Pieneearatie pee nce a ne
Beep renee te see

eS
Peete enstrimetenees|

 

 

 

 

 

 

 

 

 

 

 

 

 

 

es
Senet eaese creer
tree ep ee

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 

Cornell Aniversity Library

BOUGHT WITH THE INCOME
FROM THE

SAGE ENDOWMENT FUND

THE GIFT OF

Henry W. Sage

1891

 

BBP LIK vies iss sss unaambf Efe

 

 

 

6896-1
 

RETURN TO
ALBERT R. MANN LIBRARY

ITHACA, N. Y.

Cornell University Libra

wc ;

397 905
TEXT BOOK OF ZOOLOGY

BY

DR. J. E. V. BOAS

Lecturer in Zoology in the Royal College of Agriculture, etc.,
Copenhagen.

TRANSLATED BY

J. W. KIRKALDY
Tutor in Natural Science to the Association for the Education of Women, Oxford.

AND

E. C. POLLARD, B.Sc., Lond.,

Assistant Lecturer in Biology, University Extension College, Reading.

WITH 427 FIGURES

LONDON
SAMPSON LOW, MARSTON & COMPANY
Timited
at. Dunstay’s House
FETTER LANE, FLEET STREET, E.C.
1896.
QL 47
pet
1896 ©

A244794

LONDON :
PRINTED BY HORACE COX, WINDSOR HOUSE, BREAM’S BUILDINGS, E.C.

‘
PREFACE.

Aw English translation of Dr. Boas’s “‘ Lehrbuch der Zoologie,”
which has already appeared in two Danish and two German
editions, has been arranged in the hope that it may prove
useful to yet a larger public.

The translation is designed, in the first place, to assist
beginners in the study of Zoology ; but the needs of students of
Medicine, of Vetermary Surgery, and of Forestry have also
been kept in view. It will be noticed that Dr. Boas gives
prominence to facts rather than to theories, and of these,
such as should be of use to one or other of the classes of
readers just enumerated, or as should be most convenient for
verification.

In the German edition lists of the more important forms
belonging to the German fauna are appended to the descriptions
of the several groups: these have been replaced here by species
met with in the British Isles, and it is hoped that they will be
of special service to Naturalists. For this amount of the
subject-matter, and for this alone, are the Translators re-
sponsible: in all other respects they have merely endeavoured
to give a faithful rendering of the German text. Certain
differences appear between the English and the German, as the
book has undergone a thorough revision at the Author’s hands,
and certain portions have been deleted, whilst new matter has
been introduced.

a2
iv Preface.

The Translators desire to express their thanks to Mr. W-
E. Hoyle for suggesting that they should undertake the work,
and also for his valuable help throughout, especially for his
kindness in looking over many proof-sheets : to Prof. Newton,
for kind assistance with terms relating to the migrations of
Birds: to Prof. E. B. Poulton, Mr. Barclay Thompson, and
Dr. W. B. Benham, for many helpful suggestions. Finally,
they desire to express their indebtedness to the Radcliffe
Library, where they have not only had complete access to
cecent Zoological literature, but also every assistance in tracing
references and in procuring records for the faunistic sections.

J. W. KIRKALDY.
E. C. POLLARD.

Oxford, 1896.

 
CONTENTS

GENERAL PART.

PAGE
I. Cells and Tissues (Histology) 3
Il. Organs . 13
1. Skin 14
2. Skeleton 15
3. Musculature 16
4. Nervous system 17
5. Sense organs . 18
6. Alimentary canal 23
7. Vascular system 25
8. Respiratory organs. ; 27
9. Excretory or urinary organs ; 30
10. Reproduction and reproductive organs . : 31
11. The relations of the organs to one another.—The body cavity . 39
12. Rudimentary organs.
Ill. Fundamental Form and External Configuration of the Body . 40

Iv. Embryology or Ontogeny
Vv. Affinities of Animals—Claseification—The Doctrine of Desemit 53

VI. ee 7 58
Dispersal of animals - , 58
2. Different kinds of food and fiat effect on the eean of fis
body.—Parasitism . 62
8. Different kinds of locomotion. Their siiits upon tke aieiatiide
of animals.—Sessile forms . : 65
4, The transforming effects of the environment. . : 66
5. Stages of life—Duration of life : : , , 68
6. Protective adaptations . : , 70
7. The power of resisting ica orioate conditions 72
VII. Geographical Distribution . . . . 73
VIII. Geological Distribution . 76

Appendix.—Resemblances and differences between plants and animals 80
vi Contents.

SPECIAL PART.

Protozoa. : ee
Class 1. Gymnomyxa (Sarcodina)
Order 1. Rhizopoda
Order 2. Radiolaria
Class 2. Infusoria (Ciliata)
Class 3. Gregarinida

Celentera .
Class 1. ,Hydrozoa .
Order 1. Avdaduisties (Craspedota)
Order 2. Siphonophora . .
Order 3. Acalepha (Scyphomedusz, eas :
Class2. Anthozoa .- - - .-
Order 1. Alcyonaria (Getuasintay
Order 2. Zoantharia (Polyactinia)) .
Class3. Ctenophora. - . . .
Appendix to the Ccelentera, Spongie or Porifera .

Echinoderma . . .
Class 1. Crinoidea (Sea-Lilies).
Class 2. Asteroidea.
Order 1. Asterida
Order 2. Ophiurida
Class 8¢ Echinoidea.
Order 1, Echinoidea Rosilaite,
Order 2“, Echinoidea Irregularia
Class 4. Holothuroidea. .

Platyhelminthia
Class 1. Turbellaria
Class 2. Trematoda.
Order 1. Polystomex (Monopennité Tristate
Order 2. Distomes (Digenetic Trematodes)
Class3. Cestoda . . «. «© .
Class 4. Nemertinea (Rhynchocela)
Appendix to the Platyhelminthia: Rotifera

Nemathelminthia .
Class 1. Nematoda .
Class 2. Acanthocephala

Annelida . . .. .
Class1. Chetopoda. . - .
Order 1. Polycheta .
Order 2. Oligocheta . 7
Appendix to the Chetopoda : da
Class 2. Discophora.
Class 8. Onychophora

PAGE
85
87
87
89
91
95

98
102
103
107
109
111
113
115
118
118

122
127
130
131
133
134
138
138
138

142
143
145
146
147
149
153
156

158
158
163

165
167
172
173
174
175
177
Contents.

Appendix to the Annelida :
Polyzoa
Brachiopoda

Arthropoda
Class 1. Crustacea . i ‘
Sub-class 1. Entomostraca .
Order 1. Phyllopoda .
Order 2. Cladocera
Order 3. Xiphura
Order 4. Trilobita
Order 5. Ostracoda
Order 6. Copepoda
Order 7. Cirripedia
Sub-class 2. Malacostraca .
Order 1. Euphausiacea
Order 2. Mysidacea
Order 3. Cumacea
Order 4. Isopoda
Order 5. Amphipoda .
Order 6. Decapoda
Order 7. Stomatopoda
Class 2. Myriapoda.
Order 1. Chilopoda
Order 2. Chilognatha.
Class 3. Insecta .
Order 1. Orthoptera
\ Order 2. Rhynchota .
Order 3. Neuroptera .
Order 4. Coleoptera .
Order 5. Hymenoptera
Order 6. Lepidoptera
Order 7. Diptera
Class 4. Arachnida
Order 1. Arthrogastra
Order 2. Araneina
Order 3. Acarina
Appendix to the Arachnida :
Pentastomum
Pycnogonide
Tardigrada .

Mollusca ;
Class 1. Placophora.
Class 2. Gastropoda.

Order 1. Prosobranchiata . a

Order 2. Opisthobranchiata
Order 3. Pulmonata .
Class 3. Acephala (Lamellibranchs)
Class 4. Cephalopoda .
Order 1. Tetrabranchiata .
Order 2. Dibranchiata

vil

PAGE
178
181

184
188
193
198
195
196
198
199
200
203
207
210
211
213
214
217
219
227
227
229
230
231
252
256
260
263
267
272
275
278
281
283
284

285
286
286

287
290
291
302
303
305
306
315
322
323
viii Contents.
Vertebrata
Class 1. Leptocardii
Class2. Pisces. -. . .
Order 1. Cyclostomi .
Order 2. Selachii
Order 3. Ganoidei
Order 4. Dipnoi.
Order 5. Teleostei
Class 3. Amphibia .
Order 1. Urodela
Order 2. Anura .
Order 3. Gymnophiona
Class 4. Reptilia
Order 1. Lacertilia
Order 2. Ophidia
Order 3. Chelonia
Order 4. Crocodilia
Extinct orders of Reptiles
Class 5. Aves (Birds)

Class 6.

Order 1. Saurure
Order 2. Odontornithes
Order 3. Ratite.
Order 4. Rasores
Order 5. Natatores
Order 6. Grallatores .
Order 7. Accipitres
Order 8. Oscines
Order 9. Clamatores .
Order 10. Scansores
Mammalia .

Order 1. Monotremata
Order 2. Marsupialia .
Order 3. Insectivora
Order 4. Chiroptera
Order 5. Ungulata
Order 6. Proboscidea.
Order 7. Sirenia.
Order 8. Carnivora
Order 9. Pinnipedia .
Order 10. Cetacea
Order 11. Bruta (Edentata)
Order 12. Rodentia
Order 13. Prosimie
Order 14. Primates

Appendix to the Vertebrata: Tunicata (Ascidia)

Index

 

PAGE
324
354
356
382
383
384
386
387
391

406
407

421
422
425
426
427
430
452
453
453
455
456
458
460
461

465
466
495
496
499
500
501
510
512
513
517
520
525
527
531
532
537

541
Fie.

OE OO SO
WSNrFODDRNAA PWN EO

24,
25.
26.
27.
28.
29,
30.
31.
32.
33.

SOO SN OU me: Ro

LIST OF ILLUSTRATIONS.

An Ameeba at two different moments

A cell .

Diagram of indirect nuclear dition

Simple epithelium : A, B squamous, C columnar

Stratified epithelium : 4A squamous, B columnar

A ciliated cells, B columnar cells

Simple epithelium with a cuticle

A columnar epithelium with goblet cells, B other ana cells

Diagrams of different glands

Hyaline cartilage

Bone

Fat cells

Muscle cells and fibre

Connective tissue and smooth seanacis cells

Various ganglion cells

Diagrams of a sucker

Diagram of a nervous system . : ,

Section through a small piece of the antenna of an Insect

Auditory capsule of a Gastropod

Different forms of optic organs

Different kinds of Arthropod eyes .

Diagrams of hearts

Diagram illustrating the dial volatlont of the panies organs to the
vascular system .

Human ovum .

Diagram of an ovum with many sale shemales

Spermatozoa of different animals

Diagram of the formation of polar bodies

Diagram of fertilisation . Es

Stages in the development of an ovum ‘

Stages in the development of the ovum of a Water-snail

Section through the egg of a Chetopod at different stages of devdtenintaat

Gastrula of a marine Gastropod

Diagrammatic figures of the formation of is epibolic satiety

NW
&
OoOmMaamaoaonntoaounw se

WN NYP RRP Pe Pe eee
AnrFOON PWNHeHE OOO

29
33
33
33
34
35
42
43
43
44
Fig.

34,
35.
36.
37.

38.
39.

40.
41.
42.
43.
44,
45.
46.
47.
48,
49.
50.
51.
52.
53.
54,
55.
56.
57.
58.
59.
60.
61.
62.
63.
64,
65.
66.
67.
68.
69.
70.
71.
72.
73.
74.
75.
76.
77.

Inst of Illustrations.

Formation of the gastrula in Amphibia .

Diagram of gastrula-formation in Vertebrata with jasbial seaweed

Development of the ovum of a Crustacean

Diagrammatic sections explaining the formation of the castedla, in seein
Hydrozoa .

Diagrammatic figures of ha fotintion of the sree in the Vertebrate.

Diagrammatic transverse section showing the formation of the notochord
and of the nervous system in the Vertebrata .

Embryo of the Dog-fish with yolk sac

Diagram of a young embryo with yolk sac

Dimorphism of a Heteropteran

Two specimens of a Kallima

Two Looper Caterpillars .

An Infusorian in the free state nd aheyeted,

An encysted Infusorian which has broken up into a number of spores

Difflugia, Euglypha, and Rotalia

Nummulites distans .

Radiolarian and skeleton

Actinospherium Eichornii

Two Infusoria in various stages of conjugation

Paramecium

Vorticella .

Various Monadide

Diagrammatic figure of a Caan

Coccidium oviforme 5 ‘ : ei

Raineyan sac in a muscle fibre

Diagrammatic figures of the chief types of Gualenbaig

Cells of a Ceelenterate

Hydroid colonies and polyps 5 :

Various forms of the sexual generation of i dainrsdachie ‘

Diagram of Physophora

Diagram of Porpita

Section through a Scyphomedusan

Development of Aurelia .

Longitudinal section through a solitary Gerona

Transverse section of an Alcyonarian

Sections through various young Alcyonaria

Longitudinal and transverse sections of a Madreporarian

Portion of a massive Madreporarian

Portion of an arborescent Madreporarian

Small portion of Heliastrza

Collar cells of a Sponge

Various forms of Sponges

Diagrammatic figures explaining the radial suaanne of the Tesdaaiy:

Pedicellarie of a Sea-urchin

Diagrammatic sketch of the water iageati system of a Star-fish

78 and 79. Diagrammatic longitudinal sections of a Star-fish and of a Sea-

80.

urchin a
Diagrammatic figures of Hehinndben aie : ‘ é ‘ 5

PAGE
45
46
AT

47
48

49
49
49
54
71
71
86
86
87
89
89
91
93
94.
94.
95
95
97
97
98
100
104.
105
108
108
109
110
111
112
114
116
116
117
117
119
119
122
124,
124

125
126
Fia.

81.
82.
83.
84.
85.
86.
87.
88.

89.
90.

91.
92.
93.
94.
95.
96.
97.

98.
99.
100.
101.
102.
108.

104.

105.
106.
107.
108.
109.
110.
111.
112.

118.
114.

115.

116.
117.
118.
119.
120.
121.
122.
123.
124.
125.
126.
127.
128.

List of Illustrations.

Larve of: Star-fish, Ophiurid, Sea-urchin, Holothurian
Rhizocrinus lofotensis

Antedon .

Ventral surface of Antaion

Larve of Antedon rosacea

Antedon Eschrichtit

Diagrammatic figures explaining the guantan of a Star-fish
Diagram explaining the structure of an Ophiurid ,

Shell of a Regular Sea-urchin

Shell of an Irregular Sea-urchin

Diagrammatic longitudinal section of the spine of a Sea-urchin
Diagram of a Holothurian .
Transverse section of the body-wall ts a Halsthuriii .
Transverse section through a radius of the body-wall of a Holothurian
Nervous system of Distomum

Part of the excretory system of a Tinta

Longitudinal section through Cycloporus papillosus

Sketch of Mesostomum splendidum.

Sketch of Provortea afinis

Planaria lactea - .

Larva of a marine Turbellarian

Sketch of Liver-fluke .

Diplozoon paradoxum : : a 5 é a . .

Distomum hepaticum

Polystomum integerrimum

Snail with Leucochloridium in otis feribaistea

Tezxnia mediocanellata

Six hooked larva of T. solium

Proscolex of the same ;

Ciliated larva of Bothriocephalus ee:

Proscolex of the same &

Head of Tenia soliwm (A), of T. mediocanellata (B), nil of Bothrio-
cephalus latus (C)

Tzxnia echinococcus .

Bothriocephalus latus

Sketches of a Nemertine

Diagrammatic section of a Nimasetine

Three larval stages of a Nemertine

A, diagram of a female Rotifer: B, the ite

Transverse section of a Nematode

Hind end of a male Nematode

Intestinal Trichina

Muscle Trichina

Dochmius duodenalis

Filaria medinensis .

Heterodera Schachtii

Echinorhynchus

Larva of an Acanthocephalon

An Annelid seen from the side

PAGE
127
128
128
128
129
129
132
133
135
135
137
139
139
139
142
142
143
144,
144.
145
145
146
147
148
149
149
149
150
150
150
150

152
152
153
154
155
155
156
158
159
161
161
161
161
163
164
164
165
xil

Fia.
129.
130.
131.
132.
133.
134,
135.
136.
137.
138.
139.
140.
141.
142.
143,

144.

146.
147.
148.
149.
150.
151.
152.
153.
154.
155.
156.
157.
158.
159.
160.
161.
162.
163.
164.
165.
166.
167.
168.
169.
170.
171.
172.
173.
174,
175.
176.
177.
178.

List of Illustrations.

Nervous system in different Chetopods
Anterior end of an Annelid . s
Diagrammatic section through the skin of a Ghetopea
Anterior end of a Chetopod .
Diagrammatic sections of different Ghestopods
Diagram of the reproductive apparatus of an Earthworm.
Larva of Nereis
Myrianida fasciata :
Digestive tract, etc., of a Leech
Genital apparatus of a Leech
Peripatus
A, B, diepiaiaabia longitudinal seatnna of a Polgioons Cc Aiteninvia
Plumatella polymorpha .
Fresh-water Polyzoon
Diagrammatic longitudinal sostians of a Binkohiopod
and 145. Larve of Brachiopods
Section through a seta and the adjasant iin of an kecheoned
The last four joints of an Arthropod limb ‘
Longitudinal section through a joint of an Arthropod
Nervous system of Gammarus
Examples of typical Crustacean Gatbe
Limbs of different Crustacea .
Vascular system of the Lobster
Nauplius of Penzus
Branchipus vernalis.
Apus productus
Sida crystallina
Limulus polyphemus
Young Limulus g
A Limulus, B Belinurus, C Burypterat; D Distances
Stages in the development of Sao hirsuta
Cypris
Nauplius of an Oeteenids
Cyclops .
Various parasitic Gspapeila
A, B, Penella sagitia, C Herpyllobius arcticus
Lepas
Balanus .
Diagrammatic figures suowing tie desinaitlen fei aid fs Bulaniis,
Sacculina on the ventral side of the abdomen of a Shore-crab
The appendages of a Lobster.
Nebalia Geoffroyt
Thysanopus tricuspidatus
Boreomysis megalops
Mysis-nauplius
Diastylis neapolitana
1 Arga, 2-3 Cymothoa : ‘
1 Cepon elegans, 2-3 Portunion Kossmanni
Apseudes Latreillet

PAGE
166
166
168
168
168
171
171
172
175
176
77
179
180
181
182
183
185
186
186
187
189
190
191
192
194
194
195
196
197
198
198
199
199
200
202
202
203
208
204
207
208
210
211
212
212
213
214
215
216
Fie.
179.

180.
181.
182.
183.
184,
185.
186.
187.
188.
189.
190.
191.
192.
193.
194.
195.
196.
197.
198.
199.
200.

201.
202.
203.
204.
205.
206.
207.
208.
209.
210.
211.
212.

213.
214,

215.
216.
217.

218.
219.
220.
221.

222.
223.
224,
225.

List of Illustrations.

An Amphipod.

Transverse section of the thorax of ne

1, 2 Caprella acutifrons, 3 Cyamus mysticeti

Palemon.

Zowa of a Prawn

Mysis-stage of Penzus

A young Lobster-larva

Newly-hatched Crayfish

Phyllosoma

Larve of a Crab

Squilla

Digestive tract of Lithobius .

Newly-hatched larva of a Diplopod

Head and anterior body segments of a Sadlopandtes

Transverse sections: A of a Chilopod, B, D of different Diplopods

Antenne of various Insects

Diagram of the mouth parts of various Insects

Diagrammatic transverse sections of the proboscis of various Insects

Transverse section through the thorax of a Beetle

Diagram of the principal anatomical points in an Insect

Nervous system of various Insects

Diagrammatic longitudinal section of the head of an aaaes with wudiiag
mouth-parts

Diagram of the chief trunks of the tracheal system of an Insect.

Portion of a trachea from a Gall-fly larva

Apparatus for closing the trachea of a Beetle

Portion of the heart of an Insect

Ovariole of an Insect

Female genital organs of the Cockchafer

Male genital organs of the same .

Females of three allied species of Geometride

Blastophaga grossorum

Larva, pupa, and imago of a Sphinx

Larva and pupa of a Wasp

Termes lucifugus

Lepisma .

Abdomen of Machilis

Phyllozera vastatria

1 Cimen lectularius, 2 Pediculus capitis, 3 Phthirius pubis

Chrysopa .

Panorpa communis .

Boreus hiemalis 7 ‘

1-4 Xenos Rossti, 5 X. Peckii

A Abdomen with ovipositor of one of the Mkonetie: B Transverse sac
of the spine and the lobes .

Heads of Honey-bees

Psyche

Culex

-Gastrus . é 2

xi

PAGE.
217
218.
218.
220:
221
222
224
224
225:
226.
227
228.
228.
229
230
231
232
233
235.
237
237

268
271
274.
xiv

Fie.

226.
227.
228.
229.
230.
231.
232.
233.
234.
235.
236.
237,
238.
239.
240.
241,
242.
243,
244,
245,

246.

247,
248.
249,

250.

251.
252.

253.
254,
255.

256.
257.

258.

259.

260.
261.

262.
263.
264.
265.
266.

267.

268.

269.
270.
271.

Inst of Illustrations.

Pulex irritans . : :

Diagram of the anatomy of a “Spider

Alimentary canal of a Spider :

Sexual apparatus of one of the Phalusgitdies

A Scorpion

Diagram of the cniisiee of a “Tyroglyphus

Female of Pentastomum tanioides .

Pycnogonum :

Diagrammatic a Ste a Mardirrads .

Portion of the radula of a Cephalopod .

Diagrammatic longitudinal section of the mouth of a Gieumios

Diagram of the central nervous system in various Mollusca

Chiton

Diagrammatic fignss of 2 a Bicinaped

Diagrams of various forms of Gastropod shells

The shells of two examples of a tropical land Snail

Shell of a Snail (Paludina) é

Diagram of the nervous system in relation to ihe. sitotriaty sai

Male Periwinkle

Female Periwinkle. :

Diagram of the genitalia of various is Gastnopod 5

Larva of a Gastropod

Carinaria

Cleodora .

Cleodora .

Pneumodermon

A transverse section saath a iarabiRbcsal

Transverse sections through two Lamellibranchs.

Lamellibranch removed from the shell .

Tapes decussatus

Right shell valves of two different Tienelitheaadh

Diagrammatic transverse sections through the shell of Tesmetittieansihay
with internal (A, A’) and external (B, B’) ligaments

Diagrammatic longitudinal section of a Lamellibranch

Larve of Cardium .

Mya arenaria .

Teredo navalis

Diagram of a decapodous Cieshalinpeil

Nautilus . i

Diagrammatic figures of various Cephalonoa shalla

Diagrammatic transverse sections through the eyes of various Gaphalopoda

Diagram of the heart, etc., of a Cephalopod .

An octopodous Decapod in which the hectocotylised saition of the steht
arm is very well developed 3

Diagrammatic figures to illustrate the ralations bole the Chitons aiid
the Cephalopods ‘ 7

Diagram of a vertebra and fis parts eiiniiabed willl it

Diagram of the skeleton of the fore-limb of a higher Vertebrate

Longitudinal section of a joint

PAGE
278
279
280
281
282
284
285
286
286
288
288
289
291
292
292
293
293
296
298
299
300
301
303
304
304
304
306
307
308
308
309

311
313
313
314
315
316
317
318
319
320

321

322
326
328
329
Fia.

272.

273.
274.
275,

276.
277,
278.
279.
280.
281.
282.
283.
284.
285.

286.
287.
288.
289.
290.
291.
292.

293.
294.
295.
296.

297.

298.

299.

300.
301.
302.
308.
304.
305.

306.

307.

308.
309.
310.
311.
312.
313.
314.
315.
316.
317.

List of Illustrations. XV

PAGE

Diagrammatic vertical longitudinal section vee the brain of a
Vertebrate 5 : : . 3830
Horizontal longitudinal sation Hnongh ts ignite of a 5 Veibaate a - 331
Central nervous system of a Tortoise . < . 332
Diagrammatic representation of the desdlepmant of fia wurtebiate eye . 334
Diagrammatic section through the orbit, A of a Fish, B of a Mammal . 885
Pineal eye of a Lizard . : ‘ , . 837
Diagram of the auditory organ of a Gartetiate : . : . 338
Diagram of various developing teeth . ; ‘ 5 . 3839
Section through a tooth to show the structure of the settina ; 5 . 840
Portion of the upper jaw of a Lizard. 2 4 : : . 840
Diagram to explain the structure of the scdeanteey , : ‘ - . 842
Anterior portion of Chick embryo. ‘ = : , - 848
Heart of an Amphibian. : 344

Diagrammatic longitudinal Sitios oe 4s head a fren Be of the
body to show the position of the heart and pericardium . . 845
Diagrams of the arterial arches of various Vertebrata : . 847
Diagram of the end of a urinary tubule of a Vertebrate  . ‘ . . 848
Testis, kidney, etc., of an Amphibian 349
Testis, embryonic kidney, etc., of the embryo of a Bakes vedionaia, 349
Diagram of a pronephros ‘i : ‘ 2 ‘i i . 850
Section through the ovary of a ities 7 é : - . 3851

Illustrating the development of the embryonic membranes in a Bird
embryo. . z F x a . 853
Diagrammatic ratigttadtnal sogtion of Seana : - 855
Transverse section through the anterior region of the belly of oe 355
Diagrammatic section of the skin of a Teleostean 2 3 : . 3856
Portion of a fin with spiny rays and soft rays : 2 3 r . 358
Skeleton of a Trout i . 859
Longitudinal sections through ides wuctaieal eotuian of various Fish . . 360
End of the tail of various Fish 2 ‘ ‘ ‘ - 861
Skull of a Perch . : : 5 5 : . 863
Skull and visceral arches of A a Shark, Ba Pike. i 3 < - 864
Skull of a Cod : “ : j : : ‘i - 865
Shoulder-girdle and foredint of a | Bete é . - 866
Skeleton of fore-limb of A Shark, B Polypterus, C Amia, D Cod. ‘ . 867
Sensory papilla of a young Teleostean . _ ‘ 7 : 5 e . 869
Sternarchus curvirostris . F 2 : : . . 3871
Horizontal section through the lisad of deawehies : $ - 5 . 3872
Horizontal section through the head ofa Cod. é ‘ 5 . - 372
Transverse section of a gill arch in various Fish . : A - : - 873
Longitudinal section of the heart of different Fish  . - ‘ -  « 876
Young Pike at different stages. 7 7 : , ‘ ! ; . 380
Larva of Trachypterus . f 3 é : * = . . a - 880
A Ray embryo, B Shark con ° : 5 : . “ . 3 - 3881
Chimera monstrosa ; i : 2 - 884
Lepidosteus . ‘ ji ‘ : 5% . . A ‘i . . « 885
Ceratodus : . Fi . . . . : . : : - 886

Protopterus annectens . ‘ : ‘ i . 886
Xvi

Fia.
318.

319.
320.
321.
322.
323.

324.

325.
326.
827.
328.
329.
330.
331.
332.
333.
334.
335.
336.
337.
338.
339.
340.
341.
342.
343.
344.
345.
346.
347,

348.

349.

350.
351.
352.
353.
354,
355.
356.
357.
358.
359.
360.
361.
362.
363.
364,
365.
366.

List of Illustrations.

Skeleton of a Urodele

Visceral arches of a Salamander

Skull of a Frog 5
Sternum and snsnidanistinls of a ‘Silauandas
Sternum and shoulder-girdle of a Frog
Pelvis and last vertebre of a Frog

Pelvis of Frog

Transverse section of head of a

Head of a Urodelan larva

Tadpoles .

Arterial arches of the Grodan

Larve of the large Triton

Skull of a Stegocephalon ‘ ‘ : :
Embryo of Epicrium glutinosum

Sections through scales of Reptiles
Transverse section of the atlas of a Vertebrate
Diagram of axis

Skull of a Lizard

Hyoid of a Lizard .

Skull of a Boa constrictor

Skull of a Crotalus.

Sternum and shoulder girdle of stove
Carpus of a Turtle .

Carpus of a Lizard.

Pelvis of a Lizard

Brain of a Lizard

Vertical section of eye of Lizard and of Snakes
Diagrams of various lungs

Head and neck of an Alligator

Diagram of the heart and arterial vdlisg of a Crocodile
Poison tooth of a Crotalus

Poison gland and poison fang of a Sika

Tail end of a Crotalus

Skull of a Gavial

An Ichthyosaurian

A Plesiosaurian

A Pterodactyle

Iguanodon é

Fore and hind limbs of a Dinosaurian .

Portion of a feather

Diagrams of feathers with aftershafts .

_Down and feather of young Bird .

Tails of various Birds

Skeleton of a Raven

Skull of a Raven

Diagrams illustrating ageaiaae of beak in Birds
Skull of young Chick

“Hyoid of the Fowl . ‘ é
Sternum and shoulder girdle of fh Ravan .

PAGE
392
393
394
395
395
396
396
396
398
398

403
405

408
409
409
411
411
412
412
413
414
414
414
415
415
417
418
419
423
424,
425.
427
427
428
428
429
430
431
432
432
433
436
438
438
439
439
Fia.
367.
368.
369.
370.
371.
872.
373.
874,
375.
376.
377.
378.
379.
380.
381.
382.
383.
384.
385.
386.
387.
388.
389.
390.

391.

392.

393.
» 394.
395.

396.
397.
398.
399.

400.
401.

402.

403.
404.
405.
406.
407.

408.

List of Illustrations.

Manus of a young Ostrich

Foot of a young Chick .

Pelvis of a young American Ostrich.

Brain of a Pigeon .

Eye of a Bird.

Lungs of a Chick sitchin

Lungs of a Pigeon .

Section through the trachea and bronchus of a Bird . ‘

Diagram of the heart and arterial arches of Crocodile and Bird .

Reproductive organs of a Hen

Reproductive organs of a Cock

Archeopteryx :

Longitudinal section of a fade

A claw, B nail, C hoof

Longitudinal section of the tip of a Mammalian digit. és 7

Tips of toes seen from below .

Axis vertebra of a young Platypus

Sternum and clavicle of a Kangaroo

Skull of a Dog

Skull of an old Pig :

Right half of the shoulder girdle of a young “liber

Right half of the shoulder girdle of a young Ape

Left half of the pelvis of a young Ornithorynchus

Left half of the pelvis of a new-born Calf

Tibia of a one-year-old Horse

Diagrammatic transverse section of ihe head of a aiaienal to show the
relations of the auditory organ .

Dentition of a Mole

The teeth of a Pig, showing the ascline eit

A, incisor of a Dog shortly after it has come into use; B, the same tooth
in an old Dog

Longitudinal section agit the haa and neck of a Dog

Small portion of a mammalian lung

Heart and arterial arches of Mammalia F

The terminal portions of the gut, of the urinary and eit apparatus in
the females of various Mammalia ‘

The Millerian ducts and urinogenital sinus of various Mammalia

Diagrammatic longitudinal section of the cloaca (or rectum) and copulatory
organs, A of a Crocodile, B of a Monotreme, C, D of various other
Mammalia .

Placenta of a Mammal . :

Right hind foot of: A Phalangista, B a Raleiee, C Chorepus

Fore-foot of : A Tapir, B Rhinoceros, C Horse

Left fore-foot of Anchitherium, Hipparion, and Horse .

Manus of: A Pig, B Stag, C Camel

Diagrammatic longitudinal section of the dpiscont A of a Camel, B of an
ordinary Ruminant, C of a Tragulus

Skeleton of a Mastodon .

xvii

PAGE
440
440
441
442
443
446
446
447
448
449
449
452
467
469
470°
470
472
473
474,
475
477
477
478
478
479

481
483
484,

486
488
489

490
491
XVlil List of Illustrations.

Fig. PAGE
409. Longitudinal sections of molar teeth, A—B, various species of Mastodon,

C Elephant . , z ‘5 3 i A j . 511
410. Skull of Dinotherium  . : < 512
411. The teeth of the permanent dentition ‘of the left half of the skull of a

Dog, and the milk dentition of the same . : : 3 ‘ ‘ . 513
412. The same of a Cat . 3 ‘ _ . 513
413. The teeth of the left half of the upper jaws ae r Dee, B Beas, C Marten,

D Badger, EF Viverid, F Hyena, G Lion . : : i ° . 514
414. Pes of a young Sea Elephant » oe 8 : 518
415. Upper teeth of the Sea Elephant. .  . ; . 518
416. Right anterior appendage of a Pilot Whale . . 520
417. Skull of a Dolphin . s . - a ; . 521
418. Skull of a Mystacocete . ; ‘ 521
419. Diagrammatic transverse section of the aiterin eo of the head of a

- Balenopterid . ; ‘ z 5 ‘ : : ‘ . 522
420. Skull of a Pilot Whale . ‘ . 524
421. A Manus of the Great Anteater, B of the avactoal Aetoutes 526
422, Right ramus of the mandible: A of a Rabbit, B of an Agouti 527
423. Transverse sections of molars of various Rodents E é . 528
424, Left hind foot of a Maki es 531
425. A diagram of Appendicularia, B deigeaas of an daptdion larva . 537
426. Diagrammatic longitudinal section of an Ascidian 538

427. Diagram of a Salpa 540

 
GENERAL PART.

I. Cells and Tissues (Histology).

Tue name Protozoa is given to a group of animals of very
simple organisation, which form the lowest grade in the animal
kingdom. It is well to begin a study of zoology by considering the
Amceba, one of the many animals belonging to this group, because,
in order to appreciate animal organisms in general, it is extremely
important to understand thoroughly a simple creature such as this.
The Ameceba is a microscopic organism which is frequently found
in fresh water. Its shape is irregular and indefinite. It consists of a
substance called protoplasm, a finely granular, viscid substance,
which, on chemical analysis, is found to consist of a number of different
constituents, albumen being one of the most important. Protoplasm
also contains a considerable quantity of
water and of various other materials.
In the protoplasm is a rounded or oval
body, the nucleus, and in this again
is a smaller spherical body, the nu-
cleolus. The Amceba possesses a
number of qualities, the most obvious
of which is its power of movement:
small processes, called pseudopodia,
are thrust out from the surface, by the _ Fig. 1. An Amoeba at two
‘ different moments. & nucleus
streaming of part of the general sub- 4 vacuole, n ingested food.—After
stance of the animal towards certain Gegenbaur.
points; the pseudopodia then disappear,
and new ones are formed; but apart from this the protoplasm is in
constant motion, as is shown by the way the granules move about.
The mobility of the protoplasm gives the Amceba the power of loco-
motion, whereby it can glide through the water, past any given object,
with greater or less rapidity. Movements m ay take place without an
external stimulus, they are then said to be spontaneous: in other
cases there is such a stimulus ; a movement, often the drawing-in of
the pseudopodia, follows contact with some object, but the movement
proceeds from the Ameeba itself, it is not directly caused by the

B 2

 
A General Part.

external stimulus, this simply gives the organism an occasion for
moving, The power of reacting to stimuli is called irritability.
The Ameba is further characterised by building up its own substance
from materials which it has taken from the environment, i.e., it
feeds: it does this by surrounding other little organisms, and
inanimate particles, with its pseudopodia, and absorbing them into
its protoplasm, expelling, after a time, that part of the food which
cannot be assimilated. Besides these solid particles, the Amoeba
absorbs water, and also free oxy gen, which is present in all natural
waters, and which is absolutely necessary for its existence, since it
cannot live in water which does not contain this gas, even if all other
necessary conditions are fulfilled. The oxygen unites with some of
the carbon present in the protoplasm, forming carbon dioxide, which
is got rid of; the Amceba is, as it were, a little machine, in which,
just as in a steam-engine, carbon is burnt; a certain amount of
energy is liberated by this combustion, and is manifest as motion. So
much is clear and certain, but there are many unknown steps in the
activity of the little machine: by the combination of the oxygen and
carbon, the complex constituents of protoplasm are broken down, and
simultaneously, new compounds, principally water and nitrogenous
matter (uric acid), are formed. -:The latter is of no use to the Amceba,
but must be got rid of; it collects, as waste material dissolved in
water, in little cavities in the protoplasm, called vacuoles, and by
their contraction (or rather, the contraction of the protoplasm round
them) the contents are expelled. It is evident, therefore, that a
partial destruction of the complicated materials of the Amceba is
constantly going on, so that its mass is diminished, but the food
taken in makes good this loss, and even produces a surplus, so
that the Amceba grows—it actually increases in bulk. In close
relation with this is the last important quality of the Amceba, its
power of multiplying by fission. In this process the nucleus
first breaks in two, a constriction of the protoplasm follows, and
finally, it is separated into two nearly equal pieces, each with its own
nucleus.

All the characters just mentioned distinguish the Ameba as
living, as an organism (though of the simplest kind), in contrast
to the lifeless particles which occur near it in the water. Death,
which is caused by a change in the external conditions (e.g. by too
great heat), deprives the Amcba of all these qualities.

In their principal features the rest of the Protozoa are
all essentially similar to the Amcba. A few variations may
arise by the formation of a hard, protecting part (skeleton) of
lime or silica, in, or round, the protoplasm: or its outer layer
may be of a firmer consistency than the rest, so that, although
it retains its mobility (the movements of the granules and rough
alterations of shape, affecting the whole body, may still be observed),
Cells and Tissues. 5

there is no protrusion of true pseudopodia. Oil-globules and like
matters may be differentiated in the protoplasm: the surface of the
body may be covered with fine, hair-like protoplasmic structures,
called cilia, which exhibit constant waving movements, etc. (For
details, see special part— Protozoa,” p. 85).

All other animals, the Metazoa, begin life as ova, small
corpuscles of living protoplasm provided with a nucleus, and at this
stage agree, in all essential respects, with the Amoeba. Unlike
Protozoa, however, they do not remain in this state: the ovum or egg
-divides into a number of segments, each with its own nucleus, but,
instead of separating from one another, they remain in connection;
such segments are called cells; the essential properties of the ovum,
as also of the Amceba, are possessed by each one, and the body of the
Metazoon attains its definite form by repeated division and differen-
tiation of the cells. The perfect Metazoon, then, is an intimate
association of cells like an Amceba, but showing greater or smaller
modifications.

Cells consist of protoplasm, like that of the Ameba, either
throughout their existence, or only in the young stages. There is,
in the protoplasm, a vesicular nucleus con-
taining a watery liquid (achromatin), and a
network of delicate threads (the chromatin).
One or more rounded nucleoli are also frequently
present, often appearing as thickened spots in
the network. The cells are capable of di-
viding; division is preceded by peculiar
changes in the network, then the nucleus
divides, and finally the protoplasm separates
into two pieces. The cell exhibits all the other Fig. 2. A cell. n
essential properties of the Amceba; it absorbs Pie Ga
oxygen, takes in food, and so on. protoplasm.—-Orig.

It has recently been shown for many cells that the
protoplasm consists of a homogeneous matrix, and of numerous fine threads
besides the granules just mentioned. Sometimes many nuclei are present
in a cell, which is then considered to be an incompletely divided cell-mass
the nucleus has divided, but no division of the cell body has resulted.

The division of the nucleus is, in a few cases, direct; it simply
constricts in one place, and then separates into two pieces. As a rule, however,
nuclear division is indirect, and then it takes place in a complicated way,
as follows: First, the whole nuclear network forms a long coiled thread
(Fig. 3,1), which breaks up into a number of rod-like or curved pieces,
the chromosomes; next, the nuclear membrane disappears (Fig. 3,2), and
each chromosome splits lengthways in two (Fig. 3,3); but before this, two
little bodies, the centrosomes, from which fine threads radiate to the chromo-
somes, may be noticed in the protoplasm.* Then these threads shorten,

 

 

* One or two centrosomes may be noticed lying near the nucleus in many resting
cells (t.¢., cells which are not ready for division). Possibly they are as constant a
constituent of the cell as is the nucleus.
6 General Part.

and the halves of the chromosomes, apparently, are (Fig. 3, 4) thereby drawn
away from each other, so as to form two separate groups (Fig. 3,5). Hach
group is the beginning of a new nucleus, for its chromosomes unite again to
form a new network, and a nuclear membrane arises round it (Fig, 3,6). Before
this happens, however, the protoplasm begins to divide into two parts corre-
sponding to the new nuclei.

Fig. 3. Diagram of
indirect nuclear division.
c centrosome. See text.
—Orig.

 

Each cell of the animal body has an entity of its own, but it
differs from the Amceba, in that it is a member of, and to a certain
extent subordinate to, a great whole. The degree of its independence
varies, however, very considerably. Some cells, called wandering
cells, retain throughout life a very considerable freedom, and,
in nearly all respects, remain on a level with the Amoeba. They
have the power of protruding pseudopodia, and each moves about
by itself, freely, in the spaces of the body: moreover, whilst most
other cells (see the section on the alimentary canal) can only absorb
food in a liquid form, the wandering cells can also take up hard
particles and dissolve them. Sometimes this peculiarity seems to be
exerted even against the organism itself: for instance, in those cases
where (as in the metamorphosis of Insects) some organs atrophy—
without the death of the creature itseli—the wandering cells eat up
the dead parts and digest them. They devour also foreign bodies,
such as Bacteria, which have got into the body. The blood
corpuscles of most invertebrate animals,* and the white blood
corpuscles of the Vertebrata, are wandering cells. There are still
other free cells, viz., the red blood corpuscles of Vertebrates, which

 

* All the Metazoa, with the exception of the Vertebrata, belong to this group.
Cells and Tissues. 7

resemble wandering cells in their isolation, but differ from them in
that they have not the power of independent amceboid movement ;
they are just carried along passively by the blood.

Most of the cells of the animal body are, however, fixed, they
‘are immovably united to one another and, as they cannot protrude
pseudopodia, are fairly constant in shape. These fixed cells aré
variously modified in the adult: they are specialised, in
correlation with differentiation of function. Usually, cells which are
modified in the same or in similar ways, are arranged in groups, and
such groups are called tissues. Four principal kinds of tissue
may be recognised: epithelial, skeletal, muscular, and
nervous.

1. The name epithelium is used to designate those tissues
which form a thicker or thinner covering to the outer or inner surface
of the body, and which
consist simply of a num- 5 A B
ber of closely apposed
cells. Hpithelial cells
generally consist of pro-
toplasm, in which there
may be excretions such
as pigment granules,

oil globules, etc.: they

$ A Fig. 4. A Simple squamous epithelium, surface view ;
Wary 3 shape 2 a ave Bthe same in section. C Section of simple columnar
squamous, the height  epithelium.—After Gegenbaur.

less than the breadth ;
others columnar, the height greater than the breadth; or the breadth
and the length may be approximately the same.

The epithelial cells are joined together by small quantities of intercellular
cement-substance: often, too, there are delicate strands of protoplasm
passing from cell to cell.

 

  

Fig. 5. A Stratified squamous epithelium. B Stratified columnar epithelium.—
After Gegenbaur.

Epithelia may be simple or stratified. Simple epithelium
consists of a single layer of closely adherent cells, which may either
be flattened (simple squamous epithelium) or cylindrical (columnar
epithelium), or about equal in height and breadth (cubical epithelium).
Stratified epithelium consists of several layers of cells, or, to
8 General Part.

be more precise, it is many cells deep, for the cells are generally not
arranged in layers. Whilst the deeper-lying cells are usually
undifferentiated, the most superficial, or several of the outer layers,
exhibit many modifications. Sometimes they are flattened, and the
epithelium is termed stratified squamous epithelium ; or the outermost
layer consists of cylindrical cells, when it is known as stratified
columnar epithelium.

The free surfaces of the cells, whether of simple or of stratified
epithelium, may be provided with cilia, delicate hair-like processes,
which are in constant motion. These are called ciliate cells,
or if only one large hair, a flagellum, is present, flagellate cells.
Sometimes isolated groups of such cells are found in simple, or in the
superficial layer of stratified epithelium ; or, again, they may compose
the whole, or almost the whole, layer (of course, the outer layer
only in stratified epithelium). This is commonly called ciliate
epithelium.

Fig. 6. A Ciliated cells. B Columnar cells,
with a cuticular plate (c).—Orig.

   

Fig. 7. Simple epithelium, with a cuticle (c).
Orig.

Not infrequently the epithelial cells secrete, at their free edge, a
firmer substance,a cuticular plate (often called the cuticular
border) ; the cuticular deposits of neighbouring cells usually become
closely connected, so as to form a continuous covering or cuticle,
which occasionally attains a considerable thickness and hardness.

Fig. 8. A Columnar
epithelium, with goblet
cells, from one of these
mucus is escaping. B
Other gland cells.—Orig.

 

 

The primary function of the epithelium is to form a protecting
covering for the other tissues, but it often performs a second, viz.,
that of secreting materials, usually fluids, which are either of great
importance to the body, or else need to be discharged from it (urea).
Isolated gland cells, usually of a peculiar form, are often met with in
epithelia, such are the goblet cells of many animals. They havea
Cells and Tissues. 9

central cavity, wherein is contained the substance separated from the
protoplasm (e.g., mucus), and this escapes to the exterior through an
aperture. Secreting cells commonly consist of a long thin neck,
wedged between the adjacent epithelial cells, and a wide sac-shaped
inner part, lying in the deeper tissues. All secreting cells derived
from the general epithelium are called glandular cells, for
any part of the animal body which forms a secretion is considered
to be a gland. Sometimes glandular activity is distributed over
a large, continuous area of the epithelium, which is - usually
invaginated into the subjacent connective tissue; such are true
glands. In its simplest form the gland is a flat patch of cells,
a pit, a small sac, or a longer tube; but the tube itself may form
evaginations, and these on their part may possess branches, and so

 

Fig. 9. Diagrams of different true glands. The secreting cells are dotted. 1 The
‘simplest form; the secreting cells are not invaginated. 2—5 Different kinds of simple
glands. 6 Branched tubular gland. 7 Racemose gland.—Orig.

on; so that a compound gland is made up of a complex system of
canals (the walls of which consist of a single layer of epithelium),
held together and supported by connective tissue (see below). In
these large glands, the ends of the branches only secrete, whilst the
rest of the system serves as a reservoir and as a means of exit.
Such a distinction into secreting portion and duct, may be
noticed even in very simple glands. Sometimes the ends of the
canals exhibit a rounded enlargement, when the gland is called
racemose, to distinguish it from the tubular gland, which is
without this expansion.

For the development of sensory epithelium, see “ Sense-organs.”

2. Skeletal tissue is characterized by the great prominence
of the intercellular substance. In an early stage of develop-
ment it consists, like epithelia, of cells only; but later, the cells,
though they always remain simple and undifferentiated themselves,
secrete some form of intercellular substance which constitutes the
chief part of the hard structures, and gives them their great
importance in the animal body. Of skeletal tissues, connective
10 General Part.

tissue, cartilage, and bone are recognised. In the first of these
the intercellular substance is more or less soft, and the cells
are of various shapes, fusiform, stellate, flat. There are three
kinds of connective tissue:—cellular, in which the
intercellular substance is but slightly developed, often forming
only a membranous partition between the large vesicular cells:
mucous or gelatinous, with a homogeneous and jelly-like
intercellular substance (cells rounded or stellate): and
fibrillar connective tissue, where the intercellular substance is
composed of delicate threads, among which are often branched
elastic fibres; when these are very numerous, the tissue is called
elastic tissue. The intercellular substance of cartilage is firmer,
it is usually homogeneous (hyaline cartilage), or it may contain elastic
fibres (elastic cartilage). In this kind of tissue, which is principally
found in the Vertebrata, the cells are, as a rule, rounded. Bone is

   

Fig. 10. Hyaline cartilage—Adapted Fig. 11. Bone. — After
from Gegenbaur. Gegenbaur.

 

characterized by a yet greater hardness, on account of the lime salts
(especially phosphate of lime), which are deposited in the intercellular
substance.* The cells are stellate, with anastomosing processes.
This tissue occurs only in the Vertebrata.

Fat cells are sometimes present in the connective tissue;
when they are very abundant, the tissue is termed adipose. The
cells contain drops of fat or oil, which
may increase in number to such an
extent that they run together to form
one large drop. In this case the cell

Fig.12. A-B Young fatcells. C Soe: Eee et a 8 delicate
Older fat cell, with a very large layer of protoplasm surrounding a
oil-drop.—Orig. large drop of oil. Connective tissue
cells may also contain pigment (usually dark); these are known
as pigment cells (chromatophores).

 

 

* Sometimes lime salts are deposited in cartilage (calcified cartilage).
Cells and Tissues. 11

3. In muscular tissue the cell-protoplasm is partially or
entirely modified into a peculiar contract ile substance, which
does not move spontaneously, but only contracts in response to
some stimulus.* It differs in another respect also from other
protoplasm: the movement of the muscle cell always occurs in a
definite way: first, there is a shortening and thickening of the
cell followed by a lengthening and narrowing, so that it has assumed
its original condition by the end of the movement. The streaming
movements seen in the Amceba, which are characteristic of protoplasm
in general, are never found in the contractile substance of muscle
cells.

The simplest form of muscular tissue is composed of smooth
muscle cells, which are spindle-shaped, elongate or ribbon-like,
and pointed or occasionally forked at
both ends. A nucleus is present in
each, lying either in the middle of the
cell, surrounded by a small quantity
of protoplasm, or on one side of the
contractile substance, enveloped in a
varying amount. The contractile
substance is homogeneous and. shin-
ing, and is destitute of granules or
transverse striation, though it may
sometimes be longitudinally striped.
The muscles of most of the Inverte-
brata, with the exception of the
Arthropoda, consist of this tissue, and
it is found also in Vertebrates, in the iii a Gg BRR ete wl
walls of the digestive tract. To (a witha large residue of protoplasm),
the smooth are nearly allied the ¢ trantvereely stristed muscle cell,
; ransversely striated muscle fibre.—
striped muscle cells, the only Orig.
essential difference being that the
contractile substance of the latter has a transversely striated
appearance, due to its division into regularly alternating discs of
different refrangibility: it occurs, for example, in the Vertebrate
heart.

The transversely striated muscle fibres differ from the
striped muscle cells in that they are multinucleate. A striped muscle
fibre originates as a simple cell with one nucleus, which divides repeat-
edly without corresponding division of the cell, and in the perfect fibre,
the nuclei lie either in or upon the surface of the contractile substance.
The fibre is not only transversely striped, but a more or less distinct
longitudinal striation, depending on the very delicate fibrillee of which
the fibre is composed, may also be noticed. The whole muscle fibre is

a b

  

 

* As to the source of the stimulus, see below.
12 General Part.

enveloped by a thin sheath, the sarcolemma, which is wanting in
smooth as well as in striped muscle cells. The fibres are usually
cylindrical, and are rounded, rarely branched or forked, at the ends;
they are often of considerable length. In the Arthropoda the whole,
and in the Vertebrata the greater

RB 4 5 part, of the musculature consists of

striated muscle fibres, which like the
striped muscle cells, contract with
greater rapidity, and with greater
force, than the smooth muscle cells.

Muscle cells and fibres may not only
form large tracts of tissue, but they may
also occur as isolated secondary constitu-
ents of the connective tissue; where
these are very numerous and the connective
tissue is scanty, an appearance of muscular
tissue is produced. This shows the inti-
mate relation between connective tissue
cells and muscle cells, which is further
demonstrated, in the case of the scattered
muscle elements, by the occurrence of
connective tissue cells which have been

1 2 partially modified into muscle cells. Some-

: ahead times, like epithelial cells, muscle cells are
ee on held together by cement substance.

(2) which is undergoing transformation 4. Nervous tissue. The
its mule cel, Fromthe w28"7 contraction of muscle cells* is
Flemming. brought about by stimuli received

from ganglion cells, each of
which has a thread-like prolongation often of considerable length
(Fig. 15, 2). At its free end each of these processes breaks into a
tuft of branches which lie closely upon the muscle cell; sometimes
a process gives off branches on its course, and these are attached to
muscle cells. Besides these long processes, the ganglion cell may
also give origin to numerous shorter branching offshoots, which do
not pass to muscle cells.

Ganglion cells of this description are called motor: there
is another kind, the sensory (Fig. 15, 4), which are, externally,
just like the motor ones, but receive, by their long processes,
impressions from the outer world. The process may, for instance,
go to the epithelium covering the surface of the body, and branch
between its cells. (See the section on Sense Organs, p. 18).

The ganglion cells occur in groups, comprising both kinds. They
are attached to one another by some of the prolongations; those
of one cell do not as a rule, however, pass directly to another, but

 

 

* Under muscle cells, smooth and striped muscle cells and also muscle fibres are
included.
Cells and Tissues. 13

ramify over it or its processes (Fig. 15, 3). There is yet a third kind
of ganglion cell connected with neither epithelium nor muscle, but
only with other ganglion cells (Fig. 15, 1).

It may be noticed here that many gland cells, like muscle cells, only
become active when they receive a stimulus from a ganglion cell; in glands,
therefore, terminal branches of ganglion processes are present in great numbers.

 

 

 

 

 

 

 

 

Fig. 15. Various ganglion cells, ete. 1 Ganglion cell, with dendritic, but without the
longer processes. 2 Motor ganglion cell connected to a muscle cell m by a nerve fibre n.
8 Two ganglion cells connected with one another. 4 Sensory ganglion cell, with its nerve
fibre branching in the epithelium e. 5 Sensory ganglion cell g, with two long processes;
b the terminal tuft of the process. 6 Sense cells s; b the terminal 1uft of an efferent
nerve fibre; a ganglion cell below.— Orig.

The long processes of ganglion cells are called nerve
fibres, and according to their connection with muscle or with sense
cells, they are called motor or sensory: the short processes
are termed dendrites. Sometimes nerve fibres originate not in
ganglion, but in sensory, cells (Fig. 15, 6): the epithelial cells
are, in this case, usually tall, narrow cells, with a tuft or fringe of
cilia at the free end; they pass, on the inner side, into long delicate
processes, which are intimately connected with ganglion cells, for
the end breaks up into a fine anastomosis, which is closely apposed
to a ganglion cell or its processes. Such epithelial cells are called
sensory cells, and the prolongations, sensory nerve fibres.

The nerve fibres are frequently enveloped in sheaths of specially developed
connective tissue. Most of those in Vertebrates have a double sheath, a strongly
refringent fatty medulla within, and an outer neurilemma or sheath
of Schwann. Some vertebrate nerve fibres are covered with a neurilemma
only.

 

II. Organs.

Although the animal body forms a connected whole, yet in most
Metazoa a varying number of more or less independent or gans may
be distinguished, each composed of one or more of the tissues already
14 General Part.

described. The more general characteristics of these organs will now
be studied. ~

There is a very slight differentiation of organs in the lowest Metazoa, the
. Ceelentera; but this group is peculiar in many respects (see Special Part).

1. The Skin.

The skin which forms the external limit of the body consists, in
the simplest cases, of an epithelium only, the epidermis. It
frequently includes, however, a layer of connective tissue also, the
dermis. In most Metazoa the epidermis is a simple epithelium,
consisting of squamous or columnar cells, and often ciliated; in the
Vertebrata alone, it is a stratified epithelium, of which the outer
cells are horny and thus form a protective covering for those beneath :
this is represented in many other Metazoa by the cuticle (Cheetopoda,
Insecta, and others). The dermis is a layer of connective tissue of
varying thickness, and of a firm consistency, lying beneath the
epidermis; it is not generally sharply marked off from the neighbour-
ing structures, in most Vertebrates it passes gradually into the loose
sub-cutaneous connective tissue. In the lower Metazoa calcareous
deposits of different sizes and shapes are frequent in the dermis
(Echinoderms) and among the Vertebrata there are often bony plates
(scales of Fish). Muscle cells also are very common.

Glands, both unicellular and true glands, of diverse function, are
often found in the skin, such as mucous glands, stink glands, oil or
sweat glands. Various appendages, such as hairs or bristles, may
be present, but under these names are comprised structures of very
different kinds. The chetze of Chetopoda, for example, are solid
cuticular processes, arising as a secretion from certain epidermal cells ;
the sete of Arthropods are also cuticular, but they are hollow, and
contain an epidermal core. Mammalian hairs, on the other hand,
consist of horny epidermal cells.

Suckers are specially modified muscular portions of the skin, serving in
many animals as organs of adhesion. They usually stand out from the surface
in the form of small thick-walled
cups with smooth edges, the convex
side towards the skin, and the con-
cave side free. The sucker generally
works somewhat in the following
way: its edge is pressed against a
foreign object (Fig. 16, A), and by
the contraction of the muscles

2 ; 3 abundant in its walls, the space
dik cane teameen ee on between the two increases (Fig. 16,
skin, s sucker, wu foreign body. See text—  B), so that a chamber is formed
Orig. wherein the pressure of the air or

water is sub-normal, while the ex-
ternal pressure on the outer wall of the sucker holds it firmly to the object.

Suckers of this description occur in Flat-worms, Leeches, Cuttle-fish, some
Mammals, etc.. but other adhesive organs are also found. Some animals

 
IT, Organs. 1, The Skin. 2. Skeleton. 15

have areas of sticky skin by which they can adhere to other bodies (Amphibian
larvee), others can hold fast by simple adhesion,* applying a surface which is
smooth and damp, but not sticky, to the for eign object (Tree-frog); others again
can fix themselves by means of hooks, &c.

The colour of the skin depends, in many cases, upon cells containing pigment
granules, present either in the dermis or the epidermis (or in both). The
pigment varies in chemical composition. Sometimes the blood in the dermal
blood-vessels shows through the skin (cocks’ combs). The colour of the skin may,
however, depend on totally different circumstances: for instance, interference
colours* are known, which are due to the peculiar structure of the skin,
e.g., the stratification of cuticle or dermis; the well-known metallic colours are
often caused thus. The skin, or its derivatives, is sometimes white (e.g...
hair of Mammalia); this occasionally depends upon the presence of tiny air
vesicles.

Moulting is frequent in animals; the outer layer of the
epidermis, either the cuticle (Insecta, Crustacea), or the stratum
corneum (Vertebrata) becomes loosened from the rest of the skin,
and is thrown off all at once, or more rarely in pieces. Such a
moult is always accompanied by a new formation of cuticle or of
stratum corneum, which has always begun before the animal casts
the old one.

Mucous membrane is the name given to the skin-like lining of the-
cavities of the body which open directly on to the outer surface (e.g. the
digestive tract); it consists of an epithelium supported by a layer of connective:
tissue, corresponding with the epidermis and dermis of the skin.

2. Skeleton.

The protective structures found upon, or the calcifications and
ossifications present in, the skin, which have just been referred to,.
frequently attain a considerable thickness, hardness, and coherence,
and then form the supporting organ of the body, the skeleton,
under which name all the hard parts are included. The skeletal
elements of the skin, the exoskeleton, owes its origin either
to the epidermis, as, e.g., in the Lobster, where the well-developed
thick calcareous cuticle forms the supporting structure, or, as in the
Snail, whose shell is the secretion of certain epidermal cells; or to
the dermis, e.g. the numerous calcareous plates forming the shell of
the Sea-urchin, or the bony plates which compose the carapace of the
Turtle. In many animals, however, especially in the Vertebrata
there is also a firm supporting framework, the endoskeleton
which lies within the body and is quite independent of the skin: it
consists chiefly of cartilage and bone, and is often present in
addition to the exoskeleton, with some portions of which it may

be intimately connected (Tortoise).
The exoskeleton comes to have, in most cases, a protective as well as a
supporting function, often indeed, this is its principal duty, e.g., Molluscs and

 

* See Text-book of Physics.
16 General Part.

Chelonians. This is true, also, although in a more limited sense, for the
endoskeleton, which usually not only supports the body but also protects
certain of the organs, e.g., the skull and vertebral column of the Vertebrata
protecting the central nervous system.

3. Muscular System.

Muscular tissue occurs as a subordinate component of many
organs, e.g., the skin, the alimentary canal. It is, however, the
principal and essential constituent of muscles, those organs which
cause movements of the body as a whole, of individual portions of it,
or of its appendages, and which, taken together, constitute the
muscular system. In many of the lower animals which have
neither exo- nor endo-skeleton, the musculature is closely adherent
to the skin, and forms a continuous layer beneath it. In many
worms, there is such a body-wall, causing movements of the
animal by its contractions. The formation of an exoskeleton
has a great influence upon the development of the musculature,
especially when the former is divided into a number of movable
pieces (as in Crustacea, etc.) ; the continuous coat is then separated
into a number of more or less independent strands, the muscles,
extending between adjacent portions of the skeleton and causing them
to move upon one another. The muscles are still, however, connected
with the skin, of which the skeleton is indeed, in this case, only a
part. The connection ceases, where, as in the Vertebrata, an endo-
skeleton is developed, for the muscles are now attached to this, and
movements of the body are chiefly caused by movements of its
different parts.

It has already been stated that the essential part of a muscle is
muscular tissue, but this is not its only constituent, a certain amount
of connective tissue is usually present, surrounding and holding
together the muscle elements, and often forming tendons at the ends
of the organ. The tendons are thinner than the muscle proper, often
narrower, and are composed exclusively of fibrous connective tissue.
They make it possible for the contractile, thicker part of the muscle,
to be at a considerable distance from the spot at which the force is
applied. The name tendon has been used to designate not only these
connective tissue organs, but also others of a like significance, but ofa
different structure, as will be seen in the detailed account of the
Arthropoda.

In the lower Metazoa movement of the body is caused at least in part,
by the cilia of the epidermis (or of some portion of it). This is especially the
case in many minute free swimming larve (Ceelentera, Echinoderma, Chetopoda,
Mollusca), which are driven about by ciliary movements. In these forms
there is an actual locomotor apparatus consisting of cilia, which either cover the
whole body uniformly, or are restricted to definite lines or rings. In the adult,
on the other hand, the ciliated cells are but seldom of locomotor importance
(Platyhelminths, Rotifers).
\
IT. Organs. 4. Nervous System. 17

4. Nervous System.

Ganglion cells and nerve-fibres are usually aggregated, the
groups of ganglion cells are known as ganglia, the bundles of
nerve-fibres as nerves. It generally happens that most of the
ganglia are connected to form a central nervous system,
from which spring
the nerves supplying
muscles, sense organs,
and so on, all these
nerves are included
in the peripheral
nervous system;
nerve fibres are, of
course, present also
in the central nervous
system, and especially
in the strands con-
necting the ganglia.
Similarly the gangha
do not occur exclu-

sively in the central Sacee
nervous system, al- ,

though they are con- ma
nected with it, even

when situated in

remote parts of the

body. "(I
Nerves are called

motor or sensory, =

consisting respec-

tively of motor or

eee faba oe Fig. 17. Diagram of a nervous system. cg—cg" ganglia

are, however, mixed, of the central nervous system, 1—1’ and t—t” longitudinal

and contain both kinds and transverse connective fibres. sa sensory cells. s nerve

fibres, springing from them. g peripheral ganglion, each
of fibres. Nerves of whose cells gives off two fibres, one branching in the

usually branch during epidermis ep, the others going to cg. s sensory fibre,
: mee which arises in cells lying in cg, and branches in ep’.
their course, dividing b motor fibre, which goes to a muscle m.—Orig.

gradually into thin- -

ner and thinner strands, consisting of fewer and fewer fibres.
The central nervous system is, as it were, the “ Exchange” of the

body; by the motor nerves it transmits impulses to the muscular

elements and thus controls their movements; by the sensory nerves

it receives impressions sent from the different sense organs.

 

a

Mm

:

Lf
=

oye
a
<A

=e

I

SSA

Sas

SS

——
SS

 

* Sensory nerves are further classified as nerves of touch, taste, smell, hearing, or
sight.

Cc
18 General Part.

The sympathetic nervous system, present in many animals, consists
of ‘a series of small ganglia and nerve trunks, from which nerves are given off
to the digestive tract (in the Vertebrata to other viscera also and to the vascular
system). The sympathetic system is comparatively independent of the central
nervous system, although it is connected with it; the muscle cells of an organ
supplied by it, contract without impulse from the central system, they are
involuntary muscles, and receive the necessary stimulus from the sympathetic
ganglion cells.

5. Sense Organs.

An animal receives impressions from the outer world by
means of the sense organs, which are usually modified tracts
of epidermis. They are always closely connected with the nervous
system either by nerve fibres springing from ganglion cells
(within or external to the central nervous system) and ramifying
amongst the cells of the sense organ (Fig. 17, ep, and ep’); or by
fibres originating. in the sense cells of such an organ (p. 17) and
passing to the ganglia (Fig. 17, sa).

Sense organs may be classified as simple or complex; to the former
class the organs of touch, of smell, and of taste are usually referred,
since they are of a simpler structure than the organs of hearing and sight,
which are often very complicated.

The sense of touch contrasts with the other senses in that it
is distributed over the whole, or the greater part, of the surface of
the body; the entire skin, especially the epidermis, is, therefore, a
sense organ. In some cases, e.g., in the Vertebrata, nerve fibres pass
to these portions of the skin and ramify amongst the epidermal cells ;
in others, e.g., amongst Annelida and Mollusca, special tactile cells,
each furnished at its free surface with one or more hair-like
processes,* and continued at the other end into a nerve fibre,t occur
amongst the ordinary epidermal cells. In some animals the skin
is furnished with warty or filamentous processes, provided with
numerous tactile cells, or with a rich nerve supply, and, therefore,
important as tactile organs.

Amongst Vertebrates, certain tactile nerve fibres, as already mentioned,
innervate the epidermis, but others terminate in the dermis. The latter are

sometimes enveloped in concentric laminz of connective tissue, pacinian bodies,
or the nerve endings may be of a different form.

Olfactory Organs are acted upon by gaseous matters in a
peculiar way; they can be ascribed with perfect certainty to only a
small proportion of forms, viz., existing terrestrial animals. They are
formed of epithelium, derived from the epidermis, in which there are
tall, thin, sensory cells, each with a tuft or tufts of sensory hairs at

 

* Sometimes these tactile, and other such, sensory cells are very like ciliate
epithelium ; the hairs are, however, not actively, but merely passively movable.

+ Sometimes only a narrow external part of the sense cell is situated between the
other epidermal cells, whilst the thicker part, with the nucleus, lies in the subjacent
connective tissue. ‘

t{ These may also occur internally—e.g. in the mesentery of the cat.
IT. Organs. 5. Sense Oryans. 19

the tip, and continued at the other end into a nerve fibre, which
passes to the front part of the brain. Amongst Insects, which have
been proved by many experiments to possess a very acute sense of
smell, the olfactory organs are situated upon the antenne. These are
provided with delicate hairs, which, like arthropod hairs in general,
are evaginations of the cuticle; they are very thin walled, generally
seated in small depressions, and into each, a thread-like process
extends from one or more underlying sense cells (Fig. 18).
Whilst these insectan structures are
probably true olfactory organs, there are ES pogh
numerous contrivances to which, even in . |
this book, the same name is applied, but
with doubtful right. This is the case with
all the “olfactory organs” of aquatic
animals, which seldom or never come in
contact with air. The olfactory pits of
Fish, which, from their position, &c., are
homologous* with the olfactory organs of
higher Vertebrates, can, for instance, hardly
be really olfactory. This is also true of
the delicate “olfactory hairs” present on
the antennules of many Crustacea ; like the 8% ep
above-mentioned structures in Fish they are Fig. 18. Section through a small
undoubtedly sense organs, but their special piece of the antenna of an Insect,
function is unknown: they are. perhaps, diagrammatic; c cuticle; g pit, with
organs of taste. ig ‘olfactory hair, arising avon the
in part of the cuticle ; ep epidermis,
Gustatory Organs are affected sz sense-cell.—Orig.

only by substances which occur in
a liquid form. In the Vertebrata they are represented by the
so-called taste-buds of the tongue and the walls of the mouth,
specially modified tracts of the buccal epithelium, consisting of
groups of cells, amongst which are long thin cells with a delicate
point projecting from the free end; these are, probably, the true
organs of taste. The buds are supplied with nerve fibres which
branch between the cells. In Fish, taste-buds may occur on the
external surface of the body; similar structures are found also in
many Chetopods and Molluscs (e.g., Gastropods), not only in the
buccal cavity but also externally upon the anterior end of the body.
Of a different type are the organs which appear to bring about
sensations of taste in Insects; they are short hairs placed on the
underlip, jaws, etc., and are in all essential respects like the olfactory
hairs just mentioned.

Yet other structures are included under the simple sense organs, but of their
special function nothing is definitely known. Such are the lateral line organs of

Fish (See Pisces) and Amphibia, and the similar structures in Annelids and
Molluscs.

Auditory Organs always occur as vesicles filled with fluid.
The vesicles (otocysts) are formed by epidermic invaginations, and

 

 

ie .. ** See conclusions under Section V.

c 2
20 General Part.

either remain as sacs, opening freely on the surface: or more often
are entirely cut off from the epidermis, and are therefore closed
sacs and frequently lie deep
in the body. The auditory
capsules are usually almost
spherical, but in the Verte-
brata they are more compli-
cated, as will be seen later.
The wall into which the nerve
fibres (auditory nerve) pass,
consists of a simple epi-
thelium, whose cells—all, or

only some—are provided with

5 fine hair-like processes pro-
Fig. 19. Auditory capsule of a Gastropod.

Ot otolith, N auditory nerve.—After Claus. jecting into the liquid. These

hairs are set in vibration by
sound waves, and the sensations thus caused are conducted by the
auditory nerve to the central nervous system. One or more hard
calcareous corpuscles, the otoliths, are usually suspended in
the liquid. Amongst the higher Vertebrates, various kinds of
accessory apparatus function as resonators, etc.

The auditory organ of Arthropods differs essentially from the usual type.
In Crustacea this sense is closely connected with specially developed hairs, which
are free on the surface of the body, or contained in cup-shaped invaginations. In
Insects again, there is quite a different arrangement, as will be seen in the Special
Part. ‘

It has been proved, experimentally, that the auditory capsules of many
animals have yet another function than that of bringing about impressions
of sound. They (or in Vertebrata, their semicircular canals) are of significance in
the maintenance of the normal equilibrium in an animal. If they are destroyed,
movement becomes unsteady, the animal falls on one side, etc.* In what
manner, however, the auditory organs exercise this control is not yet understood.

Optic Organs of most animals are, like the preceding sense
organs, specially developed parts of the epithelium. In its simplest
form (Fig. 20, 1,) the organ of sight is a little pigmented patch of the
epidermis, innervated by a nerve, the optic nerve (some Meduse, a
few Lamellibranchs). In other cases (Fig. 20, 2) the pigmented
epidermis forms a small open pit (some Gastropoda, Ccelentera) ; this
arrangement may be complicated by having the cuticle, which covers
the skin in many lower animals, thickened over the cells forming the
depression, so that a lens, a refractile body, is formed (Fig. 20, 3,
certain Ccoelentera). Or the cavity is deepened to form a sac with a
small external opening, which may contain a gelatinous secretion of
the epithelium (Fig. 20, 4, some Gastropods). Again, by the contrac-
tion of the aperture, and by the loss of all connection with the skin,

  

 

* In some animals, these occurrences only take place when eyes as well as ears are
destroyed, whilst the destruction of eyes alone, or of otocyst alone, has no effect.
IT, Organs. 5. Sense Organs. 21

the optic organ may come to be a closed capsule lying beneath it.
The side of the capsule away from the surface is thickened and
pigmented, and forms an organ for the perception of light, the
retina,* whilst the opposite side is thin and transparent, as is also
the skin above it (the cornea) ; the cavity of the visual organ then
contains a jelly-like mass, the vitreous-body (Fig. 2U, 5, most
Gastropods, Cheetopods). In others again, the lens, secreted by the

 

 

 

 

 

Fig. 20. Different forms of optic organ, diagrammatic. 1 optic nerve, + retina,
ep epidermis, g vitreous body, 1 lens.—Orig.

front part of the capsule, floats in the vitreous humour, and may be
regarded as a specially modified part of that body (Fig. 20, 6, some
Cheetopods and Gastropods). With the development of this lens the
optic capsule has become a true eye; and as in the human eye a real
image may be formed upon the retina, whilst the simpler forms can at
most merely differentiate between light and darkness.

In such eyes as are described above, the retina consists partly of pigmented
cells, which appear to be the true perceptive cells, and partly of colour-
less supporting cells, which apparently secrete the vitreous body. The
former frequently bear, on the ends towards the vitreous body, unpigmented,
transparent rods,

The optic organs of Arthropods exhibit a peculiar structure.
In its simplest form (Fig. 21, 4), peculiar to certain insect-larve, the
arthropod eye appears as an invaginate area of the skin, passing
directly into the general epidermis: so far, therefore, it ‘re-
sembles that represented in Fig. 20,2. The retinal or perceptive
cells are, however, always distinguished by being removed from the
surface and covered by neighbouring epidermal cells, the outer portions

 

* This name is used to denote that part of the optic organ which is actually
sensitive to light.
22 General Part.

of which are transparent, whilst they are strongly pigmented within,
as is the case also with the retinal cells, their outer rod-like ends
excepted. The cuticle covering the eye is thickened like a lens. The
next stage is represented by those eyes, in which the retinal cells have
lost all direct connection with the skin (Fig. 21, B, ocelli of Insects,
Insect-larvee and Spiders). Below the lens there is, therefore, a layer of
transparent cells, continuous with the adjacent epidermal cells, and
corresponding with those which in the simple type are pushed in
above the retina. The compound eye (Fig. 21, C, D), occurring
in most Insecta and Crustacea, consists of a large number (as many as
several thousands) of simple eyes, closely packed together, and each

 

Fig. 21. Different kinds of Arthropod eyes, diagrammatic. A, B ocelli, C, D
ommatidia from a compound eye. 7 optic nerve, r retina, s rod of retinal cell, g vitreous
body, k crystalline cone, J lens, c limit of the general cuticle, ep epidermal cells.—Orig.

possessing’ a structure similar to that just described. The compound
eye is, however, peculiar, in that the eye-elements (ommatidia) of
which it consists are very narrow and elongate, and each one consists
of only a few retinal (6—8) and vitreous cells. As in the ocellus,
each retinal cell ends above or within in a rod-like transparent piece ;
there is frequently, also, in each vitreous cell, a peculiar refractile
body, which is closely united with its fellows of the neighbouring
cells to form the so-called crystalline cone (D,k).

Essentially different from the forms of eye already described,
where the retina invariably represents a specially developed area of
the epidermis, is the visual organ of Vertebrata, whose retina is
not epidermic, but a specially modified portion of the brain. These
eyes will be described in the section Vertebrata.

Besides the types of optic organ mentioned here, there are still others found
in certain animals, but they are simply specialised portions of the epidermis
(Platyhelminths, Lamellibranchs, etc.).

It should be noticed here, that not a few animals which have no
special visual organs, are, nevertheless, sensitive to light; this is true,
IT, Organs. 5. Sense Organs. 6. Alimentary Canal. 23

for example, of Earthworms, which withdraw with the greatest
rapidity into their holes if a strong light is thrown upon their anterior
ends, where the cerebral ganglion is situated.

6. Alimentary Canal.

Like the Amoeba, Metazoan cells undergo constant metabolic
change with consequent loss of material, and this is a necessary
condition for the continuance of the vital processes. In order to
make good this loss, they must feed. Unlike the Amceba, however,
the individual cells are unable to obtain food direct from the
environment: there must be some special arrangements for nutrition:
hence the development of an alimentary canal. Food is taken
into this canal and there digested, t.e., reduced to a fluid state, so
that it can be absorbed. by the wall of the digestive tract, and carried
to the various tissues of the body. Those portions which are not
digested and absorbed pass out again (excreta).

Whilst in most animals, secretions, by means of which the food is digested,
are poured into the alimentary canal, there is another arrangement amongst
Celentera and Sponges. No such digestive juices are found here, but the food
comes in contact with epithelial cells, and is digested and absorbed directly by
them. Smaller organisms, e.g., Diatoms, may even be entirely engulfed by the
epithelial cells. This also frequently occurs among Flat-worms.

In its simplest form the digestive tract is a sac or a canal, which
communicates with the exterior by a single aperture only. This
opening then serves both as an entrance or mouth, and also as an exit
for the undigested portions of the food (Ccelentera, Flat-worms).

In most animals, however, the digestive tract has t wo openings, a
mouth and an anus. It is then usually a long tube, with the
mouth at one end, and the anus at the other. It is frequently
divided into several regions, with different functions. In the simplest
cases, only three regions can be distinguished, the fore-gut
(stomodeeum), which is often very muscular, and serves in different
ways for the ingestion of food: the mid-gut (mesenteron), which
is usually long, and in which digestion and absorption go on; and
the hind-gut (proctodeum), which serves as an excurrent canal,
and as a reservoir for undigested materials (Nematodes, Annelids).
In other cases, the fore-gut is again divided into a large buccal
cavity, often provided with organs for the prehension and retention
of prey, or for the comminution of food (teeth); and a narrow
esophagus. The mid-gut is frequently, as in Vertebrata,
divided into a capacious anterior portion, the stomach, and a
long narrow hinder part, the true gut or intestine (small intestine
of Vertebrata). The stomach is digestive, its walls are beset with
glands, which secrete a digestive fluid; whilst the intestine is
absorptive, though digestion goes on here also. More rarely the
hind-gut is also divided into several sections. Occasionally some
24 General Part.

portion of the canal is modified to form a gizzard for the
trituration ot food. In some animals, e.g., the higher Crustacea, the
hind part of the cesophagus widens out, becomes muscular, and is
furnished within with hard denticles; in other cases, as in Birds,
it is the posterior region of the stomach.

Very frequently diverticula, blind sacs of various kinds,
are found at different parts of the alimentary canal. Their function
varies: those belonging to the fore-gut serve only as provisional
reservoirs for the food which has just been taken in (crop in Birds
and Insects); those of other regions usually serve to enlarge
the canal, or to increase the digestive and absorptive surface
(diverticula of Leeches, ceca of Mammalia), but this may be effected
in other ways—by the elongation of the intestine, by delicate
foldings of the intestinal wall, or by some similar contrivance
(Vertebrata).

The digestive fluids are secreted partly by the epithelium of the
digestive tract; partly by minute glands imbedded in the wall,
especially of the stomach and intestine; and partly also by larger
glands, lying outside the alimentary canal, and communicating with it
only by means of their ducts. In many lower animals the glandular
activity is associated with the epithelium of the digestive tract
alone, whilst among more highly organised forms, the Vertebrata, for
example, it may be essentially or exclusively possessed by special
glands. The larger glands lying without the canal are variously
named, according to the region into which their ducts open ; those for
instance, which open into\the buccal cavity, and which are often of
little direct use in digestion, serving only to moisten the food and to
facilitate its onward course, are called salivary glands; whilst
those which open into the intestine are usually termed liver. The
secretions of these glands differ in different animals; the effect of the
“liver ” secretion for example, is by no means always the same.

As to its minute structure: in its simplest form, the alimentary
canal consists only of a layer of epithelium, but connective tissue and
muscle may come to surround this, so that in a more highly
specialised gut, the wall is composed of several layers: within, a
layer of epithelium coated by a connective tissue sheath, often
including numerous little glands, the two being closely adherent, and
constituting the mucous membrane ; outside this there is a sheath of
muscle cells (the muscular coat) whose contractions are of great
importance for the passage of nutriment through the canal.

In only a few Metazoa is the alimentary canal wanting. In such
cases, either there is a functional mouth to allow of the entrance of
food into the soft tissues of the body, and these perform the digestion:
or, there is no mouth, and the food passes through the skin of the
animal by endosmosis. This, however, only occurs in parasitic
animals, especially in such as live in the gut of other animals, where
IT. Organs. 3. Alimentary Canal. 7. Vascular System. 26

they are always surrounded by food in a fluid or semi-fluid condition
(Cestoda, Acanthocephala).

Unlike plants, animals cannot feed upon inorganic substances. In
addition to water, their food consists of other organisms, animals and
plants ; or of substances derived from them.

7. Vascular System.

In many of the lower animals, the digested food stuffs, after
traversing the walls of the alimentary canal, make their way
through the various tissues by a kind of endosmosis.* In most, the
arrangement is, however, somewhat more complicated; there is a
special system of branching canals which conveys the nutritive
material derived from the gut all over the body, to be absorbed
in part by the tissues, after having undergone certain changes
within the vessels. This arrangement of tubes is termed the
vascular system.

The vascular network is sometimes very complete, the ultimate
branches ramifying throughout almost all the organs and tissues:
usually, epithelia alone are non-vascular, deriving their nutriment
from the adjacent tissues. The vascular system may, on the other
hand, consist of relatively few definite channels which communicate
directly with the spaces of the body. In a well-developed
vascular system, some of the vessels are distinguished by their
greater width, and from these main trunks, others are given off
to supply the various regions of the body. These latter, again,
give off branches dividing into smaller and smaller twigs, and
finally terminating in a network of the finest vessels, traversing
the organs. The fluid flows from the larger into the smaller
trunks, and thence into the smallest of all, from which it is
conducted back into the large trunks by another set of vessels
which are also in communication with these minute ones. In
most cases there is, therefore, a circulation of the vascular
fluid or blood plasma, which is really to be regarded as
the digested food, although it must be noticed that it has
also received certain waste products of metabolism from the various
tissues. It is usually clear and colourless, more rarely coloured red
or green. Floating in it are numerous free cells, the blood
corpuscles, which are usually amceboid and colourless ;t less
frequently some of the corpuscles are of definite form (unable to
throw out pseudopodia), and red incolour. These red corpuscles,
which have the form of circular or oval discs, occur especially

 

*In many the distribution of the products of digestion is facilitated by the
branching of the alimentary canal, which is furnished with numerous diverticula
of considerable extent (e.g., Meduse, Liver-flukes).

+ Their protoplasm may, however, contain coloured granules.
26 General Part.

in the Vertebrata, where they are far more numerous than
the white ones. They are found also in many of the lower animals
(e.g., certain Chatopods and Molluscs), but in these are less
regular in form. The plasma and corpuscles together constitute
the blood, the colour of which is usually dependent upon the colour
of the fluid portion, but in the Vertebrata upon that of the
corpuscles.

The blood corpuscles usually originate in eallulae connective tissue, which
may constitute specialised organs, the lymph glands. They are therefore
connective tissue cells which have broken away from their point of origin and
entered the blood stream.

Since it is of importance that the blood should be in constant
movement, hearts are formed, i.e., the vascular walls become very
muscular in certain definite regions and can therefore pulsate,
or contract rhythmically, and thus drive the blood along.
There may be several hearts in the same animal: usually, however,
there is only one: or if there are more, one is characterised by its size
and strength, and is known as the heart; it is always in direct
connection with some of the largest vessels of the body, forming, as it
were, the centre of the whole system. The openings into the heart
are frequently guarded by peculiar folds, the valves, whose function
it is to regulate the blood stream by permitting a flow in one direction
only, blocking up the way if the blood tends to stream in the opposite
direction (see Fig. 22,1). Very often the heart. consists of several
independent divisions, which are
frequently regarded as so many
aggregated hearts. The blood then
usually flows first into a thin walled
chamber, the auricle, and from
this passes into a thicker walled,
more muscular portion, the ven -
tricle, which is, apparently, the more
important of the two. Sometimes
it happens that several auricles open
into the ventricle (many Molluscs).
The vessels in which the blood flows
towards the heart are termed veins,
those in which it flows in the opposite
direction, arteries. The finest

Fig. 22. 1 Diagram of a simple vessels of all, which form a network
heart ; 2 of one consisting of an auricle uniting the ultimate branches of
and ventricle. a ventricle, v auricle, ‘

k valve.—Orig. the arteries and veins, are termed

capillaries. They :are often
altogether wanting, when they are to some extent replaced by
portions of the body cavity, with which the veins and arteries then
communicate directly, the blood flowing from the arteries into the
sinuses and thence into the veins.

 
IT. Organs. 7. Vascular System. 8. Respiratory Organs. 27

The minute structure of the vessels varies considerably ; the lining consists of
a single layer of flattened cells, and these constitute the entire wall of the
capillaries; in other vessels the endothelial lining is usually surrounded by
connective tissue, smooth muscle fibres, etc., so that the walls of the large vessels
may be fairly thick.

For the lymphatic vessels peculiar to the Vertebrata, see that group.

8. Respiratory Organs.

The cells of the metazoan body, like the Amceba, must have
oxygen in order to live: it must therefore be continually taken into
the body, and all the cells of the different organs must be supplied.
Further, the waste-products, resulting from the constant combustion
going on in the cells, must be got rid of: one of these waste-products
is carbon-dioxide, a combination of carbon and oxygen (CO,)
whose excretion alternates regularly with the absorption of oxygen,
whilst other waste matters are got rid of in other ways (see excretory
organs). The taking in of oxygen, with the giving out of carbon-
dioxide, is known as respiration, and the organs performing this
function are called respiratory organs. Some animals (air-
breathing) obtain oxygen from atmospheric air, of which it forms
approximately one-fifth. Others, on the other hand, make use of the
free (dissolved) oxygen which occurs in all natural waters,

The vascular system, when present, plays an important part in
connection with the introduction of oxygen and the removal of
carbon-dioxide. The blood in the vessels of the skin absorbs the
former, carries it through the body, giving it up on the way ; receives
the latter and returns with 1t to the skin, where it is expired and the
oxygen inspired again (cutaneous respiration). In many animals, with
no respiratory organs, the digestive tract performs the respiratory
function. Air, or water containing air, is always swallowed with the
food, and the oxygen is absorbed during its passage through the
digestive organs (intestinal respiration). Many of the lower animals,
chiefly aquatic, but a few terrestrial (v.g., Earthworms), are destitute
of special breathing apparatus, and respiration is effected by
endosmosis, which goes on over the whole surface of the body.
These forms are almost always thin-skinned, 7.¢., they are without a
hard, thick cuticle, or any other covering difficult for oxygen to
penetrate, and are almost invariably of small size—a small body
has, of course, a relatively larger surface than a large body of the
same shape.

Most animals are, however, provided with special organs of
respiration. The universally observed principle is that water con-
taining air, or atmospheric air itself, is brought into relation with a
large thin-skinned surface, through which oxygen is taken in in large
quantities, whilst carbon-dioxide is given off; generally a capillary
net-work is distributed immediately beneath this skin.

 
28 General Part.

Those animals which are specially adapted for obtaining the
oxygen dissolved in water, usually breathe by means of gills, thin-
skinned appendages with a relatively large surface, which either
project freely from the body, or are situated in a cavity which
is in direct communication with the exterior (branchial chamber).
An increase of surface may be obtained by simple extension,
by folding or branching of the gill. When the gills are enclosed
in a cavity, there is generally some special contrivance for causing
a stream of water to pass continuously, or at least frequently,
through it (many Crustacea, e.g., the Lobster, and Pisces); and
thus it is ensured that fresh currents of water, and therefore
fresh oxygen should constantly come in contact with the gills.

Amongst air-breathing animals, the respiratory organs are, as
a rule, thin-skinned, saccular ingrowths, the lungs, com-
municating with the exterior by a larger or smaller aperture. The
respiratory surface is frequently increased by the presence of small
outgrowths, which may themselves be sacculated, until the lung
becomes much branched, and its inner surface is extraordinarily
enlarged (especially in Vertebrata). In the wall of the sac there
is usually, just as in the gills, a delicate vascular network.

A peculiar kind of lung, the system of trachew, is present in many
Arthropods, and will be described in detail for the Insects.

Just as it is necessary for the gills to come constantly in contact
with fresh supplies of water, so the air in air-breathing organs must
be continually renewed. If the air remained stationary, the
lung would cease to act as a respiratory organ, for the oxygen
would be gradually consumed, and the air loaded with carbon
dioxide. The expulsion of air always takes place by the contraction
of the organ of respiration: the inception, as a rule, by its expanding
again, so that the air remaining is rarified, and the outer air rushes in
to equalise the pressure. The special contrivances differ to a very
great extent.

The structure of the respiratory apparatus has a very great influence
upon the vascular system, whose disposition is largely deter-
mined by these organs. The following circumstance is of special
significance: it is advantageous for the organism to have the blood,
on leaving the respiratory apparatus for the other organs, as rich in
oxygen and as free from carbon-dioxide as possible, whilst, on the
other hand, it is important that blood flowing towards the respiratory
organ should take along with it as much carbon-dioxide as possible,
in order to complete the gaseous exchange. This is always effected
by the accumulation of the so-called venous blood, which has flowed
through the organs and is rich in carbon-dioxide, in a large common
reservoir, whence it is passed on to the gills or lungs. After the
carbon-dioxide has been exchanged for oxygen, the blood, which is
now distinguished as arterial, goes intoa second large blood
LT. Organs. 8. Respiratory Organs. 29

reservoir, whence it flows all over the body. This is the usual
arrangement in known animals with a respiratory apparatus and a
complete vascular system, but great variations occur within these
limits. Among many Invertebrates (Mollusca, Crustacea), the arterial
blood spaces are represented by the heart, which, as it receives blood
from the gills, is an arterial heart, and drives it all over
the body; the impure blood is carried into a large non-contractile
reservoir, a venous blood sinus, whence again it returns to the gills.

 

 

Fig 23. Diagram illustrating the usual relations of the respiratory organs a to the
vascular system. Arterial blood light, venous blood dark. See text.—Orig.

In Pisces it is entirely different: here the heart is represented by a
venous reservoir, which receives blood from the body and sends it to
the gills; it is, therefore,a venous heart. Blood goes from the
gills to the aorta, a large non-pulsatile vessel corresponding to the
arterial reservoir, and passes thence to the body. In Mammalia and
Aves, again, there is another arrangement, for, functionally, t wo
hearts are present, of which one, the right side of the organ (right
auricle and right ventricle) represents the venous reservoir, and
receives blood from the body and sends it to the lungs; whilst the
other (left auricle and left ventricle) replaces the arterial reservoir,
receives blood from the respiratory apparatus and distributes it all
over the organism.

Tt must be noticed here that the formation of special respiratory
organs is not accompanied by cessation of cutaneous and intestinal
respiration. These are, it is true, of very slight significance in many
animals, e.g., Mammalia; in others, however, they play an important
part, especially cutaneous respiration.

A red substance, hemoglobin, present in the coloured corpuscles of Vertebrates,
is of great respiratory importance, for most of the oxygen absorbed is not simply
dissolved in the blood-plasma, but enters into a loose chemical combination with
the hemoglobin, from which it is easily separated again, and is seized upon by
the tissues as the blood travels through the capillaries. When the hemoglobin
is combined with oxygen, the blood is of a bright red colour, and is called arterial

blood; when the oxygen has been given up, the blood looks dark red, and is
known as venous blood. The same, or a similar, substance is found in the red
30 General Part.

blood-corpuscles of lower animals, and is present in the red blood-plasma of
Chetopods and others. In the light-blue blood of Cephalopods, there is an
allied substance, hemocyanin, with the same function as hemoglobin, whilst
the same, or a similar, pigment also occurs in the blood of other Molluscs
and in many Arthropods. F

The constant oxidation (combustion) in the cell not only liberates

the energy manifested in the vital processes (protoplasmic movements,
muscle contractions, the peculiar behaviour of nerve-cells and
fibres), but also results in the production of heat. This heat is
dissipated rapidly from the surface of the body by radiation, and
in other ways, so that the temperature is but little higher in most
animals than that of the surrounding medium. ‘The production
of heat is of paramount importance only in the so-called warm-
blooded Vertebrates (Aves and Mammalia), and here contrivances for
its better retention are present, so that the body is kept at a constant,
tolerably high temperature, which may be very different from that of
the environment. The body requires, moreover, a certain temperature
of its own (differing in different animals), in order that its vital
processes can be normally carried on.
_ Sound-producing Organs.—Many animals are able to produce sounds
of different kinds. This faculty is mentioned here, not because it is related
to the special respiratory process, but because the sound-producing organs of
air-breathing animals (which are specially endowed with this power), are usually
connected with the respiratory apparatus. Thin lamine or folds of skin
(vocal cords), are often present at the entrance of the air passages, and
can be set in vibration by the expired air. Not only is the voice of most
Vertebrates produced in this way, but also many of the sounds made by Insects.
The utterance of sound may, however, be wholly independent of the respiratory
organs. Certain shrill and rattling noises in Insects, Crustaceans, Fish, etc., are
caused by hard surfaces being rubbed against one another. The buzzing sounds
of Bees and other flying Insects are produced by movements of the wings. These
various sounds serve partly as a means of communication with individuals of the
same species, partly to terrify enemies.

Phosphorescent Organs.—Luminosity which is met with in many animals,
especially among the Invertebrates, is closely connected with the respiratory
process. The production of light is usually confined to certain cells, in
whose protoplasm a fatty substance is present: oxygen unites with this
substance by a kind of combustion, producing light, but not necessarily heat.
Very many animals of different groups exhibit this phenomenon (though of
course the great majority are non-luminous), such as Protozoa, Ceelenterates,
Echinoderms, Chetopods, Crustaceans, Insects, Lamellibranchs, Cephalopods,
Ascidians, Fish. This luminosity has no connection with that exhibited by dead
animals, e.g., Pisces, which is caused by certain Bacteria: leaving it a question
whether the light emanates from the decomposing tissues or from the
Bacteria themselves.

9. Excretory and Urinary Organs.

By the chemical processes in the cell, certain other matters, besides
carbon-dioxide, are formed, which cannot be further employed by the
organism; the most important are the nitrogenous waste products,
urea and uric acid. For their removal, special glandular organs, the
IT. Organs. 9,10. Ewcretory, Urinary, and Reproductive Organs. 31

urinary or excretory organs (kidneys), are present in most
animals. They are usually tubular or sac-shaped glands opening on
to the surface of the body or into the hinder part of the alimentary
canal. The secretion (the urine) is either entirely liquid or it contains
hard, granular, or crystalline concretions, Sometimes a vesicle (a
urinary bladder) is formed, which serves as a reservoir for urine; it
may either be a widened region of the canal of a single gland, or of
an excurrent canal common to several. In many animals, however,
are other organs also excretory in function; amongst some
of the Cheetopoda, the cells of a certain part of the alimentary canal
secrete hard concretions,* which are, undoubtedly, urea; such occur
algo in the hind gut of the Rotifers, and in some of the liver-cells of
the Gastropoda; also in the epithelium lining the body-cayity of
certain Cheetopods, and of Sharks, urea is formed, and is eliminated
in different ways.

The waste products are, however, not always removed from the
body; in some, probably in many, cases, they are stored up in cells
which have no connection with the exterior. This occurs, ¢.g., in
certain Fly-larve where a mass of cells containing excretory deposits
surrounds the heart; in a Slug, whose true kidney is degenerate, cells
containing concretions of uric acid are scattered throughout the body
(See also Tunicata.)

The pigments so abundant in most animals, may also, in part, represent waste
products, which have accumulated in cells in the way just mentioned. In other
cases large masses of pigment are regularly removed from the body: the pig.
ment present in the cuticle, particularly in the hair and feathers,t is got rid of
by ecdysis in many animals, by the shedding of hair in Mammals, by moulting
in Birds.

10. Reproduction and Reproductive Organs.

Reproduction, the formation of new individuals, occurs in the
Animal Kingdom in two quite different ways, sexually and
asexually. Asexual reproduction will be first considered in its
two forms of fission and gemmation.

In fission, a longitudinal or transverse furrow appears on the
individual concerned, and gradually deepens, until finally, the
organism divides into two approximately equal pieces, which grow
whilst the process is going on, or after it is complete, until each has
attained the size of the parent. Less frequently division occurs
without the preceding constriction, the animal breaking suddenly into
two pieces. Gemmation differs from fission in that only a small
part of the body of the original individual develops (by rapid growth)
into a new animal, so that it is possible to distinguish between the

 

* Small bodies lying in the protoplasm.

+ The pigment present in the epidermis and hair of Mammalia is, at any rate for
the most part, not formed in situ, but is brought there by wandering cells which
migrate into the epidermis from the subjacent connective tissue.
382 General Part.

parent and bud; in fission, the two individuals are exactly
alike. These methods of reproduction are, however, not sharply
defined, so that it is often quite impossible to say whether fission or
budding has taken place. In the course of the special part, various
instances of asexual reproduction will be met with, especially in
Coelentera, Platyhelminths, Chetopoda, and more rarely in
Echinoderms, in addition to the Protozoa.

Often in gemmation or fission the new individual does not separate
completely from the other, but remains in more or less intimate
connection with it. In this case, if division is repeated, the result is a
colony or stock consisting of a varying number of animals,
produced by asexual reproduction from one original individual. The
members of the colony have lost their independence to an extent
corresponding with the closeness of their connection with one another
(see special part). Stocks or colonies occur especially in Corals,
Hydroids, Tape-worms, Polyzoa, and Tunicates.

Regeneration.—Nearly akin to asexual reproduction is the power of
replacing parts of the body which have been lost by some accident, by new
formations resulting from growth of the tissue nearest to the wound: the edges
of the epidermis form new epidermis; the connective tissue, new connective
tissue, and so on. Different animals display this faculty in very different degrees.
In Mammalia, for instance, it hardly appears at all; they can, indeed, repair
injured epidermis and the like, but the loss of larger portions of the organism
(e.g., tail, limbs) is not made good. It is more evident in certain lower Verte-
brates, e.g., Lizards, where the tail may be replaced, or in Newts, which can not
only form a new tail, but also new limbs. Amongst Invertebrates, even in so
complex an organism as the Earthworm, large tracts of the body can be
regenerated; indeed, in some animals, the power of repair is so great that,
when cut into two or more parts, they grow out into as many new animals;
the best known example of this is the Fresh-water Polyp (Hydra).

Whilst asexual reproduction occurs in some animals and is
wanting in others, all Metazoa exhibit sexual reproduction, which
consists essentially in the development of a single cell, after
liberation from the parent, into a new individual. Every cell in
the Metazoan body has not this capacity, but only certain peculiar
ones called ova. As a rule, the ovum cannot develop by itself
into a new individual; it must first be fertilised, 7.e., it must
unite with another cell, usually of a smaller size, and always with
special properties, a spermatozoon.

The ovum is generally rounded, often spherical. Like other
cells it consists of protoplasm with a nucleus, the germinal
vesicle, which often encloses a large nucleolus (or several), the
germinal spot. The ovum is often surrounded with a covering
of varying thickness, the vitelline membrane, in which may
be one or more openings for the entrance of the spermatozoon. In the
protoplasm, there are usually numerous fatty or albuminous particles,
the yolk granules, spherules, or discs, which are all called yolk
granules, or in contrast to the protoplasm in which they lie,

the deutoplasm.
IT, Organs. 10. Reproduction and Reproductive Organs. 33

Compared with other cells the ovum is almost always large: in
many cases, ¢.g., the Mammalia, it is, however, microscopically small ;
but in others where there is a large quantity of deutoplasm, it attains

Fig. 25. Diagram
of an ovum, with
many yolk-spherules.
d protoplasm. b, with
the nucleus, c, chiefly
accumulated at one
pole. — After Hert-
wig.

 

Fig. 24. Human ovum.
a vitelline membrane, }b
protoplasm, c nucleus.—
After Kélliker.

 

a colossal size (Squalide, Aves). In this case it frequently happens
that most of the protoplasm, with the nucleus, accumulates at one
pole, whilst the chief mass of the egg consists of yolk held together
by the rest: or the protoplasm forms a thin layer over the whole
surface, whilst the inside consists principally of deutoplasm (Insecta),

The spermatozoon is, at first, a single small cell consisting of
protoplasm with a nucleus, and it may remain in this condition
(Fig. 26, 1); but

as a rule, when 4 h
mature, it is not OQ* S
so simple: very : Ah h 5

frequently it con-

sists of a thickened ;

part, the head, and SS
a long, thin, whip-
like tail, by the
lashing of which
it moves actively
along. The head
consists of the mo-
dified nucleus; the
protoplasm merely

forms the tail,

which may be re- Fig. 26. Spermatozoa of different animals, 1 Crustacean
‘i (Thysanopus), 2 Crab, 3 Man, 4 Salamander (with a flattened-
garded as a giant out tail), 5 Beetle, h head (nucleus).—After different authors.

flagellum. This
kind of spermatozoon is met with in many animals belonging to
very different groups, but it may assume a variety of other forms.
Genital Organs.—The formation of ova and spermatozoa is
usually confined to special regions of the body, and as a rule, but not
always, to definite organs. The organ in which the ova are formed is
D

 
34 General Part.

called the ovary. Its structure differs largely in different animals ;
it always, however, contains egg-cells in different stages of develop
ment, held together by connective tissue. Frequently the ovary is a
hollow, glandular organ which is continued into a tubular oviduct.
The ripe ova break loose, fall into the cavity of the ovary, and reach
the exterior through the oviduct. In other cases it is a compact
organ, attached to the wall of the body cavity; the ova fall
into the body cavity and pass out by a tube opening into it at
one end and to the exterior at the other. Before leaving the body of
the parent, the ovum is often enveloped in different hard or soft
coverings (albumen, shell), secreted by glands opening into the
oviduct. Saccular evaginations are frequently present for storing the
spermatozoa received during coitus (receptacula seminis). Further,
part of the oviduct is often expanded to form a uterus in which the
eggs may be retained for some time, often until they have undergone

a part of their development.

When the ovum has attained its full size, the nucleus moves to the surface,
and divides into two. The protoplasm undergoes corresponding division, but
into two unequal parts, so that before separation, one part looks like a
little bud of the larger egg-cell: a second small cell is constricted off in

Fig. 27. Diagram of the formation of polar
bodies. In the left figure the first, in the middle
the second, polar body is shown in process of
formation; the right figure shows the ripe ovam
with both.

 

the same way; and as soon as these polar or directive bodies are
formed, the ovum is mature and ready for fertilisation. The first polar body
may sometimes divide again, so that altogether three are present. They are
formed whilst the ovum is still in the ovary, or soon after its liberation; later,
they atrophy.

The spermatozoa are formed in the testis, which contains
sperm-cells in different stages of development. The testis even more
often than the ovary has a glandular structure, and the spermatozoa
usually pass out by a duct, the seminal duct or vas deferens,
with which it is in direct connection. Organs for the transmission of
the spermatozoa into the female apparatus are often present at the
external opening of the duct (copulatory organ, penis). Sometimes
the genital products which pass from the male to the female are
enveloped in a sheath formed by the hardened secretion of certain
glands opening into the vas deferens. Such a mass is called a
spermatophore (Cephalopoda).

In most species, some individuals give rise to ova only (females),
and others to spermatozoa (males). There are, however, many
animals, e.g., many Gastropods, which produce both: these are
known as hermaphrodites. In this case there is either a
specialised ovary (or more than one) and a specialised testis in the
II. Organs. 10. Reproduction and Reproductive Organs. 35

same animal, or the ova and spermatozoa are both formed in a common
hermaphrodite gland.

In many hermaphrodites, ripe ova and spermatozoa are produced at the
same time. In others, however, either the ova are formed first and the sper-
matozoa later, so that the animal functions first as a female, then as a male
(protogynous hermaphrodites, e.g., Salpa; or they first produce spermatozoa,
later ova (protandrous hermaphrodites, e.g., certain Nematodes),

Secondary Sexual Characters.—Distinctions between males and females
other than those resulting from the different nature of the genital organs
(primary sexual characters) are of frequent occurrence. The male is provided
with special organs, or parts of the body are specially modified for holding the
female during copulation (Water-beetles) ; or they possess special weapons for
fighting with other males during the breeding season (Stags); or they are
specially ornamented with brilliant colours, peculiar excrescences, etc. (many
Birds). On the other hand, the female may be provided with organs of importance
in rearing the young ones (mammary glands of Mammalia), whilst the male
is more rarely specialised in this way (Pipe-fish). There is often a perceptible,
or even considerable, difference in the size of the sexes; sometimes the male is
larger than the female (many Mammals, Birds, and Insects), in other
cases (Birds of Prey, Round Worms) the female is the larger: the diffe-
rence is sometimes extraordinarily great, as in many parasitic Crustacea,
where the males only attain a fraction of the size of the female; or again in
an Annelid (Bonellia), where the males are microscopic, and entirely different
in appearance from the fairly large female; indeed, they were at one time
regarded as parasites of a distinct species, since they live within the oviducts.

Fertilisation is effected by the entrance of the spermatozoon
into the ovum, and their ultimate fusion. There is evidently a

peculiar mutual attraction between ova and spermatozoa; not only

1 2 3 4

a

     

Fig. 28. Diagram of fertilisation. & female pronucleus, sp male pronucleus.
In 4, union has taken place. See Text.—Orig.

does the ovum attract the spermatozoon, but at the approach of
the latter its protoplasm may rise up to form a small papilla. After
entrance, the spermatozoon loses its tail or protoplasm, if it possess
any, and its head (nucleus), which is now called the male pronucleus,
enlarges, gradually approaches the nucleus of the ovum (female
pronucleus), the two come to lie side by side, and finally fuse.
This union of the nuclei is evidently the essential part of fertili-
sation; when it has taken place the egg is able to segment and thus
to give rise to a new organism. (See Sect. 1V.—< Ontogeny.”)

The ovum is fertilised by one spermatozoon only, and as a rule only one enters

even though thousands may be swarming round. This is due to the fact that
when a spermatozoon has entered, the ovum undergoes certain changes which

D2
36 General Part.

prevent the entrance of others; in Hchinoderms, for instance, a delicate mem-
brane is secreted over the surface. In some cases, however, several sperm-cells.
penetrate the ovum (e.g., Squalide), but only a single one unites with the female
pronucleus, the rest move about in the protoplasm for some time but eventually
disappear.

For the phenomena in Protozoa corresponding to the fertilisation of Metozoa.
see Special Part.

In many cases, most Fish, Frogs, etc., fertilisation occurs in the
water outside the body of the parent. The female lays the eggs and
at the same time, or soon after, the male deposits the spermatozoa.
The genital products are mingled together, and the spermatozoa
have an opportunity of making their way into the ova. In other
cases fertilisation takes place in the oviducts of the female, intu
which the spermatozoa are introduced by the male copulatory organs.
(copulation).

Copulation is not always followed immediately by fertilisation. In many
animals spermatozoa may be retained within the body of the female for a long
time without losing their efficacy. (In Hens, two to three weeks; Bats, as many
months ; Queen-bees, three years.) Frequently the ova are very immature when.
it occurs.

As regards hermaphrodites, it is very seldom that self-fertilisation
obtains, z.+., that an ovum and a spermatozoon from the same
individual unite ; hermaphrodites almost always copulate, and then
fertilisation is either reciprocal, or one individual only, gives.
spermatozoa to the other.

Hybridisation—An ovum under ordinary circumstances is.
fertilised by a spermatozoon which has been formed in an animal
of the same species. In most cases, however, it is possible for
ova to unite with spermatozoa of a nearly allied species; indeed,
copulation between two more distantly connected species may some-.
times occur.* As a rule, such a union results in a new organism,
a hybrid, which is more or less imperfect. For instance,
hybrids, even of nearly related species are very often sterile,
w.e., they are unable to produce ripe ova or spermatozoa, although
they may be otherwise strong and well-developed animals, ¢.g., the
mule of the Horse and Ass. In other cases the hybrid is feeble and
dies young, or even does not outlive the embryonic period (hybrid
of pheasant and Domestic Fowl). On the other hand, however,
there are hybrids quite as well developed as the parent species,
and also perfectly fertile. This holds for the crosses between certain
species of Stags, different species of Pheasants, the hybrid of the
Chinese and European Goose, &c.

 

* It has been recently found by experiment, that Frog’s spawn can be fertilised
by the spermatozoa of the Newt, and the eggs of Regular Sea-urchins by the sper-
matozoa of Irregular species; but development is usually irregular and soon ceases.
On the other hand, there are nearly allied forms whose genital products will not
unite; and there are species which give remarkable results in that ova from one, A, can
be fertilised by spermatozoa from another, B, but not ova from B by spermatozoa.
from A.
IT. Organs. 10. Reproduction and Reproductive Organs. 37

Under natural conditions, hybrids occur relatively seldom. On the border-
Jand between the ranges of two species (see section V.), hybrids are, indeed,
often found, and in some groups (Fresh-water Trout), seem fairly common. The
interbreeding of species is hindered, amongst other things, by the fact that the
individuals of different species, at least in a state of nature, are generally
disinclined to pair.

Just as the offspring of a union between remote species is unhealthy, so
also is that produced by too close in-breeding; if the offspring of the same
parents, or if other near relations are mated, and this close breeding continues
for several generations, the descendants gradually show a marked deterioration
of one kind or another.

Parthenogenesis.—The development of an ovum into a new
individual is generally dependent, as already stated, on its being
fertilised: but im not a few animals, it has been observed that the
ovum can develop without fertilisation. This peculiar
modification of sexual reproduction, which occurs in Platyhelminths,
Insects, and Crustacea, is called parthenogenesis, and although
in some forms where the unfertilised ova usually atrophy, it may be
exceptional (Silk-worms), yet in other cases it is quite an ordinary
phenomenon. In many species there are whole generations which
consist exclusively of females, so that the eggs cannot possibly be
fertilised, and yet they develop nevertheless (Aphides). Amongst
other forms the male seldom or never appears. In Bees and other
Hymenoptera, all the fertilised eggs develop in a remarkable way
into females, whilst the unfertilised ova become males (see also the
Special Part, Trematoda, Aphides, Daphnide, and Insecta).

In some animals, although parthenogenesis does not occur regularly, it is yet
suggested. It has been found that development begins in an unfertilized Hen’s
egg for instance, but does not go beyond the very first stages (segmentation),
which are followed by degeneration. The same thing has been observed in the
ovum of the Rabbit.

Ova, which are, as it were, predestined not to be fertilised; which, for example,
are produced from generations consisting only of females, are peculiar in giving
origin to one polar body only (summer eggs of Daphnia). It is a question
whether the eggs of Bees, which sometimes are fertilised and sometimes are not,
throw off two polar bodies as is customary. It has been observed in some ova,
which are usually fertilised, but which can develop parthenogenetically to a
certain point, that the nucleus for the second polar body always forms; but if
fertilisation does not take place, it unites again with the egg nucleus, and
subsequently plays the part of the missing male pronucleus (Round-worms,
Star-fish).

Alternation of Generations——Some animals reproduce both
sexually and asexually: many Corals can produce new individuals by
budding as well as by ova and spermatozoa, and this is true also of
certain Annelids and Ascidians. In other cases, however, those
individuals which give rise to buds, do not produce sexual cells;
asexual reproduction is restricted to some members of the species,
sexual to others, and there is a more or less regular alternation
of sexual and asexual broods or generations; asexual individuals
produce, by gemmation or fission, sexual individuals whose fertilised
38 General Part.

ova again become asexual animals: or, two or more asexual
generations are followed by a sexual brood, these again by more
asexual generations. Such a regular alternation of sexual and
asexual broods is known as alternation of generations,
the generations may resemble one another, but usually they differ,
often very considerably (Hydroids, Tapeworms).

Heterogony.—The alternation just mentioned occurs between
sexual and asexual generations, but in many animals a generation
consisting exclusively of females, which reproduce parthenogenetically,
alternates with another which consists of males and females giving
rise to fertilised ova. There is generally some difference between the
virgin and the sexual generations. A simple form of such alternation
occurs in certain species of Gall-wasps, which cause oak-galls; a.
female generation here alternates regularly with a generation con-
sisting of males and females. The process is more complicated
in the Aphides, where, during the summer, several generations.
of females appear in succession until, finally, a sexual generation
is produced; the fertilised eggs rest through the winter and
become the first virgin brood of the next year; there are,
therefore, several parthenogenetic generations to each sexual genera-
tion. In the Vine-louse (Phyllowera) there is a further complication,
not only is the sexual very different from the parthenogenetic
generation, but of these one differs considerably from the rest. Such
an alternation of virgin and sexual (or hermaphrodite) generations
occurs not only among Insects but also in various Crustacea and
Platyhelminthia.

Amongst those animals which reproduce only by fertilised ova,
successive generations are almost always alike; a regular alternation
of generations of different appearance is found only exceptionally,
and in consequence of special conditions. In certain butterflies, for
example, two generations, consisting of both males and females, occur
annually. The winter-brood, having wintered as pups, appears in
the spring as perfect insects: their eggs give rise to the individuals
of the other generation, the summer-brood,* from which they differ
considerably in coloration (seasonal dimorphism). A hermaphrodite
Nematode (Rhabdonema nigrovenoswm), is parasitic in the lungs
of Frogs and Toads; its embryos develop into another generation
which is free-living and of separate sexes, and which is essentially
different in appearance from the hermaphrodite generation. The
embryos of the free-living generation re-enter the Amphibia, and
become hermaphrodite worms like their grandparents. Some other
Nematodes exhibit the same peculiarity: an alternation of a
hermaphrodite generation, which leads a parasitic life, with a dicecious,
free-living generation.

 

* Instead of one summer-brood, there may be two (i.e. three generations annually).
IT. Organs. 10. Reproduction. 11. The Body Oavity. 39

Under heterogony, are included all cases of regular
alternation between sexual generations, whether these
differ in appearance or in their mode of propagation, therefore alter-
nations of parthenogenetic and dicecious generations, as well as
seasonal dimorphism come under this heading.

Heredity.—The offspring produced by an animal or by a pair
of animals is, generally, when fully developed, just like its parents.
This similarity extends not only to specific characters
(see Section V.), but, in great measure, to the individual
peculiarities of the progenitors. But such features are not always
inherited, some may be passed over: frequently, also, the offspring
exhibits a greater resemblance either to the male or to the female
parent; or again, the young ones may, under the influence of the
environment differ in small points from the parents.

Sometimes characters which are present in an animal do not
appear in its offspring, but skipping that generation, are seen again
in the next. An animal may thus possess certain peculiarities which
are present, not m the parents, but in the grandparents; indeed,
characters from still further back in the line of ancestors may
reappear: this peculiarity is called atavism.

The phenomena referred to above (metagenesis and heterogony)
are not opposed to the fundamental principles of heredity. Even if
the offspring is unlike the parent, and sometimes very unlike, yet it
always bears some resemblance to an earlier generation ; no persistent
deviation is produced in these cases which may perhaps all be
regarded as regular atavisms.

11. The Relations of the Organs to One Another.—
The Body Cavity.

The organs mentioned above form the metazoan body, and are usually
held together by connective tissue. This often fills up the interspaces,
so that the animal forms a compact mass (Platyhelminthia) ; it is
not the case, however, in most animals, where there is a large body-
cavity, in which some of the organs, viz., the digestive tract, the
excretory and genital organs are enclosed, being generally fastened to
the walls by threads, or thin sheets (mesenteries) of connective
tissue.

The body cavity is often divided into compartments by septa: in
Mammalia, for example, by the diaphragm, into thorax and abdomen:
in Chetopoda by transverse septa into many compartments. The
body-cavity is usually more or less completely filled with organs
known as the “viscera,” the remaining space containing a fluid, which
is sometimes blood, since the vessels are frequently in free com-
munication with it. Besides the body cavity, other spaces may be
present, of various forms, sizes, and significance, and filled with a
40 General Part.

fluid, which is for the most part to be regarded as exuded blood
plasma. Such are the synovial cavities of Vertebrata.

12. Rudimentary Organs.

Besides the great majority of organs which evidently perform
definite functions, structures are occasionally found which are of no
importance to the animal, the so-called rudimentary organs.

The hind leg of the Greenland Whale may be cited as an example
of such anorgan. It consists of a femur and a tibia, both of which are
concealed beneath the skin, and have entirely lost their function.
The “wolf tooth” of the Horse affords another example of a
rudimentary organ ; that in the lower jaw especially, is an instance of
extensive reduction, for, though it is formed in the customary way, it
is very seldom cut. The eyes of Myxine (the hag-fish), Proteus, and
many other blind animals; the wings of Apteryx (the kiwi) and
other Struthious Birds; the minute wings of many female Butterflies
are examples of rudimentary organs.

It may seem strange that these rudimentary and functionless
organs are so generally present, but further consideration renders
their existence less incomprehensible. Rudimentary organs which
are now useless, were, in ancestral forms (see Section V.), functional
and useful parts. The adaptation of the animal to a new and peculiar
environment rendered them useless, and during the development of the
existing form, they became reduced and functionless. It must, for
example, be admitted that the Whale is descended from a Mammal,
which, like most other Mammals, was provided with well-developed
hind limbs, but these were gradually reduced by the adaptation of
the aninial to an aquatic life, while the tail came to function as the
essential locomotor apparatus. A similar explanation can be given
for the other cases cited above.

This explanation does not, however, hold for every rudimentary structure.
Such parts as the rudimentary mammary glands of male Mammals, the rudi-
mentary oviducts of male Amphibia, the rudiment of a copulatory organ in many
female animals, etc., are to be accounted for in another way. Those parts which
are always present in one sex in a well-developed and functional condition have
probably been transmitted by this sex to the other. The mammary glands, for
example, were probably, first of all, present only in the female, and have been

inherited by the male; the copulatory organs, conversely, usually present at first
only in the male, have then been transmitted to the female in an incipient state.

 

III. Fundamental Form and External
Configuration of the Body.
In a small number of animals, Echinoderma and Ccelentera,

the body is so constructed that it may be divided into a number
of nearly congruent radially-arranged segments, antimeres (rays) :
IIT, Fundamental Form, etc. 41

such animals exhibit a radial symmetry. ‘Their individual
organs must naturally either have a radiate structure also, or be
equal in number to the antimeres.

Most Metozoa are, however, bilateral in plan: the body is
capable of division into two nearly equal parts, which are similar to one
another, looking-glass-wise, but are not congruent; the parts of the body
are here symmetrically disposed in relation to a median plane.

One of these types governs the structure of all Metazoa. Neither
is, of course, ever carried out with quite mathematical precision,
but in many cases it is clearly manifested throughout the whole body.
In other cases, variations are obvious; in many Echinoderms, for
instance, the body can be cut into five parts, which, indeed, shew
many poimts of accordance, but are yet far from identical. This
is true also for many bilateral animals: amongst Vertebrates, for
example, most of the organs are usually symmetrical in form and
arrangement, but as a rule, the greater part of the digestive tract
in the adult is an exception, though in the youngest embryos it
is symmetrical; still more aberrant is the condition in others, for
the symmetrical type is clear only in certain parts of the body,
whilst in most regions it is difficult to make out (Gastropoda).

In some groups the bilaterally symmetrical body is divided
into a series of similar segments (metameres). The segmental
arrangement of many Cheetopoda is representative of the simplest
form of this metamerism. The body is composed of a number of
segmentsorrings, which, from the first to the last, are essentially
alike, both externally and internally: each ring contains a pair of
excretory organs, a pair of nerve ganglia, is provided with a pair of
parapodia, etc. Amongst other metameric animals, e.g., the Arthro-
poda, the segments are not as a rule so uniform in structure.

Amongst bilateral animals, a dorsal and a ventral side may be
distinguished, and further, an anterior and a posterior end. The
ventral side is that part of the body which is turned downwards
when the animal is moving; the other is the dorsal side: or more
exactly, that side of the body which, in the majority of animals
belonging to a large natural group, is turned downwards, is known in
all the members as the ventral surface; the overlying surface is
dorsal. In all Gastropods, for example, the ventral side is that which
is provided with the so-called foot, and this holds good for all the
group, even when, as in pelagic forms, the foot is turned upwards.
The anterior end is usually characterised by the presence of
the mouth, of certain sense organs, and of a large portion of the
central nervous system (the brain); and by being usually directed
forwards during locomotion: it is often marked off from the rest of the
body, or in some way developed in contrast to it, and then it is known
as the head. The opposite, posterior end is often also peculiar in
construction, ¢.g., it is thinner than the rest of the body, or specially
muscular, and then is called the tail.
42 General Part.

Movable appendages, which subserve locomotion, are called
limbs. They are usually elongate, and often jointed. Amceng the
lower animals they play only a small part, whilst in the Arthropods
and higher Vertebrates they become important as locomotor organs.
Of other important appendages may be mentioned the tentacles,
antennee, etc., of different animals, employed as tactile or prehensile
organs (see also under skin). The end of an outstretched appendage,
farthest from the body, is called the distal, that which is nearest,
the proximal, end.

 

IV. Embryology or Ontogeny.

Embryology treats of development from the egg to the
mature organism, that is, the changes which the individual under-
goes until it reaches the adult form. As a matter of fact, the animal
changes continually during its entire existence, and the developmental
history should really, therefore, embrace the whole life. Prac-
tically, however, it is restricted to the earlier periods, when changes.
are more obvious than they are later.

A special interest attaches to the earliest stages in most:
Metazoa, for they exhibit striking conformity, a characteristic
common type, in spite of numerous individual modifications.

1. In the simplest cases (Fig. 29), development begins with the
division of the ovum into two nearly equal cells, each of which
divides again into two, in a radial plane, so that the result of the
segmentation, as this process of, division is called, is a number of

1 2 3

cs

 

Fig. 29. Stages in the development of the ovum of a Nemertine (Lineus). 1 The
egg divided into two cells. 2 Young blastula with small segmentation cavity. 3—4
Later stage of segmentation with larger segmentation cavity. 5—6 Younger and older
gastrule. 1 seen from the surface, the rest are sections. cs segmentation cavity. ec
epiblast, en hypoblast. UT Archenteron.—After Barrois.
IV. Embryology. 43

nearly equal radial cells composing a sphere. These cells gradually
move away from one another, so as to surround a central cavity filled
with a liquid, the segmentation cavity; thus the wall of the
sphere, the so-called blastula, consists of a single layer of cells.
When this stage is reached, an invagination of half the sphere
into the other half takes place, so that it forms a cup or sac with a
double wall. The layers of this wall are separated from one another
by the segmentation cavity; when, however, as often occurs, it is
completely obliterated by the invagination, they lie close together.
This stage is known as the gastrula stage. The outer layer of
the gastrula is called the epiblast or outer germ-layer; the
inner, the hypoblast or inner germ-layer. The cavity of
the sac is called the archenteron; its opening the blastopore
or gastrula-mouth.

2. In other cases, of frequent occurrence (Fig. 30), the cells of the
blastula are not of equal size, but those which form the hypoblast are
larger (richer in yolk) than the rest. Segmentation, invagination,
etc., proceed as in case (1).

 

Fig. 80. Different stages in the development of the ovum of a Water-snail (Planorbis).
1—2 Stages in the segmentation, 3 section of a blastula (the large hypoblast cells are seen
below), 4 gastrula, en hypoblast, kh segmentation cavity, m mesoblast, o blastopore,
r polar-bodies.—After Rabl.

The early development of a large number of animals takes place
in one of these ways; Ccelentera (for these see also p. 45), Porifera,
Echinoderma, many Worms, Molluscs, one Vertebrate (Amphioxus),
Tunicata.

3. In some cases (Fig. 81) which otherwise adhere to the order
described under (2), the cells which form the hypoblast are very

 

Fig. 31. Section through the egg of a Chetopod (Nereis) at different stages of
development. In 3, the gastrula is fully formed, but the blastopore (below, to the left)
is still open; in 4 it is closed, and the formation of the mouth (s) has begun. ek epiblast,
en hypoblast, f oil globules, m mesoblast, s developing mouth. The yvitelline membrane
is removed in the first three figures, present in the last.— After Gitte.
44, General Part.

large, andthe segmentation cavity is wanting, or is very
small. In such cases the gastrula appears to be formed in a manner
different from the foregoing: the epiblast cells, which originally form a
cap upon the hypoblast, gradually grow roundit, and the hypoblast
itself often encloses no archenteron, but forms a compact mass.

In the first and second types of gastrula formation described above, the
blastula grows directly into the gastrula by a modification of some cells to form
the hypoblast (Fig. 29, 4,5). In the blastula,
the outer end of these cells is the wider,
but they gradually alter in shape until the
inner ends are wider than the others, which
results simply from a different arrangement
of their protoplasm (protoplasmic move-
ments). This change in the shape of the
cells must necessarily lead to a flattening of
one side of the blastula and then to its
invagination. Simultaneously an alteration
occurs in the epiblast cells: these become

Fig. 82. Gastrula of « marine shorter and wider, so that they can extend
Gastropod (Natica). formed in the over a large area. Whilst the invagination
at way as the gastrula in Fig. jomains, the original relations of hypoblast

, from which it differs in the Z 2 : 3 H
possession of an archenteron.— 2nd epiblast are retained. The epibolic
After Bobretzsky. gastrula (gastrula by overgrowth) described

under (3), is probably formed in the same way.
There is no need to assume that the epiblast cells get loose from the hypoblast
and grow over it. It seems that the wide outer ends of the hypoblast cells
(Fig. 33, 1) gradually become narrower, and the inner ends broader, whilst the
epiblast cells at the same time spread out, so that, by the same process as in
the invagination of the typical gastrula, they gradually enclose the hypoblast,
without its being possible to speak of an active migration of cells, and without
the contiguous surfaces of the epiblast and hypoblast cells being altered.

 

 

Fig. 33. Diagrammatic figure of the formation of the epibolic gastrula (See Text).
1 youngest, 3 oldest stage. < hypoblast. The letters a and b indicate the same points in
all three figures —Orig.

4. In many lower Vertebrata (Cyclostomi, Sturgeon, some other
Pisces, Amphibia) the blastula wall does not consist of a single layer
as in the cases mentioned above, but is many cells thick (Fig. 34, 1) ;
the cells are larger on one side of the sphere than on the other, and
contain much yolk. This part of the blastula is invaginated, and a
gastrula is formed as before (Fig. 34, 4); but part of the hypoblast
is very thick, so that it stands up into the archenteron as a large boss.
IV. Embryology. 45:

The cells composing this mass are destined to degenerate later on, and
to serve as food for the rest (food yolk). The invagination too,
occurs in a somewhat peculiar way: first of all, a fold is formed on
one side of the blastula (Fig. 34, 2), and gradually surrounds the
ovum; then it grows down over the lower portion of the egg, so that.
this comes to project into the archenteron.

 

Fig. 34. Formation of the gastrula in Amphibia, diagrammatic, longitudinal section.
1 Blastula. 2 The invagination has begun at 7 (the corresponding place in 1 is indicated
by an arrow) ; the invagination is in the form of a furrow, but does not yet surround the
ego. 8 The invagination is proceeding. 4 Perfect gastrula; the archenteron is almost
filled with a projecting part of the hypoblast, which is later dissolved and absorbed by the
embryo, ek epiblast (light), en hypoblast (shaded), g gastrula mouth, h segmentation
cavity, 4 invagination furrow, u archenteron.—Orig.

This mode of gastrula formation is readily derived from the typical one; and
indeed, simply results from the excessive thickening of the hypoblast cells.
If to the blastula figured in Fig. 29 4, there were added a large mass of
hypoblast cells, which took no active part in invagination, this would occur
as in Fig. 34.

5. This is the kind of development which occurs in many Fish,
in Reptiles and in Birds. The egg-cell contains a large amount of
yolk, practically all the protoplasm is accumulated at one pole of the
egg, and it alone segments, while the greater part of the cell remains
unsegmented; this is known as partial segmentation.
A6 General Part.

The unsegmented portion corresponds to that part in the forms
mentioned under (4), which does segment, but which unites later, and
isinvaginated with some of the adjacent cells into the remaining cell-
mass, the process taking place as in the way last mentioned (Figs.
34, 35). An enormous mass of unsegmented substance, the food

 

Fig. 35. Diagrammatic representation of gastrula-formation in Vertebrata, with
partial segmentation (Selachians, Teleostians, Reptilia, Aves); compare preceding figures ;
-the letters are the same as in these, with the exception of en’ the unsegmented part of the
hypoblast (the yolk) ; en the segmented hypoblast. It must be noticed that the yolk is
usually, relatively much greater than is figured here.—Orig.

‘
yolk, becomes enclosed by the archenteron; is gradually absorbed
by the cells; and thus serves as nutriment during development.
These animals are, moreover, peculiar, in that invagination proceeds
very slowly. An advanced stage of development is reached by the.
time that gastrulation is complete. No notice has been taken of this
in the figures.

6. In most of the Arthropoda, as in the animals just referred to,
partial segmentation obtains, but the food yolk lies centrally ;
Surrounded by the segmentation spheres, The segmentation cavity is
IV. Embryology. 47

wanting; its place is occupied to a certain. extent by food-yolk.
Invagination takes place as in the typical gastrula (1, p. 40) and the
food-yolk is gradually absorbed by the cells.

Fig. 36. Development
of the ovum of a Crus-
tacean (sections). Bl
Yolk, ek epiblast, en
hypoblast, m mesoblast,
o blastopore. — After
Heckel.

 

From the above it follows that a gastrula, always formed in
essentially the same way, is found almost universally (when the
examination has been sufficiently thorough), as a result of the
earliest development of the egg.

An aberrant gastrula-formation occurs in many Hydrozoa. No invagination
takes place here, but at different points in the blastula, cells break away from
the rest and wander into the segmen-
tation cavity to constitute the hypoblast A B
(Fig. 37 A). Sometimes the prolifera-
tion of cells is limited to one side of
the blastula (B). Possibly the mode
of hypoblast formation figured in A is
primitive: from this B can easily be
derived, and it may be a transition to the
typical gastrula, which also occurs in the
Hydrozoa.

Between the two primary germ- 1.55, he formation of the gastrala, in
layers, of which the gastrula certain Hydrozoa.
consists, a third layer, the meso-
blast or middle germ-layer, is formed in most animals (Coelentera
excepted), very soon after, or even during, the formation of the gastrula.
There is no general type of formation recognisable for this, as there is
for the gastrula. In some cases it is formed, for example, by some
few cells lying at the blastopore, at the boundary between the epiblast
and the hypoblast, breaking from their connection with the rest,
pushing between the two sheets, and after repeated division, ex-
tending between them as an independent layer (Figs. 30, 31). In
other cases it originates as a double fold or sac of hypoblast, which

 
48 General Part.

becomes nipped off from the rest of the layer, and takes up a position
between this and the epiblast (Fig. 38).

o

eA

Uitarna
PTAs

Li}

 

Fig. 38. Diagrammatic figures in explanation of the formation of the mesoblast in
the Vertebrata (transverse sections); 1 youngest, 4 oldest stage. ek, en, m, epi-, hypo-,
meso-blast.—Orig.

After the origin of the mesoblast, the organism consists of three
germ-layers, epiblast, mesoblast, and hypoblast. From these three
layers the different organs of the animal are formed; from the
mesoblast all the connective tissue, the skeleton* (in so far as it
is not a cuticular structure), the muscular tissue, the vascular system,
the excretory and genital organs; from the epiblast, the epidermis,
the nervous system, most of the sense organs; from the hypoblast,

‘the epithelial lining of the whole or of the greater part of the
alimentary canal, and its glands. ‘'he mesoblastic structures, there-
fore, constitute, at least in the higher animals, the main mass of the
body of the adult.

Of the different systems of organs, only the development of
the nervous system and digestive tract is dealt with here, and quite
briefly.

The central nervous system usually arises as a folding,
invagination or thickening of the epiblast, from which it separates later.

Among the Vertebrata, for instance,
a long furrow-like fold is formed
along the dorsal side of the animal,
and is the incipient central nervous
system (brain and spinal cord) ; it
loses its attachment later, and lies
beneath the skin, as a tube. In
some cases (e.g., Echinoderms and

Cheetopods) the primitive connec-

tion of the derivatives of the

 

Fig. 39. Diagrammatic transverse
section, showing the formation of the : :
nervous system and the notochord in epiblast (t.€., the nervous system
the Vertebrata. A young, B older stage. : . :
ch Notochord, ek, en, m epi., hypo-, meso- and the epidermis) 1s retained
blast, n nervous system.—Orig. throughout life, either over a large

area, or at least at certain points.

 

* The chorda dorsalis of the Vertebrata, however, develops from the hyzoblast, as
a fold, which is later constricted off to form a cord, dorsal to the gut.
IV. Embryology. 49

As to the development of the alimentary canal: the
primitive opening, the blastopore, usually closes, so that the hypo-.
blastic tube is represented for a long time by a closed sac. Later,
the epiblast at each end of the animal invaginates to form,
respectively, the stomodeum and the proctodeum (Fig. 41). The
epiblastic invaginations and the hypoblastic tube, break into com-
munication at their points of contact, so that the complete alimentary
canal consists consequently, partly of the primitive hypoblastic tube,
partly of these epiblastic invaginations, and to these are added, in
many animals, elements from the mesoblast lying outside the canal,
and forming its connective tissue and the muscular layers.

When the digestive tract contains much food-yolk, the young animal or

embryo is much distended: a yolk sac, an outgrowth of the alimentary canal.
containing food-yolk, and surrounded by a corresponding outgrowth of the body-.

Fig. 41. Diagram:
of a young embryo.
with yolk sac.
Longitudinal section.
Shewing also the
4 formation of mouth
and rectum. d Food
yolk, ek epi-, en
hypo-, me meso-blast,
m mouth.—Orig.

   

Fig. 40. Embryo of the Dog-fish
with a yolk sac.—Orig.

wall, is then often formed. It is frequently niinek constricted, so that its cavity is
connected with the rest of the alimentary canal only by a narrow opening. Its
size is often relatively immense, so that the young animal looks more like an
appendage of the yolk sac, than the yolk sac of the young animal. As
development advances, the sac gradually becomes smaller, and finally disappears
altogether.

Most animals are oviparous, 4e., the egg is laid, surrounded
by the egg-membranes, whether fertilised or not. Sometimes even
after it is laid, it is still a single cell, but in other cases segmentation
has already taken place, or development may be even further
advanced. Other animals are viviparous, te. the ovum stays
so long in the body of the parent, that the egg-membranes or shell
are burst before the young organism leaves it. The distinction
between oviparous and viviparous animals goes no deeper than this,
and some forms are transitional between the two, for development

E
50 General Part.

is occasionally so far advanced among oviparous animals, that the
young one hatches almost as soon as the egg is laid; whilst there
are others, whose offspring break the shell at the moment of birth.

Those eggs which are laid without other covering than a vitelline-
membrane or egg-shell, develop without receiving any nutriment
from without. Oxygen is absorbed from the environment, and
carbon-dioxide is given off, for the egg breathes just as does the
perfect animal, and cannot develop in an atmosphere devoid of
oxygen. Water also is sometimes absorbed. When the egg is laid,
surrounded by albumen (as in Birds), this is gradually used up
during the development of the young organism*, so that whilst it
is still enclosed in the shell, it receives an addition to the material
originally present in the egg-cell. In many, but by no means all,
viviparous animals, the developing organism receives food from
the parent; either certain glands opening into the uterus secrete
a nutritive liquid which is absorbed by the offspring, or part of
the embryo forms an absorptive organ which comes into intimate
relation with the uterine wall, and the young animal lives like a
parasite on the blood of the parent (Mammalia).

So long as the animal remains enclosed in the egg-membranes, or
in the body of the parent, it is called an embryo (foetus). After
birth, ¢.e., when it breaks through the egg-membranes or leaves the
parent, as a rule, it begins instantly to lead an independent life,
feeding on its own account.t| The new-born animal differs
more or less from the perfect organism. In some cases, the
distinction is relatively unimportant, as when it consists essentially
in smaller size and immature genitalia, as in many Mammalia.
In other cases the difference is greater, e.g., among Birds; fledglings,
as is well known, differ considerably in plumage from the adult.
Still more important is this difference in many other animals which
are said to undergo a metamorphosis before they attain the
perfect form. The changes undergone by the young animals, in
such cases called larve, are often very considerable, and frequently
the larva has but the slightest resemblance to the adult.

The causes and also the nature of differences between larva and
adult are of various kinds. In many cases the most obvious is that
the egg is too small for a creature like the adult to be formed from it.
The imperfect state in which many Fish are hatched is fully accounted
for by the small size of the eggs (see the paragraph on the develop-
ment of the Pike in the special part, “ Pisces ”’): in allied forms with

 

* This absorption goes on usually through the whole surface, or by only a part of
it. Occasionally the albumen is taken up into the digestive tract of the young
organism.

+ Sometimes there is a greater or less quantity of yolk within the body of the
newly born animal, and then it does not feed for a long time. (See also, remarks, p. 52,
on “ Parental instinct.”’)
'

I¥, Embryology. 51

large ova, the young ones, when they leave the embryonic membranes,
are very similar to, or almost identical in appearance with, the adult.
This holds, also, for many Crustacea, which are hatched in a very
immature condition, with only a small number of appendages (three
pairs). Here the egg is evidently too small to form an animal with
so large a number of legs as is displayed by the adult Crustacean.
It seems as if there were a minimum, differing for different animals,
for the size of the limbs, and so on. In the larger eggs found in
other Crustacea, the animals hatch at a more advanced stage of
development. ,

The differences in the conditions of life must be regarded as
another important factor in determining the differences between adult
and larval forms; they are often intimately related to the cause
just mentioned. Many marine animals, which live as adults upon the
sea-bottom, are pelagic as larve, and this has a great effect upon
the whole structure (Chetopoda, Mollusca, Crustacea). Sometimes,
for instance, among the Amphibia, the larvee are aquatic, the adults
terrestrial, which also entails great differences. The metamorphosis
of Insects seems to be connected with the difference of the functions
of the larva and of the perfect animal, for the latter lives almost
exclusively for reproduction, whilst the larva devotes itself to feeding
and growth.

In consequence of diversity in mode of life, parts are frequently
wanting in the larve which are present in the adult. On the other
hand, they often possess special organs, the so-called provisional
larvalorgans, which are absent from the perfect animal (velum
of molluscan larva, gills of Tadpoles, pro-legs of Caterpillars). These
larval organs may be so large that only a small part of the original
larval body develops into the adult, whilst the greater part atrophies
(Echinoderma).

Compared with the whole life, the larval period is usually short: as a rule
the animal attains the adult form, in most respects, long before it reaches its full
size and is sexually mature. Insects are a noteworthy exception to this rule, for
the state of perfect insect is usually assumed only when the organism has
attained its full size.

The transition from the larval state to that of the mature
animal is never sudden, as might be supposed from the actual
metamorphosis, but is always gradual. The transformation often,
however, takes place in relatively short spaces of time ;. if a larva
has been for a long time in the same condition, it may pass through
great changes quickly, so that, to a certain extent, it assumes the
adult form ata bound. This is specially marked in the Arthropoda,
since all external changes are connected with the moults; sometimes
before an ecdysis, the living part of the skin is loosened from the
cuticle and more or less altered, so that the larva, when it strips
off the old cuticle, suddenly appears in a new and changed form.

E 2
52 General Part.

As a matter of fact, these changes also take some time, and the
development only appears to be a sudden one.

It is frequently found that an animal, during its development, whether in.
the egg or in the larval state, shows certain characters, wanting in the adult,
which are proper to a lower type. Tadpoles, for instance, possess gills, and
a piscine arrangement of the greater part of the blood vascular system. Many
larval Decapoda have an exopod upon the last pair of thoracic legs, which
atrophies later, but is permanent in many lower Crustacea. Among the higher
Vertebrates, gill-slits, etc., are present in the embryo. Frequently, as in the last:
mentioned, these structures are functionless, and of a rudimentary nature.
These facts are only intelligible when it is admitted that the forms in question
were derived from the lower type, or from one near it, and that these particular
characters are retained in an early stage of development, though lost in the adult.
(see next Section).

Parental Instinct.—In many cases the egg or the embryo after
leaving the body of the parent is specially cared for by the mother, or
more rarely, by the father. The object of this is usually two-fold,
firstly, to protect the egg or young animal from dangers of all
sorts; secondly, to supply it with food. Less frequently some special
means is resorted to, in order to keep the egg or young animal at the
temperature most favourable to development (Birds). In the simplest:
cases the mother is satisfied with depositing the egg in a safe place,
(e.g., by burying it), or parental solicitude is confined to the careful
selection of the place in which the eggs are to be laid, so that the
young ones may at once find suitable food. In other cases, the
mother sits upon the eggs until the young animals hatch out, or even
after this, in order to protect and warm them: or the eggs and young
ones are carried about by her. ‘The parental instinct is still
more actively manifested in cases where the young ones are able. to
take in and digest food, but are still unable to procure it for themselves,
and are therefore fed for some time by the mother. In many instances,.
the care of the brood not only dominates the whole life of the parent,
bat may even lead to the formation of special organs, or to the
modification of those already existing, (brood sac, mammary glands,
etc.) ; In many cases, too, it closely affects the mode of development
both of the eggs and young animals, many features of which appear
to be largely determined by this factor. (See, for example, the
Myside, the Marsupials.)

Careful consideration leads to the belief that the viviparous method of
retaining the egg within the body of the mother is only a form of parental care.
The difference between providing for the embryo within the oviduct (as in
all viviparous animals), or in a pouch of the skin (Marsupials), appears to
be a purely superficial one; the aim is in both cases identical, and in both cases.
the results are the same for the parent as well as for the young animal; the
formation of some special arrangement in the former, some peculiarities in the
development of the latter.
V. The Affinities of Animals, ete. 53

V. The Affinities of Animals.—Classification.—
The Doctrine of Descent.

The innumerable animals inhabiting the earth have been separated
into many principal groups, and these again into smaller and smaller
sections. This graduated arrangement is not arbitrary, but is based
upon the degree of conformity of animals to one another, so that the
most subordinate orders comprised in a division present the greatest
conformity. The theory of species will now be discussed in some
detail.

In the first place, all those individuals are ranked as the same
‘species which show a close correspondence in all details of their
structure at the same age: further, all those individuals which pair
with one another, under normal conditions, and produce fertile
offspring, whether they resemble each other or not: finally, also,
the offspring, which may or may not be like the parents. All the
female Hares in England, for instance, belong to one species, for they
exhibit at the same age a striking similarity in all parts of the body:
to the same species, also, belong all the male English Hares, in spite
of the difference in the genitalia, since they readily copulate with the
females, and produce fertile offspring: finally, the young ones,
which, in this case, do not differ from the progenitors. In cases of
metagenesis and heterogony, on the other hand, the offspring differ
‘considerably from the parents; every second, or third, or fourth
generation is alike, but differs from the intermediate ones; all,
however, belong to the same species.

The conception of species depends, consequently, upon three
points: 1. similarity of structure; 2. possibility of interbreeding ;
3. genetic connection (descent). The similarity of different specimens
of the same species is, however, not absolute, even if those peculiarities
which result from differences of sex, of age, or of generations (in
alternation of generations, and heterogony) are overlooked. Identical
individuals are never seen; a careful examination always brings out
differences, excepting in the very smallest creatures, where they
cannot be seen: species vary, asit is said, in a greater or a less
degree. The variation is usually not striking ; externally it is generally
restricted to slight differences of colour, shape, to relative size of the
same part, or to the absolute size or weight of the whole animal.
Internally, there are corresponding small differences to be observed.
Each large mammalian species presents obvious examples of these
ordinary variations. But sometimes, variations become more con-
spicuous: for instance, Foxes are usually white underneath, but
specimens have been found with black undersides, or with black cross-
54 General Part.

markings on the shoulders, or even entirely black; and similar varia-
tions are found in many other Mammals and in Birds; male Stag-
beetles have, as a rule, very large mandibles, but individuals have
been found with mandibles whose length is only a fraction of the
usual size. Foxes, again, are sometimes destitute of the hindmost.
molar in the lower jaw, etc. All these points in which an animal

differs from the usual type, are called individual variations.
In some species two or more forms may occur, which are in some respects.
distinct from one another, and generally not connected by those transitional
forms usual with the individual varia-
tions just mentioned. This phenomenon.
is called dimorphism, if the
species occur in two different forms.
polymorphism, if there are more
than two. Dimorphism is found, for
example, in the Heteroptera, in different.
species of which, winged, as well as wing-
less forms occur. This and similar cases.
are easily derived from the ordinary
individual variations, as the result of
great individual variation, the transi-
tional forms having disappeared.
Dimorphism and polymorphism are
Pai fairly common amongst colonial animals;
Pc che ue a ata e.g., Craspedota, Siphonophora, Octac-
ea with fore cal tae wis B a tinia, Polyzoa; and here it is evidently
less form with reduced fore wings and no the result of the common life of the
hind wings.—After Riley. individuals composing the colony: since
they are in direct organic communica-
tion with one another, some have one special function, some another, and a.
natural result of this division of labour, is a differentiation of the individuals.
The dimorphism or polymorphism occurring among the Social Insects (Bees,
Ants, Termites) is due to similar causes.

When a species has a wide distribution, it frequently happens that
the individuals living in one locality differ, as a rule, in some
respects, from the inhabitants of another: the individuals of each
region are then said to form a special variety (race, sub-species).
Hares, for example, which are distributed over the greater part of
Europe, all belong to a single species, but form three groups: a
south European, whose individuals are distinguished by short, loose
fur, long ears and rust-coloured back; a Mid-Huropean, with long and
close fur; and a North-East European (in North Russia), with a coat,
longer and thicker than either of the others, and very white. These
three groups are different varieties, for though they are in general
agreement, still they usually differ from one another in the
points just noticed; but they are not different species, for each
comprises specimens which approach the type of one of the other
groups, so that they are not sharply defined. What has been said of
Hares holds good also for various species of Mammalia and Aves.
which are distributed through Europe and North Asia. The Siberian

 
V. The Affinities of Animals, etc. 55

forms constitute a special variety ; for, as a rule, they differ in some
respects from the European. On the other hand, if a group of
individuals found in a larger or smaller tract of land or water, differs
in certain characters without exception, from similar individuals
of another locality, then it forms a distinct but nearly related
species. The Wapiti Deer (Cervus canadensis) of North America, for
instance, is a different species from the European Red-Deer, but is
nearly allied to it. So also the North American Beaver 1s a different
species from the nearly related European form, since some individuals
of the first display peculiar characters (specially in the skull) which are
never present in the European, and conversely. Often it is very
difficult to determine whether a group of animals forms a variety or
an independent species ; it is difficult, in proportion as the particular
variations are constant or not, as they are present occasionally
(variety), or without exception (species), and of this it is not easy to be
perfectly certain. Practically, a group of individuals is regarded as a
definite species when transitional forms from it to another are
unknown, #.e., when no specimens exhibit even a partial oblitera-
tion of these characters, which separate them from a closely allied
species. So soon as such links are found, the group is recognised
as a variety of the other. There is no sharp limit in Nature between
a variety and a species.

The different behaviour of species and varieties in crossing also, as was
mentioned earlier, cannot be employed as an absolute specific test, for, although
hybrids of different varieties are almost always perfectly fertile, this may
also be the case with hybrids of species (see above, p. 36).

Similar species are grouped as a genus; e.g., the lion, tiger,
jaguar, cat, and others as species of one genus. Each genus of the
Animal Kingdom is designated, according to a fixed rule, by its Latin or
latinised name, which is always a single word; e.g., the genus which
includes the animals just mentioned is called Felis. A species is
known by the name of the genus with a subjoined distinguishing
name ; the latter is usually an adjective, sometimes a substantive in
apposition to the name of the genus, or a substantive in the genitive
case ; the domestic cat, for instance, is called Felis domestica, the lion,
Felis leo, the cochineal insect, Coccus cacti. Several similar genera
are collected together asa family. For example, the badger-genus
(Meles), the otter-genus (Lutra), the marten-genus (Mustela), and
others, all belong to the marten-family, Mustelidz; the family name
is usually formed by appending the termination ide to the name
of one of the genera. Several families, again, are united to form an
order, the cat-family, marten-family, bear-family, etc., form the
order Carnivora. Orders, again, constitute classes, e.g., the
Carnivora and a number of other orders belong to the class Mammalia.
Classes form phyla, e.g., the classes Mammalia, Aves, Reptilia, etc.,
form the phylum Vertebrata.
56 General Part.

This grouping of animals in grades is, as noticed above, not
arbitrary but founded on Nature itself. The animals are connected
by some degree of relationship, «e., by a more or less exact
correspondence of structure: this connection finds an incomplete
expression in the classification of the Animal Kingdom. When,
for instance, Fish, Amphibia, Reptiles, Birds, and Mammals are
comprised in one group, it is indeed implied, with sufficient clearness,
‘that all these divisions agree in certain important points of structure,
but not that they are united together like the links of a chain.
Such is, however, the case, and Amphibia follow Pisces, Reptilia,
Amphibia; Aves and Mammalia, the Reptilia. Such a connection
of forms, more intimate than the system expresses, exists in the
Animal Kingdom; a true linking together, such as that just set
forth for the principal groups of the Vertebrata is everywhere
more or less easily recognisable.

What remains now is to ask the reason of this remarkable connection
of different animals. Until a few years ago, the answer always was
that the whole situation is one of the enigmas of Nature, incom-
‘prehensible to the mind of man. Now it is universally acknowledged
that this affinity, this similarity, of different animals is an effect of
those laws which govern the resemblance between parent and child,
brother and sister, or more distant relations, viz., the laws of
heredity. The lion, the tiger, the wildcat and other species, in
virtue of a close accordance in most points of structure, all belong
to one genus, implying that they all originally sprang from one
species, which has gradually broken up into several. If bears,
martens, cats, etc., are all united in one order, it is because
they have all sprung from a common ancestor; so also for
the larger groups, Mammalia, Vertebrata. Two such groups
as Reptiles and Birds are linked together, because the latter have
arisen from the former: by gradual change, a branch from the
Reptile-stem is modified towards a Bird-form, from which the rest
have sprung.

The completion of the conception leads to the conclusion that
all animals have originated in one common primitive ancestor,
which was probably similar to the Amceba. This is the purport of the
Theory of Descent (Darwinism), according to which all the
immense multiplicity of plants and animals have gradually evolved,
in the course of enormous periods of time, from the same progenitor.

That this theory is correct is evident on the one hand, because it
not only elucidates the long-noticed “ conformity to type,” in a natural
way, but also renders intelligible an endless number of other
phenomena of the organic world: and on the other, because in spite
of strenuous efforts, facts irreconcilable with the theory have not
been found. For the most important points supporting the theory of
descent, without the acceptance of which, indeed, they are incompre-
V. The Affinities of Animals, ete. 57

hensible, see p. 40, “ Rudimentary Organs”; p. 52, some phenomena
in Embryology ; and also the Sections following, VI. to VIII.

Whilst the doctrine of descent has been talked about for a long
time, it is only in the latter part of the present century that it has
gained general acceptance, and this is primarily due to Charles Darwin
(1809—1882), especially to his work, “The Origin of Species,” which first
‘appeared in 1859. The chief value of Darwin’s work appears to consist
in his having brought together facts from all sides, demonstrating the
necessity for the acceptance of the theory. He has proved that a large number
-of facts of Zoo-geography, of Geology, of Embryology: that rudimentary organs :
that the whole theory of the relations of animals remain unintelligible if a
‘doctrine of “Special Creations” is accepted. He has also, and this is of the greatest
importance, disproved the generally received dogma of the immutability of
‘species, by an examination of the variations of animals in a domesticated as well
-as in the wild state. His theory as to the means by which the modifications
have been brought about (‘‘ Theory of Selection”) appears to be of relatively less
importance, although this was a side of his work upon which he bestowed the
greatest energy and the most extensive studies. Darwin considered that in
Nature, as in the breeding of domestic animals, a selection takes place: for
those individuals are best fitted for the struggle for existence, which are
distinguished by small favourable variations: and in this way development
advances, for the less well equipped animal goes to the wall, whilst the better
survives (Natural Selection). Whether this always occurs in Nature seems
by no means certain, and in any case there are many characters in animals which
‘are useless, and cannot therefore be explained by an appeal to Natural Selection.
Besides this factor, Darwin acknowledged the more direct influence of the
environment as a cause of variation; but the whole question seems still too far
from solution to be treated more elaborately in a Text Book such as this.

The way in which evolution has proceeded and is proceeding, is probably as
follows: the formation of varieties is the first step ; when a species has spread
over a large area, it develops differently at different places, the varieties* formed
become more sharply separated under favourable conditions and become distinct
species. A species develops to constitute a new genus if the difference
between it and the other species of the same genus becomes clearly defined ; if it
adapts itself, for example, to special conditions: by adaptation to a herbivorous
and digging life, the badger genus has developed from the genus marten. A
genus differentiated in this way may afterwards divide into several species. By
continuous progressive development, and by the accumulation of variations,
new families, new orders, etc., may arise. Hach new type is, originally, only
a specially differentiated species, but this species may split, later, into several,
each of which again may be the starting-point for new genera. From this
account, it may be supposed that the limits of the different genera, families, etc.,
are never fixed: and in many cases this is so: in many instances it is quite
-arbitrary whether one or more distinct species is reckoned as a separate genus
-or not, or whether a genus is considered as the type of a separate family or
not. In other cases, on the other hand, the limit is sharper, for many species
and genera, which might have obscured the boundary line have become extinct in
-course of time (Section VIII).

Homology, Analogy.—By the gradual modification of animals,
the individual parts of organisms have often altered very much in

course of time, not infrequently indeed an organ has lost its original

 

* In many cases new varieties have actually been produced by the transportal of
«species to new localities.
58 General Part.

function and acquired a new one. Organs or parts of the body, which
have had a common origin, may perform the same, or different,
functions; such are called homologous: the arm of a man is
homologous with the fore-leg of a dog and the wing of a bird,
although the function in each case is different. On the other hand,
it frequently happens that the same function is performed by
different organs in different animals. Those which, differing in
origin, are functionally equivalent, are said to be analogous:
the eye of a Vertebrate is, for instance, analogous with that of a
Gastropod. That branch of science, whose special task is to
trace homologies and to notice changes in organs, is called
Comparative Anatomy: together with Embryology, it
forms the Morphology of Animals. In contrast to this, it is.
the task of Physiology to study the functions of organs.

 

VI. Biology.

Biology, in the narrow sense,* treats of the habits of animals,
their relations to the environment, and so forth. Various biological
questions have already been touched upon in the sections on Organs
and on Embryology: others of more general interest will now be
considered.

l. Dispersal of Animals.

Animals are adapted to their environment in various ways; some
forms flourish in one set of conditions, others in another ; members.
of the same group, occurring in diverse situations, are differentiated
in correspondence with the environment. On the other hand, the
same environment often induces, in many respects, a similar type
in members of different groups (Fish, Whales).

Mammalia, Aves, Reptilia, Insecta, Arachnida,
and Myripoda, are emphatically terrestrial; the Amphibia,
which are partly aquatic, are less distinctive in type. There are
also many forms which, although belonging to essentially marine
groups, have become adapted to a terrestial life, such as the great
division, Pulmonata, not a few Crustacea, some Annelids.
(Earthworm, Leech), a few Platyhelminths. The land animals
have one characteristic. in common; they are provided with a
special respiratory apparatus, and almost always breathe by means
of lungs, or lung-like organs. The fauna of a place varies in
correspondence with the character of the district, of the soil and of

 

* Biology in the wider sense comprises the whole science. of organisms, the whole.
of Zoology and Botany.
VI. Biology. 1. Dispersal of Animals. 59

the flora so largely dependent upon the latter; species, genera
and even families found in forests, are in some respects different
from those met with in deserts, so that a forest-fauna, steppe-fauna,
or mountain-fauna, may be spoken of.

The animal life of fresh water has a relatively non-distinctive
stamp; of the larger groups, there is scarcely one which can be
called a special fresh water type. This fauna is composed largely
of forms which are partly undoubted land types, partly marine:
it is a peculiarly borrowed and mongrel collection. The numerous.
Pulmonata, Insects and Spiders, living in fresh water
are derived from the terrestrial fauna, which, however, gives.
absolutely no Bird or Mammal as a constant inhabitant, although not
a few of these creatures spend a part, or even the most, of their
time there. A fair number of forms is furnished by Reptiles,
most of which however, come on land now and then (Crocodiles,
Turtles). Amphibia are almost all fresh water in the larval form;
in the adult state many are, for the most part or entirely so. The fresh-
water fauna has drawn upon the sea also. Numerous Fish, whole
families of which belong almost exclusively to rivers and lakes,
a number of branchiate Gastropods, Lamellibranchs,
Crustacea, Chetopods, Polyzoa, Platyhelminths,
some Coelentera, not a few Rhizopoda, etc. <A very few of
a mammalian group modified for a sea life, the Whales, live in
fresh water. Leeches, Rotifers, Infusorians, groups
which are fresh water as well as marine, are so common in the former
that they should perhaps be regarded as fresh-water types. The
modifications which terrestrial or marine forms have undergone by
the transition, are usually not very important. The land animals
generally remain air-breathing, and the modification is practically
limited to that necessitated by the difference in mode of locomotion;
the alterations in the marine forms are also non-essential.*

The class Pisces, the phylum Mollusca, the Crustacea,
Cheatopoda, the Polyzoa, Brachiopoda, Platyhel-
minthia, Echinoderma, Celentera, Porifera, Rhizo-
poda and Radiolaria are obviously marine groups. Of these
the Brachiopoda, Echinoderma, and Radiolaria exclusively, and the
Coelentera and Porifera with few exceptions, belong to the sea. The
sea has received a large contribution from the terrestrial fauna,
especially as regards the Vertebrata. Two orders of Mammalia
the Whales and the Sirenia, the former with many genera and species,
have adapted themselves entirely to a marine life, and their structure
has undergone correspondingly important modifications; a third
Mammalian order, the Seals, are also distinctly marine, though they

 

*It is very noteworthy that many fresh-water forms do not pass through a free-
swimming larval stage, whilst their relatives in the sea do (Astacus, Lamellibranchs,
Oligochets).
60 General Part.

repair to the land for reproductive purposes. Reptiles have also
contributed to the animal life of the sea (Sea-snakes, Sea-turtles).
Amongst Birds there are none which have become entirely marine,
although many are connected more or less closely with the sea, of
those most so, the Penguin and many other Swimming Birds. Of
living Amphibia there are no entirely marine forms. Only a few
Spiders live in the sea, and hardly any Insects. Like the
terrestrial, the marine fauna is modified according to the very
different conditions existing in different parts of the ocean, the dis-
similar character of the bottom, the depth, etc. The littoral fauna is
different from that at greater depths, which again varies according
to the bottom. The salinity is also of the greatest importance, for
greater salinity is universally favourable to animal life; it suits a
greater number of species, though less salt water may also be rich in
individuals.

This is very clearly illustrated by comparing the state of the salt Kattegat
with that of the less salt Western Baltic, and the almost brackish East Baltic. In
the Kattegat there is a tolerably rich fauna, but already the north end of the
Sound, where the salinity is less, contains a scantier collection. Most species
which live in the Kattegat are represented here, but for the most part by smaller
specimens and in fewer numbers. Southwards in the Sound, as in the entire
western part of the Baltic (south of Denmark), very many of the Kattegat forms
have disappeared; others are indeed present, but dwarfed, or in the case of the
Molluscs, thin shelled. Lastly, only a fraction of the fauna of the West Baltic
is found in the fresher Hast Baltic, and this is also the case in that part of the
latter (south of Sweden), which, as regards climate, does not materially differ
from the West.

Some fresh water animals (pike, perch) may also occur on the coast in
water of slight salinity; and on the other hand, some marine animals may be
present in fresh water, the flounder (Plewronectes flesus). Also, some Fish go to
spawn either from fresh water into the sea (eels), or conversely (salmon, trout,
sturgeon). Sudden immersion in sea water is fatal to most fresh-water
animals, and most marine forms are similarly affected by fresh water. On the
other hand, many endure, to a certain extent, a gradual salting or freshening of
the water.

Temperature has often a great influence upon the dispersal
of animals; this is especially striking in the terrestial fauna
which, other conditions being the same, is much richer in hot than
in cold districts; in the very coldest, it is almost entirely absent,
or at least, reduced to a minimum. This is due not only to a higher
temperature being universally favourable to animals, but also to the
dependence of animals upon plant life, which is much affected by
temperature. Since the temperature of sea water does not sink as low as
that of the atmosphere, the sea in the coldest regions may harbour
a rich fauna, although it cannot compare with that of tropical seas.

The more general features of the dispersal of animals have now
been touched upon; in what follows, some special adaptations will
be considered.

 
VI. Biology. 1. Dispersal of Animals. 61

Cavernicolous Fauna.—The entirely dark, subterranean caves
which occur in mountains of different countries, and which
are also present beneath the water, harbour a small but peculiar
fauna. Most of the animals living in these places, in contrast to
their relatives of the daylight, exhibit very degenerate optic
organs, or these are even entirely wanting. Frequently the skin
is destitute of pigment: the blind, pale Proteus of the Carniola caves.
may be taken as a typical cave animal, and some Fish, certain
Crustacea, Insecta, Spiders, also belong to this fauna. All cave
animals, however, are not blind; some have retained their eyes, and
are consequently less suited to life in the dark.

Those animals, which burrow in the earth, and which come to the surface

seldom or only on dark nights, are like the cave forms; their eyes, too, may
be more or less degenerate (Moles).

The rich animal life of the deep sea, where no daylight
penetrates, resembles the cave fauna. The deep sea animals are often
almost destitute of pigment, and have, frequently, very degenerate
eyes, or indeed none, even when belonging to groups, the other
members of which have these organs well-developed (some deep sea.
Crustacea and Fish). Other deep sea forms are, however, furnished
with well-developed eyes, e.g., the majority of the fish, which are
considered abysmal.* Many of these Fish are phosphorescent. Among
the abysmal animals there are many which have only remote relations
elsewhere—Stalked Crinoids, peculiar Echinoids and Crustacea,
Hexactinellids, and others, so that this fauna is strikingly peculiar.

Pelagic Fauna.—Still more extraordinary are the animals
living in the open sea, at a considerable distance from land, the so-
called Pelagic Fauna. This comprises first, a number of groups,
which either never, or only exceptionally come close to shore, and
which generally do not occur elsewhere: the Radiolaria and other
groups of the Protozoa, the Siphonophora, Euphauside, Pteropoda,
Heteropoda, and Salpidz: secondly, a multitude of forms whose near
relatives live closer to land: lastly, an immense number of larve,
belonging to forms which live in the adult state at the bottom of
the sea. But what specially characterises the pelagic fauna is not so
much the number of groups peculiar to it, as the fact that in virtue
of their life in the surface waters, all the members of these different
groups have certain features in common which are, however, less well
marked in some than in others. There is, in particular, an evident
tendency towards such a modification of the animal as may enable it
to float with the greatest facility. This is attained, in some cases,
by the tissues absorbing such considerable quantities of water that the
specific gravity is only slightly greater than that of the sea; such
animals have a jelly-like appearance (Medusz, many Pteropoda and

 

* It is possible, however, that many of these live nearer the surface, and were
caught in the net as it was drawn up from the bottom.
62 General Part.

Heteropoda, Salpide). In other cases, the surface is increased, either
by the flattening of the body, by the lengthening of the limbs, or by
the formation of long spines, as in many Crustacea and their larve,
and in young Fish: in both cases it is found that the muscles causing
the movement of the animal are reduced. Sometimes the atrophy
goes so far that they become exceedingly weak, and the animal
is only capable of feeble movements. In other cases, in spite
of the weakened muscles, they are still good or even excellent
swimmers, since the body floats in the water almost without muscular
exertion. The majority of pelagic forms are further characterised
by a great transparency. Many possess as perfect optic
organs as most of their relatives, as in the case of certain pelagic
‘Cheetopods: others, on the contrary, exhibit degenerate eyes, which
is explained by the fact that many members of the pelagic fauna
‘appear on the surface of the sea only at night, remaining in greater
‘depths by day.

 

Many animals remain for their whole life near the place where
‘they were born: others stray about in search of food: ‘others, again,
undertake further migrations, usually in great numbers.

These wanderings have often a casual and irregular character.
Unfavourable conditions, for example, scarcity of food or of water,
will cause an animal to leave the usual habitat of the species, and
to seek a new home. The migrations of Locusts, of Prairie-hens, of
the Lemming, result from such causes. These wanderings but seldom
increase the range of a species: after a short time it disappears
again from the new place.

