c2L, V. I CORNELL UNIVERSITY LIBRARY BOUGHT WITH THE INCOME OF THE SAGE ENDOWMENT FUND GIVEN IN 1891 BY HENRY WILLIAMS SAGE Corneir University Library QL 615.J82 V.I %!^?,...t9,...t'ie study of fishes^ 3 1924 024 557 641 Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924024557641 GUIDE TO THE STUDY OF FISwrL. A GUIDE TO THE STUDY OF FISHES BY DAVID STARR JORDAN President cf Leland Stanford J uiilor University With Colored Frontispieces and 42"] Illustrations IN TWO Vni,UMES VOL I. " I am the wiser in respect to all knowl- edge and the better qualified for all fortunes for knowing that there is a minnow in that brfjok." — Thoreait NEW ^T)RK HENRY HOLT AND COMPANY 1905 l/'" c-^ i G Copyrig-ht, 1905 EV HENRY HOLT AND COMPANY Published March, 1905 ROBERT DRUMMOND, PRINTER, NHW YORK To trbeoJ)ore Gill, Ichthyologist, Philosopher, Critic, Master in Taxonomy, this volume is dedicated. PREFACE This work treats of the fish from all the varied points of view of the different branches of the study of Ichthyology. In general all traits of the fish are discussed, those which the fish shares with other animals most briefly, those which relate to the evolution of the group and the divergence of^ its various classes and orders most fully. The extinct forms are restored to their place in the series and discussed along with those still extant. In general, the writer has drawn on his own experience as an ichthyologist, and with this on all the literature of the science. Special obligations are recognized in the text. To Dr. Charles H. Gilbert, he is indebted for a critical reading of most of his proof-sheets ; to Dr. Bashford Dean, for criticism of the proof- sheets of the chapters on the lower fishes ; to Dr. William Emer- son Ritter, for assistance in the chapters on Protochordata; to Dr. George Clinton Price, for revision of the chapters on lancelets and lampreys, and to Mr. George Clark, Secretary of Stanford University, for assistance of various kinds, notably in the prep- aration of the index. To Dr. Theodore Gill, he has been for many years constantly indebted for illuminating suggestions, and to Dr. Barton Warren Evermann, for a variety of favors. To Dr. Richard Rathbun, the writer owes the privilege of using illustrations from the "Fishes of Xorti: and Middle America" by Jordan and Evermann. The remaining plates were drawn for this work by Mary H. Wellman, Kako Morita, and Sekko Shimada. Many of the plates are original. Those copied from other authors are so indicated in the text. No bibliography has been included in this work. A list of writers so complete as to have value to the student woulcl make viii Preface a volume of itself. The principal works and their autliors are discussed in the chapter on the History of Ichthyolog}', and with tliis for the present the reader must be contented. The writer has hoped to make a book valuable to technical students, interesting to anglers and nature lovers, and instruc- tive to all who open its pages. David Starr Jordan. Palo Alto, S.xnt.a Cl.-vr.a County, Cal., October, 1904. CONTENTS VOL. I. CHAPTER I. THE LIFE OF THE FISH (Lepomis megalotis). PAGE What is a Fish? — The Long-eared Sunfish. — Form of the Fish. — Face of the ■ Fish. — How the Fish Breathes. — Teeth of the Fish. — How the Fish Sees. — Color of the Fish.— The Lateral Line.— The Fins of the Fish.— The Skele- ton of the Fish. — The Fish in Action.— The Air-bladder.— The Brain of the Fish. — The Fish's Nest 3 CHAPTER II. THE EXTERIOR OF THE FISH. Form of Body. — Measurement of the Fish. — The Scales or E.xoskeleton. — Ctenoid and Cycloid Scales. — Placoid Scales. — Bony and Prickly Scales. — Lateral Line. — Function of the Lateral Line. — The Fins of Fishes. — Muscles 16 CH.\PTER III. THE DISSECTIOX OF THE FISH. The Blue-green Sunfish. — The Viscera. — Organs of Xutrition. — The Alimen- tary Canal. — The Spiral Valve. — Length of the Intestine 26 CHAPTER IV. THE SKELETON OF THE FISH. Specialization of the Skeleton. — Homologies of Bones of Fishes. — Parts of the Skeleton. — Names of Bones of Fishes. — Bones of the Cranium. — Bones of the Jaws. — The Suspensorium of the Mandible. — Membrane Bones of Head. — Branchial Bones. — The Gill-arches. — The Pharyngeals. — The Vertebral Column. — The Interneurals and Interhsemals.- The Pectoral Limb.— The Shoulder-girdle. — The Posterior Limb. — Degeneration. — The Skeleton in Primitive Fishes. —The Skeleton of Sharks.— The ;\rchipterygium 34 PAGE 62 X Contents CHAPTER V, MORPHOLOGY OF THE FINS OF FISHES. Origin of the Fins of Fishes.^Origin of the Paired Fins.— Development of the Paired Fins in the Embryo.— Evidences of Palaeontology.— Current The- ories as to Origin of Paired Fin.— Balfour's Theory of the Lateral Fold.— Objections.— Objections to Gegenbaur's Theory.— Kerr's Theory of Modi- fied External Gills.— Uncertain Conclusions.— Forms of the Tail in Fishes. — Homologies of the Pectoral Limb.— The Girdle in Fishes other than Dipnoans CHAPTER VI. THE ORGANS OF RESPIRATION. How Fishes Breathe.— The Gill Structures.— The Air-bladder.— Origin of the Air-bladder.— The Origin of Lungs.— The Heart of the Fish.— The Flow of Blood 91 CHAPTER Vn. THE NERVOUS SYSTEM. The Nervous System.— The Brain of the Fish.— The Pineal Organ.— The Brain of Primitive Fishes.— The Spinal Cord.— The Ner\-es 109 CHAPTER VHI. THE ORGANS OF SENSE. The Organs of Smell.— The Organs of Sight. — The Organs of Hearing. — Voices of Fishes. — The Sense of Taste. — The Sense of Touch 115 CHAPTER LX. THE ORG.ANS OF REPRODUCTION. The Germ-cells, — The Eggs of Fishes. — Protection of the Eggs. — Sexual Modi- fication 124 CHAPTER X. THE EMBRYOLOGY AND GROWTH OF FISHES. Postembryonic Development. — General Laws of Development. — The Signifi- cance of Facts of Development. — The Development of the Bony Fishes. — The Larval Development of Fishes. — Peculiar Larval Fomis. — The Devel- opment of Flounders. — Hybridism. — The Age of Fishes. — Tenacity of Contents xi PAGE Life.— Effect of Temperature on Fishes.— Transportation of Fishes.— Re- production of Lost Parts.— Monstrosities among Fishes 131 CHAPTER XL INSTINCTS, HABITS, AND ADAPTATIONS. The Habits of Fishes.— Irritability of Animals.— Nerve-cells and Fibers. — The Brain or Sensorium.— Reflex Action.— Instinct.— Classification of Instincts. — Variability of Instincts.— Adaptations to Environment.— Flight of Fishes. — Quiescent Fishes.— Migratory Fishes.— Anadromous Fishes.— Pugnacity of Fishes. — Fear and Anger in Fishes. — Calhng the Fishes. — Sounds of Fishes. — Lurking Fishes. — The Unsymmetrical Eyes of the Flounder. — Carrying Eggs in the Mouth 152 CHAPTER XII. ADAPTATIONS OF FISHES. Spines of the Catfishes. — Venomous Spines. — The Lancet of the Surgeon-fish. — Spines of the Sting-ray. — Protection through Poisonous Flesh of Fishes. — Electric Fishes. — Photophores or Luminous Organs. — Photophores in the Iniomous Fishes. — Photophores of Porichthys. — Globefishes. — Remoras. — Sucking-disks of Clingfishes. — Lampreys and Hogfishes. — The Sword- fishes. — The Paddle-fishes. — The Sawfishes. — Peculiarities of Jaws and Teeth. — The Angler-fishes. — Relation of Number of Vertebra; to Temper- ature, and the Struggle for Existence. — Number of Vertebrje: Soft-rayed Fishes; Spiny-rayed Fishes; Fresh-water Fishes; Pelagic Fishes. — Varia- tions in Fin-rays. — Relation of Numbers to Conditions of Life. — Degenera- tion of Structures. — Conditions of Evolution among Fishes 179 CHAPTER XIII. COLORS OF FISHES. Pigmentation. — Protective Coloration, — Protective Markings. — Sexual Colora- tion. — Nuptial Coloration. — Coral-reef Fishes. — Recognition Marks. — In- tensity of Coloration. — Fading of Pigments in Spirits.— Variation in Pat- tern. 226 CHAPTER XIV. GEOGRAPHICAL DISTRIBUTION OF FISHES. Zoogeography. — General Laws of Distribution.- Species Absent through Bar- riers. — Species Absent through Failure to Maintain Foothold.— Species Changed through Natural Selection.— Extinction of Species.— Barriers xii Contents Checking Movements of Marine Species. — Temperature the Central Fact in Distribution. — Agency of Ocean Currents. — Centers of Distribution. Distribution of Marine Fishes. — Pelagic Fishes. — Bassalian Fishes. Lit- toral Fishes. — Distribution of Littoral Fishes by Coast Lines. — Minor Faunal Areas. — Equatorial Fishes most Specialized. — Realms of Distribu- tion of Fresh-water Fishes. — Xorthern Zone. — Equatorial Zone. — Southern Zone. — Origin of the New Zealand Fauna 237 CHAPTER XV. ISTHMUS BARRIERS SEPARATING FISH FAUNAS. The Isthmus of Suez. — The Fish Fauna of Japan. — Fresh-water Faunas of Japan. — Faunal Areas of Marine Fishes of Japan. — Resemblance of Japan- ese and Mediterranean Fish Faunas. — Significance of Resemblances. — Differences between Japanese and Mediterranean Fish Faunas. — Source of Faunal Resemblances. — Effects of Direction of Shore Lines. — Numbers of Genera in DilTerent Faunas. — Significance of Rare Forms. — Distribution of Shore-fishes. — Extension of Indian Fauna. — The Isthmus of Suez as a Bar- rier to Distribution. — Geological Evidences of Submergence of Isthmus of Suez. — The Cape of Good Hope as a Barrier to Fishes. — Relations of Japan to the Mediterranean Explained by Present Conditions. — The Isthmus of Panama as a Barrier to Distribution. — Unlikeness of Species on the Shores of the Isthmus of Panama. — Views of Dr. Giinther on the Isthmus of Panama. — Catalogue of Fishes of Panama. — Conclusions of Evermann & Jenkins. — Conclusions of Dr. Hill. — Final Hypothesis as to Panama 255 CHAPTER X\ I. DISPERSION OF FRESH \V.\TER FISHES. The Dispersion of Fishes.— The Problem of Oatka Creek. — Generalizations as to Dispersion. — Questions Raised by Agassiz. — Conclusions of Cope. — Questions Raised by Cope.— Views of Giinther. —Fresh-water Fishes of North America.— Characters of Species.— Meaning of Species.— Special Creation Impossible.— Origin of American Species of Fishes 282 CHAPTER X\7I. DISPERSION OF ERESH-W.\TER FISHES. (Co„li„„cd.) Barriers to Dispersion of Fresh-water Fishes: Local IJarriers. — Fa\-orable Waters Have Most Species. — Water-sheds. — How Fishes Cross Water-sheds — The Suletind. — The Cas.siquiare. — Two-Ocean Pass. — Mountain Chains — U]>land Fishes. — Lowland Fishes. — Cuban Fishes. — Swampy Water sheds. — The Great Basin of Utah. — Arctic Species in Lakes. — Causes of DisTXTsion still in Operation ^ 297 Contents xiii CHAPTER XVIII. FISHES AS FOOD FOR MAN. The Flesh of Fishes.— Relative Rank of Food-fishes.— Abundance of Food- fishes.— Variety of Tropical Fishes.— Economic Fisheries.— Angling 320 CHAPTER XIX. DISEASES OF FISHES. Contagious Diseases: Crustacean Parasites.— Myxosporidia or Parasitic Proto- zoa.— Parasitic Worms: Trematodes, Cestodes.— The Worm of the Yellow- stone.— The Heart Lake Tapeworm.— Thorn-head Worms.— Nematodes. —Parasitic Fungi.— Earthquakes.— Mortality of Filefish 340 CHAPTER XX. THE MYTHOLOGY OF FISHES. The ^Mermaid. — The Monkfish. — The Bishop-fish. — The Sea-serpent 359 CHAPTER XXI. THE CLASSIFICATION OF FISHES. Ta.xonomy. — Defects in Taxonomy. — Analogy and Homology. — Coues on Classification. — Species as Twigs of a Genealogical Tree. — Nomenclature. — The Conception of Genus and Species. — The Trunkfishes. — Trinomial Nomenclature. — Meaning of Species. — Generalization and Specialization, — High and Low Forms. — The Problem of the Highest Fishes 367 CHAPTER XXII. THE HISTORY OF ICHTHYOLOGY. Aristotle. — Rondelet. — Marcgraf. — Osbeck. — Artedi. — Linnsus. — Forskal. — Risso. — Bloch.—Lacepede.—Cuvier.— Valenciennes.— Agassiz.— Bonaparte. — Giinther.— Boulenger.— Le Sueur.— Muller.—Gi'l.— Cope.— Lutken.— • Steindachner.—Vaillant.—Bleeker.—Schlegel.—Poey.— Day.— Baird.— Gar- man. — Gilbert. — Evermann.— Eigenmann. — Zittel. — Traquair. — Wood- ward. — Dean.— Eastman.— Hay.— Gegenbaur.— Balfour.— Parker.— Dollo. . 387 CHAPTER XXIII. THE COLLECTION OF FISHES. How to Secure Fishes.— How to Preserve Fishes— Value of Formalin —Rec- ords of Fishes. — Eternal Vigilance 429 xiv Contents CHAPTER XXIV. THE EVOLUTION OF FISHES. PAGE The Geological Distribution of Fishes.— The Earliest Sharks.— Devonian Fishes.— Carboniferous Fishes.— Mesozoic Fishes.— Terliary Fishes.— Fac- tors of Extinction.— Fossilization of a Fish.— The Earliest Fishes.— The Cyclostomes.— The Ostracophores.— The Arthrodires.— The Sharks.— Origin of the Shark.— The Chima;ras.— The Dipnoans.— The Crossopte- rj-gians. — The Actinopteri. — The Bony Fishes 435 CHAPTER XXV. THE PROTOCHORD.\T.\. The Chordate Animals. — The Protochordates. — Other Terms Used in Classifi- cation. — The Enteropneusta. — Classification of Enteropneusta. — Family Harrimaniidae. — Balanoglossida;. — Low Organization of Harrimaniids 460 CHAPTER XXVL THE TUNICATES, OR ASCIDI.-\NS. Structure of Tunicates. — Development of Tunicates. — Reproduction of Tuni- cates. — Habits of Tunicates. — Larvacea. — .-^scidiacea.- Thaliacea. — Origin of Tunicates. — Degeneration of Tunicates 467 CHAPTER XXVII. THE LEPTOCWRDII, OR L.^NCELETS. The Lancelet. — Habits of Lancelets. — Species of Lancelets. — Origin of Lance- lets 482 CHAPTER XXVIII. THE CYCLOSTOMES, OR LAMPREYS. The Lampreys. — Structure of the Lamprey. — Supposed Extinct Cyclostomes. — Conodontes.— Orders of Cyclostomes. — The Hyperotreta, or Hagfishes. — The Hyperoartia, or Lampreys.— Food of Lampreys. — iNIetamorphosis of Lampreys.— Mischief Done by Lampreys.— Migration or "Running" of Lampreys.— Requisite Conditions for Spawning with Lampreys.— The Spawning Process with Lampreys.— What Becomes of Lampreys after Spawning? ^86 Contents xv CHAPTER XXIX. THE CLASS ELASMOBRANCHII, OR SHARK-LIKE FISHES. The Sharks. — Characters of Elasmobranchs. — Classification of Elasmobranchs. — Subclasses of Elasmobranchs. — The Selachii. — Hassc's Classification of Elasmobranchs. — Other Classifications of Elasmobranchs. — Primitive Sharks. — Order Pleuropterygii. — Order Acanthodii. — Dean on Acanthodii. — Order Ichthyotomi 506 CHAPTER XXX. THE TRUE SHARKS. Order Notidani. — Family Hexanchida;. — Family Chlamydoselachida;. — Order Asterospondyli. — Suborder Cestraciontes. — Family Heterodontidae. — Edes- tus and its Allies. — Onchus. — Family Cochliodontida;. — Suborder Galei. — Family Scyliorhinida;. — The Lamnoid, or Mackerel-sharks. — Family Mit- sukurinidae, the Gobhn-sharks. — Family Alopiidte, or Thresher-sharks. — Family Pseudotriakidce. — Family Lamnidoe. — Man-eating Sharks. — Family Cetorhinidae, or Basking Sharks. — Family Rhineodontid^e. — The Carcharioid Sharks, or Requins. — Family Sphyrnidae, or Hammer-head Sharks. — The Order of Tectospondyli. — Suborder Cyclospondyli. — Family Squalidae. — Family Dalatiidae. — Family Echinorhinidas. — Suborder Rhinae. — Family Pristiophoridae, or Saw-sharks. — Suborder Batoidei, or Rays. — Pristidida;, or Sawfishes. — Rhinobatida?, or Guitar-fishes. — Rajidae, or Skates. — Narco- batidce, or Torpedoes. — Petalodontida;. — Dasyatidce, or Sting-rays. — Myliobatidae. — Family Psammodontids. — Family Mobulidae 523 CHAPTER XXXI. THE HOLOCEPHALI, OR CHIMERAS. The Chimaeras. — Relationship of Chimeras.— Family Chimajridte.— Rhino- chimaerida;.— E.xtinct Chima-roids.^Ichthyodorulites 561 CHAPTER XXXII. THE CLASS OSTRACOPHORI. Ostracophores.— Nature of Ostracophores.— Orders of Ostracophores.— Order Heterostraci.— Order Osteostraci.— Order Antiarcha.— Order Anaspida. ... 568 CHAPTER XXXIII. ,'\RTHRODIRr:S. The Arthrodires.— Occurrence of Arthrodires.— .Arthrognathi.— Anarthrodira.— Stegothalami.—Arthrodira.—Temnothoraci.—Arthrothoraci.— Relations of xvi Contents PAGE Arthrodires. — Suborder Cyclic. — Pakeospondylus. — Gill on PaLtospon- dylus. — Views as to the Relationships of Palfeospondylus: Huxley, Tra- quair, 1S90. Traquair, 1893. Traquair, 1S97. Smith Woodward, 1892. Dawson, 1893. Gill, 1S96. Dean, 1S96. Dean, 1S98. Parker & Has- well, 1897. Gegcnbaur, 1898. — Relationships of PaL-eospondylus 581 CHAPTER XXXIV. THE CROSSOPTERYGII. Class Teleostomi. — Subclass Crossopterygii. — Order of Amphibians. — The Fins of Crossopterygians. — Orders of Crossopterygians. — Haplistia. — Rhipidistia. — Mcgalichthyida;. — Order Actinistia. — Order Cladistia. — The Polypte- ridK 598 CHAPTER XXXV. SUBCLASS DIPNEUSTI, OR LUNGFISHES. The Lungfishes. — Classification of Dipnoans. — Order Ctenodipterini. — Order Sirenoidei. — Family CeratodontidK. — Development of Neoceratodus. — Lepi- dosirenidce. — Kerr on the Habits of Lepidosiren 609 LIST OF ILLUSTRATIONS VOL. I. PAGE Lepomis megalotis, Long-eared Sunfish 2 Lepomis megalotis, Long-eared Sunfish 4 Eupomotis gibbosiis, Common Sunfish y Ozorthe dictyogramma, a Japanese Blenny g Eupomotis gibbosus, Common Sunfish 13 Monocentris japonicus, Pine-cone Fish 16 Diodon hystrix, Porcupine-fish 17 Nemichthys avocetta, Thread-eel 17 Hippocampus liudso?iii(s, Sea-horse 17 Pepnlus paru, Harvest-fish 18 Lophius lilidon, Anko or Fishing-frog 18 Epmephelus adscensionis, Rock-hind or Cabra Mora 20 Scales of Acanthoessus bronni 21 Cycloid Scale! 22 Ponchthys porosissimus, Singing-fish 23 Apomotis cyanellus, Blue-green Sunfish 27 Chiasmodon niger, Black Swallower 29 Jaws of a Parrot-fish, Sparisoma aurojrenatum 30 Archosargus probatocephaliis, Sheepshead 31 Campostojna anomalum, Stone-roller ^2> Roccus lineatus. Striped Ba=s 35 Roccus lineatus. Lateral View of Cranium 36 Roccus lineatus. Superior View of Cranium 37 Roccus lineatus. Inferior View of Cranium 38 Roccus lineatus. Posterior View of Cranium 40 Roccus lineatus. Face-bones, Shoulder and Pelvic Girdles, and Hyoid Arch. . . 42 Lower Jaw of Amia calva, showing Gular Plate 43 Roccus lineatus. Branchial Arches 46 Phar}-ngeal Bone and Teeth of European Chub, Leuciscus cephalus 47 Upper Pharyngeals of Parrot-fish, Scarus strongylocephalus 47 Lower Phar)'ngeal Teeth of Parrot-fish, Scarus strongylocephalus 47 Pharyngeals of Italian Parrot-fish, Spansoma cretense 48 Roccus lineatus, Vertebral Column and Appendages 48 Basal Bone of Dorsal Fin, Holoptyclnus leplopterus 49 Inner View of Shoulder-girdle of Buffalo-fish, Ictiobus bubalus 51 xviii List of Illustrations PAGE Pterophryne tumida, Sargassum-fish S^ Shoulder-girdle of Sebastolohus alascanus 5^ Cranium of Sebastolohus alascanus S3 Lower Jaw and Palate of Sebastolohus alascanus 54 Maxillary and Pre-maxillary of Sehastolohus alascanus SS Part of Skeleton of Selene vomer 55 Hyostilic Skull of Chiloscyllium indicim, a Scyliorhinoid Shark 56 Skull of Heptrancltias indicus, a Notidanoid Shark 56 Basal Bones of Pectoral Fin of jNIonkfish, Squalina 56 Pectoral Fin of Heterodontus philippi 57 Pectoral Fin of Heplranchias indicus 57 Shoulder-girdle of a Flounder, Paralichthys calijornieus 58 Shoulder-girdle of a Toadfish, Batrachoides pacifiei jg Shoulder-girdle of a Garfish, Tylosiirus jodiator ^g Shoulder-girdle of a Hake, ilcrhiceins productus 69 Cladoselaclie jyleri, Restored (,- Fold-like Pectoral and Ventral Fins of Cladosclacbe jyleri gr Pectoral Fin of a Shark, Chiloscyllium 66 Skull and Shoulder-girdle of Neoceratodus jorsteri, showing archipterygium ... 63 Acanthoessus u'ardi 6q Shoulder-girdle of Acanthoessus gn Pectoral Fin of Plcuracanthus 6q Shoulder-girdle of Polypterus bichir jq Arm of a Frog ^j Plcuracanthus dechcni -. Embr)-os of Heterodontus japonicus, a Cestraciont Shark yr Polypterus coni;icus, a Crossopterygian Fish with External Gills 78 Heterocercal Tail of Sturgeon, Acipcnser slurio ga Heterocercal Tail of Bowfin, Amia calva g2 Heterocercal Tail of Garpike, Lepisostcus osseus 82 Corypha'noides carapinus, showing Leptocercal Tail g, Heterocercal Tail of Young Trout, Salnio jario g, Isocercal Tail of Hake, Mcrluccius productus g. Homocercal Tail of a Flounder, Paralichthys calijornieus gi Gephyrocercal Tail of Mola niola g. Shoulder-girdle of Amia calva gg Shoulder-girdle of a Sea-catfish, Selcnaspis dowi g6 Clavicles of a Sea-catfish, Selcnaspis doici g- Shoulder-girdle of a Batfish. Ogcocephalus radiatus gg Shoulder-girdle of a Threadfin, Polydactylus appro.ximaus gq Gill-basket of Lamprev Wcberian Apparatus and Air-bladder of Carp Brain of a Shark, Sgiiatina squalina Brain of Chimeera monstrosa . no Bram of Proloptcrus anneetcns ' ■ ■ no List of Illustrations XIX PAGE Brain of a Perch, Perca flavescens j j j Petromyzon marinus iinicolor. Head of Lake Lamprey, showing Pineal Body . 1 1 1 Chologasler cormtlus, Dismal-swamp Fish jjg Typhlichthys subterraneus, Blind Cave-iish j jg Anableps dovii, Four-eyed Fish jj- Ipnops mitrrayi , jjg Boleophthalmus chinensis, Pond-skipper i j3 Lampeira wilderi, Brook Lamprey j2o Branchiostoma lanceolatum, European Lancelet 120 Pseudupeneus macidalus, Goatfish 122 Xiphophonis helleri, Sword-tail Minnow 124 Cymatogaster aggregatiis, White Surf-fish, Viviparous, with Young 125 Goodea liiitpoldi, a Viviparous Fish 126 Egg of CaUorhynchus antarclicus, the Bottle-nosed Chimasra 127 Egg of the Hagfish, Myxiitc limosa 127 Egg of Port Jackson Shark, Heterodontus philippi 128 Development of Sea-bass, Centroprisks strialus i^j Centroprisies striatus, Sea-bass 127 Xiphias gladius, Young Swordfish j ^n Xiphias gladius, Swordfish i og Larva of the Sailfish, htiophonis, Verj' Young 140 Lan'a of Brook Lamprey, Lampeira wilderi, before Transformation 140 Anguilla chrisypa. Common Eel 140 Larva of Common Eel, Anguilla chrisypa, called Lepiocephalus grassii 141 Larva of Sturgeon, Acipenser sturio 141 Larva of Chcetodon sedentarius 142 Chxlodon capistratus. Butterfly -fish 142 Mola mola. Very Early Larval Stage of Headfish, called Ce)tlaiirus boops 143 Mola mola. Early Lan'al Stage called Molacanihus nummularis 144 Mola mola, Advanced Lan'al Stage 144 Mola mola, Headfish, Adult 146 Albula vulpes. Transformation of Ladyfish from Larva to Young 147 Development of the Horsehead-fish, Selene vomer 148 Salanx hyalocranius, Icefish 149 Dallia pectoralis, Alaska Elackfish 149 Ophiocephalus barca. Snake-headed China-fish 150 Carassius aiiratus. Monstrous Goldfish 151 Jaws of Nemichlhys avocetia 156 Cypselurus calijornicus, Flying-fish 157 Ammocrypta clara. Sand-darter 158 Fierasjer acus, Pearlfish, issuing from a Holocanthurian 159 Gobiomorus gronovii, Portuguese Man-of-war Fish 160 Tide Pools of Misaki i6r Plvchochcilus oregonensis, Squawfish 162 Ptychocheilus grandis, Squawfish, Stranded as the Water Falls 164 XX List of Illustrations PAGE Larval Stages of Plalophrys podas, a Flounder of the Mediterranean, showing Migration of Eye i74 Plalophrys lunalus, the Wide-eyed Flounder i75 Young Flounder Just Hatched, with Symmetrical Eyes I7S Pseiidoplciironecles americanus, Larval Flounder 176 Pseudopleuronecles americanus, Larval Flounder (more advanced stage) 176 Face View of Recently-hatched Flounder 177 Schilbiosjis juriosus, Mad-Tom ryg Emmydrichlhys viilcanus, Black Nohu or Poison-fish 180 Peiithis bahianus, Brown Tang 181 Slephanolepis liispidus, Common Filefish 182 Telraodon mcleagris 183 Balisles carolinensis, the Trigger-fish 184 Narcine brasiliensis, Numbfish 185 Torpedo eleclriciis, Electric Catfish 186 Astroscopus giiltalus. Star-gazer 187 Ailhoprora liicida, Headlight-fish 188 Corynolophus rcinjiardli, showing Luminous Bulb 188 Elmoplertis hicijer 189 Argyropeleeiis oljersi 190 Luminous Organs and Lateral Line of Midshipman, Porichthys nolalns 192 Cross-section of Ventral Phosphorescent Organ of Midshipman, Porichthvs notalus in. Section of Deeper Portion of Phosphorescent Organ, Porichthys nolalns 194 Lepleeheneis naucrales, Sucking-fish or Pegador 197 Caidarchus mxandricus, Clingfish jng Polistotrema slouli, Hagfish jqq Prislis zysron, Indian Sawfish 200 Prisliophorus japonicus, Saw-shark 201 Skeleton of Pike, Esox Indus 203 Skeleton of Red Rockfish, Sebaslodes miniatus 214 Skeleton of a Spiny-rayed Fish of the Tropics, Holacanthus ciliaris 214 Skeleton of the Cowfish, Laclophrys tricornis 21c Cryslallias matsushimcB, Liparid o Sebaslichlhys maliger, Yellow-backed Rockfish 218 Myoxocephalus scorpius, European Sculpin Hemilripterus americanus, Sea-raven Cycloplerus htm pus, Lumpfish Psychrolules paradoxus, Sleek Sculpin Pallasina barbala, Agonoid-fish ^ Amblxopsis spcla;us, Blindfish of the Mammoth Cave , Lucijuea subterraiica. Blind Brotula ' '^ ' 222 Jlypsypops rubicunda, Garibaldi ^^ Synanceia verrucosa, Gofu or Poison-fish -' . . ' . 229 Alliens saliens. Lizard-skipper ' ' ' 230 List of Illustrations xxi PAGE Etheostoma camurum, Blue-breasted Darter 231 Liiiramis semicintus and Chlci>asks colubrinus, Snake-eels 233 Coral Reef at Apia 234 Rudarius ercodes, Japanese Filefish 241 Tetraodon setosus, Globefish 244 Dasyates sabina, Sting-ray 246 Diplesion blennioides, Green-sided Darter 247 Hippocampus mohnikei, Japanese Sea-horse 250 Archoplites interruptus, Sacramento Perch 258 Map of the Continents, Eocene Time 270 Catdophryne jordani, Deep-sea Fish of Gulf Stream 276 Exerpes asper, Fish of Rock-pools, Mexico 276 Xenocys jessice 279 Iclaliirus piinctatus, Channel Catfish 280 Drawing the Net on the Beach of Hilo, Hawaii 281 Semotilns atromacidatits, Horned Dace 285 Leiiciscus lineatus, Chub of the Great Easin 287 Melletes papilio, Butterfly Sculpin 288 Scartichihys enosima, a Fish of the Rock-pools of the Sacred Island of Eno- shima, Japan 294 Halichares bivittatus, the Slippery Dick 297 Peristedion miniatiim 299 Outlet of Lake Bonneville 303 Hypocrilichthys analis, Silver Surf-fish 309 Erimyzon sucetta, Creekfish or Chub-sucker 315 Thaleichthys pretiosus, Eulachon or Ulchen 320 Plecoglossus altivelis, the Japanese Ayu 321 Coregonus clupeijormis, the Whitetish 321 Mullus auratus, the Golden Surmullet 322 Scomberomorus macidalus, the Spanish "Mackerel 322 Lampris luna, the Opah or Moonfish 323 Pomatomus sallairix, the Bluefish 324 Centropomus undecimalis , the Robalo 3^4 CImtodipterus jaber, the Spadefish 325 Mkropkrus dotomieu, the Small-mouthed Black Bass 325 Salvelinus fontinalis, the Speckled Trout 326 Salmo ^airdnen, the Stee'head Trout 326 Salvelinus oquassa, the Rangeley Trout 3^6 Salmo rivularis, the Steelhead Trout 3^7 Salmo henshawi, the Tahoe Trout 3^7 Salvelinus malma, the Dolly Varden Trout 3^7 Thymallus signifer, the Alaska Grayling 32S Esox liicius, the Pike 3-8 Pleurogrammus monopterygius, the Atka-fish 328 Chirosioma humboldlianum, the Pescado bianco 329 xxii List of Illustrations PAGE Pseiidupeneus maculalus, the Red Goatfish 3^9 Pseudoscariis guacamaia, Great Parrot-fish H'-' Mtigil cephalus, Striped Mullet i?P Lulianus analis, Mutton-snapper 33'^ Clupea harcngiis, Herring 33^ Gadiis callarias, Codfish 33^ Scomber scomhrus, Mackerel 33^ Hippoglossus hippoglossus, Halibut 332 Fishing for Ayu with Cormorants 2>33 Fishing for Ayu. Emptying Pouch of Cormorant 335 Fishing for Tai, Tokyo Bay 338 Brevooriia tyrannus, Menhaden 340 Exonautes imicolor, Australian Flying-fish 341 Rhinichthys aironasus, Black-nosed Dace 342 Notropis hudsonius, Wiite Shiner 343 Ameiurus catus, White Catfish 344 Catostomus ardcns, Sucker 348 Oncorhynchus tschawytscha, Quinnat Salmon 354 Oncorhynchus tschawytscha, Young Male 355 Amejurus nebidosus. Cat shes 358 "Le Monstre Marin en Habit de Moine" 360 "Le Monstre Marin en Habit d'Eveque" 361 Regalccus russeUi, Garfish 362 Rcgalccus gles?ie, Glesnaes Garfish 363 Ncmichthys avocctta. Thread-eel 365 Lactophrys tricorms, Horned Trunkfish ^-jt^ Ostracion cornutum, Horned Trunkfish 376 Lactophrys bicaudalis, Spotted Trunkfish 377 Lactophrys bicaudalis, Spotted Trunkfish (Face) 377 Lactoplirys triqueler. Spineless Trunkfish 378 Lactophrys trigoniis. Hornless Trunkfish 378 Lactophrys Irigoniis, Hornless Trunkfish (Face) 379 Bernard Germain de Lacepede 3gQ Georges Dagobert Cuvier 999 Louis Agassiz ,00 Johannes Miiller ^nq Albert Gijnther .q-i Franz Steindachner 40, George Albert Boulenger .q-, Robert CoUett ,q, Spencer FuUerton Baird ,q- Edward Drinker Cope .q_ Theodore Nicholas Gill „_ George Brown Goode __ Johann Reinhardt 409 List of Illustrations xxiii PAGE Edward Waller Claypole -og Carlos Berg ^^^ Edgar R. Waite ^^^ Felipe Poey y Aloy , j , L^on Vaillant .j, Louis DoUo .J, Decio Vinciguerra . j , Bashford Dean .j- Kakichi Mitsukuri .j- Carl H. Eigenmann .^j Franz Hilgendorf .j- David Starr Jordan .21 Herbert Edson Copeland ^21 Charles Henry Gilbert ^21 Barton Warren Evermann 421 Ramsay Heatley Traquair 425 Arthur Smith Woodward 425 Karl A. Zittel 425 Charles R. Eastman 425 Fragment of Sandstone from Ordovician Deposits 435 Fossil Fish Remains from Ordovician Rocks 436 Dipteriis valenciennesi 437 Hoplopteryx lewesiensis 438 Paratrachichthys prosthemius, Berycoid-fish 439 Cypsilurns heterurus, Flying-tish 440 LutianidcB, Schoolmaster Snapper 440 Pleuronichlhys decurrens, Decurrent Flounder 441 Cephalaspis lyelli, Ostracophore 444 Dinichtkys intermedius, Arthrodire 445 Lamna cornubica, Mackerel-shark or Salmon-shark 447 Raja stellulata, Star-spined Ray 448 HarrioHa raleighiana, Deep-sea Chimaera 449 Dipterus valenciennesi, Extinct Dipnoan 449 Holoptychius giganieus. Extinct Crossopterygian 451 Platysomus gihbosus, Ancient Ganoid-fish 452 Lepisoslens platystomus. Short-nosed Gar 452 Palceoniscum macropomum, Primitive Ganoid-fish 453 Diplomyslus humilis, Fossil Herring 453 Holcolepis lewesiensis 454 Elops saurus, Ten-pounder 4S4 Apogon semilineatus, Cardinal-fish 455 Pomolobus (BStivalis, Summer Herring 455 Bassozetus cate?ia 45^ Traduce phalus uranoscopns 456 CMarias breviceps, African Catfish 457 xxiv List of Illustrations PAGE Notropis whipplii, Silver -fin 457 Gymnothorax moringa 45° Seriola lalandi, Amber-fish 45° Geological Distribution of the Families of Elasmobranchs 459 "Tornaria" Larva of Clossobalanus minutus 403 Clossobalamis minutus 404 Harrimania maculosa 405 Development of Larval Tunicate to Fixed Condition 47i Anatomy of Tunicate 47^ Ascidia adherens 474 Styela yacutatensis 475 Styela grecleyi 47^ Cynthia superba 47^ Bolryllus magnus, Compound Ascidian 477 Botryllus magnus 47^ Botryllus magnus, a Single Zooid 479 Aplidiopsis jordani, a Compound Ascidian 479 Oikapleura, Adult Tunicate of Group Larvacea 480 Branchiostoma calijorniense, California Lancelet 484 Gill-basket of Lamprey 485 Polygnathus dubium 488 Polistotrema stoiiti, Hagfish 489 Pctromyzon marinus, Lamprey 491 Petromyzon marinus iinicolor, Mouth Lake Lamprey 492 Lampetra wilderi, Sea Larvae Brook Lamprey 492 Lampetra wilderi, Mouth Brook Lamprey 492 Lampetra camtschalica, Kamchatka Lamprey 495 Enlosphenus tridentatus, Oregon Lamprey 496 Lampetra ijuilderi, Brook Lamprey 505 Fin-spine of Onchus tenuistriatus 509 Section of Vertebrae of Sharks, showing Calcification 510 Cladoselache jyleri ji^ Cladoselache jyleri. Ventral View jij Teeth of Cladoselache jyleri cjc Acanthocssus wardi rjr Diplacanthus crassissimus cjy Climatius sciitiger cj jg Pleuracanthiis decheni rjg Pleuracanthus decheni. Restored C20 Head-bones and Teeth of Pleuracanthus decheni r2o Teeth of Didymodus bohemicus ,-20 Shoulder-girdle and Pectoral Fins of Cladodus ncilsoni 1-21 Teeth of Cladodus striatus -22 Hexanchus griseus, Griset or Cow-shark C211 Teeth of Heptranchias indicus _^ List of Illustrations xxv PAGE Chlamydoselachus angnineus, Frill-shark 525 Heterodontus jtancisci. Bullhead-shark 526 Lower Jaw of Heterodontus philippi 526 Teeth of Cestraciont Sharks 527 Egg of Port Jackson Shark, Heterodontus philippi 527 Tooth of Hybodus delabcchei 528 Fin-spine of Hybodus basanus .' 528 Fin-spine of Hybodus reticulatiis 528 Fin-spine of Hybodus eanaliculatus 529 Teeth of Cestraciont Sharks 529 Edestus vorax, Supposed to be a Whorl of Teeth 529 Helicoprion bessonowi, Teeth of 530 Lower Jaw of Cochliodus eontortus 531 Mitsukurina owstoni, Goblin-shark 53S Scapanorynchus leuisi, Under Side of Snout 536 Tooth of Lamna cuspidata 537 Isuropsis dekayi, Mackerel-shark 537 Tooth of Isuriis hastalis 538 Carcharodon megaodon 539 Cetorhinus maximus, Basking-shark 540 Caleus zyopterus, Soup-fin Shark S4i Careharias lamia, Cub-shark S42 Teeth of Corax pristodontus S43 Sphyrna zygana, Hammer-head Shark S44 Squalas acanthias, Dogfish 54S Etmopterus lucijer S46 Brain of jMonkfish, Squatina squatina 547 Prisliophorus japonicus, Saw-shark 548 Pristis pectinatus, Sawfish 55° Rhinobatus lentiginosus, Guitar-fish 55^ Raja erinacea, Common Skate 55^ Narcine brasiliensis, Numbfish 553 Teeth of Janassa lingucejormis 554 Polyrhizodus radicans 555 Dasyatis sabina, Sting-ray 55^ Aetobatis narinari, Eagle-ray 55^ Manta birostris, Devil-ray or Sea-devil 559 Skeleton of Chimara monstrosa 5^4 Chimara colliei, Elephant-fish 505 Odontotodus schrencki, Ventral Side 57° Odonlotodus schrencki, Dorsal Side 57° Head of Odonlotodus schrencki, from the Side 57i Lwiidus polyphemus, Horseshoe Crab 572 Lanarkia spinosia 5 ' ■+ Drepanaspis gmundenensis 575 xxvi List of Illustrations PAGE Pteraspis rostrala 575 Cephalaspis lyelli, Restored 576 Cephalaspis dawsoni 577 Pterichthyodes testudinarius 578 Pterichthyodes testudinarius, Side View 579 Birkenia elcgans 579 Lasianius problemalicits 580 Coccosteus cuspidatus, Restored 582 Jaws of Dinichthys hertzeri 583 Dinichthys intermedins, an Arthrodire 584 Palceospondylus gunni J91 Shoulder-girdle of Polyplenis bichir 600 Arm of a Frog 601 Polypterus congicus, a Crossopterygian Fish 602 Basal Bone of Dorsal Fin, Holoptychius leptopteriis 603 Gyroplychius microlepidotus 604 Calacanihus elegans, showing Air-bladder 604 Vndina gtilo 605 Lower Jaw of Polypterus bichir, from Below 606 Polypterus congicus 607 Polypterus delhezi 607 Erpetoiclithys calabaricus ' gog Shoulder -girdle of Neoceratodus jorsleri gog Phaneropleuron andersoni gj. Teeth of Ceratodus runcinatus gj . Neoceratodus jorsleri gj^ Archiptery'gium of Neoceratodus jorsleri gj . Upper Jaw of Neoceratodus jorsleri gjc Lower Jaw of Neoceratodus jorsleri g^g Adult Male of Lepidosiren paradoxa gj_ Lepidosiren paradoxa. Embryo Three Days before Hatching; Larva Thirteen Days after Hatching g^^ Larva of Lepidosiren paradoxa Forty Days after Hatching (,2^ Lan-a of Lepidosiren paradoxa Thirty Days after Hatching g2T Larv'a of Lepidosiren paradoxa Three Months after Hatching g2i Prolopterus dolloi g ■n a a CHAPTER I THE LIFE OF THE FISH A POPULAR ACCOUNT OF THE LIFE OF THE LONG-EARED SUNFISH, LEPOMIS MEGALOTIS *|HAT is a Fish ? — A fish is a back-boned animal which lives in the water and cannot ever live very long anywhere else. Its ancestors have always dwelt in water, and most likely its descendents will forever follow their example. So, as the water is a region very different from the fields or the woods, a fish in form and structure must be quite unlike all the beasts and birds that walk or creep or fly above ground, breathing air and being fitted to live in it. There are a great many kinds of animals called fishes, but in this all of them agree: all have some sort of a back-bone, all of them breathe their life long by means of gills, and none have fingers or toes with which to creep about on land. The Long-eared Sunfish. — If we would understand a fish, we must first go and catch one. This is not very hard to do, for there are plenty of them in the little rushing brook or among the lilies of the pond. Let us take a small hook, put on it an angle- worm or a grasshopper, — no need to seek an elaborate artificial fly, — and we will go out to the old ' ' swimming-hole ' ' or the deep eddy at the root of the old stump where the stream has gnawed away the bank in changing its course. Here we will find fishes, and one of them will take the bait very soon. In one part of the country the first fish that bites will be different from the first one taken in some other. But as we are fishing in the United States, we will locate our brook in the centre of popu- lation of our country. This will be to the northwest of Cincin- 3 4 The Life of the Fish nati, among the low wooded hills from which clear brooks flow over gravelly bottoms toward the Ohio River. Here we will catch sunfishes of certain species, or maybe rock bass or catfish: any of these will do for our purpose. But one of our sunfishes is especially beautiful — mottled blue and golden and scarlet, with a long, black, ear-like appendage backward from his gill-covers — - and this one we will keep and hold for our first lesson in fishes. It is a small fish, not longer than your hand most likely, but it can take the bait as savagely as the best, swimming away with it with such force that you might think from the vigor of its pull that you have a pickerel or a bass. But when it comes out of the water you see a little, flapping, unhappy, living plate of Fig. 2. — Long-eared Sunfish, Lepnmis mcgalotis (Rafinesque"). (From Clear Creek, Blooniington, Indiana.) Family Centmrchida-. brown and blue and orange, with fins wide -spread and eyes red with rage. Form of the Fish. — And now Ave haA'C put the fish into a bucket of water, where it lies close to the bottom. Then we take it home and place it in an aquarium, and for the first time we have a chance to see what it is Hke. AVe sec that its body is almost elliptical in outline, but with flat sides and shaped on the lower parts very much like a boat. This form we see is such as to enable it to part the water as it swims. We notice that its progress comes through the sculling motion of its broad, flat tail The Life of the Fish 5 Face of a Fish. — When we look at the sunfish from the front we see that it has a sort of face, not unlike that of higher animals. The big eyes, one on each side, stand out without eyelids, but the fish can move them at will, so that once in a while he seems to wink. There isn't much of a nose between the eyes, but the mouth is very evident, and the fish opens and shuts it as it breathes. We soon see that it breathes water, taking it in through the mouth and letting it flow over the gills, and then out through the opening behind the gill-covers. How the Fish Breathes. — If we take another fish — for we shall not kill this one — we shall see that in its throat, behind the mouth- cavity, there are four rib-like bones on each side, above the beginning of the gullet. These are the gill-arches, and on each one of them" there is a pair of rows of red fringes called the gills. Into each of these fringes runs a blood-vessel. As the water passes over it the oxygen it contains is absorbed through the skin of the gill-fringe into the blood, which thus becomes puri- fied. In the same manner the impurities of the blood pass out into the water, and go out through the gill-openings behind. The fish needs to breathe just as we do, though the apparatus of breathing is not the same. Just as the air becomes loaded with impurities when many people breathe it, so does the water in our jar or aquarium become foul if it is breathed over and over again by fishes. When a fish finds the water bad he comes to the sur- face to gulp air, but his gills are not well fitted to use undissolved air as a substitute for that contained in water. The rush of a stream through the air purifies the water, and so again does the growth of water plants, for these in the sunshine absorb and break up carbonic acid gas, and throw out oxygen into the water. Teeth of the Fish. — On the inner side of the gill-arch we find some little projections which serve as strainers to the water. These are called gill-rakers. In our sunfish they are short and thick, seeming not to amount to much but in a herring they are very long and numerous. Behind the gills, at the opening of the gullet, are some round- ish bones armed with short, thick teeth. These are called pharyn- geals. They form a sort of jaws in the throat, and they are useful in helping the little fish to crack shells. If we look at the mouth of our live fish, we shall find that when it breathes or bites it moves 6 The Life of the Fish the lower jaw very much as a dog does. But it can move the upper jaw, too, a little, and that by pushing it out in a queer fashion, as though it were thrust out of a sheath and then drawn in. If we look at our dead fish, we shall see that the upper jaw divides in the middle and has two bones on each side. On one bone are rows of little teeth, while the other bone that lies behind it has no teeth at all. The lower jaw has little teeth like those of the upper jaw, and there is a patch of teeth on the roof of the mouth also. In some sunfishes there are three little patches, the vomer in the middle and the palatines on either side. The tongue of the fish is fiat and gristly. It cannot move it, scarce even taste its food with it, nor can it use it for making a ncise. The unruly member of a fish is not its tongue, but its tail. How the Fish Sees. — To come back to the fish's eye again. We say that it has no ej^elids, and so, if it ever goes to sleep, it must keep its eyes wide open. The iris is brown or red. The pupil is round, and if we could cut open the eye we should see that the crystalline lens is almost a perfect sphere, much more convex than the lens in land animals. We shall learn that this is necessary for the fish to see under water. It takes a very convex lens or even one perfectly round to form images from rays of light passing through the water, because the lens is but little more dense than the water itself. This makes the fish near-sighted. He cannot see clearly anything out of water or at a distance. Thus he has learned that when, in water or out, he sees anything moving quickly it is probably something dangerous, and the thing for him to do is to swim away and hide as swiftly as possible. In front of the eye are the nostrils, on each side a pair of openings. But they lead not into tubes, but into a little cup lined with delicate pink tissues and the branching nerves of smell. The organ of smell in nearly all fishes is a closed sac, and the fish does not use the nostrils at all in breathing. But they can indicate the presence of anything in the water which is good to eat, and eating is about the only thing a fish cares for. Color of the Fish. — Behind the eye there are several bones on the side of the head which are more or less distinct fr(jm the skuU itself. These are called membrane bones because thev are formed of membrane which has become bony by the deposition The Life of the Fish j in it of salts of lime. One of these is called the opercle, or gill-cover, - and before it, forming a right angle, is the pre- opercle, or false gill-cover. On our sunfish we see that the opercle ends behind in a long and narrow flap, which looks like an ear. This is black in color, with an edging of scarlet as though a drop of blood had spread along its margin. When the fish is in the water its back is dark greenish-looking, like the weeds and the sticks in the bottom, so that we cannot see it very plainly. This is the way the fish looks to the fish- hawks or herons in the air above it who may come to the stream to look for fish. Those fishes which from above look most like the bottom can most readily hide and save themselves. The under side of the sunfish is paler, and most fishes have the belly white. Fishes with white bellies .swim high in the water, and the fishes who would catch them lie below. To the fish in the water ^■^^^pi, *i|| ll ; ,^^ra2|B^^^ v^llBBlJiMIBK^ A '-''j. J jliiiS^^ifetAii^iAjfe-'"^^^^" ' - Fig. 3.— Common Sunfish, Eupomotis gihboKus (Linna;us), Natural size. (From life by R. W. Shufeldt.) all outside the water looks white, and so the white-bellied fishes are hard for other fishes to see, just as it is hard for us to see a white rabbit bounding over the snow. 8 The Life of the Fish But to be known of his own kind is good for the sunfish, and we may imagine that the black ear-flap with its scarlet edge helps his mate and friends to find him out, where they swim on his own level near the bottom. Such marks are called recognition- marks, and a great many fishes have them, but we have no certain knowledge as to their actual purpose. We are sure that the ear-flap is not an ear, however. No fishes have any external ear, all their hearing apparatus being buried in the skull. They cannot hear very much: possibly a great jar or splash in the water may reach them, but whenever they hear any noise they swim off to a hiding-place, for any dis- turbance whatever in the water must arouse a fish's anxiety. The color of the live sunfish is very brilliant. Its body is cov- ered with scales, hard and firm, making a close coat of mail, overlapping one another like shingles on a roof. O^'er these is a thin skin in which are set little globules of bright-colored matter, green, brown, and black, with dashes of scarlet, blue, and white as well. These give the fish its varied colors. Some coloring matter is under the scales also, and this especially makes the back darker than the lower parts. The bright colors of the sun- fish change with its surroundings or with its feelings. AYhen it lies in wait under a dark log its colors are A-ery dark. AVhen it rests above the white sands it is very pale. AYhen it is guarding its nest from some meddling perch its red shades flash out as it stands with fins spread, as though a water knight with lance at rest, looking its fiercest at the intruder. When the sunfish is taken out of the water its colors seem to fade. In the aquarium it is generally paler, but it will sometimes brighten up when another of its own species is placed beside it. A cause of this may lie in the nervous control of the muscles at the base of the scales. When the scales lie verv flat the color has one appearance. AVhen they rise a little the shade of color seems to change. If you let fall some ink-drops between two panes of glass, then spread them apart or press them together, you will see changes in the color and size of the spots. Of this nature is the apparent change in the colors of fishes under different con- ditions. AVhere the fish feels at its best the colors are the richest., There are some fishes, too, in which the male grows very brilliant in the breeding season through the deposition of red, white, black, The Life of the Fish 9 or blue pigments, or coloring matter, on its scales or on its head or fins, this pigment being absorbed when the mating season is over. This is not true of the sunfish, who remains just about the same at all seasons. The male and female are colored alike and are not to be distinguished without dissection. If we examine the scales, we shall find that these are marked with fine lines and concentric strise, and part of the apparent color is due to the effect of the fine lines on the light. This gives the bluish lustre or sheen which we can see in certain lights, although we shall find no real blue pigment under it. The inner edge of each scale is usually scalloped or crinkled, and the outer margin of most of them has little prickly points which make the fish seem rough when we pass our hand along his sides. The Lateral Line. — Along the side of the fish is a line of peculiar scales which runs from the head to the tail. This is Fig. 4. — Ozorthe dictyogramma (Herzenstein). A Japanese blenny, from Hakodate: showing increased number of lateral lines, a trait characteristic of many fishes of the north Pacific. called the lateral hne. If we examine it carefully, we shall see that each scale has a tube from which exudes a watery or mucous fluid. Behind these tubes are nerves, and although not much is known of the function of the tubes, we can be sure that in some degree the lateral line is a sense-organ, perhaps aiding the fish to feel sound-waves or other disturbances in the water. The Fins of the Fish. — The fish moves itself and directs its course in the water by means of its fins. These are made up of stiff or flexible rods growing out from the body and joined to- gether by membrane. There are two kinds of these rays or rods in the fins. One sort is without joints or branches, tapering to a sharp point. The rays thus fashioned are called spines, and they are in the sunfish stiff and sharp-pointed. The others, lo The Life of the Fish known as soft rays, are made up of many little joints, and most of them branch and spread out brush-like at their tips. In the fin on the back the first ten of the rays are spines, the rest are soft rays. In the fin under the tail there are three spines, and in each fin at the breast there is one spine with five soft rays. In the other fins all the rays are soft. The fin on the back is called the dorsal fin, the fin at the end of the tail is the caudal fin, the fin just in front of this on the lower side is the anal fin. The fins, one on each side, just behind the gill-openings are called the pectoral fins. These correspond to the arms of man, the wings of birds, or the fore legs of a turtle or lizard. Below these, corresponding to the hind legs, is the pair of fins known as the ventral fins. If we examine the bones behind the gill-openings to which the pectoral fins are attached, we shall find that they correspond after a fashion to the shoulder- girdle of higher animals. But the shoulder-bone in the sunfish is joined to the back part of the skull, so that the fish has not any neck at all. In animals with necks the bones at the shoulder are placed at some distance behind the skull. If we examine the legs of a fish, the ventral fins, we shall find that, as in man, these are fastened to a bone inside called the pelvis. But the pelvis in the sunfish is small and it is placed far forward, so that it is joined to the tip of the " collar-bone" of the shoulder-girdle and pelvis attached together. The caudal fin gives most of the motion of a fish. The other fins are mostly used in maintaining equilibrium and direction. The pectoral fins are almost constantly in motion, and they may sometimes help in breathing by starting currents outside which draw water over the gills. The Skeleton of the Fish. — The skeleton of the fish, like that of man, is made up of the skull, the back-bone, the limbs, and their appendages. But in the fish the bones are relatively smaller, more numerous, and not so firm. The front end of the vertebral column is modified as a skull to contain the little lirain which serves for all a fish's activities. To the skull are attached the jaws, the membrane bones, and the shoulder- girdle. The back-bone itself in the sunfish is made of about l^vL■nty-fllur i.iieces, or vertebra;. Each of these has a rounded central ])art, concave in front and behind. Above this is a The Life of the Fish 1 1 channel through which the great spinal cord passes, and above and below are a certain number of processes or projecting points. To some_of these, through the mctlium of another set of sharp bones, the fins of the back are attached. Along the sides of the body are the slender ribs. The Fish in Action. — The fish is, like any other animal, a machine to convert food into power. It devours other animals or plants, assimilates their substance, takes it over into itself, and through its movements uses up this substance again. The food of the sunfish is made up of worms, insects, and little fishes. To seize these it uses its mouth and teeth. To digest them it needs its alimentary canal, made of the stomach with its glands and intestines. If we cut the fish open, we shall find the stomach with its pjdoric ca;ca, near it the large liver with its gall- bladder, and on the other side the smaller spleen. After the food is dissolved in the stomach and intestines the nutritious part is taken up by the walls of the alimentary canal, whence it passes into the blood. The blood is made pure in the gills, as we have already seen. To send it to the gills the fish has need of a little pumping-engine, and this we shall find at work in the fish as in all higher animals. This engine of stout muscle surrounding a cavity is called the heart. In most fishes it is close behind the gills. It contains one auricle and one ventricle only, not two of each as in man. The auricle receives the impure blood from all parts of the body. It passes it on to the ventricle, which, being thick-walled, is dark red in color. This passes the blood by convulsive action, or heart-beating, on to the gills. From these the blood is col- lected in arteries, and without again returning to the heart it flows all through the body. The blood in the fish flows slug- gishly. The combustion of waste material goes on slowly, and so the blood is not made hot as it is in the higher beasts and birds. Fishes have relatively little blood; what there is is rather pale and cold and has no swift current. If we look about in the inside of a fish, we shall find close along the lower side of the back-bone, covering the great artery, the dark red kidneys. These strain out from the blood a cer- tain class of impurities, poisons made from nerve or muscle waste which cannot be burned away by the oxygen of respiration. I 2 The Life of the Fish The Air-bladder.— In the front part of the sunfish, just above the strimach, is a closed sac, filled with air. This is called the air-bladder, or swim-bladder. It helps the fish to maintain its place in the water. In bottom fishes it is almost always small, while fishes that rise and fall in the current generally have a large swim-bladder. The gas inside it is secreted from the blood, for the sunfish has no way of getting any air into it from the outside. But the primal purpose of the air-bladder was not to serve as a float. In A'ery old-fashioned fishes it has a tube connecting it with the throat, and instead of being an empty sac it is a true lung made up of many lobes and parts and lined with little blood- vessels. Such fishes as the garpike and the bowfin have lung- like air-bladders and gulp air from the surface of the water. In the very little sunfish, when he is just hatched, the air- bladder has an air-duct, which, however, is soon lost, leaving only a closed sac. From all this we know that the air-bladder is the remains of what was once a lung, or additional arrange- ment for breathing. As the gills furnish oxygen enough, the lung of the common fish has fallen into disuse and thrifty Nature has used the parts and the space for another and a very different purpose. This will serv'e to help us to understand the swimr bladder and the way the fish came to acquire it as a substitute for a lung. The Brain of the Fish. — The movements of the fish, like those of every other complex animal, are directed by a central ner- vous system, r)f which the principal part is in the head and is known as the brain. From the eye of the fish a large nerve goes to the brain to report what is in sight. Other nerves go from the nostrils, the ears, the skin, and every part which has any sort of capacity for feeling. These nerves carry their mes- sages inward, and when they reach the brain they may be trans- formed into movement. The brain sends back messages to the muscles, directing them to contract. Their contraction moves the fins, and the fish is shoved along through the water. To scare the fish or to attract it to its food or to its mate is about the whole range of the eft'ect that sight or touch has on the animal. These sensations changed into movement constitute what is called reflex action, performance without thinkincr of 01 p pi J3 ftq o I d P4 14 The Life of the Fish what is being done. With a boy, many familiar actions may be equally reflex. The boy can also do many other things " of his own accord," that is, by conscious effort. He can choose among a great many jjossible actions. But a fish cannot. If he is scared, he must swim away, and he has no way to stop himself. If he is hungry, and most fishes are so all the time, he wih spring at the bait. If he is thirsty, he will gasp, and there is nothing else for him to do. In other words, the activities of a fish are nearh' all reflex, most of them being suggested and immediately directed liy the influence of external things. Because its actions are aU reflex the brain is very small, very primitive, and verv simple, nothing more being needed for automatic move- ment. Small as the fish's skull-cavity is, the brain does not half fin it. The vacant space about the little brain is filled with a fatty fluid mass looking like white of egg, intended for its protection. Taking tlie dead sunfish (for the live one we shall look after carcfullv, giving him every day fresh water and a fresh worm or snail nr liit of beef), if we cut off the upper part of the skull wc shall see the separate parts of the brain, most of them lying in pairs, side bv side, in the bottom of the brain-cavity. The largest pair is near the middle of the length of the brain, two nerve-masses (or ganglia), each one round and hollow. If we turn these over, we shall see that the nerves of the eye run into them. AVe know then that these nerve-masses receive the impressions of sight, and so they are called optic lobes. In front of the optic lobes are two smaller and more oblong nerve- masses. These constitute the cerebrum. This is the thinking part of the brain, and in man and in the higher animals it makes up the greater part of it, overla])ping and hiding the other ganglia. But the fish has not much need for thinking and its fore-brain or cerebrum is very small. In front of these are two small, slim ]irojections, one going to each nostril. These are the olfac- tr)ry lobes which receive the sensation of smell. Behind the optic loljes is a single small lobe, not divided into two. This is the cerebellum and it has charge of certain powers of motion. Under the cereljellum is the medulla, lielow Avhich the spinal cr)rd begins. Tlic rest of the spinal cord is threader] through the dilferent vertebne back to the tail, and at each joint it sends The Life of the Fish 15 out nerves of motion and receives nerves of sense. Everything that is done by the fish, inside or outside, receives the attention of the Httle branches of the great nerve-cord. The Fish's Nest. — The sunfish in the spawning time will build some sort of a nest of stones on the bottom of the eddy, and then, when the eggs are laid, the male with flashing eye and fins all spread will defend the place with a good deal of spirit. All this we call instinct. He fights as well the first time as the last. The pressure of the eggs suggests nest-building to the female. The presence of the eggs tells the male to defend them. But the facts of the nest-building and nest protection are not very well understood, and any boy who can watch them and describe them truly will be able to add something to science. CHAPTER II THE EXTERIOR OF THE FISH lORM of Body. — AVith a glance at the fish as a living organism and some knowledge of those structures which are to be readily seen without dissection, we are prepared to examine its anatomy in detail, and to note some of the variations which may be seen in different parts of the great group. In general fishes are boat-shaped, adapted for swift progress through the water. They are longer than broad or deep and the greatest width is in front of the middle, leaving the com- pressed paddle-like tail as the chief organ of locomotion. But to all these statements there are numerous exceptions. Some fishes depend for protection, not on swiftness, but on the thorny skin or a bony coat of mail. Some of these are almost globular in form, and their outline bears no resemblance to that Fig. 6. — Pine-cone FLsh, Monoccniris japonicus (HouttuTO). Waka, Japan. of a boat. The trunkfish {Ostracion) in a hard bon)- box has no need of rapid progress. I6 The Exterior of the Fish 7 Fig. 7.— Porcupine-fish, Diodon hysirix (Linnaeus). Tortugas Islands. Fig. 8. Fic. 9. Fig. 8. — Thread-eel, Nemichthys avocetta Jordan and Gilbert. Vancouver Island Fig. 9. — Sea-horse, Hippocampus hudsonius Dekay. Virginia. i8 The Exterior of the Fish Fig. 10. — Harvest^fish, Pepnlas paru (LinniEus). ^'i^ginia. /Aili^-^^'^ Fig. 11. — Anko or Fishing-frog, Lophius litulon (Jordan). Matsushima Bay, .Japan. (The sliort line in all cases shows the degree of reduction; it represents an inch of the fish's length.) The Exterior of the Fish 19 The pine-cone fish (Monocentris japonicus) adds strong fin- spines to its bony box, and the porcupine fish {Diodon hystrix) is covered with long prickles which keep away all enemies. Among swift fishes, there are some in which the body is much deeper than long, as in Aiitigonia. Certain sluggish fishes seem to be all head and tail, looking as though the body by some accident had been omitted. These, Hke the headfish (Mola mola) are protected by a leathery skin. Other fishes, as the eels, are extremely long and slender, and some carry this elongation to great extremes. Usually the head is in a line with the axis of the body, but in some cases, as the sea-horse {Hippocampus) , the head is placed at right angles to the axis, and the body itself is curved and cannot be straightened with- out injury. The type of the swiftest fish is seen among the mackerels and tunnies, where every outline is such that a racing yacht might copy it. The body or head of the fish is said to be compressed when it is flattened sidewise, depressed when it is flattened vertically. Thus the Peprilus (Fig. 10) is said to be compressed, while the fishing-frog (Lopliius) (Fig. 11) has a depressed body and head. Other terms as truncate (cut oft" short), attenuate (long-drawn out), robust, cuboid, filiform, and the like may be needed in descriptions. Measurement of the Fish. — As most fishes grow as long as they live, the actual length of a specimen has not much value for purposes of description. The essential point is not actual length, but relative length. The usual standard of measure- ment is the length from the tip of the snout to the base of the caudal fin. With this length the greatest depth of the body, the greatest length of the head, and the length of individual parts may be compared. Thus in the Rock Hind (Epinephelus adscensionis), fig. 12, the head is contained 2f times in the length, while the greatest depth is contained three times. Thus, again, the length of the muzzle, the diameter of the eye, and other dimensions may be compared with the length of the r head. In the Rock Hind, fig. 12, the eye is 5 in head, the snout i is 4f in head, and the maxillary 2|. Young fishes have the e eye larger, the body slenderer, and the head larger in proportion t than old fishes of the same kind. The mouth grows larger 20 The Exterior of the Fish with age, and is sometimes larger also in the male sex. The development of the fins often varies a good deal in some fishes with age, old fishes and male fishes having higher fins when Fig. 12. — Rock Hind or Cabra Mora of the West Indies, Epinephelus adscensionis (Osbook). Famih' Serranidcc. such differences exist. These variations are soon understood by the student of fishes and cause little doubt or confusion in the study of fishes. The Scales, or Exoskeleton. — The surface of the fish may be naked as in the catfish, or it may be covered with scales, prickles, shagreen, or bony plates. The hard covering of the skin, when present, is known as the exoskeleton, or outer skeleton. In the fish, the exoskeleton, whatever form it may assume, ma}' be held to consist of modified scales, and this is usually obviously the case. The skin of the fish may be thick or thin, bony, horny, leathery, or papery, or it may have almost any inter- mediate character. When protected by scales the skin is usually thin and tender; when unprotected it may be ossified, as in the sea-horse; horny, as in the headfish; leathery, as in the catfish; or it may, as in the sea-snails, form a loose scarf readily de- tachable from the muscles below. The scales themselves may be broadly classified as ctenoid, cycloid, placoid, ganoid, or prickly. Ctenoid and Cycloid Scales. — Nomially formed scales are rounded in outline, marked by fine concentric, rings, an(l' crossed on the inner side by a few strong radiatmg ridges and folds The Exterior of the Fish 21 They usually cover the body in.ore or less evenly and are imbri- cated like shingles on a roof, the free edge being turned back- ward. Such normal scales are of two types, ctenoid or cycloid. Ctenoid scales have a comb-edge of fine prickles or cilia ; cycloid scales have the edges smooth. These two types are not very different, and the one readily passes into the other, both being sometimes seen on different parts of the same fish. In general, however, the rnore jprimitive representatives of the typical fishes, those offiittL-abdominal ventrals and without spines in the fins, have cycloid or smooth scales. Examples are the salmon, herring, minnow, and carp. Some of the more specialized spiny-rayed fishes, as the parrot-fishes, have, however, scales equally smooth, although somewhat dift'erent in structure. Sometimes, as in the eel, the cycloid scales may be reduced to mere n.idiments buried in the skin. Ctenoid scales are beset on the free edge by little prickles or points, sometimes rising to the rank of spines, at other times soft and scarcely noticeable, when they are known as ciliate or eyelash-like. Such scales are possessed in general by the more specialized types of bony fishes, as the perch and bass, those with thoracic ventrals and spines in the fins. Placoid Scales. — Placoid scales are ossified papillae, minute, enamelled, and close-set, forming a fine shagreen. These are characteristic of the sharks, and in the most primitive sharks the teeth are evidently modifications of these primitive structures. Some other fishes have scales which appear shagreen-like to sight and feeling, but only the sharks have the peculiar structure to which Agassiz gave the name of placoid. The rough prickles of the filefishes and some sculpins are not placoid, but are re- duced or modified ctenoid scales, scales nar- rowed and reduced to prickles. Bony and Prickly Scales. — Bony and prickly scales are found in great variety, and scarcely admit of description or classification. In general, prickly points on the skin are modifi- cations of ctenoid scales. Ganoid scales are thickened and cov- ci-orl -uTi+Tn Vir^TTsr Anampl miirh like that seen in teeth, otherwise Fig. 1.3. — Scales of A canthoess us bro nni (Agassiz). (.4fter Dean.) 22 The Exterior of the Fish Fig. 14. — Cycloid Scale. essentially like cycloid scales. These are found in the garpike and in many genera of extinct Ganoid and Crossopterygian fishes. In the hne of descent the placoid scale preceded the ganoid, which in turn was followed by the cycloid and lastly by the ctenoid scale. Bony scales in other types of fishes may have noth- ing structurally in common with ganoid scales or plates, however great may be the superficial resemblance. The distribution of sca.les on the body may vary exceedingly. In some fishes the scales are arranged in very regular series; in others they are variously scattered over the body. Some are scaly everywhere on head, body, and fins. Others may have only a few lines or patches. The scales may be everywhere alike, or they may in one part or another be greatly modified. Sometimes they are transformed into feelers or tactile organs. The number of scales is always one of the most valu- able of the characters by which to distinguish species. Lateral Line. — The lateral line in most fishes consists of a series of modified scales, each one provided with a mucous tube extending along the side of the body from the head to the caudal fin. The canal which pierces each scale is simple at its base, but its free edge is often branched or ramified. In most spiny-rayed fishes it runs parallel with the outline of the back. In most soft -rayed fishes it follows rather the outline of the belly. It is subject to many variations. In some large groups {Gohiidcc, Pccciltida:) its surface structures are entirely wanting. In scale- less fishes the mucous tube lies in the skin itself. In some groups the lateral line has a peculiar position, as in the flying- fishes, where it forms a raised ridge bounding the belly. In many cases the lateral line has branches of one sort or another. It is often double or triple, and in some cases the whole back' and sides of the fish are covered with lateral lines and their ramifications. Sometimes peculiar sense-organs and occasionally eye-like luminous spots are developed in connection with the lateral line, enabling the fish to see in the black depths of the sea. These will be noticed in another chapter. The Exterior of the Fish 23 condition of the lateral line is seen in the sharks and chimaeras, in which fishes it appears as a series of channels in or under the skin. These channels are filled with mucus, which exudes through occasional open pores. In many fishes the bones of the skull are cavernous, that is, provided with cavities filled Fig. 15. — Singing Fish (with many lateral lines), Porichthys porosissitmis (Cuv. andVal.). Gulf of Mexico. with mucus. x\nalogous to these cavities are the mucous chan- nels which in primitive fishes constitute the lateral line. Function of tJie Lateral Line. — The general function of the lateral line with its tubes and pores is still little understood. As the structures of the lateral line are well provided with nerves, it has been thought to be an organ of sense of some sort not yet understood. Its close relation to the ear is beyond question, the ear-sac being an outgrowth from it. "The original significance of the lateral line," according to Dr. Dean,* "as yet remains undetermined. It appears inti- mately if not genetically related to the sense-organs of the head and gill region of the ancestral fish. In response to special aquatic needs, it may thence have extended farther and farther backward along the median line of the trunk, and in its later differentiation acquired its metameral characters." In view of its peculiar nerve-supply, "the precise function of this entire system of organs becomes especially difficult to determine. Feeling, in its broadest sense, has safely been admitted as its possible use. Its close genetic relationship to the hearing organ suggests the kindred function of determining waves of vibration. These are transmitted in so favorable a way in the aquatic medium that from the side of theory a system of 24 The Exterior of the Fish hypersensitive end-organs may well have been established. The sensory tracts along the sides of the body are certainly well situated to determine the direction of the approach of friend, enemy, or prey." The Fins of Fishes. — The organs of locomotion in the fishes Y; are knows as fins. These are composed of bony or cartilaginous rods or rays connected by membranes. The fins are divided mto two groups, paired fins and vertical fins. The pectoral fins, one on either side, correspond to the anterior limbs of the higher vertebrates. The ventral fins beloAv or behind them represent the hnider limbs. Either or both pairs may be absent, but. the ventrals are much more frequently abortive than the pec- torals. The insertion of the ventral fins may be abdominal, as in the sharks and the more generalized of the bony fishes, thoracic under the breast (the pelvis attached to the shoulder-girdle) or jugular, under the throat. When the Axntral fins are ab- dominal, the pectoral fins are usually placed very low. The paired fins are not in general used for progression in the water, but serve rather to enable the fish to keep its equilibrium. With the rays, however, the wing-like pectoral fins form the chief organ of locomotion. The fin on the median line of the back is called the dorsal, that on the tail the caudal, and that on the lower median line the anal fin. The dorsal is often divided into two fins or even three. The anal is sometimes divided, and either dorsal or anal fin may have behind it detached single rays called finlets. The rays composing the fin may be either simple or branched The branched rays are always articulated, that is, crossed by numerous fine joints which render them flexible. Simple rays are also sometimes articulate. Rays thus jointed are known. ■ as soft raj^s, while those rays which are neither jointed nor branched are called spines. A spine is usually stiff and sharp- pointed, but it may be neither, and some spines are very slen- der and flexible, the lack of branches or joints being the feature which distinguishes spine from soft ray. The anterior rays of the dorsal and anal fins are spinous in most fishes with thoracic ventrals. The dorsal fin has usu- ally about ten spines, the anal three, but as to this there is much variation in different groups. When the dorsal is di- The Exterior of the Fish 25 vided all the rays of the first dorsal and usually the first ray of the second are spines. The caudal fin has never true spines, though at the base of its lobes are often rudimentary rays which resemble spines. Most spineless fishes have such rudi- ments in front of their vertical fins. The pectoral, as a rule, is without spines, although in the catfishes and some others a single large spine may be developed. The ventrals when ab- dominal are usually without spines. When thoracic each usually, but not always, consists of one spine and five soft rays. When jugular the number of soft rays may be reduced, this being a phase of degeneration of the fin. In writing de- scriptions of fishes the number of spines may be indicated by Roman numerals, those of the soft rays by Arabic. Thus D. ^II-I, 17 means that the dorsal is divided, that the an- terio'r IportToh '-consists of twelve spines, the posterior of one spine and seventeen soft rays. In some fishes, as the catfish or the salmon, there is a small fin on the back behind the dorsal fin. This is known as the adipose fin, being formed of fatty substance covered b}^ skin. In a few catfishes, this adipose fin develops a spine or soft rays. Muscles. — The movements of the fins are accomplished by the muscles. These organs lie along the sides of the body, forming the flesh of the fish. They are little specialized, and not clearly differentiated as in the higher vertebrates. With the higher fishes there are several distinct systems of muscles controlling the jaws, the gills, the eye, the different fins, and the body itself. The largest of all is the great lateral muscle, composed of flake-like segments (myocommas) which correspond in general with the number of the vertebrse. In general the muscles of the fish are white in color. In some groups, especially of the mackerel family, they are deep red, charged with animal oils. In the salmon they are orange-red, a color also due to the presence of certain oils. In a few fishes muscular structures are modified into electric organs. These will be discussed in a later chapter. CHAPTER III THE DISSECTION OF THE FISH [he Blue-green Sunfish. — The organs found in the abdominal cavity of the fish may be readily traced in a rapid dissection. Any of the bony fishes may be chosen, but for our purposes the sunfish will serve as well as any. The names and location of the principal organs are shown in the accompanying figure, from Kellogg's Zoologv. It represents the blue-green sunfish, Apomotis cya- nclliis, from the Kansas River, but in these regards all the species of sunfishes are alike. ^A^e may first glance at the dif- ferent organs as shown in the sequence of dissection, leaving a detailed account of each to the subsequent pages. The Viscera. — Opening the body cavity of the fish, as shown in the plate, we see below the back-bone a membranous sac closed and filled with air. This is the air-bladder, a rudiment of that structure which in higher vertebrates is developed as a lung. The alimentary canal passes through the abdominal cavity extending from the mouth through the pharynx and ending at the anus or vent. The stomach has the form of a blind sac, and at its termination are a number of tubular sacs, the pyloric CEeca, which secrete a digestive fluid. Bej^ond the pylorus ex- tends the intestine with one or two loops to the anus. Con- nected with the intestine anteriorly is the large red mass of the liver, with its gall-bladder, which serves as a reservoir for bile, the fluid the liver secretes. Farther back is another red glandu- lar mass, the spleen. In front of the liver and separated from it by a membrane is the heart. This is of four parts. The posterior part is a thin-walled reservoir, the sinus venosus, into which blood enters through the jugular vein from the head and through the cardinal vein from the kidney. From the sinus venosus it passes forward into a large thin-walled chamber, the auricle. 26 3 a- c to a 3 s I 3 2 8 The Dissection of the Fish Next it flows into the thick-walled ventricle, whence by the rhythmical construction of its waUs it is forced into an arterial bulb which lies at the base of the ventral aorta, which carries it on to the gills. After passing through the fine gill-filaments, it is returned to the dorsal aorta, a large blood-vessel which ex- tends along the lower surface of the back-bone, giving out branches from time to time. The kidneys in fishes constitute an irregular mass under the back-bone posteriorly. They discharge their secretions through the ureter to a small urinary bladder, and thence into the uro- genital sinus, a smah opening behind the anus. Into the same sinus are discharged the reproductive cells in both sexes. In the female sunfish the ovaries consist of two granular masses of vellowish tissue lying just below and behind the SAvim- bladder. In the spring they fill much of the body cavity and the manv little eggs can be plainly seen. When mature they iire discharged through the oviduct to the urogenital sinus. In some fishes there is no special oviduct and the eggs pass into the abdominal cavity before exclusion. In the male the reproductive organs have the same position as the ovaries in the female. They are, however, much smaller in size and paler in color, while the minute spermatozoa appear milky rather than granular on casual examination. A vas defe- rens leads from each of these organs into the urogenital sinus. The lancelets, lampreys, and hagfishes possess no genital ducts. In the former the germ cells are shed into the atrial cavity, and from there find their way to the exterior either through the mouth or the atrial pore ; in the latter they are shed directly into the body cavity, from which they escape through the abdominal pores. In the sharks and skates the Wolffian duct in the male, in addition to its function as an excretory duct, serves also as a passage for the sperm, the testes having a direct connection with the kidneys. In these forms there is a pair of Mullerian ducts which serve as oviducts in the females; they extend the length of the body cavity, and at their anterior end have an opening which receives the eggs which have escaped from the ovary into the body cavity. In some bony fishes as the eels and female salmon the germ cells are shed into the body cavity and escape through genital pores, which, however, may The Dissection of the Fish 29 not be homologous with abdominal pores. In most other bony fishes the testes and ovaries are continued directly into ducts which open to the outside. Organs of Nutrition. — The organs thus shown in dissection we may now examine in detail. The mouth of the fish is the organ or series of structures first concerned in nutrition. The teeth are outgrowths from the Fig. ly.^Black Swallower, Chiasmodon niger Johnson, containing a fish larger than itseU". Le Have Bank. skin, primarily as modified papillae, aiding the mouth in its various functions of seizing, holding, cutting, or crushing the various kinds of food material. Some fishes feed exclusively on plants, some on plants and animals alike, some exclusively on animals, some on the mud in which minute plants and animals occur. The majority of fishes feed on other fishes, and without much regard to species or condition. With the carnivorous fishes, to feed repre- sents the chief activity of the organism. In proportion to the voracity of the fish is usually the size of the mouth, the sharp- ness of the teeth, and the length of the lower jaw. The most usual type of teeth among fishes is that of vilHform bands. VilUform teeth are short, slender, even, close-set, making a rough velvety surface. When the teeth are larger and more widely separated, they are called cardiform, like the teeth of a wool-card. Granular teeth are small, blunt, and sand-like. Ca- nine teeth are those projecting above the level of the others, usually sharp, curved, and in some species barbed. Sometimes 3° The Dissection of the Fish the canines are in front. In some families the last tooth m either jaw may be a "posterior canine," serving to hold small animals in place while the anterior teeth crush them. Canine teeth are often depressible, having a hinge at base. Teeth very slender and brushdike are called setiform. Teeth with blunt tips are molar. These are usually enlarged and fitted for crushing shells. Flat teeth set in mosaic, as in many rays and in the pharyngeals of parrot-fishes, are said to be paved or tessellated. Knifedike teeth, occasionally with serrated edges, are found in many sharks. Many fishes have incisor-like teeth, some flattened and truncate like human teeth, as in the sheepshead, sometimes with serrated edges. Often these teeth are movable, implanted only in the skin of the lips. In other cases they are set fast in the jaw. Mo^t species with movable teeth or teeth with ser- rated edges are herbivorous, while strong incisors may indicate the choice of snails and crabs as food. Two or more of these different types may be The knife-like teeth of the sharks are progressively shed, new ones being constantly formed on the inner margins of the jaw, so that the teeth are marching to be lost oA^er the edge of the jaw as soon as each has fulfilled its function. In general the more distinctly a species is a fish- eater, tlie sharper are the teeth. Usually fishes shoAV little dis- crimination in their choice of food ; often they devour the young of their own species as readily as any other. Tlie digestive ])rocess is rapid, and most fishes rapidly increase in size in the ]irocess of development. AVhen food ceases to be abundant the fishes grow more sliiwly. For this reason the same species will groAv to a larger size in large streams than in small ones, in lakes tlian in brooks. In most cases there is no absolute limit to growth, the species growing as long as it lives. But while some species endure many years, others are certainly very short- Fir,. IS. — .Jaws of a Parrot- hsh, SpiiriKiiDni (iitr(ifreniilu}ii (Val). Cuba. found in the same fish. The Dissection of the Fish 31 lived, and some may be even annual, dying after spawning, per- haps at the end of the first season. Teeth are wholly absent in several groups of fishes. They are, however, usually present on the premaxiUary, dentary, and pharyngeal bones. In the higher forms, the vomer, palatines, and gill-rakers are rarely without teeth, and in many cases the pterygoids, sphenoids, and the bones of the tongue are similarly armed. No salivary glands or palatine velum are developed in fishes. The tongue is always bony or gristly and immovable. Some- times taste-buds are developed on it, and sometimes these are found on the barbels outside the mouth. The Alimentary Canal. — The mouth-cavity opens through the pharynx between the upper and lower pharyngeal bones into the Fig. 19. — Sheepsheac (with incisor teeth), Arcliosiirgiix iirnhn'.oreiihaliis baurn). Beaufort, X. C. fWal- oesophagus, whence the food passes into the stomach. The intes- tinal tract is in general divided into four portions — oesophagus, stomach, small and large intestines. But these divisions of the intestines are not always recognizable, and in the very lowest forms, as in the lancelet, the stomach is a simple straight tube without subdivision. In the lampreys there is a distinction only of the ceso]ih- agus with many longitudinal folds and the intestine with but 32 The Dissection of the Fish one. In the bony fishes the stomach is an enlfirged area, either siphon-shaped, with an opening at either end, or else forming a bhnd sac with the openings for entrance (cardiac) and exit (pyloric) close together at the anterior end. In the various kinds of mollets {Mngil) and in the hickory shad (Dorosoma), fishes which feed on minute vegetation mixed with mud, the stomach becomes enlarged to a muscular gizzard, like that of a fowl. Attached near the pylorus and pouring their secretions into the duodenum or small intestine are the pyloric_c^ca^ These are tubular sacs secreting a pale fluid and often almost as long as the stomach or as wide as the intestine. These may be very numerous as in the salmon, in which case they are likely to become coalescent at base, or they be few or altogether wanting. Besides these appendages which are wanting in the higher vertebrates, a pancreas is also found in the sharks and many other fishes. This is a glandular mass behind the stomach, its duct leading into the duodenum and often coalescent with the bile duct from the liver. The liver in the lancelet is a long diverticulum of the intestine. In the true fishes it becomes a large gland of irregular form, and usually but not always pro- vided with a gall-bladder as in the higher vertebrates. Its secretions usually pass through a ductus cJiolodechus to the duodenum. The spleen, a dark-red lymphatic gland, is found attached to the stomach in all fish-like vertebrates except the lancelet. The lining membrane of the abdominal cavity is known as the peritoneum, and the membrane sustaining the intestines from the dorsal side, as in the higher vertebrates, is called the mesen- tery. In many species the peritoneum is jet black, while in related forms it may be pale in color. It is more likely to be black in fishes from deep water and in fishes which feed on plants. The Spiral Valve. — In the sharks or skates the rectum or large intestine is peculiarly modified, being provided with a spiral valve, with sometimes as many as forty gyrations. A spiral valve is also present in the more ancient types of the true fishes as dipnoans, crossopterygians, and ganoids. This valve greatly increases the surface of the intestine, doing away with the neces- sity for length. In the bowfin {Amia) and the garpike (Lepi- The Dissection of the Fish 33 sosteus) the valve is reduced to a rudiment of three or four con- volutions near the end of the intestine. In the sharks and skates the intestine opens into a cloaca, which contains also the urogenital openings. In all fishes the latter lie behind the orifice of the intestine. In the bony fishes and the. ganoids there is no cloaca. Length of the Intestine. — In all fishes, as in the higher ver- tebrates, the length of the alimentary canal is coordinated with the food of the fish. In those which feed upon plants the intes- FiG. 20. — Stone-roller, Campostomu anomalum (Rafinesque). Family Cyprinidw. Showing nuptial tubercles and intestines coiled about the air-bladder. tine is very long and much convoluted, while in those which feed on other fishes it is always relatively short. In the stone -roller, a fresh-water minnow {Campostoma) found in the Mississippi Valley, the excessively long intestines filled with vegetable matter are wound spool-fashion about the large air- bladder. In all other fishes the air-bladder lies on the dorsal side of the intestinal canal. CHAPTER IV THE SKELETON OF THE FISH PECIALIZATION of the Skeleton. — In the lowest form of fish-like vertebrates (BrancJiiostoma), the skeleton consists merely of a cartilaginous rod or notochord extending through the body just below the spinal cord. In the lampreys, sharks, dipnoans, crossopterygians, and sturgeons the skeleton is still cartilaginous, but grows progressively more complex in their forms and relations. Among the typical fishes the skeleton becomes ossified and reaches a very high degree of complexity. \"ery great varia- tions in the forms and relations of the difterent parts of the skeleton are found among the bony fishes, or teleostei. The high degree of specialization of these parts gives to the study of the bones great importance in the systematic arrangement of these fishes. In fact the true affinities of forms is better shown by the bcmes than by any other system of organs. In a general way the skeleton of the fish is homologous with that of man. The head in the one corresponds to the head in the other, the back-bone to the back-bone, and the paired fins, pectoral and ventral, to the arms and legs. Homologies of Bones of Fishes. — But this homology does not extend to the details of structure. The bones of the arm of the specialized fish are not by any means identical with the humerus, coracoid, clavicle, radius, ulna, and carpus of the higher vertebrates. The A-ertcbrate arm is not derived from the pectoral fin, but both from a cartilaginous shoulder-girdle with undifferentiated pectoral elements bearing fin-rays, in its details unlike an arm and unlike the pectoral fin of the speciahzed fish. The assumption that each element in the shoulder-girdle and the pectoral fin of the fish must correspond in detail to the arm of man has led to great confusion in naming the difterent 34 The Skeleton of the Fish 35 bones. Among the many bones of the fish's shoulder-girdle and pectoral fin, three or four different ones have successively borne the names of scapula, clavicle, coracoid, humerus, radius, and ulna. None of these terms, unless it be clavicle, ought by rights apply to the fish, for no bone of the fish is a true homo- logue of any of these as seen in man. The land vertebrates and the fishes have doubtless sprung from a common stock, but this stock, related to the crossopterygians of the present day, was unspecialized in the details of its skeleton, and from it the fishes and the higher vertebrates have developed the widely diverging lines. Parts of the Skeleton. — The skeleton may be divided into the head, the vertebral column, and the limbs. The very lowest of the fish-like forms {BrancJiiostoma) has no differentiated head Fig. 21. — Striped Bass, Roccu.t linealiis (Bloch). Potomac Ri^-er. or skull, but in all the other forms the anterior part of the vertebral column is modified to form a cranium for the protec- tion of the brain. In the lampreys there are no jaws or other appendages to the cranium. In the sharks, dipnoans, crossopterygians, ganoids, and teleosts or bony fishes, jaws are developed as well as a variety of other bones around the mouth and throat. The jaw-bearing forms are sometimes known by the general name of gnathostomes. In the sharks and their relatives (rays, chimteras, etc.) all the skeleton is composed of cartilage. In the more speciaHzed bony fishes, besides these bones we find also series of mem- brane bones, more or less external to the skull and composed of o _ r«s ry is also olten knowii as in.tsrriiaxillary. Lying behind the premaxillary, its anterior end attached within Jhe angle nf"*1ie premaxillary, is the"" maxillary (31), or siiprainaxillary, a flattened bone with expanded posterior tip. In the striped bass this bone is without teeth, but in many less specialized forms, as the salmon, it is provided with teeth and joined to the premaxillary^ in a different fashion. In any case its position readily distinguishes it. In some cases the max- illary is divided by one or more sutures, setting off from it one or more extra maxillary (supplemental maxillary) bones. This suture is absent in the striped bass, but distinct in the black bass, and more than one suture is found in the shad and herring. The roof of the mouth above is formed by a number of bones, which, as they often possess teeth, may be considered with the jaws. These are the palatine bones (21), one on either side flanking the vomer, the pterygoid (20), behind it and articulating with it, the mesopterygoid (22), on the roof of the mouth toward the median line, and the metapterygoid (23), lying behind this. Al- though often armed with teeth, these bones are to be considered of the general nature of the membrane bones. In some de- graded types of fishes (eels, morays, congers) the premaxillary is indistinguishable, being united with the vomer and palatines. O CO g " = o o <5^ f^ P^ > t» o -5 c^> Q »C' -^ -^ ^ ^ o "g & ;> '3 O Ph M o CO ^' ^ lO lO ^'^ 'to 2 ■ o ^ ■ .-- o ■ > O c3 "^^ (3 (i; M :z; cE ^ ci oi o ^* c4 CO Tj^ O lO lO c3 03 C8 Tt lo o r^ 00 CO CO CO CO CO ^ s 1 "rf ^- ^ Ol CO CO M CO IM '■ 6 -o 'o OJ bB 3J 0^ -S t- a> S; 9 aj " H a> Ph O cB t; t- <^ ^ < CO TjH u:j f:D ^-^ 2S (N (N (N Ss t^ 00 C-; o r-i Ci 1 — ' rt ,-1 CM (N CM v^ W- ^^ ^^ I.N T-f rt ,-1 (M (N (N '-^ w- ( y ^~* ^ y-< a oq CM The Skeleton of the Fish 43 The upper jaw of the shark is formed from the anterior por- tion of tne palatine bones, which are not separate from the quadrate, the whole forming the palatoquadrate apparatus. In the himsera and the dipnoans this apparatus is solidly united with the cranium. In these fishes the true upper jaw, formed of maxillary and premaxillary, is wanting. The Lower /aw.— The lower jaw or mandible is also com- plex, consisting of two divisions or rami, right and left, joined in front by a suture. The anterior part of each ramus is formed by the dentary bonej^^o), which carries the teeth. Behind this is the articular bone (28), which is connected by a joint to the Fig. 27. — Lower jaw of Amia calm (Linnajus), showing tlie gular plate. quadrate bone (19). Xt the lower angle of the articular bone is the small angular bone (29). In many cases another small bone, which is called splenial, may be found attached to the inner surface of the articular bone. This little bone has been called coronoid, but it is doubtless not homologous with the coronoid bone of reptiles. In a few fishes, Amia, Elopida, and certain fossil dipnoans, there is a bony gular plate, a membrane bone across the throat behind the chin on the lower jaw. The Suspensorium of the Mandible. — The lower jaw is at- tached to the cranium by a chain of suspensory bones, which vary a good deal with different groups of fishes. The articular is jointed with the flat quadrate bone (19), which lies behind the pterygoid. A slender bone passes upward (18) under the preopercle and the metapterygoid, forming a connection above 44 The Skeleton of the Fish with a large flattish bone, the hyomandibnlar (17), which in turn joins the cranium. The slender bone which thus keys together the upper and lower elements, hyomandibular and quadrate, forming the suspensorium of the lower jaw, is known as sym- plcctic (18). The hyomandibular is thought to be homologous with the stapes, or stirrup-bone, of the ear in higher animals. In this case the symplectic may be homologous with its small orbicular bone, and the malleus is a transformation of the articular. The incus, or anvil-bone, may be formed from part of Meckel's cartilage. All these homologies are however ex- tremely hypothetical. The core of the lower jaw is formed of a cartilage called Meckel's cartilage, outside which the membrane bones, dentary, etc., are developed. This cartilage forms the lower jaw in sharks, true jaw-bones not being developed in these fishes. In lampreys and lancelets there is no lower jaw. Membrane Bones of Face. — The membrane bones lie on the surface of the head, when they are usually covered by thin skin and have only a superficial connection wnth the cranium. Such bones, formed of ossified membrane, are not found in the earlier or less specialized fishes, the lancelets and lampreys, nor in the sharks, rays, and chimeras. They are chiefly characteristic of the bony fishes, although in some of these they have undergone degradation. The preorbital (49) lies before and below the eye, its edge more or less parallel with that of the maxillary. It may be broad or narrow. When broad it usually forms a sheath into which the maxillary slips. The nasal (51) lies before the pre- orbital, a small bone usually lying along the spine of the pre- maxillary. Behind and below the eye is a series of about three flat bones, the suborbitals (50), small in the striped bass, but sometimes considerably modified. In the great group of loricate fishes (sculpins, etc.), the third suborbital sends a bony process called the suborbital stay backward across the cheek toward the preopercle. The suborbital stay is present in the rosefish. In some cases, as in the gurnard, this stay covers the whole cheek with a bony coat of mail. In some fishes, but not in the striped bass, a small supraorbital bone exists over the eye, forming a sort of cap on an angle of the frontal bone. The largest uppermost flat bone of the gill-covers is known I The Skeleton of the Fish 45 as the opercle (25). Below it, joined by a suture, is the sub- open^ (26). Before it is the prominent ridge of the preopercle (24), which curves forward below and forms a more or less distinct angle, often armed with serrations or spines. In some cases this armature is very highly developed. The interopercle (27) lies below the preopercle and parallel with the lower limb. Branchial Bones. — The bones of the branchial apparatus or gills are very numerous and complex, as well as subject to im- portant variations. In many fishes some of these bones are co- ossified, and in other cases some are wanting. The tongue may be considered as belonging to this series, as the bones of the gills are attached to its axis below. In the striped bass, as in most fishes, the tongue, gristly and immovable, is formed anteriorly by a bone called the glossohyal (37). Behind this are the hasihyals (36), and still farther back, on the side, is the ceratoJiyal (35). To the basihyals is attached a bone extending downward and free behind the urohyal (38). Behind the ceratohyal and continuous with it is the epihyal (34);. to which behind is attached the narrow interhyal (33). On th^ under surface of the ceratohyal and the epihyal are attached the branchiostegals (39). These are slender rays supporting .a membrane beneath the gills, seven in number on each side in the striped bass, but much more numerous in some groups of fishes,'- The gill membranes connecting the branchiostegals are in the' striped bass entirely separate from each other. In other fishes; they may be broadly joined across the fleshy interspace between' the gill-openings, known as the isthmus, or again they may be grown fast to the isthmus itself, so that the gill-openings of the two sides are widely separated. The Gill-arches. — The gills are attached to four bony arches with a fifth of the same nature, but totally modified by the presence of teeth, and very rarely having on it any of the gill- fringes. The fifth arch thus modified to serve in mastication instead of respiration is known collectively as the lower pharyn- geals (46). Opposite these are the upper pharyngeals (45). The gill -arches are suspended to the cranium from above by the suspensory pharyngeal (44). Each arch contains three parts —the epibranchial (43), above, the ceratobranchial (42), forming the middle part, and the hy pobranchial (41), the lower part i. 46 The Skeleton of the Fish articulating with the series of hasibranchials (40) which lie behind the epihyal of the tongue. On the three bones forming the first gill-arch are attached numerous appendages called giU- rakers (47). These gill-rakcrs vary very greatly in number and form. In the striped bass they are few and spear-shaped. In FiG. 28. — Romts lineotus. Branchial arches. (After Starks.) 40. Ba,sibranchiaL 43. Epibranchial. 40. Lower pharyngeals. 41. Hypobranchial. 44. Suspensory pharyngeal. 47. Gill-rakers. 42. Ceratobranchial. 4.5. Upper pharyngeals. the shad they are very many and almost as fine as hairs. In some fishes they form an effective strainer in separating the food, or perhaps in keeping extraneous matter from the gills. In some fishes they are short and lumpy, in others wanting altogether. The Pharyngeals. — The hindmost gill-arch, as above stated, is modified to form a sort of jaw. The tooth-bearing bones above, 2 to 4 pairs, are known as upper pharyngeals (45), those below, single pair, as loiucr pharyngeals (46). Of these the lower pharyngeals are most highly specialized and the most useful in classification. These are usually formed much as in the striped bass. Occasionally they are much enlarged, with large teeth for grinding. In many families the lower pharyn- geals are grown together in one large bone. In the suckers {Catostoniida) the lower pharyngeal preserves its resemblance to a gill-arch. In the carp family (Cypriiiida:) retaining this re- semblance, it possesses highly specialized teeth. Vertebral Column. — The vertebral column is composed of a series of vertebrae, 24 in number in the striped bass and in many of the higher fishes, but varying in different groups from 16 to 18 to upwards of 400, the higher numbers being evidence of unspecializcd or more usually degenerate structure. The Skeleton of the Fish 47 Each vertebra consists of a double concave body or centrum (66). Above it are two small projections often turned back- ward, zygapophyses (71), and two larger ones, nenrapophyses (67), which join above to form the neural spine (68) and thus form the neural canal, through which passes the spinal cord from end to end of the body. Below in the vertebrae of the posterior half of the body the hcemapophyses (69) unite to form the Jiccnial spine' (70), and Fig. 29. — Pharyngeal bone and teeth of European Chub, Leuciscus cephalut (Linnceus). (After Seelye.) Fig. 30. Fig. 31. Fig. 30. -Upper pharyngeals of a Parrot-fish, Scam, strongulocephalus .. • • •- Fig. 31.-Lower pharyngeals of a Parrot-fish, Scar«.s strong yloccphalus (Blpeker). tnrough the hcemal canal thus formed passes a great artejy. The vertebrae having hsemal as well as neural spmes are known as caudal vertebrcB, and occupy the posterior part of tl|e body, usually that behind the attachment of the anal fin (j^. The anterior vertebra; known as abdominal vertebra, bound- ing the body-cavity, possess neural spines similar to those of 48 The Skeleton of the Fish the caudal vertebrae. In place, however, of the hsmapophyses are projections known as parapopJiyses (72), which do not meet Fig. 32. — Pharyngeals of Italian Parrot-fish, Sparisoma cretense (L.). a, upper; h, lower. below, but extend outward, forming the upper part of the wall of the abdominal cavity. To the parapophyses, or near them, the ribs (73) are rather loosely attached and each rib may have one or more accessory branches (74) called epipleurals. In the striped bass the dorsal vertebra are essentially similar in form, but in some fishes, as the carp and the cat- fish, 4 or 5 anterior vertebra; are greatly modified, coossified, />' f"H8. 33. — Roccvs lineatus. 64. \ Abdominal vcrfcebra>. 65. ICaudal vertebree. 66. Centrum. 67. 'Neurapophysis. 68. Iffeural spine. 69. Hsemapophysis. Vertebral column and appendages, with a typical vertebra, (.'i.fter Starks.) 70. Haemal spine. 71. Zygapophysis. '72. Parapophysis. 73. Ribs. 74. Epipleurals. 75. Interneural. 76. Dorsal fin. 77. Interha-inal. 78. Anal fin. 79. Hypural. 80. Caudal fin. and so arranged as to connect the air-bladder with the orgc^n of hearing. Fishes with vertebrae thus altered are called plecto- sponclylous. In the garpike the vertebrae are convex anteriorly, concave The Skeleton of the Fish 49 behind, being joined by ball-and-socket joints (opisthocoelian) . In most other fishes they are double concave (anxpliccelian) . In sharks the vertebrae are imperfectly ossified, a number of terms, asterospondylous, cyclospondylous, tectospondylous, being applied to the different stages of ossification, these terms referring to the different modes of arrangement of the calcareous material within the vertebra. The Intemeurals and Interhaemals. — The vertical fins are connected with the skeletons by bones placed loosely in the flesh and not joined by ligament or suture. Below the dorsal fin (76) lies a series of these bones, dagger-shaped, with the point downward. These are called intemeurals (75) and to these the spines and soft rays of the fin are articulated. In like fashion the spines and rays of the anal fin (18) are jointed at base to bones called interhcsmals (77). In certain cases tlie second interhsemal is much enlarged, made hollow and quill-shaped, and in its concave upper end the tip of the air- bladder is received. This structure is seen in the plumefishes {Calamus). These two groups of bones, interneural and inter- hsmal, are sometimes collectively called interspinals. The flat- tened basal bone^f the caudal fin (80) is known as hypural (79). The tail of the striped bass, ending in a broad plate which supports the caudal, is said to be homocercal. In more primi- tive forms the tail is turned upward more or less, the fin being Fig. 34.— Basal bone of dorsal fin, Holophjchias leptopterus (Agassiz). (After Woodward. ) largely thrown to its lower side. Such a tail as in the sturgeon is said to be heterocercal. In the isocercal tail of the codfish and its relatives the vertebrae are progressively smaller behind and the hypural plate is obsolete or nearly so, the vertebrae remaining in the line of the axis of the body and dividing the caudal fin equally. The simplest form of tail, called diphycercal, '> ',■■ ■ , 7.V ^o The Skeleton of the Fish is extended horizontally, tapering backward, the fin equally divided above and below, without hypural plate. In any form of the tail, it may through degeneration be attenuate or whipdike, a form called leptocercal. The Pectoral Limb. — The four limbs of the fish are repre- sented by the paired fins. The anterior limb is represented by the pectoral fin and its basal elements with the shoulder- girdle, which in the bony fishes reaches a higher degree of com- plexity than in any other vertebrates. It is in connection with the shoulder-girdle that the greatest confusion in names has occurred. This is due to an attempt to homologize its parts with the shoulder-girdle (scapula, coracoid, and clavicle) of higher vertebrates. But it is not evident that a bony fish possesses a real scapula, coracoid, or even clavicle. The parts of its shoulder-girdle are derived by one line of descent from the un- differentiated elements of the cartilaginous shoulder-girdle of ancestral crossopterygian or dipnoan forms. From a similar ancestry by another line of differentiation has come the am- phibian and reptilian shoulder-girdle and its derivative, the girdle of birds and mammals. The Shoulder-girdle. — In the higher fishes the uppermost bone of the shoulder-girdle is called the post-temporal (supra- scapula) (53). In the striped bass and in most fishes this bone is jointed to the temporal region of the cranium. Some- times, as in the trigger-fishes, it is grown fast to the skull, but it usually rests Ughtly with the three points of its upper end. In sharks and skates the shoulder-girdle, which is formed of a continuous cartilage, does not touch the skull. In the eels and their allies, it has, by degradation, lost its connection and the post-temporal rests in the flesh behind the cranium. The post-temporal sometimes projects behind through the skin and may bear spines or serrations. In front of the post- temporal and a little to the outside of it is the small supra- temporal (52) also usually connecting the shoulder-girdle with the skull. Below the post-temporal, extending downward and backward, is the flatfish siipraelaviclc (postcroteinporal) (^4). To this is joined the long clavicle (proscapula) (55), which runs forward and downward in the bony fishes, meeting its fellow on the opposite side in a manner suggesting the wishbone of a The Skeleton of the Fish 51 60'/ Fig. 35. — Inner view of shovilder-girdle of the Buffalo - fish, Ictiobus buhalus Rafinesque, showing the mesocora- coid(.59). (After Starks.) fowl. Behind the base of the clavicle, the sword-shaped post- clavicle (56) extends downward through the muscles behind the base of the pectoral fin. In some fishes, as the stickleback and the trumpet-fish, a pair of flattish or elongate bones called interclavicles {injraclavicles) lie between and behind the lower part of the clavicle. These are not found in most fishes and are wanting in the striped bass. They are probably in all cases merely extensions of the hypocoracoid. Two flat bones side by side lie at the base of the pectoral fin, their anterior edges against the upper part of the clavicle. These are the liypcrcoracoid (57), above, and hypocoracoid {^?,),he\o\N. These have been variously called scapula, coracoid, humerus, radius, and ulna, but being found in the higher fishes only and not in the higher vertebrates, they should receive names not used for other structures. The hypercoracoid is usually pierced by a round foramen or fenestra, but in some fishes (cods, weavers) the fenestra is between the two bones. Attached to the hypercoracoid in the striped bass are four little bones shaped like an hour-glass. These are the actinosts (160) (carpals or pterygials), which support the rays of the pec- toral fin (61). In most bony fishes these are placed much as in the striped bass, but in certain specialized or aberrant forms their form and position are greatly altered. In the anglers (Pedicidati) the " carpals " are much elongated, forming a kind of arm, by which the fish can execute a motion not unlike walking. In the Alaska blackfish (Dtillia pectoralis) the two cora- coids are represented by a thin, cartilaginous plate, imper- fectly divided, and there are no actinosts. In almost all bony fishes, however, these bones are well differentiated and distinct. In most of the soft-rayed fishes an additional V-shaped bone or arch exists on the inner surface of the shoulder-girdle near the insertion of the hypercoracoid. This is known as the meso- 52 The Skeleton of the Fish Fig. 3ii.— Sargassum-fish, Pterophryne tumida (Osbeck). One of the -\nglers. Family Antennariidte. POT Fir.. 37. — Rhoulder-girdle of Sebastolobus alascanus Gilbert. (After St.arks.) POT. Post-temporal. HYC. Hypocoracoid. CL. Clavicle. HYPC. Hypercoracoid. PCL. Post-clavicle. The Skeleton of the Fish 53 coracoid (59). It is not found in the striped bass, but is found in the carp, catfish, salmon, and all their allies. The Posterior Limbs. — The posterior limb or ventral fin (63) is articulated to a single bone on either side, the pelvic girdle (62). In the shark the pelvic girdle is rather largely developed, but in the more specialized fishes it loses its importance. In EPO V. N. E. PF. FR. Fig. 38. — Cranium of Sebastolobus alascanus Gilbert. (After Starics.) Vomer. Nasal. Ethmoid. Prefrontal. Frontal. PAS. Parasphenoid. ALS. .Alisphenoid. P. Parietal. BA. Basisphenoid. PRO. Prootic. BO. Barioccipital. SO. Supraoccipital. EO. Exoccipital. EPO. Epiotic. SPO. Sphenotie. PTO. Pterotic. the less specialized of the bony fishes the pelvis is attached at a distance from the head among the muscles of the side, and free from the shoulder-girdle and other parts of the skeleton. The ventral fins are then said to be abdominal. When very close to the clavicle, but not connected with it, as in the mullet, the fin is still said to be abdominal or subabdominal. In the striped bass the pelvis is joined by ligament between the clavi- cles, near their tip. The ventral fins thus connected, as seen in most spiny-rayed fishes, are said to be thoracic. In certain forms the pelvis is thrown still farther forward and attached at the throat or even to the chin. When the ventral fins are thus inserted before the shoulder-girdle, they are said to be jugular. 54 The Skeleton of the Fish :\Iost of the fishes with spines in the fins have thoracic ven- trals. In the fishes with jugular ventrals these fins have begun a process of degeneration by which the spines or soft rays or l-)oth are lost or atrophied. Degeneration. — By degeneration or degradation in biology IS meant merely a reduction to a lower degree of complexity or s]:)ecialization in structure. If in the process of development Fig. 39. — Lower jaw and palate of Sebastolobus alascanits. (After Starks.) VA. Palatine. MSPT. Mcsopterj'goid. PT. Pterygoid. MPT. Jletaptcrygoid. D. Dentarv. AR. Articular. .\N. Angular. Q. Quadrate. SY. ^^^^^lplectic. HM. Hvoniandibtilar. POP. Preopercle. lOP. Interopercle. SOP. Subopercle. OP. Opercle. of the individual some particular organ loses its complexity it is said to be degenerate. If in the geological history of a type the same change takes place the same term is used. Degenera- tion in this sense is, like specialization, a phase of adaptation. It dues nr)t imply disease, feebleness, or mutilation, or any ten- dency toward extinction. It is also necessary to distinguish cleark.' phases of primitive simplicity from the apparent sim- filieity resulting from degeneration. The Skeleton in Primitive Fishes.- -To learn the names of bones AA-e can deal most satisfactorily with the higher fishes, those in The Skeleton of the Fish S5 which the bony framework has attained completion. But to understand the origin and relation of parts we must begin with the lowest types, tracing the different stages in the development of each part of the system. In the lancelcts (Leptocardn), the verte- bral column consists simply of a gelatinous notochord extending from one end of the fish to the other, and pointed at both ends, no skull being developed. The notochord never shows traces of segmentation, although cartilaginous rods above it are thought to forecast apophyses. In these forms there is no trace of jaws, limbs, or ribs. In the embryo of the bony fish a similar notochord precedes the segmentation and ossification of the vertebral column. In Fic 40 ^Ma\illarv and preina.villary ot Sehm,- tolobus alascaniis. M, maxillary; PM, pre- ina.xillary. most of the extinct types of fishes a notochord more or less Fig. 41. — Part of skeleton of Selene vomer (Linna?us). The Skeleton of the Fish modified persisted tlirougli life, the vertebr^E being strung upon it spool fashion in various stages of development. In the Cyclo- stomi (lampreys and hagfishes) the limbs and lower jaw are still wanting, but a distinct skull is developed. The notochord is still present, but its anterior pointed end is wedged into the base of a cranial capsule, partly membranous, partly car- tilaginous. There is no trace of segmentation in the notochord itself in these or any other fishes, but neutral arches are fore- FiG. 42. — Hyostylic skull of ChilosajUium indinim, a Scyliorhinoid Shark. (After Parker and Haswell.) shadowed in a series of cartilages on each side of the spinal chord. The top of the head is protected by broad plates. Fig. 43. Pj^ 4_t_ I' IG. 43.— Skull (if ncplranchius indicus (GiiieUn), a notidancid shark. (.\fter Parker and Haswell.) Pig. 44.— Basal bones of pectoral fni of Monkfish, S'jualina. (After Zittel ) There are ring-hke cartilages supporting the mouth and other cartilages in connection with the tongue and gill structures The Skeleton of the Fish SI The Skeleton of Sharks. — In the Elasmobranchs (sharks, rays, chimseras) the tissues surrounding the notochord are seg- mented and in most forms distinct vertebra; are developed. Each of these has a conical cavity before and behind, with a central canal through which the notochord is continued. The form and degree of ossification of these vertebrae differ materially in the different groups. The skull in all these fishes is cartilaginous, forming a continuous undivided box containing the brain and lodging the organs of sense. To the skull in the shark is attached a suspensorium of one or two pieces supporting the mandible and the hyoid structures. In the chimsera the mandible is articu- lated directly with the skull, the hyomandibular and quadrate Fig. 4.5. Fig. 46. Fig. 45. — Pectoral fin of Heterodontus philippi. (From nature.) Fig. 46. — Pectoral fin of Heptranchias indicus (Gmelin). (After Dean.) elements being fused with the cranium. The skull in such case is said to be autostylic, that is, with self-attached mandible. In the shark it is said to be hyostylic, the hyomandibular intervening. The upper jaw in the shark consists not of maxillary and premaxillary but of palatine elements, and the two halves of the lower jaw are representatives of Meckel's cartilage, which is the cartilaginous centre of the dentary bone in the bony fishes. These jaw-bones in the higher fishes are in the nature of membrane bones, and in the sharks and their relatives all such bones are undeveloped. The hyoid structures are in the shark relatively simple, as are also the gill-arches, which vary in number. The vertical fins are supported by interneural and interhsemal cartilages, to which the soft fin-rays are attached without articulation. The shoulder-girdle is made of a single cartilage, touching 58 The Skeleton of the Fish tlie back-bone at a distance behind the head. To this cartilage three smaller ones are attached, forming the base of the pectoral fin. These are called me so pterygium, proterygium, and iiieta- pteryginm, the first named being in the middle and more distinctly basal. These three segments are subject to much varia- tion. Sometimes one of them is wanting; some- times two are grown to- gether. Behind these the fin-rays are attached. In most of the skates the shoulder-girdle is more closely connected with the anterior vertebra, which are more or less fused together. The pelvis, remote from the head, is formed, in the shark, of a" single or paired cartilage with smaller elements at the base of the fin-rays. In the males a cartilaginous generative organ, known as the clasper, is attached to the pelvis and the ventral fins. In the Elasmobranchs the tail vertebra; are progressively smaller backward. If a caudal fin is present, the last vertebra; are directed upward (heterocercal) and the greater part of the fin is below the axis. In other forms (sting-raysj the tail degenerates into a whip-like organ {lepto- ccrcal), often without fins. In certain primitive sharks (Ichth^^o- tomi), as well as in the Dipnoi and Crossopterygii, the tail is diphycercal, the vertebra; growing progressively smaller back- ward and not bent upward toward the tip. Fig. 47. — Shoulder-girdle of a Flounder, Para lirhtlojs californicus (Ayres). The Skeleton of the Fish 59 In the chimasras {Holocephali) the notochord persists and is surrounded by a series of calcified rings. The palate with the Fig. 48. — Shoulder-girdle of a Toadfish, Batrachoides pacifici (Giinther). suspensorium is coalesced with the skull, and the teeth are grown together into bony plates. The Archipterygium. — The Dipnoans, Crossopterygians, and Fig. 49. — Shoulder-girdle of a Garfish, Tjjlosurus jndialnr (.Jordan and Gilbert). Ganoids represent various phases of transition from the ancient cartilaginous types to the modern bony fishes. 