DRAPE RS He) TA ae. Se ie i ; oe ue : Us 2h es a Cornell University Library QL 48.P24 mini A MANUAL OF ZOOLOGY A MANUAL OF ZOOLOGY BY T. JEFFREY PARKER, D.Sc., F.R.S. PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF OTAGO, DUNEDIN, N.Z. AND WILLIAM A. HASWELL, M.A., D.Sc., F.R.S. PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF SYDNEY, N.S.W. REVISED AND ADAPTED FOR THE USE OF AMERICAN SCHOOLS AND COLLEGES Neto Work THE MACMILLAN COMPANY LONDON: MACMILLAN & CO., Ltp. 1900 All rights reserved CopyRIGHT, 1900, By THE MACMILLAN COMPANY. Set up and electrotyped January, 1900. Reprinted September, 1900. Norwood jress J. 8. Cushing & Co. — Berwick & Smith Norwood Mass. U.S.A. PREFACE In planning the present work the aim of the authors has been to provide a manual embodying a course of study adapted to the requirements of the student chiefly in higher classes of schools, and to some extent in junior classes of universities. To make this, within the necessarily narrow limits of space imposed, anything more than a bare synopsis, it has been necessary to restrict the extent of the ground covered. This has been done (1) by leaving out altogether certain classes of existing animals; (2) by omitting all de- scriptions of extinct groups ; (3) by dealing only very briefly with embryology. Opinions must differ as to the best selec- tion of groups for an elementary manual of this kind. But broadly, there can, it has appeared to us, be little doubt that what should be omitted, or only briefly dealt with, are the groups of rare occurrence and uncertain relationships, the greater part of the space being devoted to the more familiar representatives of the large phyla. A course of laboratory and museum instruction, supple- mented by work in the field and on the seashore, is abso- lutely necessary in order that any sound knowledge of Vv vi PREFACE zoology may be attained. The present manual does not provide such instruction, but is intended to be used in association with it, and the examples selected for de- scription are such as may under most circumstances be readily obtained. The general plan is similar to that followed in the Zext+ Book of Zoology by the same authors, but the restricted space has necessitated considerable modifications. We have not adopted the method, followed in various recent manuals, of beginning with one of the larger Invertebrata or with a vertebrate, and working from that upwards and downwards. The reasons given for such a mode of treat- ment we understand to be that if we begin with the simplest animals, the Protozoa, we discourage and embarrass the beginner by introducing him at once into a world entirely new to him, requiring him at the same time to learn the use of an entirely unfamiliar instrument the microscope. But in our opinion, the difficulty is much less than is alleged by the advocates of the alternative method, and the advantage of presenting the facts at the outset in a natural and logical order by far outweigh any such disadvantages. We are con- vinced that any general acquaintance which the student may possess beforehand with a rabbit or a crayfish will be of little real value to him when he begins to take up seriously the study of its structure. Moreover an elementary knowledge of the use of the microscope is absolutely essential to any adequate study of Zoology as an intellectual discipline, and this difficulty, such as it is, may as well be met first as last. PREFACE. vii Owing to the lamented death of Professor T. Jeffrey Parker, at a time when but little progress had been made with this work, his actual share in it has been but slight: but as it was planned between us, and the earlier parts had the advantage of his revision, and more especially as it owes a great deal to his work in the ZextBook it has been thought right to let it appear under our joint names as origi- nally intended. I have to express very great indebtedness to Professor W. Newton Parker for the pains he has taken in revising the proof-sheets and for many valuable suggestions which he has made during the progress of the work. Wiiutiam A. HASWELL. PREFACE TO THE AMERICAN EDITION Tus American edition of Parker and Haswell’s useful and concise “ Manual of Zoology” has been adapted for the use of American schools. Common American forms closely similar to the European or Australasian ones described in the English edition, have been mentioned, so that the student can use the book in examining the allied typical forms from his own country. In the majority of cases the European species differ only in trivial characteristics, so that one general description will answer for both. In a very few cases the American editor has revised and corrected views or statements not believed to be correct. For example, few, if any, American zoologists would regard Limulus as an undoubted Arachnidan. A few additional American animals have been referred to and figured, while a few cuts not reproduced in the English edition have been copied from Parker and Haswell’s “ Text-book of Zoology,” and also from Sedgwick’s “'Text- book of Zoology.” CONTENTS PREFACE TO THE ENGLISH EDITION . PREFACE TO THE AMERICAN EDITION List oF ILLUSTRATIONS INTRODUCTION Definition of zoology Binomial nomenclature Individual variations Hybrids Definition of auvohotoey Definition of histology . Definition of embryology Classification a . Phyla Organic evolution Genealogical tree Paleontology Fossils Succession of life i in time Phylogeny : : : Distribution of animals, in space al in time The plankton The necton . The benthos Definition of a fauna Zoo-geographical regions Definition of physiology Definition of ethology or binomics xi PAGE xvii ODONNMA A HWW DAH _ xil CONTENTS SECTION I PAGE PHYLUM PROTOZOA. . ‘ 7 re 14 Class 1. The Rhizopoda . ‘ : : , 14 Example of the Class — 4maba proteus . : : 14 Class 2. The Mastigophora : ‘ 34 Example of the Class — Luglena viridis 34 Class 3. The Infusoria 45 Example of the Class — Paramacium i deadlite 45 Class 4. The Sporozoa ‘ , 55 Example of the Class — .l/oecvstis waite “ ‘ 55 SECTION IT THE METAZOA . é : : . » 59 Oosperm or egg ; . ; 59 Male cell or sperm : i . : - 60 Fertilisation ; a A 60 Segmentation of the oosperm : : : : . 60 Germinal layers. 62 Tissues, epithelium i ¥ é . 63 Glands, ducts , : : 63 Connective tissues : : : » 65 Fibrous tissue : é : » 65 Fat. ; ; : é : 65 Cartilage : : : ; . 66 Bone . : . 66 Muscular tissue. . : : 66 Nerve tissue, ganglia, nerves é 66 Organs : : é 66 Exoskeleton : - ; : ‘ i ¢ 67 Endoskeleton : i : 67 Organs of digestion 3 : 68 Organs of respiration : “96 The blood : ‘ , : . 70 Blood vascular system é . . 70 Heart . . % . : . : 71 Organs of excretion. . é . $ - eT CONTENTS The brain Reproduction The phyla of the aiid ada Tabular view of the phyla SECTION III PHYLUM PORIFERA Example of the Phylum wail Ci Sin peldeionnie SECTION IV PHYLUM C@:LENTERATA Class 1. The Hydrozoa 4 Example of the Class — Ode/ia . Class 2. The Scyphozoa Example of the Class— durelia aurita Ciass 3. The Actinozoa A Example of the Class — Zeadia crassicornis Class 4. The Ctenophora . : Example of the Class — Hor agit piers : SECTION V PHYLUM PLATYHELMINTHES : $ . . Class 1. The Trematoda . Example of the Class — Distomum hepticum si Class 2. The Turbellaria Example of the Class — Planarta torva Class 3. The Cestoda Example of the Class — Tenia solium Class 4. The Nemertinea Example of the Class — Te¢rastemma SECTION VI PHYLUM NEMATHELMINTHES Class. The Nematoda Example of the Class — Ascaris hiaaieiaies xiii PAGE 71 74 75 76 go g1 gI 108 108 114 114 125 125 129 129 129 137 138 138 138 145 145 149 149 149 xiv CONTENTS SECTION VII Pay_tm ECHINODERMATA Class 1. The Asteroidea Example of the Class ~ 4stertas vulgaris Class 2, The Ophiuroidea Example of the Class — Ophioglypha lacertosa Class 3. The Echinoidea Example of the Class — Sz preva otus -Class 4. The Holothuroidea Example of the Class — //olothurta seus Class 5. The Crinoidea Example of the Class — -faédon SECTION VIII ROTIFERA, POLYZOA, AND BRACHIOPODA Class 1. Rotifera Example of the Class ~ Brachionus rudbens Class 2. Polyzoa i Example of the Class — Bugula avicularia Class 3. Brachiopoda Example of the Class -— JJagellenia flavescens . SECTION IX PHYLUM ANNULATA Class 1. The Chetopoda : Example of the Class — WVerezs aes wi. Class 2. The Hirudinea Example of the Class — Arado ene SECTION X PiryLuM ARTHROPODA Class 1. The Crustacea Example of the Class — .fs/acus fluviatilis Class 2. The Onychophora Example of the Class — Peripatus PAGE 157 157 157 169 169 170 170 173 173 174 174 178 178 178 181 181 184 184 188 188 189 203 203 212 213 213 236 236 CONTENTS Class 3. The Myriapoda ‘ Example of the Class —-Selwienda morsttans . Class 4. The Insecta Example of the Class — Peciihuiaas americana Class 5. The Arachnida Example of the Class — Scorpio SECTION XI PHYLUM MOLLUSCA 3 F Class 1. The Pelecypoda . Example of the Class — 4nodonta cygnea Class 2. The Amphineura Example of the Class — Chiton eins Class 3. The Gastropoda . Example of the Class — Helix nemoralis . Class 4. The Cephalopoda Example of the Class — Vautilus oe SECTION XII PHYLUM CHORDATA Subphylum 1. The Adelochorda Example of the Subphylum — Ballets Subphylum 2. The Urochorda Example of the Subphylum — Asctadza Subphylum 3. The Vertebrata . ‘ Examples of the Subplivlim—vaninads Pivnotipion, Pisces, ete. ‘ ‘ Division A. The Acrania Example of the Dita salen jeans Division B. The Craniata : Examples of the Division, the dogfish, iad and eunstit ‘ Class 1. Cyclostomi Example of the Class — Petromyzon marinus . Class 2. Pisces Examples of the Class — Sharks, perch, al lung fishes Xv PAGE 239 239 241 241 254 254 264 265 265 281 281 284 284 296 298 310 311 311 314 314 322 322 323 323 328 328 360 365 365 xvi CONTENTS Subclass 1. Elasmobranchii Example of the Subclass — Sey//ivei aut Hast zs Subclass 2. Holocephali (omitted) Subclass 3. Teleostomi Example of the Subclass — Selina fee 70 Subclass 4. Dipnoi Example of the Subclass — Ceratodus foster? Class 3. Amphibia : Example of the Class — Rana temporaria Class 4. Reptilia Examples of the Class — Lizards, Ay sdeoétile Class 5. Aves Example of the Class — Gotti livia Class 6. Mammalia : Example of the Class — Lepus cuniculus . PAGE 366 366 394 394 395 405 405 407 408 433 434 456 457 49! 491 mn = a mArA AM fFWhN Oa Oo” bw YH HRN NHK HN RM Mm me me me me ON ANP W NHK OW CON AN BW WN & ty oO LIST: OF ILLUSTRATIONS . Ameeba proteus . Ameeba polypodia . Quadrula, Hyalosphenia, Agedila, Difflugia . Forms of Foraminifera . F A . Shells of Foraminifera . Actinophrys sol . Actinosphzerium eichhornii . Forms of Heliozoa . Liteocircus annularis . Actinomma asteracanthion . Collozoum inerme . . Euglena viridis . Forms of Mastigophora . Forms of Choanoflagellata . Forms of Dinoflagellata . Noctiluca miliaris . . Volvox globator . Paramoecium caudatum . Forms of Ciliata . Forms of Tentaculifera . Forms of Ciliata . Vorticella . Monocystis agilis . . Gregarina . Ovum of a sea- siecse . Diagram of maturation and fenilizacen af ovum . Segmentation of the oosperm . Forms of epithelium 5 . Diagram illustrating the structure of Mende R xvii PAGE 15 18 20 22 25 26 27 29 31 32 33 35 37 39 40 41 43 47 49 51 53 54 57 60 61 62 64 65 xvili LIST OF ILLUSTRATIONS FIG 30. Sil 32 33: 34- 35+ 36. 37: 38. 39- 40. 4i. 42. 43- 44. 45- 46. 47: 48. 49. 50. 51. 2s 53- 54- 55: 56. 57: 60. 61. 62. 63. 64. 65. 66. 67. Bones of arm with biceps muscle Viscera of male frog Hydra . : gm Sycon ciliatum Sycon gelatinosum Sycon gelatinosum, ecules Sycon gelatinosum, transverse section Ascetta primordialis Section of Spongilla Skeleton of sponges Sponge spicules Obelia colony Nematocysts of Hydra . Dissection of Medusa Development of Laomedea and Badendau Structure of Hydra Petasus and Glossocodon Bougainvillea ramosa Physalia Physalia arethusa . Halistemma tergestinum Aurelia aurita, partly dissected Aurelia aurita, development . Tessera princeps Tealia crassicornis Sea-anemone, in sections Common sea-anemone . Corallium rubrum . Alcyonium palmatum 59: Tubipora musica Pennatula sulcata Flabellum curvatum Astreea pallida : Dendrophyllia nigrescens ae Nadeepaes aspera Cancrisocia on back of a crab Hormiphora plumosa Hormiphora plumosa, section of a tentacle Idyia roseola . PAGE 67 69 73 76 77 78 80 84 85 87 88 O3 96 97 99 100 102 103 106 106 107 109 II 113 115 116 118 118 119 120 121 122 123 124 125 126 127 128 FIG, 68. 69. 70. 71. 72. 73: 74- 75- . Taenia solium, proglottis 77: 78. 79: 80, 81. 82. 83. 84. 85. 86. 87. 88. 89. go. gl. 92. 93- 94. 95: 96. 97- 98. 99. 100. Ior. 102. 103. 104. 105. LIST OF ILLUSTRATIONS Distomum hepaticum, natural size Distomum hepaticum, anatomy Distomum hepaticum, development Trematodes: Amphistomum and Homalogaster Structure of a triclad turbellarian Planaria polychroa Teenia solium Tenia solium, head seapniied Development of tape-worm Cyst of Tzenia echinococcus with deup ie eet and solide Diagram of organs of a Nemertine Tetrastemma, structure Ascaris lumbricoides Ascaris lumbricoides, dissection of feet Diagram of nervous system of Nematoda is Ascaris lumbricoides, posterior end of male dissected . Trichina spiralis . Starfish, showing tube feet . : Starfish, vertical section through an arm Starfish, diagrammatic sections Asterias rubens, digestive system . Ambulacral systems of a starfish . Anthenea, dorsal surface. 7 : . Anthenea, ventral surface Ophioglypha lacertosa . Strongylocentrotus Corona of sea-urchin : Apical systems of plates of sea-urchin . Cucumaria planci Antedon ‘ Metacrinus interruptus Brachionus rubens Bugula avicularia Plumatella . Pedicellina . ; Magellania flavescens . 5 ‘ Magellania lenticularis, sagittal section PAGE 130 131 135 136 137 138 139 140 141 142 144 146 147 150 151 152 153 155 158 161 164 165 166 167 168 169 171 172 172 174 175 177. 179 182 183 184 185 186 FIG, 106. 107. 108. 109. 110, Ill, 112. 113. 114. IIs. 116, 117. 118, 119. 120. 121, 122. 123. 124. 125. 126, 127. 128, 129. 130. 131. 132. 133. 134. 135. 136. 137. 138. 139. 140. Tl. 142. 143. LIST OF ILLUSTRATIONS Nereis dumerilii, natural size Nereis dumerilii, parapodium Nereis dumerilii, sete . Nereis dumerilii, anatomy Nereis dumerilii, transverse section Section through the eye of Nereis Brain and connecting nerves of Nereis Serpulz in their tubes . Trochosphere of Eupomatus Lumbricus agricola Lumbricus, setze Hirudo medicinalis Head of Hirudo medicinalis, cesnit the three jaws Head of Hirudo quinquestriata Nephridium of the medicinal leech Transverse section of Hirudo Diagram of blood-channels of leech Astacus fluviatilis Appendages of Astacus Astacus fluviatilis, dissection from sight aie Respiratory organs of Astacus fluviatilis Thorax of crayfish, transverse section Diagram of the circulation in the crayfish Nervous system of Astacus fluviatilis Reproductive organs of Astacus fluviatilis Cancer pagurus Pagurus bernhardus Apus glacialis Development of Apus . Cyclops and Calocalanus Lepas anatifera Peripatus capensis Peripatus capensis, head, ete. Internal organs of Peripatus Scolopendra Periplaneta americana . Mouth-parts of the cockroach Pieris rapz, larva, and pupa PAGE 189 190 1gI 192 194 196 197 198 199 200 201 204 205 206 208 209 210 214 217 221 223 225 226 227 229 230 231 232 233 234 235 237 237 238 240 242 243 244 LIST OF ILLUSTRATIONS xxi FIG. PAGE 144. Carpet beetle, larva, and pupa. ‘ a ‘ 5 « 245 145. Culex and larva - , j ‘ ‘ ‘ - 246 146, Internal organs of soskisadh ; . . : . - 247 147. Periplaneta, its tracheal system . . A a : . 248 148. Periplaneta, nervous system : s : : bs + 249 149. Honey bee, quecn, worker, and drone : ‘ ‘ + 253 150. Red ant, male, worker, and female. r # % + 253 151. Euscorpio . é : ; ‘i ‘i . . + 255 152. Scorpion, ventral side . ; ri : . ‘ . 256 153. Scorpion, internal organs . : : : . y . 258 154. Epeira diadema . 3 ‘ . A a : » 259 155. Cattle tick . ; : : . : . ; : . 260 156. Itch mite. . . : . a 3 : ; . 260 157. Limulus, ventral view 3 . : : : » 261 158. Anodonta cygnea, entire animal . i : . 265 159. Anodonta cygnea, right valve, and animal : . 268 160. Anodonta, section of shell and mantle ‘ . 7 . 269 161. Anodonta cygnea, animal . ; » 270 162, Anodonta cygnea, dissection from left side : « 293 163. Anodonta cygnea, sections of gills : . ; : - 274 164. Anodonta, diagram of circulatory system. : ‘ . 276 165. Anodonta, embryo and glochidium_ @ . . . 278 166. Mytilus edulis. A ‘ : 5 i : * - 279 167. Teredo navalis_. . : : : ‘ ‘ si . 280 168. Chiton spinosus . : ; : : ‘ 4 ‘ + 281 169. Chiton, ventral view . : ; ; : . 282 170, Chiton, nephridial and genital epsieens. . a : . 283 171. Helix nemoralis . : Z 2 : : , a . 285 172. Triton nodiferus, shell : : i ‘ : . 286 173. Triton nodiferus, median section of shell : : . . 287 174. Solarium perspectivum, under side. : : : . 288 175. Terebra oculata, shell ; : ; ‘i . 289 176. Cyprea moneta, animal expanded, in its shel : . . 290 177. Doris tuberculata . : 2 4 ; ‘i : . 290 178. Shell-bearing Pteropoda : zi ; . . 291 179. Patella vulgata, animal, ventral view . r ‘ ¢ . 292 180, Limax, lung-cavity, etc. : : és és : 293 181. Triton nodiferus . . . . . a : + 294 xxll FIG. 182. 183. 184. 185. 186. 187. 188. 189. 190. Ig]. 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. LIST OF ILLUSTRATIONS Sepia cultrata Nautilus pompilius Nautilus pompilius, section of shen Spirula peronii Sepia cultrata, shell Loligo vulgaris Argonauta argo Chromatophore of denis Sepia cultrata, dissected Nautilus pompilius, anatomy Sepia officinalis, jaws Sepia officinalis, enteric canal Nautilus pompilius, oral surface of male wid Pate Balanoglossus Balanoglossus, diagrammatic sagittal section of anterior aud : Ascidia Ascidia Ascidia, diagram of ipncitumieals section Ascidia mammillata, larva Diagram of metamorphosis of larva into fixed Ascidian Botryllus violaceus Amphioxus lanceolatus, venta anit side view Amphioxus, diagram of anatomy Amphioxus lanceolatus, sections . Dogfish, fins, ete. Lacerta viridis Lepus cuniculus, lateral view ee dkeleeawr with outline sebaay . Scyllium, vertebree Lizard, vertebre of Lepus cuniculus . Scyllium canicula Lacerta agilis, three views of dell Fore and hind limbs of vertebrate, diagram Tooth, longitudinal section, semi-diagrammatic Scyllium canicula, dissection Lacerta agilis, viscera in their natural relations Circulation of a fish, diagram Scyllium canicula, brain, dorsal view PAGE 297 298 299 301 301 302 303 304 305 306 307 3°07 3°99 31 I 312 34 315 317 320 321 322 323 325 327 329 330 33t 334 335 336 338 349 34t 343 345 348 351 353 FIG, 220, 221, 222. 223. 224. 225. 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. LIST OF IILLUSTRATIONS Eye of man, diagrammatic horizontal section Petromyzon marinus : j : : Myxine glutinosa, head 2 : : . Petromyzon marinus . : : ‘ . Scyllium canicula, side view of sical : : Scyllium canicula, dissection ‘i : ‘ Diagram of the vascular system of a ish Scyllium catulus . Dogfish, egg-case Scyllium, embryo, with wile etc. Lamna cornubica European sting-ray (HeSiaphats sueiaes) Skeleton of Urolophus testaceus . Heptanchus, side view of skull Salmo fario, fins, etc. Salmo fario, caudal end of eiiebe cata Pleuronectes cynoglossus Ctenoid and ganoid scales Polypterus birchir Skull of sturgeon Salmo fario, entire skull, left site Premaxille of Sargus Hippocampus (sea-horse) Ceratodus fosteri Ceratodus fosteri, anterior partion of deeleten Rana temporaria : Rana temporaria, skeleton . ; Rana temporaria, skull, different views Rana esculenta, shoulder girdle Rana esculenta, pelvic girdle from right sae Rana temporaria, dissection from left side Rana temporaria, heart with cavities laid open Rana temporaria, arterial system, etc. . Rana temporaria, venous system, etc. Rana esculenta, brain from above and below Rana esculenta, urinogenital organs of male . Rana esculenta, urinogenital organs of female xxili PAGE 357 361 362 363 371 373 376 378 382 385 386 387 388 399 391 395 397 398 399 399 400 40 402 404 405 406 409 412 413 415 416 417 420 421 424 426 428 429 xxiv FIG. 258. 259. 260. 261. 262. 263. 264. 265. 266. 267. 268, 269. 270. 271. 272. 273. 274. 275. 276, 277. 278. 279. 280. 281. 282. 283. 284. 285. 286, 287. 288. 289. 290. 291. 292. 293- 294. 295. LIST OF ILLUSTRATIONS Rana temporaria, stages in life-history Salamandra maculosa Siren lacertina Pygopus lepidopus Hatteria punctata A Grecian tortoise, Testudo graeca . Skeleton of crocodile . Cistudo lutaria Chelone midas Skull of rattlesnake Pectoral arch and sternum of senna age Heart of monitor, Varanus . Brain of alligator, from above Pineal eye of Hatteria punctata, section Poison apparatus of rattlesnake Columba livia, diagram with most of feabices coud Columba livia, feather . i Pterylosis of Columba livia i . ‘ Columba livia, bones of the trunk Columba livia, cervical vertebra . Columba livia, sacrum of nestling Columba livia, skull of young. Columba livia, hyoid apparatus Columba livia, bones of left wing 2 Columba livia, bones of left manus of nestling Columba livia, left innominate of nestling Columba livia, bones of left hind-limb Columba livia, part of left foot of embryo Columba livia, muscles of left wing Columba livia, dissection from right side Heart of pigeon, dorsal aspect Columba livia, brain, different views Eye of pigeon Columba livia, right ‘onommidan labyrinth . ear Columba livia, male urinogenital organs Columba livia, female urinogenital organs Feather of cassowary . : Wing of nestling of Opisthocomus el of adult donee PAGE 430 432 433 437 438 439 441 442 443 445 446 448 449 451 454 458 460 462 463 464 465 466 467 468 469 47° 471 472 473 475 478 479 480 481 482 482 484 486 FIG, 296. 297. 298. 299. 300. 301. 302. 303. 304. 305. 306. 307. 308. 309. 310. 311. B12: 313. 314. 315. 316. 317. 318. 319. 320. 321. 322. 323. 324. 325. 326. 327% LIST OF ILLUSTRATIONS Gallus bankiva, domestic fowl, egg at time of hatching Lepus cuniculus, side view of skeleton with outline of body Lepus cuniculus, atlas and axis Lepus cuniculus, skull, side, and ventral view Lepus cuniculus, shoulder girdle : Lepus cuniculus, distal end of fore-leg and carpus Lepus cuniculus, innominate bones and sacrum . Lepus cuniculus, bones of hind foot Lepus cuniculus, lateral dissection of head, neck, and oo Lepus cuniculus, stomach, intestine, and liver, etc. Lepus cuniculus, heart, from right side Lepus cuniculus, the vascular system Lepus cuniculus, larynx, ventral and dorsal views Lepus cuniculus, brain, dorsal and ventral view Lepus cuniculus, two dissections of brain Lepus cuniculus, longitudinal vertical section of brain Lepus cuniculus, urogenital organs 3 Lepus cuniculus, anterior end of vagina, with ahs uterus, etc. Duck-bill, Ornithorhynchus anatinus Spiny ant-eater, Echidna aculeata Virginian Opossum, Didelphys virginiana Dasyure, Dasyurus viverrinus Rock wallaby, Petrogale xanthopus Koala, Phascolarctos cinereus Unau, or two-toed sloth Tatu armadillo, Dasypus sexcinctus Scaly ant-eater, Manis pentadactyla Aard-vark, Orycteropus capensis . Killer, Orca gladiator . Section of upper jaw, with baleen plates, of Baenoper Harbor seal, Phoca vitulina . Bat, Synotus barbastellus XXV PAGE 489 492 494 497 501 502 503 504 529 530 531 532 533 534 534 535 536 540 542 MANUAL OF ZOOLOGY INTRODUCTION Zoology, the branch of Natural History which deals with animals, is one of the two subdivisions of the great science of Biology, which takes cognizance of all orxganisms, or things having life, as distinguished from such lifeless natural objects as rocks and minerals. The second of the two subdivisions of Biology is Botany, which deals with plants. The subject-matter of Zoology, then, is furnished by the animals which inhabit the land-surface, the air, and the salt and fresh waters of the globe; the aim of the science is to find out all that can be known of these animals, their structure, their habits, their mutual relationships, their origin. The first step in the study of Zoology is the recognition of the obvious fact that the innumerable individual animals known to us may be grouped into what are called species, the members of which resemble one another so closely that to know one is to know all. The following example may serve to give the reader a fairly accurate notion of what zoologists understand by species, and of the method of naming species which has been in use since the time of the great Swedish naturalist Linnzeus. B 1 2 MANUAL OF ZOOLOGY The domestic cat, the European wild cat, the ocelot, the leopard, the tiger, and the lion are animals which agree with one another in the general features of their organisation — in the number and form of their bones and teeth, in the possession of retractile claws, and in the position and characters of their internal organs. No one can fail to see that these animals, in spite of differences of size, colour, markings, etc., are all, in the broad sense of the word, “cats.” This is expressed in the language of systematic Zoology by saying that they are so many species of a single genus. According to the system of dnomial nomenclature intro- duced by Linnzeus, each kind of animal receives two names —one the generic name, common to all species of the genus ; the other the specific name, peculiar to the species In question. Both generic and specific names are Latin in form, and are commonly Latin or Greek in origin, although frequently modern names of persons or places, with Latinised terminations, are employed. In giving the name of an ani- mal, the generic name is always placed first, and is written with a capital letter, the specific name following it, and being written, as a rule, with a small letter. For instance, to take the examples already referred to, the domestic cat is called Feds domestica, the European wild cat F. catus, the leopard /. pardus, the tiger F. Herts, the lion F. Zo. Thus the systematic name of an animal is something more than a mere appellation, since it indicates the affinity of the species with other members of the same genus: to name an animal is, in fact, to classify it. It is a matter of common observation that no two indi- viduals of a species are ever exactly alike: two tabby cats, for instance, however they may resemble one another in the general characters of their colour and markings, invariably INTRODUCTION 3 present differences in detail by which they can be readily distinguished. Jndividual variations of this kind are of universal occurrence. Moreover, it often happens that the members of a species are divisible into groups distin- guishable by fairly constant characters: among domestic cats, for instance, we find white, black, tabby, gray, and tor- toiseshell cats, besides the large long-haired Persian breed, and the tailless Manx cat. All these are distinguished as varieties of the single species, edis domestica. It is often difficult to decide whether two kinds of ani- mals should be considered as distinct species or as varieties of a Single species, and no universal rule can be given for determining this point. Among the higher animals mutual fertility is a fair practical test, the varieties of a species usually breeding freely with one another and producing fer- tile offspring, while distinct species either do not breed together or produce infertile Ayd7ids or mules. Compare, for instance, the fertile mongrels produced by the union of the various breeds of domestic dog with the infertile mule produced by the union of the horse and ass. But this rule is not without exception, and in the case of wild animals is, more often than not, impossible of application: failing it, the only criterion of a “good species” is usually the pres- ence of constant differences from allied species. Suppose, for instance, that a naturalist receives for description a number of skins of wild cats, and finds, after an accurate examination, that in some specimens the tail is two-thirds the length of the body and the skin of a uniform reddish tint with a few markings on the head, while in the rest the tail is nearly half as long as the body and the skin tawny with black stripes. If there are no intermediate grada- tions between these two sets of individuals, they will be placed without hesitation in distinct species: if, on the 4 MANUAL OF ZOOLOGY other hand, there is a complete series of gradations between them, they will be considered to form a single variable species. As, therefore, animals have to be distinguished from one another largely by structural characters, it is evident that the foundations of a scientific Zoology must be laid in Morphology, the branch of science which deals with form and structure. Morphology may be said to begin with an accurate examination of the external characters ; the divi- sions of the body, the number and position of the limbs, the characters of the skin, the positions and relations of the mouth, eyes, ears, and other important structures. Next the internal structure has to be studied, the precise form, posi- tion, etc., of the various organs, such as brain, heart, and stomach being made out: this branch of morphology is distinguished as Anatomy. And, lastly, the various parts must be examined by the aid of the microscope, and their minute structure, or Histology, accurately determined. It is only when we have a fairly comprehensive knowledge of these three aspects. of a given animal — its external charac- ters, its rough anatomy, and its histology — that we can with some degree of safety assign it to its proper position among its fellows. An accurate knowledge of the structure of an animal in its adult condition is not, however, all-sufficient. Nothing has been made more abundantly clear by the researches of the last half-century than that the results of anatomy and histology must be checked, and if necessary corrected, by Embryology — 7.c. by the study of the changes undergone by animals in their development from the egg to the adult condition. A striking instance is afforded by the common barnacles which grow in great numbers on ships’ bottoms, piers, etc. The older zoologists, such as Linnzeus, grouped INTRODUCTION 5 these creatures, along with snails, mussels, and the like, in the group Mollusca, and even the great anatomical skill of Cuvier failed to show their true position, which was made out only when Vaughan Thompson, about fifty years ago, proved, from a study of the newly hatched young, that their proper place is among the Crustacea, in company with crabs, shrimps, and water-fleas. Given a sound knowledge of the anatomy, histology, and embryology of animals, their Classification may be attempted — that is, we may proceed to arrange them in groups and sub-groups, each capable of accurate definition. The general method of classification employed by zoolo- gists is that introduced by Linnzeus, and may be illustrated by reference to the group of cats which we have already used in the explanation of the terms genus, species, and variety. We have seen that the various kinds of true cat — domes- tic cat, lion, tiger, etc.—together constitute the genus Felis. Now there is one member of the cat-tribe, the cheetah, or hunting leopard, which differs. from all its allies in having imperfectly retractile claws and certain peculiari- ties in its teeth. It is therefore placed in a distinct genus, Cynelurus, to mark the fact that the differences separating it from any species of Felis are of a more fundamental char- acter than those separating the species of Felis from one another. The nearest allies of the cats are the hyzenas, but the presence of additional teeth and non-retractile claws — to mention only two points— makes the interval between hysenas and the two genera of cats far greater than that between Felis and Cynelurus. The varying degree of differ- ence is expressed in classification by placing the hyzenas in a separate family, the Hyenide, while Felis and Cynzelurus 6 MANUAL OF ZOOLOGY are placed together in the family Aezde. Similarly the civets and mongooses form the family Viverride ; the dogs, wolves, jackals, foxes, etc., the family Cande,; bears, the family Urstde, and so on. All the foregoing animals have sharp teeth adapted to a flesh diet, and their toes are armed with claws. They there- fore differ fundamentally from such animals as sheep, deer, pigs, and horses, which have flat teeth adapted for grinding vegetable food, and hoofed feet. The differences here are obviously far greater than those between any two of the families mentioned above, and are emphasised by placing the flesh-eater in the order Carnivora, the hoofed animals in the order Ungulata. In the same way gnawing animals, such as rats, mice, and beavers, form the order Rodentia, pouched animals, such as kangaroos and opossums, the order Marsupiaa,; and so on. Carnivora, Ungulata, Rodentia, Marsupialia, etc., although differing from one another in many important respects, agree in the possession of a hairy skin and in the fact that they all suckle their young. They thus differ from birds, which have a covering of feathers, and hatch their young from eggs. The differences here are considerably more important than those between the orders of quadrupeds referred to, and are expressed by placing the latter in the class /ammavia, while birds constitute the class dves. In the same way the scaly, cold-blooded lizards, snakes, tortoises, etc., form the class keptiia, the slimy-skinned, scaleless frogs, toads, and sala- manders the class Amphiéza ; and the finned, water-breathing fishes the class Pisces. Mammals, birds, reptiles, amphibians, and fishes all agree with one another in the possession of red blood and an inter- nal skeleton — an important part of which is the backbone or vertebral column —and in never having more than two INTRODUCTION 2 pairs of limbs. They thus differ in some of the most funda- mental features of their organisation from such animals as crabs, insects, scorpions, and centipedes, which have colour- less blood, a jointed external skeleton, and numerous limbs. These differences—far greater than those between classes —are expressed by placing the backboned animals in the phylum or sub-kingdom Chorda/a, the many-legged armoured forms in the phylum Arthropoda. Similarly, soft- bodied animals with shells, such as oysters and snails, form the phylum AZollusca, polypes and jellyfishes the phylum Celenterata. And, finally, the various phyla recognised by zoologists together constitute the kingdom Azimasa. Thus the animal kingdom is divided into phyla, the phyla into classes, the classes into orders, the orders into families, the families into genera, and the genera into species, while the species themselves are assemblages of individual animals agreeing with one another in certain constant characters. It will be seen that the zvdzzdual is the only term in the series which has a real existence: all the others are mere groups formed, more or less arbitrarily, by man. To return to the animal originally selected as an example, it will be seen that the zoological position of the domestic cat is expressed as follows : — Kingdom — ANIMALIA. Phylum — Cuorpata. Class — MAMMALIA. Order — CarNIVORA. Family — Fetde. Genus — Felis. Species —F. domestica. The object of systematic zoologists has always been to 8 MANUAL OF ZOOLOGY find a natural as opposed to an artificial classification of animals. Good instances of artificial classification are the grouping of bats with birds on the ground that both possess wings, and of whales with fishes on the ground that they both possess fins and live in the water. An equally good example of a natural classification is the grouping of both bats and whales under the head of Mammalia because of their agree- ment, in all essential points of anatomy, histology, and embryology, with the hairy quadrupeds which form the bulk of that class. With the older zoologists the difficulty was to find some general principle to guide them in their arrangement of animals— some true criterion of classification. It was believed by all but a few advanced thinkers that the in- dividuals of each species of animal were descended from a common ancestor, but that the original progenitor of each species was totally unconnected with that of every other, having, as Buffon puts it, “participated in the grace of a dis- tinct act of creation.”’ To take an instance: all wolves were allowed to be descended from a pair of ancestral wolves, and all jackals from a pair of ancestral jackals, but the original pair in each case was supposed to have come into being by a supernatural process of which no explanation could or ought to be offered. Nevertheless it was obvious that a jackal was far more like a wolf than either of them was like a tiger, and that in a natural system of classification this fact should be expressed by placing the wolf and jackal in one family, the tiger in another. All through the animal kingdom the same thing occurs : no matter what group we take, we find the species com- posing it resemble one another in varying degrees, or, as it is sometimes expressed, have varying degrees of relationship to one another. On the view that each species was sepa- INTRODUCTION 9 rately created, the word relationship was used in a purely metaphorical sense, as there could, of course, be no real relationship between two groups of animals having a totally independent origin. But it was assumed that creation had taken place according to a certain scheme in the Divine Mind, and that the various species had their place in this scheme like the bits of glass in a mosaic. The problem of classification was thus to discover the place of each species in the pattern of the unknown design. The point of view underwent a complete change when, after the publication of Darwin’s Origin of Species in 1859 the Doctrine of Descent or of Organic Evolution came to be generally accepted by biologists. A species is now looked upon, not as an independent creation, but as having been derived by a natural process of descent from some pre- existing species, just as the various breeds of Domestic Fowl are descended from the little jungle-fowl of India. On this view the resemblances between species referred to above are actually matters of relationship, and species are truly allied to one another in varying degrees, since they are descended from a common ancestor. Thus a natural classification becomes a genealogical tree, and the problem of classifica- tion is the tracing of its branches. This, however, is a matter of extreme difficulty. Repre- senting by a tree the whole of the animals which have ever lived on the earth, those existing at the present day would be figured by the topmost twigs, the trunk and main branches representing extinct forms. Thus the task of arranging animals according to their relationships would be an almost hopeless one but from two circumstances: one, that remains of many extinct forms have been preserved: the other, that the series of changes undergone by an ani- mal in its development from the egg often forms an epitome 10 MANUAL OF ZOOLOGY of the changes by which, in the course of ages, it has been evolved from an ancestral type. Evidence furnished by the last-named circumstance is, of course, furnished by embry- ology: the study of extinct animals constitutes a special branch of morphology to which the name Paleontology is applied. The solid crust of the earth is composed of various kinds of rocks divisible into two groups: (1) gneous rocks, such as granite and basalt, the structure of which is due to the action of the internal heat of the globe, and which originate below the surface and are not arranged in layers or strata ; (2) Aqueous or sedimentary rocks, which arise by the disin- tegration, at the surface of the earth, of pre-existing rocks, the fragments or débris being carried off by streams and rivers and deposited at the bottom of lakes or seas. Being formed in this way by the deposition of successive layers or strata, the sedimentary rocks have a s/ratvfied structure, the lowest being in every case older than the more superficial layers. The researches of geologists have shown that there is a general order of succession of stratified rocks ; that they may be divided into three great growps, each representing an eva of time of immense but unknown duration, and that each group may be subdivided into more or fewer syszems of rocks, each representing a lesser period of time. Imbedded in these rocks are found the remains of various extinct animals in the form of what are called fossils. In the more recent rocks the resemblance of these to the hard parts of existing animals is perfectly clear; we find shells hardly differing from those we pick up on the beach, bones easily recognisable as those of mammals, birds, or fishes, and so on. But in the older rocks the fossils are in many cases so different in character from the animals existing at the present day as to be referable to no existing order. We INTRODUCTION 11 find birds with teeth, great aquatic reptiles as large as whales, fishes, molluscs, Crustacea, etc., all of an entirely different type from any now existing. We thus find that the former were in many cases utterly unlike the present animal inhabi- tants of the globe, and we arrive at the notion of a succession of life in time, and are even able, in exceptionally favourable circumstances, to trace back existing forms to their extinct ancestors. By combining the results of comparative morphology, embryology, and paleontology we get a department of Zoology called Phylogeny, the object of which is to trace the pedigrees of the various groups. There are, however, very few cases in which this can be done with any approach to exactness ; most “ phylogenies ”’ are purely hypothetical, and merely represent the views at which a particular zoolo- gist has arrived after a more or less exhaustive study of the group under discussion. Animals may also be studied from the point of view of Distribution. One aspect of this study is inseparable from Paleontology, since it is obviously necessary to mention in connection with a fossil the particular system or systems of rocks in which it occurs: thus we distinguish geological distribution or distribution in time. The distribution of recent forms may be studied under two aspects, their horizontal or geographical distribution, and their vertical or bathymetrical distribution. To men- tion the latter first, we find that some species exist only on plains, others — hence called a/ine forms —on the higher mountains ; that some marine shells, fishes, etc., always keep near the shore (4¢toral species), others live at great depths (abyssal species), while others ( Ze/agic species) swim on the surface of the ocean. Among aquatic animals, moreover, whether marine or fresh-water, three principal modes of life 12 MANUAL OF ZOOLOGY are to be distinguished. There are animals such as jelly- fishes, which float on or near the surface of the water, and are carried about passively by currents; such forms are included under the term Plank/on. Most fishes, whales, and cuttle-fishes, on the other hand, are strong swimmers, and are able to traverse the water at will in any direction ; they together constitute the MVef/on. Finally, such animals as crabs, oysters, sponges, zoophytes, etc., remain permanently fixed to or creep over the surface of the bottom, and are grouped together as the Benthas. Under the head of geographical distribution we have such facts as the absence of all land-mammals, except bats in New Zealand and the Polynesian Islands, the presence of pouched Mammals, such as kangaroos and opossums, only in some parts of America and in Australia and the adjacent islands, the entire absence of finches in Australasia, and so on. We find, in fact, that the fawna — ze. the total animal inhabitants — of a country is to a large extent independent of climate, and that the faunze of adjacent countries often differ widely. In fact, it is convenient in studying the geo- graphical distribution of animals largely to ignore the ordi- nary division into continents, and to divide the land-surface of the globe into what are called 200-geographical regions. There are still two departments of zoological science to be mentioned. As it is impossible to have a right under- standing of a machine without knowing something of the purpose it is intended to serve, so the morphological study of an animal is imperfect without some knowledge of its Physiology, ¢.c. of the functions performed by its various parts, and the way in which they work together for the welfare of the whole. Not only may we study the action of a given animal’s organs, but also the actions of the animal as a whole, its INTRODUCTION 13 habits, its relations to other animals, whether as friends, as enemies, or as prey, to the vegetable kingdom, and to its physical surroundings, such as temperature, humidity, etc. In a word, the whole question of the relation of the organism to its enwronment gives us a final and most important branch of Natural History which has been called Ethology or Bionomics. SECTION I.—PHYLUM PROTOZOA 1. THE RHIZOPODA Tue simplest members of the animal kingdom are for the most part, too small to be visible without the aid of a micro- scope, or at least so small as to appear to the unassisted eye as extremely minute specks, not distinguishable, unless in unusually active movement, from small particles of non-living matter. Representatives of this class of simple minute ani- mals are to be found living under a variety of different con- ditions; they are abundant in fresh water, running or stagnant, and they are equally numerous in the sea, while they are also to be founc living in the fluids of cavities in the bodies of higher animals. An example which will serve to illustrate some of the main features of the class is the Proteus animalcule or Ameba. Amceba (Fig. 1) is some- times to be found by searching with the aid of the micro- scope in water from stagnant pools. To the unpractised beginner it is a difficult task to discriminate between the microscopic particles of non-living matter which form the main part of the sediment at the bottom of such a pool — débris of animals, vegetable or mineral nature—and the object of which he is in search. Numerous minute bodies will doubtless be seen which their active movements among the motionless particles show to be endowed with life. But 14 SECT. I PHYLUM PROTOZOA 15 Amceba is not one of these. It is to be recognised as a glassy-looking, irregularly shaped particle with a definite out- line. From a particle of some crystalline mineral substance, to which such a description would equally well apply, Ameeba would soon be distinguishable owing to the cir- cumstance that it is constantly changing its shape. This change is effected by the pushing out of projections or processes, called pseudopods or pseudopodia ( psd), which Fic. 1.—Ameeba proteus, a living specimen. c. vac, contractile vacuole, nu, nucleus; ~sd, pseudopods. (From Parker's Biology, after Gruber.) undergo various alterations of size and shape, and may be- come withdrawn, other similar processes being developed in their place. At the same time careful watching shows that the Amceba is also, with extreme slowness, changing its position. This it effects by a kind of streaming motion. A projection forms itself on one side, and the entire substance of the Amceba gradually streams into it; a fresh projec- tion appears towards the same side, the streaming move- ment is repeated, and, by a constant succession of such movements, an extremely gradual locomotion, which it often takes very close watching to detect, is brought about. In these movements, it is to be noticed, the Amceba is influenced 16 MANUAL OF ZOOLOGY SECT. to some extent by contact with other minute objects; when the processes come in;contact with small grains of sand or other similar particles, their movements are modified in such a way that the Amceba, in its slow progress onwards, passes on one side of. them, so that it might be said to feel its way among the solid particles in a drop of sediment. Judging from the nature of the movements, we are obliged to infer that the substance of which this remarkable object is composed must be soft and semi-fluid, yet not miscible with the water, and, therefore, preserving a sharp contour. ‘These and other characteristics to be mentioned subsequently enable us to conclude that we have to do with the substance of complex chemical composition termed procoplasm, which constitutes the vital material of all living organisms whether animals or plants. In Amceba the protoplasm is clearly dis- tinguishable into two parts, an outer homogeneous, glassy- looking layer completely enclosing a more granular internal mass. Examination of the Amceba with a fairly high power of the microscope reveals the presence in its interior of two objects which with a low power we should be likely to overlook. One of these is a small rounded body of a homogeneous appear- ance, which preserves its form during all the changes which the Amceba as a whole undergoes. This is termed the nucleus (Fig. 1, uz) ; it is enclosed in an extremely delicate membrane, and consists of a protoplasmic material differing from that which forms the main bulk of the Amceba in con- taining a substance which refracts the light more strongly and which has a stronger affinity for certain colouring matters. The other minute object to be distinguished in the interior appears as a clear rounded space (¢. vac) in the protoplasm. When this is watched it will be observed to increase gradually in size till it reaches a maximum of, let us I PHYLUM PROTOZOA iy say, a fifth of the total diameter of the Amceba, when by a sudden contraction of its walls, it suddenly disappears, to reappear presently and gradually grow again to its maxi- mum size. This pulsating clear space is the contractile vacuole. By watching the Amceba carefully for some time we may be enabled to observe that the movements of the proto- plasm of the body not only effect locomotion, but are con- nected also with the reception of certain foreign particles of organic nature —ze., either entire minute animals or plants, or minute fragments of larger forms — which form the Jood of the Amoeba, —into the interior of the protoplasm. A process of the protoplasm is pressed against such a par- ticle of food, which becomes sunk in the soft substance, and passes gradually into the interior. Here it becomes surrounded by a little globule of watery fluid, and by degrees partially or wholly disappears; the part, if any, which remains, subsequently passes outwards from the pro- toplasm into the surrounding water. The matter which dis- appears evidently mixes with the protoplasm and adds to its bulk. When food is abundant the Amceba increases in bulk — more food being ingested than is required for simply main- taining the size unaltered —and soon a remarkable change takes place. The processes become withdrawn, and a fissure appears dividing the Amceba into two parts (Fig. 2). This fissure grows inwards, and the two parts become more and more completely separated from one another, till eventually the separation becomes complete, and we have two dis- tinct Amcebe resulting from the division of the one. While the protoplasm has been undergoing this division into two halves the nucleus also divides, and each of the two new Amcebee possesses a nucleus similar to the original one, € 18 MANUAL OF ZOOLOGY SECT. and developed from it by division. It is mainly by this simple process of division into two, or &/nary fission, as it is called, that reproduction or multiplication takes place in the Ameeba. Fic. 2.—Amceba polypodia in successive phases of division. The light spot is the contractile vacuole; the dark the nucleus. (From Lang’s 7ext-Book, after F. E. Schulze.) Amceba thus consists of an undivided particle of proto- plasm containing a nucleus. To such a particle the term cell is applied. In higher groups the animal when fully developed, consists of a number of such cells, usually differ- ing in character in different parts ; and simple animals, such { PHYLUM PROTOZOA 19 as Amceba, in which the entire animal consists throughout life of a single cell, are distinguished as unicel/ular from the multicellular form in which a number of cells are combined. The whole of the great group or phylwm of animals — the Protozoa — to which Amceba belongs, are distinguished from all the remaining groups of the animal kingdom — the Metazoa —by their unicellular character. Among the Protozoa a large number resemble Amceba in the possession of pseudopodia or processes of the protoplasm. The pseudopodia-bearing Protozoa constitute one of the great divisions or c/asses into which the Protozoa are divided by zoologists — the class known as the Rhizopoda. In only a comparatively small proportion of the members of this class have the pseudopodia the comparatively short and blunt shape which they have in Amceba. All the Rhizopoda with comparatively short and thick pseudopodia are grouped together to form one of the leading divisions or orders of Rhizopoda—the order Lobosa. Amoeba is one of the simplest of these. The largest among the near relatives of Ameeba is Pedomyxa, which may be as much as 8 mm. in diameter, so that it is readily visible to the naked eye; its pseudopodia are very short and broad, and, instead of a single nucleus, it contains a large number as well as many contractile vacuoles. Other Lobosa differ from Ameeba in the presence of a shell or zes¢ enclosing the protoplasm. One of these is Difiugia (Fig. 3, D), which is very common in fresh water. Difflugia has a flask-shaped test formed of agglutinated sand-grains and other foreign particles. The main bulk of the protoplasm is contained in the interior of the shell, but comparatively long pseudopodia are capable of being pushed out through the mouth of the flask. It pierces the wall of the cells of Spirogyra, inserts its pseudopods, lift- ing the entire cell-contents out and passing them into its 20 MANUAL OF ZOOLOGY SECT. body within the shell (Stokes). An even commoner member of the group is Avcedla (Fig. 3, C). Arcella has a shell much wider than that of Difflugia, convex on one side, flat on the other. In the middle of the flat surface is a rounded opening. The shell of Arcella is of a transparent, tough- Fic._3.—A, Quadrula symmetrica; B, Hyalosphenia lata; C, Arcella vulgaris; D, Difflugia pyriformis. (From Lang’s Comparative Anatomy, after Schulze and Wallich.) material, which is said to be chitinotd from the fact that it appears to resemble a substance termed chitin, of a horny consistency, very general in its occurrence in the integument of animals. This chitinoid test exhibits a minute pattern when examined under a high power of the microscope. I PHYLUM PROTOZOA 21 The bulk of the protoplasm is, as in Difflugia, enclosed within the test, but a considerable portion of it may be pushed out in the form of pseudopods. Several nuclei and a contractile vacuole are contained in the protoplasm. The body of the animal is colourless, and is attached to its test, says Stokes, “ by fine threads of its own substance.” There are several species in our fresh-water pools, among them Arcella vulgaris (Fig. 3, C). All the rest of the Rhizopoda differ from the Lobosa in having the pseudopodia in the shape of slender threads. Of these a remarkable and interesting group is the order . Foraminifera. A Foraminifer has a shell which is nearly always composed of carbonate of lime. This we can readily demonstrate by placing a drop of hydrochloric or nitric acid on a mass of the shells, when they dissolve with efferves- cence. In some Foraminifera the shell has a wide opening on the exterior as in Difflugia and Arcella; in others there is no large opening, but the wall of the shell is perforated by a number of minute pores scattered over its surface. The greater part of the protoplasm is enclosed within the shell, but part of it (Fig. 4) streams out from the single large opening, or from the pores, in the form of slender thread-like radiating pseudopodia, which, when they come in contact with one another, may coalesce, and may in this way give rise to a network. The protoplasm in the interior contains a nucleus, but no contractile vacuole. The shape of the shell is sometimes spherical, sometimes flask-shaped, sometimes oval or elliptical. Only in a comparatively small number of Foraminifera does it remain simple (z, 2) ; in the great majority, though the shell when first formed is simple, a little process or bud of protoplasm soon projects through the wide opening or through the pores; this increases in size, and becomes enclosed in a shell like the original one, 22 MANUAL OF ZOOLOGY SECT. i Ye ! WY AY Vey 3.Squammulina 4Miliota | In, ted Hy f f Fic. 4.— Various forms of Foraminifera. In 4, Miliola, 2, shows theliving animal; 4, the same killed and stained; a, aperture of shell; 4, food particles; x, nucleus; s/, shell. (From Biitschli’s Protozoa and Claus’s Zoology.) I PHYLUM PROTOZOA 23 but usually a size larger, remaining in firm connection with it, the cavities of the two remaining in communication with one another through the original opening or openings at which the bud first appeared. From this second shell in turn a bud is given off in the same manner, and the process is repeated again and again, until, instead of a single particle of protoplasm enclosed in a single shell, there is formed a composite structure, made up of a number of particles of protoplasm, each with its nucleus, and each enclosed in a shell, the whole of the shells being firmly united togethei, and the whole of the particles of protoplasm being in con- tinuity through the apertures of communication. ‘The several parts of such a compound shell, which are known as the chambers, are variously arranged in different Forami- nifera (Fig. 5), according to the way in which the succes- sive buds have been given off. In some the buds succeed one another in a straight line, and the compound shell which results (7) has consequently its chambers arranged in a straight row. Or the chambers may be developed alternately on opposite sides of the original cell (5), or with the new.chambers entirely overlapping their prede- cessors (¢). In other cases the development of the buds takes a winding course, the resulting shell having its cham- bers arranged in some form of spiral, lke the spiral of a watch-spring or of acorkscrew. Such a spiral shell (6—zz) assumes a great variety of forms in different Foraminifera, owing to differences, not only in the shape of the chambers themselves, but also in the nature of the spiral in which they are arranged. In many cases the shell is further complicated by the development of what is termed the supplemental shell (Fig. 5,6), a deposit of carbonate of lime outside the original shell, traversed by a complex system of fine canals contain- 24 MANUAT. OF ZOOLOGY SECT. ing protoplasm, and sometimes produced into a number of relatively large spines. Though the great majority of Foraminifera have dense shells composed of carbonate of lime, there are many in which the shell resembles that of Difflugia in being com- posed of foreign particles, such as sand-grains, cemented together ; these are termed the avenaceous Foraminifera ; some of these have one large opening, some a number of pores. In certain fresh-water forms, such as Gromia, the shell is chitinoid. In Gromia (Fig. 4, 7) the chitinoid shell has a wide mouth through which the protoplasm protrudes to form a layer enclosing the shell and giving off the pseudopodia. Little is known of the reproduction of the Foraminifera. But in some a remarkable mode of reproduction has been observed. The protoplasm in the interior of the shell divides up into a number of particles. Each of the bodies thus formed possesses, instead of pseudopodia, a single delicate whip-like appendage — the flage//um— which lashes to and fro and propels the embryo Foraminifer through the water. Such a flagellum-bearing embryo is termed a flaged/u(a. All the Foraminifera, with the exception of Gromia and one or two allied forms, are marine, and the greater number are pelagic —7.c., live in the surface waters of the open sea— though they occur also inshore, and at almost all depths. The pelagic Foraminifera are most abundant in warm lati- tudes, where they occur in enormous numbers. The ocean floor at depths of five hundred to twenty-eight hundred fathoms is covered in many places with a mud-like deposit which effervesces and dissolves when acid is added, and which, when examined under the microscope, is found to consist mainly of the shells of Foraminifera, which must have fallen down from above on the death of the animals. I PHYLUM PROTOZOA 25 5. Spiroloculina i1.Nummulites 9.Planorbulina Fic. 5.—Shells of Foraminifera. In 3, 4, and 5, 2 shows the surface view, and 4a section; Sa is a diagram of a coiled cell without supplemental skeleton; 86 of a similar form with supplemental skeleton (s. s#); and zo of a form with over- lapping whorls; in zva half the shell is shown in horizontal section; 4 is a ver- tical section; ., aperture of shell; 1—z5, successive chambers, 1 pene always the oldest or initial chamber. (After Carpenter, Brady, and Biitschli.) 26 MANUAL OF ZOOLOGY SECT. From the name of the genus — G/odigerina (Fig. 5, 6) — which occurs in the greatest abundance in this deposit, it is known as the Glodigerina ooze. In the deepest parts of the ocean the Globigerina ooze is entirely absent, the calcareous shells of the Foraminifera apparently becoming entirely dis- solved before they can reach such great depths. It is inter- esting to note that similar deposits were formed in previous geological periods— the beds of cha/k of the Cretaceous period consisting, like the Globigerina ooze, in great measure of the shells of Foraminifera, though apparently not formed under the same conditions of depth. Another case of massive deposition of Foraminifera in a former geological period is the Mummulitic Limestone, a bed of limestone made up, for the most part, of the shells of comparatively gigantic Foraminifera, the Nummulites (Fig. 5, zz). A Rhizopod by no means uncommon in fresh water is the so-called sun-animalcule, Actinophrys sol. The body Fic. 6.— Actinophrys sol. a, axial filaments of pseudopods; ~, nucleus; #, pseudopod. (From Lang’s Comparative Anatomy, after Greenacher.) of Actinophrys (Fig. 6) is nearly spherical, and contains a large nucleus and numerous vacuoles, some of which, situ- ated near the surface, are contractile. The most charac- teristic feature is formed by the pseudopodia, which, instead PHYLUM PROTOZOA 27 I of being comparatively short and thick, as in Amceba and in (1assy] pue Simpy] Jaye ‘vozoz047 Syyosing wor1g) ‘tayonu ‘ze felpNpaur ‘pawe saonoea apMoRIIWOD ‘9v2 "2 + xXI09 ‘7.407 tosoydoyewoays ‘4 tpayiusem Ajysry ‘uoyiod yews e& “gq ‘ustuesio0 aus oy “Y ‘ITWIONYIIG umnueydsounoy — “2 “O14 3 ed RAF AY ERK er bg BA gx J Rey PoCh ade SS A733 ste iB a ie alee z A 3 aeey iS \ \ the other Lobosa, or extremely delicate, flexible, and thread- like, as in the Foraminifera, are slender, but comparatively stiff, and stand out straight from the surface of the sphere in a radiating manner: they are capable of only very slow 28 MANUAL OF ZOOLOGY SECT. movements. The pseudopodia owe their stiffness to the presence of a rod of chitinoid material which lies in the axis of each, and extends inward toward the middle of the pro- toplasm. A large nucleus lies in the centre of the body. A good many other genera are known which have pseudopodia of the same general character as those of Actinophrys, and these are accordingly grouped together as an order of Rhizopoda — the order Heliozoa. Of these other genera of Heliozoa, Actinospherium (Fig. 7) is somewhat more com- plex in structure than Actinophrys, the protoplasm being divided into a central mass — the exdosarc — in which the vacuoles are small, and an outer layer — the ectosarc — in which they are very large. Numerous nuclei are present, and bodies containing ch/orophyl/ — the characteristic green colouring matter of plants. It frequently occurs in com- pany with Actinophrys, among the leaves of Lemna and other plants, and feeds on microscopic forms, also Rotifers (Stokes). Some of the Heliozoa, instead of being composed like Actinophrys entirely of soft protoplasm, have support- ing and protecting hard parts. Such hard, or compara- tively hard, parts in any animal, whatever form they may assume, whether that of an enclosing shell or crust, or a system of internal bones or other firm structures, are known under the general term of ske/eton. In those Heliozoa in which a skeleton occurs it is sometimes a shell of aggluti- nated sand-grains, like the shell of Difflugia, or of the arena- ceous Foraminifera; or it may consist of loosely matted needle-like bodies composed of silica (Fig. 8, 7); or there may, as in Clathrulina, be a sphere of silica, perforated by numerous openings, enclosing the protoplasm. Clathrulina elegans (Fig. 8, 3) is common in many ponds, attached to the rootlets of Lemna, or duck-weed (Stokes). Reproduction takes place, as in Amceba, by binary fission. I PHYLUM PROTOZOA 29 2.Nuclearia 3.Clathrulina Fic. 8.— Various forms of Heliozoa. 3a, the entire animal; 34, the flagellula; ¢. vac, contractile vacuole; g, gelatinous investment; 2, nucleus; Asd, pseudo- pods; s&, siliceous skeleton; sf, spicules. (From BiitSshli’s Protozoa, after Schulze and Greeff.) 30 MANUAL OF ZOOLOGY SECT. But in some genera the process of fission under some circum- stances remains incomplete, the two protoplasmic bodies to which the fission gives rise remaining connected together by a bridge or isthmus of protoplasm, instead of becoming separated off in the shape of two independent animals, as in Amceba. Further, these two bodies may each in turn divide in the same incomplete way, so that four Heliozoans are developed, all remaining connected together; and by further repetitions of the same process a structure may be formed consisting of a large number of units all connected together by living substance. A structure of this kind, formed as a result of repeated incomplete division (or, in other cases, budding) from an original simple animal, is termed a colony, and the elements or units of which it is composed are termed zooids. How such a colony of unicellular Protozoa is to be distinguished from a multicellular animal or Metazoan (p. 19) will be explained at a later stage. It will at once be apparent that the compound Foraminifera are of the nature of colonies of unicellular zooids, each occupying one of the chambers of the shell, formed as the result of a process of repeated budding. In addition to the process of multiplication by fission multiplication also takes place in some Heliozoa by a pro- cess known as the formation of sforves. In spore-formation (a form of which has already been referred to as occurring in the Foraminifera) the protoplasm breaks up into numerous small parts, each of which eventually develops into the form of the parent. Usually the Protozoan passes into a qui- escent condition before this takes place; the pseudopodia become withdrawn, and the whole becomes enclosed in a firm envelope or sforocyst; this process is known as encys/a- zon. The spores in some of the Heliozoa, when set free, are provided each with two flagella (Fig. 8, 3, 4) which 1 PHYLUM PROTOZOA 31 subsequently become lost, pseudopodia appearing in their place. The Radiolaria are marine Rhizopoda which have exceed- ingly delicate, thread-lke pseudopodia (Fig. 9, psd) and a skeleton usually composed of silica. This skeleton may be composed of loosely woven needle-like bodies or sfzczles ; more usually it is in the form of a globular, conical, star- shaped, or disc-shaped shell, perforated by numerous open- ings, and often supported by spines which radiate out from Fic, 9. — Liteocircus annularis. cen¢. caps, central capsule; ext. caps. pr, extra- capsular protoplasm; z#/. caps. fv, intra-capsular protoplasm; #, nucleus; psd, pseudopods; skel, skeleton; 2, cells of Zooxanthella. (After Biitschli, from Parker’s Bzology.) the centre; sometimes (Fig. 10) there are several such shells one within the other. In some Radiolaria the skele- ton is composed not of silica, but of a chitinoid substance called acanthin. Embedded in the protoplasm is a perfor- ated membranous sac, the central capsule (Figs. 9 and 10, cent, caps), in the protoplasm within which is a single nucleus or a number of nuclei, and a number of oil-drops. There is no contractile vacuole, but in many Radiolaria the protoplasm outside the central capsule contains numerous non-contractile vacuoles, the presence of which gives it a frothy appearance. 32 MANUAL OF ZOOLOGY SECT. Radiolaria which give rise to colonies are exceptional, but a few cases occur. In these (Fig. 11) the central capsule divides again and again giving rise to a number of central capsules which remain embedded in a firm gelatinous sub- 3, inner the two outer spheres broken cent, caps, central capsule; B, section showing the relations of the skeleton to the animal: er, s&. 2, middle, 5% au, nucleus; sk 7,0 's Protosea, alter Haeckel and Hertwig.) protoplasm, ex caps. pr, sphere of skeleton away; Fic. 10. — Actinomma asteracanthion A, the shell with portions of stance — the vacuolated protoplasm outside the central cap- sules. Such a mass, which may attain considerable size, floats about freely in the sea. I PHYLUM PROTOZOA 33 In addition to reproduction by simple binary fission, spore-formation also occurs in some of the Radiolaria. The protoplasm contained in the central capsule breaks up into small masses, each of which becomes a flagel/uda provided with a flagelluin (Fig. 44, 2, &). In most of the Radiolaria there occur in the extra-capsular protoplasm minute yellow cells (Fig. 9, 2), which multiply Fic. 11. — Collozoum inerme. A—C, three forms of the entire colony, nat. size; D, a small colony showing the numerous capsules (c. caps) and extra-capsular protoplasm with vacuoles (vac) ; E, spores containing crystals (c); mega- and microspore. (From Biitschli’s Protozoa, after Hertwig and Brandt.) independently by binary fission. It has been proved that these are microscopic unicellular plants (Zooxanthella) of the class Algze, which live in the substance of the protoplasm of the living Radiolarian. Such an intimate association between two living organisms is known as symdzosis. There can be no doubt that this association is beneficial both to the Radiolarian and to the Alga. It is characteristic of the plant cell that under the action of light and in the presence D 34 MANUAL OF ZOOLOGY SECT. of the specially vegetable green colouring matter, chlorophyll, it is able to utilise for its nutrition the carbon dioxide or “carbonic acid gas” present in the air. The carbon is seized and made use of by the plant cell for the building up of such compounds as starch and sugar, while the oxygen is set free. The animal cell, on the other hand, is continually using up oxygen and giving off carbon dioxide in the process of respiration, while it is unable, in the absence of chloro- phyll, to manufacture such substances as starch and sugar. Thus in this close association or symbiosis between the Zoox- anthella and the Radiolarian, the latter benefits the former by supplying it with carbonic acid and other substances by which it is nourished, while the Alga contributes to the respiration of the Radiolarian by the oxygen which it gives off, and to its nutrition by the sugar and other substances which it forms. 2. THE MASTIGOPHORA We have seen that the spores by which multiplication is effected in some of the Rhizopoda (Heliozoa, Radiolaria) are characterised by the presence of slendér whip-like appendages — the flagella. In a great number of Protozoa such a flagellate condition of the cell is not merely a tempo- rary larval one, as in the cases already dealt with, but is the ordinary and permanent condition of the adult animal. These permanently flagellate Protozoa constitute the class Mastigophora — a very numerous group, mostly of very small size. A good example of this class, very abundant in fresh-water pools, in which it may be present in such enormous numbers as to impart to the water a distinct green colour, is Euglena viridis (Fig. 12). Another species or variety of Auglena viridis, is so abundant at times as to colour the water blood-red (Stokes). I PHYLUM PROTOZOA 35 The body of Euglena (4, #) is spindle-shaped, and has at the blunt anterior end a depression, the gullet (F. @s), from the inner surface of which springs a single long flagellum (7). The organism is propelled through the water by the y gullet; ; Eand H, enlarged (From Parker’s Brology, after 3 ¢. vac, contractile : g euglenoid movements , resting form after binary fission »mouth; x, nucleus: es ged; G + ey, cyst; 7, flagellum; 2 A—D, four views illustratin, ; ££, Pigment spot; x (in H), reservoir. views; F, anterior end further enlar vacuole in H, reservoir in E and F , paramylum bodies Kent and Klebs.) Fic. 12. — Euglena viridis. lashing movements of the flagellum, which is always directed forwards ; it can also perform slow, worm-like movements of contraction and expansion (4—JD), but anything like the 36 MANUAL OF ZOOLOGY SECT, I free pseudopodial movements which characterise the Rhizo- poda, is precluded by the presence of a very thin skin or cuticle which invests the body. There is a nucleus (zz) near the centre of the body, and at the anterior end a con- tractile vacuole (/7, ¢. vac), leading into a large non-con- tractile space or reservoir (r) which discharges into the gullet. The greater part of the body is coloured green by the characteristic vegetable pigment, chlorophyll, and contains grains of paramylum (HH, p), a carbohydrate allied to starch. In contact with the reservoir is a bright red speck, the stigma (pe), formed of a pigment allied to chlorophyll and called hamatochrome. It seems probable that the stigma is a light-perceiving organ or rudimentary eye. Euglena is nourished like a typical green plant; it de- composes the carbon dioxide of the air dissolved in the water, assimilating the carbon and setting free the oxygen. Nitrogen and other elements it absorbs in the form of min- eral salts in solution in the water. But it has also been shown that the movements of the flagellum create a whirl- pool by which minute fragments are propelled down the gullet and into the soft internal protoplasm. There seems to be no doubt that in this way minute organisms are taken in as food. Euglena thus combines the characteristically animal (Ao/ozoic) with the characteristically vegetable (o/o- phytic) mode of nutrition. Sometimes the active movements cease; the animal comes to rest and surrounds itself with a cyst or cell-wall of cellulose (the characteristic material of the cell-wall of plants), from which, after a quiescent period, it emerges to resume active life. It is during the resting condition that reproduction takes place by the division of the.body in a median plane parallel to the long axis (G). Under certain circumstances 3.Astasiopis 2. Oikomonas (?) fp “oz n G6.Dallingeria 8a” 9.Cryptomonas ; F B.Oikomonas = AOCORB Ione i. Dinobryon 12.Syncrypta t3.Anthophysa 14.Rhipidodendron Fic. 13.