EAWTH 
 
 1C'. r i > - c;& 
 l&RAftY 
 
 BERKELEY 
 
 LIBRARY 
 
 UNIVERSITY Of 
 
 CALIFORNIA 
 
 


FISHES, LIVING AND FOSSIL 
 
Columbia SJnifatsitg Biological Series. 
 
 EDITED BY 
 
 HENRY FAIRFIELD OSBORN. 
 
 1 FROM THE GREEKS TO DARWIN. 
 
 By Henry Fairfield Osborn. Sc.D. Princeton. 
 
 2. AMPHIOXUS AND THE ANCESTRY OF THE VERTEBRATES. 
 
 By Arthur Willey, B.Sc. Lond. Univ. 
 
 3. FISHES, LIVING AND FOSSIL. An Introductory Study, 
 
 By Bashford Dean, Ph.D. Columbia. 
 
 4. THE CELL IN DEVELOPMENT AND INHERITANCE 
 
 By Edmund B. Wilson, Ph.D. J. H. U. 
 

 of DiNiCHTHYS iNTERMEDius, NEWBERRY. in front 
 
 and side views. X T V From photograph of specimen collected by Dr. William 
 Clark, in the Waverly (Lower Carboniferous) of Ohio, now in the collection of 
 Columbia College, New York. (V. p. 133.) 
 
COLUMBIA UNIVERSITY BIOLOGICAL SERIES. III. 
 
 FISHES, LIVING AND FOSSIL 
 
 AN OUTLINE OF THEIR FORMS AND 
 PROBABLE RELATIONSHIPS 
 
 BY 
 
 BASHFORD DEAN, PH.D. 
 
 INSTRUCTOR IN BIOLOGY, COLUMBIA COLLEGE, NEW YORK CITY 
 
 Wefo gfe 
 MACMILLAN AND CO. 
 
 AND LONDON 
 
 1895 
 All rights reserved 
 
EARTH 
 
 SCIENCE* 
 
 LIBRARY 
 
 . COPYRIGHT, 1895, 
 t 'f C' '^'i! I t \?Y t 1VLA.CMILLAN AND CO. 
 
 Set up and electrotyped August, 1895. Reprinted November 
 1895. 
 
 MATTHEW LIBRARY 
 
 XortoooH 
 
 J. S. Cashing & Co. Berwick & Smith. 
 Norwood Mass. U.S.A. 
 
MY FRIEND AND TEACHER 
 
 JOHN STRONG NEWBERRY 
 
 LATE PROFESSOR OF GEOLOGY IN 
 COLUMBIA COLLEGE 
 
 942316 
 
T<ov 8' ei/vSpoov a>an> TO TU>V l^Ovwv yei/os ev o,7r6 roiv 
 
 ^>CO/3tCTTat. 
 
 ARISTOTLE, Z)<? Animalibus Historiae, Lib. II., cap. xiii. 
 
PREFACE 
 
 A KNOWLEDGE of Fishes, living and fossil, is not to be 
 included readily within the limits of an introductory study. 
 In preparing the present volume it has nevertheless been 
 my object to enable the reader to obtain a convenient 
 review of the most important forms of fishes, and of their 
 structural and developmental characters. I have also en- 
 deavoured to keep constantly in view the problems of their 
 evolution. 
 
 At the end of the book a series of tables affords more 
 definite contrasts of the anatomy and embryology of the 
 different groups of fishes. And as an aid to further study 
 has been added a summarized bibliography, including 
 especially the works of the more recent investigators. 
 
 My sincere thanks are due to my friend and colleague, 
 Professor Henry Fairneld Osborn, for many suggestions 
 during the early preparation of the book, and for the care 
 with which he has later revised the proof. I must also 
 express my indebtedness to Mr. Arthur Smith Woodward 
 of the British Museum for his personal kindnesses in 
 aiding my studies. My thanks are also due to my father, 
 William Dean, for the preparation of the index. 
 
 The figures, unless otherwise stated, are from my 
 original pen drawings. 
 
 B. D. 
 
 BIOLOGICAL LABORATORY OF COLUMBIA COLLEGE, 
 May, 1895- 
 
CONTENTS 
 
 i 
 
 PAGE 
 
 Introductory. The form and movement of Fishes. Their classifica- 
 tion; geological distribution; mode of evolution. The survival of 
 generalized forms I 
 
 II 
 
 The Evolution of Structures characteristic of Fishes; e.g. (i) gills, 
 
 (2) skin defences, teeth, (3) fins, and (4) sense organs .... 14 
 
 III 
 
 The Lampreys and their Allies. Their structures and probable relation- 
 ships. The Ostracoderms and Palseospondylus 57 
 
 IV 
 
 The Sharks. Their plan of structure; prominent forms, living and 
 
 extinct; their interrelationships 72 
 
 V 
 
 The Chimaeroids. Their characteristic structures; their representatives 
 
 and relationships 99 
 
 VI 
 
 The Lung-fishes. Their structures. Extinct and recent forms. The 
 
 evolution of the group 116 
 
 xi 
 
Xii CONTENTS 
 
 VII 
 
 The Teleostomes (i.e. Ganoids and Teleosts). Typical members; their 
 
 structures and interrelationships; their probable descent .... 139 
 
 VIII 
 
 The Groups of Fishes contrasted from the Standpoint of Embryology. 
 Their eggs and breeding habits. Outlines of the development of 
 Lamprey, Shark, Lung-fish, Ganoid, and Teleost. Their larval 
 
 development 179 
 
 DERIVATION OF NAMES 227 
 
 BIBLIOGRAPHY 231 
 
 EXPLANATORY TABLES: 
 
 I. Classification of Fishes 8 
 
 II. Distribution of Fishes in Geological Time 9 
 
 III. Phylogeny of Sharks, Chimaeroids, Dipnoans .... 98 
 
 IV. Phylogeny of Teleostomes 166 
 
 V. Characters of Vertebrae, Fins, Skull (Figs. 310-315) . . 252 
 
 VI. Relations of Jaws and Branchial Arches (Figs. 310-315) . 256 
 
 VII. Heart (Figs. 316-325) 260 
 
 VIII. Gills, Spiracle, Gill rakers (Figs. 9-12, 326-331) ... 260 
 
 IX. Digestive Tract (Figs. 326-331) 263 
 
 X. Swim-Bladder (Figs. 13-19) . 264 
 
 XL Genital System (Figs. 331-337) 266 
 
 XII. Plan of Circulation in Fishes (Fig. 338) 269 
 
 XIII. Excretory System (Figs. 331-337) 270 
 
 XIV. Abdominal Pores (Figs. 331-337) 271 
 
 XV. Central Nervous System (Figs. 339-344) 274 
 
 XVI. Sense Organs 276 
 
 XVII. Integument, Lateral line 278 
 
 XVIII. Developmental Characters 280 
 
 XIX. Comparison of Phylogenetic Tables of Authors .... 282 
 
 INDEX , 285 
 
LIST OF FIGURES 
 
 FRONTISPIECE. Head of Dinichthys. 
 
 FIG. PAGE 
 
 I, 2. Moving fishes, shark and 
 
 eel 2 
 
 3. Spanish mackerel .... 3 
 
 4. Front view of Spanish 
 
 mackerel . 4 
 
 5-8. Numerical lines of fishes . 5 
 
 9-12. Gills of fishes . . .17,259 
 
 13-19. Air-bladder . . . .22, 265 
 
 20-31. Teeth and scales ... 24 
 
 32-38. Fin spines 29 
 
 39-43. Unpaired fins ... 32, 33 
 
 44-48. Caudal fin 37 
 
 49-54. Paired fins 42 
 
 55-60. Barbels and sense organs 47 
 6 1-68. Mucous canals .... 50 
 69. General anatomy of Cyclo- 
 
 stome 58 
 
 . 69 A. Skeleton of lamprey ... 58 
 70-72 A-D. Bdellostoma, Myx- 
 
 ine, Petromyzon . . 60, 61 
 
 73. Palaeospondylus 65 
 
 74. Pteraspis 66 
 
 75. Palaeaspis 66 
 
 76. 77. Plates of Pteraspis ... 66 
 
 78, 79. Cephalaspis 66 
 
 So-82. Pterichthys 68 
 
 83. General anatomy of shark . 73 
 .84. Skeleton of shark . . .75, 255 
 
 85. Vertebrae of shark .... 76 
 
 86. 86 A. Cladoselache .... 79 
 86 B. Teeth of Cladoselache . . 80 
 
 87. Acanthodes 81 
 
 88. Acanthodes, shagreen . . . 81 
 88 A. Acanthodes, teeth ... 82 
 . Climatius 82 
 
 FIG. PAGE 
 
 90. Pleuracanthus 83 
 
 90 A. Teeth of Pleuracanthus . 84 
 
 90 B. Head roof of Pleuracanthus 84 
 
 91. Cestracion 85 
 
 92. Chlamydoselache .... 87 
 
 93. Heptanchus 88 
 
 94. Squalus 89 
 
 95. Alopias 89 
 
 96. Lamna 90 
 
 96 A. Cetorhinus 90 
 
 968. Lsemargus 91 
 
 97. Squatina 91 
 
 98. 98 A. Pristis 92 
 
 99. Pristiophorus 93 
 
 100. Rhinobatis 93 
 
 101. Raja 94 
 
 102. Torpedo 95 
 
 IO2A. Dicerobatis (Cephalop- 
 
 tera) 96 
 
 103. Shark phylogeny .... 98 
 
 104. General anatomy of Chimaera 100 
 
 105. Skeleton of Chimaera . . 102 
 105 A. Ischyodus 104 
 
 1 06. Myriacanthus 105 
 
 io6A. Squaloraja 105 
 
 io6B, c. Derm plates of Myria- 
 canthus 105 
 
 107-112. Dental plates of Chimse- 
 
 roids 106 
 
 1 1 3-1 1 6 A. Spines and claspers 
 
 of Chimaeroids .... 107 
 
 117. Harriotta 108 
 
 118. Callorhynchus 109 
 
 119. Chimaera no 
 
 1 20. Chimaera, young . . . .ill 
 
 121. General anatomy of lung-fish 117 
 
XIV 
 
 LIST OF FIGURES 
 
 FIG.- PAGE 
 
 122. Skeleton of lung-fish . . .119 
 1 22 A. Jaws and skull of Protop- 
 
 terus 120 
 
 123. Dipterus 121 
 
 124. Derm bones of head of Dip- 
 
 terus 121 
 
 125. 125 A. Jaws of Dipterus . . 121 
 
 126. Phaneropleuron . . . .122 
 
 127. Ceratodus 123 
 
 128. Skeleton of Ceratodus . .123 
 
 1 28 A. Skull of Ceratodus . . .124 
 
 129. Lepidosiren 125 
 
 1 29 A. Protopterus 126 
 
 130. Coccosteus 131 
 
 131. Coccosteus, dorsal view . .132 
 
 132. Coccosteus, ventral . . .132 
 
 133. Dinichthys 133 
 
 134-137. Dinichthys, dorsal view 134 
 138-144. Mandibles of Arthrodi- 
 
 rans 137 
 
 145. General anatomy of Teleost 140 
 
 146. Skeleton of Teleost . . . 142 
 
 147. Skeleton of Ganoid . . . 144 
 
 148. Polypterus 148 
 
 149. Polypterus, head of young . 148 
 
 150. Calamoichthys 150 
 
 151. Gyroptychius 151 
 
 152. Osteolepis 151 
 
 153. Holoptychius 151 
 
 154. Eusthenopteron . . . .152 
 
 155. Coelacanthus 153 
 
 156. Diplurus 154 
 
 156 A. Undina 154 
 
 157. Lepidosteus 155 
 
 158. Elonichthys 156 
 
 159. Eurynotus 156 
 
 160. Cheirodus 157 
 
 161. Semionotus 157 
 
 162. Aspidorhynchus . . . .158 
 
 163. Microdon 158 
 
 164. Palseoniscus 159 
 
 165. Acipenser 160 
 
 1 65 A. Chondrosteus . . . .161 
 
 1 66. Scaphirhynchus . . . .162 
 
 1 66 A. Psephurus 162 
 
 i66B. Polyodon 163 
 
 167. Amia 163 
 
 1 68. Amia, gular region . . . 164 
 
 169. Caturus 164 
 
 170. Leptolepis 165 
 
 171. Megalurus 165 
 
 1 71 A. Phylogeny of the Teleo- 
 
 stomes 166 
 
 172-174. Deep-sea fishes . . .168 
 
 175. Fierasfer 169 
 
 176. Carassius 170 
 
 177. Amiurus 171 
 
 178. Callichthys 172 
 
 179. Mormyrus 172 
 
 180. Anguilla 173 
 
 181. Perca 173 
 
 182. Gadus 174 
 
 183. Pseudopleuronectes . . .175 
 
 184. Chilomycterus 176 
 
 1 84 A. Lagocephalus . . . .176 
 
 185. Hippocampus 177 
 
 1 85 A. Syngnathus 178 
 
 186-199. Eggs of fishes . . .181 
 200-215. Development of lam- 
 prey 189 
 
 216-230. Development of shark . 194 
 231-248. Development of lung- 
 fish 199, 201 
 
 249-268. Development of Ganoid 203 
 269-283. Development of Teleost 208 
 284-289. Larval sharks . . .216 
 290-295. Larval lung-fishes . .219 
 296-302. Larval sturgeons . . . 222 
 303-309. Larval Teleosts . . . 224 
 310-315. Skulls, jaws, and bran- 
 chial arches .... 254 
 316-325. Heart and conus arte- 
 
 riosus 258 
 
 326-331. Digestive tracts . . . 262 
 332-337. Urinogenital ducts and 
 
 openings 267 
 
 338. Blood-vessels of shark . . 268 
 339-344- Brain 272 
 
FISHES IN GENERA^ 
 
 INTRODUCTION 
 
 FISHES, defined in a popular way, are back-boned ani- 
 mals, gill-breathing, cold-blooded, and provided with fins. 
 It is in their conditions of living that they have differed 
 widely from the remaining groups of vertebrates. Aquatic 
 life has stamped them in a common mould and has pre- 
 scribed the laws which direct and limit their evolution ; it 
 has compressed their head, trunk, and tail into a spindle- 
 like form ; it has given them an easy and rapid motion, 
 enabling them to cleave the water like a rounded wedge. 
 It has made their mode of movement one of undulation, 
 causing the sides of the fish to contract rhythmically, 
 thrusting the animal forward. A clear idea of this mode 
 of motion is to be obtained from a series of photographs of 
 a swimming fish (Figs. 1-2) taken at successive instants : 
 thus in the case of the shark (Fig. i) the undulation of 
 the body may be traced from the head region backward, 
 passing along the sides of the body, and may be seen to 
 actually disappear at the tip of the tail. It is the press- 
 ure of the fish's body against the water enclosed in these 
 incurved places which causes the forward movement. 
 
 The density of the living medium of fishes exerts upon 
 them a mechanical influence ; they are, so to say, balanced 
 in water, free to proceed in all planes of direction, poised 
 
2 FISHES IN GENERAL 
 
 with the utmost accuracy, enabled to rise to the surface or 
 sink readily into deep water. A special organ, the 'air-,' 
 or 'swim-bladder/ has even been acquired by the majority 
 of living fishes, which, whatever may have been its origin 
 or accessory functions (v. p. 21), has certainly to an extraor- 
 
 Figs, i and 2. Movement of fishes, shark and eel. (After MAREY.) 
 
 dinary degree the power of rendering the specific gravity 
 of the fish the same as that of the surrounding water. 
 
 In an example of a swift-swimming fish some of the 
 most striking peculiarities of the aquatic form may be 
 seen. The Spanish mackerel, Scomberomorus (Fig. 3), 
 shows admirably a stout spindle-like outline ; its entire sur- 
 
FORM AND FINS 
 
 face is accurately rounded, 
 and there appear no irregu- 
 lar points which could re- 
 tard the forward motion of 
 the fish. Even in the 
 wedge-shaped head the 
 conical surface has been 
 made more perfect by the 
 tightly fitting rims of the 
 jaws, by the smoothly 
 closed gill shields, and by 
 the eyes' accurate adjust- 
 ment to the head's curva- 
 ture. Viewed from in front 
 (Fig. 4) the fish's outline 
 appears as a perfect ellipse, 
 and seems surprisingly 
 small in size : the fins, which 
 appear so prominent a feat- 
 ure in profile, can now 
 be hardly distinguished ; 
 above and below they form 
 keels, sharp and thin. In 
 side view the vertical or 
 unpaired fins are seen sur- 
 rounding the hinder region 
 of the body : they resolve 
 themselves into dorsal (D\ 
 anal (A), and caudal (C) 
 elements ; the former are 
 low and stout, elastic in pig . 3 . _ Type of swift swimming fish 
 
 their firm CUtwater margin, Spanish mackerel, Scomberomorus macula- 
 j , tus (Mitch.), J. &G. X i. (After GOODE 
 
 deeply notched and inter- i n u. s. F. c.) 
 
4 FISHES IN GENERAL 
 
 rupted posteriorly, where useless elements have been dis- 
 carded ; the caudal is 'broadly forked, stout in its support- 
 ing rays, strong in power of propulsion. At its sides a 
 remarkable ridge has been developed, functioning as a 
 horizontal keel (R) and preventing the stroke of the cau- 
 dal from varying from the vertical plane. 
 The lateral, or paired fins, pectoral and ven- 
 tral (P and F), may rotate outward and 
 arrange themselves in the line of the fish's 
 motion, so that in a somewhat horizontal 
 plane they may, like the unpaired fins, func- 
 tion as keels. When thus erected, the 
 paired fins present a firm anterior margin 
 which 'serves as a cutwater. While thus 
 somewhat similar in function to the vertical 
 fins, the ventrals and especially the pecto- 
 
 Fig. 4 .-Front . r 
 
 view of Spanish rals may acquire additional uses : they may 
 serve as delicate balancers, or may aid in 
 guiding or arresting the fish's motions. 
 
 In further conformity to aquatic needs, the entire sur- 
 face of the fish is notably slime covered, and although 
 perfectly armoured by plates and scales, yet presents no 
 point of resistance to forward motion. An internal balance, 
 moreover, has been effected between the supporting, vis- 
 ceral and muscular parts : the firm vertebral axis acquires 
 its central position, and at its anterior end the head struct- 
 ures form a compact, wedge-like mass : the body muscles 
 which give the fish its form-contour thin away on the ven- 
 tral side, permitting in the region between the head and 
 the anal fin the space occupied by the closely compacted 
 viscera : respiratory organs occupy a restricted space on 
 either side of the gullet ; the heart and its arterial trunk 
 are implanted closely in the throat in the median ventral 
 
NUMERICAL LINES 
 
 line ; the dorsal blood-vessel takes its position immediately 
 below the vertebral axis, and the air-bladder in the most 
 dorsal part of the abdominal cavity. 
 
 FIG. 5 
 
 Figs. 5-8. Numerical lines of fishes and cetaceans. The "entering angle" 
 begins at the snout-tip at the right, and extends as far as the vertical dotted line 
 (36 %, about, of the entire length) ; the " run " then begins and is continued to the 
 body terminal. 5. Striped porpoise, Phocaena lineata. 6. Spanish mackerel 
 (Cuban), Scomberomorus cavalla. 7. Humpback whale, Megaptera longimana. 
 8. Striped bass, Labrax lineatus. (All figures after PARSONS.) 
 
 In acquiring this perfect outward symmetry it is inter- 
 esting to note that the forms of fishes may be said to have 
 actually evolved the practical solution of the most theoretical 
 problems of curves and displacement in relation to sub- 
 
6 FISHES IN GENERAL 
 
 marine motion. A study of the " lines " of typical fishes by 
 naval engineers * has led to some most interesting results 
 as to the uniformity of their mathematical " normals." It 
 is found, for example, that the "entering angles " of many 
 and very different fishes are surprisingly similar (Figs. 6 
 and 8) : they thus terminate regularly (at the plane of the 
 greatest cross-section of the body) at 36 per cent of the 
 fish's total length; and the curves of the "run" (i.e. of 
 the hinder part of the trunk, from the plane of the great- 
 est cross-section to the body terminal), similar for all, are 
 smooth hollow curves, which in the forward motion of the 
 fish permit the passage of the displaced water. 
 
 It would be unreasonable to doubt that the fish form is 
 adapted to the mechanical needs of its environment, even 
 if there existed no further evidence than that of the meta- 
 morphoses of aquatic mammals. Many of these have 
 shown so complete an adaptation to water-living that it is 
 scarcely remarkable that they were early included among 
 fishes. And it is of further interest that there exist 
 transitional forms between the land-living mammals on 
 the one hand and the cetaceans on the other. In the 
 Seal it is but the initial step in the transformation that 
 has taken place ; the head and body have become bluntly 
 tapering, the hind legs displaced backward, the foot and 
 hand webbed, the hair adapted to submerged locomotion. 
 A further stage in the acquisition of the fish-like form is 
 shown in the Dugong and Manatee. And finally in the 
 Dolphin and Whale (Figs. 5 and 7) have been actually 
 attained the numerical lines of fishes (cf. Figs. 6 and 8). 
 In these cases, the mechanical conditions of aquatic living 
 have produced their result only at the greatest cost, 
 
 * '88. Parsons, Displacement and Area Curves of Fishes, Trans. Am. Soc. 
 Mech. Engineers. 
 
CLASSIFICATION j 
 
 enormous structural and physiological changes had of 
 necessity to have been attained. The frame of the 
 head and trunk has become moulded as in the fish's 
 form, contours have been elaborately filled out and 
 rounded, median dermal keels developed, vein valves lost, 
 and the legs transformed into fin-like appendages. 
 
 The form of the fish is accordingly to be looked upon as 
 cast in a more or less common mould by its environment. 
 Its internal structures, as in the cetacean, are also ob- 
 served to be modified in accordance with its external form. 
 This is a factor in the evolution of fishes which appears 
 in every group and sub-group. And it has ever stood in 
 the way of classifying them satisfactorily according to 
 their kinships. 
 
 "Fishes," used as a popular term, may include Lam- 
 preys, Sharks, Chimaeroids, Lung-fishes, and "Modern 
 Fishes" (Teleostomes), the major groups to be dis- 
 cussed in the present book. But the relative position of 
 each of these divisions must at present remain more or 
 less doubtful. The group of the Lampreys is certainly 
 widely removed from the remaining ones, standing mid- 
 way between the simplest chordate, Amphioxus, and the 
 true fishes : it is usually given a rank co-ordinate with 
 either of these, and, in fact, with all other groups 
 of vertebrates, taken collectively. Sharks, Chimaeroids, 
 Teleostomes, may be taken to represent true fishes ; and 
 each might be assigned co-ordinate rank, although geneti- 
 cally the Chimaeroids are certainly far more closely allied 
 to the Sharks than are the Teleostomes. The Lung-fishes, 
 as a widely divergent group, appear, as W. N. Parker has 
 suggested, to be reasonably entitled to a rank equivalent 
 to that of the three groups of true fishes taken together. 
 
3 FISHES IN GENERAL 
 
 The present writer has, however, retained in the main 
 the classification of Smith Woodward, in which Fishes 
 (Pisces) is looked upon as a class, and is made to include 
 as sub-classes, (I.) Sharks, (II.) Chimaeroids, (III.) Lung- 
 fishes, and (IV.) Teleostomes. A tabular grouping of the 
 fishes is shown below. And on the opposite page their 
 geological distribution is indicated. 
 
 TABLE I 
 
 A CLASSIFICATION OF FISHES 
 
 Type: CHORDATA (VERTEBRATES). 
 
 Class: Marsipobranchii, Lampreys, Pal&ospondylus, Hag, Lam- 
 prey, Ostracoderms . 
 Class : Pisces (True Fishes) . 
 
 I. Sub-class: ELASMOBRANCHII, Sharks and Rays. 
 
 Order: Pleuropterygii (Dean), Cladoselachids (Dean). 
 " Ickthyotomi (Cope), Pleuracanthids . 
 " Selachii, Sharks and Rays. 
 II. Sub-class: HOLOCEPHALI, Chimaeroids, Spook-fishes. 
 
 Order: Chimaeroidei, Squaloraiids, Myriacanthids, 
 Chimaerids. 
 
 III. Sub-class: DIPNOI, Lung-fishes. 
 
 Order: Sirenoidei, Dipterids, Phaneropleurids, Cte- 
 
 nodonts, Lepidosirenids. 
 " ? Arthrodira, Coccosteids, Mylostomids. 
 
 IV. Sub-class: TELEOSTOMI, Ganoids and Bony Fishes 
 
 (Teleosts) . 
 Order: Crossopterygii, Holoptychiids, Osteolepids, 
 
 Onychodonts, Ccelacanthids . 
 " Actinopterygii, 
 
 Sub-order: Chondrostei (Ganoids), Palceoniscoids, 
 
 Sturgeons, Garpikes, Amioids. 
 " Teleocephali, recent Bony Fishes (Tel- 
 
 eosts). 
 
 NOTE. The groups italicized are represented only in fossil forms. 
 The derivations of the scientific names are given on pp. 227-230. 
 
GEOLOGICAL DISTRIBUTION 
 
 TABLE II 
 THE DISTRIBUTION OF FISHES IN GEOLOGICAL TIME 
 
 The geological distribution of the prominent groups of fishes as here shown is in the main 
 as given by Zittel (Palaeontologie: Fische). The varying thickness of the lines denotes ap- 
 proximately increase or diminution in the number of existing genera. 
 
 
 Silurian. 
 
 Devonian. 
 
 Carbonif- 
 erous. 
 
 Permian. 
 
 
 
 H 
 
 .g 
 
 3 
 > 
 
 Creta- 
 ceous. 
 
 1 
 
 Miocene. 
 
 Pliocene. 
 
 Recent. 
 
 MarsipobrancMi. 
 
 Cyclostomes . . . 
 PPteraspids . .' . . 
 PCephalaspids . . . 
 Palaeospondylus . 
 PPterichthids . . . 
 
 Elasmobranchii. 
 Cladoselache . . . 
 Acanthodians . . . 
 Pleuracanthids . . 
 
 1 
 1 
 
 
 
 1 
 1 
 
 m 
 
 
 
 
 
 KB 
 
 
 
 
 
 
 
 un 
 
 
 
 MMB 
 
 
 
 
 
 
 
 
 Cestracionts . . . 
 
 
 
 
 
 
 
 
 
 
 
 
 Recent sharks (in- 
 cluding Notidanids) 
 
 
 
 
 
 
 
 
 
 
 
 
 Rhinobatus . . . 
 
 
 
 
 
 
 
 
 
 
 
 
 Pristis 
 
 
 
 
 
 
 
 
 
 
 
 
 Pristiophorus . . . 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Chimaeroids .... 
 
 Dipnoans. 
 Dipterus .... 
 Ceratodus .... 
 
 1 
 
 - 
 
 - 
 
 ~ 
 
 IBBB 
 
 am 
 
 
 
 
 M~ 
 
 MW 
 
 Teleostomes. 
 
 Crossopterygians . - 
 
 
 
 
 
 
 
 
 
 
 
 
 Acipenseroids . 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Perches and Bery- 
 cids 
 
 
 
 
 
 
 
 
 
 
 
 
 Siluroids .... 
 
 
 
 
 
 
 
 
 
 
 
 
 Gadoids and other 
 Teleosts .... 
 
 
 
 
 
 
 
 
 - 
 
 
 
 
 
 P 
 
I0 FISHES IN GENERAL 
 
 Fishes hold an important place in the history of back- 
 boned animals : their group is the largest and most widely 
 distributed : its fossil members are by far the earliest 
 of known chordates ; and among its living representa- 
 tives are forms which are believed to closely resemble 
 the ancestral vertebrate. 
 
 The different groups of fishes appear especially favour- 
 able for comparative study. Their recent forms are gen- 
 erally well understood, both structurally and developmen- 
 tally ; while a vast number of extinct fishes has been 
 preserved to serve as a check, as well as an aid, to theoret- 
 ical investigation. 
 
 The remarkable permanence of the different types of 
 fishes seems a striking proof of how unchanging must 
 have ever been the conditions of aquatic living. From as 
 early as the Devonian times there have been living mem- 
 bers of the four sub-classes of existing fishes, Sharks, Chi- 
 masroids, Dipnoans, and Teleostomes. Even their ancient 
 sub-groups (orders and sub-orders) usually present surviving 
 members ; while, on the other hand, there is but a single 
 group of any structural importance that has been evolved 
 during the lapse of ages, the sub-order of Bony Fishes. 
 There are many instances in which even the very types of 
 living fishes are known to be of remarkable antiquity : 
 thus the genus of the Port Jackson Shark, Cestracion 
 (Fig. 91), is known to have been represented early in the 
 Mesozoic; the Australian Lung-fish, Ceratodus (Fig. 127), 
 dates back to Liassic times;* the Frilled Shark, C/tlamy- 
 doselache (Fig. 92), though not of a palaeozoic genus, as 
 formerly supposed (Cope), must at least be regarded as 
 closely akin to the Sharks of the Silurian. 
 
 * Cf., however, Smith Woodward, The Fossil Fishes of the Hawkesbury 
 Series at Gosford. Memoirs of the Geol. Surv. of N. S. W. Pal. No. 4, 1890. 
 
MODE OF EVOLUTION U 
 
 The evolution of groups of fishes must, accordingly, 
 have taken place during only the longest periods of time. 
 Their aquatic life has evidently been unfavourable to deep- 
 seated structural changes, or at least has not permitted 
 these to be perpetuated. Recent fishes have diverged in 
 but minor regards from their ancestors of the Coal Meas- 
 ures. Within the same duration of time, on the other 
 hand, terrestrial vertebrates have not only arisen, but have 
 been widely differentiated. Among land-living forms the 
 amphibians, reptiles, birds, and mammals have been 
 evolved, and have given rise to more than sixty orders. 
 
 The evolution of fishes has been confined to a note- 
 worthy degree within rigid and unshifting bounds ; their 
 living medium, with its mechanical effects upon fish-like 
 forms and structures, has for ages been almost constant 
 in its conditions ; its changes of temperature and density 
 and currents have rarely been more than of local im- 
 portance, and have influenced but little the survival of 
 genera and species widely distributed ; its changes, more- 
 over, in the normal supply of food organisms, cannot be 
 looked upon as noteworthy. Aquatic life has built few 
 of the direct barriers to survival, within which the ter- 
 restrial forms appear to have been evolved by the keenest 
 competition. 
 
 It is not, accordingly, remarkable that in their descent 
 fishes are known to have retained their tribal features, and 
 to have varied from each other only in details of structure. 
 Their evolution is to be traced in diverging characters 
 that prove rarely more than of family value ; one form, 
 as an example, may have become adapted for an active 
 and predatory life, evolving stronger organs of progression, 
 stouter armouring, and more trenchant teeth ; another, 
 closely akin in general structures, may have acquired more 
 
I2 FISHES IN GENERAL 
 
 sluggish habits, larger or greatly diminished size, and degen- 
 erate characters in its dermal investiture, teeth, and organs 
 of sense or progression. The flowering out of a series of 
 fish families seems to have characterized every geological 
 age, leaving its clearest imprint on the forms which were 
 then most abundant. The variety that to-day maintains 
 among the 'families of Bony Fishes is thus known to 
 have been paralleled among the Carboniferous Sharks, the 
 Mesozoic Chimaeroids, and the Palaeozoic Lung-fishes and 
 Teleostomes. Their environment has retained their gen- 
 eral characters, while modelling them anew into forms 
 armoured or scaleless, predatory or defenceless, great, 
 small, heavy, stout, sluggish, light, slender, blunt, taper- 
 ing, depressed. 
 
 When members of any group of fishes became extinct, 
 those appear to have been the first to perish which were 
 the possessors of the greatest number of widely modified 
 or specialized structures. Those, for example, whose teeth 
 were adapted for a particular kind of food, or whose 
 motions were hampered by ponderous size or weighty 
 armouring, were the first to perish in the struggle for 
 existence ; on the other hand, the forms that most nearly 
 retained the ancestral or tribal characters that is, those 
 whose structures were in every way least extreme were 
 naturally the best fitted to survive. Thus generalised 
 fishes should be considered those of medium size, medium 
 defences, medium powers of progression, omnivorous feed- 
 ing habits, and wide distribution : and these might be re- 
 garded as having provided the staples of survival in every 
 branch of descent. 
 
 Aquatic living has not demanded wide divergence from 
 the ancestral stem, and the divergent forms which may 
 culminate in a profusion of families, genera, and species, 
 

 EVOLUTION !3 
 
 do not appear to be again productive of more generalized 
 groups. In all lines of descent specialized forms do not 
 appear to regain by regression or degeneration the potential 
 characters of their ancestral condition. A generalized form 
 is like potter's clay, plastic in the hands of nature, readily 
 to be converted into a needed kind of cup or vase ; but 
 when thus specialized may never resume unaltered its 
 ancestral condition : the clay survives ; the cup perishes. 
 
II 
 
 THE EVOLUTION OF STRUCTURES CHAR- 
 ACTERISTIC OF FISHES 
 
 IT will be the object of the present chapter to review 
 the gradations which occur in some of the characteristic 
 structures of fishes and to follow in some degree the 
 mode of their evolution. We may thus review the con- 
 ditions of the (i) gills, (2) skin defences (including teeth), 
 (3) fins, and (4) sense organs. 
 
 The structures of the immediate ancestor of the fishes 
 cannot be definitely inferred : the form, however, must 
 have been elongate and transversely jointed, for this con- 
 dition seems to have existed remotely before fishes in 
 the broadest sense had become evolved. This segmen- 
 tation, or metamerism, of the vertebrate body is best shown 
 among water-living forms, sometimes indeed in so perfect 
 a way as to suggest the jointed condition of an earth-worm. 
 
 The segmented body of the eel-shaped Lamprey, shown 
 in section in Fig. 69, illustrates an interesting condition 
 of vertebrate metamerism. Its entire body, from the 
 head region to the base of the tail, is composed of drum- 
 like segments which closely correspond to one another 
 in size and in component structures. Each segment 
 thus resembles its neighbours in its equal portions of the 
 vertebral column, digestive tract, nerve tube, muscle 
 plates and blood canal, and in the arrangement of these 
 parts with reference to bilateral symmetry. Motion in 
 this form requires no more of each segment than that its 
 
EVOLUTION OF STRUCTURES ^ 
 
 sides contract alternately to produce a rhythmical wave 
 passing along the entire series of segments and giving the 
 trunk an undulatory movement. 
 
 Should this elongate body now acquire a more fish-like 
 form, in attaining, for example, the power of more rapid 
 movement, it is obvious that this simple type of meta- 
 merism would undergo a series of changes. Every change 
 of outward form would be reflected on the parts not only 
 of each, but of all segments in their common relationships. 
 To perform more perfectly the functions of their location, 
 adjacent segments might become enlarged, folded, or 
 blended, and cause the most puzzling complications of 
 their component structures. One region of the body might 
 thus appear to develop at the expense of another, as in the 
 evolution of fin structures (cf. pp. 32-44), where a vertical 
 fin fold, representing the sum of the dorsal and ventral out- 
 growths of the hinder body segments, becomes reduced to 
 the lappet-like dorsal and ventral fins ; the intervening 
 substance of the fin web becoming drawn to the points 
 where greater rigidity is required. 
 
 The simple metameral character of the lamprey acquires 
 an especial interest when the different groups of fishes are 
 examined ; for it is found that all exhibit clearly body 
 segments and segmental structures in the most varied 
 stages of complexity. To trace metamerism seems, accord- 
 ingly, a mode of determining to what degree the differ- 
 ent groups have diverged from a common stem ; and to 
 compare the sums of the archaic metameral characters in 
 the different types of fishes may perhaps be looked upon 
 as one of the safest aids in determining their genetic posi- 
 tion. From the conditions of segmentation the lampreys 
 must certainly be given a lowly rank ; even with due allow- 
 ance for degeneration of structures they are clearly more 
 
jg EVOLUTION OF STRUCTURES 
 
 primitive than the most archaic sharks : while, on the 
 other hand, to the metameral type of the sharks may the 
 structures of the remaining groups of fishes be best referred. 
 
 i. AQUATIC BREATHING 
 
 Respiration in fishes is developed on the primitive chor- 
 date plan of ejecting water through gill slits perforating 
 the throat wall. The water taken in by the mouth is rich 
 in absorbed air, and, as it passes out, is well calculated to 
 oxygenate the blood suffusing the sides of the gill slits. 
 
 Among the earliest chordates there seems evidence 
 that the gill openings of the gullet were arranged with 
 reference to some form of primitive segmentation. Per- 
 haps they occurred as well in the region of the mid-diges- 
 tive tract, before their location became restricted to the 
 gullet. There has been as yet, however, little satisfactory 
 evidence * as to the number or conditions of the gill slits 
 in very primitive forms. In Amphioxus the gill arrange- 
 ment seems clearly a most specialized one : its adult con- 
 dition presents an atrium and an elaborate branchial 
 basket,! which could hardly have occurred in the lowly 
 ancestral chordate. Its early larva, however, is known, to 
 possess (but in a condition of assymmetry) but a few gill 
 slits (seven to nine) from which the many openings of the 
 adult branchial basket take their origin, a developmental 
 stage which most closely and most interestingly suggests 
 the conditions of higher forms. 
 
 * It has generally been inferred that the immediate ancestors of fishes had 
 not many gill slits, probably not more than eight or nine. A Liassic shark, a 
 Cestraciont, Hybodus (p. 85), is known to have had but five; a Permian Pleu- 
 racanthid, as in the recent Heptanchus, seven (p. 88) ; the Lower Carbonifer- 
 ous Cladoselache probably seven. 
 
 t Cf. Vol. II, of this series. Willey, Amphioxus and Other Ancestors of th& 
 Chordates. 
 
g 
 
 Figs. 9-12. Arrangement of gills of Bdellostoma (9), Myxine (10), Shark (n), and 
 Teleost (12). In each figure the surface of the head region is shown at the left. 
 
 B. Barbels. BD. Outer duct from gill chamber, BS. BO. Common opening of outer 
 ducts from gill chambers. BS. Branchial sac, or gill chamber. BS '. Branchial sac, sec- 
 tioned so as to show the folds of its lining membrane. G. Lining membrane of gullet. 
 GB. Gill bar, supporting vessels and filaments of gills. GC. Outer opening of gill cleft. 
 GF. Gill filament. GR. Gill rakers. G V. Vessels of gill. J, J '. Upper and lower jaw. 
 M. Mouth opening. N,N'. Anterior and posterior opening of nasal chamber. OP. Oper- 
 cuhim. SP. Spiracle. ST. Tendinous septum between anterior and posterior gill filaments. 
 * Denotes the inner branchial opening ; - , the direction of the water current. 
 C 17 
 
jg AQUATIC BREATHING 
 
 In the singular group of lampreys and slime eels (Mar- 
 sipobranchs, v. p. 57), the segmental arrangement of the 
 gills seems of a primitive pattern. In the Californian 
 Myxinoid (p. 59) the slits are as numerous as thirteen and 
 fourteen on either side, each opening directly from the 
 gullet to the neck surface (Fig. 9, G, *, BS\ BD). In the 
 lamprey the conditions are similar, but the number of gill 
 slits is reduced to seven. In Myxine (Fig. 10, G, BS\ BD, 
 BO) the outer portions of the canals becoming produced 
 taij-ward have merged in a single pore (Fig. 71 *). In these 
 forfrfs each gill canal has become dilated at one point of 
 its course, and in this sac-like portion the blood-suffused 
 tissues have grouped themselves into leaf-like plates (gill 
 filaments, or lamellae, BS') to increase their surface of 
 contact with the out-passing water. The dilating power 
 of this gill sac has then become specialized so that even 
 should the animal's mouth be closed, water for respiration 
 could be drawn in through the canal's outer opening : 
 from this acquired function the elaboration of bran- 
 chial muscles and a supporting framework of cartilage 
 (branchial basket, Fig. 69 A, BB) may have taken its 
 origin. 
 
 Among fishes proper many stages in the evolution of 
 gill organs are represented. They show altogether a 
 marked advance over the conditions of Fig. 9. There 
 has been a general tendency to press closely together the 
 gill pouches and to elaborate into thinner and larger 
 lamellae the blood-suffused tissue. In this process the 
 gill chamber has become slit-like, bearing gill lamellae only 
 on its front and rear margins ; its supporting tissue has con- 
 solidated into stout vertical gill bars, the gill structures in 
 general, becoming more highly perfected, tending to recede 
 from the surface. These conditions may best be illustrated 
 
GILL CHARACTERS IC; 
 
 by contrasting the highly modified gill apparatus of a bony 
 fish with the more archaic type of the shark. 
 
 In the sharks (p. 73) the gill slits pierce separately 
 the throat wall, as in the lamprey, and thus retain their 
 primitive segmental arrangement (Fig. 11). Their number 
 is usually five on either side, but in an archaic form (Hep- 
 tanchus, p. 88) may be increased to seven. Above and 
 in front of the line of gill slits occurs a small opening 
 leading into the gullet, the spiracle (SP). This, though 
 at present possessing but few gill lamellae, and therefore 
 of little respiratory value, was doubtless quite like its 
 neighbours before its gill-supporting tissue became of value 
 in suspending the lower jaw. It may now aid the mouth 
 opening in admitting water to the gills. At the left of 
 the figure (Fig. 11), the narrow slit-like openings of the 
 gill clefts are seen at GC: at the right, where the upper 
 portion of the head has been removed, the gill lamellae 
 are shown at GF\ the tissue intervening between the 
 gill pouches is reduced to a thin tendinous septum, 57", 
 at whose inner rim is the cartilaginous gill arch or bar, 
 GB, supporting the branchial vessels, G V. 
 
 In the gill region of a bony fish (Fig. 12) a number of 
 modified characters are now evident : the spiracle has 
 become obliterated; the number of gill bars reduced 
 in one form but two on either side remaining. These 
 have become closely pressed together, and bent backward, 
 receding from the surface of the head : their gill lamellae 
 have become larger and more numerous, their intervening 
 septum, ST, reduced in size. The gills no longer open 
 separately at the surface, but into an outer branchial 
 chamber formed and protected by a large overlapping 
 scale, or opercle, OP. This shield-like organ is hinged 
 at its anterior margin and opens or shuts rhythmically as 
 
20 GILL CHARACTERS 
 
 the throat muscles draw in or eject the water used in 
 respiration. On the gullet wall, the gill bars, now seen 
 to be closely drawn together, have acquired marginal 
 outgrowths, or gill rakers, GR, which form an inter- 
 locking screen across the gill openings and prevent the 
 escape of food organisms. So perfect may this apparatus 
 become that the opening and closing gill bars may retain 
 even microscopic life.* 
 
 Between the conditions of Figs, n and 12 there occur 
 many transitional forms. 
 
 To protect the gill region, specialized devices are known 
 to have been evolved early in the history of fishes, 
 the more early if, as Garman has supposed, the gill fila- 
 ments in primitive sharks protruded at the sides of the 
 head.f There are thus the gill-encasing derm frills of 
 the archaic sharks, Cladoselache, Chlamydoselache, and 
 Acanthodes (pp. 78-83), or of Chimaeroids (p. 100). These 
 protective structures, the writer believes, may well have 
 originated independently even within the limits of sub- 
 groups. They have certainly no direct relation to the 
 opercle of bony fishes. 
 
 Modes of respiration by-gill filaments have been found 
 in endless variety among fishes, clearly dependent in the 
 majority of cases upon environment. Thus fishes that 
 require a temporary existence out of water will be found 
 to have specialized spongy gill filaments and a closely fit- 
 ting gill cover to keep moistened the respiratory organs 
 (e.g. Callichthys, p. 172). 
 
 * Thus in many bony fishes, e.g. mullet or Brevoortia (menhaden), the 
 inner margins of the gill bars are fringed with what appears like the finest 
 gauze, each gill raker giving off primary, secondary, and tertiary branches. A 
 somewhat similar condition occurs in the shark, Selache (p. 90). 
 
 t This condition appears to have been possessed by the Lower Carbo- 
 niferous Cladoselache. 
 
S WIM-BLADDER 2 1 
 
 To live a longer time out of water has been rendered 
 possible only by the appearance of a lung-lil^e organ. Such 
 a structure, however, would have been of too great impor- 
 tance in the living economy of terrestrial vertebrates to 
 have had a sudden origin : it may most reasonably have 
 been derived from a similar structure occurring very gener- 
 ally among fishes. The lungs certainly resemble the swim- 
 bladder of fishes in so many important characters that it 
 seems difficult to regard these organs as morphologically 
 distinct. In itself the swim-bladder must be looked upon x 
 as an ancient and essentially a generalized structure, for 
 within the groups of fishes it has already acquired a vari- 
 ety of modified characters : appearing in a lowly condition 
 in sharks, it acquires a balancing function in the majority 
 of bony fishes ; in some forms (carp, siluroids) its function 
 connects it with the auditory organ, often by a highly 
 elaborated apparatus : while in other forms (Amia, Gar- 
 pike, Dipnoans), it is unquestionably of respiratory value. 
 The wide range in the characters of the air-bladder (cf. 
 Figs. 13-19, and Table, p. 264), even among recent fishes, 
 would naturally favour its homology with the lungs : it may 
 thus be paired or unpaired, attached by its duct to either 
 the dorsal, lateral, or ventral wall of the gullet : it may 
 present the most varied characters in its lining membrane 
 or in its vascular supply. When, moreover, it becomes of 
 respiratory value (e.g. Dipnoans, Polyptenis), the gills are 
 known to become in part degenerate. The larval history 
 of amphibians, presenting so perfect a transition between 
 gill-breathing and terrestrial vertebrates, should alone seem 
 to render more than probable the general homology of air- 
 bladder and lung an homology which a closer knowledge 
 of the conditions of the lungs of the lower urodeles (e.g. 
 Nectitrus may well be expected to establish definitely. 
 
LEP.DOSTEUS 
 AND AMIA 
 
 ERYTHRINUS 
 
 CERATODUS 
 
 POLYPTERUS 
 
 AND 
 
 CALAMOICHTHYS 
 
 LEPIDOSIREN 
 
 AND 
 PROTOPTERUS 
 
 REPTILES 
 BIRDS 
 
 MAMMALS 
 
 Figs. 13-19. Air-bladder of fishes, shown from the front and sides. Cf. p. 
 264. A. Air- or swim-bladder. AD. Air duct. D. Digestive tube. (After WILDER.) 
 13. Sturgeon and many Teleosts. 14. Amia and Lepidosteus. 15. Erythrinus, a 
 Cyprinoid Teleost. 16. Ceratodus. 17. Polypterus and Calamoichthys. 18. Lepi- 
 dosiren and Protopterus. 19. Reptiles, birds, and mammals. The diagrams illus- 
 trate the paired or unpaired character of the organ, its varied mode of attachment 
 to the digestive tube, and the smooth or convoluted condition of its lining mem- 
 brane. 
 
 22. 
 

 SCALES AND TEETH 23 
 
 The mode of origin of the lungs as an unpaired divertic- 
 ulum of the gullet is in every sense similar to that of the 
 air-bladder. 
 
 2. THE DERMAL DEFENCES OF FISHES 
 
 The dermal defences of fishes include scales, spines, fin 
 rays, armour plates, and teeth, presenting in all a wide 
 range of calcified structures. They have usually an outer, 
 or surface layer of hard enamel-like texture and an inner 
 substance heavy, stout, and bone-like. The former is de- 
 rived from the outer layer of the skin (epidermis), the 
 latter from the derma. The relation of these structural 
 parts may be well seen in a section of shark skin which 
 passes through one of its minute limy cusps, or dermal 
 denticles (Fig. 20). The outer skin layer, E', originally 
 covered the denticle, which grew outward, papilla-like, 
 beneath it ; its inner surface, in contact with the outgrow- 
 ing papilla, secreted the enamel, E, and is known as the 
 enamel organ, EO: at the cusp, however, the epidermis is 
 early worn away. The bone-like substance of the tooth is 
 clearly formed in the lower (dermal) layer of the skin, D' : 
 it is formed by the calcification of the outer layers of the 
 tip and base of the dermal papilla, leaving a vascular cavity, 
 PC, within. This limy substance, " dentine," D, presents 
 microscopically a columnar " cancellated " structure; in 
 this and in its lack of bone cells it differs structurally 
 from true (cartilage) bone. 
 
 The dermal denticle of the shark is certainly the sim- 
 plest form of a calcified skin defence : it appears to repre- 
 sent the ancestral condition of the various scales, teeth, 
 or bone plates which have been evolved in the groups of 
 fishes. It is usually of minute size, and studs closely the 
 entire surface of the skin, forming shagreen. In many 
 
27 
 
 Figs. 20-31. Mode of evolu- 
 tion of (teeth and) dermal defences. 
 
 20. Shagreen denticle of shark, X 30, 
 cross section. (After HOFER.) D. 
 Dentine. D'. Derma. E. Enamel. 
 '. Epidermis. EO. Enamel organ. 
 PC. Pulp cavity, showing nutritive 
 tubules passing into the dentine. 
 
 21. Shagreen denticle (" placoid 
 scale ") of Greenland shark, Lcemar- 
 gus, viewed from the side and (A} 
 top, enlarged. 22. Shagreen denti- 
 cles of shark, Scyllium, showing 
 mode of arrangement, x 30. 23. 
 Shagreen of sting-ray, Urogymnus, 
 nat. size. (After SMITH WOOD- 
 WARD.) 24. Ganoid dermal plates of Lepidosteus. A. Inner face of ganoid plates, 
 showing tile-like device of interlocking. 25. Variation of ganoid plates in Aetheolepis. 
 (After SMITH WOODWARD.) Plates from different regions vary in outline from cir- 
 cular to lozenge shape. 26. Coalesced ganoid plates of the siluroid Calhchlhys. 
 27. Jaw of Port Jackson shark, Cestracion. 28. Dental plate of extinct cestraciont (?), 
 Sandalodus. 29. Dental plates of jaw of sting-ray, Trygon (?). 30. Dental plates 
 of eagle-ray, Myliobatis. 31. Scales of Teleost. A. A single scale enlarged. 
 
 24 
 
EVOLUTION OF SCALES 2 $ 
 
 members of the shark group the denticles are scattered 
 over the body without traces of metameral arrangement 
 (Fig. 23) ; in others they acquire a segmental position 
 (Fig. 22). Usually the denticles possess very definite 
 shapes and regional characters ; their basal portion, where 
 implanted in the skin, may thus become of enlarged size 
 and regular outline (Fig. 21 A\ their projecting cusps 
 tapering, blunted (Fig. 23), or branched. Sometimes the 
 fusion of contiguous denticles may occur (as in the en- 
 larged blunted denticles of Fig. 23). 
 
