i! I: rr m ru LT) a m CD The STUDIO BOOK SHOP, Inc. Books, Stationery, Art OujecU. GUIDE TO THE STUDY OF FISHES A GUIDE TO THE STUDY OF FISHES BY DAVID STARR JORDAN President of I. eland Stanford Junior University With Colored Frontispieces and 427 Illustrations IN TWO VOLUMES 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 brook. " — Thoreau NEW YORK HENRY HOLT AND COMPANY 1905 nilft'0' Copyright, 1905 BY HENRY HOLT AND COMPANY Published March, 1905 To TTbeofcore (Bill, 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 ofj 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 North 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 would make Vlll Preface a volume of itself. The principal works and their authors are discussed in the chapter on the History of Ichthyology, and with this 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, SANTA CLARA COUNTY, CAL., October, 1904. ERRATA * VOL. I Frontispiece, for Paramia quinqueviltata read Paramia quinquevittata Page xiii, line 10, jor Filefish read Tilefish 39» " J5> fa Science read Sciences 52, lines 4 and 5, transpose hypocoracoid and hypercoracoid 115, line 24, for Hexagramila read Hexagrammiace 162, " 7. The female salmon does as much as the male in covering the eggs. 169, last line, for immmediately read immediately 189, legend, jor Miaki read Misaki 313, line 26, jor sand-pits read sand-spits 322» 324, 327» 357, 361, 363, 420, 428, 428, 462, 7 and elsewhere, jor Wood's Hole read Woods Hole 15, for Roceus read Roccus next to last, for masquinonqy read masquinongy 5, jor Filefish read Tilefish 26, jor 255 feet read 25 feet 26, jor infallibility read fallibility 22, jor West Indies read East Indies 23, jor -99 read -96 28, jor were read are 24, jor Geffroy, St. Hilaire read Geoffrey St.-Hilaire 25, jor William Kitchener Parker read William Kitchen Parker 32, for Enterpneusta read Enteropneusto * For most of this list of errata I am indebted to the kindly interest of Dr. B. W. Evermann. 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 Exoskeleton. — Ctenoid and Cycloid Scales. — Placoid Scales. — Bony and Prickly Scales. — Lateral Line. — Function of the Lateral Line. — The Fins of Fishes. — Muscles 16 CHAPTER III. THE DISSECTION OF THE FISH. The Blue-green Sunfish. — The Viscera. — Organs of Nutrition. — 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 Interhaemals. — The Pectoral Limb. — The Shoulder-girdle. — The Posterior Limb. — Degeneration. — The Skeleton in Primitive Fishes. —The Skeleton of Sharks.— The Archipterygium 34 x Contents CHAPTER V. MORPHOLOGY OF THE FINS OF FISHES. PAGE 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. — Homo logics of the Pectoral Limb. — The Girdle in Fishes other than Dipnoans 62 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 VII. THE NERVOUS SYSTEM. The Nervous System.— The Brain of the Fish.— The Pineal Organ.— The Brain of Primitive Fishes. — The Spinal Cord. — The Nerves 109 CHAPTER VIII. 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 IX. THE ORGANS 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 Forms. — 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 XI. 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. — Calling 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 Vertebrae to Temper- ature, and the Struggle for Existence. — Number of Vertebrae: 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. — Northern 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 Different 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 XVI. DISPERSION OF FRESH-WATER 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 XVII. DISPERSION OF FRESH-WATER FISHES. (Continued.) Barriers to Dispersion of Fresh-water Fishes: Local Barriers. — Favorable Waters Have Most Species. — Water-sheds. — How Fishes Cross Water-sheds. —The Suletind. — The Cassiquiare. — Two-Ocean Pass. — Mountain Chains. — Upland Fishes. — Lowland Fishes. — Cuban Fishes. — Swampy Water- sheds.— The Great Basin of Utah. — Arctic Species in Lakes. — Causes of Dispersion still in Operation 297 Contents xiii CHAPTER XVIII. FISHES AS FOOD FOR MAN. PAGE 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. Taxonomy. — 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. — Linnaeus. — Forskal. — Risso. — Bloch. — Lacepede. — Cuvier. — Valenciennes. — Agassiz. — Bonaparte. — Giinther. — Boulenger. — Le Sueur. — Muller. — Gill. — Cope. — Liitken. — 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. — Tertiary 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 Chimaeras. — The Dipnoans. — The Crossopte- rygians. — The Actinopteri. — The Bony Fishes 435 CHAPTER XXV. THE PROTOCHORDATA. The Chordate Animals. — The Protochordates. — Other Terms Used in Classifi- cation.— The Enteropneusta. — Classification of Enteropneusta. — Family Harrimaniidae. — Balanoglossidae. — Low Organization of Harrimaniidae 460 CHAPTER XXVI. THE TUNICATES, OR ASCIDIANS. Structure of Tunicates. — Development of Tunicates. — Reproduction of Tuni- cates. — Habits of Tunicates. — Larvacea. — Ascidiacea. — Thaliacea. — Origin of Tunicates. — Degeneration of Tunicates 467 CHAPTER XXVII. THE LEPTOCARDII, OR LANCELETS. 