— Various forms of Mastigophora. In 2, flagellate (a) and amceboid (4) phases are shown; in 5, flagellate (2) and heliozoan (4) phases; in § are shown two stages in the ingestion of a food particle (/); chr, chromatophores; ¢. vac, contractile vacuole; /, food particle; g, gullet; #2, nucleus; /, lorica; 2, protoplasm; fer, peristome; vw. z, vacuole of ingestion, (Mostly from Biit- schli’s Protozoa, after various authors.) 37 38 MANUAL OF ZOOLOGY SECT. multiple fission takes place, and fluge//ule, ¢.e., young pro- vided with flagella, are produced, which, sometimes after passing through an amoeboid stage, develop into the adult form, In the other Mastigophora the body may have a shape similar to that of Euglena, or may be longer and narrower, or, on the other hand, may be short and thick, ovoid or globular. Anterior and posterior ends are nearly always distinguishable, the former being that which is directed forwards in progression. Usually there are distinct dorsal and ventral surfaces, the former being that which is habitually directed upwards. In most cases the body is equal-sided or bilaterally symmetrical, @.e., is capable of being divided into two equal lateral portions along the median vertical plane ; but sometimes it is unsymmetrical, one side differ- ing more or less from the other. In most the body is, as in Euglena, naked ; but some have a chitinoid shell or Zovica, while others have a firm cell-wall of cellulose which may present an elaborate pattern of strips, dots, etc., and may be produced into long processes. Most of the Mastigophora are, like Euglena, free-swimming, but some are permanently attached by means of a slender stalk (Fig. 13, 70, 73, 24; Fig. 14, 7, 9). The number and arrangement of the flagella vary greatly. The number may be one, as in Euglena, or two, three, or four. In forms with two flagella these are both attached at or near the anterior end, and often take on different functions, one of them, directed forwards, being alone used in locomotion, while the other is trailed behind when the animal is swim- ming freely, or is used to anchor it to various solid bodies. In one large group of Mastigophora, the Choanoflagellata (Fig. 14), there is, surrounding the base of the flagellum, a remarkable vase-like prolongation of the protoplasm, ex- I PHYLUM PROTOZOA 39 ceedingly delicate and transparent, called the col/ar. This is contractile, and, though its precise functions are not yet ‘ (After Saville Kent.) 4.Proterospongia. 3.Polyoeca. 2.Salpingoeca. Fic. 14.— Various forms of Choanoflagellata. 24 illustrates longitudinal fission; 2c, the production of flagell- ule; ¢, collar; ¢. vac, contractile vacuole; 77, flagellum; @, lorica; 2, nucleus. 1.Monosiga. certainly known, there is evidence to show that its move- ments cause a flow of water, with minute particles in sus- pension, up the outside of the collar and down the inside, 40 MANUAL OF ZOOLOGY SECT the solid particles being then ingested in the soft protoplasm between the base of the flagellum and that of the collar. Both collar and flagellum may be withdrawn, and the animal ; nu', micronucleus; 4.Polykrikos 3. da is an undischarged, and 6a dinal flagellum; 77. 2, transverse meganucleus ly (From Biitschli’s Protozoa.) gitu: 3.Prorocentrum 3 aN vu - 2S vgs BES e235 Ve BBR 4 anf ing ; 3 eee seo ER So Beem ai e o ° “32 vo vv > g g a § < by ww flagellum; /. gv, longitudinal groove discharged stinging-capsule; chy 2g, pigment spot; Fic. 15.— Various forms of Dinoflagellata. LGlenodinium pass into an Ameeba-like or ama@dotd form. In another _ group — the Dinoflagellata (Fig. 15)—there are two fla- gella, one springing from a longitudinal groove extending along the anterior half of the body, and the other lying in a I PHYLUM PROTOZOA 41 transverse groove which completely encircles the body; the former alone acts as an organ of locomotion, the latter lies habitually in the groove and performs undulating move- ments. Noctiluca (Cystoflagellata) (Fig. 16), which is the largest member of the class, being about half a millimetre in diameter, has two flagella, one of which is modified in a remarkable manner. The body of Noctiluca is globular, with a cleft along one side so that it resembles a miniature peach. From this springs a very large and stout flagellum Fic. 16.—Noctiluca miliaris. «, the adult animal; 4, c, flagellule; dg, tentacle; J, flagellum; 7, mouth; z, nucleus. (From Lang, after Biitschli.) or zentrcle, which is marked with a number of transverse lines or striations ; and a second flagellum, of comparatively small size, lies in the gullet. Though all the Mastigophora are characterised by the possession of flagella, there are a few, such as Mastigameba (Fig. 13, Z), which also possess pseudopodia, and may be capable of amceboid movements. Nutrition is effected in a variety of different ways. Some forms live in decaying organic infusions, not taking in solid food-particles, but absorbing nourishing matter in a dis- 42 MANUAL OF ZOOLOGY SECT. solved form from the substances in the infusion. Others, living in internal cavities of the bodies of higher animals, receive, in a similar way, nourishment from the juices of the animal they infest. Organisms, whether plants or animals, which receive their nourishment in the former of these two ways, are said to be saprophytic as regards their nutrition, while such as obtain it from other living organisms are said to be farasitic. But a large proportion of the Mastigophora are neither saprophytes nor parasites, and are nourished in one of two other ways, or in both of them. Many take in minute solid particles of organic matter, usually in the form of minute living organisms. In many such cases, there is, as in Euglena, an aperture, the mouth, opening into a short passage, the gullet, by which the food is received into the protoplasm in the interior of the body; but this is not always present, and in such cases (Fig. 13, 8) the food-parti- cles are taken in by a process not unlike that which we have seen to occur in Amceba. But, on the other hand, many of the Mastigophora are not distinguishable from plants by their mode of nutrition ; and on that ground, taken in connection with their structure, which is in nearly all respects that of a typical unicellular plant, have almost equal claims to be ranked in either the vegetable or the animal kingdom. They have a cell-wall of cellulose like a plant cell, they contain chlorophyll or a red colouring matter, hematochrome, of similar composition, and they have no mouth. They must, therefore, be nourished precisely after the manner of a green plant, and, if they are assigned to the animal kingdom instead of to the vegetable, it can only be because the possession of flagella seems to ally them with forms that are of undoubted animal character. Colonies are of frequent occurrence among the Mastigo- phora. Sometimes there is a branching slender stalk I PHYLUM PROTOZOA 43 bearing a single zooid or a group of zooids at the end of each of the branches (Fig. 14, 3), the whole colony being fixed by the base of the main stalk, and the flagellum serving for the capture of food-particles and not for locomotion. Fic. 17. — Volvox globator. A, entire colony, enclosing several daughter-colonies; B, the same during sexual maturity; C, four zooids in optical section; D1—Dé5, asexual formation of daughter-colony; E, zooid which has become converted into a mass of microgametes; F, microgamete; G, megagamete surrounded by microgametes; H, zygote; a, early stages in the formation of daughter-colonies; Ji, flagellum; ov, ovy, megagametes; Ag, pigment spot; sAy, zooids containing microgametes. (From Parker’s Bzology, after Cohn and Kirchner.) Sometimes (Fig. 17) the colony is of a more massive char- acter, the zooids being embedded in a clump of gelatinous material, with the end bearing the flagellum projecting on the exterior: usually such colonies are free-swimming. 44 MANUAL OF ZOOLOGY SECT. Multiplication is effected most commonly by the simple process of binary fission (Fig. 11, 24), which may take place either in the active or in an encysted condition. In some cases the fission is muw/tiple, the protoplasm dividing not merely into two, but into a greater number of parts, each destined to develop into the adult form. We also meet in the Mastigophora with what may be regarded as the simplest mode of sexva/ reproduction. In some forms two individuals come together and become completely fused, the process being known as conjugation, and the body formed by the union of the cells being known as a zygote. The protoplasm of the latter divides by mul- tiple fission into very minute spores. These, when first liberated by the rupture of the zogote, are mere granules, but soon the flagella are developed. In some cases the con- jugating cells or gume/ves are of two sizes, union always taking place between a large cell or megagameze and a small cell or microgamete. In Volvox, which is a free-swimming spheri- cal colony (Fig. 17, £, 7, G) this difference between the two sets of conjugating cells reaches its extreme, pro- ducing a conditioi of things closely resembling what we find in the sexual reprf@uction of higher forms. Certain of the zooids enlarge and form megagametes, others divide repeatedly and give rise to groups of microgametes, each of the latter having the form of a rod-like body with two flagella. The microgametes escaping, swim about freely and conjugate with the motionless megagametes to form a zygote, which, after a time divides to give rise to a new colony. Mastigophora occur under the most various conditions, to some of which reference has been already made. Many kinds live in fresh water; others are abundant in the sea. Noctiluca and others among the marine forms are phos- + Conjugation has also been observed to occur in many Rhizopods. I PHYLUM PROTOZOA 45 phorescent, and are usually the agents by means of which the diffuse phosphorescence of the sea is produced. Others, again, are saprophytes, while others are parasites of higher animals, 3. THE INFUSORIA Often to be found in great numbers, in stagnant pools, organic infusions, etc., is Paramecium, the “ slipper-shaped animalcule,” a Protozoan of comparatively large size, about 4 mm. in length, which moves about very actively like Euglena, but with a more regular and more rapid move- ment, and by means of organs of locomotion differing in character from the flagellum of the latter. The body of Paramcecium (Fig. 18, 4, B) is covered with what appear under the microscope like small delicate hairs arranged in longitudinal rows. These are the c/a; they are in inces- sant to-and-fro vibration, and it is by their means that the Paramcecium moves about and obtains its food. In shape the body is somewhat cylindrical, rounded at the anterior and bluntly pointed at the posterior end. On one side, the ventrad, is a large oblique depression, the duccal groove (duc. gr), leading into a short gullet (gw/), which, as in Euglena, ends in the soft internal protoplasm. The proto- plasm is differentiated into a firmer superficial layer, the cortex (cort), and a semi-fluid central mass, the medulla (med), and is covered superficially by a thin cuticle. The cilia are prolongations of the cortex, and perforate the cuticle. In the cortex are found two nuclei. One of these, the meganucleus (nu), is a comparatively large ovid body; the other, the micronucleus (pa. nu), is a small rounded body closely applied to the meganucleus. Two contractile 46 MANUAL OF ZOOLOGY SECT. I vacuoles (¢. vac) are present. Each is connected with a series of radiating spindle-shaped cavities in the protoplasm which serve as feeders to it; after the contraction of the vacuole these cavities are seen gradually to fill, apparently receiving water from the surrounding protoplasm ; they then contract, discharging the water into the vacuole, the latter rapidly enlarging while they disappear from view; finally the vacuole contracts and discharges its contents externally. The cortex contains minute radially-arranged sacs called trichocysts (trch). When the animal is irritated, more or fewer of these suddenly discharge a long delicate thread (C), which, in the condition of rest, is very probably coiled up within the sac. Food, in the form of small living organisms, is taken in by means of the current caused by the cilia of the buccal groove. The food-particles, enclosed in a globule of water, or “food-vacuole” (/. vac), circulate through the proto- plasm, where the soluble parts are gradually digested and assimilated. Effete matters are egested at a definite ana/ Spot posterior to the mouth, where the cortex and cuticle are less resistant than elsewhere. The whole feeding pro- cess can readily be observed in this and other Infusoria by placing in the water some insoluble colouring matter, such as carmine or indigo, in a fine state of division, the minute particles of the colouring matter, which are taken into the mouth in the way described, being readily observed as they become received into food-vacuoles and circulate in the central protoplasm. Multiplication takes place by transverse fission (D), the division of the body being preceded by that of both nuclei. It has been proved, however, that multiplication by binary fission cannot go on indefinitely, but that after it has been repeated a certain number of Umes, it is interrupted by buc. gr nu. mu. Fic. 18, — Paramecium caudatum. A, the living animal from the ventral aspect; B, the same in optical section: the arrow shows the course taken by food-particles; C, a specimen which has discharged its trichocysts; D, diagram of binary fission; buc. gr, buccal groove; cort, cortex; cz, cuticle; c. vac, contractile vacuole; /. vac food vacuole; gu/, gullet; med, medulla; 12%, meganucleus; fa. 2%, micro- nucleus; ¢rch, trichocysts. (From Parker’s Bzology.) 47 48 MANUAL OF ZOOLOGY SECT. I conjugation. In this very remarkable and characteristic process two Paramcecia become applied by their ventral faces, but do not fuse; their meganuclei break up and dis- appear, and an interchange of the substance of the micro- nuclei of the two conjugating individuals takes place, with the result that each develops a new meganucleus, and a new micronucleus, partly formed of the substance of its own micronucleus, partly that of the other Paramcecium. The possession of cilia is the distinctive feature of the class Infusoria among the Protozoa. But in one section of the class —the order Tentaculifera — cilia are only present in the young, their place in the adult being taken by append- ages known as ¢enfacles. The form of the body in the Infusoria (Fig. 19) is very varied; it may be globular, ovoid (7), kidney-shaped (2), trumpet-shaped (3), vase- shaped (9), produced into a long, flexible, neck-like pro- cess (5), or into large paired lappets (6), flattened from above downwards, or elongated and divided into a series of segments. Most are free-swimming, but many are fixed, usually by means of a slender stalk (Q). The arrangement of the cilia also varies greatly. Some, like Paramcecium, have small cilia of uniform character distributed over the entire surface. Others have different kinds of cilia on different parts of the surface, while in others the cilia are entirely confined to certain regions. An instance of the latter arrangement is the common stalked form VordiceHa, with its allies such as Zpistyhs (9), in which the cilia are confined to the free extremity. These cilia produce rapid currents, and the ZpishZs, says Stokes, select from them anything they may want, and let the rest sweep by. In another group, again, the body, which is of flattened shape, bears on its dorsal surface a small number of very fine motionless cilia, while on its ventral the cilia are & 4.Godonella 5. be ning at 3. Stentor 8.Anoplophyra = ¢ 9.E pistylis 12.Multicilia — 13.Lophomonas a , 18.Trachelius 19.0phryoglena 15 Didinium __'6-Condylosto: phryes ma © 170 pdlinopsis Fic. 19. — Various forms of Ciliata. ga shows part of a colony, 4 a single zooid, and ¢ acouple of nematocysts; a, anus; ¢. vac, contractile vacuole; # vac, food vacuole; g, gullet; sg. #7, meganucleus; zz. 27, micronucleus; 7z¢, mouth; uu, nucleus; wfc, nematocyst; 7, tentacle; 2. #5, undulating membrane; vac, non-contractile vacuole; ws¢, vestibule. (From Biitschli’s rotozoa, after vari- ous authors.) E 49 50 MANUAL OF ZOOLOGY SECT. very strong, and are modified into the shape of hooks, bris- tles, or plates with fringed ends. The hooks and plates do not vibrate rhythmically like ordinary cilia, but are moved as a whole at the will of the animal, such Infusoria being able, in addition to swimming freely through the water, to clamber by the aid of these specially modified cilia over the surface of weeds, etc. Tentacles may be present in addition to cilia (14), and a number of other exceptional modifications (zo-z3) occur which cannot be specially re- ferred to here. In addition to cilia, many genera possess delicate sheets of protoplasm, or wndulating membranes (uw. mb) in connec- tion with the peristome. These contract so as to pro- duce a wave-like movement which aids in the ingestion of food. The #entacles, which, in the Tentaculifera (Fig. 20), take the place of cilia in the adult, are elongated cylindrical structures, capable of protrusion and retraction, and having the distal end expanded into a sucker. The tentacle is practically tubular, the core consisting of a semi-fluid proto- plasm, while the outer part is tolerably firm. Infusoria and other organisms are caught by the tentacles, the cuticle of the prey is pierced or dissolved where the sucker touches it, and the semi-fluid protoplasm can then be seen flowing down the tentacle into the body of the captor. A single tentacle alone may be present (7), or the tentacle may be branched (¢), the extremity of each of the branches being suctorial. In some forms (5) the tentacles are devoid of sucker-like extremities, and can be moved about actively to catch the prey. The meganucleus is often ovoid, as in Parameecium. In other cases it may be long and band-like (Fig. 19, 3, mg. ni), horseshoe-shaped (9), very long and constricted PHYLUM PROTOZOA 4.Dendrocometes 5. Ephelota 3.Rhyncheta TObieyedesehet oe cheldta Fic. 20. — Various forms of Tentaculifera. za and 4, two species of Podophrya; ¢,a tentacle much enlarged; 2a, Acineta jolyt ; 2b, A. tuberosa, in 6 the ani- mal has captured several small Ciliata; 8a, a specimen multiplying by budding; 8b, a free ciliated bud; ga, the entire colony; 94, a portion of the stem; gc, a liberated bud; a. organism captured as food; 4. c, brood cavity: dd, bud; ¢. vac, contractile vacuole; mg. nu, meganucleus; mz. xu, micronucleus; #, tentacle, (After Biitschli and Saville Kent.) 52 MANUAL OF ZOOLOGY SECT. at intervals so as to look like a string of beads, or branched. In nearly all cases one or more micronuclei are present. Tn Vorticella and others there is a single contractile vacuole which opens, as in Euglena, through the intermediation of a reservoir into the gullet. In other Infusoria there may be one, two, or many contractile vacuoles. In some instances the protoplasm is hollowed out by numerous non-contractile vacuoles. Trichocysts mainly occur in the forms with a uni- form coating of cilia: more complicated bodies of similar character termed nematocysts (9, ¢) occur in some cases. A mouth is absent in many parasitic forms, and nourish- ment is obtained by the absorption of the digested food of the animal in which the infusorian is parasitic. In the Tentacu- lifera, in which a mouth is also absent, nourishment is drawn in by means of the tentacles in the manner already described. In the rest there is a mouth and gullet, usually situated, as in Paramoecium, at the end of a buccal groove, or peristome. In Vorticella and its allies (Fig. 19, 9, and Fig. 22) the body is in the shape of a wine-glass, the stem of which is represented by a slender stalk (st), while the rim is the equivalent of the peristome (Zev) ; in the area which the peristome encloses is an elevated disc of protoplasm, be- tween which and the peristome on one side is the opening of the mouth (mr) : the only cilia present run in a spiral band round the peristome, round the edge of the disc, and down into the gullet (gz/7). An anal spot is present in Vorticella and many other forms; in a few there is, instead, a distinct anal aperture (Fig. 19, 2 a). A chitinoid skeleton (Fig. 21) occurs in a few forms ; usually it is bell-shaped, sometimes it is perforated by a number of apertures (7) so that it resembles in appearance the skeleton of some of the Radiolaria. A chitinoid lid or operculum (2,3, 0p) may be fixed to the edge of the peri- I PHYLUM PROTOZOA 53 stome, and when the animal is retracted into its case, accu- rately closes the mouth of the latter. Colonies occur in many of the Infusoria. Some allies of 5. Stichotricha m, contractile fibre; of, operculum. a 5 Ee <4 S68 ay oa mm 5> QO 23 Tf es oe B =§ $ H Jz 3S oe EF as = ma =o "2 38 Oo gs SS og me co soae - un wo 3 oO o 6 3 > ~ | a 4 9° a — g Q Fe <= Vorticella (Fig. 19, 9) develop highly complex colonies, the slender stalk branching again and again, and each terminal branch ending in a zooid. A remarkable colonial form is 54 MANUAL OF ZOOLOGY SECT. Dendrosoma (Fig. 20,9), one of the Tentaculifera: it has a creeping stem from which branches spring upwards, each terminating in a zooid with suctorial tentacles; and Fic. 22.---Vorticella. A, B, living specimens.in different positions; C, optical section; D!, D?, diagrams illustrating coiling of stalk; Et, E*, two stages in binary fission; E%, free zooid; F1, F2, division into mega- and microzooids; G}, G+, conjugation; H!, multiple fission of encysted form; H?, H3, develop- ment of spores; ax. /, axial fibre; cort, cortex; cz, cuticle; ¢. vac, contractile vacuole; d, disc; gv//, gullet; #z, microzooid; mt, mouth; 2%, meganucleus; per, peristome. (From Parker’s Szodogy, partly after Saville Kent.) I PHYLUM PROTOZOA 55 the single nucleus extends as a narrow branching cord throughout the axis of the entire colony. Transverse fission is the universal method of reproduc- tion; and budding also occurs. Spore-formation has been observed in a few forms. Conjugation, in the form of a temporary union of two individuals, with interchange of the substance of the micro- nuclei, occurs in many of the ciliate Infusoria. In some forms the conjugating individuals become completely fused. The effect of the process of-conjugation seems to be in- creased activity in multiplication by fission. In mode of life the Infusoria are as varied as the Mastigo- phora. Some are holozoic, some saprophytic, some parasitic. Of the parasitic forms some give rise to definite diseases in the bodies of their hosts. The skin affection known as eczema, for example, seems to be caused by the presence of parasitic Vorticellee. : 4. THE SPOROZOA In the interior of certain organs, termed the seminal vesicles, of the earthworm will often be found a parasitic Protozoan — Monocystis agilis (Fig. 23) —which exempli- fies another of the classes of the phylum, the class Sporozoa. It is flattened, elongated, pointed at both ends, and performs slow movements of expansion and contraction (4, S), reminding us of those of Euglena. There are neither pseudopodia, nor flagella, nor cilia. There is a firm cuticle, and the protoplasm is divided into a denser superficial portion, the cov7ex, and a central semi-fluid mass, the medulla. There is a large clear nucleus, but no trace of contractile vacuole, or of mouth or gullet. Reproduction takes place by a peculiar and characteristic process of spore- formation. Either a single individual, or two individuals 56 MANUAL OF ZOOLOGY SECT. closely applied together, but not actually fused, become encysted. Multiple fission then takes place, the proto- plasm becoming divided (C’) into an immense number of spindled-shaped spores, each surrounded by a strong earthworm; jJ/, young Monocystis; roup of sperm-cells of the earthworm; (After Biitschli and Huxley.) fh oung (M) ina by sperms of t d sperm-cells of earthworm, A, B, two individuals in different stages of contraction; C, cyst stis surrounde i D—F, development of c G, newly liberated Mono nz, nucleus; sf, sperms o! containing spores; Fic. 23.— Monocystis agilis. chitinoid coat, and thus differing markedly from the naked spores of Rhizopoda and Mastigophora. The protoplasm of each spore then undergoes fission, becoming divided 57 PHYLUM PROTOZOA into a number of somewhat sickle-shaped bodies, which are arranged within the spore-coat somewhat like a bundle of By rupture of the spore-coat these fadiform young, as they are termed, are liberated, and at once begin sausages. (‘vozojo4g Syosing wor) ‘syonporods ‘pgs ‘sarods jo sseu ‘gs ‘podopnasd Buoy ‘2 ‘-psg spodopnasd yroys ‘7 ‘psg sayiawojoid ‘2g ‘smaponu ‘ww $4sh9 Jo JUaUNsaAUT snoUuElad foyawoynap ‘zap %3sh0 Wo Sf vazuvsts HQ Jo yUsuidojaaap ay} uI sadeis tpadieyosip usaq aaey Sarods ayi Jo ysour YoIyM WOIY ‘22-4Y7207g ul fzeipavinp “jo suaundads omy “egy ‘7g yseo st (g2) aqtaunida ay sYIVOIADOD JO sTJao Fe “91g Teyaquda o1ajua ur pappaquia Apjred we4032079 “D Jo suauttoeds omy “W a They enter the clumps of devel- oping sperms of the earthworm, and afterwards escape into active movements, the thin end of the body moving to and fro like a clumsy flagellum. the cavity of the seminal vesicle and grow into the adult form, 58 MANUAL OF ZOOLOGY SECT. I All the Sporozoa are parasitic, and all are characterised by the absence of pseudopodia, flagella, and cilia; and of mouth and gullet, and by the formation of spores enclosed in chitinoid coats. Grevarina (Fig. 24) differ from Mono- cystis in having the medullary part of the protoplasm divided into two sections, known as the protomerite (pr), and deutomerite (dew), by a sort of partition, with, in the young condition, a third division, the ep/merite (ep) in front; and in the more complex form of the cysts, which have delicate canals or sporoducts (spd) through which the spores escape. Some of the Sporozoa ( Ceccidium and others) are parasites, not like Monocystis and Gregarina, in the cavities of organs, but in the interior of cells, such as the cells lining the intes- tine of higher animals. The various forms of the disease known as malaria in Man have been proved to be due to the presence of a Sporozoan (Hemameba laverant) which in- vades and destroys, at a certain stage in its life-history, the red corpuscles of the blood. Another form (Apiosoma digeminum) causes the Texas fever in cattle, the infection being carried by ticks. ‘These parasites cause high fever, anemia, bloody urine, and the number of red-blood corpus- cles is diminished in one week to one-sixth of the normal amount. Badesia doris in the blood of the ox causes the dis- ease known as hemoglobinurea, and another form produces a similar disease insheep. A parasite of the tzetse fly, which is a flagellate heematozoan, is the cause of the tzetse disease in southern Africa. These organisms live in the marrow and lymphatics, and flush at intervals into the general blood stream. The disease is communicated by the tzetse fly from the wild game, the herds of which are the fester spots which maintain the disease. The silkworm disease called pedrine is due to one of the Myxosporidia, Glugea bomébyets, which inhabits all the tissues of the caterpillar of Bomdyy mort. SECTION II.—THE METAZOA Waite the Protozoa are predominantly unicellular, and of extremely simple structure, the rest of the animal kingdom, grouped together under the comprehensive title of Metazoa, are all multicellular in the adult condition, and have, except in some of the lowest groups, a more or less elaborate struc- ture owing to the presence of complicated systems of organs for carrying on the various functions of animal life. Such an animal as a lobster or a frog, for example, may readily be ascertained to be made up of a complicated system of parts, —skeleton, muscles, digestive organs, blood vessels, and so on, — and it requires only the most superficial micro- scopic examination of the substance of these various parts to render it evident that each is built up of an immense multitude of cells. A lobster or a frog, however, or any other Metazoan, consists, in the earliest stage of its exist- ence, of a single cell, the oosperm, formed by the union of a male cell or sperm with a female cell or ovum. The ovum (Fig. 25) is usually spherical in shape, with one or more enclosing membranes, with cell-protoplasm enclosing a large nucleus (germinal vesicle, as it is often termed in this case), in which are contained one or more small, rounded bodies (germinal spot or spots). The ovum may contain, in addition to the protoplasm, a quantity of non- protoplasmic material or yoék. 59 60 MANUAL OF ZOOLOGY SECT. Before the changes begin which lead to the formation of the multicellular Metazoan, another cell, the made cel/ or sperm, has to unite with the ovum or female cell. Before this takes place, the ovum throws off portions of its substance (Fig. 26, ol) in the form of two little rounded bodies — the polar bodies. This preliminary process is known as the maturation of the ovum. The male cell or sperm is a relatively small cell, usually motile, which penetrates into Fic, 25.— Ovum of a Sea-Urchin, showing the radially striated cell-membrane, the rotoplasm, containing yolk-granules, the large nucleus (germinal vescicle), with ts network of chromatin_and a large nucleolus (germinal spot). (From Bal- four’s Embryology, after Hertwig.) the ovum, and coalesces with it—the coalescence being what is termed fertilisation or impregnation —and the immediate result being that, instead of separate ovum and sperm, we have a compound body, the oosferm, formed by their union, but not differing at first in any marked degree from the simple ovum, and containing a single nucleus representing both the nucleus of the sperm and that of the ovum, On impregnation follows the process of segmentation of the oosperm. The nucleus first divides into two; then the Bag THE METAZOA 61 Fic. 26. — Diagram illustrating the maturation and fertilisation of the ovum. A, formation of first polar globule; B, beginning of fertilisation, sperms approaching the micropyle or aperture in the enclosing membrane of the ovum through which the sperm enters; C, forma- tion of the male pronucleus; D, approximation of the male and female pronuclei; E, forma- tion of segmentation-nucleus; 9 cent, female centrosome; of cent, male centrosome (the centrosomes are cell-structures not further referred to in this work); wzevz, egg-membrane; microp, micropyle; fol, polar bodies; 9 pron, female pronucleus; ¢ pron, male pronu- cleus; seg. xucl, segmentation nucleus. 62 MANUAL OF ZOOLOGY SECT. substance of the protoplasm becomes cleft into two parts (Fig. 27), each half containing one of the nuclei, so that two complete cells result. This process, it will be observed, is essentially the same as the d:vary fission of Amceba and other Protozoa: in the Metazoan, however, the two cells do not become separated from one another as the two parts of the divided Amceba do, but remain in contact and undergo further changes. Each of them divides (Fig. 27) Fic. 27. — Various stages in the segmentation of the oosperm. (From Gegenbaur's Comparative Anatomy.) in the same manner into two— four cells being thus formed ; the four divide to form eight, the eight to form sixteen, and so on; until, by this process of division and sub- division, the oosperm becomes segmented into a large number of comparatively small cells. In this mass of cells an arrangement into layers, the germina/ layers, becomes by and by discernible; and from these layers of cells are developed eventually all the parts of the body of the Metazoan. Ir THE METAZOA 63 This mode of development is, however, not entirely with- out parallel among the Protozoa. In the colonial Volvox (p. 43, Fig. 17) it will be remembered that male cells or microgametes (sperms) and female cells or megagametes (ova) are developed, and that by the coalescence of a microgamete with a megagamete a compound cell, the zygote (oosperm), is formed, which undergoes division to give rise to an adult Volvox. As the various parts become gradually moulded from the cells of the germinal layers, the form and arrangement of the cells of the different parts become modified in different ways, so that the cellular structure comes to differ widely; and, as a result, we find in the fully formed animal a variety of different kinds of material, — tissues, as they are termed, — such as muscle, bone, gristle, nerve, all derived from the cells of the germinal layers. Of such tissues the following are the most important. An efctheium is a thin stratum of cells covering some surface, external or internal ; it may be one cell thick, or several cells thick. The cells of which an epithelium is composed vary greatly in form in different cases (Fig. 28): they may be beset at their free surfaces with cilia (a), like the cilia of the Infusoria, or with flagella, like those of the Mastigophora (7), or may be amoeboid (A), sending out pseudopodia like a Rhizopod. The epithelium which covers the outer surface is known as the epidermis or deric epithelium ; that which lines the interior of the digestive organs is the ezéric epithelium. Glands (Fig. 29) are formed by modification of epithe- lial cells. In many cases a single cell of the epithelium forms a gland, which is then termed a wnicellular gland (A, B). The secretion (or substance which it is the func- tion of the gland to form or collect) gathers in such a case in the interior of the cell, and reaches the surface of the 64 MANUAL OF ZOOLOGY SECT. Fic 28.— Various forms of epithelium. a, ciliated epithelium; 4, columnar; d, sur- face view of the same, c, tessellated; ¢, the same from the surface; Sf flagellate epithelium with collars; g, flagellate epithelium without collars; 4, epithelium of intestine with psendopodia; 2, stratified epithelium; 4, deric epithelium of a marine planarian with pigment cells, rod cells, and sub-epithelial glands. (From Lang’s Comparative Anatomy.) II THE METAZOA 65 epithelium through a narrow proiongation of the cell, which serves as the duct of the gland. In other cases the gland is multicellular (D, G), formed of a number of cells of the epithelium, lining a depression or infolding, simple or com- plex in form, of the latter. In the central cavity of such a Fic. 29 — Diagram to illustrate the structure of glands. A, unicellular glands in an epithelium; 4, unicellular glands lying below epithelium and communicating with the surface by narrow processes (ducts); C, group of gland cells; D, group of gland cells lining a depression; & and F, simple multicellular gland; G, branched multicellular gland. (From Lang.) gland the secretion collects to reach the surface through a passage, the duct. The general name of connective tissues is applied to a number of tissues which play a passive part in the economy of the animal, connecting and supporting or protecting the various organs. Sometimes connective tissue is gelatinous in character, sometimes fidrous. Fat or adipose tissue is F ! 66 MANUAL OF ZOOLOGY SECT. usually developed by modification of fibrous connective tissue, the cells becoming distended with oily matter. Cartilage is a firm but elastic material, readily cut with a knife, which forms an important constituent of the skeleton in higher animals. Bone differs from cartilage in being much denser and harder, owing to its being strongly impregnated with limey matter (carbonate and phosphate of lime). Muscular tissue is the material by means of which nearly all the movements of the Metazoa are effected. It consists of bundles of microscopic fibres, which in the living condi- tion have the special property of contractility, contracting, 7.e. becoming shorter and thicker, when stimulated. Bundles or bands of these form the organs known as muscles. Verve ussue, which is the sensitive, conducting, and stimulating tissue of the body, consists of nerve-cells and nerve-fibres ; groups of the former constitute zerve-ganglia, bundles of the latter form zerves. Associated with the multicellular character of the Metazoa is the possession of a variety of different parts or organs adapted to carrying out different functions in the life of the animal. Such a formation of organs is faintly fore- shadowed in the unicellular body of the Protozoa; the contractile vacuoles, the nucleus, the pseudopodia, flagella, and cilia, the gullet, etc., are all to be looked upon as organs subserving certain functions. But in the Metazoa, with the exception of some of the lower groups, the development of organs for the carrying on of the functions of animal life — organs of locomotion, organs for protection and support, organs of digestion, respiration, and reproduction — is carried much further. Some of the chief functions which are carried on in the body of an animal have already been briefly referred to in ba THE METAZOA 67 the account of the Protozoa. The special study of these constitutes, as already pointed out in the Introduction, the science of Physiology, which forms accordingly an important part of the study of Zoology, and a part to which frequent reference will be made in dealing with the structure of the various groups of animals. The various internal parts of an animal are supported and protected by the sz and the sele‘on. The skin or in- tegument consists of a layer of cells — the efidermis — with, Fic. 30.— Bones of the human arm and fore-arm with the biceps muscle, showing the shortening and thickening of the muscle during contraction and the conse- quent change in the relative position of the bones — viz., flexion of the fore-arm on the upper arm. (From Huxley’s Physiology.) superficial to it, in many animals, a non-cellular layer known as the cuticle, and below it usually a fibrous layer, the dermis. The skeleton is, as already explained in the section on the Protozoa, a system of hard parts, external or internal, serving for the protection and support of the softer substance of the body. When these hard parts are external they form an exoskeleton, when internal an endoskeleton. An exoskeleton is formed by the thickening and hardening of portions of one or other of the layers of the integument, —cuticle, epidermis, or dermis. An endoskeleton usually 68 MANUAL OF ZOOLOGY SECT. consists either of cartilage, or of bone, or of both. The parts of the skeleton in the higher animals, whether external or internal, usually consist of a number of distinct pieces which are movably articulated together, and these have the additional important function of serving for the attachment of muscles, constituting a jointed framework on which the muscles act in bringing about the various movements of the body and its appendages (Fig. 30). The nutrition of the Metazoa is in some cases, as in some of the Protozoa, effected by food being absorbed in a dissolved form through the general surface. In the great majority, however, the food, liquid or solid, is received through an opening —the mouth—into a cavity in the interior of the body—the agestive or enteric cavity. In most cases this has the form of a longer or shorter tube or canal, beginning at the mouth and ending at a second exter- nal opening —the anus. This digestive or enteric canal consists usually of a number of different parts, through which the food passes in succession, each part having its special function to perform in connection with nutrition. In most cases there are organs in the neighbourhood of the mouth serving for the seizure of food ; these may be simply #exzacles, or soft, finger-like appendages, or they may have the form of jaws, by means of which the food is not only seized but torn to pieces, or ground into small fragments, in the process of mastication. In general we can distinguish in the enteric canal a buccal cawty, a pharynx, an esophagus or gullet, a stomach, and an intes#ine. It is in the stomach and anterior part of the intestine that the food becomes acted upon by certain digestive secretions, the effect of which is to render the various ingredients soluble, and thus fitted to be absorbed through the wall of the enteric canal, so as to reach the various parts of the body and supply them with nourish- II THE METAZOA 69 ment. These digestive secretions are partly produced by the cells of the epithelium of the canal, which are modified to form unicellular or multicellular glands (p. 65), partly by certain large special digestive glands, sadivary glands, liver, and pancreas. The nutrient parts of the food are by this means so acted upon that they are ready to be absorbed, and in most animals pass into the blood, to be distributed Fic. 31. General view of the viscera of a male dog from the right side. a, stomach; 4, urinary bladder; c, small intestine; ’ cloacal aperture; d, large intestine; ¢, liver; /, bile duct: g, gall bladder; h. ‘spleen; z, lung; &, larynx; 2, fat body; #z, testis; 2, ureter: 0, kidney; #, pancreas; s, cerebral hemi- sphere; sp, spinal cord; 7, tongue: z#, auricle; uz, urostyle; v, ventricle; v.s, vesicula seminalis; w, optic lobe; «, cerebellum; y, Eustachian recess; z, nasal sac. (From Marshall ) throughout the body. The insoluble and indigestible ingre- dients of the food pass on through the posterior part of the intestine, and reach the exterior through the anal aperture as the feces. A supply of oxygen is necessary for the carrying on of the chemical changes in the tissues on which vital activity is dependent. At the same time, as a result of these changes, 470 MANUAL OF ZOOLOGY SECT. carbonic anhydride (carbonic acid gas) is constantly being produced. The taking in of oxygen and giving off of car- bonic anhydride is the process of respiration. The task of facilitating the entry of oxygen and the passage outwards of carbonic anhydride is in most of the Metazoa performed by a set of organs known as organs of respiration, but in many respiration takes place through the general surface, and special organs for carrying on this function are absent. When organs of respiration are present, they are either processes or gills (6ranchie) adapted for the respiration of air dissolved in water; or /vmgs or other cavities which are adapted for the direct respiration of air. Through the thin membrane lining the gill, or lungs, the oxygen passes and enters the blood in vessels immediately underneath the membrane, to be conveyed, like the food, throughout the system and supplied to the several parts. At the same time the carbonic anhydride, brought to the gill or lung by the same means, passes outwards into the surrounding water or air, and is thus got rid of. The blood consists of a fluid plasma, in which float numerous cells — the d/oed corpuscles. Sometimes the blood is colourless ; usually it is bright red, owing to the presence of a red colouring matter, termed Aemoglobin, which is sometimes confined to certain of the corpuscles, sometimes diffused throughout the plasma. Haemoglobin has a strong affinity for oxygen, and is thus of importance in connection with respiration. In order to carry on its functions as a conveyer of nutriment and of oxygen throughout the body, the blood flows in a system of vesse/s —the dood vascular system — which ramify throughout all the organs. Through this system of vessels it is driven in a more or less regular course, either by pulsating contractions of the muscular W THE METAZOA 7 walls of the blood-vessels themselves, or by the agency of a special organ, the Aear?. ‘Ihe heart is essentially a sac with muscular walls. Its cavity is in communication with the main blood-vessels, and its walls contract regularly and drive the blood through the system of vessels, the direction of flow being regulated by a system of valves. The nitrogenous waste-matters which are produced as a result of the chemical changes that accompany vital action in the various organs, are separated out and got rid of bya system of organs known as the ovgans of excretion, or renal organs —this process of elimination being known as the process of renal excretion. It is by means of the nervous system that the animal receives impressions from the exterior and from the internal organs, and that the various internal parts are brought into vital communication with one another. The nervous system extends as a complicated system of nerves or bundles of nerve-fibres throughout all parts of the body. Large aggregations of nerve-cells and nerve-fibres forming the centres of the system are known as nerve-ganglia. When one of these, or a group of them, situated towards the anterior end, preponderates in size over the others, it is termed the drazn. Forming an important part of the nervous system are the organs of the special senses, — sight, hearing, smell, and taste, each of which is an organ adapted for the reception of impressions of a special kind from the exterior, — the impressions of light, of sound waves, of the particles and substances that produce the sensations of smell and taste. The less specialised sense of touch and of heat and cold is diffused generally over the integument, in which there are frequently special cells, or groups of cells, with nerve-fibres terminating in them, that are concerned with such sensations. 92 MANUAL OF ZOOLOGY SECT. The organs of sexual reproduction are the gona:ts, in which male and female cells or sperms and ova are produced, with the gonoducts or canals by which these cells reach the exterior. The gonads in which male cells or sperms are produced are called #szes, and their ducts are the sferm-ducts, The gonads in which female cells or ova are formed are called ovarves, and their ducts ovitucts. Sometimes testes and ovaries occur in distinct male and female individuals, when the animal is said to be unisexual, or to have the sexes distinct. In other cases both ovaries and testes occur in the same individual, when the animal is said to be hermaphrodite, or to have the sexes united. In some instances the same gonad produces both sperms and ova— assuming the character of a hermaphrodite gonad or ovo-testis. In many animals the ova are fertilised by the sperms after they have passed out from the body, and the develop- ment takes place externally —a condition which is known as oviparity. But in others the ova are fertilised while still in the ovary or oviduct of the parent, and the development may take place in the oviduct, usually in a special dilated part of the latter —the wéerus—so that the young only escape to the exterior after they have attained a compara- tively advanced stage of their development— when the animal is said to be wivparous. Besides the sexual process of reproduction by means of ova and sperms, there are in many classes of animals various asexual modes of multiplication. One of these — the process of simple fission —has been already noticed in connection with the reproduction of Protozoa. The forma- tion of sfores is an asexual mode of multiplication which occurs only in the Protozoa, and has been described in the account of that group. Multiplication by dudding takes II THE METAZOA ™ place in a number of different classes of animals. In this form of reproduction a process or dud (Fig. 32, 6d) is given off from some part of the parent animal; this bud sooner or later assumes the form of the complete animal, and may become detached from the parent either before or after its Fic. 32. —Fresh-water polype (hydra), two specimens, the one expanded the other contracted, showing multiplication by budding. 4d1 4d% dd, buds in various stages of growth, (From Parker's Bzology.) development has been completed, or may remain in perma- nent vital connection with it. When the buds, after becoming fully developed, remain in vital continuity with the parent, a sort of compound animal, consisting of a greater or smaller number of con- nected units, is the result. Such a compound organism is 74 MANUAL OF ZOOLOGY SECT. termed a co/ony, and the component units are termed zoozds. In some cases such a colony is produced by a process which is more correctly termed éncomplete fission than budding. The various systems of organs, — digestive, circulatory, nervous, excretory, etc.,— present under one form or an- other in all the higher groups of animals, are variously arranged and occupy various relative positions in different cases, producing a number of widely different plans of animal structure. According as their structure conforms to one or another of these great plans, animals are referred to one or another of the corresponding great divisions or pryta of the animal kingdom. That animals do present widely differing plans of structure is a matter of common knowledge. We have only to compare the true fish, such as cod, haddock, etc., in a fishdealer’s shop with the lobsters and the oysters, to recognise the general nature of such a distinction. The first named are characterised by the possession of a backbone and skull, with a brain and spinal cord, and of two pairs of limbs (the paired fins) : they belong to the great vertebrate or backboned group — the division Vertebrata of the phylum Chordata. The lobsters, on the other hand, in which these special verte- brate structures are absent, possess a jointed body enclosed in a hard jointed case, and a number of pairs of limbs also enclosed in hard jointed cases, and adapted to different purposes in different parts of the body — some being feelers, others jaws, others legs: their general type of structure is that which characterises the phylum Arthropoda. The oysters, again, with their hard calcareous shell secreted by a pair of special folds of the skin constituting what is termed the mantle, and with a special arrangement of the nervous system and other organs which need not be described here, are referable to the phylum Jfo//usca. Other familiar Ir THE METAZOA 75 animals are readily to be recognised as belonging to one or other of these great phyla) A prawn, a crab, a bluebottle fly, a spider, are all on the same general plan as the lobster: they are jointed animals with jointed limbs, and they have the internal organs occupying similar positions with relation to one another. They are all members of the phylum Arthropoda. Again, a mussel, a snail, a squid, are all to be. set side by side with the oyster as conforming to the same general type of structure ; they are all members of the phylum Afollusca. Finally a dog, a lizard, a fowl, are obviously nearer the fish: they all have skull and backbone, brain and spinal cord, and two pairs of limbs; they are all members of the great group Chordata. Altogether twelve phyla are to be recognised, viz. : — I. Protozoa VII. Molluscoida Il. Porifera VIII. 2chinodermata III. Calenterata IX. Annulata IV. Platyhelminthes X. Arthropoda V. Nemathelminthes XI. Mollusca VI. Zrochelminthes XII. Chordata SECTION III. —PHYLUM PORIFERA Tue Porifera, or sponges, belong to the lowest group of the Metazoa. They live fixed to the surface of rocks, or to submerged timber or seaweeds, so as to be incapable of locomotion; and have, in most cases, a general form which suggests the vegetable rather than the animal kingdom. But, in essentials, as will presently become evident, the sponges are distinctly animal in character, and the resemblances to plants are entirely superficial. The majority of sponges are compli- cated and difficult to understand, owing to their elaborate mode of branching and the fusion of the branches, and to the exceed- ingly intricate character of the skeletal parts, aside from their cellular structure. . Some, however, are free from these com- Fic 33. Syconcili- plications ; and it is in one of these that eee), the main characteristics of sponges are best studied. Such a simple form is Sycon, a small sponge living attached to rocks on the seashore towards or below low-water mark. Sycon gelatinosum* has the form of a tuft, one to three inches long, of branching 1 This is an Australasian species, but the following account will apply in all essential respects to Sycon ciliatum (Fig. 33) and S. clarkii of the coast of New England. 76 SECT. III : PHYLUM PORIFERA 17 cylinders (Fig. 34), all connected together at the base, where it is attached to the surface of seaweeds, rocks, or other solid bodies submerged in the sea. It is flexible, though of tolerably firm consistency. On the outer surface are to be detected, under the microscope, groups of minute pores — the zzhalant pores. At the free end of each of the cylindrical branches is a small but distinct opening, sur- rounded by what appears like a delicate fringe. When the branches are bisected longitudinally (Fig. 35), it is found that the terminal openings (g) lead into narrow passages, Fic. 34. —Sycon gelatinosum. Entire sponge, consisting of a group of branching cylinders (natural size). wide enough to admit a stout pin, running through the axis of the cylinders; and the passages in the interior of the various branches join where the branches join—the pas- sages thus forming a communicating system. On the wall of the passages are numerous fine apertures which require a strong lens for their detection. The larger apertures at the ends of the branches are the oscw/a of the sponge, the pas- sages the paragastric cavities. If the living Sycon is placed in sea-water with which has been mixed some carmine pow- der, it will be noticed that the minute particles of the carmine seem to be attracted towards the surface of the 78 MANUAL OF ZOOLOGY SECT. sponge, and will often be seen to pass into its substance through the minute pores already mentioned as occurring in groups between the elevations on the outer surface. This would appear to be due to the passage of a current of water Fic. 35.—Sycon gelatinosum. A portion slightly magnified; one cylinder (that to the right) bisected longitudinally to show the central paragastric cavity opening on the exterior by the osculum, and the position of the incurrent and radial canals; the former indicated by the black bands, the latter dotted. 7 marks the position of three of the groups of inhalant pores at the outer ends of the incurrent canals; 0, osculum. into the interior of the sponge through these minute open- ings dotted over the surface; and the movement of the floating particles shows that a current is at the same time flowing out of each of the oscula. A constant circulation of 111 PHYLUM PORIFERA 79 water would thus appear to be carried on — currents moved by some invisible agency flowing through the walls of the sponge to the central paragastric cavities, and passing out again by the oscula. If a portion of the Sycon is firmly squeezed, there will be pressed out from it first sea-water, then, when greater pressure is exerted, a quantity of gelatinous-looking matter, which, on being examined microscopically, proves to be partly composed of a protoplasmic material consisting of innumerable, usually more or less broken, cells with their nuclei, and partly of a non-protoplasmic, jelly-like substance. When this is all removed there remains behind a toughish, felt-like material, which maintains more or less completely the original shape of the sponge. This is the se/e/on or supporting framework. A drop of acid causes it to dissolve with effervescence, showing that it consists of carbonate of lime. When some of it is teased out and examined under the microscope, it proves to consist of innumerable, slender, mostly three-rayed microscopic bodies (Fig. 36, sf) of a clear, glassy appearance. These are the calcareous spicules which form the skeleton of the Sycon. Covering the outer surface of the sponge is a single layer of flattened, scale-like cells — the ectoderm (Fig. 36, ec) — through which project regularly arranged groups of needle- like and spear-like spicules (5f'). The paragastric cavities are lined by a layer of cells (e7), which are like those of the ectoderm in general shape; this is the endoderm of the paragastric cavity. Running radially through the thick wall of the cylinders are a large number of regularly arranged straight passages. Of these there are two sets, those of the one set—the éucurrent canals (fC) — nar- rower, and lined by ectoderm similar to the ectoderm of the surface; those of the other set—the radial or ii uu \ \ \Nh i Ne dc \ . vi Fic. 36. —Sycon gelatinosum. ‘l'ransverse section through the wall of a cylinder (parallel with the course of the canals), showing one incurrent canal (/C), and one radial (2) throughout their length; sf, triradiate spicules; sf', oxeote spicules of dermal cortex (dc); sf'’, tetraradiate spicules of gastral cortex (ge); ec, ectoderm; ex, endoderm; fz, pore membrane; Z/, prosopyles; af, apopyle; dz, diaphragm; exc, excurrent passage; PG, paragastric cavity; ev, early embryo; e7', late embryo. The arrows indicate the course of the water through the sponge 80 SECT. lI PHYLUM PORIFERA 81 flagellate canals (&) —rather wider, octagonal in cross- section, and lined by endoderm continuous with the lining of the paragastric cavity. The incurrent canals end blindly at their inner extremities, not reaching the paragastric cavity; externally each becomes somewhat dilated, and the dilations of neighbouring canals often communicate. These dilated parts are closed externally by a thin membrane— the pore membrane, perforated by three or four openings — the inhalant pores already referred to. The flagellate canals are blind at their ower ends, which lie at a little distance below the surface ; internally, each communicates with the paragastric cavity by a short, wide passage, the excurrent canal (exc). Incurrent and flagellate canals run side by side, separated by a thin layer of sponge substance, except at certain points, where there exist small apertures of com- munication — the prosopyles ( pp) — uniting the cavities of adjacent incurrent flagellate canals. The ectoderm lining of the incurrent canals is of the same character as the ectoderm of the outer surface. The endoderm (/) of the flagellate canals, on the other hand, is totally different from that which lines the paragastric cavity. It consists of cells of columnar shape, ranged closely together so as to form a continuous layer. Each of these flagellate endoderm cells, or collared cells, as they are termed, is not unlike one of the choanoflagellate Protozoa (p. 38) ; it has its nucleus, one or more vacuoles, and, at the inner end, a single, long, whip-like flagellum, surrounded at its base by a delicate, transparent, collar-like upgrowth, similar to that which has already been described as occurring in the Choanoflagellata. If a portion of a living specimen of the sponge is teased out in sea-water, and the broken fragments examined under a tolerably high power of the microscope, groups of these collared cells will be detected here and G 82 MANUAL OF ZOOLOGY SECT. there, and in many places the movements of the flagella will be readily observed. It is to these movements that the formation of the currents of water passing along the canals is due. The short passage or excurrent canal, which leads inwards from the flagellate canal to the paragastric cavity, differs from the former in being lined by flattened cells similar to those of the paragastric cavity ; it is partly separated from the flagellate canal by a thin diaphragm (Fig. 36, @), perforated by a large circular central aperture — the apopyle (ap) — which is capable of being contracted or dilated ; its opposite aperture of communication with the paragastric cavity, which is very wide, is termed the gast7¢ ostium of the excurrent canal. The effect of the movement of the flagella of the cells in the flagellate canals is to produce currents of water running from without inwards along the canals to the paragastric cavity. This causes water to be drawn inwards through the prosopyles from the incurrent canals, and, indirectly, from the exterior through the perforated membranes at the outer ends of the latter. Between the ectoderm of the outer surface and of the incurrent canals, and the endoderm of the inner surface and of the flagellate canals, are a number of spaces filled by an intermediate layer — the mesoderm or mesoglea — in which the spicules of the skeleton are embedded. The spicules (Fig. 36, sf.), each of which is developed in a single cell of the middle layer, are regularly arranged, and connected together in such a way as to protect and support the soft parts of the sponge. Most are, as already noticed, of triradiate form. Large numbers, however, are of simple spear-like or club-like shape (sf'). The sexual reproductive cells —the ova (Fig. 36, ov) and sgerms — are developed Il PHYLUM PORIFERA 83 immediately below the flagellate endoderm cells of the flagellate canals, and in the same situation are to be found developing embryos (ev, em'). The simplest sponges are vase-shaped or cylindrical in form, either branched or unbranched, and, if branched, with or without anastomosis or coalescence between neigh- bouring branches. But the general form of the less sim- ple sponges differs widely from that of such a branching cylinder as is presented by Sycon (Fig. 34). From the point to which the embryonic sponge becomes attached, it may spread out horizontally, following the ir- regularities of the surface on which it grows, and forming a more or less closely adherent encrustation like that of an encrusting lichen. In other cases the sponge grows at first more actively in the vertical than in the horizontal direction, and the result may be a long, narrow structure, cylindrical or compressed, and more or less branched. Sometimes vertical and horizontal growth is almost equal, so that event- ually there is formed a thick, solid mass of a rounded or polyhedral shape, with an even, or lobed, or ridged surface. Very often, after active vertical growth has resulted in the formation of a comparatively narrow basal part or stalk, the sponge expands distally, growing out into lobes or branches of varying forms, and frequently anastomosing. Sometimes after the formation of the stalk with root-like processes for attachment, the sponge grows upwards in such, a way as to form a cup or tube with a terminal opening. Sometimes the sponge grows from a narrow base of attach- ment into a thin flat plate or lamella; this may become divided up into a number of parts or lobes, which may exhibit a divergent arrangement like the ribs of an open fan. 84 MANUAL OF ZOOLOGY SECT. Sycon belongs to a type of sponges intermediate between the very simplest forms on the one hand, and the more Fic. 37.— Ascetta primordialis. A portion of the wall of the vase-like sponge removed to show the para- gastric cavity, (After Haeckel.) the middle one, though it complex on the other. The simplest and most primitive of known sponges is one named Ascetta primordialis (Fig. 37). It is vase-shaped, contracted at the base to form a sort of stalk, by the expanded extremity of which it is attached; at the oppo- site or free end is the circular osculum. So far there is a considerable resemblance to Sycon gelatinosum,; but the structure of the wall in Ascetta is extremely simple. Regu- larly arranged over the sur- face are a number of small rounded apertures, the in- halant or incurrent pores ; but, since the wall of the sponge is very thin, these apertures lead directly into the central or paragastric cavity, the long passages or canals through which the communication is effected in Sycon being absent. The wall consists of the same three layers as in Sycon; but contains a small number of spicules, is very thin ; the endoderm, which lines the Ill PHYLUM PORIFERA 85 paragastric cavity, consists throughout of flagellate collared cells similar to those of the flagellate canals of Sycon. The majority of sponges, however, are more complicated in structure than Sycon. One of the causes of their complexity being that the canals, instead of being simple and straight, become branched, forming a system, often highly complicated, of ramifying channels. In these more complex sponges the flagellate collared cells are confined to CEN e ee bake We ye im ee Fic. 38. — Vertical section of a fresh-water sponge (Spongilla), showing the arrange- ment of the canal-system, C, ciliated chambers; D/P, dermal pores; £2, excurrent_canals; GO, openings of the excurrent canals; PG, paragastric cavity; SD, subdermal cavities; O, osculum. (Modified from Leuckart and Nitsche’s diagrams.) certain rounded dilatations of the canals—the flagellate chambers. Moreover, in the more complex forms the development of branches from the originally simple sponge, and the coalescence of neighbouring branches with one another, greatly obscure the essential nature of the sponge as a colony of zooids similar to the branches of Sycon; and this effect is increased by the development of a variety of infoldings of the ectoderm which appear in the higher forms. 86 MANUAL OF ZOOLOGY SECT. The elements of the se/e¢on differ in character in the two sub-classes into which the sponges are divided. In the Calearea, of which Sycon is an example, they consist of calcareous spicules, usually triradiate in form. In the Non-Calearea the skeleton either consists of spongin fibres alone (Fig. 39, A), or of séliceous spicules alone, or of a combination of spongin fibres with siliceous spicules (ZB) : in some (Myxospongie) skeletal parts are altogether absent. Spongin is a substance allied to silk in compo- sition ; the fibres are exceedingly fine threads, which branch and anastomose, or are woven and felted together in such a way as to form a firm, elastic supporting structure. The siliceous spicules (Fig. 40) are much more varied in shape than the spicules of the Calcarea, and in a single kind of sponge there may be a number of widely differing forms of spicules, each form having its special place in the skeleton of the various parts of the sponge-body. In most Non- Calcarea siliceous spicules and spongin fibres combine to form the supporting framework, the relative development of these two elements varying greatly in different cases. But in certain groups of the Non-Calcarea, including the common washing sponges, spicules are completely absent, and the entire skeleton consists of spongin. In some Non-Calcarea which are devoid of spicules, the place of these is taken by foreign bodies — shells of Radiolaria, grains of sand, or spicules from other sponges (Fig. 39, C). In others, again, such as the Venus’s flower-basket (Zuplectella), the glass- rope sponge (Ayalonema), and others, the skeleton consists throughout of siliceous spicules bound together by a siliceous cement. Reproduction in the Sponges is effected either sexually or asexually. The process by which, in all but the simplest forms of sponges, a colony of zooids is formed from the ll PHYLUM PORIFERA 87 originally simple cylinder or vase, may be looked upon as an asexual mode of reproduction by budding. Asexual A.Euspongia | B.Pachychalina Fic. 39. — Microscopic structure of the skeleton in various sponges. A, Euspongia, network of spongin fibres; B, Pachychalina, spongin strengthened by siliceous spicules; C, Spongelia, spongin strengthened by various foreign siliceous bodies, fragments of spicules of other sponges, etc. (After Vosmaer.) 88 MANUAL OF ZOOLOGY SECT. multiplication also assumes the form in some cases of a process of production of internal buds in the shape of groups of cells called gemmules, which eventually become detached and develop into new individuals. In the fresh- water sponges (Spongiliid@) multiplication takes place very actively by means of such gemmules, each of which is a spherical group of cells enclosed in an envelope composed of peculiarly shaped siliceous spicules, termed amphidises (Fig. 40, right side). All sponges multiply by a sexual process — by means of male cells, or sperms, and female Fic. 40. — Various forms of sponge spicules. (From Lang's Text Book.) cells, or ova. Ova and sperms are developed in the same sponge, but rarely at the same time. The cell destined to form sperms divides into a number of small cells, giving rise to a rounded mass of sperms. The latter, when mature, have oval or pear-shaped heads and a Jong taper- ing appendage or tail. Each cell destined to form an ovum enlarges, and eventually assumes a spherical form. After a sperm has penetrated into its interior and effected impreg- nation, it usually becomes enclosed in a brood-capsule formed for it by certain neighbouring cells, and in this situation, still enclosed in the parent sponge, it undergoes in PHYLUM PORIFERA 89 the earlier stages of its development. Eventually it becomes free as a ciliated larva, which pursues a free existence for a time, swimming about by the agency of the cilia, till after a time it becomes fixed and develops into the adult form. Fresh-water sponges (.Spongi/ide) live in rivers, lakes, etc. Marine sponges occur in all seas, and at all depths, from the shore between tide marks to the deepest abysses of the ocean. Sponges do not appear to be edible by fishes, or even the higher crustaceans or molluscs. Countless lower animal forms, however, burrow in their substance, if not for food, at least for shelter, and the interior of a sponge is frequently found to be teeming with small crustaceans, annelids, mol- luscs, and other invertebrates. None of the sponges are true parasites. The little boring sponge, Cona, burrows in the shells of oysters and other bivalves, and even into solid limestone, but for protection and not for food. But the sponge frequently lives in that close association with another animal or plant to which the term messmatetsm, or commensalism is applied — associations which benefit one or both. Thus some species of sponge are never found grow- ing except on the backs or legs of certain crabs. In these cases the sponge protects the crab and conceals it from its enemies, while the sponge benefits by being carried from place to place, and thus obtaining freer oxygenation. Cer- tain cirripede crustaceans (members of the order to which the barnacles and acorn-shells belong) are invariably found embedded in certain species of sponge. Frequently a sponge and a zoophyte grow in intimate association, so that they seem almost to form one structure. Thus the glass-rope sponge (Ayalonema) is always found associated with a zoophyte (fa/yéhea), and there are many other in- stances. Sponges often also grow in very close association with certain low forms of plants (.4/@). SECTION IV.—PHYLUM CCELENTERATA In the previous section we saw that the simplest type of sponge has the general character of a cylinder, closed at one end and open at the other, and having the walls perforated by minute pores, and composed of three layers, —ectoderm, mesogloea, and endoderm, the last consisting of collared flagellate cells. In such an organism as this, imagine the pores to disap- pear, the internal cavity thus coming to communicate with the exterior by a single terminal aperture; the mesogloea to be replaced by a very thin, structureless layer containing no cells; the endoderm cells to lose their collars; and a circlet of arm-like processes, or tentacles, formed of the same layers as the body-wall, to be developed round the terminal aperture. The result would be a foMfe, and would serve as a type of the general structure of the group of animals with which we are now concerned. The most familiar examples of Coelenterata are the horny, seaweed-like hydroids, or, as they are sometimes called, “zoophytes,” to be picked up on every sea-beach, jelly- fishes, sea anemones, and corals. The phylum is divided into four classes as follows : — Class 7.— Hydrozoa, including the fresh-water polypes, zoophytes, many jellyfishes,—mostly of small size,—and a few stony corals. 