6o The Skeleton of the Fish In the Ichtliyotomous sharks, Dipnoans, and Crossoptery- gians the segments of the pectoral limb are arranged axially, or one beyond another. This type of fin has been called arcJii pterygium by Gegenbaur, on the theory that it represents the condition shown on the first appearance of the pectoral fin. This theory is now seriously questioned, but it will be convenient to retain the name for the pectoral fin with segmented axis fringed on one or both sides by soft rays. Fig. 50. — Shoulder-girdle of a Hake, Merluccius produrtu.'i (Ayres). The archipterygium of the Dipnoan genus Xeoceratodns is thus described by Dr. Gunther (" Guide to the Study of Fishes," p. 73) : " The pectoral hmb is covered with small scales along the middle from the root to the extremity, and is surrounded by a rayed fringe similar to the rays of the vertical fins. A muscle s[)lit into numerous fascicles extends all the length of the fin, which is flexible in every part and in every direction. The cartilaginous framework supporting it is joined to the scapular arch by a broad basal cartilage, generally single, sometimes The Skeleton of the Fish 6i showing traces of a triple division. Along the middle of the fin runs a jointed axis gradually becoming smaller and thinner towards the extremity. Each joint bears on each side a three-, two-, or one-jointed branch." In the genus Lepidosiren, also a Dipnoan, the pectoral limb has the same axial structure, but is without fin-rays, although in the breeding season the posterior limb or ventral fin in the male is covered with a brush of fine filaments. This structure, accordmg to Prof. J. G. Kerr,* is probably without definite function, but belongs to the "category of modifications so often associated with the breeding season (cf. the newts' crest) com- monly called ornamental, but which are perhaps more plausibly looked upon as expressions of the intense vital activity of the organisms correlated with its period of reproductive activity." Professor Kerr, however, thinks it not unlikely that this brush of filaments with its rich blood-supply may serve in the function of respiration, a suggestion first made by Professor Lankester. * Philos. Trans., Lond., igoo. CHAPTER V MORPHOLOGY OF THE FINS I RIGIN of the Fins of Fishes. — One of the most interest- ing problems in vertebrate morphology, and one of the most important from its wide-reaching relations, is that of the derivation of the fins of fishes. This resolves itself at once into two problems, the origin of the median fins, which appear in the lancelets, at the very bottom of the fish-like series, and the origin of the paired fins or limbs, which are much more complex, and which first appear with the primitive sharks. In this study the problem is to ascertain not what theoreti- cally should happen, but what, as a matter of fact, has happened in the early history of the fish-like groups. That these struc- tures, with the others in the fish body, have sprung from simple origins, growing more complex with the demands of varied conditions, and then at times again simple, through degenera- tion, there can be no doubt. It is also certain that eacii struc- ture must have had some element of usefulness in all its stages. In such studies we have, as Hsckel has expressed it, " three ancestral documents, paleontology, morphology, and onto- geny " — the actual history as shown by fossil remains, the side- light derived from comparison of structures, and the evidence of the hereditary influences shown in the development of the individual. As to the first of these ancestral documents, the evidence of paleontology is conclusive where it is complete. But in very few cases are we sure of any series of details. The records of geology are hke a book with half its leaves torn out, the other half confused, displaced, and blotted. Still each record actually existing represents genuine history, and in paleontology we must in time find our final court of appeal in all matters of biological origins. The evidence of comparative anatomy is most completely secured, but it is often indecisive as to relative age and primi- 62 Morphology of the Fins 63 tiveness of origin among structures. As to ontogeny, it is, of course, true that through heredity " the Hfe-history of the indi- vidual is an epitome of the Hfe-history of the race." " Onto- geny repeats phylogeny," and phylogeny, or line of descent of organisms and structures, is what we are seeking. But here the repetition is never perfect, never nearly so perfect in fact as Ha^ckel and his followers expected to find it. The demands of natural selection may lead to the lengthening, shortening, or distortion of phases of growth, just as they may modify adult conditions. The interpolation of non-ancestral stages is recognized in several groups. The conditions of the individual development may, therefore, furnish evidence in favor of cer- tain theories of origins, but they cannot alone furnish the abso- lute proof. In the process of development the median or vertical fins are doubtless older than the paired fins or limbs, whatever be the origin of the latter. They arise in a dermal keel which is developed in a web fitting and accentuating the undulatory motion of the body. In the embryo of the fish the continuous vertical fin from the head along the back and around the tail precedes any trace of the paired fins. In this elementary fin-fold slender supports, the rudiments of fin-rays, tend to appear at intervals. These are called by Ryder ray-hairs or actinotrichia. They are the prototype of fin-rays in the embryo fish, and doubtless similarly preceded the latter in geological time. In the development of fishes the caudal fin becomes more and more the seat of propulsion. The fin-rays are strengthened, their basal supports are more and more specialized, and the fin-fold ultimately divides into distinct fins, the longest rays developed where most needed. That the vertical fins, dorsal, anal, and caudal, have their origin in a median fold of the skin admits of no question. In the lowest forms which bear fins these structures are dermal folds, being supported by very feeble rays. Doubtless at first the vertical fins formed a continuous fold, extending around the tail, this fold ultimately broken, by atrophy of parts not needed, into distinct dorsal, anal, and caudal fins. In the lower fishes, as in the earlier sharks, there is an approach to this condition of primitive continuity, and in the embryos 64 Morphology of the Fins of almost all fishes the same condition occurs. Dr. John A. Ryder points out the fact that there are certain unexplained ex- ceptions to this rule. The sea-horse, pipefish, and other highly modified forms do not show this unbroken fold, and it is want- ing in the embryo of the top-minnow, Gambnsia affims. Never- theless the existence of a continuous vertical fold in the embryo is the rule, almost universal. The codfish with three dorsals, the Spanish mackerel with dorsal and anal finlets, the herring with one dorsal, the stickleback with a highly modified one, all show this character, and we may well regard it as a certain trait of the primitive fish. This fold springs from the ectoblast or external series of cells in the embryo. The fin-rays and bony supports of the fins spring from the mesoblast or middle series of cells, being thrust upward from the skeleton as supports for the fin-fold. Origin of the Paired Fins. — The question of the origin of the paired fins is much more difficult and is still far from settled, although many, perhaps the majority of recent writers favor the theory that these fins are parts of a once continuous lateral fold of skin, corresponding to the vertical fold which forms the dorsal, anal, and caudal. In this view the lateral fold, at first continuous, became soon atrophied in the middle, while at either end it is highly specialized, at first into an organ of direction, then into fan-shaped and later paddle-shaped organs of locomo- tion. According to another view, the paired fins originated from gill structures, originally both close behind the head, the ventral fin migrating backward with the progress of evolution of the species. Evidence of Paleontology. — If we had representations of all the early forms of fishes arranged in proper sequence, we could decide once for all, by evidence of paleontology, which form of fin appears first and what is the order of appearance. As to this, it is plain that we do not know the most primitive form of fin. Sharks of unknown character must have existed long before the earliest remains accessible to us. Hence the evidence of paleontology seems confiicting and uncertain. On the whole it lends most support to the fin-fold theory. In the later Devonian, a shark, CladoselacJie fyleri, is found in which the paired fins are lappet-shaped, so formed and placed as to suggest Morphology of the Fins 65 their origin from a continuous fold of skin. In this species the dorsal fins show much the same form. Other early sharks, con- stituting the order of Acanthodei, have fins somewhat similar, but each preceded by a stiff spine, which may be formed from coalescent rays. Long after these appears another type of sharks represented by Pleuracanthus and Cladodiis, in which the pectoral fin is a Fig. 51. — Cladoselache fyleri (^fewbe^ry), restored. Upper Devonian of Ohio (After Dean.) jointed organ fringed with rays arranged serially in one or two rows. This form of fin has no resemblance to a fold of skin, but accords better with Gegenbaur's theory that the pectoral limb was at first a modified gill-arch. In the Coal Measures are found also teeth of sharks {Orodontidce) which bear a Fig. 52,— Fold-like pectoral and ventral fins of Cladondache jyhri. (XHer Dean.) Strong resemblance to still existing forms of the family of HeterodontidcB, which originates in the Permian. The existing Heterodontida; have the usual specialized form of shark-fin, with three of the basal segments especially enlarged and placed side 66 Morphology of the Fins by side, the type seen in modern sharks. Whatever the primi- tive form of shark-fin, it may well be doubted whether any one of these three {Cladoselache, Plenracanthns, or Heterodontus) actually represents it. The beginning is therefore unknown, though there is some evidence that Cladoselache is actually more nearly primitive than any of the others. As we shall see, the evidence of comparative anatomy may be consistent with either of the two chief theories, while that of ontogeny or em- bryology is apparently inconclusive, and that of paleontology is apparently most easily reconciled with the theory of the fin- fold. Development of the Paired Fins in the Embryo. — According to Dr. John A. Ryder (" Embryography of Osseous Fishes," 1882) "the paired fins in Teleostei arise locally, as short longitudinal folds, with perhaps a few exceptions. The pectorals of Lepisostens originate in the same way. Of the paired fins, the pectoral Fig. .5.3. — Pectoral fin of shark, Chiloscyllium. {Mter Parker and Haswell.) or anterior pair seems to be the first to be developed, the ventral or pelvic pair often not making its appearance until after the absorption of the yolk-sac has been completed, in other cases before that event, as in Salino and in Gambusia. The pectoral fin undergoes less alteration of position during its evolution than the posterior pair." In the codfish (Gadns callarias) the pectoral fin-fold "ap- pears as a slight longitudinal elevation of the skin on either side of the body of the embryo a little way behind the auditory vesicles, and shortly after the tail of the embryo begins to bud out. At the very first it appears to be merely a dermal fold, and in some forms a layer of cells extends out underneath it from the sides of the body, but does not ascend into it. It Morphology of the Fins 67 begins to develop as a very low fold, hardly noticeable, and, as gro\\rth proceeds, its base does not expand antero-posteriorly, but tends rather to become narrowed, so that it has a peduncu- lated form. With the progress of this process the margin of the fin-fold also becomes thinner at its distal border, and at the basal part mesodermal cells make their appearance more notice- ably within the inner contour-line. The free border of the fin- fold grows out laterally and longitudinally, expanding the por- tion outside of the inner contour-line of the fin into a fan-shape. This distal thinner portion is at first without any evidence of rays ; further than that there is a manifest tendency to a radial disposition of the histological elements of the fin." The next point of interest is found in the change of position of the pectoral fin by a rotation on its base. This is associated with changes in the development of the fish itself. The ventral fin is also, in most fishes, a short horizontal fold and just above the preanal part of the median vertical fold which becomes anal, caudal, and dorsal. But in the top-minnow (Gambusia), of the order Haplomi, the ventral first appears as " a little papilla and not as a fold, where the body-walls join the hinder upper por- tion of the yolk-sac, a very little way in front of the vent." " These two modes of origin," observes Dr. Ryder, " are therefore in striking contrast and well calculated to impress us with the protean character of the means at the disposal of Nature to achieve one and the same end." Current Theories as to Origin of Paired Fins. — There are three chief theories as to the morphology and origin of the paired fins. The earliest is that of Dr. Karl Gegenbaur, supported by various workers among his students and colleagues. In his view the pectoral and ventral fins are derived from modifications of primitive gill-arches. According to this theory, the skeletal arrangements of the vertebrate limb are derived from modifica- tions of one primitive form, a structure made up of successive joints, with a series of fin-rays on one or both sides of it. To this structure Gegenbaur gives the name of archipterygium. It is found in the shark, Pleiiracantlnis, in Cladodus, and in all the Dipnoan and Crossopterygian fishes, its primitive form being still retained in the Australian genus of Dipnoans, Neocera- todus. This biserial archipterygium with its limb-girdle is 68 Morphology of the Fins derived from a series of gill-rays attached to a branchial arch. The baclavard position of the ventral fin is due to a succession of migrations in the individual and in the species. As to this theory, Mr. J. Graham Kerr observes: ' ' The Gegenbaur theory of the morphology of vertebrate limbs thus consists of two very distinct portions. The first, that the archipterygium is the ground-form from which all other forms of presently existing fin skeletons are derived, concerns us only indirectly, as we are dealing here only with the origin Fig. .54. — Skull and .shoulder-girdle of Neoceratodus forsteri (Giinther), showing the archipterygium. of the limbs, i.e., their origin from other structures that were not limbs. "It is the second part of the view that we have to do with, that deriving the archipterygium, the skeleton of the primitive paired fin, from a series of gill-rays and involving the idea that the limb itself is derived from the septum between two gill-clefts. " This view is based on the skeletal structures within the fin. It rests upon (i) the assumption that the archipterygium is the primitive type of fin, and (2) the fact that amongst the Selachians is found a tendency for one branchial ray to become larger than the others, and, when this has happened, for the base of attachment of neighboring rays to show a tendency to migrate from the branchial arch on to the base of the larger or, as we may call it, primary ray; a condition coming about which, were the process to continue rather farther than it is known to do in actual fact, would obviously result in a struc- Morphology of the Fins 69 ture practically identical with the archipterygium. Gegenbaur suggests that the archipterygium actually has arisen in this way in phylogeny." The fin-fold theory of Balfour, adopted by Dohrn, Weiders- heim, Thacher, Mivart, Ryder, Dean, Boulenger, and others, and Fig. 55. — Acanthoessus icardi (Egerton'). Carboniferous. Family Acanthoessidw. (After WoodAvard.) now generally accepted by most morphologists as plausible, is this: that "The paired limbs are persisting and exaggerated portions of a fin-fold once continuous, which stretched along each side of the body and to which they bear an exactly similar Fig. 56.— Shoulder-girdle of Acan- thoessus. (After Dean.) Fig. .57. — Pectoral fin of Pleiiracantlius. (After Dean.) phylogenetic relation as do the separate dorsal and anal fins to the once continuous median fin-fold." "This view, in its modern form, was based by Balfour on his observation that in the embryos of certain Elasmobranchs 7° Morphology of the Fins the rudiments of the pectoral and pelvic fins are at a very early period connected together by a longitudinal ridge of thick- ened epiblast — of which indeed they are but exaggerations. In Balfour's own words referring to these observations: 'If the account just given of the development of the limb is an accu- rate record of what really takes place, it is not possible to deny that some light is thrown by it upon the first origin of the ver- tebrate limbs. The facts can only bear one interpretation, viz., that the limbs are the remnants of continuous lateral fins.' "A similar view to that of Balfour was enunciated almost synchronously by Thacher and a little later by Mivart — in each case based on anatomical investigation of Selachians — mainly Fig. .58. — Sh(iuldcr-f;irdlc of Pohjpterus bichir. Specimen from the Wiite Xile. relating to the remarkable similarity of the skeletal arrange- ments in the paired and unpaired fins." A third theory is suggested by Mr. J. Graham Kerr {Cam- bridge Plitlos. Trans., 1899), who has recently given a summary of the theories on this subject. Mr. Kerr agrees with Gegenbaur as to the primitive nature of the archipterygium, but beheves that it is derived, not from the gill-septum, but from an external gill. Such a gill is well developed in the young of all the living sharks, Dipnoans and Crossopterygians, and in the latter tj^pes of fishes it has a form analogous to that of the archipter^^gium, although without bony or cartilaginous axis. We may now take up the evidence in regard to each of the different theories, using in part the language of Kerr, the para- Morphology of the Fins 71 graphs in quotation-marks being taken from his paper. We may first consider Balfour's theory of the lateral fold. Balfour's Theory of the Lateral Fold. — "The evidence in regard to this view may be classed under three heads, as onto- genetic, comparative anatomical, and paleontological. The ultimate fact on which it was founded was Balfour's discovery that in certain Elasmobranch embryos, but especially in Tor- pedo (Narcobatis), the fin rudiments were, at an early stage, connected by a ridge of epiblast. I am not able to make out what were the other forms in which Balfour found this ridge, but subsequent research, in particular by Mollier, a supporter of the lateral-fold view, is to the effect that it does not occur in such ordinary sharks as Prist hinis and Musteliis, while it is to be gathered from Balfour himself that it does not occur in Scyllium {ScyliorJiinns). " It appears to me that the knowledge we have now that the longitudinal ridge is confined to the rays and absent in the less highh? specialized sharks greatly diminishes its security as a basis on which to rest a theory. In the rays, in corre- lation with their peculiar mode of life, the paired fins have undergone (in secondary development) enormous ex- tension along the sides of the body, and their continu- ity in the embryo may well be a mere foreshadowing of this. "An apparently powerful support from the side of embry- ology came in Dohrn and Rabl's discoveries that in Pristiiirus all the interpterygial myotomes produce muscle -buds. This, however, was explained away by the Gegenbaur school as being merely evidence of the backward migration of the hind limb — successive myotomes being taken up and left behind again as the limb moved farther back. As cither explanation seems an adequate one, I do not think we can lay stress upon this body of facts as supporting either one view or the other. The Fig. .59. — .\.nn of a frofr. 72 ' Morphology of the Fins facts of the development of the skeleton cannot be said to support the fold view ; according to it we should expect to find a series of metameric supporting rays produced which later on become fused at their bases. Instead of this we find a longi- tudinal bar of cartilage developing quite continuously, the rays forming as projections from its outer side. "The most important evidence for the fold view from the side of comparative anatomy is afforded by (i) the fact that the limb derives its nerve supply from a large number of spinal nerves, and (2) the extraordinary resemblance met with be- tween the skeletal arrangements of paired and unpaired fins. The believers in the branchial-arch hypothesis have disposed of the first of these in the same way as they did the occurrence of interpterygial myotomes, by looking on the nerves received from regions of the spinal cord anterior to the attachment of the limb as forming a kind of trail marking the backward migration of tlie limb. "The similarity in the skeleton is indeed most striking, though its weight as evidence has been recently greatly dimin- ished by the knowledge that the apparently metameric segmen- tation of the skeletal and muscular tissues of the paired fins is quite secondary and does not at all agree with the meta- mery of the trunk. What resemblance there is maj^ well be of a homoplastic character when we take into account the simi- larity in function of the median and unpaired fins, especially in such forms as Raja, where the anatomical resemblances are especially striking. There is a surprising dearth of paleonto- logical evidence in favor of this view." The objection to the first view is its precarious foundation. Such lateral folds are found only in certain rays, in which they may be developed as a secondary modification in connection with the peculiar form of these fishes. Professor Kerr observes that this theory must be looked upon and judged: "Just as any other view at the present time regarding the nature of the vertebrate limb, rather as a speculation, brilliant and suggestive though it be, than as a logically constructed theory of the now known facts. It is, I think, on this account allowable to apply to it a test of a character which is admittedly very apt to mislead, that of 'common sense.' Morphology of the Fins 73 " If there is any soundness in zoological speculation at all, I think it must be admitted that the more primitive vertebrates were creatures possessing a notochordal axial skeleton near the dorsal side, with the main nervous axis above it, the main viscei^a below it, and the great mass of muscle lying in myotomes along its sides. Now such a creature is well adapted to move- ments of the character of lateral flexure, and not at all for movements in the sagittal plane — which would be not only difficult to achieve, but would tend to alternately compress and extend its spinal cord and its A'iscera. Such a creature would swim through the water as does a Cj'Clostome, or a LepiJosireii, or any other elongated vertebrate without special swimming organs. Swimming like this, specialization for more and more rapid movement would mean flattening of the tail region and ts extension into an at first not separately mobile median tail- fold. It is extremely difficult to my mind to suppose that a new purety sunniining arrangement should have arisen involving up-and-down movement, and which, at its first beginnings, while useless as a swimming organ itself, must greatly detract from the efficiency of that which already existed." Objections to Gegenbaur's Theory. — We now return to the Gegenbaur A'iew — that the limb is a modified gill-septum. "Resting on Gegenbaur's discovery already mentioned, that the gill-rays in certain cases assume an arrangement showing great similarity to that of the skeletal elements of the archip- terygium, it has, so far as I am aware, up to the present time received no direct suj3port whatever of a nature comparable with that found for the rival view in the fact that, in certain forms at all events, the limbs actually do arise in the individual in the way that the theory holds they did in phylogeny. No one has produced either a form in which a gill-septum becomes the limb during ontogeny, or the fossil remains of any form which shows an intermediate condition. "The portion of Gegenbaur's view which asserts that the biserial archipterygial fin is of an extremely primitive charac- ter is supported by a large body of anatomical facts, and is rendered further probable by the great frequency with which fins apparently of this character occur amongst the oldest known fishes. On the lateral-fold view we should have to 74 Morphology of the Fins resrard these as independently evolved, which would imply that fins of this type are of a very perfect character, and in that case we may be indeed surprised at their so complete disap- pearance in the more highly developed forms, which followed later on." As to Gegenbaur's theory it is urged that no form is known in vv'hich a gill-septum develops into a limb during the g^o^vth of the individual. The main thesis, accordmg to Professor Kerr, "that the archipterygium was derived from giU-rays, is supported only by evidence of an indirect character. Gegen- baur in his very first sugestion of his theory pointed out, as a great difficulty in the way of its acceptance, the position of the Fir,. (iO. — Pleumcanthuf; decheni (Goldfuss). (-\fter Dean.) limbs, especially of the peh'ic limbs, in a position far removed from that of the branchial arches. This difficulty has been entirely removed by the brilliant work of Gegenbaur's followers, who have shown from the facts of comparative anatomv and embryology that the limbs, and the hind limbs especially, ac- tually have undergone, and in ontogeny do undergo, an extensive backward migration. In some cases Braus has been able to find traces of this migration as far forward as a point iust behind the branchial arches. Now, when we consider the numbers, the enthusiasm, and the ability of Gegenbaur's dis- ciples, we cannot help being struck by the fact that the only evidence in favor of this derivation of the limbs has been that which tends to show that a migration of the limbs backwards has taken place from a region somewhere near the last bran- chial arch, and that they have failed utterly to discover any intermediate steps between gill-rays and archiptervgial fin. And if for a moment we apply the test of common sense we cannot but be impressed by the improbability of the evolution of a gill-septimi, which in all the lower forms of fishes is fixed Morphology of the Fins 7S firmly in the body-wall, and beneath its surface, into an organ of locomotion. "May I express the hope that what I have said is suflicient to show in what a state of uncertainty our views are regarding the morphological nature of the paired fins, and upon what an vi(\'; \^ •^ -^ a Fig. 61. — Embryos of Heterodnntus japonicus Maclay and Macleay, a Ces- traciont shark, showing the backward migration of the gill-archfs and the fonvard movement of the pectoral fin. a, b, c, representing different stages of growth. (After Dean.) exceedingly slender basis rest both of the two views which at present hold the field ? ' ' As to the backward migration of the ventral fins. Dr. Bash- ford Dean has recently brought forward evidence from the embryo of a very ancient type of shark {Heterodoutits japonicus) that this does not actually occur in that species. On the other 76 Morphology of the Fins hand, we have a forward migration of the pectoral fin, which gradually takes its place in advance of the hindmost gill-arches. The accompanjdng cut is from Dean's paper, " Biometric Evidence in the Problem of the Paired Limbs of the Verte- brates" (American Naturalist for November, 1902). Dean con- cludes that in Hcterodoutiis "there is no evidence that there has ever been a migration of the fins in the Gegenbaurian sense." "The gill region, at least in its outer part, shows no affinity during proportional growth with the neighboring region of the pectoral fin. In fact from an early stage onward, they are evi- dently growing in opposite directions." Kerr's Theory of Modified External Gills. — "It is because I feel that in the present state of our knowledge neither of the two \dews I have mentioned has a claim to any higher rank than that of extremely suggestive speculations that I venture to sav a few words for the third view, which is avowedly a mere speculation. "Before proceeding with it I should say that I assume the serial homology of fore and hind limbs to be beyond dispute. The great and deep-seated resemblances between them are such as to. my mind seem not to be adequately explicable except on this assumption. " In the Urodela (salamanders) the external gills are well- known structures — serially arranged projections from the body- wall near the upper ends of certain of the branchial arches. When one considers the ontogenetic development of these organs, from knob-like outgrowth from the outer face of the branchial arch, covered with ectoderm and possessing a meso- blastic core, and which frequently if not alwa^^s appear before the branchial clefts are open, one cannot but conclude that they are morphologically projections of the outer skin and that they have nothing whatever to do with the gill-pouches of the gut-wall. Amongst the Urodela one such gill projects from each of the first three branchial arches. In Lcpidosiren there is one on each of the branchial arches I-IV. In Polvptenis and Calaiiioichtliys {ErpetoicJitJiys) there is one on the hyoid arch. Finally, in many Urodelan larva; we have present at the same time as the external gills a pair of curious structures called balancers. At an early stage of my work on Lcpidosiren, Morphology of the Fins 77 while looking over other vertebrate embryos and larvag for pur- poses of comparison, my attention was arrested by these struc- tures, and further examinations, by section or otherwise, convinced me that there were serial homologues of the external giUs, situated on the mandibular arch. On then looking up the literature, I found that I was by no means first in this view. Rusconi had long ago noticed the resemblance, and in more recent times both Orr and Maurer had been led to the same conclusion as I had been. Three different observers having been inde- pendently led to exactly the same conclusions, we may, I think, fairly enough regard the view I have mentioned of the morphological nature of the balancers as probably a correct one. "Here, then, we have a series of homologous structures pro- jecting from each of the series of visceral arches. They crop up on the Crossopterygii, the Dipnoi, and the Urodela, i.e., in three of the most archaic of the groups of Gnathostomata. But we may put it in another way. The groups in which they do not occur are those whose young possess a very large yolk-sac (or which are admittedly derived from such forms). Now wherever we have a large yolk-sac we have developed on its surface a rich network of blood-vessels for purposes of nutrition. But such a network must necessarily act as an extraordinarily efficient organ of respiration, and did we not know the facts we might venture to prophesy that in forms possessing it any other small skin-organ of respiration would tend to disappear. "No doubt these external gills are absent also in a few of the admittedly primitive forms such as, e.g., (Neo-) Ceratodiis. But I would ask that in this connection one should bear in mind one of the marked characteristics of external gills — their great regenerative power. This involves their being extremely liable to injury and consequently a source of danger to their possessor. Their absence, therefore, in certain cases may well have been due to natural selection. On the other hand, the presence in so many lowly forms of these organs, the general close similarity in structure that runs through them in different forms, and the exact correspondence in their position and rela- tions to the body can, it seems to me, only be adequately ex- plained by looking on them as being homologous structures 78 Morphology of the Fins inherited from a common ancestor and consequently of great antiquity in the vertebrate stem." As to the third theory, Professor Kerr suggests tentatively that the external gill may be the structure modified to form the paired limbs. Of the homology of fore and hind limbs and consequently of their like origin there can be no doubt. The general gill-structures have, according to Kerr, "the primary function of respiration. They are also, however, pro- vided with an elaborate muscular apparatus comprising elevators, depressors, and adductors, and larva; possessing them may be seen every now and then to give them a sharp backward twitch They are thus potentially motor organs. In such a Urodele as Aniblystoma their homologues on the mandibular arch are used as supporting structures against a solid substratum exactly as are the limbs of the young Lcpidosireii. "I ha\'e, therefore, to suggest that the more ancient Gna- thostomata possessed a series of potentially motor, potentially Fig. ()'2. — Pvbjpterus congirux, a Crnsftnpteriigian fish from the Congo River, \oung, v.ith external gills. (After Boulenger.) supporting structures projecting from their visceral arches ; it was inherently extremely probable that these should be made use of when actual supporting, and motor appendages had to be developed in connection with clambering about a solid sub- stratum. If this had been so, we should look upon the limb as a modified external gill ; the limb-girdle, with Gegenbaur, as a modified branchial arch. "This theory of the vertebrate paired limb seems to me, I confess, to be a more plausible one on the face of it than either of the two which at present hold the field. If untrue, it is so dangerously plausible as to surely deserve more consideration than it appears to have had. One of the main differences be- tween it and the other two hypotheses is that, instead of deriving Morphology of the Fins 79 the swimming -fin from the walking and supporting limb, it goes the other way about. That this is the safer line to take seems to me to be shown by the consideration that a very small and rudimentary limb could only be of use if provided with a fixed point d'appui. Also on this view, the pentadactyle limb and the swimming-fin would probably be evolved independently from a simple form of limb. This would evade the great diffi- culties which have beset those who have endeavored to estab- lish the homologies of the elements of the pentadactyle limb with those of any type of fully formed fin." Uncertain Conclusions. — In conclusion we may say that the evi- dence of embryologv in this matter is inadequate _ though possibly favoring on the whole the fin-fold theorv ; that of morphology is inconclusive, and probably the final answer may be given by paleontology. If the records of the rocks were complete, they would be decisive. At present we have to decide which is the more primitive of two forms of pectoral fin actually known among fossils. That of Cladoselaclie is a low, horizontal fold of skin, with feeble rays, called by Cope ptychopterygium. That of Pleuracanthus is a jointed paddle-shaped appendage with a fringe of rays on either side. In the theory of Gegenbaur and Kerr Pleuracanthus must be, so far as the limbs are concerned, the form nearest the primitive limb-bearing vertebrate. In Balfour's theory Cladoselaclie is nearest the primitive type from which the other and with it the archipterygium of later forms may be derived. Boulenger and others question even this, believing that the archipterygium in Pleiiracantlius and other primitive sharks and that in Neoceratodus and its Dipnoan and Crossopterygian allies and ancestors have been derived independently, not the latter from the former. In this view there is no real homology between the archipterygium in the sharks possessing it and that in the Dipnoans and Crossopterygians. In the one theory the type of Pleuracanthus would be ancestral to the other sharks on the one hand, and to Crossopterygians and all higher vertebrates on the other. With the theory of the origin of the pectoral from a lateral fold, Pleuracanthus would be merely a curious specialized offshoot from the primitive sharks, without descend- ants and without special significance in phylogeny. 8o Morphology of the Fins As elements bearing on this decision we may note that the tapering unspecialized diphycercal tail of Pleuracanthits seems very primitive in comparison with the short heterocercal tail of CladosclacJic. This evidence, perhaps deceptive, is balanced b^'the presence on the head of PleiiracantJius oi a highly special- ized serrated spine, evidence of a far from primitive structure. Certainly neither the one genus nor the other actually repre- sents the ]irimitive shark. But as Cladoselache appears in geological time, long before Pleiiracanthiis, Cladodus,, or any other shark with a jointed, archipterygial fin, the burden of proof, according to Dean, rests with the followers of Gegenbaur. If the remains found in the Ordovician at Caflon City referred to Crossopterygians are correctly interpreted, we must regard the shark ancestr}' as lost in pre-Silurian darkness, for in sharks of some sort the Crossopterygians apparently must find their remote ancestry. Forms of the Tail in Fishes. — In the process of develop- ment the median or vertical fins are, as above stated, older than Fig. C.3. — Heterocercal tail of Sturgeon, Actpenser sturio (Linnaeus). (After Zittel.) the paired fins or hmbs, whatever be the origin of the latter. They arise in a dermal keel, its membranes fitting and accentuat- ing the undulatory motion of the body. In this elementary fin-fold slender supports (actinotrichia), the rudiments of fin-rays, appear at intervals. In those fins of most service in the movement of the fish, the fin-rays are strengthened, and their basal supports speciahzed. Dean calls attention to the fact that in fishes which swim, Morphology of the Fins 8 i when adult, by an undulatory motion, the paired fins tend to disappear, as in the eel and in all eel-like fishes, as blennies and eel-pouts. The form of the tail at the base of the caudal fin varies in the different groups. In most primitive types, as in most embryonic fishes, the vertebra; grow smaller to the last (diphy- cercal). In others, also primitive, the end of the tail is directed upward, and the most of the caudal fin is below it. Such a tail is seen in most sharks, in the sturgeon, garpike, bowfin, and in the Ganoid fishes. It is known as heterocercal, and finally in ordinary fishes the tail becomes homocercal or fan- shaped, although usually some trace of the heterocercal condi- tion is traceable, gradually growing less with the process of development. Since Professor Agassiz first recognized, in 1833, the dis- tinction between the heterocercal and homocercal tail, this matter has been the subject of elaborate investigation and a number of additional terms have been proposed, some of which are in common use. A detailed discussion of these is found in a paper by Dr. John A. Ryder "On the Origin of Heterocercy" in the Report of the U. S. Fish Commissioner for 1884. In this paper a dynamic , or mechanical theory of the causes of change of form is set forth, parts of this having a hypothetical and somewhat uncertain basis. Dr. Ryder proposes the name archicercal to denote the cylin-. droidal worm-like caudal end of the larva of fishes and amphibi- ans before they acquire median fin-folds. The term lophocercal{ is proposed by Ryder for the form of caudal fin which consists of a rayless fold of skin continuous with the skin of the tail, the inner surfaces of this fold being more or less nearly in contact. To the same type of tail Dr. Jefi:ries Wyman in 1864 gave the name protocercal. This name was used for the tail of the larval ray when it acquires median fin-folds. The term impUes, what cannot be far from true, that this form of tail is the first in the stages of evolution of the caudal fin. To the same type of tail Mr. Alexander Agassiz gave, in _ 1877, the name of leptocardaal, on the supposition that it repre- sented the adult condition of the lancelet. In this creature, 82 Morphology of the Fins however, rudimentary basal rays are present, a condition differ- ing from that of the early embryos. ■^ The diphycercal tail, as usually understood, is one in which the end of the vertebral column bears "not only hypural but also epural intermediary pieces which support rays.'l The term is used for the primitive type of tail in Avhich the vertebrae, lying horizontally, grow progressively smaller, as in Xeocera- t'odiis, Protoptents, and other pipnoans and Crossopterygians. The term was first appHed by McCoy to the tails of the Dipnoan genera Diplopterns and Gyropty chins, and for tails of this type it should be reserved. The heterocercal tail is one in which the hindmost A-ertebra3 are bent upwards. The term is generally applied to those Fig. 64. Fig. 6.3 Fig. 6-1. — Het-crocercul tail o[ Bowfin, Amia calva (Linna-us). (.Vt'ter Zittel.) Fig. 6.5. — Heterocercal tail of Garpike, Le]>ifiosteus osscus (Linnseus). fishes only in which this bending is considerable and is exter- nally evident, as in the sharks and Ganoids. The character disappears by degrees, changing sometimes to diphvcercal or leptocercal by a process of degeneration, or in ordinarv fishes becoming Jwmocercal. Dr. Ryder uses the teiTn heterocercal for all cases in which any upbencling of the axis takes place, even though it involves the modification of but a single ver- tebra. With this definition, the tail of salmon, herring, and even of most bony fishes would be considered heterocercal, and most or all of these pass througli a heterocercal stage in the course of development. The term is, however, usually restricted to those forms in which the curving of the axis is evident with- out dissection. Morphology of the Fins '3 The homocercal tail is the fan-shaped or symmetrical tail common among the Teleosts, or bony fishes. In its process of development the individual tail is first archicercal, then lophocercal, then diphycercal, then heterocercal, and lastly homo- FiG. 66. — Cortjphwnoides carapinus (Goode and Bean), showing leptocercal tail. Gulf Stream. cereal. A similar order is indicated by the sequence of fossil fishes in the rocks, although some »fpmis_of dip Uyx^ercal tail may be produced by degeneration ofT;he heterocerca/ tail, as suggested ty Dr. Dollo and Dr. Boulenger, who divide dij_hycereal tails into primitive and secondary. The peculiar tapering tail of the cod, the vertebras growing progressively smaller behind, is termed isocercal by Professor Cope. This form differs little from diphycercal, except in its supposed derivation from the homocercal type. A similar form is seen in eels. The term leptocercal has been suggested by Gaudry, 1883, for those tails in which the vertebral column ends in a point. We may, perhaps, use it for all such as are attenuate, ending in a long point or whip, as in the MacrfJtridcc, or grenadiers, the sting-rays, and in various degenerate members of almost every large group. The term gephyrocercal is devised by Ryder for fishes in which the end of the vertebral axis is aborted in the adult, leaving the caudal elements to be inserted on the end of this axis, thus bridging over the interval between the vertical fins, Fig. 67. — Heterocercal tail of Young Trout, Salmo fnrio (Linnteus). (After Parlier and Haswell.) Morphology of the Fins as the name [yecpvpo^, bridge; xepKos, tail) is intended to indicate. Such a tail has been recognized in four genera only, Fig. 6S. — Isocereal tail of Hake, Merluccius productus (Ayres). -,f:'^" Fig. 09. — Homoccrcal tail of a Flounder, Paralichthys californicuf!. Mola, Ranzania, Fierasjer, and Echwdon, the head-fishes and the pearl-fishes. Morphology of the Fins The part of the body of the fish which Hes behind the vent is known as the urosome. The urostyle is the name given to a modified bony structure, originaUy the end of the noto- chord, turned upward in most fishes. The term opistJiure is suggested by Ryder for the exserted tip of the vertebral column, which in some larvas {Lepisosteus) and in some adult fishes (Fistularia, CJt-iiuccra) pro- jects beyond the caudal fin. The urosome, or posterior part of the body, must be regarded as a prod- uct of evolution and ' specializa- tion, its function being largely that of locomotion. In the theo- retically primitive fish there is no urosome, the alimentary canal, as in the worm, beginning at one end of the body and terminating at the other. Homologies of the Pectoral Limb. — Dr. Gill has made an elaborate attempt to work out the homol- ogies of the bones of the pectoral limb.* From his thesis we take the following: "The following are assumed as premises that will be granted by all zootomists: " I. Homologies of parts are best determinable, cateris pari- bus, in the most nearly related forms. "2. Identification should proceed from a central or deter- minate point outwards. "The applications of these principles are embodied in the following conclusions : " I. The forms that are best comparable and that are most nearly related to each other are the Dipnoi, an order of fishes at present represented by Lepidosiren, Protopterus, and Cera- FiG. 70. — Gephyrocercal tail of Mola mola (LinnEPUs). (After Ryder.) * Catalogue of the Families of Fishes, 1872. 86 Morphology of the Fins iodiis, and the Batrachians as represented by the Ganocephala, Salamanders, and Salamander-hke animals. " 2. The articulation of the anterior member with the shoul- der-girdle forms the most obvious and determinable point for comparison in the representatives of the respective classes. The Girdle in Dipnoans.— " The proximal element of the anterior Fig. 71. Fig. 72. Fig. 71. — Shoulder-girdln of ,1mm calra (LinncEUs). Fig. 72. — Shoulder-girdle of a Sea Catfish, Sdenaspis dowi, limb in the Dipnoi has almost by common consent been regarded as homologous with the liiimerns of the higher vertebrates. " The humerus of Urodele Batrachians, as well as the extinct Ganocephala and Labyrinthodontia, is articulated chiefly with the coracoid. Therefore the element of the shoulder-girdle with which the humerus of the Dipnoi is articulated must also be regarded as the coracoid (subject to the proviso hereinafter stated), unless some specific evidence can be shown to the con- trary. No such CAddence has been produced. " The scapula in the Urodele and other Batrachians is entirely or almost wholly excluded from the glenoid foramen, and above Morphology of the Fins 87 the coracoid. Therefore the corresponding element in Dipnoi must be the scapula. " The otlier elements must be determined by their relation to the preceding, or to those parts from or in connection with which they originate. All those elements in immediate connec- tion with the pectoral fin and the scapula must be homologous as a whole with the coraco-scapular plate of the Batrachians; that is, it is infinitely more probable that they represent, as a whole or as dismemberments therefrom, the coraco-scapular ele- ment than that they independently originated. But the homo- geneity of that coraco-scapular element forbids the identification of the several elements of the fish's shoulder-girdle with regions of the Batrachian's coraco-scapular plate. " And it is equally impossible to identify the fish's elements with those of the higher reptiles or other vertebrates which have developed from the Batrachians. The elements in the shoulder- FlG. -Cla-\dcles of a Sea Catfish, Selenaspis rlowi (Gill). girdles of the distantly separated classes may be (to use the terms introduced by Dr. Lankester) homoplastic, but they are not homogenetic. Therefore they must be named accordingly. The element of the Dipnoan's shoulder-girdle, continuous down- ward from the scapula, and to which the coracoid is closely appHed, may be named ectocoracoid. "Neither the scapula in Batrachians nor the cartilaginous extension thereof, designated suprascapula, is dissevered from the coracoid. Therefore there is an a priori improbability 88 Morphology of the Fins against the homology Avith the scapula of any part having a distant and merely ligamentous connection with the humerus- bearing element. Consequently, as an element better represent- ing the scapula exists, the element named scapula (by Owen, Gunther, etc.) cannot be the homologue of the scapula of Ba- trachians. On the other hand, its more intimate relations with the skull and the mode of development indicate that it is rather an element originating and developed in more intimate connec- tion with the skull. It may therefore be considered, with Parker, as a posttcniporal. ' ' The shoulder-girdle in the Dipnoi is connected by an azvgous differentiated cartilage, swollen backwards. It is more prob- able that this is the homologue of the stcniuiii of Batrachians, and that in the latter that element has been still more differ- entiated and specialized than that it should haA^e originated dc novo from an independently developed nucleus. The Girdle in Fishes Other than Dipnoans. — ' ' Proceeding from the basis now obtained, a comparative examination of Fig. 74. — Shoulder-girdle of a Batfish, Ogcocephalus rndiatuR (Mitchill). Other types of fishes successively removed by their affinities from the Lepidosirenids may be instituted. "With the humerus of the Dipnoans, the clement of the Polypterids (single at the base, but immediately divaricating and with its limbs bordering an intervening cartilage which supports the pectoral and its basilar ossicles) must be homolo- gous. But it is evident that the external elements of the Morphology of the Fins 89 so-called carpus of the teleosteoid Ganoids are homologous with that element in Polypterids. Therefore those elements cannot be carpal, but must represent the humerus. " The element with which the homologue of the humerus, in Polypterids, is articulated must be homologous with the anal- ogous element in Dipnoans, and therefore with the coracoid. The coracoid of Poh^pterids is also evidently homologous with the corresponding element in the other Ganoids, and the latter consequently must be also coracoid. It is equally evident, after a detailed comparison, that the single coracoid element of the Ganoids represents the three elements developed in the gen- eralized Teleosts (Cyprinids, etc.) in connection with the basis of the pectoral fin, and, such being the case, the nomenclature should correspond. Therefore the upper element may be named Fig. 75. — Shoulder-girdle of a Threadfin, Pohjdadylus approximans (Lay and Bennett). hypercoracoid; the lower, hypocoracoid; and the transverse or median, mesocoracoid. " The two elements of the arch named by Parker, in Lepidosi- ren, ' supraclavicle ' (scapula) and 'clavicle' (ectocoracoid) seem to be comparable together, and as a whole, with the single element carrying the humerus and pectoral fin in the Crossop- terygians {Polypterus and Calamoichthys) and other fishes, and therefore not identical respectively with the 'supraclavicle' and ' clavicle ' (except in part) recognized by him in other fishes. As this compound bone, composed of the scapula and ectocora- coid fused together, has received no name which is not ambig- go Morphology of the Fins uous or deceptive in its homologous allusions, it may be desig- nated as proscapula. " The posttemporal of the Dipnoans is evidently represented by the analogous element in the Ganoids generally, as well as in the typical fishes. The succeeding elements (outside those already alluded to) appear from their relations to be de- veloped from or in connection Avith the posttemporal, and not from the true scapular apparatus ; they may therefore be named posttemporal, postcrotemporal, and tcleotcmporal. It will be thus seen that the determinations here adopted depend mainly (i) on the interpretation of the homologies of the elements with which the pectoral limbs are articulated, and (2) on the application of the term 'coracoid.' The name 'coracoid,' originally applied to the process so called in the human scapula and subsequently extended to the independent element homologous with it in birds and other vertebrates, has been more especially retained (e.g., by Parker in mammals, etc.) for the region including the glenoid cavity. On the assumption that this may be preferred by some zootomists, the preceding terms have been applied. But if the name should be restricted to the proximal element, nearest the glenoid cavity, in Avhich ossification commences, the name paraglenal given by Duges to the cartilaginous glenoid region can be adopted, and the cora- coid would then be represented (in part) rather by the element so named by Owen. That eminent anatomist, however, reached his conclusion (only in part the same as that here adopted) by an entirely different course of reasoning, and by a process, as it may be called, of elimination; that is, recognizing first the so-called 'radius' and 'ulna,' the 'humerus,' the 'scapula,' and the ' coracoid ' were successively identified from their rela- tions to the elements thus determined and because they were numerically similar to the homonymous parts among higher ver- tebrates." CHAPT]i:R VI THE ORGANS OF RESPIRATION OW Fishes Breathe. — The fish breathes the air which is dissolved in water. It cannot use the oxygen which is a component part of water, nor can it, as a rule, make use of atmospheric air. The amount of oxygen rec^uired for the low vegetative processes of the fish is comparatively small. .Vccorcling to Dr. Giinther, a man consumes 50,000 times as much oxygen as a tench. But some fishes demand more oxygen than others. Some, like the catfish or the loach, will survive long out of water, while others die almost in- stantly if removed from their element or if the water is allowed to become foul. In most cases the temperature of the blood of the fish is but little above that of the water in which they live, but in the mackerel and other muscular fishes the temperature of the body may be somewhat higher. Some fishes which live in mud, especially in places which become dry in summer, have special contrivances b}^ which they can make use of atmospheric air. In a few primitive fishes (Dipnoans, Crossopterygians, Ganoids) the air-bladder re- tains its original function of a lung. In other cases .some peculiar structure exists in connection with the gills. Such a contrivance for holding water above the gills is seen in the climbing perch of India (Anabas scandeus) and other members of the group called Labyrinthici. In respiration, in fishes generally, the water is swallowed through the mouth and allowed to pass riut through the giU- openings, thus bathing the gills. In a few of the lower types a breathing-pore takes the place of the gih-openings. The gills, or branchiae, are primarily folds of tlic skin lining the branchial cavity. In most fishes they form tleshy fringes or laminae throughout wliich the capillaries are distrib- uted. In the embryos of sharks, skates, chimasras, lung-fishes, 31 The Organs of Respiration 92 and Crossopterygians external gills are developed, but m the more specialized forms these do not appear outside the^ gdl- cavity. In some of the sharks, and especially the rays, a spiracle or open foramen remains behind the eye. Through this spiracle, leading from the outside into the cavity of the mouth, Avater is drawn downwards to pass outward over the giUs. The presence of this breathing-hole permits these animals to lie on the bottom without danger of inhaling sand. The Gill-structures.— The three main types of gihs among fishes are the foUowing: (a) the purse-shaped gills found in the hagfishes and lampreys, known as a class as Marsipobranchs, or purse-gihs. These have a number (5 to 12) of sac-like depres- sions on the side of the body, lined wath giU-fringes and capil- laries, the whole supported by an elaborate branchial basket Fig. 76.— GiU-l>asket of Lamprey. {M%ev Deau.) formed of cartilage. (b) The plate-gills, found among the sharks, rays, and cliim;eras, thence called Elasmobranchs, or plate-gills. In these the gill-structures are flat lamin;E, attached by one side to the gill-arches. {c) The fringe-gills found in ordinary fishes, in which the gill-filaments containing the capil- laries are attached in two rows to the outer edge of each gill- arch. The so-called tuft-gills (Lophobranchs) of the sea-horse and pipefish are like these in structure, but the filaments are long, Avhile the arches are very short. In most of the higher fishes a small accessory gill (pseudobranchia) is developed in the 'skin of the inner side of the opercle. The Air-bladder. — The aird^ladder, or swim-blaclder, must be classed among the organs of respiration, although in the higher fishes its functions in this regard are rudimentary, and in sume cases, it has taken collateral functions (as a hydrostatic The Organs of Respiration 93 organ of equilibrium, or perhaps as an organ of hearing) which have no relation to its original purpose. The air-bladder is an internal sac possessed by many fishes, but not by all. It lies in the dorsal part of the abdominal cavity above the intestines and below the kidneys. In some cases it is closely adherent to the surrounding tissues. In others it is almost entirely free, lying almost loose in the cavity of the body. In some cases it is enclosed in a bony capsule. In the alHes of the carp and catfish, which form the majority of fresh-water fishes, its anterior end is connected through a chain of modified vertebra; to the ear. Sometimes its posterior Fig. 77. — Weberian apparatus and air-bladder of Carp. AVeber.) (From Giinther, after end fits into an enlarged and hollow interhaemal bone. Some- times, again, a mass of muscle lies in front of it or is otherwise attached to it. Sometimes it is divided into two or three parts by crosswise constrictions. Sometimes it is constricted longitudi- nally, and at other times it has attached to it a complication of supplemental tubes of the same character as the air-bladder itself. In still other cases it is divided by many internal parti- tions into a cellular body, similar to the lung of the higher vertebrates, though the cells are coarser and less intricate. This condition is evidently more primitive than that of the empty sac. The homology of the air-bladder with the lung is evident. This is often expressed in the phrase that the lung is a developed air-bladder. This is by no means true. To say that the air- bladder is a modified and degenerate lung is much nearer the 94 The Organs of Respiration truth, although we should express the fact more exactly to say that both air-bladder" and lung are developed from a primi- tive cellular breathing-sac, originally a diverticulum from the ventral walls of the oesophagus. The air-bladder varies in size as much as in form. In some fishes it extends from the head to the tail, while in others it is so minute as to be scarcely traceable. It often varies greatly in closely related species. The common mackerel (Scomber scoinbnis) has no air-bladder, while in the closely related colias or chub mackerel (Scoiiiber japorJcns) the organ is very evident. In other families, as the rock-fishes {Scorpccnidcc), genera with and those without the air-bladder are scarcely distinguishable externally. In general, fishes which lie on the bottom, those which inhabit great depths, and those which swim freely in the open sea, as sharks and mackerel, lack the air-bladder. In the " sharks, rays, and chima^ras there is no trace of an air-bladder. In the mackerel and other bony fishes without it, it is lost in the process of development. The air-bladder is composed of two layers of membrane, the outer one shining, silvery in color, with muscular fibres, the inner well supplied by blood-vessels. The gas within the air-bladder must be in most cases secreted from the blood-\'essels. In river fishes it is said to be nearly pure nitrogen. In marine fishes it is mostly oxygen, with from 6 to lo per cent of carbonic- acid gas, while in the deep-sea fishes oxygen is greatly in excess. In LopJwlatilits, a deep-sea fish, Professor R. AV. Tower finds 66 to 69 per cent of oxygen. In Trigla lyra Biot records 87 per cent. In Dentex deiiicx, a shore fish of Europe, 40 per cent of oxygen was found in the air-bladder. Fifty per cent is recorded from the European porgy, Pagnis pagnts. In a fish dying from suffocation the amount of carbonic -acid gas (COJ is greatly increased, amounting, according to recent researches of Pro- fessor Tower on the weak-fish, Cynoscioii regal is, to 24 to 29 per cent. This shows conclusively that the air-bladder is to some degree a reservoir of oxygen secreted from the blood, to which channel it may return through a kind of respiration. The other functions of the air-bladder have been subject to much question and are still far from understood. The follow- ing summary of the various views in this regard we copy The Organs of Respiration 95 from Professor Tower's paper on "The Gas in the Swim-bladder of Fishes " : "The function of the swim-bladder of fishes has attracted the attention of scientists for many centuries. The role that this structure plays in the life of the animal has been inter- preted in almost as many ways as there have been investigators, and even now there is apparently much doubt as to the true functions of the swim-bladder. Consequently any additional data concerning this organ are of immediate scientific value. "Aristotle, writing about the noises made by fishes, states that ' some produce it by rubbing the gill-arches . . . ; others by means of the air-bladder. Each of these fishes contains air, by rubbing and moving of which the noise is produced.' The bladder is thus considered a sound-producing organ, and it is probable that he arrived at this result by his own investiga- tions. " Borelli (De Motu Animalium, 1680) attributed to the air- bladder a hydrostatic function which enabled the fish to rise and fall in the water by simply distending or compressing the air-bladder. This hypothesis, which gives to the fish a volitional control over the air-bladder — it being able to compress or distend the bladder at pleasure — has prevailed, to a greater or less degree, from the time of Borelli to the present. To my knowl- edge, however, there are no investigations which warrant such a theory, while, on the other hand, there are many facts, as shown by Moreau's experiment, which distinctly contradict this belief. Delaroche (Annales du Mus. d'Hist. Nat., tome XIV, 1807- 1809) decidedly opposed the ideas of Borelli, and 3'et advanced an hypothesis similar to it in many respects. Like Borelli, he said that the fish could compress or dilate the bladder by means of certain muscles, but this was to enable the fish to keep the same specific gravity as the surrounding medium, and thus be able to remain at any desired depth (and not to rise or sink). This was also disproved later by Moreau. Delaroche proved that there existed a constant exchange between the air in the air-bladder and the air in the blood, although he did not con- sider the swim-bladder an organ of respiration. "Biot (1807), Provencal and Humboldt (1809), and others made chemical analyses of the gas in the swim-bladder, and ^6 The Organs of Respiration found I to 5 per cent of CO^, i to 87 per cent of 0^, and the remriindcr nitrogen. The most remarkable fact discovered about this mixture Avas that it frequently consisted almost entirely of oxygen, the per cent of oxygen increasing with the depth of the water inhabited by the fish. The reasons for this phenomenon have never been satisfactorily explained. "In 1820 Weber described a series of paired ossicles Avhich he erroneously called stapes, malleus, and incus, and which con- nected the airdDladder in certain fishes with a part of the ear — the atrium sinus imparls. Weber considered the swim-bladder to lie an organ by which sounds strikmg the body from the outside are intensified, and these sounds are then transmitted to the ear by means of the ossicles. The entire apparatus would thus function as an organ, of hearing. Weber's views remained practically uncontested for half a centur3^ but re- cently much has been written both for and against this theory. Whatever the \'irtues of the case may be, there is certainly an inviting field for further physiological investigations regarding this subject, and more especially on the phenomena of hearing in fislics. "Twenty years later Johannes iluUer described, in certain Siluroid fishes, a mechanism, the so-called ' elastic-spring ' ap- paratus, attached to the anterior portion of the air-bladder, which ser\-ed to aid the fish in rising and sinking in the water according as the muscles of this apparatus were relaxed or con- tracted to a greater or lesser degree. This interpretation of the function of the ' elastic-spring ' mechanism was shown by Sorensen to be untenable. Miiller also stated that in some fish, at least, there was an exchange of gas between blood and air- bladder- -the latter having a respiratory function — and regarded the gias in the air-bladder as the result of active secretion. In Malaptentriis (Torpedo eleciricits) he stated that it is a sound- producing organ. "Hasse, m 1873, published the results of his investigations on the functions of the ossicles of AYeber, statmg that their action Avas that of a manometer, accjuainting the animal with the degree nf pressure that is exerted by the gases in the air- bladder agamst its walls. This pressure necessarily varies with the dhTerent depths of water which the fish occupies. Hasse The Organs of Respiration 97 did not agree with Weber that the ear is affected by the move- ments of these ossicles. "One year later Dufosse described in some fishes an air-blad- der provided with extrinsic muscles by whose vibration sound was produced, the sound being intensified by the air-bladder, which acted as a resonator. He also believed that certain species produced a noise by forcing the gas from the air-bladder through a pneumatic duct. "At about the same time Moreau published his classical work on the functions of the air-bladder. He proved by ingenious experiments that many of the prevailing ideas about the action of the air-bladder were erroneous, and that this organ serves to equilibrate the body of the fish Avith the water at any level. This is not accomplished quickly, but only after sufficient time for the air in the bladder to become adjusted to the increase or decrease in external pressure that has taken place. The fish, therefore, makes no use of any muscles in regulating the volume of its air-bladder. The animal can accommodate itself only gradually to considerable changes in depth of water, but can live equally comfortably at dift'erent depths, provided that the change has been gradual enough. Moreau's experiments also convinced him that the gas is actually secreted into the air- bladder, and that there is a constant exchange of gas between it and the blood. In these investigations he has also noticed that section of the sympathetic-nerve fibres supplying the walls of the air-bladder hastens the secreting of the gas into the empty bladder. Since then Bohr has shown that section of the vagus nerA^e causes the secretion to cease. Moreau noticed in one fish (Trigla) having an air-bladder supplied with muscles that the latter serv^ed to make the air-bladder produce sound. "Again, in 1885, the Weberian mechanism was brought to our attention with a new function attributed to it by Sagemehl who stated that this mechanism exists not for any auditory purposes ,nor to tell the fish at what level f>i the water it is swimming, but to indicate to the fish the \'ariations in the atmos- pheric pressure. Sorensen tersely contrasts the views of Hasse and Sagemehl by saymg that ' Hasse considers the air-bladder with the Weberian mechanism as a manometer; Sagemehl re- gards it as a barometer.' The theory of Sagemehl has, naturally o8 The Organs of Respiration enough, met with Uttle favor. Sorensen (1895) held that there is but little evidence for attributing to the air-bladder the func- tion of a lung. It is to be remembered, however, that, accord- ing to Sorenscn's criterion no matter what exchange of gases takes place between blood and air-bladder, it cannot be con- sidered an organ of respiration, 'unless its air is renewed by mechanical respiration.' "Sorensen also refutes, from anatomical and experimental grounds, the many objections to Weber's theory of the function of the ossicles. He would thus attribute to the air-bladder the function of hearing; indeed in certain species the only reason for the survival of the air-bladder is that ' the organ is still of acoustic importance; that it acts as a resonator.' This idea, Sorensen states, is borne out by the anatomical structure found in Misgiiniiis and Clilarias, which resembles the celebrated 'CoUadon resonator.' This author attributes to the air-bladder with its ' elastic spring' and various muscular mechanisms the production of sound as its chief function." Origin of the Air-bladder. — In the more primitive forms, and proliably in the embryos of all species, the air-bladder is joined to the oesophagus by an air-duct. This duct is lost entirely in the adult of all or nearly all of the thoracic and jugular fishes/ and in some of the abdominal forms. The lancelets, lampreys, sharks, rays, and chimosras have no air-bladder, but in the most primitive forms of true fishes (Dipnoans and Crossoptery- gians), having the air-bladder cellular or lung-like, the duct is^ well developed, freely admitting the external air which the fisly may rise to the surface to swallow. In most fishes the duct^ opens into the oesophagus from the dorsal side, but in the more primitive forms it enters from the ventral side, like the wind- pipe of the higher vertebrates. In some of the Dipnoans the air-bladder divides into two parts, in further resemblance to the true lungs. The Origin of the Lungs. — The following account of the func- tion of the air-bladder and of its development and decline is con- densed from an article by \h. Charles Morris:* "If now we seek to discover the original purpose of this * The Origin of Ltmgs: A Chapter in Evolution. American Naturalist December, iSq2. The Organs of Respiration 99 organ, there is abundant reason to believe that it had nothing to do with swimming. Certainly the great family of the sharks, which have no bladder, are at no disadvantage in changing their depth or position in the water. Yet if the bladder is necessar)^ to any fish as an aid in swimming, why not to all? And if this were its primary purpose, how shall we explain its remarkable variability? No animal organ with a function of essential im- portance presents such extraordinary modifications in related species and genera. In the heart, brain, and other organs there is one shape, position, and condition of greatest efficiency, and throughout the lower forms we find a steady advance towards this condition. Great variation, on the other hand, usually indicates that the organ is of Httle functional importance, or that it has lost its original function. Such we conceive to be the case with the air-bladder. The fact of its absence from some and its presence in other fishes of closely related species goes far to proA-e that it is a degenerating organ; and the same is shewn by the fact that it is useless in some species for the pur- pose to which it is applied in others. That it had, at some time in the past, a function of essential importance there can be no question. That it exists at all is proof of this. But its modern variations strongly indicate that it has lost this function and is on the road towards extinction. Larval conditions show that it had originally a pneumatic duct as one of its essential parts, but this has in most cases disappeared. The bladder itself has in many cases partly or wholly disappeared. Where pre- served, it seems to be through its utility for some secondary purpose, such as an aid in swimming or in hearing. That its evolution began very long ago there can be no question ; and the indications are that it began long ago to degenerate, through the loss of its primitive function. " What was this primitive function ? In attempting to answer this question we must first consider the air-bladder in relation to the fish tribe as a Avhole. No shark or ray possesses the air- bladder. In some few sharks, indeed, there is a diverticulum of the pharynx which may be a rudimentary approach to the air-bladder; but this is very questionable. The conditions of its occurrence in the main body of modern fishes, the Teleostean, we have already considered. But in the most ancient Hving orders loo The Organs of Respiration of fishes it exists in an interesting condition. In every modern Dipnoan, Crossopterygian, and Ganoid tlie air-bladder has an efi:'ective pneumatic duct. This in the Ganoids opens into the dorsal side of the oesophagus, but in the Dipnoans and Cros- sopterygians, like the windpipe of lung-breathers, it opens into the ventral side. In the Dipnoans, also survivors from the re- mote past, the duct not only opens ventrally into the oesophagus, but the air-bladder does duty as a lung. Externally it differs in no particular from an air-bladder; but internahy.it presents a cellular structure which nearly approaches that of the lung of the batrachians. There are three existing representatives of the Dipnoans. One of these, the Australian lung-fish {Neocera- todus) has a single bladder, which, however, is provided with breathing-pouches having a symmetrical lateral arrangement. It has no pulmonary artery, but receiA^es branches from the artcria ccdiaca. In the other two forms, Lcpidosireu and Protop- tcnis, the kindred ' mudfishes ' of the Amazon basin and tropi- cal Africa, the bladder or lung is divided into two lateral cham- bers, as in the land animals, and is provided with a separate pulmonary artery. " The opinion seems to have been tacitly entertained by physiologists that this employment of the air-bladder by the Dipnoans as a lung is a secondary adaptation, a side issue from its original purpose. It is more likely that this is the original purpose, and that its degeneration is due to the disap- pearance of the necessity of such a function. As regards the gravitative employment of the bladder, the Teleostean fishes, to which this function is confined, are of comparatively modern origin ; Avhile the Dipnoans are surviving representati^'es of a very ancient order of fishes, which flourished in the Devonian age of geology, and in all probability^ breathed air then as now; and the Crossopterygians and Ganoids, which approach them in this particular, are similarly ancient in origin, and were the ancestors of the Teleosteans. The natural presumption, there- fore, is that the duty which it subserved in the most ancient fishes was its primitive function. " The facts of embryology lend strong support to this hypo- thesis. For the air-bladder is found to arise in a manner very similar to the development of the lung. They each begin as an The Organs of Respiration loi outgrowth from the fore part of the ahmentary tract, the only difference being that the air-bladder usually rises dorsally and the lung ventrally. The fact already cited, that the pneumatic duct is always present in the larval form in fishes that possess a bladder, is equally significant. All the facts go to show that the introduction of external air into the body was a former function of the air-bladder, and that the atrophy of the duct in manv cases, and the disappearance of the bladder in others, are results of the loss of this function. " Such an elaborate arrangement for the introduction of air into the body could have, if we may judge from analogy, but one purpose, that of breathing, to which purpose the' muscular and other apparatus for compressing and dilating the bladder, now seemingly adapted to gravitative uses, may have been origi- nally applied. The same ma}^ be said of the great development of blood-capillaries in the inner tunic of the bladder. These may now be used only for the secretion of gas into its interior, but were perhaps originally employed in the respiratory secre- tion of oxA'gen. In fact all the circumstances mentioned — the similarity in larval development between the bladder and lung, the larval existence of the pneumatic duct, the arrangements for compressing and dilating the bladder, and the capillary vessels on its inner tunic — point to the breathing of air as its original purpose. " It is probable that the Ganoid, as well as the Dipnoan, air- bladder is to some extent still used in breathing. The Dipnoans have both lungs and gills, and probably breathe with the latter in ordinary cases, but use their lungs when the inland waters in which they live become thick and muddy, or are charged with gases from decomposing organic matter. The Ganoid fishes to some extent breathe the air. In Polyptenis the air-bladder re- sembles the Dipnoan lung in having lateral di\'isions and a ventral connection with the oesophagus, while in Lcpisostcns (the Amer- ican garpike) it is cellular and lung-Hke. This fish keeps near the surface, and may be seen to emit air-bubbles, probably taking in a fresh supply of air. The American bowfin, or mud- fish {Amia), has a bladder of the same lung-like character, and has been seen to come to the surface, open its jaws widely, and apparently swallow a large quantity of air. He I02 The Organs of Respiration considers tliat both Lcpisostens and Aiiiia inhale and exhale air at somewhat regular intervals, resembling in this the salaman- ders and tadpoles, 'which, as the gills shrink and the lungs in- crease, come more frequently to the surface for air.' "As the facts stand there is no evident line of demarcation between the gas-containing bladders of many of the Teleosteans, the air-containing bladders of the others and the Ganoids, and the lung of the Dipnoans, and the indications are in favor of their having originally had the same function, and of this being the breathing of air. " If now we ask what were the conditions of life under which this organ was developed, and what the later conditions which rendered it of no utilitv as a lung, some definite answer mav be giA-en. The question takes us tiack to the Devonian and Silurian geological periods, during which the original dcA-elopment of the bladder probably took place. In this era the seas were thronged with fishes of several classes, the Elasniobranchs among others, followed by the Dipnoi and Crossopter\"gians. The sharks were without, the Dipnoans and Crossopterygians doubtless with, an air-bladder — a difference in organization which was most likely due to some marked difference in their life-habits. The Elasmo- branchs were the monarchs of the seas, against whose incursions the others put on a thick protective armor, and probablv sought the shallow shore waters, while their foes held chief possession of the deeper waters Avithout. " "We seem, then, to perceive the lung-bearing fishes, driven bv their foes into bays and estuaries, and the waters of shallow coasts, ascending streams and dwelling in inland waters. Here two influences probably acted on them. The waters they dwelt in Avere often thick with sediment, and were doubtless in many instances poorly aerated, rendering gill-breathing difficult. And the land presented conditions likely to serve as a strong induce- ment to fishes to venture on shore. Its plant -hfe was abundant, while its only animal inhabitants seem to liaA'c been insects, worms, and snails. There can be little doubt that the active fish forms of that period, having no enemies to fear on the land, and much to gain, made active efforts to obtain a share of this vegetable and animal food. Even to-day, when they haA'e nu- merous foes to fear, many fishes seek food on the shore, and The Organs of Respiration 103 some even climb trees for this purpose. Under the conditions of the period mentioned there was a powerful inducement for them to assume this habit. " Such conditions must have strongly tended to induce fishes to breathe the air, and have acted to develop an organ for this purpose. In addition to the influences of foul or muddy water and of visits to land may be named that of the drying-out of pools, by which fishes are sometimes left in the moist mud till the recurrence of rains, or are even buried in the dried mud during the rainless season. This is the case with the modern Dipnoi, which use their lungs under such circumstances. In certain other fresh-water fishes, of the family Ophiocephalidae, air is breathed while the mud continues soft enough for the fish to come to the surface, but during the dry period the animal remains in a torpid state. These fishes have no lungs, but breathe the air into a simple cavity in the pharynx, whose open- ing is partly closed by a fold of the mucous membrane. Other Labyrinthici, of similar habits, possess a more developed breathing organ. This is a cavity formed by the walls of the pharynx, in which are thin laminae, or plates, which undoubtedly perform an oxygenating function. The most interesting member of this family is Aiiabas scandens, the climbing perch. In tliis fish, which not only leaves the water, but is said to climb trees, the air-breathing organ is greatly developed. The labyrinthici, moreover, have usually large air-bladders. As regards the occa- sional breathing of air by fishes, even in species which do not leave the water, it is quite common, particularly among fresh- water species. Cuvier remarks that air is perhaps necessary to every kind of fish ; and that, particularly when the atmosphere is warm, most of our lacustrine species sport on the surface for no other purpose. " It is not difficult to draw a hypothetical plan of the develop- ment of the air-bladder as a breathing organ. In the two fami- lies of fishes just mentioned, whose air-bladders indicate that they once possessed the air-breathing function and have lost it, we perceive the process of formation of an air-breathing organ beginning over again under stress of similar circumstances. The larval development of the air-bladder points significantly in the same direction. In fact we have strong reason to believe that I04 The Organs of Respiration air-breathing in fishes was originally performed, as it probably often is now, by the unchanged walls of the ce-sophagus. Then these walls expanded inwardly, forming a simple cavity, partly closed by a fold of membrane, like that of the Ophiocephahdae. A step further reduced this membranous fold to a narrow open- ing, leading to an inner pouch. As the air-breathing function developed, the opening became a tube, and the pouch a simple lung, with compressing muscles and capillary vessels. By a con- tinuation of the process the smooth-walled pouch became saccu- lated, its surface being increased by folding into breathing cells. Finally, a longitudinal constriction divided it into two lateral pouches, such as we find in the lung of the Dipnoans. This brings us to the verge of the lung of the amphibians, which is but a step in advance, and from that the line of progress is un- broken to the more intricate lung of the higher land animals. " The dorsal position of the bladder and its duct would be a difrlculty in this inquiry, but for the fact that the duct is occa- sionally ventral. This dorsal position may have arisen from the upward pressure of air in the swimming fish, which would tend to lift the original pouch. But in the case of fishes which made frequent visits to the shore new influences must have come into play. The effect of gravity tended to draw the organ and its duct downward, as we find in the Crossopterygians and in all the Dipnoans, and its increased use in breathing required a more extended surface. Through this requirement came the pouched and cellular lung of the Dipnoans. Of every stage of the process here outlined examples exist, and there is great reason to be- lie\'e that the development of the lung followed the path above pointed out. "When the carboniferous era opened there may have been many lung- and gill-breathing fishes which spent much of their time on land, and some of which, by a gradual improvement of their organs of locomotion, changed into batrachians. But with the appearance of the latter, and of their successors, the reptiles, the relations of the fish to the land radically changed. The fin, or the simple locomotor organ, of the Dipnoans could not com- pete with the leg and foot as organs of land locomotion, and the fish tribe ceased to be lords of the land, where, instead of feeble prey, they now found powerful foes, and were dnven back to The Organs of Respiration 105 their native habitat, the water. Nor did the change end here. In time the waters were invaded by the reptiles, numerous swim- ming forms appearing, which it is hkely were abundant in the shallower shore-line of the ocean, while they sent many repre- sentatives far out to sea. These were actively carnivorous, making the fish their prey, the great mass of whom were doubt- less driven into the deeper waters, beyond the reach of their air- breathing foes. " In this change of conditions we seem to perceive an adequate cause for the loss of air-breathing habits in those fishes in which the lung development had not far progressed. It may indeed have been a leading influence in the development of the Teleostean or bony fishes, as it doubtless was in the loss of its primitive function by, and the subsequent changes of, the air-bladder. "Such of the Crossopterygians and Dipnoans as survived in their old condition had to contend with adverse circumstances. Most of them in time vanished, while their descendants which still exist have lost in great measure their air-breathing powers, and the Dipnoans, in which the development of the lung had gone too far for reversal, have degenerated into eel-like, mud- haunting creatures, in which the organs of locomotion haA'e become converted into the feeble paddle-like limbs of Neocera- todus and the filamentary appendages of the other species. " As regards the presence of a large quantity of oxygen in the bladders of deep-swimming marine fishes, it not unlikely has a respiratory purpose, the bladder being, as suggested by Semper, used as a reservoir for oxygen, to serve the fish when sleeping, or when, from any cause, not actively breathing. The excess of oxygen is not due to any like excess in the gaseous contents of sea-water, for the percentage of oxygen decreases from the surface downward, while that of nitrogen remains nearly un- changed. In all cases, indeed, the bladder may preserve a share of its old function, and act as an aid in respiration. Speaking of this, Cuvier says: 'With regard to the presumed assistance which the swim-bladder affords in respiration, it is a fact that when a fish is deprived of that organ, the production of car- bonic acid by the branchife is very trifling,' thus strongly indi- cating that the bladder still plays a part in the oxygenation of the blood. io6 The Organs of Respiration "Under the hypothesis here presented the process of evolu- tion involved may be thus summed up. Air-breathing in fishes was originally performed by the unchanged walls of the oesoph- agus perhaps at specially vascular localities. Then the wall folded inward, and a pouch was finally formed, opening to the air. The pouch next became constricted off, with a duct of con- nection. Then the pouch became an air-bladder with respira- tory function, and finally developed into a simple lung. These air-breathing fishes haunted the shores, their fins becoming con- verted into limbs suitable for land locomotion, and in time developed into the lung- and gill-breathing batrachia, and these in their turn into the lung-breathing reptilia, the loco- motor organs gradually increasing in efficiency. Of these pre- batrachia we have existing representatives in the mud-haunt- ing Dipnoi, with their feeble limbs, fn the great majority of the Ganoid fishes the bladder served but a minor purpose as a breathing organ, the gills doing the bulk of the work. In the Teleostean descendants of the Ganoids the respiratory ftmction of the bladder in great measure or wholly ceased, in the majority of cases the duct closing up or disappearing, leaving the pouch as a closed internal sac, far removed from its place of origin. In this condition it served as an aid in swimming, perhaps as a survival of one of its ancient uses. It gained also in certain cases some connection with the organ of hearing. But these were makeshift and unimportant functions, as we may gather from the fact that many fishes found no need for them, the bladder, in these cases, decreasing in size until too small to be of use in swimming, and in other cases completely disappearing after having travelled far from its point of origin. In some other cases, above cited, the process seems to have begun again, in modem times, in an eversion of the wall of the oesophagus for respiratory purposes. The whole process, if I have correctly conceived it, certainly forms a remarkable organic cycle of de- velopment and degeneration, which perhaps has no counterpart of similarly striking character in the whole range of organic life." The Heart of the Fish. — The heart of the fish is simple in structure, small in size, and usually placed far forward, just behind the branchial cavity, and separated from the abdominal The Organs of Respiration 107 cavity by a sort of "diaphragm" formed of thickened peri- toneum. In certain eels the heart is remote from the head. The heart consists of four parts, the sinus venosus, into which the veins enter, the auricle or atrium, the ventricle, and the arterial bulb at the base of the great artery which carries the blood to the gills. Of these parts the ventricle is deepest in color and with thickest walls. The arterial bulb varies greatly in stnicture, being in the sliarks, rays. Ganoids, and Dipnoans muscular and provided with a large number of internal valves, and contracting rhythmically like the ventricle. In the higher fishes these structures are lost, the walls of the arterial bulb are not contractile, and the interior is without valves, except the pair that separate it from the ventricle. In the lancelet there is no proper heart, the function of the heart being taken by a contractile blood-vessel situated on the ventral side of the alimentary canal. In the Dipnoans, which are allied to the ancestors of the higher vertebrates, there is the beginning of a division of the ventricle, and sometimes of the auricle, into parts by a median septum. In the higher verte- brates this septum becomes more and more specialized, sepa- rating auricle and ventricle into right and left cavities. The blood in the fish is not returned to the heart after purification, but is sent directly over the body. The Flow of Blood. — The blood in fishes is thin and pale red (colorless in the lancelet) and with elliptical blood-corpuscles. It enters the sinus venosus from the head through the jugular vein, from the kidney and body walls through the cardinal vein, and from the liver through the hepatic veins. Hence it passes to the auricle and ventricle, and from the ventricle through the arterial bulb, or conus arteriosus to the ventral aorta. Thence it flows to the gills, where it is purified. After passing through the capillaries of the gill-filaments it is collected in paired arteries from each pair of gills. These vessels unite to form the dorsal aorta, which extends the length of the body just below the back-bone. From the dorsal aorta the subclavian arteries branch off toward the pectoral fins. From a point farther back arise the mesenteric arteries carrying blood to the stomach, in- testine, liver, and spleen. In the tail the caudal vein carries blood to the kidneys. These secrete impurities arising from io8 The Organs of Respiration waste of tissues, after which the blood again passes to the heart through the cardinal vein. From the intestine the blood, charged with nutritive materials in solution, is carried by the portal vein to the liver. Here it again passes by the liepatic sinus to the sinus venosiis and the heart. The details of the circulatory system vary a good deal in the different groups, and a comparative study of the direction of veins and arteries is instructive and interesting. The movement of the blood in fishes is relatively slow, and its temperature is raised but little above that of the surround- ing water. CHAPTER VII THE NERVOUS SYSTEM [HE Nerves of the Fish. — The nervous system in the fish, as in the higher vertebrates, consists of brain and spinal cord with sensory, or afferent, and motor, or efferent, nerves. As in other vertebrates, the nerve substance is divided into gray matter and white matter, or nerve-cells and nerve-fibres In the fish, however, the whole nervous system is relatively small, and the gray matter less developed than in the higher forms. According to Gunther the brain in the pike (Esox) forms but y^^-^ part of the weight of the body; in the burbot (Lota) about ^^tj part. The cranium in fishes is relatively small, but the brain does not nearly fill its cavity, the space between the dura mater, which lines the skull-cavity, and the arachnoid membrane, which envelops the brain, being filled with a soft fluid containing a quantity of fat. The Brain of the Fish. — It is most convenient to examine the fish-brain, first in its higher stages of development, as seen in the sunfish, striped bass, or perch. As seen from above the brain of a typical fish seems to consist of five lobes, four of them in pairs, the fifth posterior to these and placed on the median line. The posterior lobe is the cerebellnm, or metenceph- alon, and it rests on the medulla oblongata, the posterior portion of the brain, which is directly continuous with the spinal cord. In front of the cerebellum lies the largest pair of lobes, each of them hollow, the optic nerves being attached to the lower surface. These are known as the optic lobes, or mcseiiceplialou In front of these lie the two lobes of the cerebrum, also called the hemispheres, or prosencephalon. These lobes are usually smaller than the optic lobes and solid. In some fishes they are crossed by a furrow, but are never corrugated as in the brain 109 ijQ The Nervous System of the higher animals. In front of the cerebrum lie the two small olfactory lobes, Avhich receive the large olfactory nerve from the nostrils. From its lower surface is suspended the hy- pophysis or pituitary gland. In most of the bony fishes the structure of the bram does not differ materially from that seen in the perch. In the stur- Fourth ventricle. Mesencephalon (optic lobes). Metencephalon (medulla). Epencephalon (cerebellum). Fio. 78. Fig. 79. Fig. 80. Fig. 78. — Brain of a Shark (Squatina squaUna L.). (.\fter Dean.) I. First cranial nerve (olfactory). V. Fifth cranial nerve. P. Prosencephalon (cerebrum). VII. Seventh cranial nerve. E. Epiphysis. V-i. T. Thalamencephalon. M. II. Second cranial nerve. MT. IV. Fourth cranial nerve. EP. Fig. 79. — Brain of ChinKcra monstrosa. (After Wilder per Dean.) Fig. 80. — Brain of Protopterus annectens. (After Burckhardt per Dean.) geon, however, the parts are more widely separated. In the Dipnoans the cerebral hemispheres are united, while the optic lobe and cerebellum are very small. In the sharks and rays the large cerebral hemispheres are usually coalescent into one, and the olfactory nerves dilate into large ganglia below the nostrils. The optic lobes are smaller than the hemispheres and also coa- lescent. The cerebellum is very large, and the surface of the The Nervous System I 1 1 medulla oblongata is more or less modified or specialized. The brain of the shark is relatively more highly developed than that of the bony fishes, although in most other regards the latter are more distinctly specialized. The Pineal Organ.— Besides the structures noted in other fishes the epiphysis, or pineal organ, is largely developed in sharks, and traces of it are found in most or all of the higher vertebrates. In some of the lizards this epiphysis is largely developed, bear- -EP Fig. 82. (After Dean.) II. Second cranial nerve. IV. Fourth cranial nerve, v. Fifth cranial nerve. VII. Seventh cranial nerve. VIII. Eighth cranial nerve. IX. Ninth cranial nerve. X. Tenth cranial nerve. Fig. 81. Fig. 81. — Brain of a Perch, Perca flavescens. R. Olfactory lobe. P. Cerebrum (prosencephalon). E. Epiphysis. M. Optic lobes (mesencephalon). EP. Cerebellum (epencephalon). ML. Medulla oblongata (metencephalon). I. First cranial nerve. Fig. 82. — Petromyzon marinus unicolor (Dekay). Head of Lake Lamprey, showing pineal body. ("After Gage.) ing at its tip a rudimentary eye. This leaves no doubt that in these forms it has an optic function. For this reason the struc- ture wherever found has been regarded as a rudimentary eye, and the "pineal eye" has been called the "impaired median eye of chordate" animals. It has been supposed that this eye, once possessed by all vertebrate forms, has been gradually lost with the better de- 1 1 2 The Nervous System velopment of the paired eyes, being best preserved in reptiles as "an outcome of the hfe-habit which concealed the animal m sand or mud, and allowed the forehead surface alone to protrude, the median eye thus preserving its ancestral value in enabling the animal to look directly upward and backward." This theory receives no support from the structures seen in the fishes. In none of the fishes is the epiphysis more than a nervous enlargement, and neither in fishes nor in amphibia is there the slightest suggestion of its connection with vision. It seems probable, as suggested by Hertwig and maintained by Dean that the original function of the pineal body was a nervous one and that its connection with or development into a median eye in lizards was a modification of a secondary character. On consideration of the evidence, Dr. Dean concludes that "the pineal structures of the true fishes do not tend to confirm the theory that the epiphysis of the ancestral vertebrates was con- nected with a median unpaired eye. It would appear, on the other hand, that both in their recent and fossil forms the epiphy- sis was connected in its median opening with the innervation of the sensory canals of the head. This view seems essentially confirmed by ontogeny. The fact that three successive pairs of epiphyseal outgrowths have been noted in the roof of the thala- mencephalon * appears distinctly adverse to the theory of a median eye." f The Brain of Primitive Fishes. — The brain of the hagfish dift'ers widely from that of the higher fishes, and the homologies of the different parts are still uncertain. The dift"erent ganglia are all solid and are placed in pairs. It is thought that the cerebellum is wanting in these fishes, or represented by a narrow commissure {corpus restijorme) across the front of the medulla. In the lamprey the brain is more like that of the ordinary fish. In the lancelet there is no trace of brain, the band-like spinal cord tapering toward either end. The Spinal Cord. — The spinal cord extends from the brain to the tail, passing through the neural arches of the different ver- tebrae when these are developed. In the higher fishes it is cyHn- * The thalamcnccphalon or the intcrbrain is a name given to the region of the optic thalanii, between the bases of the optic lobes and cerebrum t Fishes Recent and Fossil, p. 55. The Nervous System i i 3 drical and inelastic. In a few fishes (head-fish, trunk-fish) in which the posterior part of the body is shortened or degener- ate, the spinal cord is much shortened, and replaced behind by a structure called cauda equina. In the head-fish it has shrunk into "a short and conical appendage to the brain." In the Cyclostomes and chimera the spinal cord is elastic and more or less flattened or band-like, at least posteriorly. The Nerves. — The nerves of the fish correspond in general in place and function with those of the higher animals. They are, however, fewer in number, both large nerve-trunks and smaller nerves being less developed than in higher forms. The olfactory nerves^ or first pair, extend through the ethnoid bone to the nasal cavity, which is typically a blind sac with two roundish openings, but is subject to many variations. The optic nerves, or second pair, extend from the eye to the base of the optic lobes. In Cyclostomes these nerves run from each eye to the lobe of its own side. In the bony fishes, or Teleostei, each runs from the eye to the lobe of the opposite side. In the sharks, rays, chimseras, and Ganoids the two optic nerves are joined in a chiasma as in the higher vertebrates. Other nerves arising in the brain are the third pair, or ner- vus ociilormn motorins, and the fourth pair, nervus trochlearis, both of which supply the muscles of the eye. The fifth pair, nervus trigeminus, and the seventh pair, nervus facialis, arise from the medulla oblongata and are very close together. Their various branches, sensory and motor, ramify among the mus- cles and sensory areas of the head. The sixth pair, nervus ab- ducens, passes also to muscles of the eye, and in sharks to the nictitating membrane or third eyelid. The eighth pair, nervus acousticus, leads to the ear. The ninth pair, glosso-pharyngeal, passes to the tongue and pharynx, and forms a ganglion connected with the sympathetic system. The tenth pair, nervus vagus, or pneumogastric nerve, arises from strong roots in the copus restiforme and the lower part of the medulla oblongata. Its nerves, motor and sensory, reach the muscles of the gill-cavity, heart, stomach, and air-bladder, as well as the muscular system and the skin. In fishes covered with bony plates the skin may be nearly or quite without sen- I 1 4 The Nervous System sory nerves. The eleventh pair, nerviis accessorius, and twelfth pair, nennis hypoglossns, are wanting in fishes. The spinal nerves are subject to some special modifications, but in the main correspond to similar structures in higher ver- tebrates. The anterior root of each nerve is without ganglionic enlargement and contains only motor elements. The posterior or dorsal root is sensory only and widens into a ganglionic swell- ing near the base. A sympathetic system corresponding to that in the higher vertebrates is found in all the Teleostei, or bony fishes, and in the body of sharks and rays in which it is not extended to the head. CHAPTER VIII THE ORGANS OF SENSE I HE Organs of Smell. — The sense-organs of the fish cor- respond in general to those of the higher vertebrates. The sense of taste is, however, feeble or wanting, and that of hearing is muffled and without power of acute discrimina- tion, if indeed it exists at all. According to Dr. Kingsley (Vert. Zool., p. 75), "recent experiments tend to show that in fishes the ears are without auditory functions and are solely organs of equilibration." The sense of smell resides in the nostrils, which have no re- lation to the work of breathing. No fish breathes through its nostrils, and only in a few of the lowest forms (hagfishes) does the nostril pierce through the roof of the mouth. In the bony fishes the nostril is a single cavity, on either side, lined with delicate or fringed membrane, well provided with blood-vessels, and with nerves from the olfactory lobe. In most cases each nasal cavity has two external openings. These may be simple, or the rim of the nostril may be elevated, forming a papilla or even a long barbel. Either nostril may have a papilla or barbel, or the two may unite in one structure with two open- ings or with sieve-like openings, or in some degenerate types (Tro- pidichtJiys) with no obvious openings at all, the olfactory nerves spreading over the skin of a small papilla. The openings may be round, slit -like, pore-like, or may have various other forms. In certain families of bony fishes (Pomacentridcr, Cichlid(E, Hexagram- ida), there is but one opening to each nostril. In the sharks, rays, and chimeras there is also but one opening on either side and the nostril is large and highly specialized, with valvular flaps controlled by muscles which are said to enable them ' ' to scent actively as well as to smell passively." In the lancelet there is a single median organ supposed to 115 ii6 The Organs of Sense be a nostril, a small depression at the front of the head, covered bv ciliated membrane. In the hagfish the single median nostril pierces the roof of the mouth, and is strengthened by carti- laginous rings, like those of the windpipe. In the lamprey the single median nostril leads to a blind sac. In the Barramiinda (Neoceratodus) there are both external and internal nares, the former being situated just within the upper lip. In all other fishes there is a nasal sac on either side of the head. This has usually, but not always, two openings. There is little doubt that the sense of smell in fishes is rela- tively acute, and that the odor of their prey attracts them to Fig. 83. — Dismal Swamp Fish, Chologaster cormitus Agassiz. Supposed ancestor of Typhlichthys. Virginia. Fig. 84.— Blind Cavefish, Tijphlichthys sublerraneus Girard. Kentucky. Mammoth Cave, it. It is known that flesh, blood, or a decaying carcass will attract sharks, and other predatory fish are drawn in a similar manner. At the same time the strength of this function is yet to be tested by experiments. The Organs of Sight. — The eyes of fishes differ from those of the higher vertebrates mainly in the spherical form of the crys- talhne lens. This extreme convexity is necessary because the lens itself is not very much denser than the fluid in which the fishes live. The eyes vary very much in size and somewhat in form and position. They are larger in fishes hving at a mod- erate depth than in shore fishes or river fishes. At great depths The Organs of Sense 117 as a mile or more, where all light is lost, they may become aborted or rudimentary, and may be covered by the skin. Often species with very large eyes, making the most of a little light or of light from their own luminous spots, will inhabit the same depths with fishes having very small eyes or eyes apparently useless for seeing, retained as vestigial structures through heredity. Fishes which live in caves become also blind, the structures showing everj^ possible phase of degradation. The details of this gradual loss of eyes, whether through reversed selection or hypothetically through inheritance of atrophy produced by disuse, have been given in a number of memoirs on the blind fishes of the Missis- sippi Valley by Dr. Carl H. Eigenmann. In some fishes the eye is raised on a short, fleshy stalk and can be moved about at the will of the fish. It is said that the vision of the pond-skipper, Periophthalmus, when hunting insects on the mud fiats of Japan or India is "quite equal to that of a frog." It is known also that trout possess keen Fig. 85. — Four-eyed Fish, Anableps dovii Gill. Tehuantepec, Mexico. eyesight, and that they show a marked preference for one sort or another of real or artificial fly. Nevertheless the vision of fishes in general is probably not very precise. They apparently notice motion rather than outline, changes rather than objects, while the extreme curvature of the crystaUine lens would seem to render them all near-sighted. In the eyes of the fishes there is no lachrymal gland. True eyelids no fishes possess ; the integuments of the head pass over the eye, becoming transparent as they cross the orbit. In some fishes part of this integument is thickened, covering the eye fully although still transparent. This forms the adipose eyelid char- acteristic of the mullet, mackerel, and lady-fish. Many of the sharks possess a distinct nictitating membrane or special eyelid, moved by a set of muscles. The iris in most fishes surrounds a ii8 The Organs of Sense round pupil without much power of contraction. It is fre- quently brightly colored, red, orange, Ijlack, blue, or green. In fishes, Uke rays or flounders, which lie on the bottom, a dark lobe covers the upper part of the pupil — a curtain to shut out light from above. The cornea is little convex, leaving small space for aqueous humor. In two genera of fishes, Anahleps, Dialoininus, the cornea is divided by a horizontal partition into Fig. 86. — Ipnops murraiji Giinther. two parts. This arrangement permits these fishes, which swim at the surface of the water, to see both in and out of the medium. Aiiableps, the four-eyed fish, is a fresh-water fish of tropical America, which swims at the surface like a top-minnow, feeding on insects. Dialommiis is a marine blennv from the Panama region, apparently of similar habit. In one genus of deep-sea fishes, Ipnops, the eyes are spread Fig. S7. — Pond-skipper, Bokophthalmus chinensis (Osbeck). Bay of Tokj'O, Japan; from nature. K. Morita. (Eye-stalks shrunken in preservation.) out to cover the whole upper .surface of the head, being modi- fied as luminous areas. Whether these fishes can see at all is not known. The position of the optic nerves is described in a previous chapter. In ordinary fishes there is one eye on each side of the head, but in the flounders, by a distortion of the cranium, both ap- The Organs of Sense 119 pear on the same side. This side is turned uppermost as the fish swims in the water or when it hes on the bottom. This distortion is a matter of development. The very young flounder swims with its broad axis vertical in the water, and it has one eye on either side. As soon as it rests on the bottom it begins to lean to one side. The lower eye changes its axis and by de- grees travels across the face of the fish, part of the bony inter- orbital moving with it across to the other side. In some soles it is said to pass through the substance of the head, reappearing on the other side. In all species which the writer has examined the cranium is twisted, the eye moving with the bones ; and the frontal bone is divided, a new orbit being formed by this division. In most northern flounders the eyes are on the right side in the adult, in tropical forms more frequently on the left, these distinctions corresponding with others in the structure of the fish. In the lowest of the fish-like forms, the lancelet, the eye is simply a minute pigment-spot situated in the anterior wall of the ventricle at the anterior end of the central nervous system. In the hagfishes, which stand next highest in the series, the eye, still incomplete, is very small and hidden by the skin and mus- cles. This condition is very different from that of the blind fishes of the higher groups, in which the eye is lost through atrophy, because in life in caves or under rocks the function of seeing is no longer necessary. The Organs of Hearing. — The ear of the typical fish consists of the labyrinth only, including the vestibule and usually three semicircular canals, these dilating into sacs which contain one or more large, loose bones, the ear-stones or otoliths. In the lampreys there are two semicircular canals, in the hagfish but one. There is no external ear, no tympanum, and no Eustachian tube. The ear-sac on each side is lodged in the skull or at the base of the cranial cavity. It is externally surrounded by bone or cartilage, but sometimes it lies near a fontanelle or opening in the skuU above. In some fishes it is lirought into very close connection with the anterior end of the air-bladder. The latter organ it is thought may form part of the apparatus for hearing. The arrangement for this purpose is especially elaborate in the carp and the catfish families. In these fishes and their relatives I 20 The Organs of Sense (called Ostariophysi) the two vestibules are joined in a median sac {sinus impar) in the substance of the basioccipital. This communicates with two cavities in the atlas, which again are supported by two small bones, these resting on a larger one Fig. SS. — Brook Lamprey, Lainpctrn inhlcri Jordan and Evermann. (After Gage.) Cayuga Lake. in connection with the front of the air-bladder. The system of bones is analogous to that found in the higher vertebrates, but it connects with the air-bladder, not with an external tympanum. The bones are not homologous with those of the ear of higher animals, being processes of the anterior vertebrse. The tym- panic chain of higher vertebrates has been thought homologous with the suspensory of the mandible. The otoliths, commonly two in each labyrinth, are usually large, firm, calcareous bodies, with enamelled surface and peculiar Fig. 89. — European haxLceXei, Branchiostoma lanceolatum (FaMas). (After Parker and HasweU.) grooves and markings. Each species has its own form of otolith, but they vary much in different groups of fishes. In the Elasmobranchs (sharks and rays) and in the Dipnoans the ear-sac is enclosed in the cartilaginous substance of the skull. There is a small canal extending to the surface.of the skull, ending sometimes in a minute foramen. The otoliths in these fishes are soft and clialk-likc. The Organs of Sense i 2 1 b The lancelet shows no trace of an ear. In the cyclostomes, hagfishes, and lampreys it forms a capsule of relatively simple structure conspicuous in the prepared skeleton. The sense of hearing in fishes cannot be very acute, and is at the most confined to the perception of disturbances in the water. Most movements of the fish are governed by sight rather than by sound. It is in fact extremely doubtful whether fishes really hear at all, in a way comparable to the auditory sense in higher vertebrates. Recent experiments of Professor G. H. Parker on the kilHfish tend to show a moderate degree of auditory sense which grades into the sense of touch, the tubes of the lateral line assisting in both hearing and touch. While the killifish responds to a bass-viol string, there may be some fishes wholly deaf. Voices of Fishes. — Some fishes make distinct noises variously described as quivering, grunting, grating, or singing. The name grunt is applied to species of HcBmulon and related genera, and fairly describes the soimd these fishes make. The Spanish name ronco or roncador (grunter or snorer) is applied to several fishes, both sci^noid and hsemuloid. The noise made by these fishes may be produced by forcing air from part to part of the com- plex air-bladder, or it may be due to grating one on another of the large pharyngeals. The grating sounds arise, no doubt, from the pharyngeals, while the quivering or singing sounds arise in the air-bladder. The midshipman, Porichthys notatus, is often called singing fish, from a peculiar sound it emits. These sounds have not yet been carefully investigated. The Sense of Taste. — It is not certain that fishes possess a sense of taste, and it is attributed to them only through their homology with the higher animals. The tongue is without deli- cate membranes or power of motion. In some fishes certain parts of the palate or pharyngeal region are well supplied with nerves, but no direct evidence exists that these have a function of discrimination among foods. Fishes swaUow their food very rapidly, often whole, and mastication, when it takes place, is a crushing or cutting process, not one likely to be affected by the taste of the food. The Sense of Touch. — The sense of touch is better developed among fishes. Most of them flee from contact with actively 122 The Organs of Sense moving objects. Many fishes use sensitive structures as a means of exploring the bottom or of feehng their way to their food. The barbel or fleshy filament wherever developed is an organ of touch. In some fishes, barbels are outgrowths from the nostrils. In the catfish the principal barbel grows from the rudimentary maxillary bone. In the homed dace and gudgeon the little barbel is attached to the maxillary. In other fishes barbels grow from the skin of the chin or snout. In Fig. 90. — Goat-fish, Pseudxipeneus macxdatus (Bloch). Woods Hole. the goatfish and surmullet the two chin barbels are highly specialized. In Poly mixta the chin barbels are modified branchiostegals. In the codfish the single beard is little developed. In the gurnards and related forms the lower rays of the pectoral are separate and barbel-like. Detached rays of this sort are found in the thread-fins (Polyneiindcc), the gurnards {Triglidcc), and in various other fishes. Barbels or fleshy flaps are often developed over the eyes and sometimes on the scales or the fins. The structure of the lateral line and its probable relation as a sense-organ is discussed on page 23. It is probable that it is associated with sense of touch, and hearing as well, the internal car fieing ririginally "a modified part of the lateral-Une system," as shfjwn by Parker,* who calls the skin the lateral line and the ear " three generations of sense-organs." * See Parker, on the sense of hearing in fishes, American NaturaUst for March, 1903. The Organs of Sense 123 The sense of pain is very feeble among fishes. A trout has been known to bite at its own eye placed on a hook, and similar insensibility has been noted in the pike and other fishes. " The Greenland shark, when feeding on the carcass of a whale, allows itself to be repeatedly stabbed in the head without abandoning its prey." (Gijnther.) CHAPTER IX THE ORGANS OF REPRODUCTION JIHE Germ-cells. — In most fishes the germ-cells are pro- duced in large sacs, ovaries or testes, arranged sym- metrically one on either side of the posterior part of the abdominal cavity. The sexes are generally but not always similar externally, and may be distinguished on dissection by the difference between the sperm-cells and the ova. The ovary Fig. 91. — Sword-tail Minnow, nnale, X iphophorus helleri Heckel. modified as an intromittent organ. VeTa Cruz. The anal fin with its eggs is more yellow in color and the contained cells appear granular. The testes are whitish or pinkish, their secre- tion milk-like, and to the naked eye not granular. In a very few cases both organs have been found in the same fish, as in Scrranus, which is sometimes truly hermaphrodite. All fishes, however, seem to be normally dioecious, the two sexes in different individuals. Usually there are no external genital organs, but in some species a papilla or tube is developed at the end of the urogenital sinus. This may exist in the breeding season only, as in the fresh-water lampreys, or it may persist through life as in some gobies. In the Elasmobranchs, carti- laginous claspers, attached to the ventral fins in the male, serve as a conduit for the sperm-cells. 124 Tht Organs of Reproduction 125 The Eggs of Fishes. — The great majority of fishes are ovipa- rous, the eggs being fertihzed after deposition. The eggs are laid in gravel or sand or other places suitable for the species, and the milt containing the sperm-cells of the male is discharged over or among them in the water. A very small quantity of the sperm- fiuid may impregnate a large number of eggs. But one sperm- cell can enter a particular egg. In a number of families the species are ovoviviparous, the eggs being hatched in the ovary or in a dilated part of the oviduct, the latter resembling a real uterus. In some sharks there is a structure analogous to Fig. 92. — White Surf-fish, viviparous, with young, Cymatogaster aggregatus Gibbons, San Francisco. the placenta of higher animals, but not of the same structure or origin. In the case of viviparous fishes actual copulation takes place and there is usually a modification of sorae organ to effect transfer of the sperm-cells. This is the purpose of the sword- shaped anal fin in many top-minnows {Pccciliida;), the fin itself being placed in advance of its usual position. In the surf-fishes {EmbiotocidcB) the structure of part of the anal fin is modified, although it is not used as an intromittent organ. In the Elas- mobranchs, as already stated, large organs of cartilage (claspers) are developed from the ventral fins. In some viviparous fishes, as in the rockfishes (Sebastodes) and rosefishes (Sebastes), the young are very minute at birth. The Organs of Reproduction 127 In others, as the surf -fishes (Embioiocidcc), they are relatively large and few in number. In the viviparous sharks, which con- stitute the majority of the species of living sharks, the young are large at birth and prepared to take care of themselves. The eggs of fishes vary very much in size and form. In Fig. 94. — Egg of Callorhynchus antarrticus, the Bottle-nosed Chima?ra. (After Parker and Haswell.) those sharks and rays which lay eggs the ova are deposited in a homy egg-case, in color and texture suggesting the kelp in which they are laid. The eggs of the bull-head sharks {Heterodon- ius) are spirally twisted, those of the cat-sharks (Scyliorhitiidcc) are quadrate with long filaments at the angles. Those of rays are wheelbarrow -shaped with four "handles." One egg-case Fig. 9.5. — Egg of the Hagfish, Myxine limosa Girard, showing threads for attach- ment. (After Dean.) of a ray may sometimes contain several eggs and develop several young. The eggs of lancelets are small, but those of the hagfishes are large, ovate, with fibres at each side, each with a triple hook at tip. The chimaera has also large egg-cases, oblong in form. In the higher fishes the eggs' are spherical, large or small according to the species, and varying in the firmness of their 28 The Organs of Reproduction outer walls. All contain food-yolk from which the embryo in its earlier stages is fed. The eggs of the eel (Anguilla) are micro- scopic. According to Gunther 25,000 eggs have been counted in the herring, 155,000 in the lumpfish, 3,500,000 in the halibut, 635,200 in the sturgeon, and 9,344,000 in the cod. Smaller numbers are found in fishes with large ova. The red salmon has about 3500 eggs, the king salmon about 5200. Where an oviduct is present the eggs are often poured out in glutinous masses, as in the bass. When, as in the salmon, there is no oviduct, the eggs lie separate and do not cohere together. It is only -^^ath the latter class of fishes, those in which the eggs remain distinct, that artificial impregnation and hatching is practicable. In this re- ,^, , r J . . , I,-,- ■ gard the value of the salmon and bnark, Heterodontus phdippi ° (Laci'pede). (After Parker and trout is predominant. In some fishes, HaswcU.) especially those of elongate form, as the needle-fish (Tylositnis), the ovary of but one side is developed. Protection of the Young. — In most fishes the parents take no care of their eggs or j^oung. In some catfishes (Platystaciis) the eggs adhere to the under surface of the female. In a kind of pipefish (Solenostomns), a large pouch for retention of the eggs is formed on the belly of the female. In the sea-horses and pipefishes a pouch is formed in the skin, usually underneath the tail of the male. Into this the eggs are thrust, and here the young fishes hatch out, remaining until large enough to take care of themselves. In certain sea catfishes {Galeiclitliys, Couo- rhynchos) the male carries the eggs in his mouth, thus protecting them from the attacks of other fishes. In numerous cases the male constructs a rough nest, which he defends against all in- truders, against the female as well as against outside enemies. The nest-building habit is especially developed in the stickle- FlG Egg of Port Jackson The Organs of Reproduction 129 backs {Gasterosteida:), a group in which the male fish, though a pygmy in size, is very fierce in disposition. In a minnow of Europe {RJiodcns ainanis) the female is said to deposit her eggs within the shells of river mussels. Sexual Modification. — In the relatively few cases in which the sexes are unlike the male is usually the brighter in color and with more highly developed fins. Blue, red, black, and silvery-white pigment are especially characteristic of the male, the olivaceous and mottled coloration of the female. Sometimes the male has a larger mouth, or better developed crests, barbels, or other appendages. In some species the pattern of coloration in the two sexes is essentially dift'erent. In various species the male develops peculiar structures not found in the female, and often without any visible purpose. In the chimfera a peculiar cartilaginous hook armed with a brush of enamelled teeth at the tip is developed on the forehead in the male only. In the skates or true rays (Raja) the pectoral fin has near its edge two rows of stout incurved spines. These the female lacks. In the breeding season, among certain fishes, the male sometimes becomes much brighter by the accumulation of bright red or blue pigment accompanied by black or white pig- ment cells. This is especially true in the minnows {Notropis), the darters (Etlieostoma) , and other fresh-water species which spawn in the brooks of northern regions in the spring. In the minnows and suckers homy excrescences are also developed on head, body, or fins, to be lost after the deposition of the spawn. In the salmon, especially those of the Pacific, the adult male becomes greatly distorted in the spawning season, the jaws and teeth being greatly elongated and hooked or twisted so that the fish cannot shut its mouth. The Atlantic salmon and the trout show also some elongation of the jaws, but not to the same extent. In those fishes which pair the relation seems not to be per- manent, nor is there anything to be called personal affection among them so far as the writer has noticed. There is no evidence that the bright colors or nuptial adorn- ments of the males are enhanced by sexual selection. In most species the males deposit the sperm -cells in spawning-grounds 130 The Organs of Reproduction without much reference to the preference of the females. In general the brightest colors are not found among viviparous fishes. None of tlie groups in which the males are showily colored, while the females are plain, belong to this class. The brightest colors are found on the individuals most mature or having greatest vitality. CHAPTER X EMBRYOLOGY AND GROWTH OF FISHES EGMENTATION of the Egg.