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. — Metamorphosis 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 ? 486 Contents xv CHAPTER XXIX. THE CLASS ELASMOBRANCHII, OR SHARK-LIKE FISHES. PAGE The Sharks. — Characters of Elasmobranchs. — Classification of Elasmobranchs. — Subclasses of Elasmobranchs. — The Selachii. — Hasse'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 Hexanchidae. — Family Chlamydoselachidae. — Order Asterospondyli. — Suborder Cestraciontes. — Family Heterodontidae. — Edes- tus and its Allies. — Onchus.— Family Cochliodontidae. — Suborder Galei. — Family Scyliorhinidae. — The Lamnoid, or Mackerel-sharks. — Family Mit- sukurinidae, the Goblin-sharks. — Family Alopiidae, or Thresher-sharks. — Family Pseudotriakidae. — Family Lamnidae. — Man-eating Sharks. — Family Cetorhinidae, or Basking Sharks. — Family Rhineodontidas. — The Carcharioid Sharks, or Requins. — Family Sphyrnidae, or Hammer-head Sharks. — The Order of Tectospondyli. — Suborder Cyclospondyli. — Family Squalidae. — Family Dalatiidae. — Family Echinorhinidae. — Suborder Rhinae. — Family Pristiophoridae, or Saw-sharks. — Suborder Batoidei, or Rays. — Pristididae, or Sawfishes. — Rhinobatidae, or Guitar-fishes. — Rajidae, or Skates. — Narco- batidae, or Torpedoes. — Petalodontidae. — Dasyatidae, or Sting-rays. — Myliobatidae. — Family Psammodontidae. — Family Mobulidse 523 CHAPTER XXXI. THE HOLOCEPHALI, OR CHIMERAS. The Chimasras. — Relationship of Chimaeras. — Family Chimaeridae. — Rhino- chimaeridae. — Extinct Chimaeroids. — 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. ARTHRODIRES. The Arthrodires. — Occurrence of Arthrodires. — Arthrognathi. — Anarthrodira. — Stegothalami. — Arthrodira. — Temnothoraci. — Arthrothoraci. — Relations of xvi Contents PAGE Arthrodires. — Suborder Cycliae. — Palaeospondylus. — Gill on Palaeospon- dylus. — Views as to the Relationships of Palaeospondylus: Huxley, Tra- quair, 1890. Traquair, 1893. Traquair, 1897. Smith Woodward, 1892. Dawson, 1893. Gill, 1896. Dean, 1896. Dean, 1898. Parker & Has- well, 1897. Gegenbaur, 1898. — Relationships of Palaeospondylus 581 CHAPTER XXXIV. THE CROSSOPTERYGII. Class Teleostomi. — Subclass Crossopterygii. — Order of Amphibians. — The Fins of Crossopterygians. — Orders of Crossopterygians. — Haplistia. — Rhipidistia. — Megalichthyidae. — Order Actinistia. — Order Cladistia. — The Polypte- ridae 598 CHAPTER XXXV. SUBCLASS DIPNEUSTI, OR LUNGFISHES. The Lungfishes. — Classification of Dipnoans. — Order Ctenodipterini. — Order Sirenoidei. — Family Ceratodontidae. — Development of Neoceratodus. — Lepi- dosirenidae. — 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 gibbosus, Common Sunfish 7 Ozorthe dictyogramma, a Japanese Blenny. . . •. 9 Eupomotis gibbosus, Common Sunfish 13 Monocentris japonicus, Pine-cone Fish 16 Diodon hystrix, Porcupine-fish 17 Ncmichthys avocetta, Thread-eel 17 Hippocampus hudsonius, Sea-horse 17 Pepnlus paru, Harvest -fish 18 faphius litulon, Anko or Fishing-frog 18 Epinephelus adscensionis, Rock-hind or Cabra Mora 20 Scales of Acanthoessus bronni 21 Cycloid Scale 22 Ponchthys porosissimus, Singing-fish 23 Apomotis cyanettus, Blue-green Sunfish 27 Chiasmodon niger, Black Swallower 29 Jaws of a Parrot-fish, Sparisoma aurojrenatum 30 Archosargus probatocephalus, Sheepshead 31 Campostoma anomalum, Stone-roller 33 Roccus lineatus, Striped Ba=s 35 Roccus lineatus. Lateral View of Cranium 36 Roccus lineatus. Superior View of Cranium 37 Roccus Uneatus. 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 Pharyngeal Bone and Teeth of European Chub, Leuciscus cephalus 47 Upper Pharyngeals of Parrot-fish, Scarus strongylocephalus 47 Lower Pharyngeal 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, Holoptychius leptopterus 49 Inner View of Shoulder-girdle ot Buffalo-fish, Ictiobus bubalus 51 xviii List of Illustrations Pterophryne tumida, Sargassum-fish 52 Shoulder-girdle of Sebastolobus alascanus 52 Cranium of Sebastolobus alascanus 53 Lower Jaw and Palate of Sebastolobus alascanus 54 Maxillary and Pre-maxillary of Sebastolobus alascanus 55 Part of Skeleton of Selene vomer 55 Hyostilic Skull of Chiloscyllium indicum, a Scyliorhinoid Shark 56 Skull of Heptranchias indicus, a Notidanoid Shark '. 56 Basal Bones of Pectoral Fin of Monkfish, Squatina 56 Pectoral Fin of Heterodontus philippi 57 Pectoral Fin of Heptranchias indicus. 57 Shoulder-girdle of a Flounder, Paralichthys calif ornicus 58 Shoulder-girdle of a Toadfish, Batrachoides pacifici 59 Shoulder-girdle of a Garfish, Tylosurus fodiator 59 Shoulder-girdle of a Hake, Merluccius productus 60 Cladoselache fyleri, Restored 65 Fold-like Pectoral and Ventral Fins of Cladoselache jyleri 65 Pectoral Fin of a Shark, Chiloscyllium 66 Skull and Shoulder-girdle of Neoceratodus jorsteri, showing archipterygium ... 68 Acanthoessus wardi 69 Shoulder-girdle of Acanthoessus > 69 Pectoral Fin of Pleuracanthus 69 Shoulder-girdle of Polypterus bichir 70 Arm of a Frog 71 Pleuracanthus decheni. •.,.,.. 