The migrations may, however, have a more regular character,
such as those undertaken annually by Fish and Birds: at one
time of year they inhabit one place, at another time another place,
from which they then return to the first, and so on. Among many
Fish, the migrations are due to a search, at a fixed time of year, for a
suitable breeding-ground; whilst the flight of Northern Birds towards
the South is really explained by -their not finding enough food for
the winter in their summer home. (For details see these groups.)

2. Different kinds of Food and their effect on
the form of the Body.—Parasitism.

The food of animals is of very different kinds. It may be
vegetable, consisting of living or dead plants; or animal,
consisting of living animals or carrion. Some animals eat a
variety of things both animal and vegetable, others are, however,
much restricted, e.g., to a few species of plants. Some feed on
organisms of relatively very small size, others consume animals
larger than themselves.
VI. Biology. 2. Different Food, etc—Parasitism. 63

In many cases it is evident that the kind of food exercises a very
great influence on the structure of the animal. This influence
manifests itself primarily in the form of the digestive tract.
In allied animals, its length is generally greater in herbivorous
than in carnivorous individuals; among the Mammalia, for example,
it is much longer in Ruminants than in Carnivora. Many other
variations in the alimentary canal result from the differences in food ;
this is specially marked in the buccal cavity, in the hard structures
serving for the prehension and comminution of the food, e.g., the teeth
of Vertebrata. Among the Mammalia this is very apparent; the
teeth of a Cat, for instance, may be compared with those of a Horse,
or again, the teeth of different Carnivora, Cat, Dog, Bear, etc., with one
another. Since the modification and insertion of the teeth again
affects, for example, the structure of the skull, the influence of the
food extends indirectly to other systems.

The nature of the food, further, often affects the locomotor
organs, and the entire external conformation. This is very evident
in the Insecta, where the slender, active larva of the Carabus, with
its elongate limbs, running about after its food, may be contrasted
with the maggot-like larvee of the Curculionide and Longicornia,
which either have only rudimentary legs or are entirely apodous, and
live in the midst of plenty. Frequently, again, the limbs of
predaceous animals function secondarily as prehensile organs
and are correspondingly modified. As the limbs are affected, so
also are the sense organs, especially the eyes, by the nature, and
particularly by the greater or less activity of the prey. Carnivores
often possess large, well developed eyes, whilst herbivores, whose food
is plentiful, have smaller or even degenerate optic organs. Insects
also afford characteristic illustrations of this.

This does not mean that the locomotor or sensory organs of herbivorous
animals, whose food is plentiful, are always poorly developed. Amongst the
Mammalia there are numerous herbivores rivalling Carnivora in this respect,
as Stags, Antelopes. In these cases the high state of development of these
parts affords a means of escaping the pursuit of the Carnivora.

A discussion of the direct and indirect influence of food leads on to
a consideration of Parasites. Those animals are called parasites
which live upon or in other livig animals known as the hosts, and
feed at their expense; either upon some part of the body (e.g., its
blood), or upon food taken in and digested by it, as in the Tape-
worms. They may be temporary or stationary. The former
do not stay continuously on the host, but seek it out at intervals
simply for the sake of food, whilst the stationary parasites remain
constantly upon or within it. Parasites have, indeed, been
classified according as they live on the outer surface or in the
interior of the host, as ecto- or endo-parasitic. A sharp
line cannot be drawn between these two groups, since the
64 General Part.

boundary between the external and internal organs is not clearly
defined. Most parasites do not spend their whole lives as such,
but lead an independent existence at one time or another. Some
are, for example,: parasitic when young, but free-living as adults
(the Gadflies), whilst others, conversely, are first free-living and
later on become parasitic (parasitic Crustacea). This mode of life
has a marked effect on the structure of the animal: it is often
relatively slight in the temporary parasites, and in those stationary
ectoparasites which can move about freely on the body of the
host; but very great in most stationary ecto- or endo-parasites.
The fact that nutriment is plentiful and immediately accessible
exercises its usual effect: the power of locomotion is decreased; a
more or less complete reduction of the limbs is seen: the sense
organs, further, e.g., the eyes, are much affected: most stationary
forms, especially the endoparasites, are blind. Organs of adhesion, on
the other hand, are frequently well-developed, as suckers, hooks;
or certain limbs are modified for this purpose. Parasitism, moreover,
exerts a definite influence upon the whole life. A natural result is,
for instance, that the animal must generally undertake migrations,
1.¢e., that it must not spend the whole of its life, from the ovum to
sexual maturity, in the same host, but must be actively or passively
transported at some period into another. Besides this one migration,
there are often others. Many parasites regularly produced as eggs
in one host, or in the free state, live for some time in another, the
intermediate host, and finally attain sexual maturity in a third.

Parasites belong to various sections of the Animal Kingdom. There are,
nevertheless, certain large groups of which none or only a few individuals are
modified in this direction. Among the Vertebrata, only a single Fish: so also
only a few Molluscs, Chetopods, Celenterates, and absolutely no Echinoderms
live in this way. The Arthropoda, especially the Crustacea, furnish a large
contingent, which are for the most part, ectoparasites, the Crustacea, exclu-
_ sively upon aquatic animals, the others almost as exclusively upon land animals.
Further, amongst Annelids, a great many Leeches are ecto-parasites : most of the
Nemathelminths are endoparasitic : whilst of the numerous parasitic Platy-
helminths, some are endo- and some ecto-parasitic. The parasitic Round- and
Flat-worms are frequently called intestinal (Entozoa). Many Protozoa lead
this life, Gregarines, many Infusoria, etc. Many of the members of all the chief
divisions of animals must serve as hosts, especially the Vertebrata, which
principally on account of their large size, complicated structure, and relatively-
long life, afford an excellent scene of action for parasites, both internal and
external. Many of these creatures are limited as regards the choice of a host;
some live, for instance, always in one species, never in any other; others are
confined to a few allied forms; others, again, have a larger, but always a
restricted choice. The same parasite, for instance, cannot live indiscriminately
in a Fish and in a Mammal. On the other hand, it frequently happens that
the same form lives, at different periods of development, in animals of a very
different systematic position; Echinorhynchus, for example, is found, when
young, in Arthropods, as an adult, in Vertebrates.

Some animals, e.g., some Leeches, form a transition from the predatory to the
temporary parasitic condition, for sometimes they eat small animals, and
VI. Biology. 3. Different Kinds of Locomotion, ete. 65

sometimes suck the blood of larger ones. Other animals, as certain Fly-larve,
may be both carrion feeders and parasites. Again, there are forms which are a
transition to the parasites, in so far as they live in other animals, but do not
feed at their expense; at most they take a moderate share at meal - times
(commensalism).

3. Different Kinds of Locomotion.— Their Effects
upon the Structure of Animals.—Sessile Forms.

The movements of animals are known to be very diverse. Many,
especially lower animals (Worms, etc.), craw] bymeans of contractions
of the muscles of the body-wall, or by movements of the cilia upon the
surface. Others swim: this is often accomplished by movements of
the whole body, or by the greater part of it; or it may be effected by
means of limbs. Walking and running, on the other hand, are
absolutely dependent on the presence of limbs. Springing move-
ments are of various kinds: amongst aquatic animals, some part of
the body strikes upon the water (decapodous Crustacea); amongst
terrestrial forms, a jump generally results from violently jerking the
limbs off the ground. Flying is always effected by means of
specially developed limbs, just as burrowing and climbing,
well-known forms of locomotion.

Each of the kinds of movement mentioned, which may be com-
bined, to a certain extent, in the same individual, may influence the
structure of the animal more or less deeply. This is clearly manifest
when allied groups, typically distinguished from one another by
different modes of locomotion, are compared. A great many of the
specially marked differences between Fish and the higher Vertebrates,
are to be ascribed to diversities of movement. In Pisces, limbs are but
slightly developed, the body muscles, and those of the powerful tail,
much more so, in accordance with the needs of an aquatic life. Inthe
most decided walking types of Vertebrata, the Mammalia, the tail is
reduced, the dorsal and caudal muscles also, but the limbs are well
developed. That all this is a result of a difference in locomotion is
borne out by the fact that if Mammalia are adapted, as an exception,
to a swimming life, they again come to resemble Fish. This is the
case in Whales, which are derived from terrestrial Mammalia: their
limbs have atrophied under the influence of an aquatic life, whilst
the tail is developed as a powerful locomotor organ. In like
manner the difference between a Shrimp and a Crab depends princi-
pally upon the former being a springing and swimming animal,
whilst the latter is distinctly an ambulatory form. The different
burrowing types (Mole, Mole-cricket), may also be compared with
their nearest relations. The kind of movement does not, however,
always leave so clear a mark upon the structure as in the cases
mentioned. The adaptation is not always so exact, the modification
not always so complete as in these: other swimming Mammals may

F
66 General Part.

be compared, for example, with the Whale; Seals, Otters; or
other digging forms with the Mole; the Mole-cricket and Rabbits,
Dung-Beetles.

Sessile Animals.—In spite of the fact that the power of free-
locomotion is specially characteristic of the Animal Kingdom, there
are yet many forms which are fixed to one spot for at least the
greater part of their lives. The fixation usually results from
a certain part of the surface of the animal coming into connection
inseparably with a foreign object, a stone, a dead Mollusc-shell, or
the surface of another animal; the connection is often effected by
a cuticular secretion. Frequently, as in many Chetopods, the
connection is less intimate, for the shell only, with which the animal
is not in direct union, from which, it may escape, is fixed to the
foreign object. The transition from the free-living to the sessile
form, is given by those animals which, though capable of locomotion,
yet generally remain for some time (days or years) in the same
place (some Gastropods, Lamellibranchs, Fresh-water Polyps, and
others).

The immediate and very natural result of a sessile life is the
atrophy of the locomotor organs. The mouth in sessile forms
(Corals, Hydroids, Tubiculous-worms, Polyzoa, Brachiopoda) is very
often surrounded with long, prehensile arms or tentacles, which
are adapted either for seizing those animals which happen to come
near, or, by means of their ciliated border, for driving small organ-
isms into it. In other sessile animals (Vorticella, Sponges, Oysters),
the, tentacles are wanting, but small organic particles are conveyed
to the digestive organs by ciliary currents. This mode of life is
further obviously favourable to the formation of colonies: most
colonies are sessile, especially those which are arborescent.

4. The Transforming Effects of the Environment.

In the foregoing paragraphs, cases of adaptation to the
environment have been examined: some facts illustrating its direct
influence upon organisms will now be considered.*

It is a matter of universal observation that organs, at least in
many cases, improve with use, whilst they degenerate with disuse.
This may be seen, on the one hand, in the great development of the
arm, in people employed in manual labour: on the other, in the
feebler condition of this part, in those whose work is entirely mental.
Similar facts are also known for domestic animals.

It has further been proved in various instances that a special
food may have a modifying effect upon the colour of certain
birds. A reddish-yellow colour may be quickly produced in

 

* There is still much to be done in this connection so that the following remarks
must be taken somewhat tentatively.
VI. Biology. 4. Transforming Effects of Environment. 67

canaries by feeding them with cayenne pepper. Pigeons fed on meat
-have the gizzard modified like that of a bird of prey (thin-walled),
whilst, conversely, the stomach of an ordinary flesh-eating bird (Gull)
is so modified by a diet of corn that it becomes like that of a grain-
eating bird.

Interesting experiments have been made upon the transforming
influence ofan alterationin salinity. A Crustacean living in
salt lakes, Artemia salina, nearly related to the fresh water Bran-
chipus, is modified, by gradual increase in salinity, into another
form, which has been described as a peculiar and different species,
A, milhausenti. The modification does not arise immediately in one
and the same individual; it is gradual, extending through many
generations. Conversely if A. milhausenit is placed in slightly salt
water it becomes A. salina. Further, if the water is freshened by
degrees, until it is finally quite fresh, A. salina is gradually modified
in the other direction, so that at last it assumes the characters of the
genus Branchipus.

Animals may also be affected by variations in light; the cave
form Proteus, whitish under normal conditions, becomes speckled or
brownish if exposed to the light; for the pigment, usually absent,
now develops in the skin. If Sticklebacks are put in a glass with
a white bottom, they turn quite pale in the course of a few days,
and if they are kept five or six weeks under these conditions, the
dark colour does not return, even when they are put in a glass with
a dark ground.* Similar observations have been made upon other
fish. It has been found in not a few species of Butterflies, that the
colour of the pupa really depends upon the colour of the background
upon which the larva rests during the days immediately preceding
pupation. If the larva has lived on a light background (e.g. a light
wall), the pupa will be light, and vice-versé. In this, as in the other
cases mentioned, the action of light upon the skin of the animal
is evidently the primary cause.

Among Butterflies, noteworthy observations have also been made
as to the influence of temperature. If certain pupe are kept at
a low temperature, the colour of the Butterfly varies from the normal.

The seasonal dimorphism already mentioned, is probably originally
called forth by the effect of a different temperature upon the pupe: and as a
matter of fact, when the summer pupe are exposed to a lower temperature,
specimens may appear which are like the winter-brood.

In many cases animals are curiously affected by settling in a
new locality, no further cause being ascertainable. A few
examples will illustrate this. In 1870, a few wild Turkeys were

 

* The change depends upon the fact that the pigment-cells (chromatophores) of
the skin have almost entirely atrophied. This definite change in the colour of the
skin must not be confused with the colour change occurring in many animals
(Cephalopoda, Chameleon), which depends on the alternate contraction and relaxation
of the chromatophores.

F2
68 General Part.

taken to a small island near California. They multiplied very rapidly,
and ten years later numerous descendants inhabited the island, but
the weight of the specimens had fallen to one-third of that of
the birds introduced; in the course of a few generations they had
assumed a pigmy form. The effect of island life generally appears to
result in the formation of dwarfs. Changes in other respects have
resulted from the removal of animals into new surroundings. <A
peculiar form of Wild Rabbit has been produced in course of time
in the island of Porto Santo; it seems to be a distinct species, possess-
ing special colour-markings, etc. This has sprung from Spanish Rabbits,
which were imported 400 or 500 years ago. Trout were introduced
into New Zealand about twenty years ago; their progeny varies now
in certain points in the operculum, from the European species.

The influence of different external conditions upon the organism
is very clearly exhibited in domestic animals. Many of the
peculiarities exhibited by domestic races are simply the product of
local conditions, special food, etc.

It should be pointed out that the nature of the above explanations
is unintelligible. Why <Artemia should undergo modifications, as a
result of migrating into fresh water: why pigment should be deve-
loped in Proteus when it is exposed to the light: is not as yet exactly
understood. These facts are, however, of great importance, since they
demonstrate that the peculiarities of different faunas, the adaptation to
different kinds of food, the modification and degeneration of parasites,
mentioned in the preceding paragraphs, are in all probability, at
least to a great extent, the effects of external causes.

5. The Stages of Life.——Duration of Life.

A number of stages may easily be distinguished in the life of
most animals. The first stage is the embryonic period; a second, the
ensuing time of youth; a third, the period of complete development ;
and this, finally, may be followed by a state of retrogression.

The embryonic period has already (p. 50) been sufficiently de-
scribed. The time of youth extends from birth until the animal
becomes sexually mature (i.., produces ripe ova or spermato-
zoa), and therewith has almost attained its ultimate size and form.
During the adult period development is almost stationary, and the
organism passes quite gradually into the senile period, when the
organs suffer partial degeneration, and are functionally less active.
The whole strength of the organism, moreover, fails, so that it readily
falls a victim to adverse influences. This state is, however, only
clearly seen amongst the higher Vertebrata (Mammalia and Aves). It
need scarcely be said that the different phases are by no means
sharply demarcated.
VI. Biology. 5. The Stages of Life—Duration of Life. 69

In each year and in each stage of life there are, often, regularly
recurring periods. For many animals, there is, daily, a period of
activity and a period of rest. Many sleep during the latter, .e.,
they fall into a peculiar state of unconsciousness, in which the
activity of the organs is actually lessened (Mammals, Birds). The
time of rest usually occurs in the night, the period of activity in the
day ; but it is well known that some rest in the day, whilst they
become energetic in the evening or at night (nocturnal animals).

The year is similarly divided for very many animals into two
great periods, one of which is devoted to active life, during which
the daily activity and rest may naturally alternate: the other
to repose. This is specially the case with animals of the temperate
and frigid zones, which are, for the most part, rendered entirely
passive by the cold of winter, when their vitality is reduced to a
minimum (e.g., hibernating insects). Many Mammals (Bears, Dormice)
fall during this time into “winter sleep” (hibernation), a state
resembling ordinary sleep, but of an intensified kind. The un-
consciousness is deeper, the activity of the organs decidedly
less, and the temperature of the body may fall several degrees.
Similarly the resting period of tropical forms may occur during the
dry season, and in certain English animals the hottest summer-
time may occasion a summer sleep (Harthworms, Reptiles,
Amphibia).

Many animals, especially those of cold climates, have an annual
breeding season, at which time the ova and spermatozoa are
ripe, and when pairing takes place. At other times the ovaries and
testes are in a state of relative inactivity, and the sexual impulse is
extinguished. In warm countries, at least in most cases, such a
period does not occur. Many animals, whose nearest relatives in the
temperate zone have a limited period for breeding, reproduce all the
year round. It must also be noticed that the periodicity of marine
forms is less pronounced than that of land animals; ripe ova are
found in some marine animals throughout the year in cold regions.
This diversity naturally depends on the fact that the variations of
temperature are much less in sea-water than in air.

 

Death, ie, the final cessation of all manifestations of life,
usually occurs in consequence of the functional passivity of a vital
organ: If, for instance, the heart of a Vertebrate ceases to contract,
the body is deprived of a necessary condition of existence, viz., the
supply of blood laden with oxygen, and all the organs and tissues
gradually die. Anexact moment of death cannot be spoken
of: if a Mammal be killed by a violent blow on the head, move-
ments of the heart and respiratory organs, of course, cease almost
immediately, and the animal is said to be dead: but many of the
70 General Part.

tissues continue to live for many hours the muscles are capable
of contraction, etc.

Death may occur in any period of life: in forms which produce
very numerous ova, the majority of specimens invariably die in the
embryonic or larval stages, only a small proportion attaining sexual
maturity. This results almost always from detrimental influences
in the environment. The existence of most animals terminates
because they are killed or eaten by others: many fall victims
to pathogenic parasites, principally Bacteria and Fungi; others,
again, succumb to the effects of climatic changes. Death,
conditioned by the normal internal state of the body, occurs rarely :
even when an animal appears to die of old age, or when, as is
frequently the case, it dies, necessarily, after a single production
and discharge of ova or spermatozoa, external conditions may
still be an agent.

The duration of life in animals, the time over which life
can extend under favourable circumstances, varies enormously
for different forms: in some, it may be limited to a few weeks or
less, in others it may extend to a hundred years or more. The
rule may be generally laid down that in a natural group, the
larger species live longer than the smaller, just as their develop-
mental period is longer: the Elephant lives more than a hundred
years, the Horse, seldom more than thirty; the Mouse, only a few;
Large Insects often live several (the Cockchafer, e.g., four), smaller
ones, a year, or even a few months only. In some, the duration of
life is very definite (e.g., most Insects die soon after laying their
eggs), amongst others it is quite unlimited.

6. Protective Adaptations.

It is well-known that most animals are preyed upon by others,
and, as a rule, they do not confront the enemy defenceless, but are
protected in different ways.

The means of protection are sometimes offensive: the prey
itself practically attacks the aggressor. The weapons used in defence
are sometimes such as are used in other cases for attack: a carnivore,
for instance, tears its prey to death with its teeth, and also uses them
as defensive weapons when it is attacked. As a rule, animals resist
their enemies with any means at their disposal; Mammals with
hard hoofs, kick; if provided with strong claws, they scratch;
many insect larve pour out a malodorous or sticky secretion. The
caudal spines of some Rays; the stink-glands of many Insects and
of the Skunk (Mephitis), whose disagreeable secretion is ejected to
drive away the enemy, are special weapons of defence.

Other animals try to frighten the enemy by violent cries,
by terrifying movements, by bristling the feathers or hair.
V1. Biology. 6. Protective Adaptutions. 71

Other means of protection are of a purely defensive nature,
and here there is a great diversity. Many animals try to escape
danger by flight, and many weak and defenceless forms have
remarkable powers in this direction (e.g. Antelopes). Others save
themselves by hiding. Many offer resistance in the shape of a
specialised protective covering (a prickly skin, a stiff coat of mail).
Not a few Insects are characterised by a repulsive taste or odour, and
by this keep the enemy at a distance; many animals are protected,
whether in motion or at rest, by their resemblance to their sur-
roundings (protective resemblance) ; many, on account of their green
colour, are difficult to distinguish from their food-plant ; many, again,
are concealed by the leaf-like appearance of the wings or other parts:
the most delusive resemblance is perhaps found in some Indian
diurnal Butterflies (Kallima) which can scarcely be distinguished

 

Fig. 48. Two specimens of a Kallima Fig. 44. Two looper caterpillers (Geo-
settled, with closed wings, between withered metra betularia).
leaves.—After Wallace.

from the dry leaves of the trees or shrubs whereon they rest with
folded wings. Among European Lepidoptera, a Bombyx (Gastropacha
querctfolia) also exhibits a remarkable similarity to dry leaves. Other
Insects are like withered twigs, e.g. some Looper-caterpillars (Fig. 44),
which extend motionless from a branch, attached only by the hinder
end.

It seems specially remarkable that some animals which are
protectively modified have come to resemble, externally, others
which are from some cause unpleasant to their enemies, and
therefore, are comparatively unmolested (mimicry). In South
America, for instance, there lives a group of Butterflies (the Heli-
conidee), poor fliers, with conspicuous colouring but with so unpleasant
a smell, that they are rejected by Birds; certain other Butterflies,
living with these, but not possessing their odour, are remarkably like
72 General Part.

them in shape and colour and are thereby protected from the attacks
of Birds. Not a few moths (Clearwings) of which specimens live
in England are, in external appearance, extraordinarily similar to
Hymenoptera, which are protected by the possession of stings.

7. The Power of Resisting Unfavourable
Conditions.

Most cold-blooded animals can remain alive in spite of a consider-
able decrease of temperature, so long as the fluids in the body do
not freeze; and in many the water in the tissues does not freeze even
if the temperature of the body sinks several degrees below zero. Some
animals are so constituted that they revive after being frozen through
and through ; although as a rule, the injury occasioned is so great that
death ensues. In a dry state, some animals can withstand a very
great fall of temperature, even to many degrees below zero; for
instance, small dried Nematodes have been exposed to a temperature
of —19°, and have revived afterwards. Not a few forms are still
active at freezing point; others, however, are exhausted and
stupified, and many, long before it has sunk to this. The warm-
blooded Vertebrates, also, whose temperature under normal conditions
is fairly constant, may endure a considerable decrease of heat, but die
Jong before freezing point is reached: Rabbits, whose normal heat is
31° or 82° C., die if it sinks to 15°. Hibernation forms an exception,
for here the temperature falls to within a few degrees of freezing,
without danger to life.

Very often the outer layers of the body are of such a nature that they serve
to protect the inner part against cold: fur, in many Mammals; panniculus
adiposus (blubber) of Seals and Whales. To escape the winter cold, many
animals betake themselves underground (Earthworms), or, if aquatic, to the
warmer waters below the surface or to the mud at the bottom.

Warm-blooded animals suffer more from a rise in the tempera-
ture than from a fall. As soon as there is a rise of a few
degrees above the normal they die. Protoplasm coagulates at
40°—50° C., and therefore they cannot endure a higher temperature
than this. Possibly dried animals alone form an exception.

When small pools dry up, their inhabitants seem to disappear ;
but when they fill again with water, the same animals usually re-
appear very soon. This depends, principally, upon the fact that many
eggs have a hard covering which resists desiccation. Many Protozoa
also can secrete a similar capsule; more rarely the creature can
endure a real drying-up, a withdrawal of much water from the
tissues. This has been demonstrated for some forms: a Nematode
(Tylenchus tritict) may, after remaining for a long time in a com-
pletely desiccated and shrivelled state, revive, when it is put in
water again, absorbing it into the tissues; this is true also of
many other small Nematodes, and for Rotifers and Tardigrada,
VI. Biology. VII. Geographical Distribution of Animals. 73

which live in earth or on plants (moss). Most animals, however,
die when water is withdrawn to any considerable extent, whilst many
(e.g., Gastropods) sustain no injury from a slight deprivation.

Whilst some animals can scarcely live a day without food, others
can endure hunger for a considerable time without injury:
Frogs, snakes, and many others can live several months without
food. Sometimes animals can hold out for a very long time if they
are supplied with water alone, although they soon die if this can-
not be obtained. Many fast periodically; the periods of rest in
particular, which so many undergo, are simultaneous with periods
of starvation. It has been shown for some Fish (Salmon) that
before, or during, the breeding season they take no food for many
weeks, and the digestive tract becomes quite shrunken up: the same
thing, occurs also in certain other forms. Moreover, many Insects,
in the perfect state (which is here the breeding time also), can
take no food on account of the rudimentary condition of their
mouth-parts. During the period of starvation the body naturally
loses in weight, for oxidation of the tissues still continues. Often
when such a period approaches, masses of fat are stored up in the
body, and are consumed whilst it lasts (Bears, Insect-larve before
pupation) ; or reserves may be provided in other ways (crystalline
style of Lamellibranchs).

Whilst many animals, if deprived of oxygen, die instanta-
neously, or after a few minutes, there are others which can
dispense with it for a considerable time, even for many days.
Such animals as the Frog, indeed, can live in an atmosphere
destitute of oxygen: only after several hours does a certain dulness
occur, followed by an apparent death, from which the frog can
recover if it has not continued too long. Many Insects, Worms, etc.,
exhibit a similar peculiarity. Since the production of carbon-
dioxide continues, combustion must be carried on by means of
the oxygen stored up in the cells.

 

J

VII. The Geographical Distribution of
Animals,

Wuen the great divisions of the surface of the earth are compared
with one another, it is found that animal life is possessed of a consider-
able diversity of character, and this is true for different land faunas
(including fresh-water), as well as for marine. The animals which
live in South America are different from those inhabiting Europe;
the fauna of the East Indian coasts differs from that occurring round
Europe, and so on.
74 General Part.

As regards terrestrial and fresh water faunas, it is found that
the surface of the earth may be divided into a number of large
z00-geographical regions, each of which harbours a fauna,
distinguishing it, in certain respects, from the rest. Of such regions,
the following have been established :

1. The Palearctic region: Europe, Temperate Asia, Africa
north of the Atlas Mountains.

2. The Nearctic region Greenland and North America,
to North Mexico.

3.The Ethiopian region: Africa south of the Atlas
Mountains, Madagascar, South Arabia.

4. The Oriental region: India and Further India, with
the adjacent islands.

5. The Australian region: Australia, with some islands
which belong, geographically, to Asia.

6. The Neotropical region: South America, the Antilles,
South Mexico and Central America.

Each of these regions is distinguished by the possession of a
number of animals not occurring in the others, and giving it its
special characteristics, which may be more or less definite. The
regions are subdivided: the Palearctic region is separated into
four sub-regions: the European, including Europe, with the
exception of the South European peninsulas; the Mediterranean,
districts around the Mediterranean Sea; the Siberian, the greater
part of Northern Asia; the Manchurian, the eastern part of the
Chinese Empire, and Japan; each of these divisions is characterized
by lesser peculiarities.

This diversity of animal life results from many causes. Tempera-
ture plays a great part, and explains, for example, why tropical
regions present a richer and more varied fauna than cold countries,
and it is further evident that certain groups and species are suited to
a warm, others to a cold climate. By no means all the peculiarities
of the large areas can be explained in this way: that, for instance, a
large number of species occurs in the Palearctic region, but not in the
Nearctic, cannot be ascribed entirely to the influence of temperature
or other climatic conditions; for large tracts of both regions agree in
these respects ; and many of the animals which are characteristic of the
one can flourish abundantly in the other. This experiment has been
made with several species, among them the Common Sparrow, which
was introduced into North America, and has so increased there that it
has become a perfect pest. The same is true also of other regions:
with a single exception, the only Mammals in Australia are
Monotremes and Marsupials, and the reason for this cannot be that
others are unsuited to the country, for large numbers of European
animals are established there, and thrive exceedingly ; the Rabbit, for
instance, has run wild, and is now counted by millions. There must,
consequently, be other causes.
VIL. Geographical Distribution of Animals. 75

On a closer inquiry into these causes, it is found that large regions
are generally separated from one another by natural barriers of different
kinds—large seas, high mountains, extensive wildernesses—difficult to
surmount. That each region retains its own peculiar fauna, is primarily
to be ascribed to the fact that the animals have lived for a long time
as a relatively circumscribed group, and during this separation have
been modified in one direction, whilst their relations elsewhere have
developed in others. The differentiation of two regions, which were
originally continuous and in conformity, but now are separated, has
been explained as follows: on the one hand a number of peculiar
forms has originated in each; on the other, some of the original forms
have survived in one region and become extinct in the other. In this
way it is easy to understand, for example, the great faunistic
differences of the Neotropical and Ethiopian regions, which present
similar physical conditions, but are divided by extensive seas, so that
for immensely long periods of time they have probably had no
connection. If some of the regions in sharp z0o0-geographical contrast
are less clearly separated geographically (e.g., India and Australia)
it is probably due to their having been more definitely divided at an
earlier period. On the other hand, the circumstance that the
Palearctic and the Nearctic regions, for instance, which are now
absolutely distinct, exhibit in many points a considerable similarity—
a number of Mammals is common to both regions, and other types are
represented in both by nearly allied species—is plainly explicable, on
the ground that in early times, and even relatively late, these regions
were more closely connected than they are now. The diversities and
similarities of the zoo-geographical regions may consequently be
regarded to a great extent, as the result of alterations in
the conditions of the earth’s surface.

Regions similar to these may also be established for marine
animals, especially for littoral forms. They do not, of course,
coincide with the terrestrial divisions ; the fauna of the east coast of
South America, for instance, belongs to one region, that of the west
coast to another, and so on. The abysmal fauna, on the other
hand, has, for the most part, the same characters in all seas. Many
abysmal species have the widest geographical distribution; this is
quite intelligible since the physical conditions, the temperature, etc.,
are relatively uniform, and there seem to be no impassible barriers.
This holds also for the pelagic fauna, which, throughout the warm
zones, exhibits a very uniform character though in the cold seas,
both north and south, it is of a somewhat different type: since other
natural barriers are wanting, temperature is here of paramount
importance.

 
76 General Part.

VIII. The Geological Distribution of
Animals.

Geology, the history of the evolution of the earth, shows that
animal life has existed during immeasurable periods of time;
and further that the fauna through these ages has by no means
been always the same as at present, but has been subject to a series
of extraordinarily great changes. The animal remains of
different periods, enclosed in the earth’s crust, are the source of
this knowledge.

The presence of such traces in the earth’s crust is intelligible from the
following considerations. In all natural waters, but especially in the sea, there
is a constant deposition of finer or coarser particles, which may be either in
solution or in suspension in the water: the waves, assisted by atmospheric
action, tear off portions of the coast, and the débris is laid down again, the
coarser sand or gravel at once, in the shallower places; the very fine, which is
set in motion by the slightest ripple, only at greater depths, where the waves
do not penetrate. Rivers carry down to the sea great quantities of alluvium, into
which sink the dead shells of numberless minute marine organisms: in this way
the sand, gravel, or mud of the ocean bed, forms compressed deposits, which, in
course of time, often harden into solid masses of shale, limestone or sandstone.
The deposits are stratified: the end of one stratum and the beginning of
another are important as indicating either an interruption in the sedimentation
or the beginning of a different formation. The same thing occurs on a small
scale in great inland seas.

Such a formation of strata has taken place from the earliest times, and
in so far as animals have lived in water, or have chanced to fall in after death,
their remains are imbedded mm the deposits. These stores of animal remains
would, however, avail little, were they inaccessible; but the great changes
which have occurred in the earth’s surface in the cowrse of ages and which
are always taking place, have put the beds, even of oceans and of inland seas,
within reach. Parts of the surface, which in earlier times were covered by
the sea, are now, in consequence of elevations, dry land, and therefore may
be investigated, and with great facility, for at many places and in many
ways natural sections of the strata have been produced, so that remains
buried in the bed of the sea at different epochs have been brought to light.
The same thing has often occurred in fresh-water beds.

The animal remains which have been found in the earth’s strata
are, as a rule, grouped under the general term of petrifactions
or fossils. The former name is, however, not absolutely correct,
for “petrified” remains are only exceptionally found. As a rule, only
the hardest of the calcified parts have been preserved ; traces of the
soft parts occur quite rarely, and then usually as impressions in the
stone, which must in these cases be of a very fine grain: impressions
of Hydrozoa, for example, are sometimes found in the Bavarian
lithographic slate, originally a calcareous silt. The hard parts
occurring in the strata are in many cases relatively unaltered; the
VII. Geological Distribution of Animals. 77

shells of Molluscs, Echinoderms, etc., are often but little changed,
so also are the bones of Vertebrata, except that the organic sub-
stances disappear, and only calcareous matters remain, so that fossil
bones are lighter than fresh ones. In other cases, the bones or
shells have been infiltrated with other matters, such as the silica
dissolved in the water. For instance, Echinoid shells of the
Cretaceous period are found, filled with silicates (flint); or silicated
bones, as hard as stone, penetrated throughout with silica. To
such cases, the term “ petrified” may be correctly applied. Often
the hard parts themselves are not found, but merely their
impressions in the stone in which they were imbedded. Some-
times the shells, originally filled with silica, have later been dissolved
away, so that only the cast remains, a mass of flint with an impression
of the interior of the shell on its surface.

It is evident that the conception of the fauna of early times to
be formed from the study of fossils (Paleontology), must be
very incomplete. Only an extremely small proportion of the animals
of a given period are preserved in deposits; by far the greater number
disappear without a trace. Of these there are, in the first place, all
those which possess no skeleton, so that they vanish entirely with
few exceptions. Of the rest, the terrestrial forms are preserved only
in favourable cases, for,all those which are left after death, on dry
land, soon disappear entirely. Aquatic animals, especially marine
forms, with hard structures in or round them, stand, on the other
hand, a better chance of being preserved; but of these, by far
the greater number vanish, even when they are not devoured by
other animals, for by no means every part of the ocean bed is fit
for their permanent preservation. As for the parts which, in earlier
times, were really imbedded in a suitable place, and so were preserved,
many have been lost again, for the strata have been disturbed by
voleanic action, for example, which destroys all traces of life.
Finally, it must be noticed that only an extremely small proportion
of the materials contained in the strata now, is accessible to the
investigator: most of it is only too well preserved. All this must be
taken into consideration in estimating the importance of the con-
ception of the fauna of byegone ages, supplied by the examination
of fossils.

Now it is clear, from this inquiry, that animal life has gradually
undergone great changes from the oldest times until now; the
different periods (see p. 79), into which the history of the earth
may be divided, were characterized by different floras and faunas
whose remains are preserved in the strata, where they have been
ever since. The more remote the time, the more different is the
animal (and plant) life from that now existing. The animals found
in the older formations may, for the most part, be classified without
difficulty to-day, in the phyla and classes arranged for existing forms.
78 General Part.

They belong, however, without exception, to different genera and
species, often, also, to families and orders not occurring in this age,
and, moreover, large divisions, forming the most conspicuous part of the
present fauna, did not then exist. So, for instance, the Vertebrata,
from the oldest formation to the Devonian, are represented only by
Fish, whilst Amphibia, Reptiles, Birds and Mammals are entirely
wanting. From what has been said above it will be seen that these
observations must be interpreted with great caution, for the absence
of certain animals from a given formation does not necessarily mean
that they did not live in that period. This much, however, can
be said: had the group been largely represented in that early time,
some remains at least would probably have been found. The nearer
the period in which the formation was laid down to the present day,
the more closely does the fauna resemble that now existing.

This agrees with what must be expected on the theory of
descent. An opinion is expressed by the opponents of this
theory that, were it correct, the contents of the strata should fur-
nish a far more complete phylogeny: and they say further that
there is, even in the oldest fossiliferous formation, the Cambrian, a
small fauna, which, though poor, is still far more specialised than
the original fauna could be, according to this hypothesis. The
first objection is already disposed of by the foregoing remarks,
from which it is evident that our knowledge of primeval times must
necessarily be extremely incomplete; and as for the second
objection, it must be pointed out that the oldest known animals
are not necessarily the earliest to have existed ; it is quite possible that
they had a long line of unknown ancestors. Geology can show below
this formation others still older, which probably were also formed
under water, but were so modified (metamorphosed) in course of time
that it would not be extraordinary if the then existing fauna, which
may have consisted chiefly of soft forms, had left no trace.*

When the appearance, in course of time, of individual groups is
observed, a similar impression of the small number of facts against
the doctrine of descent, is gained. This is, for example, the case with
the classes of the Vertebrata: if a Vertebrate pedigree based on a
consideration of the structure of the different Vertebrate groups is
designed, Amphioxus being excluded, the following arrangement
results. The Pisces are the most primitive and from them arose
the Amphibia, from the Amphibia again, the Reptilia, and from
these, on one side, Aves, on the other, Mammalia. The story
from the earth’s strata corresponds closely with this. Fish are the
only Vertebrates of the Silurian and Devonian. The earliest Amphibia
are found in the Carboniferous. In the great formation following,

 

* From the nature of some of these old strata it can with certainty be asserted
that organisms must have assisted in their formation; this is especially indicated by
the presence of chalk, graphite, and anthracite.
VIII. Geological Distribution of Animals. 79

the Permian, are the first Reptiles; in the Trias, the first Mammals ;
and in the Jurassic, the earliest Birds. A study of special examples
gives a similar result. Amongst living Mammalia the Horse, as is
well-known, is in some respects, e.g., the structure of the foot, a very
peculiar and aberrant form. The horse itself appears late ;
the true horse, Hquus, with a single toe on each foot, as in the living
form, first occurs in the upper Pliocene, but its near relative,
Hipparion, having the middle toe, and also the second and fourth in a
reduced form, lived in the early Miocene and on into the Pliocene.
In the lowest strata of the Miocene, before the appearance of
Hipparion, a third genus, Anchitherium, is found, more remotely
related to the horse, from which the structure of its teeth shows a
considerable removal: it has, however, the same toes as Hippari n,
but better developed, and in this respect it approaches the genus
Palzxotherium, of the Eocene. In attempting to reconstruct this
phylogeny from anatomical considerations, it is certain that
Equus must be derived from MHipparion; Hipparion from
Anchitherium; and the latter from Paleotheriwm, or some nearly
related form: and with this the geological succession agrees closely.

A similar genealogy may be drawn up for many other groups,
although the imperfect knowledge of extinct forms often renders it
impossible.

TABLE OF FOSSILIFEROUS FORMATIONS.

Quaternary Pleistocene.

Tertiary Phocene.

or Miocene.
Cainozoic Escene.

Secondary Cretaceous.
or Jurassic.
Mesozoic Triassic.

Permian.
Primary Carboniferous.
Ob Devonian.
Paleozoic ee
Silurian.

Cambrian.

 
80 General Part.

Appendix.

 

Resemblances and Differences between Plants and
Animals.

Now that the most important features in the structure of animals in
general have been studied, a consideration of the relations of the Animal
Kingdom to the other great division of the organic world, the Vegetable
Kingdom, may not be out of place.

Both plants and animals are composed of cells; in the simplest forms of
a single cell only, but usually of a great number. The cells consist, at least when
young, of protoplasm. and generally (perhaps always) in plants as well as
animals, contain a nucleus. The protoplasm of plants displays the same
essential characters as that of animals (see pp. 1—4); it exhibits the power of
movement; it possesses irritability; it feeds, by taking up. materials from the
environment; it absorbs oxygen and gives off carbon-dioxide. The cells grow,
and multiply by fission. Sexual reproduction, i.e., the formation of a new
organism from a single cell after its union with one from another individual
of the same species, occurs in most plants as well as in most animals.

In considering the differences between the two kingdoms, the lowest
unicellular plants and animals, the Protophyta and the Protozoa will, at first, be
disregarded, whilst the Metazoa and the multicellular plants are contrasted.

In general construction there are important differences. Animals, with
very few exceptions, possess an alimentary canal, a cavity into which food
is taken, and in which it is digested and absorbed; it is specially characteristic
of this system that it appears at a very early stage of development. Anything
homologous, or even only analogous with, the digestive canal is entirely wanting
in plants, which take in their food through the surface in a liquid or gaseous
form. This is not, however, an absolute distinction, for an alimentary canal
is absent from some animals (e.g., the Tape-worms). Further, a muscular
and a nervous system are wanting in all plants, whilst these organs apparently
occur in all Metazoa: sense organs, which in their simplest form, as sense-
cells, are probably represented in all Metazoa, are never present in plants: a
vascular system and special excretory organs are also peculiar to the
Animal Kingdom, although they do not occur in every member of it. On the
whole, it may be said that plants exhibit in internal organisation, only a very
slight indication of that specialisation of organs which is, comparatively, so
pronounced in animals. The so-called organs of plants are only special regions
and appendages of the body.

Quite as significant is the contrast in the tissues composing the body.
In animals, the cells, originally undifferentiated, develop in very different
ways. Some remain in their primitive condition, others secrete an intercellular
substance, varying in structure and chemical composition ; in others, the proto-
plasm becomes modified into a peculiar contractile substance. In plants,
the cells are almost always surrounded with cell-walls, consisting of cellulose,
and the internal differentiation of the body, as far as its tissues are concerned,
depends, principally, upon a variation in the form of the cell or upon the thick-
ness, toughness, etc., of the cellulose wall, and less upon modifications of the
protoplasm, which always remains protoplasm, unless, as in many adult cells, it
has disappeared entirely.
Appendia. 81

With regard to food, there is a wide difference between animals and the
great majority of plants. Animals feed upon other organisms, or on organic
substances ; they cannot build up new tissues, nor repair the waste occasioned
by vital activity, with inorganic materials alone, although, of course, these
occur as constituents of the food (water, calcareous salts). Plants, on the
other hand, can feed exclusively upon inorganic substances, and in correlation
with this, some of their cells are provided with a peculiar green substance,
chlorophyll, which enables them, in the presence of light, to separate and
assimilate the carbon from the carbon-dioxide in the air. This power is not
possessed by animal cells, which are always destitute of chlorophyll*: on the
other hand, there are not a few plants (e.g. all the Fungi), from which it is also
absent. These cannot, therefore, assimilate carbon from the air, but, like
animals, must obtain it from organic substances.

Finally, in contrast to plants, animals possess sensibility and the powe1
of voluntary movement, which seems to be a mark of absolute distinction
between plants and the Metazoa.

From the foregoing remarks, there can never be any doubt as to whether a
given organism is a multicellular plant or a Metazoon, at all events, if a
careful examination has been made; but it is otherwise with the unicellular
organisms. They cannot be considered in the light of the differences
characteristic of multicellular plants and animals, just enumerated: indeed, it
is impossible to speak of alimentary canal, of musculature, of nervous system,
or of systems of organs at all, in unicellular animals; for the most part it is
difficult to say whether sensation and voluntary motion are exhibited or not;
and the mode of feeding is no absolute test (cf, above). To divide the
unicellular organisms between the two kingdoms is, to a certain extent arbitrary,
but since chlorophyll is peculiar to plants, and never present in the Metazoa,
it is justifiable to regard all organisms containing this colourmg matter as
plants: on the other hand, the numerous unicellular organisms which are
destitute of chlorophyll must not be regarded as animals without some further
demonstration: for it is undoubtedly wanting in many plants, and its absence is
not therefore adequate proof that the organism is an animal. Further, it
must be taken for granted that those organisms with a cellulose cell-wall
belong to the vegetable kingdom; whilst, on the other hand, those which exhibit
in their protoplasm a differentiation recalling the cell-modification of the
Metazoa (the muscle-like protoplasm in the Infusoria), should be classed as
animals. All those, moreover, which ingest solid food are considered to be
animals; but for many “animals” even this does not hold, and their location is
purely a matter of custom.

 

* It has been stated that chlorophyll is present in some animals, but this supposed
chlorophyll has been proved either to be some other green colouring matter, or to
belong to Alge parasitic in the animal.

&
SPECIAL. PART.

Systematic View.

Tur Animal Kingdom may be classified as follows :—

Sub-Kingdom I.: Protozoa.
Unicellular animals: they may be colonial, but then the
members of the colony are essentially alike.

Sub-Kingdom ITI.: Metazoa.

Multicellular animals: the cells are differentiated (division of
abour) ; alimentary canal, nervous and muscular systems, etc. The
Metazoa are subdivided into the following Phyla :—

Phylum 1. Cclentera.—Radiate animals of a very simple
structure; body saccular, composed of three layers enclosing a
digestive cavity. No anus. No body-cavity. The different organs
present elsewhere in the Metazoa are but slightly indicated here.
—Appendix: Sponges.

Phylum 2. Echinoderma.—Radial symmetry. Body-cavity.
Specialised systems of organs. Calcifications in the body-wall. A
vascular system. A special water vascular system in connection
with tube-feet. Larva bilateral.

Phylum 3. Platyhelminthia. — Bilaterally symmetrical,
unsegmented animals, without body-cavity ; usually without vascular
system or anus. A branched excretory apparatus with peculiar
terminations.—Appendix: Rotifera.

Phylum 4. Nemathelminthia. — Bilaterally symmetrical,
unsegmented animals of a cylindrical shape, with body-cavity and
anus.

Phylum 5. Annelida.—Bilaterally symmetrical, segmented
animals, with relatively similar segments. Limbs, when present,
unjointed. Thin cuticle. Body-cavity, vascular system (usually),
and anus present. Segmented ventral nerve cords, connected with.
a pair of ganglia lying above the pharynx. Hyes feeble. A pair
of tubular excretory organs in most segments (segmental organs),
—Appendix: Polyzoa, Brachiopoda,

Phylum 6. Arthropoda.—Bilaterally symmetrical segmented
animals, with variously modified somites. Limbs jointed. Dermal
skeleton formed from a well-developed cuticle. Body-cavity. Heart

G 2
84 Systematic View.

on the dorsal side. Nervous system as in Annelida. Highly
specialized optic organs (compound eyes). Segmental organs always
much reduced in number or entirely wanting.

Phylum 7. Mollusca.—Bilaterally symmetrical unsegmented
animals. A ventral muscular foot. A fold of skin, the mantle,
covering part of the body. No continuous cuticle. A part of the
integument secretes a shell which is closely adherent to the animal
at certain points. Body-cavity. Dorsal heart. A pair of gangha
above and beneath the pharynx, no ventral nerve cord. Usually a
lingual ribbon armed with rows of chitinous teeth. Segmental
organs reduced in number.

Phylum 8. Vertebrata.—Bilaterally symmetrical animals;
certain parts of the body (skeleton, musculature) segmentally arranged.
Usually two pairs of limbs, never more. Body-cavity. Ventral heart.
Central nervous system in the form of a continuous thick-walled
tube along the dorsal side, generally enlarged anteriorly. Beneath
this an elongate rod, the chorda dorsalis (notochord), which forms
the basis of the usually highly specialised endoskeleton.—Appendix :
Tunicata.
Sub-Kingdom I,

Protozoa.

It has already been noticed in the general part that the animals
included in the group Protozoa are simple cells, each individual
consisting of a single cell only. In certain cases, however, several
individuals may be united to form colonies, approaching the
metazoan condition, where each individual consists of groups of cells.
There is, however, an essential difference between a protozoan colony
and a metazoan individual, since the former consists of cells which
are identical in the more important respects, whilst the cells of the
latter vary in structure and in function, division of labour having
occurred.

In all the Protozoa, the body consists of protoplasm with a
nucleus; in many there are numerous nuclei. The nucleus is
usually spherical or oval, but sometimes more elongate. The protoplasm
frequently contains vacuoles, small cavities filled with a fluid;
some of these are contractile, te. they contract and enlarge
alternately as the fluid is expelled or fresh supplies are obtained from
the cell substance. Their contraction is, of course, dependent upon pro-
toplasmic movements, since they have no definite walls. Apparently
their function is essentially excretory, and in various forms uric
acid has been found in their contents. Not infrequently different
substances are secreted by the protoplasm, such as oil globules,
pigment granules, and so forth. Very often, too, it secretes
skeletal structures usually consisting of lime or silica; these
will be considered in greater detail under the Rhizopods and Radio-
larians.

Many Protozoa, like the Amoeba, can protrude pseudopodia
from any part of the body, so that its external form is constantly
changing. In others this power of amoeboid movement is entirely
wanting, the outer layer of protoplasm being firmer than the inner
softer portion, from which, however, it is often not.sharply marked
86 Protozoa.

off (Infusoria): or the outer layer may constitute a definite and
well-defined, although flexible, coat, as in the ectoplasm of Grega-
rines. In both cases the body is, however, usually capable of
considerable change of shape. Where the form is fairly constant,
the body is often beset with cilia or flagella, varying in size and
number. Almost all the Protozoa are microscopic in size.

Reproduction, like multiplication in all other cells, occurs
by fission; the nucleus dividing first and then the protoplasm.
Usually the fission is binary, but very often the animal breaks up
simultaneously into a large number of small individuals (spores).
Sometimes division occurs by a process of gemmation, a small
portion being constricted off to form a new individual.

A great many forms, of various divisions, have the power
of encysting if the conditions are unfavourable, emerging
again when they improve. The body becomes spherical and
secretes a membrane of varying thickness over its whole surface,
and in this state it is able to survive complete desiccation: thus
encystation occurs if the water in which the organism is living
begins to dry up: or, again, if it is too stagnant, or when the
food is’exhausted, or, after the animal has ingested a large supply
of food, when it remains at rest until digestion is completed.

 

Fig. 45. Fig. 46.

Fig 45. An Infusorian in the free state (left), and encysted (right). N nucleus (macro-
nucleus).—After Balbiani.

Fig. 46. An encysted Infusorian which has broken up into a number of spores, now
in the act of leaving the cyst.— After Fourquet.

Lastly, it may encyst before undergoing fission. The
protoplasm then divides into spores (frequently a very large.
number), which later on leave the cyst (cf, the Gregarines; the
same thing also occurs in other forms, e.g., in the Infusoria).

In many Protozoa, conjugation may sometimes be observed: two
individuals of the same species approach one another and fuse, a
fusion of the nuclei also occurring. This conjugation recalls the
fertilisation of the Metazoa, which also consists in a fusion
of two cells and their nuclei. Very often it is followed by repedted -
Class 1. Gymnomyxa. Order 1. Rhizopoda. 87

division (cf. the Gregarines), just as in the Metazoa, fertilisation is
succeeded by active cell division. For the conjugation of the
Infusoria, see that group.

Gymnomyxa.. : . i With pseudopodia.
Infusoria. Body covered with cilia t

Gregarina. Without cilia Without pseudopodia.

Class 1. Gymnomyxa. (Sarcodina.)

The numerous forms belonging to this class are all possessed of
the power of protruding pseudopodia, by means of which they
move about, and ingest their food. Most of them are provided with
a skeleton, harder portions within or around the protoplasm, varying
in form and in chemical composition. They are for the most part
marine.

Order 1. Rhizopoda.

In some Rhizopoda, for instance, in the Amceba, which has
already been mentioned, there is no skeleton. Most of them, however,
are furnished with a protective structure in the form of a shell,
which surrounds the greater part of the body. In the simplest cases
the shell is cap-shaped, with a single large opening through which
the protoplasm projects. In others it is complicated by being

 

Fig. 47. A (Diflugia) and B (Euglypha), two imperforate fresh-water Rhizopods, with
chitinous shells ; in A small foreign bodies are fastened to the shell. m nucleus, p psendo-
podia. C Marine Rhizopod (Rotalia).—A after Stein, B after Hertwig and Lesser, C after
M. Schultze.
88 Protozoa.

multilocular, i.¢., divided by transverse septa into several small
cavities, which, however, communicate by small pores in the septa,
so that the protoplasm is continuous. Such shells are either
straight or spirally coiled, a character which may also obtain in
the unilocular shells; and they often closely resemble a nautilus
shell in miniature. Both unilocular and multilocular shells may
either be perforate, 1%e., having besides the larger opening,
numerous fine pores, through which the protoplasm may extend;
or they may be imperforate, without such apertures. In
the Perforata and in some Imperforata the shell les actually
within the protoplasm, for its surface is covered by the
overflow of protoplasm. The shells either consist of a chitinous
material, to which grains of sand or other foreign bodies are often
firmly cemented; or they are composed entirely of calcium
carbonate as in most marine forms (the calcareous shell may
also be strengthened by the incorporation of foreign bodies).

The protoplasm is usually homogeneous throughout, but some-
times there is a superficial layer which differs from the rest in its
hyaline appearance and in the absence of granules, although not
sharply separated off from the inner granular portion. Pigment
granules frequently occur in the protoplasm ; there are often vacuoles,
which are as a rule non-contractile. The nucleus is of simple
spherical form; occasionally there are several, sometimes many,
present. The pseudopodia are either broad lobes (Fig. 1,
Fig 47 A), or delicate threads which then radiate out in great
numbers, and frequently anastomose (Fig. 47 C) ; these thin pseudopodia
are often of considerable length, and may be even as much as ten
times as long as the shell. The animal moves by means of its
pseudopodia, crawling about at the bottom of the sea, over plants,
etc.; by means of them also, it surrounds microscopic organisms or
decayed organic fragments, and thus feeds upon them.

Comparatively little is known as to their reproduction,
Simple binary fission has been observed in various Rhizopods ;
in the forms with shells, one of the newly-developed individuals
usually constructs a new shell, whilst the other remains in the old
one; or both may leave the original shell, and form new ones.
Sometimes, also, a large number of smaller individuals may arise
within an older organism.

Some of the Rhizopods inhabit freshwater; some are found in
moss or damp earth, a few upon dung, a few are parasitic (e.g. Amwba
coli, in the human intestine). The majority, however, are marine,
they are usually found crawling about on marine plants, colonial
animals, or on the ground, usually at no great depth. A few forms
are Pelagic, swimming about in the open sea, often in great numbers ;
as they die their shells sink to the bottom, where they are
met with in the extensive deposits composed of their remains
Class 1. Gymnomyxa. Order 1. Rhizopoda. 89

(Globigerina). Similar beds of Rhizopod shells have also been
deposited in earlier times, and these, though in a more or less
fragmentary condition, form a consider-
able part of important geological strata
(chalk).

Amcbe with lobate pseudopodia and without
shells (¢f., p. 3-5) occur both in salt and fresh
water. Several genera. with simple unilocular
chitinous shells (sometimes covered with foreign
bodies) are found in fresh water (Fig. 47 A, B). Fig. 48. Nummulites distans,
One of the numerous marine shell-bearing forms, ae ge size A the figure .

j * v "2 0] a - e le: represents al example
which are often extremely fragile, is drawn it. hich has been longitudinally
Fig. 47 C. Among the very numerous fossilforms gissected: that on the right,
may be mentioned the genus Numinulites (Fig. 48), a transverse section. — After
distinguished by its size, which is, for a Protozoon, Archiac and Haime.
enormous.

 

Order 2. Radiolaria.

The Radiolaria differ from the MRhizopoda, in possessmg a
central capsule, a porous membrane enclosing the greater
portion of their protoplasm. Outside the central capsule there
is a thin protoplasmic sheath, and outside this again, a thinner
or thicker sheath of gelatinous material. The body is typically

 

Fig. 494. Diagrammatic figure of a Radiolarian from which the skeleton has
been removed. c central capsule, g jelly veil, k nucleus, p pseudopodia.— Orig.
Fig. 49 B. Skeleton of a Radiolarian.—After Haeckel.

spherical; but the deviations from this type are numerous. In
addition to the capsule, there is usually a well-developed
skeleton, which generally consists of silica {occasionally of an
organic substance); it varies considerably in the different forms. In
some it consists of a number of isolated spines which radiate from the
90 Protozoa.

centre of the animal, perforate the contral capsule and the various
soft layers and project all over the surface. In others it forms a
latticed sphere perforated by many large apertures whilst spines
sometimes radiate from it to the surface (Fig. 49, B). In others
again, there are several such spheres, enclosed one within the other
and connected by radial spines crossing from one sphere to another ;
if there are two such spheres one lies within, the othor outside the
central capsule ; if there are three, the innermost may lie within the
central nucleus. In other cases the shell is more discoid or dome-
shaped; altogether the skeletons of this division offer the greatest
variety of beautiful forms.

Within the protoplasm of the central capsule there is a nucleus
(sometimes several); in that external to the capsule there are non-
contractile vacuoles; white, red, and yellow oil globules; and red,
yellow, and brown pigment. Delicate pxrendopodia usually
radiate on al] sides from the thin layer of protoplasm surrounding the
central capsule; they often anastomose. ‘They perforate the trans-
parent jelly veil and project into the water as long filaments. In the
protoplasm cxternal to the capsule there are numerous vacuoles
which may also occur in the portions of the pscudopodia lying
in the jelly veil, so that the whole of the jelly has a vesicular,
foamy appearance.* Food, consisting of unicellular plants and
animals, ix caught by the pseudopedia and drawn into the
protoplasm.

The reproductive processes are imperfectly known. In some
forms the contents of the central capsule have been observed to
break up into a number of smaler cells cach furnished with from
one to three long flagella, “swarm spores,” whose ultimate fate is
unknown ; it is only certain that the capsule bursty and the spores
become free-swimming.t Some Radiclaria, in consequence of repeated
division, form colonies, the individuals of which are connected by
a common jelly veil.

Small yellow cells are frequently found in the Radiolaria ;
their existence used often to be cited as one of a number of points
indicating the multicellular structure of this group. Recent researches
have, however, demonstrated that they are really independent
organisms, small Algw, which are parasitic in the Radiolaria, or
more correctly, commensal with them, for the organism scoms rather to
profit than'to suffer by their presence, since like othor plants they

* The vacuoles, at least in some of the Radiolaria, contain a watery fluid of a less
specific gravity than sea water. The protoplasm contracts in response to some
externa] stimulus (¢.g., the violent movements of the water), some of the vacuoles are
burst and the animal sinks; after a storm, therefore, there are no Radiolaria to be
found at the surface. They rise again later on, in consequence of the reappearance of
the vacuoles.

+ Sometimes in one and the same central capsule two kinds of spores arise, Jurger
and smaller, macro- and micro-spores.
Class 1. Gymnomyxa. Order 2. Radiolaria. 91

give out free oxygen which is required by the hosts for respiratory
purposes (symbiosis).

The Radiolaria are exclusively marine; they are frequent in
the open sea, and live at very various depths, though chiefly near the
surface, where, especially in warmer zones, they occur in enormous
numbers and in a great variety of forms. Like the shells of the
pelagic Rhizopods, the silicious skeletons of the Radiolaria also sink
to the bottom, where they form the chief constituent of the extensive
deep sea deposits found in some regions.

Fig. 50.
Actinospherium
Bichornti. k nu-
cleus, n food par- |. __.
ticles, v vacuoles. “
(After RK. Hertwig).

 

A small group of Protozoa, the Heliozoa is found in fresh water, rarely -
in the sea. They differ from the Radiolaria in the absence of a central capsule,
but in most other respects agree with this group. When a skeleton is
present, it is silicious (trellissed spheres or spines); the pseudopodia are radially
disposed. Of the freshwater forms, Actinosphwrium Hichhornii, which attains
the size of a pin’s head, may be mentioned. The protoplasm is very vesicular,
and contains numerous nuclei. There is no silicious skeleton, but the
pseudopodia are supported by firm axial threads of organic material.

Class 2. Infusoria (Ci/iata).

The Infusoria possess a thin external layer (ectosarc) of a firmer
consistency than the rest of the protoplasm (endosarc), and in
consequence cannot protrude pseudopodia. The body, which is
usually round, oval, or somewhat more elongate, is, however,
92 Protozoa.

flexible to a certain extent, and may alter in form. The ectosare
is absent from two spots on the surface; one of these serves
for the ingestion of food, and is termed the mouth, whilst
through the other, the anus, undigested material is ejected.
The two openings are usually situated at opposite extremities of the
body ; the end where the mouth lies is termed anterior, the other
posterior. The mouth usually opens at the base of a funnel, which
is often fairly deep, whilst the anus is only visible as a slit, when
excreta are ejected. The Infusoria are all provided with cilia,
which constitute the chief locomotor apparatus. In some forms they
are distributed over the whole surface, and are then often arranged
in longitudinal rows; in others, some of the cilia are specially
developed as spines or hooks, or there may be one or several rows
of these between the other cilia; specially common is the presence
of a spiral row of powerful cilia, at the anterior end of the body,
by means of which the food is driven into the mouth. In others,
again, the whole covering, with the exception of this row, or this
row and one other, is completely lost.* Hard skeletal structures
like those of the Gymnomyxa do not occur here; but some of the
Infusoria secrete round the body a gelatinous or membranous shell,
beaker-shaped or tubular, nto which their protoplasm may be with-
drawn: the relation between the animal and its shell is the same as
that between a tubicolous worm and its tube. The shell is generally
attached to a foreign object, but it is carried about by some marine
Infusoria.

In the protoplasm there is a large macronucleus, which
may be round, sausage-shaped, ribbon-like, or moniliform (Fig. 52),
and one or more smaller micronuclei; rarely there are several
macronuclei. Near the surface are the contractile vacuoles,
which excrete the water they contain through one or more fine
pores, and then take up a fresh supply from the protoplasm. In
the outer portion of the protoplasm there are frequently delicate
threads of a contractile substance, muscle fibrille: fat
globules and pigment granules also occur in the endosarc.

The Infusoria reproduce by fission (Fig. 52), which usually
occurs at right angles to the long axis, and is thus transverse; it
is preceded by a division of both macronucleus and micronucleus.

Whilst permanent conjugation is rarely met with here, a tem-
porary fusion of two individuals, which separate again later, occurs
very frequently. They are adherent over a limited area, and during

 

*In some Infusoria there are the so-called membranelle, vibrating, laminate
structures, each of which is regarded as a short row of fused cilia. The “undulating
membranes,” long, vibratile ribbons attached by one edge, are also to be regarded
as membranelle, which have arisen from long rows of cilia.
Class 2. Infusoria. 93

(and after) the union, a series of changes occurs in the nucleus,.
with a partial exchange of nuclear material.*

The details of the process are as follows: the macronucleus becomes irregular,
breaks into several fragments, and is completely absorbed into the protoplasm.
At the same time, the micronucleus divides into several pieces (Fig. 51, 2),
which with one exception, disappear (Fig. 51, 3), the remaining portion divides.
into two parts (Fig. 51 4), one of which migrates into the other animal (Fig. 51,
5, 6), so that a mutual exchange of micronuclei occurs. The organisms then

2 3 4 5 6

EBAOVYRD

Fig. 51. Two Infusoria in various stages of conjugation. Diagrammatic. n-
micronucleus, N' macronucleus. The micronucleus of the one individual is left clear, that.
of the other, dark. See the text.—Orig.

    

separate. The two micronuclei, one of which is derived from each of the:
conjugates, fuse, and by the division of the nucleus thus formed, a new macro-
nucleus, and a new micronucleus arise.

The food of the Infusoria consists principally of unicellular plants.
and animals—Bacteria, Diatoms, Flagellata, other Infusoria, etc..
In many the food is brought to the mouth by ciliary currents, as
described above; in others, the edges of the mouth (which are often
supported by tiny rod-like structures) effect the prehension of prey.
The Infusoria are for the most part extremely active little organisms,
swimming by means of their covering of cilia, or by the contractions.
of the body: or gliding about over foreign bodies. Not a few are
temporarily or permanently fixed, and several of these form colonies
by incomplete fission or budding. Both as regards individuals
and species, they are abundantly represented in freshwater:
they congregate principally about decaying plants or animals. A
proportionately smaller number occur in the sea; one division of
shell-bearing Infusoria is pelagic, its members swimming in the open
sea together with Radiolaria and pelagic Rhizopods. Some live as.
parasites on the skin of fish or other aquatic animals; and it is by
no means rare to find them in the alimentary canal of different
Vertebrata. When the ponds in which they live become dried up,
great numbers in the encysted condition may be carried away by

 

* Conjugation usually occurs after the animals have been for some time rapidly
increasing by division, and have exhausted the food supply. When there is a constant
and abundant supply of nutrition, conjugation does not take place, and fission con—
tinues ; the consequence of this, however, is the degeneration and finally the death of.
the individual.
94 Protozoa.

winds, together with other dust, and thus they appear quickly
wherever it is possible for them to exist. ;
1. Of the innumerable fresh-water Infusoria, the following common forms

may be mentioned: Paramecium, body oval, covered with uniform rows of cilia
Stylonychia, oval, with a series of cilia, anteriorly, leading to the mouth, and

Fig. 52. Fig. 53.

 

Fig. 52.°1 An Infusorian (Paramecium). 2—4 The same in various stages of
division; in 2 the mouth and contractile vacuole are re-duplicated ; in 3 the macro- and
micro- nuclei are much elongated and constricted, in 4 they have divided, cv contractile
vacuole, cv’ newly-formed vacuole, 0 mouth, o’ newly-formed mouth, N macro-, n micro-
nucleus.— After Biitschli.

Fig. 58. Vorticella; lower portion of the stalk not drawn. na food particles,
s stalk. Other letters as in Fig. 52.—After Biitschli.

with strong spiny or hook-like cilia ventrally; Vorticella (Bell-animalcule),
a stalked Infusorian furnished with spirally arranged cilia at the anterior end, but
otherwise naked; mouth and anus situated in a common groove, anteriorly: at
the opposite end arises a stalk, through which runs a muscular thread. By
means of the stalk, which is frequently very long, the animal attaches itself to
various foreign bodies. The Vorticelle may sometimes break free from their
stalks, and become free-swimming.* Many form branched colonies.

2. Many species belonging to the genus Tintinnus, etc., and bearing very
beautiful chitinous shells, are sometimes found in great numbers in the
open sea.

3. As an example of parasitic Infusoria, Balantidiwm coli may be mentioned ;
it is always present in the large intestine of the Pig, and more rarely in Man.
The body is egg-shaped, uniformly covered with cilia, but with a somewhat
stronger series near the mouth. Other Infusoria occur, e.g., in the paunch of
Ruminants, and in the large intestine of the Horse.

 

* The conjugation of the Vorticellids is interesting. It occurs between a larger
sessile individual or macrozoid, and a smaller free-swimming microzoid. The latter
attaches itself to the larger one, and conjugation occurs in the ordinary way; after
the exchange of the micronucleus, however, the protoplasm of the microzoid is
absorbed into that of the macrozoid, and the empty cuticle of the former drops off.
Class 2. Infusoria. 95

Under the term Flagellata is included a large number of diverse unicellular
animals, which are all, characterised by the possession of a single powerful
flagellum. These organisms
do not, however, constitute A B Co
a natural division: some of
them seem to be most closely
allied to the Infusoria, and in
any case undoubtedly belong
to the Animal Kingdom.
Others are certainly vege-
table organisms, provided
with chlorophyll (ef. p. 81),
whilst yet others are of very
doubtful position. Among
the Flagellates possessing
animal characters may be
mentioned the Mona-
dinide, small organisms
provided with one or several
flagella at the anterior end,
ocemring in vast numbers Fig. 54. Various Monadidz. <A Cercomonas

in decaying substances and musce (from the duodenum of the house-fly). B Bodo
in the alimentary canal of ovatus, C Hexamita rostrata. ¢ contractile vacuole,

various animals; some 7” nucleus.—After Stein.

species are invariably pre-

sent in the stomach of the Ruminants, the cecum of the Pig, the rectum of
Frogs and Toads; whilst some have been found in the alimentary canal of Man.

  

Class 83. Gregarinida.

The Gregarines which are, without exception, parasitic, are, like
the Infusoria, unable to protrude pseudopodia, but are distinguished
from these, amongst other things, by the absence of cilia. The
unicellular body is usually, although not always, surrounded by a
definite coat: the protoplasm is usually divided into two layers,
the inner granular and the outer clearer, not, however, sharply

 

 

 

Fig. 55. Diagrammatic figure of a Gregarine. 1 a single individual, 2 two conjugating
individuals, 3 two such encysted, 4 the same, completely fused, 5 they have divided into
spores, 6 within the spores falciform young are formed, 7—9 a spore at various stages of
development strongly magnified.— Orig.
96 Protozoa.

separated. There is almost invariably only a single round nucleus.
The Gregarines are mostly elongate ; in many the cell is divided into
an anterior smaller, and a posterior larger, section (the nucleus being
in the latter) separated by a thin septum; in others, on the contrary,
the cell is quite simple. Sometimes at the anterior end, there is a
proboscis-like process which is often armed with hooks, and forms
an organ for attachment to the intestinal wall of the host. The
Gregarines move about within the host by contraction, expansion,
or flexure of the body, movements dependent on the streaming of the
protoplasm. Food is absorbed over the whole surface by endosmosis,
but no solid material is taken in.

Reproduction is very characteristic. It begins by the
rounding of the body and the secretion of a cyst; sometimes the
actual firm wall of the cyst is surrounded by a gelatinous envelope.
This encystation is usually preceded by the conjugation of
two individuals, which come into connection without, however, fusing
at first; true fusion only occurs after encysting. A single
individual may, however, also encyst. The contents of the cyst divide
into a varying number of smaller cells, spores, each of which
becomes surrounded with a separate coat. Lastly, the contents of each
spore divide to form a small number of most minute cells, usually of
elongate form, the falciform young (pseudonavicelle). These
are liberated by the bursting of the coat; their further development
has not been followed, but it is probable that each develops into a
Gregarine. In this group, therefore, reproduction consists essentially
in a repeated division of the original cell, usually preceded by
conjugation.

The Gregarines occur as parasites in a large number of Metazoa
belonging to the most widely separated groups: Echinoderms,
Flatworms, Chetopods, Arthropods, Molluscs, Vertebrates; the
Myriapoda and Insecta may be mentioned as groups which are
specially liable to infection. They occur both in the various cavities
of the body (e.g., in the alimentary canal) and also in the tissues.

Of numerous forms recorded the following may be cited as
examples :

1. Porospora gigantea, very common in the alimentary canal of the Lobster,
a very long narrow Gregarine, which attains the length (enormous for a
Protozoon) of 16 m/m.

2. Coccidium oviforme, small (035 m/m. long), egg-shaped forms which
frequently occur in the bile ducts of the Rabbit, occasionally in Man (where
they may cause fatal disease). Whilst young, the Coccidia are naked cells,
but later encyst. In this condition they resemble the eggs of certain
parasitic worms for which they have been sometimes mistaken. After encysting
they pass into the intestine with the bile, and thence escape with the excreta.
Development then proceeds to a further stage: the contents of the cyst
divide into four spores, within each of which two falciform young develop.
If such a spore-containing coccidian cyst is taken in by a rabbit with its

®
Class 8. Gregarinida. 97

food, the cyst wall apparently dissolves and the young wander through the
bile ducts into the liver and there develop into Coccidia.

3. Embedded in the trans-
verse muscle fibres of many
Mammalia, e.g., very frequently
in the Pig, there occur small
bodies, the so-called Rainey’s
or Miescher’s corpuscles
(Sarcocystis). They are cylin-
drical or spindle-shaped bodies,
varying in length (up to several

 

 

D

m/m.), each enclosed in a single Fig. 56. Coccidiwm oviforme, A—B encysted,
musclefibre. Hachissurrounded C—D formation of spores and falciform young.—
by a coat, and consists of a After Leuckart.

protoplasmic mass containing

a large number of small falciform young ;

each surrounded by a thin mem-
brane. Rainey’s sacs are now usually
regarded as organisms allied to the
Gregarines; the groups of falciform
young are considered comparable to
the spores of a Gregarine. If this
comparison prove correct it would still
be a peculiarity of these organisms that
the formation of the spores and falci-
form young begins very early, before
the growth of the sac is complete (the
falciform young occurring even in
very small forms), and goes on quite
gradually, so that fresh portions of
protoplasm are constantly forming
spores and falciform young. The
method of infection is unknown: they
do not usually appear to be very in-
Jurious; and so far they have not been
found in Man.

the latter are arranged in groups.

 

Fig. 57. 1 Raineyian sac in w muscle
fibre, 2 the tip of one highly magnified, 3
various falciform young.—After Leuckart.
Sub-Kingdom II.

Metazoa.

Phylum 1. Celentera.

Taz Coelentera are chiefly distinguished by the extreme simplicity
of their structure, and by the slight degree of differentiation in their
organisation. They occupy a more primitive position than any other
Metazoa known.

Various types of Ceelentera are met with. In the simplest
case, the body consists of a longer or shorter sac, one end of which

  
  

 

 
 
   
  
  
 
 
  
 
  

      
 

 
  
 

 

   
  

       

 

    

        
   
      
    
 
 

    

 

 

 
 

2 7 an SUP Ny,
a & SEXO mO
= oes fs ae ea}
HE EH Ae YA ES
He. Eben, Ha | (ee Ee
HE Ebly FE Sey
He EH Be ES
Hy EH ey Ey?
Ae me a
yj Ei Oo ios]
be =e om
/ [ ¥el [3]
w Ke Fo
se TSA
a DTT tt

Fig. 58. Diagrammatic figures of the chief types of Coelentera. A the simplest form,
B medusa, ( coral type. «1 endoderm, m mesoglea, y ectoderm, » mouth, n’ external
aperture of the stomadsum of a coral polyp.—Orig.

is open, the other closed (Fig. 58 A). The body-wall consists of an
external layer of cells, theectoderm; within this a thin
sheath of structureless jelly, the mesoglea, and most internally
another cellular layer, the endoderm, lining the cavity of the sac ;
the ectoderm and endoderm are continuous at the open end of
the tube, the mouth. It is evident, therefore, that such a
Ccelenterate differs but little from a gastrula, the difference
Ceelentera. 99

consisting in the presence of a gelatinous layer between the inner
and outer layers of cells, the two latter corresponding with the
hypoblast and epiblast of the gastrula. In addition to this, however,
as will be seen more fully later on, the cells of each layer are
not all similar as in the gastrula, but have been developed in
different ways, some as muscle cells, others as nerve cells, etc.

Allied to this simpler form, and capable of being derived from it
are other types of somewhat more complicated structure. Very
often (Fig. 58, B) the lower closed end of the sac is broadened out to
form a convex disc, so that the animal resembles an old-fashioned
candlestick. The discoid portion consists of the same layers as the
rest of the body ; the mesoglea is, however, especially well developed
on the convex side, and the two lamine of the endoderm, which cover
respectively the upper and the lower walls of the cavity in this
portion, are fused in certain regions, so that instead of a flat simple
cavity there is a regular system of canals; at the lines of fusion
the endoderm shrinks to a thin membrane. Whilst Ccelentera of
the first and simplest type are usually sessile, those just described, the
medusoid forms, are generally free-swimming; the disc is turned
upwards in swimming, the opening of the sac downwards.

A third type occurs in the coral polyps (Fig. 58, C).
Here the cavity of the sac is very wide, and its upper portion is
invaginated, so that the true mouth is situated at the base of the
turned in portion or stomodeum.

The Ceelentera are usually provided with soft appendages, the
tentacles, which are outgrowths or evaginations of the body-wall and
consist of the same layers; they are usually found near the mouth,
but in the meduse are carried out on to the edge of the disc.

In the whole structure of the body, e.g., in the arrangement of the
appendages just mentioned, and in the distribution of the canals in
the disc of meduse, a more or less sharply marked radial
symmetry is evinced, such that the chief axis, about which the
yadial structures are arranged, corresponds with the central axis of
the sac. The number of rays differs in the various Ccelenterate
groups; most frequently the body is divided into four, or a multiple
of four rays, in others into six, or a multiple of six.

The ectoderm, which forms the outer covering of the body
(analogous with the epidermis of Metazoa), is a peculiar epithelial
layer, the cells of which are developed in very various ways.
Some are simple epithelial cells, either flat or cylindrical, and pro-
vided with one or more cilia; such cells are quite comparable with
the epidermal cells of other Metazoa, and on this account they are
termed true epidermal cells. Others, like these and occurring
among them, differ in that their inner ends are modified to
form contractile fibrils, so that their outer protoplasmic portions
perform the function of epithelial cells, their inner portions of muscle

H 2
100 Celentera.

fibres; such cells, which only occur among Coelentera, are termed
epithelio-muscle cells.* They may, however, lose their
close connection with the rest of the epithelium, and may lie
within this as simple muscle cells; then the non-contractile
portion of the protoplasm, together with the nucleus, lies as in
the muscle cells of many other animals on one side (the outer) of
the contractile fibril. Further between the true epidermal cells, or

|

   

 

oe

 

Fig. 59. Cells of a Coelenterate (Actinian). wu epithelio-muscle cell, b muscle cell,
c—d ganglion cells, e sensory cells, f nettle cell, g nematocyst with everted head.—Partly
after Hertwig, partly Orig.

between the epithelio-muscle cells, sensory cells may be present.
Each of these bears at its outer free end, a single delicate sensory
hair, whilst its inner end is produced into one or several fine threads.
Between the inner ends of the other cells, or entirely below these,
lie certain cells which from their general appearance must be re-
garded as ganglion cells; from each, several delicate fibrils run
out in various directions, and ramify among the similar fibrils
of the sensory cells. In the ectoderm, there are, moreover, a number
of nettle cells, each of which bears a fine hair at its outer end,
and encloses a so-called nematocyst, a tiny bladder-like structure,.
containing a coiled thread, which under certain conditions, notably
if the animal is irritated, can be shot out with great force; within
the threads is an irritative fluid, which may cause a burning sensation
in the skin of man, more powerful in some forms than in others,
whilst it paralyses or kills smaller animals. lastly, there are
beaker-shaped cells which secrete the mucus with which these
forms are so often covered (gland cells). It must be noticed,
further, that the cells which have been described as constituting
the ectoderm, are not uniformly distributed over the whole body,
but on the contrary, occur very unequally in different regions ;

 

* Quite recently it has been stated that epithelio-muscle cells occur also in
Echinoderma and some Cheztopoda.
Ceelentera. 101

some portions being much richer in muscle cells, ganglion cells,
etc., than others. It may also be mentioned here that, in some
Ceelentera, part of the body is surrounded by a cuticle, secreted
by the ectoderm ; further, certain portions of the ectoderm may be
modified to form simple optic or auditory organs.

The endoderm, corresponding with the epithelium lining the
alimentary canal of other Metazoa, and originating from the
endoderm of the gastrula, is, structurally, very like the ectoderm,
since besides simple epithelial cells, epithelio-muscle cells, muscle
cells, sensory cells, ganglion cells, thread cells, and gland cells may
also be present. As regards details, e.g., the form of the cells, the
differences between the two layers are by no .means insignificant.*

The mesoglea in some forms is a thin structureless sheath
without cells. In others it is better developed, and cells from the
ectoderm and endoderm migrate into it, so that it becomes like a
connective tissue. Occasionally, in the Ctenophora, some of the
cells which have wandered in, develop into muscle and ganglion
cells. In the mesoglea of some Ceelentera hard structures may
develop, but these will be described later.

Ova and spermatozoa develop in the ectoderm in some
cases, in the endoderm in others, arising as the modification of
the ordinary cells of the layer. In general they are developed
in definite regions of the body, which may then be termed, by_
analogy, ovaries and testes, but in some forms they are irregularly
distributed.

From the foregoing description it will be seen that there is
extraordinary simplicity of structure among the Celentera. For
the most part the animal consists throughout life of the two layers of
the gastrula, the only further development being the various
modifications of the constituent cells. An actual mesoblast, arising
in other Metazoa as a special mass or masses of cells from which
large portions of the body are developed, is absent. The muscle
elements and the sexual cells (ova and spermatozoa), which are
elsewhere formed from the mesoblast, develop here from the ectoderm
and endoderm. For the most part it is almost impossible to speak of
organs as in other Metazoa; in any case there is very little
specialisation. Thus, a central nervous system which, even in very
simple Metazoa, is usually well-developed, can hardly be distinguished;
at most, the ganglion cells are more closely collected in some places
than in others. Excretory, vascular, and respiratory organs there
are none; and a body-cavity is never developed.

 

* In the inner layer of various Celentera (Actinia, Meduse, Hydroids), great
numbers of green or yellow cells are frequently found, each surrounded by
a definite cellulose cell-wall. These were formerly regarded as a part of the
animal, but as a matter of fact they are unicellular plants (Alege), which have
taken up their abode within the organism (¢f. Radiolaria).
102 Ceelentera.

On the other hand, reproduction is often fairly complex.
A metamorphosis is very general, the animal leaving the egg as
avery simple organism, ciliated and free-swimming, but without
tentacles; whilst later, usually after it has become sessile, it is
modified to a greater or less extent. Moreover, asexual repro-
duction by fission or budding often attains considerable importance ;
and colonies are frequently formed. In many species a regular
alternation of generations occurs.

The Ccelentera are almost all marine, only quite a few inhabit
fresh water. Their nettle cells enable them to prey upon even
relatively large and powerful animals, which are digested by the
endoderm cells of the gastric cavity, the indigestible portions being
thrown out through the mouth.

Class 1. Hydrozoa.

This group is characterised by the general occurrence of an
alternation of generations, and by the great dis-
similarity of the sexual and asexual generations.

The asexual generation (the polypoid individuals), presents
the simplest ccelenterate form, which consists of a simple sac with the
mouth at one end and the body-wall of the usual layers (cf. Fig. 58, A) ;
at the upper end of the animal there is a varying number of
tentacles, which are usually arranged some little distance from
the centre of the disc. The polyps are usually attached (often
immovably) by their free ends to some foreign object. Most of them
form colonies by budding.

The sexual generation, the medusoid individuals, are
characterised by the broadening out of that portion of the body
which corresponds to the lower end of the polyp, to form a circular
convex disc, the umbrella (ef. Fig. 58, B) in which the middle
layer is specially well-developed on the convex side; radial processes
of the alimentary canal extend into the disc as the radial canals,
the ends of which are generally united by a ring canal running
round the umbrella close to its edge. The medusa is typically free-
swimming (for exceptionssee the Hydromeduse and Siphonophora) with
the disc turned upwards ; from the centre of the umbrella depends a
tubular portion corresponding to the upper extremity of the polyp,
and forming a longer or shorter manubrium perforated by the
mouth. From the edge of the bell hang contractile marginal tenta-
cles which are richly supplied with nettle cells; simple auditory
and optic organs are present on the margin, and below the
epidermis (at any rate, in the Hydromeduse), numerous nerve cells
are distributed all round the disc, forming a nerve ring with
their processes. On the concave lower side, there is a layer of
Class 1. Hydrozoa. 103

circular muscle fibres, often tranversely striped, which make
the umbrella extremely concave when they contract, and thus move
the whole animal. As a rule, the meduse are of separate
sexes; the formation of ova and spermatozoa will be considered
in the individual orders.

A ciliated larva develops from the fertilised egg, fixes itself, and
develops tentacles; polyps which have originated in this way may
form colonies, but some remain solitary. The medusoid form arises
again as a bud from the polyp, or by its transverse fission. More
rarely the egg of the medusa develops direct into a new medusa,
in which case the polypoid form (and with it, alternation of generations)
does not occur.

In structure, the Hydrozoa generally display a markedly radial
symmetry; the number of rays is usually four or some multiple of
four, more rarely six.

Order 1. Hydromeduse. (Craspedota).

The polyp generation consists of hydroids, which usually form
colonies, but are occasionally solitary. The tubular, often extremely
elongated, body of the polyp is almost always surrounded by a
cuticle, which forms a chitinous case, usually thin, more rarely
thick and calcified. This does not surround the whole body; a
portion of the upper part remains uncovered. Sometimes the tube
has a cup-shaped expansion above, into which the naked, broader,
tentacle-bearing portion of the polyp can be withdrawn. The
tentacles are arranged in one or more circles below the mouth,
or more irregularly at the upper end of the animal (Fig. 60.)
They are not generally hollow as im Corals, but possess a solid
axis formed of a single row of endoderm cells; outside this there
is a continuation of mesoglea, and most externally ectoderm with
abundant nettle cells. The colonies formed by the polyps are
generally small compared with those of the corals (cf. below), of
which the solitary individuals are similarly very much larger.
Sometimes the colonies are formed on a definite system of branch-
ing: the polyp developed from the egg continually increases in
length, whilst at the same time it forms lateral buds, of which the
oldest are at the base; these develop into new individuals (lateral
polyps), which again branch in the same way as the main stem. In
other cases the growth of the first polyp ceases; only one or two
lateral branches arise from it, each of which stops growing after
forming one or two buds (cf. the cymose branch-system of plants).
The lower end of the colony is provided with hollow, root-like
outgrowths of the body-wall, covered by the cuticle; by means
of these stolons, which are sometimes connected to form a
104 Celentera.

network, occasionally giving rise to several stems, the colonies may
be closely attached to the substratum.

On account of the feeble skeleton (cuticle) the colonies are
frequently supported by various bodies occurring in the water,
winding round or creeping over them.

Very frequently the polyps of one colony are not all alike; for
instance, those persons which bear the medusa-buds are often
somewhat different from the rest, having smaller tentacles or none

 

Fig. 60. 1 Hydroid colony (Syncoryne fructicosa). Natural size. 2 two polyps of
the same, one with medusoid buds, one of which is about to break free. 3 larva of another
hydroid (Cordylophora lacustris). 4—6 the same after attachment.—After Allman.

at all, or even possessing no mouth: in this case the cuticle
covers the whole body, and certain individuals (nutritive polyps),
which do not produce such buds, perform the function of nutrition

for the whole colony.
In some Hydroids there is yet a third kind of individual, thin, mouthless,
and very short, and bearing tentacles provided with a great number of thread-
Class 1. Hydrozoa, Order 1, Hydromedusce. 105

cells. Ifthe colony be disturbed, these individuals roll themselves up in a spiral
fashion and then uncoil again. The tentacles are absent from others, which
seem then to function only as the tactile apparatus, whilst in the former case
they may perhaps be regarded as defensive polyps (dactylozooids),

The medusoid generation formed by budding from the
polypoid generation, usually attains only a small size in this Order.
Round the edge of the disc runs a thin collar-like, horizontal inturned
ledge, the velwm, which narrows the opening of the bell (hence
the name Craspedota).* The edge of the umbrella is entire and
bears the naked sense organs, either auditory or optic (rarely

 

<= Fig. 61. Various forms of the sexual generation of Hydromedusoids. Dia-
grammatic longitudinal sections. A free living medusa. B sessile, relatively little modified
medusa. C—D more modified forms. E—F the most degenerate form. EF without umbrella.
Fa simple knob-like outgrowth from the polyp, g sexual cells, m mouth, + radial canal,
t tentacle, » velum.—Orig.

both in the same individual). There is usually a small number of
simple radial canals (48) in the umbrella, connected by a
marginal ring canal. Ova and spermatozoa develop in these
canals, or on the outer wall of the manubrium; they arise in some
forms from the ectoderm, in others from the endoderm; in
some species, the ova appear in the endoderm, the spermatozoa in
the ectoderm, or vice versd.

 

* Kpdomedov, a border.
106 Celentera.

The sexual generation, however, is by no means invariably so
well developed. In very many Hydromeduse, the medusoid buds
do not separate from the hydroids, but remain firmly attached.
Such sessile meduse (Fig. 61) remain in a more or less
incomplete condition; in some cases, an umbrella with marginal
tentacles develops, but the tentacles are small; in others, the latter
are altogether absent, although the umbrella is well developed;
in others, again, the umbrella itself is degenerate; and lastly, it also
is wanting, so that the medusa consists simply of a mouthless
manubrium with, in the most degenerate forms, no cavity (Fig. 61, F;
Hydra). Without knowledge of the various transitional stages,
these small medusoid buds, which are never more than incipient,
would be regarded simply as organs of the polyp. The medusoid
bud, like the free-swimming medusa, always contains the sexual

cells, ova or spermatozoa, and new polyps or colonies arise from
these.

In the Hydromeduse an alternation of generations as just described, generally
occurs ; there are, however, not a few exceptions. In various forms the ova do
not develop into polyps, but give rise directly to meduse ; from these a hydroid
generation is altogether absent. Other deviations from the typical mode of
reproduction may be noticed, such, for instance, as the occurrence, in some forms,
of an asexual multiplication of the meduse, which produce other medusa like
themselves, as buds from the manubrium or the margin of the disc. These
species also possess a hydroid generation, and the medusxw formed by budding
propagate sexually.

The majority of Hydromeduse are marine, numerous examples
occurring in the northern seas. A considerable number both of
hydriform and medusiform persons are phosphorescent. Quite a
few, of which the genus Hydra is the best known, occur in fresh
water. ’

1. Of the marine forms the Milleporide deserve special consideration.
It has been mentioned above that stolons, surrounded by a continuation of the
chitinous covering of the polyp. usually arise from the lower end of the hydroid
stock, and often anastomose to form networks. These are sometimes of considerable
extent, and gives rise to a large number of small polypoid stocks or isolated
polyps. In the genus WMillepora and allied forms the chitinous case is
calcified, and since new stolons are constantly being formed above the older
ones, the soft parts of which die away, these animals build regular coral-like
colonies, sometimes of considerable size. The outer layer is made up of
living stolons, from which the polyps arise, whilst the inner portion of the coral
consists of the calcified walls of dead stolons. The Milleporide, which occur
exclusively in warm seas, play a not unimportant part in the formation of coral
reefs.

2. The Fresh-water Polyp (Hydra), a small, elongate, solitary form,
without a chitinous cuticle; round the mouth, is a circlet of long tentacles
(410), which, like the whole body, contract vigorously when irritated. The
animal often remains for a long time in one place, e.g., with the lower end attached
just below the surface of the water; but it is able to crawl about like a leech.
If an animalcule comesin to the vicinity of an attached Hydra, it is seized by the
tentacles, paralysed by the nettle-cells, and conveyed to the mouth. Hydra has
Class 1. Hydrozoa. Order 1. Hydromeduse. 107

the power of budding, but never forms a colony, since the new individuals soon
separate from the parent. The medusoid generation is represented by wart-like
outgrowths from the body-wall in which ova or spermatozoa develop. Hydra
is noted for its enormous power of regeneration; an individual may be cut
into several pieces, each of which can develop into a complete animal.

Order 2. Siphonophora.

The Siphonophora are closely allied to the Hydromedusz,
differing from them, primarily, in that the colonies are free-swimming.
The colonies correspond with those of the Hydroids, and like them
consist of variously modified polyps. Further, they also bear
meduse or medusa-buds, which again may develop in various
ways. These diverse individuals are borne upon a common stem
(hydrosoma), which is usually either a long tube or a flat disc; at
the upper end it is furnished with an air sac (pneumatocyst), or
if it is discoid, it encloses several small air spaces, which enable
the colony to float. The hydrosoma is to be regarded either as a
much elongated, or a much flattened polyp; of which the air sacs
are invaginations, each communicating by a fine aperture with the
exterior.

The polypoid generation occurs in the following principal
forms:—1l. Nutritive persons (gastrozooids), saccular polyps,
with a mouth, and with only a single tentacle* arising close to its base ;
which, however, attains a considerable length, and is provided with
lateral branches and numerous “ batteries’? of nettle cells; this
tentacle may be absent. The gastrozooids of the same stock may
sometimes vary considerably in size. 2. Feelers (hydrocysts),
with tentacles like the gastrozooids, but without a mouth.
3. Tentacle-like persons (dactylozooids), which arise
independently from the stem, and must not be confused with
tentacles; they have no mouth and are furnished with nettle
cells.t

The medusoid generation arises either from the hydrosoma
of the colony at the base of the hydrocysts, or of the gastrozooids;
it appears in the following forms: (1) Fertile meduse (gono-
zooids), or medusoid buds with sexual cells, corresponding exactly
to the medusoid generation of the Hydromeduse ; if the medusz are
set free—a rare occurrence among the Siphonophora—they look
exactly like the free Medusz of the Hydromeduse (they are provided
with a velum, etc.); as a rule however, they remain in situ
throughout life, and then resemble the sessile meduse of the

 

*In certain Hydroids also each polyp possesses only a single tentacle.

+ Such tentacle-like individuals occur at the margin of the discoid stem in the
genus Porpita (Fig. 63).
108 - Ocelentera.

latter. (2) Swimming bells (nectocalyces), sessile and sterile
meduse, without manubrium or mouth, but with well-developed
umbrella and velum, by the contractions of which the colony moves
about. (38) Covering pieces (hydrophyllia), like the necto-
calyces, but with the umbrella reduced to a stiff plate; they serve
as coverings for other individuals.

Fig. 62. Fig. 63.

CLEE AD LEZ LTE LLL HEED, S

    
 

Fig. 62. Diagram of a Siphonophoran with
an elongated hydrosoma (Physophora); the
digestive cavities are drawn black.—Orig.

Fig. 63. Diagram of a Siphonophoran with
a disc-like hydrosoma (Porpita).—Orig.

General lettering: d covering piece, f ten-
tacle, l air sac, mf fertile Meduse, N large
Gastrozooid, n, small] ditto, p disc with small
air cavities, s swimming bell, ta feeler, te
teutacle-like person.

A colony of the Siphonophora consists of these individuals, but
they are not always all present; the swimming bells may for instance
be absent, in which case the colony drifts passively; the covering
pieces may also be wanting; the number and arrangement of the
individuals, and consequently the form of the colony, is extremely
varied.

The Siphonophora are true pelagic animals, are almost ex-
clusively limited to tropical and warm seas (e.g., frequent in the
Mediterranean).

As examples may be mentioned: Physophora and its allies (Fig. 62), with
long hydrosoma, terminating in a small pneumatophore, and with numerous
nectocalyces on the upper part of the stem; Physalia with huge pneumatocyst
and bearing gastrozooids and hydrocysts (with long tentacles), without hydro-
phyllia or nectocalyces; Porpita (Fig. 63) with disc-like circular hydrosoma
Class 1. Hydrozoa. Order 2. Siphonophora. 109

enclosing numerous pneumatocysts, and bearing the various individuals on
the underside (a large gastrozooid centrally, dactylozooids at the edge, no
nectocalyces or hydrophyllia); Velella like the previous forms, but the disc is.
elliptical with an upright keel. All met with in the Mediterranean.

Order 3. Acalepha (Scyphomeduse, Acraspeda).

The medusoid generation is usually represented by transparent
animals of fair size. The edge of the mouth is prolonged into four
oral tentacles with which the prey is caught. Similar processes,
but as a rule less well developed, may occur in the Hydromedusze.
The canal in the manubrium widens out in the umbrella to form the
gastric cavity, which may extend into a number of large radial out-
growths (gastric pouches): and the radial canals, often branched, also.
arise from it. It contains a number of tentacular threads, the gastral
filaments, which are absent from the Hydromedusez ; also the gonads,
ovaries and testes, usually in the form of four folded bands ;.

Gs.

‘ » |

   
  
     
 

fs

  
 

SH

AS od
SS

Fig. 64. Section through a Scyphomedusa passing between two oral tentacles. d hood’
covering one of the tentaculocysts, h sub-genital pit, m mouth, 0 ovary, r tentaculocyst,
rk vadial canal, ¢ gastric portion of enteric cavity, t’ radial portion of ditto, te gastral
filament.—Orig.

beneath each of these, on the under side of the umbrella, there is a
cavity separated from the enteric cavity by a thin septum (h Fig. 64) ;.
this is pushed out when the genitalia are well-developed, so that
they appear to depend from the oral side of the umbrella. The
ova and spermatozoa which usually occur in different individuals,
fall into the enteric-cavity, and escape through the mouth.
The cells from which they originate, are endodermal. The
umbrella in which the mesoglea attains a considerable thickness,
has eight notches in its margin; in each notch, covered by
a lappet of the umbrella, there is a small round marginal body
which bears an auditory, often also an optic organ. Along
the edge of the umbrella, there is often a considerable number
of marginal tentacles, usually of a considerable length; a velum,
on the other hand, is wanting. The ova of Awrelia develop, as.
110 Celentera.

far as the larval stage, in saccular evaginations of the oral arms
of the parent; others pass through the early stages in similar
outgrowths of the radial canals.

The polypoid generation. When the ciliated larva,
developed from the egg’, leaves the parent, it attaches itself to some
foreign body, and grows into a small polyp with a circlet of tentacles.

 

Fig. 65. The development of Aurelia. 1 free larva. 2 the polyp, a short
time after attachment. 3 the same somewhat later. 4 transverse fission. 5 later stage.
-6 the polyp after the separation of a number of young Meduse. 7—9 the young Meduse
at various stages of development. 7—8 viewed from below. 9 from the side.—After
M. Sars.

Like Hydra, this polyp may form buds, which separate off and
‘develop into adults like the parent, but no true colony is formed. The
polyp, which is at first relatively short, gradually grows to a con-
‘siderable length, becoming cylindrical, with a conical base. Next,
a number of annular constrictions appear, dividing the main portion
of the body into a series of discs, which separate from each other,
and, breaking away from the polyp, form small Medusex. In
exceptional cases the polyp generation is absent, the medusa-egge
developing direct into a new medusa.
Class 1. Hydrozoa. Order 3. Acalepha. 111

The Acalepha, several of which are phosphorescent, occur only
in the sea. The following may be cited as examples :—

1. The Common Jelly-fish (Awrelia aurita), with disc only slightly convex,
bearing at its margin numerous short tentacles; the marginal bodies include
both auditory and optic organs (tentaculocyst). The enteric cavity is produced
into four short radial sacs, containing the four gonads, each shaped like the edge
of a human ear. The mouth is provided with four large oral tentacles. Like
its allies, this animal contains a large amount of water (95—96 per cent.
water, 45 per cent. dry substance). Very abundant in N. European seas.

2. Cyanea capillata, a large and beautiful medusa, which is specially
characterised by the arrangement of the extraordinarily long marginal tenta-
cles in eight groups, on the under surface of the much lobed disc. The
nematocysts cause an intensely burning sensation in thin-skinned portions of
the human body. Commonly found with Aurelia.

Class 2. Anthozoa.

The body is cylindrical, and. contains a large internal digestive
cavity, into which the upper region of the body-wall is invagi-
nated to form the stomodeum, as
already explained. The external
opening of the stomodeum is
usually termed the mouth, but it
must be remembered that the
‘true mouth, the entrance into the
digestive cavity (homologous, with
the mouth of a medusa) is
situated at the lower end of the
stomadeum. The former may be
termed the external mouth,
the latter, theinternal mouth.
Within the enteric cavity there are
‘perpendicular radial mesenteries,
reaching from the stomodzum to
the body-wall above,* whilst below,
the inner edge is free (something
Tike the dissepiments of a poppy-
head). The number of mesen- Fig. 66. Longitudinal section through

teries varies (8 12 etc.). At the * solitary Anthozoon, diagrammatic; the
f 4 i section passes through a mesentery on the

upper end of the animal there right side, but between two on the left.
is a circle of tentacles (in v endoderm, mi mesoglea, y ectoderm,
‘ . m internal, m’ external mouth, s stomo-
exceptional cases several circles) deum, ¢ tentacle.—Orig.

the number corresponding with that

 

 

*In most Actinia, which possess a large number of mesenteries, only some
‘reach from the body-wall to the stomodeum, in the others, the inner border is free
for its whole length.
112 Ceelentera.

of the mesenteries. These tentacles are hollow evaginations of the
body-wall and correspond in position with the spaces between the
mesenteries; they are richly provided with nematocysts. The some-
what discoid expanse within the circle, in the centre of which is the
mouth, is termed the oral disc, the lower flattened extremity of
the body the pedal disc.

Each mesentery is a fold of endoderm, covering a lamina of
mesoglea, which arises from the mesoglea of the body-wall
(See Fig. 67). Along the inner edge are cord-like thickenings,

much coiled and provided with

= = nettle and gland-cells; these

: ie are termed mesenterial
filaments; they play an
all-important part in digestion ;
which, indeed, is probably
effected by them alone.* The

Fig. 67. Transverse sections of an Al. OV and spermatoz - 2
cyonarian. Diagrammatic. A through the develop in the mesenteries

stomodeum. B lower down. s stomodeum . .
h gastric cavity, mu muscle. The ectoderm by the modification of endo-

is represented by an entire line; the endoderm dermal cells; the part of a
dotted; the mesoglea shaded.— After v. imesent ery in which they occur

Koch. ;
is thickened, and may be termed

ovary or testis. The Anthozoa are usually of separate sexes,
only in exceptional cases hermaphrodite. They generally develop
hard parts, which will be considered under the different

orders.

The Anthozoa, like other Celentera, exhibit a radial symmetry, which is,
however, rarely completely carried out. In transverse section, the stomodeum
is almost always oval, the external mouth slit-like, and thusa median plane
is defined. Each end of the oval corresponds with a tentacle; moreover, the
muscles in the mesenteries usually form a thickening on the one side only;
the thickenings may occur on either side, but are always arranged sym-
metrically with regard to the median plane noticed above (see Fig. 67,
which shows the arrangement in an Alcyonarian).

In many of the Zoantharia (at all events, in most of the Actinians), the
stomodeum is furnished with two thickly-ciliated grooves, corresponding with
the two ends of the oval; when the stomodeum is elsewhere pressed together
these two grooves remain open, and probably serve to maintain the current of
water necessary for respiration. In many of the Alcyonaria there is a
similar groove, characterised by deep epithelium and long cilia at one side only ;
the ciliary current here sets from without inwards, in other regions of the
stomodeum in the opposite direction.

In most corals asexual reproduction occurs by budding
or fission. The young animals thus formed separate from the

 

 

* From the lower end of the mesenteries in some Actinia, there arise peculiar free
threads, similar in structure to the filaments and very rich in thread cells; they
may be shot out through the body-wall, and serve for attack or defence (acontia).
Class 2. Anthozoa. 1138

parent only in exceptional cases; as a rule they remain connected
and thus colonies arise. These usually consist of a great number
of individuals, and frequently attain a very considerable size. An
alternation of generations occurs but rarely, since the same indivi-
dual can reproduce both sexually and asexually.

The Anthozoon leaves the egg as a larva without tentacles,
swimming about by means of cilia. Later it attaches itself and
attains the adult form. Only a few (e.g., the Actinians) retain
a capacity for locomotion throughout life, and even then to a very
limited extent.

The Anthozoa, all of which are marine, are predaceous animals.
By means of their tentacles they seize their prey, paralyse it, and pass
it through the stomodeum into the digestive cavity. When
undisturbed, they remain with their tentacles quietly extended; if
irritated, the tentacles and all the soft portions of the body are
instantly contracted.

Order 1. Alcyonaria (Octactinia).

The members of this group possess only eight mesenteries, and
corresponding with these, eight branched pinnate tentacles.
In the mesoglea there is a number of almost microscopic calcareous
spicules. These are provided with knobs or sharp points,
are of various colours, and are less numerous in the upper than in the
lower region of the body, so that the former can be retracted into the
lower firmer portion. The spicules, which are for the most part not
very closely connected, arise in cells which have wandered in from
the ectoderm.

Only a very few species are solitary; most of them form
colonies. Occasionally the individuals of a colony are united by
thin stolons containing canals which are in communication with the
gastric cavities. More often, the lower, harder portions of the polyps are
united by large connecting regions (ccenenchyme), consisting chiefly
of mesoglea, which may be perforated by numerous canals. These
canals are lined with endoderm, and put the individuals of the
colony in communication with each other (for the connection
of individuals in the Organ-pipe Coral, see below). The external
form of the colony is very varied; not infrequently it is
arboriform; and then there is usually an axial skeleton
in the stem and branches, formed in the Red Coral by the fusion of
innumerable calcareous spicules, and consequently situated in the
mesoglea. The axial skeleton of the Gorgonide is quite different in
structure: the voung colony secretes a horny mass on its pedal
surface: between it and the foreign body to which it is attached,

I
114 Coelentera.

this becomes gradually more convex, growing up with the colony;
it is secreted by the ectoderm and is a true cuticular structure
(cf. Fig. 68 C). The axial skeleton of Jsis which is to a great extent
calcified, is similar in its relations.

 

Fig. 68. Sections through young colonies of various Aleyonaria (diagrammatic). The
layers of the body indicated as in Fig. 67. A simplest mode of communication between
the individuals. B young colony of Aleyonium. C ditto of a Gorgonian axial skeleton,
figured black.—After v. Koch.

It is of interest to notice the constant presence, in various Alcyo-
narians, of arrested individuals (siphonozooids) amongst the normal
persons (autozooids). In the most extreme cases, they have no
tentacles and differ in other respects from autozooids; in other
cases the difference is less pronounced. Their chief function appears
to be the reception and ejection of water, and is thus respiratory.
They are very common among the Pennatulids, but are also
found in Alcyonium and Coralliwm rubrum, although not in the
Gorgonide.

Of the forms belonging to this group, the following may be
mentioned :

1. Dead Men’s Fingers (Alcyonium digitatum) form yellow or whitish
leathery colonies of an irregular bulky shape, with short thick branches. The
gastric-cavities are continued back from the free, upper, soft portions of the
individuals, as slightly sinuous tubes reaching far down into the stem, and
are connected by fine canals. No axial skeleton. Common on English
coasts.

2. Organ-pipe Coral (Tubipora) forms massive colonies, consisting of
long tubular zooids, arranged almost parallel to one another; the individuals
of the colony are not connected by cenenchyme, but by transverse platforms,
containing a network of tubes communicating with the gastric cavities. In
each individual the spicules (with the exception of those in the upper soft portions
of the body) are united to form a hard tubular mass : in the transverse platforms
they are fused into calcareous plates connected with the tubes. In the Indian
and Pacific Oceans.

3. The Gorgonide (genus Gorgonia and others) form arboriform colonies
with hard, dark, horny axes both in the main stem and branches; the rest of
the colony covering the horny axis is termed the ‘ cortex,” contains numerous
spicules, and may be perforated by canals. On the surface of the dried colony
Class 2. Anthozoa. Order 1. Alcyonaria. 115

may be seen small pits, in which the free, soft portions of the individuals were
situated. In some forms (Rhipidigorgia) the branches of the colony all lie in
the same plane and partially coalesce, so as to constitute a perforated plate.
Chiefly in warmer seas, some species in the Mediterranean. Isis approaches
the Gorgonide, but the axis consists of a series of calcareous joints limited
by horny transverse septa, One species in the Mediterranean.

4, The Precious Coral (Corallium rubrum). Branching colonies, with
hard, calcareous axis. Both axis and cortex are of a beautiful red colour, the
free portions of the individuals are white. In the Mediterranean.

5. Sea-feathers (genus Pennatula and others). The colonies consist of a
lower naked stalk and an upper, broader, often feather-like region, from which
the individuals. project. Within the axis of the colony there is a calcareous
unbranched rod. They are found at the bottom of the sea, with the stalk
sticking into the ground, and if disturbed, they bore their way deep down.
The phosphorescent, red, feather-like Pennatula phosphorea occurs in the
North Sea.

Order 2. Zoantharia (Polyactinia).

The number of mesenteries is either a multiple of six, or a
large indefinite number. The tentacles, which are simple, almost
always correspond in number with the mesenteries, and in most forms,
as in the Alcyonarians, there is a skeleton which is, however, very
different in character. It is limited exclusively to the lower region
of the body, and consists of a continuous, very porous or thick
mass of calcium carbonate, whilst the upper portion is entirely
without skeletal structures. The skeleton corresponds closely with
the general form of the animal, and usually consists of the
following parts: a discoid basal-plate, bearing a tubular
theca and a number—12, 24, 48—of radial septa which are
fused with the theca and basal-plate, and often with each other
also. :

From this description it might be supposed that the theca represented a
calcification occurring in the outer body-wall; the septa, similar hardenings in
the mesenteries and the basal plate in the lower discoid portion of the animal.
As a matter of fact, however, this is not the case. In the first place, it must be
noticed that the skeleton is not developed in the mesoglea as was formerly
believed, but is an external secretion of the ectoderm. As soon as the
tiny free-swimming larva settles, it secretes, upon its attached surface, a
thin calcareous disc, which becomes, later, the basal-plate. Next, the
septa appear upon this plate, gradually growing taller and more plate-like,
until, covered by the soft tissues of the pedal disc, they project into the
gastric cavity, between the twelve soft mesenteries which have already
been formed. A further secretion from the attached surface now appears,
as a ring-like ridge upon the basal plate, the beginning of the theca; the ridge
grows into a tall cylinder, covered like the septa by a fold of the basal disc, and
also projecting into the ccelenteron ; it lies some little distance within the soft
body-wall. Other septa may develop later between those of the original set, and
these again have nothing to do with the mesenteries. It may also be remarked
that, in some Corals, the basal-plate may project up on to the lateral wall of the

pe
116 Celentera.

animal (as in Fig. 69 A), so as to form a cylindrical calcareous deposit
external to the body-wall (and of course external to the theca); this is the
epitheca. The skeleton is thus a purely external, cuticular
structure, secreted by the ectoderm. :

 

Fig. 69. A diagrammatic longitudinal section of a Madre; orarian which has only just
attached itself, passing between two septa. B transverse section of the lower end of the
same. For the sake of simplicity, only 6 septa and 6 mesenteries are drawn, instead of 12.
i endoderm, m internal mouth, m’ external mouth, mi mesoglea, sk mesentery ; st septum,
t tentacle, y ectoderm. The skeleton is drawn black.— Orig.

Between the septa in the lower portion of the animal, small, calcareous
transverse beams or platforms often develop, passing from one septum to another
(synapticule). In the lower region, the septa often fuse in the middle, and
from the point of fusion there usually arises one or more vertical columellae.
All the septa are not equally well-developed; those last formed do not reach so‘
far in as the older ones, with which they alternate regularly. In proportion as the
animal grows in height, the lower portions of the septa and the theca thicken so
that the lower part of the skeleton becomes more solid and compact than the
upper. In older animals the soft parts withdraw from the lower portions,
leaving this region of the skeleton naked.

The majority of Zoantharia,
especially those which are fur-
nished with a skeleton, form
colonies by budding or by
longitudinal fission ; the colonies
usually consist of a great num-
ber of individuals. In budding,
a lateral evagination arises from
the body-wall and gradually
develops into a new individual;
longitudinal fission occurs by
the formation of a new mouth
on the oral disc, the latter
becoming oval, and finally divid-

Fig. 70. Portion of amassive Madre. ing to form two (see Fig. 70),
porarian; two individuals (one on the right whilst a corresponding division
above, one centrally) in the act of dividing : ‘
iongitudinally.—After Dana. of the whole animal occurs.

Just as in the Alcyonaria, the

 
Class 2. Anthozoa. Order 2. Zoantharia. 117

gastric cavities are connected by a system of fine canals. ‘The
outer form of the colony corresponds with that of the skeleton,
and is very varied. Some forms are
arborescent, others massive, the individuals
situated close together like the cells of
honeycomb ; the upper portions into which
the skeleton does not extend are for the
most part independent, whilst the portions
surrounded by the skeleton are fused
with the neighbouring individuals, either
throughout their whole length or in the
lower region only. Sometimes, but this
is only exceptionally the case, the con-
nection between adjacent polyps is still
more intimate; the oral openings are
indeed separated, but the gastric cavities
communicate freely, and in the dry skeleton, Fig.71. Portion of an arbor-
each individual is not, as in other cases, °8cent Madreporarian.
on which increases by budding.—
indicated by a star separated from others After L. Agassiz.

by its theca; but a whole row of in-

dividuals is indicated by a groove, from the sides of which the
septa project: in correspondence with this arrangement, the
tentacles are not situated in circles round
the mouths, but in a double row along the
groove (Fig. 72).

Only in somewhat rare instances, do the new in-
dividuals. formed by budding or fission, separate
off from the parent. This happens, for instance,
in the Actinia without skeletons, in which budding
as well as fission, both transverse and longitudinal,
may occur. In some forms with a calcareous Fig. 72. Small portion of the
skeleton, the buds or individuals formed by fission surface of a Coral in which the

; . : . . individuals are incompletely
may, in rare cases, separate, taking with them a aépurated aliasinaat. ices

portion of the calcareous skeleton. The Mush- 6a) apertures may be noticed ;
room Coral (Fungia), a solitary form, which tentacles in two rows.—After
lies freely on the bottom of the sea, and attains M. Edwards and Haime.

a considerable size, develops in this way by

the transverse fission of a small attached solitary coral (or from a colony
consisting of quite a few individuals). After fission, the individuals separate
and undergo further growth.

Coral reefs, which are so frequently met with in the seas of
the Torrid Zone, and which may be even miles in length, owe their
origin chiefly to different calcareous Zoantharia. Besides these,
certain other animals, notably certam Hydroids (Millepura,
p. 106) also assist in the formation of the reef. The reef consists
in part of skeletons of dead colonies, in part of living colonies, which
have attached themselves to the latter. Upon and within the reef
there live a great number of other animals, which are to some extent

 

   
      

   

Le
Beeb es ne

Bee TT
ey BS)

 
118 Coelentera.

adapted to this peculiar mode of life, so that it is possible to speak
of a special reef fauna. Coral reefs are a very characteristic feature
of tropical seas.

1. Almost the only representatives of the order occurring in northern seas,
are the Actiniaria (Sea-anemones, Sea-roses); solitary forms without skeletons,
mostly of relatively large size, and usually with several whorls of tentacles.
They have a broad pedal dise below, by which they attach themselves to foreign
objects ; they are capable of slow locomotion. Several species on English coasts.

2. The Madreporaria, forms provided with a calcareous skeleton, belong
almost exclusively to warm seas, where they occur in great abundance, usually
in colonies, but occasionally solitary; a few species are met with in the
Mediterranean.

Class 3. Ctenophora.

The Ctenophora may be regarded as meduse from which the manubrium is
absent, and the umbrella so convex and so much narrowed that the sub-umbrella
cavity forms a tube of varying width, at the base of which lies the mouth, the
entrance into the alimentary canal. Hight narrow streaks may be seen passing
round the surface of the body like the meridians of a globe; each of these
lines or ribs, as they are called, is composed of a series of tiny lamine, con-
sisting of transverse rows of cilia fused together; these plates constitute the chief
locomotor apparatus of the animal. Many of the Ctenophora possess two long
branched tentacles, which arise from opposite sides of the body, and can
be withdrawn into special pouches. Thereare no other appendages. The mouth
leads into a small digestive cavity, the so-called infundibulum, from which
arise other canals running along the ribs. At the upper pole of the body there
is an auditory organ. Thread cells are absent.

An eight-rayed plan is to a certain extent indicated, but is not followed
throughout. As a matter of fact, the body can only be divided into two
symmetrical portions: «a two-rayed arrangement is seen, e.g. in the disposition
of the tentacles, the branches of the alimentary canal, etc.

The Ctenophora, of whose structure only certain important points have been
noticed above, whilst others have been altogether ignored, are hermaphrodite
without an alternation of generations, and occupy a somewhat isolated position
among the Celentera. They mostly occur in warm seas; all are pelagic.

It is specially interesting to note that the larve of some forms often attain
sexual maturity quite soon after leaving the egg, and may lay fertile ova; but
this: only occurs during the warm seasons: the sexual organs then degene--
vate, and the larve develop into normal individuals, which again become
sexually mature (cf. pedogenesis of Insects).

Of the various forms may be mentioned Beroé, barrel-shaped, with a wide sub-
umbrella cavity, without tentacles ; Cydippe, spherical, with a narrow cavity and
long tentacles; Cestws veneris (Venus’s girdle), with body much compressed
and elongated to a ligamentous form structure. All these occur in the
Mediterranean, the first two also on English coasts.

APPENDIX TO THE CoELENTERA:
Spongie or Porifera (Sponges).

The Sponges form a very peculiar group of animals of low organisa-
tion, which is usually placed near to the Ccelentera, but whose
systematic position is not yet determined.
Spongue or Porifera,. 119

In the simplest form (Fig. 74 A), the body, which is always
attached to some foreign object, consists of a sac open at the upper
end, and composed of three layers. Of these, the
ectoderm consists of flattened cells, each furnished
with a flagellum; the middle layer, of a mass of con-
nective tissue ; and the endoderm, again, of a special
form of flagellate cell (Fig. 73), peculiar in bearing
at the free end a thin drainpipe-like tube, within
which is the flagellum (collar cells). The cavity
of the sponge (exhalent canal) not only com-
municates with the exterior by the large opening
(osculum), butalso by inhalent canals, which
perforate the wall and open by pores. The inhalent yy, 73. Collar
current of water passes through the pores into the cells ofaSponge.
large cavity, and out through the osculum; the k gellar.
movement is kept up by the flagella.

The simplest of these types occurs only in a minority of the
Sponges (in certain calcareous forms). In others, it is complicated by

 

  

Fig. 74. Various forms of Sponges; diagrammatic longitudinal sections. o osculum,,
p pores.—Orig.

saccular evaginations of the exhalent canal (Fig. 74 B). The
lining of collar cells is limited to these chambers, whilst the main
cavity is lined by a flat epithelium ; the inhalent canals open into the
evaginations. In others (Fig. 74 C, the left side of the figure), the
evaginations are, again, provided with smaller pouches, and in these
alone, collar cells are found; they are, therefore, termed the
flagellate chambers; they communicate with the exterior by
branching inhalent canals. Finally, the chambers may be racemose,
that is, they may be connected with the main branches by longer or
' shorter stalks (Fig. 74 C, the right side of the figure). In all cases,
120 Spougie or Porifera.

the water enters at the pores, vasses through the various canals and
cavities, and finally leaves the Sponge by the osen>em. Mone scopiie
particles. which serve for the nourishment of the amimal, enter with
the water: the collar cells take these up, and later, eject the
umiigestal portions, The current of water is undoubtedly also of
the ereatest importance for respiration.

Tn some sporess the pores kad into irveswtsr cavities oecurming below
the surface. the subcortical erypts. fe which canals arise and
run to the flagellate chambers.

The middle layer noticed above forms the chief w:s~s ef the body,
it usually consists of a sort of commective tisste with celanvens inter
cellular substance. In this tissue, besides fixed cells some of which
may be piemental, there are ameeboid wandering cells
which move about in the mass of jelly, Here also hard parts are
almost slways developed and form ao more or “ess comected
skeleton. | Ths consists either of a network af horny tibres:
or of fine calcareous spicules, which may be semple. or
possessed of three or four branches. radiating out in ditferent
directions: or there isa silicious skeleton of a very different
kind, composed ef isclared spicules connected by a mass of cement
substanee, or of silicieus fibres. The siiciexs spicules are
either sample and needle-lke, or of more corpicared and aften very
beautiful forms anchors, asters, ete.). Not infrequently the
ealeareous or siiciens spicules project partially from the surface
of the body, Im some Sponges the skeleton is) exclusively
calcareous; in others entirely sihvious; im others again. horny.
In many forms, however, it is both homy and sihviens, though
caleareous spicnles and horny fibres never oceur together. Besides
the structures already mentioned muscle cells are present in’ the
middle layer; and it is sid that uerve cells are also found
there. Im some Sponges snpertivial sensory cells are present
M certain regions.

Vory frequently Sponges multiply asexnally, forming colonies
of variens kinds, the individuals of which are only im ai few
eases Clearly distinguishable, whilst they are, for the most part,
so Intimately connected with their neighbours that, externally, the
number of osenla alone proves that there is more than one individual,
In some terms, however, after gemmation, the new individnals
separate off and develop independently, In Fresh-water Sponges
there is a peculiar mode of asexual reproducnon: portions of the
animal encyst im small capsules formed within it, and after a
resting stage develop into new individuals Yvemmuls,

With these exceptions, Sponges reproduce mm the usual way by
ova and spermatozoa, which are formed either in the same
Individual or colony, or in different ones. The ovum is naked and
capable of ameeboid movement; it develops withm the body of the
Spongie ar Porijera, 121

Parent into a ciliated Tarva, which attaches itself after a short
Independent existence, and grows nto a new animal.

The external form of the Sponge (or the Sponge-coleny) is
extremely varied; it may be massive, more elongate goblet-shaped,
diseoid, or quite irregular. All are sessile, and the majority are
Marine; only a few ocenr in fresh water.

Of numerons forms only a few will be mentioned.

1, The Bath Sponge (Euspongia), of which diverse species and
varieties are the object of important fisheries in the Mediterranean, possesses an
exclusively horny skeleton, especially characterised by its great elasticity: it
ean be completely dried without breaking. Fresh sponges are blackish in
colour, and only when the soft parts are removed do they become lighter.

2. Vitreous sponges (Heroetinellide) are silicious forms. characterised
by the striking beanty of the skeleton. which is like spun-glass. A well-known
form of this group is the beautiful Philippine Venus’s Flower-basket (Euplectella
uspergilium), whieh like several of its allies. lives at considerable depths.

& Boring Sponges (Visa), small silicions forms which can cat their
way into limestone, and lamellibranch or gastropod shells—doubtless by means
of a chemical secretion. In stones or shells which they inhabit (they attack not
only dead shells, but also the outer portions of the shells of living Molluses).
there is a system of cavities filled by the body of the Sponge. and communicating
with the exterior by fine perforations of the surface of the shell or stane. The
Boring Sponges play an important part in nature, dissolving away shells and rocks.
Abundant in all Evrpesn seas.

4. Fresh Water Sponges (Spongilla fluciatiis, and other species).
abundant in fresh water in England, form colenies of various forms (branching.
massive), attached to water plants or piles) The external form of the
colony ts determined by the substance upan which it is growing. It is a
Siivions form with simple spienles. In the antumn 21 mumber of gemmuke
arise. rest during the winter, and undergo further development early in the
following year.
Phylum 3. Echinoderma.

The Echinoderma were formerly grouped with the Coolentera as
Radiata, on account of their both exhibiting a radial symmetry
and in spite of their differing much in other respects; in the
Echinoderms, there is an early development of mesoblast; a body-
cavity, a circulatory and a water-vascular system are present.

 

Fig. 75. Diagrammatic figures explaining the radial structure of the Echinoderma.
1 Star-fish from beneath. 2 Sea-urchin from beneath. 8 Sea-urchin. lateral view.
4 Holothurian from the side. a anus, o mouth, r radius, 7 inter-radius, | lines indicating
the scissions by which the animal may be divided into rays, ¢ tentacle-—Orig.

The characteristics of the fundamental form ofa regular
Kchinoderm are as follows: the body is usually pentamerous, 1.¢., it
may be divided into five approximately identical rays (antimeres)
by five scissions meeting in the principal or median axis,
The external form of the body varies in accordance with the length
of this axis; when it is longer than the transverse, the body is
elongate; when the axes are equal, or the transverse is slightly longer,
it is almost spherical; if the principal axis is much shorter, the body
becomes discoid. All these various types are connected by transitional
forms. The mouth lies at one pole of the principal axis, the oral
pole. The surface of the body may be divided by meridians into
ten segments, five of which, termed radii, bear the tube-fcet
Echinoderma. 123

(to be described in detail below), and alternate regularly with the
other five, called inter-radii.

The radial type of structure is not only indicated externally, but is
also conspicuous in most of the internal organs «se below), although
it is never completely carried out; there are always deviations, in
some systems at least, and these are very considerable in many
forms (for details, see the various groups, especially the Echinoids'.

It is characteristic of the Echinoderms that, in almost all,
calcifications of varying size and form occur in the connective
tissue of the body-wall. Sometimes they are small, almost micro-
scopic deposits, often very beautiful in form: small perforate plates,
wheels or anchors; sometimes larger lamine movably or immovably
connected together. With the exception of some quite small deposits,
all the calcifications are porous and spongy. In most cases they are
present in such numbers that they form a considerable portion of the
whole mass ; occasionally (Holothurians) they are more subordinate.*
Calcifications may occur not only in the body-wall, but also in other
regions, e.g., in the wall of the stwne-canal (see below) and in the
pharynx of the Holothurians.

The skin is, as a rule, ciliated and often brightly coloured. In
connection with it, there are various appendages, many of which
are calcified like the body-wall. This is the case for instance in the
movable spinest usually present, part of which is calcareous
matter, although connective tassue and epidermis are by no means
wanting. A peculiar form of appendage, the so-called pedicellarie,
also oceurs in Starfish and Sea-urchins. Each consists of two or
three short calcified valves connected at one end, whilst the free ends
are often provided with curved tips capable of snapping together like
pincers; the pedicellariz are usually borne upon a longer or shorter
movable stalk, supported proximally by a calcareous rod. They serve
as defensive organs; small animals are seized and held fast until
they die; excreta and foreign particles are also removed from the
surface of the animal by their agency.

Among the appendages of the Echinoderms. the tube-feet are
of special interest; they are soft, delicate, usually cylindrical
structures, the free ends of which are either furnished with suckers
or rounded; only in the former case do they serve as organs of
attachment. They may stretch out to a considerable length, and
then have the appearance of very long thin threads, whilst in the
contracted condition, they shrink up to a small fraction of their former

 

* The calcifications lie in connective tissue covered by the epidermis. In regions
where the body is exposed to friction, the soft covering may, however, be rubbed off,
so that they become partially bare (tips of the spines of Sea-urchins, portions
of the surface of the Ophiurids, etc.).

+ Frequently the spines are not altogether simple in structure, but are forked and

soon. Sucheg.arethe paxille of some Starfish, bearing a rosette of fine points
at the end of the shaft.
124

Echinoderma.

size. The tube-feet which end in suckers, may serve as locomotor organs,
since they can stretch out and attach themselves to foreign objects, and

 

Fig. 76. Pedicellariag of a
Sea-urchin closed and open. Proxi-
mal portion of the stalk not
drawn.— Orig.

then contract so as to draw the body after
them; when they are rounded at the
ends, they usually have a tactile func-
tion. Within the feet there are cavities
connected with the water-vascular
system peculiar to the Echinoderms.
The water-vascular system,
a series of tubes, containing a fluid, and
lined with a ciliated epithelium, consists
of a ring-canal surrounding the
alimentary canal close to the mouth, and
of five branched radial canals in
connection with it. The ring-canal, which
is usually beset with a number of vesi-
cular outgrowths (polian vesicles), com-
municates with the exterior by the so-
called stone-canal,* which is at-
tached to a perforated plate, the

madreporite, lying in the body-wall, and allowing of the passage
of water. The radial canals lie along the middle of each radius

Vy

 

giving off a tiny vessel, provided
with a small swelling or ampulla,
to each tube-foot. Water is driven
into the tube-feet by the contrac-
tion of the water-vessels and
ampulle, and causes their elonga-
tion ; when, however, they contract,
it is driven back into the canals.t
In most Holothurians, and in
Crinoids, the stone-canal (or canals,
for there may be several) is not
connected with the surface, but
opens into the body-cavity by one
or more apertures, through which
the fluid is taken into the water-
vascular system. In the Crinoids,
the body-wall is perforated by fine

Fiz. 77. ‘ Diagrammatic sketch of the pores, through which the sea-water
water-vascular system ofa Star-

fish. ap ampulla, k ring - canal,

ma passes into the body-cavity.

madreporite, p polian vesicle, r radial The water-vascular system of the larva
canal, s tube feet, st stone canal.—Modified ;, always in direct communication with

from Gegenbaur.

the sea-water by a stone-canal opening

at the surface. Here, too, there is always only a single stone-canal.

 

* This name is derived from the fact that the wall of the canal often contains calcareous
deposits. + Amceboid cells, like those of blood, float in the water-vascular fluid.
Echinod erma. 125

The water-vascular system has no connection with the true blood-
vascular system; so that the Echinoderms possess two separate
sets of vessels containing fluid. In the blood-vascular system
there is a circular vessel round the mouth, from which arise numerous
branches, amongst them, the radial vessels. In Starfish and Ophiurids,
there is a second circular vessel, lying farther from the mouth, and
connected with the former by a vascular plexus. There is no heart.

The alimentary canal differs considerably in the various.
groups. It may be noticed here, that whilst the mouth is always
situated at one pole, the anus (which is usually present) lies in one of
the inter-radii, although in some forms it is quite near the aboral pole.

Special respiratory organs are usually little developed, or:
entirely absent. They are of various forms: “respiratory trees” in
Holothuria, dermal-branchie in Starfish, and tufted gills at the
mouth of Sea-urchins; these will be considered in greater detail
under the different groups.

Excretory organs are as yet unknown in this group. A glandular
organ lying along the stone-canal, which was formerly regarded as a heart, has.

more recently been considered to be excretory, but in reality it appears to be a
‘lymphatic ” organ, in which the blood corpuscles are developed.

Fig. 78.

   
 

Fig. 78 and 79. Diagram-.
matic longitudinal section
of a Star-fish and of u Sea-
urchin, pass’ng through a
radius on the right, an inter--
radius on the left. a anus,
4 gut, k body-wall, | cecum
of the gut, m mouth, ma
madreporite, radial nerve,
o in Fig. 78 eye, in Fig. 79
sensory spot, p ampulla, 7r-
radial canal, s stone canal,
sk skeletal plate. The Polian
vesicles, etc. are left out.—
Orig.

The nervous system in all Echinoderms consists of a nerve
ring round the mouth, from which nerve cords pass off to the radii.
In Starfish and Crinoids both the ring and the radial nerve cords lie-
126 Echinoderma.

in the epidermis, whilst in other forms they have sunk farther in. As
to sense organs, the small eyes present at the tips of the
arms of Starfish must be mentioned. Small eyes are also present in
certain Holothurians (Synapta), at the base of the tentacles; and
lastly, optic organs have been described in some of the Sea-urchins
where they are distributed in larger numbers over the whole surface
of the body. Vesicular auditory organs are known only in
some of the Holothurians.

Reproduction, with a few exceptions, is sexual, and the
Echinoderms are almost all of separate sexes. The male and
female organs are usually very similar in form, but they may generally
be distinguished without microscopic examination, since the ovary is
yellow or red, the testis white. As a rule they are radially arranged,
in each inter-radius an ovary or testis, or a small group of these; some-
times they are absent from one or more inter-radii, as in Irregular
Sea-urchins ; or they may be present in one only, as in the Holothurians.
They may be saccular or branched, and each opens by a pore upon its
inter-radius; in some forms near to the aboral pole, in others at some
distance from this; or again, quite close to the mouth.

Fertilisation generally occurs after the deposition of the ova, which
are usually small. Some few Echinoderms are, however, viviparous, and
in these, of course, fertilisation takes place within the body of the parent. In
some forms the ova are carried about by the parent, either protected by the
spines or in special pits in the surface of the body; some Starfish form a kind
of brood-pouch by bending the arms down over the eggs.

The development of the Echinoderms is of special interest,
for a complicated metamorphosis often occurs: the larval

       

Sa y

\ )

3 ae eet?
A B

Fig. 80. Diagrammatic figures of the principal forms of young ‘Echinoderm larve.
A, B, C seen from below; A’ is A from the left side. a anus, f ciliated ridge, m mouth.
The saddle-shaped concave region is shaded. For the rest, see the text.—Orig.

oe Ss
C

A!

form, unlike the adult, shows no trace of a radial structure, but on
the contrary is bilaterally symmetrical, and all groups
conform to a common type, excepting the Crinoids and a few
others. The simplest form (see Fig. 80), seen in young larve,
Echinoderima. 127

is almost spherical, somewhat longer than broad, with a saddle-
shaped depression on the ventral surface. The edge of the -addle
is a thickened ridge covered with cilia, which enables the animal
to swim. The mouth is situated anteriorly in the depression, the

anus is posterior to the hinder edge of the ciliated ridge. In front,
the ridge bounds a projecting lappet (6 Fig. 50 A), which in some
cases is only connected by a narrow bridge with the rest of the
convex surface (Fig. 30 B, Holothurian), or again, may even be
completely cut off from it, forming a special island in the concave
region, surrounded by a small ciliated ridge (Fig. SC, Starti-h'.
In older larve, the ciliated rim is more or less lobed, usually forming
long processes or arms, which are then frequently supported by
delicate internal calcareous rods. as in the Ophinrids and Sea-urchins.
After some time, a portion of the larva undergoes complicated
modifications to form the body of the adult, whilst the rest gradually
shrivels up. The final product of the metamorphosis is a small
animal possessing the chief features of the adult, although differing
from it in many respects, e.g., in the small number of tube-feet.
The adult is thus produced by a remodelling of the larval
body, large portions degenerating whilst others become further
developed and modified. Im some Echinoderms, especially in those

 

Fig. $1. Larve of: A Starfish. B Ophiurid, C Sea-urchin. D Holothurian.—After
J. Maller.
which are viviparous, a metamorphosis does not occur; or it is not
obvious; or it 1s modified in various ways.

Asexual reproduction occurs in only a few forms; see
Astercidea and Holothuroidea. All the Echinoderma are marine,
living at various depths; they crawl] about at the bottom, or are
sessile: only exttephonully are they capable of swimming. The
group is represented in the oldest fossihterous strata, and on account
of its abundance. and the frequent presence of a well-developed
dermal skeleton, fossils are very numerous.

Class 1. Crinoidea | Seq-Zilies).

The Crinoids are primarily distinguished from other Echinoderms,
in that, either in the adult condition, or at least in the early staves
following free larval existence, they are attached to the sea-bottom,
128 Echinoderma.

or to some foreign object, by a stalk arising from the middle of
the dorsal surface. The actual body is small in comparison with
the whole size of the animal, usually soft and flat on the up-turned

Fig. 83.

 

Fig. 82. Rhizocrinus lofotensis.

Fig. 83. Antedon.
Fig. 84. The up-turned surface (ventral side) of Antedon ; the ten arms are cut away

not far from their bases. 4 anus, at the tip of a papilla; f furrow, m mouth, p pinnule.
—Orig.

ventral surface (or oral pole), firm and arched on the dorsal side.
From the margin of the body arises a number of arms, usually five
or ten, which divide frequently, sometimes repeatedly. A series of
lateral branches or pinnules arises on either side of the arms,
Class 1. Crinoidea. 129

like the barbs of a feather. The dorsal surface is covered all over,
even to the pinnules, with large, thick, calcareous plates, closely set
together, forming in each arm a series of vertebra-like joints, and
upon the body a calyx, in which the viscera are disposed. All these

Fig. 85,

 

Fig. 85. lTarve of Antelon rosacea at various stages of
development. 1 and 2 young free-swimming larve; in the
latter, considerable portions of the adult skeleton are already
deposited. 3 larva shortly after fixation. g gastrula-mouth,
p pedal disc, r body, s stalk.—After Wyville Thompson.

Fig. 86. Another species of Antedon (Antedon Eschrichtii)
x4; in the sessile condition.—After Levinson.

 

ossicles, which make up a considerable portion of the body, are
calcifications of the dorsal wall. The stalk, too, is chiefly composed
of a series of calcareous joints; the cirrhi, filiform, or rarely root-
like or branched processes, frequently arise from it, and contain
similar calcifications. In contradistinction to the dorsal, the ventral
surface of both body and arms is usually soft and little calcified.
The mouth lies centrally (rarely excentrically) on the ventral
surface, and a short distance off is the anus at the tip of a
small conical tube in one of the inter-radii. Five ciliated furrows,
ambulacral grooves, radiate from the mouth, and if only

K
180 Etchinoderma.

five arms are present, one is produced along each; whilst, if there
are ten, each groove forks just as do the arms, and sends a small
furrow to each pinnule. Along each edge of the furrows both
of the arms and of the pinnules there is a row of small, soft feet or
suckers (so-called tentacles) ; a water vessel runs below it, and gives off
branches to the feet. (For the stone-canal, seep. 124). The
genitalia, which are similar in both sexes, extend as long tubes through
the arms’ and give off branches to the pinnules; these branches alone
produce ripe reproductive cells, whilst the main trunk is sterile: the
ova and spermatozoa escape by small openings in the pinnules, the
latter having become much swollen by the ripe genital products.

Development is known’ only for Antedon, which as an adult
has no stalk. The ovate body of the newly-hatched larva is provided
with four ciliated girdles and with a tuft ‘of cilia at the hinder pole.
After swimming freely for some time it attaches itself by one end, which
elongates, to form a stalk, whilst the arms bud out at the other pole.
Later on, the body with the arms breaks from the stalk, and the animal
is free-swimming for the rest of its life.

The stalked Crinoids are almost exclusively abysmal, whilst those
which are free-swimming usually occur in shallow water near the
coast. Crinoids feed upon microscopic organisms which are driven to
the mouth by ciliary movements in the furrows already mentioned. In
earlier geological periods, especially in the Silurian and Cretaceous,
they were as common as they: are now scarce, and were principally
represented by stalked, forms, in fact entirely so down to the Jurassic.
Genera, species, and individuals, were all abundant.

The following may be mentioned as examples of present-day
forms :—

1. Rhizocrinus lofotensis, a small, long-stalked (to 8-c/m) form, with five
(occasionally 4, 6, or 7) simple arms; the end of the stalk is provided with
branching root-like cirrhi, by which it attaches itself to objects at the bottom
of the sea, whilst elsewhere there are none. The animal was first met with off
the Lofoden Islands, at depths of 100—300 fathoms, but afterwards, also at great
depths in various other localities.

2. - Sea Palms (Pentacrinus) are large animals with ten arms, which may
divide repeatedly ; the strong stalk is beset with whorls of jointed cirrhi down its
whole length. At great depths in warm seas.

8. Antedon or Comatula, a stalk-less Crinoid, with ten or more arms. In
the young stalked condition, cirrhi occur only at the junction of the stalk and the
body; these cirrhi persist after the animal has broken away, and by means of
them, Antedon can climb upon various foreign objects, whilst it can swim with
its arms. A. rosacea occurs in the Mediterranean and the Atlantic.

,

Class 2. Asteroidea,

In this class the body is always discoid (the principal axis
short) and drawn out into a number of arms (usually five), for the
radii are better developed than the inter-radii. The tube-feet
Class 2. Asteroidea. 13]

are developed only on the ventral (oral) surface, which, unlike that of
the Crinoids, is considerably more calcified than the dorsal side. The
alimentary canal is very short and almost radially symmetrical. The
Asteroidea are divisible into two fairly dissimilar orders, the Star-
fish, and the Brittle-stars.

In some of the Starfish and Brittle-stars with six arms or more, reproduc-
tion by fission has been observed; the disc divides transversely, so that
two individuals are formed, each consisting of half a disc and half the number
of arms; they attain the perfect form later by regeneration. Other Star-
fish divide by throwing off the arms; a new individual develops from each,
whilst the disc buds out new ones at the old scars. Whilst such an asexual
multiplication occurs in a few forms only, a great capacity for regeneration
is common to all, occurring both in Asteroids and Ophiurids ;* lost arms are
easily renewed, even if several are destroyed at the same time, and, especially
among the Ophiurids, there are individuals which are almost perpetually
engaged in regenerating lost parts.

Order 1. Asterida (S/arjish).

The flattened body consists of a disc with five or more arms,
broadest at the base near the point of origin, and narrowing towards
the tip. The disc and arms pass directly into each other without
any distinct limit. The length of the latter varies very much, for in
some they are many times longer than the breadth of the disc, whilst
in others they are only just indicated, so that the whole animal looks
like a pentagonal plate, and there are all possible intermediate
forms between these two extremes.

The mouth which is without armature, lies in the middle of the
oral surface ; it leads into a spacious gastric cavity, circular in form,
and with much-folded walls, the so-called stomach. This gives off
(sometimes in pairs) tent long-branched caca, two extending into
each arm; they are glandular and pour their secretion into the
stomach, A circle of short, and also glandular, ceeca arises from the
stomach above the large ones, close to the anus; this is a small
aperture almost in the centre of the dorsal surface, lying in an inter-
radius, close to, but not at, the aboral pole: it is wanting in some
forms. The madreporite, which is perforated like a sieve, also
lies aborally in one of the inter-radii. Along the ventral side of
each arm runs the ambulacral groove, which is continued on
to the ventral surface of the oral disc as far as the mouth. The
tube-feet are situated in this groove, generally arranged in two,
occasionally in four, rows; each is usually provided with a sucker at

 

* Also in the Crinoids.

+ In forms with five arms; with a larger number of arms there is a corresponding
increase in the number of ceca. ;

K 2
132 Echinoderma.

its tip. At the distal end of each groove, there is an unpaired
filiform structure, which bears on its lower surface close to the base,
several small red eye-spots: since the tips of the arms are
curved upwards, the eyes look up in spite of their position on the
ventral surface. The genital apertures usually occur on the
dorsal surface of the disc; two or more tiny openings in each inter-
radius. The body-wall is much calcified, especially on the ventral
surface; a series of yoke-like calcareous plates movably jointed

 

A B

Fig. 87. Diagrammatic figures explaining the structure of a Starfish. A oral,
B aboral view; in B some of the internal organs are figured. bl cecum of the stomach,
k genital gland, k’ genital pore, m madreporite, 0 mouth, s tube-feet, t stomach, 6 eye-
spots.— Orig.

together, and each consisting of a pair of closely-connected calcifica-
tions, roofs in the ambulacral groove: the radial water-vessel and
the radial nerve lie ventral to these ossicles. The upper side of the
body is less strongly calcified; numerous delicate thin-walled out-
growths of the body-wall, which may be regarded as gills, project
from it: they are not connected with the vascular system, nor do
they contain blood-vessels. Dorsally, at the edges of the arms, and
ventrally, as far as the margins of the ambulacral grooves, numerous
movable or fixed spines may occur together with pedicellaria,
which are sessile, or provided with short stalks.

In order to ingest large animals, Lamellibranchs, Sea-urchins, and
the like, the Starfish evert the stomach through the mouth, so as to
cover the prey, which is killed by the action of the digestive juices,
and its soft parts dissolved and absorbed. Smaller animals are
received entire into the non-everted stomach, the indigestible portions
Class 2. Asteroidea. Order 1. Asterida, 133

being thrown out again from the mouth, for the anus plays only a
subordinate part.

The species of Starfish are numerous, and occur in all seas. The
following may be cited as examples:

1. Asterias rubens, a five-rayed form, with the tube-feet arranged in four
rows, and each foot furnished with a sucker. Very common in North European
seas, occurring on the shores and to considerable depths. It is inimical to Oyster
beds, also causing havoc by devouring Fish caught in nets or on hooks. Those
from deeper water attain a breadth of 50 c/m., the littoral ones are much
smaller.

2. Solaster, Starfish of considerable size, with a large number of arms (about
ten), tube-feet with suckers, in two rows. In North European seas.

Order 2. Ophiurida (Brittle Stars).

The arms, usually five in number, are long and narrow, and do
not meet at their bases; the edge of the disc between each two arms
is usually straight, or somewhat
bulging. In addition, the dorsal
walls of the arms, by a different
arrangement of the ossicles, generally
differ somewhat in appearance from
that of the disc; so that they seem
to be well marked off from this,
especially when examined from above.
They differ, further, from those of the
Starfish, in the absence of ambulacral
grooves; the ventral surface. is flat,
and usually covered with calcareous
ossicles which lie ventral to the radial
water-vessel ; dorsal to it are vertebra-
like ossicles, which constitute the
chief part of the arm, and are similar
to those of the Starfish, although iy, es; Dies Beating Hh
developed somewhat differently. The structure of an Ophiurid, seen from
tube-feet, which are without suckers, below. * slit-like aperture of a bursa,

: . m madreporite, o mouth, p one of the
are arranged in two series on the ossicles from the ventral surface of the
ventral surface, near the margin of Sms # ee a pad he
the arms; and on the disc, near to month, ta denticles—Orig.
the mouth. The aboral surface of
the arms is usually covered with large calcareous plates, that of the
disc is generally soft, with larger or smaller calcifications. The
arms are very flexible, and are capable of a serpentine movement.
The circular mouth lies in a stellate depression, the corners of
which are in the inter-radii, and are furnished with denticles.
The stomach is a wide sac, occupying the greater portion of the

 
134, n Echinoderma.

body; large caeca are wanting, there are only short pouches, which
do not extend into the arms. There is no anus. The opening or
openings of the stone canal are in the madreporite, which lies close
to the mouth. On the lower side of the disc, close to the bases
of the arms, there are ten narrow slits, leading into the same number
of sacs,* which have a respiratory significance (burse). On
their walls are the genital glands; ova and spermatozoa
escape into the sacs, and leave the body through the slits.
Eyes, pedicellarie, and gills are absent, but longer or shorter
spines, which are important in locomotion, occur especially along
the edges of the arms.

Those Ophiurids which are unable to evert the stomach, feed upon
dead animals, or upon such as are not capable of resistance; they
enaw their food with the denticles mentioned above.

1. True Brittle-stars (genus Ophiura, etc.). With five (rarely a
larger number) of simple arms; occurring in all seas, and represented in those of
northern Europe by a number of nearly allied species. Some are spiny, others

smooth. They may often be found climbing over foreign objects with the aid of
their arms.

2. Astrophyton, distinguished from the true Ophiurids by the fact that the
five arms, which can be rolled up towards the mouth, are much branched.
The dermal skeleton is somewhat less developed than in the true Ophiurids, and
they can swim like the Antedons. They attain a considerable size. Species of
this genus occur in northern seas, but are much less abundant than the former.

Class 3. Hchinoidea (Sea-urchins).

In some Sea-urchins the body is almost spherical, but in most,
on account of the shorter main axis, it is flattened or occasionally
discoid; arms are completely absent. The greater portion of the
body-wall is furnished with immovably connected calcareous plates.
In the so-called Regular-urchins, with spherical body
(the transverse axes being of about equal lengths), there are
twenty rows of these plates extending meridionally from one end
of the principal axis to the other. Ten of the rows bear fine pores,
each plate having one or several pairs ;f each pair of pores corre-
sponds with a tube-foot. In each radius there are two series of
these, pore or ambulacral plates, whilst in each inter-
radius there are two interambulacral plates. The latter are
often broader than the pore plates, and like these are covered with
larger or smaller, nearly hemispherical knobs, each of which bears

 

* Sometimes twice this number of slits is present, each of the original ones being
divided by a transverse bridge; but the number of sacs remains the same.

+ Each pore plate bears primitively only a single pair of pores; in consequence

of the fusion of several plates, however, there are several pairs in most of the Regular-
urchins.
Class 3. Echinoidea. 135

a small, smooth, wart-like elevation ; the largest knobs occur on the
imperforate interambulacral plates. The upper ends of the twenty
rows of plates touch upon a circle of ten apical plates, five

 

Fig. 89. Shellofa Regular Sea-urchin, Tozxopneustes Droebachiensis (young
specimen, enlarged), from above (4) and from below (B). The radii are dark. g genital
plate, m madreporite, o ocular plate. In the middle of A is the anal area with the anus,—
Orig.

 

Fig 90. Shell of an Irregular Sea-urchin, Brissopsis lyrifera (young specimen,
enlarged), from above (A) and below (B). (The radii in A are not dark enough).
Posteriorly in A the anal area may be seen. The white bands are are with very small
spines.—Orig.

large and five small, with which they are immovably connected ; in
each inter-radius lies one of the larger, in each radius one of the
smaller plates. Each of the larger plates is pierced by the opening
of a genital gland, and they are therefore termed the genita
136 Echinoderma.

plates. One of them is larger than the others, and is the
madreporite, for it exhibits, besides the sexual aperture, a number
of other delicate pores, allowing of the entrance of water into the
stone canal which is attached at this point. Hach of the five smallor
plates is similarly perforated by an opening, smaller than the genital
pore, through which a nerve passes, to be distributed to the skin in
the region of the aperture; this spot is particularly sensitive; the
plates are termed ocular plates, because it was formerly
believed that each bore an eye. Tho apical plates surround a small
membranous region, the anal area, in which the anus opens,
usually somewhat excentrically ; it is provided with small, movably-
connected, calcareous plates. The lower ends of the ambulacral
and interambulacral series of ossicles surround a large space, the
peristome, on which also there is no connected skeleton, though
it is furnished with a certain number of largcr or smaller cal-
careous plates; the mouth is central.

The skeletal plates in the regular Nea-urchins are arranged
on this plan; other less regular types may be derived from. it.
A simple departure occurs in certain Nea-urchins, which are
yet considered as “regular”; for although the shell is ovate,
instead of round, the general structure conforms to this type
(genus Lchinometra). The so-called Irregular Sea-urchins
are more aberrant; the whole of the anal aren has moved
from the circle of apical plates, into one of the inter-radii, and lics
between two rows of interambulacral plates at some distance from
the apex, occasionally even close to the oral area; the apical plates
draw together dorsally, and the regular structure of the shell may be
almost completely retained, even the spherical form, The inter-
radius, in which the anal area lics, is termed posterior,
The loss of radial symmetry is greater if, as in many Irregular
Sea-urchins (Fig. 90 B), the mouth no longer lics in the centre of
the ventral surface, but more anteriorly; this has a marked effect
upon the whole structure of the animal, since the mouth bas not
moved into a radius, but retains its position at the lower pole of the
principal axix, where it is still the meeting-place of all the radii
and inter-radii, Hence, some important alterations must uecessarily
result; the development of both radii and inter-radii is csscntially
changed (see Fig. 90 B). Twenty rows of plates may, however,
still be noticed, as in the regular forms; and the ocular and
genital plates remain as before, excepting that the latter are usually
only four, or even fewer, in number. Many of the Irregular Kehinoids
(see Fig. 90), are also peculiar in that the ambulacral plates arc
differently developed on the dorsal and ventral sides of the sholl, in
correspondence with differences in the tube-fect, to be described;
often, too, the ambulacral plates of the anterior radius differ from
the rest.
Class 3. Echinoidea. 137

Movable calcareous spines articulate with the smooth prominences
of the numerous tubercles mentioned above, and are attached to the
shell by muscle fibres. In the Regular Urchins
the spines are usually of considerable importance;
in some, they are very long and thick, and serve
as locomotor organs, accessory to the tube-feet ; in
irregular forms, on the contrary, they remain small
and thin, or even bristle-like. All the spines in
the same individual, however, are by no means of
equal size ; those with the large kind also exhibit
smaller, or even quite tiny, ones. The spines are
straight, and rounded in section; but some are
curved and flattened. Like the shell, the spines
are calcifications of the body-wall, and like the
shell also, they are covered with a soft superficial ;
layer, which is, however, often worn away from ie ae :
the tip.* Stalked or sessile pedicellariz are longitudinal section
also articulated with the shells (cf. p- 124). Se Pan

In the Regular Sea-urchins the tube- & tubercle, v wart-
feet are usually all alike; at the end of each is ike ‘process: ‘of ‘the

same, p spine, m
a sucker, supported by a perforated calcareous  museles.—Orig.
plate ; occasionally those on the dorsal surface are
pointed and compressed. In many Irregular Urchins, how-
ever, several forms occur: 1. true tube-feet with suckers; 2. a
similar kind, but with rounded ends; 3. a brush-like form, with

 

numerous threads at the ends, modified as tactile organs, and occur-
ring near the mouth; 4. dermal branchie, we., leaf-like
appendages, notched at the edges, present on the dorsal surface.

The mouth in the regular and in some of the irregular forms,
is armed with a circle of five very powerful calcareous teeth,
supported on a somewhat complicated framework of calcareous pieces,
the so-called ‘‘Aristotle’s lantern’’; in most of the irregular
forms, however, there are no teeth. The alimentary canal is
a long, cylindrical, much-coiled tube, occupying the greater portion
of the shell cavity. The position of the anus has been already
described.

In the Regular Urchins the lantern is again surrounded and supported by a
calcareous ring provided with five upwardly directed processes, and connected to
the lower rim of the shell. In these forms the masticatory apparatus occupies a
considerable part of the whole cavity. The so-called siphon, or accessory
intestine, is a very peculiar structure occurring in most Echinoids. It consists of a
fine canal, running parallel to the gut for part of its length, and opening into it
at either end; in some forms this canal is wanting, and instead there is a
groove on the inner side of the gut. It is conceivable that the accessory intestine
arose by the constriction of a groove such as this.

 

* In very large spines the soft covering may be present only at the base.
138 Echinoderma.

The peristome, in most of the regular forms, bears ten dendritic
outgrowths of the body-wall, the oral branchiz, close to the edge of
the shell ; in others, however, they are wanting.

On the ventral side of the shell, close to the peristome, there are attached to
the pore-plates of most Echinoids tiny globular structures, with short stalks and

a glassy, calcareous skeleton. These so-called spheridia are probably sense-
organs, possibly gustatory or olfactory.

Urchins occur in all seas, and are abundant both in genera

and species. They were also well represented in earlier geological
periods.

Order 1. Echinoidea regularia (Regular
Sea-urchins).

The anal area lies at the upper pole. The body is usually
wpproximately spherical. Spines strong. Teeth present. Dermal
branchiz usually present.

The Regular Sea-urchins feed partly upon other animals, e.g., large
Crustacea, which they catch by means of their tube-feet; partly upon
the Polyzoan and Hydroid colonies attached to them, and also to a
certain extent upon Alge. Some of them use their teeth to form
small cavities in the rocks in which they live.

As examples may be given: Cidaris, with long strong spines, without dermal
branchie ; Echinus, with smaller spines, to which Toxopneustes (Fig. 89) is
closely allied; Hcehinometra, with an oval shell. The genus Asthenosoma
differs from other Urchins, in that the skeletal plates, which are imbricate, are
movably connected.

Order 2. Echinoidea irregularia (irregular
Sea-urchins).

The anal area has moved into an inter-radius. The body
is round or, more often, ovate. Spines small, often bristle-like.
Usually toothless. Dermal branchie absent.

1. Shield-urchins or Clypeastride (genus Clypeaster, and others)
differ from other Irregular Sea-urchins in the possession of teeth. Shell thick ;
mouth in the centre of the ventral surface. Rarely found in European seas.

2. Heart-urchins or Spatangide (genus Spatangus, etc.), toothless,
shell usually thin, mouth moved forwards. Feed by ingesting material from the
bottom of the sea. Several species in the North Sea, among them Brissopsis
lyrifera (Fig. 90).

Class 4. Holothuroidea (Sea-Cucumbers).

In the Holothurians the principal, is always longer than the lateral,
axis, usually several times as long, so that the body is cucumber-,
sausage-, or worm-shaped. In correlation with this, the Holothurians
Class 4. Holothuroidea. 139

do not rest on one pole as do other Echinoderms, but upon one side of
the body ; and, as a consequence, one side is often specially developed
or even flattened (Fig. 98), so that external radial symmetry is more
or less destroyed ; the side turned downwards is termed ventral,
the other ‘dorsal.

Fig. 92. Fig. 93.

 

 

Fig. 92. Diagram of » Holothurian; the body-wall is cut through and spread
out. a anus, c Cuvierian organs, g gonad, k ring canal, kp calcareous ring, | respiratory
tree, ma madreporite, p polian vesicle, + radial water vessel, t gut, te tentacles.—Modified
from Ludwig.

Fig. 93. Transverse section of the body-wall of a Holothurian, diagrammatic. a
Radial water vessel, 1 longitudinal muscle, n radial nerve (the white spot above n is the
radial blood vessel), ¢ transverse muscle, v body-wall.—After Ludwig.

Fig. 94. Transverse section through » radius of the body-wall of a Holothurian.
ap ampulla, 6 radial blood vessel, s tube-foot; other letters as in the preceding figure. —
After Ludwig.

Another feature which is very characteristic of the Holothurians
is the softness of the body-wall; the wall is indeed, as in other
Kchinoderms, provided with calcifications, but to so slight an extent
as to render it impossible to speak of a dermal skeleton. The calcifi-
cations are usually in the form of minute, often microscopic, particles
140 EHchinoderma.

of varied and often beautiful form, anchors, wheels, etc.; they
are sometimes large, scale-like, and projecting. The anterior region
of the digestive tract, is, however, surrounded by a number (usually
ten) of large calcareous plates, forming a calcareous ring, from
which various muscles take their origin.

The tube-feet of some forms are arranged in five radial longi-
tudinal rows (Fig. 75, 4), just as in the Sea-urchins; in others they
are more irregularly distributed over the whole surface. Sometimes
the dorsal tube-feet do not possess suckers, and herein differ from
those on the ventral surface; or they may be wanting on the
dorsal side; or again they may be altogether absent.

The mouth is surrounded by a circle of tentacles (10-30),
which are usually branched (plumose or arboriform). They are
hollow, and like the tube-feet, are connected with the water vascular-
system ; each is traversed by a large vessel, which arises from a radial
canal, or occasionally direct from the ring canal, and is usually
provided with an ampulla. Probably the tentacles are to be regarded
as specially modified tube-feet. In most, the stone canal (or canals,
for there are often several present), is not connected with the
body-wall, but opens by means of a perforated madreporite into
the body cavity.

The alimentary canal is a cylindrical tube, which is
usually longer than the principal axis, and forms a large loop.
The mouth and anus are situated at opposite poles.

In most Holothurians two “respiratory trees” open, either
separately, or by a short, common stem, into the rectum; they are
large, hollow, arboriform organs by which water is taken into the
rectum and expelled again; their function is respiratory. In some
forms “Cuvierian organs” are also attached to the rectum;
they are saccular or racemose glandular structures of unknown
function. The genitalia are only developed in one inter-
radius: the sexual aperture is situated dorsally, usually close to
the tentacles. Most Holothurians are of separate sexes, some few
are hermaphrodite.

In the body-cavity of some forms (Synapta and its allies), especially on
the mesenteries, there are small stalked, slipper-shaped bodies, the cavities of

which are lined with long cilia: the significance of these ciliate organs is
unknown.

Many forms feed, like the Spatangide, by ingesting sand and mud,
with the contained organic particles; others remain with outstretched
tentacles and from time to time draw them, one after another, into
the mouth in order to obtain the small organisms which have become
entangled in their branches. They crawl slowly about by means of
their tube-feet; many bury themselves in the sand. They occur in

all seas.
Many react to a powerful stimulus (a rough touch, or the like) by energetically
contracting the body-wall, so that a large portion of the alimentary canal and
Class 4. Holothuroidea. 14]

other viscera is forced out through the anus. The lost organs are replaced by
regeneration. Other forms (Synapta) when irritated, constrict transversely
and break into several pieces.

The following may be cited as examples: Cucumaria, tube-feet in five double
rows from the mouth to the anus, arborescent tentacles: Holothwria, with
scattered tube-feet, conical on the dorsal surface, cylindrical on the ventral,
tentacles peltate: Psolus, with the tube-feet confined to the flattened ventral
surface, calcareous scales dorsally: Synapta, without tube-feet, vermiform, with
small tentacles, and microscopic calcareous anchors in the transparent skin. The
genera mentioned are all found in European seas. Recently a number of peculiar
abysmal forms, with flattened ventral surface, and long processes of the body,
have been discovered (Elpidia and others),

 
Phylum 3. Platyhelminths (Matworms).

The Platyhelminths are bilaterally symmetrical, unsegmented,

and usually almost flat.

The body is soft, and appendages are

wanting, though ventrally, muscular suckers are frequently present.
There is no body-cavity, all the organs are imbedded in a mass of

Fig. 95.

|

<7
=

    
      
       
   
    
  

  

Ct

LS

  

(

—
a

B
x

——=

  

oe

Le

age

Lome er \
a

   
  

=

Al
L

     

PE
peti eel

     
 
 

LO
. ‘\

Fig. 96,

 

Fig. 95. Nervous system
of Distomum (viewed from
the dorsal side, the ventral
suckers showing through). +
dorsal nerve, sn lateral nerve,
b ventral nerve, d digestive
tube, s anterior, s’ posterior,
sucker.—After Gaffron.

Fig. 96. Part of the
excretory system of
a Flatworm ; diagrammatic.
—Orig.

soft connective tissue ;
the anus, and also the
vascular system are
usually absent (the
Nemertines excep-
ted). The diges-
tive tract iseither
a simple sac, or it is
branched ; it is want-
ing in many parasitic,
and even in some free-
living, forms. ‘The
central nervous
system is repre-
sented by a paired
nerve-ganglion, which
lies anteriorly, and
from which the nerves
to the different parts
of the body issue.
From the hinder end
of the brain, several
longitudinal = stems
arise, and are fre-
quently united by

delicate transverse commissures. Sometimes eyes are present, more
rarely auditory organs; they are situated anteriorly, are simple

in structure, and small in size.

The excretory apparatus is

in the form of a much branched system of thin-walled tubes, which
Platyhelminths. Class 1. Turbellaria. 143

usually open in the hind region of the body by a single or double
aperture: occasionally several openings are present. The principal
tube sometimes exhibits a contractile enlargement just in front of the
aperture (urinary bladder). The finest terminal branches of the
canal-system are especially characteristic ; each ends in a little cup-
shaped swelling, closed by a large cell (flame cell), which bears,
on the side turned towards the lumen of the tube, a very powerful
flagellum. Similar flame cells may also be fuund at other points in
the wall of the tube. The male and female genitalia (Fig. 99)
are usually present in the same individual, and are, as a rule, of a
very complicated structure; testes and ovaries are often present in
‘great numbers, and, besides these, various organs accessory to each
system, as also a uterus. The genital aperture is usually ventral.
Generally there isa copulatory organ.

Amongst the accessory sexual organs, the yolk-gland (vitellariwm),
which is of very common occurrence, may be specially noticed. In it the
so-called yolk-cells are formed, to be enclosed with the ovum in the egg
membranes, and to serve later as food for theembryo. Shell-glands are
generally present; their secretion, when hard, forming the firm shell surrounding
the eggs of many forms.

A. Without anus or vascular system. Hermaphrodite with complicated

genitalia. <a

1. Turbellaria. As a rule free-living, surface ciliated, alimentary
canal generally present.

2. Trematoda. Parasites, without cilia. Alimentary canal
present.

3. Cestoda. Parasites, without cilia. Alimentary canal: always
‘absent. As a rule form chains.

B. With anus and vascular system. Separate sexes. Genitalia simple.
4. Nemertina.

Class 1. Turbellaria.

The Turbellaria are animals of varying, but usually small, size.
The body is uniformly ciliate, which is important for locomotion
as well as for respiration; some are active, many magnificently

 

Fig. 97. Longitudinal section through a Turbellarian (Cycloporus papitlosus), to show
the situation of the pharynx. Of the organs caught in section only the gut is figured.
m mouth, p retracted pharynx, r dorsal papilla, s sucker, ¢ gut; g male, 2 female
aperture, enlarged Adapted from Lang.
144 Platyhelminths.

coloured. Sometimes nematocysts, like those of the Ccelentera, are
found in the skin. Eyes in varying number, and sometimes
auditory organs, are present; there is frequently a pair of short
tentacles upon the front end, whilst the rest of the body is usually
bare; a little sucker is, however, often present on the ventral
surface. The mouth is ventral, sometimes near the anterior end,
sometimes in the mid-

Fig. 98. Bags OR dle, or again near the

hind end; it leads
into a buccal cavity,
which is often fur-
nished with a peculiar
retractile, muscular
pharynx. This is
a longer or shorter
canal, open at both
ends, and firmly at-
tached by one end
to the hind part of the
buccal cavity, whilst
the other end can be
everted through the
mouth to seize the
food. In other cases
the so-called pharynx
is simply a specially
muscular portion of
Fig. 98. Sketch of arhabdoccelous Turbellarian (Meso- i a sealisar the biel

stomum splendidum) showing the digestiye tract da, and the : :
cerebral nerve mass c; ge genital aperture, m mouth, s cavity, and is not pro-

pharynx. Enlarged.—After v. Graff. es Tan af
Fig. 99. Sketch of a rhabdocwlous Turbellarian (Pro- trasible. . or
vortex affinis) with the genitalia. d yolk-sac, g glands in cases even this is

connection with the male apparatus, ge genital aperture, absent. The mouth
o eye, ov ovary, p penis, s pharynx (the gut is omitted), f a
t testis, v vas deferens. Enlarged.—After v. Graff. communicates with

the true gut, which,
in some forms (Rhabdoceela), is a simple sac, whilst in others it is
branched like the veins of a leaf (Dendroccela). Some forms (Accela)
have no digestive tract, even though the mouth is still present ; food
is taken in and digested in the soft parenchymatous tissue of the
body. The hermaphrodite genital apparatus opens on
the ventral side, either by a common aperture or by separate pores.
for the male or female glands. In some members of the group,
reproduction by transverse fission occurs; some marine
Turbellaria undergo a metamorphosis. The larva is free-
swimming, and is furnished with processes which do not appear in.

the adult.