— The egg of the fish de- velops only after fertilization (amphimixis). This process is the union of its nuclear substance with that of the sperm-cell from the male, each cell carrying . its equal share in the function of heredity. When this process takes place the egg is ready to begin its segmentation. The eggs of all fishes are single cells containing more or less food- yolk. The presence of this food-yolk affects the manner of segmentation in general, those eggs having the least amount of food-yolk developing most typically. The simplest of all fish- like vertebrates, the lancelet (Branchiostoma) has very small eggs, and in their early development it passes through stages that are typical for all many-celled animals. The first stage in development is the simple splitting of the egg into two halves. These two daughter cells next divide so that there are four cells ; each of these divides, and this division is repeated until a great number of cells is produced. The phenomenon of repeated di- vision of the germ-cell is called cleavage, and this cleavage is the first stage of development in the case of all many-celled animals. Instead of forming a solid mass the cells arrange themselves in such a way as to form a hollow ball, the wall being a layer one cell thick. The included cavity is called the segmentation cavity, and the whole structure is known as a blastula. This stage also is common to all the many-celled animals. The next stage is the conversion of the blastula into a double- walled cup, known as a gastrula by the pushing in of one side. All the cells of the blastula are very small, but those on one side are somewhat larger than those of the other, and here the wall first flattens and then bends in until finally the larger cells come into contact with the smaller and the segmentation cavity is entirely obliterated. There is now 131 132 Embryology and Growth of Fishes an inner layer of cells and an outer layer, the inner layer being known as the endoblast and the outer as the ectoblast. The cavity of the cup thus formed is the archenteron and gives rise primarily to the alimentary canal. This third well-marked stage is called the gastrula stage, and it is thought to occur either typically or in some modified form in the development of all metazoa, or many-celled animals. In the lampreys, the Ganoids, and the Dipnoans the eggs contain a much greater quantity of yolk than those of the lancelet, but the segmenta- tion resembles that of the lancelet in that it is complete; that is, the whole mass of the egg divides into cells. There is a great difference, however, in the size of the cells, those at the upper pole being much smaller than those at the lower. In Pctromyzon and the Dipnoans blastula and gastrula stages result, which, though differing in some particulars from the corresponding stages of the lancelet, may yet readily be compared with them. In the hagfishes, sharks, rays, chima^ras, and most bony fishes there is a large quantity of yolk, and the protoplasm, instead of being distributed evenly throughout the egg, is for the most part ac- cumulated upon one side, the nucleus being within this mass of protoplasm. When the food substance or yolk is consumed and the little fish is able to shift for itself, it leaves the egg-envelopes and is said to be hatched. The figures on page 135 shoAv some of the stages by which cells are multiplied and ultimately grouped together to form the little fish. Post-embryonic Development. — In all the fishes the develop- ment of the embryo goes on within the egg long after the gastrula stage is passed, and until the embryo becomes a complex body, composed of many differing tissues and organs. Almost all the development may take place within the egg, so that when the young animal hatches there is necessary little more than a rapid growth and increase of size to make it a fuUy developed mature animal. This is the case with most fishes: a little fish just hatched has most of the tissues and organs of a full-grown fish, and is simply a small fish. But in the case of some fishes the young hatches from the egg before it has reached such an ad- vanced state of development, and the young looks very dift'erent from its parent. It must yet undergo considerable change before it reaches the structural condition of a fully developed Embryology and Growth of Fishes 133 and fully grown fish. Thus the development of most fishes is almost wholly embryonic development— that is, development within the egg or in the body of the mother— while the develop- ment of some of them is to a considerable degree post-embry- onic or larval development. There is no important difference between embryonic and post-embryonic development. The de- velopment is continuous from egg-cell to mature animal and, whether inside or outside of an egg, it goes on with a degree of regularity. While certain fishes are subject to a sort of meta- morphosis, the nature of this change is in no way to be com- pared with the change in insects which undergo a complete metamorphosis. In the insects all the organs of the body are broken down and rebuilt in the process of change. In all fishes a structure once formed maintains a more nearly continuous integrity although often considerably altered in form. General Laws of Development. — The general law of develop- ment may be briefly stated as follows : All many-celled animals begin life as a single cell, the fertilized egg-cell ; each animal goes through a certain orderly series of developmental changes which, accompanied by growth, leads the animal to change from single-cell to many-celled, complex form characteristic of the species to which the animal belongs; this development is from simple to complex structural condition ; the development is the same for all individuals of one species. While all animals begin development similarly, the course of development in the dif- ferent groups soon diverges, the divergence being of the nature of a branching, like that shown in the growth of a tree. In the free tips of the smallest branches we have represented the various species of animals in their fully developed condition, all standing clearly apart from each other. But in tracing back the development of any kind of animal we soon come to a point where it very much resembles or becomes apparently identical with some other kind of animal, and going farther back we find it resembling other animals in their young condition, and so on until we come to that first stage of development, that trunk stage where all animals are structurally alike. Any ani- mal at any stage in its existence differs absolutely from any other kind of animal, in this respect: it can develop into only its own kind. There is something inherent in each develop- 134 Embryology and Growth of Fishes ing animal that gives it an identity of its own. Although in its young stages it may be indistinguishable from some other species of animal in its young stages, it is sure to come out, when fully developed, an individual of the same kind as its parents were or are. The voung fish and the young salamander may be alike to all appearance, but one embryo is sure to develop into a fish, and the other into a salamander. This certainty of an embrvo to become an individual of a certain kind is called the law of heredity. \Tewed in the light of development, there must be as great a difference between one egg and another as between one animal and another, for the greater difference is included in the less. The Significance of Facts of Development. — The significance of the process of development in any species is yet far from com- pletely understood. It is believed that many of the various stages in the development of an animal correspond to or repeat the structural condition of the animal's ancestors. Naturalists believe that all animals having a notochord at any stage in their existence are related to each other through being descended from a common ancestor, the first or oldest chordate or back- boned animal. In fact it is because all these chordate animals — the lancelets, lampreys, fishes, batrachians, the reptiles, the birds, and the mammals — have descended from a common ancestor that they all develop a notochord, and those most highly organized re- place this by a complete back-bone. It is believed that the de- scendants of the first back-boned animal have, in the course of many generations, branched off little by little from the original type until there came to exist very real and obvious differences among the back-boned animals — difi:erences which among the liv- ing back-boned animals are familiar to all of us. The course of development of an individual animal is believed to be a verv rapid and evidently much condensed and changed recapitula- tion of tlie history which the species or kind of animal to which the developing individual belongs has passed through in the course of its descent through a long series of gradually changing ancestors. If this is true, then we can readily understand why the fish and the salamander and the tortoise and bird and rabbit are all alike in their eariier stages of development, and gradually Embryology and Growth of Fishes 135 come to differ more and more as they pass through later and later developmental stages. Development of the Bony Fishes.* The mode of develop- ment of bony fishes differs in many and apparently important regards from that of their nearest kindred, the Ganoids. In their eggs a large amount of yolk is present, and its relations to the embryo have become widely speciaHzed. As a rule, the egg of a Teleost is small, perfectly spherical, and enclosed in delicate but greatly distended membranes. The germ disc is especially small, appearing on the surface as an almost trans- parent fleck. Among the fishes whose eggs float at the sur- d Fig. 97. — Development of Sea-bass, Centropristes striatuf: (Linnaeus). a, egg prior to germination; 6, germ-disk after first cleavage; c, germ-disk after third cleavage; d, embryo just before hatching. (After H. V. Wilson.) face during development, as of many pelagic Teleosts, e.g., the sea-bass, Centropristes striatns, the yolk is lighter m specific gravity than the germ ; it is of fluid-like consistency, almost transparent. In the yolk at the upper pole of the egg an oil globule usually occurs; this serves to lighten the relative weight of the entire egg, and from its position must aid in keeping this pole of the egg uppermost. In the early segmentation of the germ the first cleavage plane is established, and the nuclear divisions have taken place for the second; in the latter the third cleavage has been com- pleted. As in other fishes these cleavages are vertical, the third parallel to the first. A segmentation cavity occurs as a central space between the blastomeres, as it does in the sturgeon and garpike. In stages of late segmentation the segmentation cavity is *This account of the normal development of the Teleost fishes is condensed from Dr. Dean's "Fishes Living and Fossil," in which work the details of growth in the Teleost are contrasted with those of other types of fishes. 136 Embryology and Growth of Fishes greatly flattened, but extends to the marginal cells of the germ- disk ; its roof consists of two tiers of blastomeres, its floor of a thin film of the unsegmented substance of the germ; the mar- ginal blastomeres are continuous with both roof and floor of the cavity, and are produced into a thin film which passes downward, aroimd the sides of the yolk. Later the segmenta- tion cavity is still further flattened; its roof is now a dome- shaped mass of blastomeres ; the marginal cells have multiplied, and their nuclei are seen in the layer of the germ, below the plane of the segmentation cavity. These are seen in the sur- face view of the marginal cells of this stage ; they are separated by cell boundaries only at the sides ; below they are continuous in the superficial down -reaching layer of the germ. The mar- ginal cells shortly lose all traces of having been separate ; their nuclei, by continued division, spread into the layer of germ flooring the segmentation cavity, and into the delicate film of germ which now surrounds the entire yolk. Thus is formed the periblast of the Teleost development, which from this point on- ward is to separate the embryo from the yolk; it is clearly the specialized inner part of the germ, which, becoming fluid- like, loses its cell-walls, although retaining and multiplying its nuclei. Later the periblast comes into intimate relations with the growing embryo; it lies directly against it, and ap- pears to receive cell increments from it at various regions; on the other hand, the nuclei of the periblast, from their intimate relations with the yolk, are supposed to subserve some func- tion in its assimilation. Aside from the question of periblast, the growth of the blastoderm appears not unlike that of the sturgeon. From the blastula stage to that of the early gastrula, the changes have been but slight ; the blastoderm has greatly flattened out as its margins grow downward, leaving the segmentation cavity apparent. The rim of the blastoderm has become thickened as the ' germ-ring' ; and immediately in front of the dorsal lip of the blastopore its thickening marks the appearance of the embryo. The germ-ring continues to grow downward, and shows more prominently the outline of the embryo ; this now terminates at the head region ; while on either side of this point spreads out tailward on either side the indefinite laver of out- Pi o 2 138 Embryology and Growth of Fishes groAving mesoderm. In the next stage the closure of the blas- topijre is rapidly becoming completed; in front of it stretches the Avidened and elongated form of the embryo. The yolk-plug is next replaced by periblast, the dorsal lip by the tail-mass, or more accurately tlie dorsal section of the germ-rim ; the coelen- teron under the dorsal lip has here disappeared, on account of the close a]3proximation of the embrvo to the periblast ; its last remnant, the Kupffer's A'esicle, is shortly to disappear. The germ-layers become confluent, but, unlike the sturgeon, the flattening of the dorsal germ-ring does not permit the forma- tion of a neurenteric canal. The process of the development of the germ-layers in Teleosts ajijjcars as an ablircA'iated one, although in many of its details it is Ijut imperfectly known. In the development of the medullary groo\'e, as an examjjle, the following peculiarities exist : the medullary region is but an insunken mass of cells without a trace of the groove-like surface indentation. It is only later, Avhen becoming separate from the ectoderm, that it ac- quires its rijunded character; its cellular elements then group themselves symmetrically with reference to a sagittal plane, Avhere later, by their dissociation, the canal of the spinal cord is formed. The gnwvth of the entoderm is another instance of specialized development. In an early stage the entoderm exists in the axial regiijn, its thickness tapering away abruptly on either side; its lower surface is closely apposed to the periblast; its dorsal tliickemng Avill shortly become separate as the noto- chord. In a fijllowing stage of development the entoderm is seen to arch upward in tlie median line as a preliminary stage in the formation of the cavity of the gut. Later, bv the approxi- mation of the entoderm-cells in the median A'entral line, the condition is reached Avliere the completed gut-ca\'itv exists. The formation of the mesoderm in Teleosts is not definitely understood. It is usually said to arise as a process of ' de- lammation,' i.e., detaching itself in a mass from the entoderm. Its origin is, howcA'er, looked upon generallv as of a specialized and secondary character. The mode of formation of the gill-slit of the Teleost does not dilfer from that in other groups; an evagination of the entoderm coming in contact with an invaginated tract of Embryology and Growth of Fishes 139 ectoderm fuses, and at this point an opening is later estab- lished. The late embryo of the Teleost, though of rounded form, is the more deeply implanted in the yolk-sac than that of the sturgeon; it is transparent, allowing notochord, primitive seg- ments, heart, and sense-organs to be readily distinguished ; at about this stage both anus and mouth are making their appear- ance." The Larval Development of Fishes.* — "When the young fish has freed itself from its egg-membranes it gives but little Fig. 99. — Young Sword-fish, Xiphias gladius (Linn;tus). (After Liitken.) suggestion of its adult form. It enters upon a larval ex- istence, which continues until maturity. The period of change of form varies widely in the different groups of fishes, from a few weeks' to longer than a year's duration ; and the extent Fig. 100. — Sword-fish, Xiphias gladius (LinniEus). (After Day.) of the changes that the larva undergoes are often surprisingly broad, investing every organ and tissue of the body, the imma- ture fish passing through a series of form stages which dift'er one from the other in a way strongly contrasting with the mode of growth of amniotes; since the chick, reptile, or mammal emerges from its embryonic membranes in nearly its adult form. The fish may, in general, be said to begin its existence as *This paragraph is condensed from Dean's "Fishes Living and Fossil" 1 40 Embryology and Growth of Fishes a larva as soon as it emerges from its egg-membranes. In somx' instances, however, it is difScult to decide at what point the lar\'al stage is actually initiated: thus in sharks the excessive amount of yolk material which has been provided for the growth Fio. 101. — Larva of the Sail-fish, htiophor^is. very young. (After Liitken.) of the larva renders unnecessary the emerging from the egg at an early stage ; and the larval period is accordingly to be traced back to stages that are still enclosed in the egg-mem- branes. In all cases the larval life may be said to begin when Fig. 102. — Larva of Brook Lamprey, Lampetra wilderi, before transformation, being as large as the adult, toothless, and more distinctly segmented. the following conditions have been fulfilled : the outward f onn of the larva must be well defined, separating it from the mass of yolk, its motions must be active, it must possess a continuous vertical fin-fold passing dorsally from the head region to the Fig. 103. — Common Eel. Angnilla chrisijpa Rafinesque. Family AngidUidce. body terminal, and thence ventrally as far as the yolk region; and the following structures, characteristic in outward appear- Embryology and Growth of Fishes 141 ance, must also be established: the sense-organs — eye, ear, and nose — mouth and anus, and one or more gill-clefts. Among the different groups of fishes the larval changes are brought about in widely different ways. These larval pecu- FiG. 104. — Larva of Common Eel, Anguilla chrisypa (Rafinesque), called Lepto cephotus grassii. (After Eigenmann.) liarities appear at first of far-reaching significance, but may ultimately be attributed, the writer believes, to changed environ- mental conditions, wherein one process may be lengthened, another shortened. So, too, the changes from one stage to another may occur \^'ith surprising abruptness. As a rule, it may be said the larval stage is of longest duration in the Cyclo- stomes, and thence diminished in length in sharks, lung-fishes. Ganoids, and Teleosts; in the last-named group a very much curtailed (i.e., precocious) larval life may often occur. The metamorphoses of the newly hatched Teleost must finally be reviewed; they are certainly the most varied and striking of all larval fishes, and, singularly enough, appear to be crowded into the briefest space of time ; the young fish, hatched often as early as on the fourth day, is then of the Fig. 10.5. — Larva of Sturgeon, Acipenser sturio (Linna?>is). (After Kupffer, per Dean.) most immature character; it is transparent, delicate, easily injured, inactive ; within a month, however, it may have assumed almost every detail of its mature form. A form hatching three millimeters in length mav acquire the adult form before it be- comes much longer than a centimeter." Peculiar Larval Forms. — The young fish usually differs from the adult mainly in size and proportions. The head is larger 142 Embryology and Growth of Fishes in the young, the fins are lower, the appendages less developed, and the body more slender in the young than in the adult. But to most of these distinctions there are numerous exceptions, and in some fish there is a change so marked as to be fairly called a metamorphosis. In such cases the young fish in its first condition is properly called a larva. The larva of the lamprey {Peiromyzou) is nearly blind and toothless, with slender head, and was long sup- posed to belong to a different genus {Ainnioca^tes) from the adult. The larva of sharks and rays, and also of Dipnoans and Crossopterygians, are provided with bushy external gills, Fig. 106.— Larva (called Tholichthys) of Chtrtodon sedentariiis (Poey). Cuba. (After Liitken,) Fig. 107. — Butterfly-fish, Chcvtodon capistratus Linnaeus. Jamaica. which disappear in the process of development. In most soft-rayed fishes the embryonic fringe which precedes the Embryology and Growth of Fishes 143 development of the vertical fins persists for a considerable time. In many young fishes, especially the Chatodontida and their allies (butterfly-fishes), the young fish has the head armed with broad plates fonned by the backward extension of certain membrane-bones. In other forms the bones of the head are in the young provided with long spines or with serrations, which vanish totally with age. Such a change is noticeable in the swordfish. In this species the production of the bones of the snout and upper jaw into a long bony sword, or weapon of offense, takes place only with age. The young fish have jaws more normally formed, and armed with ordinary teeth. In the head- fish {Mola mola) large changes take place in the course of growth, and the young have been taken for a different tvpe of fishes. Ampng certain soft- rayed fishes and eels the 3'oung is often developed in a pecu- liar way, being verv soft, translucent, or band-like, and formed of large or loosely aggregated cells. These pecu- liar organisms, long known as FlO- lOS.— Moto mola (LinniFus). Very leptocephah, have been shown ^^'^^' ''^^^^l «t^g«^ °f '^'^ ^l^T\ '"^"^ Centaurus ooops. (Alter Kichard.gon.) to be the normal young of fishes when mature very different. In the ladyfish (Albnla) Dr. Gilbert has shown, by a full series of specimens, that in their further growth these pellucid fishes shrink in size, acquiring greater compactness of body, until finally reaching about half their maximum length as larvje. i\fter this, acquiring essentially the form of the adult fish, they begin a process of regular growth. This leptocephalous condition is thought by Gunther to be due to arrest of growth in abnormal individuals, but this is not the case in Albula, and it is probably fully normal in the conger and other eels. In the surf -fishes the larvae have their vertical fins greatly elevated, much higher than in the adult, while the body is much more closely compressed. In the deal-fish (Tracliypterus) the form of the body and fins changes greatly with age, the body becoming more elongate and the fins lower. The differences be- tween different stages of the same fish seem greater than the 144 Embryology and Growth of Fishes Fig 109. — Main mnln (Linn;pus). Early larval stage, called Molacanthii~s num- mularis, f After Rvder.) Fig. 110. — Mola mola (Linnseus). Advanced larval stage. (After Ryder.) Embryology and Growth ot Fishes 145 differences between distinct species. In fact with this and with other forms which change with age, almost the only test of species is found in the count of the fin-rays. So far as known the numbers of these structures do not change. In the moon- fishes {CarangidcE) the changes with age are often very con- siderable. We copy Liitken's figure of the changes in the genus Selene (fig. 113). Similar changes take place in A/ec/?s, Vomer, and other genera. The Development of Flounders. — In the great group of flounders and soles {Heterosoniata) the body is greatly com- pressed and the species swim on one side or lie flat on the bot- tom, with one side uppermost. This upper side is colored like the bottom, sand-color, gray, or brown, while the lower side is mostly white. Both eyes are brought around to the upper side by a twisting of the cranium and a modification or division of the frontal bones. When the young flounder is hatched it is translucent and symmetrical, swimming vertically in the water, with one eye on either side of the head. After a little the young fish rests the ventral edge on the bottom. It then leans to one side, and as its position gradually becomes horizontal the eye on the lower side moves across with its frontal and other bones to the other side. In most species it passes directly under the first intemeurals of the dorsal fin. These changes are best observed in the genus Platophrys. Hybridism. — Hybridism is very rare among fishes in a state of nature. Two or three peculiar forms among the snappers {Lutianus) in Cuba seem fairly attributable to hybridism, the single specimen of each showing a remarkable mixture of char- acters belonging to two other common species. Hybrids may be readily made in -artificial impregnation among those fishes with which this process is practicable. Hybrids of the different salmon or trout usually share nearly equally the traits of the parent species. The Age of Fishes. — The age of fishes is seldom measured by a definite period of years. Most of them grow as long as they live, and apparently live until they fall victims to some stronger species. It is reputed that carp and pike have lived for a century, but the evidence needs verification. Some fishes, as the salmon of the Pacific {Oncorhynchus) , have a definite period 146 Embryology and Growth of Fishes of growth (usually four years) before spawning. After this act all the individuals die so far as known. In Japan and China Fin. 111. — Headfish (adult), Mnln mola (I.iiinanis). Virsrinia. the Ice-fish (Salaux), a very long, slender, transparent fish allied to the trout, may possibly be annual in habit, all the indi- viduals perhaps dying in the fall to be reproduced from eggs in the spring. But this alleged habit needs verification. Tenacity of Life. — Fishes dift'er greatly in tenacity of life. In general, fishes of the deep seas die at once if brought near the surface. This is due to the reduction of external pressure. The internal pressure forces the stomach out through the mouth and may burst the air-bladder and the large blood-vessels. Marine fishes usually die very soon after being drawn out from the sea. Embryology and Growth of Fishes 147 Some fresh-water fishes are very fragile, dying soon in the air, often with injured air-bladder or blood-vessels. They will die uiauiiiuijuu -z^ '^>mm -^-^ri Fig. 112. — Alhula vulpes (Linnaeus). Transformation of the Ladyfish, from the translucent, loosely compacted larva to the smaller, firm-bodied young. Gulf of California. (After Gilbert.) even sooner in foul water. Other fishes are extremely tena- cious of life. The mud-minnow (Umbra) is sometimes ploughed up in the half -dried mud of Wisconsin prairies. The related Alas- Embryology and Growth of Fishes 149 kan blackfish (Dallia) has been fed frozen to dogs, escaping alive from their stomachs after being thawed out. Many of the cat- fishes {SiluridcB) will live after lying half-dried in the dust for hours. The Dipnoan, Lepidosiren, lives in a ball of half-dried Fig. 114. — Ice-fish, Salanx hijalocranius Abbott, Family Salangidw. Tient- sin, China. mud during the arid season, and certain fishes, mostly Asiatic, belonging to the group Labyriiithici, with accessory breathing organ can long maintain themselves out of water. Among these is the China-fish (Opliioccphalns), often kept alive in the Chinese settlements in California and Hawaii. Some fishes can readily Fig. 11.5. — Alaska Blackfish, Dallia pectoralis (Bean). St. Michaels, Alaska. endure prolonged hunger, while others succumb as readily as a bird or a mammal. The Effects of Temperature on Fish. — The limits of distribu- tion of many fishes are marked by changes in temperature. Few marine fishes can endure any sudden or great change in this regard, although fresh-water fishes adapt themselves to the seasons. I have seen the cutlass-fish (Tnchutrus) benumbed with cold off the coast of Florida while the temperature was still above the frost-line. Those fishes which are tenacious of life and little sensitive to changes in climate and food are most successfully acclimatized or domesticated. The Chinese carp I CO Embryology and Growth of Fishes {Cypnmts carpio) and the Japanese goldfish (Carassius aitratns) have been naturahzed in almost all temperate and tropical river basins. AVithin the Umits of clear, cold waters most of the salmon and trout are readily transplanted. But some similar Fig. 116. — Snake-headed China-fish, Opiiioccphahis barca. India. (After Day.) fishes (as the grayling) are very sensitive to the least change in conditions. ]\lost of the catfish (Siliirida:) will thrive in almost any fresh waters except those which are very cold. Transportation of Fishes. — The eggs of species of salmon, placed in ice to retard their development, have been successfully trans- planted to great distances. The quinnat-salmon has been thus transferred from California to Australia. It has been found possible to stock rivers and lakes with desirable species, or to restock those in which the fish-supply has been partly destroyed, through the means of artificially impregnated eggs. The method still followed is said to be the discovery of J. L. Jacobi of Westphalia (about 1760). This process permits the saving of nearly all the eggs produced by the individuals taken. In a condition of nature very many of these eggs would be left unfertilized, or be destroyed by other animals. Fishes are readily kept in captivity in properly constructed aquaria. Un- less injured in capture or transportation, there are few species outside the deep seas' which cannot adapt themselves to life in a well-constructed aquarium. Reproduction of Lost Parts. — Fishes have little power to re- produce lost parts. Only the tips of fleshy structures are, thus restored after injury. Sometimes a fish in which the tail has been bitten off will survive the injury. The wound will heal, leaving the animal with a truncate body, fin-rays some- times arising from the scars. Embryology and Growth of Fishes 151 Monstrosities among Fishes. — Monstrosities are rare among fishes in a state of nature. Two-headed young are frequenth' seen at salmon-hatcheries, and other abnormally divided or united young are not infrequent. Among domesticated species monstrosities are not infrequent, and sometimes, as in the gold- FiG. 117. — Mon.strous Goldfish (bred in Japan), Carassius auraius (LinnaBus). (After Giinther.) fish, these have been perpetuated to become distinct breeds or races. Goldfishes with telescopic eyes and fantastic fins, and with the green coloration changed to orange, are reared in Japan, and are often seen in other countries. The carp has also been largely modified, the changes taking place chiefly in the scales. Some are naked (leather-carp), others (mirror-carp) have a few large scales arranged in series. c CHAPTER XI INSTINCTS, HABITS, AND ADAPTATIONS HE Habits of Fishes. — The habits of fishes can hardly be summarized in any simple mode of classification. In the usual course of fish-life the egg is laid in the early spring, in water shallower than that in which the parents spend their lives. In most cases it is hatched as the water grows warmer. The eggs of the members of the salmon and cod families are, however, mostly hatched in cooling waters. The young fish gathers with others of its species in little schools, feeds on smaller fishes of other species or of its own, grows and hanges until maturity, deposits its eggs, and the cycle of life begins again, while the old fish ultimately dies or is devoured. Irritability of Animals. — All animals, of whatever degree of organization, show in life the quality of irritability or response to external stimulus. Contact with external things produces some effect on each of them, and this effect is something more than the mere mechanical eft'ect on the matter of which the animal is composed. In the one-celled animals the functions of response to external stimulus are not localized. The}- are the property of any part of the protoplasm of the body. In the higher or many-celled animals each of these functions is spe- cialized and localized. A certain set of cells is set apart for each function, and each organ or series of cells is released from all functions save its own. Nerve-cells and Fibres. — In the development of the indi- vidual animal certain cells from the primitive external layer or ectoblast of the embryo are set apart to preside over the rela- tions of the creature to its environment. These cells are highly specialized, and while some of them are highly sensitive, others are adapted for carrying or transmitting the stimuli received by the sensitive cells, and still others have the function of receiv- Instincts, Habits, and Adaptations 153 ing sense-impressions and of translating them into impulses of motion. The nerve-cells are receivers of impressions. These are gathered together in nerve-masses or ganglia, the largest of these being known as the brain, the ganglia in general being known as nerve-centres. The nerves are of two classes. The one class, called sensory nerves, extends from the skin or other organ of sensation to the nerve-centre. The nerves of the other class, motor nerves, carry impulses to motion. The Brain, or Sensorium. — The brain or other nerve-centre sits in darkness, surrounded by a bony protecting box. To this main nerve-centre, or seiisoriuiii, come the nerves from all parts of the body that have sensation, the external skin as well as the special organs of sight, hearing, taste, and smell. With these come nerves bearing sensations of pain, temperature, muscular effort — all kinds of sensation which the brain can receive. These nerves are the sole sources of knowledge to any animal organism. Whatever idea its brain may contain must be built up through these nerve-impressions. The aggregate of these impressions constitute the world as the organism knows it. All sensation is related to action. If an organism is not to act, it cannot feel, and the intensity of its feeling is related to its power to act. Reflex Action. — These impressions brought to the brain by the sensory nerves represent in some degree the facts in the animal's environment. They teach something as to its food or its safety. The power of locomotion is characteristic of animals. If they move, their actions must depend on the indi- cations carried to the nerve-centre from the outside ; if they feed on living organisms, they must seek their food; if, as in many cases, other Hving organisms prey on them, they must bestir themselves to escape. The impulse of hunger on the one hand and of fear on the other are elemental. The sensorium receives an impression that food exists in a certain direction. At once an impulse to motion is sent out from it to the muscles necessary to move the body in that direction. In the higher animals these movements are more rapid and more exact. This is because organs of sease, muscles, nerve-fibres, and the ner\'e- cells are all alike highly speciaUzed. In the fish the sensation is slow, the muscular response sluggish, but the method remains the same. This is simple reflex action, an impulse from the I ^4 Instincts, Habits, and Adaptations en\aronment carried to the brain and then unconsciously re- flected back as motion. The impulse of fear is of the same nature. Reflex action is in general unconscious, but with ani- mals, as with man, it shades by degrees into conscious action, and into volition or action "done on purpose." Instinct. — Dift'erent animals show differences in method or degree of response to external influences. Fishes will pursue their prev, flee from a threatening motion, or disgorge sand or gravel swallowed with their food. Such peculiarities of dif- ferent forms of life constitute the basis of instinct. Instinct is automatic obedience to the demands of conditions external to the nervous system. As these conditions vary with each kind of animal, so must the demands vary, and from this arises the great variety actually seen in the instincts of different animals. As the demands of life become complex, so do the in- stincts. The greater the stress of environment, the more perfect the automatism, for impulses to safe action are necessarily ade- quate to the duty they have to perform. If the instinct were inadequate, the species would have become extinct. The fact that its individuals persist sliOAVS that they are provided with the instincts necessary to that end. Instinct differs from other allied forms of response to external condition in being hereditary, continuous from generation to generation. This sufiicientlv dis- tinguishes it from reason, but the line between instinct and reason and other forms of reflex action cannot be sharply drawn. It is not necessary to consider here the question of the origin of instincts. Some writers regard them as "inherited habits," while others, with apparent justice, doubt if mere habits or voluntary actions repeated till they become a "second nature" ever leave a trace upon heredity. Such investigators regard instinct as the natural survival of those methods of automatic response which were most useful to the life of the animal, the individual having less eft'ective methods of reflex action perish- ing, leaving no posterity. Classification of Instincts. —The instincts of fishes may be roughly classified as to their relation to the individual into egoistic and altruistic instincts. Egoistic instincts are those which concern chiefly the indi- vidual animal itself. To this class belong the instincts of feed- Instincts, Habits, and Adaptations 155 ing, those of self-defense and of strife, the instincts of play, the climatic instincts, and environmental instincts, those which direct the animal's mode of life. Altruistic instincts are those which relate to parenthood and those which are concerned with tlie mass of individuals of the same species. The latter may be called the social instincts. In the former class, the instincts of parenthood, may be included the instinct of courtship, reproduction, home-making, nest- building, and care for the young. Most of these are feebly developed among fishes. The instincts of feeding are primitively simple, growing com- plex through complex conditions. The fish seizes its prev by direct motion, bvit the conditions of life modify this simple action to a verv great degree. The instinct of self-defense is even more varied in its mani- festations. It may show itself either in the impulse to make war on an intruder or in the desire to flee from its enemies. Among carnivorous forms fierceness of demeanor serves at once in attack and in defense. Herbivorous fishes, as a rule, make little direct resistance to their enemies, depending rather on swiftness of movement, or in some cases on simple insignificance. To the latter cause the abundance of minnows, anchovies, and other small or feeble fishes may be attributed, for all are the prey of carnivorous fishes, which they far exceed in number. The instincts of courtship relate chiefly to the male, the female being more or less passi^'e. Among many flshes the male makes himself conspicuous in the breeding season, spread- ing his fins, intensifying his pigmented colors through mus- cular tension, all this supposedly to attract the attention of tlie female. That this purpose is actually accomplished by such display is not, however, easily proved. In the little brooks in spring, male minnows can be found with warts on the nose or head, with crimson pigment on the fins, or blue pigment on the back, or jet-black pigment all over the head, or with varied com- bination of all these. Their instinct is to display all these to the best advantage, even though the conspicuous hues lead to their own destruction. The movements of many migratory animals are mainly con- 156 Instincts, Habits, and Adaptations trolled by the impulse to reproduce. Some pelagic fishes, espe- cially flying fishes and fishes allied to the mackerel, swim long distances to a region favorable for a deposition of spawn. Some species are known only in the waters they make their breeding homes, the individuals being scattered through the wide seas at other times. RIanv fresh-water fishes, as trout, suckers, etc., for- sake the large streams in the spring, ascending the small brooks Fig. lis. — .laws of Xonichihj/s orocetia Jordan and Gilbert. Avhere they can rear their young in greater safety. Still others, known as anadromous fishes, feed and mature in the sea, but ascend the rivers as the impulse of reproduction grows strong. An account of these is given in a stibsequent paragraph. Variability of Instincts. — AVhen we study instincts of ani- mals with care and in detail, we find that their regularity is much less than has been supposed. There is as much variation in regard to instinct among individuals as there is with regard to other characters of the species. Some power of choice is found in almost every operation of instinct. Even the most machine-like instinct shows some degree of adaptability to new conditions. On the other hand, in no animal does reason show entire freedom from automatism or reflex action. "The funda- mental identity of instinct with intelligence," says Dr. Charles O. Whitman, "is shown in their dependence upon the same structural mechanism (the brain and nerves) and in their re- sponsive adaptabilitv." Adaptation to Environment. — In general food-securing struc- tures are connected with the mouth, or, as in the anglers, are hung as lures above it ; spines of offense and defense, electric organs, poison-glands, and the Hke are used in self -protection ; the bright nuptial colors and adornments of the breeding sea- son are doubtfully classed as useful in rivalry; the egg-sacs, nests, and other structures or habits may serve to defend the young, while skinny flaps, sand or weed-like markings, and Instincts, Habits, and Adaptations ^57 many other features of mimicry serve as concessions to the en- vironment. Each kind of fishes has its own ways of life, fitted to the con- ditions of environment. Some species lie on the bottom, flat, as a flounder, or prone on their lower fins, as a darter or a stone- roller. Some swim freely in the depths, others at the surface of the depths. Some leap out of the water from time to time, as the mullet (Mugil) or the tarpon (Tarpon atlanticus). Flight of Fishes. — Some fishes called the flying-fishes sail through the air with a grasshopper-like motion that closely imi- tates true flight. The long pectoral fins, wing-like in form, cannot, however, be flapped by the fish, the muscles serving Fig. 119 — Catalina Flying Fish, CypsUurus calijornicus (Cooper). Santa Barbara. only to expand or fold them. These fishes live in the open sea or open channel, swimming in large schools. The smaU species fly for a few feet only, the large ones for more than an eighth of a mile. These may rise flve to twenty feet above the water. The flight of one of the largest flying fishes {CypsUurus cali- jornicus) has been carefully studied by Dr. Charles H. Gilbert and the writer. The movements of the fish in the water are extremely rapid. The sole motive power is the action under the water of the strong tail. No force can be acquired while the fish is in the air. On rising from the water the movements ir8 Instincts, Habits, and Adaptations of the tail are continued until the whole body is out of the water. When the tail is in motion the pectorals seem in a state of rapid vibration. This is not produced by muscular action on the fins themselves. It is the body of the fish which vibrates, the pectorals projecting farthest having the greatest ampUtude of movement. While the tail is in the water the ventral fins are folded. AVhen the action of the tail ceases the pectorals and ventrals are spread out wide and held at rest. They are not used as true vings, but are held out firmly, acting as parachutes, enabHng the bodv to skim through the air. When the fish begins to fall the tail touches the water. As soon as it is in the water it begins its motion, and the body with the pectorals again begins to vibrate. The fish may, by skimming the Avater, regain motion once or twice, but it finally falls into the water with a splash. While in the air it suggests a large dragon-fly. ViCr. 120. — Sand-darter, Ammncriiptn clirrn (.Jordan and Jlerk). Dcs Momp.t: River The motion is verv swift, at first in a straight line, but is later defiected in a curve, the direction bearing little or no relation to that of the wind. When a vessel passes through a school of these fishes, they spring up before it, moving in all directions, as grasshoppers in a meadow. Quiescent Fishes. — Some fishes, as the lancelet, lie buried in the sand all their lives. Others, as the sand-darter (Avimocrvpta pellucida) and the hinalea (Jiilis gaimani), bury themselves in the sand at intervals or to escape from their enemies. Some live in the cavities of tunicates or sponges or holothurians or corals or oysters, often passing their whole lives inside the cavitv of one animal. Many others hide themselves in the interstices of kelp or seaweeds. Some eels coil themselves in the crevices of rocks or coral masses, striking at their prey like snakes. Some sea-horses cling by their tails to gulfweed or sea-wrack. Many Instincts, Habits, and Adaptations 159 little fishes {Gobiomorns, Carangiis, Psencs) cluster under the stinging tentacles of the Portuguese man-of-war or under ordinary •jellyfishes. In the tide-pools, whether rock, coral, or mud, in all regions multitudes of little fishes abound. As these localities are neglected by most collectors, they have proved of late years a most prolific source of new species. s^^^^Mv^^S?^'^' |5%a-^ii^-^ Fig. 121. — Pearl-fish, Fierosfer aciis (LinnEPus), issuing from a Hololhurian. Coast of Italy. (After Emery.) The tide-pools of Cuba, Key West, Cape Flattery, Sitka, Una- laska, Monterey, San Diego, ilazatlan, Hilo, Kailua and Waiana; in Hawaii, Apia and Pago-Pago in Samoa, the present writer has found peculiarly rich in rock-loving forms. Even richer are the pools of the promontories of Japan, Hakodate Head, Misaki, Awa, Izu, Waka, and Kagoshima, where a whole new fish fauna unknown to collectors in markets and sandy bays has been brought to light. Some of these rock-fishes are left buried in the rock weeds as the tide flows, lying quietly until it returns. Others cling to the rocks by ventral suckers, while still others depend for their safety on their powers of leaping or on their quickness of their movements in the water. Those of the latter class are often brilhantly colored, but the others mimic closely the alga? or the rocks. Some fishes live in the sea only, some prefer brackish water. Some are found only i6o Instincts, Habits, and Adaptations in the rivers, and a few pass more or less indiscriminately from one kind of water to another. Migratory Fishes. — The movements of migratory fishes are mainly controlled by the impulse of reproduction. Some pelagic fishes, especially those of the mackerel and flying-fish families, swim long distances to a region favorable for the deposition of spawn. Others pursue for equal distances the schools of men- haden or other fishes which ser\^e as their prey. Some species are known mainly in the waters they make their breeding homes, as in Cuba, Southern Cali- fornia, Hawaii, or Japan, the individuals being scattered at other times through the wide seas. Anadromous Fishes. — Many fresh-water fishes, as trout and suckers, forsake the large streams in the spring, ascending the small brooks where their young can be reared in greater safety. Still others, known as anadromous fishes, feed and mature in the sea, but ascend the rivers as the impulse of reproduction grows strong. Among such fishes are the salmon, shad, alewife, stur- geon, and striped bass in American waters. The most remark- able case of the anadromous instinct is found in the king salmon or qtunnat {Oncorhyiichns ischaivytsclia) of the Pacific Coast. This great fish spawns in November, at the age of four years and an average weight of twenty-two pounds. In the Columbia RiA-er it begins running with the spring freshets in March and April. It spends the whole summer, without feeding, in the ascent of the ri\'er. By autumn the individuals have reached the mountain streams of Idaho, greatly changed in appearance, Fig. 122. — Portuguese Man-of-war Fish, Gohiomorus gronovii. Family Siroinateidiie. o H td o' l62 Instincts, Habits, and Adaptations discolored, worn, and distorted. The male is humpbacked, with sunken scales, and greatly enlarged, hooked, bent, or twisted jaws, with enlarged dog-hke teeth. On reaching the spawning beds, which may be a thousand miles from the sea in the Columbia, over two thousand in the Yukon, the female de- posits her eggs in the gravel of some shallow' brook. The male covers them and scrapes the gravel over them. Then both male and female drift tail foremost helplessly down the stream ; none, so far as certainly known, ever survive the reproductible act. The same habits are found in the five other species of salmon in the Pacific, but in most cases the individuals do not start so early nor run so far. The blue-back salmon or redfish, however, does not fall far short in these regards. The salmon of the Atlantic has a similar habit, but the distance traveled is ever^'^vhere much less, and most of the hook-jawed males drop down to the sea and survive to repeat the acts of reproduction. Catadroiiioiis fishes, as the true eel (AugiiiUa), reverse this order, feeding in the rivers and brackish estuaries, apparently finding their usual spawning-ground in the sea. Pugnacity of Fishes. — Some fishes are A'ery pugnacious, al- ways ready for a quarrel with their own kind. The stickle- backs show this disposition, especially the males. In Hawaii the natives take advantage of this trait to catch the Uu {Myripristis Fig. 124. — Sqwaw-fish, Plijchocheilus orcgonensis (Richardson). Columbia River. munijan), a bright crimson-colored fish found in those waters. The species Uves in crevices m lava rocks. Catching a live one, the fishermen suspend it by a string in front of the rocks. It remains there with spread fins and flashing scales, and the others come out to fight it, when all are drawn to the surface bv a Instincts, Habits, and Adaptations 163 concealed net. Another decoy is substituted and the trick is repeated until the showy and quarrelsome fishes are all secured. In Siam the fighting-fish {Belta ptignax) is widely noted. The following account of this fish is given by Cantor ; * "When the fish is in a state of quiet, its dull colors pre- sent nothing remarkable; but if two be brought together, or if one sees its own image in a looking-glass, the httle creature becomes suddenly excited, the raised fins and the whole body shine with metallic colors of dazzling beauty, while the pro- jected gill membrane, waving hke a black frill round the throat, adds something of grotesqueness to the general appearance. In this state it makes repeated darts at its real or reflected antag- onist. But both, when taken out of each other's sight, instantly become quiet. The fishes were kept in glasses of water, fed with larvse of mosquitoes, and had thus lived for many months. The Siamese are as infatuated with the combats of these fish as the Malays are with their cock-fights, and stake on the issue considerable sums, and sometimes their own persons and fami- lies. The license to exhibit fish-fights is farmed, and brings a considerable annual revenue to the king of Siam. The species abounds in the rivulets at the foot of the hills of Penang. The inhabitants name it 'Pla-kat,' or the 'fighting-fish'; but the kind kept especially for fighting is an artificial variety culti- vated for the purpose." A related species is the equally famous tree-climber of India {Anabas scandens). In 1797 Lieutenant Daldorf describes his capture of an Anabas, five feet above the water, on the bark of a palm-tree. In the efi:ort to do this, the fish held on to the bark by its preopercular spines, bent its tail, inserted its anal spines, then pushing forward, repeated the operation. Fear and Anger in Fishes. — From an interesting paper by Surgeon Francis Day f on Fear and Anger in Fishes we may make the following extracts, slightly condensed and with a few slight corrections in nomenclature. The paper is written in amplifi- * Cantor, Catal. Malayan Fishes, 1850, p. 87. Bowring, Siam, p. 155, gives a similar account of the battles of these fishes. t Francis Day, on Fear and Anger in Fishes, Proc. Zool. Society, London, Feb. 19, 1878, pp. 214-221. Instincts, Habits, and Adaptations 165 cation of another by Rev. S. J. Whitmee, describing the behavior of aquarium fishes in Samoa. The means of expression in animals adverted to by Mr. Darwin (excluding those of the ears, which would be out of place in fishes) are: sounds, vocally or otherwise produced; the erection of dermal appendages under the influence of anger or terror, which last would be analogous to the erection of scales and fin-rays among fishes. Regarding special expressions, as those of joy, pain, astonishment, etc., we could hardly expect such so well marked in fishes as in some of the higher animals, in which the play of the features often aft'ords us an insight into their internal emotions. Eyes* destitute of movable eyelids, cheeks covered with scales, or the head enveloped in dermal plates, can scarcely mantle into a smile or expand into a broad grin. We possess, however, one very distinct expression in fishes which is absent or but slightly developed in most of the higher animals, namely, change of color. All are aware that when a fish sickens, its brilliant colors fade, but less so how its color may be augmented by anger, and a loss of it be occasioned by depression, the result of being vanquished by a foe. Some forms also emit sounds when actuated by terror, and perhaps in times of anger; but of this last I possess no decided proofs. Similar to the expression of anger in Betta is that of the three-spined stickleback (Gasterosteus aculeatus).] After a fight between two examples, according to Couch, "a strange altera- tion takes place almost immediately in the defeated party: his gallant bearing forsakes him; his gay colors fade away; he becomes again speckled and ugly; and he hides his disgrace amongst his peaceable companions who occupy together that part of the tub which their tyrants have not taken possession of; he is, moreover, for some time the constant object of his conqueror's persecution." Fear is shown by fish in many ways. There is not an angler unacquainted with the natural timidity of fishes, nor a keeper in * Couch (Illustrations, etc., p. 305) says: " The faculty of giving forth bril- liant light from the eyes is said to have been observed by fishermen in the blue shark, as in a cat." t Couch, " British Fishes," 1865, vol. iv. p. 172. I 66 Instincts, Habits, and Adaptations charge of a salmon-pass, who does not know how easy it is for poachers to deter the salmon from venturing along the path raised expressly for his use. Among the coral reefs of the Andaman Islands I found the little Chroiiiis Icpisurns abundant. As soon as the water was splashed they appeared to retire for safety to the branching coral, where no large fish could follow them; so frightened did they become that on an Andamanese diving from the side of the boat, they at once sought shelter in the coral, in which they remained until it was removed from the sea. In Burma I ob- ser\'ed, in 1S69, that when weirs are not allowed to stretch across the rivers (which Avould impede navigation), the open side as far as the bank is studded with reeds ; these, as the water passes over them, cause vibration, and occasion a curious sound alarming the fishes, which, crossing to the weired side of the river, become captured. Hooker, alluding to gulls, terns, AA'ild geese, and pelicans in the Ganges \'alley, observes: "These birds congregate by the sides of pools and beat the water with A'iolence. so as to scare the fish, which then become an easy pre}" — a fact which was, I believe, first indicated by Pallas during his residence on the banks of the Caspian Sea."* Fishes, under the influence of terror, dash about with their fins expanded, and often run into places which must destroy them. Thus droves and droves of sardines in the east, impelled by the terror of pursuing sharks, bomtos, and other voracious fishes, frequently throw them- selves on the shores in enormous quantities. Friar Odoric, who visited Ceylon about 1320, says: "There are fishes in those seas which come swimming towards the said country in such abundance, that for a great distance into the sea nothing can be seen but the backs of fishes, which, casting themselves on the shore, do suffer men for the space of three days to come, and to take as many of them as they please, and then they return again into the sea." f Pennant tells us that the river bullhead {Cotius gobio) "de- posits its spawn in a hole it forms in the gravel, and quits it with great reluctance." General Hardwicke tells how the * Himalayan Journals, vol. i. p. So. t Hakluyt, vol. ii. p. 37. Instincts, Habits, and Adaptations 167 gouramy {Osphromenus gonramy), in the Mauritius, forms a nest amongst the herbage growing in the shallow water in the sides of tanks. Here the parent continues to watch the place with the greatest vigilance, driving away any interloping fish. The amphibious walking-fish of Mysore (OpJiiocepJialus striatus) appears to make a nest very similar to that of the gouramy, and over it the male keeps guard ; but should he be killed or cap- tured, the vacant post is filled by his partner. (Colonel Puckle.) When very young the fishes keep with and are defended by their parents, but so soon as they are sufliciently strong to capture prey for themselves they are driven away to seek their own subsistence. (See Fishes of India, p. 362.) But it is not only these monogamous amphibious fishes which show an affec- tion for their eggs and also for their fry, but even the little Etroplus maculatus has been observed to be equally fond of its ova. "The eggs are not very numerous and are deposited in the mud at the bottom of the stream, and, when hatched, both parents guard the young for many days, vigorously attacking any large fish that passes near them." * Although the proceedings of the members of the marine and estuary genus of sea-cat {Tachysitnis) and its allies show not quite so distinctly signs of affection, still it must be a well-developed instinct which induces the male to carry about the eggs in its mouth until hatched, and to remove them in this manner when danger is imminent. I have taken the ova just ready for the young to come forth out of the mouth and fauces of the parent (male) fish; and in every animal dissected there was no trace of food in the intestinal tract. Calling the Fishes. — At many temples in India fishes are called to receive food by means of ringing bells or musical sounds. Carew, in Cornwall, is said to have called the gray mullet together by making a noise like chopping with a cleaver. Lacepede relates that some fishes, which had been kept in the basins out of the Tuileries for more than a century, would come when called by their names, and that in many parts of Ger- many trout, carp, and tench are summoned to their food by the sound of a bell. These instances are mostly due to the * Jerdon, " Madras Journal of Literature and Science," 1S49, P- i43- I 68 Instincts, Habits, and Adaptations fishes having learned by experience that on the hearing certain sounds they may expect food. But Lacepede mentions that some were able to distinguish their individual names; and the same occurs in India. Lieutenant Connolly* remarked upon seeing numerous fishes coming to the ghaut at Sidhnath to be fed when called; and on "expressing our admiration of the size of the fish, 'Wait,' said a bystander, 'until you have seen Raghu.' The Brahmin called out his name in a peculiar tone of voice ; but he would not hear. I threw in handful after hand- ful of ottah (flour) with the same success, and was just leaving the ghaut, despairing and doubting, when a loud plunge startled me. I thought somebody had jumped off the bastion of the ghaut into the river, but was soon undeceived by the general shout of 'Raghu, raghu,' and by the fishes, large and small, darting away in every direction. Raghu made two or three plunges, but was so quick in his motions that I was unable to guess at his species." [It may be said in relation to these stories quoted by Dr. Day, that they probably belong to the m^^tholog}' of fishes. It is very doubtful if fishes are able to make any such discrimination among sounds in the air.] Sounds of Fishes. — Pallcgoix states that in Siam the dog's- tongue (Cyiioglossiis) is a kind of sole; it attaches itself to the bottom of boats, and makes a sonorous noise, which is more musical when several are stuck to the same boat and act in concert (a'oI. i. p. 193). These noises can scarcely be due to anger or fear. Sir J. Bowring (vol. ii. p. 276) also remarks upon having heard this fish, "which sticks to the bottoms of the boats, and produces a sound something like that of a jew's- harp struck slowly, though sometimes it increases in loudness, so as to resemble the full tones and sound of an organ. My men have pointed me out a fish about four inches long as the author of the music." Some years since, at Madras, I (Dr. Day) obtained several specimens of a fresh-water Siluroid fish {Macroiics vittatns) which is termed the "fiddler" m ]\Iysore. I touched one which was on the wet ground, at which it appeared to become ver)^ irate, erecting its dorsal fin, making a noise resembling the buzzing of * " OLservations on the Past and Present Condition of Onjein," Journal of the Asiatic Society of Bengal, vi, p. S20. Instincts, Habits, and Adaptations 169 a bee. Having put some small carp into an aquarium contain- ing one of these fishes, it rushed at a srriall example, seized it by tlie middle of its back, and sliook it like a dog killing a rat' at this time its barbels were stiffened out laterally like a cat's whiskers. Many fish when captured make noises, perhaps due to terror. Thus the Caraiigiis hippos, Tctraodoii, and others grunt like a hog. Darwin (Nat. Joum., vol. vii) remarks on a catfish found in the Rio Parana, and called the armado, which is remark- able for a harsh grating noise when caught by hook and line; this noise can be distinctly heard when the fish is beneath the water. The cuckoo-gurnard (Trigla piiii) and the maigre {Pseiido- scicrna aqiiila) utter sounds when taken out of the water; and herrings, when the net has been drawn over them, have been observed to do the same: "this effect has been attributed to an escape of air from the air-bladder; but no air-bladder exists in the Cottns, which makes a similar noise." The lesser weaver (Tracliiims) buries itself in the loose soil at the bottom of the water, leaving only its head exposed, and awaits its prey. If touched, it strikes upAvards or sideways; and Pennant says it directs its blows with as much judgment as a fighting-cock. (Yarrell, vol. i. p. 26.) Fishermen assert that wounds from its anterior dorsal spines are more venomous than those caused by the spines on its gill-covers. As regards fighting, I should suppose that, unless some por- tion of the body is peculiarly adapted for this purpose, as the rostrum of the swordfish, or the spine on the .side of the tail in the lancet-fishes, we must look chiefly to the armature or covering of the jaws for weapons of offense. Lurking Fishes. — Mr. Whitmee supposes that most carniv- orous fish capture their prey by outswimming them ; but to this there are numerous exceptions; the angler or fishing- frog {Lophis piscatoriiis) , "while crouching close to the ground, by the action of its ventral and pectoral fins stirs up the sand and mud; hidden by the obscurity thus produced, it elevates its anterior dorsal spines, moves them in various directions by way of attraction as a bait, and the small fishes, approaching either to examine or to seize them, immmediately become the i^o Instincts, Habits, and Adaptations prey of the fisher." (Yarrell.) In India we find a fresh- water Siluroid (Chaca lophioides) which "eonceals itself among the mud, from which, by its lurid appearance and a number of loose filamentous substances on its skin, it is scarcely distinguishable ; and with an immense open mouth it is ready to seize any small prey that is passing along." (Ham. Bu- chanan.) In March, 1868, I obtained a fine example of Ich- ihyscopits lebeck (Fishes of India, p. 261), which I placed in water having a bed of mud; into this it rapidly worked itself, first depressing one side and then another, until only the top of its head and mouth remained above the mud, whilst a constant current was kept up through its gills. It made a noise, half snapping and half croaking, when removed from its native ele- ment. In the Royal Westminster Aquarium, says Dr. Day, is a live example of the electric eel {Electro pliorns electricns) which has in its electric organs the means of showing when it is affected by anger or terror. Some consider this curious prop- erty is for protection against alligators: it is certainly used against fishes for the purpose of obtaining food ; but when we remember how, when the Indians drive in horses and mules to the waters infested by the eels, they immediately attack them, we must admit that such cannot be for the purpose of preying upon them, but is due to anger or terror at being disturbed. (Day.) Carrying Eggs in the Mouth. — Many catfishes {SilnridcB) carry their eggs in the mouth until hatched. The first and most complete account of this habit of catfishes is that by Dr. Jef- fries Wyman, which he communicated to the Boston Society of Natural History at its meeting on September 15, 1857. In 1859, in a paper entitled "On Some Unusual Modes of Gesta- tion," Dr. Wyman published a full account of his observa- tions as follows, here quoted from a paper on Surinam fishes by Evermann and Goldsborough: "Among the Siluroid fishes of Guiana there are several species which, at certain seasons of the year, have their mouths and branchial cavities filled either with eggs or young, and, as is believed, for the purpose of incubation. My attention was first called to this singular habit by the late Dr. Francis W. Instincts, Habits, and Adaptations 171 Cragin, formerly United States consul at Paramaribo, Surinam. In a letter dated August, 1854, he says : " 'The eggs you will receive are from another fish. The dif- ferent fishermen have repeatedly assured me that these eggs in their nearly mature state are carried in the mouths of the parent till the young are relieved by the bursting of the sac. Do you either know or believe this to be so, and, if possible, where are the eggs conceived and how do they get into the mouth ? ' "In the month of April, 1857, on visiting the market of Paramaribo, I found that this statement, which at first seemed to be very improbable, was correct as to the existence of eggs in the mouths of several species of fish. In a tray of fish which a negro woman oft'ered for sale, I found the mouths of several filled with either eggs or young, and subsequently an abun- dance of opportunities occurred for repeating the observation. The kinds most commonly known to the colonists, especially to the negroes, are jara-bakka, njinge-njinge, kccpra, makrede, and one or two others, all belonging either to the genus Bagrtts or one nearly allied to it. The first two are quite common in the market, and I have seen many specimens of them ; for the last two I have the authority of negro fishermen, but have never seen them myself. The eggs in my collection are of three different sizes, indicating so many species, one of the three having been brought to me without the fish from which they were taken. "The eggs become quite large before they leave the ovaries, and are arranged in three zones corresponding to three succes- sive broods, and probably to be discharged in three successive years; the mature eggs of a jara-bakka 18 inches long measure three-fourths of an inch in diameter; those of the second zone, one-fourth; and those of the third are very minute, about one- sbcteenth of an inch. "A careful examination of eight specimens of njinge-njinge about 9 inches long gave the following results: "The eggs in all instances were carried in the mouths of the males. This protection, or gestation of the eggs by the males, corresponds with what has been long noticed with regard to other fishes, as, for example, Syngiiathus, where the mar- 172 Instincts, Habits, and Adaptations supial pouch for the eggs or young is found in the males only, and GasterostcHs, where the male constructs the nest and pro- tects the eggs during incubation from the voracity of the females. "In some individuals the eggs had been recently laid, in others they were hatched and the foetus had grown at the ex- pense of some other food than that derived from the yolk, as this last was not proportionally diminished in size, and the fa-tus weighed more than the undeveloped egg. The number of eggs contained in the mouth was between twenty and thirty. The mouth and branchial cavity were very much distended, rounding out and distorting the whole hyoid and branchiostegal region. Some of the eggs even partially protruded from the mouth. The ova were not bruised or torn as if they had been bitten or forcibly held by the teeth. In many instances the foetuses were still alive, though the parent had been dead for many liours. " \o young or eggs were found in the stomach, although the mouth was crammed to its fullest capacity. "The above observations apply to njinge-njinge. With re- gard to jarra-bakka, I had but few opportunities for dissection, but in several instances the same conditions of the eggs were noticed as stated above; and in one instance, besides some nearly mature foetuses contained in the mouth, two or three were squeezed apparently from the stomach, but not bearing any marks of violence or of the action of the gastric fluid. It is probable that these found their way into that last cavity after death, in consequence of the relaxation of the sphincter which separates the cavities of the mouth and the stomach. These facts lead to the conclusion that this is a mouth gestation, as the eggs are found there in all stages of development, and even for some time after they are hatched. "The question will be very naturally asked, how under such circumstances these fishes are abie to secure and swallow their food. I have made no observations bearing upon such a ques- tion. Unless the food consists of very minute particles it would seem necessary that during the time of feeding the eggs should be disgorged. If this supposition be correct, it would give a very probable explanation of the only fact which might be con- sidered at variance with the conclusion stated above, viz., that Instincts, Habits, and Adaptations 173 we have in these fishes a mouth gestation. In the mass of eggs with which the mouth is fiUecl I have occasionaUy found the eggs, rarely more than one or two, of another species. The only way in which their presence may be accounted for, it seems to me, is by the supposition that while feeding the eggs are disgorged, and as these fishes are gregarious in their habits, when the ova are recovered the stray eggs of another species may be introduced into the mouth among those which natu- rally belong there." One of the earliest accounts of this curious habit which we have seen is that by Dr. Gunther, referring to specimens of Tachysiiriis fissiis from Cayenne received from Prof. R. Owen: "These specimens having had the cavity of the mouth and of the gills extended in an extraordinary manner, I was induced to examine the cause of it, when, to my great surprise, I found them filled with about twenty eggs, rather larger than an ordi- nary pea, perfectly uninjured, and with the embryos in a for- ward state of development. The specimens are males, from 6 to 7 inches long, and in each the stomach was almost empty. "Although the eggs might have been put into the mouth of the fish by their captor, this does not appear probable. On the other hand, it is a well-known fact that the American Silu- roids take care of their progeny in various ways; and I have no doubt that in this species and in its allies the males carry the eggs in their mouths, depositing them in places of safety and removing them when they fear the approach of danger or disturbance." The Unsymmetrical Eyes of Flounders. — In the two great families of floimders and soles the head is unsymmetrically formed, the cranium being twisted and both eyes placed on the same side. The body is strongly compressed, and the side pos- sessing the eyes is uppermost in all the actions of the fish. This upper side, whether right or left, is colored, while the eye- less side is white or very nearly so. It is well known that in the very young flounder the body rests upright in the water. After a httle there is a tendency to turn to one side and the lower eye begins its migration to the other side, the interorbital bones or part of them moving before 174 Instincts, Habits, and Adaptations it. In most flounders the eye seems to move over the surface of the head, before the dorsal fin, or across the axil of its first ray. In the tropical genus Platophrys the movement of the eye is most easily followed, as the species reach a larger size than do most flounders before the change takes place. The lar\'a, while symmetrical, is in ah cases transparent. In a recent study of the migration of the eye in the winter Fig. 120. Fig. 127. Figs. 126, 127. — Larval stages of Platophrys podas, a flounder of the Mediterranean, showing the migration of the eye. (After Emery.) flounder {Psendoplenronectes ainericanus) Mr. Stephen R. Wil- liams reaches the following conclusions: ■ I. The young of Limanda ferniginea (the rusty dab) are probably in the larval stage at the same time as those of Pseu- dopleiironectes americanus (the winter flounder). 2. The recently hatched fish are symmetrical, except for the relative positions of the two optic nerves. 3. The first observed occurrence in preparation for meta- morphosis in P. americanus is the rapid resorption of the part of the supraorbital cartilage bar which lies in the path of the eye. 4. Correlated with this is an increase in distance between Instincts, Habits, and Adaptations '75 the eyes and the brain, caused by the growth of the facial carti- lages. 5. The migrating eye moves through an arc of about 120 degrees. Fig. 12s. — Platophrys lunatus (Linnteus), the Wide-eyed Flounder. Family Pleuronectidce. Cuba, (From nature by Mrs. H. C. Naish.) 6. The greater part of this rotation (three- fourths of it in P. americanns) is a rapid process, taking not more than three days. 7. The anterior ethmoidal region is not so strongly influ- enced by the twisting as the ocular region. 8. The location of the olfac- tory nerves (in the adult) shows Fig. 129. — Young Flounder, just that the morphological midline hatched, with symmetrical e)-es. , „ ^-u • ; iT-.^ 1 . (After S. R. Williams.) toUows the mterorbital septum. 9. The cartilage mass 'lying in the front part of the orbit of the adult eye is a separate anterior structure in the larva. 10. With unimportant differences, the process of meta- morphosis in the sinistral fish is parallel to that in the dextral fish. 11. The original location of the eye is indicated in the adult by the direction first taken, as they leave the brain, by those cranial nerves having to do wdth the transposed eye. 176 Instincts, Habits, and Adaptations 12. The only well-marked asymmetry in the adult brain is due to the much larger size of the olfactory nerve and lobe of the ocular side. 13. There is a perfect chiasma. 14. The optic nerve of the migrating eye is ^always anterior to that of the other eye. "The why of the peculiar metamorphosis of the Pleuro- ncctidcc is an tmsolved problem. The presence or absence of a swim-bladder can have nothing to do with the change of habit of the young flatfish, for P. aiucricaiins must lose its air- bladder before metamorphosis begins, since sections shoAved no Fig. 130. — Larval Flounder, Pseiidoplciironecfes omertcanus. (After S. R.Williams.) Fig. 131. — Larval Flounder, Pseudopleuronecle'i amcricanuf:. (AfterS. R. Williams.) evidence of it, whereas in Lopliopsctta niaciilata^ ' the window- pane flounder,' the air-sac can often be seen by the naked eye up to the time when the flsh assumes the adult coloration, and long after it has assumed the adult form. '' Cunningham has suggested that the weight of the fish acting upon the lower eye after the turning would press it toward the upper side out of the way. But in all probability the planktonic larva rests on the sea-bottom little if at all before metamorphosing. Those taken by ]\'Ir. AA^ilUams into the labora- tory showed in resting no preference for either side vmtil the eye was near the midline. Instincts, Habits, and Adaptations 177 " The fact that the change in all fishes is repeated during the development of each individual fish has been used to support the proposition that the fiatfishes as a family are a comparatively recent product. They are, on the .other hand, comparatively ancient. According to Zittel flatfishes of species referable to genera living at present, Rhombus (Botlius) and Solca, are found in the Eocene deposits. These two genera are notable in that Bothits is one of the least and Solca the most unsymmetrical of the Plciironcctidcc. ' ' The degree of asymmetry can be cor- related with the habit of the animal. Those r. , ,„ ,, iiG. 132. — iace view of fishes, such as the sole and shore-dwelling recently hatched Floun- flounders, which keep to the bottom are the der. (After s. R. Wil- most twisted representatives of the family, 'i^ms.) while the more freely swimming forms, like the sand-dab, summer flomider, and halibut, are more nearly symmetrical. Asymmetry must be of more advantage to those fishes which grub in the mud for their food than to those which capture other fishes; of the latter those which move with the greatest freedom are the most symmetrical. "This deviation from the bilateral condition must have come about either as a ' sport ' or by gradual modification of the adults. If by the latter method — the change proving to be ad- vantageous — selection favored its appearing earlier and earlier in ontogony, until it occurred in the stages of planktonic life. Metamorphosis at a stage earlier than this would be a distinct disadvantage, because of the lack of the customary planktonic food at the sea-bottom. At present some forms of selection are probably continually at work fixing the limit of the period of metamorphosis by the removal of those individuals which attempt the transformation at unsuitable epochs; for instance, at the time of hatching. That there are such individuals is shown by Fullarton, who figures a fish just hatched ' antici- pating the twisting and subsequent unequal development ex- hibited by the head of Pleuronectids.' Those larva:; which remain pelagic until better able to compete at the sea-bottom 178 Instincts, Habits, and Adaptations become the adults which fix the time of metamiorphosis on their progeny." (S. R. Williams.) So far as known to the writer, the metamorphosis of floun- ders ahvays occurs while the individual is still translucent and swimming at the surface of the sea before sinking to the bottom. CHAPTER XII ADAPTATIONS OF FISHES PINES of the Catfishes. — The catfishes or homed pouts (Siluridw) have a strong spine in the pectoral fin, one or both edges of this being jagged or serrated. This spine fits into a pecuHar joint and by means of a sHght downward or fonvard twistcan be set immovably. It can then be broken more easily than it can be depressed. A slight turn in the opposite direction releases the joint, a fact known to the fish and readily learned by the boy. The sharp spine inflicts a jagged wound. Fig. 133. — Mad-tom, Schilbeodes furioms Jordan and Meek. Showing the poisoned pectoral spine. Family Siluridce. Neuse River. Pelicans which have swallowed the catfish have been known to die of the wotmds inflicted by the fish's spine. When the catfish was first introduced into the Sacramento, according to Mr. Will S. Green, it caused the death of many of the native "Sacra- mento perch" {Archoplites interruptiis). This perch (or rather bass) fed on the jonxig catfish, and the latter erecting their pectoral spines in turn caused the death of the perch by tear- ing the walls of its stomach. In like manner the sharp dorsal and ventral spines of the sticklebacks have been known to cause the death of fishes who swallow them, and even of ducks. In Puget Sound the stickleback is often known as salmon-killer. 179 i8o Adaptations of Fishes Certain small catfishes known as stone-cats and mad-toms (Noturiis, Schilbeodcs), found in the rivers of the Southern and Middle Western States, are provided with special organs of offense. At the base of the pectoral spine, which is sometimes very jagged, is a structure supposed by Professor Cope to be a poison gland the nature of which has not yet been fully ascer- tained. The wounds made by these spines are exceedingly painful like those made by the sting of a wasp. They are, however, apparently not dangerous. Venomous Spines. — Many species of scorpion-fishes (Scor- pcrim, Syiiauccia, Pclor, Ptcrois, etc.), found in warm seas, as well as the European Aveavers {TracJiiiius), secrete poison '.f^ "'•^'•iiyf Fig. 134. — Black Nohu, or Poi.son-fish, Emmjjdrichthys ndcnniis .Jordan. A species with stinging spines, showing resemlilance to kimps of lava among which it lives. Family Scorpcmidw. From Tahiti. from under the skin of each dorsal spine. The wounds made by these spines are very exasperating, but are not often danger- ous. In some cases the glands producing these poisons form an oblong bag excreting a milky juice, and placed on the base of the spine. In Thalassopliryuc, a genus of toad-fishes of tropical America, is found the most perfect system of poison organs known among fishes. The spinous armature of the opercle and the two spines of the first dorsal fin constitute the weapons. The details are known from the dissections of Dr. Gunther. According to his * observations, the opercle in Tlialassopliryuc "is very narrow, * Gunther, Introd. to the Study of Fishes, p. 192. Adaptations of Fishes i8i vertically styliform and very mobile. It is armed behind with a spine eight lines long and of the same form as the hollow- venom -fang of a snake, being perforated at its base and at its extremity. A sac covering the base of the spine discharges its contents through the apertures and the canal in the interior of the spine. The structure of the dorsal spines is similar. There are no secretory glands imbedded in the membranes of the sacs and the fluid must be secreted by their mucous membrane. The sacs are without an external muscular layer and situated im- mediately below the thick, loose skin which envelops the spines at their extremity. The ejection of the poison into a living animal, therefore, can only be effected as in Synanceia, by the pressure to which the sac is subjected the moment the spine enters another body." The Lancet of the Surgeon-fish. — Some fishes defend themselves by lashing their enemies with their tails. In the tangs, or surgeon- fishes {Tenthis), the tail is provided with a formidable weapon, Fig. 1.3.5.— Brown Tang, Teuthi.'< bahianus (Ranzani). Tortugas, Florida. a knife-like spine, with the sharp edge directed forward. This spine when not in use slips forward into a sheath. The fish, when alive, cannot be handled without danger of a severe cut. In the related genera, this lancet is very much more blunt and immovable, degenerating at last into the rough spines of Balistapus or the hair-like prickles of Monacanthus. 82 Adaptations of Fishes Spines of the Sting-ray. — In all the large group of sting- rays the tail is provided with one or more large, stiff, barbed spines, which are used with great force by the animal, and are capable of piercing the leathery skin of the sting-ray itself. There is no evidence that these spines bear any specific poison, but the ragged wounds they make are always dangerous and often end in gangrene. It is possible that the mucus on the surface of the spine acts as a poison on the lacerated tissues, rendering the wound something very different from a simple cut. Protection Through Poisonous Flesh of Fishes. — In certain groups of fishes a strange form of self-protection is acquired by Fig. 1.36. — Common Filefish, Sicphanolepix hixpidus (Linna?us). Virginia. the presence in the body of poisonous alkaloids, by means of which the enemies of the species are destroyed in the death of the individual devoured. Such alkaloids are present in the globefishes {Tctraodontidcc), the filefishes {Monacaiithns), and in some related forms, while members of other groups (Batrachoididcr) are imder suspicion in this regard. The alkaloids produce a disease known as cigua- tera, characterized by paralysis and gastric derangements. Severe cases of ciguatera with men, as well as with lower animals, may end fatally in a short time. The flesh of the filefishes (Stepbanolepis tomentosus), which Adaptations of Fishes i8' the writer has tested, is very meager and bitter, having a de- cidedly offensive taste. It is suspected, probably justly, of be- ing poisonous. In the globefishes the flesh is always more or less poisonous, that of Tetraodon hispidns, called muki-muki, or death-fish, in Hawaii, is reputed as excessively so. The poi- sonous fishes have been lately studied in detail by Dr. Jacques Pellegrin, of the Museum d'Histoire Naturelle at Paris. He shows that any species of fish may be poisonous under certain circumstances, that under certain conditions certain species are poisonous, and that certain kinds are poisonous more or less at Fig. 137. — Tetraodon meleagns (Lacepede). Riu Kiu Islands. all times. The following account is condensed from Dr. Pelle- grin' s observations. The flesh of fishes soon undergoes decomposition in hot climates. The consumption of decayed fish may produce serious disorders, usually with symptoms of diarrhoea or erup- tion of the skin. There is in this case no specific poison, but the formation of leucomaines through the influence of bacteria. This may take place with other kinds of flesh, and is known as botolism, or allantiasis. For this disease, as produced by the flesh of fishes, Dr. Pellegrin suggests the name of ichthyosism. It is especially severe in certain very oily fishes, as the tunny, the anchovy, or the salmon. The flesh of these and other fishes occasionally produces similar disorders through mere indiges- tion. In this case the flesh undergoes decay in the stomach. 184 Adaptations of Fishes In certain groups (wrasse-fishes, parrot-fishes, etc.) in the tropics, individual fishes are sometimes rendered poisonous by feeding on poisonous mussels, holothurians, or possibly polyps, species which at certain times, and especially in their spawning season, develops alkaloids which themselves may cause cigua- tera. In this case it is usually the very old or large fishes which are liable to be infected. In some markets numerous species are excluded as suspicious for this reason. Such a list is in use in the fish-market of Havana, where the sale of certain species, elsewhere healthful, or at the most suspected, was rigidly Fig. 13S. — The Trigger-fish, Bahsies caroUnensis Ginelin. New 1 prohibited under the Spanish regime. A list of these suspicious fishes has been given by Prof. Poey. In many of the eels the serum of the blood is poisonous, but its venom is destroyed by the gastric juice, so that the flesh may be eaten with impunity, unless decay has set in. To eat too much of the tropical morays is to invite gastric troubles, but no true ciguatera. The true ciguatera is produced by a specific poisonous alkaloid. This is most developed in the globefishes or pufters (Tetraodon, Splieroidcs, Tropidichthvs, etc.). It is present in the filefishes (Moiiacantlms, Alutcra, etc.), prob- ably in some toadfishes (BatracJiotdes, etc.), and similar com- pounds are found in the flesh of sharks and especially in sharks' livers. Adaptations of Fishes 185 These alkaloids are most developed in the ovaries and testes, and in the spawning season. They are also found in the liver and sometimes elsewhere in the body. In many speeies other- wise innocuous, purgative alkaloids are developed in or about the eggs. Serious illness has been caused by eating the roe of the pike and the barbel. The poison is less virulent in the species which ascend the rivers. It is also much less developed in cooler waters. For this reason ciguatera is almost confined to the tropics. In Havana, Manila, and other tropical ports it is of frequent occurrence, while northward it is practically un- known as a disease requiring a special name or treatment. On the coast of Alaska, about Prince William Sound and Cook Inlet, Fig. 139. — Numbfish, Narcine hrasiliensis Henle, showing eleiiric cells. Pensacola, Florida. a fatal disease resembling ciguatera has been occasionally pro- duced by the eating of clams. The purpose of the alkaloids producing ciguatera is con- sidered by Dr. Pellegrin as protective, saving the species by the poisoning of its enemies. The sickness caused by the specific poison must be separated from that produced by ptomaines and leucomaines in decaying flesh or in the oil diffused through it. Poisonous bacteria may be destroyed by cooking, but the alka- loids which cause ciguatera are unaltered by heat. It is claimed in tropical regions that the germs of the bu- bonic plague may be carried through the mediation of fishes which feed on sewage. It is suggested by Dr. Charles B. Ash- i86 Adaptations of Fishes mead that leprosy may be so carried. It is further suggested tliat the custom of eating the flesh of fishes raw almost uni- versal in Japan, Hawaii, and other regions may be responsible for the spread of certain contagious diseases, in which the fish acts as an intemiediate host, much as certain mosquitoes spread the germs of malaria and yellow fever. Electric Fishes. — Several species of fishes possess the power to inflict electric shocks not unlike those of the Leyden jar. This is useful in stunning their prey and especially in confound- ing their enemies. In most cases these electric organs are evidently developed from muscular substance. Their action, which is largely voluntary, is in its nature like muscular action. The power is soon exhausted and must be restored by rest and food. The eft'ects of artificial stimulation and of poisons are parallel with the effect of similar agents on muscles. In the electric rays or torpedos (Narcobatidcr) the electric organs are large honeycomb-like structures, "vertical hexag- FiG. 140. — Electric Catfish, Torpedo rlecfriais (Gmelin). Congo River. (After Boulenger.) onal jirisms," upwards of 400 of them, at the base of the pec- toral fins. Each prism is filled "with a clear trembhng jeUy-like substance." These fishes give a shock which is communicable through a metallic conductor, as an iron spear or the handle of a knife. It produces a peculiar and disagreeable sensation not at all dangerous. It is said that this living battery shows all the known qualities of magnetism, rendering the needle mag- netic, decomposing chemical compounds, etc. In the Nile is an electric catfish {Tor pain dcctriciis) having similar powers. Its electric organ extends over the whole body, being thickest Ijclow. It consists of rhomboidal cells of a firm gelatinous substance. The electric eel {Electro pJiorns dcctriciis), the most powerful Adaptations of Fishes 187 of electric fishes, is not an eel, but allied rather to the sucker or carp. It is, however, eel-like in form and lives in rivers of Brazil and Guiana. The electric organs are in two pairs, one on the back of the tail, the other on the anal fin. These are made up of an enormous number of minute cells. In the electric eel, as in the other electric fishes, the nerves supplying these organs are much larger than those passing from the spinal cord for any other pur- pose. In all these cases closely related species show no trace of the electric powers. Dr. Gilbert has described the electric powers of species of star-gazer {Astroscopus y-grcccinn and A. zcpliyrcits), the electric cells lying under the naked skin of the top of the head. Electric power is ascribed to a species of cusk (Uropliycis rcgius), but this perhaps needs verification. Photophores or Luminous Organs. — ^lany fishes, cliiefly of the deep seas, develop organs for producing light. These are known as luminous organs, phosphorescent or- gans, 01 photophores. These are independently developed in four entirely unrelated groups of fishes. This differ- ence in origin is accomjianied by corresponding difference in structure. The best-known type is found in the Iniomi, including the lantern-fishes and their many relatives. These ma}^ have luminous spots, differ- w i88 Adaptations of Fishes entiated areas round or oblong which shine star-hke in the dark. These are usually symmetrieally placed on the sides of ""^-^^^^s^ Fig. 142.— Headlight Fish ^iSlinprora lucid i Goode and Bean. Gulf Stream. the body. They may have also luminous glands or diffuse areas which are luminous, but which do not show the specialized structure of the phosphorescent spots. These glands of similar nature to the spots are mostly on the head or tail. In one Fig. 143. — Coriinohjilnit; rcinhnrdii (Liitkon), showing luminous I:)ull5 (modified after Tjiitkcn). Family Ccratiidir. Deep .sea off Greenland. genus, .Ethoprora, the luminous snout is compared to the hcad- litjht f>f an engine. Adaptations of Fishes 189 Entirely different are the photophores in the midshipman or singing-fish {Porichthys), a genus of toad-fishes or Batra- choididcr. This species Hves near the shore and the luminous spots are outgrowths from pores of the lateral line. In one of the anglers (Corynolopliiis rciiihardti) the complex bait is said to be luminous, and luminous areas are said to occur on the belly of a very small shark of the deep seas of a d Fig. 144. — Etmopterus hicifer Jordan and Snyder. Mi aki, Japan. Japan (Etmoptenis lucifer). This phenomenon is now the sub- ject of study by one of the numerous pupils of Dr. Mitsukuri. The structures in CorynolopJiiis are practically unknown. Photophores in Iniomous Fishes. — In the Inioini the luminous organs have been the subject of an elaborate paper by Dr. R. von Lendenfeld (Deep-sea Fishes of the Challenger. Ap- pendix B). These he divides into ocellar organs of regular form or luminous spots, and irregular glandular organs or luminous areas. The ocellar spots may be on the scales of the lateral line or on other definite areas. They may be raised above the surface or sunk below it. They may be simple, with or without black pigment, or they may have within them a reflecting surface. They are best shown in the MyctopJiidcc and StomiatidcB, but are found in numerous other families in nearly all soft-rayed fishes of the deep sea. The glandular areas may be placed on the lower jaw, on the barbels, under the gill cover, on the suborbital or preorbital, on the tail, or they may be irregularly scattered. Those about the eye have usually the reflecting membrane. In all these structures, according to Dr. von Lendenfeld, the whole or part of the organ is glandular. The glandular part is at the base and the other structures are added distally. The primitive organ was a gland which produced luminous slime. I no Adaptations of Fishes To this in the process of specialization greater complexity has been added. The luminous organs of some fishes resemble the supposed original structure of the primitive photophore, though of course these cannot actually represent it. The simplest type of photophore now found is in Astroncsthes, in the form of irregular glandular luminous patches on the surface of the skin. Fig. 14.5. — Argyropclecus ulfersi Cuvier. Gulf Streani. There is no homology between the luminous organs of any insect and those of any fish. Photophores of Porichthys. — Entirely distinct in their origin are the luminous spots in the midshipman {Poriclitliys iwtatits), a shore fish of California. These have been described in detail by Dr. Charles Wilson Greene (late of Stanford University, now of the University of Missouri) in the Journal of Alorpliology, XV., p. 667. These are found on various parts of the body in connection with the mucous pores of the lateral lines and about the mucous pores of the head. The skin in Poriclitliys is naked, and the photophores arise from a modification of its epidermis. Each is spherical, shining white, and consists of four parts — the Adaptations of Fishes 1 9 1 lens, the gland, the reflector, and the pigment. As to its func- tion Prof. Greene observes: " I have kept specimens of Porichthys in aquaria at the Hop- kins Seaside Laboratory, and have made numerous observations on them with an effort to secure ocular proof of the phospho- rescence of the living active fish. The fish was observed in the dark when quiet and when violently excited, but, with a single exception, only negative results were obtained. Once a phosphorescent glow of scarcely perceptible intensity was observed when the fish was pressed against the side of the aquarium. Then, this is a shore fish and quite common, and one might stippose that so striking a phenomenon as it would present if these organs were phosphorescent in a small degree would be observed by ichthyologists in the field, or by fisher- men, but diligent inquiry reveals no such evidence. " Notwithstanding the fact that PoricJitliys has been observed to voluntarily exhibit only the trace of phosphorescence men- tioned above, still the organs which it possesses in such num- bers are beyond doubt true phosphorescent organs, as the fol- lowing observations will demonstrate. A live fish put into an aquarium of sea-water made alkaline with ammonia water ex- hibited a most brilliant glow along the location of the well- developed organs. Not only did the lines of organs shine forth, but the individual organs themselves were distinguish- able. The glow appeared after about five minutes, remained prominent for a few minutes, and then for twenty minutes gradually became weaker until it was scarcely perceptible. Rubbing the hand over the organs was followed always by a distinct increase in the phosphorescence. Pieces of the fish containing the organs taken five and six hours after the death of the animal became luminous upon treatment with ammonia water. " Electrical stimulation of the live fish was also tried with good success. The interrupted current from an induction coil was used, one electrode being fixed on the head over the brain or on the exposed spinal cord near the brain, and the other moved around on dift'erent parts of the body. No results fol- lowed relatively weak stimulation of the fish, although such currents produced violent contractions of the muscular system I02 Adaptations of Fishes of the body. But when a current strong enough to be quite painful to the hands while handling the electrodes was used then stimulation of the fish called forth a brilliant glow of light apparently from every weU-developed photophore. All the lines on the A-entral and lateral surfaces of the body glowed with a beautiful light, and continued to do so while the stimu- lation lasted. The single weU-developed organ just back of and below the eye was especially prominent. No luminosity was observed in the region of the dorsal organs previously de- scribed as rudimentarv in structure. I was also able to produce Fig. 146. — Luminous organs and lateral line of Jlid.shipman, Pnrichlluis notatux Girard. Family Batrachoididcc. Monterey, California. (After Greene.) the same effect by galvanic stimulation, rapidly making and breaking the current bv hand. "The light produced in Porichtliys was, as near as could be determined by direct observation, a white light. When pro- duced by electric stimulation it did not suddenly reach its maximal intensity, but came in quite graduallv and disappeared in the same way when the stimulation ceased. The light was not a strong one, only strong enough to enable one to quite easily distinguish the apparatus used in the experiment. " An important fact brought out by the above experiment is that an electrical stimulation strong enough to most violently stimulate the nervous system, as shown by the violent con- tractions of the muscular system, may still be too weak to produce phosphorescence. This fact gives a physiological con- Adaptations of Fishes 193 firmation of the morphological result stated above that no specific nerves are distributed to the phospliorescent organs. " I can explain the action of the electrical current in these experiments only on the supposition that it produces its effect by direct action on the gland. " The experiments just related were all tried on specimens of the fish taken from under the rocks where they were guarding Fig. 147. — Cross-section of a ventral phosphorescent organ of the Midshipman, Forichthys nolaius Girard. I, lens; gl, gland; r, reflector; W, l)lood; p, pig- ment. (.\ftpr Greene.) the young brood. Two specimens, however, taken by hooks from' the deeper water of Monterey Bay, could not be made to show phosphorescence either by electrical stimulation or by treatment with ammonia. These specimens did not have the high development of the system of mucous cells of the skin exhibited by the nesting fish. My observations were, how- IQA Adaptations of Fishes ever, not numerous enough to more than suggest the possibility of a seasonal high development of the phosphorescent organs. " Tavo of the most important parts of the organ have to do with the phvsical manipulation of Hght— the reflector and the lens, respectively. The property of the reflector needs no dis- cussion other than to call attention to its enormous deA^elop- ment. The lens cells are composed of a highly refractive sub- stance, and the part as a whole gives every evidence of hght refraction and condensation. The form of the lens gives a theoretical condensation of light at a very short focus. That snch is in reality the case, I have proved conclusively by e.^ami- nation of fresh material. If the fresh fish be exposed to du-ect Fii;. 148. — Section of the deeper portion of pho.sphorescent organ of Porichlhys iiotatus, higlily magnified. (After Greene.) sunlight, there is a reflected spot of intense light from each phosphorescent organ. This spot is constant in position with reference to the sun in whatever position the fish be turned and is lost if the lens be dissected away and onh^ the reflector left. With needles and a simple microscope it is comparatively easy to free the lens from the surrounding tissue and to examine it directly. When thus freed and examined in normal saline, I have found by rough estimates tliat it condenses sunlight to a bright point a distance back of the lens of from one-fourth to one-half its diameter. I regret that I have been unable to make precise phvsical developments. " The literature on the histological structure of known phos- phorescent organs of fishes is rather meager and unsatisfactory. Von Lendenfcld describes twelve classes of phosphorescent organs from deep-sea fishes collected by the Cliallcnger expe- Adaptations of Fishes 195 dition. All of these, however, are greater or less modifications of one type. This type includes, according to von Lendenfeld's views, three essential parts, i.e., a gland, phosphorescent cells, and a local gangHon. These parts may have added a reflector, a pigment layer, or both ; and all these may be simple or com- pounded in various ways, giving rise to the twelve classes. Blood-vessels and nerves are distributed to the glandular por- tion. Of the twelve classes direct ocular proof is given for one, i.e., ocellar organs of MyctopJiwin which were observed by Willemoes-Suhm at night to shine 'like a star in the net.' A-'' on Lendenfeld says that the gland produces a secretion, and he supposes the hght or phosphorescence to be produced either by the ' burning or consuming ' of this secretion by the phos- phorescent cells, or else by some substance produced by the phosphorescent cells. Furthermore, he says that the phos- phorescent cells act at the ' will of the fish' and are excited to action by the local ganglion. " Some of these statements and conclusions seem insufficiently grounded, as, for example, the supposed action of the phos- phorescent cells, and especially the control of the ganghon over them. In the first place, the relation between the ganglion and the central nervous system in the forms described by von Lendenfeld is very obscure, and the structure described as a ganglion, to judge from the figures and the text descriptions, may be wrongly identified. At least it is scarcely safe to ascribe ganglionic function to a group of adult cells so poorly preserved that only nuclei are to be distinguished. In the second place, no structural character is shown to belong to the ' phosphorescent cells ' by which they may take part in the process ascribed to them.* "The action of the organs described by him may be explained on other grounds, and entirely independent of the so-called 'gangHon cells' and of the 'phosphorescent cells.' * The cells which von Lendenfeld designates ' phosphorescent cells ' have as their peculiar characteristic a large, oval, highly refracting body imbedded in the protoplasm of the larger end of the clavate cells. These cells have nothing in common with the structure of the cells of the firefly known to be phos- phorescent in nature. In fact the true phosphorescent cells are more probably the ' gland-cells ' found in ten of the twelve classes of organs which he describes. ic)6 Adaptations of Fishes " Phosphorescence as appHed to the production of Hght by a living animal is, according to our present ideas, a chemical action, an oxidation process. The necessary conditions for producing it are two — an oxidizable substance that is luminous on oxida- tion, i.e., a photogenic substance on the one hand, and the pres- ence of free oxygen on the other. Every phosphorescent organ must have a mechanism for producing these two conditions; all other factors are only secondary and accessory. If the gland of a firefly can produce a substance that is oxidizable and luminous on oxidation, as shown as far back as 1828 by Farada}' and confirmed and extended recently by AVatase, it is conceivable, indeed probable, that phosphorescence in Myctoplimn and other deep-sea forms is produced in the same direct way, that is, by direct oxidation of the secretion of the gland found in each of at least ten of the twelve groups of organs described by von Lendenfeld. Free oxygen may be supplied directly from the blood in the capillaries distributed to the gland which he describes. The possibility of the regulation of the supply of blood carrying oxygen is analogous to what takes place in the firefly and is wholly adequate to account for any 'flashes of light' 'at the will of the fish.' " In the phosphorescent organs of PoriditJiys the only part the function of which cannot be explained on physical grounds is the group of cells called the gland. If the large granular cells of this portion of the structure produce a secretion, as seems probable from the character of the cells and their behavior toward reagents, and this substance be oxidizable and luminous in the presence of free oxygen, i.e., photogenic, then we have the conditions necessary for a Hght-producing organ. The numerous capillaries distributed to the gland will supply free oxygen sufficient to meet the needs of the case. Light pro- duced in the gland is ultimately all projected to the exterior, either directly from the luminous points in the gland or reflected outward by the reflector, the lens condensing all the rays into a definite pencil or slightly diverging cone. This explanation of the light-producing process rests on the assumption of a secreti/3n product with certain specific characters. But com- paring the organ with structures known to produce such a sub- stance, i.e., the glands of the firefly or the photospheres of Eu- Adaptations of Fishes i 97 phausia, it seems to me the assumption is not less certain than the assumption that twelve structures resembling each other in certain particulars have a common function to that proved for one only of the twelve. " I am inclined to the belief that whatever regulation of the action of the phosphorescent organ occurs is controlled by the regulation of the supply of free oxygen 'by the blood-stream flowing through the organ; but, however this may be, the essen- tial fact remains that the organs in PoriclitJiys are true phos- phorescent organs." (Greene.) Other species of PoriditJiys with similar photophores occur in Texas, Guiana, Panama, and Chile. The name midshipman alludes to these shining spots, compared to buttons. Globefishes. — The globefishes (Tetraodou, etc.) and the por- cupine-fishes have the surface defended by spines. These fishes have an additional safeguard through the instinct to swallow air. When one of these fishes is seriously disturbed it rises to Fig. 149. — Sucking-fi.sh, or Pegador, LepUcheneis naucratef (Linn;i'us>. ^'irginia. the surface, gulps air into a capacious sac, and then floats belly upward on the surface. It is thus protected from other fishes, although easily taken by man. The same habit appears in some of the frog-fishes (Anteniiarins) and in the Swell sharks (Ccpha- loscyllium) . The writer once hauled out a netful of globefishes (Tetrao- dou hisptdiis) from a Hawaiian lagoon. As they lay on the bank a dog came up and sniffed at them. As his nose touched them they swelled themselves up with air, becoming visibly two or three times as large as before. It is not often that the lower animals show surprise at natural phenomena, but the attitude of the dog left no question as to his feeling. Remoras.— The different species of Remora, or shark-suckers, fasten themselves to the surface of sharks or other fishes and are carried about by them often to great distances. These 198 Adaptations of Fishes fishes attach themselves by a large sucking-disk on the top of the head, which is a modified spinous dorsal fin. They do not harm the shark, except possibly to retard its motion. If the shark is caught and drawn out of the water, these fishes often instantly let go and plunge into the sea, swimming away with great celerity. Sucking-disks of Clingfishes. — Other fishes have sucking- disks differently made, by which they chng to rocks. In the gobies the united ventrals have some adhesive power. The blind goby {Typhlogobiits califoriiiensis) is said to adhere to rocks in dark holes by the ventral fins. In most gobies the adhesive power is slight. In the sea-snails {Li parididcc) and lumpfishes (Cvclopteridcc) the united ventral fins are modified into an Fig. 1.50. — Cliugfish, Cuiihirchus mirandricus (GirarJ). Monterey, California. elaborate circular sucking-disk. In the clingfishes (GobiesocidcF) the sucking-disk lies between the ventral fins and is made in part of modified folds of the naked skin. Some fishes creep OA'er the bottom, exploring it with their sensitive barbels, as the gurnard, surmullet, and goatfish. The suckers (Catostomits) test the bottom with their thick, sensitive lips, either puckered or papillose, feeding by suction. Lampreys and Hagfishes. — The lampreys suck the blood of other fishes to which they fasten themselves b}' their disk-like mouth armed with rasping teeth. The hagfishes {Myxiiic, Epiatiriiis) alone among fishes are truly parasitic. These fishes, worm-like in form, have round mouths, armed wdth strong hooked teeth. They fasten them- seh-es at the throats of large fishes, work their way into the muscle without tearing the skin, and finally once inside devour all the muscles of the fish, leaving the skin unbroken and the viscera undisturbed. These fishes become living hulks before Adaptations of Fishes 199 they die. If lifted out of the water, the slimy hagfish at once sHps out and swims quickly away. In gill-nets in Monterey Bay great mischief is done by hagfish (Polistotrema stonti). It is a curious fact that large numbers of hagfish eggs are taken from the stomachs of the male hagfish, which seems to be Fiu. 151. — Hagfish, Polistotrema stouii (Lockington). almost the only enemy of his own species, keeping the numbers in check. The Swordfishes. — In the swordfish and its relatives, the sail- fish and the spearfish, the bones of the anterior part of the head are grown together, making an efficient organ of attack. The sword of the swordfish, the most powerful of these fishes, has been known to pierce the long planks of boats, and it is supposed that the animal sometimes attacks the whale. But stories of this sort lack verification. The Paddle-fishes. — In the paddle-fishes {Polyodon spatula and Psephurus gladins) the snout is spread out forming a broad paddle or spatula. This the animal uses to stir up the mud on the bottoms of rivers, the small organisms contained in mud constituting food. Similar paddle-like projections are developed in certain deep-water Chimseras (Harrtottia, Rhino- chimcBra), and in the deep-sea shark, Mitsnkurina. The Sawfishes. — A certain genus of rays (Pristis, the saw- fish) and a genus of sharks {Pristiophorus, the saw-shark), pos- sess a similar spatula-shaped snout. But in these fishes the snout is provided on either side with enamelled teeth set in sockets and standing at right angles with the snout. The animal swims through schools of sardines and anchovies, strikes Adaptations of Fishes 201 right and left with this saw, destroying the small fishes, who thus become an easy prey. These fishes live in estuaries and river mouths, Pristis in tropical America and Gruinea, Pristi- ophorns in Japan and Australia. In the mythology of science, the Fig. 153. — Saw-shark, Pristiophorus ja-ponicvs Giinther. Specimen from Nagasaki. sawfish attacks the whale, but in fact the two animals never come within miles of each other, and the sawfish is an object of danger only to the tender fishes, the small fry of the sea. Peculiarties of Jaws and Teeth. — The jaws of fishes are sub- ject to a great variety of modifications. In some the bones are joined by distensible ligaments and the fish can swallow other fishes larger than itself. In other cases the jaws are excessi\-ely small and toothless, at the end of a long tube, so ineft'ective m appearance that it is a mar\'el that the fish can swallow any- thing at all. In the thread-eels (Nemichthys) the jaws are so recurA-ed that they cannot possibly meet, and in their great length seem worse than useless. In some species the knife-Hke canines of the lower jaw pierce through the substance of the upper. In four different and wholly unrelated groups of fishes the teeth are grown fast together, forming a homy beak like that of the parrot. These are the Chimasras, the globefishes (Tciroadoii), and their relatives, the parrot-fishes (Scants, etc.), and the stone-wall perch (OplegnatJms). The structure of the beak varies considerably in these four cases, in accord with the dif- ference in the origin of its structures. In the globefishes the 202 Adaptations of Fishes jaw-bones are fused together, and in the Chimasras they are solidly joined to the cranium itself. The Angler-fishes. — In the large group of angler-fishes the first spine of the dorsal fin is modified into a sort of bait to attract smaller fishes into the capacious mouth below. This structure is typical in the fishing-frog {Lophius), where the fleshy tip of this spine hangs over the great mouth, the huge fish lying on the bottom apparently inanimate as a stone. In other related fishes this spine has different forms, being often reduced to a vestige, of little value as a lure, but retained in accordance with the law of heredity. In a deep-sea angler the bait is enlarged, provided Avith fleshy streamers and a luminous body which serves to attract small fishes in the depths. The forms and uses of this spine in this group constitute a very suggestive chapter in the study of specialization and ulti- mate degradation, when the special function is not needed or becomes ineft'ective. Similar phases of excessive development and final degrada- tion may be found in almost every group in which abnormal stress has been laid on ,a particular organ. Thus the ventral fins, made into a large sucking-disk in Liparis, are lost alto- gether in Paralipans. The very large poisoned spines of Pterois become very short in Aploactis, the high dorsal spines of Citnla are lost in Alectis, and sometimes a very large organ dwindles to a very small one within the limits of the same genus. An example of this is seen in the poisoned pectoral spines of Scliilbeodcs. Relation of Number of Vertebrae to Temperature and the Strug- gle for Existence. — One of the most remarkable modifications of the skeleton of fishes is the progressive increase of the number of vertebrae as the forms become less specialized, and that this particular form of specialization is greatest at the equator.* It has been known for some years that in several groups of * See a more technical paper on this subject entitled " Relations of Tempera- ture to VertebrEe among Fishes," published in the Proceedings of the United States National Museum for 1S91, pp. 107-120. Still fuller details are given in a paper contained in the Wilder Quarter-Century Book, 1893. The substance IS also included in Chapter VIII of foot-notes to Evolution: D. Appleton & Co. Adaptations of Fishes 203 fishes (wrasse-fishes, flounders, and "rock-cod," for example) those species which inhabit northern waters have more vertebras than those living in the tropics. Certain arctic flounders, for example, have sixty vertebra; tropical flounders have, on the average, thirty. The significance of this fact is the problem at issue. In science it is assumed that all facts have significance, else they would not exist. It becomes necessary, then, to find out first just what the facts are in this regard. Going through the various groups of non-migratory marine fishes we find that such relations are common. In almost every group the number of vertebrce grows smaller as we approach the equator, and grows larger again as we pass into southern lati- tudes. Taking an average netful of fishes of difTerent kinds at different places along the coast, the variation would be evi- dent. At Point Barrow or Cape Farewell or North Cape a Fig. 1.54. — Skeleton of Pike, Esox lucius Linnaeus, a river fish with many vertebrae. seineful of fishes would perhaps average eighty vertebrae each, the body lengthened to make room for them; at Sitka or St. Johns or Bergen, perhaps sixty vertebrae; at San Francisco or New York or St. Malo, thirty-five; at JIazatlan or Pensacola or Naples, twenty-eight; and at Panama or Havana or Sierra Leone, twenty-five. Under the equator the usual number of vertebra in shore fishes is twenty-four. Outside tropical and semitropical waters this number is the exception. North of Cape Cod it is virtually unknown. Number of Vertebrae. — The numbers of vertebnc in different groups may be summarized as follows : Lancelets. — Among the lancelets the numbers of segments range from 50 to 80, there being no vertebnc. Lampreys. — In this group the number of segments ranges from 100 to 150. jQA Adaptations of Fishes Ehisiiiohranclis.