74 Embryos of Heterodontus japonictis, a Cestraciont Shark 75 Polypterus congicus, a Crossopterygian Fish with External Gills 78 Heterocercal Tail of Sturgeon, Acipenser sturio 80 Heterocercal Tail of Bowfin, Amia calva 82 Heterocercal Tail of Garpike, Lepisosteus osseus 82 Coryphanoides carapinus, showing Leptocercal Tail 83 Heterocercal Tail of Young Trout, Salmo fario 83 Isocercal Tail of Hake, Merluccius productus 84 Homocercal Tail of a Flounder, Paralichthys calijornicus 84 Gephyrocercal Tail of Mola mola 85 Shoulder-girdle of Amia calva 86 Shoulder-girdle of a Sea-catfish, Selenaspis dowi 86 Clavicles of a Sea-catfish, Selenaspis dowi 87 Shoulder-girdle of a Batfish, Ogcocephalus radiatus 88 Shoulder-girdle of a Threadfin, Polydactylus approximans 89 Gill-basket of Lamprey 92 Weberian Apparatus and Air-bladder of Carp 93 Brain of a Shark, Squatina squatina no Brain of Chimara monstrosa no Brain of Protopterus annectens no List of Illustrations xix Brain of a Perch, Perca flavescens ........................................ m Petromyzon marinus unicolor. Head of Lake Lamprey, showing Pineal Body, in Chologaster cornutus, Dismal-swamp Fish ................................. 116 Typhlichthys subterraneus, Blind Cave-fish ................................ 116 Anableps dovii, Four-eyed Fish .......................................... 117 Ipnops murrayi ........................................................ 118 Boleophthalmus chinensis, Pond-skipper ................................... 118 Lampetra wilderi, Brook Lamprey ....................................... 120 Branchiostoma lanceolatum, European Lancelet ............................ 120 Pseudupeneus maculatus, Goatfish ........................................ 122 Xiphophorus helleri, Sword-tail Minnow .................................. 124 Cymatogaster aggregatus, White Surf-fish, Viviparous, with Young ............ 125 Goodea luitpoldi, a Viviparous Fish ....................................... 126 Egg of Callorhynchus antarcticus, the Bottle-nosed Chimaera ................. 127 Egg of the Hagfish, Myxine limosa ....................................... 127 Egg of Port Jackson Shark, H eterodontus philippi ......................... 128 Development of Sea-bass, Centropristes striatus ........... ................. 135 Centropristes striatus, Sea-bass ........................................... 137 Xiphias gladius, Young Swordfish ....................................... 139 Xiphias gladius, Swordfish .............................................. 139 Larva of the Sailfish, Istiophorus, Very Young ............................ 140 Larva of Brook Lamprey, Lampetra ivilderi, before Transformation .......... 140 Anguilla chrisypa, Common Eel ......................................... 140 Larva of Common Eel, Anguilla chrisypa, called Leplocephalus grassii ....... 141 Larva of Sturgeon, Acipenser sturio .......................... . ........... 141 Larva of Chcetodon sedentarius ........................ , .................. 142 Chcetodon capistratus, Butterfly-fish ....................................... 142 Mola mola, Very Early Larval Stage of Headfish, called Centaur us boops ...... 143 Mola mola, Early Larval Stage called Molacanthus nummularis .............. 144 Mola mola, Advanced Larval 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 pecloralis, Alaska Elackfish ....................................... 149 Ophiocephalus barca, Snake-headed China-fish ............................ 150 Carassius auratus, Monstrous Goldfish ................................... 151 Jaws of Nemichthys avocetta ............................................ 156 Cypselurus californicus, Flying-fish ....................................... 157 Ammocrypta clara, Sand-darter .......................................... 158 Fierasfer acus, Pearlfish, issuing from a Holocanthurian ..................... 159 Gobiomorus gronovii, Portuguese Man-of-war Fish ......................... 160 Tide Pools of Misaki ................................................... 161 Ptychocheilus oregonensis, Squawfish ..................................... 162 Ptychocheilus grandis, Squawfish, Stranded as the Water Falls ............... 164 xx List of Illustrations PAGE Larval Stages of Platophrys podas, a Flounder of the Mediterranean, showing Migration of Eye 174 Platophrys lunatus, the Wide-eyed Flounder 175 Young Flounder Just Hatched, with Symmetrical Eyes 175 Pseudopleuronectes americanus, Larval Flounder 176 Psendopleuronectes americanus, Larval Flounder (more advanced stage) 176 Face View of Recently-hatched Flounder 177 Schilbiosus furiosus, Mad-Tom 1 79 Emmydrichthys vulcanus, Black Nohu or Poison-fish 180 Teuthis bahianus, Brown Tang 181 Stephanolepis hispidus, Common Filefish 182 Tetraodon meleagris 183 Batistes carolinensis, the Trigger-fish 184 Narcine brasiliensis, Numbfish 185 Torpedo electricus, Electric Catfish 186 Astroscopus guttatus, Star-gazer 187 ALthoprora lucida, Headlight-fish 188 Corynolophus reinhardti, showing Luminous Bulb 188 Etmopterus lucijer 189 Argyropelecus oljersi 190 Luminous Organs and Lateral Line of Midshipman, Porichthys notatus. ....... 