90 SECT. IV PHYLUM CCELENTERATA 91 Class 2.— Seyphozoa, including most of the large jelly- fishes. Class 3.-—— Actinozoa, including the sea-anemones, and the vast majority of stony corals. Class g.—Ctenophora, including certain peculiar jelly- fishes known as ‘“comb-jellies.”’ 1. THE HYDROZOA Obelia, which is a good example of the class, is a common zoophyte occurring in the form of a delicate, whitish, or light brown, almost fur-like growth on the wooden piles of piers and wharfs. Ovelia commissuralis occurs on the coast of New England almost at low-water mark, being exposed only at the lowest tides. With it, north of Cape Cod, may be found Odelia gelatinosa, a rather stouter species, but similar in general appearance. Odea genicudata is abundant on Laminaria or the “devil’s apron,” giving the fronds when submerged a downy appearance. The following account refers to a common European species: It consists of branched filaments about the thickness of fine sewing cotton; of these, some are closely adherent to the timber, and serve for attachment, while others are given off at right angles, and present at intervals short lateral branches, each terminating in a bud-like enlargement. The structure is best seen under a low power of the microscope. The organism (Fig. 41) is a colony, consisting of a common stem or axis, on which are borne numerous zooids. The large majority of the zooids have the form of little conical structures (P, z-P, 4), each’ enclosed in a glassy, cup-like investment or hydrotheca (Ath), and produced dis- tally into about two dozen arms or /entacles (7): these zooids are the pohpes or hydranths. Less numerous, and 92 MANUAL OF ZOOLOGY SECT. IV found chiefly towards the proximal region of the colony, are long cylindrical bodies or d/astostyles (b/s), each enclosed in a transparent case, the gonangium or gonotheca (gth), and bearing numerous small lateral offshoots, varying greatly in form according to their stage of development, and known as medusa-buds (m.bd). By studying the development of these structures, and by a comparison with other forms, it is known that both blastostyles and medusa-buds are zooids, so that the colony is #imorphic, having zooids of three kinds. To make out the structure in greater detail, living speci- mens should be observed under a high power. A polype is then seen to consist of a somewhat cylindrical, hollow body, of a yellowish colour, joined to the common stem by its proximal end and produced at its distal end into a conical elevation, the manudrium or hypostome (mnb), around the base of which are arranged the twenty-four tentacles in a circle. Both body and manubrium are hol- low, containing a spacious cavity, the eteron (ent), which communicates with the outer world by a mouth (mth), an aperture placed at the summit of the manubrium. The mouth is capable of great dilatation and contraction, and accordingly the manubrium appears now conical, now trumpet-shaped. Under favourable circumstances small organisms may be seen to be caught by the tentacles and carried towards the mouth to be swallowed. ‘The hydro- theca (Av) has the form of a vase or wine-glass, and is perfectly transparent and colourless. When irritated — by a touch, or by the addition of alcohol or other poison — the polype undergoes a very marked contraction: it suddenly withdraws itself more or less completely into the theca, and the tentacles become greatly shortened and curved over the manubrium (P. 2). ae eR BA Fic, 41.—Obelia sp. A, portion of a colony, with certain parts shown in longi- tudinal section; B, medusa; C, the same, with reversed umbrella; D, the same, oral aspect; Bd. 7, 2, buds; dls, blastostyle; c@, ccenosarc; ect, ectoderm ; end, endoderm ; ext, enteric cavity: gt#, gonotheca (gonangium) : At, hydro- theca; 7, lithocyst; #.4d, medusa-bud: #6, manubrium; szsg?, mesoglea; mth, mouth; #, perisarc; P. 2, 2, 3, ¢, polypes; rad.c, radial canal; 7, tentacle; v/, velum. 5 93 94 MANUAL OF ZOOLOGY SECT. The various branches of the common stem show a very obvious distinction into two layers: a transparent, tough, outer membrane, of a yellowish colour and horny con- sistency, the ferisarc (f), and an inner, delicate, granular layer, the ce@nosarc (ce), continuous by a sort of neck or constriction with the body of each hydranth. The ccenosarc is hollow, its tubular cavity being continuous with the cavities of the polypes, and containing a fluid in which a flickering movement may be observed, due to the presence of vibrating cilia. In the blastostyle both mouth and tenta- cles are absent, the zooid ending distally in a flattened disc ; the hydrotheca of the polype is represented by the gono- theca (g#), which is a cylindrical capsule enclosing the whole structure, but ultimately becoming ruptured at its distal end to allow of the escape of the medusa-buds. These latter are, in the young condition, mere hollow off- shoots of the blastostyle: when fully developed they have the appearance of saucers attached by the middle of the convex surface to the blastostyle, produced at the edge into sixteen very short tentacles, and having a blunt process, the manubrium, projecting from the centre of the concave sur- face. They are ultimately set free through the aperture in the gonotheca as little medusz or jellyfish (B-D), which will be described hereafter. The microscopical structure of Obelia reminds us, in its general features, of that of such a simple sponge as Ascetta, but with many characteristic differences. The body is composed of two layers of cells, the ectoderm and the endoderm, the latter ciliated; between them is a very delicate transparent membrane, the mesoglea or supporting lamella, which, unlike the intermediate layer of sponges, contains no cells and is practically structureless. The perisare or transparent outer layer of the stem shows Iv PHYLUM CCELENTERATA 95 no cell-structure, but only a delicate lamination. It is, in fact, not a cellular membrane or epithelium, like the ecto- derm and endoderm, but a cwécle, formed, layer by layer, as a secretion from the ectoderm cells (see p. 67). It is of chitinoid or horn-like consistency, and, like the lorica of many Protozoa, serves as a protective external skeleton. Embedded in the ectoderm are numerous clear, ovoid bodies, the stnging-capsules or nematocysts (Fig. 42), serving as weapons of offence. Each consists (A) of a tough, ovoid capsule, full of a gelatinous material, and invaginated at one end in the form of a hollow process continued into a long, coiled, hollow thread. The whole apparatus is developed in an interstitial cell called a cnzdoblast (cnb), which, as it ap- proaches maturity, migrates towards the surface, and becomes embedded in one of the large ectoderm cells. At one point of its surface the cnidoblast is produced into a delicate pro- toplasmic process, the cnidocil or trigger-hair (enc) : when this is touched — for instance by some small organism brought into contact with the waving tentacles— the cnidoblast un- dergoes a sudden contraction, and the pressure upon the stinging-capsule causes an instantaneous eversion of the thread (B), at the base of which are minute barbs. The threads or the gelatinous substance are poisonous and exert a numbing effect on the animals upon which the Obelia preys. The structure of the Medusaze — formed as we have seen by the development of medusa-buds liberated from a ruptured gonangium — yet remains to be considered. The convex surface of the bell or umbrella (Fig. 41, B-D) by which the zooid was originally attached to the blastostyle, is distinguished as the ex-wmbrella, the concave inner surface as the sub-umbrella. From the centre of the sub-umbrella proceeds the manubrium (mz), at the free end of which is 96 MANUAL OF ZOOLOGY SECT. the four-sided mouth (ch). Very commonly as the medusa swims the umbrella becomes turned inside out, the sub- Fic. 42.— Nematocysts of hydra. A, undischarged; B, discharged; C, nerve- supply; ed, cnidoblast; exe, cnidocil; xz, nucleus; wfc, nematocyst; xz.c, nerve-cell. (From Parker’s Svodogy, after Schneider.) umbrella then forming the convex surface, and the manu- brium springing from its apex (Fig. 41, C). Iv PHYLUM CCELENTERATA 97 The mouth (Figs. 41, C, D, and 43, msh) leads into an enteric cavity which occupies the whole interior of the manubrium, and from its dilated base sends off four delicate tubes, the radial canals (rad. c), which pass at equal distances from each other through the substance of the umbrella to its margin, where they all open into a circular canal (cir. c), running parallel with and close to the margin. By means of this system of canals the food, taken , i \j et oto Fic. 43. ~ Dissection of a medusa with rather more than one-quarter of the umbrella and manubrium cut away (diagrammatic). The ectoderm is dotted, the endo- derm striated, and the mesoglcea black. c7r. c, circular canal; exd. lam, endoderm lamella; gow, gonad; 7, lithocyst; #2, manubrium; 1¢4, mouth; rad, c, radial canal; v/, velum. in at the mouth and digested in the manubrium, is dis- tributed to the entire medusa. The edge of the umbrella is produced into a very narrow fold or shelf, the velwm (Fig. 43, v/), and gives off the tentacles (7), which are sixteen in number in the newly-born medusa (Fig. 41, D), but which are very numerous in the adult. At the bases of eight of the tentacles— two in each quadrant — are minute globular sacs (7), each containing a H Missing Page Missing Page ee Ae SCALE FoH A wh fic 45.—Hydra. A vertical section of entire animal; B, portion of transverse section, highly magnified: C, two large ectoderm cells: D, endoderm cell of H viridis; ¥, large nematocyst; I’, small nematocyst; G, sperm; a, ingested diatom; éd.1, ba.2, buds: chr, chromatophores; c/, cnidoblast; cc, cnidocil; ect, ectoderm; end, endoderm; ext. cav, enteric cavity; evt caz, its prolonga- tion into the tentacles; /7, flagellum; Ay/, hypostome or manubrium; zw? c, in- terstitial cells; 7. fx, muscle processes; ath, mouth; msg/, mesoglea; xct, large, and z#c}, small nematocysts; 7, nucleus, ov, ovum; ovy, ovary; psd, pseudopods; sfy,spermary; vac, vacuole, 100 SECT. IV PHYLUS CCOELENTERATA 101 tome and a circlet of from six to eight tentacles surrounding the mouth. It is ordinarily attached, by virtue of a sticky secretion from the proximal end, to weeds, etc., but is capable of detaching itself and moving from place to place after the manner of a looping caterpillar. The tentacles are hollow, and communicate freely with the enteron. There is no perisarc. Buds are produced which develop into Hydre ; but these are always detached sooner or later, so that a permanent colony is never formed. ‘There are no special reproductive zooids, but simple ovaries (ovy) and testes (spy) are developed, the former nearer the proximal, the latter nearer the distal end of the body. In nearly all the remaining Hydrozoa that do not form colonies the form assumed is not that of the AoZype, but that of the medusa (Fig. 46), a polype stage never being developed, and the animal resembling in all essential respects the medusz of Obelia; the chief difference of importance being the presence of sense-organs in the form of hollow, club-shaped appendages, the sentaculocysts, con- taining calcareous bodies of 4¢h7ztes. These simple free- swimming medusiform Hydrozoa (Z7achytine) develop ova and sperms which give rise to free-swimming ciliated larvee ; but the latter, instead of becoming fixed and developing into plant-like colonies, remain free, and develop directly into medusz like those from which they originated. The fixed zoophyte stage is thus absent in the life-history, and an alternation of generations is not recognisable. In the colonial Hydrozoa, which constitute the great majority of the class, the colony in most instances resem- bles that of Obelia in being a fixed structure consisting of a slender branching stem, covered over by perisarc, and bear- ing zooids and blastostyles. In many the perisarc is produced to form hydrothece and gonothece for the 102 MANUAL OF ZOOLOGY SECT. protection of the polypes and blastostyles respectively ; but in others (Fig. 47) these protecting structures are absent. The polypes resemble those of Obelia in all es- = ° 3 ° ° ° 0 @ ° 9 n ctr. c, circular canal; gon, gonad; 2d, manubrium; ah, mouth; recurrent canal; 7, tentacle; 7c, tentaculocyst; ¢g, tongue; v/, velum. e ae a 3 c a a ae o Ba _ ees o $85 Oss ° vu “ ses ana E23 Se oO SES & sential respects, but differ in the number and arrangement of the tentacles and other minor points. In many meduse are developed from blastostyles as in Obelia, and when fully formed become free. The shape of the medusa Iv PHYLUM CCELENTERATA 103 differs in different forms, more particularly as regards the umbrella. There is always a manubrium, with gastric ® Fic. 47.— Bougainvillea ramosa. A, entire colony, natural size; B, portion of the same magnified ; C, immature medusa ; ctr. c, circular canal; cz, cuticle or perisarc ; end. cav, enteric cavity ; 4yd, polype or hydranth ; yf, hypostome or manubrium ; sed, medusa; 2d, manubrium ; rad. c, radial canal ; ¢, tentacle ; v, velum, (From Parker’s Bzology, after Allman.) This is closely allied to the New England B, supercilians. 104 MANUAL OF ZOOLOGY SECT. cavity, and a marginal and four radial canals, and a velum is universally present. But lithocysts are not present in all, their place being taken by specks of red or black pigment —the oce/Z or rudimentary eyes —at the bases of the ten- tacles. The number and arrangement of the tentacles is subject to considerable variation. The gonads are some- times, as in Obelia, developed in the radial canals, some- times in the manubrium. In size the medusz range from about 1 up to 400 millimetres (16 inches) in diameter. In many of the zoophytes, however, the medusz never become detached from the colony, developing the ova and sperms without becoming free. In such cases the charac- teristic medusa structure is more or less imperfectly de- veloped, and in many forms is not at all recognisable, the buds corresponding to those which in Obelia give rise to medusze merely developing into rounded outgrowths termed Sporosacs, in the interior of which the ova and sperms are formed. The reproductive buds are not in all cases formed, as in Obelia, on distinct, peculiarly modified, mouthless zooids. In many instances, whether they are destined to give rise to meduse or sporosacs, the buds spring directly from the ccenosarc, or from the ordinary zooids. A small group of Hydrozoa—the Hydrocorallina — in- cluding the Millepores (A@iVepora) and Sfvlaster, form colonies, the supporting material of which, instead of being chitinoid, is of calcareous and stony character, like the substance of a coral. The colonies of Hydrozoa are not in all instances at- tached, like those of Obelia and the othér hydroid zoo- phytes. In one large order, the Siphonophora, the colonies of zooids float or swim freely in the sea. In some Siphono- phora there are no organs for active locomotion, and the Iv PHYLUM CCELENTERATA 105 colony drifts about, completely at the mercy of wind and tide, buoyed up by a bladder-like float or pneumatophore containing air. Such a passively floating form is the Portuguese Man-of-war (Physalia) (Figs. 48, 49) which has an elongated float, pointed at the ends, and produced above, along its upper edge, into a crest or sail (cv). At one end is a minute aperture communicating with the exterior. From the under side of the float hang polypes (J), feelers, groups of medusa-buds looking like bunches of grapes of a deep blue colour, and long retractile tentacles, sometimes several feet in length, and containing batteries of stinging- capsules powerful enough to sting the hand as severely as a nettle. ‘The male reproductive buds remain attached and take the form of sporosacs, while the female buds apparently become detached as free meduse. Physalia arethusa is common in the West Indies, and, borne northward by the Gulf Stream, is occasionally met with on the coast of southern New England, and off Nova Scotia. In such a Siphonophoran as Halistemma (Fig. 50), on the other hand, there is a long, slender, flexible stem or coenosarc, at the upper end of which is a comparatively small float. Next to this come a number of closely set, transparent structures (zc), having the general characters of unsymmetrical medusz without manubria, each being a deep, bell-like body, with a velum and radiating canals. During life these szimming-bells or nectocalyces contract rhythmically, —z.e., at regular intervals,—thus serving to propel the entire organism through the water. Below the last negtocalyx the character of the structures borne by the stem changes completely: they are of several kinds, and are arranged in groups which follow one another at regular intervals. Some of these are unmistakable polypes (f) differing, 106 MANUAL OF ZOOLOGY SECT. si ANAT dd ‘ ‘ APS’ POA ¢ % 5 SON g i £4 a o¢€ Sasser Mecca as ah Sy 0! nn soa ‘Move yunt Z i ~ Fic. 48 —Physalia. The living animal Fic. 49.— Physalia arethusa, natural floating on the surface of the sea. cv, size. (After Agassiz.) crest ; f, polype ; A, pneumatophore, float, or air-sac. (After Huxley.) Iv PHYLUM CGELENTERATA 107 OS ce a U 2b ws ea of ey WX 7 ia i & : SZ g AN & S we 710o Fic. 50 —Halistemma tergestinum. A, the entire colony; B. 4 single group of zooids; c@, coenosarc; dz, dactylozooid; #f4, hydrophyllium or bract; xc?, nectocalyx or swimmuing-bell; xéc. battery of nematocysts; #. polype; fx, pneumatophore or float; s, s', sporocysts; 7, tentacle, (After Claus.) 108 MANUAL OF ZOOLOGY SECT. however, from those we have hitherto met with, in having no circlet of tentacles round the mouth, but a single, long, branched tentacle (¢) arising from its proximal end, and bearing numerous groups or “ batteries” of stinging-capsules (ntc). Others are dactylozooids or feelers (dz) —mouth- less polypes, each with an unbranched tentacle springing from its base. Near the bases of the polypes and dactylo- zooids spring groups of sporosacs (B, s, s‘), some male, others female; and finally delicate, leaf-like transparent bodies —- the braces or hydrophyllia (hph) — partly cover the sporosacs. Halistemma occurs in the Atlantic and Mediter- ranean. A closely related form (Agalmopsis cara) occurs off the coast of New England. 2. THE SCYPHOZOA Aurelia, which may be taken as an example of the Scyphozoa, is the most common of our larger jellyfishes, and is often found cast up on the sea-shore, where it is readily recognisable by its gelatinous saucer-shaped umbrella, from eight to twelve, and sometimes fifteen inches in diam- eter, having near the centre four red or purple horseshoe- shaped bodies — the gonads — lying embedded in the jelly. The general arrangement of the parts of the body (Fig. 51) is very similar to what we are already familiar with in the hydrozoan jellyfishes (Figs. 41 and 43). Most con- spicuous is the concavo-convex umbrella, the convex sur- face of which, or ex-umbrella, is uppermost in the ordinary swimming position. The outline is approximately circular, but is broken by eight notches, in each of which lies a pair of delicate processes, the marginal lappets (mg. ip) with a peculiar sense-organ,; between the pairs of lappets the edge Iv PHYLUM CCELENTERATA 109 of the umbrella is fringed by numerous close-set marginal tentacles (2). In the centre of the lower or sub-umbrella surface is a four-sided aperture, the mowth (m¢h), borne at the end of Fic. 51 —Aurelia aurita. Ventral view—two of the oral arms are removed; a@.7.c, radial canal; gon, gonads; z.7.c, radial canal; mg. /p, marginal lappet; mth, mouth; ov. a, oral arm; g.7.c, radial canal; s.g.f, sub-genital pit; ¢, tentacles. an extremely short and inconspicuous manubrium: sur- rounding it are four long delicate processes, the oral arms 110 MANUAL OF ZOOLOGY SECT. (or. a), situated one at each angle of the mouth and uniting round it. At a short distance from each of the straight sides of the mouth is a nearly circular aperture leading into a shallow pouch, the swd-genital pit (s. g. p), which lies immediately beneath one of the conspicuously coloured gonads (gor). The mouth leads by a short tube or gwHez, contained in the manubrium, into a spacious stomach, which is produced into four wide inter-radial gastric pouches, which extend about halfway from the centre to the circumference. In the outer or peripheral wall of each gastric pouch are three small apertures, leading into as many radial canals (arc, irc, prc), which pass to the edge of the umbrella and then unite in a very narrow circular canal. Each gonad (go.) is a horseshoe-shaped frill-like structure situated on the floor of the gastric pouch. When mature, its products — ova or sperms — are discharged into the stomach, and pass out by the mouth. The sexes are lodged in distinct individuals. Lying parallel with the inner or concave border of each gonad is a row of delicate filaments supplied with stinging- capsules. These are the gastric filaments. their function is to kill or paralyse the prey taken alive into the stomach (compare Fig. 53, g./). The development and life-history of Aurelia present several striking and characteristic features. The impreg- nated egg-cell or oosperm becomes converted into a closed two-layered sac or flanula (Fig. 52, A), similar to that of a Hydrozoon. The planula swims about by means of the cilia with which its ectodermal cells are provided, and, after a brief free existence, settles down, loses its cilia, and be- comes attached by one pole. At the opposite pole a mouth is formed. On two opposite sides of the mouth hollow Iv PHYLUM CCZLENTERATA 11 Fic. 52. — Aurelia aurita, development A, planula: B, C, formation of the gullet or stomodeum; D, transverse section of young scyphula; E, scyphula; F, longitudinal section of same; G, division of scyphula into ephyrule; H, ephy- rula from the side; J, the same from beneath. In A D and F the ectoderm is unshaded, the endoderm striated, and the mesogleea dotted. a, lobes of umbrella; #774, manubrium; stk, mouth; sf, septal funnel; s¢, stomodaeum; z, tentacle: ¢z, taenioles, or gastric ridges. (From Korschelt and Heider’s Embryology ) 112 MANUAL OF ZOOLOGY SECT. processes grow out, forming the first two tentacles; soon two others appear at right angles to these. Subsequently other tentacles appear. At the same time the attached or proximal end is narrowed into a stalk-like organ of attach- ment (E). The outcome of all these changes is the metamorphosis of the planula into a polype (F), not unlike a Hydra. The Scyphozoon-polype is called a Scrphula. The Scyphulasome- times multiplies by budding. After a time it undergoes a process of transverse fission (G), becoming divided by a series of constrictions which deepen until the polype assumes the appearance of a pile of saucers, each with its edge produced into eight bifid lobes. Soon the process of constriction is completed, the saucer-like bodies separate from one another, ° and each, — except the first topmost one, which falls off and dies, — turning upside down, begins to swim about as a small jellyfish called an Aphyruda (H, I), which grows rapidly and eventually develops into the adult Aurelia. The rest of the Seyphozoa resemble Aurelia in the gen- eral features of their structure, but there is a good deal of variation in certain points (Fig. 52). Thus the umbrella, instead of being a saucer-shaped disc, as in Aurelia, is often conical or cup-shaped or cubical. In some, tentaculocysts are not developed, and in others the oral arms are absent. Lucernaria differs somewhat widely from the rest in being attached by means of a short stalk developed from the centre of the ex-umbrella. In the AAdzostomee the mouth is obliterated by the union of the bases of the oral arms, the food being taken in through a large number of minute orifices scattered over the surface of the arms, and leading into a system of fine canals, which join together to form larger canals, eventually opening into the gastric cavity. Many of the Scyphozoa pass through an alternation of generations Iv PHYLUM CCELENTERATA 113 similar to that which has been described in the case of Aurelia, with a fixed scyphistoma stage; but in others the ciliated larvee developed from the ova give rise directly to Fic. 53.—-Tessera princeps. A, external view; B, vertical section; g._/, gastric filament; gon, gonad; 7.x.¢, tentacle; ed, manubrium; mth, mouth; £.7.t, tentacle: s¢, stomach; ¢m, tzeniole or gastric ridge. Antarctic Ocean. (After Haeckel.) jellyfishes like the parent, without the intercalation of any ‘fixed stage. The Scyphozoa are all marine, and the majority are pelagic, t.e., swim freely in the surface waters of the ocean. I 114 MANUAL OF ZOOLOGY SECT. A few inhabit the deep sea, and have been dredged from as great a depth as 2000 fathoms. Nearly all are free- swimming in the adult state; some, however, live on coral- reefs or mud-banks, and are found resting, in an inverted position, on the ex-umbrella; and a few, such as Lucernaria, are able to attach themselves at will by a peduncle. Many are semi-transparent and glassy, but often with brilliantly coloured gonads, tentacles, or radial canals. In many cases the umbrella, oral arms, etc., are highly coloured, and some species are phosphorescent. They are all carnivorous, and, although mostly living on smaller organisms, are able, in the case of the larger species, to capture and digest crustaceans and fishes of considerable size. 3. THE ACTINOZOA The simplest and most familiar of the Actinozoa are the Sea-anemones, which are to be found attached to rocks, seaweeds, shells, etc., on the sea-shore. When expanded a sea-anemone has the form of a cylindrical column attached to a rock or other support by a broad dase. The distal or free surface of the column, termed the dsc or peristome, bears in the middle an elongated, slit-like aperture—the mouth, Springing from the disc and encircling the mouth are numerous cylindrical zzfrc/es, disposed in circlets, their total number being some multiple of five. Obviously the sea-anemone is a polype, formed on the same general lines as a polype of the Hydrozoa. But certain important differences from the Hydrozoan polype become manifest when we examine the internal structure (Fig. 54). The mouth does not lead at once into a spacious undivided enteric cavity, but into a short tube (gv/), having the form of a flattened cylinder, which hangs downward IV PHYLUM CCELENTERATA 115 into the interior of the body, and terminates in a free edge. This tube is called the gude¢ or stomodeum. Its inner surface is marked with two longitudinal grooves (sgh), known as the gullet-grooves or siphonoglyphes. The gullet does not simply hang freely in the interior cavity, but is connected with the body-wall by a number of radiating WIth ost.? m1es.3. 713.2 Fic. 54.—Tealia crassicornis. Dissected specimen; gon, gonads; gz?, gullet; Z m, longitudinal muscle; 4%, lappet; es. z, primary, mes. 2, secondary, mes. 3, tertiary mesenteries; ses. F, mesenteric filaments; mth, mouth; ost. 1, ost. 2, ostia or aperture in mesenteries; Z. 7, parietal muscle; sgfh, siphonoglyphe; s. #, sphincter muscle; #4. #, transverse muscle. partitions, the complete or primary mesenteries (mes. I) ; between these are incomplete secondary mesenteries (mes. 2), which extend only part of the way from the body-wall to the gullet, and “rtiary mesenteries (mes. 3), which are hardly more than ridges on the inner surface of the body- 116 MANUAL OF ZOOLOGY SECT. wall. Thus the entire enteric cavity of a sea-anemone is divisible into three regions: (1) the gwdlet or stomodeum, communicating with the exterior by the mouth, and opening The ectoderm ac, acontium; cz, cinclis or aperture in gloza black. i , intermesenteric chamber; mes, mesentery; ses. /, mesenteric -wall; gv, gullet: zit. mcs. c¢ ; mth, mouth; as¢, ostium; Z, pore; #, tentacle. is dotted, the endoderm striated, the meso; body filament Fic. 55. — Diagrammatic vertical (A) and transverse (B) sections of a sea-anemone. below into (2) a single main digestive cavity, the stomach, which gives off (3) a number of radially arranged cavities, the inter-mesenteric chambers. The free edges of the mesenteries below the gullet are produced into curious Iv PHYLUM CCELENTERATA 117 twisted cords, the mesenteric filaments (mes. F), answering to the gastric filaments of Scyphozoa. Stinging-capsules occur in the ectoderm, and are also very abundant in the mesenteric filaments. They resemble in general character the nematocysts of Hydrozoa, but are of a more elongated form, and the thread is usually provided at the base with very numerous slender barbs. In virtue of possessing both stinging-capsules and gland- cells, the mesenteric filaments perform a double function. The animal is very voracious, and is able to capture and swallow small fishes, molluscs, sea-urchins, etc. The prey is partly paralysed before ingestion by the nematocysts of the tentacles, but the process is completed, after swallowing, by those of the mesenteric filaments. Then, as the captured animal lies in the stomach, the edges of the filaments come into close contact with one another and practically surround it, pouring out at the same time a digestive juice secreted by their gland-cells. Sea-anemones are dicecious, the sexes being lodged in distinct individuals. The gonads—ovaries or testes—are developed in the substance of the mesenteries (Fig. 54, gon), a short distance from the edge, and, when mature, often form very noticeable structures. The development of sea-anemones resembles, in its main features, that of Scyphozoa, but there is no alternation of generations. Our common sea-anemone, Metridium marginatum (Fig. 56), lives under stones near low-water mark. Two main divisions or sub-classes of the Actinozoa are recognised,—the Zoantharia and the Alcyonaria, the former including the sea-anemones, the Madrepores, and other stony corals, and the horny black corals; the latter the “dead men’s fingers,” red coral, organ-pipe coral, “sea-fans,” and “sea-pens.” The principal distinguishing 118 MANUAL OF ZOOLOGY SECT. features of the two sub-classes are, that in the Zoantharia the tentacles and mesenteries are usually very numerous, and are arranged, as a rule, in multiples of five or six, and Fic. 56.— The common Sea-anemone. Fic. 57. —Corallium rubrum, portion of P (After Emerton.) colony. Enlarged twice. (After Lacaze- Duthiers.) that the tentacles are simple in form; while in the Alcyo- naria (Fig. 58) the tentacles and mesenteries are always eight in number, and the tentacles are pinnate, z.e., each of them consists of a main stem with two rows of lateral branchlets. Only the sea-anemones (with a few exceptions) and a few Madrepore corals remain simple, the rest all giving rise to more or less extensive colonies, of a variety of differ- ent forms, by continuous budding. ‘The structure of the zooids is similar to that of the sea-anemone in all essential respects. In many of the Alcyonaria two forms of zooids are to be distinguished in each colony (dimorphism of the zooids), ordinary zooids, and siphonozoords, which are smaller, and are devoid of tentacles and of gonads. Iv PHYLUM CCELENTERATA 119 None of the sea-anemones have a true skeleton ; in some, however, there is a thick cuticle, and several kinds enclose themselves in a more or less complete tube, which may be largely formed of discharged nematocysts. In some Alcyo- Fic. 58.—Alcyonium palmatum. A, entire colony natural size; B, spicules. editerranean Sea. (After Cuvier.) naria, such as the “ dead men’s fingers ” (A/cyonium, Fig. 58), the skeleton consists of minute, scattered, irregular deposits of carbonate of lime called spicules. Alcyonium carneum occurs below tide-mark off the New England coast. In Tubipora (the “ organ-pipe coral’’) (Fig. 59) there is a con- 120 MANUAL OF ZOOLOGY SECT. tinuous calcareous tube for each polype. In the red coral of commerce (Fig. 57), which inhabits the Mediterranean Sea, there is an extremely hard calcareous branched rod which extends as an axis through the ccenosarc. In the black corals (.dv/pacthes and allies) there is a horn-like axis ; and in Gorgonia there is a similar skeleton, some- times partly calcareous, with the addition of numerous spicules. In the sea-pens (Fig. 60) the colony is supported by an un- branched horny axis. Pennatula aculeata lives in deep water in the North Atlantic. In the Madrepore corals we have a skeleton of an entirely different type, consisting, in fact, of a more or less cup-like calca- reous structure secreted from the ectoderm of the base and column of the polype. When formed by a solitary polype such a “ cup- Fic. 59. — Tubipora musica. Skel- coral” is known as a corallite ; eton of entire colony. Natural, Pia A cen IndianQcean jn the majority of species a large number — sometimes many thou- sands — of corallites combine to form a corad/um, the skele- ton of an entire coral-colony. The structure of a corallite is conveniently illustrated by that of the solitary genus F/adelum (Fig. 61, A, B). It has the form of a short conical cup, much compressed, so as to be oval in section. Its wall or ¢heca is formed of dense stony calcium carbonate, the proximal end pro- duced into a short stalk or peduncle. From the inner Iv PHYLUM CCELENTERATA 121 surface of the theca a number of radiating partitions, the septa, proceed inwards or towards the axis of the cup, some of them meeting in the middle to form an irregular central mass or columella, which in some kinds of corals forms an independent, pillar-like structure arising from the middle of the base. In the living condition the polype fills the whole interior of the corallite, and projects beyond its edge to a greater or less degree according to its state of expan- sion. The septa alternate with the mesenteries, each being in- vested by an in-turned portion of the body-wall; so that, though having at first sight the appear- ance of being internal structures, they are really external, lying alto- gether outside the enteric cavity, and are in contact throughout with the ectoderm. 7 The almost infinite variety in form of the compound corals is Fic._60.—Pennatula sulcata. s 3 . Entire colony. Natural size. due, in the main, to the various Z, lateral branch. (After methods of budding. According pee to the mode of budding, massive corals are produced in which the corallites are in close contact with one another, as in Astrea (Fig. 62); or tree-like forms, such as Den- adrophyllia (Fig. 63, A), in which a common calcareous stem, the cenenchyma, is formed by calcification of the ccenosarc,' and gives origin to the individual corallites. 1See p. 94. 122 MANUAL OF ZOOLOGY SECT. ST Ta Sapo Tse oe =o L af. orev I > i Fic. 164.— Diagram of the circulatory system of Anodonta. Vessels containing aérated blood red, non-aérated blue. @/ dr. v, afferent brancbial veins; ao, aorta; art.s, artery to mantle; a7? 2, artery to body generally; az, auricle; ef. br. 7, efferent branchial veins; 2p. v, nephridial veins; fc, pericardium; wv, ventricle; v.c, venacava. The arrows show the direction of the current. visceral mass with the foot; the two pedal ganglia are so closely united as to form a single bilobed mass. From each cerebro-pleural ganglion there further proceeds a long cere- bro-visceral connective which passes directly backwards through the kidney, and ends in a visceral ganglion (v. gn) XI PHYLUM MOLLUSCA 277 placed on the ventral side of the posterior adductor muscle. The visceral, like the pedal ganglia, are fused together. Sensory organs are poorly developed, as might be expected in an animal of such sedentary habits. In connection with each visceral ganglion is a patch of sensory epithelium form- ing the so-called olfactory organ or, better, osphradium, the function of which is apparently to test the purity of the water entering by the respiratory current. Close to the pedal ganglion a minute otocyst is sometimes found. Sen- sory cells — probably tactile — also occur round the edge of the mantle, and especially on the fimbriz of the inhalant siphon. . The sexes are separate. The gonads (Fig. 162, gov) are large, paired, racemose glands, occupying a considerable portion of the visceral mass amongst the coils of the intes- tine ; the testis is white, the ovary reddish. The gonad of each side has a short duct which opens (g. af) on the sur- face of the visceral mass just in front of the renal aperture. In the breeding season the eggs, extruded from the gen- ital aperture, pass into the suprabranchial chamber and so to the cloaca. There, in all probability, they are impregnated by sperms introduced with the respiratory current. The oosperms are then passed into the cavities of the outer gills, which they distend enormously. Thus the outer gills act as brood-pouches, and in them the embryo develops into a peculiar larval form known as Glochidium. The Glochidium (Fig. 165) has a bivalved shell produced ventrally into incurved hooks beset with spines. After a time it is ejected from the mantle-cavity and falls to the bottom of the water, where it lies until it has the oppor- tunity of becoming attached to the gills or skin of a fish. Fixed firmly by means of the hooked valves the larva remains as an external parasite for about ten weeks, becoming en- 278 MANUAL OF ZOOLOGY SECT. cysted by an overgrowth of the skin or mucous membrane of their host. In the meantime a metamorphosis is taking place, and when the young mussel becomes free it has begun to assume the form and structure of the adult. The majority of the members of the class Pelecypoda resemble the fresh-water mussel in the main features above described. They are bilaterally symmetrical, laterally com- pressed, with a mantle consisting of paired right and left lobes, secreting a bivalved calcareous shell. A distinct head is never present. There is on the ventral surface a muscu- D.--~ Fic 165.— A, advanced embryo of Anodonta; B, free glochidium. /, provisional byssus: s, shell; sh, hooks ; sv, adductor muscle ; so, sense organs; w, cilia. (From Korschelt and Heider’s Embryology. ) lar foot ; there are two abductor muscles, and there are two pairs of gills. But, on looking over a collection of shells of various bivalves, it will be found that certain of them differ from that of the fresh-water mussel in not having the two valves of the shell alike. This inequality between the two valves of the shell is strongly marked in the scallops, and even more so in the oysters. The oysters are also examples of Pelecypods, which have only one adductor muscle instead of two; and the oyster, which is unable to XI PHYLUM MOLLUSCA 279 move from place to place, and in the case of some species is permanently fixed to some rock or other solid body by the substance of the larger valve, has no foot. The inhalant and exhalant siphons are sometimes absent, sometimes much longer than in the fresh-water mussel, as in the clam (Mya arenaria). Posterior to the foot there is in many Pelecypods a gland termed the dyssus gland, secreting silky threads which serve to attach the animal temporarily or permanently, as, for example, in the sea mussel (AZpilus) (Fig. 166). In most Pelecypoda the gills (ctenidia, p. 271) Fic. 166.— Mytilus edulis, attached by byssus (By) toa piece of wood. F, foot; S, exhalant siphon. (From the Cambridge Natural History.) are simpler in character than in the fresh-water mussels. In one group, Protobranchia (Nucula, etc.), they take the form of a pair of plume-like organs, and are primitive in shape and structure. A remarkably modified member of this class of molluscs is the ship-worm, Zeredo, which is very destructive to ships’ timbers, piles of jetties, etc. -The valves of the shell are extremely small, and the general surface of the mantle secretes a continuous shelly tube lining the burrow in which the elongated worm-like body of the mollusc lies. Highly 280 MANUAL OF ZOOLOGY SECT. developed eyes are present in a row round the edge of the Fic. 167.—Teredo navalis, in a piece of timber. P, pallets; SS, siphons; T,tube; V, valve; of shell. (From the Caméridge Natural History.) mouth in the scallop (fecten) and a few others. Although none of the Pelecy- poda are microscopic, they present a considerable range in size, from the little fresh-water Cyc/as, about 1 cm. long, to the giant clam (Z7- dacna gigas) of the Indian and Pacific Islands, which is sometimes 60 cm. (two feet) in length and 500 pounds in weight. The nacre- ous inner layer of the shell of the pearl oyster (JA/eleagrina marga- ritifera), which is of unusual thick- ness, constitutes the “ mother-of- pearl” of commerce, employed for many ornamental purposes. Pearls are deposits of nacre formed around sand grains or other foreign bodies, either between the mantle and shell, or in the soft parts in the pearl oyster and the pearl mus- sel (Unio complanatus), etc. Most Pelecypoda are sluggish in habit, progressing only by slow movements of the foot, and some are permanently fixed during adult life by the byssus. The scallops, however, swim freely by clapping the valves together. The cockles (Cardium), Trigonia, etc., jump by sudden movements of the foot, XI PHYLUM MOLLUSCA 281 and the razor-fish (So/em) jerks itself forward by suddenly withdrawing its very large foot, and thus ejecting water through the siphons. The only parasitic genus is /7/0- valva, found in the gullet of a Holothurian. Pelecypoda are abundant both in fresh water and the sea ; the marine forms are mainly littoral. None are pelagic or terrestrial. 2. THE AMPHINEURA A class of molluscs which comprises only a small number of repre- sentatives, most of them of rare occurrence and of simple organisation, is the Amphineura. With the exception of the Chitons these have no shell and are devoid of a foot, so that though probably related to the more typical molluscs, and to be referred to the same phylum, they are wanted in some of the most characteristic features exhibited by the members of the other classes. All the Amphineura are bilaterally symmetri- cal, more or less elongated molluscs, with the mouth at the anterior and the anus at the posterior end. The commonest, as well as the most highly organised, of the Amphineura are the Chitons, marine molluscs which are to be found adhering firmly, like limpets, to rocks and stones on the “4 seashore, or in deep water. The body is dorso-ventrally compressed, convex above, and presents below a broad flat foot (narrow in Chitonel/us), which acts not only as an organ for effecting creep- ing movements, but also as a sucker for enabling the animal when at rest to Fic. 168 — Chiton spinosus, dorsal 3 o view. (From the Caméridge adhere firmly, like a limpet, to the sur- Natural History.) face ofa rock. The most remarkable external feature of the Chiton is the presence on the dorsal surface of a calcareous shell (Fig. 168), made up of no fewer than eight trans- versely elongated pieces or valves, arranged in a longitudinal row, artic- 282 MANUAL OF ZOOLOGY SECT. ulating together and partly overlapping one another. They are some- times partly, sometimes completely, covered over by the mantle. Each valve consists of two very distinct layers, a more superficial and a deeper, the latter formed of a compact calcareous substance, the former perfo- rated by numerous vertical canals for the lodgment of the sense organs, to be presently referred to. External to the valves the dorsal integu- ment (mantle) of Chiton and its allies is usually beset with a number of horny or calcified tubercles and spicules. The mantle develops only very slight lateral flaps, and under cover of these are a series of small gills or ctenidia (Fig. 169, c¢z), to the number of fourteen to eighty. The mouth and anus are both median, situ- ated at the anterior and posterior extremities respectively. The buccal cavity always contains a well-developed odontophore. The in- testine is elongated and coiled. There are salivary glands and a large paired liver. There is a well-developed heart, consisting of a median ventricle and two lateral auricles. The pericardial cavity in which it lies is a space of con- siderable extent in the posterior region of the body, below the two last valves of the shell. arn The central part of the nervous sys- Fic. 169.—Chiton, ventral view. tem comprises an cesophageal nerve- an, anus; cfen, ctenidia; /t, foot; : i mant, mantle edge; #0, mouth. ring, consisting of a thicker dorsal (Alter, Relseneet:) cerebral portion not differentiated into ganglia, and a thinner ventral ézccal commissure. Two pairs of longi- tudinal nerve-cords, pedal and fallial, are given off from this poste- riorly. The former, which give off nerves to the foot, are joined by numerous commissures passing beneath the enteric canal. The large cords contain nerve-cells throughout their length. The conspicuous organs of special sense present on the head of Gas- tropods (see p. 289) are absent in the Chitons. A pair of processes situated in front at the sides of the mouth have the character of labial palps. Remarkable sensory organs, the micresthetes and the megales- thetes, lie in the canals already mentioned as occurring in the super- XI PHYLUM MOLLUSCA 283 ficial layer of the shell valves. The megalaesthetes may take the form of eyes, with cornea, lens,spigment layer with iris, and retina. There are two symmetrical nephridia (Fig. 170) opening internally into the pericardium by a ciliated funnel-like opening (7. perz. ap), and Fic. 170. —Chiton, nephridial and genital systems. am, anus; cten, ctenidia; gen. ap, genital aperture; gox, gonad; goxod, gonoduct; mo, mouth; neph. af, nephridial aperture; 7. ferz. af, aperture from nephridia to pericardium, (From Simroth, after Haller and Lang.) opening on the exterior (wepfh. af), between two of the posterior ctenidia. Each consists of a looped main tube, into which open numerous minute tubules which ramify among the viscera. The sexes are distinct. The testis and ovary (go) are similar in appearance, Missing Page Missing Page as 286 af .. MANUAL OF ZOOLOGY SECT. on the axis. When the obliquity is very slight (Fig. 174), the spiral is nearly flat; when the obliquity is great, an elongated tapering shell, such as that represented in Fig. 175, is the result. Sometimes the later whorls completely Fic. 172. — Shell of Triton nodiferus. Natural size. New Zealand. cover over the earlier ones, so that the spiral form of the shell is concealed. Sometimes only the apical portion of the shell is spiral, the remainder being a straight or sinuous cylinder. The mouth of the shell has usually a prominent margin or XI PHYLUM MOLLUSCA 287 peristome, which is sometimes entire and continuous, some- times is broken by a deep notch or a spout-like prolonga- tion or cana/, formed in connection with the development Fic. 173. — Longitudinal median section of the shell of Triton nodiferus. of a spout-like prolongation of the mantle, the sphon, which lies in it. The mouth of the shell in many Gastro- poda is capable of being closed by means of an operculum 288 MANUAL OF ZOOLOGY SECT. borne on the foot. In some terrestrial forms in which an operculum is absent, the opening may be closed up during winter by a layer of hardened mucous matter to which the name of epiphragm is applied. Lateral folds of the mantle are in some of the Gastropoda (Fig. 176) reflected over the shell, and may completely cover it. In some cases these folds unite by their edge, so that the shell comes to be enclosed ina complete sac of the mantle; such enclosed shells are always imperfectly developed and incapable of covering the body. Thus in 4/éysza (the “Sea-hare’’) and Fic. 174. — Shell of Solarium perspectivum from the under side. (From the Cambridge Natural History.) other allied forms the shell is greatly reduced, thin and horny, and concealed within the mantle, while in the nudibranch (Fig. 177), members of the same sub-order, it is entirely absent. The shell is also completely absent in some of the pelagic forms (AHeteropoda and Preropoda); in others, though present and external, it is too small to enclose the animal. In the slugs the shell is vestigial and concealed by the mantle. The Gastropoda have a well-marked head, separated from the body by a constriction or zeck. The mouth, XI PHYLUM MOLLUSCA 289 situated at the anterior end of the head on its ventral aspect, is in many instances provided with a protrusible probosis or in¢rovert, sometimes of considerable length. On the dorsal surface of the head are a pair of tentacles which vary a good deal in shape, but are usually cylindrical or club- shaped. In most cases the eyes are situ- ated on tubercules at the bases of the ten- tacles, or elevated towards the middle; but in the snails and slugs (Pu/monata) (Fig. 171) the eyes are elevated on the extremities of a second, longer pair of tentacles (oc. zent) placed behind the first. The mantle is usually developed into a fold, the mantle-flap, originally posterior, but subsequently becoming shifted round to the right-hand side. This covers over a cavity, the mande-cavity, situated ante- riorly, in which are situated the anal and nephridial apertures and the ctenidia. The edges of the mantle-flap may become united together in such a way as to form a cham- ber opening on the exterior by a compara- tively narrow opening. In many the edges of this aperture are drawn out into a spout- like prolongation open ventrally, the siphon, which lies in the corresponding prolongation of the peristome of the shell, and serves as a channel for the ingress and egress of water. In some Gastro- Fic. 175. — Shell of Terebra oculata. pods, however, there is no definite mantle-cavity, the anus, nephridial apertures, and ctenidia merely lying under cover of a comparatively slightly developed: lateral mantle-flap. uu 290 MANUAL OF ZOOLOGY SECT. The foo¢ varies in the extent of its development in the different families of the class. It usually presents an elongated, flat, ventral surface on which the animal creeps Fic. 176. — Cyprea moneta (Cowrie). Showing the mantle, provided with marginal tentacles, partly enveloping the shell. yr, branchia; M, M, mantle; F, foot; T, tentacles at the edge of the mantle. (From Cooke, after Quoy and Gaimard.) by wave-like contractions of the muscular tissue. In the typical Gastropods the foot is usually distinguishable into three parts, a middle part or mesopodium which is the most goc ‘eck. a ‘Odo 2.08 vos 9 0 O8er OG 0 cr PEs fo9 eon Fic. 177.—Doris (Archidoris) tuberculata. a, anus; dr, branchie; , penis; rh, rh, tentacles. (From the Cambridge Natural History.) important, with a smaller anterior propodium and posterior metapodium. The whole foot becomes reduced in a few Gastropods that remain fixed. The metapodium very fre- XI PHYLUM MOLLUSCA 291 quently bears a disc or stopper, the operculum, usually horny, or partly calcified, by means of which the aperture of the shell is closed when the animal is retracted. In some forms, such as the sea-hares (Af/ysta), the foot develops a pair of lateral lobes, the efzpodia, which act as fins; and in the Pteropods (Fig. 178), which are specially modified for a pelagic existence, these constitute the largest part of the foot. The organs of respiration in the majority of the aquatic Gastropoda are in the form of gills or céenzdia, usually plume- shaped appendages consisting of a central stem bearing two Fic. 178. — Shell- een Ptero enone S,f, fins; 2, liver; 0, ovary; sh, shell. From Cooke, after Souleyet.) rows of compressed filaments or lamellee, or a single row. Two ctenidia may be present or only one may be developed; they are enclosed in the mantle-cavity. In the Nudibranchs two ctenidia are absent, but their place as breathing organs is taken by a number of secondary branchiga, sometimes simple, sometimes branched or pin- nate processes, which are distributed over the dorsal surface, as in Zolis, or as in Dorts (Fig. 177), forming a circlet surrounding the anus, or, as in Pleurophylidia, a row on each side beneath the mantle-flap. 292 MANUAL OF ZOOLOGY SECT. In the limpets (P/e/a and its allies!) (Fig. 179) the true ctenidia are represented only by a pair of vestiges, and respiration is carried on by a number of secondary branchiz (g. 7) in the form of lamellz situated between the short lateral fold of the mantle and the foot. In the Pul- monata, and in some members of other groups, ctenidia are absent, and the mantle-cavity, completely enclosed except ge ole nie ip ve) Ss Fic. 179. — Patella vulgata, seen from the ventral side. /, foot; g.7, circlet of gill lamella; 2. e, edge of the mantle; #7, attachment muscle; s/, slits in the attachment muscle; sf, shell; 7, efferent branchial vessel; z', aorta; ve, smaller vessels. (From the Cambridge Natural History.) for a small rounded opening, has the function of a pu/- monary sac or lung (Fig. 180), its roof being richly sup- plied with blood-vessels; in the aquatic forms its function is apparently as much hydrostatic as respiratory. In some of the Pulmonata there is a return to a completely aquatic mode of respiration accompanied by the development of 1 Our common eastern American limpet is -femc@a testudinalis, XL PHYLUM MOLLUSCA 293 Secondary gills— vascular processes of the wall of the mantle-cavity. Puly Fic. 180.— Pulmonary cavity and related parts in a slug (Limax). aort, aorta: aur, auricle; neph, nepheidiue: eric, pericardium, laid open; px/. af, pul- monary aperture; 4z/. v, pulmonary vein with its ramifications; ect, rectum; ur, ureter; vent, ventricle. (After Pelseneer.) Digestive Organs. — In many Gastropods there is a long proboscis capable of being everted and retracted, at the extremity of which the mouth is placed. A single curved horny jaw lies on the roof of the buccal cavity in the Pul- monata; in most marine Gastropoda the place of this is taken by two lateral pieces. A characteristic feature of the alimentary canal of the Gastropoda, which, however, they share with some Amphi- neura and with the Cephalopoda, is the possession of an odontophore and radula, situated in a thick-walled chamber, the éuccal cavity, into which the mouth opens. From the floor of the cavity rises an elevation, the odontophore, which is somewhat elongated in the direction of the long axis of the body and compressed laterally. Over the summit of the odontophore runs longitudinally a narrow strap-like body, the radula or Lingual ribbon (Fig. 181, vad), beset Missing Page Missing Page 296 MANUAL OF ZOOLOGY SECT. such as the limpets, ear-shells, cowries, tritons, whelks, and cones. The latter includes the water-breathing sea-hares and nudibranchs and the air-breathing snails and slugs. The chief general points of distinction between the two groups are that in the Streptoneura the visceral nerve-cords are twisted into a figure 8, and the sexes are separate, while in the Euthyneura the twisting of the nerve-cords is absent and the sexes are united in the same individual. Only a few aberrant families of Gastropoda are parasites. Most are aquatic, all the most primitive forms being in- habitants of the sea. Of the marine families the majority move by creeping over the sea-bottom, some burrowing in mud or sand, some in solid rock; some are able to float in a reversed position, adhering to frothy mucus secreted by the glands of the foot; certain exceptional forms such as Vermetus are fixed in the adult condition by the substance of the shell. A few families—the Heteropoda and the Pteropoda— are specially modified for a pelagic mode of existence, and swim through the water by flapping move- ments of the lobes of the foot, which act as fins. Gastro- pods are found at considerable depths — up to nearly three thousand fathoms — in the ocean. Many forms, however, are inhabitants of fresh water, while many Pulmonata are terrestrial, and occur even towards the summits of the highest mountains. 4, THE CEPHALOPODA The class Cephalopoda, including the cuttle-fishes, squids, Octopi, argonauts, and Nautili, is the highest of the Mollusca, its members being very much more active and powerful in their movements than the rest of the Mollusca, and much more highly endowed as regard their higher senses. The XI PHYLUM MOLLUSCA 297 body (Figs. 182, 183, 185, 187) is bilaterally symmetrical. The foot, instead of extending along the ventral surface Fic. 182.— Sepia cultrata. Entire avira picwed from the dorsal aspect. New ealand. of the body in the region behind the mouth, as it does in Pelecypoda and Gastropoda, occupies a more anterior posi- 298 MANUAL OF ZOOLOGY SECT. tion, and surrounds the mouth. A distinct head is pres- ent, and the foot assumes the appearance of a system of appendages of the head. In the cuttle-fishes (Fig. 182), Fic. 183.— Nautilus pompilius, diagrammatic lateral view of a female specimen enclosed in its shell. cart, cartilage; cten, ctenidia; 4d, hood; 7u/, funnel; Jaws, jaws; mant, mantle: mant', dorsal mantle-fold overlapping the coil of the shell; ss, position of lateral mass of muscle; zd, nidamental glands; seft, first septum; szfh, siphuncle. (After Keferstein.) squids (Fig. 187), Octopi, and Argonauts (constituting the sub-class Dibranchiata) the main part of the foot is composed XI PHYLUM MOLLUSCA 299 of either eight or ten long, highly extensible and contractile appendages, the avms, the inner surfaces of which are beset with numerous suckers, rendering them powerful grasping organs. These are arranged in a circlet surrounding the mouth. The posterior part of the foot appears to be repre- sented by the /uzne/, a wide tube through which water is Fic. 184. — Section of the shell of Nautilus pompilius, showing the septa (s, s), the septal necks (s. #., 5. 2.), the siphuncle (sz, represented by dotted lines), and the large body-chamber (ck). (From the Cambridge Natural History.) driven out from the mantle-cavity. In the Nautili (Fig. 183), (sub-class Tetrabranchiata), the place of the arms with their suckers is taken by a number of lobes bearing sheathed tentacles surrounding the mouth, and a funnel is also pres- ent, though it does not form a complete tube. 300 MANUAL OF ZOOLOGY SECT. To compare such a cephalopod as a cuttle-fish or squid with a fresh-water mussel or a snail, it is advisable to place it in a position which it quite naturally assumes when not swimming, with the head and its arms downwards and the body sloping away from this upwards and backwards. In this position we distinguish antero-dorsal and postero- ventral surfaces, oral and aboral extremities, and right and left borders. A shell is present in nearly all Cephalopods, but is only external in the female argonaut and in Nautilus. In the latter (Fig. 184) it is in the form of a flat spiral, the interior of which is divided by a series of transverse partitions or septa into a corresponding series of chambers. The last chamber opens widely on the exterior, and this alone lodges the body of the animal, the remaining chambers being filled with gas. Perforating the middle of all the septa in succession is a spiral tube — the s7phunc/le — continuous with the centro- dorsal region of the visceral prominence. In the course of its growth the body of the Nautilus shifts forwards at intervals into a newly formed chamber, and a new sep- tum is formed closing the latter off from the cavity last occupied. The Nautilus inhabits the coral reefs of the Pacific, at a depth of a few fathoms. Of existing Dibranchiata, Sprrula (Fig. 185) alone has a shell comparable to that of Nautilus. The shell of Spirula is of spiral form, the turns of the spiral, however, not being in close contact. Internally it is divided into chambers by a series of septa, and these are perforated by a siphuncle. Again, as will be seen by comparing Figs. 183 and 18s, the relation of the soft parts to the shell is the reverse of what obtains in Nautilus, the shell of Spirula curv- ing backwards, that of Nautilus forwards. Moreover the shell of Spirula is an internal structure, being almost com- XI PHYLUM MOLLUSCA 301 pletely covered by the mantle. Its shell has been found cast ashore on Nantucket. In the other Dibranchiata the shell may consist of three parts, —a horny pen or pro-ostracum, a calcareous guard, and a part termed the phrag- mocone. The last, which alone repre- sents the shell of Sprru/a, has the form of a cone divided internally by a series of septa perforated by a si- phuncle. These parts are most com- pletely developed in the extinct genus Belemnites, in which the shell con- sists of a straight, conical, chambered phragmocone, with a siphuncle, en- closed in a calcareous sheath, the guard, pro- duced into a horny or calcareous plate, the pro-ostracum. In the cuttle-fish of the Medi- Fic. 185.— Spirula peronii, lateral view. d, terminal sucker; 7, funnel; sy, s9, projecting portions of the shell, the internal part of which is indicated by dotted lines. (From Cooke.) Fic 186.—Shell of Sepia cultrata, posterior view, reduced. septa of the terranean Sea (Seg7a) the shell is a leaf-like body, with a rounded and comparatively broad oral end, and a narrower aboral pro- vided with a sharp projecting spine. The main mass of the shell consists of numerous, closely arranged, thin lamine of calcareous composition, between which are interspaces containing gas. The spine-like projecting point represents the guard, and the main substance of the shell is to be looked upon as the pro-ostracum and phragmocone, the latter being represented by the calcareous 302 MANUAL OF ZOOLOGY SECT. lamellae. In Zofigo' (the squids) the shell (Fig. 187, B) is long, narrow, and completely horny ; it corresponds to the pro-ostracum, the phragmocone being entirely absent. Fic. 187.—Loligo vulgaris. A, entire animal, dorsal view; B, horny internal shell or pen. (Irom Keferstein ) In Octopus the shell is represented only by a pair of rudiments with which muscles are connected. In 47vonauta there is no shell in the male, but the female has an external shell (Fig. 188) of a remarkable character. This is a deli- 1 Our common American species is Lolige peal. XI PHYLUM MOLLUSCA 303 cate spiral structure, the internal cavity of which is not divided into chambers. It is not secreted by the mantle like the shells of other Mollusca, but by the surfaces of a pair of the arms ending in expanded disc-like extremities, which become applied to its outer surface; its chief func- tion is to carry the eggs. The argonaut inhabits deep water, 70 to roo miles off the coast of New England, its shells being in very rare cases found cast ashore on our coast south of Cape Cod. r¥ re) B. Fic. 188. — Shell of Argonauto argo. In addition to the shell there is in all the Cephalopoda an internal skeleton of cartilage supporting and protecting the nerve-centres and other parts. The cuttle-fishes and other Dibranchiata when alive will be observed to undergo frequent changes of colour, and blushes of different hues are to be noticed passing over the surface. These are due to the presence of numerous con- tractile, pigment-containing cells or chromatophores, situated in the deeper layers of the integument over the entire 304 MANUAL OF ZOOLOGY SECT. surface, which contract and expand under nervous influence (Fig. 189). On the postero-ventral aspect of the body the mantle encloses a wide cavity, the mantle-cavity (Figs. 190, 191), in which the ctenidia are lodged, and on the wall of which are situated the anal, excretory, and reproductive apertures. The mantle-cavity communicates at its oral end by a wide slit with the exterior; but this is capable of being closed, Fic. 189. — Chromatophore of Sepia, magnified. #zc, nuclei in wall of sac; pigm, pigment ; rad. mus, .adiating strands of muscle, (After Vogt and Jung.) so that, when the walls of the cavity coutract, a stream of water is ejected through the funnel, and the animal is propelled in the aboral direction. Swimming is also effected in the Dibranchiata by means of a pair of fins in the shape of muscular, lateral flaps. The ctenidia (c/n) are plume- like, and are either two (Dibranchiata) or four (Zetra- branchiatfa) in number. The mouth is provided with a pair of horny or calcified jaws (Fig. 192, B) similar in shape to the jaws of a parrot. The buccal cavity contains an odontophore. Opening into XI PHYLUM MOLLUSCA 305 mantl.cart liv St inka: acnid Fic. 190. —Sepia cultrata, female seen from the posterior aspect, the wall of the mantle-cavity divided along the middle line and the two flaps thus formed spread out so as to expose the contents. ac. #¢d, accessory nidamental glands; an, anal aperture with its lateral appendages; “4, membranous fold attaching the ctenidium to the wall of the mantle-cavity ; 7/, external opening of funnel: zu. cart, infundibular cartilage; zz. s, ink-sac; zk. d, ink-duct; dzg, ligamentous band which extends from the anterior wall of the mantle-cavity to the ovary, cut across; /2v, liver; 2. cten, left ctenidium ; 7. meph, left nephridial aperture : xd, left nidamental gland; Z. st. g, left stellate ganglion: ant. cart, mantle cartilage 5 mo, mouth; mzs, neck muscles; ov, ovary ; ovzd, oviduct; rec, rectum. x 306 MANUAL OF ZOOLOGY SECT. the terminal part of the intestine close to the anal aperture is the duct of a peculiar gland — the ink gland (Fig. 193, 7). This secretes a black substance, the 7, which is discharged when the animal is irritated or alarmed, and mingling with the water in the mantle-cavity is discharged as a dark cloud, under cover of which the animal may elude the pursuit of an enemy. The heart and vascular system reaches a high stage of development. The heart consists of a median ventricle and HAUS C.visc.ab~cte 72 Wb.t neph af Post os ae Fic. 191. —Nautilus pompilius, interior of mantle-cavity of a male specimen with the postero-ventral wall reflected. a. 2. neph. af, oral left nephridial aperture ; an, anus: cten, ctenidia: 2. ¢ af, left reproductive aperture: /. av/. os, left oral osphradium ; 2 vise af, left viscero-pericardial aperture; szazz, flaps of mantle; pen, penis; p 2. neph ap, aboral left nephridial aperture: Z. r. neph. ap, aboral right nephridial aperture; fost. os, aboral osphradia; ». wsc. ap, right viscero- pericardial aperture. two or four elongated lateral auricles or branchio-cardiac vessels conveying the blood from the ctenidia to the ventricle. The nervous system is highly developed, and its principal central parts, representing the cerebral, pedal, and visceral ganglia of other molluscs, with their commissures and con- XI PHYLUM MOLLUSCA 307 nectives, form a ring round the gullet. There are a pair of large eyes situated on the head. In the cuttle-fishes and other Dibranchiata these have a highly complicated structure, Fic. 193. — Sepia officinalis, enteric canal. a@, anus; 6. d, one of the bile ducts; 4 2, buccal mass; c, cecum; 2z, ink-sac; 7. d, ink-duct; J, jaws; 2, Z, liver lobes; @, cesoph- agus; #, pancreatic appendages!; Fic. 192. — Sepia officinalis, jaws. A, zz vr, rectum; s. g, salivary glands; situ, B, removed and slightly enlarged. st,stomach (From the Cambridge (Fromthe Cambridge Natural History.) Natural History.) and contain representatives of all the principal parts of the eye of a fish or other vertebrate. In Nautilus the eye is of 1 This organ is by Sedgwick regarded as renal in its nature, being the unpaired portion of the kidneys, (See Sedgwick’s Text-bo0k of Zoology, i, PP. 433) 437-) 308 MANUAL OF ZOOLOGY SECT. much simpler structure. There is a pair of otocysts, and sensory processes or depressions supposed to be olfactory are also present. Osphradia occur only in Nautilus. There are either two (Dibranchiata) or four (Zefra- branchiata) nephridia, which are in the form of sacs opening into the mantle-cavity, and in the Dibranchiata communi- cating with the pericardium. Through each of these runs one of the principal veins, round which the secreting tissue of the nephridium is aggregated. The sexes are distinct. The ova are always large, con- taining a large quantity of yolk. No metamorphosis, such as is general in other groups of Mollusca, is known to occur in any Cephalopod. The Cephalopoda are all marine, and range from tidal limits to a considerable depth. Squids swim like fishes in schools, rising to the surface and darting out of the water, and sometimes leaping so vigorously as to fall on the decks of large vessels. A large number are pelagic. They are, nearly without exception, carnivorous. In length they range from an inch or two to as much as fifty feet—the gigantic members of the group, such as Architeuthis, being by a long way the largest of invertebrate animals, and like the other classes of Mollusca they are most abundant in tropical and warm temperate seas. As already stated, the class is divided into two sub-classes, the Dibranchiata and the Tetrabranchiata — the latter com- prising only the Nautili (in addition to many fossil forms), the former including all the rest of the living members of the class. In the former the forefoot assumes the character of acirclet of either eight or ten arms bearing suckers sur- rounding the mouth. The funnel forms a complete tube. The shell is usually internal; when external its cavity is not divided by septa. There are two ctenidia, two nephridia, XI PHYLUM MOLLUSCA 309 and two auricles. An ink gland is present. In the latter, on the other hand, the forefoot has the character of lobes bearing tentacles; the funnel does not form a complete Fic. 194. — Oral surface of a male (A) and female (B) Nautilus pompilius in an expanded state, 4 natural size, linear. a@, shell; 4, external annular lobe carry- ing 19 tentacles on each side, and anteriorly enlarged to form the hood; c, right and left inner lobes, each carrying 12 tentacles in the female, and divided in the male into two parts; d, posterior inner lobe; e, oral cone; /, tentacles of the outer annular lobe projecting from their sheaths; g, two anterior tentacles of this lobe belonging to the hood; 7, superior, #, inferior, ophthalmic tentacle; /, eye; 2, lamellated organ on the posterior inner lobe of the female; 7, paired lami- nated organ on each side of the posterior inner lobe of the female; 0, funnel; p, spadix; g, antispadix. (After Bourne, from Sedgwick.) tube. There is an external, chambered, spiral shell. There are four ctenidia, four nephridia, and four auricles. The ink gland is absent, SECTION XII.— PHYLUM CHORDATA Tue Phylum Chordata comprises all the vertebrate ani- mals (fishes, amphibians, reptiles, birds, and mammals), together with the Urochorda or Ascidians, and the Adelo- chorda or Balanoglossus and its allies. ‘The name Chordata is derived from one of the most important of the few but striking common features by which the members of this extensive phylum are united together—the possession, either in the young condition, or throughout life, of a structure termed the chorda dorsalis or notochord. This is a cord only of cells, typically developed from the endoderm, extending along the middle line on the dorsal side of the enteric cavity, and on the ventral side of the central part of the nervous system. It becomes enclosed in a firm sheath and forms an elastic supporting structure. In the Vertebrata (with the exception of Amphioxus and the lam- preys and hag frstres) it becomes in the adult replaced more or less completely by a segmented bony or cartilaginous axis — the spinal or vertebral column. Another nearly uni- versal common feature of the Chordata is the perforation of the wall of the pharynx, either in the embryonic or larval condition only, or throughout life, by a system of clefts — the branchial clefts; and a third is the almost universal presence at all stages, or only in the larva, of a cavity or system | of. cavities, the vewvrocele, tr the-mnrtertor-ofthe—bery, lying above the central nervous system. 310 SECT. XII PHYLUM CHORDATA 1. THE ADELOCHORDA Of somewhat doubtful relationships both to one another and to the other Chordata are cer- tain remarkable marine animals which have been grouped together under the name of Hemichorda or Adelochorda. These are Balanoglossus and its allies, which occur in shallow water on the coasts of most of the warmer parts of the world, and two are deep- sea animals, Khabdopleura and Cephalodiscus. Balanoglossus (Fig. 195) is a soft-boclied, cylindrical, worm-like animal, the surface of which is uniformly ciliated. It is divisible into three regions: in front there is a large, club- shaped, hollow organ — the frodosczs , imme- diately behind the proboscis and encircling its base is a prominent fold—the col/ar; the third region or én is long and nearly cylin- drical, but somewhat depressed. Balanoglossus lives in the sea, burrowing in sand or mud by means of its proboscis. It occurs as far north as Salem, Mass., between tide-marks. Numerous glands in the integu- ment secrete a viscid matter to which grains of sand adhere in such a way as to form a fragile temporary tube. The proboscis (Fig. 195, £7, Fig. 196, prod) has muscular walls; its cavity opens on the exterior usually by 4 single minute aperture—the prodoscis pore (Fig. 196, prob. po) —rarely by two. The collar (Fig. 195, co) is also muscular, and contains one cavity or two (right and left) separated from one another by dorsal and ventral mesenteries, and completely cut off from the proboscis. The collar cavity com- municates with the exterior by a pair of collar pores —ciliated tubes leading into the first gill-slit or first gill-pouch. 