 
Class 1. Turbellaria. 145
The Turbellaria live in fresh-, or salt-water, or even on land in

damp places. By means of the ciliary movements, and by slight
movements of the body-muscles, they glide through the water and

Fig. 100. Fig. 101.

 

Fig. 100. Planaria lactea, a fresh-water Turbellarian, with everted pharynx.—After
O. Smidt.

Fig. 101. Larva of a marine Turbellarian, enlarged.—After Lang.

over any foreign objects found therein. They feed upon other
animals, e.g., small Crustacea, which are seized by the pharynx and
sucked out.

Both terrestrial and fresh-water forms occur in England; of the latter, species
of the genus Planaria (branched gut) which sometimes attain a length of
2 c/m. (Fig. 100) are the best known. Many species are found in all seas.

Class 2. Trematoda.

The Trematodes, all of which are parasitic, are nearly allied
to the Turbellaria, differing from them in that the superficial cilia
of the larva are lost later; they are usyally pale or inconspicuous in
colour. The body, which is of a firmer consistency than that of the
Turbellaria, is provided with a definite cuticle, which sometimes
bears little spines, and is furnished with a varying number of small
suckers, sometimes also with chitinous hooks. These adhesive
organs are specially developed in ecto-parasitic forms. Eyes
are wanting in the internal parasites, whilst in the external ones
they are often present. The mouth is frequently situated at the
base of a sucker, and usually at the anterior end of the body. It
leads into a pharynx with muscular walls, which acts as a
pumping apparatus. The pharynx is continued into the true gut; this
is rarely a simple sac, more often* forking into two lateral branches,

 

* In the asexual generations of many forms the gut is, however, only a simple sac;
in others it is entirely wanting. (See the description of Distomum hepaticum given
below). ;

L
146 Platyhelminths.

which in some forms give off more delicate branches (Fig. 102), in
others are unbranched (Fig. 95). The genital openings are
usually on the ventral side close together, and far forward. The
Trematodes are invariably hermaphrodite, but in some (see below)
female parthenogenetic generations occur.

The ectoparasitic forms pass through a
ciliated larval stage, during which they
swim freely in the water. The reproduc-
tion of most of the endoparasites is
far more complicated. The different gene-
rations alternate with one another, a her-
maphrodite being followed by one or more
parthenogenetic generations, so that a
heterogony occurs. A _ ciliated larva
hatches from the fertilised egg of the
hermaphrodite generation, migrates into a
lower animal, generally a Gastropod, and
there develops into an imperfect female,
within whose body the eggs are formed;
an alimentary canal is wanting or occurs as
fluke, showing alimentary ® Simple sac. The eggs produced by this
canal x 2. 9, anterior, s. generation develop without fertilisation in
evi eggs PRN hie body of the parent, and these individuals,

in some forms, constitute the hermaphro-
dite generation, after they have been received into another host (a
Vertebrate). In others, however, they form a second female (partheno-
genetic) generation, which then produces the hermaphrodites. These
are always far superior to the others in size and in complexity of
organisation, and in many forms they alone are known.

 

Order 1. Polystomeze (Monogenetic Trematodes).

Almost always ectoparasitic: with usually more than two suckers,
often possessing hooks: without heterogony. The majority are
parasitic upon Fish (skin and gills).

1. The genus Tristomwm includes large species (to almost 2 c/m long);
characterised by a very large sucker at the hind end, and two smaller ones
anteriorly ; they are parasitic on many marine Fish.

2. Polystomum integerrimum (Fig. 105), lives in the urinary bladder of the
Frog; anteriorly there are four eyes; posteriorly six large suckers, and a number
of hooks of different sizes. The eggs are laid in the spring, pass to the exterior
through the cloacal aperture of the host, and develop in the water in the course
of some weeks. The larva is furnished with a ciliated girdle, with eyes, and with
a circle of sixteen hooks upon a disc at the posterior end; the sucker of the adult
is absent. The larva wanders into the gill cavity of the tadpole, where it loses the
cilia and develops one or two pairs of suckers; it remains there until the gills of
Class 2. Trematoda. Order 1. Polystomec. 147

the host begin to atrophy, and then wanders (probably through the alimentary
canal of the Frog) into the urinary bladder, where its further development takes
place.

3. Diplozoon paradoxum, “the Double-animal,” lives in the gills of different
fresh-water Fish. The larva is furnished with cilia, which atrophy after it has
attached itself to the gills. The young parasite is an elongate animal with two
suckers in front and several behind ; there is, further, a median ventral sucker, and

A 8 Ww

RY

he ®

. of

88S a
Ko )
~6 cas

4

 

Fig. 103. Diplozoon paradoxum. A free-swimming larve. B single individual.
C two individuals which have begun to unite, the left has seized the dorsal papilla of the
right with its ventral sucker. D The same after fusion, each has seized the dorsal papilla
of the other. b ventral sucker, d gut, h adhesive apparatus of the posterior end, m mouth,
rv dorsal papilla.—After Zeller.

upon the dorsal side, just about opposite to this, a conical papilla. After some
time the young animals unite in pairs, in such a way that one seizes the dorsal
hump of another with its ventral sucker, and the latter turns round to clasp the
dorsal hump of the former in a similar manner, so that the animals are fastened
together cross-wise. They coalesce and remain attached throughout life. After
the fusion, the animal still grows considerably.

Order 2. Distomex (Digenetic Trematodes).

Endoparasites with one or two suckers, or wholly destitute of
them: with a heterogony. The hermaphrodite generation occurs in
Vertebrates, the parthenogenetic in lower animals.

1. Distomum hepaticum, the Liver-fiuke. The hermaphrodite generation
frequently occurs in the bile ducts, especially of Sheep and Cattle (more rarely of
other Mammalia); length, 3 c/m. Besides the anterior sucker which surrounds
the mouth, there is a small ventral one at some distance from it. The animal
feeds upon blood. The microscopic ova are carried by the bile into the digestive
tract of the host, and are conveyed thence to the exterior. If they fall into
water or some damp place, each hatches into a ciliated larva provided with two
eyes ; and a small papilla at the front end, by means of which it bores through
the skin of a particular species of fresh-water Snail, Limnzus truncatulus ; if this
little Snail is not forthcoming, the larva perishes. In the Snail, the ciliated
covering is lost, and numerous ova are formed in the small accelous animal, the
sporocyst (first asexual generation), during its growth. The ova
hatch within the sporocyst, and each develops into a small animal, a redia
{second asexual generation), differmg from the parent, in the poss2ssion

i 2
148 Platyhelminths.

of a pharynx and a simple sac-shaped gut. The redia break through the
maternal body-wall and wander about in the Snail, consuming its liver. In
these, eggs are again formed, which become “cercariw,” with a branched
alimentary canal and a caudal appendage. They escape through an opening
in the maternal tissues, and later from the body of the Snail also. The cercaria
swims actively for some time in the water, then it attaches itself to some plant,
loses its tail, and secretes a mucous-substance which hardens into a cyst round
the body. If it be swallowed with the food by a Sheep or an Ox, the capsule

AY)

PN
of) b= osely
XN JOP)
1
2

  

Fig. 104. Distomum hepaticwum. 1 newly hatched larva. #¢ boring papilla, o eve.
2 the same (young sporocyst of the first generation), after it has entered the snail and
lost its ciliated coat. kovum. 3 adult sporocyst of the first generation. 4 redia of the
second generation. f Limb-like projection, h;—h, cercarie developing within the redia,
k cercaria-embryo, m mouth, ta gut, v genital aperture. 5 cercaria, Ku glands, whose
secretion forms the capsule. S,—S, suckers, ta gut. All the figures are enlarged.—After
Thomas; 4 slightly altered.

is dissolved by the gastric juice, and the young Trematode wanders into the
liver, where it attains sexual maturity (the hermaphrodite generation).
Encysted Liver-flukes are found not only on water, but also on land plants, for
the Snail frequently leaves the water and wanders about in the adjacent
meadows.

2. Leucochloridium paradoxum is a parthenogenetic trematode, parasitic in
Succinea amphibia, a Gastropod inhabiting damp places. This peculiar form has
the appearance of a sac with numerous branches, some of which attain a very
great development, forming thick, brightly coloured rods, which push their way
into the tentacles of the Snail, and expand them enormously. Different insect-
eating Birds tear the “ rods” out of the Snail, which may go on living with a new
branch of the Leucochloridium in its tentacle. In the digestive tract of these
Class 2. Trematoda. Order 2. Distomee. 149

Birds, as also in that of various Marsh-birds which devour the whole Snail, the
young Trematodes contained in the “rods” undergo their complete development,
and become the normal hermaphrodite generation, which has been described
under the name Distomum macrostomum.

Fig. 106.

  

B Cc

Fig. 105. Polystomum integerrimum, from the central side. m Mouth, s sucker,
t gut.—After Zeller.

Fig. 106. A Snail, with Leuchochloridium paradozum in both tentacles. B the same,
taken out of the Snail. C Distomum macrostomum. p penis, s, fore-, s, hind-sucker, t gut.
A and B natural size, C x 20.—After Zeller.

Class 3. Cestoda (Zapeworms).

The Cestoda differ from the Trematoda, with which they are
nearly related, in that they have no digestive tract, and almost
always form chains by budding.

A cestode chain consists, at first, of an asexual individual, the so-
called “head” (scolex), which is provided at the anterior end with

 

Fig. 107. Tania mediocanellata, part of the chain, natural size.—After Leuckart.

suckers, hooks, or other organs of adhesion. Behind the head follows
a larger or smaller number of segments (proglottides), 7.¢., sexual
individuals of different developmental grades, and of different sizes,
150 Platyhelminths.

which are separated from one another by constrictions; the segments
nearest to the head are the youngest, those farthest off, the oldest and
largest ; new segments are constricted off from the hind part of the
head. When the development of the segments has gone so far that
they contain ripe eggs in large numbers, they separate from the
chain ; in some cases, they break off at an earlier stage, and grow
independently ; in others, they remain in connection. The number of
segments in a chain may increase from quite afew to many hundreds.*

The adult worm occurs exclusively in the gut of the Verte-
brata, to the wall of which it attaches itself by the organs of adhesion
on the head. It feeds by absorbing the contents of the gut through
the skin. The Tapeworm does not, however, spend its whole life in
the same place, or in the same host. At a younger stage, as a

Fig. 108. Fig. 109 b. Fig. 110. Fig. 111.

i oh

ae
yi

if ay
A
Hf ae
NN
Fig. 108. Six-hooked larva of T. solium.

a1.
i )
Fig. 109. Proscolex of the same Tzenia, with (a) inpushed, (b) evaginated
head.
Fig. 110. Ciliated larva of Bothriocephalus latus.
Fig. 111. Proscolex of above.
All figures enlarged. After Leuckart.

 

proscolex, it lives in another host, and in a different part of the
body. It then often consists only of the head; in other cases, of
the head and of a number of joints, which are, however, never
ripe. Asecond host now devours the first, and thus a transference
of the parasite occurs, and it attains sexual maturity. The tem-
porary host is usually infected by taking the eggs, (or the
segments containing eggs), which have passed from the permanent
host with the excreta, into its alimentary canal. Hach egg contains,
one larva, a small round organism provided with six hooks, which,

 

* According to the opinion put forward by many observers in recent times, the
Cestode chain is not a stock, but is a single individual, with a great number of
gonads. But this view is contradicted by the fact that in some Cestoda, even after
separation, the segments are capable of growth, become ripe, copulate, and thereby
testify abundantly to their independent individuality.
Class 3. Cestoda. 151

after its shell is dissolved by the digestive fluids,* bores through
the wall of the gut and becomes a proscolex.

As regards their structure the Tapeworms are, excepting for the
absence of the alimentary canal, closely connected with the Trema-
todes. The genitalia are hermaphrodite, of a very complicated
nature ; in each segment, there is a separate genital apparatus, which
has no connection with those of the other segments. The genital
aperture is either on the ventral side of the segment, or on its margin.

The parasitic genera, Amphilina (in the Sturgeon), and Caryophylleus (in the
Carp), seem to be a transition towards the Trematodes, for they do not form
chains, The unsegmented body contains but one reproductive apparatus ;
like the rest of the Cestoda, they have no gut, and agree also with them in
certain special arrangements of the genitalia. Some other Tapeworms are like
the above-mentioned forms, in so far as they appear to be entirely unsegmented,
although they exhibit essentially different arrangements, for an inner segmentation
is clearly manifest in the multiplicity of the reproductive organs. Among
such forms, a separation of the reproductive individuals does not occur, and a
chain of this kind may be compared with a Coral-colony, some of whose
polyps are in closer connection than usual. As an example of Cestodes
showing this external continuity, but internal metamerism, the Strap-worm,
Ligula simplicissima, parasitic in the digestive tract of different Water-birds (in
Fish in the cystic stage), may be mentioned. /

Most of the Tapeworms of Mammalia and Aves belong to the
genera, Tvenia and Bothriocephalus, chiefly to the former. Numbers
of other genera are known particularly in Pisces.

1. Tenia. The head is furnished with a circle of four suckers. Upon the
middle of the anterior end there is, in many species, a crown of recurved hooks,
which may be numerous, and situated upon an elevation (rostellum) ; in others,
however. the hooks may be entirely wanting. The ripe proglottis may be
elongate or short and wide; it contains a branched uterus. The genital aperture
is usually at the edge of the segment.

(a) . soliwm lives in the alimentary canal of Man. The scolex with a crown
of hooks, the ripe proglottides considerably longer than broad; the former about
as large as a pin’s-head, the latter 5 m/m broad. The chain attains a length
of about 3. to 34 m. The ripe proglottides, and the thick-shelled eggs, con-
taining embryos pass out with the excreta. If they be eaten by a Pig, the
egg-shell dissolves, and the six-hooked larva bores through the gut into the body,
where it usually takes up its abode in the muscles, more rarely in the heart
or brain; there it grows considerably, and turns into a bladder-worm or
proscolex (Cysticercus cellulosx), a cestode head of the same appearance as that
of the adult Tapeworm, but with an appendage behind in the form of a vesicle
the size of a pea, filled with fluid, in which the head is invaginated. When it is
taken into the digestive tract of Man, the bladder atrophies and the head develops
into the Cestode-chain. More rarely the proscolices are found in various other
Mammals. They sometimes occur in Man in places where they may prove fatal,
in the brain, eye, or wall of the heart. Man, like the Pig, may occasionally
take in eggs containing embryos through the mouth.

(b). T. mediocanellata (=T. saginata, LEvcK.), also found in the digestive tract
of Man; in most countries more common than T. soliwm. The head without

 

* This shell is not an egg-shell in the usual acceptation of the term, but a
membrane secreted by the embryo. The “eggs” are, in reality, ency sted embryos.
152 Platyhelminths,

rostellum, but with very powerful suckers. The branches of the uterus are
more numerous than in J. solium, which this species usually resembles closely ;
it attains a length of 7—8
A B Cc m. The development as
: before. The bladder-worm,
almost exclusively in the
muscles of Cattle, is very
much like that of 7. soliwm,
but a little smaller.
(ce) T. ceenurus. With
érown of hooks; in the
digestive tract of the dog;
s lem. long. The bladder-
a worm (Cenurus cerebralis),

Fig. 112. “Head ” of Tenia solium (A), of T. medio- lives in the brain of Sheep,

canellata (B), and of Bothriocephalus latus (C).—Orig. in which it induces gid-

diness. It becomes very
large (as large as a Hen’s egg or more), and produces, by budding, numerous
scolices, so that there is a colony of Cestode-heads in the same vesicle.

(d) T. echinococcus. A very small Cestode (at most 5 m/m. long), with 3—4
proglottides; in the alimentary canal of the Dog. The bladder, the Echinococcus,
in the liver and other organs of Cattle, Sheep, Pigs, and Man, often attains a
considerable size (that of a child’s head or more), and is surrounded by a thick,
stratified cuticle. Many small heads, as in ZT. cenurus, bud out from the
vesicle, but in 7. echinococcuws are always formed as little invaginations of
the wall (see Fig. 113 B), the so-called brood-capsules. The Echinococcus

  

 

 

Fig. 118. Tenia echinococcus. A Tapeworm enlarged.—After
Leuckart.—B diagrammatic section through a cyst, v wall, ¢
cuticle, y brood-capsule, y' the same in an incipient state—Orig.

 

occurring in Man—rare in most places, but common in Mecklenburg, Iceland,
and Australia—is distinguished by often attainimg an enormous size, and by
having within the original bladder many smaller daughter vesicles (brood-
capsules), which exhibit the same structure as the former. The brood-capsules
seem to arise by a modification of heads which have broken free from the wall of
the parent bladder.

(e) T. cucumerina. ‘75 m. long. The head provided with a retractile
proboscis-like process, with several circles of hooks. Ripe proglottides oval.
Class 3. Cestoda. 153

Very common in the Dog and Cat, rare in Man (children). The proscolex,
which has no bladder, lives in the Dog-louse (Trichodectes canis); according to
modern opinions, in the Dog-flea also.

2. Bothriocephalus. The head with two long sucking grooves, without true
suckers and without hooks. The genital apertures are on the ventral side of the
proglottides, which are always short and wide. Uterus an unbranched coiled

 

Ape ee

SE ae

 

 

 

 

 

 

 

 

Fig. 114. B. latus, part of the chain, natural size—After Leuckart.

canal. B. latus, the broad Tapeworm of Man, common in the Russian Baltic
provinces, Finland, in W. Switzerland, though extremely rare in England,
attains a length of 8—9 m. The proscolex lives in the flesh of the Pike, and
other fresh-water Fish. It is long, without a bladder (1 c/m. long). How the Fish
are infected is not known. The eggs of the Tapeworm develop in water, the newly
hatched larve are provided with a covering of cilia and within them the six hooks
are found as usual. It has not, however, been found possible to infect the
Fish with the larve, so that it is conceivable that the worm lives first in another
host. On the other hand, it has been shown by experiment that the Pike-
proscolex transferred to the digestive tract of Man (and the Dog) develops into
B. latus.

Class 4. Nemertinea (2/ynchocela)

The Nemertines are, as a rule, elongate, often even ribbon-like,
animals of considerable size. The skin is ciliated all over. At
the front end, on each side, is a slit-like, thickly-ciliate pit, a sense-
organ, which is also present in some Turbellarians; dorsally and
anteriorly there is usually a number of small eyes. Quite at the
front end of the animal there is an opening leading into a deep eversible
blind sac, the proboscis. At the bottom of the sac, there is, in
many forms, a pointed stylet, which, when the proboscis is everted,
lies on its tip; frequently a poison gland opens close beside
it. In others the spine is not present, but the proboscis is furnished
with numerous nettle-cells. When retracted (Fig. 115 C) it is sur-
rounded by a muscular proboscis-sheath, and the space between
them is filled with fluid. The proboscis is everted by contractions of
154 Platyhelminths.

its sheath. A long muscle, the retractor, passes from its inverted
end to the sheath, and this pulls in the everted organ (see Fig. 115 D).
Its function is defensive and prehensile; it is not connected with
the digestive tract. This begins in front and ventrally (behind
the proboscis pore) in a slit-like mouth, and runs through the body
as a canal, furnished usually with small lateral evaginations, and
opening in the anus at the posterior end.

A B CG D

TO

   

ISN

LDL

 
   

   

IS

 
 

B

  
  
        

   

LD

OO

Rapea BELA Arle Wd el scah Wea

7

    

 

 

 

\
.

  

ARETA

 

 

 

 

 

 

DODO DOLDD

 

i)

 

 

 

 

SED
enn

 

Fig. 115. A Sketch of a Nemertine, showing the nervous system, B do. with
blood vascular system, ( ditto with gut and proboscis, D ditto front end with everted
proboscis. Diagrammatic. a Anus, ¢ ciliated groove, aa gut, g poison gland, | lateral vessel,
m retractor muscle, 7 probscis, ro proboscis opening, rs proboscis sheath, s lateral nerve
cord, ¢ transverse vessel.—Orig.

The nervous system is very like the usual flatworm type; the
proboscis sheath passes between the cerebral commissures. From the
cerebral ganglion of either side arises a lateral nerve, running
backwards, and containing numerous nerve-cells; the two cords
are often connected by delicate transverse commissures, passing
above and below the alimentary canal, and from them many
nerves arise. The excretory organs are similar in structure
to those of other Flatworms. Besides the ciliated grooves and eyes
Class 4. Nemertinea. 155

already mentioned, there are auditory vesicles ina few forms.
In contrast to other Flatworms, the Nemertines possess a vascular
system, usually consisting of three principal longitudinal trunks,
two lateral, and one dorsal, which
come into relation with one
another anteriorly and _pos-
teriorly, and are besides con-
nected by transverse vessels.
The blood flows from behind
forwards in the dorsal vessel,
from before backwards in the
lateral vessels; it is colourless
or red. The Nemertines are

almost always of separate Fig. 116. Diagrammatic transverse section
sexes; the sexual organs are ft Nomen 0 Donel vst ered
much simpler in structure than muscle, 1 lateral nerve cord, p proboscis, ps
those of other Platyhelminths. proboscis sheath, r circular muscle.

Many ovaries or testes are

present, opening by one duct on the side of the body. There are
no accessory and no copulatory organs.

Some Nemertines undergo a metamorphosis, which is
aberrant, in that the principal part of the larval body atrophies.
The larva, which is sometimes of a peculiar form (Fig. 117) is free-
swimming.

 

 

Fig. 117. Three larval stages of 4 Nemertine; the oldest larva (C) is the
so-called pilidium. ¢ flagellum, g gastrula mouth, e and e’ invagination of the skin, from
which a great part of the final Nemertine body arises; m stomach, oe cesophagus.—After
Metschnikoff.
156 Platyhelminths.

The Nemertines are for the most part marine, living usually at
the bottom of the sea. Some are fresh-water or terrestrial. They
feed upon other animals.

One form living in European seas, Lineus longissimus, sometimes attains
a length of 13 m., with a breadth of 8 m/m. Most species are a few centi-
metres, some only a few millimetres long.

APPENDIX TO THE PLATYHELMINTHS.
Rotifera (Wicel Animalcules).

The Rotifers are usually microscopic creatures, which in size,
habitat, and mode of life resemble the Infusoria. The posterior part
of the body, the foot, is narrowed, separated from the trunk,
and provided with a pair of short appendages or with an adhesive
disc at the tip. At the anterior end, there is a more or less
well-developed (sometimes scalloped) trochus, the rotatory organ,
whose edge is beset with strong cilia. It serves two purposes; in the
first place it is of use in swimming, and secondly, by means of the

 

Fig. 118. A Diagram of the anatomy of a female Rotifer, lateral view. Bthe
male. a anus, c ganglion, cb contractile bladder, d yolk sac, ex excretory organ, k ovary,
m stomach, o mouth, oc eye, r wheel organ, s pharynx, ¢ testis, g male aperture.—Orig.
(with assistance from Plate’s figures).

currents set up by it, small particles are driven into the under-
lying mouth. The trunk, in some forms, is covered by a hard
chitinous shield, the lorica (a specialised thickening of the
cuticle covering the whole body), which may be armed with spines.
In other cases both trunk and foot exhibit delicate constrictions
which simulate a segmentation, but there is never a corre-
sponding arrangement internally. The foot is often articulated
with the body, so that by its help the animal can crawl about like
Rotifera. 157

a leech. The mouth leads into a muscular pharynx, furnished
with several emall jaws, which are continually being struck one
against the other. The digestive tract is usually short and
simple, and the anus is generally dorsal, at the base of the
foot, though in some forms it is wanting. The nervous system
is of the flat-worm type, cerebral ganglia anteriorly with nerves
springing from them; one or two eyes are often present at the
front end. The excretory organs closely resemble those
of the Platyhelminths; there is a pair of principal tubes with
smaller branches, whose club-shaped terminal swellings are like
those of the Flat-worms. The principal ducts open, after having
united to form a contractile vesicle, into the hinder part of the
gut or cloaca. There is no vascular system. The Rotifera
are of separate sexes. Ina few forms only are the sexes alike,
usually they are extraordinarily different ; the males are smaller than
the females, they are entirely destitute of a mouth, and the digestive
tract is rudimentary, so that they can take in no nourishment;
they live for only a few days; they have no lorica, even when the
female has one, and the trochus is small; they are less numerous than
the females, and in many genera were long unknown. The short
oviduct * opens, as a rule, into the cloaca; the vas deferens dorsally
at the base of the foot. The Rotifera lay two different kinds of
eges, viz. thin-shelled, unfertilised summer eggs, which
develop parthenogenetically ; and the thick-shelled fertilised
winter eggs, which do not hatch until long after they are laid.
The young ones do not undergo a metamorphosis.

In a common fresh-water Rotifer, Hydatina senta, two kinds of females are
found. The one does not copulate and lays only summer eggs, which give rise
to females; the other is capable of copulating, and when this takes place, lays
winter eggs, or if this does not occur, summer eggs, which hatch into males.
Whether similar conditions obtain for other forms is still uncertain, although
probable.

Much doubt exists as to the systematic position of the Rotifers; they have
been sometimes placed with the Arthropoda, sometimes with the ‘“ Vermes.”
From the facts which have lately come to light with regard to their structure,
it is probable that they must have been derived from the Platyhelminths (see
especially the excretory apparatus).

The Rotifers are usually active and free-swimming, some, however,
are fixed. For the most part they live in fresh-water, a small number
in the sea. Some forms which occur in damp earth or on plants
(moss) can withstand complete desiccation, but this is not the case
with those living in water. A few are parasitic.

 

* The (usually unpaired) ovary is connected with a yolk-gland which produces a
mass of yolk, to be absorbed by the ovum.

 
Phylum 4. Nemathelminthes (Rownd-worms).

The two groups of this phylum are so very different from one
another, that it is a matter of great doubt whether they should be
put together. Common to both groups are the elongate, cylindrical
body, and the muscular body-wall which encloses a well-defined

body-cavity. Cilia are absent. The sexes are always separate.

It is as yet impossible to say to which of the other phyla the Round-worms are
most nearly allied. From what is known, up to the present, of their anatomy,
they seem to present no characteristic affinities with any other groups.

Class 1. Nematoda (Ziread-worms).

The smooth body is almost always elongate and cylindrical, often
filiform, and usually pointed at both ends. It is covered with a light,
thick, elastic, cuticle, beneath
which is a thin hypodermis, and
under this is a single layer of
muscle cells, of different shapes,
and often very large. The mus-
culature is, however, interrupted by
four so-called longitudinal aree,
ridges of the hypodermis, which
traverse the length of the body, one
in the mid-dorsal, one in the mid-

ventral line, and one on each side,
é dividing the muscular sheath into four

Fig.119. Transverse section of a lon git - di : al bands. Of the
Nematode, diagrammatic. 6 ventral, four longitudinal arez, the lateral are
i gut, ¢ excretory organ, h skin, 9 the best developed. The mouth is at
gonad, m muscle-cell, r dorsal area, s
lateral area.—Orig. the front end of the body ; sometimes

a distinct buccal cavity lined with a
stiff cuticle is present, but in most forms, this is not the case. The
rest of the digestive tract, which takes a straight course through the

 
Nemathelminthes. Class 1. Nematoda. 159

body, is composed of three sections : a muscular cesophagus, which acts
as a pump, a peculiar intestine devoid of muscles, and a short
muscular rectum. The anus is on the ventral side, near the hind end
of the body. The central nervous system consists of a nerve-ring,
provided with ganglion-cells, ranning round the cesophagus; several
nerves are given off from this, two of which are specially important,
one passing along the mid-dorsal, the other along the mid-ventral
line. The ventral nerve ends posteriorly in a small ganglion. As to
sense organs, the little tactile papillw, which are always
present anteriorly and posteriorly (the latter especially in the males),
must be mentioned; in some free-
living Nematodes, small eyes
have been found at the anterior
end. The excretory ap-
paratus seems to be represented > Yd
by a pair of delicate tubes, which e hal
traverse the lateral arew, and open Ad
anteriorly upon the under surface
in a common aperture. The
genitalia, in the female, con-
sist of two long, coiled tubes,
which open by a short common
duct, rather anteriorly upon the
ventral surface. Each canal con- 8-----
sists of two regions, not sharply
demarcated, the ovary and the
oviduct; the latter is frequently
much distended in the gravid .
female, and serves as uterus, or as Fig. 120. Hind end ~ a eels
brood-pouch for the numerous ova. Nematode, longitudinal section. Dia-
In the male, testis and vas deferens etammatic. cl cloaca, d gut, m retractor
. muscle of the spicule, s sheath of spicule,
are represented by a single, as a w body-wall.—Orig.
rule, long coiled canal opening into
the rectum, which thus represents a cloaca. The canal exhibits
two parts, of which the vas deferens is the shorter and wider, the
testis the longer and thinner. The male is usually provided
with copulatory organs, one, or at most two, curved chitinous
needles, the so-called spicula, which lie im sacs opening
into the upper wall of the cloaca. In copulation, the spicula are
protruded through the anus and introduced into the female genital
aperture ; in some forms, the cloaca is everted at the same time (see
below for the special arrangements in Trichina and Strongylus).
The female usually surpasses the male in size; sometimes also,
other striking differences occur. The Nematodes, as a rule, lay
eggs enclosed in a thick shell; frequently the development is con-
siderably advanced when the egg is laid; not a few are viviparous.

  
160 Nemathelminthes.

There is usually no pronounced metamorphosis, although the young
one sometimes differs from the adult. Asexual reproduction does
not occur. Most Nematodes are parasitic; some, mostly small
forms, are, however, free-living, in fresh-water, damp earth, or in
the sea, some in decayed substances or living plants. Many of the
parasitic forms live in different hosts, at different periods, or are free
for one period, parasitic for another. The habits of these animals

are of peculiar interest.

_ 1. The Common Round-worm (Ascaris), often of considerable size,
anteriorly three prominent well-developed lips, forming a conical projection
marked off from the rest of the body. The human Ascaris, A. lumbricoides is
frequent in the small intestine, especially numerous in children, and then not
without danger: also in Pigs. It probably feeds upon intestinal mucus, not
upon blood. According to recent observations, infection is simply caused by the
ova, which pass out from the host with the excreta, chancing to enter the mouth.
On reaching the stomach the shell is dissolved by the gastric juice,* so that the
embryos are set free. The female may attain a length of 40 c/m., the male of
25 c/m., both are usually about half as long. A. megalocephala of the Horse is
somewhat larger than A. lwmbricoides ; A. mystax of the Cat and Dog is consider-
ably smaller, the female 12 c/m., the male 6 c/m., and is easily recognised by the
wing- or ridge-like fold of skin on either side of the anterior end.

2. The Maw-worm (Oxyuris vermicularis). With three rudimentary lips;
at the anterior end, dorsal, and ventral longitudinal folds of skin. Female with
thin, pointed, elongate, spike-like hind-end, 1 ¢/m. long; male without this “ tail,”
smaller and less common than the female. Common in the large intestine of man
(especially children), feeding on its contents, often present in very large numbers,
and then causing serious suffering. Infection probably takes place in the same
way as with Ascaris. A much larger species (0. curvula) in the caecum of the
horse.

8. The Strongylide (genera Strongylus, Eustrongylus, Dochmius),
are especially characterised by the presence of a cup-shaped bursa, surrounding
the cloacal aperture in the male, which serves as an organ of adhesion during
copulation, and is supported by radial rib-like thickenings (Fig. 123 A). Spicula
are also present as usual. Most of the Strongylide are blood-suckers; the
mouth is large, and furnished with chitinous teeth or spines.

(a) Eustrongylus gigas, the female may be 1 m. long (12 m/m. thick), the
male ‘3m. In the pelvis of the kidney (i.e., the anterior widened part of the
ureter) in the Dog, Otter, Seal, etce., very rare in Man. Life history unknown.

(b) Dochmius duodenalis (Fig. 123), the female may be 2 ¢/m. long, the male
1c/m. Mouth with strong hooked teeth ; a very dangerous blood-sucking parasite,
living in the small intestine of Man. In the tropics and in warm climates (Brazil,
Egypt, Italy); also farther north, e.g., in some mining districts of Germany
(“Egyptian Chlorosis”’). The ova leave the parent and its host, to undergo their
development in damp earth or quagmires, where the larve live for some time.
Then they encyst (the capsule has the elongate form of the animal, and is pro-
bably a loosened cuticle), and in this state are probably introduced with drinking-
water, or in some such way.

(c) Strongylus armatus, the Palisade W orm (the latter name comes from
a row of chitinous spicules along the edge of the mouth), female to 5 c/m., male
2—3 c/m. Very frequent in the large intestine (especially in the cecum) of the

 

* The egg-shell, just as in most other intestinal parasites, cannot be dissolved in
the intestine, the ova must pass through the stomach for this to be effected.
Fig. 121.
Fig. 122.
Fig. 123.
Fig. 124.

 

Class 1. Nematoda. 161

Fig. 124,

Fig. 122.

 

SEAS

STORM AT
oe cere

 

Intestinal-Trichina, A 9, B g.—After Leuckart.
Muscle-Trichina lying in its capsule.—Orig.

Dochmius duodenalis, A ¢, BY .—After Leuckart.

Filaria medinensis (Guinea-worm). Natural size.—After Leuckart.

Mu
162 Nemathelminthes.

Horse. In the youngest stage it is free and is probably swallowed by the Horse
with drinking-water ; it lives at first in certain arteries (especially in the anterior
mesenteric artery), which suffer, in consequence, a pathological change (worm-
aneurism). Later it passes into the gut, and attains sexual maturity. How the
wanderings to and from the artery occur is not yet known, Neither the presence
of the worm in the artery nor in the gut seems to affect the health of the Horse
directly ; but a clot from the aneurism may occasion a stoppage in the intestinal
vessel, and thereby a dangerous, often fatal, illness. Other Strongylidew live in
various domestic animals, among them the dangerous S. filaria in the lung of
the Sheep.

4. Trichocephalus dispar, very frequent in the large intestine, especially the
cecum of Man, rare in England; the front part of the body is drawn out to a
long, thin thread, which bores into the mucous membrane of the gut; may attain a
length of 5c/m. The embryo develops within the egg-shell in damp places or in
water, and is taken, still enclosed by the shell, into the digestive tract of the host,
where it hatches and undergoes further development.

5. The Trichina (Trichina spiralis), The body of the sexually mature
animal, the so-called Intestinal-trichina, is very thin; the female, 3 to
35 m/m., the male, 15 m/m., long; the female aperture lies far forward; the
hind end of the male, with two cones, cloaca eversible, serving as a copulatory
organ; spicula wanting. In the mature state in the smull intestine of Man and
other Mammals, especially in the Pig and the Rat. The Intestinal-trichina
produces a large number of microscopic larvee whilst within the gut of the host
(each female at least about 1500), which at once bore through the intestinal wall
into the body-cavity of the same host, and thence migrate into the muscles,
where each enters a muscle-fibre, causing it to swell up. The outer part of the
swollen muscle-fibre hardens into a citron-shaped capsule round the young
Trichina, which, meantime, has grown considerably (to 1 m/m. long), and now
lies spirally coiled in the pulpy mass filling the capsule; the capsule, after
some months, is infiltrated with calcareous salts, and becomes hard and opaque.
If an animal, which contains such encysted Muscle-trichina, is eaten by
another (in which the Trichina can live), the capsules are dissolved in the stomach,
the Trichine are freed, pass to the intestine, and attain sexual maturity in the
course of a few days. They then copulate, and within a week after their
entrance into a new host, the female intestinal form produces the first embryos.
The female usually lives in the intestine only five or six weeks, and then dies;
the adult male lives for a still shorter time. As Muscle-trichinew, they can,
however, live even several years; old forms often become calcified, and then
die. Man is infected by partaking of raw pork; the Pig, by eating a Rat; the
latter, probably, by devouring the sweepings of the slaughter-house, or a dead
comrade. Trichinosis is really caused by the wanderings of the young Trichina,
and by its first sojourn in the muscle; when the wandering is over and the
Trichina is encysted, the symptoms of disease cease, but recovery is often very
gradual, and many cases terminate fatally.

6. The Threadworms (genus, Filaria, etc.) are very elongate animals,
living as a rule, in parts of the host other than the gut, chiefly in connective
tissue. Amongst them are:

(a) The Guinea-orMedina-worm (F.[Dracunculus] medinensis) living
in the connective tissue under the skin or between the muscles of man; only,
however, in warm regions of the Old World. The female alone is known; it
attains a length of 80 c/m. In the adult, the digestive tract is atrophied, the anus
is absent, food is taken by absorption through the body-wall. The greater part
of the body-cavity is occupied by the enormous mouthless oviduct, in which there
are several million embryos. The irritation produced by the parasite, causes
small abscesses through which the mature worms make their escape. The larva
Class 1. Nematoda. 163

bores into a Cyclops in which it undergoes certain changes. In Man, infection is
probably the result of accidentally swallowing the Cyclops in drinking water.

(b) Filaria immitis (female to 25, male to 17 c/m), in the heart and hypo-
dermal connective tissue of the Dog; the young forms in the blood. Common in
Eastern Asia, rare in Europe. In the tropics the young Filurie are also found
in the blood of Man.

7. Mermis. Filiform aproctous Round-worms inhabiting various Insects,
out of which they finally bore into damp earth, where they become sexually
mature, copulate, and lay their eggs. The larve bore their way again into the
tissues of Insects. The genus Gordius, far removed in structure from the
typical Nematoda, and living, in the adult state, in fresh water, presents a
similar, but more complex, life-history.

8. The Anguillide are a group of Nematodes, which are, for the most part.
very small, and usually free-living, occurring in water, in different decaying
substances, or in living plants. As examples, the following may be mentioned :

(a) Tylenchus tritici, the Eel-worm. In grains of wheat there is sometimes
found a fibrous mass, which, upon closer examination, proves to be a number
of small dried-up Nematodes; they are restored to
animation by moistening. When such “ergots’” are
sown with sound grains, the Nematodes leave them and
mount the growing wheat plants, upon which they may be
met with between the glumes; later they bore into the
grains, in which they become mature and lay their eggs.
The young ones hatch from these and are found in the
ergots arising by modification of the grains.

(b) Heterodera schachtii, another Eel-worm, produces
the so-called root-knot. The larva bores into the delicate
roots of the beet (and various other plants), and attains
maturity there. The ripe female, which is distinguished by Fig. 125. Hetero-
its short, citron-shaped form, pushes the hinder end of its qdera Schachtii.
body out from the root, causing the epidermis of the root Female fastened to a
to split. The elongate male, on the other hand, bores 00t-fibre. Enlarged.
entirely out, and seeks the female for fertilization. The a
impregnated female later (Fig. 125), by the degeneration of
the organs, becomes a brood pouch full of ova and larve,and finally drops off theroot.

(c) Anguillula aceti, the Vinegar worm, livesinsour paste and in vinegar.

 

Class 2. Acanthocephala (Ziorn-headed Worms).

The body is cylindrical, elongate, often transversely wrinkled, and
fairly hard. There is an eversible process,the so-called proboscis,
at the anterior end, which is beset with many rows of backwardly
directed chitinous hooks; the rest of the body is usually smooth.
In the skin there is a peculiar vascular net-work, continued
into two long bodies (the lemnisci), which spring from the body-
wall, in the anterior region of the body-cavity. A digestive
tract is entirely wanting. Food is absorbed through the
surface, and the vascular system and the lemnisci probably carry the
nutritive fluid from the skin over the rest of the body. The nervous
system is represented by a ganglion lying in the forepart of the
body, at the base of the proboscis, from which nerves run backwards
and forwards. There are no sense organs. ‘The Acanthocephala

Mu 2
164 Nemathelminthes.

possess an excretory apparatus, similar to that of the
Platyhelminths, i.e., provided with the typical terminal branches. It
opens into the peidast or vas deferens*. Ova are found free in the
body-cavity of the female in different stages of development; only
one oviduct is present, which, although somewhat complicated in
structure, is, essentially, a canal open at both ends; the ova enter by
the anterior opening: the posterior one is efferent, and opens at the
hind end of the body. The male is usually smaller than the female,
and possesses two testes; their efferent ducts unite to form a common
vas deferens, beset with glands, and opening at the posterior end of
the body in a tolerably wide eversible bursa.

All the Acanthocephala belong to the one genus Echinorhynchus ;
they live, in the adult state, in the alimentary canal of Vertebrata,
with the proboscis
fixed in the mucous
membrane, and they
feed upon the contents
of the intestine. Their
development is
of interest. The eggs
of H. Proteus (one of
the forms whose life-
history is best known)
living in the gut of
different Fresh-water
Tish, escape with the
excreta of the Fish,
and are consumed by
a small Crustacean,
Gammarus pulex, in

whose alimentary

Fig. 126. Echinorhyrchus.—After Leuckart. canal the elongate
Fig. 127. Larva of one of the Acanthocephala.—After larve hatcht out.

ean The front end of the
larva is provided with a boring apparatus consisting of ten spines
(see Fig. 127), by means of which it traverses the intestinal wall
into the body-cavity of the Crustacean. Here it wanders about,
grows, and gradually assumes the form of the adult. If the
Crustacean be eaten by a Fish, the parasite gets into the alimentary
canal, and here attains sexual maturity. . gigas, the female of which
may attain a length of 50 c/m. (the male only 9 c/m.), lives, in the
adult state, in the digestive tract of the Pig; as a larva, in the larve
of the Rose-chafer (Cetonia anrata) and other Tinmielliiconnia

Fig. 127.

  

 

* The excretory organs do not, as in the Flatworms, spread over the whole body,

but are limited to a small region.
+ It is noteworthy that the oviducal canal has a lateral opening, through which
the unripe eggs, taken up by the oviduct, pe again into the body- -cavity, whilst

the ripe ones pass through the canal.
Phylum 5. Annelida.

The elongate, bilaterally-symmetrical body consists of a number of
somites or segments, which are separated externally by con-
strictions ; the segments resemble each other to a certain extent both
in their internal and external structure, although they are never all
identical, the first or several anterior segments and the last always
differing from the rest. Frequently, too, there are other differences,
but, even when these variations are considerable, certain common
features are always retained.

 

Fig. 128. Annelid seen from the side; diagram of alimentary canal, of the nervous
system, and the segmental organs. m mouth, a anus,c cerebral ganglion, b sub-cesophageal
ganglion, s segmental organ.—Orig.

The body is covered by a thin cuticle. The mouth is close
to the front end. The alimentary canal, consisting of several regions,
usually traverses the body without convolutions, although not in-
frequently it is provided with lateral evaginations; the anus is at
the hind end. The central nervous system (Fig. 129) consists
of a paired cerebral ganglion above the anterior end of the
digestive tract, and two nerve cords passing from this round the
buccal cavity and then running close together below the alimentary
canal in the ventral body-wall. In each segment these nerves swell out
into a pair of ganglia; the two ganglia of a segment are united by a
longer or shorter commissure. The cords often lie close to one another,
or are even fused, in which case the ganglia of each pair are united.
By fusion of several consecutive segments, the ganglia are aggregated
and even coalesced. From the cerebral and ventral ganglia nerves
go to the corresponding segments. As to sense organs, tactile
threads (tentacles, etc.) are often present, and also eyes: the latter;
which are usually few in number and simple in structure, are
166 Annelida.

specially found on the anterior part of the body, but sometimes
also on other segments. Auditory vesicles are more rarely
present. The vascular system (Fig. 130) is usually very
well developed ; there

A B C is, as a rule, a longi-
tudinal vessel on the
dorsal side, the dorsal
vessel, and a similar
one on the ventral side,
the ventral vessel;
these are united by
transverse vascular
arches. The dorsal
trunk, sometimes, also,
some of the transverse
vessels, is pulsatile, and
performs the functions.
ofa heart; the blood-
stream is from behind,
forwards in the dorsal
vessel; in the ventral
vessel in the opposite
direction. From these
trunks smaller branches
go to different parts, to
Fig. 129. Nervous system of different Chetopods the gut, Ohta also to the

(B Serpula, C Aphrodite). c cerebral ganglion, g gills when these are
ventral ganglia, o eye.—After Quatrefages. present. The vascular
fluid is usually coloured ;

as a rule red, sometimes yellow or green. The vascular system in some
forms (Cheetopods) is completely separated from the body-cavity
which contains a special colourless fluid. In other cases, e.g., in Leeches,
this system communicates with the body-cavity, which, moreover,
is here of small extent, and modified to form vascular sinuses.*
In certain Cheetopods the vascular system is entirely wanting.

 

 

Fig. 130. Anterior end of an Annelid, with alimentary canal and vascular
system figured. Diagrammatic. m mouth, 1 dorsal vessel, b ventral vessel, p pulsatile
transverse vessel.—Orig.

 

* The opinion has recently been advanced, that in Leeches there is no communica-
tion between the vascular system and the spaces which represent the body-cavity.
Annelida. 167

Jn most segments, there is a pair of segmental organs;
each is usually a tightly-coiled glandular canal, opening at one
end into the body-cavity by a ciliated funnel, and at the other,
ventro-laterally, to the exterior (in Chatopoda, at the base of the
ventral parapodia) ; the outer region, near the external pore, is often
swollen into a vesicle. These are the excretory organs
(nephridia) of the Annelids,* but they often perform another function
in permitting the exit of ova and spermatozoa. The sexual
organs are very diversely arranged (see below) ; some Annelids are
of separate sexes, some are hermaphrodite.

The Annelids in many respects come rather close to the Nemertines,
from which they are probably to be derived. If the two lateral nerve-cords
of the latter moved ventrally and approached one another, and formed
swellings at the origins of the transverse nerves, the chief portions of the Annelid
nervous system would be represented. The dorsal vessel of the Nemertines
corresponds entirely with that of the Annelids, the lateral vessels of the
Nemertines are united to form the Annelid ventral vessel, and in both groups
the arch-like transverse vessels are similar. Many Annelids possess two ciliated
grooves corresponding with those of the Nemertines. It is also of great interest
that many Annelid larve are furnished with a provisional excretory apparatus,
the so-called ‘‘head-kidney,’’ provided, at least in many chetopod
larve, with closed end-branches, just as is the permanent excretory
apparatus of the Flatworms, with which it indisputably corresponds. The
segmentation of the body, the peculiar segmental organs, the formation of a
body-cavity, etc., are, however, important points, distinguishing the Amnelids
from all Flatworms.

Class 1. Chatopoda.

The body is divided by distinct constrictions into a large number
of segments. With the exception of the anterior and posterior
somites, each usually bears four so-called parapodia, two on
each side (Fig. 133). These are short processes of the body-wall of
different forms, each bearing a bundle of chitinous bristles (cheetz),
which are sunk in deep saccular invaginations of the skin. The
cheta, which is a cuticular structure, is secreted by a large cell
at the bottom of the invagination. The bundle may be moved by
muscles attached to the lower ends of the cheta-sacs. The chetze
are of various and often elegant shapes; sometimes the outer moiety
is jointed upon the shaft-like part; the point is often hooked, or
the end may be pectinate. The cheetee may be so long as to look
like long thin hairs, or they may be very short. In very many
Cheetopods, there is in each bundle of cheetz, a peculiarly developed
thick and stiff, often dark one, the aciculum, which is implanted

 

*In some Chetopods, the epithelial cells of the body-cavity also secrete waste
substances, which are probably taken up by the funnels of the nephridia and carried
to the exterior.
168 Annelida.

much deeper than the others. Very frequently the two parapodia of
the same side are confluent, either for their whole length, or only

Fig. 131. Fig. 132.

  

Fig. 1381. Diagrammatical section through the skin of a Chetopod. ec cuticle, ep
epidermis, ep’ epidermal cell, which secretes the cheta, b, m muscle-sheath, m’ muscle
of the lower end of the cheta-sac.—Orig.

Fig. 132. Anterior end of a Chetopod (diagrammatic). h prostomium, m oral segment,
with c the oral tentacles; e the next segment.—Orig.

at the base, so that there appears to .be only one on each side,
but each has still its own bundle of chaete and its own aciculum. In
other cases, the upper parapodium is rudimentary or entirely absent.
The parapodia may be lobed, large, and well-developed; or they

A B Cc D

 

¢

Fig. 133. Diagrammatic sections of different Chetopods. In B the two parapodia
are confluent, in C the notopodium (with the exception of the cirrus) is rudimentary, in D
(Earth-worm) the parapodia are represented only by two bristles. ww aciculum, g gill,
ce dorsal, c’ ventral cirrus.—Orig.

are quite insignificant processes of the skin, or are merely repre-
sented by their chete, which then are planted directly in the
Class 1. Cheetopoda. 169

body-wall (e.g. in Earthworms). Very rarely the parapodia are
present without chete; in some forms they are entirely absent
from certain segments. ‘There is often a dorsal and a ventral
cirrus, tentacle-like appendages, arising from the upper side of the
dorsal parapodium (notopodium), and the under side of the ventral
parapodium (neuropodium) respectively. In some forms, the dorsal
cirri on some or all of the segments are large, and form lamelle or
elytra, covering the upper surface of the animal.

The two anterior segments differ from the others. The first seg-
ment, the prostomium, which overhangs the mouth, has no
parapodia, but a number (usually 1—9, in many tubicolous forms a
much larger number, in others none at all) of thread-like appendages,
the so-called palpi and tentacles. The second segment, the
peristomium, which usually bears the mouth, although sometimes
this is still further back, is provided with a rudimentary parapodium
on each side, carrying few chete or none, but one or two well-
developed, forwardly directed cirri, the so-called tentacular
cirri. One or more of the ordinary segments may be fused with
the peristomium, which, like the prostomium, may be destitute of
appendages; in this case, their parapodia and cirri more or less
resemble the oral appendages. Frequently the oral and following
somites are fused and are difficult to distinguish. The terminal seg-
ment is without cheetee, and is often furnished with two long processes,
the anal-cirri.

The integument is covered with a thin continuous cuticle,
but, in spite of this, is often ciliated over certain limited tracts. The
skin, with the underlying muscle-layer, forms a strong body-wall,
which encloses a spacious body-cavity, very often divided into a series
of compartments by transverse septa, corresponding to the con-
strictions between the segments. These septa, which are naturally
traversed by the alimentary canal, and the blood vessels, are also
perforated by holes to allow of the passage of the ccelomic fluid.
Sometimes the septa are replaced by strands, which pass from the
body-wall to the alimentary canal.

The anterior region of the digestive tract is usually a muscular
pharynx, which may be everted like a proboscis. It is frequently
provided with chitinous teeth, or hooks, in larger or smaller
numbers. The rest of the alimentary canal is generally a straight tube,
with constrictions at places where it is encroached on by the body-
wall, more rarely it is coiled; in some short forms (Sea-mouse) the
gut is furnished with a double row of ceca. The anus is, as a rule,
situated at the posterior end of the body.

The eyes, which are, however, absent from many Chetopods,
belong to the type figured in Fig. 20, 5—6. They usually number from
two to four, and are situated on the prostomium; in certain Tubicole,
however, on its thread-like appendages; in a few other forms, on
170 Annelida.

several of the body segments. One pair (or more) of auditory
vesicles is present in some (e.g., Lugworm), in the neighbourhood
of the cerebral ganglion.

In one division of the Chetopods, gills of different forms, tufted,
pectinate, or filiform, are present on certain of the segments, one pair
to each somite. They occur on the dorsal surface, at the bases of the
notopodia. In many Tubicole (e.g., Serpwla) the prostomial threads
also serve as gills. Most of the Chetopods, however, possess no
special respiratory apparatus.

The genital organs are very different in the Polycheta
and Oligocheta, the two groups into which the Chetopods are
divided. The former are almost always of separate sexes: ova
or spermatozoa are as a rule formed in a great number of segments
on the inner side of the body-wall, or on the septa, so that many
ovaries or testes are present, which, do not appear as well-defined
organs, but only as thickened spots in the wall; the genital
products fall into the body-cavity, and pass out through the nephridia.
The Oligocheta are, on the other hand, hermaphrodite, and the
ovaries and testes, which are more definite organs, are present in
only a few segments, one pair in each; there is always only one
pair of ovaries, one or two of testes. The Oligocheta are
further distinguished by having special oviducts and vasa deferentia,
which, like the nephridia, open into the body-cavity by ciliated
funnels; but there are also nephridia in these segments, so that
these canals cannot be homologous with segmental organs. Instead
of an oviduct, there is, in some forms, only a pair of slits in the
body-wall.

In the Earth-worms (Fig. 134) the spermatozoa do not complete their develop-
ment in the testis, but the cells from which they are formed break loose, and are
received in a number of definite sacs (vesicule seminales) which are situated
just within the body-wall and open by pores into the body-cavity. Here they
develop into spermatozoa. In some forms there is a similar receptacle for
the ova. In the Earthworms (and other Oligocheta) there are, further, sacs
(spermathece), which open on to the surface, not into the body-cavity, and
during reciprocal copulation, receive spermatozoa from the other animal.

The nervous system, vascular system, and excre-
tory apparatus, have been referred to in the general account of
the Anvelida.

The development of the Polycheta is effected by a distinct
metamorphosis, which is not found in the Oligocheta. The
larve are free-swimming, and provided with cilia, which, in some
forms, extend evenly over the whole body; in others, constitute a
well-defined band on the often discoid anterior end, and frequently
a second ring at the posterior end; or there may be a large number
of ciliated bands. The body of the larva is at first short, parapodia
are absent or present in small numbers; it gradually attains a con-
siderable length, dividing into numerous segments provided with
Class 1. Cheetopoda. 171

parapodia. Sometimes eyes and auditory organs, which do not
occur in the adult, are present.

 

 

  

Fig. 134.
Q @
6 be Ve 4
10

1

#2

13

ve! the

 

Fig. 134. Diagram of the reproductive apparatus of an Earth-worm; the animal is.
dissected from the mid-dorsal line and spread out. 8—14, 8th to 14th bristle-bearing seg-
ments. o ovary, od oviduct, sb vesicula seminalis, sy spermatheca, ¢ testis, vd vas deferens,
vd’ its outer end, @ receptaculum ovorum. The transverse lines represent the septa.—Orig..

Fig. 135. Larva of Nereis. a anus, m mouth, o eye.—After Gitte.

Asexual reproduction occurs in not a few members of
both groups. In some cases there is a simple transverse fission;
the animal divides into two nearly equal parts, the posterior of which
forms a new mouth, prostomium, etc., before the separation; whilst the
anterior produces a new hind end. In other cases budding
takes place; the hindmost segment (or a number of posterior
segments) elongates and develops into a new individual, which then
separates from the parent. Sometimes before separation, the latter
begins to produce from its new posterior end, a second new individual
in front of the first formed: the process may be repeated, so that a
chain arises, consisting of a parent and several buds, of which the
hindmost is the oldest and longest, and that nearest the parent
is the youngest (Fig. 136). It will, however, easily be seen that a
sharp line cannot be drawn between the fission and budding of
Cheetopods; in both cases certain of the posterior segments of the
original individual become a new individual; in the former a large
number of somites pass over into the new animal, in the latter only
172 Annelida.

a few, or a single one. In some forms it has been found that tho
individuals which produce buds develop no genitalia, whilst these
are present in forms produced
by budding, so that a regular
alternation of genera-
tions occurs; in other cases,
however, both kinds of indi-
viduals are sexual,

Most Chatopods are marine,

 

ES (REA a EB and for the most art creep

ot Ye S ANN GN oP |

YS a) i Ny LSS ea about on, or burrow into, the soft
He eA OP md ?

bottom*; others (Oligochiwtse)
live in like manner in fresh-
water or in damp earth; many
forms, which usually live on the
bottom, are yet able to swim
by serpentine movements. A
few are, however, truly pelagic,
and like other pelagic animals
, are transparent and provided
4" with cyes, which for Amnelids
ie (00> 6 Gla Moment Gtpiepea: “Ne St temmons eizey. A ene
(Myrianida fasciata), with very long dorsal siderable number form tubes,
cirri—After H. Milne Edwards. consisting of foreign particles,
mud, clay, sand, small stones,
fragments of gastropod or lamellibranch shells, or rhizopod sliclls
cemented together by the secretion of certain skin glands; the
separate particles are either irregularly united or neatly fitted into
one another like a mosaic. The glands often secrete a chitinous
tube, on which are plastered foreign bodies: in other forms the case
consists exclusively of the hardened secretion of the skin glands,
and is then either chitinous or calcareous. The tube increases in size
as the growth of the animal advances: lines of growth may be clearly
discerned just as on a snail-shell. The tube is either fastened to
some foreign object or lies free; rarely the animal carries it about.
Some Cheetopods, which are provided with strong pharyngeal teeth,
lead a predatory life, others feed on algwe; many are mud and carth-
feeders, living on organic particles contained in mud, sand, or earth,

 

Order 1. Polycheta.

The prostomium and the peristomium are usually furnished with
appendages (cirri); eyes are frequently present. The chet are
borne upon true parapodia frequently provided with cirri; gills may

 

* Some species can bore into rock, stone, or clay, but how they do it is not
understood.
Class 1. Cheetopoda. Order 1. Polycheta. 173:

be present. Sexes separate (with some exceptions). A metamorphosis.
Marine.

The following forms are given as examples of this very numerous
group.

1. The Nereidz (Nereis) have a very elongate body. The prostomium is
furnished with four small eyes. Noto- and neuro-podia fused; gills absent. The
protrusible pharynx has a pair of hard chitinous jaws. One species of this
genus (N. diversicolor) is common on English coasts, creeping, or swimming, or
boring into the sand.

2. The Polynoide exhibit a form which, in comparison with that of other
Chetopods, is usually very short and broad, and is especially distinguished by
having on the dorsal side a varying number of large scale-like epidermal plates ;
these plates are modified dorsal cirri, and are only present on a few segments,
the others being provided with cirri of the ordinary form. Gills are want-
ing. Polynoé squamata with rough, uneven dorsal plates; the Sea-mouse
(Aphrodite aculeata), has the dorsal scales covered with the very long felt-like
cheetz of the notopodia, forming a felted mat over the back of the animal; other
dorsal chete are thin hairs with a metallic lustre, and others again are stiff,
thick opaque spines. Both on English coasts.

3. The Lugworm (Arenicola piscatorum). Front part of cylindrical body
swollen, skin rough. Prostomium and peristomium without appendages; eyes
wanting. Noto- and neuro-podia separate, short; the latter a low transverse
ridge with a few hooked chete standing from it; both without cirri. Gills
present only in the middle region of the body, but here well-developed. Para-
podia wanting on the hindmost third of the body. The proboscis without teeth.
The Lugworm lives in the sand, burrowing close to the shore; it swallows the
sand for the sake of the contained organic particles, the excreta are deposited on
the shore, above the holes, as castings. Very frequent on these coasts (used as
bait for fish).

4, The Serpulide (Serpula) live in fixed calcareous tubes. which are either
irregularly or spirally coiled. When undisturbed, the anima! projects from
the tube a large number of long threads provided with a double row of delicate
lateral branches, which are arranged in two groups on the prostomium. These
feather-like threads are respiratory. and by means of their cilia drive micro-
scopic organisms into the mouth. One of the threads is specially strong,
without lateral branches, and with a calcareous operculum of varying form at
the end. When the animal is irritated it withdraws the whole bunch of threads
into the tube, which it closes with the operculum. At the anterior end of
the animal the notopodia are provided with hair-like chete, the neuropodia
with hooked chet, whilst the converse is the case on the greater part of the
posterior extremity. Several species on sea-weeds, stones, etc., on English coasts.

Order 2. Oligocheta.

The prostomium and peristomium are almost always without ap-
pendages. The parapodia are represented only by bundles of chzetee
(quite a few in each bundle), no cirri; gills wanting. Hermaphrodite.
No metamorphosis.

The Oligocheta live with few exceptions in fresh water or in the
earth. Compared with the Polycheta there are few species,

1. Earthworms (Lumbricus) have elongate cylindrical bodies pointed
anteriorly, Each segment is provided with four bundles of cheta, with only two
174 Annelida.

‘chete in each bundle. Eyes are absent. Just in front of the middle is the
elitellum, a thickened region of skin, covering several segments; and containing
a large number of glands, whose mucous secretion holds the individuals together
during copulation, and possibly also forms the cocoon in which the eggs are laid.
In each cocoon there is generally a large number of eggs. The pharynx is not
eversible; jaws are wanting. Harthworms of different species live in cultivated
‘soil, in which they burrow, and upon which they feed. They consume dead vege-
table matter, also assisting its decomposition by drawing it into their holes and
‘pouring over it a salivary liquid. The excreta are deposited for the most part at
the surface, whither the animal usually repairs only at night. In severe cold, as
in very great heat, the worm leaves the surface soil, and goes into the substrata ;
here the holes are long, usually perpendicular, and lined with an excreted
‘substance. There is generally an expansion at the bottom, where the animal
lies in a drowsy condition, as much as 2 to 3 m. below the ground. By these
habits, especially by devouring soil and replacing it on the surface in the form of
excreta, the Harthworm does more than any other animal to promote the natural
elaboration of the soil, and attains thereby a paramount importance in the economy
of nature. When a place is deserted by Harthworms on account, e.g., of an
inadequate supply of moisture, the surface soil changes and assumes a dry turfy
character; should this occur in a forest, natural planting, by self-sowing, ceases,
and unless man interfere, the wood gradually becomes a moor.

2. The Naide (Nais) are small (seldom more than 1 c/m. long), thin, and
transparent; there are usually two eyes on the prostomium. The chete of the
dorsal bundle are long and hair-like, those of the ventral bundle short and hooked.
Asexual reproduction is of frequent occurrence. The Naidze live amongst
the vegetation in fresh water. Tubifex rivulorum, a reddish worm, common in
fresh water, is related to Nais. It forms burrows in the mud, from which, so
long as it is undisturbed, the hinder part of its body protrudes in constant
motion. Often many specimens are found close together, so that the surface of
the mud seems to be coloured red in places; at the slightest movement of the
water, the animals withdraw, and the red colour vanishes.

Under the term Gephyrea is usually included a number of vermiform
animals, regarded as constituting a special class of the Annelids. When some
forms which have proved to be Molluscs, have been removed from the group, the
remainder are evidently aberrant, peculiarly modified, Chaetopods.
Some still possess chaete similar to those of the Chetopods, but in small
numbers, and not arranged in bundles. External segmentation is in-
variably wanting; instead of the double ventral ganglion chain, there is a single
stout nerve cord without ganglionic swellings; it splits anteriorly into two
cords encircling the buccal-cavity, and uniting with the often very slightly
developed cerebral ganglion. The nephridia are very large, but few in
number, at most three pairs, often only one pair, or a single one. They serve
as efferent ducts for the genital products which are formed on the walls of the
body-cavity. The sexes are separate; a metamorphosis occurs similar to
that of the typical Chetopod. It is significant that at an early stage, segmen-
tation of the body is sometimes indicated. Their habits resemble those of the
majority of Chetopoda; they are all marine. An interesting form, Bonellia
viridis, occurs in various European seas (e.g., the Mediterranean) ; the female
possesses at the front end of the short saccular body, a very long tentacle-like
prostomium, whose anterior end is forked (body, 5 c/m.; prostomium, 1—2 m.) ;
only two chet are present, and one segmental organ. The pigmy male is
quite differently proportioned; it is 1—2 m/m. long, and like a Turbellarian,
uniformly ciliated, with neither mouth nor anus, and without prostomium ; it
lives in the nephridium of the female.
Class 1. Chetopoda. 175

Class 2. Discophora (Zeeches).

The body is always flattened with sharp lateral edges, rarely
cylindrical. The segments are externally divided, each into several
small annuli, by transverse furrows, so that the number of segments
appears many times greater than it is in reality (the same thing occurs
in some Chetopods). Parapodia and chaetz are always
wanting; with few exceptions, no branchiz are present. The
posterior end of the body is modified into a sucker ; around the mouth
there is also an adhesive disc, which in some is cup-shaped like the
hinder one, whilst in others, it consists of a long, jointed upper lip,
and a shorter underlip.

The digestive tract consists of three sections: the pharynx,
the crop, and the rectum. In one group, the Gnathobdellide,

 

Fig. 137. Digestive tract, nervous system and excretory organs of a Leech in outline.
aanus, 6 diverticulum, c cerebral ganglion, e rectum, g sub-cesophageal ganglion, m sucker,
se nephidium.—After Leuckart.

the pharynx is muscular, and furnished in front with jaws,
three prominent, longitudinal, chitinous ridges, with teeth on
their sharp edges, which work like little saws to cut holes in
the skin of the prey, so that the fluids may be pumped out of its
body by the pharynx. In the other division, the Rhyncobdellidez, on
the other hand, a thin, muscular tube, the proboscis, is attached
to the end of the thin-walled pharynx. It may be stretched out from
the mouth and pointed, so as to bore through the integument of the
prey. The crop is a straight, wide tube, which is almost always
provided with a number of paired diverticula; the capacity of the
crop and its diverticula allows of the ingestion of a large amount of
food. The intestine is narrow, and opens dorsally above the sucker.

A number of eyes is always present upon the anterior end of the
animal; in some Fish-leeches on the hind margin of the posterior
sucker also.

The Leeches are always hermaphrodite; they possess two long
or round ovaries, which open far forward on the ventral side in a
common efferent duct: albumen glands open into the oviduct. The
round testes are present in great numbers, 6—12 pairs, one pair in a
segment; on either side there is a long vas deferens, into which all the
testes of the same side open by short ducts: the two vasa deferentia
176 Annelida.

finally unite and open by an unpaired aperture in front of the female
pore. The eggs are laid in chitinous capsules (cocoons), usually
several together, with a certain amount of
albumen. The capsules, which are formed by a
hardened secretion of the skin-glands, have vithor
a smooth surface, or are, as in the Medicinal
Leech, covered with a spongy case (hardened
frothy mucus). The young ones leave the cocoon
in the form of the adult.

Each egg is, of course, covered by an egg-mem)rane :
the embryo of the Gnathobdellidw, where the eges are
very small, soon bursts this covering, and lies free in the
albumen, upon which it feeds, and thus grows rapidly.
It is in this stage very different from its later forms, and
possesses several provisional organs (pharynx, muscles,
etc.), which atrophy, and are replaced by the permanent
organs before it leaves the cocoon. The Gnathobdellidw
may therefore be said to undergo a metamorphosis
within the cocoon. In the Rhynchollecllidw, whose
eggs are larger, this does not occur.

The Leeches, which, compared with the Chato-
poda, form a small group, are relatively well repre-
scented in fresh water; still « considerable number
are marine. Some are terrestrial (in the tropics),
others frequently go on shore. They are predatory,
Fig. 138. Genital or are temporary parawites, sucking the blood of

apparatus of a Leech.  Jarger animals ; some are stationary parasites. ‘Choy
n ventral nerve cord, ’

0 ovary, w oviduct, creep ubout in the well-known manner by means

t testis, vd vas defe’ of their suckers, but are also able to swim by
rens, vs coiled part of ‘ ‘ ’
vd, g glands, p penis, Serpentine movements of the body.

—After Spengel. 1. Gnathobdellide. With jaws. Anterior «adhesive

organ divided into an upper and a lower hp. Eggs
small; the young ones undergo a kind of metamorphosis within the cocoon.
All fresh-water or terrestrial.

(a) The Medicinal Leech (Hirudo medicinalis), a fresh-water form,
varying in colour, occurring in different parts of Europe, and in England. Its
jaws are very strong and have pointed teeth. The dorsal surface is a ereenish-
grey, with reddish longitudinal stripes, flecked with black: the ventral surface is
paler, but speckled. Ten eyes. The spongy egg-capsules are laid on land, in banks,
To this genus belongs the well-known East Indian Land-lecch (H. ceylonien).
Hzxmopis vorax is allied to the Medicinal-leech, which it resembles in shape and
size, It is indigenous to 8. Europe and N. Africa. It frequently enters the
nostrils, pharynx, and throat of different Mammals with drinking-water, and may
occasion serious inconvenience.

(b) The Horse-leech (Aulastomwm gulo). Very common in fresh water
in England, of a similar size to the Medicinal-leech. It is frequently mistaken
for Hemopis vorax. The jaws are less developed than in the Medicinal-leech. It
attacks no Mammal, but lives on Harthworms and small aquatic animals. It is
greenish-black above and yellowish-brown below. Ten eyes. The egg-capsules
are like those of the Medicinal-leech, and are laid on land. Species of the genus
Nephelis are also frequently met with in fresh water; they are shorter and

 

on

>
(O

 

 

Vv \
A

 

Vl
=
“l
Class 2. Disvophora. 177

narrower, and possess only eight eyes and very weak rudimentary jaws; the
cocoons are smooth, and are fastened to water plants.

2. Rhynchobdellidw. With proboscis. Anterior organ of adhesion,
cup-shaped. Eggs large; no metamorphosis. Fresh-water and marine.

(a) Clepsine, a small, flattened leech, almost as hard as cartilage, which is
frequently found in fresh water. The eggs, enclosed in a very thin cocoon, and
the young ones, are carried about on the underside of the body of the parent,
which then seems to be hollowed out like a cup.

(b) The Fish-leech (Piscicola), with cylindrical
body and bell-shaped sucker at both ends; lives as a
parasite upon most species of marine fish. Nearly
related to this is the large Pontobdella muricata, with
large integumentary warts; upon Skates in the North
Sea.

Norts.—A little worm, parasitic upon the Crayfish
(on the gills and elsewhere), Branchiobdella astaci, is
usually put with the Leeches. It approaches the Cheto-
poda in some points, and by some authorities is counted
as one of this group. The body is cylindrical, the anterior
sucker indistinct ; it possesses two jaws and a gut without
diverticula. The conditions of the genitalia recall those
of the Oligocheta.

Class 3. Onychophora.

This division includes only the genus Peripatus,
which may be regarded as a Chetopod adapted for
terrestrial life.

In external appearance the Peripatus species are
most like caterpillars. The body is elongate and
cylindrical, the segments not externally demarcated.
The skin is granular, and delicately striated trans-
versely. At the anterior end there is a pair of ringed
tentacles (these appendages may be ringed also in the
Cheetopoda), and a pair of simple eyes of the kind
shown in Fig. 20, 5. In the mouth there is a pair of jaw-
like masticatory organs. The rest of the body consists
of similar segments, each of which bears a pair of
indistinctly jointed, stumpy limbs, ending in two
claws. The muscles are composed of smooth
muscle cells. The nervous system is characterised
by separation of the ventral cords, which are joined by
many delicate transverse strands, whilst only feeble
swellings are present in each segment. The alimen-
tary canal is a straight tube; the anus lies at the
posterior end of the body. The heart is dorsal, and is
a tube provided with lateral slits; other vessels are Fig. 139. Peripatus
wanting. The respiratory organs consist of a from the dorsal side,—
well-developed system of air-carrying tubes, which After Balfour.
ramify in the body and open upon the surface in many
delicate, irregularly-distributed, respiratory apertures.§ In most segments there
is a pair of segmental organs, similar to those of other Annelids: they

N

 
178 Annelida.

open into the body-cavity by large funnels,* and to the exterior by delicate
apertures at the bases of the limbs. The sexes are separate: the paired gonads
open at the posterior end. The species, as a whole, is viviparous.

Recently Peripatus has been very generally classed with the Arthropoda,
chiefly on account of the presence of the air-tubes mentioned above, which are
like the tracheze of Insecta, and Myriapoda. But there are weighty facts for
the other side: the eyes are of the same kind as those of the Chetopods, and
quite different from the Arthropod type; a complete set of segmental organs is
never found elsewhere in the Arthropoda; in the Tracheata, indeed, they are
entirely wanting ; also the character of the muscle cells is altogether opposed
to a relationship with the Arthropods which exhibit striated muscle fibres.
Under the circumstances it seems best to regard the air-tubes as merely
analogous with the trachex, attributing their presence to a terrestrial life,
whilst they are (cf. Insecta) the cause of the degeneration of the vascular system.

The species of this group live exclusively in warm climates in both hemi-
spheres (W. Indies, Cape, and elsewhere), in damp places, in rotten wood, etc.

APPENDIX TO THE ANNELIDA.

Each of the groups now to be discussed, the Polyzoa and the
Brachiopoda, occupies an isolated position in the Animal
Kingdom: it is doubtless therefore most correct to treat them as two
special phyla. They were formerly placed with the Mollusca, with
which, however, they are not at all closely allied. From the most
recent researches, it seems that their nearest relatives—though even
these are sufficiently remote—are the Annelids, wherefore they are
taken in this connection.

Polyzoa (Moss-animals).

With a single exception, all the Polyzoa form colonies by
budding ; individual members attain to only a small size, but the
extent of the whole colony may be very considerable. The rather
short body of each zooid is usually divided into a fore and a
hind portion: the latter is covered with a firm, thick, some-
times spiny, chitinous investment, the ectocyst, which is often
calcified. The front part is, on the other hand, quite soft, and
bears at its anterior extremity, a wreath of long ciliated tentacles
(the lophophore). In the great majority of forms, this is a simple
circle, but sometimes there is a large sinus on one side, which
gives it a kidney, or horseshoe, shape. The whole of the front part
can be withdrawn into the hinder part by means of a long muscle
(Fig. 142). The wall of the front part is then introverted to form a
sheath round the retracted tentacles (tentacle-sheath). In one
section of the marine Polyzoa (the Chilostoma) there is, at the anterior

 

* According to some accounts the segmental organ ends in a closed, thin-walled
vesicle, not in a funnel.
Polyzoa. 179

end of the chitinous case, a movable, chitinised fold of the wall, which
acts as an operculum to the mouth of the tentacle-sheath, when
the soft part of the body is retracted. The mouth is at the anterior
end in the midst of the circle of tentacles; the anus lies at this end

   
  

  

=
a

eee biel

  

 

ee EO

|
y
|

A B Cc

Fig. 140. A—B Diagrammatic longitudinal sections of a Polyzoon, A expanded,
B retracted. a anus, b hind-end, e rectum, f fore-end, 1 operculum, m stomach, n nerve
ganglion, 0 mouth, s cesophagus, ¢ tentacle. The chitinous covering is indicated by a wide
black line, the soft wall of the body is shaded. C avicularia (diagrammatic), 1 oper-
culum, m its muscles, ta gut.—Orig.

also, not far from the mouth, and is usually just without, seldom
within, the lophophore. The alimentary canal is, therefore, in
the form of a loop; it is made up of an cesophagus, a stomach
provided with a cecum, and a rectum. The food, consisting of
microscopic particles, is driven into the mouth by the cilia of the
tentacles. The central nervous system consists of a nerve
ganglion, which is situate on the side of the cesophagus near the anus,
and of a nerve-ring surrounding the cesophagus. Nerves from the
ganglion pass to the different parts of the body. Optic and auditory
organs are wanting ; so are a vascular system, and special respiratory
organs ; the lophophore is, however, doubtless of respiratory import-
ance. Excretory organs have hitherto been foundin only a few
Polyzoa, in the form of two short canals, opening at one end into the

nN 2
180 Polyzoa.

body-cavity, and at the other, to the exterior by a common aperture,
near the lophophore.* The Polyzoa usually have a large body-cavity,
filled with a liquid in which
amceboid cells are found;
it contains, besides the ali-
mentary canal, a cord, the
funiculus (Fig. 142),
stretching from the stomach
to the body-wall, upon which,
or upon the inner side of the
body-wall, ova and sperma-
tozoa appear, both, usually,
in the same individual ; special
sexual ducts are absent, the
genital products (or embryos)
pass out through ‘holes in the
body-wall, or through the
excretory organs. Generally,
the fertilised ovum undergoes
its earliest development within
the body of the parent, in
many marine forms, in a
special invagination of the
body-wall (ocecium).

Among the freshwater Poly-
zoa reproduction is effected by

 

Fig. 141. Plwmatella polymorpha, a fresh-
water Polyzoon. Enlarged.—After Kripelin. means of statoblasts, as
well as by fertilised ova. The

statoblasts are small, discoid
bodies arising upon the funiculus by a peculiar process of budding. They are
produced chiefly towards the end of the summer, and rest during the winter,
developing, in the next year, into a new colony. Each is provided with a hard
ornamental shell, in whose edge there are small air cavities. The new animal is
formed from a mass of cells within.

In many forms a very remarkable degeneration of the lophophore and
alimentary canal occurs, constituting the so-called “brown body,” from which
these parts are, after a time, reconstructed.

The colonies formed by the Polyzoa are of very different
kinds. Some are much branched (Fig. 141), and either stand erect
from, or creep over, some foreign object; others are laminate, lying
upon the substratum or standing upright: or they may be more
massive. The colony is almost always fixed; a single freshwater form

(Cristatella) is free.
Amongst many of the Chilostoma, dimorphism, like that in the
Hydrozoa, occurs. Specially common among the ordinary individuals

 

* These canals do not seem to form excretory products themselves, but serve as
a means of exit for cells, loosened from the epithelium of the body-cavity, in whose
protoplasm certain nitrogenous waste products are secreted.
Polyzoa. 181

are the so-called avicularia (Fig. 140 C), small individuals, destitute
(or with only rudiments) of tentacles, mouth, and digestive tract, but

with a large movable oper-
culum, which can open and
shut. The best developed
avicularia resemble crabs’
claws or birds’ beaks, for
the tip of the operculum
is bent like a hook, and
bites upon an outgrowth of
the body. They seem to
be a kind of defensive
person, to catch the animals
crawling over the surface
of the colony. More rare
are the vibracula, also
small reduced persons,
whose operculum is deve-
loped into a long whip-
like process, which sweeps
over the surface of the

colony.
The Polyzoa undergo a
metamorphosis. There

is a free-swimming larva,
whose cilia are either evenly
distributed over the body,
or restricted to special
regions (ciliated ridges or

     

m

nal

Fig. 142. Fresh-water Polyzoon, bi-
sected. Diagrammatic. a anus, e excretory aperture,
m mouth, mu muscle, 2 nerve ganglion, st statoblast
on the funiculus.—Orig.

tufts) ; sometimes there is
a hard cuticle or shell upon part of the body, usually it is entirely
naked.

They are very numerous in all seas; a few live in fresh water.

The fresh-water forms, which are found on water plants, etc., generally have a
horseshoe-shaped lophophore ; and form a delicate branched colony, which is not
raised much above its support: but some species grow erect, neighbouring
branches supporting one another reciprocally, and thus forming large clumps.
Amongst the marine forms are the Membraniporidz, which may often be seen
forming calcareous incrustations upon the surfaces of all large sea-weeds.

Brachiopoda.

The body is generally enclosed within two calcareous, or rarely,
chitinous shells, somewhat like those of the Lamellibranchs, with which,
therefore, the Brachiopoda were in times past associated. As a matter
of fact the two groups are in no wise nearly related to one another,
182 Brachiopoda.

and that the presence of the shells does not denote a relationship is
evident from the circumstance that those of the Brachiopoda are

dorsal and ventral, whilst in the Lamellibranchs they are right and
left.

 

Fig. 143. Diagrammatic longitudinal section of a Brachiopod. d digestive tract,
e excretory organ, h heart, n nerve ganglion, o mouth, s shell, with the mantle lying within
it, st peduncle, ¢ tentacle.—Orig.

Compared with the whole extent of the animal, the actual
body is of very small size, and very short. Two large mantle-
folds, lining the inside of the shell, spring from it. The shells
are secreted by the mantle, and are to be regarded as cuticular
structures. Unlike the Lamellibranch valves they are not connected
by a ligament; but in some forms they are attached by a hinge
posteriorly. Chitinous bristles, implanted in pits in the skin
are often present along the edge of the mantle. From the posterior
end of the body there usually springs a process, the peduncle,
which projects from between the valves, or from a hole in the hinder
part of the dorsal shell: in some species it is longer than the rest
of the body, in others it is very short. Most of these animals are
fixed to foreign objects by means. of the peduncle, but some are free.
In young Brachiopods a circle of tentacles surrounds the
mouth, but during development, an in-pushing of the wreath occurs,
which results in its becoming kidney- or. horseshoe-shaped and
gradually both branches of the horseshoe are drawn out into long
arms beset with a double row of tentacles: the arms are usually
spirally coiled, and lie between the mantle-lobes; they serve as a
respiratory organ, and also waft food (minute organisms) into the
mouth with their cilia; frequently they are supported internally by a
variously shaped (e.g., ribbon-like) calcareous structure, which is
connected with the dorsal valve. The alimentary canal may
be short or long; curiously enough, in most Brachiopods an anus is
wanting, when present it is on the right side of the body. There is
a well-developed liver. The central nervous system is repre-
sented by a nerve-collar surrounding the cesophagus, swelling out on
Brachiopoda. 183

the underside into a ganglion, from which the nerves proceed. There
are neither optic nor auditory organs. The vascular system is
well-developed; a saccular heart lies above the digestive tract. The
excretory apparatus consists of one or two pairs of tubular
organs which open at one end into the body-cavity by a ciliated
funnel, and to the surface at the other exhibiting a great re-
semblance to the segmental organs of the Annelids. They
serve, at the same time, as a means of exit for the genital products,
which are formed on the wall of the body-cavity. The Brachiopoda
are of separate sexes.
The ciliated larva swims
about freely. Its body is some-
times divided (Fig. 144) by
constrictions into segment-
like sections. Eyes may be
present at the front end, and
provisional bundles of bristles
(Fig. 145) behind. (Cf. the
Cheetopods).

The Brachiopoda are ex-
clusively marine; they are
as numerous in warm as in

Fig. 145.

  

Figs. 144 and 145. Larvae of two
cold seas; there are, however, ° Brachiopods. — After Lacaze- Duthiers and

but few species. They were Kowalevsky.

very numerous in early times,

and are known from the Cambrian formations. They were well
represented in the Silurian, the Devonian, and the Jurassic.

As examples may be cited: Terebratula, living as well as fossil, dorsal and
ventral shells convex, the former drawn out into a beak-like process, pierced by
an aperture for the short peduncle, by which the animal attaches itself to
stones, etc.; in other similar forms there is a notch at the same place. Dorsal
valve with a loop-like brachial skeleton. Lingula, extant and fossil, two thin, flat,
horny, almost equal, hingeless shells; peduncle very long, surrounded by a sandy
tube.

 
Phylum 6. Arthropoda.

The body is divided into a number of segments demarcated
externally by constrictions, and provided with jointed limbs,
which constitute efficient locomotor organs: it resembles, therefore,
the Annelid body in the former respect, but differs in the latter.
Moreover, there is a greater dissimilarity in the formation of the
body segments than in the Annelids; among the Arthropoda, the
body (exclusive of the head), is usually divided into two or more
regions, which are distinguished by a special modification of the
constituent segments, and the individual segments of each region
often differ considerably from one another. This dissimilarity is
manifest both externally and internally. Furthermore, the limits
between certain of the somites are often obliterated so that they
come to be more or less intimately united to form a compound
structure, the origin of which can only be made out from a comparison
with other forms, or from a study of the development. The most
anterior region of the body, the head, is always composed of several
fused segments ; some of the appendages thus brought together serve
for feeding, and are called mouth-parts; there are usually, also, one
or two pairs of feelers or antenne.

In the majority of Arthropods, three pairs of mouth-parts are present; the
first are the mandibles, usually strong hard-biting organs; the second and
third are known respectively as the first and second maxilla; they are
almost always more feebly developed than the mandibles. These three pairs may
be augumented by others called maxillipeds, when more segments are
included in the head.

As in the Annelids again, the body, with its appendages, is
invested by a cuticle, secreted by the epidermis. It differs in an
apparently trifling, but in its results very important, respect from that
of the Annelids; for it is usually of a much greater thickness
and hardness than in these, forming as it were an armour for
the body, an exoskeleton. Only at the constrictions between
the segments, both of the body proper and of the limbs, does it retain
Arthropoda. 185

a certain thinness, so that movement can take place at these points.
All Arthropods moult* periodically, at least, as long as growth
continues; the cuticle loosens from the underlying tissue, breaks
at some point, and is cast off as a whole (z.e., the animal creeps
out of it) after the epidermis has secreted a new cuticle. This is
thin and soft at first, but becomes thick and hard later. Such
periodic ecdyses are indispensable
for growth, for the stiff, un-
yielding cuticle allows only of very
slight increase in the size of the
body. The growth of the animal
would therefore cease, if the sur-
rounding case were not now and
again thrown off and replaced by
a new and roomier one. Upon
the body, there are larger or
smaller tracts of sete, evagina-
tions of the cuticle, each containing
a process of the soft epidermis;
the cuticle at the base of the hair
is thinner, so that it can move
about. The cuticle consists of
chitin, an organic substance, of
a horny appearance, chemically
however, quite different from horn.
Lime salts, principally carbonate Fig. 146. Section through a hair and

2 ‘ : the adjacent skin of an Arthropod; dia-
of lime, are often deposited in the grammatic. c cuticle, d thin part at the exit
chitin, especially in the Crustacea. of the hair h; ep epidermis.—Orig.

The skin is never ciliate among
the Arthropoda, nor indeed is any other organ; in fact ciliated
cells are entirely absent.

The muscular system is closely connected with the skin;
the formation of a segmented exoskeleton, however, necessitates
important deviations, from the Annelid type. Instead of a
continuous musculature beneath the skin, there is usually a large
number of separate muscles passing from one segment to another,
and attached by their extremities to the inner side of the skin:
by their contraction the segments of the body, as also the
joints of the appendages, move upon one another. The muscles
are often connected by the so-called tendons, which, in the
Arthropods, always consists of invaginations of the cuticle, sur-
rounded of course by a corresponding invagination of the epidermis

 

 

 

 

*In many (all?) Annelids (e.g., Leeches) and in Nematodes, « similar ecdysis
occurs.
186 Arthropoda.

(Fig. 148). They are thrown off with the rest of the cuticle at
each moult and renewed. The muscular tissue of the Arthropods
consists of striated, multinucleate muscle fibres.

Fig. 147. Fig. 148.

 

Fig. 147. The last four joints of an arthropod limb with their muscles: diagrammatic.
U articulation, B and b flexors, S and s extensors, u places where two joints touch one
another, and the articular membrane is very narrow; 1 terminal, 2 penultimate joint, etc.
—Orig.

Fig. 148. Longitudinal section through a joint of an Arthropod : diagrammatic.
c cuticle, ep epidermis, 1 articular membrane, M muscle, o opening of the tendon to which
the muscle is attached.—Orig.

The nervous system agrees closely with that of the Annelids.
Just as in these animals there is a pair of ventral ganglia in each
segment, connected with those of the adjacent segments by a double
nerve cord. Fromthe most anterior of these ganglia spring two nerve
cords, which run round the cesophagus to unite with a paired
ganglion mass, the cerebral ganglion, lying in the head. This
often attains to a very considerable size, which is correlated, amongst
other things, with the development of certain sense organs, situate on
the head, the compound eyes. The ventral ganglia often exhibit
remarkable differences from those of the Annelids, differences which
are due to the above-mentioned dissimilarity in the formation of the
segments and their grouping into different regions. In well-developed
segments for example the ganglia are large, whilst a fusion of many
segments is accompanied by a fusion of their ganglia. In some cases,
Arthropoda. 187

indeed, all the ventral ganglia may unite into a single unsegmented
mass; this is always accompanied by the shortening of the body,
as in Crabs. Sometimes ganglia are shifted during
development, so that those belonging to one segment
move further forward; but the nerves arising from
such a pair are distributed to the segment to which
they properly belong. The members of a pair are
united by a commissure, which is almost always short,
often so short that they appear to be fused; this
is often the case, also, with the connectives of
consecutive pairs.

Sense organs. The formation of a cuticular
skeleton results in the restriction of the sense of touch
to certain spots on the surface of the body. In
particular many sete become tactile; beneath the
epidermis lie one or more sensory cells, each of
which sends a filiform process into the seta from one
end, and a nerve fibre from the other end, to the
central nervous system. Hairs, provided with a thin
cuticle, and occurring upon the first antenne of
Crustacea, act as olfactory organs; so also do
the peg-shaped processes upon the antenne of Insects
(see p. 19): like the tactile structures, they are con-
nected with sensory cells. Auditory organs
are found in many Crustacea, and in some Insects ;
these will be considered in the several groups. Optic
organs, which reach such a high stage of de-
velopment among the Arthropoda, appear in two
forms; as simple eyes, or ocelli, and as compound
eyes. The most important points in the structure
of these eyes have already been noticed in the General
Part, pp. 21, 22. In most of these animals there is a Ligaen dea

y vous system of
pair of compound eyes, as well as several ocelli, but Gammarus.

: : c¢ brain, o eye,
in others ocelli only are developed. i feck apie cal

The digestive tract usually runs through panels, I first
the body as a tolerably straight tube; the mouth is at ee ae ee
the anterior end, and is usually ventral; the anus
is posterior. Salivary glands and a liver may or may not be present.

 

Vascular system. The heart, which is usually tubular,
corresponds to the dorsal vessel of the Annelids, and is found on
the dorsal side, above the digestive tract. It is furnished with venous
ostia, generally several pairs, through which the blood enters the
heart from the surrounding blood-space, the pericardium: the
pericardium receives the blood from the gills (lungs) when such are
present, or from the body. In other respects, the vascular system of
188 Arthropoda.

different Arthropods presents very considerable variations, which will
be dealt with later; in a few forms (Acarines, small Crustacea), it
is entirely wanting. The blood is usually a colourless fluid, with
colourless, amceboid blood corpuscles.

From some small Crustacea respiratory organs are entirely »
absent; generally, however, there are either gills, or peculiar air-
breathing organs (See special classes).

Excretory organs. The segmental organs, familiar
in the Chetopods, occur again in one division of the Arthropods, but

reduced to a small number, two pairs; the antennary and shell. --

glands of Crustacea (see this group) are modified segmental
organs. In Insecta, Myriapoda, and Arachnida there is, on the other
hand, no trace of such structures; instead, they possess the so-called
Malpighian tubes, long glandular canals, which open into the
hind gut and perform an excretory function.

Genitalia. The Arthropoda are, with few exceptions, of
separate sexes: the male and the female glands closely resemble
one another. There is never more than one pair of genital glands,
and this is frequently united or even fused to form an unpaired
organ. From each gonad springs a duct (the oviduct or vas deferens),
which opens on the ventral side, always in front of the anus; the
ducts are frequently united for the last part of their course, and then
there is only one aperture. Even when the glands are connected or
fused there are generally two ducts.

Class 1. Crustacea.

The head is never sharply marked off from the rest of the body
{as is the case among Insecta, for example), but some of the thoracic
segments are usually fused with it. It bears, besides the eyes, which
will be dealt with later, two pairs of antenne (the antennule
and the antenne), and three pairs of jaws, the mandibles and
the first and second maxillew. The antenne are usually elon-
gate, whip-like appendages, consisting of a short, jointed, basal piece,
or peduncle, and a long, flexible end-piece, composed of many
joints; or the peduncle may bear two such filaments. The most
important part of the mandibles is a hard, unsegmented, basal
piece, the true mandible, which is provided, as a rule, on the inner
side with a sharp dentate edge, and often with a rough, grinding
surface. The sharp edge, as well as the grinding surface, works against
the corresponding parts of the other mandible. The basal part often
bears a smaller jointed appendage, a “palp.”” The other pairs of
jaws are not nearly as strong as the mandibles: they are lamellate,
and the inner edge is divided into several lobes, beset with stiff sete ;
Class 1. Crustacea. 189

they also often possess a small end-piece, a palp. The rest of the
body bears a varying number of limbs, arising on the ventral
side, one pair to each segment. The terminal segment is frequently
apodous, so also may be some of the others. In rare instances all
these appendages are almost or quite identical, but usually those of
the different segments are more or less dissimilar. Frequently, for
instance, the foremost are nutritive in function, and are correspondingly
modified, and are then called maxillipeds; the hindmost may be
swimming organs, whilst others, again, are ambulatory. The limbs
are, in short, highly specialised in form and function.

It is, however, possible to reduce all the limbs to a common
ty pe, not only those which belong to the trunk, but also those of the
head, #.e., the second antenne,* and the three pairs of jaws. <A typical
crustacean limb consists of
the following parts: (1) a 7 B
main stem or endopod,
composed of a number of
joints, and constituting the
chief part of the limb; (2)
an outer branch or exo-
pod springing from the
second joint of the endopod;
unjointed, or at least not
divided into special pieces
moving upon one another ;
usually flat, and provided
with marginal sete; (3) an
ep ip od arising from the Fig. 150. Example of typical crustacean
basal joint of the endo- limbs. 4 thoracic limb of Nebalia. Blast maxil-

liped of a larval Prawn. 1-—7 joints of the stalk.
pod, always unsegmented, ex exopod, ep epipod. Enlarged.—Orig.

usually sparsely setose, thin
skinned, and as a rule subserving respiration. Exopod or epipod,t
or both, may be absent, so that the limb consists of the endopod only;
and even this may be more or less degenerate. On the other hand
certain joints of the endopod may be specially well-developed, as,
for instance, the basal joint of the mandible.t| The exopod may be
flat or round, curled or uncurled, etc.

Among other cephalic structures must be noticed the carapace
(or shell), a backwardly-directed, mantle-like fold, arising from the

 

 

* The first antenne, though often called limbs, do not agree with the rest of the
appendages, but exhibit peculiar relations (the exopod is always absent from the
second joint, etc.) ; like the eye-stalks they are to be regarded as special appendages,
which function as the supports of special sense organs (olfactory and auditory).

+ The epipod is always absent from the appendages of the head.

{ The true functional mandible is merely the basal joint developed as a cutting or
grinding organ ; its jointed appendage, the palp, represents the rest of the endopod.
190 Arthropoda.

hind part of the head, and covering a greater or less part of the body.
It is frequently concrescent with the thorax along the mid-dorsal line.
Sometimes the mid-line of the shell is softer than the rest, so that it is
divided into two movable halves, which surround the body like a

 

Fig. 151. Limbs of different Crustacea; the exopod is dotted. A swimming leg of
Branchipus. B swimming leg of a Copepod. C second maxilla of a Decapod.
D mandible of a Copepod. s endopod, 1, 2, 3 its joints, p palp, ep epipod.—Orig.

lamellibranch shell. The outer surface of the shell is usually covered
with a thick, hard cuticle, so that it forms a really protective covering ;,
the inner surface, is, on the other hand, softer. The carapace is very
characteristic of the Crustacea, although it is absent from many forms.

The cuticle covering the body is often of a considerable thick-
ness and hardness, the chitin always containing lime salts (carbonate
of lime) in varying quantity.

The olfactory organs are situated on the antennules, the
function appearing to be restricted to long, soft, thread-like sete.
Auditory organs are known only in some Malacostraca (see
Myside, Decapoda). Optic organs may be represented either by
the nauplius-eye, consisting of a single eye-spot in the median
line of the head, or of a small group of them, or by a pair of large
compound eyes on the sides of the head, often placed upon movable
or immovable stalks. In some forms both median and paired eyes are
present, in some only the former, in many only the latter. In numerous.
cases the nauplius-eye is present in the larva, but atrophies later.

The digestive tract begins anteriorly on the ventral surface
of the head, in a mouth opening between the mandibles. It is often
bounded before and behind by projecting folds of skin, the upper,
or the under lip. The alimentary canal is a straight tube, which
opens upon the terminal segment of the body. A liver is usually
present.

Respiratory organs, The Crustacea, for the most part,
breathe the oxygen dissolved in water. In many, particularly in
small thin-skinned forms, special respiratory organs are wanting ;
then the whole surface of the body, or the greater part of it, performs
Class 1. Crustacea. 191

this function. In others, again, certain parts of the body are specially
developed as gills. Sometimes the thin-skinned inner side of the
carapace serves as a breathing apparatus; in other cases, the
flattened epipod, or some other part of the limb, acts as a gill; in yet
others, the gills are special, usually branched, appendages, springing
from the limbs or from the side of the body. These true gills,
which are usually characterised by the possession of a close and
delicate vascular network, may be supplemented by either the whole,
or a part, of the surface of the body.

Some of the terrestrial Crustacea breathe atmospheric air, and here, peculiar
respiratory organs are sometimes developed. This is, e.g., the case in Birgus
latro, an Hast Indian form related to the Hermit-crab; the gills are very small,
but the branchial-cavity, enclosed by the sides of the carapace, serves as an
air-breathing organ, and is, therefore, provided with large vascular excre-
scences of the surface, arising from the inner side of the carapace. In a true
hermit-crab, Cenobita, the soft skin of the abdomen serves as a respiratory
organ, and is furnished with a vascular network for this purpose. In some
terrestrial Isopods the abdominal limbs have branched invaginations of the skin
which take in air and serve as breathing apparatus.

The vascular system exhibits a variety of modifications. In
some forms, it is represented only by the heart, which drives the
blood into the spaces between the organs; in a few cases, even
this is wanting. A poorly-developed vascular system is usually
correlated with a small body, and with the absence of special
respiratory organs. When these are present, there is, as a rule, a

 

Fig. 152. Vascular system of the Lobster, diagrammatic; the vessels which
carry arterial blood, light, the others, dark ; the arrows indicate the direction of the blood.
stream. g gills, h heart, p pericardium, v venous sinus, v' vessel thence to the gill, a’ from
the gill to the heart.— After Gegenbaur.

better-developed system, and definite vessels, although these may
fail im many parts of the body, so that the blood flows in the
spaces between the organs; the vascular system is consequently not
entirely closed. The circulation in gill-bearing Crustacea is as
follows (see Fig. 152): The blood is driven from the heart, through
more or less perfect arteries into the different parts of the body ; after
it has received carbon-dioxide, and given up oxygen here, it collects
192 Arthropoda.

in large blood reservoirs, whence it is passed on to the gills. After
receiving fresh supplies of oxygen, it travels through special vessels
to the pericardium, enters the heart through the ostia, and then
recommences the circulation.

Excretory organs. Two pairs of tubular organs, probably
representing the segmental organs of the Annelids, are found in the
Crustacea. The inner opening is wanting; they are usually of con-
siderable size and much coiled. The foremost pair, the antennary-
glands, open on the basal joints of the second antenne ; the
second, the shell-glands,* at the base of the second maxille.
Both pairs are seldom developed in the same animal; frequently one
pair is present, and atrophies later, when the other is formed.t Often
both are absent.

The great majority of Crustacea are of separate sexes. The
genital organs open ventrally, asarule at a considerable distance
from the posterior end, and usually by two distinct openings. The
apertures of the oviducts are, in many forms, further forwards than
those of the vasa deferentia. Not infrequently, parthenogenesis
occurs (see Branchipus, Apus, the Daphnids).

The development of the Crustacea is usually connected
with a very distinct metamorphosis, for the young one,

when it leaves the egg,

< is essentially different

from the adult. The

difference depends,
amongst other things,
upon the smaller number
of segments and limbs
possessed by the larva ;
and further upon the
different structure and
even function of these
limbs. A large number
of Crustacea leave the
egg in the so-called
nauplius-state; as
small, compact creatures,
furnished only with the
Fig. 153. Nauplius of Peneus. Enlarged.— first and second antennze
After Fr. Miiller. and the mandibles. These
appendages are all de-

 

* This name is connected with the fact that the glands often (e.g.,in Apus) lie for
the most part in the carapace.

+Among the Entomostraca, the shell-gland is universally present
in the adult, the antennary gland in the larva; whilst, conversely, the adult
Malacostracan exhibits the antennary-gland, the larva, the shell-gland.
Class 1. Crustacea. 1938

veloped as tolerably powerful swimming organs, the posterior
antenne and the mandibles (which last are wholly different
from their adult form) are each provided with a long setose
exopod. The larva possesses only the nauplius eye, the paired
(lateral) eyes are entirely wanting. It is actively free-swimming,
grows gradually in length; the other limbs arise, and after a series
of changes simultaneous with ecdyses, it finally attains the adult
form. Amongst other Crustacea, however, the young one hatches
at a more advanced stage, provided with several pairs of limbs, etc.
(see below).

- Most Crustacea are marine; some creep about at the bottom of
the sea, others are excellent swimmers; many are pelagic; the
majority are free-swimming in the larval state. A few live in
fresh water, others on land or in damp places

The Crustacea are divided into two sub-classes: Entomostraca
and Malacostraca. The latter group forms a circumscribed
whole, whilst the Entomostraca comprise several, and in some cases
only distantly related, groups.

Sub-Class 1]. Entomostraca.
Order 1. Phyllopoda,

The head is furnished with a nauplius eye, and with com-
pound, stalked or sessile lateral eyes; the jaws are usually
feebly developed, sometimes also the antennew. The head is generally
followed by a thorax composed of numerous segments; each thoracic-
somite bears a pair of strong, flat, leaf-like limbs, which
serve both as natatory organs and also as gills, and are about
equally developed on all the segments. The terminal joints of the
body are apodous (abdomen) ; on the most posterior is a pair of
jointed or unjointed backwardly-directed appendages. In the
majority of forms the body is entirely or partially covered with
a carapace which arises from the head. The Phyllopoda hatch
as nauplii. Most members of this small group live in fresh
water, as a rule in little pools. The eggs can endure complete
drought; some even do not develop until they have lain dry for
some time.

1. Branchipus possesses a pair of stalked, movable lateral eyes: the
carapace is wanting. The second antenna of the male is modified, to
hold the female during copulation. The thorax bears eleven pairs of legs, the
abdomen is nine-jointed, the caudal appendages unjointed. The organisms
belonging to this genus are transparent, elongate, and minute (1—2 e/m. in
length) ; found in fresh-water pools; they swim about constantly with the ventral
side upwards. The species of the nearly related genus Artemia (see page 67),

O
194, Arthropoda. Class 1. Crustacea.

live in salt lakes on flat sea coasts, or in inland seas (Utah); some of these
forms reproduce parthenogenetically, males appearing only now and

again (A. salina in South Europe).

 

Fig. 154. Branchipus vernalis g. a, anterior, a, posterior antenna, f rostrum,
o stalked-eye, p penis, r caudal appendage, I, II, XI: first, second, eleventh thoracic
segments. XII, XIII, the two anterior abdominal segments.—After Packard.

2. Apus is provided with a broad, feebly-arched carapace, which covers
the body with the exception of the hindmost part. The lateral eyes are
sessile, situated close to one another and near the little nauplius eye on the

   
    

  
   

GQae:
Lire
LT)

 
  
 
  

YH
(CC

iG

 

 
 
 

      
   
       

G

A
a

<

    

             

  

Fig. 155. Apus productus, seen from below.
a antenna, an anus, l upper lip, md mandible, p, first
leg, r caudal appendage (ends cut off), S carapace.—

After H. Milne Edwards.

  
  
  

dorsal side of the head. The
antenne are very small. There
are about sixty pairs of leaf-like
legs, whose endopod, as in other
Phyllopods, is drawn out into
lobes prolonged in the most
anterior pair, to form long,
jointed threads. In the female,
the wide exopod of the eleventh
pair is curved like a watch-
glass, and the epipod lies upon
it as a cover, so that the two
together form a little box, in
which theeggs arecarried about.
The caudal appendages are
long jointed threads. The shell-
glands lie in the carapace, and
are visible through the skin.
The individuals of this species
are of a very considerable size
(several c/m. long). They are
brownish or greenish creatures
with a thin exoskeleton. They
occur, especially in spring, in
small fresh-water lakes (often
in those which dry up in the’
course of the summer), swim-
ming with the ventral surface
upwards. Usually, and in some
species exclusively, females only
are found, males occur but
seldom. Reproduction is as
a rule parthenogenetic.

3. The genera Estheria,
Sub-Class 1. Entomostraca. Order 1. Phyllopoda. 195

Limnadia, etc., afford a transition to the next order; they are distinguished
by having the carapace divided into two movable halves, provided externally with
a very hard cuticle, and surrounding the whole body; the valves shut together as
do those of Lamellibranchs, for which they might be mistaken. Further, the
lateral eyes are very near one another or even united; the second antennz are
very strong and provided with two jointed filaments, the exopod and the distal
part of the endopod respectively, whilst the first antennz attain only a small
size.

Order 2. Cladocera.

The Daphnids must be regarded as peculiarly developed Phyllopods
with a small number of limbs, and a large compressed
bivalve carapace enclosnmg the body with the append-
ages; upon the head there is a large compound eye, which is
mounted upon a short stalk and is movable; it arises from the
fusion of the lateral eyes, and is enclosed in a special socket, formed
by the upgrowth of a fold of skin; there is usually also a small
unpaired nauplius-eye. The first antenne are generally short, and
provided with olfactory hairs. The second antenne are
powerful biramous natatory organs. Besides the mandibles

 

Fig.156. A Daphnid, Sida crystallina, with eight winter eggs in the brood-pouch.
«, first, ag second, antenna, an anus, d gut, h heart, m mouth, o eggs, oe eye, ov ovary,
r caudal fork, S carapace.—After Weismann.

there is a feebly developed pair of maxille. The short thorax is
provided with laminate nectopods like the limbs of the Phyllopoda,
though there are only four to six pairs. The abdomen is curved
downwards, and has two pointed, unsegmented caudal appendages at
the tip. There is a powerful pulsatile heart anteriorly and dorsally,

o 2
196 Arthropoda. Class 1. Crustacea.

but special vessels are wanting. A well-developed shell-gland is
present. Some Daphnids differ from the usual type now described,
in that the carapace is wanting, or is only feebly developed, that the
body is elongate, and that the thoracic-limbs are aberrant in form.

The Daphnids are small (at most a few m/m. long), transparent
animals, which are mostly fresh-water, though a few are marine;
they move through the water by jumps (Water-fleas). During the
summer, usually only females are found, producing partheno-
genetically large, thin-shelled “summer eggs,” which are
“brooded ” in the cavity between the trunk and the carapace; the
young ones leave the brood-pouch almost in the condition of the
parent; in autumn males appear also. The fertilised ova, “ winter
eggs” (“resting eggs”’), which are thicker-shelled than the summer
ones, usually pass the winter
inapeculiar case (Ephippium),
formed by the thickened
cuticle of the whole or part
of the carapace, and thrown
off by the female together
with the eggs. The winter
eggs develop in the spring ;
in some forms the young ones
hatch out of the winter eggs
as nauplii.

Order 3. Xiphosura.

In the living Xiphosura,
which comprise only a single
genus, Limulus (the King-
crab), the body is divisible
into two unsegmented parts,
the cephalo-thorax and
the abdomen, which are
movably articulated ; each of
these regions is composed
of anumber of fused segments.
The cephalo-thorax is strongly
arched, the sides are thin and
continued down to form a
shield-shaped structure, which

Fig. 157. Limulus polyphemus; , from covers in the ambulatory

below: reduced. 1—6 ambulatory appendages, appendages. A carapace ie
o operculum of the gill-bearing limbs, the edges U a a 1
of which are seen one behind the other. wanting. pon e dorsa

surface there is a pair of large

 
Sub-Class 1. Entomostraca. Order 2. Cladocera. 197

compound sessile eyes; the nauplius eye is represented by a
pair of ocelli, placed near together. Antenne and jaws are
entirely wanting. Ventrally there are six pairs of jointed
ambulatory limbs, all of which are, in the female, furnished
with chele (cf. Decapoda), whilst in the male these are frequently
wanting from some of the limbs.

- The six pairs of walking legs surround the mouth, which is far
back; the first pair, which is much smaller than the others, is
in front of the mouth; the basal joints are beset with spines, so
as to serve also as masticatory organs. On the ventral side of the
abdomen thereare five pairs of lamellate limbs; the members
of a pair are concrescent at the bases of their inner edges; and each
limb bears on its posterior side a number of broad, low, branchial
lamelle. From the hinder edge of the cephalo-thorax arises a
pair of similar lamellate but more chitinised and gill-less appendages,
which coalesce in the middle-line, and cover the gill-bearing limbs as
an operculum. On the posterior side of the operculum, in
both male and female, are the two genital apertures. The body
terminates in a long, movably-jointed, pointed caudal-spine.
The exoskeleton is tolerably hard, of a horny consistence and
colour.

The young Limulus hatches at a comparatively advanced stage.
When newly-hatched it is peculiar in having a jointed abdomen
and slightly developed caudal-spine.

 

Fig. 158. Young Limulus. A dorsal, B ventral.—After Kingsley,

The few extant species of this group are large (to over ‘5 m. long),
and come from the coasts of Asia and America. The caudal-spine
plays a not unimportant part in locomotion, for it is used to push the
body forwards. The Xiphosura are carnivorous.

Some of the extinct forms exhibit a segmented abdomen like that
‘of the young Limulus (+.g. Belinwrus, from the Carboniferous). More
198 Arthropoda. Class 1. Crustacea.

remotely related to the King-crabs are the genera Hurypterus (Silurian)
and others, with a relatively smaller cephalothorax, with five pairs of

 

Fig. 159. <A Limulus, B Belinurus, C Eurypterus, D a Trilobite (Dalmanites
socialis).
locomotor appendages, bearing a general resemblance in size and
shape to those of Limulus, and with a large jointed abdomen and a
short caudal-spine.

Order 4. Trilobita.

The flat, oval body of the Trilobites is divided into three regions
(see Fig. 159 D); cephalothorax, thorax, and abdomen, of which the
thorax is usually the largest.

The cephalothorax is unsegmented, its anterior and ‘lateral
edges are curved, but its posterior one straight; the lateral angles are
not infrequently prolonged into backwardly directed spines. Placed
close together on the dorsal side, there is usually a pair of large,
sessile, compound eyes. The thorax consists of a number (2—26)
of movable, short, wide segments. The abdomen is formed of
a number of fused segments, whose
limits are sometimes clear, but
usually indistinguishable. Two
longitudinal furrows traverse almost
the entire length of the dorsal side,
from one end of the body to the

: other, marking out the surface into

Fig. 160.—Stages in the development of A
a, Trilobite (Sao hirsuta).—After Barrande, 2 median (tergum) and two
lateral areze (p le ur x). Theventral
surface, with the appendages, was probably very soft and thin-
skinned, whilst the dorsal was hard. In only a few cases have
indubitable traces of the ventral surface and the limbs been found,

 
Sub-Class 2. Entomostraca. Order 4. Trilobita. 199

so that the structure of the appendages cannot be spoken of with
certainty; they were probably soft and feeble like those of the
Phyllopods. Some Trilobites had the power of rolling themselves
up like Oniscus. As regards their development, it is known that
they possessed a smaller number of segments in the young than in
the adult state.

The order of Trilobites comprises numerous species, all of which
are extinct. The group flourished especially in the Silurian, was
more sparsely represented in the Devonian, and died out in the
Carboniferous Period. Many specimens are of very considerable size.

Order 5. Ostracoda.

From superficial observations, the Ostracoda appear to be very like the
Daphnidw, from which, however, they prove to be very different on a closer
examination. The body is short and compressed, and may, with the limbs, be
entirely enclosed in the very hard shell; this is divided into two parts, which can
be opened and shut like the valves of a mussel shell. In the anterior part of the
animal, there is a nauplius-eye, sometimes divided into two; and, in some
forms, also a pair of movable lateral eyes. The first and second antenne
are much modified, and provided with long, swimming sete; both, but especially
the second pair, are natatory and locomotor. The three pairs of jaws are all well
developed. Besides these appendages, only two pairs of slender, jointed thoracic
legs are present. The most posterior part of the body is curved downwards, and
usually terminates in two lamellate appendages. As regards the internal

Fig. 161. Fig. 162.

 

Fig. 161. Cypris. oc nauplius eye, an', an? first and second antenna, md mandible,
mo, ma? first and second maxille, p', p* first and second legs, c tail: enlarged.—After
Zenker.

Fig. 162. Nauplius of an Ostracod. s shell, the other letters as in Fig. 161.—After
Claus.

structure, it must be noticed that many have no heart. Sexual dimorphism is
well marked (in the structure of the limbs, etc.) ; the colossal size to which the
spermatozoa attain is worthy of note; in the species Cypris ovum, for example,
the total length is 2 m/m., 7.e., more than three times as long as the whole
animal. Many leave the egg in the nauplius state, provided only with
antenne and mandibles; the shell is usually already developed.

The Ostracoda are animals of small size, occurring both in salt and fresh
water.
200 Arthropoda. Class 1. Crustacea.

Order 6. Copepoda.

The order Copepoda comprises a large number of free-living
forms, and also a multitude of parasites, which conform, on the whole,
to the same type, although they are often considerably modified in
accordance with their peculiar mode of life.

The free-living Copepods will be first considered. The body
is divided into three regions, cephalothorax, thorax, and
abdomen. On the cephalothorax there is a nauplius-
eye, consisting of two, three, or more ocelli, and attaining a
considerable size in some pelagic forms; lateral eyes, on the
other hand, are always wanting. The cephalothorax bears,
further, two pairs of antenne, both of which are well-
developed. The anterior antenne& are usually the longer,

 

 

 

 

 

Fig. 163. Cyclops. a nauplius, b—d later stages of development, e adult animal
(only the Jeft mandible and maxilliped, and the right maxille are figured): enlarged.

and serve as natatory organs; in the males they are frequently
used also for holding the female during copulation; they are then
bent in the middle, and the distal can close upon the proximal part.
The mandibles are usually provided with palps, the palp often
possesses a small exopod (Fig. 151 D). Behind the mandibles
are the two pairs of maxille and a pair of maxillipeds.
Sub-Class 1. Entomostraca. Order 6. Copepoda. 201

The thorax consists of five segments, of which the foremost is
frequently united with the cephalothorax; each segment, or only
the first four, bears a pair of swimming legs, consisting of
a short peduncle with two rami; the outer ramus represents the
exopod; the inner, together with the peduncle, the endopod. The
abdomen is reduced and apodous, and is composed of the last five
segments of the body; at its posterior end there is a pair of unjointed
lamellate, or pointed, caudal appendages, between which the anus is
situated. The vascular system _ is poorly developed; the
heart usually wanting. Special respiratory apparatus
is also absent. The eggs are carried about by the female,
enclosed in one or two egg-sacs, which consist of a hardened glandular
secretion, and are attached to the base of the abdomen. The egg
hatches into an oval nauplius, with a nauplius-eye, and the
appendages (antenne, mandibles) characteristic of this developmental
stage, by means of which it swims actively about in the water. The
other limbs bud out gradually as the body increases in length.

These Copepods are small aquatic animals, which are fresh-
water as well as marine, and are frequently found in immense
numbers; the sea may be tinted red, over large tracts, by their
presence. The principal food of the great shoals of Herring consists,
at least in many places, of some species of this group, which
furnishes also a considerable contribution to the food of the Whale-
bone Whale.

Species of the genus Cyclops, carrying two egg-sacs, are common in the
fresh waters of England.

The Parasitic Copepods comprise a multitude of different forms
living on (seldom in) different aquatic, usually marine, animals,
They are frequent upon Fish (especially on the skin and gills), also
on Worms, Molluscs, etc; they often attain a larger size than the
free-living forms (several c/m.). Some of them (Fig. 164, 1-2) e.g.,
Fish-lice (Caligus), differ relatively little from the free-living forms.
The mandibles are modified as stabbing organs (stylets), which are
enclosed in a tube, the proboscis, formed by the concrescence of
the upper and under lips; some of the limbs (second antennz, second
maxille, maxillipeds) are modified to prehensile hooks (adhesive
organs) ; but in other respects those occurring, for instance, on the
skin of fish, are not strikingly different from the free-living forms,*
the sexes are not very dissimilar, and male as well as female, is
locomotor, not fixed to one spot on the host. In others the altera-
tion is greater, the adaptation to parasitié life closer; this is specially
evident in the female. The modifications, which differ in extent in

 

*It may be noted that the first antennz, which, in free-living Copepods, are
generally very long, tend here to be rather short. The first maxilla is rudimentary,
the eye may or may not be present. Not infrequently (e.g. in Caligus), the body is
flattened, and accommodated to the surface of the host.
202 Arthropoda. Class 1. Crustacea.

different forms, are in the direction of clumsiness, deformity, and im-
mobility; the abdomen degenerates, the segmentation is obliterated,

 

4

Fig. 164. Various parasitic Copepoda: 1 Nogagus borealis, male from the ventral
side. 2 Caligus rapaz, female from above. 38 Chondracanthus gibbosus, female from
below (g¢ the male). 4 Brachiella thynni, female. 5 Male of the same species (more
enlarged). a,—da, first and second antenne, f caudal appendages, hk second maxilla,
kf maxilliped, p,—p, first—fourth pairs of legs, 0 egg-sac.—1, 2, 4, 5 after St. enstrup and
Liitken, 3 after Claus.

those limbs, which do not serve as organs of adhesion, atrophy, or
become functionless ; this applies especially to the true legs, which
are either wanting, have
degenerated to mere ves-
tiges (Fig. 165 B), or have
become large thick ap-
pendages, without sete,
exhibiting only feeble in-
dications of their original
form. Often such parasitic
Crustacea are provided

with peculiar outgrowths,
Fig.165. A, Penella sagitta (parasitic on certain : >
Fish), 9, natural size. B anterior end enlarged. rendering their Hy peaneiee

p' first, p! fourth pair of legs, 0 egg-sac. C Herpyl- still more striking. As @

lobius arcticus (parasitic on Cheetopods), 9 enlarged, rule they are blind. Where
oegg-sac. The irregularly lobed part is sunk in the Z Wipes
body of the host.—After Steenstrup and Liitken. the reduction is most ad-

vanced, the entire animal

 
Sub-Class 1. Entomostraca. Order 6. Copepoda. 203

is a sac without limbs (Fig. 165 C), and with only two longer or
shorter (often thread-like) egg-sacs. It is immovably attached to
the host, in some cases by means of the second antennz, the second
maxille or the maxillipeds modified into long arms; in others by
means of the whole front part of the animal, which is imbedded in
the body of the host. The males of the more strongly modified
forms are usually pigmy, attain only a small fraction of the size
of the females, and asa rule are attached to them in the neighbourhood
of the genital aperture; they are not usually so entirely modified as
the females may be, as a rule they have several pairs of limbs, etc.
The parasitic Copepods, like the free-living ones, are hatched as
nauplii, which swim freely about, and after some moults reach a
state like that of the free-living adult. The parasites owe their ultimate

deformity to a “retrograde metamorphosis” occurring after fixation.

In some parasitic Crustacea, e.g., Lernza branchialis, living on the gills of the
Cod, the male and female are fairly alike up to the time of copulation, presenting
a tolerably normal copepod form ; after pairing, however, the female grows con-
siderably, and becomes quite distorted, whilst the male perishes; wherefore no
male is found with the adult female Lernza.

Order 7. Cirripedia.

The Cirripeds are furnished with a sort of protecting shield, the
so-called mantle, which is attached to the rest of the auimal only

Fig. 166. Fig. 167.

 

 

Fig. 166. Lepas. The right half of the mantle is removed, the body shown in longi-
tudinal section. After Claus.

Fig. 167. Balanus. The right half of the mantle and shell taken away.—After Darwin.
a and b the paired valves of the mantle, wu scutum, b tergum, c unpaired dorsal valve,
carina. a, anterior antenne, an anus, k cement gland, 1 liver, m adductor muscle of
mantle, m’ retractor muscle, o’ female aperture, od oviduct, ov ovary, p penis, r shell,
sl vas deferens, t testis.
204 Arthropoda. Class 1. Crustacea.

at the head end, whilst it covers the rest of the body loosely ; the
enclosed cavity communicates with the exterior only by a slit on the
ventral side. In one of the chief groups of the Cirripeds, the Lepadidee
(Barnacles), the mantle is prolonged anteriorly into a thick, shorter or
longer peduncle, by means of which the animal attaches itself to
some foreign object. In most Lepadide (e.g., the genus Lepas), the
mantle is provided externally with five calcareous plates or valves, of
which one, the carina, is narrow, and lies along the dorsal edge of the
mantle, whilst the remaining four, scuta and terga, two on each
side, cover a larger or smaller part of the lateral surface of the mantle ;
that part of the surface which these plates leave bare (in Lepas, only
the marginal furrows between the plates, in others the greater part),
is covered with a thin cuticle, which also clothes the peduncle, the
inner side of the mantle, and the body; the valves are specially
well-developed parts of the cuticle. In some Lepadide, besides
these five plates, a number of large and small plates (lateralia)
occurs at the edge of the peduncle and the rest of the mantle
(Fig. 168 B). In the Balanide (Sea-acorns), another important divi-
sion of the Cirripeds, the peduncle is wanting, but the animal is still
fixed, and indeed by the same part of the mantle as in the Lepadidee

the adhesive surface is large and provided with a calcareous
covering. The lateralia (Fig. 168 B,d), are in a line with the

A B Cc D

  

Fig. 168. Diagrammatic figures, shcwing the trarsiticn ficm Leyas to Palanus
A Lepas, B Pollicipes, C a Balanid with many lateralia, d (Calophragmus), D Balanus
s peduncle, a—d valves, a scutum, b tergum, c carina, d lateralia. The lettering is the
same for all the figures.—Orig.

carina (c), and are connected to form a hard shell, the testa,
which surrounds the greater part of the animal like a box. The
testa rarely consists of a large number of plates in several circles (Fig.
168 C), but more frequently of a smaller number (6—8) of large
plates in one circle (D, d—c). A lid (operculum) for the box
is furnished by the rest of the mantle with the four large plates (a, b)
Sub-Class 1. Entomostraca. Order 7. Cirripedia. 205

of Lepas, which here are relatively small, and at this point there is a
narrow slit leading into the mantle-cavity.

As for the appendages, the first pair of antenne is

present in a very rudimentary state; in the Lepadide it occurs on the
adhesive surface of the peduncle ; in the Balanidz in a corresponding
position. A cement-gland opens on each antenna, and its
secretion serves for the attachment of the animal. The second
antenne, on the other hand, are wanting entirely in the adult.
There are usually three pairs of jaws, none of which are well-
developed. The ventral side of the body, which, as is evident from
Figs. 166, 167, is turned upwards, bears six pairs of cirri, each
consisting of a two-jointed shaft, with two multiarticulate, very-
flexible, whip-like rami; the outer is the exopod, the shaft and the
other branch, the endopod. The cirri, whose rami are fringed with
sete, can be extrnded through the mantle-slit and withdrawn again ;
they serve to waft into the mantle-cavity the little organisms which
form the food of the animal, and when in motion the cirri stretch
through the slit close together, then widen out like a fan, come
together again, and are drawn back with a jerk. Among the
Balanide the anterior are considerably shorter than the posterior
cirri. The body is usually indistinctly segmented, and frequently
bears at its tip a pair of small joimted or unjointed caudal ap-
pendages. The adult has only a double nauplius-eye, whilst
lateral eyes are wanting. Heart and blood vessels are
absent.
_ The ventral ganglion chain is much concentrated; in the Balanide,
the ventral ganglia are all united to a single large nerve mass. The digestive
tract terminates at the end of the body. Among the Lepadide gills are
present in the form of thin-skinned whip-like appendages, springing from the
bases of one or more of the thoracic legs. These appendages, possibly
representing the epipods, are wanting in the Balanide, which are, however,
provided with a pair of large folded gills arising within the mantle on either
side. In a degenerate state they are also present in the Lepadide, where
they have a different function, viz., that of carrying the ovigerous lamelle
(see below).

In contrast to almost all other Crustacea, most of the Cirripedia
are hermaphrodite. Among the Lepadide, the ovaries lie in
the peduncle, among the Balanidz on the adhesive surface ; an oviduct
opens on each side of the body; the branched testis is situate
in the body proper; the seminal ducts open by a common aperture
on the tip of an elongate copulatory organ, posteriorly. It is
very curious that in certain Lepadidzw, besides the hermaphrodite
individuals, very small males occur, attached to the former in the
mantle-cavity or at its opening. These complemental males*

 

* In others an actual separation of sexes occurs; the female possesses the usual
form, the males are pigmy, like the complemental males.
206 Arthropoda. Class 1. Crustacea.

are sometimes like the hermaphrodite individuals in structure, in
other cases they are very degenerate. The eggs are cemented
together into large ovigerous lamelle and remain in the
mantle-cavity, until the larve are developed.

The Cirriped leaves the egg as anauplius of the usual kind,
which after moulting acquires the so-called cypris form; the
name indicates a certain resemblance to Cypris (Ostracoda). In this
state, during which the animal, just as in the nauplius state, is
free-swimming, the first pair of antenne is well developed, and has
an adhesive disc on the penultimate joint; the second antenne have
vanished, but six pairs of thoracic limbs are present, and resemble
those of the Copepoda; besides the nauplius.eye, there is a pair of
large compound lateral eyes, and a bivalve carapace
surrounding the body. After a time the organism attaches itself by
the antenne, the secretion of the cement-gland flows through them,
and fixes the animal permanently to the spot selected. The large
eyes atrophy, though the unpaired eye remains; the swimming legs
gradually change to cirri, their rami increasing in length, and
by a series of modifications, the animal attains the lepas or balanus
state.

All the Cirripedia are marine.

1. The Lepadide (Barnacles) are provided with a longer or shorter ped-
uncle; the mantle with five (or more) valves. Many attach themselves to some
object which floats in the sea (ships, floating pieces of pumice-stone, etc.); this
happens, e.g., in the genus Lepas, whose five calcareous valves cover almost the
whole surface of the mantle. Others, ¢.g., Scalpellum (like the Pollicipes
figured in Fig. 168 B), with numerous valves and with complemental males,
attach themselves to immovable objects, generally at great depths.

The genus Inthothrya, which bores holes in chalk and coral by means of deli-
cate chitinous spines projecting from the very thick peduncle, belongs also to the’
Lepadide ; and, further, the very different genus Alcippe, with distinct sexes (the
female has only the first, fifth, and sixth pairs of cirri, the male is a dwarf with-
out a- digestive tract, etc.), bores holes in dead gastropod shells. A peculiar
parasitic Barnacle, Anelasma squalicola, is found embedded in the skin of
certain Sharks, firmly attached by delicate branched threads which arise from
its peduncle. The cirri are without setz (recalling the limbs of certain parasitic
Copepoda), the mantle destitute of calcareous plates.

2. The Balanide (Sea-acorns) are sessile, and possess a shell, formed
usually of a single circle of plates, with an operculum, which consists of four
valves, and has a median slit (see above). Here belongs the genus Balanus,
often occurring in great numbers on large stones on the sea-shore, where the
animal is sometimes covered with water, sometimes uncovered. Other genera
are found upon the Turtle, or on the skin of the Whale (with the lower end
beneath the epidermis; Coronula, and others).

3. The Rhizocephala, which are modified in correlation with a parasitic life,
form the most peculiar division of the Cirripedia, and, if the adult alone were
examined, would seem to be far removed from the typical members of the order.
The body is divided into two regions: an anterior, consisting of much-branched
threads, imbedded in the body of the host, and a posterior, sac-like part, which
hangs outside the host, and is in connection with the front part by a short
Sub-Class 1. Entomostraca. Order 7. Cirripedia. 207

peduncle; the threads of the anterior region twine round the internal organs
of the host, and absorb food by endosmosis; they are comparable, both in general
appearance and in function, with the roots of a plant. The saccular part is
covered by a soft mantle; the mantle cavity, in which the eggs are retained,
communicates with the exterior only by a small aperture. Digestive tract and
limbs are altogether wanting. The Rhizocephala undergo «a metamorphosis

Fig. 169. A Rhizo-
cephalon (Sacculina),
3, on the ventral side of
the abdorren of a Shore
Crab; the Crab is seen
from below, with the
abdomen artificially
stretched out.—Orig.

 

whose first stages are like those of a normal Cirriped (nauplius, cypris); after
attachment to the host, however, the animal undergoes a modification, which
results in the above-described abnormal structure. They are parasitic upon
Decapoda; one species (Sacculina carcini), for instance, is very commonly found
on the ventral side of the abdomen of the Common Crab (Carcinus mcenas) of
European coasts; another (Peltogaster paguri) on the abdomen o the Hermit-
crab (the “roots” in both cases permeate the whole body of the host, whose
genitalia do not ripen). :

Sub-Class 2. Malacostraca.

In contrast to the Entomostraca, where the number of segments
and of limbs varies within very wide limits, there is a typical
number in the Malacostraca, which is never exceeded, but which
may be reduced in some forms by the loss of some segments or
pairs of appendages.

The body is divided into three regions: the head, the
thorax, consisting of eight segments, and the abdomen, of
seven. From the head arises in most orders a carapace,
which never covers more than the thorax (often not the whole
of it), and leaves the thoracic limbs and abdomen uncovered (eéf.,
the Daphnide, the Phyllopoda, and others); the carapace is
always confluent with a certain part of the dorsal side of the thorax,
whilst its sides are free; its outer surface is covered with a hard
cuticle, which often attains a considerable thickness. The head bears,
further, a pair of large compound lateral eyes, which are usually
stalked and movable, whilst the nauplius-eye is generally absent from
208 Arthropoda. Class 1. Crustacea.

the adult animal; the antennules, each consisting of a three-jointed
peduncle and two multiarticulate filaments, of which the outer bears
the olfactory sete (the inner is often absent) ; the antenne, in which
the peduncle is five-jomted, and produced into a multiarticulate

Vk Mk Hk Ef Ef, Ef;

 

Fig. 170. The appendages of a Lobster, 6; all of the left side and viewed
from below. In the upper row are represented: antennule (A,), antenna (A,), mandibles,
first and second maxilla (Vk, Mk, Hk), the three maxillipeds (Kf,—;). In the middle row
the ambulatory legs. In the lower row the abdominal appendages. i endopod, ¥ exopod,
b epipod, g gill, opening of antennary gland.—Orig.
Sub-Class 2. Malacostraca. 209

filament, whilst a lamellate unjointed exopod very often arises from
its second joint; finally, a pair of powerful mandibles, with
frequently a three-jointed palp, and two pairs of maxille, both of
a flattened form. The thorax, whichis not sharply marked off from
the head, and whose segments (all, or a few) are often completely
fused, bears eight pairs of limbs, consisting typically (see
Fig. 150, B), of a slender seven-jointed endopod, the basal
joint bearing a flat, unsegmented epipod; whilst from the second
joint springs a usually narrower exopod, fringed with sete and
multiarticulate. Frequently either exopod, epipod, or both, are
wanting, and as a result of concrescence, the endopod may have fewer
than seven joints. The eight pairs of thoracic feet are seldom all
alike ; usually the first, or the first two or three, pairs are modified as
maxillipeds, subserving the functions of nutrition; whilst the
rest serve for locomotion, or are developed as prehensile organs. The
abdomen is typically seven-jointed; it is usually filled up with
powerful muscles, and forms a true locomotor apparatus, whilst
the viscera are for the most part located in the thorax. Each of
the six anterior segments usually bears a pair of appendages, the
abdominal limbs, consisting of a two-jointed peduncle and two
rami, the outer of which represents the exopod; these are
usually natatory organs (swimmerets). The last pair of
abdominal appendages is generally different from the rest; it is
directed backwards, often broad, and with a short peduncle; with the
seventh somite, which is always apodous, it frequently forms the caudal
fin. Amongst other characters common to the group, the following
must be noticed: the region of the fore-gut following the short
cesophagus forms a gizzard, lined with chitin, and furnished with
hard denticles and with sete. The rest of the digestive tract is
tubular ; the anus is on the ventral surface of the last abdominal
segment; the liver, which is composed of a number of tubes, opens
into the gut bebind the gizzard; the heart is usually short and wide,
sometimes more elongate, and almost always provided with three (or
fewer) pairs of ostia; the ovaries are generally partly fused; the
oviducts are, however, separate, and open on the under side of the
ante-penultimate (sixth) thoracic segment, or on the basal joint of its
appendages; the testes are usually like the ovaries; the seminal!
ducts open on the last (eighth) thoracic segment, or on the basal
joints of the eighth thoracic limbs.

Norse.—The genus Nebalia forms a transition from the Entomostraca, and
especially the Phyllopoda, with which it should be grouped, to the Malacostraca.
It lives in the Mediterranean, the North Sea, on the coast of Greenland, and
elsewhere. The body is divided into head, thorax, and abdomen; the thorax is
eight-jointed, with eight similar pairs of appendages, which are like those of
other Phyllopoda. Each appendage (Fig. 150 A) is seven-jointed, lamellate, with
broad exo- and epipod. The abdomen is eight-jointed, and, as in the Phyllopoda.

P
210 Arthropoda. Class 1. Crustacea.

is provided with a pair of caudal appendages at the tip; the abdominal appen-
dages (six pairs) are, however, like those of the Malacostraca. A large part of the
body with the limbs (not the thorax alone, as in the Malacostraca), is covered.

 

Fig. 171. Nebalia Geoffroyi. VIII Highth thoracic segment, 1, 7 first and seventh
abdominal segment; A,—Ag, first and second antenne, ( head; H, Hg first and sixth
abdominal appendages; K,, Kg first and eighth thoracic appendages; o eye, p mandibular
palp, r caudal appendage, S carapace (left-side removed).—After H. Milne-Edwards.

by a large, compressed carapace, which lies loosely over the thorax, without
undergoing concrescence with it. On the whole, the animal exhibits a curious
combination of the characters of the Phyllopoda and the Malacostraca.

SYNOPSIS OF ORDERS.

Stalked eyes. ( 6. Decapoda

Carapace present, usually well- | 7. Stomatopoda ?) No brood-pouch.
developed. 1. Euphausiacea

Second antenna with exopod. ( 2. Mysidacea. Brood-pouch

Sessile eyes. 3. Cumacea present.

Carapace small or absent. 4. Isopoda One pair of

Second antenna without exopod. \ 5. Amphipoda maxillipeds.

Order 1. Euphausiacea.

The Euphausiacea are transparent, prawn-1 ike animals, a
few c/m. long, which live in great numbers in the open sea. They
differ from all Malacostraca in that none of the thoracic
feet are modified as maxillipeds, but all the eight pairs,
though the last two may be degenerate, are essentially alike, and all
‘Sub-Class 2. Malacostraca. Order 1. Huphausiacea. 211

are locomotor: each consists of a seven-jointed, long and thin
endopod, and a strong exopod, fringed with sete, and serving
as a natatory organ: there is also an e pipod which is much-branched,
except in the case of the first pair, and hangs free on the side of the
animal, acting as a gill. Eyes, antennew, carapace, abdomen, and
swimmerets are like those of the Prawn (q.v.). The EHuphausiacea are

 

 

Fig. 172. Thysanopus tricuspidatus. 1—7 first and seventh abdominal segments;
A,—Ag first and second antenne; Hy; third abdominal appendage: K,, Ky, K; first,
second, and seventh thoracic limbs; K,er and Kew exopod of the third and eighth thoracic
limbs ; ep epipod of the eighth thoracic limb ; LZ phosphorescent organ; S carapace.—After
Sars.

also characterised by the retention of the nauplius eye throughout
life; the possession of peculiar eye-like phosphorescent
organs on the eye-stalk, on the basal joint of the second and
seventh thoracic limbs, and on the ventral side of the first four
abdominal somites; and by hatching as free-swimming nauplii.
The order, which is relatively poor in species, is represented both
in warm and in cold seas (Thysanopus, Euphausia, etc.) ; some
species form an important part of the food of the Whale-bone
Whale.

Order 2. Mysidacea.

This order is divided into two groups, the true Myside and the
Lophogastride, which latter group is confined to great depths, and
comprises many curious and aberrant forms. The following account refers only
to the true Myside.

The general appearance of the Mysidz, as of the Euphausiacea, is
prawn-like. The body is, however, less compressed and more
rounded, and the abdomen does not exhibit the very obvious bend of
the Prawns (and Huphausia). Hach of the thoracic limbs is furnished

PQ
212 Arthropoda. Class 1. Crustacea.

with a swimming ramus, the exopod, but only the first pair possess
epipods.

The first pair of thoracic appendages is modified to form
maxillipeds; the second pair is also different from the rest. The
abdominal appendages, with the exception of the last pair (those of »
the caudal fin) are, in the females always, in the males often, feebly

 

Fig. 173. Boreomysis megalops, one of the Myside, 9. 1, 6 first and sixth abdomina
segments ; 4,—Ag first and second antenne ; ex exopod of the last thoracic appendage ;
H, fifth abdominal appendage ; KX, Kg thoracic appendages, md mandibular palp ; Ot Otolith,
R brood sac, § carapace.—After Sars.

developed. An auditory vesicle is found in the inner ramus
of the last pair of abdominal appendages, it is furnished internally
with a number of hairs supporting a large otolith (the Myside
are the only Crustacea possessing an auditory organ in such a
position). The inner, membranous side of the carapace is provided
with a close vascular network, and acts as a
respiratory organ. The epipod of the first
thoracic limb is situated within the branchial
cavity, and its movements cause a constant current
of water through the chamber. From the inner
sides of the basal joints of some of the thoracic
appendages arise thin, curved lamelle, which
together form a ventral brood-sac (marsupium)
to serve for the protection of the eggs and larve.
The young ones leave the eggs as nauplii with
the three usual pairs of appendages (antenne and
aaa eae mandibles), but are incapable of free movement ;
nauplius, seen they feed on the food yolk derived from the egg,
from below (en- and only leave the brood-pouch when they have
larged). a,, do first :
and second antennz, @cquired the general appearance of the adult.
md ‘mandible—Orig. Some Myside are found in the open sea,
others are littoral: the genus Mysis, for example,
lives on the coasts of Northern Europe; it is a transparent feebly
pigmented animal occurring in shoals.

 
Sub-Class 2. Malacostraca. Order 3. Cumacea. 213

Order 3. Cumacea.

The animals of this order are indeed related to those foregoing,
but they do not possess the same prawn-like appearance, and are
somewhat aberrant in many respects. The dermal skeleton is hard
and brittle. The carapace is so small that it only covers the
anterior part of the thorax, whilst the five hindmost thoracic
segments are bare.* The lateral eyes are sessile, small,
usually fused into one; the antenna has no exopod. Of the
thoracic appendages some have a swimming ramus,
and others have not. The first is a maxilliped, and, just as
in the Myside, it is the only one which bears an epipod, which is
here provided with a large lamellate gill; the second joint of the
maxilliped is furnished with hooks, so that it can be fastened to

 

Fig. 175. Diastylis neapolitana, 4 Cumacean. V and VIII, fifth and eighth thoracic
segments ; 1, 2, 7 first, second, and seventh abdominal segments; ez exopod of a thoracic
foot; H, sixth abdominal appendage; K,, Kg fourth and eighth thoracic appendages ;
o eye, S carapace.—After Sars.

its fellow. The second thoracic legs also differ from the succeeding
ones (as in the Myside), the thoracic feet are, moreover—especially
is this the case with the last pair—more adapted for walking than
those of the Myside and Euphauside. The abdomen is long, thin,
straight, and very movable. Of the abdominal appendages, the
female exhibits only the last, which are backwardly directed,
slender, and not lamellate, and incapable of acting as a caudal fin ;
the males usually possess the other appendages also. The females
are furnished with a brood-pouch, formed by the union of lamellate
appendages of the thoracic feet just as in the female Mysis. The
young ones hatch as non-motile nauplii, like those of the last
mentioned order; when they leave the marsupium they are like
the adult, but they are still without the last pair of thoracic legs,
which are developed later (see Isopoda).

The Cumacea are small animals which live on the sea-bottom at
some depth. They are met with on British coasts.

 

* Among the Myside, too, the carapace has not coalesced with these five segments,
but extends over the greater part of them (the last two segments are alone
uncovered dorsally).
214 Arthropoda, Class 1. Crustacea.

Order 4. Isopoda.

The body is dorso-ventrally compressed, enclosed in a hard,
often brittle, dermal skeleton ; the abdomen is short, at most with six
segments, for the last (seventh) is absent. Of the remaining segments
the terminal one is usually large: owing to fusion there often appear
to be fewer than six. The carapace is absent; the eyes
(lateral) are sessile, the exopod of the second antenna is
usually wanting. The first thoracic segment is fused with the head,
but the remaining seven are free, movable, and well
developed. The first thoracic appendage is modified as a maxilli-
ped; its inner edge is usually provided with hooks, by means of
which it may be coupled with its fellow. The other seven pairs of

 

Fig. 176. 1 Aega; 1—3 Cymothoa, dorsal and ventral. JI and VII second andeighth
thoracic segments ; 1, 2, 6 first, second, and sixth abdominal segments; H, sixth abdominal
leg; Ky, K, etc. second, fourth, etc. thoracic limbs; R plate of brood-pouch.—After
H. Milne Edwards.

thoracic feet are powerful ambulatory appendages, without
exopod and without epipod. The abdominal appendages are pecu-
liar in having the inner ramus of some of their number modified as
a gill; this ramus is membranous, and provided with a delicate, close
capillary net-work ; as a rule, there are no other respiratory organs.
The Isopoda possess a marsupium under the thorax, formed of
the lamellate appendages of the basal joints of the thoracic limbs,
as in the Myside; the young ones leave the egg as non-motile
nauplii, with three pairs of stumpy appendages; or they may be
Sub-Class 2. Malacostraca. Order 4, Isopoda. 215

destitute of limbs; when they leave the brood-pouch they usually
possess the general form of the perfect animal, but they still lack
the last pair of thoracic legs.

Some of the Isopods are marine, some fresh-water, and others
terrestrial (in damp places). They are essentially adapted for walk-
ing or for running, but some swim by means of the abdominal

appendages. Many are parasitic.

1. In the North Sea live, for example, several species of Idothea, relatively
elongate animals, with the last pair of abdominal appendages modified to form
a valve-like operculum, covering over the others. One species of this genus
(I. tricuspidata), which lives on the shore among the sea-weed, is characterised
by exhibiting many different colour variations (speckled in different ways).
Further, the small Gribble (Limnoria terebrans), which gnaws holes in the
wood-work of harbours, etc., and is sometimes very destructive.

2. The flat, long-legged Asellus (Asellus aquaticus) is common in fresh-
water lakes amongst decaying vegetation.

3. Many species of Oniscide are terrestrial (e.g., genus Oniscus). They are
characterised by the rudimentary first antenna, and by the very minute terminal
segment of the abdomen. In addition to the usual arrangement of gills, some
possess a kind of lung; the outer lamina of some of the abdominal appendages
encloses a branching cavity, with a slit-like aperture, which has undoubtedly a
respiratory function. The Oniscide are light-avoiding animals, of insignificant
colour; some (Armadillidium) can roll themselves up like some of the Myriapods,
to which they have a superficial resemblance.

4, The numerous parasitic Isopods live principally upon Fish and Crustacea.
They offer a gradation in adaption to a parasitic life, similar to that in the

 

Fig. 177. 1 Cepon elegans, a Bopyride from the branchial cavity of a Crab, 2 (the male
3 is fixed to the base of the abdomen). Dorsal view. 2—8 Portunion Kossmanni, ¢
(from the right) and 9 (from the left), an Entoniscide, which is parasitic in a Crab;
& enlarged much more than ?.

II—VIII thoracic segments, 1—6 abdominal segments, 3’ lateral process of the third
abdominal segment (these processes light, the abdominal appendages dark), C head (+
first thoracic segment), Ca abdomen, H,, H;, Hg first, fifth, sixth abdominal appendages,
R marsupial lamelle.—After Giard and Bonnier.
216 Arthropoda. Class 1. Crustacea.

parasitic Copepoda. The genus Aega, for example (Fig. 176, 1), which comprises
blood-suckers living on the skin of Fish, is only slightly modified; the second, third,
and fourth thoracic legs are indeed provided with hooks, and adapted for pro-
hension, but the animal is able to move freely about, and is furnished with large
eyes ; sexual dimorphism is not pronounced. More adapted to the parasitic life
is the clumsy Cymothoa,* related to Aega (Fig. 176, 2-3), with or without small
eyes, with seven pairs of hook-hearing appendages; living in the mouth and gill-
cavity of Fish. Still more modified are the Bopyridae (eg., Bopyrus),
parasitic in the gill-cavity of Prawns and other Decapoda; the females are
symmetrical, without eyes, and with tiny hook-bearing appendages (Fig. 177, 1);
the segments of the wide thorax are immovably united: the males possess a
more normal Isopod form, but they are of a very small size (dwarf males), and

fixed to the abdomen of the female. The females of the Hntoniscide
(Entoniscus, etc., Fig. 177, 2-3), parasitic in certain Crustacea are almost, or
entirely apodous, and altogether very remarkable in form; the pigmy males
are relatively normal in structure, although somewhat reduced in size. The
larvee of the parasitic Isopoda always exhibit a normal isopod form, and are
free-swimming.

5. The Tanaide (the genera Tanais, Apseudes, etc.), form a small
division of the Isopoda, which differs in several respects from the foregoing, and
approaches the Myside and Cumacea. The organisms belonging here have only
six free thoracic segments, for the first two of these (not the first only, as in most
Isopods) are fused with the head. There is a small carapace, united

 

Fig. 178. Apseudes Latreillei, 2, 3, 4, 8 second, third, etc. thoracic appendages ;
A,—Ay first and second antenne ; ew exopod of the second thoracic appendage; H, sixth
abdominal appendage; o eye.—After Sars.

dorsally with the two segments, which are fused on to the head, whilst its lateral
part is free, and just as in the Myside, its inner membranous surface has a
respiratory function. Below the carapace, on each side, is the soft epipod
of the first thoracic appendage, which keeps up a current of water just as
in the latter. The eyes are on short, fixed stalks, clearly marked off from
the rest of the head. The exopod of the second antenna is sometimes present.
The second and third thoracic feet, of which the first pair is modified

 

* An interesting observation has been made for Cymothoa and a few other parasitic
Isopoda; unlike all other Malacostraca, they are hermaphrodite. During
youth the individuals function for a time as males; the female genitalia are only
developed later, when the male organs atrophy.
Sub-Class 2. Malacostraca. Order 4. Isopoda. 217

to form the chele, are often provided with rudimentary, but distinct,
exopods. The abdominal appendages do not serve as gills.
They occur on all European coasts,

Order 5. Amphipoda.

The Amphipoda are like the Isopoda in many respects ; there is
no carapace, the eyes are sessile, there are seven free thoracic
segments; the first thoracic appendages are maxillipeds, the others
are ambulatory, consisting merely of endopod, etc. An important
difference is that the abdominal appendages do not act as gills,
but the organs of respiration are peculiar, lamellate, membranous
processes of the inner side of the basal joint of some of the thoracic
legs.* The exoskeleton is usually not so hard as in the Isopoda.

 

Fig. 179. An Amphipod nearly related to Gammarus (somewhat enlarged). A,—A,
first and second antenne, 1 maxilliped, 2, 3 second and third thoracic feet, @ brood-pouch,
g gill, H3, Hy, Hg third, fourth, and sixth abdominal feet.—After Sars.

The abdomen is seven-jointed (the terminal segment small). The
maxillipeds are fused at their bases. Some of the walking legs,
chiefly the anterior ones, are also prehensile organs, since the terminal
joint can move upon the penultimate. The basal joint of these
appendages (especially of the first four pairs) is laminate and
directed downwards, which gives the body a compressed appearance
(the thorax itself is not compressed, Fig. 180). The first three pairs
of abdominal limbs are powerful swimming legs, the
three hindmost, on the other hand are smaller, somewhat stiff and
turned back. The Amphipoda have just sucha marsupium as have
the Isopoda, but the larva do not leave the eggs until all the limbs
are developed.

 

* This process cannot be taken as representing the epipod, which arises from the
outer side of the basal joint (see Fig. 180).
218

Arthropoda. Class 1. Crustacea.

Most of the members of this group are active organisms swimming
and hopping about in the water; the former is effected by means of

 

the first three pair of abdominal limbs, the
latter by the flexure of the caudal appendage.
Other forms (see below) are less energetic.
Numerous species and individuals are marine,
occurring on the shore as well as in deeper
water, and in the open sea. A few are fresh-
water ; some live among seaweed of the shore,
or far from the coast on damp ground. A
few are parasitic.

Fig. 180. Transverse section of the thorax of Gam-
marus (enlarged). 1, 2 first and second joints of a leg, and
brood pouch; 6 one of its constituent lamine, g gill,
h heart, o ovary, t gut, 1 liver, n ventral ganglion.—Adapted
from Sars.

1. The Fresh-water Shrimp (Gammarus) may be taken as a repre-
sentative of the typical Amphipod. Eyes fairly small, second and third thoracic

 

Fig. 181.

1—2 Caprella acutifrons, from above and from the left. 3 Cyamus

mysticeti, from above. III—VIII Thoracic segments. A, firstantenne. Ca Rudimentary
abdomen. g gill, K,—K, second—eighth thoracic legs.—1, 2 after Mayer, 3 after Liitken

(adapted).
Sub-Class 2. Malacostraca. Order 5. Amphipoda. 219

feet prehensile. Marine and fresh water: G. locusta, common on all Huropean
coasts; the nearly allied G. fluviatilis frequent in fresh water; the blind
G. (Niphargus) puteanus in springs.

2. Many genera of the Hyperidz are found in the open sea; these are
transparent Amphipods, with colossal eyes; some of them live in jelly fish and
other transparent forms; in the common Aurelia, for instance, the species
Hyperia galba is often found.

3. The genus Caprella, Skeleton Shrimp, characterised by rudimentary
abdomen (reduced to a blunt process, and destitute of appendages), and the
possession of only six free thoracic segments (two of them being fused with the
head). The body is long and thin, almost filiform; the second and third pairs
of thoracic limbs form chele (the first pair of these is small, the other large) ; of
the fourth and fifth pairs only the basal joint and the gill lamella are present
(gills are absent from all the other appendages), the sixth to the eighth are true
ambulatory legs. Caprella is marine, and wanders about slowly over seaweeds
and colonial animals. Cyamus is nearly allied; its six free thoracic segments
are each produced on either side into a long process bearing a leg at the tip, so
that the body is flat and isopodan in appearance; in other respects very like
Caprella. Parasitic on the skin of the Whale, devouring its thick epidermis.

Order 6. Decapoda.

The well-developed carapace is fused with all eight thoracic
segments dorsally, but the lateral parts are free (branchiostegites),
and between them and the trunk there is, on either side, a roomy
cavity, the branchial chamber. The eyes are placed
on movable stalks, the antennules have as a rule (excepting
in Crabs) a lamellate, unjointed exopod. Of the thoracic legs
(see Fig. 170, p. 208), the three anterior pairs are modified to
form maxillipeds; the first pair is much flattened, as are also the
first and second maxille; the other two pairs differ but little from
the rest of the thoracic feet, but are usually much shorter. The
remaining five pairs of thoracic appendages are known as ambu-
latory legs. They are essentially walking legs, but one or
more pairs (usually the front pair) are generally modified to form
claws (chele), the penultimate joint being elongated into a strong
process, against which the terminal joint bites. Such are used either
exclusively, or in addition to their normal function, as prehensile
organs. The maxillipeds have, as a rule, a very well-developed,
slender exopod, which is almost always absent from the ambula-
tory legs; an epipod may be present on both sets of thoracic
limbs, and always projects into the gill-cavity. The gills arise
from the epipods, from the sides of the thorax, and from the arthro-
dial membranes, between the thorax and its appendages. Each
consists of an axis with two series of lamelle, or with a large
number of filaments ; of such gills there are from five to twenty odd
on each side. They are situate in the branchial cavity, into which
water usually enters at the base of the thoracic feet, flows over the
220 Arthropoda. Class 1. Crustacea.

gills, and leaves it again at its anterior end; the current is kept up
by the constant vibrations of the large flat setose exopod of the
second maxille. The last (sixth) pair of abdominal legs, when
present, forms, with the terminal (seventh) segment, the broad
caudal fin; of the other five pairs, the first and second of the male
are, as a rule, partially or completely modified to form copulatory
organs. The development of the abdomen is, in other respects,
very different in the different forms.

ee

 

Fig. 182. Palemon. 1—7 abdominal segments, A,—A,, first and second antenne,
A,ew exopod of the latter; H;, H, third and sixth abdominal appendages; K, third
thoracic appendage (= third maxilliped) ; K, fourth thoracic appendage (= first ambulatory
limb) ; Kg eighth thoracic appendage (= 5th ambulatory); S carapace.—After H. Milne
Edwards.

The Decapoda are furnished with a pair of auditory organs,
situated in the basal joint of the antennules. In many (Prawns,
Lobsters, and others), each is a depression of the skin which opens on to.
the upper surface of the joint, and encloses peculiar jointed setz (auditory
hairs), which are set in motion by the sound waves. Resting upon
the auditory hairs are grains of sand and the like, which are intro-
duced into the sac by the animal, and take the place of otoliths. In
others the vesicle is closed, but contains similar auditory hairs, and
sometimes an otolith secreted by its walls; in yet other forms with
a closed sac (Crabs), the otolith is wanting. In the simplest cases of all
(certain Prawns) there is no depression at the spot corresponding with
the auditory sac of other forms, but there is a number of auditory
Sub-Class 2. Malacostraca. Order 6. Decapoda. 221

hairs* upon the skin. Such free auditory hairs may occur
also in Crustacea possessing the vesicle, and may be present in other
regions (e.g., upon the abdomen). The Decapoda possess a very
strong gizzard, often with large, calcareous, masticatory teeth. In
depressions in its side walls there are often to be found two rounded
calcareous masses, which are absorbed before a moult (“ crabs’ eyes,”
or gastroliths). There isa large antennary gland, the “green
gland,” opening by a small aperture in the base of the antenna.

As the eggs leave the oviducts they are firmly fixed on to the
swimmerets of the female, which never possesses a marsupium, but
in spite of this almost always carries the eggs about; not, how-
ever, the larve, or these only for a short time. The young ones
almost always undergo a com-
plete metamorphosis. Only
in a small number does a
free-swimming nauplius
represent the first stage, e.g.,
in the Prawn, Penwus (see
below), and in some allied
forms. The majority are
further developed before
hatching, having attained
the so-called zowa stage,t
in which condition the animal
moves by the appendages
which later form the maxil-
lipeds, and at this stage
are not connected with feed-
ing, but are solely natatory
in function. Swimming is
chiefly effected by the exo-
pods of these appendages.
The zoza displays further,
the nauplius eye and lateral
eyes, the two pairs of antenne
as ae ae a = 183. Zowa of a Prawn enlarged.

3 o—Kf,; second and third mavsillipeds.—After
but the ambulatory legs, and Claus.
the swimmerets, have not yet
appeared, or are only incipient, and the posterior part of the thorax,
and theabdomen, are not so pronounced as they become later. Theforms,
which hatch as nauplii, pass through the zoea stage later. In many

 

 

* This is also the case in the Euphauside.

+ Decapoda at this stage were formerly regarded as adult organisms, and described
under the generic name of Zowa; hence the name for these larve.
222 Arthropoda. Class 1. Crustacea.

Decapods the zovea is followed by the “mysis-stage” (so-called
on account of its resemblance to the perfect Mysis), in which the
development of the ambulatory limbs is completed, and the
animals swim actively by means of their exopods and the posterior
maxillipeds; the swimmerets are still absent, or only imperfectly
developed. This stage is followed by the praw n-stage, in which the
exopods of the ambulatory limbs atrophy, whilst the swimmerets
are strongly developed, and form powerful swimming-organs, enabling
the animal, which in this, as well as the foregoing stages, is entirely or
almost transparent, to move actively about in the surface waters. For
one division of the Decapoda, the Natantia, the prawn-stage corresponds
with the adult; they remain throughout life in this state, the

 

Fig. 184. Mysis-stage of Penevs (enlarged). I—V the five ambulatory limbs
with long exopods and short endopods.—After Claus.

swimmerets being the permanent natatory-organs; in another
division, the Reptantia, the prawn-stage is not permanent, but after
some time, the abdominal limbs, with the exception of the sixth pair,
atrophy ; they cease to be swimming-organs, the animal becomes
opaque, and the power of swimming is lost.

Some Decapoda (e.g., the Lobster), hatch at the mysis-stage, and consequently
only pass through this and the prawn-stage. Others (e.g., Crabs) pass direct
from the Zoea to the prawn, missing out the mysis-stage, i.e. at no
time are the ambulatory limbs provided with swimming rami.

The Decapoda constitute a very large group, including the largest
forms among the Malacostraca. Most of the species are marine; a
comparatively small number (Cray-fish, some Prawns) are fresh-

water; whilst a few are terrestrial.

Sub-Order 1. Natantia (Prawns).

The skeleton of the Prawns is not very hard, it is merely
horny ; the animal is transparent or semi-transparent ; the body is
compressed (Fig. 182) ; the abdomen strong and curved, and
Sub-Class 2. Malacostraca. Order.6. Decapoda. 223

incapable of being straightened out. The carapace has a strong,
compressed and serrated frontal spine (rostrum). On the second
antenna is a large lamellar exopod ; there are long flexible flagella on
both pairs of antenne, and large eyes borne upon long stalks. The
ambulatory appendages are thin and feeble; the third
maxillipeds long and leg-like. The abdominal limbs, with
powerful peduncle and long laminz, are strong swimming-organs ;
from the inner edge of the inner ramus springs an appendage with
small hooks at the tip, by means of which each swimmeret is coupled
with its fellow, so that the two move incompany. Prawns are for the
most part active swimmers, propelling themselves forwards through
the water by paddling-movements of the first five pairs of swim-
merets, whilst they are able to shoot backwards by powerful flexure of
the posterior portion of the abdomen and the caudal fin.

Some forms differ from the rest in that‘they take up their abode in Sponges,

etc., and are more or less modified in correlation with this semi-parasitism; the
eyes and antenne having become small, and so on.
Of the very numerous, mostly small, forms, only a few are quoted :
1. Peneus is a genus of large Prawns reaching the size of a Cray-fish,
which live only in warm seas (two species in the Mediterranean). They are
compressed and elongate, with small claws on the first three pairs of ambulatory

legs. Penzus, and some of its relatives, are distinguished from all other
Decapods in that they hatch as nauplii (Fig. 153).

2, The genus, Palemon, is of frequent occurrence in European seas (Fig.
182). In this form only the first two pairs of ambulatory limbs are chelate; it
hatches, like the great majority of Prawns, as a zoxa, and later, passes
through a mysis-stage. Several species of this genus are edible, as also the
Common Shrimp (Crangon vulgaris), which differs in many respects from Palemon,
and lives in the sand on the coasts of Great Britain.

Sub-Order 2. Reptantia.

The skeleton is generally thick, hard, and much calcified; the
animal opaque and coloured. The body is round or flat; the
abdomen, in some cases, very powerful and muscular, in others.
very degenerate; the rostrum short, not compressed. The
exopod of the second antenna is short or absent; the antennary
flagella usually feeble, the eyes small, with shorter stalks
than in Prawns. The second to the fifth pairs of ambulatory
legs are more or less powerful walking organs; the first pair
is, as a rule, much stronger than the rest, provided with large claws.
and held up during locomotion ; the third maxilliped is short and not
leg-like. The abdominal legs are never swimming organs in the
perfect animal, with the exception of the sixth pair: they have, in the
female, the primary function of carrying the eggs, whilst in the male
the first two pairs serve as copulatory organs; the three following
are of little importance in the males, and consequently are often
absent or degenerate. The sixth pair forms, in some, a well-
224, Arthropoda. Class 1. Crustacea.

developed caudal fin, in others (Crabs), which have a feeble abdomen, it
is entirely wanting. The adult Reptantia move on the sea-bottom by
means of their strong ambulatory legs (which in Prawns are of quite
subordinate locomotor importance), whilst they are incapable of
actually swimming ;* those which have a muscular abdomen can shoot
backwards like the Prawns.

1. The Lobster (Homarus vulgaris) is a large dark-blue Crustacean with
a very muscular tail and wide fin; second antenna, with exopod, and a long,
powerful flagellum. The first pair of ambulatory legs are strong chele, of which

one (sometimes the right, sometimes the left) is the larger, and is beset with more
knob-like teeth than the other; the second and third pairs are also chelate, but

Fig. 185. Fig. 186.

 

GOSS

Fig. 185. Quite a young Lobster-larva (Mysis-stage), dorsal and lateral views,
enlarged.—After Sars.
Fig. 186.—Newly hatched Cray-fish, enlarged—After Huxley.

are no stronger than the remaining two pairs. The Lobster does not pass
through a zoea stage, but at hatching is already provided with all the
ambulatory limbs, which, like the third maxilliped, bear swimming rami, by
means of which the almost transparent animal rows itself through the water.
The mysis-stage is followed by a prawn-stage, from which, finally, the perfect
animal emerges. Common on European coasts, especially on the coast of Norway;
an allied species is caught in quantities on the coast of North America.

2. The Cray-fish (Astacus fluviatilis) is in most respects like the
Lobster (three pairs of chele, etc.), but differs from it, among other things, in
that the body is smaller and somewhat thicker, that the large chele of the first
pair are equal, and that the feeler of the second antenna is shorter and weaker.
With reference to the development, the Oray-fish behaves very differently,
not only from the Lobster, but also from almost all Decapods. When the young
one leaves the egg it is already in most respects like the adult animal; in
particular, all the ambulatory legs are nearly as well developed, and have no

 

* Some Crabs, in which the last pair of thoracic appendages is much flattened,
execute by their means a sort of swimming movement.
Sub-Class 2. Malacostraca. Order 6. Decapoda. 225

exopods. Of the abdominal limbs the last pair, however, is not yet present. It
is evident from this that the Cray-fish does not pass through a mysis-stage, nor,
so far as is known, through a prawn-stage. The young ones cling for a time
to the abdominal limbs of the parent.

3. The Craw-fish (Palinurus) are large, spiny Crustaceans, which
resemble Lobsters in most respects, although they differ in that none of the
ambulatory limbs (all of which are of about equal strength) are modified as chele;
the second antenna is provided with a very long and strong flagellum. A species
living on English coasts, P. vulgaris, can produce a creaking sound by

tS

or
v

 

Fig. 187. Phyllozoma, slightly enlarged. The four best developed pairs of appendages
are: third maxilliped, first to third ambulatory legs.

rubbing the peduncle of the second antenna against a median projection of
the head. Scyllarus is nearly-related to the Craw-fish, but differs from it in that
the long multiarticulate feeler is replaced by a short, broad, unsegmented plate.
The larva in both genera is very singular, hatching in the mysis-stage,
although the hinder thoracic feet are not yet present; it is called Phyllosoma,
and is chiefly characterised by its leaf-like and flattened form; the carapace,
through which the branching of the liver may be seen, is a flat plate, and does
not cover over the whole thorax; the latter is a roundish disc, at whose edge the
long locomotor limbs (the third maxillipeds and the ambulatory legs with small
‘swimming-rami) are articulated. The abdomen is an unimportant appendage.