192 Cross-section of Ventral Phosphorescent Organ of Midshipman, Porichthys notatus 193 Section of Deeper Portion of Phosphorescent Organ, Porichthys notatus 194 Leptecheneis naucrates, Sucking-fish or Pegador 197 Caularchus m(zandricus,.C\ingfish 198 Polistotrema stouti, Hagfish 199 Pristis zysron, Indian Sawfish 200 Pristiophorus japonicus, Saw-shark 201 Skeleton of Pike, Esox lucius 203 Skeleton of Red Rockfish, Sebastodes miniatus 214 Skeleton of a Spiny-rayed Fish of the Tropics, Holacanthus ciliaris 214 Skeleton of the Cowfish, Lactophrys tricornis 215 Crystallias matsushima, Liparid 218 Sebastichthys maliger, Yellow-backed Rockfish 218 Myoxocephalus scorpius, European Sculpin 219 Hemitripterus americanus, Sea-raven 220 Cyclopterus lumpus, Lumpfish 220 Psychrolutes paradoxus, Sleek Sculpin 221 Pdllasina barbata, Agonoid-fish 221 Amblyopsis spelceus, Blindfish of the Mammoth Cave 221 Lucifuga subterranea, Blind Brotula 222 Hypsypops rubicunda, Garibaldi 227 Synanceia verrucosa, Gofu or Poison-fish 229 Alticus saliens, Lizard-skipper. 230 List of Illustrations xxi PAGE Etheostoma camurum, Blue-breasted Darter 231 Liuranus semicintus and Chlevastes 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 Caulophryne jordani, Deep-sea Fish of Gulf Stream 276 Exerpes asper, Fish of Rock-pools, Mexico 276 Xenocys jessice 279 Ictalurus punctatus, Channel Catfish 280 Drawing the Net on the Beach of Hilo, Hawaii 281 Semotilus atromaculatus, Horned Dace 285 Leuciscus lineatus, Chub of the Great Easin 287 Melletes papilio, Butterfly Sculpin 288 Scartichthys enosinuz, a Fish of the Rock -pools of the Sacred Island of Eno- shima, Japan 294 Halichares bivittatus, the Slippery Dick 297 Peristedion miniatum 299 Outlet of Lake Bonneville 303 Hypocritichthys 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 Whitefish 321 Mullus auratus, the Golden Surmullet 322 Scomberomorus maculatus, the Spanish Mackerel 322 Lampris luna, the Opah or Moonfish 323 Pomatomus saltatrix, the Bluefish 324 Centropomus undecimalis, the Robalo 324 Cluzlodipterus faber, the Spadefish 325 Micropterus dolomieu, the Small-mouthed Black Bass 325 Salvelinus fontinalis, the Speckled Trout 326 Salmo gairdnert, the Steelhead Trout 326 Salvelinus oquassa, the Rangeley Trout 326 Salmo rivularis, the Steelhead Trout 327 Salmo henshawi, the Tahoe Trout 327 Salvelinus malma, the Dolly Varden Trout 327 Thymallus signijer, the Alaska Grayling 328 Esox lucius, the Pike 328 Pleurogrammus monopterygius, the Atka-fish 328 Chirostoma humboldtianum, the Pescado bianco 329 xxii List of Illustrations PACK Pseudupeneus maculatus, the Red Goatfish 329 Pseudoscarus guacamaia, Great Parrot -fish 330 Mugil cephalus, Striped Mullet 330 Lutianus analis, Mutton-snapper 331 Clupea harengus, Herring 331 Gadus callarias, Codfish 331 Scomber scombrtis, Mackerel 332 Hippoglossus hippoglossus, Halibut 332 Fishing for Ayu with Cormorants 333 Fishing for Ayu. Emptying Pouch of Cormorant 335 Fishing for Tai, Tokyo Bay 338 Brevoortia tyrannus, Menhaden 340 Exonautes unicolor, Australian Flying-fish 341 Rhinichthys atronasus, Black-nosed Dace 342 Notropis hudsonius, White Shiner 343 Ameiurus catus, White Catfish 344 Catostomus ardens, Sucker 348 Oncorhynchus tschawytscha, Quinnat Salmon 354 Oncorhynchus tschawytscha, Young Male 355 A mnurus nebtdosus. Cat "shes 358 "Le Monstre Marin en Habit de Moine" 360 "Le Monstre Marin en Habit d'Eveque" 361 Regalecus russelli, Garfish 362 Regalecus glesne, Glesnaes Garfish 363 Nemichthys avocetta, Thread-eel 365 Lactbphrys tricornis, Horned Trunkfish 373 Ostracion cornutum, Horned Trunkfish 376 Lactophrys bicaudalis, Spotted Trunkfish 377 Lactophrys bicaudalis, Spotted Trunkfish (Face) 377 Lactophrys triqueter, Spineless Trunkfish 378 Lactophrys trigonus, Hornless Trunkfish 378 Lactophrys trigonus, Hornless Trunkfish (Face) 379 Bernard Germain de Lace"pede 399 Georges Dagobert Cuvier 399 Louis Agassiz 399 Johannes Miiller 399 Albert Giinther 403 Franz Steindachner 403 George Albert Boulenger 403 Robert Collett 403 Spencer Fullerton Baird 407 Edward Drinker Cope 407 Theodore Nicholas Gill 407 George Brown Goode 407 Johann Reinhardt - 409 List of Illustrations xxiii PAGE Edward Waller Claypole 409 Carlos Berg 409 Edgar R. Waite 409 Felipe Poey y Aloy 413 Leon Vaillant 413 Louis Dollo 413 Decio Vinciguerra 413 Bashford Dean 4*17 Kakichi Mitsukuri 417 Carl H. Eigenmann 417 Franz Hilgendorf 417 David Starr Jordan 421 Herbert Edson Copeland 421 Charles Henry Gilbert 421 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 Dipterus valenciennesi 437 Hoplopleryx lewesiensis 438 Paratrachichthys prosthemius, Berycoid-fish 439 Cypsilurus heterurus, Flying-fish 440 Lutianida, Schoolmaster Snapper 440 Pleuronichthys decurrens, Decurrent Flounder 441 Cephalaspis lyelli, Ostracophore 444 Dinichthys intermedius, Arthrodire 445 Lamna cornubica, Mackerel-shark or Salmon-shark 447 Raja stellulata, Star-spined Ray 448 Harriotta raleighiana, Deep-sea Chimaera 449 Dipterus valenciennesi, Extinct Dipnoan 449 Holoptychius giganteus, Extinct Crossopterygian 451 Platysomus gibbosus, Ancient Ganoid-fish 452 Lepisosteus platystomus, Short-nosed Gar 452 Palceoniscum macropomum, Primitive Ganoid-fish 453 Diplomystus humilis, Fossil Herring 453 Holcolepis lewesiensis 454 Flops saurus, Ten-pounder '. 