311 prominences formed by gion: co, collar; gem, genital ridges; hep, (After Spengel.) _6r, branchial re hepatic caeca; fr, proboscis. Entire animal. Fic. 195. — Balanoglossus. 312 MANUAL OF ZOOLOGY SECT. On the dorsal surface of the anterior part of the trunk is a double row of small slits —the g2//-s/its (Fig. 195, 67,) — each row situated in a longitudinal furrow; these slits increase in number throughout. The cara. § ven.v a@ors.v Fic. 196. —Balanoglossus. Diagrammatic sagittal section of anterior end. card. sg, cardiac sac; dv, diverticulum (supposed notochord); dors. 2, dorsal nerve strand; dors. sz, dorsal sinus; dors. v, dorsal vessel; 220, mouth; prod, pro- boscis; prob. po, proboscis pore; prod. skel, proboscis skeleton; vent. 2, ven- tral nerve strand; zext wv, ventral vessel. (After Spengel.) ccelom of the trunk is divided into two lateral closed cavities by a verti- cal partition (dorsal and ventral mesenteries). The mouth (Fig. 196, 7o0,) is situated ventrally at the base of the proboscis, within the collar, Into the dorsal half of the anterior portion XII PHYLUM CHORDATA 313 of the alimentary canal open the internal gill-openings. The gill- pouches are supported by a chitinoid skeleton consisting of a number of separate parts. The posterior part of the alimentary canal is a nearly straight tube with, in its middle part, paired hepatic caca (Fig. 195, hep), which bulge outwards in a series of external prominences. Posteriorly it terminates in an anal aperture situated at the posterior extremity of the body. Throughout its length it lies between the dorsal and ventral divisions of the vertical partition, which act as mesenteries. In front the dorsal wall of this anterior portion of the alimentary canal gives off a diverticulum (Fig. 196, dv), the lumen of which extends nearly to the anterior end. This diverticulum consists of epithelium with gland cells and of a sort of retiform connective tissue; it is supposed to be homologous with the zofochord of the typical Chordata. There is a blood-vascular system with dorsal (dors. v) and ventral (vend. v) longitudinal trunks. The nervous system consists of dorsal (dors. 2) and ventral strands (vezd¢. 7), which extend throughout the length of the body. The part of the dorsal cord which lies in the collar lies deeper than the rest, and contains a canal or a number of spaces. Between the collar and the trunk the dorsal and ventral strands are connected by a ring-like thickening. ‘There are no organs of special sense. The sexes are separate; the ovaries and testes are saccular organs arranged in a double row along the branchial region of the trunk and further back; they open on the exterior by a series of pores. The course of the development differs in different species. In some it is comparatively direct; in others there is a metamorphosis. In the latter case the embryo assumes a larval form termed 7ornarza, which is somewhat like an Echinoderm larva, with 9 pair of ciliated bands, one of which is considered pree-oral, and the other post-oral, and an independent circlet of strong cilia at the posterior end. Usually associated with Balanoglossus are two aberrant animals — Cephalodiscus and Rhabdopleura — formerly regarded as Polyozoa. These both resemble Balanoglossus in having the body divided into three parts or regions —a proboscis, with a proboscis cavity, a col/ar with a collar-cavity communicating with the exterior by a pair of collar- pores, and a ¢runk with two distinct lateral cavities; and in the presence of astructure resembling a notochord with the same relations to the 314 MANUAL OF ZOOLOGY SECT, nervous system as in Balanoglossus. They both differ from Balano- glossus in having the alimentary canal bent on itself, so that the anal opening is situated not far from the mouth, in the presence of tentacles arising from the collar; and in the comparatively small size of the proboscis. 2. THE UROCHORDA Still more unlike a vertebrate in general appearance than Balano- glossus, and yet, as the earlier stages show, indubitably to be assigned to the Chordate phylum, are the Ascidians or Sea-squirts and their allies. Sea-squirts are familiar objects on rocky sea- shores, where they occur often in large associa- tions, adhering firmly to the surface of the rock. They also live free in sand and in mud, at differ- ent depths, some being deep-sea forms. When touched the Ascidian ejects with considerable force two fine jets of sea-water, which are found to proceed from two apertures on its upper end. The shape of the Ascidian, however, can only be profitably studied in the case of specimens that are completely immersed in the sea-water, specimens not so immersed always undergoing contraction. In an uncontracted specimen 1 (Fig. 197) the general shape is that of a short cylinder with a broad base by which it is fixed to the rock, The free end presents a large rounded aperture, and some little distance from > cnt it on one side is a second of similar character. Fic. 197.--Ascidia, en- ‘ tire animal seen from The former aperture is termed the ova/, the aie ean side. latter the aériad. A strong current of water will be noticed, by watching the movements of floating particles, to be flowing steadily in at the former and out of the latter. When the animal is removed from the water both apertures become narrowed, so as to be almost completely closed, by the contrac- 1 The European species, whose anatomy is here described, is approxi- mately represented by our common large Ascidia cadlosa, which lives in deep water off the Maine coast. XI PHYLUM CHORDATA 315 tion of sphincters of muscular fibres which surround them. At the same time the walls of the body contract, streams of water are forced out through the apertures, and the bulk becomes considerably reduced. Fic. 198. — Dissection of Ascidia from the right-hand side. The greater part of the test and mantle has been removed from that side so as to bring into view the relations of these layers and of the internal cavities and the course of the alimen- tary canal, etc. az, anus; ar. af, atrial aperture; exd, endostyle; gon, gonad; gonod, gonoduct; hyp, hypophysis; 4p. d, duct of hypophysis; #anz, mantle; ue. gn, nerve-ganglion; @s. af, aperture of cesophagus; ov. af, oral aperture; pA, pharynx; stom, stomach; tev, tentacles; fest, test. (After Herdman.) The outer layer of the body-wall is composed of a tough translucent substance forming a thick des¢ or /unze (Fig. 198, ¢est). This proves, 316 MANUAL OF ZOOLOGY SECT. when analysed, to consist largely of the substance ce//zose, which has already been referred to (p. 36) as a characteristic component of the tissues of plants, and which is rare in its occurrence in the animal kingdom. When the test is divided (Fig. 198), the soft wall of the body or mantle (mant), as it is termed, comes into view, and the body is found to be freely suspended within the test, attached firmly to the lat- ter only round the oral and atrial apertures. he mantle follows the general shape of the test, and at the two apertures is produced into short and wide tubular prolongations, which are known respectively as the ova/ and atrial siphons (Fig. 199, atr. siph). These are continuous at their margins with the margins of the apertures of the test, and round the openings are the strong sphincter muscles by which closure is effected. Within the body-wall is a cavity, the afréal or peribranchial cavity (a@¢r. cav) communicating with the exterior through the atrial aperture. The oral aperture leads by a short and wide oral passage into a chamber of large dimensions, the pharyviex or branchial chamber (ph). This is a highly characteristic organ of the Urochorda: Its walls are pierced by a number of slit-like apertures, the stigmata (Fig. 199, stig) arranged in transverse rows. Through these the cavity of the pharynx communicates with the atrial or peribranchial cavity, which completely surrounds it except along one side. The edges of the stigmata are beset with numerous strong cilia, the action of which is to drive currents of water from the pharynx into the atrial cavity. It is to the move- ments of these cilia lining the stigmata that are due the currents of water already mentioned as flowing into the oral and out of the atrial apertures, the ciliary action drawing a current in through the oral aperture, driving it through the stigmata into the atrial cavity, whence it reaches the exterior through the atrial aperture. The stigmata are all vertical in position; those of the same row are placed close together, separated only by narrow vertical bars; neighbouring rows are sepa- rated by somewhat thicker horizontal bars ; in all of these bars run blood-vessels. It has been already mentioned that the atrial cavity does not com- pletely surround the pharynx on one side. This is owing to the fact that on the side in question, which is ventral in position, the wall of the pharynx is united with the mantle along the middle line. Along the line of adhesion the inner surface of the pharynx presents a thickening in the form of a pair of longitudinal folds separated by a groove. To 4 Xi PHYLUM CHORDATA 317 this structure, consisting of the two ventral longitudinal folds with the groove between them, the term ezdosty/e is applied. The cells covering orsiph fest ~ érv alrcav mant rf ery dors.v an gonoa venly visc.or oncar card.viso Fic. 199. — Ascidia, diagram of longitudinal section from the left-hand side, the test and mantle removed. atv. cav, atrial cavity; afr. sipf, atrial siphon; 47. car, branchio-cardiac vessel; card. visc, cardio-visceral vessel; gonod, gonoduct; hi, heart; iy, hypophysis; mant, mantle; x. gv, nerve-ganglion; @s, cesopha- gus; ov, ovary; rect, rectum; s¢zg, stigmata; stow, stomach ; fez. tentacles; test, testis; t”. v, transverse vessel; vent. v, ventral vessel; vzsc. 7, viscero- branchial vessel. (After Herdman.) the endostyle are large cells of two kinds — c//ated cells and gland cells, —the former beset at their free ends with cilia, the action of which is IN BUNN. unseen JERMM 318 MANUAL OF ZOOLOGY SECT. to drive floating particles that come within their influence outwards towards the oral aperture, the latter secreting and discharging 4 viscid mucous matter. Anteriorly the endostyle is continuous with a ciliated ridge which runs circularly round the anterior end of the pharynx. In front of this circular ridge, and running parallel with it, separated from it only by a narrow groove, is another ridge of similar character; these are termed the feri-pharyngeal ridges, the groove between them is the peri-pharyngeal groove. Dorsally, 7.e,, opposite the endostyle, the posterior peri-pharyngeal ridge passes into a median, much more prominent, longitudinal ridge, the dorsa/ /amina, which runs along the middle of the dorsal surface of the pharynx to the opening of the cesophagus. The mucus secreted by the gland cells of the endostyle forms viscid threads which entangle food-particles (microscopic organ- isms of various kinds); the cilia of its ciliated cells drive these forwards to the peri-branchial groove, around which they pass to the dorsal lamina, and the cilia of the cells of the latter drive them backwards to the opening of the cesophagus. Some little distance in front of the anterior peri-pharyngeal ridge, at the inner or posterior end of the oral siphon, is a circlet of delicate tentacles (Fig. 198, fend). The cesophagus leads from the pharynx (near the posterior end of the dorsal lamina) to the stomach, which, together with the intestine, lies embedded in the mantle on the left-hand side. The stomach is a large fusiform sac. The intestine is bent round into a double loop, and runs forwards to terminate in an aad aperture, situated in the atrial cavity. There is no liver; but the walls of the stomach are glandular, and a system of delicate tubercles which ramify over the wall of the intestine is supposed to be of the nature of a digestive gland. The Ascidian has a well-developed blood system. The heart is a simple muscular sac, situated near the stomach ina pericardium forming part of the primitive ccelom. Its mode of pulsation is very remarkable. The contractions are of a peristaltic character, and follow one another from one end of the heart to the other for a certain time; then follows a short pause, and, when the contractions begin again, they have the opposite direction. Thus the direction of the current of blood through the heart is reversed at regular intervals. The nervous system is of an extremely simple character. There is a single nerve-ganglion, which lies between the oral and atrial apertures, embedded in the mantle. This is elongated in the dorso-ventral direc- XII PHYLUM CHORDATA 319 tion, and gives off at each end nerves which pass to the various parts of the body. Lying on the ventral side of the nerve-ganglion is a gland — the sz/- neural gland, A duct runs forward from it and opens into the cavity of the pharynx; the termination of the duct is dilated, and this terminal dilatation is folded on itself in a complicated way to form a tubercle, the dorsal tubercle, which projects into the cavity of the pharynx. The excretory system is represented by a single nephridium, which consists of a mass of clear vesicles, without a duct, lying in the second loop of the intestine. The sexes are united. The ovary and the testis are closely united together, and lie on the left-hand side of the body in the intestinal loop. Continuous with the cavity of each is a duct — oviduct or spermi- duct, as the case may be — which opens into the atrial cavity close to the anus. So far we have met with no feature that could with certainty be looked upon as indicating alliances with the Chordata. But, though the adult Ascidian is devoid of any such features, there is in the course of its life- history « larval stage in which Chordate affinities are unmistakably indicated. In this stage the young Ascidian is free-swimming, and in general shape bears some resemblance to a minute tadpole, consisting of an oval trunk and a long, laterally compressed tail. The tail is fringed with a caudal fin, which is merely a delicate outgrowth of the thin test covering the whole of the surface; running through the delicate fringe are a series of strize presenting somewhat the appearance of the fin-rays of a fish’s fin. At the anterior end are three processes, the adhesive papille. In the axis of the tail is the notochord (oto), which at this stage consists of a cylindrical cord of gelatinous substance enclosed in a layer of cells. Parallel with this runs, on the dorsal side, the narrow cau- dal portion of the nerve-cord, and at the sides are bands, or muscular fibres. Inthe trunk the nerve-cord is dilated, and, further forwards, expands into a vesicle, the sezse vesicle (sens. ves) with an otocyst (oto) and a well-developed eye (eye). The enteric canal is distinguishable into pharynx, cesophagus, stomach, and intestine. The pharynx opens on the exterior by the mouth: in its ventral floor the endostyle (ed) has become developed; its walls are pierced by stigmata, the number of which varies; a ciliated sac opens into it below the trunk part of the nerve-cord. The atrial cavity has become formed round the phar- ynx, and opens on the exterior by asingle aperture (a/), The heart 320 MANUAL OF ZOOLOGY SECT. and pericardial cavity have become developed. In this tailed, free- swimming stage the larva remains only a few hours; it soon becomes fixed by the adhesive papillee, and begins to undergo the redrogressive metamorphosis by which it attains the adult condition. The chief changes involved in the retrogressive metamorphosis (Figs. 200 and 201) are increase in the number of pharyngeal stigmata, the diminution, and eventually the complete disappearance, of the tail with the contained notochord and caudal part of the nerve-cord, the dis- appearance of the eye and the otocyst, the dwindling of the trunk part of the nervous system to a single ganglion and the formation of the reproductive organs. ‘Lhus, from an active, free-swimming larva, with well-developed organs of special sense, and provided with a notochord and well-developed nervous system, there is a retrogression to the fixed poo st a Reese SS oe a, Fic. 200 — Free-swimming larva of Ascidia mammillata, lateral view. adh, adhe- sive papille; a/z, alimentary canal; afr, atrial aperture; cz/. gr, ciliated groove; end, endostyle; eye, eye; med, nerve-cord; moto, notochord; ofo, otocyst; sexs. ves, sense vesicle; st7g, earliest stigmata, (From Korschelt and Heider, after Kowalewsky.) inert adult, in which all the parts indicative of affinities with the Ver- tebrata have become aborted. A remarkable feature of the Ascidians is that, though many remain simple, others give rise to colonies by a process of budding. In some of these compound forms, distinguished as the Comeposite Ascidians, the tests of the zooids are united together to form a mass of gelatinous consistency in which the zooids of the colony lie embedded (Fig. 202). These compound forms, such as Amaroucium, are common on the New England coast in shallow water. A minute animal which swims about in the surface waters of the sea has in most respects an extremely close resemblance to the tailed larva X XII PHYLUM CHORDATA 321 Fic. 201. — Diagram of the metamorphosis of the free, tailed larva into the fixed Ascidian. A, stage of free-swimming larva; B, larva recently fixed; C, older fixed stage. adh, adhesive papillz; atr, atrial cavity; cz. gv, ciliated groove: end, endostyle; ht, heart; med, ganglion of trunk; ~. g, nerve-ganglion; 10%0, notochord; ov, oral aperture; rect, rectum; sews és, sense vesicle: st7g, stig- mata: sto/, stolon; 4, tail. (From Korschelt and Heider, after Seeliger.) Y 322 MANUAL OF ZOOLOGY SECT. of an Ascidian, being of similar shape, with a tounded body and a long tail-like appendage attached to the ventral side, and with a distinct notochord. This, however, is an adult animal, known as 4ppendicula- ria. It never becomes fixed and retains permanently its chordate characteristics. Fic. 202. — Botryllus violaceus. +, oral apertures; c/, opening of common cloacal chamber. (After Milne-Edwards.) A number of other Urochorda are permanently free-swimming, but these are all almost, if not quite, as thoroughly metamorphosed as the Ascidians, so that their true affinities only become clear when their life-histories are followed. 3. THE VERTEBRATA The Sub-phylum Vertebrata comprises the lancelets, the lampreys and their allies, the fishes, the amphibians, the reptiles, the birds, and the mammals. The lancelets occupy an extremely isolated position with regard to the other mem- XII PHYLUM CHORDATA 323 bers of the sub-phylum, and are best regarded as consti- tuting by themselves a division, which, for reasons which will be manifest shortly, is designated Acrania, the rest of the sub-phylum being known as Cramiata. A. THE ACRANIA This isolated group, the Acrania, comprises only a single family, the two genera (Branchiostoma and Asymmetron) of which are distin- guished from one another by comparatively slight differences. Branchiostoma (more widely known under the name of Amphioxus), the lancelet, is a small transparent animal, occurring in the sea near the shore and burrowing in sand; its length does not exceed 5.3 cm. mpl alrp ven ifr PMP aT EMC he aes orhd JOD ambpl Fic. 203. Amphioxus lanceolatus. A. ventral; B, side view of the entire animal. an, anus; atrf, atriopore; cd. f, caudal fin; ez, cirri; dors. f, dorsal fin; dors. f. r. dorsal fin-rays; gon, gonads; mt/, metapleure; yom, myomeres; nch, notochord; ov. Ad, oral hood; vent. /, ventral fin; vent /. r, ventral fin- rays. (After Kirkaldy.) or less than two inches. Its form will be obvious from Fig. 203. The body is elongated, pointed at either end, and compressed. The anterior two-thirds is roughly triangular in transverse section, presenting right and left sides, inclined towards one another, above, and a convex ven- tral surface. The posterior third is nearly oval in section, the right and left sides meeting above and below in a somewhat sharp edge. Extending along the whole of the dorsal border is a median longi- tudinal fold, the dorsal fin (dors. f); this is continued round the 324 MANUAL OF ZOOLOGY SECT, posterior end of the body and extends forwards, as the ventral fin (vent. f), as far as the spot where the oval gives place to the trian- gular transverse section. The portion of the continuous median fold which extends round the pointed posterior extremity of the body is somewhat wider than the rest, and may be distinguished as the caudal jin (cd. f). In the anterior two-thirds of the body there is no median ventral fin, but at the junction of each lateral with the ventral surface is a paired longitudinal fold, the metapleure (mpl), which extends forward to the oral hood mentioned in the next paragraph. Below the pointed anterior extremity is a large median aperture surrounded by a frill-like membrane, the oral hood ( or. hd), the edge of which is beset with numerous tentacles or cz77z, The oral hood encloses a cup-shaped cavity or vestibule, al the bottom of which is the mouth (Fig. 204, mth). Immediately in front of the anterior termina- tion of the ventral fn and partly enclosed by the metapleures is a rounded aperture of cunsiderable size, the atrzpure (atrp), and a short distance from the posterior extremity of the body is the aus (ai), placed unsymmetrically on the left side of the ventral fin. The post- anal portion of the body is distinguished as the zaz?. Amphioxus ordinarily lives with the greater part of the body buried in sand, only the anterior end with the expanded oral hood protruding. It also swims in the vertical position, and frequently lies on one side on the sand; it burrows, head foremost, with great rapidity. It occurs on the American coast as far north as Cape Hatteras. A current of water is constantly passing in at the mouth and out at the atriopore. The muscular layer (my) is remarkable for exhibiting metameric segmentation. It consists of a large number — about sixty — of muscle segments or myomeres, separated from one another by partitions of connective tissue, the myocommas, and having the appearance, in a surface view, of a series of very open V’s with their apices directed forwards (Figs. 203 and 204). The chief of the skeletal or supporting structures of the lancelet is the notochord (Figs. 203 and 204, zch), a cylindrical rod, pointed at both ends, and extending from the anterior to the posterior end of the body in the median plane. It lies immediately above the enteric tract and between the right and left myomeres. It is composed of a peculiar form of cellular tissue, known as nodochordal tissue, formed of large vacuolated cells extending from side to side of the notochord, and having the nuclei confined to its dorsal and ventral regions. Around PHYL 325 M CHORDATA U XII ‘sapoequa) IeElaa ‘7 "7@ Sumyaa ‘7aa ‘Aer-uy pexyues “4 -f zuae@ ‘uy yeayuea {f y7aa :ps0d Jeutds ‘po -gs :(payop) ro pue pooy yer jo uojajays ‘ys ‘xuAreyd ‘yg :pooy peso ‘py f 20 sud A10ioeyO ‘¢ “70 teipiiydeu ‘yg tproysujou *y2« tsarawodu ‘okw ty Mout ‘ygwe ‘raat ‘47 LauTysayul uz !peuos ‘zoF tyods-aha ‘gs ‘7 ‘ajsvojeydaoua *w7 “wa + Aer -uy [esiop *4f“scop ‘uy yesiop f ‘s4op $woyss ‘7H land ‘477 tpeued [eUad ‘9 -ywa2 tuy [epnes YprvI ‘por PeouEsq Arepuosas ‘2 «ag ‘Around {1 +29 Se] surey peryoueiq Aiwpuoses *z yes cy :Areunsd ‘1 “gas 4p ‘jauuny umorg “f* eg tsajajo jerouesq 12 49 sureig ‘4g :a1odouje ‘¢ pu. J, pelvic ly removed to show the anchial apertures: v re; pct. 7, pectoral fin } myc, Myocommas; mynz, myomeres; x. a, nasal apertu (From Parker’s Bzology.) mth, mouth 6, spiracle; v. 7, ventral fin. mn; S§; , anus; ¢c. ad. /, caudal fin; d.f.7,d f.2, dorsal fins; e, eye; ext. dr. ap, external br: muscles. az lateral line; Fic. 206.— Side view of Dogfish (Mustelus antarcticus), with a strip of skin in the middle of the bod 330 MANUAL OF ZOOLOGY SECT. bearing teeth; near the mouth are a pair of smaller aper- tures — the nostrils or nasal apertures, and at the sides of the head region are the pair of conspicuous eyes ; while further back the pair of prominent auricles or pin- ne, with the wide apertures at their bases, mark very conspicuously the position of the auditory organs in the Fic. 207. — Lacerta viridis. (After Brehm.) rabbit, less clearly indicated in the lizard, and still less in the dogfish. On the lower (ventral) surface, towards ‘the posterior end of the trunk, will be observed in all three apertures which serve as the orifices through which the intestine and the ducts of the urinary and genital organs communicate with the exterior. A further resemblance XII PHYLUM CHORDATA 331 between the lizard and the rabbit consists in the presence of twu pairs of jointed limbs, anterior and posterior, the principal divisions of which correspond in their general arrangement. In the dogfish these are found to be rep- resented by very different-looking structures, the paired fins. At this point all external resemblance ceases, and we see nothing but differences. The skin of the dogfish, though almost smooth, is harsh to the touch, and, when we examine it with a lens, this is found to be due to the presence of innumerable minute hard gran- Fic. 208. — Lepus cuniculus. Lateral view of skeleton with outline of body. ules, set closely together so as to give the surface the charac- ter of a fine file. The general shape of the body is adapted to cleaving the water rapidly,—long and narrow, nearly fusiform, pointed at the ends, — and the fins are obviously swimming organs. The fins are all of the same general character, so far as their superficial appearance is con- cerned ; they are all of the nature of flap-like outgrowths, thick at the base, where they are obviously supported by hard parts, thinner towards the margins, where their sole 332 MANUAL OF ZOOLOGY SECT. support is a series of slender fibres of horny character. Besides the two pairs of fins which have already been re- ferred to as taking the places of the anterior and posterior pairs of limbs in the lizard and rabbit, certain others are to be recognised which are of a totally different character, being median or unpaired; these, which are not in any way represented in either the lizard or the rabbit, are the two dorsa/, the single ventral, and the single caudal, the last fringing the tail. Behind the eye in the dogfish will be noticed a small aperture which seems to occupy very nearly the position occupied by the opening of the ear in the rabbit. This opening, however, the sfzvac/e, does not lead into the ear, but into the cavity of the pharynx. Further back- there are, on each side, five slit-like apertures in a row: these are the dranchial or gill-clefts, and are not present in the lizard or the rabbit. In the living fish it will be observed that there are regular movements of the mouth, spiracles, and branchial clefts, indicating that water is being rhythmi- cally taken in through the mouth and expelled by the spiracles and branchial clefts. Those are the movements of respiration. The mouth is situated some little distance behind the anterior extremity of the head, on the ventral side. In front of it are the nasal openings (nostrils), which are also ventrally situated. In the lizard the surface is covered with a system of overlapping horny scales. The head is separated from the trunk by a distinct constricted region, the veck. The tail is extremely long and narrow. The two pairs of limbs, anterior and posterior, or pectoral and pelvic, are adapted to running on the surface of the ground. Each consists of three divisions, — arm, fore-arm, and hand,—the anterior xu PHYLUM CHORDATA 333 limb, thigh, leg, and foot in the posterior; and each hand and each foot contains five slender digits, each provided at its extremity with a curved and pointed horny claw. Slight rhythmical movements of dilatation and contraction of the anterior portion of the trunk are the movements of respiration, by means of which air is alternately drawn into and expelled from the lungs through the nostrils. In the rabbit the place of the scales of the lizard is taken by the coating of hairs constituting the fur. The limbs present the same main divisions as in the lizard, though the proportions of the parts are very different, and the hind foot has only four toes. Between the head and trunk the neck region is more sharply marked off than in the lizard. Aris- ing from the posterior part of the head, behind the eyes, are a pair of very prominent auditory pinne or auricles, at the base of each of which is the corresponding ear-opening. Movements of respiration resembling those of the lizard, but much more marked, are to be detected in the living animal. When the skeletons of these three animals are examined and compared, it will be found that they are constructed on the same general plan with differences in details. In the dogfish it is mainly composed of cartilage; in the others, mainly of bone. In all there is a rod-like axis, the spzna/ or vertebral column supporting the trunk and tail, but not continued into the head, where its place is taken by the skull, The spinal column consists of a row of similar segments, the verfebr@, which articulate with one another. Each vertebra consists of a neutral solid portion, the cen- trum or body; an arch of bone or cartilage, the zewvral arch, situated on the dorsal side of the centrum, and cer- tain processes. The series of centra form together a strong axial support for the entire body and tail; the series of 334 MANUAL OF ZOOLOGY SECT. neural arches enclose a canal, the neural canal, on the dorsal side of the centra. By the interlocking of certain processes — the articulating processes — of the neural arches the vertebrae in the lizard and rabbit are yet more firmly united together. In the dogfish the centra have deeply concave anterior and posterior faces, so that when the vertebrae are in posi- Fic. 209. — A, three trunk vertebra of Scyllium from the side; B, a single trunk vertebra viewed from one end; C, three caudal vertebre from the side; D, a single caudal vertebra from one end. c, centrum; 4, a, hemal arch; w. a, neural arch; ¢7. or, transverse process, (After Hasse.) tion there are hollows of considerable extent between the centra formed by the apposition of these concave faces. This form of centrum is termed amphicelous. The entire spinal column is distinguishable into two regions, — the region of the ¢-w#& in front and the region of the ¢az/ xu PHYLUM CHORDATA 335 behind. In the region of the trunk the vertebree bear very small ribs in the form of short rods of cartilage; in the caudal region ribs are absent; but each vertebra bears, in addition to the neural arch, a ventrally situated arch of similar shape — the hema/ arch. In both the lizard and the rabbit the vertebree are com- posed entirely of bone. In the former the centra have concave anterior and convex posterior surfaces— and the vertebre are accordingly said to be procelous. In the lat- ter the surfaces are flat, and the discs of fibro-cartilage, the inter-vertebral discs, are intercalated between the vertebra. Fic. 210. —Vertebre of Lizard. A, anterior, B, posterior, view of a thoracic ver- tebra; C, lateral, D, anterior, view of atlas vertebra; E, lateral view of axis. cent, centrum; Ay, hypapophysis of axis; /at, lateral piece of atlas; /zg. liga- mentous band dividing the ring of the atlas into two; ev, neural arch of atlas; od, odontoid process; pr. zy, pre-zygapophysis; ff. zy, post-zygapophysis; 74, rib; sf, spine; vent, ventral piece of atlas. In both the spinal column is divisible into five regions, — the cervical, the thoracic, the Lembar, the sacraé, and the caudal. The cervical region is the most anterior. In the rabbit the vertebre of the cervical region are devoid of ribs; in the lizard they have short ribs with the exception of the first three. The first and second vertebre in both the rabbit and the lizard are specially modified in connection with the movements of the head on the trunk. The vertebre of the 336 MANUAL OF ZOOLOGY SECT. thoracie region are characterised by the possession of 77s, which, in the case of the most anterior, are connected with the breast-bone or sternum by slender cartilaginous szernadl ribs. In the Zeméar region there are no ribs. The sacral region is distinguished by its relations with the hind limb. The cauda/ region, short in the rabbit, very long in the lizard, lies behind the sacral. The ribs connected with the thoracic vertebre are slender curved rods, which lie in the side walls of the anterior part of the trunk; the most anterior of them with their continuations, the sternal ribs, form half-loops extending from the spinal column dorsally Fic, 211. ~ Lepus cuniculus. A, atlas and axis, ventral aspect; ed, odontoid pro- cess of axis. B, lateral view of axis; ayr?, articular facet for occipital condyle; od, odontoid process; ft. sy, post-zygapophysis; sf, neural spine. C, thoracic vertebrae, lateral view. cent, centrum; fac, facet for rib; set, metapophysis; pr. sy’, pre-zygapophysis; fz. zy, post-zygapophysis; 7d, rib; sf, spinous process. to the sternum ventrally. The szernum or breast-bone, absent in the dogfish, lies in the middle of the wall of the ventral region of the trunk. Jn the lizard it is a rhomboidal plate of cartilage ; in the rabbit it is bony, and divided up into a number of segments known as the stevncbre. In the embryo of each of the three forms used as illus- trations, the spinal column passes through a stage in which it consists merely of a continuous cylindrical rod of cells — the votochord, corresponding to the notochord of Amphi- oxus-—— which becomes enclosed in a sheath, In some XII PHYLUM CHORDATA 337 Craniates it never passes beyond this stage, but remains of the nature of a persistent notochord, as it is termed. But in the great majority the notochord becomes enclosed in a sheath of cartilage, and thus becomes divided up into a number of segments. Eventually ossification sets in, and the series of completely formed bony vertebrae becomes developed. As already mentioned, the spinal column does not extend into the head region. The skeleton of this region is the complex cartilaginous or bony structure known as the sul. The chief part of this is a case, the cran‘vm, in the interior of which the brain is lodged, and the walls of which afford support to three pairs of organs of special sense, —the nasal or olfactory organs in front, the eyes in the middle, and the ears or auditory organs behind. The cavity of the cranium opens behind by a rounded foramen, the foramen magnum, into the anterior end of the neural canal enclosed by the neural arches of the vertebra ; and the posterior region of the cranium articulates movably with the first vertebrae of the spinal column. In addition to the cranium the skull or skeleton of the head comprises certain. elements known as the wsceral arches. The foremost of these forms the jaws, the second is the Ayozd, and mainly supports the tongue, the remainder are the dranchial arches. In the dogfish the cranium remains in the primitive condition of a cartilaginous case, with complete walls and floor, but with the roof partly formed of fibrous membrane. In the lizard and rabbit the substance of the cartilage is replaced by a number of cartilage bones, t.e, bones which take the place of pre-existing cartilage, to which are super- added a number of membrane bones, 1.¢., bones, the site of which was not preoccupied by cartilage ; the whole united together so as to form a structure of considerable com- z MANUAL OF ZOOLOGY SECT, 338 C738 “TM Jay) ‘(49 °xeo) sadepyreo perpouerg-e1yxe YIM A[[eUsa}xXa payaUUO are YOUAr ‘(4 +49 ‘4 49) sAei yeryoueig YO uaats aie ‘nu109 piddy pu repnqrpuewoAy ayy wos sv [pea se fasayy Woy !(S-7 v 4g) SyoIE [eLyouLIG aay ayy 9M0d (#7 Ay) NUIOD piosy ayy uodn Zurmoyjog “way) yywa payoauuos ade (g7) sadeynavo jeiquy jews pue (87 47) syuawesi] omy Aq wintueso a4} 0} payoene osje st ave aaddn ayy 1! (42-47) nu1os prody ayy 0) Mojaq JUaWYy ree Burais pue ‘smel (47) amo] pue (f gz) seddn ayy yoddus 0} Burdjay ‘(we -'y) repnqipuewody ay} st ajusdes Aioyipue ayy YM payeynonsy ‘seareu (S$ “@ay) [eululedity pue (2 “ZA/) ando aly 10y sammyiade wsas aie yiqio ayy Uy (4) xvaq 10 Windsor ay) Jo Saderies ayy pure ‘(7 ye) ajusdvo Arojo eyo ayy ‘(~2) WqIO MOT[OY aya ‘(7 "pxy) a_nsded Aroyipne Sunoaload ayy smoys (47) NUL OY fF -BEMOTWBD WINI[TAIG JO [[MAS JO MaIA BPIS — “Iz “Ol pee PPR Ory. XU PHYLUM CHORDATA 339 plexity. The visceral arches in the dogfish are composed of a system of rods of cartilage. The first visceral arch forms the upper and lower jaws, between which the open- ing of the mouth is situated. The jaws are connected on each side with the skull behind by means of a cartilage known as the hyomandibular, which is a part of the second or hyoid arch; the rest of the hyoid arch and the branchial arches, which are five in number, lie in the lateral and ven- tral walls of the pharynx and support the gills. In both the lizard and the rabbit the branchial arches are not present as such, the only well-developed visceral arches being the first and second. The upper jaw is formed of certain membrane bones, and in the lower jaw also the cartilage completely disappears, its place being taken by bones which are early completely united together, so as to form the bony lower jaw or mandible. In the lizard the mandible articulates on each side with the pos- terior region of the skull through the intermediation of a bone known as.the guwadraze, which is an element of the ‘first visceral arch. In the rabbit the articulation between the mandible and the skull is direct, no quadrate inter- vening. The skeleton of the limbs in the dogfish differs widely from that of the lizard and rabbit. In all three we dis- tinguish the limb-arch from the skeleton of the free part of the limb itself. The limb-arch (pectoral or pelvic) is a cartilage or a system of bones with which the base of the free part of the limb articulates, and has the function of connecting the limb with the trunk and serving for the origin of many of the muscles moving the limb. In the dogfish the entire skeleton of the limbs is composed of cartilages which are so arranged as to support the thin broad expanse of the fin. In both the lizard and the Fic. 213. —Skull of Lacerta agilis. A, from above; B, from below; C, from the side. ang, angular: av, articular: das oc. basi-occipital; das. pty, basi-pterygoid processes; fas sph, basi-sphenoid; col, epi-pterygoid; cor, coronary; dent, dentary; eth, ethmoid; ¢x ec, ex-occipital: ert. vax, external nares; for mag, foramen magnum: /r, frontal; z¢. vax, internal nares; 7, jugal; der, lacyr- mal: ax, maxilla; was, nasal; oc cond, occipital condyle; o/f, olfactory capsule; of. of, apisthotic: opt n, optic nerve; fal, palatine: far, parietal; par. parasphenoid; fav. 7, parietal foramen; A wr, pre-maxille; fr. fr, pre- frontal; /éy, pterygoid, #Z4. 0rd, post orbital: qu, quadrate; s. ang, supra- angular; s 074, supra-orbitals; sg, squamosal; supra. ¢.1, supra-temporal 1; supra ¢.2, supra-temporal 2; ‘ans, transverse; supra oc, supra-occipital; vow, vomer. (After W. K Parker. ) 340 SECT, XII PHYLUM CHORDATA 341 rabbit the skeleton of the limbs is constructed on a general plan, common to the limbs of all Craniata but the fishes, and known as the fexéadacty/e, in allusion to the five digits in which the limb typically terminates. In the pectoral limb the upper arm has a single long bone known as the humerus; at its proximal end this is movably articulated with the pectoral arch. The forearm contains two long 1 / —g! actb CL \ HU FE uv v cnulo cn.2 SO dst.1 O§ D&-dst. 5 dsts—p Oe asb.5 micps mtcp.6 mts. mlts.5 ph ph ph MY 1 WV Vv Qn WV Im Fic. 214. — Diagrams of the fore (A) and hind (B) limbs with the limb-girdles. acté, acetabulum; g/, glenoid cavity; #. cor, procoracoid; I’, digits Cartilage bones —cn.1, en.2, centralia; COR, coracoid; dst. 5-1, distalia; FE, femur; FI, fibula; fi, fibulare; HU, humerus; IL, ilium; int, intermedium; IS, ischium; mtcp. 1-5, metacarpals; mt. ts. 1-5, metatarsals; ph, phalanges; PU, pubis; RA, radius; ra, radiale; TI, tibia; ti, tibiale; UL, ulna; ul, ulnare, membrane bone; CZ, clavicle. bones — radivs and w/na — articulating proximally with the distal end of the humerus. The skeleton of the hand con- sists of three principal parts,— the carpus, the metacarpus, 342 MANUAL OF ZOOLOGY SECT. and the phalanges. The carpus or wrist consists of a num- ber of small irregularly shaped bones arranged in two trans- verse rows, proximal and distal, with a central bone between the rows. The mefacarpus consists of five narrow bones forming the support of the basal parts of the five digits, and articulating proximally with the distal row of carpals. The rest of the skeleton of the digit is formed of a row of small bones, the phalanges, the last of which — wagual phalanx —is modified in shape to support the horny claw. The skeleton of the hind-limb corresponds closely with that of the fore-limb. The pelvic arch consists on each side of three bones which become firmly united together, one of these, the zm, is dorsal in position, the other two, pzdes and ischium, are ventral, the pubis being anterior to the ischium. ‘The ilia articulate firmly with the sacral region of the spinal column ; the pubes unite ventrally in an articu- lation known as the pubic symphysis, and in the lizard the ischia are similarly connected. Laterally where the three bones unite is a cup-like cavity — the acetabulum — which forms the socket for the head of the thigh-bone. The thigh has a single long bone, the femur. The leg has two bones, the #éza and fiula, the former, which is internal, being the larger of the two, and the latter in the rabbit not being distinct from the former towards the distal end. In the foot are a number of ¢a/sa/ bones correspond- ing to the carpals of the hand, a series of mecfafarsals corre- sponding to the metacarpals and a series of phalanges. When the skin of the trunk of the dogfsh is removed there will be found immediately beneath it a thick layer of muscle. This is distinctly divided into segments or myomeres Similar to those of Amphioxus, and this, with the division of the vertebral column into segments or vertebrae (which, however, do not exactly correspond in arrangement XII PHYLUM CHORDATA 343 with the myomeres), indicates that the body, like that of Nereis or an Arthropod, is metamerically segmented. In the lizard and rabbit the metamerism of the muscular sys- tem, though distinguishable at an early stage, becomes lost in the adult, and the muscles take on a much more compli- cated arrangement. On the jaws are a series of teeth, the function of which is to seize the food, and in the rabbit cut it into fragments, and crush it into yet smaller particles, in order to prepare it for the process of digestion. In the dogfish the teeth are numerous and of uniform character throughout, small with sharp points directed backwards. At their bases they are fixed to the surface of the cartilage of the jaw by means of dense fibrous tissue. In the lizard the teeth are also of uniform § character (homodont dentition). They are of a simple conical shape, and fixed to the bone of the jaws. In the rabbit the teeth are distinctly visible into sets, dif- fering from one another in shape and function (heterodont dentition). Their bases are lodged in sockets or a/veot in the substance of the jaws. The structure of the tooth is the same in all three cases. The main mass of the tooth consists of dentine, a densely Fic. 215. — Longitudinal ‘ é F section of a tooth, semi- calcified material permeated by delicate diagrammatic.’ PH, = i pulpcavity; PH", open- parallel tubules. The free surface is ingofsame; ZZ, den- covered with a layer of still harder mate- wimei (From Wieder. rial, the ename/, and the basal portion is “1™* 177%.) covered with a layer of cement, which is similar in micro- scopic structure to bone. 344 MANUAL OF ZOOLOGY SECT. XU The anterior part of the cavity into which the mouth leads is the ducca/ cavity, the posterior part is the pharyrx, On the floor of the buccal cavity is, in the lizard and in the rabbit, a mobile muscular prominence, the songue, repre- sented in the dogfish by a much less prominent and little mobile process. From this a wide tube leads backwards to open into a spacious chamber, the stomach. From the stomach the intestine, a more or less coiled tube, leads eventually to the anal aperture. In the dogfish and in the lizard the anus opens into a chamber, the c/oaca, which also receives the ducts of the urinary and reproductive organs. In the rabbit a cloaca is absent, and the anus is separate from the urino- genital opening. The mucous membrane of the enteric canal contains numerous glands, the secretions of which play an important part in digestion ; the most important of these secretions is the gastric juice secreted by the glands of the stomach. In addition, special large digestive glands are present producing secretions, also having the function of acting on the various components of the food in such a way as to facilitate the passage of the useful ingredients from the cavity of the alimentary canal to the blood-vessels. In the rabbit these special large digestive glands are the sadvary glands, the fiver, and the fancrcas, in the dogfish and lizard the salivary glands are absent, though in the latter there are numerous small glands, the ducca/ glinids, in the wall of the buccal cavity. The secretion of the salivary glands, the sa/va, enters the cavity of the mouth through the ducts of the glands. It contains a ferment, pspadin, which has the property of converting starch into sugar. The liver is in all three a relatively large organ, fixed by folds of peritoneum to the dorsal wall of the abdominal cavity and divided by fissures into a number of lobes. Its ‘suaiajap Sea [Yep “2 {e110v [eIUaA ‘ow “2 fa[olyUaA ‘2 ‘4ajain “en tmefiaddn ‘C-7 ‘snus jeyuagomm ‘s «92 ‘smsay ‘sz ‘onBuo0y ‘uz ‘snsouaa snus “z's taayva perids ‘72 gs ssteuruas e[Nasaa ‘aas ‘sa toes wads ‘s “gs tuaaids ‘7¢s ! poo eurds ‘po «gs tapends ‘gs trai] Jo aqoy ysis ‘47 «2 ‘pues Teqot (28 yo.e tumiysor your aajad. ‘vag :kpog Areynyid “7g :uopeydaouasoid ‘sg :Apoq jeauid ‘zg :xudseyd ‘yg Syode perojoad ‘v “9g tseaioued ‘ung !aqo] odo 7 -3¢0 taqo] Aroyoeslo ‘7 “Yo tsayoue [einau ‘wy “z ‘eyeSuojqgo el[npow (290 ‘pane ‘raat jo aqoy yay “2 “7 tel ramoy ‘f-7 tAoupry ‘py ‘ourjsajur Guz ‘soinjiode Terqoueiq [BULayUL ey 2g 7 ‘yp 4g “2 tsoyore peurey fv “7 +{[M2{8 JO Joor ur ayjauejuoy ‘20f 1uAptpida ‘pzga sapojUaA palyy ‘wazp :ei10e Jesiop ‘ov “p tuinjeqaiaa ‘949 sumrueio “er segues ‘x7 BOBO] 72 SUlaA [epNed ‘2 “pr !yoeUIO}s Jo uONIOd seIpIeD “78 “p2 ssnsoliayze snuod Yew “2 sjedy-Iseq ‘fy *g ‘a8epn1e9 lerqouviq-seq ‘<9 g ‘apiune ‘vy —-xoe]q 1qaq19A ay) JO spua paytoyes ays :paiop St asepyied ayy, “YyIZua| Foy Itay) ur santaeo (2v2 -w) [wanau pue ‘(20d ‘peg ) [elprvoiiad ‘(av2 “pgn) eurwopqe ay} osodxa 0} se os aueld ueipaw ay ul Aeme yno st [jem-Apog ay Jo apis ya] ayy, ‘opts YP] 24) Woy (BINIIUeD UNIT[ADG) YSPsoq Jouonsassiq — -grz ‘og an pyp en fen gi0 9 O49 s2 0D 2/ 9b 724 pe wie ft i al Gee mau Pate IS Slory fp 87 souL Spa pia 345 346 MANUAL OF ZOOLOGY SECT. duct, the dz/e duct, conveys its secretion, the é2/, into the most anterior part of the intestine known as the duo- denum. The duct gives off a diverticulum which expands into a rounded sac, the gadl-bladder; this acts as a recep- tacle for the bile when it is not required. The bile has an important action on the fatty matters of the food, converting them into an emuésion and decomposing a small proportion into glycerine and fatty acid. In addition to secreting the bile the liver has another function to perform: it acts as a storehouse for surplus carbohydrates absorbed from the food. The carbohydrates —compounds of the nature of starch and sugar — are converted in the liver into a sub- stance known as g/ycogen or animal starch, which becomes stored up in the cells to be given out again to the blood as it is required for nutrition during the intervals of fasting ; this function of the liver is known as the g@ycogenic function. The pancreas, which is a much smaller gland than the liver, produces a secretion, the pancreatic juice, which has the effect of converting starch into sugar, proteids into soluble modifications known as fepéones, and of assisting in the emulsification of fats. The duct of the pancreas also opens into the duodenum. The nutrient matters of the food, rendered soluble by the action of the various digestive fluids, pass into the blood contained in the blood-vessels in the wall of the enteric canal, and are thus conveyed through- out the body to be distributed. The fatty matters, however, pass into a system of minute vessels — the /ac#a/s — which ramify in the wall of the intestine. The lacteals are not blood-vessels, but belong to the Avwphatic vascular system to be referred to presently. The lacteals combine together and in the rabbit open into a large trunk — the “horacic duct — by means of which the absorbed emulsion, or chyée as it is termed, is conveyed to one of the great veins. XII PHYLUM CHORDATA 347 The body-cavity in which the enteric canal and other organs are contained is lined with a membrane, the fev7- toneum. This is reflected over the surface of the contained structures, and folds of it serve to suspend the various organs and connect them together. The best developed of these folds is the mesentery (defective in the dogfish), by means of which the intestine is attached to the dorsal wall of the body-cavity. The organs of respiration of the dogfish are gz//s adapted for receiving oxygen from the air dissolved in sea-water ; those of the lizard and the rabbit are lungs adapted for breathing air directly. The movements of respiration have been already referred to. In the dogfish these movements have the effect of causing water to be taken in by the mouth, and to pass out from the pharynx to the exterior through the gill-slits. In passing out, the water flows over the gills, which are sets of vascular elevations on the walls of a series of five pairs of chambers—the Jdranchial sacs opening internally into the pharynx, and externally communicating with the surrounding water through the branchial slits. In this way the needed oxygen is constantly being taken up, and the carbon dioxide given off. The walls of the branchial sacs are supported by the hyoid and branchial arches. Inspiration and expiration of air in the lizard and rabbit take place through the nostrils. The nasal chambers into which the nostrils lead communicate internally with the mouth-cavity or the pharynx through a pair of apertures known as the zaérnal or posterior nares. On the floor of the pharynx behind the root of the tongue is a slit-like aperture, the g/o¢#s, opening behind into a chamber known as the Zarynx, the wall of which is supported by cartilages. From the larynx the air passes backwards along a tube, the trachea, the wall of which is supported by numerous rings 348 MANUAL OF ZOOLOGY SECT. of cartilage. The trachea bifurcates when it enters the body-cavity, each of the two branches, or d7vnchi as they Oe are termed, passing to the corresponding lung. In the lizard the lung is in essence a thin-walled sac with elas- tic walls. In the wall of the sac immediately out- side, the delicate internal epithelium is a rich net- work of blood-vessels, into the blood contained in which oxygen from the air in the cavity of the lung readily passes, while the carbonic acid is at the same time given off. In the rabbit the lung is of much more complicated structure, but the essential relations are the same. In the lizard the lungs lie in the anterior part of the general body-cavity. In the rabbit the anterior part of the body-cavity, containing the lungs and the heart, is separated off from the posterior part, Fic. 217.— Lacerta agilis. General view +s of the viscera in their natural relations. containing the greater por- &/, urinary bladder; Cz, post-caval vein; 4; ‘ Do vectim: CB, gallbladder; A, tion of the enteric canal and heart; Lg, Lg’. the lungs; AZ, stomach; AMD, small intestine; Oe, cesophagus; other organs, by a muscular Pun, pancreas; Tyr, trachea. (After Whiedersheim.) partition concave posteri- XII PHYLUM CHORDATA 349 orly,—the daphragm, — the anterior portion of the cavity being known as the cavity of the ¢zorax, and the posterior as that of the abdomen. : Hunn The air in the lungs, as it is constantly QhEe ely ah and gaining carbon dioxide, requires to be frequently renewed ; and the respiratory movements which have already been referred to are the movements indicative of this renewal ; in the movement of vespf/ration air is drawn into the lungs, which become fully distended ; in that of expiration, the greater part of the air is driven out again, and the lung collapses. In the rabbit inspiration and expiration are effected by the movements of the ribs and of the diaphragm, by which the dimensions of the cavity of the thorax are increased or diminished. The blood-vascular system is highly developed in all the three examples. The blood is of a red colour, owing to the presence of red corpuscles containing a red colouring matter termed hemoglobin. The blood-vessels are of three kinds, — arteries, veins, and capillaries. The arteries have firm and elastic walls, which do not collapse when the vessel is empty; they contain arterial blood, z.¢., blood which contains abundance of oxygen. The veins have thin, non-elastic walls which col- lapse when the vessel is empty and contain valves ; the con- tained venous blood is darker in colour than the arterial, and has been deprived of oxygen in the tissues. Both arteries and veins ramify extensively, the ultimate branches being of very small size. Connecting together the ultimate branches of the arteries and the ultimate branches of the veins is a system of microscopic vessels — the capillaries. The /eart is ventral and anterior in position. In the dog- fish it will be found to lie in a space, the pericardial cavity, between the two rows of gills, and separated behind from the 350 MANUAL OF ZOOLOGY SECT. general body-cavity (abdomen) in which the majority of the internal organs are contained, by a transverse fibrous parti- tion. It consists of four chambers, — the s¢nus venosus, aust- cle, ventricle, and conus arteriosus. The venous blood enters the sinus venosus from the great veins and passes through the other three chambers in succession in the order given. All the chambers contract rhythmically, and by their con- tractions the blood is propelled from chamber to chamber, and finally driven out from the heart, its passage in the opposite direction being prevented by the presence of valves. These are placed in the openings leading from chamber to chamber, and are so arranged that while they permit the ready passage of the blood in the direction above given, they close up the opening when pressure is exerted in the opposite direction ; thus, for example, when the auricle contracts, the valve guarding the opening leading back into the sinus venosus closes that opening, while the valve in the opening leading into the ventricle opens freely, and the blood passes readily in that direction. The ventricle is by far the most muscular of the four chambers, since it is mainly by its contractions that the blood is forced through the system of vessels. The blood which is forced out from the heart by the contractions of the ventricle passes into a series of vessels which carry it all to the gills. Here it enters a system of capillaries in the gills, and these being separated from the surrounding water only by a thin mem- brane, oxygen readily enters the blood, and the carbon dioxide collected in the various tissues and organs of the body is given off. The blood then enters a set of larger vessels, which combine to form a large trunk, the dorsal aorta. Branches from this distribute blood to all parts of the body, where it enters the systems of capillaries, and whence it is carried back again to the heart by the verns. xl PHYLUM CHORDATA 351 In the lizard the heart and the circulation are somewhat more complicated than in the dogfish. ‘There is a sinus venosus as before. The auricle is completely divided into two chambers, right and left, by a partition. Into the right auricle the sinus venosus drives the venous blood from the great veins ; into the left open the pulmonary veins, bring- ing the oxygenated blood from the lungs. Both the auricles open into the ventricle, the cavity of which is partly divided by a septum. From the ventricle are given off the main arteries (systemic arteries) which branch throughout all parts Fic. 218 — Diagram illustrating the course of the circulation in a fish. Vessels containing aérated blood, red; those containing non-aérated blood, blue; lym- phatics, black. B, capillaries of the body generally; E, of the enteric canal; G, of the gills; K, of the kidneys; L. of the liver; T, of the tail. a. 47. a, afferent branchial arteries; az, auricle; c. a, conus arteriosus; d@. ao, dorsal aorta; e. dx. a, afferent branchial arteries; %. 4 wv, hepatic portal vein; 4. v, hepatic vein; éc, lacteals; 7y, lymphatics; fy. cv. v, pre-caval veins; 7. p. 7, renal portal veins; s. v, sinus venosus; v, ventricle; v. ao, ventral aorta. The arrows show the direction of the current. of the body, and the pu/monary arteries, which pass direct to the lungs. By various arrangements of the parts which need not be described at present, the venous blood from the right auricle is mainly guided into the pulmonary arte- ries, and passes to the lungs to obtain oxygen and part with its carbon dioxide ; while the arterial blood is mainly guided 352 MANUAL OF ZOOLOGY SECT. to the systemic arteries. A certain degree of mixing, how- ever, of the venous and arterial currents takes place as they pass through the ventricle. In the rabbit this mixing of the arterial and venous cur- rents is entirely prevented, owing to the ventricle being completely divided into two chambers — right and left. The right auricle opens into the right ventricle, and fills it with venous blood from the great veins. From the right auricle the blood is driven through a pulmonary artery to the lungs. From the lungs the oxygenated blood is returned by means of the pulmonary veins to the left auricle; from the left auricle it enters the left ventricle, and from the latter is driven out through the system of systemic arteries to all parts of the body. There are thus two distinct cur- rents of blood constantly passing simultaneously through the heart, but entirely cut off from one another, viz., a venous current on the right side and an aréria/ on the left. The blood of the rabbit has a much higher temperature than that of the dogfish or lizard. In all the three examples the veins which carry the venous blood towards the heart from the stomach, intestine, and pancreas unite together to form a large vein, the hepatic portal, which ramifies in the substance of the liver, and forms the main source of the blood supply of that organ. In the dogfish and lizard, but not in the rabbit, veins con- vey blood from the posterior region to the kidneys, forming what is termed a vena/ portal system. The nervous system is highly developed. The central nervous system consists of the brain and spinal cord. The brain is, as already stated, contained in the cavity of the cranium ; the spinal cord, continuous with the posterior end of the brain, extends through the neural canal roofed over by the series of neural arches of the vertebree. XII PHYLUM CHORDATA 353 ‘The spinal cord is similar in essential respects in all three examples. It is a cylindrical cord of nerve matter, having running along the middle of its dorsal surface a fissure, the VH Lot Fic. 219. — Dorsal view of the brain of Scyllium canicula, The posterior division of the brain is the medulla oblongata (V/H/), on the dorsal surface of which is skown one of the central ventricles (7. rho). The large cerebellum (H#) nearly covers the optic lobes (WA’). The diencephalon (ZH) shows in the middle one of the central ventricles, and the place of attachment of the oe body (Gf). The prosencephalon (VH) gives off the olfactory lobes (Tro, L. ol). The following nerves are shown: optic (//), trochlear (/V/’), trigeminal (Vv ), facial (V//), auditory (V///), glossopharyngeal (/4°), and vagus (1). (From Wiedersheim.) dorsal longitudinal fissure, and along the middle of its ven- tral surface, a second fissure, the ventral longitudinal fissure. 2A 354 MANUAL OF ZOOLOGY SECT, Through its substance from end to end runs a narrow canal, the central canal. In the brain of the dogfish the most anterior portion is a thick mass of nerve matter indistinctly divided into two lateral portions by a shallow depression. This is the pro- sencephalon of the fore-brain. A pair of lobes given off from this in front are the olfactory lobes. The prosencepha- lon with a narrow region, diencephalon or thalamencephaien, behind it, constitute the fore-drain. Behind the fore-brain a pair of oval lobes, the offic /odes, constitute the dorsal portion of the mid-brain, which comprises, in addition, a thick mass of longitudinal nerve-fibres, lying below, and connecting the hind-brain with the fore-brain. An elon- gated median mass, indistinctly divided into lobes, is the cerebellum, the anterior portion of the hind-brain. The posterior division of the hind-brain, — medudla oblongata, — broad in front, tapers posteriorly where it passes into the spinal cord. The central canal of the spinal cord expands in the me- dulla oblongata into a wide shallow cavity, roofed over only by a thin membrane ; this is known as the fourth ventricle. From this runs forwards a narrow passage, the zver or ague- duct of Sylvius, expanding in front in the thalamencephalon into a laterally compressed cavity, the “ird ventricle. From this are given off a pair of /tteral ventricles, passing into the prosencephalon, each giving off a prolongation into the corresponding olfactory tube. The roof of the third ventricle is very thin; it is pro- duced into a slender process — the epiphysis or pineal body. Its side walls are formed of two masses, the optic thalami ; its floor is produced into a hollow prolongation, the /7/fien- dibulum, to the end of which a vascular body, the Aypophysis or pituitary body is applied. XII PHYLUM CHORDATA 355 In the brain of the lizard the same parts are recognisa- ble as in the dogfish, the chief differences being that the prosencephalon is deeply divided by a median longitudinal fissure into two lobes, the cerebral hemispheres, and that the cerebellum is very small. In the rabbit also we rec- ognise the same parts. But the whole brain is larger in pro- portion to the bulk of the body; the cerebral hemispheres are much more highly developed, and the cerebellum is not only of large relative size, but is of complicated structure. ‘The peripheral nervous system consists of the spinal and cerebral nerves given off from the spinal cord and the brain respectively, with their ramifications through all parts of the body. A pair of spinal nerves emerge from the neural canal between each adjoining pair of vertebrae. Each spinal nerve arises from the spinal cord by two roots—a dorsal and a ventral; the former is dilated into a ganglion. Experiments prove that the dorsal root contains the sensory fibres of the nerves, z.¢., those fibres which are concerned in carrying impulses from the various parts to the nerve centres to be translated in consciousness into sensations. When, for example, the skin of some part of the body is touched, the impulse by means of which we become con- scious of the contact passes from the surface through branches of the spinal nerves, and enters the spinal cord through the dorsal root, in order to be transmitted to the brain. The ventral root, on the other hand, contains the motor fibres ; the fibres through which impulses which lead to the contraction of muscles pass outwards from the central nervous system. More or less extensive intercommunications take place between the spinal nerves that are situated opposite the origin of the limbs ; these sprnal nerve plexuses give off the nerves to the limbs. 356 MANUAL OF ZOOLOGY SECT, The cerebral or cranial nerves correspond pretty closely in their general arrangement in the three examples. The offactory nerve-fibres, which originate from the olfactory lobes, the epzic nerves, which are derived from the thalamen- cephalon, and the ava/fory nerves which originate from the medulla oblongata, are the nerves of the special senses of smell, sight, and hearing respectively, the first ending in the epithelium of the nasal cavities, the second in the retina of the eye, and the third in the epithelium of the interior of the inner ear. Other cranial nerves supply the muscles that move the eyeball, the skin of the head, the muscles of the jaws, the tongue, pharynx, heart, stomach, etc. The structure of the eye is in all essential respects the same in all the three examples; such differences as there are will be referred to later. The eye of a bullock or a sheep, being larger, may with advantage be substituted. The eyeball is globular, and is encased in a rough opaque capsule, the scderotic. It lies in the cavity of the orbit, and is capable of being turned about in various directions by a number of muscles inserted into it. On the side of the eyeball directed towards the light, the opaque sclerotic is replaced by a transparent membrane, the cornea, which forms a window through which the rays of light enter the eye. Within the sclerotic is a more delicate pigmented layer, the chorord. ‘Towards the cornea the choroid passes into a circular pigmented diaphram, the zris, the opening of which is known as the fugi7. Through the pupil, the size of which is capable of being increased or diminished, the light is admitted into the interior of the eye. The sen- sitive part of the eye, the part on which the image produced by the rays of light proceeding from an object must fall in order to produce the sensation of sight, is a soft gray layer lining that part of the cavity of the eye which lies within the XI PHYLUM CHORDATA 357 iris. The rays of light are brought to a focus on the retina mainly by means of the crystalline lens, a firm, glassy body situated within the iris. The cornea also assists in this, as does a gelatinous substance, the w¢reous humour, which fills the part of the cavity of the eyeball internal to the lens. The ear in the dogfish is imbedded in the cartilage of the posterior part of the skull (auditory region). It con- sists of a somewhat complicated structure termed the Fic. 220. —— Diagrammatic horizontal section of the eye of man. c, cornea; ch. choroid (dotted); C. P, ciliary processes; e. c, epithelium of cornea; ¢. ¢7, conjunctiva; fc, yellow spot; /, iris; Z, lens; ON, optic nerve; OS, ora serrata; o-x, optic axis; # c. R, anterior non-visual portion of retina; P. Z, pigmented epithelium (black); AR, retina; sf. 2, suspensory ligament; Sc/, sclerotic; V’. H, vitreous body. (From Foster and Shore’s Physzology.) membranous labyrinth, with soft walls and an_ internal epithelium in which the fibres of the auditory nerve termi- nate. Contained in the interior of the labyrinth is a fluid, the endolymph, in which there are suspended particles of 358 MANUAL OF ZOOLOGY SECT. carbonate of lime, the o#dths. In ‘the lizard and rabbit there are superadded to this, the essential part of the ear, certain accessory parts. The most important of these is the Avmpanum or drum of the ear. This is a cavity to the outside of the auditory region of the skull (the region in which the membranous labyrinth is enclosed). The tym- panum communicates with the pharynx through a passage known as the Eustachian passage. Externally the cavity of the tympanum is closed by a tense, drum-like membrane, the “’mpanic membrane. The tympanic membrane is set in vibration by the waves of sound, and the vibrations are transmitted across the tympanic cavity by a slender rod of bone (in the lizard) or a chain of minute bones (in the rabbit). The inner end of the rod or chain of bones is inserted into a membrane covering over a small aperture in the outer wall of the auditory region of the skull, which forms the inner wall of the tympanic cavity, and by this means the vibrations are communicated to the endolymph of the membranous labyrinth and affect the terminations of the auditory nerve-fibres. In the lizard the tympanic membrane is nearly on a level with the skin of the head, and its position is conspicuously indicated by a brown patch situated behind the eye. In the rabbit the tympanic membrane is more deeply sunk, and a wide passage, the passage of the outer ear, leads to it from the exterior. The ear of the rabbit also differs from that of the lizard in the presence of the prominent auricle or pinna of the ear to which reference has been already made. The Aidneys, or organs of renal excretion, though they differ in form in the three examples are not widely different in essential structure. Their function is the secretion of urine, which consists of water containing various nitrogenous waste matters in solution. Essentially the kidney is a mass XI PHYLUM CHORDATA 359 of tubules by whose agency the process of secretion is car- ried on, the whole being richly supplied with blood-vessels. Eventually the tubules open into a duct, the w7eter. In the lizard and the rabbit there is present a median thin-walled sac, the w/?nary bladder, in which the urine is stored, to be discharged at intervals. In the rabbit the ureters open into the bladder, and the latter opens on the exterior by a median canal, the wze¢hra. In the lizard the ureters and the bladder have independent openings into the cloaca, and the bladder is filled only by regurgitation from the latter chamber. The sexes are distinct in all three. There are two éesées, each with its duct or vas deferens. In the female there are two ovaries, which are solid bodies in which the ova lie im- bedded. In the dogfish, when mature, the ova are of large size, containing a great quantity of food-yolk. The ova of the rabbit are extremely small, while those of the lizard are of a size intermediate between those of the other two. Each ovum is enclosed in a follicle — the Graafian follicle — with a wall composed of small cells. When the ovum approaches maturity the follicle projects on the surface of the ovary, and eventually the wall becomes ruptured and the ovum escapes into the body-cavity. The oviducts, of which there are two, are not connected with the ovaries, each opening anteriorly into the body- cavity by a wide opening. In the dogfish and the lizard the oviducts remain practically distinct from one another throughout; in the rabbit the posterior parts are united to form a median chamber, the body of the wéerus, and a median passage, the vagzna, leading to the exterior. The ova in all three, when discharged from the ovaries, enter the wide openings of the oviducts and are impregnated during their passage backwards. In both the dogfish and the lizard each fertilised ovum becomes enclosed while in the oviduct 360 MANUAL OF ZOOLOGY SECT. in a tough she//, and is discharged when development has only begun. In the rabbit the fertilised ovum is received into the uterus and there undergoes its development, the young rabbit when born differing little, save in size, from the adult. The nourishment of the fe/ws or uterine young of the rabbit is effected by means of a special vascular structure known as the p/acenéa, by means of which nutrient material passes from the blood of the mother to that of the foetus ; and after birth the young rabbit receives its nourishment for a time exclusively from the secretion of a set of glands of the mother—the mammary or milk glands. CLASS I. CYCLOSTOMI The iowest of existing Craniate Vertebrates are certain fish-like animals known as “lampreys” and “hag-fishes,”’ or “slime-fishes,” which are looked upon as constituting the class of Craniata, to which the name of Cyclostomi is ap- plied. Of them it is here possible only to make the briefest mention. The lampreys (Fefromyzon and other genera) and the hag-fishes or slime-fishes (A/ xine and Bdellostoma) are somewhat eel-like in general shape, that is to say, they have a long and narrow body without marked external dis- tinction into regions, and with a soft and slimy integument. Of the fins of such a fish as the dogfish the median or un- paired series alone are represented, paired fins corresponding to the limbs of the higher Craniata being entirely absent. There is a dorsal fin divided into two in the lampreys, undi- vided in the hag-fishes, which is continued asa tail fin round the posterior or caudal extremity of the body. On the lower or ventral surface of the anterior or head-end is a deep hollow — the buccal funnel, much more conspicuous in the lampreys than in the hags, at the bottom of which the small xit PHYLUM CHORDATA 361 opening of the mouth is situated. There are no jaws, but on the inner surface of the buccal funnel and on the tongue —a fleshy (?) process below the opening of the mouth. In Myxine the funnel is edged with slender, flexible processes or tentacles. At the sides of the head are the eyes, well developed and conspicuous in the lamprey, imperfect and buried beneath the skin in Myxine, and on the upper surface is a single median aperture, the nostril. Further back at Ni pre Fic. 22t.