4. The Hermit-crabs (Pagurus) are characterised by having the abdomen
modified into a large membranous sac with hardly any muscles, but almost
entirely occupied by the large liver, and the gonads, which have moved down
from the thorax. The abdomen is concealed in an empty gastropod shell which the
animal carries about; it is always asymmetrical; its ventral side is
entirely membranous, but dorsally there are traces of the tergal portions of
the abdominal segments, as thin plates separated by large soft-skinned inter-
spaces: the last two segments alone are somewhat harder; the penultimate
bears a small pair of abdominal appendages by which, with the help of the
seventh segment, the animal keeps in the shell. Of the other abdominal append-
ages only those of the left side are present (the first pair is often
entirely wanting). The ambulatory legs are also peculiar; the first pair are
strong chele, the second and third simple walking legs, the fourth and fifth are

Q
226 Arthropoda. Class 1, Crustacea.

very small and assist in holding the animal in its shell; the fifth have also the
work of cleaning out the gill-cavity* into which they are introduced from behind.
The Hermit-crabs hatch as zo# and pass directly from this condition to the
prawn-state, in which they swim about by means of the abdominal appendages;
the abdomen at this time is muscular and perfectly symmetrical. At the con-
clusion of this stage the animal seeks a small empty shell which it later exchanges
for others of a gradually increasing size. Hermit-crabs are found in all seas.
P. Bernhardus lives in the North Sea and in the English Channel, and lodges in
the shell of the Whelk.

5. Crabs (Brachywra) are a division of the Decapoda, consisting of
many genera, and very rich in species, forming, as it were, the summit of
this sub-order; for on the one hand the perfection of the posterior
thoracic legs as ambulatory organs, on the other, the reduction
of the abdomen, here reaches its climax. The body is broad (the
cephalothorax frequently wider than long), the abdomen is much flattened,
short, and feeble, and is turned up on the ventral side of the thorax; in the
female it is wider than in the male. The antenne are short, the second antenna,
has no exopod; the last maxillipeds are laminate, covering the other mouth parts
like folding-doors. Only the first pair of ambulatory appendages are chelate,
the rest are strong walking legs. The sixth pair of abdominal legs (those
of the caudal fin) are wanting; in the female the eggs are carried by the
second to the fifth (the first pair is, as a rule, missing); in the male, only the first
and second pairs, which form the copulatory organs, are present. The Crabs
hatch as zowe with the first and second maxillipeds developed as natatory
organs (the third pair is not developed in this way); the crab-zowa is often
characterised by having long spines on its short carapace. There is no mysis-
stage, but the young one passes through a prawn-stage (the so-called megalops),
in which it is in most respects like the adult animal, but the more powerful
abdomen is backwardly directed, and is provided with appendages which act
as swimmerets. Finally the abdomen and its appendages become reduced, the

 

Fig. 188. A, zowa of a Crab, B—C prawn-stage from above and from the side,
enlarged (in C the walking legs are for the most part cut off). A,, A, first and second
antenne, 1—3 maxillipeds, H, last abdominal leg, T dorsal spine.—After Rathke.

 

* In some Prawns (probably many) the first, somewhat feeble, ambulatory legs are
put to the same use. They are pushed into the cavity from in front and below, and
brush over the gills to clean them.
Sub-Class 2. Malacostraca. Order 6. Decapoda. 227

tail doubles up, and the Crab is henceforth a creeping animal. The Shore Crab
(Carcinas menas) occurs in great numbers on the coasts of England and other
parts of Europe. Like other Crabs it is an active, crafty, predaceous animal,
which makes strenuous resistance when attacked. The large and broad, thick-
shelled form, Black-clawed Crab or Punger (Cancer pagurus), also
lives on English coasts in deeper water.

Order 7. Stomatopoda.

The Stomatopoda are Malacostraca with large stalked eyes,
with a carapace, and with a powerful abdomen. The
carapace is, however, relatively small, and the four posterior thoracic
segments are free, movable, strongly built, and not covered by it.
The abdomen is strong, almost straight, with the usual six pairs of
appendages, of which the hindmost forms the tail fin, together with
the seventh segment, whilst those of the other five pairs are all strong,

 

Fig. 189. Squilla. VIII eighth thoracic segment ; 1, 7 first and seventh abdominal
segments; A,, A, antenne; g gill; H,, H, first and sixth abdominal appendages ;
K,, Kg second and eighth thoracic appendages ; 0 eye; S carapace.—After Liitken.

swimming feet, coupled together, and bearing on their outer rami,
large, branching gills. Of the eight pairs of thoracic limbs, the
first five are all prehensile ; the last joint can be folded back upon
the penultimate. The second pair is specially well developed. The
last three pairs of thoracic appendages are feeble walking legs. The
Stomatopoda do not carry their eggs about. The young animal passes
through a metamorphosis, the first stages of which are not
accurately known. The more advanced larvae are delicate and
transparent, but otherwise very like the adult ; they are characteristic
members of the pelagic fauna.

The group, which includes relatively few and fairly uniform
members, belongs to warm seas. A noteworthy species, Squalla
mantis, is found on English coasts.

Class 2. Myriapoda (Centipedes).

The multiarticulate, usually elongate body, is covered with a
chitinous skin, which may, or may not, be calcified. The head is
clearly defined, and is provided on either side with a group of
ocelli, more rarely with true lateral compound eyes; it bears also

Q 2
228 Arthropoda.

one pair of antenne, which are simply filiform or feebly clavate,
and the usual three pairs of jaws, or two only. The body is
not divided further into regions, but consists usually of a large
number of essentially similar segments, which bear short cylindrical
legs, each composed of a simple series of joints (6—7).

The Myriapoda resemble the Insecta in their internal structure.
The alimentary canal is generally straight, and is divided
into a narrow cesophagus, a cylindrical mesenteron, and a narrower
hind-gut ; salivary glands open close to the mouth; at the junction
of the mesenteron and hind-gut, open two (or more rarely four)
Malpighian tubules (ef. Insecta) ; the anus is in the terminal
segment. There is no liver. The heart is a long dorsal tube
with paired lateral slits, through which blood enters; it gives off an
anterior, and a series of lateral arteries, whilst the
blood also flows through the various slits and spaces
of the body. The Myriapods, like Insects, have a
system of air-carrying tubes,a tracheal system,
which ramifies throughout the body, and opens by
stigmata, generally at the base of certain of the
pairs of legs. The nervous system is of the
usual arthropod type ; the ventral nerve ganglia are
generally equally developed in correspondence with
the uniform development of the body segments. The
ovaries or testes are always fused into an
unpaired organ, which in the Chilopoda, opens

 

Fig. 190. Digestive tract of Lithobius (Chilopoda). a anus,
h hind-gut, m mesenteron, s salivary gland, w Malpighian tubule,
v cesophagus.—After Plateau.

Fig. 191. Newly-hatched larva of a Diplopod.—After Metsch-
nikoff.

 

ventrally at the end of the body, in front of the anus, by a single
aperture; whilst in the Diplopoda, a pair of genital pores lies between
the second and third pairs of legs, and thus far forward on the
ventral side of the body. In this last group, the limbs of the
seventh segment are usually modified in the males, to form copulatory
Class 2. Myriapoda. 229

organs, which are filled before coitus, with spermatozoa, and inserted
in the genital aperture of the female.*

In most Diplopoda (e.g. Iulus) the eggs are laid in masses, covered by a small
mound, perforated at its apex, and formed of earth and a glandular secretion.
Glomeris, however, surrounds each egg with a spherical covering of earth.

The Diplopoda and some Chilopoda have, when they leave the
egg, fewer segments and appendages than later; in the former, the
newly-hatched young ones have usually only three pairs of legs (that
of Iulus is quite apodous) ; in the latter there are seven pairs. Other
Scolopendridz have the full number on hatching.

The Centipedes constitute a relatively small division. They are,
without exception, terrestrial ; inhabiting damp, shady places, under

leaves, in the soil, etc.

In most points they are so nearly allied with the large class following, the
Insects, that it might be thought best to incorporate them with that group.
They are, however, regarded here as a distinct class, because they offer certain
peculiarities which would mark them off as very aberrant Insects, and interfere
with the clear definition of that group.

Order 1. Chilopoda (Scolopendras).

The head is flat and bears three pairs of jaws, of which the first
maxille have very often undergone concrescence in the mid-line.
The basal joint of the second
maxilla also coalesces with its
fellow of the other side, whilst the
other joints form a palp. The rest
of the body, which often consists
of a very large number of segments,
is flattened dorso-ventrally ; the legs
arise far apart from one another
(Fig. 193 A), from the soft, lateral
portions of the segment, one pair
to each segment. The foremost
pair of legs is very different
from the rest; it is very strongly
developed, and forms a pair of stout,
hook-like organs, at the tip of which
is the opening of a poison gland Fig. 192. Head and anterior trunk
(the Pp oison-claw s) . The last segmentsofa Scolopendra, from below.
pair alsa 48 usually somewhat antenna (the greater part cut off),

; j k first maxilla (the greater part covered),
modified, being longer than the  / palp of second maxilla, p' first pair of

legs, b its fused basal joints, p? second
others and turned back. It Dade Of legs. —Orie.
has already been remarked that
the genital organs open at the posterior end.

 

 

*In one genus of the Diplopoda, Glomeris, the terminal pair of legs forms the
copulatory organs.
230 Arthropoda.

The Scolopendras, of which several species are luminous, are
active and predaceous, killing their food with the poison-claws. In
temperate zones the few species are relatively small; they attain to an
important size in the Tropics (to a foot long). In England, there
are several species of Lithobius, and others.

Order 2. Chilognatha or Diplopoda.

Only two pairs of jaws, generally termed mandibles and maxzille,
are present. The structure of the body is very peculiar: whilst the
two legs of each pair arise far apart in the Chilopoda, separated by a
wide sternal plate, here they are articulated near to one another on
the ventral side. Moreover, most segments bear two pairs of legs,
indicating that each segment has really arisen by the fusion of two.
The four segments following the head have not, however, more than
one pair of legs each; indeed, one of them is altogether apodous.
The shape of the segments varies: in some (Fig. 198 B) they are

A B. Cc D
Fig. 193. Transverse sections: A Of a Chilopod. B—D Of different Diplopoda
(B Iulus, D Glomeris), F lateral outgrowth.—Orig.

cylindrical ; in others each segment is a compressed cylinder, but
possesses a short lateral process, which gives the body a more flattened
appearance (Fig. 193 C) ; in others, again, the body is itself flattened,
convex dorsally and concave ventrally (Fig. 198 D). The legs,
which are feeble and thin, are turned out; they are all essentially
alike (excepting those which serve in the males as copulatory organs,
see above). It has already been stated that the genital apertures are
anterior and that copulatory limbs are present.

The members of this order are sluggish animals, which live on
decaying or soft vegetable matter or animal remains. When dis-
turbed, they roll themselves together.

Occurring in England are Iulus, with an elongate, cylindrical body; and

Glomeris, with short, semi-cylindrical body, composed of so few segments that
it bears a superficial resemblance to Armadillidiwm.
Class 3. Insecta. 231

Class 3. Insecta.

The insectan body is divided into three sections: head, thorax,
and abdomen. The head is sharply marked off from the thorax,
and is usually freely movable: on each side there is a sessile com-
pound eye consisting of a very large number (twenty to many
thousands) of small ocelli, covered externally by convex facets ;
each of these is usually hexagonal in shape, and corresponds in
position with an ocellus. In many Insects the eyes occupy a very
large part of the head (in many Diptera, for instance, almost the
whole of it). In form they are most frequently circular, but often
kidney-shaped, and so on. Occasionally the compound eyes are

1 2 3 4 5 6 7

 

Fig. 194. Antenne of various Insects. 1 bristle-like, 2 filiform, 3 moniliform,
4 pectinate, 5—7 clavate (7 with laminate club).—After Judeich and Nitsche.

replaced by small groups of ocelli* (Collembola), or by a single
ocellus on each side (Fleas and Lice). In many Insects, there
are from one to three ocelli on the middle of the head, in addition
to the compound eyest (cf., the nauplius eye of Crustacea). From the
head, arises a pair of antenne or feelers, which either
consist of a limited number of well-developed joints, or of a large
number of very short ones. The form of the antenne is very varied ;
at the simplest, they are filiform or bristle-like, but they are some-
times moniliform (much. constricted at the joints), pectinate (the
joints being produced on one or on both sides into processes), or
clavate (club-shaped).

The head also bears the mouth and the surrounding mouth-
parts, which vary greatly in form, though all may be referred
to a common type. The simplest and most primitive condition is
presented by the biting mouth-parts of the Orthoptera, the
Coleoptera, the Neuroptera, and the Hymenoptera, where an upper

 

* Only the adult Insect is referred to here ; for larval arrangements, see below.
+ Absent from nearly all Beetles.
232 Arthropoda.

lip and three pairs of jaws occur. The upper lip (labrum)
is a broad, movable unpaired plate, situated in front of the
mouth. Behind the labrum are the mandibles, which are very

 

B
-

 

Fig. 195. Diagrams of the mouth parts of various Insects. A An Insect with biting
mouth-parts, Ba Butterfly, C a Fly. 1 labrum, 2 mandible, 3 first maxilla.

c cardo, s stipes, f’ galea, f” lacinia, p, palp. 4 Second maxilla=labium. c¢ submentum,
s mentum, f’glossa, f” paraglossa of ligula, p palp, f proboscis of B and C.— Orig.

1 2 3

much like those of the Crustacea in general structure, though as
the palp is always wanting, each consists of a single, unsegmented_
piece, which can be moved inwards (towards the middle line) or
outwards; its inner surface forms a cutting edge, and at its base
Class 3. Insecta. 233

there is a grooved or tuberculate grinding denticle, the latter being
best developed in the herbivorous forms, whilst the former is more
prominent in predaceous Insects. The first maxilla usually con-
sists of six to eight joints, of which the basal joint (cardo) is short, the
second (stipes) large, and produced into two long lobes, the inner
(galea) being usually fringed with stiff setee along its outer edge; the
outer (Jacinia), in several forms, consisting of two joints. Sometimes
only a single lobe is present. The rest of the maxilla, which
usually consists of four to six jomts, forms a curved palp. The first
maxille are prehensile and gustatory in function, whilst the mandibles.
are masticatory ; sometimes, however, the former also assist in masti-
cation. The second maxille are similar to the first, but are
distinguished by the fact that the two cardines are always fused to
form a single plate (mentum); the stipes, too, are more or less
completely fused, and the lobes are often considerably modified as
compared with those of the first maxille; the palps are like those of
the first maxille, but never consist of more than four joints. The
second maxilla are usually spoken of as the labium, their palps
as the labial palps, the lobes as glosse and paraglosse. The
labium is, of course, not comparable with the lower lip of the
Crustacea; it is, like the mandible and first maxille, a pair of limbs,
and corresponds with the second maxille of the Crustacea, whilst
the lower lip of the latter is a membranous fold which is not repre-
sented in the Insects. The labium here forms the posterior, as the
labrum forms the anterior, boundary of the mouth.

In Insects with sucking mouth-parts the same elements
occur, but modified in different ways in accordance with the change
of function. Inthe Lepidoptera, the labrum is simply a short,

 

Fig. 196. Diagrammatic transverse section of the proboscis of: A Butterfly,
B Rhynchota, C Tabanas (Gad-fiy), D Musca (another of the Diptera in which
mandibles and first maxille are wanting). sw sucking tube through which the fluid passes
to the mouth; s salivary tube, o labrum, m mandibles, k first maxille, u labium, h hypo-
pharynx.—Orig.

broad plate with no special significance; the mandibles are rudi-
mentary or absent. The first maxille on the other hand are
well-developed ; each possesses only a single lobe, which is elongate
and gutter-like, forming, with its fellow of the other side, a long
tube, open at the end; this tube is the sucking apparatus, the
234 Arthropoda,

proboscis of the butterfly. Maxillary palps are present, but
feeble. The unpaired portion of the labium is not well developed,
but the palps are large setigerous lobes, enclosing the proboscis,
which is spirally coiled when not in use, In the Rhynchota the
suctorial tube is formed by the mandibles, which are represented
by two compressed blades without palps ; two grooves run down the
inner surfaces of the blades, which are so fitted together that they
form two tubes, an upper and a lower. The proximal opening of the
lower tube lies close to the opening of the duct of the salivary gland,
and saliva passes down it, to be mixed with the food before it is
sucked up into the mouth through the upper, wider canal. At the
sides of the mandibles lie two other dagger-like organs, the modified
first maxille, pointed like them, and thus adapted to act as
stabbing weapons; their palps are wanting, both pairs of appendages
are inserted in deep pits, and can be protruded or withdrawn. ‘The
labium is characterised by the fusion of the palps, so that the
whole lower lip is an unpaired structure of three or four joints,
hollowed out like a gutter, and forming a sheath surrounding the
mandibles and first maxille. This sheath is open above, but the
opening is simply a slit along most of its length, widening out only
at the base, where it is covered by the triangular labrum. Formerly
the labium of the Rhynchota was regarded as the functional tube, but
it is now known to be simply a case for the sucking tube proper, which
is formed from the mandibles. In the Diptera the relations are as
follows: In the most perfectly developed mouth parts (e.g., in
the Gnat and the Gad-fly [Tabanus]) there is a labium of consider-
able length, much hollowed out on its under surface ; beneath this lie
the flattened, sword-like mandibles, which together with the labrum
form the proboscis. Below the mandibles lies an unpaired, narrow,
flattened piece, the hy popharynx, which arises posteriorly from
the labium ; it is traversed by the salivary tube which opens at its
tip. Next below lie the firsts maxillz, which, like the mandibles,
are long, narrow, blade-like stabbing or cutting organs ; a large palp
arises from the base of each. All these parts are enclosed by a long
furrowed 1a bium, which has no palp, and lke that of the Rhynchota,
only forms a case for the rest of the mouth parts; the maxillary palps
alone are not surrounded by the labium, but project freely at its base.
In other Diptera (e.g., House-flies), the mandibles and first maxille
(with the exception of the basal portions of the latter and their palps)
are wanting ; in this case, the place of the mandibles is supplied by the
hypopharynx, which closes the labial groove below. In the
Hymenoptera most of which possess simple biting mouth parts,
these may, as in the Bees, be both biting and sucking: the mandibles
performing the former, the first maxille and labium together
subserving the latter, function.
Class 3. Insecta. 285

The thorax is composed of three segments: prothorax, meso-
thorax, and metathorax. Usually the last two are immovably
united, the pro-thorax freely articulated. Hach bears a pair of legs,
which are divided into the following parts: coxa, trochanter,
femur, tibia, and tarsus; each of the first four consists of a
single joint only, whilst the tarsus is generally multiarticulate. The
coxa and trochanter are usually short, the femur and tibia long, the
former thicker than the latter; articulating with the lower end of
the tibia there is generally a pair of movable spines (spurs). The
tarsus in many Insects consists of five joints (sometimes of fewer),
and usually bears at its tip two movable hooks, the claws. The
legs are true loco-
motor organs; in
walking, the animal
rests on the lower
side of the tarsus,
which is often hairy ;
the distal end of the
femur is turned out-
wards, that of the
tibia downwards, the
tip of the tarsus out-
wards; in the first

pair of legs the foot aoe ae 1 section cheauel: the thorax of
= . a Beetle (diagrammatic). a! elytra, a? wings, k body-wall;
is forwardly directed, ¢ coxa, t (upper) trochanter, t’ (lower) tibia, ta tarsus, wu
in the last pair back-  claws.— Orig.

wardly. In many

forms the legs, or some of them, have another function besides that
already mentioned. The front pair in the Cockchafer serve not
only for ambulatory purposes but also for digging; in others the
legs are so modified in connection with the secondary office, that
their primitive function is lost. The first pair in the Mole-
cricket, for instance, is only used for digging; the same pair in
Water-scorpions for organs of prehension ; the last pair in the Locust
forms a springing apparatus, whilst in Dytiscus it is pre-eminently
natatory in function.

 

The thorax usually bears two pairs of wing's, which arise dorso-
laterally from the meso- and meta-thorax. Each wing is a large,
laminate, tegumentary outgrowth, which primitively possesses the
same layers as the rest of the skin, 7.e., is covered on each side
with a chitinous layer (cuticle), within which, on each side, is an
epidermal layer, whilst between the two epidermal layers run
tracheew, nerves, etc. When the wing is fully developed, however,
the soft parts disappear, so that it then consists of little else than
two closely apposed chitinous plates. The wings articulate with
236 Arthropoda.

the thorax, and are moved by a muscular apparatus; they are
usually thin transparent plates, in which a network of somewhat
thicker, more firmly chitimised, and darker ribs occur: not in-
frequently they are sparsely or entirely covered with sete (see
the Lepidoptera). The two pairs are often almost identical in form
and size, more frequently, as in certain Libellulide, they differ
somewhat in these respects; sometimes the anterior, sometimes the
posterior, pair is the larger. During flight, they are spread laterally,
but when at rest, they turn somewhat backwards, so as to cover
the abdomen, and the wings of the first pair overlie the second
ones, which are then often folded like a fan.* In correlation with
this, the anterior wings have been modified, in many Insects (Locusts,
Beetles), to form wing-cases, or elytra; they are thicker and
harder, and serve chiefly or exclusively to cover and to protect the
posterior pair during rest, whilst their locomotor importance is
lost; the hind wings, which are usually large, lie beneath them,
folded longitudinally or transversely. The elytra attain their greatest.
development in Beetles (Fig. 197), where they not only protect the
posterior wings most efficiently, but also the dorsal surface of the
abdomen (which is, therefore, softer than the ventral side); for
their inner edges are straight, and fit closely together, and their
outer edges are coincident with the lateral body-wall. It results,
therefore, that in many Beetles, which are apterous, or have rudi-
mentary wings only, well-developed elytra are, nevertheless, present.
Another modification of one pair of wings occurs in the Diptera, where
the hind ones are developed as small club-like appendages
(halteres), the significance of which is not clear, but which are
certainly not organs of flight. In a number of Insects belonging to
various groups, the wings are rudimentary, or altogether absent;
many of these forms are parasitic.

The abdomen, the posterior apodous region of the body, consists.
of ten or fewer segments, which are usually freely articulated, although
occasionally some of them are fused; there is not generally such a
deep constriction between the thorax and abdomen as between the
head and thorax. In each abdominal segment a dorsal and a ventral
plate (tergum and sternum) is usually distinguishable, connected by
softer portions. In some Insects (Mole-cricket, Dragon-fly), the
posterior end of the abdomen bears a pair of jointed or unjointed.
anal cerci, which turn backwards, but otherwise there are no.
abdominal limbs or limb-like appendages.T

 

* But occasionally the first pair of wings are folded when at rest.

+ In some genera belonging to the Thy sanura, a group which consists entirely
of apterous Insects with biting mouth parts, there are, on the ventral side of the
abdominal segments, small paired appendages, which are not jointed, but which are
quite like limbs in their mode of origin. It must be mentioned, too, that in many
insectan embryos, definite rudiments of limbs bud out from the first abdominal.
segments (sometimes from several), but these atrophy before hatching.
Olass 3. Insecta. 237

The chitinous cuticle in Insects is not calcified, but, not-
withstanding this, it frequently attains a very considerable firmness,
and is often of great thickness; below, there is an epidermis often
called hypodermis, usually a single layer of cells. In connection
with the skin, there are frequently skin-glands; of these may

bg A Oh a LRAT

* oes ,

.
“&

 

 

 

 

 

Fig. 198. Diagram of the principal anatomical points in an Insect. 1—3 first and
third pairs of legs cut away. a anus, c cerebral ganglion, ch mesenteron, ¢ proctodzum,
g genital aperture, h heart, k crop, m mouth, n ventral ganglion, sp salivary gland,
wu Malpighian tubule, e ovary.—Orig.

be mentioned, the stink-glands on the ventral side of the thorax, in
the Hemiptera; the anal-glands of the Carabide; the wax-glands
of Apidz and of Cocci. Some are gland-cells, some true glands;
sometimes they are represented by simple, flat, thickened portions of
the epidermis (wax glands of Bees).

The nervous system is characterised by the great size to
which the cerebral ganglion often attains. The most anterior of the
ventral series, the sub-
oesophageal, is situated
in the head, like the cerebral a B
ganglion, and gives off
branches to the mouth-parts.
This is succeeded by three
single or paired ganglia, one
for each thoracic segment,
and lastly, by a series of
abdominal ganglia. Often,
however, some of these fuse ;
the second and third thoracics
may, for instance; the pos-
terior abdominals also, or the
second and third thoracics

Fig. 199. Nervous system of an
ant (A), a cockchafer (B), and a blue-
bottle (C). h cerebral ganglion, u
sub-cesophageal ganglion, 1—3 the
three thoracic ganglia, w,—a 3 ab-
dominal ganglia, w fused abdominal
ganglia, sp passage for the ceso-
phagus.—After Brandt.

 
238 Arthropoda.

and all the abdominal ganglia may unite to form a single mass,
which, in extreme cases, includes also the first thoracic ganglion.

Sense organs. Olfactory organs occur as short, delicate,
thin-walled hairs, which receive filiform processes from sense-cells
lying beneath ihrem: (Fig. 18); they occur on the antenne, often situated
in pits. Auditory organs probably occur in the majority of In-
sects, since there is direct proof that many can perceive sounds; and
indirectly, it is probable that, since many can produce noises, they can
also perceive them ; these organs are, however, at present only known
with certainty for quite a few forms. In the Grasshoppers, there is
on the side of the first abdominal segment a thin membrane (the
“tympanum,” a specially developed portion of the skin), stretched at
the bottom of a depression. Beneath the membrane there are peculiar
cells, each inclosing a delicate pin-like body, and connected with a
nerve fibre. It is believed that the membrane is caused to vibrate by
sound waves, and that this reacts on the cells described ; the sound
is intensified by a tracheal bladder, which lies close to the tympanum,
and serves as a resonator. Auditory organs of a somewhat different
structure occur in the Locusts on the tibie of the first pair of legs.
In other cases there are cells like those described above, but without
tympanum or resonator, and it is supposed that these may also be
regarded as simple auditory apparatus. For eyes, the account on
p. 281, and the description of the structure of Arthropod eyes given
in the General Part, may be consulted.

Alimentary canal. In Insects with sucking mouth-parts,
strong muscles run from the buccal cavity to the inner side of the
head: the cavity of the mouth is enlarged by their contraction, and
thus the fluid into which the proboscis is dipped is drawn in. One or
more pairs of salivary
glands open into the mouth.
The rest of the alimentary
canal, which may be
straight or looped, is made
up of the cesophagus, the
mesenteron, and the proc-

Fig. 200. Diagrammatic longitudinal section of todeum. The ces oph agus

the head of an insect with sucking mouth-parts. jg usually narrow in front,
su sucking tube, m buccal cavity, mu muscles which nl : :
widen the latter, @ cesophagus.—Orig. but swells out behind into

a crop, which is either
a sivule dilation or a special pouch-like appendage connected with
the rest of the cesophagus by a narrow duct; this is the case in
many suctorial Insects. The crop serves as a reservoir for the food.
Occasionally the terminal part of the cesophagus is particularly
muscular, provided with hard parts on the imner surface, and
serves as a gizzard. The mesenteron is the essential digestive
portion, though the secretion of the salivary glands assists in this

 
Class 3. Insecta. 239

connection ; it is also the absorptive region; it is saccular,
and sometimes separated into several sections. The epithelium
of the alimentary canal secretes the digestive fluid; sometimes
small evaginations, which project externally from the alimentary
canal as warts or papille, may have this function; there is never
a specialised liver. The proctodeum is usually divided into an
anterior narrower and a posterior wider portion ; the anus is situated

Fig. 201.

   

 

       

   

l)

   

|

 
  
  

 

 

 

E--4----2 Fig. 201. Diagram of the
; chief trunks of the tracheal
system of an Insect; the
central nervous system is also
shown. a antenna, o eye, st’
anterior stigma, J longitudinal
trunk.—After Kolbe.

Fig. 202. Portion of a

¢ trachea from a Gall-fly

\ larva (somewhat diagrammatic).
z @ cell of the wall.—Orig.

BAA A

 

on the terminal segment. The Malpighian tubules, delicate
unbranched, brightly-coloured (white, yellow, brown, or green) tubes,
open into the proctodzum at its junction with the mesenteron. There
is usually only a small number, four to six, when they reach a con-
siderable length ; in the Hymenoptera and some of the Orthoptera,
however, there is a much larger number of shorter tubes. These
constitute the excretory apparatus,
240 Arthropoda.

The respiratory organs are represented by a system of
tubes containing air, the trachez, which branch over the whole
body, winding about among the organs and communicating with the
exterior by the stigmata, which, like the whole system, are
symmetrically disposed. There are at most ten pairs of stigmata, one
pair on the mesothorax, one on the metathorax, and one on each of the
eight anterior abdominal segments, where they lie between the sterna
and terga; there are no stigmata on the head or prothorax.* The
stigmata are usually slit-like apertures, which are frequently provided
with marginal sete (Fig. 203 s), overlying the opening and pre-
venting the entrance of foreign bodies; the same end may be
attained in other ways. A short transverse stem usually runs in-

A B Fig. 203. Apparatus for
closing the trachea of a Beetle
(diagrammatic). A the appa-
ratus by itself, opened. B The
trachea with the apparatus
closed. The apparatus consists
of three chitinous pieces which
surround the trachea like a
ring; the piece (b) is as long as
the two others together; one
of these (a) sends out a process
for the attachment of a muscle
(m), which takes its origin from
the third piece (c). When the
‘muscle contracts, a and ¢ are pushed against b, and the trachea is clamped between
the three pieces. s stigma, t trachea.—Orig.

 

wards from the stigma to open into one of the main tracheal trunks,
a varying number of which traverse the whole length of the animal,
connected with each other by several transverse vessels and giving
-off numerous branches which anastomose over the whole body.
Occasionally the longitudinal trunks are absent, and the trachea
arising from each stigma breaks up directly into a number of branches
which are entirely independent of the rest. Some of the trachez
may be dilated to form vesicles, which vary in size, but are some-
times quite large. These vesicles have no actual respiratory signifi-
cance, but serve to decrease the specific gravity of the body, and are
thus of importance in flight; in other words the tracheal system is
not only respiratory, but in many forms is also aérostatic. All
the tracheze are covered by a thin chitinous cuticle which, in the
coarser tubes (but not in the vesicular dilations), is supported by a
delicate spiral thickening. Respiration is effected by move-
ments of the abdomen; by its contraction part of the air is forced out
from the trachez, and when it expands again a fresh supply enters.

 

* The position of some of the stigmata may often be changed, those belonging to
the mesothorax may lie between the prothorax and mesothorax (Fig. 201) or even,
.as in caterpillars, on the prothoyax.
Class 3. Insecta. 241

In order that the air shall have access to the most distant branches
of the system, the trachea arising from the stigma, possesses a
peculiar apparatus by which it may be completely closed; when this
is effected, and the abdomen contracts, air cannot escape from the
stigma, and is, therefore, driven into the ultimate branches and into
the vesicles. When the abdomen is relaxed, and the closing
apparatus opened, a new supply of air streams in; then by the
contraction of the abdomen, and the simultaneous closing of the
stigma, this fresh supply is driven again into the finest branches and
vesicles. By repetition of these processes, the tracheal system is
filled with air, and the vesicles completely expanded; this is of
especial significance in its function as erostatic apparatus; and
before flight, individuals may be seen expanding with air thus
pumped in.

The trachee arise as epidermal invaginations, which branch freely, and
unite to form the large longitudinal trunks; they secrete a cuticle just as does
the epidermis. The apertures of the invaginations form the stigmata. At an
ecdysis, the cuticle of the trachew is also renewed, the old cuticle being thrown
out through the stigmata.

In a number of aquatic insectan larvee (Dragon-flies, May-flies, Neuroptera),
the tracheal system is closed, 1«.e. without open stigmata. The oxygen s
‘obtained endosmotically from the water by means of the “tracheal gills,”
membranous appendages, with large surfaces, and containing a close trachea!
network.

In addition to the respiratory and aérostatic function, the tracheal system of
many Insects is also concerned in the production of sounds. Thin
membranous folds often occur within the trachez, close to the stigmata; they
are set in vibration by the air entering the trachee, and thus produce a sound
(buzzing of Flies and of Cockchafers). The noises made by Insects are also
brought about in many other ways. Flies, Bees, and Gnats, all of which produce
sounds by the vibration of the tracheal folds, can also make humming noises by
the rapid movements of the wings. Others rub various parts of the surface
of the body against one another. The male Grasshopper, for instance, rubs a
dentate ridge of the tibia of the last leg against the elytron of the same
‘side; others again, strike some part of the body against a foreign object (the
Fiddler-beetles for instance, knock their heads against the wall of the
passages they have gnawed in wood, and thus cause the well-known ticking
sound).

Some Insects are luminous in the dark. The light proceeds from large
cells situated within the body beneath transparent arez of the skin, and depends
‘upon the oxidation of certain substances present in the cells, which are therefore
surrounded by a close tracheal network.

The vascular system is but little developed, a circum-
stance correlated with the high specialisation of the respiratory
apparatus. Since air is carried direct to all parts of the body, the
importance of the blood as oxygen-carrier is necessarily limited. In
the dorsal region of the abdomen there is a tubular heart, closed
behind, open in front, and constricted into a series of chambers
corresponding with the abdominal segments; each chamber is fur-
nished with a pair of ostia provided with valves, and there are

B
242 Arthropoda.

also valves at the limits of the chambers. The heart, as in other

Arthropods, lies in a spacious cavity, the pericardium, which is
bounded above by the dorsal wall of the

abdomen, below by a perforate plate of con-
nective tissue interlaced with muscle fibres.
The heart and a tubular extension of its
anterior end, the aorta, are the only vessels,
the blood circulates in spaces between the
organs in a fairly regular current. After

Fig. 205.

      

 

yo
Soa

  
 

=

  

Ly

(2

  

TZ
4

   

ws

AN
mJ

CS

  
    

   
   
   

 
 
 

 
 
 
   

  
    

 

     
   

   
 

Fig. 204. RS

is traversing the body it enters the peri-

\ Eo} cardium, and from this, in consequence of the

Be dilatation of the heart and the opening of the

0: ostia, into the heart itself, whence it is again

A BRS driven out through the aorta into the sinuses
. of the body.

r fo He Genital organs. The female, as in

Een other Arthropoda, possesses a pair of ovaries.

” s _Hach consists of a varying number of tubules:

, ‘¢  (evarioles) which usually extend like fingers

Danis

from the anterior end of the oviduct. Each
ovariole is surrounded by a thin membrane
and is immature anteriorly, consisting of
small homogeneous cells; further back there
are larger cells, young ova, lying in the
middle of the tube, and surrounded by
smaller cells, which provide them with
nutriment and also secrete the shell

Fig. 204. Portion of the
heart of an Insect, dia-
grammatic. 7 constriction
between two chambers, k
valves, s venous ostia.—
Orig.

Fig. 205. Ovariole of
an Insect, diagrammatic.
@ young ovum, @ mature
ovum, s shell, + empty lower
extremity of the ovarian
tubule (an egg has just
escaped).—Orig.

(chorion), for the fully developed egg. The
mature ova occupy the posterior ends of the
ovarioles, and pass thence into the oviduct ;
when an egg passes into the latter the cor-
responding portion of the ovarian tubule:
shrinks, and thus the egg next in front is
brought nearer to the duct. The two
oviducts unite to form an unpaired
portion, the vagina,* which opens ventral

to the anus, either freely on the surface
or into a cloaca, an invagination occurring at the hinder end of
the body. There is usually an evagination of the vagina which
serves aS a receptaculum seminis and one, or a pair of
accessory glands which secrete either a sticky fluid to attach the ova
to foreign bodies, or the mucus surrounding them (e.g., in Insects
which lay their eggs in water) ; sometimes there is also an evagination

*In some few Insects (Thysanura, Ephemera), the vagina is wanting, and both
ducts open direct on the postero-ventral surface of the body (c¢f., Crustacea).
Class 3. Insecta. 243

of the vagina to form the bursa copulatrix, into which the penis
of the male is inserted in copulation.* Not infrequently there is at the
female aperture, an ovipositor (Locusts), consisting of compli-
cated knife-like or dagger-shaped lamine, or a sting (Hymenoptera),
or the last abdominal segments, which then are thin and elongate, and

Fig. 206. Fig. 207.

 

Fig. 206. Female genital organs ofthe Cockchafer. On the right, the ovarioles
are lying together in the natural position; on the left they are separated, and two are
cut away. g vagina, k glands which open into the receptacula, | oviduct, o segments of
the ovarioles containing almost ripe ova, o’ regions of the same, containing immature ova,
p bursa copulatrix, r anterior, r’, r’ posterior buds of the ovarian tubules, s glands,
sg receptacula ovorum.—Orig.

Fig. 207. Male genital organs of the same (penis not drawn). b vesicula
seminalis, g vas deferens, k glandular appendages, r widened region of the duct of the
same, ¢ testis, consisting of six seminal pouches.—Orig.

may be telescoped, serve in this capacity (Diptera and others). The
chorion is often very hard, frequently covered with a delicate and
regular sculpturing, and always provided with one or more openings,
the micropyles, through which the spermatozoa may enter.
The outer form of the eggs varies: it may be spherical, oval, discoid,
rough, stalked, etc.

The male genitalia are for the most part a repetition of those of
the female. There is a pair of testes, each consisting of several
long seminal tubes or shorter seminal pouches, situated at the
end of the vas deferens. The two vasa deferentia unite to form a

 

*In the Lepidoptera the bursa copulatrix is peculiar, in that it is not as in other
forms, a simple evagination of the vagina, but is a tube, open at both ends, one end
leading into the vagina, the other on to the surface of the body; so that here the
female genital organs have two pores, that into the bursa serving for copulation,
whilst the vaginal opening proper allows only of the escape of the eggs.

R 2
244 Arthropoda.

single duct,* which opens in a similar position to the vagina of the
female. Each of the vasa deferentia widens posteriorly to form a
vesicula seminalis. Special glandular appendages frequently
open into these ducts, or into their common portion. There is a more
or less complicated copulatory organ, an evagination of the
body-wall through which the terminal portion of the seminal duct is
continued, and capable of partial or complete retraction when not
in use; in many, it may possess hard chitinous portions, and lies
hidden within the cloaca, from which it may be protruded during

copulation.

A fairly marked sexual dimorphism occurs very often in Insecta,
due largely to the different parts played by the male and female in repro-
duction. Frequently the males possess apparatus which is wanting in the
females, or certain portions of the body are specially developed; for example,
the large mandibles of the Stag-beetle, the huge eyes of the male Honey-bee,
the well-developed antenne of the male Cock-chafers and many Butterflies,
the broad front feet of male Water-beetles; such developments, if they are
in any way explicable, are attributable to the struggles carried on by the
males for the possession of the female (Stag-beetle); or, in the case of special
prominence of sensory organs, they result from the needs of the male in seeking
for the less active female, or the parts serve as organs of retention during copula-
tion (Water-beetles). More rarely some portion of the body of the female is

specially developed; in the female

1 2 3 Nut-weevil (Balaninus nucum), the
proboscis is longer than in the male,
as it is used to gnaw through the
young nuts, in which the eggs are
deposited. Not infrequently the
sexes differ in size, the pre-
ponderence being usually on the
side of the female; this may be

Fig. 208. Females of three allied species of * .
Geometrida (1 Hibernia progemmaria, 2 H. due simply to the great bulk of

aurantiaria, 3 H. defoliaria), to show the suc. the ova. There are very often,
cessive stages in the degeneration of the wings— also, differences in colour and

After Ratzeburg. form, but these, like many plastic

differences (e.g., those between the
male and female Oryctes), are, as a rule, not apparently capable of explanation.
As already mentioned, the male is usually more active than the female,
and in correlation with this, sexual dimorphism may be carried very far,
various parts of the body of the female may be considerably modified or
atrophied. In not a few Lepidoptera for instance, the wings of the female are
considerably shortened, so that they have become useless as organs of flight, or
they are quite rudimentary, or have vanished altogether ; in some forms, indeed,
degeneration goes still further, the legs are feeble, or are not developed, so that
the animal sinks into a maggot-like state, which is as different from the male as
possible. The converse, when the female has greater activity, may also occur,
although more rarely; Fig. 209 for instance, shows a species of small Gall-
fly (Blastophaga grossorum), which lives as a larva in the tiny seeds of the

  

 

* This duct (like the vagina) may be absent (Ephemera, and uw few others), and
the vasa deferentia then open separately.
vy

Class 3. Insecta. 245

fig; the male never leaves the fruit in which it has passed its early existence, and
in consequence of this is clumsy and apterous, whilst the female must seek for
young figs in which to deposit the eggs, and is active and winged.

 

Fig. 209. Blastophaga grossorum. A Q (2). B & (4!).—After P. Mayer.

Many species of Insects are remarkable, in that a large number of
individuals remain sterile throughout life, and thus take no part in
the propagation of the species; these individuals possess, as a rule,
distinct rudiments of sexual organs, which, however, never develop
far enough to form fertile genital products (or they are deficient in
some other way, so that the individuals cannot take any part in
reproduction) ; such sterile individuals are always, in some Insects
(Bees and Ants), incompletely developed females ; in others (Termites),
both males and females. The occurrence of such sterile individuals
depends upon the fact that these Insects are social, and form larger or
smaller colonies; it is an expression of a division of labour within
the colonies, the care of the brood, etc., being relegated to the sterile
individuals, whilst the reproductive faculty is exercised by relatively
few, which, however, produce an enormous number of offspring (cf.,
the division of labour in Hydroid colonies).

Parthenogenesis has been shown to occur in many Insects.
In many cases, it is an exceptional occurrence ; the female of the
silkworm moth for instance (Bombya mort), if unfertilised, can still
lay eggs, most of which atrophy, though they may develop in the
usual way. The same thing is known for many other Lepidoptera.
In other cases, parthenogenesis is of more regular occurrence ;
in some Insects it is the rule, males appearmg only occasionally;
so in certain Lepidoptera, e.g., Psyche heliz, in which the female is
apterous and maggot-like, whilst the male is normal in form: or
the males may appear with the females, but in small numbers, and
apparently without, as a rule, copulating, as in Cynips rose, a well-
known rose Gall-fly: or, as in some of the Saw-flies and Gall-flies,
reproduction is apparently exclusively parthenogenetic, in which
case the species consists entirely of females ; or in certain generations
only, reproduction may be exclusively parthenogenetic. Another
246 Arthropoda.

regular occurrence of parthenogenesis is found in many social
Hymenoptera where the males originate from unfertilised, the females
from fertilised, ova. Not infrequently, parthenogenetic reproduction
alternates regularly with the usual sexual mode, so that there is
heterogony; either each unisexual generation alternates with
a true sexual one (Gall-flies), or the sexual is followed by several
parthenogenetic generations (Aphides). Usually, the parthenogenetic
generations differ somewhat from the other; sometimes, if there
are several such successive generations, these also differ from each
other.

In some of the Diptera (Cecidomyia) eggs may arise prematurely in the
larva, and develop direct without fertilisation into viviparous larve, the parent
larva dies, whilst the young ones grow, and either give rise in the same way to
another generation or become perfect insects. Thus parthenogenesis may occur
precociously, when there is otherwise no sexual reproduction. This process is
known as pedogenesis.

Insects are usually oviparous, but the parent is most solicitous in
ensuring that the newly-hatched larve shall be well supplied with
nourishment; this is generally accomplished by laying the eggs in
places where suitable food is present, but occasionally by the collec-
tion of a supply of food where the eggs are deposited (certain Dung-
beetles, Sand-wasps) ; more rarely the parental instinct is more
highly evolved, and the female brings a fresh supply of food each day
to the brood. In a few Insects the eggs are only laid when the
embryo is about to be hatched; others are viviparous, embryonic
development being completed within the oviduct. A peculiar
arrangement is met with in the Forest-flies (Hippobosca), in which not
only is the egg completely developed within the oviduct, but the larva
remains there for some time feeding upon the secretion of certain
glandular appendages.

The majority of Insects on leaving the egg do not resemble the
adult, but undergoa metamorphosis; only in a few cases, e.g.,
Lice and various other apterous forms, are the changes so insignificant
that it is impossible to speak of a true metamorphosis. Meta-
morphosis may be more or less thorough ; two chief types may, there-
fore, be distinguished, complete or holometabolous, and in-
complete or hemimetabolous.

In hemimetabolous Insects (Orthoptera, Rhynchota) the newly-
hatched larva differs chiefly from the adult or imago only in that it
is apterous. In other respects the differences are slight, the
number of joints in the antenne may be fewer, the head relatively
larger than in the adult and so on. The transition from the first larval
stage to the adult occurs gradually ; wings begin to appear,* small at
first, but increasing at each ecdysis, until after the last moult they are
fully formed and functional: at the same time the other portions of

 

* Such larve, possessed of incipient wings, are often termed nymphs.
Class 3. Insecta. 247

the body have attained their definite form. In some hemimetabolous
Insects the differences between larva and adult are, however,
much greater, attributable to essential differences in habits. These
distinctions are very well marked in the Libellulide and the
Ephemeride, which are aquatic during larval life, but terrestrial as
adults; in the larve of these forms the tracheal system is closed,
and they breathe by means of tracheal gills (see p. 241); in the adult,
on the contrary, the usual relations obtain. Considerable differences
may also be noticed in several other points, e.g., in the dispositions
of the mouth-parts of the Libellulids: these differences hold
throughout the whole larval life until the last ecdysis, but, just as in
other forms, the wings develop gradually. At the last ecdysis all the
special larval characters disappear as at one stroke, although, as a
matter of fact, the changes have gone on gradually within the cuticle
during the last phases. When the wings are completely developed,
and functional, the insect moults no more, and growth ceases.

The Ephemeride, which, as already mentioned, are aquatic as larve, are peculiar
in that the insect on leaving the water has feeble, though functional, wings, but
immediately after, the final ecdysis occurs and it appears with completely
developed wings. At this stage, in which it is capable of flight, but not
perfectly developed, it has been termed a sub-imago.

Holometabolous Insects (Coleoptera, Hymenoptera, Lepi-
doptera, and Diptera) differ from the hemimetabolous forms, in that
there isa complete dissimilarity between the larva and the adult;
in that the larval stages exhibit, externally, no gradual approach
to the adult form; lastly, and this is the most important characteristic
of a complete metamorphosis, in that between the larval and imaginal
stages, a special period of pupation intervenes, during which the
animal does not feed and is generally quiescent. During this resting-
stage a series of significant changes occurs in the body.

The larva of a holometabolous insect is distinguished from the
imago in the following points: the small ocelli situated medianly on
the head are absent, and the compound eyes are replaced by a group
of ocelli on each side of the head (these may, however, be altogether
wanting): the antenne are almost always short, and consist of
a small number of joints: the mouth-parts constitute a biting
apparatus, even if those of the adult are suctorial, and if the latter
has biting mouth-parts they are always essentially different in form:
the legs are short, with fewer joints, and more uniform than in the
adult; they have usually only a single claw: wings are altogether
absent: the thorax is small, the abdomen large: the cuticle,
except over the head, is generally more delicate than in the
imago: the nervous system usually consists of a number of separate
ganglia even in those forms in which it is later much concentrated
(cf. Fig. 210) ; the alimentary canal is often very different, and this
to a striking degree where the larval habits differ much from those
248 Arthropoda.

of the adult (e.g., in Lepidoptera, Fig. 210).* In many the salivary
glands are modified to form a pair of silk glands, whose secre-
tion forms a protective covering for the larva, either alone, or with
the assistance of foreign particles which it binds together. This
covering or cocoon is usually developed for protection during
pupation.1 The tracheal system also exhibits striking deviations, for

 

Fig. 210. Larva, pupa, and imago of a Lepidopteran (Sphinx) with various
organs in situ; somewhat diagrammatic. All three figures of the same magnification.
b legs, c brain, ch mesenteron, e proctodeum, h heart, + sub-cesophageal ganglion, k head,
@ cesophagus, s proboscis, f testis. 1—3 three thoracic ganglia. J, II, III, IV the four
first abdominal ganglia.— Adapted from Newport.

some of the stigmata which are open in the imago are closed in the
larva, or conversely; the structure of the stigmata may also vary.
In the body-cavity of the larva there are large masses of fat, the fat
bodies, which are to a great extent used up during metamorphosis,
if they are not entirely absent from the adult. The genital organs
are only incipient. ;

During larval life, the Insect moults repeatedly, and gradually
increases in size, usually without an actual change of form. When

 

* In certain insectan larve (e.g., the larve of Bees and Ant-lions) a peculiar condition
obtains, in that the proctodeum into which the Malpighian tubules open, is not in
connection with the mesenteron; but both the posterior end of the latter and the
anterior end of the former are closed. Only after metamorphosis do the two
communicate.

+ In the larve of the Ant-lions (and presumably in their allies) the secretion from
which the silk of the pupa-case is constructed, is probably formed in some of the
Malpighian tubules (¢f., the analogous conditions of some Fish where the kidneys
secrete mucous threads).
Class 3. Insecta. 249:

the definite size is attained, however, it appears suddenly to change
its external form in a number of essential points, and then after
moulting, it appears asa pupa. The pupa displays externally, a
very close approach to the imaginal form; the wings are fairly
prominent, and the compound eyes are also present, the legs and
antennz resemble those of the adult insect, and this is also the case
with the mouth-parts, but all the appendages are still somewhat:
indefinite in outline, and not distinctly jointed; like the incipient
limbs in the body of an embryo, they are not yet functional; they
lie immovable upon the body, the general form of which is very like
that of the imago (relative development of thorax and abdomen, etc.) ;.
internally, however, the pupa at the moment of the last ecdysis,
is still in reality in the larval condition. The important changes.
which have occurred in external structure, have not, of course, taken
place so suddenly as they appear to have done; they have all been
ready at the close of larval life; the wings may, for instance, have
developed long before this as invaginations of the body-wall, and
when the larval skin is thrown off for the last time, they are
evaginated, and appear as outgrowths of the body; the legs have
already grown within their chitinous cases, and may be seen there,
folded up, towards the end of larval life. At this time, the insect is
inert, and remains as quiet as possible, for the modifications have
made its appendages, to a certain extent, functionless. The changes
are continued during the pupal stage; the external form of the body
alters underneath the protective cuticle, and within, the larval organs
are gradually modified into those of the adult (see Fig. 210), so that
there is a considerable difference in the organs at the beginning and
end of pupation,although apparently the animal remains unaltered
during the whole time. Many pup are quiescent; true locomotion
occurs in only a few forms (e.g., Gnat-pup, which are aquatic, and
must move about on the surface of the water to obtain air), and then
is brought about by movements of the abdomen, which also effect
respiration. When all the changes are at last concluded, the
chitinous pupa-case splits, and the imago emerges. When all
the appendages are unfolded, and the cuticle has hardened, the
development is in all essentials complete. The adult never
moults, it does not grow, or at least, not more than the chitinous
coat will permit.

The changes which are undergone at the close of the larval period and during
pupation, are not limited to a transformation of the parts already present, but in
addition, there is a general destruction and dissolution of many larval organs ; in
some Insects, only a small portion of the larva actually forms the imago, whilst a
larger part undergoes dissolution, and serves for the nourishment of the rest.
The amceboid blood-corpuscles of the larva play an important part in this process,
in that they feed upon and digest the tissues as they die, passing on the nourish-

ment thus obtained to the actively growing organs of the animal. This process of
dissolution is carried to very great lengths in a large number of Diptera, whose
250 Arthropoda.

larve differ extraordinarily from the adult, both in appearance and in habits (e.g.,
the Blow-flies, and many others).

The larve of metabolous Insects occur in a number of
different forms. Of special modifications may be mentioned the
peculiar type occurring in the Lepidoptera and Tenthredinidz, specially
characterised by the presence, on the ventral side of the cylindrical
body, of a number of so-called prolegs, small muscular dermal
outgrowths which play an important part
in locomotion; such larve are termed
caterpillars or (in the Tenthredinide)
pseudo-caterpillars. In a number
of larve of different orders, legs are
altogether wanting; such forms,
termed maggots, are usually pale, blind
creatures, which are concealed in plants as
parasites, etc.; occasionally they are more
motile (aquatic forms, e.g., Gnat-larvee).
The most degenerate occur among the
Blow-flies and other Diptera; these
oe pete ny eg (mogsot) are termed he adless maggots, since
B Pupa of the same from even the head is not clearly developed,
Below) saben Batzeburg: whilst it is very striking in many other

forms in consequence of its thick brown
cuticle. Many larve, which lead a hidden existence in the earth,
or in cavities in wood, etc., without being maggots, 7.e., without loss
of the thoracic limbs, have habits like those of most maggots; they
are blind, or almost so, with short or feeble legs, and soft, fat bodies.

In most holometabolous Insects, the body hardly changes at all during the
whole of larval life. In others, however, it has a different appearance at different
ages, a fact which is chiefly connected with changed habits. This is the case in
Meloé and its allies; the larve hatch as small active organisms, provided with
legs. They crawl about on plants,and attach themselves to certain Bees, in whose
dwellings, after changing into maggot-like creatures, they pass the rest of their
larval life, feeding upon the stores of their hosts.

The pupe do not exhibit such a variety of form as the larvae,
but here, too, there are many which are interesting to note. The
Lepidoptera, for instance, have a peculiar pupa (chrysalis), in which
the antenne, mouth-parts, legs, and wings, lie close on to the body,
and are hard and chitinous all over their outer surfaces, as is also the
rest of the body where it is not covered by these parts; the limbs,
therefore, appear to adhere to the sides of the body, and it looks as
if they were all covered by a coat of varnish. In many of the
Diptera, the chitinous cuticle is considerably hardened previous to
pupation, and when it is later separated from the subjacent soft parts,
it is not as usual thrown off, but remains as a hard capsule round
the thin-skinned pupa, and thus serves as a protective case; it is
only thrown off when the imago breaks through (coarctate pupa).

 
Class 3. Insecta. 251

The larva, in many species, forms a similar protective case, a cocoon,
before pupating; it consists of spun silk, or of various particles
bound together, and the pupa rests within it (Lepidoptera, Hymenop-
tera, some Coleoptera, and others).

In some of the Hymenoptera, w peculiar developmental stage is inserted
between the larva and the pupa, or more correctly, there are two pupal stages.
The fully-grown larva first forms a so-called pseudopupa, with just the
beginnings of wings, legs, and so on, and not till later does the insect enter the
true pupal stage, characterised by larger wings and legs, and generally by a
greater approximation to the imago.

The metamorphosis is indicative of a definite division of
labour in the animal’s life. The larval period is a time for
eating and growing; the life of the imago is devoted to
reproduction; at metamorphosis growth terminates, the animal
usually takes no more food than is necessary to make good the loss
due to vital activity, and it dies when reproduction has been accom-
plished. In some cases, the distinction between the two periods is
especially well-marked; the imago takes no food at all, and thus
the vegetative and reproductive periods are sharply separated.
Even if the perfect form does feed, the fact that it no longer under-
goes ecdyses shows that growth has really ceased. The few Insects
(Termites) in which the abdomen of the adult increases enormously
in size, in consequence of the great development of the ovary, form
in some sort an exception to this.

According to this account the metamorphosis of Insects is in marked contrast
to that of other animals, e.g., of the Crustacea, in which the conclusion of larval
life, and the cessation of growth are by no means coincident.

The duration of life in Insecta is almost always sharply
limited and fairly short. Usually the whole life (including the
phases of egg, larva, pupa, and imago) lasts only one year; in nota
few, e.g., in the Aphides it is a matter of months only: in others
(many larger forms) it continues during several, usually a fairly
definite number, of years (the Cockchafer, for instance, lives usually
for four years). Of the whole life the larger part is generally
occupied by the larval stage, and only a small portion by the
imaginal period; the imago usually lives for only quite a short time,
not infrequently for a few days or even for a few hours. Only
exceptionally do instances of longevity (several years) in the imago
occur. Honey bees have been observed to live five years in captivity,
Ants even twelve.

The members of this group afford an emphatically terrestrial
type of animal, their organisation being closely adapted to life on land
or in the air. Not a few are, however, modified, so that they may live
for their whole life, or during the larval stage only, in fresh water.
Few are marine, e.g., larvee of flies which occur in the mud on flat sea-
shores. Some (Coleoptera, Heteroptera and others) live on the coast
at spots which are only dry at ebb-tide, whilst at the flood they are
252 Arthropoda.

covered with water, so that their inhabitants are excluded from the
air for hours together ;* the Halobatide are the only actually marine
forms, and these lead a life on the open sea like that of their near
allies, the Hydrometride, in freshwater.t Various Insects (Pediculide,
Mallophagidee, Pulicide, etc.), live as imagines, or, during the whole
of their life, as parasites on various Vertebrates; others are parasitic
only as larve upon, or in, various other animals, whilst they lead
a free existence as perfect-insects.

The Insecta are richer in species than any other class of animals.
According to one reckoning they make up four-fifths of all species; of
Insects again, one half are Beetles.

A Orthoptera Biting mouth-parts.
tabola { 8 P
Heminetabola Rhynchota Sucking ,, 5
Neuroptera
Coleoptera i Biting ,, 3
Holometabola Hymenoptera
Lepidoptera ‘i .
Diptera SUCKMAG, <2, es

Order 1. Orthoptera.

The Orthoptera are hemimetabolous Insects with biting
mouth-parts. The labium shows more clearly than in other
forms that it has arisen by the fusion of a pair of jaws, the
individual portions of which are usually easily recognisable. The
wings are generally closely veined, but in other respects differ
considerably. Frequently the number of abdominal segments is.
large; the abdomen is usually furnished with two shorter or
longer jointed or unjointed, anal cerci. This order includes very
various forms; of the types given below, numbers one to six have
the front pair of wings modified to form leathery elytra, whilst in
the rest all the wings are similar.

1. Grasshoppers (genus Acridium, and others). The limbs of the last.
pair are long, springing legs with thickened tibia. The front wings form long,
narrow, somewhat thickened elytra, below which lie the broad hind wings folded
up like fans. The prothorax is large, the antenne short and filiform (at most
only twenty-four joints), auditory apparatus (see p. 238) on the first abdominal
segment. The males make a noise by rubbing a dentate ridge of the femur of
the last leg against the elytron. The females have no ovipositor. Various small
species are often met with in great numbers in the fields. Certain species (some
large, others small) are common in warm countries as “migratory Locusts”
(e.g., Acridium migratorium) ; these, after increasing enormously in some locality,
migrate in incredibly large numbers, utterly destroying all vegetation in the
regions through which they pass.

 

* This is also the case with some of the Arachnida (Mites and Pseudoscorpions)
and Scolopendras.

+The Lice parasitic on Seals are also marine.
Class 3. Insecta. Order 1. Orthoptera. 253

2. Locusts (genus Locusta and others) resemble the previous group in
habits, in the structure of the wings and hind legs, etc., but differ in certain other
important characters. The antenne are bristle- Tike, eualy very long, and
always composed of numerous short joints. On the tibie of each of the front
legs there are two auditory organs (whilst there are none on the abdomen), and
the males make sounds by rubbing the basal portion of one elytron, the under-
side of which is provided with a transversely ridged edge, over a corresponding
portion of the other. The female possesses a long, sabre-like ovipositor. One
of the best known species is the large bright green Locusta viridissima, which,
like Locusts in general, devours both animal and vegetable food. Nearly allied to
the Locusts are the Crickets (Gryllidx), which agree with them in the pos-
session of multiarticulate antenne, and in the position of the auditory organs
and the vocal apparatus, but differ in the shorter hind legs and the long
cerci (the cerci of hoth Locusts and Grasshoppers are very short), and generally,
too, in that the posterior portions of the wings which are folded up, are not
covered by the elytra, but project from these as a pair of pointed appendages.
Here belong the Cricket (Gryllus domesticus), in bake-houses and similar
warm places; and the Field-cricket (G. campestris), common in arid fields,
and making passages in the ground; both with well-developed elytra, the female
with projecting ovipositor: further the Mole-cricket or Earth-crab
(Gryllotalpa vulgaris), whose front legs are developed as enormously powerful
digging limbs; with very large prothorax, short elytra, and no ovipositor ; they
lead a subterranean existence, feeding upon plants and animals: all three in
Great Britain.

3. Cockroaches (Blatta); flattened forms, with long bristle-like antenne,
and strong running legs with large femurs; the fore-wings are thin elytra,
partially overlapping; the abdomen has two anal cerci posteriorly; the head
is covered by the anterior edge of the prothorax. Often both pairs of wings,
especially in the females, are short or rudimentary. The eggs are laid in
chiti: .us capsules, which are carried about for a long time by the female,
projecting half out of the genital aperture; each capsule contains a number of
eggs lying in two rows. Two large species of this group, one of which is the
well-known “Black-beetle” (B. [Periplaneta] orientalis), have been intro-
duced from the tropics into Europe, where they live in houses; several species
occur in the open in England.

4. The Mantide are allied to the Cockroaches, but differ in various
respects. The body is on the whole more elongate, the prothorax being
especially long. The first pair of legs is prehensile, with large coxe, strong
femurs with two rows of spines, and tibie also furnished with two rows of
spines, which can be folded back upon the femurs; with these appendages the
animal seizes its prey, which consists of other Insects. Wings well developed;
in other respects like the Cockroaches ; joimted cerci. The ova are attached to
plants in groups, swrounded, as in Cockroaches, by a capsule formed as a
glandular secretion. A large green species of this genus (M. religiosa, the
Praying Mantis), occurs in South Europe.

5. Earwigs (Forficula), somewhat flattened Insects, which are chiefly
characterised by the condition of the wings. The elytra are quite short plates,
which do not completely cover the thin hind wings, although the latter are much
folded. The larger part of the abdomen is left uncovered by the wings; it is
strongly chitinised, freely movable, and possesses, posteriorly, a pair of un-
jointed cerci, curved to form a pair of pincers. The Karwigs usually remain
hidden by day; they live principally upon vegetable food. The females brood
over the eggs. Several species occur in England.

6. The Stick- and Leaf-insects (Phasmidz), form a small division
of the Orthoptera, including a number of aberrant species; they are only
254 Arthropoda.

indigenous to warm countries. Amongst them is the apterous genus,
Bacillus, whose long body, together with the elongate legs, looks like a dry
branched twig; some species in South Europe. In the Hast Indian, Phylliwm
siccifolium, the Leaf-insect, the broad abdomen and elytra are leaf-like.

7. The Termites, (genus Termes, and others) possess four large, thin
wings, which are all alike, and cannot be folded up. The antenne are short,
and moniliform, the legs are like one another. The Termites are specially
remarkable for living in large colonies, including, besides fertile males and
females, a large number of apterous and blind individuals in which the sexual
organs (in some examples male, in others, female) remain in an immature
condition. Some of these wingless individuals are possessed of larger heads
and more powerful mandibles, and are termed “soldiers,” whilst the others
are termed “workers”; the nest is made by the workers, either by gnawing
passages and chambers in tree-trunks and lining them with a layer of excreta,
or by constructing such dwellings out of excreta and earth. They often
form extensive tunnels in the ground. The soldiers defend the nest against
attack. Before pairing the males and females leave the nest, fly about for a

 

Fig. 212. Termes lucifugus. 1 Worker. 2 Sol-
dier. 3 Male or female, with wings. 4 Female
shortly after flight. 5 Female later, with enlarged
abdomen.—After Lespés.

 

short time, lose their wings, and the majority die, only a few making their way
back to the nest, where copulation occurs. Then, in many forms, the abdomen
of the female enlarges to an extraordinary extent. Besides the winged males
and females there are apparently others which, as regards the structure of the
wings, remain at one of the older larval stages, in which merely short stumps are
present; they do not leave the nest, and only become functional if none of the
males or females which flew from the nest return. Some species differ in certain
respects from this description; many of their habits are by no means thoroughly
understood. The Termites, also called “ White Ants,” live chiefly in the tropics,
but there are two species in South Europe (one of which is figured in Fig.
212); they often do a large amount of damage by making their nests in wood-
work, and by eating clothes or furniture.

8. The Dragon-flies (Libellulidz) possess four large wings almost equal
in size, and closely veined. The head is very movable, with large compound eyes
and three accessory eyes, short antennz, strong mandibles, no first maxille or
Class 3. Insecta. Order 1. Orthoptera. 255

labial palps, but with a very broad labium. The legs feeble. Abdomen usually
elongate with two unjointed cerci. Extremely good fliers, seizing their prey
(e.g. Butterflies) upon the wing.* The larve inhabit fresh water, and are
characterised by the modification of the labium into a long eversible prehensile
organ (the mask), and further by the closure of all the stigmata; respiration is.
effected by means of tracheal gills which in some cases are lamellate and situated
at the end of the abdomen, whilst in others they are represented by a number of
folds developed in the rectum; in the latter case the rectum receives and ejects
water rhythmically. The larve of the last species move by spirting the water out.
of the rectum. Here belongs the genus Libellula, in which the hind wings are:
broader at the base than at the tip, and the large eyes are pushed together into
the middle of the head; the larva: with rectal branchiew: also the delicate slim
Agrion-species (Demoiselle flies) in which the hind wings are narrower at their:
bases than at the ends, the eyes are wide apart and the larve possessed of three
external gills.

9. May-flies (genus Ephemera and others) are usually small insects.
with four thin wings, of which the hinder are smaller than the anterior. The
mouth-parts of the imago are rudimentary; the
abdomen with three anal filaments posteriorly. The
larve live in water, and like the Dragon-flies possess
a closed tracheal system and leaf-like or branched
tracheal gills, situated in a row along each side of
the abdomen; they exhibit three thread-like ap-
pendages, as does the imago. The larve are pre-
daceous, and have well-developed mouth-parts ; some
of them dig passages in banks. The May-flies pass
through a sub-imaginal stage (ef. p. 247) ; as imagines
they take no food, and many species live for only a
few hours during the night, metamorphosis occurring
in the evening; others a few days; whilst the larval
life, at least in some cases, lasts for two years.
Several species common in England.

10. Book-lice (Troctes), are small apterous
Orthoptera, which chiefly occur between old paper,
in collections of Insects, and so forth ; together with
their winged relatives (Psocus), which live in forests,
they form a special small family within the order.

ll. To this order also belong the Mallophagidez, !
small, flat, lice-like animals, with fairly hard chitinous Fig. 213.  Sugar-mite.
exoskeleton; the head is broader than the prothorax, (Zepisma).
and carries the usual biting mouth-parts, of which
the mandibles are specially well developed. The antenne have from three to five
joints, there is one ocellus on each side of the head, but this may he absent..
The tarsus consists of one or two joints with one or two claws; at the lower
end of the tibia is a process against which the claws may be bent back,
the legs are thus adapted to gripping hairs or the barbs of feathers. The
numerous species of this division all live upon Mammalia and Birds, gnawing:
the epidermis, hairs and feathers. The chief species ocewring on Mammalia.

 

 

* Copulation is very peculiar among the Dragon-flies. The second abdominal
segment of the male is enlarged, and furnished with a copulatory apparatus. Before
pairing, this is filled with spermatozoa from the vas deferens, which opens at the end
of the body. The operation is effected by flexure of the abdomen. The male then
seizes the female round the neck by means of the cerci, and the female arches its body
so that the abdominal extremity reaches the male copulatory organ, and coitus is
effected.
206 Arthropoda.

belong to the genus Trichodectes, each of our common domestic animals possess-
ing its own species (ZT. canis on the dog); on Birds, there is a number of species
of other genera (no fewer than six are known, for
instance, from the Domestic Fow!).

APPENDIX TO THE ORTHOPTERA.

The Thysanura are allied to the Orthoptera; they
are apterous forms, most of which are ametabolous, and
possess rudimentary abdominal limbs; the
mouth-parts are like those of the Orthoptera. The
Thysanura may be the most ancestral of all living
Insects, the absence of wings is probably primitive,
whilst in other forms it is acquired (through parasitism,
etc.). Of the forms belonging here may be mentioned :
Machilis, with compound lateral eyes, three ocelli, and
eight pairs of rudimentary abdominal appendages; and
the sugar-mite (Lepisma saccharina, Fig. 218),
which, instead of the compound eye, possesses a group
of ocelli on each side, and has only two pairs of ab-
dominal limbs; the latter is covered with bright silvery
scales (flattened hairs), and is very active; common in
houses. : f

Fig. 214. Abdomen Allied to the Thysanura are the Collembola, genus
of Machilis seen from Podwra, ete., also apterous and characterised by a
below. f first, f last forked process arising from the tip of the abdomen on
abdominal appendage, op 2 : ss
ovipositor, 7, 7 cerei the ventral surface by means of which springing move-
(cutaway).—AfterOude- ments are accomplished; they are small, and are
mans. frequently found among fallen leaves, or in similar
places.

 

Order 2. Rhynchota or Hemiptera.

The Rhynchota, like the Insects of the previous order, are hemi-
metabolous. The mouth-parts are modified to form a suctorial
apparatus, the proboscis, the structure of which has been
already described (p. 234). In some, the proboscis projects in front,
in others it is turned back under the body.

Sub-Order 1. Homoptera.

The fore and hind wings are usually alike, and both membranous* ;
the fore wings larger than the hind. The head is large. The proboscis
arises from its ventral side posteriorly, close to the thorax. All suck
the juices of plants.

1. The Cicadas (Cicada), are large, rather bulky forms; the male makes
a peculiar noise by means of the metathoracic stigmata, which are provided with
vocal cords; the tone is intensified by complicated resonators. The female

 

* Not infrequently the fore wings are leathery over their whole extent.
Class 3. Insecta. Order 2. Rhynchota or Hemiptera. 257

deposits the eggs in branches of trees by means of an ovipositor; the larvae,
whose fore legs are adapted for digging, make their way down into the earth,
where they feed upon the juices of roots; they only leave the earth just before
metamorphosis, climb into a tree and moult for the last time: the imagines
suck young shoots. This division is confined to warm countries, but there is a
single species in England. In North America the Seventeen-years
Cicada (Cicada septendecim) occurs: its development lasts seventeen years (a
variety of the same species has a period of development which lasts thirteen
years).

2. The Frog-hopper (Aphrophora spwmaria) is a small Homopteran,
peculiar in that the soft, thin-skinned larva, which lives on the juices of
various plants, surrounds itself with a foamy secretion (cuckoo spittle). This
insect belongs to the family Cicadellide, of which there are several other
species in Britain; most of them can spring long distances.

3. The Green-flies (Aphidx) form a large family of the Homoptera, the
members of which are characterised by the bulky, thin-skinned body, feeble legs,
sparse veining on the wings, and small size; very often the wings are absent,
especially from the females; they are inert aninials, living together in colonies.
Many of them possess glands for the secretion of delicate wax threads which
‘surround the body as a woolly mass; in many, also, there is a pair of glands
‘opening posteriorly on the dorsal side of the abdomen, by two apertures which are
situated either on papille, or at the top of long projecting tubes; these glands
secrete a fatty substance.* Heterogony usually occurs; several virginal genera-
tions are followed by a generation of males and females.

(a) Aphides, Green-flies in a restricted sense of the word, are green or black,
soft-bodied Insects, with but little power of movement. They live in large
colonies, and are extremely abundant on the leaves of all kinds of herbaceous
and woody plants; they have fairly long antenne, and two long tubes on the
abdomen. In the course of the summer, several successive generations of
females occur, which possess no seminal pouch, and which reproduce partheno-
genetically ; the eggs develop in the oviducts, so that the Insects are viviparous ;
some of these females have wings, but the majority are apterous. Finally, in the
autumn, there is a generation of usually wingless females and winged males,
which copulate, produce eggs, and die. These eggs give rise to the first female
‘generation the following spring.

(b) The Vine-louse (Phylloxera vastatriz), famed on account of the
terrible devastation it works in vineyards, especially those of France ; indigenous
to North America, where it does no great harm, it was accidentally introduced
into Europe a few decades ago with American vines. The tubes are wanting
on the abdomen, and it has shorter legs and antenne than Aphis. In
the spring, wingless females appear and feed on the roots, causing knotty
swellings. Each lays about thirty or forty unfertilised eggs, from which a
generation of individuals like the parent arises. In this way, from five to eight
similar generations occur during the summer. At last, from the eges of the
apterous females, a generation of winged females develops. They leave the roots
before metamorphosis (and, therefore, when the wings are incipient only), and
betake themselves to the shoot part of the vine, where each deposits about four
unfertilised eggs. These eggs are of two sizes: from the larger, females hatch
out, from the smaller, males. Both sexes are small, apterous, with rudimentary
mouth-parts, and no alimentary canal, so that no food can be taken, After
impregnation, each female lays a single egg, which before being deposited,

 

* « Honeydew,” a sweet sticky fluid, the excreta of the Aphides, occurs upon the
plants on which they are living.

8
258 Arthropoda.

occupies the greater portion of the small body. These eggs rest during the
winter, and in spring develop into the first virginal generation. Besides the
fertilised eggs, a number of apterous parthenogenetic females persist during the
winter, in the larval stage, firmly attached to the roots of the vines.*

 

Fig. 215. Phyllozera vastatriz. 1 Young female of one of the apterous parthenogenetic
generations. 2 Older ditto, from the ventral surface. 3 Adult female of the winged
generation. 4 Female of true sexual generation (the ovum shows through the skin).
5 Male. All the figures of equal magnification After Cornu.

(c.) Various Aphides produce characteristic galls on trees and bushes..
Chermes abietis, for instance, by sucking at young pine shoots causes cone-
like galls by shortening and broadening the needles. Pemphigus spirothece
forms a spiral gall on the petioles of poplars; crumpled or saccular galls are
caused on elm leaves by various Aphides, and so on.

4, The Scale-insects (Coccidx) are allied to the Aphides, but differ
from them in various respects. Sexual dimorphism is usually very marked.
The female is cumbrous, apterous, and short-legged, and is usually somewhat
motile only in youth, later becoming fixed to one place, where the eggs are laid.
Soon after oviposition the coccus dies, but the body which has gradually shrunk
to a thin arched shield remains as a protection to the eggs. Very often the
female is covered dorsally by a continuous layer of wax secreted by the skin
glands; sometimes the eggs are surrounded by fine wax threads. The male
possesses well-developed fore wings (with few veins), whilst the hind wings are
rudimentary and like halteres or altogether absent; the mouth-parts are
rudimentary. The larve resemble young females. It is a very remarkable
fact that the males (not the females) pass through a resting pupa-stage,

 

* In addition, it may be noticed that in exceptional cases, wingless parthenogenetic.
females may occur attached to the vine leaves, where they produce galls.
Class 3. Insecta. Order 2. Rhynchota or Hemiptera. 259

and thus, unlike all other members of the group, are holometabolous.
In several of the species it has been proved that the females can reproduce
parthenogenetically. Several forms differ in certain respects from this descrip-
tion of the Coccide ; in some the females are locomotor throughout life and do
not remain attached over the eggs; there are others, again, in which both sexes
possess four wings, and which thus offer a transition to the Aphides. As
examples may be mentioned: Aspidiotus nerti, the shield-like female of which
is frequently met with on the oleander; similar forms are very abundant on
uncultivated trees. Coccus cacti, the Cochineal-insect, lives on certain
Mexican species of cactus; the males are dipterous and have long cerci. The
females are wingless and bulky; they do not cover the eggs with their bodies,
but surround them with wax threads as do many of the Aphides; the cochineal of
commerce consists of their dried bodies. To this family belongs also the
Shellac-insect (Coccus lacca), which is found in the Hast Indies on certain
species of figs, causing the flow of a resinous substance, shellac, from the tree :
and the Kermese-insect (Lecanium ilicis), which lives on a species of oak-
tree in South Europe; from the spherical females a dye is obtained.

Sub-Order 2. Heteroptera (us).

The fore and hind wings are dissimilar, the latter thin, membranous
and adapted to flight; the former modified as elytra, which are
not thickened and leathery for their whole length, but only for
their basal halves or rather more, and the thin tips, when at
rest, overlap; the distinction into the two regions may, how-
ever, be quite effaced. The elytra cover the greater portion of
the mesothorax, the metathorax, and the abdomen, but a triangular
median portion of the mesothorax (scutellwm) remains uncovered.
The proboscis arises anteriorly from the head, which is generally
small; the prothorax is large and freely movable, the whole body is
usually flattened. In the land forms a pair of stink glands opens on
the ventral surface of the metathorax, and the secretion has an
extremely offensive odour. The Heteroptera feed on the fluids of
plants or animals (Insecta, Vertebrata).

1. Land-bug (Geocores) is the common term for a large number of
bugs (forming several families), characterised by the possession of well-
developed autenne and a long proboscis. Most of them are terrestrial; some
feed on plants, others are predaceous, sucking other Insects; some live as
parasites on Vertebrata. Many are gorgeously coloured. Abundant in temperate
zones, and especially so in the tropics. The Bed-bug (Cimex [Acanthia]
lectulartus) is a flattened, brownish, apterous (rudiments of the fore wings
only are present) form, which lives as a temporary parasite upon Man. It
came originally from the East Indies. Here also belongs the Hydrometra, a
slim, elongate form, which runs about actively upon its middle and hind legs
on the surface of freshwater; the legs of the first pair are considerably
shorter than the others, but are fairly strong, and are used for catching Insects
upon which it feeds; the abdomen is rather small, hardly longer than the
thorax. Closely allied to the Hydrometride are the Halobatide, which run about
on the open sea: they are distinguished by the extraordinarily small size of the
abdomen.

s 2
260 Arthropoda.

2. Water-bugs (Hydrocores) have short antenne and a short proboscis;
they live in water, which they are, however, able to leave, in order to fly in the
air. Allare predaceous. Of forms found in England, the Water-scorpion
(Nepa), belongs here, a flat, darkly-coloured insect, which is very common,
crawling about at the bottom of fresh water; the front legs are prehensile,
the tibize can be folded into grooves on the femurs, posteriorly there are
two filiform grooved processes, which together form a tube (the respiratory
tube), at the base of which lies a pair of stigmata: also the Water-boatman
(Notonecta) with long, outwardly directed hind legs, covered with setz on the
tibie and tarsi; these are swimming organs.

3. Lice (Pediculidz), a small group of ametabolous parasitic Insects, are
probably to be regarded as peculiarly modified Heteroptera. The head is narrow,
with short antenne, and an ocellus on each side; the suctorial apparatus, which can
be completely withdrawn into the head through an opening at the tip, consists
essentially of a short, thick tube, provided at the end with a few hooks, through
which a second thinner tube, the actual sucking tube, can be protruded; the
more exact structure of the latter is not definitely known. The legs, which
are short and strong, end in chele; the tarsus, consisting of one joint, bears a
very powerful claw, which bites against a process arising from the lower end of
the tibia. Wings are altogether absent, the abdomen is large, broad, and
tough. The large eggs (nits) are stuck on to the hairs of the host.

    

Fig. 216. 1 Cimex lectularius. 2 Pediculus capitis. 3 Phthirius pubis. All
enlarged.—After Taschenberg.

Lice only occur upon Mammalia, living as stationary parasites upon the skin,
sucking the blood; they grasp the hair by means of their legs. The follow-
ing species occur on Man: Pediculus capitis and P. vestimenti, which are
very similar, the former living exclusively in the hair of the head; the latter
on the naked portions (or, more correctly, the sparsely hairy), of the body; also
Phthirius pubis on the hairy portions of the body, with the exception of the
head (in the hair of the pubic region, the beard, etc.), distinguished by the great
breadth of the thorax and abdomen. Other species, on domestic Mammalia.

Order 3. Neuroptera.

The Neuroptera are holometabolous Insects, with four
similar, thin wings, and biting mouth-parts,. The
antenne are usually multiarticulate; in some, the mouth-parts are
well developed ; in others, rudimentary. The prothorax is freely
movable; the wings in some are closely vemed, like those of the
Libellulide ; in others, there are fewer veins. The larva are pro-
vided with legs, but in other respects, are very diverse. The pupa
is peculiar in seeking a convenient spot for the completion of
Class 3. Insecta. Order 3: Neuwroptera. 261

metamorphosis ; if it is enclosed in a cocoon, it bites its way out for
this purpose. The following may be taken as examples:

1. Ant-lions (Myrmeleon). Fore and hind wings large and similar, almost
of equal size, with a delicate close veining; the antenne, fairly short and thick,
somewhat club-shaped; the mouth-parts well developed. In their habits very
like the Libellulide. The larve to which the name of “ Ant-lions ” was originally

Fig. 217. Fig’ 218.

 

Fig. 219.

 

 

 

Fig. 217. Chrysopa. a Imago, b larva, c-—d pupa, e—f pupa cases (f opened), g eggs,
h egg enlarged.—After Taschenberg.
Fig. 218. Panorpa communis, 3.

Fig. 219. Boreus hiemalis, 4.

given, have large slender mandibles, which are hollowed out ventrally ; into these
grooves, the elongate first mavxille fit, so that each mandible, with its maxilla,
forms a hook perforated by a.canal;.the canal leads into the mouth, which is
closed but for this. The larva sits in a funnel-like pit in the sand, and catches
passing Insects which fall in by accident, or in consequence of a shower of sand
which it throws over them with its head. The prey is devoured with the
help of the hooks already mentioned. Closely allied to the Ant-lions, is the
Golden-eye (Chrysopa), a small delicate greenish insect, with large wings.
It resembles the Ant-lions in the main points of its structure, but differs, among
other things. in its long, bristle-like antennz. The greenish larva, “ Aphis-lion,”
is also similar to larval Ant-lions, but it moves freely about on trees and eats
Aphides. The eggs are attached by long stalks to leaves. Some species are very
common in Great Britain.
262 Arthropoda.

2. TheScorpion-flies (Panorpa), are characterised by the snout-like
elongation of the head; the males by the presence of pincers at the end of the
abdomen, which like the sting of the Scorpion, may be curved upwards. Wings
small and uniform, body and legs slender. Actively predaceous; length about
10 m/m. The larva (with prolegs) lives in the earth, upon decaying matters.
P. communis abundant everywhere in the summer. Another form is the springing,
apterous (possessing rudiments of wings), Boreus hiemalis, about 4 m/m. long,
which occurs in the imaginal state, from October to March, sometimes even on
glaciers. Larva, like that of Panorpa. In Great Britain.

3. Spring-flies or Caddis-flies (genus, Phryganea and others).
Wings hairy or scaly; the hind wings, which are broader than the fore, are
folded beneath the latter ; the veining is less pronounced than in the Ant-lions.
The antenne are long, the mouth-parts rudimentary and functionless. The
larve are aquatic; the abdomen is long and cylindrical, bearing thread-like
tracheal gills laterally, and hidden in a tube formed of fragments of plants, snail
shells, or stones, often very regular in construction; the particles of which the
tube is composed, are held together by a web. When the animal moves about,
the head, legs, and thorax protrude from the tube ; it is attached to the tube by
means of two hook-like caudal cerci, and often by stout outgrowths of the first
abdominal segment. In some forms, the tube is attached to some foreign body,
a large stone or the like, and, in all before pupation, it is fastened to some object
in the water, and is then closed by a network of threads; the pupa, like the
larva, possesses tracheal gills.

The small group, Strepsiptera, has been regarded by some authorities as
belonging to the Neuroptera; its systematic position is, however, doubtful. The
larve (genera, Xenos, Stylops, etc.), live in the larve, and, later, in the imagines of
Bees and Wasps, the host undergoing metamorphosis in spite of the presence of
the parasite. Before pupating, the strepsipteran larva pushes half-way out
of the body of the host between two abdominal rings; and here the pupa may be
found with one end projecting. Sexual dimorphism is wel!-marked; the male
possesses well-developed eyes and legs (without claws), and large hind wings,

 

  

Fig. 220. 1—4 Xenos Rossii. 5 X. Peckii. 1 Newly-hatched'larva. 2 Fully grown
female larva. 3 Female (imago): 4 Fully grown male larva. 5 Male (a fore-wing).—
1—4 after v. Siebold, 5 after Kirby.

which can be folded up lengthways, whilst the fore wings are quite rudimentary.
The female is maggot-like, without limbs, wings, or eyes; it does not leave the
host, but pushes out a portion of its body, and is there sought out by the male,
and fertilised. The embryos are developed within the body of the parent, and
hatch out as hexapod larve, which move actively about in the host, and later,
bore into its larve, where they become maggot-like. In the larva, and in the
adult female, an anus is wanting.
Class 3. Insecta. 263

Order 4. Coleoptera (Beeties.)

The Coleoptera are holometabolous and have biting mouth-parts ;
the fore wings are modified to form elytra. The exoskeleton is usually
very firm, often brightly coloured. The head, which is partially sunk
into a depression of the prothorax, bears a pair of compound eyes of
diverse form; sometimes they are reniform, and the inpushing on
the front edge is in some cases so deep that each is divided into an
upper and a lower portion, and thus there are two compound eyes on
each side. Ocelli are almost always absent. The antenne usually
consist of eleven joints, but the number may be increased to about
thirty, or reduced to four; in different species their form varies
considerably. The mandibles differ according to the food; they are
slender in predaceous forms, thicker in herbivorous; the mentum is
usually a well-developed, firmly-chitinised plate, whilst the rest of the
lower lip, with the exception of the palp, is usually only feebly
developed. The prothorax is large, strongly-chitinised, and freely
articulated with the mesothorax; between the prothorax and meso-
thorax there is a deep constriction. The mesothorax and metathorax,
of which the latter is best developed, are immovably connected; they
are covered above by the elytra so as to leave a scutellum; the most
anterior portion of the mesothorax is covered by the hinder edge of
the prothorax. The tarsus is usually five-jointed, but there are not a
few exceptions to this. The fore wings are elytra, and during
rest they meet along the mid-dorsal line or may even be folded the
one over the other, whilst their lateral edges wrap round the lateral
edges of the body (Fig. 197) ; they thus form a very complete covering
not only for the hind wings but also for the dorsal surface of the
mesothorax and metathorax, and usually for most of the abdomen;
they are generally very hard. More rarely they are short, so that
the larger portion of the abdomen remains uncovered; in some
they overlap along the mid-line. The posterior are true wings, thin
and membranous, with few veins; when at rest they are usually
folded not only lengthways but also transversely. In not a few
they are rudimentary or they may be absent, but in spite
of this, the elytra are generally just as well developed, since
they afford a covering for the abdomen; both pairs of wings are
wanting in only a very few cases. The abdominal somites are
divided into tergal and sternal half-rings, which are frequently
somewhat displaced; there are always fewer sterna (four to seven)
than terga (usually eight); the latter are less strongly chitinised
as far as they are covered by the elytra, the dorsal surface of the
abdomen is thus softer than the ventral. The larve vary con-
siderably in form; they usually possess legs but may be maggot-like.
Only a few of the most important families of this extraordinarily large
order are mentioned here.
264 Arthropoda.

1. The Carabidez (genus Carabus, and many others), active, slim,
usually dark-coloured beetles, with long powerful legs; antenne filiform,
mandibles slender, projecting; first maxilla with a two-jointed lacinia. The
tarsi of the first pair of limbs in the males are very often broad and hairy below,
enabling them to hold the females firmly; the other tarsi are long and thin. In
not a few the hind wings are rudimentary. The larve, which, like the adults.
are almost always predaceous, are usually darkly-coloured, with a group of
ocelli on each side, and with well-developed legs, each with two claws; in other
coleopterous larve there is usually only a single claw on each foot. The Tiger-
beetles (Cicindela) are small Carabids characterised by their bright colours.
(green, etc.). The larva is paler than that of most of the Carabide, and exhibits.
a pair of hooks on the back; it lives in a burrow in the ground, where it lies in wait
for its prey. The Dytiscide (genus, Dytiscus, and others) are to be regarded.
as a type of Carabide specially developed for an aquatic life; in most respects
they resemble the Carabids, but differ from them in the broad, oval body, and in
the modification of the hind legs as natatory organs, the tarsi being broad and.
hairy at the edges. In the males, the first three joints of the front tarsi are still
broader than in the Carabide, and are furnished with ventral suckers (modified
sete). They come to the surface to breathe; by night they usually leave the
water and fiy about. The larve are also aquatic, and are slender: the
legs are fringed with sete; their most striking peculiarity consists in the
perforation of the thin mandibles by a fine canal, which opens at the tip and.
leads at the other end into the mouth (the canal is really a groove with apposed
edges, cf., the poison tooth of snakes), whilst but for this the mouth is completely
closed. The prey is sucked out by these mandibles. Allied to the Dytiscide is
another group of Water-insects, the W hirligigs (Gyrinus), small forms which
usually swim about actively on the surface of the water in the sunshine. They
are distinguished by several features: the middle and hind legs are modified to
form short, broad, flattened, fin-like natatory organs, whilst the longer front legs
are normal in structure, and are used as organs of attachment when the insect
dives. Hach eye is divided into an upper and a lower portion, of which the
former looks upwards, the latter downwards. The larve correspond with those
of the Dytiscide in the structure of the mandibles, etc., but differ from them in
the possession of closed stigmata and a row of filiform branchie along the sides of
the abdomen.

2. Staphylinide (genus Staphylinus, and others), distinguished by the
small size of the elytra; the larger portion of the very movable abdomen is
uncovered, but it is well chitinised dorsally; the hind wings are folded across
twice, in order to find room under the elytra. The body is elongate, the
antenne filiform, or somewhat clavate. The adult generally lives upon decaying
plant and animal substances. The larve are like those of the Carabide, but
possess only a single claw on each foot (or more correctly, the tarsus itself is
pointed) ; they are provided with two jointed cerci, and the anus is situated on a
tubular projection. They feed as do the adults, or are predaceous. This family
is extraordinarily rich in species.

3. The Carrion-beetles (Silphidz) have the antenna clavate, or at least,
somewhat thickened at the tips. In some forms, the elytra cover the whole of the
abdomen ; in others, its tip is left uncovered. They are, as a rule, carrion-
feeders. The genus Silpha has slightly clavate antennez, elytra covering the
whole of the abdomen, and the body of a flat, oval form. The larve are broad
and flattened, firmly chitinised, and they forage for themselves; both larve
and adults usually feed upon dead animals, for which they seek. The
Burying-beetles (Necrophorus) have markedly clavate antenne, elongate
bodies and short elytra usually coloured with black and red bands, leaving the
Class 3. Insecta. Order 4. Coleoptera. 265

hinder end of the body uncovered. They make a noise by rubbing the dorsal
surface of the fifth abdominal somite, which is provided with two transversely
ribbed ares, against the hinder edges of the elytra. Several generally unite to
bury small Mammalia, etc., removing the earth below the body, in which they lay
their eggs. The larve are pale and bulky, but possess legs and eyes, and feed
upon the carrion buried by the foresight of their parents; they do not forage for
themselves like the larve of the Silphide.

4. Dermestidae (genus Dermestes and others), small, with clavate
antenne; the surface of the body covered over a greater or less extent
with short close-set sete. The larve are provided with numerous upright
sete ; the pupa remains within the displaced larval skin, which thus serves as
pupa-case. The Dermestide and their larve feed upon dead animal substances,
and are often injurious to woollens and furs, and to museum specimens.

5. Lamellicornia or Scarabeide. <A family of Beetles very
rich in species, and comprising many beautiful and characteristic forms; each
of the last three (or more) joints of the antenne is expanded like a leaf on
one side, and these lamine, when laid upon one another, form a clavate swelling.
The eye has a deep notch in front, into which the lateral edge of the head
extends. The front legs are emphatically adapted for digging, with flattened
spiny tibize and cylindrical coxe; and to the same end the prothorax is very
powerfully developed. The whole body is usually fairly bulky. The males are
often very unlike the females, with outgrowths on the head, prothorax, etc. The
larve are whitish (with the exception of the much chitinised head), fat, thin-
skinned, sparsely setose, and usually blind ; the legs are rather feeble, the abdomen
curved, its end often swollen and saccular. Both larve and adults feed upon
plants or dung. Amongst others, the following belong to this family : The Cock-
chafer (Melolontha vulgaris), the males distinguished from the females by larger
clubs to the antenne ; the larva lives upon roots, the imago on leaves ; the whole
duration of life extends over four years in Britain. Rose-chafers (Cetonia)
are green and shiny ; the elytra are notched at the lateral edges, so that after
spreading the hind wings, they can be folded back along the dorsal surface, and
the insects can fly with closed elytra; the larva lives in rotten wood and in Ants’
nests. Oryctes nasicornis is a large brown Lamellicorn, the males of which have
large projections on the head; the larve occur in tan, etc. Dung-beetles
(Coprophaga) live as larve, chiefly on the dung of Ungulata; larve and adults of
the genus Aphodius, for instance, are found in abundance in cow dung; the
female of genus Copris digs « hole in the ground, lays an egg in it, and adds a
small piece of manure to serve as food for the larva when it hatches out.
Geotrupes, bulky, blue insects, the eyes completely divided into upper and lower
portions, strong digging legs; mode of life similar to that of the forms last
mentioned. The Stag-heetle (Lucanus cervus), is the most striking of
English Beetles; the male has a large square head, and huge antler-like
mandibles, which are very variable in size; the antennz are geniculate with long
basal joints, the club pectinate, the processes being not laminate, but denticulate
and far apart; the larve live in rotten oak trees. More abundant is the allied
Dorcus parallelopipedus, a small form in which the mandibles of the male are
very little enlarged; the larve in rotten heechwood.

6. The Skip-jacks (Hlateridz, genus Hluater, etc.) are usually small
with flattened bodies of an ellipsoid form. The prothorax is long, and pro-
vided, posteriorly, with a spine, which fits into a pit in the mesothorax, so that
very considerable movement can take place. When the prothorax is raised
the spine is supported against the edge of the depression, and on its being
suddenly allowed to shoot back into the pit the animal strikes the ground
with considerable force, and thus is jerked up. The leap upwards may occur
266 Arthropoda.

when the animal is in the natural position, as well as when it is on its back. Tho
head is sunk deeply into the prothorax, the antenne are serrate or pectinate. The
larve (Wire-worms) are long, sometimes almost wiry and firmly chitinised,
with legs, but without eyes; the last segment large and varying in form. These
Insects are for the most part phytophagous. The Buprestide (genus Buprestis
and others) are allied to the Elateride, which they closely resemble in form,
in the relations of the head, and in the serrate antennz ; they differ, however,
amongst other things, in the absence of the springing apparatus. The larve
are whitish, blind, apodous; the prothorax into which most of the head is sunk,
is usually very large and broad, the abdomen narrow; they usually live upon
wood, as do longicorn larve, which they closely resemble. The Buprestide
are specially abundant in the Tropics, where large and beautiful forms are
met with; in temperate countries there are relatively few, and they are mostly
small.

7. The Malacodermata are characterised by the unusual softness of the
exoskeleton, the elytra, for instance, crumpling up when dried. The head is
generally more or less hidden beneath the front edge of the broad, shield-shaped
prothorax. The elytra fit closely together along the back as usual. The
Glow-worms (Lampyris), represented in Britain by two species, belong here;
in these the head is covered by the prothorax, the females have neither elytra
nor wings, and look like larve; the adults of both sexes and the larve (which
feed upon Molluscs) have phosphorescent organs on the ventral side of the
abdomen. In the allied genus Telephorus (which is not luminous) the head
projects freely; in the summer several species are found on flowers.

8. The Vesicantia are heteromerous, ie. the tarsi of the front
and middle legs are five-jointed, those of the hind legs, four-jointed.* The
head is constricted posteriorly to form a neck, the prothorax is narrower than the
elytra, which are not so hard as in most Beetles. The claws are cleft; blistering
materials are contained in the body. The ova are laid in holes in the earth; the
newly-hatched larve possess eyes and well-developed legs, and crawl about
on plants, attaching themselves to certain Bees and entering their nests with
them; when the Bee lays an egg the parasite leaves its host and remains in the
cell, where it first devours the egg, and then undergoes a metamorphosis, becoming
a clumsy, blind, short-legged creature, which devours the supplies intended for the
bee-larva. To this group belongs also the Oil-beetle (Meloé), with no hind wings
and with short elytra, which do not fit together, but overlap: also the Spanish-
fly (Lytta vesicatoria), a beautiful emerald green beetle. with well-developed
elytra and wings: rare in England, whilst Meloé is common. The Meal-
worm (Zenebrio molitor), a brown, elongate insect, like the Carabide, belongs
to another family of Heteromera. The larva resembles that of the Elateride,
and is well-known in meal and corn.

9. Longicorns (Cerambycide, genus Cerambyx, etc.) The tarsi are
broad, and apparently consist of only four joints, the last being short and
difficult to see (Beetles with this type of foot are termed tetramerous).
They are for the most part large with long heads, long antenne in the
males often strikingly developed, and emarginate eyes. The larve which
live in wood, and especially in dead trees, gnawing out long tunnels, are
whitish, long and somewhat flattened ; broader in front, without (or with feebly-
developed) eyes, with very small legs (or quite apodous). The Leaf-beetles
(Chrysomelide) ate apparently very different from the Cerambycide ; they are,
however, closely allied, and possess a tarsus of the same form. The body is

 

* The families already mentioned have usually five-jointed tarsi on all the legs,
and are termed pentamerous.
Class 3. Insecta. Order 4. Coleoptera. 267

generally bulky and much arched, the head more or less covered by the pro-
thorax, the antenne shorter than the body, the colouring bright; but there are
also more elongate forms resembling the Cerambycide (Donacia). The larve
are mostly coloured, with eyes and well-developed limbs; most of them live upon
leaves.

10. Weevils (Curculionide ; genus Curculio, etc.): tarsi like those of the
Cerambycide. They are usually small with head prolonged in front into
a shorter or longer probosciform process, at the tip of which are the small but
well-developed mouth-parts. The antenne are clavate and usually geniculate,
with a long peduncle. The elytra bend over the edge of the abdomen; the wings
are not infrequently absent; the exoskeleton usually very hard. The larve are
apodous, curved, and, with the exception of the brown head, whitish, and
usually blind. Both larve and adults are phytophagous (eating leaves, bark,
wood, roots), the former are almost always hidden. Many genera and species in
Britain. Closely allied are the Tomicidz, small cylindrical forms with short
head and no proboscis (this is the most important difference between the
Tomicide and the Curculionide), short geniculate antenne with thick clubs ;
eyes reniform ; the larve like those of the weevils.* Before laying the eggs the
female usually gnaws a longer or shorter passage, at the junction of the wood
and bark, in a tree which is either sickly or has recently died, but is still fairly
rich in sap; rarely is a healthy tree bored. A number of eggs is laid along the
sides of this tunnel, each in a small depression; and when the larva hatches
it proceeds to make for itself a tunnel, which is gradually lengthened and
widened as the creature increases in size; the larval passages branch off almost
directly at right angles to the original one, and, like it, rum along at the
junction of the wood and bark. There are all kinds of deviations from this
typical arrangement in the different forms. To the Tomicide belong some of
‘the worst enemies of forestry (especially pine trees), Tomicus typographus (the
Printer), and many others, which may do an enormous amount of harm in
the course of a short time if some accident, e.g., wreckage by wind, affords a
quantity of suitable brood material, enabling the pests to increase very rapidly.
Their destructiveness is due less to their normal breeding than to the fact that
if they are once present in large numbers they will also lay their eggs in sound
trees; moreover the adults of some species are injurious, in that they eat young
buds (Hylesinus piniperda), gnaw the roots of young plants, and so on.

ll. Ladybirds (Coccinellide) have apparently only three joints in each
tarsus, but actually four, of which the penultimate is very short (trimerous).
They are small, often almost hemispherical, or somewhat ovate; the head is
‘small, with short clavate antenne, and sunk into the prothorax; the legs are
short. Larve and imagines both resemble those of the Chrysomelide, but both
are predaceous, feeding upon Aphides,.

Order 5. Hymenoptera.

The Hymenoptera are holometabolous with biting
mouth-parts and four membranous wings. The head is
short and broad, and deeply constricted off from from the prothorax,

 

* The Tomicide are not to be confounded with the Death-watch (Anobium). The
latter possesses a body similar in form and also gnaws wood, but it belongs to quite
a different family and is easily distinguished by its round eyes, by the antenne only
slightly thickened at the tip, and by the possession of pentamerous tarsi; the larve
have legs (small and like those of the Scarabzide) and eat irregular labyrinthine
tunnels in dead, dry wood, e.g., in furniture, which is often destroyed by them.
268 Arthropoda.

never sunk into it; sometimes, indeed, it is situated on a stalk-like
process of the prothorax. The usual mouth-parts are present, and of
these, the mandibles are powerful biting organs. In some Hymenop-
tera—but these are in the minority—the “ tongue,” which is formed by
the concrescence of the ligule, is elongate and gutter-like ventrally, and
surrounded by a tube formed of the long, flattened, labial palps and
blades of the first maxille (only a single blade of each being present) ;
by means of the tongue and its sheath, sweet liquids are sucked up
into the mouth. The prothorax is but feebly developed, the dorsal is
separated from the ventral portion, and is firmly fused on to the meso-
thorax, whilst the latter (with the first pair of legs) is movable. Meso-
thorax and metathorax are usually immovably united, but in the Saw-
flies and Wood-wasps they are freely articulated. The legs are character-
ised by the size of the cox; the trochanter is often divided into two
joints (in the Tenthredinide, Uroceride, Cynipidee and Ichneumonide) ;
the first joint of the pentamerous tarsus is much longer than the
following (metatarsus). The front pair of wings is almost always
much larger than the hind pair; both are veined, but not very
closely ; those of the same side are connected by a row of small
hooks on the anterior edge of the hind wing, which fasten into
the curved hinder edge of the front one; thus, during flight, the

 

Fig. 221. A Abdomen with ovipositor of one of the Uroceridew. The spine (a) is
pushed out from the groove (d) in which it lies when at rest ; this groove is continued from b
into the two long lobes c, which surround the terminal portion of the spine. B Transverse
section of the spine and the lobes, enlarged. a b and a’ b’ lobes (= ¢ in A), c d,e and e’ the
three acicular pieces of the sting.—After Graber.

two act as one continuous lamina. At the base of the front wing,
there is a projecting scale which covers the base of the hind
wing. In all the Hymenoptera, the first abdominal segment is
immovably united with the metathorax, and in the majority (<.e., in
all with the exception of the Tenthredinide and Uroceride), there is
a deep constriction between this and the following abdominal
segments; the abdomen is thus said to be stalked, but it must
not be forgotten that the constriction occurs not between the two
regions, but in the abdomen itself; the segments following the
constriction are usually narrower than the first. At the hinder
Class 3. Insecta. Order 5. Hymenoptera. 269

end of the female, there is a hollow stabbing or boring apparatus,
through which the eggs pass when being laid, and with which,
im many cases, a prick or cut is made in an animal or plant, for
the reception of the egg; this is the ovipositor of forms
described under 1 and 2; in others (8 to 6), the spine is not
simply an ovipositor, but also acts asa sting; a poison gland opens
into it, and the secretion runs down the canal of the spine; with
this, other animals may be pierced, either in self-defence or with
other objects (see the Sand-wasps). The great majority of the
larve are whitish, blind grubs; only in the Tenthredinide and
Uroceride do they depart from this type, having legs, etc. (see
below). The larve generally form cocoons for pupation.

1. Saw-flies (Tenthredinide). Abdomen sessile, z.e., without constriction,
broad and short; in the females, a short, serrated ovipositor, with which small
cuts are made in leaves for the reception of the eggs. Mesothorax and metathorax
movably articulated, trochanter two-jointed, fairly close veining in the wings.
Some of the Saw-flies reproduce parthenogenetically, either exclusively (P), or in
addition to reproduction by fertilised eggs. The larve are coloured, cylindrical,
and eruciform (caterpillar-like); they usually possess six to eight pairs of
prolegs without hooks, besides the thoracic legs (ef., the Lepidoptera), and an
ocellus on each side of the head; they live on trees and other plants, destroying
the leaves. Closely allied are the Wood-wasps, genus Sirex, etc. (Uroceridx), in
which the abdomen is long, cylindrical, and provided with a longer ovipositor,
whilst in other respects they resemble the Tenthredinidz ; the larve live in wood,
in which they gnaw long winding passages; they are blind, whitish animals, with
three pairs of short thoracic legs, but no prolegs.

2. Gall-flies (Cynipidz), small Insects in which the abdomen is short,
compressed, lenticular, with an ovipositor arising from the ventral surface ; wings
with very little veining ; two-jointed trochanter. The larve live in galls; the
female bores into living portions of plants (leaves, stems, buds) by means of
her spine, and deposits an egg in the hole thus made; later, the plant tissue
swells up in different ways characteristic for each species, in consequence of the
presence of the larva, for it lives in, and upon, the gallthus formed. Some galls
are concamerated, #.e., several eggs are introduced close together into one plant,
and one continuous gall is formed round all the larve. In many species of
Cynipide, which are found in great numbers on oak-trees, a regular alternation -
of parthenogenetic and true sexual generations is observed (one of each annually);
the two generations are dissimilar, and cause galls very different in appearance.
Other Oak Gall-flies are apparently all females. Allied to the Cynipide is a
very large group, the Ichneumon-flies (Ichneuwmonidz), usually very small
in size, but often possessed of long ovipositors ; their larve live as parasites in
(rarely upon) insect larve, pupz, and ova, caterpillars being especially attacked ;
some are parasitic in other Ichneumon larve. When the egg of an Ichneumon is
laid in that of another insect, the parasitic larva lives and develops at the expense
of the egg, and the latter degenerates. Those Ichneumons, which are parasitic
in larvee, usually complete their growth before the pupation of the host, they
then break through its skin and pupate close beside it whilst it dies; or the
host pupates first, and the parasite pupates within it; the former then dies, and
the latter only leaves the pupal skin of the host when it has attained the
imaginal state. The Ichneumon larva, which possesses very imperfeet mouth-
parts, apparently feeds upon the blood of its host (except when parasitic in an
egg); there may be one, or several, or many in the same individual. In some
270 Arthropoda.

Ichneumons, parthenogenetic reproduction has been observed ; for the most part,
males arise from the fertilised eggs.

38. Sand-wasps (Crabronidex, Pompilidw). These, like the following
groups, have a simple trochanter, a stalked abdomen, and a sting. They are
active forms, and are chiefly characterised by their mode of life; they catch
Insects, and their larve, or Spiders, paralyse them by a sting in the ventral nerve
cord, and store them in burrows, which they make in the earth or in wood; they
lay one egg in each passage and then close it up; the larva feeds upon the stores
thus collected. Other forms divide the burrows up into cells hy means of clay
partitions, and deposit one egg in each cell; others again form branching tunnels,
and place one egg, with a supply of food, in each branch. More rarely they
bring fresh supplies of food to the larva daily. The allied Gold-wusp
(Chrysis), is a beautiful, metallic-looking insect, with a very hard chitinous
exoskeleton. This is especially firm on the abdomen, which is much arched above,
but concave below, and appears to be made up of a few large segments, the last
being telescoped. The antennew are geniculate. The body may be rolled up, so
as to present only the hard exoskeleton to the stings of the Sand-wasps, in
whose nests they lay their eggs. The larve live as ecto-parasites upon the Sand-
wasp larve.

4. Ants (Formicariz) are distinguished from other Hymenoptera in that
the second (or second and third) abdominal segment is considerably thinner
than the following, and is provided with an upright scaley, or knob-like
outgrowth; the antenna are geniculate. Ants form colonies, consisting of
males, females, and workers; the latter being females with imperfectly developed
sexual apparatus: both males and females have large wings, but those of the
latter are thrown off after copulation: the workers, on the other hand, are quite
apterous. In some species two kinds of workers are met with, some with
large heads (soldiers), others with smaller heads (true workers). Some Ants (of
course only females and workers) possess stings, others have only the corre-
sponding poison glands, the secretion from which is squirted into the wound
made by the mandibles. The nests, which consist of irregular chambers and
labyrinthine passages, are, in most cases, tunnelled in the earth, or gnawed out in
stumps of trees; the burrowing forms generally pile up the earth they dig
out above the nest, and thus form a hillock, into which the nest is continued;
others (e.g., the Red-forest ant, Formica rufa), construct mounds of pine-
needles, leaves, and so on; others again, build nests in hollow trees, constructing
the walls of sawdust, etc., cemented together with saliva. Ants are omnivorous ;
the larve are fed by the workers upon comminuted food. The habits of these
insects are of the greatest interest, and in many species the most remarkable
conditions may he observed. There are, for example (occurring in England),
species which steal larve and pupe from the nests of others, and bring them to their
own; the workers, which develop from these, form a necessary contingent of the
working staff of the marauders, or may have to do all the work, even to feeding
their masters. In a Mexican species the abdomen of some workers is much
swollen in consequence of the enormous dilation of the crop, which is filled with
a honey-like fluid; these workers remain in the nest whilst others are out seeking
for honey; on their return the latter give their booty to the inactive forms, which
thus serve as regular reservoirs for the honey supplies of the nest. Besides Ants,
an ant-hill harbours (just as in the case of the Termite nests) quite an insect
fauna on a small scale, the members of which are known as Myrmecophilous
Insects, eg., several small Beetles, many of which are found here exclusively.
The relations between Ants and Aphides are well known, the Ants greedily
sucking up the sweet excretion of the latter; many ants even carry Aphides
into their nests, and keep them as “domestic animals.”
Class 3. Insecta. Order 5. Hymenoptera, 271

5. True wasps (Vesparie), are characterised by geniculate antennz, reni-
form eyes, long and projecting mandibles; the front wings are folded during rest.
Some of them are solitary forms, leading an existence like that of the Sand-wasps;
others, among them the genus Vespa (Paper-wasps, Hornets), live in large or
small colonies, consisting of males, females, and workers (females with imperfect.
sexual apparatus, but with wings), and build ingeniously constructed nests.
These consist of one or more horizontal! combs, each composed of a number of
closely apposed prismatic hexagonal tubes closed at one end, the so-called cells,
which are arranged perpendicularly with the openings downwards, and are used
as dwellings for the larve and pupe; the combs may be connected by shafts,
and the whole nest be surrounded by a loose or firm covering. The material
chiefly used for the nest is a mass formed of finely masticated wood or bark,
which, when dry, has the appearance of paper. The larve are fed upon com-
minuted Insects. The whole population of the nest dies in the late autumn, with
the exception of the young fertilised females. They survive the winter, and in the
following spring found a new colony, the completion of which is accomplished
later by the workers to which they give rise; the nest, which is often large, is
thus the work of a single summer.

6. Bees (Apiariz) are usually very hairy, the antenne are geniculate, the
eyes not emarginate, the tongue elongate, the gale and lacinie, and the labial
palps are often very long and flat; the tibi# and tarsi of the hind legs are
usually broad. Some Bees form colonies of males, females, and winged workers
(sterile females); others are solitary. The Honey-bee (Apis mellifica) is a
colonial form, and there is only a single fertile female (the queen) in each nest ;
the hatching of a new female is a signal for a division of the colony, to form
a new swarm; the Honey-bees build combs of the wax secreted by integumentary
glands upon the abdomen; the combs are arranged perpendicularly, and consist
of two layers of hexagonal horizontally placed cells, closed at one end, the
openings being laterally directed. The larve from which fertile females arise,
live in special, large, roundish cel!s, situated at the edge of the comb; the other
cells are used partly for the workers and male larve, partly for the storage of
honey and pollen (hee-bread); the honey is carried to the hive in the crop, the

 

Fig. 222. Heads of Honey-bees. a Queen, > worker, c male.—After Ratzeburg.

pollen is kneaded up and carried in a depression of the tibiz, surrounded by hairs
(sete), the so-called “basket,” which occurs only in the workers. The whole
colony survives the winter, and this without hibernating; a fairly high tempera-
ture prevails in the nest. The male bees (drones) have very large eyes, and like
the queens are much larger than the workers; they develop from unfertilised
eggs. Closely allied to the Honey-hee is the Bumble-bee (Bombus), which
forms small colonies, and lives in nests in holes in the ground; each colony is
founded by a single large fertilised female which has survived the winter, and
when complete, is made up of a few large females, some smaller females which
only lay drone eggs, a number of workers, and males. Both fertile females and
272 Arthropoda.

workers possess “baskets”; they do not build cells, but the eggs are laid each
upon a little lump of bee-bread and honey, into which the young larva gradually
eats, increasing in size by the ingestion of new material; before pupating, it
spins a glossy ovate covering; this cocoon which has been wrongly regarded as a
cell, may sometimes be used for the storage of food, after the Bumble-bee has
crawled out of it. The females of many Solitary-bees form small cavities
in the earth or in wood, or true cells of sand, loam, or pieces of leaves. Pollen
‘or honey is stored in these cells, and one egg is laid in each, and then it is
closed; the larve feed on the stores, the female taking no further trouble
about them. The females, as well as the workers of some of the solitary
Bees, possess baskets; in others, the pollen is collected on the thick hairy
‘covering of the hind legs, or on the hairy ventral surface of the abdomen.
Not a few of the solitary forms are parasitic (Cuckoo-bees), laying their eggs
in the stores of other Bees, so that their larve may live at the expense of these
supplies.

Order 6. Lepidoptera.

The Lepidoptera are holometabolous Insects, with four
equally developed wings, and with sucking mouth
parts. The whole animal is well covered with hairs. The head is
freely movable; the multiarticulate antenne are filiform or bristle-
like, clavate, or pectinate, etc. For the structure of the mouth
parts, see p. 238. The three thoracic segments are intimately
connected, the prothorax small, the mesothorax large. The wings
are large, covered with minute coloured imbricating scales (flattened
sete), or “dust,” which usually form a complete covering over
the veins and the rest of the surface ; the fore wings are longer,
but generally also narrower than the hind ones. The latter very
often bear on the anterior margins, close to the point of origin, a
strong bristle, or group of stiff bristles, (retinaculum), which fits
into a small ring on the ventral surface of the fore wing; by this
means the two wings of the same side are coupled. At the base
of the fore wing there is a specially developed scale, just as in the
Hymenoptera, but often still larger than in this group. The legs
are feeble, with large coxe and pentamerous tarsi, the basal
joint being much longer than the rest (cf. the Hymenoptera).
There is no deep constriction between the thorax and abdomen,
and the latter is therefore “sessile.” The larve, “ caterpillars,”
are of a very distinct type. They are cylindrical, with a long
abdomen, bearing prolegs; they are almost exclusively phytophagous,
and for the most part lead a free existence upon leaves, and in
connection with this, and in contradistinction to most other insect
larve, they are often brightly coloured: the exoskeleton is fairly soft,
with the exception of the firmly chitinised head and prothorax.
‘There are five or six ocelli on each side of the head, a pair of short,
three-jointed antenne, and the usual biting mouth-parts. The thorax
is provided with three pairs of short legs, each with a single claw.
Class 3, Insecta. Order 6. Lepidoptera. 273

‘On the long abdomen there are usually five pairs of prolegs (one
pair on each of the segments three to six, and one pair on segment
nine), sometimes a smaller number, and then usually two pairs (in the
Geometers on segments six and nine), most rarely (in a single genus of
the Tineidz) six pairs. The prolegs are provided at their lower ends
either, as in the Microlepidoptera, with a circle of movable hooks,
curved outwardly, with respect to the centre of the circle; or in the
Macrolepidoptera, with a row of hooks on the inner side, and curved
inwards: the prolegs are thus adapted for clasping thin branches.*
Caterpillars may be distinguished from the very similar larve of the
Tenthredinide by the greater number of ocelli, the smaller number of
prolegs, and by the presence of hooks on the latter. The pupa is
characterised by the way in which all the appendages (wings,
legs, etc.) lie close to the body; all the external surfaces are firmly
chitinised (whilst the surfaces lying against one another are but
feebly so), so that it looks as if it had been varnished. The larve
possess spinning-glands, which open on to the labium, and many
of them before pupating either spin a complete cocoon; or form
a case by binding together various particles by means of the silk;
whilst others spin only a few threads; not a few surround themselves
still earlier with a saccular case, open at one end, which they carry
about with them.

The Lepidoptera are allied to the Hymenoptera, especially to the Tenthre-
dinide ; they agree with the latter in the form of the legs (metatarsus, coxa), in
the presence of a covering-scale at the root of the fore wing, in the feeble
‘development of the prothorax, and in the structure of the larva.

Sub-Order 1. Microlepidoptera.

The prolegs of the larve have a complete circle of hooks, the
head is directed forwards; they live, for the most part, in conceal-
ment, either tunnelling in leaves, stems, or wood, or lying between
leaves held together by the threads which they spin, ete. The pupx
usually have transverse rows of spines on the dorsal side of the
abdomen. The adults are, with few exceptions, of small size, with
slender bodies.

1. Tineide, small forms with narrow wings, bordered with a fringe of
hairs. The members of this group are numerous: they are often beauti-
fully coloured, but, as rule, very small. Among them are the Clothes-
moths, Tinea pellionella, and T. tapezella ; the larva of the former species lives
upon fur and woollen materials; it lies in a sac, open at both ends, formed of
particles gnawed off the material and spun together; and here it pupates. The

 

* The row of hooks corresponds with the inner portion of the circle, and the
unilateral type of foot may be derived from the other by supposing the outer half
of the circle to have disappeared. The last pair of prolegs in the Microlepidoptera,
too, do not possess a complete circle, but a row in which the hooks are curved forward.

t
274 Arthropoda.

larva of T. tapezella, which is somewhat larger, spins on the outside of the fur, a
long thin-walled tube within which it can move about; the portion of fur or
woollen material covered by the case, is eaten away from the surface.

2. The “Leaf-rollers” (Tortricidz) are, on the
whole, somewhat larger than the Tineide, the wings
broader, with a shorter marginal fringe. The larve very
frequently—but by no means in all forms—live in and
upon leaves which they have spun together. A larva,
which is often found in the core of “ worm-eaten” apples,
belongs to one species of this division (Tortria pomo-
nana), other species are injurious forest pests (Tortrix
buoliana, etc.).

3. The Wood-borers (Xylotropha). A small
family, the members of which are usually distinguishable
from other Microlepidoptera by their much larger size.
Here belongs the Goat-moth (Cossus ligniperda),
a large, brownish-grey moth (about 80 m/m. across the
wings); the larva which is almost naked, and rose-red
dorsally gnaws passages in poplars, osiers, and other
trees. Further, the wasp-like Clearwings (Sesia,)
with transparent, almost scaleless wings, the whitish
larve of which live in trees or in the stems of shrubs.

4. The Case-bearers (Psyche), are charac-
terised by great sexual dimorphism, the females are
grub-like, wings and legs are absent, whilst the males
look like ordinary moths. The larva is surrounded by
a sac spun out of fragments of plants or grains of sand,
the female remains within this larval case. One species
of the genus, Psyche helix, which forms a spiral case of
fine particles of sand, usually reproduces partheno-
genetically, males only appear now and again.

  

é

  

Sub-Order 2. Macrolepidoptera.

The prolegs of the larve have a unilateral
series of hooks, the head turns downwards;

Fig. 223. Psyche. a they lead a free life upon plants, feeding on
male, b male pupa, c y P Pp 2 g
female, d female pupa, leaves. The pupe have no transverse rows

e sac containing female, of spines on the abdomen. The adults are
f sac containing male M
larva.—After Taschen. usually of considerable size.

berg. 1. The Bombycide are bulky forms with dull faded

colours, usually of somewhat indistinct patterns; the
wings are broad and overlap when at rest ; the antenne of the male are pectinate
on each side, those of the female bristle-like or denticulate; the proboscis is
small. The larve are usually hairy, often, indeed, very hairy. The pupa lies:
within a cocoon formed either of spun threads alone, or of these together with
hairs thrown off from the larva, etc. The Bombycide are nocturnal, the males
flying about to seek for the inactive females; in some species the latter have
only rudimentary wings. To the Bombycide belong the Silkworm (Bombyx
mori), which came originally from China, and the cocoons of which afford the
chief supply of the silk used in industries; the imago is white, the larva
naked, and (unlike all other Bombycide) provided with a small horn at the
hinder end of the body. Silk is also obtained from several other species.

 
Class 3, Insecta. Order 6. Lepidoptera. 275

Others, again, are among the most deadly enemies to the cultivation of Pine-
trees; the Pine-lappet (Bombyx pini) and the Black-arch (B. monacha).
Allied to the Bombycide are the Noctuide with bristle-like antenne (often
denticulate in the males), rather narrow wings, well-developed proboscis; the
larve usually naked. Certain caterpillars of the Noctuide (e.g., the larve of
the Rustic, Agrotis segetwm), are often pests upon young plants, turnips,
potatoes, etc.

2. The Loopers (Geometride) are somewhat like the Bombycide in
appearance, they have broad, thin wings, bristle-like antenne (often pectinate in
the males). The almost naked caterpillar only possessing the hindmost pair
of prolegs is very characteristic. It moves like a leech, by alternately
straightening and arching the body (the thoracic feet and the prolegs func-
tion as do the fore and hind suckers of a Leech). In some species the female
has more or less degenerate wings (Fig. 208).

38. The Hawk-moths (Sphingidz). The body is short and spindle-shaped,
with a conical pointed abdomen, long, narrow fore wings, small hind wings, long
proboscis, and pointed antenne triangular in cross-section. When at rest the
wings lie horizontally. They are large excellent fliers; the larve are naked,
and the abdomen bears a curved horn.

4. The Butterflies (Rhopalocera) have a slender body, clavate
antenne, and broad wings, which, when at rest, are held perpendicularly ;
they exhibit beautiful, clear colours, and fly by day. The larve often
possess branching, spiny outgrowths, otherwise they are naked or sparsely
hairy. The pupe are characterised by their remarkably angular form; usually
they are simply attached by a single silken thread round the body, more rarely
they lie in a loose cocoon. Two of the best known forms may be mentioned:
the Cabbage-butterfly (Pieris brassicx, etc.), with white wings with small
dark spots (the larve on cabbages), and the Small Tortoiseshell
(Vanessa wrtice), with reddish brown wings, flecked with black (the hairy
larve live upon stinging nettles).

Order 7. Diptera.

The Diptera are holometabolous with reduced hind
wings and sucking mouth-parts. The head bears a pair
of large eyes, which, in the males, where they are best developed,
often touch in the mid-dorsal line. In the majority (Flies) the
antenne are short, and consist of only three well-developed
joints (of which, however, the last can usually be proved to be com-
posite), whilst in the Midges they are long and multiarticulate. The
mouth-parts are used for sucking the juices of plants or animals;
the chief features of their structure are given on p. 234. The three
thoracic segments are fused; the prothorax is small. The
rings of the first pair have few veinings, are well-developed and
adapted for flight; the hind wings are reduced to halteres, which
are in active motion during flight; their function is not definitely
ascertained. The legs have long coxe, long basal joints to the
tarsi, and often two or three small cushions (pads) on the
terminal joints. The abdomen is either sessile or separated from

Tt 2
276 Arthropoda.

the thorax by a constriction. The larve are invariably
maggots, t.e., the thoracic appendages are absent. Some, however,
still possess a hard chitinised head furnished with eyes, antennae, and
mouth-parts. In others on the contrary, the head is not well
marked, eyes are absent, the antenne absent or very degenerate, the
mouth-parts represented by a pair of darkly-coloured chitinous hooks
(mandibles ?). The larvee live in water, in decaying substances, in or
upon plants, or as parasites. In those Diptera whose larve have well
developed heads, the pupz are like those of the Lepidoptera, the
appendages lying close to the body; in those with “headless” grubs
the pupz remain within the last hardened larval skin (coarctate
pupe).

1. Midges (Nemocera) are usually slender with long antenne, which
in the males are often furnished with long hairs. The wings are narrow, the legs
long and thin. To mention afew forms: Gnats (Culex) antenne of fourteen
joints, with long hairs in the male; maxillary palps in the male longer than the
proboscis; the females alone possess mandibles, and stab and suck blood: the
larve are aquatic; they have only two stigmata, situated on a terminal process
(respiratory tube); the pupa is motile, and has two upright respiratory tubes at
the front end of the body; both larve and pupe usually hang suspended by these
respiratory tubes from the surface of the water. The Daddy-long-legs or

Crane-flies (Tipula) are
a m b large Midges, the larve of
which live in meadows, or
inrotten wood. The Gall-
flies (Cecidomyjia, etc.) are
very small delicate forms,
the larve of which, like the
Cynipide, frequently live in
galls (one of these for in-
stance, C. fagi, lives in the
well-known pointed gall of
beech leaves) ; many species,
however, do not form galls,
but the larve are found in
living or dead plants. In
some species of this group,
Fig. 224. Culea. a larva (head downwards), b pupa, pedogenesis is known to
c perfect insect.—After Taschenberg. occur (see p. 246). The
Sand-fly (Simulia), a
small fly-like Midge, the females of which, like Culex, are blood suckers; several
of the notorious “ Mosquitos” of warm countries are species of this genus;
others, Black-flies, eg., S. columbaczensis, of Hungary, are sometimes, when
they occur in large numbers, a terrible plague to cattle, since they sting them in
thin-skinned places, and the result of the wound is inflammation, fever, or even
death. The larve of this genus are aquatic.

2. Gad-flies (Tabanide); the antenna is said to be three-jointed, but
the last joint is constricted, and therefore consists of more than three joints.
The head is short and broad, with very large eyes; the mandibles are only present
in the female ; the abdomen is flattened; the larve are cylindrical, living in the
earth. The females suck blood from Mammalia, and are, for instance, great
plagues to Horses in summer.

 
276 Arthropoda.

the thorax by a constriction. The larve are invariably
maggots, t.e., the thoracic appendages are absent. Some, however,
still possess a hard chitinised head furnished with eyes, antennz, and
mouth-parts. In others on the contrary, the head is not well
marked, eyes are absent, the antennz absent or very degenerate, the
mouth-parts represented by a pair of darkly-coloured chitinous hooks
(mandibles ?). The larve live in water, in decaying substances, in or
upon plants, or as parasites. In those Diptera whose larve have well
developed heads, the pupe are like those of the Lepidoptera, the
appendages lying close to the body; in those with “headless” grubs

the pup remain within the last hardened larval skin (coarctate
pupe).

1. Midges (Nemocera) are usually slender with long antenne, which
in the males are often furnished with long hairs. The wings are narrow, the legs
long and thin. To mention afew forms: Gnats (Culex) antenne of fourteen
joints, with long hairs in the male; maxillary palps in the male longer than the
proboscis ; the females alone possess mandibles, and stab and suck blood: the
larvee are aquatic; they have only two stigmata, situated on a terminal process
(respiratory tube); the pupa is motile, and has two upright respiratory tubes at
the front end of the body; both larve and pup usually hang suspended by these
respiratory tubes from the surface of the water. The Daddy-long-legs or

Crane-flies (Tipula) are
é ¢ b large Midges, the larve of
which live in meadows, or
inrotten wood. The Gall-
flies (Cecidomyia, etc.) are
very small delicate forms,
the larvae of which, like the
Cynipide, frequently live in
galls (one of these for in-
stance, C. fagi, lives in the
well-known pointed gall of
beech leaves); many species,
however, do not form galls,
but the larve are found in
living or dead plants. In
some species of this group,
Fig. 224. Culew. a larva (head downwards), b pupa, pedogenesis is known to
c perfect insect.—After Taschenberg. occur (see p. 246). The
Sand-fly (Simulia), a
small fly-like Midge, the females of which, like Culex, are blood suckers; several
of the notorious “ Mosquitos” of warm countries are species of this genus;
others, Black-flies, e.g., 8. columbaczensis, of Hungary, are sometimes, when
they occur in large numbers, a terrible plague to cattle, since they sting them in
thin-skinned places, and the result of the wound is inflammation, fever, or even
death. The larve of this genus are aquatic.

2. Gad-flies (Tabanide); the antenna is said to be three-jointed, but
the last joint is constricted, and therefore consists of more than three joints.
The head is short and broad, with very large eyes; the mandibles are only present
in the female ; the abdomen is flattened; the larve are cylindrical, living in the
earth. The females suck blood from Mammalia, and are, for instance, great
plagues to Horses in summer.

 
278 Arthropoda.

pupates immediately after birth. On the Horse (and Cow) the active, winged
Horse-tick (Hippobosea equina) is found; in the wool of Sheep, the wingless
Sheep-tick (Melophagus ovinus). The same mode of propagation is followed
by the closely allied, small, blind, wingless Bee-louse (Braula ceca) parasitic
on Honey-bees.

The Fleas (Aphaniptera) are usually placed close to the Diptera, though
probably incorrectly. The body of these Insects is compressed, the colour bright
‘yellow to dark brown, the head small with a
1 single ocellus on each side (instead of the com-
pound eye), the antenne small, clavate, and lying
in a pit behind the eye. The mouth-parts are
adapted for sucking, but are very different in
structure from those of the Diptera. The actual
sucking-tube consists of the very long labrum
which is grooved ventrally, and the two mandibles,
which forma half-open tube; the first maxille
are short, pointed, and provided with a four-
jointed palp of considerable length ; they form,
together with the labium which carries two three-
jointed palps, a kind of sheath for the true
sucking-tube; a hypopbarynx is absent. There
are three distinct thoracic segments each bearing
a pair of long powerful legs (the hind legs being
Fig. 226. Pulex irvitans. somewhat stronger than the others) with very
1 imago, 2 larva, 3 pupa.— large coxe and pentamerous tarsi; they are
Atter Taschenberg. apterous. They live as parasites upon Mammalia
and Birds. The larve have neither eyes nor
legs; the whitish body is cylindrical, somewhat hairy; the mouth-parts are
biting; before pupating 'they spin cocoons. They live in sweepings, etc. Pulew
irvitans is a parasite upon Man; and other species of the same genus also
occur upon various other animals. The Chigoe or Jigger (Sarcopsylla
penetrans) of the tropical regions of America sucks the blood of Man and
other animals; the fertilised female bores into the skin, and as the ova develops
the abdomen enlarges enormously, reaching the size of a pea; the aperture
into the small cavity in the skin in which the parasite is situated is filled up
by the hind end of the body, so that the eggs can be conveniently deposited ;
after oviposition it dies.

 

Class 4. Arachnida.

The body is divided into a cephalothorax and an apodous
abdomen. The cephalothorax is usually unsegmented; the
abdomen, which is generally short, is segmented in some forms,
unsegmented in others; sometimes the two regions are separated by a
deep constriction (in the true Spiders), but usually there is no distinct
separation: sometimes the whole body is fused into a single
unsegmented mass (in the Mites). The cephalothorax is usually
furnished, anteriorly, with a varying number of ocelli, grouped in
different ways, compound eyes are never present. Antenne are
absent. There are two pairs of jaws, termed the cheliceree and the
Class 4. Arachnida. 279

pedipalpi. The chelicerez, which lie in front of the mouth,
consist of two or three joints, and are entirely different from the
mandibles of Insects and Crustacea; in many (e.g., in the Scorpions)
they are in the form of small chele. The pedipalpi are usually
leg-like, longer or shorter; the basal joint is often furnished with a

 

Fig. 227. Diagram of the anatomy of 4 Spider. a anus, 6 cecum of mesenteron,
b’ its anterior end, b” branches of the cecum extending into the legs which are here cut
away); ¢c cerebral ganglion connected with the ventral ganglionic mass, d mesenteron,
g poison glands, H heart, k, chelicerze, k pedipalpi, 1 hepatic duct, L lung-sac, Le liver,
M Malpighian tubules, M, dilation of the rectum into which M open, o eyes, ov ovaries,
S large silk glands, 8’ smaller do., T opening of the tracheal system, Z spinnerettes, ?
female genital aperture—Modified from Krieger.

kind of grinding ridge, whilst the rest of the joimts are either all
‘simple, and form a strong palp, or the two distal joints are modified
to form larger or smaller chele. Behind the pedipalpi are four
pairs of legs (ambulatory appendages), which are usually all
similar, and generally consist each of seven joints.

According to the usual interpretation, the cephalothorax of the Arachnida
corresponds to the head and thorax of Insecta, the chelicere represent the
mandibles, the pedipalpi the first mavxille, whilst the first walking legs are
comparable with the second maxille (the labium), and the remaining legs
with those of Insects. Against this view, however, may be mentioned, among
other things, the structure of the chelicere, which are totally unlike the mandibles
of Insects (consisting of several joints, etc.). Moreover, the Arachnida, on the
whole, differ so essentially from the Insecta that it is impossible to make a
special comparison of this nature. It would, therefore, appear very doubtful
whether the jaws of the Arachnida can be compared with those of other
Arthropods; more probably they are thoracic limbs, which in correlation
with the degeneration of the head, have taken on the function of jaws; in
this case the mouth would have moved back to lie between the thoracic
limbs.*

The skin in most Arachnids is not so hard as in the Insects,
usually the cuticle is leathery, often setose. Among the glands

of the skin, the spinning glands, present in certain divisions

 

* As in Limulus, with which the Spiders are in no way allied, a view that has
been incorrectly held by some authorities.
280 Arthropoda.

(Spiders, Pseudoscorpions, and others) must be specially noticed.
The nervous system is of the usual Arthropod type, but
characterised in most forms by the
fact that all the ventral ganglia
are fused into a single mass; a
series of distinct ganglia occurs in
quite a few (e.g. the Scorpions).
Of special sense organs only
the eyes mentioned above are
known; but since some Arachnids
can produce sounds, it is very
probable that auditory organs are
also present. The alimentary
canal is characterised by the
presence of several ceca arising
from the anterior portion of the
mesenteron and extending some
distance into the legs. In the
Spiders, a single large curved
cecum arises on each side from
the mesenteron, is directed for-
wards and gives off branches which
enter the bases of the legs; the

; front ends of the two ceca lie close
- ee ea ae paren together above the fore gut (Fig.
b’ its anterior end, b” lateral branches of 228), and in many Spiders, unite

the same, into which the Malpighian . : .
tulidise open, @ leealia dubte, sa neeen: at this point. Salivary glands are

teron, 0 esophagus, o’ suctorial stomach, present, and, unlike Insecta, many
HMstieen ape OEe Arachnida possess a large liver

consisting of numerous tubules
situated in the abdomen. In most Arachnida there are Malpighian
tubules, like those of the Insecta.* The respiratory organs
are represented either by trachee, which open to the surface by
a small number of stigmata, or by so-called lungs; the latter are
invaginations of the skin, each of which is again provided with
a series of flat evaginations, lying close together like the leaves
of a book; each form of respiratory organ may occur alone,
or both may be present in the same individual. The vascular
system is often better developed than in Insects ; in the Scorpions.
for instance, which are provided with lungs, there is a circula-
tion similar to that of many Crustacea; the blood flows from the
heart through a number of arteries; the venous blood collects in

 

 

~ * In a variety of Arachnida (Scorpions, Phalangiide, etc.) there is, in the cephalo-
thorax, a pair of large coxal glands which usually open at the base of the third
pair of limbs. They have been regarded as excretory, and considered to be segmental
organs; the correctness of this interpretation is doubtful.
Class 4. Arachnida. 281

a large ventral blood sinus, and passes thence to the lungs, from
which the now arterial blood returns to the pericardium, and enters.
the heart through the ostia; the heart of the Scorpions is a long
tube, divided, as in the Insects, into a series of chambers (eight), each
provided with a pair of ostia. In other Arachnida, the heart is.
shorter, and has a smaller number of these
ostia, the vascular system is less complete, the,
blood flowing into large sinuses between the
organs. As in other Arthropoda, there is a pair
of ovaries in the female, a pair of testes
in the male; the two glands, whether ovaries
or testes, are frequently partially united, and
the ducts open by a common aperture, far
forward on the ventral surface of the abdomen.
In the Phalangiide and the Acarineg, the gonads
are united at one end, the other ends being
* prolonged into the oviducts (or vasa deferentia). Bi, 2. Paxwal
These soon unite to form a single canal, which apparatus of one of
thus arises from a circle formed by the genital ‘the Phalangiidae.
. ‘ ; o ovary, u swelling of the

glands and their two ducts. Sexual dimorphism ong ‘oviduct, op ovi-
is frequently displayed. The Arachnida only ee ee

occasionally undergo a metamorphosis; After Gegenbaur.
the newly-hatched animals are generally like
the adults, but sometimes the last pair of limbs is wanting.

Like Insecta, the Arachnida are emphatically terrestrial and
fresh-water forms; many are parasitic. Besides the Pycnogonide,
whose position here is not without some doubt, a few of the
Acarine are marine.

 

Order 1. Arthrogastra.

The members of this order, which includes a number of very
different forms, are distinguished from the two following orders,
in that the abdomen is segmented. The chelicere are
generally chelate. Respiration is effected by lungs or trachee.

1. The Scorpions (Scorpionidx) possess a more elongate body than the
rest of the Arachnids. The cephalothorax, which is not constricted off from the
abdomen, bears in the middle line, dorsally, two ocelli, and anteriorly on each
side, a small group (two to five); the chelicere are short, strong chele; the
pedipalpi, which forcibly recall the large chele of the Crayfish, are of considerable
length (as long as, or longer, than the legs), and each is furnished with strong
claws, the four pairs of legs are well developed. Of the thirteen abdominal
segments, the last six are much narrower than the anterior, and form a very movable
tail (post-abdomen), which the animal curls up over the rest of the body so
as to carry it with the tip pointing forwards; this tip, the sting, bears the
openings of two poison glands, which lie in the anterior swollen portion of the
282 Arthropoda.

terminal joint. The anus is situated in the membrane between the last and
the penultimate somites. Anteriorly, on the ventral surface of the abdomen,
just behind the legs, there arises a pair of flattened, unsegmented appendages
{the pectines), the posterior edges of which are toothed; their significance is
unknown. Close to them lies the genital
aperture; on the broad portion of the
abdomen (pre-abdomen) there are also, on
the ventral surface, four pairs of slit-like
stigmata, the openings of the same number
of lung-sacs. The Scorpions are fairly
large animals; they are viviparous, the
young ones remain with the parent for the
first few weeks, but the latter dies before
long. They occur in the tropics and in
the warmer regions of the temperate zones
(two species in S. Europe). They remain
in one place, feeding upon Insects and
Arachnids, which they seize with their
chele, and kill by a stab of the sting.

2. The Pseudoscorpions (genus
Chelifer and others) recall at first sight
the Scorpions, which they resemble in the
structure of the chelicere and pedipalpi.
They differ, however, in many respects.
The abdomen consists of eleven somites;
Fig. 230. Scorpion, seen ven- its hinder region is not developed as a

ee St ac aan post-abdomen, and a sting is absent; further,

genital aperture, kpectines, ochelicerw, Tespiration is by trachew, which open
w pedipalpi, s stigmata, 1—4 legs— by two pairs of stigmata on the ventral
After M. Edwards. surface of the abdomen. Anteriorly there

are one or two eyes on each side of the
cephalothorax, but these may sometimes be absent. On the ventral surface
of the abdomen, near to the genital pore, is a number of small papillae,
perforated by the apertures of the spinning glands. The ova and the
larve, which are hatched in a very imperfect condition, are carried about
on the ventral surface of the body; the former are bound together
into a mass. The Pseudoscorpions are small; they live beneath bark, in
moss, old books, collections of Insects, and so forth; they feed upon Mites,
Book-lice, ete.

3. The Harvest Men (Phalangiidx)* have a short, arched body, which is not
sharply divided into cephalothorax and abdomen. The cephalothorax, which
consists of three indistinct and immovably connected segments, bears a pair of
eyes dorsally, like the two median eyes of Scorpions; the chelicere have small
chele, the pedipalpi are antenniform, much shorter than the extremely long legs,
which are characterised by the division of the proximal joint into a number of
smaller segments. The abdomen consists of eight ill-defined segments, it is
provided, anteriorly, with a pair of stigmata leading into a system of trachee.
The Phalangiide are peculiar in that the males possess a long extensile copulatory
organ, the females a long eversible ovipositor; the genital aperture is anterior.
At first sight they look very like long-legged Spiders, and are chiefly met with in
the dwellings of mankind.

 

 

* This description does not apply to a few aberrant forms.
Class 4. Arachnida. .Order 2. Araneina. 288

Order 2. Araneina (Spiders),

The Spiders may be distinguished from other Arachnidas by the
separation of the cephalothorax from the abdomen by a deep
constriction. Both regions are unsegmented, but newly-hatched
animals show indications of abdominal segmentation. Anteriorly the
cephalothorax bears a group of six to eight ocelli, arranged in various
ways. The chelicere consist of a simple, strong basal joint, and a
claw-like terminal segment, at the tip of which opens a poison gland.
The pedipalpi are antenniform, with broad basal joints; the terminal
joint in the adult males is modified, hollowed out, etc., and thus
adapted for introducing the spermatozoa into the genital aperture of
the female; it is often very complicated in form. The legs are very
strong, often of considerable length. Anteriorly, on the ventral
surface of the abdomen, there are always two stigmata, each leading
into a lung-sac; in a few Spiders, posterior to these, there is a
second pair, which either (Mygale) lead into a similar pair of lung-
sacs, or (Argyroneta) lead intotraches. In most of the Spiders,
however, this second pair of stigmata is wanting, instead there is an
unpaired stigma posteriorly, just in front of the spinnerettes, and
this leads into a variously modified system of tracheze. The majority
of this group possess both lungs and trachewe; a smaller
number have only lungs, but in this case there are four. Posteriorly,
below the anus, there are four or six spinnerettes, fairly large
processes beset with a larger or smaller number of short, fine tubes (in
Epeira, altogether about 700); at the apex of each of these is the
aperture of a silk gland, which lies in the abdomen. These spinning
glands may vary considerably in structure, even in the same animal,
and may give rise to different secretions. As the substance is
pressed out through the tubules it hardens to form fine threads;
in many Spiders which form webs some of these threads remain sticky.
By means of the feet the fine threads may be woven together into
coarser ones; all Spiders spin cocoons for their eggs, many form
webs or tubes, in which they live. The genital aperture lies
anteriorly on the abdomen. The males are often smaller than the
females, sometimes the difference is so great that, although in other
respects the structure is normal, they have been termed dwarf
males. Spiders feed chiefly upon Insects which they kill with
their chelicere. There are very many species, but the group
is very uniform, and is abundantly represented in temperate
countries.

As examples may be mentioned: the Bird-spiders (Mygale), large tropical
forms, thickly covered with hairs, and possessing four lung-sacs; they will even
attack and consume small Vertebrata; the common Cross-spider (Epeira
diadema), which, like the House-spider (Tegenaria domestica), spins webs,
and often lives in or near houses; the Water-spider (Argyroneta aquatica)
284 Arthropoda.

abundant in small pieces of water, where it builds a bell-like web, the cavity
of which is filled with air, carried by the animal from the surface of the water
in its velvety covering of hairs.

Order 3. Acarina (Mites).

The Mites are small, frequently even microscopic Arachnids, in
which the cephalothorax and abdomen are generally fused
into a single mass. They possess from one to three pairs of eyes, or
none at all. The mouth-parts are usually short. The pedipalpi,
as well as the cheliceree, may be chelate, they are sometimes used
for biting, sometimes for stabbing. A heart has only been demon-
strated in some of the Acarines; special respiratory organs are
frequently absent, but in many there is a tracheal system,
opening by a pair of stigmata. On hatching, the Mites possess only
three pairs of legs, the fourth pair develops later; in other respects
also, the larvee may differ more or less from the adult. Many
undergo a resting period before moulting.

The genital aperture, as in
other Arachnida, is situated
anteriorly on the ventral sur-
face of the abdomen. In some
females (Tyroglyphus, probably
also in the Sarcoptide), there
is, besides, the ordinary genital
opening, a second one pos-
teriorly, just in front of the

Fig. 231. Diagram of the anatomy of a Tyro- ae By uy, pieh the spermatozoa
glyphus ; legs cut off. a anus, c cerebral ganglion, ane: received during copulation,
d mesenteron, k, chelicera, k, pedipalp, M Malpighian whilst the anterior serves as
tube, m ventral ganglionic mass, Ov ovary; 9 aper- the oviducal pore.
ture of the oviduct, ?’ copulatory aperture.—Orig. 1. Trombidiide, ved,velvety,

quadrangular animals, some of
which are among the largest of the Mites. The larve live as parasites on
Phalangium, Spiders and Insects; the adults are predaceous. The Water-
mites (Hydrachna and others), are roundish animals, often of a red colour,
which swim about in the water by means of their hairy legs; the hexapod
larve are parasitic on aquatic Insects, whilst the adults are usually free-living
(one species of this group is in the adult stage parasitic upon the gills of
the Fresh-water Mussel). The Beetle-mites (genus Gamasus) frequently occur
on Beetles, Bumble-bees, etc. They are small animals, with an oval, flattened,
rather hard, brownish body; they run about freely on the body of the host. An
allied, but thin-skinned form, the common Bird-mite (Dermanyssus avium)
occurs on Birds (Fowls, Canaries), and sucks their blood; like some of the
Hemiptera, it is a temporary parasite preying upon the Birds by night. The
Ticks (Iwodes) are flat, with a fairly hard, but very extensible exoskeleton ;
they can move about, but attach themselves to Mammals, Birds, and Reptiles,
in order to suck their blood; the female increases enormously in size when
gorged. The species of the Genus Tyroglyphus (Cheese-mites and Flour-mites),
live in old cheese, meal, and many other half-dried organic substances; they
are white, shining, almost microscopic animals. All these Mites, with the
exception of Tyroglyphus, possess trachez.

 
Olass 4. Arachnida. Order 3. Acarina. 285

2. Itch-mites (Sarcoptide) are microscopic, blind, without trachee, and
generally with suckers at the tips of the feet; they live as stationary parasites
on Mammals and Birds, and feed either upon the skin or upon exuded lymph.
There is a marked sexual dimorphism, and it is interesting to note that copula-
tion occurs before the females have reached the adult form, and whilst the ovary
is still entirely undeveloped. Here belongs the human Itch-mite (Sarcoptes
scabiet) which burrows in the epidermis; the female has suckers on the two
anterior pairs of legs, the small males also have them on the fourth pair.
Various nearer or more distant allies live in and on the skin of other Mammalia
and Birds, causing mange. Peculiar microscopic Mites of elongate form and with
short legs, destitute of suckers (Demodex.folliculorum) occur in the hair follicles
of the human nose; they are quite harmless, but a variety of the same species
which is parasitic upon Dogs, causes a very bad skin disease in this animal.

3. Gall-mites (Phytoptus) are microscopic, with elongate bodies, and
are easily distinguished from other Mites by the possession of only the two
anterior pairs of legs. They suck the sap of plants and thus cause various
abnormal growths of leaves and buds of many,
especially woody, plants. A

APPENDIX TO THE ARACHNIDA.

2 mA ifs

The three groups following are very peculiar, &S~
and their systematic position is not at all certain ; 7
they are generally, however, regarded as belonging
to the Arachnida, and this is probably true for
the first two. They are, however, so very aberrant
in all respects that they are best considered in an
appendix.

The Pentastoma (Pentastomum) live para-
sitically in various Vertebrata; they are animals
of very considerable size, and at first sight are
very like short-jointed Tapeworms. The body is
elongate, usually flattened, and separated by
furrows into a large number of short segments ;
the segmentation is, however, only external and
does not affect the internal structure; the limbs Par,
are only represented by two pairs of chitinous
hooks which are situated anteriorly not far from
the mouth. The alimentary canal is a straight
tube, the anus posterior. The male genital
aperture lies far forward on the ventral surface,
the female pore close to the anus; the genitalia
recall those of the Arachnida. The central
nervous system is reduced to a ventral ganglion
below the pharynx anda. ring. arising from it
to run round this. Sensory, respiratory, and
circulatory organs are absent. Pentastomum Fig. 232. Female of Penta-
tenioides, when sexually mature, inhabits the  stomum taenioides. ad gut, h
nares and frontal sinuses of the Dog and the hooks, oe esophagus, ov ovary,
Wolf (female 8 c/m. and upwards, male 2 c/m. pares eee va oviduet.—
long). The ova escape with the mucus of the Pee Bet
nose, and each contains a young Pentastomum,
possessing two pairs of small hooked legs. If these ova are ingested by a Hare
or Rabbit, the egg shell is dissolved in the stomach, and the small animal makes
its way into the liver, where it grows considerably, but does not become sexually
mature. Immature Pentastoma are also now and then found in other Mammals,

 
286 Arthropoda.

and in Man himself; if an organ containing such parasites be devoured by a Dog,
they wander into the nasal cavities and complete their development.

The Pycnogonida, or Crab-spiders, have a very rudimentary
abdomen; the cephalothorax is narrow and divided into four segments. The
most anterior is elongated to form a snout-like process, at the tip of which is the
mouth ; the cephalothorax bears four ocelli, a pair of chelicere which are usually
clawed, and a pair of antenniform pedipalps, though both these pairs of limbs may
be absent; and also four pairs of eight-jointed legs, which may be thick or
very elongate, and which always make up the main mass of the body. In
the males, at the base of the first pair of legs, there is a pair of jointed,
leg-like appendages, to which the eggs are attached; these appendages
may also sometimes occur in the females, which do not carry the eggs. The
ceca of the alimentary canal extend far into
the legs. Respiratory organs are wanting, but
a heart is present. There is a pair of ovaries,
or of testes, which unite posteriorly and send
branches into all the legs; ova and spermatozoa
escape by apertures in the second joints of all, or
of some of the legs. The newly-hatched larve are
unsegmented, and possess only three pairs of
limbs, of which the anterior represent small chele,
and are modified to form the chelicere of the
adult; the second and third pairs are short; the
latter apparently degenerate, whilst the second
form pedipalpi. Sometimes the larve are
parasitic in Hydrozoa. The Pycnogonide are marine, crawling slowly about at
the bottom of the sea. In northern seas both short-legged (Pyenogonum) and
long-legged forms (Nymphon) occur.

The Tardigrada, or Bear-animalcules, are microscopic animals, which
live in moss, in gutters, and in fresh water. They are elongate, indistinctly seg-
mented, and possess four pairs of stumpy unjointed legs, which have claws at
the tips, and by means of which they crawl slowly about. A pair of stylet-
shaped stabbing organs may be protruded from the mouth. Respiratory
and circulatory organs are absent: on the other hand they possess a pair of

 

Fig. 233. Pycnogonum.

 

Fig. 234. Diagrammatic figure of a Tardigrade, ¢ viewed from the left side. a anus,
bg ventral ganglion, ¢ cerebral ganglion, d gland, ex excretory organ (?), m stomach, 0 mouth,
p pharynx, ¢ testis. 1—4 four legs.—Orig. (with the use of figures by Plate.)

small eyes and a fairly well-developed nervous system, consisting of a large
cerebral ganglion and several distinct ventral ganglia. The sexes are separate;
the males are much more rare than the females. If the water, in which the
Tardigrada are living, dries up, they shrink to small granules, and may pass
years in this condition ; when they are moistened again they swell out and again
become active. The systematic position of this small group is still uncertain, and
their location amongst the Arachnida appears to be hardly justified.
Phylum 7. Mollusca.

The body is unsegmented, very varied in form, and without
jointed appendages. The skin is soft, often ciliated over large tracts;
the cuticle absent or (usually) very thin. The body-wall forms,
ventrally, a muscular foot, which is either discoidal or com-
pressed, and, on account of its great contractility, forms an important
locomotor organ. Anteriorly there is a more or less well-developed
head with a mouth, often also with tentacles and eyes. Above
the foot and head there is a fold of skin, the mantle, which
extends round the whole animal; in some instances it is narrow;
in others it forms a large lamellar expansion on either side of the
body (Lamellibranchs) ; in others again it is better developed either
at the anterior or the posterior end than elsewhere (Gastropods,
Cephalopods), forming a pouch, the pallial chamber, between
the body and the mantle (k in Fig. 239 and 268 B). In the
majority, the greater part of the animal is covered by an open
shell, secreted by the skin, with which it is usually only
connected at isolated spots, whilst for the most part it les free
upon the upper surface of the body. The shell is never cast (like.
the cuticle of Arthropoda), but is continually increased im size by
the formation of new material at the edge, whilst it is thickened by
deposits from within; it consists of a substance, conchiolin,
something like chitin, but differing from it chemically, and usually so
thoroughly impregnated with calcareous salts, principally
carbonate of lime, that these constitute the chief part of the
shell.

The alimentary canal usually exhibits a large expansion,
the stomach; the anus is either at the hind end of the animal or is.
moved to one side. Salivary glands opening into the mouth
are generally, and a well-developed liver invariably, present. In
the majority of the Mollusca (with the exception of all Lamellibranchs)
there is, on the floor of the mouth a muscular pad, the tongue,
covered on its upper surface with a thin, stiff membrane, the
radula, or lingual ribbon, on which are arranged transverse rows.
288 Mollusca.

of delicate, chitinoid teeth of various forms, with their points
projecting backwards. The teeth in one row may be all similar, but
very frequently some differ from the others; each row is definitely
arranged, and a median tooth is usually present, on either side of which
the other teeth are symmetrically disposed. The successive rows are
generally similar. The anterior eud of the radula is continually being

Fig. 235. Fig. 236.

 

Fig. 235. Portion of the radula
of a Cephalopod.—Orig.

Fig. 236. Diagrammatic longitudinal
section of the mouth of a Gastropod.
k jaw, o mouth, r radula, rs radula sac,
sp cesophagus.— Orig.

 

worn down and rubbed away ; the posterior end lies in a narrow sac,
the radula-sac, which is frequently very deep; new teeth are
formed at its end, and the radula is gradually pushed out from it.
Besides this organ, which is very characteristic of the Mollusca, there
occur also within the cavity of the mouth other hard structures,
varying in form (also composed of a substance like chitin), which may
be termed jaws.

The respiratory organs are for the most part gills of
various kinds, usually occurring in the mantle cavity, which on this
account may also be termed the branchial chamber. In some forms
gills are wanting, and the mantle chamber may then (as in the
Gastropoda) serve as a pulmonary organ; from others special
respiratory organs are altogether absent. The vascular system
is for the most part well developed, although the blood flows partly
through spaces between the organs. The heart consists of one or
two (in the Nautilus as many as four) auricles into which the
blood flows from the gills (or pulmonary chamber), and a thick-
walled ventricle, which receives it from the auricles, and drives
it into the body. The venous blood collects in one or more large
‘spaces which supply the respiratory apparatus. The excretory
organs or kidneys are saccular, and have each two openings,
of which one lies on the surface of the animal, whilst the other
leads into the so-called pericardium, a portion of the body-cavity
surrounding the heart. The number of the kidneys varies (one to
Mollusca. 289

four); they clearly correspond with the segmental organs of the
Cheetopoda.*

The nervous system is peculiar; the typical arrangement is
as follows (Fig. 237 B): above the anterior portion of the alimentary
canal lies a pair of cerebral ganglia, connected by a com-
missure ; from these a nerve cord runs, on either side, round the
cesophagus to a pair of pedal ganglia, lying in the foot,
which are likewise connected by a commissure; behind the cerebral
ganglia lie a pair of pleural ganglia, joined by one pair of
connectives to the cerebral, by another to the pedal ganglia. From

   

9 g 4g

 

Fig. 237. Diagram of the central nervous sys tem in various Mollusca.
A—B Gastropods, C—D Lamellibranchs. h cerebral ganglion, f foot, p pleural ganglion,
ig visceral ganglion, ¢ visceral loop, » pedal nerve.—Orig.

each pleural ganglion there arises a nerve cord, which is usually
long, and runs posteriorly through the body, uniting with that
of the other side to form a loop termed the visceral loop:
the visceral ganglia lie upon it, posteriorly. Great differences
appear in the various Molluscs; the nerve cords may be long or
short, sometimes so short that all the ganglia lie close together
and fuse to form a single mass (Fig. 237 D).

The cerebral ganglia apparently correspond with the same structures in the
Cheetopoda, the pedal ganglia with the first ventral pair of the same; one pair of
nerves, the pedal nerves, which proceed from the pedal ganglia and run
posteriorly, and, in various Molluscs (e.g., in Chitons and certain Gastropods,
Fig. 237 A), are very thick, and are connected by fine transverse cords, probably
correspond with the ventral nerve cords of the Chetopods. The pleural ganglia
and the visceral nerves must be regarded as new structures.

 

*In many Mollusca—Cephalopoda, many Lamellibranchs, several Gastropoda—
certain parts of the epithelial covering of the pericardium are glandular. Similar
epithelium may occur upon evaginations of the auricles, or there may be true
glandular evaginations of the pericardial wall. Apparently all these structures,
which are called indiscriminately pericardial glands, are excretory organs.
The waste substance formed in the cells, partly as concretions, is doubtless got rid of
by the kidneys.

Tu
290 Mollusca.

Upon the head of the Gastropoda and Cephalopoda there is
a pair of eyes, which usually conform to one of the types figured
in Fig. 20, 2,4-6 (p. 21); occasionally they are also present on
other parts of the body. In Chitons and Lamellibranchs, cephalic
eyes are wanting; if any are present in these animals they occur on
other parts of the body. The Mollusca possess a pair of auditory
vesicles with one or more calcareous otoliths (cf. Fig. 19, p. 20);
the auditory vesicles are situated near the pedal ganglia, but the
nerves which supply them (auditory nerves) proceed direct from the
cerebral ganglia. The tentacles which are universally present in
Gastropods are to be regarded as tactile organs; in other
Mollusca, other appendages, papille, etc., have a like function. One
or a pair of sensory organs (specialised portions of the skin) regarded
as olfactory,- occurs in the mantle cavity of most Gastropods and
various Lamellibranchs ; behind the eyes in the Cephalopoda there is
usually a pair of pits with a similar significance.

Reproductive organs. In some Mollusca there is a pair
of gonads, each with its duct; but frequently there is only a
single gland and duct, or the glands are fused, the ducts, separate
and so on. In other respects, also, the reproductive system offers
great diversity ; many forms are hermaphrodite, others are bisexual ;
the ducts are often furnished with accessory apparatus; usually
peculiar copulatory organs of various kinds are present (see the
various classes). Parthenogenesis is unknown within this group, as
is also asexual reproduction.

The majority of the Mollusca undergo a metamorphosis;
the larva swims by means of a velum, a discoid expansion of the
head with a ciliated margin; often, however, it is represented
only by a crown of cilia upon the head (cf., the larva of the
Cheetopoda).

The Mollusca are pre-eminently aquatic, chiefly marine
animals: many Gastropoda, however, live on land, but for the most
part in damp places. They are not only very abundant at the
present day, but in earlier periods were represented by a great
diversity of forms, and their shells are among the most numerous of
fossils.

Class 1. Placophora (Chitons).

The Chitons, which were formerly incorrectly placed in the next
class, are a small group of Mollusca possessing a well-marked
bilateral symmetry almost throughout; there is here no trace
of the torsion so characteristic of Gastropods. They are rather
flattened, somewhat convex, oval animals, with a large discoid foot
ventrally. Dorsally there are eight transverse shell-plates, which
are broad, calcareous and imbricate ; these, like the smaller calcareous
Class 1. Placophora. 291
plates, spines, and bristles, which cover the edge of the dorsal surface,
are true cuticular structures. The mantle is represented only by
a narrow fold which runs round the whole body, dorsal to the head
and foot (Fig. 268 A); it covers a series of plumose gills on either
side. The head, which is not very well marked, bears neither eyes
nor tentacles; on the other hand, eyes occur irregularly on the
dorsal surface in several forms; they are situated at the tips of
the soft projections of skin which
perforate the shell-plates, and thus
apparently on the shell-plates them-
selves. The nervous system is
chiefly characterised by the fact that
two of the cords which spring from
the pedal ganglia and run posteriorly
(see p. 289) are very strong and are
connected by numerous transverse
cords. A well-developed radula
is present; the anus is posterior
and median. The heart lies above
the rectum, it is possessed of two
auricles, arranged symmetrically on
either side of the ventricle. There
is a pair of elongate branched
Kidneys, opening into the mantle. P88 ohipn viewed hm
groove, one on either side, just mouth, f foot, k gills, g genital pore,
anterior to the anus. The sexes 7% winary aperture, a anus.—Orig.
are separate ; ovary and testis single,
but the ducts paired, and opening on either side a little in front of
the excretory pores in the mantle-groove. The larve are oval,
provided with a velum, and two eyes which later undergo degeneration.
The smaller species of eyeless Chitons occur on British coasts; the
larger forms live in the warmer seas.

Formerly another small group of bilaterally symmetrical Mollusca was also
placed with the Gastropoda, namely, the Scaphopoda (genus Dentalium,
Elephants-tusks, etc.), in which the elongate body is surrounded by a slightly
curved, conical shell open at both ends. Further details of this group which is

in many respects very aberrant and isolated in position, cannot, however, be given
here.

 

Class 2. Gastropoda.

The structure of the Gastropods is most easily comprehended on
the supposition that they have arisen by the modification of a Chiton
in the following way (cf, Fig. 268A and Fig. 239). The dorsal
surface has become much arched, generally indeed drawn out into a
long sac, the ventral portion of which is surrounded by the lower

v2
292 Mollusca.

margin of the mantle-fold. At the anterior end of the sac, the mantle-
furrow is much accentuated, forming a deep pouch, the mantle-
cavity, opening ventrally; posteriorly the furrow is shallow, just as
in the Chitons. Most of the
organs (alimentary canal,
liver, gonads, etc.) are con-
tained in this saccular region,
whilst the lower portion of
the body is almost without
viscera; the sac is covered by
a calcareous shell. In con-
sequence of this peculiarity
of structure, the body of the
animal is naturally divided
into two portions, the soft

Fig. 239. Diagrammatic figure of a Gastro- visceral hump, the lower
pod seen from the left side (the shell removed). oui dary of wiih iaaudieatad

a anus, f foot, k mantle cavity, m stomach, mu

shell muscle, 0 mouth, op operculum. Besides by the edge of the mantle,
the parts indicated by letters, certain portions of ad tral ti ‘
the nervous system are also drawn, viz., cerebral ®2@ @ vVentra portion, im-
and pleural ganglia (seen above the cesophagus), cluding the foot and head.

 

and pedal ganglion (below the esophagus). The .
dotted line indicates the boundary of the mantle : The head is : usually
chamber.— Orig. fairly well defined; it bears

a pair of tentacles, which,
in terrestrial forms, can be invaginated like the finger of a
glove, and withdrawn into the head, but in other forms, are only
strongly contractile. In some Gastropods (Opisthobranchs), behind
these there is another pair of tentacles, which may often be concealed
within depressions on the head, and whose surface is frequently

A B Cc D
Fig. 240. Diagrams of various forms of Gastropod shells seen from the

left side. A-—B slightly curved; C spiral shell in which the successive coils do not
touch ; D ditto, in which the coils lie closely upon each other (the common type).—Orig.

much folded; they are regarded as olfactory organs. Besides these,
a pair of small eyes is generally situated upon the head; they
are sometimes borne at the tips of special tentacle-like stalks (as in
the Common Snail), but are usually placed directly upon the head
Class 2. Gastropoda. 293

itself or on the side of the tentacles. The foot is generally a
flat, very contractile disc, occupying the whole ventral surface of
the lower portion of the body.

The soft, thin-skinned visceral sac is covered by a tubular shell,
open at one end, closed at the other, and becoming gradually wider
towards the open end. Only in rare instances is the tube straight or
slightly curved, usually it is a spiral, the concavity of which
corresponds, in Gastropods, with the ventral side of the visceral sac
(see Fig. 239). The individual coils of the shell almost invariably
touch one another, and are, indeed, closely united. Some discoidal
shells form a flat coil, like a watch-spring ; usually, however, the
closed end of the tube is drawn out on one side, so that the axis of
the shell describes a spiral round a cone. The form of most
Gastropod shells is, therefore, conical, although many are widely
aberrant from this, on account of the very different form of shell-
tube. If a shell be placed so that the axis of the cone stands
perpendicular, with its apex (the closed end) uppermost, and the
mouth towards the observer (Fig. 241), the aperture then either

Fig. 241. Fig. 242.

 

Fig. 241. The shells of two examples of a tropical
land Snail (Bulimus perversus). A left-handed spiral.
B right-handed spiral.—After v. Martens.