 The evolution of the more perfect body armouring of 
 fishes from shagreen denticles has not been followed in 
 minor details. It appears, however, that the calcifica- 
 tion of the skin which occurs superficially in the dermal 
 papillae of the shark may in other fishes be traced oc- 
 curring in deeper and deeper layers of the derma : the 
 papillae at the surface accordingly lose their functional 
 importance, and tend to disappear, while the calcified 
 tissue of the derma representing morphologically the 
 basal region of the denticles is coming to occupy more 
 and more definite tracts. These processes have already 
 taken their origin within the group of sharks. 
 
 An interesting condition in the subsequent evolution of 
 the dermal armouring is illustrated in Fig. 25, and has 
 been described by Smith Woodward. The circular bone 
 plate of the figure is a calcified dermal tract which still 
 retains, scattered generally over its surface, traces of 
 shagreen tubercles : from this shark-like condition a 
 well-marked gradation in the form of the derm plates 
 may be traced in different body regions of the same 
 fish : according to metameral needs there are acquired 
 rectangular or lozenge-shaped outlines. In Fig. 24 these 
 bone or " ganoid " plates are seen to constitute a com- 
 
2 6 EVOLUTION OF SCALES 
 
 plete but flexible body armouring, made additionally 
 strong by an interlocking articulation of its elements 
 (24 A). 
 
 In this form the enamel-like surface layer ("ganoine") 
 of the ganoid plates is believed to be derived from the 
 dentine substance, and not deposited by the epidermis : 
 they bear numerous shagreen denticles during an early 
 period of life. 
 
 The most complete encasement of a fish's body by 
 dermal plates is shown in Fig. 26, v. p. 172. The met- 
 ameral conditions have here permitted extended fusions, 
 a single dermal plate enclosing the upper, or lower 
 division of the muscle-plate of either side. 
 
 The thin horn-like scales of the majority of recent 
 fishes, e.g. carp or perch (Fig. 31 A) are probably 
 derived from a condition not widely different from that 
 of Fig. 24. They take their origin, however, in a deeper 
 layer of the derma, thence grow outward, arising as 
 if from deep and flattened pockets. Their substance 
 becomes horn-like, rather than limy, and they enlarge in 
 outline, rather than in thickness. Their hinder margins, 
 often crenulate, overlap widely the neighbouring scales ; 
 their arrangement is in direct relation to the underlying 
 metameres, and their surface is densely slime-coated. 
 The dermal armouring they thus constitute is both light, 
 tough, and flexible. 
 
 Degeneration of scales is shown to occur in many 
 types. In some forms their size may become micro- 
 scopic (eel), in others enormously enlarged (mirror carp). 
 In cases they may entirely disappear (leather carp). 
 The fusions of the dermal plates of the trunk-fish or 
 of the sea-horse (p. 177) are probably degenerate. 
 
TEETH 27 
 
 Teeth 
 
 Teeth have long been known to represent the dermal 
 defences of the mouth rim. In this region they have 
 become of especial value in the living economy of verte- 
 brates seizing, holding, cutting, or crushing the food- 
 material. They have here accordingly been retained and 
 specialized. In the sharks the dermal denticles of the 
 mouth rim are often identical in shape and pattern with 
 those of the entire body surface : they differ only in 
 their larger size. Their arrangement in many rows still 
 presents clearly their metameral character. 
 
 The forms of teeth acquired among the different groups 
 of fishes suggest closely the evolution of the more modi- 
 fied dermal defences. In general, they are found to vary 
 widely according to their function or location ; those near- 
 est the dermal margin of the mouth usually retaining 
 the cusp-like and more primitive features. Thus in the 
 jaw of Port Jackson shark (Fig. 27, v. p. 85), the teeth of 
 the symphysial region clearly represent shagreen denti- 
 cles ; while those deeper in the mouth, large and blunt, 
 serve as crushing or "pavement " teeth. These must evi- 
 dently be looked upon as standing in the same relation to 
 the anterior cusps, as do the bone plates of Fig. 25 to the 
 derm denticles of Fig. 23 ; the fused crushing teeth have 
 still retained their metameral arrangement. The dental 
 plates (Fig. 30) of a ray, Myliobatis (p. 96) show more 
 perfect conditions for crushing ; they are uniform in size, 
 tightly set, and present a smooth, mosaic-like surface. A 
 still more perfect fusion of the dental elements occurs in 
 a ray, closely akin to Myliobatis ; all lateral elements have 
 here been fused, but their metameral sequence has been re- 
 tained (Fig. 29). In Fig. 28 is shown a dental plate of a 
 
2 3 TEETH AND SPINES 
 
 fossil shark (?), Sandalodus, which probably represents a 
 condition of complete fusion ; it would accordingly cor- 
 respond to the sum of the dental elements of half of the 
 jaw of Fig. 27. 
 
 In more highly modified fishes the tooth-producing 
 region has become greatly extended ; teeth are present not 
 only on the jaw rims, but deep in the mouth cavity, 
 studding its floor and roof, and occurring even on the 
 tongue, gill bars, and pharynx. 
 
 Fin Spines 
 
 Primitive dermal defences appear to have played a 
 prominent part in the formation of fin spines. The clus- 
 tering of dermal cusps on the exposed margin of a fin 
 may have been an important initial step toward the for- 
 mation of a rigid cutwater. The anterior margin of the 
 fin of Fig. 49 is whitened with a fusion of dermal tuber- 
 cles which must have formed a firm encrusting support ; 
 the extension of the calcification of the bases of the tu- 
 bercles would accordingly be the mode of origin of a fin 
 spine. In Fig. 32 is shown a spine that appears largely 
 of this origin. A similar spine (Fig. 33) shows its dermal 
 tubercles not only at its sides, but in a most marked 
 way at its hinder margins. In Fig. 34, representing the 
 " sting " of the sting ray, a series of dermal spines, bear- 
 ing rows of minute denticles are seen to arise in a meta- 
 meral succession. A condition somewhat similar is known 
 in the Carboniferous shark, Edestus (Fig. 35), whose spine, 
 often of gigantic size, is of special interest, since it shows 
 how important a part in spine-formation may be taken by 
 the dermal defences of many successive metameres. The 
 spine is clearly segmented, and as its separate elements 
 (Fig. 37) are bilaterally symmetrical (Figs. 36 and 38), its 
 
FIN SPINES 
 
 position was probably in the median line of the body. 
 The well-marked, backward curve of the spine suggests 
 
 34 
 
 Figs. 32-38. Fin spines. 32. Fin spine and pectoral fin of Acanthodian. 
 33. Hybodus (cestraciont shark). 34. Sting-ray, Trygon. 35. Edestus heinrichsii 
 (Carboniferous shark, known only from its spine), side view of spine. X \. 36, 
 37, 38. Dorsal view, separated element and transverse section of Edestus spine. 
 
 that fin structures could not well have existed behind it. 
 Each separate element has an elongated basal portion, 
 
go EVOLUTION OF FINS 
 
 which apparently was imbedded in the integument ; its 
 gouge-like form (Figs. 37 and 38) permitted it to be firmly 
 apposed to its anterior and posterior neighbours. Each 
 median enamelled cusp represents apparently the sum of 
 the shagreen papillae, occurring in the median-dorsal region 
 of each metamere, its gouge-like underlying portion the 
 metameral calcification of the bases of the denticles. 
 
 What has been the mode of origin of the primitive 
 derm cusps is a puzzling question. It is significant, per- 
 haps, that they occur in primitive forms (sharks) in con- 
 nection with the sense organs of the lateral line (p. 50), 
 and that they are in this region retained in a number 
 of archaic forms (Polypterus, p. 148, Callichthys, p. 172), 
 which have in all other body parts evolved protective derm 
 plates.* It is certain that for the sensory groove of the 
 lateral line, no more simple, protective devices could have 
 arisen than conical elevations of skin. Arising in this 
 region, they may have extended their protective functions 
 over the entire body surface. 
 
 3. THE EVOLUTION OF FINS 
 
 Fins are the organs of progression adapted to the 
 needs of aquatic living. A fish, balanced in its living 
 medium, acquires, as has been seen, a boat-like form, 
 enabling it to pierce the water in the least resisting 
 \manner. 1 Its appendages, when they come to arise, must 
 reasonably be looked to to fulfil the mechanical condi- 
 tions of aquatic motion in order to propel to the best 
 advantage the lightly balanced and boat-shaped mass. 
 Fins might thus be expected to arise as keel-like struct- 
 
 * In the sensory canals of the head of Chimsera, the presence of scattered 
 bony plates, protective in function, v. p. 1 14, would suggest the concentration 
 of the marginal cusp elements for more perfect protection. 
 
MEDIAN FINS 31 
 
 ures, i.e. as ridges in the direction of the fish's axis or 
 line of motion. 
 
 Fish fins have long been distinguished as vertical (me- 
 dian, or unpaired) or lateral (paired), the former function- 
 ing both as keel and means of propulsion, the latter as 
 accessory and specialized balancing organs.^ 
 
 Median Fins 
 
 Median fins are unquestionably the older. They exist 
 in the simplest condition in those fishes whose axis is long 
 and whose motion is undulating. Indeed, the sole swim- 
 ming requisite is here the continuous dermal keel which 
 passes down the back from the head to the body terminal, 
 and extends thence forward on the ventral side. The 
 undulatory motion of the body is well transmitted to the 
 surrounding medium by the exaggerated undulation of 
 this long, waving fin web. This condition was probably 
 the ancestral one in the evolution of fishes. It represents 
 the simplest metamerism ; it occurs as the adult condition 
 in the lampreys (p. 57), and as the embryonic or larval 
 stage in all fishes, appearing before any traces of paired 
 fins are known ; .it is even adverse to their specialization : 
 should life habits require undulatory motion, paired fins 
 must inevitably tend to disappear (eel, p. 173 ; Cala- 
 moichthys, p. 150). 
 
 From this condition the further evolution of the un- 
 paired fins may thus be theoretically outlined. 
 
 The primitive continuous dermal fin could have been 
 of little value in active movement : its more rapid undu- 
 lations could not have greatly increased the rate of motion, 
 since its web, lacking in supports, would not have retained 
 its rigidity. As the simplest means of strengthening the 
 fin fold, " actinotrichia " (Ryder), appear to have been early 
 
32 EVOLUTION OF FINS 
 
 evolved (Fig. 39, T) ; these are slender, unjointed fin sup- 
 ports, passing from the body wall to the margin of the 
 fin, appearing to arise without relation 
 to the underlying body segments. The 
 more rapid undulations of the contin- 
 uous fin would next cause nodes to 
 arise ; and at other points the greatest 
 mechanical stress would occur. These 
 portions of the fin web would accord- 
 ingly become prominent, while the in- 
 tervening or useless parts would dimin- 
 ish in width and tend to disappear. The 
 body terminal (tail, caudal fin) has now 
 * become the seat of propulsion : dorsal 
 and ventral fins arise as lobate elements 
 of the fin fold, functioning as vertical 
 keels in the region of the body where 
 mechanical stress demands them (v. Fig. 
 40), increasing in size as the intervening 
 portions of the web gradually disappear. 
 Their rate of growth is doubtless af- 
 fected by the appearance of the paired 
 fins ; for even at an early period of de- 
 velopment these are known to have an 
 important function in balancing the fish. 
 The lappet-shaped fins (Fig. 40) next 
 acquire more rigid supports. Cartilagi- 
 nous rod-like elements arise within the 
 fin web, arranged in metameral sequence, 
 representing, perhaps, fusions of actino- 
 trichia. As shown in Fig. 40, these car- 
 Fig- 39- Hypothet- tilaginous "radials" R, appear to be 
 
 ical ancestral shark. Let- 
 ters as on p. 33. largest and stoutest in the widest por- 
 
MEDIAN FINS 
 
 33 
 
 tions of the fin lobe, and thence to taper in size toward 
 the nodal points of the web. Each radial appears shortly 
 to segment off a proximal joint, or "basal" cartilage, B, to 
 secure a more perfect attachment with the wall of the body. 
 The subsequent evolution of the fins appears to have 
 been determined by two modifications of growth, the 
 clustering of the radial and basal elements, and the 
 encroachment of newly formed marginal (distal) rays 
 
 FIQ.40 
 
 43 
 
 Figs. 40-43. Evolution of unpaired fins. 40. Plan of reduction of vertical fin 
 web into its dorsal, anal, and caudal elements. 41. Arrangement of fin supports 
 in primitive fin {Cladoselache) . 42. Plan of archaic unpaired fin in (larval) shark. 
 43. Unpaired fin of fossil Crossopterygian, Holoptychius, (After SMITH WOOD- 
 WARD.) - 
 
 A. Anal fin. B. Cartilaginous basal (fin support). C. Caudal fin. D. Dermal 
 margin of fin. D' . Anterior and D". Posterior dorsal fin. K. Cartilaginous radial 
 (fin support). T. Actinotrichia. 
 
 upon the functions of the older fin supports. Three 
 stages in this metamorphosis will be seen in Figs. 41-43. 
 The first illustrates the dorsal fin of an ancient shark 
 (Cladoselache, p. 79), and will at once be seen to present 
 most primitive conditions^: It closely resembles the theo- 
 
34 ANAL AND DORSAL FINS 
 
 retical dorsal fin, D' or Z>" of Fig. 40. The form of the 
 fin suggests the lobate constriction of the continuous fin 
 web ; its radial supports, R, extend from the body wall to 
 the margin of the fin, and between them traces of actino- 
 trichia are to be seen. The anterior margin of the fin 
 must now function as a strong cutwater, its supporting 
 elements, both radial and basal, tightly clustering. A fin 
 of this character could evidently have possessed a greater 
 freedom of lateral movement in its hinder than in its an- 
 terior part ; and thus the clustering of the fin supports 
 becomes of especial significance. The region of move- 
 ment, restricting itself to the hinder part of the fin, 
 permits extensive fusions of the supporting cartilages 
 anteriorly, and leads ultimately to exceedingly complex 
 conditions. The dorsal fin of a Coal Measures fish (Ho- 
 loptychius, p. 15.1) has thus (Fig. 43) specialized the power 
 of lateral movement in the highest degree. The length 
 of the fin has, in the first place, become greatly compressed, 
 a process which seems to have resulted in implanting the 
 anterior basals, B, deeply into the integument and in 
 fusing them : the posterior basals then appear to have 
 been everted from the surface of the body. Here they 
 still retain their segmental arrangement, but are irregular 
 in shape and reduce in size distally. 
 
 An important part is taken by the dermal margin of 
 the fin in modifying the size of the older fin supports. 
 The simplest form of a dorsal fin of a recent shark (Fig. 
 42) has thus more than half of its functional area of a 
 dermal origin, although in other regards it resembles 
 closely the conditions of Fig. 41. The dermal margin of 
 the fin has apparently increased to the detriment and 
 consequent reduction of the cartilaginous elements ; -it 
 produces in its secondary structures light flexible horn- 
 
CAUDAL FIN 35 
 
 like rays, which prove stronger and more serviceable than 
 the heavier radials ;. it seems more capable of adapting 
 the fin for special uses. 
 
 Accordingly, in many forms of recent fishes, notably 
 bony fishes, the entire fin is found to become of dermal 
 origin ;. The radio-basals, greatly reduced in number and 
 size, extend no further outward than the base of the fin ; 
 they are usually small and irregular, and are often deeply 
 sunken within the body wall. 
 
 After this glimpse at the mode of origin of the vertical 
 fins, i.e. dorsals and anals, the history of the final vertical 
 
 fin, the tail, and of the paired fins may next be reviewed. 
 
 f 
 The Caudal Fin 
 
 The tail, or caudal fin, is the main organ of aquatic 
 propulsion, and it is doubtless on this account that it 
 presents so wide a range in its structure and outward 
 form. From the earliest times there are found fishes of 
 all groups whose tail shapes are tapering (diphycercal, Fig. 
 47), unsymmetrical (Jieterocercal, Figs. 45, 46), or squarely 
 truncate (homocercal, Fig. 48), as the mechanical needs 
 in swimming may have demanded. 
 
 The following summary of the mode of evolution of 
 the caudal fin seems to be warranted by study of fossil 
 and embryonic forms. The vertical fin fold of the ances- 
 tral fish was probably carried around the body terminal 
 and strengthened by constant actinotrichia (Fig. 39 C), a 
 condition similar to that (Fig. 44) of an early larval 
 stage of living fishes (protocercy). This caudal structure, 
 however, could have proven Ba value only in sluggish 
 undulatory motion. The functional needs, which gave 
 rise to radials anteriorly, have in the tail region produced 
 firmer and stouter fin supports. These appear both on the 
 
2 6 CAUDAL FIN 
 
 dorsal and ventral sides, but, unlike the radials of the anal 
 or dorsal fins, do not segment off basal elements. They 
 first occur in the region of the base of the caudal, as in 
 the embryonic stage (Fig. 44, R), since, perhaps, it is in this 
 region that the greatest stress occurs in propulsion. It 
 is not until a later stage that their metameral sequence 
 is extended backward to the tip of the vertebral axis 
 (Fig. 40, Q. 
 
 With the origin of cartilaginous supports there seems 
 to have arisen a mechanical need for enlarging the ventral 
 lobe of the caudal; -ft is here certainly that in the majority 
 of early forms the radials appear longer and stouter, giv- 
 ing rise to the condition of heterocercy of Figs. 45 and 46. 
 The greater functional importance of the radials of the 
 ventral region, R+H, is acquired contemporaneously with 
 the upturning of the end of the vertebral axis. In the 
 tail of a Lower Carboniferous shark (Fig. 46, v. p. 79), an 
 extreme degree of heterocercy has been acquired before 
 the radials of the lower lobe have extended themselves in 
 the hindmost region of the vertebral axis ;,the ventral web 
 of the upper tail lobe, accordingly, is still strengthened 
 by minute (dermal) rays, which the writer believes homol- 
 ogous with actinotrichia ; , 6n the fin's dorsal side the 
 radials have been abruptly upturned with the notochord, 
 and are fused into a compact cutwater. 
 
 The plan of structure of the shark's caudal fin (Fig. 45) 
 may in its most primitive form prove to be the ancestral 
 one of fishes ; if this is the case it would give rise to the 
 types of caudal fins of Figs. 47 and 48. That it has given 
 rise to the latter form cannot be doubted, for even in the 
 adult condition of the fin the notochord, N> may be seen 
 passing to the upper lobe of the tail ; the essential out- 
 ward form of this truncated, or homocercal, tail had already 
 
Figs. 44-48. Evolution of caudal fin. 44. Embryonic caudal of Amia. 45. Hetero- 
 cercal caudal of shark, Cestracion. 46. Heterocercal caudal of Cladoselache. 47. Diphy- 
 cercal caudal of Polypterus. (After L. AGASSIZ.) 48. Homocercal caudal of Teleost. 
 (After RYDER.) 
 
 D. Dermal fin supports. L. Lateral line. M. Spinal cord. MC. Membranous caudal. 
 N. Xotochord. N+, and R+N. Neural spines, including probably radial and basal 
 elements. R. Radials. R+H. Haemal arch and spine ; includes as well, probably, radial 
 and basal elements. 
 
 37 
 
38 PRIMITIVE CAUDAL FIN 
 
 been acquired in ancient sharks (Fig. 46). The fin of Fig. 
 
 47, however, has not generally been looked upon as derived 
 from shark-like conditions ;/it has, on the other hand, been 
 thought to be most nearly of the ancestral form. The 
 vertebral axis does not appear to be upturned, and the 
 ventral and dorsal lobes of the fin remain nearly sym- 
 metrical, or diphycercal. This form of the caudal fin, on 
 the other hand, has been noted to present many degener- 
 ate characters, arid to the writer* it seems more reasona- 
 ble to regard the diphycercal condition as in many cases 
 directly descended from the heterocercal. This might be 
 effected by the terminal portion of the vertebral rod abort- 
 ing (as in Fig. 47, N), and the upper and lower lobes of the 
 tail becoming pressed backward until their hinder margins 
 appose in the axial line.f The form of diphycercy which 
 is seen in Fig. 1 19 is unquestionably of little morphological 
 value ;,ft occurs commonly in deep-sea fishes of every group, 
 and must be looked upon as a degenerate condition result- 
 ing from impeded motion under the conditions of bathyb- 
 ial, or deep-sea living. 
 
 The cartilaginous supports of the caudal, like those of 
 other unpaired fins, become greatly reduced in size by the 
 encroachment of dermal rays. In the tail of the fossil 
 shark (Fig. 46) the cartilaginous supports, R, extend to the 
 very margin of the fin :. an the modern shark (Fig. 45) a 
 large part of the functional fin area has become of second- 
 ary, or dermal origin, D, In the caudals of Figs. 47 and 
 
 48, distinct dermal rays, D, are seen, extending from the 
 body wall to the fin margin, splitting and segmenting dis- 
 tally in becoming more perfectly specialized in function. 
 The cartilaginous supports, R + Nand R + H, must now be 
 
 * Journal of Morphology, IX, i, 1894. 
 t Gephyrocercy of Ryder. 
 
PAIRED FINS 29 
 
 looked upon as including the elements of both the radials 
 and the haemal or neural processes and spines. 
 
 The Paired Fins 
 
 The paired fins of fishes claim an especial interest as 
 the precursors of the limbs of the land-living vertebrates. 
 In this light they have been widely studied, and many 
 schemes have been devised for the comparison of the parts 
 of the five-fingered extremity, or cheiropterygium, of the 
 amphibian with the fin structures of many fishes. The un- 
 satisfactory character of these homologies, however, is felt 
 at the present time more generally than ever, and many 
 morphologists believe with Dr. Mollier * that the ancestral 
 form of the terrestrial limb cannot be found in any of the 
 known types of paired fins^^^^T**" 
 
 Among fishes, on the other hand, there appears to be a 
 well-marked unity of plan in the varied forms of the 
 paired fins and there exists so perfect a gradation in 
 structural characters in the different forms that it seems 
 impossible to doubt their genetic kinship. Which fin, 
 however, must be looked upon as the ancestral type is still 
 disputed. Professor Gegenbaur has long maintained that 
 the fin of Fig. 54 (or, better, the pectoral fin of Fig. 147!) 
 is to be looked upon as the most primitive form, or Archip- 
 terygium. It is a leaf-shaped fin, whose principal carti- 
 laginous supports are arranged in a row from base to tip 
 in the position of a mid-rib tf and whose minor fin supports 
 are grouped more or less symmetrically on either side of 
 this axis (cf. Figs. 53, 54, 121, 123, 126). The archipteryg- 
 ium is believed by Gegenbaur to have had a centrifugal 
 origin : it arose behind the gill region, representing in its 
 
 * SB. Gesell.f. Morph. Munchen, 1894, p. 17. 
 
 t Gegenbaur, Das Flossenskelet der Crossopterygier. Cf. Morph. JB, 1894. 
 
40 LATERAL FOLD FINS 
 
 supporting substance the fusion of the cartilages of the 
 hindmost gill bars.; in its outward growth the median axis of 
 the fin was first produced, the minor supports then arrang- 
 ing themselves on both anterior and posterior margins. 
 The fin of Fig. 52 was believed to represent a specially 
 evolved (or "monoserial") form of the archipterygiumr.the 
 hindmost of its elements, B, was homologized with the 
 primitive fin stem, along whose posterior (post-axial) mar- 
 gin the elements, R, no longer occurred. The structures 
 of Fig. 53 were adduced as a transitional stage in the dif- 
 ferentiation of the biserial archipterygium (Fig. 54) into the 
 monoserial form of Fig. 52. 
 
 The theory of Gegenbaur as to the origin and evolution 
 of the paired fins cannot be said to be in any way generally 
 supported at the present time. The opposing view, that 
 of their derivation from a continuous lateral dermal fin 
 fold, based on the work of Thacher, Balfour, Mivart, 
 Dohrn, Wiedersheim, and others, is widely accepted, and 
 continues to gain supporting evidence on the sides both 
 of embryology and palaeontology. 
 
 In the following discussion of the paired fins the 
 writer has mainly followed the recent studies of Wieders- 
 heim.* 
 
 The paired fins are believed to have arisen as balancing 
 organs, accessory in function to the vertical fins. They 
 probably occurred early in the line of descent as a response 
 to a need for balancing the fish's body, at the time when 
 the vertical fin was separated into caudal, dorsal, and anal 
 elements. There can be little doubt that they first arose 
 in the line of the fish's motion, and are known primitively 
 (Figs. 49, 50), as a pair of keel-like lateral lappets arising 
 somewhat ventrally, and directed outward and downward. 
 
 * Das Gliedmassenskelet der Wirbdthiere, 1893. 
 
PAIRED FINS 4I 
 
 The foremost pair appears anteriorly not far behind the 
 gill region : from its position it has certainly the more im- 
 portant mechanical function in balancing the fish's length 
 on this account becoming more widely modified in form 
 and function as the pectoral fins. The hinder pair, or ven- 
 tral fins, though in the plane of the pectorals, has a more 
 ventral position, the hinder borders converging in the 
 region of the anus. The ventral fins are certainly placed 
 in the most motionless region of the fish: they are little 
 affected by either the lateral or upward movements of the 
 body ; and remain accordingly smaller in size and simpler 
 in structure than the pectoral fins. That there may have 
 existed in primitive fishes a third (post-ventral) pair of fins 
 is by no means improbable (cf. T. J. Parker, Ref. p. 244), 
 although its presence has not as yet been satisfactorily 
 demonstrated. 
 
 The paired fins thus appear to have been derived from a 
 continuous dermal fold, similar in every way to that giving 
 rise to the vertical fins. They appear, moreover, to have 
 undergone the same mode of evolution in their structures' 
 as have the dorsal or anal fins. The unpaired fin fold as it 
 passed forward on the ventral side of the body may primi- 
 tively have forked in the anal region, and given rise on 
 either side to a lateral fold. In these might next appear 
 an anterior and posterior pair of lappets, pectoral and 
 ventral fins, whose positions would be determined by 
 mechanical needs, and whose size would increase as the 
 intervening and useless portion of the dermal fold disap- 
 peared. In the subsequent history of pectoral and ventral 
 fins, supporting elements, actinotrichia, radials, and basals, 
 would arise in the same way as in the unpaired fins, and a 
 similar metamorphosis of the fin form would take place, 
 owing to the concrescence of these elements and to the 
 
FIG. 49 
 
 Figs. 49-54. Evolution of paired fins. 49-50. Pectoral and ventral fins of Cladose- 
 lache. X 5. 51. Pectoral fin of Acanthodian, Parexus. (After SMITH WOODWARD.) 52. 
 Pectoral fin of Heptanchus. (After GEGENBAUR.) 53. Pectoral fin of Xenacanthus 
 (Pleuracanthus.) (After A. FRITSCH.) 54. " Archipterygial " pectoral fin of Ceratodus. 
 (After HOWES.) 
 
 B. Basal. D. Dermal. R. Radial. 
 
 42 
 
PAIRED FINS . 43 
 
 subsequent encroachment of the dermal fin margin. These 
 conditions may be briefly illustrated. The paired fins of a 
 primitive shark (Figs. 49, 50, v. p. 79) appear as the actual 
 lappet-shaped remnants of a continuous dermal fold. The 
 ventral fins (Fig. 50) have clearly retained even the out- 
 ward shape of the fin fold ; the supporting elements are 
 arranged in metameral order ; the radials, R, are unjointed, 
 extending from body wall to fin margin ; the basals, agree- 
 ing in number with the radials, are uniform in size, and as 
 yet unfused. The pectorals, acquiring more special func- 
 tions (Fig. 49), are enlarged in size, their basals, B, becom- 
 ing compressed and obscure. In these fins the effect of 
 concrescence is admirafry marked ; the anterior fin margins, 
 pressed tail-ward in their plane of growth, become firm and 
 rigid, their elements stout and compact ; the basals, re- 
 sponding to this outward need, cluster more firmly together, 
 are compressed and fused, their anterior elements, largest 
 and stoutest, become inturned, their posterior elements, 
 slightest and most clearly metameral.* 
 
 The next stage in the evolution of the paired fins is 
 clearly comparable to that already noted as occurring in 
 the dorsal fin of Holoptychius (Fig. 43), where the line of 
 basals, fusing compactly into a plate-like mass, had in- 
 turned its anterior, and f protruded its posterior tip ; a 
 change apparently slight, but great in functional impor- 
 tance. Up to this stage the fin has been firmly implanted 
 in the body wall ; its motion, probably slight upward or 
 downward, served but to balance the fish, its fin rays, 
 tending to concentrate anteriorly, functioned as an efficient 
 cutwater. This process of concentration in the anterior 
 fin margin may have resulted, the writer believes, in the 
 
 * The effect of the enlarged and clustering dermal denticles in strengthen- 
 ing the cutwater margin of the fin has already been noted (p. 28). 
 
44 PAIRED FINS 
 
 formation of fin spine, as in Acanthodian * (Figs. 32, 51, 
 and p. 81). But the protrusion of the line of the basals 
 must have brought with it a new use in the economy of 
 fish motion. The plane of the fin could now be directed 
 upward or downward ; the fin would become a direct aid 
 in propulsion ; it would acquire a paddle-like function ; it 
 could also be extended sideways as a check to motion. 
 Under these circumstances it is not unnatural that the 
 region of the concrescence of the fin rays should now be 
 transferred from the fin's anterior to the more useful pos- 
 terior (now distal) margin, and that the fin rays, as well as 
 the line of basals, should acquire a more jointed structure, 
 suited to flexible motions. The course of the differentia- 
 tion of fin structures may be traced from this point on- 
 ward, as Wiedersheim has shown, by means of a series of 
 gradational stages : from the conditions of Fig. 49 we may 
 in the present figures pass to those of Fig. 52, thence to 
 those of Figs. 53 and 54. In the pectoral fin of a modern 
 shark (Fig. 52) the basal cartilages, B, may still be com- 
 pared with those in the older form (Fig. 49 B] ; their distal 
 element (B, at the right of the figure), however, protrudes 
 from the body wall and is becoming surrounded by clus- 
 tered radials, R ; the cartilaginous elements, it is here 
 noted, have been placed in competition with the dermal 
 elements, and have already yielded them over half of the 
 fin area. In the next stage of the evolution, as in the 
 pectoral fin of a Permian shark (Pleuracanthus, p. 83, Fig. 
 53), the line of the basals is seen to boldly protrude from 
 the body wall and to have become distinctly jointed ; the 
 radials have surrounded its distal end, and taken a position 
 
 * This homology proposed by the writer has not been accepted by Smith 
 Woodward; the spine is unquestionably encased outwardly by dermal den- 
 ticles. 
 
PAIRED FINS 45 
 
 along the outer half of the hinder margin of the fin stem ; 
 the dermal region of the fin, D, has notably increased. 
 Indeed, the fin area in the modern bony fishes (Fig 145, 
 PF) may become entirely dermal, and the basal supports 
 greatly reduced and metamorphosed. In a final type of 
 fin (Fig. 54) the line of the basals has become widely spe- 
 cialized, and the characters of the archipterygium have 
 been attained : the fin stem is long, tapering, jointed ; the 
 radials occur as clearly along the hinder as along the ante- 
 rior margin; and, as in Figs. 52, 53, dermal rays contrib- 
 ute largely to the fin area. This form of fin may be noted 
 as most closely approximating in function the limb type of 
 land-living vertebrates. 
 
 It has recently been urged that the lateral fold origin of 
 the paired fins as thus described is not confirmed by devel- 
 opmental studies, the especial ground for this belief 
 being that in sharks these fins appear, even in very early 
 stages, as paired lappet-like outgrowths, destitute of inter- 
 vening fin membrane. The perfected fin fold is therefore 
 claimed to represent nothing more than a specialization to 
 bottom-living, since this condition is known to maintain in 
 earlier stages and in more primitive metamerism in the 
 development of skates : and as skates (p. 93) are well known 
 to represent a comparatively recent offshoot from the stem 
 of the sharks, it is accordingly inferred that the chief proof 
 of the lateral fold doctrine is destroyed. 
 
 Since these objections, however, were raised, the struct- 
 ural conditions of the ancient shark of Figs. 49 and 50 
 have been described, and may be looked upon as the 
 weightiest evidence of the origin of paired fins from lat- 
 eral folds. Nor does it seem to the present writer that 
 the early character of the fin-fold metamerism of skates 
 is to be looked upon as an unexpected condition. Their 
 
4 6 
 
 SENSE OK CANS OF FISHES 
 
 broad longitudinal fins, specialized to bottom-living, become 
 fashioned in an ancestral mould ; and it seems not unnatu- 
 ral that they tend to reacquire their latent primitive form 
 at an early period. On the other hand, the fin-fold condi- 
 tion of the shark might be less perfectly shown on account 
 of processes of accelerated development. 
 
 4. THE CHARACTERS OF THE SENSE ORGANS OF FISHES 
 
 It has already been seen that the conditions of aquatic 
 living have caused fishes to evolve adaptive structural char- 
 acters, such as body form, specialized metamerism, organs 
 of progression, and dermal investiture. It is not, accord- 
 ingly, unnatural to expect that, from the same causes, the 
 condition of the sense organs may have been strikingly 
 modified. 
 
 The sense of "feeling" using the word in its general 
 meaning has been of especial value in fishes, and tactile 
 organs appear to be independently developed in all fish 
 groups whose living habits demand them. In the form of 
 barbels they thus occur in members of the various divis- 
 ions of bony fishes, as cod (cusk, Ophidium) (Fig. 55), 
 drum-fish, Pogonias (Fig. 56), or sculpin, Hemitripterus 
 (Fig. 57). Their form may be lobate, thread-like, or villose ; 
 they are often surprisingly similar in size, position, and 
 innervation ; they usually appear on the inferior head 
 surface, most often in the anterior throat region, in the 
 position most exposed to tactile impressions. The thread- 
 like barbels of the catfishes (Fig. 58, p. 171) are arranged 
 in pairs about the margin of the mouth ; the longest lat- 
 eral pair is connected with the marginal bone (maxillary) 
 of the upper jaw and directed at will. In other mud-living 
 forms, sturgeons (Fig. 160), the barbels have arisen on the 
 under side of the shovel-like snout, directly in advance of 
 
Figs. 55-60. Barbels and tactile sense organs. (After GOODE in U. S. F. C.) 
 55. Cusk, Ophidium. 56. Drum-fish, Pogonias. 57. Sea-raven, Hemitripterus. 
 58. Catfish, Amiurus. 59. Spoon-bill sturgeon, Polyodon (ventral view of snout). 
 60. Sea-robin (Gurnard), Prionotus. 
 
 47 
 
4 8 
 
 BARBELS AND LATERAL LINE 
 
 the protractile sucking mouth. There can be little doubt 
 that the most aberrant tactile organ in fishes is the long 
 spatulate rostrum of the paddle-fish (Polyodon) of the Mis- 
 sissippi (Fig. 59) : the sense organs are here known to be 
 most highly specialized, although their intimate structure 
 is as yet not understood. Tactile organs are often to be 
 found upon fin structures, especially those of the anterior 
 body region. In the sea-robin, Prionotus (Fig. 60), the sen- 
 sory structures are borne by three anterior fin rays ; these 
 are greatly enlarged, lose their connecting fin web, and 
 can be moved at will in a variety of ways. In all cases 
 the barbels appear to be true and highly specialized 
 organs of touch, and the end organs are comparable ap- 
 parently with the touch papillae of higher forms. Of their 
 extreme sensitivity there can be no doubt, and as far as 
 can be judged from their innervation, it would appear that 
 their function is tactile rather than gustatory, as has been 
 suggested. The limits of these processes, however, are 
 no doubt poorly defined in aquatic living. 
 
 The Lateral Line 
 
 The sense organs, generally known as the lateral line, 
 or mucous canal system, are looked upon as essentially 
 peculiar to fishes. In the form of a 'lateral line,' they 
 are arranged more or less segmentally along the median 
 line of either side of the body and form a conspicuous 
 feature in the outward appearance of the fish (Figs. 87, 
 104, LL, 121, LL, 145, LL). Often by striking colora- 
 tion, the lateral line is rendered even more prominent, 
 passing from the head to the tail as a pale or brightly 
 coloured band, against the dusky side of the fish. In the 
 region of the head, however, this sensory structure is, as 
 a rule, no longer conspicuous : it dips below the skin sur- 
 
LATERAL LINE ORGANS ^ 
 
 face and becomes a series of interconnecting tubes, which 
 pass along the most exposed ridges of forehead, cheek, 
 orbit, and jaw rim. Here in different regions, these sen- 
 sory mucous tubes may become dilated, constricted, or 
 ramose, and may communicate with the surface by occa- 
 sional or numerous pores. 
 
 The mucous canal system has long been a subject of 
 study and investigation. It is looked upon generally as a 
 sensory organ, adapted to the conditions of aquatic living, 
 but its function has not been definitely established. How 
 it was acquired, or how its ancestral conditions have been 
 modified in the present groups of fishes, must at present 
 be looked upon as in many ways doubtful. 
 
 The simplest conditions of the mucous canal system 
 appear to exist in primitive sharks : and to these the 
 writer believes that the modified sense canals in other 
 fishes may best be referred. 
 
 The ancestral condition of the lateral line of sharks 
 appears to have been represented in an open continuous 
 groove,* lined with ciliated sense cells, and protected 
 only by an overcropping margin of shagreen denticles 
 (Fig. 61). In this condition it at least exists in the 
 ancient sharks of Figs. 86, 87, 92, and in the Chimaera 
 (Fig. 104). That the canals of the head region were also 
 primitively of this character appears exceedingly prob- 
 able : they are thus retained in the adult Chimaera (Fig. 
 104, M.C)j 
 
 In the modern forms of sharks the condition of the 
 
 * It is to be noted that this condition occurs in deep-sea fishes : it here is 
 evidently an adaptation to their peculiar environment, which causes an early 
 ontogenetic stage to be permanently retained. 
 
 f In Callorhynchus this condition has been largely lost : the outer margins 
 of the sensory groove have sealed over. 
 E 
 
FIG. 6.1 
 
 68 
 
 I'll 
 
 N 
 
 Figs. 61-68. Mucous canals (lateral-line organs). 61. Chlamydoselache, , groove-like 
 lateral line. (After CARMAN.) 62. Plan of lateral line of sharks, longitudinal section. 
 63. Plan of sensory end buds (lateral line). 64. Sensory tracts of head of larval Amia. 
 65. Surface openings of tubules of sensory tracts of head of adult Amia. 66. Ramification 
 of sensory tubules in dermal plate of Amia. 67. Cycloid scales of Amia, showing the 
 openings of the tubules of the lateral line. 68. Cycloid scale of the lateral line of Amia, 
 showing the course of the sensory tubule. (Figs. 64-68 after ALLIS.) 
 
 N. Nerve supply. S. Sensory tissue. * Denotes an outer opening ; -* the direction 
 of an incoming stimulus. 
 
 50 
 
LATERAL LINE ORGANS tj r 
 
 sensory canals suggests the modifications to which the 
 open sensory groove has been subjected. There are thus 
 forms in which the canal becomes more and more deeply 
 sunken in the integument, and acquires a tubular char- 
 acter by the fusing together of its outer margins. The 
 section of the lateral line of the Greenland shark, Lce- 
 margus (Fig. 62, v. p. 90), shows the tube-like sensory 
 canal well sunken from the surface, but retaining met- 
 ameral openings at the points. The sensory cells, S, 
 are no longer, as in Fig. 61, scattered evenly along the 
 floor of the canal ; they now occur in metameral masses 
 supplied with a distinct nerve branch, N, located in the 
 region immediately below the external tubules. When 
 sunken in the integument, the sensory canal is known to 
 have acquired supporting structures to enable its tubular 
 character to be maintained ; in the Cretaceous shark, 
 Mesiteia, an elaborate series of surrounding calcified rings * 
 were thus evolved. 
 
 Further changes in the mucous canal are often accom- 
 panied by the subdivision of the external apertures ; each 
 of the openings of Fig. 62 might by this process give rise 
 to a series of minute surface pores, as at vS in Fig. 65, or 
 enlarged, showing the collecting mucous canals in Fig. 66. 
 This ramose mode of termination of the external tubules 
 has been admirably described by Allis f in the ontogeny of 
 a ganoid ; in a larval stage (Fig. 64, S, S, S), the condi- 
 tion of the sensory canals is seen to differ little from 
 those shown in section in Fig. 62 ; although imbedded 
 in the integument, occasional pores are seen, S, S, to 
 open to the surface ; these subsequently by repeated sub- 
 division give rise to the great number of minute open- 
 
 * A condition somewhat similar has been noted (Leydig) in Chimsera. 
 t On the Lateral Line System of Amia calva. J. of Morph., 1889. 
 
C 2 LATERAL LINE 
 
 ings already noted in Fig. 65. A process of this kind 
 is carried to great lengths among the fishes which 
 develop horn-like scales, as Amia, herring, or cod : in the 
 scales of the lateral line region the distal tubules appear 
 at the surface as a cluster of pores, as shown in Fig. 67, 
 or in the detached scale of Fig. 66. 
 
 The organs of the lateral line (of a bony fish) shown 
 in section in Fig. 63 are regarded by the writer as of 
 a highly modified character. They appear to have been 
 derived from the conditions of Fig. 62 ; the end organ, 
 S, corresponds with that, S, of the preceding figure ; its 
 size, however, has greatly increased, and the intervening 
 sensory tube has been lost ; its metameral opening at 
 the surface corresponds with that of Fig. 62 ; the nerve 
 supply, N, is now seen to have secured a more perfect 
 relation to the end organs. 
 
 The original significance of the lateral line system as 
 yet remains undetermined. As far as can be judged from 
 its development, it appears intimately, 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 further and further backward 
 along the median line of the trunk, and in its later differ- 
 entiation acquired its metameral characters. 
 
 A significant feature of its development is its peculiar 
 innervation. Its lateral tract is innervated by a specially 
 evolved root of the vago-glossopharyngeal group, but its 
 head region is supplied by a similar root of the facial 
 nerve (perhaps also by the trigeminus ; cf. Collinge, Ref. 
 p. 248). 
 
 In view of this innervation, the precise function of this en- 
 tire system of end organs becomes especially difficult to de- 
 termine. Feeling, in its broadest sense, has safely been 
 
PINEAL EYE ^ 
 
 admitted as its possible use. Its close genetic relationship 
 with the hearing organ suggests the kindred function of 
 determining waves of vibration. These are transmitted in 
 so favourable a way in the aquatic living medium, that from 
 the side of theory a system of hyper-sensitive end organs 
 may well have been specialized. The sensory tracts along 
 the sides of the body are certainly well situated to deter- 
 mine the direction of the approach of friend, enemy or 
 prey. 
 
 The Pineal Eye 
 
 The presence or absence in fishes of \hepineal end organ, 
 the "unpaired median eye of chordates," may finally be 
 noted, since the condition of the epiphysis and its associ- 
 ated structures in fishes has an important bearing on 
 general vertebrate morphology. 
 
 It is well known that in many forms of reptiles there 
 exists, at the distal end of the epiphysis, a well-defined 
 sensory capsule, whose structure shows unquestionably its 
 optic function. It has seemed to many, therefore, that 
 throughout the chordates the epiphysis has been primi- 
 tively associated with a median eye, which has degenerated 
 as the paired eyes became better evolved. That it has 
 been retained in an almost perfect condition in reptiles 
 has accordingly been looked upon as an outcome of a 
 life habit which concealed the animal in sand or mud, 
 and allowed the forehead surface alone to protrude : 
 the median eye thus preserving its ancestral value in 
 enabling the animal to look directly upward and backward. 
 
 If this view as to the presence of a parietal eye in the 
 ancestral vertebrate is to be generally accepted, one would 
 naturally suggest that the organ should be present, at all 
 events to a recognizable degree, in some of the varied forms 
 
54 PINEAL EYE 
 
 of the lowest vertebrates extant, fishes and amphibia. If 
 there are no suggestions of its visual nature among these 
 forms, one would be inclined to believe with O. Hertwig, 
 that the epiphysis was originally of a different function 
 and that its connection with a median eye may have been 
 altogether of a secondary character. 
 
 The evidence as to the presence, primitively, of a median 
 eye in fishes is certainly far from satisfactory : * in all the 
 forms of recent fishes, no structure has been found associ- 
 ated with the epiphysis which, by the broadest interpreta- 
 tion, could be looked upon as suggesting a visual function. 
 It is possible that fishes and amphibia may, in their extant 
 forms, have lost all definite traces of this ancestral organ on 
 account of some peculiar condition of their aquatic living. 
 On this supposition, evidence of its presence might be 
 sought in the pineal structures of the earliest Palaeozoic 
 fishes whose terrestrial kindred, and probable descend- 
 ants, may alone have retained the living conditions which 
 fostered its functional survival. 
 
 It is accordingly of interest to find that in a number 
 of fossil fishes the pineal region retains an outward median 
 opening, whose shape and position suggest that it may have 
 enclosed an optic capsule. If the median eye existed in 
 these forms, it may well have been passed along in the line 
 of descent through the early amphibia (where substantial 
 traces of a parietal foramen occur, e.g. as in Cricotus) to 
 the ancestral reptiles. This view is greatly strengthened, 
 as Beard has shown, by the presence in the lamprey of a 
 pineal end organ (optic?). 
 
 The evidence, however, that the median opening in the 
 head shields of ancient fishes actually enclosed a pineal 
 
 * Hertwig (Mark), Handbook of Embryology of Vertebrates, and Cattie, v. 
 Ref. p. 250. 
 
PINEAL EYE 
 
 55 
 
 eye, is now felt by the present writer to be more than ques- 
 tionable. The remarkable pineal funnel of the Devonian 
 Dinichthys (Fig. 134) is evidently to be compared with 
 the median foramen of Ctenodus and Palcedaphus ( = Sire- 
 noids, p. 122) ; but this can no longer be looked upon as 
 having possessed an optic function, and thus practically 
 renders worthless all the evidence of a median eye pre- 
 sented by fossil fishes. It certainly appeared that in the 
 characters of the pineal foramen of Dinichthys there ex- 
 isted strong grounds for believing that a median visual 
 organ was present : its opening was in the pineal plate, 
 midway between the orbits (PN, Fig. 134). At the surface 
 it was of minute size (X, Fig. 136), but below (Fig. 137) 
 it flared out into a funnel-like form, shown in longitudinal 
 section in Fig. 137 A. The peculiar character of this 
 opening seemed to render it especially fitted for a visual 
 function ; the minute external opening forms an image 
 near the plane of the visceral opening of the funnel, with- 
 out the specialization of a lens, an image so perfect that 
 it might readily be photographed. It is evident, accord- 
 ingly, that if an optic capsule were enclosed by this fora- 
 men, it would have enabled its possessor to have looked 
 directly upward and backward ; and, without the need of 
 developing lens-like and focussing structures, it could have 
 readily received the images of all outer objects near or 
 remote. 
 
 But the function of this pineal foramen, unfortunately 
 for speculation, could not have been optical. It occurs in 
 a fish (Titanichthys) closely related to Dinichthys, and, 
 as the writer * has recently found, is of a distinctly paired 
 
 * He is obliged by accumulating evidence to abandon his former view that 
 the pineal foramen of Dinichthys contained a specialized optic capsule (TV. Y. 
 Rep. of Fisheries, 1891, pp. 310-314). 
 
^6 PINEAL EYE 
 
 character, its visceral and outer openings bearing grooves 
 and ridges which demonstrate that the pineal structures 
 must not only have been paired, but must have entered 
 the opening in a way which precludes the admission of 
 the epiphysis. It is now, therefore, that the pineal fora- 
 men which has been described in Siluroids * becomes 
 of especial interest, since its contained structures are ap- 
 parently connected with the lateral line system of paired 
 nerves. 
 
 It must for the present be concluded, accordingly, that 
 the pineal structures of the true fishes do not tend to con- 
 firm the theory that the epiphysis of the ancestral verte- 
 brates was connected with a median unpaired eye ; it would 
 appear, on the other hand, that both in their recent and 
 fossil forms, the epiphysis was connected in its median 
 opening with the innervation of the sensory canals of 
 the head. This view, it is now interesting to note, seems 
 essentially confirmed by ontogeny. The fact that three 
 successive pairs of epiphysial outgrowths have been noted 
 in the roof of the thalamencephalon, appears distinctly 
 adverse to the theory of a median eye. 
 
 *Dean, N. Y. Rep. of Fisheries, 1891, and Klinckowstrom, Anat. Anz., 
 1893, viii, p. 561. 
 

 Ill 
 
 THE LAMPREYS AND THEIR ALLIES 
 
 THE relations of the more primitive chordates to the 
 true fishes have not been considered in the present dis- 
 cussion. A brief account, however, must be given of the 
 Cyclostomes, or Marsipobranchii, which are represented in 
 the recent lampreys and hags. 
 
 The three prominent forms of Cyclostomes are figured 
 on a following page (Figs. 70-72, A-D). They are eel- 
 like in shape, but are lacking both in paired fins and in 
 an under jaw. Their mouth is of a rounded form, and 
 is suctorial ; when closing, its lateral margins draw to- 
 gether. Their skeleton is of the simplest character, mem- 
 branous rather than cartilaginous ; its elements are never 
 more highly differentiated than those shown in the ac- 
 companying figure (Fig. 69, A). 
 
 Bdellostoma is shown in surface view in Figs. 70 and 
 72 A, and in sagittal section in Fig. 69. It is looked 
 upon as the most archaic form of the living Cyclostomes. 
 Barbel-like structures surround its mouth region ; its nasal 
 canal (Fig. 69, N and C) has a forward opening at the 
 snout, and a hinder one piercing the roof of the pharynx, 
 a very exceptional character in fishes ; its tongue, stud- 
 ded with rows of rasp-like teeth,* may be greatly everted, 
 
 * The teeth of Myxinoids are cuticular structures, and may well have been 
 evolved within the limits of the group. Beard has homologized them with the 
 teeth of sharks, but his determination of the presence of true enamel has not 
 been confirmed (Ayers). 
 
 57 
 
THE LAMPREYS eg 
 
 as in Fig. 72, A, and then drawn in by stout tongue 
 muscles, T (Fig. 69) ; its digestive tube is almost straight, 
 terminating at the base of the tail region at A ; the 
 region of the gullet, OE, is pierced by a number of 
 branchial openings, varying from seven to fifteen, often 
 assym metrical. The body cavity is an extremely large 
 one for the size of the contained viscera. An unpaired 
 fin, supported by delicate, unbranched (dermal) rays is 
 restricted to the hindmost part of the body. Passing 
 down the side is a row of mucous pouches by which a 
 remarkable supply of slime is secreted. The living animal 
 is enabled, by the peculiar character of this slimy secre- 
 tion, to render a pailful of water jelly-like in consistency. 
 