— Among sharks and skates the usual num- ber of segments is from loo to 150 and upwards. In the extmct species as far as known the numbers are not materially different. Tlie Carboniferous genus, Plcnracanthus, has about 115 vertebrae. The CJninccras have similar numbers; Chimccra monstrosa has about 100 in the body and more than as many more in the fila- mentous tail. Cvdicc. — Palcrospoidyliis has about 85 vertebras. Arthrodircs. — There are about 100 vertebrae in Coccosteus. Dipnoans. — In Protopterits there are upwards of 100 vertebra, the last much reduced in size. Figures of Neoceraiodiis show about 80. Crossoptcrvgians. — Polyptcrus has 67 vertebrae; Erpetichthys, no; Uudina, about 85. Oauoids. — In this group the numbers are also large — 95 in Aiiiia, about 55 m the short-bodied Microdon. The Sturgeons all liaA'c more than 100 vertebrae. Soft-rayed Fishes. — Among the Telcostei, or bony fishes, those which first appear in geological history are the Isospondyli, the allies of the salmon and herring. These have all numerous A-ertel)r;e, small in size, and none of them in any notable degree modified or specialized. They abound in the depths of the ocean, but there are comparatively few of them in the tropics. The Salmonidic which inhabit the rivers and lakes of the north- ern zones have from 60 to 65 vertebrae. The Myciophidcr, Stomiatidcc, and other deep-sea forms have from 40 upwards in the few species in which the number has been counted. The group of Clitpeidcc is nearer the primitive stock of Isospondyli than the salmon are. This group is essentially northern in its distribution, but a considerable number of its members are found within the tropics. The common herring iClitpca Jiarangits) ranges farther into the arctic regions than any other. Its vertebras are 56 in number. In the shad {Alosa sapidissinia), a northern species which ascends the rivers, the same number is recorded. The sprat (Cliipea spratins) and sardine {Sardinia pilchardus), ranging farther south, have from 48 to 50, while in certain small herrings {Sardinella) which are strictly confined to tropical shores the number is but 40. Allied to the herring are the anchovies, mostly tropical. The northern- Adaptations of Fishes 205 most species, the common anchovy of Europe (Engraulis enchra- sicolus), has 46 vertebrse. A tropical species {Anchovia browni) has 41. There are, however, a few soft-rayed fishes confined to the tropical seas in which the numbers of vertebrje are still large, an exception to the general rule. Among these are Albula viilpes, the bonefish, with 70 vertebras, Elops saurits, the ten-pounder, with 72, the tarpon {Tarpon atlanticns), with about 50, and the milkfish, Chanos chanos, with 72. In a fossil Eocene herring from the Green River shales (Dip- lomystns) I count 40 vertebrae ; in a bass-like fish {Mioplosus) from the same locality 24 — these being the usual numbers in the present tropical members of these groups. The great family of Sihiridcc, or catfishes, is represented in all the fresh waters of temperate and tropical America, as well as in the warmer parts of the Old World. One division of the family, containing numerous species, abounds on the sandy shores of the tropical seas. The others are all fresh-water fishes. So far as the vertebrae in the Silnrida; have been examined, no conclusions can be drawn. The vertebra in the marine species range from 35 to 50 ; in the North American forms, from 37 to 45 ; and in the South American fresh-water species, where there is almost every imaginable variation in form and structure, the numbers range from 28 to 50 or more. The Cyprimdae (carp and minnows), confined to the fresh waters of the northern hemi- sphere, and their analogues, the Characinidcc of the rivers of South America and Africa, have also numerous vertebra, 36 to 50 in most cases. In general we may say of the soft-rayed fishes that very few of them are inhabitants of tropical shores. Of these few, some -which are closely related to northern forms have fewer vertebrae than their cold-water analogues. In the northern species, the fresh-water species, and the species found in the deep sea the number of vertebra; is always large, but the same is true of some of the tropical species also. The Flounders. — In the flounders, the halibut and its rela- tives, arctic genera (Hippoglossus and Atheresthes), have from 49 to 50 vertebras. The northern genera {Hippoglossoides, Lyopsetta, and Eopsetta) have from 43 to 45; the members of 2o6 Adaptations of Fishes a large semitropical genus {Paralichthys) of wide range have from 35 to 41 ; while the tropical forms have from 35 to 37. In the group of turbots and whiffs none of the species really belong to the northern fauna, and the range in numbers is from 35 to 43. The highest number, 43, is found in a deep-water species {Monolene), and the next, 40, in species (Lepidorhombus, Ortliopsetta) which extend their range well toward the north. Among the plaices, which are ah northern, the numbers range from 35 to 65, the higher numbers, 52, 58, 65, being found in species {Glyptocephalus) which inhabit considerable depths in the arctic seas. The lowest numbers (35) belong to shore species {PleuronichtJiys) which range well toward the south. Spiny-rayed Fishes. — Among the spiny-rayed fishes the facts are more striking. Of these, numerous families are chiefly or wholly confined to the tropics, and in the great majority of all the species the number of vertebra; is constantly 24, — 10 in the body and 14 in the tail (10+14). This is true of all or nearly all the Bcrycidcc, Scrranidcr, Sparidcr, Scicrnidcc, Chccto- doiitidcv, Hccmididcr, Gerrida;, Gobiidcr, AamtJiiiridcc, Mugilidcc, Spliyrccnidar, Mullidcr, Poniaceiitridar, etc. In some families in which the process of reduction has gone on to an extreme degree, as in certain PlcctognatJi fishes, there has been a still further reduction, the lowest number, 14, exist- ing in the short inflexible body of the trunkfish (Ostracion), in which the vertebral joints are movable only in the base of the tail. In all these forms the process of reduction of vertebrse has been accompanied by specialization in other respects. The range of distribution of these fishes is chiefly though not quite wholly confined to the tropics. Thus Batistes, the trigger-fish, has 17 vertebra;; Mouacantlms and Aliitcra, foolfishes, about 20; the trunkfish, Ostracion, 14; the puffers, Tetraodon and SpJier aides, 18; CantJiigastcr, 17; and the headfish, Mala, 17. Among the Pediculates, Malthe and Antcnnarius have 17 to 19 vertebrae, while in their near relatives, the anglers, Lophiidcc, the number varies with the latitude. Thus, in the northern angler, Lophins piscatoriiis, which is never found south of Cape Hatteras, there are 30 ver- tebras. In a similar species, inhabiting the north of Japan (Lo- phins litulon), there are 27. In another Japanese species, ranging Adaptations of Fishes 207 farther south, Lophtomus setigeriis, the vertebras are but ig. Yet in external appearance these two fishes are almost iden- tical. It is, however, a notable fact that some of the deep-water Pedictilates, or angling fishes, have the body very short and the number of vertebrae correspondingly reduced. Dibranclms atlan ticus, from a depth of 3600 fathoms, or more than 4 miles, has but 18 vertebrae, and others of its relatives in deep waters show also small numbers. These soft-bodied fishes are simply ani- mated mouths, with a feeble osseous structure, and they are perhaps recent offshoots from some stock which has extended its range from muddy bottom or from floating seaweed to the depths of the sea. A very few spiny-rayed families are wholly confined to the northern seas. One of the most notable of these is the family of viviparous surf -fishes (Einbiotocidcc), of which numerous species abound on the coasts of California and Japan, but which enter neither the waters of the frigid nor of the torrid zone. The surf- fishes have from 32 to 42 vertebrae, numbers which are never found among tropical fishes of similar appearance or relation- ship. The facts of variation with latitude were first noticed among the Labridcr. In the northern genera {Labrits, Tantoga, etc.) there are 38 to 41 vertebrae; in the semitropical genera iCreni- labrns, Bodianiis, etc.), 30 to ^3' in the tropical genera (Haii- chceres, XyricJithys, Thalassoma, etc.), usually 24. Equally striking are the facts in the great group of Pareio- plitcB, or mailed-cheek fishes, composed of numerous families, diverging from each other in various respects, but agreeing in certain peculiarities of the skeleton. Among these fishes the family most nearly related to ordi- nary fishes is that of the Scorpccnidcc iscorpion-fishes, etc.). This is a large family containing many species, fishes of local habits, swarming about the rocks at moderate depths in all zones. The species of the tropical genera have all 24 vertebrae. Those genera chiefly found in cooler waters, as in California, Japan, Chile, and the Cape of Good Hope, have in all their species 27 vertebra;, while in the arctic genera there are 31. Allied to the Scorpcenida:, but confined to the tropical or semitropical seas, are the Platycephalidce, with 27 vertebra;, and 2o8 Adaptations of Fishes the Cephalacanthidcc (flying gurnards), with but 22. In the deeper waters of the tropics are the Peristeditdcc , with 33 vertebrae, and extending farther north, belonging as much to the temper- ate as to the torrid zone, is the large family of the Triglida: (gur- nards) in which the vertebra; range from 25 to 38. The family of Agonidce (sea-poachers), with 36 to 40 vertebrae, is still more decidedly northern in its distribution. Wholly con- fined to northern waters is the great family of the Cottida (scul- pins), in which the A^ertebrae ascend from 30 to 50. Entirely polar and often in deep waters are the LiparididcE (sea-snails), an offshoot from the Cottida, with soft, limp bodies, and the vertebra 35 to 65. In these northern forms there are no scales, the spines in the fins ha^-e practically disappeared, and only tlie anatomy shows that they belong to the group of spiny-rayed fishes. In the Cydoptcrida: (lumpfishes), likewise largely arc- tic, the body becomes short and thick, the back-bone inflexible, ami the vertebras are again reduced to 28. In most cases, as the number of vertebrae increases, the body becomes propor- tionally elongate. As a result of this, the fishes of arctic waters are, for the most part, long and slender, and not a few of them approach the form of eels. In the tropics, however, while elongate fishes are common enough, most of them (always ex- cepting the eels) have the normal number of vertebrae, the greater length being due to the elongation of their individual vertebrae and not to their increase in number. Thus the very slender goby, Gohiondhts oceaniciis, has the same number (25) of vertebras as its thick-set relative Gobiits soporator or the chubby Lophogobins cypruioides. In the great group of blenny-like fishes the facts are equally striking. The arctic species are very slender in form as compared with the tropical blennies, and this fact, caused by a great increase in the number of their vertebra;, has led to the separation of the group into several famiUes. The tropical forms composing the family of Blenniidw have from 28 to 49 vertebra;, while in the arctic genera the numbers range from 75 to 100. Of the true Blenniidw, which are all tropical or semi-tropical, Blenniiis has 28 to 35 vertebrae; Salarias, 35 to 38; Lcpisoma, 34; Cliniis, 49; Cristiceps, 40. A fresh-water species of Cris- ticeps found in Australia has 46. Blennioid fishes in the arctic seas are Anarrhidias, with 76 vertebrae; Anarrhidithys , with Adaptations of Fishes 209 100 or more; Lunipenus, 79; Pholis, 85; Lycodes, 112; Gyninelis, 93. Lycodes and Gymnelis have lost all the dorsal spines. In the cod family {Gadidcc) the number of vertebrae is usu- ally about 50. The number is 51 in the codfish (Gadus callarias), 58 in the Siberian cod {Elegiims navaga), 54 in the haddock (Melanogrammus ceglifinus), 54 in the whiting (Merlangus mer- langiis), 54 in the coalfish {PollacJiins virens), 52 in the Alaskan coalfish {Theragra cJialcogramma) , 51 in the hake {Merlitcciiis merliiccius). In the burbot {Lota lota), the only fresh-water codfish, 59; in the deep-water ling (Molva niolva), 64; in the rocklings (Gaidropsarns), 47 to 49. Those few species found in the Mediterranean and the Gulf of Mexico have fewer fin-rays and probably fewer vertebrse than the others, but none of the family enter warm water, the southern species living at greater depths. In the deep-sea allies of the codfishes, the grenadiers or rat-tails (ALicrouridcr), the numbers range from 65 to 80. Fresh-water Fishes. — Of the families confined strictly to the fresh waters the great majority are among the soft-rayed or physostomous fishes, the allies of the salmon, pike, carp, and catfish. In all of these the vertebra are numerous. A few fresh-water families have their affinities entirely with the more specialized forms of the tropical seas. Of these the Centrarchidcc (comprising the American fresh-water sunfish and black bass) have on the average about 30 vertebra, the pirate perch 29, and the Percidcs, perch and darters, etc., 35 to 45, while the SerranidcB or sea-bass, the nearest marine relatives of all these, have constantly 24. The marine family of damsel-fishes (Poina- centrida) have 26 vertebras, while 30 to 40 vertebras usually exist in their fresh-water analogues (or possibly descendants), the Cichlido', of the rivers of South America and Africa. The sticklebacks {Gasterosteidce), a family of spiny fishes, confined to the rivers and seas of the north, have from 31 to 41 vertebras. Pelagic Fishes. — Among the free-swimming or migratory pelagic fishes, the number of vertebra; is usually greater than among their relatives of local habits. This fact is most evident among the scombriform fishes, the allies of the mackerel and tunny. All of these belong properly to the warm seas, and the reduction of the vertebra; in certain forms has no evident rela- 2IO Adaptations of Fishes tion to the temperature, though it seems to be related in some degree to the habits of the species. Perhaps the retention of many segments is connected with that strength and swiftness in the water for which the mackerels are preeminent. The variations in the number of vertebra; in this group led Dr. Gunther to divide it into two famihes, the CarangidcB and Scotnbrida\ The Carangidw or Pampanos are tropical shore fishes, local or migratory to a sUght degree. All these have from 24 to 26 vertebrte. In their pelagic relatives, the dolphins {Cory- phccna), there are from 30 to 33; in the opah (Laiuprts), 45; in Brama, 42; while the great mackerel family (ScombridcB) , all of whose members are more or less pelagic, have from 31 to 50. "The mackerel (Scomber scomhriis) has 31 vertebrse; the chub mackerel (Scomber japonicus), 31 ; the tunny (Thminus thynnus), 39; the long-finned albacore (Germo alalonga), 40; the bonito (Sarda sarda), 50; the Spanish mackerel (Sconiberomorns macii- latiis), 45. Other mackerel-like fishes are the cutlass-fishes (Trichiiiridcr), which approach the eels in form and in the reduction of the fins. In these the vertebra; are correspondingly numerous, the num- bers ranging from 100 to 160. Aplianopiis has loi vertebrse ; Lepidopns, 112; Trichnrns, 159. In apparent contradiction to this rule, however, the pelagic family of swordfishes (XipJiias), remotely allied to the mackerels, and with even greater powers of swimming, has the vertebrae in normal number, the common swordfish having but 24. The Eels. — The eels constitute a peculiar group of soft-rayed ancestry, in which everything else has been subordinated to muscularity and flexibility of body. The fins, girdles, gill- arches, scales, and membrane bones are all imperfectly developed or wanting. The eel is perhaps as far from the primitive stock as the most highly "ichthyized" fishes, but its progress has been of another character. The eel would be regarded in the ordinary sense as a degenerate type, for its bony structure is greatly simplified as compared with its ancestral forms, but in its eel-like qualities it is, however, greatly specialized. All the eels have vertebrae in great numbers. As the great majority of the species are tropical, and as the vertebrje in very few of Adaptations of Fishes 2 i i the deep-sea forms have been counted, no conclusions can be drawn as to the relation of their vertebra) to the tempera- ture. It is evident that the two families most decidedly tropical in their distribution, the morays {M ura-indcc) and the snake-eels {O.phidUhyida;) , have diverged farthest from the primitive stock. They are most "degenerate," as shown by the reduction of their skeleton. At the same time they are also most decidedly " eel- like," and in some respects, as in coloration, dentition, muscular development, most highly specialized. It is evident that the presence of numerous vertebral joints is essential to the sup- pleness of body which is the eel's chief source of power. So far as known the numbers of \'ertebr£e in eels range from 115 to 160, some of the deep-sea eels (Netniclithys, Nettastonia, GordiicJithys) having much higher numbers, in accord with their slender or whip-like forms. Among the morays, Miirccua Helena has 140; Gymnothorax meleagris, 120; G. nndidatiis, 130; G. moringa, 145; G. concolor, 136; Ediidna catenata, 116; E. nebulosa, 142; E. zebra, 135. In other families the true eel, Angnilla angnilla, has 115; the conger-eel, Leptocephalns conger, 156; and Mnrcenesox cinerens. Variations in Fin-rays. — In some families the number of rays in the dorsal and anal fins is dependent on the number of vertebrae. It is therefore subject to the same fluctuations. This relation is not strictly proportionate, for often a variable number of rays with their interspinal processes will be inter- posed between a pair of vertebra;. The myotomes or muscular bands on the sides are usually coincident with the number of vertebra. As, however, these and other characters are de- pendent on differences in vertebral segmentation, they bear the same relations to temperature or latitude that the vertebra; themselves sustain. Thus in the Scorpccmdcc, Sebastes, and Scbastolobns arctic genera have the dorsal rays xv, 13, the vertebra; 12-^19- The tropical genus Scorpcsna has the dorsal rays xii, 10, the ver- tebra; JO +14, while the genus Sebastodes of temperate waters has the intermediate numbers of dorsal rays xii, 12, and ver- tebra 1 2 -f- 1 .'^ . 2 1 2 Adaptations of Fishes Relation of Numbers to Conditions of Life. — Fresh-water fishes have in general more vertebrae than marine fishes of shallow waters. Pelagic fishes and deep-sea fishes have more than those which live along the shores, and more than localized or non-migratory forms. To each of these generalizations there are occasional partial exceptions, but not such as to invalidate the rule. The presence of large numbers of vertebras is noteworthy among those fishes which swim for long distances, as, for example, many of the mackerel family. Among such there is often found a high grade of muscular power, or even of activity, associated with a large number of vertebrae, these vertebrae being individ- ually small and little differentiated. For long-continued mus- cular action of a uniform kind there would be perhaps an ad- vantage in the low development of the vertebral column. For muscular alertness, moving short distances with great speed, the action of a fish constantly on its guard against enemies or watching for its prey, the advantage would be on the side of a few vertebras. There is often a correlation between the free- swimming habit and slenderness and suppleness of the body, which again is often dependent on an increase in numbers of the vertebrfil segments. These correlations appear as a dis- turbing element in the problem rather tham as furnishing a clew to its solution. In some groups of fresh-Avater fishes there is a reduction in number of vertebrae, not associated with any degree of speciaHzation of the indi\'idual bone, but correlated with simple reduction in size of body. This is apparently a phenomenon of degeneration, a survival of dwarfs, where con- ditions are unfavorable in full growth. All these effects should be referable to the same group of causes. They may, m fact, be combined in one statement. All other fishes now extant, as well as all fishes existing prior to Cretaceous times, have a larger number of vertebne than the marine shore fishes of the tropics of the present period. There is good reason to believe that in most groups of spiny-rayed fishes, those with the smaller number of segments are at once the most highly organized and the most primitive. This is true among the blennies, the sculpins, the flounders, the perches, and probably the labroid fishes as well. The present writer once Adaptations of Fishes 2 1 3 held the contrary view, that the forms with the higher numbers were primitive, but the evidence both from comparative anatomy and from palaeontology seems to indicate that among spiny- rayed fishes the forms most ancient, most generalized, and most synthetic are those with about 24 vertebrte. The soft-rayed fishes without exception show larger numbers, and these are still more primitive. This apparent contradiction is perhaps explained by Dr. Boulenger's suggestion that the prevalence of the same number, 24, in the vertebras of various families of spiny- rayed fishes is due to common descent, probably from Cretaceous berycoids having this number. In this theory, perches, spa- roids, carangoids, chjedodonts, labroids, parrot-fishes, gobies, flounders, and sculpins must be regarded as having a common origin from which all have diverged since Jurassic times. This view is not at all unlikely and is not inconsistent with the facts of palaeontology. If this be the case, the members of these and related families which have larger numbers of vertebra must have diverged from the primitive stock. The change has been one of degeneration, the individual vertebrae being reduced in size and complexitv, with a vegetative increase in their num- ber. At the same time, the body having the greater number of segments is the more flexible though the segments themselves are less specialized. The primitive forms live chiefly along tropical shores, while forms with increased numbers of vertebras are found in all other localities. This fact must be considered in any hypothesis as to the causes producing such changes. If the development of large numbers be a phase of degeneration the causes of such degeneration must be sought in the colder seas, in the rivers, and in the oceanic abysses. What have these waters in common that the coral reefs, the lava crags, and tide-pools of the tropics have not? It is certain that the possession of fewer vertebras indicates the higher rank, the greater specialization of patrts, even though the many vertebrae be a feature less primitive. The evolution of fishes is rarely a movement of progress toward complexity. The time movement in some groups is accompanied by degra- dation and loss of parts, by vegetative repetition of structures, and often by a movement from the fish-form toward the eel- 21 A Adaptations of Fishes form. Water life is less exacting than land life, having less vari- ation of conditions. It is, therefore, less effective in pushing Fig. 1.5.5. — Skeleton of Red Rockfish, Sehastodcs miniatus Jordan and Gilbert. California. forward the differentiation of parts. AVhen vertebrse are few in number each one is relatively larger, its structure is more complicated, its appendages larger and more useful, and the fins with which it is connected are better developed. In other words, the tropical fish is more intensely and compactly a fish, with a better fish equipment, and in all ways better fitted for the busi- ness of a fish, especially for that of a fish that stays at home. In the center of competition no species can aff'ord to be handicapped by a weak back-bone and redundant vertebrse. Fig. 156.— Skeleton of a spiny-rayed fish of the tropics, Holacanthus ciliaris (Linna-us) . Those who are thus weighted cannot hold their own. They must change or perish. The conditions most favorable to fish life are among the rocks Adaptations of Fishes 215 and reefs of the tropical seas. About the coral reefs is the center of fish competition. A coral archipelago is the Paris of fishes. In such regions is found the greatest variety of surroundings, and therefore the greatest number of possible adjustments. The struggle is between fish and fish, not between fishes and hard conditions of life. No form is excluded from the com- petition. Cold, darkness, and foul water do not shut out com- petitors, nor does any evil influence sap the strength. The heat of the tropics does not make the sea-water hot. It is never sultry or laden with malaria. From conditions otherwise favorable in arctic regions the majority of competitors are excluded by their inability to bear the cold. River life is life in isolation. To aquatic animals river life has the same limitations that island life has to the Fig. 1.57.— Skeleton of the Cow-fish, Lactophnjs tricornis (Linni-eus). animals of the land. The oceanic islands are far behind the continents in the process of evolution in so far as evolution im- plies specialization of parts. In a like manner the rivers are ages behind the seas, so far as progress is concerned, though through lack of competition the animals in isolation may be farthest from the original stock. Therefore the influences which serve as a whole to intensify fish life, to keep it up to its highest effectiveness, and which tend to rid the fish of every character or structure it cannot "use in its business," are most eft'ective along the shores of the tropics. One phase of this is the retention of low numbers of vertebrse, or, more accurately, the increase of stress on each individual bone. Conversely, as the causes of these changes are still in opera- 2i6 Adaptations of Fishes tion, we should find that in cold waters, deep waters, dark waters, fresh waters, and inclosed waters the strain would be less, the relapses to less complex organization more frequent, the numbers of vertebree would be larger, while the individual vertebrce would become smaller, less complete, and less per- fectly ossified. This in a general way is precisely what we do find in exam- ining the skeletons of a large variety of fishes. The cause of the increased numbers of vertebra; in cold waters or extratropical waters is as yet unknown. Several guesses have been made, but these can scarcely rise to the level of theories. To ascribe it to natural selection, as the present writer has done, is to do little more than to restate the problem. As a possible tentative hypothesis we may say that the retention of the higher primitive traits in the tropics is due to continuous selection, the testing of individuals by the greater variety of external conditions. The degeneration of extra- tropical fishes may be due to isolation and cessation or reversal of selection. Thus fresh waters, the arctic waters, the oceanic abysses are the "back woods" of fish life, localities favorable to the retention of primitive simplicity, ecpally favorable to subsequent degeneration. Practically all deep-sea fishes are degenerate descendants of shore fishes of various groups. Monot- ony and isolation permit or encourage degeneration of tvpe. Where the struggle for existence is most intense the higher struc- tures will be retained or developed. Among such facts as these derived from natural selection the cause of the relation of tem- perature to number of vertebrc-e must be sought. How the Cretaceous berycoids first acquired their few vertebra and the high degree of individual speciahzation of these structures we may not know. The character came with the thoracic ventrals with reduced number of rays, the ctenoid scales, the toothless maxillary, and other characters which have long persisted in their subsequent descendants. An exception to the general rule in regard to the number of vertebra; is found in the case of the eel. Eels inhabit nearly all seas, and everywhere they have many vertebrae. The eels of the tropics are at once more specialized and more degraded. They are better eels than those of northern regions, but, as the Adaptations of Fishes 2 1 7 eel is a degraded type, they have gone farther in the loss of structures in which this degradation consists. It is not well to push this analogy too far, but perhaps we can find in the comparison of the tropics and the cities some suggestion as to the development of the eel. In the city there is always a class which follows in no degree the general line of development. Its members are specialized in a wholly different way. By this means they take to them- selves a field which others have neglected, making up in low cunning what they lack in humanity or intelligence. Thus, among fishes, we have in the regions of closest compe- tition this degenerate and non-fishlike type, lurking in holes among the rocks, or creeping in the sand; thieves and scaven- gers among fishes. The eels thus fill a place otherwise left un- filled. In their way they are perfectly adapted to the lives they lead. A multiplicity of vertebral joints is useless to the tropical fish, but to the eel strength and suppleness are every- thing. No armature of fin or scale or bone is so desirable as its power of escaping through the smallest opening. With the elongation of the body and its increase in flexibility there is a tendency toward the loss of the paired fins, the ventrals going first, and aftenvards the pectorals. This tendency may be seen in many groups. Among recent fishes, the blennies, the eel- pouts, and the sea-snails furnish illustrative examples. Degeneration of Structures. — In the lancelet, which is a primitively simple organism, the various structures of the body are formed of simple tissues and in a very simple fashion. It is probable from the structure of each of these that it has never been very much more complex. As the individual develops in the process of growth each organ goes as it were straight to its final form and structure without metamorphosis or especial alterations by the way. When this type of development occurs, the organism belongs to a type which is primitively simple. But there are other forms which in their adult state appear feeble or simple, in which are found elements of organs of high complexity. Thus in the sea-snail (Liparis), small, weak, with feeble fins and flabby skin, we find the essential anatomy of the sculpin or the rose- fish. The organs of the latter are there, but each one is re- duced or degenerate, the bones as soft as membranes, the spines 2l8 Adaptations of Fishes obsolete or buried in the skin. Such a type is said to be de- generate. It is very different from one primitively simple, and Fig. 1.5s;. — Liparid, Crysto.lUas matsushimce (Jordan and Snyder). Family Lipa- rididce. Matsushima Bay, Japan. it is likely in its earlier stages of development to be more complex than when it is fully grown. In the evolution of groups of fishes it is a common feature that some one organ will be the center of a special stress, in view of some temporary importance of its function. By the Fig. 1,59. — Yellow-Ijacked Kockfish, ScbaxlichtJujs maligcr Jordan and Gilbert Sitka, Alaska. process of natural selection it will become highly developed and highly specialized. Some later changes in conditions will ren- Adaptations of Fishes 219 der this specialization useless or even harmful for at least a part of the species possessing it. The structure then undergoes de- generation, and in many cases it is brought to a lower estate than before the original changes. An example of this may be taken from the loricate or mailed-cheek fishes. One of the primitive members of this group is the rockfish known as priestfish (Sebas- todes mystiiius). In this fish the head is weakly armed, cov- ered with ordinary scales. A slight suggestion of cranial ridges and a slight prolongation of the third suborbital constitute the Fig. 160. — European Sculpin, Mi/oxoccphahm scorpius (lAnnxas). Gulf, Arctic America Cumljerland chief suggestions of its close affinity Avith the mailed-cheek fishes. In other rockfishes the cranial ridges grow higher and sharper. The third suborbital extends itself farther and wider. It becomes itself spincjus in still others. Finally it covers the whole cheek in a coat of mail. The head above becomes rough and homy and at last the whole body also is enclosed in a bony box. But while this specialization reaches an extraordinary degree in forms like Agoniis and Peristedion, it begins to abate with Coitus, and thence through Cottiiiiciilns, Psychrolutes, Li- paris, and the like, and the mailed cheek finds its final degra- dation in Parliparis. In this type no spines are present any- where, no hard bone, no trace of scales, of first dorsal, or of ventral fins, and in the soft, hmp structure covered with a fragile, scarf-like skin we find little suggestion of affinity with the strong rockfish or the rough-mailed Agoniis. Yet a study of the skeleton shows that all these loricate forms 220 Adaptations of Fishes constitute a continuous divergent series. The forms figured con- stitute only a few of the stages of speciahzation and degradation which the members of this group represent. Fk!. 161. — Sea-raven, Uemitripterus americanus (Gmelin). Halifax, Nova Scotia. Some of the features of the habits and development of certain fresh-water fishes are mentioned in the following chapter. The degeneration of the eye of the blind fishes of the caves Fig. 162. — Lumpfish, Cycloplervs hnnpus (Linnaeus). Eastport, Maine of the Mississippi Valley, Ainblyopsis, TypJiUchihys, and Trog- lichthys, have been very fully studied by Dr. Carl H. Eigen- mann. Adaptations of Fishes 221 According to his observations " The history of the eye of Amblyopsis spelceus may be divided into four periods: Fig. 16.3. — Sleek Sculpin, Psycltrolutes paradoxus (Giinther). Puget Sound. " (a) The first extends from the appearance of the eye till the embryo is 4.5 mm. long. This period is characterized by Fig. 164. — Agonoid-fish, Pa??a.sma barbata (Steindachner). Port Mulgrave, Alaska. a normal palingenic development, except that the cell division is retarded and there is very little growth. " (b) The second period extends till the fish is 10 mm. long. It is characterized by the direct development of the eye from Fig. 16.5. — Blind-fish of the Mammoth Cave, Amblyopsis spelwus (DeKay). Mammoth Cave,, Kentucky. the normal embryonic stage reached in the first period to the highest stage reached by the Amblyopsis eye. " (c) The third, from 10 mm. to about 80 or 100 mm. It is characterized by a number of changes which are positive as con- 222 Adaptations of Fishes trasted with degenerative. There are also distinct degenera- tive processes taking place during this period. " (d) The fourth, 80-100 mm. to death. It is characterized by degenerative processes only. "The eye of Amblyopsis appears at the same stage of growth as in normal fishes developing normal eyes. The eye grows but little after its appearance. "All the developmental processes are retarded and some of them give out prematurely. The most important, if the last, is the cell division and the accompanying growth that provide material for the eye. ' ' The lens appears at the normal time and in the normal way, but its cells never divide and never lose their embryonic char- acter. "The lens is first to show degenerative steps and disappears entirely before the fish is 10 mm. long. "The optic nerve appears shortly before the fish reaches 5 ^^^^^^^^^HHRSS^^^^^^^^^^ IVl '■' >! i^^^l fe^hjuj- 1 S-J^" Mk V, ^^^^l^^^^^^l ■i^^H Fig. 166. — Blind Brotula, Lucijvga siibterranea (Poey), .showing vi\-iparous haliit. Joignan Cave, Pinar del Rio, Cuba. Photographed by Dr. Eigenmann. mm. It does not increase in size with the growth of the fish and disappears in old age. "The scleral cartilages appear when the fish is 10 mm. long; they grow very slowly, possibly till old age. There is no constant ratio between the extent and degree of ontogenic and phylogenic degeneration. "The eye is approaching the vanishing point through the route indicated by the eye of TroglicJitliys rostally diflerent nature, and scarcely less bright than those of the male. Nuptial Coloration. — Nuptial colors are those which appear on the male in the breeding season only, the pigment after- wards vanishing, leaving the sexes essentially alike. Such colors are found on most of the minnows and dace (Cvpruuihr) of the rivers and to a less degree in some other fresh-water fishes, as the darters {Ethcostoiiiiiia:) and the trout. In the The Colors of Fishes 231 minnows of many species the male in spring has the skin charged with bright pigment, red, black, or bright silvery, for the most part, the black most often on the head, the red on the head and body, and the silvery on the tips of the fins. At the same time other markings are intensified, and in many species the head and sometimes the body and fins are covered with warty excrescences. These shades are most distinct on the most vigor- FiG. 170. — Blue-breasted Darter, Etheostoma cnmurum (Cope), the most brilliantly colored of American river-fishes. Cumberland Gap, Tennessee. ous males, and disappear with the warty excrescences after the fertilization of the eggs. Nuptial colors do not often appear among marine fishes, and in but few families are the sexes distinguishable by dift'erences in coloration. Recognition-marks. — Under the head of "recognition-marks" may be grouped a great variety of special markings, which may be conceived to aid the representatives of a given species to recognize each other. That they actually serve this purpose is a matter of theory, but the theory is plausible, and these mark- ings have much in common with the white tail feathers, scarlet crests, colored wing patches, and other markings regarded as recognition- marks among birds. Among these are ocelli, black- or blue-ringed with white or yellow, on various parts of the body ; black spots on the dorsal fin; black spots below or behind the eye; black, red, blue, or yellow spots variously placed ; cross-bars of red or black or green, with or without pale edges; a blood-red fin or a fin of shining blue among pale ones; a white edge to the tail; a yellow, blue, or red streamer to the dorsal fin, a black tip to the pectoral 232 The Colors of Fishes or ventral; a hidden spot of emerald in the mouth or in the axil; an almost endless variety of sharply defined markings, not directly protective, which serve as recognition-marks, if not to the fish itself, certainly to the naturalist who studies it. These marks shade off into an equally great variety for which we can devise no better name than "ornamentation." Some fishes are simply covered with brilliant spots or bars or reticu- lations, their nature and variety baffling description, while no useful purpose seems to be served by them, unless we stretch still more widely the convenient theory of recognition-marks. In many cases the markings change with age, certain bands, stripes, or ocelli being characteristic of the young and gradu- ally disappearing. In such cases the same marks will be found permanent in some related species of less dift'erentiated colora- tion. In such cases it is safe to regard them as ancestral. In case of markings on the fins and of elaborate ornamenta- tion in general, it is best defined in the oldest and most vigorous individuals, becoming intensified by degrees. The most bril- liantl}' colored fishes are found about the coral reefs. Here may be found species of which the groimd color is the most intense blue, others are crimson, grass-green, lemon-yellow, jet-black, and each with a great variety of contrasted mark- ings. The frontispiece of this volume shows a series of such fishes drawn from nature from specimens taken in pools of the great coral reef of Apia in Samoa. These colors are not pro- tective. The coral masses are mostly plain gray, and the fishes which lie on the bottom are plain gray also. Nothing could be more brihiant or varied than the hues of the free-swimming fishes. What their cause or purpose may be, it is impossible to say. It is certain that their intense activity and the ease with which they can seek shelter in the coral masses enable them to , defy their enemies. Nature seems to riot in bright colors where her creatures are not destroyed by their presence. Intensity of Coloration. — In general, coloration is most in- tense and varied in certain families of the tropical shores, and especially about coral reefs. But in brilliancy of individual markings some fresh-water fishes are scarcely less notable, especially the darters (Etheostomiua) and sunfishes (Centra)- cliida') of the streams of eastern North America. The brio-ht The Colors of Fishes 233 3 a I w 3 p p ta rtt s 3 a. 234 The Colors of Fishes The Colors of Fishes 235 hues of these fresh-water fishes are, however, more or less con- cealed in the water by the olivaceous markings and dark blotches of the upper parts. Coral-reef Fishes. — The brilliantly colored fishes of the trop- ical reefs seem, as already stated, to have no need of pro- tective coloration. They save themselves from their enemies in most cases by excessive alertness and activity {Chatodon, Pomacentrns), or else by burying themselves m coral sand ( fulis gaimard), a habit more frequent than has been suspected. Every large mass of branching coral is full of lurking fishes, some of them often most brilliantly colored. Fading of Pigments in Spirits. — In the preservation of speci- mens most red and blue pigments fade to whitish, and it requires considerable care to interpret the traces which may be left of red bands or blue markings. Yet some blue pigments are abso- lutely permanent, and occasionally blood-red pigments persist through all conditions. Black pigment seldom changes in spirits, and olivaceous markings simply fade a little without material alteration. It is an important part of the work of the systematic ichthyologist to lea^ to interpret the traces of the faded pigment left on specimens he may have occasion to ex- amine. In such cases it is more important to trace the mark- ings than to restore the ground color, as the ground color is at once more variable with individuals and more constant in large groups. Variation in Pattern. — Occasionally, however, a species is found in which, other characters being constant, both ground color and markings are subject to a remarkable range of varia- tion. In such cases the actual unity of the species is open to serious question. The most remarkable case of such variation known is found in a West Indian fish, the vaca, which bears the incongruous name of Hypoplectrus unicolor. In the typical vaca the body is orange with black marks and blue lines, the fins checkered with orange and blue. In a second form the body is violet, barred with black, the head with blue spots and bands. In another form the blue on the head is wantmg. In stiU another the body is yellow and black, with blue on the head only. In others the fins are plain orange, without checks, and the body yehow, with or without blue stripes and spots, and 236 The Colors of Fishes sometimes with spots of black or violet. In still others the body may be pink or brown, or violet-black, the fins all yellow, part black or all black. Finally, there are forms deep indigo-blue in color everywhere, with cross bands of indigo-black, and these again may have bars of deeper blue on the head or may lack these altogether. I find no difference among these fishes ex- cept in color, and no way of accounting for the differences in this regard. Certain species of puffer {Tetraodon setosus, of Panama, and Tctraodoi! nigropitiictatns, of Polynesia) show similar remark- able variations, being dark gray with white spots, but varying to indigo-blue, lemon-yellow, or sometimes having coarse blotches of either. Lemon-yellow varieties of several species are known, and these may be due to a failure of pigment, a sort of semi- albinism. True albinos, individuals wholly without pigment, are rare among fishes. In some cases the markings, commonly black, will be replaced by a deep crimson which does not fade in alcohol. This change happens most frequently among the Scorpccnidcc. i\n example of this is shown in the frontispiece of Volume II of this work. The Japanese okose or poison- fish (Iiiiiincits) is black and gray about lava-rocks. In deeper water among red alg:e it is bright crimson, the color not fading in spirits, the markings remaining the same. In still deeper water it is lemon-yellow. i--- CHAPTER XIV THE GEOGRAPHICx\L DISTRIBUTION OF FISHES OOGEOGRAPHY.— Under the head of distribution we consider the facts of the actual location of species of organisms on the surface of the earth and the laws by whicli their location is governed. This constitutes the subject-matter of the science of zoogeograpliy. In physical geography we maj' prepare maps of the earth or of any part of it, these bringing to prominence the physical features of its surface. Such maps show here a sea, there a plateau, here a mountain chain, there a desert, a prairie, a peninsula, or an island. In political geography the maps show their physical features of the earth as related to the people who inhabit them and the states or powers which receive or claim their allegiance. In zoogeography the realms of the earth are con- sidered in relation to the species or tribes of animals which inhabit them. Thus series of maps could be drawn representing those parts of North America in which catfishes or trout or sunfishes are found in the streams. In like manner the distri- bution of any particular fish as the muskallonge or the yellow perch could be shown on the map. The details of such a map are very instructive, and their consideration at once raises a series of questions as to the cause behind each fact. In science it must be supposed that no fact is arbitrary or meaningless. In the case of fishes the details of the method of diffusion of species afford matters of deep interest. These are considered in a subsequent chapter. The dispersion of animals may be described as a matter of space and time, the movement being continuous but modified by barriers and other codnitions of environment. The ten- dency of recent studies in zoogeography has been to consider 237 238 The Geographical Distribution of Fishes the facts of present distribution as the resuh of conditions in the past, thus correlating our present knowledge with the past relations of land and water as shown through paleontology. Dr. A. E. Ortmann weU observes that "x\ny division of the earth's surface into zoogeographical regions which starts exclusively from the present distribution of animals without considering its origin must always be unsatisfactory." We must therefore consider the coast-lines and barriers of Tertiary and earUer times as well as those of to-day to understand the present distribution of fishes. General Laws of Distribution. — The general laws governing the distribution of all animals are reducible to three very simple propositions. Each species of animal is found in every part of the earth having conditions suitable for its maintenance, unless (a) Its individuals have been unable to reach this region through barriers of some sort; or, (b) Having reached it, the species is unable to maintain itself, through lack of capacity for adaptation, through severity of competition with other forms, or through destructive condi- tions of environment ; or else, (c) Having entered and maintained itself, it has become so altered in the process of adaptation as to become a species dis- tinct from the original type. Species Absent through Barriers. — The absence from the Jap- anese fauna of most European or American species comes under the first head. The pike has never reached the Japanese lakes, though the shade of the-lotus leaf in the many clear ponds would suit its habits exactly. The grunt * and porgies t of our West Indian waters have failed to cross the ocean and there- fore have no descendants in Europe or Asia. Species Absent through Failure to Maintain Foothold. — Of species under (6), those who have crossed the seas and not found lodgement, we have, in the nature of things, no record. Of the existence of multitudes of estrays we have abundant evidence. In the Gulf Stream off Cape Cod are every year taken many young fishes belonging to species at home in the Bahamas and which find no permanent place in the New England fauna. In * nonunion. ■\ Calamus. The Geographical Distribution of Fishes 239 like fashion, young fishes from the tropics drift northward in the Kuro Shiwo to the coasts of Japan, but never finchng a per- manent breeding-place and never joining the ranks of the Japa- nese fishes. But to this there have been, and will be, occasional exceptions. Now and then one among thousands finds per- manent lodgement, and by such means a species from another region will be added to the fauna. The rest disappear and leave no trace. A knowledge of these currents and their in- fluence is eventual to any detailed study of the dispersion of fishes. The occurrence of the young of many shore fishes of the Hawaiian Islands as drifting plankton at a considerable distance from the shores has been lately discovered by Dr. Gilbert. Each island is, in a sense, a "sphere of influence," affecting the fatina of neighboring regions. Species Changed through Natural Selection. — In the third class, that of species changed in the process of adaptation, most insular forms belong. As a matter of fact, at some time or another almost every species must be in this category, for isola- tion is a source of the most potent elements in the initiation and intensiflcation of the minor dift'erences which separate re- lated species. It is not the preservation of the most useful features, but of those which actually existed in the ancestral individuals, which distinguish such species. Natural selection must include not only the process of the survival of the fittest, but also the results of the survival of the existing. This means the preservation through heredity of the traits not of the species alone, but those of the actual individuals set apart to be the first in the line of descent in a new environment. In hosts of cases the persistence of characters rests not on any special use- fulness or fitness, but on the fact that individuals possessing these characters have, at one time or another, invaded a cer- tain area and populated it. The principle of utility explains survivals among competing structures. It rarely accounts for qualities associated with geographical distribution. Extinction of Species. — The extinction of species may be noted here in connection with their extension of range. Prof. Herbert Osborn has recognized five different types of elimina- tion. 240 The Geographical Distribution of Fishes I. That extinction which comes from modification or pro- gressive evolution, a relegation to the past as the result of a transmutation into more advanced forms. 2. Extinction from changes of physical environment which outrun the powers of adaptation. 3. The extinction which results from competition. 4. The extinction from extreme specialization and limitation to special conditions the loss of which means extinction. 5. Extinction as a result of exhaustion. As an illustration of No. i, we may take almost any species which has a cognate species on the further side of some barrier or in the tertiary seas. Thus the trout of the Twin Lakes in Colorado has acquired its present characters in the place of those brought into the lake by its actual ancestors. No. 2 is illustrated by the disappearance of East Indian types (Zandns, Platax, Toxotes, etc.) in Italy at the end of the Eocene, perhaps for climatic reasons. Extinction through competition is shown in the gradual disappearance of the Sacra- mento perch (Archoplitis interruptus) after the invasion of the river by catfish and carp. From extreme specializaion certain forms have doubtless disappeared, but no certain case of this kind has been pointed out among fishes, unless this be the cause of the disappearance of the Devonian mailed Ostracophorcs and ArtJirodircs. It is not likely that any group of fishes has perished through exhaustion of the stock of vigor. Barriers Checking Movement of Marine Fishes. — The limits of the distribution of individual species or genera must be found in some sort of barrier, past or present. The chief bar- riers which limit marine fishes are the presence of land, the presence of great oceans, the differences of temperature arising from differences in latitude, the nature of the sea bottom, and the direction of oceanic currents. That which is a barrier to one species may be an agent in distribution to another. The common shore fishes would perish in deep Avaters almost as surely as on land, while the open Pacific is a broad highway to the albacore or the swordfish. Again, that which is a barrier to rapid distribution may be- come an agent in the slow extension of the range of a species. The great continent of Asia is undoubtedly one of the greatest of barriers to the wide movement of species of fish, yet its long shore-line enables species to creep, as it were, from bay to bay, The Geographical Distribution of Fishes 24 i or from rock to rock, till, in many cases, the same species is found in the Red Sea and in the tide-pools or sand-reaches of Japan. In the North Pacific, the presence of a range of half- submerged volcanoes, known as the Aleutian and the Kurile Islands, has greatly aided the slow movement of the fishes of the tide -pools and the kelp. To a school of mackerel or of flying-fishes these rough islands with their narrow channels might form an insuperable barrier. Temperature the Central Fact in Distribution. — It has long been recognized that the matter of temperature is the central fact in all problems of geographical distribution. Few species in any group freely cross the frost-line, and except as borne by Fig. 173. — Japanese file-fi.sh, liudarius ercodes Jordan and Snyder, ^\'akanoura, Japan. Family M onacanlhida: . oceanic currents, not many extend their range far into waters colder than those in which the species is distinctively at home. Knowing the average temperature of the water in a given region we know in general the types of fishes which must inhabit it. It is the similarity in temperature and physical conditions which chiefly explains the resemblance of the Japanese fauna to that of the Mediterranean or the iVntilles. This fact alone 242 The Geographical Distribution of Fishes must explain the resemblance of the iVrctic and Antarctic faunae, there being in no case a barrier in the sea that may not some time be crossed. Like forms lodge in like places. Agency of Ocean Currents. — We may consider again for a moment the movements of the great currents in the Pacific as agencies in the distribution of species. A great current sets to the eastward, crossing the ocean just south of the equator. It extends past Samoa and passes on nearly to the coast of Mexico, touching the Galapagos Islands, Clipperton Island, and especially the Revillagigedos. This may account for the number of Polynesian species found on these islands, about which they are freely mixed with immi- grants from the mainland of Mexico. From the Revillagigedos * the current moves northward and westward, passing the Hawaiian Islands and thence onward to the Ladrones. The absence in Hawaii of most of the charac- teristic fishes of Polynesia and ilicronesia may be in part due to the long detour made by these currents, as the conditions of life in these groups of islands are not very different. North- east of Hawaii is a great spiral current, moving with the hands of the watch, forming what is called Fleurieu's Whirlpool. This does not reach the coast of California. This fact may help to account for the almost complete distinction in the shore fishes of Hawaii and California. f No other group of islands in the tropics has a fish fauna so isolated as that of Hawaii. The genera are largely the ordinary tropical types. The species are largely peculiar to these islands. The westward current from Hawaii reaches Luzon and For- mosa. It is deflected to the northward and, joining a north- ward current from Celebes, it forms the Kuro Shiwo or Black Stream of Japan, which strews its tropical species in the rock pools along the Japanese promontories as far as Tokio. Then, turning into the open sea, it passes northward to the Aleutian Islands, across to Sitka. Thence it moves southward as a cold * Clarion Island and Socorro Island. t A few Mexican shore fishes, ChaHodon humcralis, Galeichthys dasyccphahts, Hypsoblennius parvipinnis. have been wrongly accredited to Hawaii by some misplacement of labels. The Geographical Distribution of Fishes 243 current, bearing Ochotsk-Alaskan types southward as far as the Santa Barbara Islands, to which region it is accompanied by species of Aleutian origin. A cold return current seems to extend southward in Japan, along the east shore perhaps as far as Matsushima. A similar current in the sea to the west of Japan extends still further to the southward, to Noto, or beyond. It is, of course, not necessary that the movements of a species in an oceanic current should coincide with the direction of the current. Young fishes, or fresh-water fishes, would be borne along with the water. Those that dwell within floating bodies of seaweed would go whither the waters carry the drift- ing mass. But free-swimming fishes, as the mackerel or flying- fishes, might as readily choose the reverse direction. To a free- swimming fish the temperature of the water would be the only consideration. It is thus evident that a current which to certain forms would prove a barrier to distribution, to others would be a mere convenience in movement. In comparing the Japanese fauna with that of Australia, we find some trace of both these conditions. Certain forms are perhaps excluded by cross-currents, while certain others seem to have been influenced only by the warmth of the water. A few Australian types on the coast of Chile seem to have been carried over by the cross-currents of the South i\tlantic. It is fair to say that the part taken by oceanic currents in the distribution of shore fishes is far from completely demon- strated. The evidence that they assist in such distribution is, in brief, as follows: 1. The young of shore fishes often swim at the surface. 2. The young of very many tropical fishes drift northward in the Gulf Stream and the Japanese Kuro Shiwo. 3. The fatmal isolation of Hawaii may be correlated with the direction of the oceanic currents. Centers of Distribution. — We may assume, in regard to any species, that it has had its origin in or near that region m which it is most abundant and characteristic. Such an assumption must involve a very large percentage of error or of doubt, but in considering the mass of species, it may represent essential truth. In the same fashion we may regard a genus as being autochthonous or first developed in the region where it shows 244 The Geographical Distribution of Fishes the greatest range or variety of species. Those regions where the greatest number of genera are thus autochthonous may be regarded as centers of distribution. So far as the marine fishes are concerned, the most important of these supposed centers are found in the Pacific Ocean. First of these in importance is the East-Indian Archipelago, with the neighboring shores of India. Next would come the Arctic Pacific and its bounding islands, from Japan to British Columbia. Third in importance in this regard is Australia. Important centers are found in temperate Japan, in California, the Panama region, and in New Zealand, Chili, and Patagonia. The fauna of Polynesia is almost entirely derived from the Indies ; and the shore fauna of the Red Sea, the Bay of Bengal, and Madagascar, so far as genera are con- cerned, seems to be not really separable from the Indian fauna generallv. I know of but six genera which may be regarded as autoch- thonous in the Red Sea, and nearly all of these are of doubtful Fig. 174.— Globe-fi.sh, Tctraodon seiosvs Rosa Smith. Clarion Island, Mexico. value or of uncertain relation. The many pecuhar o-enera de- scribed by Dr. Alcock, from the dredgmgs of the Livcstigator m the Bay of Bengal, belong to the bathybial or deep-water series, and will all, doubtless, prove to be forms of wide dis- tribution. In the Atlantic, the chief center of distribution is the West Indies; the second is the Mediterranean. On the shores to the northward or southward of these regions occasional genera have The Geographical Distribution of Fishes 245 found their origin. This is true especially of the New England region, the North Sea, the Gulf of Guinea, and the coast of Argentina. The fish fauna of the North Atlantic is derived mainly from the North Pacific, the differences lying mainly in the relative paucity of the North Atlantic. But in certain groups common to the two regions the migration must have been in the opposite direction, exceptions that prove the rule. Distribution of Marine Fishes. — The distribution of marine fishes must be indicated in a different way from that of the fresh-water forms. The barriers which limit their range fur- nish also their means of dispersion. In some cases proximity overbalances the influence of temperature ; with most forms questions of temperature are all-important. Pelagic Fishes. — Before consideration of the coast-lines we may glance at the differences in vertical distribution. Many species, especially those in groups allied to the mackerel family, are pelagic — that is, inhabiting the open sea and ranging widely within limits of temperature. In this series some species are practically cosmopolitan. In other cases the genera are so. Each school or group of individuals has its breeding place, and from the isolation of breeding districts new species may be conceived to arise. The pelagic types have reached a species of equilibrium in distribution. Each type may be found where suitable conditions exist, and the distribution of species throws little light on questions of distribution of shore fishes. Yet among these species are all degrees of localization. The pelagic fishes shade into the shore fishes on the one hand and into the deep-sea fishes on the other. Bassalian Fishes. — The vast group of bassalian or deep-sea fishes includes those forms which live below the line of ade- quate light. These too are localized in their distribution, and to a much greater extent than was formerly supposed. Yet as they dwell below the influence of the sun's rays, zones and surface temperatures are nearly alike to them, and the same forms may be found in the Arctic or under the equator. Their dift'erences in distribution are largely vertical, some living at greater depths than others, and they shade off by degrees from bathybial into semi-bat hybial, and finally into ordinary pelagic and ordinary shore types. Apparently all of the bassalian fishes 246 The Geographical Distribution of Fishes are derived from littoral types, the changes in structure being due to degeneration of the osseous and muscular systems and of structures not needed in deep-sea life. The fishes of the great depths are soft in substance, some of them blind, some of them with very large eyes, ah black in color, and very many are provided with luminous spots or areas. A large body of species of fishes are semi-bathybial, inhabitmg depths of 20 to 100 fathoms, showing many of the characters of shore fishes, but far more Avidely distributed. Many of the remarkable cases of wide distribution of type belong to this class. In moderate depths red colors are very common, cor- responding to the zone of red algce, and the colors in both Fig 175 — stiiic;-ra\ , Dn^yiiti'! -^abina Le Sueur. Galveston. cases are perhaps determined from the fact that the red rays of light are the least refrangible. A certain number of species are both marine and fresh water, inhabiting estuaries and brackish waters, while some more strictly marine ascend the rivers to spawn. In none of these cases can any hard and fast line be drawn, and some groups which are shore fishes in one region will be represented by semi- bathybial or fluviatile forms in another.* * The dragoncts {Call ion y)niis) arc shore fishes of the shallowest waters in Europe and Asia, but inhabit considerable depths in tropical America. The sea-robins (Priouotits) are shore fishes in Massachusetts, semi-bathybial fishes at Panama. Often Arctic shore fishes become semi-bathj'bial in the Temper- ate Zone, living in water of a given temperature. A long period of cold weather will sometimes bring such to the surface. The Geographical Distribution of Fishes 247 Littoral Fishes. — The shore fishes are in general the most highly specialized in their respective groups, because exposed to the greatest variety of selecting conditions and of competi- tion. Their distribution in space is more definite than that of the pelagic and bassalian types, and they may be more defi- nitely assigned to geographical areas. Distribution of Littoral Fishes by Coast-lines. — Their distri- bution is best indicated, not by realms or areas, but as form- ing four parallel series corresponding to the four great north and south continental outlines. Each of these series may be represented as beginning at the north in the Arctic fauna, practically identical in each of the four series, actually identical in the two Pacific series. Passing southward, fonns are arranged according to temperature. One by one in each series, the Arctic types disappear; subarctic, temperate, and semi-trop- ical tvpes take their places, giving way in turn to south-tem- perate and Antarctic forms. The distribution of these is modi- fied by barriers and by currents, yet though genera and species may be dift'erent, each isotherm is represented in each series by certain general types of fishes. Fig. 176.— Green-sided Darter, Di.pIe.non hiennimdcs Rafinesque. Clinch River. Family PerrirUc. Passing southward the two American series, the East At- lantic and the East Pacific, pass on gradually through temperate to Antarctic types. These are analogous to those of the Arctic, and in a few cases they are generally identical. The AA'est Pacific (East Asian) series is not a continuous hnc on account of the presence of Australia, the East Indies, and Polynesia. The irregularities of these regions make a numl:)er of subserics, which break up the simphcity expressed in the idea of four 248 The Geographical Distribution of Fishes parallel series. Yet the fauna of Polynesia is strictly East Indian, modified by the omission or alteration of species, and that of Australia is Indian at the north, and changes to the southward much as that of Africa does. In its marine fishes, it does not constitute a distinct "realm." The East Atlantic (Europe-African) series follows the same general lines of change as that of the West Atlantic. It extends, -however, only to the South Temperate Zone, developing no Antarctic elements. The relative shortness of Africa explains in large degree, as already shown, the similarity between the tropical elements in the two Old-World series, as the similarity in tropical elements in the two American series must be due to a former depression of the connecting Isthmus. The practical unity of the Arctic marine fauna needs no explanation in view of the present shore lines of the Arctic Ocean. Minor Faunal Areas. — The minor faunal areas of shore fishes may be grouped as follows ; East Atlantic. Icelandic, British, Mediterranean, Guinean, Cape. West Atlantic. Greenlandic, New England, Virginian, Austroriparian , Floridian, Antilkean, Caribbean, Brazilian, Argentinan, Patagonian. East Pacific. Arctic, Aleutian, Sitkan, Califomian, San Diegan, Sinaloan, Panamanian, Peruvian, Revillagigedan, Galapagan, Chilian, Patagonian. West Pacific. Arctic, Aleutian, Kurile, Hokkaido, Nippon, Chinese, East Indian, Polynesian, Hawaiian, Indian, Arabian, Madagascarian, Cape, North Australian, Tasmanian, New Zealand, Antarctic. Equatorial Fishes Most Specialized. — In general, the dif- ferent types are most highly specialized in equatorial waters. The processes of specific change, through natural selection or The Geographical Distribution of Fishes 249 other causes, if other causes exist, take place most rapidly there and produce most far-reaching modification. As elsewhere stated, the coral reefs of the tropics are the centers of fish-life, the cities in fish-economy. The fresh waters, the arctic waters, the deep sea and the open sea represent forms of ichthyic back- woods, regions where change goes on more slowly, and in them we find survivals of archaic or generalized types. For this rea- son the study in detail of the distribution of marine fishes .of equatorial regions is in the highest degree instructive. Realms of Distribution of Fresh-water Fishes. — If we consider the fresh-water fishes alone we may divide the land areas of the earth into districts and zones not differing fundamentally with those marked out for mammals and birds. The river basin, bounded by its shores and the sea at its mouth, shows many resemblances, from the point of view of a fish, to an island considered as the home of an animal. It is evident that with fishes the differences in latitude outweigh those of con- tinental areas, and a primary division into Old World and New World would not be tenable. The chief areas of distribution of fresh-water fishes we may indicate as follows, following essentially the grouping proposed by Dr. Giinther : * Northern Zone. — With Dr. Giinther we may recognize first the Northern Zone, characterized familiarly by the presence of sturgeon, salmon, trout, white-fish, pike, lamprey, stickleback, and other species of which the genera and often the species are identical in Europe, Siberia, Canada, Alaska, and most of the United States, Japan, and China. This is subject to cross- division into two great districts, the first Europe-Asiatic, the second North American. These two agree very closely to the northward, but diverge widely to the southward, developing a variety of specialized genera and species, and both of them pass- ing finally by degrees into the Equatorial Zone. Still another line of division is made by the Ural Mountains in the Old World and by the Rocky Mountains in the New. In both cases the Eastern region is vastly richer in genera and species, as well as in autochthonous forms, than the Western. The reason for this lies in the vastly greater extent of the river * " Introduction to the Study of Fishes." 250 The Geographical Distribution of Fishes Vir, 177. — Japanese Sea-horse. U ippor_ampns molnnkei Bleelcer. Alisaki, Japan. The Geographical Distribution of Fishes 251 basins of China and the Eastern United States, as compared with those of Europe or the CaHfornian region. Minor divisions are those which separate the Great Lake region from the streams tributary to the Gulf of Mexico; and in Asia, those which separate China from tributaries of the Caspian, the Black, and the Mediterranean. Equatorial Zone. — The Equatorial Zone is roughly indicated by the tropics of Cancer and Capricorn. Its essential feature is that of the temperature, and the peculiarities of its divisions are caused by barriers of sea or mountains. Dr. Giinther finds the best line of separation into t^^•o divisions to lie in the presence or absence of the great group of dace or minnows,* to which nearly half of the species of fresh- water fishes the world over belong. The entire group, now spread every%Yhere except in the Arctic, South America, Aus- tralia, and the islands of the Pacific, seems to have had its origin in India, from which region its genera have radiated in every direction. The Cyprinoid division of the Equatorial Zone forms two districts, the Indian and the African. The Acyprinoid division includes South America, south of Mexico, and all the islands of the tropical Pacific lying to the east of Wallace's line. This line, separating Borneo from Celebes and Bali from Lompoe, marks in the Pacific the western limit of Cyprinoid fishes, as well as that of monkeys and other important groups of land animals. This line, recognized as very important in the distribu- tion of land animals, coincides in general with the ocean current between Celebes and Papua, which is one of the sources of the Kuro Shiwo. In Australia, Hawaii, and Polynesia generally, the fresh- water fishes are derived from marine types by modification of one sort or another. In no case, so far as I know, in any island to the eastward of Borneo, is found any species derived from fresh-water families of either the Eastern or the Western Conti- nent. Of coiirse, minor subdivisions in these districts are formed by the contour lines of river basins. The fishes of the Nile differ from those of the Niger or the Congo, or of the streams of Mada- * Cyprinidffi. 2 (-2 The Geographical Distribution of Fishes gascar or Cape Colony, but in all these regions the essential character of the fish fauna remains the same. Southern Zone. — The third great region, the Southern Zone, is scantily supplied Avith fresh-water fishes, and the few it pos- sesses are chiefly derived from modifications of the marine fauna or from the Equatorial Zone to the north. Three districts are recognized — Tasmania, New Zealand, and Patagonia. Origin of the New Zealand Fauna. — The fact that certain peculiar groups are common to these three regions has attracted the notice of naturalists. In a critical study of the fish fauna of New Zealand,* Dr. Gill discusses the origin of the four genera and seven species of fresh-water fishes found in these islands, the principal of these genera (Galaxias) being represented by nearly related species in South Australia, in Patagonia,! the Falkland Islands, and in South Africa. According to Dr. Gill, we can account for this anomaly of distribution only by supposing, on the one hand, that their ancestors were carried for long distances in some unnatural manner, as (a) having been carried across entombed in ice, or (b) being swept by ocean currents, surviving their long stay in salt water, or else that they were derived (c) from some widely distributed marine type now extinct, its descendants restricted to fresh water. On the other hand. Dr. Gill suggests that as "community of type must be the expression of community of origin," the pres- ence of fishes of long-estatilished fresh-water types must imply continuity or at least contiguity of land. The objections raised by geologists to the supposed land connection of New Zealand and Tasmania do not appear to Dr. Gill insuperable. It is well known, he says, "that the highest mountain chains are of com- paratively recent geological age. It remains, then, to consider which is the more probable, (i) that the types now common in distant regions were distributed in some unnatural manner by the means referred to, or (2) that they are descendants of forms once wide-ranging over lands now submerged." After considering questions as to change of type in other groups, Dr. Gill is inclined to postulate, from the occurrence of species of the * " A Comparison of Antipodal Fauna;," 1887. ■\ Galaxias, Ncochanna, Prototroctes, and Rclropinna. The Geographical Distribution of Fishes 253 trout-like genus Galaxias, in New Zealand, South Australia, and South America, that "there existed some terrestrial pas- sage-way between the several regions at a time as late as the close of the Mesozoic period. The evidence of such a connec- tion afforded by congeneric fishes is fortified by analogous rep- resentatives among insects, moUusca, and even amphibians. The separation of the several areas must have occurred little later than the late Tertiary, inasmuch as the salt-water fishes of corresponding isotherms found along the coast of the now widely separated lands are to such a large extent specifically different. In general, change seems to have taken place more rapidly among marine animals than fresh-water representatives of the same class." In this case, when one guess is set against another, it seems to me that the hypothesis first suggested, rather than the other, lies in the line of least logical resistance. I think it better to adopt provisionally some theory not involving the existence of a South Pacific Antarctic Continent, to account for the dis- tribution of Galaxias. For this view I may give five reasons: 1. There are many other cases of the sort equally remark- able and equally hard to explain. Among these is the presence of species of paddle-fish and shovel-nosed sturgeon,* types char- acteristic of the Mississippi Valley, in Central Asia. The pres- ence of one and only one of the five or six American species of pike t in Europe ; of one of the three species of mud-minnow in Austria,! the others being American, Still another curious case of distribution is that of the large pike-like trout of the genus Hncho, one species (Hiicho hiicho) inhabiting the Danube, the other {Hiicho blackistoni) the rivers of northern Japan. Many such cases occur in different parts of the globe and at present admit of no plausible explanation. 2. The supposed continental extension should show per- manent traces in greater similarity in the present fauna, both of rivers and of sea. The other fresh-water genera of the re- gions in question are different, and the marine fishes are more * The shovel-nosed sturgeon (Scaphirynchus and Kessleria) and the paddle- fish {Polyodon and Psephurus). f Esox luciiis. J Umrba, the mud-minnow. 2 54 The Geographical Distribution of Fishes different than they could be if we imagine an ancient shore connection. If New Zealand and Patagonia were once united other genera than Galaxias would be left to show it. 3. VCe know nothing of the power of Galaxias to survive submergence in salt water, if carried in a marine current. As already noticed, I found young and old in abundance of the commonest of Japanese fresh-water fishes in the open sea, at a distance from any river. Thus far, this species, the hakone * dace, has not been recorded outside of Japan, but it might well be swept to Korea or China. Two fresh-water fishes of Japanese origin now inhabit the island of Tsushima in the Straits of Korea. 4. The fresh-water fishes of Polynesia show a remarkably wide distribution and are doubtless carried alive in currents. One river-goby t ranges from Tahiti to the Riu Kiu Islands. Another species, J originally perhaps from Brazil through Mexico, shows an equally broad distribution. 5. We know that Galaxias with its relatives must have been derived from a marine type. It has no affinity with any of the fresh-water families of either continent, unless it be with the Salmonidffi. The original type of this group was marine, and most of the larger species still live in the sea, ascending streams only to spawn. When the investigations of geologists show reason for believing in radical changes in the forms of continents, we may accept their conclusions. That geological evidence exists which seems to favor the existence of a former continent, Ant- arctica, is claimed on high authority. If this becomes well estabhshed we may well explain the distribution of Galaxias with reference to it. But we cannot, on the other hand, regard the anomalous distribution of Galaxias alone constituting proof of shore connection. There can be no doubt that almost every case of anomalies in the distribution of fishes admits of a possi- ble explanation through " the slow action of existing causes." Real causes are always simple when they are once known. All anomalies in distribution cease to be such when the facts necessary to understand them are at our disposal. * Lcuciscus hakucnsis. f Elcolris fusca. J Awaous gciitvittatus. CHAPTER XV. ISTHMUS BARRIERS SEPARATING FISH FAUNAS HE Isthmus of Suez.— In the study of the effect of the Isthmus of Suez on the distribution of fishes we may first consider the alleged resemblance between the fauna of the Mediterranean and that of Japan. Dr. Gunther claims that the actual identity of genera and species in these two regions is such as to necessitate the hypothesis that they have been in recent times joined by a continuous shore-line. This shore-line, according to Prof. A. E, Ortmann and others, was not across the Isthmus of Suez, but farther to the northward, probably across Siberia. The Fish Fauna of Japan. — For a better understanding of the problem we may give a brief analysis of the fish fauna of Japan. The group of islands which constitute the empire of Japan is remarkable for the richness of its animal life. Its variety in climatic and other conditions, its nearness to the great con- tinent of Asia and to the chief center of marine life, the East Indian Islands, its relation to the warm Black Current or Kuro Shiwo from the south and to the cold currents from the north, all tend to give variety and richness to the fauna of its seas. Especially is this true in the group of fishes. In spite of the political isolation of the Japanese Empire, this fact has been long recognized and the characteristic types of Japanese fishes have been well known to naturalists. At present about 900 species of fishes are known from the four great islands which constitute Japan proper — Hondo, Hokkaido, Kiusiu, and Shikoku. About 200 others are known from the volcanic islands to the north and south. Of these 11 00 species, about fifty belong to the fresh waters. These are all closely allied to forms found on the mainland of Asia, from which re- 255 256 Isthmus Barriers Separating Fish Faunas gion all of them were probably derived. In general the same genera appear in China and with a larger range of species. Fresh-water Faunas of Japan. — Two faunal areas of fresh waters may be fairly distinguished, although broadly overlap- ping. The northern region includes the island of Hokkaido and the middle and northern part of the great island of Hondo. In a rough way, its southern boundary may be defined by Fuji Yama and the Bay of IMatsushima, It is characterized by the presence of salmon, trout, and sculpins, and northward by stur- geon and brook-lampreys. The southern area loses by degrees the trout and other northern fishes, while in its clear waters abound various minnows, gobies, and the famous ayu, or Japanese dwarf salmon, one of the most delicate of food fishes. Sculpins and lampreys give place to minnows, loaches, and chubs. Two genera, a sculpin * and a perch, t besides certain minnows and catfishes, are confined to this region and seem to have originated in it, but, like the other species, from Chinese stock. Origin of Japanese Fresh-water Fishes. — The question of the origin of the Japanese river fauna seems very simple. All the types are Asiatic. AVhile most of the Japanese species are dis- tinct, their ancestors must have been estrays from the main- land. To what extent river fishes may be carried from place to place by currents of salt water has never been ascertained. One of the most wideh^ distributed of Japanese river fishes is the large hakone dace or chub.t This has been repeatedly taken by us in the sea at a distance from any stream. It would evidently survive a long journey in salt water. An allied species § is found in the midway island of Tsushima, between Korea and Japan. Faunal Areas of Marine Fishes in Japan. — The distribution of the marine fishes of Japan is mainly controlled by the tem- perature of the waters and the motion of the ocean currents. Five faunal areas may be more or less clearly recognized, and these may receive names indicating their scope — Kurile, Hok- kaido, Nippon, Kiusiu, Kuro Shiwo, and Riu Kiu. The first or Kurile district is frankly subarctic, containing species charac- teristic of the Oehotsk vSea on the one hand, and of Alaska on * Rheopresbe. % Lcuciscus hakitcnsis Gunther. t Bryttosus. § Lcuciscus jouyi. Isthmus Barriers Separating Fish Faunas 257 the other. The second or Hokkaido * district includes this northern island and that part of the shore of the main island of Hondot which lies to the north of Matsushima and Noto. Here the cold northern currents favor the development of a northern fauna. The herring and the salmon occupy here the same economic relation as in Norway, Scotland, Newfoundland, and British Columbia. Sculpins, blennies, rockfish, and floun- ders abound off the rocky shores and are seen in all the markets. South of Matsushima Bay and through the Island Sea as far as Kobe, the Nippon fauna is distinctly one of the temperate zone. Most of the types characteristically Japanese belong here, abounding in the sandy bays and about the rocky islands. About the islands of Kiusiu and Shikoku, the semi-tropical elements increase in number and the Kiusiu fauna is less char- acteristically Japanese, having much in common with the neigh- boring shores of China, while some of the species range north- ward from India and Java. But these faunal districts have no sharp barriers. Northern fishes J unquestionably of Alaskan origin range as far south as Nagasaki, while certain semi-tropical § types extend their range northward to Hakodate and Volcano Bav. The Inland Sea, which in a sense bounds the southern fauna, serves at the same time as a means of its extension. While each species has a fairly definite northern or southern limit, the boundaries of a faunal district as a whole must be stated in the most general terms. The well-known boundary called Blackiston's Line, which passes through the Straits of Tsugaru, between the two great islands of Hondo and Hokkaido, marks the northern boundary of monkeys, pheasants, and most tropical and semi-tropical birds and mammals of Japan. But as to the fishes, either marine or fresh water, this line has no significance. The northern fresh- water species probably readily cross it; the southern rarely reach it. We may define as a fourth faunal area that of the Kuro * Formerly, but no longer, called Yeso in Japan. t Called Nippon on foreign maps, but not so in Japan, where Nippon means the whole empire. 1 Pleuronichthys cornutus, Hexagrammos otakii, etc. § As Halichwres, Teirapiurus, Callionymus, Ariscopus, etc. 258 Isthmus Barriers Separating Fish Faunas Shhvo district itself, wliich is distinctly tropical and contrasts strongly with that of the inshore bays behind it. This warm " Black Current," analogous to our Gulf Stream, has its origin in part from a return current from the east which passes west- ward through Hawaii, in part from a current which passes be- tween Celebes and New Guinea. It moves northward by way of Luzon and Formosa, touching the east shores of the Japa- nese islands Kiusiu and vShikoku, to the main island of Hondo, Fig. 17S. — Sacramento Perch, Archoplites interrwptus Girard. Family Centrarchidm. Sacramento River. flooding the bays of Kagoshima and Kochi, of AVaka, Suruga, and Sagami. The projecting headlands reach out into it and the fauna of their rock-pools is distinctly tropical as far to the northward as Tokio. These promontories of Hondo, Waka, Ise, Izu, Misaki, and Awa have essentially the same types of fishes as are found on the reefs of tropical Polynesia. The warmth of the off-shore currents gives tlie fauna of Misaki its astonishing richness, and the wealth of life is by no means confined to the fishes. Corals, crustaceans, worms, and mollusks show the same generous pro- fusion of species. A fifth faunal area, closely related to that of the Black Cur- rent, is formed by the volcanic and coral reefs of the Riu Kiu Archipelago. This fauna, so far as known, is essentially East Indian, the genera and most of the species being entirely iden- tical with those of the islands about Java and Celebes. Isthmus Barriers Separating Fish Faunas 259 Resemblance of the Japanese and Mediterranean Fish Faunas. — It has been noted by Dr. Gunther that the fish fauna of Japan bears a marked resemblance to that of the Mediterranean. This hkeness is shown in the actual identity' of genera and species, and in their relation to each other. This resemblance he proposes to explain by the hypothesis that at some recent period the two regions, Japan and the Mediterranean, have been united by a continuous shore-line. The far-reaching character of this hypothesis demands a careful examination of the data on which it rests. The resemblance of the two faunal areas, so far as fishes are concerned, may be stated as follows : There are certain genera * of shore fishes, tropical or semi-tropical, common to the Medi- terranean and Japan, and wanting to California, Panama, and the West Indies, and in most cases to Polynesia also. Besides these, certain others found in deeper water (100 to 200 fathoms) are common to the two areas, f and have been rarely taken elsewhere. Significance of Resemblance. — The significance of these facts can be shown only by a fuller analysis of the fauna in ques- tion, and those of other tropical and semi-tropical waters. If the resemblances are merely casual, or if the resemblances are shown by other regions, the hypothesis of shore continuity would be unnecessary or untenable. It is tenable if the resem- blances are so great as to be accounted for in no other way. Of the genera regarded as common, only two J or three are represented in the two regions by identical species, and these have a very Avide distribution in the warm seas. Of the others, nearly aU range to India, to the Cape of Good Hope, to Australia, or to Brazil. They may have ranged farther in the past ; they may even range farther at present. Not one is confined to the two districts in question. As equahy great resemblances exist between Japan and .Vustralia or Japan and the AVest Indies, the case is not self-evident without fuller comparison. I shah * Of these, the principal ones arc Oxysiomus, Myrus, Puerus. Spams, Macror- hamphosus, CepoUi, Callionymus, Zeus, Uranuscopas, Lcpidoirigla, Chchdunith- thys. t Among these are Bcryx, Helicolcnus. Lotdla, Ncttasiuina, Ccntrolophus, Hoplosiethns, Aulopits, Chlorophthalmiis, Lophutcs. X Beryx, Hoplostethits. 26o Isthmus Barriers Separating Fish Faunas therefore undertake a somewhat fuller analysis of the evidence bearing on this and similar problems with a view to the con- clusions which may be legitimately drawn from the facts of fish distribution. Differences between Japanese and Mediterranean Fish Faunas. — AVe may first, after admitting the alleged resemblances and others, note that differences are equally marked. In each re- gion are a certain number of genera which we may consider as autochthonous. These genera are represented by many species or by many individuals in the region of their supposed origin, but are more scantily developed elsewhere. Such genera in Mediterranean waters are Crenilabrns, Labrus, Spicara, Pagel- lus, M alius, Boops, Spondyliosoma, Oblata. None of these occiirs in Japan, nor have they any near relatives there. Japanese autoch- thonous types, as Psendoblenniiis, Vcllitor, Duymccria, Anopliis, Histiopterus, Monocentnis, Oplegnathns, Plecoglosstis, range south- ward to the Indies or to Australia, but all of them are totally unknown to the Mediterranean. The multifarious genera of Gobies of Japan show very little resemblance to the Mediter- ranean fishes of this family, while blennies, labroids, scaroids, and scorpaenoids are equally diverse in their forms and alliances. To the same extent that likeness in faunas is produced by con- tinuity of means of dispersion is it true that unlikeness is due to breaks in continuity. Such a break in continuity of coast- line, in the present case, is the Isthmus of Suez, and the unlike- ness in the faunas is about what we might conceive that such a barrier should produce. Sources of Faunal Resemblances. — There are two main sources of faunal resemblances; first, the absence of any barriers permitting the actual mingling of the species ; second, the hke- ness of temperature and shore configuration on either side of an imperfect barrier. Absolute barriers do not exist and ap- parently never have existed in the sea. If the fish faunas of different regions have mingled in recent times, the fact would be shown by the presence of the same species in each region. If the union were of a remote date, the species would be changed, but the genera might remain identical. In case of close physical resemblances in dift'erent regions, as in the East Indies and West Indies, like conditions would favor Isthmus Barriers Separating Fish Faunas 261 the final lodgement of like types, but the resemblance would be general, the genera and species being unlike. Without doubt part of the resemblance between Japan and the Mediterranean is due to similarity of temperature and shores. Is that which remains sufficient to demand the hypothesis of a former shore- line connection? Effects of Direction of Shore-line. — We may first note that a continuous shore-line produces a mingling of fish faunas only when not interrupted by barriers due to climate. A north and south coast-line, like that of the East Pacific, however unbroken, permits great faunal differences. It is crossed by the different zones of temperature. An east and west shore-line lies in the same temperature. In all cases of the kind which now exist on the earth (the Mediterranean, the Gulf of Mexico, the Car- ibbean Sea, the shores of India), even species will extend their range as far as the shore-line goes. The obvious reason is because such a shore-line rarely offers any important barrier to distribution, checking dispersion of species. We may, there- fore, consider the age and nature of the Isthmus of Suez and the character of the faunas it separates. Numbers of Genera in Different Faunas. — For our purposes the genera must be rigidly defined, a separate name being used in case of each definable difference in structure. The wide- ranging genera of the earlier systematists were practically cos- mopolitan, and their geographical distribution teaches us little. On the other hand, when we come to the study of geological distribution, the broad definition of the genus is the only one usually available. The fossil specimens are always defective. Minor characters may be lost past even the possibility of a guess, and only along broad lines can we achieve the classifica- tion of the individual fossil. Using the modem definition of genus, we find in Japan 483 genera of marine fishes; in the Red Sea, 225; in the Mediter- ranean, 231. In New Zealand 150 are recorded; in Hawaii, 171; 357 from the West Indies, 187 from the Pacific coast of tropical America, 300 from India, 450 from the East-Indian islands, and 227 from Australia. Of the 483 genera ascribed to Japan, 156 are common to the Mediterranean also, 188 to the West Indies and Japan, 169 to 262 Isthmus Barriers Separating Fish Faunas the Pacific coast of the United States and Mexico. With Hawaii Japan shares 90 genera, with New Zealand 62; 204 are common to Japan and India, 148 to Japan and the Red Sea, most of these being found m India also. Two hundred genera are common to Japan and Australia. From this it is CA'ident that Japan and the ilediterranean have much in common, but apparently not more than Japan shares with other tropical regions. Japan naturally shows most likeness to India, and next to this to the Red Sea. Proportion- ately less is the resemblance to Australia, and the likeness to the Mediterranean seems much the same as that to the AYest Indies or to the Pacific coast of America. But, to make these comparisons just and effective, we should consider not the fish fauna as a whole ; we should limit our dis- cussion solely to the forms of ecjuatorial origin. From the fauna of Japan we may eliminate all the genera of Alaskan- Aleutian origin, as these could not be found in the other regions under comparison. We should eliminate all pelagic and all deep-sea forms, for the laws wdiicli govern the distribution of these are very different from those controlling the shore fishes, and most of the genera ha\'e reached a kind of equilibrium over the world. Significance of Rare Forms. — We may note also, as a source of confusion in our investigation, that numerous forms found in Japan and elsewhere are very rarely taken, and their real distribution is unknown. Some of these will be found to have, in some unexpected cjuarter, their real center of disper- sion. In fact, since these pages were AA'ritten, I have taken in Hawaii representatives of three * genera which I had enumer- ated as belonging chiefly to Japan and the West Indies. Numerous other genera common to the two regions have since been obtained by Dr. Gilbert. Such species may inhabit oceanic plateaus, and find many halting places in their circuit of the tropical oceans. AYe have already discovered that Madeira, St. Helena, Ascension, and other volcanic islands con- stitute such halting places. We shall find many more such, Avhen the dee]ier shore regions are explored, the region between market-fishing and the deep-sea dredgings of the Challenger and * Antigonia, Etclis, Eminclichthys. Isthmus Barriers Separating Fish Faunas 263 the Albatross. In some cases, no doubt, these forms are verging on extinction and a former wide distribution has given place to isolated colonies. The following table shows the contents, so far as genera are concerned, of those equatorial areas in which trustworthy cata- logues of species are accessible. It includes only those fishes of stationary habit living in less than 200 fathoms. It goes without saying that considerable latitude must be given to these figures, to allow for errors, omissions, uncertainties, and differences of opinion. Distribution of Shore Fishes. — .1. Japan and tlie Mediterranean. Genera* chiefly confined to these regions 2 Genera of wide distribution 77 Total of common genera 79 Total in both regions 399 Genera above included, found in all equatorial regions 55 General found in most equatorial regions 11 Genera more or less restricted 13 79 B. Japan and the Red Sea. Genera t chiefly confined to these two regions. . 2 Genera of wide distribution 109 Total genera common in Total in both regions 424 * Lepadogaster, Myrus; Lophotes, thus far recorded from Japan, the Medi- terranean, and the Cape of Good Hope, is bassalian and of unknown range. Beryx, Trachichthys, Hoplostethus, etc., are virtually cosmopolitan as well as semi-bassalian. t In this group we must place Cepola, Callionymus, Pagrus, Sparus, Beryx, Zeus, all of which have a very wide range in Indian waters. X Cryptocentrus, Asterropteryx. The range of neither of these genera of small shore fishes is yet well known. 264 Isthmus Barriers Separating Fish Faunas C. Japan and Hawaii. Genera chiefly confined to these regions 3 Genera of wide distribiition 79 Total genera common 82 Total in both regions 396 D. Japan and Australia. Genera chiefly confined to these regions 13 Genera of wide distribution (chiefly East In- dian) 122 Total genera common 135 Total in both regions 533 E. Japan and Panama. Genera chiefly confined to these regions 2 Genera of wide distribution . 89 Total genera common 91 Total in both regions 499 F. Japan and tlie West Indies. Genera chiefly confined to these regions 5 Genera of wide distribution 108 Total genera common 113 Total in both regions 520 G. The Mediterranean aitd tlie Red Sea. Genera confined to the Suez region o Genera of wide distribution (chiefly Indian) ... 40 Total genera common 40 Total in both regions 295 H. West Indies and the Mediterranean. Genera chiefly confined to the equatorial At- lantic jj Genera of wide distribution eg Total ^Q Total in both regions ^.y^ Isthmus Barriers Separating Fish Faunas 265 /. West Indies and Paiiaiua. Genera chiefly confined to equatorial America . 68 Genera of wide distribution loi Total genera common 169 Total in equatorial America 376 /. Hawaii and Panama. Genera chiefly confined to the regions in ques- tion 9 Genera of wide distribution 74 Total genera common 77 Total in both regions 323 K. Hawaii and tlie East Indies. Genera chiefly confined to Hawaii 4 Genera of wide distribution in the equatorial Pacific 123 Genera confined to Hawaii and the West In- dies I Suniinary. Genera (shore fishes only) in the Mediterra- nean Sea 144 Genera in the Red Sea 191 Genera in India 280 Genera in Japan (exclusive of northern forms) 334 Genera in Australia 344 Genera in New Zealand 108 Genera in Hawaii 144 Genera about Panama 256 Genera in West Indies 299 Extension of Indian Fauna. — From the above tables it is evi- dent that the warm-water fauna of Japan, as well as that of Hawaii, is derived from the great body of the fauna of the East Indies and Hindostan ; that the fauna of the Red Sea is derived in the same way; that the fauna of the Mediterranean bears no especial resemblance to that of Japan, rather than to other 266 Isthmus Barriers Separating Fish Faunas elements of the East Asiatic fauna in similar conditions of tem- ]ierature, and no greater than is borne by either to the West Intlies; that the faunas of the sides of tlie Isthmus of Suez have relativelv little in common, while those of the tAVO sides of the Isthmus of Panama show large identity of genera, al- though few species are common to the two sides. Of the 255 genera recorded from the Panama region, 179, or over 70 per cent., are also in the West Indies, while 68, or more than 30 per cent, of the number, are limited to the two regions in ques- tion. The Isthmus of Suez as a Barrier to Distribution. — With the aid of the above table we may examine further the rela- tion of the fauna of Japan to that of the Mediterranean. If a continuity of shore-line once existed, it would involve the ob- literation of the Isthmus. With free connection across this isthmus the fauna of the Red Sea must have been once practically the same as that of the Alediterranean. The pres- ent differences must be due to later immigrations to one or the other region, or to the extinction of species in one locality or the other, through some kind of unfitness. In neither region is there evidence of extensive immigration from the out- side. The present conditions of water and temperature differ a little, but not enough to explain the difference in faunse. The Red Sea is frankly tropical and its fauna is essentially Indian, much the same, so far as genera are concerned, as that of southern Japan. The Mediterranean is at most not more than semi-tropical and its fishes are characteristically European. Its tropical forms belong rather to Gumea than to the East Indies. With the Red Sea the Mediterranean has very httle in common, not so much, for example, as has Hawaii. Forty genera of shore fishes (and only fifty of all fishes) are identical in the two regions, the Mediterranean and the Red Sea. Of those, every one is a genus of wide distribution, found in nearly all warm seas. Of shore fishes, only one genus in seven is com- n:on to the two regions. Apparently, therefore, we cannot assume a passage across the Isthmus of Suez within the life- time of the present genera. Not one of the types alleged to be peculiar to Japan and the Mediterranean is thus far known in the Red Sea. Not one of the characteristically abundant Isthmus Barriers Separating Fish Faunas 267 Mediterranean types * crosses the Isthmus of Suez, and the dis- tinctive Red Sea and Indian typesj arc equally wanting m the Mediterranean. The only genera which could have crossed the Isthmus are certain shaUow-water or brackish-water forms, sting-rays, torpedoes, sardines, eels, and mullets, widely dif- fused through the East Indies and found also in the Mediter- ranean. The former channel, if one ever existed, had, therefore, much the same value in distribution of species as the present Suez Canal. Geological Evidence of Submergence of the Isthmus of Suez. — Yet, from geological data, there is strong evidence that the Isthmus of Suez was submerged in relatively recent times. The recognized geological maps of the Isthmus show that a broad area of post-Pliocene or Pliocene deposits constitutes the Isth- mus and separates the nummtditic hills of Suez from their fel- lows about thirty miles to the eastward. The northern part of the Isthmus is alluvium from the Nile, and its western part is covered with drifting sands. The Red Sea once extended farther north than now and the Mediterranean farther to the southeast. Assuming the maps to be correct, the Isthmus must have been open water in the late Pliocene or post-Pliocene times. Admitting this as a fact, the difference in the fish fauna would seem to show that the waters over the submerged area were so shallow that the rock-loving forms did not and could not cross it. Moreover, the region was very likely overspread with silt- bearing fresh waters from the Nile. To such fishes as Chcctodon, Holocentnts, TJialassoma of the Red Sea, or to Crenilabrus, Boops, and Zeus of the Mediterranean, such waters would form a barrier as effective as the sand-dunes of to-day. Conclusions as to the Isthmus of Suez. — We are led, there- fore, to these conclusions: 1. There is no evidence derivable from the fishes of the recent submergence of the Isthmus of Suez. 2. If the Isthmus was submerged in Pliocene or post-Pho- cene times, the resultant channel was shallow and muddy, so * As Crenilabrus, Labrus, Symphodiis, Pagellus, Spondyliosonta, Sparisoiiia. t As Chwtodon, Lethrinus, Monotaxis, Glyphisodon, etc. 268 Isthmus Barriers Separating Fish Faunas that ordinary marine fishes or fishes of rock bottoms or of deep waters did not cross it. 3. It formed an open water to brackish-water fishes only. 4. The types common to Japan and the I\Iediterranean did not enter either region from the other by way of the Red Sea. 5. As most of these are found also in India or Australia or both, their dispersion was probably around the south coast of Africa or by the Cape of Good Hope. 6. In view of the fact that numerous East Indian genera, as Zanclus, Enoplosus, Toxotes, Epluppits, Platax, TeittJiis, Acan- ihunis (Mouoceros), Myripristis occur in the Eocene rocks of Tuscany, Syria, and Switzerland, we may well .suppose that an open watenvay across Africa then existed. Perhaps these forms were destroyed in European waters by a wave of glacial cold, per- haps after the Miocene. As our knowledge of the Miocene fish fauna; of Europe is still imperfect, we cannot locate accurately the period of their disappearance. About half the species found in the Eocene of Italy belong to existing genera, and these genera are almost all now represented in the Indian fauna, and those named above with others are confined to it. The study of fishes alone furnishes no adequate basis for mapping the continental masses of Tertiary times. The known facts in regard to their distribution agree fairly with the pro- visional maps lately published by Dr. Ortmann (Bull. Philos. Soc, XLI). In the Eocene map (Fig. 179) the Mediterranean extends to the northward of Arabia, across to the mouth of the Ganges. This extension would account for the tropical. Eocene, and Miocene fish fauna of Southern Europe. The Cape of Good Hope as a Barrier to Fishes. — The fishes of the Cape of Good Hope are not well enough known for close comparison with those of other regions. Enough is known of the Cape fauna to show its general relation to those of India and Australia. The Cape of Good Hope lies in the South Tem- perate Zone. It offers no absolutely impassable barrier to the tropical fishes from either side. It bears a closer relation to either the Red Sea or the Mediterranean than they bear to each other. It is, therefore, reasonable to conclude that the transfer of tropical shore fishes of the Old World between the Atlantic and Pacific, in recent times, has taken place mainly Isthmus Barriers Separating F'ish Faunas 269 around the southern point of Africa. To pelagic and deep-sea fishes the Cape of Good Hope has offered no barrier whatever. To ordinary fishes it is an obstacle, but not an impassable one. This the fauna itself shows. It has, however, not been passed by many tropical species, and by these only as the result of thousands of years of struggle and point-to-point migration. Relations of Japan to Mediterranean Explainable by Present Conditions. — We may conclude that the resemblance of the Mediterranean fish fauna to that of Japan or India is no more than might be expected, even had the present contour of the continents been permanent for the period of duration of the present genera and species. An open channel in recent times would have produced much greater resemblances than actually exist. The Isthmus of Panama as a Barrier to Distribution. — Con- ditions in some regards parallel with those of the Isthmus of Suez exist in but one other region — the Isthmus of Panama. Here the first observers were very strongly impressed by the resemblance of forms. Nearly half the genera found on the two sides of this isthmus are common to both sides. Taking those of the Pacific shore for first consideration, we find that three-fourths of the genera of the Panama fauna occur in the West Indies as well. This identity is many times greater than that existing at the Isthmus of Suez. Moreover, while the Cape of Good Hope offers no impassable barrier to distribution, the same is not true of the southern part of South America. The subarctic climate of Cape Horn has doubtless formed a complete check to the movements of tropical fishes for a vast period of geologic time. Unlikeness of Species on the Shores of the Isthmus of Panama. — But, curiously enough, this marked resemblance is confined chiefly to the genera and does not extend to the species on the two shores. Of 1400 species of fishes recorded from tropical America north of the Equator, only about 70 are common to the two coasts. The number of shore fishes common is still less. In this 70 are included a certain number of cosmopolitan types which might have reached either shore from the Old World. 270 Isthmus Barriers Separating Fish Faunas Isthmus Barriers Separating Fish Faunas 271 A few others invade brackish or fresh waters and may pos- sibly have found their way, in one way or another, across the Isthmus of Nicaragua. Of fishes strictly marine, strictly lit- toral, and not known from Asia or Polynesia, scarcely any species are left as common to the two sides. This seems to show that no waterway has existed across the Isthmus within the lifetim.e, whatever that may be, of the existing species. The close resemblance of genera shows apparently with almost equal certainty that such a watenvay has existed, and within the period of existence of the groups called genera. How long a species of fish may endure unchanged no one knows, but we know that in this regard great differences must exist in dif- ferent groups. Assuming that different species crossed the Isthmus of Panama in Miocene times, we should not be sur- prised to find that a few remain to all appearances unchanged ; that a niuch larger number have become ' ' representative ' ' species, closely related forms retaining relations to the envi- ronment to those of the parent form, and, finally, that a few species have been radically altered. This is exactly what has taken place at the Isthmus of Panama with the marine shore fishes. Curiously enough, the movement of genera seems to have been chiefiy from the At- lantic to the Pacific. Certain characteristic genera* of the Panama region have not passed over to the Pacific. On the other hand, most of the common generaf show a much larger number of species on the Atlantic side. This may be held to show their Atlantic origin. Of the relatively small number of genera which Panama has received from Polynesia, t few have crossed the Isthmus to ap- pear in the West Indian fauna. Views of Earlier Writers on the Fishes of the Isthmus of Panama. — The elements of the problem at Panama may be better under- stood by a glance at the results of previous investigations. * Hoplopagrits, Xenidilliys, Xcnislius, Xcnocys, Microdcsmus, Ccrdale, Cratiniis, Azevia, Microlepidotus, Orthoslcechus, Isaciclla, etc. t Hmnulon, Anisotremus, Gerrcs, Centra poimis, Galcichlliys, llypoplcctrus, Mycteroperca, UlcEma, Stellifer, Micropogon, Bodianus, Micros paihodon. % Among these are perhaps Teiithis (Acanilmrus) , llisha, Salarias, Myri- pristis, Thaiassoma. Some such which have not crossed the Isthmus are Cirrhitus, Sectator, Sebastopsis, and Lophiomus. 272 Isthmus Barriers Separating Fish Faunas In i860 r)r. Gunther, after enumerating the species exam- ined by him from Panama, reaches the conclusion that nearly one-third of the marine fishes on the two shores of tropical America will be found to be identical. He enumerates 193 such species as found on the two coasts; 59 of these, or 31 per cent. of the total, being actually identical. From this he infers that there must have been, at a comparatively recent date, a de- pression of the Isthmus and intermingling of the two faunas.* Catalogue of Fishes of Panama. — In an enumeration of the fishes of the Pacific coast in 1885,! the present writer showed that Dr. Giinther's conclusions were based on inadequate data. In my list 407 species were recorded from the Pacific coast of tropical America — twice the number enumerated by Dr. Gunther. Of these 71 species, or 17-3- per cent., were found also in the Atlantic. About 800 species are known from the Caribbean and adjacent shores, so that out of the total number of 1,136 species but 71, or 6 per cent, of the whole, are common to the two coasts. This number does not greatly exceed that of the species common to the West Indies and the Mediterranean, or even the West Indies and Japan. It is to be noted also that the number 71 is not very definitely ascertained, as there must be considerable difference of opinion as to the boundaries of species, and the actual identity in several cases is open to doubt. This discrepancy arises from the comparatively limited rep- resentation of the two faunas at the disposal of Dr. Gunther. He enumerates 193 marine or brackish-water species as found on the two coasts, 59 of which are regarded by him as specific- ally identical, this being 31 per cent, of the whole. But in 30 of these 59 cases I regard the assumption of complete identity as erroneous, so that taking the number 193 as given I would reduce the percentage to 15. But these 193 species form but a fragment of the total fauna, and any conclusion based on such narrow data is certain to be misleading. Of the 71 identical species admitted in our list, several {e.g., Mold, Thnniius) are pelagic fishes common to most warm seas. * "Fishes of Central America," 1S69, 397. t Proc. U. S. .\fal. Mus., 1S85, 393. Isthmus Barriers Separating Fish Faunas 273 Still others {e.g., Trachunis, Carangus, Diodon sp.) are cosmo- politan in the tropical waters. Most of the others {e.g., Gobius, Gerres, Centropomus, Galeichthys sp., etc.) often ascend the rivers of the tropics, and we may account for their diffusion, perhaps, as we account for the dispersion of fresh-water fishes on the Isthmus, on the supposition that they may have crossed from marsh to marsh at some time in the rainy season. In very few cases are representatives of any species from opposite sides of the Isthmus exactly alike in all respects. These differences in some cases seem worthy of specif c value, giving us "representative species" on the two sides. In other cases the distinctions are very trivial, but in most cases they are appre- ciable, especially in fresh specimens. Further, I expressed the belief that "fuller investigation will not increase the proportion of common species. If it does not, the two faunas show no greater resemblance than the simi- larity of physical conditions on the two sides would lead us to expect." This similarity causes the same types of fishes to persist on either side of the Isthmus while through isolation or otherwise these have become different as species. This conclusion must hold so far as species are concerned, but the resemblance of the genera on the sides has a signifi- cance of its own. In 1880* Dr Giinther expressed his views in still stronger language, claiming a still larger proportion of the fishes of trop- ical America to be identical on the two sides of the continent. He concluded that "with scarcely any exceptions the genera are identical, and of the species found on the Pacific side, nearly one-half have proved to be the same as those of the Atlantic. The explanation of this fact has been found in the existence of communications between the two oceans by channels and straits which must have been open tiU within a recent period. The isthmus of Central America was then partially submerged, and appeared as a chain of islands similar to that of the Antilles; but as the reef-building corals flourished chiefly north and east of these islands and were absent south and west of them, reef fishes were excluded from the Pacific shores when the com- munications were destroyed by the upheaval of land." * Introduction to the "Study of Fishes," iS8o, p. 280. 274 Isthmus Barriers Separating Fish Faunas Conclusions of Evermann and Jenkins. — This remark led to a further discussion of the subject on the part of Dr. B. W. Evermann and Dr. 0. P. Jenkins. From their paper on the fishes of Guaymas * I make the following quotations : "The explorations since 1885 have resulted (i) in an addi- tion of about 100 species to one or other of the tvi^o faunas; (2) in sliowing that at least two species that were regarded as identical on the two shores f are probably distinct; and (3) in the addition of but two species to those common to both coasts, t "All this reduces still further the percentage of common species. "Of the no species obtained by us, 24, or less than 21 per cent., appear to be common to both coasts. Of these 24 species, at least 16, from their wide distribution, would need no hypothesis of a former waterway through the Isthmus to account for their presence on both sides. They are species fully able to arrive at the Pacific shores of the Americas from the warm seas west. It thus appears that not more than eight species, less than 8 per cent, of our collection, all of which are marine species, require any such hypothesis to account for their occurrence on both coasts of America. This gives us, then, 1,307 species that should properly be taken into account when considering this question, not more than 72 of which, or 5.5 per cent., seem to be identical on the two coasts. This is very different from the figures given by Dr. Giinther in his 'Study of Fishes.' "Now, if from these 72 species, admitted to be common to both coasts, we subtract the 16 species of wide distribution — so wide as to keep them from being a factor in this problem — we have left but 56 species common to the two coasts that bear very closely upon the waterway hypothesis. This is less than 4.3 per cent, of tlie wliole number. "But the evidence obtained from a study of other marine life of that region points to the same conclusion. *Proc. U. S. Nat. Mas., 1891, pp. 12.1-126. t Cilharichlhys spiloplcnis and C gilbcrti. X Ilcciinilon stcindadiiicri and Gyinnoihorax castaneus of the west coast probably being identical with //. schranki and Gyvinothorax funebris of the east coast. Isthmus Barriers Separating P'ish Faunas 275 "In 1 88 1, Dr. Paul Fischer discussed the same question in his 'Manual de Conchyliologie,' pp. 168, 169, in a section on the Molluscan Fauna of the Panamic Province, and reached the same general conclusions. He says : ' Les naturalistes Americians se sont beaucoup preeoccupes des espcces de Panama qui paraissent identiques avec celles des Antilles, ou qui sont representatives. P. Carpenter estime qu'il en existe 35. Dans la plupart des cas, I'identite absolue n'a pu etre constantee et on a trouve quelques caracteres distinctifs, ce qui n'a rien d'etonnant, puisque dans I'hypothese d'une origine commune, les deux races pacifique et atlantique sont separee depuis la periode Miocene. Voici un liste de ces especes representatives ou identiques.' Here follows a list of 20 species. 'Mais ces formes semblables,' he says, 'constituent un infime minorite (3 per cent.).' "These facts have a very important bearing upon certain geological questions, particularly upon the one concerning the cold of the Glacial period. " In Dr. G. Frederick Wright's recent book, 'The Ice Age in North America,' eight different theories as to the cause of the cold are discussed. The particular theory which seems to him quite reasonable is that one which attributes the cold as due to a change of dift'erent parts of the country, and a depression of the Isthmus of Panama is one of the important changes he considers. He says: 'Should a portion of the Gulf Stream be driven through a depression across the Isthmus of Panama, into the Pacific, and an equal portion be diverted from the Atlantic coast of the United States by an elevation of the sea-bottom between Florida and Cuba, the consequences would necessarily be incalculably great, so that the mere existence of such a pos- sible cause for great changes in the distribution of moisture over the northern hemisphere is sufficient to make one hesitate before committing himself unreservedly to any other theory; at any rate, to one which has not for itself independent and adequate proof.' "In the appendix to the same volume Mr. Warren Upham, in discussing the probable causes of glaciation, says : ' The qua- ternary uplifts of the Andes and Rocky Mountains and of the West Indies make it nearly certam that the Isthmus of Panama 276 Isthmus Barriers Separating Fish Faunas has been similarly elevated during the recent epoch. ... It may be true, therefore, that the submergence of this isthmus was one of the causes of the Glacial period, the continuation of the equatorial oceanic currents westward into the Pacific having Fig. ISO.— Cauhphryne jordani Goode and Bean, a deep-sea fish of the Gulf Stream. Family Cera/iidtr. greatly diminished or wholly diverted the Gulf Stream, which carries warmth from the tropics to the northern Atlantic and northwestern Europe.' Fig. 181.