454 Apogon semilineatus, Cardinal-fish 455 Pomolobus cestivalis, Summer Herring 455 Bassozetus catena 456 Trachicephalus uranoscopus 456 Chlarias breviceps, African Catfish 457 xxiv List of Illustrations PAGE Notropis whipplii, Silver -fin 457 Gymnothorax moringa 458 Seriola lalandi, Amber-fish 458 Geological Distribution of the Families of Elasmobranchs 459 "Tornaria" Larva of Glossobalanus minutus 463 Glossobalanus minutus 464 Harrimania maculosa 465 Development of Larval Tunicate to Fixed Condition 471 Anatomy of Tunicate 472 Ascidia adharens 474 Styela yacutatensis 475 Styela greeleyi 476 Cynthia superba 476 Botryttus magnus, Compound Ascidian 477 Botryllus magnus 478 Botryttus 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 stouti, Hagfish 489 Petromyzon marinus, Lamprey 491 Petromyzon marinus unicolor, Mouth Lake Lamprey 492 Lampetra ivilderi, Sea Larvae Brook Lamprey 492 Lampetra ivilderi, Mouth Brook Lamprey 492 Lampetra camtschatica, Kamchatka Lamprey 495 Entosphenus tridentatus, Oregon Lamprey 496 Lampetra ivilderi, Brook Lamprey 505 Fin-spine of Onchus tenuistriatus 509 Section of Vertebrae of Sharks, showing Calcification 510 Cladoselache jyleri 514 Cladoselache jyleri, Ventral View 515 Teeth of Cladoselache jyleri 515 Acanthoessus wardi 515 Diplacanthus crassissimus 517 Climatius scutiger 518 Pleuracanthus decheni 519 Pleuracanthus decheni, Restored 520 Head-bones and Teeth of Pleuracanthus decheni 520 Teeth of Didymodus bohemicus 520 Shoulder-girdle and Pectoral Fins of Cladodus neilsoni 521 Teeth of Cladodus strialus 522 Hexanchus griseus, Griset or Cow-shark 523 Teeth of Heptranchias indicus 524 List of Illustrations xxv PAGE Chlamydoselachus anguineus, Frill-shark 525 Heterodontus jrancisci, 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 delabechei 528 Fin-spine of Hybodus basanus 528 Fin-spine of Hybodus reticulatus 528 Fin-spine of Hybodus canaliculatus 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 contortus 531 Mitsukurina owstoni, Goblin-shark 535 Scapanorynchus lewisi, Under Side of Snout 536 Tooth of Lamna cuspidata 537 Isuropsis dekayi, Mackerel-shark 537 Tooth of Isurus hastalis 538 Carcharodon mega'odon 539 Cetorhinus maximus, Basking-shark 540 Galeus zyopterus, Soup-fin Shark 541 Carcharias lamia, Cub-shark 542 Teeth of Cor ax pristodontus 543 Sphyrna zygcena, Hammer-head Shark 544 Squalas acanthias, Dogfish 545 Etmopterus lucifer 546 Brain of Monkfish, Squatina squatina 547 Pristiophorus japonicus, Saw-shark 548 Pristis pectinatus, Sawfish 550 Rhinobatus lentiginosus, Guitar-fish 551 Raja erinacea, Common Skate 552 Narcine brasiliensis, Numbfish 553 Teeth of Janassa linguajormis 554 Polyrhizodus radicans 555 Dasyatis sabina, Sting-ray 556 Aetobatis narinari, Eagle-ray 558 Mania birostris, Devil-ray or Sea -devil 559 Skeleton of Chimcera monstrosa 564 Chinuzra colliei, Elephant-fish 565 Odontotodus schrencki, Ventral Side 570 Odontotodus schrencki, Dorsal Side 570 Head of Odontotodus schrencki, from the Side 571 Limulus polyphemus, Horseshoe Crab 572 Lanarkia spinosia 574 Drepanaspis gmundenensis 575 xxvi List of Illustrations PAGE Pteraspis rostrata 575 Cephalaspis lyelli, Restored 576 Cephalaspis dawsoni 577 Pterichthyodes testudinarius ." 578 Pterichthyodes testudinarius, Side View 579 Birkenia elegans 579 Lasianius problematicus 580 Coccosteus cuspidatus, Restored 582 Jaws of Dinichthys hertzeri 583 Dinichthys intermedius, an Arthrodire 584 Palceospondylus gunni 591 Shoulder -girdle of Polypterus bichir 600 Arm of a Frog 601 Polypterus congicus, a Crossopterygian Fish 602 Basal Bone of Dorsal Fin, Holoptychius leptopterus 603 Gyroptychius microlepidotus 604 Ccdacanthus elegans, showing Air-bladder 604 Undina gulo 605 Lower Jaw of Polypterus bichir, from Below 606 Polypterus congicus 607 Polypterus delhezi 607 Erpetoichthys calabaricus 608 Shoulder-girdle of Neoceratodus forsteri 609 Phaneropleuron andersoni 613 Teeth of Ceratodus runcinatus 614 Neoceratodus forsteri 614 Archipterygium of Neoceratodus forsteri 614 Upper Jaw of Neoceratodus forsten 615 Lower Jaw of Neoceratodus forsteri 616 Adult Male of Lepidosiren paradoxa 619 Lepidosiren paradoxa. Embryo Three Days before Hatching; Larva Thirteen Days after Hatching 620 Larva of Lepidosiren paradoxa Forty Days after Hatching 621 Larva of Lepidosiren paradoxa Thirty Days after Hatching 621 Larva of Lepidosiren paradoxa Three Months after Hatching 621 Protopterus dolloi 622 (N 3> •S •~ I 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, Lepomis megalotis (Rafinesque). (From Clear Creek, Bloomington, Indiana.) Family Centrarchidw. brown and blue and orange, with fins wide -spread and eyes red with rage. Form of the Fish. — And now we have 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 like. We see 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 flat and gristly. It cannot move it, scarce even taste its food with it, nor can it use it for making a noise. 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 eyelids, 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 from the skull itself. These are called membrane bones because they are formed of membrane which has become bony by the deposition The Life of the Fish 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 FIG. 3. — Common Sunfish, Eupomotis gibbosus (Linnaeus). 