 Bdellostoma occurs plentifully in the bays of the Pacific 
 coast of America, notably at Monterey, California. It is 
 active in its movements, is carnivorous, and is well known 
 to take a baited hook. Its numbers make it an enemy of 
 the fishermen, entangling and sliming their set lines, and 
 destroying the captured fish. It is said to feed at night, 
 although little is yet known of its general habits of living. 
 None but adult specimens have thus far been observed. 
 
 The Hagfish, Myxine glutinosa (Fig. 71, and 72, 7?), is in 
 many regards similar to Bdellostoma ; it differs mainly in 
 the character of its unpaired fin and in its branchial struct- 
 ures (Figs. 9, 10). As already noted, the outer ducts of the 
 gills, instead of opening separately at the surface as in 
 Fig. 70, are drawn together tail-ward, and terminate on 
 either side in a common ventral opening (Fig. 71, at the 
 point*). The unpaired fin is almost lacking in supports; 
 its ventral origin is even as far forward as the branchial 
 openings ; the anus, as a slit-like opening, pierces it in 
 the tail region. As in Bdellostoma, the nasal canal begins 
 at the snout, and at its hinder opening pierces the roof of 
 
60 
 
 i 
 
LAMPREYS AND HAGS 
 
 61 
 
 the pharynx ; this, with other related conditions, has caused 
 Myxine and Bdellostoma to be included in a sub-group 
 of Cyclostomes, as Myxinoids, or Hyperotretes* In each 
 genus there is possibly no more than a single valid species. 
 Myxine is a well-known form : it occurs along the Atlan- 
 tic coast at moderate depths. It is exclusively carnivorous, 
 
 Fig. 12. A-D. Ventral aspects of heads of (A) 
 Bdellostoma (after AYERS) ; (B) Myxine (after GCJN- 
 THER) ; (C) Ammoccetes (after GiJNTHER) ; (D) Pe- 
 tromyzon (after GUNTHER). 
 
 often boring its way into the abdominal 
 cavity of (diseased or injured) fishes, and 
 with them is brought to market; it is 
 also taken not infrequently by line fisher- 
 men. The smallest example that has 
 thus far been described is 6 cm. in length ; it was 
 recorded by Beard. (V. Ref. p. 239). 
 
 The Lamprey, Petromyzon, is the most perfectly studied 
 member of the Cyclostomes. Its species are common 
 to the continents of the northern hemisphere ; and in 
 South America and Australia there occur very closely 
 allied genera, as Mordacia and Geotria. The largest 
 lamprey, P. marinus (Fig. 72, and C, D\ is known to 
 attain a length of nearly four feet ; it occurs in the coast 
 
 * v. Glossary, p. 228. 
 
5 2 THE LAMPREYS 
 
 rivers, ascending them in numbers in the springtime 
 (April) on the way to the spawning grounds (v. p. 182). 
 During its adult life it is supposed to be exclusively car- 
 nivorous, to some degree, perhaps, parasitic, although many 
 doubt that it is truly parasitic in the sense of entering the 
 body cavities of healthy fishes. It certainly is often taken 
 attached to other fishes, as shark, sturgeon, or salmon. 
 
 Immature lampreys differ so strikingly from the adults 
 that they were formerly regarded as species of a separate 
 genus, Ammoccetes (v. p. 215). In feeding habits the am- 
 moccete is widely unlike the mature form ; it is toothless 
 (Fig. 72, C), and in part mud-eating, i.e. vegetivorous. 
 
 Petromyzon must be regarded as the most highly organ- 
 ized of Cyclostomes. Its mouth has no longer the fring- 
 ing barbels of Myxinoids, which suggest, according to 
 Pollard, the buccal cirrhi of Amphioxus, it has acquired 
 stout supporting cartilages and a funnel-shaped form, 
 studded with a series of conical teeth, as shown in Fig. 
 72, C. The teeth of the hinder mouth region now appear 
 almost as though they were supported by a mandibular 
 cartilage ; the tongue, as in other Cyclostomes, bears the 
 teeth which are probably of the greatest functional impor- 
 tance. The nasal canal of Petromyzon has its outer opening 
 on the dorsal surface of the head ; its inner end, however, 
 does not perforate the roof of the mouth, although produced 
 backward as a blind sac, closely apposed to the pharynx. 
 Petromyzonts are, accordingly, arranged as the sub-group 
 Hyperoartia, in contrast to the Myxinoids. 
 
 Further structural characters, which the lamprey seems 
 to have derived from simpler conditions, may be noted in 
 its unpaired fin, gill chamber, nervous system, and skele- 
 ton. The unpaired fin has subdivided into dorsal and 
 caudal elements, and is now supported by well-marked 
 
AFFINITIES OF LAMPREYS 63 
 
 rays, which (sometimes) bifurcate. The branchial region of 
 the adult lamprey's gullet is restricted to a pouch-like 
 diverticulum (v. p. 263 and Fig. 326). A 'sympathetic' 
 nervous system, and a ' lateral line ' has appeared : the 
 latter passes down the side in two branches, one above 
 and one below the median lateral plane : its end organs 
 are the pouches of nervous epithelium which in Myxi- 
 noids are scattered generally over the body surface. The 
 skeletal structures of the lamprey (Fig. 69, A) indicate 
 well-marked advances : a stouter supporting tissue of car- 
 tilage-like character has appeared ; the brain case is partly 
 roofed over ; neural processes, NP t a branchial basket, 
 BB, and a series of mouth cartilages are especially note- 
 worthy. 
 
 Affinities of the Cyclostomes 
 
 The relations of the group, Cyclostomi, to the earlier 
 chordates, and, on the other hand, to fishes, have been by 
 no means definitely established. Dohrn and others have 
 suggested that the Cyclostomes are greatly degenerate, and 
 are even closely akin to the recent bony fishes, as perch 
 or cod. Their views have been based upon several struct- 
 ural characters, notably vestigial organs, such as the ap- 
 pendages at the sides of the cloacal opening of Petromyzon 
 which were believed to represent pelvic fins ; and there was 
 further taken into consideration the belief that the entire 
 group was one of degenerate life habits. The views of these 
 writers, however, do not appear to be confirmed by later 
 studies, and the belief is becoming more and more general 
 that Cyclostomes represent a very ancient chordate stem 
 whose ancestral form is most nearly exemplified by Bdel- 
 lostoma. Parasitism has been acquired to a limited degree, 
 but does not appear to have affected the general characters 
 
64 KINSHIPS OF CYCLOSTOMES 
 
 of the group. Among its primitive features are to be in- 
 cluded : skeleton and muscles, continuous vertical fin, gill 
 characters (p. 260), viscera (p. 263), urino-genital organs 
 (pp. 266, 270), nervous and circulatory systems (pp. 260, 
 269, and 274). With these must be taken into account: 
 absence of mandible* and of paired fins and girdles; and in 
 addition the remarkable conditions of metamerism (p. 14). 
 
 Little more that a vague kinship between lampreys and 
 fishes has been established by the study of living forms. 
 And, on the other hand, it would appear equally impracti- 
 cable to obtain evidence bearing upon this problem from 
 the side of palaeontology. All that is known of the recent 
 Cyclostomes more than suggests that their soft body struct- 
 ures would prove most unfavourable to fossilization. It 
 would be only, therefore, in the event of some of their 
 ancient members possessing calcified structures that palae- 
 ontology would be able to offer a clue as to their ancient 
 affinities. 
 
 Upon the problem of their descent the evolution of 
 fishes has, however, an undoubted bearing, in suggesting 
 the lines and effects of aquatic evolution and the perma- 
 nence of generalized types. It certainly tells of the ex- 
 treme slowness of the evolution of aquatic forms and con- 
 vinces us that the ancestral Cyclostome could only have 
 occurred in a time stratum exceedingly remote. Palaeon- 
 tology cannot perhaps hope to obtain more than sugges- 
 tions of the ancestral forms, although these, from their 
 generalized characters, may well have survived during geo- 
 
 * The cartilages of the mouth region of Cyclostomes have been homologized 
 with the structures of gnathostomes ; Pollard recently (Anat. Anz. ix, pp. 
 349-359) ascribes a cirrhostomial origin to the mouth parts of a Teleostome 
 (catfish), which the writer cannot believe has been demonstrated; variations 
 in the number, shape, and function of the cartilages of the mouth rim of 
 Cyclostomes might well have occurred within the limits of this ancient group. 
 
A FOSSIL LAMPREY 65 
 
 logical ages. It can, however, show that Cyclostomes are 
 not the degenerate descendants of shark-like forms ; and 
 if only by analogies in the evolution of fishes it may 
 still be able to demonstrate with fair probability their 
 genetic kinships. It may, for example, 
 prove that in the most ancient time there 
 existed undoubted Cyclostomes, and that 
 these in many and most specialized forms 
 were even then branching-off twigs of a 
 great descent tree. In such an event an 
 inference would certainly be the more 
 reasonable which derived the advancing 
 line of fish descent from the genealogical 
 tree of the more primitive Cyclostomes, 
 than that vice versa. 
 
 It is now accordingly of especial inter- 
 est that the fossil remains of what seems 
 undoubtedly a lamprey (Fig. 73) have been 
 discovered in the Devonian ; and this, to- 
 gether with a better knowledge of the 
 ancient and curious chordate group, Os- 
 tracoderms, may, it is hoped, lead to some 
 solution of the Cyclostome puzzle. 
 
 The Ostracoderms 
 
 Fig. 73. The De- 
 vonian Cyclostome, 
 Palaospondylus gunni, 
 T. X 4. (After TRA- 
 
 Ostracoderms, as they are called from QUAIR.) Achanarras 
 
 quarry, N. Scotland. 
 
 their shell-like, dorsal and ventral derm 
 plates, are certainly the oldest known remains of verte- 
 brates.* In their simpler forms they occur in the Upper 
 Silurian ; they flower out in a variety of types in the De- 
 vonian, and shortly become extinct. In the present con- 
 
 * The earlier (Ordovician) vertebrate remains described by Walcott are as 
 
 yet uninterpretable. 
 F 
 
FIG. 74 
 
 Figs. 74-79. Pteraspis (restored) . X 5. (After LANKESTER.) Lower Old Red 
 Sandstone, Herefordshire. 75. Palceaspis americana, Claypole. X 4. (Restoration after 
 CLAYPOLE, somewhat modified by the writer.) 76. Pteraspis, dorsal shield, slightly 
 restored. (After LANKESTER.) 77. Pteraspis, ventral shield (" Scaphaspis ") , showing 
 mucous canals. (After SMITH WOODWARD.) 78. Cephalaspis lyelli, side view. (Re- 
 stored by LANKESTER.) 79. Cephalaspis lyelli, dorsal aspect. X 5. (After L. AGASSIZ.) 
 Specimen from Old Red Sandstone, Forfarshire. A C. Rhomboidal scales from different 
 body regions. B. Tessera from middle layer of head shield. 
 
 66 
 
OSTRA CODERMS 
 
 6 7 
 
 nection they may be described, if only to indicate that 
 they are in no way closely connected with the ancient 
 shark types (p. 78), and that they are accordingly of but 
 indirect interest in the descent of jaw-bearing vertebrates. 
 
 Ostracoderms may readily be reduced to three general 
 types, Pteraspid, Cephalaspid, and Pterichthid. The first, 
 oldest, and probably simplest occurs in the Lower Old 
 Red Sandstone of Herefordshire. It was provided with 
 arched back and breastplate (Figs. 74, 76, 77), from whose 
 anterior lateral notches a pair of eyes protruded ; the sur- 
 face of these plates (Fig. 77) appears to have been grooved 
 for sensory canals. Pteraspis, as seen in the restoration, 
 had a snout plate, a dorsal spine, and a body casing of 
 rhomboidal scales ; its mouth was probably in the region 
 immediately below the eyes, in front of the margin of the 
 well-rounded ventral plate ; this was generally regarded as 
 the dorsal plate of a kindred genus, " Scaphaspis" Closely 
 related is the American Pteraspid, Palceaspis (Claypole), 
 from the Upper Silurian of Pennsylvania (Fig. 75) ; this 
 form lacks the dorsal spine of the English species ; it has a 
 well-marked lateral plate intervening between those of the 
 back and ventral side, and, according to its discoverer, 
 Professor Claypole, possessed pectoral fins similar to those 
 seen in Fig. 123. Its hinder trunk region is unknown. 
 
 Cephalaspis, the second type of Ostracoderm, is from 
 the Old Red Sandstone of Scotland (Figs. 78, 79). It was 
 curiously suggestive of a trilobite, and with little doubt 
 mimicked this ancient crustacean in its life habits. Its 
 most prominent feature is a crescent-shaped head, with 
 sharp rounded margin like a saddler's knife. This is 
 protected dorsally by but a single plate, arching upward 
 and backward ; at its summit was a pair of closely apposed 
 eyes, and near its flattened rim were pouch-like sensory 
 
Fig. 80 
 
 SL 
 
 Figs. 80-82. Pterichthys testudinarius, Ag. ; restored by R. H. TRAQUAIR, from the 
 dorsal aspect (80), ventral aspect (8i),and lateral aspect (82). The double dotted lines 
 indicate the grooves of the sensory canal system ; and in the trunk, the thick lines repre- 
 sent the exposed borders of the plate, the thin line showing the extent of the overlap. 
 
 ADL. Anterior dorso-lateral. AMD. Anterior median dorsal. A VL. Anterior ventro- 
 lateral. EL. Extra-lateral (or operculum). L. Labial. MOCC. Median occipital. PM. 
 Premedian. PDL. Posterior dorso-lateral. PMD. Posterior median dorsal. PVL. Pos- 
 terior ventro-lateral. SL. Semilunar. (Figure from SMITH WOODWARD.) 
 
 68 
 
PTERICHTHYS AND CEPHALASPIS 
 
 69 
 
 organs. The angles of the head plate are in some genera 
 produced most acutely, and bear spines which served prob- 
 ably in progression. The body walls were encased in 
 metameral derm plates, which became arched in the 
 median line to serve as a dorsal fin. A heterocercal tail 
 and an anal fin were also present. Problematical opercu- 
 lar flaps protruded at the sides of the head plate, and 
 represented (as is now known) a continuation of the elastic 
 middle layer of the head plate. 
 
 Pterichthys must be looked upon as the culminating 
 type of these anomalous forms (Figs. 80-82). As in some 
 Cephalaspids, there are two body regions that are cui- 
 rassed, head and thorax. The tail portion is encased 
 in dermal plates; it bears a dorsal * fin and a clumsy 
 heterocercal tail. In the consolidation of its armoured 
 parts the elements are usually clearly indicated. The 
 curious arm-like jointed appendages at the lateral head 
 angle were formerly regarded as homologous with the 
 opercular flaps of Cephalaspid, but are now known to be 
 nothing more than the lateral head angles produced and 
 specialized (i.e. jointed for locomotion). The strengthen- 
 ing spine of the dorsal fin is also but a primitive speciali- 
 zation of the body integument ; it is formed by a pair of 
 the bent scales of the dorsal ridge, and is not, therefore, 
 homologous with the radial fin cartilages of fishes. 
 
 In Cephalaspids and Pterichthids there occurs a pineal 
 plate (or its equivalent) which may have been either 
 movable or fixed. In this are to be found the paired eyes 
 and the socket of a median unpaired eye (?). In all of 
 these singular forms mouth parts * are wanting. In 
 
 * Smith Woodward has since described a pair of inturned labial plates in 
 the mouth of Pterichthys. Their position suggests that the sides of the mouth 
 rim might become apposed, as in the Cyclostomes. 
 
70 KINSHIPS OF OSTRACODERMS 
 
 no instance has a trace of endoskeletal parts been ob- 
 served. 
 
 The more that is determined of the structural characters 
 of Ostracoderms, the less is it possible to accept the 
 views as to their affinities with forms other than "fishes," 
 either (Cope) as to their permanent larval-ascidian char- 
 acters, or (Patten) as to their relationships with arachnids. 
 Their general kinship is certainly to the fishes. Accord- 
 ing to Smith Woodward, the markings appearing on the 
 visceral surface of head tests indicate the presence of 
 gill pouches ; in some forms clearly marked furrows sug- 
 gest the possession of vertical semicircular canals ; fish-like 
 sense organs occur (Fig. 77) ; and their derm plates, in 
 their cancellated atid bone-like characters, cannot well be 
 likened to the exoskeletal parts of invertebrates. 
 
 The lamprey-like form, Palceospondylus gunni, Traquair 
 (Fig. 73), in the Lower Devonian is by many looked upon 
 as the actual solution of the Cyclostome, and even of the 
 Ostracoderm puzzle. This interesting fossil was discov- 
 ered by Dr. Marcus Gunn, in the Lower Old Red Sand- 
 stone of Caithness, and was described in several papers by 
 Traquair (Trans. Edin. Soc., 1892-1894). It is of very 
 small size, commonly of about an inch in length, but is 
 admirably preserved (Fig. 73). There can be no doubt 
 that Palaeospondylus possessed a ring-like mouth sur- 
 rounded by barbels like those of a Myxinoid, and that it 
 lacked paired fins. But as a Cyclostome it must have 
 highly specialized, having the same relation to the more 
 primitive Cyclostomes of its day, as had the minute Acan- 
 thodians (p. 81) to the existing sharks. It had thus a 
 remarkably large caudal fin with elaborately bifurcating 
 supports ; it had evolved stout, ring-like vertebrae, even in 
 the caudal region, which had developed stout neural proc- 
 
PAL& OSPOND YLUS 7 r 
 
 esses. Its skull was highly evolved : in its anterior part 
 were represented, according to Traquair, the palatine car- 
 tilages ; the brain case was complete, and the auditory 
 capsules were of relatively enormous size. The lateral 
 plates of the neck region are as yet uninterpretable. 
 
 From the evidence of Palaeospondylus, accordingly, it 
 may reasonably be inferred that lamprey-like forms existed 
 in highly specialized conditions, even at the beginning of 
 Devonian times. If they then existed, it is of course not 
 impossible, and perhaps even not improbable, that their 
 offshoots may have culminated in the Ostracoderms, as 
 Smith Woodward has suggested. These can certainly 
 belong to no gnathostome stem. Their organs, though 
 often highly specialized, were yet of the most primitive 
 order, lack of paired appendages,* softness of axial parts, 
 lowly sense organs; even the dermal plates, elaborate in 
 their subdivision or ornamentation, or in the special uses, 
 as "opercula," "pectoral fins," or " fin rays,"f are yet but 
 primitive specializations of the exoskeleton. 
 
 * The presence of paired fins in Palaeaspis, as determined by Claypole, has 
 not been confirmed. The present writer, to whom the type specimens were 
 kindly shown by their describer, must regard these structures as elasmo- 
 branchian (Chimseroid?) spines, in crushed condition, accidentally associated 
 with the head region of the fossil. 
 
 t It is obvious that these structures are but analogous to the opercular and 
 fin structures of fishes, and would tend to separate, rather than closen, the 
 ties of kinship of these groups. 
 
IV 
 
 THE SHARKS 
 
 ALL true fishes may conveniently be grouped into the 
 four sub-classes that have been noted (p. 8) in the introduc- 
 tory chapter. These are now in turn to be considered, and 
 in this review the principal forms, fossil and recent, of each 
 group must be exemplified. From the standpoint of their 
 structural and developmental characters, a general idea of 
 the mutual relationships of the fishes may finally be 
 deduced. 
 
 The sub-class Elasmobranchii, which includes the sharks 
 and rays, is usually regarded as representing most nearly 
 the persistent ancestral condition of fishes, and, indeed, of 
 all other jaw-bearing vertebrates. As a group it should 
 certainly be taken first in the present discussion, as a con- 
 venient basis of comparison. 
 
 Sharks and rays should be looked upon at the beginning 
 as the representatives of the oldest, most widely diffused, 
 and possibly largest group of fishes. In their living 
 forms they suggest but faintly the number and variety of 
 their fossil kindred. It is generally thought that the his- 
 tory of this group, when more perfectly determined, is to 
 furnish the most important evidence as to the general 
 lines of descent of the fishes. 
 
 72 
 
73 
 
74 STRUCTURES OF SHARKS 
 
 Structural Characters 
 
 The definition of a shark emphasizes its cartilaginous 
 skeleton, investiture of shagreen, uneven (heterocercal) tail, 
 and its separate and slit-like gill openings. Its more defi- 
 nite characters may well be summarized in the accompany- 
 ing figure (Fig. 83). 
 
 I. The SKELETON is cartilaginous (cf. Fig. 83, 84, and 
 p. 252), sometimes calcified generally, but always (in recent 
 forms) lacking in dermal bones. Behind the simple, trough- 
 like brain case the vertebral rod, beginning at the occip- 
 ital condyles, is clearly segmented ; the notochord is often 
 retained, especially in the tail region, NC, but is encroached 
 upon by the cartilaginous rings, centra, C, arising metamer- 
 ally in its sheath (Fig 85). The vertical supports of each 
 centrum include a well-marked ventral plate, the haemal 
 arch and spine, HER, which' in the tail region probably 
 represents as well the cartilaginous elements of the fin 
 support, and a pair of small dorsal plates, the neurals 
 and interneurals, NP, 1C, each capped by a neural spine, 
 NS. The fin supports compare closely in structure with 
 the vertebral processes ; they form a large part of the 
 functional fin, and preserve clearly, both in basal and 
 radial parts, thpr metameral character. This -segmental 
 arrangement is also characteristic of the supporting ele- 
 ments of the cavity of the mouth and throat. These con- 
 stitute the " visceral arches" (cf. p. 256) which pass 
 backward from the rim of the mouth to the region of the 
 pectoral fin. The first visceral arch strengthens the rim of 
 the mouth ; it is margined with teeth and functions as jaws,* 
 
 * The writer believes that the upper element of the mandibular arch is to 
 be regarded as the palatoquadrate cartilage, rather than the pre-spiracular 
 ligament. 
 
75 
 
76 STRUCTURES OF SHARKS 
 
 P and M. The second arch serves as the principal support 
 of the jaw hinge, HM, while holding in position, ventrally, 
 the hinder arches; it also supports the tongue, and forms 
 the hinder border of the spiracle (p. 19). The succeeding 
 arches, usually five in number, are the bearers of the func- 
 tional gills, their jointed structure permitting the dilating 
 and contracting movements of breathing. 
 
 As a further skeletal element of the Elasmobranchs the 
 sub-notochordal rod is to be mentioned. It is present in 
 the larval stages of sharks, and appears to persist in the 
 adult Cladoselache (p. 79). It is a prominent structure 
 of the hinder body region, passing along, like a second 
 
 notochord, immediately below the 
 vertebral axis. Its significance is 
 unknown. 
 
 II. The INTEGUMENT of the 
 sharks, as has been noted (p. 23), 
 is studded with shagreen denticles, 
 Fi S- 85. Vertebrae of often in metameral arrangement. 
 
 shark (Squatina) , longitudinal 
 
 section. (After ZITTEL ) These have been shown to corre- 
 
 "pond dearly with the teeth. 
 
 centrum. iv. Intervertebral The Soft Structures characteristic 
 
 space, w. Centrum. . 
 
 of the Elasmobranchs include : 
 
 III. GILLS, arranged metamerally (p. 19) ; the most 
 anterior one partly functional in the spiracle, SP. 
 
 IV. SENSE ORGANS OF THE LATERAL LINE, in some 
 forms in an open sensory groove, in others sunken and 
 constricted in metameral pouches. 
 
 V. BRAIN, simple in its segmental characters and 
 cranial nerves (v. p. 274). 
 
 VI. NASAL ORGAN, EYE AND EAR, as shown on p. 276. 
 
 VII. RENAL AND REPRODUCTIVE SYSTEMS (p. 270), ab- 
 dominal pores (p. 271). 
 

 FOSSIL SHARKS jj 
 
 VIII. DIGESTIVE TUBE with a single bend, 5, /, the 
 intestine provided with a spiral valve (p. 263), terminat- 
 ing, together with the ducts of the renal and reproduc- 
 tive organs, in a common cloaca, CL (p. 266). Liver, Z, 
 spleen, and pancreas large ; mesenteries simple but greatly 
 fenestrated ; air bladder absent. 
 
 IX. HEART with a contractile arterial cone, CA, con- 
 taining several rows of valves (p. 260) ; circulatory system 
 in general as described on p. 269. 
 
 X. " CLASPERS " developed at the hinder margin of 
 the ventral fins as the intromittent organ of the male. 
 They are rudimentary in the female, CL'. Each clasper 
 is the trough-like hinder rim of the fin, which becomes 
 transformed into the compact, elongated, tube-like sperm 
 canal. Its tip is often studded with elongated shagreen 
 denticles whose recurved cusps retain it in copulo. 
 
 Fossil Sharks 
 
 Of all fishes, sharks certainly suggest most closely in 
 their general structures the metameral conditions of the 
 Cyclostome : it should also be noted that they possess the 
 greatest number of body segments, in some instances 
 over three hundred, known among vertebrates. Little is 
 known, however, of the primitive stem of the sharks, and 
 even the lines of descent of the different members of the 
 group can only be generally suggested. The development 
 of the recen forms has yielded few results of undoubted 
 value to the phylogenist : it would appear as if palaeon- 
 tology alone could solve the puzzles of their descent. 
 
 The history of fossil sharks has as yet been but imper- 
 fectly outlined. The remains of the more ancient forms 
 have usually proven so imperfectly preserved that little 
 could be determined of their structural characters. Spines, 
 
7 g PALEOZOIC SHARKS 
 
 teeth, shagreen denticles, have proven the antiquity of the 
 shark stem and the wealth and variety of its fossil forms ; 
 they have provided the evidence that even in Silurian 
 times there lived sharks whose exoskeletal specializa- 
 tions had progressed further than in their recent kindred : 
 that in the Carbon there occurred the culminating-point 
 in their differentiation, when specialized sharks existed 
 whose varied structures are paralleled only by those of 
 existing bony fishes, sharks fitted to the most special 
 environment ; some minute and delicate ; others enormous, 
 heavy, and sluggish, with stout head and fin spines, and 
 elaborate types of dentition. 
 
 But the detached fragments of the fossil sharks can give 
 little satisfactory knowledge of their general structures. 
 The simpler the form of the shark, indeed, the less liable 
 is it to become fossilized. The more generalized of the 
 ancient sharks must thus remain structurally unknown 
 until more perfect fossils come to be found. To this event 
 the discoveries of the past few years have certainly yielded 
 most encouraging aid. Several forms of sharks of the 
 Lower Carbon and Permian have been obtained in a con- 
 dition of admirable preservation, and have already con- 
 tributed materially to the morphology of Elasmobranchs. 
 Other early forms may be forthcoming which will be found 
 to have retained sufficient of the characters of their an- 
 cestors to warrant more definite views as to the general 
 relationships of fishes. 
 
 Of the three primitive forms of fossil sharks lately 
 described : the earliest, from the Ohio Waverly (Lower 
 Carbon) is Cladoselache, Dean ; a later and puzzling form, 
 from the Carboniferous, is Chondrenchelys, Traquair ; the 
 latest from the Permian and Coal Measures, is Pleiiracan- 
 tkus, Agassiz. The only early shark type that had previ- 
 
CLADOSELACHE 
 
 79 
 
 ously been structurally known was that of the aberrant 
 and highly specialized Acanthodian of the Coal Measures. 
 
 Cladoselache is the most primitive, as well as the oldest, 
 of these ancient sharks. It is relatively of small size, 
 varying in the length of its species from two to six feet. 
 Its outward form, as restored by the writer, is seen in Fig. 
 86, and in ventral view in Fig. 86 A. The shape is clearly 
 
 Fig. 86. Cladoselache fyleri, Newb. X $. Restoration by writer. After speci- 
 men in the museum of Columbia College from Cleveland shales, Ohio. 
 Fig. 86 A. Cladoselache fyleri ; ventral aspect. 
 
 that of a modern shark; the fins, too, in their size and 
 position, have somewhat of a modern look ; and at the 
 base of the tail occurs the small horizontal keel of many 
 living forms. But in spite of these peculiarities, Cladose- 
 lache must be looked upon as the most archaic, and, in 
 many ways, the most generalized of known sharks ; its 
 paired fins are but the remnants of the lateral fold (p. 43), 
 serving alone as balancers ; the tail, curiously specialized, 
 is widely heterocercal, its hinder web lacking supports in 
 the upper lobe (p. 36) ; the vertebral axis is notochordal ; 
 
g o CLADOSELACHIAN SHARKS 
 
 and the writer now finds that an exceedingly simple con- 
 dition existed in the neural and haemal arches ; they prove 
 to be of moderate size and thickness, each a tapering rod 
 of cartilage, forked at its base ; each body segment con- 
 tains a single neural and haemal spine, closely alike in size. 
 Unlike modern sharks, Cladoselache was without claspers : 
 its eggs must have been fertilized after their deposition, as in 
 the majority of fishes other than Elasmosbranchs. The gill 
 openings, at least seven (probably nine) in number, appear 
 as in the restoration, to have been shielded anteriorly by 
 a dilated dermal flap. A spiracle was probably present. 
 The jaws were slender, and apparently hyostylic (p. 257) ; * 
 the teeth are of the pattern of shagreen denticles, but occur 
 
 Fig. 86 B. Teeth of (" Cladodus") Cladoselache. X . The above forms 
 occur in different regions of the mouth. 
 
 in clusters (^Cladodus" Fig. 86, B). The mouth was ter- . 
 minal in its position. The nasal capsule was apparently 
 not connected with the mouth by a dermal flap. The eye 
 was protected by several rings of rectangular plates, clearly 
 shagreen-like in character. The integument was finely 
 studded with minute lozenge-shaped denticles, and was 
 everywhere lacking in membrane bones. The lateral line 
 retained its groove-like character. 
 
 The shark, Acanthodes (Fig. 87), of the Coal Measures 
 is now to be regarded (Smith Woodward) as a member of 
 a highly specialized Palaeozoic group. And its many spe- 
 cialized structures added to its greatly reduced size 
 
 * As Claypole's recent figure seems to demonstrate. Am. Geol.^Jan. 
 
ACANTHODES 
 
 81 
 
 may, perhaps, have been the cause of its extinction. 
 The present writer believes that Cladoselache may well 
 have represented the ancestral form of the Acanthodian. 
 The generalized structures of the former have given place 
 to a perfected dermal armouring, and a completed series 
 
 Fig. 87. Acanthodes wardi, Egert. X about J. (Restoration slightly modified 
 after SMITH WOODWARD.) Coal Measures, England. 
 
 of balancing fins. In Acanthodes the shagreen denticles 
 have thus become greatly enlarged and thickened, their 
 flattened and enamelled surfaces wedging closely to- 
 gether (Fig. 88) ; and on the roof of the head and 
 mouth traces of membrane bones have appeared. Around 
 
 'Pig. 88. Acanthodes gracilis,Eeyr. Shagreen. X about i ff . (After ZlTTEL.) 
 a. Outer face. b. Inner face. c. Isolated denticle. 
 
 the eyes the many shagreen plates of Cladoselache have 
 fused into a group of four. Supporting the dermal gill 
 frills, there have also appeared rows of minute sculptured 
 plates (corresponding, perhaps, to those, BR, of Fig. 
 145), homologous, apparently, with shagreen denticles. 
 
82 
 
 ACANTHODIAN SHARKS 
 
 Further resemblances to Cladoselache are to be traced in 
 the position of the fins, gill slits, eyes, mouth, nasal cap- 
 sule, and in the structures of the caudal fin (Kner), and of 
 the lateral line. The teeth, however, are no longer of the 
 derm-denticle pattern ; they have become few in number, 
 large, and "degenerate" in their fibrous structure (Fig. 
 88, A}. The fins are clearly more per- 
 fect balancing organs than those of 
 the older shark ; their anterior rim is 
 Fig. 88 A. -Teeth of formed by a stout spine, representing, 
 Acanthodopsis wardi. x i. the present writer believes, the con- 
 
 From sketch after speci- 
 men in British Museum. cresccnce of the radial fin supports ; 
 
 it is heavily crusted over with the 
 
 calcifications of shagreen denticles. The functional fin 
 area has thus become dermal, and is lacking in supports, 
 excepting in the pectoral fin. This, as the most highly 
 specialized of all the body fins (p. 41), appears in some 
 cases to have evolved strengthening (dermal) jays in its 
 proximal portion (as in Figs. 87 and 32). 
 
 Fig. 89. Climatius scutiger, Egert. X i. (From ZlTTEL, after POWRIE.) 
 Old Red Sandstone, Forfarshire. 
 
 In connection with these fin structures the remarkable 
 Acanthodian, Climatius (Fig. 89), should finally be men- 
 tioned. In this form the paired fins are represented by a 
 series of fin spines whose size grades backward from the 
 pectoral region ; a series of paired fins appear, therefore, 
 
PLE URA CAN THUS 
 
 to have been present, 
 and suggest strongly 
 continuous fin-fold char- 
 acters. (V. p. 40.) 
 
 Pleuracanthus (Fig. 
 90), the third of the 
 well - known Palaeozoic 
 sharks, is widely differ- 
 ent from the Acantho- 
 dian : it suggests a tran- 
 sitional form between 
 the generalized Cladose- 
 lachian, on the one hand, 
 and the Dipnoan on the 
 other ; or, more accu- 
 rately, it demonstrates 
 that the stems of shark 
 and lung-fish were at one 
 time drawn very closely 
 together. It has thus 
 far occurred only in the 
 Carbon and Permian, 
 but may reasonably be 
 expected in lower hori- 
 zons as a contemporary 
 of the earliest lung- 
 fishes. 
 
 Pleuracanthus is in 
 many ways the most in- 
 teresting and suggestive 
 member of the shark 
 group ; for it destroys 
 many of our conventional ideas as to the general characters 
 
8 4 
 
 PLEURACANTHID SHARKS 
 
 Fig. 90 A. Teeth of Pleuracanthus. 
 (After DAVIS.) 
 
 XJ. 
 
 essential to sharks. That it was actually a shark cannot 
 be doubted ; its gills, six or seven in number, opened 
 separately to the surface ; its teeth (Fig. 90 A) were 
 typically shark-like, arranged in many rows on Meckelian 
 and palatoquadrate cartilages ; a tuberculated dorsal spine 
 was present ; claspers occurred in the male ; the vertebral 
 column, although notochordal, N, presented intercalary 
 
 plates, 1C, and the 
 jaw was essentially 
 hyostylic, HM. On 
 the other hand, 
 many of its struct- 
 ures are clearly tran- 
 sitional to the Dip- 
 noan: the pelvic fins 
 are shark-like, with 
 the radial supports, 
 R, arising from but 
 one side of the line 
 of basals, B ; but the 
 pectoral fin is typi- 
 cally archipterygial, 
 and the caudal diphy- 
 cercal, as in the lung- 
 fishes. In this re- 
 gard the continuous 
 dorsal fin, with its separate basals and radials, B and R, is 
 again noteworthy. But most singular of all the features 
 of this lung-fish-like shark were its integumentary charac- 
 ters ; shagreen tubercles had disappeared on the body sur- 
 face, and derm bones had appeared roofing the head : their 
 arrangement (Fig. 90 B) is strikingly similar to that of the 
 lung-fish of Fig. 124. 
 
 Fig. 90 B. Dermal bones of the head roof of 
 Pleuracanthus. X 5. (After DAVIS.) 
 
CHONDRENCHEL YS g 5 
 
 The final form of Palaeozoic shark whose structural char- 
 acters have in any way been described is Chondrenchelys. 
 It appears to have somewhat resembled the Pleuracanthid 
 in its elongate form and tapering tail ; but as yet the 
 details of its structure have not been discovered. In its 
 vertebral characters it had certainly made a marked ad- 
 vance ; the notochord had become greatly constricted ; 
 and well-marked centra and arches were present. These 
 appear to have been highly calcified, and show a peculiar 
 
 Fig. 91. Port Jackson shark, Cestracion philippi (?) . X ^. (After GARMAN.) 
 Australia. A. Ventral. B. Anterior, and C. Dorsal aspect of head. 
 
 beaded or fretted structure which in this form is appar- 
 ently unique. 
 
 Other ancient sharks, as far as can be inferred from 
 fragmental structures, appear to have closely resembled 
 forms that are still extant. 
 
 Such unquestionably were the Cestracionts, a group 
 of sharks especially abundant in the early Palaeozoic 
 seas, judging from the numbers of their fin spines and 
 
36 PORT JACKSON SHARKS 
 
 pavement teeth that have been preserved. Their bygone 
 role was certainly a long and important one. In some 
 of their forms they could have differed but little from 
 their single survivor, the Port Jackson shark, Cestracion 
 (Heterodontus) (Fig. 91, A, B, C). In others, the denti- 
 tion and dermal defences suggest a wide range in evo- 
 lution. Their general character appears to have been 
 primitive, but in structural details they were certainly 
 specialized ; thus their dentition had become adapted to a 
 shellfish diet, and they had evolved defensive spines at 
 the fin margins, sometimes even at the sides of the head. 
 In some cases the teeth remain as primitive shagreen 
 cusps on the rim of the mouth, but become heavy and 
 blunted behind ; in other forms the fusion of tooth clus- 
 ters may present the widest range in their adaptations for 
 crushing ; and the curves and twistings of the tritoral sur- 
 faces may have resulted in the most specialized forms of 
 dentition (e.g. Janassas, Petalodonts, Cochliodonts, and Psam- 
 modonts of the Coal Measures) which are known to occur 
 not merely in sharks but among all vertebrates. Equally 
 interesting may prove the evolutional details of other 
 cestraciont structures when they come to be known. 
 Ray-like proportions may well have been evolved even 
 among the earliest Palaeozoic forms. 
 
 The surviving member of this group, Cestracion, sug- 
 gests in itself the adaptations of a bottom-living form in 
 its greatly enlarged pectorals. Its genus, however, has 
 not been traced earlier than the Mesozoic, although its 
 comparatively generalized dentition (Fig. 27) suggests a 
 far more remote descent. 
 
 It is of interest to note that Cladoselache approaches in 
 its dentition the characters of the primitive Cestracionts 
 (e.g. Synechodus). 
 
88 
 
 PRIMITIVE LIVING SHARKS 
 
 Recent Sharks 
 
 The forms of Sharks and Rays 
 common at the present time are 
 generally looked upon as closely 
 related genetically, although 
 their lineage cannot be defi- 
 nitely traced. As far as palae- 
 ontological evidence goes, they 
 may well have been derived 
 from a single Palaeozoic an- 
 cestor. 
 
 Perhaps of all recent forms, 
 Chlamydoselache (Fig. 92), and 
 Notidamis (Heptanchus, or Hep- 
 tabranchias) (Fig. 93), which are 
 universally regarded as "primi- 
 tive," have inherited most di- 
 rectly the features of this gen- 
 eralized Palaeozoic form. But 
 which of these two sharks must 
 be regarded as resembling its re- 
 mote ancestor the more closely 
 seems to the writer a very doubt- 
 ful matter. Chlamydoselache 
 derives its great interest from 
 its late discovery (1884, Gar- 
 man), rareness, and Pleuracan- 
 thid type of teeth (Fig. 92, A) ; 
 but now that it has been taken 
 in numbers comparatively 
 in deep water, one is inclined 
 to believe that many of its 
 
RECENT SHARKS 
 
 8 9 
 
 "primitive" features, like its eel-like shape, may partly be 
 due to its environment : its resemblance, moreover, to the 
 Pleuracanth has since been found to be of a superficial 
 character. Notidanus, on the other hand, adds to its 
 primitive characters the presence of no less than seven 
 
 Fig. 94. The horned dog-fish, Squalus acanthias, L. 
 in U. S. F. C.) Atlantic. 
 
 X J. (After GOODE 
 
 gill slits, a feature which morphologists generally are 
 inclined to regard as of great significance. 
 
 The many forms of recent sharks have certainly not 
 diverged widely from the stem of descent which Notidanus 
 may well represent : they retain the sub-cylindrical body 
 form, specializing more or less to environment; in deep- 
 sea genera the body length appears proportionally in- 
 
 Fig. 95. The thrasher shark, Alopias vulpes (GmeL), Bonap. 9. X T V. Atlantic. 
 
 creased : predatory forms, such as Squalus, Alopias, Lamna 
 (Figs. 94, 95, 96), acquire great size and strength, travel 
 great distances, and are enabled to become cosmopolitan. 
 Among the minor details to which their evolution has 
 been carried, may be noted : the pattern, size, and arrange- 
 
9 o 
 
 RECENT SHARKS 
 
 ment of teeth and shagreen denticles ; the calcification of 
 the vertebrae (great differences sometimes occurring in the 
 same genus, e.g. Scyllium), the size, disposition, and num- 
 
 Fig. 96. The mackerel shark, Lamna cornubica (Gmel.), Fleming. X sV. 
 North Atlantic. 
 
 her of the fins, the more or less pouch-like character of 
 the sensory canals. 
 
 In the basking shark, Cetorhinus (Selache) (Fig. 96 A), 
 widely specialized conditions occur in the gill rakers, 
 which enable the throat to retain the smallest food organ- 
 
 Fig. 96 A. The basking shark, Cetorhinus maximus, (L.) Blainville. cf. 
 X sV. (After GOODE in U. S. F. C.) 
 
 isms. In another shark, Lcemargus (Fig. 96 B\ the eggs 
 are probably fertilized after being deposited, a condition 
 unique among recent Elasmobranchs. 
 
SQUATINA AND PRISTIS gj 
 
 The different families of the existing sharks appear to 
 to have been already differentiated during the early Meso- 
 zoic times. The ancient shark-like form had then given 
 place to the flattened and rostrated types, adapted to the 
 
 Fig. 96 B. The Greenland shark, Lcemargus borealis, L. X &. (After G0NTHER.) 
 
 conditions of bottom living and to the special character of 
 their shell-fish or crustacean diet. 
 
 One of the earliest offshoots from the main selachian 
 stem appears to have been Squatina (Fig. 97), popularly 
 known as the monk-fish, or angel-fish. As early as the 
 Mesozoic times it was existing, differing but little from the 
 recent species. Its general shape is shark-like, although its 
 
 Fig. 97. The monk-, or angel-fish, Rhlna squatina. ?. X &. Atlantic, 
 Mediterranean, Pacific. 
 
 head and trunk are clearly depressed. This, together with 
 its enlarged pectoral fins, enables it to take a position 
 closer to the bottom. 
 
 The recent saw-fish, Pristis (Figs. 98, 98 A), is next to 
 
02 SA W-FISHES 
 
 be mentioned as a form somewhat transitional from shark 
 to ray. Its body, as may be seen in the figure, has been 
 strikingly flattened, the gill openings changing their posi- 
 tion from the lateral to the ventral side, but the fins re- 
 taining in general the selachian characters. Its singular 
 rostrum with lateral spike-like teeth is unquestionably a 
 
 Fig. 98. The saw-fish. Pristis pectinatus, Latham. ?. 
 seas. (After GOODE in U. S. F. C.) 
 
 highly specialized organ. Pristis is thus far known not 
 earlier than the Eocene, but its close connection genetically 
 with the ancient and more generalized Pristiophorus is 
 usually conceded. 
 
 Pristiophorus (Fig. 99) is certainly more closely allied 
 to the sharks : its gill slits have not as yet acquired their 
 ventral position, and its rostrum suggests the ancestral 
 
 Fig. 98 A. Saw-fish, ventral view. 
 
 conditions of that of Pristis. Its barbel-like structures, 
 however, distinguish this form clearly from all other 
 Elasmobranchs. It is known to have occurred as early 
 as the Jura. 
 
 The Skates or Rays are well known to represent the 
 most highly modified survivors of the ancient stem of the 
 
SKA TES 
 
 93 
 
 sharks ; they appear comparatively late in time, and may 
 well be regarded as the culminating forms of the specializ- 
 ing bottom-living sharks of the Mesozoic. Whether they 
 are directly descended from forms like Squatina or Pristio- 
 
 Fig. 99. Pristiophorus (cirratus). 
 
 (After JAEKEL.) Australia. 
 
 phorus must be looked upon as exceedingly doubtful, as 
 the depressed body form may possibly have arisen 
 independently in these different families. The most 
 nearly ancestral form of the skates appears to have sur- 
 survived in Rhinobatus (Fig. 100). The shark-like body 
 form is here most nearly retained, and its fin structures 
 
 Fig. loo. Rhinobatus planiceps. ?,. X }. (After CARMAN.) (The lower 
 portion of the figure showing ventral side.) S. Spiracle. GO. Gill slits. 
 
 are the least specialized ; these transitional characters of 
 Rhinobatus become more prominent in view of its ancient 
 occurrence : its genus was clearly defined as early as the 
 Oolite. 
 
94 
 
 FLATTENED SHARKS 
 
 The body form of the Skate (Fig. 101) has become 
 admirably adapted to bottom living; it is exceedingly 
 flattened anteriorly, its head and trunk and paired fins 
 fusing so perfectly that from the surface view one could 
 not define their limits ; the tail region, on the other hand, 
 has dwindled away to rod-like or whip-like proportions. 
 
 Fig. ioi. The barn-door skate, Raja Icevis, Mitch, 
 in U. S. F. C.) 
 
 1 . x J. (After GOODE 
 
 In the process of flattening, the gill openings take their 
 appearance early in the ventral side of the body, and the 
 pectoral fins, enlarging rapidly, press closely forward at 
 the side of the flattened head, fusing with its tissues. 
 Motion is now accomplished by the gentle undulation 
 of the long horizontal fin margin : and the enlarged 
 
AFFINITIES OF THE ELASMOBRANCHS 
 
 95 
 
 anterior element of the fin stem, by being raised or de- 
 
 pressed, comes to direct the upward or downward motion 
 
 of the fish. In this mode of movement seems to have 
 
 been paralleled the undulation of the ancestral fin fold. 
 
 On the fish's dorsal side colour adaptations have become 
 
 marked, the ventral 
 
 aspect becoming de- 
 
 ficient or wanting in 
 
 pigment. In its hab- 
 
 its the skate mimics 
 
 the colour of the 
 
 bottom and glides 
 
 along inconspicuous- 
 
 ly, apparently with- 
 
 out movement ; when 
 
 alarmed, it will press 
 
 its enlarged and flat- 
 
 tened fins so closely 
 
 to the bottom that it 
 
 appears to adhere, 
 
 and is to be dislodged 
 
 only with the great- 
 
 est efforts. 
 
 Two of the aber- 
 
 rant forms Of rays are 
 
 shown in Figs. 102 
 
 and 1 02 A. The for- 
 
 mer, the Torpedo, is remarkable on account of its electric 
 
 organs ; the latter, Dicerobatis, on account of the great 
 
 breadth of its pectorals, and its enormous size. 
 
 pig. 102. The torpedo, Torpedo occidcnta- 
 
 * x * (After GOODE in u. S. 
 
96 KINSHIPS OF SHARKS 
 
 Affinities 
 
 In concluding the present chapter, the probable affini- 
 ties and interrelationships of the Elasmobranchs may be 
 summarized as follows (v. Fig. 103) : 
 
 1. Of all known stems that of the shark is most nearly 
 ancestral in the line of jaw-bearing vertebrates. 
 
 2. A generalized form not unlike Cladoselache might 
 well represent the ancestor of Pleuracanthid, as well as 
 of the primitive Cestraciont, of Acanthodes, and of the 
 modern sharks and rays. 
 
 Fig. 102 A. The mantis, or devil ray, Cephaloptera (Dicerobatis) d 
 (After GUNTHER.) Tropical seas. 
 
 raco. 
 
 3. On the evidence of the Permian Pleuracanthids, 
 lung-fishes (Dipnoans) and the earliest bony fishes 
 (Crossopterygians) are to be derived from an advancing 
 shark type. 
 
 4. From the ancestral stem of the recent sharks 
 Cestracionts were the most early differentiated : it is one 
 of their more generalized forms, Cestracion, that has alone 
 
KINSHIPS OF SHARKS ^ 
 
 survived among the widely evolved genera and families of 
 Palaeozoic times. 
 
 5. The more primitive types of modern sharks, Chlamy- 
 doselache, Notidanus, represent in an almost differentiated 
 condition the Palaeozoic phylum. 
 
 6. The modern rays are derived in early Mesozoic times 
 from the main shark stem, not (in the opinion of the 
 writer) descended from Cestracionts, Pristids, Pristiopho- 
 rids, or even (?) Rhinids. 
 
 7. Chimaeroids, next to be discussed, represent the most 
 ancient of known offshoots from the (Pre-Silurian ?) sharks : 
 they are not degenerate in their essential structures, nor 
 are they connected with the ancestral phylum of the lung- 
 fishes, save through a common descent from early shark- 
 like ancestors. 
 
 These results the writer has expressed in the diagram 
 on the following page. The diverging phyla are indicated 
 as they are represented historically ; their primitive con- 
 currence with the main line of descent is suggested by 
 dotted lines. 
 
Ancestral Elasmobranch. 
 
 (TABLE III) 
 
 Cladoselache. 
 
 thodian. 
 
 - Pleuracanthid. 
 
 CXENO- 
 ZOIC. 
 
 Fig. 103. Scheme suggesting the interrelationships of Sharks, Chimaeroids, 
 and Lung-fishes. 
 
 98 
 
THE CHI1VLEROIDS 
 
 CHIM^ROIDS are shark-like in their general characters, 
 but cannot be looked upon as in any strict sense closely 
 associated with the Elasmobranchs. They constitute the 
 second of the more important groups of fishes. Their 
 typical representative is the Chimaera, spook-fish, or sea- 
 cat (Fig. 119). 
 
 Structural Characters 
 
 The typical structures of Chimaera are shown in the dis- 
 section given in Fig. 104. Its thick, round, and blunted 
 head tapers away gradually to the tip of a diphycercal tail, 
 C. The body surface is generally smooth. The paired fins 
 are somewhat shark-like, but their dermal margins have be- 
 come greatly enlarged, tapering distally to an acute point ; 
 the foremost dorsal fin provided with an anterior spine folds 
 like a fan and may be depressed into a sheath, SH, in the 
 body wall ; this fin and the hinder ones are largely dermal, 
 D', basal and radial supports existing only at B\ R'. The 
 gill arches, BA, may be seen to be closely drawn together; 
 their outer openings are now reduced to the slit-like aper- 
 ture beneath the dermal flap, OP. Teeth exist in the 
 form of dental plates, closely fused with the jaws ; as 
 shown in the figure, D, three of these occur in each side, 
 a single one on the mandible, an anterior and posterior on 
 
 99 
 
li^l 
 
 !tti 
 
 v o O. o "* 
 
 A 
 
 
 100 
 
STRUCTURES OF CHIM&ROIDS IO i 
 
 the upper jaw (" premaxillary " and "palatine") ; they are 
 studded with hardened points, or "tritors" (Figs. 109-112). 
 The sense organs are similar to those of sharks ; the nasal 
 capsule, NAS, has both an anterior and a posterior* open- 
 ing, O, O', the latter within the cavity of the mouth. 
 