-— Petromyzon marinus. Ventral (A), lateral (B), and dorsal (C) views of the head. 47. c/. 1, first gill-cleft; duc. /, buccal funnel; eye, eye; mth, mouth; na. ap, nasal aperture; /, papilla: #2, pineal area; ¢. 7, ¢. 2, ¢. 3; teeth of buccal funnel; 4g, teeth of tongue. (After W. K. Parker.) Yer of dartote the sides of the head are, in the lamprey, a series of seven pairs of slits, the gill-slits, leading to the gill-pouches ; in Bdellostoma there are six pairs of small gill-slits, in Myxine only a single aperture on each side. The skeleton is very unlike that of the true fishes, and ae MANUAL OF ZOOLOGY SECT. XI is in some respects extremely primitive. The spinal col- umn is represented merely by a thick persistent notochord, enclosed in a sheath, with, in the lampreys, small carti- na.ap B Sate fl oes.ct.d Fic. 222. — Head of Myxine glutinosa (A) and of Bdellostoma forsteri (B), from beneath. 4x. af, branchial aperture; 47, cd. z, first branchial cleft; #¢, mouth; na. apf, nasal aperture; oes. ct. d, esophageo-cutaneous duct. The smaller open- ings in A are those of the mucous glands, (After W. K. Parker.) laginous processes representing neural and hemal arches. The skull is cartilaginous, and is peculiarly modified. Be- hind it in the lamprey is a remarkable basket-like apparatus, pavo wiory possed apistiq ‘x “a fanBuoy ‘7 ‘7 :smsousA “4 $anu0} jo aposnur 90 syeuvo peuids ‘v2 “7% 1 saBepyies [eyo nf ‘af Saunsazut ‘7742 UIA qeynsnt nq Mojaq eAoors 64s op ‘op p ‘Ulea [euIpaes Io] "7 ‘f sapUINe OVI snsouaa snuts ySnorty WEA [eUy eyoe peryuaa ‘ov 2 Lepotiyuaa (7 (Ue “A SONBUOY JO TOJOWAJOI “7 “1 “fo syayns ‘sa tyoor erueto ‘pu spioo yeurds ‘fee wiorg) “aUTSOIT OFUT JaT]NS wWosy (hiatozo07 § Jaysed seq jerqouersq Jo 7 fsaposuu [eIuas Sue 2 TWN[IA 972 142% snuis ‘2 “s :ja]{NS Sarpunosins snuys y soyenoid 7 m g sadvjyred [es10p IOL19} ‘ou fou saynsdeo jeseu :Aqawo peoong ‘ze + aotrayur ff 2 :juaumngaz ut fyeuvo yeinau jo anss suado ano yey taddn oy} eq [EUIPNSU] esque ‘7 "2 ¢ Asoyeridsar {7 “4 suopua} Sit ‘ d ‘og ‘freao ‘20 :jauuny peoonq vu syonod Areyinyid © 87 :oBepaies pensuy] -1seq 0} Tolazue aieyd | jo ainyiede jeuiay sod ‘py *g swmipreotie pensany oF poyoure asey! 1seq puryaq aed [eseq Jo O[NoLMeE MOYs 07 pauedo pue syed snourde3129 ayy, pue Mojaq ainye' oyou ay} JO yJeays 243 ‘gpeuray Jo UOQIesSIqg ‘SHULIvUT UOZATHOI}ed — “ae OL] 363 364 MANUAL OF ZOOLOGY SECT. composed of cartilaginous processes. This branchial basket, as it is termed, supports the gill-sacs. The gill-sacs, of which there are either six or seven pairs, are the organs of respiration, representing the gills of the true fishes. In the lamprey each of these communicates with the exterior by the corresponding gill-slit, and inter- nally opens into a common passage, the respiratory tube which leads in front into the buccal cavity. In Bdellostoma each gill-pouch has its own internal opening through a narrow tube into the pharynx, as well as its external open- ing through a small gill-slit. In Myxine, on the other hand, though éach pouch has a separate internal commu- nication with the pharynx, the tubes leading outwards from the gill-pouches of each side all join to form a common tube, which opens on the exterior by the single gill-slit. The other systems of organs are not so remarkable. The alimentary canal, the heart, and the brain are not widely different from those of the true fishes. A peculiar feature is that there is only a single nasal sac (opening by the single nasal aperture already referred to) instead of the pair developed in all other Craniates ; in Myxine its cavity com- municates by a passage with the cavity of the mouth. In the lamprey, in addition to paired eyes having the typical vertebrate structure, there is connected with a lobe in the roof of the fore-brain a median or pineal eye of simpler structure and imperfectly understood function. Lampreys live mainly in rivers and estuaries. Their food consists chiefly of small aquatic animals, such as worms, small crustaceans, etc.; but they also sometimes attach themselves to the bodies of fishes, by means of the sucker- like buccal funnel, and rasp off portions of the flesh with the horny teeth of the tongue. Myxine actually makes its way into the interior of the bodies of large fishes, such as the xi PHYLUM CHORDATA 365 cod, consuming the flesh in its passage, and thus becomes for a time an internal parasite the only example among -the Vertebrata of sucha condition. In the free state Myxine usually lies buried in the sand, with only the anterior end, with the nasal aperture, projecting on the surface. By means of the passage leading from the nasal sac to the mouth, water passes in and out through the nasal aperture, and the process of respiration is carried on while the ani- mal remains almost completely hidden. The geographical distribution of the Cyclostomi is some- what remarkable. Fe/romyzon is found on the coasts and in the rivers of Europe, North America, Japan, and West Africa. Of the allied genera one, /chthyomyzon, occurs on the western coast of North America; another, AZordacia, in Tasmania and Chili; a third, Geo¢ria, in the rivers of Chili, Australia, and New Zealand. Myxine occurs in the North Atlantic and on the Pacific Coast of South America, includ- ing the Straits of Magellan; Bdellostoma on the coasts of South Africa, New Zealand, and Chili. CLASS II. PISCES The class Pisces or Fishes includes the Elasmobranchii or cartilaginous fishes (sharks, dogfishes, and rays), the Teleo- stomi or bony fishes (such as perch, pike, mackerel, cod, sole, salmon, sturgeon, and bony pike), and the Dipnoi or lung-fishes. In these the organs both of respiration and of locomotion are adapted for an aquatic mode of life. The chief and, in the majority, the only organs of respiration are the gills, which are in the form of series of vascular processes attached to the branchial arches and persisting throughout life. The organs of locomotion are the paired pectoral and the pelvic fins, and the unpaired dorsal, 366 MANUAL OF ZOOLOGY SECT. ventral, and caudal; these are all supported by fin-rays of dermal (p. 372) origin. A hard external covering of scales developed in the dermis is usually present. In the en- doskeleton the notochord is usually replaced more or less completely by cartilaginous or bony vertebrae; there is a well-developed skull and a system of well-formed visceral arches, of which the first forms the upper and lower jaws, the latter movably articulating with the skull, and both nearly always bearing teeth. An air-bladder is frequently present, and in certain exceptional cases acquires the function of a lung or chamber for breathing air. Sub-class I. Elasmobranchii A dogfish may be selected as a convenient example of the sub-class and of the class Pisces. Dogfishes occur at slight depths off the coasts in all quarters of the globe. The commonest European forms are the rough hound (Se/ium canicula), the lesser spotted dogfish (S. catésus), the piked dogfish ( Acanthias vulgaris), and the smooth hound (Mustelus vulgaris). Allied species of the southern hemi- sphere are Scy@ium, Acanthias, and ALlustelus anarcticus. On the coast of Northeastern America the common dogfish is Mustelus canis, For the description which follows, any of these species will be found to serve very well. A slight general account of the dogfish has already been given in the introduction to the Craniata ; this has now to be extended and supplemented. The general shape (Fig. 206) may be described as fusiform ; at the anterior or head-end it is broad and depressed ; posteriorly it tapers gradually and is compressed from side to side. The head terminates anteriorly in a short blunt snout. ‘The tail is narrow and bent upwards towards the extremity. The entire surface is xt PHYLUM CHORDATA 367 covered closely with very minute hard placotd scales or dermal teeth somewhat larger on the upper surface than on the lower. These are pointed, with the points directed somewhat backwards, so that the surface appears rougher when the hand is passed over it forwards than when it is passed in the opposite direction. When examined closely, each scale is found to be a minute spine situated on a broader base. The spine consists of dentine covered with a layer of enamel; the base is composed of bone, and the whole scale has thus the same essential structure as a tooth. Along each side of the head and body runs a faint depressed longitudinal line or slight narrow groove, — the 4ateral Line. As in fishes in general, two sets of fins are to be recognised, — the wupaired or median fins, and the pazred or lateral. These are all flap-like outgrowths, running vertically and longitudinally in the case of the median fins, nearly horizontally in the case of the lateral; they are flexible, but stiffish, particularly towards the base, owing to the presence of a supporting framework of cartilage. Of the median fins, two — the dorsa/— are situated, as the name indicates, on the dorsal surface: they are of triangular shape ; the anterior, which is the larger, is situated at about the middle of the length of the body, the other a little further back. The cawzda/ fringes the tail; it consists of a narrower dorsal portion and a broader ventral, continuous with one another round the extremity of the tail, the latter divided by a notch into a larger, anterior, and a smaller, posterior lobe. The tail is heterocercal, z.¢,, the posterior extremity of the spinal column is bent upwards and lies in the dorsal portion of the caudal fin. The ventral or so-called ana/ fin is situated on the ventral surface, opposite the interval between the anterior and posterior dorsals ; it resembles the latter in size and shape. 368 MANUAL OF ZOOLOGY SECT. Of the /ateral fins there are two pairs, the pectoral and the pelvic. The pectoral are situated at the sides of the body, just behind the head. The ge/vzc, which are the smaller, are placed on the ventral surface, close together, in front of the middle of the body. In the males the bases of the pelvic fins are united together in the middle line, and each has connected with it a clasper or copulatory organ. The latter is a stiff rod, on the inner and dorsal aspect of which is a groove leading forwards into a pouch-like depression in the base of the fin. The mouth —a transverse, somewhat crescentic opening — is situated on the ventral surface of the head, near its anterior end. In front and behind it is bounded by the upper and lower jaws, each bearing several rows of teeth with sharp points directed backwards. The nostrils are sit- uated one in front of each angle of the mouth, with which each is connected by a wide groove, the zasobuccal groove. A small rounded aperture, the sfivac/e, — placed just behind the eye,—leads into the large mouth-cavity or pharynx. Five pairs of slits running vertically on each side of the neck, the branchial slits, also lead internally into the mouth- cavity. A large median opening on the ventral surface at the root of the tail, between the pelvic fins, is the opening leading into the cloaca, or chamber forming the common outlet for the intestine and the renal and reproductive organs. A pair of small depressions, the aédominal pores, situated behind the cloacal opening, lead into narrow passages open- ing into the abdominal cavity. The skeleton is composed entirely of cartilage, with, in certain places, depositions of calcareous salts. As in Verte- brates in general, we distinguish two sets of elements in the skeleton, —the axial set and the appendicular, the former comprising the skull and spinal column, the latter the limbs and their arches. xIl PHYLUM CHORDATA 369 The spinal column is distinguishable into two regions, — the region of the trunk and the region of the tail. In the trunk region each vertebra (Fig. 209, 4) consists of a centrum (¢), neural arch (vz@), and transverse processes (¢r. pr). In the caudal region there are no transverse processes, but inferior or hemal arches (D,h. a) take their place. The centra of all the vertebrae are deeply biconcave or amphi- celous, having deep conical concavities on their anterior and posterior surfaces. Through the series of centra runs the notochord, greaély constricted in the centrum itself, dilated in the large spaces formed by the apposition of the amphiccelous centra of adjoining vertebree. The concave anterior and posterior surfaces of the centra are covered by a dense calcified layer, and eight radiating lamelle of calcified material run longitudinally through the substance of the centrum itself. Each neural arch consists of a pair of rod-like neural processes, which form the sides, and two pairs of compressed neural plates (one placed opposite the centrum, the other or énéercalary cartilage, opposite the interval between adjoining centra), which form the roof of the arch, together with usually two nodules — the repre- sentatives of neural spines — which form the keystones. The transverse processes are very short: connected with each of them is a cartilaginous rudimentary 77d about half an inch in length. The cranium (Fig. 224) is a cartilaginous case, the wall of which is continuous throughout, and not composed, like the skulls of higher vertebrates, of a number of distinct ele- ments (bones) fitting in together. At the anterior end is a rostrum, consisting of three cartilaginous rods converging as they extend forwards and meeting at their anterior ends. At the sides of the base of this are the o/fuctory capsules (off. cb),—thin rounded cartilaginous sacs opening widely 2B 370 MANUAL OF ZOOLOGY SECT. below, —the cavities of the two capsules being separated from one another bya thin septum. The part of the roof of the cranial cavity behind and between the olfactory capsules is formed, not of cartilage, but of a tough fibrous membrane, and the space thus filled in is termed the anéertor fontanelle ; in contact with the lower surface of the membrane is the pineal body, to be afterwards mentioned in the account of the brain. Each side wall of this part of the skull presents a deep concavity, the oré7t over which is a ridge-like prominence, the supra-orbital crest, terminating anteriorly and posteriorly in obscure processes termed respectively the pre-orbital and post-orbital processes. Below the orbit is a longitudinal 72/ra-orbita/ ridge. Behind the orbit is the a/rtorv region of the skull (aud. cp), a mass of cartilage in which the parts of the mem- branous labyrinth of the internal ear are embedded. On the upper surface of this posterior portion of the skull are two small apertures situated in a mesial depression. These are the openings of the agueductus vestibuli (endolymphatic ducts), leading into the vestibule of the membranous laby- rinth. Behind this again is the occipital region, forming the posterior boundary of the cranial cavity, and having in the middle a large rounded aperture, the foramen magnum, through which the spinal cord contained in the neural canal and protected by the neural arches of the vertebrae becomes continuous with the brain, lodged in the cranial cavity. On either side of this is an articular surface, the occipital condyle, for articulation with the spinal column. A number of smaller apertures or foramina, chiefly for the passage of nerves, perforate the wall of the skull. In close connection with the cranium are a number of cartilages composing the wiscera/ arches (Fig. 224). These are incomplete hoops of cartilage, mostly segmented, which 37! CHORDATA PHYLUM XII XII OIL “MM joy) “(49 +a) sadepyszeo perpoursq-erjxa YIM AT[eusazxXa poyoauuod are yoy ‘(,< 4g 4 +497) SheI peryuesg Yo sone ae Gaaiee prody puv xzejnqipuewody ay3 wos Se jam se ‘asaya wor 1(S-7 ‘v 4g) Sayore jeryoueIg aay 9y3 aWOD (72°47) NUIOD proAy U3 uodn Surmoyjoy ‘wayy ym payoauuod ale (97) sadeyyaes yeiqey [feuls pue (47 197) squswiest, omy Aq wield ay) 0} payore osje st mel raddn aq !(#2 47) nuios prosy ayi 0} Mojaq Uae Surats pure ‘smef (/:7) ramo, pue (f:¢7) aaddn ayy yoddns 0} Burdjay ‘(ve -fy) repnqipuewody yj st ajnsdeo Aroypne ayy yA pajejnoury “saaisu (S “2,z7) yeurwasiy pue (2 -2az) sudo ays 10y sammjiade usas aie jiqio ayi ul “(4) YBaq IO UINIySOI ayy Jo SaSepies ay) pue ‘(g7 fo) ansdeo A10DeFIO ay} ‘(40) y1qi0 Mo]foy oui ‘(¢2 ‘pxy) ajnsded Aroypne Bunsafoid ayy smoys (4) wWhlues ayy, “R[MOTURO TANTTTAIG Jo [NYS Jo MOIA aplg — ‘bee “OLY pouq, Udhy ayro 3772 MANUAL OF ZOOLOGY SECT. lie in the sides and floor of the mouth-cavity or pharynx. The first of these forms the upper and lower jaws. The upper jaw, or palato-guadrate (up. 7), consists of two stout rods of cartilage firmly bound together in the middle line and bearing the upper (or anterior) series of teeth. The lower jaw, or Afeckel’s cartilage (2. 7), likewise consists of two stout cartilaginous rods firmly united together in the middle line, the union being termed the sympAyscs. At their outer ends the upper and lower jaws articulate with one another by a movable joint. In front the upper jaw is connected by a ligament with the base of the skull. Immediately behind the lower jaw is the Avord arch. This consists of two cartilages on each side, and a mesial one in the middle below. The uppermost cartilage is the hyo-man- dibular (hy. m) ; this articulates by its proximal end with a distinct articular facet on the auditory region of the skull; distally it is connected by ligamentous fibres with the outer ends of the palato-quadrate and Meckel’s cartilage. The lower lateral cartilage is the cerato-hval (hy. cn). Both the hyo-mandibular and cerato-hyal bear a number of slender cartilaginous rods — the branchial rays of the hyoid arch (47. r). The mesial element, or dasz-Aya/, lies in the floor of the pharynx. Behind the hyoid arch follow the dranchial arches, which are five in number. Each branchial arch con- sists of several cartilages and bears branchial rays. The skeleton of all the fins — paired and unpaired — pre- sents a considerable degree of uniformity. The main part of the expanse of the fin is supported by a series of flattened segmented rods, the p/erigiophores or cartilaginous fin-rays, which lie in close apposition; in the case of the dorsal fins these are calcified along their axes. At the outer ends of these are one or more rows of polygonal plates of cartilage. On each side of the rays and polygonal cartilages are a RI PHYLUM CHORDATA 373 number of slender horny fibres of dermal origin. In the smaller median fins there may be an elongated rod of carti- lage constituting the skeleton, or cartilage may be entirely absent. In the pectoral fin (Fig. 225) the fin-rays are supported on three dasal cartilages articulating with the pectoral arch. he latter is a strong hoop of cartilage in- complete dorsally, situated immediately behind the last of Fic 225, — Ventral view of pectoral arch of Scyllium with right pectoral fin. The pectoral arch is divisible into dorsal (Acé. g) and ventral ( pct. g') portions, separated by the articular facets (a7¢. /) for the fin The pectoral fin is formed of three basal cartilages (4s, 7-3) and numerous radials (vad); its free edge is supported by dermal rays (d./. ~). (Modified from Marshall and Hurst.) the branchial arches. It consists of a dorsal, or scapular, (pet. g) and a ventral, or coracoid, portion (pct. g'), the coracoid portions of opposite sides being completely con- tinuous across the middle line, while the scapular are sepa- rated by a wide gap in which the spinal column lies. Between the two portions are the three articular surfaces for the three basal cartilages. The three basal cartilages of 374 MANUAL OF ZOOLOGY SECT. the fin are named, respectively, the anterior, pro-pterygium (4s. 2), the middle, meso-prerygium (6s. 2), and the pos- terior, mefa-pterygium (bs.3). Of these the first is the smallest, and the last the largest. The pe/vic fz has only a single basal cartilage, articulating with the pelwze arch, with which also one or two of the fin-rays articulate directly. The pelvic arch is a nearly straight bar of cartilage which runs transversely across the ventral surface of the body, just in front of the cloacal opening. The mouth leads into a very wide cavity, the pharynx (Fig. 216, ph), into which opens at the sides the internal apertures of the branchial clefts and of the spiracle. From this runs backwards a short wide tube, the esophagus (gut), which passes behind into the stomach. The stomach is a U-shaped organ, with a long left limb (¢d. s¢) continuous with the cesophagus, and a short right (fy/. s¢) passing into the intestine. At the fZy/orus—the point where the stomach passes into the intestine —is a slight constriction followed by a thickening. The zzéestine consists of two parts, —small intestine or duodenum, and large intestine. The former is very short, only an inch or two in length. The latter (¢z¢) is longer and very wide ; it is divisible into two portions, — the co/on in front and the rectum behind. The former is very wide and is characterised by the pres- ence in its interior of a spiral valve, a fold of the mucous membrane which runs spirally round its interior and both retards the too rapid passage of the food, and affords a more extensive surface for absorption. The rectum differs from the colon in being narrower and in the absence of the spiral valve ; it opens behind into the cloaca. There is a large “iver (2. Iv, r. dr) consisting of two elon- gated lobes. A rounded sac, the ga//-dladder, lies em- bedded in the left lobe at its anterior end. The duct of xu PHYLUM CHORDATA 375 the liver, the 4z/ duct, runs from the liver to the intes- tine. Proximally it is connected with the gall-bladder and by branch ducts with the right and left lobes of the liver. It opens into the commencement of the colon. The pancreas (pan) is a light-coloured compressed gland consisting of two main lobes with a broad connecting isthmus lying in the angle between the right-hand limb of the stomach and the small intestine. Its duct enters the wall of the small intestine and runs in it for about half an inch, opening event- ually at the point where the small intestine passes into the colon. Connected with the rectum on its dorsal aspect is an oval gland, the rectal gland (ret. g/), about three-quarters of an inch in length. The spleen (spl) is a dark-red or purple body attached to the convexity of the U-shaped stomach, and sending a narrow lobe along the right-hand limb. The organs of respiration in the dogfish are the g7/s, situated in the five g7/-pouches. Each gill-pouch is an antero-posteriorly compressed cavity opening internally into the pharynx and externally by the gill-slit. The walls of the pouches are supported by the branchial and hyoid arches with their rays, the first pouch being situated between the hyoid and first branchial arches, the last between the fourth and fifth branchial arches. On the anterior and posterior walls of the pouches are the g7//s, each hemibranch consisting of a series of close-set parallel folds or plaits of highly vascular mucous membrane. Separating adjoining gill-pouches and supporting the gills are a series of broad interbranchial septa, each containing the corresponding branchial arch with its connected branchial rays. The most anterior hemibranch is borne on the posterior surface of the hyoid arch. The last gill-pouch differs from the rest in having gill-plaits on its “SUDdIOJap SBA ‘pp @ BIO’ [BIYUDA fon «2 F9]D1IWUAA {2 tIalaIn ‘en uaa snus “2 "sy taayea qeatds 72 ge tsipeuruas LINAISAA Sres “92 Pioo eurds ‘po s/s fapoerids ‘Ys t1aai jo aqoy WRU ez 4 Spurs Jeyar 2F pac twmaysos oe v ag ‘Spog Arena zY *uoprydaouasoad ‘sae ‘Apog jeaurd v7g vxudavyd tye tysse peroyad ‘vy yg tsearourd tvs taqoy “aqo] ArOqDE}[0 GT fje “sayoue jeanau ‘vy ‘2 PEyESUTqo vypnpau ‘7qo pou ‘IAAI JO aqoy yay ‘47 D, tael qamol ‘f 7 * Aaupiy “Py (qi tsaimady perp ueiq peusayur 6.2 29 7 Ge eg cz tsayoue pewuay tv “WSYMYS Jo Jvor ur apjauezuoy fwe/ ssi Spipida tyrgy pay ‘orp ivis0w [usiop ‘ey p Sunjjaqaiaa ‘g.c9 Sunes 867 Suaquas fs teoeo]o 79 fuiaa Jepnes ‘2 ‘po tyoewuoys Jo uons0d sepieo 8 (p? isnsouarye snuos ‘zen sa tpedy-seq “ly “9 ‘a8ulytes Jerpouviq-iseq “4g -g ‘apne tay “ASE Wiqajiaa ay) Jo spua payiyer ayy Spanop si adepies ayy, yBua] ayoym ways ur sanacs (2H +7) Peano pur ‘(av poy) [erpresiiad ‘(.2779 “pov) yeulwmopqe ayj asodxa oj sr os auejd ueipou ayy ur Aeme pnd st [peMm-Apog ay} Jo apis yal tavfiaddn (f-w tsnuis jeyuasoan ‘sy «#2 tsnsay ‘s7 fanSuo1 ‘Sug ‘snso foes utads ts gs suaalds tgs ayouyuaa 2D vp sPIT? O19 2 Magn Ul Te OP hyo yt ee lear aDu PUL “OPIS Ya] ey wWoay (eMoTAv. wMNTTTAIg) YsyZop jo uondessi(] — ‘9zz ‘DI 376 SECT. XII PHYLUM CHORDATA 377 anterior wall only. On the anterior wall of the spiracle is a rudimentary gill, the psewdo-branch or spiracular gill, in the form of a few slight ridges. The deart is situated in the pericardial cavity, on the ventral aspect of the body, in front of the pectoral arch and between the two series of branchial pouches. The heart consists of four chambers, — sénus venosus (s.v), auricle (au), ventri- cle (v), and conus arteriosus (c. art), through which the blood passes in the order given. The sznus venosus.is a thin- walled, transverse, tubular chamber, into the ends of which the great veins open. It opens into the auricle by an aper- ture, the s¢mu-auricular aperture. The auricle is a large, triangular, thin-walled chamber, situated in front of the sinus venosus and dorsal to the ventricle. Its apex is directed forwards, and its lateral angles project at the sides of the ventricle ; it communicates with the ventricle by a slit-like aperture guarded by a two-lipped valve. The ventricle is a thick-walled, globular chamber, forming the most conspicu- ous part of the heart when looked at from the ventral sur- face. From it the conus artertosus runs forwards as a medium stout tube to the anterior end of the pericardial cavity, where it gives off the ventral aorta. It contains two transverse rows of valves, anterior and posterior, the former consisting of three, the latter of three or four. The ventral aorta (Fig. 227, v. a0) gives origin to a series of paired affer- cent branchial arteries (a. br. a), one for each branchial pouch. From the gills the blood passes by means of the efferent branchial arteries (e.b6r.a). These efferent vessels form a series of loops, one running around the margin of each of the first four internal branchial clefts: a single vessel runs along the interior border of the fifth branchial cleft and opens into the fourth loop. The four main efferent bran- "eVIO€ [ELJUDA ‘ov, 2 apojuer ‘2 ‘snsousa snus ‘2 ‘s !yseuoys “zs {UDA oneunads ‘2 gs iusajds ‘7¢s tAroyie Oneuads v £ tulaa welaepoqns ‘2 72s | Ataye uelAvpogns ‘vy ‘79s sulaA [evar ‘a 4 ‘ules jeiod jeuar ‘2g # tAroyv [eUel ‘V4 SuloA eaes-aid 42 29 4 iseaisued ‘ug SAlaye dWajuasaul ‘vy “sue tuloa pedal (2 gop viaay ‘47 {Aoupry ‘y fulea zepnBnf{ ‘a -f touysaqur “yee Susan owl “72 tArayre OvIE ‘vy 72 sUleA oneday ‘2 -y ‘ulea yeylod ayeday ‘2 g'y ‘Asaqae oneday ‘vy y ypeuod ‘waF \Araqie jerypouviqg Ualaya ‘PY 49 (9 :¥110e [esIOp ‘op "p .UTeA JeUIpAeo V2 p47 :Ataye el] ‘vy “77 UIA [epnes “2 “ps ‘AroyIe [epnes ‘wv ‘pr isnsouejie snuos yey 9 tAlaye pnorws ‘wy ‘2 ‘syed jeryouesq ‘s—7 "79 49 ‘aptine ‘nv :Atoq1e [eTyOURIG quaiaye ‘v 2g “P ‘antq poopy paresge-uoU Zurureyuod asoy3 ‘pas poojg payezge Sujusejuoo sjassaq YY _& JO woaysAs 1ejnosea ay} jo WeaseIq: §=4ze “DIY a'708 as SECT. XII PHYLUM CHORDATA 379 chial vessels run inwards and backwards from the loops under cover of the mucous membrane of the roof of the mouth to unite in a large median trunk — the dorsal aorta (¢@.a0). From the first efferent vessel, that from the first or hyoidean gill, arises the carotid artery, which runs for- wards and bifurcates to form the ¢zéernal and external carotid arteries (¢.a@), supplying the head with arterial blood. The dorsal aorta rans backwards throughout the length of the body-cavity, giving off numerous branches, and is continued as the caudal artery (cd.a), which runs in the canal enclosed by the inferior arches of the caudal vertebre. The veins are very thin-walled, and the larger trunks are remarkable for their dilated character, from which they have obtained the name of szzuses, though they are true vessels and not sinuses in the sense in which the word is used in dealing with the Invertebrates. The venous blood is brought back from the head by a pair of jugular or anterior cardinal sinuses (7. v), and from the trunk by a pair of Josterior cardinal sinuses (crd.v). At the level of the sinus venosus the anterior and posterior car- dinals of each side unite to form a short, nearly transverse sinus, the precaval sinus or ductus Cuviert ( pr.cv.v) which is continued into the lateral extremity of the sinus venosus. There are two fortal systems of veins, the renal portal and the hepatic portal (h.p.v), by which the kidneys and liver, respectively, are supplied with venous blood. The caw- dal vein (cd. v), which brings back the blood from the tail, running, along with the caudal artery, through the inferior arches of the vertebrze, divides on entering the abdominal cavity into right and left rvexa/ portal veins (7. p.v), which end in a number of afferent renal veins supplying the kidneys. The hepatic portal vein (4. p.v) is formed by the conflu- 380 MANUAL OF ZOOLOGY SECT. ence of veins derived from the intestine, stomach, pancreas, and spleen, and runs forwards to enter the liver a little to the right of the middle line. The blood from the liver enters the sinus venosus by two hepatic sinuses (h. v) placed close together. The fore-brain consists of a rounded, smooth prosen- cephalon (Fig. 219, V. H), divided into two lateral parts by a very shallow median longitudinal groove. From its antero- lateral region each half gives off a thick cord, which dilates into a large mass of nerve matter, the o/factory lobe (L. of), closely applied to the posterior surface of the correspond- ing olfactory capsule. The diencephalon (2) is com- paratively small; its roof is very thin, while the floor is composed of two thickish masses, the optic thalami. At- tached to the roof is a slender tube, the epiphysis cerebri or pineal body (Gp), which runs forwards and terminates in a slightly dilated extremity fixed to the membranous part of the roof of the skull. Projecting downwards from its floor are two rounded bodies, the /oé7 infertores, which are dilated portions of the znfundibulum ; and attached to this, behind, is a thin-walled sac ,— the petwitary body or hypophysis cerebri having a pair of thin-walled vascular lateral diverticula, — the sacet vasculosi, and having on its ventral surface a median tubular body attached at its posterior end to the floor of the skull. In front of the infundibulum, and also on the lower surface of the diencephalon, is the opie chiasma, formed by the decussation of the fibres of the two optic nerves. The mid-brain (A¢/7) consists of a pair of oval optic lobes dorsally, and ventrally of a band of longitudinal nerve-fibres corresponding to the crura cerebri of the higher vertebrate brain. The cerebellum (/777) is elongated in the antero- posterior direction, its anterior portion overlapping the optic lobes, and its posterior the medulla oblongata, Its XII PHYLUM CHORDATA 381 surface is marked with a few fine grooves. The medulla oblongata (V4), broad in front, narrows posteriorly to pass into the spinal cord. The fourth ventricle (F.rho) is a shallow space on the dorsal aspect of the medulla oblongata covered only by a thin vascular membrane, the choroid plexus ; it is wide in front and gradually narrows posteriorly. At the sides of the anterior part of the fourth ventricle are a pair of folded ear-shaped lobes, the corpora restiformia. The fourth ventricle is continuous behind with the cen- tral canal of the spinal cord. In front it is continuous with a narrow passage, the z7ev (z#er), which opens anteriorly into a wider space, the dacale or third ventricle (dia) occupying the interior of the diencephalon. From this opens in front a median prosocele, which gives off a pair of paraceeles (fara) extending into two lateral portions of the prosen- cephalon. A series of nerves arise in pairs from the brain and spinal cord. From the spinal cord the nerves arise segmentally, one pair corresponding to each myomere, and pass through apertures in the neural arches of the vertebrae. Each arises by two roots, a dorsal and a ventral. The dorsal root is dilated into a ganglion, and contains only sensory fibres ; the ventral root is non-ganglionated, and is motor. A longitudinal ganglionated sympathetic nerve, extending along the dorsal region of the ccelome, is connected with the spinal nerves, and sends branches to the viscera, blood- vessels, etc. From the brain arise ten pairs of nerves, some of which are sensory, others motor, others mixed. Three are the nerves of the principal sense organs: the first, or o/faczory, supplying the organ of smell (Fig. 228, o/f s) ; the second, or optic, the retina of the eye, and the eighth, or auditory, the organ of hearing. The third, or ocudomotor, the fourth, 382 MANUAL OF ZOOLOGY SECT. or frochlear (path), and the sixth, or adducent, go to the muscles of the eye; the fifth, or “vgeminal (oph. V, mx. V, mnd. VW), to the snout and jaws ; the seventh, or facial (oph. Fic. 228.—Scyllium catulus. Dissection of the brain and spinal nerves from the dorsal surface ‘The right eye has been removed. The cut surfaces of the cartilaginous skull and spinal column are dotted. The ophthalmicus profundus and the buccal branch of the facial are not represented. cd. r-c¢. 5, branchial clefts; ef, epiphysis; ext. rect, external rectus muscle of the eye-ball; g/. ph, glossopharyngeal; ov. can, horizontal semicircular canal; Ay. mud. VII, hyo- mandibular portion of the facial; 7”f 0d/, inferior oblique muscle; zwt rect, internal rectus muscle; at. vag, lateral branch of vagus; mx. J", maxillary division of the trigeminal; o/f cfs, olfactory capsule; o/f s, olfactory sac; ae V. VIZ, superficial ophthalmic branches of trigeminal and facial; path, fourth nerve; f/, J°//, palatine branch of facial; sf. co, spinal cord; ‘sfzr, spiracle; s. rect, superior rectus muscle; s. 02, superior oblique; vag, vagus; vest, vestibule. (From Marshall and Hurst.) VIL, pl. VI, hy. mnd. VIL), to the palate, lower jaw, and hyoid arch; the ninth, or glossopharyngeal (g/. ph), to the XII PHYLUM CHORDATA 383 hyoid and first branchial arches; and the tenth, or vagus (vag), to the remaining branchial arches, as well as to the heart, stomach, and lateral line. Besides the lateral line, which is probably the seat of a delicate tactile sense, and the tongue, which is presumably an organ of taste, there are the three pairs of characteristic sensory organs, the structure and position of which are very characteristic of vertebrates. These are the olfactory organs, the eyes, and the auditory organs. The o/factory organs are a pair of cup-like sacs on the under side of the snout, en- closed in the olfactory capsules and opening externally by the nostrils. They are lined with mucous membrane, which is raised up into ridges so as to increase the surface. The general structure of the eyes has already been described (p. 356). The ear consists of the membranous labyrinth (p- 357), which is enclosed in the cartilage of the auditory region of the skull. It consists of a sac called the vestibule (Fig. 228, vest), with which are connected three tubes, called from their form the sem/circular canals. Two of these, the anterior and posterior canals, are vertical in position, and are united with one another at their adjacent ends; at the other end each is dilated to form a bulb-like swelling, the ampulla. The third, or horizontal canal (Aor. can), opens at each end into the vestibule, and has an ampulla at its anterior end. The vestibule gives off a tube, the endolymphatic duct, which opens at the auditory aperture already referred to on the top of the head. Endolymph containing otoliths (p. 358) fills the interior of the labyrinth, and it is immediately surrounded externally by a space con- taining a similar watery fluid, the perz/ymph. The fibres of the auditory nerve are distributed to various parts of the internal epithelium of the vestibule and semicircular canals. There seems little doubt that the membranous labyrinth 384 MANUAL OF ZOOLOGY SECT. has not only an auditory, but also an equilibrating function, z.e., that the fish is enabled by its means to maintain its equilibrium in the water. ‘The kidneys (Fig. 227, %) are long flat lobulated bodies lying one on each side of the backbone in the posterior part of the abdominal cavity. From the ventral surface of each spring numerous delicate ducts which unite inte a single tube, the wre/er, opening directly into the cloaca in the female, in the male into a small paired cham- ber, the wrogenifal sinus (ug. s), which opens into the cloaca (¢/). In the male dogfish the testes are a pair of large soft organs situated in the body-cavity, and united with one another posteriorly. From the anterior end of each arise numerous delicate efferent ducts, which enter a long convo- luted spermiduct or vas deferens (v. def) leading posteriorly to the urogenital sinus. In the female there is a single ovary suspended to the dorsal body-wall by a fold of peri- toneum. In the adult it is studded all over with rounded projections, the ova. There are two oviducts, a right and a left, which extend along the whole length of the dorsal wall of the ceelom below the kidneys. Anteriorly they unite with one another below the gullet, and just in front of the line and at the point of junction is a single aperture of con- siderable size, by which both tubes communicate with the ccelom ; posteriorly they open into the cloaca. About the anterior third of each oviduct is narrow; its posterior two- thirds is wide and distensible, and at the junction of the parts is a yellowish glandular mass, the she/-gland. Internal impregnation takes place, the spermatic fluid of the male being passed, by means of the claspers, into the ovi- ducts of the female. The ova, when ripe, break loose from the surface of the ovary into the ccelom, and thence pass, XII PHYLUM CHORDATA 385 through the common aperture, into one or other of the ovi- ducts, where fertilisation (p. 393) occurs. As it passes into the dilated portion of the oviduct, the oosperm (p. 60) of Scyllium becomes surrounded by a horn-like egg-shell (Fig. 229), secreted by the shell-gland, and having the form of a pillow-case produced at each of its four corners into a long tendril-like process. The eggs are laid among seaweed, to which they become attached by their tendrils. In some other dogfshes (Acanthias, Afus- telus) a mere vestige of the egg-shell is formed, and the eggs undergo the whole of their development in the oviducts, the young being eventu- ally born alive with the form and proportions of the adult. The great size of the egg is due to the immense quantity of yolk { which it contains; its protoplasm is almost entirely aggregated at one pole in the form of a small disc. When segmentation of the oosperm takes place, it affects the protoplasm alone, the inactive yolk taking no part in the process. The disc of protoplasm divides to form a little Fic. 229. — Dogfish, egg-case. heap of cells, the d/astoderm, situ- peer ated at one pole of the undivided sphere of yolk. The blastoderm subsequently spreads out as a sheet of cells over the yolk which it ultimately completely encloses. While this extension of the blastoderm is taking place, its middle part becomes raised up into a ridge-like thick- 2c 386 MANUAL OF ZOOLOGY SECT. ening, which is moulded, step by step, into the form of the embryo fish. The head, trunk, and tail acquire dis- tinctness, and become more and more clearly separated off from the bulk of the egg, the latter taking the form of a yolk-sac attached by a narrow stalk to the ventral surface of the embryo (Fig. 230). In this condition the various parts of the adult fish can be recognised, but the proportions are different, and the Fic. 230.— A, embryo of Scyllium with yolk-sac (x 13); B, under-side of head enlarged. 4. 7, branchial filaments protruding through gill-clefts; 47. /', branchial filaments projecting through spiracle; cd /, caudal fin; d@ /, dorsal fins; e,eye; ex. dx”, ap external branchial apertures, »v¢/, mouth; va, nostrils; pet. /, pectoral fin: pz. _f, pelvic fin; st, yolk-stalk; uv. f/, ventral fin; y&. s, yolk-sac, (After Balfour, slightly altered ) head presents several peculiarities. The gill-filaments (47. /) are so long as to project through the external branchial apertures and the spiracle (47. 7) in the form of long threads abundantly supplied with blood-vessels, and apparently serving for the absorption of nutriment — the albumen in the egg-shell in the case of Scyllum, secretions of the ovi- duct in the viviparous forms. Besides this mode of nutrition the yolk-sac communicates with the intestine by a narrow duct, through which absorption of its contents is constantly XII PHYLUM CHORDATA 387 going on. By the time the young fish is ready to be born or hatched, the greater part of the yolk-sac has been drawn into the ccelom, a mere vestige of it still dangling from the ventral surface of the body. In all the most important features of their organisation there is a considerable degree of uniformity ene the Elasmobranchii. In general shape the sharks (Fig. 231), for the most part, are somewhat fusiform and slightly compressed laterally. In the rays (Fig. 232), on the other hand, there is great dorso- Fic. 231. — Shark (Lamna cornubica). (From Dean’s Fishes.) ventral compression. The head is in many cases produced forwards into a long rostrum, which is of immense length and bordered with triangular teeth in the saw-fish shark (Pristiophorus) and saw-fish ray (Prist#s). In the hammer- head shark the anterior part of the head is elongated trans- versely. There are well-developed median and paired fins. The caudal fin is well developed, and, as a rule, strongly hetero- cercal in the sharks and shark-like rays, feebly developed in most of the latter group. The dorsal and ventral fins are large in the sharks, the former completely divided into two; in the rays the dorsal fin is usually small, and the ven- 388 MANUAL OF ZOOLOGY SECT, tral absent. The paired fins are very differently developed in the two groups. In the sharks both pairs are well devel- oped, the pectoral being the larger. In the rays or skates the pectoral fins are extremely large, very much larger than the pelvic, fringing the greater part of the length of the flattened body, and becoming prolonged forwards on either Fic. 232. — European sting-ray (Urolophus cruciatus). (After Giinther.) side and even in front of the head, so that the animal presents the appearance of a broad fleshy leaf. In all recent Elasmobranchs the male has, connected with the pelvic fins, a pair of grooved appendages, the claspers or prerygodia, which subserve copulation. The mouth is situated on the ventral surface of the head, usually a considerable distance from the anterior extremity. XII PHYLUM CHORDATA 389 In front of each angle of the mouth on the ventral surface is the opening of one of the olfactory sacs, each of which is connected by a groove, the naso-buccal groove, with the mouth-cavity. Behind the mouth, on the dorsal surface in the rays, and at the side in the sharks, is the spiracle. Along the sides of the neck in the sharks, and on the ven- tral surface in the rays, is on either side a row of slit-like apertures, the branchial slits or branchial clefts. These are usually five in number on each side; but in Aexanchus and Chlamydoselachus there are six, and in Heptanchus seven. A large cloacal opening is situated just in front of the root of the tail, and a pair of small openings placed in front of it, the addominal pores, lead into the abdominal cavity. When the integument develops any hard parts, as is the case in the majority of the Elasmobranchs, they take the form, not of regular scales, as in most other fishes, but of numerous hard bodies, which vary greatly in shape, are usually extremely minute, but are in some cases developed, in certain parts of the surface, into prominent tubercles or spines. When these hard bodies are, as is commonly the case, small and set closely together in the skin, they give the surface very much the character of a fine file; and the skin so beset, known as “shagreen,” is used for various polishing purposes in the arts. This is the péacotd form of exoskeleton, to which reference has been already made. Each of the hard bodies has the same structure as a tooth, being composed of dentine, capped with enamel, and sup- ported on a bony base, representing the cement or crusta petrosa of the tooth, The dermal fin-rays are horny. The skeleton is composed of cartilage, with, in many cases, deposition of bony matter in special places, notably in the jaws and the vertebral column. The entire spinal column 390 MANUAL OF ZOOLOGY SECT. may be nearly completely cartilaginous (Hexanchus and Heptanchus), but usually the centra are strengthened by K "Cl 5, ay nas \\ Wy Fic. 233. —Skeleton of sting-ray (Urolophus testaceus), ventral view. @.7z. A, anterior vertebral plate; das. 47, basi-branchial plate; 4”. 7-r..5, branchial arches The branchial rays are represented as having been removed, the round dots indicate their articulations with the arches c¢/, skeleton of clasper; 4. mz, hyomandibular; Ay, hyoid arch; /aé, labial cartilage; /zg, ligament connecting the hyomandibular with the palato-quadrate and Meckel’s cartilage; mck, Meckel’s cartilage; os. pt, mesopterygium; wf pz, metapterygium of pectoral fin; wd. pt', metapterygium of pelvic fin; as, nasal cartilage; fal, palato- quadrate; fect, pectoral arch; A/, pelvicarch; pro. p?, propterygium; sf, spiracu- lar cartilage. XI PHYLUM CHORDATA 391 radiating or concentric lamelle of calcified cartilage or bone, or they may be completely calcified. They are deeply amphiccelous, the remains of the notochord per- sisting in the large spaces between the concave surfaces of contiguous centra. In the rays the anterior part of the spinal column becomes converted into a continuous solid cartilaginous and bony mass— the anterior vertebral plate (Fig. 233, @. v. £). Two main regions only are distinguish- Fic. 234.— Lateral view of the skull of Heptanchus. ck, Meckel's cartilage; pal. gu, palato-quadrate; Zt, ord, post-orbital process of the cranium, with which the palato-quadrate articulates. (After Gegenbaur.) able in the spinal column —the pre-caudal region and the caudal, the latter being distinguished by the presence of in- ferior or hamal arches. In the pre-caudal region short ribs may be developed, but these are sometimes rudimentary or entirely absent. The skull is an undivided mass of cartilage, hardened, in many cases, by deposition of osseous matter, but not con- taining any separate bony elements. In all, the jaws are 392 MANUAL OF ZOOLOGY SECT. connected with the skull through the intermediation of a hyomandibular cartilage, or proximal element of the hyoid arch; in the great majority this is the sole articulation of the jaws with the skull posteriorly, and the skull is on that account said to be Ayosf#ic ; but in Hexanchus and Hep- tanchus (Fig. 234) the upper jaw has a direct articulation with the skull behind the orbit, and the arrangement is termed ayphistylic. There are always five pairs of bran- chial arches, except in Hexanchus and Chlamydoselachus, which have six, and Heptanchus, in which there are seven. The basal cartilages of the pectoral fin are typically three, as in the dogfish, but there are sometimes four, and the number may be reduced to two. There are usually two such cartilages in the pelvic fin, and one alone may be present. Electric organs — organs in which electricity is formed and stored up, to be discharged at the will of the fish — occur in several Elasmobranchs. They are best developed in the electric rays (Zorpfedo and Hypnos) in which they form a pair of large masses running through the entire thick- ness of the body between the head and the margin of the pectoral fin. By means of the electric shocks which they are able to administer at will to animals in their immediate neighbourhood, these torpedo rays are able to ward off the attacks of enemies and to kill or paralyse their prey. Teeth are developed in all on the palato-quadrate or upper jaw and Meckel’s cartilage or the lower jaw. They are arranged in several parallel rows, and are developed from a groove at the back of the jaw, successive rows coming to the front, and, as they become worn out, falling off and becoming replaced by others. In the sharks the teeth are usually large and may be long, narrow, and pointed, 1 Torpedo occidentalis occurs on the southern coast of New England. XII PHYLUM CHORDATA 393 or triangular with serrated edges, or made up of several sharp cusps; in the rays, however, the teeth are more or less obtuse, sometimes, as in the eagle rays, forming a “con- tinuous pavement of smooth plates covered with enamel, adapted to crushing food consisting of such objects as shell-fish and the like. The various divisions of the evzertc canal are similar in all members of the class to what has already been described in the case of the dogfish. A spiral valve is always present in the large intestine, though its arrangement varies con- siderably in the different families. The rectum always ter- minates in a cloaca into which the urinary and genital ducts also lead. The respiratory organs have in all the same general arrangement as in the dogfish. The inter-branchial septa are of considerable breadth and the gill-filaments are attached to them along their entire length. The heart also has in all essential respects the same structure throughout the group, the most characteristic feature being the presence of a conus arteriosus which is rhythmically contractile and contains several rows of valves. Impregnation is internal in all the Elasmobranchii with the exception of the Greenland shark (Lemargus), the claspers acting as intromittent organs by whose agency the semen is transmitted into the interior of the oviducts. In all Elasmobranchs the ova are very large, consisting of a large mass of yolk with, on one side, a disc of protoplasm, the germinal disc. The ripe ovum ruptures the delicate wall of the follicle in which it is enclosed and escapes into the abdominal cavity to enter one of the oviducts, as already stated in the case of the dogfish. Impregnation takes place in the oviduct, and in the oviparous forms the impregnated ovum becomes enclosed in a chitinous shell secreted by the 304 MANUAL OF ZOOLOGY SECT, shell-gland. Enclosed in the shell, the form of which varies in different groups, the egg passes to the exterior and under- goes development until the young fish is fully formed, when it escapes by rupturing the egg-shell. In the viviparous forms, on the other hand, the ovum undergoes its develop- ment in the uterus; and the young fish, when it escapes to the exterior, has assumed all the features of the adult. The habits of the active, fierce, and voracious sharks, which live in the surface waters of the sea waging war on all and sundry, are in strong contrast with those of the more sluggish rays, which live habitually on the bottom, usually in shallow water, and feed chiefly on crustaceans and molluscs, with the addition of such small fishes as they can capture. As a group, the Elasmobranchs, more particularly the sharks, are distinguished by their muscular strength, the activity of their movements, and also by the acuteness of their senses of sight and smell. The only deep-water Elasmobranch known is a species of ray, which extends to a depth of over 600 fathoms. Sub-class III. Teleostomi ! The great majority of existing fishes belong to the sub- class Teleostomi. As a matter of convenience we may look upon the Teleostomi as consisting of two main divisions, — the Teleostei, in which are included all the commonest and most familiar fishes, such as the perch, pike, mackerel, cod, sole, herring, eel, salmon, etc., and the Ganoidei or Ganoids, such as the sturgeon, body pike (Lefidoseus), and bow-fin (dmia) of North America, and the Folpterus of the Nile. They are distinguished from Elasmobranchs by the posses- 1Sub-class II, the small group Holocephali, or Chimzeras and their allies, is one of the groups-omitted from this work. See Preface. XII PHYLUM CHORDATA — 395 sion of an operculum or gill-cover, by the absence of a cloaca, by having the primary skull and shoulder-girdle complicated by the addition of membrane-bones, and by possessing bony instead of horn-like fin-rays. A typical Teleostomian, such as a trout (Fig. 235)? or a herring, has a long compressed body nearly half of which is formed by the tail, pointed anterior and posterior ends, a large vertical tail-fin, a head of moderate size, and a terminal mouth. Such a form is eminently fitted for progression through the water. But from this characteristic fish form Fic. 235.—Salmo fario. a. 7, adipose lobe of pelvic fin; az, anus; c. /, caudal fin; @./. 7, first dorsal; df 2, second dorsal or adipose fin; @. /, lateral line; a operculum; gc¢. 7, pectoral fin; Av. /, pelvic fin; v. f, ventral fin, (After ardine.) there are many striking deviations. The body may be greatly elongated and almost cylindrical, as in the eels; or of great length and strongly flattened from side to side, as in the ribbon-fishes ; or the head may be of immense pro- portional size and strongly depressed, as in certain shore- fishes, such as the fishing-frog ; or, as in the beautiful reef- fishes, the whole body may be as high as it is long. The mouth sometimes has a ventral position, as in the Elasmo- branchs, with the snout prolonged over it; this is the case, 1 Our common brook trout in the northeastern states is Sadmo fontinalis, 396 MANUAL OF ZOOLOGY SECT. for example, in the sturgeons (Fig. 240). On the other hand, in the ground-feeding “ star-gazers ’’ and some others, the lower jaw is underhung like that of a bull-dog, and the mouth becomes dorsal in position. A deak may be pro- duced by the elongation of the upper jaw, as in the sword- fish, or of the lower jaw, as in the half-beak or czar-fish, or of both jaws as in the bony pike. An operculum or gill-cover (of), a flap which covers the gills of each side and bounds in front the single, usually crescentic gill-opening, is always present, and is supported by four membrane bones. Ventrally the operculum is pro- duced into a thin membranous extension, the dranchio- stegal membrane, which is in nearly all cases supported by a series of bony rays. Spiracles are absent except in certain of the Ganoids. There are dorsal, ventral, and caudal median fins. The dorsal is usually divided into two; in a few it is partly or wholly supported by a series of finlets. The caudal is in the majority of a type to which the term homocercal is applied. The homocercal caudal fin is divided into two equal or sub-equal lobes, upper and lower, so that it appears symmetrical externally, though the posterior portion of the spinal column which supports it is strongly bent upwards and terminates in the upper lobe. In some of the Ganoids, however, this upward curvation of the caudal part of the spinal column does not occur, and the tail is symmetrical internally as well as externally ; in these the tail is said to be diphycercal. In many Ganoids the tail is Aeterocercal, as in nearly all the Elasmobranchs (p. 367). In some Teleos- tomi dorsal, caudal, and ventral fins are united into a con- tinuous fold. The dermal fin-rays of the caudal fin and a portion or all of those of the rest of the fins are slender flexible rods divided into a series of short segments and XU PHYLUM CHORDATA 397 usually branching at the free ends. In many, however, the anterior portions of the dorsal, ventral, and pelvic fins are supported not by flexible jointed rays, but by stiff unjointed sharp spines. The paired fins, pectoral and pelvic, are usually thin and flexible, supported mainly, or exclusively, by jointed rays. The pectorals always retain their normal position, just behind the gill-cleft, but the pelvics always become more or less shifted forwards from their typical position beside the vent; when they are not placed as far forwards as the Fic. 236. —Salmo fario. Caudal end of vetebral column. CN,centrum; D.F.R, dermal fin-rays; H. SP, hemal spine; H. ZYG, hemal zy gapophysis; N. SP. neural spine; N. ZYG, neural zygapophysis; UST, urostyle, middle of the abdomen, they are said to be abdominal in position ; when further forwards, nearly beneath the pectorals, they are said to be thoracic ; when still further, actually in front of the pectorals and beneath the throat, they are said to be jugudar in position. A very remarkable deviation from the typical form occurs in the flat-fishes (Pleuronectide, including the soles, plaice, flounders, turbots, etc.). The body (Fig. 237) is very deep and strongly compressed ; the fish habitually rests on the bottom, in some species on the right, in others on the 398 MANUAL OF ZOOLOGY SECT. left side. The under side is usually pure white, the upper dark. The eyes are both on the upper side, and the skull is distorted so as to adapt the orbits to this change of position. / Lit \ Ll haeg fe ply Fic. 237. — Pleuronectes cynoglossus (craig-fluke), from the right side. a. f, dorsal fin; 7 ¢, left eye; Act /, pectoral fin; Az. /, pelvic fen; ~. ¢, right eye; vf, ventral fin, (After Cuvier.) In many Teleostei, such as the eels, the skin is devoid of hard parts; but in most cases there is an exoskeleton developed in the derm. In the majority this takes the form of scales, rounded plates of bone embedded in pouches of the derm, and overlapping one another from behind for- wards. When the free border of the scales presents an even curve, they are called cye/u/ scales; when the free edge is produced into small spines, they are distinguished as cfenotd scales (Fig. 238). In exceptional cases the scales may be so large and strong as to form a rigid armour. 1 Our common flounders are Paralichthys dentafus trom the southern coast of New England, and Pseudopleuronectes americanus from the coast north of Cape Cod. XII PHYLUM CHORDATA 309 Sometimes there is an armour formed of stout bony plates, or scuées, while in other cases, as in the “ file-fishes,” the exoskeleton takes the form of minute spines like the Fic. 238. — A, ctenoid scale; B, ganoid scale. (After Giinther.) shagreen of sharks, or as in many globe-fishes of long bony spines ; lastly, in Polypterus (Fig. 239) and Lepidosteus are found rhomboid or ganoid scales in the form of rhomboidal plates of bone covered externally by a layer of enamel or ganoin and joined together by pegs and sockets. : im j orm pols’ RU an uf Fic. 239. — Polypterus birchir. A, entire animal; B, ventral view of throat. az, anus; 4x. 7, branchiostegal membrane; c. f, caudal fin; @. f, dorsal finlets; zag. f/, jugular plates; na, nostril: pct. f, pectoral fin; gv. /, pelvic fin; v._/, ven- tral fin. (After Cuvier.) In the sturgeon the spinal column consists of a persistent notochord with cartilaginous arches ; in the rest bony verte- bree are present, the centres of which are nearly always bi-concave. 400 MANUAL OF ZOOLOGY SECT. In the sturgeons (Fig. 240) and their allies the cranium is an undivided mass of cartilage with a few isolated carti- lage bones, and covered over dorsally by membrane bones. In most of the other members of the group it is mainly or entirely composed of numerous cartilage and membrane bones (Fig. 240). Both upper and lower jaws are bounded by membrane bones (/. wx, wx, dent). The jaws are con- nected with the skull by the intermediation of a hyomandib- & t Fic. 240.— Skull of sturgeon, with the membrane bones removed. a, pharyngo- branchial; .4/, antorbital process: AA’, articular; 4, epibranchial: c, cerato- branchial; C, notochord: Cv, basi-branchials; @, hypobranchial; De, dentary; GK, auditory capsule; 4/1/, hyomandibular; Ay, hyoid cornu; /A, inter-hyal; Md, mandible; Na, nasal capsule; Gé, neural arches; PF, post-orbital pro- cess; PQ, palato-quadrate; Ps. Ps'. Ps'', parasphenoid; Psp, neural spines; Qu, quadrate: 2 rostrum: RZ, ribs; Sf. NV, foramina for spinal nerves; Sy, symplectic, J/7S vertebral column; 2, vagus foramen; /-I”, branchial arches. (From Wiedersheim’s Comparative -uatomy.) ular (Ayem) which, however, probably does not correspond with the cartilage so named in the dogfish and other Elas- mobranchs. The pectoral arch is complicated by the addi- tion of membrane bones, of which the most constant are a pair of large clavicles. The pelvic arch is vestigial or absent. Two genera of Teleostomi possess electric organs, — the electric catfish (J/alaplerurvus) and the electric eel (Gim- notus) ; the former occurs in fresh waters of tropical Africa, 401 PHYLUM CHORDATA XII and the latter in Brazil and the Guyanas. Some Teleostomi ((97v499748 4 SWIdYsiaplaad WOT) ‘yeAy-seq ‘aFunzZ ‘onooidurks ‘7gads :xenorado-qns ‘gogns ‘onouayds Yoyds ‘yeydio90-vidns ‘2208 ‘ayexpenb ‘pond ‘onorayd ‘4agg sproBAsaid ‘7g ‘aejnoiado-aad ‘goveg ‘eyprxew-aid ‘rm ‘yejaired “evg ‘ounered yog sielnosiado ‘go ‘syeiqzo-qns ‘o tyeseu ‘so ‘eyprxew ‘re ‘prosAroydeyour ‘z¢zz sprosAsaidosaw ‘g¢ame ‘yesnl ‘af ‘renoxado-sayut ‘gozuz !prody pue afqipuew yim ‘apis ya] aqi woy ‘gq f(amnsy jo y9]) apis wsr ay} UO padoulad SsUOg SUeIqUIDUT 94) YA ‘yIwouEq WOY “WY "[[NYs eyT, ‘eleodw9, eUeY— gre ‘O1y On the ventral surface of the skull is a large T-shaped parasphenoid (PA. SPA), its stem underlying the base of the cranium, while its two arms ex- tend outwards beneath the auditory capsules. paired vomers (VO). 4i4 MANUAL OF ZOOLOGY SECT, The palato-quadrate cartilage is unossified ; but in relation to its anterior portion is a palatine (PAL) membrane bone and to its posterior portion a prerygoid (PTG). The former is a slender rod-like bone directed transversely on the lower surface of the skull. The latter is a larger three-rayed bone, having an anterior, an inner, and a posterior arm. The posterior portion of the palato-quadrate cartilage, the guad- rate or suspensorium (sus), connects the lower jaw with the posterior region of the skull. Internally it is covered over by the inner and posterior arm of the pterygoid ; externally a hammer-shaped membrane bone, the sguamosal (SQ) is applied to it. The upper jaw is formed by three mem- brane bones, the small premaxilla (PACX ) in front, then the long narrow maxil/a (ZX ), and finally the short guad- ratojugal (QU. JU) which is connected posteriorly with the quadrate. The mandible contains on each side a per- sistent Meckel’s cartilage as a sort of core, ossified at its anterior end, outside which are two membrane bones. The hyoid is a squarish plate of cartilage (4. Ay) with two pairs of processes (a.¢. hy, p. c.hy), the posterior of which is ossified. The scapula is ossified and is connected by its dorsal edge with a swpra-scapula (Fig. 247, 8. SCP) formed partly of bone, partly of calcified cartilage, and developed from the dorsal region of the embryonic shoulder-girdle. The coracoid (Fig. 249, Co) is also ossified, while the procora- coid is represented by a bar of cartilage, having a membrane bone, the clavicle (C7), closely applied to it. The supra- scapula overlaps the anterior vertebre ; the coracoid and procoracoid are connected ventrally by a cartilage, the epi- coracoid (Co'), which is in close contact with its fellow of the opposite side in the middle ventral line, so that the entire shoulder-girdle, like that of the dogfish, forms a single inverted arch. xu PHYLUM CHORDATA 41s Passing forwards from the anterior ends of the united epicoracoids is a rod of bone, the episternum (Ep), tipped by a rounded plate of cartilage, the omosternum ; and passing backwards from their posterior ends is a similar but larger bony rod, the sternum (S?), also tipped by a cartilaginous plate, to which the name xiphisternum (An) is applied. Fic. 249.— Rana esculenta. The shoulder girdle from the ventral aspect. Co, coracoid; Co', epicoracoid; CZ, clavicle; G, glenoid cavity; 2%, episternum; Fe, fenestra between procoracoid and coracoid; KC, cartilage separating scapula and clavicle; A, xiphisternum; 2, junction of epicoracoids; S, scapula; St, sternum. (From Wiedersheim’s Comparative Anatomy.) The four limbs deviate from the typical structure (p. 341) chiefly in the fusion of the radius and ulna into a single radio-ulna (Fig. 247, RA. UL) and in the presence of only four complete digits with a vestigial one on the radial side. In all probability the latter represents the pollex,.and the 416 MANUAL OF ZOOLOGY SECT. complete digits are the second to the fifth of the typical hand. Six carpals only are present. The pelvic arch (Figs. 24.7 and 250) is very peculiarly modified; it re- sembles in form a bird’s “ merry- thought,” consisting of two long curved bars articulating in front with the transverse processes of the sacral vertebra and uniting posteriorly in an irregular vertical disc of mingled bone and cartilage which bears on each side a deep, hemispherical acetabulum (Fig. 250, G) for the ar- ticulation of the thigh-bone. The curved rods are the ea (ZZ, P); they expand posteriorly and unite ium Fnac bu with one another in the median plane ve epee )dnatony.) to form the dorsal portion of the disc and about one-half of the acetabulum. The posterior portions of the disc and the acetabulum are furnished by the zschza (Zs), fused with one another in the sagittal plane, and their ventral portions by the similarly united pudes (An). The ilium and ischium are formed of true bone, the pubis of calcified cartilage ; the union of the elements in the median plane is called the symphysis. In the Aznd-liméd the tibia and fibula are fused to form a single tibio-fbula (Fig. 247, TI. FI), and the two bones in the proximal row of the tarsus, namely, the tibiale or as/raga- /us (AST) and the fibulare or caleaneum (CAL), are greatly elongated and provide the leg with an additional segment. There are three tarsals in the distal row, one of which ap- pears to represent a central, another the first distal carpal, and the third the fused second and third. There are five Fic. 250 — Rana esculenta. Pelvic girdle from the right XII PHYLUM CHORDATA 417 well-developed digits, and on the tibial side of the first is a spur-like structure or ca/ar (C), formed of three bones, a metatarsal and two phalanges: such a rudimentary digit is called a pre-hallux. The mouth leads into a wide éduccal cavity having in its roof the posterior nares (Fig. 251, p. na), a pair of projec- tions due to the downward bulging of the large eyes, and the el ZF; ts pr paget gt cng ZL rin vs.sem , oe crbh s Blin hat alys sped 7G ah F hea ust | ur el pe Fic 251.— Rana temporaria. Dissection from the left side; the viscera somewhat displaced. az, anus; 6.d, bile duct; 4. hy, body of hyoid; 42, urinary bladder; 47’, its opening into cloaca; ¢ art, conus arteriosus; célm, cerebellum; cé, cloaca; cz. 3, centrum of third vertebra; cf. ad, corpus adiposum; cvb h, cere- bral hemisphere: d. Zy. s, dorsal lymph sinus; dz, duodenum; ef. cor, epicora- coid; es. ¢, Eustachian tube; /R. PA, fronto-parietal; g/, glottis; gut, gullet; iL, ilium; 1s, ischium; Ad, kidney; 7. az, left auricle; 2 dzg, left lung; 7r, liver; mM. MCK, mento-meckelian; . a. 7, neural arch of first vertebra; olf 2, olfactory Inbe; oft 7, optic lobe; 0. sT, omo- and epi-sternum; fcd, peri- cardium; PILV, premaxilla; fz, pancreas; f za, posterior naris; fx, pubis; ret, rectum; ». Zag, right lung; s. zzf, small intestine; sf. cd, spinal cord; SPH. ETH, sphenethmoid; sf/, spleen; s¢, stomach; s. 7, sinus venosus; fg, tongue; ¢s, testis; #7, ureter; 27’, its aperture into the cloaca; uST, urostyle; v, ventricle; v dy.s, ventral lymph sinus; vo. ¢, vomerine teeth; ws. sem, vesicula seminalis, Lustachian tubes (eus. t, vide infra). On its floor is the large fongue (fg), attached in front and free behind, where it ends in a double point ; by means of its muscles it can be 2E 418 MANUAL OF ZOOLOGY SECT, suddenly projected, point foremost, from the mouth, and is used in the capture of insects. Immediately behind the tongue is the glottis (g/). Teeth are arranged in a single series round the edge of the upper jaw, attached to the pre- maxilla and maxillze; there is also a small patch of teeth (vo. 2) on each vomer just internal to the posterior nostril. The teeth are small conical bodies, their bases ankylosed to the bones ; their only use is to prevent the polished or slimy bodies of the prey — insects and worms — from slipping out of the mouth. The buccal cavity narrows towards the pharynx, which leads by a short gullet (gu/) into a stomach (s?) consisting of a wide cardiac and a short, narrow pyloric division. The duodenum (du), or first portion of the swall intestine, passes forwards parallel with the stomach; the rest of the small intestine is twisted into acoil. The large intestine or rectum (re?) is very wide and short, and passes without change of diameter into the cloaca (¢/). The “ver (/r) is two-lobed ; between the right and left lobes lies a large gadl-bladder. The pancreas (pn) is an irregular gland surrounding the bile duct, into which it pours its secretion ; the sA/cen (sf7) is a small, red globular body attached near the anterior end of the rectum. The lungs (2 lig, r. dng) are elastic sacs lying in the anterior part of the ccelom above the heart and liver ; their size and appearance vary greatly according to their state of distention. Each contains a spacious cavity, and has its walls raised into a complete network of ridges abundantly supplied with blood-vessels. The two lungs open anteriorly into a small /aryngo-tracheal chamber which communicates with the mouth by the narrow slit-like g/odt’s. The walls of the laryngo-tracheal chamber are supported by a cartilagi- nous framework, and its mucous membrane is raised into a xII PHYLUM CHORDATA 419 pair of horizontal folds, the vocal chords, by the vibration of which the croak of the frog is produced. In breathing, the frog keeps its mouth closed, and, by depressing the floor of the mouth draws air into the buccal cavity through the nostrils. The floor of the mouth is then raised, the nostrils are closed, and the air is forced through the glottis into the lungs. The skin is also an important respiratory organ. The pericardium (Fig. 251, ped) is not a separate cham- ber, as in fishes, but the heart, enclosed in a pericardial membrane, lies in the general coelomic cavity between the gullet above and the epicoracoids below. ‘The heart con- sists of a sinus venosus (Figs. 251 and 252, s.v), right and left auricles (7. au, /. au), a ventricle (v, vf), and a conus arteriosus (¢. a7). As in Dipnoi, the sinus venosus opens into the right auricle, the pulmonary veins into the left ; a striking advance is seen in the greatly increased size of the left auricle and its separation by a complete partition, the septum auricularum (Fig. 252, spt. aur), from the right. The two auricles open by a common auriculo-ventricular aperture, guarded by a pair of valves (au. v. v), into the sin- gle ventricle. The conus springs from the right side of the base of the ventricle ; it is separated from the latter by three small semilunar valves, and is traversed obliquely along its whole length by a large flap-like longitudinal valve (/) which springs from its dorsal wall and is free ventrally. The conus passes without change of diameter into a dudbus aorte, the two being separated by a semilunar valve and by the free end of the longitudinal valve. The bulbus gives off two branches, right and left, each of them divided by two longi- tudinal partitions into three vessels, — an inner or anterior, the carotid trunk (car. tr), a middle, the systemic trunk or aortic arch, and an outer or posterior, the pulmo-cutaneous 420 MANUAL OF ZOOLOGY SECT, trunk (pul. cu. tr). The carotid and systemic trunks com- municate separately with the bulbus, the two pulmo-cuta- neous trunks communicate with the anterior end of the conus by a single aperture placed just below the free end of the longitudinal valve. cangl cara Fic. 252.