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 hel£>s 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. Over 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. When it lies in wait under a dark log its colors are very dark. When it rests above the white sands it is very pale. When 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 very flat the color has one appearance. When 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. Where 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 striae, 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 line. 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, io 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 brain 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 twenty-four pieces, or vertebrae. Each of these has a rounded central part, 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 medium 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 pyloric caeca, 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 stomach, 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 very 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 serve to help us to understand the swim- 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, of 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 effect that sight or touch has on the animal. These sensations changed into movement constitute what is called reflex action, performance without thinking of 3 3 & (4 -~> 2 £ 1 I eg § i 1.0 I 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 possible 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 will 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 nearly all reflex, most of them being suggested and immediately directed by the influence of external things. Because its actions are all reflex the brain is very small, very primitive, and very simple, nothing more being needed for automatic move- ment. Small as the fish's skull-cavity is, the brain does not half fill 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 the dead sunfish (for the live one we shall look after carefully, giving him every day fresh water and a fresh worm or snail or bit of beef), if we cut off the upper part of the skull we shall see the separate parts of the brain, most of them lying in pairs, side by 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. We 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, overlapping 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 projections, one going to each nostril. These are the olfac- tory lobes which receive the sensation of smell. Behind the optic lobes is a single small lobe, not divided into two. This is the cerebellum and it has charge of certain powers of motion. Under the cerebellum is the medulla, below which the spinal cord begins. The rest of the spinal cord is threaded through the different vertebrae 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 little 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 |ORM of Body. — With 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 Fish, Monocentris japonicus (Houttuyn). Waka, Japan. of a boat. The trunkfish (Ostraciori) in a hard bony box has no need of rapid progress. 16 The Exterior of the Fish FIG. 7. — Porcupine-fish, Diodon hystrix (Linnaeus). Tortugas Islands. FIG. 8. FIG. 9. FIG. 8. — Thread-eel, Nemichthys avocetta Jordan and Gilbert. Vancouver Island. FIG. 9. — Sea-horse, Hippocampus hudsoniiis Dekay. Virginia. i8 The Exterior of the Fish FIG. 10. — Harvest-fish, Peprilus paru (Linnaeus). Virginia. FIG. 11. — Anko or Fishing-frog, Lophius litulon (Jordan). Matsushima Bay, Japan. (The short 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 Antigonia. Certain sluggish fishes seem to be all head and tail, looking as though the body by some accident had been omitted. These, like the headfish (Mola mold) 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 (Lophius) (Fig. n) has a depressed body and head. Other terms as truncate (cut off 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 head. In the Rock Hind, fig. 1 2 , the eye is 5 in head, the snout is 4f in head, and the maxillary 2f. Young fishes have the eye larger, the body slenderer, and the head larger in proportion 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 (Osbeck). Family Serranidce. 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, may 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. — Normally formed scales are rounded in outline, marked by fine concentric rings, and crossed on the inner side by a few strong radiating ridges and folds. The Exterior of the Fish 21 They usually cover the body more 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 more primitive representatives of the typical fishes, those with 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 different in structure. Sometimes, as in the eel, the cycloid scales may be reduced to mere rudiments 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 FIQ 13 _Scales of some sculpins are not placoid, but are re- Acanthoessus bronni duced or modified ctenoid scales, scales nar- (Agassiz). (After 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- ered with bony enamel, much like that seen in teeth, otherwise 22 The Exterior of the Fish essentially like cycloid scales. These are found in the garpike and in many genera of extinct Ganoid and Crossopterygian fishes. In the line 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 scales on the body may vary exceedingly. In some fishes the scales FIG. 14.