— Excrpes asper Jenkins and Evermann, a fish of the rock-iiools, Guayraas, Mexico. Family Blenniidce. "Any very recent means by which the fishes could have passed readily from one side to the other would have resulted in making the fish faunas of the two shores practically identical; but the time that has elapsed since such a waterway could have Isthmus Barriers Separating Fish Faunas 277 existed has been long enough to allow the fishes of the two sides to become practically distinct. That the moUusks of the two shores are almost wholly distinct, as shown by Dr. Fischer, is even stronger evidence of the remoteness of the time when the means of communication between the two oceans could have existed, for ' species ' among the moUusks are probably more persistent than among fishes. "Our present knowledge, therefore, of the fishes of tropical America justifies us in regarding the fish faunas of the two coasts as being essentially distinct, and beheving that there has not been, at any comparatively recent time, any waterway through the Isthmus of Panama." It is thus shown, I think, conclusively, that the Isthmus of Panama could not have been depressed for any great length of time in a recent geological period. Conclusions of Dr. Hill. — These writers have not, however, con- sidered the question of generic identity. To this we may find a clue in the geological investigations of Dr. Robert T. Hill. In a study of "The Geological History of the Isthmus of Panama and Portions of Costa Rica," Dr. Hill uses the follow- ing language: "By elimination we have concluded that the only period of time since the Mesozoic within which communication be- tween the seas could have taken place is the Tertiary period, and this must be restricted to the Eocene and Oligocene epochs of that period. The paleontologic evidence upon which such an opening can be surmised at this period is the occurrence of a few California Eocene types in the Atlantic sides of the tropical American barrier, within the ranges of latitude between Gal- veston (Texas) and Colon, which are similar to others found in California. There are no known structural data upon which to locate the site of this passage, but we must bear in mind, however, that this structure has not been completely explored. " Even though it was granted that the coincidence of the oc- currence of a few identical forms on both sides of the tropical American region, out of the thousands which are not common, indicates a connection between the two seas, there is still an absence of any reason for placing this connection at the Isth- mus of Panama, and we could just as well maintain that the 278 Isthmus Barriers Separating Fish Faunas locus thereof might have been at some other point in the Cen- tral American region. "The reported fossil and living species common to both oceans are littoral forms, which indicate that if a passage existed it must have been of a shallow and ephemeral character. "There is no evidence from either a geologic or a biologic standpoint for believing that the oceans have ever communi- cated across the Isthmian regions since Tertiary time. In other words, there is no evidence for these later passages which have been established upon hypothetical data, especially those of Pleistocene time. "The numerous assertions, so frequently found in litera- ture, that the two oceans have been frequently and recently connected across the Isthmus, and that the low passes indic- ative of this connection still exist, may be dismissed at once and forever and relegated to the domain of the apocryphal. A few species common to the waters of both oceans in a predomi- nantly Caribbean fauna of the age of the Claiborne epoch of the Eocene Tertiary is the only paleontologic evidence in any time upon which such a connection may be hypothesized. "There has been a tendency in literature to underestimate the true altitude of the isthmian passes, which, while probably not intentional, has given encouragement to those who think that this Pleistocene passage may have existed, ilaack has erroneously given the pass at i86 feet. Dr. J. W. Gregory states 'that the summit of the Isthmus at one locahty is 154 feet and in another 287 feet in height.' The lowest isthmian pass, which is not a summit, but a drainage col, is 287-295 feet above the ocean. ' ' If we could lower the isthmian region 300 feet at present, the waters of the two oceans would certainly commingle through the narrow Culebra Pass. But the Culebra Pass is clearly the headwater col of two streams, the Obispo flowing into the Chagres, and the Rio Grande flowing into the Pacific, and has been cut by fluviatile action, and not by marine erosion, out of a land mass which has existed since Miocene time. Those who attempt to establish Pleistocene interoceanic channels through this pass on account of its present low altitude must not omit from their calculations the restoration of former rock Isthmus Barriers Separating Fish Faunas 279 masses which have been removed by the general leveUing of the surface by erosion." In conclusion, Dr. Hill asserts that "there is consideraVjle evidence that a land barrier in the tropical region separated the two oceans as far back in geologic history as Jurassic time, Fig. 182. — Xenocys jessice .Jordan and BoUman. Galapagos Island.s. Family Lutianidce . and that that barrier continued throughout the Cretaceous period. The geological structure of the Isthmus and Central American regions, so far as investigated, when considered aside from the paleontology, presents no evidence by which the former existence of a free communication of oceanic waters across the present tropical land barriers can be established. The paleontologic evidence indicates the ephemeral existence of a passage at the close of the Eocene period. All lines of inquiry — geologic, paleontologic, and biologic — give evidence that no connection has existed between the two oceans since the close of the Oligocene. This structural geology is decidedly opposed to any hypothesis by which the waters of the two oceans could haA^e been connected across the regions in Miocene, Pliocene, Pleistocene, or recent times." Final Hypothesis as to Panama. — If we assume the correct- ness of Dr. Hill's conclusions, they may accord in a remarkable degree -VAnth the actual facts of the distribution of the fishes about the Isthmus. To account for the remarkable identity of genera and divergence of species I may suggest the following hypothesis : 2»0 Isthmus Barriers Separating Fish Faunas During the lifetime of most of the present species, the Isth- mus has not been depressed. It was depressed in or before Pliocene time, during the hfetime of most of the present genera. We learn from other sources that few of the extant species of fishes are older than the PHocene. Relatively few genera go back to the Eocene, and most of the modern families appear to begin in the Eocene or later Cretaceous. In general the Miocene may be taken as the date of the origin of modern genera. The channel formed across the Isthmus was relatiA'ely shallow, excluding forms inhabiting rocky bottoms at consider- able depths. It was wide enough to permit the infiltration from Fig. 1S3. — Channel Catfish, IdaJurns pinirtntus CRafinesquc). Illinois River. Family Siluridcp. the Caribbean Sea of numerous species, especially of shore fishes of sandy bays, tide pools, and brackish estuaries. The currents set chiefly to the Avestward, favoring the transfer of Atlantic rather than Pacific types. Since the date of the closing of this channel the species left on the tAvo sides have been altered in varying degrees by the processes of natural selection and isolation. The cases of actual specific identity are few, and the date of the establishment as species, of the existing forms, is subsequent to the date of the last depression of the Isthmus. We may be certain that none of the common genera ever found their way around Cape Horn. ^lost of them disappear to the southward, along the coasts of Brazil and Peru. While local oscillations, inA'olving changes in coast-lines, have doubtless frequently taken place and are still going on, the past and present distribution of fishes does not alone give adequate data for their investigation. Isthmus Barriers Separating Fish Faunas 281 Further, it goes without saying that we have no knowledge of the period of time necessary to work specific changes in a body of species isolated in an alien sea. Nor have we any data as to the effect on a given fish fauna of the infiltration of many species and genera belonging to another. All such forces and results must be matters of inference. The present writer does not wish to deny that great changes have taken place in the outlines of continents in relatively recent times. He would, however, insist that the theory of such changes must be confirmed by geological evidence, and evidence from groups other than fishes, and that likeness in separated fish faunas may not be conclusive. Fig. 184. — Drawing the net on the beach of Hilo, Hawaii. Photograph by Henry W. Henshaw. CHAPTER XVI DISPERSION OF FRESH-WATER FISHES * ISPERSION of Fishes. — The methods of dispersion of fishes may be considered apart from the broader topic of distribution or the final results of such dispersion. In this discussion we are mainly concerned with the fresh-water fishes, as the methods of distribution of marine fishes through marine currents and by continuity of shore and water ways are all relatively simple. The Problem of Oatka Creek. — When I was a boy and went fishing in the brooks of western New York, I noticed that the different streams did not always have the same kinds of fishes in them. Two streams in particular in Wyoming County, not far from my father's farm, engaged in this respect my special attention. Their sources are not far apart, and they flow in opposite directions, on opposite sides of a low ridge — an old glacial moraine, something more than a mile across. The Oatka Creek flows northward from this ridge, while the East Coy runs toward the southeast on the other side of it, both flowing ulti- mately into the same river, the Genesee. It does not require a very careful observer to see that in these two streams the fishes are not quite the same. The streams themselves are similar enough. In each the waters are clear and fed by springs. Each flows over gravel and clay, through alluvial meadows, in many windings, and with elms and alders "in ah its elbows." In both streams we were sure of finding trout, f and in one of them the trout are still abun- dant. In both we used to catch the brook chub,t or, as we * This chapter and the next are m substance reprinted from an essay pub- hshed by the present writer m a voKimc called Science Sketches. A. C. Mc- Clurg & Cii., Chicago. t Sa/rclinus }o}ili)ialis ^litchiU. X Seiiwlilus atronitiLiilaliis ilitchill. 2S2 Dispersion of Fresh-water Fishes 283 called it, the "horned dace"; and in both were large schools of shiners* and of suckers. f But in every deep hole, and espe- cially in the millponds along the East Coy Creek, the horned poutj swarmed on the mucky bottoms. In every eddy, or in the deep hole worn out at the root of the elm-trees, could be seen the sunfish,§ strutting in green and scarlet, with spread fins keeping intruders away from its nest. But in the Oatka Creek were found neither horned pout nor sunfish, nor have I ever heard that either has been taken there. Then besides these nobler fishes, worthy of a place on every schoolboy's string, we knew by sight, if not by name, numerous sm.aller fishes, darters !| and minnows,1i which crept about in the ' gravel on the bottom of the East Coy, but which we never recognized in the Oatka. There must be a reason for differences like these, in the streams themselves or in the nature of the fishes. The sun- fish and the horned pout are homedoving fishes to a greater extent than the others which I have mentioned; still, where no obstacles prevent, they are sure to move about. There must be, then, in the Oatka some sort of barrier, or strainer, which keeping these species back permits others more adven- turous to pass ; and a wider knowledge of the geography of the region showed that such is the case. Farther down in its course, the Oatka falls over a ledge of rock, forming a consider- able waterfall at Rock Glen. Still lower down its waters dis- appear in the ground, sinking into some limestone cavern or gravel-bed, from which they reappear, after some six miles, in the large springs at Caledonia. Either of these barriers might well discourage a quiet-loving fish; while the trout and its active associates have some time passed them, else we should not find them in the upper waters in which they alone form the fish fauna. This problem is a simple one ; a boy could work it out, and the obvious solution seems to be satisfactory. * Notropis cumulus Rafinesque. ■\ CatOiiomus commersoui (Laccpedc). J Ameiurus nielas Rafinesque, § Eupomotis gibbosus Linna:us. \\Eihcostoma flabellare Rafinescjue. T[ Rhinichihys alronasus MitchiU. 284 Dispersion of Fresh-water Fishes Generalizations as to Dispersion. — Since those days I have been a fisherman in many waters, — not an angler exactly, but one who fishes for fish, and to whose net nothing large or small ever comes amiss ; and wherever I go I find cases like this. We do not know all the fishes of America }'et, nor all those well that we know by sight ; stiU this knowledge will come with time and patience, and to procure it is a comparatively easy task. It is also easy to ascertain the more common inhabitants of any given stream. It is difficult, however, to obtain nega- tive results which are really results. You cannot often say that a species does not live in a certain stream. You can only affirm that you have not yet found it there, and you can rarely fish in any stream so long that you can find nothmg that you have not taken before. Still more difficult is it to gather the results of scattered observations into general state- ments regarding the distribution of fishes. The facts may be so few as to be misleading, or so numerous as to be confusing, and the few writers who have taken up this subject in detail have found both these difficulties to be serious. AVhatever general propositions we may maintain must be stated with the modifying clause of " other things being equal" ; and other things are never quite equal. The saying that "Nature abhors a generalization" is especially applicable to all discussions of the relations of species to environment. Still less satisfactory is our attempt to investigate the causes on which our partial generalizations depend, — to attempt to break to pieces the "other things being equal" which baffle us in our search for general laws. The same problems, of course, come up on each of the other continents and in all groups of animals or plants; but most that I shall say will be confined to the question of the dispersion of fishes in the fresh waters of North America. The broader questions of the boundaries of faunas and of faunal areas I shall bring up only incidentally. Questions Raised by Agassiz.— Some of the problems to be solved were first noticed by Prof. Agassiz in 1850, in his work on Lake Superior. Later (1854), in a paper on the fishes of the Tennessee River,* he makes the following statement: * On Fishes from Tennessee River, Alabama. American Journal of Science and Arts, xvii., 2d series, 1854, p. 26. Dispersion of Fresh-water Fishes 285 " The study of these features [of distribution] is of the greatest importance, inasmuch as it may eventually lead to a better understanding of the intentions implied in this seemingly arbi- trary disposition of animal life. ... "There is still another very interesting problem respecting the geographical distribution of our fresh-water animals which may be solved by the further investigation of the fishes of the Tennessee River. The water-course, taking the Powell, Clinch, and Holston Rivers as its head waters, arises from the moun- FiG. 1S5. — Homed Dace, Semohlus atromaculatiui (Mitchill). Aux Plaines River, Ills. Family Cyprinida:. tains of Virginia in latitude 37°; it then flows S.W. to latitude 34° 25', when it turns W. and N.W., and finally empties into the Ohio, under the same latitude as its source in 37°. "The question now is this: Are the fishes of this water sys- tem the same throughout its extent? In which case we should infer that water communication is the chief condition of geo- graphical distribution of our fresh-water fishes. Or do they differ in different stations along its course? And if so, are the differences mainly controlled by the elevation of the river above the level of the sea, or determined by climatic differences cor- responding to dift'erences of latitude? We should assume that the first alternative was true if the fishes of the upper course of the river differed from those of the middle and lower courses in the same manner as in the Danube, from its source to Pesth, where this stream flows nearly for its whole length under the same parallel. We would, on the contrary, suppose the second alternative to be well founded if marked dift'erences were ob- served between the fish of such tracts of the river as do not 286 Dispersion of Fresh-water Fishes materially differ in their evolution above the sea, but flow under dift'erent latitudes. Now, a few collections from different sta- tions alons this river, like that sent me by Dr. Newman from the vicinity of Huntsville, would settle at once this question, not for the Tennessee River alone, but for most rivers flowing under similar circumstances upon the surface of the globe. Nothing, however, short of such collections, compared closely with one another, will furnish a reliable answer. . . . Who- ever wiU accomplish this survey will have made a highly valu- able contribution to our knowledge." Conclusions of Cope. — Certain conclusions were also sug- gested by Prof. Cope in his excellent memoir on the fishes of the Alleghany region* in 1868. From this paper I make the following quotations: "The distribution of fresh-water fishes is of special impor- tance to the questions of the origin and existence of species in connection with the physical conditions of the waters and of the land. This is, of course, owing to the restricted nature of their habitat and the impossibility of their making extended migrations. With the submergence of land beneath the sea, fresh-water fish are destroyed in proportion to the extent of the invasion of salt water, while terrestrial vertebrates can re- treat before it. Hence every inland fish fauna dates from the last total submergence of the country. " Prior to the elevation of a given mountain chain, the courses of the rivers may generally have been entirely dift'erent from their later ones. Subsequent to this period, they can only have tmdergone partial modifications. As subsecjuent sub- mergences can rarely have extended to the highlands where such streams originate, the fishes of such rivers can only have been destroyed so far as they were unable to reach those ele- vated regions, and preserve themselves from destruction from salt water by sheltering themselves in mountain streams. On the other hand, a period of greater elevation of the land, and of consequent greater cold, would congeal the waters and cover their courses with glaciers. The fishes would be driven to the neighborhood of the coast, though no doubt in more * On the Distribution of Fresh-water Fishes in the Alleghany Region of Southwestern Virginia. Journ. Aead. Nat. Sei., Phila., iS6S, pp. 207-247. Dispersion of Fresh-water Fishes 287 southern latitudes a sufficient extent of uncongealed fresh waters would flow by a short course into the ocean, to perserve from destruction many forms of fresh-water fishes. Thus, through many vicissitudes, the fauna of a given system of rivers has had opportunity of uninterrupted descent, from the time of the elevation of the mountain range, in which it has its sources. . . . "As regards the distinction of species m the disconnected basins of different rivers, which have been separated from an early geologic period, if species occur which are common to any two or more of them, the supporter of the theory of distinct creations must suppose that such species have been twice created, once for each hydrographic basin, or that waters flow- ing into the one basin have been transferred to another. The developmentahst, on the other hand, will accept the last propo- sition, or else suppose that time has seen an identical process and similar result of modification in these distinct regions. jhub of the Great Basin, Leuctscus lincntus (Girard). Yellow.stone Park. Family Cyprinidw. Heart Lake, "Facts of distribution in the eastern district of North America are these. Several species of fresh-water fishes occur at the same time in many Atlantic basms from the Merrimac or from the Hudson to the James, and throughout the Mississippi Valley, and in the tributaries of the Great Lakes. On the other hand, the species of each river may be regarded as pertaining to four classes, whose distribution has direct reference to the character of the water and the food it offers: first, those of the tide-waters, of the river channels, bayous, and sluggish waters near them, or in the flat lands near the coast; second, those of the river channels of its upper course, where the currents are 288 Dispersion of Fresh-water Fishes more distinct; third, those of the creeks of the hill country; fourth, those of the elevated mountain streams which are sub- ject to falls and rapids." In the same paper Prof. Cope reaches two important general conclusions, thus stated by him : "I. That species not generally distributed exist in waters on different sides of the great water-shed. "II. That the distribution of the species is not governed by the outlet of the rivers, streams having similar discharges (Holston and Kanawha, Roanoke and Susquehanna) having Fig. 1S7. — Butterfly-sculpiii, Melletes papilio Bean, a fish of the rock-pools. St. Paul, Pribilof Islands. less in common than others having different outlets (Kanawha, or Susquehanna and James). "In view of the first proposition, and the question of the origin of species, the possibility of an original or subsequent mingling of the fresh waters suggests itself as more probable than that of distinct origin in the different basins." Questions Raised by Cope. — Two questions in this connec- tion are raised by Prof. Cope. The first question is this: "Has any destruction of the river fauna; taken place since the first elevation of the AUeghanies, when the same species were thrown into waters flowing in opposite directions ? " Of such destruc- tion by submergence or otherwise. Prof. Cope finds no evidence. The second question is, "Has any means of communication Dispersion of Fresh-water Fishes 289 existed, at any time, but especially since the last submergence, by which the transfer of species might occur? " Some evidence of such transfer exists in the wide distribution of certain species, especially those which seek the highest streamlets in the moun- tains; but except to cah attention to the cavernous character of the Subcarboniferous and Devonian limestones, Prof. Cope has made little attempt to account for it. Prof. Cope finahy concludes with this important generali- zation : "It would appear, from the previous considerations, that the distribution of fresh-water fishes is governed by laws similar to those controlling terrestrial vertebrates and other animals, in spite of the seemingly confined nature of their habitat." Views of Giinther. — Dr. Giinther * has well summarized some of the known facts in regard to the manner of dispersion of fishes : "The ways in which the dispersal of fresh-water fishes has been affected were various. They are probably all still in opera- tion, but most work so slowly and imperceptibly as to escape direct observation ; perhaps they will be more conspicuous after science and scientific inquiry shall have reached a somewhat greater age. From the great number of fresh-water forms which we see at this present day acclimatized in, gradually acclimatizing themselves in, or periodically or sporadically mi- grating into, the sea, we must conclude that under certain cir- cumstances salt water may cease to be a barrier at some period of the existence of fresh-water species, and that many of them have passed from one river through salt water into another. Secondly, the headwaters of some of the grandest rivers, the mouths of which are at opposite ends of the continents which they drain, are sometimes distant from each other a few miles only. The intervening space may have been easily bridged over for the passage of fishes by a slight geological change affect- ing the level of the water-shed or even by temporary floods ; and a communication of this kind, if existing for a limited period only, would afford the ready means of an exchange of a num- ber of species previously peculiar to one or the other of these river or lake systems. Some fishes provided with gill-openings * Introduction to the Study of Fishes, iSSo, p. 211. 200 Dispersion of Fresh-water Fishes so narrow that the water moistening the gills cannot readily evaporate, and endowed, besides, with an extraordinary degree of vitality, like many Siluroids {Chlarias, Callichthys), eels, etc., are enabled to wander for some distance over land, and may thus reach a water-course leading them thousands of miles from their original home. Finally, fishes or their ova may be acci- dentally carried by water-spouts, by aquatic birds or insects, to considerable distances." Fresh-water Fishes of North America. — We now recognize about six hundred species * of fishes as found in the fresh waters * The table below shows approximately the composition of the fresh-water fish fauna of Europe, as compared with that of North America north of the Tropic of Cancer. Families. Europe. N. America- Lamprey Petromyzonidcn 3 species. S species. Paddle-fish Polyodoniida: — " s " Sturgeon Acipenscridcr 10 " 6 " Garpike Lepisosteidte — " •; " Bowfin Ajiiiido' — " i " Mooneye Hiodotttidn' — " 3 " Herrina: Cliipeidce 2 " c " Gizzard-shad Dorosomidcs — " i " Salmon Salmonidcn 12 " 28 " Characin Characinida; — " i " Carp Cyprinidcs 61 " 230 " Loach CobitidcB 3 " — " Sucker Catoslom-idce — " iji " Catfish Silurida: i " 2^ " Trout-perch Percopsida: — " 2 " Blindfish Ainblyopsida; — " g " Ivillifish Cypriitodontidu! 3 " r2 " Mud-minnow UmhridiP i " 2 " Pike Esocidts i " cj " Alaska blackfish Dalliida; — " j " Eel A iigiUllidiS 2 " I " Stickleback Gasterosteida; 3 " y " Silverside Atlicrinidce 2 " 2 " Pirate perch Iphrcdoderida: — " i " Elassoma Elassoiiiidcr — " 2 " Sunfish Centrarchidcr . ... — " ^7 " Perch Pjrcida; ^ 1 1 " Iji. Bass bcrranidte i " ^ " Drum Sciaenidm — " j " Surf-fish Embiotocid(S — " j " Cichlid Cichlid(£ — " 2 .< Goby Cobiidcv 2 " 6 " Sculpin CottidcF 2 " 21 Blenny Blcnuiida; 3 ■' I_ .. Cod Gadida i " j .. Flounder Plcnroncctidue i " .< Sole Solcidj: i " j Total; Europe, 21 families; 126 species. North America, 34 families* 590 species. A few new species have been added since this enumeration was made' According to Dr. Giinther (Guide to the Study of Fishes, p. 243), the total number of species now known from the temperate regions of Asia and Eiirrine Dispersion of Fresh-water Fishes 291 of North America, north of the Tropic of Cancer, these repre- senting thirty-four of the natural famihes. As to their habits, we can divide these species rather roughly into the four cate- gories proposed by Prof. Cope, or, as we may call them, (i) Lowland fishes; as the bowfin,* pirate-perch, f large- mouthed black bass, J sunfishes, and some catfishes. (2) Channel-fishes; as the channel catfish, § the mooneye, || garpike,T[ buffalo-fishes,** and drum.ff (3) Upland fishes; as many of the darters, shiners, and suckers, and the small-mouthed black bass.|t (4) Moimtain-fishes ; as the brook trout and many of the darters and minnows. To these we may add the more or less distinct classes of (5) lake fishes, inhabiting only waters which are deep, clear, and cold, as the various species of whitefish §§ and the Great Lake trout; II II (6) anadromous fishes, or those which run up from the sea to spawn in fresh waters, as the salmon, 7"il sturgeon,*** shad,ttt and striped bass;nt (7) catadromous fishes, like the eel,§§§ which pass doAvn to spawn in the sea; and (8) brackish- water fishes, which thrive best in the debatable waters of the river-mouths, as most of the sticklebacks and the killifishes. As regards the range of species, we have every possible gra- dation from those which seem to be confined to a single river, and are rare even in their restricted habitat, to those which are is about 360. The fauna of India, south of the Himalayas, is much more extensive, numbering 625 species. This latter fauna bears little resemblance to that of North America, being wholly tropical in its character. * Amia calva Linnaeus. t Aphredoderus sayanns Gilliams. J Micropterus sahnoides Lacepede. § Ictalurus punctatus Rafinesque. II Hindon tergisus Le Sueur. Ij Lepisosteus osseiis I.inna--us. ** Ictiobus bubalus, cypriiiclla, etc. ft Aplodinotus gruniiiens Rafinc-sque. %% Micropterus dolomicu Lacepede. §§ Coregomis clupeiformis, Argyrosomus artcdi, etc. II II Cristivomer nnmayctsh Walbaum. ^1| Salnio salar Linna;us. *** Acipenser stitrio and other species. ttt Alosa sapidissima Wilson. XXX Roccus lineatus Bloch. §§§ Angiiilla chrysypa Raf. 292 Dispersion of Fresh-water Fishes in a measure cosmopolitan,* ranging everywhere in suitable waters. Characters of Species. — Still, again, we have all degrees of constancy and inconstancy in what we regard as the charac- ters of a species. Those found only in a single river-basin are usually uniform enough; but the species having a wide range usually vary much in different localities. Such variations have at different times been taken to be the indications of as many different species. Continued explorations bring to light, from year to year, new species; but the number of new forms now discovered each year is usually less than the number of recognized species which are yearly proved to be untenable. Four complete lists of the fresh-water fishes of the United States (north of the Mexican boundary) have been published by the present writer. That of Jordan and Copeland,t published in 1S76, enumerates 670 species. That of Jordan J in 1878 con- tains 665 species, and that of Jordan and Gilbert § in 18S3, 587 species. That of Jordan and Evermann || in 1898 contains 5S5 species, although upwards of 130 new species were detected in the twenty-two years which elapsed between the first and the last list. Additional specimens from intervening localities are often found to form connecting links among the nominal species, and thus several supposed species become in time merged in one. Thus the common channel catfish Tj of our rivers has been de- scribed as a new species not less than twenty-five times, on account of differences real or imaginary, but comparatively tri- fling in value. * Thvis the chub-sucker {Erimyzon sucelta) in some of its varieties ranges everywhere from Maine to Dakota, Florida, and Texas; while a number of other species are scarcely less widley distributed. t Check List of the Fishes of the Fresh Waters of North America, by David S. Jordan and Herbert E. Copeland. Bulletm of the Buffalo Society of Natural History, 1876, pp. 133-164. I A Catalogue of the Fishes of the Fresh Waters of North America. Bul- letin of the United States Geological Survey, 1S7S, pp. 407-442. § A Catalogue of the Fishes Known to Inhabit the Waters of North America North of the Tropic of Cancer. Annual Report of the Commissioner of Fish and Fisheries for 1884 and 1885. !1 Check List of the Fishes of North and Middle America. Report of the U. S. Commissioner of Fisheries for 1895. II Ictaluriis punctalus Rafmcsque. Dispersion of Fresh- water Fishes 293 Where species can readily migrate, their uniformity is pre- served; but whenever a form becomes locahzed its representa- tives assume some characters not shared by the species as a whole. When we can trace, as we often can, the disappearance by degrees of these characters, such forms no longer represent to us distinct species. In cases where the connecting forms are extinct, or at least not represented in collections, each form which is apparently different must be regarded as a distinct species. The variations in any type becpi and marine fishes from the Gulf. Channel-cats, sharks, sea-crabs, sunfishes, and mullets can all be found there to- gether. It is therefore to be expected that the lowland fauna of all the rivers of the Gulf States would closely resemble that of the lower ;\Iississippi ; and this, in fact, is the case. The streams of southern Florida and those of southwestern Texas offer some peculiarities connected with their warmer climate. The Floriila streams contain a few peculiar fishes;! while the rivers of Texas, with the same general fauna as those farther north, haA'e also a few distinctly tropical types, J immi- grants from the Lowlands oi Mexico. Cuban Fishes. — The fresh waters of Cuba are inhabited by fishes unlike those found in the United States. Some of these are e\'i(lcntly indigenous, derived in the waters they now in- hafiit directly from marine forms. Two of these are eyeless species, § inhabiting streams in the caverns. They have no relatives in the fresh waters of any other region, the blind fishes !1 of our caves being of a whoUy different type. Some of the Cuban fishes arc common to the fresh waters of the other AVest Indies. Of Northern types, onl}' one, the alligator gar,"" is found in Cuba, and this is evidently a filibuster immigrant from the coasts of I^lorida. Swampy Watersheds. — The low and irregular watershed which separates the tributaries of Lake Michigan and Lake Erie from those of the Ohio is of httle importance in determining the range of species. Many of the distinctively Northern fishes are found in the headwaters of the Wabash and the Scioto. The considerable difference in the general fauna of the Ohio Valley as compared with that of the streams of Michigan is due to the higher temperature of the former region, rather than * Lepisosteus tristirchus. t Jordanella, Riviilns, Hetcrandria, etc. J Heros, Tetragonoptcrtis . § Liicifuga and Stygicola, fishes allied to the cusk, and belonging to the family of Brotulida:. \\ Ainblyopsis, Typhlichihys. T[ Lepisosteus irisiccclius. Barriers to Dispersion of River Fishes 315 to any existing barriers between the river and the Great Lakes. In northern Indiana the watershed is often swampy, and in many places large ponds exist in the early spring. At times of heavy rains many species will move through con- siderable distances by means of temporary ponds and brooks. Fishes that have thus emigrated often reach places ordinarily inaccessible, and people finding them in such localities often imagine that they have "rained down." Once, near Indian- apolis, after a heavy shower, I found in a furrow in a corn-field a small pike,* some half a mile from the creek in which he should belong. The fish was swimming along in a temporary - brook, apparently wholly unconscious that he was not in his native stream. Migratory fishes, which ascend small streams to spawn, are especially likely to be transferred in this way. By some such means any of the watersheds in Ohio, Indiana, or Illinois may be passed. Fig. 193. — Creekfish or Chub-sucker, Erimyzon sucetta (Laci^p^de). Nipisink Lake, Illinois. Family Catostomidw. It is certain that the Hmits of Lake Erie and Lake Michigan were once more extended than now. It is reasonably prob- able that some of the territory now drained by the Wabash and the Illinois was once covered by the waters of Lake Michi- gan. The ciscof of Lake Tippecanoe, Lake Geneva, and the lakes of the Oconomowoc chain is evidently a modified de- scendant of the so-called lake herring, t Its origin most likely *Esox vermiculatus Le Sueur. t Argyrosomus sisco Jordan. J Argyrosomus artedi Le Sueur. -} I 6 Barriers to Dispersion of River Fishes dates from the time when these small deep lakes of Indiana and AYisconsm were connected with Lake Michigan. The changes m habits wliich the cisco has undergone are consider- able. The changes in external characters are but trifling. The presence of the cisco in these lakes and its periodical disappear- ance—that is, retreat into deep water when not in the breeding season — have given rise to much nonsensical discussion as to whether any or all of these lakes are still joined to Lake Michigan bv subterranean channels. Several of the larger fishes, properly characteristic of the Great Lake region,* are occasionally taken in the Ohio Ri\-cr, where they are usually recognized as rare stragglers. The difference in physical conditions is probably the sole cause of their scarcity in the Ohio basin. The Great Basin of Utah. — The similarity of the fishes in the dift'erent streams and lakes of the Great Basin is doubtless to be attributed to the general mingling of their waters which took place during and after the Glacial Epoch. Since that period the climate in that rcgiim has grown hotter and drier, until the over- flow fif tlie \Tirious lakes into the Columbia basin through the Snake Ri\-er has long since ceased. These lakes have become isolated from each other, and many of them have become salt or alkaline and therefore uninhabitable. In some of these lakes certain species may now have become extinct which still remain in others. In some cases, perhaps, the dift'erences in surround- ings may have caused divergence into distinct species of what was once one parent stock. The suckers in Lake Tahoe f and those in Utah Lake are certainly now dift'erent from each other and from those in the Columbia. The trout + in the same waters can be regarded as more or less tangible species, while the w^hite- fishes§ show no differences at all. The clift'erences in the present faunas of Lake Tahoe and Utah Lake must be chiefly due to influences which have acted since the Glacial Epoch, when the whole Utah Basin was part of the drainage of the Columbia. Arctic Species in Lakes. — Connected perhaps with changes * As Lola maculosa; Pcrcopsis gullata: Esox inasquinongy. t L alostoiHus tahoensis, in Lake Tahoe; Caiosiomns iiiacroclieilus and dis- cobolus, in the Cokimbia; Calostoiiius jccundus, Catostonuis ardens; Chasmisies liorus and Panlosteus gcticrosus. in Utah Lake. J Salmo henshawi and virginalis. \ Coregonus williamsoni. Barriers to Dispersion of River Fishes 317 due to glacial influences is the presence in the deep waters of the Great Lakes of certain marine types,* as shown by the explora- tions of Professor Sidney I. Smith and others. One of these is a genus of fishes, t of which the nearest allies now inhabit the Arctic Seas. In his review of the fish fauna of Finland, J Professor A. J. Malmgren finds a number of Arctic species in the waters of Fin- land wliich are not found either in the North Sea or in the southern portions of the Baltic. These fishes are said to " agree with their 'forefathers' in the Glacial Ocean in every point, but remain comparatively smaller, leaner, almost starA^ed." Professor Loven§ also has shown that numerous small animals of marine origin are found in the deep lakes of Sweden and Finland as well as in the Gulf of Bothnia. These anomalies of distribution are explained by Loven and Malmgren on the supposition of the former con- tinuity of the Baltic through the Gulf of Bothnia with the Glacial Ocean. During the second half of the Glacial Period, according to Loven, "the greater part of Finland and of the middle of Sweden was submerged, and the Baltic was a great gulf of the Glacial Ocean, and not connected with the German Ocean. By the gradual elevation of the Scandinavian Continent, the Baltic became disconnected from the Glacial Ocean and the Great Lakes separated from the Baltic. In consequence of the gradual change of the salt water into fresh, the marine fauna became gradually extinct, with the exception of the glacial forms men- tioned above." It is possible that the presence of marine types in our Great Lakes is to be regarded as due to some depression of the land which would connect their waters with those of the Gulf of St. Lawrence. On this point, however, our data are still incomplete. To certain species of upland or mountain fishes the depression of the Mississippi basin itself forms a barrier which cannot be passed. The black-spotted trout, || very closely related species * Species of My;is and other genera of Crustaceans, similar to species described by Sars and others, in lakes of Sweden and Finland. t Triglopsis thompsoni Girard, a near ally of the marine species Oncocottiis quadncornis L. X Kritisk Ofversigt af Finlands Fisk-Fauna, Helsingfors, 1863. § See Giinther, Zoological Record for 1864, p. 137. II Salnw fario L., in Europe; Salmo labrax Pallas, etc., in Asia; Salmc gairdneri Richardson, in streams of the Pacific Coast; Salmo perryi. in J^pan; 3 I 8 Barriers to Dispersion of River Fishes of which abound in all waters of northern Asia, Europe, and western North America, has nowhere crossed the basin of the Mississippi, although one of its species finds no difficulty in passing Bering Strait. The trout and whitefish of the Rocky Moun- tain region are all species diiTerent from those of the Great Lakes or the streams of the Alleghany system. To the grayling, the trout, the whitefish, the pike, and to arctic and subarctic species generally, Bering Strait has evidently proved no serious obstacle to diffusion ; and it is not unlikely that much of the close resemblance of the fresh-water faunse of northern Europe, Asia, and North America is due to this fact. To attempt to decide from which side the first migration came in regard to each group of fishes might be interesting ; but without a wider range of facts than is now in our possession, most such attempts, based on guess- work, would have little value. The interlocking of the fish faunas of Asia and North America presents, however, a number of inter- esting problems, for migrations in both directions have doubtless taken place. Causes of Dispersion Still in Operation. — One miglit go on indefinitely with the discussion of special cases, each more or less interesting or suggestive in itself, but the general conclusion is in all cases the same. The present distribution of fishes is the result of the long-continued action of forces still in operation. The species have entered our waters in many invasions from the Old World or from the sea. Each species has been subjected to the various influences implied in the term "natural selection," and under varying conditions its representatives have undergone many different modifications. Each of the six hundred fresh- water species we now know in the United States may be con- ceived as making every year inroads on territory occupied by other species. If these colonies are able to hold their own in the struggle for possession, they will multiply in the new condi- tions, and the range of the species becomes widened. If the surroundings are different, new species or varieties may be formed with time ; and these new forms may again invade the territory of the parent species. Again, colony after colony of species Salmo clarki Richardson, throughotat the Rocky Mountain range to the Mexican boundary and the headwaters of the Kansas, Platte, and Missouri. Barriers to Dispersion of River Fishes 3 1 9 after species may be destroyed by other species or by uncongenial surroundings. The ultimate result of centuries on centuries of the restlessness of individuals is seen in the facts of geographical distribution. Only in the most general way can the history of any species be traced ; but could we know it all, it would be as long and as event- ful a story as the history of the colonization and settlement of North America by immigrants from Europe. But by the fishes each river in America has been a hundred times discovered, its colonization a htmdred times attempted. In these efforts there is no co-operation. Every individual is for himself, every struggle a struggle of life and death ; for each fish is a cannibal, and to each species each member of every other species is an aHen and a savage. CHAPTER XVIII FISHES AS FOOD FOR MAN HE Flesh of Fishes. — Among all races of men, fishes are freely eaten as food, either raw, as preferred by the Japanese and Hawaiians, or else as cooked, salted, dried, or r)therwise preserved. The flesh of most fishes is white, flaky, readily digestible, ami Avith an agreeable flaA'or. Sonie, as the salmon, are charged \\'ith oil, which aids to gi\'e an orange hue known as salmon Color. (. )thers ha\-e colorless oil Avhich mav be of various con- sistencies. Some have dark-red flesh, which usually contains a hca\"y oil which becomes acrid when stale. Some fishes, as the sharks, have tough, coarse flesh. Some have flesh which is watery and coarse. Some are watery and tasteless, some dry and tasteless. S()me, otherwise excellent, have the muscular area, which constitutes the chief edible part of the fish, filled whh small Ijones. Relative Rank of Food-fishes. — The writer has tested most of the noted food-fishes of the Northern Hemisphere. When Fig. 194. — Eulaclion, or Ulclien. Thaleichihy.t pretiosus Girard. Colunil)ia lliver. Family Argentinida. properly cooked (for he is no judge of raw fish) he would place first in the ranks as a food-fish the eulachon, or candle-fish ( ThalcicJithys pacificits) . 320 Fishes as Food for Man 321 This little smelt, about a foot long, ascends the Columbia River, Frazer River, and streams of southern Alaska in the spring in great numbers for the purpose of spawning. Its flesh is white, very delicate, charged with a white and very agree- FiG. 195. — Ayu, or Japanese Samlet, Plecoglossas altivelis Schlegel. Tanagawa, Tokyo, Japan. able oil, readily digested, and with a sort of fragrance peculiar to the species. Next to this he is inclined to place the ayu iPlecoglossns altivelis), a sort of dwarf salmon which runs in similar fashion in the rivers of Japan and Formosa. The ayu is about as large Fig. 196. — Whitefisli, Coregonvi rhipHformia Mitchill. Eeorse, Midi. as the eulachon and has similar flesh, but with little oil and no fragrance. Very near the first among sea-fishes must come the pampano 322 Fishes as Food for Man of the Gulf of Mexico, with firm, white, {TracJiinotns carolinns) finely flavored flesh. The red surmullet of Europe (Miillus barbatus) has been long famed for its deUcate flesh, and may perhaps be placed next. Two related species in Polynesia, the mimu and the Fig. 197. -Golden Surmullet, MuUus auratus Jordan & Gilbert. Wood's Hole, Mass. kumu (Pscndiipeneiis bifasciatits and Pscudupeneus porpJiyreus), are scarcely inferior to it. Side by side with these belongs the whitefish of the Great Lakes {Coregoniis clapciformis). Its flesh, delicate, slightly Fig. 198. — Spanish Mackerel, Scomberomorus maculatus MitchiU. Family Scombridw. Key West. gelatinous, moderately oily, is extremely agreeable. Sir John Richardson records the fact that one can eat the flesh of this fish longer than any other without the feeling of cloying. The salmon cannot be placed in the front rank, because, however excellent, the stomach soon becomes tired of it. The Spanish mackerel (Scomberomorus maculatus) , with flesh at once rich and delicate, the great opah (Lampris luna), still richer and still o •a to o o p o 2 p 324 Fishes as Food for Man more delicate, the bluefish {Pomatomus saltatrix) similar but a little coarser, the ulua {Carangus sem), the finest large food-fish of the South Seas, the dainty California poppy-fish, miscalled " Pampano " {Palometa simillima), and the kingfish firm and Fig. 200.— Bluefish, Pomatomus saltatrix (L.). New York well-flavored (Sconiberomoriis cm'alla). represent the best of the fishes allied to the mackerel. The shad (Alosa sapid issima), with its sweet, tender, finely oily flesh, stands also near the front among food-fishes, but it sins above all others in the matter of small bones. The weak- fish (Cytioscioii iiobilis) and numerous relatives rank first among Fk;. 201. — lUibulo, Crntropumiis mhleriinnlis (Rloelil. Florida. those with tender, white, savorous flesh. Among the bass and perch-like fishes, common consent places near the first the striped bass {Roceiis lineatus), the bass of Europe [DicentrarcJiits lahrax), the susuki of Japan (Latcolahrax japonicus), the red tai of Japan (Pagriis major and P. cardiiialis), the sheep's-head (Ardiosargiis prohatoccphaliis), the mutton-fish or Pargo CriolLi of Cuba (Lutiatiits analis), the European porgy {Pagrus pagnis), Fishes as Food for Man 325 the robalo (Centropomus imdecimalis), the uku (Aprion vires- cens) of Hawaii, the spadefish {Cluctodipicrtis faber), and the black bass {Micropterus doloinieu). -a£L ■ast. Fig. 202. — Spadefish, ChoBtodiplerus faber (L.). Virginia. i»^ Fig. 203. — Small-mouthed Black Bas.s, MicTopterux linlom.ieu (Lacepede). Potomac River. The various kinds of trout have been made famous the Avorkl over. All are attractive in form and color; all are gamy; all 326 Fishes as Food for Man have the most charming of scenic surroundings, and, finally, all are excellent as food, not in the first rank perhaps, but well above the second. Notable among these are the European Fig. 204.— Speckled Trout (male), Salvelinus fontmalis (Mitchill). New York. Fig. 205. — Piainbow Trout, Snlmo irideu >; Giblions. Sacramento River, California. Fig. 206. — Rangeley Trout, Salvelinus oquassa (Girard). Lake Oquassa, Maine. charr {Salvelinus alpinns), the American speckled trout or charr (Salvelinus fontinalis) , the Dolly Varden or malma {Salvelinus malnia), and the oquassa trout {Salvelinus oquassa). Scarcely Fishes as Food for Man 327 less attractive are the true trout, the brown trout, or forelle (Salmo fario), in Europe, the rainbow-trout (Salmo irideiis), Fig. 207. — Steelhead Trout, Salmo gairdneri Richardson. Columbia River. the steelhead (Salmo gairdneri), the cut -throat trout (Salmo clarkii), and the Tahoe trout (Salmo henshawi), in America, Fig. 20s. — Tahoe Trout, Salmo henshawi Gill & Jordan. Lake Tahoe, California. and the yamabe (Salmo perryi) of Japan. Not least of all these is the flower of fishes, the grayling (Tliymalliis) , of differ- ent species in different parts of the world. Fig. 209.— The Dolly Varden Trout, Salvelinus malma (Walbaum). Lake Fend H'nrpHle THaho. fAfter Evermann.l d'Oreille, Idaho. (After Evermann.) Other most excellent food-fishes are the eel (Angiiilla species), the pike {Esox Indus), the muskallonge (Esox masqninonqy) , the sole of Europe (Solea 5o/ka. Fig. 211. — Pike, Esox lucius L. Ecorse, Mich. Fim 1 liinnh ihllinniiin (V.'il.). Ijakc ('li:ilrn, Clt\ lit \1. \IM1. prefer in general the large parrot-fishes (as Psendoscarns jordani in Hawaii), or else the voung of mullet and similar species. Abundance of Food-fishes. — In general, the economical value of any species depends not on its toothsomeness, but on its abundance and the ease with which it may be caught and pre- FlG 214. — Red Goutfish. nr S;iliiiiiiic1c. Pxfvrhippiiens mnriilnliix 1'>1ih-1i. Fainilv Mii/h'ilie (Sunniilli'ts). served. It is said that more individuals of the herring (Cltipca harengus in the Atlantic, Clnpea pallasi in the Pacific) exist than of any other species. The herring is a good food-fish and when- ever it runs it is freely sought. According to Bjornson, wherc\-er the school of herring touches the coast of Norway, there a \'illage springs up, and this is true in Scotland, Newfoundland, and 33' Fishes as Food for Man fi-.nn Killisnnr) in Alaska to Otaru in Japan, and to Strielok ni Sil.eria. Goode estimates the herring product of the North Atlantic at 1,500,000,000 pounds annually, Huxley used these words: In 1 88 1 Professor Fig. 21.5. — Great Parrot-fisli, iir Guacamaia, Pseudoscarus guacamaia Bloch & Schneider. Florida. " It is said that 2,500,000,000 or thereabout of herrings are every year taken out of the North Sea and the Atlantic. Suppose we assume the number to be 3,000,000,000 so as to be quite safe. It is a large number undoubtedly, but what does Fii;. 21lj. — Striped Mullet, M\ujil cephalus (Ij.). Wood's Hole, Mass. it come to? Not more than that of the herrings which may be contained in one shoal, if it covers half a dozen square miles, and shoals of much larger size are on record. It is safe to say that scattered through the North Sea and the Atlantic, at one and the same time, there must be scores of shoals, any one of Fishes as Food for Man 331 which would go a long way toward supplying the whole of man's consumption of herrings." The codfish (Gadns callarias in the Atlantic; ikiJiis uiacro- '"-'■M^^^ l-'iG. 217. — Mutton-snapper, or Par^o crioUo, Lulianuf! analis (Cuv. ^t Val.). Key West. Fig. 21s. — Herring, Clupca harengus L. Ni-w York. Fig. 219. — Codfish, Gadas callarias L. Eastport, Maine. cephalus in the Pacific) likewise swarms in all the nortliern seas, takes the hook readily, and is better food when salted and dried than it is when fresh. 3n '-> Fishes as Food for Man Next in economic importance probably stands the mackerel of the Atlantic (Scomber scombrns), a rich, oily fish which bears saltme better than most. Fic. 220. — Mackerel, Scomber scombrus L. New York. Not less important is the great king-salmon, or quinnat (On- corhv.icJiiis tschaivytscha), and the still more valuable blued^ack salmon, or red-fish {Oiicorhyiicluis ncrka). I'iG. 221.--H.alilivit, IlippiMilossii.-i hipiioijlossiix (Liniia'usl. St. Paul Island, Bering Sea. (Pliolograph by U. 8. Fur Seal Caiu.uission.) The salmon of the ^\tlantic (Salino salar), the various species of sturgeon (Acipciiscr). the sardines (Saniiiiclla), the halibut (Hil-'pof^lossiis), are also food-fishes of great importance. Fishes as Food for Man 333 Variety of Tropical Fishes. — In the tropics no one species is represented by enormous numbers of individuals as is the case in colder regions. On the other hand, the number of species regarded as food-fishes is much greater in any given port. In Havana, about 350 different species are sold as food in the mar- kets, and an equal number are found in Honolulu. Upward of 600 different species appear in the markets of Japan. In Eng- land, on the contrarv^ about 50 species make up the list of fishes commonly used as food. Yet the number of individual fishes is probably not greater about Japan or Hawaii than in a similar stretch of British coast. Economic Fisheries. — Volumes have been written on the eco- nomic value of the different species of fishes, and it is not the purpose of the present work to summarize their contents. Fio. 222. — Fishing for Avu witli Cormorants in tlie Tanii'j;awa, near Tokyo. (After" pliotograph by J. O. Snyder l>y Sekko Sliiiriada.) Equally voluminous is the Hterature on the subject of catch- ing fishes. It ranges in quality from the quaint wisdom of the " Compleat Angler" and the delicate wit of " Little Rivers " to elaborate discussions of the most economic and effective forms and methods, of the beam-trawl, the purse-seine, and the cod- ^ o A Fishes as Food for Man fish hook In general, fishes are caught in four ways— by baited hooks by spears, by traps, and by nets. Special local methods, such as the use of the tamed cormorant * in the ca-tchmg of the ayu, by the Japanese fishermen at Gifu, may be set aside for the 'moment, and all general methods of fishing come under • one of these four classes. Of these methods, the hook, the spear, the seine, the beam-trawl, the gill-net, the purse-net, the sweep-net,, the trap and the weir are the most important. The use of the hook is again extremely varied. In the deep sea long, sunken lines, are sometimes used for codfish, each bait- ed with many hooks. For pelagic fish, a baited hook is drawn swiftly over the surface, with a "spoon" attached which looks like a Hvmg fish. In the rivers a line is attached to a pole, and when fish are caught for pleasure or for the joy of being in the Avoods, recreation rises to the dignity of angUng. Angling may be accomplished with a hook baited with an earth- worm, a grasshopper, a living fish, or the larva of some insect. The angler of to-day, however, prefers the artificial fly, as belong more workmanhke and also more effective than bait-fishing. The man who fishes, not for the good company of the woods and brooks, but to get as many fish as possible to eat or sell, is not an angler but a pot-fisher. The man Avho kills all the trout he can, to boast of his skill or fortune, is technically known as a trout-hog. Ethically, it is better to He about your great catches of fine fishes than to make them. For most anglers, also, it is more easy. Fisheries. — With the multijdicity of apparatus for fishing, there is the greatest variety in the boats which mav be used. The fishing-fleet of any port of the wxirld is a most interesting * The cormorant is tamed for this purpose. A harness is pUaced about its wings and a ring about the lower part of its neek. Two or three birds may be driven by a boy in a shallow stream, a small net behind him to drive the fish down the river. In a large river like that of Gifu, where the eor- morants are most used, the fishermen hold the birds from the boats anel fish after dark by torchlight. The bird takes a great interest in the work, darts at the fishes with great eagerness, and fills its throat and gular pouch as far down as the ring. Then the bo)' takes him out of the water, holds him by the leg and shakes the fishes out into a basket. When the fishing is over the ayu arc preserved, the ring is taken ofi; from the bird's neck, and the zako or minnows are thrown to him for his share. These he devours greedily. Fishes as Food for Man 335 object, as are also the fishermen with their quaint garb, plain speech, and their strange songs and calls with the hauling in of the net. For much information on the fishing apparatus in use in Fig. 223. — Fishing for .\yu in the Tanagawa, Japan. Emptying the poucli of the cormorant. (Photograph by J. O. Snyder.) America the reader is referred to the Reports of the Fisheries in the Tenth Census, in 1880, under the editorship of Dr. George Brown Goode. In these reports ('joikIc, Stearns, Earle, Gilbert, Bean, and the present writer have treated very fully of all eco- nomic relations of the American fishes. In an admirable work entitled "American Fishes," Dr. Goode, with the fine literary -1^6 Fishes as Food for Man touch of which he was master, has fully discoursed of the game- and food-fishes of America with especial reference to the habits and methods of capture of each. To these sources, to Jordan and Evermann's " Food and Game Fishes of North America," and to many other works of similar purport in other lands, the reader is referred for an account of the economic and the human side of fish and fisheries. Angling. — It is no part of the purpose of this work to de- scribe the methods or materials of angling, still less to sing its praises as a means of physical or moral regeneration. We may perhaps find room for a first and a last word on the subject; the one the classic from the pen of the angler of the brooks of Staf- fordshire, and the other the fresh expression of a Stanford stu- dent setting out for streams such as Walton never knew, the Purissima, the Stanislaus, or perchance his home streams, the Provfi or the Bear. " And let me tell you, this kind of fishing with a dead rod, and laying night-hooks, are like putting money to use; for they both Avork for the owners when they do nothing but sleep, or eat, rir rejoice, as you know we have done this last hour, and sat as quietly and as free from cares under this sycamore as Virgil's Tityrus and his Meliboeus did under their broad beech- tree. Xo life, my honest scholar, — no life so happy and so pleasant as tlie life of a well-governed angler; for when the lawyer is SAvallowed up with business and the statesman is pre- venting or contriving plots, then Ave sit on the cowslip-banks, hear the birds sing, and possess ourseh-es in as much quietness as tliese silent silver streams which Ave noAv see ghde so quietly by us. Indeed, my good scholar, Ave may say of angUng, as Dr. Boteler said of straAvberries, ' Doubtless God could have made a better berry, but doubtless God never did' ; and so, if I might be judge, 'God ncA-er made a more calm, quiet, innocent recrea- tion than angling. ' "I'll tell jrou, scholar, Avhen I sat last on this primrose-bank, and looked doAvn these meadoAvs, I thought of them as Charles the Emperor did of Florence, ' That they were too pleasant to be looked on but only on holidays.' "Gentle Izaak! He has been dead these many years but his disciples are still faithful. When the cares of business lie Fishes as Food for Man 337 heavy and the sound of wheels jarring on cobbled streets grows painful, one's fingers itch for the rod; one would away to the quiet brook among the pines, where one has fished so often. Every man who has ever got the love of the stream in his blood feels often this longing. " It comes to me each year with the first breath of spring. There is something in the sweetness of the air, the growing things, the 'robin in the greening grass' that voices it. Duties that have before held in their performance something of pleas- ure become irksome, and practical thoughts of the day's work are replaced by dreamy pictures of a tent by the side of a moun- tain stream — close enough to hear the water's singing in the night. Two Hght bamboo rods rest against the tent-pole, and a little column of smoke rising straight up through the branches marks the supper fire. Jack is preparing the evening meal, and, as I dream, there comes to me the odor of crisply browned trout and sputtering bacon — was ever odor more delicious? I dare say that had the good Charles Lamb smelled it as I have, his 'Dissertation on Roast Pig' would never have been written. But then Charles Lamb never went a-fishing as we do here in the west — we who have the mountains and the fresh air so boimdlessly. "And neither did Izaak Walton for that matter. He who is sponsor for all that is gentle in angling missed much that is best in the sport by living too early. He did not experience the exquisite pleasure of wading down mountain streams in supposedly water-proof boots and feeling the water trickling in coolingly; nor did he know the joy of casting a gaudy fly far ahead with a four-ounce rod, letting it drift, insect-like, over that black hole by the tree stump, and then feeling the sea- weed line slip through his fingers to the ivhirr of the reel. And, at the end of the day, supper over, he did not squat around a big camp-fire and light his pipe, the silent darkness of the moun- tains gathering round, and a Ijasketful of willow-packed trout hung in the clump of pines by the tent. Izaak's idea of fishing did not comprehend such joy. With a can of worms and a crude hook, he passed the day by quiet streams, threading the worms on his hook and thinking kindly of all things. The day's meditations over, he went back to the village, and, may- 33^ Fishes as Food for Man hap, joined a few kindred souls over a tankard of ale at the sign of the Red Lobster. But he missed the mountains, the water rushing past his tent, the bacon and trout, the camp- FiG. 224.— Fishing for Tai, Tokyo Bay. (Photograph by J. 0. Snyder.) fire— the ]ihysical exaltation of it all. His kind of fishing was angling purely, while modern AValtons, as a rule, eschew the worm. OxywjDAO.oa-viX'Vvu.S \oKvoivvo%\r\s Cftiud.t.'jAu?^ ^q-vaVo . ,^, .,,,„, ,<1«/M REEK XT Al'IA, SAMOA. FISHES FROTvi a I'OvJi. IN I iTE L(.)KAL kj>i.i -^ Fishes as Food for Man 339 "To my mind, there is no real sport in any kind of fishing except fly-fishing. This sitting on the bank of a muddy stream with your bait sunk, waiting for a bite, may be conducive to gentleness and patience of spirit, but it has not the joy of action in wliich a healthy man revels. How much more sport is it to clamber over fallen logs that stretch far out a-stream, to wade slipping over boulders and let your fly drop caressingly on ripples and swirling eddies and still holes! It is worth all the work to see the gleam of a silver side as a half-pounder rises, and, with a flop, takes the fly excitedly to the bottom. And then the nervous thrill as, with a deft turn of the wrist, you hook him securely — whoever has felt that thrill cannot forget it. It will come back to him in his law office when he should be thinking of other things; and with it will come a longing for that dear remembered stream and the old days. That is 'the hold trout-fishing takes on a man. "It is spring now and I feel the old longing myself, as I always do when life comes into the air and the smell of new growth is sweet. I got my rod out to-day, put it together, and have been looking over my flies. If I cannot use them, I can at least muse over days of the past and dream of those to come." (WALDEii.\R Young.) CHAPTER XIX DISEASES OF FISHES ONTAGIOUS Diseases. — As compared with other ani- mals the fishes of the sea are subject to but few specific diseases. Those in fresh waters, being more isolated, are more frequently attacked by contagious maladies. Often these diseases are very destructive. In an "epidemic" in Lake Mendota, near Madison, AA^is., Professor Stephen A. Forbes reports a death of 300 tons of fishes in the lake. I have seen similar conditions among the landlocked alewife in Cayuga and Seneca Lakes, the dead fishes being piled on the beaches so as to fill the air with the stench of their decay. Crustacean Parasites. — The external parasites of fishes are of little injury. These are mainly lerna^ans and other crustaceans ^.>^ ^ Ftg. 22.5.— Menhaden, Brevoortia tyrrinnus (Latrobe). Wood's Hole, Ma.ss. (fishdice) in the sea, and in the rivers different species of leeches. These may suck the blood of the fish, or in the case of certain crustaceans which lie under the tongue, steal the food as it passes along, as is done by Cymothoa prccgiistator, the "bug" of the mouth of the menhaden (Brevooriia tyrannus). 340 0A2 Diseases of Fishes The relation of this crustacean to its host suggested to Latrobe, its discoverer, the relation of the "foretaster" in Roman times to the tyrant whom he served. A similar commensation exists in the mouth of a mullet (Mitgil hospes) at Panama. The writer has received, through the courtesy of I\Ir. A. P. Lundin, a specimen of a fijdng-fish (Exouautcs uiiicolor) taken off Sydney, AustraHa. To this are attached three large copepod crustaceans of the genus Peiiella. the largest over tAvo inches long, and to the copepods in turn are attached a number of barnacles (Con- cJiodcrma virgatinii) so joined to the copepods as to suggest strange flowers, like orchids, growing out of the fish. Myxosporidia, or Parasitic Protozoa. — Internal parasites are very numerous and varied. Some of them are bacteria, giving rise to infectious diseases, especially in ponds and lakes. Others are myxosporidia, or parasitic protozoans, which form warty ap- pendages, which burst, discharging the germs and leaving ulcers Fig. 227. — Black-nosed Daee, Rhinichthys atronasus {Mitchill). East Coy Creek, W. N. Y. Showing black spots of parasitic organisms. (From life by Mary Jordan Edwards.) in their place. In the report of the U. S. Fish Commissioner for 1892, Dr. R. R. Gurley has brought together our knowl- edge of the protozoans of the subclass Myxosporidia, to which these epidemics are chiefly due. These creatures belong to the class of Sporozoa, and are regarded as animals, their nearest relatives being the parasitic Gregarinida, from which they differ m having the germinal portion of the spore consisting of a single protoplasmic mass instead of falciform protoplasmic rods as in the worm-like Gregarines. The Myxosporidia are parasitic on fishes, both fresh-water and marine, especially beneath the epidermis of the gills and fins and in the gall- bladder and urinary bladder. In color these protozoa are Diseases of Fishes 343 always cream-white. In size and form they vary greatly. The cyst in which they lie is filled with creamy substance made up of spores and granual matter. Dr. Gurley enumerates as hosts of these parasites about sixty species of fishes, marine and fresh-water, besides frogs, crustaceans, sea-worms, and even the crocodile. In the sharks and rays the parasites occur mainly in the gall-ducts, in the minnows within the gill cavity and epidermis, and in the higher fishes mainly but not exclusively in the same regions. Forty- seven species are regarded by Gurley as well defined. The diseases produced by them are very obscurely known. These parasites on American fishes have been extensively studied by Charles Wardall Stiles, Edwin Linton, Henry B. Ward, and others. According to Dr. Linton the parasitism which results from infection with protozoan parasites will, of all kinds, be found to Fig. 22s. — White Shiner, Notropis hudsonius (Clinton), with cysts of parasitic psorosperms. (After Gurley.) be the most important. Epidemics among European fish have been repeatedly traced to this source. The fatality which attends infection with psorosperms appears to be due to a sec- ondary cause, however, namely, to bacilli which develop within the psorosperms (Myxoboliis) tumors and give rise to ulceration. The discharge of these ulcers then disseminates the disease. " Brief mention of the remedies there proposed may appro- priately be repeated here. Megnin sees no other method than to collect all the dead and sick fishes and to destroy them by fire. Ludwig thinks that the waters should be kept pure, and that the pollutions of the rivers by communities or industrial establishments should be interdicted. Further he says: 344 Diseases of Fishes "That most dangerous contamination of the water by the Myxosporidia from the ulcers cannot of course be stopped en- tirely, but it is evident that it will be less if all fishermen are impressed with the importance of destroying all diseased and dead fish instead of throwing them back into the water. Such destruction must be so effected as to prevent the re-entry of the germs into the water. " Railliet says that it is expedient to collect the diseased fish and to bury them at a certain depth and at a great distance from the watercourse. He further states that this was done Fig. 229. — White Catfish, Am.eiurus calus (Linnteus), from Potomac River, infested by parasitic protozoa, Ichthyophthirus multifilis Fouquet. (After C. W. Stiles.") on the ileuse Avith success, so that at the end of some years the disease appeared to have left no trace." Parasitic Worms : Trematodes. — Parasitic worms in great variety exist in the intestinal canal or in the liver or muscular substance of fishes. Trematode worms are most common in fresh-water fishes. These usually are sources of little injury, especially when found in the intestines, but they may do considerable mischief when encysted within the body cavity or in the heart or liver. Dr. Linton describes 31 species of these worms from 25 different species of American fishes. In 20 species of fishes from the Great Lakes, 102 specimens, Dr. H. B. AVard found 95 speci- mens infected Avith parasites, securing 4000 trematodes, 2000 acanchocephala, 200 cestodes, and 200 nematodes. In the bowfin (Amia calva), trematodes existed in enormous numbers. Cestodes. — Cestode worms exist largely in marine fishes, the adults, according to Dr. Linton, being especially common in the spiral A-alve of the shark. It is said that one species of Diseases of Fishes 545 human tape-worm {Botlirioccphalus tcciiia) has been got from eating the flesh of the European tench [Tinea iitica). The Worm of the Yellowstone. — The most remarkable case of parasitism of worms of this type is that given by the trout of Yellowstone Lake (Salmo clarki). This is thus described by Dr. Linton: " One of the most interesting cases of parasitism in which direct injury results to the host, which has come to my atten- tion, is that afforded by the trout of Yellowstone Lake {Salmo clarki). It was noticed by successive parties who visited the lake in connection with government surveys that the trout with which the lake abounded were, to a large extent, infested with a parasitic worm, which is most commonly in the abdom- inal cavity, in cysts, but which in time escapes from the cyst and tunnels into the flesh of its host. Fish, when thus much afflicted, are found to be lacking in vitality, weak, and often positively emaciated. "It was my good fortune, in the summer of 1890, to visit this interesting region for the purpose of investigating the para- sitism of the trout of Yellowstone Lake. The results of this special investigation were published in the Bulletin of the U. S. Fish Commission for 1889, vol. ix., pp. 337-358, under the title' A Contribution to the Life-history of Dibothrium cordi- ceps, a Parasite Infesting the Trout of Yellowstone Lake.' "I found the same parasite in the trout of Heart Lake, just across the great continental divide from Yellowstone Lake, but did not find any that had tunneled into the flesh of its host, while a considerable proportion of the trout taken in Yellow- stone Lake had these worms in the flesh. Some of these worms were as much as 30 centimeters in length when first removed; others which had lain in water a few hours after removal before they were measured were much longer, as much as 54 centi- meters. They are rather slender and of nearly uniform size throughout, 2.5 to 3 millimeters being an average breadth of the largest. I found the adult stage in the intestine of the large white pelican (Pelccaniis crythrorhynchits), which is abun- ant on the lake and was found breeding on some small islands near the southern end of the lake. " In the paper alluded to above I attempted to account for •746 Diseases of Fishes two things concerning this parasitism among the trout of Yel- lowstone Lake : First, the abundance of parasitized trout in the lake; second, the migration of the parasite into the mus- cular tissue of its host. The argument cannot be well sum- marized in as short space as the requirements of this paper demand. It is sufficient to say that what appear to me to be satisfactory explanations are supplied by the peculiar condi- tions of distribution of fish in the lakes of this national park. Until three or four years ago, when the U. S. Fish Commission stocked some of the lakes and streams of the park, the condi- tions with relation to fish life in the three principal lakes were as follows; Shoshone Lake, no fish of any kind; Heart Lake, at least three species, Saliiio clarki, Lettcisais liiieatiis, and Catostoniiis ardciis; Yellowstone Lake, one species, Salnio clarki. Shoshone and Yellowstone Lakes are separated from the river systems which drain them by falls too high for fish to scale. Heart Lake has no such barrier. The trout of Yellowstone Lake are confined to the lake and to eighteen miles of river above the falls. Whatever source of parasitism exists in the lake, therefore, must continue to affect the fish all their lives. They cannot be going and coming from the lake as the trout of Heart Lake may freely do. If their food should contain eggs of parasites, or if the waters in which they swim should contain eggs or embryos of parasites, they would be continually exposed to infection, with no chance for a vacation trip for recuperation. To quote from my report ; "'It follows, therefore, from the peculiar conditions sur- rounding the trout of Yellowstone Lake, that if there is a cause of parasitism present in successive years the trout are more liable to become infested than they would be in waters where they had a more varied range. Trout would become infested earlier and in greater relative numbers, and the life of the para- sites themselves — that is, their residence as encysted worms — must be of longer duration than would be the ,rule where the natural conditions are less exceptional. . . . There are probably not less tlian one thousand pelicans on the lake the greater part of the time throughoutthe summer, of which at any time not less than 50 per cent, are infested with the adult form of the parasite, and, since they spend the greater part of Diseases of Fishes 347 their time on or over the water, disseminate milKons of tape- worm eggs each in the waters of the lake. It is known that eggs of other dibothria hatch out in the water, where they swim about for some time, looking much like ciliated infusoria. Don- nadieu found in his experiments on the adult dibothria of ducks that the eggs hatched out readily in warm water and very slowly in cold. If warm water, at least water that is warmer than the prevailing temperature of the lake, is needed for the proper development of these ova, the conditions are supphed in such places as the shore system of geysers and hot springs on the west arm of the lake, where for a distance of nearly three miles the shore is skirted by a hot spring and geyser formation, with numerous streams of hot water emptying into the lake, and large springs of hot water opening in the floor of the lake near shore. " 'Trout abound in the vicinity of these warm springs, pre- sumably on account of the abundance of food there. They do not love the warm water, but usually avoid it. Several persons with whom I talked on the subject while in the park assert that diseased fish — that is to say, those which are thin and affected with flesh worms — are more commonly found near the warm water; that they take the bait readily but are logy. I fre- quently saw pelicans swimming near the shore in the vicinity of the warm springs on the west arm of the lake. It would appear that the badly infested or diseased fish, being less active and gamy than the healthy fish, would be more easily taken by their natural enemies, who would learn to look for them in places where they most abound. But any circumstances which cause the pelican and the trout to occupy the same neighbor- hood will multiply the chances of the parasites developing in both the intermediate and final host. The causes that make for the abundance of the trout parasite conspire to increase the number of adults. The two hosts react on each other and the parasite profits by the reaction. About the only enemies the trout had before tourists, ambitious to catch big strings of trout and photograph them with a kodak, began to frequent this region, were the fish-eating birds, and chief among these in numbers and voracity was the pelican. It is no wonder, there- fore, that the trout should have become seriously parasitized. 348 Diseases of Fishes It mav be inferred from the foregoing statements that the rea- son Avhy the parasite of the trout of Yellowstone Lake migrates into the muscular tissue of its host must be found in the fact that the life of the parasite within the fish is much more pro- longed than is the case where the conditions of life are less exceptional. " The case just cited is probably the most signal one of direct injury to the host from the presence of parasites that I have seen. I shall enumerate more briefly a few additional cases out of a great number that I have encountered in my special investigations on the entozoa of fishes for the U. S. Fish Commission." Many worms of this type abound in codfishes, bluefishes, striped bass, and other marine fishes, rendering them lean and unfit for food. The Heart Lake Tape-worm. — Another very interesting case of parasitism is that of the large tape-Avorm (Ligiila catostomi) infecting the suckers, Catostomus ardciis, in the warm waters Fig. 230. — Sucker, Catostomus ardens (.Jordan & Gilbert), from He.irt Lake, Yellow- .'itone Park, infe.sted by a flatworm, Ligida catostomi Linton, itself probabty a l:ir\'a (if Dibothrinm. (."^.fter Linton.) of Witch Creek, near Heart Lake, in the Yellowstone Park. Of this Dr. Linton gives the following account : "In the autumn of 1SS9 Dr. David Starr Jordan found an interesting case of parasitism in some ^^oung suckers (Catos- ioniiis aniens) which he had collected in Witch Creek, a small stream which flows into Heart Lake, in the Yellowstone National Park. Specimens of these parasites were sent to me for identi- fication. They proA-ed to be a species of ligula, probably iden- tical with the European Ligtda simplicissinia Rud., which is Diseases of Fishes 349 found in the abdominal cavity of the tench. On account of its larval condition in which it possesses few distinctive char- acters, I described it under the name Ligula catostomi. These parasites grow to a very large size when compared with the fish which harbors them, often filling the abdominal cavity to such a degree as to give the fish a deceptively plump appear- ance. The largest specimen in Dr. Jordan's collection meas- ured, in alcohol, 2 8.5 centimeters in length, 8 millimeters in breadth at the anterior end, 1 1 millimeters at a distance of 7 millimeters from the anterior end, and 1.5 millimeters near the posterior end. The thickness throughout was about 2 mil- limeters. The weight of one fish was 9.1 grams, that of its three parasites 2.5 grams, or 27 J per cent, the weight of the host. If a man weighing 180 pounds were afflicted with tape- worms to a similar degree, he would be carrying about with him 50 pounds of parasitic impedimenta. " In the summer of 1890 I collected specimens from the same locality. A specimen obtained from a fish 19 centimeters in length measured while living 39.5 centimeters in length and 15 millimeters in breadth at the anterior end. Another fish 15 centimeters in length harbored four parasites, 12, 13, 13, and 20 centimeters long, respectively, or 58 centimeters aggregate. Another fish 10 centimeters long was infested with a single parasite which was 39 centimeters in length. ' ' These parasites were f oimd invariably free in the body cavity Dr Jordan's collections were made in October and mine in July of the following year. Donnadieu has found that this parasite most frequently attains its maximum develop- ment at the end of two years, It is probable, therefore, that Dr. Jordan and I collected from the same generation. Since these parasites, in this stage of their existence, develop, not by levying a toll on the food of their host, after the manner of intestinal parasites, but directly by the absorption of the serous fluid of their host, it is quite evident that they work a positive and direct injury. Since, however, they lie quietly in the body cavity of the fish and possess no hard parts to cause irritation, they work their mischief simply by the passive abstraction of the nutritive juices of their host, and by crowding the viscera into confined spaces and unnatural positions. The worms, in oro Diseases of Fishes almost every case, had attained such a size that they far ex- ceeded in bulk the entire viscera of their host. ' ' From the fact that the examples obtained were of compar- atively the same age, it may be justly inferred that the period of infection to which the fish are subjected must be a short one. I did not discover the final host, but it is almost certain to be one or more of the fish-eating species of birds which A'isit that region, and presumably one of which, in its migrations, pays but a brief visit to this particular locality. This parasite was found only in the young suckers which inhabit a warm tributary of AA'itch Creek. They were not found in the large suckers of the lake. These young Catostonii were found in a single school, associated with the young of the chub (Lencisciis Uiicatiis), in a stream whose temperature was 95° F. near where it joined a cold mountain brook whose temperature was 46° F. We seined several hundred of these young suckers and chubs, ranging in length from 6 to 19 centimeters. The larger suckers were nearly all infested with these parasites, the smaller ones not so much, and the smallest scarcely at all. Or, to give con- crete examples: Of 30 fish ranging in length from 14 to 19 cen- timeters, only one or two were without parasites ; of 45 speci- mens averaging about 10 centimeters in length, 15 were infested and 30 were not; of 65 specimens averaging about 9 centimeters in length, 10 were infested and 55 were not; of 62 specimens less than 9 centimeters in length, 2 were infested and 60 were not. None of the chubs were infested with this parasite. "The conditions under which these fish were found are worthy of passing notice. The stream which they occupied flowed with rather sluggish current into a swift mountain stream, which it met almost at right angles. The school of young chubs and suckers showed no inclination to enter the cold water, even to escape the seine, but would dart around the edge of the seine, in the narrow space between it and the bank, in preference, apparently, to taking to the colder water. When not disturbed by the seine they would swim up near to the line which marked the division between the cold and the warm water, and seemed to be gazing with open mouth and eyes at the trout which occasionally darted past in the cold stream. The trout appeared to avoid the warm water, while Diseases of Fishes 351 the chubs and suckers appeared to avoid the cold water. It may be that what the latter really avoided was the special preserve of the trout, since large chubs and suckers are found in abundance in the lake, which is quite cold, a temperature of 40° F. having been taken b}' us at a depth of 124 feet. " Since the eggs of this parasite, after the analogy of closely related forms, in all probability are discharged into the water from the final host and hatch out readily in warm water, w-here they may live for a longer or shorter time as free-swimming planula-like forms, it will be observed that the sluggish current and high temperature of the water in which these parasitized fish occur give rise to conditions which are highly favorable to infection. "It may be of passing interest to state here what I have recorded elsewhere, that ligulae, probably specifically identical with L. catostomi, form an article of food in Italy, where they are sold in the markets under the name maccaroni piatti; also in southern France, where they are less euphemistically but more truthfully called the ver blanc. So far as my information goes, this diet of worms is strictly European. "It is not necessary to prove cases of direct injury resulting from the presence of parasites in order to make out a case against them. In the sharp competition which nature forces on fishes in the ordinary struggle for existence, any factor which imparts an increment either of strength or of weakness may be a very potent one, and in a long term of years may determine the relative abundance or rarity of the individuals of a species. In most cases the interrelations between parasite and host have become so adjusted that the evil wrought by the parasite on its host is small. Parasitic forms, like free forms, are simply developing along the lines of their being, but unlike most free forms they do not contribute a fair share to the food of other creatures." Thorn-head Worms. — The thorn-head worms called Acan- thocephala are found occasionally in large numbers in different kinds of fishes. They penetrate the coats of the intestines, producing much irritation and finally waxy degeneration of the tissues. According to Linton, there is probably no practical way of ^ r2 Diseases of Fishes counteracting the bad influences of worms of this order, since their larval state is passed, in some cases certainly, and m most cases probably, in small crustacea, which constitute a constant and necessary source of food for the fish. The same remark which was made in .another connection with regard to the dis- posal of the viscera of fish applies here. In no case should the viscera of fish be throAvn back into the water. In this order the sexes are distinct, and the females become at last veritable sacs for the shelter and nourishment of enormous numbers of embryos. The importance, therefore, of arresting the devel- opment of as many embryos as possible is at once apparent. Nematodes. — The round worms or nematodes are very especially abundant in marine fishes, and particularly in the young. The study of these forms has a large importance to man. Dr. Linton pertinently observes : "Where there is exhaustive knowledge of the thing itself the application of that knowledge toward getting good out of it or averting evil that may come from it first becomes possible. For example, a knowledge of the Hfe-history of Trichina spiralis and its pathological effects on its host has taught people a sim- ple Avay of securing immunity from its often deadly effects. A knowledge of the life-histories of the various species of tasniffi which infest man and the domestic animals, frequently to their serious hurt, has made it possible to diminish their numbers, and may, in time, lead to their practical extinction. " So with the parasites of fishes. AVhenever for any reason or reasons parasitism of any sort becomes so prevalent with any species as to amount to a disease, the remedy will be suggested, and in some cases may be practically applied. If, for example, it were thought desirable to counteract the influences which are at work to cause the parasitism of the trout of Yellowstone Lake, it could be very largely accomplished by breaking up the breeding-places of the pelican on the islands of the lake. With regard to parasitism among the marine food-fishes, the remedy while plainly suggested by the circumstances, might be difficult of application. Yet something could be done even there, if it were thought necessary to lessen the amount of parasitism. If such precautions as the destruction of the para- sites which abound in the viscera of fish before throwing them Diseases of Fishes 353 back into the water, and if no opportunity be lost of killing those sharks which feed on the food-fishes, two sources of the prevalence of parasites would be affected and the sum total of parasitism diminished. These remarks are made not so much because such precautions are needed as to suggest possible apdications of knowledge which is alread}^ available." Parasitic Fungi. — Fishes are often subject to wounds. If not too serious these will heal in time, with or without scars. Some lost portions may be restored, but not those including bone fin-rays or scales. In the fresh waters, wounds are usu- ally attacked by species of fungus, notably Saprolegnia ferox, Saprolcgnia mixta, and others, which makes a whitish fringe over a sore and usually causes death. This fungus is especially destructive in aquaria. This fungus is not primarily parasitic, but it fixes itself in the slime of a fish or in an injured place, and once established the animal is at its mercy. Spent salmon are very often attacked by this fungus. In America the spent sal- mon always dies, but in Scotland, where such is not the case, much study has been given to this plant and the means by which it may be exterminated. Dr. G. P. Clinton gives a useful account of the development of Saprolegnia, from which we take the following : " The minute structure and life-history of such fungous forms have been so thoroughly made out by eminent specialists that no investigation along this line was made, save to observe those phenomena which might be easily seen with ordinary microscopic manipulations. The fungus consists of branched, hyaline filaments, without septa, except as these are found cutting off the reproductive parts of the threads. It is made up of a root-like or rhizoid part that penetrates the fish and a vegetative and reproductive part that radiates from the host. The former consists of branched tapering threads which pierce the tissues for a short distance, but are easily pulled out. The function of this part is to obtain nourishment for the growth of the external parts. Prostrate threads are found running through the natural slime covering the fish, and from these are produced the erect radiating hypha; so plainly seen when in the water. The development of these threads appears to be very rapid when viewed under the microscope, although the ;54 Diseases of Fishes growth made under favorable conditions in two days is only about a third of an inch. From actual measurements of fila- ments of the fungus placed in water and watched under the microscope, it was found that certain threads made a growth of about 3000 microns in an hour. Two others, watched for twenty minutes, gave in that time a growth of 90 and 47 microns respectively; and yet another filament, observed during two periods of five minutes each, made a growth of 28 microns each time. In ordinary cultures the rate of growth depends upon the condition of the medium, host, etc." Professor H. A. Surface thus speaks of the attacks of Sapro- Icgiiia on the lamprey: "The attack that attends the end of more lampreys than does an}- other is that of the fungus (Saprolcgiiia sp.). This looks like a gray slime and eats into the exterior parts of the animal, finally causing death. It covers the skin, the fins, the eyes, the gill-pouches, and all parts, like leprosy. It starts where the lamprey has been scratched or injured or where its mate has held it, and develops verj' rapidly when the water is Fig. 231. — Quinnat Salmon, Oncorhynchus tschawytscha (Walbaum). Monterey Bay. (Photograph by C. Rutter.) warm. It is found late in the season on all laniprej^s that have spawned out, and it is almost sure to prove fatal, as we have repeatedly seen with attacked fishes or lampreys kept in tanks or aquaria. With choice aquarium fishes a remedy, or at least a palliative, is to be found in immersion in salt water for a few minutes or in bathing the affected parts with listerine. Since these creatures complete the spawning process before the fun- goid attack proves serious to the individual, it can be seen that it affects no injurjr to the race, as the fertilized eggs are left to Oh ^ ^ Si ^ >. G T3 C, CO •^ O t-, ■:> Xi '-^ r- C^4 r' 5^ ^ o o r- Ph c 3 o 35^ Diseases of Fishes come to maturitA'. Also, as it is nature's plan that the adult lampreys die after spawning once, we are convinced that death would ensue without the attack of the fungus ; and in fact this is to be regarded as a resultant of those causes that produce death rather than the immediate cause of it. Its only natural remedy is to be found in the depths of the lake (450 feet) where there is a uniform or constant temperature of about 39° Fahr., and where the light of the noon-day sun penetrates with an intensity only about equal to starUght on land on a clear but moonless night. " As light and heat are essential to the development of the fungus, which is a plant growth and properly called a water mold, and as their intensity is so greatly diminished in the depth of the lake, it is probable that if creatures thus attacked should reach this depth they might here find relief if their physical condition were otherwise strong enough to recuperate. However, we have recently observed a distinct tendency on the part of fungus-covered fishes to keep in the shallower, and consequently w'armer, parts of the water, and this of course results in the more rapid growth of the sarcophytic plant, and the death of the fishes is thus hastened. "All kinds of fishes and fish-eggs are subject to the at- tacks of such fungus, especially after having been even slightly scratched or injured. As a consequence, the lamprey attacks on fishes cause wounds that often become the seat of a slowly spreading but fatal fungus. We have seen many nests of the bullhead, or homed pout (Ameinrns ncbulosits), with all the eggs thus destroyed, and we have found scores of fishes of vari- ous kinds thus killed or dying. It is well known that in manj^ rivers this is the apparent cause of great m rtality among adult salmon. Yet we really doubt if it ever attacks uninjured fishes that are in good strong physical condition which have not at least had the slime rubbed from them w^hen captured. It is contagious, not only being conveyed from one infested fish to another, but from dead flies to fishes." (For a further discus- sion of this subject see an interesting and valuable :\lanual of Fish Culture, by the U. S. Fish Commission, 1897.) Earthquakes.— Occasionally an earthquahe has been known to kill sea-fishes in large numbers. The Albatross obtained Diseases of Fishes 357 specimens of Sternoptyx diaphana in the Japanese Kuro Shiwo, killed by the earthquakes of 1896, which destroyed fishing villages of the coast of Rikuchu in northern Japan. Mortality of Filefish. — Some years ago in the Gulf Stream off Newfoundland an immense mortahty of the filefish (Loplio- latilus chamccleonticeps) was reported by fishermen. This hand- some and large fish, inhabiting deep waters, died by thousands. For this mortality, which almost exterminated the species, no adequate cause has been found. As to the destruction of fresh-water fishes by larger ene- mies, we may quote from Professor H. A. Surface. He says there is no doubt that these three species, the lale lamprey {Petromyzon mariuns unicolor), the garpike {Lepidostetis osseus), and the mud-puppy {Necturns maculosus), named "in order of destructiveness, are the three most serious enemies of fishes in the interior of this State [New York], each of which surely destroys more fishes annually than are caught by all the fish- ermen combined. The next important enemies of fishes in order of destructiveness, according to our observations and belief, are spawn-eating fishes, water-snakes, carnivorous or predaceous aquatic insects (especially larvae), and piscivorous fishes and birds." The lamprey attaches itself to larger fishes, rasping away their flesh and sucking their blood, as shown in the accompanying plate. CHAPTER XX THE MYTHOLOGY OF FISHES [HE Mermaid. — A word may be said of the fishes which have no existence in fact and yet appear in popular Hterature or in superstition. The memiaid, half woman and half fish, has been one of the most tenacious among these, and the manufacture of their dried bodies from the head, shoulders, and ribs of a monkey sealed to the body of a fish has long been a profitable industry in the Orient. The sea-lion, the dugong, and other marine mammals have been mistaken for mermaids, for their faces seen at a distance and their movements at rest are not inhuman, and their limbs and movements in the water are fishlike. In China, small mermaids are very often made and sold to the curious. The head and torso of a monkey are fastened ingeniously to the body and tail of a fish. It is said that Lin- naeus was once forced to leave a town in Holland for question- ing the genuineness of one of these mermaids, the property of some high official. These monsters are still manufactured for the "curio-trade." The Monk-fish. — Many strange fishes were described in the Middle Ages, the interest usually centering in some supposed relation of their appearance with the affairs of men. Some of these find their way into Rondelet's excellent book, "Histoire Entiere des Poissons," in 1558. Two of these with the accom- panying plate of one we here reproduce. Other myths less interesting grew out of careless, misprinted, or confused ac- counts on the part of naturahsts and travelers. " In our times in Norway a sea-monster has been taken after a great storm, to which all that saw it at once gave the name of 359 360 The Mythology of Fishes monk ; for it had a man's face, rude and ungracious, the head shorn and smooth. On the shoulders, hke the cloak of a monk, were two long fins instead of arms, and the end of the body was finished by a long tail. The picture I present was given me by the very illustrious lady, Margaret de Valois, Queen of Navarre, Fig. 234. — " Le monstre marin en habit de Maine." (After Rondelet.) who received it from a gentleman who gave a similar one to the emperor, Charles V., then in Spain. This gentleman said that he had seen the monster as the portrait shows it in Nor- way, thrown by the waves and tempests on the beach at a place called Dieze, near the town called Denelopoch. I have seen a similar picture at Rome not differing in mien. Among the sea- beasts, Pliny mentions a sea-mare and a Triton as among the creatures not imaginary. Pausanias also mentions a Triton." Rondelet further says: The Mythology of Fishes 361 The Bishop-fish. — "I have seen a portrait of another sea- monster at Rome, whither it had been sent with letters that affirmed for certain that in 1531 one had seen this monster in a bishop's garb, as here portrayed, in Poland. Carried to the king of that country, it made certain signs that it had a great desire to return to the sea. Being taken thither it threw itself instantly into the water." The Sea-serpent. — A myth of especial persistency is that of the sea-serpent. ]\Iost of the stories of this creature are sea- man's yarns, sometimes based on a fragment of wreck, a long strip of kelp, the power of sug- gestion or the incitement of alcohol. But certain of these tales relate to real fishes. The sea-serpent with an uprearing red mane like that of a horse is the oarfish (Regaleciis), a long, slender, fragile fish com- pressed like a ribbon and reaching a length of 2^ feet. We here present a photograph of an oarfish (Regalecus riis- selli) stranded on the Cali- fornia coast at Newport in Orange County, California. A figure of a European species (Regalecus glesne) is also given showing the fish in its uninjured condition. Another reputed sea-serpent is the frilled shark (Chlamydoselachits angineus), which has been occasionally noticed by seamen. The struggles of the great killer (Orca orca) with the whales it attacks and destroys has also given rise to stories of the whale struggling in the embrace of some huge sea-monster. This description is correct, but the mammal is a monster itself, a relative of the whale and not a reptile. 235; — "Le monstre marin en habit d' Eveque." (After Rondelet.) k. ' o 264 The Mythology of Fishes It is often hard to account for some of the stories of the sea- serpent. A gentleman of unquestioned intelligence and sincer- ity lately dercribed to the writer a sea-serpent he had seen at short range, 100 feet long, swimming at the surface, and with a head as large as a barrel. I do not know what he saw, but I do know that memory sometimes plays strange freaks. Little venomous snakes with flattened tails {Platyiiriis, Pclamis) are found in the salt bays in many tropical regions of the Pacific (Gulf of California, Panama, East Indies, Japan), but these are not the conventional sea-serpents. Certain slender fishes, as the thread-eel {NcniicJitJiys) and the wolf-eel (Auarrhichtliys), have been brought to naturalists as young sea-serpents, but these of course are genuine fishes. Whatever the nature of the sea-serpent may be, this much is certain, that while many may be seen, none will ever be caught. The great swimming reptiles of the sea vanished at the end of Mesozoic time, and as living creatures will never be known of man. As a record of the Mythology of Science, we may add the following remarks of Rafinesque on the imaginary garpike (Litholcpis adamajitinus), of which a specimen was painted for him by the wonderful brush of Audubon : "This fish may be reckoned the wonder of the Ohio. It is only found as far up as the falls, and probably lives also in the Mississippi. I have seen it, but only at a distance, and have been shown some of its singular scales. Wonderful stories are related concerning this fish, but I have principally relied upon the description and picture given me by Mr. Audubon. Its length is from 4 to 10 feet. One was caught which weighed 400 pounds. It lies sometimes asleep or motionless on the surface of the water, and may be mistaken for a log or snag. It is impossible to take it in any other way than with the seine or a very stn-jng hook; the prongs of the gig cannot pierce the scales, which are as hrad as flint, and even proof aeainst lead bahs! Its flesh is not good to eat. It is a voracious fish. Its vulgar names are diamond-fish (oAving to its scales being cut like diamonds), devil-fish, jackfish, garjack, etc. The snout is large, convex above, xQvy obtuse, the eyes small and black; nostrils small, round before the eyes; mouth beneath the eves 366 The Mythology of Fishes transversal with large angular teeth. Pectoral and abdominal fins trapezoidal. Dorsal and anal fins equal, longitudinal, with many rays. The whole body covered with large stone scales, lying in oblique rows; they are conical, pentagonal penta;dral, with equal sides, from half an inch to one inch in diameter, brown at first but becoming the color of turtle-shell wh.n dry. They strike fire with steel and are ball-proof! " CHAPTER XXI CLASSIFICATION OF FISHES JAXONOMY. — Classification, as Dr. Elliott Coues has well said* is a natural function of "the mind which always strives to make orderly disposition of its 'cnowledge and so to discover the reciprocal relations and interdependencies of the things it knows. Classification pre- supposes that there do exist such relations, according to which we may arrange objects in the manner which facilitates their comprehension, by bringing together what is like and separating what is unlike, and that such relations are the result of fixed inevitable law. It is therefore taxonomy (ra^z?, away ; yojAo?, law) or the rational, lawful disposition of observed facts." A perfect taxonomy is one which would perfectly express all the facts in the evolution and development of the various forms. It would recognize all the evidence from the three ances- tral documents, paleontology, morphology, and ontogeny. It would consider structure and form independently of adaptive or physiological or environmental modifications. It would regard as most important those characters which had existed longest unchanged in the history of the species or type. It would regard as of first rank those characters which appear first in the history of the embryo. It would regard as of minor importance those which had arisen recently in response to natural selection or the forced alteration through pressure of environment, while fundamental alterations as they appear one after another in geologic time would make the basal characters of corresponding groups in taxonomy. In a perfect taxonomy or natural system of classification animals would not be divided into groups nor ranged in linear series. We should imagine * Key to North American Birds. 367 -7 68 Classification of Fishes series variously and divergently branched, with each group at its earlier or lower end passing insensibly into the main or primi- ti\-e stock. A very little alteration now and then in some structure is epoch-making, and paves the way through speciali- zation to a new class or order. But each class or order through its LiAvest types is interlocked with some earlier and otherwise di\'erging group. Defects in Taxonomy. — A sound system of taxonomy of fishes should be an exact record of the history of their evolu- tion. But in the limitations of book-making, this transcript must be made on a flat page, in linear series, Avhile for centuries and perhaps forever whole chapters must be left vacant and others dotted everywhere with marks of doubt. For science demands that positive assertion should not go where certainty cannot folLiw. A perfect taxonomy of fishes would be only possible through the study, by some Artedi, Muller, Cuvier, Agassiz, Traquair, Gill, or Woodward, of all the structures of all the fishes which have ever lived. There are many fishes living in the sea which are not yet known to any naturalist, many others are known from one or two specimens, but not yet accessible to students in other continents. Many are known externally from specimens in bottles or drawdngs in books, but have not been studied thoroughly by any one, and the vast multitude cjf species have perished in Paleeozoic, Mesozoic, and Tertiary seas without leaving a tooth or bone or fin behind them. With all this goes human infallibility, the marring of our records, such as they are, by carelessness, prejudice, depend- ence, and error. Chief among these defects are the constant mistaking of analogy for homology, and the inability of men to trust their own eyes as against the opinion of the greater men who have had to form their opinions before all evidence was in. Because of these defects, the current system of classifi- cation is always changing with each accession of knowdedge. The result is, again to quote from Dr. Coues, "that the natural classification, like the elixir of life or the philosopher's stone, is a goal far distant." Analogy and Homology. — Analogy, says Dr. Coues, "is the apparent resemblance between things really unlike — as the wing of a Ijird and the wdng of a butterfly, as the lungs of a bird and Classification of Fishes 369 the gills of a fish. Homology is the real resemblance, or true relation between things, however different they may appear to be — as the wing of a bird and the foreleg of a horse, the lungs of a bird and the swim-bladder of a fish. The former com- monly rests upon mere functional, i.e. physiological, modifi- cations; the latter is grounded upon structural, i.e., morpho- logical, identity or unity. Analogy is the correlative of physi- ology, homology of morphology; but the two may be coinci- dent, as when structures identical in morphology are used for the same purposes, and are therefore physiologically identical. Physiological diversity of structure is incessant, and continu- ally interferes with morphological identity of structure, to obscure or obliterate the indications of affinity the latter would otherwise express clearly. . . . We must be on our guard against those physiological appearances which are proverbially deceptive! " "It is possible and conceivable that every animal should have been constructed upon a plan of its own, having no resem- blance whatever to the plan of any other animal. For any reason Ave can discover to the contrary, that combination of natural forces which we term life might have resulted from, or been manifested by, a series of infinitely diverse structures; nor would anything in the nature of the case lead us to suspect a community of organization between animals so different in habit and in appearance as a porpoise and a gazelle, an eagle and a crocodile, or a butterfly and a lobster. Had animals been thus independently organized, each working out its life by a mechanism peculiar to itself, such a classification as that now under contemplation would be obviously impossible ; a morpho- logical or structural classification plainly implying morphologi- cal or structural resemblances in the things classified. "As a matter of fact, however, no such mutual independence of animal forms exists in nature. On the contrary, the mem- bers of the animal kingdom, from the highest to the lowest, are marvel ously connected. Every animal has something in com- mon with all its fellows — much with many of them, more with a few, and usually so much with several that it differs but little from them. "Now, a morphological classification is a statement of these 37° Classification of Fishes gradations of likeness which are observable in animal structures, and its objects and uses are manifold. In the first place, it strives to throw our knowledge of the facts which underlie, and are the cause of, the similarities discerned into the fewest possible general propositions, subordinated to one another, ac- cording to their greater or less degree of generality; and in this way it answers the purpose of a memoria technica, without which the mind would be incompetent to grasp and retain the multifarious details of anatomical science." Coues on Classification. — It is obvious that fishes like other animals may be classified in numberless ways, and as a matter of fact by numberless men they have been classified in all sorts of fashions. "Systems," again quoting from Dr. Coues, "have been based on this and that set of characters and erected from this or that preconception in the mind of the systematist. . . . The mental point of view was that every species of bird (or of fish) was a separate creature, and as much of a fixture in nature's museum as any specimen in a naturalist's cabinet. Crops of classifications have been sown in the fruitful soil of such blind error, but no lasting harvest has been reaped. . . . The genius of modern taxonomy seems to be so certainly right, to be tending so surely even if slowly in the direction of the desired consummation, that all differences of opinion we hope will soon be settled, and defect of knowledge, not perversity of mind, is the only obstacle in the way of success. The taxonomic goal is not now to find the way in which birds (or other animals) may be most conveniently arranged, but to discover their pedigree, and so construct their family tree. Such a genealogical table, or pJiylnm {(pvXov^ tribe, race, stock), as it is called, is rightly considered the only taxonomy worthy the name — the only true or natural classification. In attempting this end, we proceed upon the beHef that, as explained above, all birds, hke all other animals and plants, are related to each other genetically, as oft'spring are to parents, and that to discover their generic relations is to bring out their true affinities — in other words, to reconstruct the actual taxonomy of nature. In this view there can be but one ' natural ' classification, to the perfecting of which all increase in our knowledge of the structure of birds infallibly and inevitably tends. The classification now in use Classification of Fishes 371 or coming into use is the result of our best endeavors to accom- plish this purpose, and represents what approach we have made to this end. It is one of the great corollaries of that theorem of evolution which most naturalists are satisfied has been demon- strated. It is necessarily a morphological classification; that is, one based solely upon considerations of structure or form {nop(f>ii^ form, morphe), and for the following reasons: Every offspring tends to take on precisely the form or structure of its parents, as its natural physical heritage; and the principle involved, or the law of heredity, would, if nothing interfered, keep the de- scendants perfectly true to the physical characters of their progenitors; they would 'breed true' and be exactly alike. But counter influences are incessantly operative, in consequence of constantly varying external conditions of environment; the plasticity of organization of all creatures rendering them more or less susceptible of modifications by such means, they become unlike their ancestors in various ways and to different degrees. On a large scale is thus accomplished, by natural selection and other natural agencies, just what man does in a small way in producing and maintaining different breeds of domestic ani- mals. Obviously, amidst such ceaselessly shifting scenes, de- grees of likeness or unlikeness of physical structure indicate with the greatest exactitude the nearness or remoteness of organisms in kinship. Morphological characters derived from the examination of structure are therefore the surest guides we can have to the blood relationships we desire to establish ; and such relationships are the ' natural affinities ' which all classifi- cation aims to discover and formulate." Species as Twigs of a Genealogical Tree. — In another essay Dr. Coues has compared species of animals to " the twigs of a tree separated from the parent stem. We name and arrange them arbitrarily in default of a means of reconstructing the whole tree according to -nature's ramifications." If one had a tree, all in fragments, pieces of twig and stem, some of them lost, some destroyed, and some not yet separated from the mass not yet picked over, and wished to place each part where he could find it, he would be forced to adopt some system of nat- ural classification. In such a scheme he would lay those parts together which grcAV from the same branch. If he were corn- 372 Classification of Fishes pelled to arange all the fragments in a linear series, he would place together those of one branch, and when these were finished he would begin with another. If all this were a matter of great importance and extending over years or over many lifetimes, with many errors to be made and corrected, a set of names would be adopted — for the main trunk, for the chief branches, the lesser branches, and on down to the twigs and buds. A task of this sort on a world-wide scale is the problem of systematic zoology. There is reason to believe that all animals and plants sprang from a single stock. There is reasonable certainty that all vertebrate animals are derived from a single origin. These vertebrate animals stand related to each other, like the twigs of a gigantic tree of which the lowermost branches are the aquatic forms to which we give the name of fishes. The fishes are here regarded as compsed of six classes or larger lines of descent. Each of these, again, is composed of minor divisions called orders. The different species or ultimate kinds of ani- mals are grouped in genera. A genus is an assemblage of closely related species grouped around a central species as type. The type of a genus is, in common usage, that species with which the name of the genus was first associated. The name of the genus as a noun, often with that of the species which is an adjec- tive in signification if not in form, constitutes the scientific name of the species. Thus Petromyzon is the genus of the com- mon large lamprey, marinns is its species, and the scientific name of the species is Petromyzon niarinus. Petromyzon means stone-sucker; marinus, of the sea, thus distinguishing it from a species called fluviatilis, of the river. In like fashion all ani- mals and plants are named in scientific record or taxonomy. Technical names are necessary because vernacular names fail. Half a million kinds of animals are known, while not half a thousand vernacular names exist in any language. And these are always loosely used, half a dozen of them often for the same species, one name often for a dozen species. In the same way, whenever we undertake an exact descrip- tion, we must use names especially devised for that purpose. We cannot use the same names for the bones of the head of a fish and those of the head of a man, for a fish has a different series of bones, and this series is different with different fishes. Classification of Fishes 373 Nomenclature. — A family in zoology is an assemblage of related genera. The name of a family, for convenience, always ends in the patronymic ida, and it is always derived from the leading genus, that is, the one best known or earliest studied. Thus all lampreys constitute the family Petromyzonidcc. An order may contain one or more families. An order is a division of a larger group; a family an assemblage of related smaller groups. Intermediate groups are often recognized by the pre- fixes sub or super. A subgenus is a division of a genus. A subspecies is a geographic race or variation within a species; a super-family a group of allied families. Binomial nomenclature, or the use of the name of genus and species as a scientific name, was introduced into science as a systematic method by Lin- naeus. In the tenth edition of his Systema Naturas, published in 1758, this method was first consistently applied to animals. By common consent the scientific naming of animals begins with this year, and no account is taken of names given earlier, as these are, except by accident, never binomial. Those authors who wrote before the adoption of the rule of binomials and those who neglected it are alike "ruled out of court." The idea of genus and species was well understood before Linnsus, but the specific name used was not one word but a descriptive phrase, and this phrase was changed at the whim of the difter- ent authors. Nomenclature of Trunkfishes. — Examples of such names are those of the West Indian trunkfish, or cuckold {Ostracion Pig 939 —Homed Trunkfish, Cowfish, or Cuckold, Lactophrys tricornis (Linnceus) . Charleston, S. C. tricorne, Linna;us). Lister refers to a specimen in 1686 as " Piscis triangularis capiti cornutu cui e media caiida cutanea ■7 74 Classification of Fishes aculeits longns erigitiis." This Artedi alters in 1738 to Ostra- c-ioii triangulatiis acitleis diiobus in capite et unico longiore superne ad candam. This is more accurately descriptive and it recog- nizes the existence of a generic type, Ostracion, or tninkfish, to cover all similar fishes. French writers transformed this into various phrases beginning " Coffre triangulaire a trois cornes," or some similar descriptive epithet, and in English or German it was likely to wander still farther from the original. But Lin- naeus condenses it all in the word tricornis, which, although not fully descriptive, is still a name which all future observers can use and recognize. It is true that common consent fixes the date of the begin- ning of nomenclature at 1758. But to this there are many exceptions. Some writers date genera from the first recog- nition of a collective idea under a single name. Others follow even species back through the occasional accidental binomials. Most British writers have chosen the final and completed edition of the Systema Naturre, the last work of Linnaeus, in 1766, in preference to the earlier volume. But all things con- sidered, justice and convenience alike seem best served by the use of the edition of 1758. Synonymy and Priority. — Synonymy is the record of the names applied at different times to the same group or species. AVith characteristic pungency Dr. Coues defines synonymy as " a burden and a disgrace to science." It has been found that the only way to prevent utter confusion is to use for each genus or species the first name applied to it and no other. The first name, once properly given, is sacred because it is the right name. All other later names whatever their appro- priateness are wrong names. In science, of necessity, a name is a name without any necessary signification. For this reason and for the further avoidance of confusion, it remains as it was originally spelled by the author, obvious misprints aside, re- gardless of all possible errors in classical form or meaning. The names in use are properly written in Latin or in Latinized Greek, the Greek forms being usually preferred as generic names, the Latin adjectives for names of species. Many species are named in honor of individuals, these names beino- usually given the termination of the Latin genitive, as Sebas- Classification of Fishes 375 todes gillii, Liparis agassizi. In recent custom all specific names are written with the small initial; all generic names with the capital. One class of exceptions must be made to the law of priority. No generic name can be used twice among animals, and no specific name twice in the same genus. Thus the name Diabasis has to be set aside in favor of the next name Ihcmidoii, because Diabasis was earlier used for a genus of beetles. The specific name Pristipoma hiunilc is abandoned, because there was al- ready a hnmile in the genus Pristipoma. The Conception of Genus. — In the system of Linmcus, a genus corresponds roughly to the modern conception of a family. Most of the primitive genera contained a great variety of forms, as well as usually some species belonging to other groups dis- associated from their real relationships. As greater numbers of species have become known the earlier genera have undergone subdivision until in the modern systems almost any structural character not subject to intergradation and capable of exact definition is held to distinguish a genus. As the views of these characters are undergoing constant change, and as different writers look upon them from different points of view, or with different ideas of convenience, we have constant changes in the boundaries of genera. This brings constant changes in the scientific names, although the same specific name should be used whatever the generic name to which it may be attached. We may illustrate these changes and the burden of synonymy as well by a concrete example. The Trunkfishes. — The horned trunkfish, or cuckold, of the West Indies was first recorded by Lister in 1686, in the descrip- tive phrase above quoted. Artedi, in 1738, recognized that it belonged with other trunkfishes in a group he called Ostracion. This, to be strictly classic, he should have written Ostracium, but he preferred a partly Greek form to the Latin one. In the Nagg's Head Inn in London, Artedi saw a trunkfish he thought different, having two spines under the tail, while Lister's figure seemed to show one spine above. This Nagg's Head specimen Artedi called "Ostracion triangidatus diiobus aculeis in fronte ct totideni in into ventre subcaudalesque binis." Next came Linnaeus, 1758, who named Lister's figure and 376 Classification of Fishes the species it represented, Ostracion tricornis, which should in strictness have been Ostracion tricorne, as oarpaKwv, a Uttle box, is a neuter diminutive. The Nagg's Head fish he named Ostracion quadricornis. The right name now is Ostracion tri- cornis, because the name tricornis stands first on the page in Linngeus' work, but Ostracion quadricornis has been more often used by subsequent authors because it is more truthful as a descriptive phrase. In 1798, Lacepede changed the name of \^.