 The visceral parts are decidedly shark^ike^fte! 3ige** 
 tive tube is straight (p. 263) ; the intestine, /, with a spiral 
 valve of three turns ; the liver, L, is prominent ; the 
 kidney, K, reproductive organs, T, and their ducts, VD, 
 SS y VS, and abdominal pores are as in sharks ; the intes- 
 tine, however, opens directly to the surface, A, separating 
 an anal from a urogenital aperture, UG. The mesenteries 
 are string-like. 
 
 The male fish is provided with a highly specialized intro- 
 mittent organ, CL ; it has a supplemental clasping organ, 
 VC, at the front margin of each ventral fin, V (cf. also Fig. 
 116 and Fig. ii6#), and a retractile spine in the region of 
 the forehead, MSP (cf. Figs. 113 and 115). 
 
 The skeleton of a Chimaeroid is shown in the following 
 figure (Fig. 105). Its structure is cartilaginous. The ver- 
 tebral axis is notochordal ; its sheath, lacking in definite 
 centra, is strengthened anteriorly by a series of calcified 
 rings. In the anterior region of the trunk, neural proc- 
 esses, interneurals, and neural spines, NP, IN, NS, to- 
 gether with haemal processes, occur as in sharks ; toward 
 the tail region they fade away, and before joining with 
 the head at the occipital condyles, OC, they fuse into a 
 compact mass, joining with the basal supports of the 
 dorsal fin. 
 
 The cranium is of a highly compacted structure; its 
 vertical height has been greatly produced ; the orbits, OR, 
 are of great size and are separated from each other by a 
 membranous septum. The snout region is greatly meta- 
 
ifl 
 
 * sea 3-^5 s- 
 
 .a a<u-aOt; = ? 
 a g-g* > 
 
 *^ !/)- r-*w. -^^CC-^ 
 
 i 
 
 ^5 oO a 
 
 102 
 
STRUCTURES OF CHIMJZROIDS , IO ^ 
 
 morphosed ; the mandible appears to be autostylic, or artic- 
 ulated directly with the skull cartilage, PQ. The gill 
 arches are shark-like, b\ '"he hyoid arch appears far less 
 modified than in sharks ; its upper element, HM, is thus 
 unconnected with either th: skull or the joint of the jaw; 
 its distal element, CH, has, however, developed a series of 
 specialized supports for the dermal gill shield, OP. The 
 study of the fin supports shows the dorsal elements, B + R, 
 representing probably the radial and basal elements to- 
 gether, arranged in a single row margined distally by the 
 longitudinal ligament, LL, supporting the dermal func- 
 tional fin, D. The paired fins are readily reduced to the 
 plan of those of Fig. 84; their girdles, however, seem to 
 have acquired more modified characters, their ventral and 
 dorsal elements greatly increasing in size. 
 
 Chimasroids as a group have received but a small share 
 of the attention paid to the other fishes ; their living 
 forms are few and comparatively rare ; their embryology 
 and larval history are unknown ; and their life habits have 
 been suggested only in the work of Dr. Giinther (Chal- 
 lenger Report). His record of the taking of immature 
 specimens of Chimara at great depths seems thus far the 
 most important clue as to the conditions of their living 
 and breeding.* 
 
 Fossil Chimaroids 
 
 Fossil Chimaeroids have left behind them very imperfect 
 records of the history of their group. Like the sharks, 
 little more than their dental plates and fin spines have 
 usually been preserved. The structures of some of their 
 ancient members appear to have differed little from those 
 just described in the recent Chimaera. In Ischyodus t 
 
 * Cf. also Goode and Bean, on Harriott^ P. U. S. Nat. Mus., XVII. 471-473. 
 
FOSSIL CHIMsEROIDS 
 
 a Jurassic form (Fig. 105 A), the skeletal structures are 
 readily comparable to those of Fig. 105. In the case of 
 two of the Mesozoic genera, however, the evolution of 
 the Chimaeroids had evidently attained a high degree 
 of specialization : Myriacanthus and Squaloraja, whose par- 
 tial restoration has been attempted in Figs. 106 and 
 io6A, must be both looked upon as highly modified forms ; 
 their snouts and frontal spines are greatly enlarged, and 
 their dental plates (Figs. 107 and 108) widely divergent 
 from the general Chimaeroid type : in Myriacanthus a series 
 of membrane bones occurs in the head region (Fig. 106, 
 B, C). In Squaloraja a horizontally flattened body shape 
 parallels the development of the ray-like form of sharks. 
 
 Fig. 105 A. The Mesozoic Chimaeroid hchyodus. X |. (After ZlTTEL.) 
 
 Living Chimceroids 
 
 The Chimaeroids of to-day must be looked upon as the 
 survivors of a group comparatively numerous in Mesozoic 
 times : the few existing forms accordingly, from the palae- 
 ontological standpoint, acquire an exceptional interest. 
 They have been grouped under three genera, Harriotta, 
 Callorhynchns, and Chimara. The first of these (Fig. 
 117, A, B, C) has been only recently discovered, and but 
 a few examples have been taken ; it merits especial atten- 
 tion, since it is unquestionably the most shark-like of 
 known Chimaeroids. In the male it lacks entirely the 
 frontal spine and has its claspers in an exceedingly un- 
 
FOSSIL CHIM&ROIDS 
 
 105 
 
 X "o 
 
 differentiated condition. The eggs are evidently fertilized 
 after they have been extruded. 
 
 The second genus, Callorhynchus, is represented by but 
 
"|t|! 
 
 * S f 
 
 106 
 
FIG. 113 
 
 MC 
 
 114 
 
 ^^^^ 
 
 116 
 
 sc v 
 
 Figs. 113-116 A. Spines and clasping organs of Chimaeroids. 113. Clasping spine 
 of the forehead of male Chimcera colliei. X 6. 114. Myriacanthus dorsal spine. (After 
 L. AGASSIZ.) 115. Frontal spine of male Squaloraja. (From SMITH WOODWARD.) 
 116. Ventral fin and clasping organs of male Chimcera colliei. X i. 116 A. View of tip 
 of hinder clasper (intromittent organ), when the three tips are drawn together. 
 
 A. Anus. A V, Anterior rim of ventral fin, specialized as a clasping organ. BC. Body 
 of the posterior clasper (intromittent organ). D. Dermal denticles. DS. Dermal spine- 
 like denticles. D T. Dermal tubercles. GD. Urinogenital aperture. J. Jointed base of 
 inner ventral element of intromittent organ. MC, Mucous canal. S. Sheath of frontal 
 spine. SC. Sperm groove of inner face of clasper. V. Ventral fin. 
 
 10 7 
 
i I' 
 
 Fig. 117. Harriotta raleighana, Goode and Bean. tf. X \. Anew genus 
 of Chimasroid a bathybial form. A. Ventral view, showing rudimentary claspers. 
 B, C. Immature specimens. 
 
 108 
 
CALL ORHYNCHUS 
 
 a single species, C. antarcticus. It is said to be common in 
 the Straits of Magellan, and is popularly known as the 
 Bottle-nosed Chimaera (Fig. 118, A, B). Its remarkable 
 snout is well supplied with sense organs, and its pad-like 
 dilation in front of the mouth is evidently of barbel-like 
 function ; it illustrates closely, no doubt, the remarkable 
 snout process of Myriacanthus. Callorhynchus is shark- 
 like in its general shape; and its caudal, dorsal and ventral 
 
 Fig. 118. The bottle-nose Chimaera, Callorhynchus antarcticus, ?. X &. From 
 Magellan Straits. A. Dorsal aspect. B. Ventral view of head. (After GARMAN.) 
 
 fins correspond closely in appearance and structure with 
 those of certain sharks ; the greatly enlarged pectoral fins 
 have, however, a more highly specialized character ; they 
 stand boldly out from the sides of the body, and their 
 bases are rounded and muscular. The mucous canals 
 (Garman) have paralleled the saccular or tubular struct- 
 ures of the majority of sharks. The mandible (Fig. no) 
 shows but a single broad tritoral area. 
 
110 
 
 RECENT CHIM&ROIDS 
 
 Chimaera, the third genus of the recent forms, is well 
 represented in the commoner form, C. monstrosa (Fig. 1 19, 
 A, B). This species is widely distributed in the Mediter- 
 ranean and Atlantic, taken usually in deep water; it is the 
 largest of the living species, often attaining a yard in 
 length. Its occurrence is usually erratic : in a favourable 
 locality, as at Messina, months often elapse before one is 
 taken ; at other times many will be brought in in the 
 course of a few days. The Portuguese species, C. affinis, 
 
 Fig. 119. The sea-cat, Chimcera monstrosa, 
 snout. B. Front view of head. (After GARMAN.) 
 
 X 5. A. Ventral view of 
 
 is said to be numerous in the deep fishing grounds ; the 
 writer has seen it in the Lisbon market, where from its 
 low price it evidently ranks with the sharks as a food fish. 
 The smaller Pacific C. colliei (Fig. 104), rarely half a yard 
 in length, differs sharply from the other species, and is 
 therefore often given rank as a distinct genus, Hydro- 
 lagus, Gill. The writer learns from his friend Dr. Bean 
 
AFFINITIES OF CHIM&ROIDS IIZ 
 
 that it occurs abundantly in the shallow waters of Van- 
 couver ; it is there well known as the "rat fish," and may 
 often be seen in the neighbourhood of the docks, swim- 
 ming slowly at the surface. 
 
 The shape of the body of Chimaera seems in some re- 
 gards to have diverged from the more shark-like form of 
 Callorhynchus. Its organs have become concentrated in 
 the pectoral region, and the disturbance in the curve 
 normals of the fish seems to have caused the shortening of 
 the snout, and the sudden dwindling of the hinder trunk 
 region; the tail, with its thread-like terminal, the opis- 
 thure (Fig. 120), is accordingly to be looked upon as de- 
 
 Fig. I2O. Chimcera monstrosa, tf. Juv. X about . (After L. AGASSIZ.) 
 The anterior ventral clasper is noted at X; the tail terminates in a thread-like 
 opisthure. 
 
 generate. In the anterior region, however, a number of 
 what seem to be primitive characters have been retained ; 
 the mucous canals are groove-like ; and the dental plates 
 (Figs. 109, 109^) exhibit a series of tritoral areas. 
 
 Affinities 
 
 All that is known of Chimaeroids, living or fossil, gives 
 but little definite knowledge of the kinships or evolution 
 of the group. Their shark-like structures cannot be shown 
 to have taken their origin from shark-like conditions. 
 Thus the dental plates even of the most ancient forms 
 do not suggest their derivation from shagreen cusps ; the 
 
! j 2 CHIM^R OIDS 
 
 beak-like jaws of the Devonian Rhynchodus (Fig. in), 
 of the Devonian Ptyctodus, or of the Mesozoic genera, 
 e.g. Ischyodus (Fig. 112), differ little in their structures 
 from those of their living kindred (Figs. 109, 109 A, 1 10). 
 The tritors accordingly are only doubtfully to be derived 
 from the fusion of the primitive basal substance of the teeth 
 with the tissue of the jaws. But the history of Chimae- 
 roids tells of their ancient importance and of the diversity 
 of their forms, and demonstrates that they cannot be con- 
 nected with other existing forms of fishes. In Liassic 
 times their specialized members bore the same relation to 
 Chimaera as did the aberrant Cestracionts of the Coal 
 Measures to the simpler sharks. In their dental evolution 
 they had even reached a more specialized condition than 
 the Cochliodonts (Cestracionts ?). Thus in Myriacanthus 
 and Squaloraja, "all anterior prehensile teeth have disap- 
 peared, and the growth of the dental plates, instead of 
 taking place exclusively at the inner border, seems to have 
 gradually extended to the whole of the attached surface. 
 The Chimaeridae exhibit an advance in the circumstance 
 that all the dental plates are thickened, while the hinder 
 upper pair are both closely apposed in the median line and 
 much extended backward " (Smith Woodward).* Squaloraja 
 had certainly attained a high degree of evolution in the 
 calcified vertebral rings, and in its specialized girdles, fins, 
 and clasping organs. Myriacanthus, on the other hand, 
 while retaining its ancient vertebral characters, had evolved 
 a well-marked series of membrane bones. 
 
 One cannot deny that the study of Chimseroids as a 
 group emphasizes many of their structural affinities to 
 the sharks. They resemble them in their cartilaginous 
 skeleton, fins and girdles, " claspers," integument, and 
 
 * Cat. Fossil Fishes II, xvi. 
 
KINSHIPS OF CHIM^.ROIDS U^ 
 
 sense organs : they present similar visceral characters, 
 spiral intestine, heart, gills, abdominal pores, renal and 
 reproductive organs. 
 
 Their more important divergences from the plan of 
 elasmobranchian structure may thus be summarized : 
 
 I. SKULL AND MANDIBLE (v. pp. 252, 256). The mandi- 
 ble articulates directly with what appears to be the carti- 
 lage of the cranium, i.e. without the hyoid-arch element 
 serving as the suspensorium (Autostylic, p. 257). 
 
 II. FINS, paired (Wiedersheim) and unpaired (Ryder), 
 and fin defences. The first dorsal, armed with an anterior 
 spine, is so specialized that it folds like a fan, and may be 
 depressed into a receptive sheath. The tail is (second- 
 arily) diphycercaL 
 
 III. SKIN DEFENCES AND TEETH. Shagreen tubercles 
 occur in Chimaeroids and are in every way shark-like. 
 They are scattered thickly over the entire dorsal region 
 in Menaspis* sparsely in Squaloraja. They occur in the 
 head region and on the spines in Myriacanthus (Figs. 106 
 C, 1 14) ; and on the head, spine, and clasper tips of recent 
 forms (Figs. 113 D, 116 D). But dermal bones also occur, 
 as in Myriacanthus (Fig. 106 B), which do not outwardly 
 resemble the structures of ancient sharks shown, e.g. in 
 Fig. 90 B. The dermal plates protecting the suborbital 
 sensory canal of Chimaera (Fig. 104, DP) must be looked 
 upon as specialized defences, not as degenerate remnants 
 of a complete dermal armouring (Pollard). And the dental 
 plates, as already noted (p. 99), are altogether unshark-like ; 
 their tritors are few in number and constant in position, 
 suggesting an origin from more superficial tooth centres, 
 but these in turn, like the toothplates of Cestracionts, may 
 have been evolved from shagreen denticles. 
 
 * Jaekel, SB. d. Gesell. nat. Freunde, Berlin, 1891, Nr. 7. 
 
 I 
 
U4 
 
 CHIMAEROIDS 
 
 IV. GILL ARCHES. The gills have become drawn 
 closely together as in the more highly evolved types of 
 fishes (e.g. bony fishes), and are enclosed by a protective 
 dermal flap which fringes the sides of the head. The con- 
 centration of the arches and the appearance of the dermal 
 shield suggest, however, the conditions we have seen in 
 ancient sharks (Cladoselache, Chlamydoselache, Acantho- 
 des), and cannot be given significance as the ancestral 
 form of the opercular apparatus of Teleostome. Even 
 the similar conditions of the Chimaeroid and ancient 
 shark may well have been evolved independently. It is 
 interesting to note that in Chimaeroids the spiracle is 
 absent. 
 
 V. BRAIN. The brain structure is archaic. Its gen- 
 eral plan is, however, more 'shark-like than Dipnoan 
 (Wilder, Ref. p. 244). 
 
 VI. LATERAL LINE. The sensory canals possess many 
 distinctive features ; they retain their groove-like charac- 
 ter, but become widely sacculated and dilated, especially 
 in the snout region. 
 
 VII. CLASPING SPINE. The forehead clasper of the 
 male has been a well-marked character of Chimaeroids 
 from Liassic time. It folds anteriorly into a receptive 
 groove ; its distal end, studded with recurved spines, 
 serves in the recent forms for strongest retention. It 
 seems to represent morphologically the anterior spine of 
 a dorsal fin (cf. Pleuracanthus, p. 83). 
 
 In spite of these differences, however, the kinships of 
 the Chimaeroids seem unquestionably nearer the stem of 
 the sharks than that of other fishes. On existing evi- 
 dence the Chimaeroid could not have been derived from 
 either Teleostome or lung-fish ; nor, on the other hand, 
 could any of the larger groups of fishes be reasonably 
 
AFFINITIES OF CHIM&ROIDS r ! 5 
 
 derived from its conditions as ancestral. The dentition 
 of Chimaeroids alone is so remarkable that no direct proc- 
 ess of differentiation could convert it into the structures of 
 lung-fish or Ganoid. A number of archaic features draw 
 fishes together in the lines of their descent, but they can- 
 not be interpreted as linking the Chimaeroids with the 
 Dipnoans, or the Dipnoans with the Chimaeroids. Auto- 
 stylism, often adduced to ally these groups, differs widely 
 in its characters in each (p. 254) : and the apparent similar- 
 ities in dental plates and membrane bones are closely 
 paralleled by the sharks. The diphycercal tail of the 
 Chimaeroid can be made no standard of comparison, since 
 it is evidently a secondary structure, arising within the 
 limits of the group, as it may well have done among 
 sharks (Pleuracanthus) or Teleostomes (Polypterus, eel). 
 
 If the sum of the general characters of Chimaeroids be 
 considered, their affinities would clearly be to the most 
 ancient sharks. Their structures are not so widely at vari- 
 ance with those of Elasmobranchs that they cannot rea- 
 sonably be derived from their more generalized conditions 
 in vertebral characters, cranium, mandible, girdles, fins, 
 membrane bones, gills. Absence of swim-bladder is again 
 strikingly shark-like. Like the ancient sharks, they have 
 been well adapted for survival by evolving but few special- 
 ized structures (e.g. dentition, gills). Their ventral clasp- 
 ing organs separate them clearly from the Dipnoans. 
 Until the discovery of Harriotta the frontal clasping spine 
 remained as one of the most distinctive features of Chi- 
 maeroids ; its high degree of specialization in Liassic times 
 is alone significant of the antiquity of their descent. 
 
VI 
 
 
 
 THE LUNG-FISHES 
 
 LUNG-FISHES, or Dipnoans, have long been looked upon 
 as the linking type between amphibians and fishes. In 
 some regards of structure they approach the primitive 
 sharks ; in others, they resemble so closely the salamanders 
 that they were recently regarded by W. N. Parker as worthy 
 of a class by themselves, intermediate between fishes and 
 amphibians. As with the Chimaeroids, their few surviving 
 members give but a mere suggestion of the former size 
 and importance of the group. 
 
 Structural Characters 
 
 The general structural plan of a Dipnoan is shown in 
 the adjoining figure (Fig. 121), taken from a dissection of 
 the African form, Protopterus. Its thick, spindle-shaped 
 body, enclosed in rounded, horn-like scales, CS, terminates 
 in a diphycercal tail, CF. The head is salamander-like 
 both in shape and in slimy integument. The paired fins 
 (schematized in the figure, PF, VF) are archipterygial. 
 
 The head region is characterized by a cartilaginous brain 
 case, roofed by dermal bones, HR\ a mandible, MA, 
 directly articulated with the skull (autostylic) ; an anterior 
 and posterior nares, NO, the former opening under the 
 lip, the latter within the mouth ; a row of small, compressed 
 (unsegmented) gill arches, GA, whose single outer aperture 
 
 116 
 
r- w> _. -a 
 _ o .5 I- 
 
 . ctf 3 X! 5 
 ^ y "O >- 
 
 2 -3 ' S o 
 ^ rt ^.- 
 
 30 
 8 
 
 _ 
 
 < 2 
 *-) 
 
 
 \ ^ ; 
 
 'srl 
 
 s--s 
 
 n; 
 
 g 1 a 2 1 
 
 SW O 
 ~ "3 
 
! ! 3 L UNG-FISHES 
 
 is guarded by an operculum, OP. The stunted external 
 gills which here protude, EB, are sometimes looked upon 
 as significant of an ancestral condition (Garman, Wieders- 
 heim). 
 
 The viscera are somewhat shark-like in their features. 
 They include a short digestive tract, with well-marked 
 spiral intestinal valve, SIV\ a fenestrated dorsal mesen- 
 tery, DM\ a large, elongate liver, L\ a heart whose 
 arterial cone, CA, contains transverse rows of valves ; a 
 cloaca, abdominal pores (or pore), A ; and a rectal caecum, 
 CC (v. p. 263). The elongate kidney, K, the ovary, O V y 
 with its many small eggs, and the long, paired, sacculated 
 air-bladder (lung) may be named as among the least shark- 
 like of its visceral characters. 
 
 The skeleton of a Dipnoan (Fig. 122) is almost entirely 
 cartilaginous. A stout notochord, encased in a heavy 
 sheath, NCH, passes from the skull to the tip of the tail : 
 vertebral centra encroach upon it only in the caudal region, 
 C. Dorsal and ventral processes, arranged in metameral 
 sequence, extend from the notochordal sheath outward and 
 become distally the cartilaginous supports of the dermal 
 unpaired fin. The proximal elements might thus be re- 
 garded as neural, N, NS, or haemal processes and spines, 
 the distal elements as equivalent to the basal and radial fin 
 supports, B + R. A stout, longitudinal ligament, LL, 
 serves to connect the outer ends of the cartilaginous 
 processes, as well as the proximal ends of the dermal fin 
 rays. The ribs are probably the homologues of the haemal 
 processes ; the most anterior pair, greatly enlarged, extends 
 downward on either side as the occipital ribs, OR, special- 
 ized in the function of the air-bladder. 
 
 The structure of the paired fin is normally of the 
 archipterygial form of Fig. 54. In Protopterus, however, 
 
120 
 
 LUNG-FISHES 
 
 (Fig. 122), this plan of structure is somewhat obscured by 
 the rudimentary character of the radial and basal elements, 
 R 4- D, although the fin stem presents a well-marked 
 jointed character, B. The pelvic girdle, a solid plate of 
 cartilage, is produced anteriorly into a narrow median out- 
 growth, PG, and laterally into a pair of dorsal spurs, PG'. 
 The shoulder girdle is composed on either side of a large 
 ventral element, SG, which meets its fellow in the median 
 ventral line, and of a short dorsal element, SG', which 
 connects it with the skull. 
 
 Fig. 122 A. Jaws and skull of Protopterus annectans, figured in front and side 
 aspects, showing paired dental plates, x i. (After NEWBERRY.) 
 
 M. Dental plates of (dentary) mandible; P. of palatopterygoid ; V. of vomer. 
 
 In the head region (v. pp. 252, 254), the brain case is 
 cartilaginous, with, however, a few true bone centres (e.g. 
 epiotic) appearing; the roofs of the skull and mouth, 
 together with the mandible, are well sheathed by dermal 
 bones, as FP, N, PP, DN, AG. Paired dental plates 
 fringe the rim of the mandible (Fig. 122 A, M), the 
 vomerine region (V), and the anterior end of the palato- 
 pterygoids (P). 
 
 Fossil Lung-fishes 
 
 The structures of the recent Dipnoans can as yet be but 
 imperfectly compared with those of fossil forms. Their 
 ancestral conditions can only be determined when more 
 
121 
 
j 2 2 L UNG-FISHES 
 
 perfect evidence is discovered as to their kinship and the 
 lines W their descent. 
 
 In the history of fishes, Dipnoans are known to have been 
 early a dominant group. In some regards, one of their 
 ancient forms bore many resemblances to the Pleura- 
 canthid shark, which, although known at present only in 
 a later period, may well have been its contemporary. But 
 the range in the forms of Dipnoans occurring in the early 
 Palaeozoic indicates the remote antiquity of their origin. 
 They had even then evolved exoskeletal characters which 
 are scarcely less specialized than those of existing forms. 
 
 Fig. 126. A restoration of the Devonian lung-fish, Phaneropleuron. X \. 
 
 Dipterus, of the Old Red Sandstone (Fig. 123), had a 
 complete body armouring of cycloidal scales, a head roofing 
 of dermal plates (Fig. 124), and well-calcified jaw rims 
 (Figs. 124, 125, 125^4). Its fin rays were dermal in 
 structure, its paired fins were archipterygial, its tail and 
 its dorsal fins separate and lobate. Its mucous canals had 
 become elaborately adapted to the body scales (lateral line, 
 Fig. 123) and head plates, piercing the latter with minute 
 pores, as in Figs. 65, 66. Anterior and posterior nares are 
 indicated under the rim of the upper jaw (Fig. 125, 12). 
 Marginal teeth have disappeared ; a pair of elaborate dental 
 plates on the mouth roof (palatine) are apposed by a simi- 
 lar pair in the hinder part of the mandible (splenial). 
 
 The Carboniferous Ctenodus was a nearly allied form. 
 
 Another Devonian lung-fish, Phaneropleuron (Fig. 126), 
 
123 
 
124 
 
 LUNG-FISHES 
 
 was similar to Dipterus in its skeletal characters. Its elon- 
 gate diphycercal tail was continuous with the dorsal and 
 anal (?) elements; in this, and in the retention of marginal 
 cusp-like teeth, it resembled the Pleuracanthid sharks. 
 
 Living Forms 
 
 The three forms of living lung-fishes may reasonably be 
 looked upon as the survivors of the more generalized Palaeo- 
 zoic forms. Ceratodus, the 
 Australian genus, appears to 
 have retained most perfectly 
 the ancestral conditions ; it 
 has probably remained almost 
 unmodified from the early 
 Mesozoic times,* and presents 
 close affinities to the Coal 
 Measure family, Ctenodontidce, 
 and even to the Devonian 
 Dipterids. Its outward ap- 
 pearance is shown in Fig. 
 
 127, and its skeleton in Fig. 
 
 128. The latter is seen to 
 resemble closely the charac- 
 
 Fig. 128 A. Skull of Ceratodus. 
 Seen from the ventral side. (After ters of Fig. 122; its paired 
 
 'ToLpitai rib. d . Dental plates. fins are archipterygial ; the 
 
 na. Anterior and posterior nares. P. mouth is lacking in marginal 
 Palatine. PSph. Paraspenoid. Ft. . 
 
 Pterygoid. Qu. Quadrate. Vo. Vomer. Cutting plates (cf. V, Fig. 
 
 122 A). The dental plates 
 
 of the palatine and splenial regions (Fig. 128 A) are seen 
 to correspond clearly with those of Figs. 125, 125 A. 
 
 Ceratodus had long been known to the colonists of 
 
 r. p. 10. The recent genus, according to Dr. Gill, is to be distinguished 
 
 as Neoceratodus. 
 
THE RECENT LUNG-FISHES 
 
 125 
 
 Queensland as a plentiful food-fish, a "salmon" in size and 
 taste, although, curiously enough, it remained undescribed 
 until 1870 (Krefft, and Gunther). After this its develop- 
 mental history was eagerly awaited, in the hope that it 
 would reveal the affinities of the Dipnoans to the sharks, 
 amphibians, and in general to the early chordates. About 
 ten years ago Caldwell was sent to Queensland by the 
 
 Fig. 129. The South American lung-fish, Lepidosiren paradoxa, Natter. X . 
 (From NICHOLSON, after NATTERER.) A front view of the mouth is shown at B. 
 
 Royal Society, and succeeded in securing a set of the 
 embryonic stages, but his results still remain unpublished. 
 A second set of embryos was collected in 1891 by Semon, 
 from whose recent paper a summary is later given (p. 198). 
 The development of Ceratodus, however, as far as it is at 
 present known, has proven in many ways unsatisfactory to 
 the phylogenist ; its abbreviated growth stages cannot be 
 
126 
 
 LUNG-FISHES 
 
 looked upon as furnishing clearly the ancestral history of 
 
 Dipnoans. 
 
 The two remaining forms of recent lung-fishes, Lepi- 
 
 dosiren and Protopterus, 
 resemble each other so 
 closely that Ayers has 
 contended that they 
 should be regarded as 
 distinct only specifically. 
 Lepidosiren, the South 
 American form (Fig. 
 129), was discovered by 
 its describer, Natterer, 
 in 1837 in the upper 
 Amazon. It then, for 
 many years, succeeded 
 in eluding the collectors, 
 and was known as one 
 of the rarest specimens 
 of foreign museums. In 
 1887 it was, however, re- 
 discovered in Paraguay, 
 where it appears to have 
 long been known as a 
 food-fish. Its structures 
 are now regarded as en- 
 titling it unquestionably 
 to the rank of a distinct 
 genus. 
 
 Protopterus, common 
 in the White Nile and 
 Congo (Fig. \2()A), has 
 long been the " Lepido- 
 
RELATIONSHIPS OF LUNG-FISHES 12 y 
 
 siren" of dealers, often of museums. It is the best known 
 of Dipnoans, on account, partly, of the ease with which it 
 may be transported alive. In the hardened mud cocoons 
 with which it encases itself during the dry season, it is 
 readily dug out of the stream bed and packed for exporta- 
 tion. When placed in tepid water, the cocoon dissolves 
 and the fish shortly revives. 
 
 Relationships 
 
 A review of our knowledge of Dipnoans gives but little 
 satisfactory suggestion as to their relations as a group. 
 They must certainly be looked upon as an advancing 
 phylum from which the amphibia may early have diverged. 
 Their many amphibian characters have been lately em- 
 phasized by W. N. Parker. On the other hand, the 
 evidences of the kinship of Dipnoans to the other types 
 of fishes can only be interpreted as the common con- 
 vergence of the ancient phyla toward the structures of the 
 ancestral form of fish. Thus we find that the types of 
 Devonian lung-fishes can only be distinguished from 
 those of the contemporary Teleostomes by the pattern 
 of arrangement of the plates of the head roof,* a condition 
 which has led Smith Woodward to believe that these 
 groups had already diverged before the appearance of 
 dermal bones. 
 
 Lung-fishes have unquestionably many structures which 
 may have been derived from the more generalized condi- 
 tions of the sharks ; and as a group they may not unrea- 
 sonably be looked upon as descended from the primitive 
 elasmobranchian stem. Their ties of kinship to the sharks 
 
 * The present writer regards this distinction as somewhat provisional; 
 median head plates are nominally characteristic of Dipnoans (Fig. 124), but, 
 as in the sturgeons and siluroids, they are also well known among Teleostomes. 
 Protopterus has, moreover, a symmetrical arrangement of the head plates. 
 
I2 8 RELATIONSHIPS OF LUNG-FISHES 
 
 have now been closened by the proof that their paddle- 
 shaped fins may be directly deduced from a "monoserial 
 archipterygium," and that their diphycercal caudal, formerly 
 regarded as most primitive in plan, may have been acquired 
 secondarily after a condition of heterocercy (W. N. Parker, 
 Traquair, Dean). 
 
 The resemblances of Dipnoans to Elasmobranchs might 
 be summarized in the following structures : 
 
 I. VERTEBRAL AXIS. Its notochordal condition and 
 simple metameral, neural, and haemal elements suggest the 
 conditions of Cladoselache (p. 80) ; in that ancient form, 
 however, the vertebral processes had not come into rela- 
 tion with the unpaired fins. 
 
 II. SKULL. The chondrocranium is as yet largely re- 
 tained ; as yet no dentigerous membrane bones of the 
 mouth rim (maxillary and premaxillary) have appeared. 
 
 III. TEETH. These are clearly of an elasmobranchian 
 order; the tubercles of the dental plates (Fig. 125) suggest 
 closely a shagreen pattern ; in Phaneropleuron, marginal 
 cusps have even been retained. The palatine and splenial 
 plates parallel strikingly some of the forms of Cestraciont 
 dentition. 
 
 IV. BRAIN. Its structures are of an advancing elasmo- 
 branchian order, annectent with reptilian (Ceratodus) and 
 amphibian types (Protopterus).* 
 
 V. VISCERAL CHARACTERS. Heart, gills, digestive tract, 
 vessels, mesenteries. 
 
 The closely corresponding characters of Phaneropleuron 
 and Pleuracanthus might be looked upon as independently 
 acquired ; but in view of the many nearnesses of their 
 phyla, these characters may reasonably be regarded as 
 proof of genetic kinship. 
 
 * Burckhardt. 
 
ARTHRODIRAN LUNG-FISHES 
 
 The advancing structures of the Dipnoan include, in 
 addition : 
 
 I. EXOSKELETAL SPECIALIZATIONS. Head-roofing der- 
 mal bones (cf., however, Pleuracanthid) and cycloidal scales. 
 In early forms (Dipterus) these appeared at the surface 
 and were apparently enamelled. In recent forms they 
 are deeply sunken in the integument (Prototerus). They 
 suggest closely the structures of Crossopterygian (p. 149). 
 
 II. ARTICULATION OF THE MANDIBLE. This is auto- 
 stylic, somewhat as in Chimaeroid (v. p. 256). Its homol- 
 ogy is obscure. 
 
 III. AIR-BLADDER, (v. p. 264). 
 
 IV. ABSENCE OF VENTRAL "CLASPERS" (cf., however, 
 Cladoselache). 
 
 V. TRUE POSTERIOR NARES (amphibian). 
 
 VI. THE GREAT SIZE OF THE CELLULAR ELEMENTS OF 
 
 ALL TISSUES (amphibian); THE GLANDULAR STRUCTURES 
 OF THE EPIDERMIS (amphibian). 
 
 VII. CIRCULATORY CHARACTERS : the three-chambered 
 heart ; aortic arches. 
 
 VIII. LIMB STRUCTURE. This, however, is not to be 
 interpreted as in any way directly transitional to cheirop- 
 terygium. 
 
 The Arthrodiran Lung-fishes 
 
 The ARTHRODIRA, as Smith Woodward has shown, may 
 provisionally be regarded as an order of extinct and highly 
 specialized lung-fishes. They occur geologically among the 
 earliest fishes, and include a number of (Devonian) forms 
 whose peculiar characters and gigantic size must have made 
 them among the most striking members of ancient fauna. 
 The group might be regarded as standing in the same rela- 
 tion to the ancient Dipnoan s as Acanthodians to the Cla- 
 
ARTHRODIRAN LUNG-FISHES 
 
 doselachian sharks. As recently as 1887 its members were 
 associated by Traquair with Pterichthys, but the discovery 
 of jaws, specialized dentition, fin spines, and highly evolved 
 pelvic fins at once separate this group from the lowly 
 Ostracoderms. 
 
 American Arthrodirans, described mainly by Newberry 
 and v by Claypole, have proven of especial interest. They 
 occur from the Silurian to the Coal Measures. The giant 
 predatory member of this group, Dinichthys (Frontispiece, 
 and Figs. 133-137), attained a length of ten feet. Titan- 
 ichtkys, less formidable in armour and dentition, may well 
 have been twenty-five feet in length. These forms occur 
 almost exclusively in the Waverly of Ohio. Their discovery 
 has here been due to the efforts of Dr. William Clark 
 of Berea, Rev. William Kepler of New London, and Mr. 
 Jay Terrell of Linton ; and most of the type specimens 
 have been preserved in the museum of Columbia College, 
 New York. 
 
 The European member of this group is a small, fresh- 
 water (?) form, Coccosteus, especially abundant in the Old 
 Red Sandstone of Scotland. It has thus far yielded the 
 most complete material for study, and its structural char- 
 acters might accordingly be described, since they are 
 probably common to all members of the group. 
 
 The lateral view of Coccosteus is shown in Fig. 130, the 
 dorsal aspect of the anterior region in Fig. 131, and the 
 ventral view of the visceral region in Fig. 132. It will 
 accordingly be seen that the general shape of the body 
 of this Arthrodiran was somewhat depressed ; that the 
 head, shoulder, and stomach regions were protected by 
 bony plates ; and that the trunk region was lacking in 
 armouring, and short in relative length. In well-preserved 
 fossils the space occupied by the notochord, N, is seen to 
 
COCCOSTEUS I ^ l 
 
 pass from the region of hinder plates of the body armour 
 to that of the tip of the tail. This is seen to be bordered 
 by neural and haemal processes, N t H y which in size and 
 character are somewhat comparable with those of Protop- 
 terus or Pleuracanthus. The dorsal fin presents a meta- 
 meral series of supporting cartilages (radial and basal, DR, 
 DB). The basal supports of each pelvic fin have become 
 compressed into a flattened plate, VB. Pelvic fins were 
 present, but there have as yet been found no traces of 
 pectoral appendages. In Dinichthys Newberry believed 
 that a pectoral fin spine was present, and that this fin was 
 
 Fig. 130. The Devonian Arthrodiran, Coccosteus decipiens, Ag x X 4. Old Red 
 Sandstone, Scotland. (Side view, restored ; slightly modified, after SMITH WOOD- 
 WARD.) 
 
 A. Articulation of head with trunk. DB, Cartilaginous basals of dorsal fin. 
 DR. Cartilaginous radials of dorsal fin. H. Haemal arch and spine. MC. Mu- 
 cous canals. A^. Neural arch and spine. U. Median unpaired plate of hinder 
 ventral region. VB. Basals of ventral fin. VR. Radials of ventral fin. 
 
 probably Siluroid-like (p. i/i), but this view has not been 
 confirmed. 
 
 The head of Coccosteus was clearly flattened, with 
 orbits and nasal openings near its anterior margin ; it 
 was roofed by a stout buckler of closely fitted dermal 
 plates (Fig. 131), whose outer surface was tuberculate, 
 enamelled, and furrowed by sensory grooves, MC. The 
 arrangement of the dermal plates of Coccosteus was early 
 (1861) compared by Huxley with that of recent Siluroids, 
 
132 
 
 AR THR ODIRAN L UNG-FISHES 
 
 an analogy afterward supported by Newberry, Dean, and 
 recently, on account of the similar characters of the sen- 
 sory canals, by Pollard. In their conclusions, however, 
 fundamental characters of structure seem to have been 
 overlooked in the unlikeness of Arthrodiran to Tele- 
 ostome. The inner structure of the cranium of Arthro- 
 
 PM 
 
 PO 
 
 FIG. 131 
 
 Figs. 131, 132. Coccosteus decipiens. Dorsal view of dermal armouring. X J. 
 (After TRAQUAI-R.) 132. Ventral plates. (After TRAQUAIR.) 
 
 ADL. Antero-dorso-lateral. AL. Anterolateral. A VM. Antero-ventro-lateral. 
 C. Central. E. Ethmoid. EO. Epiotic. IL. Inferior lateral. M. Marginal. 
 MC. Mucous canals. MD. Median dorsal. MO. Median occipital. MV. Me- 
 dian ventral. O. Opercular. PDL. Postero-dorso-lateral. PL. Posterior lateral. 
 PM< Premaxillary. PN. Pineal. PO. Preorbital. PTO. Postorbital. PVL. 
 Postero-ventro-lateral. SO. Suborbital. 
 
 dira was evidently entirely cartilaginous ; in a Russian 
 Coccosteid, according to Smith Woodward, the base of the 
 brain case (parachordal cartilages) has been preserved and 
 shows a " tubular canal originally occupied by the anterior 
 
STRUCTURES OF ARTHRODIRAN j^ 
 
 extremity of the notochord." Gill arches and opercula are 
 not definitely known. The mandible was attached directly 
 to the skull (autostylic). The jaws were shear-like, their 
 margins usually with pointed teeth, whose bases fuse with 
 the tissue of the jaw and constitute dental plates. In 
 all forms, as in Dinichthys (Frontispiece), there appear to 
 have been three pairs of these "plates," those forming the 
 rim of the mandible below, and those of the vomerine 
 and palatine regions (" premaxillary " and "maxillary") 
 above.* This arrangement of the dental plates somewhat 
 resembles the Dipnoan's. Those of the Arthrodiran, how- 
 ever, appear to have been movable, and suggest a dental 
 condition elsewhere unknown among vertebrates. 
 
 Fig. 133. Restoration of Dinichthys intermedius, Newb. X &. Cleveland 
 Shales, Ohio. 
 
 The body armouring of dermal plates is characteristic of 
 the group. A carapace, cape-like in shape, begins at the 
 head angle and broadens out backward and dorsally 
 towards the median line. It consists of a single median 
 spade-shaped element, which forms the strong ridge of the 
 back, and a flanking of lateral plates, all compactly joined. 
 The rigid shield that is thus formed is movably connected 
 with the head ; an elaborate joint, formed on either side 
 between the anterolateral dorsal plate, Fig. 131, ADL, and 
 the "epiotic," EO, whence the name Arthrodira, must 
 
 * According to Dr. Clark, an additional symphysial pair of dental plates 
 was present in both upper and lower jaw (Dinichthys). 
 
134 
 
 AR THR ODIRAN L UNG-FISHES 
 
 have permitted the head to be thrown backward to a 
 degree which suggests the thoracic joint of an Elater. 
 On the ventral side of the trunk there occurs a flattened 
 plastron (Fig. 132) : its dermal -elements are connected by 
 overlapping margins ; they are lighter, and in some forms 
 (Fig. 135) lack the tuberculate surface of the dorsal 
 plates. Dorsal and ventral shields are connected by stout 
 lateral elements (Fig. 132, 7Z), which, passing ventrally, 
 
 FIG. 135 
 
 137 A 
 
 Figs. 134-137. Dermal plates of Dinichthys. 134. Associated plates of head 
 and shoulders. 135. Plates of ventral armouring. (After A. A. WRIGHT). 136. 
 Pineal plate of Dinichthys intermedius, surface view. 137. Pineal plate of Dinich- 
 thys terrelli, visceral aspect. 137 A. Pineal plate, in sagittal section. 
 
 ADL. Antero-dorso-lateral. A VL. Antero-ventro-lateral. A VM. Antero- 
 ventro-median. E. Ethmoid. EO. Epiotic. MO. Median occipital. PN. 
 Pineal. PO. Preorbital. PTO. Postorbital. PVL. Postero-ventro-lateral. SO. 
 Suborbital. X. External aperture, and -* , the axis of the pineal funnel. 
 
 meet in the median line, and become the anterior support- 
 ing rim of the plastron. By some writers these have been 
 homologized as " clavicles." 
 
 In further detail little is known of the anatomy of 
 
STRUCTURES OF ARTHRODIRAN 
 
 135 
 
 Arthrodirans. Sensory canals have been described chan- 
 nelling the surface of the dermal plates of the dorsal side. 
 In the body region of Coccosteus evidence of a lateral line 
 occurs (Smith Woodward) in a white calcified band fossilized 
 in the region of the space of the notochord. In this form, 
 too, an endoskeletal plate is known, (Fig. 130, U) occurring 
 in the median line in the region of the vent, which must 
 be regarded as " suggesting an internal element of support 
 occurring in the vertical septum between the right and 
 left halves of some paired organ (S. W.)." The character 
 of the dermal investiture of the trunk has apparently 
 not been described ; it may therefore be of interest to 
 note that the museum of Columbia College has recently 
 acquired two of the hinder dorsal plates of Dinichthys 
 which clearly indicate the presence of integument. The 
 plates are covered by a crinkled epidermis, whose irregular 
 surface traceries resemble the roughened finish of Turkey 
 morocco. This leather-like surface is seen to have been 
 continued over the margin of the plates along the side 
 of the trunk ; traces of scales or tubercles are altogether 
 lacking, and its appearance suggests that it may have been 
 degenerate in structure. 
 
 Among Arthrodirans there occurs a series of most inter- 
 estingly evolved forms ; and it is found more and more 
 evident that they, with other lung-fishes, may have repre- 
 sented the dominant group in the Devonian period, as 
 were the sharks in the Carboniferous, or as are the 
 Teleosts in modern times. There were forms which, 
 like Coccosteus, had eyes at the notches of the head 
 buckler; others, as Macropetalichthys, in which orbits 
 were well centralized ; some, like Dinichthys and Titan- 
 ichthys, with the pineal foramen present ; some with 
 pectoral spines (?) ; some with elaborately sculptured derm 
 
136 
 
 AR THR ODIRAN L UNG- FISHES 
 
 plates. Among their forms appear to have been those 
 whose shape was apparently sub-cylindrical, adapted for 
 swift swimming ; others (Mylostomd) whose trunk was 
 depressed to almost ray-like proportions. In size they 
 varied between that of a perch and that of a basking 
 shark. In dentition (Figs. 138-144) they presented the 
 widest range in variation, from the formidable shear-like 
 jaws of Dinichthys to the lip-like mandibles of Titan- 
 ichthys, the tearing teeth of Trachosteus, the wonderfully 
 forked, tooth-bearing jaw tips of Diplognathus, to the 
 Cestraciont type, Mylostoma. The latter form has hitherto 
 been known only from its dentition, but now proves to be, 
 as Newberry and Smith Woodward suggested, a typical 
 Arthrodiran. 
 
 The puzzling characters of the Arthrodirans * do not 
 seem to be lessened with a more definite knowledge of 
 their different forms. The tendency, as already noted, 
 seems to be at present to regard the group provisionally as 
 a widely modified offshoot of the primitive Dipnoans, bas- 
 ing this view upon their general structural characters, 
 dermal plates, dentition, autostylism. But only in the 
 latter regard could they have differed more widely from 
 the primitive Elasmobranch or Teleostome, if it be ad- 
 mitted that in the matter of dermal structures they may 
 clearly be separated from the Chimaeroid. It certainly 
 is difficult to believe that the articulation of the head of 
 Arthrodirans could have been evolved after dermal bones 
 had come to be formed, or that a Dipnoan could become 
 so metamorphosed as to lose not only its body armouring 
 
 * The writer believes that the Arthrodirans may as well be referred to the 
 sharks as to the lung-fishes; as far as existing evidence goes, they certainly 
 differed more widely from the lung-fishes than did the lung-fishes from the 
 ancient sharks. They may, perhaps, be ultimately regarded as worthy of rank 
 as a class. 
 
FIG. 138 
 
 144 
 
 Figs. 138-144. Mandibles of Arthrodirans : Cleveland Shale, Ohio. 138. 
 Mylostoma variabllis, Xewb., visceral aspect. 139. Titanichthys clarki, Newb., 
 visceral aspect, x g. 140. Trachosteus, Newb., outer aspect. X 5. 141. Diplo- 
 gnathus, Newb., outer aspect. X J. 142. Diplognathus, seen from dorsal side. 
 143. Diplognathns, visceral aspect. 144. Dinichthys intermedius, outer aspect. X 5. 
 
 137 
 
ARTHRODIRAN LUNG-FISHES 
 
 but its pectoral appendages as well. The size of the 
 pectoral girdle is, of course, little proof that an anterior 
 pair of fins must have existed, since this may well have 
 been evolved in relation to the muscular supports of 
 plastron, carapace, trunk, and head. The inter-movement 
 of the dental plates, seen especially in Dinichthys, is a 
 further difficulty in accepting their direct descent from 
 the Dipnoans. 
 
VII 
 THE TELEOSTOMES 
 
 ALL fishes not to be grouped among Sharks, Chimae- 
 roids or Lung-fishes, have been included in the fourth 
 sub-class, Teleostomi. In this are to be merged the two 
 time-honoured groups, Ganoids* and Teleosts, since it is 
 now found that there are absolutely no structures of the 
 one group that are not possessed by members of the other. 
 The terms, therefore, "Ganoid" and "Teleost," must 
 be used in a popular and convenient, rather than in an 
 accurate sense ; the former to denote the " old-fashioned " 
 Teleostome, with its rhombic bony body plates, and carti- 
 laginous endoskeleton ; the latter, the modern "bony fish," 
 with rounded, horn-like scales and its calcified endo- 
 skeleton. 
 
 Teleostomes present so wide a range of variation that 
 it becomes exceedingly difficult to include in a single 
 definition their minor structural characters. 
 
 As a basis for the comparison of the Teleostomes, the 
 characteristic structures of a single type, e.g. the Perch, 
 might conveniently be taken. From these conditions, 
 typical of a modern and highly specialized form, the simple 
 structures of the ancient, more primitive, and ancestral 
 Ganoids may afterward be readily understood. 
 
 * The term Ganoid, as here vised (as far as p. 147), includes the Crossopte- 
 rygians as well. 
 
 139 
 
140 
 
STRUCTURES OF TELEOST l ^ l 
 
 General Anatomy 
 
 In the Teleost (Fig. 145) the shortened and muscular 
 body appears admirably adapted to the conditions of 
 aquatic motion. Anteriorly it is broad and deep, its 
 trunk muscles firmly attached to the bony prongs of the 
 enlarged base of the skull, DCR, and to the solid, compact, 
 calcified vertebrae, V, and their stout processes. The 
 fish's tapering sides are encased in horn-like cycloidal 
 scales, CS, a light, flexible armour, whose elements over- 
 lap, defending every point, and whose smooth and slime- 
 coated surface provides the least possible resistance to 
 motion. The fins, D, C, A, PF y VF, are light and strong, 
 erectile and depressible ; their rays are thin, narrow, spine- 
 like, strong ; they are entirely dermal, their cartilaginous 
 supports sinking within the body wall, RB. The caudal 
 is large and fan-shaped (homocercal), its crowded rays 
 providing admirably its needed strength ; its stout basal 
 supports, compacted beneath the tip of the notochord, JVC, 
 show that its form is modified heterocercy. The pectoral 
 fin, PF t has now taken its position high in the side of the 
 body ; its basi-radial supporting elements are reduced to a 
 proximal row of a few small irregular plates. 
 