— Cycloid 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 (Gobiidce, Pceciliidce) 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 Lateral Line as a Mucous Channel. — The more primitive 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), Porichlhys porosissimus (Cuv. and Val.). Gulf of Mexico. with mucus. Analogous to these cavities are the mucous chan- nels which in primitive fishes constitute the lateral line. Function of the 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 * Fishes Recent and Fossil, p. 52. 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 are knows as fins. These are composed of bony or cartilaginous rods or rays connected by membranes. The fins are divided into 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 below or behind them represent the hinder 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 ventral 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 rays, 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- nominal 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. XII-I, 17 means that the dorsal is divided, that the an- terior portion 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 by 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 vertebra. 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 Zoology. It represents the blue-green sunfish, Apomotis cya- nellus, from the Kansas River, but in these regards all the species of sunfishes are alike. We 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 caeca, which secrete a digestive fluid. Beyond 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 28 The Dissection of the Fish Next it flows into the thick-walled ventricle, whence by the rhythmical construction of its walls 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 small 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 yellowish tissue lying just below and behind the swim- bladder. In the spring they fill much of the body cavity and the many little eggs can be plainly seen. When mature they are 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 Miillerian 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. 17. — Black Swallower, Chiasmodon niger Johnson, containing a fish larger than itself. 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 villiform bands. Villiform 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 in 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 brush-like 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. Knife-like 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. Most 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 over the edge of the jaw as soon as each has fulfilled its function. In general the more distinctly a species is a fish- eater, the sharper are the teeth. Usually fishes show little dis- crimination in their choice of food ; often they devour the young of their own species as readily as any other. The digestive process is rapid, and most fishes rapidly 'increase in size in the process of development. When food ceases to be abundant the fishes grow more slowly. For this reason the same species will grow to a larger size in large streams than in small ones, in lakes than 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- FIG. 18. — Jaws of a Parrot- fish, Sparisoma aurofrenatum (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 premaxillary, 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. — Sheepshead (with incisor teeth), Archosargus probaiocephalus (Wal- baum). Beaufort, X. C. 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 oesoph- 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 enlarged area, either siphon-shaped, with an opening at either end, or else forming a blind sac with the openings for entrance (cardiac) and exit (pyloric) close together at the anterior end. In the various kinds of mollets (Mugil) 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 caca. 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 cholodechus 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 (Amid} 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, Campostoma anomalum (Rafinesque). Family Cyprinidce. 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 (Branchiostoma) , 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. Very great varia- tions in the forms and relations of the different 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 bones 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 vertebrate 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 specialized 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 different 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 (Branchiostoma) has no differentiated head FIG. 21. — Striped Bass, Roccus lineatus (Bloch). Potomac River. 