- FiG 240. — Horned Tmnkfish, Ostracion cornutum Linna'us. East Indies. (After Bleeker.) Lister's fish to Ostracion listeri, a needless alteration which could only make confusion. In 18 18, Dr. Samuel Latham Mitchill, receiving a specimen from below New Orleans, thought it dift'erent from tricornis and quadricornis and called it Ostracion scxcornutns; Dr. Hol- ard, of Paris, in 1857, named a specimen Ostracion maculatus, and at about the same time Bleeker named two others from Africa which seem to be the same thing, Ostracion guincensis and Ostracion gronovii. Lastly, Poey calls a specimen from Cuba Acanthostracion polygonins, thinking it different from all the rest, which it may be, although my own judgment is other- wise. This brings up the question of the generic name. Among trunkfishes there are four-angled and three-angled kinds, and of each form there are species with and without horns and spines. The original Ostracion of Linnsus we may interpret as being Ostracion cnhicus of the coasts of Asia, a species similar to the Ostracion rJiinorliynchns. This species, cnhicus, we call the type species of the genus, as the Nagg's Head specimen of Artedi was the type specimen of the species quadricornus, and' the one that was used for Lister's figure the type specimen of tricornis. Ostracion cnhicus is a four-angled species, and when the Classification of Fishes 377 trunkfishes were regarded as a family {Osiraciidcc), the three- angled ones were set off as a separate genus. For this two names were offered, both by Swainson in 1839. For trigonus, a species without horns before the eyes, he gave the name Lac- ^*^'«ai>.. s-V'f:-,-.,::v.A..,«-'..j.^^^'.ic - * -' Fig. 241. — Spotted Trunkfish, Lactophrys hicaudalis (Linnsus). Cozumel Lsland, Yucatan. toplirys, and for triqiietcr, a species without spines anywhere, the name of RJiiiiesomus. Most recent American authors have placed the three-cornered species which are mostly American in one genus, which must therefore be called Lactophrys. Of this name Rhinesoinus is a synonym, and our species should stand as Lactophrys tricornis. The fact that Lactophrys as a word (from Latin Icctus, smooth; Greek o ^:^30S| 409 4.IO The History of Ichthyology described the collections of the Thetis, on the thores of the New S(juth Wales. From Austria the voyage of the frigate Xovara has yielded large material which has been described by Dr. Rudolph Kner. The cream of many voyages of many Danish merchant vessels has been gathered in the " Spoha Atlantica " and other truly classical papers of Christian Frederik Liitken, of the Uni\'er- sity of Copenhagen, one of the most accomplished naturalists of recent times. F. H. von Kittlitz has written on the fishes seen by him in the northern Pacific, and earlier and more important we may mention the many iehthyological notes found in the records of travel in !\Iexico and South America by Alexander von Humboldt { 1 796-1 859). The local faunal work in various nations has been very extensive. In Great Britain we may note Parnell's " Natural History of the Fishes of the Firth of Forth," published in Edin- burgh in 1838, Wilham Yarrell's "History of British Fishes" (1859), the earlier histories of British fishes by Edward Dono- van and by William Turton, and the works of J. Couch (1862) and Dr. Francis Day (1888), possessing similar titles. The work of Day, with its excellent plates, will long be the standard account of the relatively scant fish fauna of the British islands. H. G. Seeley has prepared (18S6) also a useful synopsis of "The Fresh-water Fishes of Europe." We may here notice without praise the pretentious work of WilHam Swainson (1838-39). W. Thompson has written of the fishes of Ireland, and Rev. Richard T. Lowe and J. Y. Johnson have done most excellent work on the fishes of Madeira. F. McCoy, better known for work on fossil fishes, mav be mentioned here. The fish fauna of Scandinavia has been described more or less fully by S. Kroyer (1840), Robert Nilsson (1855), Fries and likstrom {1836), Robert Collett, Robert Lilljeborg, and F. A. Smitt, Viesides special pa]>ers by other writers, notably Reinhardt, L. Esmarck, Japetus Steenstrup, Lutkcn, and A. W. Malm. Reinhardt, Kroyer, Ltitken, and A. J. Malmgren have Avritten of the Arctic fishes of Greenland and Spitzbergen. In Russia, N.irclmann has described the fishes of the Black The History of Ichthyology 411 Sea (" Ichthyologie Pontiquc," Paris, 1840) and Eichwald those of the Caspian. More recently, S. Herzcnstein, Warpachow- sky, K. Kessler, B. N. Dybowsky, and others have written of the rich fauna of Siberia, the Caucasus, and the scarcely known sea of Ochotsk. Stephan Basilevsky has written of the fishes of northern China. A. Ivowalevsky has contributed very much to our knowledge of anatomy. Peter Schmidt has studied the fishes of the Japan Sea. In Germany and Austria the chief local works have been those of Heckel and Kner on the fresh-water fishes of Austria (1858) and C. Th. von Siebold on the fresh-water fishes of Central Europe (1863). German ichthyologists have, however, often extended their view to foreign regions where their charac- teristic thoroughness and accuracy has made their work illu- minating. The two memoirs of Eduard I^iippell on the fishes of the Red Sea and the neighboring parts of Africa, "Atlas zu der Reise im Nordlichen Afrika," 1828, and " Neue AVirbel- thiere," 1837, rank with the very best of descriptive literature. Gunther's illustrated " Fische der Slidsee," published in Ham- burg, may be regarded as German work. The excellent colored plates are mostly from the hand of Andrew Garrett. Other papers are those of Dr. AYilhelm Peters on Asiatic fishes, the most important being on the fishes of Mozambique. J. J. Heckel, Rudolph Kner, and Franz Steindachner, successively directors of the iluseum at Vienna, have written largely on fishes. The papers of Steindachner cover almost every part of the earth and are absolutely essential to any systematic study of fishes. No naturalist of any land has surpassed Stein- dachner in industry or accuracy, and his work has the advan- tage of the best illustrations of fishes made by any artist, the noted Eduard Konopicky. In association with Dr. Doder- lein, formerly of Tokyo, Dr. Steindachner has given an excel- lent account of the fishes of Japan. Other German writers are J. J. Kaup, who has worked in numerous fields, but as a whole with little skill. Dr. S. B. Klunzingcr, Avho has gi\'en excellent accounts of the fishes of the Red Sea, and Dr. Franz Hilgendorf, of the University oi Berlin, whose papers on the fishes of Japan and other regions have shown a high grade of taxonomic insight. A writer of earUer date is W. L. von Rapp, 412 The History of Ichthyology who wrote on the " Fische den Bodensees." J. F. Brandt has written of the sturgeons of Russia, and Johann ]\Iarcusen, to whom Ave owe much of our knowledge, of the Aformyri of Africa. In Italy, Charles Lucien Bonaparte, Prince of Canino, has pubhshed an elaborate "Fauna Itahca" (1838) and in numer- ous minor papers has taken a large part in the development of ichthyology. Many of the accepted names of the large groups (as Elasmobranchii, Heterosomata, etc.) were first suggested bv Bonaparte. The work of Rafinesque has been already noticed. 0. G. Costa published (about 1850) a "Fauna of Naples." In recent times Camillo Ranzani, of Bologna, wrote on the fishes of Brazil and of the Mediterranean. Giovanni Canestrini, Deeio A'inciguerra, Enrico Hillyer Giglioli, Luigi Doderlcin, and others have contributed largely to our knowledge of Italian fishes, Avhile Carlo F. Emery, F. de Filippi, Luigi Faccioki, and others have studied the larval growth of dift'erent species. Camillo Ranzani, G. G. Bianconi, Domenico Nardo, Cristdforo Bellotti, Alberto Perugia, and others have con- tributed to difi'erent fields of ichthyology. Nicholas jVpostolicles and, still later, Horace A. Hoft'man and the present writer, have written of the fishes of Greece. In France, the fresh-Avater fishes are the subject of an impor- tant work by Emile Blanchard (1866), and Emile Moreau has given us a convenient account of the fish fauna of France. Leon A'aillant has written on various groups of fishes, his monograph of the American darters (Etheostomiiiff) being a master] )iece so far as the results of the study of relatively scanty material Avould pemiit. The "Mission Scientifique au Mex- ique," by \'ailkmt and F. Boeourt, is one of the most valuable contributions to our knowledge of the fishes of that region. Dr. 11. E. Sauvage, of Boulognc-sur-Mcr, has also written largely on the fishes of Asia, Africa, and other regions. Among the most important of these are the " Poissons de ]\Iadagascar," and a monograph of the sticklebacks. Alexander Thominot and Jacques Pellegidn have also written, in the Museum of the Jardm des Plantes, on difl'ercnt groups of fishes. Earher writers were Constant Dtuneril, Al]dionse Guiehenot, L. Bris- sot de Barneville, H. Hollard, an aide anatomist, and Bibron, an associate of Auguste Dumeril. Fei.ipf. Poey y Aloy. \: IK noD(M}DOi: Leon Vaillant. J' 413 414 The History of Ichthyology In Spain and Portugal the chief work of local authors is that of J. V. B. Bocage and F. de Brito Capello on the fishes of Portugal. So far as the fishes of Spain are concerned, the most valuable memoir is Steindachner's account of his travels in Spain and Portugal. The principal studies of the Balkan region have also been made by Steinclachner. Jose Gogorza y Gon- zalez, of the Museum of ^ladrid, has given a list of the fishes of the Philippines. A still more elaborate list, praiseworthy as a beginning, is the work of the Reverend Padre Casto de Elera, professor of Natural History in the Dominican College of Santo Tomas in Manila. In Holland, the chief great works have been those of Schlegel and Pieter van Bleeker. Professor H. Schlegel, of the University of Leyden, described the fishes collected about Nagasaki by Ph. Fr. de Siebold and Biirger. His work on fishes forms a large folio illustrated by colored plates, a volume of the " Fauna Japonica," published in Leyden from 1843 to 1847. Schlegel's work in every field is characterized by scrupulous care and healthful conservatism, and the "Fauna Japonica" is a most useful monument to his rare powers of discrimination. Pieter von Bleeker (1819-78), a surgeon in the Dutch West Indies, is the most voluminous writer in ichthyology. He began his work in Java without previous training and in a YQj-y rich field where almost e\'er}'thing was new. With many mistakes at first he rose to the front by sheer force of industry and patience, and his later work, while showing much of the "personal ecpation," is still thoroughly admirable. At his death he was engaged in the pubheation of a magnificent folio work, "Atlas Ichthyologique des Indes Orientales Neerlan- daises," iUustrated by colored plates. This work remams about two-thirds completed. The writings of Dr. Bleeker constitute the chief source of our knowledge of the fauna of the East Indies. Dr. \'an Lidth de Jeude, of the University of Leyden, is the author of a few descriptive papers on fishes. To Belgmm we may assign part at least of the work of the eminent Belgian naturalist, George Albert Boulenger, now long connected Avith the British Museum. His various valu- able papers on the fishes of tlie Congo are published under the The History of Ichthyology 415 auspices of the "Congo Free State." To Belgium also we may ascribe the work of Louis Dollo on the morphology of fishes and on the deep-sea fishes obtained by the "Expedition Ant- arctique Beige." The fish fauna of Cuba has been the lifelong study of Dr. Felipe Poey y Aloy (1799-1891), a pupil of Cuvier, for a half century or more the honored professor of zoology in the Uni- versity of Havana. Of his many useful papers, the most exten- sive are his " Memorias sobre la Historia Natural de la Isla de Cuba," followed by a "Repertorio" and an "Enumeratio" in which the fishes are elaborately catalogued. Poey devoted himself solely to the rich fish fauna of his native island, in which region he was justly recognized as a ripe scholar and a broad- minded gentleman. A favorite expression of his was " Comme naturaliste, je ne suis pas espagnol: je suis cosmopolite." Before Poey, Guichenot, of Paris, had written on the fishes collected in Cuba by Ramon de la Sagra (1810-60). His account was published in Sagra's " Historia de Cuba, " and later Philip H. Gosse (1810-1888) wrote on the fishes of Jamaica. Much earlier, Robert Hermann Schomburgk (1804-65) wrote on the fishes of British Guiana. Other papers on the Carib- bean fishes were contributed by Johannes Miiller and F. H. Troschel, and by Richard Hill and J. Hancock. Besides the work in South America of ilarcgraf, Agassiz, Reinhardt, Liitken, Steindachner, Jenyns, Boulenger, and others already named, we may note the local studies of Dr. Carlos Berg in Argentina, Dr. R. A. Philippi, and Frederico T. Delfin in Chile, Miranda-Ribeiro in Brazil, with Garman, J. F. Abbott, and others in recent times. Carl H. Eigenmann and earlier Jordan and Eigenmann have studied the great col- lections made in Brazil by Agassiz, Steindachner has de- scribed the collections of Johann Natterer and Gilbert those made by Dr. John Casper Branner. The most recent exam- inations of the myriads of Brazilian river fishes have been made by Dr. Eigenmann. Earher than any of these (1855), Francis de Castelnau (1800-65) described many Brazihan fishes and afterwards numerous fishes of Australia and southern Africa. Alphonse Guichenot, of Paris, contributed a chapter on fishes to Claude Gay's (1800-63) "History of Chile," and J. J. von 41 6 The History of Ichthyology Tschudi, of St. Gallen, published an elaborate but uncritical "Fauna Peruana" with colored plates of Peruvian fishes. In Xew Zealand, F. W. Hutton and J. Hector have pub- lished a valuable work on the fishes of New Zealand, to which Dr. GiU added useful critical notes in a study of "Antipodal Faunas." Later Avriters have given us a good knowledge of tlie fishes of Australia. Notable among them are Charles DeVis, AA'illiam Macleay, H, de iliklouho-Maclay, James Douglas Ogilby, and Edgar R. Waite, Clarke has also written on "Fishes of New Zealand." The most A'aluable work on the fishes of Hindustan is the elaborate treatise on the "Fishes of India" by Surgeon Francis Day. In this all the species are figured, the groups being arranged as in Gunther's catalogue, a secjuence which few non- British naturalists seem inclined to foUoAv. Cantor's " ]\Ialayan F'ishes" is a memoir of high merit, as is also McClelland's work on Indian fishes and the still earlier work of Francis Buchanan Hamilton on the fishes of the Ganges. We may here refer to Andrew Smith's papers on the fishes of the Cape of Good Hope and to R. I. Playfair and A. Gtinther's "Fishes of Zanzibar." T. C. Jerdon, John Edward Gray, E. Tyrwhitt Bennett, and others have also written on the fishes of India; J. C. Bennett has published several excellent papers on the fishes of Poly- nesia and the East Indies. In Japan, fallowing the scattering papers of Thuntierg, Tilesius, and Hriuttuyn, and the monumental work of Schlegel, numerous species have been recorded by James Carson Bre- voort, Gunther, Gill, Eduard Nystrom, Hilgendorf, and others. About 1S84 Steindachner and Doderlein published the A'al- uable " Fische Japans," based on the collections made, about Tokyo by Dr. Doderlein. In 1S81, ilutokichi Namiye, then assistant curator in the Imperial University, pulTished the first list of Japanese fishes by a native author. In igoo. Dr. Chiyomatsu Ishikawa, on the " Fishes of Lake Biwa," Avas the first Japanese author to venture t(3 name a new species of fish (I'sriidogobio zczcra). This reticence was due not whollv to lack of self-confidence, but rather to the scattered condition of the literature of Japanese ichthyology. For this reason no Japanese author has ever felt that any given undetermined 417 41 8 The History of Ichthyology species was really new. Other Japanese ichthyologists of promise are Dr. Kamakichi Kishinouye, in charge of the Imperial lisherics Bureau, Dr. Shinnosuke :\Iatsubara, director of the Imperial Fisheries Institute, Keinosuke Otaki, S. Hatta, S. Xozawa, T. Kitahara, and Miehitaro Sindo, and we may look for others among the pupils of Dr. Kakichi Mitsukuri, the dis- tinguished professor of zoology in the Imperial University. The most recent, as well as the most extensive, studies of the fishes of Japan were made in 1900 by the present writer and his associate, John Otterbein Snyder. The scanty pre-Cuvieran work on the fishes of North America has been already noticed. Contemporary with the early Avork of Cuvier is the worthy attempt of Professor Samuel Latham ]\Iitchill (i 764-1 831) to record in systematic fashion the fishes of New York. Soon after followed the admirable work of Charles Alexandre Le Sueur (1780-1840), artist and naturalist, who Avas the first to study the fishes of the Great Lakes and the basin of the Ohio. Le Sueur's engravings of fishes, in the early publications of the Academy of Natural Sciences in Philadelphia, are still among the most satisfactory representations of the species to which they refer. Constan- tine Samuel Rafinesque (i 784-1842), the third of this remark- able but very dissimilar trio, published numerous papers descrip- tive of the species he had seen or heard of in his various botan- ical ramljles. This culminated in his elaborate but untrust- worthy " Ichthyologia Ohiensis." The fishes of Ohio received later a far more conscientious though less brilliant treatment at the hands of Dr. Jarcd Potter Kirtland (i 793-1877), an eminent physician of Cleveland, Ohio. In 1842 the amiable and scholarly James EUsworth Dekay (1799-1851) published his detailed report on the fishes of the "New York Fauna," and a little earlier (1836) in the "Fauna Boreah-Americana" Sir John Richardson (i 787-1865) gave a most A'aluable and accu- rate account of the fishes of the Great Lakes and Canada. Almost simultaneously, Rev. Zadock Thompson (1796-1856) ga^-e a catalogue of the fishes of \"ermont, and David Humphreys Storer (1804-91) began his work on the fishes of Massachu- setts, finally expanded into a "Synopsis of the Fishes of North America" (1846) and a "History of the Fishes of Massachu- The History of Ichthyology 4 1 9 setts" 1853-67). Dr. John Edwards Holbrook (1794-1871), of Charleston, pubhshed (1855-60) his invaluable record of the fishes of South Carolina, the promise of still more impor- tant work, which was prevented by the outbreak of the Civil War in the United States. The monograph on Lake Superior (1850) and other publications of Louis Agassiz (1807-73) have been already noticed. One of the first of Agassiz's stu- dents was Charles Girard (1822-95), who came with him from Switzerland, and, in association with Spencer FuUerton Baird (1823-87), described the fishes from the United States Pacific Railway Sirrvej^s (1858) and the United States and Mexican Boundary Surveys (1859). Professor Baird, pri- marily an ornithologist, became occupied with executive mat- ters, leaA'ing Girard to finish these studies of the fishes. A large part of the work on fishes published by the United States National iluseum and the United States Fish Commission has been made possible through the direct help and inspiration of Professor Baird. Among those engaged in this work, James William Milner (1841-80), Marshall Macdonald (1836-95), and Hugh M. Smith may be noted. Most eminent, however, among the students and assistants of Professor Baird was his successor, George Brown Goode (1851-99), one of the most accomplished of American natu- ralists, whose greatest work, "Oceanic Ichthyology," pub- lished in collaboration with his long associate. Dr. Tarleton Hoffman Bean, was barely finished at the time of his death. The work of Theodore Nicholas Gill and Edward Drinker Cope has been already noticed. Other faunal writers of more or less prominence were William Dandridge Peck (1763-1822) in New Hampshire, George Suck- ley (1830-69) in Oregon, James William Milner (1841-80) in the Great Lake Region, Samuel Stehman Haldeman (181 2- 80) in Pennsylvania, WilUam O. Ayres (1817-91) in Connecti- cut and California; Dr. John G. Cooper (died 1902), Dr. Wil- liam P. Gibbons and Dr. William N. Lockington (died 1902) in CaHfomia; Philo Romayne Hoy (1816-93) studied the fishes of Wisconsin, Charles Conrad Abbott those of New Jersey, Silas Steams (1859-88) those of Florida, Stephen Alfred Forbes and Edward W. Nelson those of Illinois, Oliver Perry Hay, 420 The History of Ichthyology later known for his work on fossil forms, those of ^Mississippi, Alfredi) Duges, of Guanajuato, those of Central Mexico. Samuel Garman, at Harvard University, a student of Agassiz, is the author of numerous valuable papers, the most notable being on the sharks and on the deep-sea collections of the Albatross in the Galapagos region, the last illustrated bA' plates of most notable excellence. Other important mono- graphs of Garman treat of the Cyprinodonts and the Discoboli. The present writer began a " Systematic Catalogue of the Fishes of North America" in 1875 in association with his gifted friend, Herbert Edson Copeland (1849-76), Avhose sudden death, after a few promising beginnings, cut short the under- taking. Later, Charles Henry Gilbert (i860-), a student of Professor Copeland, took up the work and in 1883 a "Synop- sis of the Fishes of North America" -was completed by Jordan and Gilbert. Later, Dr. Gilbert has been engaged in studies of the fishes of Panama, Alaska, and other regions, and the second and e'^largecl edition of the "Synopsis" was completed in 1898, as the "Fishes of North and Middle America," in col- laboration with another of the writer's students. Dr. Barton Warren Evemiann. A monographic review of the Fishes of Puerto Rico was later (1900) completed by Dr. Evertnann, together with numerous minor works. Other naturalists ■whom the Avriter mav be proud to claim as students are Charles Leslie McKay (1854-83), drowned in Bristol Bay, Alaska, while engaged in explorations, and Charles Henry Bollman (1S68- 8q), stricken with fever in the Okefinokee Swamps in Georiga. Still others were Dr. Carl H. Eigenmann, the indefatigable investigator of Brazilian fishes and of the blind fishes of the caves ; Dr. Oliver Peebles Jenkins, the first thorough explorer of the fishes of Hawaii ; Dr. Alembert Winthrop Brayton, explorer of the streams of the Great Smoky ilountains ; Dr. Seth Eugene Jleek, explorer of Mexico ; John Otterbein Snvder, explorer of Mexico, Japan, and Hawaii ; EdAvin Chapin Starks, explorer of Puget Sound and Panama and investigator of fish osteology. Still other naturalists of the coming generation, students of the present writer and of his life-long associate. Professor Gilliert, have eontriliuted in various degrees to the present fabric of American ichthyology. Among them are ImI Charles Hpinky (_;ii,i)1' fe=w^ liAirid.v Wakkkn EvekhanW 421 422 The History of Ichthyology j\lrs. Rosa Smith Eigenmann, Dr. Joseph Swain, Wilbur Wilson Thnburn (1859-99), Fi-ank Cramer, Alvin Seale, Albert Jeffer- son AVoolman, Phihp H. Kirsch (1860-1902), Cloudsley Rutter (died 1903), Robert Edward Snodgrass, James Francis Abbott, Arthur White Greeley, Edmund Heller, Henry Weed Fowler, Keinosuke Otaki, ]\Iichitaro Sindo, and Richard Crittenden McGregor. Other facts and conclusions of importance haA-e been con- tributed by various persons with whom ichthyology has been an incident rather than a matter of central importance. The Fossil Fishes.* — The study of fossil fishes was begun sys- tematically during the first decades of the nineteenth century, for it was then realized that of fossils of backboned animals, fishes were the only ones which could be determined from early Palaeozoic to recent horizons, and that from the diversity of their forms they could serve as reliable indications of the age of rocks. ^Vt a later time, when the CA'olution of vertebrates began to be studied, fishes were examined with especial care with a A-icw of determining the ancestral line of the Amphibians. The earliest work upon fossil fishes is, as one would naturally expect, of a purely systematic value. Anatomical observa- tirjns Avere scanty and crude, but as the material for study increased, a more satisfactory knowledge was gained of the structures of the various major groups of fishes; and finally by a comparison of anatomical results important light came to be thrown upon more fundamental problems. The study of fossil fishes can be divided for convenience into three periods: d) That which terminated in the luag- nitui opus of J^ouis Agassiz ; (II) that of the S3'stematists whose major works appeared between 1845 and the* recent publica- tion of the Catalogue of Fossil Fishes of the British iluseum (from this period date many important anatomical observa- tions); and (III) that of morphological work, roughh^ from 1870 to the present. During this period detailed considera- tion has been giA-en to the ph}dogeny oi special structures, to the proljablc lines of descent of the groups of fossil fishes, and to the relationships of terrestrial to aquatic vertebrates. * For these paragraphs on the history of the study of fossil fishes th( writer is indebted t.. the kind interest of Professor Bashford Dean. The History of Ichthyology 423 First Period. — The Work of Louis Agassiz. — The real beginning of our knowledge of fossil fishes dates from the pubHcation of the classic volumes of Agassiz, " Recherches sur les Poissons Fossiles (Neuchitel, 1833-44)." There had previously existed but a fragmentary and widely scattered Uterature; the time was ripe for a great work which should bring together a knowledge of this important vertebrate fauna and the mu- seums throughout Europe had been steadily growing in their collections of fossils. Especially ripe, too, since the work of Cuvier (1769-1832) had been completed and the classic an- atomical papers of J. Miiller (1802-56) were appearing. And Agassiz (1807-73) was eminently the man for this mission. At the age of one and twenty he had already mapped out the work, and from this time he devoted sixteen active years to its accomplishment. One gets but a just idea of the person- ality of Agassiz when he recalls that the young investigator while in an almost penniless position contrived to travel over a large part of Europe, mingle with the best people of his day, devote almost his entire time to research, employ draughts- men and lithographers, support his own printing-house, and in the end publish his " Poissons Fossiles " in a fashion which would have done credit to the wealthiest amateur. With tireless energy he collected voluminous notes and drawings number- less; he corresponded with collectors all over Europe and prevailed upon them to loan him tons of specimens; in the meanwhile he collated industriously the early but fragmental literature in such works as those of de Blainville, Munster, Murchison, Buckland, Egerton, Redfield, W. C. Williamson, and others. Hitherto less than 300 species of fossil fishes were known; at the end of Agassiz's work about 900 were described and many of them figured. It is easy to see that such a work made a ready basis of future studies. Doubtless, too, much is owing to the personal energy of Agassiz that such keen interest was focused in the collection and study of fossil fishes during the middle of the nineteenth century. The actual value of Agassiz's work can hardly be overestimated; his figures and descriptions are usu- ally clear and accurate. And it is remarkable, perhaps, that in view of the very wide field which he covered that his errors 424 The History of Ichthyology are not more glaring and numerous. Upon the purely scien- tific side, however, one must confess that the " Poissons Fossiles " is of minor importance for the reason that as time has gone by it has been found to yield no generalizations of fundamental value. The classification of fishes advocated by Agassiz, based upon the nature of the scales, has been shown to be convenient rather than morphological. This indeed Agassiz himself ap- pears to realize in a letter written to Humboldt, but on the other hand he regards his creation of the now discarded order of Ganoids, which was based upon integumental characters, as his most important contribution to the general study of ichthyology. And although there passed through his hands a series of forms more complete than has perhaps been seen by any later ichthyologist,* a series which demonstrates the steps in the evolution of the various families and even orders of fishes, he is nowhere led to such important philosophical conclusions as was, for example, his contemporary, Johannes Miiller. And even to his last day, in spite of the light which palaeontology must have given him, he denied strenuously the truth of the doctrine of evolution, a result the more remarkable since he has even given in graphic form the geological occurrence of the vari- ous groups of fishes in a way which suggests closely a modem phylogenetic table, and since at various times he has empha- sized the dictum that the history of the individual is but the epitomized history of the race. The latter statement, which has been commonly attributed to Agassiz, is clearly of much earUer origin; it was definitely formulated by von Baer and Meckel, the former of whom even as early as 1834 pronounced himself a distinct evolutionist. Second Period.— Systematic Study of Fossil Fishes. — On the ground planted by Agassiz, many important works sprang up within the next decades. In England a vigorous school of palaeichthyologists was soon flourishing. Many papers of Egerton date from this time, and the important work of Owen on the structure of fossil teeth and the often-quoted papers of Huxley in the ''British Fossil Remains." Among other workers may be mentioned James Powrie, author of a number of papers upon Scottish Devonian fossils; the enthu- * Dr. Arthur Smith Woodward excepted. 425 426 The History of Ichthyology siastic Hugh Miller, stone-mason and geologist ; ilontague Brown, Thomas Atthey, J. Young, and AA'. J. Barkas, students upon Coal Measure fishes; E. Ray Lankester, some of whose early papers deal with pteraspids; E. T. Xewton, author of important works on chimaeroids. The extensive works of J. W. Davis deal with fishes of many groups and many horizons. Mr. DaA'is, like Sir Philip Gray Egerton, was an amateur whose de\-otion did much to ad\'ance the study of fossil fishes. The dean of British pakeichthyology is at present Dr. R. H. Tra- quair, of the Edinburgh iluseum of Science and Arts. During four decades he has devoted himself to his studies with rare energy and success, author of a host of shorter papers and numerous memoirs and reports. Finally, and belonging to a younger generation of palscontologists, is to be named Arthur Smith W(iodward, curator of vertebrate palaeontology of the British Museum. Dr. AA'oodward has already contributed many scores of papers to palasichthj'ology, besides publishing a four-\-olume Catalogue of the Fossil Fishes of the British Museum, a compendial work whose value can only be appre- ciated adequately by specialists. In the United States the study of fossil fishes Avas taken up by J. H. and W. C. Redfield, father and son, prior to the work of Agassiz, and there has been since that time an active school of American workers. Agassiz himself, however, is not to be included in this list, since his interest in extinct fishes became almost entirely unproductive during his life in America. Foremost among these workers was John Strong Newberry (1822-92), of Columbia College, whose publications deal with fishes of many horizons and whose work upon this conti- nent is not unlike that of Agassiz in Europe. He was the author of many state reports, separate contributions, and two mono- graphs, one upon the palaeozoic fishes of North America, the other upon the Triassic fishes. Among the earlier palaeontolo- gists were Orestes H. St. John, a pupil of Agassiz at Harvard, and A. H. Worthen (1813-88), director of the Geological Sur- vey of IlHnois; also W. Gibbes and Joseph Leidy. The late E. D. Cope (1840-97) devoted a considerable portion of his labors to the study of extinct fishes. E. W. Claypole, of Buch- tel College, is next to be mentioned as having produced note- The History of Ichthyology 427 worthy contributions to our knowledge of sharks, pala;aspids, and arthrodires, as has also A. A. Wright, of Oberhn College. Among other workers may be mentioned O. P. Hay, of the American Museum; C. R. Eastman, of Harvard, author of important memoirs upon arthrodires and other forms; Alban Stewart, a student of Dr. S. W. AVilliston at Kansas Univer- sity, and Bashford Dean. Among Canadian palaeontologists G. F. Matthew deserves mention for his work on Cyathaspis, Principal Dawson for interesting references to Mesozoic fishes, and J. F. Whiteaves for his studies upon the Devonian fishes of Scaumenac Bay. Belgian pala?ontologists have also been active in their study of fishes. Here we may refer to the work of Louis Dollo, of Brussels, of i\lax Lohest, of P. J. van Beneden, of L. G. de Koninck, of T. C. "Winckler, and of R. Storms, the last of whom has done interesting work on Tertiary fishes. Foremost among Russian palasichthyologists is to be named C. H. Pander, long-time Academician in St. Petersburg, whose elaborate studies of extinct lung-fishes, ostracophores, and crossopterygians published between 1856 and i860 will long stand as models of careful work. We should also refer to the work of H. Asmuss and H. Trautschold, E. Eichwald and of Victor Rohon, the last named having published many important papers upon ostracophores during his residence in St. Petersburg. German palaeichthyologists include Otto Jaekel, of Berlin; 0. M. Reis of the Oberbergamt, in Munich; A von Koenen, of Gottingen; A. Wagner, E, Koken, and K. von Zittel. .Among Austro-Htmgarians are Anton Fritsch, author of the Fauna der Gaskoklef or Illations Boemens; Rudolf Kner, an active student of living fishes as well, as is also Franz vSteindachner. French palseichthyologists are represented by the veteran H. E. Sauvage, of Boulogne-sur-Mer, V. Thollicre, M. Bron- gniart, and F. Priem. In Italy Francesco Bassani, of Naples, is the author of many important works dealing with Mesrizoic and Tertiary forms; also was Baron Achille di Zigno. Robert CoUett, of Bergen, and G. Lindstrom are worthy representatives of Scandinavia in kindred Avork. Third Period. — Morphological Work on Fossil Fishes. — Among the writers who have dealt with the problems of the rela- 428 The History of Ichthyology tionships of the Ostracophores as well as Palaospondylus and the Arthrodires may be named Traquair, Huxley, New- berry, Smith-Woodward, Rohon, Eastman, and Dean; most recently William Patten. Upon the phylogeny of the sharks Traquair, A. Fritsch, Hasse, Cope, Brongniart, Jaekel, Reis, Eastman, and Dean. On Chima^roid morphology mention may be made of the papers of A. S. Woodward, Reis, Jaekel, Eastman, C. D. Walcott, and Dean. As to Dipnoan relation- ships the paper of Louis DoUo is easily of the first value; of especial interest, too, is the work of Eastman as to the early derivation of the Dipnoan dentition. In this regard a paper of Rohon is noteworthy, as is also that of Richard Semon on the development of the dentition of recent Neoceratodus, since it contains a number of references to extinct types. Interest notes on Dipnoan fin characters have been given by Traquair. In the morphology of Ganoids, the work of Traquair and A. S. Woodward takes easily the foremost rank. Other important works are those of Huxley, Cope, A. Fritsch, and Oliver P. Hay. Anatomists. — Still more difficult of enumeration is the long list of those who have studied the anatomy of fishes usually in connection with the comparative anatomy or development of other animals. Pre-eminent among these are Karl Ernst von Baer, Cuvier, Geffroy, St. Hilaire, Louis Agassiz, Johannes Mtiller, Carl Vogt, Carl Gegenbaur, William Kitchener Parker, Francis M. Balfour, Thomas Henry Huxley, Meckel, H. Rathke, Richard Owen, Kowalevsky, H. Stannius, Joseph Hyrtl, Gill, Boulenger, and Bashford Dean. Other names of high authority are those of Wilhelm His, Kolliker, Bakker, Rosenthal, Gottsche, Miklucho-Macleay, Weber, Hasse, Retzius, Owsjannikow, H. Miiller, Stieda, Marcusen, J. A. Ryder, E. A. Andrews, T. H. Morgan, G. B. Grassi, R. Semon, Howard Ayers, R. R, AA'right, J. P. McMurrich, C. O. Whitman, A. C. Eyclesheimer, E. Pahis, Jacob Reighard, and J. B. Johnston. Besides all this, there has risen, especially in the United States, Great Britain, Nonvay, and Canada and Australia, a vast literature oi commercial fisheries, fish culture, and anglino-, the chief workers in which fields we may not here enumerate even bv name. CHx\PTER XXIII THE COLLECTION OF FISHES fOW to Secure Fishes. — In collecting fishes three things are vitally necessary— a keen eye, some skill in adapting means to ends, and some willingness to take pains in the preservation of material. In coming into a new district the collector should try to preser\'e the first specimen of every species he sees. It may not come up again. He should watch carefully for specimens which look just a little different from their fellows, especially for those which are duller, less striking, or with lower fins. Many species have remained unnoticed through generations of col- lectors who have chosen the handsomest or most ornate speci- mens. In some groups with striking peculiarities, as the trunk- fishes, practically all the species were known to Linneeus. No collector could pass them by. On the other hand, new gobies or blennies can be picked up almost every day in the lesser kno-wn parts of the world. For these overlooked forms — her- rings, anchovies, sculpins, blennies, gobies, scorpion-fishes — the competent collector should be always on the watch. If any specimen looks different from the rest, take it at once and find out the reason why. In most regions the chief dependence of the collector is on the markets and these should be watched most critically. By paying a little more for unusual, neglected, or useless fish, the supply of these will rise to the demand. The word passed along among the people of Onomichi in Japan, that "Ebisu the fish-god was in the village" and would pay more for okose (poison scorpion-fishes) and umiuma (sea-horses) than real fishes were worth soon brought (in 1900) all sorts of okose and umiuma into the market when they were formerly left neglected on the beach. Thus with a little ingenuity the mar- kets in any country can be greatly extended. 429 430 The Collection of Fishes The collector can, if he thinks best, use all kinds of fishings tackle for himself. In Japan he can use the "dabonawa" long lines, and secure the fishes which were otherwise dredged by the Challenger and Albatross. If dredges or trawls are at his hand he can hire them and use them for scientific purposes. He should neglect no kind of bottom, no conditions of fish life which he can reach. Especially important is the fauna of the tide-pools, neg- lected by almost all collectors. As the tide goes down, espe- cially on rocky capes which project into the sea, myriads of little fishes will remain in the rock-pools, the alga;, and the clefts of rock. In regions like California, where the rocks are buried with kelp, blennies will lie in the kelp as quiescent as the branches of the algas themselves until the flow of water returns. A sharp three-tined fork Avill help in spearing them. The water in pools can be poisoned on the coast of ilexico with the milky juice of the "hava" tree, a tree which yields strychnine. In default of this, pools can be poisoned by chloride of lime, sulphate of copper, or, if small enough, by formaline. Of all poisons the commercial chloride of lime seems to be most effective. By such means the contents of the pool can be secured and the next tide carries away the poison. The water in pools can be bailed out, or, better, emptied bv a siphon made of small garden-hose or rubber tubing. On rock}' shores, dynamite can be used to advantage if the col- lector or his assistant dare risk it and if the laws of the country do no prevent. Jlost efTective in rock-pool work is the help of the small boy. In all lands the collector will do well to take him into his pay and confidence. Of the hundred or more new species of rock-pool fishes lately secured by the writer in Japan, fully two-thirds Avere obtained by the Japanese boys. Equally effective is the "muchacho" on the coasts of Mexico. Masses of coral, sponges, tunicates, and other porous or hollow organisms often contain small fishes and should be care- fully examined. On the coral reefs the breaking up of large masses is often most remunerative. The importance of securing the young of pelagic fishes by tow-nets and otherwise cannot be too strongly emphasized. The Collection of Fishes 431 How to Preserve Fishes. — Fishes must be permanently pre- served in alcohol. Dried skins are far from satisfactory, except as a choice of difficulties in the case of large species. Dr. Giinther thus describes the process of skinning fishes: "Scaly fishes are skinned thus: With a strong pair of scissors an incision is made along the median line of the abdomen from the foremost part of the throat, passing on one side of the base of the ventral and anal fins to the root of the caudal fin, the cut being continued upward to the back of the tail close to the base of the caudal. The skin of one side of the fish is then severed with the scalpel from the underlying muscles to the median line of the back; the bones which support the dorsal and caudal are cut through, so that these fins remain attached to the skin. The removal of the skin of the opposite side is easy. More difficult is the preparation of the head and scapu- lary region. The two halves of the scapular arch which have been severed from each other by the first incision are pressed toward the right and left, and the spine is severed behind the head, so that now only the head and shoulder bones remain attached to the skin. These parts have to be cleaned from the inside, all soft parts, the branchial and hyoid apparatus, and all smaller bones being cut away with the scissors or scraped off with the scalpel. In many fishes which are provided with a characteristic dental apparatus in the pharynx (Labroids, Cyprinoids), the pharyngeal bones ought to be preserved and tied with a thread to their specimen. The skin being now prepared so far, its entire inner surface as well as the inner side of the head are rubbed with arsenical soap; cotton-wool or some other soft material is inserted into any cavities or hol- lows, and finally a thin layer of the same material is placed between the two flaps of the skin. The specimen is then dried under a slight weight to keep it from shrinking. "The scales of some fishes, as for instance of many kinds of herrings, are so dehcate and deciduous that the mere handling causes them to rub oft" easily. Such fishes may be covered with thin-paper (tissue paper is the best) which is allowed to dry on them before skinning. There is no need for removing the paper before the specimen has reached its destination. "Scaleless fishes, as siluroids and sturgeons, are skinned in 432 The Collection of Fishes the same manner, but the skin can be rolled up over the head ; such skins can also be preserved in spirits, in which case the traveler may save to himself the trouble of cleaning the head. ' ' Some sharks are known to attain to a length of thirty feet, and some rays to a width of twenty feet. The preservation of such gigantic specimens is much to be recommended, and although the difficulties of preserving fishes increase with their size, the operation is facilitated, because the skins of all sharks and rays can easily be preserved in salt and strong brine. Sharks are skinned much in the same way as ordinary fishes. In rays an incision is made not only from the snout to the end of the fleshy part of the tail, but also a second across the widest part of the body. When the skin is removed from the fish, it is placed into a cask with strong brine mixed with alum, the head occupying the upper part of the cask ; this is necessary, because this part is most likely to show signs of decomposition, and therefore most requires supervision. When the preserving fluid has become decidedly weaker from the extracted blood and water, it is thrown away and replaced by fresh brine. After a week's or fortnight's soaking the skin is taken out of the cask to allow the fluid to drain off; its inner side is covered with a thin layer of salt, and after being rolled up (the head being inside) it is packed in a cask the bottom of which is covered with salt ; all the interstices and the top are likewise filled with salt. The cask must be perfectly water-tight." Value of Formalin. — In the field it is much better to use formalin (formaldehyde) in preference to alcohol. This is an antiseptic fluid dissolved in water, and it at once arrests decay, leaving the specimen as though preserved in water. If left too long in formalin fishes swell, the bones are softened, and the specimens become brittle or even worthless. But for ordi- nary purposes (except use as skeleton) no harm arises from two or three months' saturation in formalin. The commercial formalin can be mixed with about twenty parts of water. On the whole it is better to have the solution too weak rather than too strong. Too much formalin makes the specimens stiff, swollen, and intractable, besides too soon destroying the color. Formalin has the advantage, in collecting, of cheapness and of ease in transportation, as a single small bottle will make The Collection of Fishes 433 a large amount of the fluid. The specimens also require much less attention. An incision should be made in the (right) side of the abdomen to let in the fluid. The specimen can then be placed in formalin. When saturated, in the course of the day, it can be wrapped in a cloth, packed in an empty petroleum can, and at once shipped. The wide use of petroleum in all parts of the world is a great boon to the naturalist. Before preservation, the flshes should be washed, to remove slime and dirt. They should have an incision to let the fluid into the body cavity and an injection with a syringe is a useful help to saturation, especially with large fishes. Even decay- ing fishes can be saved with formalin. Records of Fishes. — The collector should mark localities most carefully with tin tags and note-book records if possible. He should, so far as possible, keep records of life colors, and water-color sketches are of great assistance in this matter. In spirits or formalin the life colors soon fade, although the pat- tern of marking is usually preserved or at least indicated. A mixture of formalin and alcohol is favorable to the preserva- tion of markings. In the museiun all specimens should be removed at once from formalin to alcohol. No substitute for alcohol as a per- manent preservative has been found. The spirits derived from wine, grain, or sugar is much preferable to the poisonous methyl or wood alcohol. In placing specimens directly into alcohol, care should be taken not to crowd them too much. The fish yields water which dilutes the spirit. For the same reason, spirits too dilute are ineft'ective. On the other hand, dehcate fishes put into very strong alcohol are Hkely to shrivel, a condition which may prevent an accurate study of their fins or other structures. It is usuahy necessary to change a fish from the first alcohol used as a bath into stronger alcohol in the course of a few days, the time depending on the closeness with which fishes are packed. In the tropics, fishes in alcohol often require attention within a few hours. In formalin there is much less difficulty with tropical fishes. Fishes intended for skeletons should never be placed in formalin. A softening of the bones which prevents future 434 "The Collection of Fishes exact studies of the bones is sure to take place. Generally alcohol or other spirits (arrack, brandy, cognac, rum, sake "vino") can be tested with a match. If sufficiently concen- trated to be ignited, they can be safely used for preservation of fashes. The best test is that of the hydrometer. Spirits for perrnanent use should show on the hydrometer 40 to 60 above proof. Decaying specimens show it by color and smell and the collector should be alive to their condition. One rot- ting fish may endanger many others. With alcohol it is neces- sary to take especial pains to ensure immediate saturation. Deep cuts should be made into the muscles of large fishes as well as into the body cavity. Sometimes a small distilling apparatus is useful to redistil impure or dilute alcohol. The use of formalin avoids this necessity. Small fishes should not be packed v/ith large ones; small bottles are very desirable for their preservation. All spinous or scaly fishes should be so wrapped in cotton muslin as to prevent all friction. Eternal Vigilance. — The methods of treating individual groups of fishes and of handling them under dift'erent climatic and other conditions are matters to be learned by experience. Eternal vigilance is the price of a good collection, as it is said to be of some other good things. Mechanical collecting — pick- ing up the thing got without effort and putting it in alcohol without further thought — rarely serves any useful end in science. The best collectors are usually the best naturalists. The col- lections made by the men who are to study them and who are competent to do so are the ones which most help the progress of ichthyolog}^ The student of a group of fishes misses half the collection teaches if he has made no part of it himself. CHAPTER XXIV THE EVOLUTION OF FISHES ||HE Geological Distribution of Fishes. — The oldest un- questioned remains of fishes have been very recently made known by Mr. Charles D. Walcott, from rocks of the Trenton period in the Ordovician or Lower Silurian. These are from Canon City in Colorado. Among these is cer- tainly a small Ostracophore (Asteraspis desideratus). With it are fragments (Dictyorhabdiis) thought to be the backbone of a Fig- 246. — Fragment of Sandstone from Ordovician depo.sits, Canon City, Colo., showing fragments ot scales, etc., tfie earliest known traces of vertebrates. (From nature.) Chimaera, but more likely, in Dean's view, the axis of a cephalo- pod, besides bony, wrinkled scales, referred with doubt to a sup- posed Crossopterygian genus called Eriplydiius. This renders certain the existence of Ostracophores at this early period, but their association with Chiniccras and Crossopterygians is question- able. Primitive sharks may have existed in Ordovician times, but thus far no trace of them has been found. The fish-remains next in age in America are from the Bloom- field sandstone in Pennsylvania of the Onondaga period in the 435 43' The Evolution of Fishes upper Silurian. The earliest in Europe are found in the Lud- low shales, both of these localities being in or near the horizon of the Niagara rocks, in the Upper Silurian Age. It IS, however, certain that these Lower Silurian remains do not represent the beginning of fish-life. Probably Ostracophores, and Arihrodires, with perhaps Crossopterygians and Dipnoans, m^ Fig- 247, — Fossil fish remains from Ordovician rocks, Canon Citj', Colo. (After (Walcott.) a. Scale of Eriptychius amencanus Walcott. Famil}'- Holopty- chiidaef b Dermal plate of Asteraspis desideratus Walcott. Family Asterolepidai. c Dictyorhabdus priscus Walcott, a fragment of uncertain nature, thought to be a chorda! sheath of a Chimara, but probably part of a Cephalopod (Dean). ChirruBrida:? existed at an earlier period, together perhaps with unarmed, limbless forms without jaws, of which no trace whatever has been left. The Earliest Sharks. — The first actual trace of sharks is found in the Upper Silurian in the form of fin-spines (Onchus), thought to belong to primitive sharks, perhaps Acanthodeans possibly to Ostracophores. With these are numerous bony shields of the mailed Ostracophores, and somewhat later those of the more highly specialized Arthrodires. Later appear the teeth of CochUodontidcB, with Chimasras, a few Dipnoans, and Crossopterygians. Devonian Fishes. — In the Devonian Age the Ostracophores increase m size and abundance, disappearing with the beginning The Evolution of Fishes 437 of the Carboniferous. The Arthrodires also increase greatly in variety and in size, reaching their culmination in the De- vonian, but not disappearing entirely until well in the Carbon- iferous. These two groups (often united by geologists under the older name Placoderms) together with sharks and a few Chimaeras made up almost exclusively the rich fish-fauna of Devonian times. The sharks were chiefly Acanthodean and Psammodont, as far as our records show. The supposed more primitive type of Cladoselache is not known to appear before the latter part of the Devonian Age, while Pleiiracanihus and Cladodns, sometimes regarded as still more primitive, are as yet found only in the Carboniferous. It is clear that the records of early shark life are still incomplete, whatever view we may adopt as to the relative rank of the different forms. Chimaeroids occur in the Devonian, and with them a considerable variety of Crossopterygians and Dipnoans. The true fishes appear also in the Devonian in the guise of the Ganoid ancestors and rela- tives of Palcconisciim, all with diamond-shaped enameled scales. In the Devonian, too, we find the minute creature Palceospon- dyliis, our ignorance of which is concealed under the name Cyclia:. Carboniferous Fishes. — In the Carboniferous Age the sharks increase in number and variety, the Ostracophores disappear, and Fig. 248. — Dipterus valenciennesi Af!,aiifi\z, a, Dipnoan Woodward.) (After Dean, from the Arthrodires follow them soon after, the last being recorded from the Permian. Other forms of Dipnoans, Crossopterygians, and some Ganoids now appear giving the fauna a somewhat more modem aspect. The Acanthodei and the Ichthyotonn pass away with the Permian, the latest period of the Carboniferous Age. Mesozoic Fishes. — In the Triassic period which follows the Permian, the earliest types of Ganoids give place to forms ap- 438 The Evolution of Fishes proaching the garpike and sturgeon. The Crossopterygians rapidly decline. The Dipnoans are less varied and fewer m number; the primitive sharks, with the exception of certain Cestracionts, all disappear, only the family of Orodoniidw remain- ing Here are found the first true bony fishes, doubtless derived from Ganoid stock, the allies and predecessors of the great group of herrings. Hernng-like forms become more numerous in the Jurassic, and with them appear other forms which give the fish- fauna of this period something of a modem appearance. In the Jurassic the sharks become divided into several groups, Nottdani, Scyllioid sharks, Lamnoid sharks, angel-fishes, skates, and finally Carcharioid sharks being now well differentiated. Chimaeras are still numerous. The Acanthodei have passed away, as well as the mailed Ostrachopores and Arthrodires. The Dipnoans and Fig. 249. — Hoplopteryx lewesiensis (Mantell), restored, English Cretaceous. Family Berycidce. (Aiter Woodward.) Crossopterygians are few. The early Ganoids have given place to more modern types, still in great abundance and variety. This condition continues in the Cretaceous period. Here the rays and modern sharks increase in number, the Ganoids hold their own, and the other groups of soft-rayed fishes, as the smelts, the lantern-fishes, the pikes, the fiying-fishes, the berycoids and the mackerels join the group of herring-like forms which represent the modern bony fishes. In the Cretaceous appear the first spiny-rayed fishes, derived probably from herring-like forms. These are allies or ancestors of the living genus Bcrvx. The Evolution of Fishes 439 Dr. Woodward observes: "As soon as fishes with a completely osseous endoskeleton began to predominate at the dawn of the Cretaceous period, specializations of an entirely new kind were rapidly acquired. Until this time the skull of the Actinopterygii had always been remarkably uniform in type. The otic region of the cranium often remained incompletely ossified and was never prominent Fig. 2.50. — A living Berycoid fish, Paratrachichthys ■proathemuis Jordan & Fowler. Missiki, Japan. Family Berycidcc. or projecting beyond the roof bones; the supraoccipital bone was always small and covered with the superficial plates; the maxilla invariably formed the greater part of the upper jaw, the cheek-plates were large and usually thick; while none of the head or opercular bones were provided with spines or ridges. The pelvic fins always retained their primitive remote situation, and the fin-rays never became spines. During the Cretaceous period the majority of the bony fishes began to exhibit modifi- cations in all these characters, and the changes occurred so rapidl}^ that by the dawn of the Eocene period the diversity observable in the dominant fish-fauna was much greater than it had ever been before. At this remote period, indeed, nearly all the great groups of bony fishes, as represented in the exist- ing world, were already differentiated, and their subsequent modifications have been quite of a minor character." 440 The Evolution of Fishes Tertiary Fishes. — With the Eocene or first period of the Tertiary great changes have taken place. The early famihes of bony fishes nearly all disappear. The herring, pike, smelt, Fk;. 211. — Flyincr-fish, Cyp.9i7ur»,s hetrrnru.': (Rafinesque). Family Exnrcetida: Wood's Hole, Mass. salmon, flying-fish, and berycoids remain, and a multitude of other forms seem to spring into sudden existence. Among these are the globefishes, the trigger-fishes, the catfishes, the Fig. 2.52. — The Schoolmaster Snapper, a Pereh-like fish. Key West. Family LiiliaiiichT. eels, the morays, the butterfly-fishes, the porgies, the perch, the bass, the pipefishes, the trumpet-fishes, the mackerels, and the John-dories, with the sculpins, the anglers, the flounders, the blennies, and the cods. That all these groups, generalized and specialized, arose at once is impossible, although all seem The Evolution of Fishes 441 to date from the Eocene times. Doubtless each of them had its origin at an eariier period, and the simultaneous appearance is related to the fact of the thorough study of the Eocene shales, which have in numerous localities (London, Monte Bolca, Licata, Mount Lebanon, Green River) been especially favorable for the preservation of these forms. Practically fossil fishes have been thoroughly studied as yet only in a very few parts of the earth. The rocks of Scotland, England, Germany, Italy, Switzerland, Syria, Ohio, and Wyoming have furnished the great bulk of all the fish remains In existence. In some regions perhaps collections will be made which will give us a more just Fig. 2.5.3. — Decurrent Flounder, Pleuronichlhys denirrens .Jordan i (i San Francisco. prt. conception of the origin of the different groups of bony fishes. ' We can now only say with certainty that the modern families were largely existent in the Eocene, that they sprang from ganoid stock found in the Triassic and Jurassic, that several of them were represented in the Cretaceous also, that the Berycoids were earliest of the spiny-rayed fishes, and forms allied to herring the earliest of the soft-rayed forms. Few modern families arose before the Cretaceous. Few of the modern genera go back to the Eocene, many of them arose in the Miocene, and few species 442 The Evolution of Fishes have come down to us from rocks older than the end of the Pliocene. The general modern type of the fish-faunas being determined in the latter Eocene and the Miocene, the changes which bring us to recent times have largely concerned the abundance and variety of the individual species. From geo- logical distribution we have arising the varied problems of geographical distribution and the still more complex conditions on which depend tlie extinction of species and of types. Factors of Extinction. — These factors of extinction have been recently formulated as follows by Professor Herbert Osborn, He considers the process of extinction as of five different types: "(i> That extinction which comes from modification or progressive evohition, a relegation to the past as a result of tlie transmutation into more ath'anced forms. (2) Extinction from changes of physical environment which outrun the powers of adaptation. (3) Tlie extinction which results from com- petition. (4) The extuiction %Yhich results from extreme spe- cialization and limitation to special conditions the loss of which means extinction. (5) Extinction as a result of exhaustion." Fossilization of a Fish. — AA^'hen a fish dies he leaves no friends. His body is at once attacked by hundreds of creatures ranging fr'im tlie one-celled protozoa and bacteria to individuals of his own species. His flesh is devoured, his bones are scattered, the gelatmous substance in them decays, and the phosphate of lime is in time dissolved m the water. For this reason few fishes of the millions wliich die each year leave any trace for future prescrA'ation. At the most a few teeth, a fin-spine, or a bone buried in the clay might remain intact or in such condition as to be recognized. But now and then it happens that a dead fish may fall in more fortunate conditions. (3n a sea bottom of fine clay the bones, or even the whole body, may be buried in such a way as to be sealed up and protected from total decomposition. The flesh will usually disappear and leave no mark or at the most a mere cast of its surface. But the hard parts, even the muscles may persist, and now and then they do persist, the salts of lime unchanged or else siHcified or subjected to some other form of cliemical substitution. Only the scales, the teeth, the bones, the spines, and the fin-rays can be preserved in the rocks of sea or The Evolution of Fishes 443 lake bottom. In a few localities, as near Green River in Wyo- ming, Monte Bolca, near Verona, and Mount Lebanon in Syria, the London clays, with certain quarries in Scotland and lith(j- graphic stones in Germany, many skeletons of fishes have been found pressed flat in layers of very fine rock, their structures traced as delicately as if actually drawn on the smooth stone. Fragments preserved in ruder fashion abound in the clays and even the sandstones of the earliest geologic ages. In most cases, however, fossil fishes are known from detached and scattered frag- ments, many of them, especially of the sharks, by the teeth alone. Fishes have occurred in all ages from the Silurian to the present time and probably the very first lived long before the Silurian. The Earliest Fishes. — No one can say what the earliest fishes were like, nor do we know what was their real relation to the worm-like forms among which men have sought their presumable ancestors, nor to the Tunicates and other chordate forms, not fish-like, but still degenerate relatives of the primeval fish. From analogy we may suppose that the first fishes which ever were bore some resemblance to the lancelet, for that is a fish-like creature with every structure reduced to the lowest terms. But as the lancelet has no hard parts, no bones, nor teeth, nor scales, nor fins, no traces of its kind are found among the fossils. If the primitive fish was like it in important respects, all record of this has probably vanished from the earth. The Cyclostomes. — The next group of living fishes, the Cyclostomes, including the hagfishes and lampreys, — fishes with small skull and brain but without limbs or jaws, — stands at a great distance above the lancelet in complexity of struc- ture, and equally far from the true fishes in its primitive sim- plicity. In fact the lamprey is farther from the true fish in structure than a perch is from an eagle. Yet for all that it may be an offshoot from the primitive line of fish descent. There is not much in the structure of the lamprey which may be pre- served in the rocks. But the cartilaginous skull, the backbone, fins, and teeth might leave their traces in soft clay or hthographic stone. But it is certain that they have not done so in any rocks yet explored, and it may be that the few existing lampreys owe their form and structure to a process of degradation from a more complex and more fish-like ancestry. The supposed 444 The Evolution of Fishes lamprey fossil of the Devonian of Scotland, Palcrospondylus, lias little in common with the true lampreys. The Ostracophores.— Besides the lampreys the Devonian seas sAvarmcd with mysterious creatures covered with an armor of plate, fish-like in some regards, but limbless, without true jaws and very different from the true fishes of to-day. These are called Ostracophori, and some have regarded them as mailed lamprevs, but they are more likely to be a degenerate or eccen- tric offshoot from the sharks, as highly modified or specialized lampreys, a side offshor)t which has left no descendants among recent forms. Recently IVofessor Patten has insisted that the resemblance of their head-plates to those of the horseshoe crab iLiiunliis) is indicative of real affinity. Among these forms in mail-armor are some in which the jointed and movable angles of the head suggest the pectoral spines of some catfishes. But in spite of its resemblance to a fin, the spine in PicricJitJiyodcs is an outgrowth of the ossified skin and has no more homology with the spines of fishes than the mailed plates have with the bones of a fish's cranium. In none of these fishes has any trace of an internal skeleton been Fig. 2.')4. — An Ostracophore, CcphntaspiK bielli Agassiz, restored. Devonian. (After Agassiz, per Dean.) found. It must have retained its primitive gelatinous character. There are, however, some traces of eyes, and the mucous channels of the lateral line indicate that these creatures possessed some other special senses. AA'hatever the Ostracophores may be, they should not be in- cluded within the much-abused term Ganoidei, a word which was once used in the widest fashion for all sorts of mailed fishes, but little tiy little restricted to the hard-scaled relatives and ances- tors of the garpike of to-day. The Arthrodires. — Dimly seen in the vast darkness of Paleo- zoic time are the huge creatures known as Arthrodires. These arc mailed and helmeted fishes, limbless so far as we know, The Evolution of Fishes 445 but with sharp, notched, turtle-like jaws quite different from those of the fish or those of any animal alive to-day. These creatures appear in Silurian rocks and are especially abundant in the fossil beds of Ohio, where Newberry, Claypole, Eastman, Dean and others have patiently studied the broken fragments of their armor. Most of them have a great casque on the head -tf^ <^^^*V^V^ i Fig. 2.55. — An Arthrodire, Dinichthys intermedius Newberry, restored. Devonian, Ohio. (Family after Dean.) with a shield at the neck and a movable joint connecting the two. Among them was almost every variation in size and form. These creatures have been often called ganoids, but with the true ganoids like the garpike they have seemingly nothing in common. They are also different from the Ostracophores. To regard them with Woodward as derived from ancestral Dipnoans is to give a possible guess as to their origin, and a very unsatisfactory guess at that. In any event these have all passed away in competition with the scaly fishes and sharks of later evolution, and it seems certain that they, like the mailed Ostra- cophores, have left no descendants. The Sharks.— Next after the lampreys, but a long way after them in structure, come the sharks. With the sharks appear for the first time true hmbs and the lower jaw. The upper jaw is, however, formed from the palate, and the shoulder- girdle is attached behind the skull. "Little is known," says Professor Dean, "of the primitive stem of the sharks, and even the Unes of descent of the different members of the group can only be generally suggested. The development of recent forms has yielded few results of undoubted value to the phylogenist. It would appear as if paleontology alone could solve the puzzles of their descent." 446 The Evolution of Fishes Of the very earliest sharks in the Upper Silurian Age the remains are too scanty to prove much save that there were sharks in abundance and variety. Spines, teeth, fragments of shagreen, show that in some regards these forms were highly specialized. In the Carboniferous Age the sharks became highly varied and extensively specialized. Of the Paleozoic types, however, all but a single family seems to have died out, leaving Cestraciontes only in the Permian and Triassic. From these the modem sharks one and all may very likely have descended. Origin of the Sharks. — Perhaps the sharks are developed from the still more primitive shark imagined as without limbs and with the teeth slowly formed from modification of the ordinary shagreen prickles. In determining the earliest among the several primitive types of shark actualh^ known we are stopped by an undetermined question of theory. What is the origin of paired limbs.'' Are these formed, like the unpaired fins, from the breaking up of a continuous fold of skin, in accordance with the view of Balfour and others? Or is the primitive limb, as supposed by Gegenbaur, a modification of the bony gill- arch? Or again, as supposed by Kerr, is it a modification of the hard axis of an external gill? If we adopt the views of Gegenbaur or Kerr, the earliest type of limb is the jointed arclii pterygium, a series of consecutive rounded cartilaginous elements with a fringe of rays along its length. Sharks possessing this form of limb (IclitJiyoioini) appear in the Carboniferous rocks, but are not known earlier. It may be that from these the Dipnoans, on the one hand, may be descended and, on the other, the true sharks and the Chimseras; but there is no certainty that the jointed arm or archipterygium of the Dipnoans is derived from the similar pectoral fin of the Ichthyotomi. On the other hand, if we regard the paired fins as parts of a lateral fold of skin, we find primitive sharks to bear out our conclusions. In Cladoselache of the Upper Devonian, the pectoral and the ventral fins are long and low, and arranged just as they might be if Balfour's theory were true. Acan- thoessus, with a spine in each paired fin and no other rays, might be a specialization of this type or fin, and Climatius, with rows of spines in place of pectorals and ventrals, might be held to The Evolution of Fishes 447 bear out the same idea. In all these the tail is less primitive than in the Ichthyotomi. On the other hand, the vent in Cladose- lache is thought by Dean to have been near the end of the tail. If this is the case, it should indicate a very primitive character. On the whole, though there is much to be said in favor of the primitive nature of the Iclitliyotoiiii (Pleuracantlius) with the tapering tail and jointed pectoral fin of a dipnoan, and other traits of a shark, yet, on the whole, Cladoselache is probably nearer the origin of the shark-like forms. The relatively primitive sharks called Notidani have the weakly ossified vertebrae joined together in pairs and there are six or seven gill-openings. This group has persisted to our day, the frilled shark (Chlamydoselachns) and the genera Hexan- chtts and Heptranchias still showing its archaic characters. Here the sharks diverge into two groups, the one with the vertebra better developed and its calcareous matter arranged star-fashion. This forms Hasse's group of Asterospondyli, the typical sharks. The earliest forms (Orodoutida:, Heterodontida) approach the Notidani, and so far as geological records go, precede all the other modern sharks. One such ancient type, HeierodontHs, including the bull-head shark, and the Port Fig. 256. — Mackerel-shark or Salmon-shark, Lanina cornubica (Gmelin). Santa Barbara, Cal, Jackson shark, still persists. The others diverge to torm the three chief groups of the cat-sharks {Scyliorhinus, etc.), the mackerel-sharks {Lamna, etc.), and the true sharks {Car- charhias, etc.). In the second group the vertebrae have their calcareous matter arranged in rings, one or more about the notochordal center. In all these the anal fin is absent, and in the process of speciali- 448 The Evolution of Fishes zation the shark gradually gives place to the flattened body and broad fins of the ray. This group is called Tectospondyli. Those sharks of this group with one ring of calcareous matter in each vertebra constitute the most primitive extreme of a group representing continuous evolution. From Cladosdadie and Clilainydoselachits through the sharks to the rays we have an almost continuous series which reaches its highest development in the devil rays or mantas of the tropical seas, Manta and Alobnla being the most specialized genera and among the very largest of the fishes. However dift'erent the rays and skates may appear in form and habit, they are structurally similar to the sharks and have sprung from the main shark stem. Fig. 2.57. -Star-spined Ray, Raja stellulata Jordan & Gilbert. Monterey, Cal. The Chimseras.— The most ancient offshoot from the shark stem, perhaps datmg from Silurian times and possibly separated at a period earlier than the date of any known shark, is the group of Holocephali or Chimseras, shark-like in essentials, but differing widely in details. Of these there are but few living forms and the fossil types are known only from dental plates and fin-spines. The living forms are found m the deeper seas the world over, one of the simplest in structure being the newly dis- The Evolution of Fishes 449 covered Rhinochimara of Japan. The fusion of the teeth into overlapping plates, the covering of the gills by a dermal flap, the complete union of the palatoquadrate apparatus or upper jaw with the skull and the development of a pecuhar clasping Fig. 2.5S. — A Deep-sea Chimj^ra, Hnmoltn mleighiana Goode k Bean. Gull t^treani. Spine on the forehead of the male are characteristic of the Chi- maeras. The group is one of the most ancient, but it ends with itself, none of the modern fishes being derived from Chimseras. The Dipnoans. — The most important offshoot of the primitive sharks is not the Chimseras, nor even the shark series itself, but the groups of Crossopterygians and Dipnoans, or lung-fishes, with the long chain of their descendants. With the Dipnoan appears Fig. 259. — An extinct Dipnoan, Diplerus ralennennesi Agassiz. Devonian. (Alter Pander.) the lung or air-bladder, at first an outgrowth from the ventral side of the oesophagus, as it still is in all higher animals, but later turning over, among fishes, and springing from the dorsal side. At first an arrangement for breathing air, a sort of accessory gill, it becomes the sole organs of respiration in the higher forms, while in the bony fishes its respiratory function is lost altogether. The air-bladder is a degenerate lung. In the Dipnoans the shoulder-girdle moves forward to the skull, and the pectoral limb, a jointed and fringed archipterygium, is its 450 The Evolution of Fishes characteristic appendage. The shark-hke structure of the mouth remains. The few hving lung-fishes resemble the salamanders in many regards, and some writers have ranged the class as midway between the primitive sharks and the amphibians. These forms show their intermediate characters in the develop- ment of lungs and in the primitive character of the pectoral and ventral limbs. Those now extant give but little idea of the great variety of extinct Dipnoans. The living genera are three in number — Neoccratodits in Australian rivers, Lepidosiren in the Amazon, and Proiopterns in the Nile. These are all mud- fishes, some of them livmg through most of the dry season encased in a cocoon of dried mud. Of these forms Neoceratodns is certainly the nearest to the ancient forms, but its embryology, owing to the shortening of its growth stages due to its environ- ment, has thrown little light on the question of its ancestry. From some ally of the Dipnoans the ancestry of the am- phibians and through them that of the reptiles, birds, and mam- mals may be traced, although a good deal of evidence has been produced in favor of regarding the primitive crossop- terygian or fringe fin as the point of divergence. It is not un- likely that the Crossopterygian gave rise to Amphibian and Dipnoan alike. In the process of development we next reach the charac- teristic fish mouth in which the upper jaw is formed of maxillary and premaxillary elements distinct from the skull. The upper jaw of the shark is part of the palate, the palate being fused with the quadrate bone which supports the lower jaw. That of the Dipnoan is much the same. The development of a typical fish mouth is the next step in evolution, and with its appearance we note the decline of the air-bladder in size and function. The Crossopterygians. — The fish-like mouth appears with the group of Crossopterygians, fishes which still retain the old- fashioned type of pectoral and ventral fin, the archipterygium. In the archaic tail, enameled scales, and cartilaginous skeleton the Crossopterygian shows its affinity with its Dipnoan ancestry. Thus these fishes unite in themselves traits of the shark, lung- fish, and Ganoid. The few living Crossopterygians, Polypterus and Erpetoichthys, are not very different from those which pre- The Evolution of Fishes 451 vailed in Devonian times. The larvas possess external gills with firm base and fringe-like rays, suggesting a resemblance to the pectoral fin itself, which develops from the shoulder-girdle just below it and would seem to give some force to Kerr's con- tention that the archipterygium is only a modified external Fig. 260. — An extinct Crossopten'gian, Holoptychius giganieus Agassiz (1S35). (Alter Agussiz, per Zittel.) gill. In Polypterns the archipterygium has become short and fan-shaped, its axis made of two diverging bones with flat cartilage between. From this type it is thought that the arm of the higher forms has been developed. The bony basis may be the humerus, from which diverge radius and ulna, the carpal bones being formed of the intervening cartilage. The Actinopteri. — From the Crossopterygians springs the main branch of the true fishes, known collectively as Actinopteri, or ray-fins, those with ordinary rays on the paired fins instead of the jointed archipterygium. The transitional series of primi- tive Actinopteri are usually known as Ganoids. The Ganoid differs from the Crossopterygian in having the basal elements of the paired fins small and concealed within the flesh. But other associated characters of the Crossopterygii and Dipnoans are preserved in most of the species. Among these are the mailed head and body, the heterocercal tail, the cellular air- bladder, the presence of valves in the arterial bulb, the presence of a spiral valve in the intestine and of a chiasma in the optic nerves. All these characters are found in the earlier types so far as is known, and all are more or less completely lost or altered in the teleosts or bony fishes. Among these early types is every variety of form, some of them being almost as long 452 The Evolution of Fishes as deep, others arrow-shaped, and every intermediate form being represented. An offshoot from this hne is the bowfin (Anna calva), among the Ganoids the closest hving ahy of the bony Fin. 2()1. — An ancirnt Ganr.id fish, Plnli/sotiius gibbosus Blainville. r'amiiy Plah/somidn'. (Alter Woodward.) fishes, sliowing thstinct affinities with the great grouji to which the herring and salmon bckjng. \ear relatives of the bowfin ilourished in the !\Iesozoic, among them some with a forked tail. Fig 2ri2. — A living Ganoid fi.sh, the Short-nosed Oar, Lrpixnslciis plalystomus Rafinesque. Lake Erie. and some Avith a very long one. From Ganoids of this tvpe the vast majority of recent fishes may be descended. Another branch of Ganoids, divergent from both garfish and bowfin and not recently from the same primitive stock, included the sturgeons (Acipenser, Scaphirhynchns, Kcsslcna) and the paddle-fishes (Po/_vo(ion iind Pscphurus). All these are regarded by Woodward as degenerate descendants of the earliest Ganoids. Palceoniscida:, of Devonian and Carboniferous time. 454 The Evolution of Fishes The Bony Fishes. — All the remaining fishes have ossified instead of cartilaginous skeletons. The dipnoan and ganoid traits one by one are more or less completely lost. Through these the main line of fish development continues and the various groups are known collectively as bony fishes or teleosts. The earhest of the true bony fishes or teleosts appear in Meso- FiG. 26.5. — A primitive Herring-like fish, Holcolepis lewesiensis Mantell, restored. Family Elopidic. English Chalk. (After Woodward.) zoic times, the most primitive forms being soft-rayecl fishes Avith the vertebrae all similar in form, allied more or less remotely to the herring of to-day, but connected in an almost unbroken series with the earliest ganoid forms. In these and other soft- rayed fishes the pelvis still retains its posterior insertion, the Fig. 266.— Ten-pounder, EIops saurus L. An ally of the earliest bony fishes. Virginia. ventral fins being said to be abdominal. The next great stage in evolution brings the pelvis forward, attaching it to the shoulder- girdle so that the ventral fins are now thoracic as in the perch and bass. If brought to a point in front of the pectoral fins, a feature of speciahzed degradation, they become jugular as in the codfish. In the abdominal fishes the air-bladder still re- tains its rudimentary duct joining it to the oesophagus. From the abdominal forms allied to the herring, the huge The Evolution of Fishes 455 array of modern fishes, typified by the perch, the bass, the mackerel, the wrasse, the globefish, the sculpin, the seahorse, and the cod descended in many diverging hnes. The earliest of the spine-rayed fishes with thoracic fins belong to the type Fig. 267. — Cardinal-fish, a perch-like fish, Apogon semilineatus Schlegel. Misaki, Japan. of Berycidce, a group characterized by rough scales, the reten- tion of a primitive bone between the eyes, and the retention of the primitive larger number of ventral rays. These appear in the Cretaceous or chalk deposits, and show various attributes Fig. 268. — >Summer Herring, Pomolohus astivalis (Mitchill). Potomac River. Family Clupeida'. of transition from the abdominal to the thoracic type of ven- trals. Another line of descent apparently distinct from that of the 456 The Evolution of Fishes herring and salmon extends through the characins to the loach, carps, catfishes, and electric eel. The fishes of this series have the anterior vertebrae coossified and modified in connection with the hearing organ, a structure not appearing elsewhere among fishes. This group includes the majority of fresh-water fishes. Fig. 269. — Fish with jugular ventral fins, Bassozetus catena Goode & Bean. Family Brotulidcc. Gulf Stream. Still another great group, the eels, have lost the ventral fins and the bones of the head have suffered much degradation. The most highly developed fishes, all things considered, are doubtless the alUes of the perch, bass, and sculpin. These fishes Fig. 270. — A specialized liony fi.sh, Trachicephalus vranoscopus. Family Scor- pccnida. From Swatow, China. have lost the air-duct and on the whole they show the greatest development of the greatest number of structures. In these groups their traits one after another are carried to an extreme and these stages of extreme specialization give way one after another to phases of degeneration. The specialization of one The Evolution of Fishes 457 organ usually involves degeneration of some other. Extreme specialization of any organ tends to render it useless under other conditions and may be one step toward its final degradation. We have thus seen, in hasty review, that the fish-like verte- brates spring from an unknown and possibly worm-like stock, Fig. 271. — An African Catfish, Chlarias breviceps Boulenger. Congo River. Family Chlariidcc. (After Boulenger.) that from this stock, before it became vertebrate, degenerate branches have fallen off, represented to-day by the Tiinicates and Enteropneustans . We have seen that the primitive verte- brate was headless and limbless and without hard parts. The lancelet remains as a possible direct offshoot from it ; the cyclo- FiG. 272. — Silverfin, Notropis whipplii (Girard). White River, Indiana. Family Cyprinida:. stome with brain and skull is a possible derivative from archaic lancelets. The earhest fishes leaving traces in the rocks were mailed ostracophores. From an unknown but possibly lamprey- like stock sprang the sharks and chima:'ras. The sharks de- veloped into rays in one right line and into the highest sharks along another, while by a side branch through lost stages the primitive sharks passed into Crossopterygians, into Dipnoans, or lung-fishes, and perhaps into Ostracophores. All these types 458 The Evolution of Fishes and others aboiond in the Devonian Age and the early records were lost in the Silurian. From the Crossopterygians or their ancestors or descendants by the specialization of the lung and limbs, the land animals, at first amphibians, after these rep- tiles, birds, and mammals, arose. Fig. 273. — Moray, Gymnothorax moringa Bloch. Family Murcenidce Tortugas. In the sea, by a line still more direct, through the gradual emphasis of fishdike characters, we find developed the Crossop- tervgians with archaic limbs and after these the Ganoids with fish-like limbs but othenvise archaic; then the soft-rayed and finally the spiny-rayed bony fishes, herring, mackerel, perch. Fig. 274. — Amber-fish, Seriola Inlandi (Cuv. & Val.). Famil_v Carangulre. Wood's Hole. which culminate in specialized and often degraded types, as the anglers, globefishes, parrot-fishes, and flying gurnards; and from each of the ultimate lines of descent radiate infinite branches tih the sea and rivers are filled, and almost every body of water has fishes fitted to its environment. -a u ■§ o 6 o c O < c a o =1 CD a o Id o ■n 6 O o s a 1 8i a o 5 □ o •a o O P 5 o _ J ■i ^ y 3 ? 3 a ^ 5 q J 2 9i o EH cr a; 3^ 8i d P •5 1 1 ft o £ ft s o Pliocene Miocene Eocene Cretaceous Jurassic Triassic Permian Coal Measures ! j ! 1 Sub-Carbon- iferous Devonian Silurian Ordovician Geological Distribution of the Families of Elasmobranchs. 459 CHAPTER XXV THE PROTOCHORDATA I HE Chordate Animals. — Referring to our metaphor of the tree with its twigs as used in the chapter on classification we find tlie fislies with the higher verte- brates as parts of a great branch from whicli the lower twigs have mostly perished. This great branch, phylum, or line of descent is known in zoology as CJiordata, and the organisms associated with it or composing it are chordate animals. The chordate animals are those which at some stage of life possess a notochord or primitive dorsal cartilage which divides the interior of the body into two cavities. The dorsal cavity contains the great nerve centers or spinal cord ; the ventral cavity contains the heart and alimentary canal. In all other animals which possess a body cavity, there is no division by a notochord, and the ganglia of the nervous system if existing are placed on the ventral side or in a ring about the mouth. The Protochordates. — ilodern researches have shown that besides the ordinary backboned animals certain other creatures easily to be mistaken for moUusks or worms and being chordate . in structure must be regarded as offshoots from the vertebrate branch. These are degenerate allies, as is shown by the fact that their vertebrate traits are shown in their early or larval development and scarcely at all in their adult condition. As Dr. John Sterling Ivmgsley has weh said: "Many of the species start m life Avith the promise of reaching a point high in the scale, but after a while they turn around and, as one might say, pursue a downward course, which results in an adult which displays but few resemblances to the other vertebrates." In the Tunicates or Ascidians (sea-squirts, sea -pears, and salpas), which constitute the class known as Tiuiicata or Urochordata, 460 The Protochordata 461 there is no brain, the notochord is confined to the tail and is usually present only in the larval stage of the animal when it has the form of a tadpole. In later life the animal usually becomes quiescent, attached to some hard object, fixed or float- ing. It loses its form and has the appearance of a hollow, leathery sac, the body organs being developed in a tough tunic. There are numerous families of Tunicates and the species are found in nearly all seas. They suggest no resemblance to fishes and look like tough clams without shells. The internal cavity being usually fiUed with water it is squirted out through the two apertures when the animal is handled. The class Enicropncusta {Addocho-rda, or Hcmichordata), includes the rather rare worm-like foi-ms related to Balauoglossiis. Bateson has shown that these animals possess a notochord which is devel- oped in the anterior part of the body. They have no fins and before the mouth is a long proboscis. Gill-slits are found in the larval tunicate. In Balauoglossiis these persist through life as in the fishes. The remaining chordate forms constitute the vertebrates proper, not worm -like nor moUusk-like, the notochord not disappearing with age, except as it gives way, by specialized segmentation to the complex structures of the vertebral column. These vertebrates, which are permanently aquatic, are known in a popular sense as fishes. The fish, in the broad sense, is a backboned animal which retains the homologue of the back- bone throughout life, which does not develop jointed limbs, its locomotive members, if present, being developed as fins, and which breathes through life the air contained in water by means of gills. This definition excludes the Tunicates and Enteropneusta on the one hand and the Amphibia or Batrachia with the reptiles, birds, and mammals on the other. The Amphibia are much more closely related to certain fishes than the classes of fishes are to each other. Still for purposes of systematic study, the frogs and salamanders are left out of the domain of ichthyology, while the Tunicata and the Enterop- neusta might well be included in it. The known branchiferous or gill -bearing chordates living and extinct may be first divided into eight classes — the Enterop- neusta, the Tunicata, the Leptocardii, or lancelets, the Cyclostovii A.6z The Protochordata or lampreys, the Elasmobranchii, or sharks, the Ostracophori the Arihrodira, and the Tcleostoini, or true fishes. The first t^A'o groups, being very primitive and in no respect fishdike in appearance, are sometimes grouped together as Proto- chordata, the others with the liigher Cliordates constituting the \'crtcbrata. Other Terms used in Classification. — The Leptocardii are some- times called Acraniata (without skull), as distinguished from the higher groups, Craniota, in which the skull is developed The Leptocardii, Cyclostomi, and Ostracophori are sometimes called Agnatha (without jaws) in contradistinction to the Giiath- osio)iii(jaw mouths), which include the sharks and true fishes with the higher vertebrates. The sharks and Teleostomes are sometimes brought together as Pisces, or fishes, as distin- guished from other groups not true fishes. To the sharks and true fishes the collective name of Lyrijera has been given, these fishes having the harp-shaped shoulder-girdle, its parts united below. The Ostracophorcs and Artlirodircs agreeing in the bony coat of mail, and both groups now extinct and both of uncertain relationship, have been often united under the name of Placoderiiis, and these and many other fishes have been again erroneously confounded with the Ganoids. Again, the Teleostomi have been frequently divided into three classes — Crossoptcrygii, Dipncnsti or Dipnoi, and Actinopterygii. The latter may be again divided into Gaiioidei and Teleosiei and all sorts of ranks have been assigned to each of these groups. For our purposes a division into eight classes is most convenient, and lowest among these we may place the Eiitcro- piteiista. The Enteropneusta. — ]\Iost simple, most worm-like, and per- haps most prmiitive of ah the Cliordates is the group of worm-shaped forms, forming the class of Enterpncusta. The class of Euteropuciista, also called Adelochorda or HcmicJiordata, as here recognized, consists of a group of small marine anmials allied to the genus Bahiiioglossiis, or acorn-tongues (/ia'Aaro? acorn; yXojcraa, tongue). These are Avorm-hke creatures with fragile bodies iDuried in the sand or mud, or liA'ing under rocks of the seashore and in shallow waters, where they He coiled in a spiral, with little or no motion. From the surface of the body The Protochordata 463 a mucous substance is secreted, holding togetner particles by which are formed tubes of sand. The animal has a peculiar odor like that of iodoform. At the front is a long muscular proboscis, very sensitive, capable of great extension and con- traction, largely used in burrowing in the ground, and of a brilliant orange color in life. Behind this is a collar which overlaps the small neck and conceals the small mouth at the base of the proboscis. The gill-slits behind the collar are also more or less concealed by it The body, which is worm-like, extends often to the length of two or three feet. The gill-slits in the adult are arranged in regular pairs, there being upwards of fifty in number much like the gill-slits of the lancelet. As the animal grows older the slits become less conspicuous, their openings being reduced to small slit-like pores. In the interior of the proboscis is a rod-like structure which arises as an outgrowth of the alimentary canal above the mouth. In development and structure this rod so resembles the notochord of the lancelet that it is regarded as a true notochord, though found in the anterior region only. From the presence of gill-slits and notochord and from the develop- ment and structure of the central ner\'ous system Balano gloss us was recognized by William Bateson, who studied an American species, DolicJwglossiis kowalevskii, at Hamp- ton Roads in Virginia in 1885, and at Beau- fort in North Carolina, as a member of the Chordate series. Unlike the Tunicates it represents a primitively simple, not a degen- erate, type. It seems to possess real affinities with the worms, or possibly, as some havcj thought, with the sea-urchins. A peculiar little creature, known as Tor- naria, was once considered to be the larva of a starfish. It is minute and transparent, floating on the surface of the sea. It has no visible resemblance to the adult i?a/aHog/o5.?zt5, Fir, 27.5 — 'Tomana" , , 1 • • 1 i_ Larva of Glossohalami s but it has been reared m aquaria and shown „„„,,,„<,. (AiterMinot.) to pass into the latter or into the related genus Glossobalamts. No such metamorphosis was found by 464 The Protochordata Bateson in the more primitive genus Dolichoglossus, studied by him. This adult animal may be, indeed, a worm as it appears, but the presence of gill-slits, the existence of a rudimentary notochord, and the character of the central nervous system are distinctly hshdike and therefore vertebrate characters. With the Chordates, and not with the worms, this class, Enterop- FiG. 276. — Glossobalanus minutus, one of the higher Enteropneustans. (After Minot.) neiista {evreftov, intestine; nvelv, to breathe), must be placed if its characters have been rightly interpreted. It is possibly a descendant of the primitive creatures which marked the transition from the archaic worms, or possibly archaic Echino- derms, to the archaic Chordate type. It is perhaps not absolutely certain that the notochord of Balanoglossns and its allies is a true homologue of the notochord of the lancelet. There may be doubt even of the homologies of the gill-slits themselves. But the balance of evidence seems to throw Balatioglossus on the fish side of the dividing line which separates the lower Chordates from the worms. It may be noticed that Hubrecht regards the proboscis of various marine Nemertine worms as a real homologue of the notochord, and other writers have traced with more or less success other apparent or possible homologies between the Chordate and the Annelid series. Classification of Enteropneusta. — Until recently the Enterop- neitsta have been usually placed m a single family or even in a single genus. The recent researches of Professor J. AV. Spengel of Giessen and of Professor William Emerson Ritter of the Uni- versity of California, have shown clearly that the group is much larger than had been generally supposed, with numerous species The Protochordata 465 in all the warm seas. In Spengel's recent paper, "Die Benen- nung der Enteropneusten-Gattungen," three famihes are recog- nized with nine genera and numerous species. At least seven species are now known from the Pacific Coast of North America. Family Harrimaniidae. — In Harriuiaiiia viacidosa, lately de- scribed by Dr. Ritter from Alaska, the eggs are large, with much food yolk, and the process of development is probably, without Tornaria stage. A second species of Harriniania (H. kiip- jeri) is now recognized from Norway and Greenland. This genus is the sim- plest in structure among all the Enter- ^ Fig. 277. — Harrunama macii- opneustans and may be regarded as the losa (Ritter), the lowest of lowest of known Chordates, the most Ltpt^rfron. "Tx.^^. worm-like of back-boned animals. (After Ritter.) In Dolichoglossns ko'valevskii the species studied by Bateson on the Virginia coast, the same simplicity of development occurs. This genus, with a third, Stereobalanus {canadensis), constitutes in Spengel's system the family of HarrimaniidcB. Balanoglossidae. — The family GlandicepitidcB contains the genera Glandiceps, Spengelia, and Schizocardium. In the BalanoglossidcB (Ptychoderid(£ of Spengel) the eggs are very small and numerous, with little food yolk. The species in this family pass through the Tornaria stage above described, a condition strikingly like that of the larval starfish. This fact has given rise to the suggestion that the Enteropneusta have a real affinity with the Echinoderms. The Balanoglossidcc include the genera Glossohalanus, Bala- noglossus, and Ptychodera, the latter the oldest known member of the group, its type, Ptychodera ftava, having been described by Eschscholtz from the Pacific Coast in 1825, while Balaiio- glossiis clavigeriis was found by Delia Chiaje in 1829. Low Organization of Harrimaniidae. — Apparency the Harri- maniida:, with simpler structure, more extensive notochord, and direct development, should be placed at the bottom as the most primitive of the Enteropneustan series. Dr. Willey, however, regards its characters as due to degeneration, and considers the 466 The Protochordata more elaborate Balanoglossida: as nearest the primitive type. The case in this view would have something in common with that of the Larvacea, which seems to be the primitive Tuni- cates, but which may have been produced by the degeneration of more complex forms. CHAPTER XXVI THE TUNICATES, OR ASCIDIANS TRUCTURE of Tunicates.— One of the most singular groups of animals is that known as Ascidians, or Tuni- cates. It is one of the most clearly marked yet most heterogeneous of all the classes of animals, and in no other are the phenomena of degeneration so clearly shown. Among them is a great variety of form and habit. Some lie buried in sand ; some fasten themselves to rocks ; some are imbedded in great colonies in a gelatinous matrix pro- duced from their own bodies, and some float freely in long chains in the open sea. All agree in changing very early in their development from a free-swimming or fish-like condition to one of quiescence, remaining at rest or drifting with the current. Says Dr. John Sterling Kingsley: "Many of the species start in life with the promise of reaching a point high in the scale, but after a while they turn around and, as one might say, pursue a downward course which results in an adult which displays but few resemblances to the other vertebrates. Indeed, so different do they seem that the fact that they belong here was not suspected until about thirty-five years ago. Before that time, ever since the days of Cuvier, they were almost universally regarded as moUusks, and many facts were adduced to show that they belonged near the acephals (clams, oysters, etc.). In the later years when the facts of development began to be known, this association was looked on with suspicion, and by some they were placed for a short time among the worms. Any one who has watched the phases of their development cannot help believing that they belong here, the lowest of the vertebrate series." 467 468 The Tunicates, or Ascidians The following account of the structure and development of the Tunicate is taken, with considerable modiflcafon and condensation, from Professor Kingsley's chapter on the group in the Riverside Natural History. For the changes suggested I am indebted to the kindness of Professor William Emerson Ritter : The Tunicates derive their name from the fact that the whole body is invested with a tough envelope or " tunic." This tunic or test may be either gelatinous, cartilaginous, or leathery. In some forms it is perfectly transparent, in others it is trans- lucent, allowing enough Hght to pass to show the colors of the viscera, while in still others it is opaque and variously colored. The tunic is everywhere only loosely attached to the body proper, except in the region of the two openings now to be mentioned. One of these openings occupies a more or less central position, while the other is usuahy at one side, or it may even be placed at the opposite end of the body. On placing one of the Ascidians in a glass dish and sprinkling a little car- mine or indigo in the water, we can study some of the func- tions of the animal. As soon as the disturbance is over, the animals will open the two apertures referred to, when it will be seen that each is surrounded with blunt lobes, the number of which varies with the species. As soon as they are opened a stream of water will be seen to rush into the central opening, carrying with it the carmine, and a moment later a reddish cloud will be ejected from the other aperture. From this we learn that the water passes through the body. Why it does so is to be our next inquiry. On cutting the animal open we find that the water, after passing through the first-mentioned open- ing (which may be called the mouth) enters a spacious cham- ber, the walls of which are made up of fine meshes, the whole appearing like lattice-work. Taking out a bit of this network and examining it under the microscope, we find that the edges of the meshes are armed with strong cilia, which are in constant motion, forcing the water through he holes. Of course, the supply has to be made good, and hence more water flows in through the mouth. This large cavity is known as the branchial or pharyngeal chamber. It is, according to Professor Ritter, "as we know from the embryology of the animal, the greatly The Tunicates, or Ascidians 469 enlarged anterior end of the digestive tract ; and as the holes, or stigmata, as they are technically called, are perforations of the wall for the passage of water for purposes of respiration, they are both morphologically and physiologically comparable with the gill openings of fishes." There can be no doubt, there- fore, that the pharyngeal sac of Ascidians is homologous with the pharynx of fishes. Surrounding the mouth, or branchial orifice, just at its entrance into the branchial chamber is a circle of tentacles. These are simple in some genera, but elaborately branched in others. In close connection with the cerebral ganglion, which is situated between the two siphons, there is a large gland with a short trumpet-shaped duct opening into the branchial sac a "ittle distance behind the mouth. The orifice of the duct is just within a ring consisting of a ciliated groove that extends around the mouth outside the circle of branchial tentacles. On the opposite side of the mouth from the gland the ciliated groove joins another groove which is both ciliated and glandular, and which runs backward along the upper floor of the pharyn- geal sac to its posterior extremity. This organ, called the endostyle, is concerned in the transportation of the animal's food through the pharyngeal sac to the opening of the oesopha- gus. Comparative embryology makes it almost certain that the subneural gland with its duct, described above, is homologous with the hypophesis cerebri of true vertebrates, and that the endostyle is homologous with the thyroid glands of vertebrates. The water after passing through the branchial network is received into narrow passages and conducted to a larger cavity — the cloacal or atrial chamber. The general relations can be seen from our diagram, illustrating a vertical and horizontal section. From the atrial chamber the water flows out into the external world. Now we can readily see how in the older works naturalists were misled as to the affinities of the Tunicates. They re- garded the tunic as the equivalent of the mantle of the mol- lusks, while the mcurrent and excurrent openings corresponded to the siphons. In one genus, Rhodosouia, the resemblance was even stronger, for there the tunic is m two parts, united 470 The Tunicates, or Ascidians by a hinge line, and closed by an adductor muscle. How and why these views were totally erroneous will be seen when we come to consider the development of these animals. At the bottom of the pharnygeal sac is the narrow oesophagus surrounded with cilia, which force a current down into the digestive tract. The branchial meshes serve as a strainer for the water, and the larger particles which it contains fah down until they are within reach of the current going down the oesophagus. After passing through the throat, they come to the stomach, where digestion takes place, and then the ejectamenta are carried out through the intestine and poured into the bottom of the atrial cavity. The heart lies on the ventral side of the stomach and is surrounded by a well-developed pericardium. The most re- markable fact connected with the circulation is that the heart, after beating a short time, forcing the blood through the vessels, will suddenly stop for a moment and then resume its beats; but, strange to say, after the stoppage the direction of the circu- lation is reversed, the blood taking an exactly opposite course from that formerly pursued. This most exceptional condition 'was first seen in the transparent Salpa, but it may be witnessed in the young of most genera. AVe have already referred to the branchial chamber. The walls of this chamber, besides acting as a strainer, are also respiratory organs. The meshes of which they are composed are in reality tubes through which the blood circulates and thus is brought in contact with a constantly renewed supply of fresh water. The central nervous system in the adults of all except the Larvacea is reduced to a single gangUon placed near the mouth thus indicating the dorsal side. In forms like Cynthia it holds the same relative position with regard to the mouth, but by the doubling of the body (to be explained further on) it is also brought near the atrial aperture, where it is shown in our first diagram. Development of Tunicates. — The sexes are combined in the same individual, though usually the products ripen at different times. As a rule, the earlier stages of the embryo are passed inside the cloacal chamber, though in some the development occurs outside the body. As a type of the development we The Tunicates, or Ascidians 471 will consider that of one of the solitary forms, leaving the many curious modifications to be noticed in connection with the species in which they occur. This will be best, since these Fig 278. — Development of the larval Tunicate to the fixed condition. (From Seeliger, per Parker & Haswell.) a, larva; b, intermediate stage; c, adult. forms show the relationship to the other vertebrates in the clear- est manner. The egg undergoes a total segmentation and a regular gas- trulation. Soon a tail appears, and under the microscope the young embryo, which now begins its free life, appears much 472 The Tunicates, or Ascidians like the tadpole of the frog. It has a large oval body and a long tail which lashes about, forcing the animal for^vard with a wriggling motion. Nor is the resemblance superficial; it pervades every part of the structure, as may be seen from the adjacent diagram. The mouth is nearly terminal and com- municates with a gill-chamber provided with gill-clefts. At the posterior end of the gill-chamber begins the alimentary tract, which pursues a convoluted course to the vent. In the tail, but not extending to any distance into the body, is an axial cylinder, the notochord, which here, as in all other verte- brates, arises from the hypoblast ; and above it is the spinal cord (epiblastic in origin), which extends forward to the brain, above the gill-chamber. Besides, the animal is provided with organs of sight and hearing, which, however, are of peculiar construction and can hardly be homologized with the correspond- ing organs in vertebrates. So far the correspondence between the two types is very close, and if we knew nothing about the later stages, one would without doubt predict that the adult tuni- cate would reach a high point in the scale of vertebrates. These high expectations are never ful- filled ; the animal, on the contrarv, pursues a retrograde course, re- sulting in an adult whose relation- ship to the true vertebrates never would have been suspected had its embryology remained unknown. After the stage described this retrograde movement begins . From various parts of the body lobes grow out, armed on their extremi- ties with sucking-disks. These Fig. 279.-Anatomy of Tunicate. ''^'''^ ^°™*^ ^" contact with some (After Herdman, per Parker A- subaquatic obiect and adhere to Haswell.) .^ „i it. ihen the notochord breaks down, the spinal cord is absorbed, the tail follows suit, the intestine twists around, and the cloaca is formed, the result being much like the diagram near the head of this section. In forms The Tunicates, or Ascidians 473 like Appendicularia, little degeneration takes place, so far as is known, the tail, with its notochord and neural chord, persisting through life. Reproduction of Tunicates. — jVs to the reproduction of the Tunicates, Dr. Ritter writes: " In addition to the sexual method of reproduction, many tunicates reproduce asexually by budding. The capacity for bud reproduction appears to have been ac- quired by certain simple Ascidians in connection with, probably as a result of, their having given up the free-swimming life and become attached and consequently degenerate. " Instructive as the embryonic development of the creatures is from the standpoint of evolution, the bud method of de\'elop- ment is scarcely less so from the same point of view. The development of the adult zooid from the simple bud has been conclusively shown to be by a process in many respects funda- mentally unlike that by which the individual is developed from the egg. We have then in these animals a case in which prac- tically the same results are reached by developmental processes that are, according to prevailing conceptions of animal oi^gani- zations, fundamentally different. This fact has hardly a parallel in the animal kingdom." Habits of Tunicates. — The Tunicates are all marine, some float- ing or swimming freely, some attached to rocks or wharves, others buried in the sand. They feed on minute organisms, plants, or animals, occasional rare forms being found in their stomachs. Some of them possess a single median eye or eye- like structure which may not do more than recognize the presence of light. No fossil Tunicates are known, as they possess no hard parts, although certain Ostracoderms have been suspected, though on very uncertain grounds, to be mailed Tunicates, rather than mailed lampreys. It is not Hkely that this hypothesis has any sound foundation. The group is divided by Herdman and most other recent authorities into three orders, viz., the Larvacea, the Ascidiacea, and the Thaliacea. Larvacea. — In the most primitive order the animals are minute and free-swimming, never passing beyond the tadpole stage. The notochord and the nervous chord persist through hfe, the latter with ganglionic segmentations at regular m- tervals. The species mostly float in the open sea, and some 474 The Tunicates, or Ascidians of them form from their own secretions a transparent gelatinous envelope called a "house." This has two apertures and a long chamber "in which the tail has room to vibrate." The order consists of a single small family, Appendiculariida:-. The lowest type is known as Kowalevskia, a minute creature without heart or intestine found floating in the Mediterranean. It is in many respects the simplest in structure among CI wr date animals. Oiko pleura (Fig. 288) is another genus of this group. Ascidiacea. — In the Ascidiacea the adult is usually attached to some object, and the two apertures are placed near each other by the obliteration of the caudal area. The form has been compared to a "leathern bottle with two spouts." The suborder Ascidicc simplices includes the solitary xVscid- ians or "sea-squirts," common on our shores, as Avell as the social forms in which an individual is sur- rounded by its buds. The common name arises from the fact that when touched they contract, squirting water from both aper- tures. The Ascidiidcc comprise the most familiar solitary forms, some of them the largest of the Tunicates and represented on most coasts. In the MolguUdtr and most Ascidicc compositcB the young hatch out in the cloaca, from which "these tadpoles swim out as yellow atoms," while in a new genus, Enkerdiiiania, described by Ritter, fromt he coast of California, the embryos are retained through their whole larval stage in the oviduct of the parent. They form, ac- (After cordmg to Kmgsley, adhesive processes on the body, but those of Alolgida cannot use them in becoming attached to rocks, since they are entirely in- closed in a peculiar envelope. This envelope is after a while very adhesive, and if the little tadpole happens to touch any part of himself to a stone or shell he is fastened for life. Thus " I have frequently seen them adhere by the tail, while the anterior part was making the most violent struggles to escape. Soon, howex-er, they settle down contentedly, absorb the tail, and in a few weeks assume the adult structure." Fig. 2S0.