— Rana temporaria The heart from the ventral aspect with the cavities laid open. a, a’. bristle in left carotid trunk; az. v. v, auriculo-ventricular valves; 4,4’, bristle in left systemic trunk; ¢,c’, bristle in left pulmo-cutaneous trunk; cary a, carotid artery; car gi, carotid plexus; ¢ avt, conus arteriosus; car. tr, carotid trunk; 2, az, left auricle; g. a, lingual artery: @ 7, longitudinal valve; Aud. cu. tr, pulmo-cutaneous trunk; fz/ v, aperture of pulmonary veins; y.au, right auricle; s av. af, sinu-auricular aperture; sft. aur, septum auricu- larum; v.v', valves; wd, ventricle. After being bound together in the way described for a short distance, the carotid, systemic, and pulmo-cutaneous trunks separate from one another. The carotid trunk divides XI PHYLUM CHORDATA 421 Fic. 253. —Rana temporaria. The arterial system, with the heart, lungs, kidneys, and left testis, from the ventral aspect. car, carotid artery; car. gl, carotid gland; c. art, conus arteriosus; car. tr, carotid trunk; c@/. mes, coeliaco- mesenteric artery; cz, cutaneous artery; @. ao, dorsal aorta; dz, duodenal artery; gs, gastric artery; 4, hepatic artery; z/, iliac artery; zw, intestinal arteries; #d, kidney; 7. av, left auricle; Zg, lingual artery; pu/, pulmonary artery; fx/. cu. tr, pulmo-cutaneous trunk; 7. az, right auricle; 7, renal arteries; s#/, splenic artery; sys. ¢r, systemic trunk; sf, spermatic artery; ts, testis; v, ventricle, 422 MANUAL OF ZOOLOGY SECT. into carotid (Figs. 252, car. a and 253, car) and Aingual (2) arteries for the supply of the head, the former having at its base a small swelling, the carotid gland (car. gl), consisting of a plexus of blood-vessels. The systemic trunks curve round the gullet and unite with one another above it to form the dorsal aorta (ad. ao), from which, or from one of the systemic trunks themselves, the arteries to all parts of the body, except the head, the lungs, and the skin, are given off. The pulmo-cutaneous trunk divides into two, a pulmonary artery (pul) to the lung, and a cusaneous artery (cw) to the skin. The blood from the head and fore-limbs is returned by veins which unite to form a pair of large trunks, the pre- cavals, which open separately into the sinus venosus. One portion of the blood from the hind-limb is carried forward by a vein which unites with its fellow of the oppo- site side to form the abdominal vein (Fig. 254, ad), which passes forwards, in the ventral body-wall, to the level of the sternum, where it turns inwards and divides into two branches, both breaking up into capillaries in the liver. Just as it enters the liver it is joined by the Aepate portal vein (Ap. pt), bringing the blood from the stomach, intes- tine, spleen, and pancreas. The rest of the blood from the hind-limb is carried by the vena/ portal vein to the corresponding kidney. The blood is collected from the kidneys by the rena/ veins (rn), which unite to form the large unpaired fost-caval vein (pt.cv). This passes forward through a notch in the liver, receives the hepatic veins (hp) from that organ, and finally opens into the sinus venosus. Thus the blood from the hind-limbs has to pass through one of the two portal systems on its way back to the heart ; part of it goes by the renal portal veins to the kidneys, and thence by the renal xu PHYLUM CHORDATA 423 veins to the post-caval, part by the abdominal vein to the liver, and thence by the hepatic veins to the post-caval. Lastly, the blood which has been purified in the lungs is returned by the pu/monary veins (pul) directly to the left auricle. It will be perceived that the blood poured into the right auricle is mostly impure or venous, that poured into the left fully aérated or arterial. When the auricles contract, which they do simultaneously, each passes its blood into the corresponding part of the ventricle, which then instantly contracts, before the venous and arterial bloods have time to mix. Since the conus arteriosus springs from the right side of the ventricle, it will at first receive only venous blood, which, on the contraction of the conus, might pass either into the bulbus aorte or into the aperture of the pulmo-cutaneous trunks. But the carotid and systemic trunks are connected with a much more extensive capillary system than the pulmo-cutaneous, and the pressure in them is proportionally great, so that it is easier for the blood to enter the pulmo-cutaneous trunks than to force aside the valves between the conus and the bulbus. A fraction of a second is, however, enough to get up the pressure in the pulmonary and cutaneous arteries, and in the meantime the pressure in the arteries of the head, trunk, etc., is constantly diminishing, owing to the continual flow of blood towards the capillaries. Very soon, therefore, the blood forces the valves aside and makes its way into the bulbusaorte. Here again the course taken is that of least resistance ; owing to the presence of the carotid gland the passage of blood into the carotid trunks is less free than into the wide, elastic, systemic trunks. These will, therefore, receive the next portion of blood, which, the venous blood having been mostly driven to the lungs, will be a mixture of venous and 424 MANUAL OF ZOOLOGY SECT. Fic. 254. —Rana temporaria. The venous system with the heart, lungs, liver, kidneys, and right testis, from the dorsal aspect. add, abdominal vein; 47, brachial vein; cd, cardiac vein; ds. dmb, dorso-lumbar vein; dz, duodenal vein; ext. Ju, external jugular vein; fre, femoral vein; gs, gastric vein; 4, hepatic vein; Ap pt, hepatic portal vein; zv#, intestinal veins; zv¢. 7x, internal jugular vein; &d, kidney; 2. az, left auricle; /zg, lung: dvr, liver; ms. cx, musculo- cutaneous vein; pr. cv, pre- -caval vein; fz. cz, post- caval vein; pu/, pulmonary vein; pv, pelvic vein; . av, right auricle; 2, renal veins; »w. ft, renal portal vein; s¢, sciatic vein; sf, splenic vein; sft, spermatic vein; s. v, sinus venosus; zs, testis; ces, vesical veins. XII PHYLUM CHORDATA 425 arterial. Finally, as the pressure rises in the systemic trunks, the last portion of blood from the ventricle, which, coming from the left side, is arterial, will pass into the carotids and so supply the head. The dmphatic system is very well developed, and is remarkable for the dilatation of many of its vessels into immense {ph sinuses. Vhe lymph is pumped into the veins by two pairs of Jymph-hearts, one situated beneath the supra-scapulz, the other beside the posterior end of the urostyle. The drain (Fig. 255) has avery small cerebellum (H 7), large optic lobes (A7 #7), a well-developed diencephalon, and large hemispheres and olfactory lobes, the latter fused in the median plane. The first spinal nerve performs the function of the hypoglossal, one of the cranial nerves of higher Vertebrates supplying the muscles of the tongue: it passes out between the first and second vertebrae. The spinal cord is short, and ends in a delicate filament, the filum ‘erminale. In correspondence with the number of vertebre there are only ten pairs of spinal nerves, of which the second and third unite to form a brachial plexus giving off the nerves to the fore-limb, while the seventh to the tenth join to form a lumbo-sacral plexus giving off the nerves to the hind-limb. The offactory sacs have each two openings: the anderior naris or external nostril and the fosterior naris (Fig. 251, p- na), or internal nostril, which opens into the mouth immediately external to the vomer. The eye and the auditory organ have the usual structure, but in connection with the latter there is an important accessory organ of hearing not hitherto met with. Bounded externally by the tympanic membrane, and internally by the outer wall of the auditory capsule, is a considerable space, 426 MANUAL OF ZOOLOGY SECT. the “tympanic carrty (caw), which communicates with the mouth by the short Eustachian tube already noticed (Fig. 251, ews. 2), So that a probe thrust through the tympanic membrane from outside passes directly into the mouth. In Fic. 255.— Rana esculenta. The brain. A, from above; B, from below. ch oft, optic chiasma; AH, cerebellum; Ay, pituitary body: //, infundibulum; L. ol, olfactory lobe; AZed, spinal cord; ALAM, mid brain; A.A, medulla ob- longata; 7h. oft, optic thalamus; Jy. oft, optic tract; /°A, cerebral hemi- sphere; ZH, diencephalon; /—X, cerebral nerves; A’//. (1), hypoglossal (first spinal) nerve. (From Wiedersheim’s Comfarative Anatonty ) the roof of the tympanic cavity lies a slender rod of bone and cartilage, the columella, its head, or extra-columella, attached to the inner surface of the tympanic membrane, its II PHYLUM CHORDATA 427 handle united to the s/afes, a nodule of cartilage which is fixed in the membrane of the fenestra ovalis (p. 358). Sonorous vibrations striking the tympanic membrane are communicated by the columella and stapes to the fenestra ovalis, thence to the perilymph, and thence to the mem- branous labyrinth. The connection of the Eustachian tube with the mouth obviates undue compression of the air in the tympanic cavity. The kidneys (Figs. 251 and 253, Ad, and Figs. 256 and 257, JV) are flat, somewhat oval bodies of a dark red colour, lying in the posterior region of the ccelom. On the ventral face of each is an elongated, yellow adrenal, and irregularly scattered nephrostomes occur on the same surface. They do not, however, communicate with the urinary tubules, but with the renal veins, and serve to propel the lymph from the ccelom to the venous system. The ureters (Ur) pass backwards from the outer borders of the kidney, and open into the dorsal wall of the cloaca (C7). Opening into the cloaca on its ventral side is a bilobed, thin-walled, and very delicate sac, the urinary bladder (Fig. 251, 4/), into which the urine passes by gravitation from the cloaca when the anus is closed. The “estes (Fig. 256, Ho) are white ovoid bodies lying immediately ventral to the anterior ends of the kidneys, to which they are attached by folds of peritoneum. From the inner edge of each pass a number of delicate vasa efferentia, which enter the kidney and become connected with the urinary tubules. The spermatic fluid is thus passed into the urinary tubules and carried off by the ureter, which is therefore a urinogenital duct in the male frog. A vesicula seminalis opens by numerous small ducts into the outer side of the ureter. Attached to the testis are lobed bodies of a bright yellow colour, the fatdodies (FX). 428 MANUAL OF ZOOLOGY SECT. The ovaries (Fig. 257, Oz) are large folded sacs, on the surface of which the black and white ova project. A fat- body is attached to each. The oz7duets (Od) are greatly convoluted tubes, the narrow anterior ends of which open into the coelom by small apertures ( Of) placed close to the bases of the lungs. Their posterior ends are wide and thin-walled (C7), and open into the cloaca (P). The ova break loose from the surface of the ovary and enter the cce- lomic apertures of the ovi- ducts, the walls of which are glandular, and secrete an albuminous fluid having the property of swelling up in water. The eggs receive a coating of this substance as they pass down the ovi- ducts, and are finally stored up in the thin-walled pos- terior portions of those Fic. 256.—Ranaesculenta Urinogenital : ‘ organs of the male. -f, dorsal aorta; tubes, which in the breed- Cl, cloaca; Cv, post-caval vein; AK, fat . : bodies; HO, testes; .V, kidneys; S, ing season become im- apertures of ureters into cloaca; Ur, 3 ureters. (From Wiedersheim’s Com- mensely dilated and serve parative clnatony.) ‘ : as uteri. The eggs are laid in water in large masses ; each has one black and one white hemisphere, the former always directed upwards, and is sur- rounded by a sphere of jelly. During oviposition the male sheds his spermatic fluid over the eggs, and the sperms making their way through the jelly impregnate them. XII PHYLUM CHORDATA 429 When the embryo escapes from the egg by the rupture of the egg-membrane it swims about as a little fish-like creature or fadpole, with two pairs of branched external gills and a Fic. 257.—Rana esculenta. Urinogenital organs of the female. J, kidneys; Od, oviduct; Oz#, its coelomic aperture; Ov, left ovary (the right is removed); P, cloacal aperture of oviduct; S.S', cloacal apertures of ureters; U#, uterine dilatation of oviduct. (From Wiedersheim’s Comparative Anatomy.) long tail. There is no mouth, and eyes have not yet become developed. On the lower surface of the head is a pair of 430 MANUAL OF ZOOLOGY SECT, suckers by which the tadpole is able to attach itself to water-weeds. Soon a pair of external gills appears, the mouth and gill-slits are formed, and the eyes appear. The mouth is small, bounded by lips beset with horny papillee, Fic. 258.—Rana temporaria. Stages in the life-history, from the newly-hatched Tadpoles (1) to the young Frog (8). 2a is a magnified view of 2. (From Mivart.) and provided with a pair of horny jaws. The enteric canal grows toa great length and is coiled like a watch-spring, and the tadpole browses upon the water-weeds which form its XII PHYLUM CHORDATA 431 staple food, though it also eats decaying leaves and the flesh of dead animals. Soon the external gills show signs of shrivelling, and at the same time zv/ernad gills, like those of fishes, are devel- oped on the branchial arches. A fold of skin, the operculum, appears on each side, in front of the gills, growing from the region of the hyoid arch, and extends backwards until the gill-slits and external gills are covered and there is only a single small external branchial aperture on each side. On the right side the operculum soon unites with the body-wall so as to close the branchial aperture, but on the left side the opening remains for a considerable time as the sole exit of the water. At this time the tadpole is to all intents and purposes a fish. The lungs now appear, and the larva is for a time truly amphibious, rising periodically to the surface to breathe air ; the single branchial aperture, however, soon closes, and henceforth respiration is purely aérial. In the meantime the limbs are developed. The hind- limbs appear as little rounded buds, one on each side of the root of the tail. The fore-limbs arise beneath the operculum, and are therefore hidden at first; soon, however, they emerge by forcing their way through the operculum. As the limbs increase in size, the tail undergoes a progressive shrinking. The mouth widens, the intestine undergoes a relative diminution in length, and vegetable is exchanged for animal diet. The little tailed frog can now leave the water and hop about upon land ; its tail is soon completely absorbed, and the metamorphosis is complete. The frogs and toads are all closely allied as regards all the main features of their structure —the chief differences between the many genera and species being in such super- ficial characteristics as coloration and proportions. In 432 MANUAL OF ZOOLOGY SECT, some teeth are altogether absent; in others the webs between the toes are not developed; in some tree-frogs (74/a and allied genera) the toes terminate in sucking discs. A less superficial point of divergence from the structure of the common American frogs is to be observed in some members of the group, such as the tree-frogs and toads (7fi7a, Bufo, and others), in which the two halves of the shoulder-girdle, instead of being firmly united in the mid- Fic. 259. — Salamandra maculosa. (After Cuvier.) dle line, overlap one another. In one small group the tongue is absent. In some, again, there is no fish-like, gill- bearing larva or tadpole — the young animal emerging from the egg with the limbs formed, with no gills and no tail. All the frogs and toads are grouped together to form an order of Amphibia — the Anura or tailless Amphibia. The newts and salamanders (Fig. 259), with a number of other less widely known forms, differ from the frogs and toads in the possession in the adult of a well-developed tail. These constitute the order Urodela or tailed Amphibians. Of these tailed Amphibians, some, such as the newts and XIL PHYLUM CHORDATA 433 salamanders, lose both gills and gill- slits completely in the adult: while in others (such as Proteus, Necturus, and Siren), either gills are retained through- out life, or, as in the American Meno- poma, or hell-bender, gill-slits remain as a permanent record of their pres- ence in the larva. In some of the tailed Amphibians the limbs are well- developed; in others they are very small. Widely different in many respects from both the Anura and Urodela are 2 group of Amphibia—the Gyzzno- phiona —which are quite snake-like in appearance, owing to the elongated and narrow form of the body and the entire absence of limbs. The group is represented by the blind snake (Ce- cia) of Central and South America. CLASS IV. REPTILIA The class Reptilia comprises the lizards and snakes, the tuataras, the turtles and tortoises, and the alligators and crocodiles. On a superficial com- parison of these with the Amphibia, it might be inferred that there is a close alliance between the two groups; but this impression becomes weakened when a closer examination is made of ; the structure and development, and it oe ee 2F 434 MANUAL OF ZOOLOGY SECT. at length becomes evident that in the Reptilia we have to do with a class of Vertebrates which stand on a dis- tinctly higher plane than the Amphibia. One significant feature of the Reptilia which marks them off sharply from the Amphibia is that the lungs are the sole organs of respiration, gills never being developed at any stage. Another is the development in the embryo of two struc- tures known as the amnion and the allantois, not devel- oped in lower groups of Vertebrates, but present in the embryos of all the higher. The amnion is a thin membrane which covers over the body of the embryo, the space between it and the latter being tensely filled with a watery fluid. The amnion thus forms a sort of water-cushion, protecting the delicate and fragile embryo from the effects of any shocks which may be sustained by the eggs. The allantois, repre- sented in the frog by the urinary bladder, is a membranous structure developed as a hollow outgrowth of the enteric canal at its posterior end. It becomes highly vascular, and acts as an embryonic respiratory organ. There are four well-marked orders of living reptiles : — 1. The Squamata, comprising the Lacertilia or lizards (including the iguanas, monitors, skinks, geckos, chameleons, and others), and theSphidia or snakes (including the vipers and rattlesnakes, pythons, boas, sea-snakes, etc.). 3. The Rhynchocephalia, including only the New Zealand Tuatara (Hatterta). g. The Chelonia, including the land tortoises, soft tor- toises, river and marsh tortoises, and the turtles. . The Crocodilia, including the crocodiles, gavials, the alligators and caimans. The most striking external difference between a typical lizard (Fig. 207) and the frog are in the covering of scales in the case of the former, the comparative smallness of its XII PHYLUM CHORDATA 435 head, and the presence of a distinct neck, the great length of the caudal region, the shortness of the limbs, and the approximate equality in length of the anterior and posterior pairs. The anterior limbs are situated just behind the neck, springing from the trunk towards the ventral surface. The fore-limb, like that of the frog, is divided into three parts, the upper-arm or dvachium, the fore-arm or anfi- brachium, and the hand or manus; there are five digits provided with horny claws, the first digit or pollex being the smallest. The hind-limbs arise from the posterior end of the trunk towards the ventral aspect; each, like that of the frog, consists of three divisions — thigh or femur, shank or crus, and foot or ges. The pes, like the manus, termi- nates in five clawed digits, of which the first or hallux is the smallest. The head is somewhat pyramidal, slightly de- pressed; the openings of the external nares are situated above the anterior extremity. The mouth is a wide slit- like aperture running round the anterior border of the head. At the sides are the eyes, each provided with upper and lower opaque movable eyelids, and with a transparent third eyelid or néctitating membrane, which, when withdrawn, lies in the anterior angle of the orbit. Behind the eye is a circular brown patch of skin, — the Ampanic membrane, — corresponding closely to that of the frog, but somewhat sunk below the general level of the skin. The trunk is elongated, strongly convex dorsally, flatter at the sides and ventrally. At the root of the tail on the ventral surface is a slit-like transverse aperture — the anus or cloacal aperture. The tail is cylindrical, thick in front, gradually tapering to a narrow posterior extremity; it is nearly twice as long as the head and trunk together. There is an exoskeleton of horny epidermal scaées covering all parts, differing in size in different positions. 436 MANUAL OF ZOOLOGY SECT. In some groups of lizards the tail is comparatively short and thick; and in others it is depressed and expanded into a leaf-like form. In the chameleons the long and tapering tail is used as a prehensile organ, the coiling of which round branches of the trees in which the animal lives, aids in maintaining the balance of the body in climbing from branch to branch. In the limbs there is likewise a considerable amount of variation in the different groups of the Lacertilia. Moder- ately long pentadactyle limbs, like those of Lacerta, are the rule. In the chameleons both fore- and hind-limbs become prehensile by a special modification in the arrangement and mode of articulation of the digits. In these remarkable arboreal reptiles the three innermost digits of the manus are joined together throughout their length by a-web of skin, and the two outer digits are similarly united ; the two sets of digits are so articulated that they can be brought against one another with a grasping movement much analogous to the grasping movements of a parrot’s foot or the hand of man. A similar arrangement prevails in the pes, the only difference being that the two innermost and three outermost digits are united. In some groups of Lacertilia, on the other hand, such as the blind-worms (.imgués), limbs are entirely absent, or are represented only by mere vestiges ; and numerous intermediate gradations exist between these and forms, such as Lacerta, with well-developed limbs. The limbless lizards, such as the glass-snake, and Pygopus (Fig. 261), bear a very close resemblance to the snakes, not only in the absence of the limbs, but also in the general form of the body and the mode of locomotion. The body of a snake is elongated, narrow, and cylindrical, usually tapering towards the posterior end, sometimes with, more usually without, a constriction behind the head. In XII PHYLUM CHORDATA 437 the absence of limbs, the beginning of the short caudal region is only indicated by the position of the cloacal open- ing. The fore-limbs are never represented even by vestiges ; in some pythons there are inconspicuous vestiges of hind- limbs, in the form of small claw-like processes. The mouth of the snake is capable of being very widely opened by the free articulation of the lower jaw, and it is this mainly which distinguishes it from the snake-like lizards. But other, less Fic. 261.— Pygopus lepidopus. (After Brehm.) conspicuous, points of distinction are the absence of movable eyelids in the snake, and also the absence of a tympanum. Hatteria, the New Zealand Tuatara (Fig. 262), the only living representative of the Rhynchocephalia, is a lizard-like reptile with a well-developed laterally-compressed tail, and pentadactyle extremities, very similar to those of a typical lizard. The upper surface is covered with small granular scales, and a crest of compressed spine-like scales runs along the middle of the dorsal surface. The lower surface is covered with transverse rows of large squarish plates. 438 MANUAL OF ZOOLOGY SECT. In the Chelonia (Fig. 263) the body is short and broad, enclosed in a hard “shell,” consisting of a dorsal part or carapace and a ventral part or flastron. These are firmly united, apertures being left between them for the head and neck, the tail and the limbs. The neck is long and mobile ; the tail short. The limbs are fully developed, though short. In some (land and fresh-water tortoises) they are provided each with five free digits terminating in curved horny claws ; in the turtles the digits are closely united together, and the Fic. 262.—Hatteria punctata. (After Brehm.) ’ limb assumes the character of a “flipper” or swimming paddle. ‘The cloacal aperture is longitudinal. The Crocodilia, the largest of living reptiles, have the trunk elongated and somewhat depressed, so that its breadth is much greater than its height. The snout is prolonged, the neck short, the tail longer than the body and compressed laterally. The limbs are relatively short and powerful, with five digits in the manus and four in the pes, those of the latter being partly or completely united by webs of skin. XII PHYLUM CHORDATA 439 The eyes are very small; the nostrils placed close to the end of the snout and capable of being closed by a sphincter muscle. The cloacal aperture is a longitudinal slit. Characteristic of the Squamata is the development in the epidermis of horny plates, the sca/es, which cover the entire surface, overlapping one another in an imbricating manner. Sometimes they are similar in character over all parts of the surface ; usually there are specially developed scales — the Fic. 263. — Grecian tortoise (Testudo greca). (After Brehm.) head shields — covering the upper surface of the head. In the majority of snakes the ventral surface is covered with a row of large transversely elongated scales, the ven¢ra/ shields. In some lizards (chameleons and geckos) the scales are reduced and modified into the form of minute tubercles or granules. In some lizards special developments of the scales occur in the form of large tubercles or spines. In the snake-like Amphisbeenians there are no true scales, 440 MANUAL OF ZOOLOGY SECT. with the exception of the head shields, but the surface is marked out into annular bands of squarish areas. In addition to the modification of the scales, the integu- ment of the chameleons is remarkable for the changes of colour which it undergoes, these changes being due to the presence in the dermis of pigment cells which contract or expand under the influence of the nervous system, in a way that reminds one of the integument of the Cephalopoda. In the Chelonia, scales, when developed, are confined to the head and neck, the limbs and the tail, but in all of them, with the exception of the soft tortoises, both dorsal and ven- tral surfaces are covered by a system of large horny plates. A series of horny head-shields usually cover the dorsal sur- face of the head. Beneath the horny plates of the dorsal and ventral surfaces are the bony carapace and plastron, partly composed of dermal bones, but so intimately united with elements derived from the endoskeleton that the entire structure is best described in connection with the latter (Pp. 443)- In the Crocodilia, the dorsal surface is covered with longi- tudinal rows of sculptured horny plates, beneath which are bony dermal scutes of corresponding form. The ventral surface of the body is covered with scales like those of a lizard. The horny plates of the dorsal surface of the tail are elevated into a longitudinal crest. A periodical ecdys7s or casting and renewal of the outer layers of the horny epidermis takes place in all the Reptilia. Sometimes this occurs in a fragmentary manner; but in snakes and many lizards the whole comes away as a con- tinuous slough. The vertebre are always fully ossified. Only in the geckos and Hatteria are the centra amphiccelous, with XII PHYLUM CHORDATA remnants of the notochord in the inter-central spaces. In most of the others the centra are proccelous, a ball-like con- vexity on the posterior surface of each centrum projecting into a cup-like concavity on the anterior face of the next. The various regions of the spinal column are well marked in most of the lizards, in the Chelonia, and in the Croco- dilia (Fig. 264). In the snakes and many of the snake-like lizards only two regions are distinguishable —. pre - caudal and caudal. In the others there is a sacral region com- prising two vertebra, which have strong transverse pro- cesses for articulation with the ilia. The first and sec- ond vertebrz are always modi- fied to form an atlas and axis. Ribs are developed in connection with all the ver- tebre of the pre-sacral or pre- caudal region; in the caudal region they are usually replaced by inferior arches. In the fly- ing lizards (Draco) a num- ber of the ribs are greatly produced, and support a pair . s Hi, humerus; (From U, ulna. T, tibia; D, thoracic region of spinal column; F, fibula; Fe, femur; ! C, caudal region; Z,ischium; Z, lumbar region; A, radius; Az, ribs; S, sacrum; Sc, scapula; Sta, abdominal ribs; Fic. 264.— Skeleton of crocodile. Zittel.) 442 MANUAL OF ZOOLOGY SECT. of wide. flaps of skin at the sides of the body, acting as wings or rather as parachutes. In Hatteria and Crocodilia (Fig. 264) each rib has connected with it posteriorly a flat- tened curved cartilage, the wxcinaze. Fic. 265.— Cistudo lutaria. Skeleton seen from below; the plastron has been removed and is represented on one side. C. costal plate; Co, coracoid; e, ento- lastron; £f, epiplastron; F, fibula; /e, femur; HY, humerus; //, ilium; Zs, ischium; //, marginal plates; .V, nuchal plate; 7é, pubis; Pro, pro-cora- oe ea pygal plates; A, radius; Sc, scapula; 7, tibia; U, ulna. (From ittel. In the Chelonia (Fig. 265) the total number of vertebre is always smaller than in the members of the other orders. The cervical and the caudal are the only regions in which the vertebrze are movable upon one another. The vertebree XII PHYLUM CHORDATA 443 of the trunk, usually ten in number, are immovably united together. Each of the neural spines, from the second to the ninth inclusively, is expanded into a flat plate, and the row of neural plates (Fig. 266, V), thus formed constitutes the median portion of the carapace. The ribs are likewise immovable; a short distance from its origin each passes into a large bony costt/ plate (C), and the series of costal plates uniting by their edges form a large part of the cara- pace on either side of the row of neural plates. The cara- pace is made up of the neural and costal plates supplemented by a row of margina/ plates (Figs. 265 and 266, 47) running along the edge, and nuchal (Vu) and pygal (Py) plates Fig. 266.— Chelone midas. Transverse section of skeleton. C, costal plate; C’, centrum; 4, marginal plate; P, lateral element of plastron; 2, rib; V’, expanded neural plate. (After Huxley.) situated respectively in front of and behind the row of neural plates. The bony elements of the plastron of the Chelonia are an anterior and median plate and six pairs of plates —the six pairs probably being of similar nature to the abdominal ribs of the Crocodilia. The sternum in the Lacertilia is a plate of cartilage with a bifid posterior continuation. In the Ophidia and Chelonia it is absent. In the Crocodilia it is a broad plate with a posterior continuation or hy~osternum, extending backwards as far as the pelvis. 444 MANUAL OF ZOOLOGY SECT. A series of ossifications — the abdominal ribs, with a mesial abdominal sternum —-\ie in the wall of the abdomen in the Crocodilia (Fig. 264, Séz), and similar ossifications occur also in the monitors and in Hatteria. The elements of the plastron of the Chelonia are probably of a similar character. In the s&z// ossification is much more complete than in the Amphibia, the primary chondrocranium persisting to a considerable extent only in some lizards and in Hatteria, and the number of bones is much greater. The parasphenoid is reduced, and its place is taken by large basi-occipital, basi-sphenoid, and pre-sphenoid bones. The lower jaw articulates with the skull through the interme- diation of a quadrate bone, which is movable in the lizards and snakes, fixed in Hatteria, the Chelonia, and Crocodilia. A remarkable feature of the skull of the snakes (Fig. 267), is the free articulations of the bones of the jaws, permitting of the mouth being opened very wide so as to allow the passage of the relatively large animals which the snake swallows whole ; this wide opening of the mouth is further aided by the two halves of the mandible not being firmly fixed together anteriorly, but merely connected together by means of elastic tissue, so that they are capable of being widely separated from one another. In accordance with their purely aérial mode of respira- tion, the zsceral arches are much more reduced in the Reptilia than in the Amphibia in general. The only well- developed post mandibular arch is the hyoid, and even this may undergo considerable reduction (Ophidia). The branchial arches, except in so far as they may contribute to the formation of the tracheal rings, are not represented in the adult, with the exception of most Chelonia, in which the first branchial arch persists. XII PHYLUM CHORDATA 445 In the lizard (Fig. 268) and crocodiles there is a cross- shaped membrane-bone, the ¢aderclavicle or episternum (epist), in relation to the pectoral arch and sternum. In the limb- less lizards the pectoral arch may be absent or may be well developed ; it is completely wanting in all snakes. In the pelvic arch the ischium is separated from the pubis by a wide space not developed in the Amphibia. “Slight vestiges of hind- limbs occur in some pythons alone among the Ophidia. XN Fic. 267. — A, lateral view of skull of rattlesnake (Crotalus). 2. O, basi-occipital; B.S, basi-sphenoid; £. O, exoccipital; 7. O, fossa ovalis; La, conjoined lac- rymal and pre-frontal; Z. /, articulation between lacrymal and frontal; Mx, mandible; 47x, maxilla; Ma, nasal; P?, palatine; Px, pre-maxilla; P. Sph, pre-sphenoid; Pt, pterygoid; Qx, quadrate; Sg, squamosal; //. V, foramina of exit of the second and fifth cranial nerves. B, transverse section at point lettered Bin Fig. A; 7, trabecule. (After Huxley.) In the lizards teeth are present in the pre-maxillz, the maxilla, the mandible, and usually the palatines. These are in most lizards small and simple, and uniform in shape and arrangement. A Mexican Lizard, Heloderma, which also occurs in Utah and Arizona, differs from all the rest in gpESTER JERMAIN HUNN. 446 MANUAL OF ZOOLOGY SECT, having teeth which are perforated for the ducts of poison- glands. In the snakes (Fig. 267) teeth are rarely devel- oped on the pre-maxillee, but are present on the maxille, palatines, pterygoids, and sometimes the transverse bones, as well as the dentary of the mandible. They may be of the same nature throughout, solid, elongated, sharp-pointed teeth, which are usually strongly recurved, so that they have the character of sharp hooks, their function being rather to Fic. 268. — Pectoral arch and sternum of a lizard (Lacerta agilis). cd, clavicle; cor, coracoid; ef. cor, epicoracoid; epzst, episternum; gen, glenoid cavity for head of humerus; fv. cor, pro-coracoid; ~ 7 — ~. 4, first to fourth sternal ribs; se, scapula; st, sternum; swfra. sc, supra-scapula. (After Hoffman.) hold the prey and prevent it slipping from the mouth while being swallowed than to masticate it. _Non-venomous snakes possess teeth only of this character. In the venomous snakes, more or fewer of the maxillary teeth assume the character of poison-fangs. These are usually much larger than the ordinary teeth, and either grooved or perforated by a canal XII PHYLUM CHORDATA 447 for the passage of the duct of the poison-gland. In the vipers there is a single large curved poison-fang with small reserve-fangs at its base, these being the only teeth borne by the maxilla, which is very short; in the venomous colu- brine snakes the poison-fangs are either the most anterior or the most posterior of a considerable range of maxillary teeth. In the vipers the large poison-fang is capable, owing to the maxilla in which it is fixed being movable on a hinge-joint, of being rotated through a considerable angle, and moved from a nearly horizontal position, in which it lies along the roof of the mouth, embedded in folds of the mucous mem- brane, to a nearly vertical one when the snake opens his mouth to strike its prey. In Hatteria there are pointed, triangular, laterally- compressed teeth, arranged in two parallel rows, one along the maxilla, the other along the palatine. The teeth of the lower jaw, which are of similar character, bite in between these two upper rows, all the rows becoming worn down in the adult in such a way as to form continuous ridges. Each pre-maxilla bears a prominent, chisel-shaped incisor, represented in the young animal by:two pointed teeth. In the young Hatteriaa tooth has been found on each vomer — a condition exceptional among reptiles. In the Chelonia, teeth are entirely absent, the jaws being invested in a horny layer in such a way as to form a structure like a bird’s beak. The Crocodilia have numerous teeth which are confined to the pre-maxille, the maxillz, and the dentary. They are large, conical, hollow teeth, devoid of roots, each lodged in its socket or alveolus, and each becoming replaced, when worn out, by a successor developed on its inner side. In the enteric canal of the Reptiles the principal special features to be noticed are the muscular, gizzard-like stomach 448 MANUAL OF ZOOLOGY SECT. of the Crocodilia, the presence of a rudimentary cecum at the junction of small and large intestines in most Lacertilia and in the Ophidia, and the presence of numerous large cornified papillee in the cesophagus of the Turtles. The Reptiles have all an elongated ¢rachea, the wall of which is supported by numerous cartilaginous rings. The anterior part of this is dilated to form the larynx, the wall of which is supported by certain spe- cial cartilages —the cricoid and the arytenoids. The trachea bifurcates posteri- orly to form two bronchi, right and left, one passing to each lung. The Zungs of the Lacer- tilia and Ophidia are sim- ple and sac-like, like those of the frog. In the Croco- dilia and Chelonia they are of a more complex char- acter, being divided inter- Fic. 269. — Heart of monitor (Varanus) guarded by valves. dissected to show the cavity of the ventricle and the vessels leading out from it. A. A’, auricles; Ao, dorsal aorta; Ap. Ap’, pulmonary arteries; Asc, subclayian artery ; Ca. Ca’, caro- tids; RA. RA, roots of dorsal aorta; Trea, innominate trunk: V, ventricle; t, right aortic arch; *, left aortic arch, (From Wiedersheim. y nally by septa into a number of chambers. In the heart (Fig. 269) the sinus venosus is always distinct, and is divided into two parts by a septum; its aperture of communication with the right auricle is There are always two quite distinct xil PHYLUM CHORDATA 449 auricles, as in the Amphibia, the right receiving the venous blood from the body, the left the oxygenated blood brought from the lungs by the pulmonary veins. But a vital point of difference between the heart of the reptile and that of the am- phibian is that in the former the ventricle is al- ways more or less com- pletely divided into right and left portions. Inallthe Lacertilia, Ophidia, and Chelonia the ventricle is incompletely divided by a septum which does not entirely cut off the two portions of the cavity from one another. But in the Crocodilia the cavity is completely divided, so that we may ‘speak of distinct right and left ventricles. The drain of Reptiles is somewhat more highly organised than that of the Amphibia. The cerebral hemispheres are well de- veloped in all. The mid- brain consists usually of Fic. 270.— Brain of alligator, from above. B. ol., olfactory bulb; G. #, epiphysis ; FH, cerebellum ; Ae, spinal cord; MA, optic lobes; MWA, medulla oblongata ; VH, cerebral hemispheres ; /— XJ, cra- nial nerves ; 1, 2, first and second spinal nerves. (After Wiedersheim.) two closely approximated oval optic lobes. The cerebellum 2G 450 MANUAL OF ZOOLOGY SECT. is always of small size, except in the Crocodilia (Fig. 270), in which it is comparatively highly developed, and consists of a median and two lateral lobes. The eyes are relatively large, with a cartilaginous sclerotic in which a ring of bony plates is developed in some cases. Most reptiles have both upper and lower eyelids and nicti- tating membrane. The greater number of the geckos and all the snakes constitute exceptions, movable eyelids being absent in both these groups. In the chameleons there is a single circular eyelid with a central aperture. The middle ear is absent in the snakes, though a colu- mella auris is present, embedded in muscular and fibrous tissue. Developed in close relation to the epiphysis there is in many lizards (Lacerta, Varanus, Anguis, Grammatophora, and others) and in Hatteria, a remarkably eye-like organ — the pineal eye (Fig. 271), which is situated in a foramen of the cranial roof immediately under the integument, and covered over by a specially modified, transparent scale. Like the epiphysis itself, the pineal eye is developed as a hollow outgrowth of the roof of the diencephalon; the distal end of this becomes constricted off as a hollow sphere, while the remainder becomes converted into a nerve. The nerve degenerates before the animal reaches maturity, so that the organ would appear—though evidently, from its structure, an organ of sight — to have now entirely or nearly lost its function. Though fertilisation is always internal, most Reptilia are oviparous, laying eggs clothed in a tough, parchment-like or calcified shell. These are usually deposited in holes and left to hatch by the heat of the sun. In the crocodiles they are deposited in a rough nest and guarded by the mother. In all cases development has only progressed to a very early XII PHYLUM CHORDATA 451 stage when the deposition of the eggs takes place, and it is only after a more or less prolonged period of incubation that the young, fully formed in almost every respect, emerge from the shell and shift for themselves. Many lizards, Fic. 271. — Section of the pineal eye of Hatteria punctata. g, blood-vessels: /, cavity of the eye filled with fluid; 4, capsule of connective tissue: 27, lens; #2, molecular layer of the retina; 7, retina; s¢, stalk of the pineal eye; -r, cells in the stalk. (From Wiedersheim, after Baldwin’Spencer.) however, and a few snakes are viviparous, the ova being developed in the interior of the oviduct, and the young reaching the exterior in the completely formed condition. 452 MANUAL OF ZOOLOGY SECT. The lizards are for the most part terrestrial animals, usually extremely active in their movements and endowed with keen senses. The majority readily ascend trees, and many kinds are habitually arboreal ; but the chameleons are the only members of the group which have special modi- fications of their structure in adaptation with an arboreal mode of life. The skinks and the amphisbzenians are swift and skilful burrowers. The geckos are enabled by the aid of the sucker-like discs on the ends of their toes to run readily over vertical or overhanging smooth surfaces. A few lizards, on the other hand, live habitually in fresh water. The flying lizards (Draco) are arboreal, and make use of their wings — or, to speak more accurately, aéroplane or para- chute (thin folds of skin supported by the greatly produced ribs)— to enable them to take short flights from branch to branch. Chalmydosaurus and certain other genera are exceptional in frequently running on the hind-feet, with the fore-feet entirely elevated from the ground. A tolerably high temperature is essential for the maintenance of the vital activities of lizards, low temperatures bringing on an inert condition, which usually passes, during the coldest part of the year, into a state of suspended animation or hibernation. The food of lizards is entirely of an animal nature. The smaller kinds prey on insects of all kinds, and on worms. Chameleons, also, feed on insects, which they capture by darting out the extensile tongue covered with a viscid secretion. Other lizards supplement their insect diet, when opportunity offers, with small reptiles of various kinds, frogs and newts, small birds and their eggs, and small mam- mals, such as mice and the like. The larger kinds, such as the monitors and iguanas prey exclusively on other ver- tebrates ; some, on occasion, are carrion-feeders. Most lizards lay eggs enclosed in a tough calcified shell. These XII PHYLUM CHORDATA 453 they simply bury in the earth, leaving them to be hatched by the heat of the sun. Some, however, are viviparous ; in all cases the young are left to shift for themselves as soon as they are born. Snakes are also usually extremely active and alert in their movements ; and most are very intolerant of cold, under- going a hibernation of greater or less duration during the winter season. Many live habitually on the surface of the ground—some kinds by preference in sandy places or among rocks, others among long herbage. Some (tree- snakes) live habitually among the branches of trees. Others (fresh-water snakes) inhabit fresh water; others (sea-snakes) live in the sea. The mode of locomotion of snakes on the ground is extremely characteristic, the reptile moving along by a series of horizontal undulations brought about by contractions of the muscles inserted into the ribs, any inequalities on the surface of the ground serving as fulcra against which the free posterior edges of the ventral shields (which are firmly connected with the ends of the ribs) are enabled to act. The burrowing blind- snakes and other families of small snakes feed on insects and worms. All the rest prey on vertebrates of various kinds — fishes, frogs, lizards, snakes, birds and their eggs, and mammals. The pythons and boas kill their prey by constriction, winding their body closely round it and draw- ing the coils tight till the victim is crushed or asphyxiated. Some other non-venomous snakes kill with bites of their numerous sharp teeth. The venomous snakes sometimes, when the prey is a small and weak animal such as a frog, swallow it alive: usually they first kill it with the venom of their poison-fangs. When a venomous snake strikes, the poison is pressed out from the poison-gland by the contraction of the masseter 454 MANUAL OF ZOOLOGY SECT. (Fig. 272, dc), one of the muscles which raise the lower jaw: it is thus forced along the duct (Gc) to the aperture (sa), and injected into the wound made by the fang. The effect is to produce acute pain with increasing lethargy and weakness, and in the case of the venom of some kinds of snakes, paralysis. According to the relative amount of the poison injected and the degree of its virulence (which differs not only in different kinds of snakes, but in the same snake under different conditions) the symptoms may result in death, or the bitten animal may recover. The poison is a _? pre Yipee dL teh o C9 s . os 3 EE RE Fic. 272.— Poison apparatus of rattlesnake. 4, eye; Gc, poison-duct entering the poison-fang at ¢ ; Av, muscles of mastication partly cut through at * ; A/c, masseter or constrictor muscle; Mc’, continuation of the constrictor muscle to the lower jaw ; 4, nasal opening; S, fibrous poison-sac ; 2, tongue; sa, opening of the poison-duct ; 2 pouch of mucous membrane enclosing the poison-fangs. (From Wiedersheim. ) clear, slightly straw-coloured or greenish liquid ; it preserves its venomous properties for an indefinite period, even if completely desiccated. The poisonous principles are cer- tain proteids not to be distinguished chemically from other proteids which have no such poisonous properties. Immu- nity against the effects of the poison, and relief of the symp- toms after a bite has been inflicted, have been found to be conferred by injections of the serum of animals which have XII PHYLUM CHORDATA 458 been treated with injections of increasing doses of the poison. The majority of snakes are viviparous. Some, however, lay eggs, which, nearly always, like those of the oviparous lizards, are left to be hatched by the heat of the sun, some of the Pythons being exceptional in incubating them among the folds of the body. Hatteria lives in burrows in company with mutton-birds (Puffinus), and feeds on insects and small birds. It lays eggs enclosed in a tough parchment-like shell. The eggs are laid in November, and the embryos pass the winter in a state of hibernation unknown to any other vertebrate embryo, not emerging from the egg until nearly thirteen months have elapsed (Dendy). Of the Chelonia some (land-tortoises) are terrestrial ; others (fresh-water tortoises) inhabit streams and ponds, while the sea-turtles and luths, or leather-backed turtles, inhabit the sea. Even among reptiles they are remarkable for their tenacity of life, and will live for a long time after severe mutilations, even after the removal of the brain; but they readily succumb to the effects of cold. Like most other reptiles, the land and fresh-water tortoises living in colder regions hibernate in the winter; in warmer latitudes they sometimes pass through a similar period of quiescence in the dryseason. The food of the green turtles is exclusively vegetable ; some of the land tortoises are also exclusively vegetable feeders; other Chelonia either live on plant food, together with worms, insects, and the like, or are com- pletely carnivorous. All are oviparous, the number of eggs laid being usually very great (as many as 240 in the sea- turtles) ; these they lay in a burrow carefully prepared in the earth, or, in the case of the sea-turtles, in the sand of the sea-shore, in a round hole about fifteen or twenty inches i ‘ 4 456 MANUAL OF ZOOLOGY SECT. deep and ten inches in diameter, and having covered them over, leave them to hatch. ~The crocodiles and alligators, the largest of living reptiles, are in the main aquatic in their habits, inhabiting rivers, and, in the case of some species, estuaries. Endowed with great muscular power, these reptiles are able, by the move- ments of the powerful tail and the webbed hind-feet, to dart through the water with lightning-like rapidity. By lying in wait motionless, sometimes completely submerged with the exception of the extremity of the snout bearing the nostrils, they are often able by the suddenness and swiftness of their onset to seize the most watchful and timid animals. In the majority of cases the greater part, and in some the whole, of their food consists of fishes; but all the larger and more powerful kinds prey also on birds and mammals of all kinds, which they seize unawares when they come down to drink or attempt to cross the stream. On land their movements are comparatively slow and awkward, and they are correspondingly more timid and helpless. The Crocodilia are all oviparous, and the eggs, as large in some species as those of a goose, are brought forth in great numbers (sometimes too or more), and either buried in the sand or deposited in rough nests, CLASS V. AVES In many respects birds are the most highly specialised of Craniata. As a class they are adapted for aerial life, and almost every part of their organisation is modified in ac- cordance with the unusual environment. The non-conduct- ing covering of feathers; the modification of the fore-limbs as wings, of the sternum and shoulder-girdle to serve as xi PHYLUM CHORDATA 457 origins of the wing-muscles, and of the pelvic girdle and hind-limbs to enable them to support the entire weight of the body on land; the perfection of the respiratory system, producing a higher temperature than in any other animals, — all these peculiarities are of the nature of adaptations to cee hester J. Hunn The common or domestic pigeon is known hester. many varieties which differ from one another in size, proportions, coloration, details in the arrangements of the feathers, and in many points of internal anatomy. The following description refers especially to the common dovecot pigeon. In the entire bird (Fig. 273) the plump trunk appears to be continued insensibly into the small, mobile head, with its rounded brain-case and prominent deak formed of the upper and lower jaws covered by horny sheaths. The head, neck, and trunk are invested in a close covering of feachers, all directed backwards and overlapping one another. Posteriorly the trunk gives origin to a number of outstanding feathers which constitute what is ordinarily called the tail. From the anterior region of the trunk spring the wngs, also covered with feathers, and, in the position of rest, folded against the sides of the body. The legs spring from the hinder end of the trunk, but, owing to the thick covering of feathers, only the feet are to be seen in the living bird, each covered with scaées and terminating in four digits (dg r'— dg 4'), three directed forwards and one backwards. In order to make a fair comparison of the outer form with that of other craniate types, it is necessary to remove the feathers. When this is done the bird is seen to have a long, cylindrical, and very mobile neck, sharply separated both from head and trunk. The true tail is a short, conical projection of the trunk, known as the wropygium, and giving 458 MANUAL OF ZOOLOGY SECT. origin to the group of large feathers (7c?) to which the word “tail” is usually applied. On the dorsal surface of the uropygium is a papilla bearing on its summit the opening of Fic. 273. —Columba livia. The entire animal from the left side with most of the feathers removed. ad.dg. rmx, ad-digital remex; a/ sf,ala spuria; ax, anus; au ap, auditory aperture; cd. mg, cubital remiges; cr, cere; @g. J, 2, 3, digits of manus; dg 7’, 2’, 3’, 4', digits of pes; Aw ff, humeral pteryla; dg, ligament of remiges; mad. dg rmg, mid-digital remiges; a, nostril; xc. me, nictitating membrane; 0. g?, oil gland; pr. dg rmg, pre-digital remiges; Jr. pig, pre- patagium; Af pfgm, post-patagium; xc, mesial rectrix of right side; vcé’, sacs of left rectrices; sf. A¢, spinal pteryla; ¢s. s#éts, tarso-metatarsus; v. aft, ventral apterium, or featherless space. XII PHYLUM CHORDATA 459 a large gland, the oz/-g/and (0. g/), used for lubricating or “preening” the feathers. The wings show the three typical divisions of the fore- limb, upper arm, fore-arm, and hand, but the parts of the hand are closely bound together by skin, and only three imperfectly marked digits, the second (dg 2) much larger than the first (dg z) and third (dg 3), can be distinguished. In the position of rest the three divisions of the wing are bent upon one another in the form of a Z: during flight the entire wing is straightened out at right angles to the trunk. In the hind-limb the short thigh is closely bound to the trunk: the foot is clearly divisible into a proximal portion, the /arso-metatarsus (¢s. més) and four digits, of which one, the hallux (dg z'), is directed backwards, the others, the second, third, and fourth of the typical foot, forwards. The mouth is terminal and is guarded by the elongated upper and lower beaks; it has, therefore, a very wide gap. On each side of the base of the upper beak is a swollen area of soft skin, the ceve (cr) surrounding the woséi/ (7a), which has thus a remarkably backward position. The eyes are very large, and each is guarded by an upper and a lower eyelid and a transparent nictitating membrane (met. m). A short distance behind the eye is the auditory aperture (au. ap), concealed by feathers in the entire bird, and lead- ing into a short external auditory meatus, closed below by the tympanic membrane. The anus or cloacal aper- ture (az), is a large, transversely elongated aperture placed on the ventral surface at the junction of the uropygium with the trunk. The exoskeleton is purely epidermal, like that of the lizard, which it also resembles in consisting partly of horny scales. These cover the tarso-metatarsus and the digits of the foot, and are quite reptilian in appearance and structure. 460 MANUAL OF ZOOLOGY SECT. Each digit of the foot is terminated by a claw which is also a horny product of the epidermis, and the beaks are of the same nature. The rest of the body, however, is covered by feathers, a unique type of epidermal product found nowhere outside the present class. Fic. 274.— Columba livia. A, proximal portion of a remex. ca/, calamus; zaf. umib, inferior umbilicus; rch, rachis; sup. umd, superior umbilicus. B, filo- plume. C, nestling-down. (C, from Bronn’s Thzerretch.) A feather (Fig. 274) is an elongated structure consisting of a hollow stalk, the ca/amus or quill (ca7), and an ex- panded distal portion, the vex//um or vane. At the proximal end of the quill is a small aperture, the zxfertor umbilicus (inf. umb), ito which fits, in the entire bird, a XII PHYLUM CHORDATA 461 small conical prolongation of the skin, the feather papilla. A second extremely minute aperture, the superior umbilicus (sup. umb), occurs at the junction of the quill with the vane on the inner or ventral face of the feather, z.c., the face adjacent to the body. The vane has a longitudinal axis or rachis (rch) contin- uous proximally with the quill, but differing from the latter in being solid. To each side of the rachis is attached a kind of membrane forming the expanded part of the feather and composed of dards, delicate thread-like structures which extend obliquely outwards from the rachis. In an uninjured feather the barbs are closely connected so as to form a con- tinuous sheet, but a moderate amount of force separates them from one another, and it can readily be made out with the aid of a magnifying glass that they are bound together by extremely delicate oblique filaments, the dardudes, having the same general relation to the barbs as the barbs themselves to the rachis. Adjacent barbules interlock by means of a system of min- ute hooklets and flanges, and in this way the parts of the feather are so bound together that the entire structure offers great resistance to the air. Among the contour feathers which form the main cover- ing of the bird and have the structure just described, are found filoplumes (Fig. 274, B), delicate hair-like feathers having a long axis and a few barbs, devoid of locking apparatus, at the distal end. Nestling pigeons are covered with a temporary investment of down feathers (C), in which also there is no interlocking of the barbs: when these first appear each is covered by a horny sheath like a glove finger. Feathers, like scales, arise in the embryo from papille of. the skin formed of derm with an epidermal covering. The papilla becomes sunk in a sac, the /eather-follicle, from 462 MANUAL OF ZOOLOGY SECT. which it subsequently protrudes as an elongated feather-gerim, its vascular dermal interior being the /eather-pulp. The horny substance of the feather is formed from the epidermis of the feather-germ. The feathers do not spring uniformly from the whole sur- face of the body, but from certain defined areas (Fig. 275), Fic, 275.— Pterylosis of Columba livia. A, ventral: B, dorsal. a@/. At, alar pteryla or wing-tract; ¢. pz, cephalic pteryla or head-tract: cd. At, caudal pteryla or tail-tract; cr fz, crural pteryla; cv. aft, cervical apterium or neck- space; f/m. ft, femoral pteryla; Az. ft, humeral pteryla; /a¢ aft, lateral apterium; sf f#, spinal pteryla; 7. af¢, ventral apterium; 7 £é, ventral pteryla. (After Nitsch.) the feather tracts or preryle (sp. pt, hu. pi, etc.), separated from one another by featherless spaces or apseria (v. aft, etc.), from which only a few filoplumes grow. In the wings and tail certain special arrangements of the feathers are to be distinguished. When the wing is stretched XU PHYLUM CHORDATA 463 out at right angles to the trunk, twenty-three large feathers (Fig. 273) are seen to spring from its hinder or post-axial border: these are the remiges or wing-quills. Twelve of them are connected with the ulna and are called cuditals or secondaries (cb. rmg). The rest are known as primaries. In the tail there are twelve long rectrices (rc¢) or tail-quills springing in a semicircle from the uropygium. The whole feather-arrangement is known as the peerylosis. car Fic. 276.—Columba livia. The bones of the trunk. acy. cov, acrocoracoid; a. tr, anti-trochanter; ac¢éé, acetabulum; car, carina sterni; cd. v, caudal verte- br; cor, coracoid; cv. 7, cervical ribs; f ¢vs, probe passed into foramen triosseum; fxr, furcula; gi. cv, glenoid cavity; 2, ilium; 7s, ischium; 7s. for, ischiatic foramen; od¢, x, obturator notch; px, pubis; pyg. st, pygostyle; scp. scapula; s. sc, syn-sacrum; sz, sternum; sz. r, sternal ribs; th. wT, first, and th. u. 5, last thoracic vertebra; zc, uncinates; vr. 7, vertebral ribs. The vertebral column is distinguished from that of most other Craniata by the great length and extreme mobility of the neck, the rigidity of the trunk region, and the shortness of the tail. There are fourteen cervical vertebre, the last two of which have double-headed ribs (Fig. 276, cv. 7) each 464 MANUAL OF ZOOLOGY SECT. having its proximal end divisible into the Aead proper articu- lating with the centrum of the vertebra, and a ¢wberc/e with the transverse process: their distal ends are free, not uniting with the sternum. In the third to the twelfth there are vestigial ribs (Fig. 277, 78), each having its head fused with the centrum, and its tubercle with the transverse process. The whole rib thus has the appearance of a short, backwardly directed transverse process perforated at its base. The centra of the cervical vertebre differ from those of all other Vertebrata in having saddle-shaped surfaces, the anterior face (Fig. 277, A) being concave from side to side and convex from above downwards. This peculiar form of vertebra is distinguished as heteroce/lous. The first two vertebra, the atlas and axis, are specially modified. The atlas is a ring- like bone with an articulation on its anterior surface for the single occipital condyle of the skull. ie. aye alata Tela Rae The ands has projecting forwards vical vertebra; A, anterior; from its centrum, a peg-like pro- B, posterior face. a. cyyy an- terior zygapophysis; cv, cen- cess, the odontoid process, which trum; z.@,neural arch; fp. syg, posterior zygapophysis: 7, b; lies in the lower part of the ring vrb. f, vertebrarterial foramen. of the atlas. Between the last cervical vertebra and the pelvic region come four thoracic vertebrae (Fig. 276), the first three united into a single mass, the fourth free. They all bear ribs, each consisting of a vertebral (7. 7) and a sternal (s¢. 7) portion, and articulating with the vertebra by a double head. Springing from the posterior edge of the vertebral rib is an uncinaze (Fig. 276, wc), resembling that of Hatteria XII PHYLUM CHORDATA 465 and the crocodile, but formed of bone and ankylosed with the rib. Following upon the fourth thoracic are about twelve vertebrz all fused into a single mass (Fig. 276, s. sev), and giving attachment laterally to the immense pelvic girdle. The whole of this group of vertebra has, therefore, the function of a sacrum, differing from that of a reptile in the large number of vertebrae composing it. The first of them bears a pair of free ribs, and is, therefore, the fifth or last thoracic (¢4. v. 5). The next five or six have no free ribs, and may be looked upon as lumbar (Fig. 278, /'—s*). Fic. 278.—Columba livia. Sac- Next come two sacral vertebre rum of a nestling (about 5 fourteen days old), ventral (c') homologous with those of aspect. cl, centrum of first 7 anal sacral vertebra; c!, centrum of the lizard. The remaining five fifth caudal; c. 7, first sacral : : rib; 21, centrum of first lumbar; vertebra of the pelvic region are 2, of third lumbar; s?, of fourth lumbar; s, of sixth lumbar; caudal. Thus the mass of ver- zr. p, transverse process of i : ‘ first lumbar; ¢7. ', of fifth tebrae supporting the pelvic girdle lumbar; ¢ #", of first sacral. :d 5 , (From Parker’s Zootomy.) in the pigeon is a compound sacrum, or syz-sacrum, formed by the fusion of the posterior thoracic, all the lumbar and sacral, and the anterior caudal vertebrae. The syn-sacrum i¢ followed by six free caudals and the vertebral column ends posteriorly in an upturned, compressed bone, the pygost/e or ploughshare-bone (Fig. 276, pyg. sé), formed by the fusion of four or more of the hindermost caudal vertebre. The sternum (Fig. 276, st) is one of the most character- 2H 466 MANUAL OF ZOOLOGY SECT. istic parts of the bird’s skeleton. It is a broad plate of bone produced ventrally, in the sagittal plane, into a deep keel or carina sterni (car), formed, in the young bird, from a separate centre of ossification. The posterior border of the sternum presents two pairs of notches, covered, in the recent state, Fic. 279. —Columba livia. Skull of young specimen. A, dorsal; B, ventral; C, left side. ad. s, alisphenoid; ax, angular; av, articular; 4 0, basi-occipital ; d. dentary; ¢. 0, ex-occipital; ex, aperture of Eustachian tube; f. », foramen magnum; /r, frontal; 2.0, s, inter-orbital septum; jz, jugal; Zc, lachrymal; /. s, lambdoidal suture; ». eff, mesethmoid; wa, maxilla; mx ?, maxillo-palatine process; wa, wa’, na"', nasal; 0. c, occipital condyle; or. Jr, orbital plate of frontal; fa, parietal; fa. s, parasphenoid (rostrum); Pi, palatine: p wx, pre- maxilla; p/, pterygoid; gz, quadrate; s. az, supra-angular; s 0, supra-occipital * sg, squamosal; ¢y, tympanic cavity; II.—XII, foramina for cerebral nerves. (From Parker’s Zootomy.) XII PHYLUM CHORDATA 467 by ligament; its anterior edge bears a pair of deep grooves for the articulation of the coracoids. The skudl (Fig. 279) is distinguished at once by its rounded brain-case, immense orbits, and long pointed beak. The foramen magnum (f #) looks downwards as well as backwards, so as to be visible in a ventral view, and on its anterior margin is a single, small, rounded, occipital condyle (0. ¢). Most of the bones, both of the cranial and facial regions, are firmly ankylosed in the adult, and can be made out only in the young bird. The premaxille (Fig. 279, £. mx) are united into a large triradiate bone which forms practically the whole of the upper beak. The maxille (Fig. 279, mx), on the other hand, are small, and have their anterior ends produced inwards into spongy maxzllo- palatine processes (Fig. 279, mx.p). The slender poste- rior end of the maxilla is continued backwards by an equally slender jugal (jz) and quadrato - jugal to the quadrate. The latter (Fig. 279, g#) is a stout three- rayed bone articulating by fic. 280 --Columbia livia. Hyoid ap- : paratus. The cart:laginous parts are two facets with the roof dotted. 4. 4.7, basi-branchials; 4 Ay, : : si-hyal; c. dr, -b hial; of the tympanic cavity, and ee ae ae Bee ep : branchial. presenting below a condyle for articulation with the mandible: the mandible of the young bird consists of a cartilage bone, the articular (Fig. 279, ar), and four membrane bones, which all coalesce in the 468 MANUAL OF ZOOLOGY SECT. adult. The hyoid apparatus (Fig. 280), is of characteristic form, having an arrow-shaped body (é. 4) with a short pair of anterior cornua (¢c. Ay) derived from the hyoid arch, and a long pair of posterior cornua (¢. 7., ep. dr) from the first branchial. The colu- mella is a rod-shaped bone ankylosed to the stapes, anc bearing at its outer end a three- rayed cartilage or ex- tra-columella fixed to the tympanic mem- brane. The showlder-girdle (Fig. 276) is quite un- like that of other Cra- niates. There is a pair of stout, pillar - like coracoids (cor) articu- lating with deep facets on the anterior border of the sternum and directed upwards, for- wards, and outwards. The dorsal end of each is produced into an acrocoracoid — process (acer. cor), and below this, to the posterior Fic. 281. Columba livia. Skeleton of the left aspect of the bone, is wing. cp. métcp, carpo-metacarpus; Az, hu- 2 merus; pf.z, phalanx of first digit; #i.2', attached by ligament a Ota Stel die Cee eke sabre-shaped scapula foramen: va, radius; va’, radiale; #2, ulna; ud’, ulnare. (scp) which extends xu PHYLUM CHORDATA 469 backwards over the ribs, and includes, with the coracoid, an acute angle, the coraco-scapular angle. The glenoid cavity (g/. cv) is formed in equal proportion by the two bones ; in- ternal to it the scapula is produced into an acromion process. In front of the coracoids is a slender V-shaped bone, the Jurcula (fur) or “ merrythought,” the apex of which nearly reaches the sternum, while each of its extremities is attached by ligament to the acromion and acro-coracoid processes of the corresponding side in such a way that a large aper- ture, the foramen triosseum (7. trs) is left between the three bones of the shoulder- girdle. The furcula is a mem- brane bone and_ represents fused’ clavicles and __inter- clavicle. Equally characteristic is the skeleton of the fore-limb. The humerus (Fig. 281, hw) is a large, strong bone, with a greatly expanded head and a prominent ridge for the in- ye. 282, — Columba livia. Left manus sertion o: the pectoral muscle. nit Ca ee The radius (ra) is slender ©: 2, ulnare; cp 1. 2,3, meta carpals; #4. 7, phalanx of first digit; and nearly straight, the nina 2fJ-o%-4> palene’s of second stouter and gently curved. Sys bas ulna. “(Eom There are two large free car- pals, a radiate (ra') and an wlnare (w/'), and articulating with these is a bone called the carpo-metacarpus (cp. micp), consisting of two rods, that on the preaxial side strong and nearly straight, that on the postaxial side slender and curved, fused with one another at both their proximal and distal 470 MANUAL OF ZOOLOGY SECT. ends; the proximal end is produced pre-axially, into an outstanding step-like process. The study of its development shows that this bone is formed by the union of the distal carpals with three meta- carpals (Fig. 282), the second and third of which are the two rod-like portions of the bone, the first, the step-like projection. Articulating with the first nfetacarpal is a single pointed phalanx (ff. 7); the second metacarpal bears two phalanges, the proximal one ( p#. 2') produced postaxially into a flange, the distal one (pA. 2") pointed; the third metacarpal bears a single pointed phalanx (fA. 3). ac ae olf % pu Fic. 283.— Columba livia. Left innominate of a nestling. The cartilage is dotted. ac, acetabulum; a. ¢v, anti-trochanter; 77, pre-acetabular; and 27’, post-acetab- ular portion of ilium: zs, ischium; 7 s. f, ischiatic foramen; 0d. /, obturator notch; gz, pubis. (From Parker’s Zootomy.) The pelvic girdle (Fig. 283). The sium (i7) is an immense bone, attached by fibrous union with the whole of the syn-sacrum and becoming ankylosed with it in the adult. As usual it furnishes the dorsal portion of the acetab- ulum. The ventral portion of the acetabulum is furnished in about equal proportions by the pubis and ischium (Fig. 283): it is not completely closed by bone, but is perforated by an aperture covered by membrane in the recent state. Both pubis and ischium are directed sharply XII PHYLUM CHORDATA 471 backwards from their dorsal or acetabular ends, and lie nearly parallel. Neither is- chium nor pubis unites ven- trally with its fellow to form a symphysis. In the hind-limb the femur (Fig. 284, fe) is a compara- tively short bone. Its proxi- mal extremity bears a promi- nent frochanter (tr) and a rounded head (Ad). Its dis- tant end is produced into pulley-like condyles. Articu- lating with the femur is a very long bone, the 7#z0- tarsus (#. ts) ; its distal end is pulley-like, not concave like the corresponding ex- tremity of the tibia of other Amniota. The study of its development shows that the pulley-like distal end of the bone (Fig. 285, #') con- sists of the proximal tarsals, —astragalus and calcaneum, —which at an early period unite with the tibia and give rise to the compound shank- bone of the adult. The dua (Fig. 284, 7%) is very small, much shorter than the tibia, and tapers to a point at its distal end. e, femur; 7, fibula; 2d, head; mtts.7, rth digit; ¢z. ¢s, tibio-tarsus; ts. wztts, Bones of the left hind-limb. cx. 7, cnemial process; first metatarsal; Aas, patella; A. 7, phalanx of first digit; A%. 4, phalanx of fou tarso-metatarsus; ¢”, trochanter. Fic. 284. — Columba livia. 472 MANUAL OF ZOOLOGY SECT. Following the tibio-tarsus is an elongated bone, the zarso- metatarsus (ts. mitts), presenting at its proximal end a con- cave surface for the tibio-tarsus, and at its distal end three distinct pulleys for the articulation of the three forwardly directed toes. In the young bird the proximal end of this bone is a separate cartilage (Fig. 285, #°), repre- senting the distal tarsals, and followed by three distinct metatarsals, belonging respectively to the second, third, and fourth digits. To the inner or preaxial side of the tarso-metatarsus, near its distal end, is attached by fibrous tissue a small irregular bone, the first metatarsal (md¢¢s.z). The back- wardly directed hallux has two pha- langes, the second or inner toe three, the third or middle toe four, and the fourth or outer toe five. In all four digits the distal or ungual Fic. 28s. — Columba livia, phalanx is pointed and curved, and Part of left foot of a: “ hatched embryo (magni. Serves for the support of the horny fied). The cartilage is dotted’: onils ss seconds “Glas mil. 3, third; and wl. 4, +e : fourth metatarsal dictibies A further peculiarity is the fact ae aes | «that the larger proportion of the oa ee (From Parker's bones contain no marrow, but are filled during life with air, and are therefore said to be pneumatic. The cavities of the various bones open externally in the dried skeleton by apertures called pneumatic foramina (Fig. 281, pn. for), by which, in the entire bird, they communicate with the air-sacs (vide infra). As might naturally be expected, the muscles of the fore- limb are greatly modified. ‘The powerful downstroke of the XII PHYLUM CHORDATA 473 wing, by which the bird rises into and propels itself through the air, is performed by the fectoradis (Fig. 286, pct), an immense muscle having about one-fifth the total weight of the body; it arises from the whole of the keel of the sternum (car. s¢), from the posterior part of the body of hu Fee prpligm probe na lg tnsbr lnsace |jextep.rd Pralg Fic. 286.