Fig. 242. Shell of a Snail (Paludina) in which a
large part of the wall towards the observer is broken
away. 7 umbilicus, s columella.—Orig.

 

lies to the right of the axis, and the shell is said to be a right
handed spiral; or it lies to the left of the axis, giving a left-handed
spiral. The shell is borne by the animal in such a way, that its
point, if a right-handed spiral, is towards the right (and points
upwards and backwards) ; or if a left-handed spiral, towards the left
(upwards and backwards). Right-handed spirals are much more
common than left; in some species the one kind occurs, in others, the
other ; as individual variations, examples of the left-handed spiral may
be found among forms in which the right is normal ; but it is very rare
to find both forms equally common in the same species. In some
294 Mollusea.

Gastropods, the shell-tube is coiled in such a way that a
large cavity is left in the middle, surrounded by the turns of
the shell, and open below; usually, however, the coils lie upon
one another, so that this cavity, the umbilical-tube, is very
narrow; and frequontly, its outer opening, the umbilicus, is
closed by the last coil. Those portions of tho spiral which im-
mediately surround the umbilical-tube, form a kind of central column,
the columella.

Growth of the shell occurs as follows: new material is secreted
by the thickened edge of the mantle, and is deposited at the rim of
the aperture, and thus increase in length takes place; growth appears
to be intermittent, in the course of a short time a large portion is
added, then a longer period of rest occurs, and so on. ‘I'he portion
of newly-formed shell substance, which covers and grows on to the
older coils, is usually thinner than the remaining free portion, and is
often difficult to make out. In addition to this deposit at the mouth,
calcareous material is also laid down within the shell, over the
whole surface of the visceral mass, and in this way an increase in
thickness iy effected. ‘The small, oldest coily at the apex of the
shell may, by this means, become filled with lime: occasionally such
portions get broken away. Besides the new formation of calcareous
material, » reabsorption of the older part frequently occurs ;
for instance, it may occasionally be observed that before the period of
growth begins, superficial portions of the old shell, near to the
mouth, become loosened and worn away where the new shell will
later be deposited ; internally, too, an absorption of the conccaled
portions of the shell takes place, by means of which the septa between
successive coils may be much thinned, or, completely dissolved. ‘Tho
Gastropod shell consists chiefly of calcium carbonate, with a small
amount of conchiolin; there is usually a thin, uncalcified horny layer,
superficially, which is easily removed.

Transverse sections of shells vary in form, they ure rarely circular, usually
somewhat compressed, occasionally even elliptical. In some instances, the younger
coils may almost, or entirely, surround the older ones, so that the latter are
nearly, or completely, hidden from without. The axis of the conical shell is
sometimes long, sometimes short; in the latter case, the shell approaches a discoid
form. In some cases the coils are very numerous, and the cross-Kection of the
tube increases gradually in size; in others there are only a few turns, which
increase rapidly in diameter. In not a few Gastropods, when growth has ceased,
the mouth of the shell takes on a peculiar form, becomes thickened, and widened ;
in others, even in young animals, there is a peculiar rim (thickened and
rough), round the mouth and at the close of each period of growth a new rim is
formed, so that the old mouths are indicated by special regions in the shell. (For
the notch in the shell for the branchial syphons, see below). The shells are often
brightly coloured, and rough with finer or coarser sculpturings on the surfuce,
etc. Sometimes the edge of the mantle is specially well developed, wraps over the
edge of the shell, and secretes a bright layer over the surface (¢.y., in Cowries,
Cypria).
Class 2. Gastropoda. 295

In the majority of the Gastropods the shell is formed in the way
described above; there are, however, exceptions. In some forms (e.g.,
Vermetus) it is coiled in quite an irregular spiral; this is correlated
with its firm attachment to some foreign object; the regular spiral
twisting of snail shells is connected with the fact that a regular
spiral shell can be more easily carried than a long and straight or
an irregular one. In some forms, which are free-living whilst young,
but sessile later, the shell is, at first, regular, but then grows
straight or irregular. In others it is hardly possible to speak of a
tube, the whole shell is a simple basin, and the visceral hump, a soft
pad on the dorsal surface (Limpets, Patella). In many Gastropods
the shell and viscera are rudimentary, or altogether absent; the
viscera are then situated in the lower portion of the body. In some
cases, in which the shell is rudimentary, or feebly developed, it is
partially or completely enclosed in a fold of the skin.

The visceral sac, for the most part, lies freely within the shell, but
it is firmly connected with it in several places, namely, where the
columellar muscle arises from the columella. This muscle lies
on the ventral side of the visceral sac, and thence runs into the lower
portion of the body, which it withdraws into the shell when the animal
is disturbed.

In many of the Gastropods there is a plate of conchiolin, or
conchiolin and calcium carbonate, on the upper surface of the
hinder portion of the foot. When the whole animal is retracted
into the shell, the foot is drawn togethcr in such a way that this
plate hes below, forming a lid or operculum. The operculum
is firmly fused to the animal beneath, and grows by the secretion
of new material from the skin; sometimes growth occurs in such
« way that the operculum displays a spiral line on its upper surface;
this, however, is only rarely the case.

The true operculum which is firmly united to the animal, and gradually
increases in size, must not be confounded with the winter operculum
(epiphragma). The latter is usually as thin as paper, occasionally somewhat
thicker; and occurs, ¢.g., in species of Helix, being very thick and firm in
H. pomatia. When the animal is about to hibernate it withdraws into its shell
and the epiphragm is formed at the mouth. It consists of a hardened calcified
mucus, and is not attached to the animal, but at the end of the winter is
thrown off, a new one being formed each year.

The skin is soft and slimy; the mucus is secreted by unicellular
glands which open in great numbers on the surface of the body.
In many of the Pulmonata, larger skin glands, which also secrete
mucus, are present. In the Prosobranchiata there is a peculiar
patch of glandular epithelium on the inner side of the mantle, the
so-called “mucous-gland.” In some Gastropoda, in addition
to mucus, these glands also secrete a fluid, “ purple,’ which, under
the action of light becomes of a permanent violet colour.
296 Mollusca.

The central nervous system consists of paired cerebral,
pedal, and pleural ganglia, and a varying number of visceral ganglia,
which are connected with one another as shown on p. 289. In the

opisthobranch and pulmonate
B Gastropods, the visceral cord
runs posteriorly, forming a
loop between the two pleural
ganglia and lying below the
digestive tract throughout
the whole of its course. In
all the Prosobranchiata on
the other hand, the visceral
loop twists round the digestive
tube in a peculiar way; the
nerve cord arising from the
left pleural ganglion runs
below the gut, then crosses

/ above the gut to the left side,

_ ball Os and then again crosses this

LU L time above the gut to run
Fig. 243. Diagram of the central nervous anteriorly, ending in the right

system in relation to the alimentary canal pleural ganglion (F ig. 243 B).

(A in an Opisthobranch, Bina Proso- i : q
branch). h cerebral, p pleural, f pedal, i This peculiar arrang ement of

visceral-ganglia; ¢ alimentary canal.—Orig. the nervous system pre-

supposes changes in the
position of most of the organs. Of sense-organs, the eyes
have already been mentioned; for the auditory organs the account
given on p. 290 for the Mollusca in general may be referred to. In
most of the Gastropods there is, within the mantle-cavity, a
specialised portion of skin covered with a peculiar epithelium,
often folded and richly supplied with nerves; it lies near the gill,
and when two gills are present two such osphradia also occur.
There is no doubt that they are sense organs, and they are considered
to be olfactory.

With regard to the alimentary canal, it is important to
notice that the anus usually lies on the right side* of the mantle-
cavity quite asymmetrically ; only in a few isolated forms among
those Gastropods in which the shell is lost, is it symmetrical in
position (see the Opisthobranchs). In the mouth there isa radula

 

 

 

 

 

 

 

 

 

 

* Just as in other animals which are asymmetrical in some respects (e.g. Mammalia),

so in Gastropoda, such a departure from the usual arrangement of organs occurs, that;

all which are usually right come to lie on the left side, and conversely (inversio

viscerwm) ; the anus is left instead of right and so on. This happens sometimes

in the case of forms with shells in a left-handed spiral ; but there are forms with such
shells in which the torsion has not occurred, even the anus being on the right.
296 Mollusca.

The central nervous system consists of paired cerebral,
pedal, and pleural ganglia, and a varying number of visceral ganglia,
which are connected with one another as shown on p. 289. In the

opisthobranch and pulmonate

A B Gastropods, the visceral cord

runs posteriorly, forming a
loop between the two pleural
gangha and lying below the
digestive tract throughout
the whole of its course. In
all the Prosobranchiata on
the other hand, the visceral
loop twists round the digestive
tube in a peculiar way; the

nerve cord arising from the
left pleural ganglion runs
below the gut, then crosses

above the gut to the left side,
ik eS and then again crosses this

y

 

 

 

.

 

 

 

 

 

i
time above the gut to run

Fig. 248. Diagram of the central nervous anteriorly, ending oo the right
system in relation to the alimentary canal pleural ganglion (F 1g. 243 B ) .

(A in an Opisthobranch, Bina Proso- :
branch). h cerebral, p pleural, f pedal, + This peculiar arrangement of

visceral-ganglia; ¢ alimentary canal.—Orig. the nervous system pre-

supposes changes in the
position of most of the organs. Of sense-organs, the eyes
have already been mentioned; for the auditory organs the account
given on p. 290 for the Mollusca in general may be referred to. In
most of the Gastropods there is, within the mantle-cavity, a
specialised portion of skin covered with a peculiar epithelium,
often folded and richly supplied with nerves; it lies near the gill,
and when two gills are present two such osphradia also occur.
There is no doubt that they are sense organs, and they are considered
to be olfactory.

With regard to the alimentary canal, it is important to
notice that the anus usually lies on the right side* of the mantle-
cavity quite asymmetrically; only in a few isolated forms among
those Gastropods in which the shell is lost, is it symmetrical in
position (see the Opisthobranchs). In the mouth there isa radula

 

* Just as in other animals which are asymmetrical in some respects (e.g. Mammalia),
so in Gastropoda, such a departure from the usual arrangement of organs occurs, that
all which are usually right come to lie on the left side, and conversely (inversio
viscerum) ; the anus is let tt instead of right and so on. This happens sometimes
in the case of forms with shells in a left-handed spiral ; but there are forms with such
shells in which the torsion has not occurred, even the anus being on the right.
298 Mollusca. ‘

In the Gastropods there is usually one saccular kidney,
opening into the pericardium, and also to the exterior; if a mantle-
cavity is present, the kidney opens into it, otherwise on the right
side of the animal. It is usually much folded on its inner surface,
and is sometimes much branched. Occasionally there are two
kidneys.

Fig. 244. Male Peri-
winkle (Littorina) re-
moved from the shell and
viewed from above; mantle
cut along the right side
and turned over to the left.
a@ anus, d mucous gland,
f foot, g osphradium, h
heart, & gill, U liver, m edge
of the mantle, . kidney,
nm’ urinary aperture, p
penis, + seminal groove,
s seminal duct, ¢ testis.—
After Souleyet, modified.

 

The generative organs (Fig. 246) differ very considerably
in the different groups; they have, however, this in common, that the
genital aperture is almost always on the right side, and usually within
the mantle-chamber when this is present. The Prosobranchiata,
which are almost invariably of separate sexes, display the
simplest arrangement. In these the ovary and testis, one of each
alone being present, are exactly alike externally. The oviduct is a
convoluted tube, widened in one region, and opening into the mantle-
cavity. The seminal duct in most opens in the same position as the
oviduct, and from the genital aperture a groove ruus along the
surface of the body to the penis, which is situated on the nght
side of the head; the groove runs down the copulatory organ to
its apex. In others this seminal groove has become a closed canal,
Class 2. Gastropoda. 299

and the sperm duct opens only at the apex of the penis, which
cannot be withdrawn by invagination, as in other Gastropoda.
Glandular appendages of the sexual organs are usually wanting in
the Prosobranchiata. The Opisthobranchiata and Pulmo-
nata are hermaphrodite, and ova and spermatozoa are
formed in one and the same organ, the hermaphrodite

Fig.245. Female Peri-
winkle (Littorina) dis-
sected as Fig. 244; some
portions of the body-wall
and some of the organs
(kidney, pericardium), are
also opened. a anus, ge
genital pore, h ventricle,
ma stomach, » kidney,
od oviduct, ov ovary, sd
salivary gland, sp ceso-
phagus, v auricle, z spirally
coiled radula sac.—After
Souleyet, modified.

 

gland. The duct is in some of the Opisthobranchs common to
both ova and spermatozoa, and then a common genital aperture is
present; from this a groove runs along the skin to the apex of
the copulatory organ. In most Opisthobranchiata and in the
Pulmonata the duct is common only to a certain extent, for it
splits a short distance from the hermaphrodite gland into two
canals, an oviduct and a vas deferens, which usually open
close together, the vas deferens at the apex of the penis, which
is here furnished with an actual canal, not simply with a

groove. The penis can be invaginated in all Pulmonates and
Opisthobranchs. In these groups, especially in the air-breathing
300 Mollusca.

snails, the sexual apparatus possesses numerous accessory organs,
albumen glands (which manufacture the albumen to surround
the eggs), mucous glands (which secrete mucus during copulation),
spermathece, etc.* Copulation in the hermaphrodite Gastropods is
reciprocal.

A B Cc D E

 

Fig. 246. Diagram of the genitalia of various Gastropoda. Sexual gland in each case
dotted. A—C Prosobranchiata, A female, B and C males; D Opisthobran-
chiata; HOpisthobranchiata and Pulmonata. 9 oviduct, ?’ female
genital aperture, g sperm duct, g’ male genital opening, ¢ hemaphrodite duct, p penis,
r seminal groove.—Orig.

The terrestrial Pulmonata lay their eggs in the earth, each egg is surrounded
by a large mass of albumen _ which is covered by a more or less calcified,
round or oval, shell; the latter is very like that of a Bird’s egg. In the fresh-
water Pulmonata each egg is similarly covered by a mass of albumen and a very
thin transparent outer shell, but a number of such eggs lie in a common mass
of jelly (adhering to plants, etc.) ; those of the Opisthobranchs, and of some of
the Prosobranchs, are similarly arranged; in most Prosobranchs (e.g., the Whelk),
however, several eggs lie without separate shells in a common mass of albumen,
which is surrounded by a leathery capsule; the capsules, which often adhere
together in groups, are of very diverse, and often strange shapes. Several of

 

* In some terrestrial Pulmonata (eg., the common species of Helix) there is a
“dart-sac,” an evagination of the oviduct close to the external genital aperture,
in which a calcareous body, somewhat of the form of an arrow, the “ dart,’ is
secreted ; it is extruded during copulation, and is to be regarded as an excitatory
organ.
Class 2. Gastropoda. 301

the Prosobranchiata and Pulmonata are viviparous, the eggs developing within
the oviduct.

The eggs of Gastropods are always small, and undergo total
segmentation. In the Prosobranchs and Opisthobranchs the larva
passes through a metamorphosis; when it leaves the egg it
usually possesses a well-developed velum, by means of which it moves
about in the water: the foot on the contrary is only feebly developed.
The young Pulmonates have no velum, and
undergo no such transformation.

Amongst those Prosobranchs which lay egg capsules
containing many eggs, a few, or only one in each capsule
develops, the undeveloped eggs are swallowed by the
young animal as it swims about in the albumen. Fre-
quently the young of such forms undergo metamorphosis
within the egg-capsule, which they leave when the velum
has disappeared, the foot is formed and the body has
reached a considerable size (Whelk, etc.).

The Gastropods are, for the most part, creep-
ing animals, gliding over surfaces by means of
undulatory contractions of the foot; not a few
(e.g., freshwater forms) have the power of at-
taching themselves, so to speak, to the surface
of the water with the foot upwards, the visceral mass hanging below,
and, in this position, they are able to move slowly along. Some
smaller divisions of marine Gastropods are distinguished by the fact
that they can effect actual swimming movements by means of the
modified foot, or by some special organ. The majority of the
Gastropods (the Opisthobranchs, and by far the greatest number
of the Prosobranchs) live in the sea, not a few in fresh water
(some Pulmonata and some of the Prosobranchiata), many are
terrestrial (the majority of the Pulmonata and some of the
Prosobranchiata).

 

Fig. 247. Larva of
a Gastropod (Opistho-
branch). f foot, 2 au-
ditory organ, op opercu-
culum, s shell, v velum.

The following table gives a summary of the chief characters of the
Gastropoda:

Prosobranchiata.

Sexes separate.

Visceral loop in the form
of an 8.

The auricle anterior to
the ventricle.

Respiration (usually) by
a gill.

Penis projecting freely.

Metamorphosis,

Opisthobranchiata.

Hermaphrodite.
Visceral loop, U-shaped.

The auricle usually poste-
rior to the ventricle.
Respiration by gills.

Penis capable of invagina-
tion.
Metamorphosis,

Pulmonata.
Hermaphrodite.
Visceral loop, U-shaped.

The auricle anterior to
the ventricle.

Respiration by a pul-
monary chamber.

Penis capable of invagi-
nation.

No Metamorphosis,
802 Mollusca.

Order 1. Prosobranchiata.

To this division, the essential characters of which are set forth in
the preceding table, belong the majority of the shell-bearing
marine Gastropoda, some of the fresh-water forms and some
of the air-breathing terrestrial forms. Practically all the Proso-
branchiata possess a shell, usually a well-developed spiral, with or
without a notch or canal; occasionally the shell is cap-like. An
operculum is usually present. There is generally a single gill within
the mantle-cavity. Some are herbivorous, others feed upon living or
dead animals.*

1. Marine forms. This division is represented by numerous forms; in
the tropics, especially, there are many large and beautiful species; in colder seas
they are also numerous, but mostly small and inconspicuous. Among those
very common on British coasts may be mentioned: the Periwinkles
(Litiorina), small, thick-shelled Gastropods, without the syphonal notch, which
may be found in great numbers on rocks close to the shore: the Whelk
(Buccinum undatum), a large form, with a short syphonal canal, living in some-
what deeper water, and much used for bait: the Pelican’s Foot (Aphorrhais
‘pes pelicani), the mouth of whose shell is prolonged into several claw-like
processes: Limpets (Patella), forms with basin-like shells, which remain for
a long time on the same spot.

2. Fresh-water forms. The following forms occur in Britain and
elsewhere: the River Snail (Paludina vivipara), tolerably large (as much
as 4c/m. high), with conical shell (Fig. 242), viviparous; the young when born
are similar to the adults, and nearly as large as peas; the eggs are each* enclosed
ina capsule containing a rich supply of albumen, and remain in the much-widened
oviduct of the female; metamorphosis occurs within the egg-capsule. The
allied genus Bithynia is oviparous, and comprises smaller forms. Another
species, Neritinia, belongs to a family also met with in the sea; the shell is
hemispherical, the inner edge of its opening flattened.

3. Cyclostoma elegans is a terrestrial form occwring in Great Britain ;
it breathes by means of a lung, but may easily be distinguished from the
Pulmonata by the presence of an operculum.

The Heteropoda constitute a peculiar pelagic group of the Prosobranchiata.
They are almost transparent and large-eyed, with a large compressed foot,
by means of which they move through the water; the foot is a perpendicular
muscular plate, with a sharp ventral edge, and has only retained the ordinary
gastropod condition at one spot, in the form of a sucker situated at its edge
(the sucker may, however, be absent). In some cases the visceral hump is very
well developed, and enclosed in a compressed discoid spiral shell; the foot carries
an operculum, and can be withdrawn into the shell. In others (Fig. 248) the
visceral sac is small, and provided only with a cap-shaped shell, whilst the lower
portion is relatively huge, has no operculum, and naturally cannot be with-
drawn into the shell. Lastly, there are some in which the visceral mass is still

 

* Jn certain Prosobranchiata (Natica) there is, on the lower side of the
proboscis, a sucker-like area, the epithelium of which secretes an acid. When the
animal lays this against the shell of another Mollusc it forms a hole in the latter,
through which the proboscis can enter to devour the soft portions of the prey.

‘
Class 2. Gastropoda. Order 1. Prosobranchiata. 303

smaller, and which possess no shell at all. As larve all have shell and operculum.
The Heteropoda are actively predaceous, and swim with the ventral side turned
upwards ; they occur in all warm seas; various forms, for instance, are found in
the Mediterranean.

 

Fig. 248. One of the Heteropoda (Carinaria). f foot with a posterior sucker (su),
g |gill projecting from the mantle cavity, m mouth, s shell, & keel on the shell—After
Souleyet.

Order 2. Opisthobranchiata.

Some Opisthobranchs are provided with a visceral hump; a shell,
which is usually spiral; a mantle-cavity enclosing a gill; sometimes,
also, like the Prosobranchiata, with an operculum: often, however,
the shell is somewhat aborted, and most of the members of the
group (Nudibranchiata) have completely lost it, and with it
the visceral hump and mantle-cavity ; the viscera have sunk into the
lower portion of the body ; the nephridial and genital apertures, and
frequently the anus also, are situated on the right side above the foot.
In the Nudibranchs, as a rule, the ordinary gill is absent, and is then
generally replaced by special outgrowths of the skin, varying in form.
It is particularly interesting that the nudibranch larva is furnished
with shell and operculum ; both being later thrown off. All Opistho-
branchiata, of which the naked forms usually display gorgeous
colours, are marine, occurring in cold as well as in warm seas.

1. Of shell-bearing Opisthobranchs may be mentioned: the Bubble
(Bulla), with bulging shell, the apex of which lies in a depression; common in
warmer seas, allied genera in Northern seas. In some allied forms the shell
is surrounded by folds of skin; these fuse with one another, and may com-
pletely enclose the shell, which is then always thin (internal shell); such, for
instance, is the case in the genus Aplysia (Sea-hare), which inhabits the Medi-

terranean and other warm seas, and is also met with on the south coast of
England,
304 Mollusea.

2. Among the Nudibranchiata, the Doridide (genus, Doris, etc.)
are peculiar in that the anus is situated posteriorly on the dorsal surface, and
surrounded by a circle of plumose gills. The
Aolidew (genus, Molis, etc.) have unbranched
gills dorsally; a process extends into each from
the liver, which is much branched and not sharply
marked off from the gut. Many Nudibranchs are
without gills (e.g., Elysia, Limapontia), and often
have a striking superficial resemblance to the
Flatworms. All the forms mentioned are met with
in Northern seas.

To the Opisthobranchiata belong two aberrant
groups of pelagic animals, which have usually, but
not quite correctly, been placed together under the

Fig. 249. A Euptero- name, Pteropoda. The first of these divisions,
pod (Cleodora). m mouth, the Thecosomata (EHupieropoda), is distinguished
r Poet eee of foot, among other things by the breadth of the anterior
: ore muscular portion of the foot, which forms a pair

of fin-like locomotor organs; the posterior region

(f’, Fig. 249) is covered on its under surface with long close-set cilia,
by which microscopic organisms are driven into the mouth. The mouth lies
anteriorly between the fins, and is surrounded by a pair of lip-folds, which

 

Fig. 250. Fig. 251. ,

 

Fig. 250. One of the Eupteropoda (Cleodora) with simple tubular shell_—After
Souleyet.

Fig. 251. One of the Pterota (Pnewmodermon). In B the arms are furnished with
suckers and two hooked processes are projecting ; in A these are all withdrawn. a anus,
an tentacles, b and b’ gills, f—f’ foot, v fin— After Souleyet.

unite in part, and thus prevent the escape of the animalcule secured by the
current of the cilia. The visceral mass is well developed, and enclosed in a shell,
which, in some forms, is spirally twisted (and then an operculum is usually
present), but in the majority, is straight, or slightly curved and symmetrical.
Class 2. Gastropoda. Order 2. Opisthobranchiuta. 305

The Eupteropoda are among the most abundant and most characteristic pelagic
animals ; they are blind, and are specially frequent towards evening on the surface-
waters, both in warm and cold seas. The other group assigned to the Pteropoda,
the Gymnosomata (Pterota), have no shell; they have a small, often almost rudi-
mentary, foot; and move by means of two special fin-like muscular appendages,
which are situated anteriorly, close to the foot, but do not represent any portion
of it. Various organs of prehension, “arms” with suckers, etc., may extend
from the mouth of these animals, (Fig. 251 B); the Pterota are most predaceous,
and attack in particular the defenceless Eupteropoda, whose distribution corre-
sponds with their own. Clione limacina, a well-known species, occurring abun-
dantly on the coast of Greenland, and attaining a length of as much as 4 ¢/m.,
feeds upon a Eupteropod with a spiral shell, Limacina helicina.

Order 3. Pulmonata.

Tn the Pulmonata, just as in the Opisthobranchiata, some forms—
the majority, indeed—carry shells, and possess a well-developed visceral
hump, whilst others are naked, and have no such hump, the viscera
being sunk into the lower portion of the body. ‘The two groups
differ, however, in that in the Pulmonata, even if the shell and visceral
sac be absent, the mantle-cavity is still present on the upper surface
of the animal as a pouch, covered by a shield-shaped mantle; the
inner side of the mantle in the naked, as well as in the shell-bearing,
forms, is provided with a rich vascular network. ‘The opening which
leads into the mantle-chamber is not, as in other Gastropoda, a broad
slit, but is merely a pore on the right side; the shell never has a
syphonal notch, and an operculum is wanting. Between the shell-
bearing and the naked Pulmonata there is a complete series of
intermediate forms; in some, the shell is not large enough to contain
the whole animal, unless the air be dry, for the molluscan body
increases in size in damp air; there are others possessing a regularly
formed shell, which is, however, so small, that it only covers the
reduced visceral hump, whilst the rest of the animal can never be
withdrawn into it; or the visceral sac has completely disappeared,
and the small plate-like shell covers the mantle only ; again, the shell
is a small thin plate which lies beneath the mantle ;* or it may be
only represented by isolated calcareous granules, which lie attached to
the mantle (the latter is the case, for instance, in the Great Black-
slug) ; or it is entirely absent. The Pulmonata live on land and in
fresh water, and feed chiefly upon vegetable substances. As already
mentioned, they breathe air; some Fresh-water Snails (Limneeus),
however, possess, especially in youth, the power of taking water into
the mantle-chamber, and obtaining the dissolved oxygen from it.

 

* In one form (Parmacella), the young animal possesses a small external shell,
which, later, becomes covered by the mantle, so that the older animal possesses an
“internal” shell. In other forms, an “internal” shell occurs in youth, and is
dependent upon similar occurrences in embryological stages; the sac in which the
shell lies, is an invagination of the skin,

x
306 Mollusca.

1. The terrestrial Pulmonata (Stylommatophora) are characterised
by the position of the eyes, which are at the tips of eye-stalks, exactly similar
to the tentacles, and like these, capable of invagination into the head. To this
group belong both shell-bearing and naked forms. Among the former may be
mentioned the genus Heliz, to which the small Garden Snail (H. hortensis),
and the large Edible Snail (H. pomatia) belong; among the latter are the
Great Black-slug (Arion ater), and the smaller, destructive, grey, Common Slug
(Limax agrestis).

2. The freshwater Pulmonata (Basommatophora) have sessile eyes,
situated at the base of the tentacles, which cannot be invaginated. To this
group belong the numerous species of the Pond Snail (Limnzus), with pointed
shell, and of Planorbis, with discoid shell; both genera are common everywhere
in fresh water, and are represented by large and small species: some of the
Limnzidz lead an amphibious life, being met with on land as well as in water.

Class 3. Acephala (Lamellibranchs).

The body of the Lamellibranchs, unlike that of the Gastropoda,
is usually bilaterally symmetrical, except as regards the
coils of the alimentary canal. The anus is posterior, the genital
and nephridial apertures, etc., are symmetrically disposed. The
following is a general account of the structure of a Lamellibranch :
the body proper is rather small in comparison with the whole
size of the animal; the mantle-fold is developed on either side
in the form of a large lamina, dependent like a curtain. On each
side, also, just below the point of origin of the mantle, two gill
lamelle arise and hang down within it. The foot is ventral,
and is usually keel-shaped. There
are four large labial palps in
front of the mouth. A specialised
head is absent. The whole animal
is generally enclosed in a symmetrical,
laterally compressed, bivalve shell.

The foot is, asa rule, not very
well marked off from the trunk ; most
often it is only a compressed longi-
tudinal keel on the ventral surface.
In some forms it is longer and more
projecting (sometimes geniculate) ; in
a few cases it is linguiform (Mussels) ;
in others there is a true pedal disc.

b It is the most important locomotor
wor ne = ee aii, organ of the Lamellibranchs, and can
branch (diagram). 6 ligament, f be protruded from the shell by being
a ae oe distended with blood, whilst if the
Orig. animal is disturbed, it is withdrawn
by means of muscles arising from the inner surface of the shell,

 
Class 3. Acephala. 307

In a few forms (eg., the Oyster) it is altogether wanting; in
others it is rudimentary or small.

Each gill isa lamella, the upper edge of which is attached to
the body ; the lower portion, almost half the lamella, is bent round*
and closely apposed to the upper half (just as one half of a folded
sheet of paper lies upon the other); in the outer gill the reflexed
portion lies external to, in the inner gill internal to, the upper portion.
The edge of this reflexed portion is, in some cases, free, in others
it is concrescent with the body close to the point of origin of the
gill lamella, either throughout its whole extent or for part of its
length only. The gill lamella consists of delicate filaments extending
dorso-ventrally ; they are sometimes free, only adhering to one
another by “ciliated junctions” (Mytilus), but are usually firmly
united by interfilamentar junctions, so that the gill lamella shows a
trellis-work. The reflexed portion of the gill lamella is usually
united with the upper portion by similar “ ciliated junctions” (Fig.
252). On the surface of the gill lamelle is a thick covering of
cilia, by which the water is kept circulating through the meshes, and
small, solid bodies are conducted towards the mouth by means of
the ciliary currents on the surfaces of the gills.

In some Lamellibranchs (Fig. 253.4), each gill lamella projects
behind the foot in a free point; the
two points of the same side have, A B
however, undergone concrescence
along their dorsal edges.t In others
the point has become concrescent at
its hindmost tip, with the posterior
part of the mantle (Mussels). In
others again (Fig. 253 B), the right
and.left inner portions of the gills
coalesce behind the foot along
their reflexed edges, and similarly
the outer gills with the mantle; in
this case, in the posterior region of Fig. 253. Transverse sections through
the mantle-cavity, an upper portion the posterior regions of two Lamelli-
of the cavity (suprabranchial) jg  branchs after the removal of the shells,

to show the relations of the hinder
separated from the rest,andextends ends of the gills. kr body, k

Zs mantle, g inner, g? outer gill, h supra-
into the cloaca. eo ada ; branchial portion of the mantle cavity.
The mantle is divided into —Orig.

two symmetrical portions, a right
and a left mantle-lobe, which lie external to the gills. Each
lobe is a thin lamina, the edge of which, the pallial muscle,

 

 

* Only in a few Lamellibranchs are the gills not reflexed.

+ The two gill lamelle of each side, in all probability, together represent a plumose
gill with two series of filaments ; sometimes the two lamelle originate from a common
basis,

x 2
808 Mollusca.

is, however, somewhat thicker, and provided with transverse muscle
fibres. The upper ends of these fibres are firmly attached to the
so-called pallial line (sve below) on the inner side of the shell, and
by their contraction withdraw the margin of the mantle within its
edge: along the free edge occur numerous tactile tentacles. The
edges of the two mantle lobes are perfectly free from each other;
in a few forms only (e.g., the Oysters), as a rule, they are partially
concrescent, so that the large opening between them is divided
into two or several divisions. In the simplest cases (e.g., in the
Mussels), only the most posterior portion is separated from the rest,
the edges of the mantle being connected for a short distance; in
such there is a small pos-
terior opening, the cloacal
aperture, through which
water and excreta escape
from the mantle-cavity,
and a very large open-
ing through which water
streams in, and the foot
can be protruded. In
others (Fig. 254) the large

Fig. 254. ALamellibranch removed from the epee just mentioned 18
shell, seen from the left side. a and b points of divided into an anterior

concrescence along the edge of the mantle, r left, large aperture for the fo
r right edge of mantle, f foot,m and m! ends of the ge ap : h ot,
adductors.—Orig. and a posterior smaller pore

for the inhalent current of
water, the mantle-lobes having concresced for a longer or shorter
distance ;* thus the originally single slit is divided into three:
posteriorly the cloa-
cal aperture, below
this the inhalent
aperture, through
which the water
streams in, and an-
terior to, and below,
this, the pedal ori-
fice, through which
the foot may be pro-
truded, the last being
much larger than the
other two. The cloacal
and inhalent apertures
Fig. 255. A Lamellibranch (Tapes decussatus) with are often drawn out

partially separated syphons. The arrows indicate the into two tubes, the
direction of the streams of water. 1 foot. ?
cloacal and res-

 

 

 

*The edges of the mantle may lie closely apposed in these regions without
pndergoing concrescence. :
Class 3. Acephala. 309

piratory syphons, which can be protruded from the shell, and
may attain a considerable length; usually they are connected
together, and then appear externally like a single tube (sometimes
forked at one end), but this is divided internally into two by a
septum; they are rarely separated externally. In the forms
with these syphons the edges of the mantle have often undergone
concrescence over so large an extent that the pedal opening is
considerably decreased.

The shell lies external to the mantle, but closely upon it. It
is divided into two halves, connected above by a flexible band, the
ligament, which will be further described below. The two halves
of the shell are, as a rule, essentially similar; they are more or

   

ov —-------

 

Fig. 256.—Right shell valves of two different Lamellibranchs, seen from within.
A with simple, B with incurved pallial line, b ligament, 1 pallial line, m impressions of
adductor muscles, w umbo, s hinge.—Orig. |

less convex, and usually exhibit a projecting hump dorsally, the
so-called umbo (the oldest portion of the shell), which generally lies
nearer to the anterior than the posterior end. The upper edge of each
valve usually possesses a tooth or ledge, which fits in between
corresponding portions of the other half, forming a hinge (cardo);
in not a few this is absent, or only feebly developed. When the
shell is closed the edges of the valves fit closely together, so that the
soft parts of the animal are completely shut in: occasionally, however,
the shell is cleft in one or more places, posteriorly ; for instance, in
those which are provided with large syphons, and anteriorly in those
which are attached by means of a byssus (p. 811). The closure of the
shell is effected by adductor muscles, usually two in number,
which run transversely across the animal, one in the anterior, the

m
310 Mollusca.

other in the posterior, region, and are attached to the interior
of the shell; occasionally one such muscle only is present (e.g., in the
Oyster). The attachment of an adductor to the shell is indicated by a
sharply defined area, a muscular impression, of which there
are two on the inner side of each valve. Besides these, there are
frequently smaller impressions, which correspond with the attach-
ments of the pedal muscles; further, the so-called pallial line,
from which the muscle-fibres of the pallial muscle arise ; in those
Lamellibranchs which have no syphons, it runs parallel to the edge of
the shell some distance from it (integripalliate) ; in those which have
syphons it usually traces out a notch, extending from behind forwards
(sinupallate) (Fig. 256, B); and along this the muscles of the
syphons arise, being specially developed portions of the pallial muscle ;
since these muscles arise more anteriorly, the syphons can be with-
drawn into the shell. Three layers may be usually distinguished ,in
the shell: an outer horny layer in some (e.g., Mussels), very
definite ; in others, indistinct; and two layers consisting principally
of calcium carbonate, which make up the chief part of the shell;
of these, the inner layer is sometimes iridescent (mother of
pearl).

The flexible band which holds the two valves of the shell together,
the so-called ligament, consists of an outer, flexible, but inelastic
layer (an extension of the outer layer of the shell), and an inner,
elastic portion of radially arranged fibres. In many forms, this
ligament has a large, very convex surface, exteriorly ; and is termed
an external ligament: in others, it is enclosed between the
upper edges, displaying a very small portion externally, whilst it is
convex inwardly, and is then termed an internal ligament.
Its action is essentially the same in the two cases (cf., Fig. 257). If
a shell, furnished with an interna] ligament, is closed by the
contraction of the adductor muscles, the inner elastic portion of the
ligament is compressed, and when the muscles relax, the valves of the
shell are once more driven apart. In the shells provided with an
external ligament, the elastic substance of the ligament undergoes
a compression, or arching together, within the outer inelastic sheath,
and on the relaxation of the muscles, the effect is the same as in shells
with internal ligaments.* The action of the ligament is purely
mechanical, and occurs after the death of the animal just as in life.
It must also be mentioned that its position is either directly below the
umbo, or more usually, posterior to it. Only in very incompletely
developed shells (¢.g., Teredo) is the ligament altogether wanting, and
the shell-valves completely separate.

 

* The usual statement, that a stretching of the external ligament must occur on
closure of the shell, is incorrect.
Class 8. Acephala. 311

The shell increases in size by the addition at its margin of new
material, secreted by epithelial cells at the edge of the mantle ; it
increases also in thickness, since the outer surface of the mantle,

 

Fig 257. Diagrammatic transverse sections through the shell of Lamellibranchs with
internal (A, 4’) and external ligaments (B, B’). In A and B the shell is drawn
open, in A’ and B’ shut, b elastic portion of the ligament, b’ outer inelastic portion of the
same; m adductor.—Orig.

and, in the upper region, the surface of the body, continually deposit
new layers within it.

The shells of some Lamellibranchs differ from the usual type in being very
asymmetrical: in the Oyster and some Scallops, for instance, only one valve
is convex, the other being flat. A lesser asymmetry, quite insignificant in most
instances, occurs in many others, (e.g., the hinge-teeth of the two valves fit in
between one another; at those places where a tooth is present in the one valve,
there must be a depression in the other). Other forms are characterised by the
fact that the shell covers only a small portion of the body (Teredo, and others).
Pearls are calcareous deposits from the outer side of the mantle round foreign
bodies, which have got by accident between the mantle and the shell; they are
either firmly attached to the inner side of the shell, or else lie quite freely ; they
occur in various forms. Some species, with elongate bodies and imperfect shells,
either build a tube of small foreign bodies welded together, or (more frequently)
secrete a calcareous tube, with which the small valves of the shell are sometimes
united.

In connection with the skin, the formation of byssus threads,
which occurs in one group, must be specially noticed. These threads
are horny fibres, which are secreted by the epidermal cells in a
depression of the foot, and im a groove connected with it. They
constitute organs of attachment in some species (e.g., in the Mussels),
one end remaining in connection with the animal, whilst the other
is firmly fixed to some foreign body. Others bind small stones
together by means of the byssus threads, and thus form a kind of
nest, in which they take up their abode.

In many Lamellibranchs, where'no byssus is formed, a rudimentary byssus
gland may nevertheless be present. Some forms possess this thread only in the
larval stage, losing it when adult.
312 Mollusca.

The pleural ganglion in Lamellibranchs is almost always
fused with the cerebral ganglion, avd the connective between the
pleural and pedal ganglia is fused with that between the cerebral
and pedal, so that to all appearance the pleural ganglion and its cord
are absent (Fig. 2387 D). In some forms, however, the two are
independent; the cord only partially so{ which gives conditions
closely approaching to those of the Gastropoda. Eyes are only
present occasionally, and then are always situated, often in large
numbers, along the edge of the mantle; in the siphonate forms, at
the tips of the syphons. For example, in the Scallops (Pecten)
there is along the edge of the mantle a series of eyes of somewhat
complex structure. An olfactory organ, a specially modified
portion of the epidermis supplied with nerves, corresponding with
that of the Gastropoda, is present in many, near the anus.

The mouth isa transverse slit at the anterior end of the body,
below the anterior adductor muscle. It is bounded above and below
by an upper and lower lip respectively, each of which is drawn out on
both sides into a usually well-developed labial palp. The labial
palps are covered with numerous cilia; these serve to drive into the
mouth the small particles, microscopic plants and animals, which are
present in the water taken into the mantle-cavity. Radula and
jaws are absent. A short cesophagus leads from the mouth into a
stomach, which is often provided with a cecum ; in the latter
is contained the so-called crystalline stylet, a gelatinous,
transparent body which is secreted by the epithelium of the cecum,
developing when food is plentiful (in the summer), and redissolving
during scarcity (in winter); it probably represents a-reserve of
nourishinent, and is present in almost all Lamellibranchs.* A
well-developed liver surrounds the stomach, and opens into it by
several apertures. The intestine is coiled several times; its posterior
portion runs along the dorsal side of the animal, and finally passes
dorsal to the posterior adductor muscle to open at the hind end of
the body. The ventricle is situated on the dorsal side of the
animal above the rectum ; it generally divides into two branches which
surround the gut and unite below it, so that it is ring-shaped,
“perforated by the rectum.” There are two auricles, one on each
side, which receive the blood from the gills and carry it to the
ventricle. The vascular system is imperfect; in the gills there is,
however, a rich network of capillaries. The kidneys are a pair of
sac-like organs which are often more or less intimately connected
with each other (the organs of Bojanus) ; each opens by an aperture
situated laterally below the origin of the inner gills; and also into
the pericardium. Most of the Lamellibranchs are of separate
sexes, a few (ey., the Oyster) are hermaphrodite. Ovary and

 

* A crystalline style is also present in some Gastropoda.
Class 8. Acephala. 313

testis are present as paired branched organs ramifying between the
other viscera, in the foot, or (¢.g., in the Mussel) in the mantle;
they open on either side close to the nephridial aperture, or the

 

Fig. 258. Diagrammatic longitudinal section of a Lamellibranch. a
anus, br gill, « cerebro-pleural ganglion, e rectum, f foot, fy pedal ganglion, g generative
gland, g’ genital aperture, h ventricle, i visceral ganglion, k caecum containing the crystalline
stylet, | liver, m anterior, m’ posterior adductor, ma stomach, » kidney, n’ external renal
aperture, o mouth, p mantle, pd pericardial gland, pe pericardium, v auricle.— Adapted
from Rankin.

duct unites with that of the kidney, so that a common urino-genital
aperture is present on each side.* Sometimes the fertilised eggs
develop in the space between the lamelle of the outer gills of the
female.

Marine Lamellibranchs undergo
a metamorphosis similar to
that of the marine Gastropods ;
the newly-hatched larva moves by
means of a velum; eyes are
frequently present anteriorly, but
disappear later. Such a free-swim-
ming larva does not occur in most
fresh-water forms, and a velum is
not developed or is only transitorily au Se, wee eh hae
present in the embryo. (Cardinm); in the older a small shell s

All Lamellibranchs are aquatic, is developed, v velum.—After Lovén.
the majority marine. They

 
   

q

“PMR

 

 

* In some the reproductive organ opens into the kidney itself, in certain cases even
close to the reno-pericardial aperture.
314 Mollusca.

feed upon small organisms, Diatoms, etc., which are contained in the
inhaled water. They can crawl slowly along by means of the foot,
which they press upon or into the ground; some can take leaps by
its means. In exceptional cases they can move rapidly through
the water by quickly opening and shutting the shell. Some
are able to work themselves into the soft sandy, or muddy ground
by means of the foot, so that the cloacal and inhalent apertures alone
project, and many pass most of their lives buried in this way; the
formation of shorter or longer syphons is in correlation with this.
Some even have the power of boring into hard substances, wood,
limestone, etc., grinding the material away with the foot in which
tiny silicious bodies (?) are embedded. Some forms have the shell
firmly attached to the surroundings by means of a calcareous
secretion, and have, of course, lost the power of locomotion. As
has been mentioned above, such an attachment may be also
effected by the byssus thread; the animals so attached remain for a
long time in the same place, but may leave it by throwing off the
byssus; the Dreissena mentioned below is, for example, attached
during summer to foreign bodies just below the surface of the water,
in the autumn the byssus is discarded and the animal retreats to
the bottom.

As examples the following may be mentioned :

1. The Oyster (Ostrea edulis) possesses only one adductor ; the ligament
is internal; the foot absent; the right valve flat, the left convex and adherent to
various foreign bodies: on English coasts. Related to the Oysters are the
Scallops (Pecten) with a radially ribbed shell, of which the anterior and
posterior halves are similar. In several species the left valve is flat, the right
convex; in others both are alike convex; internal ligament; eyes at the edge
of the mantle; one adductor; small foot: species in the North Sea, English
Channel, etc.

2. The Mussel (Mytilus edulis), characterised by the position of the
umbo at the anterior end of the rather thin shell; and possessing a long internal
ligament and a powerful byssus, by means of which the animal attaches itself to
stones, etc.. very abundant on British coasts; if it lives in stagnant water
(harbours) a poisonous substance is secreted by the liver. The allied, some-
what smaller Dreissensia polymorpha, inhabits fresh water ; originally a native of
South-East Europe, it has spread during the present century over the whole
continent. Another allied form is the almost cylindrical, elongate Lithodomus
lithophaqus, which bores into limestone; a Mediterranean form.

 

Fig. 260. Mya arenaria. f foot, i cloacal opening, u respiratory opening.—After
Meyer and Mobius.
Class 3. Acephala.

315

3. The Freshwater Mussels (Anodonta) are large, egg-shaped,
thin-shelled Lamellibranchs, abundant in freshwater. The numerous eggs

hatch in the outer gills of the female, and the larve
escape by the cloacal aperture. These larve are provided
with long, sticky threads, which float in the water and
adhere easily to passing Fish; when this occurs the young
Mussel attaches itself firmly to the Fish by means of the
teeth present on the lower edge of each valve of the shell;
it is then covered by a growth of the skin, and for a time
leads a parasitic life upon the Fish, which it forsakes
again later. The River Mussel (Unio) and the River
Pearl Mussel (Margaritana margaritifera), which are com-
mon in England, are allied forms. The latter manufactures
some of the pearls of commerce. The true Pearl Mussel
(Meleagrina margaritifera), which forms the best pearls, belongs
to another family of Lamellibranchs; it is found in the Indian
and Pacific oceans.

4. The Gaper (Mya arenaria) is distinguished by the
possession of « very long syphon (formed, of course, by the
fusion of two tubes), and by the way the shells gape open
behind; the edges of the mantle are concrescent to a large
extent. It occurs on the beach on the coast of Britain, buried
more than a foot deep.

5. The Ship-worm (Leredo navalis) is a vermiform,
elongate Lamellibranch, in which the edges of the mantle
have undergone concrescence to # large extent; and a pair
of very small shell-valves, which ave not connected by a
ligament, are present anteriorly; and two partially separated
syphons posteriorly. It is a marine form ocewring in wood
(piles or ships), in which it bores long tubes, lined with a
calcareous secretion; the external aperture and the portion of the
tube next this are narrow, and were formed by the animal when
young; further in it is wider and cylindrical: the animal is
unable to leave the tube, its anterior end is in the innermost
portion of the tube, the syphons at the mouth: common on the
coasts of Europe: very destructive. In the allied genus, Pholas
(Piddock), which bores into limestone, wood, etc., the body is
shorter, the shell better developed than in Teredo ; itis phos-
phorescent: present in Huropean seas.

Class 4. Cephalopoda.

The body is externally, and for the most part,
internally, bilaterally symmetrical. It falls naturally
into two regions, the head and the body. The
head is very well developed ; the mouth is anterior ;
and in all Dibranchiata (7.e., in all Cephalopoda, except
Nautilus) is surrounded by eight long muscular arms.*
In some Dibranchiata, i.e., in the Decapoda, there are

 

 

 

 

 

 

Fig. 261.
Teredonavalis.
a shell, 6 foot,
c mantle, e
syphons.

 

* In certain of the Cephalopods some, or all, of the eight arms are connected at thei
bases, or further up, by a thin web of skin (just as are the toes of mine svinndue

Mammals and Birds).
316 Mollusca.

two more long, so-called “tentacular arms” within the other
eight. All (the tentacular ones only towards the tips) are
furnished with numerous muscular suckers, ranged along the
inner sides, 7.¢e., towards the
mouth. These suckers are
sessile in the Octopods, usually
stalked in the Decapods; in
the latter (but not in the
Octopods) there is a chitinous
ring at the margin of the
sucker, and it is usually finely
denticulate at its edge. In
certain Decapods some of the
suckers may be metamor-
.phosed into hooks by lateral
elongation of the ring. In
the Tetrabranchiata (Nau-
tilus) numerous thin ten-
tacles are arranged in
several circlets round the
mouth, instead of the one
circle of arms. They may be
withdrawn into  tentacle-
sheaths which are partially
concrescent, forming hand-
like plates, from the edges
of which the tentacles arise ;
they have no suckers. On
the head there is a pair of
large eyes, which will be
described later.

The body, whose under
surface corresponds with the
posterior side of the visceral
hump of Gastropods, is short
and thick in the Octopods
oy and Nautilus, more elongate
Fig. 262. Diagram of a decapodous in the Decapods: in the latter

Cephalopod viewed from below, mantle cut j¢ ig furnished with a pair of
through down one side and turned over to the

other. «a anus in the posterior end of the funnel, horizontal fins, which arise
f fin, g genital aperture, i gill, m Se laterally and somewhat dor-
a PSR rae erento sally, and are usually situated

near the posterior end of
the animal. At the junction of the head and body there is a trans-
verse slit ventrally, leading into the spacious mautle-cavity

(see Fig. 268 B), which extends over the whole length and width of

 
Class 4. Cephalopoda. 317

the animal on the ventral surface. It is bounded externally by a
mantle, which is usually very muscular and thick, and, in many
cases, prolonged into a low fold behind the head on the upper
surface. From the opening of the mantle-cavity projects the anterior
end of the funnel, a tube open at both ends, and attached dorsally
to the dorsal wall at the boundary of the head; the funnel is a true
tube in the Dibranchiata only; in Nautilus it is a plate rolled up
like a paper bag; it corresponds to the foot of other Mollusca. The
animal takes water into the mantle-cavity by the large aperture,
but expels it through the funnel by the contraction of the mantle
and the pressure of its edge upon the body. In the funnel there
is frequently a small tongue-like flap, which is attached posteriorly,
the anterior end being free, so that it acts as a valve, preventing
the entrance of water. The laminate gills lie in the mantle-cavity,
one pair in the Octopods and Decapods, two pairs in Nautilus.

 

Fig. 263. Nautilus, the shell sawn through. 0 eye, ¢ funnel, te tentacle ; s the syphon,
h a fold of skin which overlaps the shell.—After v. Martens.

In Nautilus the body is enclosed by a shell, which, as in
the Gastropods, is an epidermal secretion. It is spiral, but sym-
metrical ; the convexity corresponds to the ventral side of the animal
(see Fig. 263) ; the coils touch one another. The shell is multi-
locular, being divided by arched transverse septa into nume-
rous chambers, of which the outermost and largest contains the
body, whilst the others contain air; each septum is perforated by
a hole, through which a thin tube, the siphuncle, an extension of the
318 Mollusca.

posterior end of the body, runs through the whole length of the shell.*
In some extinct nautiloid forms the shell was straight
(Orthoceras) ; in others slightly curved or rolled into an incom-
plete spiral; in others it formed a perfect spiral, of which the
successive coils did not touch. In the living genus Spirula, one of
the decapodous Cephalopods, there is a spiral multilocular
shell (Fig. 264 A) like that of the Nautilus, but the dividual turns
do not touch, and the shell is coiled in the opposite direction, the
convexity corresponding to the dorsal surface; only a small portion
of the body is contained in the shell, of which the outer chamber
is small, and the shell itself is completely enclosed by folds of skin
which have wrapped round and coalesced. In certain extinct
decapodous forms there is also a multilocular shell (Fig. 264 B, C),
but this is usually straight and drawn out into a plate-like portion
anteriorly; im living Decapoda (with the exception of Spirula)
this piece is almost the only part of the shell which persists;
the posterior spiral, which in extinct forms was concamerated, has
become quite rudimentary or is entirely absent. In these forms the

A B Cc D Ez

 

 

Fig. 264. Diagrammatic figures of various Cephalopod shells viewed from the side.
A Spirula; B Spirulirostra (extinct) ; C Belemnites (extinct) ; in B and C the posterior
portion of the shell is prolonged in a strong spiny process; D Conoteuthis (extinct) ;
E Ommatostrephes (living). p plate-like portion of the shell—Orig.

 

* Jt is assumed that the septa are formed by the animal’s withdrawing from the
outermost as the shell grows at the mouth, and secreting a new septum in front of the
last formed ; the cord elongates simultaneously.
Class 4. Cephalopoda. 319

shell is usually a thin, horny, elongate plate, occasionally it is some-
what thicker, with a calcareous layer below the horn (Sepia) ; it is
completely enclosed in a cavity on the dorsal surface, an invagina-
tion of the outer skin. ‘This so-called ‘internal shell”
corresponds with the external shell of Nautilus, and like it is an
epidermal secretion. In the Octopods the shell is altogether absent.
(For the very aberrant shell of Argonauta, see below, p. 323).

The skin is characterised by its constantly changing colour, due
to the presence of stellate pigment cells which can contract and
expand (chromatophores). The so-called ink-sac, a peculiar
gland connected with the skin, is usually a pear-shaped bag in
which an inky fluid is secreted; it opens into the mantle-cavity
close behind or even into the anus, and when the animal is in danger
the fluid can be poured through the funnel, rendering the water
black.

The Cephalopoda possess a true, although feebly-developed,
internal skeleton in the form of pieces of cartilage, of
which the cartilaginous capsule in the head, surrounding the central
nervous system, the auditory organs, and in part the eyes, is the
most important. Besides this capsule there are usually several smaller
pieces in various regions of the body.

The nervous system is peculiar in that all the large nerve
masses, cerebral, pedal, pleural, and visceral ganglia, are closely
collected round the cesophagus, and are directly connected by the
shortening of the commissures. The eyes are large, and in many

Sooo
eas

  

S

A

 

Fig. 265. Diagrammatic transverse sections through the eyes of various Cephalopoda.
A Nautilus, B, C different Dibranchiates. ep epidermis, h cornea, 7 iris, J inner, l? outer
portion of the lens, n optic nerve, r retina, 7f eyelid. Orig.

forms attain a high development. The simplest occur in Nautilus
(Fig. 265 A), where they are deep, saccular, epidermal invaginations ;
the cavity communicates with the exterior by a small opening (the
eye belongs to the type figured in Fig. 20, 4, but a lens is wantin g).
In the other Cephalopoda a closed optic vesicle is developed,

    
 
820 Mollusea.

and is further provided with a lens; the inner half of which is
secreted by the epithelium of the optic vesicle ; the outer half by the
epidermis. Moreover, at the periphery of the eye, a large fold like
an eyelid is present, forming a cavity round the eye; in some
Decapoda (igopside, Fig. 265 B) this cavity is widely open; in the
rest (Myopside) and in the Octopoda (Fig. 265 C) the fold extends
completely round the eye, and the aperture leading into the cavity
is very small; where the fold. lies above the lens it is transparent,
‘and is termed the cornea. In the cavity thus formed there
is a second small pigmented fold, which displays a certain resem-
blance to the iris of the Vertebrata, and is also designated by
that name. A depression of the skin situated laterally on the head
behind the eyes and supplied by a nerve from the brain, is regarded
asan olfactory organ.

The mouth is surrounded by a projecting fold of skin, the lip,
within which are two powerful horny jaws, an upper and a lower;
the former bites within the edge of the latter, and the two together
are very similar to a parrot’s beak inverted. In the mouth, which is
furnished with muscular walls, there is a radula like that of the
Gastropoda. The anus lies far forward on the ventral side of the
body in the mantle-chamber, in the median line. A stomach, a large
liver, and usually salivary glands are present. The heart consists
of a ventricle and as many auricles as there are gills, that is,

 

Fig. 266. Diagram of the heart, etc. of a Cephalopod. h ventricle, f auricle, u, u
arteries, vh branchial heart, vt’ vein to the gill, yf vein from the gill, g gill—Orig.

four in Nautilus, two in other Cephalopods. In the Dibranchiata
the large veins which carry the blood to the gills are known as
branchial hearts; they are enlarged at the entrance of the gills
and contractile. The kidneys, two pairsin Nautilus, one pair in
the Dibranchiata, are saccular organs opening into the pallial chamber
by paired apertures. In some of the Dibranchiata the two are
partially fused, but each has its own opening. The kidneys exhibit
racemose evaginations of the large adjoining veins which have
pushed the closely attached wall of the kidney into its cavity; these
evaginations appear to hang freely into the cavity.
Class 4. Cephalopoda. 321

The reproductive organs are similarly arranged in the
male and female, the Cephalopoda being bisexual. There is a pair of
ovaries or testes; neither is directly connected with the duct,
but each is enclosed in a thin-walled sac, from which this arises. In
some forms two symmetrical oviducts are present, and these open
one on either side behind the anus into the pallial chamber ; in others,
one, usually the right, duct is wanting. The nidamental glands
open close to the genital aperture in many female Cephalopods ; their
secretion is used in the formation of the egg capsules. In some
there are paired vasa deferentia, but usually one, the left, alone is
present. The spermatozoa are bound into elongate, almost filiform,
spermatophores, which are formed in a gland connected with
the vas deferens.

Specially worthy of note is the manner in which the spermato-
phores of the Dibranchiata are transferred to the female; this is
effected by one arm of the male, which is peculiarly modified,
“hectocotylised,” for this purpose. In the Decapoda, it is
usually an arm of the fourth pair (occasionally of the first) ; in the
Octopoda, one of the third pair, rarely both. The form of this arm
varies; it may be spatulate at the tip, and provided with a wide
ridge lone the edge (Octopods), or the suckers may be absent or
modified in the middle or at the base (Decapods). The modification
is greatest in some of the Octopods (e.g., in the Argonauta to be
mentioned below), where the arm is used exclusively for copulation ;
it is enclosed in a sac until needed, and in coitus is thrown off

 

Fig. 267. An Octopod in which the hectocotylised portion (h) of the right arm

is a well developed. ¢ funnel, 1—4 first and fourth arms of the right side.—After
Verri

and remains, filled with spermatozoa, within the pallial chamber of
the female. Here it may continue motile for some time, which led
to its being regarded as a peculiar parasite, described under the
name of Hectocotylus ; later, it was considered by some observers
to be a much modified male, and finally its true nature was
discovered. In the males of Nautilus there is, on the left side, a

Y
322 Mollusea.

small group of metamorphosed tentacles, which are possibly of service
in copulation.

The eggs are either heaped together in masses of mucus or
are enclosed in firm capsules. They are of relatively large size ;
segmentation is partial, and the embryo often possesses, for a time,
a large yolk sac, depending between the arms. There is no
metamorphosis, the newly-hatched form resembling the adult.

The Cephalopoda, which are all marine, are for the most part,
predaceous, seizing their prey (e.g., Crustacea) with their arms; the
latter are also used for crawling, especially in the Octopods.
They may swim by the movement of the fin backwards and
forwards ; a hurried fight backwards, usually accompanied by a
discharge of ink, may be effected by the ejection of the water from
the pallial chamber through the funnel. The Decapods are the best
swimmers, whilst the Octopods usually crawl better. Many
Cephalopods (especially the Decapods, but some Octopods too)
often- occur in shoals in the open sea; others are more littoral.
They are mostly found in warm seas.

 

Fig. 268. Diagrammatic figures to illustrate
the relations between the Chitons (A) and

the Cephalopods (B); profile; f foot (funnel), iL

h head, k mantle cavity, r rim of the mantle,

whose upper boundary is indicated by a dotted @)

line, o eye.—Orig. A ¢,

It is conceivable that the cephalopod type was derived from a chiton-like
form by enormous development in the height of the dorsal surface, by the
deepening of the mantle furrow on the posterior side of this upgrowth, by the
great development of the head, and the reduction of the foot.

Order 1. Tetrabranchiata.

There are numerous arms (tentacles) without suckers. The funnel
is a plate rolled upon itself. The eyes have no lens. There are four
gills (four auricles, four kidneys); no ink sac; an external shell,
Class 4. Cephalopoda. Order 1. Tetrabranchiata. 823

The Tetrabranchiata are at the present day only represented by the genus
Nautilus, of which there are two species in the Indian and the Pacific Oceans;
they may crawl upon the ground or swim at the surface. In former times (even
as early as the Silurian) this division was very numerous, partly represented by
forms with straight or curved shells (¢., p. 318).

The Ammonites are a large group of extinct animals, in which the shell
is multilocular like that of the Nautilus, with perforated septa, spiral or straight,
curved, etc., but differing from it in that the perforations lie close to the convex
side, whilst, in Nautilus, they are usually median; and also in that the septa are
strongly sinuous at the fusion with the shell: many were possessed of an
operculum (aptychus). The Ammonites first occur in the Silurian formations,
and die out in the Cretaceous. Their systematic position is quite uncertain;
they are mentioned here on account of the resemblance the shell bears to that of
Nautilus, but it cannot be affirmed that they are allied to it.

Order 2. Dibranchiata.

There are eight or ten arms with suckers. The funnel is tubular ;
the eyes have a lens. There are two gills (two auricles, two kidneys) ;

an ink sac; an internal shell, or, none.

1. Decapods (Decapoda). Ten arms, suckers stalked, and with chitinous
rings; shell present, body elongate and with fins. To this group belong, for
example: Sepia officinalis, which occurs abundantly in European seas, and whose
thick shell, formed of fine calcareous laminze (0s sepie of the chemist) is
turned to various technical uses. Here too, belongs the Sea-clerk (Loligo
vulgaris), occurring in the same places, and possessed of a thinner horny shell.
Further, the gigantic Architeuthus, a pelagic animal several metres long, but not
otherwise differing from the common decapod type. The so-called ‘“thunder-
bolts,” which are especially abundant in the Cretaceous strata, and which, on
account of the displacements, consequent on the Glacial Period, occur also in the
glacial deposits of North Europe, are the posterior tongue-shaped ends of the
shells of certain extinct Cephalopods (Belemnites).

2. Octopods (Octopoda). Hight arms, suckers sessile and without horny
rings, no shell; thick body without fins. Here belongs, for example, Octopus
vulgaris, a large animal with long arms, small round body; abundant in the
Mediterranean. Also Argonauta argo, the females of which are characterised by
the compression of the first pair of arms, and their extension posteriorly, to
form two lamellz, reaching round the body; these secrete, on the inner side, a
thin, cap-like calcareous shell, to protect the body, and to contain the eggs. It
is at no point closely adherent to the upper surface of the animal. The male
possesses a hectocotylus, but the first pair of arms is normal in structure, and it
has no shell. Argonauta is a pelagic animal.

 
Group 8. Vertebrata.

General review. The Vertebrata are bilaterally symmetrical.
There is a dorsal central nervous system, of which the
anterior end is usually enlarged to form the brain, whilst the rest
forms an elongate spinal cord. Below the nervous system lies
another cord, the notochord or chorda dorsalis; skeletal struc-
tures are usually developed round these two. Below the notochord is
the alimentary canal, the mouth is anterior, the anus ventral, usually
some little distance from the posterior end. The heart lies anteriorly
below the digestive tract. ‘There is a pair of kidneys and a pair
of gonads; the ducts of both these open near the anus, or into the
posterior portion of the gut. Alimentary canal, heart, etc., lie
in a spacious body-cavity. Optic, auditory and olfactory
organs, are present anteriorly. The body is naturally divisible
into the following regions: (1) the head, with the brain, sense-
organs, and mouth; (2) the trunk, extending from the head to
the anus, and enclosing the body-cavity with its contained organs, and
usually furnished with two pairs of appendages, the limbs ; these last,
especially in the higher Vertebrata, play an important part in
locomotion; (38) the tail, the muscular termination of the body,
forming a powerful locomotor organ in the Pisces, but usually of
subordinate importance in the higher Vertebrata. In the higher forms,
from Reptilia upwards, the anterior portion of the trunk forms a neck;
that is, the body-cavity is drawn away from the anterior end of the
trunk ; and organs (e.g., the heart) which in other forms occur there,
have also moved back, so that this portion is practically without viscera,
and forms a muscular stalk-like connection between head and trunk,
which is of the greatest importance in connection with the free
movement of the head.

The epidermis consists, in Amphiovus, of a simple epithelium
of cylindrical cells ; in other Vertebrata there is a stratified squamous
epithelium of varying thickness. In Pisces all the epidermal cells
Vertebrata. 825

are soft and protoplasmic, but in all other groups the outer portion
of the epidermis consists of cornified cells, so that an outer
stratum corneum, and an inner stratum mucosum (Rete
Malpighii), in which the cells are protoplasmic, may be dis-
tinguished. In the Amphibia the stratum corneum is only one
or two cells thick, in the higher Vertebrata thicker; in various
regions of the body it is developed in different ways, and in certain
parts may attain a very considerable thickness and great hardness.
The claws, for instance, of Reptiles, Birds, and Mammals, are
thickened portions of the stratum corneum which surround the last
joint of the digit. Hedysis in the Vertebrata consists in a
throwing off of the stratum corneum, either in one piece (Amphibia,
some Reptilia), or bit by bit. Below the epidermis is a layer of
connective tissue, the dermis, which varies in thickness and
firmness, and is connected with the subjacent parts by the loose
subcutaneous connective tissue; in the dermis there are
numerous smooth muscle cells or transversely striped muscle fibres,
and below, but still connected with it, there are, especially in the
higher Vertebrata, the continuous laminate cutaneous muscles con-
sisting of transverse muscle fibres. In the cells of both epidermis
and dermis there is frequently a deposit of pigment. Glands
of many kinds belong to the skin. In the Fish, between the outermost
cells of the epidermis, there are beaker-shaped cells which
secrete mucus; true glands are not generally present, although
in other Vertebrata they attain a great development, sunk into,
or below, the dermis and opening through the epidermis. In
members of all the classes of Vertebrata, with the exception of the
Lancelet (Amphiowus), ossifications are present in the dermis
forming plates of varying thickness (scales of Pisces, etc.). Sometimes
these plates attain a considerable size, and may be united to form
an exoskeleton which surrounds some portion of the body
(some Fish, Tortoises, a few Mammals), and are often intimately
connected with the endoskeleton, especially in the head region.

The endoskeleton is, at very early stages of development,
represented only by the notochord, a cord or rod of cellular
connective tissue, lying below the central nervous system. In
Amphioxus the adult skeleton consists almost exclusively of the
notochord (Fig. 298, p. 355), but in all other Vertebrates, other
skeletogenous structures develop; largely around, and in connection
with, the chorda. They surpass the notochord in size, and it is, in
fact, almost obliterated by the newly-developed skeleton. The latter
consists partly of cartilage, partly of bone; even when the adult
skeleton is principally bone, it usually consists at first of cartilage,
which is gradually absorbed and replaced by bone, .e., it ossifies:
or it is covered by bony plates, membrane-bones, beneath
which it may persist: or it may disappear altogether.
326 Vorlobrrbe.

The axial skeleton, fe, the endo-ekeleton of the body with
the exclusion of that of the linbs, will now be considered, fi xome
Wishes mm continuous cortilagineus shemtl aries round the
chordy in the trunk and tail rogions; this dibe is closed above by u
series of short tectiform pieces, or wrelos, which surrowoid the spinal
cord, Tnomost Vortobrata the cartilaginous shoath is, howover, divided
into w number of pieces, usually ono for cach ureh, and those together
surround the notochord.  ‘Pheso piocos, which aro termed contra,
differ considerably in form und structure; sometimes tho enelosed
notochord persists to a gro oxtont, in other casos it is very des
generate or vanishes almost complotoly. A contrum, togobhor with its
arch, is termed a vertobras arch ond centrum uro asually firmly
united and consist of cartilinge or bone. tn the
region of the tail numerous inforior archos
wre attached to the contra, thoy resemble the
superior arches, and encloxe the large caudal
vessol. = From tho vertebrm, vieriolus  “procenKeN
arise; above, from cach oreh, a noural spine ;
laterally, transverse processes, arliculiur processes
wilh articular facote, which lio upon those of
succeeding vortebrio, and soon ribs aro attached
to most of the trunk vertebrin, excupting tho
witorior and posterior ones, one pair to each
vertebra, They aro cartilaginoas or bony rods
which serve as a support to the body-wall; in the

 

or

Fig. 269. Din-
gram of w vorto-

bro and the parts
connected with it.
ch notochord, h cen-
trum, 6 neural arch,
+ neural spine, m
spinal cord, r rib,
br sternum.—Orig.

higher Vertebrata they are partly connectod below
by a sternum, an unpaired, usually partially
or completely ossificd cartilage, sittmdod in’ the
body-wall; it is absent from Fish, and though
present in Amphibian, is not connected with the

ribs. In higher Vertebrata (Roptilin, Aves,
Mammalia, and to some extent even in the Amphibia), the series of
trunk vertebrin may be divided into several regions: L cervieul
vertebra, with or without small ribs; 2. thorucice verlobri,
with well-developed ribs; 3. lumbar vertebras, suececding the
thoracics, with no ribs; 4 saeral vertebra, to which the
pelvis is attached, These regions cannot be distinguished in Pisces,
where the trank vertebra: are usually all similar,
The primitive cephalic skeleton is a
cranium, enclosing the brain, protecting
olfactory organs, whilst the auditory apparatus is imbedded in its
walls. Ite ventral wall is with the vertebras, and
surrounds the anterior end of the notochord—a very degenerate
structure in the adult. In the embryo the cranium is entirely
cartilaginous, and this is occasionally the case in the adult also,
though « certain amount of fibrous tissue is present, filling in the

strong capsule, the
alyo the optic and

continuous
Vertebrata, 327

gaps in tho cartilage; but during tho dovelopment of some forms,
tho cartilage is partially or ontively rephicod by bone. ‘The bone
hore, as in othor regions, oceupios tho exact position of the
curtilage; the luther is gradually absorbed, bone developing: simul-
taneously tn its place, For the most part, however, the bonos of
tho skull dovelop in the form of plates, moubrance bones, which
arise in the neighbouring (issue, and lie external to the chondro-
erauiua, pactly covering the gaps moutioncd above, partly covering
the cartilage itself. This may persist to a greater or less oxtont
below the motbrno bones (eg. ta many Tolooster, or it may
ontively disappear. Tho adult skull ts, therotore, made up partly of
bones, proformed in curtilige (of whieh a small amount romatus to
connect tho soparate pieces), aud partly of mombraue boues (joined
togothor by connective tissue) ; the soparate bones are often partly or
ontively fusod in tho adult. Ou otthor side of the skull we attached a
number of viscoral archos (Mig. 80b cy p. 864), which, like the
skull, are origiually cartilaginous > they aro curved bars lying im the
wull of the mouth; veutrolly, the corresponding arches of the two sidos
otthar uuite directly (the tirst avoh) ; or thoy are connected by a series
of unpaired cartilaginous or bony pieces, or by a single one (copilir
ov basi-branohials). Tho first viscoral arch, the mandibular areh,
ms Stronger than the succeoding ones aud is divided into uppor and
lowor portions, the palato-quadrato and the mandibular
or Mookel’s cartilage. The vest, the hy otd, ts usually also
woll doveloped. Pho rest uro termod gill arehes; in Bish and
Amphibia there are usually four, tive, or more, though gonerally
wt most, one or two. ta most Vortobrata the visceral arches, like
othor parts of the skeleton, become, tn the course of dovelopmont,
partially or completely replied, or covered by boue; the patato-
qiurdeate by tho pakoting, pterygwotd, and quadrate bones; Mockel’s
cartilage, by oue or tore bouos, ete. The maxilla and promasilla
avo tudependont of the gill arches; they are paired bones, present
in most Vertobrata, and forming the anterior boundary of the mouth ;
thoy develop in counoctive tissttio, aud have uo curtiligiuous portions,

Tho foro-liinbs are connected with the body by the shoulder
girdte, whteh consists on cither sale of a cartilaginous or bouy arch,
sittaited tn the autertor rogtou of tho bodys sometimes the two arches
wre unttod below, but usually thoy are separate. LE ossttied, each arch
may generally be seen to coustst of a dorsal shoulder blade
(scapula), wbove the potut of articulation of the limb, or glenoid cavity,
and a yeutral coraeotd: in front of the latter there is usually a
spovial boue, the collar-bone (eleviclo).  Coracoid and clavicle
are ustatly attached autortorly to the sternum who thas ts present.
The skeleton of the tove-tineb ttself ts laminate tn Pisces, consisting
vt radivtly arranged cartilaginous or bony pieces. (For details
see below under Pisces.) ta all other Vertebrata the skeleton of the
328 Vertebrata.

fore-limb conforms to one type: articulating with the shoulder girdle
by its upper end is a long bone, the humerus; to its lower end
are attached two other long bones, the radius
and ulna, together forming the fore-arm;
at the proximinal end of the ulna there is
usually a process, the olecranon, which
projects over the radius. At the lower end
of the fore-arm is the carpus (wrist),
consisting, when completely developed, of
two transverse rows of small cartilages or
bones (carpals), three in the proximal,
radiale, intermedium, ulnare, and
five in the distal row, one for each meta-
carpal: a small bone or cartilage (or
sometimes two) lies between these rows,
the centrale. To the carpus, which
undergoes many modifications, there are
attached five (or fewer, rarely more) series
of cartilaginous or bony pieces, of which
the proximal in each row is termed ‘a
metacarpal, the others phalanges;
whilst the metacarpals usually lie close
together and are enclosed in a common skin,
the digits are, for the most part, free.
ie. 2%, Diagram of The pelvic girdle, like the shoulder
the skeleton of the fore- girdle, is a paired or unpaired cartilaginous
limb of a higher Verte- : i ‘
brate. H humerus, Rradius, OF bony arch, affording an articulation for the
U ulna, u ulnare, ¢ inter. hind limbs. In Fish, it is independent of the
ee ae vertebral column; but in other Vertebrata,
to fifth digits.—Orig. it is almost invariably fused with one or more
vertebree, the sacrals, on either side. Like
the shoulder girdle, each half is divisible, in all excepting Fish, into
a dorsal portion, above the acetabulum (the point of articulation
of the hind limb), the ilium, and a ventral piece which is, however,
usually divided into anterior and posterior parts, pubis and ischium;
the latter is usually articulated with the corresponding bone of the
other side. Ilium, ischium, and pubis are always separate bones in
young animals, and are connected by cartilage, of which, indeed,
the whole pelvis originally consists; later, however, the three bones
more or less completely fuse with one another. The skeleton of
the hind limb corresponds closely with that of the fore limb, in
Fish and other Vertebrata ; in the latter, there is a femur (thigh-
bone), corresponding with the humerus; a shank corresponding
with the forearm, and consisting of a tibia and a fibula; a
tarsus (ankle), consisting of two rows of bones (tarsals); in
the proximal row, tibiale, intermedium, fibulare; five

 
Vertebrata. 829

in the distal; and a centrale (rarely two); five metatarsals
and five toes, each composed of several phalanges.

The bony or cartilaginous pieces are united simply by a
connective tissue sheath which lies between them, or more rarely by
cartilage, in which case there is but little power
of movement between the parts. If the move-
ment be greater, a joint is usually present ;
that is, the skeletal pieces are separated at their
adjacent ends by a slit-like space (the joint-
cavity), filled with a small amount of fluid, and
are only united by a capsule of connective
tissue surrounding this cavity. The apposed
surfaces of these skeletal pieces, the articular
surfaces, are smooth and accommodated ;
to one another, but are very diverse in form; Fig. 271.  Longitu-
they are almost always covered with a thin i oe hes aa
layer of cartilage (articular cartilages), a of the joint,h periosteum,
remnant of that of which the whole bone | capsule, kn articular

bo les i" : y . cartilages.— AfterGegen-
primitively consisted. The connective tissue in  pbaur.
the region of the joint is often in part modified
into firmer cords or ligaments, which reach from one bone to the
other. With the exception of the articular surfaces, bones are
everywhere covered by a fibrous connective tissue, the periosteum
cartilage is similarly covered by the perichondrium.

 

Bones, unless they are unusually thin, do not consist simply of osseous tissue,
but have cavities within them containing connective tissue and vessels. The
outer portion usually consists of a firm mass of compact bone, which
is perforated only by small canals (Haversian canals); the inner portion,
on the contrary, usually consists of spongy or cancellous bone in
which canals and spaces (marrow spaces), preponderate, separated by fine
trabecule and lamine. In the middle of long bones, there is frequently an
expanded cavity, filled usually with adipose tissue, the marrow cavity. In
cartilages, too, 4 smaller number of fine canals are usually present, containing
connective tissue and blood vessels.

Since the skeleton of Vertebrata is an internal one, the muscu-
lature is principally external, in contrast to Arthropoda, where
it lies within the skeleton. The muscles may be classified as those
of the trunk and those of the limbs. In Amphioxus and Pisces the
body muscles consist chiefly of large continuous masses, disposed on
the sides of the trunk and tail, not closely connected with the
skeleton, and divided by thin sheets of connective tissue into a
ttumber of segments; besides these, there are smaller muscles for
the movement of the visceral skeleton, the fin rays, etc. The limb
muscles are, as a rule, feebly developed in the Pisces. Similar
arrangements occur, in part, in the Amphibia, whilst in the higher
Vertebrata the musculature both of trunk and limbs is separated
into numerous individual muscles, extending from one bone to
330 Vertebrata.

another, and closely united to these at their ends; the limb muscles
are usually also very powerful. They consist of striated fibres, bound
together by connective tissue. Usually they terminate in tendons,
which consist of fibrous connective tissue; the tendons are not
infrequently, especially in Mammalia and Aves, of considerable
length. Sometimes they may be ossified to a greater or less extent,
and often small “sesamoid bones” develop in those portions
which pass over a bone, having cartilaginous surfaces towards
the bone; the knee-cap (patella) of Birds and Mammals is a
sesamoid bone.

The central nervous system arises in the Vertebrata
along the dorsal surface of the animal, as a grooved infolding
of the epiblast (Fig. 39, p. 48), which is later cut off from the rest of
the layer, and lies as a tube below the skin. In Amphioxus it remains
in this state throughout life; in others it is modified anteriorly,
to forma brain, in contradistinction to the rest, the spinal cord.
The lumen of the cord usually persists as a narrow canal (the
central canal) in the spinal cord, in the form of larger cavities (the
ventricles) in the brain. The brain is, from very early stages, divided
by grooves into three regions, of which the first and last are again
sub-divided into two. There are thus five sections: primary
and secondary fore-brain (thalamencephalon, prosen-

 

Fig. 272. Diagrammatic vertical longitudinal section through a vertebrate brain.
f cerebrum, me thalamencephalon, mi mid-brain, b cerebellum, e medulla, t olfactory lobes,
k epiphysis, tr hypophysis, ¢ pituitary body.— Orig.

cephalon); mid-bram (mesencephalon); primary and
secondary hind-brain (metencephalon, myelencephalon);
they lie one behind the other, and can be distinguished throughout
the whole series of Vertebrata, trom Pisces upwards, although in
other respects the structure of the brain, as a whole, and of its
various parts, exhibits great variety. The most anterior section,
the prosencephalon, or cerebrum, which is usually well deve-
loped, and, especially so in higher Vertebrata (Birds and Mammals),
is generally divided into two halves (the cerebral hemispheres) by
a longitudinal fold which dips into it from above and before, and
these hemispheres are prolonged anteriorly into a pair of small
hollow bodies, the olfactory lobes; the wall of the cerebrum
is much thickened both above and below. The thalam-
Vertebrata. 331
encephalon is always relatively small; its wall is only thickened
below and at the sides, dorsally it is very thin; a small process
extends from it to end above in a small body which varies considerably
in form, the pineal gland (epiphysis): ventrally, the wall is
evaginated to form a funnel-like pit, the infun-
dibulum, witha peculiar appendage, primitively
au invagination of the epithelium of the mouth,

the pituitary body (hypophysis). The
thickened lateral portions of the thalamen-
cephalon are termed optic thalami. The

cerebrum and the thalamencephalon are separated
by a deep transverse fold dorsally. The mid-
brain has a thickened upper wall divided into
two halves (the optic lobes) by a longi-
tudinal furrow, and in the Mammalia is also
divided by a transverse groove, so that there
are four lobes, hence the name, corpora quad-
rigemina. The cerebellum, which is specially
well developed in Birds and Mammals, has, usually,
a much thickened upper wall, extending posteriorly
over the medulla, whose dorsal boundary is, on

 

the contrary, very thin, whilst in other respects
this portion of the brain is similar to the spinal
cord, into which it is continued posteriorly without
any sharp demarcation. The spinal cord
extends through the vertebral column, as an almost
cylindrical rod dwindling to a point posteriorly ;
at the two regions where the nerves for the limbs
originate, it is usually somewhat enlarged. Brain
and spinal cord may be seen even with the naked
eye to consist of two substances, the grey
matter and the white matter; the former
consists of very numerous ganglion cells, which
lie embedded in a peculiar kind of connective
tissue (neuroglia), the latter consists of nerve

Hori-
zontal longitudinal
section through the
brain of a Vertebrate.
Diagrammatic. f
cerebrum, me thala-
mencephalon, mi mid-
brain, b cerebellum,
e medulla, 1, 1 the
cavities of the cere-
bral hemisphere (ven-
tricult laterales), 3
cavity in the thala-
mencephalon = (ven-
triculus tertius), a
that of the mid-brain
(aqueductus Sylvit),
4 that of the hind
brain (ventriculus
quartus).—Orig.

Fig. 273.

fibrils.

Often, ¢.g., in Mammualia, the primitive relations of the vertebral column and
spinal canal have undergone a change, for, owing to the more rapid growth of
the former, the hind end of the spinal canal is left empty. The result of this
again is that the posterior spinal nerves run within the canal for some distance
before making their exit.

The brain and spinal cord are surrounded by three connective tissue sheaths.
Most externally lies a fibrous, hard covering, the dura mater, which invests
the inner surface of the skull closely, whilst in the Mammalia, a special portion
of the periosteum lines the spinal canal; the dura mater frequently forms
large folds stretching between the different sections of the brain. Next to the
nervous matter lies a very vascular covering, the pia mater, and between
this and the dura is the thin arachnoid membrane; this last is not
332 Vertebrata.

distinguishable from the pia mater in Fish, and in other
Vertebrata they are closely connected. A number of
pairs of nerves arise from the brain, in part sensory
(tactile, olfactory, optic, and auditory), and in part motor ;
they are principally distributed to the head. From the
thalamencephalon and the optic lobes arise the optic
nerves, which are remarkable for crossing at their
point of origin; the nerve of the right eye thus arises to
the left of the median line, and crosses over. The
simplest case of sucha crossing or chiasma occurs in
many of the Teleostei, where the two nerves simply
cross, without entering into any closer connection. In most
other Vertebrata, on the contrary, the optic nerves ex-
change some fibres at the chiasma, so that, whilst the
main portion of the nerve which originates on the right
side runs to the left eye, a few of its fibres bend round
and join the other optic nerve, which, for its part, also
gives up some nerve fibres to its fellow. Of the other
cranial nerves, the olfactory arise from the olfactory lobes,
the others mostly from the ventral side of the medulla.
One of these, the vagus, is remarkable in that it not only
sends branches to the head, but also posteriorly, to supply,
for example, certain portions of the alimentary canal. The
spinal nerves usually leave the vertebral canal laterally,
one pair between every two successive vertebre ; each nerve
originates from the cord in two roots, of which the dorsal
is furnished with a small ganglion close to its point of
origin, and contains exclusively sensory nerve fibres, whilst
the ventral root consists of motor fibres only. The nerves
supplying the limbs originate in a number of spinal nerves,
connected together into so-called plexuses (brachial plexus
and lumbar plexus,for the fore and hind limbs respectively).
A peculiar system is the so-called sympathetic ner-
vous system, the principal part of which is a pair of
stout nerve cords running ventral to the vertebral column,
and only connected to the spinal cord and brain by small
connectives. The sympathetic nerves, which branch over
the alimentary canal and other viscera, are provided with
a great number of ganglia; the movements of the parts
which they supply (e.g., the muscles of the alimentary
canal) are involuntary.

Concerning the tactile and gustatory organs
of the Vertebrata, see the General Part, pp. 18—19.

The olfactory organs are, in the Fish,
a pair of large pits on the surface of the head,
covered by an epithelium, in which are sensory
cells. In other Vertebrata, it is only in .early
embryonic stages that the olfactory organs are
such superficial elongate pits (Fig. 283) ; gradually
each pit becomes overgrown by the surrounding
parts, so that it forms a tube with an anterior and
a posterior orifice, of which the former opens

 

 

 

 

 

 

f cerebrum, m optic lobes, b cerebellum, e medulla oblongata, & epiphysis, a and a’ swellings

Fig. 274. Central nervous system of a Tortoise.
in the regions from which the nerves for the limbs arise.—After Bojanus.
Vertebrata. 393

freely on to the surface of the head, the latter into the mouth,
within the upper jaw (the premaxilla and maxilla develop in those
parts which have grown over the olfactory pits). Thus the anterior
end of the head becomes perforated by two tubes which are usually
close together, and separated only by a thin septum; in the tubes,
there is a limited region containing the olfactory cells. The lining
often projects as large folds, which may be supported within by bony
or cartilaginous pieces (the turbinals). For further details, see the
various classes.* In those Vertebrata, in which the olfactory
apparatus consists of two tubes leading from the upper surface
of the head to the mouth, they have still another function, for air
for the respiratory organ enters through them.

The eye or optic bulb consists externally of the sclerotic
coat, a firm connective tissue sheath, varying in thickness and often
strengthened with cartilaginous or bony plates: it becomes trans-
parent anteriorly to form the cornea. Within the sclerotic there
lies the darkly coloured vascular coat, the choroid, and within this,
again, the retina, connected with the sclerotic and choroid by
the optic nerve, which perforates them. In the cavity of the eye-
ball, towards the exterior is the lens, consisting chiefly of long
filiform cells; in aquatic animals it is usually almost round,
in terrestrial forms more flattened. Behind the lens lies the
vitreous humour, a gelatinous connective tissue mass; the
cavity between the lens and the cornea is filled with lymph, the
aqueous humour. In front of the lens there is a circular
extension of the choroid, the muscular pigmented iris, whose
circularly arranged muscle cells respond involuntarily to the action
of the light, and so narrow the aperture, that less light enters when
the illumination is brilliant. The opening of the iris, the pupil,
is either round or elliptical, in the latter case either vertical
or horizontal. The choroid itself is provided just behind the lens
with numerous meridional folds, the ciliary processes, which
are slightly developed or wanting in Pisces.

With regard to the development of the eye, it may be noted,
that at an early stage of ontogeny, the fore brain forms anteriorly
on either side a vesicular evagination, the primary optic
vesicle, which is connected with the brain by a short stalk, whilst
its distal portion lies close below the skin. Then follows an invagina-
tion of the outer part of this vesicle, so as to form a double-walled

 

*In some Reptiles and most Mammals, there is a peculiar saccular or tubular
paired organ, Jacobson’s organ, in close connection with the olfactory
apparatus; its epithelium contains olfactory cells, and it receives fibres from the
olfactory nerves. In Reptilia (Snakes and Lizards), it is a small sac lying below the
nose, and opening anteriorly into the mouth; in Mammalia, it is a long tube, closed
behind, running below the mucous membrane of the nose, on either side of the
lower edge of the nasal septum ; and opening usually in a fine canal (duct of Stensen),
which leads into the mouth; more rarely it opens direct into the nose,
334 Vertebrata.

capsule, the secondary optic vesicle, whilst the stalk
elongates; then the cavity of the stalk diminishes as does also the
cavity between the two layers of the vesicle (1.e., the cavity of the
primary optic vesicle). The stalk forms the optic nerve, and
the wall of the vesicle forms the retina; the outer layer becomes
very thin and forms a sheath of strongly pigmented cells (the
pigmented layer of the retina, tapetum nigrum), whilst the
rest of the retina is formed from the thick inner layer. At the

 

Fig. 275. Diagrammatic representation of the development of the vertebrate eye.
1 section through the head at an early stage. -2 somewhat later stage: the incipient lens,
and the invagination of the optic vesicle may be seen. 3—4 further development: con-
striction of the lens, formation of the secondary optic vesicle. 5 the other chief parts of
the eye are formed. ch choroid, ep epidermis, ep’ epidermal portion of the cornea, g vitreous
humour, h cornea, hj brain, ¢ iris, 1 lens, m mesoderm, n optic nerve, » primary optic
vesicle, 7 retina, S sclerotic, ¢ pigment layer (external sheath of the retina).—Orig.

time when the primary optic vesicle is becoming capsular, the lens
begins to form. It develops as an invagination, which is finally
completely cut off from the rest of the epidermis and takes up its
position below this and opposite to the optic capsule. The trans-
parent lens develops from this epithelial sac by further modification
of the cells. The remaining portions of the vertebrate eye then
form round this essential part: the connective tissue between the
lens and the retina forms the vitreous humour, the covering to
the lens forms the cornea; between the latter and the lens there
Vertebrata. 335

is a space in which the aqueous humour is secreted ; outside the
retina, the choroid with the iris, and the sclerotic, develop from
the surrounding connective tissue.

From this account it will be clear that the sensory, that is, the essential, part
of the vertebrate eye, has a different origin from the retina of invertebrate
animals. The origin of the vertebrate eye may be imagined thus: originally a
vesicular evagination of the brain served for the perception of light, and later a
lens, etc., developed and closed the optic vesicle, which had been modified in the
meanwhile. Cf. also the pineal eye described below, which is similarly a vesicular
evagination of the brain. It must also be mentioned here that in certain lower
forms from which eyes are absent, part of the central nervous system is sensitive
to light (see p. 22).

The retina of the Vertebrata, like that of many other animals, possesses
rod-like refringent bodies which form a special layer (rods and cones) ; it differs
however, in that the rods are not in that part of the retina which is towards
the light. They lie directly upon the pigment sheath, and in order to reach
them the light has to traverse all the other layers of the retina. A considerable
number of thin layers is distinguished in the fully developed retina.

The eye lies in a deep basin-like cavity on the side of the head
surrounded by loose connective tissue; this depression, the orbit,
is arched over above by the skull; frequently too, it is more or less

completely bounded in front, below, and behind by osseous or carti-

 

 

Fig. 276. Diagrammatic section through the orbit A of a Fish, B of « Mammal!
© conjunctiva palpebrarum; c’ c. oculi; h cornea; l upper; 1 lower eyelid; m superior,
m’ inferior rectus muscles ; » optic nerve; o bulb of the eye; v retractor bulbt. The skin
is represented by a thick black line, the connective tissue dotted, the wall of the orbit
(consisting of bones, muscles, etc.) shaded by oblique lines).—Orig.

laginous pieces. The cornea is generally directly continuous with
the skin, which is usually soft and flexible in this region, so that the
eye can move within the orbit without hindrance. The movements
are brought about by muscles, which arise from the skull, and are
attached to the eye-ball, There are almost always four rectus eye
836 Vertebrata.

muscles (musculi recti), superior, inferior, internal, and external, and
two oblique muscles (musculi obliqui). The recti, which are
usually attached to the skull, close to the point where the optic
nerve perforates it, and to the eyeball, in a circle a short distance
from the cornea, move the eye upwards, downwards, inwards, or
outwards ; the oblique muscles, which are usually attached to the
anterior or nasal wall of the orbit, and above or below to the optic
bulb, cause it to rotate on its axis which runs approximately
through the middle of the cornea. Besides these, there is, in not
a few animals (Amphibia, Reptilia, Mammalia), a muscle which with-
draws the eye-ball (retractor bulbi) ; this muscle surrounds the optic
nerve, and springs from a point close to the optic foramen.

Excepting in Pisces, a circular fold of skin, which can be drawn
over the cornea, arises a short distance from, and almost parallel
to, it. This fold consists of upper and lower portions, the upper
and lower eyelids, whose edges meet when they are drawn
over the eyes; in the Mammalia the upper lid is best developed ;
in other animals, the lower. Just below the portion of skin covered
by the eyelids there is usually a thin and soft membrane, which
is termed the conjunctiva bulbi.* In many Reptiles, in Birds, and
in many Mammals there is a nictitating membrane, a fold
of skin developed in the inner corner of the eye, within the true
eyelids. In the two first-mentioned groups it is large, semi-trans-
parent, and moved by a special muscle; in the Mammalia it is not
so well-developed.t Connected with the eyes are various glands,
opening below the eyelid or nictitating membrane, and serving to
keep the cornea and the inner side of the eyelid damp and smooth.
In Pisces such glands are altogether absent, whilst in all other
Vertebrates one or more are present. There is generally a
lachrymal gland which opens behind (at the outer corner
of the eye), usually by several apertures, on the inner side of the
lower or of the upper eyelid,{ anda Harderian gland, which
opens anteriorly in the inner corner of the eye (usually within the
nictitating membrane if this is present) ; the secretion of the former
is usually more watery, of the latter more fatty in composition.
Part of the secretion from these glands runs through a tube, the
lachrymal canal, which has several openings in the inner
corner of the eye and discharges into the nose. (‘The lachrymal
canal is primitively a trough-like epiblastic invagination which
becomes constricted to form a canal; see Fig. 283 ANr).

 

* The soft inner covering of the eyelids is termed conjunctiva palpebrarum.

+ In many Fish immovable folds of the skin, otherwise like eyelids, lie round
the eye. In some Sharks there is a movable nictitating membrane.

¢ Only in Mammalia some (often the majority) of the openings of the lachrymal
glands are on the upper eyelid, . 7
Vertebrata. 337

A peculiar third unpaired eye, the pineal eye (parietal eye), in
connection with the pineal body, has been recently described in some Lizards
(e.g., in the common Lacerta, Blind-worm, and others). It lies in a small perfora-
tion of the upper wall of the skull (in the parietal bone, or between this and the
frontal), close below the skin, which is at this spot partially transparent. It
consists of a vesicle formed of a simple epithelium, the upper portion forming a
lens-like thickening, whilst the lower part is much pigmented (retina). In
other Lizards the same structure occurs in the same position in a more
rudimentary form, as a simple vesicle, which does not resemble an eye, but is
unpigmented, and without a lens. A structure like the first described occurs
also in the Cyclostomi, where, however, it is covered by the skull, which
is often somewhat thin at this place, and may even, like the skin above it, be
transparent. In various other Vertebrates also, facts are known which point to a

  

Fig. 277. Pineal eye of a Lizard; diagrammatic. A brain and upper wall of the
skull, the latter cut through; B pineal eye alone, in section. V, Z, M, H cerebrum,
thalamencephalon, optic lobes, cerebellum; h skin, s roof of skull, o unpigmented portion
of skin below which the pineal eye lies, in a ‘hole in the roof of the skull; p epiphysis,
t hypophysis, 2 optic nerve. LZ lens, R retina, N nerve of pineal eye.—Orig. (using
Spencer’s figures).

connection between the pineal gland and the exterior. In the Selachians the
pineal gland is filiform, and its distal end lies in a hole in the dorsal wall of the
skull, covered entirely by skin; so far as is known it possesses no optic structure.
In the Anura also, the epiphysis, which is short at first, elongates during larval
life into a long thread, with a terminal enlargement; the thread perforates the
skull-wall, and the swelling lies on the upper side of the head, directly beneath
the epidermis.

The auditory organs, one on either side, arise in the embryo
as vesicular invaginations of the epidermis, which gradually sink in
deeper, and become surrounded by the cartilage of the skull (later often
by bone). The invagination remains for some time connected with the
exterior by means of a canal, but later is usually completely cut off
from the skin, so that the developing organ is a closed sac; in some
cases, however (the Selachians), the canal persists throughout life
as an open tube. The vesicle does not retain its primitively simple
form, but is modified, so that the auditory organ in its adult condition

Z
338 Vertebrata.
consists of a saccular chamber, and three semi-circular canals;
the latter are tubes opening at both ends into the vesicle, to which
they are attached like hollow handles. The sac itself is divided by a
constriction into two portions, the sacculus and the utriculus; the
canals open into the latter, and each possesses a swelling at one end
(ampulla). The sacculus usually bears an evagination (ductus
cochlearis), which is, in Fish, Amphibians, and many Reptiles, a
short minute pouch; in some Reptiles (the Crocodiles) and in the
Birds, a longer tube; but attains its highest development in the
Mammalia, where it forms a long spiral canal. This whole vesicle,
which consists of epithelium, surrounded by a thin layer of connective
tissue, is termed the membranous
labyrinth. This is the essential
auditory organ which occurs in all
Vertebrata, Amphioxus alone ex-
cepted, and usually includes all
the parts named. There are certain
cells in the epithelium provided
with one or more processes, to
which the branches of the auditory
nerve are distributed, and which
are closely connected with the sense
Ge BRS, hand sat dhe aettiows of hearing. In the labyrinth there
organ (membranous labyrinth) of a Ver- are otoliths, either small
tebrate, @ ampulla, b semicircular canal, orystals or larger calcareous bodies
s sacculus, u utriculus (s+wu auditory :
vesicle), sg cochlea.—Orig. (Teleostei). The membranous laby-
rinth, which is inclosed in the
lateral wall of the skull, constitutes in Fish the whole auditory
apparatus; in other Vertebrata various accessory structures
are usually connected with it (tympanic-cavity, Hustachian tubes,
tympanum, ear-bones), which will be considered in the different
groups.

Those portions of the skull which closely surround the membranous labyrinth
are often (e.g., in the Mammalia) more compact in structure than the rest of the
bone, and may be entirely separated, giving exactly the form of the enclosed
membranous labyrinth: this is termed the bony labyrinth.

The alimentary canal is divisible into the following parts:
buccal cavity, esophagus, stomach, small intestine, and rectum. Of
the structures connected with the spacious buccal-cavity, the
teeth will be considered first.

The teeth, both in structure and development, are essentially
characteristic of the Vertebrata. They are present not only in the
mouth, but in many Fish (especially in the Selachians) on the skin
also. They occur within the mouth in all classes (with the exception
of the Lancelet, Amphioxus), although they are frequently absent.
In the simplest case (Fig. 279 A) the formation of teeth occurs

 
Vertebrata. 339

in the following way: a papilla of the dermis, or of the corresponding
connective tissue of the mucous membrane, grows into the epidermis,
or what is the same thing, the epithelium of the mouth. This papilla
secretes, on its upper surface, a covering of dentine, a substance
as hard as bone, the structure of which will be considered later; whilst
the cylindrical cells, constituting the lowest layer of the epithelium,
covering the papilla, secrete on their under sides a layer of still harder
material, the enamel. Between the papilla and the epithelium

 

 

Fig. 279. Diagram of various developing teeth. To the left in each figure a very
young one is represented, followed to the right by an older or several older teeth in
succession. A simplest form, B-—-C more complicated forms.. Enamel black; dentine
perpendicularly shaded; connective tissue dotted. b connective tissue, eo enamel organ,
ep epithelium, ep’ epithelial papi'la (incipient enamel organ), ep” older epithelial papilla,
p dermal papilla (pulp of tooth).—Orig.

a hard cap is thus formed, which consists within of a layer of dentine,
secreted by the papilla, and externally of a layer of enamel, secreted
by the epithelium; the two layers are inseparably connected, and
together make up the young tooth. The dentine is gradually thickened
by the secretion of new material by the papilla, which at the same time
becomes smaller, and is finally often reduced to a relatively small
structure, the pulp, within the tooth. The enamel is increased
by the deposition of new material on its surface, it never
attains so great a thickness as the dentine, and is often not
distributed over the whole tooth, but occurs only at its apex. As a
rule, however, development is somewhat more complicated (see Fig.
279 B—C); before the formation of the papilla a thickening of
the epithelium. occurs at a given spot, and in connection with it there
is an ingrowth into the connective tissue (ep’), which is usually so deep
that the point of the tooth does not project at all into the true layer of
epithelium, but lies exclusively in the sunken portion (Fig. 279 ();
this latter often only retains its connection with the epithelium by a
thin cord, and, indeed, is often completely separatcd from it. In other

z2
340 Vertebrata.

respects, however, the tooth develops in exactly the same way as in
the other case: a papilla grows up to the portion of epithelium that
has sunk in, and so on. Dentine has a certain resemblance to
bone, consisting of cells and a calcified inter-
cellular substance. They differ, however, in
that each of the cells of dentine (odontoblasts)
possesses only a single long, filamentous
process, provided with delicate lateral branches,
which run transversely through the whole of
the dentine, parallel to neighbouring pro-
cesses ; whilst the cell itself, with its nucleus,
ee aes is never enclosed in the intercellular substance,
atooth toshow the strneture but lies on the upper surface of the papilla.
of the dentine; diagram- The dentine is thus provided with numerous
matic. d dentinal tubes, ‘ ne
o odontoblasts on the inne,  @elicate canals, each containing a cell process ;
side of the dentine—Orig. for as the dentine increases in thickness
the processes gradually elongate. The enamel
is a very hard substance, consisting chiefly of calcium phosphate,
which in the Mammalia, at least, is composed of thread-like prisms,
whilst in many lower forms it appears more homogeneous. It is a
cuticular secretion of the lowest layer of epithelial cells.** The
fully-formed tooth, which varies considerably in form (though all
varieties are modifications of the cone), may have its tip pushed
through the mucous membrane by the growth of adjoining parts,
and may be attached by its lower end to the subjacent bones

 

Fig. 281. Portion of upper jaw of a
Lizard (Iguana) seen from the inner side ;
soft parts removed. k jaw bone, to the inner
side of which the teeth are firmly ankylosed
by a porous mass of bone b. T'—T* three
teeth which are about to fall out, the lower
ends being more or less absorbed (T" least,
T® most); t'—t? the corresponding incom-
pletely developed replacement teeth.—Orig.

 

(or cartilage) by a fibrous portion of connective tissue, or a small
osseous mass, the socket, which develops between the tooth and |
the bone. In Mammalia and some others, the teeth are placed in
alveoli, deep cavities in the bone, into which the lower end of
the tooth is sunk. The teeth are, of course, subjected to much,
and often rough, usage, and only remain for a limited time in the
mouth. They then fall out and new ones are formed; and thus

 

* For the cement, which is only present in Mammalia, see that section,
Vertebrata. 341

there is a succession of teeth; before falling out a tooth
loses its connection with the bone, the socket is reabsorbed. (For
the special conditions of replacement in Mammalia, see that
group).

Among other hard parts connected with the oral cavity, and occasionally
occurring among the Vertebrata, may be mentioned certain horny
structures, locally thickened and hardened portions of the cuticle, which
are developed here just as on the outer skin: the horny teeth of Cyclo-
stomes and Monotremes, the horny jaws otf Aves, Chelonia, and others.

The tongue projects from the floor of the mouth, and is inti-
mately connected with the visceral skeleton, especially with its
unpaired portions. It is a feeble structure in Fish, but in Mammals it
is well-developed, muscular, and very movable, and thus of great
importance in introducing food into the mouth. It exhibits a great
diversity of form, as will be noticed more particularly in the various
groups: it is rarely altogether absent. Various glands are also
connected with the mouth, pouring into it secretions which serve to
moisten the food, etc.; they are absent from Fish, but are developed
in all other groups. As a rule they are embedded in the wall of the
buccal cavity, but in the Mammalia some lie apart from it, and only
communicate with it by their ducts ; here they have, moreover, attained
to a considerable size as “salivary glands”; this is only
exceptionally the case in other groups.

Developmentally, the thyroid gland is also connected with the mouth.
It arises* as one or more evaginations of the floor of the oral cavity, from
which, however, it soon separates, and later forms a large. independent, duct-
less gland, which consists chiefly of epithelial sacs, filled with fluid. and united
by connective tissue. The function of the thyroid was until recently a complete
riddle ; medical researches of the last few years, however, have demonstrated
with certainty that it forms a product of vital importance, which is carried by
the blood to the rest of the body. The enigmatical thymus also arises as
a series of evaginations, which separate later from the buccal cavity. It is
well developed in embryos and young animals (in many young Mammalia it is
an extensive organ, stretching far back into the thorax), but it degenerates in
after life. In the adult the thymus consists chiefly of cellular connective
tissue.

The esophagus is short and wide in Fish and Amphibia,
but in Reptiles and Birds may be longer, in consequence of the
formation of a neck ; in the Mammalia it is not only fairly long, but
also rather narrow, although capable of great distension, whilst in
all the others it is very wide. The stomach is a wider region
varying in form, with innumerable small tubular glands in its walls.
The small intestine is a straight tube in the Cyclostomes and
some other Fish, but is usually coiled. In Fish, Amphibia, and many
Reptiles it is still comparatively short: in Birds and Mammals on the
contrary, it attains a considerable length, several times the length of

* According to general opinion, the thyroid corresponds to the endostyle in the
branchial sac of Ascidians (q.v.).
342 Vertebrata.

the body. In correlation with the importance of the small intestine
as an organ of absorption there are various arrangements for increas-
ing its inner surface, folds arranged in a network, or papilla (villi),
the latter chiefly occurring in the Mammalia. At the anterior end of
the small intestine opens the duct (or ducts) of the liver, a very
large, often lobed gland, consisting of very numerous lobules; the
duct (bile duct) is usually provided with a saccular expansion, the
gall bladder, which forms a reservoir for the hepatic secretion,
the bile. Close to the opening of the bile duct into the gut is the orifice
of another large gland, the pancreas, which, like the liver, is
usually extensive ; it is absent
A B from some Fish. Besides
these larger glands external
to the intestine, there are
frequently numberless small
tubular or racemose glands
lying in its wall (eg., in
the Mammalia). The terminal
°°, portion of the alimentary
canal is the rectum, which
is wider than the small intes-
Fig. 282. Diagram to explain the structure of mae In Oe V ertebrata ut
the mesentery: transverse section of the is short, and is then straight
lemon (eek ld), a? tha: pdion of figs out. es JO Only alles # Bustiton
rounding the gut; m mesentery, formed of two , length in the Mammalia;
layers ; + spinal cord.—Orig. here it is termed the lar ge
intestine, the term rec-
tum being reserved for the termination only. In many Vertebrata
the hinder end of the rectum acts as a cloaca, the urinary
and genital ducts opening into it. At its anterior end, at its junction
with the small intestine, the rectum (or large intestine) is often
provided in Reptiles and Mammals with one, in Birds with two, ceca
of varying length. The anus is situated ventrally at the base of
the tail, it is either round or a longitudinal or transverse slit.

:

 

The alimentary canal in the embryo is for some time a straight tube running
through the body-cavity along its dorsal surface, invested with a thin connective
tissue membrane, the peritoneum, which covers all the organs in the body-
cavity. Later it leaves the body-wall and sinks deeper into the cavity, drawing
its peritoneal covering with it, so that in the adult it is suspended by a large fold
of the peritoneum (Fig. 282). Where they do not surround the alimentary canal
the two layers of this fold lie close together, and form the mesentery, which
appears as a thin connective tissue lamina between the upper body-wall and the
digestive tract. Similar mesenteries may also be formed for other organs in the
body-cavity.

The respiratory organs of Vertebrata are sometimes
gills, sometimes lungs, the latter occurring in almost all
(with the exception of Amphioxus, the Cyclostomes, the Selachians,
Vertebrata. 343

and some others), whilst the former are limited to Fish and the
larve of Amphibia. The gills usually consist of very vascular
lamine arranged in a single series on the sides of the gill-clefts;
the latter are a series of large lateral slits, which lie closely
behind each other as perfora-
tions in the wall of the
oral-cavity. The clefts are
separated by septa, in which
lie the visceral arches men-
tioned above (see also Pisces).
It is of great interest that in
the embryos of all higher
Vertebrata (Reptilia, Aves, Ry.
Mammalia), which at no time
of their lives breathe by gills,
similar visceral clefts occur ;
they do not, however, bear
gill filaments, and they close
again later.

The lungs arise as an
unpaired evagination of the
alimentary canal, at the junc-
tion of the buccal-cavity and
cesophagus. During further
development, this evagination
does not usually remain simple, =
pat divides into two-sacs, right FE 28, Andor potion of Chick
and left, communicating with —lachrymal canal (still a groove), Ex incipient left
the alim entary canal by a, limb, Gh auditory vesicle, H fore brain, Hz heart,

; Db liver, Ls lens of eye, Lw body wall, M mouth,
common tube. Each sac, 1n Mg rudiment of stomach, Mh mid-brain, Ok upper

the simplest alee grows into coat chide ch Gace oe ao
a large, thin-walled bag, the be observed, Uk lower jaw.—Atter His.
wall of which is richly sup-

plied with blood vessels (e.g., in the common Newt). Usually,
however, the inner surface of the pulmonary sac becomes increased by
evaginations, which remain united by connective tissue, so that the
outer surface of the lung appears almost smooth. In some instances
(e.g., the Frog) each lung contains a large central cavity and the
evaginations are short; in others, the latter become longer and
branching, whilst the central cavity is smaller (Reptilia); in the
highest condition (im the Mammalia) the original sac is so much
branched that it forms an arborescent organ, the finest branches of
which end in tiny thin-walled vesicles. Over the walls of these
minute sacs a fine capillary network is spread, whilst the trunk and
the larger branches become thick-walled and firm, forming a kind of
skeleton for the rest of the lung. Further, both larger and smaller

Mh.

   

Gh.

Lv.
844 Vertebrata.

branches are covered by connective tissue, so that the ramifications
cannot be seen from without. On the inner surface of the lung there
is usually, as has already been mentioned, a delicate vascular net-
work; this is not, however, the case in most Fish; here the lung,
which is usually an unpaired organ, has no such network, and
therefore no respiratory function; it simply possesses the power of
diminishing the specific gravity of the animal, and is termed the
swim-bladder. A respiratory lung is only possessed by the
Dipnoi and a few others. The unpaired, usually tubular, portion
which connects the two lungs with the alimentary canal, the wind-
pipe (trachea), varies much in length, usually in correlation with
the form of the neck; it is generally strengthened by cartilaginous
or bony rings, and in most Vertebrata (Amphibia, Reptilia, Aves,
Mammalia, and some Pisces) it opens ventrally into the alimentary
canal; in most Pisces, however, it opens dorsally. In the anterior,
specially modified portion of the trachea, the larynx, there is,
in many forms (Anura, Lacertilia, Crocodilia, Mammalia), a pair
of projecting membranous folds, the vocal cords, which are set
in motion by the currents of air and thus produce the voice.
Circulatory organs. In the Fish the heart consists of
three successive parts, atrium, ventricle, and conus
arteriosus.* he atrium is a thin-walled sac lying above the
ventricle which has thick spongy walls; the conus is tubular.
Each portion encloses a simple
cavity as does the large venous
sac, the sinus venosus, which
lies in front of the auricle and
brings into it the venous blood
from the body. Inthe Amphibia
the conus is well-developed, and the
ventricle, with its spongy walls, is
undivided, like that of Pisces. The
atrium, on the other hand, is
separated by a thin septum into
right and left auricles; the sinus
venosus is also divided. The left
a Pm. sides of the sinus and the corre-
fis 20k Hiss ofan Amphibians sponding auricle receive the blood
is removed by a horizontal section; from the lungs, the right that from
partly disgrammatio. spongy wall of the rest of the body (for details see
e ventricle, k valves, o opening o: e me
sinus venosus into the left auricle, 0’ Amphibia). In the Reptilia
Opes of the sinud venoms inte ‘he the atrium and the, ¢losely eon:
right auricle, s auricular septum, v wall Ec es % :
of auricle.—Orig. nected sinus are divided just as in
the Amphibia; butthe specialisation

 

 

* The conus is rudimentary in many Fish.
Vertebrata. 345

of the heart has proceeded further, the ventricle is at least imperfectly
divided, and in the Crocodilia is completely separated by a perfect
septum into right and left chambers, in communication with the
corresponding auricles. The conus is rudimentary or absent.
Birdsand Mammals exhibit conditions very similar to those in
Crocodiles; the auricles and ventricles are completely divided ; the
conus is absent. Valves which regulate the flow of the blood
are always present at the junction of the auricle and ventricle and
also in the conus, or when this is absent, at the limit of the ventricle.
Auricles, ventricles, and conus are composed chiefly of striated
muscle cells.

It must be noticed that the auricle and ventricle are simple during the
embryonic life of the higher Vertebrata, the septa being formed later.

A B

      

1
'
™

Fig. 285. Diagrammatic longitudinal section through the head and front end of the
body to show the position of the heart and the pericardium. A Fish, B higher
Vertebrate. c posterior boundary of the skull (the rest of which is not drawn), h ventricle,
1 body-cavity, m buccal-cavity, 0 cesophagus, s septum or pericardium, v stomach.—Orig.

The heart is ventral to the alimentary canal; in Pisces it lies close to the
head in a special portion of the body-cavity (Fig. 285 A), closed off from the
rest by a transverse septum. In other Vertebrata it has moved further
back, and therefore this septum is sacculated, and forms a pouch round the heart,
the pericardium, which projects some way back into the general body-cavity.

A large ventral aorta springs from the heart in Fish and
gives off a branch to each gill-arch, the afferent branchial
arteries; there are usually ‘five pairs altogether in Selachians
(gill-arches 2—6), and four pairs in the Teleostei (gill-arches
3—6). The blood, after passing through the capillaries of the gills
of each arch, proceeds through the efferent branchial
arteries tothe aorta, a large unpaired artery running below the
vertebral column, and giving off branches to the various organs. The
large arteries of the head (carotids) arise from the first efferent
branchial artery ; if a functional lung is present, it usually receives
blood from a branch of the last efferent branchial artery. The
Amphibia generally exhibit similar arrangements during larval
life. Later the afferent and efferent arteries unité to form four
simple arterial arches on either side, which run directly into the
aorta. Of these, the third is usually atrophied in the adult; the
346 Vertebrata.

second, on the contrary, is especially well developed, and supplies
most of the blood for the aorta; the first arch practically supplies the
head only; the fourth, the lungs. The second often loses its connec-
tion with the other arches, so that it alone forms the aorta. In other
Vertebrata, the third arch is wanting; and it must also be noticed
that the primitively simple arterial trunk is divided into two or three
branches, of which one is exclusively connected with the last arch.
In the Reptilia the arrangements are otherwise essentially similar
to those of the Amphibia; in Birds and Mammalia, on the
other hand, a further reduction has occurred, for the aorta is formed
from one of the second arches only ; from the right in Birds, from
the left in Mammals. The connections between the first and second,
and the second and fourth arches, which may still occur in the
Reptiles, are absent from Birds and Mammals. (For details see the
various groups.)

In Fish, the embryo develops six simple arterial arches on either side, which
run along the six primary visceral arches, and unite to form the aorta; the first
of these, and in Teleostei, etc., the second also, degenerates, whilst the others
split into afferent and efferent branchial arteries. Further, in almost all other
Vertebrata these six arterial arches are present in the embryo; then some of
them gradually atrophy, and thus are obtained the adult conditions already
described. The appearance of arterial arches and visceral clefts in the embryos

of higher Vertebrata (Reptilia, Aves, Mammalia) seems to prove that these have
been derived from forms with branchial respiration.

With regard to the venous system, it must be mentioned that
the venous blood from the alimentary canal, spleen, and other viscera
does not go direct to the heart, but is collected into a large trunk, the
portal vein, which enters the liver, and branches to form a
capillary net-work. The blood is collected again into hepatic
veins, which carry it to the heart. In Fish, Amphibia, and Reptiles
such an arrangement also obtains for the kidney, the renal portal
system: veins from the tail and hind limbs proceed to the kidney,
and break up into capillaries, from which other veins arise and go to
the heart. In Fish and Amphibia it not infrequently happens that
several large veins are pulsatile (venous hearts); at these
points, Just as in the heart, transversely striped muscle cells are
present. The veins, but not the arteries, are provided throughout
with valves, which direct the current of blood. In the Verte-
brata a well-developed capillary network is present, connect-
ing the smallest arteries and veins. The blood corpuscles are
of two kinds: amceboid white corpuscles, few in number; and
discoid red corpuscles, constant in form, usually oval and nucleate,
but in the Mammalia circular, biconcave, and without a nucleus. They
impart the red colour to the blood, the plasma itself being colourless.

Occasionally an artery or vein breaks up suddenly into numerous branches,
lying close together, and frequently anastomosing, and uniting again to form a
single vessel. Such a network is termed a rete mirabile (swim-bladder of Fish,
kidney, ete.).
Vertebrata. 347

 

D E F

Fig. 286. Diagrams of the arterial arches of various Vertebrata. A embryonic
condition, B Fish, C Urodele, D Reptile (Lizard), HF Bird, F Mammal.
The atrophied vessels are represented by dotted lines. k and h the two first embryonic
arches which almost entirely atrophy. 1—4 the four posterior arches. 1’ and 3’ the first
and third afferent branchial arteries, 1/’ and 3” efferent branchial arteries. 2 in D and F
second left arches, 2’ in D, E and F second right arches. a, b, ¢ vessels into which the
ventral aorta is divided in Reptiles, Birds, and Mammals. ao aorta, ca carotid, p pulmonary
artery, s (in F) artery of left limb, s (in B) and st ventral aorta.— Orig.
348 Vertebrats.

Peculiar to the Vertebrata is the so-called lymphatic system,
a special system of canals and spaces, distributed over the whole of
the body, and containing fluid. Its function is in part to reabsorb
the plasma which has escaped from the capillaries into the tissues,
in part to take up fluid nutritive substance (chyle) from the
wall of the alimentary canal, and to carry both imto the blood.
Its principal trunks open into certain large veins. In the lower
Vertebrata (Pisces, Amphibia, Reptilia), the lymph vessels occur
partly as sheaths round the arteries and veins, whilst they are
elsewhere represented by special vessels which are, however, to some
extent irregular in form, sometimes wide or saccular. There are
often large lymph sinuses, e.g., below the skin in the Frog. Usually
near the point of entrance into the veins, the large lymph vessels
are rhythmically contractile, the lymph hearts; in the Frog, for
instance, there is a pair posteriorly on the dorsal surface; they are
absent from the Mammalia, but present in all other classes. The
fluid in the lymphatics is colourless or whitish, and contains numerous
leucocytes, identical with the white blood corpuscles. They are
formed in very cellular portions of the connective tissue attached
to the lymphatics, and, breaking loose, are carried away by the
lymph ; this tissue frequently forms specialised rounded bodies, the
so-called lymph follicles, which, especially in the Mammalia,
are collected into large lymphatic glands. An organ in
connection with the true vascular system, which serves also for the
production of white blood corpuscles, is the spleen, a dark-red
body of considerable size, situated in the abdomen near the stomach.

The red blood corpuscles are formed chiefly in the spleen and in
marrow. The epithelial lining of some of the blood
vessels in these parts is much thickened and stratified ;
cells of this epithelium develop into blood corpuscles,
break off and enter the vascular current.

The kidneys, which lie on the dorsal
wall of the body-cavity,consist of innumerable
long, coiled glandular tubules, the urinary
tubules, bound together by connective
tissue. The closed end of the tubule, which
is somewhat expanded, is imvaginated to
form a capsule (Bowman’s capsule),
by the inpushing of a small rete mirabile, the

Fig. 287. Diagram of glomerulus. This results from the break-
ae ae e . fant ing up of a small artery, its capillaries again
uw urinary tubule, which uniting into a single artery, which, later,
ae ee Likes oe goes to form the capillary network of the
funnel, f, the other in a kidney. The thin walls of the glomerulus
oe See ae appear to excrete the watery part of the
—Orig. urine, osmotically, whilst the salts are sepa-

rated by the kidney tubules. In many Fish

 
Vertebrata. 349

(Selachians), and in the Amphibia, branches arise from the urinary
tubules and run to the surface of the kidney to open there by
ciliated funnels (nephrostomes), so that they communicate
directly with the body-cavity. The urine escapes through the
ureters, which open either into the cloaca, or else by a single
orifice near the anus. For the urinary bladder see the
different groups.

In Fish* and Amphibia, each kidney is connected with the
testis of the same side by fine transverse canals, so that the
spermatozoa can escape through the urinary tubules and ureters.
Usually the testis is only thus connected with the anterior and
often narrow end. At an early stage of development a pair of
embryonic kidneys is developed in Reptilia, Aves, and
Mammalia, and these for some time act as the excretory organs.
Later, however, they are replaced by another pair, quite independent
of the first, the adult kidneys, which are functional throughout

Fig. 288. Fig. 289.

Fig. 288. Testis, Kid-
ney, ete, of an Amophi-
bian, diagrammatic. €
cloaca, ¢ testis, w anterior,
wu posterior portion of
kidney, ug ureter, ug’ ducts
of posterior portion of
kidney which open into the
hindmost portion of the
ureter.—Orig.

Fig. 289. Testis, em-
bryonic kidney, ete.
of the embryo of a higher
Vertebrate ; diagrammatic.
c cloaca, ¢ testis, anterior
portion of embryonic kidney
(which forms the epididy-
mis), wu’ posterior portion
which atrophies, wy duct of
embryonic kidney (seminal
duct).—Orig.

 

life. The embryonic kidneys and their ducts (Wolffian ducts) which
open into the cloaca, are lost in the female, whilst in the male the
testis becomes connected by fine tubules with the anterior portion of
the embryonic kidney, and this part persists throughout life as the

 

* The aberrant conditions of the Teleostei are disregarded here. See Pisces.
350 Vertebrata.

epididymis. This consists of numerous coiled tubes, and lies
close to the testis receiving the spermatozoa from it, and carrying
them to the segmental duct, which serves as the seminal duct
(vas deferens) of the adult. The posterior portion of the
embryonic kidney atrophies, and the epididymis loses its original
excretory function. It follows, from this: description, that the
embryonic kidneys of Reptilia, Aves, and Mammalia correspond
with the permanent organs of Pisces and Amphibia, whilst those of
the adult are, on the other hand, quite new structures.

A pair of organs lying far anterior in the bhody-cavity is distinguished by the
term head kidneys (pronephros)*: each consists of one or more glandular

tubes. One end of each tube opens by a funnel into the
f body-cavity, the other is connected with a duct. the

segmental duct, opening into the cloaca. Opposite the
funnels a large glomerulus projects from the body-wall.
This head kidney appears in the embryo as yet another
urinary organ, but before long it gradually disappears,t
the duct, however, remains as the ureter of Fish and
Amphibia, and the Wolffian duct of higher Vertebrata.
In the latter the pronephros is rarely functional, and
is very poorly developed; in Amphibia and many Fish
on the other hand, it is for some time the functional
excretory organ both in the embryo, and sometimes also
in the young animal.

In the Vertebrata there is usually a pair of supra-
renal bodies (sometimes separated into several
portions), organs whose significance is still unknown.
They are mentioned here since they usually lie close to
the kidneys, with which, however, they do not come into
any further relation. The suprarenal organs are usually
yellow or brown in colour, and consist of connective
tissue, in which are embedded strings of cells or vesicles.

They are very vascular, and well supplied with nerves.
Fig. 290. Diagram of a The Vertebrata typically possess two ovaries,
pronephros. eaaorta, é :
g—g (left) glomeruli, g although in many Fish they are fused, and one
(below and to the right) ig generally abseut from Birds; they are firmly

duct of embryonic kid-
ney, t funnels.—Orig. attached to the dorsal body-wall, and are covered

by a simple epithelium, from which there are
inpushings into the subjacent connective tissue even in early
developmental stages. These invaginated regions separate from
the superficial epithelium as small roundel groups of cells, in
which there is a central larger cell, surrounded by a sheath of
smaller ones. Such a group is termed a Graafian follicle,
the central cell is the young ovum, which gradually increases, and

 

 

 

 

* In relation with this, the kidney of Fish and Amphibia, and the embryonic kidney
of the higher Vertebrata may be termed the mesonephros, and the adult kidney of the
latter, the metanephros.

+In certain Teleostei it persists throughout life as an excretory organ; in many
others it persists in a modified condition, but in the adult no longer excretes urine,
Vertebrata. 851

often attains an enormous size. The cells round the ovum secrete
a vitelline membrane, which is sometimes very thick.
The cells constitute, in all Vertebrata, a single layer round the
egg, and usually remain in this condition; only in the Mammalia
do they divide, so that the young egg is surrounded by
several layers. Here a split appears later in the cellular mass
(Fig. 291, s), and gradually enlarges, so that the ripe Graafian
follicle of Mammalia looks like a hollow ball of cells, whilst the
ovum, surrounded by a proliferation of cells, projects into the cavity.
The ripe ova are shed into the body-cavity by the
bursting of the Graafian follicles. They vary in size in the different
Vertebrata; they are smallest,
microscopic even, in the Mammalia,
largest in Birds and Selachians.
Where the ova are large, they
project from the surface of the
ovary, so that it looks very uneven ;
in Birds, it appears racemose,
whilst in Mammalia, on the con-
trary, it is usually a small, smooth,
roundish body. The ova gene-
rally escape by the Millerian
ducts, a pair of long tubes
each opening at one end by a
ciliated funnel into the body-cavity
(usually near the ovary of the
same side), at the other end into Fig. 291. Section through the ovary
the cloaca, or to the exterior by of a Mammal; diagrammatic. e epithelium

‘ ‘ on the surface of the ovary, e’ invaginated
a special aperture in the region portion of epithelium, g’ young Graafian

of the anus. (For the aberrant f collicle, g somewhat older do., s split,
: : ‘ @ egg, k nucleus of egg.—Modified from

relations of ovary and oviduct in  Wiedersheim.

many Pisces, see that group.)

The testes, of which there is also a pair, usually lie like the
ovaries, on the dorsal wall of the -body cavity (see the Mammalia for
the change of position which may occur during development). They
consist of numerous coiled glandular tubes (seminal tubules), which
are closely packed, and in which the spermatozoa are produced by
the modification of the constituent cells. For the methods by which
the spermatozoa escape from the body, see above, pp. 349, 350. For
copulatory organs, see the different groups.

Rudiments of the Miillerian ducts, varying in size, often occur in the male
(Selachii, Amphibia, Mammalia), just as vestiges of the mesonephros (parovarium)

and its duct (Gartner’s duct), may sometimes be found in the female (e.g., in the
Ruminants).

The majority of the Vertebrata are of separate sexes. Only in some species
of Teleostei are ova and spermatozoa formed in the same individual, #.e., there is
true hermaphroditism; both genital products develop in a common gland,

 
352 Vertebrata.

the eggs in one region, the spermatozoa in another. In not a few others
it may be noticed as a quite regular occurrence, that the sexual glands have in
some measure a dual character, being, for the most part, either ovary or testis,
but having a small portion of the ovary forming a testis, or of the testis forming
an ovary. These small portions do not, however, form ripe sexual products. So
also, a portion of the testes of the Toad (Bufo) resembles an ovary, but it does not
produce ripe ova.* As rare abnormalities, such relations may also obtain in the
higher Vertebrata (¢.g., in Mammalia); for instance, a testis may occur on one
side, an ovary on the other: or the gland of each side may possess in part, the
structure of a testis ; in part, that of an ovary: but in this case ripe genital cells
of both kinds are apparently not produced. More common than these true
hermaphrodites are the so-called pseudo-hermaphrodites, which
possess testis or ovary alone, but show the characters of the other sex in the
ducts or the structure of the copulatory organs; amongst the domestic animals
for instance, it is by no means rare to find males which possess very well-
developed Miillerian ducts, like those of the female. Certain normal arrange-
ments may be regarded as slight indications of pseudo-hermaphroditism ; e.g,
the presence of rudimentary Millerian ducts in the male, which has been
already mentioned, or the rudimentary copulatory organs in certain females
(clitoris of Mammalia, etc.).

Most Vertebrates are oviparous. The egg, when laid, is
sometimes surrounded by a gelatinous mass (Amphibia); in other
cases by a horny shell (Selachii); or again, by a tough or brittle
calcareous shell (Reptilia, Aves), which encloses, besides the egg-cell,
a mass of albumen, which will later be gradually absorbed by the
embryo ; all the coverings are secreted by the glands of the oviducts.
Many Vertebrata are, however, viviparous, embryonic develop-
ment occurring in the oviduct of the mother (or in Teleostei in the
hollow ovary). In the simplest cases, the egg, surrounded by
the usual coverings (shell, etc.), develops within the body of the
parent without the assistance of any additional nourishment; the
ducts of the female simply afford protection to the egg (e.g., in
many Reptilia): ovoviviparous animals. An approach to this
condition occurs in many oviparous forms, where the egg when
laid contains a more or less fully-developed embryo, the first part
of development occurring within the body of the parent, the conclu-
sion externally (e.., in the common Ringed Snake). In other
viviparous animals the embryo lies in, and is nourished by, a fluid,
secreted usually by the wall of the oviduct, which it absorbs into the gut
or through the skin (Zoarces, some Rays, Marsupials) ; in others, again,
processes from the embryo grow into the wall of the oviduct and serve
for the absorption of blood from the mother, upon which the foetus
is, as it were, parasitic (Mammalia, one Reptile, and Selachians).

 

* According to the interpretation of some observers, the Hag (Myzine) is a true
hermaphrodite, which is male whilst young, later female. The correctness of
this conclusion must still remain doubtful ; certain it is that in some male specimens
of this form, the anterior portion of the sexual gland has the character of an unripe
ovary, whilst the posterior part constitutes a testis; but whether this region later
develops into a ripe ovary, or whether, like the similar part in the male Toad, it
remains in this condition, cannot be decided from the investigations so far made,
Vertebrata. 353

Segmentation of the ovum is total in some of the
Vertebrata—Amphioxus, Cyclostomi, Ganoidei, Amphibia (with the
exception of Ceecilia and several others), and most Mammalia; in
others, in which the egg is large, segmentation is partial (Selachii,
Teleostei, Reptilia, Aves, Monotrema). As in the lower animals
a gastrula is formed, Amphioxus offering the simplest instance
(see p. 43), the formation in others being more complicated (pp. 43-45) ;
the mode of gastrula formation in Mammalia is not yet fully
elucidated. Most Vertebrate embryos are for a long time provided
with a yolk-sac (see p. 49), which attains a huge size in some (e.g., the
Selachians), but has usually vanished or is no longer visible when the
animal is born (¢.e., leaves the egg-shell or the body of the parent.)
In Reptilia, Aves, and Mammalia (the amniote Vertebrata), certain
peculiar conditions may be observed: the embryo is surrounded by
several embryonic membranes, which develop as special
outgrowths of the young animal. These are embryonic organs and

are thrown off at birth. ©

In the Hen’s egg, at a very early stage of development, a fold, consisting of
epiblast and the outer layer of mesoblast, is formed round that portion which
will develop into the embryo itself, as distinct from the yolk-sac portion. This
fold gradually grows round the whole embryo, its walls meet and fuse, and thus
a cavity is formed above, limited by the inner layer of the coalesced fold,
This inner layer is now called the amnion whilst the outer layer, which is

 

 

Cc D

Fig. 292. Iustrating the development of the embryonic membranes in a
bird embryo ; diagrammatic longitudinal sections of various stages. In A the development
of the membranes has not begun. ek epiblast, en hypoblast, mm mesoblast (broader line),
am amnion, am’ folds from which the amnion and serous membrane originate, s sercus
membrane, al allantois, b! food yolk, ¢ gut,—Orig. (partly after older figures).

AA
354 Vertebrata.

continuous below with the covering of the yolk sac, is termed the serous
membrane. Further, there grows into the cavity between the serous membrane
and the amnion, an outgrowth from the hinder part of the gut, consisting of an
inner layer of hypoblast and an outer layer of mesoblast. This outgrowth,
the allantois, grows gradually into a compressed sac of considerable size,
lying between the amnion and the serous coat, and communicating by a duct
with the gut. The allantois is very vascular, and serves partly as a reservoir
for the urinary excretions, partly asa respiratory organ. Similar conditions
obtain in other Birds, Reptiles,and Mammals ; in the last-mentioned the allantois
unites with the serous membrane to form vascular outgrowths, which grow into
the wall of the uterus and serve as nutritive apparatus (placenta).* In Fish and
Amphibia these embryonic membranes are wanting.

The Vertebrata occupy a somewhat isolated position in the Animal
Kingdom, and so far no close connection with other phyla has been
proved. Of the five chief divisions of the Vertebrata, excluding
Amphioxus, Pisces and Amphibia contrast, in many respects (see the
summary below), with the Reptilia, Aves, and Mammalia, which ‘are
likewise allied in many ways; the first two are united under the
heading Anamnia, the others as Amniota. On the other
hand, however, the Amphibia display many points in common with
the Amniota as opposed to the Fish (cf., the left of the summary).

1. Leptocardii

Skeleton of limbs not di- ( ‘| Embryonic membranes ab-

vided into arm, forearm, sent.

finger, etc. Ist and 2nd vertebre not
Stratum corneum absent. specially developed.
Olfactory organ a pit. 2 2. Pisces Gills present at least in the
Eyelids absent. young forms.
Auditory ossicles absent. Mesonephros functional kid-
Auricle of heart not divi- ney of adult.

ded. L Ventricle not divided.

Skeleton of limbs divided [ 3 Amphibia )
into arm, fore arm,
finger, etc.

Stratum corneum present.

Olfactory organ with ex-

se

Embryonic membranes de-
veloped.

4. Reptilia Ist and 2nd vertebre de-

veloped as atlas and axis.

wa

 

 

ternal and internal aper- Gills absent.

tures. 5. Aves Mesonephros_ replaced by
Eyelids present. metanephros.
Auditory ossicles. Ventricle completely or
Auricle of heart divided. | 6. Mammalia incompletely divided.

Class 1. Leptocardii (Zancelets).

The body is elongate, compressed, and pointed at each end; along
the back and the ventral side of the tail is a fin; limbs are absent.
The skeleton is represented by a well-developed notochord,
running the whole length of the body, and pointed anteriorly and

 

* A structure similar to the embryonic membranes occurs in the Insecta and
several Worms.
Class 1. Leptocardu. 300

posteriorly. Above this lies the central nervous system,a
long cord-like organ without specialised brain; its central canal
communicates with the exterior in front. There is an unpaired
eye in the form of a pigmented spot in the anterior part of the

 

 

Fig. 293. Diagrammatic longitudinal section of Amphioxus.
gill sac, m stomach, 2» central nervous system, p atrium, p’ atriopore.—Orig.

a@ anus, ¢ notochord, k

nervous system; paired eyes and auditory organs are absent. The
musculature isarranged as in Fish, the muscle-fibres transversely
striated. Below the notochord lies the alimentary canal,
beginning at the anterior end of the animal with a mouth, surrounded‘
by a number of projecting tentacles (cirrhi), this leads into a large
pharynx, perforated by numerous transverse slits, and extending
back through a large region ‘of the body. Behind, the pharynx leads
into the stomach, which is furnished with a large evagination, the
liver; the intestine is short and straight and opens ventrally, not far
from the hind end, so that the length of the tail is not great. The gill-
clefts do not lead direct to the exterior, but open into an atrium,
surrounding the pharynx, and this again opens
ventrally, anterior to the anus. In quite young
animals the branchial clefts open on the surface, but
later a longitudinal fold develops above them on
each side, and eventually grows round them, the
two uniting on the ventral surface. The vascular
system is remarkable for the absence of a
specialised heart, but all the vessels are

 

pulsatile. Below the pharynx is an unpaired vessel, Fig. 294.

which receives the venous blood from the body, and ‘Transverse _ sec-
i tion through the

sends branches to the gill bars; from the latter the anterior region

blood is collected into an aorta running below the
notochord. A hepatic portal system is present as in
other Vertebrata. Red blood corpuscles are wanting.
Numerous short ciliated tubes, arranged in a row on
either side, serve for excretory organs; each
tube has a single dorsal opening into the atrium,
several into the body-cavity. The sexes are separate.

of the body of
Amphioxus; dia-
grammatic. n
spinal cord, ch
notochord, g pha-
rynx, p atrium,
k gonad.—Orig.

The sexual

organs are represented by several pairs of ovaries or testes, which

AA 2
356 Vertebrata.

lie in the body-wall on the side towards the atrium; ova and
spermatozoa escape into this by the bursting of the organs, and are
ejected through the mouth. Segmentation is total, a blastula is
formed, the epiblast and hypoblast cells are little differentiated
(gastrula formation of the type depicted in Fig. 29); the embryo
hatches early, and the short larva swims by means of the cilia which
cover the surface. ‘

The class Leptocardii, which only includes the genus Amphioxus,
occupies in many respects the most primitive position among Vertebrata
(skeleton, nervous system, development, etc.), whilst in other respects it
is very peculiar and far from ancestral (atrium, etc.).

The colourless Amphiowus lanceolatus, reaching about 7 c/m. long,
occurs on European coasts, buried in sand,

Class 2. Pisces. (Fish)

The body is usually compressed and spindle-shaped ; head, body
and tail pass gradually into each other, the last is very muscular;
there is no neck, and movement of the head is usually very limited.
Many Fish differ more or less considerably from this general type; for
instance, some are so strongly compressed laterally that the animal
resembles a perpendicular plate ; im others, the head and body are
flattened dorso-ventrally ; in others again, the body is so elongated as
to be vermiform, or, on the contrary, it may be extraordinarily short
and bulky. Unpaired fins occur dorsally and ventrally upon the tail,
and on the dorsal side of the body. Usually two pairs of rather feeble,
flattened limbs are present; sometimes the posterior, or even both
pairs, are wanting. It is characteristic of the Fish that the hind limbs,
the pelvic fins, have often moved far forwards; close, or even anterior
to, the fore limbs or pectoral fins.

The somewhat thin epidermis, as already mentioned, has no
stratum corneum; goblet cells are often present, and their
secretion imparts to the skin its slimy character. The dermis often
contains ossifications, of which the best known are the so-called
scales, thin, bony plates lying in cavities of the dermis; they are

 

Fig. 295. Diagrammatic
section of the skin of a Teleos-
tean, to show the scales. 1
dermis, e epidermis, s scale.— -
Orig. .

 

often so loosely connected with the latter, and lie so close to the surface,
covered only by a thin connective tissue sheath and the epidermis,
that they are easily loosened by the movements of the animal and
fall off. They are usually imbricate, the overlapping edge being
posterior, and are then regularly arranged in rows. Cycloid
Class 2. Piven, 357

and ctenoid scales are distinguished ; in the latter the posterior
edge is finely denticulate. Scales, which are especially frequent in
the Teleostei, are simply one form of dermal ossification, and are
not sharply demarcated from others, bony plates, scutes, spines, etc.,
which are present in many Fish. The placoid scales (dermal
denticles) covering the whole surface of many Selachians, and
present also in various other Pisces, are entirely different. ‘They are
identical in structure and development with the buccal teeth, consisting
of dentine and enamel formed in the ordinary way; they do not lie
in the dermis, as do most dermal ossifications,* but their upper
portion projects from the skin; they fall out and are replaced, whilst
dermal ossifications usually grow with the growth of the animal, and
are neither deciduous nor successional. The form of these dermal
teeth varies, sometimes they have many points; usually they are
small, but may reach a considerable size. In those Teleostei and
Ganoidei which possess dermal denticles, their lower end is usually
connected with the dermal ossifications.t

The unpaired fins are folds of skin usually supported by
hard parts. At a certain stage in development, frequently even in
the newly-hatched animal, more often during embryonic life, the
unpaired fins are represented by a continuous fold, which runs
medianly along the dorsal surface of the body and tail, round its
tip and ventral side, along part of the body. In certain cases, this
ridge remains undivided throughout life, but the ventral portion in
front of the anus always disappears; usually, however, it breaks
into three or more sections, of which-those on the dorsal surface
are termed dorsal fins; that round the tail, the caudal fin;
and those ventral to the tail, anal fins. When fully developed,
hard portions, the so-called fin rays, are generally present. In
the Selachians, “horny rays” occur; horny, elastic, structureless
fibres, stretching from the base of the fin to the edge; they lie in
several layers in each fin, which is stiff and incapable of folding.§
Instead of these, there are in the unpaired fins of Ganoids, Dipnoans,
and Teleosteans, a series of rod-like dermal ossifications, the bony
rays, which lie as supports within the fin. Of such rays, two chief
forms may be distinguished, soft rays and spinose rays,
between which there are, however, intermediate forms. A soft ray

 

* Not infrequently, however, the true dermal ossifications have a large surface,
or a projecting point, bare.

+ The fine tooth-like points along the hind border of the ctenoid scales, which are
merely special portions of these, are not to be confounded with the dermal denticles.

{ The name is not a very happy one, since it is here applied to parts which develop
in connective tissue, and are entirely distinct from the true horny structures of
Vertebrata.

§ A series of cartilaginous rays occurs in the Cyclostome fin.
358 Vertebrata.

is a bony rod, which is jointed, 7.e., is divided transversely into a
number of short pieces connected by connective tissue; moreover,
it is more or less deeply split at its apex into several branches,
which are also jointed. Some, however, do not show this splitting,
and in others (Fig. 296 w’) the jointing is limited to the tip of
the ray, or is absent altogether. Each
soft ray consists of two symmetrical halves,
closely apposed, and corresponding the
one with the other. The spinose rays are
stiff, pointed, unsegmented bony rods ;
they also are composed of two halves,
which are either closely connécted or fused.
Intermediate forms also occur, which,
though not jointed, are yet flexible. Whilst
soft rays are present in all Pisces, and
especially in those with bony rays, the
spinose rays only occur in some of them,
Fig. 296. Portion of a fn 2d then are almost invariably confined to
eh es y ne y ; (pend the front of the fin; they are absent from
Saal heroes diagrammatic the caudal fin. The bony rays are capable
Orig. of depression and erection, the membrane
being folded together and then expanded:
Sometimes the skin is absent from several successive rays (free
rays). For the endoskeleton connected with the unpaired fins,
interspinal bones, etc., see below. Along the edge of the limbs, the
pectoral and pelvic fins, which are usually very short,
there isa fin border which is of similar structure to that of the
unpaired fin, furnished in the Selachians with horny rays,* in Ganoids,
Dipnoans, and Teleosteans with bony rays (soft or spinose). Spiny
rays are very rarely present in the pectoral, but are more abundant
anteriorly in the pelvic fin, and in this case occur also in dorsal and
anal fins. For the sense organs of the skin (lateral line, etc.), see
below.

Phosphorescent organs occur in some Fishes; they are peculiarly
modified portions of skin which look like larger or smaller spots; their structure
is as yet not quite understood. Such organs are fairly common in the Deep-sea
Fish, but are also present in some pelagic forms.

Jn many Pisces (Cyclostomes and Selachians), the skeleton,
with the exception of the notochord, consists entirely of cartilage,
which is, however, usually to some extent calcified, 2.e., calcareous
salts are absorbed by the intercellular substance ; in others (Ganoidei,
Dipnoi, Teleostei), the cartilage which originally forms the whole

 

* The edge of the fin and the horny rays are specially well developed in the paired
fins of the Sharks. In the Rajide, on the other hand, the cartilaginous rays belonging
to the limb skeletons to be mentioned below, reach almost to the edge of the fin, and
in connection with this the horny rays in the pectoral and pelvic fins are little
developed, or altogether absent.
359

Pisces.

Class 2.

The

vertebral column (Fig. 298), is not infrequently represented

; ‘ZISseBV¥ “"T 104sY¥—'e[pALs rapjnoys
out 30 souo0q ouwrq Mout raddu 1p —g9p ‘sfva teSoysorouvrq ep ‘mol samo] GE—pe ‘umnpNosedoseyut gg ‘uMTNoOAedoqns gE ‘tNNoIedoaal
0g ‘wnynoredo gz ‘afa oy} pulyeaq pue Moped S[VIIqioqns GT ‘BI[IxeM QT ‘ey[Ixemerd ~T “4yuoAyT, B jo uozoPAyYG “16% ‘SW

 

     

    

     

ALANS LOO
J

 

Ag) H

PS IE EE El

Ton : 8
Ae e DB ie ho
LEER EP RG CA

 

Z

AWS
ie enenass,
LAL Lo

ee Z “Phy

skeleton, is more or less completely replaced by true bone.

         

(in the Cyclostomes, some Selachians, Dipnoans, and cartilaginous

Ganoids) by a continuous tube of cartilage or connective tissue which
360 Vertebrata.

surrounds the chorda, is not divided into vertebra, and carries the
upper arches (the arches may even be absent, e.g., the Hag-fish
Myzine). Usually, however, this tube is broken up into a number of
pieces, the vertebrae, united by connective tissne. The vertebrae
are short tubular bodies, thickened so that
the lumen is narrowed centrally and thinner
at each end, where there are concavities,
connected with each other by a small median
opening (like that of an hour-glass): they are,
therefore, biconcave (amphiccelous) ver-
tebree. They surround the notochord which
is much constricted intravertebrally, so that
it resembles a string of beads. In some
Sharks, in which the vertebral column is
not divided into vertebra, the intravertebral
constrictions are already indicated by ring-

 

Fig. 298. Longitudinal
sections through the verte- 3 : : : .
bral column of various like thickenings on the inner side of the

Fish ; schematic. In A and : . : 4
Ba continuous cartilaginous COUtinuous cartilaginous sheath (Fig. 298 B).

tube is still present, in C Dorsally, each vertebra usually bears a
this is divided into centra neural arch* which is often produced
(h), g boundary of two | :
centra, ch notochord.—Orig. into a neural spine; often, also, on the trunk
vertebre, there are transverse pro-
cesses, which bend down at the beginning of the tail to form
the hemal arches, united just as are the dorsal ones. In the
Selachians the vertebre consist of cartilage often partially calcified;
in the bony Ganoids and Teleosteans they consist entirely of bone ;
or partly of bone, partly of cartilage.

The part of the vertebral column at the end of the tail, and its
relation to the caudal fin, deserves special consideration. In a small
number of Fish (Cyclostomi, Dipnoi) the hinder end of the vertebral
column is straight and there is an almost equal portion of the tail fin
above and below it, the upper portion being congruent with the lower ;
the tail is then said to be ppbarcercal, In most Fish, on the
other hand, the posterior vertébre turn upwards; the lower portion of
the fin is then usually better developed than the upper, and the tail
is called heterocercal. In most Sharks, the cartilaginous
Ganoids and Lepidosteus, this condition is very evident. In the
Teleostei (Fig. 299 D) it also obtains, but the turned up
portion consists, not of separate vertebre, but of a single bony or
cartilaginous piecet surrounding the end of the notochord, and often
uniting with the last or last few lower arches, to form the most

 

* The spaces between the arches are filled in by cartilaginous intercalaria in
Selachians and the cartilaginous Ganoids, and thus the tube round the spinal cord is
completed.

+ In some Teleostei (Fig. 299 C) the curved portion is longer, and includes several
vertebre besides the rod-like part.
Class 2. Pisces. 861

posterior joint of the vertebral column; below this apparently last
joit, there is usually a portion supported by rays, and almost
congruent with its upper portion, so that the tail appears to be
diphycercal ; this is termed a_homocercal tail. As a matter of
fact, however, it is just like the heterocercal, since the end of the
vertebral column is bent upwards, and the dorsal portion of the fin
is smaller than the ventral (see Fig. 299 D). In many, actually
heterocercal, forms, in which a great length of the vertebral column
is bent up, there is an approach to the same structure; since the
end of the tail, as regards the exterior, is divided into two almost
equal portions: a dorsal, into which the vertebral column is pro-
longed, and a ventral, consisting exclusively of rays (Fig. 299 A, B).

    

Fe
SS

Fig. 299. End of the tail of various Fish: Ad Sturgeon, B Pike, C Salmon,
DCod. h vertebral column, h’ bent up termination of the same, 6 upper arch, ¢ neural
spine, » lower arch, n’ last lower arch, united with h’. In C the bent portion of the
vertebral column is still fairly well developed (it is enclosed between the two halves of the
caudal fin rays of which the left are removed in the figure), in D, which represents the usual
‘Teleostean condition, it is on the contrary very small._—Partly original, partly a copy.

In the embryo, and in many cases also, in the newly-hatched animal
(Teleostei), the notochord is for some time a straight rod; later the
posterior end bends up, and is relatively much larger than in the
adult.

Well developed, bony, or partly ossified ribs are attached to the
transverse processes of the trunk vertebrae in most Ganoids, Teleo-
steans, and Dipnoans; in the Selachians the ribs are wanting or
very short; they are absent also from the Cyclostomes. There is
862 Vertebrata.

no sternum and the ribs do not meet ventrally. The dorsal and anal
fins of Selachians are each supported by a laminate skeleton extend-
ing, on the one hand, into the base of the fin, and on the other,
between lateral myotomes of the trunk and tail. Each consists of a
number of cartilaginous pieces arranged like the skeleton of the
pectoral and pelvic fins. In Ganoids, Dipnoans, and Teleosteans, it
is replaced by the interspinous processes, usually dagger-like
bones, lying between the muscle plates, and united with the neural
spines; or, on the ventral side of the tail, with the haemal spines
by connective tissue: the interspinous bones which do not extend into
the fin bear each a single movably articulated ray. A pair of short
bones is usually intercalated between the ray and the interspinal.
The caudal fin is attached directly to the upper and lower arches
which are partly separated from the vertebre at the hinder end of
the tail.

The skull in Cyclostomes and Selachians is entirely carti-
laginous, but in the latter is frequently calcified on the surface ;
in the cartilaginous Ganoids also there is a similar thick-walled
cartilaginous capsule, but here it is partly covered with membrane
bones; in bony Ganoidei, Dipnoi and Teleostei, it consists originally
of cartilage, which is later not merely covered by membrane bones
but is also partly ossified, i.e., replaced by bone; although some,
often a considerable portion, of the cartilage is retained throughout
life. The base of the skull, where it comes in contact with the spinal
column, is usually hollowed like a vertebra; and on either side of
the foramen magnum, there is often an articular surface, which
corresponds with a similar one on the first vertebra. The eye lies in
a lateral cavity protected above by a roof-like projection of the skull,
which, in most Teleostei, is compressed between the eyes to a thin
cartilaginous or membranous partition, with the cranial cavity
prolonged as a narrow canal for the olfactory lobes above it. There
is a pair of smaller cavities anteriorly for the olfactory organs.

In the Teleostei, and in the bony Ganoids as a whole, the skull consists of a
larger or smaller amount of cartilage and a number of separate bones. The
cartilage bones (formed by ossification of the cartilage) are: four occipitals
(basi-,supra-, and two ex-occipitals); of which all four, or the first and
the last two alone, bound the foramen magnum; in the region of the labyrinth
the most important is the petrosal or prootic, there are in addition
the epiotic and opisthotic; in the basal and lateral regions in front of
the parts just mentioned are the sphenoids (ali-, orbito-, and basi-
sphenoid); dorsal ossifications anterior and posterior to the orbit of each
side, the pre- and postfrontals; one or two ossifications at the anterior
end of the cartilaginous skull, the ethmoids. The following are membrane
bones: dorsal and anterior, a pair of nasals; thenapair of frontals (some-
times united, e.g., in the Cod) behind these again a pair of parietals, lateral to
which on each side is a squamosal; ventrally a long flat unpaired bone
which covers the greater part of the floor of the skull, the parasphenoid;
and anterior to this the similarly azygos vomer. Besides these, others
Class 2. Pisces. 363

may be present but are less constant. In the Dipnoi some of these bones
occur but cartilage persists to a large extent. In the cartilaginous Ganoids,
as already mentioned, only membrane bones are found, among them a parasphenoid,
frontals, parietals, and several smaller bones dorsally.

 

Fig. 300. Skull of a Perch, A dorsal, B ventral. 1 frontal, 2 prefrontal, 3
ethmoid, 4 postfrontal, 5 basioccipital, 6 parasphenoid, 7 parietal, 8 supraoccipital, 9 epiotic,
10 exoccipital, 11, prootic, 12 squamosal, 13 opisthotic, 14 alisphenoid, 16 vomer.—After
Cuvier and Valenciennes.

The dorsal membrane bones of the head are in many Fish very superficial in
position, covered only by a thin layer of connective tissue and epidermis (Sturgeon,
bony Ganoids, many Teleosteans) ; in others, the overlying connective tissue is
thicker.

A large number of visceral arches* usually seven pairs,
occasionally more (some Sharks), are suspended from, or situated
near to, the skull. The members of the first pair are united ventrally,
whilst the others are attached to a series of unpaired, cartilaginous,
or bony pieces (basibranchials). The most anterior, the
mandibular arch, consists, in the Sharks, of an upper and a
lower cartilaginous piece; the former, which is connected in front
with the corresponding one of the other side, is termed the palato-
quadrate, or less happily, the upper jaw; the latter, the
mandibular cartilage, or lower jaw. The two portions are
jointed together. The mandibular arch, the best developed, is loosely
connected with the skull in the Sharks, and forms the framework of
the mouth. The second, the hyoid, is similarly divided into two
parts ; the upper is fastened to the skull above, whilst its lower end is
attached by connective tissue to the mandibular. The other

 

* The Cyclostomi are excluded from this deseription of the visceral arches. The
arrangements in this group are much modified and difficult to understand.
364 Vertebrata.

five (occasionally six or seven) arches, the branchial arches,
are each divided into several pieces, and bear on their outer borders
delicate cartilaginous rays (removed in Fig. 301), which support
the septa between the gill-clefts; similar rays are also present on the

 

ZA. "%,
ee LEI),
$

Fig. 301. A skulland visceral arches of a Shark, B the same of a Pike; the
arches are in part artificially separated ; premaxilla and maxilla separated in B. First arch
dotted, second shaded : br, —br; first to fifth branchial bars (third—seventh visceral arches),
c basibranchials, d dentary, g palato-quadrate, gb palatine, hm upper portion of the hyoid
arch (in B hyomandibular), h rest of the same, k mandible, o orbit, g quadrate, s symplectic,
v—v” pterygoids (v ecto-, v’ endo-, v’’ metapterygoid).—Orig.

hyoid).* In the Ganoidei, Dipnoi, and Teleostei, there
are also seven visceral arches. The upper portion of the man-
dibular arch, the palato-quadrate, meets its fellow of the other
side in the cartilaginous Ganoids, whilst in all others it
remains distinct. This portion is intimately connected below, with
the lower end of the upper portion of the hyoid arch, which is

 

* As regards visceral arches, the Rays, on the whole, resemble the Sharks, but
the hyvid shows certain peculiarities, which cannot be gone into more closely here. In
many Sharks there are anteriorly, close to the gill-bars of each side, w pair of feebly-
developed cartilaginous bars (the labial cartilages), which may perhaps be regarded as
rudimentary first visceral arches.
Class 2. Pisces. 365

articulated above with the skull, and thus serves as suspensorium
for the mandibular, which, therefore, possesses no direct connec-
tion with the skull. This connection of the upper portions of
the mandibular and hyoid arches is specially close in the Teleosteans
and bony Ganoids, forming a continuous whole, in which the cartilage
is, for the most part, replaced by bone; it is less evident in the
cartilaginous Ganoids, although here, also, the two portions are
closely connected (for the Dipnoi, see below): the mandibular
cartilage, which is now, however, more or less replaced and covered by
bone, and the hyoid, which is likewise more or less ossified, are
attached at the same point. Of the five branchial arches
which are usually partly ossified, or covered by bony plates, the last
is very short in the bony Ganoids and Teleosteans, the lowest joint
alone being present. The last branchial bars, which usually carry
numerous teeth, are termed the inferior pharyngeal bones.
The uppermost joints of some of the other gill-bars are toothed in a
similar way, and are called the superior pharyngeal bones.

 

Fig. 302. Skull ofa Cod. h—j’ skull, hy hyomandibular, hy’ lower portion of the
hyoid, io interoperculum (see p. 374), | quadrate, m premaxilla, o (left) maxilla, o (right)
operculum, p pterygoid, pr preoperculum, s suborbitals, so suboperculum, st branchi ostegal
rays, (p. 374), ¢ basibranchials, w mandible.

In the Teleostei, the upper portion of the mandibular archis
represented by the following bones: below and behind by the quadrate, with
articular surfaces for the mandible; then by several bones, which are termed
pterygoids; and anteriorly, by the palatine. The lower portion of
the mandibular arch is a cartilage, the upper end of which is ossified and bears
articular facets, whilst the rest is a thin cartilaginous rod (Meckel’s
cartilage), surrounded by membrane hones, of which the most important
366 Vertebrata.

is the large dentigerous dentale, which meets its fellow of the other side
anteriorly. The upper portion of the hyoid, which is united with the
corresponding part of the mandibular arch, is represented by two bones; a
large one, the hyomandibular, articulated with the skull, and a smaller,
lower ossification, the symplectic. For the membrane bones connected with
the hyoid, see below, under the gill apparatus.

In the Dipnoi, the upper portions of the mandibular and hyoid arches are
concrescent, and partly ossified, thus possessing so far, the same relations as in

the Teleostei; the arcade thus formed is, however, connected immovably with
the skull.

In the Ganoids and Teleosteans, two membrane bones
arise anteriorly on either side of the head, quite independent of the
visceral arches: an intermaxilla or premaxilla, and a
maxilla, which is sometimes represented by several bones, and
is situated behind, or behind and within, the former; the premaxille
are connected in the midline, and with the maxille, are usually
somewhat loosely connected to the anterior end of the skull, forming
the upper margin of the mouth, whilst the bones lying upon the
mandibular cartilage form the lower edge.

The shoulder girdle is,inthe Selachians, an unpaired
cartilaginous arch, sometimes divided into two pieces, which lies behind

 

Fig. 303. Shoulder girdle and fore limb of a Perch. a’, a”, b, c, mem-
brane bones (6 clavicle), e, f the actual shoulder girdle (e scapula, f coracoid), g radialia,
h fin rays.

the gill bars, and reaches up on to the side of the head. In the
Ganoids and Teleosteans it is divided into two halves, one on
either side of the body, and closely united to each part is a series of
membrane bones, of which the largest is a long, flattened, somewhat
Class 2. Pisces. 367

arched bone, the clavicle. This series of bones is fastened above
to the hinder end of the skull. In the Chondrostei the cartilage of
the shoulder girdle is always very well developed in spite of the
presence of membrane bones; in the Holostei, and the Teleostei, the
original part of the shoulder girdle is usually much reduced in size,
and is represented only by a small plate, attached to each clavicle.
In the Teleosteans two ossifications are present in this plate, the
scapula and coracoid. In the Dipnoi relations similar to
those of the Chondrostei obtain. The skeleton of the fore limb
consists, in the Selachians, of a number of flattened cartilages :
at the base of the limb are three large ones articulated to the
shoulder girdle, the basalia, and to the edge of these is attached a
larger number of jointed cartilaginous rays, the radialia. These
he close together in the Sharks, but in the Rays, where they are very
long, they are somewhat further apart. In the Ganoids this
skeleton is reduced in size, the radialia are shorter, the basalia

 

Fig. 304. Skeleton of fore limbs of A Shark, B Polypterus, C Amia (a Ganoid), D Cod.
a, b, ¢ basalia (b’ ossification in b), r radialia, st fin rays (not all drawn).—Chiefly after
Gegenbaur.

usually less well developed, or partly absent; there is often an
ossification of some parts. In the Teleostei the original
skeletogenous supporting pieces are very small, the fin-border
preponderating ; the basalia are absent; the radialia are short and
few in number: they occur only as a transverse row of four, or fewer,
short rods, attachmg the fin to the shoulder girdle, they are partly
ossified, and have been incorrectly termed “carpals”; a few short
cartilaginous pieces may also be present. The Dipnoi are very
different ; there is a median, long, jointed, cartilaginous bar, bearing, in
the genus Ceratodus, two series, in Protopterus, a single row only, of
cartilaginous, jointed rays. (In Lepidosiren, the radialia are entirely
wanting).
368 Vertebrata.

The pelvis, which is not connected with the vertebral column
in Fish, is, in the Selachians, an unpaired transverse ventral cartilage.
In the Dipnoi, too, it is an unjointed cartilaginous plate. In the
Ganoids and Teleosteans it is divided into two halves, closely apposed
to one another, and except in the Chondrostei it is partially, or entirely,
ossified. The hind limb closely resembles the fore limb in
structure ; in the Selachians there are two large basalia provided with
radialia; in the Ganoids the basalia are degenerate or absent ;
this is also the case in the Teleostei, in which the skeleton of the hind
limb is represented by a few short radialia only, it is even less
developed than the fore limb. In the Dipnoi the conditions are
the same for both hind and fore limbs.

The muscular system is distinguished by the feeble condi-
tion of the limb muscles, as compared with the powerful development
of the trunk and tail musculature, which extends along the whole
length of the body in the form of four large muscle plates, two on
each side. EKach of these is broken up, by transverse septa
(myocommata), into a series of short segments, corresponding to the
vertebree in number (myomeres): in the dorsal muscles, and the
caudal portions of the ventral muscles, the septa are bent in a
peculiar way. In these muscles there are in many Fish numerous
fine rib-like bones, the epipleurals, which are attached at one end
to the ribs or to the vertebre. They are ossifications in the
myocommata and serve as supports to the muscles.

The electric organs present in many Pisces generate electricity, which
can be discharged at will: for instance, when the animal is caught. The
essential elements of these organs are plates, modified muscle fibres, for
the entire organ is a modified muscle: it is richly supplied with nerves, and
fibres enter each plate and branch freely on one side. The plates are bound
together by connective tissue; the organ is frequently composed of closely
apposed columns, each of which consists of a number of plates. The electric
organs lie in different regions of the body in different Fish; the most powerful
apparatus is thatof the Electric Skate (Torpedo), of the Sheath-fish or
Thunderer (Malapterurus), and of the Electric Hel (Gymnotus); but
feebler organs also occur in some other forms, e.g., in our native Skates (Raja),
where they are elongate spindles lying one on either side of the tail.

The brain of Pisces is of small size, and does not fill the
cranial cavity, which is chiefly occupied by the dura mater, a
membrane of considerable thickness, consisting chiefly of adipose
tissue. The olfactory lobes are usually large, and often of
considerable length, since the olfactory organ lies anteriorly, far
away from the brain. In many Teleostei, the fore brain is very
small, smaller than the mid brain; the hind brain, on the other
hand, is usually very well developed.

The olfactory organs generally occur at the anterior end
of the head, as a pair of pits whose mucous membrane is usually in
radial folds. The opening of each pit is single in many forms (some
Class 2. Pisces. 369

Teleosteans, Selachians) ; in others, a transverse membranous bridge,
varying in width, divides the opening into two, anterior and posterior
nares, of which the anterior may occasionally be drawn out into a
narrow tube; in many Selachians, this bridge is only represented by
a flap, arising from one side, and overlying the aperture without being
attached to the other.

In the Dipnoi, the nasal openings are peculiar, in that both lie within the
edge of the upper lip. In the Cyclostomes, the two olfactory pits are
united to form a deep unpaired tubular sac, the floor of which lies closely upon
the roof of the mouth; in Myzxine, it perforates the roof of the mouth,
and consists of a tube open at both ends, connecting the oral cavity with the
exterior.

Taste buds, as already mentioned (p. 21), are present in
many Fish (Teleostei), not only in the mouth, but scattered over the
surface of the body.

Groups of peculiar sense-organs occur in connection with the
skin ; they consist of modified epidermal cells, some of which bear
sensory hairs; and are thus not unlike taste-buds, from which, how-
ever, they differ in form. These sensory papille are supplied
with nerves, and may lie free upon the surface of the body (e.g.,
in most Teleostei), in which case they often bear a cylindrical tube,
a cuticular structure, which surrounds and protects the hairs
(Fig. 305 r). In other cases, those portions of the skin to which they
belong, have sunk in to form small sacs, opening to the exterior
(Ganoids) ; or the sacs have become
long tubes filled with mucus, running
below the skin, provided at one end
with an expansion in which the sensory
cells lie, whilst at the other, they
open to the surface (on the head in
Selachians). Further, similar groups
of cells are present in the lateral
line which occurs in most Fish.
This is a narrow tube (an invagination
of the skin), lying close below the
surface, and extending along each
side of the body. It usually divides
into several branches on the head, He She. e ; ; ;
one branch running over the summit 4 S0nng Welecshaan. + the> hose cidls
of the head, another above the eye, bearing hairs.—After F. E. Schultze.
a third below the eye—both the
latter reaching the snout—a fourth along the lower jaw. The
lateral line is richly supplied with nerves, and communicates
with the exterior by a number of openings; sometimes, indeed,
it is a partially open groove; in many Teleostei, it runs along
the side of the body and tail through a series of perforated

 

BB
370 Vertebrata.

scales ;* on the head they are partly enclosed by special, tubular,
membrane bones, of which there is, for instance, usually a series
below the eye (Fig. 302 s), partly surrounded by the ordinary bones
of the head.