-~Ascidia ad- hcerens Ritter. Glacier Bay, Alaska, Ritter.) The Tunicates, or Ascidians 475 In the family Cynthiidce the brightly-colored red and yellow species of Cynthia are known as sea-peaches by the fishermen. The sea-pears, Boltenia, are fastened to long stalks. These have a leathery and wrinkled tunic, to which algcc and hydroids freely attach themselves. Into the gill-cavity of these forms Fig. 281. — Stijela yacuiatensia (Ritter), a simple Ascidian. FamiU- Mnlgn- lida. Yaku tat Bay, Alaska (After Kitter.) small fishes, blennies, gobies, and pearl-fishes often retreat for protection. The social Ascidians constitute the Clavellinidcc . They are similar to the Ascidiida in form, but each individual sends out a bud which forms a stem bearing another individual at the end. By this means large colonies may be formed. The suborder, Ascidia: compositor, contains the compound Ascidians or colonies enveloped in a common gelatinous "test." These colonies are usually attached to rock or seaweed, and the individuals are frequently regularly and symmetrically arranged. The bodies are sometimes complex in form. 476 The Tunicates, or Ascidians In the Botryllidw and Polystyelidcc the individuals are not segmented and in the former family are arranged in star-shaped groups about a common cloaca, into which the atrial siphons of the different individuals open. The group springs by budding from the tadpole, or larva, which has attached itself to some object. ^ 1^ i#. I Fig. 2S2. Fig. 2S3. Fig. 282. — Styela greeleyi Ritter. Family Molgulidcv. Lukanin, Pribilof Islands. (After Ritter.) Fig. 283. — Cynthia superha Ritter. A Tunicate from Pugct Sound. Family Cynlhiidte. (After Ritter.) These forms are often brightly colored. Botryllns gonldi is a species very common along our North Atlantic coast, forming gray star-shaped masses sometimes an inch across on eel-grass {Zoster a) and on flat-leaved seaweeds. Goodsiria dura, a repre- sentative of the Polyslyelidir, is one of the most common Ascid- ians on the California coast southward, where the brick-red The Tunicates, or Ascidians 477 masses incrusting on seaweeds of various kinds, and on other Ascidians, are frequently thrown ashore in great quantities during heavy storms. In Didemnidcc the body is more complex, of two parts, called the "thorax" and "abdomen." In Amarcecinm, the "sea pork " of the fishermen, the body is in three parts and the indi- viduals are very long. These some- times form great masses a foot or more long, "colored like boiled salt pork, but more translucent." Other families of this type are the DistomidcB and the Polycli- nida:. In the suborder Lucim, includ- ing the family PyrosomidcE, the colonies are thimble-shaped and hollow, the incurrent openings being on the outer surface of the thimble, the outgoing stream open- ing within. Pyrosoma is highly phosphorescent. In the tropical ^^^ 284. -Botryllns magnus Ritter. seas some colonies reach a length A compound Ascidian. Shumagin „ , . , J- . T. • . , Islands, Alaska. (After Ritter.) of two or three feet. It is said that a description of a colony was once written by a naturalist on a page illumined by the colony's own light. "Each of the individuals has a number of cells near the mouth the function of which is to produce the light." Thaliacea. — In the order Thaliacea the Tunicates have the two orifices at opposite ends of the body. All are free-swimming and perfectly transparent. The principal family is that of Salpidw. The gill-cavity in Salpa is much altered, the gills projecting into it dividing it into two chambers. In these forms we have the phenomena of alternation of generations. A sexual female produces eggs, and from each hatches a tadpole larva which is without sex. This gives rise to buds, some at least of the individuals arising which in turn produce eggs. In the family Salpida; two kinds of individuals occur, the 478 The Tunicates, or Ascidians solitary salpa, or female, and the chain salpa, or bisexual males. The latter are united together in long bands, each individual forming a link in the chain held together by spurs extending from one to the next. From each solitary individual a long process or cord grows out, this dividing to form the chain. Each chain salpa produces male reproductive organs and each de- FiG. 285. — Bntri/Uus magnus Ritter. Part of colony. (After Hitter.) velops as weU a single egg. The egg is developed within the body attached by a sort of placenta, while the spermatozoa are cast into the sea to fertilize other eggs. From each e'^-^ develops the solitary salpa and from her buds the chain of bisexual creatures. Dr. AV. K. Brooks regards these as nursinc; males, the real source of the egg being perhaps the sohtary female. Of this extraordinary arrangement the naturalist- poet Chamisso, who first described it, said: "A salpa mother is not like its daughter or its own mother, but resembles its sister, its granddaughter, and its grandmother." But it is misleading to apply such terms taken from the individuahzed htiman relationship to the singular communal system developed by these ultra-degenerate and strangely specialized Chordates. The Tunicates, or Ascidians 479 The Salpas abound in the warm seas, the chains often cov- ering the water for miles. They are perfectly transparent, and the chains are often more than a foot in length. In Doliolum the body is barrel- shaped and the gills are less modified than in Salpa. The alternation of generations in this genus is still more complicated than in Salpa, for here we have not only a sexual and a non-sexual generation, the individuals of which dift'er from each other, but there is further a differentiation among the asexu- ally produced individuals themselves; so that we have in all three instead of two sorts of animals in the complete life cycle. Besides the proliferating stolon situated on the ventral side, the bud-producing individual possesses a dorsal process larger than the stolon proper. Fig. 286. — Botryllus magniis Ritter, a single Zooid. Shu- magin Islands, Alas- ka. (After Ritter.) The buds become completely severed from the true stolon at an early stage and Fig 287 — ApKdinpsis jordnni Ritter, a tonipound Ascidian. Lukanin Beach, Pribilof Islands. (Alter Ritter.) actually crawl along the side of the parent up to the dorsal process, upon which they arrange themselves in three rows, two lateral and one median. The buds of the lateral rows become nutritive and respiratory zooids, while those of the 480 The Tunicates, or Ascidians median row, ultimately at least, give rise in turn to the egg- proclucing mdividuals. Origin of Tunicates. — There can be little doubt that the Tiiiitcaia form an offshoot from the primitive Chordate stock, and the structure of their larva in connection with that of the lancelet throws a large light on the nature of their common parents. "We may conclude," says Dr. Arthur Willey, "that the proximate ancestor of the Vertebrates was a free-swimming animal intermediate in organization between an Ascidian tad- pole and Amphioxus, possessing the dorsal mou'.h, hypophysis, Fig. 2SS. — Adult Tunic.ite of the group Lanacea, Oikopleura. Family Appcndicuhinuhi. (After Fol, per Parker A- Haswell.) and restricted notochord of the former and the myotomes, coelomic epithelium, and straight alimentary canal of the latter. The ultimate or primordial ancestor of the Vertebrates would, on the contrary, be a worm-like animal whose organization was approximately on a level with that of the bilateral an- cestors of the Echinoderms." Degeneration of Tunicates. — There is no question, further- more. Professor Ritter observes, "that most of the group has undergone great degeneration in its evolutionary course. Just what the starting-point was, however, is a matter on which there is considerable dift'erence of opinion among authorities. According to one view, particularly championed by Professor W. K. Brooks, Appcndicularia is very near the ancestral form. The ancestor was consequently a small, marine, free-swimming creature. From this ancestor the Ascidiacea were evolved largely through the influence of the attached habit of life, and the tadpole stage in their development is a recapitulation of the ancestral form, just as the tadpole stage in the frog's life is a repetition of the fish ancestry of the frog. The Tunicates, or Ascidians 48 i "According to the most common view Appendicularia is not an ancestral form at all, but is the tadpole stage of the Ascidiacea that has failed to undergo metamorphosis and has become sexually mature in the larval condition, as the larva of certain Amphibians and insects are known to never pass into the adult state but reproduce their kind sexually in the larval condition. By this view the tadpole of such Ascidian as Ciona, for example, represents more closely the common ancestor of the group than does any other form we know. This view is especially defended by Professor K. Heider and Dr. Arthur Willey." CHAPTER XXVII THE LEPTOCARDII, OR LANCELETS (HE Lancelet. — The lancelet is a vertebrate reduced to its very lowest terms. The essential organs of ver- tebrate life are there, but each one in its simplest form unspecialized and with structure and function feebly differen- tiated. The skeleton consists of a cartilaginous notochord in- closed in a membranous sheath. There is no skull. No limbs, no conspicuous processes, and no vertebras are present. The heart is simply a long contractile tube, hence the name Leptocardii (from \e7TTi'>?, slender; KapSia, heart). The blood is colorless. There is a hepatic portal circulation. There is no brain, the spinal cord tapering in front as behind. The water for respira- tion passes through very many gill-slits from the pharynx into the atrium, from which it is excluded through the atripore in front of the vent. A large chamber, called the atrium, extends almost the length of the body along the A'entral and lateral regions. It communicates with the pharynx through the gill- slits and with the exterior through a small opening in front of the vent, the atripore. The atrium is not found in forms above the lancelets. The reproductive organs consist of a series of pairs of seg- mentally arranged gonads. The excretory organs consist of a series of tubules in the region of the pharynx, connecting the body-cavity with the atrium. The mouth is a lengthwise slit without jaws, and on either side is a row of fringes. From this feature comes the name Cirrostoini, from cirrus, a fringe of hair, and a-To/Aa, mouth. The body is lanceolate in form, sharp at either end. From this fact arises a third name, A)npliioxns, from ajAdn, both; oiiv^, sharp. Dorsal and anal fins are de- veloped as folds of the skin supported by very slender rays. 4S2 The Leptocardii, or Lancelets 483 There are no other fins. The ahmentary canal is straight, and is differentiated into pharynx and intestine ; the liver is a blind sac arising from the anterior end of the intestine. A pigment spot in the wall of the spinal cord has been interpreted as an eye. Above the snout is a supposed olfactory pit which some have thought to be connected with the pineal structure. The muscular impressions along the sides are very distinct and it is chiefly by means of the variation in numbers of these that the species can be distinguished. Thus in the common lance- let of Europe, Branchiostoina lanccolatiiin, the muscular bands are 35+14 + 12=61. In the common species of the Eastern coasts of America, Brandiiostoma carihcDum, these are 35+14 + 9 = 58, while in the California lancelet, Br anchio stoma cali- forniensc, these are 44 + 16+9=69. Habits of Lancelets. — Lancelets are slender translucent worm- like creatures, varying from half an inch {Asymmetron lucaya- num) to four inches {Br anchio stoma calijornicnse) in length. They live buried in sand in shallow waters along the coasts of warm seas. One species, Amphioxides pelagicns, has been taken at the depth of 1000 fathoms, but whether at the bottom or floating near the surface is not known. The species are very tenacious of life and will endure considerable mutilation. Some of them are found on almost every coast in semi-tropical and tropical regions. Species of Lancelets. — The Mediterranean species ranges north- ward to the south of England. Others are found as far north as Chesapeake Bay, San Diego, and Misaki in Japan, where is found a species called Brandiiostoma belclieri. The sands at the mouth of San Diego Bay are noted as producing the largest of the species of lancelets, Brandiiostoma calijornicnse. From the Bahamas comes the smallest, the type of a distinct genus, Asymmetron lucayanum, distinguished among other things by a projecting tail. Other supposed genera are Amphioxides {pelagicns), dredged in the deep sea off Hawaii and supposed to be pelagic, the mouth without cirri; Epigonichtliys icnltdliis), from the East Indies, and Heteroplenron {bassaniim), from Bass Straits, Austraha. These little animals are of great interest to anatomists as giving the clue to the primitive structure of vertebrates. While possibly these have diverged widely from 484 The Leptocardii, or Lancelets their actual common ancestry with the fishes, they must ap- proach near to these in many ways. Their simplicity is largely primitive, not, as in the Tunicates, the result of subsequent degradation. The lancelets, less than a dozen species in all, constitute a single family, Branchiostovnida;. The principal genus, Branchi- ostoiiia, is usually called Amphioxus by anatomists. But while T'T ^„ *iiL_e 2fe&^ Fig. 289. — California Laneelet, Branchiostoma calijorniense Gill. (From San Diego.) the name Amphioxus, like laneelet, is convenient in vernacular use, it has no standing in systematic nomenclature. The name Braiichiostonia was given to lancelets from Naples in 1834, by Costa, while that of Amphioxus, given to specimens from Corn- wall, dates from Yarrell's work on the British fishes in 1836. The name Amphioxus may be pleasanter or shorter or more familiar or more correctly descriptive than Branchiostoma, but if so the fact cannot be considered in science as affecting the duty of priority. The name Acraniata (without skull) is often used for the lower Chordates taken collectively, and it is sometimes applied to the lancelets alone. It refers to those chordate forms which have no skull nor brain, as distinguished from the Crauiota, or forms with a distinct brain having a bony or cartilaginous capsule for its protection. Origin of Lancelets. — It is doubtless true, as Dr. Willey sug- gests, that the Vertebrates became separated from their worm- like ancestry through "the concentration of the central nervous system along the dorsal side of the body and its conversion The Leptocardii, or Lancelets 485 into a hollow tube." Besides this trait two others are common to all of them, the presence of the gill-slits and that of the noto- chord. The gill-slits may have served primarily to relieve the stomach of water, as in the lowest forms they enter directly into the body-cavity. The primitive function of the notochord is still far from clear, but its ultimate use of its structures in affording protection and in furnishing a fulcrum for the muscles and limbs is of the greatest importance in the processes of life. Fig. 289a, — Gill-basket of Lamprey. CHAPTER XXVIII THE CYCLOSTOMES, OR LAMPREYS }he Lampreys. — Passing upward from the lancelets and setting aside the descending series of Tunicates, we have a long step indeed to the next class of fish-like vertebrates. During the period this great gap represents in time we have the development of brain, skull, heart, and other differentiated organs replacing the simple structures found in the lancelet. The presence of brain without hmbs and without coat-of- mail distinguishes the class of Cyclostoines, or lampreys (kvkXos, round; a-rofia, mouth). This group is also knov/n as Marsipo- hranchi {luapainiov, pouch; fipayxos, gill); Dermopteri (depjua, skin; nrepov, fin); and Myzontes {/uvCdco, to suck). It includes the forms known as lampreys, slime-eels, and hagfishes. Structure of the Lamprey. — Comparing a Cyclostome with a lancelet we may see many evidences of specialization in struc- ture. The Cyclostome has a distinct head with a cranium formed of a continuous body of cartilage modified to contain a fish-like brain, a cartilaginous skeleton of which the cranium is evidently a differentiated part. The vertebrae are undeveloped, the notochord being surrounded by its membranes, without bony or cartilaginous segments. The gills have the form of fixed sacs, six to fourteen in number, on each side, arranged in a cartilaginous structure known as "branchial baske^ " ffig. 289a), the elements of Avhich are not clearly homologous Kvith the gill-arches of the true fishes. Fish-like eyes are develop/d on the sides of the head. There is a median nostril associated with a pituitary pouch, which pierces the skull floor. An ear-capsule is developed. The brain is composed of paired ganglia in general appearance resembling the brain of the true fish, but 4S6 The Cyclostomes, or Lampreys 487 the detailed homology of its different parts offers considerable uncertainty. The heart is modified to form two pulsating cavities, auricle and ventricle. The folds of the dorsal and anal fins are distinct, supported by slender rays. The mouth is a roundish disk, with rasping teeth over its surface and with sharper and stronger teeth on the tongue. The intestine is straight and simple. The kidney is represented by a highly primitive pronephros and no trace exists of an air-bladder or lung. The skin is smooth and naked, some- times secreting an excessive quantity of slime. From the true fishes the Cyclostomes differ in the total absence cf limbs and of shoulder and pelvic girdles, as well as of jaws. It has been thought by some writers that the limbs were ancestrally present and lost through degeneration, as in the eels. Dr. Ayers, following Huxley, finds evidence of the ancestral existence of a lower jaw. The majority of observers, however, regard the absence of limbs and jaws in Cyclo- stomes as a primitive character, although numerous other features of the modem hagfish and lamprey may have resulted from degeneration. There is no clear evidence that the class of Cyclostomes, as now known to us, has any great antiquity, and its members may be all degenerate offshoots from types of greater complexity of structure. Supposed Extinct Cyclostomes. — No species belonging to the class of Cyclostomes has been found fossil. We may reason theoretic- ally that the earliest fish-like forms were acraniate or lancelet- like, and that lamprey-like forms would naturally follow these, but this view cannot be substantiated from the fossils. Lance- lets have no hard parts whatever, and could probably leave no trace in any sedimentary deposit. The lampreys stand between lancelets and sharks. Their teeth and fins at least might occasionally be preserved in the rocks, but no structures cer- tainly known to be such have yet been recognized. It is how- ever reasonably certain that the modern lamprey and hagfish are descendants, doubtless degraded and otherwise modified from species which filled the gap between the earliest chordate animals and the jaw-bearing sharks. Conodontes. — Certain structures found as fossils have been from time to time regarded as Cyclostomes, but in all such 488 The Cyclostomes, or Lampreys cases there is doubt as to the real nature of the fossil relic in question or as to the proper interpretation of its relationship. Thus the Coiiodonics of the Cambrian, Silurian, and Devonian have been regarded as lingual teeth of extinct Cyclostomes. The Cyclicc of the Devonian have been considered as minute lampreys, although the vertebral segments are highly specialized, to a degree far beyond the condition seen in the lampreys of to-day. The Ostracophores have been regarded as mon- c oo,^ D 7 ,1. J !,■ -a- A strous lampreys 'n coat of Fig. 290. — Poh/gnathus dubium Hmde. f J A Conodont from the New York De- mail, and the possibility of a vonian. (After Hindc.) , • . r '\ ^i lamprey origin even tor Arthro- dires has been suggested. The Cyclicv and Ostracophori were apparently without jaws or limbs, being in this regard like the Cyclostomes, but their ancestry and relationships are wholly problematical. The nature of the Conodontes is still uncertain. In form they resemble teeth, but their structure is different from that of the teeth of any fishes, agreeing with that of the teeth of annelid worms. Some have compared them to the armature of Trilobites. Some fifteen nominal genera are described by Pander in Russia, and by Hinde about Lake Erie and Lake Ontario. Some of these, as Drcpaniodus, are simple, straight or curved grooved teeth or tooth-like structures; others, as Prioniodns, have numerous smaller teeth or denticles at the base of the larger one. Orders of Cyclostomes. — The known Cyclostomes are natu- rally divided into two orders, the Hypcroircta, or hagfishes, and the Hyperoariia, or lampreys. These two orders are very dis- tinct from each other. While the two groups agree in the general form of the body, they differ in almost every detail, and there is much pertinence in Lankester's suggestions that each should stand as a separate class. The ancestral forms of each, as well as the intervening types if such ever existed, are left unrecorded in the rocks. The Hyperotreta, or Hagfishes. — The Hypcroircta {vnZpoa, pal- The Cyclostomes, or Lampreys 489 ate; rperos, perforate), or hagfishes, have the nostril highly developed, a tube-like cylinder with cartilaginous rings pene- trating the palate. In these the eyes are little developed and the species are parasitic on other fishes. In Polistotrema stoiiti, the hagfish of the coast of California, is parasitic on large fishes, rockfishes, or flounders. It usually fastens itself at the throat or isthmus of its host and sometimes at the eyes. Thence it works very rapidly to the inside of the body. It there devours all the muscular part of the fish without breaking the skin or the peritoneum, leaving the fish a living hulk of head, skin, and bones. It is especially destructive to fishes taken in gill-nets. The voracity of the Chilean species Polistotrema domheyi is equally remarkable. Dr. Federico T. Delfin finds that in seven hours a hagfish of this species will devour eighteen times its own weight of fish-flesh. The intestinal canal is a simple tube, through which most of the food passes undigested. The eggs are large, each in a yellowish horny case, at one end of which are barbed threads by which they cling together and to kelp or other objects. In the California hagfish, Polistotrema stouti, great numbers of these eggs have been found in the stomachs of the males. Similar habits are possessed by all the species in the two families, Myxinidce and Eptatretidce. In the Myxinida the Fig. 291. — California Hagfish, Polislolrcma stouti Loclcington, gill-openings are apparently single on each side, the six gills being internal and leading by six separate ducts to each of the six branchial sacs. The skin is excessively slimy, the ex- tensible tongue is armed with two conedike series of strong teeth. About the mouth are eight barbels. 49© The Cyclostomes, or Lampreys Of Myxiiie, numerous species are known — Myxine gliitinosa, in the north of Europe; 2i[yxinc liinosa, of the AA^est Atlantic; Mvxiiic aiistralis. and several others about Cape Horn, and I\Ivxiiic ganuaii! in Japan. All live in deep waters and none ha\-e been fully studied. It has been claimed that the hagfish is male when young, many individuals gradually changing to female, but this conclusion lacks verification and is doubtless without foundation. In the EptatrctiJcr the gill-openings, six to fourteen in number, are externally separate, each with its own branchial sac as in the lampreys. The species of the genus Eptatrctns (Bdcllostouia, Heptatrenm, and Hoiiiea, all later names for the same group) are found only in the Pacific, in California, Chile, Patagonia, South Africa, and Japan, In general appearance and habits these agree with the species of Myxine. The species with ten to fourteen gill-openings {clviibcy!: stoiiti) are sometimes set oft' as a distinct genus {Polis- ioirciiia), but in other regards the species differ little, and fre- quent individual variations occur. Eptatrctns hiirgeri is found in Japan and Eptatrctns forstcri in Australia, The Hyperoartia, or Lampreys. — In the order Hypcroartia, or lampreys, the single nostril is a blind sac which does not pene- trate the palate. The seven gill-openings lead each to a sepa- rate sac, the skin is not especially covered with mucus, the eyes are well developed in the adult, and the mouth is a round disk armed with rasp-like teeth, the comb-like teeth on the tongue being less developed than in the hagfishes. The intestine in the lampreys has a spiral valve. The eggs are small and are usually laid in brooks away from the sea, and in most cases the adult lamprey dies after spawning. According to Thoreau, "it is thought by fishermen that they never return, but waste away and die, clinging to rocks and stumps of trees for an in- definite period, a tragic feature in the scenery of the river-bottoms worthy to be remembered with Shakespeare's description of the sea-floor." This account is not far from the truth, as re- cent studies have shown. The lampreys of the northern regions constitute the family oi PctroiuyzonidiC. The larger species iPctroinyzoii, Eiitosplicinis) live in the sea, ascending rivers to spawn, and often becomine The Cyclostomes, or Lampreys 491 land-locked and reduced in size by living in rivers only. Such land-locked marine lampreys {Petromyzoti inariiiiis imico'.or) breed in Cayuga Lake and other lakes in New York. The marine forms reach a length of three feet. Smalle; lampreys of other genera six inches to eighteen inches in length remain all their lives in the rivers, ascending the little brooks in the spring, clinging to stones and clods of earth till their eggs are deposited. These are found throughout northern Europe, northern Asia, and the colder parts of North America, belonging to the genera Lampetra and Iclitliyoiiiyzon. Other and more aberrant genera from Chile and Australia are Gsotria and Mordacia, the latter forming a distinct family, MordaciiJcc. In Gcotria, a large and peculiar gular pouch is developed at the throat. In Macroph- thahnia chiloisis from Chile the eyes are large and conspicuous. Food of Lampreys. — The lampreys feed on the blood and flesh of fishes. They attach themselves to the sides of the various species, rasp off the flesh with their teeth, sucking the blood till the fish weakens and dies. Preparations made by students of Professor Jacob Reighard in the University of Michigan show clearly that the lamprey stomach contains muscular tissue as well as the blood of fishes. The river species do a great deal of mis- FiG. 292. — Lamprey, Pctromtjzon marinus L. Wood's Hole, Mass. chief, a fact which has been tlie subject of a valuable investiga- tion by Professor H. A. Surface, who has also considered the methods available for their destruction. The flesh of the lam- prey is wholesome, and the larger species, especially the great sea lamprey of the Atlantic, Pctroniyzon marinus, are valued as food. The small species, according to Prof. Gage, never feed on fishes. Metamorphosis of Lampreys. — All lampreys, so far as known, pass through a distinct metamorphosis. The young, known as the Ammocwtes form, are slender, eyeless, and with the mouth 492 The Cyclostomes, or Lampreys narrow and toothless. From Professor Surface's paper on "The Removal of Lampreys from the Interior Waters of New York" \ve have the following extracts (slightly condensed) : "In the latter part of the fall the young lampreys, Petro- iiiv^oii mariiuis iiuicolor, the variety land-locked in the lakes of Central New York, metamorphose and assume the form of the adult. They are now about six or eight inches long. The externally segmented condition of the body disappears. The i^v Fig. 294. Fig. 295. Mouth of Lake Lamprej-, Fig. 293. Fig. 29.3. — Petronujzon marinus vnicolor (De Kay) Cayuga Lake. ( After Gage.) Fig. 294. — Lampetra v:ilderi Jordan & Evermann. Larv burrow in a glass filled with sand. (After Gage.) Fig. 29.5. — Lampetra wilda'i Jordan it Evermann. Mouth of Brook Lamprey Cayuga Lake. (After Gage.) brook lamprey in its eyes appear to grow out through the skin and become plainly visible and functional. The mouth is no longer filled Avith verti- cal membranous sheets to act as a sieve, but it contains nearly one hundred and fifty sharp and chitinous teeth, arranged in rows that are more or less concentric and at the same time presenting the appearance of circular radiation. These teeth are very strong, with sharp points, and in structure each has the appearance of a hollow cone of chitin placed over another cone or papilla. i\ little below the center of the mouth is the oral opening, which is circular and contains a flattened tongue Avhich bears finer teeth of chitin set closely together and arranged in two interrupted (appearing as four) curved roAvs extending The Cyclostomes, or Lampreys 493 up and down from the ventral toward the dorsal side of the mouth. Around the mouth is a circle of soft membrane finally surrounded by a margin of fimbria; or small fringe. This com- pletes the apparatus with which the lamprey attaches itself to its victims, takes its food, carries stones, builds and tears down its nest, seizes its mate, holds itself in position in a strong current, and climbs over falls. Mischief Done by Lampreys. — " The most common economic feature in the entire life history of these animals is their feeding habits in this (spaw .nig) stage, their food now consisting wholly of the blood (and fieshj of fishes. A lamprey is able to strike its suctorial mouth against a fish, and in an instant becomes so firmly attached that it is very rarely indeed that the efforts of the fish will avail to rid itself of its persecutor. AVhen a 1am- prev attaches itself to a person's hand in the aquarium, it can only be freed by lifting it from the water. As a rule it will drop the instant it is exposed to the open air, although often it will remain attached for some time even in the open air, or may attach itself to an object while out of water. " Nearly all lampreys that are attached to fish when they are caught in nets will escape through the meshes of the nets, but some are occasionally brought ashore and may hang on to their victim with bulldog pertinacity. "The fishes that are mostly attacked are of the soft -rayed species, having cycloid scales, the spiny-rayed species with ctenoid scales being most nearly immune from their attacks. We think there may be three reasons for this: ist, the fishes of the latter group are generally more alert and more active than those of the former, and may be able more readily to dart away from such enemies ; 2d, their scales are thicker and stronger and appear to be more firmly imbedded in the skin, consequently, it is more difficult for the lampreys to hold on and cut through the heavier coat-of-mail to obtain the blood of the victim; 3d, since the fishes of the second group are wholly carnivorous and in fact almost exclusively fish-eating when adult, in every body of water they are mor.e rare than those of the first group, which are more nearly omnivorous. Accorrling to the laws and requirements of nature the fishes of the first group must be more abundant, as they become the food for those of the 494 """he Cyclostomes, or Lampreys second, and it is on account of their greater abundance that the lampreys' attacks on them are more observed. " There is no doubt that the buUhead, or horned pout {Aineiu- rns iicbiilosiis), is by far the greatest sufferer from lamprey attacks in Cayuga Lake. This may be due in part to the slug- gish habits of the fish, which render it an easy victim, but -it is more likely due to the fact that this fish has no scales and the lamprey has nothing to do but to pierce the thick skm and find its feast of blood ready for it. There is no doubt of the excellency of the bullhead as a food-fish and of its increasing favor with mankind. It is at present the most important food- and market-fish of the State (New York), being caught by bushels in the early part of June when preparing to spawn. As we have observed at times more than ninety per cent, of the catch attacked by lampreys, it can readily be seen- how verv serious are the attacks of this terrible parasite which is surely devastating our lakes and streams. Migration or "Running" of Lampreys. — "After thus feeding to an unusual extent, their reproductive elements (gonads) be- come mature and their alimentary canals commence to atrophy. This duct finally becomes so occluded that from formerly being large enough to admit a lead-pencil of average size when forced through it, later not even liquids can pass through, and it becomes nearly a thread closely surrounded by the crowding reproductive organs. When these changes commence to ensue, the lampreys turn their heads against the current and set out on their long journeys to the sites that are favorable for spawn- ing, which here may be from two to eight miles from the lake. In this migration they are true to their instincts and habits of laziness in being carried about, as they make use of any avail- able object, such as a fi h, boat, etc., that is going in their direc- tion, fastening to it with their suctorial mouths and being borne along at their ease. During this season it is not infre- quent that as the Cornell crews come in from practice and lift their shells from the water, they find lampreys clinging to the bottoms of the boats, sometimes as many as fifty at one time. They arc likely to crowd up all streams flowing into the lake, inspecting the bed of the stream as they go. Thev do not stop until they reach favorable spaAvning sites, and if they The Cyclostomes, or Lampreys 495 find unsurmountable obstacles in ttieir way, sucli as vertical falls or dams, they turn around and go down-stream until they find another, up which they go. This is proved every spring by the number of adult lampreys which are seen temporarily in Fall Creek and Cascadilla Creek. In each of these streams, about a mile from its mouth, there is a vertical fall over thirty feet in height which the lampreys cannot surmount, and in fact they have never been seen attempting to do so. After clinging with their mouths to the stones at the foot of the falls for a few days, they work their way down-stream, care- FiG. 296. — Kamchatka Lamprey, Lampetra camtschatica (Tilesius). Kamchatka. fully inspecting all the bottom for suitable spawning sites. They do not spawn in these streams because there are too many rocks and no sand, but finally enter the only stream fthe Cayuga Lake inlet) in which they find suitable and accessible spawn- ing sites. " The three-toothed lampreys {Entosphenus tridentatns) of the West Coast climb low falls or rapids by a series of leaps, holding with their mouths to rest, then jumping and striking again and holding, thus leap by leap gaining the entire distance. " The lampreys here have never been known to show any tendency or ability to climb, probably because there are no rapids or mere low falls in the streams up which they would run. In fact, as the inlet is the only stream entering Cayuga Lake in this region which presents suitable spawning condi- tions and no obstructions, it can be seen at once that all the lampreys must spawn in this stream and its tributaries. "In 'running' they move almost entirely at night, and if they do not reach a suitable spawning site by dayHght, they will cling to roots or stones during the day and complete their journey the next night. This has been proven by the positive 5 I -c , C3 y J 3' The Cyclostomes, or Lampreys 497 observation of individuals. Of the specimens that run up early in the season, about four-fifths are males. Thus the males do not exactly precede the females, because we have found the latter sex represented in tlie stream as early in the season as the former, but in the earlier part of the season the number of the males certainly greatly predominates. This pro- portion of males gradually decreases, until in the middle of the spawning season the sexes are about equally represented, and toward the latter part of the season the females continue to come until they in turn show the greater numbers. Thus it appears very evident in general that the reproductive in- stinct impels the most of the males to seek the spawning ground before the most of the females do. However, it should be said that neither the males nor the females show all of the entirely sexually mature features when they first run up-stream in the beginning of the season, but later they are perfectly mature and 'ripe' in every regard when they first appear in the stream. When they migrate, the}? stop at the site that seems to suit their fancy, many stopping near the lake, others pushing on four or five miles farther up-stream. AVe have noted, however, that later in the season the lower courses become more crowded, showing that the late comers do not attempt to push up-stream as far as those that came earlier. Also it thus follows, from what was just said about late-running females, that in the latter part of the season the lower spawning beds are especially crowded with females. In fact, during the early part of the month of June we have found, not more than half a mile above the lowest spawning bed, as many as five females on a spawning nest with but one male; and in that immediate vicinity many nests indeed were found at that time with two or three females and but one male. " Having arrived at a shoal which seems tn present suitable conditions for a spawning nest, the inrlividual or pair commences at once to move stones with its mouth from the centre to the margin of an area one or two feet in diameter. When many stones are thus placed, especially at the upper edge, and they are cleaned quite free of sediment and alg;e, both by being moved and by being fanned with the tail, and wlien the proper condition of sand is '"ound in the bottom of the basin thus formed. 498 The Cyclostomes, or Lampreys it is ready to be used as a spawning bed or nest. A great many nests are commenced and deserted. This has been left as a mystery in publications on the subject, but Ave are well con- Adnced that it is because the lampreys do not find the' requi- sites or proper conditions of bottom (rocks, sand, etc., as given below) to supply all their needs and fulfill all conditions for ideal sites. This desertion of half -constructed nests is just what would be expected and anticipated in connection with the ex- planation of 'Requisite Conditions for Spawning,' given below, because some shallows contain more sand and fewer stones, and others contain many larger stones but no sand, while others contain pebbles lying over either rocks or sand. The lamprej^s remove some of the material, and if they do not find all the essentials for a spawning nest, the site is deserted and the creatures move on. Requisite Conditions for Spawning with Lampreys. — "For a spawning site two conditions are immediately essential — proper conditions of water and suitable stream bed or bottom. Of course with these it is essential that no impassable barriers (dam or falls) exist between the lake and the spawning sites to prevent migration at the proper 'running' season. Lampreys wdl not spawn where there is no sand lying on the bottom between the rocks, as sand is essential in covering the eggs (see remarks on the ' Spawning Process ' ) ; neither will they spawn where the bottom is all sand and small gravel, as they cannot take hold of this material with their mouths to con- struct nests or to hold themselves in the current, and they would not find here pebbles and stones to carry over the nest while spawning, as described elsewhere. It can thus be seen that, as suggested above, the reason they do not spawn in Fall Creek and Cascadilla Creek, between the lake and the falls, is that the beds of these streams are very rocky, being covered only with large stones and no sand. There is no doubt that the lampreys find here suitable conditions of water, but they do not remain to spawn on account of the absence of the proper conditions of stream bed. Again, they do not spawn in the lower course of the inlet for a distance of nearly two miles from the lake, because near the lake the bed of the stream is composed of silt, while for some distance above this (up- The Cylcostomes, or Lampreys 499 stream) there is nothing but sand. Farther up-stream are found pebbles and stones commingled with sand, which com- bination satisfies the demands of the lampreys for material in constructing nests and covering eggs. The accessibility of these sites, together with their suitable conditions, render the inlet the great and perhaps the only spawning stream of the lake; and, doubtless, all the mature lampreys come here to spawn, excepting a few which spawn in the lower part of Six-mile Creek, a tributary of the inlet. "As the course of the stream where the beds abound is divided into pools, separated by stony ripples or shallows, the nests must be made at the ends of the pools. Of the spawning beds personally observed during several seasons, nine-tenths of the entire number were formed just above the shallows at the lower ends of the pools, while only a few were placed below them. An advantage in forming the nest above the shoals rather than below it is that in the former place the water runs more swiftly over the lower and middle parts of such a bed than at its upper margin, since the velocity decreases in either direction from the steeper part of the shallows ; and any organic material or sediment that would wash over the upper edge of the nest is thus carried on rather than left as a deposit. When formed below the shallows, owing to the decreased velocity at the lower part of the nest compared with that at the upper, the sediment is likely to settle in the hollow of the nest, and, through the process of decay of the organic material, prove disastrous or unfavorable for the developing embryos. "The necessity of sand in the spawning bed indicates the explanation of why we see so many shallows which have no spawning lampreys upon them, while there are others in the same vicinity that are crowded. There will be no nests formed if there is too little or too much sand, not enough or too many stones, or stones that are all too small or all too large. The stones must vary from the size of an egg to the size of a man's hand, and must be intermingled with sand without mud or rubbish. " The lampreys choose to make their spawning nests just where the water flows so swiftly that it will carry the sand a short distance, but will not sweep it out of the nest. This 500 The Cyclostomes, or Lampreys condition furnishes not only force to wash the sand over the eggs when !aid, but also keeps the adult lampreys supplied with an abundance of fresh water containing the dissolved air needed for their very rapid respiration. Of course in such rapid water the eggs are likely to be carried away down-stream, but Nature provides against this by the fact that they are ad- hesive, and the mating lampreys stir up the sand with their tails, thus weighing down the freshly laid eggs and holding them in the nest. Hence the necessity of an abundance of sand at the spawning site." The Spawning Process with Lampreys. — ' ' There is much in- terest in the study of the spawning process, as it is for the mainte- nance of the race that the lampreys risk and end their lives; and as they are by far the lowest form of vertebrates found within the United States, a consideration of their actions and apparent evidences of instinct becomes of unusual attraction. Let us consider one of those numerous examples in which the male migrates before the female. When he comes to that portion of the stream where the conditions named above are favorable, he commences to form a nest by moving and clearing stones and making a basin with a sandy bottom about the size of a common wash-bowl. Several nests may be started and deserted before perfect conditions are found for the com- pletion of one. The male may be joined by a female either before or after the nest is completed. There is at once harmony in the family; but if another male should attempt to intrude, either before or after the coming of the female, he is likely to be summarily dealt with and dismissed at once by the first tenant. As soon as the female arrives she too commences to move pebbles and stones with her mouth. " Sometimes the nest is made large enough to contain several pairs, or often unequal numbers of males and females ; or they may be constructed so closely together as to form one con- tinuous ditch across the stream, just above the shallows. Many stones are left at the sides and especially at the upper margin of the nest, and to these both lampreys often chhg for a few minutes as though to rest. While the female is thus quiet, the male seizes her with his mouth at the back of her head, clinging as to a fish. He presses his body as tightly as possible The Cyclostomes, or Lampreys 501 against her side, and loops his tail over her near the vent and down against the opposite side of her body so tightly that the sand, accidentally coming between them, often wears the skin entirely off of either or both at the place of closest contact. In most observed instances the male pressed against the right side of the female, although there is no unvarying rule as to position. The pressure of the male thus aids to force the eggs from the body of the female, which flow very easily when ripe. The vents of the two lampreys are thus brought into close proximity, and the conspicuous genital papilla of the male serves to guide the milt directly to the issuing spawn. There appears to be no true intromission, although definite observa- tion of this feature is quite difficult, and, in fact, impossible. During the time of actual pairing, which lasts but a few seconds, both members of the pair exhibit tremendous excitement, shaking their bodies in rapid vibrations and stirring up such a cloud of sand with their tails that their eggs are at once con- cealed and covered. As the eggs are adhesive and non-buoyant, the sand that is stirred up adheres to them immediately and covers most of them before the school of minnows in waiting just below the nest can dart through the water and regale themselves upon the eggs of these enemies of their race; but woe to the eggs that are not at once concealed. We would suggest that the function of the characteristic anal fin, which is possessed only by the female, and only at this time of year, may be to aid in this A^astly important process of stirring up the sand as the eggs are expelled; and the explanation of the absence of such a fin from the ventral side of the tail of the male may be found in the fact that it could not be used for the same purpose at the instant when most needed, since the male is just then using his tail as a clasping organ to give him an essential position in pairing. As soon as they shake together they commence to move stones from one part of the nest to another, to bring more loose sand down over their eggs. They work at this from one to five minutes, then shake again, thus making the intervals between mating from one to five minutes, with a general average of about three and a half minutes. "Although their work of moving stones does not appear to be systematic in reference to the placing of the pebbles, or ^02 The Cyclostomes, or Lampreys as viewed from the standpoint of man, it does not need to be so in order to perfectly fulfill all the purposes of the lampreys. As shown abo^'e in the remarks on the spawning habits of the brook lampreys, the important end which they thus accomplish is the loosening and shifting of the sand to cover their eggs; and the more the stones are moved, even in the apparently indiscriminate manner shown, the better is this purpose achieved. Yet, in general, they ultimately accomplish the feat of moving to the lower side of the nest all the stones they have placed or left at the upper margin. At the close of the spawning season when the nest is seen with no large pebbles at is upper margin, but quite a pile of stones below, it can be known that the former occupants completed their spawning process there; but if many small stones are left at the upper edge and at the sides, and a large pile is not formed at the lower edge, it can be known that the nest was forsaken or the lampreys removed before the spawning process was completed. The stones they move are often twice as heavy as themselves, and are some- times even three or four times as heavy. Since they are not attempting to build a stone wall of heavy material, there is no occasion for their joining forces to remove stones of extraor- dinary size, and they rarely do so, although once during the past spring (1900) we saw two lake lampreys carrying the same large stone down-stream across their nest. Although this place was occupied by scores of brook lampreys, there were but three pairs of lake lampreys seen here. It is true that one of these creatures often moves the same stone several times, and many even attempt may times to move a stone that has already been found too heavy for it; but sooner or later the rock may become undermined so that the water will aid them, and they have no way of knowing what they can do imder such circtmistances until they try. Also, the re- peated moving of one stone may subserve the same purpose for the lamprey in covering its eggs with sand as would the less frequent removal of many. "When disturbed on the spawning nest, either of the pair will return to the same nest if its mate is to be found there' but if its mate is in another place, it will go to it, and if its mate is removed or killed, it is likely to go to any part of the The Cyclostomes, or Lampreys 503 stream to another nest. When disturbed, they often start tip-stream for a short distance, but soon dart down-stream with a veloctiy that is almost incredible. They can swim faster than the true fishes, and after they get a start are generally pretty sure to make good their escape, although we have seen them dart so wildly and fractically down-stream that they would shoot clear out on the bank and become an easy victim of the collector. This peculiar kind of circumstance is most likely to happen with those lampreys that are becoming blinded from long exposure to the bright light over the clear running water. If there is a solitary individual on a nest when dis- turbed, it may not return to that nest, but to any that has been started, or it may stay in the deep pool below the shallows until evening and then move some distance up-stream. When the nest is large and occupied by several individuals, those that are disturbed may return to any other such nest. We have never seen evidence of one female driving another female out of a spawning-nest; and from the great number of nests in which we have found the numbers of the females exceeding those of the males, we would be led to infer that the former live together in greater harmony than do the males. "Under the subject of the number of eggs laid, we should have said that at one shake the female spawns from twenty to forty. We once caught in fine gauze twenty-eight eggs from a female at one spawning instant. In accordance with the frequency of spawning stated, and the number of eggs contained in the body of one female, the entire length of time given to the spawning process would be from two to four days. This agrees with the observed facts, although the lampreys spend much time in moving stones and thoroughly covering the nests with sand. Even after the work of spawning and moving stones is entirely completed, they remain clinging to rocks in various parts of the stream, until they are weakened by fungus and general debility, when the gradually drift down-stream. " In forming nests there is a distinct tendency to utilize those sites that are concealed by overhanging bushes, branches, fallen tree-tops, or grass or weeds, probably not only for con- cealment, but also to avoid the bright sunlight, which sooner or later causes them to go blind, as it does many fishes when 504 The Cyclostomes, or Lampreys they have to hve in water without shade. Toward the end of the spawning season, it is very common to see bhnd lampreys clmging helplessly to any rocks on the bottom, quite unable to again find spawning-beds. However, at such times they are generally spent and merely awaiting the inevitable end. "As with the brook lamprey, the time of spawning and duration of the nesting period depend upon the temperature of the water, as does also the duration of the period of hatching or development of the embryo. They first run up-stream when the water reaches a temperature of 45° or 48° Fahr., and com- mence spawning at about 50°. A temperature of 60° finds the spawning process in its height, and at 70° it is fairly completed. It is thus that the rapidity with which the water becomes heated generally determines the length of time the lampreys remain in the stream. This may continue later in the season for those that run later, but usually it is about a month or six weeks from the time the first of this species is seen on a spawning-nest until the last is gone. What becomes of Lampreys after Spawning? — "There has been much conjecture as to the final end of the lampreys, some writers contending that they die after spawning, others that they return to deep water and recuperate, and yet others compromise these two widely divergent views by saying that some die and others do not. The fact is that the spawning process completely wears out the lampreys, and leaves them in a physical con- dition from which they could never recover. They become stone-blind; the alimentary canal suft'ers complete atrophy; their flesh becomes very green from the katabolic products, which find the natural outlet occluded ; they lose their rich yellow color and plump, symmetrical appearance; their skin becomes torn, scratched, and worn oft" in many places, so that they are covered with sores, and they become covered Avith a parasitic or sarcophytic fungus, which forms a dense mat over almost their entire bodies, and they are so completely debili- tated and worn out that recovery is entirely out of the question. What is more, the most careful microscopical examination of ovaries and testes has failed to reveal any evidence of new gonads or reproductive bodies. This is proof that reproduc- tion could not again ensue without a practical rebuilding of The Cyclostomes, or Lampreys 505 the animals, even though they should regain their vitality. A. Mueller, in 1865, showed that all the ova in the lamprey were of the same size, and that after spawning no small re- productive bodies remained to be developed later. This is strong evidence of death after once spawning. "One author writes that an argument against the the(jry of their dying after spawning can be found in the fact that so few dead ones have been found by him. However, many can be found dead if the investigator only knows how and where to look for them. We should not anticipate finding them in water that is shallow enough for the bottom to be plainly seen, as there the current is strong enough to move them. It is in the deep, quiet, pools where sediment is depositing that the dead lampreys are dropped by the running water, and there they sink into the soft ooze. "The absence of great numbers of dead lampreys from visible portions of the stream cannot be regarded as important evidence against the argument that they die soon after spawn- ing once, as the bodies are very soon disintegrated in the water. In the weir that we maintained in 1898, a number of old, worn- out, and fungus-covered lampreys were caught drifting down- stream; some were dead, some alive, and others dying and already insensible, but none were seen going down that appeared to be in condition to possibly regain their strength." Fig, 297a. — Brook Lamprey, Lampdra Wilderi, (After Gage.) CHAPTER XXIX THE CLASS ELASMOBRANCHII OR SHARK-LIKE FISHES (HE Sharks. — The gap between the lancelets and the lampreys is a very wide one. Assuming the primi- tive nature of both groups, this gap must represent the period necessary for the evolution of brain, skull, and elaborate sense organs. The interspace between the lampreys and the nearest fish-like forms which follow them in an ascending scale is not less remarkable. Between the, lamprey and the shark we have the development of paired fins with their basal attach- ments of shoulder-girdle and pelvis, the formation of a lower ;'aw, the relegation of the teeth to the borders of the mouth, the development of separate vertebrae along the line of the notochord, the development of the gill-arches, and of an ex- ternal covering of enameled points or placoid scales. These traits of progress separate the Elasmobranchs from all lower vertebrates. For those animals which possess them, the class name of Pisces or fishes has been adopted by numerous authors. If this term is to be retained for technical purposes, it should be applied to the aquatic vertebrates above the lam- preys and lancelets. We may, however, regard fish as a popular term only, rather than to restrict the name to members of a class called Pisces. From the bony fishes, on the other hand, the sharks are distinguished by the much less speciahzation of the skeleton, both as regards form and substance, by the lack of membrane bones, of air-bladder, and of true scales, and by various pecuHarities of the skeleton itself. The upper jaw, for example,, is formed not of maxillary and premaxillary, but of elements which in the lower fishes would be regarded as belonging to the palatine and pterygoid series. The lower jaw is formed 506 The Class Elasmobranchii or Shark-like Fishes 507 not of several pieces, but of a cartilage called Meckel's cartilage, which in higher fishes precedes the development of a separate dentary bone. These structures are sometimes called primary jaws, as distinguished from secondary jaws or true jaws de- veloped in addition to those bones in the Actiiioptcri or typical fishes. In the sharks the shoulder-girdle is attached, not to the skull, but to a vertebra at some distance behind it, leaving a distinct neck, such as is possessed or retained by the verte- brate higher than fishes. The shoulder-girdle itself is a con- tinuous arch of cartilage, joining its fellow at the breast of the fish. Other peculiar traits will be mentioned later. Characters of Elasmobranchs. — The essential character of the Elasmobranchs as a whole are these : The skeleton is cartilagi- nous, the skull without sutures, and the notochord more or less fully replaced or inclosed by vertebral segments. The jaws are peculiar in structure, as are also the teeth, which are usually highly specialized and found on the jaws only. There are no membrane bones; the shoulder-girdle is well developed, each half of one piece of cartilage, and the ventral fins, with the pelvic-girdle, are always present, always many-rayed, and abdominal in position. The skin is covered with placoid scales, or shagreen, or with bony bucklers, or else it is naked. It is never provided with imbricated scales. The tail is diphycercal, heterocercal, or else it degenerates into a whip-like organ, a form which has been called leptocercal. The gill-arches are 5, 6, or 7 in number, with often an accessory gill-slit or spiracle. The ventral fins in the males (except perhaps in certain primi- tive forms) are provided with elaborate cartilaginous appen- dages or claspers. The brain is elongate, its parts well separated, the optic nerves interlacing. The heart has a contractile arterial cone containing several rows of valves; the intestine has a spiral valve ; the eggs are large, hatched within the body, or else deposited in a leathery case. Classification of Elasmobranchs. — The group of sharks and their ahies, rays, and ChimJEras, is usuahy known collective^ as Elasmobranchii (elaa-z-iog, blade or plate; /3pdyx"S, giU)- Othcr names apphed to ah or a part of this group are these; Sdachii (o-eAajos, a cartilage, the name also used by the Greeks for the gristle-fishes or sharks); Plagiostomi (nXayw?, obhque; (jTOjia, 5° 8 The Class Elasmobranchii or Shark-like Fishes mouth); Cliondropterygii {x'^y^po?., cartilage; nrepiti, fin); and Antacca {dvTaKaios, sturgeon). They represent the most primitive known type of jaw-bearing vertebrates, or Gnatho- stouii iyraOoi, jaw; aTOf-ia, mouth), the Chordates without jaws being sometimes called coUectively Agnatha {d-yvaOos, without jaws). These higher types of fishes have been also called collectively Lyrifcra, the form of the two shoulder-girdles taken together being compared to that of a lyre. Through shark- like forms all the higher vertebrates must probably trace their descent. Sharks' teeth and fin-spines are found in all rocks from the Upper Silurian deposits to the present time, and while the majority of the genera are now extinct, the class has had a vigorous representation in all the seas, later Palseozoic, Mesozoic, and Cenozoic, as well as in recent times. Most of the Elasmobranchs are large, coarse-fleshed, active animals feeding on fishes, hunting down their prey through superior strength and activity. But to this there are many exceptions, and the highly specialized modern shark of the type of the mackerel-shark or man-eater is by no means a fair type of the whole great class, some of the earliest types being diminutive, feeble, and toothless. Subclasses of Elasmobranchs. — ^With the very earliest recog- nizable remains it is clear that the Elasmobranchs are already divided into two great divisions, the sharks and the Chimaras. These groups we may call subclasses, the Scladiii and the Holo- cepliali, or Chismopnea. The Scladiii, or sharks and rays, have the skull hyostylic, that is, with the quadrate bone grown fast to the palate which forms the upper jaw, the hyomandibular, acting as suspen- sorium to the lower jaw, being articulated directly to it. The palato-quadrate apparatus, the front of which forms the upper jaw in the shark, is not fused to the cranium, although it is sometimes articulated with it. There arc as many external gill-slits as there are gill-arches (5, 6, or 7), and the gills are adnate to the fiesh of their own arches, without free tips. The cerebral hemispheres are grown together. The teeth are sepa- rated and usually strongly specialized, being primitivelv modified from the prickles or other defences of the skin. There is no fn mtal holder or bony iKJok on the forehead of the male. The Class Elasmobranchii or Shark-like Fishes 509 The subclass Holocephali, or Chiincrras, differ from the sharks in all this series of characters, and its separation as a distinct group goes back to the Devonian or even farther, the earliest known sharks having Httle more in common with Chimasras than the modem forms have. The Selachii. — There have been many efforts to divide the sharks and rays into natural orders. Most writers have con- tented themselves with placing the sharks in one order {Squall or Galei or Plenroirenii) having the gill-openings on the side, and the rays in another {Raj(T, Batoidei, Hypotrema) having the gill-openings underneath. Of far more importance than this superficial character of adaptation are the distinctions drawn from the skeleton. Dr. Gill has used the attachment of the palato-quadrate apparatus as the basis of a classification. The Opistharthri (Hexanchida:) have this structure articulated with the postorbital part of the skull. In the Prosarthri {Hetero- dontidcB) it is articulated with the preorbital part of the skull, while in the other sharks (Anarthri) it is not articulated at all. But these characters do not appear to be always important. Chlamydoselachus, for example, differs in this regard from Heptranchias, which in other respects it closely resembles. Yet, in general, the groups thus characterized are undoubtedly natural ones. Basse's Classification of Elasmobranchs. — In 1882, Professor Carl Hasse proposed to subdivide the sharks on the basis of the structure of the individual vertebra. In the lowest group, a Fig. 298. — Fin-spine of Onchus tenuistriatus Agassiz. (After Zittel.) hypothetical order of Polyospondyli, possibly represented by the fossil spines called Onchus, an undivided notochord, perhaps swohen at regular intervals, is assumed to have represented the vertebral column. In the Diplospondyli {Hexanchida;) the im- 5IO The Class Elasmobranchii or Shark-like Fishes perfectly segmented vertebriE are joined in pairs, each pair having two neural arches. In the Asterospondyli or ordinary- sharks each vertebra has its calcareous lamella radiating star- like from the central axis. In the Cyclospondyli {Sqnalida;, etc.) the calcareous part forms a single ring about the axis, and in the Tcctospoiidyli {Sqnatiiia, rays, etc.) it forms several 2 3 Fig. 299. — Section of vertebra^ of sharks, showing calcification. (After Hasse.) 1. Cydosiiondi/li {Squaliis) ; 2. Teciospondyli (Squatina); .3. Asterospondyli {Carcharlas). rings. These groups again are natural and correspond fairly with those based on other characters. At the same time there is no far-reaching difference between Cyclospondyli and Teciospondyli, and the last-named section includes both sharks and rays. Nothing is known of the Polyospondyli, and they may never have existed at all. The Diplospondyli do not differ very widely from the earlier Asterospondyli {Cestraciontes) which, as a matter of fact, have preceded the Diplospondyli in point of time, if we can trust our present knowledge of the geological record. Other Classifications of Elasmobranchs. — Characters more fun- damental may be drawn from the structure of the pectoral fin. In this regard four distinct types appear. In Acaiiihocssiis this fin consists of a stout, stift' spine, with a rayless membrane attached behind it. In Cladoselache the fin is low, with a very long base, like a fold of skin (ptychoptery^^iiini), and composed of feeble rays. In Pleiiracantlius it is a jointed axis of many segments, with a fringe of slender fin-rays, corresponding in structure to all appearance to the pectoral fin of Dipnoans and The Class Elasmobranchii or Shark-like Fishes 5 1 1 Crossopterygians, the type called by Gegenbaur archipterygium on the hyopthesis that it represents the primitive vertebrate limb. In most sharks the fin has a fan-shape, with three of the basal segments larger than the others. Of these the mesop- terygium is the central one, with the propter ygium before it and the metapterygium behind. In the living sharks of the family of Hetcrodontidcr, this form of fin occurs and the teeth of the same general type constitute the earliest remains dis- tinctly referable to sharks in the Devonian rocks. Primitive Sharks. — Admitting that these four types of pec- toral fin should constitute separate orders, we have next to consider which form is the most primitive and what is the line of descent. In this matter we have, in the phrase of Haeckel, only the "three ancestral documents. Palaeontology, Morphol- ogy, and Ontogeny." Unfortunately the evidence of these documents is incom- plete and conflicting. So far as Palaeontology is concerned, the fin of Cladoselache, with that of Acanthocssus, which may be derived from it, appears earliest, but the modern type of pectoral fin with the three basal segments is assumed to have accompanied the teeth of Psammodonts and Cochliodonts, while the fin of the Chimasra must have been developed in the Devonian. The jointed fin of Cladodus and Pleura- canthns may be a modification or degradation of the ordinary type of shark-fin. Assuming, however, that the geological record is not perfect and that the fin of Cladoselaclie is not clearly shown to be pr'mi- tive, we have next to consider the evidence drawn from mor- phology. Those who with Balfour and others (see page 69) accept the theory that the paired fins are derived from a vertebral fold, will regard with Dean the fin of Cladoselaclie as coming nearest the theoretical primitive condition. The pectoral fin in Acanthoessiis Dean regards as a specialized derivative from a fin like that of Cladoselaclie, the fin-rays being gathered together at the front and joined together to form the thick spine characteristic of Acanthocssus. This view of the morphology of the fin of Acanthoessiis is not accepted by 5 I 2 The Class Elasmobranchii or Shark-like Fishes Woodward, and several different suggestions have been recorded. If with Gegenbaur we regard the paired fins as derived from the septa between the gill-shts, or with Kerr regard them as modified external' gills, the whole theoretical relation of the parts is changed. The archipterygmm of Pleiiracanthtis would be the nearest approach to the primitive pectoral limb, and from this group and its alhes ah the other sharks are descended. This central jointed axis of Pleuracanthus is re- garded by Traquair as the equivalent of the metapterygium in ordinary sharks. (See Figs. 44, 45, 46.) According to Traquair: "The median stem [of the archip- terygium], simplified, shortened up and losing all its radials on the postaxial side, except in sometimes a few near the tip, becomes the metapterygium, while the mesopterygium and propterygium are formed by the fusion into two pieces of the basal joints of a number of preaxial radials, which have reached and become attached to the shoulder-girdle in front of the m.etapteryglum . ' ' According to Dr. Traquair, the pectoral fin in Cladodns neilsoni, a shark from the Coal Measures of Scotland, is "appar- ently a veritable uniserial archipterygium midway between the truly biserial one of Pleuracanthus and the pectoral fin of ordi- nary sharks." Other authors look on these matters differently, and Dr. Traquair admits that an opposite view is almost equally probable. Cope and Dean would derive the tribasal pectoral of ordinary sharks directly from the ptychopterygium or fan- like fold of Cladoselache, while Fritsch and Woodward would look upon it as derived in turn from the CcratodnsAAie fin of Pleura- canthus, itself derived from the ptychopterygium or remains of a lateral fin-fold. If the Dipnoans are descended from the Crossopterygians, as Dollo has tried to show, the archipterygium of Pleuracanthus has had a dift'erent origin from the similar-appearing limb of the Dipnoans, Diptcms and Ccratodus. In such case the archipterygium would not be the primi- tive pectoral limb, but a structure w^hich may have been inde- pendently evolved m two different groups. In the vicAv of Gegenbaur, the Crossopterygians and Dip- noans with ah the higher vertebrates and the bony fishes would The Class Elasmobranchii or Shark-like Fishes 5 1 3 arise from the same primitive stock, ancestors, or allies of the Ichthyotomi, which group would also furnish the ancestors of the Chimcsras. In support of this view, the primitive pro- tocercal or diphycercal tail of Pleuracanthus may be brought in evidence as against the apparently more specialized hetero- cercal tail of CladosclacJie. But this is not conclusive, as the diphycercal tail may arise separately in different groups through degeneration, as DoUo and Boulenger have shown. The matter is one mainly of morphological interpretation, and no final answer can be given. On page 68 a summary of the various arguments may be found. Little light is given by embryology. The evidence of Paleontology, so far as it goes, certainly favors the view of Balfour. Omitting detached fin-spines and fragments of uncertain character, the earliest identifiable remains of sharks belong to the lower Devonian. These are allies of Acanthoessus. Cladoselache comes next in the Upper Devonian. Pleuracanthus appears with the teeth and spines supposed to belong to Cestraciont sharks, in the Carboniferous Age, The primitive-looking Notidani do not appear before the Triassic. For this reason the decision as to which is the most primitive type of shark must therefore rest unsettled for the present and perhaps for a long time to come. The weight of authority at present seems to favor the view of Balfour, AViedersheim, Boulenger, and Dean, that the pec- toral limb has arisen from a lateral fold of skin. But weight of authority is not sufficient when evidence is confessedly lacking. For our purpose, without taking sides in this controversy, we may follow Dean in allowing Cladoselache to stand as the most primitive of known sharks, thus arranging the Elasmobranchs and rays, recent and fossil, in six orders of unequal value — Pleura pterygii, Acanthodei, Ichthyotoini, Notidani, Astcrospoiidyli, and Tectospondyli. Of these orders the first and second are closely related, as are also the fourth and fifth, the sixth being not far remote. The true sharks form the culmination of one series, the rays of another, while from the Ichthyotomi the Cros- sopterygians and their descendants may be descended. But this again is very hypothetical, or perhaps impossible ; while, on 514 The Class Elasmobranchii or Shark-like Fishes the other hand, the relation of the Chimaeras to the sharks is stiU far from clearly understood. Order Pleuropterygii. — The order of Pleiiropterygii of Dean {nXevpov, side; nrepvB,, fin), called by Parker and Hasweh Clado- sdaclica, consists of sharks in which the pectoral and ventral fins have each a very wide horizontal base fptychopterygium), without jointed axis and without spine. There are no spines in any of the fins. The dorsal fin is low, and there were proba- bly two of them. The notochord is persistent, without inter- calary cartilage, such as appear in the higher sharks. The caudal fin is short, broad, and strongly heterocercal. Appar- ently the ventral fin is without claspers. The gill-openings were probably covered by a dermal fold. The teeth are weak, being modified denticles from the asperities of the skin. The lateral line is represented by an open groove. The family of Cladoselachidw consists of a single genus Cladoselachc from the Cleveland shale or Middle Devonian of Ohio. Cladoscladic jyleri is the best-known species, reaching a length of about two feet. Dean regards this as the most primitive of the sharks, and the position of the pectorals and ventrals certainly lend weight to Balfour's theory that they were originally derived from a lateral fold of skin. I am recently informed by Dr. Dean that he has considerable evidence that in Cladoselache the anus was subtcrminal. If this statement is verified, it would go far to establish the primitive character of Cladoselache. Order Acanthodei. — Near the Pleuropterygii, although much more highly developed, we may note the strange group of Acan- FiG. 300. — Cladoselache fi/lcri (Newberry"), restored. Upper Devonian of Ohio. (After" Dean.) tliodei {aKavdoS?/^, spinous) . These armed fishes were once placed among the Crossopterygians, but there seems no doubt that Woodward is right in regarding them as a highly specialized aber- rant offshoot of the primitive sharks. In this group the pairea The Class Elasmobranchii or Shark-like Fishes 5 i 5 fins consist each of a single stout spine, nearly or quite destitute of other rays. A similar spine is placed in front of the dorsal Fig. .301. — Cladoselache pjUri (Newberry), restored. Ventral view. (After Dean.) fin and one in front of the anal. According to Dean these spines are each produced by the growing together of all the Fig. 302. — Teeth of Cladoselache fyleri (Newberry). (After Dean.) fin-rays normally belonging to the fin, a view of their mor- phology not universally accepted. The dermal covering is highly specialized, the shagreen den- FlG. 303. — Acanthoessus loardi (ERorton). Carboniferous. Family Acanlhoessida:. (After Woodward.) tides being much enlarged and thickened, often set in lit- tle squares suggesting a checker-board. The skull is covered with small bony plates and membrane bones form a sort of ring about the eye. The teeth are few, large, and "degenerate 5i6 The Class Elasmobranchii or Shark-like Fishes in their fibrous structure." Some of the species have certainly no teeth at all. The tail is always heterocercal, or bent upward at tip as in the Cladoselache, not diphycercal, tapering and horizontal as in the Ichihyotomi. The lower Acanthodeans, according to Woodward, "are the only vertebrates in which there are any structures in the adult apart from the two pairs of fins which may be plausibly in- terpreted as remnants of once continuous lateral folds. ' In Climatius, one of the most primitive genera (see Fig. 305), there exists, according to Woodward, and as first noticed by Cope, between the pectoral and pelvic (or ventral) fins a close and regular series of paired spines, in every respect identical with those supporting the appendages that presumably correspond to the two pairs of fins in the higher genera. They may even have supported fin membranes, though specimens sufficiently well preserved to determine this point have not yet been dis- covered. However, it is evident that dermal calcifications attained a greate development in the Acantlwdei than in any of the more typical Elasmobranchs, and we may look for much additional information on the subject when the great fishes to which the undetermined Ichthyodorulites pertained became known." (See Fig. 305.) The Acanthodci constitute three families. In the Acan- hocssidcv- there is but one short dorsal fin opposite the ana\ and clavicular bones are absent. The gill-openings being pro- vided with "frills" or collar-like margins, perhaps resembled those of the living genus Chlaniydosclachus , the frilled shark. The pectoral spine is very strong, and about the eye is a ring of four plates. The body is elongate, tapering, and compressed. AcantJwessus of Agassiz, the name later changed by its author to Acauthodcs, is the principal genus, found in the Devonian and Carboniferous. The species of Acaiitliocssus are all small fishes rarelv more than a foot long, with very small teeth or none, and with the skin well armed with a coat-of-mail. Acaiitliocssus broniii is the one longest known. In the earliest species knoAvn, from the Devonian, the ventral fins are almost as large as the pec- torals and nearly midway between pectorals and anal. In the later species the pectoral fins become gradually larger The Class Elasmobranchii or Shark-like Fishes 5 1 7 and the ventrals move forward. In the Permian species the pectorals are enormous. Traqiiairia pygmcea, from the Permian of Bohemia, is a di- minutive sharklet three or four inches long with large scales, slender spines, and apparently no ventral fins. In the genus Cheiracantlms the dorsal fin is placed before the anal. In Acanthodopsis the teeth are few, large, and triangular, and the fin-spines relatively large. The IsdinacantJiidcv have no clavicles, and two dorsal fins. Ischnacantlius gracilis of the Devonian has a few large conical teeth with small cusps between them. The Diplacanthidcr, with two dorsal fins, possess bones interpreted as clavicles. The teeth are minute or absent. In Diplacanthus striatus and Diplacanthus longispiniis of the Lower Fig. .304. — Diplacanthus crassissimus Duff. Devonian. Family Diplacanthidce. (After Nicliolson). (Restoration of jaws and gill-openings; after Traquair.) Devonian stout spines are attached to the shoulder-girdle between the pectoral spines below. In the very small sharks called Climatins the fin-spines are very strong, and a series of several free spines occurs, as above stated, on each side between the pectoral and ventral fins, a supposed trace of a former lateral fold. In Paraxus the first dorsal spine is enormously enlarged in size, the other spines remaining much as in Climatius. Dean on Acanthodei. — In his latest treatise on these fishes, "The Devonian Lamprey," Dr. Dean unites the Pleiiropterygii and Acanthodei in a single order under the former name, re- 51 8 The Class Elasmobranchii or Shark-like Fishes garding AcaiitJiocssits as an ally and perhaps descendant of the primitive Cladoselache. Dr. Dean observes: "In the foregoing classification it will be noted that the Acanthodia are regarded as included under the first order of sharks, Pleuropterygii. To this arrangement Smith Wood- ward has already objected that the spines of Acanthodians cannot be regarded as the homologues of the radial elements of the Cladoselachian fin (which by a process of concrescence have become fused in its interior margin), since he believes the structure to be entirely dermal in origin. His criticism, however, does not seem to me to be well grounded, for, although Fig. 305. — Chmaiius scutiger Eserton, restored. Family Diplacanlhidce. (After Powrie, per Zittel.) all will adm't that Acanthodian spines have become incrusted, and deeply incrusted, with a purely dermal calcification, it does not follow that the 'nterior of the spine has not had primi- tively a non-dermal core. That the concrescence of the radial supporting elements of the fin took place pari passu with the development of a strengthening dennal support of the fin margin was the view expressly formulated in my previous paper on this subject. It is of interest in this connection to recall that the earliest types of Acanthodian spines were the widest, and those which, in spite of their incasing dermal cal- cification, suggest most clearly the parallel elements represent- ing the component radial supports. There should also be recalled the many features in which the Acanthodians have been shown to resemble Cladosclaclic." From these primitive extinct types of shark we may pro- ceed to those forms which have representatives among livino- fishes. From Cladosclaclie a fairly direct series extends throuoh The Class Elasmobranchii or Shark-like Fishes 5 1 9 the Notidani and Cestraciontes, culminating in the Lamnoid and Galeoid sharks. Still another series, destitute of anal fin, probably arising near the Acanihodei, reaches its highest development in the side branch of the Batoidei or rays. The Holocephali and Dipneusti must also find their origin in some of these primitive Fig. 306. — Pleuracanthus decheni Goldfuss. Family Pleuraco.nthtdce. (After Roemer, per Zittel.) types, certainly not in any form of more highly specialized sharks. Woodward prefers to place the Tectospondyli next to the Ichthyotomi, leaving the specialized sharks to be treated later. There is, however, no linear system which can interpret natural affinities, and we follow custom in placing the dogfishes and rays at the end of the shark series. 520 The Class Elasmobranchii or Shark-like Fishes Order Ichthyotomi. — In the order Ichthyotomi {ix^vs, fish; TO)xbi, cutting ; named by Cope from the supposed segmentation Fig. 307. — Pleuracanthus decheni, restored. (After Brongniart.) The anterior anal very hypothetical. of the cranium; called by Parker and Haswell Pleuracanthea) the very large pectoral fins are developed each as an archip- terygium. Each fin consists of a long segmented axis fringed on one or both sides with fin- rays. The notochord is very simple, scarcely or never con- stricted, the calcifications of its sheath "arrested at the most primitive or rhachitomous stage, except in the tail." This is the best defined of the orders of Fig. 308. Fig. 309. Flo. 308. — Head-bones and teeth of PleuTacanthus decheni Goldfuss. (After Davis, per Dean.) Fig. 309. — Teeth of Didymodus hohemicus Quenstadt. Carboniferous. Family Pleuracanlhidtv. (After Zittel.) sharks, and should perhaps rank rather as a subclass, as the Holocephali. Two families of Ichthyotomi are recognized by Woodward, the PleuracanthidcB and the Cladodontida . In the Pleuracanthida the dorsal fin is long and low, continuous from head to tail, and the pectoral rays are in two rows. There is a long barbed spine with two rows of serrations at the nape. The Class Elasmobranchii or Shark-like Fishes 521 The body is slender, not depressed, and probably covered with smooth skin. The teeth have two or more blunt cusps, some- times with a smaller one between and a blunt button behind. The intemeural cartilages are more numerous than the neural spines. The genera are imperfectly known, the skeleton of Pleuracanthus decheni only being well preserved This is the type of the genus called Xenacanthus which, according to Wood- ward, is identical with Pleuracanthus, a genus otherwise known from spines only. The denticles on the; spine are straight or hooked backward, in Pleuracanthus {Iwvissimus), the spine being flattened. In Orthacanthus (cylindricus) , the spine is cylindrical in section. The species called Dittodus and Didy- modus are known from the teeth only. These resemble the Fig. 310. — ^Shoulder-girdle and pectoral fins of Cladodm; neilsoni Traquair. teeth of Chlamydoselachus. It is not known that Dittodus pos- sesses the nuchal spine, although detached spines like those of Pleuracanthus lie about in remains called Didynwdns m the Permain rocks of Texas. In Dicranodus texensis the palato- quadrate articulates with the postorbital process of the cranium, as in the Hexanchidce, and the hyomandibular is slender. A genus, Chondrenchelys, /rom the sub-Carboniferous of 52: The Class Elasmobranchii or Shark-like Fishes Scotland, is supposed to belong to the Pleuracanthidw, from the resemblance of the skeleton. It has no nuchal spine, and no trace of paired fins is preserved. The Cladodontidm differ in having the "pectoral fin de- veloped in the form of a uniserial archipterygium intermediate between the truly biserial one of Pie nr acanthus and the pectoral fin of modern sharks." The numerous species are known mainly from detached teeth, especially abundant in America, the earliest being in the Lower Carboniferous. One species, Cladodiis nelsoni (Fig. 310), described by Traquair, from the sub -Carboniferous of Scotland shows fairly the structure of the pectoral fin. In Cladodiis iiiirabilis the teeth are very robust, the crown consisting of a median principal cone and two or three large lateral cones on each side. The cones are fairly striate. In Lanibdodiis from Illinois there are no lateral cones. Other genera are Dicciitrodns, Phwbodus, Carcliaropsis, and Hyhocladodiis. Fig. 3U.— Teeth of Cladodiis striatiix Agassiz. (After Davis.) Carboniferous. CHAPTER XXX THE TRUE SHARKS RDER Notidani. — We may recognize as a distinct order, a primitive group of recent sharks, a group of forms finding its natural place somewhere between the CladoselacJiidcc and Hctcrodoniidw, Vjoth of which groups long preceded it in geological time. The name Notidani {Notidaniis, voaridavoi, dry back, an old name of one of the genera) may be retained for this group, which corresponds to the Diplospondyli of Hasse, the Opis- tharthri of Gill, and the Protoselachii of Parker and Haswell. The Notidani are characterized by the primitive structure of the spinal column, which is without calcareous matter, the centra being imperfectly developed. There are six or seven branchial arches, and in the typical forms not in Chlamydoseladius) the palato-quadrate or upper jaw articulates with the postorbital Fig. 312. — Griset or Cow-shark, Hexanchus grisevs (Gmelin). Currituck Inlpt, N.C. region of the skull. The teeth are of primitive character, oi different forms in the same jaw, each with many cusps. The fins are without spines, the pectoral fin having the three basal cartilages (mesopterygium with propterygium and metapte- rygium) as usual among sharks. The few living forms are of high interest. The extinct species are numerous, but not very different from the living species. 523 524 The True Sharks Family Hexanchidse.— The majority of the living Notidanoid sharks belong to the family of HexanchidcB. These sharks have six or seven gill-openings, one dorsal fin, and a relatively simple organization. The bodies are moderately elongate, not eel- shaped, and the palato-quadrate articulates with the post- orbital part of the skull. The six or eight species are found sparsely m the warm seas. The two genera, Hexanchus, with six, and Heptranchias, with seven iertebr^e, are fotmd in the Mediterranean. The European species are Hexanchus grisens, the cow-shark, and Heptranchias cinereus. The former crosses to the West Indies. In California, Heptranchias niaculatus Fig. 313. — Teeth of Heptranchias indicus Gmelin. and HexancJiits coriniis are occasionally taken, while Heptran- chias dcani is the well known Aburazame or oil shark of Japan. Heptranchias indicus, a similar species, is found in India. Fossil Hcxancliidcv exist in large numbers, all of them re- ferred by Woodward to the genus Notidanus (which is a later name than HexancJms and Heptranchias and intended to in- clude both these genera), differing chiefly in the number of gill- openings, a character not ascertainable in the fossils. None 'if these, however, appear before Cretaceous time, a fact which may indicate that the simplicity of structure in Hexanchus and Heptranchias is a result of degeneration and not altogether a mark of primitive simplicity. The group is apparently much The True Sharks 5^5 younger than the Cestraciontes and Httle older than the Lam- noids, or the Squaloid groups. Heptranchias niicrodon is com- mon in EngHsh Cretaceous rocks, and Heptranchias primigenius and other species are found in the Eocene. Family Chlamydbselachidse. — Very great interest is attached to the recent discovery by Samuel Garman of the frilled shark, Chlamydoselachus anguineiis, the sole living representative of the Chlamydoselachidce. Fig. 314. — -Frill-shark, Chlamydoselachus anguineus Garman. From Misaki, Japan. (After Gunther.) This shark was first found on the coast of Japan, where it is rather common in deep water. It has since been taken off Madeira and off the coast of Norway. It is a long, slender, eel-shaped shark with six gill-openings and the palato-quadrate not articulated to the cranium. The notochord is mainly persistent, in part replaced by feeble cyclospondylic vertebral centra. Each gill-opening is bordered by a broad frill of skin. There is but one dorsal fin. The teeth closely resemble those of Dittodus or Didymodus and other extinct Ichthyotomi. The teeth have broad, backwardly extended bases overlapping, the crown consisting of three slender curved cusps, separated by rudimentary denticles. Teeth of a fossil species, Chlamy- doselachus lawleyi, axe recorded by J. W. Davis from the Pliocene of Tuscany. Order Asterospondyli.— The order of Asterospondyli comprises the typical sharks, those in which the individual vertebrae are well developed, the calcareous lamellae arranged so as to radiate, star-fashion, from the central axis. All these sharks possess two dorsal fins and one anal fin, the pectoral fin is normally 526 The True Sharks developed, with the three basal cartilages; there are five gill- openings, and the tail is heterocercal. Fig. 315.— Bullhead-shark, Hcterodontii.^ francisci (Girard). San Pedro, Cal. Suborder Cestraciontes. — The most ancient types may be set off as a distinct suborder under the name of Cestraciontes or Prosartliri. Fig. 3)0. — Lower jaw of Hetfrodontus philippi. From Australia. Family Hetcro- dontida:. (After Zittel.) These forms find their nearest allies in the Notidani, which they resemble to some extent in dentition and in having the palato-quadrate articulated to the skull although fastened The True Sharks 527 farther forward than in the Notidani. Each of the two dorsal fins has a strong spine. Family Heterodontidae. — Among recent species this group contains only the family of Hetcrodontidcc, the bullhead sharks, or Port Jackson sharks. In this family the head is high, with usually projecting eyebrows, the lateral teeth are pad-like, ridged or rounded, arranged in many rows, different from the D Fig. 317. Fig. 31S. Fig. 317. — Teeth of Cestraciont Sharks. (After Woodward.) d, Synechodus duhrisianus JIackie; e, Heterodontus can-alicidalus Egerton; /, Hyhodus striatulus Agassiz. (After Woodward.) Fig. 31s. — Egg of Port Jackson Shark, Heterodontus phdippi (Lac6pede). (After Parker & Haswell.) pointed anterior teeth, the fins are large, the coloration is strongly m rked, and the large egg-cases are spirally twisted. All have five gill-openings. The living species of Heterodontidcr are ound only in the Pacific, the Port Jackson shark of Australia, Heterodontus philippi, being longest known. Other species are Heterodontus francisci, common in California, Heterodontus japonicHS. in Japan, and Heterodontus zebra, in China. These small and harmless sharks at once attract attention by their peculiar forms. In the American species the jaws are less 528 The True Sharks contracted than in the Asiastic species, called Heterodontus. For this reason Dr. Gill has separated the former iinder the name of Gyropleiirodits. The differences are, however, of slight value. The genus Heterodontus first appears in the Jurassic, where a number of species are known, one of the earliest being Heterodontus jalcifer. Three families of Cestraciontes are recognized by Hay. The most primitive of these is the group of Orodontidce. Orodus, from the Lower Carboniferous, has the teeth with a central crown, its surface wrinkled. Of the Heterodontidce, Hyho- dus, of the Carboniferous and Triassic, is one of the earliest and largest genera, characterized by elongate teeth of many Fig. 3i9.-Toothof H„bodusde-C^^V^' different in different parts of the labechei Charlesworth. (After jaw, somewhat as in the HexanchidcF, Woodward.) , ,. • , •, ■ i the median points being, however, always longest. The dorsal fins are provided with long spines serrated behind. The vertebrae with persistent notochord show qualities intermediate between those of Hexancliidm and Hetero- FiG 320. — Fin-spine of Hybodus basaniis Egerton. Cretaceous. Familj' Hetero- dontidce. (After Nicholson.) doiitidcc, and the same relation is shown by the teeth. In this genus two large hooked half -barbed dermal spines occur behind each orbit. Fir ^21 — Fin-spme ot Hiibodu\ uticidatiis Agassiz (After Zittel.) Pahcospiiiax, with short stout spines and very large pectoral fins, formerly regarded as a dogfish, is placed near Hcterodoiitus by Woodward. Acrodus, from the Triassic, shows considerable resemblance to Heterodontus. Its teeth are rounded and without cusps. The True Sharks 529 Most of these species belong to the Carboniferous, Triassic, and Jurassic, although some fragments ascribed to Cestraciont sharks occur in the Upper Silurian. Astera- canthus, known only from fin-spines in the Jura, probably belongs here. It is a singular fact first noted by Dr. Hay, that with all the great variety of sharks, ten families in the Carboniferous age, repre- sentatives of but one family. Meter odontidcB, are found in the Triassic. This family may be the parent of all subsequent sharks and rays, six families of these appearing in the Jurassic and many more in the Cretaceous. Edestus and its Allies. — Certain monstrous structures, hitherto thought to be fin-spines. Fig. 322. Fig. 323. Fig. 322. — Fin-spine of Hybodus canaliculatus Agassiz. Fig. 323. — Teeth of Cestraciont Sharks. (After Woodward.) a, Hybodus laevis Woodward (after Woodward); b, Heterodontus rugosus Agassiz; c, Hybodus delabechei Charlesworth. are now shown ^ / Dr. Eastman and others to be coalescent teeth of Cestraciont sharks. These remarkable Ichthyodorulites are characteristic structures Fig. 324. — Edestus vorax Leidig, supposed to be a whorl of teeth. (After Newberry.) of sharks of unknown nature, but probably related to the Heterodontidce . Of these the principal genera are Edestus, Helicoprion, and Campylo prion. Karpinsky regards these ornate serrated spiral structures as whorls of unshed teeth 53' The True Sharks cemented togther and extending outside the mouth, "sharp, piercing teeth which were never shed but became fused in whorls as the animals grew." Dr. Eastman has, however, shown that these supposed teeth of Edestus are much like those of the C ochliodontidcB , and the animals which bore them should doubtless find their place Fig. 325. — Helicoprion bessonowi Karpinsky. Teeth from the Permian of Krasnonfimsk, Russia. (After Karpinsky.) among the Cestraciont sharks, perhaps within the family of HeterodonU'dcr. Onchus. — The name Ojicliiis was applied by Agassiz to small laterally compressed spines, their sides ornamented with smooth or faintly crenulated longitudinal ridges, and with no denti- cles behind. Very likely these belonged to extinct Cestraciont sharks. Onchus murchisoni and Onchus tenutstriatus occur in the Upper Silurian rocks of England, in the lowest strata in which sharks have been found. To a hypothetical group of primitive sharks Dr. Hasse has giA'cn the name of Polyospondyli. In these supposed The True Sharks 531 ancestral sharks the vertebras were without any ossification, a simple notochord, possibly swollen at intervals. The dorsal fin was single and long, a fold of skin with per haps a single spine as an anterior support. The teeth must have been modified dermal papillae, each probably with many cusps. Probably seven gill-openings were developed, and the tail was diphycercal, ending in a straight point. The finely striated fin-spines not curved upward at tip, called Onchus from the Upper Silurian of the Ludlow shales of England and else- where, are placed by Hasse near his Polyspondylous sharks. Such spines have been retained by the group of Chimaras, supposed to be derived from the ancestors of Onchus, as well as by the Heterodontidac and Sqiialidcc. Family Cochliodontidae. — Another ancient family known from teeth alone is that of Cochliodontidce. These teeth resemble those of the Heterodontida:, but are more highly specialized. The form of the body is tm- known, and the animals may have been rays rather than sharks. Eastman leaves them near the Petalodontidcs, « which group of supposed /| rays shows a similar denti- ^ tion. The teeth are convex in form, strongly arched, hohowed at base, and often Fig. 326.-Lower jaw of CoMwdus contortus Agassiz. Carboniferous. (After Zittel. ) marked by ridges or folds, being without sharp cusps. In each jaw is a strong posterior tooth with smaller teeth about. The elaborate speciahzation of these ancient teeth for crushing or grinding shells is very remark- able. The species are chiefly confined to rocks of the Car- boniferous age. Among the principal genera are Helodus, Psephodus, Sandalodus, Venustodus, Xystrodiis, Deltodus, Paci- lodus, and Cochliodus. Concerning the teeth of various fossil sharks. Dr. Dean observes: "Their general character appears to have been primi- tive, but in structural details they were certainly specialized. Thus their dentition had become adapted to a shellfish diet, and they had evolved defensive spines at the fin margins, some- rT2 The True Sharks times at the sides of the head. In some cases the teeth remain as primitive shagreen cusps on the rim of the mouth, but be- come heavy and bluntish behind; in other forms the fusion of tooth clusters may present the widest range in their adapta- tions for crushing; and the curves and twistings of the tri- toral surfaces may have resulted in the most specialized forms of dentition which are known to occur, not merely in sharks but among all vertebrates." In this neighborhood belongs, perhaps, the family of Tamio- hatidcE, known from the skull of a single specimen, called Tamio- batis vetustus, from the Devonian in eastern Kentucky. The head has the depressed form of a ray, but it is probably a shark and one of the very earliest known. Suborder Galei. — The great body of recent sharks belong to the suborder Galei, or Euselachii, characterized by the astero- spondylous vertebrae, each having a star-shaped nucleus, and by the fact that the palato-quadrate apparatus or upper jaw is not articulated with the skull. The sharks of this suborder are the most highly specialized of the group, the strongest and largest and, in general, the most active and voracious. They are of three types and naturally group themselves about the three central families ScyliorhinidcE, Lamnidw, and Carchariidce {Galeorhinidce). The Asterospondyli are less ancient than the preceding groups, but the modem families were well differentiated in Mesozoic times. Among the Galei the dentition is less complex than with the ancient forms, although the individual teeth are more highly specialized. The teeth are usually adapted for biting, often with knife-like or serrated edges; only the outer teeth are m function ; as they are gradually lost, the inner teeth are moved outward, gradually taking the place of these. We may place first, as most primitive, the forms without nictitating membrane. Family Scyliorhinidae. — The most primitive of the modem families is doubtless that of the Scyliorhinidce, or cat-sharks. This group includes sharks with the dorsal fins both behind the ventrals, the tail not keeled and not bent upward, the spiracles present, and the teeth small and close-set. The species The True Sharks 533 are small and mostly spotted, found in the warm seas. All of them lay their eggs in large cases, oblong, and with long filaments or strings at the comers. The cat-sharks, or rous- settes, Scyliorhinus canicula and Catulus stellaris, abound in the Mediterranean. Their skin is used as shagreen or sand- paper in pohshing furniture. The species of swell-sharks (Cephaloscylium) {C. uter, in California; C. ventriosus, in Chile; C. laticeps, in Australia; C. umbratile, in Japan) are short, wide-bodied sharks, which have the habit of filling the capacious stomach with air, then floating belly upward like a globe-fish. Other species are found in the depths of the sea. Scylio- rhinus, Catulus, and numerous other genera are found fossil. The earliest is Palcroscyllium, in the Jurassic, not very dif- ferent from Scyliorhinus, but the fins are described as more nearly like those of Giiiglymostoma. Close to the Scyliorhinidw is the Asiatic family, Hemi- scylliidcB, which differs in being ovoviviparous, the young, according to Mr. Edgar R. Waite, hatched within the body. The general appearance is that of the ScyliorhinidcB, the body being elongate. Cliiloscyllium is a well-known genus with sev- eral species in the East Indies. Chiloscylliimi modestum is the dogfish of the Australian fishermen. The Orectolobidw are thick- set sharks, with large heads provided with fieshy fringes. Orec- tolobus barbatus {Crossorhinus of authors) abounds from Japan to Australia. Another family, Ginglymostomidce, differs mainly in the form of the tail, which is long and bent abruptly upward at its base. These large sharks, known as nurse-sharks, are found in the warm seas. Ginglynwstoma cirrhatum is the common species with Orectolobus. Stegostoma tigrinum, of the Indian seas and north to Japan, one of several genera called tiger- sharks, is remarkable for its handsome spotted coloration. The extinct genus Pseudogaleus (voltai) is said to connect the Scyliorhinoid with the Car chart old sharks. The Lamnoid or Mackerel Sharks. — The most active and most ferocious of the sharks, as well as the largest and some of the most sluggish, belong to a group of families known collectively as Lamnoid, because of a general resemblance to the mackerel- 534 The True Sharks shark, or Lariina, as distinguished from the blue sharks and white sharks alhed to Carcharias {Carcharhinus). The Lamnoid sharks agree with the cat-sharks in the absence of nictitating membrane or third eyehd, but differ in the an- terior insertion of the first dorsal fin, which is before the ven- trals. Some of these sharks have the most highly specialized teeth to be found among fishes, most effective as knives or as scissors. Still others have the most highly specialized tails, either long and flail-like, or short, broad, and muscular, fitting the animal for swifter progression than is possible for any other sharks. Tlie Lamnoid families are especially numerous as fossils, their teeth abounding in all suitable rock deposits from Mesozoic times till now. Among the Lamnoid sharks numerous families must be recognized. The most primitive is perhaps that of the OdoiitaspididcB (called Carcliar-iidcc by some recent authors), now chiefly ex- tinct, with the tail unequal and not keeled, and the teeth slender and sharp, often with smaller cusps at their base. Odontaspis and its relatives of the same genus are numerous, from the Cretaceous onward, and three species are still extant, small sharks of a voracious habit, living on sandy shores. Odon- taspis littoralis (also known as Carcharias littoralis) is the com- mon sand-shark of our Atlantic coast. Odontaspis taurus is a similar form in the Mediterranean. Family Mitsukurinidae, the Goblin-sharks. — Closely allied to Odontaspis is the small family of Mitsuknrinidcc, of which a single living species is known. The teeth are like those of Odontaspis, but the appearance is very different. The goblin-shark, or Tenguzame, Mttsukuriiia owstoni, is a very large shark rarely taken in the Kuro Shiwo, or warm " Black Current" of Japan. It is characterized by the development of the snout into a long flat blade, extending far beyond the mouth, much as in Polyodon and in certain Chimasras. Several specimens are now known, all taken by Capt. Alan Owston of Yokohoma in Sagami Bay, Japan. The original specimen, a young shark just born, was presented by him to Professor Kakichi Mitsukuri of the University of Tokyo. From this our figure was taken. The largest specimen now known is in the United States National Museum and is fourteen feet in . -i o 3 g o r^b The True Sharks length. In the Upper Cretaceous is a very similar genus, Scapanorhynchus (lewisi, etc.), which Prof essor Woodward thinks may be even generically identical with Mitsukurina, though there is considerable difference in the form of the still longer rostral plate, and the species of Scapanorhynchus differ among themselves in this regard. Mitsukurina, with Heterodontus, Heptranchias, and Chlamy- dosclachc, is a very remarkable survival of a very ancient form. Fig. .32S. — Scapajwrhi/nchiix leii-if;i Davis. Family Mitsukurinida: Under side of .snout. (.AJter Woodward.) It is an interesting fact tliat the center of abundance of all these relics of ancient life is in the Black Current, or Gulf Stream, of Japan. Family Alopiidae, or Thresher Sharks. — The related family of Alopiidcv contains probably but one recent species, the great fox-shark, or thresher, found in all warm seas. In this species, Alopias inilpcs, the tail is as long as the rest of the body and bent upward from the base. The snout is verj^ short, and the teeth are small and cLise-set. The species reaches a length of about twenty-five feet. It is not especially ferocious, and the current stories of its attacks on whales probably arise from a mistake of the observers, who have taken the great killer, Orca, for a shark. The killer is a mammal, allied to the por- poise. It attacks the whale with great ferocitv, clinging to its flesh by its strong teeth. The whale rolls over and over, throwing the killer into the air, and sailors report it as a thresher. As a matter of fact the thresher very rarely if ever attacks any animal except small fish. It is said to use its tail in round- ing up and destroying schools of herring and sardines. Fossil teeth of thresher-sharks of some species are found from the ]\Iiocene. Family Pseudotriakidse. — The Pscndolriakidcc consist of two species. One of these is Psciidoiriakis inicrodoii, a laro-e shark The True Sharks 537 with a long low tail, long and low dorsal fin, and small teeth. It has been only twice taken, off Portugal and off Long Island. The other, the mute shark, Pseiidotriakis acrales, a large shark with the body as soft as a rag, is in the museum of Stanford University, having been taken by Mr. Owston off Misaki. Family Lamnidse. — To the family of Lavni-idcc proper belong the swiftest, strongest, and most voracious of all sharks. The chief distinction lies in the lunate tail, which has a keel on either side at base, as in the mackerels. This form is especially favorable for swift swim- ming, and it has been independently de- veloped in the mackerel-sharks, as in the mackerels, in the interest of speed in move- ment. The porbeagle, Lamna coniubica, known as salmon-shark in Alaska, has long been noted for its murderous voracity. About ^^.^^^ ^^g.-Tooth or Lam- Kadiak Island it destroys schools of na cuspidata Agassiz. 11 ii .u £ T J Oligocene. Fainilv salmon, and along the coasts of Japan, and Lamnidce. (After Xirh- especially of Europe and across to New olson.) England, it makes its evil presence felt among the fishermen. Numerous fossil species of Lamna occur, known by the long knife-like flexuous teeth, each having one or two small cusps at its base. Fig. 330 — Mackerel-shark, Isuropsis dekaiii Gill Pensarola, In the closely related genus, Isitriis, the mackerel-sharks, this cusp is wanting, while in Isuropsis the dorsal fin is set farther back. In each of these genera the species reach a length of 2o to 25 feet. Each is strong, swift, and voracious. 538 The True Sharks Isiints oxyrhynchus occurs in the Mediterranean, Isnropsis dekayi, in the Gulf of Mexico, and Isuropsis glauca, from Hawaii and japan westward to the Red Sea. Man-eating Sharks. — Equally swift and vastly stronger than these mackerel-sharks is the man-eater, or great white shark, Carcharodon carcharias. This shark, foimd occasionally in all warm seas, reaches a length of over thirty feet and has been known to devour men. According to Linnaeus, it is the animal which swallowed the prophet Jonah. " Jonam Prophetum," he observes, "ut veteris Herculem trinoctem, in hujus ventriculo tri- ^"/.;«r«.!~'^fc°!lafc dui spateo bcEsisse, verosimile est." (Agassiz). Mio- j^ ^g beyond comparison the most vo- cene. Family Zynm- ._,,., . , ^^ o ludce. (After Nich- racious of tish-hke animals. Near boquel, "'^""■^ California, the writer obtained a speci- men in 1880, with a young sea-lion (Zalophus) in its stomach. It has been taken on the coasts of Europe, New England, Caro- lina, California, Hawaii, and Japan, its distribution evidently girdling the globe. The genus Carcliarodon is known at once b}' its broad, evenly triangular, knife-like teeth, with finely serrated edges, and without notch or cusp of any kind. But one species is now living. Fossil teeth are found from the Eocene. One of these, Carcliarodon juce^alodoii (Fig. 332), from fish-guano deposits in South Carolina and elsewhere, has teeth nearly six inches long. The animal could not haA'e been less than ninety feet in length. These huge sharks can be but recently extinct, as their teeth have been dredged from the sea-bottom by the Cliallenger in the mid-Pacific. Fossil teeth of Lamna and Isiirus as well as of Carcharodon are found in great abundance in Cretaceous and Tertiary rocks. Among the earlier species are forms which connect these genera verv closely. The fossil genus Otodns must belong to the Lamnidcc. Its massive teeth with entire edges and blunt cusps at base are common in Cretaceous and Tertiary deposits. The teeth are formed much as in Lanina, but are blunter, heavier, and much less effective as instruments of destruction. The extinct genus Corax is also placed here by Woodward. The True Sharks 539 Family Cetorhinidse, or Basking Sharks.— The largest of all living sharks is the great basking shark (Ceiorhinus maximus), constituting the family of CetorhinidcB. This is the largest of all fishes, reaching a length of thirty-six feet and an enormous Fig. 332. — Carcharodon megalodon Charlesworth. (After Zittel.) Miocene. Family Lawnida weight. It is a dull and sluggish animal of the northern seas, almost as inert as a sawlog, often floating slowly southward in pairs in the spring and caught occasionally by whalers for its liver. When caught, its huge flabby head spreads out wide on the grotind, its weight in connection with the great size of the mouth-cavity rendering it shapeless. Although so clumsy and without spirit, it is said that a blow with its tail will crush f^o The True Sharks an ordinary whaleboat. The basking shark is known on all northern coasts, but has most frequently been taken in the Xorth Sea, and about Monterey Bay in California. From this locality specimens have been sent to the chief museums of Europe. In its external characters the basking shark has much m common with the man-eater. Its body is, however, rela- Fig. .333, — Basking Shark, Cetorhinus maximus (Gunner). France. tivclv clumsy forward; its fins are lower, and its gill-openings are much broader, almost meeting under the throat. The great difference lies in the teeth, which in Cetorhiiiiis are very small and weak, about 200 in each row. The basking shark, also called elephant-shark and bone-shark, does not pursue its prey, but feeds on small creatures to be taken without effort. Fossil teeth of CctorJiinus have been found from the Creta- ceous, as also fossil gill-rakers, structures which in this shark are so long as to suggest whalebone. Family Rhineodontidas. — The whale-sharks, Rhineodontida:, are likewise sluggish monsters with feeble teeth and keeled tails. From Cetorlmins they differ mainly in having the last gill-opening above the pectorals. There is probably but one species, Rhi)ieodon typicns,oi the tropical Pacific, straying north- ward to Florida, Lower California, and Japan. The Carcharioid Sharks, or Requins. — The largest family of re- cent sharks is that of Cardiariida: (often called Galeorhinidcr, or (jaleidcc), a modem offshoot from the Lamnoid type, and especially characterized by the presence of a third eyelid, the nictitating membrane, which can be drawn across the eye from The True Sharks 54 1 below. The heterocercal tail has no keel; the end is bent up- ward; both dorsal fins are present, and the first is well in front of the ventral fins; the last gill-opening over the base of the pectoral, the head normally formed ; these sharks are ovovivipa- rous, the young being hatched in a sort of uterus, with or without placental attachment. Some of these sharks are small, blunt-toothed, and innocuous. Others reach a very large size and are surpassed in voracity only by the various Lanniidcc. The genera Cv)n'a5 and Mnsteliis, comprising the soft -mouthed or hound-sharks, have the teeth flat and paved, while well- developed spiracles are present. These small, harmless sharks abound on almost all coasts in warm regions, and are largely used as food by those who do not object to the harsh odor of Fig. 334. ^Soup-fin Shark, Galeus zyopterus (Jordan & Gilbert). Monterey. shark's flesh. The best-known species is Cynias canis of the Atlantic. By a regular gradation of intermediate forms, through such genera as Rhinotriacis and Triakis with tricuspid teeth, we reach the large sharp-toothed members of this family. Galeus (or Galeorhinus) includes large sharks having spiracles, no pit at the root of the tail, and with large, coarsely serrated teeth. One species, the soup-fin shark (Galeus zyopterus), is found on the coast of California, where its fins are highly valued by the Chinese, selling at from one to two dollars for each set. The delicate fin -rays are the part used, these dissolving into a finely flavored gelatine. The liver of this and other species is used in making a coarse oil, like that taken from the dogfish. Other species of Galeus are found in other regions, Galeus galeus being known in England as tope, Galeus japonicus abounding in Japan. Galeocerdo differs mainly in having a pit at the root of the tail. Its species, large, voracious, and tiger-spotted, are found 542 The True Sharks in warm seas and known as tiger-sharks {Galeocerdo macidatus in the Atlantic, Galeocerdo tigrinus in the Pacific). The species of Carcharias {CarcharJiinus of Blainville) lack the spiracles. These species are very numerous, voracious, armed with sharp teeth, broad or narrow, and finely serrated on both edges. Some of these sharks reach a length of thirty feet. They are very destructive to other fishes, and often to fisher}' apparatus as well. They are sometimes sought as food, more often for the oil in their livers, but, as a rule, they arc rarely caught except as a measure for getting rid of them. Of the many species the best known is the broad-headed Carcharias lamia, or cub-shark, of the Atlantic. This the writer has taken with a great hook and chain from the wharves at Key West. These great sharks swim about harbors in the tropics, acting as Fig. 335. — (-'ub-shark, Carcharias Imnia Rafinesque. Florida. scavengers and occasionally seizing arm or leg of those who venture within their reach. One species {Carcharias iiicara- gnciisis) is found in Lake Nicaragua, the only fresh-water shark known, although some run up the brackish mouth of the Ganges and into Lake Pontchartrain. Carcharias japonicus abounds in Japan . A closely related genus is Prionace, its species Prionace glauca, the great blue shark, being slender and swift, with the dorsal farther back than in Carcharias. Of the remaining genera the most important is Scoliodon, small sharks with obhque teeth which have no serrature. One of these, Scoliodon ierrcc-iwvce, is the common sharp-nosed shark of our Carolina coast. Fossil teeth representing nearly ah of these genera are common in Tertiary rocks. Probably allied to the Carchariidce is the genus Corax, containing large extinct sharks of the Cretaceous wath broad- The True Sharks 543 triangular serrate teeth, very massive in substance, and without denticles. As only the teeth are known, the actual relations of the several species of Corax are not certainly known, and they may belong to the Lam- nidcB. Family Sphymidae, or Ham- mer-head Sharks. — The SpJiyrni- d(B, or hammer -headed sharks, are exactly like the Carcha- riidcB except that the sides of the head are produced, so as to give it the shape of a ham- Fig. 336.— Teeth of Corax mer or of a kidney, the eye prlstodonius. being on the produced outer edge. The species are few, but mostly widely distributed ; rather large, voracious sharks with small sharp teeth. The true hammer-head, Sphyrna zygcena, Fig. 337, is common from the Mediterranean to Cape Cod, California, Hawaii, and Japan. The singular form of its head is one of the most ex- traordinary modifications shown among fishes. The bonnet-head {Sphyrna tihiiro) has the head kidney-shaped or crescent-shaped. It is a smaller fish, but much the same in distribution and habits. Intermediate forms occur, so that with all the actual dift'erences we must place the SpJiyrnidoe all in one genus. Fossil hammer- heads occur in the Miocene, but their teeth are scarcely different from those of Carcharias. Sphyrna prisca, described by Agassiz, is the primeval species. The Order of Tectospondyli. — The sharks and rays having no anal fin and with the calcareous lamelte arranged in one or more rings around a central axis constitute a natural group to which, following Woodward, we may apply the name of Tecto- spondyli. The Cyclospondyli {Squalida:, etc.) with one ring only of calcareous lamellae may be included in this order, as also the rays, which have tectospondylous vertebrae and differ from the sharks as a group only in having the gill-openings relegated to the lower side by the expansion of the pectoral fins. The group of rays and Hasse's order of Cyclospondyli we may consider each as a suborder of Tectospondyli. The origin The True Sharks 54^ of this group is probably to be found in or near the Cestraciontes, as the strong dorsal spines of the SqiiaUda resemble those of the Heterodontida:. Suborder Cyclospondyli.— In this group the vertebra; have the calcareous lamelte arranged in a single ring about the cen- tral axis. The anal fin, as in all the tectospondylous sharks and^ rays, is wanting. In all the asterospondylous sharks, as in the Ichthyotomi, Acantliodei, and Chimccras, this fin is present. It is present in almost all of the bony fishes. All the species have spiracles, and in all are two dorsal fins. None have the nictitating membrane, and in all the eggs are hatched internally. Within the group there is considerable variety of form and structure. As above stated, we have a perfect gradation among Tedospondyli from true sharks, with the gih-openings lateral, to rays, which have the gill-opening on the ventral side, the great expansion of the pectoral fins, a character of relatively recent acquisition, having crowded the gill-openings from their usual position. \~ Family Squalidae. — The largest and most primitive family of Cyclospondyli is that of the Sqnalidcc, collectively known as dogfishes or skittle-dogs. In the Sqnalidcc each dorsal fin has a stout spine in front, the caudal is bent upward and not keeled, and the teeth are small and varied in form, usually not all alike in the same jaw. The genus Sqitaliis includes the dogfishes, small, greedy sharks abundant in almost all cool seas and in some tropical Fig. 338. — Dogfish, Squalus acanthias L. Gloucester, Mass. waters. They are known by the stout spines in the dorsal fins and by their sharp, squarish cutting teeth. They are largely sought by fishermen for the oil in their livers, which is used to adulterate better oils. Sometimes 20,000 have been taken in one 54^ The True Sharks haul of the net. They are very destructive to herrings and other food-fishes. Usually the fishermen cut out the hver, throwing the shark overboard to die or to be cast on the beach. In northern Europe and Xew England Sqiialns acanthias is abun- dant. Sqiiahts siicklii replaces it in the waters about Puget Sound, and Sqitalns mitsitkitrii in Japan and Hawaii. Still others are found in Chile and Australia, The species of Sqiialiis live near shore and have the gray color usual among sharks. Allied forms perhaps hardly different from Sqiiahis are found in the Cretaceous rocks and have been described as Coitrophoroides. Other genera related to Sqiialiis live in greater depths, from loo to 600 fathoms, and these are violet -black. Some of the deep- water forms are the smallest of all sharks, scarcely exceeding a -Etmopierus lucijer Jordan it Snyder. Misaki, Japan. foot in length. Etiiioptcriis spiiiax lives in the [Mediterranean, and teeth of a similar species occur in the Italian Pliocene rocks. Etuwptcrits liicifcr* a deep-water species of Japan, has a ' brilliant luminous glandular area along the sides of the bell3^ Other small species of deeper waters belong to the genera Centrophorus, Cejitroscyniuus, and Deaiiia. In some of these species the scales are highly specialized, pedunculate, or having the form of serrated leaves. Some species are Arctic, the others are most abundant about ilisaki in Japan and the Madeira Islands, two regions especially rich in semibathybial types. Allied to the Sqiialidcr is the small family of Oxynotidcr with short bodies and strong dorsal spine. Oxyiiotus centrina is found in the Mediterranean, and its teeth occur in the Miocene. Family Dalatiidee. — The Dalatiidce, or scymnoid sharks, differ from the Squalida almost solely in the absence of dorsal spines. The smaller species belonging to Dalatias (Scymnorhinus, or Scymnus), Dalatias licha, etc., are very much like the dog- * Dr. Peter Schmidt has made a sketch of this little shark at night from a living example, using its own light. H'f?' (Jf The True Sharks 547 fishes. They are, however, nowhere very common. The teeth of Dalatias major exist in Miocene rocks. In the genus Somniosus the species are of very much greater size, Somniosus microcephalus attaining the length of about twenty-five feet. This species, known as the sleeper-shark or Greenland shark, lives in all cold seas and is an especial enemy of the whale, from which it bites large masses of flesh with a ferocity hardly to be expected from its clumsy appearance. From its habit of feeding on fish-oft'al, it is known in New England as "gurry-shark." Its small quadrate teeth are very much like those of the dogfish, their tips so turned aside as to form a cutting edge. The species is stout in form and sluggish in movement. It is taken for its liver in the north Atlantic on both coasts in Puget Sound and Bering Sea, and I have seen it in the markets of Tokyo. In Alaska it abounds about the salmon canneries feeding on the refuse. Family Echinorhinidae. — The bramble-sharks, Echinorhimdcc , differ in the posterior insertion of the very small dorsal fins, and in the presence of scattered round tubercles, like the thorns of a bramble instead of shagreen. The single species, Echinorhi- niis spinosiis reaches a large size. It is rather scarce on the coasts of Europe, and was once taken on Cape Cod. The teeth of an extinct species, Echinorhinns richardi, are found in the Pliocene. Suborder Rhinae. — The suborder Rhino; in- cludes those sharks having the vertebrae tecto- spondylous, that is, with two or more series of calcified lamella;, as on the rays. They are transitional forms, as near the rays as the sharks, although having the gill-openings rather lateral than inferior, the great pectoral fins being separated by a notch from the head. The principal family is that of the angel- fishes, or monkfishes {Squatinida:). In this group the body is depressed and flat like that of a ray. The greatly enlarged pectorals form a sort of shoulder in front alongside of the gill-openings, which has suggested the bend of the angel's wing Fig. .340.— Brain of Monkfish, Squatina aqualina L. (After Dumeril.) 54! The True Sharks The dorsals are small and far back, the tail is slender with small fins, all these being characters shared by the rays. But one genus is now extant, widely diffused in warm seas. The species if really distinct are al! very close to the European Sqnatina squatina. This is a moderate-sized shark of sluggish liabit feeding on crabs and shells, which it crushes with its small, pointed, nail-shaped teeth. Ntimerous fossil species of Sqnatina are found from the Triassic and Cretaceous, Sqnatina alifera being the best known. Family Pristiophoridae, or Sawsharks. — Another highly aber- rant family is that of the sawsharks, Pristiophoridcc. These are small sharks, much like the Dalatiida in appearance, but with the snout produced into a long flat blade, on either side of which is a Fig. 341 — Sawshark, Fr/s^iop/iorws /opomais Giinther. Specimen from Nagasaki. row of rather small sharp enameled teeth. These teeth are smaller and sharper than in the sawfish (Pristis) , and the whole animal is much smaller than its analogue among the rays. This saw must be an effective weapon among the schools of herring and anchovies on which the sawsharks feed. The true teeth are small, sharp, and close-set. The few species of sawsharks are marine, inhabiting the shores of eastern Asia and Aus- tralia. PristiopJiorus japoiiicus is found rather sparsely along the shores of Japan. The vertebra? in this group are also tecto- spondylous. Both the Sqnati)ia and Pristiophorns represent a perfect transition from the sharks and rays. We regard them as sharks only because the gill-openings are on the side, not The True Sharks 549 crowded downward to the under side of the body-disk. As fossil, Pristiophorus is known only from a few detached verte- bras found in Germany. Suborder Batoidei, or Rays.