— Columba livia. The principal muscles of the left wing; the greater part of the pectoralis (fcz) is removed. car. st, carina sterni; c/, furcula; cor, coracoid; cor. dr. br, coraco-brachialis brevis: cor. br, lg, coraco- brach’alis longus; ¢f. s¢, corpus sterni; ext. cp. rd, extensor carpi radialis; ext. cp. x/, extensor carpi ulnaris; 77. cf, w/. flexor carpi ulnaris; g?. c, glenoid cavity; an, head of humerus; /z’, its distal end; Act, pectoralis; Act’ , its cut edge: pct’’, its insertion; prx. br, pronator brevis: fr. ig, pronator longus; pr. plgm, pre- patagium; A¢. _pigm, post-patagium; sd c/z, sub-clavius; sé. clv’, its tendon of insertion passing through the foramen triosseum, and dotted as it goes to the humerus; és. acc, tensor accessorius; 75. ér, tensor brevis; ¢us. lg, tensor longus; Zs. 2. f, tensor membrane posterioris alz. that bone (cf. s¢), and from the clavicle (¢2), filling nearly the whole of the wedge-shaped space between the body and the keel of the sternum, and forming what is commonly called the “breast” of the bird. Its fibres converge to their insertion (fc?') into the ventral aspect of the humerus 474 MANUAL OF ZOOLOGY SECT. XII (hu, hu'), which it depresses. The elevation of the wing is performed, not, as might be expected, by a dorsally placed muscle, but by the swvdb-clavius (sb. cv), arising from the anterior part of the body of the sternum, dorsal to the pectoralis, and sending its tendon (sd. c/z') through the foramen triosseum to be inserted into the dorsal aspect of the humerus. In virtue of this arrangement, the end of the foramen acting like a pulley, the direction of action of the muscle is changed, the backward pull of the tendon raising the humerus. Digestive Organs. — The mouth (Fig. 287) is bounded above and below by the horny beaks, and there is no trace of teeth. The congue (tng) is large and pointed at the tip. The pharynx leads into a wide and distensible gu//et (gud), which soon dilates into an immense reservoir or crop (crp) situated at the base of the neck, between the skin and the muscles and immediately in front of the sternum. In this cavity the food, consisting of grain, undergoes a process of maceration before being passed into the stomach. From the crop the gullet is continued backwards into the stomach, which consists of two parts, the proventriculus (pron) and the gissard (giz). The proventriculus appears externally like a slight dilatation of the gullet, but its mucous mem- brane is very thick and contains numerous gastric glands so large as to be visible to the naked eye. The gizzard has the shape of a biconvex lens; its walls are very thick and its lumen small. The thickening is due mainly to the im- mense development of the muscles which radiate from two tendons, one on each of the convex surfaces. The epi- thelial lining of the gizzard is very thick and horny, and of a yellow or green colour: its cavity always contains small stones, which are swallowed by the bird to aid the gizzard in grinding up the food. Fic. 287. Columba livia. Dissection from the right side. The body-wall, with the vertebral column, sternum, brain, etc., are in sagittal section; portions of the gullet and crop are cut away and the cloaca is opened; nearly the whole of the ilium is removed, and the duodenum is displaced outwards. @. ao, aortic arch; bd. 1, bd. 2, dvile-ducts; &. fadr, bursa Fabricii; cé/, cerebellum; ce, right coecum; cfdm, coprodeum; cr, cere; crd. h, left cerebral hemisphere; crf, crop; cv. v. 7, first cervical vertebre; dz. cw, diacele; dwt, dentary; duo, duodenum; ezs. af, aperture of Eustachian tubes; g7z, gizzard (dotted behind the liver); g?, glottis; gw/, gullet; Zz, ilium: 72. 0d. sf, inter-orbital septum; Ad, right kidney; dwg, right lung; Z~, liver (right lobe); ma, bristle passed from nostril into mouth; 042. sep, oblique septum; o. g/, oil gland; ped, pericardium; pmx, pre-maxilla; fx, pancreas; px. 6, pineal body; pzd. 1-3, pancreatic ducts; pv. cv, right pre-caval; prdm, proctodeum; fry, proventriculus (dotted behind liver); At. cv, post-caval; pty. 6, pituitary body: Ayg. st, pygo- style; 7. az, right auricle; ». dr, right bronchus; rect, rectum; 7 vut, right ventricle; sf. cd, spinal cord; sf/, spleen (dotted behind liver); s. 724, sinus rhomboidalis; s. scr, syn-sacrum; s¢, carina sterni; syx, syrinx; ¢. v. JZ, first, and th. v. 5, fifth thoracic vertebrae: ‘ug, tongue: fr, trachea; fs, right testis; ur, aperture of left ureter; ~7dm, urodxum; v. d/, aperture of left vas deferens, 475 476 MANUAL OF ZOOLOGY SECT. The duodenum (duo) leaves the gizzard quite close to the entrance of the proventriculus and forms a distinct loop enclosing the pancreas. The rest of the small intestine is called the zm (z/m) : it passes without change of diameter into the rectum or large intestine (rcZ), the junction between the two being marked only by a pair of small blind pouches or ceca (cw). The c/oaca is a large chamber divided into three compartments. There are small dvece/ glands opening into the mouth, but none that can be called salivary. The Aver (/) is large, and is divisible into right and left lobes, each opening by its own duct (4. d@. 7, 6. d. 2), into the duodenum: there is no gall bladder. The pancreas (pf) is a compact reddish gland lying in the loop of the duodenum, into which it discharges its secretion by three ducts (fz. d. z~7). A thick-walled glandular pouch, the dursa Fabric (6. fabr), lies against the dorsal wall of the cloaca in young birds, and opens into the cloaca: it atrophies in the adult. The spleen (sf/) is an ovoid red body, of unusually small proportional size, attached by peritoneum to the right side of the proventriculus. There are paired ¢hyrords at the base of the neck ; and, in young pigeons, there is an elongated thymus on each side of the neck. The adrenals (Fig. 292, adr) are irregular yellow bodies placed at the anterior ends of the kidneys. The glottis (Fig. 287, g/) is situated just behind the root of the tongue and leads into the Zavux, which is supported by cartilages, but does not, as in other vertebrates, function as the organ of voice. From the larynx an elongated tube, the ¢rachea or windpipe, the wall of which is supported by numerous bony rings, runs back along the ventral aspect of the neck to enter the body-cavity, where it divides into the right (7. 47) and left dronchz, one passing to each of the lungs. XI PHYLUM CHORDATA 477 At the junction of the trachea with the bronchi is found the characteristic vocal organ, the sy7x (s)"), occurring in no other class. The dungs (Fig. 287, /ug) are very small in comparison with the size of the bird, and are but slightly distensible, being solid, spongy organs, not mere bags with sacculated walls, as in Amphibia and many reptiles. Their dorsal sur- faces fit closely into the spaces between the ribs and have no peritoneal covering ; their ventral faces are covered by a strong sheet of fibrous tissue, the pu/monary aponeurosis or pleura, a special development of the peritoneum. Into this membrane are inserted small, fan-like costo-pulmonary mus- cles, which arise from the junction of the vertebral and sternal ribs. Each main bronchus gives off secondary bronchi, and these branch again, sending off tubes which end blindly near the surface of the lung and give off blind dilations commonly known as alveo#. In addition to these, each main bronchus also gives off branches which end in a series of thin-walled air-sacs, which lie in the body-cavity, and are in communi- cation with the pneumatic cavities of the bones. The Acar? (Fig. 288) is of great proportional size, and like that of the crocodile consists of four chambers, 2.¢., the right and left auricles, and right and left ventricles. There is no sinus venosus, that chamber being, as it were, absorbed into the right auricle (Fig. 288, A, 7. av). The right ventricle (Fig. 288, B) partly encircles the left, the former having a crescentic, the latter a circular cavity in transverse sections. The left auriculo-ventricular valve has the usual membranous structure consisting of two flaps connccted with the wall of the ventricle by tendons, but the corresponding valve of the right side (R. V) is a large muscular fold, very characteristic of the class. 478 MANUAL OF ZOOLOGY SECT. The right auricle receives the right and left pre-cavals (x. pre, 1. pre) and the post-caval ( pzc), the left, four large pulmonary veins (f. 7). The left ventricle (Fig. 288, 2 v7), as in the crocodile, gives origin to the right aortic arch (a. ae), but the right ventricle (7. vz) gives off only one trunk, the pulmonary artery, which soon divides into two TUN Fic. 288.—A, heart of the pigeon, dorsal aspect. @. ao, arch of aorta; 4”. a, brachial artery; 4>. 7, brachial vein; ¢.c, common carotid: 77, jugular; 2. az, left auricle; 2. 2 a, left pulmonary artery; /. 7, left ventricle; pe. v, left pre- caval; fic, post- caval: é 7, pulmonary veins; 7. av. x. az’, right auricle; 7 pa, right pulmonary artery; 7. pre, right pre- caval: run, right ventricle. B, heart of a bird with the right ventricle opened L. Vv, septum ventriculorum; R. Ni right ventricle; V, right auriculo-ventricular valve, (A, from Parker’s Zootomy; B, from Headley’ s Birds.) (7. p.a.,2p.a). The left aortic arch is absent in the adult, and it is the right alone which is continued into the dorsal aorta. The result of this is that the systemic arteries re- ceive pure arterial blood from the left side of the heart, and the only mingling of aérated and non-aérated blood is in the Xu PHYLUM CHORDATA 479 capillaries. This is perhaps the most important physiologi- cal advance made by birds over reptiles. The aortic arch curves over the right bronchus to reach the dorsal body-wall, and then passes directly backwards as the dorsal aorta. Fic 289.— Columba liyia The brain; A, from above; B, from below; C, from the left side. cé, cerebellum; c. 4, cerebral hemispheres; 7, flocculus; 7%/, in- fundibulum; 2. 0, medulla oblongata; 0. /, optic lobes; o. ¢, optic tracts; pz, pineal body; II-XIII, cerebral nerves; sf. 7, first spinal nerve. (From Parker’s Zootomy.) The Jvacn completely fills the cranial cavity, and is re- markable for its short, broad, rounded form. The cerebellum 480 MANUAL OF ZOOLOGY SECT. (Fig. 289, ¢. 2) is of great size, and has a large median portion and two small lateral lobes or floccud’ (7) ; the surface of the middle lobe is marked by grooves passing inwards in a radiating manner and carrying with them the grey matter, the extent of which is thus greatly increased. The hemz- Spheres (c. h) extend backwards to meet the cerebellum, and the optic lobes (0. 2) are thereby pressed outwards so as to take up a lateral instead of the usual dorsal position. Fic. 290 — The eye. A, in sagittal section; B, the entire organ, external aspect; cn, cornea; ch, choroid; c?. pr, ciliary processes; zr, iris; 2, lens; off nv, optic nerve; pct, pecten; 77, retina; sc/, sclerotic; seZ. p/, sclerotic plates. (After Vogt and Yung.) The ere (Fig. 290) is not even approximately globular, but has the form of a biconvex lens. Sclerotic plates are present, and there is a large fccf’ in the form of a plaited and strongly pigmented membrane projecting into XII PHYLUM CHORDATA 481 the cavity of the eye from the entrance of the optic nerve. The auditory organ (Fig. 291) is chiefly distinguished from that of reptiles by the great development of the coch/ra. The tympanic cavity and columella have the same arrange- ment as in the frog; the narrow Eustachian tubes open by a common aperture (Fig. 287, eus. ap) in the roof of the pharynx. The Aidneys (Fig. 287, 2d, Figs. 292 and 293, &) have a very characteristic form. Each is a flattened organ divided into three main lobes and fitted closely into the hollows of the pelvis. The ureters (ur) are narrow tubes passing directly backwards to open into the middle compart- ment, or the cloaca. The destes (Figs. 287 and 292, Fic. 291.— Columba livia. The 3 : ‘ right membranous labyrinth, zs) are ovoid bodies, varying greatly in size according to the season, attached by the perito- neum to the ventral surfaces of the anterior ends of the kidneys. From the inner border of each outer aspect; FA, ampulla of posterior canal; FB, posterior canal: HA, ampulla of hori- zontal canal; AB, horizontal canal; Zag, cochlea or lagena; mr, membrane of Reissner; ph, basilar part of cochlea; S, sacculus; SA, ampulla of anterior canal; SZ, anterior (canal. From Wiedersheim, af- ter Hasse.) goes off a convoluted vas def- erens (va@), which passes backwards, parallel with the ureter, to open into the cloaca on the extremity of a small papilla. The posterior end of the spermiduct is slightly enlarged to form a vesicwla seminalis (v.s). The female organs (Fig. 293) are remarkable for the more or less complete atrophy of the right ovary and oviduct. 21 482 MANUAL OF ZOOLOGY SECT. The £/f ovary (ov) is a large organ in the adult bird, its surface studded with follicles or ovisacs, varying in size from about 15 mm. in diameter downwards, and each containing a single ovum. The “ff oviduct (2 od) is long and convoluted ; its anterior end is enlarged to form a wide, membranous ccelomic funnel (Z od@") into which the Fic. 292,—Columba livia Male Fic. 293. —Columba livia. Female urino- urino-genital organs. adr, ad- genital organs. c/.2, urodeum; cd. 3, renal; cZ 2, urodeum; c¢/ 3, proctodzum; &, kidney; ¢. od, left ovi- proctodaum; 4, kidney; Zs, duct; ¢. od’, its cloacal aperture; 2. od'', testis, that of the right side dis- its coelomic funnel; 2. od''', its coelomic placed; », ureter; wr’, aper- aperture; ov, ovary; ». od, right oviduct; ture of ureter; wa, vas deferens; vr. od', its cloacal aperture: 27, ureter; va’, its cloacal aperture; 7. s, ur’, its cloacal aperture, (From Parker’s vesicula seminalis, (From Par- Zootomry.) ker’s Zootomy.) ripe ova pass on their liberation from the ovisacs ; the rest of the tube has thick, muscular walls, lined with glandular epithelium, and opens into the urodeum. Internal impregnation takes place. As the ova or XII PHYLUM CHORDATA 483 “yolks” pass down the oviduct, they are invested with the secretions of its various glands ; first with layers of a/éumen or “ white,”’ next with a parchment-like shell-membrane, and lastly with a white calcareous she//. They are laid, two at a time, in a rough nest, and are ¢zcubazed or sat upon by the parents for fourteen days, the temperature being in this way kept at about 40° C. (104° F.). At the end of incubation the young bird is sufficiently developed to break the shell and begin free life. It is covered with fine down, and is fed by the parents with a secretion from the crop, the so-called “ pigeon’s milk.” Of recent birds two main divisions are recognised — the Ratitee and the Carinate — the former comprising only the emus (Dromeus), cassowaries (Casvartus), and kiwis (Apeeryx), the South American ostriches (Aea), and the true ostriches (S/ru¢hio) ; and the latter including all the rest. One of the most characteristic features of birds in general is the covering of feathers — peculiar epidermal structures which differ widely in shape and arrangement from their equivalents, the horny scales of reptiles and the hairs of mammals. The arrangement of the feathers follows closely that briefly described as observable in the pigeon, with great diversity in detail. The distribution of the contour feathers in feather tracts or pteryle separated from one another by featherless tracts or afferta is almost universal in the Carinatee, but is not distinguishable in the Ratite except in the young condition. In many birds each feather has a secondary vein or after-shaft, as it is termed, springing from the main shaft near the umbilicus, and sometimes (Fig. 294) this may be as large as the main shaft itself. A shedding or “moulting” of the feathers takes place at regular intervals, usually annually —a new set of feathers growing from the pulps of the old ones. 484 op n> SN % os Uses (Osos CG boos So MANUAL OF ZOOLOGY SECT. (From Headley.) Feather, showing after-shaft and disconnected barbs. Fic. 294. —Casuarius (Cassowary). The colours of feathers present great variety. Black, brown, red, orange, and yellow colours are due to the pres- ence of definite pigments, ze. are absorption colours. White, and in some cases yellow, is produced by the total reflection of light from the spongy, air- containing substance of the feather, there being, as in nearly all other natu- ral objects, no such thing as a white pigment. Blue, violet, and in some cases green, are produced by the light from a brown pigment becoming bro- ken up as it passes through the super- ficial layer of the feathers in its passage to the eye; no blue or violet pigments occur in feathers, and green pigments are very rare. The beautiful metallic tints of many birds are entirely the result of structure, owing their existence to a thin, transparent, superficial layer, which acts as a prism: in such feathers the colour changes according to the relative position of the bird and of the eye of the observer with regard to the source of light. There is also infinite variety in the general coloration of birds. In many the colouring is distinctly protective, harmonising with the environment, and even changing with the latter, as in the ptarmigan, which is greyish brown in summer, white in winter, the former XII PHYLUM CHORDATA 485 hue helping to conceal the bird among herbage, the latter on snow. Frequently, as in pheasants and birds of paradise, the female alone is protectively coloured, while the male presents the most varied and brilliant tints enhanced by crests, plumes or tufts of feathers on the wings, elongated tail, etc. etc. These have been variously explained as “ courtship colours” for attracting the female; as due simply to the exuberant vitality of the male bird, or as helping to keep the number of males within proper limits by rendering them conspicuous to their enemies. Such ornaments as the bars and spots on the wings and tail of many gregarious birds, such as plovers, fully exposed only during flight, and often widely different in closely allied species, have been explained as “ recog- nition marks,” serving to enable stragglers to distinguish between a flock of their own and of some other species. The toothless jaws with the horny sheaths forming the bill are universal in the class. But the dimensions and form of the bill vary very widely in different groups of birds. It may be extremely short and wide for catching moths and other flying insects, as in swifts and goatsuckers ; short and conical for eating fruit, as in finches; strongly hooked for tearing the bodies of animals, as in birds of prey, or for rending fruits of various kinds, as in parrots ; long, conical, and of great strength, as in storks; slender and elongated, as in swifts, ibises, and curlews; broad and flattened for feeding in mud, as in ducks and geese; expanded at the end, as in spoonbills; immensely enlarged, as in hornbills and toucans. It is most commonly bent downwards at the tip, but may be straight or curved upwards, as in the avocet, or bent to one side, as in the New Zealand crook-billed plover. It is sometimes, as in the toucans, brilliantly coloured, and there may also be bright coloration of the cere, as in the macaws, and of naked spaces on the head, 486 MANUAL OF ZOOLOGY SECT, as in the cassowaries. In the latter the head is produced into a great horny prominence or “ casque,” supported by an elevation of the roof of the skull. The cere is frequently absent. The nostrils are placed at the base of the beak, except in Apteryx, in which they are at the tip. The essential structure of the wing — apart from its feathers —is very uniform. As a rule all three digits are devoid of claws, as in the pigeon, but the ostrich has claws on all Fic. 295 — A, wing of nestling of Opisthocomus ; B, wing of adult Apteryx both from the inner (ventral) aspect; cd, z, first cubital remex; dg. 1, dg. 2, dg. 3, digits; pr. pig, pre-patagium; pz, Ag, post-patagium. (A, after Pycraft; B, after T. J. Parker.) three digits; rhea on the first, and sometimes the second and third; the cassowary, emu, and kiwi (Fig. 295, B) on the second; and the crested screamer (Chauna) and two other species, and, as a rare abnormality, the common fowl and the goose, on the first. With these exceptions, the XII PHYLUM CHORDATA 487 hand of the adult bird has lost all the characters of a fore- foot ; but in the young of the hoatzin ( Opisthocomus) claws are present on the first two digits (Fig. 295, A), which are sufficiently mobile to be used in climbing. Besides the true claws, horny spurs are sometimes present on the carpus and metacarpus. There is almost every gradation in the proportional length of the hind-limb, from birds in which nothing but the foot projects beyond the contour feathers, and even the toes may be feathered, to the long-legged storks and cranes, in which the distal part of the tibio-tarsus is covered with scales as well as the foot. In aquatic forms a fold of skin or wed is stretched between the toes, sometimes including all four digits, as in the cormorants ; sometimes leaving the hallux free, sometimes forming a separate fringe to each digit, as in the coots and grebes. As to the toes them- selves, the commonest arrangement is for the hallux to be directed backwards, and Nos. 2, 3, and 4 forwards, but in the owls No. 4 is reversible, ze. can be turned in either direction, and in the parrots, woodpeckers, etc., it, as well as the hallux, is permanently turned backwards. In the swifts, on the other hand, all four toes turn forwards. The hallux is frequently vestigial or absent, and in the ostrich No. 4 has also atrophied, producing the characteristic two- toed foot of that bird. The following are the most essential general features of the skeleton of birds. More or fewer vertebrz from the regions in front of and behind the sacral fuse with the true sacral vertebree to form the composite syn-sacrum. The posterior caudal vertebra are fused together to form a pygostyle. The bones of the skull early unite, the sutures becoming entirely obliterated. There is a single rounded occipital condyle. The premaxillae are very large and form the 488 MANUAL OF ZOOLOGY : SECT. greater part of the upper jaw. The sternum is broad, and is usually provided with a prominent keel or carina as in the pigeon, but the carina is absent in the Ratite, and is rudimentary or absent in some flightless Carinate. The clavicles and interclavicle unite to form a furcula. The distal carpals and metacarpals unite to form a carpo- metacarpus. The pubes and ischia run downwards and backwards parallel with one another; and neither the pubes nor the ischia unite in a symphysis, but remain widely separated at their distal ends, except in the ostrich, in which the pubes unite distally, and the South American ostriches in which the ischia unite while the pubes remain free. Universally characteristic of the skeleton of the hind- limb is the union of the tibia with the proximal element of the tarsus to form a tibio-tarsus, and of the distal element of the tarsus with the second, third, and fourth metatarsals to form a tarso-metatarsus, the ankle-joint being situated between these bones. The skeleton always contains air- cavities to a greater or less extent. The presence of crop, proventriculus, and gizzard, as in the pigeon, is universal among birds. The gizzard is most powerful in grain-eating birds, thinner-walled in flesh-eaters. There is a pair of cceca in most birds at the junction of the large and small intestines. The voice of birds is always produced not in the larynx, as in other higher vertebrates, but in a syrinx situated either, as in the pigeon, at the junction of the trachea and bronchi, or at the anterior ends of the bronchi, or the posterior end of the trachea. The system of air-sacs connected with the bronchi described in the account of the pigeon is of universal occurrence. The temperature of the blood is always high. The heart in all has the same main features as in the pigeon: it has four distinct chambers, two auricles and two ventricles, and XII PHYLUM CHORDATA 489 there is a single aortic arch, situated on the right side. In the brain the most characteristic points’ are the short rounded hemispheres, the large folded cerebellum produced forwards to meet the hemispheres, and the laterally placed optic lobes. The internal ear has a large curved cgchlea, and the eye has a pecten. The right ovary and oviduct are more or less completely aborted. Fic. 296. —Gallus bankiva (domestic fowl). Semi-diagrammatic view of the egg at the time of hatching. a, air-space; a/4, dense layer of albumen; 2/6’, more fluid albumen; 4/, blastoderm; c&, chalaza; sh, shell; sh. m, shell-membrane; sh. 1, sh, 2, its two layers separated to enclose air-cavity. (From Marshall’s Embryology, slightly altered.) The ovum is always large, owing to the great quantity of food-yolk ; the protoplasm forms a small germinal disc at one pole. Impregnation is internal, and as the incipient egg or oosperm passes down the oviduct, it is coated by successive secretions from the oviducal glands. It first receives a coat of thick, viscid e/bumen (Fig. 296, a/b), which, as the egg 490 MANUAL OF ZOOLOGY SECT. rotates during its passage, becomes coiled at either end into a twisted cord, the chadasa (ch). Next, more fluid albumen (alb') is deposited layer by layer, then a tough, parchment- like shell-membrane (sh. m) and finally a calcareous shell (sh). The shell-membrane is double, and at the broad end of the egg the two layers are separate and enclose an air- cavity (@). The shell may be white or variously coloured by special pigments: it consists of three layers, and is traversed by vertical pore-canals, which are unbranched in the Carinate and in Apteryx, branched in the other Ratite. The eggs may be laid on the bare ground or on the rocks by the seashore, as in penguins and auks, or on the ledges on inaccessible cliffs as in the sooty albatross (Diomedea Jfuliginosa) ; but as a rule a mes¢ is constructed for their reception by the parent birds. This may be simply a hole in the sand, as in the ostrich ; a mere clearing on the hill- side surrounded by a low wall of earth, as in the wandering albatross (Diomedea exulans) ; or a cylinder with excavated top, built of grass, earth, and manure, as in the mollymawks (Diomedea melanophrys, etc.). It may take the form of a burrow, as in many petrels, kingfishers, and sand-martins, or it may be more or less elaborately built or woven of sticks, moss, leaves, hair, or feathers, showing every stage of con- structive skill from the rude contrivance of sticks of the pigeon and eagle, to the accurately constructed cup- or dome-shaped nests of many familiar Passeres. In the tailor- bird (Orchotomus) it is formed of leaves sewn together, the beak acting as needle: in a Malayan swift (CollocaHa) it is largely built of the secretion of the bird’s buccal glands. After the egg is laid, the process of development is ar- rested unless the temperature is kept up to about 40° C. (104° F.) : this is usually done by the heat of the body of the parent birds, one or both of which sit upon, or ¢ncu- xII PHYLUM CHORDATA 491 bate, the eggs until the young are hatched, but in the Aus- tralian mound-makers (AZegapodius) the eggs are buried in heaps of decaying vegetable matter, the decomposition of which generates the necessary heat. CLASS VI. MAMMALIA The class Mammalia, the highest of the Vertebrata, com- prises the Monotremes and Marsupials, the hoofed and clawed quadrupeds, the whales and porpoises and sea-cows, the rodents, bats, and insectivores, the lemurs and apes, and the human species. All mammals, though many are aquatic, are air-breathers throughout life, lungs being, as in reptiles and birds, the sole organs of respiration. The blood of mammals has a high temperature, resembling in that re- spect the blood of birds, and differing from that of reptiles and amphibia. The scales of reptiles and the feathers of birds are replaced in mammals by peculiar epidermal struc- tures, the hairs, usually developed in such quantities as to form a thick soft covering or fur. The rabbit (Lepus cuniculus) will serve as a convenient example of the class.! The rabbit (Fig. 297) is a four-footed or quadrupedal ani- mal, having the whole surface of its body covered with soft fur. The head bears below its anterior extremity the mouth in the form of a transverse slit bounded by soft lips. The upper lip is divided by a longitudinal cleft, running back- wards to the nostrils and exposing the chisel-shaped zuczsor teth. Behind the incisor teeth the hairy integument pro- jects on each side into the cavity of the mouth. At the end of the snout, above the mouth, are the nostrils in the shape 1 The following account will apply in all but very slight details to our cotton-tail rabbit or to our American hare. 492 MANUAL OF ZOOLOGY SECT. of two oblique slits. The large eyes, situated at the sides of the head, have each three eyelids, an upper and a lower hairy lid, and an anterior hairless third eyelid or mécttating membrane, supported by a plate of cartilage. Vebrisse — very long stiff hairs— are scattered above and below the eyes and on the snout. Behind the eyes and a little nearer the summit of the head, are a pair of very long flexible and movable external ears or g7nn@. These are somewhat spout-shaped, expanding distally and are usually placed vertically with the concavity directed laterally and some- Fic. 297-—Lepus cuniculus. Lateral view of skeleton with outline of body. what forwards, leading to the external auditory opening. The neck is a distinct constriction, but relatively short as compared with the neck of the pigeon. The ¢ruz is distin- guishable into “rerax in front and addomen behind. On the ventral surface of the abdomen in the female are four or five pairs of little papilla — the “eas. At its posterior end, below the root of the tail, is the aza/ opening, and in front of this in the male is the fers, with a smal] terminal wrinogenital aperture and with the zestes, each in a prominent scvota/ sac, at the sides : and in the female XIL PHYLUM CHORDATA 493 the opening of the wz/ya. The tail is very short and covered with a tuft of fluffy hair. The fore- and hind-timds, both of which take part in loco- motion and in supporting the weight of the animal, differ considerably in size—the fore-limbs being much shorter than the hind-limbs. Both have the same general divisions as in the lizard. The upper arm is almost completely hidden by the skin, being applied closely against the side of the body. The manus is provided with five digits, each terminating ina horny claw. The thigh is also almost hidden by: the skin; the Zes has four digits only, all provided with claws. The spinal column of the rabbit is divisible, like that of the pigeon, into five regions — the cervical, the thoracic, the lumbar, the sacral, and the caudal. In the cervical region there are seven vertebree ; in the ¢horacic twelve or some- times thirteen, in the Zvzmédar seven, or sometimes six, in the sacral four, and in the cauda/ about fifteen. The centra of the vertebrae in a young rabbit consists of three parts —a middle part, which is the thickest, and two thin discs of bone — the efzphyses — anterior and posterior, applied respectively to the anterior and posterior faces of the iniddle part or centrum proper. Between successive centra in an unmacerated skeleton and thin disc-like plates of fibro-cartilage — are the inder-vertebral discs. The first vertebra or a/as (Fig. 298, B) resembles the cor- responding vertebra of the pigeon in being of the shape of a ring without any solid centrum like that of the rest. On the anterior face of its lateral portions are two concave arti- cular surfaces (arf) for the two condyles of the skull. The second vertebra or axzs (B and C) bears on the anterior face of its centrum a peg-like process — the odontoid process (od) —which fits into the ventral part of the ring of the atlas. 494 MANUAL OF ZOOLOGY SECT. The thoracic vertebre all have elongated spines. The transverse processes are short and stout; each bears near its extremity a small, smooth articular surface or éudercular facet for the tubercle of arib. On the anterior and posterior borders of each vertebra is a little semi-lunar facet, the capitular facet, situated at the junction of the centrum and the neural arch. The two contiguous semi-lunar facets of successive vertebree form between them a cup-like concavity into which the head or capi¢udum of a rib is received. Fic. 298. — Lepus cuniculus. A, atlas and axis, ventral aspect. od, odontoid pro- cess of axis. B, lateral view of axis. a@r?, articular facet for occipital condyle; od, odontoid process; ff. sv, post-zygapophysis; sf. neural spine. C, thoracic vertebra, lateral view. cez?, centrum; fac, facet for rib; #zet, metapophysis; pr. 2y, prezygapophysis; ff. zy, post-zygapophysis; 7, rib; sf, spinous process. In the lumbar region the spines are comparatively short, and both transverse processes and bodies are devoid of facets. The sacral vertebre are firmly ankylosed together to form a single composite bone, the sacvwm. The first and second bear great expanded lateral plates — sacral ribs — with roughened external surfaces for articulation with the ilia. Of the caudal vertebrae the more anterior resemble those of the sacral region and have similar processes ; but as we pass backwards in the caudal region all the processes gradu- XII PHYLUM CHORDATA 495 ally diminish in size, the most posterior vertebra being represented merely by nearly cylindrical centra. There are twelve pairs of 7zés, of which the first seven are true ribs, t.e. are connected by their cartilaginous sternal ribs with the sternum; while the remaining five, the so- called false or floating ribs, are not directly connected with the sternum. All, except the last four, bear two articular facets, one on the vertebral extremity or capitulum, and the other on a little elevation or ¢wbercée situated at a little dis- tance from this, the former for the bodies, the latter for the transverse processes of the vertebree. The sternum (Fig. 300) consists of six segments or szerne- bre. The first or manubrium sterni or presternum is larger than the rest, and has a ventral keel. With the last is con- nected a rounded cartilaginous plate, the xphisternum. The skuil (Fig. 299), if we leave the jaws out of account, is not at all unlike that of the pigeon in general shape. The length is great as compared with either the breadth or the depth; the maxillary region, or region of the snout (corresponding to the beak of the pigeon), is long in pro- portion to the rest, the orbits closely approximated, being separated only bya thin inter-orbital partition, and the optic . foramina united into one. But certain important differences are to be recognised at once. One of these is in the mode of union of the constituent bones. In the pigeon, as we have seen, long before maturity is attained, the bony ele- ments of the skull, originally distinct, become completely fused together so that their limits are no longer distinguish- able. In the rabbit, on the other hand, such fusion between elements only takes place in one or two instances, the great majority of the bones remaining distinct throughout life. The lines along which the edges of contiguous bones are united— the sutures as they are termed —are sometimes 496 MANUAL OF ZOOLOGY SECT. XII straight, sometimes wavy, sometimes zig-zagged, serrations of the edges of the two bones interlocking ; in some cases the edges of the bones are bevelled off, and the bevelled edges overlap, forming what is termed a sgvamous suture. Another conspicuous difference between the skull of the rabbit and that of the pigeon is in the mode of connection of the lower jaw, which in the former articulates directly with the skull, the quadrate, through which the union is effected in the pigeon, being apparently absent. Certain large apertures which are distinguishable are readily identified with the large openings in the skull of the pigeon. In the pos- terior wall of the skull is a large rounded opening, the foramen magnum, flanked with a pair of smooth rounded elevations or condvées for articulation with the first vertebra, these obviously corresponding to the single condyle situated in the middle below the foramen in the pigeon. A large opening situated at the end of the snout and looking forwards obviously takes the place of the externa/ nares of the pigeon ; and a large opening in the roof of the mouth leading forward to the external nasal opening, plainly represents, though much wider and situated further back, the ¢zerna/ or poste- rior nares of the pigeon ; while the rounded tubular opening situated at the side of the posterior part of the skull, some distance behind the orbit, is evidently the same as the auditory aperture of the pigeon. Surrounding the large opening of the foramen magnum are the bones of the occiprfa/ region of the skull, the supra-ex- and éas?-occipitals. The first of these (s. 0c ) is a large plate of bone above the foramen magnum. The ex-oceipitals lie at the sides of the opening and each bears the greater part of the somewhat oval prominence or condyle with which the corresponding surface of the atlas or first vertebra articulates. The dast-occipitaé is a median plate of bone, almost horizontal I.0C Fic. 299. — Lepus cuniculus. Skull: A, lateral view; B, ventral view. ang. proc, angular process of mandible; as, ali-sphenoid (external pterygoid process); 4, oc, basi-occipital ; 6. sph, basi-sphenoid; cod, condyle; /r, frontal; zz? pa, inter-parietal; 7x, jugal; cr, lacrymal; max, maxilla; vas, nasal; oft. fo, optic foramen; o. sph, orbito-sphenoid; Za, parietal; Za/, palatine; fal max, palatine plate of maxilla; par. oc, par-occipital pro- cess; pal. p. maz, palatine process of pre-maxilla; f. max, pre-maxilla; fer, periotic; pt, pterygoid; %.¢. sg, post-tympanic process of squamosal; s. oc, supra-occipital; sg, squamosal; ty. 6x/, tympanic bulla; vo, vomer; zyg. max, zygomatic process of maxilla. 2K 497 498 MANUAL OF ZOOLOGY SECT. in position, which forms the floor of the most posterior part of the cranial cavity ; it bears the lower third of the occipital condyles. Articulating in front with the basi-occipital is a plate of bone, also horizontal in position, which forms the middle part of the floor of the cranial cavity. ‘This is the bast-sphenoid ; on its upper surface is a depression, the se//a turcica or pituitary fossa, in which the pituitary body rests. In front of it is another median bone of laterally compressed form, the pre-sphenoi’. Connected laterally with the basi- sphenoid and pre-sphenoid are two pairs of thin irregular plates, the af-sphenoid (as) behind and the ordito-sphenoid (0. sph) in front. The ali-sphenoids are broad wing-like bones, each produced below into a bilaminate process, the plerygod process. The boundary of the anterior part of the brain case is completed by a narrow plate of bone, the ervbriform plate of the e¢hmoi?, perforated by numerous small foramina for the passage of the olfactory nerves. This cribriform plate forms a part of a median vertical bone, the mesethmord, the remainder of which, or /amina perpendicularis, forms the bony part of the partition (completed by cartilage in the unma- cerated skull) between the nasal cavities. Fused with the mesethmoid are two lateral, thin-twisted bones, the e¢2mo- turbinals, and with its inferior edge articulates a long median bone with a pair of delicate lateral wings, the zomer. Roof- ing over the part of the cranial cavity, the walls and floors of which are formed by the sphenoid elements, is a pair of membrane bones, the fariefals (pa), and further forward another pair, the frontals (fr). Between the supra-occipital and the parietals is a median ossification, the /nter-parietal (it, pa). Below the parietal and frontal is a broad bone (sg), the superior margin of which is bevelled off. This is the sguamosal. It gives off in front a strong zgomatic process, XI PHYLUM CHORDATA 499 which curves outwards, then downwards, and finally forwards, to unite with the 7wga/ in the formation of the sygomatic arch. Below the root of the process is a hollow, the glenoid fossa. Between the occipital and parietal bones, below and behind the squamosal, are the qnpanic and periotic bones. The tympanic forms the bony part of the wall of the external auditory meatus; below it is dilated to form a process (4'. dvZ) projecting on the under surface of the skull, the Juda tympani. The periotic (f. 0Z) is a bone of irregular shape enclosing the parts of the membranous labyrinth of the internal ear; externally it presents two small openings, the fenestra ovalis and fenestra rotunda, visible only when the tympanic is removed. The periotic and tympanic are ankylosed together, but are loosely con- nected with the surrounding bones. Roofing over the olfactory cavities are two flat bones, the zasals (nas). In front of the nasals are the pre-maxille —large bones which form the anterior part of the snout, bear the upper incisor teeth, and give off three processes. The maxille (max), which form the greater part of the upper jaw and bear the premolar and molar teeth, are large, irregularly shaped bones, the upper surfaces of which are spongy. They give off internally horizontal processes, the palatine processes, which unite to form the anterior part of the bony palate. A strong process which is given off from the outer face of each maxilla and turns outwards and then backwards to unite with the zygomatic process of the squamosal and thus complete the zygomatic arch, is a separate bone in the young, the malar or jugal (ju). The rest of the narrow bony palate, forming the roof of | the mouth and the floor of the nasal cavities, is formed by the palatine plates of the palatine bones. The pterygords are small irregular bones, each of which articulates with 500 MANUAL OF ZOOLOGY SECT. the palatine in front and the ali-sphenoid behind. The lachrymals are small bones, one situated in the anterior wall of each orbit, perforated by a small aperture — the lachrymal foramen. The mandible, or lower jaw, consists of two lateral halves or rami, which articulate with one another in front by a rough articular surface or symphysis, while behind they diverge like the limbs of a letter V. In each ramus is a horizontal portion (anterior), which bears the teeth, and a vertical or ascending portion, which bears the articular surface or condyle for articulation with the glenoid cavity of the squamosal ; in front of the condyle is the compressed coronoid process. The angle where the horizontal and as- cending processes meet gives off an inward projection or angular process. The hyo’, which, as in the pigeon, is the only other post-oral visceral arch represented in the adult, consists of a stout thick body or éasi-Aya/, a pair of small anterior cornua or cerato-hyals, and a pair of long backwardly directed cornua or ¢hyro-hvals. The auditory ossicles, contained in the cavity of the middle ear, and cut off from the exterior, in the unmacerated skull, by the tympanic membrane, are extremely small bones, which form a chain extending, like the columella auris of the pigeon, from the tympanic membrane externally to the fenestra ovalis internally. The elements of the pectoral arch (Fig. 300) are fewer than in the pigeon. There is a broad thin triangular scapu- lar, the base or vertebral edge of which has a thin strip of cartilage (the swpra-scapular cartilage) continuous with it. Along the outer surface runs a ridge, the sfine,; the spine ends below in a long process, the acremion process (a), from which a branch process or mefacromion (ma) is given XII PHYLUM CHORDATA 501 off behind. At the narrow lower end of the scapula is a concave surface, the glenoid cavity, into which the head of the humerus fits, and immediately in front of this is a small inwardly curved process, the coracotd process (c), which is represented by two separate ossifications in the young rabbit. A slender rod, the clavicle (cl), is con- nected with the acromion process externally and with the sternum internally by means of fibrous tissue. At the proximal end of the humerus are to be recognised: (1) A rounded head for ar- ticulation with the glenoid cavity of the scapula ; (2) externally a greater; and (3) in- ternally a lesser tuber- osity for the insertion of muscles. At the distal end are two ar- ; ; ticular surfaces, one OS ee a Be sung eee e men @, acromion; af, pre-scapular fossa; large and pulley-like, ¢, coracoid; cZ, ossified clavicle; ma, meta- cromion; mss, meso-scapular segment; ost trochlea, for the ulna ; pre-sternum; Pe, pre-coracoid; £/, post-scapu- the other smaller, capt- lar fossa; sv, sternal ribs. (After Flower.) zellum, for the radius: laterally are two prominences or condyles, an internal and an external. The radius and ulna are firmly fixed together so as to be incapable of movement, but not actually ankylosed. The radius articulates proximally with the humerus, distally with the scaphoid and lunar bones of the carpus. The ulna pre- sents on the anterior aspect of its proximal end a deep fossa, the greater sigmoid cavity, for the trochlea of the humerus ; the prominent process on the proximal side of this is the 502 MANUAL OF ZOOLOGY SECT. olecranon process. Distally it articulates with the cunei- form. The carpal bones (Fig. 301), nine in number, are all small bones of irregular shape. Eight of these are arranged in two rows, a proximal and a distal; the ninth, cenzérale (cent), lies between the two rows. The bones of the proxi- mal row are—taken in order from the inner to the outer side — scaphoid (sc), lunar (orsemi-lunar) (dun), cuneiform (cun), and pist- form. Those of the dis- tal row are reckoned in the same order, “rapeztum (77pm), trapezoid (tps), magnum (mag), and unci- Jorm (unc). Fic. 301. —Lepus cuniculus. Distal end The five metacarpals are of fore-arm and carpus, dorsal view, the al] small but relatively nar- bones bent towards the dorsal side so as to be partly separated: cent, centrale; row and elongated bones cun, cuneiform; dz, lunar; mag, mag- ? num; rad, radius; sc, scaphoid; tr/z, the first being smaller than trapezoid: ¢7f7v, trapezium; 222, ulna; unc, unciform; /-I’, bases of metacar- the rest. Each of the five pals. (After Krause.) eis digits has three phalanges, except the first which has only two. The distal (ungual) phalanges are grooved dorsally for the attachment of the horny claw. The pelvic arch (Fig. 302) contains the same elements as in the pigeon, but the union of the ilium with the sacrum is less intimate, the acetabulum is not perforated, and the pubes of opposite sides unite ventrally in a svphyszs (sy). The ilium and ischium meet in the acetabulum or articular cavity, which they contribute to form for the head of the femur, but the remainder of the cavity is bounded, not by XII PHYLUM CHORDATA 503 the pubis, but by a small intercalated ossification, the cotylowd bone. The tum (a7) has a rough surface for articulation with the sacrum. Between the pudis (pub) in front and the ¢schiwm (isch) behind is a large aperture, the obturator foramen (obt). The femur has at its proximal end a prominent ead for articulation with the acetabulum, external to this a prominent process, the great trochanter, and internally a much smaller, the Zesser trochanter, while a small process or chird trochanter is situated on the outer border a little below the great trochan- ter. At its distal end are two prominences or condyles, with a depres- sion between them. Op- posite the knee-joint, or articulation between the femur and the tibia, is a small bone or knee-cap, the patella. The tibia has at its proximal end two articular surfaces for the condyles of the fe- mur ; distally it has also Fic. 302.— Lepus cuniculus. Innominate two articular surfaces, bones and sacrum, ventral aspect. acet, . acetabulum; 27, ilium; zsck, ischium; oé¢, one, internal, for the obturator foramen; fxd, pubis; sacr, sacrum; sy, symphysis. astragalus, the other for the calcaneum. The fibula is a slender bone which becomes completely fused distally with the tibia. The tarsus consists of six bones of irregular shape arranged in two rows, one of the bones, the navicular (Fig. 303, zav), being intercalated between the two rows. 504 MANUAL OF ZOOLOGY SECT. In the proximal row are two bones, the as/ragalus (ast) and the calcaneum (cal), both articulating with the tibia; the calcaneum presents behind a long caécaneal process. The distal row contains three bones, the mesocuneiform, ectocunet- form, and cuboid (cub) ; the ento- cuneiform, which commonly forms the most internal member of this row in other mammals, is not pres- ent as a separate bone. There are four metatarsals, the hallux or first digit being absent. Each of the digits has three pha- langes, which are similar in character to those of the manus. The ccelom of the rabbit differs from that of the pigeon in being divided into two parts by a trans- verse muscular partition, the aa- phragm. The anterior part, or thorax, contains the heart and the roots of the great vessels, the lungs and bronchi, and the posterior part of the cesophagus. The posterior part or addomen contains the stom- ach and intestine, the liver and : pancreas, the spleen, the kidneys, Fic. 303.—Lepus cuniculus. P Skeleton of pes; asz, astrag- ureters and urinary bladder, and the alus; ca/, calcaneum; cv, f cuboid; cv, cuneiforms? organs of reproduction. eMC The teeth (Fig. 299) are lodged in sockets or afveoti in the pre-maxille, the maxille, and the mandible. In the pre-maxille are situated four teeth, the four upper incisors. Of these the two anterior are very long, curved, chisel-shaped teeth, which are XII PHYLUM CHORDATA 505 devoid of roots, growing throughout life from persistent pulps. Enamel is present as a thick layer on the ante- rior convex surface only, which accounts for the bevelled- off character of the distal end, the layer of enamel being much harder than the rest, which therefore wears more quickly away at the cutting extremity of the tooth. The second pair of incisors of the upper jaw are small teeth which are lodged just behind the larger pair. In the lower jaw are two incisors, which correspond in shape with the anterior pair of the upper jaw. The remaining teeth of the upper jaw are lodged in the maxille. Canines, present in most mammals as a single tooth on each side, are here entirely absent, and there is a considerable space, or dastema, as it is termed, between the incisors and the teeth next in order, the pre-molars. Of these there are three in the upper jaw and two in the lower. They are long, curved teeth devoid of fangs, the first smaller than the others. Behind the pre- molars are the mo/ars, three on each side both in the upper and lower jaws. Opening into the cavity of the mouth are the ducts of four pairs of salivary glands. On the floor of the mouth is the muscular tongue, covered with a mucous membrane which is beset with many papille. The roof of the mouth is formed by the fa/aze. The anterior part, or hard palate, is crossed by a series of transverse ridges of its mucous membrane. The posterior part, or soft palate, ends behind in a free pendulous flap (the wzzdz) in front of the opening of the posterior nares. Behind the mouth or buccal cavity proper is the pharynx. The pharynx is divided into two parts, an upper or asa/ division, and a lower or duccal division, by the soft palate. Into the nasal division open in front the two posterior nares and at the sides the openings of the Zustachian tubes. The nasal division is continuous mes.elhy 506 MANUAL OF ZOOLOGY SECT. with the buccal division round the posterior free edge of the soft palate. From the buccal division leads ventrally the slit-like opening of the glottis into the larynx and trachea; overhanging the glottis is a leaf-like movable flap (Fig. 304, ef) formed of a plate of yellow elastic cartilage covered with mucous membrane: this is the epiglottis. Behind, the pharynx becomes continuous with off Z mes.elh — (i ve Tho eX ge erb rel.ing Fic. 304. — Lepus cuniculus. Lateral dissection of the head, neck, and thorax. The head and spinal column are represented in mesial vertical section: the left Jung is removed; the greater part of the nasal septum is removed so as to show the right nasal cavity with its turbinals. @ort, dorsal aorta; 4. Ay. basi-hyal; cd, cerebellum; crv, cerebral hemispheres: cov. 7, curonary vein; da, diaphragm: ef, epiglottis: ew, opening of Eustachian fate’ inte pharynx; Jar, larynx; LGU, left jugular vein; 27 sd. a, left subclavian artery: 2. sé. 7, left subclavian vein; med, medulla; mes. eth, mesethmoid: 72-, tré, maxilla-turbinal; as, esophagus; olf, olfactory lobe; f?. a, pulmonary artery; B. MAX, pre-manilla; pr. st, pre- sternum; ft. c, post-caval vein; +. Zzg, root of left lung with bronchus and pul- monary veins and artery cut across; s. g7, sub-lingual salivary gland; s. #2. g/d, sub-maxillary salivary gland; s¢, sternebrae; zg, tongue; 7, trachea; #74, ethmo-turbinals; ve/. /, soft palate. the asephagus or gullet (as). The latter is a narrow but dilatable muscular tube, which runs backwards from the pharynx through the neck and thorax to enter the cavity of the abdomen through an aperture in the diaphragm, and opens into the stomach. XII PHYLUM CHORDATA 507 The stomach (Fig. 305) is a wide sac, much wider at the end (cardiac), at which the cesophagus enters, than at the opposite or fyZoric end, where it passes into the small intestine. The small intestine is an elongated, narrow, greatly coiled tube, the first part of which or duodenum (du and du) forms a U-shaped loop. The large intestine is a wide tube, the first and greater part of which, termed the colon, has its walls sacculated, a structure which is absent in the short, straight posterior part or rectum (ret). At the junction of the small with the large intestine is a very wide blind tube, the ca@cm, which is of considerable length and is marked by a spiral constriction, indicating the presence in its interior of a narrow spiral valve. At its extremity is a small, fleshy, finger-like vermiform appendix. The intestine, like that of the pigeon, is attached through- out its length to the dorsal wall of the abdominal cavity by a mesentery or fold of the lining membrane or peritoneum. The “ver is attached to the diaphragm by a fold of the peritoneum. Its substance is partly divided by a series of fissures into five lobes. A thin-walled gall-bladder lies in a depression on its posterior surface. The common éz/e duct, (¢. 6. d@) formed by the union of the cyste duct from the gall-bladder and hepatic ducts from the various parts of the liver, runs to open into the duodenum near the pylorus. The pancreas (pn) is a diffused gland in the fold of mesentery passing across the loop of the duodenum. Its single duct, the pancreatic duct (pn. @), opens into the distal limb of the loop. The heart (Fig. 306) is situated in the cavity of the thorax, a little to the left of the middle line, and lies between the two pleural sacs enclosing the lungs. The peri- cardial membrane enclosing the heart consists of two layers, a parietal, forming the wall of the pericardial cavity, and a Fic. 305.— Lepus cuniculus. The stomach, duodenum, posterior portion of rectum and liver (in outline) with their arteries veins, and ducts. A. the ceeliac artery of another specimen (both x #). The gullet is cut through and the stomach some- what displaced backwards to show the ramifications of the coeliac artery (ca. a); the duodenum is spread out to the right of the subject to show the pancreas (pu); the branches of the bile duct (c. &. d), portal vein (f. v) and hepatic artery (4. a), are supposed to be traced some distance into the various lobes of the liver. @. #2. a, anterior mesenteric artery; caz, caudate lobe of liver, with its artery, vein, and bile duct; c. 6. 2, common bile duct; cd. st, cardiac portion of stomach; c. 27. a, common iliac artery; ca@. a, coeliac artery; cy a, cystic artery; cy. d, cystic duct: d@. ao, dorsal aorta; dz, proximal, and du’, distal limbs of duodenum; a a@, duodenal artery; du. ha, in (A), duodeno-hepatic artery; g. @, gastric artery and vein; g. 4, gall-bladder; 4. a, hepatic artery; &. d, left bile duct; 2. c, left central lobe of liver, with its artery, vein, and bile duct; 2. gv, lieno-gastric vein; 2. /, left Jateral lobe of liver, with its artery, vein, and bile duct: ss, branch of p esenteric artery and vein to duodenum; ms.7, mesorectum: mw 7, chief mesenteric vein; @&s, cesophagus; /. 7. a, posterior mesenteric artery; # #2. v, posterior mesenteric vein; fz, pancreas; pr. d, pancreatic duct; ~ 7, portal vein; Ay. s¢, pyloric portion of stomach; ret, rectum; » c, right central lobe of liver, with artery, vein, and bile duct; spe, Spigelian lobe of liver, with its artery, vein, and bile duct; 52, spleen; sf. a, splenic artery. (From Parker’s Zootomy.) 508 SECT. XII PHYLUM CHORDATA 509 visceral, immediately investing the heart. Between the two is a narrow cavity containing a little fluid, the pericardial fiuid. In general shape the heart resembles that of the pigeon, with the apex directed backwards and slightly to the left, and the base forwards. Like that of the pigeon, it contains right and left auricles and right and left ventricles, the right and left sides of the heart having their cavities completely separated off from one another by inter-auricular and inter-ventricular partitions.- Fic. 306.— Lepus cuniculus. Heart, seen from the right side, the walls of the right auricle and right ventricle partly removed so as to expose the cavities. ao, aorta; f. ov, fossa ovalis; 7. Av. c, opening of pre-caval; 1 pap, musculi papillares; Az. c, post-caval; ff. c’, opening of post-caval; ». prc, nght pre- ove r. pul, right pulmonary artery; sew. v, semi-lunar valves; ¢77, tricuspid valve. Into the right auricle open three large veins, the righ? and deft pre-caval veins and the single postcaza/, the first into the anterior part, the second into the left-hand side of the posterior portion, and the third into the dorsal surface. Projecting forwards from it is an ear-like auricular appendix. On the septum is an oval area where the partition is thinner 510 MANUAL OF ZOOLOGY SECT. XII than elsewhere; this is the fossa ovais, it imarks the position of an aperture, the foramen ovale, in the foetus. The cavity of the right auricle communicates with that of the right ventricle by the wide right auriculo-ventricular opening. This is guarded by a valve, the ¢ricuspid, com- posed of three membranous lobes or cusps, so arranged and attached that while they flap back against the walls of the ventricle to allow the passage of blood from the auricle to the ventricle, they meet together across the aperture so as to close the passage when the ventricle contracts. The lobes of the valve are attached to muscular processes of the wall of the ventricle, the mzsculi papillares, by means of tendinous threads called the chorde tendinee. The right ventricle, much thicker than the auricle, forms the right side of the conical apical portion, but does not extend quite to the apex. Its walls are raised up into muscular ridges called columne carnea. It gives off in front, at its left anterior angle, the pulmonary artery, the entrance to which is guarded by three pouch-like sem-/unar valves. The left auricle, like the right, is provided with an auricular appendix. Into this cavity on its dorsal aspect open together the right and left pulmonary veins. A large left auriculo-ventricular opening leads from the cavity of the left auricle into that of the left ventricle ; this is guarded by a valve, the mz¢ra/, consisting of tvo membranous lobes or cusps with chordz tendineze and musculi papillares. In the walls of the ventricle are columnz carnee rather more strongly developed than in the right. At the basal (anterior) end of the left ventricle is the opening of the aorta, guarded by three semi-lunar valves similar to those at the entrance of the pulmonary artery. The coronary arteries, which supply the muscular substance of the heart, Svs tidy Fic. 307.—Lepus cuniculus The vascular system. The heart is somewhat dis- placed towards the left of the subject; the arteries of the right and the veins of the left side are in great measure removed. a, arch of the aorta; a. efg, internal mammary artery; a. f, anterior facial vein; @. mm, anterior mesenteric artery; a. fh, anterior phrenic vein; az. v, azygos vein; br, branchial artery: ¢.7.a, common iliac artery; ca, coeliac artery; d@.ao, dorsal aorta; e.c, external carotid artery; ¢. 2/7. a, external iliac artery; ¢ 77. v, external iliac vein: @ ju, external jugular vein: fu. @, femoral artery; 1. v, femoral vein; 4. v, hepatic veins; 7. ¢, internal carotid artery; 7. ¢s, intercostal vessels; 7. fu, internal jugular vein; ¢ Z, ilio-lumbar artery and vein; 77, innominate artery; ¢. az, left auricle; 7. c¢.c, left common carotid artery; 7. prc, left pre-caval vein; Z. uv, left ventricle; 7. sc, median sacral artery; #. a, pulmonary artery; p. epg, epigastric artery and vein; # //, posterior facial vein; 4. 7, posterior mesenteric artery; #. £2, posterior phrenic veins; ffc, post- caval veins; p. v, pulmonary vein; 7, renal artery and vein; 7. av, right auricle; 7. ¢. ¢, right common carotid artery; 7. prc, right pre-caval vein; 7. v, right ventricle; s¢/. a, right sub-clavian artery; sel. v, sub- clavian vein; spm, spermatic artery and vein; vs. 5, superior vesical artery and vein; z/, uterine artery and vein; 7'7, vertebral artery. (From Parker’s Zootomy.) git 512 MANUAL OF ZOOLOGY SECT. are given off from the aorta just beyond the semi-lunar valves. The corresponding vein opens into the terminal part of the left pre-caval. The pulmonary artery divides into two, a right and a left, each going to the corresponding lung. The aorta gives origin to a system of arterial trunks by which the arterial blood is conveyed throughout the body. It first runs forwards from the base of the left ventricle, then bends round the left bronchus, forming the arch of the aorta (Fig. 307, a), to run backwards through the thorax and abdomen, in close contact with the spinal column, as the dorsal aorta (ad. ao). The system of caza/ veins which open into the right auricle consists of the right and /eft pre-cavals and of the single post-caval. From the liver the blood is carried to the post-caval by the Aepavic veins. The hepatic portal system consists, as in other vertebrates, of a series of veins conveying blood from the various parts of the alimentary canal to the liver, the trunks of the system uniting to form the single large portal vein (Fig. 307, p.v). There is no renal portal system. Respiratory Organs. — The /arynx (Fig. 308) is a cham- ber with walls supported by cartilage, lying below and somewhat behind the pharynx, with which it communicates through a slit-like aperture. It contains the vocal cords. Leading backwards from the larynx is the ¢rachea or wind- pipe (Fig. 308, 77), a long tube, the wall of which is sup- ported by cartilaginous rings which are incomplete dorsally. The trachea enters the cavity of the thorax and there divides into the two érenchi, one passing to the root of each lung. The /ungs (Fig. 304) are enclosed in the lateral parts of the cavity of the thorax. Each lung lies in a cavity lined by a membrane — the cavity of the plewral sac or pleural XII PHYLUM CHORDATA 513 membrane. The right and left pleural sacs are separated by a considerable interval owing to the development in the partition between them of a space, the mediastinum, in which lie the heart and other organs. The lung is attached only at its root where the pleural membrane is reflected over it. In this respect it differs widely from the lung of the bird. It differs also in its minute structure. The bronchus entering at the root divides and subdivides to form a ramifying system of tubes, each of the ultimate branches of which, or “rminal bronchioles, opens into a Fic. 308. —Lepus cuniculus. Larynx: A, ventral view; B, dorsal view; ary, arytenoid: cr, cricoid; ef, epigiottis; savt, cartilage of Santorini; th, thyroid, tr, trachea, (From Krause, after Schneider, ) minute chamber or 7nfundibilum, consisting of a central passage and a number of thin-walled azr-vesicles or alveolt given off from it. The spleen is an elongated, compressed, dark red body situated in the abdominal cavity in close contact with the stomach, to which it is bound by a fold of the peritoneum. The ¢kymus, much larger in the young rabbit than in the adult, is a soft mass, resembling fat in appearance, situated in the ventral division of the mediastinal space below the base of the heart. The ¢hyrozd is a small brownish, bilobed glandular body situated in close contact with the ventral surface of the larynx. a5; 514 MANUAL OF ZOOLOGY SECT. The neural cavity, as in the pigeon, contains the central organs of the cerebro-spinal nervous system, the éra7v and spinal cord. Vhe brain (Fig. 309) of the rabbit contains og. —Lepus cuniculus. Wiedersheim ) 3 me the same principal parts as that of the pigeon, with certain differences, of which the following are the most important. The surface of the cerebral hemispheres (Fig. 309, f. 4, XII PHYLUM CHORDATA 515 Fig. 310, ¢. 4), which are relatively long and narrow, presents certain depressions or sulci, which, though few and indis- tinctly marked, yet divide the surface into lobes or con- volutions not distinguishable in the case of the pigeon or the lizard. A slight depression, the Sy/tun fissure, at the side of the hemisphere separates off a lateral portion or temporal lobe (Fig. 311, ch”) from the rest. There are very large club-shaped olfactory lobes at the anterior ex- tremities of the cerebral hemispheres. Connecting together the two hemispheres is a commissural structure, the corpus callosum (Fig. 310, cp. cZ), not present in the pigeon ; this runs transversely above the level of the lateral ventricles. Below the corpus callosum is another characteristic structure of a commissural nature, the fornix (4. fo), a narrow median strand of longitudinal fibres which bifurcates both anteriorly and posteriorly. Below the corpus callosum, between it and the fornix, the thin inner walls of the hemispheres (septum lucidum) (sp. lu.) enclose a small, laterally compressed cav- ity, the so-called fi/th ventricle or pseudocele; this is not a true ventricle, but merely a space between the closely apposed hemispheres. The lateral ventricles of the cerebral hemispheres are much more extensively developed than in the brain of the pigeon, and of somewhat complex shape. The floor of the anterior portion of the lateral ventricle is formed of an eminence of gray matter, the corpus striatum (cp. s). The right and left corpora striata are connected together by a narrow transverse band of white fibres, the anterior commissure (a. Co). The diaccele (v*) is a laterally compressed cavity. From the posterior part of the roof of the diaccele arises the peduncles of the pineal body, and just beyond their point of origin is the posterior commissure (p. co), a delicate trans- 516 MANUAL OF ZOOLOGY SECT. verse band of fibres connecting together the posterior parts of the optic thalam:. The latter (0. #) are large Fic. 310.— Lepus cuniculus. Two dissections of the brain from above (nat. size). In A, the left parencephalon 1s dissected down to the level of the corpus callo- sum; on the right the lateral ventricle is exposed. In B, the cerebral hemi- spheres are dissected to a little below the level of the anterior genu of the corpus callosum; only the frontal lobe of the left hemisphere is retained; of the right, a portion of the temporal lobe also is left; the velum interpositum and pineal body are removed, as well as the greater part of the body of the fornix, and the whole of the left posterior pillar; the cerebellum is removed with the exception of a part of its right lateral lobe; @ co, anterior commissure; @. fo, anterior pillar of for- nix; @. pu, anterior peduncles of cerebellum; 3. 0, body of fornix: cé1, superior vermis of cerebellum: c¢é?, its lateral lobe; ¢c. gz, corpus geniculatum; c. 4, cere- bral hemisphere; ch. #2, choroid plexus: cf. c/, corpus callosum; cf. s, corpus striatum; c. xs, corpus restiforme; @.f, dorsai pyramid; 77, flocculus: Ap m2, hippocampus major; 7. co, middle commissure: 0. 71, anterior; o 22, posterior lobes of corpora quadrigemina; o. ¢#, optic thalamus; of, optic tract, p co, pos- terior commissure; # /o, posterior peduncles of cerebellum; 4 va, fibres of pons Varolii forming middle peduncles of cerebellum; sf. 7, septum lucidum; st Z, stria longitudinalis; ¢ s, teenia semicircularis; v. vz, valve of Vieussens; v*, third ventricle; v4, fourth ventricle. (From Parker's Zootomy.) masses of mixed gray and white matter forming the lateral portions of the diencephalon ; they are connected together xII PHYLUM CHORDATA 517 by a thick mass of gray matter, the middle or soft commis- sure (m. co) passing across the diaccele. The floor of the diencephalon is produced downwards into a mesial rounded process, the ¢wber cinereum or infundibulum (inf) to which the pituitary body is attached. In front of this, on the ventral aspect of the brain, is a thick curved transverse band of nerve fibres, the united optic tracts, from the ante- rior border of which the optic nerves are given off. Behind the tuber cinereum‘is a rounded elevation, the corpus mammuillare (¢. ma). In the mid-brain the dorsal part is remarkable for the fact that each optic ode is divided into two by a transverse furrow, so that two pairs of lobes, the corfora guadrigemina, are produced. On the ventral region of the mid-brain the crura cerebvt are far more prominent than in the lower groups. In the hind-brain the cerebellum (Fig. 310, cb', cb") is very large ; it consists of a central lobe or vermis and two lateral lobes divided by very numerous fissures or sulci into a large number of small convolutions. Each lateral lobe bears an irregularly shaped prominence, the flocculus. On section (Fig. 311, cd) the cerebellum exhibits a tree-like pattern (arbor vite), brought about by the arrangement of the white and gray matter. On the ventral aspect of the hind-brain a flat band of transverse fibres, the pons Varolit, connects together the lateral parts of the cerebellum. The cranial nerves are similar to those of the pigeon in most respects, differing in some of the particulars of their arrangement and distribution. The rabbit, like most other vertebrates, possesses a sympathetic nervous system, consisting of a series of ganglia united together by commissural nerves and giving off branches to the various internal organs. In the organs of special sense the following special 518 MANUAL OF ZOOLOGY SECT. features are to be seen when a comparison is made with the pigeon. In the eye, the sclerotic is composed entirely of dense fibrous tissue ; the pecten is absent. In the ear the principal point of difference is in the special development of the cochtea. This part of the membranous labyrinth, instead of retaining the simple curved form which it pre- sents in the bird, is coiled on itself in a close spiral of two and a half turns. olf CLE a inf on a _ MO 7 A\ ™.€0. Phe YPN. ack, 5, 2 a & Fic. 311. — Lepus cuniculus. Longitudinal vertical section of the brain (nat. size). Letters as in the preceding figure; in addition, cé, cerebellum, showing arbor vitae; ¢. c, crus cerebri; c41, parencephalon; c/?, temporal lobe: ¢. wa, corpus mammillare; /. 1, foramen of Monro; zz/, infundibulum; @y, lyra; #2. 0, me- dulla oblongata; 0. ch, optic chiasma; of, olfactory lobe; pty, pituitary body; vi. zp, velum interpositum; v. vz, valve of Vieussens; //, optic nerve. © (From Parker's Zootomy.) The special features of the middle ear with its auditory ossicles have been already referred to. The kidneys are of somewhat compressed oval shape, with a notch or Azévs on the inner side. They are in close contact with the dorsal wall of the abdominal cavity. the right being somewhat in advance of the left. Towards the hilus the tubules of the kidney converge to open into a wide chamber, the ses, which forms the dilated commencement of the ureter. When the kidney is cut XII PHYLUM CHORDATA 519 across, its substance is seen to be divided into a central mass or medudla and a peripheral portion or cortex. An adrenal (suprarenal) bedy lies in contact with the anterior end of each kidney. he wreter (Fig. 312, ur) runs back- ur al an aaa Fic. 312.