 The skeleton is completely calcified. The vertebral axis 
 has undergone entire segmentation, the notochord persist- 
 ing only between the cup-shaped faces of the centra ; the 
 vertebral arches and processes have merged with the 
 centra, and those of the hinder region, A 7 , H, with prob- 
 ably the basal fin supports as well. Ribs, R, usually with 
 intersupporting processes, strengthen the walls of the 
 visceral cavity, and represent calcifications of the myocom- 
 mata, rather than transverse processes of the vertebrae. 
 The skull is formed of compact bony elements ; its carti- 
 
" 
 
 fl l 
 
 a 1 1 4 8 
 
STRUCTURES OF TELEOST I43 
 
 laginous brain case is replaced by many definite osseous 
 elements. The floor and roof of the skull, the face region, 
 jaws, gill arches, and their protecting parts, are all encased 
 by an elaborate series of membrane bones ; these, however, 
 must be noted as deeply embedded in the body tissue, 
 DCR, DN, A, Q, PT, SM, BR, O. The membrane bones 
 of the jaw rim maxillary, premaxillary, and dentary, MX, 
 PMX, DN bear teeth, and are especially characteristic 
 of the Teleostomes ; those overlapping and protecting the 
 gill arches (GA), O, fO, PO, SO, usually four in number, 
 are also characteristic of the group. The skull is hyostylic. 
 As to the visceral parts. The gill arches, GA, are 
 reduced in number, usually widely bent backward, and 
 closely crowded together ; their gill filaments are enlarged 
 and specialized. The heart lacks the arterial cone with its 
 transverse series of valves ; in its place a stout bulbus, B, 
 forms the base of the aorta. The digestive tract is tubular, 
 long, and coiled ; its intestine, G, lacks a spiral valve, and 
 terminates at the body surface, AN, not in a cloaca ; its 
 glands include a series, often great in number, of pyloric 
 caeca (pancreas). An air-bladder, AB, is present, which 
 may, or may not, retain its communication with the gullet. 
 The ovary, with its many small eggs, and the kidney, dorsal 
 to it, have often a common external opening in a urino- 
 genital papilla, UG, in either side of which abdominal pores 
 may occur. The nervous system and sense organs (pp. 275, 
 277) have many peculiarities : the roof of the fore brain is 
 non-nervous ; the nasal openings appear in the dorsal side 
 of the head, NO, and are separate; the eye has specialized a 
 vascular, nutritive structure, \hzproctssusfalciformis, pro- 
 jecting from the region of the entrance of the optic nerve 
 into the vitreous cavity of the capsule ; the optic nerves 
 cross in passing to the eyes, but their fibres do not fuse. 
 
144 
 
 TELEOSTOMES 
 
 Such in outline are 
 the essential structures 
 ofaTeleost. They may 
 now be briefly con- 
 trasted with the more 
 important characters of 
 the Ganoids. 
 
 In skeletal structures 
 the Perch (Fig. 146) 
 may be strikingly con- 
 trasted with the most 
 nearly ancestral form 
 of Ganoid (Fig. 147). 
 In this, Polypterus (p. 
 148), the skeleton re- 
 .tains a semi-calcified 
 condition. Its verte- 
 bral centra are practi- 
 cally separate from the 
 arches ; its ribs, R, are 
 equivalent to the trans- 
 verse processes ; its ac- 
 cessory ribs, AR, to 
 the "ribs "of Teleosts. 
 The cartilaginous brain 
 case is notably re- 
 tained; the membrane, 
 or dermal bones, of the 
 head roof, as F, P, SP, 
 PO, O, are clearly 
 scale -like, with an 
 enamelled surface, sim- 
 ilar in character to 
 
GANOIDS AND TELEOSTS 
 
 145 
 
 those of Dipterus. The shoulder girdle includes outer 
 dermal elements, DSG. The external parts of the unpaired 
 fins are dermal; but their cartilaginous supports are re- 
 tained, RB, even in the tail region. The caudal fin may 
 be regarded as either diphycercal or heterocercal. The 
 exposed parts of the paired fins, it is especially interesting 
 to note, are only in part dermal ; the two rows of carti- 
 laginous supports are retained in a condition very similar 
 to that of sharks, R B\* two of the basal elements of the 
 pectoral fin, however, have retained the rod-like form in 
 strengthening the front and hinder margin of the fin. 
 
 In visceral structures the Ganoids exhibit the fol- 
 lowing noteworthy characters : a greater number of gill 
 arches ; a spiracle ; a short and almost straight digestive 
 tube, with spiral valved intestine ; a shark-like pancreas ; 
 an arterial cone, with many rows of valves ; a cellular air- 
 bladder, like that of a Dipnoan ; primitive conditions in the 
 urinogenital apparatus ; shark-like characters in the ner- 
 vous system and sense organs ; a chiasma of the optic 
 nerves, (pp. 260-279). 
 
 Relationships and Descent 
 
 Johannes Miiller, when separating Ganoids from Tele- 
 osts, recognized clearly even at that early date (1844) that 
 the majority of the structural differences of these forms 
 were bridged over in exceptional instances ; there were 
 thus Teleosts with bony body plates, as well as, it was 
 afterwards found, a Ganoid (Amta, p. 163) with herring- 
 like cycloidal scales. But he believed that three structural 
 characters of the Ganoids separated them constantly from 
 all Teleosts, and warranted the integrity of the groups. 
 
 * Contrast Gegenbaur's view that this fin represents the simplest known 
 condition of the archipterygium. Ref. on p. 248. 
 L 
 
TELEOSTOMES 
 
 These distinguishing characters were : 
 
 I. A contractile arterial cone, containing rows of valves. 
 
 II. An intestinal spiral valve. 
 
 III. The interfusion (chiasma) of the optic nerve. 
 
 It was not until these differences were shown to be of 
 little morphological importance that the two groups were 
 merged in that of Teleostomi (Owen, 1866). Thus transi- 
 tional characters in the arterial cone of Butrinus (p. 258) 
 were discovered by Boas : the Teleost Cheirocentrus was 
 found to present ganoidean intestinal characters ; and the 
 optic chiasma, as Wiedersheim * demonstrated, could no 
 longer be regarded as of taxonomic or morphological 
 value. 
 
 The descent of the Teleostomes, likefthat of the other 
 groups, has long been a matter of speculation. Their affini- 
 ties with the Dipnoans are generally admitted (Gunther, 
 Gegenbaur, Haeckel, Smith Woodward). Rabl derives them 
 directly from a selachian stem, regarding the Dipnoans 
 as later evolved ganoidean forms. Beard, on the other 
 hand, even goes so far as to entirely separate the Teleo- 
 stome stem from that of the shark, lung-fish, and amphibian, 
 deriving it with a close kinship to Petromyzonts, from the 
 earliest vertebrates. Palaeontology, however, has lately 
 been giving rich contributions to this disputed problem, 
 and there can at present be little doubt that the conditions 
 in fossil fishes have demonstrated that in most ancient 
 times Dipnoan and Teleostome were closely approximated. 
 Although even in the earliest fossils they may be distin- 
 guished (e.g. by the arrangement of the head-roofing derm 
 bones, v. p. 127), yet, as Smith Woodward has noted, forms 
 occur too clearly transitional to indicate anything less 
 
 * One form of lizard was shown to possess a chiasma of the optic nerves; 
 in its neighbouring genus the nerves were found to cross without fusion. 
 
INTERRELATIONSHIPS OF TELEOSTOMES 
 
 than genetic kinship. The Crossopterygian, whose ancient 
 structure is well known, may well have been derived from 
 an ancestor common to the Ctenodont (Dipnoan) and 
 Holoptychian (Fig. 153) ; so that the gradual nearing of the 
 Teleostome stem to that more fixed, of the Dipnoan, is a 
 strong suggestion as to its derivation. The later descent 
 of the Ganoids from an ancestor closely akin to, if not 
 identical with the Crossopterygian, is usually conceded. 
 Teleosts first occurring in Cretaceous are by evidence of 
 fossils the almost undoubted survivors of an extensive 
 group of transitional Mesozoic Ganoids (p. 165). But 
 whether all Teleosts are to be deduced from a single 
 ganoidean phylum can at present hardly be established. 
 Thus catfishes, or Siluroids, appear in many structural 
 regards closely akin to the .sturgeon (p. 160) ; but as their 
 fossil remains are lacking before the Eocene when, how- 
 ever, they appear to have been in every way as highly 
 evolved as in recent forms little clue has been given to 
 their descent. 
 
 Teleostomes may, in the present connection, be briefly 
 characterized under their two principal subdivisions. 
 
 I. CROSSOPTERYGIAN, the more archaic group, uniting 
 characters of shark, lung-fish, and Ganoid, retaining the 
 ancient cartilaginous fin bases, radials, and basals in their 
 lobate fins; in some forms (Holoptychius, Fig. 153), the 
 concrescence of the basal parts of unpaired fins passing 
 through the same evolution as those of paired fins. 
 Represented in the surviving Polypterus (" Bichir " of 
 the White Nile, Fig. 148), and in the slender Polypteroid 
 Calamoichthys (of Calabar), and in the extinct Holoptych- 
 ius, Undina, Diplurus, and Coelacanthus. 
 
 II. ACTIXOPTERYGIAN, the spine-finned Teleostomes. 
 Fins supported by dermal rays ; ancient fin support greatly 
 
148 
 
 TELE OS TOMES 
 
 Fig. 148. 
 bichir. x J. 
 
 The Nile bichir, Polypterus 
 White Nile. (Modified after 
 
 Dors aspect. B. view of throat re- 
 
 gion, showing jugular (gular) plates and ven- 
 tral elements of the dermal shoulder girdle. 
 
 reduced, implanted with- 
 in body wall. Includes 
 Chondrosteans (" Gan- 
 oids ") and Teleocephali 
 (" Teleosts "). 
 
 I. CROSSOPTERYGIANS 
 
 The CROSSOPTERYG- 
 IANS, as palaeontology 
 has demonstrated, are 
 the most ancient Tele- 
 ostomes. In their struct- 
 ural characters espe- 
 cially in the fins, skeleton, 
 nervous system they 
 are clearly to be sepa- 
 rated from the neigh- 
 bouring Ganoids. And 
 their transitional charac- 
 ters have not as yet been 
 clearly demonstrated. 
 
 Polypterus (Figs. 148, 
 A, B, 149) and its kindred 
 genus, Calamoichthys 
 (Fig. 150), stand alone 
 as the survivors of the 
 Crossopterygian group. 
 They have diverged but 
 little from their Devo- 
 nian kindred, and demon- 
 strate in the most inter- 
 esting way the persistent 
 survival of fishes. From 
 
RECENT CROSSOPTERYGIAN 
 
 149 
 
 their isolated position, these recent forms become of ex- 
 treme interest to the morphologist, and from the side of 
 their development, when this comes to be studied, they are 
 expected to throw the greatest light on the relations of the 
 primitive Teleostome to the sharks and Dipnoans, on the 
 one hand, and to the Ganoids on the other. 
 
 Polypterus * presents the exoskeletal characters of the 
 ancient Crossopterygians, and the typical conditions of 
 their lobate pectoral fins; the dermal plates of its head 
 region are tuberculate as in Dipnoans, but, unlike 
 these, their arrangement, as in all Teleostomes, is dis- 
 
 Fig. 149. Polypterus lapradei. (After STEINDACHNER.) 
 well-grown larva showing external gill, EG. 
 
 Head region of 
 
 tinctly paired, i.e. "ethmoids," frontals, parietals, occipi- 
 tals (Fig. 148 A), including a pair of gular plates in the 
 
 throat region, 
 
 Among the structures peculiar to the 
 
 * Polypterus occurs in the Nile, but is rarely taken below the Cataract. It 
 was noted, however, from near Cairo in the Description d" 1 Egvpte, and a spec- 
 imen in the possession of Professor Innes of the College of Medicine, Cairo, was 
 taken near Boulak a few years ago. It is known by the Arabs near Assuan, 
 and is here occasionally taken in the fykes at the beginning of the flooding- 
 season. The remarkable series of Polypterus in the Vienna collection was 
 collected in the White Nile, although some of these specimens, Dr. Stein- 
 dachner has stated personally to the writer, were taken in Middle Egypt. It 
 seems evident to the writer, from the results of his collecting-trip from Cairo 
 to Assuan, April and May, 1892, that abundant material of Polypterus is not 
 readily secured below the Second Cataract. Until, therefore, the interior of 
 Egypt is made more accessible to foreigners, developmental stages can hardly 
 be hoped for. 
 
 f As in some of the fossil lung-fishes. 
 
jj TELE OS TOMES 
 
 recent forms may be included the fringing dor- 
 sal fin, the tubular nasal opening (Fig. 149), 
 and an external gill in Polypterus (Steindach- 
 ner), EG, in the late larval stages. 
 
 Calamoichthys is unquestionably a divergent 
 member of the stem of Polypterus ; its form, 
 becoming elongated, has acquired a general un- 
 dulatory movement ; the paired fins have accord- 
 ingly diminished in relative size, the ventral fins 
 
 g, finally disappearing. 
 
 Little is known of either the living or breed- 
 
 ^ ing habits of Crossopterygians : in these they 
 might naturally be expected to resemble the 
 
 Ganoids. 
 
 | 
 
 Fossil Crossopterygians 
 
 A number of the fossil kindred of Polypterus 
 "I are shown in the succeeding figures (Figs. 151- 
 
 \ Gyroptychius and Osteolepis, Devonian genera 
 g> (Figs. 151, 152), are certainly most nearly in 
 
 JSP the ancestral line of the recent forms. Like 
 pjj 
 
 many sharks and fossil Dipnoans, they present 
 a heterocercal tail, a single anal fin, and a pair 
 of dorsals. The pectoral fin of Osteolepis is 
 becoming a typical archipterygium. 
 
 Holopty chins, another Devonian form (Fig. 
 153), approaches even more closely the dipnoan 
 types : the scales are cycloidal ; its paired fins 
 IP are distinctly archipterygial ; and the caudal 
 
 region, reduced in length, is becoming meta- 
 morphosed into the typical diphycercal form by the ten- 
 dency of the second dorsal and anal fin to coalesce with 
 
FOSSIL CROSSOPTERYGIANS jjjj 
 
 the caudal. In these forms a number of paired gular 
 plates may occur. 
 
 In a closely related genus, Eusthenopteron, also of 
 
 Fig. 151 
 
 152 
 
 Fig. i^i. Gyroptychius. x \. Old Red Sandstone, Scotland. (After SMITH 
 WOODWARD.) 
 
 Fig. 152. Osteolepis. X 4. Old Red Sandstone, Scotland. (Restoration 
 from SMITH WOODWARD, after PANDER.) 
 
 Devonian age (Fig. 154, A, ), the structure of the basal 
 parts of the unpaired fins is exceedingly interesting ; the 
 radial supports are unfused, while the basals, merged in a 
 
 Fig. 153. Holoptychius andersoni. Old Red Sandstone, Scotland. 
 
 single plate, have come into especial relation with the 
 axial skeleton ; the subsequent stage of their differentia- 
 
FOSSIL CROSSOPTERYGIANS 
 
 153 
 
 tion has been noticed in Fig. 43. The condition of the 
 caudal fin of Eusthenopteron is also worthy of note ; the 
 tip of the notochord is retained although the functional 
 portion of the fin is derived from the more anterior 
 body region. The vertebral arches are here clearly sug- 
 gestive of the conditions of the Dipnoan. 
 
 CcflacantkuS) common in the Coal Measures (Fig. 155), 
 is the most specialized of the Crossopterygians ; it has 
 retained all of the archaic structures of its kindred, yet 
 has concealed them under the outward appearance of a 
 recent bony fish ; the general contours of its head, trunk, 
 scales and fins resemble strikingly those of a dace or 
 
 Fig. 155. Ceelacanthus elegans, Newb. x |. Coal Measures, Ohio. 
 A. Position of calcified swim-bladder. 
 
 chub ; but on closer view the paired fins are found to be 
 archipterygial, the scales enamelled and sculptured, the 
 true caudal fin the degenerate stump of the notochord ; 
 the functional caudal has been formed of the enlarged fin 
 rays of the dorsal and anal region. Traces of a calcified 
 air-bladder, A, are often preserved. 
 
 Diplurus and a closely related genus, Undina (Figs 156, 
 156 A), may finally be noted among the highly evolved 
 Crossopterygians. They appear in the Mesozoic when the 
 majority of their kindred have disappeared ; they have as- 
 sumed peculiar characters and have apparently reached the 
 point of differentiation when they shortly become extinct. 
 
154 
 
 TELEOSTOMES 
 
 Diplurus has become excessively shortened in its body 
 length ; the head is of relatively enormous size ; its derm 
 bones are squamous, and appear to have been deeply 
 implanted in the integument ; teeth have disappeared ; 
 
 Fig. 156. Diplurus longicaudatus , Newb. X \. Triassic, Boonton, NJ. 
 
 A. Position of calcified swim-bladder. A" '. Second anal fin (now the ventral 
 portion of the functional caudal) . BR. Radial and basal fin supports. C. Caudal 
 fin (degenerate). D, Hindmost dorsal fin (now the dorsal portion of the func- 
 tional caudal). J. Jugular. 
 
 scales have become exceedingly thin and are rarely pre- 
 served. Fin structures are apparently of a degenerate 
 character ; their cartilaginous bases, when showing, appear 
 
 Fig. r$6 A. Undina gulo, Egert. 
 (Restoration after SMITH WOODWARD.) 
 
 Lower Lias of Lyme Regis. 
 
 to have become reduced to single plates, as BR ; the 
 caudal is the elongate tip, of the vertebral axis ; the 
 functional caudal, now elongate and diphycercal, is formed 
 
CAN OWE AN FORMS !^ 
 
 by dorsal and anal elements, D, A" y as in Coelacanthus. 
 The boundary line of the calcified air-bladder, A, is often 
 preserved. 
 
 II. ACTINOPTERYGIANS 
 
 A. Chondrosteans (Ganoids}. Ganoids agree with the 
 Crossopterygians in their exoskeletal characters, although 
 usually lacking in gular plates. The most important 
 differences between these groups have been reduced to 
 those of fin structures ; the Ganoids have no longer the 
 lobate form of the paired fins ; their basal fin supports 
 have become greatly reduced and are usually represented 
 by a single row of a few metamorphosed elements in the 
 
 Fig. 157. The short-nosed gar-pike, Lepidosteus platystomus, Raf. x \. Mis- 
 sissippi basin. (After GOODE in U. S. F. C.) 
 
 most proximal region of the fin. The transitional stages 
 if they exist between the lobate and the monoserial 
 fins have not as yet been demonstrated. 
 
 Fossil Forms 
 
 From the middle of the Palaeozoic period to the end of 
 the Mesozoic there seems to have been a culminating time 
 of forms like the still existing Gar-pike (Fig. 157); their 
 fossils are generally the most numerous, and, on account 
 partly of their strong body armouring of interlocking 
 rhombic plates, the most perfectly preserved of fossil 
 fishes. They usually exhibit the structural characters 
 
TELEOSTOMES 
 
 which Lepidosteus has retained, while diverging widely on 
 all sides in matters of shape, size, special dentition, and 
 
 Fig. 158. Elonichthys (Kkabdolepis) macropterus (Giebel), Bronn. x \. 
 (After L. AGASSIZ.) Lower Permian, Rhenish Prussia. 
 
 features of the body armouring, characters, apparently, 
 of minor morphological importance. But a few of the char- 
 acteristic types of the early Ganoids can be noted in the 
 present connection. Some of the more important have 
 been figured in Figs. 158-164. 
 
 ig- 159- Eurynotus crenatus, Agassiz. x . (After TRAQUAIR.) Calcif- 
 erous Limestone, Scotland. 
 
 Thus Elonichthys (Fig. 158) was a form which had 
 evolved a small size and narrow sculptured body plates ; 
 
FOSSIL GANOIDS 
 
 157 
 
 Eurynotiis (Fig. 159) had attained a great depth of body 
 and prominent dorsal fin ; Cheirodus (Fig. 160) was dis- 
 tinctly flattened ; Semionotus (Fig. 161) was small, with 
 
 Fig. 160. Cheirodus granulosus, Young, x \. Coal Measures, Scotland. 
 (After TRAQUAIR.) 
 
 elaborate fin conditions ; Aspidorhynchus (Fig. 162) had a 
 remarkable pointed snout and a reduced number of body 
 
 Fig . 161 . Semionotus 
 Keuper, Stuttgart. 
 
 , Fraas. X }. (From ZlTTEL, after FRAAS.) 
 
 plates ; Microdon (Fig. 163), flattened like Cheirodus, had 
 
 evolved an admirable series of crushing teeth (-Pycnodont). 
 
 And, finally, is to be mentioned Palaoniscus (Fig. 164), 
 
 a form whose abundance, numerous species, and long sur- 
 
158 
 
 TELEOSTOMES 
 
 viva! (Palaeozoic-Mesozoic) have made it the most widely 
 known of fossil fishes. Of all extinct Ganoids there 
 
 Fig. 162. Aspidorhynchus acutirostris, Agassiz. X f. (After ZlTTEL.) Jura, 
 Solenhofen. 
 
 appears to attach to Palaeoniscus the greatest morphological 
 interest ; on the one hand, it seems closely akin to the 
 
 ^Fig. 163. Microdon wagneri, Thiolliere. X \. (From ZlTTEL, after THIOL- 
 LIERE.) Jura, Cerin. 
 

 LIVING GANOIDS 
 
 159 
 
 recent gars, and, on the other, even as evidently to the 
 sturgeons ; of all fossil kindred of these living forms, it 
 seems most nearly in the ancestral line. 
 
 Fig. 164. PalcBoniscus macropomas, Agassiz. X |. (After restoration of 
 TRAQUAIR.) Upper Permian. 
 
 Ganoids certainly outrank the Crossopterygians in the 
 number and variety of their ancient forms. Their few 
 living representatives give but little idea of the importance 
 of the group, and can suggest but faintly the lines of its 
 evolution. 
 
 Living Types 
 
 The recent Ganoids include the Gar-pike, the Sturgeons, 
 and Amia. The first is of especial interest in connecting 
 the group most closely with the Crossopterygians, the last 
 as best illustrating the intermediate stage between the 
 Ganoids and Teleosts. 
 
 The Gar-pike, Lepidosteus (Fig. 157), resembles Polyp- 
 terus in many characters of skeleton and dermal defences. 
 It is a form not uncommon in the fresh waters of North 
 America, and is especially abundant in the Mississippi, 
 Great Lakes, and rivers of the Southern States. In South 
 Carolina the writer has known the gar-pikes to occur in 
 such numbers that they would fill the shad nets, and for 
 many days render this fishery impracticable. They some- 
 times attain a length of six feet, and are said to become 
 
! 60 TELE OS TOMES 
 
 as aggressive as sharks. They are remarkably tenacious 
 of life, and their complete armouring of dermal plates 
 renders them practically invulnerable. 
 
 In development Lepidosteus has apparently more prim- 
 itive features than Acipenser (v., p. 207 ; also Jour, of 
 Morph. XI, No. i). 
 
 Of all recent Ganoids, Lepidosteus must certainly be 
 looked upon as retaining most perfectly the structural 
 Characters of the most abundant and probably the most 
 generalized Palaeozoic and Mesozoic forms. Its genus, it 
 is true, is not known to occur earlier than the Eocene, but 
 its structures scales, fins, labyrinthine teeth and partially 
 calcified skeleton are known to have been possessed, 
 
 Fig. 165. The sturgeon, Acipenser sturio, L. X jV- Streams entering North 
 Atlantic. (After GOODE in U. S. F. C.) 
 
 even in their details, by a number of the older genera and 
 families. 
 
 The Sturgeons, Acipenser > Scaphirhynchus , Psephurus* 
 Polyodon, must in many ways be looked upon as of a highly 
 adaptive or even retrogressive character. There is strong 
 evidence that in their descent a large proportion, and, in- 
 cases, all of their dermal armouring has been lost, and that 
 their cusp-like ancestral teeth have either disappeared or 
 are retained in a rudimentary condition. 
 
 The interrelationships of the four surviving forms of 
 sturgeons have not as yet been definitely suggested ; transi- 
 tional fossil forms have thus far been lacking, and the 
 relative importance of the different structures in the recent 
 
THE STURGEONS l ^ l 
 
 genera cannot, therefore, be determined for purpose of 
 comparison. 
 
 The genus of the common sturgeon, Acipenser, is the 
 most completely studied of the recent forms. It includes 
 twenty or more "species," varying in length from one 
 (A. brevirostris, of the Eastern United States) to ten yards 
 (A. huso, of Russia), and is altogether one of the most valu- 
 able food-fishes of the rivers, lakes, and coasts of the north- 
 ern hemisphere. It is a sluggish, bottom-feeding fish, 
 common in muddy streams. Its broad and pointed snout, 
 sensory barbels, and greatly protractile jaws are the most 
 striking differences from the Palaeoniscoid ; its dermal 
 
 Fig. 165 A. Chondrosteus acipenseroides. X \. From Lias of Lyme Regis. 
 (Restoration of skeleton after SMITH WOODWARD.) 
 
 armouring has become reduced to the five longitudinal 
 bands of body plates,* but is more perfect in the tail 
 region ; its skeleton retains an entirely cartilaginous con- 
 dition. In its larval stage conical teeth are known to be 
 present, and the entire series of dermal plates are much 
 larger in relative size. 
 
 A figure of Chondrosteus, a Liassic sturgeon, may here 
 
 * It is interesting to note that in Palaeoniscoids there is sometimes a notice- 
 able tendency for the five rows of plates, dorsal, and the paired lateral and 
 ventral, to increase in size, suggesting the first steps in the origin of the derm 
 plates of Acipenser. 
 M 
 
TELE OS TOMES 
 
 parenthetically (Fig. 165 A) be inserted ; it is of especial 
 interest as suggesting an approximation of the type of the 
 modern sturgeon to that of the Palaeoniscoid ; its snout is 
 shorter than in Acipenser ; its jaws larger, and apparently 
 less protrusible ; its dermal plates of the head region, 
 including the branchiostegals, are clearly of the ancient 
 pattern, and the fins, fin supports, and vertebral characters, 
 
 Fig. 166. The shovel-nose sturgeon, Scaphirhynchus platyrhynchus (Raf.), 
 Gill. X \. Mississippi basin. (After GOODE in U. S. F. C.) 
 
 together with the general small size of the fish, suggest 
 intermediate conditions. 
 
 Of the remaining sturgeons, the shovel-nose, ScapJii- 
 rhynchus (Fig. 166), of the Mississippi and of Central Asia, 
 seems to possess the closest relations to Acipenser; 
 although it is apparently a more modified form, on account 
 of its elongate body shape and flattened snout, it still 
 retains many interesting and archaic features. Among 
 
 Fig. i66A. Psephurus gladius, Gun. x \. Rivers of China. (After GUNTHER.) 
 
 these it includes the most complete dermal armouring of 
 recent forms, its hinder body region being entirely encased. 
 Psephiirus (Fig. i66A), of the Chinese rivers, and Poly- 
 odon, or Spatularia (Fig. 166 B\ of the Mississippi, are 
 the other forms of living sturgeons. Their greatly elon- 
 gate snouts, giving them the popular names of Spoonbills, 
 Paddle-fish, Spear-fish, are among the most remarkable 
 
STURGEONS AND AMIA 
 
 163 
 
 sensory appendages of fishes. They have been but little 
 studied, and their relations to Acipenser have never been 
 satisfactorily determined. They have certainly many feat- 
 
 Fig. i66B. The spoon-bill sturgeon or paddle-fish, Polyodon spatula (Walb.), 
 J. and G. X |. Ventral and side view. Mississippi basin. (After GOODE.) 
 
 ures in skeletal parts, fin structures, lateral line organs, 
 jaws, teeth, which can only be looked upon as of primitive 
 character ; on the other hand, their highly specialized ros- 
 trum, degenerate opercula, and want of dermal amouring 
 would suggest an early divergence from the main stem of 
 the sturgeons. To the writer, Psephurus seems the more 
 generalized of these peculiar forms. 
 
 Fig. 167. The bowfin, Amia calva, L. X \. (After GOODE in U. S. F. C.) 
 Central and Eastern United States. 
 
 Amia calva (Fig. 167) is the last of the recent Ganoids 
 to be noted. Its distribution corresponds closely with 
 that of the gar-pike ; it is a common form, worthless as 
 
1 64 
 
 TELEOSTOMES 
 
 a food-fish, but deemed worthy of a host of local names, 
 as : Bowfin, Grindle, Dog-fish, Mud-fish, Sawyer, Joseph 
 
 Grindle, Lawyer-fish. Its 
 interest, as already sug- 
 gested, is in its close kin- 
 ship to the Teleosts on 
 the one hand, and to the 
 sturgeons and gars on the 
 other. Its cycloidal scales, 
 its fin structure, and cal- 
 cified skeleton seemed of 
 so modern a character, 
 that it was long included 
 among the members of 
 the herring group; only 
 after a closer examination 
 did its primitive struct- 
 ures become apparent. 
 It is one of the few Gan- 
 oids which possess a gular 
 plate (Fig. i68,/#g-). Like 
 that of Lepidosteus, its 
 air-bladder is cellular, and of respiratory value (Wilder). 
 
 Fig. 168. Amia. Ventral view of jaw 
 region, x i. (After ZITTEL). 
 
 brs. Branchiostegal rays. h. Cerato- 
 hyal. jug. Jugular plate, md. Mandible. 
 
 Fig. 169. Caturus furcatus. x J. (From SMITH WOODWARD, after AGAS- 
 SIZ.) Lithographic stone (Upper White Jura), Solenhofen. 
 
 The relations of Amia become of especial interest, in 
 view of the number and range of its fossil kindred. Its 
 
TELEOST-LIKE GANOIDS 
 
 I6 S 
 
 group is known to have attained its prominence at a later 
 geological time than the other Ganoids ; it is doubtless 
 derived, more or less directly, from the main ganoidean 
 stem. Three of the more typical Mesozoic forms are 
 shown in Figs. 169, 170, 171, in Caturus, Leptolepis, and 
 
 Fig. 170. Leptolepis sprattiformis. X f . (From SMITH WOODWARD.) Lith- 
 ographic stone, Solenhofen. 
 
 Megalurus. To these amioid forms the ancestry of the 
 (majority of the) Teleosts is reasonably to be traced. 
 
 A general scheme of the phylogeny of the Teleostomes 
 is suggested on the adjoining page (Fig. 171 A). 
 
 B. Teleocephali (Teleosts?) This group, popularly known 
 as that of the bony fishes, or Teleosts, includes as great 
 a proportion perhaps as 95 per cent of the kinds of fishes 
 
 Fig. 171. Megalurus elegant is simus, Wagner. 
 Solenhofen. 
 
 X |. (After ZlTTEL.) Jura, 
 
 living at the present time. The immense number of their 
 genera and species is doubtless suggestive of the form 
 changes which occurred during the flowering periods of 
 the sharks, chimaeroids, or lung-fishes. 
 
 Teleosts have diverged most widely of all fishes from 
 
1 66 
 
 TELEOSTOMES 
 
 what seem to have been their primitive structural condi- 
 tions. Their skeleton has become highly calcined, its ele- 
 ments multiplying, fusing, and specializing. The notochord 
 has practically disappeared, owing to the complete formation 
 of bony vertebne. The derm bones of the head, which in 
 
 ANCESTRAL 
 TELEOSTOME 
 
 (TABLE IV) 
 
 PALAEOZOIC 
 
 PALAEONISCOID 
 
 LEP.OOST'E'us'^siLUKo.D I p^^ME \\\\\\\\ LopHOB ** NCH 
 
 POLYPTERUS AM.A ME ACANTHOPTtRYS.AN BYPATH 
 
 Fig. 171 A. The Phylogeny of the Teleostomes. 
 
 the ancestral Ganoid were at the surface, enamel-coated,* 
 are now deep-seated in the head, resembling true cartilage 
 bones ; their surfaces are usually deeply furrowed or ridged, 
 
 * The enamel of Ganoid plates (ganoine) appears to be derived from the 
 underlying bony tissue, not deposited by the overlying epidermis (enamel 
 organ) . 
 
EVOLUTION OF TELEOSTS 
 
 I6 7 
 
 and their character is often squamous. Scales are widely 
 specialized, thin, horn-like, ornate, overlapping their outer 
 margins, their inner rims set deeply but loosely in dermal 
 pockets (Fig. 31). Fins are dermal structures, their ancient 
 basal supports hardly to be distinguished ; the primitive 
 tail structure is so masked by clustered and fused skeletal 
 elements that its heterocercy is scarcely apparent. In 
 short, the most widely modified conditions can be shown 
 to exist in Teleosts in almost every structural character, 
 as in gills, teeth, opercula, circulatory and urinogenital 
 organs, sensory structures, and nervous system. They 
 have evidently been competing keenly in the struggle for 
 survival, for in every detail of form or structure the most 
 varied conditions exist. In addition to these structural 
 adaptations of Teleosts, changes in coloration have been 
 rendered possible by the transparency of their scales ; and 
 in their different families these changes have taken place 
 often with striking results : adaptive coloration, brilliant, 
 dull, mottled, inconspicuous, occurs with a range of varia- 
 tion which is not surpassed even by the colours of birds. 
 
 It is not remarkable, therefore, that members of the 
 different groups of Teleosts should often parallel each 
 other in structural likenesses, when placed under the same 
 environmental conditions. Each organ, in fact, rrtay be- 
 come a centre of variation, and confuse the line of the 
 descent of the minor groups ; for the keenest judgment 
 cannot select of all these varying structures those which 
 can definitely be made the standards of general comparison. 
 Environment, like a mould, has impressed itself upon 
 forms genetically remote, and in the end has placed them 
 side by side, apparently closely akin, similar in form and 
 structure. 
 
 A striking instance of changes due to environment is 
 
i68 
 
 TELEOSTOMES 
 
 well known in the case of Deep-sea Fishes, in their acquir- 
 ing a characteristic shape under the conditions of abyssal 
 life. The head region of these forms becomes greatly 
 exaggerated in size, and the trunk tapers suddenly away 
 toward the tip of the pointed tail. The tissues become 
 extremely modified, soft, porous, delicate, often trans- 
 parent ; skeletal parts are deficient in lime, and loosely 
 articulated. Many organs are retained in curiously unde- 
 veloped or aborted conditions ; the vertebral axis is noto- 
 
 Figs. 172-174. Deep-sea fishes. (After GUNTHER.) 172. Paraliparis bathy- 
 bius. 640 fathoms. 173. Bathyonus compressus, 1400 fathoms. 174. Notacanthus 
 sexspinis. 1800 fathoms. 
 
 chordal ; gill arches, as many as six (?) in number, may open 
 freely to the surface, never enclosed by opercula ; sensory 
 canals remain as open grooves as in the most generalized 
 fishes ; paired fins are retained either in an undeveloped 
 condition or are not produced at all. Absence of light has 
 been not without its effects ; body colours are usually dark 
 and meaningless ; while, on the other hand, when eyes still 
 
DEEP-SEA TELEOSTS AND FIERASFER 
 
 169 
 
 occur, a widely modified series of integumentary phos- 
 phorescent organs are often evolved as lures by predatory 
 forms. It is evident, in the case of deep-sea fishes, that 
 the simple condition of their structures does not separate 
 them widely in point of descent from more specially 
 evolved Teleosts. Intermediate forms, occurring in shal- 
 lower water, often connect them clearly with different, and 
 widely distinct, groups of bony fishes. In this way the 
 
 Fig. 175. Fieras/er acus, Kaup. X |. 
 cucumber in southern waters. 
 
 (After EMERY.) Commensal of sea- 
 
 forms which are shown in Figs. 172, 173, 174 are severally 
 connected with the cottid, the cod and the salmon, al- 
 though the striking similarity of their outward structures 
 would naturally lead one to regard them as far more 
 intimately related. 
 
 Another interesting instance of the modification of a 
 fish's form by its living conditions has often been noted in 
 the case of Fierasfer (Fig. 175). This small Teleost lives 
 as a commensal in the branchial chamber of the sea-cucum- 
 
TELEOSTOMES 
 
 ber, and from its peculiar life habit retains permanently 
 a number of its embryonic characters ; it has thus its 
 elongated larval form, a functional pronephros, a noto- 
 chordal skeleton and immature fin conditions (Emery, 
 Ref. p. 249). 
 
 To what degree the structures of fishes may be varied 
 by artificial selection is an interesting question, but one 
 that has as yet received little attention even from those 
 who have made artificialization an especial study. In the 
 instance of the Goldfish it is well known how wide a 
 
 Fig. 176. Goldfish, Carassius auratus ("Telescope" variety). X i. (After 
 
 TXTTUT?!? ~\ lotion 
 
 GUNTHER.) Japan. 
 
 variation has been produced in colour, size, and proportions. 
 Fin structures are elaborately developed, long, drooping, 
 lace-like, often to a degree which must render progression 
 both slow and difficult. Even the eyes have been made 
 to become large and protruding (Telescope-fish, Fig. 176). 
 In carp the variation in scale character, due to artificializa- 
 tion, is also to be mentioned. It is natural, perhaps, that 
 artificial selection has been most successfully practised 
 
CA TFISHES 
 
 I/I 
 
 among these forms which compete most actively for 
 survival. 
 
 To conclude the present chapter, several forms of Tele- 
 osts may be briefly discussed as especially characteristic 
 of the group, namely the catfish, Mormyms, eel, perch, 
 cod, flodnder, porcupine-fish, sea-horse. 
 
 TJ*e catfish, representing the Siluroids, has, as already 
 noted, many structural affinities to the sturgeon, and is, 
 perhaps, a direct descendant of some early type of Mesozoic 
 Palaeoniscoid. It is a representative of a large and wide- 
 spread family, usually of river fishes. Its habits are slug- 
 
 Fig. 177. The bull-head (catfish), Amiurus melas (Raf.), Jord. and Cope- 
 land. X . (After GOODE in U. S. F. C.) Eastern North America. 
 
 gish and mud-loving. Its trunk is heavy, rounded, and 
 without Teleostean scales ; its broad mouth margin is pro- 
 vided with barbels ; the fin rays of its dorsal and pectoral 
 fins /fuse into a stout, serrate, erectile spine. In North 
 American forms armouring derm plates are developed 
 only on the head roof (Fig. 177). Closely akin to these 
 are the Asiatic genera, and the single European species, 
 Silunis glanis, the gigantic We Is of the Danube. The 
 Nile is of interest if only for its forms of catfish to 
 parallel the shapes and structures of the recent Teleosts. 
 
172 
 
 TELEOSTOMES 
 
 In South America the catfish is a regnant type, and is 
 remarkable for the variety as well as for the number and 
 size of its forms. Many, completely armoured (Fig. 178), 
 are strongly suggestive of Ganoids. Their armouring is 
 
 Fig. 178. South American Siluroid, Callichthys armatus. X i. 
 GUNTHER.) Upper Amazon. 
 
 (After 
 
 metameral and archaic, their sensory canals primitive in 
 structure and arrangement. 
 
 Mormyrus, like the catfish, appears to have long been 
 divergent from the main stem of the Teleosts. Its species 
 
 Fig. 179. Mormyrus oxyrhynchus. x |. (After GUNTHER.) Nile. 
 
 are restricted to the Nile, one the long-nosed M. oxyrhyn- 
 chus (Fig. 179) figuring prominently in Egyptian myth. 
 In many of its structures it is archaic, as in axial skeleton, 
 fins, dermal characters, sensory canals ; in others, e.g. hear- 
 
EEL-LIKE FORMS 
 
 173 
 
 ing organ, it is most highly specialized. Its group is an 
 interesting one, and has been but little studied. 
 
 The Eel (Fig. 180) might well be taken as one of the 
 
 Fig. 180. The eel, Anguilla vulgaris, Turton. X \. (After GOODE in U. S. 
 F. C.) Europe, South Asia, North Africa, North America. 
 
 fish forms evolved by special environment. Living in soft 
 river bottoms, a serpent-like movement in progression has 
 gradually been acquired ; its form has, therefore, become 
 elongated and rounded, and the internal structures corre- 
 spondingly modified. Fin structures have accordingly been 
 
 V-' 
 
 Fig. 181. The perch, Perca americana (=Jluviatilis?), Schrank. X k. (After 
 GOODE in U. S. F. C.) 
 
 metamorphosed, ventral fins lost, tail degenerated, and a 
 continuous dorsal and ventral secondarily evolved ; scales 
 have become reduced in size, supplanted by mucous layers. 
 
TELE OS TOMES 
 
 Similarity in eel-like form, e.g. as of Murcena, is not in 
 itself indicative of direct kinship. (Apodes.) 
 
 The Perch (Fig. 181) has long been taken as a repre- 
 sentative Teleost. Perfect in its "lines," its compact, 
 wedge-like shape cleaves the water by vigorous thrusts of 
 a strong broad caudal ; its fins are stout, supported by 
 spinous rays ; its dermal armouring light, smooth, and flex- 
 ible ; its colour is brilliant under its transparent scales. 
 So adapted is it to its environment that its organ of static 
 equilibrium, the air-bladder, has lost its valvular connec- 
 tion with the gullet. Of existing fishes about one-half are 
 essentially percoid. (Acanthopterygii.} 
 
 Fig. 182. The codfish, Gadus morrhua, L. X &. (After GoODE in U. S. 
 F. C.) North Atlantic. 
 
 The Cod (Fig. 182) is scarcely less important as a repre- 
 sentative Teleost. Its structural differences may perhaps 
 represent the result of a competition less active than that 
 of the perch in the struggle for survival. Heavy in body, 
 its sluggish form has become blunted and rounded; its 
 fins are depressed, their rays soft and yielding; its scales 
 are reduced in size, colours less vivid; its swim-bladder 
 loses its connection with the gullet. As many, perhaps, 
 as one quarter of the existing genera of fishes may be 
 assigned to this type. (Anacant/iini.) 
 
 The Flounder (Fig. 183) should be mentioned as a singu- 
 
FLOUNDERS AND PORCUPINE-FISHES ^5 
 
 lar instance of environmental evolution, its flattened body 
 adapting itself both in shape and colour to its bottom 
 living. Its entire side, not the ventral region, as in the 
 rays, is flattened to the bottom. The unpaired fins now 
 become of especial value ; they increase in size, and their 
 undulatory movements enable the fish to swim rapidly yet 
 retain its one-sided position ; ventral fins become useless, 
 and degenerate. The further adaptations of the flat fish 
 include its pigmentation only on the upper or light-exposed 
 side, and the rotation of the eye fro'm the blind to the upper 
 
 Fig. 183. The winter flounder, Pseudopleuronectes americanus (Walb.), Gill. 
 X \. (After GOODE in U. S. F. C.) North Atlantic. 
 
 side, in this giving one of the most remarkable cases of 
 adaptation known among vertebrates. (Heterosomata.} 
 
 The Porcupine-fish (Fig. 184) may be referred to as 
 another singular result of environmental evolution. Its 
 globular and inflatable form bespeaks slowness of motion 
 and helplessness if exposed to changes of temperature 
 or current. Its fins are reduced and feeble, suited, how- 
 ever, to its tranquil habitat ; its fused jaws, parrot-like, 
 show in how special a way its food is best secured. It 
 has evolved a protective casing of enormous needle-like 
 scales, whose shape parallels that of the derm denticles 
 
TELEOSTOMES 
 
 of the shark. As a somewhat transition form to the more 
 usual conditions of the Teleost, the Rabbit-fish has been 
 figured (Fig. 184^). (Plectognathi.) 
 
 Fig. 184. The porcupine-fish, Chilomycterus geometricus (Schn.), Kaup. x 
 (After GOODE in U. S. F. C. report.) Warmer Atlantic. 
 
 Fig. 184 A. The rabbit-fish, Lagocephalus Iczvigatus (L.), Gill. X \. (After 
 GOODE in U. S. F. C.) Northeast Atlantic. 
 
 A final, perhaps the most bizarre, instance of adapta- 
 tion among Teleosts is that of the Sea-horse (Fig. 185). 
 In spite of its many structural oddities, its genetic kin- 
 ship with the Sticklebacks (Hemibranchiates) cannot be 
 doubted. Yet to have attained its present form its evolu- 
 tion must have been carried along a widely divergent path. 
 It may, in the first place, have fused the lines of its meta- 
 meral scales, dividing off the surface of its elongate body 
 
SEA-HORSE AND PIPE-FISH 
 
 177 
 
 in sharp-edged rectangles, whose corners became produced 
 as spines. At this stage of evolution its appearance might 
 well be represented by (Fig. 185 A) the kindred Pipe-fish. 
 To secure more perfect anchorage in its algous feeding- 
 ground, its body terminal must now have discarded its fin 
 membranes and become prehensile, probably the most 
 remarkable adaptation in the 
 entire class of fishes, since it 
 causes metameral organs to 
 change the plane in which they 
 function from a horizontal to a 
 vertical one. As a probable de- 
 velopment of prehensilism, three 
 changes may next have been 
 wrought : the flexure of the neck 
 region, the thickening of the 
 trunk, and the metamorphosis 
 of the fins. The first change 
 may have been brought about 
 by the normal position of the 
 fish's axis becoming, as is well 
 known, vertical ; the head then 
 assumes its normal horizontal 
 plane and thus parallels mildly 
 the cranial flexure of higher ani- 
 mals. The enlargement of the 
 
 Fig. 185. The sea-horse, Hip- 
 
 trunk region is evidently of static pocampus heptagonus, Raf. x j. 
 
 i T-i. i<. *.- c ^i- (After GOODE in U. S. F. C.) East 
 
 value. The alteration of the po- ^ oast of North America> 
 sition, size, and degree of move- 
 ment of the pectoral fins, the loss of the ventrals and the 
 changed function, now one of propulsion, of the dorsal, 
 appear clearly the result of the altered plane of the fish's 
 motion. Further structural changes might with interest 
 
TEtEOSTOMES 
 
 be followed, as in characters of viscera, gills, and endo- 
 skeleton. In its life habits mimicry is strongly evinced ; 
 
 Fig. 185 A. The pipe-fish, Syngnathus acus J, L., showing abdominal pouch. 
 X i. (After GtJNTHER.) Coasts of Europe and Africa. 
 
 the well-known genus Phyllopteryx, whose entire body 
 surface develops pigmented appendages, is with difficulty 
 to be distinguished from a rough-shaped seaweed. (LopJw- 
 Itranchii.} 
 

 
 VIII 
 THE DEVELOPMENT OF FISHES 
 
 THE groups of fishes have hitherto been contrasted 
 in the structures of their living and fossil forms. They 
 should next be reviewed in the light of their mode of 
 development ; for the developmental stages of the Shark, 
 Lung-fish, or Teleostome might be expected, according 
 to time-honoured belief, to furnish important evidence 
 as to their descent and interrelationships. The younger 
 stages of the various forms of fishes should thus suggest 
 their ancestral characters : the developing Teleost should 
 approach the Ganoid ; the Lung-fish and the Ganoid 
 should resemble their supposed elasmobranchian ancestor. 
 
 But the embryology of fishes is in this regard very 
 inconclusive, if at present in any important way sugges- 
 tive. The majority of the forms, including some of the 
 most important, are developmentally unknown ; yet suffi- 
 cient is known of the representative members of the 
 groups to show the most perplexing characters. On the 
 one hand, the developmental processes of forms which are 
 regarded by the morphologist as closely akin seem often 
 widely distinct; and, on the other hand, the fishes which 
 should, a priori, exhibit an archaic mode of development 
 actually present complex processes of early growth which 
 can only be interpreted as highly specialized. In fact, 
 there are far greater differences in the developmental plans 
 
 179 
 
DEVELOPMENT OF FISHES 
 
 of the closely related Ganoid and Teleost, than in those of 
 a Reptile and a Bird ; and even among the members of the 
 single group, Teleosts, there are more striking embryolog- 
 ical differences than those between Reptiles and Mammals. 
 Adaptive characters have entered so largely into the plan 
 of the development of fishes that they obscure many of 
 the features which might otherwise be made of value for 
 comparison. And until the controversies regarding some 
 of the most fundamental principles in embryology e.g. 
 the importance of the loss or gain of food yolk shall be 
 decided, it seems impracticable to use the plan of develop- 
 ment as in any strict sense a guide in phylogeny. 
 
 It is, accordingly, rather with the view of contrast- 
 ing the groups of fishes, whose external features have 
 hitherto been compared, that the present chapter seems 
 of especial importance. They may briefly be reviewed in 
 their (A) spawning habits, (B) the mode of fertilization 
 of their eggs, (C) their embryonic, and (D) larval de- 
 velopment. 
 
 A. EGGS AND BREEDING HABITS 
 
 The eggs of typical fishes in Figs. 186-199, illustrate 
 how wide a range occurs in their shapes and sizes. All 
 are of about actual size, except Figs. 189-191, which have 
 been reduced about two-thirds. From the figures the 
 character of the egg membranes may also be contrasted. 
 
 Among Cyclostomes, which are usually looked upon 
 as of close genetic kinship, there appears a striking dif- 
 ference in the characters of the eggs. Those of Bdello- 
 stoma and Myxine (Figs. 186, 187) are large and bluntly 
 spindle-shaped, encased in a horn-like capsule ; those, on 
 the other hand, of Petromyzon are minute, spherical, and 
 enclosed in delicate and jelly-like membranes (Fig. 188). 
 
Figs. 186-199. Eggs and egg cases of fishes. All of about actual size except 189-91 ; 
 these have been reduced about two-thirds. 186. Bdellostoma: germ disc (?) at upper pole 
 and in 186 A terminal hook processes and micropyle. (After AYERS.) 187. Myxine. (After 
 STEENSTRUP.) 187 A. Terminal process. 188. 'Petromyzon marinus. 189. Shark, Scyllium. 
 (After GtNTHER.) 189 A. Skate, Raja. 190. Port Jackson shark, Cestracion. (After 
 GUNTHER.) 191. Chimaeroid, Callorhynchus. (After GiJNTHER.) 192. Lung-fish, Ceratodus. 
 (After SEMON.) 193. Ganoid, Lepidosteus. 194. Ganoid, Acipenser. 195. Siluroid, Arius, 
 showing larva. (After GiJNTHER.) 196. Teleosts : sea-bass, Serranus, and 197. shad, Alosa. 
 198. Blenny, Blennius, showing attached egg capsules. 199. Enlarged Blennius (after 
 GuiTEL) , showing mode of attachment of capsule. 
 
 181 
 
j3 2 DEVELOPMENT OF FISHES 
 
 The eggs of Myxinoids are probably deposited at a 
 single time ; at first extruded by pressure of the body 
 wall ; then drawn out string-like, one egg following 
 another, attached by hooked and thread-like processes 
 (Figs. 186^4, 187 A). Little is known, however, of the 
 actual breeding habits of Myxinoids, either as to locality, 
 mode, or season ; individuals of Myxine and Bdellostoma 
 with ripe spawn have never been taken even in the 
 most favourable regions. It is supposed that their spawn- 
 ing does not occur in the immediate neighbourhood of 
 the shore, since detached eggs have been dredged in the 
 deeper water. Their breeding time is probably in the 
 early spring, although possibly intermittent spawning 
 takes place. In Myxine, according to Putnam,* the bulk 
 of the eggs may be deposited as late as the beginning of 
 winter. 
 