The eyes of Fish are, as a rule, relatively large. The lens
is spherical. Movable eyelids are absent; but the eye is often
surrounded by a low circular ridge of skin, and in some species by
larger, but immovable folds; in the Mackrel and the Herring, for
instance, there is a transparent fold in front of, and behind, the eye,
which partly covers it.

The scelerotic usually consists of an outer connective tissue layer, and
an inner cartilaginous layer, varying in thickness (very thick, e.g., in the
Sturgeon) ; in the Teleostei the cartilage, in the vicinity of the cornea, is partly
replaced by two bony plates, which sometimes attain a considerable importance,
and may unite to form a ring. The choroid consists of several layers:
usually there is an external lustrous, tunica argentea, a thin coat of con-
nective tissue, with an abundant deposit of crystals; the tapetum lucidum, a
membrane with a metallic lustre, whose cells are filled with crystals, occurs in
Selachii, and Chondrostei, though it is absent from other forms. In the Teleostei
there is usually a so-called choroid gland in the choroid coat: it is a large
horseshoe-shaped rete mirabile near the optic nerve ; this group usually possesses
also a processus falciformis, a low fold of the choroid, which runs along the
inner side of the optic bulb, from the entrance of the optic nerve to the lens. In
certain Squalide there is a nictitating membrane, which can be drawn

over the eye by a special muscle.
The auditory organ is only represented by the membranous

labyrinth, which is enclosed in the lateral wall of the skull; within,
towards the cranial capsule, the labyrinth is often not completely
surrounded by cartilage or bone, but is simply separated from the
brain-cavity by connective tissue. In the Selachians, the cavity
of the labyrinth opens to the exterior at the surface of the head
by a canal, the ductus endolymphaticus ; in others this canal is
present, but closed at its outer end. In the Teleostei and bony
Ganoids, a large flattened otolith is present in the sacculus, a
smaller one in the evagination from the sacculus, and yet a third
in the anterior portion of the utriculus. In some Fish these are
replaced by bundles of delicate crystals, or by rounded bodies.

The labyrinth is in a reduced condition in the Cyclostomes, having only
one or two semicircular canals, unlike all other Vertebrata.

The buccal cavity is usually provided with teeth, which in
Selachians,t are situated upon the palato-quadrate and mandibular
cartilages; in the Holostei and Teleostei upon a number of different
bones: on the premaxilla, maxilla, and mandible, the palatine and

 

* The meaning of this is, of course, that the scales in question have developed
round the tube after it was formed.

+ Besides the well-developed teeth of the jaws, the Selachians often possess
numerous minute teeth on other parts of the wall of the mouth, on its roof and
floor, and on the gill bars.
Class 2. Pisces. 371

pterygoid, the branchial bars (especially the superior and inferior
pharyngeal bones), the basibranchials of the visceral skeleton, and
the vomer; they may, however, be wanting from one or other of
these bones. The teeth are of somewhat diverse form: most often
pointed, conical, slightly curved, and more or less powerful ; in other
cases they are low, rounded, grinding teeth (Rajidee, certain Teleostei) ;
or compressed and triangular (Squalide); or chisel-shaped, resem-
bling the incisors of Man (teeth on the premaxilla and mandible
of certain Teleosteans). Very often they are extremely numerous,
covering the bones like a mosaic; on the jaw there is frequently
only a single row of teeth, or a row of larger, outside a row of
smaller, denticles. They are either attached to the subjacent bone
by connective tissue, and then often partly movable, or they are
implanted in bony sockets. They are renewed throughout the whole
life, the old teeth fall out as the connection between them and the
cartilage or bone gives way, or if a socket is present this is absorbed.
The usual conical, piscine teeth are chiefly prehensile, and the points
are therefore turned backwards and inwards; they are movable so
that the point may assume another position. Teeth of other forms
are used for biting or masticating the food.

The cesophagus is so short and wide that the mouth passes almost
directly into the stomach. In most Teleosteans a varying number of
short, blind, glandular sacs (1—100), the appendices pyloriccee, open
into the anterior part of the small intestine, close to the stomach. In
Cyclostomes, Selachians, and Ganoids, there is a spiral valve in
the small intestine, a large projecting fold, attached to the inner
side of the gut, and almost filling up its cavity ;* it is absent from the
Teleosteans. The large intestine is quite a short tube.

 

Fig. 306. A fish with pectoral anus (Sternarchus curvirostris). A lateral view, B
ventral view of head end. a anus, o mouth.—After Boulenger.

In some Fish (e.g., the Plaice), the anus does not lie at the boundary of trunk
and tail, as in all higher Vertebrata, but has moved forwards, sometimes even far on
to the trunk. The anal fin in such cases follows the anus, and usually takes up
its position close behind it.

 

* Exceptionally, in some Squalide, the fold springs from the gut-wall in an almost
straight line, it is then broad and rolled like a piece of paper. ‘ oe

BB 2
372 Vertebrata.

The branchial apparatus. In Selachians the wall
of the buccal-cavity is perforated posteriorly, by five, rarely six or
seven, large oblique slits on either side; they lie in close succession,

   
  
 
  
  
  
  
 
 
 
  
  

Fig. 307. Horizontal section
through the head of a Shark
(Acanthias): diagrammatic. The
visceral arches are dotted, the
gill lamella shaded. br,, br,
br, first, third, and fifth gill
bars, c septum, g upper portion
of the first visceral arch (palato-
quadrate cartilage), h hyoid
arch, k body wall, 1 body cavity,
m oral cavity, 2 olfactory pit,
@ esophagus, s gill rakers
yy, (straining apparatus), sp, first,
\--¢ sp; fifth gill cleft.—Orig.

Fig. 308. Horizontal section
through the head of a Teleostean
(Cod), dorsal to the mouth:
somewhat diagrammatic. Let-
ters as in Fig. 307, with the
exception of: g upper portion
of the first visceral arch (here
ossified), op operculum, sp ex-
ternal aperture of the branchial
cavities.—Orig.

QP
Class 2. Pisces. 373

and are separated by perpendicular plates. A gill bar lies at the
inner or oral edge of each of these septa, which for the rest, is spread
out by the cartilaginous rays arising from the bar (see p. 364). The
outer opening of the cleft or branchial pouch is smaller than
the inner; the first lies between the hyoid and the first branchial
arch, those following between arches one and two, two and three,
three and four, four and five, respectively. On both anterior and
posterior walls, but in the last gill pouch only on the anterior, is a
vertical row of flat, horizontal membranous folds, arranged one above
the other; these are the gill lamellw. Thusthe Selachians
usually possess nine rows of lamelle on each side, the first on the
posterior side of the hyoid, the other eight on the anterior and
posterior sides of the first four gill bars. Hach lamella is again beset
with fine transverse folds. Besides these five gill pouches there is in
most of the Selachians an anterior tubular pouch, the spiracle,
between the upper portions of the hyoid and mandibular arches ; it
may contain a rudimentary series of gill lamelle, and it opens to the
exterior, by a relatively small aperture on the surface of the head.
The Cyclostomes resemble the Selachians in the most important
respects ; the gill pouches, however, are tubular with a median enlarge-
ment; both internal and external openings are small; the lamelle
are situated in the widened part. The relations of the gill apparatus

 

Fig. 309. Transverse section of a gill arch in various Fish. A Shark, B
Chimera (see p. 384), 0 Sturgeon, D—E different Teleosteans; diagrammatic. ~
b gill bar, c septum, s gill rakers. Gill lamella shaded.—Orig.

in Ganoidei, Dipnoi, and Teleostei, differ considerably
trom those of the Selachii. In all these groups the five external
openings of the gill slits are covered by the operculum, a strong
membrane arising from the hyoid, and supported by bony plates and
374 Vertebrata.

rods. The septa between the gill clefts have become narrower, espe-
cially in the Teleostei, whilst in the Selachians they are broad plates,
not completely covered by gill lamellz, so that there is a free edge
externally; this is absent from the group just mentioned, and the
outer ends of the gill-lamelle project to a certain extent over the
outer margin of the septum: this is the case in the Teleosteans,
where the narrow, pointed lamine usually arise by a short basal
portion from the much reduced septum. In these groups the two
series of lamine belonging to one gill-bar constitute a gill, of
which four pairs are present; the cavity within the operculum, into
which the gills project, is called the branchial chamber. In
Ganoids, and Dipnoans, a series of gill-lamelle is often still present on
the posterior side of the hyoid, within the operculum, the opercular
gill; whilst it is rudimentary, or wanting in the Teleostei: the
spiracle is also retained in the Sturgeon and Polypterus.

The operculum is attached to the hyoid, and contains flat and rod-like
membrane bones (Fig. 320). In the Teleostei, along the posterior edge
of the upper portion of the hyoid, is a long bone, the preoperculum,
behind this are three large flat ones, operculum, sub- and inter-
operculum; and from the lower portion of the hyoid, arises a series of
thin curved pieces, the branchiostegal rays, embedded in the lower
membranous portion of the operculum. The external opening of the branchial
chamber is usually a large slit, in some Fish (e.g., the Hel), however, the hinder
border of the operculum is concrescent with the body to such a large extent, that
only a small lateral aperture remains.

In most Pisces, water enters the buccal-cavity through the
mouth, which is then closed, whilst the tongue is raised, and the
operculum pressed in, so that the water is driven through the gill-
slits over the gill lamelle. In the Selachians, the water is
taken in, not by the mouth, but by the spiracle. In the Cyclo-
stomes, it is generally both received and ejected by the external
branchial aperture. At the inner edge of the gill-bars is a more or
less well-developed straining apparatus, the gill-rakers,
whose function is to prevent the solid bodies, which enter the
oral-cavity with the water, from passing into the gill-sacs or
branchial chamber. In the Selachians, the Dipnoans, and the
cartilaginous Ganoids, this apparatus usually consists of a double
series (single on the hyoid and the last gill-arch) of cartilaginous
rods, on the inner edge of the gill-arch; the rods of the anterior
rows on each arch dovetail with those of the posterior row on the
preceding bar. In the Teleostei they are often replaced by bony
outgrowths, which may be dentigerous; the anterior series of the
first gill-arch is often composed of very long rods, projecting over
the cleft between the first arch and the hyoid, upon which they do
not occur. For the rest, they are developed to very different extents
in different Teleosteans, in some, e.g., the Herring, very well deve-
loped ; in others, quite insignificant.
Class 2. Pisces. 375

In Cyclostomes and Selachians, structures corresponding with the
lungs of the higher Vertebrata are wanting. On the other hand,
a true lung, which is not only homologous with that of Amphibia
and others, but is actually functional as a respiratory
organ, occurs in some bony Ganoids (Lepidosieus and Amia),
in the Dipnoans, and also in a few Teleosteans. This lung is
unpaired or incompletely divided into two; it lies dorsal to the
alimentary canal, and opens by a wide aperture into the cesophagus.
Within, it is furnished with folds, just as in the Frog’s lung; air
can be inhaled and exhaled through the mouth. These Fish have, in
addition to the lung, gills which also serve as respiratory organs.*
In the rest, a lung is also usually present; it does not act as a
respiratory organ, but rather as hydrostatic apparatus,
and is termed a swim-bladder. The swim-bladder is an
‘unpaired air-containing sac, often rather thick-walled, and situated
below the vertebral column, dorsal to the alimentary canal; in many
Fish it communicates with the cesophagust by a long, narrow tube,
the pneumatic duct; in others, such a connection is present
only in the embryo, closing and disappearing later. The swim-
bladder is sometimes incompletely divided into anterior and posterior
portions (Carp), by a transverse constriction ; or it may be provided
with evaginations. The gas contained in the swim-bladder is not
taken direct from the atmosphere, but is excreted from the vessels
lying in the walls ; they often form close circumscribed retia mirabilia,
projecting as “red bodies” on the inner side of the bladder.

Many Fish, e.g., the common freshwater forms, in which the air-bladder is not >
respiratory, nevertheless come occasionally to the surface and gulp in atmospheric
air through the mouth; this is soon sent out again. It probably has to do with
an oral respiration of subordinate importance. In a few Fish in connection
with this,a special respiratory apparatus is developed; for instance,
in some Siluroids (Saccobranchus), there is a sac-like evagination on each side of
the oral cavity which serves as a lung. It opens into the mouth in front of
the first gill-bar, and extends far back into the body; so also in a kind of Eel
(Amphipnous), an East Indian form, which lives in holes in the ground, and
whose gills are very degenerate. In the Hast Indian Climbing Perch (Anabas),
which often wanders on to land, and has similarly feebly-developed gills, there
are peculiar pleated lamine (supported by modified portions of the gill-hars),
which act as respiratory organs, in the upper part of the branchial chamber.
In others, eg., the Loach (Cobitis), intestinal respiration ocews;
air is inhaled through the mouth, and passed on to those parts of the ali-
mentary canal, which are specially vascular; the air which is not absorbed
escapes from the anus, together with excreted carbonic acid gas.

Many Pisces can produce sounds. The wall of the swim-bladder is made
to vibrate by the action of certain skeletal muscles which are applied to it,
as in the Gurnard; or particular bony surfaces may be rubbed against one

 

* Some Fish can survive a drought, during which the gills are functionless for some
time.

+ In some, the pneumatic duct opens further back, into the stomach.
376 Vertebrata.

another, as in the Siluroids, where the bases of well-developed rays may play
against the subjacent bones.

The heart, which is situated anteriorly (see Fig. 285 A), is
usually almost bilaterally symmetrical. In Selachii, Ganoidei,
and Dipnoi, it consists of a large thin-walled auricle; of a
ventricle lying ventral to this, with thick walls of a spongy
nature, owing to the numerous offsets passing into them from the
small cavity; and lastly, of a tubular conus arteriosus, from
the anterior end of which the trunk of the branchial arteries arises,
and in which several rows of membranous watch-pocket valves are

B Cc

 

Fig. 310. Diagrammatic longitudinal section of the heart of different Fish. A of a
Fish with well-developed conus, B of Amia, C of a Teleostean; in B and C the auricle is cut
away. a auricle, b bulbus arteriosus, which is only just indicated in Amia, c conus
arteriosus, k valves, s sinus venosus, ¢t cardiac aorta, v ventricle.—Orig.

situated. All three sections are red, and their walls are furnished
with striated muscle-cells. In the Teleostei, the conus is, as a
rule, quite rudimentary (extremely short and without musculature),
and is provided with but two valves; only in a few cases (from the
family of the Herrings) is it somewhat more significant, although still
very short; and in a single genus (Butirinus) there are two rows
of valves.* In the Cyclostomes a conus is wanting. In Pisces there
is usually a transverse row of valves between the auricle and
ventricle, and between the sinus venosus (see below) and the auricle.
From the anterior end of the conus, or of the ventricle when the
former is absent, arises a longer or shorter cardiac aorta, which

* In one of the Holostei, Amia, the conus is much shortened, and exhibits only three
rows of valves.
Class 2. Pisces. 377

in the Teleostei, is much swollen, and provided with thick.
walls just at the point of origin. This enlargement, the bulbus
arteriosus,* is whitish like the other arteries, and contains
simply smooth muscle-cells, whilst the conus, with which it was.
until recently included, is red, and possesses striated muscle-
cells. The cardiac aorta sends a branch to each gill-bearing
arch; if the opercular gill is well developed, a branch also goes
to this, but not if it is rudimentary. These branches, the
afferent branchial arteries, run from below upwards, along
the hinder edge of the gill-bar, and give to each gill lamella a twig,
which breaks into capillaries. From each lamella, there arises, again,
a small vessel, which, with those like it from the same visceral
arch, forms an efferent branchial artery.t This runs near
to the afferent artery, and unites dorsally with the corresponding
vessels from other visceral arches, to form the aorta, which runs
backwards, just beneath the vertebral column, and gives off branches
to various parts of the body. All the veins flow into the sinus
venosus, which opens into the auricle. The blood entering the
heart is thus venous, reaches the gills in this condition, becomes.
arterialised there, and thence flows into the arteries.

There is, therefore, a complete separation of arterial, from venous, blood in
Pisces, and the condition of the vascular system accords with the general plan.
given on pp. 28, 29. Some Fish, however, which possess other respiratory organs
as well as gills, form an exception, for in them the arterial and venous blood is.
more or less mixed. In Lepidosteus, for example, the lung receives from the
aorta, arterial blood, to be further oxydised, whilst the pulmonary veins, which
thus carry blood very rich in oxygen, unite with the large veins, bringing venous.

‘blood from the rest of the body. The heart and gills thus receive mixed blood.
In the Dipnoi, where the lung, as in higher Vertebrata, receives blood from
the last arterial arch (the last efferent branchial vessel), there are special

contrivances to partially remedy the defect, but these are too complicated to be
gone into here.

The piscine kidneys are usually elongate organs, and in many
Teleostei, in which they lie above the swim-bladder close against
the vertebral column, extend{ the whole length of the body from
head to tail, and are often united$ behind. In the Selachians and

* A similar swelling is present in Amia, but in no other Pisces excepting the
Teleostei ; whilst in this genus the wall is little thickened.

+ These efferent branchial vessels are frequently, but incorrectly termed,
branchial veins, and the afferent vessels simply distinguished as “ branchial
arteries.” In some Fish, instead of one, two efferent vessels may arise from each gill-
bar.

{ The most anterior portion of this long kidney is the persistent pronephros, which
is frequently very large in the adult, but has usually not an excretory function.

§ A very interesting modification of the kidney occurs in the male Sea Stickleback
(Spinachia vuigaris), which binds various foreign bodies together by fine mucous.
threads, and thus forms a nest for the eggs. The mucus of which these threads.
consist is manufactured in the kidneys; some of the gland cells of the
urinary tubules are modified to secrete mucus, and are of different appearance from the
rest of the cells.
378 Vertebrata.

Dipnoans, the urinary ducts open into the cloaca; in others they unite
and open behind the anus, either together with the gonaducts,
or by a special aperture behind the genital pore. The last is the case
in most Teleostei, where there are three openings, one behind the
other; first the anus, then the genital pore, finally the urinary
aperture.*

In the Teleostei the urinary (and the genital) aperture is usually
situated on a small, soft process, the papilla urogenitalis. The
posterior porticn of the urinary duct is usually wide, and forms
a bladder: in the Selachians a pair of bladders is present; in
the Teleosteans one only, an expansion of the common portion of the
ducts.

Female genitalia. In Selachians, Ganoids,t and
Dipnoans, the ovary resembles that of most other Verte-
brata, and there is a pair of Millerian ducts, each usually
opening anteriorly into the body-cavity by a funnelf{; in the
Selachians and Dipnoi they open posteriorly into the cloaca, whilst
in the Ganoids they unite with the excretory duct, and open behind
the anus by an unpaired aperture. In the Selachians there is on
each oviduct a swollen portion with glandular walls, which secrete
the horny capsule, surrounding one or more eggs in most of
these animals. In the Teleostei, Miiller’s ducts are altogether
wanting; the ovaries are hollow and vary in form; each is
prolonged into a short, tubular duct, which unites with its fellow
of the other side to open behind the anus. The ovary thus displays
relations extremely different from those of all other Vertebrata, but
similar to those occurring in many lower animals, e.g., the Mollusca.
The ova break away from the much-folded inner wall, and fall into
the cavity of the ovary, escaping to the exterior through the duct.
The two ovaries are frequently fused posteriorly (e.g., in the Cod), or
throughout their whole length (as in Zoarces) ; and the duct is then
unpaired. When ripe, in the spawning season, the Teleostean ovaries
are often extremely large.

Only two families differ from the condition just described. Inthe Salmon
and the Hel the ovaries are solid, the eggs fall into the body-cavity, and
escape by an unpaired opening § in the body-wall, behind the anus (porus geni-

talis). The Cyclostomes, which only possess a single ovary, are otherwise
similar to the Salmonide.

 

* In some Fish, viz., Selachians, Ganoids, and certain Teleosteans (the Salmon
family) there is in this region, on either side of the anus, a pair of small openings,
the so-called abdominal pores, which perforate the body-wall, and put the
body-cavity in communication with the exterior. Their significance is unknown.

+ With the exception of Lepidosteus, which seems to resemble the Teleostei.

t In the Selachians the Miillerian ducts are united anteriorly, so that there is only
a single funnel for the two. In some Sharks only one ovary is developed.

§ Which is not to be confounded with the abdominal pores mentioned above (*).
Class 2. Pisces. 379

Male genitalia. In the Selachians the spermatozoa
escape by the anterior portion of the kidney, often termed
epididymis; this is in connection with the testis, and the duct
arising from it unites posteriorly with those from the rest of the
kidney, and serves really as a seminal duct, for the epididymis is
of very slight importance in excretion. In the females, also, this
region is very little developed. In the Ganoids, too, the sperm
makes its way out through the kidney; numerous transverse canals
run from the testis to the kidney (of which no part is specially
modified), to communicate with the urinary tubules* In the
Teleostei such a connection with the kidney does not occur,
the testis is prolonged directly into a seminal duct,t and like the
ovaries, the ripe testes are tolerably large, elongate, often lobed,
or (eg., in the Cod), pleated bodies; the vasa deferentia unite
behind to form an unpaired duct, which has, in some forms,
a special opening behind the anus, in front of the urinary
aperture, whilst in other cases there is a common urino-genital
opening.

In the Cyclostomes, the spermatozoa from the unpaired testis fall into the

body-cavity, and escape through an opening of the abdominal wall just as do the
ova.

Copulatory organs occur in all Selachians, where a portion
of the hind limb in the male, is modified into a somewhat compli-
cated rolled organ (Fig. 314), which is used in copulation (ef. the
copulatory organs of decapod Crustaceans). On the other hand,
copulatory organs are absent from most other Fish, and the sper-
matozoa (“milt’’) are usually not introduced into the body of the
female, but are poured over, or near to, the eggs when they are laid.

In certain viviparous Teleostei (Anableps) there is a long process behind
the anus, with the urino-genital opening at its apex. This process, which
serves as a copulatory organ, is the metamorphosed anal fin, which has
fused with the urino-genital papilla. There are similar organs in some other
viviparous Teleosteans. In all viviparous Fish there must, of course, be a direct
transference of the spermatozoa from the male to the female, but copulatory
organs are by no means always present.

Not a few Fish display striking sexual dimorphism; in the males
certain fins may be specially well developed, or they may possess a specially
brilliant colouring. Sometimes (e.g., the Stickleback) the male is distin-
guished by striking colours during the reproductive season, which disappear
later on. The males are usually smaller than the females (e.g., the Hel).

For hermaphroditism in Fish, see p. 351.

The eggs vary considerably in size (from the size of a pin’s head
to that of a Hen’s egg and upwards), they are largest in the Selachians,
smaller in the Teleostei, where each is covered by a thin transparent
vitelline membrane sometimes furnished with a micropyle. The eggs

 

* The arrangement of the seminal ducts of the Dipnoi is not understood.

+ The Salmon and the Eel are like the others in this respect.
380 Vertebrata.

of numerous marine forms (e.g., the Cod), float at the surface of
the water; others are deposited at the bottom; or are attached
In the Selachians they are

to water plants (e.g., the Herring).

 

 

 

Fig. 811. Young Pike; A just hatched, B, B’
eleven days old, C and D still older. In A the tail
is still straight, in @ and D markedly heteroceral.
a anal fin, c chorda, d dorsal-, p pectoral-, u caudal-

fin, « anus.—After Sundevall.

enclosed in a horny capsule,
which is often flattened and
quadrangular with the
corners drawn out into
threads. Some Fish are
viviparous (eg., most
Selachians), and develop-
ment takes place in a
widened portion of the
oviduct (uterus), which
is provided with glomerular
vascular folds; also some
Teleosteans whose eggs
develop in the cavity of the
ovary (e.g., the viviparous.
Blenny). In some few
forms there is a special
arrangement for the pro-
tection of the eggs and
brood ; the males of the
Stickleback (and of various.
other Teleostei) build nests,
in which the eggs are
hatched ; the males of the

Pipe-fish carry the eggs and sometimes also the brood about
with them, firmly attached to the abdomen, or enclosed in special
folds of the skin. This is the case also in various Fish occurring
abroad. More rarely the eggs are protected in the same way by

the female.

 

Fig. 312. Larva of a Fish (Trachypterus) which, in the adult, is extraordinarily long,

ribbon-like, and without the fin filaments.
Class 2. Pisces. 381

It is quite correct to speak of a metamorphosis in many
Teleosteans, since the young one leaves the egg in a very imperfect
condition, differing much from the adult; often the caudal extremity
of the vertebral column is still straight; there is a continuous dorsal
and ventral fin, etc. (Fig. 311 A). It may often happen that the
transition from this state to the adult form is not a simple, gradually
advancing development; but the larva not infrequently displays
special characters for a long time after leaving the egg, which do not
occur in the newly-hatched young, nor in the adult. Especially
in the Pelagic Fauna, abundant large-eyed ‘leleostean larve are
met with, possessing enormous spines, and fin appendages, struc-
tures which recall those observed in many pelagic crustacean larve,
e.g. the Crabs (Fig. 312). For the peculiar development of the
Lampreys, see p. 382.

The embryos of Selachians (Fig. 313) are distinguished by the
possession of a huge yolk sac, and also by the projection from the gill-slits of

numerous long gill-filaments, processes from the gill-lamelle. These
filaments are embryonic organs, and atrophy before birth.

Most Fish are predaceous, only a few feed upon plants or mud.
‘The majority are marine, but many are freshwater (some species are

 

Fig. 3138. Ray embryo, B Shark embryo with exte:nal gills (k). d yolk sac (not
completely drawn; removed in 4).

both) ; a few wander upon land. They often migrate from one
place to another in the sea, or from the sea into fresh water and
back. They usually occur in shoals. Fish make their way through
the water by movements of the whole body, and by lateral movements
of the tail; the Teleostei can also progress slowly by undulations of
all the fins (paired and unpaired).*

 

: *A very singular movement, suggesting flight, occurs in the Rajide, brought
about by the powerful fore limbs.
382 Vertebrata.

Fish, which are represented to-day by such numerous genera and
species, have also played an important part in earlier periods;
the Teleosteans, which preponderate at the present time, arose
comparatively late; whilst the Ganoids, which now include a few
species only, were for long very abundant.

SYNOPSIS OF THE ORDERS.

Skeleton entirely cartila- 7
ginous. Cyclostomi

Horny or cartilaginous rays.

Scales absent.

Operculum absent. Selachii

Swim-bladder absent. L Conus arteriosus well-de-
veloped.

}

: : |
Skeleton..of cartilage and.) Genel asi ES walvednantectiue:

a

 

bone. Miillerian ducts present.
Bony rays. Div wot
Scales present. P
Operculum present. Conus rudimentary.
Swim-bladder or lung pre- . Spiral valve absent.
Tel t
sent. L cities Millerian ducts absent.

Order 1. Cyclostomi.

The Cyclostomes form a small group, differing in many respects
from other Pisces. The body is cylindrical, vermiform and apodous ;
the skin is naked ; the skeleton is entirely cartilaginous; the noto-
chord is unconstricted ; ribs are absent. There is a complicated oral
and branchial skeleton, which can with difficulty be reduced to the
common type of piscine visceral skeleton. There are usually six or
seven (in a few, a still larger number) gill-pouches on each side
(see p. 373); the mouth is provided with horny teeth, but
true teeth are absent; the olfactory organ is unpaired; the caudal
extremity straight; and there is a continuous dorsal fin (cf. in other
respects, the account given for Fish in general.

The Cyclostomes are most nearly allied to the Selachians; their peculiar
characters are without doubt to be attributed partly to their peculiar mode of
life, as parasites or carrion-feeders.

1. The Nine-eyes or Lampreys (Petromyzon) have a circular suck-
ing mouth with horny teeth; seven small gill-apertures on each side leading
into gill-pouches; which do not open directly into the mouth, but into a short
tube ventral to the esophagus, closed behind but anteriorly in communication
with the mouth. Eyes are well developed. The Lampreys attach themselves by
suction to living Fish, which they devour; they also feed on smaller animals.
Three species live in England; two are marine, but can make their way up
into fresh water—P. Marinus, up to lm. long, and the small P. Fluviatilis,
(Pricke) ; whilst the third and smallest species (P. Planert) is exclusively a fresh-
water form. Lampreysundergoa metamorphosis; the larve (Ammocetes),
which in P. Planeri may be three or four years old and of a considerable size
Class 2. Pisces. Order 1. Cyclostomi. 383.

before a change occurs, are very different in form from the adult; horny teeth
are absent, the eyes are very small, and the gill-sacs open directly into the mouth.
They live in mud.

2. The Hag-fish (Myzine) has rudimentary eyes; the mouth is surrounded
by tactile tentacles ; the gill-sacs (six on each side) are long tubes expanded in
the middle, each opening direct into the pharynx, whilst the outer regions of
each side unite, to open by a common aperture some way back; though in an.
allied foreign form, Bdellostoma, they open separately. Hag-fish, of which
M. glutinosa is very common in N. European seas, and reaches as much as.
30 c/m. in length, bore into dead (and living?) Fish; they secrete enormous
masses of mucus.

Order 2. Selachii.

The skeleton consists entirely of cartilage, which may, however,
be partially calcified; bone is altogether wanting. A conus
arteriosus is present, and a spiral valve in the gut. There are
five, rarely six or seven, gill-clefts on each side; often a spiracle,
but no operculum, excepting in Chimera. There is no swim-
bladder. The whole surface of the skin is often covered with teeth.
In the fins, which cannot be folded together, there are horny rays.
The mouth is on the ventral side of the head. Parts of the pelvic
fins in the male serve as copulatory apparatus. Eggs very large..
Almost exclusively marine.

1. The Sharks (Squalidz) are animals of the ordinary piscine form,
generally elongate and somewhat circular in section. The skin is usually thickly
covered with small teeth. Along the edge of the jaw there are, as a rule, one or
two rows of teeth, usually triangular in form, and replaced by others from the-
mucous membrane within the jaws: definitely heterocercal. Of the numerous forms
the following may be specially mentioned: the Common Spiny Dog-fish
(Acanthias vulgaris), 1 m. long, with a spine (a strongly developed placoid scale)
anteriorly on each of the dorsal fins; anal fin absent; viviparous: found in the.
North Sea and Baltic: the Dog-fish (Scyllium canicula), somewhat smaller ;
oviparous, egg-capsule quadrangular, and attached to Alge by long tendril-like
appendages from the corners; common on the coasts of Britain: the Blue
Shark (Carcharias glaucus), the voracious man-eating form, 3 m. or 4m. long,
occurring in the Mediterranean, abundant in the Tropics: the Hammer-
headed Shark (Sphyrna), with each side of the head drawn out into a longer:
or shorter process, at the end of which is the eye; one species in the Mediterranean:
the Greenland Shark (Scymnus borealis), which reaches 8 m. in length,
is caught in great numbers for the sake of the fat liver; on the coast of Iceland:
still larger (up to 12m.) is the Giant Shark (Selache maxima), in which
the external gill-clefts are very large slits; the eyes very small; teeth small and.
poorly developed ; the inner edge of the gill-bars, with a series of very long teeth,
forming a fine comb, which acts as a straining apparatus, to retain the small.
Crustacea on which this giant feeds, after the manner of the Whalebone Whale.

2. The Skates (Rajide) are chiefly distinguished by the flattened form
of the head and body, by the thin, whip-like tail, which is often almost destitute.
of fins, and by the enormous development of the pectoral fins, which arise like
horizontal plates from the sides of the body, so as to form a disc with it and the
head, and to relegate the gill-slits, over which they lie, to the ventral surface; the
eyes and spiracle are on the dorsal side. Amongst other characters it must be
mentioned that the skin is usually naked over a greater or less extent; that.

.
B84 Vertebrata.

some of the remaining placoid scales form large spines; and that the buccal teeth
are low knobs (sometimes pointed) or plates, which are arranged in several rows
-and form a mosaic over the edges of the jaws. In general appearance, therefore,
the Skates differ considerably from the Sharks. The skate type is not always
developed to the same extent; in some forms the pectoral fins are smaller, the tail
more powerful; whilst, on the other hand, there are Sharks (Squatina, the Sea-
-angel), which are somewhat flattened, with the eyes turned upwards, and large
horizontal pectoral fins reaching antero-posteriorly along the sides of the head, but
not attached to it. There is indeed a complete series of transitional forms, between
the usually slim shark type, to the most extreme ray type with its discoid shape,
wider than it is long, and with its thin caudal whip. In British seas there
are several species (chiefly of the genus Raja), all typical Rays. Of forms
belonging to the Southern seas may be mentioned the Hlectric Skates
(Torpedo), and the Saw-fish (Pristis); the former are well known on account
of their powerful electric organs, which lie on either side of the head; in the
Sawfish the snout is drawn out into a long, straight, narrow plate, with a series of
large, laterally directed, teeth on each edge. Both the Electric Skates and the
Saw-fish, but especially the latter, belong to the more shark-like Rays, with toler-
ably powerful tail. Both genera occur in the Mediterranean.

3. The Cat-fishes (Holocephali) genus Chimera, etc., form a small
division of the Selachians, which differ from their allies, and approach the
following orders chiefly in the possession of an operculum (which is, how-
-ever, not supported by skeletal plates); the gill lamella completely cover the side
-of the septum, but do not project over its outer rim (Fig. 309B). The skin is

 

Fig. 314. Chimera monstrosa, 3.

-for the most part naked, the mouth armed with a small number of large teeth.
The upper portions of the mandibular and hyoid arches are attached to the skull.
In other respects they exhibit for the most part the characters of other Selachians.
One species, Ch. monstrosa, is abundant in the Mediterranean, on the coast
of Norway. and elsewhere.

Order 3. Ganoidei.

The skeleton consists of cartilage and bone; conus arteriosus and
spiral valve are present; an operculum supported by bony plates ;
often a spiracle; swim-bladder or true lung. The skin usually
Class 2. Pisces. Order 3. Ganoidei. 3885

provided with bony plates or scales (ganoid scales) ; dermal denticles
may also. be present, but in small numbers. Bony rays occur in the
folding fins.

This group was formerly very well represented ; few of its members
are living, however, at the present day.

Sub-Order 1. Chondyostei (Cartilaginous Ganoids).

The skeleton is, for the most part, cartilaginous; only membrane
bones are present. ‘The mouth ventral. The tail heterocercal.

1. Sturgeons (Accipenser) have five rows of large bony plates arranged
along the body (one row being median) dorsally, and manyj small plates
irregularly placed; dorsally upon the head are large bony plates, which cover
the chondrocranium : the mouth is small, edentulous (the young, however, have
teeth, and sometimes small teeth occur on the gill-bars of the adult); on the
ventral side of the often elongate snout there are tactile tentacles: a spiracle
is present. A. sturio, which attains a length of several metres, inhabits North
European seas, wandering up into the rivers to spawn; there are several other
species in the Caspian and Black Seas, and in the large rivers of Russia
(Sterlet, A. ruthenus, A. huso, etc.).

2. The Spoon-billed Sturgeons (Spatularia) differ from
Accipenser in that the snout is prolonged into a large horizontal blade, and the
skin is almost without hard parts; in the mouth weak teeth are developed. In
North American and Chinese rivers.

Sub-Order 2. Holostei (Bony Ganvids.)

The skeleton is for the most part ossified. The mouth anterior.
Large, rhomboidal, enamelled* scales, which may be partly dove-
tailed together, or, more rarely, scales like those of the Teleosteans.
Usually (Lepidosteus, Amia) the respiratory organ is a true lung.
All existing forms are freshwater.

1. Polypterus. Long dorsal fin, with strong fin-rays, usually fan-shaped at
the tip, and not connected together; no anal fin; caudal fin rounded, feebly
heterocercal (the bent-up portion of the spinal column is very small). Large
rhomboidal scales. A spiracle. In Africa (e.g., in the Nile).

2. The Bony Pike (Lepidosteus). Snout much elongated; short dorsal
and anal fins; well-marked heterocercality, the caudal fin being almost entirely

 

Fig. 315. Lepidosteus.

 

* The scales are covered externally by a smooth layer, commonly called “ enamel ” :
but it is not true enamel, like that of the teeth, it is only an external, polished, dense
layer of bone.

cc
386, : Vertebrata.

ventral to the long, bent-up portion of the spinal column (Fig. 299 B). Rhom-
boidal scales. Several species in N. America.

3. Amia. Externally almost exactly like a Teleostean; it has cycloid
scales. For its chief characteristics see p. 375, foot-note *: p. 377, foot-note *;
Fig. 304 C; Fig. 310 B. It occurs in North America.

Order 4. Dipnoi.

The skeleton is partially ossified; the conus arteriosus spirally
coiled and provided inside with a longitudinal fold formed of
modified valves; a spiral valve in the intestine; the operculum is
supported by bony plates; the lung is functional; the skin
provided with scales, the fins with unsegmented, soft, bony rays.
Both anterior and posterior nares lie within the mouth. The limbs
are either long, pointed plates, with a median, segmented, cartila-
ginous rod, from either side of which a series of cartilaginous rays
arise ; or they are filiform, with a similar, but more or less reduced
skeleton. The tail is pointed and diphycercal; notochord uncon-
stricted and well-developed; a few large teeth in the mouth.
Exclusively freshwater.

This aberrant group, which at the present day is represented by a few forms
only, is most nearly allied to the Ganoids, especially the Holostei. The structure
of the conus is remarkable, recalling the condition in the Amphibia (q.v.); in
connection with it are certain peculiarities in the structure of other parts of the
heart, by which a partial separation of blood from the lung and from the rest

of the body is effected. The structure of the limbs, the position of the nares,
etc., is also very peculiar.

 

Fig. 316. Ceratodus. After Gitinther.

1. The Mud-fish or Barramunda (Ceratodus) is a large, elongate
animal, pointed at both ends; with large scales; large, broad limbs; dorsal,
caudal and anal fins continuous. It inhabits the rivers of Australia.

 

Fig. 317. Protopterus annectens.
Class 2. Pisces. Order 4. Dipnoi. 387

2. Protopterus annectens, the African Lung-fish, has very long, thin limbs;
it possesses some small, thread-like membranous appendages at the upper ends of
the gill apertures; these possibly have a respiratory function; the gills of the
first and second arches are absent. In other external respects it is similar to
Ceratodus. If the water in which it is living dries up, it buries itself in the
ground, and surrounds itself by a hard mucous capsule, in which it can remain
for a long time without water (this is not the case with Ceratodus). An allied
form (Lepidosiren paradoxa) occurs in 8. America.

Order 5. Teleostei.

The skeleton consists of cartilage and bone; chiefly the latter.
The conus arteriosus is rudimentary, a bulbus arteriosus is present.
There is no spiral valve in the intestine; the operculum is bony ;
there is no spiracle; the skin is provided with scales or bony
knobs, plates, etc.; dermal denticles are usually absent, but may be
present in small numbers. The fins can be folded and are provided
with bony rays.

Sub-Order 1. Physostomi.

Swim bladder connected with the alimentary canal by a
pneumatic duct; pelvic fins far back, close to the anus; spinose rays

usually absent ; scales cycloid.

1. The Herring family (Clupeidz). Body elongate and compressed:
large, easily deciduous, cycloid scales; only one dorsal fin; teeth feeble. To
this family belong: the Herring (Clupea harengus), and the. Sprat
(Cl. sprattus); the Sardine (Cl. pilchardus); the Shad, (Cl. alosa) all
common on British coasts; the last makes its way into rivers (e.g., the Severn)
to spawn; all these very similar forms have a row of carinate scales along the
ventral side. The true Anchovy (Engraulis encrassicholus), without these
modified scales, and with elongate snout: in the Mediterranean, occasionally in
northern seas.

2. The Salmon family (Salmonide). Scales small, or of medium size.
Two dorsal fins, of which the posterior is rayless and adipose. Chiefly in fresh-
water. Amongst the species occurring in the British Isles: the Salmon
(Salmo salar), marine, migrating into rivers to spawn; the closely-allied
Common Trout (S. fario), in fresh water; the Sea- or Salmon-trout
(S. trutéa): the Char (sub-genus, Salvelinus), in mountain lakes. The species
of Coregonus (C. thymallus, the Grayling; C. pollan, the Fresh-water
Herring;) are edentulous, or have only small teeth, whilst the genus, Salmo,
has large ones.

3. The Pike family (Hsocidz). Small scales; dorsal fins far back;
flattened, elongate snout; mouth large, with numerous ‘teeth; some of them
large. Few species; the common Pike (Hsow lucius), abundant in fresh water.

4, The Carp family (Cyprinide). Body compressed, with larger or
smaller scales; one dorsal fin; bones of the mouth entirely edentulous
the lower pharyngeal bones are, however, provided with powerful grinding-teeth,
which work against a thick horny plate on the under side of the skull; usually
barbules on the edge of the mouth; freshwater fish, feeding partly upon
decayed plants. Of the numerous forms, may be mentioned: the Car p (Cyprinus

co 2
388 Vertebrata.

carpio), with four barbules on the upper edge of the mouth (introduced from Asia) :
the Prussian Carp (Carassius vulgaris), without barbules, but otherwise
similar: the Gold-fish (Car. auratus), from China: the Barbel (Barbus
vulgaris), with four barbules, of which two are at the tip of the snout: the small
Gudgeon (Gobio fluviatilis): the Roach (Leucisus): the Tench (Tinca
vulgaris), with small scales in a thick slimy skin: the small Bitterling
(Rhodeus amarus), females provided at spawning-time with a long ovipositor
bearing the genital pore at the tip, by means of which the eggs are laid in the
branchial chambers of the Freshwater Mussels (Unio): the Bream (Abramis
brama), with high, laterally compressed body: the Loach (Cobitis), small fish
with elongate, sometimes eel-like, bodies; very small scales concealed beneath the
skin ; six or more barbules, intestinal respiration (see p. 375). All these, except the
Gold-fish and the Bitterling, are indigenous to the British Isles.

5. The Silurus family (Stluridz), The body never has the ordinary
scales; it is either naked, or provided with large bony plates (dermal denticles
may be present); maxille very poorly developed; barbules and an adipose fin
usually present. Freshwater Fish, which are represented by numerous interesting
tropical forms. The Sheat-fish (Silurus glanis), naked, with quite small
dorsal fin far forward, long anal fin, two long and four short barbules, small
eyes; as much as 4 m. long; the only European representative of the family,
occurs in England. The electric Silurid (Malapterurus electricus), with adipose
fin (but otherwise without a dorsal fin), more than 1 m. long, in Africa. The
Loricaria, skin covered with large bony plates, in 8. America.

6. The Eel family (Murenidz). Body snake-like, smooth or with small
scales; without pelvic fins; dorsal, caudal, and anal fins continuous; small gill-
slits; small eyes. The Hel (Anguilla vulgaris), with scales; spawns in the sea,
probably in deep water; the young, whilst still transparent, wander into fresh
water, returning to the sea later. The Conger-eel (Conger vulgaris), scale-
less, attains a considerable size (2 m.); in the North Sea.) The Murena
(Gymnothorax murxna), apodous, even the pectoral fins being absent; in the
Mediterranean. To another family of snake-like Physostomi belongs the
Electric Eel (Gymnotus electricus), of S. America; anus close to the head;
anal fin long; no dorsal and pelvic fins; the large electric organs along the
ventral side reaching to the tip of the tail.

Sub-Order 2. Aphysostomi.

No pneumatic duct. Pelvic fins, generally moved far forwards.
Spinose rays usually present (not in sub-divisions, 1—3).

1. Mackrel-pikes (Scomberesocidz). Cycloid scales; dorsal fin short,
far back; pelvic fins far back; no spinose rays. The Gar-pike
(Belone vulgaris) has mandible and premaxilla elongated to form a beak, beset
with fine teeth; body elongate; bones green; in the North and Baltic Seas.
The Flying-fish (Heocetus) distinguished by the enormous development
of the pectoral fins, by means of which it can take short flights across the
surface of the ocean; in tropical seas (one species in the Mediterranean).

2. The Cod-fish family (Gadide). Body somewhat elongate with
small cycloid scales; usually two or three dorsal, and one or two anal fins;
pelvic in front of the pectoral-fin, no spinose rays; often a barbule on the
lower jaw. To the genus Gadus, with three dorsal and two anal fins,
belong: the Codfish (G. morrhua), which occurs in immense shoals in the
North Atlantic, up to 1.5 m. in length; the Haddock (G. zglefinus), numerous,
eg. in the North Sea; both these have barbules: the Hel-pout (Lota

'
Class 2. Pisces. Order 5. Teleostei. 389

vulgaris) in fresh water, has a short anterior, and a long posterior dorsal fin
(the latter corresponds to the two dorsal fins of Gadus); an anal fin, and one
barbule. To an allied family (Ophidiide) belong the Sand-eels (Ammo-
dytes), small and elongate with no mandibular teeth; with projecting lower
jaw: without pelvic fone with long dorsal and anal fins; on the coasts of
Britain. To the same family belongs also the genus Fierasfer, the species of
which take up their abode in the cloaca of Holothurians (without being actually
parasitic, since they feed upon small animals): an allied genus, Enchelyophis,
is a true parasite.

3. Flatfish (Plewronectide). The body is a laterally compressed disc ;
both eyes on the same side, in some species on the right, in others on the left
(in a few species, some individuals have the eyes on the right, others on the
left); the blind side is white and turned downwards, the other coloured; the
mouth is often somewhat asymmetrical, being larger on the blind side where
the premaxilla and maxilla are better developed; dorsal and anal fins very long,
anus far forwards; pelvic fins in front of the pectorals; no spinose rays. The
lurve are perfectly symmetrical, with the eyes on either side of the body, and
the animal swims with the ventral surface downwards; later, one eye moves
round to the other side, and the animal lies upon one side. Amongst the
forms inhabiting British seas are: the Plaice (Pleuronectes platessa), eyes right
(very rarely left); scales smooth: the Dab (Pl. limanda), eyes right; scales
rough: the Flounder (Pl. flesus), with rough bony knobs; eyes usually right
but frequently left; it occurs not only in the sea, but also in fresh water:
the Sole (Solea vulgaris) disc not so wide as the foregoing; eyes right; the
Halibut (Hippoglossus vulgaris), also with eyes on the right, attains a con-
siderable length (2 m.): the Turbot (Rhombus maximus), with bony warts, and
the Brill (Rh. levis) with small smooth scales, both with the eyes on the left side.

4, The Perch family (Percidz). Scales ctenoid; two dorsal fins,
which are generally, however, united, the anterior with only spinose rays; pelvic
fins below the pectorals; operculum with spines. To this family belong the
Common Perch (Perca fluviatilis), and the Pope (Acerina cernua) with
fused dorsal fins. Both are freshwater, the former occurring also in brackish
water, and are found in England. To an allied family ay the Climbing
Perch (Anabas) mentioned before (p. 375).

5. The Wrasses (Labride) recall the Perch in fete external appear-
ance, but are distinguished by the fusion of the lower pharyngeal bones, and
especially by a pad-like thickening of skin (the lip) along the edge of the
mouth. To this family, which is represented by several small species in the
North Sea belongs the Parrot-fish (Scarus); in this form the edge and
a portion of the front of the premaxilla and maxilla, are beset with teeth,
which are connected with each other, and with the rest of the jaw by means of
a bony mass, so that a continuous cutting edge is formed. Grinding teeth,
united in the same way, occur on the superior and inferior pharyngeals. The
Parrot-fish, which belong exclusively to warm seas (one species in the
Mediterranean), can bite through even branches of Coral.

6. “Peter’s Thumb” (Trachinus draco) is a somewhat elongate form
with a short head and small cycloid scales; with two dorsal fins, the posterior
being long and possessing soft fin-rays, the anterior quite short and with spinose
rays; pelvic fins in front of pectorals. On the operculum is a bony spine, with
two poison glands, lying i in grooves on its surface, and opening at its tip;
similar glands in the spiny rays of the dorsal fins.* Abundant in the North
Sea; usually seen with the larger part of the body buried in the sand.

 

* Similar poison organs occur also in a few other tropical Fish.
390 Vertebrata.

7. The Squamipinnes. Fish with spiny fins, with very high, much
compressed bodies, and with gorgeous colours; the scales extend some way
on to the unpaired fins. In warm seas.

8. The Cataphracti. Body usually without the ordinary scales, naked
or with large bony plates; one of the suborbitals is well developed, and reaches
back to the preoperculum; pelvic fins below the pectorals. Here belong:
the Sea Scorpion (Cottus scorpius), with a large head, naked skin, spines
on the head; abundant in the North Sea: in the rivers of Great Britain is
found the small River Bull-head, or Miller’s Thumb (Cottus gobio),
about 15 c/m. in length: the small Armed Bullhead (Agonus cataphractus),
with bony plates on the body and with numerous barbules: the Grey
Gurnard (Trigla gurnardus), with mailed head; small scales; and the lowest
rays of the pectoral fins free, digitiform, and used in crawling; in British seas.
In the Flying Gurnard (Dactylopterus volitans) each pectoral fin is divided
into two portions, one of which is very large, and by its means the animal can
lift itself above the surface of the water; in other respects it resembles the
two previous forms; in the Mediterranean.

9. The Sticklebacks (Gasterosteide) resemble the preceding family
as regards the suborbital bones; the spiny-rayed portion of the dorsal fin
consists of free rays; each of the pelvic fins, which are a little behind the
pectorals, consists of a long spiny and of a short, soft ray; no scales, but
large dermal plates; the males often build nests. The Sticklebacks (Gaster-
osteus) are small forms, occurring in fresh and brackish water: the Three-
spined Stickleback (G. aculeatus), with three spiny rays in the dorsal fin,
and the Ten-spined Stickleback (G. pungitius), with about ten, both
in Great Britain: the Sea Stickle (Spinachia vulgaris) is exclusively
marine (North Sea, etc.); very elongate, with long, thin tail; and fifteen free,
spiny rays.

10. Mackrel family (Scomberidx). Spiny fins; body elongate, slightly
compressed, with small scales; posterior portion of dorsal and anal fins broken
up into a number of small pieces; pelvic fins below the pectorals; here
belong: the Mackrel (Scomber scomber), common on European coasts, and
the Tunny (Lhynnus vulgaris), common in the Mediterranean, rarer in
northern seas. Allied to these are the Sucking-fish (Hcheneis); the anterior
dorsal fin is modified into a suctorial apparatus, extending on to the head, and
by it the animal attaches itself to large fish, ships, and so forth Further,
the large Sword-fish (Xiphias gladius), with the upper jaw elongate and
beak-like, and without pectoral fins; abundant in the Mediterranean, also
occasionally in northern seas.

ll. The Blennies (Blenniide). Body usually almost eel-like, with very
small scales; usually a long dorsal and anal fin; * pelvic fins small, in front
of the pectorals. Here belong: the Viviparous Blenny (Zoarces vivi-
parous), very abundant in the North Sea; up to 40 c/m. long: the Wolf-
fish (Anarrhichas lupus), large, with well-developed, strong, conical teeth in
front, and grinding teeth further back in the mouth; no pelvic fins; feeds
upon Lamellibranchs, etc.; in northern seas.

12. The Gobies (Gobius), small, with tolerably soft spiny rays, chiefly
distinguished by the fusion of the pelvic fins, which lie below the pectorals. To
another family belongs the Lump-fish (Cyclopterus luwmpus), with the pelvic
fins fused, and, moreover, modified to form a sucker; the Sea-hare is a short,
clumsy form with bony spines in the skin; in British Seas.

 

* In Zoarces and Anarrhichas there are a few spiny rays posteriorly in the
otherwise soft dorsal fin; in the genus Centronotus (Butter-fish) the whole dorsal fin
consists of spiny rays; in others, again, all the rays are soft.
Class 2. Pisces. Order 5. Teleostet. 391

18. The Pediculati, with bulky, naked body; head often large; gill-
opening small; pelvic fins in front of the pectorals, the latter stalked; the
radialia, which are short in other Teleostei, are long here; the anterior portion
of the dorsal fin consists of a number of free rays. The only form occurring in
Northern Seas is the large Frog-fish (Lophius piscatorius), flattened; with
a huge mouth; the free dorsal rays elongate, the most anterior with a soft
appendage at its tip.

14. The Plectognathi are fish of very varied appearance, which agree
in having the premaxille and maxille, contrary to the general rule, firmly
attached to the skull; pelvic fins absent. Chiefly animals of very aberrant form
inhabiting the warmer seas. The Trunk-fish (Ostracion), short, with
flattened abdomen, peculiar in that most of the body is covered by a thin armour
formed of polygonal bony plates, firmly connected together; the small tail and
the fins alone are movable. The Sea Hedgehog (Diodon) is beset with
bony spines, which stand up when the animal puffs itself out; this is effected by
filling a sac-like evagination of the esophagus with air, which is taken in through
the mouth ; the creature then lies in the water with the ventral surface upwards ;
the dentition recalls that of the Parrot-fish. The Sun-fish (Mola or
Orthagoriscus) is a large pelagic form, much compressed and very short, the
body forming a perpendicular oval disc; the caudal fin is a ridge along the
hinder. edge of the animal, dorsal and anal fins high.

15. The Sea-adder family (Syngnathide). Body elongate, covered
with bony plates; snout drawn out into a tube, at the apex of which lies the small
edentulous mouth; pelvic fins absent; gill-lamelle on each bar in quite small
numbers, but much folded; external branchial aperture small. The eggs are
carried by the males on the lower side of the body and tail, sometimes simply
adhering to this; in other cases enclosed in two longitudinal folds or in a sac.
The animals swim by a very rapid undulating movement of the rather short
dorsal fin (or of the pectorals, if these are present). Various forms inhabit
northern seas; species of the genus Syngnathus, Nerophis, etc., in the last of
which only the dorsal fin is present. The Sea-horses (Hippocampus), with
finless, prehensile tail; ventrally curved head; and spiny outgrowths on head and
body, swini in a perpendicular position; usually in warm seas; one species,
abundant in the Mediterranean;’also occurs in the North Sea.

Class 3. Amphibia.

The head, unlike that of Pisces, is, in Amphibia, generally
clearly defined, and is usually capable, to some extent, of free move-
ment, although there is no distinct neck. The head, and usually
the body also, is somewhat flattened. The tail, when present, is
compressed and strongly developed, though not nearly so muscular
as in Fish; dorsally, it passes gradually into the trunk, but
ventrally, is more sharply limited. The limbs have reached a higher
stage of development than in Pisces: they are separated by joints
into several regions, of which the distal is divided into digits.
They have been modified to form ambulatory organs, which,
compared with those of the Mammalia, at least in one of the principal
groups (the Urodela), are small and feeble.

The epidermis in the adult exhibits a thin stratum
corneum, only one or two cells thick, which, as in many Reptiles,
392 Vertebrata.

is periodically shed entire, and replaced by a new one (ecdysis).
This layer is harder in some regions than in others, ¢.g., certain
spots on the fore-limb of the Frog in the breeding season. Claws
are absent. Rounded, saccular glands, opening to the sur-
face, and distributed all over the body, occur in connection with
the skin; they usually secrete a slimy fluid, which keeps it moist;
in some forms, there are also small mucous glands, and larger
poison glands, which may be so closely aggregated in some
regions as to cause projections; such are the “ parotids” behind
the head in the Toad and the Land Salamander; the secretion is
injurious to many animals, and thus serves as a means of defence.
True scales, like those of many Fish, are present in the dermis of
many Gymnophiona; in other forms, large membrane bones* may
be present in certain regions of the skin; or there may be calcareous
deposits in the dermis, as in old Toads. Like Pisces, the Urodela are
furnished with an unpaired fin, which extends along the back for
some distance, sometimes even from the head, round the tail to the
ventral surface, as far as the anus; it never exhibits fin rays: it is
usually better developed in the males than in the females, and here
it is most prominent during the breeding season. Except during
larval life (see below) it is absent from all other Amphibia.

The skeleton is for the most part ossified, although there are,
as in many Fishes, considerable tracts of cartilage, especially in the
skull. In the Perennibranchiata and Gymnophiona, the centra are
amphicclous and the notochord is large; in others, on the

Ped

ey
cee gee

 

Fig. 318. Skeleton of a Urodele (Menopoma).

 

* Scales were also present in the dermis of many extinct Amphibia (Labyrinth-
odonta).
Class 3. Amphibia. 393:

contrary, it is intervertebrally constricted, the vertebre articu-~
lating by joints; in the Urodela the vertebre are opisthoce-
lous (concave behind, convex in front); in the Anura usually
procclous (convex behind, concave in front). Just as in Pisces,
but in contradistinction to the classes following, the second cervical
vertebra is not specially modified (cf, Reptilia). The first, with
which the head articulates, and the last or sacral vertebra, to which
the pelvis is attached, differ from all the others. The caudal verte-
bre of the Urodela are provided with hemal arches; in the
Anura, where they are twice as numerous in the larva as in the
adult, they are fused into a long, unjointed bone, the urostyle*
(Fig. 323 0). The ribs never reach the sternum; in some extinct
Amphibia (Stegocephala) they were well-developed; in all living
forms they are, however, very degenerate ; they are best developed
in the Urodela and Gymnophiona, where they are short processes
usually present on all the trunk vertebra except the first; im the
Urodela they occur on the anterior caudal vertebre also. In the
Anura the ribs are rudimentary, and in the adult usually fused with
the long transverse processes. The sternum (Fig. 321-22) is not
connected with the ribs, but is closely attached to the lower portion of
the shoulder girdle; in the Urodela it is a short cartilaginous plate,
with the insertion of the coracoid at its anterior edge; in the Anura
it is often partially ossified, and closely connected with the coracoids.
The cranial skeleton is in many points very similar to that of
the Ganoids and Teleostei. Considerable portions of the cartilaginous

 

Fig. 319. The visceral arches of the Salamander, seen from below; 4 larva, B adult.
c basibranchials, c’ the last (separated from the others in the adult), k mandible, h hyoid
arch, br 1—4 first to the fourth gill-bars, | occipital condyles, o eye. After Rusconi.

fe

 

* The tail is not visible externally, for the long ilia, which are attached by their
anterior ends to the sacral vertebra, extend backwards almost parallel to the urostyle ;
the latter is of about the same length as the ilia, so that their glenoid cavities are
close to its tip.
394 Vertebrata.

skull are retained throughout life, covered for the most part by
membrane bones. There are two articular condyles on the
occipital. The premaxille and maxille are closely adherent to the
anterior solid portion of the skull; they are not movable as in the
Teleosteans. The upper part of the mandibular arch, the palato-
quadrate, is fused to the hinder part of the skull; sometimes, as
in the Anura, it is also fused to the front part by its anterior end ;
it remains partly cartilaginous. In the larva there are usually,
besides the mandibular and hyoid arches, four pairs of cartilaginous
branchial arches, which degenerate to some extent in the
metamorphosis; in the Urodela, the first two pairs persist. The
basibranchials, hyoid, and branchial arches, are together termed the
hyoid.

Of the skull bones, besides those already noticed, the following must be
mentioned. In the cartilaginous cranium itself there develops a pair of
exoccipitals which almost completely surround the foramen magnum, and
which bear the occipital condyles; anterior to these on either side is the
petrosal, and at the front end of the cranium, the sphenethmoid.
The skull is covered dorsally by apair of nasals behind the external nares, and
a pair of frontals and parietals (in the Anura those of each side fuse
into a single bone) ; ventrally there isa parasphenoid (¢f., Fish) and, anterior
to this on each side, the vomer. In the palato-quadrate cartilage

     

pt oP ys

Fig. 320. Skull of a Frog (Rana esculenta). (A) from the dorsal (B) from the
ventral surface. c cartilaginous lateral portions of the skull, e sphenethmoid, e’ cartilaginous
nasal capsule, fn nasal bone, fp fronto-parietal, h’ stylo-hyoid, i premaxilla, j quadrato-jugal,
m maxilla, m’ quadrate, v exoccipital, op cartilage between the latter and the prootic p,
p’ anterior portion of prootic, with a large nerve foramen (p”), pl palatine, pt pterygoid,
pt’ posterior portion of the pterygoid, s parasphenoid, t—i’ squamosal, v vomer.—After
Ecker. ‘

there is, at the point of junction with the lower jaw, an insignificant ossification,
the quadrate, and behind, the cartilage is covered by a large membrane bone,
the squamous; the pterygoid extends anteriorly, and in front of this
there is in the Anura a transverse palatine attached to the skull by its inner
end. In this group, too, a thin bony rod, the jugal or quadrato-jugal,
stretches from the quadrate to the maxilla. The rami of the mandible
consist, as in Fish, of several bones.
Class 3. Amphibia. 395

The shoulder girdle of the Urodela is represented by
a cartilaginous arch on either side, in which two regions are dis-
tinguished, one dorsal the other ventral, is the glenoid for the arm.
The dorsal portion, the scapula, is narrower than the ventral,
the coracoid, which partially overlaps its fellow of the other
side. The lower part of the scapula is ossified to a varying extent,
the ossification often reaches into the coracoid region, but the upper
and lower portions of the girdle remain cartilaginous (Fig. 321). In
the Anura (Fig. 322), the coracoid is perforated by a large
foramen, and thus separated into anterior and posterior portions, the
latter ossified, the former not ossified, but covered by a membrane
bone, the clavicle; the right and left coracoids either overlap or

Fig. 321. Fig. 322.

 

Fig. 321. Sternum and shoulder girdle of a Salamander. s¢ sternum.
co coracoid, sc scapula.

Fig. 322. The same parts ofa Frog. st sternum, ep omosternum, co posterior region
of coracoid, se lower portion of scapula, sc’ upper portion of the same, cl clavicle. The
-cartilaginous parts in this and the preceding figure dotted.— After Ecker.

fit close together in the median line as in the Frog.* The scapula in
the Anura is divided into upper and lower parts, both ossified, but the
upper only partially. The fore limb consists of the same chief
parts as in the higher Vertebrata. The carpus, especially in the
Anura, usually conforms closely to the typical arrangement. In
extant Amphibia there are never more than four fingers; the
number of phalanges varies. In the Anura the two bones of the
forearm are fused.

Each half of the pelvis in the Urodela consists of a narrow upper
portion, the ilium, and a lower broader part, the ischio-pubis,
which is connected medianly with its fellow, and in which there is

 

* In some Anura (e.g., the Frog) there is, in the middle line, anterior to the coracoid,
a special, partly-ossified cartilage, which has been termed the episternum,
although it has no connection with the sternum, and although the episternum of other
Vertebrata is purely membrane bone. It is probably to be regarded as a special
development of the coracoid.
396 Vertebrata.

usually a single ossification only. Anteriorly the pelvis is prolonged
into a narrow, unpaired, usually Y-shaped, cartilage (cartilago
ypsiloides. In the Anura the ilia are backwardly-directed bony
rods; the ischio-pubes have fused to form a compressed vertical
disc. The hind limb closely resembles the fore limb in
structure. In the Anura the tibia and fibula are fused, and the two

Fig. 324.

 

Fig. 323. Pelvis and last vertebre of a Frog, from
above. a acetabulum, c urostyle, il ilium, ip ischio-
pubis, 7—9 vertebree (9 sacral vertebra).—Orig.

Fig. 324. Pelvis of the same viewed from the
left side. cacartilage. The other letters as in Fig. 323.
—Orig.

 

proximal tarsals (the third is absent) are very long and powerful.
The hind limb usually has five digits.

The musculature of the body and tail, in the amphibian
larva, is very similar to that of Pisces; it is separated into four

Fig. 325. Transverse section of the
hind end of the head of young Frog to
. show the tympanic cavity; dia-
Vf grammatic. Cartilage and bone closely
dotted. f tympanum (at the point

Lee, where the letter is situated the colu-
COs --A  mella is attached to the tympanic
Teed membrane), h brain, hy hyoid, k palato-
a quadrate cartilage, k’ lower jaw, | mem-
branous labyrinth (quite diagram-
matic), m mouth,t tympanic cavity
in which the columella lies.—Orig.

   

iz

longitudinal muscle plates, each of which is divided into a series of
segments by thin transverse septa; in the adult Urodela the relations
are little altered, whilst in the Anura great modifications occur. The
brain is small, the cerebellum very little developed.
Class 8. Amphibia, 397

The olfactory organs are two canals which lead from the
outer side of the head into the mouth, and open there behind the
edge of the jaw; the external nares can be opened and closed.
Eyelids are wanting in the larve, in the Perennibranchiata, and in
the Gymnophiona, which have rudimentary eyes; where they are
present only the lower one is movable, it is often semi-transparent,
and like a nictitating membrane. lLacrymal glands are absent,
although a lacrymal canal occurs in the adult; a Harderian gland is,
on the other hand, present.

Auditory apparatus. In most Anura, a short, wide canal;
the tympanic cavity extends from the posterior region of the
mouth behind the first gill-bar towards the exterior, it is not open
at the surface, but is closed in by a thin membrane, the tympanum.
The canal traverses that region of the skull which encloses the
membranous labyrinth, and is perforated in the region of the sacculus
by a foramen (fenestra ovalis), The fenestra is covered by a small
cartilaginous plate, the expanded end of a partially ossified rod,
the ear-bone (columella awris), whose other end is attached to
the tympanum (Fig. 325). In other Amphibia (some Anura,
e.g., the Toad; all Urodela and Gymnophiona), the tympanic cavity
and membrane are wanting; but all possess the fenestra ovalis
and the columella.

Alimentary canal. Teeth may be present on maxille,
premaxille, mandibles, vomers, and pterygoids, exceptionally also on
the parasphenoid ; in living Amphibia they are always small and
simple in form. The tongue is better developed than in Pisces ; it is
attached by its under surface to the floor of the mouth, in such a
way, however, that the edge is free. It is characteristic of the
Anura that the posterior tip, which is free and sometimes bifid,
is especially well developed; whilst the anterior edge, which is
insignificant, is attached in front, so that the tongue can be flicked
out of the mouth from behind forwards. In some Urodela it can
be stretched out upon a kind of shaft, projecting from its ventral
surface. The tongue is absent from Pipa and an allied genus. The
csophagus is short and wide, the intestine short.

The respiratory organs of Amphibia are gills or
lungs, the former will be considered first.

In the urodelan larva there are, on either side, four gill-slits,
the first between the hyoid and the first gill-bar, the last between the
third and fourth gill-bars. Each bar bears on its outer edge a thin
membranous plate, and the series is covered by a thick membranous
fold without ossifications, which corresponds to the operculum of
Fish. The plates correspond to the septa between the gill-clefts in
Fish, but bear no gill lamelle. At the dorsal end of each of the first
three pairs of clefts there is, however, a gill, not covered by the oper-
398 Vertebrata.

culum, and consisting of a stem and two rows of lamelle (Fig. 326).
These gills persist throughout life in the Perennibranchs, where
they are somewhat more complicated (branched) ; the embryos of
some Gymnophiona* possess similar gills (see Fig. 831). The
larve of the Anura also are furnished for a short time after
hatching with three pairs of external gills, like those of the larval

Fig. 326. Head, etc., of a
Urodelan larva, diagrammatic
(in the figure more of the thin
plates is seen than in reality, etc.).
k operculum, p thin plate on the
first gill bar.—Orig.

 

Urodeles ; they are, however, soon covered by the operculum, which
is well developed, and covers gills and gill-clefts, concrescing
posteriorly with the surface of
the body. A large branchial
cavityt results, communicating
with the exterior by a single
aperture,{ usually on the left
side. The gills enclosed in this
cavity atrophy, and in their
place numerous branched “in-
ternal gills,” structures
peculiar to the anuran larve,
arise on the outer edge of all
the four bars. Asin Selachians,
etc., there is usually an imperfect
straining apparatus at
Fig. 827. 4 Young Tadpole of a the inner edge of the gill-bar,

frog (lateral view) ; B somewhat older from jn guch forms as are provided
below; C still older larva with internal

gills. 1, 2, 3 the three external gills, u with external gills. It is repre-
anus, > hind limb, g branchial aperture, sented on each arch by one or

mu caudal muscles, n nares, o mouth, op
operculum, s organ of adhesion.—C orig., A two (one on the first and fourth

and B with the assistance of figures by Ecker. gill-bars, two on each of the
others) rows of short processes

 

 

* In other embryos of this division there is, instead of such gills, one very vascular
lamina on each side.

+ The opercula of the two sides are continuous ventrally (Fig. 327 B), concrescing
posteriorly to enclose a single cavity.

{ In Pipa, and an allied genus, there are two openings, one on either side.
Class 3... Amphibia. 3899:

which dovetail with those of adjacent arches. In the larval Anura
with internal gills, this straining apparatus reaches a high pitch
of perfection, so that it is able to exclude even the very finest
particles from the branchial-cavity and the delicate membranous
gill-tufts within it. For the branchial vessels, see below.

The lungs, occurring in all Amphibia, are two saccular organs,
which in some forms (e.g., Newts, Proteus) are quite simple, in
others (Salamanders, Anura), are provided with short, thick-set
evaginations (Fig. 345 B). In the Gymnophiona, the right lung is
much shorter than the left. The trachea, which is almost always
very short, opens by a longitudinal slit into the back of the mouth; it
is supported by several cartilages, and in the Anura, contains vocal
cords, which are absent from all the others. To effect an inspira-
tion, the animal depresses the soft parts between the rami of the lower
jaw, by shutting the mouth, and draws air into the buccal-cavity
through the open nares; these are now closed and the lower wall of
the buccal-cavity is raised, so that the air is forced into the trachea ;
it is forced out by the contraction of the body-wall and its pressure
upon the elastic lungs.

In some Salamanders, e.g., two species in 8. Europe, the lungs are rudimentary
or entirely absent. Respiration is effected by means of the skin (of great import-
ance in this connection in all Amphibia) and the buccal cavity, where inspiration
and expiration proceed in the usual way.

The vocal cords of the Anura are made to vibrate by the expired air, and thus
sounds are produced. In the males of many species, this noise may be intensified
by means of evaginations of the posterior region of the buccal-cavity, which can
be blown out at pleasure into thin-walled sacs of considerable size. A pair of
such resonators is present; in some (e.g., the Tree Frog), they unite to form a
single unpaired vesicle, which is, however, connected with the mouth by two.
openings. The Urodela can produce sounds, although they have no vocal cords.

The heart (Fig. 284) differs from that of most Fish in that the
atrium is divided by a septum into two auricles, right and left;
the latter is the smaller, and receives blood from the lungs, whilst
the right receives blood from the rest of the body. The septum is
often pierced by larger or smaller apertures, and is thus imperfect.
The ventricle is undivided, and shows no trace of separation ;
as in Fish, its wall is thick and spongy, the small spaces open-
ing into the central cavity; the auriculo-ventricular apertures are
guarded by valves. The conus arteriosus, which arises in
front from the right side of the ventricle, is usually a well-developed
tube, somewhat spirally curved. It displays at each end a trans-
verse row of valves, and is in addition provided with a longi-
tudinal fold, which is connected with a valve of the anterior
row, and projects into the cavity of the conus (for its significance
see below).

The arterial system in amphibian larve is piscine in char-
acter: an afferent branchial artery, arising from a very short ventral
aorta, runs to, an efferent artery runs from, each gill-bearing gill-
400 Vertebrata.

bar; the efferent branchials unite to form the aorta. In urodelan
larvee a single arterial arch runs to the last branchial bar, which is
destitute of gills; the pulmonary artery arises from this, or, in
the larval Anura, from the last efferent branchial artery; the
carotids, vessels to the head, spring from the first efferent
branchial artery.

At the metamorphosis the gill vessels degenerate, and the afferent
and efferent branchial arteries unite* to form simple arterial
arches, which, like their precursors, the efferent branchial arteries,

B

  

Fig. 328. Arterial arches of the Urodela: diagrammatic. A larva, B
adult. ao aorta, br gill (removed from the second and third arches), ca carotid, p pul-
monary artery, st conus arteriosus; 1—1l’ first, 2 second, 3 third, 4—4’ fourth arterial
arches, la—3a first—third afferent branchial arteries ; 1b—3bh first—third efferent branchial
.arteries.—Orig.

unite to form the aorta. The first, however, usually lose their
connection with the others, and simply supply the head with blood;
the fourth also generally become independent, and form only the
pulmonary arteries; and the third arterial arches, in many cases,
atrophy completely. When this occurs, and if at the same time the
first and fourth arches have no connection with it, the aorta is
formed by the second arterial arches only, which are better
developed than the others. The aorta of Amphibia is sometimes
formed by a single pair of arterial arches, sometimes by several.
The Gymnophiona in the adult condition are very similar to the
others ; the vascular system of the larva is at present unknown.

 

* In the larva of the Urodeles the afferent and efferent branchial arteries are con-
nected by a small vessel at the base of the gill (anastomosis), and this ree at the
metamorphosis.
Class 3. Amphibia. 401

In the larval Urodeles that part (4 Fig. 828 A) of the fourth arterial arch
which lies between the ventral aorta and the point of origin of the pulmonary
artery is much narrower than the pulmonary, whilst the rest (4/) of this arterial
arch is as wide as the latter: the pulmonary artery in the larva evidently
receives direct the chief mass of the blood from the vessel formed by the
union of the three efferent branchial arteries, i.e., arterial blood. In the adult
the relative sizes of the different sections of the fourth arterial arch are
exactly reversed (Fig. 328 B).

In the larve generally the circulation is essentially piscine. In the
adult, in spite of the single ventricle, the arterial blood from the lungs is to
some extent separated from the venous blood; the arrangements are, however,
too complicated to be more closely gone into here. Suffice it to say that by
means of the spiral valve of the conus almost all the arterial blood from the
left auricle flows into the first two pairs of arterial arches, whilst the venous
blood from the right auricle goes partly into these, partly into the third and
fourth pairs; the fourth pair, as already mentioned, gives rise to the pulmonary
arteries, which receive entirely venous blood, whilst that in the systemics is
“ mixed.”

From the fourth arterial arch, larger or smaller branches go to the skin; in
the Anura especially, there is a very large cutaneous artery, which therefore
carries venous blood; and as a matter of fact, the skin is here of great respira-
tory importance; but the blood thus oxydised, mixes with that of the other
veins, and goes to the right auricle. On the whole, the separation is very
incomplete.

The ureters open into the cloaca, which has a ventral outgrowth
serving aS a urinary bladder. The latter, which is often
drawn out into two points, is not directly connected with the ureters,

but opens separately into the cloaca.

The ovaries vary in size, according to the time of year; in
the breeding season they are very large. The Miillerian ducts
are long, coiled tubes, which are thickest at the breeding season,
on account of the great development of the albumen glands lying in
their walls ; they open into the abdomen by funnels, situated quite
anteriorly, and far distant from the ovaries; the ripe ova are wafted
to the funnels by movements of the cilia upon a portion of the
abdominal epithelium; they usually open separately into the cloaca
by their other ends. In the Anura, the hinder portion of the oviduct
is expanded into a vesicle, which is filled with ova at spawning time.
The testes (Fig. 288), are connected with the urinary tubules of the
anterior end of the kidney, which, in the Urodela is smaller than
the posterior end, and the spermatozoa pass out through the ureter ;
the duct of the anterior portion of the kidney is, moreover, in many
cases, almost completely separated from the other renal ducts with
which it unites only just before the common opening into the cloaca.
In the males, there is a rudimentary Miillerian duct on each side.

Actual copulation takes place only in the Gymnophiona;
the eversible cloaca of the male serving as an intromittent organ.
In the Anura, the male clasps the female with the fore limbs, and as
the eggs leave the cloaca, pours the sperm over them; fertilisation

DD
402 Vertebrata.

thus takes place in the water. The fore limbs are stronger in the
males than in the females, and in many forms are furnished, in
the breeding season, with rough horny warts, especially on the
hands, so that they can grip more firmly. The male Urodele
deposits the spermatophores, which consist of masses of jelly
containing spermatozoa, and vary in form, at the bottom of the
water. The female then moves over them, so that they become
attached to the cloacal opening; they are taken into the cloaca
where the spermatozoa penetrate into little sacs in the wall, which
serve as receptacula seminis. Here fertilisation occurs within the body
of the female.

As already mentioned, there is, in the Toads (Bufo), at the anterior end of
the testis, a small body, which resembles an unripe ovary in structure. In
the females of this genus, a corresponding portion of the ovary is similarly
developed ; it is especially noticeable in young females, but degenerates later.

A pair of yellow bodies containing fat, and often very conspicuous, is attached
to the reproductive glands in Amphibia, and is frequently in close connection
with them. These are the so-called fat bodies, which are digitiform in
Aunura, and originate by modification of a portion of the ovary or testis.

The eggs are usually laid in fresh water, surrounded by a thin
albuminous coat, which swells up in the water to a thick gelatinous
capsule. They are either laid singly (rarely) or in rows, strings, or
‘masses. They vary in size from two to about ten m/m. in diameter.
Segmentation is usually total, but the segmentation spheres are
larger at one pole (cf., p. 45, and Fig. 34); the larger eggs, how-
ever, undergo partial segmentation. Rarely, as in the Salamander,
the ovum develops within the oviduct. The eggs or brood are
protected in various Amphibia: Pipa, Alytes obstetricans, Cecilia,
etc. (see below).

The metamorphosis, which all Amphibia undergo, is
specially characteristic of the group. The larve, as already men-
tioned, ‘are provided with well-developed gills; the circulation and
the disposition of the vascular system are almost identical with
those of Fish; lungs are already present, but have as yet no re-
spiratory function. At the metamorphosis a significant change
in structure and mode of life occurs; the gills atrophy and the
lungs become functional, involving amongst other alterations, great
modifications in the vascular system (cf. p. 400). The differences
between larva and adult are not, however, confined to these; in
many other respects the former approaches the piscine type; for
instance, there is no stratum corneum; lateral line organs are
present ; they always lie free, and even bear delicate cylinders like
those of Fish.* Eyelids are absent; a continuous fin is present at
first, but disappears in later larval life, and the visceral skeleton is

 

*The sensory papille also occur in adult aquatic Urodeles, but here the
cylinders are wanting.
Class 3. Amphibia. 403

much more piscine (p. 394) early, than in final stages. When the
tadpoles hatch, they are generally somewhat unlike the fully-developed
larval form; for example, the limbs are not present, or are merely
indicated, and, on the ,

head, there are frequently Z

organs of attachment, @ ZB

which atrophy after atime 4 7 ee

(Fig. 327 A—B, and 329A). age oe :
The metamorphosis SS «

itself, that is, the change
from the larval to the
perfect form, is completed
somewhat suddenly; the
changes are accomplished
In quite a short time.
The size attained before 4
metamorphosis varies ;
closely allied species often
differ considerably in this

respect ; for example, with- ve 329. Larve of the large Triton. A newly
: hatched, from the side and below. B 12 days old.
in the genus Rana, She <@ shout & #ecka old, (A x about 5, B 3—4,
larva of the Edible F rog C scarcely x 2). aanus, f fore limb, g gills, s organ

a very large, that of the of attachment.—After Rusconi.

Grass Frog, on the other

hand, rather small; growth is not usually completed at metamorphosis
(as in Insects) but continues for some time.* In some Urodela, viz.,
in certain Tritons, it has been noticed that the larvae sometimes
grow beyond their customary size, and become sexu ally mature
as larve; whether they afterwards undergo metamorphosis is
unknown. The same thing occurs normally in the larva of a
Mexican Salamander the Axolotl (Siredon mexicanus), at least in
those individuals which have been kept in confinement ; they are, as
a rule, sexually mature during the larval period, and do not
undergo a metamorphosis ; this happens only exceptionally, and then
before sexual maturity. Lastly, there are a few Urodela, the
Perennibranchiata (genus Proteus, etc.), which remain in
the larval condition and never assume the adult form. These forms
are like larve in all respects excepting the development of the
reproductive organs ; in some points, however, they have undergone
degeneration ; in Proteus, for instance, the lungs, compared with the
size of the animal, are very poorly developed, and they are of just
as little respiratory significance as in the larva. The retrogressions
are in part of such a character as to render it possible to state

 

 

* The larve of a South American Frog (Pseudis paradoxa) are huge.

DD?
404, Vertebrata.

4

definitely that these forms are no longer capable of
undergoing metamorphosis.*

In two genera of the Urodela, Menopoma and Amphiuma, the gills atrophy,
but the gill-slits persist, and in many respects the animals remain in a larval, or
more correctly, in an intermediate condition.

All living Amphibia are freshwater or terrestrial, they are almost
always small or of a medium size, and feed upon Insects and other
small animals. In earlier times they were to a certain extent
represented by larger forms (see below). With regard to the
Geographical Distribution, the remarkable fact, that Urodela belong
almost exclusively to the temperate regions of the Northern
Hemisphere, may be noticed.

Order 1. Urodela.

The tail is well developed ; the fore and hind limbs about equal,
and feeble. The larva has three external gills on each side.

1. Newts (Triton) have a compressed tail, and on the dorsal side of the
body, both dorsal and ventral to the tail, is a fin, which is most marked at the
breeding season, and largest in the males. At spawning time they live in water,
otherwise on land (the male, however, frequently in water); the eggs are laid in
the spring, singly, or in short strings on aquatic plants. The newly-hatched
larva (Fig. 329 A) exhibits posteriorly on the head, a pair of stalk-like processes,
by means of which it attaches itself to plants; for limbs, there are only wart-like
processes, the incipient fore limbs; they develop gradually, the anterior first ;
the organs of attachment soon disappear. Larval life usually lasts some
months. In England are found the Large Water Newt (TY. cristatus),
with a rough skin; the Small Newt (7. tzxniatus), the commonest species;
the Palmated Smooth Newt (T. helveticus), with a filiform tip to its tail,
rare; the last two are about the same size, the first considerably larger.

2. The Salamander (Salamandra maculosa) is an animal of considerable
size (up to 18 ¢/m) ; velvet black, with large irregular yellow spots; no trace of a
fin; tail rounded. In Central and South Europe; viviparous; the young ones
quite differently coloured; they are born with gills, and both pairs of limbs, and
then only are aquatic. It is of interest that the embryo has much longer gill
lamin whilst still within the oviduct, than it has later. The Black Alpine
Salamander (8S. atra), allied to the one just described, and quite black, occurs
in the Alps; viviparous, bearing only two young ones at a time, one in each
oviduct (S. maculosa produces a greater number at a birth). There are several
eggs in the oviduct, besides the one which develops, but they merely coalesce,
and furnish nutrition for the embryo. The embryo has extraordinarily large
gills, which surround a great part of the body before birth, but atrophy later;
metamorphosis thus occurs within the body of the parent; the Alpine Salamander
is born on dry land, and is never aquatic.

3. The Axolotl (Stredon mexicanus) is distinguished as already mentioned
-by the fact that, in captivity at least, it does not usually undergo a metamorphosis,
but becomes sexually mature in the larval state. The form which does undergoa

 

 

* For instance, in Proteus, that portion of the fourth arterial arch which lies
between the ventral aorta and the point of origin of the pulmonary artery is absent,
but it is indispensable for the adult Amphibian.
Class 3. Amphibia. Order 1. Urodela. 405

metamorphosis (Amblystoma meaicanwm) is similar to a Salamander. The
Axolotl, which is indigenous to Mexico, is oviparous; when first hatched, it is
just like the triton larva of the same stage.

4. Under the name, Perennibranchiata, are collected all the Urodela
described above (p. 403) as retaining gills and other larval characteristics
throughout life. Amongst these is the blind, pale, elongate Proteus anguwineus,
which has rudimentary eyes, and three digits on each foot; in subterranean lakes in
Austria. Furthermore, the genus, Menobranchus, less elongate, with four digits
on each foot, and Stren lacertina, which may attain a length of 1 m., with
horny jaws; vermiform, without hind limbs; both in N. America. The genera,
Menopoma and Amphiuma (the latter vermiform ; with four very small limbs, each
with two or three digits), lose their gills as already mentioned, but retain the gill-
slits and several other larval characters. Nearly allied to Menopoma, is the
Japanese Giant Salamander (Cryptobranchus japonicus), in which the
branchial clefts are closed.

Related to the living Urodela are the Stegocephala (primitive Amphibia), a
large group, which lived in the Carboniferous, Permian, and Triassic periods, and
of which a few were remarkable for their great size ; skulls are known of 1:5 m.
long. The skull has a larger number of membrane bones than in existing
Amphibia; there is, for example, a double supraoccipital and several others.*
The skull bones are often scarred externally, and this signifies that they were
located close below the surface, covered only by a thin skin; sometimes there
are furrows on the head, for the branches of the lateral line, recalling those

 

Fig. 330. Skull of 4 Stegocephalon (Tre:
matosaurus), from below (A), from above (B), and
from the side (QC). 1 Orbit, 2 external nares, 3 internal:
nares, 4 foramen magnum. a occipital, b parietal,
ce frontal, d parasphenoid, g palatine and pterygoid,
t nasal, v vomer, # occipital condyles. The other
letters distinguish various membrane bones.

 

of many Fish. As in the Amphibia of to-day there were two occipital condyles.
The notochord was, to a large extent, persistent, the centra often biconcave;
ribs sometimes long.t Some Stegocephala have five digits on the fore limbs.
The sclerotic coat of the eye (unlike that of existing Amphibia) usually had a
ring of bony plates. In the skin of the ventral surface (rarely on the dorsal)

 

* Between the parietals there is often « fairly large parietal foramen, which
indicates the presence of a parietal eye (see p. 337).

+ The head often forcibly recalls that of the bony Ganoids.

{The sternum was cartilaginous, but there was an episternum and a
clavicle, like those of the Lacertilia.
406 Vertebrata.

bony scales were developed. The surface of the teeth, in some of the
Stegocephala, has deep, compressed spiral folds, which, especially at the bases,
stretch far into the mass, and in transverse section look like curved lines; hence
the name Labyrinthodonta, which has been given to this group, but
which only suits one section of the members, since the rest have teeth of
simple structure.

Order 2. Anura.

There is no projecting tail in the adult. he hind limbs, which
are always more powerful than the anterior, are Jumping or swim-
ming legs, and have a larger or smaller web between the toes. Lower
jaw edentulous. Larva at first with external, later with internal,
gills,

The young larve (Fig. 327 A—B) are small, elongate animals, having
three external gills on each side, and a pair of sucker-like sticky organs on the
head, by means of which they attach themselves firmly to plants, etc.; limbs are
absent. After a few days the external gills are covered by an operculum, and
atrophy, whilst internal gills arise on all the gill-bars (see above, p. 398). Simul-
taneously the form of the body changes, head and trunk together become almost
spherical, as distinct from the powerful tail with its large fin (Fig. 327 C); the
adhesive apparatus disappears. The larva (tadpole), which has horny jaws and a long
coiled gut, feeds upon decayed vegetables, dead animals, or mud; it is an active
swimmer. Of the gradually developing limbs the anterior lie within the branchial
cavity during the whole of larval life; that is to say the points at which they
project are covered, like the gill-bars, by the operculum. The fore limbs break
through the outer wall of the branchial cavity, but this only occurs at the meta-
morphosis when the tail dwindles; the teeth develop (that is if the adult has
teeth), the small mouth enlarges, etc.

1. Frogs (Rana) have teeth in the upper jaw; a smooth skin; round
pupil; long, strong hind limbs, with perfect webbing between the toes. The
eggs are laid in large masses. The following species inhabit the British
Isles: the Common or Grass Frog (Rana temporaria), which usually
lives on land, and betakes itself to the water only at the breeding season, the
early spring, in contradistinction to the large Edible Frog (R. esculenta),
which lives the whole year through in water, and which swims and springs better
than the others; it spawns later also, and its larve attain a considerable size.

2. Tree Frogs (Hyla, etc.), are distinguished from others in having a
sucking-dise at the tip of each toe. The green Hyla arborea, which is usually
found on trees, except during the breeding season, occurs over most of Europe.

3. Land Frogs, or Frog-toads (Pelobatide) differ from true Frogs.
in the short hind legs; erect pupil; and warty skin. The following European
forms may be noted: the Orange-speckled Toads (Bombinator igneus
and B. bombinus), ventral surface black and yellow; Pelobates fuscus, hind foot
with a horny knob, sharp as a knife on its inner side; the larva reaches a still
greater size than that of the Edible Frog ; Alytes obstetricans, of which the males
wrap the eggs round their hind legs and carry them about with them until the
larve are ready to hatch, when they go into the water and the larve leave the
egg-shells.

4. The Toads (Bufo) are edentulous, have shorter hind limbs than the
Frogs, and an imperfect web between the hind toes, transverse pupils, warty skin.
The eggs are laid in long strings. In England: the Common Toad
Class 3. Amphibia. Order 2. Anura. 407

(B. vulgaris) and the Natterjack Toad (B. calamita), with a longitudinal
yellow stripe down the back.

5. The Surinam Toad (Pipa americana), a large, flattened Amphi-
bian, with small eyes, no tongue, no teeth, with large webs between the
hind toes. With the help of the male, the fertilised eggs are placed on the
back of the female: a small depression forms for each egg, in which it develops,
and where metamorphosis takes place. S. America.

Order 3. @ymnophiona.

The body elongate, vermiform, and apodous ; the tail rudimentary,
eyes degenerate; skin with ring-like
grooves on. the surface, often contain-
ing bony scales.

The Gymnophiona (genus Cecilia
and others) live in the earth in warm coun-
tries; they feed on Harthworms and such
animals. The embryology is well known
only for a single species, living in the
East Indies, Epicriwm glutinosum. This
form lays its eggs in a hole in the ground,
coils its body round them, and does not
leave them until they are hatched. The
completely developed embryo possesses three
pairs of gills, similar to those of sala-
mander larve, rudimentary hind limhs, and
a short tail, provided with a fin.* It ?
loses its gills on hatching, and _betakes Fig. 331. Embryo of Epi-

 

itself to the water, where it lives for some crium  glutinosum, removed
time. from the egg.—After Sarasin.

Class +. Reptilia.

As regards external form, the body is very like that of the
Urodela, but differs in the presence of a more pronounced neck.
The powerful tail is not sharply demarcated from the body, and is
often quite round in section. The limbs are generally, as in the
Urodela, small, and feeble as compared with those of the two following
classes ; elbow and knee are turned outwards; the tail is usually
still important as a locomotor organ.

The skin is provided with a hard stratum corneum, which is shed
entire at certain periods (several times a year), in Snakes and some
Lizards; the former draw off the “slough” inside out, the latter
crawl out of it. In the majority of Lizards, however, the horny
layer is moulted in large pieces, in the Chelonia and Crocodilia in

 

* It is very remarkable that the egg increases in size after it is laid, until the
diameter becomes twice as great, and the embryo weighs almost four times as much as
the new-laid egg. This is probably consequent, to a great extent, upon an absorption
of water, but possibly the egg also takes in « secretion from the cutaneous glands of
the female.
408 Vertebrata.

quite small shreds; the very hard and thick portions of the stratum
corneum are not thrown off. The surface of the body is covered with
so-called scales, which are, however, quite different in structure
from those of Fish. The reptilian scutes may be termed dermal
warts; they are usually flattened, lie close together, and are
regularly arranged. In the furrows between the scales, the corneum
is thin, on their surface, thicker. In some cases, e.g. in Geckos and
others, the scales are simple round warts, granular scales. On

      

Wy TT Zo

 

Fig. 332. Longitudinal section through various scales of Reptiles: diagrammatic.
A granular scales, B shield, C splint scales, D do. with ossifications. h cuticle, s mucous
ayer of the epidermis, | dermis, 0 bony plates.— Orig.

the head, sometimes also upon other parts of the body, there may
be shields, ie., large flat plates, separated from their neighbours
by regular grooves. In most cases, the scale is drawn out posteriorly
into a point, which overlaps the one followimg, true scales; if
these are much broader than they are long, as on the ventral side of
the body in Snakes, they are termed splints. Not infrequently
the scutes are developed into longer or shorter spinose scales,
as in many Ground Iguanas, and on the back of some Tree Iguanas,
etc. True scales have often a small median keel (e.g., in many
Snakes). Occasionally, ossifications occur in the dermis; there
is, for example, in each scute of the Blind-worm, a small bony plate;
in the Crocodilia, there are similar but larger plates in the dermis;
and in the Chelonia they are very large, and often connected by
sutures, thus making a continuous bony shell round the animal ;
the boundaries do not correspond with the grooves between
the scutes). Skin glands are but slightly developed in the
Reptilia; there is, however, e.g, im many Lizards, a row of large
glands on the thigh (their openings are termed femoral pores ; or, in
front of the anus, pre-anal pores); in the Crocodilia also, and in many
Chelonia, large isolated skin glands occur. The digits, in contra-
distinction to those of the Amphibia, are provided with claws,
peculiar horny structures, covering the last phalanx like a cap;
they are not affected by the ecdysis; they grow gradually from
within, and are simultaneously worn away at the surface.
Class 4, Reptilia. 409

Tn the adult, the skeleton is only to a slight extent carti-
laginous ; it consists almost entirely of bone. The notochord has
usually disappeared; only in the Geckos does it persist as a
‘continuous cord extending the whole length of the vertebral column.*
The centra usually articulate; they are generally proccelous ;
in the Crocodilia, there are cartilaginous discs between them.t
The vertebral column is usually divisible into more regions than
in the Amphibia: first, there is a variable number of cervical
vertebra, without ribs or with short ones; then a number
provided with longer ribs, the thoracic vertebra; these are
often followed by several ribless lumbar vertebre; then the
sacral vertebra, usually two, to the transverse processes of
which the pelvis is attached (occasionally, especially in certain extinct
Reptilia, there is a larger numbers of sacrals) ; lastly, the caudal
vertebra,{ without ribs. Inthe Snakes, however, in consequence
of the absence of limbs, these distinctions do not hold; all the
cervical and dorsal vertebre, with the exception of the first, bear
well-developed ribs; there are no sacrals, and therefore trunk and
caudal vertebree only can be distinguished. The first two cervicals,
the atlas and axis, are peculiar in form (Fig. 333). The centrum

Fig. 333. Diagrammatic
transverse section of the
atlas of one of the higher
Vertebrata. 6, arch of the
atlas, 1 odontoid process,
x bony plate, t ligament.—
‘Orig.

Fig. 334. Diagram of
axis. 1lcentrum of atlas,
2 centrum of axis, b) arch
of axis.—Orig.

 

of the former is fused with the second, forming a process (the
odontoid) at its anterior end. The first vertebra is, therefore,
merely a bony ring formed by an arch, bridged below by a bony

 

*In the young Lacerta, etc., considerable portions of the chorda dorsalis are
present in the centra, but they disappear later.

+Transverse processes are especially well-developed in the Crocodilia ;
here they are large on most of the vertebre, although elsewhere they are most
prominent in the tail. Frequently (e.g., in the Snakes) an unpaired process arises
from the ventral side of the centrum of many of the vertebre, the ventral spine.
Definite articular processes (zygapophyses) are present; in the Snakes and some
Lizards (Iguana), besides these, there arises from the anterior side of each
neural arch, a single process, with two articular facets (zygosphene), each of which
fits into a pit (zygantrum) in the preceding vertebra, and thus the connection is made
‘still firmer.

t In most Lizards, the tail breaks with peculiar readiness ; this is correlated with
the fact that in the middle of each caudal centrum, there is an uncalcified transverse
‘disc. After fracture, the tail grows again.
410 Vertebrata.

plate. The lower portion of this ring receives the odoutoid process,
and is separated from the upper, through which the spinal cord
passes, by a broad connective tissue ligament. The thoracic ribs
consist of an upper bony region and a lower portion, which is often
cartilaginous ; the latter is sometimes, ¢.g., in Crocodiles, divided into
two parts: from the bony portion a flat backwardly-directed
process (processus uncinatus) is occasionaHy given off (Crocodiles).
The anterior, or true, ribs are attached to the sternum, in Lacertilia,
Crocodilia, and, many extinct forms ; the posterior ribs are free (false
ribs) ; no such distinction can be made in the Chelonia and Ophidia,
for a sternum is not present. The ribs are partly fused to the dermal
skeleton in Chelonia. In Crocodilia, small ribs, which for the most
part articulate by two heads, like the thoracic ribs, occur on all
the cervical vertebrae ; the same points may be observed in Lizards,
where, however, there are none on the atlas. The posterior cervical
ribs become successively longer, so that there ix a gradual transition
from cervical to thoracic vertebre.* Azygos, forked bones, the
hemal arches, occur ventrally, in Lizards and Crocodiles,
between the caudal vertebrae, but have not coalesced with them. The
sternum (Fig. 339) which is absent from the Chelonia and
Ophidia, is usually a short rhomboidal plate, which sometimes (e.g.,.
in Crocodiles) is prolonged posteriorly into a long narrow process;
it is cartilaginous, and is usually calcified. Connected with the
sternum anteriorly is a flat, longish membrane bone, the epi-
sternum, which partly covers it and is often drawn out anteriorly
into two processes one on either side.

The skull consists principally of bone, and in many Reptiles is.
compressed between the orbits to form a perpendicular plate
of cartilage or even partly of mere fibrous connective tissue, the
interorbital septum ; the brain is situated behind this plate; in front of
it lies the olfactory organ. There is only one occipital condyle
below the foramen magnum. The premaxillet and maxille
are firmly attached to the skull, as are also the bones formed in the
place of the palato-quadrate ; viz., most posteriorly, the quadrate
which bears the articular facets for the lower jaw ; in front of this the
pterygoid; and still further forward the palatine; the two
last bones extend forwards from the quadrate, inwards from the large
maxille. The extraordinary mobility possessed by the palato-pterygo-
quadrate arcade, in connection with the maxilla, in Snakes, is
remarkable ; the quadrate in Lizards is also, to some extent, movable,
but quite immovable in the Crocodilia and Chelonia, in which groups,
the palatines, pterygoids and maxille are fixed. The lower jaw

 

* There is a number of narrow membrane bones, the so-called abdominal
ribs, in the abdominal wall of Crocodiles, which must not be confused with true ribs.
They have no connection with vertebre, and are, not like ribs, preformed in cartilage.

+ In Snakes and many Lizards the premaxille are fused.
Class 4, Reptilia. 411

consists of several bones : of these the most anterior may be anchylosed
with its fellow of the other side, as in Chelonia. The hyoid

 

7
Fig. 335. Land 3 Skullof a Lizard (Varanus).—2 and 4 ofa Crocodile, dorsal and
ventral. C occipital condyle, Ch posterior nares, co columella, E Eustachian tube, Fr frontal,
Ju jugal, L in 2 lachrymal (in 1 4 membrane bone present in some forms), Mz maxilla,
Na nasal, Ob basi-, Ol ex-, Os supra-occipital, Pa parietal, Pal palatine, Pf postfrontal,
Prf prefrontal, Pt pterygoid, Px premaxilla. Q quadrate, Qj (and the lower @ in 1) quadrato-
jugal, Spd basisphenoid, Sq squamosal, Tr transverse bone, Vo vomer.—After Gegenbaur.

apparatus, v.e., the visceral skeleton, with the exception of the first
visceral arch (the quadrate, pterygoid, palatine and mandible),

consists, in the Chelonia and Lacertilia,
of an unpaired portion, the body of the
hyoid, corresponding to the basi-
branchials of Fish, and two pairs of
cornua which represent the hyoid
and the first gill-bar respectively ;* in
Crocodiles and Snakes only a single
pair of horns is present, in the latter
group the whole apparatus is very
poorly developed.

The most important bones of the
reptilian skull, besides those already
mentioned, are the following: the occi-
pitals, a supra-, basi-, and two
ex-occipitals, surrounding the foramen
magnum; the petrosal, in front of the

I

|

  

Fig. 3836. Hyoid of a Lizard.
¢ body of the hyoid (copula), br, first.
gill bar.—After Walter.

* In some Lizards there are traces of two cornua representing the second gill-bar.
AL? Vertebrata.

‘exoccipitals; the squamosal, inthe same region, projects far forwards in
Snakes, and is connected with the quadrate ; the basisphenoid, in front of the
basi-occipital, and like this, an ossification in the lower wall of the skull. A
parasp henoid is not developed (cf., Fish and Amphibia). The anterior wall
of the brain-case is often unossified and membranous, sometimes with isolated
ossifications. Dorsally there is a number of bones; the parietals, which are
generally (Snakes, Lizards, Crocodiles) fused; the frontals, an unpaired bone,
in Crocodiles and many Lizards; the post-frontals, behind, the pre-
frontals, in front of, and the lachrymals, below, the orbit (the last is
present only in Lacertilia and Crocodilia); the nasals behind the external
nares. Below the orbit and behind the maxilla, there is usually a jugal, and
from this to the quadrate stretches the quadrato-jugal; a paired or unpaired
vomer lies ventrally, in front of the palatine. Extending from the pterygoid
to the maxilla, there is in Crocodiles, Lizards, and Snakes, the peculiar
transverse bone which is peculiar to the Reptilia. There is yet another
peculiar bone in many Lizards, the columella, extending almost perpen-
-dicularly from the parietal to the pterygoid.

The shoulder girdle of the Reptilia is very like that of the
Amphibia. In Lacertilia, which will be considered first, it is

 

Fig. 337. Left half of the skull of a Boa constrictor, seen from the side (and
somewhat from above).— Orig.

Fig. 338. Do. of a large Crotalus (Craspedocephalus atrox).—Orig.

Fr frontal, h ear bone, Mz maxilla, Nunasal, Os supra-occipital, Pa parietal, Pal palatine,
Pe petrosal, Pf postfrontal, Prf prefrontal, Pt pterygoid, Px premaxilla, Q quadrate, Sq
ssquamosal, Tr transverse bone, 1, 2, 3 bones of the lower jaw.
Class 4. Reptilia. 413:

represented on each side by an arched, partially ossified plate, which
articulates below with the front edge of the sternum. A scapula
is distinguishable above the glenoid, and below this a coracoid,
which is usually divided by one or two large fenestra into two or
three regions. The scapula is divided into an upper and a lower
portion, of which the former consists of calcified cartilage, the latter
of bone; it is connected with the coracoid by a suture or is fused
with it. A clavicle reaches from the scapula to the epi-
sternum. In the Crocodilia the shoulder blade is almost
entirely ossified, only the upper edge being cartilaginous (supra--
scapula) ; the coracoid is a simple bone, and the clavicle is absent.
In the Chelonia the coracoid is divided, as in the Lizards, into:
anterior and posterior regions, which are, however, quite separate ;
the former, the precoracoid, is fused with the scapula, which it meets.

 

Fig. 389. Sternum and shoulder girdle of Lacerta spread out, the scapula
in reality bends upwards. The right clavicle has been removed. aglenoid for the humerus,
cl clavicle (in the species figured perforated by a large fenestra), co coracoid, co’ cartila-
ginous epicoracoid, ep episternum, r ribs (cut away), sc scapula (here anchylosed to the
coracoid), sc’ cartilaginous supra-scapula, st sternum.—Orig.

at a right angle; the latter, the postcoracoid, is a separate bone.
In the Ophidia the shoulder girdle is altogether wanting. With
regard to the fore limb it must be noticed that the ulna is
the stronger of the two bones of the forearm. In the Chelonia
the nine primitive bones are present in the carpus (sometimes
some are fused); in the Lizards, too, the carpus is little modified
whilst in the Crocodilia it is distinguished by the large size of
the two proximal bones, and by the degeneration or fusion of
the distal carpals. Attached to the outer side of the carpus there.
is usually a sesamoid bone, the pisiform. The number of
414 Vertebrata.

fingers is usually five, but may be smaller; the phalanges vary in
number ; in the Lizards they are generally as follows: two in the
thumb, three in the second, four in the third, five in the fourth,
three in the fifth digit.

Fig. 340. Fig. 341. Fig. 342.

 

Fig. 340. Carpus of a Turtle. U lower portion of the ulna, R of the radius,
uw ulnare, 4 intermedium, r radiale, c centrale, 1—5 carpals first to fifth; s pisiform: I—V
metacarpals.—After Gegenbaur.

Fig. 341.—Carpus of a Lizard (Lacerta agilis).—Modified from Gegenbaur.

Fig. 342.—Left half of pelvis of a Lizard (Varanus). Jl Tlium, a its hind end,
.Js ischium, P pubis, t acetabulum.—After Gegenbaur.

The pelvis is composed of three bones on each side, the ventral
portion being separated by a large fenestra into anterior and posterior
parts, which ossify separately, the pubis and the ischium;
they are connected medianly with their fellows of the other side; all
three bones generally take part in the formation of the acetabulum.
A pelvis is usually altogether absent from the Ophidia, but occasion-
ally rudiments of it are present, ¢.g., in the Peropoda with rudimentary
hind limbs. In the tarsus* some of the bones are always fused ;
it is important to note, that the proximal row of tarsals with which the
centrale is also connected, is usually closely united with the distal end
-of the leg, and movement in the ankle occurs between the proximal
and distal rows of tarsals, whilst there is very little or none between
the leg and the proximal row (cf. Mammalia).t The toes are like
the fingers ; five are usually present; the number of joints varies : in
Lizards beginning with the hallux, as a rule, two, three, four, five,
four.

The brain of Reptilia is generally rather small. In some forms,
especially in Crocodiles, the cerebrum attains relatively large

 

*In Crocodilia the pubis is, however, excluded from the acetabulum, which is
formed by ilia and ischia alone.

+ As regards special arrangements it may be mentioned that the bone of the
proximal row, which corresponds with the caleaneum of Mammalia, is provided in the
-Crocodilia with a similar process (tuber calcis),
Class 4. Reptilia. 415

proportions, just as does the cerebellum, which in Lacertilia and
‘Ophidia forms simply a narrow ridge in front of the medulla oblongata.
Olfactory organs, the
nasal capsules, occupy the front
end of the head, and are sepa-
rated from one another by the
nasal septum. ach capsule is
a fairly roomy cavity, usually
provided with a large projecting
fold, the turbinal; the ex-
ternal nares are small, the
imternal usually open far for-
wards in the mouth, and are
often prolonged into a groove
on the roof; in Crocodiles,
however, this groove, by the
curving over and concrescence
of its edges, has become a tube,
opening far back in the mouth
(Fig. 346), and covered below Fig. 348. Brain of a Lizard from above
by portions at the maxilla, te = from Pe aS cr gee ae
cerebrum, mi optic lobes, cerebellum,

at alga AL Set hyn, ty oda eek ob Ga wid brata Soy

ptic rgans. The : :

vee : be seen the lower portion of the epiphysis.—
‘sclerotic is usually partly carti- After T. Jeffery Parker.

laginous, and in Lacertilia and

Chelonia, though not in Ophidia and Crocodilia, it exhibits a
ring of thin, bony plates, the sclerotic ring, surrounding the
cornea. In Lizards, a process, projecting freely into the vitreous
humour, and corresponding to the pecten of Birds, arises from

 

Fig. 344. A Vertical
section of the eye and
eyelids of a common
Lizard, B the same of a
Snake; both diagram-
matic. h cornea, o upper,
uw lower eyelid, o bulb of the
seye (in outline).—Orig.

 

‘the inner wall of the optic bulb, at the entrance of the optic nerve ;
in others it is absent or rudimentary. An upper and a lower
eyelid are present, of which the former is only slightly movable,
whilst the latter can be moved across the eye as in Amphibia. The
lower lid is often somewhat transparent centrally (e.g., in the common
416 Vertebrata.

Lacerta); in certain other Lacertilians quite transparent. In the
Ascalabotida, a few other Lizards, and in the Snakes, it is
not only transparent, but remains drawn over the eye, with its upper
edge fixed to the upper eyelid, so that there is an enclosed space in front
of the eye ; these animals seem to be unable to “shut” the eye, the
transparent lid looking like a cornea, but as a matter of fact it is.
always closed. There is usually a nictitating membrane.
Besides a lachrymal gland, a lachrymal duct and a Harderian gland
are also present. For the parietal eye, see p. 337.

Auditory organ. The cochlea of most Reptilia is as little
developed as in Fish and Amphibia, and is only a small evagination ;
in the Crocodilia, however, it reaches a much higher stage of devel-
opment, as a fairly large, closed tube. The outer wall of the skull,
which lies above the cochlea, is pierced in the Reptilia by an opening,
covered by connective tissue, the fenestra rotunda; above the
sacculus there is, as in Amphibia, a fenestra ovalis, which is
closed by a process of the pro-otic. There is usually a tympanic
cavity, closed towards the surface bya tympanic membrane,*
which lies in a shallow groove, not, as in Amphibia, at the level of
the rest of the skin. The tympanic cavity in the Lacertilia, as in the
Amphibia, communicates directly with the mouth by a wide aperture ;
in the Chelonia and Crocodilia, on the other hand, by a narrow
canal, the Eustachian tube. The Crocodiles are peculiar in
that the tympanic cavity is connected with air spaces in the
wall of the skull, and that the two Hustachian canals open by a
common aperture into the mouth, not far behind the internal nares.
In the Ophidia and some Lacertilia tympanic cavity and membrane
are entirely absent. There is a columella, like that of the
Amphibia; its flattened portion fits into the fenestra ovalis, and
the other end is attached to the tympanum, when there is one. An
“external ear” occurs, in the Crocodilia, as a flap or fold of
the skin covering the drum externally.

Teeth occur, in most Reptiles, on premaxilla, maxilla, and
mandible ; in Snakes (in which the premaxilla is usually edentulous)
and in Lizards, they are often present on the palatine and pterygoid
also, whilst they are entirely absent from the Chelonia. They are
usually attached to the bones by osseous tissue; only in the Crocodilia
are they implanted in sockets. Replacement teeth are formed con-
tinuously throughout life; the old ones fall out; the osseous
substance which attached them to the bones and the lower portions
of the teeth themselves, being reabsorbed. The teeth are usually
simple, most often conical; sometimes distally compressed and
pointed ; sometimes they are knob-like. Usually, all the teeth in one

 

* A tympanic cavity is present in Chameleons, and is closed externally by an
undifferentiated portion of skin. A specially developed tympanum is wanting.
Class 4. Reptilia. 417

animal are identical in form (homodont). (For the poison teeth of
snakes, see p. 423, and Fig. 348). The tongue, which is attached
behind free in front, is very varied in form; in the Crocodilia and
Chelonia, it is but slightly movable, with a short tip, and incapable
of protrusion; whilst in the Lacertilia, it has generally a long, often
very long, and bifid, tip; in the Ophidia, too, the tongue is long,
narrow, and bifid, and can be stretched far out of the mouth; here,
and in one division of the Lacertilia also, it can be withdrawn into
a sheath on the floor of the mouth. (For the peculiar tongue of
the Chameleons, see p. 422). The csophagus is long, and
capable of considerable distension. The stomach of Crocodiles
is very muscular, provided on each side with a tendinous disc, to
which the muscle cells are attached ; it suggests the gizzard of Birds.
The small intestine varies in length, the rectum is short.
Respiratory organs. The trachea of Reptilia is long,
and its wall is strengthened with numerous cartilaginous rings. The

 

 

 

Fig. 345.—Diagrams of various lungs. A Triton, B Frog or small Lizard, ( Tortoise,
D Turtle. 6b bronchus, h cavity of the lung, a evagination of the lung. Connective tissue
dotted.— Orig.

anterior portion, the larynx, is furnished with special pieces of

cartilage, and in some Lacertilia (Geckos, Chameleons), as well as in

the Crocodilia, possesses a pair of vocal cords which do not occur in

others. The entrance from the mouth is through a longitudinal slit

behind the tongue. At the hinder end, the trachea divides into two
EE

«
418 Vertebrata.

shorter or longer bronchi,* one for each lung. The lungs are of
very diverse forms, which may, however, all be referred to a common
type. The simplest occurs in many small Lizards (e.g., Lacerta) ;
here, just as in the Anura, there is a capacious sac, with numerous
short (and very closely connected) evaginations, which are again
provided with still smaller outgrowths. In the Tortoises
(Emys), the posterior region of the lung is similar to that of
Lizards, but the anterior larger portion has been drawn out to a
narrow tube with a number of evaginations, some very large and
deep, which are again provided with smaller pits, all being bound
together by connective tissue. In Turtles (Chelonia), the posterior
portion of the lung has also become narrow, and is furnished with
deep outgrowths ; in the anterior region, there are transverse rods of
cartilage in the walls of the bronchi, not in the sacs. The arrange-
ments in the Crocodilia are similar, but the rods of cartilage have
become rings like those of the trachea.t Amongst special conditions,
it may be mentioned that the lungs of the elongate, apodous
Lizards (eg., the Blind-worm), are of unequal length, the right
being the longer. In Snakes, too, the right lung is the larger; as

 

Fig. 346. Head and neck of an Alligator; posterior portion cut in longitudinal
section. /f transverse fold behind the tongue, g brain (only indicated), | trachea (longitudinal
section), l’ its opening, » left external naris, n’ left internal naris (the posterior portion of
the nasal tube is cut into), s skull, sp esophagus (opened), wu lower jaw, « tongue.—Orig.

 

* Sometimes (Snakes, some Lizards) the bronchi are so short, that the two lungs
open directly into the hinder end of the trachea.

+ The lungs of some large Lizards are like those of the Chelonia and Crocodilia ;
others occupy an intermediate position. Among the Reptiles, the size of the
animal has a direct influence on the structure of the lung; the most complicated
structure (i.e., the relatively largest respiratory surface) is shown by the largest forms,
of., General Part, p. 28.
Class 4. Reptilia. 419
a rule the left is rudimentary or absent. The Snakes are also peculiar,
in that, whilst the anterior portion of the lung is like that of a Lizard’s ;
posteriorly, it is simply a smooth unfolded sac which receives ‘blood,
not from the pulmonary, but from one of the systemic arteries ;
this portion is entirely without respiratory significance. The
Chameleons (and some other Lacertilia) are characterised by
the possession of thin-walled, finger-like sacs extending from the
lungs between the viscera. The animal can fill these with air so
that the size of the body is noticeably increased. Inspiration,
in the majority of cases, is effected as follows: the capacity of the
trunk is increased by movements of the ribs, so that the air in
the elastic lungs is rarified, and external air rushes in through the
nares to equalise the pressure; expiration is brought about
by reversed movements of the ribs. In the Chelonia, where the
ribs are immovable, inspiration results from the contraction of a
special diaphragm-like muscle in the
tbody-cavity (cf., the Mammalia).

In the Crocodilia the inner nares open, as
already noticed, far back in the mouth. On
the back of the tongue (Fig. 346) there is
‘a projecting, stiff, transverse fold, which, when
the mouth is opened, lies against the palate
and separates a posterior cavity into which the
internal nares open above, the trachea below.
‘In consequence of this arrangement the animal
can lie in the water with its mouth open wait
ing for prey, and if only the snout with the
external nares is above the surface can breathe
quietly.

In consequence of the development
of a neck, the heart in Reptiles is
further from the head than in Amphibia
and Fish. The atrium is separated
into a larger right, and a smaller left,
auricle, of which the latter receives the
blood from the lungs, the former, that
from the rest of the body. The ventricle

 

Fig. 347.

Diagram of the

shows only the beginning of a division
into two, for the septum is still in-
complete; in the Crocodilia alone the
right and left ventricles are completely
separated, and connected only with the
right and left auricles respectively, so
that the arterial pulmonary, and the
venous systemic blood are entirely

heart and arterial arches of a

Crocodile. a right, a’ left
auricle. v and »’ vight and left
ventricles, 1, 1’ cavotids (arterial
arch 1); 2, 2’ right and left aortic
arches (arterial arch 2); ¢ thin part
of 2’, after giving off the vessel m
to the intestine ; 4, 4’ pulmonary
arteries (arterial arch 4), ao aorta.
—Orig.

separated within the heart. The conus is either rudimentary or
absent, so that the arterial trunk springs direct from the ventricle.

EE 2
420 Vertebrata.

It is not, however, single, as in the Pisces and some Amphibia ;
but is divided into three vessels derived from three pairs of
arterial arches, viz., 1, 2, and 4. The first of these vessels
forms the carotids (arterial arch 1) and the right aortic arch (the
right arch of the second pair); the second is prolonged into the
left aortic arch (the left arch of the second pair), whilst the third
forms the pulmonary arteries (arterial arch 4). At the origin of
each vessel there is a transverse row of valves. The carotids and
the right aortic arch arise from the left ventricle and carry arterial
blood, whilst the pulmonaries and the left aortic arch are given
off from the right ventricle and carry venous blood. In conse-
quence of this arrangement, the head is supplied with pure blood,
whilst the aorta carries mixed blood, for it is formed of the union of
two arches, of which one contains arterial, the other venous, blood.

In the Crocodilia, thelarger portion of venous blood from the left aortic arch goes
direct to the alimentary canal, by a vessel (m) which it gives off before it unites
with the right aortic arch, so that in the aorta arterial blood preponderates.* In
other Reptiles, in which the ventricular septum is quite imperfect, the blood
is mixed within the heart itself, but here various arrangements prevent the:
mixing from being as complete as might be expected. The whole mechanism.
is too complicated to receive more detailed consideration here.

The kidneys are somewhat elongate, lobulated organs, lying
posteriorly in the body-cavity ; the urinary tubules have no open
funnels as in the Amphibia. The ureters discharge separately into
the cloaca, not into the urinary bladder. There is a urinary bladder
in Lacertilia and Chelonia, not in Ophidia or Crocodilia; it is an
evagination of the ventral wall of the cloacat; the openings of the
ureters are not far from the opening of the bladder.

The two ovaries are racemose when ripe in consequence of the
large size of the ova; the oviducts (Miiller’s ducts) are of the ordinary
type, and open separately into the cloaca. In Snakes, in correspond-
ence with the elongation of the body, the ovaries lie one in front
of the other. The testis is connected, by an epididymis of fine
tubules, with a sperm duct which opens into the cloaca. Copu-
latory organs of two kinds are met with. In the Lacertilia.
and Ophidia there is a pair of these organs; on each side,
quite close to the anus, there is an opening leading into a sac or
tube, which extends back below the skin of the tail, and is to be
regarded as an invagination of the skin; this sac can be everted, and
then displays on its surface a spiral groove, along which the sperm
can travel when the organ (which is often provided with spines or

 

* The right arterial arch (and the carotids) communicates with the left arterial arch
by means of an opening in the septum between the two vascular trunks; mixing of.
the blood, however, occurs only to a very limited extent at this spot.

4+ In the Chelonia, besides the unpaired urinary bladder, a pair of similar sacs of.
unknown significance opens into the cloaca.
Class 4. Reptilia. 421

folds) is inserted into the cloaca of the female ; the sac is withdrawn by
a muscle attached to its end. In the Crocodilia and Chelonia,
the penis is, on the other hand, an unpaired, solid, linguiform organ
which is attached to the ventral wall of the cloaca, and can be
protruded from the anus ; it bas a seminal groove on its upper surface.

The eggs of Reptiles are relatively large. During their passage
through the cloaca, they are surrounded by albumen and a calcareous
shell, which in Lacertilia and Ophidia, is usually leathery and tough,
in Crocodilia and most Chelonia hard and brittle, like a Bird’s egg-
shell. ‘The shell is usually oval, occasionally round, the latter in
most of the Chelonia. The eggs of not a few Ophidia and some
Lacertilia remain so long in the oviducts, that the young ones are
born alive. The eggs of such forms are usually provided with shells
which are thrown off at birth. Segmentation is partial, food yolk
abundant; the embryo is surrounded by embryonic membranes
(see p. 353). The animal, when newly hatched, is in most respects
like the adult.

In the fully-developed embryos of Ophidia and Lacertilia, there is a median
tooth on the upper jaw (a true tooth) which is used to cut through the egg-shell.
The embryos of Crocodilia and Chelonia have, at the tip of the snout, a wart-
like, very cornified projection, with which to break the shell.

The Reptilia are for the most part terrestrial; but a few
are amphibious, for they live partly in the water (sea or freshwater),
partly on land; most of them prey on other animals (Insects,
Vertebrata, etc.). They are numerous in the tropics, occur sparingly
in temperate regions, and are absent from colder zones. At earlier
periods of the earth’s history,in Mesozoic times, this division
was much better represented, and, in part, by much larger forms
than at the present time.

Synopsis oF Existing Orpers or ReEpribia.

{1.Lacertilia. Usually with limbs. Scales ven-
Movable quadrate. Anus | trally. Rami of lower jaw firmly anchylosed.
atransverseslit. Paired { 2. Ophidia. Without limbs. Splints ventrally.
copulatory organs. | Rami of lower jaw connected by an eiastic ligu-
ment.

Quadrate immovable. (3. Chelonia. Hdentulous. Continuous bony
| ease round the body.

Anus not a transverse ee ‘
slit. Penis unpaired. A. . oe ius ae Teeth in sockets. Heart with

Order 1. Lacertilia (Lizards).

For the characters of the Lacertilia, compare the above summary,
and the general description of the Reptilia. Of the numerous forms,
a few examples are given below.
422 Vertebrata.

1. Lizards (Lacerta) have a long round tail; well-developed limbs; small
dorsal scales, larger ones ventrally, usually arranged in longitudinal rows;
tongue well-developed and bifid. In England, the two very similar species, the
Sand Lizard (ZL. agilis) andthe CommonLizar4d (L. vivipara) are abundant.
Allied are the Varanids (Varanus), large, tropical, old-world forms with
long bifid tongue.

2. Iguanas (Iguanidz), Lacertilia with small scales; and a thick, slightly-
bifid tongue; many have spines, ridges, and so forth on the skin. They fall
into two natural groups, belonging to the Old and the New World; the former
acrodont (7.¢., with teeth fused to the edge of the jaw), the latter pleuro-
dont (teeth on the inner side of the jaw, Fig. 281). Within both groups, there are
elongate, long-legged, long-tailed forms (Tree Iguanas), and bulky, flat,
short-tailed forms (Ground Iguanas); between these, there is no sharp
distinction, as there are many intermediate forms. A peculiar genus of
small tree Iguanas, the Flying Lizards or Dragons (Draco volans),
have the false ribs not in the body-wall, but lying turned outwards, to form on
either side supports for a large fold of the skin, which acts as a patagium.
East Indies.

3. The Blind-worm (Anguis fragilis), an apodous Lizard, with long tail
and movable eyelids; viviparous; abundant in England. It belongs to the
family of the Skinks (Scincoidei), which are characterised by smooth, flattened
scales, and a short, flat tongue; within this family, there are forms with well-
developed limbs, and a relatively short body ; forms with more or less degenerate
limbs and a longer body; and lastly, apodous species like the Blind-worm. The
other species belong to warmer countries; some occurring on the coasts of the
Mediterranean.

4. Chameleons (Chamzleo) constitute a very peculiar group of Lizards.
The slit between the eyelids is very narrow, the latter almost entirely cover the eye-
ball, to which they are attached, and with which they move; the tongue, which
can be withdrawn into a sheath, is club-like, of considerable length, and can be
projected some way from the mouth; the fingers or toes of each foot have grown
together into two bundles, each consisting of two or three digits, which are united
almost to the tip, but separated from the other bundle down to the tarsus; the
two bundles are s: turned that they work together like the limbs of a
pair of tongs, and may be used for seizing branches; body compressed ; tail
curled up; scales very small; the power of the Chameleons to change their
colour is very well known: in warmer countries (especially Africa) ; one species
in Andalusia.

5. The Geckos (Ascalabote) are characterised by the presence of suckers
on the lower side of the toes, and of eyelids like those of Snakes (see p. 415) ;
usually flattened animals, with compressed scales; in warm countries (even in
S. Europe).

6. Ringed Lizards (genus Amphisbena, etc.), short-tailed, elongate,
cylindrical forms, with very small eyes; usually apodous (or with only small
fore limbs) ; scales quadrangular, not imbricating, arranged in transverse rings;
mode of life like that of the Ccecilias; in warm countries (one species in
S. Europe).

Order 2. Ophidia. (Snakes.)

Snakes, which are nearly related to Lizards, are characterised by
the absence of limbs (occasionally there are rudiments of the hind
ones); the structure of the eyelids already mentioned (p. 415) ;
Class 4. Reptilia. Order 2. Ophidia. 423

by the absence of a tympanum and tympanic cavity; the very
long body, the relatively short tail; the broad scutes covering the
ventral surface ; the connection of the mandibular rami by an elastic
ligament; the great mobility of the quadrate and the whole jaw
apparatus ; and by the long, bifid tongue. They are distinguished
from apodous Lizards by the possession of the elastic ligament,

 

Fig. 348. A Poison tooth of a Crotalus, seen from in front and partly from the
outside; B the same tooth cut through longitudinally; C Poison tooth of Naja tri-
pudians, seen in similar view ; D transverre section of the same; # Transverse section of
the tooth of a Crotalus. jf groove, g poison canal, o upper, o’ lower opening of the poison
canal, p pulp cavity.—Orig.

by the absence of sternum and shoulder girdle (of these parts there
are at least rudiments in the Lizards), and by the rudimentary hyoid.

On account of the power of widening the buccal cavity, dependent
on the great mobility of jaws and palate, and the absence of a
sternum, the Snakes are able to take in very large prey; they feed
at long intervals (as much as several months). Some snakes (Protero-
glypha and Solenoglypha) are provided with large poison teeth,
with a deep groove on the front side; the edges of the groove may be.
closed or even fused, but it is open at the apex of the tooth. Only
one of these teeth is present at a time, anteriorly, in the maxilla of
either side, and the aperture leading into its canal is connected at the
424 Vertebrata.

base with a poison gland* behind the head, which is to be
regarded as a specially developed buccal gland. In the mucous
membrane of the mouth, behind the poison fang, there are several
replacement teeth at various stages
of development. When the tooth is
not in use it is covered by a fold of
the mucous membrane ; it is brought
forward by a movement of the
maxilla, with which it is immovably
connected. In the Vipers the maxilla
is very short and edentulous, except
for the poison fangs ; in the Protero-
Fig. 349. Poison gland and glypha it bears several other small,

poison fang of a Snake; dia- 1 n on uw nak
grammatic. k gland, g duct of the e ne teeth, In one BYSEP ak S see

same, ka poison canal,o upper,o’ lower One or more of the posterior
opening.— Orig. maxillary teeth is provided with an
open groove on the anterior side:
grooved teeth. It has been stated that these teeth (always ?)
are likewise connected with poison glands, and that small animals
die soon after being bitten by them.
A few examples of this large group are given below.

I. Giant snakes (Peropoda) exhibit rudiments of the hind limbs in the
form of a small claw-like process on either side of the anus. Teeth simple.
Large snakes belong here: Python (up to about 10 m. long), several species in
Asia and Africa; the females incubate their eggs (the warmth of the body
while brooding considerably exceeds that of the environment): Boa constrictor,
in South America, up to about 6 m.

2. The Colubride, like those which follow are destitute of posterior
appendages; teeth simple. In Britain, the Ringed Snakes (Tropidonotus
natriz), easily recognised by two large yellow patches on the back of the head:
AAsculapius’ Snake (C. Mseulapii) is probably the species venerated by
the ancient Romans. Numerous forms in warm countries.

3. The Opisthoglypha possess in the posterior portion of the maxilla one or
several grooved teeth. The Whip-snakes (Dryophis, etc.), a group indigenous
to the Tropics; distinguished by their extraordinarily long, thin body and pointed
head; they live in trees.

4. The Proteroglypha are venomous snakes, which have, anteriorly, in the
maxilla a poison gland with a fine groove on the front side (ef. Fig. 348 C—D),
and behind this, small simple teeth.

a. The Cobra (Naja tripudians) can spread out the skin behind the head
into a wide hood, for the anterior ribs are turned outwards; a pair of spectacles
is represented on this hood; 2 m. long; India. The Coral snake (Elaps) is
ringed with black and red; small; in South America. Several other genera
in warm countries.

b. The Sea Snakes (genus Hydrophis, etc.), specially characterised by
the very compressed tail and the very small scale-like ventral splints; numerous

 

 

* The poison gland opens quite freely on the wall of the mouth, as does the upper
aperture of the poison fang; the two apertures, however, lie close together, with the
edge of that of the gland round the opening in the tooth, so that the poison cannot
flow into the mouth (ef. Fig. 349).
Class 4. Reptilia.

Order 2. Ophidia. 425

species in the Indian and Pacific Oceans; usually small (rarely longer than the
Ringed Snake, often smaller); their bite is dangerous.

5. The Solenoglypha or Vipers.

The large poison fang is the only tooth in

the maxilla, it has no groove anteriorly; the head is usually broad behind, and
sharply marked off from the body.
a. Common Viper or Adder (Vipera berus), with a zig-zag line

down the back; viviparous;
abundant in Hngland, _ es-
pecially upon sandy heaths.
The somewhat larger Sand-
viper (Vipera ammodytes),
with upwardly directed pro-
eess on the snout, lives on
the Mediterranean coasts, in
Austria, and in South Bavaria,

b. The Pit Vipers
(Crotalide) are characterised
by the possession of a deep
pit on either side between the
eye and the naris. To this
group belong most of the
dangerous snakes occurring in
warm countries. The Rattle-
shake (Crotalus) differs from
the rest, in possessing at the

 

Fig. 350. Tail end of a Crotalus with eleven
caps (1 the oldest, 11 the youngest). B the same
cut through longitudinally, v vertebral column,
v’ several fused vertebra, forming the last joint of the
vertebral column (the surrounding soft parts dotted) ;
the caps in section indicated by a thick line. As a
comparison of the two figures shows, only the anterior
portion of each cap, with the exception of the oldest,
projects as an arched ring, the rest being covered by

tail end, several loose rattling, the next older cap.—After Garman.

horny caps, fitting into one

another, the remains of cast skins (see Fig. 350). Several species (to over 2 m.)
in North and South America. Species of Trigonocephalus, usually smaller, but
very dangerous, live in India and America.

Order 3. Chelonia (/estudinata).

The edentulous jaws are covered by a horny sheath with a sharp
edge. Large dermal plates are present, which usually fit into
ove another at the edges, so as to form a continuous bony shell
round that part of the body. There is a large opening in front for
the head and fore limbs, and behind for the tail and hind limbs.
Dorsally, there are three longitudinal rows of bony plates, of which
the middle row is connected with the vertebre (vertebral plates),
whilst the two others are fused with the ribs of each side, one for
each rib. Besides these three rows there is, externally, a series of
small marginal plates. Ventrally, there are two rows; there is
an anterior unpaired piece, probably corresponding to the epi-
sternum of other Reptiles, and in front of this a pair, which may
represent the clavicles. These bony plates do not form so complete
a shell in all Chelonians; in the Turtles, for instance, the plates do
not fit close together, but large portions of unossified leathery skin
are left between their edges. The regions in which the dermal
armour lies are usually covered, externally, by large horny shields
426 Vertebrata.

(tortoiseshell), separated by grooves; their boundaries do not corre-
spond with those of the bony plates, although the arrangement is
similar. The rest of the body is covered by small scutes ; small bony
plates may develop in some scales, as in certain Lacertilia.

The Chelonians feed partly on plants, partly on animals. They
are dull, sluggish creatures, terrestrial, freshwater, or marine. Many
are able to withdraw head and limbs within the edge of the shell.

1. Mud Turtles (Emydz), mostly flattened animals, with webbed toes ;
live in freshwater, but many can also walk about on land. More exclusively
aquatic is the Freshwater Tortoise (genus Trionyz, etc.), with large
swimming feet (each with three claws), shell without horny plates; ferocious
animals; Asia, Africa, North America.

2. Tortoises (Testudinide), closely allied to the Mud Turtles; differing
ehiefly in the much arched carapace, and the very short feet, in which the toes
have grown together and which possess short claws (club-footed). The Grecian
Tortoise (Testudo Greca) inhabits South Europe.

3. Turtles (Cheloniz) have a flattened carapace and immovably connected
toes without claws, or with rudiments only; the fore limbs much larger than the
hind, forming a strong fin-like steering apparatus. They attain a consider-
able size; live in the sea, but the eggs are laid on land, buried in the sand. One
species in the Mediterranean.

cr
So

Order 4. Crocodilia. (Crocodiles).

This order differs from other living Reptiles, and approaches Birds
and Mammals in many respects: as in the divided ventricle, the
structure of the brain and the cochlea, and also in the thecodont
dentition (teeth in sockets). The Crocodiles have large heads with
the nares on the upper side of the snout, webs between the hind
toes, and a long compressed swimming tail; claws present only on
the three inner toes of each foot; five toes on the forefeet, four
on the hind. In the skin there are numerous bony plates (especially
on the dorsal side). The anus is a longitudinal slit. For the way
they breathe with the mouth open in the water, and’ for other
peculiarities, see above.

Crocodiles, which may attain a length of about ten metres, live in
warm countries in fresh water, rarely on the sea-shore, but they also
frequent the land; they are rapacious beasts and carrion feeders. The
eggs are laid on land, either buried in earth or among decaying plants,
etc.; the female guards them, and sometimes also the young ones.

The Crocodilia of the present day may be divided into three groups; (1)
Alligators (Alligator), with short snout and imperfectly webbed hind feet ; the
fourth tooth of the lower jaw bites into a cavity in the upper jaw; America
(one species in Hast Asia): (2) True Crocodiles (Crocodilus), with long snout
and complete webbing between the hind toes; the fourth tooth of the lower jaw
bites into a notch on the side of the upper jaw; in both the Old and the New
World: (3) Gavialide (Rkamphostoma), with very long, slender snout and
complete webs; the fourth tooth of the lower jaw bites into a notch; India.
Class 4. Reptilia. Order 4. Crocodilia. 427

For the rest, these three groups are connected by intermediate forms; there are-
species of Crocodiles which approach the Alligators, and a Gavial which forms a
connecting link with the Crocodiles.

The oldest Crocodiles known, from the Triassic (Belodon and others) are-
specially characterised by their resemblance to Lacertilia and Chelonia with

 

 

 

Fig. 351. A Skull of a Gavial, Bof a Teleosaurus. n’ internal nares, p palatine, v
pterygoid. ;

respect to the position of the internal nares; the palatines and pterygoids.
do not form a canal, but the internal nares open much farther forward than in
those now living. The Crocodiles from the Jurassic, and some of those from the
Cretaceous formations (Teleosaurus [Fig. 351 B], etc.) approach the extant
forms in this respect; for the palatines, but not the pterygoids, are connected
to form a canal, and the nares are thus moved much further back. All these:
older forms differ also from those of to-day in the possession of biconcave
vertebre. On the other hand the Tertiary and some of the Cretaceous forms.
exactly resemble those now existing; the pterygoids take part in the formation
of the nasal canal, and the centra are procelous. The Crocodiles of different
periods afford a very interesting series.

 

Whilst many extinct Reptiles, eg., the Crocodiles just mentioned,
as well as many others, are allied to the orders of the present day, there are
also many forms constituting orders which are without living representatives.
Several of these groups are of considerable interest, and the most important
will now be briefly considered.

The Ichthyosaurians occupy a position among the Reptiles similar to that
of the Whales among Mammals, and they are very suggestive of this group. The

 

Fig. 352. An Ichthyosaurian.

head, especially the snout, is of huge size. the neck uncommonly short, the
tail very long and powerful; both pairs of limbs are formed like the fins of a
Whale: they are short, broad plates, all the bones of which are immovably
connected and much shortened; the digits, of which there were often more than
five on each foot, were enclosed in a common skin, and without claws, and the
number of joints to each digit was very great, though each joint was very
428 Vertebrata.

short. Among other characters, it may be mentioned, that the sclerotic of
the large eye was provided with a ring of bony plates; the vertebral centra
were very large and strongly biconcave, the pelvis was not connected with the
vertebral column, the hind limbs weaker than the fore, the teeth in a continuous
furrow in the edge of the jaw, a character which also occurs in several other
animals (e.g., certain Whales). The Ichthyosaurians were marine, some of very
great size (10m. and more); they lived in Triassic, Jurassic, and Cretaceous
times.

The Plesiosaurians, another extinct type of marine Reptile, are in some
respects like the Ichthyosaurians, in others very different from them. The
head is small, sometimes even very small; the neck, on the contrary, is long ;
longest in those with the smallest head. The compressed piscine form of body
which obtains in the Ichthyosaurians is absent here. Fore and hind limbs,

 

Fig. 353. A Plesiosaurian.

as in the latter, are clawless, and like the fins of a Whale; they are, however,
usually larger than in the Ichthyosaurians, the bones are not so much shortened,
and the number of digits does not exceed five. They attain a length equal to
that of the Ichthyosaurians. Triassic, Jurassic, Cretaceous.

    

Fig. 354. A Pterodactyle,
from Zittel.

restored.—Modified

  

The Pterodactyles (Pterosauria: genera Ptero-
dactylus, Ramphorhynchus,  etc.), were specially
characterised by the modification of the fore limbs
as actual organs of flight. Hach fore limb had four
digits, of which the three inner (Nos. 1, 2, 3), were
not particularly developed, whilst the fourth, next
to the middle finger, was much elongated, and formed
the edge of the large patagium; this membrane,
of which several impressions have been found, was
stretched from that finger to the body. The head,
especially the anterior part, is of considerable size ;
in the sclerotic there was a bony ring; teeth are
usually present and placed in sockets; the sternum
is provided with a keel, possibly for the attachment
of the pectoral muscles, which moved the wings; the
Class 4. Reptilia. 4.29)

bones are pneumatic (as in Birds). The Pterodactyles, which occupy among
Reptiles a position comparable with that of Bats among Mammals, were for
the most part small animals, and lived in Jurassic and Cretaceous times.

coracoid, f fibula,

5 fifth finger, 4 fourth toe, co

f
a)

its posterior process, r cervical ribs, ra radius, sc scapula,

 

1 pollex,

il ilium, ts ischium, mt metatarsus, n nares, o orbit, p pubis, p’

st sternum, u ulna.—Modified from Dollo,

 

 

 

 

Fig. 355. Igwanodon, one of the bird-like Dinosaurians.

 

The Dinosaurians (Dinosauria) are a group of Reptiles consisting of
numerous forms, which are of the greatest interest on account of their affording
a link between Reptiles and Birds. Within this division there are forms
which stand tolerably near to other Reptiles, and again, forms which more closely
approach Birds. The Dinosaurians were terrestrial anima!s, chiefly of consider-.
430 Vertebrata.

able, some of colossal size, bigger than the largest extant terrestrial Mammals
(in one species the thigh-bone is 2—3 m. long, and very thick); though small
forms also occur. The limbs are powerful; in some, fore and hind legs are about
equal in length, but generally the former are smaller, sometimes even much
-feebler than the hind limbs, and many Dinosaurians moved almost entirely upon
the latter, possibly springing along; among those with stronger hind limbs some
were digitigrade, whilst other Reptiles are plantigrade; the tail is long
and powerful. The pelvis is very remarkable; the ilia are much prolonged
in front of the acetabulum, agreeing with Birds not with Reptiles, and in those
Dinosaurians which have small fore limbs (e.g., Iguanodon, Fig. 355), the pubis
-also is very peculiar in form: a long thin process (p') arises from its base, and

 

Fig. 356. A—B fore and hind limbs of one of the Dinosaurians, which are some
way from birds (Morosaurus grandis). C—D Do. of w bird-like Dinosaur (Camptonotus
dispar). a tarsus, ¢ coracoid, d toes, d’ fingers, f femur, g fibula, h humerus,  ilium,
k ischium, m metatarsus, m’ metacarpus, r radius, s scapula, sk pubis, t tibia, wu ulna.—
After Marsh.

reaches back, in a direction almost exactly opposite to that of the main branch,
lying close against, and parallel to the ischium, which is often long and thin.
There is a larger number of sacral vertebre than in other Reptiles (four or more)
and these are fused. Among other characters, it may be mentioned, that the
proximal series of tarsals is in many cases immovably attached to the tibia (or
fused with it); the tibia has a long projecting ridge on its front face. The
forms of the femur and tibia are very different from those of other Reptiles
and very birdlike. (See also the remarks made below upon avian skeletons.)
The Dinosaurians lived in Triassic, Jurassic, and Cretaceous times.

Class 5. Aves (Birds).

The most striking peculiarity of the avian body lies in the
structure of the limbs, the hind are exclusively developed for
walking, or hopping (sometimes, also, for swimming), whilst the fore
Class 5. Aves. 431

limbs are never adapted for terrestrial Idcomotion, but, with few
exceptions, for flight. The body is usually borne upon the hind
limbs in a semi-erect position; it rests only upon the toes, not on
the very slender metatarsus. The

neck is of considerable length and st

very movable, the trunk is short;
the tail in all existing Birds is

short, but the large steering preven LF lt’
feathers* give it an appearance
of greater length. The face portion, yee
the beak, is peculiarly modified ;
it is usually elongate, and covered
with a horny sheath.

The skin is almost entirely
covered with feathers, com-
plicated appendages consisting of s
cornified epidermis cells. They
arise as dermal papille but soon
sink into sac-like pits in the skin,
the feather follicles; the feather
develops from the epidermal layer
covering the papilla.t Feathers
exhibit a great diversity of form,
The contour feathers (penne)
are firm, the distal parts at least ea ;

: 7 * Fig. 357. Portion of a feather:
reaching the surface and forming diagrammatic. s shaft, a barb, st bar-
the outer contour of the bird (in bules of an anterior row with hooks, st’
distinction to the down which  Qover the latter and seize thom by means
lies below); they consist of the of the hooks on the edges.—Orig.
following parts: the proximal
portion is a short, cylindrical, hollow quill (calamus) which is
imbedded in the feather-follicle, a more or less deep
dermal pit. The quill is continued into the shaft (rachis) which
consists externally of a hard cuticle, within of a loose horny
mass; and is thinner at the tip. (Quill and shaft together form
the stem [scapus] of the feather.) From the shaft there arises on
each side a series of barbs which are again furnished with
barbules; the barbs and shaft together, are termed the vane
(vextllum). Atthe distal portion of the shaft, and this may form
a larger or smaller portion of the feather, the barbs are stiff and
compressed (their flat surfaces turned towards those of neighbouring

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

* When, in the description of Birds,a long or short tail is mentioned, this
always refers to the length of the steering feathers.

+ It is, however, only the first plumage of young Birds, which develops as papille
on the surface; the later feathers arise as similar papille, which lie, however, at the
base of the follicle of the preceding feathers.
432 Vertebrata.

barbs), and furnished with relatively short barbules, of which, those
on the anterior row, lie obliquely above the posterior row of the
preceding barb. Further, each barbule of the anterior row is
provided with a series of delicate hair-like microscopic appendages,
some of which are curved at their tips, to hook into the hinder row of
the preceding barb; by means of these hooklets, the barbs are
attached together into a continuous lamina. In the proximal

Fig 358.

 

 

 

 

A B c

Fig. 358. Diagrams of various feathers to elucidate the varied development of the
aftershaft; vane only in outline.—Orig.

Fig. 359. A Down of a young Bird, resting upon the tip of the succeeding feather which
is still surrounded by a horny sheath (h). s quill of the down feather. B tip of a contour
feather with some down barbs still attached. Diagrammatic.—Orig.

portion of the vane, the barbs are softer and thinner, the barbules
long and soft, but without hooks; this portion, which is covered by
other feathers, has thus a soft, loose, downy character. At the
junction of quill and shaft, there usually arises from the inner side
of the feather, a smaller, thinner shaft (the aftershaft), which
bears a double row of soft barbs; the after shaft and its barbs may
be termed the accessory vane. -This appendage is sometimes well-
developed (e.g., Fowls, Fig. 358 A); usually, however, it is somewhat
feeble (B); its shaft is often rudimentary, so that the accessory
vane is only represented by a tuft of barbs arising close together (C).
Of the contour feathers, the flight and steering feathers
(remiges, rectrices) must be noticed, the strongest, stiffest, usually
Class 5. Aves. 433

longest feathers on the body; as a rule, they have no aftershafts,
and the down-like proximal portion is very small, or is absent ;
they lie in very deep feather-follicles, the remiges in a row along
the outer edge of the fore-arm and hand, the rectrices on the tail.

In the extinct Archxopteryx, the rectrices were arranged in two longi-
tudinal rows, one on either side of the long tail. In some existing Birds
also, they occur in two distinct oblique rows on the much shortened tail; in
others, this part is so very short that
the longitudinal series form a curved A B
transverse row.

The down feathers (plume),
whichare generally completely covered
by the contour feathers, differ from
them, in that the whole vexillum is
similar to the proximal portion in the
latter; they consist of soft barbs,
which are often very long and beset
with long barbules without hooks, the
shaft is thin and feeble, often even
quite rudimentary, so that the barbs
arise close together at the distal end
of the quill. There is often an
aftershaft on the down feathers ;
not infrequently it is almost as large
as the main shaft. The down feathers Cc
are usually whitish or grey, whilst Fig. 360. Tail of: A Archeopterya,
the contour feathers vary much in une free mena
colour. The two types described the rectrices. f apertures of feather
pass gradually into each other ; there sane tia, Roane coe
are plume which, in virtue of their matically indicated).—Orig.
strong shafts, etc., approach the
penne, and modified penne which are so loose and soft, or which
possess so small a portion with hooks, that they form a transition to
the plume.

A special form of pluma is the so-called filoplume, a delicate feather
with long thin shaft, in which the barbs are few in number, and at the tip of
the shaft only; they occur in almost all Birds, arising close to the contour
feathers.”

Among peculiarly developed feathers, the following may be mentioned:
ospreys, which grow on certain parts of the head in many Birds and have
no barbs, or only a few, at the base of the shaft; the penne, in the Ratite,
from which hooks are entirely absent, even from the stiff distal barbs, and which,
in the Cassowaries.and Emeus, are further remarkable in that the main and
aftershafts are equally well developed; the remiges of the Cassowary, in
which the long stiff shafts are entirely without barbs.

Newly hatched Birds are, as is well known, usually covered, over larger or
smaller tracts, with down feathers, which generally consist only of a short
quill and a tuft of barbs (Fig. 359 A); occasionally (Ducks, Ostriches), besides
the quill, there is a thin shaft with barbs. These down-feathers are connected »

FF

 

 
434 Vertebrata.

with the distal ends of the succeeding penne, and in many Birds the loose
down quill is split by the developing feather in such a way, that the soft down
barbs remain for some time at the tip of the distal barbs of the adult feather,
looking like a soft external portion (Fig. 359 B). The down is really to be
regarded as a modified distal extremity of the feather to which it is attached.

The contour feathers are not usually distributed regularly over the
whole body, but only over certain regions, the so-called feather
tracts (pteryle), which are regularly, but somewhat differently,
arranged in different birds; there is, for instance, a pteryla along the
mid-dorsal line, another on the outer side of the thigh, etc. The
intermediate tracts (apteria), bear down feathers, which are also
present in the feather tracts, between the penne, or they are entirely
destitute of feathers; the apteria are covered by the contour feathers
of neighbouring tracts. There is an almost equal distribution of
feathers over the whole body in the Ratites (where there is no down
unless the entire plumage be regarded as down feathers), in the
Penguins and a few others.

At regular intervals, usually once a year, all the feathers are
thrown off, and are simultaneously replaced by new ones; this is
known as moulting; in northern Birds it usually takes place in
the course of a few weeks in the autumn. Besides this, a
spring moult often occurs; many Birds indeed, change some
of their feathers in spring, so that there is a partial (rarely a complete)
ecdysis ; in many cases, however, the distinction between winter and
summer plumage is dependent upon this second moult. In some, the
specially coloured edges of many feathers are thrown off in the spring,
and the appearance of the plumage is thus considerably changed ;
in others there is an actual change in the colour of the feathers them-
selves, sometimes to a striking extent. This change of colour is the
more remarkable since the feathers consist exclusively of horny
material, and thus represent a dead portion of the body; the
alterations are probably to be attributed to chemical changes,
independent of the vital functions.

The feather is surrounded, for some time after its tip has projected from the
feather-follicle, by a thin tubular horny sheath, which binds the barbs
together; this sheath is gradually thrown off. The so-called “powder down,”
which is found on some Birds, e.g., the Herons, is composed of feathers which grow
continuously from the feather-follicle (just as the teeth of certain Mammalia grow
from persistent pulps), whilst at the same time their free ends are worn off; the
powder comes from the crumbling away of the horny sheath, which is constantly
renewed at the proximal end.

Attached to the follicles of the larger feathers there are usually small
muscles, by which, for example, the rectrices can be spread out like a fan, the
ordinary penne raised, etc.

Feathers are probably to be regarded as modified reptilian scales ;
indications of this are afforded by their origin from papille. Birds
also possess true scales, exactly like those of the Reptiles, but
occurring only on the hind feet; these scales are of various forms:
Class 5. Aves. 435

knobs, plates, splints. The spur of the Cock and other male
gallinaceous Birds, which is provided with an internal ossification
firmly attached to the metatarsus, is a peculiar, large, conical
scale; this spur is present in the Hen also, but usually as a simple,
wart-like scale.* Claws are present on the toes of the hind foot;
in perching forms they are long, curved, and pointed; in ground
Birds, shorter and thicker. They are often entirely absent from the
fore limbs; but there is frequently a small, often rudimentary,
claw on the pollex, and not seldom there is another such claw on
the second digit, but this is generally rudimentary ; it may sometimes
be present in the young one, and lost later; in the Ostriches of
Africa both claws are of fair size and well developed. In all living
forms the claw of the third finger is wanting; but in Archzopteryx
well-developed claws are present on all three digits, a fact which
can be determined with certainty from the form of the last finger
(Fig. 378). The edges of the jaw and the adjacent parts of the head,
the beak, are usually covered by a thick, hard mass of horn, often
with sharp edges ; occasionally this is partly or entirely replaced by
a thinner and softer horny sheath. An ecdysis of the whole skin
like that of many Reptiles, does not occur in Birds; the stratum
corneum is thrown off in small portions.

Birds usually possess only one pair of integumentary glands, the
large, round uropygial glands, which are situated dorsally on
the short tail; they lie close together, and their apertures are near
each other, generally on a small papilla. Each gland consists of
numerous tubes, opening into a large central cavity, which is
continued into the duct; in some each gland has several ducts.
They secrete a lubricating fluid, which the Birds remove with their
bills for preening their feathers ; they are largest in aquatic species,
and are absent from the Ostriches, some Parrots, and a few others.

The skeleton. The vertebral column may be divided into
regions similar to those of Reptiles. The cervical vertebre
are numerous; there may be as many as twenty, very loosely articu-
lated with each other. The first and second vertebrae, as in the
Reptilia, are developed as atlas and axis (the centrum of the atlas
is fused with that of the axis, etc.). Further, the articular surfaces
of the cervical vertebre are saddle-shaped (each centrum is,
anteriorly, concave from right to left, convex dorsoventrally, and,
posteriorly, convex from right to left, concave dorsoventrally) ; in
Archopteryx and some of the Odontornithes (Ichthyornis) the sur-
faces of the centra were flat or feebly biconcave. For the cervical
ribs see below. The thoracic vertebra, in contradistinction
to the cervicals, are somewhat few in number, and but slightly

 

* On the fore limbs too, similar spurs may also occur, but these must not be
confused with the claws mentioned above.

FRQ2
436 Vertebrata.

movable; sometimes, even, fused together; the articular surfaces of
the centra are usually like those of the cervicals. The last, or the
last two or three thoracics, the lumbar, sacral, and some of the

    
     

QS S77
eee *

Oe ee ee

 

 

——

== = =o

Fig. 361. Skeleton of a raven. 1, 2, 3 first—third fingers, 1’ and 4’ first and fourth
toes, ca carpus, cl clavicle, co coracoid (nearly covered by h), f fibula, h humerus, il ilium,
i’ anterior portion of this, is ischium, mc, and me, first and third metacarpals, mt large
metatarsals (consisting of the fused ‘metatarsals 2—4), mt first metatarsus, 1 nares,
p’ pubis, + cervical ribs, ra radius, sc scapula, st sternum, w ulna.—Orig.

caudal vertebre, are fused. together and furnish an attachment for
the pelvis, whilst_a distinct lumbar region is wanting, and the pelvis
lies immediately behind the rib-bearing region. In all existing Birds
Class 5. Aves. 437

the number of free caudal vertebre® is small, usually from six
to eight ; the terminal bone, however, which is much compressed, is
a fusion of several short vertebra, separate in young Birds. The tail
vertebrae are, like the tail itself, short; though in Archzopteryx
(Fig. 878) there was a long, thin tail of a reptilian type, and con-
sisting of a number of vertebrae, some of which were elongate.
Short ribs are attached to the cervical vertebre, and like
the thoracic ribs have two articular processes; they are fused
in the adult, though separate in young forms. The cervical ribs
gradually increase in length posteriorly, and remain separate
throughout life, thus affording a transition to the thoracic ribs,t
which consist of two bony portions connected at an angle; the ventral
portion is attached to the sternum, and from the hinder edge of the
dorsal part arises a narrow oblique process (processus wncinatus),
which overlaps the next rib; im young Birds it is a separate bone.
The sternum is completely ossified and very large, covering the
greater part (or at least a large part) of the ventral region of the
body. It is almost always furnished with a large projecting keel, to
which some of the muscles of flight are attached, and which is only
absent from certain forms with rudimentary wings (e.g., Ratite) ;
here the sternum itself is smaller than usual. Posteriorly it is often
perforated or notched on either side, the gaps being covered with
connective tissue. There is no episternum.

The skull usually resembles that of the Reptiles very closely ;
among living forms, especially that of the Lizards; there is only
one occipital condyle; the quadrate is reptilian, as also the
conditions of the palatine and pterygoid; the region between
the large orbits is compressed into a perpendicular bony lamina,
the interorbital or orbital plate, which may be partially
membranous. The prominent premaxille, which fuse early to
form a single bone, are characteristic of Birds; they form the entire
edge of the beak, and also send a long branch, almost to the frontals,
between the external nares. The maxilla, on the other hand, are
relatively small, and lie within the posterior portions of the pre-
maxille. The lower end of the large, very movable quadrate
is connected with the beak (the premaxilla and maxilla) by a bony
bridge formed of the pterygoid posteriorly, the palatine anteriorly ;
the pterygoid and palatine are both elongate bones, and in most
Birds they slide upon the thickened lower rim of the orbital plate
mentioned above at their point of contact. From the lower end of
the quadrate to the beak there runs yet another bony bridge, the

 

* The caudal centra are biplanar.

+ Usually, the first vertebra, bearing ribs attached to the sternum, is termed the
first thoracic; the transition from cervicals to thoracies is, however, quite gradual,
and this distinction is artificial. ,
438 Vertebrata.

jugal, external to that already noticed; it is a thin rod of bone,
and is formed posteriorly by the quadratojugal, medianly by
the jugal, and anteriorly by a process of the maxilla; in the
adult these bones are often anchylosed. The beak is attached
above to the rest of the skull, by the upper portion of the. pre-

Fig. 362. Fig. 363.

   

     

i ok
g ¥

 

 

Fig. 362. Skull of a Raven from the ventral
side. g foramen magnum, j jugal, mz maxilla,
ns nasal septum, pa palatine, pt pterygoid, q
quadrate, v vomer.—Orig.

Fig. 363. Diagrammatic figures to illustrate
the movement of the beak in Birds. nm nasal
septum, h posterior membranous portion of this,
o orbit, l quadrate, k jugal, v pterygoid, g palatine.
In A the bill is raised, in B lowered.—Orig.

 

maxilla, and by the nasal, which lies behind the nares; the posterior
portions of these bones (premaxille and nasals) are, however,
flattened, thin, and elastic,* and since the lower part of the nasal
septum is membranous, Birds are able to move the beak up
and down. The movement upwards is effected by the. forward
motion of the lower end of the quadrate, by which the two bony
bridges are pushed forwards, and pressed against the lower, hinder
portion of the beak, so as to send its point upwards ; the movement
downwards, on the other hand, is the result of the retraction of the
quadrate. As for other characters, it may be noticed, that most of
the sutures have disappeared, even in the young animal, owing to
the fusion of the bones; further the cranial-cavity is very large as
compared with that of most Reptiles.

 

*In the Parrots and some others which have a specially movable beak, this bony
mass is interrupted by a narrow strip of connective tissue.
Class 5. Aves. 439

The skull consists of almost the same bones as that of Reptiles (but pre-
and post-frontals, transverse bone, and columella are always wanting). The
vomer is an unpaired bone of varied form, sometimes compressed, sometimes
fairly broad, etc., lying below the hinder portion of the nasal septum, and
connected behind with the palatine, in the movement of which it takes part. The
lachrymal lies at the anterior edge of the orbit, and in many Birds remains
distinct throughout life. The lower jaw consists of several bones on each side,
of which the anterior (dentary), in all living Birds, fuses very early with its fellow
of the other side; in extinct toothed forms (Odontornithes), on the contrary, they
remained separate.

Fig. 364. Fig. 365.

   

SS

Fig. 364. Skull of two days old Chick. a alisphenoid, d
dentary, f frontal, j jugal, | lachrymal, ma maxilla, 1 nasal, na outer
cartilaginous wall of the nasal cavity, o orbital plate, ol ex-, os supra-
occipital, p parietal, pa palatine, pm premaxilla, pt pterygoid, q¢
quadrate, qj quadratojugal, sy squamosal, st ear bones. The parts
which are still cartilaginous are dotted, the membranous portions
shaded.—After K. Parker.

Fig. 365. Hyoid of the Fowl. h hyoid (anterior horn), br first
branchial arch (posterior horn).—After K. Parker.

 

The hy oid consists of an unpaired, partially ossified median rod
(copule), to which is added (not invariably) a pair of very
short anterior cornua, and a pair of long posterior
cornua, the first branchial arch. The median rod is usually
divided into two or three pieces, lying one behind the other.
The cornua are not closely connected with the skull; the posterior
pair bend round the back part of the skull, but in the Woodpeckers,
where the tongue is specially protrusible, they curve up more
anteriorly, even as far forward as the base of the beak.

The shoulder girdle (Fig. 366) consists of the usual elements.
Both scapula and coracoid are completely ossified; the former
is a flat, narrow, sabre-shaped bone, which is generally connected
with the coracoid at an acute or right angle; the coracoid is,
as a rule, rather long and narrow as compared with that of the
Reptiles, but yet very strong; its lower broad end articulates with
the anterior edge of the sternum. In Ratite, and in some Odont-
ornithes, which were also incapable of flight, the two bones lie more
440 Vertebrata.

nearly in a line, and fuse with age; in these forms, the coracoid is
short and broad. The clavicles are two long thin bones, fused
ventrally (in most Birds) to form the merrythought (furcula),
which is attached to the anterior end of the sternal keel, by a
ligament, passing from the: point of fusion. Hach of the other
extremities of the fork is attached to the dorsal end of one of the
coracoids, from which it is otherwise separated by a large fenestra.
In the Ratite and some others, the clavicles are rudimentary or

 

Fig. 366. Sternum and
shoulder girdle of the
Raven, viewed from the
left side. cl clavicle, co cora-
coid, sc scapula, st sternum.—
Orig.

Fig. 367. Manus of a
young Ostrich (Struthio).
a, b carpals which remain
separate, c carpals of distal
row (already united, later to
be fused with the metacarpals),
m, m?, m* first—third meta-
carpals (still distinct), r radius, u ulna, 1a and 1b phalanges
of the pollex, 2a—2c second digits, 3 third digit.—Orig.

Fig. 368. Foot of a young Chick, mt !— first—
third metatarsals (the metatarsals 2—4 are already fused, but there are traces of their
original distinctness), ¢ tibia, ta and ta’ proximinal distal portion of the tarsus.—Orig.

 

absent. The fore limb is usually very long. The ulna is much
more powerful than the radius; the carpus of the adult consists
of two separate bones only.* The manus is veryslim, and never
exhibits more than three fingers with their metacarpals; the fourth and
fifth fingers of Reptiles are absent. Of the three metacarpals,
the first is short, the two others much longer; all three are fused in
the adult, the second and third, however, only at the two ends, not

 

* One of these is the radiale, the other corresponds to the ulnare and intermedium.
The carpals of the distal row are represented by two bones which fuse with the
metacarpus.
Class 5. Aves. 441

for the whole length ; only in Archaeopteryx were they separate. The
pollex has one or two joints, the second digit two or three, the
third only one (rarely two); in Archeopteryx alone, the third
possessed three or perhaps four joints. In Birds which are capable
of flight, the arm when at rest lies along the body with the elbow
backwards; the forearm is directed anteriorly, and les along the
arm, the ulna outwards, and the hand is curved at the wrist, so that
it lies along, and external to, the forearm, with the point backwards,
the inner edge (with the pollex) outwards.

The pelvis closely resembles that of the Dinosaurians, but it is
further specialised (cf., p. 430). The ilium is elongate, and is
fused with a number of vertebra (cf., p. 436); it is connected with
the other two bones at the acetabulum, which lies at its lower edge,
and in the formation of which, all three take part; they are all fused
in the adult. The ischium, a strong bone directed backwards,

-runs almost parallel to the posterior portion of the ihum; in most

 

Fig. 369. Pelvis of a young American Ostrich (Rhea). “1 ilium, is ischium,
1 acetabulum (with large perforation), p—p’ pubis.— Orig.

Birds, its hinder portion is firmly anchylosed in old age with the
ilium, whilst in Odontornithes and Struthious Birds it is either
quite free or only fused with the ilium posteriorly. The most
remarkable part of the avian pelvis is, however, the pubis. This
is a long thin bone stretching backwards parallel to the ischium,
with which it usually partially anchylosed. In some Birds (Odont-
ornithes, Ratite, Gallinacez), there is a short process (p, Fig. 369)
at the upper end of the pelvis, just in front of the acetabulum;
but it is usually absent. It corresponds to the chief part of the
pubis of Dinosaurians, and to that bone itself in other Reptiles, whilst
the rest of the pubis (p’) corresponds with the posterior pubic
process of Dinosaurians. Further, it must be noticed that
the pelvis of Birds is almost always quite open below, since neither
the ischium nor the pubis is fused with its fellow. In the hind
limb, the femur is relatively short; the fibula thin, imperfect, and
pointed at its lower end (except in Archeopteryx) ; the tibia is long
and strong, and is furnished above, on the anterior surface, with a
442 Vertebrata.

well-developed crest (a similar crest occurs in the Dinosaurians, but
is very feeble in other Reptiles). There is usually a patella. The
structure of the tarsus is interesting. As in the Reptiles, it is
divided into proximal and distal portions, between which there is
a very perfect joint; the tarsals of the proximal row are distinct from
the tibia in the young animal, but in the adult are fused so as to leave
no trace. In the same way, the distal portion fuses with the meta-
tarsus, so that in the adult there is apparently no tarsus. The foot
never consists of more than four toes, there is never any trace of
the fifth or of its metatarsal. Metatarsals two, three, and four,
are long, and only separate in the embryo; later they fuse almost
down to the toes, forming a long thin bone (the tarso-metatarsus) ;
on the other hand, the first metatarsal is separate, but much shorter
than the others, and attached to these at its distal end. The hallux
which is usually directed backwards, consists of two phalanges,
the second digit of three, the third of four, and the fourth of five’
(as a rule); all as in Lacertilia and Dinosauria. Of the forwardly
directed toes the middle one (No. 3) is usually the longest; the
hallux may be large, but is often rudimentary or absent.