—Lepus cuniculus. The urogenital organs. A, of male; B, of female, rom the left side (half nat. size). The kidneys and proximal ends of the ureters, and in B, the ovaries, Fallopian tubes and uteri are not shown. ax, anus; 62, urinary bladder; c. c, corpus Cavernosum; c.s, corpus spongiosum; c. &, Cowper’s gland; g° c/, glans clitoridis; g. f, glans penis; 4. g7, perineal gland; . g7', aperture of its duct on the perineal space; #7, anterior, Pee » posterior, and ir’, lateral lobes of prostate; rc, rectum; ». gé, rectal gland; w. & @, urino- genital aperture; #. #z, uterus masculinus; ur, ureter; va, vagina; v4, vesti- bule; wv. d, vas deferens. (From Parker's Zootomzy.) wards to open not into a cloaca but directly into the urinary bladder (bl). The latter is a pyriform sac with elastic walls which vary in thickness according as the organ is 520 MANUAL OF ZOOLOGY SECT. dilated or contracted. In the male the openings of the ureters are situated much nearer the posterior narrower end or neck than in the female. In the male rabbit the ¢s/es are oval bodies, which, though in the young animal they occupy a similar position to that which they retain throughout life in the pigeon, pass backwards and downwards as the animal approaches maturity until they come to lie each in a scrotal sac situated at the side of the urogenital opening. The cavity of each scrotal sac is in free communication with the cavity of the abdomen by an opening, the zmguinal canal. A convo- luted efedidymis, closely adherent to the testis, forms the proximal part of the vas deferens. The vasa deferentia (vd) terminate by opening into a urogenital canal, or urethra, into which the neck of the urinary bladder is con- tinued. A prostate gland (pr) surrounds the commence- ment of the urethra, the neck of the bladder, and the terminal parts of the vasa deferentia. A diverticulum of the urethra, the werus masculinus (um), les embedded in the prostate gland close to the neck of the bladder. A small pair of ovoid glands, Cowfer’s glands (c. g/l), lie just behind the prostate close to the side of the urethra. The terminal part of the urethra traverses a cord of vascular tissue, the corpus spongiosum (c. s), which forms the dorsal portion of the penis. A loose fold of skin, the prepuce, encloses the penis. In the female the ovaries are small ovoid bodies attached to the dorsal wall of the abdomen behind the kidneys. The Graafian follicles enclosing the ova form only very small rounded projections on their outer surface. The ovéducés in the anterior part of their extent (/a//opian tubes) are very narrow and slightly convoluted. They open into the abdominal cavity by wide funnel-shaped openings, XII PHYLUM CHORDATA 521 with fimbriated or fringed margins. Posteriorly each passes into a thick-walled wterus. The two uteri open sepa- rately into a median tube, the vagina (va). The vestibule (Fig. 312, vd), or urogenital canal, is a wide median passage, into which the vagina and the bladder open. On its ventral wall is a small, hard, rod-like body, the c/vorts, corresponding to the penis of the male, and composed of two very short corpora cavernosa attached anteriorly to the Slt Zut fi Lt rue Fic. 313. —Lepus cuniculus. The anterior end of the vagina, with the right uterus, Paflopian tube, and ovary (nat. size). Part of the ventral wall of the vagina 1s ~ removed, and the proximal end of the left uterus is shown in longitudinal section Fi. t, Fallopian tube; 77. z', its peritoneal aperture; 2. w#, left uterus; 7. w¢’, left os uteri; ». «¢, right uterus; 7. wt’, right os uteri; s, vaginal septum; va, vagina. (From Parker's Zootomy.) ischia, with a terminal soft conical glans clitoridis (g. cl). The vulva, or external opening of the vestibule, is bounded laterally by two prominent folds, the /abza mayora. The rabbit is viviparous. The ovum, which is of rel- atively small size, after it has escaped from its Graafian follicle, passes into the oviduct, where it becomes fertilised, and reaches the uterus, in which it develops into the fedus, 522 MANUAL OF ZOOLOGY SECT. as the intra-uterine embryo is termed. The young animal escapes from the uterus in a condition in which all the parts have become fully formed, except that the eyelids are still closed, and the hairy covering is not yet completed. As many as eight or ten young are produced at a birth, and the period of gestation, z.¢., the time elapsing between the fertilisation of the ovum and the birth of the young animals is thirty days. Fresh broods may be born once a month throughout a considerable part of the year, and, as the young rabbit may begin breeding at the age of three months, the rate of increase is very rapid. During intra-uterine life the young rabbit is nourished by an organ called the p/acenza, formed by an intimate union between certain structures, the foetal membranes, derived from the embryo, and a specially modified part of the wall of the uterus. By means of the placenta a close connection is established between the blood-system of the foetus and that of the parent, and nourishment is thus received by the former from the latter. After birth the young rabbits are nourished for a time wholly by the milk or secretion of the mammary glands of the mother. The following are the principal general features which characterise the Mammalia as a class : — The Mammalia are air-breathing vertebrates, with warm blood, and with an epidermal covering in the form of hairs. The bodies of the vertebra are in nearly all mammals ossified each from three independent centres, one of which develops into the centrum proper, while the others give rise to thin discs of bone, the epiphyses. Also charac- teristic of the spinal column of mammals are the discs of fibro-cartilage termed inter-vertebral discs, which intervene between successive centra. XII PHYLUM CHORDATA 523 The skull has two condyles in connection with the atlas, instead of the single condyle of the reptiles and birds ; and the lower jaw articulates with the skull in the squamosal region without the intermediation of the separate quadrate element always present in that position in birds and reptiles. Each of the long bones of the limbs is composed in the young condition of a central part or shaft and terminal epiphyses, the latter only becoming completely united with the shaft at an advanced stage. In the pectoral arch the coracoid of the birds and reptiles is usually represented only by vestiges, which unite with the scapula in the adult. Mammals are typically @phyodont, i.e., have two sets of teeth — a milk or deciduous set, and a permanent set ; some are monophyodont, t.e., have only one set. The teeth are thecodont, i.e., the base of each tooth is embedded in a distinct socket or alveolus in the substance of the bone of the jaw; and nearly always the teeth in different parts of the jaw are clearly distinguishable by differences of shape into incisors, canines, and grinding teeth, z.e., are heterodont ; in some instances the teeth are all alike (Aomodont). A cloaca is absent except in the Prototheria. A movable plate of cartilage, the epiglottis, overhangs the glottis or passage leading from the pharynx into the cavity of the larynx. A partition of muscular fibres, usually with a tendinous centre, the diaphragm, divides the cavity of the body into two parts, — an anterior, the thorax, containing the heart and lungs, and a posterior, the abdomen, containing the greater part of the alimentary canal with its associated glands, the liver and pancreas, and the renal and reproductive organs. The lungs are freely suspended within the cavity of the thorax. The heart is completely divided into two halves, a right and a left, between which there is no aperture of 524 MANUAL OF ZOOLOGY SECT, communication. Each half consists of an auricle and a ventricle, opening into one another by a wide opening, guarded by a valve composed of three membranous cusps on the right side, two on the left. The right ventricle gives off the pulmonary artery ; the left gives off the single aortic arch, which passes over to the left side, turning round the left bronchus in order to run backwards as the dorsal aorta. The blood is warm. The red blood-corpuscles are non- nucleated and usually circular. The two cerebral hemispheres, in all but the monotremes and marsupials, are connected together by a band of trans- verse fibres, the corpus callosum, not represented in the lower vertebrates. The dorsal part of the mid-brain is divided into four optic lobes, the corpora quadrigemina. On the ventral side of the hind-brain is a transverse band of fibres, the pons Varolii, by which the lateral portions of the cerebellum are connected together. The ureters, except in the Prototheria, open into the bladder. Mammals are all, with the exception of the monotremes, viviparous. The feetus is nourished before birth from the blood-system of the parent through a special development of the foetal membranes and the lining membrane of the uterus, termed the placenta. After birth the young mam- mal is nourished for a longer or shorter time by the milk or secretion of the mammary glands of the parent. The class Mammalia is divisible into two main divisions or sub-classes, the Prototheria and the Theria. The Prototheria are mammals in which the mammary glands are devoid of teats ; the oviducts are distinct through- out, and there is a cloaca into which the ureters and the urinary bladder open separately. In the centra of the vertebre the epiphyses are absent or more imperfectly de- XII PHYLUM CHORDATA 525 veloped ; the bones of the skull early coalesce by the oblit- eration of the sutures; there is a large coracoid articulating with the sternum, and a T-shaped episternum, and there is a pair of epipubic (marsupial) bones. In the brain a corpus callosum is absent. The ova are discharged in an early stage of their development, enclosed in a tough shell. This sub-class comprises a single living order, the Mono- tremata, including the duck-bill or Platypus ( Orndthorhyn- chus) and spiny ant-eater (Echidna). The Theria are mammals in which the mammary glands are provided with teats; the oviducts are united in a longer or shorter part of their extent, and there is no cloaca, the ureters opening into the base of the bladder. ‘The centra of the vertebree possess distinct epiphyses ; the bones of the skull in most instances do not completely coalesce, most of the sutures remaining distinguishable throughout life; the coracord is represented by vestiges, and an episternum is absent as a distinct bone. The early development of the young takes place in the uterus. Of the Theria again there are two sections, the Metatheria or Marsupialia and the Eutheria. The section Metatheria comprises all the pouch-bearing mammals or marsupials, such as the opossums, the dasyures, the bandicoots, the wombats, the phalangers, and the kan- garoo, nearly all, with the exception of the opossums, con- fined to the Australian region. They are characterised by the possession of a pouch or marsupium, within which the young, born in rudimentary and helpless condition, are sheltered. They also possess a pair of peculiar bones, the epipubic or marsupial bones (present also in the Prototheria), attached to the pubes. In the Eutheria marsupium and marsupial bones are absent. This section comprises the great majority of 526 MANUAL OF ZOOLOGY SECT. mammals, which, when the fossil forms are left out of account, are capable of being arranged in nine orders : — 1. Edenfata, comprising the sloths, ant-eaters, and arma- dillos. 2. Cefacea, including the whales, porpoises, and dolphins. 3. Strenia, or dugongs and manatees. 4. Ungulata, avery large order, comprising among others, the horses, tapirs, and rhinoceroses, the ruminants (camels, oxen, sheep, goats, antelopes, giraffes, and deer), the pigs and hippopotami, the hyraxes, and the elephants. Fic. 314. — Duck-bill (Oruithorhynchus anatinus). (After Vogt and Specht.) 5. Carnivora, or the cats, dogs, bears, weasels, and otters, and the seals and walruses. 6. Rodentia, a large order, including, among many others, the rats and mice, hares and rabbits, squirrels, beavers, and porcupines. 7. Lnsectivera, including the moles, shrews, and hedge- hogs. 8. Chiroptera, or bats, and fruit-eating bats (flying foxes). xu PHYLUM CHORDATA 527 9. Primates, comprising the lemurs, apes, and monkeys, and the human species. The two genera of the Prototheria, Ornithorhynchus and Echidna, differ somewhat widely from one another in gen- eral appearance. The former (Fig. 314) has the surface covered with a close soft fur, and has the upper jaw pro- duced into a depressed muzzle, not unlike the beak of a duck, covered with a smooth, hairless integument. The eyes are very small, and there is no auditory pinna. The legs are Fic. 315.—Spiny Ant-eater (Echidna aculeata). (After Vogt and Specht.) short, and the five digits end in strong claws, and are con- nected together by a web, so that the limbs are equally adapted for burrowing and for swimming. The tail is elon- gated and depressed, covered with fur. The male has a sharp-pointed, curved spur on the inner side of the foot, having the duct of a poison-gland opening at its apex. Echidna (Fig. 315) has the body covered above with strong-pointed spines, between which are coarse hairs; the 528 MANUAL OF ZOOLOGY SECT. lower surface is covered with hair only. The jaws are pro- duced into a rostrum which is much narrower than that of Ornithorhynchus. The eyes are small, and there is no audi- tory pinna. ‘The tail is vestigial. The opossums (Didelphjyide) (Fig. 316) are arboreal rat-like marsupials, with elongated naked muzzle, with well- developed, though nailless, opposable hallux, and elongated prehensile tail. The Dasyuride (Australian native cats, tasmanian devil, thylacine, etc.) have the pollex often rudi- Fic. 316. — Virginian Opossum (Didelphys virginiana). (After Vogt and Specht.) mentary, the foot four:toed, the hallux, when present, small and clawless, and the tail not prehensile. The bandicoots (Peramelive) are burrowing marsupials, the size of which varies from that of a large rat to that of a rabbit. They have an elongated pointed muzzle, and, in some cases, large auditory pinne. ‘The first and fifth digits of the fore-foot are vestigial or absent, the remaining three XII PHYLUM CHORDATA 529 nearly equally developed. In the hind-foot the fourth toe is much longer and stouter than the others, while the second and third are small and slender, and united together by a web of skin, and the first is vestigial or absent. The marsu- plum has its opening directly backwards. The wombats (Phascolomyide) are large, heavy, thick- bodied, burrowing animals, with short flattened heads, short thick limbs, provided with strong claws on all the digits except the hallux, and with the second, third, and fourth of Fic. 317. — Dasyure (Dasyurus viverrinus). (After Vogt and Specht.) the hind-foot partly connected together by skin. The tail isvery short. The kangaroos and their allies (AZacropodide) (Fig. 318) are adapted, as regards their limbs, for swift terrestrial locomotion. They have a relatively small head and neck, the fore-limbs small, and each provided with five digits; the hind-legs long and powerful ; rapid progression is effected by great springing leaps, with the body inclined forwards and the fore-limbs clear of the ground. The foot is narrow and provided with four toes, the hallux being absent ; the two inner (second and third) small and 2M Missing Page Missing Page 532 MANUAL OF ZOOLOGY SECT. elongated snout, with the mouth as a small aperture at its extremity, small eyes, and the auditory pinna sometimes small, sometimes well developed. There are five digits in the fore-foot, of which the third has always a very large, Fic. 320. — Unau, or two-toed sloth (Cholepus didactylus). (After Vogt and Specht.) curved, and pointed claw, rendering the manus an efficient burrowing organ. The toes of the hind-foot, four or five in number, are sub-equal and provided with moderate-sized XII PHYLUM CHORDATA 533 claws. ‘The tail is always very long, and is sometimes pre- hensile. The body is covered with long hair. In the armadillos (Dasypodide@) (Fig. 321) the head is comparatively short, broad, and depressed. The number of complete digits of the fore-foot varies from three to five ; these are provided with powerful claws, so as to form a very efficient burrowing organ. The hind-foot always has five digits with smaller claws. ‘The tail is usually well developed. Fic. 321. — Tatu armadillo (Dasyfus sexcinctus). (After Vogt and Specht.) The most striking external feature of the armadillos is the presence of an armour of bony dermal plates. This usually consists of a scapular shield of closely united plates covering the anterior part of the body, followed by a series of trans- verse bands separated from one another by hairy skin, and a posterior pelvic shield. The tail is also usually enclosed in rings of bony plates, and a number protect the upper surface of the head. Dasypus occurs in southwestern Texas. In the scaly ant-eaters (Manis) (Fig. 322) the head is produced into a short pointed muzzle, The limbs are short 534 MANUAL OF ZOOLOGY SECT. Fic. 322 —Scaly apt-eater (Van's pevtadactyla), (After Vogt and Specht.) Fic. 323. — Aard-vark (Orycteropus capensis). (After Vogt and Specht.) XII PHYLUM CHORDATA 535 and strong, with five digits in each foot. The upper surface of the head and body, the sides of the latter, and the entire surface of the tail are covered with an investment of rounded horny epidermal scales. The lower surface is covered with hair, and there are a few coarse hairs between the scales. There are five digits in both manus and pes. The aard-varks (Fig. 323) have a thick-set body, the head produced into a long muzzle with a small tubular mouth, the pinne of great length, the tail long and thick. The fore- limbs are short and stout, with four toes. ‘The hind-limb wil ii LEON TR ii uh til Fic 324.—Killer (Orca gladzator). (After True.) is five-toed. The surface is covered with thick skin with sparse hairs. The Cetacea (Fig. 324), among which are the largest of existing mammals, are characterised by the possession of a fusiform fish-like body, tapering backwards to the tail, which is provided with a horizontally expanded caudal fin divided into two lobes or “ flukes,” and a relatively Jarge head, not separated from the body by any distinct neck. A dorsal 536 MANUAL OF ZOOLOGY SECT. median fin is usually present. The fore-limbs take the form of flippers, with the digits covered over by a common integu- ment and devoid of claws ; the hind-limbs are absent. ‘The mouth is very wide ; the nostrils are situated on the summit of the head, and the auditory pinna. is absent. Hairs are : completely absent, or are rep- resented only by a few bristles about the mouth. In the whale-bone whales (Fig. 325) the nostrils have two exter- nal slit-like apertures ; in the toothed whales, porpoises, and dolphins, on the other hand, the two nostrils unite to open by a single crescentic valvular aperture. In the Sirenia also the body is fish-like, with a horizontal caudal fin, the fore-limbs flip- per-like, the hind-limbs absent, and the integument almost hairless. But the body is dis- tinctly depressed, and the head is by no means so large Facet aera aesamges a" gat in proportion as in the Ceta- Owen.) cea, and has a tumid truncated muzzle, not far back from the extremity of which the nostrils are situated. There is no dorsal fin. In the Ungulata vera the claws or nails of other mammals are replaced by thick solid masses, the Avofs, investing the ungual phalanges and bearing the weight of the body. The number of digits is more or less reduced, and the limbs as a XII PHYLUM CHORDATA 537 whole are usually specially modified to act as organs of swift locomotion over the surface of the ground, their move- ments being restricted by the nature of the articulations to antero-posterior movements of flexion and extension. The metacarpal and metatarsal regions are relatively very long. In the sub-order Artiodactyla (or cattle, sheep, antelopes, giraffes, deer, camels, pigs, and hippopotami) the third and fourth digits of each foot form a symmetrical pair, and in the majority are the only digits that are completely devel- oped. Characteristic of the ruminants are the cephalic appendages known as horns and anders. The horns of the oxen, sheep, goats, and antelopes, sometimes developed in both sexes, sometimes only in the males, are horny sheaths supported on bony cores, which are outgrowths of the frontal bones. In the giraffes the horns, which are short and occur in both sexes, are bony structures covered with soft skin, and not at first attached by bony union to the skull, though sub- sequently becoming firmly fixed. The antlers of the deer, which, except in the case of the reindeer, are restricted to the male sex, are bony growths enclosed only while immature in a layer of skin, the “ velvet,’’ covered with very soft short fur. Antlers are shed annually, and renewed by the growth of fresh vascular bony tissue from the summit of a pair of short processes of the frontal bones, the pedicles. In the pigs the legs are relatively short, and the two lat- eral toes of both manus and pes are fully developed, though scarcely reaching the ground. The surface is covered with a scanty coat of coarse bristles. There is a truncate mobile snout, the anterior end of which is disc-shaped and free from hairs. A remarkable feature of the males is the development of the canine teeth of both jaws into large, upwardly curved tusks. In the hippopotami the body is of great bulk, the limbs 538 MANUAL OF ZOOLOGY SECT. very short and thick, the head enormous, with a transversely expanded snout, prominent eyes, and small pinne. The tail is short and laterally compressed. ‘The toes are four in each manus and pes, all reaching the ground. The surface is naked, with only a few hairs in certain positions ; the skin is of great thickness. In the sub-order Perissodactyla (horses, tapirs, rhinoce- roses) the third digit is either the only complete one in both fore- and hind-foot (horses) or there are only three digits, second, third, and fourth in each (rhinoceroses), or there are four in the fore-foot and three in the hind (tapirs). The horses (guide) have the distal divisions of the limbs slen- der, the metacarpals and metatarsals nearly vertical to the surface of the ground, the single hoof massive and with a broad lower surface. Though the head is elongated, the nasal region is not produced into a proboscis. The tail is short or moderately long, and is either beset throughout with a large number of very long coarse hairs, or with a tuft of such specially developed hairs at the extremity. A mane of similar large hairs usually runs along the dorsal surface of the neck. ‘There is a wart-like callosity above the wrist, and in the true horses a second a little below the heel or “hock.” The tapirs have the body more massive than the horses, and the limbs, especially the distal segments, shorter and stouter. The nasal region is produced into a short proboscis. The surface is beset with a scanty covering of hairs. The tail is vestigial. In the rhinoceroses the body is extremely massive, the limbs short and stout, each digit provided with a hoof-like nail. There is a short soft muzzle. Either one or two remarkable median horns are borne on the nasal region, not attached directly to the skull ; these are epidermal structures which are formed of a dense aggregation of slender fibre- Xu PHYLUM CHORDATA 539 like elements. The eyes are small, the auditory pinna well developed. The surface is devoid, or nearly devoid, of hairs, and the skin is enormously thick, and in some species thrown into deep folds. The tail is narrow and of moderate length. The hyraxes are small, somewhat rabbit-like animals, with slender limbs and vestigial tail. There are four func- tional digits in the manus and three in the pes, all provided with short flat nails, except the innermost of the pes, which has a curved claw. The body is covered with soft fur. The elephants, the largest of existing terrestrial mammals, have the limbs much more typically developed than in the true Ungulates, there being five comparatively short digits, enclosed in a common integument, in each foot, all of them in the fore-, and three or four in the hind-foot terminating in a broad flat nail. The limbs are very stout and pillar-like, and the thigh and leg when at rest are in a straight line instead of being, as in the Ungulata vera, placed nearly at- right angles to one another—a circumstance which gives a characteristic appearance to the hind-quarters. The nasal region is produced into a proboscis or “ trunk,” a mobile cylindrical appendage, longer than the rest of the head, at the extremity of which the nostrils are situated. There is in the male a pair of enormous tusks, the incisors of the upper jaw. The eyes are small, the pinna of the ear enor- mous. The tail is small. The skin is very thick and pro- vided with only a scanty hairy covering. In the Carnivora the typical number of digits is sometimes present, or, more usually, there are five in the fore- and four in the hind-foot, or four in both. The extremities of the digits are provided with compressed curved claws, which may be very long and sharp, when they are capable, when not in use, of being retracted into a sheath of skin situated 540 MANUAL OF ZOOLOGY SECT. at their bases; or relatively short and blunt, when they are incompletely or not at all retractile. The otters (Luira) differ from the rest in having short limbs with the toes connected by webs of skin. The Pinnipedia, or seals and walruses (Fig. 326), have the proximal segments of the limbs short, so that the arm and thigh and nearly all the fore-arm and leg are enclosed in the common integument of the trunk, and the manus and pes elongated. The earless seals (Phocide) are much more completely adapted to an aquatic life than the eared seals Fic. 326.— Harbor Seal (Phoca vitulina). (Otartide) and walruses (Zitchechid@), being unable to flex the thigh forwards under the body, so that the hind-limbs may aid in supporting the weight, and thus being only able to drag themselves along very awkwardly when on dry land. The pinna of the ear is absent in the earless seals and walruses, well developed in the eared seals. The surface in all is covered with a thick soft fur. In the fur seals there are two kinds of hairs, those of the one kind being longer and coarser and scattered through the more numerous shorter and finer hairs composing the fur proper. A remarkable . XI PHYLUM CHORDATA 541 feature of the walruses is the presence of a pair of large tusks, the enlarged canine teeth, projecting downwards from the upper jaw. Though some of the rodents (beavers, water voles) are aquatic, some (squirrels and tree-porcupines) are arboreal, while others (the majority of the order) lead a terrestrial life and are active burrowers ; they are on the whole a very uniform group, and exhibit few such remarkable modifica- tions as are to be observed in some of the other orders of mammals. They are nearly all furry animals with five-toed, plantigrade, or semi-plantigrade limbs. The tail is usually elongated, and may be naked or covered with fur; but sometimes, as in the rabbits and hares, it is very short. A few special modifications, however, have to be noted in cer- tain families of rodents. The flying squirrels have on each side a fold of skin, the patagium, which serves as a parachute. The African flying squirrels (Anomalurus) are remarkable also on account of the presence of a series of overlapping horny scales on the lower surface of the basal part of the tail. The Jerboas (Yzpus) and their allies are characterised by the great relative length of the hind-limbs—the mode of locomotion of these remarkable rodents being by a series of leaps not unlike the mode of progression of the kangaroo — and by the reduction of the number of the toes to three in some of them. The porcupines (Ays#7cid@) have numerous elongated spines or “ quills’? among the hairs of the dorsal surface, and some of them have prehensile tails. The Insectivora are, in general, small, furry, burrowing mammals with plantigrade limbs and an elongated muzzle. But there is a considerable range of modification within the order in adaptation to different modes of life. The cobegos ( Galeopithecus) have a fold of skin extending along each side of the neck and body and continued between the hind-legs, 542 MANUVAL OF ZOOLOGY SECT. enclosing the tail; the fore- and hind-feet are both webbed, and the tail is prehensile. The hedgehog (Zrinaceus) has the surface beset with pointed spines. The moles (Za/a) and their allies, which are active burrowers, have the limbs very short and stout and provided with extremely strong claws. The jumping shrews (Aacrosceledide) have slender limbs adapted to progressing by leaps on the surface of the ground. The Chiroptera (Fig. 327) are the only mammals which are capable of active flight. The fore-limbs have the seg- Fic. 327.— Bat (Synotus barbastellus). (After Vogt and Specht.) ments greatly elongated, especially the fore-arm and the four ulnar digits, and these support a thin fold of the integu- ment which stretches to the hind-limbs and constitutes the wing. A fold also extends between the hind-limbs and may or may not involve the tail. The pollex is much shorter than the other digits, directed forwards, and terminates in a well-developed curved claw ; in the Megachiroptera, but not in the Microchiroptera, the second digit also has a claw; the other digits are always clawless. The position of the hind- limbs is peculiar, and the knee is directed backwards instead XI PHYLUM CITORDATA 543 of forwards as in other mammals ; the five digits of the foot are all provided with claws. So complete is the adaptation of the limbs to the purpose of flight that bats are only able to shuffle along with great difficulty on the ground, though with the aid of their claws they are able to climb and to suspend themselves from branches of trees by the hind-feet, In the lemurs and their allies (ProsimiZ) the body is slender, and the limbs adapted for an arboreal existence. The hallux is divergent from the other digits of the foot and opposable to them, and the same holds good, in some cases, of the pollex. In some, all the digits are provided with claws, or all but the hallux. More commonly all the digits are provided with flat nails, except the second of the pes, which always has a claw. The eyes are very large. The muzzle is sometimes elongated, sometimes short ; the nostrils are slit-like. The tail is sometimes absent or short ; more usually it is greatly elongated, but it is never prehen- sile. The surface is always covered with soft fur. Of the remaining groups of Primates the Hapilide or marmosets are small squirrel-like animals with all the digits except the hallux provided with pointed claws, with the pollex incapable of opposition, the tail non-prehensile, and without cheek-pouches or callous patches over the ischia. The Cebide, or American monkeys, resemble the Hapalidz in the negative characters of the absence of ischial callosities and of cheek-pouches, and of the power of opposition in the hallux. But the limbs are much longer, the digits are all provided with flat nails, and the tail is frequently prehensile. The Cercopithecide, or baboons and macaques, all have brightly coloured bare callous patches of skin (callosities) over the ischia, and most of them have cheek-pouches for the storage of food. All the digits are provided with flat nails. The tail may be long or short or absent; when present it is 544 MANUAL OF ZOOLOGY SECT. XII. never prehensile. The pollex when developed is always opposable to the other digits. In the Simiidee or man-like apes, a tail is never developed, and there are no cheek- pouches ; ischial callosities are only present in the gibbons. The gibbons can walk in an upright position without the assistance of the fore-limbs; in the others, though in pro- gression on the surface of the ground, the body may be held in a semi-erect position with the weight resting on the hind- limbs, yet the assistance of the long fore-limbs acting as crutches is necessary to enable the animal to swing itself along. INDEX Aard-vark, 535. Abactinal end, of starfish, 158. Acanthias vulgaris, 366. Acanthin, 31. Acetabulum, 342; of frog, 416, Aciculum of Annelids, 190. Acineta, 51. Acmezea testudinalis, 292, a Acrania, 323. Acromion process, 500, Actinobolus, 49. aActinomma asteracanthion, 32. aActinophrys sol, 26, 28. ‘Actinospherium, 27, 28. Actinostome, 158. Actinozoa, 91, 114. Adamsia palliata, 123. Adelochorda, 311. Adrenals, of birds, 476; of frog, 427. Agalmopsis cara, 108. Air-bladder, 403. Air-sacs, of birds, 472, 477; of in- sects, 248. Air-vesicles, 513. Albatross, 490. Alcyonaria, 118, 119. Alcyonium carneum,119; palmatum, Ig. Alisphbenoid, 498. Allantois, 434. Alligator, 434, 438, 456; brain, 449. Alveolus, 504. Amaroucium, 320, Ambulacral groove, 160, 161, Ambulacral pores, 161. Ambulacrum, 160, Amnion, 434. 2N Ameeba, 14, 19; polypodia, 18; pro- teus, 14. Amphiccelous vertebrae, 334. Ampbhineura, 281. Amphibia, 407. Amphidises, 88, Amphioxus lanceolatus, 323. Amphistomum, 136. Ampulla, 162, «Anemone, sea, 115, 117. Anguis, 436. Animalcules, wheel, 178. Annelida, 188, 191. Annulata, 188. Annuli of leeches, 203. Anodonta cygnea, 265, 270, 273, 274; fluviatilis, 265; circulatory system, of, 276, Anolis, 328. Anomalurus, 541. Anoplophyra, 49. Ant-eater, 526, 531; scaly, 533; spiny, 525: 527. Antedon, 175. Antelope, 526, 537 Antenna, 219. Antennule, 219. Antlers, 537. Anthenea, 167. Anthophysa, 37. Anthrenus scrophularize, 245. Antipathes, 120. Ant, red, 253; neuter, 253; soldier, 253; worker, 253. Anura, 432. Anus, 46; of Antedon, 175; of star- fish, 159; absent in starfish, 170; of 545 546 round worms, 149; of birds, 459; of reptiles, 435; of scorpion, 255. Aorta, of mammals, 512; of molluscs, | 275; of vertebrates, 350. Ape, 544. Aphides, 250. Apiosoma bigeminum, 58. Apis mellifica, 253; parthenogenesis in, 250. Aplacophora, 284. Aplysia, 288, 291. Apopyle, 82. Appendicularia, 322, Appendix vermiformis, 507. Apteria, 462, 483. Apteryx, 483. Apus glacialis, 232, 275. Arachnida, 254; lungs or pulmonary sacs, 257. Arachnidium, 259. Arbor vitae of cerebellum, 517. Arcella vulgaris, 20. Arch, heemal, 335, 369; hyoid, 337, 372; pectoral, 339, 373, 406, 445, 446, 500; neural, 410; pelvic, 339, 416, 445, 470, 502. Arches, branchial, 337, 372, 407; vis- ceral, 337, 379 444- Archidoris tuberculata, 290. Archipterygium, 406, Architeuthis, 308. Argonauta argo, 302, 303. Arteries, of vertebrates, 349, 379, 419, 422; coronary, 510; pulmonary, 352, 407; systemic, 351. Arthropoda, 212. Armadillo, 526, 533. Artiodactyla, 537- Aristotle’s lantern, 171. Ascaris lumbricoides, 149,151; suilla, 149. Ascetta primordialis, 84. Ascidia callosa, 314; 320. Ascidians, 314; blood system, 318; heart, 318; larva of, 319; nervous system, 318. mammillata, INDEX | Aspredo, 404. | Astacus fluviatilis, 213, 221. s\sterias rubens, 157; vulgaris, 157. Asteroidea, 157. Astraea, 121; pallida, 123. Astragalus, 504. Asymmetron, 323. Atlas, 493; of birds, 464. Atriopore, 326. Atrium, 326. Auditory capsules, 410, Aurelia aurita, 108, 111. Auricles, of birds, 477; of mammals, 510; of rabbit, 333; of sharks, 377; of vertebrates, 350, 407. Aves, 456. Avicularium, 181. Axis, 493; of birds, 464. Babesia bovis, 58. Baboon, 543. Balanoglossus, 311, 313. Bandicoot, 525, 528. Barbs, of feathers, 461. Barbules, 461. Basi-sphenoid, 498. Bat, 526, 542. Bdellostoma, 360, 361, 364. Beak, of birds, 457; of bivalve shells, 267; of Brachiopod shells, 184; of czar fish, 396; of sword fish, 396. Bear, 526. Beaver, 526, 541. Bee, 250; honey, 253; parasites, 252. Beetle, carpet, 245. Belemnites, 301. Bells, swimming, 105. Beroé, 128. Bile, 346. Bill, of birds, 485; modifications of, 48s. Binomial nomenclature, 2. Biology, definition of, 1. Bionomics, 13. Birds, 456; colors of, 484; egg, 483, 489, 490; limbs of, 459; mouth of, 459; voice of, 488; wings of, 459. INDEX Bladder, air, 403; gall, 346, 374; of molluscs, 275; swimming, 403; urinary, 519; of crustacea, 224; frog, 427; vertebrates, 359. Blastoderm, of sharks, 385. Blastostyle, 92. Blood, 70; corpuscles, 70; of insects, 249; vascular system of insects, 249; of birds, 488; of starfish, 162; of vertebrates, 349, 422, 423. Blood-vessels, 70; of annelid worms, I93, 207, 260; of crustacea, 224, 226; nemertean worms, 148. Body-cavity of starfish, 160. Body, pituitary, 354. Bojanus, organ of, 275. Bombyx mori, 58. Bone, 66. Bone quadrate, 339. Bones, of birds, 472; cartilage, 337, 411; epipubic, 525; marsupial, 325; membrane, 937). 411. Bothriocephalus latus, 145. Botryllus violaceus, 322. Bougainvillea ramosa, 103; cilians, 103. Brachionus rubens, 179. Brachiopoda, 184. , Bract, 108. Bradypodide, 531. Brain, 71; of annelid worms, 195, 197, 208 ; of birds, 479; of crustacea, 227; of insects, 249; of Peripatus, 239; of mammals, 514; of reptiles, 449; of shark, 353, 380; fore, 354. Branchellion, 211. Branchial basket of lamprey, 364. Branchiz, of annelid worms, I99; secondary in Gastropod molluscs, 2gI. Branchiostoma, 323. Breast-bone, 336. Brittle-stars, 169. Bronchi, of birds, 476; of lizard, 348; of mammals, 512. Bronchioles, 513. Bud, 73. super- 547 Budding, 72. Buds, medusa, 92. Bufo, 432. Bugula avicularia, 182, Bulbus aortz, 403, 419. Bulla tympani, 499. Bursa Fabricii, 476. Buthus carolinianus, 259. Byssus, 279. Calamus, 460, Calcaneum, 416, 504. Calcarea, 86, Calcar, of frog, 417. Camel, 526, 537. Canal, of gastropod shell, 287; ingui- nal, 520; neural, 334; radial, 97. Cancer irroratus, 231; pagurus, 230. Cancrisocia, 124. Capillaries of vertebrates, 349. Capitulum, 495. Capsule, central, 31. Carapace, 214; of crustacea, 233. Cardium, 280, Carina sterni, 466, Carinate, 483. Carnivora, 6, 526, 539. Carpal bones, 502. Carpo-metacarpus, 469. Carpus, 341. Cartilage, 66; cerato-hyal, 372; hyo- mandibular, 339, 372; intercalary, 369; Meckel’s, 372. Casque, 486, Cassowary, 483. Cat, 2, 5,7, 526. Caudal vertebrze, 335. Cavity, atrial, 315; pericardial, 315, 349- Cavity, buccal, 293, 294; of verte- brates, 344, 459, 505. Cebide, 543. Cell, 18; flame, 132, I40. Cells, adhesive, 127; pigment, 303. Cellulose, in ascidian test, 315. Cement, of tooth, 343. Centrale, 502. 548 Centra, of birds, 464; of mammals, 493; of vertebrae, 333. Cephalodiscus, 311, 313. Cephalopoda, 296. Cephalothorax of arachnida, 254. Ceratium, 40. Ceratodus fosteri, 405. Cercaria, 134; of fluke-worm, 134. Cercopithecide, 543. Cere, 459, 486; absence of, 486. Cerebellum, 354; of birds, 479, 489; of mammals, 517. Cerebral hemispheres, 355, 480, 514, 524. Cervical vertebrae, 335. Cestoda, 138. Cestus, 128. Cetacea, 526, 535. Cheetopoda, 188. Chalaza, 490. Chalk, how formed, 26. Chameleon, American, 328. Chauna, 486, Chela, of arachnida, 256; of crusta- cea, 218, 219. Cheliceres, 257, 262. Cheliped, 218. Chelonia, 434, 438, 455. Chiasma, optic, 380. Chilaria of Limulus, 262. Chilopoda, 240. Chiroptera, 526, 542. Chitin, 20. Chitonellus, 281. Chiton spinosus, 281. Chlamydosaurus, 452. Chlamydoselachus, 389. Chlorophyll, 28. Choanoflagellata, 38. Chorda dorsalis, 310, Chordata, 310. Chromatophores, 303, 304. Chrysalis, 252. Chyle, 346. Ciliata, 49. Circulation of frog, 423. Cirri of amphioxus, 323. INDEX Cirrus, of annelid worms, 191; of cri- noids, 175; of fluke-worms, 130. Cistudo lutaria, 442. Clam, 279; giant, 280. Claspers, of sharks, 368. Classification, 5, 8. Clathrulina elegans, 28, 29. Clavicle, 414, 501. Clavicles, of sturgeon, 400. Claws, 486; of birds, 460, 486. Cliona, 89. Clitellum, 201. Clitoris, 527. Cloaca, 344, 407, 476; of Prototheria, 523; of sharks, 393. Cnidoblast, 95. Cnidocil, 95. Cobego, s54r. Coccidium, 58. Cochlea, of birds, 489; of mammals, 518. Cockle shell, 280. Cockroach, 242, 243, 247. Cocoon, of earthworms, 201. Codonella, 49. Coeca, of fluke-worms, 131; hepatic, of Amphioxus, 326; hepatic, of Balanoglossus, 313; hepatic, of in- sects, 248; intestinal, of starfish, 165; pyloric, of starfish, 163; rec- tal, of birds, 476; worms, 193. Coecilia, 433. Ccelenterata, go. Ceelom, of mammals, 504; of mol- luscs, 271; of starfish, 160; of worms, IoI. Ceenenchyma, rar, Coenosare, 94. Collar, 39. Collozoum inerme, 33. Colocalanus, 234. Colonies, 42. Colony, 30. Colors of birds, 484. Columba livia, 457. Columella, 285; of birds, 468; of corals, 121. INDEX Column, spinal, ‘333, 369; spinous, 335; vertebral, 335; of frog, 410. Comb-jellies, 125. ‘ Commissures of brain, 515. Conchiolin, 269, Condyle of skull of birds, 467. Condyles, of bird’s leg, 471; occipi- tal, of frog, 411. Condylostoma, 49. Conjugation, 44, 48, 55. Conus arteriosus, 350, 419; of Dipnoi, 407 ; of sharks, 377; of Teleostomi, 403. Coracoid bone of birds, 468. Corallite, 120. Corallum, 120, Corallium rubrum, 118. Coral, red, 120. Cord, spinal, 353. Cords, vocal, of frog, 419; of mam- mals, 512. Cornea of eye of Crustacea, 228. Corona of Echinoidea, 170, 172. Corpora, cavernosa, 521; quadri- gemina, 517; restiformia, 381. Corpus, callosum, 515; mammillare, 517; spongiosum, 520; striatum, igs. Cortex, 45,55; of kidneys, 519. Cowrie, 290. Crab, 124, 230; hermit, 231; king, 260. Craniata, 323, 328. Cranium, 328, 337; of sharks, 369. Crayfish, 213. Crinoidea, 174; stalked, 176. Crocodilia, 434, 438, 456. Crop, of birds, 474, 488; of insects, 246; of leeches, 205. Crura cerebri, 380, 517. Crustacea, 213. Cryptomonas, 37. Ctenidia, 271, 279, 282, 291, 304. Ctenophora, 91, 125. Cubitals, 463. Cuboid, 504. Cucumaria planci, 174. Cucumber, sea, 173. 549 Cuneiform, 502, 504. Cuticle, 95; of nematoid worms, 151, Cuttlefish, 296, 300. Cyclas, 280, Cyclidium, 49. Cyclops, 156, 234. Cyclostomi, 360, Cydippe, 126. Cypraea moneta, 290. Cyst, daughter of tape worms, 143; mother of tape worms, 143. Cysticercoid embryo, 143. Cysticercus, 143. | Cystoflagellata, 41. Dactylozooids, 108. Dallingeria, 37. Dasypus sexcinctus, 533. Dasyurus, 525, 528, 529. Deer, 526, 537- Dendrocometes, 51. Dendrophyllia, 121, 124. Dendrosoma, 51, 54. Dentine, 343. Dentition, heterodont, 343; dont, 343. Deutomerite, 58. Devil, tasmanian, 528. Diaccele, 515. Diaphragm, 349, 504, 523. Dibranchiata, 298, 300, 301, 308. Dictyocysta, 53. Didinium, 49. Difflugia, 19, 21, 24; pyriformis, 20. Digestion, 69; in vertebrates, 344, 346. Digestive glands of starfish, 164. Digit, 341; of birds, 459; of frog, 409; of mammals, 502. Dimorpha, 37. Dimorphism, 118. Dinobryon, 37. Dinoflagellata, 4o. Dicecious worms, 148. Diophrys, 49. Diphyodont dentition, 523. Diplomita, 37. homo- 55° Diplopoda, 240. Dipnoi, 365, 405. Diptera, 243, 245. Dipus, 541. Disc, trochal, 178. Discorbina, 25. Disease, cattle, 58; silkworm, 58. Distomum hepaticum, 129, 135. Distribution, bathymetrical, 11; geo- graphical, 11; geological, 11; zoo- geographical, 11. Division, self, 18, 44. Dog, 526. Dogfish, 366. Dolphin, 526, 536. Dorippe facchino, 124. Doris tuberculata, 290, 291. Down feathers, 461. Draco, 441, 452. Dracunculus medinensis, 156. Dromezus, 483. Duck-bill, 525. Duct, 65; ejaculatory, of leech, 210; pneumatic, 403. Dugong, 526. Duodenum, 346; of birds, 476; of mammals, 507. Ear, of bird, 459; of crustacea, 228; of frog, 426; of mammals, 518; of vertebrates, 383. Earthworm, 201, 202. Ecdysis, 440. Echidna, 525, 527. Echinaracbnius parma, 173. Echinodermata, 157. Echinoidea, 170. Ectoderm, 79. Ectoprocta, 183. Ectosare, 28. Eczema, caused by a parasitic vorti- cella, 55. Edentata, 526. Egg, 59, 60; segmentation of, 60. Egg-shell, 360; of bird, 483; of mol- luses, 265; of sharks, 384. Eggs, of crocodiles, 456; demersal, INDEX 405; of frog, 428; pelagic, 405; of reptiles, 451; of sharks, 385; of turtles, 455; summer and winter, 180; of reptiles, 452. Elasmobranchii, 365. Electric catfish, 400. Electric eel, 400. Elephant, 526, Elytra, 245. Embryo, ciliated, of flat-worms, 133; cysticercoid, 143; hexacanth, 141. Embryology, 4. Embryo of shark, 386. Emu, 403. Enamel, 343. Encystation, 30. Endoderm, 79. Endolymph, 357. Endopodite, 216, Endoprocta, 181, Endosarc, 28. Endoskeleton, 67. Endostyle, 317, 319. Enteron, 92. Entomostraca, 232. Entovalva, 281. Eolis, 291. Epeira diadema, 259. Ephelota, 51. Ephyrula, 112. Epicoracoid bone, 414. Epidermis, 63. Epiglottis, 506. Epimerite, 58. Epipharynx of insects, 250. Epiphragm, 288. Epiphysis cerebri, 354, 380. Epipodia, 291. Epipodite, 218. Episternum, of frog, 415; of reptiles, 445- Epistoma of crustacea, 216, Epistylis, 48, 49. Epithelium, 63, 64; deric, 63. Equida, 538. Ethmoid, 498. Ethmo-turbinals, 498. INDEX Ethology, 13. Euglena viridis, 34, 36. Euplectella, 86. Eupomatus, trochosphere of, 199. Eurypterida, 260. Euspongia, 87. Eustachian tube, 358, 417, 505. Eutheria, 525. Euthyneura, 295. Evolution, 9. Excretion, 71. Excretory pore of nematoda, 152. Excretory system of nematoda, 152. Excretory vessels of flat-worms, 132; of nemertean worms, 148. Exoccipital bones of frog, 411; of mammals, 496. Exopodite, 216. Exoskeleton, 67; of sea urchin, 157, of starfish, 157. Eye, of birds, 459, 480, 489 ; choroid of, 356; compound, of crustacea, 228 ; iris of, 356; of frog, 408; of insects, 250; of mammals, 518; median, of amphioxus, 328; of molluscs, 280, 283, 289, 307; of nemertean worms, 148; of nereis, 196; pineal, 364, 450; pupil of, 356; of starfish, 160; of vertebrates, 356, 425, 450. Eyeball, 356. Eyelid, of frog, 408. Eye-spot, of fluke-worm, 133. Eye-stalk, 216, 219. Facets of eye, 228. Facial nerve, 382. Fallopian tubes, 520. Fat bodies of frog, 427. Fauna, 12. Feather, follicle of, 461; germ of, 462; papilla of, 461; pulp of, 462; tracts, 462. Feathers, 460, 483; colors of, 484; contour of, 461; cubital, 463; primaries, 463; rectrices, 463; secondaries, 463. Feather-stars, 174. 551 Felis, 2, 5, 7. Femur, 342; of birds, 471. Fibula, 342, 416; of birds, 471. Fibulare, 416. Filoplumes, 461. Fimbrize of mussel, 266. Finger, index, 409. Fins; 992, 965, 972% lateral, 363; median, 367; paired, 367; rays of, 365; of shark, 406; unpaired, 367. Fin-skeleton, of ceratodus, 406. Fish, circulation in, 351. Fishes, 365 ; bony, 394; cartilaginous, 365; teeth of, 4o2. Fission, binary, 18, 28, 44. Flabellum, 120; curvatum, 122. Flagellula, 24, 33, 38. Flagellum, 24, 33, 36, 38; of crustacea, 219. Flat-fish, 397. Flat-worms, 137. Flight, muscles of, in birds, 474. Flocculi, of bird’s brain, 480. Flounder, 397. Fluid, coelomic, 191. Fluke-worm, 129, 135. Foeces, 69. Foetus, 360, 521. Folliculina, 49. Fontenelle, 570. Foot, of frog, 409; of molluscs, 266, 280, 281, 290. Foramen magnum, 337. Foramina, 370; pneumatic, 472. Foraminifera, 21, 25, 26. Formica rufa, 253. Fornix, 515. Fossils, Io. Fox, flying, 526. Frog, brain, 425; eyes, 408; limbs, 408; metamorphosis of, 429; mouth, 408; nervous system, 425; nostrils, 408. Frondicularia, 25. Frontal bones of frog, 411; of lizard, 340. Fronto-parietal bones, 411. 552 Funnel of Cephalopoda, 299, 304. Furcula, 488. Galeopithecus, 541. Gametes, 44. r Ganglion, optic, 249; of mussel, cere- bro-pleural, 276; pedal, 276; vis- ceral, 276. Ganodei, 394. Gastrolith, 222. Gastropoda, 284. Generations, alternation of, 98. Genital opening of flat-worms, 130. Genital plates of Echinoidea, 172, Geotria, 365. Germinal spot, 59. Germinal vesicle, 59. Gestation, 522. Gibbon, 544. Gill-cover, 2T4. Gill-slits of Balanoglossus, 312. Gill, spiracular, 377. Gills, 70; of annelid worms, 199; of crustacea, 222; of frog, 431; of molluscs, 267, 271, 279, 282, 291, 304 ; secondary, 293; tracheal, 248; of vertebrates, 347, 375- Giraffe, 526, 537. Girdle, pelvic, of birds, 470. Gizzard, of birds, 474, 488; of insects, 247. Gland, 63; byssus, 279; Cowper's, 520; digestive, 27; digestive of starfish, 164; green, 224; mam- mary, 360; milk, 360; of fluke- worm, 133; ovoid, 166; prostate, 520; rectal, 375; salivary, 69; sali- vary of vertebrates, 344; shell, 133, 233, 384; subneural, 319. Glands, buccal, 476; clitoridis, 521; thyroid, 476. Glenodinium, qo. Globigerina, 25, 26; 00ze, 26, Glochidium, 277. Glossocodon, Io2. Glottis, 347, 418; of birds, 476. Glugea bombycis, 58. INDEX Glycogen, 346. Goat, 526. Gonads, 72; of mussel, 277. Gonangium, 92, 95. Gonopoda, 216s Gonopore of nematoid worms, 150. Gonotheca, 92. Graafian follicle, 359, 520. Gregarina, 57, 58. Gromia, 22, 24. Groove, buccal, 45. Growth, lines of, in bivalve shells, 267. Guinea worm, 156, m Gymnophiona, 433. Gymnotus, 400. Heemameeba laverani, 58, Heemal arch, 335. Heematochrome, 36. Hag-fish, 360. Hair, trigger, 95. Halistemma, I05, 107. Hallux, of birds, 459; of frog, 410. Hand of frog, 409. Hapilidze, 543. Hare, 526; American, 491. Hatschek, groove of, 328. Hatteria, 437, 455. Heart, 71; of birds, 477, 488; of crus- tacea, 224; of Dipnoi, 407; of frog, 419; of mammals, 507; of mol- luses, 275, 294, 306; of reptiles, 448; of sharks, 377; of vertebrates, 349. Hedgehog, 526, 542. Heliozoa, 28, 29. Hell-bender, 433. Heloderma, 445. Hemichorda, 311. Hemiptera, 243. Hemispheres, cerebral, 355. Hen’s egg, 489. Hepato-pancreas, 222. Heptanchus, 389, 390, 392. Hermaphroditism, in flat-worms, 132. Heteropoda, 288, 296. Hexanchus, 389, 392. .| Hilus of kidney, 518. INDEX Hinge of bivalve shells, 267 ; teeth, 267. Hippocampus, 4o4. Hippopotamus, 526, 537. Hirudinea, 203. Hirudo, eyes of, 209; lateral sense- organs, 209; medicinalis, 204; quinquestriata, 206, Histology, 4. Hoatzin, 487. Hock, 538. Holothuria edulis, 173; floridana, 73. Holothuroidea, 173. Homalogaster, 136. Hoof, 536. Hormiphora plumosa, 126. Horns, 537. Horse, 526, 538; sea, 404. Host, of guinea worm, 156; of para- sitic worms, 134, 142, 144. Hound fish, rough, 366. Humerus, 341; of birds, 469. Hyalonema, 89. Hyalosphenia lata, 20. Hybrids, 3. Hydatids, 143. Hydra, 73, 96, 99, 100. Hydranths, 91. Hydrocorallina, 104. Hydrophyllia, 108. Hydrotheca, 91. Hydrozoa, 90, 91. Hydrula, 98. Hyla, 432. Hyoid apparatus of birds, 468; of frog, 411; of mammals, 500. Hypopharynx, 244. Hypophysis cerebri, 354, 380. Hyposternum, 443. Hypostome, 92. Hyrax, 526, 539. Hystricidze, 541. Ichthyomyzon, 365. Idyia roseola, 128. llium, 342; of birds, 470, 476; of frog, 416; of mammals, 503. 553 Imago, 251. Incisor teeth of rabbit, 491. Incubation, 483, 490. Infundibulum, 127, 354, 380; of brain, 513, 517. Infusoria, 45. Ink gland of Cephalopoda, 306, Ink sac of Cephalopoda, 306. Insecta, 241; abdomen, 242; head, 242: thorax, 242; appendages of head, 242; of thorax, 242; muscu- lar force of, 252. Insectivora, 526, 541. Interclavicle, 445. Intestine of vertebrates, 374, 418, 447. Introvert, 289. } Ischium, 342; of bird, 470; of frog, 416. Itch mite, 260. Jaws, of Cephalopoda, 304; of leech, 205; of Peripatus, 239; of starfish, 159; upper, of frog, 410; of verte- brates, 343. Jellyfish, go. Jerboa, 541. Kangaroo, 525, 529. Kidneys, of birds, 481; of frogs, 427; of mammals, 518; of molluscs, 275, 283, 295; of vertebrates, 358, 384. King crab, 260, 263. Kiwi, 483. Koala, 531. Labia majora, 521. Labrum, of Arachnida, 256; of in- sects, 242; of Limulus, 262; of Myriapoda, 240. Lacerta viridis, 330. Lachrymal bones, soo. Lachrymal foramen, 500. Lacrymaria, 49. Leemargus, 393. Lagena, 25. Lamellz of molluscan gills, 272, 274. Lamellibranchiata, 265. 554 Lampreys, 360, 364. Lamp-shells, 184. Larva, of annelid worms, 199; of in- sects, 251. Larynx, 347; of birds, 476; of mam- mals, 506, 512. Laurer, canal of, 133. Layers, germinal, 62. Leech, eyes of, 209; sense-organ of, 209; medicinal, 203. Legs, of crustacea, 218+ of insects, 244, of mammals, 493: of reptiles, 435+ Lemur, 543. Lens, crystalline, 357. Lepas anatifera, 235. Lepidoptera, 251. Lepidosiren, 405. Lepus cuniculus, 491. Limb of vertebrates, 332, 459, 493. Limpet, 285, 292. Limulus, 260, 263. Line, lateral, 367, 383; pallial, 267. Lingula pyramidata, 187. Liteocircus annularis, 31. Lithite, 98. Lithocysts, 98. Liver, 69; of birds, 476; of frog, 418; of vertebrates, 374. Liver-fluke, 129, 135; of vertebrates, 344, 507. Lizards, 436; 452. Lobe, temporal, of mammals, 515. Lobes, olfactory, 354, 380; optic, 480. Lobosa, I9. Loligo pealii, 302; vulgaris, 302. Lophomonas, 49. Lophophore, of Brachiopods, 186; of Polyzoa, 181. Lorica, 38; of Rotifers, 180. Loxosoma, 181. Lucernaria, 112. Lumbar vertebre, 335. Lumbricus agricola, 200. Lunar bones, 502. flying, 441; habits, INDEX of birds, 477; of fishes, 365, 405; of frog, 418, 431; of lizards, 348, 448; of mammals, 512; of molluscs, 292. Lutra, 540. Lymphatic vessels, 425. Macaque, 543. Macropodide, 529. Macrosceledidz, 542. Madrepora aspera, 124. Madrepore, 120, Madreporic canal, 165. Madreporite, 159. Magellania flavescens, 185; lenticu- laris, 186. Magnum, 502. Malacostraca, 232. Malapterurus, 400, Malar bone, 499. Malaria caused by Protozoa, 58. Malphigian tubes, 248. Mammalia, 491. Mammary glands, 360. Manatee, 526. Mandible, of vertebrates, 339, 500. Mandibles, of crustacea, 217, 219; of insects, 242; of Myriapoda, 2qo, Manis, 533. Mantle, of ascidians, 315 ; of molluscs, 266, 289; cavity, 271, 289, 304. Manubrium, 92, 94, 95, 109. Marmoset, 543. Marsupium, 525. Mastigamceba, 37, 41. Mastigophora, 34. Maxilla, of crustacea, 218, 219; of insects, 242, Maxillary palpus of insects, 242. Maxilliped, 218, Medulla, 45, 55; of kidney, 519; ob- longata, 354. Medusa-buds, 92. Megagamete, 4q. Megaleesthetes, 282. Meganucleus, 45, 50. Lungs, 70; book, of Arachnida, 257 ; Megapodius, 491. INDEX Meleagrina margaritifera, 280. Membrane, branchiostegal, 396; nic- titating, 435; tympanic, 408, 435; undulating, 50. Menopoma, 433. Merostomata, 260. Mesentery, 115, 347, 507. Mesoglezea, 94. Mesopodium, 290. Metacarpus, 342. Metacrinus interruptus, 177. Metagenesis, 98. Metametes, 189. Metamorphosis, of crustacea, 235; of frog, 429; of insects, 251; retro- grade, of ascidians, 320. Metapleure, 323. Metapodium, 290. Metatarsal bones, 504. Metatarsus, 342. Metatheria, 525. Metazoa, 19, 59. Metridium marginatum, 117. Mice, 526. Micreesthetes, 282, Microgamete, 44. Micronucleus, 45. Miliola, 22. Milk, pigeon’s, 483. Mill, gastric, of crawfish, 220. Millepora, 104. Mite, 260; itch, 260. Mole, 526, 542. — Molar teeth, sos. Mollusca, 264; characters of, 364; naked, 291, 296. Molluscoidea, 184. Monkey, 543. Monocystis agilis, 55, 56. Monotremata, 525. Monosiga, 39. Mordacia, 365. Morphology, 4. Mound-maker bird, 491. Mouth, 92; of fishes, 368, 374; of fluke-worms, 130; of frog, 408, 417. Mud-fish, 405. 555 Multicilia, 49. Muscle, adductor, of bivalve shells, 268, 271. Muscle, of birds, 472; of vertebrates, 342- Mussel, fresh water, 265, 270, 273, 274; brain of, 276; nervous system of, 276; sea, 279. Mustelus anarcticus, 366; canis, 366; vulgaris, 366. Mya arenaria, 279. Myomeres, 342. Myriapoda, 239. Myrmecophaga, 531. Mytilus edulis, 279. Myxine, 360; glutinosa, 362, 364. Myxospongiz, 86. Nacre of shell, 269. Naked molluscs, 291, 296. Name, generic, 2; specific, 2. Nares, 347, 417, 425, 505; of mam- mals, 496. Nauplius, 233. Nautilus pompilius, 298, 300, 306, 309. Nectocalyces, 105. Necturus, 433. Nematelminthes, 149. Nematocysts, 52, 95, 96. Nematoda, 149. Nematodes, 154. Nemertean worms, 145. Nemertinea, 145. Nephridia, of Amphioxus, 327; of annelids, 196; of leech, 207, 208; of molluscs, 275, 283, 295, 308. Nephridiopores, 203. Nephrostomes of frog, 427. Nereis dumerilii, 189, I92, virens, 189. Nerve cord of Amphioxus, 328. Nerve-pentagon, 162. Nerves, 71; auditory, 356; cranial, 356; cerebral, 356; hypoglossal, 425; olfactory, 356, 381; optic, 356, 381, 517; peripheral, 355. Nervous system, of annelids, 195; of 194; 556 crustacea, 227; of insects, 249; of molluscs, 275, 282, 295, 296, 306; of Nematoda, 152; of nemertean worms, 148; of flu&ke-worm, 132; of starfish, 162; of tape-worm, 149; of vertebrates, 355, 380, 381. Nest, birds’, 490. Neuroceele, 310. Neuropodium of annelid worms, 190. Newt, 432. Nictitating membrane, 408, 435, 492. Noctiluca miliaris, 41. Nodosaria, 25. Nomenclature, binomial, «. Nostrils, in Apteryx, 486; of birds, 459; of frog, 408. Notechord, 910; 913, 924; 336, (337, 366, 406. Notochordal sheath, 325. Notopodium of annelid worms, Igo. Nuclearia, 29. Nucleus, 16, 45. Nucula, 279. Nudibranch molluscs, 291, 296. Nummulites, 25. Nyctotherus, 49. Obelia, 99; commissuralis, 91; gela- tinosa, 91; geniculata, 91. Ocelli, 104. Ocellus of insects, 250. Octopus, 302. Ocular plates of Echinoidea, 172. Odontoid process, 493. Odontophore, 293, 304. (Esophagus of starfish, 163; of in- sects, 246. Oikomonas, 37. Oil glands ot birds, 459. Olfactory capsules, 410. Olfactory pit of Amphioxus, 328. Olfactory sacs of frogs, 425. Oligochzeta, 202. Ommatidia, of crustacea, 228; insects, 250. Omosternum, 415. Onychophora, 236, of INDEX Oosperm, 59, 60, 62. Opalinopsis, 49. Operculum, 52; of bony fish, 396; of Dipnoi, 407 ; of gastropod molluscs, 291, 295; genital, of scorpion, 257; of Limulus, 262; of Polyzoa, 181. Ophioglypha lacertosa, 169. Ophiuroidea, 169. Ophrydium, 53. Ophryodendron, 51. Ophryoglena, q9. Opisthocomus, 487. Opossum, 525, 528. Optic chiasma, 380. Optic lobes, 380, 480. Optic thalami, 354, 516; of sharks, 380. Orbito-sphenoid, 498. Organs, 66, Ornithorhynchus, 525, 527. Osculum, 77. Osphradium, 277, 295; in Nautilus, 308. Ossicles, ambulacral, 161; auditory, 500; of starfish, 157. Ostium, 82. Ostrich, 483. Otaridze, 540. Otocysts, 98; of mussels, 277; of Cephalopods, 308. Otoliths of vertebrates, 358. Otter, §26, 540. Ovaries, of birds, 482 ; of frog, 427, 428; of mammals, 520; of shark, 384; of starfish, 107; of vertebrates, 359. Ovary, 101, 133; of crustacea, 228. Oviducts, of birds, 482; of crustacea, 229; of mammals, 520; of verte- brates, 359, 428. Ovum, 59, 60; fertilization of, 61; maturation of, 61; of mammals, 521; of vertebrates, 359, 384. Oxen, 526, 537. Oyster, pearl, 280, Pachychalina, 87. Pzedogenesis in insects, 251, INDEX Pagurus bernhardus, 231. Palzeontology, Io, Palate, 505. Palatine bone, 414, 499. Pallial line, 267. Pallium, 266, Palpi, of annelid worms, 189; of mol- luses, 271, 282. Palpus of insectgy2q2. Palythoa, 89. es Pancreas, 69, 344, 346, 375, 418, 507; of birds, 476. Pancreatic appendages of molluscs, 307- Papilla, adhesive, of nemertean worms, 146. Papulze of starfish, 159. Paraglossze of insects, 243. Paralichthys dentatus, 398. Parameecium caudatum, 45, 47. Paramylum, 36. Parapodia of annelids, 189. Parasitic worms, 156. Parasphenoid bone of frogs, 413. Parietal bones of frogs, 413. Parthenogenesis, in insects, 250; in Rotifers, 180. Patagium, 541. Patella, 292; of mammalian leg, 503. Pearl, mother of, 269; mussel, 265, 280; oyster, 280, Pebrine, 58. Pecten, 280; of eye of bird, 480, 489. Pectines of scorpion, 257. Pedalion, 180. Pedicellina, 181, 184. Pedicellariz, 159. Pedicles, 537. Pedipalpi, 256; of spider, 259. Peduncle, 120. Pelagic animals, 291, 308. Pelecypoda, 265, 278, 280. Pelomyxa, I9. Pelvic arch, 445. Pelvic fin, 374, 406. Pelvis of mammalian kidney, 518. 557 Penis, of fluke-worms, 130; of mam- mals, 520; nematoid worms, setz of, 149. Pennatula aculeata, 120; sulcata, rar. Pen of cuttle-fish, 301. Pentacta frondosa, 173. Peptones, 346. Peramelidz, 528. Pericardium, 295; of frog, 419; of molluses, 271. Perilymph, 383. Periostracum, 268, Periotic bones, 499, Peripatus, 236. Periplaneta americana, 242, Perisarc, 94. Perissodactyla, 538. Peristome, 52, 163, 287. Peristomium, 189. Peritoneum, 347; of annelid worms, 197. Pinna, auditory, 333. Pinnipedia, 540. Pinnules of crinoids, 176. Pipe fish, 404. Pisces, 365, 394; teeth of, 4o2. Placenta, 360. Placophora, 284. Plaice, 397. Planaria, lugubris, 138; polychroa, 138; torva, 138. Plankton, 12. Planorbulina, 25. Planula, 98, 110. Plates, in reptiles, 443. Platyhelminthes, 129, Platypus, 525. Pleopoda, 216. Pleural membrane, 513. Pleura sac, 513. Pleurobrachia, 128. Pleuronectes cynoglossus, 398. Pleuronectidze, 397. Petasus, 102, Petromyzon, 360; marinus, 361, 363. Phalanges, 342, 502, 530; ungual, 342. Pharynx, of Amphioxus, 325; of an- 558 nelid worms, 193; of leech, 205; ascidian, 365; of mammals, 505; of vertebrates, 344. Phascolomyida, 529. Phocidze, 540. Phragmocone, 301. Piylogenes, 11. Phylum, 7, 74, 75. Physalia arethusa, 105. Physiology, 12. Pieris rapie, 244. Pig, 526, 537- Pigeon, domestic, structure of, 457. Pigeon's milk, 483. Pigment cells of molluscs, 303. Pineal body, 354, 380; eye, 364, 450. Pleurophyllidia, 2gt. Ploughshare, 465. Pneumatic duct, 403. Pneumatophore, 105. Podobranchiz, 224. Podomeres, 214. Podophrya, 51. Poison apparatus of reptiles, 454. Poison fang of reptiles, 447, 453, 454- Poison glands, of scorpion, 255; | of spider, 259; of reptiles, 453. Poison, of reptiles, 454; immunity against, 454. Polar bodies, 60. Polian vesicles, 165. Polychzeta, 199. Polykrikos, 40. Polyoeca, 39. Polype, 90. Polypterus birchir, 399. Polyzoa, 181. Pons Varolii, 517. Porcupine, 526, 541. Pore, excretory, of fluke-worms, 130; of round-worms, 149. Porifera, 76. Porpoise, 526, 536. Portuguese man-of-war, Ios. Post-abdomen, 255. Potamobia pallipes, 213, 221. Prze-abdomen, of scorpions, 255. INDEX Pre-maxillze, 499. Pre-hallux, 417. Premaxilla of frog, 414. Prepuce of mammals, 520. Pre-sphenoid, 498. Presternum, 495. Primates, 527, 543. Pristiphorus, 387. Pristis, 387. Proboscis, of an’ corms, 193; of Balanoglossus, 371; of gastropod molluscs, 289, 293; of leech, 211; of nemertean worms, 145; sheath of, 146. Process, articulating, 334; odontoid, 464. Procoracoid bone of frog, 414. Proglottis, Tyo. Pro-ostracum, 301. Pro-otic bones of frog, 411. Propodium, 290. Prorocentrum, 4o. Prorodon, 49. Prosencephalon, 380. Prosimii, 543. Prosopyle, 81. Prostomium of annelids, 189. Proterospongia, 39. Proteus, 433. Protobranchia, 279. Protomerite, 58. Protoplasm, 16. Protopodite, 216. Protopterus, 405. Prototheria, 524. Prototroch, 295. Protozoa, 14. Proventriculus of birds, 474, 488. Pseudoceele, 515. Pseudopleuronectes americanus, 398. Pseudopodia, Is. Pteropoda, 288, 291, 296. Pterygiophores, 372. Pterygodia, 388. Pterygoid, bones, 414, 499. Pterygoid process, 498. Pterylae, 462. INDEX Pterylosis, 462, 463. Ptyalin, 344. Pubis, 342; of birds, 470; of frog, 416: of mammals, 503. Pulmonary sacs of Arachnida, 257. Pupa, 251. Pygopus, 436, 437. Pygostyle, Pyxicola, Quadrate bo Quadrato-jugal, 414. Quadrula symmetrica, 20. Quill, 460. Rabbit, 331, 491, 526. Rachis, 461. Radiale, 469. Radiolaria, 31. Radio-ulna of frog, 415. Radius, 341, 501; of bird, 469. Radula, 293. Radula sac, 293. Rana esculenta, 408, 415, 429; tem- poraria, 408, 412, 413, 417, 420, 421; metamorphosis of, 430. Rat, 526. Ratitae, 483. Rattlesnake, skull of, 445. Ray, 388, 394; electric, 392; sting, 388. Razor fish, 281. Rectrices, 463. Rectum, of molluscs, 271; of mam- mals, 507. Remiges, 463. Reproduction, 18, 24, 72. Reptilia, 433. Respiration, 70; of vertebrates, 332, 349- Rhabdopleura, 311. Rhinoceros, 526, 538. Rhipidodendron, 37. Rhizopoda, 14, 19. Rhizostomez, I12. Rhyncheta, 51. Rhynchocephalia, 434- Ribbon, lingual, 293- 559 Rib, 336. Ribs, of birds, 463, 494; false, 495; floating, 495. Rodentia, 526, 541. Rostellum, 140. Rostrum, 216. Rotalia, 22. Rotifera, 178. Ruminants, 526. Sac, scrotal, 520. Saccammina, 25. Sacral vertebrae, 335. Sacrum, 494. Salamander, 432. Salamandra maculosa, 432. Salmo, fario, 395, 401; fontinalis, 395. Salmon, Burnet, 405. Salpingoeca, 39. Sapropbytes, 45. Saprophytic, 42. Saw-fish, 387. Scales, ctenoid, 398; cycloid, 398; ganoid, 399; of legs of birds, 459; placoid, 367; of reptiles, 435, 439. Scallop shell, 280. Scaphoid, 502. Scapula, 414; of birds, 468. Sclerotic, 356; plates of bird's eye, 480. Scolex, 140. Scolopendra, 240. Scorpion, 255, 259; anatomy of, 258; carapace of, 255. Scuta, 240. Scutes of bony fishes, 399. Scutigera, 240. Scyllium, canicula, 338, 345, 366, 371, 376; catulus, 366. Scyphozoa, 91, 108. Scyphula, 112. Sea-hare, 288, 291, 296. Sea-horse, 404. Sea-squirts, 314. Sea-urchins, 170. Seal, 526, 540; earless, 540. Segmental organs of annelids, 196. 560 Segmentation of egg, 60. Segments of worms, 189. Sella turcica, 498. Sense organ, 108. Sense organs of leech, 209; of mol- luses, 282. Sepia cultrata, 297, 301, 305. Septa, 121; of annelid worms, 191. Serpula, 198. Setze, of annelids, 190, 201; olfactory, of crustacea, 228; penial, 149, 150, 153: Setigenous sac of annelids, 190. Shark, Greenland, 393. Sheath, proboscis, of nemertean worms, 146. Sheep, 526, 537. Shell, Cephalopod, 300. Shell-fish, 266. Shell-gland of fluke-worm, 133. Shell-glands, 133; of crustacea, 233. Shell membrane, 490; nacre of, 269; periostracum, 269; prismatic layer of, 269; supplemental, 23; vesti- gial, 288. Shells, dextral, 285; sinistral, 285. Shields of reptiles, 439. Ship-worm, 279. Shoulder-girdle, of birds, 468; frog, 414. Shrew, 526; jumping, 542. Simiide, 544. Sinistral shells, 285. Sinus venosus, 350, 407, 419. Siphon, of molluscs, 266; of gastro- pod mollusc, 289. Siphonoglyphes, 115. Siphons of ascidians, 315. Siphonozooids, 118, Siphophora, 104. Siphuncle, 300. Siren, 433. Sirenia, 526, 536. Skeleton, 28, 67; of birds, 487; of fish, 368; of sponges, 79. Skull, autostylic, 407; of birds, 467; of frog, 410; of mammals, 495; of INDEX of reptiles, 444; of vertebrates, 328, 333, 337, 339- Slits, branchial, of sharks, 368 ; gill, of Amphioxus, 326; of Balanoglos- sus, 312. Sloth, §26, 93%, $72. Slug, 288, 293. Snail, 284. Snake, 436, 44 parous, 455; Soldier ant, 253. Sole, 297. Solen, 281. Species, 3; abyssal, 11; alpine, 11; littoral, 11; pelagic, r1, 24. Sperm, 59. Spermiduct of shark, 384. Sphaerophrya, 51. Sphenethmoid bone of frog, 411. Spicule, 31, 119. Spicule of sponge, 79, 88. Spider, 259. Spine, caudal, of Limulus, 262. Spines, ambulacral, 159; neural, 369. Spinnerets, 259. Spiracle of shark, 332, 368, 386. Spiroloculina, 25. Spirula peronii, 300, 301. Spleen, 375, 418; of birds, 476; of mammals, 513. Sponges, 76. Spongelia, 87. Spongilla, 85, 89. Spores, 30. Sporocyst, 30, 134 ; of fluke-worm,134. Sporoduct, 58. Sporozoa, 55. Spot, anal, 46. Spur of birds, 487. Squamata, 434. Squamosal bone, 414, 498. Squammulina, 22. Squid, 296, 300. Squirrel, 526, 541; flying, 541. Starfish, 157. Stentor, 49. Sternebrze, 336, 495. S, 436; Ovi- » 455+ INDEX Sternum, 255, 336; of birds, 465, 488; of frog, 415; of reptiles, 443. Stichotricha, 53. Stickleback, 406. Stigma, 36. Stigmata, of ascidians, 315; of in- sects, 248; of scorpion, 257. Stomach, of m' ls, 506; of star- fish, 163; of vertebrates, 374, 418. Stomach, sucking, of insects, 246. Stomodzeum of Nematoda, 152. Stomogastric nerves, 195. Stone-canal of Echinoderms, 165. Strepsiptera, 252. Streptoneura, 295. Strongylocentrotus, 171. Struthio, 483. Sturgeon, 399, 400. Stylaster, 104. Stylet of nemertean worms, 145. Sucker of distoma, 130, 136. Suprascapular bone of frog, 414. Suspensorium, 414. Sutures of skull, 496. Swan mussel, 265. Swift, 490. Swimming, act of in squid, 304, 308. Sycon ciliatum, 76; gelatinosum, 76. Sylvian fissure, 515. Symbiosis, 33. Symmetry, bilateral, of worms, 130; radial, 176. Sympathetic nerves of vertebrates, 381, 517. Symphysis, of jaw, 500; pubic, 352, 502; of frog, 416. Synapta, 174. Syncrypta, 37. Syncytial ectoderm, 151. Syngnathus, 404. Syn-sacrum, 465, 487. Syrinx, 488. 20 561 Tadpole, 429. Teenia coenurus, 143; echinococcus, 143, 144; saginata, I42, 144; ser- rata, 142; solium, 139, 141, 144. Tail, diphycercal, 396; heterocercal, 367, 396; homocercal, 367, 396. Tailor bird, 490. Talpa, 542. Tape-worms, 138, 144; human, 138, 141. Tapir, 526, 538. Tarso-metatarsus, 472. Tarsus, 342, 411, 503; of insects, 244. Tealia crassicornis, 115. Teeth, dermal, 467; heterodont, 523; homodont, 523; thecodont, 523; of leech, 205 ; of sharks, 392; of shells, 267; stomach, of crawfish, 220; of vertebrates, 343, 418, 446, 504; ca- nine, 505; incisor, 504; molar, 505; premolar, 505. Teleostei, 394. Teleostomi, 394. Telson, 217. Tentacles, 48, 50, 91; of annelid worms, 189; of crinoids, 176; of molluscs, 289; of starfish, 160. Tentaculifera, 48, 50, 51. Tentaculocysts, Ior, Terebra oculata, 289. Terebratulina septentrionalis, 187. Teredo navalis, 279, 280. Tergum, 255. Tessera princeps, I13. Test, 19; of ascidians, 315. Testes, 101, 132; of birds, 481; of crustacea, 228 ; of fluke-worm, 132; of frog, 427; of mammals, 520; of Nematoda, 153; of starfish, 167; of vertebrates, 359. Tetrabranchiata, 299, 308. Tetramita, 37. Tetrastemma, 147. Texas cattle disease, 260. Texas cattle fever, 58. Theca, 92, 120. Thecodont teeth, 523. 562 Theria, 524, 525. Thoracic vertebrae, 335. Thorax, of insects, 241; of mammals, 504. Thuricola, 53. Thylacine, 528. Thymus, 513; of birds, 476. Thyroid, 513. Thyroid glands, 476. Tibia, 342, 416. Tibio-fibula of frog, 416. Tibio-tarsus of birds, 471. Tick, 260; cattle, 260. Tintinnidium, 49. Tissues, 63. Toad, 432. Toe, great, of frog, 410. Toes, of birds, 487. Tongue, of birds, 474; of frog, 417; of vertebrates, 344. Torpedo occidentalis, 392. Trachea, of birds, 476; of mammals, 512; of reptiles, 347, 448. Trachez of insects, 248. Trachelomonas, 37. Trachelius, 49. Trachosphere of molluscs, 295. Trachylinge, 102. Trapezium, 502. Trapezoid, 502. Tree, genealogical, 9. Trematoda, 134; ectoparasilic, 137. Trichechidee, 540. Trichina spiralis, 154. Trichocysts, 46. Triclad Turbellaria, 137. Tridacna gigas, 280. Trigeminal nerves, 382. Trigger-hair, 95. Trigonia, 280. Triton nodiferus, 286, 294. Trochanter, 471, 503. Trochosphere of annelid worms, 201. Trout, 395. Tuatara, 437, 438. Tube-feet,of Echinoidea,170 ; of Holo- thuroidea, 173; of starfish,160, 161. INDEX Tubipora musica, 119. Tunic of ascidians, 315. Turbellaria, 137. Turbot, 397. Turtles, 434, 438, 455. Tympanic bones, 499. Tympanum, 358; of frog, 408. Tzetse fly, 58. Ulna, 341, 501; of birds) 469. Ulnare, 469. : : Umbilicus of feather, 460. Umbo of shells, 267, Umbrella, 95. Una, 592. Unciform, 502. Ungulata, 526, 536. Unio complanatus, 265, 280; mar- garitifer, 265. Urchin, sea, egg of, 60. Urchins, cake, 173; heart, 173. Ureter, 359; of frog, 427; of mam- mals, 519; of shark, 384. Urethra, 359, 520. Urinary tubes, 248. Urine, 358. Urnatella, 181. Urochorda, 314; larva, 319. Urodela, 432. Urolophus testaceus, 390. Uropoda, 217. Uropygium, 457, 463. Uterus, masculinus, 520; of Nema- toda, 154; of tape-worm, 140; of vertebrates, 359; of worms, 133. Sere Vacuole, contractile, 17, 36, 45; food, 46. Vagina, of leech, 211; of vertebrates, 359; 521. Vagus nerve, 383. Valve, spiral, 374; of shark, 393, 402. Valves, mitral, 510; semi-lunar, 510; of shells, 265. Vane of feather, 460. Variation, 3. Vascular system of a fish, 378. INDEX Vas deferens, of fluke-worm, 132; of mammals, 520; of vertebrates, 359; of worms, 132. Vein, pulmonary, 407, 423; portal, 422. Veins, hepatic, 352; pulmonary, 351; of vertebrates, 349, 359, 379. Veliger, 295. Velim, 97, Ait, Velvet, of deer horns, 537. Ventricle, of brain, fourth, 354, 380; lateral, 354; third, 354; fifth, 514. Ventricles of heart of vertebrates, 350. Venus'’s flower-basket, 86 ; girdle, 128. Vermetus, 296. Vermiform appendix, 507. Vermis, 517. Vertebra, 333, 440, 463 ; amphiccelous, 334, 440; heteroccelous, 464; pro- coelous, 335, 410, 441. Vertebrata, 322; brain of, 354; cir- culation of, 349; nervous system of, 350; respiration of, 349. Vertebral column, 333, 369; of birds, 463; of frog, 410; of mammals, 493. Vesicles, Polian, 165; racemose, 166 ; Tiedemann's, 166. Vesicula seminalis of worms, 133. Vessels, water, of flat worms, 132; of Platyhelminths, 132. Vexillum, 460. Vibrissze of rabbit, 492. Visceral arches, 337, 444. Visceral mass of molluscs, 270. renal 563 Visceral nerves, of crustacea, 227; of worms, 195. Viviparity, 72. Voice of birds, 488. Vole, 541. Volvox globator, 43, 44. Vomer bone, of frog, 413. Vorticella, 48, 52,54; parasitic, 55. Vulva, 521. Wallaby, 530. Walrus, 526, 540. Wasp, 250. Weasel, 526. Whale, 526, 536. Wheel animalcules, 178. Whelk, 296. Wings, of birds, 459; muscles of, 474; of insects, 244; veins of, 244. Wombat, 529. Worker ant, 253. Worm, blind, 436. Xiphosura, 260, 263. Xiphisternum, 415. Yolk-sac, of shark, 386, Zocecium, 181. Zooid, 30, 91. Zoology, definition of, 1. Zoophytes, go. Zooxanthella, 33. Zygomatic arch, 499. Zygomatic process, 498. Zygapophysis of frog, 410. A TEXT-BOOK OF ZOOLOGY BY T. JEFFERY PARKER, D.Sc., F.R.S. Professor of Biology in Untuersitty of Otago, Dunedin, N.Z. AND WILLIAM A. HASWELL, M.A., D.Sc., F.R.S. Professor of Biology in the Untversity of Sydney, N.S.W. In two volumes, containing many illustrations Cloth. 8vo. 2 vols. $9.00, net “The book deserves a warm welcome, and ... will be found an invaluable aid not only to students of zodlogy, but also to a large num- ber of those whose main interest lies in other branches of scientific study. 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After a general introduction and a section upon ‘General Structure and Physiology,’ there are presented in turn the twelve phylums recognized, viz.: Protozoa, Porifera, Coelen- terata, Platyhelminths, Nemathelminths, Trochelminths, Molluscoida, Echinodermata, Annulata, Arthropoda, Mollusca, and (occupying the whole of the second volume) Chordata, corresponding nearly with Vertebrates. The discussion of each class is based upon a more or less detailed account of the anatomy and development of one or more forms, fairly representative and commonly available. The second volume also contains a discussion of the mutual relationships of the Chordata and of the twelve phyla. The last seventy pages are devoted to Geographic Distribution, the Philosophy and History of Zodlogy, and Modern Literature; seven of the sixty writers recommended being American.” — The Nation. THE MACMILLAN COMPANY NEW YORK CHICAGO BOSTON SAN FRANCISCO EXPERIMENTAL MORPHOLOGY BY CHARLES BENEDICT DAVENPORT, Ph.D. Lustructor in Zodlogy in Harvard University PART I. PART II. Effects of Chemical and | Effects of Chemical and Physical Agents upon Physical Agents upon the Protoplasm Growth Cloth. 8vo. $2.60, net Cloth. 8vo. $2.00, net “The material which is discussed has been well digested and is well arranged, and the style is on the whole clear and concise. The book is a readable one, and the descriptions and criticisms of the methods employed in experimentation, and the bibliographical lists at the conclusion of each chapter, con- tribute materially to the value the book possesses for both the morphologist and the physiologist.” — Sczence. “In this second instalment of his valuable treatise, Dr. Davenport considers the effects of chemical and physical agents on growth. 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