 The spawning habits of Petromyzon, on the other hand, 
 have been especially favourable for observation. The eggs 
 are deposited in shallow and clear water and the move- 
 ments of the fish may readily be followed. In the small 
 stream at Princeton,! for example, the lampreys make their 
 appearance about the middle of May and remain on the 
 spawning grounds two or three weeks. Their "nests" 
 are seen scattered thickly on the gravelly shoals, often but 
 a few feet apart. Each will be occupied by several males 
 and a single female, the latter conspicuous on account of 
 greater size. When spawning, the lampreys press together 
 and cause a flurry in the water at the moment when the 
 eggs and milt are emitted. This portion of eggs will now 
 
 * As observed at Grand Menan. Pro. Bost. Soc. Nat. Hist. Feb. '74. 
 
 t Professor McClure and Dr. O. S. Strong have here repeatedly observed 
 the spawning lampreys; it is to their account that the writer is here indebted. 
 Compare, also, the excellent account given recently by Professor Gage. 
 Ref. p. 234. 
 
EGGS OF ELASMOBRANCHS 
 
 183 
 
 be covered with a thin layer of sand or gravel, the 
 spawners always returning to the same nest, and a sec- 
 ond, third, and more tiers of eggs will be added. When 
 the eggs have finally been deposited, the nest is fortified 
 by a dome-like mass of pebbles and stones, which the lam- 
 preys carefully drag to the spot. The nest is thus marked 
 out as well as protected, and is said to be made of partial 
 use during the following season. The hatching of the 
 eggs takes place within about a fortnight. 
 
 The eggs which Sharks and Rays deposit are usually 
 enclosed in a stout, horn-like capsule ; this is in general of 
 oblong or rectangular outline, its surface smooth or ridged ; 
 the case of the egg of Scyllium (Fig. 189), shows thread- 
 like terminal processes, while these in the ray (Fig. 189^) 
 are stout and spine-like. A great variation may exist in 
 the size of the egg and in the character of its envelopes 
 among the different groups of Elasmobranchs. The egg 
 of the Port Jacksqn shark, Cestracion (Fig. 190), is of enor- 
 mous size and possesses an extremely thick, spiral-rimmed, 
 pear-shaped capsule ; that of the Greenland shark, L&mar- 
 gus, is said to be spherical and relatively small, and to be 
 deposited unprotected by capsule. 
 
 The breeding habits of Elasmobranchs are but imper- 
 fectly known. With the exception, perhaps, of Laemargus, 
 the sexes copulate.* The clasping appendages of the male 
 are inserted either singly or together into the cloaca and 
 oviduct of the female, and the eggs appear to be fertilized 
 in the uppermost portion of the oviduct. The egg then 
 becomes surrounded by a glairy albuminous envelope, and 
 thereafter by the secretion of the oviducal gland, which in 
 the lower oviduct hardens into the horny capsule. The 
 
 * The copulation of sharks has been but rarely observed (c.g. by Bolau in 
 Hamburg ; cf. Ref. on p. 241). 
 
1 84 
 
 DEVELOPMENT OF FISHES 
 
 majority of sharks and rays are viviparous ; the eggs are 
 retained in the lowermost portion of the oviduct (uterus) 
 and the embryo establishes a "placental" circulation, the 
 vascular yolk sac becoming adherent to the walls of the 
 uterus. Other sharks deposit their eggs, and their mode 
 of oviposition has been observed. The egg (Fig. 189), 
 when slightly protruded from the cloaca, is rubbed against 
 brush-like objects, and when its terminal processes become 
 finally entangled, the egg is withdrawn. The processes of 
 the egg case which leave the body last, the longer ones, 
 are often greatly straightened out when the egg is depos- 
 ited ; subsequently their elastic character causes them 
 to curl tightly, and often to secure a firm attachment 
 to neighbouring objects. The eggs of oviparous skates 
 (Fig. 189 A) are said to be deposited on sand flats near 
 the mark of low water. Mr. Vinal N. Edwards of Wood's 
 Holl, Massachusetts, believes that they are implanted ver- 
 tically in the sand, and, from the occurrence of "beds" 
 of skate eggs, that the fishes are singularly local in their 
 places of spawning. Eggs of Elasmobranchs* are often 
 many months in hatching ; the young fish finally escapes 
 through a slit at the end of the egg case. 
 
 Nothing is known definitely of the breeding habits of 
 Chimaeroids. The mode of copulation of the sexes is 
 doubtless similar to that of sharks. Their clasping organs 
 are highly specialized sperm ducts, and the hook-bearing 
 organs at the anterior margin of the ventral fin, and on 
 the forehead of the male, function in all probability in 
 retaining the female. The forehead spine could certainly 
 prove of such service if the position of the fishes during 
 mating was at all similar to that figured for Scyllium by 
 
 * In the case of Scyllium the eggs are deposited about six days after they 
 have been fertilized ; they then hatch in from 200 to 275 days. 
 
EGGS OF FISHES 
 
 I8 5 
 
 Bolau.* The egg case of Callorhynchus (Fig. 191) is 
 essentially shark-like ; it is of spindle-shaped outline, and 
 its broad, fringing margin gives it an almost seaweed-like 
 appearance. The egg is believed to be deposited in deep 
 water. 
 
 The spawning of but one of the three existing Lung- 
 fishes has been recorded. Ceratodus, according to Semon, 
 has a spawning season extending over several months ; it 
 deposits its eggs in shallow water, scattering them broad- 
 cast. The female fish is attended by several males, and 
 the emission of eggs and milt appears to be simultaneous. 
 The egg (Fig. 192) lacks a horny capsule, but is amply 
 protected by a thick, jelly-like hull. It hatches during the 
 second week. 
 
 Eggs of Ganoids are shown in Figs. 193, 194. They 
 are encased in a jelly-like envelope, especially viscid in the 
 case of sturgeon. When deposited, they speedily adhere 
 to whatever they touch, and often remain attached until 
 the time of hatching. The spawning grounds are in 
 shallow water ; the fish occur in numbers during a few 
 days of May and June, each female attended by several 
 males : ova and milt are emitted simultaneously, at short 
 intervals. The eggs develop rapidly, hatching in about a 
 week. 
 
 The eggs of Teleosts present the utmost variety in 
 number, form, membranes, and mode of deposition. In 
 some forms (Embiotocids, Blenniids, Cyprinodonts) they 
 may even develop within the ovarian tissue, establishing 
 there a "placental" circulation. They have been fertilized 
 within the fish, the anal fin spine of the male having in 
 some cases been metamorphosed into a copulatory organ. 
 The eggs of Siluroids (Fig. 195) are generally of large size, 
 
 *V. Ref. p. 241. 
 
I $6 DEVELOPMENT OF FISHES 
 
 and somewhat adhesive; they are deposited in "nests," i.e. 
 bowl-like depressions, and are attended by the male fish.* 
 Other adhesive eggs are those of carp, Ckristiceps, Batra- 
 chus. Eggs of Salmonids are deposited loosely in " nests " 
 on a clean, gravelly bottom; their membranes are thick 
 and parchment-like. On the other hand, the majority of 
 pelagic fishes produce eggs which float (Figs. 196, 197) ; 
 of these the membranes are extremely hygroscopic and 
 transparent, and an oil globule, located in the yolk region 
 of the egg, serves to diminish its specific gravity. The 
 egg membranes of a number of Teleosts, e.g. Blennies 
 (Fig. 199), appear essentially shark-like ; a horn-like cap- 
 sule is evolved, whose terminal processes afford it a firm 
 attachment. Aberrant modes of oviposition are not lack- 
 ing ; the South American Siluroid, Aspredo, as is well 
 known, carries its eggs attached to its ventral surface ; the 
 pipe-fishes and sea-horses, Siphostoma, Solenostoma, Hip- 
 pocampus, have specialized a pouch-like fold of the abdo- 
 men and of the ventral fins, which serves to retain the 
 eggs and larvae. It is curious to note that this remark- 
 able condition occurs only in the male. 
 
 The breeding habits of Teleosts are in general like those 
 of Ganoids ; their spawning season is usually during the 
 spring and summer, but is seldom of very brief duration. 
 The hatching of the eggs depends largely upon water 
 temperature, and may vary from a few days to several 
 months (Salmo). 
 
 B. THE FERTILIZATION PHENOMENA 
 
 The processes of the maturation and fertilization of 
 the egg have as yet shown but minor differences in the 
 
 * In several genera they are carried about in the gill chamber of the male, 
 thus ensuring aeration. 
 

 EARLY DEVELOPMENT 
 
 I8 7 
 
 groups of fishes. In the forms which have thus far been 
 studied * there have been few noteworthy variations from 
 what appear the normal conditions of vertebrates. The 
 sperm usually gains admission to the egg through a micro- 
 pyle in the egg membranes which becomes formed imme- 
 diately after the extrusion of the polar bodies. A sperm 
 cell, invariably a single one, participates in the actual 
 fertilization. This may occur directly by the formation of 
 a single male pronucleus, as e.g. in Petromyzon, Teleosts ; 
 while in the sharks, on the other hand, Riickert describes 
 a multiple fertilization (polyspermy), where many male 
 pronucleif are formed, the one nearest in position fusing 
 subsequently with the female pronucleus. An inter- 
 mediate condition seems to be retained in the sturgeon, 
 where several (six to nine) micropyles have been noted, 
 although but a single one occurs in the kindred Ganoid, 
 Lepidosteus (Mark, Ref. p. 249). 
 
 C. THE EMBRYONIC DEVELOPMENT 
 
 When the egg of a fish is deposited, it contains but the 
 elements of a single cell. Its size and its enveloping 
 membranes may vary widely, but its constituents are con- 
 stant, cytoplasm and nucleus. The size of the egg in 
 different fishes varies with the amount of food material, 
 or yolk, stored away in its cytoplasm ; the enormous egg 
 of the shark differs from the minute egg of the lamprey 
 strikingly in this regard. But even in the minute lamprey 
 egg there is a certain amount of yolk material present. 
 
 In every egg there can usually be distinguished at sight 
 
 * Lamprey by Kupffer and Bohm, and Calberla ; Sharks by Ruckert ; Te- 
 leostomes by Hoffman, Agassiz and Whitman, Kupffer, Bohm, and others. 
 
 t These appear later to undergo karyokinesis, and are thereafter to be 
 regarded as supplemental merocytes (p. 195). 
 
DEVELOPMENT OF FISHES 
 
 an upper and a lower zone : the latter rich orange in colour, 
 caused by the settling of the heavier yolk material ; the 
 former lighter in colour, containing the nucleus of the egg, 
 and originating the growth processes. 
 
 The less the amount of yolk in the lower, or vegetative, 
 region, the smaller is naturally the egg, and the more 
 obscure becomes the limit of the upper zone, or germ, or 
 animal pole, as it is indifferently called. In the yolk- 
 filled egg of the shark, on the other hand, the upper zone 
 becomes reduced to a mere "germ disc" on the surface of 
 the egg (Fig. 216, GD). If but little yolk is present, the 
 early growth processes, i.e. the splitting of the germ cell, 
 or egg, into many cells, or blastomeres, to give rise to the 
 embryo, affect the entire egg. If, however, much % yolk is 
 present, the cells at first multiply only at the animal pole, 
 and the yolk-filled region, remaining unsegmented, fur- 
 nishes the nutriment for the cell growth above. 
 
 In the present outline of the development of fishes, 
 the following types are reviewed : 
 
 I. Petromyzon ; II. Shark ; III. Lung-fish ; IV. Ganoid ; 
 V. Teleost. 
 
 I. The Development of Petromyzon 
 
 The egg of Petromyzon is of small size (Fig. 188), and 
 is poorly provided with yolk material ; in surface view one 
 can only distinguish the germinal from the yolk region by 
 its slightly lighter colour. In the side view of the egg of 
 Fig. 200, the beginning of the first cleavage plane is seen ; 
 a vertical plane, passing through the egg, completes the 
 stage of the two blastomeres of Fig. 201. The nuclei were 
 at first close to the upper, or animal, pole, but they shortly 
 take their position somewhat above the plane of the egg's 
 equator. A second cleavage plane is again vertical, ap- 
 
FIG. 200 
 
 201 
 
 202 
 
 EC 
 
 204 
 
 EN 
 
 Figs. 200-215. Development of lamprey, Petromyzon planeri. Figs. 200-204, 208-212 
 X 18, others X about 30. 200, 201. First cleavage, beginning and concluded. 202. Third 
 cleavage. 203. Fourth cleavage, in section, showing beginning of segmentation cavity. 204, 
 205. Early and late blastulae, in section. 206, 207. Early and late gastrulae, in section. 208, 
 210, 212. Early embryos showing growth of head end. 209, 211. Sagittal sections of early 
 embryos showing differentiation of organs. 213, 214. Transverse sections of early embryos. 
 215. Sagittal section of newly hatched larva, Ammocostes. (Figs. 211, 215, after GOETTE, others 
 after v. KUPFFER.) 
 
 BP. Blastopore. C. Coelenteron. CH. Notochord. DL. Dorsal lip of blastopore. EC. 
 Ectoderm. EN. Entoderm. EP. Epiphysis. G. Gut. H. Heart. M. Central nervous 
 system. MES. Mesoblast. N. Nasal pit. NC. Neurenteric region. S. Mouth pit, stomo- 
 dceum. SC. Segmentation cavity. T. Thyroid gland. Y. Yolk and yolk cells. 
 
DEVELOPMENT OF FISHES 
 
 proximately at right angles to the first ; the third, which 
 shortly appears, is horizontal (Fig. 202), giving rise to the 
 stage of eight blastomeres ; this plane, passing slightly 
 above the equator, causes the upper blastomeres to be 
 slightly smaller in size than those of the lower hemisphere. 
 The amount of yolk in the egg, it is accordingly inferred, 
 although not sufficient to prevent the passage of cleavage 
 planes, is enough, nevertheless, to retard the nuclear cleav- 
 ages in the region of the lower, or vegetative, pole. In 
 Fig. 203, showing a vertical section of the following 
 stage, another horizontal cleavage has been established in 
 the upper part of the egg ; the segmentation cavity is seen 
 in the centre of the figure arising as the central space 
 between the blastomeres. This is seen to have become 
 greatly enlarged in Fig. 204, a slightly later stage where 
 in vertical section is seen a greatly increased number of 
 blastomeres. Repeated cleavage of all blastomeres now 
 continues regularly, and results in the production of a 
 blastula, a smooth-surfaced cell mass containing the seg- 
 mentation cavity, SC (in section, Fig. 205) ; this is seen 
 to be located in the region of the animal pole. In the 
 next developmental stage, gastrula, seen in section in 
 Fig. 206, the primitive digestive tract, coelenteron, C, is 
 appearing ; it arises as an indentation of the side of the 
 blastula. The ccelenteron, soon greatly increasing in depth, 
 reduces in size and finally obliterates the segmentation cav- 
 ity, taking the position, C, shown in section in Fig. 207. 
 Here the segmentation cavity has practically disappeared ; 
 the surface opening of the ccelenteron is the blast op ore, 
 BP\ the cell layer of the gastrula's surface is the ecto- 
 derm, EC\ the cell layer lining the ccelenteron is the en- 
 toderm, EN: the ccelenteron, it will be seen, is closely 
 apposed to the ectoderm at the left of the figure, the 
 
DEVELOPMENT OF LAMPREY l g l 
 
 future dorsal region of the embryo ; on this side the 
 margin of the blastopore is known as the dorsal lip, DL, 
 while to the right the ventral lip is seen greatly enlarged 
 by the yolk-bearing cells, Y. A somewhat later stage 
 (Fig. 208) shows the blastopore as a narrowly constricted 
 opening, BP, whose dorsal lip is slightly raised at its left- 
 hand margin. The head of the embryo is to arise near 
 the opposite pole (as in Fig. 210), and is thence to elon- 
 gate into neck and trunk (Fig. 212). A sagittal section of 
 a stage, slightly older than Fig. 208, shows admirably the 
 structures of the embryo that have thus far been differ- 
 entiated (Fig. 209). Contrasting with Fig. 207, it will 
 thus be seen that the coelenteron, arising at BP, has 
 become greatly elongated ; at its blind end its lining mem- 
 brane, entoderm, EN, is in contact with an indented por- 
 tion of the ectoderm, at 5, where later the opening of the 
 mouth will be established ; and that ventrally the coelen- 
 teron has given off a pouch which passes into the yolk, and 
 will later be differentiated as the liver. That the entire 
 dorsal wall of the coelenteron has become thickened, con- 
 stitutes the main difference between the sections of Figs. 
 207 and 209 ; there have, in other words, arisen between 
 the entoderm and ectoderm of Fig. 207 the central ner- 
 vous system, or medullary cord, M, and the notochord, CH. 
 The origin of these structures may best be traced in the 
 cross-section of a slightly earlier stage (Fig. 213) ; the 
 coelenteron, or gut, is at G, the ectoderm at EC, the yolk 
 cells intervening at Y\ and the notochord and medullary 
 cord, CH, and M, in the sagittal region immediately be- 
 tween the gut and the ectoderm. In the medullary region 
 the ectoderm cells are seen pressed together, growing down- 
 ward and sidewise, forming altogether a compact cell cord * 
 
 * As in Teleosts, but unlike other vertebrates. 
 
DEVELOPMENT OF FISHES 
 
 passing down the back of the embryo ; the notochord is aris- 
 ing from the differentiating cells of the roof of the gut. In 
 the cross-section shown in Fig. 214, the subsequent con- 
 ditions of these structures may be seen ; the medullary 
 nerve cord, M, is now in section elliptical, separated dor- 
 sally from the ectoderm, and its cellular elements are of 
 more uniform size, arranged with bilateral symmetry, its 
 central lumen having not as yet appeared ; the notochord, 
 now constricted off from the wall of the gut, takes upon 
 it its characteristic form and structure. It is, however, 
 in the differentiation of the walls of the gut that this 
 section is of especial interest ; the gut is seen to have 
 greatly enlarged, and at the expense of the yolk material ; 
 its lining membrane, entoderm, EN, is now directly ap- 
 posed to the outer germ layer, ectoderm, EC. The middle 
 germ layer, mesoderm, MES, out of which cartilage, 
 muscular and connective tissue, are formed, is now seen 
 taking its origin as paired evaginations of the dorsal wall 
 of the gut. The mesoderm shortly loses its connection 
 with the entoderm, and by the rapid increase of its cellular 
 elements rapidly invests the remaining embryonic struct- 
 ures ; its segmental character may be seen in the surface 
 view shown in Fig. 210, its dorsal portions appearing as 
 the primitive segments. 
 
 Later developmental stages are shown in the sagittal 
 sections, Figs. 211, 212. These may best be compared 
 with Fig. 209. In Fig. 211 the head end of the body has 
 greatly elongated, and with it the gut cavity has dilated ; 
 entoderm is now composed of very minute cells, whose 
 nuclei are suggested by dots ; the yolk has become more 
 definitely restricted to the region of the hinder gut ; the 
 blastopore is still seen ; at its lips the germ layers are 
 alone fused. 
 
DEVELOPMENT OF FISHES 
 
 II. The Development of the Shark 
 
 On the side of embryology a shark presents many points 
 of striking contrast to the lamprey ; yet it may in many 
 regards be looked upon as archaic in its developmental 
 characters. Its contrasting structures (together with those 
 of lung-fish, Ganoid, and Teleost) may best be reviewed 
 in the table, p. 280. 
 
 The egg of the shark is of large size, richly provided 
 with yolk material. When removed from its membranes, 
 it is seen to be of a bright orange colour ; its form is elon- 
 gated, and the weight of its pasty substance causes it to 
 assume a flattened ovoid (Fig. 216). At the upper pole of 
 the egg is a small, light-coloured spot, the germ disc, GD, 
 which figures prominently in the early stages of develop- 
 ment. It would represent the lamprey's entire egg, if one 
 could imagine a point of the lower pole of the latter hugely 
 dilated with yolk. It is in the region of this germ disc 
 alone that every process of development as far as gastrula- 
 tion occurs. 
 
 The segmentation of the germ disc is shown in Figs. 
 217-220. In the first of these (Fig. 217) the germ is seen 
 to be sharply marked off from the surrounding yolk by a 
 circular band ; two cleavages have traversed it in the form 
 of narrow grooves separating the blastomeres. In Fig. 
 218 the fifth cleavage has been completed; the furrows 
 dividing irregularly the surface of the germ disc fade away 
 at its periphery. Fig. 219 represents a vertical section of 
 the germ disc at this stage ; the upper, finely dotted layer, 
 thinning away at either side, is the germ disc ; the coarsely 
 granular material below is the yolk ; the depth of the 
 cleavage furrows is seen, and it will be noted that up to 
 this stage of development there have been no horizontal 
 
FIG. 216 GD 
 
 218 
 
 219 
 
 Y CH 
 
 Figs. 216-230. Development of shark, Scyllium (mainly). (All but 216 after BAL- 
 FOUR.) 216. Egg freed from case showing germ disc GD. 217. Germ disc at second 
 cleavage. 218. Germ disc at fifth (?) cleavage. 219. Vertical section of similar stage. 
 220. Vertical section of slightly older germ disc. 221. Blastula. 222. Early gastrula. 
 223. Blastoderm showing early growth of embryo. 224-226. Slightly later stages of growth 
 of embryo. 227. Stage showing early embryo and mode in which the blastoderm sur- 
 rounds yolk. 228. Early embryo viewed as a transparent object. 229, 230. Transverse 
 sections of early embryo. 
 
 A. Anal invagination. A U. Auditory vesicle. BP. Dorsal lip of blastopore. C. 
 Coelenteron. CF. Tail folds. CH. Notochord. CP. Cephalic plate. EC. Ectoderm. 
 EN. Entoderm. G. Gut. GD. Germ disc. GS. Gill slits. H. Heart. HE. Head 
 eminence. M, Central nervous system. M' '. Yolk nuclei, merocytes. MES. Mesoblast. 
 NC. Neurenteric canal. OP. Optic vesicle. PS, Primitive segments. .S. Mouth pit, 
 stomodaeum. SC. Segmentation cavity. 
 
 194 
 
DEVELOPMENT OF SHARK 
 
 195 
 
 cleavages. A stage in which early horizontal cleavages 
 are represented is shown in Fig. 220. This may well be 
 compared with the last figure ; the germ disc, while not 
 increasing in diameter, is now seen to have multiplied its 
 blastomeres by horizontal cleavages ; it is converted into 
 a plug-shaped mass of cells, sunken into the yolk material. 
 At M' are cell nuclei, which have found their way into the 
 adjacent yolk, and which there acquire a developmental 
 importance. They become the so-called merocytes, or 
 yolk nuclei. 
 
 The section of the germ shown in Fig. 221 represents 
 a subsequent stage of development ; the blastomeres, by 
 continued subdivision, have become greatly reduced in size, 
 and are clearly to be distinguished from the smooth-sur- 
 faced, yolk-like material lying beneath. Merocytes, M', 
 are apparent in the superficial layer of the yolk ; they are 
 supposed to serve a twofold function, on the one hand, to 
 elaborate the yolk material and fit it for the embryo's use ; 
 on the other, to supply the cells which are being con- 
 tinually added to the germ's margin. In the figure a large 
 cavity is shown to exist between the yolk and the mass of 
 blastomeres. This cavity has been identified as the seg- 
 mentation cavity, SC, and the developmental stage as the 
 blastula ; it is as though the lower hemisphere of the 
 lamprey's blastula (Fig. 205) had become enormously 
 enlarged, and all traces of the cells in the floor of its 
 segmentation cavity lost, except in the layer of the 
 metamorphosed cells, the merocytes. 
 
 In the next growth process the extent of the germ area 
 becomes greatly increased ; the thick blastula is now 
 thinned out into a surface layer of regular cells, an en- 
 larging disc-like blastoderm, which will eventually grow 
 around and enclose the entire egg. The blastoderm of 
 
196 
 
 DEVELOPMENT OF FISHES 
 
 Fig. 223 is a pale-coloured circular membrane of about a 
 half inch in diameter lying on the surface of the egg. 
 Sectioned at an earlier stage (Fig. 222) the blastoderm is 
 seen to present the following contrast to the blastula of 
 Fig. 221 : the floor of the segmentation cavity has flattened, 
 and a sharp rim forms the outline of the blastoderm ; at 
 one side this rim is seen to protrude ov 7 er the yolk mass, 
 leaving a narrow, fissure-like cavity between. This stage 
 is identified as the gastrula ; the fissure-like cavity, the 
 coelenteron ; its marginal blastoderm, the dorsal lip of the 
 blastopore ; its ventral lip, the entire yolk mass. 
 
 The growth of the embryo's form takes its origin at the 
 blastopore's dorsal lip. In Fig. 223 the rim of the blasto- 
 derm is seen indented near the point CF, and its thicken- 
 ing at this region becomes more and more marked in 
 subsequent stages ; on the other hand, the anterior por- 
 tion of the blastoderm, growing continually on all sides, 
 becomes excessively thin, flattening itself tightly to the 
 yolk, and reducing the segmentation cavity to the small 
 area indicated at SC. The growth of the embryo in the 
 mid-region of the blastopore's dorsal lip may next be 
 followed in the stages, Figs. 224, 225, 226. The inden- 
 tation of the rim may thus be seen to assume a creese- 
 like thickening, thrusting forward its blunt end, the head 
 eminence, HE, over the blastoderm ; at the points CF, 
 the tail eminences, the rim of the blastoderm is thick, 
 protruding, appearing to be pressing together in the 
 median line, and causing the body of the embryo to be 
 actually pushed into form and thrust above the level of 
 the blastoderm. In Fig. 225 the sides of the embryo are 
 separated dorsally by a deep groove, the medullary furrow, 
 the future canal of the central nervous system. In Fig. 
 226 this is seen at a more advanced stage ; its hinder 
 

 DEVELOPMENT OF SHARK 
 
 I 9 7 
 
 portion has been roofed over by the coalesced sides, and 
 the process of enclosing the groove is being continued 
 anteriorly, although the head end of the embryo is now 
 flattened out as the prominent cephalic plate. 
 
 In the stage figured in 227, the form of the embryo has 
 been acquired : the head in the manner already outlined, 
 the tail by the coalescence and subsequent outgrowth 
 of the tail folds, CF. The entire embryo now rises above 
 the blastoderm, as this continues to enclose the yolk. In 
 the figure the yolk has thus been more than half enclosed ; 
 its final appearance is seen in the oval space outlined by a 
 dotted line behind the embryo. 
 
 The origin of the germ layers is not as readily traced 
 as in the Cyclostome. Ectoderm is the most clearly 
 marked; even in the blastula (Fig. 221) it has appeared 
 as an outer single-celled stratum clearly differentiated 
 from the underlying cells. Entoderm is only to be 
 seen on the dorsal wall of the ccelenteron : the ventral 
 entoderm (cf. Fig. 222) is merged with the yolk. Meso- 
 derm takes its origin from the inner layer on either side 
 of the median line, but it arises as a solid cell mass 
 instead of as the pouch-like diverticula in Petromyzon. 
 Cross-sections of an embryo represented by Fig. 224 
 have been figured in Figs. 228 and 229 ; the former is of 
 the hinder region and illustrates the mode of growth of the 
 mesoderm, MES\ the latter across the head region, 
 shows that in this region the mesoderm is separated 
 from the inner layer. Both sections show the simple 
 character of the medullary groove, and the latter section 
 the mode of origin of the notochord, CH t i.e. as an axial 
 thickening of the entoderm. 
 
 An embryo of about the stage of Fig. 227 is extremely 
 delicate and may readily be viewed as a transparent object. 
 
198 
 
 DEVELOPMENT OF LUNG-FISH 
 
 By this time (Fig. 230) it will be seen that its prominent 
 organs have already been differentiated. There are thus : 
 medullary canal, M, with optic, OP, and auditory, AU, 
 vesicles ; gut with gill slits, 5, neurenteric canal, NC, 
 and suggestion of mouth, S, and anus, A ; notochord, 
 CH\ segmented mesoderm (primitive segments), PS, 
 and heart, H. The medullary groove was converted into 
 a canal, as has been already suggested, by the oyerroofing 
 and fusion of the summits of the medullary ridges ; its 
 anterior dilatation is the brain ; the gut, G, communicates 
 freely below with the yolk mass ; it is a cavity, a portion 
 of the coelenteron that has been constricted off with the 
 embryo ; its openings, the mouth, anus, and gill slits, are 
 secondary, acquired after there have been established in 
 these regions fusions of entoderm and ectoderm ; the 
 neurenteric canal, NC, a communication between medul- 
 lary tube and gut, is a structure acquired in the stage of 
 Fig. 226, where the hinder medullary groove was roofed 
 over, allowing, in the region of the tail folds, a communi- 
 cation to exist between medullary canal and ccelenteron. 
 The notochord has by this stage been completely sepa- 
 rated from the entoderm ; it already assumes a supporting 
 function. 
 
 III. The Development of Ceratodus 
 
 The development of a Lung-fish has thus far been de- 
 scribed (Semon) only from the outward appearance of the 
 embryo. The egg of Ceratodus (Fig. 192) is seen without 
 its covering membranes, enlarged, in Fig. 231. Its upper 
 pole is distinguished by its fine covering of pigment. The 
 first fine planes of cleavage are shown in Figs. 232-236 ; 
 and from these it will be seen that the yolk material of the 
 lower pole is not sufficient to prevent the egg's total seg- 
 
234 
 
 239 
 
 244 
 
 245 
 
 246 
 
 Figs. 231-247. Development of lung-fish, Ceratodus. (After SEMON.) X 4-7. 
 231. Egg immediately before cleavage. 232, 233. First cleavage, seen from above and 
 from the side. 234. Second cleavage, seen from above. 235, 236. Third cleavage, 
 seen from above and from the side. 237. Blastula. 238, 239. Gastrulae showing 
 closure of blastopore. 240. Early embryo, seen from the side. 241. Early embryo 
 showing medullary folds (head). 242. Tail region of same embryo. 243. Tail region 
 of slightly later stage. 244. Head region of same embryo. 245-247. Later embryos. 
 
 A V. Auditory vesicles. BP. Blastopore. GS. Gill slits. M. Mouth pit. MF. 
 Medullary folds'. O. Olfactory lobes. OP. Optic vesicles. PN. Primitive kidney, 
 pronephros. PS. Primitive segments. Y. Yolk mass. 
 
 199 
 
200 DEVELOPMENT OF FISHES 
 
 mentation. The first plane of cleavage is a vertical one, 
 passing down the side of the egg (Fig. 233) as a shallow 
 surface furrow, not appearing to entirely separate the sub- 
 stance of the blastomeres, although traversing completely 
 the lower hemisphere (Fig. 232). A second vertical furrow 
 at right angles to the first is seen from the upper pole in 
 Fig. 234 ; it is essentially similar to that of Fig. 233. The 
 third cleavage of Fig. 235 is again a vertical one (as in all 
 other fishes, but unlike Petromyzon), approximately meridi- 
 onal ; its furrows appear less clearly marked than of earlier 
 cleavages, and seem somewhat irregular in occurrence. The 
 fourth cleavage is horizontal above the plane of the equator. 
 Judging from Semon's figure (Fig. 236), at this stage the 
 furrows of the lower pole seem to have become fainter, if 
 not entirely lost. A blastula showing complete segmenta- 
 tion is seen in Fig. 237 ; the blastomeres of the upper 
 hemisphere are the more finely subdivided ; the conditions 
 of the segmentation cavity may be expected to prove 
 similar to those of Fig. 205. Two stages of the gastrula 
 are shown in Figs. 238 and 239, showing a full view of the 
 blastopore. In the earlier one (Fig. 238) the dorsal lip of 
 the blastopore is crescent-like ; in the later (239) the 
 blastopore acquires its oblong outline, through which the 
 yolk material is apparent ; its conditions may later be 
 compared to those of a Ganoid (Figs. 254, 255). 
 
 The growth of the embryo is illustrated in the remaining 
 figures (Figs. 240-248). A side view of an early embryo 
 is shown in Fig. 240 ; at the top of the egg to the right is 
 the head region, to the left the blastopore and tail. The 
 surface view of the head region (Fig. 241), the medullary 
 folds, MF, may be compared with those of Fig. 225, 
 although they are low and widely separated ; the axial 
 seam is referred to by Semon as a demonstration of the 
 
DEVELOPMENT OF LUNG-FISH 2 QI 
 
 theory of the embryo's concrescence. In the hinder region 
 of the same embryo (Fig. 242) the blastopore is still 
 apparent, BP, reduced to a narrow, fissure-like aperture ; 
 around it is the tail mass, corresponding generally to CF 
 of Fig. 226 ; and encircling all is the hinder continuation 
 of the medullary folds. 
 
 The next change of the embryo is strikingly amphibian- 
 like ; the medullary folds rise above the egg's surface, and, 
 arching over, fuse their edges in the median dorsal line. 
 In Fig. 243, the tail region of a slightly older embryo, this 
 process is clearly shown ; the medullary folds, MF y are 
 seen closely apposed in the median line ; hindward, how- 
 ever, they are still separate, and through this opening the 
 blastopore, BP, may yet be seen. At this stage primitive 
 segments are shown at PS\ in the brain region in Fig. 
 244 the medullary folds are still slightly separated (cf. CP, 
 Fig. 226). 
 
 Two views of an 
 older embryo are fig- 
 ured (Figs. 245 and 
 246), where the fish- 
 like form may be rec- 
 ognized. The medul- Fig- 248. Embryo of Ceratodus, near the time 
 of hatching. 
 
 lary tolas have com- GS. GUI slits. M. Mouth pit. OP. Optic vesi- 
 
 pletelv fused in the deS ' PN ' Primitive kidne y. pronephros. T. Tail 
 * ' eminence. 
 
 median line, and the 
 
 embryo is coming to acquire a ridge-like prominence; 
 optic vesicles and primitive segments are apparent, and 
 at BP the blastopore appears to persist as the anus. The 
 continued growth of the embryo above the yolk mass, 
 Y, is apparent in Fig. 247; the head end has, however, 
 grown the more rapidly, showing gill slits, GS, auditory, 
 optic, and nasal vesicles, AU, OP, and O, at a time when 
 
202 DEVELOPMENT OF GANOID 
 
 the tail mass has hardly emerged from the surface. Pro- 
 nephros has here appeared at PN (cf. with Fig. 247, Fig. 
 210). It is not until the stage of the late embryo of Fig. 
 248 that the hinder trunk region and tail come to ' be 
 prominent. The embryo's axis elongates and becomes 
 'straighter ; the yolk mass is now much reduced, acquiring 
 a more and more oblong form, lying in front of the tail, T, 
 in the region of the posterior gut (cf. Figs. 211 and 212). 
 The head, and even the region of the pronephros, PN, 
 are clearly separate from the yolk sac ; the mouth, M, is 
 coming to be formed. 
 
 IV. The Development of Ganoids 
 
 The development of Ganoids is next to be outlined. 
 The eggs of the sturgeon and gar-pike are poorly provided 
 with yolk. They have still, however, a greater amount 
 than those of the lamprey or lung-fish, and in many 
 regards of development suggest nearnesses to the Elasmo- 
 branchs. 
 
 The egg of the sturgeon shown in Fig. 249 shows 
 clearly two distinct zones ; the upper, blotched with pig- 
 ment at the animal pole, is pale in colour; the lower, rich 
 in yolk, is orange-coloured, well speckled with pigment. 
 The early cleavages appear at first only in the upper pale- 
 coloured area which corresponds apparently with the germ 
 disc of the shark's egg. In Fig. 250 there have been 
 two cleavages, vertical and at right angles to each other ; 
 these have sharply traversed the germ area, the earlier 
 one being now produced slightly into the yolk region of 
 the egg only, however, as a slight surface furrow. The 
 third cleavage (Fig. 251) presents a stage closely corre- 
 sponding with that of Ceratodus of Fig. 235, its plane tend- 
 ing to pass parallel to the first cleavage : the germ disc 
 
FIG. 249 
 
 250 
 
 251 
 
 252 
 
 258 EC/T EN NC 259 
 
 Figs. 249-268. Development of Ganoids, Acipenser and (last four figures) Lepi- 
 dosteus. x about 12. 249. Egg immediately before cleavage. 250. Second cleavage. 
 251. Third cleavage. 252. Blastula. 253. Vertical section of blastula. 254. Early 
 gastrula. 255. Late gastrula. 256. Vertical section of late gastrula. 257. Early 
 embryo. 258. Sagittal section of same stage. 259, 260. Head and tail regions of 
 slightly later embryo. 261. Transverse body section of hinder body region of same 
 stage. 262, 263. Head and tail regions of late embryo. 264. Embryo immediately 
 before hatching. 265. Lepidosteus' blastula. 266. Vertical section of early gastrula. 
 267. Late gastrula. 268. Embryo, showing mode of separation from yolk. 
 
 BP. Dorsal lip of blastopore. C. Coelenteron. EC. Ectoderm. EN. Entoderm. 
 F. Pectoral fin. GS. Gill slits. H. Heart. HE. Head eminence. KV. Kupffer's 
 vesicle. LC. Marginal limit of coelenteron. M. Mouth pit. MC. Medullary canal. 
 MES. Mesoblast. NC. Neurenteric canal. OL. Olfactory pits. OP. Optic vesicles. 
 PX. Primitive kidney, pronephros. PS. Primitive segments. SC. Segmentation 
 cavitv. T. Tail eminence. VL. Ventral lip of blastopore. Y. Yolk, yolk mass. 
 YP. 'Yolk plug. 
 
 203 
 
DEVELOPMENT OF FISHES 
 
 is deeply cut by the furrows ; the yolk area, however, only 
 superficially ; the shallow furrow of the first cleavage on 
 the yolk hemisphere now passes through the lower pole ; 
 the second cleavage, passing downward, has made a shal- 
 low groove extending half-way between the rim of the 
 germ area and the lower pole of the egg. It is the great 
 amount of yolk in the lower hemisphere that retards the 
 cleavage of the blastomeres. In Fig. 252 the entire 
 germ area has become subdivided into a mass of small 
 cells, while the large, irregular blastomeres of the yolk 
 hemisphere are separated only by superficial furrows. 
 This stage, the blastula, is seen in section in Fig. 253: 
 the yolk, unsegmented, occupies the lower hemisphere ; 
 the germ area contains a segmentation cavity, SC, with 
 a roofing of small cells, and a floor of irregular cells half 
 engulfed in a deep, underlying zone transitional between 
 germ and yolk. 
 
 An early gastrula is seen in Fig. 254 : the more rapid 
 multiplication of the cells of the germ region has given 
 rise to a down-reaching cap of cells, whose boundary is 
 here sharply marked off from the large and imperfect yolk 
 cells of the lower hemisphere. At BP, the rim of the cell 
 cap, or blastoderm, is sharply distinct from the yolk ; it is 
 the dorsal lip of the blastopore ; the remaining portion of 
 the rim is, generally speaking, the remainder of the rim 
 of the blastopore ; more accurately it is the circumcres- 
 cence margin of Hertwig. The late gastrula of Fig. 255 
 shows the greatly increased extent of the blastoderm : its 
 margin is continually reducing the size of the blastopore, 
 BP\ on its dorsal lip at HE, the outline of the embryo 
 is appearing. A sagittal section of this stage (Fig. 256) 
 shows at BP the dorsal, and at VL the ventral, lip of the 
 blastopore ; at YP the yolk material appears at the egg's 
 
DEVELOPMENT OF GANOID 205 
 
 surface as a plug-like mass ; at SC is the segmentation 
 cavity. The dorsal lip of the blastopore is seen to be far 
 longer than the ventral lip ; its rim is the more inflected, 
 at KV occurring a recessus which the writer compares 
 to the Kupffer's vesicle of Teleost development; the 
 cavity, C, coelenteron, between the wall of the blastopore 
 and the yolk mass is in this region the largest. The 
 germ layers in this stage, EC, MES, EN, are seen to 
 be confluent at the blastopore's rim ; at the termina- 
 tion of the coelenteron, entoderm and mesoderm are 
 merged ; the ectoderm forms the roof of the segmenta- 
 tion cavity. 
 
 The form of the embryo next becomes more definitely 
 established. In Fig. 257 the blastopore, much reduced 
 in size, is seen at BP ; its thickened rim is whitish in 
 colour; the darkened area, whose boundary is LC, is the 
 coelenteron, seen faintly through the translucent margin 
 of the blastopore ; the embryo is the opaque area of the 
 blastopore's dorsal lip, terminating anteriorly in the dilated 
 tract, H, the head region. In a sagittal section of a 
 slightly later stage (Fig. 258), the relations of germ 
 layers, EC, MES, EN, coelenteron, C, and yolk mass, 
 Y, may be compared with those of the section (Fig. 256), 
 wherein the region YP corresponds to that of NC. A 
 thin ectoderm will now be seen to have enclosed the 
 entire egg ; the segmentation cavity has disappeared ; the 
 rim of the blastopore, becoming continually constricted, 
 causes the yolk material to recede from the surface, and 
 leaves the blastopore disappearing, as the blunt diver- 
 ticulum of NC. The neurenteric canal, NC, is the last 
 communication between the surface of the egg and the 
 coelenteron ; this has become established before the blas- 
 topore closes in the stage of Fig. 257 at its dorsal lip; 
 
206 DEVELOPMENT OF FISHES 
 
 the medullary furrow of the embryo has here been the 
 deepest, and has been bridged over by a coalescence of 
 its margins. At the anterior end of the embryo the 
 inner, EN, and middle, MES, germ layers become 
 greatly thinned, in the region where the heart is shortly 
 to arise. 
 
 The next stage of development is represented in Figs. 
 259, 260, showing front and hinder regions of the same 
 embryo. The curiously flattened mode of growth char- 
 acteristic of the sturgeon is here very apparent ; the 
 embryo has surrounded over three-fourths of the egg's 
 circumference, yet has not risen above its surface curva- 
 ture ; the head region is especially flattened ; mouth, M, 
 heart, H, gill slits, GS, brain, and optic vesicles are broadly 
 spread out : the fourth ventricle at MC, the pronephros 
 at PN, the primitive segments at PS. In the tail region 
 the medullary folds appear at M, the pronephric duct at 
 PN, the neurenteric canal at NC. A favourable section 
 through the hinder body region of an early embryo is 
 shown in Fig. 261 ; it illustrates the mode of origin of the 
 following structures : the notochord as an axial thickening 
 of entoderm, EN, immediately under MC] the medullary 
 canal, as an infolding of (an under, or formative layer of) 
 the ectoderm, its sides, folding over dorsally, coming to fuse 
 in the median line; the mesoderm, MES, as in sharks, 
 arising (partly) from the entoderm on either side of the 
 notochord. 
 
 The later stage, shown in Figs. 262 and 263, may be con- 
 trasted with Figs. 259 and 260; the head region, though 
 still greatly flattened out, is now rising above the surface ; 
 the trunk region is becoming prominent ; the tail is bud- 
 ding out, and separating from the egg surface ; sense 
 organs are well outlined, and pectoral fins, F, elasmobran- 
 
DEVELOPMENT OF TELEOST 2O/ 
 
 chian in character, are appearing. An embryo shortly 
 before hatching is next figured (Fig. 264) ; the head has 
 now entirely lost its flattened character; the mouth in- 
 vagination occurs at M\ the tail, much elongated, is 
 compressed laterally, and already presents the dermal 
 embryonic fin ; the yolk sac is attached along the an- 
 terior body region, in a position more nearly that of the 
 shark than of the lung-fish. 
 
 Of the two Ganoids, sturgeon and gar-pike, the latter, 
 as the writer has pointed* out, * has the more shark-like 
 developmental features. Its segmentation is incomplete, 
 since the yolk pole of the egg is at no time traversed even 
 by superficial furrows. The blastoderm, or cell cap, is 
 early apparent, and is clearly marked off by a furrow from 
 the irregular marginal blastomeres (Fig. 265). It resem- 
 bles closely the segmented germ disc of an Elasmobranch, 
 and the irregular marginal blastomeres may be compared 
 to merocytes. The section of a late blastula of Fig. 266 
 does not differ widely from that of the shark of Fig. 221 ; 
 a segmentation cavity is present, whose floor is smooth, 
 and contains a well-marked zone of merocytes, M\ the 
 smaller quantity and firmer consistency, perhaps, of the 
 yolk do not, on the other hand, permit the blastula to 
 occupy the sunken position of that of the shark. In the 
 gastrula of the gar, further, a well-marked notch appears 
 at the dorsal lip (as in this stage, Fig. 223, of the shark), 
 representing the primitive blastopore. And, finally, the 
 form of the embryo rises boldly from the surface, and 
 early presents the well-marked head and tail eminences, 
 HE and T, of Fig. 268, comparable with Figs. 225 and 
 227. 
 
 * Am. J. Morph., Vol. XI, No. I. 
 
FIG. 269 
 
 270 
 
 272 
 
 P G 
 
 EN 
 
 Figs. 269-283. Development of Teleost, Serranus atrarius. (After H. V. WILSON.) 
 Fig. 276 X 25. 269. Egg immediately prior to segmentation, showing position of germ 
 disc and of oil globule. 270. Germ disc after first cleavage. 271. Germ disc after third 
 cleavage. 272. Vertical section of blastula. 273. Vertical section of blastula, showing 
 origin of periblast. 274. View of marginal cells of blastula of similar stage. 275. Growth 
 of blastoderm around yolk mass. 276. A slightly later stage, showing growth of embryo. 
 277. Continued growth of embryo and reduction in size of the blastopore. 278. Sagittal 
 section of tail region of embryo of last figure. 279, 280, 281. Cross-sections of embryos, 
 showing successive stages in the development of notochord, gut, neuron, mesoblast. 282. 
 Cross-section of young embryo, showing the mode of formation of gill slit. 283. Embryo 
 shortly before hatching. 
 
 A. Anus. AU. Auditory vesicle. BP. Dorsal lip of blastopore. Cff. Notochord. 
 EC. Ectoderm. EN. Entoderm. G. Gut. GD. Germ disc. GR. Germ ring. GS. 
 Gill slit. H. Heart. HP. Head process. KV. Kupffer's vesicle. M. Spinal nervous 
 system. MES. Mesoblast. MP. Marginal periblast cells. OG. Oil globule. OL. Ol- 
 factory pit. OP. Optic capsule. P. Periblast. PS. Primitive segments. SC. Segmen- 
 tation cavity. SCH. Subnotochordal rod. TM. Tail mass. Y. Yolk. 
 
 208 
 
DEVELOPMENT OF TELEOST 2 OQ 
 
 V. The Development of Teleost 
 
 The mode of development of bony fishes differs in 
 many and apparently important regards from that of 
 their nearest kindred, the Ganoids. In their eggs a large 
 amount of yolk is present, and its relations to the embryo 
 have become widely specialized. 
 
 As a rule, the egg of a Teleost is small, perfectly spheri- 
 cal, and enclosed in delicate but greatly distended mem- 
 branes (Fig. 269). The germ disc, GD, is especially 
 small, appearing on the surface as an almost transparent 
 fleck ; it may occupy the same position as in the other 
 fishes, or, as in the figure, it may occur at the lowermost 
 pole. Among the fishes whose eggs float at the surface 
 during development, as of many pelagic Teleosts, e.g. the 
 Sea-bass, Serranus atrarius, to which all the accom- 
 panying figures refer, the yolk is lighter in specific 
 gravity than the germ; it is of fluid-like consistency, 
 almost transparent. In the yolk at the upper pole of 
 the egg an oil globule, OG, usually occurs ; this serves 
 to lighten the gravity of the entire egg, and from its 
 position must aid materially in keeping this pole of the 
 egg uppermost. 
 
 The early segmentation of the germ is seen in Figs. 
 270, 271. In the former, the first cleavage plane is estab- 
 lished, and the nuclear divisions have taken place for the 
 second ; in the latter, the third cleavage has been com- 
 pleted. As in other fishes these cleavages are vertical, 
 the third parallel to the first. A segmentation cavity, 
 SCj occurs as a central space between the blastomeres, 
 as it does in the sturgeon and gar-pike. 
 
 Stages of late segmentation are seen in section in Figs. 
 272, 273. In both the segmentation cavity, SC, is greatly 
 
DEVELOPMENT OF FISHES 
 
 flattened, but extends to the marginal cells of the germ 
 disc ; in Fig. 272 its roof consists of two tiers of blasto- 
 meres, its floor a thin film of the unsegmented substance 
 of the germ ; the marginal blastomeres are continuous 
 with both roof and floor of the cavity, and are produced 
 into a thin film which passes downward, around the sides 
 of the yolk. In Fig. 273 the segmentation cavity is still 
 further flattened ; its roof is now a dome-shaped mass of 
 blastomeres ; the marginal cells have multiplied, and their 
 nuclei are seen in the layer of the germ, P, below the 
 plane of the segmentation cavity. These are seen at MP 
 in the surface view of the marginal cells of this stage 
 (Fig. 274) ; they are separated by cell walls only at the 
 sides ; below they are continuous in the superficial down- 
 reaching layer of the germ. The marginal cells, MP, 
 shortly lose all traces of having been separate; their 
 nuclei, by continued division, spread into the layer of germ 
 flooring the segmentation cavity, and into the delicate film 
 of germ which now surrounds the entire yolk. Thus is 
 formed the periblast of teleostean development, which from 
 this point onward is to separate the embryo from the yolk ; 
 it is clearly the specialized inner part of the germ, which, 
 becoming fluid-like, loses its cell walls, although retaining 
 and multiplying its nuclei. It would accordingly corre- 
 spond to that portion of the germ of the sturgeon in Fig. 
 253 which lies below the plane of the segmentation cavity, 
 and which extends downward at the sides of the yolk ; in 
 this case, however, the surface outlines of the cells have 
 not been lost. It will be seen from later figures (Figs. 
 278-282) that the periblast, P, comes into intimate rela- 
 tions with the growing embryo ; it lies directly against 
 it, and appears to receive cell increments from it at various 
 regions ; on the other hand, the nuclei of the periblast, 
 
DEVELOPMENT OF TELE OS T 211 
 
 from their intimate relations with the yolk, are supposed 
 to subserve some function in its assimilation. 
 