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, chimaeras, etc.) all the skeleton is composed of cartilage. In the more specialized bony fishes, besides these bones we find also series of mem- brane bones, more or less external to the skull and composed of CO CM 00 •s. ^ PH s 2 ;§. ill •* 2 O O •• • X *M « o rtt *^ ^^ •15 a O 3 s :§• E C5 «J § S '•§ 2 •2 a CU 3 w £ 3 § • c S 2-s. The Skeleton of the Fish 39 ossified dermal tissues. Membrane bones are not found in the sharks and lampreys, but are developed in an elaborate coat of mail in some extinct forms. Names of Bones of Fishes. — In the study of the names of the bones of fishes it will be more convenient to begin with a highly specialized form in which each of the various structures is present and in its normal position. To this end we present a series of figures of a typical form, choosing, after Starks, the striped bass (Roccus lineatus) of the Atlantic coast of the United States. For this set of plates, drawn from nature by Mrs. Chloe Lesley Starks, we are indebted to the courtesy of Mr. Edwin Chapin Starks. The figures of the striped bass illustrate a noteworthy paper on "The Synonymy of the Fish Skeleton," published by the Washington Academy of Science in 1901. Bones of the Cranium. — The vomer (i) is the anterior part of the roof of the mouth, armed with small teeth in the striped bass and in many other fishes, but often toothless. The eth- moid (2) lies behind the vomer on the upper surface of the skull, and the prefrontal (3) projects on either side and behind the ethmoid, the nostrils usually lying over or near it and near the nasal bone (51). Between the eyes above are the two frontal (4) bones joined by a suture. On the side behind the posterior angle of the frontal is the s phenolic (5) above the posterior part of the eye. Behind each frontal is the parietal (6). Behind the parietal and more or less turned inward over the ear-cavity is the epiolic (7). Between the parietals, and in most fishes rising into a thin crest, is the supraoccipital (8), which bounds the cranium above and behind, its posterior margin being usually a vertical knife-like edge. The plerolic (9) forms a sort of wing or free margin behind the epiotic and over the ear- cavity. The opisthotic (10) is a small, hard, irregular bone behind the pterotic. The exoccipital (n) forms a concave joint or condyle on each side of the basioccipital (12), by which the vertebral column is joined to the skull. The parasphenoid (13) forms a narrow ridge of the roof of the mouth, connecting the vomer with the basioccipital. In some fishes of primitive struc- ture (Salmo, Beryx] there is another bone, called orbitosphenoid, on the middle line above and between the eyes. The basis phe- 40 The Skeleton of the Fish noid (14) is a little bone above the myodome or tube in which runs the rectus muscle of the eye. It descends toward the parasphenoid and is attached to the prootic. The prootic (15) is an irregular bone below the ear region and lying in advance of the opisthotic. The alisphenoid (16) is a small bone in the roof of the mouth before the prootic. These sixteen bones FIG. 25. — Roccus lineatus. Posterior view of cranium. 6. Parietal. 9. Pterotic. 12. Basioccipital. 7. Epiotic. 10. Opisthotic. 8. Supraoccipital. 11. Exoccipital. (with a loose bone of specialized form, the otolith, within the ear-cavity) constitute the cranium. All are well developed in the striped bass and in most fishes. In some specialized forms they are much distorted, coossified, or otherwise altered, and their relations to each other may be more or less changed. In the lower forms they are not always fully differentiated, but The Skeleton of the Fish 41 in nearly all cases their homologies can be readily traced. In the sharks and lampreys the skull constitutes a continuous cartilaginous box without sutures. In the dipnoans and other forms having a bony casque the superficial bones outside the cranium may not correspond to the cartilaginous elements of the soft skull itself. Bones of the Jaws. — The bones of the jaws are attached to the cranium by membranes only, not by sutures, except in a few peculiarly specialized forms. The Upper Jaw. — The premaxillary (32) lies on either side and forms the front of the upper jaw. Its upper posterior tip or premaxillary spine projects backward almost at right angles with the rest of the bone into a groove on the ethmoid. There is often a fold in the skin by which this bone may be thrust out or protracted, as though drawn out of a sheath. When the spines of the premaxillary are very long the upper jaw may be thrust out for a considerable distance. The premaxil- lary is also often known as intermaxillary. Lying behind the premaxillary, its anterior end attached within the angle of the premaxillary, is the maxillary (31), or supramaxillary, 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 oft 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 meso pterygoid (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. ill Is III _ ^H