— The suborder of Batoidei, Raja:, or Hypotrema, including the skates and rays, is a direct modern offshoot from the ancestors of tectospondylous sharks, its char- acters all specialized in the direction of life on the bottom with a food of shells, crabs, and other creatures less active than fishes. The single tangible distinctive character of the rays as a whole lies in the position of the gill-openings, which are directly below the disk and not on the side of the neck in all the sharks. This difference in position is produced tiy the anterior encroach- ment of the large pectoral fins, which are more or less attached to the side of the head. By this arrangement, which aids in giving the body the form of a flat disk, the gill-openings are limited and forced downward. In the Sqnatiiiidcc (angel-fishes) and the Pristioplwridcu (sawsharks) the gill-openings have an inter- mediate position, and these families might well be referred to the Batoidei, with which group they agree in the tectospondy- lous vertebraj. Other characters of the rays, appearing progressively, are the widening of the disk, through the greater and greater de- velopment of the fins, the reduction of the tail, which in the more specialized forms becomes a long whip, the reduction, more and more posterior insertion, and the final loss of the dorsal fins, which are always Avithout spine, the reduction of the teeth to a tessellated pavement, then finally to flat plates and the retention of the large spiracle. Through this spiracle the rays breathe while lying on the bottom, thus avoiding the danger of introducing sand into their gills, as wcmld be done if they breathed through the mouth. In common with the cyclospon- dylous sharks, all the rays lack the anal fin. The rays rarely descend to great depths in the sea. The dift'erent mcmliers have varying relations, but the groujj most naturally divides into thick-tailed rays or skates iSarcura) and whip-tailed rays or sting-rays {Masticiira). The former are much nearer to the sharks and also appear earliest in geological times. Pristididse, or Sawfishes. — The sawfishes, Pristididas, are long, shark-like rays of large size, having, Hke the sawsharks, the ^^o The True Sharks snout prolonged into a very long and strong fiat blade, with a series of strong enameled teeth implanted in sockets along either side of it. These teeth are much larger and much less sharp than in the sawsharks, but they are certainly homolo- gous with these, and the two groups must have a common de- scent, distinct from that of the other rays. Doubtless when taxonomy is a more refined art they will constitute a small suborder together. This character of enameled teeth on the snout would seem of more importance than the position of the gill-openings or even the flattening and expansion of the body. The true teeth in the sawfishes are blunt and close-set, pave- ment-like as befitting a ray. (See Fig. 152.) The sawfishes are found chiefly in river-mouths of tropi- cal America and West Africa: Pristis pectinatus in the West Flu. 312. — Sawfish, Pristis pectinatus Latham. Pensacola, Fla. Indies ; Pristis zephyreus in western Mexico ; and Pristis pecti- natus in the Senegal. They reach a length of ten to twenty feet, and with their saws they make great havoc among the schools of mullets and sardines on which they feed. The stories of their attacks on the whale are without foundation. The writer has never found any of the species in the open sea. They live chiefly in the brackish water of estuaries and river-mouths. Fossil teeth of sawfishes occur in abundance in the Eocene. Still older are vertebrae from the Upper Cretaceous at Maes- tricht. In Propristis scJiwciiifurtlii the tooth-sockets are not yet calcified. In Sclcrorhynchus ataviis, from the Upper Cretaceous, the teeth are complex in form, with a "crimped" or stellate base and a sharp, backward-directed enameled crown. Rhinobatidse, or Guitar-fishes. — The Rhinobatidcc (guitar- fishes) are long-bodied, shovel-nosed rays, with strong tails ; they are ovoviviparous, hatching the eggs within the body. The body, like that of the shark or sawfish, is covered with nearlv uniform shagreen. The numerous species abound in all warm seas; they are olive-gray in color and feed on small animals of the sea- The True Sharks 551 bottoms. The length of the snout differs considerably in different species, but in all the body is relatively long and strong. Most of the species belong to Rhinobatns. The best-known American species are Rhinobatns lentiginosus of Florida and Rhinohatus prodnctus of California. The names guitar-fish, fiddler-fish, etc., refer to the form of the body. Numerous fossil species, alhed to the recent forms, occur from the Jurassic. Species much like Rhinobatns occur in the Cretaceous and Eocene. Taniiobatis vetnstns, lately described by Dr. Eastman from a skull found in the Devonian of eastern Kentucky, the oldest ray-like fish yet known, is doubtless the type of a distinct family, Tamiobatida:. It is more likely a shark however than a ray, although the skull has a flattened ray-like form. Fig. 343. — Guitar-fish, Rhinohatus lentiginosus Garman. Charleston, S. C. Closely related to the RJiinobatidw are the Rhinida (Rham- phobatidce), a small family of large rays shaped like the guitar- fishes and foimd on the coast of Asia. Rhina ancyiostoma extends northward to Japan. In the extinct family of Astrodermidce, allied to the Rhino- batidcE, the tail has two smooth spines and the skin is covered with tubercles. In Belemnobatis sismonda: the tubercles are conical; in Astrodermns platypterns they are stellate. Rajidae, or Skates. — The RajidcE, skates, or rays, inhabit the colder waters of the globe and are represented by a large number of living species. In this family the tail is stout, with two- rayed dorsal fins and sometimes a caudal fin. The skin is variously armed with spines, there being always in the male two series of specialized spinous hooks on the outer edge of the pectoral fin. There is no serrated spine or "sting," and in all the species the eggs are laid in leathery cases, which are ss^ The True Sharks "wheelbarrow-shaped," with a projecting tube at each of the four angles. The size of this egg-case depends on the size of the species, ranging from three to about eight inches in length. In some species more than one egg is included in the same case. Most of the species belong to the typical genus Raja, and these are especially numerous on the coasts of all northern regions, where they are largely used as food. The flesh, although rather coarse and not well flavored, can be improved by hot butter, and as " raie au beurre noir" is appreciated by the epicure. The rays of ah have smaU rounded teeth, set in a close pavement. Some of the species, known on our coasts as "barn-door skates," reach a length of four or five feet. Among these are Raja lasvis and Raja occUata on our Atlantic coast. Raja binocn- •''^. (f ,,.,<. '^'"^ / tj Fig. 344. — Common Skate, Raja erinacea ilitchill. Wood's Hole, Mass. laia in California, and Raja tengii in Japan. The small tobacco- box skate, brown with black spots, abundant on the New England coast, is Raja erinacea. The corresponding species in Cali- fornia is Raja inoruata, and in Japan Raja kcnojei. Numerous other species. Raja batis, clavata, circiilaris, fullonica, etc., occur on the coasts of Europe. Some species are variegated in color, with eye-like spots or jet-black marblings. Still others, living in deep waters, are jet-black with the body very soft and The True Sharks 553 limp. For these Garman has proposed the generic name Mala- corhimis, a name which may come into general use when the species are better known. In the deep seas rays are found even under the equator. In the south-temperate zone the species are mostly generically distinct, Psammobatis being a typical form, differing from Raja. Discobatiis sinensis, com- mon in China and Japan, is a shagreen-covered form, looking like a Rhinobatns. It is, however, a true ray, laying its eggs in egg-cases, and with the pectorals extending on the snout. Fossil Rajidcc, known by the teeth and bony tubercles, are found from the Cretaceous onward. They belong to Raja and to the extinct genera Dyiiatobatis, Oncobatis, and Acanthobatis. The genus ArtJiroptcrits (rileyi), from the Lias, known from a large pectoral fin, with distinct cylindrical- jointed rays, may have been one of the Rajidcc, or perhaps the type of a distinct family, Arthropterida. Narcobatidse, or Torpedoes. — The torpedoes, or electric rays {Narcobatida), are characterized by the soft, perfectly smooth Fig. 345. — Numbfish, Narcme hrasiliensis Henle, showing electric cells. Pensacola, Fla. skin, by the stout tail with rayed fins, and by the ovoviviparous habit, the eggs being hatched internaUy. In all the species is developed an elaborate electric organ, muscular in its origin and composed of many hexagonal cells, each filled with soft fluid. These cehs are arranged under the skin about the l)ack 554 The True Sharks of the head and at the base of the pectoral fin, and are capable of Ijenumbing an enemy by means of a severe electric shock. The exercise of this power soon exhausts the animal, and a certain amount of rest is essential to recovery. The torpedoes, also known as crampfishes or numbfishes, are peculiarly soft to the touch and rather limp, the substance consisting largely of watery or fatty tissues. They are found in all warm seas. They are not often abundant, and as food they have not much value. Perhaps the largest species is Tctrouarcc occidentalis, the crampfish of our Atlantic coast, black in color, and said some- times to weigh 2 00 pounds. In California Tetronarce cali- f arnica reaches a length of three feet and is very rarely taken, in warm sandy bays. Tetronarce nobiliana in Europe is much like these two American species. In the European species, Narcobatns torpedo, the spiracles are fringed and the animal is of smaller size. To A'arcine belong the smaller numbfish, or " entemedor, " of tropical America. These have the spiracles close behind the eyes, not at a distance as in Narcobatns and Tetronarce. A'arciuc brasilioisis is found throughout the West Indies, and Narcine entemedor in the Gulf of California. Astrapc, a genus with but one dorsal fin, is common in southern Japan. Fossil Xareobatiis and Astrapc occur in the Eocene, one speci- men of the former nearly five feet long. A'ertebra^ of Astrape occur in Prussia in the amber-beds. Petalodontidae. — Near the Squatinidcc, between the sharks and the rays, Woodward places the large extinct family of Petalodontidcv, with coarsely paved teeth each of which is elongate with a central ridge and one or more strong roots at base. The best-known genera are Jatiassa and Petalodus, widely distributed in Carboniferous time. fanassa is a broad fiat shark, or, perhaps, a skate, covered with smooth shagreen. The large pectoral fins are grown to the head ; the rather large ventral fins are separated from them. The tail is small Fig. .3-tG.— Teeth of Janassa lin- gufcformis Attley. Carl:)oni('erous. Family Petalodonlidaj. (After Nicholson.) The True Sharks 5SS Fig. 347. — PnJi/rhizodus radicans Agas- siz. Family Pelalodontidoe. Carbon- iferous of Ireland. (After McCoy.) and the fins, as in the rays, are without spines. The teetli bear some resemblance to those of Myliobatis. Janassa is found in the coahmeasures of Europe and America, and other genera extend upward from the Sub- carboniferous hmestones, dis- appearing near the end of Car- boniferous time. Petalodiis is equaUy common, but known only from the teeth. Other widely distributed genera are Cienoptychins and Polyrhizodns. These forms may be intermediate between the skates and the sting-rays. In dentition they resemble most the latter. Similar to these is the extinct family of Pristodontidcc with one large tooth in each jaw, the one hollowed out to meet the other. It is supposed that but two teeth existed in life, but that is not certain. Nothing is known of the rest of the body in Pristodns, the only genus of the group. Dasyatidae, or Sting-rays. — In the section Masticiira the tail is slender, mostly whipdike, without rayed dorsal or caudal fins, and it is usually armed with a very long spine with saw- teeth projecting backward. In the typical forms this is a very effective weapon, being wielded with great force and making a jagged wound which in man rarely heals without danger of blood-poisoning. There is no specific poison, but the slime and the loose cuticle of the spme serve to aggravate the irregu- lar cut. I have seen one sting-ray thrust this spine through the body of another lying near it in a boat. Occasionally two or three of these spines are present. In the more specialized forms of sting-rays this spine loses its importance. It be- comes very small and not functional, and is then occasionally or even generally absent in individuals. The common sting-rays, those in which the caudal spine is most developed, belong to the family of Dasyatidcr. This group is characterized by the small skate-like teeth and by the non-extension of the pectoral rays on the head. The skin is smooth or more or less rough. These animals lie flat on the sandy bottoms in nearly all seas, feeding on crabs and shellfish. All hatch the eggs within the body. The genus Urolophiis has a 556 The True Sharks rnunded disk, and a stout, short tail with a caudal fin. It has a strong spine, and for its size is the most dangerous of the sting- rays. Urolophus halleri, the Cahfornia species, was named for a young man who was stung by the species at the time of its first discovery at San Diego in 1863. Urolophus jamaicensis abounds in the West Indies, Urolophus inundus at Panama, and Urolo- phus fuscus in Japan. None of the species reach Europe. The true sting-ray (stingaree, or clam-cracker), Dasyatis, is more widely diffused and the species are very closely related. In these species the body is angular and the tail whip-like. Some Fig. 348. — Sting-ray, Dasyatis sahina Le Sueur. Galveston. of the Species reach a length of ten or twelve feet. None have any economic value, and all are disliked by fishermen. Dasyatis pastinaca is common in Europe, Dasyatis ccntrura along our Atlantic coast, Dasyatis sabiiia ascends the rivers of Florida, and Dasyatis dipternra abounds in the bay of San Diego. Other species are found in tropical America, while still others {Dasyatis akajei, kuhlii, zngci, etc.) swarm in Japan and across India to Zanzibar. Pteroplatca, the butterfly-ray, has the disk ver^^ much broader than long, and the trivial tail is very short, its httle spine more often lost than present. Different species of this genus circle the globe: Ptcroplatea maclura, on our Atlantic coast; Ptero- platca marmorata, in California; Pteroplatca japonica, in Japan; The True Sharks ^^y and Pteroplatea altavela, in Europe. They are all very much alike, oHve, with the brown upper surface pleasingly mottled and spotted. Sting-rays of various types, Taniiira, Urolophns, etc., occur as fossils from the Eocene onward. A complete skeleton called Xiphotrygon aciitidcns, distinguished from Dasyatis by its sharp teeth, is described by Cope from the Eocene of Twin Creek in Wyoming. Vertebrae of Urolophns are found in German Eocene. Cyclobatis (oligodactylits), allied to Urolophns, with a few long pectoral rays greatly produced, extending over the tail and forming a rayed wreath-like projection over the snout, is known from the Lower Cretaceous. Myliobatidse. — The eagle-rays, Alyliobattdcc, have the pec- toral fins extended to the snout, where they form a sort of rayed pad. The teeth are very large, flat, and laid in mosaic. The whip-like tail is much like that in the Dasyatidcs, but the spine is usually smaller. The eagle-like appearance is suggested by the form of the skull. The eyes are on the side of the head with heavy eyebrows above them. The species are destructive to clams and oysters, crushing them with their strong fiat teeth. In Aeiobatus the teeth are very large, forming but one row. The species Aetobatiis narinari is showily colored, brown with yellow spots, the body very angular, with long whip-like tail. It is found from Brazil to Hawaii and is rather common. In RIyliobatis: the teeth are in several series. The species are many, and found in all warm seas. Myliobatis aqitila is the eagle-ray of Europe, Myliobatis californicus is the batfish of California, and Myliobatis tobijei takes its place in Japan. In Rhinoptera the snout is notched and cross-notched in front so that it appears as if ending in four lobes at the tip. These "cow-nosed rays," or " whipparees," root up the soft bottoms of shallow bays in their search for clams, much as a drove of hogs would do it. The common American species is Rhinopteriis bonasus. Rhinoptera steindachneri lives in the Gulf of California. Teeth and spines of all these genera are common as fossils from the Eocene onwards, as well as many of the extinct genus, Ptychodns, with cyclospondylous vertebrae. Ptyclwdns main- milaris, rugosns, and decurrens are characteristic of the Creta- 5S^ The True Sharks ceous of England. Myliobatis dixoni is common in the Euro- pean Eocene, as is also Myliobatis toliapicus and Aetobatis Fig. 349 — Eagle-ray, Aetobatis narinari (Euphrasen). Cedar Keys, Fla. irregularis. Apocopodoii scriacus is known from the Cretaceous of Brazil. Family Psammodontidae. — The Psaiiiuiodoiitidcc are known only from the teeth, large, fiat, or rounded and finely dotted or roughened on the upper surface, as the name Psantjuodus {i/:djj/.io£, The True Sharks 559 sand ; oSovs, tooth) would indicate. The way in which the jaws lie indicates that these teeth belonged to rays rather than sharks. Numerous species have been described, mostly from the Subcarboniferous limestones. Archcrobatis gigas, perhaps, as its name would indicate, the primeval skate, is from the Subcarboniferous Hmestone of Greencastle, Indiana. Teeth of numerous species of Psammodiis and Copodus are found in ^ Fig. 350. — Devil-ray or Sea-de^al, Mania lirostris (Walhaum). Florida. many rocks of Carboniferous age. Psammodiis rugosus com- mon in Carboniferous rocks of Europe. Family Mobulidae. — The sea-devils, Mobididcc, are the mightiest of all the rays, characterized by the development of the anterior lobe of the pectorals as a pair of cephalic fins. These stand up like horns or ears on the upper part of the head. The teeth are small and flat, tubercular, and the whip-like tail is with or without spine. The species are few, little known, and in- ordinately large, reaching a width of more than twenty feet and a weight, according to Risso, of 1250 pounds. When har- pooned it is said that they will drag a large boat with great swiftness. The manta, or sea-devil, of tropical America is 560 The True Sharks ^ Mania birostris. It is said to be much dreaded by the pearl- fishers, who fear that it will devour them "after enveloping them in its vast wings." It is not likely, however, that the manta devours anything larger than the pearl-oyster itself. Mania hamilioni is a name given to a sea-devil of the Gulf of California. The European species Mobnla edentula reaches a similarly enormous size, and Mobiila hypostoma has been scantily described from Jamaica and Brazil. Mobiila japonica occurs in Japan. A fcetus in my possession from a huge specimen taken at Misaki is nearly a foot across. In IMobula (Ceplialoptera) there are teeth in both jaws, in Mania (Ceratoptera) in the lower jaw only. In Ccraiobatis from Jamaica (C. robertsi) there are teeth in the upper jaw only. Otherwise the species of the three genera are much alike, and from their huge size are little known and rarely seen in collections. Of Mobulidcs no extinct species are known. CHAPTER XXXI THE HOLOCEPHALI, OR CHIMERAS HE Chimaeras. — Very early in geological times, cer- ^. tainly as early as the middle Silurian, the type of Chiiiiccras diverged from that of the sharks. Hasse derives them directly from his hypothetical primitive Polyo- spondyli, by way of the Acanthodei and Ichthyotomi. In any event the point of divergence must be placed very early in the evolution of sharks, and this suggestion is as likely as any other. The chief character of Chimeras is found in the autostylic skull, which is quite different from the hyostylic skull of the sharks. In the sharks and in all higher fishes the mandible is joined to the skull by a suspensorium of bones or cartilages (quadrate, sym- plectic, and hyomandibular bones in the Teleost fishes). To this arrangement the name hyostylic is given. In the Chimsera there is no suspensorium, the mandible being directly attached to the cranium, of which the hyomandibular and quadrate elements form an integral part, this arrangement being called autostylic. The palato-quadrate apparatus, of which the upper jaw is the anterior part, is immovably fused with the cranium, instead of being articulated with it. This fact gives the name to the subclass Holocephali {o\oz, whole or solid; KecpaX?'/, head). Other characters are found in the incomplete character of the back-bone, which consists of a scarcely segmented notochord differing from the most primitive condition imagined , only in being surrounded by calcareous rings, no lime entering into the composition of the i.otochord itself. The tail is diphycercal and usually prolonged in a filament (leptocercal). The shoulder- girdle, as in the sharks, is free from the skull. The pectoral fins are short and broad, without segmented axis or archiptery- cfii r()2 The Holocephali, or Chimaeras gium and without recognizable analogue of the three large cartilages seen in the sharks, the propterygium, mesopterygium, and metapterygium. In the mouth, instead of teeth, are de- veloped flat, bony plates called tritors or grinders, set endwise in the front of the jaws. The giUs are fringe-like, free at the tips as in ordinary fishes, and there is a single external opening for them all as in true fishes, and they are covered with a flap of skin. These structures are, however, quite different from those of the true fishes and are doubtless independently de- veloped. There is no spiracle. The skin is smooth or rough. In the living forms and most of the extinct species there is a strong spine in the dorsal fin. The ventral fin in the male has complex, usually trifid, claspers, and an analogous organ, the cephaHc holder, is developed on the front of the head, in the adult male. This is a bony hook with a brush of glistening enameled teeth at the end. The eggs are large, and laid in oblong or elliptical egg-cases, provided with silky filaments. The eggs are fertihzed 5&tegr they are extruded. Mucous chan- nels and lateral line are highly developed, being most complex about the head. The brain is essentially shark-like, the optic nerves form a chiasma, and the central hemispheres are large. The teeth of the Chimasras are thus described by Woodward, vol. 2, pp. 36, 37: " In all the known families of Chimasroids, the dentition consists of a few large plates of vascular dentine, of which certain areas ('tritors') are specially hardened by the depo- sition of calcareous salts within and around groups of medullary canals, which rise at right angles to the functional surface. In most cases there is a single pair of such plates in the lower jaw, meeting at the symphysis, while two pairs are arranged to oppose these above. As a whole, the dentition thus closely resembles that of the typical Dipnoi (as has often been pointed out) ; and the upper teeth may be provisionally named pala- tine and vomerine until further discoveries shall have revealed their precise homologies. The structures are sometimes de- scribed as 'jaws,' and regarded as dentaries, maxillae, and premaxilliE, but the presence of a permanent pulp under each tooth is conclusive proof of their bearing no relation to the familiar membrane-bones thus named in higher fishes." The Holocephali, or Chimaeras 563 Relationship of Chimaeras. — As to the origin of the Chimasras and their relation to the sharks, Dr. Dean has this recent ("The Devonian Lamprey") and interesting word: "The Holocephah have always been a doubtful group, anatomy and pateontology contributing but imperfect evidence as to their position in the gnathostome phylum. Their em- bryology, however, is still undescribed, except in a brief note by T. J. Parker, and it is reasonably looked to to contribute evidence as to their line of descent. The problem of the relation- ships of the ChimEeroids has long been of especial interest to me, and it has led me to obtain embryonic material of a Pacific species of one of these forms. It may be of interest in this connection to state that the embryology of this form gives the clearest evidence that the wide separation of the Selachii and Holocephali is not tenable. The entire plan of develop- ment in Cliimara coUiei is clearly like that of a shark. The ovulation is closely like that of certain of the rays and sharks: the eggs are large, the segmentation is distinctly shark-like; the circular blastoderm overgrows the yolk in an elasmobranchian manner. The early embryos are shark-like; and the later ones have, as T. J. Parker has shown, external gills, and I note further that these arise, precisely as in shark-embryos, from the posterior margin of the gill-bar. A spiracle also is present. A further and most interesting developmental feature is the fact that the autostylism in Chinicrra is purely of secondary nature and is at the most of ordinal value. It is found that in a lar\'a of Chimccra measuring 45 mm. in length, the palato -quadrate cartilage is still separated from the skull by a wide fissure. This becomes gradually reduced by the con- fluence of the palato-quadrate cartilage with the skull, the fusion taking place at both the anterior and posterior ends of the mesal rim of the cartilage. The remains of the fissure are still well marked in the young Chimara, four inches in length; and a rudiment of it is present in the adult skull as a passage- way for a nerve. Regarding the dentition; it may also be noted in the present connection that the growth of the dental plates in ChmcEra suggests distinctly elasmobranchian con- ditions. Thus on the roof of the mouth the palatine plates are early represented by a series of small more or less conical 564 The Holocephali, or Chima;ras elements which resemble outwardly, at least, the 'anlagen' of the pavement teeth in cestraciont sharks." Family Chimgeridee. — The existing Chimasras are known also as spookfishes, ratfishes, and elephant-fishes. These are divided by Garman into three families, and in the principal family, the Cliimcrridcc, the snout is blunt, the skin without plates, and the dorsal fin is provided with a long spine. The flat tritors Fig. 351. — Skeleton of Chimirra monstrosa Linnaeus. (After Dean.) vary in the different genera. The single genus represented among living fishes is CJiiincrra, found in cold seas and in the oceanic depths. The best-known species, ChinuTra colliei, the elephant-fish, or chimara of California, abotuids in shallow waters of ten to twenty fathoms from Sitka to San Diego. It is a harmless fish, useless except for the oil in its liver, and of special interest to anatomists as the only member of the family to be found when desired for dissection. This species was first found at Monterey by Mr. Collie, naturalist of Captain Beechey's ship, the Blossom. It is brown in color, with whitish spots, and reaches a length of 2\ feet. As a shallow-water form, with certain difterences in the claspers and in the tail, Chimccra collici is sometimes placed in a distinct genus, Hydro- lagus. Other species inhabit much greater depths and have the tail produced into a long filament. Of these, Chuiurra monstrosa, the sea-cat of the north Atlantic, has been longer known than any other Chimfera. Chimccra afjinis has been dredged in the Gulf Stream and oft' Portugal. Cluiiicrra pJian- tasma and Clnmara mitsuknrii are frequently taken in Japan The Holocephali, or Chimsras 565 and the huge jet-black Chimara piirpiirascens in Hawaii and Japan. None of these species are valued as food, but all impress the spectator with their curious forms. The fossil Chimccridce, although numerous from Triassic times and referred to several genera, are known chiefly by their teeth with occasional fin-spines, frontal holders, or impressions of parts of the skeleton. The earhest of chimieroid remains has 4 t3^^ "^"'«m, ,_ Fig. 352. — Elephant-fish, Chimcera colliei Lay & Bennett. Monterey. been described by Dr. Charles D. Walcott * from Ordovician or Lower Silurian rocks at Canon City, Colorado. Of the species called Dictyorhabdus priscus, only parts supposed to be the sheath of the notochord have been preserved. Dr. Dean thinks this more likely to be part of the axis of a cephalopod shell. The definitely known CJiimccridcB are mainly confined to the rocks of the Mesozoic and subsequent eras. Ischyodiis priscus iavitus) of the iower Jura resembles a modern chimasra. Granodus oweni is another extinct chimera, and numerous fin-spines, teeth, and other fragments in the Cretaceous and Eocene of America and Europe are referred to EdapJiodon. A species of Chinicsra has been recorded from the Pliocene of Tuscany, and one of Callorhynchus from the greensand of New Zealand. Other American Cretaceous genera of chimieroids are Adylognathus, Bryactiniis, Isotcrnia, Leptomylus and SpJiagepcca. Dental plates called Rhynchodus are found in the Devonian. Rhinochimaeridse. — The most degenerate oi existing chima^ras belong to the family of Rhinochimasridcc , characterized by the long flat soft blade in which the snout terminates. This struc- * Bulletin Geol. Soc. America, 1S92. 5 66 The Holocephali, or ChimsEras ture resembles that seen in the deep-sea shark, Mitsnkurina, and in Polyodou. In Rhinochhnara pacifica of Japan the teeth in each jaw form but a single plate. In Harriotta raleighana, of the Gulf Stream, they are more nearly as in Chimara. Both are bathybial fishes, soft in texture, and found in great depths. The family of CallorUynchidcr, or Antarctic Chimaeras, includes the bottle-nosed Chimaera (Callorhynchiis callorhynchus) of the Patagonian region. In this species the snout is also produced, a portion being turned backward below in front of the mouth, forming a sensory pad well supplied with nerves. Extinct Chimaeroids. — According to AVoodward, three other families are recognizable among the extinct forms. The Ptyctodontids are known from the teeth only, a single pair of large, laterally compressed dental plates in each jaw, with a few hard tritoral areas. These occur in Silurian and Devonian rocks. Ptyctodns obliqnns from the Devonian of Russia is the best-known species. Other genera are RJiyn- chodits and Palccomyliis. The Sqiialorajidcc have the head depressed and the snout produced in a flat rostrum, as in Harriotta. There is no dorsal spine, and the teeth are a few thin curved plates. The frontal holder of the male is well developed. The few species occur in the Lias. Sqiialoraja dolicliognatJios is known from numerous fragments from the Triassic in England and Scotland. Clialcodiis perniianus is found in German Permian. The RIyriacaiitliidcc have the body elongate, with dermal plates on the head and a long straight spine in the dorsal fin. The frontal holder is large. The species, few in number, are found in i\Iesozoic rocks. MyriacaiitJiiis paradoxus is the best- known species. Of another species, CJiimccropsis paradoxa, a skeleton about three feet long has been found which shows a number of peculiar traits. The skin is covered with ribbed shagreen scales. The dorsal fin has a large spine with retrorse serrations behind. The tail is slim, and the pectoral and ven- tral fins are very large. Bony plates with conical spines protect the neck. The teeth are large and angular, of peculiar form. Ichthyodorulites. — The term ichthyodorulite {ixdvs, fish; dopv, lance; XiBo?, stone) is applied to detached fin-spines, dermal spmes, and tubercles belonging to unrecognized species of The Holocephali, or Chimasras 567 sharks and chimeras. Some of these are serrated, others entire, some straight, some curved, and some with elaborate armature or sculpture. Some doubtless belong to Cestraciontes, others to Pleuracanthida ; some to Sqnalida;, some to chimaeras, and others, perhaps, to forms still altogether unknown. CHAPTER XXXII THE CLASS OSTRACOPHORI * I STRACOPHORES. — Among the earliest vertebrates act- ually recognized as fossils belongs the group known as Ostracophori {ocrrpaKoz, a box; (popeco, to bear). These are most extraordinary creatures, jawless, apparently limb- less, and enveloped in most cases anteriorly in a coat of mail. In tvpical forms the head is very broad, bony, and horseshoe- shaped, attached to a slender body, often scaly, with small fins and ending in a heterocercal tail. What the mouth was like can only be guessed, but no trace of jaws has yet been found in connection with it. The most remarkable distinctive character is found in the absence of jaws and limbs in connec- tion with the bony armature. The latter is, however, sometimes obsolete. The back-bone, as usual in primitive fishes, is de- veloped as a persistent notochord imperfectly segmented. The entire absence of jaw structures, as well as the character of the armature, at once separates them widely from the mailed Arthro- Jircs of a later period. But it is by no means certain that these structures were not represented by soft cartilage, of which no traces have been preserved in the specimens known. * This ,^roup was first called by Cope Ostracoderiiii — a name preoccupied for the group" of bony trunkfishes, Oslracidcu. The still earlier name of Placodcrmi, chosen by McCoy (1S4S), was intended to include Arthrodires as well as Ostracophores. Rohon (1892) calls the group Proioccphali, and to the two orders he assigns the names Asf^idorhmi and Aspidoccphali. These groups correspond to Hclcrostraci and Osleostraci of Woodward, Another name of early date is that of Aspidoganoidei, given by Professor Gill in 1S76, but not defined until 1896. These fishes are, however, not "Ganoids" and the name Ostracophori seems to receive general preference. The group Pcl- iaccphalaia of Patten corresponds essentiaUy to Ostracophori, as does also the order Hypostomata of Gadow. =;68 The Class Ostracophori 569 Nature of the Ostracophores. — The Ostracophores are found in the Ordovician or Lower Silurian rocks, in the Upper Silu- rian, and in the Devonian. After the latter period they dis- appear. The species are very numerous and varied. Their real affinities have been much disputed. Zittel leaves them with the Ganoids, where Agassiz early placed them, but they show httle homology in structure with the true Ganoids. Some have regarded them as aberrant Teleosts, possibly as freakish catfishes. Cope saw in them a huge mailed group of archaic Tunicates, while Patten has soberly and with considerable plausibility urged their affinity* to the group of spiders, es- pecially to the horseshoe-crabs {Liiuulns) and their palaeozoic ancestors, the Eurypteridcc and Merostomata. The best guess as to the affinities of the Ostracophores is perhaps that given by Dr. Ramsey H. Traquair ("Fossil Fishes of the Silurian Rocks of the South of Scotland," 1899). Tra- quair regards them as highly aberrant sharks, or, more exactly, as being derived, like the Chimasras, from a primitive Elas- * According to Professor Patten's view, the close resemblance of the shields of Pteraspis to those of contemporaneous Euryplerids indicates real affinity. But the Eurypterids are related to the spiders and to Liinulus. The only reason for thinking that Pteraspis is a fish at all lies in its resemblance to Cepkalaspis, which is in several ways fish-like, althovigh its head shield is much like that of Liiuulus. All these resemblances in Patten's \'ie\v indicate real affinity. Patten considers the Ptcraspids as derived from prmiitive arachnid or spider-like forms having a bony carapace as L-iiiiulns has. From Pteraspis he derives the other Ostracophores, and from these the sharks and other vertebrates, all of which appear later in time than the earliest Ostra- cophores. This view of the origin of vertebrates is recently urged with much force by Professor Patten (Amer. Nat., 1904, 1S27). Most naturalists regard such resemblances in specialized structures on the outside of an animal as parallelisms due to likeness in conditions of life. The external structure in forms of really difi^erent nature is often similarly modified. Thus certain catfishes, pipefishes, sea-moths, and agonoid fishes are all provided with bony plates not unlike those of ganoid fishes, although indicative of no real alVinity with them. Commonly the ancestry of vertebrates is traced through euterop- neustans to soft-bodied worms which have left no trace in the rocks. In the same conneetion. Professor Patten suggests that the lateral fold from which many writers have supposed that the limbs or paired fins of \-erte- brates is evolved is itself a resultant of the fusion of the fringing appendages on the sides of the body. Such appendages are found in the primiti\'e mailed arachnoids and in Limntus. They are shown very plainly in Patten's restora- tion of Cepkalaspis. About thirty of them of a bony nature and jointed to the body occur on either side between the gill opening and the vent. 57° The Class Ostracophori nil ibrancli stock. In favor of this view is the character of their armature, the bony plates themselves to be regarded as formed by the fusion of shagreen grains or scales. According to Tra- quair: "Specialization from the most specialized fonn, Lanar- kia. has been accompanied by (i) fusion of the spinelets {Lanar- kia) or shagreen grains {Thelodns) into plates, scutes, and rhombic scales, supported by hard matter developed in a deeper /■'■ _- - . ''^ /^ ■4 ^ <* Fig. 3.53. Fig. 354. Fig. 353.— 0(^o?itotodi(s schrencki (Pander) (Tremalaspis), ventral side. Island of Oesel. (After Patten.) Fig. 354.—Odontotodtis schnncki (Pander) (Tremataspis) , dorsal side. Island of Oesel. (After Patten.) layer of skin, and (2) alterations in the pectoral fin-flaps, which, becoming covered up by the postero-lateral plates inDrcpanaspis, are finally no longer recognizable in the Pteraspidw." Woodward leaves their exact relationship undefined, while others have regarded them as mailed lampreys, at any rate to be excluded from the Gnatliostoini, or jaw-bearing series. The apparent absence of true jaws, true limbs, and limb-girdles certainly seems to separate them widely from true fishes, but these characters are negative only, perhaps due to degeneration, and at any rate they are not yet absolutely determined. Cer- tainly they offer no positive proof of affinity with the modem Cyclostomes. The Class Ostracophori 571 Dr. Traquair regards the Hctcrostraci or most primitive Ostracophores as most certainly derived from the Elasmo- branchs. Other writers have attacked the integrity of the group of Ostracophores, questioning the mutual relationship of its component parts. Reiss, for example, regards the asso- ciation of the Osteostraci with the Hctcrostraci as "unbegrundet" and "-unheilvoll," while Ray Lankester, as quoted by Traquair, affirms that "there is absolutely no reason for regarding Cepha- laspis as allied to Ptcraspis beyond that the two genera occur Fig. 355. — Head of Odontotodus schrencki Pander, from the side. (After Patten.) in the same rocks, and still less for concluding that either has any connection with Pterichthys." Elsewhere Lankester states that the Heterostraci are associated at present with the Osteo- straci, "because they have, like Cephalaspis, a large head-shield, and because there is nothing else with which to associate them." Patten, on the other hand, seems inclined to deny the rank of Heterostraci and Osteostraci as even separate orders, regarding them as very closely related to each other as also to their sup- posed spider-like ancestors. But the consensus of opinion favors the belief that the four orders usually included under this head are distinct and at the same time are really related one to another. For our purposes, then, we may regard the Ostracophori as a distinct class of vertebrates. By placing it after the Elasmobranchs we may indicate its probable descent from a primitive shark- like stock. On this subject Dr. Dean remarks: "The entire problem of the homology of the dermal plates and ' scales ' in the Ostra- cophores and Arthrognaths is to the writer by no means as clear as previous writers have conceded. From the histologi- cal standpoint, admitting the craniote nature of the vaso- dentine and cancellous layers in the dermal plates, it never- theless does not follow that they have been derived from the The Class Ostracophori 57- actual conditions of the dermal denticles of the ancestral Gnatho- st. .me, as were unquestionably the dermal plates of Teleostomes and Dipnoans. It seems equally if not more probable, on tlie other hand, that the dermal armoring of the distinct groups ma)' have had an altogether different mode of origin, the product Fig. 356. — The Horseshoe Crab or King-crab, Limulus polyphfmu^ Linna?us. Sup- posed by Professor Patten to be an ally of the Ostracophores ; usually re- garded as related to the Spiders. of a crude evolution which aimed to strengthen the skin by a general deposition of calcareous matter throughout its entire thickness. The tuberculation of plates thus acquired might have become an important step in the development of a more superficial type of armoring which is most preferably represented bv the dermal denticles of Selachians. Not, in passing, need the presence of a mucus-canal system in the early plated forms be of greater morphological importance than a foreshadowing of the conditions of Gnathostomes, for this system of organs The Class Ostracophori 573 might serve as well as evidence, in a general way, of relationship with Marsipobranchs. Nor is this evidence the more conclu- sive when we reflect that no known type of Gnathostome, recent or fossil, possesses open sensory grooves in distinct dermal plates. The presence, furthermore, of a dorsal fin and a 'truly piscine heterocercal tail,' as noted by Traquair, is by no means as Gnathostome-like as these structures at first glimpse appear. For they lack not m.erely the characteristic radial supports of fishes, but even actinotrichia. Their mode of support, on the other hand, as Smith Woodward points out, is of a more gener- ahzed nature, bent scales, homologous with those of the adja- cent body region, taking the place of the piscine external sup- ports." The actual position in the system to be finally as- signed to the Ostracophores is therefore still uncertain. Orders of Ostracophores. — Four orders of Ostracophori are now usually recognized, known in the systems of Woodward and Traquair as Heterostraci, Osteostraci, Antiarcha, and Anaspida. The former is the most primitive and perhaps the most nearly allied to the sharks, the second is not very remote from it, the last two aberrant in very different directions. Hay places the Antiarcha with the Arthrodira under the superorder of Placodermi. Order Heterostraci. — The Heterostraci (erepos, different ; oarpa- Koz, box) have no bone-corpuscles in the coat of mail. This typically consists of a few pieces above, firmly united and traversed by dermal sense-organs or "lateral lines." The ventral shield is simple. Four families are recognized by Traquair as constituting the Heterostraci, these forming a con- tinuous series from shark-like forms to the carapace-covered Pteraspis. In the most primitive family, the Thelodontidcc ,* the head and trunk are covered with small scales or tubercles of dentine and not fused into large plates. The tail is slender and heterocercal, the caudal fin deeply forked. Until lately these tubercles were regarded as belonging to sharks, and they are still regarded by Traquair as evidence of the affinity of the Heterostraci with the Acanthodei. Dr. Traquair thinks that a flap or laj pet-like projection behind the head may be * Called Coilolepidii by Pander and Traquair, but Ccelolepis is a later synon)mi of Thetodus. r74 The Class Ostracophori a pectoral fin. The three known genera are Thelodus, Lanarkia, and Atcleaspis. In Thelodus the scales consist of a base and a crown separated by a constriction or neck. Thelodus scoUcus, Thelodus pagei, and Thelodus planus are found in the Silurian rocks of Scotland. Other species, as Thelodus tulensis of Russia, extend to the Upper Devonian. In Lanarkia the large sharp scales have an expanded base like the mouth of a trumpet. Lanarkia Iwrrida and L. spimdosa are found in the shire of Lanark in Scotland. In Ateleaspis (tessclatits) the skin is covered with small polygonal plates. The lateral flaps or possibly fins take the form of flat rhombic sculp- Fig. 357. — Lanarkia spinosa Traquair. Upper riilunan. Family Thelodontidcc . (After Traquair.) tured scales. In this genus the eyes seem to be on the top of the head. In the Psammosteidcc of the Devonian the head is covered with large plates which are not penetrated by the sense-organs. These plates are covered with minute, close-set tubercles, covered with brilliant ganoid enamel and with finely crimped edges. According to Dr. Traquair, these tubercles are shagreen granules which have coalesced and become united to plates formed in a deeper layer of the skin, as in Ateleaspis the minute scales have run together into polygonal plates. These crea- tures have been considered as "armored sharks," and Dr. Traquair regards them as really related to the acanthodean sharks. Nevertheless they are not really^ sharks s.t all, and they find their place with the Pteraspis and other longer known Heterostracans. The family of Drepanaspida; consists of a single recently known species, Drepanaspis gnmndenensis , found in a pyritized condition The Class Ostracophori 57S in purple roofing-slate in Gmiinden, Germany. This fish, which reaches a length of about two feet, has a broad head, with eyes on its outer margin, with a slender body and heterocercal tail. The head has a broad median plate and smaher polygonal ones. The flaps, supposed to represent the pectoral fins, are here cased in immovable bone. No trace of internal skeleton is Fig. 358. — Drepanaspis gmundenensis Schluter. Upper Silurian, Ginunden, Germany. (After Traquair.) found by Traquair, who has given the restoration of this species, but the mouth has been outlined. The best known of the Heterostracan families is that of Pteraspidcr. In this family the plates of the head are coalesced in a large carpace, the upper part originally formed of seven coalesced pieces. A stout dorsal spine fits into a notch of the carapace. The slender body is covered with small scales and Fig. 359. — Pteraspis rostrata Agassiz. Devonian. Family Pteraspidce . (After Nicholson.) ends in a heterocercal tail. The dermal sense-organs are well developed. Pteraspis rostrata occurs in the Lower Devonian. Other gen(jra are PaUsaspis and Cyrthaspis. Order Osteostraci. — The Osteostraci (oVreoK, bone; ocrrpaKoi^ box) (called Aspidocephali by Rohon) have bone-corpuscles in the shields, and the shield of the back is in one piece without 576 The Class Ostracophori lateral-line channels or sense-organs. Ventral shield single. The order includes three famiUes. The Cephalaspida: have the shields tuberculate, the one between the eyes fixed, and the anterior body-shields are not fused into a continuous plate. The best known of the numerous species is Cephalaspis lyelli from the Lower Devonian of England. Hemicy- claspis mnrchisoni occurs in the Upper Silurian of England, and the extraor- dinary Cephalaspis dawsoni in the Lower Devonian of Gaspe, Canada. Eukcraspis pnstiilifera has the head- shield very slender and armed with prickles. In the Thyestidcr the anterior bodv-scales are fused into a continuous plate. Tliyestis and Didymaspis are genera of this type. The Odontotodon- tidcr (Tnviiataspida:) have the shield truncate behind, its surface finely punctate, and the piece between the eyes not fixed. Odontotodiis * sdirenki is found in the Upper Silurian of the Island of Oesel in company with species of Thyestes. The Eiiphaiieropidcc are represented in the Devonian of Quebec. Order Antiarcha. — The Antiarcha (avri, opposite; apxoi', anus) have also bone-corpuscles in the plates, which are also enameled. The sense-organs occupy open grooves, and the dorsal and ventral shields are of many pieces. The head is jointed on the trunk, and jointed to the head are paddle-like appendages, covered with bony plates and resembling limbs. There is no evidence that these erectile plates are real limbs. They seem to be rather jointed appendages of the head-plate, erectile on a hinge like a pectoral spine. There are traces of ear-cavities, gill-arches, and other fish-like structures, but nothing sug- gestive of mouth or limbs. This group contains one family, the Asterolepidcc, with numer- ous species, mostly from Devonian rocks. The best known genus is Ptcnchthyodes,'t in which the anterior median plate * This name, inappropriate or meaningless, is older than Troiiataspjs. t The earlier name of Picrichthys has been already used for a genus of liv- ing fishes. Fig. 360. — Cephalaspis lyelli Agassiz, restored. (After Agassiz.) The Class Ostracophori S71 of the back is overlapped by the posterior dorso-lateral. Pter- ichthyodes milleri from the Lower Devonian, named by Agassiz for Hugh Miller, is the best known species, although numer- ous others, mostly from Scottish quarries, are in the British Fig. 361. — Cephalaspis dawsoni Lankester. Lower Devonian of Canada. Family CephalaspidcE. (After Woodward.) In the square a portion of the tubercular surface is shown. Museum. Asterolepis maximus is a very large species from the same region, known from a single plate. Bothriolepis canadensis is from the Upper Devonian of Scaumenac Bay near Quebec, numerous specimens and fragments finely preserved having been found. Microhrachium dicki with the pectoral appendages small occurs in the Devonian of Scotland. The earliest remains of Ostracophori are found in Ordovi- cian or Lower Silurian rocks of the Trenton horizon at Canon 578 The Class Ostracophori City, Colorado. These consist of enormous numbers of small fragments of bones mLxed with sand. With these is a portion of the^ head carapace of a smaU Ostracophore which has been named by Dr. Walcott Asteraspis desiderata and referred provi- sionally to the family of Asterolepidcz, which belongs otherwise to the Lower Devonian. Fig. 362 -Pterichthyodes testudinariiis (Agassiz), restored. Lower Devonian Family Asterolepida-. (After Traquair and others.) With these remains are found also scales possibly belonging to a Crossopterygian fish (Eriptycliiits). These remains make it evident that the beginning of the fish series lies far earlier than the rocks called Silurian, although fishes in numbers are not elsewhere known from rocks earlier than the Ludlow shales of the Upper Silurian, corresponding nearly to the Niagara period in America. In the Ludlow shales we find the next appearance of the The Class Ostracophori 570 Ostracophores, two families, Thelodontidw and BirkeniidcE, being there represented. ^ Order Anaspida. — Recently a fourth order, Anaspida (a, without; daTtis, shield), has been added to the Ostracophori through the researches of Dr. Traquair. This group occurs Fig. 363. — Pterichthyodes tesludinariiis Agassiz, side view. (After Zittel, etc.) in the Upper Silurian in the south of Scotland. It includes the single family Birkeniidcc, characterized by the fusiform body, bluntly rormded head, bilobate, heterocercal tail, and a median row of hooked spinous scales along the ventral margin. No trace of jaws, teeth, limbs, or internal skeleton has been Fig. 364. — Birkenia ehgans Traquair. Upper Silurian. (After Traquair.) fotmd. Unlike other Ostracophores, Birkenia has no cranial buckler with orbits on the top, nor have the scales and tubercles the microscopic structure found in other Ostracophores. In the genus Birkenia the head and body are completely covered by tubercular scutes. The gill-openings seem to be represented by a series of small perforations on the sides. A dorsal fin is present. Birkenia elegans is from the Ludlow and Downstonian rocks of southern Scotland. Lasianitts problematiciis from the same rocks is very similar, but is scaleless. It has a row of ventral plates like those of Birkenia, the only other hard parts it 58o The Class Ostracophori possesses being a number of parallel rods behind the head, homologous with the lateral series of Birkenia. Lasianius is therefore a specialized and degenerate representation of Bir- FiG. 365. — Lasianius problemaHcus Traquair. Upper Silurian. (After Traquair.) keiiia, differing somewhat as "the nearly naked Phanerosteon differs from other Palmoniscida whose bodies are covered with osseous scales." CHAPTER XXXIII ARTHRODIRES JHE Arthrodires.— Another large group of extinct fishes mailed and helmeted is included under the general name of Arthrodira* {apOpos, joint; del/ja, neck), or Arthrognathi {apdpos, yvaOo;, jaw) , the latter term recently framed by Dr. Dean with a somewhat broader application than the former. These fishes differ from the Ostracophores, on the one hand, in the possession of jaws and in the nature of their_armored covering. On the otherTiand, the nature of these jaws, the lack of differentiation of the skeleton, and the uncertain charac- ter of the_- limbs separate them still more widely from the true fishes. Their place in the system is still unknown, but their origin seems as likely to be traceable to Ostracophores as to any other group. The head in all the species is covered with a great bony helmet. Behind this on the nape is another large shield, and *"The name Artlirodira as given to Coccosteans, as distinguished from the Antiarcha, is not altogether a satisfactory one, since at least from the time of Pander the head of Pterichthys (Asterole pis) is known to be articu- lated with the armoring of the trunk in a way closely resembling that of Coc- costeiis. This term may, however, be retained as a convenient one foi the order of Coccosteans, in which, together with other differentiating features, this structure is prominently e\-olved. A renewed exammation of the sub- ject has caused me to mcline strongly to the belief, as abo\-e expressed, that Pterichlhys and Coccosteans are not as widely separated in phylogcn\' as Smith Woodward, for example, has maintained. But, as far as present e\-i- dence goes, they appear to me certainly as distinct as fishes are from am- phibia, or as reptiles are from birds or from mammals." (Dean.) The naine Placodernii used by McCoy in 1848 was applied to the Ostra- cophores as well as to the Arthrodires . Hay revi\-es it as the name of a super- order to include the Antiarcha and the Arllirodira, the former bein,g detached from the Ostracophores. This superorder is equivalent to the subclass A:y- gostei of Hay. 58r 58: Arthrodires between the two is usually a huge joint which Dr. Dean com- pares to the hinge of a spring-beetle (Elater). As to the presence of limbs, no trace of pectoral fin or anterior hmb has been found. Dean denies the existence of any struc- tures corresponding to either limb, but Woodward figures a supposititious posterior Hmb in Coccosteus, finding traces of basal bones which may belong to it. These monstrous creatures have been considered by Wood- ward and others as mailed Dipnoans, but their singular jaws are quite unlike those of the Di'pneusti, and very remote from anv structures seen in the ordinary fish. The turtle-like man- dibles seem to be formed of dermal elements, in which there lies little homologv to the jaws of a fish and not much more with the jaAvs of Dipnoan or shark. The relations with the Ostracophores are certainly remote, though nothing else seems to be any nearer. They have no affinity with the true Ganoids, to which A'aguely limited group manv writers have attached them. isor is there any sure foundation to the view adopted by Woodward, that they are to be considered as armored oft'shoots of the Dipnoans. According to Dean we might as well refer the Arthrodires to the sharks as to the Dipnoans. Dean further observes ("Fishes Living and Fossil"): "The puzzling characters of the Arthrodirans do not seem to be lessened by a more definite knowdedge of their dift'erent Fig. 306. — Coccosteus cusjrldalus Agassiz, restored. Lower Devonian. (After Traquair, per Woodward.) forms. The tendency, as already noted, seems to be at present to regard the group proA'isionally as a widely modified oft'shoot of the primitive Dipnoans, basing this view upon their o-eneral structural characters, dermal plates, dentition, autostyhsm. But only in the latter regard could they have differed more Arthrodires 583 widely from the primitive Elasmobranch or Teleostome, if it be admitted that in the matter of dermal structures they may be clearly separated from the Chima;roid. It certainly is difficult to beheve that the articulation of the head of Arthro- dirans could have been evolved after dermal bones had come to be formed, or that a Dipnoan could become so metamorphosed as to lose not only its body armoring, but its pectoral appen- X^"^ ■-""'^~\tj dages as well. The size of the ^^^<^'Z^j\r^^,^^^ pectoral girdle is, of course, little ■ ^^ '"' proof that an anterior pair of f,^ mi .-^^i Muy.ys hertz^H fins must have existed, since this Newberry. Upper Devonian. Ohio. 11 1 , , , . (After Newberry.) may well have been evolved m relation to the muscular supports of plastron, carapace, trunk, and head. The intermovement of the dental plates, seen es- pecially in Dinichthys, is a further difficulty in accepting their direct descent from the Dipnoans." Occurrence of Arthrodires. — These fishes occur in abundance from the Silurian times to the Mesozoic. In the Devonian their gigantic size and thick armor gave them the leading position among the hosts of the sea. Among the genera there occurred "series of forms most interesting as to their evolution." It is found more and more evident," says Dr. Dean ("Fishes, Living and Fossil," pp. 135, 136) " that the Arthrodirans may have rep- resented the dominant group in the Devonian period, as were the sharks in the Carboniferous, or as are the Teleosts in modem times. There were forms which, like Coccostens, had eyes at the notches of the head-buckler ; others, like Macropetalichthys, in which orbits were well centralized ; some, like Dinichthys and Titanichthys, with the pineal foramen present; some with pectoral spines (?); some with elaborately sculptured dermal plates. Among their forms appear to have been those whose shape was apparently subcylindrical, adapted for swift swim- ming; others {Mylostoma) whose trunk was depressed to almost ray -like proportions. In size they varied from that of the perch to that of a basking shark. In dentition they presented the widest range in variation, from the formidable shear-like jaws of Dinichthys to the lip-like mandibles of Titanichthys, the tearing teeth of Trachosteus, the wonderfully forked tooth- 584 Arthrodires bearing jaw-tips of Diplognathtis, to the Cestraciont type, Mylo- stoma. The latter form has hitherto been known only from its dentition, but now proves to be, as Newberry and Smith Wood- ward suggested, a typical Arthrodiran." Classification of Arthrodira. — Our knowledge of the system- atic relations of the Arthrodira is mostly of recent origin. Woodward refers most of the remains to the best known genus Fio. 368. — An Arthrodire, Dinichthiis intermedius Newberry, restored. Devonian, Ohio. (After Dean.) Coccostciis, and recognizes as families the CoccosteidcB, Mylostomi- dcr, Astcrosteida:, and PJiyllolcpidcc. Dr. Bashford Dean in different papers has treated these fishes in great detail. In a recent paper on the "Relationships of the Arthrognathi " * he recognizes the group as a class coor- dinate with Cyclostomi and Elasmobranchii. This class, which he calls Arthrognatlii, is first divided into two suborders, Auar- tJirodira, without joint at the neck, and ArtJirodira, with such a joint. The former comprises one order, Stcgotlialaiui, and the latter two orders, Tcnuwtlioraci and ArtJirotlioraci. The foUowine is Dr. Dean's definition of these orders and their component families : Arthrognathi. — ' ' Chordates whose anterior body region is encased in dermal elements, and divisible by a more or less definite partition into head and trunk. Dermal plates which surround the mouth function as jaws. No evidence of branchial arches. Column notochordal, showing no traces of centra; well- marked neural and ha;mal elements. Paired limbs [absent or uncertain]. Dermal plates consisting typically of two layers, the superficial tuberculate, the inner bony with radiatino- la- * Memoirs New Yorlv Academy of Sciences, 1901. Arthrodires S^5 mellae. Orbits situated near or at the margin of the head-shield and separated from one another by fixed integumental plates. A pineal funnel present situated in a fixed plate. A mucous system whose canals radiate from the preoccipital region." Anarthrodira. — " Arthrognaths in which the cranial and dorsal regions are separated by a fixed partition whose dorsal rim is overlapped and concealed by superficial plates. Of these a large median dorsal element is present which extends back- ward superficially from the region near the pineal funnel. Also a pair of elements which overlie the position of the external occipital joint. Suborbital plates apparently absent. Jaw elements undescribed." Stegothalami (crre;/oj, roof; ddXa/nos, chamber). — "Anarthro- dires in which the cranio-dorsal septum is vertical and deep, its height equal apparently to that of the arch of the head- shield. By this deep partition the latter appears to inclose two chambers (whence the ordinal name). Orbits inclosed by pre- and postorbital plates, ilucous system lacks a postorbital canal." One family, the Alacropetalichthyidcs, thus defined: "Stegothalami with large orbits and well-arched cranio- dorsal shield. Dorso-central shield long, wide, gomphoidal, extending backward to the hinder margin of the shield and bordered by all plates save the postorbitals and marginals. Pineal funnel small and obscure." Macro petalichthys sullivanti from Ohio Devonian rocks, and AlacropetalichtJiys agassizi from the Devonian of Germany, are important species of this group. The Asierosteidcc perhaps constitute a second family in this order. The single species Asterosteus stenocephalits is from the Devonian of Ohio. Arthrodira. — "Arthrognaths in which the dorsal armoring is separated into dorsal and cranial elements, the latter attached to the former movably by means of a pair of peg-and-socket joints. The interval lying between cranial and dorsal armor- ing does not appear to have been protected by plates, and in the median line, instead of the cranio-central of the Anarthro- dires, there are separate elements, median occipital, median dorsal, and perhaps others. Suborbital plates present. Jaws of three r86 Arthrodires pairs of elements. Ventral armoring of two pairs of lateral and two median elements." Temnothoraci (re'/^/'cy, to cut; OopaS, thorax). — "Arthrodires whose cranial and dorsal shields are closely apposed, separated only by a transverse fissure-like interval (whence the ordinal name) ; interarticulation of cranial and dorsal shields little developed. Head-shield elliptical in outline as far as the line of the transverse division. The anterior rim of the shoulder-shield flattened at its sides, suggesting a rudiment of the vertical partition of the Anarthrodira. Suborbital plate is present, but takes no part, apparently, in the ventral boimdary of the orbit, this being formed, as in the Anarthrodira, by the pre- and postorbital elements. Jaws, ventral armoring, and endo- skeleton not definitely known." One family, Chelonidithyidcr, thus defined: "Temnothoraci Avith orbits relatively small in size and situated well forward in the head-shield. Occipital elements produced antero-posteriorly, the external occipital forming the posterior lateral angle of the head, no projection of the head occurring in the region of the marginal plate. Median occipital trapezoidal. Centrals take part in the median boundary of the orbits, and embrace the pineal plate. Median dorsal with poorly developed keel and terminal process." HcicrostcHs asimissi (perhaps to be called IchtJiyosanroidcs spinosits) is a gigantic species from the Lower Devonian of Li\'onia. Allied to this species is Honwstiiis miller i from Scotland, celebrated as the "Asterolepis of Stromness" in Hugh Miller's "Footsteps of the Creator." x-\nother notable species is Hoiiios- tiiis fonuosissinuis from the Lower Devonian of Russia. Arthrothoraci. — "Arthrodires whose dorsal shield articu- lates Avith the head-roof by a conspicuous and movable peg- and-socket joint, and leaves a definite interval (unprotected?) between the two armorings. Orbits marginal, bounded in- teriorly not by the suborbital element. In the head-shield the postero-lateral angles formed by the marginal plate {Phlyctcc- naspisf), the occipital border concave. A dorsal fin is present, supported by endoskeletal elements." Five families, the most important being the Coccostcidcc, thus defined: Arthrodires 587 " Arthrothoraci with head-shield hexagonal in outline. Median occipital trapezoidal, margins underlapped conspicu- ously by the external occipitals. Prefrontals meet below pineal plates, thus occluding this element from contact with centrals. The median dorsal plate elongated, terminating in an acute heavy point; no definite ventral keel; its anterior border approaches the head-shield more closely than in related families. Cranio- dorsal joint relatively small. Postero-dorso-lateral large." (?A pair of spines occurs in the pectoral region.) The best-known species is Coccosteiis cuspidatus {decipiens) of the Lower Red Sandstone or Devonian of Scotland. The family of Dinichthyide consists of "Arthrothoraci with stout trenchant jaws, whose cutting surfaces have worn away marginal teeth. Plates heavy. Head-shield with conspicuous lateral indentation to form dorsal border of orbit. Preorbitals separated by rostral and pineal elements, the latter passing baclavard between the anterior ends of the centrals. Cranio- dorsal joint conspicuous. Median dorsal shovel-shaped, nearing a stout keel with a large neck and with heavy gouge-shaped terminal. Postero-dorso-lateral relatively small in size." Di- nichthys hertzeri and numerous other species are described from the Devonian and Carboniferous rocks of Ohio. The TitanichthyidcB are "Arthrothoraci with slender edentu- lous jaws bearing a longitudinal sulcus. Plates squamous. Head-shield wide, with indentations to form dorsal border of orbit. Cranio-dorsal joint complete, but of relatively small size. Median dorsal with lateral border indented with rudimentary keel and with flat and rounded terminal. Antero-dorso-lateral with an area of overlap on median border." Titanichthys agas- sizi is a gigantic mailed fish from the Lower Carboniferous of Cleveland, Ohio. The MylostomidcB are ' ' Arthrothoraci with dental elements in the character of crushing plates. Cranial shield wide, rounded anteriorly, deeply indented in nuchal margin ; orbital rim not apparent in dorsal aspect. Central separated from marginal." Mylostoma terrelli is based on jaws from Cleveland, Ohio. The SelenosteidcB are "Arthrothoraci with jaws studded witli cuspidate teeth ; the mandibular rami rounding out anteriorly or presenting diverging tips , bearing teeth in the symphysis . Cranial ^88 Arthrodires shield deeply concave on lateral margins, no orbital rim here ap- parent. Nuchal border deeply indented. (Centrals separate from marginals.) Cranio-dorsal hinges large in size. Dorsal armoring reduced antero-posteriorly, giving an almost zone-like appear- ance. Dorso-median crescent-shaped, with feeble keel and knob." Sclciiostciis glaber is described by Dean from the Cleve- land shales. Relations of Arthrodires. — To complete our account of the Arthrodira we may here summarize Dr. Dean's reasons for separat- ing its members from true fishes on the one hand and from the Ostracophores on the other. "First. The Arthrodira cannot be strictly included among the Pisces. According to the definition of the latter class its members are Craniotes possessing the following characters: a, dermal defenses which in their simplest terms can be re- duced to the shagreen denticles of the Elasmobranch ; b, a series of definite gill-arches whose foremost elements are meta- morphosed into hyoid and mandibular apparatus; c, paired fins, or their equivalents. In the first of these regards I think it can be shown that the remarkable character of the dermal plates in the Arthrognaths approaches rather that of the Ostra- cophores than that of the Pisces. In certain of these forms, Trachosteiis, for example, the tuberculated plates are made up of inner and outer elements, each with tubercles, which denote a distinctly difterent mode of origin from that of any known type of fish. The absence of remains of gill-arches in the Ar- thrognaths would be not a series objection to including these forms among Pisces, especially in view of the fact that carti- laginous gill-arches are rarely preserved even in favorable fossils. But that their presence is more than doubtful is in- dicated by the peculiar character of the 'jaws' in these forms. For the character of these structures is such as to suggest that they are not homologous with the branchial-arch jaws of the true fishes, but are rather parallel structures which owe their origin to distinctly exoskeletal elements, i.e., that they were derived from dermal plates surrounding the mouth, which be- came mobile, and whose edges became apposed as sectorial structures. I Avould in this connection call attention to the fact that the 'mandibles,' ' prcmaxillary,' and 'maxillary' Arthrodires 589 dental plates * were not fixed in the sense in which these ele- ments are in the true Pisces. On the evidence of several types, Dinichthys, Titanichthys, Mylostoma, Trachostens, Diplognathus, and other of the American forms, MacropctalicJithys f excepted, there is the clearest proof that each element of the jaws had a considerable amount of independent movement. On account of the mobility of these elements the name Arthrognathi is suggested. Thus the mandibular rami could change the angle of inclination towards each other, as well as their plane with reference to the vertical axis. So, too, could the ' premaxillas ' be protracted like a pair of bent fingers, and it is more than probable that the 'maxillae' had a considerable amount of inde- pendent movement. In connection with these characters it is also important to note that the blades of the 'mandible' show nowhere the faintest trace of an articular facet for attachment to the cranium. In short, the entire plan of the mandibu- lar apparatus in these forms is strikingly unfish-like, although one will frankly confess that it is remarkable that these forms should have paralleled so strikingly the piscine conditions, to the extent of producing mandibular rami margined with teeth, and an arrangement of toothed elements on the 'upper jaw' which resembles superficially the premaxillary and maxillary structures of teleostomes, or the vomero-palatine structures of lung-fishes and chimaeras. ' ' In the matter of paired fins there seems little evidence to conclude that either pectoral or pelvic fins were present. In spite of the researches upon these forms during the past half- century, no definite remains of pectoral fins have been de- scribed. The so-called pectoral spines described for Dinich- thys by Newberry, whatever they may be, certainly are not, * It will be recalled that there is no ground for concluding that the "man- dibular rami' possessed an endoskeletal core, and were comparable, there- fore, to the somewhat mobile jaws of Elasmobranchs. On the other hand, there is the strongest evidence that they are entirely comparable to adjacent dermal plates. Histologically they are identical, and in certain cases their exposed surfaces bear the same tuberculation. t The similarity of Macropelalichthys to Dinichthyids in the general matter of the dermal plates is so complete that I have had no hesitation in associating it with the Arthrognaths. (Cf. Eastman.) The circumstance that its "jaws" have not yet been found has to a large degree been due to the lack of energy on the part of local collectors. In the corniferous quarries near Delaware, Ohio, this fossil is stated to be relatively abundant. rgo Arthrodires as far as the present evidence goes, pterygial, nor are the similar structures in Brachydirus* The sigmoid element, described as a 'pelvic girdle' by Smith Woodward, in Coccosteus, a struc- ture which appears to occur in a small species of Dinichthysit), may as reasonably be interpreted as a displaced element of the armor-plates of the trunk. In Coccosteus, as far as I am aware, it occurs in well-preserved condition in but a single specimen. "In referring to the singular joint between the shoulder- plates and the hinder margin of the cranitmi Smith Woodward has called attention to one of the striking features of the group. It is one, however, which, as a functional structure, i.e., a joint, characterizes only a portion of its members; and in these the region in which vestiges of the joint are sought is overlaid and concealed by dermal plates. Such are the conditions in Macro- petaliclitlivs (with transitional characters in Tracliostens and in ]\Iylostoina). For this form a special subclass (or order) may be created which we may term Anarthrodira. "Second. The --1 r//»-og«a//n cannot well be included in any other class. It would certainly be more convenient to retain the Arthrognaths among the Ostracophores, regarding them as a fourth subclass, were it not that they difTer from them in so marked a way in the presence of well-marked vertebral arches, of supports for the impaired fin, and in the possession of ' jaws.' In these regards — add to them the (probable if not certain) absence of the paired paddle -like ' spines ' — they stand certainly further from the Antiarcha than these from the Osteostraci, or than the latter from the Heterostraci. It appears to me desirable, therefore, that the Arthrodira and the Anarthrodira be brought together as a separate class. Should subsequent researches demonstrate a closer affinity with the Ostracophores, the Arthrognathi can be regarded as of rank as a subclass, with the orders Anarthrodira and Arthrodira." t * It is by no means impossible that there may ultimately be found pectoral elements to correspond in a general way with the paddle-like "spines" of the Antiarcha. t The group Placodcrmi, created by McCoy (1S4S) as a "family" for the reception of Coccosteus and Pterichthys might then be justly elevated to rank as a class, superseding the Ostracof>hori of Cope (iSoi), The latter group might, however, be retained as a subclass, and include the Hetero- straci and Osteostraci as ordinal divisions. Arthrodires 591 In a recent paper Dr. Otto Jaekel unites Arthrodires and Ostracophores under the name Placodermi. He regards Pteraspis as a larval type, Asterolepis as one more specialized. In Coccosteus he claims to find a pelvic girdle as well as a more segmented skeleton. He regards ah of these as true fishes, the Coccostcidcc as ancestral, related on the one hand to the Cross- opterygians, and on the other to the Stegocephali and other ancestral Amphibians. Suborder Cyclise. — We may append to the Arthro- dira as a possible suborder the group called CyclicB by Dr. Gill, based on a single imperfectly known species. Few organisms discovered in recent times have excited as much interest as this minute fish- like creature, called PalcFOspondylns guniii, dis- covered in 1890 by Dr. R. H. Traquair in the flagstones of Caithness in Scotland. Many speci- mens have been obtained, none more than an inch and a half long. Its structure and systematic position have been discussed by Dr. R. H. Traquair, by Woodward, Gill, Gegenbaur, and recently by Dean, from whose valuable memoir on "The Devonian Lamprey " we make several quotations. Palaeospondylus. — According to Dr. Traquair : " The PalcBospondyliis giinni is a very small organism, usually under one inch in length, though exceptionally large specimens occasionally measure one inch and a half. ... It has a head and vertebral column, but no trace of jaws or limbs and, strange to say, all the specimens are seen only from the ventral aspect as is shown by the relation of the neural arches to the vertebral centra. " The head is in most cases much eroded. ... It is di- vided by a notch . . . into two parts. . . . The anterior Fig. 369. — Palnospondylus gunni Tra- quair. Devonian. (After Traquair and Dean. ) fg2 Arthrodires part shows a groove the edges of which are elevated, while the surface on each side shows two depressions, like fenestra, though perliaps they are not completely perforated, and also a groove partially divided off, posteriorly and externally, a small lobe. In front there is a ring-like opening . . . surrotmded by small pointed cirri, four ventrally, at least five dorsally, and two long lateral ones which seem to arise inside the margin of the ring instead of from its rim like the others. The posterior part of the cranium is flattened, but the median groove is still ob- servable. Connected with the posterior or occipital aspect of the skull are two small narrow plates which lie closely along- side the first half-dozen vertebrae. "The bodies of the vertebra are hollow or ring-like, and those immediately in front are separated from each other by perceptible intervals; their surfaces are marked with a few little longitudinal grooves, of which one is median. They are provided with neural arches, which are at first short and quad- rate, but towards the caudal extremity lengthen out into slender neural spines, which form the dorsal expansion of a caudal fin, while shorter haemal ones are also developed on the ventral aspect." Dr. Traquair concludes that "there seems to be no escape from the conclusion that the little creature must be classed as a j\larsipobranch." "If Palaospondylits is not a Marsipo- branch, it is quite impossible to refer it to any other existing group of vertebrates." Gill on Palaeospondylus. — In 1S96 Dr. Gill proposed to regard Palaospoudylus provisionally as the type of a distinct order of Cyclostomes to be called Cyclicc {kvkXo^, circle), from the median ring on the head, Avhether nostril or mouth. Dr. Gill observes: "Assuming the correctness of Dr. Traquair's description and figures, we certamly have a remarkable combination of char- acters. On the one hand, if the 'median opening or rim' is indeed nasal, the animal certamly cannot be referred to the class of Selachians or of Teleostomcs. On the other hand, the cranium and the segmental vertebral column indicate a more advanced stage of development of the vertebrate line than that from the living Marsipobranchs must have originated. We Arthrodires rg? may, therefore, with propriety isolate it as the representative not only of a peculiar family {Palaospondylida;), but of an order or even subclass (Cyclise) of vertebrates which may provisionally (and only provisionally) be retained in the class of Marsipobranchs. " The group may be defined as Monorrhines with a continu- ous (?) cranium, a median nasal (?) ring, and a segmented ver- tebral column. "The differences between the Hypcroartia and Hypero- treta are very great, and Prof. Lankester did not go much too far when he elevated those groups to class rank. Among the numerous distinctive characters are the great differences in the auditory organs. Perhaps the organs of Palaospondyliis might be worked out in some specimen and throw light on the subject of affinities. At present even the region of the auditory organs is not exactly known and we are now at a loss to orient the several parts of the cranium. In fact, the question of the relations of Palccospoiidylits is a very open one." Views as to the Relationships of Palaeospondylus. — Dr. Dean thus summarizes in a convenient and interesting fashion the views of dift'erent students of fossil fishes in regard to Palao- spondyliis: Huxley. — A "baby Coccosteus." Traquair, 1890. — "Certainly not a Placoderm, its resem- blance to a supposed 'baby Coccosteus' being entirely decep- tive. The appearance of the head does remind us in a strange way of the primitive skull of Myxine, a resemblance which is ren- dered still more suggestive by the apparent complete absence of the lower jaw, or of limbs or limb-girdles." Traquair, 1893. — "It seems, indeed, impossible to refer the organism to any existing vertebrate class, unless it be the Mar- sipobranchs or Cyclostomata. " Does not believe it a larval form, because the possible adult is unknown, and because of the highly differentiated vertebra;. Granting his interpretation of the parts of the fossil, "there seems no cscaj)e from the con- clusion that the little creature must be classed as a Marsipo- branch." Traquair, 1897. — "The question of the affinities of PaUco- spondylus is left precisely where it was after I had written mv last paper on the subject." ro^ Arthrodires Smith Woodward, 1892. — "It seems to possess an impaired nose, lip cartilages in place of functional jaws, and no paired limbs ; thus agreeing precisely with the lampreys and hagfishes, of which the fossil representatives have long been sought. It is extremely probable, therefore, that Palaospondylus belongs to this interesting category." Dawson, 1893. — PalcEOSpondylas suggests " the smaller snake- like Batrachians of the Carboniferous and Permian; and I should not be surprised if it should come to be regarded as either a forerunner of the Batrachians or as a primitive tad- pole." Gill, 1896. — "The group to which Palooospondyliis belongs may be defined as Monorrhines with a continuous (') cranium, a median nasal (?) ring, and a segmented vertebral column " ' ' The cranium and segmented vertebral column indicate a more advanced stage of development of the vertebrate line than that from which the living ilarsipobranchs must have originated. We may, therefore, with propriety isolate it as the representative not only of a peculiar family {Palcrospondy- lida-), but of an order or even subclass (Cyclicc) of vertebrates which may provisionally (and only provisionally) be retained in the class of Marsipobranchs." Dean, 1896. — "Place it with the Ostracoderms among the curiously specialized offshoots of the early Chordates, but this position would be at the best rmsatisfactory." Dean, 1898. — " Palccospondylus should not be given a place — even a provisional one — among the Marsipobranchs." To be accepted "as the representative of the new subclass (or class) Cycliae constituted for it by Professor Gill." Parker & Haswell, 1897. — "There is some reason to regard that Palcrospondylns is referable to the Cyclostomes." "A distinctly higher type than recent forms." Gegenbaur, 1898. — " Discovery of Palccospondylus one of the highest importance. If this organism stands in no way near the Cyclostomes, the tentacles lose their higher importance, since they also occur in other groups." "Through Palccospon- dylus came also the attempt (Pollard) to deduce the presence of the tentacular condition in the higher forms." {AIcni.~ln this Gegenbaur has not consulted the literature accurately. At Arthrodires 595 the time of founding his " Cirrhostomal Theory" Pollard was unaware of the discovery of Palaospondylus). " Ich muss sagen, das die positive Behauptung der einen wie der anderen Deutung mir sehr unsicher scheint, da auch an den iibrigen Resten des Kopfskelets keine bestimmmten Uebereinstimmungen mit anderen Organismen erweisbar sind. Es ist daher auch nicht zu vermuthen, dass sogar an Beziehung zu Froschlarven gedacht ward. Unter diesen Umstanden mochte ich jene im Verhaltniss zum Kopfe wie zum gesammten Korper bedeutende, von Cirren umstellte Eingangsoffnung als nicht einer Nase, sondern einem Munde oder beiden zugleich angehorig betrachten. Zu einem dem Cyclostomenriechorgan vergleichbaren Ver- halten fehlen alle Bedingungen." Relationships of Palaeospondylus. — The arguments for and against the supposition that Palaospondylus is a Cyclostome may be here summed up after Professor Dean, The vertebral column agrees with that of the lamprey in having the notochord in part persistent. On the other hand, the vertebra have continuous centra, showing definite processes. Those of the different regions are differentiated. These con- ditions are quite unlike those seen in the lamprey. The cranitim is massive, over twice as large proportionally as that of the lamprey. In the latter type the cranium forms but a small portion of the bulk of the head ; in Palaospondylus, on the other hand, the cranium bears every sign of having filled the contour of the head. Moreover, if the region ad- jacent to the structure is admitted to be that of the eye, and few, I believe, will doubt it, then the brain-cavity must, by many analogies, have been much larger than that of a Mar- sipobranch. Also the auditory capsules must have been of extraordinary size. In short, there is very little about the cranium to suggest the structures of Cyclostomes. The "oral cirri" suggest somewhat the barbels of the nose and mouth of a hagfish. They, however, resemble even as much in arrangement and greater number the buccal cirri of Amphioxus. On the other hand, similar mouth-surrounding tentacles are evolved independently in many groups of fishes, siluroids, sharks, forms like Pogonias, Hemitripterus. A possi- rgS Arthrodires bility further exists that the "cirri" may turn out to be remnants of cranial or facial structures of an entirely different nature. In fact the very uncertain preservation of these parts renders their evidence of little definite value. In but one specimen, as far as I am aware, is there any evidence of the presence of ventral cirri. The jaw parts in Palccospoiidylus are unknown. It is possi- ble that the A'entral rim of the "nasal ring" may prove to be the remains of the Meckehan cartilage (the cartilaginous core of the lower jaw). It is possible that certain very faint ray-like markings noted b}^ Professor Dean may be the basalia of paired fins. In such case Palccospoiidylus can have no affinity with the lampreys. Dr. Dean asserts that the presence of these, in view of the wide dissimilarity in other and important structures, is sufficient to remove Palaospondyliis from its provisional position among the Cyclostcmes. The postoccipital plates may represent a pectoral arch. It is, however, much more likely, as Dr. Tra- quair has insisted, that the supposed rays are due to the reflection of light from striations on the stone, and that the creature had no pectoral limbs. The caudal fin, with its dichotomous rays, is essentially like the tail of a lamprey. This condition is, however, found in other groups of fishes, as among sharks and lung-fishes. It is, moreover, doubtful whether the rays are really dichoto- mous. It is possible that Palccospoiidylus may be, as Huxley sug- gests, a larval Arthrodire. It is not probable that this is the case, but, on the other hand, Palccospondylns seems to be an immature form. According to Dr. Dean, it is more likely to prove a larval Coccosteus, or the young of some other Arthrodire, than a lamprey. Against this view must be urged the fact that the tail of Palccospoiidylus is not heterocercal, a fact veri- fied by Dr. Traquair on all of his many specimens. It is more hke the tail of a lamprey than that of Coccosteus. It is, how- ever, certain that it cannot be placed in the same class with the living Cyclostonics, and that it is far more highly specialized than any of them. In a still later paper (1904) Dr. Dean Arthrodires 597 shows that the fossil might as easily be considered a Chimacra as a lamprey, and repeats his conviction that it is a larval form of which the adult is still unrecognized. We cannot go much farther than Dr. Dean's statement in 1896, that it belongs "among the curiously specialized offshoots of the early Chordates." CHAPTER XXXIV THE CROSSOPTERYGII j LASS Teleostomi. — We may unite the remaining groups of fishes into a single class, for which the name Teleos- tomi (reXeo?, true; arojiia, mouth), proposed by Bona- parte in 1838, may be retained. The fishes of this class are characterized by the presence of a suspensorium to the man- dible, by the existence of membrane-bones (opercles, sub- orbitals, etc.) on the head, by a single gill-opening leading to gill-arches bearing filamentous gills, and by the absence of claspers on the ventral fins. The skeleton is at least partly ossified in all the Teleostomi. More important as a primary character, distinguishing these fishes from the sharks, is the presence typically and primitively of the air-bladder. This is at first a lung, arising as a diverticulum from the ventral side of the oesophagus, but in later forms it becomes dorsal and is, by degrees, degraded into a swim-bladder, and in very many forms it is altogether lost with age. This group comprises the vast majority of recent fishes, as well as a large percentage of those known only as fossils. In these the condition of the lung can be only guessed. The Teleostomi are doubtless derived from sharks, their relationship being possibly nearest to the IcJithyotomi or to the primitive Cliimccras. The Dipnoans among Teleostomi retain the shark-like condition of the upper jaw, made of palatal elements, which may be, as in the Chimara, fused with the cra- nium. In the lower forms also the primitive diphycercal or protocercal form of tail is retained, as also the archipterygium or jointed axis of the paired fins, fringed with ravs on one or both sides. 59s The Crossopterygii 599 We may divide the Teleostomes, or true fishes, into three subclasses: the Crossopterygii, or frmge-fins; the Dipneusti, or lung-fishes; Actinopteri, or ray-fins, including the Ganoidei and the Teleostei, or bony fishes. Of these many recent writers are disposed to consider the Crossopterygii as most primitive, and to derive from it by separate lines each of the remaining sub- classes, as well as the higher vertebrates. The Ganoidei and Teleostei (constituting the Actinopteri) are very closely related, the ancient group passing by almost imperceptible degrees into the modern group of bony fishes. Subclass Crossopterygii. — The earliest Teleostomes known belong to the subclass or group caUed after Huxley, Crossop- terygii {Kpoacro;, fringe; nrepvS, fin). A prominent character of the group lies in the retention of the jointed pectoral fin or archip- terygium, its axis fringed by a series of soft rays. This char- acter it shares with the IclitJiyotomi among sharks, and with the Dipneusti. From the latter it dift'ers in the hyostylic cra- nium, the lower jaw being suspended from the hyomandibular, and by the presence of distinct premaxillary and maxillary elements in the upper jaw. In these characters it agrees with the ordinary fishes. In the living Crossopterygians the air- bladder is lung-like, attached by a duct to the ventral side of the oesophagus. The lung-sac, though specialized in struc- ture, is simple, not cellular as in the Dipnoans. The skeleton is more or less perfectly ossified. Outside the cartilaginous skull is a bony coat of mail. The skin is covered with firm scales or bony plates, the tail is diphycercal, straight, and end- ing in a point, the shoulder-girdle attached to the cranium is cartilaginous but overlaid with bony plates, and the branchios- tigals are represented by a pair of gular plates. In the single family represented among living fishes the heart has a muscular arterial bulb with many series of valves on its inner edge, and the large air-bladder is divided into two lobes, having the functions of a lung, though not cellular as in the lung-fishes. The fossil types are very closely allied to the lung-fishes, and the two groups have no doubt a common origin in Silurian times. It is now usually considered that the Crossopterygian is more primitive than the lung-fish, though at the same time 6oo The Crossopterygii more nearly related to the Ganoids, and through them to the ordinary fishes. Origin of Amphibians. — From the primitive Crossopterygii the step to the ancestral Amphibia, which are likewise mailed and semi-aquatic, seems a very short one. It is true that most writers until recently have regarded certain Dipneustans as the Diptcridce as representing the parents of the Amphibians. But the weight of recent authority, Gill, Pollard, Boulenger, Dollo, and others, seems to place the point of separation of the higher vertebrates with the Crossopterygians, and to regard the lobate pectoral member of Polypterus as a possible source of the five-fingered arm of the frog. This view is still, however, ex- tremely hypothetical and there is still much to be said in favor of the theory of the origin of Amphibia from Dipnoans and in Fig. .370.— -Shoulder-girdle of Polypterus bichir. Specimen from the White Nile. favor of the view that the Dipnoans are also ancestors of the Crossopterygians. In the true Amphibians the lungs are better developed than in the Crossopterygian or Dipnoan, although the lungs are finally lost in certain salamanders which breathe through epithe- lial cells. The gills lose, among the Amphibia, their primitive importance, although in Proteus angiiineiis of Austria and Nectmus maculosus, the American "mud -puppy" or water-dog, these persist through life. The archipterygium, or primitive fin, gives place to the chiropterygium, or fingered arm. In The Crossopterygii 6oi Fig. 371.— Arm of a frog. this the basal segment of the archipterygium gives place to the humerus, the diverging segments seen in the most special- ized type of archipterygium (Polypterus) become perhaps radius and ulna, the intermediate quadrate mass of cartilage possibly becoming carpal bones, and from these spring the joints called metacarpals and phalanges. In the Amphibians and all higher forms the shoulder-girdle retains its primitive insertion at a distance from the head, and the posterior limbs remain abdominal. The Amphibians are there- fore primarily fishes with fingers and toes instead of the fringe -fins of their an- cestors. Their relations are really with the fishes, as indicated by Huxley, who unites the amphibians and fishes in a primary group, Ichthyopsida, while reptiles and birds form the contrasting group of Sanropsida. The reptiles differ from the Amphibians through accelera- tion of development, passing through the gill-bearing stages within the egg. The birds bear feathers instead of scales, and the mammals nourish their young by means of glandular secretions. Through a reptile-amphibian ancestry the birds and mammals may trace back their descent from palaeozoic Crossopterygians. In the very young embryo of all higher vertebrates traces of double-breathing persist in all species, in the form of rudimentary gill-slits. The Fins of Crossopterygians. — Dollo and Boulenger regard the heterocercal tail as a primitive form, the diphycercal form being a result of degradation, connected with its less extensive use as an organ of propulsion. Most writers who adopt the theory of Gegenbaur that the archipterygium is the primitive form of the pectoral fin are likely, however, to consider the diphycercal tail found associated with it in the Ichthyotomi, Dipneusti, Crossopterygii as the more primitive form of the tail. From this form the heterocercal tail of the higher sharks and 6o2 The Crossopterygii Ganoids may be derived, this giving way in the process of de- velopment to the imperfectly homocercal tail of the salmon, the homocercal tail of the perch, and the isocercal tail of the codfish and its allies, the gephyrocercal and the leptocercal tail, tapering or whip-like, representing various stages of degenera- tion. Boulenger draws a distinction between the protocercal Fk -Polyplcriis rongicus. a Crossopterygian fish from the Congo River. Young, witii external gills. (After Boulenger.) tail, the one primitively straight, and the diphycercal tail modified, like the homocercal tail, from an heterocercal ancestry. Orders of Crossopterygians. — Cope and Woodward divide the Crossof^tcrygia into four orders or suborders, Haplistia, RJiipi- distia. Actinistia. and Cladistia. To the latter belong the exist- ing species, or the family of Polypteridcr, alone. Boulenger unites the three extinct orders into one, which he calls Osteolepida. In all three of these the pectorals are narrow with a single basal bone, and the nostrils, as in the Dipneustans, are below the snout. The differences are apparently such as to justify Cope's division into three orders. Haplistia. — In the Haplistia the notochord is persistent, and the basal bones of dorsal and anal fins are in regular series, much fewer in number than the fin-rays. The single family TarrassiidcB is represented by Tarrasins probleinaticus, found by Traquair in Scotland. This is regarded as the lowest of the Crossopterygians, a small fish of the Lower Carboniferous, the head mailed, the body with small bony scales. Rhipidistia. — In the Rhipidistia the basal bones of the median fins ("axonosts and baseosts") are found in a single piece, not separate as in the Haplistia. Four families are recognized, HoloptychiidaB, Megalichthyidcr, Osteolepida, and Onychodontidcr, the first of these being considered as the nearest approach of the Crossopterygians to the Dipnoans. The Crossopterygii 603 The HoloptychiidcB have the pectoral fins acute, the scales cycloid, enameled, and the teeth very complex. Holoptychiiis nohilissimus is a very large fish from the Devonian. Glyptolepis leptopterus from the Lower Devonian is also a notable species. Dendrodus from the Devonian is known from detached teeth. In the Ordovician rocks of Caiion City, Colorado, Dr. Wal- cott finds numerous bony scales with folded surfaces and stellate ornamentation, and which he refers with some doubt to a Crossopterygian fish of the family HoloptychndcE. This fish he Fig. 373. — Basal bone of dorsal fin, Holoptycldus leptojUerus (Agassiz). (After Woodward) names Eriptychius aniericanits. If this identification proves cor- rect, it will carry back the appearance of Crossopterygian fishes, the earliest of the Teleostome forms, to the beginning of the Silurian, these Canon City shales being the oldest rocks in which remains of fishes are known to occur. In the same rocks are found plates of Ostracophores and other fragments still more doubtful. It is certain that our records in palaeontology fall far short of disclosing the earliest sharks, as well as the earliest remains of Ostracophores, Arthrodires, or even Ganoids. Megalichthyidse. — The MegalichthyiJiF (wrongly called " Rhizo- dontidw ") have the pectoral fins oljtuse, the teeth relatively simple, and the scales cycloid, enameled. There are numer- ous species in the Carboniferous rocks, largely known from fragments or from teeth. Megalichthys, Strepsodiis, Rhizo- dopsis, Gyroptychiiis, Tristidiopterns, Ensthenopteron, Cricodiis, and Smiripterus are the genera; Rhizodopsis sauroidcs from the coal-measures of England being the best-known species. The Osteolepidcc differ from the Megalichthyidcc mainly in the presence of enameled rhomboid scales, as in Polypteriis and 6o4 The Crossopterygii Lcpisostens. In Glypiopomns these scales are sculptured, in the others smooth. In Osteolepis, Thursius, Diplopterus, and Glvptopoinns a pineal foramen is present on the top of the head. This is wanting in Parabatrachiis (Megalichthys of authors). In Osteolepis, Thursius, and Parabatrachiis the tail is heterocercal, '..'■s^^^- • . jaw of Poiypte-a^tier largely from those of bony fishes, ap- bdow"''"'" *'™" preaching the teeth of reptiles. The external gill of the young, first discovered by Steindachner in 1869, consists of a fleshy axis bordered above and below by secondary branches, themselves fringed. In form and structure this resembles the external gills of amphibians. The Crossopterygii 607 It is inserted, not on the gill-arches, but on the hyoid arch. Its origin is from the external skin. It can therefore not be compared morphologically with the gills of other fishes, nor with the pseudobranchitE, but rather with the external gills of larval sharks. The vertebrae are very numerous and bi- FiG. 378. — Polypierus congicus, a Crossopterygian fish from the Congo River. Young, with e.\ternal gills. (After Boulenger.) concave as in ordinary fishes. Each of the peculiar dorsal spines is primitively a single spine, not a finlet of several pieces as some have suggested. The enameled, rhomboid scales ari in movable oblique whorls, each scale interlocked with its neighbors. The shoulder-girdle, suspended from the cranium by post- temporal and supraclavicle, is covered by bony plates. To the small hypercoracoid and hypocoracoid the pectoral fin is at- tached. Its basal bones may be compared to those of the sharks, mesopterygium, propterygium, and metapterygium, which may with less certainty be again called humerus, radius, Fig. 'il%.—Polypteriu delhezi Boulenger. Congo River. and ulna. These are covered by flesh and by small imbricated scales. The air-bladder resembles the lungs of terrestrial vertebrates. It consists of two cylindrical sacs, that on the right the longer, then uniting in front to form a short tube, which enters the oesophagus from below with a slit-hke glottis. Unlike the lung of the Dtpneusti, this air-bladder is not cellu- lar, and it receives only arterial blood. Its function is to assist the respiration by gills without replacing it. 6o8 The Crossopterygii The Polypteridse. — All the Polypterida; are natives of Africa. Two genera are known, no species having been found fossil. Of Polypterns, Boulenger, the latest authority, recognizes nine species: six m the Congo, Polypterns congiciis, P. delhezi, P. ornatipinnis, P. weeksi, P. palnias, and P. retropinnis; one, P. lapradei, in the Niger ; and two in the Nile, Polypterns bichir and P. endlicheri. Of these the only one known until very recently was Polypterns bichir of the Nile. These fishes in many respects resemble the garpike in habits. They live close on the mud in the bottom of sluggish waters, moving the pectorals fan-fashion. If the water is foul, they rise to the siirface to gulp air, a part of which escapes through the gill-openings, after which they descend like a flash. In the breeding season these fishes are very active, depositing their eggs in districts flooded in the spring. The eggs are very numerous, grass-green, and of the size of eggs of millet. The flesh is excellent as food. The genus Erpetoichthys contains a single species, Erpetoich- iJiys calabaricns* found also in the Senegal and Congo. This Fig. 380. — Erpetoichthys calaharicus Smith. Senegambia. (After Dean.) Species is very slender, almost eel-like, extremely agile, and, as usual in wriggling or undulating fishes, it has lost its ventral fin. It lives in shallow waters among interlaced roots of palms. When disturbed it swims like a snake. * This genus was first called Erpetoichthys, but the name was aftenvards changed by its author, J. A. Smith, to Calamoiclithys, because there is an earlier genus Erpiclilhys among blcnnies, and a H erpetoichthys among eels. But these two names, both wrongly spelled for Herpetichthys, are sufficiently different, and the earlier name should be retained. "A name in science is a name without necessary meaning" and without necessarily correct spelling. Furthermore, if names are spelled differently, they are different, whatever their meaning. The efforts of ornithologists, notably those of Dr. Coues, to spell correctly improperly formed generic names have shown that to do so consistently would throw nomenclature into utter confusion. It is well that generic names of classic origin should be correctly formed. It is vastlv more important that they should be stable. Stability is the sole function of the law of priority. CHAPTER XXXV SUBCLASS DIPNEUSTI,* OR LUNG-FISHES HE Lung-fishes. — The group of Dipneusti, or lung- fishes, is characterized by the presence of paired fins consisting of a jointed axis with or without rays. The skull is autostyhc, the upper jaw being made as in the Chimaera of palatal elements joined to the quadrate and fused with the cranium, without premaxillary or maxillary. The dentary bones are little developed. The air-bladder is cellular, used as a lung in all the living species, its duct attached to the Fig. 381. — Shoulder-girdle of Neoceratodus forsleri Giinther. (After Zittel.) ventral side of the oesophagus. The heart has many valves in the muscular arterial bulb. The intestine has a spiral valve. The teeth are usually of large plates of dentine covered with enamel, and are present on the pterygo-palatine and splenial bones. The nostrils are concealed, when the mouth is closed, under a fold of the upper lip. The scales are cycloid, mostly not enameled. The lung-fishes, or Dipneusti (Sis^ two; Ttveiv, to breathe), arise, with the Crossopterygians, from the vast darkness of * This group has been usually known as Dipnoi, a name cho.scn by Johannes Miiller in 1845. But the latter term was first taken by Leuckart in 1821 as a name for Amphibians before any of the Uving Dipneusti were known. We therefore follow Boulenger in the use of the name Dipneusti. suggested by Hsckel in 1866. The name Dipnoan may, however, be retained as a ver- nacular equivalent of Dipneusti. 609 6io Subclass Dipneusti, or Lung-fishes Palfeozoic time, their origin with that or through that of the latter to be traced to the Ichthyotomi or other primitive sharks. These two groups are separated from all the more primitive fish-like vertebrates by the presence of lungs. In its origin the lung or air-bladder arises as a diverticulum from the ali- mentary canal, used by the earliest fishes as a breathing-sac, the respiratory functions lost in the progress of further di- vergence. Nothing of the nature of lung or air-bladder is found in lancelet, lamprey, or shark. In none of the remaining groups of fishes is it wholly wanting at all stages of develop- ment, although often lost in the adult. Among fishes it is most completely functional in the Dipneusti, and it passes through all stages of degeneration and atrophy in the more specialized bony fishes. In the Dipneusti, or Dipnoans, as in the Crossopterygians and the higher vertebrates, the trachea, or air-duct, arises, as aboA'c stated, from the ventral side of the oesophagus. In the more specialized fishes, yet to be considered, it is transferred to the dorsal side, thus avoiding a turn in passing around the oesophagus itself. From the sharks these forms are further distinguished by the presence of membrane-bones about the head. From the Actinopteri (Ganoids and Teleosts) Dipnoans and Crossopterygians are again distinguished by the presence of the fringe-fin, or archipterygium, as the form of the paired Umbs. From the Crossopterygians the Dipnoans are most readily distinguished by the absence of maxillary and pre- maxillary, the characteristic structures of the jaw of the true fish. The upper jaw m the Dipnoan is formed of palatal ele- ments attached directly to the skull, and the lower jaw con- tains no true dentary bones. The skull in the Dipnoans, as in the Chiuuvra, is autostylic, the mandible articulating directly with the palatal apparatus, the front of which forms the upper jaw and of which the pterygoid, hyomandibular and quadrate elements form an immovable part. The shoulder-girdle, as in the shark, is a single cartilage, but it supports a pair of super- ficial membrane-bones. In all the Dipnoans the trunk is covered with imbricated cvcloid scales and no bony plates, although sometimes the scales are firm and enameled. The head has a roof of well- Subclass Dipneusti, or Lung-fishes 6 i i developed bony plates made of ossified skin and not corre- sponding with the membrane-bones of higher fishes. The fish- like membrane-bones, opercles, branchiostegals, etc., are not yet dift'erentiated. The teeth have the form of grinding-plates on the pterygoid areas of the palate, being distinctly shark-like in structure. The paired fins are developed as archipterygia, often without rays, and the pelvic arch consists of a single cartilage, the two sides symmetrical and connected in front. There is but one external gill-opening leading to the gill-arches, which, as in ordinary fishes, are fringe-like, attached at one end. In the young, as with the embryo shark, there is a bushy external gill, which looks not unlike the archipterygium pec- toral fin itself, although its rays are of dift'erent texture. In early forms, as in the Ganoids, the scales were bony and enam- eled, but in some recent forms deep sunken in the skin. The claspers have disappeared, the nostrils, as in the frog, open into the pharynx, the heart is three-chambered, the arterial bulb with many valves, and the cellular structure of the skin and of other tissues is essentially as in the Amphibian. The developed lung, fitted for breathing air, which seems the most important of all these characters, can, of course, be traced only in the recent forms, although its existence in all others can be safely predicated. Besides the development of the lung we may notice the gradual forward movement of the shoulder-girdle, which in most of the Teleostomous fishes is attached to the head. In bony fishes generally there is no distinct neck, as the pogt-temporal, the highest bone of the shoulder-girdle, is articulated directly with the skull. In some specialized forms { Batistes, Tctraodon) it is even immovably fused with it. In a few groups (Apodes, Opisthomi, Heteromi, etc.) this connection ancestrally possessed is lost through atrophy and the slipping baclavard of the shoulder-girdle leaves again a distinct neck. In the Amphib- ians and ah higher vertebrates the shoulder-girdle is dis- tinct from the skull, and the possession of a flexible neck is an important feature of their structure. In all these higher forms the posterior limbs remain abdominal, as in the sharks and the primitive and soft -rayed fishes generally. In these the pelvis or pelvic elements are attached toward the middle 6 1 2 Subclass Dipneusti, or Lung-fishes of the body, giving a distinct back as well as neck. In the spiny-rayed fishes the "back" as well as the neck disappears, the pelvic elements being attached to the shoulder-girdle, and in a few extreme forms (as Ophidion) the pelvis is fastened at the chin. Classification of Dipnoans. — By Woodward the Dipneusti are divided into two classes, the Sirenoidei and the Arthrodira. We follow Dean in regarding the latter as representative of a distinct class, leaving the Sirenoidei, with the Ctenodipterini, to constitute the subclass of Dipneusti. The Sirenoidei are divided by Gill into two orders, the Monopneumona, with one lung, and the Diplopneunioiui, with the lung divided. To the latter order the Lcpidosirenidcv belong. To the former the Ccratodontidcc, and presumably the extinct families also belong, although nothing is known of their lung structures. Zittel and Hay adopt the names of Ctenodipterini and Sirenoidei for these orders, the former being further characterized by the very fine fin-rays, more numerous than their supports. Order Ctenodipterini. — In this order the cranial roof-bones are small and numerous, and the rays of the median fins are very slender, much more numerous than their supports, which are inserted directly on the vertebral arches. In the UronemidcB the upper dentition comprises a cluster of small, blunt, conical denticles on the palatine bones; the lower dentition consists of similar denticles on the splenial bone. The vertical fins are continuous and the tail diphycercal. There is a jugular plate, as in Amia. The few species are found in the Carboniferous, Uronemus lobatus being the best-known species. In Dipteridce there is a pair of dental plates on the palatines, and an opposing pair on the splenials below. Jugular plates are present, and the tail is usually distinctly heterocercal. In Phaneropleuron there is a distinct anal fin shorter than the very long dorsal; Phaneropleuron andersoni is known from Scotland, and Scaumenacia curta is found at Scaumenac Bay in the Upper Devonian of Canada. In Dipterus there are no marginal teeth, and the tail is heterocercal, not diphycercal, as in the other Dipnoans gener- ally. Numerous species of Dipterus occur in Devonian rocks. Subclass Dipneusti, or Lung-fishes 6 1 3 In these the jugular plate is present, as in Uronemus. Dipterus valenciennesi is the best-known European species. Dipterus nelsoni and numerous other species are found in the Chemung and other groups of Devonian rocks in America. In the CtenodontidcB the tail is diphycercal, and no jugular plates are present in the known specimens. In Ctenodus and Sagenodus there is no jugular plate and there are no marginal teeth. The numerous species of Ctenodus and Sagenodus belong Fig. 383. — Phaneropleuron andersoni 'H.uxley; restored; Devonian. (After Dean.) chiefly to the Carboniferous age. Ctenodus wagneri is found in the Cleveland shale of the Ohio Devonian. Sagenodus occiden- talis, one of the many American species, belongs to the coal- measures of Illinois. As regards the succession of the Dipneusti, Dr. Dollo re- gards Dipterus as the most primitive, Scaumenacia, Uronemus, Ctenodus, Ceratodus, Protopterus, and Lepidosiren following in order. The last-named genus he thinks marks the terminus ■ of the group, neither Ganoids nor Amphibians being derived from any Dipnoans. Order Sirenoidei. — The living families of Dipneusti differ from these extinct types in having the cranial roof-bones re- duced in number. There are no jugular plates and no marginal teeth in the jaws. The tail is diphycercal in all, ending in a long point, and the body is covered with cycloid scales. To these forms the name Sirenoidei was applied by Johannes Muller. Family Ceratodontidae. — The CeratodontidcB have the teeth above and below developed as triangular plates, set obliquely each with several cusps on the outer margin. Nearly all the species, representing the genera Ceratodus, Gosfordia, and Con- chopoma, are now extinct, the single genus Neoceratodus still existing in Australian rivers. Numerous fragments of Cera- todus are fovmd in Mesozoic rocks in Europe, Colorado, and 6 14 Subclass Dipneusti, or Lung-fishes India, Ccratodus latissimus, figured by Agassiz m 1838, being the best- known species. The abundance of the fossil teeth of Ceratodus renders the discovery of a hving representative of the same type a matter of great interest. In 1870 the Barramunda of the rivers of Queensland was described Fig. 38.3. — Teeth of Ceratodus runcinatus Plie- ninger. Carboniferous. (After Zittel.) by Krefft, who recognized its rela- tionship to Ceratodus and gave it the name of Ceratodus forsteri. Later, generic differences were noticed, and it was separated as a distinct group by Castelnau in 1876, under the name of Neoceratodus (later called Epicera- todus by Teller) . Neoceratodus forsteri and a second species, Neoceratodus mio- lepis, have been since very fully dis- cussed by Dr. Giinther and Dr. Krefft. Pig. 385.— Archlpterygium of Neoceratodus forsteri Gilntlier. rS o «, Subclass Dipneusti, or Lung-fishes 615 They are known in Queensland as Barrainimda. They inhabit the rivers known as Burnett, Dawson, and Mary, reaching a length of six feet, and being locally much valued as food. From the salmon-colored flesh, they are known to the settlers in Queens- land as "salmon." According to Dr. Gunther, "the Barra- munda is said to be in the habit of going on land, or at least on mud-flats ; and this assertion appears to be borne out by the fact that it is provided with a lung. However, it is much more probable that it rises now and then to the surface of the water in order to fill its lung with air, and then descends again until the air is so much deoxygenized as to render a renewal of it necessary. It is also said to make a grunting noise which may be heard at night for some distance. This noise is proba- bly produced by the passage of the air through the oesophagus when it is expelled for the purpose of renewal. As the Barra- munda has perfectly developed gills besides the lung, we can hardly doubt that, when it is in water of normal composition and sufficiently pure to yield the necessary supply of oxygen, these organs are sufficient for the purpose of breathing, and that the respiratory function rests with them alone. But when the fish is compelled to sojourn in thick muddy water charged with gases, which are the products of decomposing organic matter (and this must be the case very frequently during the droughts which annually exhaust the creeks of tropical Australia), it commences to breathe air with its lung in the way indicated above. If the medium in which it happens to be is perfectly unfit for breathing, the gills cease to have any function ; if only in a less degree, the gills may still continue to assist in respiration. The Barra- munda, in fact, can breathe by either ^ „^„ .,, . „ „ ' -' , Fig. 386. — Lpper jaw of Neocera- gills or lung alone or by both simul- todusforsteri Gimtber. (After taneously. It is not probable that ' '^ '' it lives freely out of water, its limbs being much too flexible for supporting the heavy and unwieldy body and too feeble 6i6 Subclass Dipneusti, or Lung-fishes generally to be of much use in locomotion on land. How- ever, it is quite possible that it is occasionally compelled to leave the water, although we cannot believe that it can exist AMthout it in a lively condition for any length of time, " Of its propagation or development we know nothing except that it deposits a great number of eggs of the size of those of a newt, and enveloped in a gelatinous case. We may infer that the young are provided with external gills, as in Pro- toptcrus and Polyptcrus. "The discovery of Ccratodiis does not date farther back than the year 1S70, and proved to be of the greatest interest, not only on account of the relation of this creature to the other living Dipneusti and Ganoidei, but also because it threw fresh light on those singular fossil teeth which are found in strata of Triassic and Jurassic formations Yu!. 3S7 _Lower iaw of ii^ various parts of Europe, India, and ,\,acer„tndn.'' apposed in the median line; hindward, h<.)A\-ever, they are still separate, and through this opening the lilastop(jrc may yet be seen. At this stage primitive segments Subclass Dipneusti, or Lung-fishes 6 i 9 are shown ; in the brain region the medullary folds are still slightly separated. In an older embryo the fisli-like form may be recognized. The medullary folds have completely fused in the median line, and the embryo is coming to acquire a ridgedike prominence, optic vesicles and primitive segments are apparent, and the blastopore appears to persist as the anus. The continued growth of the embryo above the yolk mass is apparent ; the head end has, however, grown the more rapidly, showing gill-slits, auditory, optic, and nasal vesicles, at a time when the tail mass lias hardly emerged from the surface. Pronephros has here appeared. It is not until the stage of the late embryo that the hinder trunk region and tail come to be prominent. Tlie em- bryo's axis elongates and becomes straighter; the yolk mass is now much reduced, acquiring a more and more oblong form, lying in front of the tail in the region of the posterior gut. The head and even the region of the prone pJiros are clearly separate from the yolk-sac ; the mouth is coming to be foiTned. According to Eastman (Ed. Zittel), the skeleton of Xco- ceratodiis is less developed and less ossified than that of its supposed Triassic ancestors. A similar rule holds with regard to the sturgeons and some Amphibians. Lepidosirenidse. — The family Lepidosircnidcc, representing the suborder Dtploueumoiia, is represented by two genera of mud- fishes found in streams of Africa and South America. Lepidosiren paradoxa was discovered by Natterer in 1837 in tributaries of the Amazon. It was long of great rarity in Fia. 38 8.— Adult male of Lepidosiren parndoxii, Fitzingcr. (After Kerr.) collections, but quite recently large numbers have been ob- tained, and Dr. J. Graham Kerr of the University of Cambridge has given a very useful account of its structure and develop- ment. From his memoir we condense the following record of its habits as seen in the swamps in a region known as Gran Chaco, which lies under the Tropic of Capricorn. These swamps 620 Subclass Dipneusti, or Lung-lishes m the rainy season have a depth of from two to four feet, be- coming entirely dry in the southern winter (June, Julyj. Kerr on the Habits of Lepidosiren. — The loalach, as the Lepi- dosircn is locally called, is normally sluggish, wriggling slowly about at the bottom of the swamp, using its hind limbs in irregular alternation as it clambers through the dense vegeta- tion. More rapid movement is brought about by lateral strokes of the large and powerful posterior end of the body. It burrows with great facility, gliding through the mud, for which form of movement the shape of the head, with the ,»*«*!""»*- g^'^'^ '<^ v^'^^t Fig. 389.— Embryo (3 days before hatching) and larva (13 days after hatching) of Lepidosiren pa racloxd Fitziuger. (After Kerr.) upper lip overlapping the lower and the external nostril placed witlnn the lower lip, is admirably adapted. It feeds on plants, .alg;e, and leaves of flower-plants. The gills are small and quite unaljle to supply its respiratory needs, and the animal must rise ti) the surface at intervals, Hke a frog. It breathes with its lungs as continuously and rhythmically as a mammal, the an- l:.eing inhaled through the mouth. The animal makes no Vocal sound, the older observation that it utters a cry like that of a cat being doubtless erroneous. Its strongest sense is that Mf smell. In darkness it grows paler in color, the black Subclass Dipneusti, or Lung-fishes 621 chromatophores shrinking in absence of light and enlarging in the sunshine. In injured animals this reaction becomes much less, as they remain pale even in daylight. In the rainy season when food is abundant the Lepidosiren eats voraciously and stores great quantities of orange-colored fat in the tissues between the muscles. In the dry season it ceases to feed, or, as the Indians put it, it feeds on water. When the water disappears the Lepidosiren burrows down into the mud, closing its gill-openings, but breathing through the mouth. As the mud stiffens it retreats to the lower part of its burrow, Fig. 390. — Larva of Lepidosiren paradoxa 30 days after hatching. (After Kerr.) where it lies with its tail folded over its face, the body sur- rounded by a mucous secretion. In its burrow there remains an opening w^hich is closed by a lid of mud. At the end of the Fig. 391.— Larva of Lepidosiren paradoxa 40 days after hatching. (After Kerr.) dry season this hd is pushed aside, and the animal comes out when the water is deep enough. When the waters rise the presence of Lepidosirens can be found only by a faint quivering FiG. 892 Larva of Lepidodren paradoxa 3 months after hatching. (After Kerr.) movement of the grass in the bottom of the swamp. When taken the body is found to be as slippery as an eel and as mus- cular. The eggs are laid in underground burrows in the black 622 Subclass Dipneusti, or Lung-fishes peat. Their galleries run horizontally and are usually two feet long by eight inches wide. After the eggs are laid the male remains curled up in the nest with them. In the spawning season an elaborate brush is developed in connection with the ventral fins. Protoptcnis, a second genus, is found in the rivers of Africa, where three species, P. aiuicctcns, P. dolloi, and P. crthiopicns, are now known. The genus has five gill-clefts, instead of four as in Lepidosiren. It retains its external gills rather longer than the latter, and its limljs are better developed. The habits of Protoptcnis are essentially like those of Lepidosiren, and the two types haA'e developed along parallel lines doubtless from a common ancestry. No fossil Lepidosirenidw are known. Fig. 393. — Protopterus doUoi Boulenger. Congd River. Family Lepid