 Aside from the question of periblast, the growth of 
 the blastoderm appears not unlike that of the sturgeon. 
 From the blastula stage of Fig. 273 to that of the early 
 gastrula (Fig. 275), the changes have been but slight ; the 
 blastoderm has greatly flattened out as its margins grow 
 downward, leaving the segmentation cavity apparent at 
 SC. The rim of the blastoderm has become thickened, 
 as the 'germ ring;' and immediately in front of BP, the 
 dorsal lip of the blastopore, its thickening, as in Fig. 255, 
 marks the appearance of the embryo. In Fig. 276 the 
 germ ring, GR, continues to grow downward, and shows 
 more prominently the outline of the embryo ; this now 
 terminates at HP, the head region ; while on either side 
 of this point spreads out tail-ward on either side the indefi- 
 nite layer of outgrowing mesoderm, MES. In the stage 
 of Fig. 277 the closure of the blastopore, BP, is rapidly 
 becoming completed ; in front of it stretches the widened 
 and elongated form of the embryo. A sagittal section 
 through a late stage of the blastopore appears in Fig. 278 ; 
 with it may be compared the corresponding region of the 
 sturgeon of Fig. 256; the yolk plug, YP, of the latter is 
 now replaced by periblast, P, the dorsal lip at BP, by 
 TM, the tail mass, or more accurately the dorsal section 
 of the germ rim ; the coelenteron under the dorsal lip 
 has here disappeared, on account of the close approxima- 
 tion of the embryo to the periblast ; its last remnant, 
 the Kupffer's vesicle, KV, is shortly to disappear. At 
 TM, the germ layers become confluent as at BP in Fig. 
 256, but, unlike the sturgeon, the flattening of the dorsal 
 germ ring, TM, does not permit the formation of a neu- 
 renteric canal. 
 
2J2 DEVELOPMENT OF FISHES 
 
 The process of the development of the germ layers 
 in Teleosts appears an abbreviated one, although in many 
 of its details it is but imperfectly known. In the develop- 
 ment of the medullary groove, as an example, the follow- 
 ing peculiarities exist : the medullary region at HP (Fig. 
 276) is but an insunken mass of cells without a trace of 
 the groove-like surface indentation of Fig. 261 or 229. 
 Its condition is figured at Mm Fig. 282. It is only later, 
 when becoming separate from the ectoderm, EC, that it 
 acquires its rounded character (Fig. 279), M; its cellular 
 elements then group themselves symmetrically with refer- 
 ence to a sagittal plane, where later by their disassocia- 
 tion (?) the canal of the spinal cord is formed (Fig. 280), M. 
 The growth of the entoderm is another instance of special- 
 ized development. In the section of the embryo of Fig. 
 279, the entoderm exists in the axial region, its thickness 
 tapering away abruptly on either side ; its lower surface 
 is closely apposed to the periblast; its dorsal thickening 
 will shortly become separate as the notochord. In a fol- 
 lowing stage of development (Fig. 280), the entoderm is 
 seen to arch upward in the median line as a preliminary 
 stage in the formation of the cavity of the gut. Later, 
 by the approximation of the entoderm cells in the median 
 ventral line, the condition of Fig. 281 is reached, where the 
 completed gut cavity exists at G. 
 
 The formation of the mesoderm in Teleosts is not defi- 
 nitely understood. It is usually said to arise as a process 
 of ' delamination,' i.e. detaching itself in a mass from the 
 entoderm. Its origin is, however, looked upon generally 
 as of a specialized and secondary character. 
 
 The mode of formation of the gill slit of a Teleost does 
 not differ from that in other groups ; an evagination of 
 the entoderm, GS (Fig. 282), coming in contact with an 
 
LARVAL FISHES 
 
 invaginated tract of ectoderm, EC, fuses, and at this point 
 an opening is later established. 
 
 In Fig. 283 has been figured a late embryo. This may 
 be compared with that of the sturgeon of Fig. 264. The 
 Teleost, though of rounded form, is the more deeply im- 
 planted in the yolk sac ; it is transparent, allowing noto- 
 chord, primitive segments, heart, and sense organs to be 
 readily distinguished ; at about this stage both anus, A, 
 and mouth, M, are making their appearance. 
 
 D. THE LARVAL DEVELOPMENT OF FISHES 
 
 When the young fish has freed itself from its egg mem- 
 branes, it gives but little suggestion of its adult form. It 
 enters upon a larval existence, which continues until matu- 
 rity. The period of metamorphosis varies widely in the 
 different groups of fishes from a few weeks' to longer 
 than a year's duration ; and the extent of the changes that 
 the larva undergoes are often surprisingly broad, invest- 
 ing every organ and tissue of the body, the immature 
 fish passing through a series of form stages which differ 
 one from the other in a way strongly contrasting with the 
 mode of growth of amniotes ; since the chick, reptile, or 
 mammal emerges from its embryonic membranes in nearly 
 its adult form. 
 
 The fish may, in general, be said to begin its existence 
 as a larva as soon as it emerges from its egg membranes. 
 In some instances, however, it is difficult to decide at what 
 point the larval stage is actually initiated : thus in sharks, 
 the excessive amount of yolk material which has been pro- 
 vided for the growth of the larva renders unnecessary the 
 emerging from the egg at an early stage ; and the larval 
 period is accordingly to be traced back to stages that are 
 still enclosed in the egg membranes. In all cases the 
 
DEVELOPMENT OF FISHES 
 
 larval life may be said to begin when the following con- 
 ditions have been fulfilled : the outward form of the larva 
 must be well defined, separating it from the mass of yolk,, 
 its motions must be active, it must possess a continuous 
 vertical fin fold passing dorsally from the head region 
 to the body terminal, and thence ventrally as far as the 
 yolk region; and the following structures, characteristic 
 in outward appearance, must also be established, the sense 
 organs, eye, ear and nose, mouth and anus, and one 
 or more gill clefts. 
 
 Among the different groups of fishes the larval changes 
 are brought about in widely different ways. These larval 
 peculiarities appear at first of far-reaching significance, 
 but may ultimately be attributed, the writer believes, 
 to changed environmental conditions, wherein one proc- 
 ess may be lengthened, another shortened. So too the 
 changes from one stage to another may occur with sur- 
 prising abruptness. As a rule, it may be said the larval 
 stage is of longest duration in (I) the Cyclostomes, and 
 thence diminished in length in (II) Sharks, (III) Lung- 
 fishes, (IV) Ganoids, and (V) Teleosts ; in the last-named 
 group, a very much curtailed (i.e. precocious) larval life 
 many often occur. 
 
 I. Larval Cyclostomes 
 
 The Cyclostome larva is represented in a stage as 
 early as that of Fig. 212 : its form is here retort-shaped ; 
 the yolk material is concentrated in the ventral region 
 immediately in front of the blastopore (the anus ?), but 
 is distributed in addition in the cells of other body regions. 
 In the section of a slightly older larva (Fig. 215), in which 
 the mouth is all but established, the form outline has 
 become regular, the bulk of the yolk, Y, restricted to the 
 
LARVAL SHARKS 
 
 215 
 
 cavity of the intestine, the only instance of this condition 
 known among fishes (Ceratodus ?), and, with but a single 
 exception (Ichthyophis),* among all other vertebrates. 
 The larval lamprey is by this time a quarter of an inch 
 long, yellowish white in colour ; its movements are slug- 
 gish, rarely more than to cause it to wriggle worm-like 
 from the bottom. A few weeks later it has acquired its 
 brownish grey colour, its fin fold is well marked, and its 
 habit is active ; it now feeds on muddy ooze rich in 
 organic matter. It 'by this time possesses the essential 
 characters of the well-grown larva, long looked upon 
 as a distinct genus, Ammoccetes. In its larval stage the 
 lamprey appears to live a number of years ; in Petromyzon 
 planeri the adult stage is said to be sometimes deferred 
 until the autumn of the fourth or fifth year. The trans- 
 formation is then a surprisingly sudden one ; the head 
 .attains its enlarged size, the mouth its ring-like and suc- 
 torial character, losing its more anterior position, and its 
 lip-like flaps (cf. Fig. 72, C, D) ; teeth are developed in place 
 of the numerous mouth papillae ; gills, formerly simpler 
 in character, opening directly from neck surface to gullet, 
 now enter the branchial chamber, a ventral diverticulum 
 of the gullet ; eyes become prominent, complete their 
 development, and attain the head surface ; unpaired fin, 
 formerly of great extent, is now reduced to its adult 
 position and proportions. 
 
 II. Larval Sharks 
 
 The larval history of Sharks has been summarized in 
 Figs. 284-289 : the younger of these stages (Figs. 284, 
 285, 286) have not as yet escaped from their egg mem- 
 branes. The hatching, in fact, of the young shark is 
 
 * The writer has not confirmed Salensky's observation upon the sturgeon. 
 
FIG. 284. 
 
 287 
 
 Figs. 284-289. Larval sharks. (Figs. 284-287 after BALFOUR.) 284. Pristiurus 
 (embryo, X 5) with yolk sac (X 2). 285, 286. Larvae of Scy Ilium. X 4. 287. Ventral 
 view of head of larval Scy Ilium, slightly younger than that of last figure. X 8. 288. Larva 
 of Acanthias. x 4. 289. Late larva of Acanthias. X |. 
 
 G. Gills. GS. Gill slits. PP. Pectoral fin. SP. Spiracle. Y. Yolk sac. VS. Stalk 
 of yolk sac. 
 
 216 
 
LARVAL SHARKS 2 I/ 
 
 an exceedingly slow one ; Pristiurus emerges from the 
 egg in about nine months, Scyllium in about seven. And 
 in consequence of the large amount of yolk stored in 
 the yolk sac, the young shark, as in Fig. 289, has fully 
 acquired its adult outward characters by the time the yolk 
 is exhausted and its sac absorbed. 
 
 In Fig. 284 is figured a stage in the development of 
 Pristiurus which may be regarded as either embryonic 
 or larval ; the form of the larva is well established ; gill 
 clefts, muscle-plates, mouth, and sense organs are present ; 
 but, on the other hand, unpaired fin and anus are lacking. 
 There is shown the abrupt constriction, characteristic of 
 Elasmobranchs, which separates the animal from the yolk 
 sac, a construction which in later stages becomes narrow 
 and tubular. The relatively larger size of the yolk sac 
 in later stages is, of course, the result of the bulkier elabo- 
 ration of the yolk material. 
 
 The youngest stage (Fig. 284) shows prominently the 
 great enlargement of the anterior end of the embryo, a 
 marked cephalic flexure, large optic capsule, and irregular 
 gill slits of graded sizes ; a tubular tail end, bulbous at 
 the terminal, where the neurenteric canal occurs ; as yet 
 the nasal pits are in close proximity to the mouth. In the 
 next stage (Fig. 285), the elongated trunk has its unpaired 
 fin, the neurenteric canal disappearing; the beginnings 
 of the pectoral fins are noticeable ; gill clefts are of more 
 uniform size ; and the anal region is indicated. In the 
 stage of Fig. 286, further advances are seen in the con- 
 stricting off of the unpaired fins, the appearance of the 
 ventral and the continued growth of the pectoral fins ; 
 in the reduced foremost gill slit (spiracle) ; in the jaw 
 region, and, in fact, in the entire shaping of the head ; 
 in the appearance of the lateral line. In the ventral head 
 
2I 3 LARVAL DEVELOPMENT 
 
 region (Fig. 287), is to be noted the prominence of the 
 mouth cavity, and the enlarged gill arches, showing by 
 this time the outbudding branchial filaments. In the 
 stage of Fig. 288, the larva begins to appear shark-like ; 
 the fins are longer and more noticeable, the anus has 
 appeared, and the branchial filaments by continued growth 
 protrude at all gill openings. The external gills thus 
 acquired are seen in a later stage (Fig. 289) to have 
 disappeared ; they have aided, however, as Beard, Turner, 
 and others have shown, in absorbing nutriment, and must 
 be looked upon as an especial organ of the larval life of 
 the animal. Fig. 289 illustrates a final larval stage : in it 
 there appear all of the structures of the adult outward form, 
 e.g. shagreen, fin spines, nictitating membrane, anterior 
 and posterior nasal openings. This larva has been esti- 
 mated to be about a year older than that of Fig. 284. 
 
 III. Larval Lung-fish 
 
 The larval history of the lung-fish, Ceratodus, as recently 
 described by Semon, seems to offer characters of excep- 
 tional interest, uniting features of Ganoids with those of 
 Cyclostomes and Amphibians. 
 
 The newly hatched Ceratodus (Fig. 290) does not 
 strikingly resemble the early larva of shark (Fig. 284). 
 No yolk sac occurs, and the distribution of the yolk 
 material in the ventral and especially the hinder ventral 
 region is suggestive rather of lamprey or amphibian ; it 
 is, in fact, as though the quantum of yolk material had 
 been so reduced that the body form had not been con- 
 stricted off from it. The caudal tip in this stage appears, 
 however, to resemble that of the shark, and as far as can 
 be inferred from surface views a neurenteric canal persists. 
 Like the shark there then exists no unpaired fin ; the 
 
FJG. 290 
 
 291 
 
 PS M 
 
 Figs. 290-295. Larval lung-fishes, Ceratodus. (After SEMON.) X 6. 290. 
 Embryo at about the time of hatching. 291. Young larva. 292. Larva of two weeks. 
 293. Larva of four weeks, ventral side. 294. Larva of six weeks. 295. Larva of ten 
 weeks. 
 
 A. Anus. A U. Auditory vesicle. E G. External gills. GS. Gill slits. H. Heart. 
 M. Central nervous system. MC. Mucous canals. O. Opercular flap. OL. Olfac- 
 tory organ. PF. Pectoral fin. PN. Pronephros. PS. Primitive segments. S. Mouth 
 pit, stomodaeum. 
 
 2I 9 
 
22O DEVELOPMENT OF FISHES 
 
 gill slits, five (?), GS, are well separated, and there is an 
 abrupt cephalic flexure. In this stage pronephros and 
 primitive segments, PS, are well marked, and are out- 
 wardly similar to those structures in Ganoid ; the mouth, 
 S, is on the point of forming its connection with the 
 digestive cavity ; the anus is the persistent blastopore ; 
 the heart, well established, takes a position, as in Cyclo- 
 stomes, immediately in front of the yolk material. 
 
 In a later stage the unpaired fin has become perfectly 
 established, the tail increasing in length ; the gill slits 
 have now been almost entirely concealed by a surrounding 
 dermal outgrowth, the embryonic operculum ; a trace of 
 the pectoral fin, PF, appears ; the lateral line is seen pro- 
 ceeding down the side of the body ; near the anal region 
 the intestine* becomes narrower and the beginnings of 
 the spiral valve appear. In a larva of two weeks (Fig. 292), 
 a number of developmental advances are noticed : the fish 
 has become opaque, the primitive segments are no longer 
 seen; the size of the yolk mass is reduced; the anal fin 
 fold appears; sensory canals are prominent in the head 
 region ; lateral line is completely established ; the rectum 
 becomes narrowed ; and the cycloidal body scales are already 
 outlined. Gill filaments may still be seen beyond the rim of 
 the outgrowing operculum. In the ventral view of a some- 
 what later larva (Fig. 293), the following structures are to 
 be noted : the pectoral fins which have now suddenly budded 
 out,f reminding one in their late appearance of the mode of 
 
 * The yolk appears to be contained in the digestive cavity as in Ichthy- 
 ophis and lamprey. 
 
 f The abbreviated mode of development of the fins is most interesting ; 
 from the earliest stage they assume outwardly the archipterygial form ; the re- 
 tarded development of the limbs seems curiously amphibian-like ; the pec- 
 torals do not properly appear until about the third week, the ventrals not until 
 after the tenth. 
 
LARVAL GANOIDS 221 
 
 origin of the anterior extremity of urodele ; the greatly en- 
 larged size of the opercular flap ; external gills, still promi- 
 nent ; the internal nares, OL, becoming constricted off into 
 the mouth cavity by the dermal fold of the anterior lip (as 
 in some sharks) ; and finally (as in Protopterus and some 
 batrachian larvae) the one-sided position of the anus. 
 
 The larva of six weeks (Fig. 294) suggests the outline 
 of the mature fish ; head and sides show the various open- 
 ings of the tubules of the insunken sensory canals ; and 
 the ' archipterygium ' of the pectoral fin is well defined. 
 The oldest larva figured (Fig. 295) is ten weeks old ; its 
 operculum and pectoral fin show an increased size ; the 
 tubular mucous openings, becoming finely subdivided, are 
 no longer noticeable ; and although the basal supports of 
 the remaining fins are coming to be established, there is 
 as yet little more than a trace of the ventrals. 
 
 IV. Larval Ganoids 
 
 The larval forms of a Ganoid, Acipenser (Figs. 296- 
 302), resemble far more closely those of the shark than of 
 the lung-fish. When newly hatched, the young sturgeon 
 (Figs. 296, 297) is attached to the well-rounded yolk sac 
 situated in the throat region, in exactly the position one 
 would expect the yolk stalk to be situated if the yolk mass 
 were larger ; it resembles the shark larva of Fig. 295 in 
 its unpaired fin, in gill slits, in olfactory, OL, optic, OP y 
 and auditory, A U, organs, and in the fact that it possesses 
 even at this stage a trace of the neurenteric canal ; on the 
 other hand, it suggests the Ceratodus larva of Fig. 291 in 
 its stout trunk region, prominent muscle segments, pro- 
 nephros, PN, and anus, A ; at the foremost corner of the 
 yolk sac are mouth pit (stomodamm, S) and heart. A 
 larva of the second day resembles in many features the 
 
298 
 
 300 
 
 301 
 
 Figs. 296-302. Larval sturgeons. (All but Fig. 302 after KUPFFER.) Fig. 299, X 18 ; 
 296-300, X 10 ; 301, X8; 302, X 5. (Enlargement approximate.) 296, 297. Larvae 
 shortly after hatching. 298. Larva two days old. 299. Mouth region of larva of third 
 day. 300. Larva of fourth day. 301. Larva of twenty-eight days. 302. Sturgeon ol 
 twelve months. 
 
 A. Anus. AU. Auditory vesicle. B. Barbel. GS, Gill slit. H. Heart. OL. Ol- 
 factory pit. OP. Optic vesicle. PF. Pectoral fin. PN. Pronephros. S. Mouth pit. 
 SP. Spiracle. 
 
 222 
 
LARVAL TELEOSTS 223 
 
 shark larva of Fig. 286: dorsal, caudal, and anal regions are 
 outlined in the unpaired fin ; a pectoral fin of a fin-fold 
 character, PF, has appeared; the spiracle, SP, is becom- 
 ing established. The mouth region is more clearly indi- 
 cated in this stage, S, but may better be seen in ventral 
 view in a slightly later larva ; here (Fig. 299) the posterior 
 lip is constricted off from the yolk region, and the anterior 
 lip is budding off near the median line a pair of the tactile 
 barbels ; the dermal fold (operculum) enclosing the gills 
 is in a condition very similar to that of Ceratodus in 
 Fig. 293. A larva of the fourth day (Fig. 300) shows 
 well-marked advances : the snout is elongated ; the opercle 
 is enclosing the gills, which are now seen to protrude as 
 external branchial ; the pectoral fin elongates and is tend- 
 ing to protrude its fin axis; body segments and heart are 
 encroaching into the region of the now elongate yolk sac ; 
 the lateral line has been formed. In a larva of four weeks 
 (Fig. 301), the essential outlines of the sturgeon may be 
 recognized, although the head appears of strikingly larger 
 proportions : barbels, nares, mouth, operculum, and spiracle 
 are as in the adult ; fins, of the mature outlines, are want- 
 ing in all save basal supports ; yolk material has long since 
 been exhausted, A very late larva (Fig. 302), supposed to 
 be twelve months old, differs outwardly from the sexually 
 mature form in but its colouring and dermal plates : those 
 of the regular rows are of great size, conspicuous in their 
 abrupt spines and well-roughened borders ; and those of the 
 remaining trunk integument are remarkably prominent ; the 
 tail of the larva shows clearly its palaeoniscoid character. 
 
 V. Larval Teleosts 
 
 The metamorphoses of the newly hatched Teleost 
 must finally be reviewed ; they are certainly the most 
 
CH M 
 
 309 
 
 Figs. 303-309. Larvae of Teleost, Ctenolabrus. (After A. AGASSIZ.) Fig. 
 309 X about 7, other figures X about 14. 303. Larva shortly after hatching. 304, 
 305. Larvae of first few days. 306, 307. Larva of one week. 308. Larva of two 
 weeks (?). 309. Final larval stage, four (?) weeks. 
 
 A. Anus. A U. Auditory vesicle. CH. Notochord. GR. Gill protecting der- 
 mal rays. H. Heart. M. Central nervous system. OL. Olfactory capsule. OP. 
 Optic vesicle. PF. Pectoral fin. -S. Stomodaeum. 
 
 224 
 
LARVAL TELEOSTS 2 2$ 
 
 varied and striking of all larval fishes, and, singularly 
 enough, appear to be crowded into the briefest space of 
 time ; the young fish, hatched often as early as on the 
 fourth day, is then of the most immature character; it 
 is transparent, delicate, inactive, easily injured ; within 
 a month, however, it may have assumed almost every 
 detail of its mature form. A form hatching three mille- 
 metres in length may acquire the adult form before it 
 becomes much longer than a centimetre. 
 
 The larval life of the common Sea-bream, or Gunner, 
 Ctenolabrus cceruleus, has been admirably figured by A. 
 Agassiz. The newly hatched fish (Fig. 303) has the yolk 
 sac appended at the throat, as a large, transparent, if 
 slightly tinted, globule ; save for its great delicacy and 
 transparency, it may generally be compared to the corre- 
 sponding larva of Acipenser (Fig. 296). By the third day 
 (Fig. 304), the yolk sac has become greatly reduced, the 
 trunk elongated, the fin fold less conspicuous ; primitive 
 segments have appeared ; the pectoral fin has arisen, but 
 is not of the elasmobranch form of the similar stage (Fig. 
 298) of sturgeon ; it is long, thin, transparent, and its 
 rapid growth indicates its metamorphosed character. The 
 mouth, S, is in this stage on the point of formation. In 
 a slightly older larva (Fig. 305), the yolk has almost dis- 
 appeared ; its gill slits, GS, and mouth have now been 
 formed, and with the latter the nasal apertures. In a fol- 
 lowing stage (Figs. 306, 307), a well-marked opercular fold 
 makes its appearance ; pectoral fins acquire their com- 
 pleted outline and the fin fold undergoes changes : ante- 
 riorly it acquires supporting actinotrichia, posteriorly the 
 dermal supports of the caudal fin appear and at their bases 
 the coalesced radio-basal s ; a ganoidean heterocercy is 
 here apparent, its distal tip the membranous opisthure, O. 
 
226 LARVAL TELEOSTS 
 
 The later larva (Fig. 308) is characterized by the appear- 
 ance of abundant pigment masses (not shown in the 
 figure) in all regions of the trunk; branchiostegal rays, 
 GR, and traces of pelvic fins are noted ; the caudal fin 
 has become separated from the dorsal and anal elements. 
 And finally, in the stage of Fig. 309, the fish, although 
 still of very small size, has acquired almost perfectly its 
 mature features ; the outward differences are only those 
 of pigmentation and fin proportions. 
 
LIST OF DERIVATIONS OF PROPER NAMES 
 
 Acanthodes, d/cavflwS^s, provided with spines. 
 Acanthopterygii, aKavQa, spine, 7rrepv, fin(ned). 
 Acipenser, d/aTnycrios, classic name of sturgeon. 
 Actinopterygii, d/ms, stout ray, 7rrepv, fin(ned). 
 Alopias, dAwTre/a'as, classic name of the fox shark. 
 Amia, d/xca, classic name of tunny( ?) . 
 Amiurus, d/xta, Amia, ovpd, tail(ed). 
 Ammocoetes, d/x/xos, sand, KOLTTTJ, (a bed) abider. 
 Anacanthini, dvd, without, aKav0a, spine. 
 Anguilla, classic name of eel. 
 Arthrodira, apOpov, joint, (?)oYs, double. 
 Aspidorhynchus, doWs, shield, pvyxs? snout. 
 
 Bdellostoma, /JSe'AAa, leech, (rro/xa, mouth. 
 
 Belonorhynchus, j3e\6vrj, classic name of gar-fish, pvyx o? > snout. 
 
 Calamoichthys, calamus, a reed, tx^, fish. 
 
 Callichthys, KaAAos, beautiful, tx^us, fish. 
 
 Callorhynchus, KoAAos, beautiful, pvyx o? ' snout. 
 
 Carassius, xP a > classic name of (sea)fish. 
 
 Caturus, Kara, on the under side, ovpd, tail. 
 
 Cephalaspis, /ce^>aA^, head, doTris, shield. 
 
 Ceratodus, Kepas, horn, dSow, tooth (ed). 
 
 Cestracion, KeWpa, classic name of (pavement-toothed) sea-fish. 
 
 Cheirodus, x et 'p hand, o8ovs, tooth (ed). 
 
 Chimaera, xfyuupaj fabulous monster, lion's head, goat's body, dragon's 
 
 tail. 
 
 Chlamydoselactrf*xAa/>i-u8os, frilled, treAdx^, shark. 
 Chondrostei, xw8pos, cartilage, otrreov, bone(d). 
 Cladoselache, for Cladodonto-selache, /cAdSos, branch, oSovs, tooth (ed), 
 
 aeAdx^ shark. 
 Climatius, /cAi]ua, a gradation (in allusion, perhaps, to the graded row 
 
 of fin spines). 
 
 227 
 
22g FISHES, LIVING AND FOSSIL 
 
 Coccosteus, KO'KKOS, rough like a berry, ocrre'ov, bone. 
 Ccelacanthus, KotAos, hollow, aKavOa, spine (d). 
 Crossopterygii, /cpocro-os, fringe or tassel, 7rrepv, fin. 
 Ctenodus, KTCIS (KTVOS), comb, oSovs, tooth(ed). 
 Cyclostomata, KwXos, circular, oro/Aa, mouth. 
 
 Dinichthys, Savos, terrible, i'x0u's, fi sh. 
 Diplognathus, SiTrAds, double (pointed), yvaflos, jaw. 
 Diplurus, SiTrAds, double, ovpd, tail(ed). 
 Dipnoi, Sipvoos, double breathing. 
 Dipterus, Sis, two, Trrepov, fin(ned). 
 
 Edestus, eSeorifc, a devourer. 
 
 Elasmobranchii, eAaoyxos, strap-like, ftpayx^ gill(ed). 
 
 Elonichthys, (?)eA.vo>, to twist, ix^? fisn - 
 
 Erythrinus, ept^pos, red-coloured. 
 
 Eurynotus, evpvs, wide, VWTOS, back(ed). 
 
 Eusthenopteron, ew^ev^s, strong, TrrepoV, fin. 
 
 Fierasfer, derivation of Cuvier uncertain, perhaps from proper name. 
 
 Gadus, classic name of cod. 
 Ganoid, yavos, enamelled. 
 Gnathostome, yvdOos, jaw, o-ro/xa, mouth. 
 
 Gyroptychius, yOpos, a circle, 7rrux>? folded (referring to the tooth 
 enamel). 
 
 Harriotta, from the proper name Harriott. 
 
 Hemitripterus, hemi, half, rpeis, three, Trrepw, fin(ned). 
 
 Heptanchus, eTrra, seven, ayx^ (referring to the compressed gill 
 
 openings). 
 
 Hippocampus, classic name, " sea-horse." 
 Holocephali, oAos, whole or complete, Ke<aA^, head. 
 Holoptychius, oAos, entire(ly), TTTV^OS, folded (referring to the tooth 
 
 enamel). 
 
 Hybodus, v/?os, hump, oSous, tooth. 
 Hyperoartia, vTrepwa, palate, aprtos, entire. 
 Hyperotretia, vTrepwa, palate, rperos, pierced. 
 
 Ichthyotomi, t'x^us, fish, re/xvco, separate (referring perhaps to the 
 
 distinctness of this group) . 
 Ischyodus, I<TXU'S, power(ful), oSovs, tooth(ed). 
 
DERIVATION OF NAMES 22Q 
 
 Laemargus, classic name of a shark. 
 
 Lagocephalus, Xeryws, rabbit, /ce^aX*/, head. 
 
 Lamna, Xaftvo, classic name for a shark. 
 
 Lepidosiren, XtTri's, scale (d), siren, salamander. 
 
 Lepidosteus, Xris, scale, oore'ov, bone. 
 
 Leptolepis, XCTTTOS, smooth or delicate, A.OUS, scale (d). 
 
 Lophobranchii, Xo<os, tuft, J3pa.y\iov, gill(ed). 
 
 Marsipobranchii, fjapa-Linov, pouch, ftpa.y\iai, gills. 
 
 Megalurus, /Aey a? ? l ar g e > oupo, tail(ed). 
 
 Microdon, fUKpos, small, oSovs, tooth (ed). 
 
 Mormyrus, classic name of a (sea) fish ( from //.op/xvpo), I murmur). 
 
 Myliobatis, /xvXwxs, pavement (toothed), /3art5, skate. 
 
 Myiostoma, /xvXos, mill(like), OTO/UUX, mouth. 
 
 Myriacanthus, /xvpwis, ten thousand, axav^a, spine. 
 
 Myxine, /xv^tvos, slimy-fish. 
 
 Onychodus, ow^, claw; oSovs, tooth (ed). 
 Ophidium, o<^>t'8tov, a snake. 
 Osteolepis, ooWov, bone, ACTTI'?, scale (d). 
 Ostracoderm, oo-rpaKiov, shell, 8e'p/xa, skin. 
 
 Palaeaspis, TroXatos, ancient, a(T7ri?, shield. 
 
 Palaeoniscus, TroAatos, ancient, OI/IO-KOS, a sea-fish. 
 
 Palaeospondylus, TroAato?, ancient, <77roV8vAos, vertebrae. 
 
 Parexus, ? Trape^w, have as one's own (referring to the peculiar nature 
 
 of the fish?). 
 
 Perca, classic name offish. 
 Petromyzon, TreVpos, stone, /xvao>, to suck. 
 
 Phaneropleuron, <^>avepos, well marked, TrAevpo, side (fins) or ribs(?). 
 Pisces, fishes. 
 
 Plagiostomi, TrAayios, transverse, OTO/AO, mouth. 
 Plectognathi, TrXexTo?, twisted, yvdOos, jaw. 
 Pleuracanthus, TrXevpa, side, a/cav^a, spine. 
 Pleuropterygii, TrXevpa, side, Trrepv^, fin(ned). 
 Pogonias, Trwywvta?, bearded. 
 Polyodon, TroXvs, many, oSwv, tooth(ed). 
 Polypterus, TroXvs, many, Trrepov, fin(ned). 
 Prionotus, TrptW, saw, vturos, back. 
 Pristiophorus, vpurns, a saw, ^>optu, to carry. 
 Pristis, TrpiVrts, a saw-fish. 
 Protopterus, Trpoiros, ancient, Trrepov, fin(ned). 
 
230 FISHES, LIVING AND FOSSIL 
 
 Psammodus, ^a/A/xos, sand, o8ovs, tooth (ed). 
 Psephurus, t/o^os, a little stone, ovpa, tail. 
 
 Pseudopleuronectes, i/^vSos, false, TrAevpw, side, vrJKrrjs, swimmer. 
 Pterichthys, Trrepv^, fin or wing, ix^^> ^ s ^' 
 
 Raja, classic name of skate. 
 
 Rhabdolepis, pa/3Sos, nail, AcVis, scale (d). 
 
 Rhina, ptvrj, a rasp. 
 
 Rhinobatus, ptVa, Rhina, /fori's, skate. 
 
 Rhynchodus, pvyx 0< *i sn out, oSov's, tooth (ed). 
 
 Scaphirhynchus, <7Ka<iW, shovel, 
 Scomberomorus, (r/co/x^pos, mackerel, /u,opiov, part. 
 Scyllium, crKvAtoi/, classic name of this shark. 
 Selachii, o-eAa^ry, shark. 
 Semionotus, o-^etoj/, a standard, VWTO?, back. 
 Silurus, classic name of fish. 
 Siphostoma, (n'^on/, tube, o-ro/xa, mouth. 
 Sirenoidei, siren, salamander, oTSos, like. 
 Squaloraja, squalus, shark, r<27, skate. 
 Squalus, classic name of a shark. 
 Squatina, a classic name of a sea-fish. 
 
 Teleocephali, reAeos, entirely, oo-re'oi/, bone, Ke<aA?j, head. 
 
 Teleost, reAeos, entirely, oareov, bone. 
 
 Teleostomi, re'Aeos, entirely, oo-reW, bone, oro/m, mouth. 
 
 Titanichthys, /////, giant, IxOvs, fish. 
 
 Torpedo, classic name (from the root of Torpor, stupefy) . 
 
 Trachosteus, rpa^'s, rough, ocrre'oi/, bone. 
 
 Trygon, rpvywv, the thorny ray. 
 
 Urogymnus, ovpd, tail, yv/xvos, naked. 
 Xenacanthus, eVos, strange, aKavOa, spine. 
 
BIBLIOGRAPHY 
 
 IN the following list the writer aims to present the more recent and 
 more important works relating to the general subject of fishes. Titles 
 have been classified, and most of the references give more or less com- 
 plete bibliographies of their special subjects. Of the journals in which 
 papers occur the principal abbreviations are as follows : 
 
 Q.J.M.S Quarterly Journal of 
 Microscopical Science. 
 
 P . Proceedings. 
 
 R. . . Report. 
 
 S . . . Society. 
 
 SB . . Sitzungsberichte. 
 
 Sci . . Science, or Scientific. 
 
 Tr. . . Transactions. 
 
 U.S.F.C United States Fishery 
 Commission. 
 
 VH . . Verhandlungen. 
 
 Z . . Zeitschrift. 
 
 A ... Archiv (or Archives) . 
 
 AH . . Abhandlungen. 
 
 Ann. N.H Annals and Magazine 
 of Natural History. 
 
 B . . . Bulletin. 
 
 C.R . . Contes rendus. 
 
 DS. . . Denkschriften. 
 
 J Journal 
 
 JB . . . Jahrbuch 
 
 JH . . . Jahreshefte 
 
 J.R.M.S . Journal of the Royal Mi- 
 croscopical Society. 
 
 MT . . Mittheilungen 
 
 The Roman numerals denote the number of the volume, the Arabic 
 numerals the pages. 
 
 WORKS ON THE GENERAL SUBJECT, FISHES 
 
 WOODWARD, A. SMITH Catalogue of Fossil Fishes in the British 
 Museum. Vols. I, II (and III). 
 
 London, i889~(95). 
 
 GUXTHER, A. ... Catalogue of the Fishes in the British 
 
 Museum. Vols. I-VIII. London, 1859-70. 
 
 GUXTHER, A. ... An Introduction to the Study of Fishes. 8vo. 
 
 pp. 720. Illustrated. Edinburgh, 1880. 
 
 GUXTHER, A. ... Fishes : Challenger Reports. Vol. I, pt. 
 VI, Vol. XXXI, pt. LXXVIII. 
 
 London, 1880-89. 
 
 GILL, T Fishes : Standard Natural History. 
 
 Boston, 1885. 
 231 
 
232 FISHES, LIVING AND FOSSIL 
 
 GOODE, G. BROWN . . Fishery Industries of U. S. U. S. F. C. 
 
 Washington, 1884. 
 
 DUMERIL, A Histoire naturelle des Poissons. Vols. 
 
 I-II (Sharks, Chimaeroids, Lung-fishes, 
 Ganoids, Lophobranchs). Paris, 1890. 
 
 AGASSIZ, L Recherches sur les Poissons Fossiles. Vols. 
 
 I-V, with Atlas volumes. 
 
 Neuchatel, 1833-43. 
 ZITTEL, K. v. ... Handbuch der Palaeontologie. Fische. 
 
 Munich, 1887. 
 ROLLESTON, G. . . . Forms of Animal Life. Second edition. 
 
 Oxford, 1888. 
 
 HUXLEY, T Manual of the Comparative Anatomy of 
 
 Vertebrated Animals. New York, 1872. 
 
 JORDAN and GUILBERT Manual of the Vertebrates of Eastern N. A. 
 McClurg. Last edition. 
 
 SKELETON. '86 BAUR, G., Squamosum, Anat. Anz. '87 Ribs, 
 Am. Nat. xxi, 942-945. '86 COPE, E. D., Caudal vertebrae, Am. 
 Phil. Soc. 243. '93 BOULENGER, G. A., Haemapophyses, Ann. 
 N.H. xii, 60-61. '92 DOLLO, L., Ribs, vertebrae, B. Sci. Fr. Belg. 
 xxiv. '87 GEGENBAUR, Occipital region, Kolliker Festschr. 1-33. 
 '79 GOETTE, A., Wirbelsaule, A. mikr. Anat. xvi, 428. '89 HAT- 
 SCHEK, Rippen, VH. Anat. Gesell. Berl. (Jena). '78 IHERING, 
 H., Wirbelverdoppelung, Zool. Anz. I, 72-74. '93 JORDAN, D. S., 
 Temperature and vertebras, Wilder Quarter Century Book, Ithaca, 
 !3-37- ' 93 KLAATSCH, H. (Vertebrae), Morph. JB. xix, 649- 
 680, and xx, 143-186. '68 KLEIN, Schadel, Wiirt. Nat. JH. 71- 
 171, and ('81) xxxvii, 326-360. '87 LUOFF, B. (Chorda and 
 Sheath), B. S. Mosc. 227-342 (442-482, German). '77 PARKER 
 and BETTANY, Morph. of the Skull, London, pp. 14-90. '89 
 POUCHET and BEAUREGARD, Traite de Osteol. Comp. Paris, 
 398-451. '87 STRECKER, C. (Condyles), A. Anat. Phys. Anat. 
 Abth. 301-338. 
 
 INTEGUMENT, TEETH. '92 AGASSIZ, A., Chromatophores, B. 
 Mus. Comp. Zool. xxiii, 189-193. '82 BAUME, A., Odont. Forsch. 
 Leip. 41-52. '77 HERTWIG, O., Hautskelet, Morph. JB. II, 
 328-395, and v ('79), 1-21. '90 KLAATSCH, H., Schuppen, op. 
 cit., 97-202 and 209-258. '45 OWEN, Odontography, London. 
 '93 RYDER, J. A., Mechanical genesis of Scales, Ann. N. H., xi, 
 243-248. '82 TOMES, C., Dental Anat. Ed. 2. 
 
BIBLIOGRAPHY: FISHES 
 
 233 
 
 FINS. '90 COPE, Homologies, Am. Nat. 401-423. '79 DAVIDOFF, 
 M., Pelvics, Morph. JB. v, 450-520, vi ('80), 125-128, 433-468. 
 '87 EMERY, C, Homologies, Zool. Anz. x, 185-189. '65 GEGEX- 
 BAUR, C., Brust Flosse, Leip. 4to, pp. 176. '7O Jen. Z., v, and 
 ('73) Archipterygium, vii. '79 Morph. JB., v, 521-525. 
 '94 Op. cit. xxi, 119-160. '89 HATSCHEK (Paired), VH. Anat. 
 Gesell. Berl. 82-90. '68 PARKER, W. K., Shoulder girdlej Ray 
 Society, Lond. pp. 237. '83 RAUTENFELD, E. V., Ventrals, Dor- 
 pat ('82), 48 pp. '79 RYDER, J. A., Bilateral symmetry, Am. Nat. 
 xiii, 41-43. '85 Unpaired fins, op. cit. xix, 90-97. '86 Em- 
 bryol. of fins, R. U. S. F. C., 981-1086. '86 Fin rays and degen- 
 eration, P. U. S. Nat. Mus. 71-82. '87 Homologies, P. Acad. 
 Philadel. 344-368. '77 THACHER, J., Homologies, Tr. Conn. 
 Acad. III. '92 WIEDERSHEIM, R., Gliedmassenskelet, Jena, 266 
 pp. '92 WOODWARD, A. S., Evolution, Nat. Sci. 28-35. 
 
 VISCERA, GLANDS, CIRCULATORY. '84 AYERS, H., Pori 
 abdominales, Morph. JB. x, 344-349. '89 Carotids, B. Mus. 
 Comp. Zool. xvii. '82 BALFOUR, F. M., Head kidney, Q. J. M. S. 
 xxx, 12-16. '87 BOAS, J. E. V., Arterienbogen, Morph. JB. xiii, 
 115-118. '79 BRIDGE, T., Pori abdominales, J. Anat. Phys. xiv, 
 81-102. '85 CLELAND, J., Spiracle, R. Br. Ass. 1069. '87 
 EBERTH, C. J., Blutplattchen, Kb'lliker Festschrift, 37-48. '66 
 GEGENBAUR, Bulbus, Jen. Z. ii, 365-375. '84 Abdominal poren, 
 Morph. JB. x, 462-464. '91 Conus, op. cit. xvii, 596, 610. '85 
 GROSGLIK, S., Kopfniere, Zool. Anz. viii, 605-611. '90 HOWES, 
 G. B., Intestinal canal and blood supply, J. Linn. S. xxiii, 381-410. 
 '64 HYRTL, J. (Hepatic and portal), SB. Acad. Wiss. Wien, 
 167-175. '85 PHISALIX, C., Rate, Paris, 8vo. '90 ROSE, C., 
 Herz, Morph. JB. xvi, 27-96. '82 SOLGER, B., Niere, A. H. Gesell. 
 Halle, xv, 405-444. '84 WELDOX, W. F. R., Suprarenals, P. 
 Roy. S. xxxvii, 422-425. 
 
 SWIM-BLADDER. '86 ALBRECHT, P., Non-homologie des 
 poumons, Paris and Brux, 44 pp. '8O DAY, F., Zool. 97-104. 
 '66 GOURIET, E., Ann. Sci. Nat. vi, 369-382. '73 HASSE, C., 
 Anat. Studien, I, Heft 4. '90 LIEBREICH, O., A. Anat. Phys. 
 Phys. Suppt. 142-161, 360-363. '85 MORRIS, C., P. Acad. Nat. 
 Sci. Philadel. 124-135, Anat. Anz. ('85) xxvi, 975-986. 
 
 NERVOUS SYSTEM AND END ORGANS. '83 BAUDELOT, E., 
 fol. Paris, 178 pp. '88 BATESOX, Sense organs, J. Mar. Biol. 
 Ass. I, No. 2. '85 BEARD, J., Branchial sense organs, Q. J. M. S. 
 xxvi. '82 BERGER, E. (Eye), Morph. JB. viii, 97-168. '84 
 BLAUE, J. (Nasal membrane), A. Anat. Phys. 331-362. '83 
 
234 
 
 FISHES, LIVING AND FOSSIL 
 
 CANESTRINI, Otoliths, Atti. Soc. Pad. viii, 280-339. '86 Hearing 
 organ, op. cit. ix, 256-282. '91 CHEVREL, R., Sympathetic, 
 These faculte des sciences, Paris. '79 DERCUM. F., Lateral line, 
 P. Acad. Phil. 152-154. '70 FEE, F., Systeme lateral, Mem. S. 
 Sci. Nat. Strasb. vi, 129-201. '73 HASSE, C., Gehororgan, Anat. 
 Stud. I, Heft 3. '88 JULIN, C., Epiphysis, B. Sci. Nord. x, 55-65. 
 '90 ? KOKEN, E., Otoliths, Z. geol. Gesell. xliii, 154. '91 
 OWSJANNIKOW, P. (Pineal eye), Rev. S. Nat. St. Petersb. 
 loo-ui. '81 RETZIUS, G., Gehororgan, Stockholm, fol. 222 pp. 
 '71 SCHULTZE, F. E., Seitenlinie, A. mikr. Anat. vi, 62. '70 
 STIEDA, L., Centralnervensystem, Z. wiss. Zool. xxi, 273-456. 
 EMBRYOLOGY. '85 HAACKE, W., Uterinaler Brutpflege, Zool. 
 Anz. viii, 488-490. HALBERTSMA, H. J., Normal en abnormal 
 Hermaphroditismus, Tijd. Nied. Dier. Ver. Amst. '87 HOCH- 
 STETTER, F., Venensystem, Morph. JB. xiii, 119-172. '86 HOFF- 
 MAN, C. K., Urogenital, Z. wiss. Zool. xliv, 570-643. '91 KUPFFER, 
 C. v., Kopfniere, VH. Anat. Gesell. 22-55. ' 90 LAGUESSE, E., 
 Rate, J. de 1'Anat. Phys. xxvi, 345-406 and 425-495. '77 
 LANKESTER, E. RAY. Germ layers, Q. J. M. S. xvii. '93 LWOFF, B., 
 Keimblatterbildung, Biol. Centralb. xiii, 40-50, 76-81. '79 MAR- 
 TENS, E. V., Hermaphroditische Fische, Naturf. 116. '80 Nuss> 
 BAUM, M., DhTerenzirung d. Geschlechts, A. mikr. Anat. xviii, 
 1-121. '89 SCHWARZ, D., Schwanzende, Z. wiss. Zool. xlix, 
 191-223. '92 VIRCHOW, H., Dotterorgan, Z. wiss. Zool. liii, 
 Suppl. 161-206. 
 
 THE CYCLOSTOMES 
 
 GENERAL. '93 AYERS, H., Bdellostoma, Woods Holl Lectures, 
 125-161. '92 BEARD, J., Lampreys and Hags, Anat. Anz. viii, 
 59-60. '91 BUJOR, P., La metamorphose de rAmmocoetes, Rev. 
 Biol. du Nord de la France, iii, pp. 97. '93 GAGE, Lake and 
 Brook Lampreys, Wilder Quarter Century Book, Ithaca, 421-493. 
 '91 HOWES, G. B., Lamprey's affinities and relationships, P. 
 Tr. Liverpool Biol. Soc. vi, 122-147. ' 89 JULIN, C., Morphologic 
 de PAmmocrete, B. Sci. France et Beige, 281-282. '90 KAENSCHE, 
 C. C., Metamorphose des Ammoccetes, Schneider's Zool. Beitrage, 
 II, 219-250. 
 
 ANATOMY, GENERAL. '86 CUNNINGHAM, J. T., Critique of 
 Dohrn's views of Cyclostome morphology, Q. J. M. S. xxvii, 265- 
 284. '88 JULIN, C., Anatomic de rAmmocoetes, B. Sci. du Nord 
 de la France, x, 265-295. '75 LANGERHANS, P., Untersuchungen 
 u. Petromyzon, VH. d. n. Gesell. Friburg, XI, Heft 3. '37 
 
BIBLIOGRAPHY: CYCLOSTOMES 235 
 
 MULLER, J., Vergleich. Anat. d. Myxinoiden, AH. K. Akad. Wiss. 
 Berlin, 65-340, 9 pis. '79 SCHNEIDER, A., Beitrage zur vergleich. 
 Anat. 4to, pp. 164, Berlin. 
 
 SKELETON. '92 BURNE, R., Branchial Basket in Myxine, P. ZooL 
 S. 706-708. '69 GEGENBAUR, C., Sketelgewebe, Jen. Z. V. '93 
 HASSE, C, Wirbel. Z. wiss. Zool. 290-305. '76 HUXLEY, T. 
 H., Craniofacial Apparatus, J. Anat. Phys. x, 412-429. ('84) 
 PARKER, W. K., Monograph of Skeleton of Petrom. and 
 Myxine, P. Roy. S., '82, 439-443 and Phil. Tr. Roy. S., '83, 373- 
 457. '78 PEREPELKINE, K., Structure de la Notochorde, B. Mosc. 
 liii, 107-108. '92 RETZIUS, G., Caudalskelet der Myxine, BioL 
 Foren. iii, 81-84. 
 
 MUSCULATURE. '75 FURBRINGER, P., Muskulatur des Kopf- 
 skelets, Jen. Z. ix, N. F. II. '67 GRENACHER, H., Muskulatur, Z. 
 wiss. Zool. xvii. '59 KEFERSTEIN (Histological), Du Bois R's. A. 
 f. Anat. 548. '82 SCHNEIDER, A., u. d. Rectus, Zool. Anz. N. 107, 
 p. 164. '52 STANNIUS, H. (Heart fibres), Z. wiss. Zool. iv, 252. 
 '52 (Histology), L'Institut, xx, 132-134, and Gb'ttin. Nachricht. 
 '51, 225-235. '82 STEINDACHNER, A., u. d. Rectus. Zool. Anz. v, 
 660. 
 
 FINS. '85 CLELAND, J., Tail of Myxine, R. Br. Ass. Adv. Sci. 1069. 
 
 INTEGUMENT, TEETH. '88 BEARD, J., Teeth of Myxinoids, 
 Nature, xxxvii, 499, and Anat. Anz. iii, 169-172. '91 BEHRENS, 
 Hornzahne v. Myxine, Zool. Anz. xiv, 83-87. '82 BLOMFIELD, 
 S. E., Thread, cells of Epidermis of Myx. Q. J. M. S. xxii, 355-361. 
 '76 FOETTINGER, A., Structure de 1'Epiderme, B. Acad. roy. d. 
 Beige, ix, No. 3. '94 JACOBY, M., Hornzahne, A. mikr. Anat. 
 117-148. '60 KOLLIKER, Inhalt d. Schleimsacke d. Epidermis, 
 Wiirzb. naturwiss. Zeitschr. i, i-io. '64 MULLER, H., Epidermis, 
 Wiirzb. naturwiss. Zeitschr. v, 43-53. '89 POGOJEFF, L., Haut, 
 A. mikr. Anat. xxxiv, 106-122. '61 SCHULTZE, M., Kolben- 
 formig Gebilde, A. Anat. u. Phys. 
 
 VISCERA, GLANDS, CIRCULATORY. '46 DUVERNOY, G. L., 
 Sinus veineux genital, C. R. xxii, 662. '76 EWART, T. C., Abdom. 
 pores, J. Anat. and Phys. x. '78 Vascular peribranchial spaces, 
 J. Anat. and Phys. xii, 232-236. '89 GAGE, S. H., Blood, P. Am. 
 S. Micros, x, 77-83, and J. R. M. S. 494. '17 HOME (Gills), Isis, 
 25-35. >93 HOWES, G. B., Abnormal gill clefts in Pet. and Myx. P. 
 Zool. S. 730-733. '87 JULIN, CH. (Two anterior gill slits), B. Acad. 
 Roy. Sci. Brux. xiii, 275-293. '88 Appareil vasculaire, Zool. Anz. 
 xi, 567-568. '94 KERKALDY, J. W., Head-kidney of Myx. Q. J. 
 