The brain, in comparison with that of the Reptiles, is large.
The hemispheres, especially, are well developed; the cere-

 

Fig. 370. Brain of a Pigeon, dorsal (A), and ventral (B). 6b cerebellum,
f cerebrum, k epiphysis, 1 olfactory lobes, mi mid-brain, r spinal cord, 8 optic nerve,
t hypophysis.—After Jeffery Parker.

bellum is likewise large; its median portion, which is clongate, and
furnished with deep transverse furrows, covers both the medulla and
the middle portion of the mid-brain, the two lobes of which are
pushed out to the sides. Of living Reptiles, the Crocodiles come
nearest to the Birds in regard to the development of the brain.

The olfactory organ is very like that of Lizards; the
external nares, on account of the length of the premaxille, are usually
Class 5, Aves. 443

some distance from the tip of the beak, and may even be at its
base; the internal nares open into the mouth, rather far forwards,
in a groove, which is partly covered by lateral longitudinal folds
(cf. Reptilia). On the outer wall of the nasal-cavity there is a
cartilaginous projection often spirally folded; which corresponds
with the turbinal of Reptilia; there are also two other more or
less well-developed folds.* The eye and its accessory structures are
also very like those of Reptiles. The optic bulb is of very consider-
able size. The front wall of the sclerotic, in which there is a circle
of bony plates (the sclerotic ring), has the form of a frustrum of a
cone ; the absent apical portion of the cone is replaced by the cornea,
which is often very convex, whilst its base is formed by the posterior
eurved portion of the sclerotic ; if the frustrum is long, and its wall,
as sometimes happens (e.g., in the Owls, Fig. 371, B) is somewhat
arched inwards, the form of the eyeball differs much from the

B

KC

 

Fig. 871~-4 Eye of a Bird, diagrammatic transverse section. c¢ cornea, ch choroid,
ct ciliary processes, ¢ iris, | lens, n optic nerve, o transverse section of bony plates, p pecten,
r retina; s external connective tissue portion, s’ internal cartilaginous portion of the
sclerotic. B Seotion through the eye of an Owl, in order to show its peculiar shape.—Orig.

ordinary spherical type, whilst in others it deviates but little from
this. A large membranous process, which is folded and pigmented,
the pecten, arises from the retina at the point of entrance of the optic
nerve, and projects freely into the vitreous humour. Of the two
eyelids, the lower is much larger and more movable than the
upper (as in Reptiles); there is a well-developed nictitating
membrane, which can be flicked across the eye by a special
muscle. The Harderian gland opens at the anterior corner of the

 

* Into the nasal cavity opens the duct of a large nasal gland, which usually
lies above the frontal bone (in Sea-gulls and others, in a longitudinal depression at the
edge of the orbit); this gland occurs in many Reptiles, but is situated in a different
region of the head.
444, Vertebrata.

eye; at the posterior, a small lachrymal gland. Astothe auditory
organ, the membranous labyrinth, especially as regards the
cochlea, is very like that of the Crocodilia. There is a short
external auditory meatus, at the base of which lies the tympanum
(cof., Reptilia) ; its opening is covered by regularly-arranged feathers
(a pinna, i.e., a movable flap of skin covering the opening, only
occurs in the Owls. In the tympanic-cavity there is an ear-bone,
like that of Reptiles: it consists of a long rod, expanding at one
end into a disc, which fits into the fenestra ovalis; whilst by the
other end, which is provided with two or three cartilaginous processes,
it is attached to the tympanum. A fenestra rotunda is present. The
Eustachian tubes, which are partially enclosed in the wall of
the skull (sphenoid bone), are united with each other, and open
into the mouth by a single aperture.

Alimentary canal. There are no traces of teeth* in any
living Birds, but in Archeopteryx and the Odontornithes, there were
simple conical teeth, placed in sockets on the edges of the jaws as
in the Crocodiles; in some of the Odontornithes, the sockets become
confluent, so as to form a continuous groove in each jaw, a condition
which may also be observed in some Mammalia. The roof of the
mouth is usually provided with backwardly directed spiny processes.
The tongue is generally flattened, narrow, stiff, and hard, and
covered with a thick, hard cuticle, which is especially well-developed
at the anterior, usually pointed, end ; occasionally it is thick and soft,
as in the Parrots and the Flamingo ; not infrequently it is rough or
prickly. The cesophagus is of considerable length and fairly
wide. In many, but by no means in all Birds, it widens out at the
base of the neck to form a crop, in some a simple expansion of the
cesophagus, from which it is not sharply marked off; in others, a
more definite sac opening into the cesophagus. It usually serves
merely as a storage for food, but in Pigeons, it has another function:
here, during the breeding season (in cock as well as in hen), the
stratified epithelium lining it becomes thickened, the superficial cells
filled with oil globules break away, and form a crumby liquid with
which the fledglings are fed. The stomach of Birds is divided
into two, usually rather sharply defined, chambers, a glandular and a
muscular portion. The glandular stomach isa short tube which
appears as a direct, somewhat widened continuation of the cesophagus;
embedded in its walls are numerous glands of two kinds: (1) large,
close-set glands secreting a digestive fluid, either distributed over
the whole wall, or limited to definite regions; and (2) quite small
tubular glands, which secrete a mucous covering for the whole inner
surface of this region. Lower down, at its junction with the next

 

*The “teeth” along the edge of the beak in, for instance, Merganser (Mergus),
are dentiform processes of the edge of the beak, and are thus horny structures.
Class 5. Aves. 445

part, the large glands are wanting, the lining becomes firmer, and
gradually passes into that of the muscular stomach. ‘This is
short and saccular, and has muscular walls; it possesses glands of
one kind only, namely, simple, close-set glandular pits, like those
which secrete the mucous layer of the other chamber. Their
secretion is, however, very peculiar; each gland forms a hard, horny
thread, which projects from its mouth, and adhering to neighbouring
threads, forms a horny lining;* it is continually being worn
away at its surface, and renewed by fresh secretion at the base of
the threads. On the outer surface of the muscular stomach, there
is a dorsal and a ventral tendinous disc, from which the muscular
elements arise. The muscles of the wall are especially strong in
herbivorous, notably in graminivorous species (e.g., Fowls and Ducks),
in which this organ is provided with a large muscle mass, plano-
convex from within outwards; whilst its cavity is very small. In
such, the muscular stomach forms a true gizzard, in which the
food may be ground by the two muscles just mentioned ; the horny
lining is very thick and hard, and sand and stones are swallowed
to assist in trituration. In insectivorous and predaceous forms the
muscular stomach, on the other hand, is thin walled, the musculature
feeble, and the cavity large. Its openings into the small intestine,
and into the glandular stomach, are close together. The small
intestine is well-developed, and longest in the herbivorous forms ;
it is continued into a rectum which is almost invariably short, and
which has a posterior widened portion, the cloaca. Two ceca usually
open at the junction of the small intestine with the rectum, and in
many herbivorous and omnivorous Birds they are of considerable
length, whilst in the carnivorous forms they are usually quite short
or rudimentary (this may also be the case in others; Pigeons, for
instance, have quite short ceeca).' There is a large brownish-red
liver provided with a gall bladder, and an elongate whitish
pancreas lying in the first loop of the small intestine.t

Many Birds disgorge the indigestible portions of their food, bones, hairs,
feathers, insect skeletons, etc., in small masses, the so-called pellets; the best
known of such pellets are thrown up by the Owls, and usually consist of skin and
bones of Mice, but various others disgorge similar ones: Swifts (insect remains),
Kingfishers (fish bones), Ravens, etc.

Respiratory.organs. - A-longitudinal slit in the mouth
close behind the tongue leads into the larynx, which is continued

 

' * In Birds of Prey and other carnivorous forms, the lining of the muscular stomach
has a softer character. é ;
+In most. young Birds, there opens on the dorsal wall of the cloaca, a small
unpaired-sac-with-a-narrow-aperture, the-bursa- Fabricii, in the-wall of which lie small-
portions of epithelium, which are indeed constricted evaginations of the epithelium of
the sac. ‘ In older forms,‘the bursa, of which the significance is unknown, is usually
degenerate or-absent:*-In! the? Struthious Birds, instead of this, there is a large.
undefined outgrowth of the cloaca. ie q
446 Vertebrata.

into a trachea of considerable length, furnished with numerous
cartilaginous or bony rings, and dividing below into two branches, one
for each lung. Unlike most other air-breathing Vertebrata there are
no vocal cords in the larynx ; but most Birds possess a peculiar lower
larynx (syrinw) at the junction of the trachea, with the upper ends
of the two large bronchi; and here the walls of the bronchi form
membranous folds (me and mi, Fig. 374), which are caused to vibrate
by the exhalent current of air (for details see below). The lungs
are spongy organs, closely apposed to the dorsal wall of the body-
cavity ; in structure, they resemble very closely those of most Reptiles.
A tubular continuation of the bronchus runs through the lung,

Fig. 372.

  

4

Fig. 372. Lungs of an eleven days Chick embryo. ¢ trachea, ? rudiments of
branchial sacs.—After Selenka.

Fig. 373. Lungs of a Pigeon. tr trachea, o apertures from the lungs into the sacs
which have been removed.—After J. Parker.

dividing and sub-dividing on its way; the delicate terminal branches
are the actual respiratory organs. All these branches are closely
bound together by connective tissue; some of them are continued
into large thin-walled air sinuses, which extend back between the
viscera, between certain of the subcutaneous muscles, and even send
long processes into many of the bones, eg., the limb bones, in
which they occupy the position of the marrow cavities; the bones
are thus to a large extent pneumatic.* This development of air
sacs is of significance, from the small specific gravity that the body
thus acquires, in other words, the lungs of Birds, like the trachex of

 

* It may be mentioned here, that Birds are not the only animals with pneumatic
bones; the Pterodactyles, and many Dinosaurians had them, which leads to the
conclusion that they, also, were provided with air sacs.
Class 5. Aves. 44:7

Insects, constitute not only a respiratory, but also an aérostat ic
apparatus.

The syrinx has usually the following structure: the two bronchi are separated
at their upper ends, where they pass into the trachea, by a median bony rod,
or septum, connected with the last tracheal ring. The inner wall of the
anterior portion of each bronchus is membranous, and is termed the intern al
tympanic membrane. The outer side of the wall of the bronchus is
strengthened by semicircles of cartilage or bone, and there is often here also a
membranous portion, the external
tympanic membrane, which, in
other cases, may be replaced by a thicken-
ing of connective tissue, projecting into
the lumen from one of the half hoops of
cartilage. The lower end of the trachea
itself, which may be termed the tym-
panum, is usually modified for the pro-
duction of voice, the last rings, for
instance, may be fused, or this portion
is compressed or widened, etc. In the
males of Merganser (Mergus) and most
Ducks, the tympanum possesses a lateral
saccular outgrowth with ossified walls,
the resonator (or the labyrinth).

To these structures accessory to the
respiratory system, the following may be
added: in the Whistling Swan, the
Crane, and others, the keel of the sternum
is thick and hollowed, with an opening Fig. 374. Section through the lower
above; within this cavity the trachea end of the trachea and the upper ends of
makes a long loop before passing back the two large bronchi ofa Bird; dia-
3 ‘ : grammatic. 6 bronchi, me external, mi
into the body ~cavity i. BOM other internal tympanic membranes, s bony sep-
birds similar coils of the trachea lie tum, ¢ drum, tr trachea. I—IV the four
below the skin or in the body-cavity: lower rings of the trachea; 1 uppermost
the tubular continuation of the bronchus —_#f-hoop of a bronchus.— Orig.
which runs through the lung (see above),
gives off branches from which numerous long parallel tubes arise, from these
are given off close-set radial, somewhat racemose, tubules, which end blindly ;
these are all bound together by connective tissue, and thus form a thick
layer round each of the parallel tubes: the air-sacs in the bones of the skull
are extensions from the tympanic and nasal cavities: several other air-sacs
of the head are connected with the latter (e.g., one in the orbit below the eye),
these reach back into the neck, and, in some birds, communicate with the
pulmonary air-sacs. Inspiration is brought about by movements of the ribs,
resulting in « forward motion of the sternum and the widening of the body-
cavity. Certain muscles, which arise from the inner side of the wall of the
body-cavity (from the ribs and sternum), and are attached to a membrane
which extends over the ventral surface of the lung, assist in the process, since
by their contraction, the lungs are expanded.

 

The heart and the large arterial trunks arising from it, offer
relations which may be shown to be a modification of those obtaining
in the Crocodiles. Both auricle and ventricle are completely divided
into right and left halves. The conus is wanting. The left aortic
448 Vertebrata.

arch (left arterial arch of the second pair), which arises in Crocodiles
from the right ventricle, is here altogether absent; the aorta is
thus exclusively formed by the right arch arising from the left
ventricle; in other respects the relations are like those of the
Crocodiles. No mixing of arterial and venous blood occurs in Birds ;

  

ao

Fig, 375. Diagram of the heart and arterial arches of a Crocodile (A) and ofa
Bird(B). a right, a’ left auricle; v right, v’ left ventricle; ao aorta. 1, 2, 4 1st, 2nd,
and 4th arterial arches of the right side, 1’ 2’ 4’ the same of the left side (c and m
see Fig. 347).— Orig.

the venous blood enters the right auricle, goes thence into the right
ventricle, and from the latter to the lungs; the arterial blood from
the lungs goes to the left auricle, thence to the left ventricle, and so
into the body.

The kidneys are long, dark-red bodies lying in the pelvic
region ,just below the vertebral column; they occupy the spaces
between the transverse processes, and are divided ventrally by
transverse constrictions into several (usually three) lobes. Sometimes
the two glands fuse, to a greater or less extent, along their inner
edges. The ureters open separately into the cloaca; a urinary
bladder is absent. The urine is semi-solid and whitish.

Of the ovaries, only the left is developed; exceptionally
there is however a rudimentary right-one; in many diurnal Birds of
Prey (Falcon, Sparrow-hawk, Buzzard) such a rudiment is large
Class 5. Aves. 449

and fairly constant. On account of the size of the eggs the Graafian
follicles project from the surface of the ovary, giving it a racemose
appearance. The left oviduct (Miillerian duct), also, is alone
well-developed, though a rudiment of the right may be present ;
during the breeding season the oviduct is long and wide, at other

Fig. 377.

 

Fig. 376. Reproductive organs ofa Hen.
d rectum, 1 oviduct, ov ovary, ¢ funnel, u uterus.—
Orig.

Fig. 377. Reproductive organs (and
ureter) of a Cock; rectum turned to one side to
show the place where the ureters and vasa deferentia
open into the cloaca. a anus, h testis, n epididymis,
s vas deferens, ur ureter.—Orig.

 

times it is a narrow tube opening, by a large funnel, into the
body-cavity ; not far from the opening into the cloaca it widens out
to form the uterus, where the shell is secreted. The testes,
both of which are well developed (although sometimes the left is
larger), lie in front of the kidneys; the vasa deferentia, each of which
arises from a small epididymis, have a convoluted course, and open
separately into the cloaca, usually on small papille. The testes are
very small, except at the breeding season, when they attain a
considerable size ; this holds also for the ovaries. A definite penis
occurs only in the males of a small number, in Struthious Birds,
Ducks, and some others; in the rest it is rudimentary or absent.

G@@
450 Vertebrata.

It is homologous with the copulatory organ of Chelonia and Crocodilia ;
it is situated on the ventral wall of the cloaca ; the free tip is directed
backwards, and is provided with a superficial groove, at the anterior
end of which the vas deferens opens, and along which the spermatozoa
pass during coitus. In Ducks the penis is spiral, in others, linguiform,
or rod-like ; the tip is usually invaginable. Where the cock-birds
have a penis, the hens usually have a rudimentary copulatory organ
(clitoris).

Very generally larger or smaller external (secondary) sexual differences
are noticeable: usually the males are somewhat larger (in Fowls, etc.), rarely
smaller than the females (in Birds of Prey); the cocks are often distinguished
by the special development of certain feathers (Peacock, Birds of Paradise), by
peculiar cuticular processes (spur‘of the Cock), or by vivid colouring.

Most Birds breed only once a year (usually in the spring), others
several times (e.y., the House Sparrow). As a rule, they live in
pairs during the breeding season, i.e, they are monogamous ;
occasionally the male has several hens, or is polygamous.

The eggs of Birds are of very considerable size, and contain a
large amount of food yolk. As they pass down the oviducts they are
covered first by a mass of albumen, then by a shell-membrane, and
finally, in the uterus, by a hard calcareous shell; all the coverings
are secreted by glands in the wall of the oviduct. The eggs are
incubated by the females alone, or by the males and females
together, rarely by the males only, this occurs in the African Ostrich
and the Phalarope (Phalaropus) ; usually the sitting Bird is provided
with brood spots, regions from which the feathers have
fallen off, so that the eggs may come into direct contact with the
warm skin. Most Birds build nests for the reception of their eggs,
but occasionally they are laid upon the bare ground. In the simplest
cases the Birds drag together a scanty collection of twigs, straws,
feathers, etc.; in others similar materials are woven into a basket-
shaped or spherical nest; occasionally the nest is built of clay, dirt, or
the like, and saliva (Swallows and others), or from saliva alone
(Salangane). The nests of some forms are built upon the ground,
and others in excavations or in natural holes in the earth (Sand-
martins, Puffins), in holes in trees (Woodpecker), on trees, etc.
Usually the males and females build the nest together. As a rule the
young Birds do not leave the nest immediately after hatching, but
remain in it for some time, and are fed by the parents (“altrices’’) ;
occasionally (“praecoces’”’) they are immediately able to feed them-
selves (usually, however, under the protection of the hen). The
newly-hatched young one generally differs considerably from the
adult ; it is either covered with down or is almost naked, and differs
in colour, and usually in the form of the beak (e.g., in many singing
Birds) ; the food, too, is often different from that of the adult (for
instance, many grain-eating Birds feed their young ones upon Insects).
Class 5. Aves. 451

The plumage, which replaces the down feathers, is usually essentially
different from that of the parent.

Many young Birds, like young Chelonia and Crocodilia, possess, on the upper
side of the beak, a small hard cuticularised knob, with which they break through

the egg (neb).

Whilst some Birds inhabit the same confined locality throughout
the year, and may therefore be called residents, others undertake
longer or shorter excursions or true migrations. Some wander about
through a large district in search of food, and are most like the
residents ; others, according to the season, leave the mountains and
betake themselves to the neighbouring valleys, or, impelled by
necessity, exchange the forest for the open country, etc. The more
conspicuous migrants travel greater distances, for they breed
every year in a cold climate, and spend the winter in a warm
country some way off. They follow special routes, which are arranged
so that, as far as possible, only those countries which resemble
the native habitat shall be touched at. Coast-birds usually take a
course along the sea-coast, or, if necessary, along rivers ; Marsh-birds
go over marshy-ground, along rivers, etc. The same route is generally
followed, whether going or returning. Most travel in large flocks,
sometimes several species in company, and as old and young fly
together, the knowledge of the way is always handed on to, and
preserved by, successive generations; Birds cannot find the way
“instinctively,” although in Birds of Passage an inherited indefinite
instinct to wander may be noticed, which shows itself in restlessness
in young caged individuals, at the time when migration occurs.
Migrations from colder regions take place at different, but for each
species definite, times, usually in the autumn, for some species even
in August and July; the return occurs from February to May, those
forms which are among the earliest to go away, returning last. Most
of the Birds of Passage, which breed in Britain, winter in South
Europe or North Africa.

It is easy to understand that wanderings in general, and also true migration,
originated in the need for food; it has been noticed that certain forms which do
not usually migrate, journey South in severe winters in search of food, whilst,
in mild winters, some Birds of Passage remain in their breeding place: on the
other hand, it may be observed, that migration is undertaken so instinctively
by most Birds that they will start even in time of plenty, so that their
wandering is no longer directly dependent upon the food supply.

Birds occur wherever there is life, although they are most
abundant in the Tropics, and constitute at the present time a very
numerous but fairly uniform class. Geologically this is the youngest of
all vertebrate classes, since the oldest avian form known, a single species
only, comes from the Jurassic, so that they were certainly very scarce
at that time; a larger number occurs in the Cretaceous (all Odont-
ornithes) and many in Tertiary formations.

aa 2
452 Vertebrata.

Synopsis of tHE Orpers or Avzus.*

1. Saurure: caudal region of vertebral
column longer than trunk; teeth present.

2, Odontornithes: caudal region shorter
than trunk ; teeth present.

3. Ratite: wings not functional; pedes |

cursorii. :

The young ones | 4. Rasores: short, slightly-curved beak; Hind toe
are covered at pedes gradarii; wing short and curved. aul
first with a thick | 5. Natatores: pedes palmati.t paral,
coat of down. 6. Grallatores: pedes vadantes. J

7. Raptatores: beak powerful and hooked; )

pedes insidentes. ind
The young ones - 8. Oscines: pedes fissi, ambulatorii, ad- Hind toe

 

on hatching are hamantes. | usually
almost naked) 9. Clamatores: pedes adhamantes, am- well-de-
and very help- bulatorii, fissi or gressorii. veloped
less. 10.Scansores: pedes scansorii. J

Order 1. Saurure.

Of this order only a single species is known, Archwopteryz litho-
graphica, from the Jurassic (lithographic slates). Archeopteryx,

 

Fig. 378. Archeopteryz. 1—3 first to third fingers, 1’ first, 4’ fourth toe, fi fibula,
tl ilium, me, first, me, third metacarpal, n nares, o orbit, r cervical rib, ra radius, u ulna,
z is possibly a joint, but perhaps due to injury (according to the second interpretation the
third finger has three joints, according to the former, four).—Orig. (with the use of figures
by Dames). .

 

* The systematic arrangement of Aves offers considerable difficulties, on account
of their great uniformity ; several of the orders given here are not natural groups.

+ For the significance of these terms, see the descriptions of the various orders.
Class 5. Aves. Order 1. Saurure. 453

of all known Birds, stands nearest to Reptiles. It is characterised
firstly by the very long tail consisting of twenty elongate vertebre,
to which the rectrices, known from impressions on the slates, were
attached in a single row on either side: and further, by the separa-
tion of the metacarpals: by the three well-developed fingers
furnished with claws (a point which may be recognised from the
form of the last phalanx): and by the presence of conical teeth on
the edges of the jaws. Among other characters it may be noticed
that the somewhat thin thoracic ribs have apparently no uncinate
processes ; that the cervical ribs are longer; that the neck and pelvic
regions are shorter; the sternal region, on the other hand, more
extensive than in Aves in general (the thoracic vertebre also appear
to have been more freely articulated than is usual); that the
surfaces of the centra are apparently biplanar (not saddle-shaped) ;
and that the lower end of the fibula is complete, not simply ending
in a point; it is even somewhat widened below. From the well-
preserved impressions of the large remiges it is proved that
Archeopteryx must have been a good flier. Its size was about that
of a Pigeon, but it is only known from two specimens, both incomplete ;
and the sternum, pelvis, and coracoid are not made out, or only
imperfectly.

Order 2. QOdontornithes (Zvothed Birds).

The Toothed Birds, of which several species are known from the
Cretaceous of North America, are on the whole very like existing
forms, though differing in the possession of teeth upon the edges of
the jaws. Some of them (Ichthyornis) possess slightly biconcave
centra ; in others (Hesperornis), the vertebrae are similar to those of
living Birds. The mandibular rami are not anchylosed anteriorly.
The pelvis is characterised by the fact that the ilium and ischium
are not fused posteriorly. For the rest, a considerable variety of
forms is grouped under this name: some were able to fly, others
possessed rudimentary wings like the Ratitee.

Order 8. Ratitee (Struthious Birds).

The most prominent character of this order is the degenerate
condition of the wings, which can never be used for flight,
and, indeed, are often quite rudimentary. The sternum has no keel.
‘The hind limbs, on which there is usually no hind toe, are generally
very powerful, and are used for running; the claws are short and
stumpy. The feathers are not arranged in tracts, but are fairly
regularly distributed over the whole body (there are, however, naked
portions, e.g., on the inner side of the fore limbs in the Ostrich and
454 Vertebrata.

Rhea) ; there is no down between the feathers; remiges and retrices
generally differ but little from the other feathers. There are no
uropygial glands.

The Ratite are placed directly after Archeopteryx and the Odontornithes
because, in several respects, they show more primitive characters than other
living forms. For instance, the palatines do not touch the lower wall of the skull,
but lie a little distance from the middle line, as in Lizards; a character which
they have in common only with a small isolated group of the Rasores* (in
Archzopteryx and the Odontornithes this portion is not preserved); the bones of
the skull remain separate longer than in Carinates, as do also the cervical ribs and
tarsal bones; the ischium does not fuse with the ilium (as in Odontornithes) or
only quite posteriorly ; the second digit of the fore limb possesses a fairly well-
developed claw. In various other points, however, they are considerably special-
ised; the condition of the wings is clearly secondary (i.e. the Ratite are
descended from flying birds); the absence of the keel is a consequence of the loss
of the power of flight and the degeneration of the pectoral muscles ; so with the
feathers, etc.

Most of the Ratites are of very considerable size; they are true
prairie animals inhabiting the warmer portions of the Southern
Hemisphere. They prefer a vegetable diet, but also eat small animals.
The males undertake the whole or most of the brooding. The young
ones are covered with down and are able to run about directly they
are hatched.

1. Ostriches (Struthionide). Beak short and broad, feathers without
aftershaft; wings relatively well developed, with pollex and large feathers;
smaller or larger feathers on the tail. Belonging to this family are: the
American Ostrich or Nandu (Rhea) with three toes; in South America:
the African Ostrich (Struthio Camelus) with only two toes (3 and 4)
of which the inner bears a large claw, whilst the outer has no claw or only
a small one; wings with very large, and tail also with fair-sized, feathers; in
Africa and West Asia.

2. Cassowaries (Dromexidz). Beak short, main-shaft and aftershaft
of equal size: wings very feeble, pollex absent, tail scarcely distinguishable ;
three toes. The Cassowary (Casuarius) with a bony ridge covered with
horn on the top of the head; a compressed beak; and on each wing five long
strong feathers without barbs: inhabiting New Guinea, the Moluccas, and the
north of Australia. The Emeu (Dromeus) with flat beak; without crest and
without naked feather shafts, occurring in Australia. To the same family belong
the extinct Moas, some of which had a hind toe. They flourished in New
Zealand several centuries ago, and some of them were of gigantic size (Dinornis
and others).

3. Kiwis (Apteryx) are small, short-legged, and short-necked birds, (about
the size of a fowl) with long thin beak, on which the nares lie close to the tip;
feathers without after-shafts ; wings quite rudimentary; hind limbs with a small
hind toe. Their food consists essentially of Harthworms; in places where
they live, the earth is riddled with borings made with the beak. They are
nocturnal animals and brood in holes in the earth, which they dig out them-
selves; New Zealand.

 

* Namely, the Tinamous (Crypturidz), a division of Rasores distinguished by
a long beak; very short rectrices, if any (so that they appear short tailed or tailless)
and a very small hind toe, if present at all. They inhabit South America.

5
Class 5. Aves. Order 4, Rasores. 455

Order 4. Rasores (Gallinaceous birds).

Beak short, slightly curved at the tip; pedes gradarii, strong
feet with small hind toe, which is articulated at a higher level
than the rest of the toes, and has a slightly curved, short com-
pressed claw; occasionally the hind toe is large. The wings are
usually short, rounded, curved. The Rasores are, as a rule, of
medium size, they are not very good fliers and generally remain
on the ground; they are mostly omnivorous, scraping up seeds,
larve, worms, etc., with their claws. Not a few are polygamous,
when the males are usually larger and more gorgeously coloured
than the females. The eggs are, as a rule, laid on the ground and
brooded by the hens; the newly-hatched chicks are stronger than
those of most other birds, and are able to run about immediately.

1. Tetraonomorphe. The nares and the base of the beak covered with thick
feathers. Metatarsus more or less feathered, without a spur. Here belong: the
Capercaillie (Tetrao urogallus) occurring in Scotland; and the Black
Grouse (T. tetriz); magnificent birds, the former the larger: in both cases
the metatarsus is completely feathered, the toes naked; polygamous; the cocks
much larger than the hens; the latter brown, the former blackish. In the genus
Lagopus, the whole foot is feathered; they are brown in summer, usually
white in winter; the European species live only in cold regions, the Alps and
elsewhere; two species are met with in Scotland, the Red grouse (L. scoticus),
which is brown all the year round, and the Ptarmigan (LZ. mutus), the
former occurring also in the Orkney Isles. The Sand Grouse (Syrrhaptes
paradowus) is characterised by long wings and short feathered feet, from which
the hind toe is wanting, the fore toes being fused; it is indigenous to the
Steppes of Western Asia, but in recent years has several times wandered in
large flocks into Europe, and has even been known to breed in Scotland.

2. Phastanomorphe. The naris naked, covered with a small arched scale.
Metatarsus of the male usually furnished with a spur (occasionally with two),
which is rudimentary in the female.

(a) The Pheasant Family (Phasianidez). Tail feathers sloped from’
a median plane like a roof: naked outgrowths usually present on the head :
spur present: sexual dimorphism well marked: South Asia. The Domestic
Fowl «Gallus domesticus), with a naked comb on its head; cock with long
curved tail coverts; descended from Jungle-fowl (G. bankiva). Further,
the Pheasant (Phasianus), of which one species (Ph. colchicus) occurs
in many places in England in a half wild condition; distinguished by their
long pointed tail (the rectrices themselves are lengthened).

(b) The Peacock Family (Pavonide). Tail flattened and fairly long;
spur present. The Peacock (Pavo cristatus), with a tuft of feathers on the
head; male with extraordinarily long tail feathers, which can be spread out:
East Indies. The Turkey (Meleagris gallopavo), head and neck naked, in
the male a soft process of skin depends from the dorsal side of the head at
the base of the beak: North America.

(c) The Partridge Family (Perdicidz). Tail flattened, short; spur
often absent. In England there occur, the common Partridge (Perdix
cinerea) and the common Quail (Coturnix communis), of which the latter
is a Bird of Passage and polygamous; both have a naked patch of skin behind
the eye; the spurs absent; male and female fairly similar. The Guinea-
456 Verlebrata.

fowl (Numida meleagris), with naked head, which bears a large bony process;
grey, with white spots; without spur: indigenous to Africa.

3. The Curassows (Cracide: genus Craw, etc.). Large, with fairly
long metatarsus, curved and pointed claws; long tail; beak covered at the
base with soft naked skin (cere), where there is often a large knob; an
upright crest of feathers, frequently curves forwards from the top of the
head: breed in trees: Mexico and South America.

4. Mound-birds or Talegallas (genus Megapodius, etc.), dis-
tinguished by the length of the claws and the powerful structure of the hind
toe, which is articulated at the level of the other toes. They are specially
remarkable in that they do not brood over their very large eggs, but deposit
them in a mound of vegetable matter, which they have collected, in a sand
heap, or in a pit dug in the sand; the eggs are then either incubated by the
warmth resulting from the fermentation of the vegetable matter, or simply by
the heat of the sun. The young ones lose the covering of down whilst still within
the egg, and hatch out with the adult plumage. Australia, the Philippines.

Order 5. Natatores (Swimming Birds).

The feet are generally pedes palmati, t.e., a membrane is
stretched between the front toes almost to their tips. As a rule
the feet are short, the claws short and flattened, the hind toe
generally very small, the lower end.of the fore leg bare and
scaly. The tail is usually short; the plumage thick and elastic.
The Natatores are able to swim by means of their hind limbs, and
not a few of them can dive, when they often use the wings as
swimming organs; others can only bring the head, neck, and fore
limbs below the water, the rest of the body remaining above. Usually
they cannot walk well; the power of flight is considerable in some
forms, in others it may be lost.

_ 1. The Gulls (Longipennes). Long, pointed wings; short hind toe; lateral
slit-like nares; tail well-developed. Most are coast-birds (some may also live near

- fresh water), feeding on Pisces and other marine animals, for which they plunge
into the sea; excellent fliers. The Gulls (Larus) are large and light-coloured,
with the tip of the beak curved; and astumpy tail; numerous species on the coast
of Great Britain: the Common Gull (L. canus), the Black-headed Gull
(L. vidibundus), the Laughing Gull (L. atricilla), the Herring Gull
(LZ. argentus), and others. The Terns (Sterna) differ from the Gulls in their
long, straight, pointed beaks, and their forked tails. Out of eight or nine species
occurring on English coasts, the Common Tern (8. hirwndo), and the
Lesser Tern (S. minuta), may be noted. An interesting form is Buffon’s
Skua (Lestris), dark in colour, with the two median rectrices longer than the
others, and the beak grooved. The Skuas follow other marine forms which have
secured any prey, seizing upon it if the possessors allow it to fall; they also fish
for themselves, and behave as true Birds of Prey, since they hunt small Birds
and Mammals. They are northern, and are met with in the Orkneys.

2. The Petrels (Tubinares). Chiefly distinguished from the preceding
groups, in that the nares are situated at the ends of two tubes lying above the
beak; usually met with in the open sea. Among those on British coasts, may
be noted, the Fulmar Petrel (Fulmarus glacialis) of the Orkneys’ and
St. Kilda’s, and the small, dark-coloured Stormy Petrel (Procellaria
Class 5. Aves. Order 5. Natatores. 457

pelagica) of the English Channel, the Atlantic, and elsewhere. The group is
represented in the Southern Hemisphere, at the Cape, etc., by the large
Albatross (Diomedea exulans), in which the hind toe is wanting.

3. Steganopodes. A large, often backwardly directed, hind toe, which is
connected by a web with the other toes, so that there is here a web between all
four (p. stegant); beak long, straight, the tip usually cwved downwards. The
Cormorant (Graculus carbo) is dark-coloured, with a narrow beak hooked
at the tip; it breeds in flocks in trees near the sea or by fresh
water; feeds upon fish; almost throughout the whole of Europe, in Great
Britain, Asia, North America (in the winter, also in Africa). The Pelican
(Pelecanus), white, with reddish or yellow touches, the beak long, straight, and
broad, hooked at the tip; the skin between the mandibular rami capable of great
distension, to form a large sac for the reception of the prey; tongue rudimentary ;
indigenous to warm countries; two species in South Europe. The Frigate
Bird (Tachypetes aquila), with long, pointed wings, forked tail, and feebly-
developed web, lives in the open sea within the Tropics; feeds chiefly upon Flying
Fish, which it catches as they fly. The Gannet (Sula bassana), with long
wings, and a long powerful, pointed beak, plunges deep into the water after its
prey; common in Iceland and the Pharoe Islands, also met with in Devonshire.

4, Pygopodes. Wings weakly developed, but with the ordinary joints; beak
of diverse form; leg, and most of the foreleg, enclosed in the body-wall, from
which the lower end projects close to the anus; tail very short; the body can be
held upright whilst walking. They dive after Fish, Shell-fish, and such like?
belong to the Northern Frigid Zones. ‘

(a) The Divers (Colymbus) usually possess pedes palmati, with a small
hind toe; a long beak, pointed and straight. Northern birds, building their nests
close to fresh water; several in England: the Great Northern Diver
(C. glacialis), the Black-throated Diver (C. arcticus), and the
Red-throated or Speckled Diver (C. septentrionalis). Grebes or
Dabchicks (Podiceps) are like the Divers, but differ in that they have no
continuous web, each fore toe having on either side a broad ridge (pedes
fissipalmati); they build a floating nest on stagnant water; several species in
Great Britain: the Red-necked Grebe (P. grisegena), the Eared
Grebe (P. auritus), the Little Grebe (P. minor), and others.

(6) The Auk Family (Alcide) is distinguished from the preceding
group by the absence of a hind toe. They breed in flocks by the sea. The
Guillemots (Uria), with fairly long, straight, pointed beak, breed chiefly on
Northern seas; three species abundant on the shores of North Britain, the
Orkneys and Shetlands. Only one species of Auk, the Little Auk (Alca
alle) breeds in Great Britain; the Razor-bill (Alca tonda) breeds in colder
countries, but is occasionally found in the North Sea in winter; related to it is
the extinct Great Auk (Alca impennis), in which the degenerate wings were
quite useless for flight. It inhabited Iceland, Newfoundland, etc. The Puffin
(Mormon fratercula) has the beak much compressed laterally and grooved ;
it digs out tunnels in the earth and nests in them; breeding chiefly on the
Northern Coasts (Iceland, etc.).

5. The Penguins (Impennes). A very aberrant group, chiefly charac-
terised by the small fore limbs, which move only from the shoulder, and
are covered with small scale-like feathers (no specially developed remiges) ;
they are of course useless as organs of flight, but are used for swim-
ming.* Like the Auks, the Penguins walk upright; the metatarsus is short

 

= Indeed, the Bird swims almost entirely by means of the fore limbs, the feet
being stretched backwards with the soles upwards, and serving as steering organs.
458 Vertebrata.

and broad, the small hind toe turned forwards: the tail is very short: the
feathers are evenly distributed over the body. They live in the Southern
Hemisphere.

6. Anseres (Lamellirostres). Large, usually broad, bill, high at the base,
flattened at the tip; most of the beak is covered by soft skin, only at the tip is
there a hard, horny plate; along the edges of the jaw there is a series of small,
usually laminate, processes; thick, soft tongue; small hind toe.

(a) Ducks (Anatinz). Small anserine forms with short neck and broad, flat
bill with a small horny plate; the male more brightly coloured than the female ;
undergo a seasonal change of colour. Birds of Passage. Among a number of Ducks
occurring in Great Britain the following may be noted: the Wild Duck (Anas
boschas), ancestor of the Domestic Duck; the Common Shieldrake or
Stock Annet (A. tadorna); the Pintail Duck (A. acuta), a regular
winter visitor; the Teal (A. crecca); the Garganey (A. querquedula);
the Shoveller or Spoon-bill Duck (A. elypeata), in which the bill is
very large and provided with long lamine at its edge. Many Ducks breed in
England, but others, e.g., the Wid geon (A. penelope), only, or usually, in more
Northern Countries. The Fuliguline differ from the Ducks in the possession
of a small flap of skin, which projects from the hind toe; further in the power
of diving: they are mostly northern forms, several occur on the English coasts :
the Tufted Duck (Fuligula cristata); the Staup Duck (F. marila). To
this division belong the Hider Ducks (Somateria mollissima), which breed
on the Faroes, in Iceland and Greenland in great numbers. The Mergansers
(Mergine, genus Mergus and others), differ from the Fuliguline in the
narrow beak, hooked at the tip and furnished with dentiform processes at the
edge. Several species in England.

(b) Geese (Anserinz). Large, fairly long-necked, and long-legged, with-
out flaps of skin on the hind toe, beak high at the base and with a large
horny plate at the tip. In contradistinction to other Lamellirostres, which
feed either upon animals or are omnivorous, Geese feed chiefly on plants,
grazing with their bills; they live upon land much more than do the others.
Usually there is no striking sexual dimorphism. The Grey Goose (Anser
cinereus), the ancestor of the Domestic Goose; the Red-breasted Goose
(A. ruficollis); the Bean Goose (A. segetum), and others occur in Britain.

(c) Swans (Cygnus). Large, very long-necked, but short-legged; the
hind toe without a flap of skin, bill high at the base, flattened at the tip. In
Temperate and Frigid Zones; those of the Northern Hemisphere, white; those of
the Southern, partially or entirely, black. Amongst others the Whistling
Swan or Wild Swan (C. musicus), and the Mute Swan (C. olor), occur
in England; the latter is frequently kept as a tame animal. The Black
Swan (C. atratus) inhabits Australia.

(4) Flamingoes (Phenicopterus) are, with regard to their very long fore-
legs and metatarsals, like the Grallatores; the neck is extraordinarily long;
the beak looks as if broken, otherwise like that of the Ducks; tongue
soft and large; web present. One species of this large Bird inhabits
Mediterranean lands, wading about on the coasts.

Order 6. Grallatores (Wading birds).

The members of this group have pedes grallarii; the lower
portion of the leg is naked, scutellate, the metatarsus long; there is
usually no web, although this is present in exceptional cases. The
head is small, the beak usually long and narrow. The neck long,
Class 5. Aves. Order 6. Grallatores. 459

much curved, and sigmoid; the feathers which cover the curves
are often long, making the whole neck look short and thick. The
food is usually of an animal nature.

1. Altinares. Beak large and strong, much longer than the rest of the head,
with firm, horny sheath, small basal nares, wings large. Birds of considerable
size, which build their nests high above the ground (in trees, etc.) and foster the
young ones.

(a) Herons (Herodii), Hind toe long, with a large claw, resting its whole
length upon the ground. In Britain there are: the Common Heron (Ardea
cinerea), abundant, nests in flocks in trees; the Common Bittern (Botaurus
stellaris), with soft plumage, brownish in colour, nocturnal; the Night Heron
(Nycticorax griseus) with thick bill, an occasional visitor ; and others.

(b) Storks (Pelargi). Hind toe short, with small claw articulated at a
higher level than the other toes. Here belong the White Stork (Ciconia
alba), and the Black Stork (C. nigra) both of which occasionally visit England.
The Adjutant or Marabou (Leptoptilus) with very powerful beak;
bare neck and head; a carrion feeder, in Africa and the Hast Indies: the
White Spoonbill (Platalea leucorodia) with much-flattened bill broad at
the tip, in South Europe, rare in England: the white Sacred Ibis (Lbis
religiosa) of ancient Egypt, distinguished by the thin, soft, curved beak, and the
naked head and neck; now rare in Egypt but abundant in the Soudan and
Southern Nubia.

2. Brevirostres. Bill short, usually fairly thick, with firm, horny sheath
and nares sub-basal. Most of them are small or of medium size and nest on
the ground; the young ones can run from the first.

(a) Plovers (Charadriidx). Small birds with or without a small hind
toe. Among those occurring in England the following may be mentioned: the
Peewit (Vanellus cristatus), with a crest of feathers on the head, hind toe
present, nests on meadow land; the Turnstone (Strepsilas interpres), with
hind toe, the short beak somewhat arched upwards, with a world-wide distribu-
tion on sea-coasts; the Oyster Catcher (Hematopus ostralegus) without
hind toe and with a long beak; the Golden Plover, (Charadrius pluvialis),
without hind toe; with short beak clubbed at the tip : an inland form, on moors, etc.
Of these, the Turnstone is only a seasonal visitor, the others are indigenous.

(b) The Bustards (Otidz). Large hen-like forms with short conical
bill; and short powerful toes; the hind toe absent; inhabiting dry treeless plains
The Large Bustard (Otis tarda) aud the Small Bustard (0. tetraz)
occasionally visit England ; the latter is a native of Mediterranean coasts.

(c) Water-fowls, Rails (Rallidz). Toes long, hind toe well developed ;
beak varying in length. As examples may be mentioned: the Water Rails
(Rallus aquaticus), beak straight, larger than the rest of the head; the Corn
Crake or Land Rail (Crew pratensis), a migratory form; the Moor-hen
(Gallinula chloropus); and the Common Coot (Fulica atra), with a ridge o
skin along each side of the fore toes; both of the latter with a naked, horny
frontal plate above the beak.

(d) Cranes (Gruidz). Large, with fairly large, straight, pointed beak ;
legs very long, toes short, hind toe small, neck long. The Common Crane
(Grus cinerea) was formerly a native of England, but long ago ceased breeding
here, and now only appears at uncertain intervals.

3. Debilirostres. Bill long and thin, often flexible, and with a soft skin
otherwise like the Brevirostres; in mode of life, true Wading Birds. The
Snipes (Scolopax), with long, straight, soft beak (Woodcock [S. rusticola],
Great Snipe [S. major], Common snipe [S. gallinago], Jack Snipe [S. gallinula]) :
460 Vertebrata.

the Sandpipers (Tringa); some indigenous, some seasonal visitors: the
Ruff (Machetes pugnaz): the Redshank (Totanus): the Godwits
(Iimosa): the Curle ws (Numenius arcuata), with very long, arched downwardly
curved beak: the Avoset (Recurvirostra avocetta), with very long, upwardly
curved beak, and incomplete webbing between the toes. All those mentioned
(and others besides) occur in England; some are Birds of Passage, others
indigenous. The Phalaropes (Phalaropus), with ridge of skin along the
toes, are Northern forms (Iceland, etc.), which occasionally stray into England.
The males alone incubate the eggs.

Order 7. Accipitres or Rapaces (Birds of Prey).

Beak short and strong, thick at the base, which is provided with a
cere, much curved and with its point directed downwards. The feet are
powerful; the strong claws are of an elongate, conical shape, pointed
and curved, forming the talons; the hind toe is usually very strong ;
pedes raptatorii. Wings large. For the most part, majestic Birds,
feeding upon their prey or upon carrion. The females are larger than
the males. The newly-hatched young ones, although well covered
with down, remain for a long time within the nest, and are fed by the
parents.

1. Diurnal birds of prey (Hemeroharpages). Head and neck feathered ;
hind toe large, articulated at the level of the fore toes, and bearing a very short
claw. They prey upon living animals.

(a) Hawks (Asturidz). Lower side of the metatarsus covered with large
horny plates; wings of medium length. Amongst British species are the
Goshawk (Astur palumbarius) and the small Sparrow-hawk (A. nisus).
The Secretary (Gypogeranus secretarius), an extraordinarily long-legged bird,
with a very long metatarsus and short toes, recalling a Wading Bird; lives in
the deserts of Africa, feeding chiefly upon Reptiles. The Buzzards (Buteo)
differ from the Hawks principally in the greater length of wing. The Harriers
(Ctreus), also with long wings, are characterised by the possession of a facial
disc, like that of the Owls.

(b) Falcons (Falconide). The hinder side of the metatarsus, with
numerous small scales. Short, powerful beak, curved from the base, and with a
large tooth-like projection on the edge, near the tip. Wings usually long. The
most important occurring in England are the Kestrel (Falco tinnunculus), the
Peregrine Falcon (Ff. peregrinus), the Hobby (F. subbuteo), and the
Merlin (F. zsalon): F. subbuteo, a migratory form wintering in South Africa ;
the others indigenous. The Gyrfalcon (F. gyrfalco) is an Arctic bird, which
occasionally visits England.

(c) Hagles (Aquilide). The metatarsus like that of Falcons, but often
feathered; beak usually longer, only curved at the tip, very strong, without
the dentiform projection; large with long wings; the Eagles (Aquila),
characterised by the well-feathered metatarsus, only occur as stragglers in
England, but are more common in the Highlands. The only two British species
are the Golden or Mountain Eagle (A. chrysaétus), and the large Sea
Eagle or White tailed Hagle (Haliaétus albicilla), in which the meta-
tarsus is only feathered over its upper half. This form feeds both upon land
animals and fish; it occurs in all parts of Europe, and wanders south to breed.
The Osprey or Fishing Hawk (Pandion haliaétus), distinguished by the
Class 5. Aves. Order 7. Accipitres or Rapaces.. 461

short beak, and by the reversible outer toe, feeds on fish; and is very
cosmopolitan, being met with in all five continents. The Kite or Glede
(Milvus regalis) is distinguished from the Eagles proper by its smaller beak and
its forked tail; abundant in England and Europe generally. To the Eagles
belongs also the Bearded Vulture (Gypaétus barbatus), in the mountainous
regions of South Europe and South Asia (at one time in the Alps). It was formerly
elassed with the Vultures, which it resembles in its mode of life (feeding chiefly
upon carrion), but the head and neck are covered with true feathers.

2. Vultures of the Old World (Saproharpages). Head and upper part of
the neck bare or covered with down ; hind toe large, articulated at the same level
as the others; talons less powerful, somewhat depressed ; wings large; numerous
small scales on the posterior side of the metatarsus. Large forms, feeding chiefly
upon carrion, and inhabiting the hotter parts of the Old World. The large
White-headed Vulture (Vultur fulvus), with the head and neck covered
with whitish down; and thesmall Alpine Vulture (Neophron percnopterus),
with naked head and very long, thin beak; live in countries bordering the
Mediterranean and in Africa.

3. Vultures of the New World (Necroharpages). Head and upper portion of
the neck usually naked; hind toe small, articulated above the level of the rest;
nasal septum perforate; very large wings; carrion feeders; in America, especially
South America. The largest species is the Condor (Sarcorhamphus gryphus) ;
another large form isthe King Vulture (S. papa), with brightly-coloured
head and neck; andthe smaller Carrion Vulture (Cathartes).

4. Owls (Nyctharpages). The back part of the head so broad that the eyes
look forwards (in other Birds of Prey they look sideways). The face is surrounded
by a circle of peculiar short feathers, the facial disc; there is also a circle of
feathers round each eye; between these rings is the large auditory opening,
Bristle feathers surround the base of the beak; the plumage is soft, usually
mottled brown ; the outer toe (fourth) is reversible, 7.e., may be turned backwards ;
the hind toe is articulated somewhat above the others; the foot and toes usually
feathered.

(a) Diurnal Owls (Striges diwnz). The ear simple, without an
operculum ; facial disc incomplete above. They hunt both by day and in the
evenings. Diurnal Owls are rare in England. The Snowy Owl (Nyctea nivea)
has been found off the Shetlands; and the Hawk Owl (Surnia nisoria) at sea,
off Cornwall, but both these are more Northern (Scandinavia). Others which are
Continental birds, occasionally visiting the British Isles, are the Great-Eared
Owl (Bubo maeimus), and the small Scops Eared Owl (Ephialtes scops),
both with two tufts of feathers on the head; and the Little Owl (Athene
noctua).

(}) Nocturnal Owls (Striges nocturne). Ear very large, with an oper-
culum ; facial dise complete. In England there are the Tawny Owl (Syrniwm
aluco), the Long-Hared Owl (Otus vulgaris), the Short-Hared Owl
(O. brachyotus), the almost cosmopolitan Barn Owl (Strix flammea), and as
an occasional visitor, Tengmalm’s Owl (Nyctale funerea).

Order 8. Oscines. (Singing Birds).

The feet are thin and delicately formed. The hind toe, which is
strong and provided with a larger claw than the others, can
be moved by itself, whilst in all other Birds it can only be
moved with the other toes, since the tendon of the hind toe is generally
462 Vertebrata.

connected with that of the fore toes, though in the Oscines it is
independent. The contour feathers of the wing are small and few in
number. In the majority the back of the metatarsus is almost covered
by two long, narrow plates, instead of being scutellate. At the lower
end of the trachea there are generally several small muscles, which are
absent from other forms (singing muscles). The nest is often rather
ingenious in construction. The Oscines feed, for the most part, upon
grain, berries, or Insects.

1. Turdiformes. Beak usually straight or slightly curved at the tip, often
with a marginal notch in front; nares basal.

(a) Singers (Sylviadz). Beak somewhat feeble, compressed, of medium
length with a shallow notch: small or medium-sized some of them noted
singers: feeding upon Insects and berries. The following English Birds, among
others, belong here: many of the Turdide; Blackbird: (Turdus merula) ; the
Ring Ouzel (2. torquatus), the Song Thrush (TZ. musicus), etc. The
Common Dipper (Cinclus aquaticus), almost the same size as the
Thrushes, dives into running water; a sedentary Bird; the Nightingale
(Luscinia philomela); and the Redbreast (ZL. rubecola); the Redstart
(Ruticilla); the Wheatear (Sawicola); the genus Sylvia (Sedge Warblers,
Reed Warblers, and Willow Warblers) dainty little forms, usually inconspicuous
in colour. The Gold-crested Regulus (Regulus), and the Wrens,
(Troglodytes parvulus) the smallest British Birds. The Wagtails (Motacilla)
with long dipping tail, near small pieces of water. The Pipit (Anthus) with
long hind claw, like the Larks.

(b) Shrikes (Laniadz) differ from the Sylviade in the strong beak, at the
edge of which is a dentiform process on either side just within the curved tip.
They catch Insects and small Vertebrates and spike them on thorns. Several
species occur in Europe, the largest, the Great Grey Shrike or Butcher-
bird (Lanius excubitor), which is as big asa Thrush, is occasionally met with in
England.

(c) The Tits (Paride) small, with soft plumage; the beak is short, fairly
thick, straight, and without a notch; the nares covered by bristles. Insect-
eaters, which breed chiefly in hollow trees and such places. Amongst English
forms are the Great Tit (Parus major), the Blue Tit (P. ceruleus), the
Long-tailed Tit (P. caudatus), etc.

(d@) The Fly-catchers (Muscicapide) have short, straight, flattened
beaks, broad at the base and with stiff bristles at the root. The Spotted
Fly-catcher (M. grisola) is a seasonal visitor to England ; two other species
are occasionally met with.

(e) The Bohemian Waxwing (Ampelis garrulus) has a rather short
beak somewhat broad at the base, and soft plumage. The most remarkable
peculiarity of these creatures is that on the remiges, and sometimes also the rectrices,
some of the branches have united with the tip of the shaft to form a spatulate
lamina. They breed in Scandinavia, but in the winter occur in great numbers on
the continent and occasionally visit England. To an allied group belongs the
Golden Oriole (Oriolus galbula), which is of a beautiful yellow, of the size
of a thrush; rare in Britain.

2. Conirostres. Beak short, thick, and conical, with nares high up. The
food consists chiefly of seeds, but the young ones are fed upon Insects.

(a) Finches (Fringilla), beak thick, without a hooked tip; the Haw-
finch (F. coccothraustes), the large English Finch, beak extraordinarily thick
and strong; the Chaffinch (F. celebs); the Mountain Finch (F. monti-

e
Class 5. Aves. Order 8. Oscines. 463

fringilla); the Greenfinch (F. chloris); the Serin Finch (F. serinus) ;
the Common Linnet (F. cannabina); the Mountain Linnet (F.
montium); the Goldfinch (F. carduelis) ; the small yellowish-green Siskin
(F. spinus); the Lesser Redpole (F. linaria); the House sparrow
(F. domestica) occurs in Europe, Asia, and North Africa, and has also been
introduced into America and Australia; has increased enormously in North
America; the Tree sparrow (F. montana); the Bullfinch (F. pyrrhula) :
all these occur in England, but the Mountain and Serin Finches and the Siskin
are rare. Among foreign forms may be mentioned the Canaries (#. canaria)
from the Canary Islands.

(b) Buntings (Emberiza), beak compressed at the tip, narrower and lower
than the mandible, the edge arched; there is usually a hard knob on the palate.
The Snow Bunting (#. nivalis), which nests in the north, and in the winter
comes to England, has no palatine knob. The Common Bunting (F.
miliaria); the Yellow Bunting or Yellow Hammer (E. citrinella) ;
the Black-headed Bunting (EH. scheniclus); the Ortolan Bunting
(#. hortulana), all occur in England, but the last is rare.

(c) Cross bills (Lowia) are chiefly characterised by the crossing of the
tips of the beak and mandible; pine-tree birds: L. curvirostra and L. pytiopsit-
tacus occasionally visit England. Allied is the Pine Grosbeak (Pinicola
[Pyrrhula] enucleator), about the size of a Thrush, with hooked tip to the beak;
a northern form of rare occurrence in England.

3. Corviformes. Strong, fairly large, almost straight beak; fairly strong
feet. For the most part large, social, and omnivorous.

(a) Starlings (Sturnus vulgaris), medium-sized, with long, straight,
compressed beak; the nares not covered with feathers. They breed in holes,
are insectivorous and indigenous. Allied is the Rose-coloured Pastor
(Pastor roseus), in which the top of the beak is feebly curved; occasionally strays
into England.

(6) Raven family (Corvidz), with very strong, anteriorly compressed,
somewhat curved beak ; the nares are covered with bristles. Large. The Raven
(Corvus corax), the largest of English Oscines, quite black in colour and
not very abundant. The black Carrion Crow (C. corone), and the partially
black Hooded Crow (C. cornix) are not separate species, but only
geographical varieties; there is a series of transitions between the two, and
they are quite fertile together. The Rook (C. frugilegus), quite black, the
bristle feathers at the base of the beak wanting in the adult. The Jackdaw
(C. monedula), slaty black, beak shorter than in the others mentioned. The
Magpie (Pica caudata), with long tail, black and white. The Jays (Garrulus
glandarius), brightly-coloured, with short beak, the tip of which is hooked. The
Nutcracker (Nucifraga caryocatactes), with long, almost straight beak.
Rare in England.

(c) Birds of Paradise (Paradiseidz), distinguished by their gorgeous
colouring and the peculiar structure of the feathers, but these points characterise
tbe males only, the females being more modestly arrayed; large, with strong,
compressed beak, and nares covered by feathers; New Guinea and adjacent
islands.

4. Swallows (Longipennes). Wings very long, feet short, beak short;
broad at the base; the angles of the mouth reach far back. Small migratory
Birds, excellent fliers; insectivorous. In England occur the Swallows
(Hirundo rustica), with brownish red throats, and the House Martins
(H. urbica), both of which build the well-known nests of mud and saliva; the
brownish-grey Sand Martins (H. riparia), which dig horizontal nesting
464 Vertebrata.

tunnels, 1m. to 15m. long in perpendicular walls of sand; and breed in the
innermost, somewhat widened portion.

5. The Common Creeper (Certhia familiaris), the Nuthatch
(Sitta cxsia), and the Wall Creeper (Tichodroma muraria) belong to a
special group of the Oscines, and are characterised by the very great size of the
hind toe, whilst the fore toes are enclosed at their roots in a common skin. The
claws are much compressed and very pointed. They are all found in England, but
the Wall Creepers are very rare. They run up the trunks of trees or up rocks.
All the Creepers have long, thin, arched beaks (longest in the Wall Creepers) ;
the Nuthatch has a straight, strong, pointed beak. The Wall Creepers are Alpine.

6. Larks (Alaudide), distinguished from all the other Oscines so far
mentioned in that the metatarsus is covered posteriorly by several small
plates. The hind toe has a long, straight claw; the beak is of medium
length, fairly strong and almost straight, the summit arched. They feed chiefly
on seeds, and nest on the ground; the following occur in England: the Sky
Lark (Alauda arvensis), the Wood Lark (A. arborea), and the Crested
Lark (A. cristata), the lastisrare. The Shore Lark (Otocoris alpestris)
is of striking appearance, it inhabits the Northern parts of Asia and Europe,
and not infrequently visits the East coast of Britain. Allied to the Larks is the
Hoopoe (Upupa epops), with long, thin, arched beak, a hind claw like theirs,
and an upright tuft of feathers on the head. Rather rare in England.
Insectivorous, migratory.

7. The Lyre Birds (Menura), fowl-like, with short, straight beak.
They are characterised especially by the peculiar, long, lyre-shaped tail of the
males. The innermost and the outermost rectrices are curved outwards, the rest
are thinly furnished with long barbs, which possess no barbules: Australia.

Order 9. Clamatores (Shricking birds).

Distinguished from the Singing Birds in that the hind toe, and
especially its claw, is less powerful and that it cannot be moved by
itself. The singing muscles are not developed.

1. The Roller (Coracias garrula). Beak of medium length, compressed
in front, broad at the base, slightly arched at the tip. Gorgeous blue-green;
about the size of a Thrush; comparatively rare in England; nests in holes in
trees ; insectivorous and migratory.

2. Swifts (Cypselidx). The mouth very large, extending back behind the
eye; beak short and weak; broad at the base and flattened; uncommonly long
wings, very small feet. Insectivorous forms like Swallows. In England occurs
the Common Swift (Cypselus apus), in which all four toes are directed
forwards; the dish-like nest is formed in holes in walls, etc., and is built of
straws and feathers, which are bound together by saliva. The Swifts are repre-
sented in the Alps and on Mediterranean coasts by the very similar, somewhat
larger, Alpine Swift (Cypselus melba), with white abdomen ; it occasionally
visits England. The Salanganes (Collocalia), with normal feet, but in
other respects like the foregoing species, live in the East Indies, and construct
their nests of saliva (edible birds-nests). To an allied family belongs the
Nightjar (Caprimulgus ewropxus), which is large, brown, and coloured like
an Owl; feather bristles at the base of the beak; nocturnal; the eggs are laid
on the bare ground. A summer visitant to Britain.

3. Humming Birds (Trochilidz). The beak is long, thin, and tubular ;
the tongue is deeply cleft and can be greatly protruded. The wings are long;
Class 5. Aves. Order 9. Clamatores. 465

the feet short. Gorgeously coloured, especially the males; often, too, some of
the feathers are of a peculiar structure. Insectivorous. To this family, which
is only met with in the warmer parts of America, belong the smallest of all
Birds.

4, The Kingfishers (Alcedinidx) have a straight, strong, angular beak ;
external and middle fore toes united up to the second joint, the
middle internal ones to the first pedes gressorii. Brightly coloured; mostly
natives of warm countries. In England the long-beaked Kingfisher (Alcedo
ispida), which lives upon Pisces and is often very destructive of the fry. The
same type of foot is found in the Bee-eater (Merops apiaster), with long,
very-pointed, slightly-arched beak; winters in South Africa, migrating into
South Europe in the summer, and occasionally flying into England. In the
Rhinoceros Birds (Bucerotidx) too, the fore toes are connected at their
roots; they are further distinguished by their very long, thick. somewhat-curved
beak, which usually bears a large process at the root. Africa and East Indies.

5. Pigeons (Columbidz), characterised by the fact that the ratner short
beak has a horny covering only at the tip, being soft at the base. The Ring-
dove (Columba palumbus), the Stock Dove (C. enas), which nests in high
trees, and the Turtle Dove (Turtur auritus)* occur in England, the last as
a seasonal visitor. The Rock Pigeon (C. livia), on the coasts of the
Mediterranean, in England, etc., is the ancestor of the numerous races of tame
Pigeons. The Migratory Pigeon (C. migratoria), of North America.
wanders in immense flocks through large districts in search of food. Numerous
other Pigeons occur in various parts of the world. An aberrant form is
Didunculus strigirostris of the Samoan Isles, distinguished by its short,
strong beak, hooked at the tip, and by the presence of two dentiform processes
on each side of the lower jaw. The extinct Dodo (Didus ineptus) was about
the size of a Swan, very clumsy, with strong legs and strong beak; on
account of the very small size of the wings it was unable to fly (sternal keel
absent); the tail, too, was very degenerate. It lived in the Mauritius, and was
extinct by the close of the seventeenth century.

Order 10. Scansores (Climbing Birds).

Distinguished from the Clamatores in that the fourth toe is turned
hack, so that they possess two fore and two hind toes (pedes
‘scansorii).

1. Cuckoos (Cuculide) have a beak of medium length and somewhat
hooked ; the fourth toe can be turned to the side. Here belongs the Common
‘Cuckoo (Cuculus canorus), an insectivorous, migratory form. which lays its
eggs in the nests of other Birds (Oscines) in order that they may do the
brooding.

2. Woodpeckers (Picidx) have a very strong, straight. angu’ar beak,
compressed at the tip and keel-like; the tongue, which can be stretched out a
very long way, is provided at the edges with delicate biwkwardly-directed
‘processes; the tail feathers are very stiff, and support the hird in climbing. They
are Forest-birds, feeding wpon wood-boring larve and other Insects, but also
upon seeds; they breed in holes in trees, which they chisel out for themselves;
they are “res dents,” ov wander about in a limited locality. In England are
found the Great Bluck Woodpecker (Picus martius), the Green Wood-

 

*The Collard or Barbary Dove (f. risorius), which is often kept tame,
lives wild in Asia and Africa.

HH
466 Vertebrata..

pecker (P. viridis); and the Spotted Woodpeckers, the Large (P-
major), the Medium (P. medius),and the Small (P. minor). The Three-toed
Woodpecker (P. tridactylus), in which the inner hind toe (hallux) is lost,
occurs in the Alps. The Wryneck (Lyn torquilla), is a near ally; beak
conical, not keel-like; the tail feathers are not stiff enough to act as a support;
migratory. visiting England in the spring.

3. Parrots (Psittacide) have an uncommonly short, thick, much arched
beak, overhanging a short mandible; the beak is freely movable; the tongue,
thick and soft. They are brightly-coloured (green, red, etc.) and plant-eating ;
they are found in the Tropics. They may be divided into several groups: (1)
Cockatoos (Plictolophinz), of Asia and Australia, with an upright tuft of
feathers on the head, often brightly-coloured plumage; (2) Parrakeets
(Sittacine), with long tails; (3) True Parrots (Psittacine), with short tails,
and without the crest of feathers on the head; (4) Lories (Trichoglossinz), of
Australia, the tip of the tongue is brush-like in consequence of numerous long»
filiform, horny papille ; (5) Stringopine, owl-like Parrots, of which there is only a
single genus in New Zealand (Stringops habroptilus). The last are nocturnal,
with soft, dark greenish plumage, living by day in holes in the ground, where
also they nest; they fly very little, or not at all (the sternal keel is reduced)
and for the most part move about on the ground.

4, Toucans (Rhamphastidz) have a very large, thick, somewhat curved
beak, which is often notched at its edges, and which is almost as long as the
whole body; the tongue is narrow, horny, and frayed out at its margin. They
are South American forms, of medium size, and with gorgeous colouring.

Class 6. Mammalia.

As regards external configuration, the Mammalia are usually
characterised by the possession of a very pronounced neck, varying
considerably in length; of a much reduced tail, with no locomotor
significance, and of little use; of limbs, so well-developed, on the
other hand, that the body is raised some distance off the ground: the
elbows are turned backwards; the knees, fingers, and toes forwards.
In many cases the animal does not rest upon the whole foot, but only
on the toes, or even their tips, whilst the rest is raised, and contributes.
to the lengthening of the limb.* Within the class, besides the
ordinary walking type, various others are specialised, such as.
springing, flying, swimming forms (¢f., Reptilia). When the body is.
adapted to a peculiar mode of life, the outer form may be very
aberrant. This is especially noticeable in certain aquatic Mammalia.
(Whales), where the neck is reduced toa minimum; the limbs are
very degenerate, whilst the tail attains enormous proportions, so that
the appearance is in the highest degree piscine.

The skin consists of the usual layers (dermis, and epidermis with
stratum corneum and stratum mucosum or Malpighii); on the surface
of the dermis there are papille extending into the Malpighian
layer. Pigment may be present in the epidermis (in both layers), and

 

* The limbs are longest, and the surfaces touching the ground smallest in the.
swiftest animals (Ungulata)
Class 6. Mammalia. 467

also in the dermis. The stratum corneum is not shed all at once, but
in minute portions.

Asarule the greater part of the skin is covered with hair, a
very characteristic feature, absent in very few cases. The hairs
consist almost entirely of cornified cells, and each is inserted in an
invagination of the skin, the hair follicle. At the base of
each follicle there is a small hair papilla, covered by an out-
growth of the stratum mucosum, by the cornification of which the
overlying hair is formed. The rest of the hair follicle is covered
by outgrowths of the mucous and horny layers of the ordinary
epidermis, the outer and inner root-sheaths; the latter
is continued below into the hair,
the former into the stratum mucosum
of the papilla; the hairs are nothing,
then, but well-defined, enormously-
developed portions of the stratum
corneum. In many of the thicker
hairs there is an inner medulla of
loosely-packed cells, surrounded by
the harder cortex; externally there
is a layer of thin, flattened cells,
the epidermis; many, especially
thin, hairs consist simply of cortex
and epidermis. In many Mammals
two kinds may be distinguished,
contour hairs and woolly
hairs; the latter finer and covered
by the others. Peculiar long stiff
“tactile hairs’? or “whiskers”
(vibrisse) are often inserted on
certain regions of the head, es-

pecially on the upper lip; they are Fig. 379. Longitudinal section of

well-developed and _ @ hair, and the connected hair
P ; : tegu larly ar follicle; diagrammatic. a outer
ranged ; their follicles lie in a blood root sheath, b connective tissue, c
space, which is in H . stratum corneum, h hair, i inner root
P 2 communication sheath, r stratum Malpighii, p hair
with blood vessels. Other peculiar _ papilla.—Orig.

stiff hairs, the eyelashes, are

often present along the edges of the eyelids. Sometimes certain of
the hairs attain immense proportions, such as the spines of the
Hedgehog and Porcupine. The hairs are, for the most part, obliquely
implanted in the skin, and are regularly arranged, usually in small
groups or tufts. Smooth muscle fibres are attached to the
base of the follicle, they arise from the dermis, and by their
contraction the hair can be erected. Nerves also run to the hairs

(or more correctly to the hair follicles), especially to the whiskers
mentioned above, which are true tactile organs.

 

HH 2
468 Vertebrata.

Like the feathers of Birds, hairs are shed at regular intervals
and replaced by new ones; each is detached from the papilla,
and a new one arises from the base of the follicle. In some
Mammalia (Man and the Apes) this moulting goes on
gradually throughout the whole year, now one hair, now another
being thrown off and replaced by a new one. In others, however,
it is confined to a short period recurring annually; and usually, for
northern forms, in the spring,* when a total ecdysis takes place, both
wool and hair being thrown off. Simultaneously new hairs arise, and
the tips of the wool hairs bud out, but complete their development
later in the year. In some animals which are dark in summer, white
in winter, there is a colour changeT of the summer coat in
late autumn, in the Alpine Hares, for instance. In others, in which
the summer and winter coats are different, a change of hair occurs in
the autumn, as well as in the spring, e.g., in Stags.

In many Mammals some portion of the body is covered by scales or plates
like those of the Reptiles (Manis, Dasypus, tails of Mice). Sometimes, ¢.g., in
Dasypus, the dermal part of each scale contains an ossification; and
besides this there are in several Mammalia, smaller or larger independent
ossifications in the dermis.

Small glands in connection with the skin are usually distributed over
almost the whole surface ; two principal kinds may be distinguished,
sebaceous and sudoriparous. The sebaceous glands are
small and racemose, and usually open into the hair follicles; rarely
directly on to the surface ; they are therefore generally absent from
hairless tracts, they secrete a fatty substance. The sudoriparous
glands are simple and tubular, with the lower portion, usually
lying in the loose layer below the skin, coiled into a knot. They also
often discharge their secretion into the hair follicles, but closer to
the surface than the sebaceous glands ; many open quite independently,
in great numbers, for instance, in certain naked tracks. Like the
sebaceous glands, too, they occur on various regions, in various
numbers, and are of various sizes. . Most of them secrete sweat ; the
secretion may, however, be more fatty; for instance, the wax-glands
of the ear are peculiar sweat-glands.

The mammary glands, common to all Mammalia, are
peculiarly modified sudoriparous glands. Those of the Mono-
tremes are of the most primitive type; here, there is, on either
side of the abdomen, a small hairy pit into which a number of large
branched sudoriparous glands open; they secrete milk. In other
Mammalia they open upon somewhat projecting papille, the
mammille, or nipples, usually several upon each (about twenty in
Man, five to eight in the Dog, two in the Horse), seldom there is only

 

* But a change of some hairs may also occur at other times.

+ Cf., change of colour in feathers, p. 434.
Class 6. Mammalia. 469

one (Ruminants). The glands or mamma, which vary in number (one
to seven, most in those animals which produce many young ones ata
time), lie in two rows on the ventral aspect of the body. They are
of considerable size and much branched; the terminations are
vesicular, and for this reason the glands were formerly regarded as
sebaceous ; comparison with those of Monotremes demonstrates, how-
ever, that they are really sudoriparous. During gestation the mammary
glands increase in size and complexity, and are functional for some
time after parturition. Milk is a watery liquid in which are suspended
numerous oil globules; these impart its white appearance. At the
close of lactation the glands become simpler again; they are usually
rudimentary in the males.

Specially modified skin glands, isolated or in patches occur more rarely, but
still fairly frequently. Asa rule the skin is invaginated to form a pit, covered
with hairs, and in this region the glands are specially prominent: such are the
interdigital glands of Sheep and other Ruminants; the so-called lachrymal pits
in front of the eyes of the Red Deer; the perinezal pouches opening, in the Dog
and other Carnivora, at the sides of the anus; the musk sac in the Musk deer, etc.
In other cases the highly-developed skin glands open freely on to the surface; a
very large one opens on the back of the Peccary; in certain Shrews there is a
region of the skin with numerous specially modified glands, etc.

On the lower side of the foot there is usually a naked elastic tract
of skin, the sole, covered by a thick but soft stratum corneum, and
provided with numerous sweat glands. In some cases it extends over
the whole ventral surface, or it is limited to certain regions, namely,
to the toes.

Like Reptiles and Birds, Mammals have cap-shaped claws at the
tips of the digits, and here also they are differentiated into two parts,

Fig. 380. A Claw
ot a Mammal (removed
from the subjacent skin),
B Nail of a monkey, C
hoof; diagrammatic. s
sole (of the claw) ; the
rest, wall.

 

a harder dorsal (and lateral) wall, and a ventral horny sole,
consisting of looser horn; the base of the claw is oblique, so that
the sole is shorter than the wall; the latter forms a horny plate,
arched longitudinally and transversely, whilst the former is flattened
470 Vertebrata.

or concave below. The wall is usually covered at the base by a
fold of skin. The nails of Monkeys differ from most claws in
that the sole is very short and consists of very soft horn (this may also
be the case in many true claws), and that the wall is but slightly
carved, either longitudinally or transversely ; in Man the sole has
practically vanished, merely an insignificant remnant of it lies below the
edge of the wall, and the “nail” is the wall only. The modifica-
tions termed hoofs, are peculiar in that they are short with blunt
ends, and the thick wall is convex transversely, but not longitudinally
(or very slightly) ; and in that the horny sole is thick and hard,
and the fold of skin at the base very poorly developed. The
peculiarity of the hoof is correlated with its function of supporting
the animal when walking, whilst in other forms the sole of the
foot serves this purpose, and the claws are used for climbing,
digging, etc., and in this connection, among other points, a solid
attachment by means of a deep fold of skin appears of special
importance.

In most Ungulata (excepting the Tapir and the Rhinoceros) there is an
intimate connection between the hoof and the sole of the foot, which is usually

L

0 a p iD t
!

\ |
ts

u

I

Fig. 381. Longitudinal
| section of the tip of a Mam-
! malian digit. Malpighian
| layer dark, a and b see p.
| 471, ba ball of the foot with
i

4

  
  
 

 

sweat glands, g last phalanx
of the digit, g’ next phalanx
(not completely drawn), h
cavity of the joint, p and t
wall, s sole, sb sesamoid bone,
J w fold of skin at the base of

* ' " the claw.— Orig.
1
|

i
|
|
g hk 8b gf La

very small here, and confined to the distal portion of the toes. In the Horse
(Fig. 382 D) the hoof is, so to speak, arched round the very small sole of
the foot (the “ frog”), so that the latter lies at the back of the hoof; relations

 

Fig. 382. Tip of toes seen from below: A Monkey, B a clawed animal, ( Rhinoceros,
D Horse, H Elk; diagrammatic. 6 sole of the foot, n edge of wall, s horny sole-——Orig.
Class 6. Mammalia. 471

somewhat similar obtain in the Pig, where, however, the sole of the foot reaches
farther back than in the Horse. Ruminants (Fig. 382 H#) display an advance
on the Pig, since the true sole reaches far forwards, and the horny sole is largely
suppressed, and only represented by a narrow rim along the lower edge of the
horny wall: further, the most anterior portion of the true sole in many
Ruminants (Red-deer, Oxen, etc.) has attained greater firmness than in others,
becoming like the horny sole, whilst in others (¢.g., the Roe and the Elk) it is as
soft as usual.

As in the Crocodiles, Chelonians, and Birds, growth of the claws is the result
of the formation of a new thin stratum corneum over the whole surface of the
subjacent Malpighian layer; thus the cap-shaped claw is pushed forwards (just
as in the growth of the horns of Ruminants, see below). In Mammals
(and Lizards), on the other hand, a large portion of the subjacent Malpighian
layer is sterile (Fig. 381 a—b), i.e., is not concerned in strengthening the wall
which is formed at the proximal margin of the layer (left of a), and pushed over
sterile part; at the tip (right of b) a formation of horny substance (¢) again
occurs. The horny wall, therefore, increases in thickness from the base up toa,
retains the same thickness up to J, thence increasing in thickness again, except
in so far as it is prevented by wear.* The horny sole, on the other hand, becomes
continuously thicker from the base to the tip.

The horn of the Rhinoceros is an enormous local thickening of the stratum
corneum ; into it extends a papilla from the dermis, covered of course with the
stratum Malpighii. The horns of Ruminants are of quite a different structure ;
each is to be regarded as a large, naked projection of skin, which is internally
ossified, and covered superficially with a firm, thick layer of horn; the structure
therefore consists of a bony mass within, the core, fused to the frontal bone;
outside this, there is a layer of connective tissue and of the stratum Malpighii, and
externally, the stratum corneum, which increases by new deposits from within,
and is thus pushed out distally; the basal edges of the individual layers of horn
appear as rings on the surface. The antlers of the Stag are very like, but
they differ in having a comparatively thin layer of horn, and a covering of
hair (“velvet”). In the Giraffe, where the antlers are of small size, the soft
parts persist round the core; in other animals, however, when they are fully
developed, the velvet shrivels over most of the surface and is rubbed off; only
the basal region, the pedicle, retains the integumentary covering. The bare
bony mass, the true antler, is loosened annually from the pedicle, and is thrown
off ; the adjacent skin then grows over the bare edges, and a new antler develops
at the same spot, covered at first with velvet. In the Giraffe, no shedding occurs.

The vertebre are usually biplanar, rarely opisthoccelous ;
they are connected by thick ligamentous discs of fibrous
connective tissue, which contain a remnant of the notochord, the
so-called nucleus pulposus, centrally. The vertebral column is
composed of the same sections as in Reptilia. There are almost
always seven cervical vertebra, t regardless of the length of the neck.
The first two of these are, as in the Reptilia, developed as atlas and
axis. Monotremes alone possess separate cervical ribs (on the

 

* In the transparent nail of Man, the bright basal portion (“lunula”’) corresponds
to the portion a in Fig. 381; a bright line near the free edge corresponds with the
spot b.

+ Exceptions: the Manatee has only six, so has one of the Sloths (Cholepus
Hoffmani), whilst another of the same genus (Ch. didactylus) has seven, and yet
another (genus Bradypus), nine.
472 Vertebrata.

last six cervical vertebra), and even here they are only separate in
early life, fusing later with the vertebree ; the posterior ones are not,
asin Reptiles and Birds, longer than the anterior. In other Mammalia,
cervical ribs are, indeed, present, the so-called transverse processes of
the cervical vertebrae ; but they are at no time separated from the
vertebrae, so that their identity can only be recognised by comparison
with other forms. The thoracic vertebre are more sharply
marked off from the cervicals than in Reptiles and Birds, since the
first bears a movable rib, articulating with the sternum. In the
lumbar region there are usually fairly large transverse processes.
There are, as a rule, twenty thoracic and lumbar vertebrz (the
number may, however, sink to fourteen, or rise to thirty); the
thoracics are twelve or thirteen, but may rise to upwards of twenty.
Of true sacral vertebra, ie., those to which the ila are
attached ; there are, as in Reptiles, usually only t wo fused together in
the adult, but in most Mammals one or more of the anterior caudal
vertebre (the false sacral vertebre) assist in forming the
sacrum. The caudal vertebre vary considerably in number

Fig. 388. Axis of a young Platypue
(Ornithorhynchus) from the left side (A),
and from behind (B). 1 centrum of the
first cervical vertebra, 2 do. of the second,
b arch, r rib, ¢’ inferior spine. In B the
arches, centrum, and ribs are shaded in
different ways.—Orig.

\

 

the anterior ones usually have well-developed transverse processes, and
often bear V-shaped bones, like those of many Reptiles, on the
ventral side; the posterior tail vertebre are always more or less
imperfectly developed, especially the last (arches and processes
degenerate).

The ribs always consist of an upper and a lower portion, of which
the latter is usually cartilaginous or only partially ossified. In the
Monotremes, yet a third portion is intercalated (cf., the Crocodilia)
between these two. The majority of the ribs, the anterior so-called
true ribs, are attached to the sternum, whilst the posterior, or
so-called false ribs, are attached to one another and to the last
true rib, or terminate quite freely (floating ribs). The rib articulates
with the transverse process of the corresponding thoracic vertebra by.
an external outgrowth, the tuberculum (generally absent from the
posterior ribs); and with the centrum by the capitulum, the true
dorsal end of the rib. The articular facet lies upon one centrum, or
between that centrum and the one in front of it. The true ribs, of
which the first is usually especially strong, become longer towards the
Ulass 6. Mammalia. 473

sacrum ; the false ribs, shorter. The sternum, which is almost
always long and narrow, consists at first of a cartilaginous mass, in
which a series of ossifications appears later; the latter usually remain
separate throughout life, so that the adult sternum retains a jointed
appearance ; occasionally they fuse to a great
extent (asin Man), The most anterior joint,
the manubrium, is generally somewhat
broader than the succeeding ones; to this
the first pair of ribs are attached, whilst the
other true ribs are attached at the junctions
of the other joints. The last joint, the
xiphisternum (processus wiphoides), with which
no ribs are connected, usually ends in a broad
cartilaginous plate. Only in the Monotremes
is there an episternum corresponding
with that of Reptiles, as in many Lizards it
is here a large T-shaped bone.

The skull of the adult consists chiefly
of bone, and exhibits but little cartilage. Not
only the small premaxilla and the large
maxilla, but also the bones belonging to
the upper portion of the gill-bars, are fused
with the skull. Of these only the palatine,
which is attached anteriorly to the premaxilla,
and the somewhat small pterygoid are
present, whilst the quadrate has dis- Wig 884 Sternum and

garoo. ¢

appeared (or at least in its usual form, see clavicle, m manubrium, 1
below under the ear) ; the lower jaw, which 71s (cutoff), # xiphisternum,
: 7‘ : zw) its cartilaginous terminal
consists of a single bone on each side, plate—Orig.
articulates directly with the skull. The two
rami are either united anteriorly by means of connective tissue,
or (in the adult) are anchylosed (Horse, Man, and _ others).
There are two occipital condyles instead of one as in
Reptiles and Birds. There is no interorbital septum as in many Reptiles,
etc.; the cranial cavity extends forwards as far as the nasal
cavities. The latter are usually very well developed; they are
separated by a plate, at first cartilaginous, later partially replaced by
bone, which arises from the anterior wall of the skull, and projects
forwards. They are also at first surrounded laterally and dorsally by
outgrowths from the anterior region of the cartilaginous cranium, but
after a time these ossify, or are covered in by membrane bones, and
then dwindle away; those portions which surround the external nares
and the adjacent regions persist, however, throughout life. In the adult
the nares are surrounded by various bones, laterally chiefly by
the maxille, dorsally by the well-developed, flattened nasals,
which touch in the median line; ventrally by the palate

 
474, Vertebrata.

 

Fig. 385. Skull of « Dog. A sawn through longitudinally; B dorsal, C ventral.
The cartilaginous parts are removed. AS lateral parts (wings) of the sphenoid, BO basi-
occipital, BS basisphenoid, CE cribriform plate, ET ethmo-turbinal, ExO exoccipital, Fr
frontal, IP interparietal, L lachrymal, Ma jugal, ME bony portion of the nasal septum
(connected behind with the cribriform plate), Mt maxillo-turbinal, Ma maxilla, Na nasal, OS
orbitosphenoid, Pa parietal, Per petrosal, Pl palatine, PM premaxilla, PS presphenoid, Pt
pterygoid, SO supraoccipital, Sq squamosal, Ty tympanic bulla, Vo vomer, ch, eh, sh
joints of the anterior cornua of the hyoid, bh body of the hyoid, th posterior cornua, an
external nares, ap and apf canalis incisivus, cd articular facets of the mandible, eam external
auditory meatus, fm foramen magnum, gf articular facet on the skull for the lower jaw, oc
occipital facets, s symphysis of the mandible.—After Flower.
Class 6. Mammalia. 475

(hard palate), which is formed of horizontal medianly apposed
portions of the premaxillee, maxille and palatines.* Behind, in the
septum between the cranium and the nasal cavities, which was originally
cartilaginous, there is a bone with numerous fine perforations for the
olfactory nerves, the cribriform plate. From the front side of
this thin, folded, bony lamelle arise, covered by a thin membrane
and projecting far into the nasal cavity ; they are known as the ethmo-
turbinal. Further forward on the outer wall, there is a bone composed
of a varying number of delicate bone lamelle, the maxillo-
turbinal, so that the greater part of the cavity is filled up.
There are larger or smaller air spaces (Fig. 386) in certain bones of the
head in connection with the nasal cavities of the Mammalia; especially
in the maxilla (maxillary sinus) and in the frontal (frontal
sinus); sometimes (in the Ox, Elephant, etc.) these smuses are

 

Fig. 886. Skull of an old Pig, sawn through longitudinally, in order to show the large
arsinuses. hcranial cavity,1l U’ air sinuses partially (l’ the frontal sinus) divided
by bony plates, s bony nasal septum.—After Bendz.

of considerable size, extend into other bones, and are divided by
incomplete septa into a number of small cavities. Amongst other
characteristics of the skull it may be mentioned here, that a bony
bridge, the zygomatic arch,t runs from the articulation of the mandible
to the maxille ; it is formed by a process of the squamous (see below),
of the jugal, and sometimes a process of the maxilla (cf., the similar
bony bridge in Reptiles and Birds which is formed of the quadrato-
jugal and jugal). The hyoid consists of an unpaired body and
two horns on each side. The anterior horn, which corresponds
to the hyoid of Fish, is usually the longer, and consists of three
movable joints ; it is attached by its upper end to the skull (prootic).

 

* The palate is perforated in front at the junction of premaxille and maxille by
two openings (canales incisivi), through which the Stensen’s ducts, mentioned on
Pp. 333, pass.

+ In some Mammals there is a process near the middle of the jugal which meets
a similar one from the frontal and forms with this a bony bridge behind the eye.
476 : Vertebrata.

The posterior horn, which corresponds to the first gill bar, is short
and unsegmented.

The foramen magnum is surrounded by four bones, the supra- basi- and
two ex-occipitals; the latter bear the condyles, which may, however, extend
on to the basi-occipital. In front of this bone lies the basisphenoid, in front
of this again, the presphenoid, both developed in the ventral region of the
cartilaginous cranium, and both provided with wing-like lateral processes (ali-
and orbito-sphenoids) which assist in forming the cranial boundaries ;
in front of the sphenoids lies the cribriform plate. The periotic
(petrosal) within which the auditory organ is situated, lies in front of the
ex-occipital: the squamous, from which the jugal arises, is attached
externally to this; and the tympanic, a circular bone over which the
tympanum is stretched, lies upon it: in many Mammalia these three bones
fuse at a very early period, and are termed together the temporal. A single
or paired bone, the interparietal, lies above the supraoccipital, and in many
cases (e.g., Man) fuses with it even in embryonic life. The parietals lie in
front of the interparietal, and anterior to these again are the frontals,
overlapping the lachrymals, upon which the lachrymal duct opens in front
of the orbit on either side. The posterior region of the nasal septum is ossified,
and forms a plate, the lamina perpendicularis, perpendicular to and fused with
the cribriform plate, whilst the anterior portion remains cartilaginous; the lower
part is formed by an unpaired compressed bone in the form of a trough, the
vomer, (difficult to homologise with the bone so-called in the lower Vertebrata).
The pre- and post-frontals, the quadratojugal, the transverse bone, and the
columella, besides the quadrate, all well-known in reptilian skulls, have dis-
appeared. In general, the bones of the mammalian skull are only separate
during youth, in later life they fuse entirely or to a great extent.

The great diversity of external form displayed by mammalian skulls is
directly dependent on the varying development of the organs within and upon it.
In this connection, the brain is of great significance; with a great development.
of this, as compared with the other organs of the head, the posterior region
of the skull preponderates over the anterior (face portion); this is the case, for
instance, in Man. ‘The heterogeneity of the teeth has also considerable
influence upon the form of the skull; their great development leads to a
corresponding hypertrophy of the bones in which they are implanted, and also
of the parts upon which the masticatory muscles are inserted. The development
of the organs of the nasal cavity, and also the varying size of the eye, are of great.
importance, whilst the presence of horns or antlers brings about an increased
development of that part of the skull to which they are attached. In large
skulls of large animals with large teeth, horns, etc., the air-sinuses often
occupy a considerable space: the large bony masses necessary to support these
parts, or to afford attachment for the muscles, are hollowed out, a point of very
great importance to the animal (e.g., Horse, Ox, Elephant). It may also be
mentioned here that the skull of the young animal often differs considerably
in external form from that of the adult: the brain is proportionately larger ;
the teeth and masticatory muscles feebler; the face portion therefore small;
the air sinuses little developed; the projections from which the masticatory
muscles arise, small or absent, etc. The skull of smaller (adult) Mammals bears
in many respects the same relation to the skulls of larger allied forms that the
young one does to the adult of the same species ; the cranial portion is larger, thé
muscular ridges smaller.

The shoulder girdle of the Monotremes is similar to
that of the Reptilia; both scapula and coracoid are well

developed; the latter is broad and flattened, divided into anterior
Class 6. Mammalia. 477

and posterior portions, and attached by its anterior end to the
sternum; a clavicle also occurs, extending from the edge of the
scapula to the episternum, just as in Reptiles. In all other
Mammalia, however, there is a considerable modification; the
coracoid* has become rudimentary, and does not reach the
sternum: it fuses early in life with the scapula, and is represented
only by a projection from the ventral end of this, the coracoid
process. The scapula is usually a broad plate, the upper part
of which generally remains cartilaginous ; it is provided on its outer

Fig. 387. Fig. 388.

 

Fig. 387. Right half of the shoulder girdle of a young Platypus. cl
clavicle, co’ anterior, co posterior portion of the coracoid, 1 glenoid cavity, sc scapula.—
Orig.

Fig. 888. Right half of the shoulder girdle of a young Ape; shoulder blade
much foreshortened. k spine of the scapula. Other letters as in the preceding figure.-—
Orig.

surface with an erect longitudinal ‘“‘spime” with a ventral pro-
jection, the acromion, to which the outer end of the clavicle
is attached ; whilst its inner end is connected with the manubrium.
In many Mammals, the clavicle is wanting (e.g., in all the Ungulata),
or is rudimentiry (Dog), and in these cases the shoulder girdle
has no direct connection with the axial skeleton; in others, e..,
in digging, climbing, and flying forms, the clavicle is a strong rod-
like bone.

The skeleton of the fore limb consists of the usual parts. The
bones of the forearm are usually either about equal in size, or the
radius is stronger, at least, at its lower end, whilst the lower portion
of the ulna is often rudimentary, though its upper end, which bears
the projecting olecranon, is usually well developed. The two bones
often cross, since the radius is articulated above to the outer, the
ulna to the inner side of the humerus, whilst below, the radius is
connected with the inner, the ulna with the outer portion of the
carpus: in other cases, however, the distal end of the ulna is pressed
right behind the radius, so that no true crossing occurs. The two

 

* In young animals, the coracoid is 1epresented by two separate ossificat.ons, which
fuse later with the scapula (¢f., Fig. 388.)
478 Vertebrata.

bones are either movable,* or are immovably bound together; in the
latter case they often fuse with increasing age. The carpus
consists of two transverse rows of bones; in the proximal row there
are usually three bones, in the distal, four, the two outer bones of the
typical five (fourth and fifth distal carpals) being fused.t At the
outer edge there is a rather large sesamoid bone, the pisiform. Of
the five digits, the pollex (first) has two phalanges, the others each
three ; only in certain, much modified forms (Whales), is the number
increased. In certain Mammalia the pollex is more freely movable
than the other fingers, so that the hand is a prehensile organ ; where
it has not this function it is usually reduced, or altogether absent.
Other fingers also may dwindle or vanish, particularly if the limbs are
specially adapted for walking or running (Ungulata): with the
decrease in number, there is an increase in power on the part of the
remainder; in such cases a fusion of metacarpals may occur. The
structure of the fore limb shows great variety in correlation with
the varied function (digging, climbing, flying). (See also the
special descriptions).

The pelvis is peculiar in that the ilia are directed backwards;
the point of attachment to the sacral vertebre lies towards its anterior,

Fig. 389. Fig. 390.

 

Fig. 389. Left half of the pelvis of w young Ornithorynchus. 1 acetabulum, ii ilium,
is ischium, ‘p pubis, # point at which the ischium and pubis unite behind. m marsupial
bone.— Orig.

Fig. 390. Left half of the pelvis of a new born Calf. oc point at which ischium and
pubis unite with one another below; the other letters as in the preceding figure.—Orig.

 

* The lower end of the radius, with the hand (which is only connnected at a
definite spot with the ulna, elsewhere with the radius), can then swing outwards; this
is especially the case in Man.

+ The carpals of Mammalia are usually distinguished by the following names: the
proximals from within outwards, scaphoid, lunar, and cuneiform; in the
distal row, trapezium, trapezoid, magnum, and unciform. In some
cases (by reduction of the number of metacarpals), some of these bones may be
absent ; or fusions may occur. Occasionally a centrale is developed between the
rows. :
Class 6. Mammalia. 479

the acetabulum at the posterior end (whilst in Reptilia the ilium
is directed forwards or antero-ventrally). The ischia and pubes of
each side fuse, and the pubes also anchylose in the mid line; as
may also the ischia; occasionally there is no connection between the
two halves of the pelvis (e.g., certain Insectivora). In the adult all
three bones of each side are completely fused.*

In the Monotremes and the Marsupials, attached to the anterior edge of the
pubis, is a pair of forwardly-directed bones, the so-called marsupial bones;
they may be regarded as ossifications in the tendons of the abdominal muscles.

Hind limbs. The tibia is always stronger than the
fibula, which is often very thin, or indeed imperfect at its lower
end, where it is usually fused with the tibia.
A large patella lies over the knee-joint,
anteriorly. There are only two bones in the
proximal row of the tarsus; the astra-
galus within, and the calcaneum, with
the much projecting heel, postero-externally.
Movement occurs between the lower end of
the fore-leg and the astragalus (or sometimes
the caleaneum), whilst movement between
the tarsals themselves is usually much limited
(cf., the very different conditions in Reptiles
and Birds). In the distal row there are four
bones,t as in the hand; between the two
rows on the inner side there isa centrale
(naviculare). Metatarsus and toes as regards”
the number of phalanges, etc., agree with
the metacarpus and fingers; and with regard
to special developments, such as reduction
in the number of toes, the relations are
usually similar. Sometimes, however, the
hand is modified differently from the foot
(e.g., in leaping or digging animals).

Other sesamoid bones are found besides
these already mentioned (pisiform, patella). namely,
below the joints between each metacarpal and the Fig. 391. Tibia of a one
first phalanx (also between each metatarsal and the year old Horse to show the
first phalanx of each toe), there are two small bones ; epiphyses e and e’.—Orig.
and below the joint, between the last and the pen-
ultimate phalanx of the finger and toe, one sesamoid bone; other smaller ones
may also occur, but less frequently.

 

 

* The two halves may be anchylosed in the mid-ventral line, and the ilia may also
fuse with the sacral vertebre. In some forms (eg., certain Edentata), the ischia may
be fused with the posterior false sacral vertebra.

+ Cuneiforms 1, 2, and 3, and the cuboid, the latter consisting of distal tarsals,.
4 and 5.
480 Vertebrata.

A general characteristic of the mammalian skeleton consists in the occurrence
of special ossifications for the end portions of many bones, especially of long
bones, and also of many processes, so that in young animals many bones consist
of several pieces, which fuse later. These special terminal ossifications are
termed epiphyses.

The brain is characteristic in many respects. The cerebrum
is of considerable size; its surface is marked by deep labyrinthine
furrows, the sulci, separated from each other by ridges, the gyri:
occasionally the surface is smooth, or almost smooth, as in ‘the
Rodents. ‘he hemispheres cover not only the thalamencephalon,
but usually the mid-brain also, and sometimes part of the cerebellum.
Peculiar to the Mammalia is the so-called corpus callosum, an
important system of transverse nerve fibres, which pass from one
hemisphere to the other; these fibres are least developed in the
Monotremes and Marsupials. The mid-brain is divided not only
by a longitudinal, but also by a transverse furrow, so that it forms
four dorsal lobes (corpora quadrigemina). The cerebellum is well
developed, its much thickened dorsal wall is divided into two median
and two lateral portions, and is transversely folded.

The size of the brain, as compared with that of the rest of the body, is closely
correlated with the intellectual level of the species under consideration (see, for
instance, the enormous development in Man). There are, however, other circum-
stances which are of great importance in this connection : noticeably it is a rule
that small Mammals have relatively larger brains than have their nearest
allies; it may be said that, on the whole, the size of the brain varies inversely as
the bulk of the animal; the Elephant, for instance, in spite of its striking
intellectual qualities. has a relatively minute brain. It may also be noticed here
that the brain of young animals is relatively larger than that of the adult.

Olfactory organs. Prominent folds, the turbinals,
project into the nasal cavities, which are usually of considerable size.
The turbinals arise from the postero-external wall, developing as
large lamellae, which become folded and coiled so as to form very
complex structures. They are supported at first by cartilage, which
becomes partly or entirely ossified, to form the maxillo- and the ethmo-
turbinals. The olfactory epithelium is situated in that part
of the mucous membrane which lines the region of the nasal cavity
nearest the cribriform plate; it is yellowish-brown in colour. ‘The rest
of the cavity has no olfactory significance; in addition to mucns-
secreting glands it has a rich vascular network which, according to
some authorities, serves to warm the air entering the lungs. The air
sacs of some of the skull bones mentioned above (p. 475-6) are out-
growths from the nasal cavity, and are lined with a continuation of
its mucous membrane.

Optic Organs. In contrast to other Vertebrata the upper
eyelid is larger and more movable than the lower. A nictitating
membrane is always present but Jess well developed than in Birds
and Reptiles, and usually not provided with special muscles ; it slips
Class 6. Mammalia. 481

over the outer surface of the eyeball when this is withdrawn into the
orbit and covers it partially or entirely. Sometimes (e.g., in Man) it
is rudimentary.

The sclerotic consists of connective tissue without cartilage* or bone ;
in some Mammalia, especially in the Whales, it is very thick. In the choro id
coat there is frequently a peculiar greenish, blue, or whitish, shimmering
membrane varying somewhat in structure, the tapetum (eg., in the Horse,
Ruminants, Carnivora). The form of the pupil varies, it is either circular
(e.g., in Man,), or a perpendicular (Cat, Fox), or horizontal slit (Horse,
Ruminants).

Auditory organ. The cochlea of Monotremes is
like that of Crocodiles and Birds; in all other Mammalia, however,
it is much longer and is spirally coiled. As in Reptiles there is a
fenestra ovalis anda fenestra rotunda. The single ear-

Fig. 392. Diagrammatic trans-
verse section of the head of a Mammal,
to show the relations of the auditory
organ; (the labyrinth is drawn propor-
tionally much too large, ete.). a
ampulla, b semi-circular canal (only one
is represented) c cochlea; sa sacculus,
u utriculus (together forming the vesti-
bule) ; round the labyrinth the cavum
perilymphaticum, black in the figure.
k bones of the skull, h malleus, am
incus, s stapes, t tympanic cavity, r
fenestra rotunda, e Eustachian tube,
tr tympanic membrane, g external
auditory meatus, 6 external ear. —
Orig. (with partial use of older

figures).

 

bone of Reptiles is broken into three, the malleus, which is connected
with the tympanum, the incus, and the stapes, the terminal disc of
which closes the fenestra ovalis ;f in the Monotremes it consists of a
plate and a single shaft; which is usually broader and perforate in
other orders, so that the ossicle becomes like a stirrup. The presence
of an external meatus is characteristic of the Mammalia; the
pit, at the base of which the tympanum is situated in Reptiles, has
become a long tube here; the inner part is often ossified (a tubular
elongation of the tympanic bone), whilst the external portion is
supported by cartilages. The external auditory meatus is usually
surrounded by the pinna, a large fold of skin varying in form
and containing a considerable amount of elastic cartilage.

 

*In the Monotremes, the sclerotic is partly cartilaginous.

__ t+ According to another interpretation the malleus is homologous with the quadrate
of Reptiles, whilst the incus is to be regarded as representing the outer portion of the
reptilian columella auris; others again regard the incus as corresponding to the
quadrate, the malleus to the upper posterior bone of the mandible of Reptiles
(articulare).

If
482 Vertebrata.

The tympanic cavity which lies enclosed in the temporal bone, is often
of considerable size, so that the surrounding bony portions (especially the
tympanic bone) are swollen to form a vesicle (bulla); sometimes the tympanic cavity
is connected with air sinuses in the neighbouring bones (ef. Crocodilia and Aves).
The walls of the eustachian tubes are usually partly ossified; they open separately
into the pharynx. In the Horse and Tapir, each Eustachian canal has a very large
thin-walled, saccular extension.

The buccal cavity in young embryos, as in most Reptiles,
is undivided. Quite soon, however, a ledge develops laterally
and above, and unites with its fellow of the other side to form a
horizontal septum, the anterior end of which (covered, of course,
on both sides with mucous membrane) is the hard palate, whilst
the hinder portion remains soft, and forms the muscular soft
palate. The cavity above the hard palate unites with the nasal
cavities (the nasal septum growing down and becoming connected
with the hard palate); the cavity above the soft palate, which com-
municates freely at its front end with the nasal cavities, remains
single, and is termed the pharynx; it includes also the posterior region
of the primitive buccal cavity. The eustachian canals open above, the
trachea below into the pharynx (Fig. 396). The buccal cavity lies
below both hard and soft palates and encloses the teeth, tongue, etc.

The teeth of Mammalia are chiefly remarkable in that their
number is small and fairly constant for a given species; that their
form is usually relatively complex ; that they are implanted in sockets ;
and especially that the mode of replacement is peculiar, for
the teeth are not, as in other Vertebrata, replaced continuously
throughout life, but only two series, the milk and the permanent
dentitions, are present, following each other in regular sequence.
It may be noticed further that the teeth are used not only for the
prehension of food, but also very largely for its mastication. In
addition to the two ordinary components of teeth yet a third is
present, the cement, occurring chiefly at the root (see below).
It is simply a sheath of osseous matter deposited by the connective
tissue surrounding the tooth; it lies external to the rest of the
tooth, and is formed last: it is not as hard as dentine.

Two parts may be distinguished in a mammalian tooth, the crown
and the root. The root is the lower,* usually narrower part, and
is often split into several branches; it is destitute of enamel,
but is covered with cement. The crown is the upper enamelled
portion, which generally projects quite freely, and is usually clearly
demarcated from the roct; for instance, by a constriction. Cement
does not occur‘in this region, excepting as an occasional layer, varying
in thickness, upon the surface of the enamel. The crown exhibits a
great diversity of form; it may be simply conical or chisel shaped,

 

*The free end of the tooth is termed the upper, the opposite the lower, end;
although this terminology is actually correct only for the teeth of the lower jaw,
Class 6. Mammalia. 483

it may be low and broad, provided with rounded or pointed tubercles,
or it may be much compressed and serrate at the edge ; or again, it
may be traversed by marked transverse or longitudinal ridges
separated by valleys, which may be so deep as to reach the base
of the crown (¢.g., in the molar teeth of the Elephant). Perpendicular
furrows may also occur on the sides of the teeth ; usually the deeper
folds are partially or completely filled with cement (in the Horse and
Elephant). During use, the enamel, especially in plicate teeth, is very
frequently worn away at all the projecting points, and the subjacent
dentine is thus laid bare; at the grinding surface, therefore, may be
seen islands of dentine surrounded by slightly elevated enamel
borders, and the latter are often again surrounded by cement
(especially in teeth of herbivorous animals). The crowns and roots of
many teeth are of almost equal length; sometimes one, sometimes the
other may, however, be the longer. The furmer especially the case with
much folded teeth, which are subjected to considerable wear and tear ;
in these the root (or roots) is often very short; the crown, on the
contrary, is very long, but it projects from the jaw for ouly part of its
length, and gradually, as the free end is worn away, the tooth is pushed
out (e.g., in the molars of the Horse). The crown has often begun to
wear down before the root is formed; in other cases there is
actually no development of a root; as the crown is worn
away above, growth takes place below, and never ceases; such teeth
are said to grow from persistent pulps (the incisors of Rodents, the
molars of many of the same group, the canines of the Boar, etc.).

The teeth are arranged in a single row along the edge of
premaxilla, maxilla, and mandible; those of the premaxilla are
designated incisors, the anterior
teeth of the maxilla, next to these,
canines; the rest, molars;
in the lower jaw the teeth which
bite just in front of the upper
canines are known by that name
also; those anterior, the incisors ;
those behind, the molars. In most
placental* Mammals the number of
teeth on each side of the jaw,t in
thesccondor permanent den- Jf, Danton aele om
tition, isnot morethan eleven, drawn in outline above or below the cor-
three incisors (i, 4, 73), one canine oe permite Gnes. third

” , ¢ canine, p premolar, m molar.—
(c), seven molars, of which the four After Ch. Tomes.
anterior are termed premolars

 

 

* The placental Mammals include all Mammalia excepting Monotremes and Mar-
supials (see p. 493).

+ One premaxilla and one maxilla are regarded as half of the upper jaw.

rr: 2
484 Vertebrata.

(p'—p*) ; the three posterior, molars (m!—m').* In the complete
first dentition, the milkdentition, which is present in the
young animal, but is lost after a time, there are eight teeth in
each half of the jaw; three incisors (di!—di*), one canine (dc),
and four molars (dp!—dp*), occupying the places in the jaw
which will be filled afterwards by the corresponding permanent
incisors, canines, and premolars, whilst the true molars have
no predecessors. The number of teeth is, however, reduced in
many forms, and the reduction affects not only molars, but even
incisors and canines. Usually it is not difficult to determine, by
comparison, which are the missing teeth. In the molar series the
reduction usually begins either at the anterior or the posterior end, so

 

Fig. 394. The teeth of a Pig showing the replacement, the jaws cut away.
v— 3 first to third incisors, c canine, p'—p* premolars, m'—m molars, di? second
deciduous incisor, dp?—dp* deciduous molars. (milk teeth shaded). Of the deciduous
teeth di}, di3, de have already fallen out; dp! is wanting in the Pig.—Orig.

that if only six molars are present the absent tooth is either the
first premolar or the last molar; if only five are present
the missing teeth will be p! and p?, or m? and mi, or again,
p' and m’. In some groups, the molars disappear first (in
the Seals); in others, the premolars (e.g., in the Rodents); in yet
others (e.g., the Cat), teeth are missing from both ends of the series.
The number of milk teeth may be similarly reduced ; if a tooth of the
permanent dentition is wanting, as a rule the corresponding milk
tooth has also disappeared; but there are several exceptions. Of
the typical deciduous molars, however, the first (dp!) is usually
absent, even when the corresponding permanent tooth (p') is
present; occasionally other milk teeth are wanting, although the
permanent ones are present; sometimes (e.g., in the Seals) they are
absorbed during embryonic life, or fall out at birth, and they are then

 

* jis the most anterior (the innermost) incisor, p' the most anterior premolar, m!
the most anterior molar, etc, e
Class 6. Mammalia. 485

very poorly developed, or evenrudimentary. The molars are usually the
most complicated teeth, whilst the incisors and canines are simpler ;
the canines are generally conical, the incisors, for the most part,
chisel-shaped. The teeth of the milk dentition usually resemble those
of the permanent set; but a given milk tooth is not always exactly
like that which is to take its place: in the Carnivora, for instance,
each milk molar is very like the permanent molar, one place further
back in the series. In some placental Mammals, there may be
conditions very different from those just described, in that a larger
number of teeth may be present. This is especially the case in
forms which, in correlation with peculiar habits, have in some
respects, descended, so to speak, to a lower zoological grade; for
instance, in the Toothed Whales, whose mode of life closely resembles
that of Fish, the teeth are uniform, usually conical in shape (homodont),
and very numerous; in animals, too, whose teeth are of subordinate
importance, there may be an increase in number accompanying a
degeneration in form and structure (e.g., in the Dasypodide). Where
there is so aberrant a condition of the permanent teeth, there
is frequently an entire absence of milk dentition. The permanent
dentition of the Marsupials differs from that of the Placentalia in
that it is composed of a larger number of teeth, and also, that the
milk dentition is represented by a single molar; for details see this
group.

The following points may be added to the description of the mammalian
dentition just given. The enamel is frequently thinner in some parts of the

Fig. 395. A Incisor of a Dog, shortly
after it has come into use; Bthe same
tooth of an old Dog; longitudinal
section. In the young tooth the pulp
cavity is very large; there is as yet no
cement (or very little); in the old tooth
the upper portion of the primitive pulp
cavity is entirely filled with dentine, and
the rest is very narrow, the cement
abundant, the tip of the tooth worn
away. c cement, d dentine, p pulp cavity,
s enamel.—Orig.

 

crown than in others; or it may be absent from certain regions (e.g., from the
posterior side of the incisors of the Rodents) ; from almost the whole tooth (in the
incisors of Elephants, enamel occurs only upon the tip of the tooth before it is
cut); or it may be completely wanting (as in many Whales). When the tooth is
cut and comes into use, it is not, as arule, completely developed; the root
is frequently not yet fully formed; the dentine has not attained its greatest
thickness ; the pulp-cavity is large, and decreases gradually as the bulk of the
dentine increases; the cement at the root of the tooth also continues to be
deposited, and in very old animals, is often of considerable thickness; whilst in
486 Vertebrata.

young animals it is scarcely indicated ; the enamel (except in teeth growing from
persistent pulps) appears to be completely developed only when the tooth comes
into use. Before falling out, the milk teeth are usually absorbed to a certain
extent in the lower portions by special cells lying in the surrounding connective
tissue.
The number of teeth will be indicated here aocariling to the following plan:

1 & (= 3 incisors above, 2 below on each side), ¢ } (= 1 canine above, 0 below),
m £ (= 6 molars above, 5 below), or pm 3 (= 3 premolars above, 3 below),
m % (= 3 molars above, 2 below). If the actual teeth present are to be expressed,
the following formula is used, the signs above the line indicating the teeth of
the upper jaw, those below, those of the lower jaw:

PPG c p? pip? mm?
2B Co p® pt m!

Some of the Mammalia are altogether edentulous, but where
this is the case with the adult (e.g., Whale-bone Whale) teeth may
have been present in embryonic life; or even in youth, such are,
however, never cut; they are absorbed.

The presence of an upper and a lower lip is characteristic
of the Mammalia. These are large, muscular folds of skin covering
the edges of the jaws and continuous with each other laterally ;

  

   

F
|
!
1
I
'
I
|
s

{
{
1
1
|
p k~betv gp z 1
Fig. 396. Longitudinal section through the head and neck of a Dog, decreased.
b hyoid, e opening of eustachian canal into the pharynx, g brain (only suggested), h frontal
sinus, hg hard palate, k epiglottis (lies above the edge of the soft palate), 1 lyssa (cf. foot
note, p. 487)), m turbinals, p anterior, p’ posterior edge of the pharynx, r spinal cord, s vocal
cords, sp oesophagus, t tonsil (see foot note, p. 487), tr trachea, v soft palate, z tongue,
2 axis, 4 fourth cervical vertebra.—Orig.

  
Class 6. Mammalia. 487

they form the cheeks and are absent only in rare cases. In some
Mammalia (e.g., many Apes, Rodents) there are cheek pouches
which serve as reservoirs for food. The tongue is very muscular,
strong, and movable, and is thus very useful in bringing food into
the mouth; it is covered on its upper surface with small, pointed
processes (papille filiformes) which are sometimes much cornified
(in the Cat) ; there is also a small number of various other processes
(p. fungiformes, circumvallatee, and foliatw), which bear taste buds.*
On the hard palate there is usually a double series of fairly hard
transverse folds, the palatal ridges, which often, e.g., in cattle,
project considerably ; or are almost or quite effaced (Man); for
the pecuhar development of the palatine ridges in the Whale-bone
Whale, see Cetacea. Besides small glands embedded in the wall,
several large salivary glands open into the buccal cavity:
viz.. the parotid, submaxillary, and sublingual.t

The pharynx is continued into the csophagus which is
usually long and narrow. The stomach is generally a short,
wide, somewhat curved tube, provided, close to the entrance of the
cesophagus, with a short, blind sac which, however, passes quite
gradually into the general cavity. In some Mammalia the stomach
is compound, #.e., is divided by constrictions into several regions (in
certain Rodents, the Whales, Ruminants, etc.) : or it is characterised
by the possession of several short, blind sacs (in the pig): or it differs
from the ordinary type in yet other ways, ¢.y., in being elongate
and intestine-like (Kangaroo). Usually it is entirely lined by a
cylindrical epithelium and its walls are furnished with numerous
glands (gastric and mucous): sometimes, however, the epithelium
of the cesophagus, which is stratified like that of the mouth, reaches
some way into the stomach, and often it may extend over a very
considerable area, in the Horse about half: in most Ruminants the
rumen, reticulum, and psalterium are lined with stratified epithelium.
The small intestine is of considerable length, longest in
herbivorous forms. That portion of the alimentary canal which
is designated rectum in Vertebrates, is generally of considerable
length in the Mammalia, usually fairly wide also, and is known as the

 

* On each side of the ventral surface of the tongue, there is a fold which often
unites with that of the other side; it is termed the “sub-lingua,” and attains its
highest development in the Prosimii, where it forms a linguiform appendage of the
true tongue. In the anterior region of the tongue (Fig. 396) there is, close to the
lower side in many Mammalia, an elongate structure, the so-called worm ( lyssa) ; it
is surrounded by loose connective tissue, and consists of muscular and connective
tissue ; sometimes it contains a cartilaginous portion, which apparently corresponds to
the anterior end of the hyoid of Lizards (Fig. 336). Behind, at the base of the tongue,
on each side, is the tonsil (tonsilla) (Fig. 396 t), a region of the mucous membrane
in which there are numerous lymph follicles. Such follicles are also embedded in
other portions of the mucous membrane of the mouth.

+ The last, however, is not a single gland, but a group of small glands, each with
its duct.
488 Vertebrata.

large intestine, the end portion alone being termed rectum.
A cecum almost always arises from the large intestine at its
junction with the small intestine ; in some animals, (e.g., the Horse),
it attams an enormous length, whilst in others (e.g., Man), it is
small, or even rudimentary.* The liver, which is situated behind
the diaphragm, is usually, but not invariably, provided with a
gall bladder (it is wanting in, e.g., the Horse), The pancreas
has generally one duct,t which opens into the anterior portion of the
small intestine, either together with, or independently of, the bile
duct.t
Respiratory Organs. The entrance to the larynx is a
longitudinal slit behind the tongue, anterior to the entrance into the
cesophagus. In front of the opening, there is a peculiar flap, the
epiglottis, which contains a large elastic cartilage ; under ordinary
conditions it is directed forwards, often reaching even up over
the edge of the soft palate (Fig. 396), but when food passes from the
mouth through the pharynx into the cesophagus, the epiglottis is let
down over the glottis. The walls of the larynx are supported by
large cartilages, viz., the cricoid behind, the large thyroid
below; in front and above, the two arytenoids. ‘The rest
of the trachea is usually strengthened for some distance
by cartilaginous rings; it branches posteriorly imto two large
bronchi, which branch again; each lung, as already stated, is an
arboriform organ, of which both the larger and finer branches are
hollow. Only the peripheral branches, which have thin walls, and
are furnished with small dilations (alveoli) are respiratory ; in
other regions the tubes have thicker walls,
provided in the larger branches with
cartilaginous rings like those of the
trachea, or with small cartilaginous plates.
All the branches are held together by
connective tissue. The lungs, with the
heart, are situated in the anterior portion
of the body-cavity, the thorax, along
Fig. 397. oe eet ie the dorsal wall of which the esophagus
Mammalian lung filled passes; whilst the rest of the alimentary
ee ve ae i pong cages canal, with the kidneys and reproductive
Fi piratory portion of : e 4 é
the lung.—After Frey. organs, lies in the posterior portion, the
abdomen. A large septum, the dia-
phragm, divides the thorax from the abdomen; it is tendinous

 

 

* In Man and some other Mammalia, the cecum is continued into a thin narrow
appendage, the processus vermiformis.

+ Occasionally the pancreas has two ducts, which either open both direct into the
gut, or one unites with the bile duct.

{ The great omentum is a specially developed portion of the mesentery, depending
in many forms over the ventral side of the stomach and the intestine.
Class 6. Mammalia. 489

centrally, elsewhere muscular: when the muscular portion contracts,
the diaphragm is flattened so as to enlarge the thorax, the very elastic
lungs are expanded, and consequently air rushes in: when the
diaphragm is relaxed, it is arched up into the thorax, the lungs are
compressed, and the air is partially expelled. The diaphragm is thus
an apparatus for effecting respiration. The muscles which
move the ribs are also of importance in this connection, since, when
the lower ends of the ribs are moved forwards, the thoracic cavity is
widened.

In many Mammals which hibernate (Bats, Hedgehogs, Marmots, Hamsters,
Myoxus), and in some others (Mole, Shrew-mouse, Mouse, Rabbit), there is a
so-called hibernating gland, a lobed mass, reaching from the thorax to
the neck, over a portion of the back; it is largest in autumn, and decreases in
size during winter. The organ consists of connective tissue with numerous large
cells containing oil-globules, and is to be regarded, like other fatty masses,
solely as a reserve of nourishment.

Vascular System. Asin Crocodiles and Birds, both atrium
and ventricle are completely divided, the left auricle receives
blood from the lungs, the right
from the rest of the body. The
pulmonary arteries (the
arterial arches of the fourth pair),
arise by a common stem from the
right ventricle. The arterial arches
of the first and second pairs
arise together by a common trunk,
the innominateartery, from
the left ventricle, and thus carry
simply arterial blood; the right
arterial arch of the second pair
only gives off the artery for the
right limb; the aorta (in contrast
to that of Birds) is formed by the
left arch of the same pair; the
first pair of arterial arches forms
the carotids as usual. Thus in
Mammalia we have, as in Aves, a
complete separation of arterial and
venous blood. A conus arteriosus ae
is absent.

 

bs 398. Heart and arterial arch
In the new-born Mammal there is of Mammalia, diagrammatic. a night,

a large opening (foramen ovale) in the left auricle, ao aorta, s and s’ sub-
septum between the two auricles, which ae arteries, v right, v’ left ventricles,
is, however, soon closed. In the same + U, 4, 2, 4, 4 arterial axches.—Orig.
way there is an open duct (the ductus

Botalli) between the second left arterial arch and the pulmonary artery
(the fourth arterial arch); after birth it degenerates to a solid cord.
490 Vertebrata.

The kidneys are short, roundish organs, with a large cavity,
the pelvis of the kidney, into the inner side of which the urinary
tubules open ; several large papille project into the pelvis from the
substance of the kidney (consisting of urinary tubulés) surrounding
it; the pelvis is continued into the ureter. A urinary bladder is
present ; for its opening and for that of the ureters, see the repro-
ductive organs.

In most Mammalia the surface of the kidney is smooth; in others (e.g., Cattle)
lobed, in others again (Bear, Seal, Whales, etc.), the kidney is branched, and
consists of numerous lobules, each of which is mounted upon a branch of the
proximal end of the ureter, whilst they are only held together by loose connective
tissue.

The ovaries are comparatively small, usually with a flat or
somewhat lobed surface; in a few Mammals only (Monotremes, the
Pig, etc.) the ovary, in consequence of the projecting Graaffian
follicles, has a racemose appearance.* The Graaffian follicles as
described above, p. 351, differ from those
of other Vertebrata in that they are pro-
vided with a large number of follicle
cells, and contain a large cavity; in
the Monotremes, however, just as in
the lower Vertebrates there is only one
layer of cells round the ovum, and
there is no cavity. Hach oviduct in
the Mammalia in general is composed of
three regions ; an anterior, usually very
narrow, portion, the fallopian tube,
with a funnel opening into the abdominal
cavity ; a median wider part, the uterus;
and a terminal sectiov, the vagina;
in the Monotremes the division between
uterus and vagina is not demarcated,

Fig. 399. The terminal portions and the oviducts open separately into
of the gut, of the urinary and 4 saccular dilation of the ventral wall
generative apparatus in the , 7
females of various Mammalia Of the cloaca, the urinogenital
ae Wee ae ee sinus, into which the urinary bladder
C other Mammalia. b bladder, ch of the two ureters also opens; all five
cloaca, ¢ rectum, u uterus, wgurino- apertures are close to its base. In the
genital duct, ul ureter, v vagina.— 7 :

Orig. Marsupials the cloaca is shortened,

so that it forms simply a shallow pit,
into which the rectum opens above, and the urinogenital sinus
below; the two vagine open separately on the floor of the urino-

 

 

* When the ovum leaves the follicle the cavity is filled with very cellular connective
tissue, which in some Mammalia increases so much in size that the follicle becomes
many times as large as it was previously; as large indeed as the whole of the rest of
the ovary. Later it degenerates to form the corpus luteum.
Class 6. Mammalia. 491

genital sinus, which contains also the aperture of the urinary
bladder, whilst those of the ureters lie on the dorsal wall of
the bladder.* In the placental Mammals there is no cloaca
in the adult; the urinogenital sinus (vestibule) and the
rectum open independently, either close together or separated
by a considerable interval. The posterior ends of the oviducts
are almost always united for a greater or less extent: either the
vagine simply; or the posterior portions, or even the whole length
of the uteri also: in the first case there are thus two entirely
separate uteri (uterus duplex), as in Rabbits; in the second, there

A B Cc D

  

Fig. 400. The Miillerian ducts and urinogenital sinus of various Mammalia. A of
a Marsupial, B uterus duplex, C@ bicornuate, D simplex, 6 opening of the
bladder into the front end of the urinogenital sinus, o external opening of the sinus,
t fallopian tube, tr funnel, wu uterus, v vagina.—Orig.

is a bicornuate uterus (uw. bicornis), as in the Horse; in the last, a
simple uterus (w. simpler), as in Man. The ureters and the
bladder are arranged as in the Marsupials.

At the junction of the vagina and the vestibule there is in many Mammalia a
thin membranous septum (hymen), perforated by a small pore, and broken
down at the first coitus. The vestibule varies very much in length; in some
forms it is very long (e.g.,in Hares), in others, very short, hardly apparent (e.g., in
Man). Very frequently, a clitoris, a rudimentary organ homologous with the
penis of the male, is present in the female; itis usually a papilla, rarely elongate,
and lies on the ventral side of the external aperture of the urinogenital sinus.
Further, there may be rudiments of the mesonephros (epoophoron, for instance, in
man) and of its duct (Gartner’s duct in the Ruminants).

Male Genitalia. In all Mammalian embryos the testest lie
close to the dorsal wall of the abdomen, just as in Reptiles and Birds,

 

*In some Marsupials the two oviducts are separate throughout their length, in
others, the vagine are united for a certain distance, but open separately into the urino-
genital sinus.

+ In many Mammalia, as in Aves (see p. 419), the testis diminishes in size after the
breeding season (Roebuck, Hedgehog, ctc).
492 Vertebrata.

and in some (Monotremes, Cetacea, Proboscidians, etc.), they retain
this position throughout life. In most species, however, at the close
of foetal life, or in early youth, each descends into an evagination of
the ventral abdominal wall; usually the two evaginations are united
externally to form a pouch-like appendage (scrotum), divided by a
septum into two compartments, each containing one of the testes ;

Fig. 401. Diagrammatic
longitudinal section of the
cloaca (or rectum) and the
copulatory organs, A
of aCrocodile, B of a
Monotreme, C—D of
various other Mammalia.
a anus, 6 urinary bladder,
cl cloaca, f corpus fibrosum,
h skin, 7 gut, r (in A) seminal
groove, in (B—D) seminal
tube, s vas deferens, u urino-
genital sinus (in C the de-
generated portion of the
sinus is dotted: w’), ur
ureter.— Orig.

 

whilst its cavity communicates with the abdomen by a duct varying
in width, which is often closed in the adult.* Inthe Monotremes
the vasa deferentia open, together with the ureters and urinary
bladder, into a deep, though narrow outgrowth of the ventral wall

 

*In some Mammalia (Insectivora, Rodentia) the testes only lie in the scrotum
during the breeding season (when they are much enlarged); at other times, in the
abdomen. 4
Class 6. Mammalia. 493

of the cloaca, the urinogenital sinus, corresponding to the
same organ in the female. In connection with the ventral wall
of the cloaca there is a penis, which differs from the homologous
organ of the Chelonia, Crocodilia, and Aves, in the closure of the
groove on the dorsal side, to form a tube, the seminal tube, opening
anteriorly into the urinogenital sinus, at the other end to the exterior
(Fig. 401, B). An elongate mass of fibrous connective tissue, the
corpus fibrosum, lies ventral to the seminal canal. In all other
male Mammalia, including the Marsupials, there is no cloaca; the
original opening of the urinogenital sinus into it has closed (Fig.
401, ©), and the sinus itself only opens to the exterior by the
seminal tube, through which the excretory products must also pass.
The copulatory organ is ventral to the anus, but in many Mammalia
it is connected with the abdominal wall (D), so that the tip is directed
forwards. ,

The seminal tube is surrounded by a vascular network, and one is contained
in the corpus fibrosum. The dilation of the vessels effects the erection of the penis.
An ossification (os penis) is often developed in the copulatory organ (Carnivora,
Apes). Various glands open into the urinogenital canal and into the seminal
tube, and their secretion escapes with the spermatozoa; among these the
prostate glands and Cowper’s glands are the most constant. A vesicula
seminalis, a saccular or branched hollow organ, which serves both as a
seminal reservoir, and also as an organ of secretion, opens, in many Mammals,
into each vas deferens, close to its union with the urinogenital sinus; or inde-
pendently into the sinus. A larger or smaller rudiment of the oviduct (uterus
masculinus) is often present.

Of the Mammalia, the Monotremes alone are oviparous;
here the egg is relatively large,* and segmentation is partial; as in
many Reptiles the egg is surrounded by a parchment-like shell. All
other forms are viviparous; an egeg-shell is always absent,
the ovum is microscopic, segmentation total. In the Marsupials
the embryo lies in the uterus surrounded by the embryonic mem-
branes, is nourished and grows by the absorption of a fluid secreted
by the uterine glands; there is not aclose connection between the
embryo and the uterine wall, and the young one is born in a condi-
tion which, in comparison with that of the new-born placental
Mammal must be considered very undeveloped ; it is nourished by
the milk of the parent for a long time after birth. In the
placental Mammals the outer embryonic membrane comes
into close connection with the uterine wall; delicate vascular branched
villi are developed on its surface and fit into corresponding crypts in
the vascular wall of the uterus, serving as organs for the absorption
of the maternal plasma. The villi are either uniformly distri-
buted over the whole surface, as in the Horse, Pig, Camel, Whale,
or are chiefly or exclusively developed in one region, which is then

 

* In Echidna the egg with its shell has a longitudinal diameter of 15 m/m., a
transverse diameter of 13 m/m,; that of Ornithorynchus is similar. me
494, . Vertebrata.

termed the placenta fretalis,* or there are several regions upon which
the villi are well-developed. This is the case in most Ruminants,
which possess a great number of small, very prominent placentae
(cotyledons) ; elsewhere a large continuous placenta, either zonary
(Carnivora, Seal, Elephant) or discoidal (in Man and othersT), occurs.
That portion of the uterine wall which is connected with the placenta
is termed the uterine placenta, p. uterina. In some cases the
villi are simply withdrawn from the pits in the uterine wall at birth
(Horse, Ruminants); in others (in all with zonary or discoidal
placenta) a portion of the mucous membrane of the uterus remains
attached to the embryonic membranes and is thrown off with them
(decidua), so that the former has, to a great extent, to be regenerated.

In the placental Mammals the serous membrane (éf,, p. 354) is closely
connected with the allantois, and partially fuses with it; the vascular
membrane thus formed is termed the chorion, and gives rise to the vascular
papille already mentioned. In older Mam-
malian embryos the amnion is much
extended, and often lies close to the allantois,
and then it immediately surrounds the
tubular peduncles of the allantois and of
the yolk sac, as with a sheath. These
peduncles (see Fig. 402), together with the
sheath, are termed the umbilical cord.

The circulation in an advanced
embryo is in several respects very different
from that of the adult, the lugs of course
are not yet functional; the oxygen which
the embryo needs is received with the plasma
from the parent. The chief points of the
circulation are the following: the arterial

_Fig. 402. Placenta ofaMammal, blood from the placenta mixes with the
ae arene am amnion, al allantois, venous blood from the posterior part of the
yolk sac; the outermost line is the Z : 5 :
serous membrane. The external layer body and flows into the right auricle, which
of the allantois is fused with the serous also receives venous blood from the anterior
membrane forming the chorion which is yegions. Part of the blood from the right
beset with branched processes—Orig. a uyicle flows into the right ventricle, thence
to the pulmonary artery, and so partly into
the lungs, partly through the ductus Botalli into the aorta; another portion
of blood from the right auricle goes through the opening in the auricular
septum into the left auricle, and from this through the left ventricle into
the main arterial trunk. A very considerable mixing of arterial and venous
blood, therefore, occurs in the embryo.

The length of time during which the placental embryo remains
in the uterus (uterine gestation) varies considerably for different
forms, though it is fairly constant for each species. As a general
rule large Mammals have a long gestation (a year or more), and

 

 

* If the villi are uniformly distributed over the whole membrane, the animal
(e.g., the Horse) is said to possessa diffuse placenta; strictly speaking there is
none.

+ Apes, Bats, Insectivores, and Rodents,
Class 6. Mammalia. Order 1. Monotremata. 495

only produce one or quite a few offspring at a birth; whilst in
small Mammalia the time is short, and several or many young ones
are born at the same time. If there are several embryos in the uterus
at once, the ova from which they develop have all been fertilised at
the same time; they are, therefore, all at about the same stage of
development, and are born in immediate succession. In some
placental forms the offspring at birth are very helpless, naked,
with closed eyes (the eyelids adhering together) ; whilst others are
more advanced, or are immediately capable of independent movement.
They are all at first nourished by milk from the parent.

The Mammalia are grouped in the following way :—

A. Oviparous Mammalia. Hgg laid, large, surrounded by a shell.
Cloaca long. One order only, the Monotremes.

A. Aplacental Mammalia. Egg small, develops in the oviduct, whose
walls secrete a fluid for the nourishment of the embryo. This is very small and
imperfectly developed at birth. Cloaca rudimentary (only present in the
female). One order only, the Marsupials.

C. Placental Mammals. The embryo develops from a smallegg: the
outer embryonic membrane is closely connected by villi with the wall of the
oviduct. Cloaca absent. All other orders of Mammalia belong here.

Order 1. Monotremata (JMonotremes).

This small group differs from other Mammalia in a number of
characteristics which bring it near the Reptilia. It is especially
remarkable that Monotremes are oviparous; that the egg is
relatively large, and is surrounded by a leathery shell; that
they possess a well-developed cloaca. Other points tending in
the same direction, are the presence of well-developed cervical
ribs, a large coracoid, a very reptilian episternum, the
absence of a scapular spine, the form of the stapes, the
straight cochlea, the presence of cartilage in the sclerotic of
the eye, the feeble development of the corpus callosum, the
whole relations of urinary and genital organs, as already
noticed. It is interesting that the temperature of the body*
is lower than in other Mammals.

That they are not incorrectly placed with the Mammalia may be
seen, however, from the fact that they accord with them, and differ from
Reptiles in the following respects: they are covered with hair, possess
sebaceous and sudoriparous glands, havea long, jomted sternum,
no quadrate, two occipital condyles, three ear bones; whilst
the mid-brain is divided into four lobes, the penis is tubular, etc.

It may also be mentioned that Monotremes possess marsupial
bones, like those of Marsupials, connected with the pelvis; further,

 

* In Echnidna under usual conditions 28° C., in Ornithorhynchys 25° C. (c). In
other Mammalia as a rule 38—39° C. y
496 Vertebrata.

it must be remembered that mammille are absent, and that
the mammary glands are primitive in character. The few known
forms are edentulous when adult, but horny teeth may be
present. Recently it has been demonstrated that the young
Ornithorhynchus has true teeth, but that they are lost later.
There is no definite external ear. The males have a horny
spur on the heel, perforated by the duct of a gland.

There are only three living species of Monotremes known, they
are mentioned below. They are of medium size, and are confined to
Australia, New Guinea, and Tasmania. Very little is known
definitely concerning the fossil remains of this group.

1. The Duck-billed Platypus (Ornithorynchus paradowus). The snout
is flattened, broad, and covered with a naked skin; at the back of the mouth on
either side of each jaw, there is a large horny tooth, and a smaller horny ridge in
front; the tail is powerful and flattened; the feet webbed; the fur soft. They
feed upon small aquatic animals. The eggs are laid two at a time, in holes dug
in the ground; the young ones, when hatched, are fed with milk by the mother.
East Australia, Tasmania. '

2. The Spiny Anteater (Hehidna aculeata). The snout is narrowed,
especially towards the tip, and covered with naked skin; the mouth small, the
tongue !ong and sticky; the body covered with hairs and spines; the tail very
short; strong digging claws. The food consists of Ants, Termites, etc. The egg
(only one is laid at a time) is placed in an unpaired saccular depression on the
ventral surface, and there incubated; the temperature of the sac rises several
degrees above that of the body. It serves later to protect the young one, and
then atrophies, forming anew before the next oviposition. The brood pouch is
absent from Ornithorynchus. Different varieties inhabit New Guinea, Australia,
and Tasmania. The three-toed Echidna (E. [Proechidna] Bruijnii), is
a near relative; it has a longer and curved bill, and only three toes on each foot,
both hind and fore, whilst #. aculeata has five. New Guinea.

Order 2. Marsupialia (Marsupials).

The leading characteristic of this group is the absence of a true
placenta; the outer embryonic membrane does not project as villi
into the uterine wall, but the embryo is nourished by a secretion of
uterine glands, and is born in a very immature and imperfect
condition. Other characters also show the low grade of the
Marsupials, as compared with all subsequent orders of Mammalia:
for instance, the corpus callosum is feebly developed ; in the female,
there is acloaca, but it is a mere pit, and the two oviducts open
separately into the urinogenital sinus. Like the Monotremes, and
unlike all other Mammals, the Marsupials have marsupial bones,
a pair of peculiar ossifications connected with the pubes and extending
forwards in the abdominal wall. They have nothing to do with the
marsupium usually present in females. This is an open saccular
cavity on the ventral side of the animal, limited by a large fold of
skin; it covers the mammille, and the young ones are placed in it
Class 6. Mammalia, Order 2. Marsupiaha. 497

immediately after birth; they are each attached immovably by
suction to one of the mammille for a long time.

The dentition of the Marsupials on the whole resembles that of
other Mammals ; they differ, however, in some points. The molars
vary within the number seven in each half of the jaw. Only a single
form with degenerate teeth has a larger number; the incisors
may, however, be as many as five above, four below. Of the seven
molars the third alone has a predecessor, the only milk tooth met
with so far in this group. The form of the teeth, especially of the
molars, varies considerably in correlation with very diverse habits.

In most points of structure the Marsupials stand nearer the placental
Mammals than do the Monotremes; mammille are present, the coracoid is
rudimentary, there is no episternum, the cochlea is spirally coiled, the penis is
essentially like that of the placental Mammals, the testes move back into a scrotum,
the ovum is very small, and segmentation is total, ete.

Most existing Marsupials live in the Australian region, the
Opossums* alone inhabit America. In earlier geological times,
however, Marsupials occurred also in other parts of the world.

At least three small )
similar incisors on each |
side of the lower jaw.
The canines larger os)
the incisors.

Opossums. f None of the toes of
| the hind leg united.

Bandicoots. 7

| Toes 2 and 3 thinner
Only one large incisor | + than 4 and 5, and united
in each ramus of the Kangaroos. | together.
lower jaw. The canine J
small or absent. J

1. Opossums (Polyprotodontia). Four or five incisors in the upper,
three or four in the lower jaw. Well developed conical canines. Molars with
cusps or tubercles. The second and third digits of the hind foot are like the
fourth and fifth, and are not united.

(a) The True Opossums (Didelphyidz) have, on the hind foot, a well-
developed, but clawless, hallux which can be opposed to the rest of the toes;
i4,e4, m2. Tail long and prehensile, almost naked, but scaly. The pouch
is well developed in some forms, rudimentary or wanting in others. They feed
upon Insects, and are small animals, living exclusively in the New World,
chiefly in South America.

(b) Native Cats, ete. (Dasywride). Hallux rudimentary or absent.
i4, Tail not developed as a prehensile organ, Carnivorous or insectivorous.
Among them the peculiar Native Cat (Dasyurus), and the long-legged,
wolf-like Tasmanian Wolf (Thylacinus), occurring only in Tasmania.
Further, the small squirrel-like Marsupial Ant-eater (Myrmecobius),
with 2 small molars, and with long, smooth protrusible tongue.

2, The Bandicoots (Peramelina) resemble the preceding group as
regards the teeth, whilst they agree with that following in the structure of the
hind feet, for the second and third toes are thin and enclosed in a common

 

* The forms cited below, which are not specially commented on, live in Australia
(some of them also in New Guinea, Tasmania, etc.).

KK
498 Vertebrata.

membrane; the hallux is wanting or rudimentary. i 8.” Whilst in other
Marsupials the fore limb has five well-developed digits, in one of the two
genera of Bandicoots (Perameles) the first and fifth fingers are very degenerate
and destitute of claws, in the other (Chwropus) they are completely absent,
and the fourth has also become rudimentary. In the True Bandicoot
(Perameles), a rudiment of the hallux is present, the fourth is the best developed
toe; in the Pig-footed Bandicoot (Cheropus) (Fig. 403 ¢), the rudiment
of the hallux is wanting, and the second, third, and fifth are very thin, almost
rudimentary.

3. Kangaroos (Diprotodontia) have usually three incisor teeth in the
upper, one in the lower jaw. The canines are absent or small, the molars with
rough cusps or transverse ridges. Of the toes of the hind foot the second and
third are weaker than the fourth or fifth, and are surrounded by a common
membrane (syndactylous). Herbivorous.

(a) Australian Opossums (Phalangistidz). The hind, are little
longer than the fore, limbs. Hallux well-developed, without a claw; opposable
(Fig. 403 A). 7%. Climbing animals. The following may be noted: the

 

Fig. 403. Right hind foot: A of Phalangista, B of the Kangaroo, C of
Cheropus. a astragalus, c caleaneum, 7 centrale (naviculare), c'—c* cuneiforms, cb cuboid
ID first to fifth toes.—After Flower.

Cuscus (Phalangista), with long prehensile tail: the Flying Phalangers
(Petaurus), with a large membrane (patagium) stretched between the fore and
hind limbs: the Koala or Australian Bear (Phascolarctos), a clumsy
ecaudate creature; in which the fingers, like those of the Chameleon, are united
in two bundles (the first and second may be opposed against the third, fourth,
and fifth): and the small, aberrant, insectivorous, Long-snouted Pha-
langer (Tarsipes) with long protrusible tongue; few rudimentary molars (4);
and rudimentary claws on all the fingers and toes with the exception of the
second and third toes of the hind foot.

(b) Kangaroos (Macropodide). Hind legs very long, adapted for
jumping ; hallux absent; toes, second and third, very thin, fourth and fifth,
Class 6. Mammalia. Order 2, Marsupialia. 499

strong (Fig. 403 B); fore limbs small; tail very strong, used as a support in
sitting. ¢ 3. Large and small forms (Halmaturus, Hypsiprymnus, etc.) in
Australia and adjacent islands.

(c) Wombats (Phascolomys). Distinguished in that they have only a
single incisor on each side, above and below (like the Rodents); all the teeth
grow from persistent pulps; the second and third hind toes only slightly weaker

than the others; tail very short; clumsy nocturnal animals.

Note —tThe recently discovered Australian Mammal, Notoryctes typhlops,
with habits like those of the Mole, is also a Marsupial. The third and fourth
digits of the fore limbs are provided with strong, compressed, digging claws
(the rest of the claws are smaller); a hard, horny plate is developed on the
dorsal side of the snout, and the head is used in digging; the eyes are rudi-
mentary ; pinne are absent. Claws are developed on all five digits of the hind
foot, whilst in other Marsupials the hallux, if present, has no claw. 7 3.

Order 3. Insectivora.

The Insectivora are small, short legged, placental Mammals; with
the snout elongated, more or less like a proboscis; and with
multicuspidate molar teeth, the front ones being usually small
and unicuspidate. They generally walk on the whole foot (planti-
grade) ; both fore and hind feet have usually five similar toes.

The canines are frequently small, some of the incisors large; clavicles are
present; eyes and pinne are usually little developed; mammille abdominal.

The Insectivora feed chiefly upon Insects, Worms, etc., rarely on
vegetable substances. They are entirely absent from Australia and
South America.

1. The Hedgehog (Hrinaceus). Spines (very thick, stiff hairs) dorsally,
usually finer or coarser hair ventrally; feet simple, tail short. It can roll itself
into a ball by the ventral flexure of the head, limbs and tail, the spiny dorsal
surface being drawn down by the contraction of the large skin muscles. Canines
absent; first incisor, above and below, larger than the rest of the incisors; the
cusps of the molars blunter than in other Insectivora ; altogether, ten teeth above,
eight below, on each side. The Common Hedgehog (E. europzus) is
distributed almost throughout the whole of Europe ; it lives both upon plant and
animal food; it hibernates for the winter.

2. The Mole (Talpa). The fore limbs are developed into very strong digging
organs; the hand is broad, with long, powerful, and almost straight, claws, and
so compressed, that the inner edge, supported by a peculiar sickle-shaped bone, is
turned downwards, whilst the palm is turned outwards; the clavicle is extremely
short and powerful, pre-sternum with a keel; the eyes are rudimentary; pinnz
absent; tail short; fur soft; dental formula complete, 44; canines of the lower
jaw like the incisors, which are small and simple (Fig. 393). The Talpide live
exclusively upon animal food, chiefly Earthworms. The English species is the
Common Mole (Z.europza). The Golden or Cape Moles (Chrysochloris)
constitute another group of fossorial Insectivora. They are blind, subterranean
animals with velvety coat; the claws and last phalanges of the second, and
especially of the third, fingers, are very powerful, the first and fourth fingers are
small, the fifth absent; the hand is not compressed. South Africa.

3 The Shrew (Sorex) is a small Insectivore, with a long tail; pointed
proboscis ; feet of simple structure; and softfur. There is only one incisor in each

K K 2
500 Vertebrata.

ramus of the mandible, it is very large, and projects forwards; the first
upper incisor is similar in form; the canines small; the cusps are in many cases
reddish-brown. The Shrews, which feed upon Insects and Worms, are represented
in Britain by the following species: the Common Shrew (Sorex vulgaris), the
Lesser Shrew (S. pygmzus), comparatively rare in England, but taking the
place of the Common Shrew in Ireland; the Water Shrew (Crossopus fodiens),
distributed over England and the South of Scotland ; all with brownteeth. Two
Musk Shrews (C. aranea and C. suavolens) occur on the continent of Europe,
but not in Britain.

4. Of foreign Insectivora, besides the Cape Moles, the following may
be mentioned: The Desmans (Myogale), aquatic forms with webbed feet;
proboscis long, tail long and scaly; possessed of musk glands: a large species,
the Russian Desman (M. moschata), with compressed tail, occurs in South
Russia; another smaller species (M. pyrenica), with cylindrical tail, in the
Pyrenees. The Jumping Shrews (Macroscelides) are saltatorial animals, with
elongate metatarsus; long proboscis; large pinnw: in Africa. Cladobates, with
powerful tail, furnished with long laterally-directed hairs; squirrel-like animals,
living in trees in Africa. The Cobego or Kaguan (Galeopithecus volans) is
in many respects an aberrant form; a patagium is stretched between the fore-
limhs, the body and the hind limbs; the edges of the lower incisors are pectinate.
It is about the size of a Cat and is herbivorous, inhabiting the South Sea
islands, the Moluccas and Philippines.

N ote.—The genus Hyrax may be mentioned here. It was formerly regarded
as an Ungulate, but appears to the author to be allied to the Insectivora; its
systematic position is, however. still very doubtful. The few species of the
genus are small rodent-like animals with soft fur; pointed snout; quite short
tail; legs of medium length: there are four well-developed digits on the fore
feet (the pollex is rudimentary), the hind foot has only three toes; all the digits
are provided with flat nails (not hoofs), except the inner toe of the hind foot
which bears a claw; there is a large sole to the foot. i 2, c 8, p £, m 3; the
grinding surface of the molars is very like that of the Rhinoceros; the inner
incisors are large, so that the dentition is somewhat rodent-like: herbivorous;
Africa and West Asia.

Order 4. Chiroptera (Bais).

The Bats are remarkable, chiefly on account of the peculiar
modification of the fore limb. With the exception of the first, all the
metatarsals and their corresponding digits are much elongated, and
a naked patagium® is stretched between them. It reaches from the
fifth finger along the arm and forearm, to the body and hind libsm ;
in front a similar membrane is stretched in the angle between the
arm and forearm, and there is frequently another between the hind
limbs and the tail. The hind feet and the short pollex are free;
of the fingers, the third and fifth are without claws; in the small
Bats, the second also; but the thumbs and the five digits of the hind
feet possess curved claws: the terminal phalanx of the clawless
digits is absent: besides the metatarsus and the digits, the arm and

* The patagium is not absolutely naked, for there are very fine hairs scattered about
on it.
Class 6. Mammalia. Order 4. Chiroptera. 501

forearm are also elongate, although tu a relatively small extent. The
hind legs are turned outwards in a peculiar way; they are thin and
feeble: a long, thin bone or cartilage, the spur, arises from the
ankle ; it lies on the edge of the membrane extending between the
hind limbs. The patagium can be folded up like an umbrella, and
laid along the body. The clavicles are long and powerful, the pre-
sternum provided with a long keel. The mammillz, one or two pairs,
are thoracic.* The Bats are nocturnal or crepuscular. Their best
mode of locomotion is flight, but they can manage to crawl on their
hind limbs and thumbs. They rest suspended by the hind feet.

1. Large Bats (Megachiroptera: genus Pteropus, the Fruit-Bats or
Flying Foxes, etc.). Claws on the first and second digits; head long;
molars with two longitudinal ridges; pinna simple: chiefly frugivorous. Large
forms inhabiting the warmer parts of the Old World and Australia.

2. Small Bats (Microchiroptera). There is no claw on the second finger ;
head short; molars with several tubercles (like those of the Insectivora); opening
into the external auditory meatus more or less completely covered by a
membranous flap of the pinna, the antitragus. They feed principally on Insects,
which they catch as they fly, discovering them by the tactile sense located in the
skin, especially of the patagium, of the pinna, whichis sometimes very large, and
of peculiar outgrowths (nasal processes), which are frequently present on the
head. Some South American forms (Vampire, Desmodus) suck the blood of
other living Mammals. The group is very rich in species, distributed over the
whole world, especially abundant in the tropics; mostly small animals. A fairly
large number of diverse forms occurs in England; among them may be noted:
several species of the genus Vesperugo, of which the Pipistrelle (V. pipis-
trellus) is the common English one. This genus is characterised by the short
antitragus, and by the possession of #55 cheek teeth: of the genus Vespertilio,
Daubenton’s Bat (V. daubentont), is a well-known British species, with a
large antitragus and ¢ cheek teeth: of the Horse-shoe Bats (Rhinolophus),
the greater (RB. ferrum-equinuwm), and the lesser (R. hipposiderus), both occur
in England although they are not very common; they are distinguished by the
complicated nose-piece. All the British species hibernate, passing the winter
suspended in hollow trees and elsewhere.

Order 5. Ungulata.

The limbs are elongate and specially adapted for walking or
running, the trunk is raised well above the ground. The metacarpus
and metatarsus are usually of considerable length; the digits are more
or less completely enclosed in a common skin (with the exclusion, how-
ever, of the last) ; the animal usually steps upon the last phalanx only,
chiefly upon the surrounding hoof (p. 470) ; the rest of the foot does
not touch the ground, but assists in lengthening the limb. ‘The first
digit and the corresponding meta-carpal or tarsal is absent from all
four limbs of all existing Ungulata. Clavicles are also wanting.

 

* Many indigenous Bats are very remarkable in that whilst copulation occurs iv.
the autumn, fertilisation of the ovum does not take place till the following spring ;
the spermatozoa are stored in the uterus of the female during hibernation.
502 Vertebrata.

Herbivorous animals, generally of considerable size, with plicate or
tuberculate molars, and usually with a long caecum.

Sub-Order 1. Perissodactyla.

The third digit is almost symmetrical, stronger than the
rest, and the median plane of the foot passes through the middle of
it; the fifth is usually absent. The femur has on its outer edge a
process (trochanter tertius), which is wanting in the Artiodactyles.
On the distal surface of the astragalus there is a large, flat, articular
facet for the naviculare, and a smaller one for the cuboid. The
rami of the lower jaw are anchylosed. The molars are folded, and,
with the exception of the first premolar, of about equal size.
Stomach simple; ceecum colossal; placenta diffuse.*

1. The Tapir (Lapirus), Fore foot with four toes (all but the pollex), hind
foot with three (hallux and minimus wanting); the third is not much stronger

 

Fig. 404. Hand (fore foot) of: A Tapir, B Rhinoceros, C Horse. R radius, u ulna
s,1,¢ proximal row of carpals (naviculare, lunare, cuneiform); p pisiform ; tm, td, m, w
distal row of carpals (trapezium, trapezoid, os magnum, unciform) ; II—V second—fifth
fingers (in B, Vis the rudimentary fifth metacarpal, in C, IT and IV denote the second and
fourth metacarpals).—After Flower.

than the second and fourth; digitigrade. 7 3, c¢4, p 4, m 3; the molars have
each two transverse ridges; the snout is elongated to form a short proboscis;
the skin is well covered with hair. One species in the Hast Indies, another in

South America. The extinct (Hocene) genus, Palxotherium, is somewhat closely

 

* Gall-bladder absent. Two abdominal mamme. At least twenty-two dorsal
vertebre.
Class 6. Mammalia. Order 5. Ungulata. 503

related to the Tapirs; it had, however, only three toes on each fore-foot, and
the molars were like those of the Rhinoceros.

2. The Rhinoceros. Both fore and hind limbs symmetrical and three-
toed; the median toe (third) somewhat stronger than the other two (second and
fourth) ; digitigrade. 71 3=8, ¢ 2, p 4, m %; incisors more or less degenerate,
no canines, strong plicate molars. Antero-dorsally in the median line of the
head one or two horns (¢f. p. 471). The skin is thick, inflexible, and very
sparsely covered with hairs; the upper lip very mobile. Limited to the warmer
parts of Asia and Africa. In Africa there are two species with smooth skin
and with two horns (Rh. bicornis and simus); in Asia a two-horned species and
also a one-horned species with large deep skin folds (Rh. unicornis, etc.). The
Woolly Rhinoceros (Rh. tichorinus), with ossified nasal septum, two
horns and an abundant covering of hair, lived in Quarternary times in Central
Europe and Siberia, together with the Mammoth.

3. The Horse Family (Equidz) is characterised by the great develop-
ment of the middle (third) as compared with the lateral toes, and by the great
length of the metatarsus. Fore and hind limbs similar. They tread upon
the hoof. Dental formula complete: 7 3, ¢ 1, p 4, m 3. Bony orbit complete
(4.e., a process from the frontal has united with a process of the zygoma behind
the eye.

(a) All Horses now living belong to the genus Equus. The second
and fourth toes are altogether absent, so that each foot has a single toe only,
the third, which with the corresponding metacarpal or metatarsal (cannon bone)
is extremely well-developed; the second and fourth metacarpals (or metatarsals)
are present in the form of long, thin bones (splint bones) on the sides of the
cannon bone. The animals tread only on the hoof upon the last phalanx;
this hoof surrounds the very small sole of the foot (ef. p. 470, Fig. 382 D). The
incisors are characterised by the possession of a large pit partially filled with
cement (the mark); the canines are well developed in the male, rudimentary in
the female; the germ of the first premolar is present in both upper and lower
jaws, but usually only develops in the upper; even there it is rudimentary, and
generally falls out early (wolf tooth); the other molars of both jaws are of about
equal size (broader in the upper than in the lower jaw); they have very long
crowns and short roots; the crowns exhibit folds and pits; these reach to the
roots and are filled with cement, which is extraordinarily well-developed here,
surrounding the crown with a thick coat; very soon after the tooth comes into
use, streaks of enamel appear upon the grinding surface, and the crown becomes
gradually worn away, so that in old Horses it is very short. In contrast to the
conditions in the Tapir and Rhinoceros, the lower portion of the ulna (or fibula)
is very weak, in part only represented by a ligament. To this genus belong:
the Zebras (EH. zebra, quagga, Burchelli, and others), with dark transverse
stripes; small hoofs; bovine tail: in South Africa. The Ass (E. asinus), with
a black stripe along the middle of the back, and a similar transverse one across
the shoulders ; small hoof; tail bovine: wild in North Africa. Two allied forms
(E. hemionus, the Dschiggetai, and EH. onager, the Kulan, in Asia). The Horse
(H. caballus) is usually larger than those just mentioned: it has larger hoofs;
the tail is covered with a large tuft of long hairs: there are naked, horny patches
on the skin both of the fore and the hind limbs, the so-called chestnuts and
ergots (in others, only on the fore limbs); native place not definitely known.

(b) Some of the Quaternary and Pliocene Horses also belong to the genus
Equus, and occurred not only in the Old World, but also in the New. Other
Pliocene forms belong to the genus Hipparion, a small form which resembles
Equus in most respects, but differs from it in that the second and fourth
digits were present on all four limbs, although only as poorly developed
504 Vertebrata. |

“accessory toes,” which did not touch the ground in walking.* Hipparion lived
in recent Miocene times as well as in the Pliocene. The Genus Anchitheriwm is
more remote from Equus; it has toes like Hipparion, but the second and fourth
are considerably stronger than in the latter, although still much weaker than the
third; the crowns of the molars are shorter than in Equus, the folding more like
that of the Rhinoceros (or Paleotherium), the cement little developed ; the wolf

A B Cc A’ B Co

“7

 

Fig. 405. Left fore foot of Anchitherium (A, A’), Hipparion (B, B’), Horse (C, 0),
from in front and from within. All similarly decreased (about +). tm trapezium, td
trapezoid, m os magnum, uw unciform. JJ, III, IV, second—fourth metacarpals, v rudi-
mentary fifth metacarpalAfter Gaudry.

tooth (first premolar) is larger, and present also in the lower jaw; the front teeth
without the mark; the ulna and fibula better developed than in Equus. This
genus, which lived in Miocene times, is very like the Eocene Paleotherium
mentioned above.

Sub-Order 2. Artiodactyla.

The third and fourth digits on both fore and hind feet are each
asymmetrical in themselves, but the two correspond, as does an
object with its image in a mirror; the median plane of the
foot passes between these two toes. The third and
fifth are smaller, do not usually touch the ground in walking, and
are situated somewhat behind the others; indeed they are often
rudimentary or absent. The trochanter tertius is wanting. The two
articular facets on the distal edge of the astragalus, for the naviculare
and cuboid, respectively, are of about equal size, and both are much
arched from before backwards ; the stomach is more or less compli-

 

* The fifth metacarpal is present (Fig. 405 B), but quite rudimentary; it may
also be present in the horse.
Class 6. Mammalia. Order 5. Ungulata. 505

cated, the cecum smaller than in the Perissodactyles; the molars
folded or tuberculate, the premolars smaller than the true molars.*

Group 1. Non-Ruminantia.

Incisors well developed; the third and fourth metacarpals or
metatarsals are almost always separate, the second and fifth digits and
the corresponding bones usually comparatively well developed; ulna
and fibula strong ; mandibular rami anchylosed ; stomach less compli-
cated than in the Ruminants; in some forms of the group (e.g., the
Common Pig), fairly simple; in others (e.g., the Hippopotamus) with
definite indications of division into several sections; there is no rumina-
tion; mammee. often along the whole ventral side; placenta diffuse.

 

Fig. 406. Manus of: 4 Pig, B Stag, CCamel. R radius, Uulna: s naviculare,
l lunar, c cuneiform, td trapezoid, m magnum, u unciform; m? and m* second and fifth
(rudimentary) metacarpals ; II—V second to fifth fingers.—After Flower.

1. Pig family (Suidx). Limbs slender; digits two and five are consider-
ably shorter than three and four, are situated somewhat behind them, and do not
usually touch the ground in walking; ball of the foot small and soft; molars
tuberculate ; there is a short proboscis ; skin with hairy covering.

(a) The Pigs (Sus) are confined to the Old World, and represented by
various species: 7 3,¢ +, p 4, m 3; the incisors of the lower jaw are directed for-
wards, those of the upper jaw downwards; the upper canines turned outwards
and upwards, the lower ones much arched (those of the male grow from persistent

 

* Gall bladder usually present. The number of dorsal vertebre less than twenty-
two (rarely more than nineteen).
506 Vertebrata.

pulps and are more curved than those of the female); the premolars are com-
pressed, the molars have broad tuberculate grinding surfaces. Here. belong the
European Wild Hog (Sus Serofa), the ancestor of the old race of the
North European Domestic Pig; most existing English breeds are
hybrids of the latter and of the Chinese pig, which was derived from one or more
species of Asiatic Wild Pigs, and differs in several respects (in the skeleton)
from the old race and from the European Wild Hog.

(b) Among other Suide the following may be noticed: the Peccaries
(Dicotyles), small forms, with a large skin gland dorsally ; the fifth hind toe is
wanting ; the canine in the upper jaw is directed downwards, but neither it nor
that of the lower jaw is of striking size; South America. In the Babyrusa
of Celebes (Porcus babyrusa) the canines of the upper jaw are turned upwards
and much curved, in the male they are enormously elongated. The Wart-hog
(Phacocherus) is chiefly distinguished by the extraordinary development of the
last molar, this tooth is also the largest in Sus; in very old animals it is the only
persisting molar; canines much like those of Sus; South Africa.

2. Hippopotami (Hippopotamide) are huge animals with thick limbs;
the second and fifth digits are very powerful; the animals place all four toes on
the ground and the sole of the foot is large; molars plicate and tuberculate ;
incisors and canines very powerful; head very large, without a proboscis, with
very broad snout, sparsely covered with hairs: only two living species; the best
known is the Hippopotamus (H. amphibius), which is distributed over large tracts
in Africa ; another smaller species (Cheropsis liberiensis), which approaches the
Suide in some respects, inhabits West Africa.

8. There are also many extinct Non-ruminants, which are in some
points like the Pigs and Hippopotami, but in others differ considerably from
them. There are, for example, various forms with molars like those of the
Ruminants, whilst in other respects they stand fairly close to the Suide; others,
like the Anoplotherium of Hocene and Miocene times, with long neck and
long legs, offer a superficial resemblance to the Ruminants, but are distinguished
from them by the possession of a complete dentition (44); by the well-developed
upper incisors ; and by the separation of the metatarsals.

Group 2. Ruminantia.

Incisors are absent from the premaxille (or the third is alone
developed) ; canine of the lower jaw usually (but not in the Camels)
like the incisors, so that there appear to be four of these in each
ramus. The molars, and to some extent the premolars also, have
each four curved longitudinal ridges, two external and two internal.
On all four limbs, the third and fourth metatarsals (or metacarpals)
are almost invariably fused, forming a single long bone (cannon
bone), whilst the second and fifth are incomplete or absent*; in the
Tragulide alone are they complete. Digits two and five are small
or absent. For the structure of the hoof, see p. 470 and Fig. 382 H.
Ulna and fibula are poorly developed; the lower end of the latter is
separate, and resembles a tarsal bone. Rami of the lower jaw

 

* The upper ends of the second and fifth are, at least in the hind foot, fused with
the third and fourth respectively, but the rest, if present, remain as small separate
bones.
Class 6. Mammalia. Order 5. Ungulata. 507

anchylosed only in the Camels, elsewhere separate. The stomach is
constricted into several portions, and after the food has been there
for some time, it is regurgitated and masticated anew. There is
usually a number of cotyledons ; but in Camels, the placenta is diffuse
like that of the Pigs and the Perissodactyles. The mamme are
abdominal.

In the majority of Ruminants (Cavicornia, Stags, Giraffes), the stomach is
divided into three sharply-defined portions. The first compartment follows
the cesophagus, and from the junction a deep groove runs along the anterior
side of the chamber, to
its opening into the
second region, the many-
plies (psalteriwm or
omasum.) The first part,
which attains a consider- 4
able size, is furnished
with several ingrowths,
one of which is very
large, and divides the
cavity into two incom-
pletely separated sub-
sections, the large
paunch (rumen), and p
the smaller honey-
comb bag (reticulum) ;
the latter is furnished
internally with a pro-
jecting network of folds;
the former with villi.
The manyplies is
furnished within with
numerous large longi-
tudinal laminz, which lie
closely together and fill
up the greater part of
the cavity. The last
portion, the reed
(abomasum) is almost Fig. 407. Diagrammatic longitudinal section of the
tubular. The rumen, ee =e es ance B a an neacamrnk
rat]. 9 ; 2 uius. sma. intes
on ee h abomasum ha reticulum (ha! portion of the rumen ae :

: : : Camel, which may be falsely compared with the reticulum
epithelium like that of of others), m manyplies, o cesophagus, + groove in the

the esophagus and the rumen, v first chamber.—Orig.

buccal cavity, and are

non-glandular; the abomasum is lined with a cylindrical epithelium, and is
furnished with glands. The food, which is not much masticated in the mouth,
forms a large bolus, passes through the esophagus, dilating it as it goes, and
reaches the rumen, where it undergoes a kind of fermentation or maceration,
until it is again brought up in small quantities into the mouth, to be masticated
and mixed with saliva. Then it passes a second time, but in a viscid condition,
through the esophagus, running, however, along the groove of the rumen, and so
reaches the psalterium, whose laminz absorb some of the fluid, and lastly it enters
thereed. Fluid substances apparently pass direct fromthe esophagus into the

 
508 Vertebrata.

manyplies through the groove of the rumen. In Camels the stomach consists
of the same compartments as in most other Ruminants, but the manyplies
is a long tube with low, longitudinal folds, and is not externally separated from
the short abomasum ; further, the abomasum is lined with cylindrical epithelium
and provided with short tubular glands.* The abomasum is furnished with
long, well-developed glandular pits, and thus an internal distinction is made
between the two chambers, the mucous membrane of the latter being of a much
greater thickness+ In the Tragulide the stomach is very like that of the
majority of Ruminants; but it is different in that the many plies, though
clearly demarcated, is rudimentary. A transition to this condition is
afforded by several other small Ruminants, in which the manyplies is very short
and little developed.

1. Camels (Camelidz). In contradistinction to other Ruminants the
last upper incisor is present and caniniform ;¢ the canine of the lower jaw, like
that of the upper, is caniniform (conical); the stomach is aberrant (see above) ;
the placenta diffuse;§ horns are absent; there are only two digits on each
foot; the hoof is small and curved, the sole is large and soft (in contradistine-
tion to all other Ruminants); they are plantigrade. The Camel genus (Camelus)
includes long-legged animals with a large fatty hump on the back; dental

13

formula, ie < ee 5 ame ;
and separated from its fellows by a diastema. In the Bactrian Camel
(C. bactrianus) of Asia, the hump is divided into two, anterior and posterior :
in the Dromedary (C. dromedarius), of Africa, Arabia, Persia, etc. it is
simple: these two essentially desert animals are only known in the tame condition
(except when they have run wild). The Llamas (Auchenia) are smaller,
without humps, and without the caniniform molar (p!); several species, both
tame and wild, occur in western South America.

2. Giraffes (Camelopardalis giraffa) possess two hairy, internally ossified,
outgrowths on the head; very long legs, fore legs longer than the hind; neck
long; Africa.

* 3. Stags (Cervide) constitute a large group of mostly slim, thin-legged,
short-tailed Ruminants; the males (and occasionally the females also) usually
bear antlers; in the fully developed condition (for structure and development see
p. 471), they are naked bony processes; at the base of each is a slightly widened
portion, the “burr” (above the lower portion, the pedicle, which remains covered
with skin). The first antlers borne by young Stags are simple, unbranched and
small; later they are larger and usually branched. The dental formula is:
i2,c} > s p %, m %.|| The following occur in Britain: the Roe (Cervus
capreolus), smaller than other European forms; the antlers of the adult with
rarely more than three tines: the Red Deer (C. elaphus), only in the High-
lands: and the Fallow Deer (C. dama), a native of the countries bordering
the Mediterranean, whence it was introduced into Central Europe and Britain

 

the first premolar of both jaws is caniniform

 

 

* Cylindrical epithelium and short glands are also present on the floor of the
“water cells” of the first chamber (cf. foot note +): for the rest these portions are
lined with non-glandular stratified epithelium.

+ In Camels the first compartment is incompletely separated by constrictions into
several parts ; the sub-sections thus formed are not, however, comparable with those of
other Ruminants. Some portions are provided with a net-work of deep folds bounding
small prismatic or honey-comb-like cavities, the so-called “water cells.”

t In the rudimentary condition i? may also sometimes be present, whilst in the
milk dentition both di? and di? are always developed.

§ Blood corpuscles, unlike those of all other Mammalia, oval.

|| A canine may or may not be present in the upper jaw (e.g., in the Red Deer).
The premolar which is absent is p!.
Class 6. Mammalia. Order 5. Ungulata. 509

probably several centuries ago. Remains of a large extinct form, the Irish
Deer (C. euryceros), characterised by the colossal size of its antlers, are found
on the Continent and in Scotland as well as in Ireland, where this animal must
have lived into the Middle Ages. The Reindeer (C. tarandus), the does of
which are characterised by the possession of small antlers, inbabits the circum-
polar lands of the Northern Hemisphere, and fossil remains are found in the
Quarternary formations of Central Hurope. The Moose Deer (C. alces) is
a clumsy long-legged animal with very spreading antlers; its range is almost
coincident with that of the Reindeer, although not extending so far north; in
former times it, too, was met with in Central Europe, but its distribution now
does not reach further west than Prussia. The Wapiti (C. canadensis) must
be mentioned as the New World representative of the closely allied Red Deer.
Further, there is the Musk Deer (Moschus moschiferus) of Asia, without
antlers, the males of which have very long canines projecting from the mouth,
and have a ventro-abdominal dermal pouch in which musk is secreted.

4. The Tragulids (Tragulidx) form a circumscribed group of small
Ruminants without antlers; in external form they are very like Stags, and are’
indeed, in most respects nearly allied to the Cervide. They are characterised
chiefly by the fact that the third and fourth metatarsals and carpals fuse late
or not at all, and that the second and fifth are complete. The manyplies is
rudimentary (see above). East Indies; Africa.

5. The Cavicornia have two horns, which, instead of being hirsute, are
covered externally by a hard thick horny layer; they are ossified internally
(of. p. 471). They are usually developed in both sexes, though occasionally rudi-
mentary or wanting in the female: 7 9, c 9, p 3, m 3; the absent premolar is
the first.

(a) Antelopes (Antilopinz) is the common term for a large number of
Ruminants which are for the most part cervine in appearance, though some
resemble Cattle. The horns are of very diverse form; in some cases they are
absent from the females. Especially abundant in Africa.*

(b) Sheep (Ovis). Snout hairy, horns transversely wrinkled, thick,
pointed, often much curved backwards and outwards; a dermal invagination
between the two large toes (interdigital pouch); two mammille. The Domestic
Sheep (Ovis aries) belongs here; the ewes have rudimentary horns or none:
of unknown descent. Among wild species may be mentioned the Mouflon
(O. musimon) of Corsica and Sardinia, and the Argali (0. ammon) of Central
Asia, besides several other Asiatic species. All wild Sheep are mountain
animals. Closely allied are the Goats (Capra) with compressed, less-curved
horns, and without interdigital sacs; mountain animals. The descent of the
Domestic Goat (C. hircus) is unknown. Among wild forms may be noted:
the Steinbock (C. ibex) of the Alps and other mountains of South Europe,
andthe Bezoar Goat (C. zgagrus) in Asia Minor, Crete, etc. The Chamois
(Capella rupicapra) is allied to the Goats; it has small upright horns curved only
at the tips; in the Alps, Pyrenees, ete. The Musk Ox (Ovibos moschatus) is
also related to the Sheep; it is a large long-haired Ruminant; with horns re-
calling those of the Buffalo; with hairy snout ; and only two mammille ; it inhabits
Arctic North America and also occurs in the Quaternary formations of Europe.

(c) Cattle (Bovine). Large, bulky animals, with broad naked nose; long
tail, with terminal tuft; no interdigital sacs ; often a dewlap (dependent fold of skin)

 

*The Prong-buck or Prong-horned Antelope (Antilocapra an-ricana)
is usually regarded as an Antelope: it is remarkable because the horns, each of which
in the adult possesses two tines, are thrown off and replaced annually. When the
horny cap is cast, bony cores are seen covered with a hairy skin, but later, a thick
horny layer is formed above the hair: when the horns are thrown off the hair goes
also. On the prairies of Western North America, :
510 Vertebrata.

on the neck and chest; four mammille; the horns usually round and smooth
curved outwards at the base, upwards at the tip. The Domestic Ox (Bos
taurus), with flat forehead, is probably descended from several wild species;
one of its ancestors is the now extinct gigantic Aurochs or Ure Ox (B.
primigenius), which lived in Britain and many parts of the continent in early
times. Nearly allied to the Domestic Cow is the tame Zebu (B. indicus), with
a fatty hump; occurring in Asia and Africa. Somewhat more remote is the
long-haired Yak (B. grunniens), of which both wild and tame forms inhabit the
mountain districts of Central Asia. The Bison (Bison) has an arched fore-
head and fairly small horns, which are far apart at the base, just as in the
genus Bos; the anterior portion of the body is humped in consequence of the
great development of several of the neural spines; the European Bison* (Bison
ewropxus) is now almost exterminated (only persisting in Lithuania and the
Caucasus); formerly it was widely distributed throughout Central Europe. The
nearly allied American species (B. americanus, “ Buffalo”) was common in large
herds in North America some time ago, but is nowrarely seen. The Buffalos
(Bubalus) are distinguished by the horns, which are very flat at the base, and
sometimes almost touch in the median line; they are poorly covered with hair ;
beasts of burden, of which, among others, a tame species descended from an
Indian form (Bub. vulgaris), is kept in South Europe.

Order 6. Proboscidea (Hephants).

Existing Elephants (Hlephas) are large, bulky, long-
legged animals, with little hair. The feet, including the metacarpals

 

Fig. 408. Skeleton of a Mastodon.—After Gaudry.

or metatarsals are short, and each has five toes bearing short hoofs ; t
there is a large sole ventral to the toes, which are enclosed in a

 

* The name Aurochs is used for this as well as for Bos primigenius.
+ Hoofs may be absent from one or two digits,
Class 6. Mammalia. Order 6. Proboscidea. 511

common membrane. The snout is produced into a long trunk,
bearing the nares and, in the Indian Elephant, a finger-like process
at the tip; it is a prehensile organ, and conveys food (plants) to the
mouth; water is sucked up into it and squirted into the mouth,
towards which the tip can be directed. The pinne are large
dependent flaps. The mamme (two) are close to the forelegs. The
head is borne upon a short thick neck, and is of colossal size;
the cranium small; extensive air sacs in the bones of the head.
Incisors absent from the lower, one on each side in the upper
jaw; this, in the males especially, is modified to form a long tusk
which is curved forwards, and is practically devoid of enamel; it
projects some distance from the mouth, and grows continuously
throughout life. Canines are absent. ‘The molars are large, with
high crowns and short roots; the crown is made up of a varying
number of compressed transverse plates coated with enamel, and

A B Cc

 

Fig. 409. Molar teeth in longitudinal section. A, B different species of Mastodon, C
Elephant ; diagrammatic, cement removed; d dentine, e enamel, k pulp cavity, r root.——
Orig.

bound together with an abundant supply of cement. There is
never more than one, or at most, two, teeth in use at the same time
in each half of the jaw: as one tooth is worn away another comes
forward and gradually takes its place; the anterior end comes into
use, whilst the posterior part is still within the jaw: it is therefore
worn away first, so that at last only the posterior end remains.
Altogether six molars appear in this way on each side; the first to
arise being the smallest.* There are only two living species: the
Indian Elephant (H. indicus), with the molar-plates numerous and
much compressed ; with relatively small pimnz; it is both wild and

 

* The six molars of the Elephant are: dp’, dp*, dp', m’, m?, m*; the premolars are
wanting in living forms, but rudiments occur in an extinct species, and also in
Mastodon,
512 Vertebrata.

domesticated: the African Elephant (£. africanus), with fewer,
thicker plates; and very large ears.

The extinct forms are numerous. The Mammoth (£. primigenius), from
the Quarternaries of Siberia and Europe, ap-
proached the Indian Elephant in build, but
had a thick coat of hair to fit it for the raw
climate. The Mastodons were aberrant forms,
with several molars in use at once; the molar
ridges are few, and not connected by cement.
Someforms had a large incisor in the mandibular
ramus turned forwards and downwards; they
also had upper incisors like those of the Elephant.
The two genera, Mastodon and Elephas, are closely
connected by their outlying forms: Tertiary. The
Miocene genus, Dinotheriwm, had relatively small
molars, like those of the Tapir; the upper incisors
were absent, but jin each jaw there is a single
: : downwardly-directed incisor.

a 410: Sleull. of Dene- The genus Dinoceras, recalls the Elephants in

; size and form, and is associated with them: it

differs, however, in many respects; there are no

incisors in the premaxilla (six in the lower jaw), but there are very large upper
canines ; the molars are small: Miocene of North America.

 

Order 7. Sirenia (Sea Cows).

The Sirenia, a small group of marine Mammalia, were formerly
classed with the Whales ; they have, however, absolutely no connection
with them. The resemblance in certain structural points, is to be
regarded as dependent upon adaptations to a similar mode of life.
In some respects this group recalls the Ungulata.

The body has asparse covering of bristles. The head is borne upon
a very short neck, but is well marked off from the trunk; the nares
lie at the end of the snout; the lips are large and thick; pinne are
absent. The trunk passes gradually into a powerful tail, at the end of
which there is a large horizontal fold of skin on each side, the two
folds together forming the “caudal fin.” The fore limbs are short
and fin-like, with the digits enclosed in a common membrane; the
thumbs are rudimentary ; the others, three-jointed (in contradistinc-
tion to the Whales); the arm is not movable at the shoulder only,
as in Whales, but also at the elbow; in the Manatee, rudimentary
hoof-like nails occur. Hind limbs are altogether wanting in all
living Sirenia, and the pelvis is vestigial; but in the Miocene genus,
Halitherium, traces of the hind limbs in the form of rudimentary
femurs have been found; the two mamme lie between the fore limbs.
In young forms, upper and lower incisors are present, but they
usually fall out, so that the adult is edentulous anteriorly ; in the
male Dugong alone, a pair of upper incisors develops into tusks; in
Class 6. Mammalia. Order 7. Sirenia. 5138

the females they are never cut, but a horny plate covers the jaw
above and below; canines are absent; the molars are small with
transverse ridges ; the Manatee has about ten in each half of the jaw,
the Dugong fewer: the stomach is complicated in structure.*

The Sirenia are herbivorous and feed upon alge; they are of
considerable size (existing forms 3 m. to 5 m.), and are found on sea
coasts and in rivers. The only representatives now living are the
Manatee (Manatus), on the Atlantic coasts of Africa and America
(and the adjacent rivers); and the Dugong (Halicore dugong), in
the Indian Ocean. The gigantic, edentulous Rhytina, Steller’s
Cow (Rhytina stelleri), is now exterminated. Until the last century
it was found in the North Pacific.

Order 8. Carnivora.

The Carnivora constitute a large group, including numerous genera
and species, which exhibit great diversity both in structure and also
in habits; certain characteristic features run through the whole
group, and all the members are reducible to a common type.

This is particularly evident with regard to the dentition,
which is most easily comprehended if that of the Dog is considered
first ; for that of other members of the group may be regarded as

Fig. 412.

  

Fig. 411. The teeth of the permanent dentition of the left half of the skull of a Dog,
and the milk dentition of the same, the latter shaded.—Orig.

Fig. 412. The same of a Cat.—Orig.

variously modified from it. There are, then, on each side of the
upper jaw of the Dog, three incisors (of which the third and outer-
most is larger than the others), one conical curved canine and six
molars (four premolars and two molars). The three anterior upper

 

* With regard to the skeleton it may be noticed that the lower jaw is very large
and heavy, very unlike that of the Whale’s, and this is true also for the rest of the
skull,

LL
514 Vertebrata.

premolars may be termed interdigitating teeth (for they usually
interlock with those of the lower jaw), each has a compressed
triangular pointed crown, and one or two smaller cusps on the
posterior edge of the triangle, the anterior one being the smallest.
The fourth premolar (p*), the sectorial or carnassial tooth,
is similarly compressed ; behind the apex there is a narrow notch in
the edge; and on the inner side a small tubercle: next to the
sectorial there follow two broad trituberculate teeth
(m! and m*), of which the anterior is the larger. The incisors and
canines of the lower jaw are like those of the upper; there are,
however, seven molars (p4, m8), the first four resembling the
interdigitating teeth ; the fifth (m1), the largest tooth of the lower jaw,
is something like the fourth premolar of the upper, and is also
termed a sectorial; its anterior portion, which is situated below
the upper sectorial, is compressed and provided with two cusps, of
which the posterior is
a little higher than
the anterior, whilst
the small posterior
portion of the tooth
is low and tubercu-
late. The last two
molars (m? and m?)
are tritubercular,
like those of the upper
jaw, but are smaller.
The modification
of the dental system
occurring in other
Carnivora tends
partly towards a
reduction of the
molar series proceed-
rae a, ing from both ends,
G e Spy hay” ae to a hyper-
Fe trophy either of the
tubercular or of
Fig. 413. The teeth of the left half of the upper jaws the sectorial portion,

of: A Dog, B Bear, C Marten, D Badger, E Viverid whilst the incisors

(Herpestes), F Hyena, G Lion. The chief point to notice is ane
the great development of the tubercular portion (m!—m?) in and canines as regards
B and D, and the degeneration of this in F—G.—Orig. number and form are

practically the same
in all. To give examples of this: in the Cat (Fig. 412), the dentition
is degenerate as compared with that of the Dog; of the six upper
molars of the latter, the first and the last have disappeared, and of
the four remaining, the first and the last are almost rudimentary ; as

 
Class 6. Mammalia. Order 8. Carnivora. 515

to the seven lower molars, both the first two and the last two are
absent. The tubercular part of the series is almost completely
atrophied, for not only are the molars (with the exception of the
rudimentary one of the upper jaw) absent, but the tubercular part
of the lower sectorial has also disappeared. In Bears, the opposite
extreme is reached ; the tubercular teeth are all present, and like the
posterior (tubercular) portion of the lower sectorial, extraordinarily
well developed, whilst the first three premolars are small, and some
fall out with maturity. For other groups see the special descriptions
and Fig. 4138.

The milk dentitions are still more nearly coincident, since with one
exception (see below), three premolars are present in each jaw, viz,, the second,
third, and fourth; the second upper interdigitates with the second and third
lower, the third is exactly like the upper permanent sectorial, the fourth in the
upper jaw is a tubercular tooth, in the lower jaw, a sectorial.* It is remark-
able that the sectorial of the permanent dentition does not occupy the
same position as does the milk sectorial, but in both upper and lower jaws, is
one place further back. Only where the number of premolars is less than
three (in the lower jaw of the Cat), is the number of milk molars less than the
typical number; the milk molar corresponding with the absent premolar (the
second) is then also wanting.

The last phalanx of each toe bears a claw which is often much
curved and can be turned upwards by means of an elastic ligament
passing from its phalanx to the penultimate ; so that in some animals
(e.g., the Cat) it does not touch the ground in walking (retractile
claws). The first digit is usually smaller than the others, and is
frequently absent from the hind limb. These animals are either
plantigrade, or digitigrade. The clavicle is poorly developed or
absent. Placentation zonary. In many forms there are, in the
region of the anus, glands or glandular pits, whose secretion has an
offensive odour.

Most of the Carnivora are of medium size, and feed either upon
other animals, or upon plants (succulent roots, berries, etc.). They
occur all the world over (with the exception of Australia), and are
most abundant in the Tropics.

The Carnivora form three large natural groups, one of which (Cynoidea)
includes the Dogs, another (Arctoidea) the Bears, Raccoons and Martens, a third
(Ailuroidea) the Cats, Viverras, and Hywenas. The differentiation is shown chiefly
in numerous minute points in the skull, a full account of which would, however,
involve so much detail, that this bare statement must suffice.

1. The Dog Family (Canidz). p 4,m2; the tubercular portions of the
molars are of medium strength. Head long, tail long, legs long, with five toes
in front, four behind; digitigrade. To this family belong the Fox (Canis
vulpes), the Polar Foxt (C. lagopus), both with perpendicular pupils; the
latter an inhabitant of the Arctic regions: the Wolf (C. lupus), with round

 

*In the milk dentition of Carnivora there is therefore the same number of
tubercular teeth as in the permanent dentition of the Cat, ie, 2.

+ In the Fox there are usually m 3.
LL2
516 Vertebrata.

pupil; in Europe, North Asia and North America, exterminated in England:
the Jackal (C. aureus), nearly allied to the Wolf; in Asia, North Africa, and
the Balkan Peninsula: the Domestic Dog (C. familiaris) probably a
descendant of the Jackal or its naer relations. An isolated canine form, the
genus Icticyon of Brazil, is distinguished by the possession of m 3 only, in other
respects, near to the rest of the Canidw. Another, the South African Otocyon
caffer has very large pinne; and is vulpine, with a pointed nose, and with more
than the typical number of molars, viz. p 4, m *.

2. The Bear family (Ursidz). p+, m2; tubercular region of the molar
series principally developed, sectorial portion degenerate (usually some of the
premolars are absent from the adult). Elongate head, very short tail; each
foot has five toes armed with very strong claws; plantigrade; animals of con-
siderable size, feeding chiefly upon plants. Here belong: the Common
Bear (Ursus arctos), which occurs on the continent, eg., in Switzerland,
Hungary, Russia, Scandinavia; it hibernates: the American Black Bear
(U. americanus) in North America, where is also the Grizzly Bear
(U. cinereus): the Sloth Bear (U. labiatus) of India, with very projecting
lips, and unusually long claws; the incisors are generally lost early: the Polar
Bear (U. maritimus), white, with hairy soles, belongs to the Arctic regions.
The Quaternary Cave Bear (U. spelwus) was larger than living forms; its
remains are frequently met with in the bone caves of Europe.

38. Raccoons (Procyonidz). p+, m2; tubercular portion of the molar
series not so pronounced as in the Bears; head longish, tail long, five toes on
each foot; plantigrade; small forms; omnivorous. Here belongthe Washing
Racoon (Procyon) and the Coatimondi (Nasua); both in America.

4, The Marten family (Mustelidz). pi+,m +4; in some, the carnassial
region of the molar series (i.e., the interdigitating teeth, the sectorial of the
upper jaw, the anterior portion of the lower sectorial) ; in others, the tubercular
portion, is most pronounced. The tail is usually well-developed; legs short,
five toes, digitigrade or plantigrade.

(a) Martens (Mustela). Small, very elongate, thin forms, prey chiefly
upon warm-blooded Vertebrates ; digitigrade; tubercular region rather small.
The following occur in Europe: the Pine-marten (M. foina), a large species
with white throat: the Polecat (M. putorius), brown; the Ferret
(M. furo) is a paler, degenerate, domesticated breed of the Polecat: the
Ermine (M. erminea), becomes white in winter; the short-tailed Weazel
(M. vulgaris), the smallest species, occurs in the British Isles: the European
Mink (M. lutreola), of the size of the Polecat, is uniformly brown, and has
webbed toes; it is aquatic, and common in Russia; it recalls the Otter. The
Sable (M. zibellina) of Siberia, stands near the Pine-marten. Allied to the
Martens, but larger and clumsier, is the Glutton (Gulo borealis), with a very
short, bushy tail, plantigrade; in Scandinavia, Russia, Siberia, North America.

(b) The Otters (Lutra) are larger, and characterised by the long, powerful
tail, webbed toes, blunt nose, and very short pinne. They are extremely good
swimmers, and feed upon fish, The Common Otter (L. vulgaris) of Britain
and other parts of Europe, inhabits fresh water as well as the sea. Allied to it
is the Sea Otter (Enhydra marina), with i 2; the hindlimbs resemble those of
Seals: on the coasts of the North Pacific.

(ec) Badgers (Meles tarus), characterised by the great development of the
molars, and of the hinder portion of the lower sectorial; plantigrade forms, with
strong digging claws on the fore limbs; omnivorous. The Skunks (Mephitis)
are allied to the Badyers, and occur in North and South America, Africa, and
Asia Minor,
Class 6. Mammalia. Order 8. Curnivora. 517

5. The Civet Family (Viverride). p +,m2; sectorial portion of the
molar series preponderatingly developed. Small animals, resembling the
Martens, with elongate body and short legs. In the warmer parts of the Old
World. The following may be noted: the Civet Cat (Viverra), one species
of which, the Genet (V. genetta), inhabits South Europe and North Africa;
and the Mongoose (Herpestes ichnewmon), of Africa and India.

6. The Hyena Family (Hyenide). p+,m+. Large, long-legged,
wolf-like, fairly long-tailed animals ; digitigrade. In the Old World, The species
of the genus Hywna are carrion feeders; the genus Proteles of South Africa,
with very feeble, small, cusped molars, preys chiefly upon lambs.

7. The Cat Family (Felidx). p 3, m1; tubercular portion of the molar
series rudimentary. Slim, elongate animals, with roundish head, long tail; four
toes on the hind foot, very much curved, compressed and pointed claws; digiti-
grade; feed almost entirely on warm-blooded animals. The Lion (Felis leo), of
a uniform, tawny colour; male with mane; Africa, West Asia, formerly in South-
East Europe: the extinct (Quarternary) Cave Lion, (F. spelza), is a near rela-
tive. The Tiger (Ff. tigris), with transverse stripes; Asia. The Jaguar
(F. onca), in the Southern districts of America; andthe Leopard or Panther
(F. pardus) of which there are several varieties in Africa and Southern Asia,
large, with circular spots. The Puma or Cougar (Ff. concolor) of median
size and uniform colour; in South America and in most of North America (the
“Panther” of the Americans). Smaller forms are: the Tiger Cats, various
small spotted forms (F. tigrina and others); the Wild Cats (F. catus), in
Central and South Europe, similar in colour to the grey Domestic Cat, but
shorter tailed; the Domestic Cat (F. domestica), which is apparently a
descendant of the Nubian Wild Cat (F. maniculata). The following are
aberrant forms: the Guepar de (F. [Cynailurus] jubata), a large-spotted, long-
legged form with claws less retractile than in other Felide; Africa and Asia ;
may also be tamed: the Lynx (F. lyna or Lyna vulgaris) distinguished by its
long legs, short tail, and the pencils of hairs on its ears (in the Lynx the first
interdigitating tooth of other Felide is generally wanting, the dental formula
being p 2, m 4); Scandinavia, Russia, etc.; formerly also in Germany. The
extinct Sabre-toothed Cats (Machexrodus) have p ,+—, m 4, and thus
the molar series is still more degenerate than in living Cats, to which, in other
respects, they are allied; the canine of the upper jaw is extremely powerful and
very long. In another extinct group, the genus Dinictis, there is, on the other
hand, a larger number of teeth than in the living forms, one additional inter-
digitating tooth and w small tubercular tooth in the lower jaw (the teeth of the
upper jaw being as in Felis): p 3, m 4.

 

Order 9. Pinnipedia,

The Pinnipedia are nearly related to the preceding group, with
which they have many characters in common; indeed they may be
regarded as Carnivora, which have been adapted to a marine life.

The limbs are short and broad and are turned back ; the proximal
part of the fore limb is concealed beneath the skin of the trunk, the
free portion bears a superficial resemblance to the pectoral tin of a
Fish: the hind limbs lie close to the trunk, with the tips of the feet
pointing backwards; they are enclosed for the greater part of their
length within the general skin; in the true Seals they are fixed in this
position, but in the Walrus and Eared Seals they may be turned so far
518 Vertebrata.

forwards, that the animal can walk upon them. Each foot has five
digits provided with straight claws; all are webbed, and the membrane
is prolonged beyond the tips of the toes as a more or less well-
developed ridge of skin. ‘The digits of the fore limb decrease in
length and strength from the first to the fifth (the first and second,
however, are about equally strong); on the hind limb the first and
fifth are stronger and usually also longer than the other three; the
tail is short; the pinne small or absent; the eyes large; the nares
mere slits, which close spontaneously by the elasticity of their walls,
but are opened by a muscular apparatus; the hair is usually close-
set, smooth, and sleek; with, sometimes, a thick covering of wool
below ; the new-born animal is generally covered with a woolly fur
which is sometimes shed before birth: the vibrissee are very strong.
Below the skin there is a thick layer of adipose tissue (blubber).

Fig. 414. Fig. 415.

 

Fig. 414. PesofayoungSea Elephant. a astra-
galus, c caleaneum, n centrale, cl—c* cuneiforms, cb cuboid ;
I—Y first-fifth toes.—After Flower.

Fig. 415. Upper teeth of the Sea Elephant; the
milk teeth are drawn below the teeth of the permanent set.
—After Flower.

 

There are usually 3 incisors (or a smaller number, rarely }) ; they
are more conical than those of the Carnivora, and do not form a
continuous cutting edge in closing: the canines are usually feebler
than in Carnivora, but otherwise similar. Of the molars, p ~ and
m +, are usually present; they are practically all alike, usually
similar to the interdigitating teeth of the Carnivores or simple and
conical; they are relatively feeble. The milk teeth are rudimentary,
they are either absorbed before, or shed quite soon after, birth.

It may also be mentioned that the hindermost portion of the skull is very
broad, whilst the interorbital region is usually much compressed. The lower jaw
is generally feeble; lachrymal bone and duct are absent; the lachrymal gland
is small, the Harderian gland well developed: the placenta, as in the Carnivores,
is zonary.
Class 6. Mammalia. Order 9. Pinnipedia. 519

The Pinnipedia are of considerable size, sometimes even gigantic ;
they are marine (a few live in large lakes, e.g., the Caspian Sea),
moving with the greatest activity by means of the very flexible
posterior portion of the body, whilst the large, backwardly-directed,
hind feet function as the caudal fin of a fish. ‘They usually come on
shore to rest, to breed, etc. ; they are littoral forms, but can only move
slowly upon land. Hared Seals and Walruses are able to walk on all
four legs; the true Seals hop along with great difficulty, arching
their backs and pushing themselves forward by means of the tail end;
they rest with the ventral surface on the ground; the fore limbs are
not generally used in locomotion. The food consists of Fish and marine
Invertebrates (Crustacea, Mollusca). They are usually polygamous;
the males are frequently, as in many other polygamous animals, con-
siderably larger than the females. They belong principally to cold
and temperate regions.

1. Eared Seals (Otariide). With small pinne; long neck; fore limbs
large; they can walk on the feet which are naked below; there is a large
ridge on all four feet, lobed on the hind ones; claws in part rudimentary
or very small (this holds for all the claws of the fore limb, and for the first
and fifth of the hind, whilst that of the middle toe of the hind limb is well
developed). The males are always much larger than the females. This group
comes nearest to the Carnivora, and many of the characteristic peculiarities
of the Pinnipedia are not well marked. Among these are the so-called Sea-
Lions or Sea-Bears, whose skins afford the well-known sealskin.* They
inhabit the southern waters of the South Hemisphere, and the northern regions
of the Pacific.

2. The Walrus (Trichechus [Odobenus] rosmarus) is devoid of pinne,
but in most respects is closely allied to the Otariide, though very peculiar
as regards the dentition. Like the Otariide this animal can support itself
on its fins, which have large borders, the ventral surface of the feet is naked;
the structure of the claw as in the Otariide.’ The young animal has i 3, ¢ 1,
m %, but several of the teeth are small and soon fall out or are never cut, so
that the adult usually possesses the following functional teeth: 7 3, ¢ 1, m 3

The upper canine is a long tusk, and continues to grow throughout life; the
other teeth are conical at first, but later worn right away. The Walrus feeds
on bivalves, worms, etc., which it grubs up with its long tusks from the bottom
of the sea. Fairly large; indigenous to the Arctic regions.

3. True Seals (Phocide). Pinne wanting; neck short; fore limbs
small. The ventral sides of the feet are hairy, and the limbs are absolutely
useless for walking; border of the feet narrow; claws for the most part well
developed. Chiefly in the Arctic regions.

(a) The genus Phoca with three upper, two lower incisors, and compressed,
multitubercular molars. The Common Seal (Ph. vitulina), occasionally
the Ringed or Marble Seal (Ph. fetida), and the Greenland Seal
(P. greenlandica), occur on the shores of Britain. Allied to Phoca is the Grey
Seal (Halicherus grypus), with conical molars, occurring on the shores of
Northern Europe, including Britain.

 

* The sealskin of commerce is deprived of the contour hairs, so that the woolly
fur alone remains; and it has, therefore, a very different appearance from the fresh
skin.
520 Vertebrata.

(b) The Hooded or Bladder-nose Seal (Cystophora cristata), with
two upper, one lower incisor. The male is characterised by the possession
of a flexible proboscis, which it dilates when angry. Polar seas. The

Sea Hlephants (C. proboscidea) are somewhat similar forms. In the Indian
and Pacific Oceans, chiefly in the southern regions.

Order 10. Cetacea (Whales).

The Whales are superficially much more like Fish than Mammals ;
as they have been completely adapted to an exclusively marine
existence, for which they are much better
suited than are other marine Mammalia
(Pinnipedia, Sirenia).

The body is piscine in form and pointed
at both ends; head, trunk, and tail, are
evenly continuous; externally there is no
trace of a neck; the tail is compressed,
extraordinarily powerful for a Mammal,
and very muscular. There is a horizontal
‘tail fin, a broad, stiff, bilateral ex-
pansion of skin, at the end of the tail.
Dorsally, there is usually a short, upright,
compressed dermal process, the dorsal
fin. The skin is smooth and shiny;
hair and skin glands are generally wanting
in the adult, at most there are a few hairs
in certain regions of the head, especially
near the edges of the mouth ;* the dermis
is very thick, and contains an extraordinary
amount of fat (blubber). Lips are absent.
The anterior limbs only are well developed
(for the rudimentary hind limbs see below) ;
they are modified into stiff, clawless plates,
only movable from the shoulder; the
fingers are enclosed in a common skin, and
their limits are not recognisable externally.
The nares open high upon the head, and

Fig. 416. Right anterior are often united into a single aperture ;
appendage ofa Pilot Whale. the eyes are small; the external auditory
H humerus, R radius, U ulna; b ‘

8 scaphoid, 1 lunar, ccuneiform; Opening extremely small, and pinne are
td trapezoid, uw unciform; F— wanting. The mammillz, one on each side,

IV first to fourth fingers, V fifth g ; 4 “
cinema IBe Tomes, are situated in pits near the anus.

 

 

* Only some of the Mystacoceti (and a South American river Dolphin Inia)
have hairs when adult. On the other hand, the embryos of almost all Whales
(both Mystacoceti and Odontoceti) have « few hairs; in the Odontoceti these only
occur above the upper jaw.
Class 6. Mammalia. Order 10. Cetacea. 521

“The cervical region of the vertebral column is very short, but
consists of the usual seven vertebra, several of which are generally
fused ; sometimes, as in the Arctic Right Whale, they are all fused

Fig. 417.

 

Fig. 417. Skull of a Dolphin (Delphinus) from the side. Decreased.—Orig.

Fig. 418. Skull of « Mystacocete (Balaena japonica), foetus. Decreased.—After
Eschricht.

C occipital condyle, Fr frontal, Ju jugal, LZ lachrymal, Mz maxilla, n naris, Na nasal,
oe exoccipital, Os supraoccipital, Pa parietal, Pal palatine, Pt pterygoid, Px premaxilla, Sq
squamosal, Ty tympanic bulla.

in the Balenopteride and some Odontoceti, on the other hand,
they are all separate, the centra are flattened discs. Very few of
the ribs are attached to the short sternum. The lumbar region is
characterised by its great length; sacral vertebree are not dis-
522 Vertebrata.

tinguishable: the entire vertebral column, with the exception of
the cervical region, is very flexible, the intervertebral discs thick.
The jaws are much elongated; the jugal in the Odontoceti is very
thin; the nasal very short, often rudimentary (best developed in
the Mystacoceti). The scapula without a spine; clavicles absent.
As was mentioned above, the bones of the fore limb are immovably
connected; there are four or five fingers; it is interesting to note
that some of these have more than three joints. There is
a vestigial pelvis in the form of two bones, one on each side, which
are neither connected with each other nor with the vertebral column:
in some of the Mystacoceti rudiments of the hind limb, the femur
and tibia, are also present, but embedded in the muscle. Lachrymal
glands and ducts are absent, but the Harderian gland is present,
and, indeed, well developed, the secretion having a fatty consistency.
The nasal cavities are a pair of tubes, oblique in the Mysta-
coceti, almost perpendicular in the Odontoceti; in the Mystacoceti,
rudimentary turbinals and small olfactory nerves are present; in the
Odontoceti the turbinals are wanting, whilst olfactory nerves may or
may not be present. In the Odontoceti the teeth are usually very
numerous, generally homodont and conical; there is no replacement.
The Mystacoceti have teeth in the embryonic condition (similar in
form to those of the Odontoceti), but they are small and are never
cut. The baleen or
whalebone in the
mouths of these Whales,
consists of two longi-
tudinal rows of strong
transverse folds of skin
depending perpendi-
cularly from the palate,
and covered with a well-
developed horny layer
which constitutes the
chief mass. The whale-
bone, therefore, is a
stiff three-cornered plate
of horn, which is, for the

most part, solid, but
Fig. 419. Diagrammatic transverse section of the i aie atic hes
anterior portion of the head of 4 Balaenopterid. as a Cavity a € base,
b cartilage, corresponding to the nasal septum of other wherein is the soft part,
Mammalia; ba whalebone, f grooves of the skin, i pre- ree f ‘i
maxilla, m maxilla, tu tongue, « mandible, v yomer— Consisting of connective

After Yves Delage. tissue and mucous mem-

brane. The whalebone
has three edges: a shorter, dorsal one, connected with the palate ;
an outer, smooth, straight one; and an inner, oblique edge, which
is the longest of the three, and much frayed out; in the imner

 
Class 6. Mammalia. Order 10. Cetacea. 528

portion there are several perpendicular notches reaching to the base.
‘The plates, of which the tirst and last of each row are the smallest, le
fairly close together on each side, and fill up a large portion of the
buccal-cavity, in the middle of which, however, a space, triangular in
transverse section, persists. When the mouth is closed, the whalebone
is covered by the lower Jaw: it serves as a filtermg apparatus; the
Mystacoceti swim for some distance with the mouth gaping open, then
close it, and the water trickles out between the baleen, leaving the
contained organisms imprisoned by the fibrous inner edge of the
blades. The whalebone is to be regarded as extraordinarily well-
developed palatal ridges (see p. 487). The salivary glands are
rudimentary or absent, the stomach is complex. The larynx extends
forwards as a tubular prolongation, surrounded by the well-developed
soft palate; thus a continuous passage between nostrils and trachea is
formed, on either side of which the food passes into the cesophagus.
The testes are retained in the abdominal cavity.

The Whales are almost all marine ; some few occur in rivers. Like
Fish, they move by undulations of the tail, and never voluntarily come
on to land. They are able to remain for considerable periods below
the water (half an hour or more). Their food consists chiefly of Fish
and marine Invertebrata. They frequent all seas, the large forms,
however, occur chiefly in the colder regions of the world. The largest
animals known belong to this group.

Sub-Order 1. Mystacoceti (Wiale-done Whales).

Edentulous, but provided with whale-bone. Two external nares,
placed more anteriorly than in the Odontoceti. Only one pair of true
ribs. The skull is extraordinarily large and bilaterally symmetrical ;
nasals relatively well-developed. The Mystacoceti feed on various
small marine animals, which live in shoals (Kuphauside, Copepoda,
etc.) ; many of the Baleenoptera also feed upon small Fish. This sub-
order includes the largest Whales.

1, The Fin-whales (Balenopteridz). With dorsal fin. On the ventral
stuface of the head and body, there are numerous deep longitudinal grooves.
Elongate animals, with relatively small head and short whalebone; narrow
pectoral fins. The Blue-whale or Sibbald’s Fin-whale (Balenoptera
Sibbaldiz), which attains a length of about 30 m.; and the rather smaller
Rorqual (B. musculus), which is abundant in North European seas, are not
uncommon off British coasts. Both of these are the objects of a regular
fishery on the coasts of northern Norway. The Lesser Fin-whale (B.
rostrata) is much smaller (the largest only 10 m.) and also occurs in the North
Atlantic. The very large Hump-back Whale (Megaptera béops), with low
hump-like dorsal fins and with very long pectoral fins, is less elongate than
most other Balenoptera ; a few have been taken off British coasts.

2. Balwnide. No dorsal fin; no ventral furrows; body less elongate ;
head relatively very large; whalebone long and narrow; pectoral fins broad. The
524 Vertebrata.

huge Greenland or Polar Whale (Balena mysticetus), up to 20 m. long;
in Greenland, etc.; now much reduced in numbers. B. biscayensis, very like the
Greenland form, occurs somewhat further south (in the North Atlantic),

Sub-Order 2. Odontoceti (Zoothed Whales).

Furnished with teeth, but no whalebone. External nares united,
to form a single aperture* situated dorsally and far back on the
head ; several true ribs. The face portion of the skull is distinctly
asymumetrical ; nasal bones rudimentary. Feed chiefly upon fish.

1. Dolphins (Delphinus) have a pointed, beak-like snout, marked off from
the forehead by a groove; numerous (twenty or more) small conical teeth in
each half of the jaw; a high dorsal fin. Animals of about 3 m. long, several
species occur on British coasts. Allied isthe Sea-hog or Porpoise (Phocena
communis), 1:5 m. long, with short blunt snout, compressed teeth (about
twenty-five in each half of the jaw); abundant in European seas. The Pilot-
whale or Black-whale (Globiocephalus melas), has teeth only in the anterior

ue
'

'

'

   

Fig. 420. Skull of a Pilot Whale, from the left side, with large mass of blubber
lying upon the snout ; this mass is divided medianly. f blubber, 6b firm layer of connective
tissue below the epidermis, which is indicated by a thick black line, w nares, | air sinus
continued on from the nasal duct.—After Murie.

portion of each jaw; the head is thick and rounded in front, with quite a short
projecting pointed snout; up to 6 m. long. It is regularly caught off the Faroe
Islands, and is a frequent, though irregular, visitor to British coasts. It feeds
principally upon Cuttle-fish. The “Grampus” or “Killer” (Orca gladiator),
somewhat larger than the Pilot-whale, with very high dorsal fin (whence it is
sometimes termed the Sword-fish), and about twelve powerful conical teeth in
each half of the jaw; feeds upon Porpoises, Seals, and Fish; very widely dis-
tributed; occurs on the west coasts of Britain.

2. Of the more aberrant Odontoceti may be mentioned, the
Cachalot or Sperm-whale (Physeter macrocephalus), a large form with
a huge head, on the flattened snout-like portion of which, there lies an immense

 

* In the Odontoceti, but not in the Mystacoceti, there are saccular outgrowths, both
from the short unpaired and also from the upper portion of the paired external nasal
duct.
Class 6. Mammalia. Order 10. Cetacea. 525

mass of blubber* (yielding spermaceti); strong, conical teeth in the lower,
rudimentary, in the upper jaw. Widely distributed; stragglers have been caught
several times off the coasts of Britain. The Bottle-nose Whale (Hyper-
oodon rostratus), with narrow, pointed snout, and the head much arched behind
this; almost edentulous (only one larger and one smaller tooth anteriorly in
each half of the lower jaw; besides this, several rudimentary teeth above and
below); in the North Atlantic, fairly abundant, ¢.g., off the Faroes, and one of
the most common Cetaceans; stranded on British shores. The Narwal
(Monodon monoceros) is characterised by the possession of a long, spirally-
twisted tusk, which sticks straight out from the mouth on the left side; in the
right side of the upper jaw, there is a similar, but much smaller tooth, which
remains within the bone; there are no other teeth;+ in the female, both are
enclosed in the jaw. As an example of an Odontocete living in fresh water, the
Ganges Dolphin (Platanista gangetica), which possesses long, thin jaws
with numerous pointed teeth, may be mentioned ; the eyes are rudimentary, and
have no lens; the skeleton is in many respects peculiar. The animal, which is
only 2 to 3 m. long, lives in the Ganges, Indus, ete. Two allied forms in rivers of
South America.

Order 11. Bruta (Hdentata).

The animals belonging to this group are peculiar in that the
teeth, when present, are imperfectly developed, and do not form
a continuous series; they are devoid of enamel, are usually all
approximately alike, and grow from persistent pulps: incisors are
absent (in one of the Dasypodide alone, the last incisor of the upper
jaw is present): there is, as a rule, no replacement. The claws are
generally long, curved, and very powerful. A number of fairly
diverse forms belong to this order; most of them are natives of hot
countries.

l. Sloths (Bradypodide: genus Bradypus, etc.). The body is covered
with long coarse hair; the head is round; the pinnw very small; % cylindrical
teeth; fore longer than hind limbs; three fingers (the second, third, and
fourth), or only two (the second and third); on the hind limbs there are always
three toes (second, third, and fourth); both fingers and toes are enclosed in a
common skin up to the terminal phalanx, which can be opposed to the palm or
sole; the claws are falciform and extremely long and powerful; tail rudi-
mentary; exclusively arboreal, feeding upon leaves; South and Central America.

2. The extinct Megatheria or Giant Sloths (Megatheriide:
genus Megatherium, Mylodon, etc.) occupy an approximately intermediate
position between the foregoing and the succeeding divisions, for they resemble:
the Sloths in respect of the head and teeth, whilst the vertebral column, the limbs
(of which the posterior are about the same length as the anterior) and the
long powerful tail are more like the corresponding, parts in Myrmecophaga.
They were herbivorous animals, generally of considerable size (the largest bigger
than the Rhinoceros), of extremely bulky structure, and with very massive bones ;

 

*In the same region of other Odontoceti, there is a thinner or thicker layer of
blubber, which in, eg., the Pilot Whale, is well developed, and gives the head its
arched form (Fig. 420).

+ There may be a few.rudimentary teeth in the upper jaw, posterior to the tusk,
526 Vertebrata.

some had small bony knobs in the skin. The remains have been found in the
Quarternary strata in various parts of America.

3. Ant-eaters (Myrmecophaga) are covered with fine or coarse hair, the
head is more or less elongate, sometimes very long; teeth are absent, the mouth
is very small, the tongue vermiform, the submaxillary glands of unusual length;
the third fingers are very large, with long falciform claws, the other fingers are
smaller or even atrophied ; the animal rests upon the outer edge of the hand in
walking; the hind feet have four or five almost equal toes with powerful claws ;
the tailis long. This group is insectivorous, feeding, e.g., upon Termites which
adhere to the long tongue by means of the sticky saliva: South America. The
Great Ant-eater (M. jubata), with coarse hair and bushy tail, lives upon
the ground, whilst the other species are, for the most part, or exclusively, arboreal,
eg., the Little or Two-toed Ant-eater (M. didactyla), which has a
short snout; fine. soft fur; a prehensile tail; and only two claw-bearing digits on
each of the fore limbs.

 

Fig. 421. A manus of the Great Anteater, B of the Two-toed Anteater,
s scaphoid, 1 lunar, c cuneiform, p pisiform, tm trapezium, td trapezoid, m os magnum,
wunciform. IJ—V digits.—After Flower.

4. Armadillos (Dasypodidz) are characterised throughout by a dorsal
covering of large flattened scales, like those of Reptiles; these scales or
plates are separated from one another by grooves, the outer surface being very
horny, whilst within each scale there is a large ossification. They lie in several
transverse rows, separated by soft skin in the median region of the back, but
in front and behind they are close together; here the ossifications are firmly
fused, and this is also the case with those of each transverse row, so that the
back is covered by large bony shields in front and behind, and in the middle
with a varying number (three to twelve) of half hoops of bone. There are
similar scales on the dorsal side of the head, on the limbs, and on the tail, but
these are wanting from the hairy ventral surface. The teeth are cylindrical, often
fairly numerous; the head is long with well-developed pinne; the legs short
with strong claws, The animal is plantigrade; it is fosgorial, essentially insec-
Class 6. Mammalia. Order 11. Brita. 527

tivorous. rather small or of medium size; some forms can roll themselves up :
South America and the southern parts of North America. Allied to them are
the extinct Glyptodons, in which all the dorsal plates were immovably
united to form a large, thick, arched coat of mail; large portions of the vertebral
column were also fused; they were extremely clumsy animals and of consider-
able size. Quaternary of South America.

5. The Cape Ant-eaters or Aardvarks (Orycteropus) are animals
of fair size; sparsely haired; with long snout and tongue; small mouth; large
pinne; powerful tail; strong, but not very long claws; possessing teeth: Africa.

6. Pangolins or Scaly Anteaters (Manis) are specially
characterised by having the dorsal region of the body covered with large,
very horny, imbricating scales, between which a few hairs appear. The head is
long ; pinnz are absent; the mouth is small and edentulous; the tongue long; the
tail is powerful; claws long and falciform. Insectivorous and representing the
Ant-eaters (which they resemble in many respects) in the tropical regions of the
Old World.

Order 12. Rodentia (Rodents).

The Rodents are primarily characterised by the peculiar
dentition. Canines are absent; there is only a single
incisor in each side of the lower jaw, situated anteriorly and
close to its fellow; there is usually also only one in the premaxilla,
placed as in the lower jaw; the incisors are long and grow from
persistent pulps, they are almost quadrangular prisms avd are
curved; the enamel only
covers the front and the
lateral edges, its surface is
sometimes reddish brown;
the free end of the tooth
is cut away obliquely like
achisel. Theupperincisors 4
have a greater curvature
than have the lower ones,
in both cases the portion
within the jaw extends far
back, m the lower usually
even to the most posterior
extremity below all the
molars. In the Leporide
there is a smaller incisor

hi i : ;

be ind the large one in the Fig. 422. Right ramus of the mandible, A of a

upper jaw ; it may also be Rabbit, B of an Agouti, from the inner side. Sockets
: of the incisors removed for their whole length to

noticed that here the lower show the different lengths of the tooth. B gives the

incisor only extends back usual rodent condition —Orig,

as far as the front end of

the molar series (Fig. 422 A). There is always a large diastema

between the incisors and molars: the molars exhibit a great

.

 
528 Vertebrata.

diversity of form; the crown is short and tuberculate; or furnished
with low transverse ridges (Mouse, Rat); or each has two fangs, but
the crown is longer and is folded both from above downward and also
laterally ; or again, the roots are quite short as compared with the
long plicate crowns; lastly, they often grow from persistent pulps,
and are provided on each side with deep, perpendicular folds

A B Cc

 

Fig. 422. Transverse sections of molars of various Rodents (at about a similar stage of
attrition). .1 Hare, B Beaver, C Field Mouse. c cement, d dentine, e enamel.—After
Owen.

which extend for some distance into the tooth, and are partially or
entirely filled with cement. On the grinding surface, therefore, there
are transverse or oblique stripes of enamel

with cement and dentine between. Occasion- Dental Formule.
ally the molars with persistent pulps (cf., the Hare. . . p 3,m 2
molars of Elephants) are even divided into a Pika . eae
series of perpendicular transverse plates with Squirrel. . ,,2,, 2
cement between them. This variety in the Beaver @ ope
form of the teeth is correlated with a diversity Sminthus wine
of habit. The molars with short crowns are Mouse . .,,%,, 3
relatively little used, the others more or very Australian

much. The number of teeth is greatest in Ret. ey

the Hares, p $, m 2; in others it is more or
less reduced from the anterior end of the series; even, as may be seen
from the accompanying list, to the exclusion of all the premolars ;*
only from quite a few forms (eg., the Australian rat, Hydromys,
belonging to the Muridz), one of the molars, namely, the last m%, is
also absent.

Whilst the articular facets for the lower jaw in most Mammalia
are in the form of transverse surfaces or pits, in most Rodents there

 

* As the corresponding milk teeth are also generally absent, and as (with the
exception of the Hares) the incisors have no predecessors, there is absolutely ng
replacement in forms destitute of premolars, :
Class 6. Mammalia. Order 12. Rodentia. 529

is a longitudinal groove, so that the mandible possesses considerable
mobility from before backwards’ (in masticating, the lower jaw moves
backwards and forwards; the enamel stripes upon the molar run in
the opposite direction, 7.e., transversely). The feet are usually small
and bear claws, and the animals are generally plantigrade. The first
digits of the manus are rudimentary or absent, whilst the other
fingers and toes are usually all present. In several forms there are
internal cheek-pouches, outgrowths of the cheeks, connected with
the buccal cavity; in some, in approximately the same position, there
are ingrowths of the skin covered with hairs (external cheek-
pouches) .*

The Rodents are widely distributed and rich in species, includ-
ing for the most part small forms which are almost exclusively
herbivorous.

1. The Rabbit family (Leporidz). 12, m 2%, the large upper

5?

incisors are grooved, the molars are plicate and grow from persistent pulps. The
genus Lepus, with m &, long pinne; very short tail; long hind limbs;t
comprises the Hare (L. Huropzus),t distributed throughout the greater part
of Europe: andthe Polar or Variable Hare (L. timidus or variabilis),
in the Northern parts of Europe and Asia, in Ireland, the Alps and the Pyrenees ;
it is white during winter in the colder regions: also the shorter-legged burrow-
ing Rabbit (L. cwuniculus), indigenous to South Europe; the Pika (Lagomys),
with m £; short pinne; shorter limbs than the Hares; ecaudate; in Siberia and
North America.

2. The Squirrel family (Sciuridz). m 5, tuberculate or plicate; the
anterior molars of the upper jaw very small; pollex rudimentary; tail hairy:
the Squirrel (Sciwrus vulgaris), with long, bushy tail; arboreal: the
Flying Squirrel (Pteromys), characterised by the possession of a patagium
between the fore and hind limbs (one European species, Pt. volans, in North
Russia). The Marmots (Arctomys) are fossorial, hibernating animals; they
are thick-set, with short pinnz and a short tail: there are two European species,
the Alpine Marmot (A. marmota), and an allied form, the Pouched
Marmot (Spermophilus citillus) of East Europe. Allied to the Squirrels is
the Beaver (Castor fiber), a fair-sized animal with + plicate molars; short
ears; large, flattened, scaly tail; and webbed toes on the hind feet: they are
excellent swimmers and diggers, and feed upon bark. Beavers were formerly
abundant in the British Isles, but are now quite extinct; they occur on the
Continent, and are, for instance, still fairly abundant in the Elbe: an allied
species (C. canadensis) occurs in North America.

3. Dormice (Myowidz). M +, with transverse bands of enamel; pollex
rudimentary ; tail long and hairy: superficially’ they somewhat resemble Squirrels
or Mice. The small, mouse-like Common Dormouse (M. avellanarius)

 

*In the maxille of Mammals generally, there is a shorter or longer canal, the
canalis infraorbitalis, through which a large nerve (the maxillary branch of the
trigeminus) runs. The canal opens in front of the orbit by a perforation termed the
infraorbital foramen. In the Rodents the infraorbital canal is quite short, and
usually very wide, and a portion of the masseter muscle passes through it.

+ The soles of the feet appear to have acomplete covering of hair, but as a matter
of fact there are small, naked, plantar cushions, which are, however, covered by the
hair of adjacent regions.

t In many books this is incorrectly termed L. timidus.
530 Vertebrata.

occurs in Britain, and is widely distributed over the Continent. Several other
species are met with in southern, or southern and eastern Europe: the Sq uirrel-
tailed Dormouse (M. glis), the largest species: the Garden Dormouse
(Mf. nitela): the Tree Dormouse (M. dryas). Allied is the Sminthus
betwlinus or vagus, in North and East Europe, very like a Mouse externally, with
m %. The Sminthus is closely allied to the Jerboa (Dipus), which is chiefly
characterised by the great length of the hind foot; this especially affects the
second to the fourth metatarsals, which are fused (the first to the fifth toes are
small or absent); the animals hop along, stepping only upon the second, third,
and fourth toes of the hind foot; the tail is long, with a tuft of hairs at the end:
desert animals; South Russia, Asia, Africa. Also allied to the Sminthus is the
blind, earless, and tailless Mole-rat (Spalax typhlus), whose habits are some-
what similar to those of the Mole; South-East Europe (e.g., South Russia) and
Western Asia.

4. Mouse Family (Muridz). M3 (occasionally 2, of., p. 528); very varied
in structure; tail longer or shorter, scaly ; pollex rudimentary. Usually of small
size.

(a) Rats and Mice (Mus). Molars tuberculate, with short crowns and
with roots; tail long, slightly hairy; pinne fairly well developed. In England
occur: the Wood Mouse, or Long-tailed Field Mouse (UM. sylvaticus),
and the Harvest Mouse (M. minutus) : the following have invaded and live in
human dwellings: the House Mouse (M. musculus), the Black Rat (M.
rattus), now rare, having been almost completely exterminated by the more
recent immigrant, the Brown Rat (M. decwmanus). Allied to the Mice is the
brightly-coloured Hamster (Cricetus frwmentarius), with cheek pouches and
short tail; somewhat larger thana Rat; Central Europe.

(b) Field Mice (Arvicola). Molars long, growing from persistent pulps,
with deep grooves on each side (grinding surface with loops of enamel) ; occasion-
ally there are short roots; tail shorter and more hairy than in the Mice; pinne
short. They burrow in the ground, and are more exclusively herbivorous
(feeding upon roots, bark, etc.) than the true Mice. The following species
occur in England: the Bank-vole (A. glareola), which affords a transition to
true Mice; the molars with short roots; pinne and tail somewhat longer than in
the rest: the Field Mouse (A. agrestis and arvalis): the Water Rat
(A. amphibius) ; the latter is the size of a Brown Rat, the others about as large
as the House Mice. Closely allied is the Lem ming (Myodes lemmus), with very
short tail, and strong claws on the fore limbs; Scandinavia; famed on account of
its migrations. Another form allied to the Field Mice is the Musquash or
Musk Rat (Fiber zibethicus), with long, compressed tail; the toes with stiff
hairs at the edges; furry animals of fairly large size, inhabiting northern
North America, and by their mode of life recalling the Beaver.

5. Hystricomorpha, a group consisting of numerous forms, differing very
much externally, but agreeing chiefly in the characteristics of the skull.* Molars
+, banded, with roots, or growing from persistent pulps.

(a) The Coypu (Myopotamus coypu), an aquatic animal of beaver-like
appearance, but smaller, and with a rounded tail; the toes of the hind foot are
webbed; South America.

(b) Porcupines (Hystricidzx), characterised by the modification of some
of the hairs into stiff spines, often of enormous thickness and considerable
length; animals of considerable size. The Common Porcupine (Hystria
cristata), in South Europe; lives in holes in the ground; tail short. In America,
there are various arboreal forms, (Cercolabes) with prehensile tails.

 

** E.g., the infraorbital foramen is huge, and the mandible is peculiar in form.
Class 6. Mammalia. Order 12. Rodentia. 531

(c) Subungulata. Claws short, hoof-like, legs for the most part long,
usually digitigrade; the number of toes on the hind foot varies; forefoot, with
four well-developed digits, and with or without a rudimentary pollex; tail small
or absent: all in South or Central America. The Pacas (Celogenys paca)
with five toes: the Agoutis (Dasyprocta): the Guinea-pig (Cavia
cobaya): the Capybara (Hydrocherus capybara); all with three toes; the
last-named is the largest of all living Rodents; in South American rivers.

Order 18. Prosimize (Lemurs).

As in the Apes, with which the Lemurs were formerly grouped,
the first digit on both fore and hind limbs is separated from the
others, and is opposable. On the hind foot, usually only the second
toe has a claw, the other fingers and toes are provided with flat
nails. The fore limbs are shorter than the hind. Of teeth, there
are at most 72, ¢ 4, p 3, m3; often, however, the number is smaller.
The upper incisors are generally small, and there is usually a median
diastema; the lower incisors and canines are all alike, narrow and
directed obliquely  for-
wards; the upper canines 2
are caniniform; all the
premolars (or the anterior
ones alone) are compressed
and triangular (the first of
the lower jaw is canini-
form); the other molars
tubercular, or each with
two transverse ridges.

Most of the Lemurs
are very hairy, many have
long tails. The skeleton
differs in many respects
from that of Apes; for
instance, the orbit is in-
complete behind, and as
in other Mammalia, remains
in widely open communi-
cation with the temporal
fossa (there is, however, as
in various other Mammals,

a closed ring of bone round

ry Z Fig. 424. Left hind foot of a Maki, ventral
the orbit) 3 the rami of the (oe ars digit; oI wooed dttta, toi, Gee).
mandible are usually sepa- Orig.

rate; the facial region of

the skull is larger in proportion to the cranial part than in

most Monkeys. The uterus has two long horns (uterus bicornis).

There is a pair of thoracic, sometimes also a pair of abdominal,’
MM 2

 
532 Vertebrata.

mamme. The Lemurs are arboreal animals feeding on fruits,
Insects, and small Vertebrates; and are usually nocturnal. They
occur only in the Old World, a considerable number in Madagascar.

1. The Makis (Lemurs). Muzzle pointed and vulpine; tail long; ¢ 2, ¢ 4.
m &; Madagascar. Allied to these are the Loris (Stenops), with short
muzzle; large eyes; tail small or absent; India.

2. The Tarsier (Tarsius spectrum) characterised by the great elongation*
of some of the tarsals (caleaneum and navicular) so that the foot appears to
have a handle; broad soft pads below the tips of the toes; toes two and three
with claws; tail long and tufted; eyes huge. Nocturnal springing animals; in
the Malay Archipelago.

3. The Aye-Aye (Chiromys madagascariensis) is peculiar in several
respects. Anteriorly, both in upper and lower jaws, there is a large tooth
growing from a persistent pulp, which recalls the incisors of the Rodents; that
in the upper jaw is an incisor, that in the lower apparently corresponds with
the outermost forwardly directed tooth of other Lemurs, i.e., seems to be a canine
(therefore the following may be given as the dental formula: ¢ 3, ¢ 9 m 4),
Hallux with nail, all the other digits with claws; the third finger exceptionally
thin (used for pulling Insects out of holes or crevices); Madagascar.

Order 14. Primates.

‘In the members of this order, Monkeys and Man, both pollex
and hallux are separated from the rest of the digits, and are more
freely movable than the latter, being usually more or less perfectly
opposable, so that the limbs may serve as organs of prehension; the
hallux in particular is usually free and movable (except in Man). As
a rule all the digits are furnished with rather feebly arched nails.
The facial region is generally short and small in comparison with that
of other Mammals, and with the cranium. There is usually not much
hair on the face. The eyes look forwards, and are placed close
together. Unlike all other Mammals, the or bit is separated from the
temporal fossa by a bony transverse septum (consisting of portions of
the jugal, the frontal, and the alisphenoid). The teeth of the
upper and lower jaw are similar, both as regards number and
structure ; in each half of the jaw there are two chisel-shaped incisors,
one canine of the usual form, two or three premolars, and, as a rule,
three (occasionally two) molars; all the molars are tuberculate, and
have short crowns. There are always two mamme only, and these
are thoracic. Of other characters it may be noticed that the anterior
cornua of the hyoid are shorter than the posterior, and that the hyoid
is not directly connected with the skull. The uterus is simplex.

The Primates are, for the most part, essentially adapted to an
arboreal life; many of them can, however, move along the ground

 

* Such an elongation of the ankle is almost unique among Mammalia; in some
allied Lemurs there is, however, an approach to this condition. (Cf. the tarsus of the
Anura.)
Class 6. Mammalia. Order 14. Primates. 533

with ease, using all four limbs, the whole of the foot or hand resting
upon the ground. In Man alone the hind limbs exclusively are used,
and are very strongly developed for terrestrial locomotion. They are
almost all tropical animals, feeding principally upon fruit.

|

7 Distance between theexternal
Hallux capable of Platyrrhine |
J

nares fairly large. External
auditory meatus unossified. A
small foramen in the septum
between the orbit and the tem-
poral fossa. p 3.

considerable movement. {

Hind limbs little or no

stronger than the fore.
‘
|
‘4
|
L

2 ) Distance between the nares
Gatarehing | small. External auditory

meatus partially ossified. No
Anthropidz | foramen in the septum between

Hallux only capable
of slight movement.
Hind limbs extraordin-

the orbit and the temporal
arily well-developed.

fossa. p 2.

Sub-Order 1. Platyrrhine.

The external nares are separated by a broad membranous bridge.
Three premolars are present both above and below; usual dental
formula: 7 3, ¢ +, p 3, m 3. No portion of the external auditory
meatus ossified. In the posterior border of the jugal there is a tiny
perforation of the septum between the orbit and the temporal fossa,
ie, the septum is not quite complete. Cacum relatively large.
Cheek-pouches and ischial callosities absent. Fore limbs usually
somewhat shorter than hind. Tail well developed, sometimes pre-
hensile. Confined to South and Central America.

1. Sapajous or Capuchin Monkeys (Cebus) have a long tail covered with hair,
and capable of being rolled up like a watch spring and coiled round branches of
trees. Inthe Howling Monkeys (Mycetes) the tail is very powerful, its
tip is naked on the ventral side and sensory, and it is developed as an organ of
attachment (the animal can even hang by it alone), i.¢., isa genuine prehensile
tail; the hyoid is large and hollowed out to receive an outgrowth of the larynx.
The Spider Monkeys (Afeles), with similar tails, are characterised by the
rudimentary nature or absence of the pollex.

2. The Marmosets (Hapalide) have a flattened nail only on the hallux;
on all the other digits on the contrary, the nails are so much arched as to be
claw-like. This small group may also be distinguished from other Platyrrhines
in that m 2 only are present. The tail is hairy, and cannot be coiled up; the
pollex has but little power of independent movement. In other respects the
Hapalide come near to the other Platyrrhines.

Sub-Order 2. Catarrhine.

The external nares are close together. Two premolars (dental
formula always: « 3, ¢ +, p $m 3). Proximal portion of the
external auditory meatus ossified over a considerable extent.
584 Vertebrata.

No perforation in the septum between the orbit and the temporal
fossa. Czcum small. Cheek-pouches frequently, ischial callosities
usually present; tail never developed into an organ of prehension,
often absent. Occur exclusively in the Old World.

1. Cynomorphe. Below each of the thick, broad ischia, there is a naked
coloured portion of the skin, an ischial callosity. Nails relatively much
arched, Tail usually present. Hind somewhat longer than fore limbs. Cheek
pouches usually present. External incisor of the lower jaw narrower than (or
the same breadth as) the inner ; first molar of the lower jaw with four tubercles.
The thorax compressed (as is usual in the Mammalia) ; the manubrium of the
sternum broad, the rest very narrow. Pelvis long and narrow; the symphysis
(the line of junction of the two halves) long, the ilia long and narrow. The
sacrum consists of three vertebra.

(a) Cercopithecide. Tail long; muzzle short; cheek pouches present;
several African species. Closely allied is the Magot or Barbary Macaque
(Inuus ecaudatus); with rudimentary knob-like tail; occurring in North Africa
and Gibraltar (the only European Ape). The Baboons (Cynocephalus), dis-
tinguished from the Cercopithecide by the very long, canine muzzle; tail long or
short; cheek pouches present. They usually remain on the ground, are only
occasionally seen in trees. Africa and Arabia.

(b) Semnopithecidx, characterised by the absence of cheek pouches; and
the division of the stomach into several sections (whilst in other Apes
it is simple). Amongst forms belonging here is S. nasieus, of Borneo,
with very long nose. Colobus, in which the pollex is wanting, is nearly allied;
Africa.

2. Anthropoid Apes (Anthropomorphe). Ischial callosities
absent or small. Nails arched in the Gibbons, more flattened in other forms.
Gibbons well clothed with hair; in the others, certain regions sparsely covered.
Tail absent (rudimentary caudal region of the vertebral column consisting of
four or five small vertebre); fore limbs longer than hind; no cheek
pouches; outer lower incisor broader than the inner, first molar of the lower
jaw with five tubercles; thorax broader than in the Cynomorphe; pelvis in
the Gibbons like that of the Cynomorphe; in others, the ilia are broader, the
symphysis is short; the sacrum consists of five vertebre.* The Anthropoid
Apes are more exclusively arboreal than are the other Catarrhine; they do not
walk like ordinary Mammalia (as the Platyrrhine do), but upon their hind legs,
supporting themselves by the knuckles of the fore limbs, or they move in other
aberrant ways. The largest Monkeys belong here.

(a) Gibbons (Hylobates) come nearest to the Cynomorphe; they possess
small ischial callosities; the nails are strongly arched; and the pelvis is long and
narrow, like that of the Cynomorphe; they are covered with thick hair, and
have extraordinarily long arms, which they swing as they walk on their hind
limbs. Smaller than those following: several species in Asia.

(}) Orang-Utang (Pithecus satyrus). Head almost conically arched
above, face very projecting, nose flattened; fore limbs very long, reaching to the
ankles when the animal stands upright; hand and foot long and narrow; hallux
fairly small; reddish brown; height up to 15 m. (measured in the upright
position): Sumatra and Borneo.

 

*In the Orang, the Chimpanzee, and the Gorilla (and in one of the Gibbons
Hylobates syndactylus), just below the skin, there are one or two large air sacs;
they proceed from the larynx, and extend on to the neck and thorax; they may be
inflated with air and enormously expanded.
Class 6. Mammalia. Order 14. Primates. 5385

(c) The Chimpanzee* (Simia troglodytes or Troglodytes niger) and the
Gorilla* (S. or 7. gorilla) correspond in most points. The forehead slopes
back, the nose is broad and flat, but projects further than in the Orang; the
fore limbs also are shorter, the hands and feet broader, the hallux large and
well-developed; both are black. The Gorilla attains a height of 1'7 m.; the
Chimpanzee is somewhat smaller. Both occur in the tropical parts of West
Africa.

Sub-Order 3. Anthropide. (Jan.)

In contrast to other Primates, the Anthropide are characterised
by the specialisation of the hind limbs as organs of loco-
motion adapted for supporting the body in an upright position
without assistance from the fore limbs. In correlation with this
they are very powerful, much longer than the fore limbs, and
extremely muscular. The hallux is but little more separated
from the other toes than these from one another,t possesses only
a slight power of independent movement and is not opposable ; it is
somewhat longer than, or about -equal in length to, the second digit,
or a very little shorter (in other Primates much shorter) ; the other
four toes are short, the metatarsus long. The pelvis is very short and
broad, the ilia in particular are very short, broad, and strongly curved ;
the symphysis is short. The fore limbs, which are very like those of
the Anthropoid Apes, are relatively weaker than in the latter; they
are extremely well developed as prehensile organs, but are of no
importance for the ordinary mode of locomotion. Another character-
istic point is the enormous development of the brain,t and the
consequent abnormal preponderance of the cranial capsule over the
slightly developed facial region: in other respects the structure of
the brain, even as regards points of detail, is very like that of the
Anthropoid Apes. Further peculiarities are the slight covering of
hair over the greater portion of the body; the small size of the canine
tooth ; and a feature which is closely connected with this, the absence
of a diastema between the external incisor and the canine of the upper
jaw larger than between the other teeth (in other Primates the canine
of the lower jaw bites into this space) ; lastly it must be mentioned
that the thoracic cavity is still broader and flatter than in the
Anthropoid Apes.

 

* Possibly several closely allied species are included under each of these titles.

+ The gap, however, is clearly deeper, and the distance between the hallux and the
second toe is greater than between the other toes; still greater and more distinct in
the embryo and young child than in the adult.

t Man, however, does not possess the largest brain as compared with the whole
weight of the body; even among the Primates, a relatively larger brain occurs in some
small forms (in one of the Hapalidew, the weight of the brain, when compared with that
of the whole body, is as 1: 20, in Man it averages 1: 40). On the other hand, the
brain of Man is much larger than in any other animal of similar size (the brain of the
Gorilla, relatively to the weight of the body, is 1: 200).
536 Vertebrata.

For the rest, Man agrees in all the chief points of structure with
the Catarrhine, particularly with the Anthropomorphe. This
coincidence obtains in all those characters by which the
Catarrhines are separated from the Platyrrhines: in the
position of the nares, the number of premolars (the dental
formula of the Anthropide is identical with that of the Catarrhinz) ;
the ossified external auditory meatus; the absence of a foramen
in the septum between the orbital and the temporal fosse; the
small cecum; etc. In particular the Anthropide agree with the
Anthropomorpha, especially the larger forms (Orang,
Chimpanzee, Gorilla), in the following points: the absence of
ischial callosities, cheek pouches, and tail; there is a rudimentary
caudal region (consisting of four or five fused vertebra); the nails
are flattened ; the external incisor of the lower jaw is broader than
the inner ; the first lower molar has five cusps ; the thoracic cavity is
broad ; the sternum broad and flattened; the broad pelvis of the
large Anthropoids approaches that of Man; the sacrum consists
in both of five vertebrae. There are also numerous other points of:
agreement. On the whole this group stands extraordinarily close to
the Anthropoid Apes, the differences are almost all such as may be
attributed to the adaptation to an upright gait ; the great development
of the brain; and the relative weakness of some portion of the
musculature, e.g., the jaw muscles. The intimate correspondence may
be to some extent masked by the development of subordinate parts ;
the skull of the Gorilla, for instance, which is more human than that
of any other Anthropoid, is at first sight very unlike that of Man, e.g.,
in the presence of projecting bony ridges, which are wanting here ;
but the appearance of these ridges is directly correlated with the great
development of the jaw and neck musculature,* whilst careful and
detailed consideration demonstrates the closest correspondence in most
points.

All Men are usually regarded as one species, Homo sapiens, divided into
a number of races. These differ, however, in some respects, quite as much as
do other species of many other groups of animals. They are considered to belong
to one species chiefly from their perfect fertility inter se (cf. p. 36), and this
often renders their division into races extremely difficult, for hybridisation has
occwred to a great extent. The more detailed study of the various races
constitutes, however, a special science, Ethnology, whose province must not be
trespassed upon here. It must, however, just be mentioned that certain races
come nearer to the Anthropoid Apes than others, although in no case is the
approximation very close. The Negro Race, for instance, is distinguished
by the broad flat nose; projecting (strongly-developed) facial region; large teeth,
obliquely set incisors; receding chin; long, narrow thoracic cavity; deep narrow
pelvis; long digits: characters which as a whole lead back to the Apes.

 

* Among other nearly allied Mammalia such ridges may be present in one form,
absent from another (Badger, Marten).
Appendix: Tunicata. 537

APPENDIX TO THE VERTEBRATA.

Tunicata (Sea-Squirts).

The Tunicata are a small group of marine animals, which were
formerly usually regarded as Mollusca, or placed with some other
division of the Invertebrata; only recently has it been demonstrated
that they are most nearly allied to the Vertebrata, a relationship
which is made specially clear by a consideration of their ontogeny.
In particular it has been shown that in early life at least they agree
with the Vertebrata in the possession of a notochord, and in the
position of the central nervous system, both fundamental
points. In spite of this, they are not, however, incorporated with the
Vertebrates, but treated of in an appendix, because the majority
undergo so peculiar a metamorphosis that the Vertebrate characters

7°

   

      

WOOF ALLEL.
LLTOIELOT ESE EEE LL

LEE E ey
i a ;
i
a ch

       
 
 
  

LOTT

    

 
      
  

LELAND

     

 

      

Fig. 425. A diagram of one of the Appendicularia, viewed from the side,
stretched out straight. B ditto of an Ascidian larva. a anus, ch chorda, g
branchial chamber, m mouth, n brain, n’ nerve cord, t gut.—Orig.

have completely disappeared in the adult, which has received an
entirely different impress: thus it is more convenient to consider
them separately.

It may also be noted here that the Tunicata, like the true Vertebrata, do not
exhibit definite affinities with any of the Invertebrata.

Insight into the characteristics of this group is best attained by a
separate consideration of its various sub-divisions belonging to it.
The following general characteristics may, however, be noticed: the
skeleton is at best only represented by the notochord, the
nervous system is feebly developed, so also are the sense
organs. The Tunicata are hermaphrodite, ovaries and testes
are continued directly into their ducts. Reproduction by budding
frequently occurs.

The Appendicularia possess the simplest and most easily com-
prehended organisation. They are tiny, transparent, free-swimming,
marine forms, with some resemblance to tadpoles. The body is
538 Vertebrata.

divisible into a roundish trunk and a flattened tail, which is
folded on to the ventral side. The wall of the capacious pharynx is
perforated on each side by a ciliated aperture, the gill-slit, which
opens on to the surface; the rest of the alimentary canal is short,
the anus is ventral. The notochord only occurs in the tail,
where, however, it is well developed. The central nervous
system is represented by a cord swollen into a bulb (the brain)
dorsal to the pharynx, and provided with smaller swellings on the
rest of its course; it is continued down the tail on the left side
of the notochord, so that the tail is really laterally compressed
and has undergone a rotation of 90°. The simple heart lies below
the alimentary canal. An otocyst is present,
but eyes are wanting.
(AA The simple Ascidians (i.c., those which

  

YA .
eo
¢ do not form colonies, genus Ascidia, etc.)
000 Z| are apparently of quite a different structure.
I y They are barrel-shaped, round, or of some
g "“f ;

other form, and, for the most part, gela-
tinous ; they are fixed by one end or by one
side. At the free end two openings are
present; one of these, the mouth, leads
into avery roomy pharynx or branchial
sac, the walls of which are perforated by
numerous ciliated clefts; these do not
lead directly on to the surface, but into
a large peribranchial cavity sur-
rounding the branchial sac, and communi-
cating with the exterior by the second
opening, the cloacal aperture. The
“YZ branchial sac is fused along one side with
the outer wall of the peribranchial cavity,

Oo ©
SSSI SSS

z

Oo

   
  

<N
SY

& N
xS oss Se
Sooocoaos
DOO ORE OC
aoaoo oO ©
Sy SY

ew

V7

fe Z Z and along this line there is a longitudinal
ELL f th tral furrow o
Ge Ly urrow, e ventra urr Tr

endostyle, with large mucus-secreting
Fig. 426. Diagrammatic and ciliated cells; along the opposite side

longitudinal section of an puns a dorsal lamina, often con-
Ascidian; the section is not , 7
quite median, but somewhat siderably folded, and connected anteriorly
lateral. a anus, cl cloacalaper- with the endostyle by a ciliated band on
ture, g branchial sac, g’ aper- : ;
tures in its wall, m mouth, x each side (the peripharyngeal bands). The
nerve ganglion, p peribranchial pharynx leads below into a rather short
cavity, t gut, B ventral, R ?+ 2 . 7
dorsal surface.—-Orig. intestine, which bends upon itself and

opens into the peribranchial cavity. The
heart lies below the alimentary canal; the current of blood is remark-
able in that it flows alternately in opposite directions through it; there
is a fairly well-developed system of vessels, the branchial sac being

especially well provided ; the blood corpuscles are all amoeboid and
Appendia: Tunicata. 589

colourless. The central nervous system is reduced to a
nerve ganglion situated between the mouth and the cloacal aperture.
Ductless vesicles varying in size perform the function of excretory
organs; they excrete hard particles, in which the presence of uric
acid has been demonstrated. The reproductive organs (an
ovary and a testis) open into the peribranchial cavity close to the
anus. The body is entirely covered with a thick gelatinous or leathery
coat, the “mantle,” a product of the epidermis.*

The difference between the Appendicularia and the adult Ascidian
is thus very great. But a comparison of the larval forms reveals
quite other relations; there is a close agreement in almost every
respect. The Ascidian larve are still more like Tadpoles than are
the Appendicularia; they have a rounded trunk, and a long com-
pressed tail with a notochord, which extends a short distance
into the trunk. Dorsal to the notochord liesthe central nervous
system, which extends along the whole tail, and has a swelling, the
brain, anteriorly ; in connection with the latter, there is an eye and
an organ which is regarded as auditory; both are remarkable in that
they lie within the cavity of the brain, and are specially developed
portions of its wall. There is as yet no peribranchial cavity, but
two simple gill slits lead from the pharynx to the surface.
As may be seen, therefore, there is very great resemblance between
these larvee and the Appendicularia. Before long, however, the larva
attaches itself, the tail dwindles; the notochord, the sense organs,
etc., degenerate ; and the animal gradually attains to the very aberrant
form of the adult Ascidian.

It is easy to see how closely the type of structure of this larva corresponds
with that of the Vertebrata (as regards the position of the nervous system, the
notochord, and the alimentary canal); the relation is still more obvious than in
the adult Appendicularia, where the rotation of the tail, etc., to some extent,
masks the conformity. It must also be noticed here that the notochord arises in
exactly the same way as in the true Vertebrata.

Some of the Tunicates (Compound Ascidians) form
colonies, throwing off thread-like outgrowths, from which new
individuals develop, in other respects independent of each other.
In other colonial forms, Ascidice composite, there is a common test:
in this case the colonies are firmly attached to some foreign body, and
form soft spongy masses, in which the individuals are embedded,
often on a stellate plan. The members of each group have usually
a common cloacal opening, but each has its own mouth. The pelagic,
free-swimming, phosphorescent Pyrosoma, also belongs here.
This colony has the form of a thick-walled tube, open at one end,
closed at the other, walls being formed by the tiny animals which are
arranged close together, their mouths opening at the surface of the

 

* The mantle is to be regarded as a much thickened cuticle. It is interesting
to note that it contains scattered cells, which are amwboid, and have migrated
from the mesoblast through the epidermis into the mantle.
540 Vertebrata. Appendia:: Tumicata.

tube, their cloacal apertures into the cavity; the water which is
taken in at the mouth thus passes into the tube, from the open end
of which it is expelled; by means of this exhalent current the
colony is driven through the water, with the closed end forwards.
The free-swimming Salpa offers a remarkable modification of
the Ascidian type. The buccal and cloacal apertures are almost at
opposite poles of the body. The branchial sac is, however, very
degenerate ; its lateral walls are absent, so that, with the exception
of the ventral region with the endostyle, only the dorsal portion
remains as a band stretching across the united branchial and peri-
branchial cavities (r, Fig. 427). The visceral mass is of insignificant
size as compared with that of the whole animal, the cavity just.
mentioned constitutes the greater part of the animal (in most
Tunicata the branchial cavity is very extensive). In the transparent
body-wall, beautiful circular muscle-bands are seen, by the contrac-

Fig. 427. Diagram of a Salpa,
a anus, cl cloacal opening, &k
branchial cavity, + gut, m muscle
bands, o mouth, p peribranchial
cavity, + dorsal lamina.—Orig.

 

tions of which water is expelled; they are homologous with a
continuous layer of muscle which is present in the body-wall of
Ascidia. The Salpide are not only remarkable in structure, but
also in affording an instance of a regular alternation of
generations. There are both solitary asexual forms
and chains consisting of a larger or smaller number of somewhat
loosely connected sexual individuals. The asexual generation
forms chains by budding; the chains remain within the body-wall
of the solitary salp until they have attained a certain development,
when they break free and swim about independently. The solitary
and colonial individuals differ somewhat from each other. The
colonial forms are remarkable in that they first give rise to eggs
which are fertilised by spermatozoa from another chain, whilst later
on they themselves produce spermatozoa. Hach individual usually
produces only a single egg, which undergoes development in the
body of the parent.

Of the forms mentioned above, various species of simple Ascidians are
widely distributed in European seas; they are attached to seaweed, stones, piles,
etc. There are species of Composite and of Appendicularia, also in
northern seas; Pyrosoma and Salpa are pelagic, and occur in the large
oceans as well as in the Mediterranean. All the Tunicata feed upon microscopic
organisms, which they take into the branchial cavity with the water.

 
Aardvark, 527
Abdomen, 193
Abdominal limbs, 209
3 pores, 378
ag ribs, 410
Abomasum, 507
Abramis brama, 388
Abysmal fauna, 61, 75
Acalepha, 109
Acanthia lectularius, 259
Acanthias vulgaris, 383
Acanthocephala, 163
Acarina, 284
Accessory intestine, 137
Accipenser, 385
#8 huso, 385
- ruthenus, 385
Pe sturio, 385
Accipitres, 460
Acephala, 306
Acerina cernua, 389
Acetabulum, 328
Achromatin, 5
Aciculum, 167
Accela, 144 :
Acontia, 112
Acraspeda, 109
Acridium, 252
as migratorium, 252
Acromion, 477
Actiniaria, 118
Actinospherium
hornii, 91
Adaptation, 66
Adder, 425
Adductor muscles, 309
Adhesive organs, 14
Adipose tissue, 10
Adjutant, 459
AMluroidea, 515
Molide, 304
Aolis, 304
Affinities of animals, 53
African Elephant, 512
» Ostrich, 450
Agonus cataphractus, 390

eich-

 

INDEX.

Agouti, 531
Agrion, 255
Agrotis segetum, 275
Air sinuses, 475-6
» frontal sinus, 475
» maxillary sinus, 475
Alaudide, 464
Albatross, 457
Alca alle, 457
»  impennis, 457
» tonda, 457
Alcedinide, 465
Alcedo, 465
Alcide, 457
Alcippe, 206
Aleyonaria, 113
Alcyonium digitatum, 114
Alga, 216
Alimentary canal, 23
Alisphenoid, 362
Allantois, 354
Alligators, 426
Alpine Marmot, 529
Alternation of Genera-
tions, 37
Altinares, 459
Altrices, 450
Alytes obstetricans, 406
Amblystoma Mexicanum,
405
Ambulacral groove, 129
ie plates, 134
American Black Bear, 516
Amia, 385, 386
Ammoceetes, 382
Ammodytes, 389
Ammonites, 323
Amunion, 353
Amniota, 354
Ameba, 3-5, 89
Ampelis garrulus, 462
Amphiccelous, 360
Ampbhilina, 151
Amphipnous, 375
Amphioxus lanceolatus,
356

 

Amphipoda, 210
Amphisbena, 422
Amphiuma, 404-5
Ampulla, 124
Anabas, 375, 389
Anamnia, 354
Anal area, 136

» cerci, 236

» cirrus, 169

» glands, 237
Analogy, 57
Anarrhicas lupus, 390
Anas, 458
Anas acuta, 458

»  boschas, 458

»  Clypeata, 458

»  crecca, 458

» penelope, 458

» querquedula, 458

> sadorna, 458 ©
Anchitherium, 503
Anchovy, 387
Anelasma squalicola, 206
Anguilla vulgaris, 388
Anguillide, 163
Anguillula aceti, 163
Anguis fragilis, 422
Ankle, 328
Annelida, 83, 165
Annuli, 175
Anobium, 267
Anodonta, 315
Anoplotherium, 506
Anser cinereus, 458

»  ruficollis, 458

»  segetum, 458
Anseres, 458
Ant-eaters, 526
Antedon, 180
Antenna, 184
Antennary gland, 192
Anthozoa, 111
Anthropide, 533, 535
Anthropoid Apes, 534
Anthropomorpha, 534
Anthus, 462
542

Antilocapra
509

Antilope, 509

Antilopine, 509

Antimeres, 40, 122

Antitragus, 501

Antlers, 471

Ant-lions, 261

Ants, 270

Anura, 406

Anus, 23

Aorta, 29

Aphaniptera, 278

Aphide, 257

Aphides, 257

Aphis, 257

Aphis-lion, 261

Aphodius, 265

Aphorrhais pes pelicani,
302

Aphrodite, 173
Aphrophora spumaria, 257
Aphysostomi, 388
Apiarie, 271
Apical plates, 135
Apis mellifica, 271
Aplysia, 303
Appendices pylorice, 371
Appendicularia, 537
Apseudes, 216
Apteria, 434
Apteryx, 454
Aptychus, 323
Apus, 194
Aqueous humour, 333
Aquila chrysaétus, 460
Aquilide, 460
Arachnida, 278
Arachnoid membrane, 331
Araneina, 283
Archeopteryx, 444
Archenteron, 43
Arches, 326
Architeuthus, 323
Arctoidea, 515
Arctomys, 529
ze marmota, 529
Ardea cinerea, 459
Arenicola, 173
Argali, 509
Argonauta argo, 323
Argyroneta aquatica, 283
Arion ater, 306
Aristotle’s Lantern, 137
Armadillidium, 230
Armadillo, 526
Artemia, 193
<< salina, 194
milhausenia, 194
Arterial blood, 28
» heart, 29
Arteries, 26
Arthrogastra, 281
Arthropoda, 83, 184
Articular cartilages, 329
Artiodactyla, 504
Arvicola, 580
a agrestis, 530

Americana,

 

Index.

Arvicola, amphibius, 530
os arvalis, 530
glareola, 530
Arytenoid cartilages, 488
Ascalabotide, 422
Ascaris, 422
Ascidiz composite, 539
Ascidians, 538
Asellus, 215
#8 aquaticus, 215
Asexual reproduction, 29
Aspidiotus nerii, 259
Ass, 503
Astacus fluviatilis, 224
Asterias rubens, 133
Asterida, 131
Asteroidea, 130
Asthenosoma, 138
Astrophyton, 134
Asturide, 460
Astur nisus, 460
»  palumbarius, 460
Atavism, 39
Ateles, 533
Athene noctua, 461
Atlas, 409
Atrium, 344
Auchenia, 508
Auditory hairs, 221
Auditory organs, 19
Auk, 457
» Great, 457
» Little, 457
Aulastomum gulo, 176
Aurelia aurita, 111
Auricle, 26
Aurochs, 510
Australian Bear, 498
a Opossums, 498
3 Region, 74
Autozooids, 114
Aves, 430
Avicularia, 181
Avoset, 460
Axial skeleton, 113
Axis, 409
Axolotl, 403, 404
Aye-aye, 532

Baboon, 534

Babyrusa, 506

Bacillus, 254

Badgers, 516

Balena biscayensis, 324

Balena mysticetus, 324

Balenide, 523

Balenoptera musculus, 523
Ws rostrata, 523
ss Sibbaldii, 523

Balenopteride, 523

Balanide, 206

Balaninus nucum, 244

Balantidium, 94

Balanus, 206

Baleen, 522

Bandicoots, 497

Bank-vole, 530

Barbary Macaque, 534

 

Barbel, 388
Barbus, 388
Barnacles, 206
Barramunda, 389
Basal plate, 115
Basi-branchials, 327
Basi-occipital, 362
Basi-sphenoid, 362
Basket, 271, 272
Basommatophora, 306
Bath Sponge, 121
Bats, 500
Bdellostoma, 383
Bean Goose, 458
Bear animalcules, 286
Beaver, 529
Bed-bug, 259
Bee-eater, 465
Bee-louse, 278
Bees, 271
Beetles, 263
Beetle-mite, 284
Belemnites, 323
Belinurus, 197
Bell-animalcule, 94
Belodon, 427
Belone vulgaris, 388
Beroé, 118
Bezoar Goat, 509
Bilateral symmetry, 41, 126
Biology, 58
Bird-mite, 284
Birds, 430

» Of Paradise, 450, 463

» of Passage, 451

» of Prey, 461

» Climbing, 465

»  Gallinaceous, 455

»  Shrieking, 464

»  Struthious, 464

» Swimming, 456

»  Toothed, 458

Wading, 458

Bird-spiders, 283
Bison, 510

» Huropeus, 510

»  Americanus, 510
Bithynia, 302
Bitterling, 388
Bittern, 459
Black-arch, 275
Black-beetle, 263
Blackbird, 462
Black-clawed Crab, 227
Black Flies, 276

» Rat, 530

5» Whale, 524
Bladder-nosed Seal, 520
Blastophaga grossorum,

244,

Blastula, 43
Blatta, 253

» orientalis, 253
Blenniidex, 390
Blenny, 390
Blind-worm, 418, 4.22
Blood, 26
Blood corpuscles, 25
Blood plasma, 25
Blubber, 518, 520
Blue-bottle, 277
Blue Whale, 525
Boa Constrictor, 424
Body cavity, 39
Bohemian Waxwing, 462
Bombinator bombinus, 406
a igneus, 406
Bombus, 271
Bombycide, 274
Bombyx monacha, 275
» mori, 275
»  pini, 274
Bone, 10
Bonellia viridis, 174
Bony labyrinth of the ear,
338
Bony Pike, 385
Book-lice, 255
Bopyride, 216
Bopyrus, 216
Boring Sponges, 121
Bos grunniens, 510
» indicus, 510
»» primigenius, 510
» taurus, 510
Botaurus stellaris, 459
Bot-flies, 277
Bothriocephalus, 151, 153
Bottle-nosed Whale, 525
Bovine, 509
Bowman’s capsule, 348
Brachiopoda, 83, 178
Brachial plexus, 332
Brachyura, 226
Bradypodide, 525
Bradypus, 525
Brain, 324, 330
Branchial arteries, 345
a chamber, 26
3 hearts, 320
a lamelle, 197
a sac, 538
Branchiobdella astaci, 177
Branchiostegite, 219
Branchipus, 193
Braula ceca, 278
Bream, 388
Breeding season, 69
Brevirostres, 459
Brill, 389
Brissopsis lyrifera, 138
Brittle-stars, 133
Bronchi, 418
Brown body, 180
» Rat, 580
Bruta, 525
Bubalus, 510
as vulgaris, 510
Bubble, 303
Bubo maximus, 461
Buccal cavity, 23
Buccinum undatum, 302
Bucerotide, 465
Buffalo, 510
Buffon’s Skua, 456
Bufo, 406

 

Index.

| Bufo, calamita, 407

» vulgaris, 407
Bugs, 259
Bulbus arteriosus, 377
Bulla, 303
Bullfinch, 462
Bull-head, 390
Bumble Bee, 271
Buntings, 463
Buprestide, 266
Buprestis, 266
Bursa copulatrix, 243

»  Habricii, 445
Burse (respiratory), 134
Burying-beetles, 264
Bustards, 459

ma Small, 459
a Large, 459

Butcher Bird, 462
Buteo, 460
Butirinus, 376
Butterflies, 275
Byssus, 308

be gland, 311

ys thread, 311
Buzzards, 460

Cabbage Butterfly, 275
Cachalot, 524
Caddis-flies, 262
Creca, 25
Cascilia, 402, 407
Calcareous valves, 204
Caligus, 201
Camelide, 508
Camels, 508
Camelus, 508
os bactrianus, 508
a dromedarius, 508
Camelopardalis giraffa, 508
Canales incisivi, 475
Canaries, 463
Cancer pagurus, 227
Canide, 515
Canines, 483
Canis aureus, 516
»  tfamiliaris, 516
» lagopus, 515
» lupus, 515
» vulpes, 515
Cape Ant-eater, 527
Capella rupicapra, 509
Cape Mole, 499
Capercaillie, 455
Capillaries, 26
Capitulum, 472
Capra, 509
»  egagrus, 509
»  hireus, 509
x»  ibex, 509
Caprimulgus europzus, 464
Capuchin Monkey, 533
Capybara, 531
Carabide, 264
Carabus, 264
Carapace, 189
Carassius auratus, 388
ye vulgaris, 388

 

5438

Carcharias glaucus, 383
Carcinus mosnas, 227
Cardo, 233, 309
Carina, 204
Carnassial tooth, 514
Carnivora, 513
Carp, 375, 387
Carpals, 328
Carpus, 328
Carrion-beetles, 264:
Cartilaga ypsiloides, 396
Cartilage, 10
Cartilaginous sheath, 326
Caryophylleus, 151
Case-bearers, 274
Cassowaries, 454
Castor canadensis, 529
» fiber, 529
Casuarius, 454
Cataphracti, 390
Catarrhine, 533
Caterpillar, 250, 272
7 fly, 277
Cat-fishes, 384
Cathartes, 461
Cattle, 509
Caudal appendages, 195
» fin, 209
» Spine, 197
Cave Bear, 516
» dion, 517
Cavernicolous fauna, 61
Cavia cobaya, 531
Cavicornia, 509
Cecidomyia, 246, 276
Cells, 5
»  Ciliate, §
» epidermal, 99
»  epithelio-muscle, 100
» fixed, 7
» flagellate, 8
» glandular, 9
» goblet, 9
» herve, 120
» nettle, 100
» pigment, 31
» sensory, 13
» simple, 85
» wandering, 6, 31
Cement, 482
_ gland, 205
Centipedes, 227
Centrale, 328, 329
Centrosome, 5
Centrum, 326
Cephalopoda, 315
Cephalothorax, 198
Cerambycida, 266
Cerambyx, 266
Ceratodus, 367, 386
Cercaria, 148
Cercolabes, 530
Cercopithecide, 534
Cerebellum, 331
Cerebral ganglia, 289
3 hemispheres, 330
Cerebrum, 330
Certhia familiaris, 464.
544,

Cervical ribs, 437, 471
- 5 vertebrae, 326
Cervide, 508
Cervus alces, 509
> canadensis, 509
»  capreolus, 508
»  dama, 508
»  elephus, 508
»  euryceros, 509
tarandus, 509
Cestoda, 143, 149
Cestus veneris, 118
Cetacea, 520
Cetonia, 265
Cheeta, 167
Chetopoda, 167
Chaffinch, 462
Chameleo, 422
Chameleon, 422
Chamois, 509
Char, 387
Charadriide, 459
Charadrius pluvialis, 459
Cheek pouches, 485
Cheese-fly, 277
» mites, 284
Chele, 219
Chelicere, 279
Chelifer, 282
Chelonia, 425
Chelonie, 426
Chequered Meat-fly, 277
Chermes abietis, 258
Chestnuts, 503
Chigoe, 278
Chilognatha, 230
Chilopoda, 229
Chimera monstrosa, 384
Chimpanzee, 535
Chiromys madagascarien-
sis, 532
Chiroptera, 500
Chitin, 185
Chitons, 290
Chlorophyll, 81, 95
Cheeropsis liberiensis, 506
Cheeropus, 498
Chondocranium, 327
Chondrostei, 385
Chorda dorsalis, 324
Chorion, 242
Choroid, 333
» gland, 370
Chromatin, 5
Chromatophores, 10
Chromosomes, 5
Chrysalis, 250
Chrysis, 270
Chrysochloris, 499
Chrysomelide, 266
Chrysopa, 261
Chyle, 348
Cicada, 256
»  septendecim, 257
Cicadellide, 257
Cicindela, 264
Ciconia alba, 459
» nigra, 459

 

Index.

Cidaris, 138
Cilia, 5, 16, 92, 95
Ciliary processes, 333
Ciliated junction, 307
Ciliate organs, 146
Cimex lectularius, 259
Cinglus aquaticus, 462
Circus, 460
Cirrhus, 129, 169, 205
Cirripedia, 203
Civet Cat, 517
Cladobates, 500
Cladocera, 195
Clamatores, 464
Class, 55
Classification, 53
Clavicle, 327
Claws, 235, 408, 435, 469
Clear wings, 274
Clepsine, 177
Climbing Perch, 389
Clione limacina, 305
Clitellum, 174
Clitoris, 450
Cloaca, 159, 342
Cloacal piace 808
yphon, 308
Clothes- othe 273
Clupea alosa, 387
a harengus, 387
»  pilchardus, 387
»  sprattus, 387
Clupeide, 387
Clypeaster, 138
Clypeastride, 138
Coarctate pupa, 250
Coatimondi, 516
Cobego, 500
Cobitis, 388
Cobra, 424
Coccidium oviforme, 96
Coccidee, 258
Coccinellide, 267
Coccus cacti, 259
»  lacca, 259
Cochineal Insect, 259
Cochlea, 444
Cockatoos, 465
Cockchafer, 265
Cockroaches, 253
Cocoons, 269
Cod, 388
Ccelentera, 83, 98
Coelogenys paca, 531
Coenenchyme, 113
Coenurus cerebralis, 152
Coleoptera, 252, 263
Collar-boné, 327
Collar-cells, 119
Collembola, 256
Collocalia, 464
Colobus, 534
Colony, 32, 66
Colour change, 434, 468
Colubride, 424
Columba, 465
5 livia, 465
- migratoria, 465

 

Columba, cenas, 465
o palumbus, 465
Columbide, 465
Columella, 116, 294, 412
ee auris, 397, 416
Columellar muscle, 295
Colymbus, 457

e arcticus, 457
ie glacialis, 457
35 septentrionalis,
457
Comatula, 180

Combustion, 4, 30
Commensalism, 65
Common Bear, 516
es Bittern, 459
is Coot, 459
ads Crane, 459
35 Creeper, 464
4 Dipper, 462
» Hedgehog, 499
ey Mole, 499
a Mouse, 529
a Porcupine, 530
- Round-worm, 160
» Seal, 519
es Shrew, 500
ss Shrimp, 223
Slug, 306
Comparative cheene 58
Complemental males, 205
Composite, 540
Compound Ascidians, 539
2» eye, 22
53 stomach, 487
Conchiolin, 287
Condor, 461
Conger-eel, 388
» vulgaris, 388
Conirostres, 462
Conjunctiva bulbi, 336
65 palpebrarum,
336

' Conjugation, 86, 96

Connective tissue, 10
Conus arteriosus, 344
Coot, 459
Copepoda, 200
Copris, 265
Coprophaga, 265
Copule, 327
Copulation, 36
Copulatory organs, 34
Coracias. garrula, 464
Coracoid, 327
Corallium rubrum, 115
Coral reefs, 117
Coregonus, 387
3 pollan, 387
53 thymallus, 387

Cormorant, 457
Corn Crake, 459
Cornea, 333
Coronula, 206
Corpora quadrigemina, 331
Corpus callosum, 480

»  brosum, 493
Corvide, 463
Corviformes, 463
Corvus corax, 463
»  cornix, 463
»  corone, 463
»  frugilegus, 463
» monedula, 463
Cossus ligniperda, 274
Cottus gobio, 890
»  scorpius, 390
Coturnix communis, 455
Cotyledons, 494
Cougar, 517
Covering pieces, 108
Cowper’s glands, 493
Coxa, 235
Coxal glands, 380
Coypu, 530
Crabronide, 270
Crabs, 226
Crab-spiders, 286
Cracide, 456
Craneflies, 276
Cranes, 459
Crangon vulgaris, 223
Cranium, 326
Craspedota, 103
Crawfish, 227
Crax, 456
Creeper, 464
7 Common, 464
sy Wall, 464
Cribriform plate, 475
Cricetus frumentarius, 530
Cricket, 253
Cricoid, 488
Crinoidea, 127
Crocodilia, 426
Crocodilus, 426
Crop, 24
Cross bills, 463
Crossopus aranea, 500
ee fodiens, 500
35 suavolens, 500
Cross-spiders, 283
Crotalide, 425
Crotalus, 425
Crow, 463
Crustacea, 190
Cryptobranchus japonicus,
405
Crystalline cone, 22
Ctenophora, 118
Cuboid, 479
Cuckoo Bees, 272
Cuckoos, 465
Cuckoo-spittle, 257
Cuculide, 465
Cuculus canorus, 465
Cucumaria, 141
Culex, 276
Cumacea, 210, 213
Cuneiform, 478, 479
Curassows, 456
Curculio, 267
Curculionide, 267
Curlews, 460
Cuscus, 498
Cuvierian organs, 140

 

Index.

Cyamus, 219
Cyanea capillata, 111
Cyclops, 201
Cyclopterus lumpus, 390
Cyclostoma elegans, 302
Cyclostomi, 382
Cydippe, 118
Cygnus, 458
atratus, 458
ig musicus, 458
# olor, 458
Cymothoa, 216
Cynailurus jubata, 517
Cynipide, 269
Cynips rose, 245
Cynocephalus, 534
Cynoidea, 515
Cynomorpha, 534
Cyprinide, 387
Cyprinus carpio, 387
Cypris (larva), 207
Cypris ovum, 199
Cypselida, 464
Cypselus, 464
Cysticercus cellulose, 151
Cystophora cristata, 520
g proboscidea,
520

2

Dab, 389
Dabchicks, 457
Dactylopterus volitans, 390
Dactylozooid, 105, 107
Daddy-long-legs, 276
Daphnia, 195
Dasypodide, 526
Dasyprocta, 531
Dasyuride, 497
Dasyurus, 497
Daubenton’s Bat, 501
Dead Men’s Fingers, 114
Death, 69
Death-watch, 267
Debilirostres, 459
Decapoda, 210, 219, 323
Decapods, 323
Deep sea fauna, 59
Defensive polyps, 105
Delphinus, 524
Demoiselle Fly, 255
Dendrocela, 144
Dental formula, 486
Dentalium, 291
Dentary, 439
Denticles, 133
Dentine, 339, 340
Dentition, 483

i Milk, 484

5 Permanent, 483
Dermal branchise, 125, 137
Dermanyssus avium, 284
Dermestes, 265
Dermestidie, 265
Desmans, 500
Desmodex folliculorum,

285

Desmodus, 501
Deutoplasm, 32

 

545

Diaphragm, 37, 488
Dibranchiata, 323
Dicotyles, 506
Didelphyide, 497
Didus ineptus, 465
Digenetic Trematodes, 147
Dimorphism, 54
Dinictis, 517
Dinoceras, 512
Dinornis, 454
Dinosaurians, 429
Dinotherium, 512
Diodon, 391
Diomedea exulans, 457
Diplopoda, 230
Diplozoon paradoxum, 147
Dipnoi, 386
Dipper, 462
Diprotodontia, 498
Diptera, 252, 275
Dipus, 530
Discophora, 175
Dispersal of Animals, 58
Distal, 42
Distomez, 147
Distomum hepaticum, 147
Divers, 457
»  Black-throated,457
» Great Northern,
457
»  Red-throated or
speckled, 457
Diverticula, 24
Division, 5
» nuclear, 5
3 » direct, 5
a »  indirect,5
Dochmius, 160
Doctrine of Descent, 53
Dodo, 465
Dog-fish, 383
Dolphin, 524
Domestic Cat, 517

ss Dog, 516
ae Goat, 509
ss Ox, 510
5 Pig, 506

oo Sheep, 509
Donacia, 267
Dorcus _ parallelopipedus,

265
Doridide, 304
Doris, 304
Dormice, 529
Dorsal, 39
Dorsal lamina, 538
Double animal, 147
Doves, 465
Draco volans, 422
Dracunculus, 162
Dragon-flies, 254
Dragons, 422
Dreissensia polymorpha,
314
Dromeide, 454
Dromeus, 454
Drones, 424
Dschiggetai, 503

NWN
546

Ducks, 458
Duck-billed Platypus, 496
Ductus Botalli, 489

55 cochlearis, 338

55 endolymphaticus,

370

Dugong, 513
Dung-beetles, 265
Dura mater. 331
Duration of life, 68, 70
Dwarf males, 216
Dytiscide, 264
Dytiscus, 264

Eagles, 460
» Golden or Moun-
tain, 460
» Sea or White-
tailed, 460
Ear-bones, 481
Eared Seals, 519
Earth Crab, 253
» Worms, 173
Earwigs, 253
Ecdysis, 31, 185
Echeneis, 390
Echidna, 496
Echinoderma, 83, 122
Echinoidea, 1384
Echinometra, 138
Echinus, 138
Ectocyst, 178
Ectoderm, 30
Ectoparasites, 63
Ectosare, 91
Edentata, 525
Edible Snail, 306
Eel, 388
Eel-pout, 388
» -worm, 163
Egg-sacs, 201
Elater, 265
Elateride, 265
Electric Eels, 388
» organs, 368
» Skates, 384
Elephants, 510
Tusks, 291
Elephas africanus 512
»  primigenius, 512
Elpidia, 141
Elysia, 304
Elytra, 236
Emberiza, 463
Embryo, 50
Embryology, 42
Embryonic membranes,
353
Emeu, 454
Emdyz, 426
Enamel, 339, 340
Enchelyophis, 389
Encystation, 86
Endoderm, 98
Endoparasites, 63
Endopod, 189
Endosare, 91
Endoskeleton, 16

 

Indea.

Endosmosis, 26, 96
Endostyle, 538
Engraulis encrassicholus,
387
Enhydra marina, 516
Enteric cavity, 111
Entomostraca, 198
Entoniscide, 216
Entoniscus, 216
Entozoa, 64
Environment, 66
Epeira diadema, 283
Ephemera, 255
Ephialtes scops, 461
Ephippium, 196
Epiblast, 43
Epibolic gastrula, 44
Epicrium glutinosum, 407
Epididymis, 350
Epiglottis, 488
Epiotic, 362
Epiphragm, 295
Epiphyses, 480
Epiphysis, 331
Epipod, 189
Epitheca, 116
Epithelial tissues, 7
Epithelium, 7
hos ciliate, 8
S simple, 7
a stratified, 7
Epoophoron, 491
Equide, 503
Equus asinus, 503
»  Burchelli, 503
»  caballus, 503
»  hemionus, 503
x  onager, 503
» quagga, 503
zebra, 503
Ergots, 163, 503
Erinaceus, 499
x europeus, 499
Ermine, 516
Esocide, 387
Esox lucius, 387
Estheria, 194
Ethiopian region, 74
Ethmoid, 362
Euphausia, 211
Euphausiacea, 210
Euplectella aspergillum,
121
Eupteropoda, 304
European sub-region, 74
Eurypterus, 198
Euspongia, 121
Eustachian tube, 416
Eustrongylus, 160
Excretory organs, 30
Exhalent canal, 119
Exoccipital, 362
Exoccetus, 388
Exopod, 189
Exoskeleton, 15, 184
External auditory meatus,
444,

” ear, 416

 

External ligament, 310
3 mouth, 111
Eyelashes, 467
Eyelids, 336
Eye-muscles, 335-6
, spots, 132
, stalk, 211

Falciform young, 96
Falco esalon, 460
»  gyrfalco, 460
»  peregrinus, 460
jz  subbuteo, 460
»  tinnunculus, 460
Falconide, 460
Falcons, 460
» Peregrine, 460
Fallopian tube, 490
Fallow Deer, 508
False ribs, 472
Family, 55
Fat bodies, 248, 402
Feathers, 431
Feather-follicle, 431
Feelers, 107, 184
Felide, 517
Felis cattus, 517
» concolor, 517
» domestica, 517
x» jubata, 517
leo, 517
» lynx, 517
»  maniculata, 517
» onca, 517
» pardus, 517
spelea, 517
» tigrina, 517
tigris, 517
Femoral pores, 408
Femur, 235, 328
Fenestra ovalis, 897, 416
33 rotunda, 416
Ferret, 516
Fertilisation, 32
Fiber zibethicus, 530
Fibula, 328
Fibulare, 328
Fiddler-beetle, 241
Field-cricket, 253
» mice, 5380
Fierasfer, 389
Filaria, 162
Filoplume, 433
Finches, 462
- Mountain, 462
o Serin, 463
Fin Whales, 523
Fish, 356
Fishing Hawk, 460
Fish-leech, 177
» lice, 201
Fission, 4, 31
Flagellata, 95
Flagellate chambers, 119
Flagellum, 33, 95, 119
Flame cell, 143
Flamingoes, 458
Flat-fish, 389
Flat-worms, 142
Fleas, 278
Floating ribs, 472
Flounder, 389
Flour-mites, 284
Fly-catchers, 462
Flying Fish, 388
»  Phalangers, 498
» Foxes, 501
» Squirrel, 529
Feetus, 50
Food-yolk, 45 >
Foot, 293
Foramen magnum, 362
es ovale, 489
Fore-arm, 328
” -gut, 23
Forest-flies, 277
Forficula, 253
Formicarie, 270
Formica rufa, 270
Fossils, 76
Fowls, 450
» Domestic, 455
» Guinea, 455
» Jungle, 455
Fox, 515
Free-living Copepods, 200
Freshwater Fauna, 59
és Mussels, 315
os Shrimps, 218
Ws Sponges, 121
ss Tortoise, 426
Frigate Bird, 457
Fringilla, 462
Frog of foot, 470
Frog, Edible, 406
» Grass, 406
» Land, 406
» Tree, 406
Frog-fish, 391
, chopper, 257
» ‘Loads, 406
Frontal, 362
Fruit Bats, 501
Falica atra, 459
Fuliguline, 458
Fuligula cristata, 458
igs marita, 458
Fulmarus glacialis, 458
Fungia, 117
Funiculus, 317
Funnel, 317
Furcula, 440

Gadflies, 276
Gadide, 388
Gadus, 388

»  weglefinus, 388

»  wmorrhua, 388
Galea, 233
Galeopithecus volans, 500
‘Gall-bladder, 342
Gall-fly, 269
Gallinula chloropus, 459
Gall-mites, 285
Gallus bankiva, 455

» domesticus, 455

 

Index.

Gamasus, 284
Gammarus, 218
= fluviatilis, 219
locusta, 219
9 puteanus, 219
Ganges Dolphin, 525
Ganglion cells, 10
Gannet, 457
Ganoidei, 384
Gaper, 315
Garden Dormouse, 530
» Snail, 306
Gar-pike, 388
Garrulus glandarius, 463
Gartmer’s duct, 351, 491
Gasterosteus, 390
ve acuteatus,
390
ss pungitius,
390
Gasterosteidx, 390
Gastric cavity, 109
x» pouch, 109
Gastropoda, 291
Gastrozooids, 107
Gastrula, 43, 98
- mouth, 43
Gastrus equi, 277
Gavialide, 426
Gecko, 417, 422
Geese, 458
Gemmation, 31, 86
Gemmule, 120
Genet, 517
Genital organs, 38
» plates, 136
Genus, 55
Geocores, 259
aot Distribution,
8

2”

Geology, 76
Geological Distribution, 76
Geometride, 275
Geotrupes, 265
Gephyrea, 174
Germinal spot, 32
= vesicle, 32

Germ-layers, 47
Gestation, 494
Giant-Sloth, 525
Gibbons, 534
Gills, 538
Gill arches, 327

» Clefts, 343

» lamelle, 306

», rakers, 374
Giraffe, 508
Gizzard, 24, 445
Glands, 14, 24
Glandular cells, 9
Glede, 461
Glenoid cavity, 327
Globigerina, 89
Globiocephalus melas, 524
Glomeris, 230
Glomerulus, 348
Glosse, 233
Glow-worms, 266

 

547

Glutton, 516
Glyptodon, 527
Gnathobdellide, 176
Gnats, 276
Goat, 509

»  -moth, 274
Gobio fluvialis, 388
Gobius, 390
Godwits, 460
Gold-crested Regulus, 462
Golden-eye, 261

» Mole, 499

» Oriole, 462
Goldfinch, 462
Goldfish, 388
Gold Wasp, 270
Gonozooid, 107
Goose, 458

» Grey, 458

»  Red-breasted, 458
Gordius, 163
Gorgonia, 114
Gorgonide, 114
Gorilla, 535
Goshawk, 460
Graafian follicle, 350
Graculus carbo, 457
Grallatores, 458
Grampus, 524
Grasshoppers, 252
Grayling, 387
Great Ant-eater, 526

» Black Slug, 306
Crebes, 457

»  Eared, 457

» Little, 457

»  Red-necked, 457
Green-finch, 462
Green-flies, 257

» gland, 221
Greenland Whale, 524
Gregarina, 87
Gregarinida, 95
Grey Seal, 519
Gribble, 215
Grizzly Bear, 516
Grooved Teeth, 424
Grouse, 455

» Black, 455

» Red, 455

55 Sand, 455
Gruide, 459
Grus cinerea, 459
Gryllide, 253
Gryllotalpa vulgaris, 253
Gryllus campestris, 253

» domesticus, 253
Gudgeon, 388
Gueparde, 517
Guinea-pig, 531

» worm, 162
Gulls, 456

,  Black-headed, 456

» Common, 456

» Herring, 456

» Laughing, 456
Gulo borealis, 516
Gurnard, 390

nw 2
548

Gurnard, Flying, 390

ae Grey, 390
Gustatory organs, 19
Gut, 23
Gymnomyxa, 87
Gymnophiona, 407
Gymnosomata, 305
Gymnothorax murena, 388
Gymunotus, 368

3 electricus, 388
Gypaétus barbatus, 461
Gypogeranus _ secretarius,

460

Gyrfalcon, 466
Gyri, 480
Gyrinus, 264

Haddock, 388
Hematopus ostralegus, 459
Hemocyanin, 30
Hemoglobin, 29
Hemopis vorax, 176
Hag-fish, 383
Hair, 467
» follicle, 467
» papilla, 467
Hairs, contour, 467
» tactile, 467
» woolly, 467
Halibut, 389
Halicherus grypus, 519
Halicore dugong, 513
Halmaturus, 499
Halobatide, 259
Hamster, 530
Hapalide, 533
Harderian gland, 336
Hare, 529
Harriers, 460
Harvest-men, 282
er Mouse, 530
Haversian canal, 329
Hawfinch, 462
Hawk, 460
» Fishing, 460
» Sparrow, 460
Hawk-moths, 275
Head, 41, 324
Head-kidney, 167, 350
Heart, 26
»  Urchins, 138
Hectocotylised arm, 321
Hectocotylus, 321
Hedgehog, 499
Heliozoa, 91
Helix, 306
»  hortensis, 306
»  pomatia, 306
Hemeroharpages, 460
Hemimetabola, 250
Hemimetabolous, 246
Hemiptera, 256
Heredity, 39
Hermaphrodite, 34
i gland, 35,
299
Hermaphrodites, protan-
drous, 35

 

Index.

Hermaphrodites, protogy-
nous, 35
Hermit Crab, 225
Herodii, 459
Heron, Common, 459
» Night, 459
Herons, 459
Herpestes ichneumon, 517
Herring, 387

| Heterodera schachtii, 163

Heterogony, 38, 146
Heteropoda, 302
Heteroptera, 259
Hexactinellide, 121
Hibernation, 69
Hibernating gland, 489
Hind gut, 23
Hipparion, 503
Hippobosca equina, 278
Hippoboscide, 277
Hippocampus, 391
Hippoglossus vulgaris, 389
Hippopotamide, 506
Hippopotamus, 506

3 amphibius,
506
Hirudo, 176
Hirundo, 463
Hobby, 460

Holocephali, 384
Holometabola, 250
Holometabolous, 246
Holostei, 385
Holothuria, 141
Holothuroidea, 138
Homarus vulgaris, 224
Homodont teeth, 485
Homology, 57
Homoptera, 256
Homo sapiens, 536
Honey-bee, 271

» dew, 257

» -comb-bag, 507
Hooded Seal, 520
Hoofs, 470
Hoopoe, 464
Hornets, 271

| Horns, 471

Horny fibres, 120
Horse, 503

»  Bot-fly, 277

» Leech, 176

» Shoe Bats, 501

» tick, 278
Hosts, 63
House-fly, 277

» Mouse, 580

» Spider, 283
Howling Monkey, 533
Humerus, 328
Humming Birds, 464
Hump-back Whale, 523
Hunger, 73
Hyena, 517
Hyenide, 517
Hybrid, 36

| Hybridisation, 386

Hydatina senta, 157

 

Hydra, 106
Hydrachna, 284
Hydrocherus capybara,
531
Hydrocores, 260
Hydrocysts, 107
Hydroid, 103
Hydromeduse, 103
Hydrometra, 257
Hydrometride, 259
Hydrophyllia, 108
Hydrophis, 424
Hydrosoma, 107
Hydrozoa, 102
Hyla arborea, 406
Hylesinus piniperda, 267
Hylobates, 534
Hymen, 491
Hymenoptera, 252, 267
Hyoid, 327
Hyperide, 219
Hyperoodon rostratus, 525
Hypoblast, 43
Hypoderma bovis, 277
Hypopharynx, 234
Hypophysis, 331
Hypsiprymuus, 499
Hyrax, 500
Hystricomorpha, 530
Hystrix cristata, 530

Ibis religiosa, 459
Ichneumon-flies, 269
Ichneumonide, 269
Ichthyornis, 453
Ichthyosaurians, 427
Icticyon, 516
Idothea, 215

» .tricuspidata, 215:

Iguanas, 422
5 Ground, 422
Er Tree, 422

Iguanide, 422

Iguanodon, 430

Tlium, 328

Imago, 249

Impennes, 457

Imperforate Rhizopoda, 88

Impressions, 77

Incisors, 483

Incus, 481

Inferior arches, 326

Infundibulum, 118, 331

Infusoria, 89, 91

Inhalent aperture, 308
» canal, 119

| Ink-sac, 317

Inner germ-layer, 43
»  root-sheath, 467
Insecta, 231
Insectivora, 499
Integripalliate, 310
Interambulacral plates, 134
Interdigital glands, 469
Interfilamentar junctions,
307
Intermedium, 328
Internal ligament, 310
Internal mouth, 111

» shell, 305, 319
Interparietal, 476
Interradii, 123
Interspinous processes,

362

Intestinal Trichina, 162
Intestine, 23
Tnuus ecaudatus, 534
Invagination, 43
Tris, 333
irish Deer, 509
frregular Sea-urchins, 138
Irritability, 4
Ischium, 328
Isis, 115
Isopoda, 210, 213
Itch-mites, 285
Tulus, 230
Ixodes, 284
Tynx torquilla, 466

Jackal, 517
Jackdaw, 463
Jacobson’s organ, 333
Jaguar, 517
Jaws, 176, 205
Jays, 463
Jelly-fish, 111
» veil, 90
Jerboa, 530
Jigger, 278
Joint, 329
Jugal, 394, 412
Jumping Shrews, 500

Kaguan, 500
Kangaroos, 498
Kermese-insect, 259
Kestrel, 460
Kidneys, 31
Killer, 524
King-crab, 196
» -fisher, 465
Kite, 461
Kiwi, 454
Knee-cap, 330
Koala, 498
Kulan, 503

Labial cartilages, 364
»  palps, 233, 306
Labium, 233
Labride, 389
Labrum, 232
Lacerta, 422
» agilis, 422
ies vivipara, 422
Lacertilia, 421
Lachrymal bone, 439
ee gland, 336
~ pits, 469
Lacinia, 233
Ladybirds, 267
Lagomys, 529
Lagopus, 455
Pe mutus, 455
oe scoticus, 455

 

Index,

Lamellibranchs, 306 i
Lamellicornia, 265
Lamellirostres, 458
Lamina perpendicularis,
476 i
Lampreys, 382 ‘
Lamppyris, 266
Lancelets, 354
Land-bug, 259
» leech, 176
Laniade, 462 :
Lanius excubitor, 462
Large Bats, 501
Larks, 464
Larus, 456
»  argentus, 456
»  atricilla, 456
» canis, 456
»  ridibundus, 456
Larva, 247
Larve, 50
Larynx, 344
Lateralia, 204
Lateral-line organs, 369
Leaf-beetles, 266
» insects, 253
»» -rollers, 274
Lecanium ilicis, 259
Leeches, 175
Lemnisci, 163
Lemming, 530
Lemurs, 531, 532
Lens, 20, 333
Leopard, 517
Lepadide, 206
Lepas, 206
Lepidoptera, 252, 272
Lepidosiren paradoxa, 367,
387
Lepidosteus, 375, 378, 385
Lepisma saccharina, 255
Leporide, 529
Leptocardii, 354
Leptoptilus, 459
Lepus, 529
cuniculus, 529
europeus, 529
timidus, 529
variabilis, 529
Lernea branchialis, 203
Lesser Fin-whale, 523
» Shrew, 500
Lestris, 456
Leuciscus, 388
Leucochloridium
doxum, 148
Libellula, 255
Libellulide, 254
Lice, 160
Ligament, 310, 329
Ligula simplicissima, 151
Limacina helicina, 305
Limapontia, 304
Limax agrestis, 306
Limbs, 42
Limnadia, 195
Limneus, 306
Limnoria terebrans, 215

para-

‘

1

 

549

Limosa, 460
Limpets, 302
Limulus, 196
Lineus longissimus, 156
Lingual ribbon, 287
Lingula, 183
Linnet, 463
» Common, 463
» Mountain, 463
Lion, 517
Lip, 486
Lithobius, 230
Lithodomus
314
Lithophrya, 206
Little Ant-eater, 526
Littoral fauna, 38
Littorina, 302
Liver, 24
Liver-fluke, 147
Lizards, 422
3 Common, 422
55 Flying, 422
3 Ringed, 422
. Sand, 422
Llamas, 508
Loach, 388
Lobster, 224
Locomotion, 65
Locomotor organs, 63
Locusta, 253
53 viridissima, 258
Locusts, 253
Loligo vulgaris, 323
Longicorns, 266
Longipennes, 456, 463
Longitudinal arez, 158
Long-tailed Field Mouse,
530
Loopers, 276
Lophius piscatorius, 391
Lophogastride, 211
Lophophore, 178
Lorica, 156
Lories, 465
Loris, 582
Lota vulgaris, 388
Lucanus cervus, 265
Lugworm, 173
Lumbar plexus, 332
» vertebra, 326
Lumbricus, 173
Lump-fish, 390
Lunar, 478
Lung-sacs, 282
Luscinea philomela, 462
e rubecola, 462
Lutra, 516
» Vulgaris, 516
Lymphatic system, 347
Lymph follicles, 348
» glands, 26
» hearts, 348
Lynx, 517
» _ vulgaris, 517
Lyre Birds, 464
Lyssa, 487
Lytta vesicatoria, 266

lithophagus,
550

Macherodus, 517
Machetes pugnax, 460
Machilis, 256
Mackerel, 390
» pikes, 388
Macrolepidoptera, 274
Macronucleus, 92
Macropide, 498
Macroscelides, 500
Madreporaria, 118
Madreporite, 124, 131
Maggots, 250
Magnum, 478
Magot, 534
Magpie, 463
Makis, 532
Malacodermata, 266
Malacostraca, 193, 207
Malapterurus, 368, 388
3 electricus,
388
Malleus, 481
Mallophagide, 255
Malpighian tubes, 188
Mamme, 469
Mammalia, 466
Mammary glands, 468
Mammille, 468
Mammoth, 512
Man, 535
Manatee, 513
Manatus, 513
Manchurian sub-region, 74
Mandibles, 184
Mandibular arch, 327
Manis, 527
Mantide, 253
Mantis religiosa, 253
Mantle, 203, 287
» folds, 182
x lobe, 307
Manubrium, 102, 105, 473
Manyplies, 507
Marabou, 459
Marble Seal, 519
Margaritina margaritifera,
315
Marine fauna, 59
Marmosets, 533
Marmots, 529
Marsupial Ant-eater, 497
Marsupials, 496
Marsupial bones, 479
Marsupium, 214, 217
Martens, 516
Martins, 463
» House, 463
35 Sand, 468
Mask, 255
Mastodons, 512
Maw-worm, 160
Maxilla, 410
Maxille, 184
Maxillipeds, 184
Maxillo-turbinal, 475
May-flies, 255
Meal-worm, 266
Meckel’s cartilage, 327

 

Index.

Medicinal Leech, 176
Medina Worm, 162
oe sub-region,
4
Medusa, 99
Medusoid generation, 102
Megachiroptera, 501
Megapodius, 456
Megaptera biéops, 523
Megatheria, 525
Megatheriide, 525
Meleagrina margaritifera,
315
Meleagris gallopavo, 455
Meles taxus, 516
Meloé, 266
Melolontha vulgaris, 265
Melophagus ovinus, 278
Membrane bones, 325
Membranelle, 92
Membraniporide, 181
Membranous labyrinth,
338
Menobranchus, 405
Menopoma, 405
Mentum, 233
Menura, 464
Mephitis, 516
Mergansers, 458
Mergine, 458
Mergus, 458
Merlin, 460
Mermis, 163
Merops apiastes, 465
Merrythought, 440
Mesencephalon, 330
Mesenterial filaments, 112
Mesenteron, 23
Mesentery, 39, 111, 342
Mesoblast, 47
Mesoglea, 98
Mesonephros, 350
Mesothorax, 235
Metacarpal, 328
Metameres, 41
Metamorphosis, 50
Metanephros, 350
Metatarsal, 329
Metathorax, 235
Metazoa, 5, 85, 98
Metencephalon, 330
Mice, 530
Microchiroptera, 501
Microlepidoptera, 273
Micronucleus, 92
Micropyle, 243
Mid-brain, 330
Middle germ-layer, 45
Midges, 276
Mid gut, 23
Miescher’s corpuscles, 91
Migrations, 62
Migratory Locusts, 252
Milk, 469
Millepora, 106
Miller’s Thumb, 390
Milvus regalis, 461
Mimicry, 71

 

Mink, 516
Mites, 284
Mola, 391
Molars, 483
Mole, 499
Mole-cricket, 253
» -rat, 5380
Mollusca, 84, 287
Monadinide, 95
Mongoose, 517
Monodon monoceros, 525
Monogenetic Trematodes,
146

Monotremes, 495
Moor-hen, 459
Moose-deer, 509
Mormon fratercula, 457
Morphology, 57
Moschus moschiferus, 509
Mosquitos, 276
Moss-animals, 178
Motacilla, 462
Mother-of-pearl, 310
Moufion, 509
Moulting, 15, 31
Mound-birds, 456
Mouth, 23
Mouth-parts, 184
Mucous gland, 295
» membrane, 24
Mud-fish, 386
» turtles, 426
Miillerian ducts, 351
Muride, 530
Murena, 388
Murenide, 388
Mus, 530
» decumanus, 530:
» minutus, 530
» musculus, 530
»  sylvaticus, 530
Musca domestica, 277
»  vomitoria, 277
Muscicapide, 462
Muscide, 277
Muscle-cells, 11
33 smooth, 11
- striated, 12
Muscle fibrille, 92
»  -trichina, 162
Muscular impression, 310
Muscular system, 16
Muscular tissues, 7
Mushroom coral, 117
Musk Deer, 509
» Rat, 530
» Shrew, 500
Musquash, 530
Mussel, 314
Mustela, 516
as erminea, 516
$3 foina, 516
bs furo, 516
5 Tutreola, 516
35 putorius, 516
% vulgaris, 516
sy zibellina, 516
Mustelide, 516
Mya arenaria, 315
Mycetes, 533
Myelencephalon, 330
Mygale, 283
Mylodon, 525
Myodes lemmus, 530
Myogale, 500
ei moschata, 500
35 pyreenica, 500
Myopotamus coypu, 530
Myoxide, 529
Myoxus avellanarius, 530
3 dryas, 530
oe glis, 530
= nitela, 580
Myriapoda, 227
Myrmecobius, 497
Myrmecophaga, 526

és didactyla,
526
es jubata, 526
Myrmecophilous Insects,

270
Myrmeleon, 261
Mysidacea, 210, 211
Myside, 211
Mysis, 212
Mysis-stage, 222
Mystacoceti, 523
Mytilus edulis, 314
Myxine, 383

“4 glutinosa, 383

Naide, 174
Nails, 470
Nais, 174
Naja tripudians, 424
Narwhal, 525
Nasal, 362

» gland, 443
Nasua, 516
Natantia, 222
Natatores, 456
Natica, 302
Native Cats, 497
Natural selection, 57
Nauplius, 192

, eye, 190

Nautilus, 323
Naviculare, 479
Nearctic region, 74
Neb, 451
Nebalia, 207
Neck, 324
Necrophorus, 264
Nectocalyces, 108
Negro, 536
Nemathelminthia, 83, 158
Nematoda, 158
Nematocyst, 100
Nemertinea, 153
Nemocera, 276
Neophron percnopterus,461
Neotropical region, 74
Nepa, 160
Nephelis, 176
Nephridia, 167
Nephroharpages, 461

 

Index.

Nereidaw, 173
Nereis, 173
Neritina, 302
Nerophis, 391
Nerve fibres, 13
» Ying, 102
Nervous system, 17
central, 17
peripheral, 17
» sympathetic, 18
» tissues, 7
Neural spine, 326
Neurilemma, 13
Neuroglia, 331
Neuroptera, 252, 260
Neuropodium, 169
Newts, 404
» Large Water, 404
»  Palmated-smooth,
404
» Small, 404
Nictitating membrane, 336
Nidamental glands, 321
Nightingale, 462
Nightjar, 464
Nine-eyes, 382
Niphargus puteanus, 219
Nits, 260
Noctuide, 275
Nocturnal animals, 71
Non-ruminantia, 505
Notochord, 324
Notonecta, 160
Notopodium, 169
Notoryctes typhlops, 499
Nubian Wild Cat, 517
Nucifraga caryocatactes,
463
Nucleolus, 3, 85
Nucleus, 3, 85, 96
» pulposus, 471
Nudibranchiata, 303
Numenius arcuata, 460
Numida meleagris, 456
Nummulites, 89
Nutcracker, 463
Nuthatch, 464
Nutritive polyps, 104, 107
Nut Weevil, 244
Nyctale funerea, 461
Nyctea nivea, 461
Nyctharpages, 461
Nycticorax griseus, 459
Nymphon, 286

2

27

Occipital, 362

- condyles, 394
Ocelli, 187
Octactinia, 113
Octopoda, 323
Octopods, 323
Octopus vulgaris, 323
Ocular plates, 136
Odobenus rosmarus, 519
Odontoblasts, 340
Odontoceti, 524
Odontoid, 409
Odontornithes, 453

 

551

Csophagus, 23
Gstride, 277
Qstrus, 277
Oil-beetle, 266
» globules, 10, 85
Olecranon, 328
Olfactory lobes, 330
is organs, 18
Omasum, 507
Omentum, 488
Oniscide, 215
Oniscus, 215
Ontogeny, 40
Onychophora, 177
Ocecium, 180
Operculum, 179, 197, 204,
295, 373, 374
Ophidia, 422
Ophidiide, 389
Ophiura, 134
Ophiuride, 133
Opisthobranchiata, 301, 303
Opisthoglypha, 424
Opisthotic, 362
Opossums, 497
Optic chiasma, 332
» lobes, 3381
» organs, 20
» thalami, 331
Oral disc, 112
» tentacles, 109
Orang-utang, 534
Orbit, 333
Orbitosphenoid, 362
Orca gladiator, 524
Order, 55
Organ-pipe coral, 114
Organs, 18
» of Bojanus, 312
Oriental region, 74
Oriolus galbula, 462
Ornithorynchus, 496
Orthagoriscus, 391
Orthoptera, 252
Orycteropus, 527
Oryctes, 244
» nasicornis, 265
Oscines, 461
Osculum, 119
Os penis, 493
Osphradia, 296
Osprey, 433, 460
Os sepiz, 323
Ossicles, 129, 133
Ossifications, 325
Ostracion, 391
Ostracoda, 199
Ostrea edulis, 314
Ostrich, 453, 454
Otariide, 519
Otide, 459
Otis tarda, 459
» tetrax, 459
Otocoris alpestris, 464
Otocyon caffer, 516
Otocysts, 19
Otoliths, 20
Otters, 516
552

Otus brachyotus, 461
» Vulgaris, 461
Outer germ layer, 43
» root sheath, 467
Ovarioles, 242
Ovary, 34
Ovibos moschatus, 509
Oviduct, 33
Ovigerous lamelle, 206
Oviparous, 47
Ovipositor, 243, 269
Ovis, 509
»  ammon, 509
» aries, 509
» Musimon, 509
Ovum, 5, 32, 34

Owls, 461
x» (a) Diurnal, 461
es Great Eared, 461
oe Hawk, 461
5 Little, 461
$3 Scops Eared, 461
35 Snowy, 461
»  (b) Nocturnal, 461
%5 Barn, 461
3 Long-eared, 461
s Short-eared, 461
a Tawny, 461
8 Tengmalm’s, 461
Oxyuris vermicularis, 160
Oyster, 314
» catcher, 459
Paca, 531
Pedogenesis, 118
Pagurus, 225

i Berhardus, 226
Palearctic region, 74
Palemon, 223
Paleontology, 77
Paleotherium, 502
Palatal ridges, 487
Palate, 482 i

», hard, 482

» soft, 482
Palatine, 394
Palato-quadrate, 327
Palinurus, 225

vulgaris, 225

Palisade Worm, 160
Pallial chamber, 287

» Line, 808

» muscle, 307
Palp, 169, 188
Paludina vivipara, 302
Pancreas, 342
Pandion haliaétus, 4.60
Pangolin, 527
Panorpa, 262

Pe communis, 262
Panther, 517
Paper-wasps, 271
Papille circumvallate, 487

»  filiformes, 487

»  foliate, 487

»  fungiformes, 487
Paradiseide, 463
Paraglosse, 233

oo

2”

»

2

a”

»?

2

 

”

Pastor, 463
Patagium, 428
Patella, 302, 330
Paunch, 507
Pavo cristatus, 455
Pavonide, 455
Paxille, 123
Peacock, 455
Pearl Mussel, 315
Pearls, 311
Peccaries, 506
Pecten, 314, 443
Pedal disc, 112

Indez.

Paramecium, 94
Parasites, 24, 63
Parasitic Copepods, 201
Parasitism, 62
Parasphenoid, 363, 394
Parental instinct, 52
Parida, 462

Parietal, 362
Parovarium, 351
Parrakeets, 465
Parrots, 446
Parrot-fish, 389
Parthenogenesis, 37
Partial segmentation, 45
Partridge, 455

Parus caudatus, 462

coeruleus, 462
major, 462

ganglia, 289
nerves,.289
orifice, 308

Pedes adhamantes, 452

ambulatorii, 452
cursorii, 452, 453
fissi, 452
fissipalmati, 457
gradarii, 452
grallarii, 458
gressorii, 452, 465
insidentes, 452
palmati, 452, 456
raptorii, 460
scansorii, 452, 465
stegani, 457
vadantes, 452

Pedicellarie, 123, 182, 187
Pediculati, 391
Pediculatide, 160
Pediculus capitis, 260

vestimenti, 260

Pedipalpi, 279
Peduncle, 182, 188, 204
Peewit, 459

Pelagic fauna, 61
Pelargi, 459

Pelecanus, 457

Pelican, 457

Pelican’s foot, 302
Pelobates fuscus, 406
Pelobatide, 406
Peltogaster paguri, 207
Pelvic girdle, 328
Pemphigus spirothece, 258
Penzus, 223

| Penguins, 457

 

Penis, 34
Penne, 431
Pennatula, 115
Pentacrinus, 180
Pentastoma, 285
Perameles, 498
Peramelina, 497
Perea fiuviatilis, 389
Perceptive cells, 21
Perch, 389
Percidsx, 389
Perdicide, 455
Perdix cinerea, 455
Perforate Rhizopoda, 88
Perennibranchiata, 405
Peribranchial cavity, 538
Pericardium, 187, 345
Perichondrium, 329
Perineal pouches, 469
Periosteum, 329
Peripatus, 177
Periplaneta orientalis, 253
Perissodactyla, 502
Peristome, 136, 138
Peristomium, 169
Peritoneum, 342
Periwinkles, 302
Peropoda, 424
Peter’s Thumb, 389
Petrel, Fulmar, 456

» Stormy, 456
Petrels, 456
Petrifactions, 76
Petromyzon, 382

53 fluviatilis,382
e marinus, 382
planeri, 382

Petrosal, 362
Phacocheerus, 506
Phalanges, 328
Phalangiide, 282
Phalangista, 498
Phalangistide, 498
Phalaropes, 460
Phalaropus, 460
Pharyngeal bones, 365
Phascolarctos, 498
Phascolomys, 499
Phasianide, 455
Phasianus, 455
33 colchicus, 455

Phasianomorphe, 455
Phasmide, 253
Pheasants, 455
Phoca, 519

»  foetida, 519

»  greenlandica, 519

»  vitulina, 519
Phocena communis, 524
Phocide, 519
Pheenicopterus, 458
Pholas, 315
Phosphorescent organs, 28,

211

Phryganea, 262
Phthirius pubis, 266
Phyllium siccifolium, 254

. Phyllopoda, 193
Phyllosoma, 225
Phylloxera vastatrix, 257
Phylum, 55
Physalia, 108
‘Physetes macrocephalus,
524
Physiology, 58
Physophora, 108
Physostomi, 387
Phytoptus, 285
Pia mater, 331
Pica caudata, 463
Picide, 465
Picus martius, 465 |
» viridis, 466 |
Piddock, 315
Pieris brassice, 275
Pig, 505
Pigeons, 465
Pigment, 31
i granules, 10, 85
Pigmy male, 201, 205
Pika, 529
Pike, 387
Pilot Whale, 524
Pineal eye, 337
» gland, 331
Pine Grosbeak, 463
d’,, Lappet, 275
» Marten, 516
Pinicola enucleator, 463
Pinna, 481
Pinnipedia, 517
Pinntes, 128
Piophila casei, 277
Pipa, 398, 402
» americana, 407
Pipistrelle, 501
Pipit, 462
Pisces, 356
Piscicola, 177
Pisiform, 414
Pithecus satyrus, 534
Pituitary body, 331
Placenta, 354
»  foetalis, 354
as uterina, 354
Placophora, 290
Plaice, 389
Planaria, 145
Planorbis, 300
Platalea leucorodia, 459
Platanista gangetica, 525
Platyhelminthia, 83, 142
Platyrrhineg, 533
Plectognathi, 391
Plesiosaurians, 428
Pleura, 198
Pleural ganglia, 289
Pleuronectes flesus, 389
5 limanda, 389
35 platessa, 389
Pleuronectide, 389
Plictolophine, 465
Plovers, 459
» Golden, 459
Plume, 433
Pneumatic duct, 375

 

Index.

Pneumatocyst, 107
Podiceps, 457
6 auritus, 457
i grisegena, 457
minor, 457
Podura, 256
Poison-claws, 229
» glands, 392, 424
» teeth, 423
Polar Bear, 516
» Fox, 515
» Hare, 529
» Whale, 523
Polecat, 516 |
Polian vesicle, 124
Pollex, 478
Pollicipes, 206
Polyactinia, 115
Polycheta, 172
Polymorphism, 54
Polynoé, 173
Polynoide, 173
Polyp, 98
Polypoid generation, 102
Polyprotodontia, 497
Polypterus, 374, 385
Polystomee, 146
Polystomum intergerri-
mum, 146
Polyzoa, 83, 178
Pompilide, 270
Pond-snail, 306
Pontobdella muricata, 177
Pope, 389
Porcupines, 530
Poreus babyrusa, 506
Pores, 119
Pore plates, 134
Porifera, 118
Porpita, 108
Porpoise, 524
Portal vein, 346
Porus genitalis, 378
Post coracoid, 413
» frontal, 362
Pouched Marmot, 529
Powder-down, 434
Preecoces, 450
Prawns, 222
Prawn-stage, 222
Praying Mantis, 253
Preanal pores, 408
Precious Coral, 115
Precoracoid, 413
Prefrontal, 362
Prehensile organs, 63
Premaxilla, 410
Premolars, 483
Primates, 532
Printer, 267 ;
Pristis, 384 ;
Proboscidea, 510
Proboscis, 153, 201, 234, 256 |
Proboscis-sheath, 153
Procellaria pelagica, 456

 

Processus falciformis, 370
se uncinatus, 410,
437

558

Processus, vermiformis, 488
3 xiphoides, 473
Proctodeum, 23
Procyon, 516
Procyonide, 516
Proechidna, 496
Proglottides, 149
Prolegs, 250
Pronephros, 350
Prongbuck, 509
Prong-horned Antelope,
509
Prootic, 362
Proscolex, 150
Prosencephalon, 330
Prosimia, 531
Prosobranchiata, 301, 302
Prostate glands, 493
Prostomium, 169
Protective adaptations, 70
Proteles, 517
Proteroglypha, 424
Proteus, 399, 403
e anguineus, 404
Prothorax, 235
Protoplasm, 38, 85
Protopterus annectens, 387
Protozoa, 3, 88, 85
Provisional larval organs,
51
Proximal, 42
Psalterium, 507
Pseudis paradoxa, 403
Pseudo-caterpillars, 250
» ~navicelle, 96 ,
» “pupa, 251
Pseudopodia, 3, 25, 85, 87,
90

Pseudo-scorpions, 282
Psittacide, 466
Psittacine, 465
Psocus, 255
Psolus, 141
Psorospora gigantea, 96
Ptarmigan, 455
Pterodactyles, 428
Pterodactylus, 428
Pteromys, 529
= volans, 529

Pteropoda, 304
Pteropus, 501
Pterosauria, 428
Pterota, 305
Pterygoid, 394
Pteryle, 434
Pubis, 328
Puffin, 457
Pulex irritans, 278
Pulmonary syphon, 297
Pulmonata, 301, 305
| Pulp, 339
Puma, 517
Punger, 227
Pupa, 249
Pupil, 333
Purple, 295
Pyche, 274

» helix, 245
554

Pycnogonide, 286
Pycnogonum, 286
Pygopodes, 457
Pyrosoma, 540
Pyrrhula, 463
Python, 424

Quadrate, 394
Quadrato-jugal, 394
Quail, 455
Queen-bee, 271

Rabbit, 529
Racoons, 516
Radial canal, 102, 109
Radiale, 328
Radial symmetry, 41, 99,
122
Radiata, 122
Radii, 122
Radiolaria, 89
Radius, 329
Radula, 287
» sac, 288
Rails, 459
» Land, 459
» Water, 459
Rainey’s corpuscles, 97
Raia, 368
Raiide, 383
Ramphorhynchus, 428
Rana, 406
» esculenta, 406
» temporaria, 406
Rapaces, 460
Rallide, 459
Rallus aquaticus, 459
Rasores, 455
Ratite, 453
Rats, 530
Rattle-snake, 425
Raven, 463
Rays, 40
Razor-bill, 457
Receptacula seminis, 34,
242
Rectrices, 432
Recurvirostra avocetta, 460
Red bodies, 375
Redbreast, 462
Red corpuscles, 25
Red Deer, 508
Red Forest Ant, 270
Redia, 147
Redpole, Lesser, 463
Redshank, 460
Redstart, 462
Reed, 507
Regeneration, 32
Regular Sea-urchins, 138
Regulus, 462
Reindeer, 509
Remiges, 432
Replacement of teeth, 482
Reproduction, 31, 86
Reproductive organs, 31
Reptantia, 223
Reptilia, 407

 

Index.

Resonators, 399
Respiration, 26
Respiratory organs, 27
> syphon, 309
53 trees, 125, 140
Rete malpighii, 325
» Mirabile, 346
Retina, 21
Retinaculum, 272
Retinal cells, 21
Rhabdoceela, 144
Rhamphastide, 465
Rhamphostoma, 426
Rhinoceros, 503
bicornis, 503

we simus, 503
= tichorinus, 503
35 unicornis, 503
Birds, 465
Rhinolophus, 501
ts ferrum-equi-
num, 501
Se hipposiderus,
501

Rhizocephala, 206
Rhizocrinus lofotensis, 130
Rhizopoda, 87
Rhodeus amarus, 388
Rhombus levis, 389
s maximus, 389
Rhopalocera, 275
Rbynchobdellide, 177
Rhyncoceela, 153
Rhyncota, 252, 256
mii: 513
-stelleri, 513
Ribs, 118, 326
Ring canal, 124
Ringed Seal, 519
Ring Ouzel, 462
River Pearl-mussel, 315
» Mussel, 315
» Snail, 302
Roach, 388
Rodentia, 527
Rodents, 527
Roe, 508
Roller, 464
Rook, 463
Rorqual, 528
Rosechafers, 265
Rostrum, 223
Rotatory organ, 156
Rotifera, 83, 156
Rudimentary organs, 40
Ruff, 460
Rumen, 507
Ruminantia, 506
Russian Desman, 500
Rustic, 275
Ruticilla, 462

Sable, 516
Sabre-toothed Cats, 517
Saccobranchus, 375
Sacculina carcini, 207
Sacculus, 338

Sacral vertebra, 326

 

Salamander, 402
7 Black Alpine,
404

- Giant, 405
a maculosa, 404
Salanganes, 464
Salinity, 60, 67
Salivary glands, 24, 341
Salmon, 387
»  fario, 387
gs salar, 387
5 trutta, 387
Salmon-trout, 387
Salpa, 546
Salvelinus, 387
Sand-eels, 389
Sand-fly, 276
Sand-pipers, 460
Sand-wasps, 270
Sapajou, 533
Saproharpages, 461
Sarcocystis, 97 ©
Sarcodina, 87
Sarcolemma, 12
Sarcophaga carnaria, 277
Sarcopsylla penetrans, 278
Sarcoptes scabieia, 285
Sarcoptide, 285
Sarcorhamphus gryphus,
461
5 papa, 461
Sardine, 387
Saururer, 452
Saw-fish, 384
» -flies, 269
Saxicola, 462
Scale-insects, 258
Scales, ctenoid, 356
»  cycloid, 357
»  Placoid, 357
» reptilian, 408
Scallops, 314
Scalpellum, 206
Sealy Ant-eater, 527
Scansores, 465
Scaphoid, 478
Scaphopoda, 291
Scapula, 327
Scarabeide, 265
Scarus, 389
Scincoidei, 422
Sciuride, 529
Sciurus vulgaris, 529
Sclerotic coat, 333
Scolex, 149
Scolopax gallinago, 459
35 gallinula, 459
oe major, 459
3s rusticola, 459
Scolopendras, 229
Scomberesocide, 385
Scomberide, 390
Scomber scomber, 390
Scorpion-flies, 262
Scorpionide, 211
Scorpions, 281
Scrotum, 492
Scuta, 204
Scutellum, 259
Scyllarus, 225
Scyllium canicula, 383
Scymnus borealis, 383
Scyphomedusz, 109
Sea-acorns, 206
», Anemones, 118
» Adder, 391
» Angel, 384
» Bear, 519
» Clerk, 323
, Cows, 512
», Cucumbers, 138
Elephants, 526
» Feathers, 115
» Gulls, 443
Hare, 303, 390
» Hedgehog, 391
» Hog, 524
» Horse, 391
», Lilies, 127
» Lion, 519
» Mouse, 173
» Otter, 515
» Palms, 130
» Roses, 118
» Scorpion, 390
» Squirts, 537
» Stickle, 377, 390
Urchins, 134
Seasonal dimorphism, 38
Sebaceous glands, 468
Secondary sexual charac-
ters, 35
Secretary, 460
Sectorial tooth, 514
Segmentation, 156
cavity, 43
Segments, 41, 184
Selache maxima, 383
Selachii, 383
Self fertilisation, 36
Semicircular canals, 338
Seminal duct, 34
Seminal tubes, 243
Semnopithecide, 534
Semnopithecus nasicus,
534
Sense of equilibrium, 20
Sense organs, 18
Sensory cells, 13
Sepia officinalis, 323
Serous membrane, 354
Serpula, 173
Serpulide, 173
Sesamoid bones, 330
Sesia, 274
Sessile forms, 65, 66
» medusa, 106
Seta, 185
Seventeen-years Cicada,
257
Sexual reproduction, 31
Shad, 387
Shark, 328
Sharks, 383
Blue, 383
Greenland, 383

”

”

 

Index.

Sharks, Giant, 383
Hammer-headed,
383
Sheat-fish, 388
Sheath of Schwann, 13
Sheep, 509
Sheep Bot-fly, 277
Tick, 278
Shell, 92, 182, 287
Shellac-insect, 259
Shell-gland, 143, 192
Shield-urchins, 138
Ship-worm, 315
Shore-crab, 227
Shoulder-blade, 327
z. girdle, 327
Shrew, 499
Shrikes, 462
3 Great Grey, 462
Sibbald’s Fin-whale, 523
Siberian sub-region, 74
Siliceous fibres, 120
Silk glands, 248
» -worm Moth, 245, 274
Silpha, 264
Silphide, 264
Siluride, 388
Silurus glanis, 388
Simia Gorilla, 535
»  Troglodytes, 535
Simulia, 276
‘i columbaczensis,
276
Sinupalliate, 310
Sinus venosus, 344:
Siphon, 137
Siphonophora, 107
Siphonozooids, 114
Siphuncle, 317
Siredon mexicanus, 403,
404
Sirenia, 512
Siren lacertina, 405
Sirex, 269
Siskin, 463
Sitta cesia, 464
Sittacine, 465
Skates, 383
Skeletal tissues, 7, 9
Skeleton, 4, 15, 85
Skeleton Shrimp, 219
Skin, 14
Skin glands, 237
Skinks, 422
Skip-jacks, 265
Skull, 327
Skunks, 516
Sleep, 69
Sloth Bear, 516
Sloths, 525
Slough, 407
Small Bats, 501
Small Tortoiseshell, 275
Sminthus betulinus or
vagus, 530
Snakes, 422
» Aisculapius, 424
Giant, 424

”

 

555

Snakes, Ringed, 424

es Sea, 424

» Whip, 424
Snipe, Common, 459

» Great, 459

» Jack, 459
Snipes, 459

Solaster, 133
Soldiers, 254, 270
Sole, 389

» (of foot), 469
Solea vulgaris, 389
Solenoglypha, 425
Solitary Bees, 272

» Corals, 117

Somateria mollissima, 458
Sorex, 499

»  pygmeus, 500

» Vulgaris, 500
Sound-producing organs,30:
Spalax typhlus, 530
Spanish-fly, 266

Sparrow, 463
ai House, 463
ie Tree, 463

Spatangide, 138
Spatangus, 138
Spatularia, 385
Species, 53
Spermatophore, 34
Spermatozoon, 32, 33
Spermophilus citillus, 529
Sperm Whale, 524
Sphenoid, 362
Sphenethmoid, 394
Spheridia, 138
Sphingide, 275
Sphyrna, 383
Spicula, 159
Spider Monkey, 533
Spiders, 283
Spinachia vulgaris, 390°
Spinal cord, 324, 330, 331,
Spines, 123, 137
Spinnerettes, 283
Spinning glands, 279
Spiny Ant-eater, 496

»  Dog-fish, 383
Spiracle, 373
Spiral valve of intestine,

371
Spleen, 348
Sponges, 83, 118
Spongie, 118
Spongilla fluviatilis, 121
Spontaneous movement, 3
Spoon-billed Sturgeon, 385
Spores, 96
Sporocyst, 147
Sprat, 387
Spring-flies, 262
Spur, 235, 435
Squalide, 383
Squamipennes, 390
Squamosal, 362
Squatina, 384
Squilla mantis, 227
Squirrel, 529
556

Squirrel-tailed Dormouse,
530
Stag, 508
Stag-beetle, 265
Stages of life, 68
Stapes, 481 \
Staphylinide, 264
Staphylinus, 264
Starfish, 131
Starlings, 463
Stationary parasites, 61
Statoblast, 180
Steganopodes, 457
Stegocephala, 405
Steinbock, 509
Steller’s Cow, 518
Stenops, 532
Stensen’s duct, 333
Sterlet, 385
‘Sterna, 456
= hirundo, 456
5 minuta, 456
Sternum, 326
Stick-insects, 253
Stickleback, Ten-spined,
390 :
55 Three-spined, ‘
390
Sticklebacks, 379, 390
Stigmata, 240
Sting, 248, 269
Stink-glands, 237
Stipes, 233
Stock, 32
Stolon, 103
Stomach, 23
Stomapoda, 210, 227
Stomodeum, 23
Stone canal, 124
Stork, Black, 459
» White, 459
Storks, 459
«Strap-worm, 151
Stratum corneum, 325, 466_
as Malpighii, 466
= mucosum, 325, 466 ©
Strepsilas interpres, 459
Strepsiptera, 262
Striges nocturne, 461
«Stringopine, 465
Stringops habroptilus, 465 |
Strix flammea, 461
Strongylide, 160
Strongylus, 160
Struthionide, 454
Sturgeons, 363, 374, 385
‘Sturnus vulgaris, 463 {
Stylets, 201 i
Stylommatophora, 306 \
Stylonychia, 94
Stylops, 262 \
Subcortical crypts, 120 !
Subimago, 247 |
Sublingua, 487 ‘
Sub-regions, 74 t
Subungulata, 521 F
Succinea amphibia, 148 !
Suckers, 14

 

. Index.

Sucking-fish, 390

Sudoriparous glands, 468

Suide, 505

Sula bassana, 457

Sulci, 480

Summer sleep, 69

Sun-fish, 391

Supporting cells, 21

Suprabranchial cavities,
307

Supraoccipital, 362
Suprarenal body, 350
Suprascapula, 413
Surnia nisoria, 461
Sus, 505
» scrofa, 505
Swallows, 463
Swan, Black, 458 1

» Mute, 458 :
» Wild or Whistling, .
458 ;

Swans, 458

Swarm-spores, 90
Swift, Alpine, 464

ay Common, 464
Swifts, 464
Swim-bladder, 344
Swimmerets, 209
Swimming bells, 108
Sword Fish, 390
Sylvia, 462
Sylviade, 462
Symbiosis, 91
Sympathetic nervous

system, 332
Synapta, 141
Synapticula, 116
Syngnathide, 391
Synovial cavities, 40
Syrinx, 446, 447
Syrnium aluco, 461
Syrrhaptes paradoxus, 455
Tabanide, 276 :
Tachina, 277
Tachypetes aquila, 457
Tenia, 151

»  ecenurus, 151 i

»  eucumerina, 151

»  echinococcus, 151 |
mediocanellata, 151
saginata, 151
Tail, 41, 324

3 diphycercal, 360

» heterocercal, 360

» homocercal, 361
Talegallas, 456
Talpa, 499

» europea, 449
Tanaide, 216
Tapetum, 481

es lucidum, 370
¥ nigrum, 333

Tapeworms, 149
Tapir, 502
Tapirus, 502
Tardigrada, 286
Tarsals, 328

i
‘

”

 

Tarsier, 532
Tarsipes, 498
Tarsus, 235, 328
Tarsius spectrum, 532
Tasmanian Wolf, 497
Taste-buds, 19
Teeth, 23, 338
Tegenaria domestica, 283
Teleosaurus, 427
Teleostei, 387
Telephorus, 266
Temporal, 476
Temperature, 60
Temporary conjugation, 92
ai parasites, 62
Tench, 388
Tendons, 185, 330
Tenebrio molitor, 266
Tentacles, 108,111, 140, 178,
292, 316
Tentacle-sheath, 316
Tentacular arms, 316
cirrus, 169
Tentaculocyst, 111
Tenthredinide, 269
Terebratula, 183
Teredo navalis, 315
Terga, 204
Tergum, 198
Termes, 254
Termites, 254
Tern, Common, 456
» Lesser, 456
Terns, 456
Terrestrial, 58
Testis, 34
Testudinata, 425
Testudinidey, 426
Testudo greca, 426
Tetrabranchiata, 322
Tetraonomorphe, 455
Tetrao tetrix, 455
»  urogallus, 455
Thalamencephalon, 330
Theea, 115
Thecosomata, 304
Theory of Descent, 56
Thigh bone, 328
Thoracic segments, 188
53 vertebree, 326
Thorax, 190
Thorn-headed Worm,
‘163
Thread-worms, 158, 162
Thrush, 462
Thunderbolts, 323
Thylacinus, 497
Thymus, 341
Thynnus vulgaris, 390
Thyroid gland, 341, 488
Thysanopus, 211
Thysanura, 250
Tibia, 235, 328
Tibiale, 328
Tichodroma muraria, 464.
Ticks, 284
Tiger, 517
Tiger-beetles, 264
Tinamou, 454
Tinca vulgaris, 388
Tinea pellionella, 273
»  tapezella, 273
Tineide, 273
Tintinnus, 94
Tipula, 276
Tissues, 7
» epithelial, 7
» muscular, 7
» nervous, 7
» skeletal, 7
Tit, Blue, 462
‘Great, 462
i ” Long-tailed, 462
Tits, 462
Toad, 406, 407
» Common, 406
» Natterjack, 407
»  Orange-speckled, 406
» Surinam, 406
Tomicide, 267
Tomicus typographus, 267
Tongue, 287, 341
Tonsil, 487
Toothed Whales, 524
Torpedo, 368, 384
Tortoises, 426
35 Grecian, 426
Tortricide, 274
Tortrix buoliana, 274
»  pomonana, 274
Totanus, 460
Toucans, 465
Toxopneustes, 138
Trachea, 417
Trachese, 240
Tracheal bladder, 238
6 gills, 241
‘5 system, 228
Trachinus draco, 389
Tragulide, 509
Transverse bone, 412
Trapezium, 478
Trematoda, 148, 145
Trichechus rosmarus, 519
Trichina spiralis, 162
Trichodectes, 256
canis, 153, 256
Trichoglossinz, 465
Trigla gurnardus, 390
Trigonocephalus, 425
Trilobita, 198
Trilobites, 198
Tringa, 460
Trionyx, 426
Tristomum, 146
Triton, 403, 404
»  evristatus, 404
»  helveticus, 404
»  teniatus, 404
Trochanter, 235
5s tertius, 502
Trochilide, 464
Troctes, 255
Troglodytes gorilla, 535
i niger, 535
8 parvulus, 462

 

Index.

Trombidiide, 284

| Tropidonotus natrix, 424

Trout, 387

_ True Seals, 519

» Wasps, 271

' Trunk, 324

»  -fish, 391

Tube-feet, 122

Tuber calcis, 414
Tuberculum, 472
Tubifex rivulorum, 174

- Tubipora, 114
. Tunica argentea, 370

Tunicata, 84, 537
Tunny, 390
Turbellaria, 143
Turbinals, 333
Turbot, 389

' Turdide, 462

Turdiformes, 462
Turdus merula, 462
»  musicus, 462
»  torquatus, 462
Turkey, 455
Turnstone, 459
Turtles, 426
Turtur auritus, 465
»  vrisorius, 465
Two-toed Anteater, 526
Tylenchus tritici, 163
Tympanic cavity, 397
i membrane, 447
Tympanic membrane, in-
ternal, 447
Tympanic membrane, ex-
ternal, 444
Tympanum, 238, 397
Tyroglyphus, 284

Ulna, 328
Uluare, 328
Umbilical cord, 494
is tube, 294
Umbilicus, 294
Umbo, 309
Umbrella, 102
Unciform, 478
Undulating membrane, 92
Ungulata, 501
Unio, 315
Upupa epops, 464
Urea, 30, 31
Ure ox, 510
Uric acid, 4, 30
Urinary bladder, 31
a organs, 30
Urine, 31
Uroceride, 269
Urodela, 404
Uropygial glands, 435
Urside, 516
Ursus americanus, 516
»  arctos, 516
»  Cinereus, 516
»  Jabiatus, 516
maritimus, 516
speleus, 516
Uterus, 490

”

 

557.

Uterus, bicornis, 490
i 3 duplex, 490
é es masculinus, 493
2 simplex, 490
" Utriculus, 338

Vacuole, 4, 85, 92
. Vagina, 242, 490
‘ Valves, 26
‘ Vampire, 501
Vanellus cristatus, 459
Vanessa urtice, 275
' Varanids, 422
. Varanus, 422
' Variable Hare, 529
Varieties, 54
Vascular system, 25
Vascular system in con-
nection with respiratory
apparatus, 28
Vas deferens, 34
Vegetable Kingdom, 80
. Veins, 26
. Velella, 109
' Velum, 105, 107, 290
‘Velvet, 471
Venus’s Flower-basket, 121
33 Girdle, 118
Venous blood, 28
re heart, 29
Ventral, 41
Ventricle, 26
Vertebra, 326
Vertebrata, 84, 324
Vesicantia, 266
Vesicles (tracheal), 240
Vesicula seminalis, 244,
493
Vespa, 271
Vespariz, 271
Vespertilio, 501
sy Daubentoni,
501
Vesperugo, 501
5 pipistrellus,501
Vestibule, 491
Vibracula, 181
Vibrisse, 467
Villi, 342
Vinegar-worm, 163
Vine-louse, 257
Vioa, 121
Vipera, 425
>»  ammodytes, 425
» berus, 425
Viper, Common, 425
» Pit, 425
Vipers, 425
Viscera, 39
Visceral arches, 327
ee ganglia, 289
sy hump, 292
25 loop, 289
Vitellarium, 143
Vitelline membrane, 32
Vitreous body, 21
re humour, 333
Be Sponges, 121
558

Viverra, 517
»  genetta, 517
Viverride, 517
Viviparous, 47, 126
Vocal cords, 30, 417
Vomer, 362
Vorticella, 94
Vultur fulvus, 461
Vulture, Alpine, 461
“a Bearded, 461
5 Carrion, 461
King, 461
White-headed,461

2»

”

Wagtails, 462
Walrus, 519
Wapiti, 509
‘Warblers, 462

Ss Reed, 462

5 Sedge, 462

33 Willow, 462
Warm-blooded animals, 30
Wart-hog, 506
Washing Racoon, 516
Water Boatman, 160

» Bugs, 260

» cells, 508
» Flea, 196
» Howls, 459
» Mites, 284
» Rat, 530

 

Index.

Water Scorpion, 260

» Shrew, 500

» Spider, 283

» vascular system, 124
Wax glands, 237
Weazel, 516
Weevils, 267
Whale-bone, 522
Ps Whales, 523
Wheatear, 462
Wheel Animalcules, 156
Whelk, 302
Whirligigs, 264
White Ants, 254

» Spoonbill, 459
Widgeon, 458
Wild Cat, 517

» Hog, 506
Wing, 235

» cases, 236
Winter sleep, 69
Wire-worms, 266
Wolf, 515
Wolffian ducts, 349
Wolf-fish, 390
Wombats, 499
Wood-borers, 274
Woodcock, 459
Wood Mouse, 530

» ~peckers, 465

» Wasps, 269

 

Woolly Rhinoceros, 503
Workers, 254, 270
Wrass, 389

Wrens, 462

Wrist, 328

Wryneck, 466

Xenos, 262 %
Xiphias gladius, 390
Xiphisternum, 473
Xiphosura, 196
Xylotropa, 274

Yellow cells, 90
» hammer, 463
Yolk gland, 143
» granules, 32
» sac, 49

Zebra, 503
Zoantharia, 115
Zora, 221
Zoarces, 390
9 vivipara, 390
BepeevernD ea regions,
4

Zooid, 178
Zygantrum, 409
Zygapophysis, 409
Zygosphene, 409
Page 118, line

» 149, Fig.
» 176, Fig.

» 274, line
» 283, line

» 1289, Fig.

ERRATA.

42, delete “ structure.”

105, for “central” read “ ventral.”

137, for “ subesophageal” read “ ventral.”
19, insert , after dorsally.

1, for “ Arachnidas ” read “ Arachnida.”
237, for “foot” read “pedal ganglion.’

» 9814, line 18, for “Dreissena” read “ Dreissensia.”

» 817, Fig. 263, for “syphon” read “ siphuncle.”

» 851, Fig. 291, for “f collicle” read “ follicle.”

» 855, Fig 293, for “ gill-sac” read “ pharynx.”

» 9888, line 37, and page 390, lines 29, 32, for “Mackrel read
“ Mackerel.”

» 478, Fig.

» 600, line

390, for “oc” read “x.”
36, for “metatarsals” read “ metacarpals.”

N.B.—The term Raptatores, used p. 452, is interchangeable with the terms

Rapaces or Accipitres, used p. 460.
 

 

 

Se eer om mecieT