2^6 FISHES, LIVING AND FOSSIL 
 
 M. S. 353-359- '90 KLINCKOWSTROM, A., Darm-u. Lebervenen 
 b. Myx. Biol. Foren. 62-67. '93 KUPFFER, C. v., Pankreas, SB. 
 Morph. Gesell. Mun. ix, 37-59. '82 LEGOUIS, P. S., Pancreas, 
 C. R. xcv, 305-308, and Ann. S. Sci. Brux. viii, 187-304. '32 
 MAYER, C., milz. Gror. Nat. xxxiv, 165-166. '76 MEYER, F., 
 Nieren, Centr. f. d. medicin. Wiss. No. 2. '39 MULLER, J., 
 Gefasse: Wundernetze, Monatsheft, Berlin, 184-186, and 272-292. 
 '39 Lymphgefasse, AH. d. Berl. Akad. '73 MULLER, W., 
 Urniere b. Myx. Jen. Z. vii. '75 Urogenital system, AH. d. 
 Ak. d. Wiss. Berl. ix. '21 OKEN, J. (Gills), Isis, 271-272, and 
 '29 VH. Gesell. Natur. Berl. 1, 133-141. ' 4 6 ROBIN, C., Systeme 
 veineux, L'Inst. xiv, 120-123. '87 THOMPSON, D'A. W., Blood, 
 Ann. N. H. xx, 231-233, and Anat. Anz. ii, 630-632. '84 WELDON, 
 W. F., Head-kidney of Bdell. Q. J. M. S. xxiv, 171-182. 
 
 NERVOUS SYSTEM, END ORGANS. '82 AHLBORN, F., Gott- 
 ing. Nachr. 677-682. '83 Z. wiss. Zool. xxxix, 191-294. '84 
 Hirnnerven, Z. wiss. Zool. xl, 286-308. '88-'89 BEARD, J., 
 Parietal eye, Nature, xxxvi, 246-298, and 340-341, also Q. J. M. S. 
 xxix, 55-73. '77 FREUD, S., Nervenwurzeln im Riickenmark, 
 SB. Ak. Wien, Ixxv. '78 Spinalganglien, SB. Ak. Wien, Ixxviii. 
 '78 GOETTE, A., Spinalganglien, A. mikr. Anat. xv, 332-338. 
 '72 HASSE, Auditory organ, Anat. Studien, I, Heft 3, and Ketel, 
 ibid. 489-541. '79 JELENEF, A. (Cerebellum), B. Pdtersb. xxv, 
 333-345. '86 JULIN, C. (Sympathetic), A. Zool. exper. vi, and 
 Anat. Anz. '87, 192-201. '87 Nerfs lateral, B. Acad. R. Brux. 
 xiii, 300-309. '92 KOHL, C., D. Auge v. Pet. u. Myx. Leip. 
 Reudnitz. br. '37 MULLER, J., Gehb'rorgan, Abh. Berl. Acad. 
 '38 Nervensystem d. Myx. Berl. Monatsber, 16-20. '85 NANSEN, 
 F., Aarsber. Berg. Mus. 55-78 (trans, in Ann. N. H. xviii, 
 209-226. '64 OWSJANNIKOW, P., Gehb'r. Me'm. Acad. St. Pe'tersb. 
 viii. '83 (Sympathetic), Arb. Naturf. Gesell. xiv, and '84 B. 
 Acad. St. Petersb. xxviii, 439-448. '88 (Pineal eye), Mem. 
 Acad. St. Petersb. xxxvi. '86 RANSOM, W. and THOMPSON, D'A., 
 Spinal and visceral nerves, Zool. Anz. ix, 421. '80 RETZIUS, 
 G., Riechepithel. A. f. Anat. u. Phys. '90 (Myxine : caudal 
 heart, nerve and sub-cutaneous ganglion cells), Biol. Untersuch. 
 Neue Folge, Stockholm, Fol. '92 Nervenendungen in der Haut, 
 des Pet., op. cit. (2) III, 37-40, and (tail structures), op. cit. iv, 
 36-41. '93 Gehirn-Auge v., Myx. op. cit. v, 27-30. And 
 Geschmacksknospen bei Pet. op. cit., 69-70. '82 ROHON, J. V., 
 Ursprung d. acusticus. SB. Ak. Wien, Ixxxv, 245-267. '84 SAC- 
 CHI, T. (Neuroglia of retina), Arch. Ital. Biol. vi, 76-96. 
 
BIBLIOGRAPHY: CYCLOSTOMES 237 
 
 '80 SCHNEIDER, A., Nerven, Zool. Anz. 330. '71 SCHULTZE, M., 
 Retina, SB. nieder-rhein Gesell. 6 Nov. '79 SELENEFF, A. (Cere- 
 bellum), B. Acad. St. Petersb. xxv, 333-343, and '80 Melanges 
 Biol. St. Petersb. x, 307-325. '88 WHITWELL, J. R., Epiphysis, 
 J. Anat. Phys. xxii, 502-504. '79 WIEDERSHEIM (Brain and 
 nerves), Zool. Anz. 589-592 and '80 in Jen. Z. xiv, 1-24. 
 
 EMBRYOLOGY. 
 
 I. General '88 GOETTE, A., Zool. Anz. xi, 160-163 and ' 90 in AH - 
 3, Entwicklungesch. d. Thiere, 5 Heft. '88 KUPFFER, C. v., SB. 
 bayer. Akad. I, 70-79, and '90 in A. mikr. Anat. xxxv, 469-558. 
 '90 NESTLER, Zool. Anz. xiii. '81 NUEL, J. B., A. d. Biol. i, and 
 '82 ii, 403-454; also J. R. M. S. ii, 26-27. 1<7 OWSJANNIKOW, B. 
 Acad. St. Petersb. xiv, 325 and '89, xxxii, 83-95, and ' 91 Ml. 
 Biol. xiii, 55-67 and B. Acad. St. Petersb. 13-55, and ' 93 Ann - 
 N. H. xi, 30-43. '81 SCOTT, W. B., O. J. M. S. xxi, 146-153, Zool. 
 Anz. ('80) 422, and Morph. JB. vii. Also '82, A. Zool. exper. 
 ix, and (pituitary body and teeth) Science, ii, 184-186, 731-732. 
 Also '88 J. of Morph. i, 253-310. '87 SHIPLEY, A. E., Q. J. M. S. 
 xxvii, 325-370, and A. Zool. expe'r. i. Also Stud. Morph. Lab. 
 Camb. iii. 
 
 II. Ovary ', Sperm, Fertilization. '93 BEARD, J., Testes with ova, 
 Anat. Anz. viii, 59-60. '87 BOHM, A. A., Befruchtung, SB. bayer. 
 Akad. 8 Feb., and A. mikr. Anat. xxxii. '77 CALBERLA, E., 
 Befruchtungsvorgang. Z. wiss. Zool. xxx, 437-486. '87 CUNNING- 
 HAM, T., Ova of Bdell. Tr. Roy. S. Edinb. xxx, 247-250, (Myxine) 
 Zool. Anz. 390-392, and Q. J. M. S. xxvii, 49-76. '91 Sper- 
 matogenesis of Myx. Q. J. M. S. xxxiii, 169-186, and Zool. Anz. 
 xiv, 22-27. '83 FERRY, L. (Internal fecundation), CR. Ixxxxvi, 
 721-722, and Ann. N. H. xi, 388. '75 GULLIVER, Spermatozoa, 
 P. Zool. S. 336. '78 KUPFFER, C. v., u. BENECKE, Befruchtung. 
 Festschr. Th. Schwann Kbnigsberg. '86 NANSEN (Protandric), 
 Myxine, Zool. Anz. 676, '87 in Bergens Mus. Aarsber, pp. 34, and 
 '89 (Q. J. M. S. 188-189) ZooL Anz - 26r - '8 NUSSBAUM, M. 
 (Eggs and spawning), A. mikr. Anat. xviii, 1-121. '89 RETZIUS, 
 Entwick. d. Myx. Biol. For. i, 22-28, Anhang. 50-51 (Dec. '88). 
 '63 STEENSTRUP, J. (Egg of Myxine), Oversigt. o. d. K. danske 
 Videnskabernes Selskabs Forh. 233-239. '87 WEBER, M. 
 (Reply to Cunningham), Zool. Anz. 318-321. Geslachtsorganenv. 
 Myx. Ned. Dierkd. Vereen, 4 pp. D. I. Afl. 3-4. 
 
 III. Organogeny. '77 CALBERLA, E., Medullarrohr, Morph. JB. iii. 
 '82 DOHRN, Hypophysis, Zool. Anz. 587-588, '83 in MT. z. Stat. 
 Neapel, iv, 172-189. '84 Visceralbogen, op. cit. v, 152-189. 
 
FISHES, LIVING AND FOSSIL 
 
 '86 Thyreoidea, op. cit. vi. '87 (Thyroid, Spiracle, Pseudo- 
 branch), op. cit. vii, 301-337- '88 Nerven u. Gefasse, op. cit. viii, 
 233. '92 HATTA, S., Germinal Layers, J. Coll. Sci. Japan, v, 
 129-147. '84 HERMS, E., Nervus acusticus, SB. math. nat. Acad. 
 MUnch. 333-354- '9 3 McCLURE, Early stages, Zool. Anz. xvi, 
 429. '85 SHIPLEY, A. C., Mesoblast and blastopore, P. Roy. S. 
 Lond. xxxix, 244-248. '86 Nervous system, P. Camb. Phil. S. 
 v, 374- ' 79 WIEDERSHEIM, Brain and spinal nerves, Zool. Anz. 
 ii, 589-59 2 - 
 
 THE OSTRACODERMS AND PAL^OSPONDYLUS 
 (Cf. SMITH WOODWARD'S Cat. Foss. Fishes.) 
 
 '85 COPE, E. D., Position of Pterichthys, Am. Nat. xix, 289-291. 
 '92 CLAYPOLE, E. W., Pteraspidian family, Q. J. Geol. S. xlviii, 
 542-562. '90 PATTEN, W., Q. J. M. S. xxxi, 359-365. '94 
 Limulus and Pteraspis, Anat. Anz. '94 ROHON, J. V. (Meta- 
 merism of Cephalaspids), Zool. Anz. 51. '88 TRAQUAIR, R. H., 
 Asterolepids, Ann. N. H. ii, 485-504, and ('89) P. Phys. Soc. 
 Edinb. 23-46. '90 Palaeospondylus. Ann. N. H. vi, 485, and 
 '93 in P. Roy. Phys. Soc. Edinb. xii, 87-94, and '94 op. cit. xii r 
 312-321. '92 SMITH WOODWARD, Forerunners of Backboned 
 Animals, Nat. Sci. i, 596-602. 
 
 THE SHARKS 
 
 GENERAL. '65 DUMERIL, A, Hist. nat. d. poissons, Tome I 
 (Sharks, Skates, and Chimaera), pp. 720, Paris. '79-'80 MIKLOUHO- 
 MACLAY, Plagiostomes of the Pacific, i, ii, iii (Anat. notes : 
 Dentition of young Cestracionts), P. Linn. S. N. S. Wales, iii r 
 306-326. '41 MULLER, u. HENLE, Syst. Beschr. d. Plagiost. 
 folio, 60 pis. Berlin. 
 
 ANATOMY, GENERAL. '85 CARMAN, Chlamydoselache, B. Mus. 
 Comp. Zool. (cf. Gunther in Challenger report). '90 JAEKEL, 
 O., Kiemenstellung u. System, d. Sel. (?) Berlin. '91 Pristi- 
 ophorus, A. f. Naturges, 15-48. LEUCKART, R., Bildung d. 
 Korpergestalt b. Rochen. Z. wiss. Zool. ii, 258. '93 MAREY 
 (Swimming movements of Ray), C. R., cxvi, 77-81. '92 MAR- 
 SHALL and HURST, Practical Zoology (Dog-fish), Putnam, N. Y. 
 '84 PARKER, T. J., Zootomy (Skate), Macmillan. '84 WILS, 
 H. B., Squatina. Lugd. Bat. 
 
 SKELETON. '85 DOHRN (Visceral arches of Skate), MT. z. Stat. 
 
BIBLIOGRAPHY: SHARKS 
 
 239 
 
 Neapel, vi. '72 GEGENBAUR, Kopfskelet, 4to, Leip. '78 HASSE, 
 C. (Vertebrae, Morph. JB. iv, 214-268, and op. cit. Supplt. 43-58, 
 and Berl. Verb. Naturw. 173-174 (Zool. Anz. i, 144-148 and 167- 
 171). Also '85, 4to, 27 pp. Leip. '84 HASWELL, W. A., P. Linn. 
 S. N. S. Wales, ix, 71-117. '78 HUBRECHT, Bronn's Klassen u. 
 Ordnungen. '64 KOLLIKER, Wirbel, Senkenb. Naturf. Gesell. v, 
 51-99. Also 4to. Frankfurt. '90 PARKER, T. J., Sternum in 
 Notidanus, Nature, xliii, 142. '78 PARKER, W. K., Skull (with 
 develop.) of shark and skate, Tr. Zool. S. x, 184-234. '84 ROSEN- 
 BERG, E., Occiput, Festschr. Dorpat. 4to, 20 pp. And '87 in SB. 
 Gesell. Dorp, viii, 31-34. '73 STEENSTRUP, J. (Gill rakers of 
 Selache), Overs. Dan. Selsk. No. i. '90 WHITE, P. J., Skull and 
 vise, skelet. of Laemargus, Anat. Anz. v, 259-261. 
 
 FINS AND GIRDLES. '81 BALFOUR, Skates, P. Zool. S. '70 
 GEGENBAUR, Skel. of, Jen. Z. v, 397-447, also (claspers) 448-458. 
 '90 HOWES, Batoid and Squaloraja, P. Zool. S. 675-688. '85 
 MAYER, P., Unpaaren Flos. MT. z. Stat. Neap, vi, 217-285. '79 
 METSCHNIKOFF, O. (Morph. of girdles), Z. wiss. Zool. xxviii, 423- 
 438. '79 MIVART, ST. G., T. Zool. S. x, 439-484. '92 MOLLIER, 
 S. (Entwickelung), Vorl. MT. Anat. Anz. vii, 351-365, also '77 
 THACHER, J., Tr. Connec. Acad. iii. 
 
 INTEGUMENT AND TEETH. '44 AGASSIZ, L., Dents et rayons, 
 4to, Neuchatel. '68 HANNOVER, A., Ecailles. (?). HARLESS, E., 
 Zahnbau v. Myliobates, 4to (?). '74 HERTWIG, O. (also develop- 
 ment), Jen. Z. viii. '72 RANVIER, L., Etranglements annulaire 
 (Rays), C. R. 1129-1132. 
 
 VISCERA, VESSELS, GLANDS. '92 ANTIPA, G., Thymus, Anat. 
 Anz. vii, 690-692. '88 AYRES, H., Carotids (Chlamydosel.) B. 
 Mus. Comp. Zool. xvii, 191-224. '78 BLANCHARD, R., Superanal 
 gland, J. de 1'Anat. Phys. xiv, 442-450, and B. S. Zool. Fr. vii, 
 399-401. '79 BRIDGE, Pori abdominales, J. Anat. Phys. '82 
 DROSCHER, W. (Histol. of gills), A. f. Nat. xlviii, 120-177. '90 
 EWART, J. C., Spiracle of Lamna, J. Anat. Phys. xxiv, 227-229. 
 '78 FURBRINGER, Excretory system, Morph. JB, 49-56. '91 
 GEGENBAUR, Cb'calanhange v. Mitteldarm, Jen. Z. (?), 180-184. 
 '90 HOWES, Kidney of Raja, J. Anat. Phys. xxiv, 407-422. '90 
 Visceral anat. of Hypnos, P. Zool. S. 669-675. '72 HYRTL, J., 
 Kopfarterien, DS. Ak. Wiss. Wien, xxxii, 263-275. '85 LIST, 
 J. H., Cloakenepithel, SB. Akad. Wien (?), and Anat. Anz. vii, 
 545-546. '80 PARKER, T. J., Spiral valve of Ray, T. Zool. S. xi, 
 49-61, and Venous system, Tr. N. Zeal. Ins. xiii, 413-418. '86 
 On the vessels of Mustelus, and ('87) on Carcharodon, P. Zool. 
 
FISHES, LIVING AND FOSSIL 
 
 S. (?). '90 PILLIET, A. (Histol. of liver), C. R. Soc. Biol. ii, 
 690-694. '82 POUCHET, G., Termin. vascul. d. la Rate, J. de 
 1'Anat. Phys. xviii, 498-502. '88 RUCKERT, J., Excretions-organe, 
 A. Anat. Phys. (Anat.), 205-278. '77 STOHR (Valves in arterial 
 conus), Morph. JB. ii, 197-228. '79 TROIS, E. F. (Carotids of 
 Oxyrhina), Atti del Inst. Ven. and '83 (Of Alopecias), op. cit. 
 '73 TURNER, W., Visceral Anat. of Laemargus, J. Anat. Phys. 
 233. '75 Spiny Shark, op. cit. '79 Pori abdominales, op. cit. 
 xiv, 1 01-102. '81 Teeth and gill-rakers of Selache, op. cit. xiv, 
 273-286. '93 VIRCHOW, H., Spritzlochkieme, SB. Gesell. n. 
 Freunde, Berl. 177-182; Augengefasse ('90) A. Anat. Phys. 
 (Phys.), 169-173. '67 MIKLUCHO-MACLAY, Schwimmblasenrudi- 
 ment, Jen. Z. iii, 448-453. 
 
 NERVOUS SYSTEM AND END ORGANS. '92 BRAUS, H., 
 Rami ventrales d. vord. Spinalnerven. Inaug. Diss. 35 pp. Jena. 
 '83 CATTIE, J. F., Epiphysis, Z. wiss. Zool. xxxix, 720-722, and 
 A. Biol. iii, 101-196. '90 CHEVREL, R., Sympathetic, A. Zool. 
 exper. v, 196 pp. '91 COGGI, A., Vdsicules de Savi (Torpedo), 
 A. Ital. Biol. xvi, 216-224. '92 EDINGER, L., Zwischenhirn, AH. 
 Senck. Gesell. xviii, 55 pp. (and Anat. Anz. vii, 472-476). '78 
 EHLERS, E., Gehirn u. Epiphyse, Z. wiss. Zool. xxx, Suppl. 607. 
 '90 EWART, J. C., Cran. nerves of Torpedo, P. Roy. S. xlvii, 
 240-291. '92 Electric organ of Skate, Phil. Trans, clxxxiii, 
 389-420 (Abs. in P. Roy. S. 474-476). '92 Sensory canals of 
 Laemargus, and Skate, Tr. Roy. S. Edinb. Nos. 5-6 (Abs. in 
 Zool. Anz. xv), 116-120. '88 FRITSCH,G., Bedeuting d. Kanalsyst 
 SB. Ak. Berl. 273-306. '88-'89 GARMAN, Lateral line (figures 
 many forms), B. Mus. Comp. Zool. xvii, No. 2. '71 GEGENBAUR, 
 Kopfnerven v. Hexanchus, Jen. Z. 497-560. '75 JACKSON, W. H., 
 and CLARKE, Brain and nerves, J. Anat. Phys. x, 75-197. '87 
 LEGER, M., Cervelet d'un Alopias, B. S. Philom. xi, 160-163. 
 '81 MARSHALL, A. M., Head cavities and nerves, Q. J. M. S. xxi, 
 72, and (with SPENCER) 469-499. '80 MERKEL, Sens, nerven in 
 d. Haut. Rostock. '70 MIKLUCHO-MACLAY, Gehirn, 4to, 74 pp. 
 Leip. '78 RETZIUS, G., Memb. Gehorlabyr. A. Anat. Phys. 
 (Anat.), 83-105. '91 REX, H. (Morph. of cran. nerves), Morph. 
 JB. xvii, 417-466. '78 ROHON, J. (Brain), DS. Ak. Wien, xxxviii, 
 43-108. '86 SANDERS, A., Phil. Trans, clxxvii, 733-764, and P. 
 R. S. xl. '89 SHORE, T. W., Vagus, J. Anat. Phys. iii, 428-451. 
 '80 SOLGER (Organs of lateral line), A. mikr. Anat. xvii. '73 
 STIEDA, L., Riickenmark, Z. wiss. Zool. xxiii, 435-442. '73 
 TODARO, F. (Gustatory buds and branch, membr.), Recherche 
 
BIBLIOGRAPHY: SHARKS 241 
 
 lab. univers. Roma. (Abs. in A. Zool. expdr.) 534-558. '91 
 VALENTI, G., Histogenesis, A. Ital. Biol. xvi, 247-252. '76 
 VIAULT, F., Histology, A. Zool. exper. v, 441-528. '83 VIGNAL, 
 Sys. ganglionaire (Ray), op. cit. i, xvii. 
 
 EMBRYOLOGY, GENERAL. '76 BALFOUR, G. M., in Q. J. M. S. 
 xiv, and Camb. J. Anat. Phys. xi, pt. I. Also '78 Monograph, 
 Macmillan, London. '90 BEARD, J., Skate, R. Fish. Board, Edin. 
 '89 EIGENMANN, C. H. and R. S., Young stages, West Am. 
 Nat. vi, 150-151. '85 HASWELL, W. A., Young Pristiophorus, P. 
 Linn. S. N. S. Wales, ix, 680-681. '77 His, W., Ueb. d. Bildung 
 v. Haifishembryonen, Z. wiss. Zool. ii, 108-124. ' 81 HOFFMANN, 
 C. K. (?), Harlem. '88 KASTSCHENKO, N., Anat. Anz. iii, 445- 
 467. '70 KOWALEWSKY, A. (Russian), Trans. Kiew. Soc. of 
 Nat. i. '52 LEYDIG, F., Mikr. Rochen u. Haie, Leip. Englemann, 
 iv, 127 pp. '76 MALM, A. W., Kongl. vet. akad. forhand. Stock- 
 holm. '42 MULLER, J. (Emb. differences of Shark and Ray), 
 fol. Berlin. '86 PERENYI, J., Torpedo, Zool. Anz. ix, No. 227, 
 433-436. '77 SCHULTZ, A., A. mikr. Anat. '92 SEDGWICK, A., 
 Q. J. M. S. xxxiii, 559-586. '64, WYMAN, Raja, Mem. Am. Acad. 
 Arts and Sciences, ix. 
 
 I. Breeding, Gestation. '73 AGASSIZ, A., P. Bost. Soc. xiv, 
 
 339. '90 ALCOCK, A., J. A. Soc. Bombay, lix, 51-56. (Of 
 Rays) '92 Ann. N. H. ix, 417-427, and x, 1-8. '79 BOLAU, H. 
 (Of Scyllium), VH. Ver. Hamb. iii, 122-130 and ('81) Z. wiss. 
 Zool. xxxv. '67 COSTE (Of Scyllium), C. R. 99-100, and Ann. 
 
 M. N. H. xix, 227. '70 HOME, E., Ovoviviparous Sharks. 
 
 '68 MACDONALD, J. D., and BARRON, CH., Heptanchus, P. Zool. S. 
 37!-373- ' 85 MATTHEWS, J. D., Oviduct of Skate, J. Anat. Phys. 
 xix, 144-149. '90 MEHRDORF, C. (Gestation), Rostock, 51 pp. 
 '72 MEYER (Scyllium), Zool. Gait. 371. '85 OERLEY, L. 
 (Gestation), Term, fiizetek. ix, 293-309. '90 PARKER, T. J., 
 Mustelus, Tr. N. Zeal. Inst. xxii, 331-333. '77 PETRI, K. R., 
 Copulationsorgane, Z. wiss. Zool. xxx, 288-385. '75 SCHENK, 
 S. L., Kiemenfader, SB. Akad. Wien. 12 pp. '79 SCHMIDTLEIN, R., 
 MT. z. Stat. Neap. 1, 61. '91 WOOD-MASON and ALCOCK, Gesta- 
 tion of Pteroplataea, P. Roy. S. xlix, 359-367, and 1, 202-209. 
 '67 TROIS, E. F. (Acanthias' gestation), Atti. Inst. Ven. 171-176. 
 '77 (Gestation of Myliobatis and Centrina), op. cit. ii, 429. 
 '77 TURNER, W., Laemargus' oviducts, J. Anat. Phys. xii, 604- 
 607, and ('85) op. cit. xix, 221-222. 
 
 II. Egg, Gastr tdation. '92 DOHRN, Schwann'schen Kerne, Anat. 
 Anz. vii, 348-351. '72 GERBE, Z., Segmentation, J. de 1'Anat. 
 
 R 
 
FISHES, LIVING AND FOSSIL 
 
 Phys. 1 81 HERRMANN, G., Spermatogenese, C. R. xciii, 858-860, 
 and '83 J. 1'Anat. Phys. xviii, 373-432. '83 HERTWIG, O. 
 (Middle germ layer), Jen. Z. xvi, 287-290. '83 HOFFMANN, C. K. 
 (Middle germ layer), Arch. Neerland. xviii, 241. '92 Endothelial 
 Anlage d. Herzens, Anat. Anz. vii, 270-273, and '93 in Morph. 
 JB. xix, 592-648. '88 KASTSCHENKO, Dotterkerne, Anat. Anz. 
 '90 (Early develop, and muscles), Zool. Beitr. ii, 251-266. '86 
 KOLLMANN, Furchung (C. R. '84), Congr. pe'r. internal, d. sc. 
 mdd. Copenhague, i, Sect. d'Anat. 50-52, and VH. d. Natur. 
 Gesell. Basle, Th. viii, Heft i. '78 LA VALLETTE, ST. GEORGE, A., 
 Spermatosomatum, Bonn, 4to, 9 pp. '79 LUTKEN, Laemargus' 
 eggs, oviduct, Vid. Medd. ('80) 56-61. '84 PERRAVEX, M. E. 
 (Egg case), C. R. xcix, 1080-1082. '89 OSTROUMOFF, A., Blasto- 
 porus u. Schwanzdarm, Zool. Anz. xii, 364-366. '85 RUCKERT, J., 
 Keimblattbildung, SB. Gesell. Morph. MUnchen, i, 48-104, and 
 '89 in Anat. Anz. iv, 353-374. '86 Gastrulation (and middle 
 germ layer), Anat. Anz. 286-287, and '87 op. cit. 97-112 and 
 151-174. '91 Befruchtung, Anat. Anz. vi, 308-322. '92 Ova- 
 rialei, vii, 107-158, Chromosomen, viii, 44-52. '86 RYDER, 
 Segmentation, Am. Nat. xx, 470-473, and B. U. S. F C. 8-10. 
 '82 SABATIER, A., Spermatogenese, C. R. xciv, 1097-1099. '75 
 SCHULTZ, A. (Ovogenesis), A. mikr. Anat. xi, 569-582. '73 
 SCHENK, S. L. (Egg and oviduct), SB. Akad. Wien, Ixxiii. 
 74 Dotterstrang, op. cit. Ixix, 301-308. '90 SCHNEIDER, A. 
 (Gastrula-muscles), Zool. Beitr. ii, 251-266. '85 SWAEN, A. 
 (Germ layers and blood), B. Acad. roy. Belgique, ix, and '86 in 
 A. de Biol. vii, 537-585. '83 TROIS, E. F., Spermatozoi, Atti. Inst. 
 Ven. and J. Microgr. vii, 193-196. '84 VAILLANT, L., Orientation 
 des oeufs dans 1'ute'rus, B. Soc. Philom. viii, 178-179. '88 ZIEGLER 
 (Mesenchyme), A. mikr. Anat. xxxii. '92 ZIEGLER, H. E. and F. 
 (Early development), A. mikr. Anat. xxxix, 56-102. 
 
 III. Integument, Skeleton. '81 BENDA, C., Dentinbildung, A. mikr. 
 Anat. xx, 246-270. '79 HASSE, C., Knorpel, Zool. Anz. ii, 
 325-329, 351-355, and 371-374- '82 Wirbelsaule, Jena ('79), 
 4to. '92 Wirbelsaule, Z. wiss. Zool. Iv, 519-531. '60 KOLLIKER, 
 A., Chorda u. Wirbel. Wiirz. '87 PERENYI, J., Chorda, peri- 
 chordal. Math. u. Naturwiss. Ber. a. Ungarn, iv, 214-217, and 
 ('89) in 218-241. '93 PLATT, JULIA B., Ectodermic cartilage, 
 Anat. Anz. 506. '78 REICHERT, Vordere Ende d. Chorda, AH. 
 Ak. Berl. 49-1 13. '84 ROSENBERG, E., Occipitalregion, Festschrift, 
 Dorpat, 26 pp. 4to. 
 
 IV. Viscera. '87 BEARD, J., Segmental duct, Anat. Anz. ii, 646-652. 
 
BIBLIOGRAPHY: SHARKS 
 
 243 
 
 '85 BEMMELEN, J. F. v. (Rudimentary gill slits), MT. z. Stat. 
 Neap, vi, 165-184. '79 BLANCHARD, R., Fingerformigen Driise, 
 MT. Emb. Inst. Schenk, iii, 179-192, and ('77) J. de 1'Anat. xlv, 
 442-450. '84 DOHRN, Kiemenbogen, Flossen, MT. z. Stat. Neap. 
 v, 102-189. '87 MAYER, P. (Circulatory), op. cit. vii, 338-370, 
 and ('88) viii, 307-373. Also Anat. Anz. ix, 185-192. '77 
 MAYER, F., Urogenitalsys. SB. Gesell. Leip. ('76), 38-44. '92 
 RABL, C., Venensys. Leuckart Festschr. 228-235. '92 RAF- 
 FAELE, F., Sist. vascolare, MT. z. Stat. Neap, x, 441-479. '88 
 RUCKERT, J., Endothel. Anlagen d. Herzens, Biol. Centralbl. 
 viii. '89 Excretionssys. Zool. Anz. xii, 15-22. '75 SEIKPER, C., 
 Urogenitalsys. Arb. a. d. Zool. Zoot. Inst. Wiirz. ii. '88 WIJHE, 
 J. W. v., Excretionsorgane, Zool. Anz. xi, 539-540, and Anat. 
 Anz. iii, 74-76, and '89 in A. mikr. Anat. xxxiii, 461-516. 
 
 V. Nervous System and End Organs. '85 BEARD, J., Cranial 
 ganglia, Zool. Anz. viii, 220-223, Anat. Anz. iii, 874-905, and 
 op. cit. '92, 191-206. '91 KILLIAN, Metamerie, VH. Anat. 
 Gesell. 85-107. '88 DOHRN (Motor fibres), MT. z. Stat. Neap. 
 viii, 441-462. '91 Augenmuskelnerven, op. cit. x, 1-40. '91 
 FRORIEP, Kopfnerven, VH. Anat. Gesell. 55-65. '92 LENHOSSEK, 
 M. v. (Spinal ganglia and cord), Anat. Anz. vii, 519-539. '85 
 ONODI, A. (Nerve roots), Ber. Math. Nat. Ungarn, ii, 310-336. 
 '89 OSTROUMOFF, A., Froriep'schen Ganglien, Zool. Anz. xii, 
 363-364. '90 PLATT, J. B., Anterior head cavities, Zool. Anz. xiii, 
 239, and '91 J. of Morph. v, 79-106, and Anat. Anz. vi, 251-265. 
 '96 PUNIS, G. C., Pineal eye, P. Phys. Soc. Edinb. 62-67. '92 
 RABL, C., Metamerie, VH. Anat. Gesell. 104-135. '80 RABL- 
 RUCKHARDT (Metamerism), Morph. JB. vi, 535-570. '93 Lobus 
 olf. impar. Anat. Anz. Sep. 15. '83 VIGNAL, W., Systeme gang- 
 lionaire, A. Zool. exper. i, 17-20. '83 VAN WIJHE (Metamerism), 
 VH. Aka. Wiss. Amsterdam. '76 WILDER, B. G., Anterior 
 brain mass, Am. J. Sci. xii, 103-106. 
 
 MORPHOLOGY OF FOSSIL SHARKS. V. ref. in S. Wood- 
 ward's Catalogue, also in present writer's article on Cladoselache, 
 '94 J. of Morph. ix, 112. In addition, '88 BROGNIART ET SAUVAGE, 
 Etudes sur le Terrain Houiller de Commentry, Liv. iii, B. de la 
 S. d. 1' Indus, miner, ii. 1-39. '93 CLAYPOLE, E. W., Cladodonts, 
 Am. Geol. 325-331, and ('95) op. cit. Jan. '93 COPE, Clado- 
 donts, Am. Nat. Sept. Also '94 J. Am. N. S. Phila. ix, 427-441. 
 '92-'94 DAVIS, J. W., Pleuracanths, Acanthodians, Tr. Dub. Roy. 
 S. '94 DEAN, B., Cladodont, Tr. N. Y. Acad. Sci. 115-119. '92 
 JAEKEL, O. (Eocene sharks), SB. Gesell. Nat. Fr. Berlin, p. 6i> 
 
FISHES, LIVING AND FOSSIL 
 
 and Cladodus, I.e. 156-158. '95 SMITH WOODWARD, Primaeval 
 
 sharks, Nat. Sci. vi, 38-44. 
 
 THE CHIMLEROIDS 
 (Cf. esp. DUMERIL, Ref. p. 238.) 
 
 '94 BEAN, T. H., Harriotta, P. U. S. Nat. Mus. xvii, 471-473. '52 
 COSTA (Anatomy), Faun, regno Napoli. '51 LEYDIG, F., Anat. 
 and Hist. Mill. A. f. Anat. Phys. xviii, 241-271. '76 HUBRECHT, 
 A., Kopfskelet, Nied. A. Zool. iii, 255-276, and '77 in Morph. JB. 
 iii, 280-282. '86 PARKER, T. J., Claspers of Callorhynchus, Nat. 
 xxxix, 635. '75 SOLGER, B. (Visceral skeleton), Morph. JB. I, 
 H. I. '37 DUVERNOY, G. Z. (Heart and vessels), Ann. d. Sc. 
 Nat. 1-16. '78 LANKESTER, E. R., Heart, P. Zool. S. 634, and 
 '79 in Tr. Zool. S. x, 493-506. '42 MULLER, J. (Nerves and 
 heart, critique of Valentin), A. f. Anat. ('43) ccliii. '89 CARMAN, 
 S., Lateral line, Mus. Comp. Zool. xvii. '70 MIKLUCHO-MACLAY 
 (Brain), Jen. Z. v, 132. '79 SOLGER, B. (Lateral line), A. mikr. 
 Anat. xvii, 95-113. '42 VALENTIN (Brain and Nebenherzen), A. 
 mikr. Anat. 25-45. '77 WILDER, Brain, P. Philadel. Acad. Sci. 
 219-250. '90 ALCOCK, Egg capsule of Callorhynchus, Ann. N. H. 
 viii, 22. '71 CUNNINGHAM, Callorhynchus' egg, Notes on the 
 N. H. of the Straits of Magellan, 340. '89 GUNTHER, Chimaera's 
 egg, A. N. H. iv, 275-280. 
 
 For literature of Fossil Chimaeroids v. SMITH WOODWARD'S 
 Catalogue. 
 
 THE LUNG-FISHES 
 
 GENERAL (NATURAL HISTORY). '94 BOHLS, Fang u. Lebens- 
 weisev. Lepidosiren. Nachr. Gesell. Gottingen, 80-83. '76 CAS- 
 TLENAU, F., Ceratodus, C. R. Ixxxiii, 1034. '92 DUBOIS, R.> 
 Respiration, "hibernation," Ann. S. Linn. Lyon, xxxix, 65-72. 
 '66 DUMERIL, A. M. C., C. R. 97-100, and Ann. N. H. xvii, 160. 
 '70 (Swim-bladder, etc.), Angers ? '94 EHLERS, E., Lepid, n. s. 
 Nachr. Gesell. Gottingen. FRITSCH, A. (Living and Fossil Lung- 
 fishes and their affinities), Prag. 4to. '87 GIGLIOLI (Rediscovery 
 of Lepidosiren), Nat. xxxv, 343, and '88, Nat. xxxviii, 112. 
 '56 GRAY, J. E., " Lepidosiren," P. Zool. S. Lon. 342. '88 HOWES, 
 Rediscovery of Lep. Nat. xxxviii, 126. '41 JARDINE, W., Ann. 
 N. H. vii, 24. '64 KRAUSS, F., Protopterus, Wiirt. nYrwiss. 
 Jahresber. 126-133. ' 70 KREFFT, Ceratodus, P. Zool. S. 221- 
 
BIBLIOGRAPHY: LUNG-FISHES 245 
 
 224, and Ann. N. H. 221-224, and ('71) P. Roy. S. 377. 
 '91 LACHMAN, H., Protop. Zool. Gart. xxxii, 129. '73 MARNO, 
 E., Protop. Zool. Gart. 44. '58-'59 MCDONNELL, R., Protop. Z. 
 \viss. Zool.x. '37 NATTERER, J., Lepid. Ann. Wien. Mus. II. 
 '94 NATURAL SCIENCE, Lepid. 324-325. '39-'41 OWEN, Lepi- 
 dosiren annectans, Tr. Linn. S. xviii. '45 PETERS, W., Protop. 
 Mill. A. '76 RAMSEY, E. P., Cerat. P. Zool. S. 698. SCHMELTZ, 
 Cerat. J. Mus. Godeffr. viii, 138. '66 SCLATER and BATES, Lepid. 
 P. Zool. S. 34. '92 SPENCER, W. B., Cerat. Viet. Natural. Melb. 
 June 10, and P. Roy. S. Viet, iv, 81-84. '89 STUHLMAN, F., 
 Cerat. SB. Akad. Wiss. BerL 32. '87 WIEDERSHEIM, Protop. 
 Anat. Anz. ii, 707-713, and R. Br. Ass. 738-740. 
 
 ANATOMY, GENERAL. '85 AYERS, H., Jen. Z. Naturwiss. xviii, 
 479-527. '87 BAUR, G., Lepid. Zool. JB. ii, 575. '4O BISCHOFF, 
 T., Lepid. Leip. '71 GUNTHER, Ceratodus, Ann. N. H. vii, 227 
 and Phil. Trans. ('72) clxi, 511-571, and P. Roy. S. 377-379, 
 Nat. Nos. 99, 100, 102. '76 HUXLEY, Ceratodus, P. Zool. S. 
 24-58. '64 KLEIN, Protop. Wiirt. n't'rwiss. Jahresber. 134-144. 
 '78 MIALL, L., Cerat. and Protop. Palaeont. S. xxxii, 1-32. '88 
 PARKER, W. N., Ber. d. Naturforsch. Gesell. Friburg, VB. iv, H. 
 3, Nat. xxxix, 9-21, and Tr. Cardiff Nat. S. xx. '91 Protop. 
 P. Roy. S. xlix, 549-554. '92 Protop. (Large memoir), Tr. R. 
 Irish Acad. xxx, 115-227. '66 PETERS, Monatsber. Ak. Wiss. 
 Berl. 12-13. 
 
 SKELETON. '93 KLAATSCH, H., Wirbel, VH. Anat. Gesell, 130- 
 132. '91 TELLER, F., Skull of Ceratodus, AH. Geol. Reichanst. 
 xv, H. 3. 
 
 MUSCLES. '72 HUMPHREY, G. M., Ceratodus and Protop. J. Anat. 
 and Phys. vi. 
 
 FINS AND GIRDLES. '86 ALBRECHT, P., Protop. Fin forked, SB. 
 Ak. Berl. 545-546. '91 BOULENGER, Protop. Renewed pectoral. 
 '83 DAVIDOFF, M., Cerat. Pelvic fin. '84 GILL, T., Shoulder 
 girdle, Ann. N. H. xi, 173-178. '83 HASWELL, W. A., Cerat. 
 Paired fins, P. Linn. S. N. S. Wales, vii, 2-11. '91 HOPLEY, C., 
 Protop. Renewed pectoral, Am. Nat. xxv, 487. '87 HOWES, G. 
 B., Cerat. Paired fins compared with sharks', P. Zool. S. 3. 
 '94 LANKESTER, E. Ray, Lepid. Villous processes of hind limbs, 
 Nat. Apr. 12. '86 SCHNEIDER, A., Zool. Anz. ix, 521-524, and 
 ('87) Zool. Beitr. ii, 97-105. '71 TRAQUAIR, R. H., Protop. Tail 
 restored, Br. Ass. R. '90 VANHOFFEN, Cerat. VH. Gesell. D. 
 Naturf. ii, 134, 
 
246 
 
 FISHES, LIVING AND FOSSIL 
 
 INTEGUMENT AND TEETH. '87 BOCKLEN, H., Cerat. Denti- 
 tion, JH. Ver. Wiirt. xliii, 76-81. '60-'61 KOLLIKER, A., Protop. 
 Histol. of Skin, Z. Naturwiss. Wiirzb. i. '65 PAULSON, M., 
 Protop. Histol. of epidermis, B. Acad. Sci. St. Pe'tersb. viii, 
 141-145. '92 ROSE, C., Zahnbau u. Zahnwechsel, Anat. Anz. vii, 
 821-839. '89 WALTHER, G., Prot. Skin, Z. f. Phys. Chem. xiii, 
 H. 5. '80 WIEDERSHEIM, R., Scales, A. mikr. Anat. xviii. 
 
 VISCERA, VESSELS, GLANDS. '80 BOAS, E. V. (Heart and 
 arteries), Morph. JB. vii, 3 2I -354- 17 8 FURBRINGER (Excretory), 
 Morph. JB. iv, 60. '76 HUXLEY, Anterior nares, P. Zool. S. 
 180. '45 HYRTL, J., Lepid. AH. d. bohm Gesell. Prag. '78 
 LANKESTER, E. R., Heart, P. Zool. S. 634, and ('79) Tr. Zool. S. 
 x, 493-506. '89 PARKER, W. N., Veins (L. cardinal), P. Zool. S. 
 145-151. '94 SPENCER, W. B., Cerat. Vessels (complete memoir), 
 Macleay Mem. Vol. Linn. S. N. S. Wales, 2-32. 
 
 NERVOUS SYSTEM, END ORGANS. '82 BEAUREGARD, H. 
 (Cranial), J. de TAnat. Phys. xvii, 230-242. '91 BURCKHARDT, 
 R., Zirbel. Anat. Anz. vi, 348-349. '92 Cent. nerv. sys. Berlin, 
 64 pp. Also Zool. Gesell. ii, 92-95, and SB. Nat. Fr. Berl. 
 23-25. '94 (Zwischenhirndach), Anat. Anz. 152. '86 FUL- 
 LIQUET, G. (Brain), A. Sci. Naturelles, xv, 94-96, and Rec. 
 Zool. Suisse, iii, 1-130. '94 PINKUS, F. (Undescribed nerve), 
 Anat. Anz. ix, 562-566, and (Cranial nerves of Protop.) Morph. 
 Arb. (Schwalbe), 275-346. '89 SANDERS, A., Cent. nerv. sys. 
 Cerat. Ann. N. H. iii, 157-188. '80 WIEDERSHEIM, Skel. and 
 cent. nerv. sys. Jen. Z. xiv, and Morph. Stud. Heft i, Jena. '82 
 WIJHE, J. W. van, Visceralskel. u. d. Nerven. Cerat. Nied. A. 
 Zool. v, 207-320. '87 WILDER, B., Brain, Am. Nat. xxi, 544-548. 
 
 EMBRYOLOGY. '86 BEDDARD, F. E., Ovarian ovum, P. Zool. S. 
 272-292, and Zool. Anz. ix, 635-637. '84 CALDWELL, W. H., 
 (Preliminary), J. and P. Roy. S. N. S. W. xviii, and ('87) in Phil. 
 Trans, clxxviii. '93 HASSE, C., Wirbelsaule, Z. wiss. Zool. Iv, 
 533-542. '93 SEMON, R. (Habits and development surface 
 views of eggs and larvae), DS. d. Med. Nat. Gesell. Z. Jena, pp. 50. 
 
 THE GANOIDS 
 
 GENERAL (NATURAL HISTORY). '70 DUMERIL, Aug. Tome 
 ii, pp. 625, Roret, Paris. '35 HECKEL, J., Scaphirhynchus, SB. 
 Akad. Wien. '71 LUTKEN (Classification), Transl. in Ann. N. H. 
 329-339. '85 ORR, H. (Phylogeny) Inaug. Dissert. Jena, 37 pp. 
 '65-'66 SMITH, J. A., Calamoichthys, P. Roy. S. Edinb. v, 654- 
 
BIBLIOGRAPHY: GANOIDS 247 
 
 659, and ('66) 457-479. '69 STEINDACHNER, F., Polypterus, SB. 
 Wien. Akad. Ix. 
 
 GENERAL ANATOMY. '87 TWANZOW, N., Scaphirhynchus, B. 
 S. Mosc. 1-41. '54 LEYDIG (Histology of Polypterus), Z. wiss. 
 Zool. v. '50 LITTANY, M., Acipenser, B. S. Mosc. xxiii, 389-445. 
 '44 MULLER, J., Bau u. Grenzen, A. f. Anat. and ('46) AH. d. 
 Berl. Akad. d. Wiss. '92 POLLARD, H. B., Polypterus, Anat. and 
 phylogeny, Morph. JB. V, 387-428, and preliminary in ('91) 
 Anat. Anz. vi, 338-343. '48 WAGNER, A., de Spatulariarum 
 Anat. Inaug. Diss. Berol. '75 WILDER, B., Notes on Am. Gan. 
 I. Respir. of Lepid. and Amia. II. Tail formation of Lepid. 
 III. Pect. fin formation of Lepid. IV. Brains of Amia, Lepid., 
 Acip., and Polyod. P. Am. Ass. Adv. Sci. xxiv, 151-193. 
 '76 Brains, Philadel. Acad. P. xxxviii, 51-53. '78 Amia and 
 Lepid. rudimentary spiracle, P. Am. Ass. (unpub'd), and Am. Nat. 
 xix, 192. And in the respiration of Amia, P. Am. Ass. 306- 
 313. '85 WRIGHT, R. R., Notes on anat. of fishes: A. Cutan- 
 sense organs. B. Spiracular cleft of Amia and Lepid. C. Aud. 
 organ of Hypophthalmus, Am. Nat. xix, 187-190 and 513. D. 
 Hyomand. clefts and pseudobranchs of Amia and Lepid. and 
 Amia, J. Anat. Phys. xix, 477-497. E. Amia's serrated append- 
 ages, Sci. iv, 511. '87 ZOGRAFF, N., Monograph (Russians) on 
 Sturgeon, Tr. S. Nat. Mosc. Hi, pp. 72. '87 Affinities of ganoids, 
 Nat. xxxvii, 70. 
 
 SKELETON. '77 BRIDGE, T., Cranium Amia J. Anat. Phys. xi, 
 605-622. '78 Polyodon, Phil. Trans, clxix, 683-734. '89 
 Cranial anat. Polypterus, P. Birmingham, Phil. S. vi, 118-130. 
 '83 CAFAUEK, F. (Prag.). '47 FRANQUE, H., Amia, Folio, 
 Berolini. '78 GOETTE, A., Wirbelsaule, A. mikr. Anat. x, 442- 
 641. '93 HASSE, C., Wirbelsaule, Z. Wiss. Zool. 76-90. '60 
 KOLLIKER, Ende d. Wirbelsaule, Leip. '20 KUHL u. HASSELT 
 Ost. of Sturgeon, Kuhl's Beitr. Zool. in Vergl. Anat. 2 Abth. 
 188-202. '51 MOLIN, R., Scheletro dell. Acipenser, SB. Acad. 
 Wien, vii, 357-378. '82 PARKER, W. K., Skull (and develop.) of 
 Acip. P. Roy. S. 142-145, of Lepidos. 443-491. '83 SAGEMEHL, 
 M. (Skull of Amia), Morph. JB. ix, 177-227. '92 SCHMIDT, L. 
 (Vertebras of Amia), Z. wiss. Zool. liv, 748-764. '85 SHUFELDT, 
 R. W., Amia, R. U. S. F. C. ('83) 747-834. '70 TRAQUAIR, R. 
 H., Calamoichthys, J. Dub. Geol. Soc. June 8. '70 Skull of 
 Polypterus, J. Anat. Phys. v, 166-183. ' 82 WIJHE, J. W. VAN, 
 Visceralskelet (u. Nerven) includes Ceratodus, Nied. A. Zool. 
 v, 207-320. 
 
248 
 
 FISHES, LIVING AND FOSSIL 
 
 MUSCLES. '85 McMuRRiCH, J. P., Head of Amia, Stud. Biol. Lab. 
 J. Hop. Univ. iii, 121-153. '82 SCHNEIDER, H., Augenmuskeln, 
 Jen. Z. xv, 215-242. 
 
 INTEGUMENT, TEETH. '78 BARKAS, W., Teeth of Lepid. Tr. 
 Roy. S. N. S. Wales, xi, 203-207. '77 MACKINTOSH, H. W., 
 Scale of Amia. (?). '80 PAWLOW, H., Teeth of Sturgeon, Arb. 
 St. Petersb. Nat. Gesell. No. 9, 494~5 8 - ' 59 REISSNER, Schup- 
 pen v. Polyp, and Lepid. A. f. Anat. '87 ZOGRAFF, N., Zahne d, 
 Knorp. gan. Biol. Centralb. vii, 178-183 and 224. 
 
 VISCERA. '86 CATTANEO, G., Olandula gastriche nell' Acip. Rend. 
 Inst. Lomb. xix, 676-682. '78 FURBRINGER, Excretory sys. Morph. 
 JB. iv, 56-60. '72 HERTWIG, R., Lymph. Driisen d. Stbrherzens, 
 A. mikr. Anat. ix, 62-79. HOEVEN, J. v. D. (Air-bladder of 
 Lepid.) 4to. (?). '91 HOPKINS, G. S., Structure of stomach 
 of Amia, P. Am. Micr. S. xxii, 165-169. '92 Diges. tracts of 
 N. A. Gan. P. Am. Ass. xli, 197. '69 HYRTL, J., Blutgefasse 
 d. aus. Kiemendeckel-Kieme v. Polyp. SB. Ak. Wien, Ix, 109-113. 
 '86 MACALLUM, A. B., Diges. tract and pancreas of Acip., Amia, 
 Lepid. J. Anat. Phys. xx, 604-636. '91 SEMON, R., Zusammen- 
 hang d. Harn- und Geschlechtsorgane, Morph. JB. xvii, 623-635. 
 '77 STOHR (Valves in conus compares sharks'), Morph. JB. ii, 
 197-228. '90 VIRCHOW, H., Spritzlochkieme v. Acip. A. Anat. 
 Phys. (Phys. Abt.) 586-588. '86 WILDER, Serrated appendages 
 of Amia, P. Am. Ass. xxxiv, 313-315. 
 
 FINS. '94 GEGENBAUR, Flossenskelet d. Crossopterygier, Morph. 
 JB. xxi, 119-160. '82 RAUTENFELD, E. V., Skel. hint. Glied- 
 massen, Inaug. Diss. Dorpat, 47 pp. '77 THACHER, J., Ventral 
 fins, Tr. Connec. Acad. iv, 233-242. '80 DAVIDOFF, M. V., 
 Skel. d. hint. Gliedmassen, Morph. JB. vi, 126-128 and 433-468. 
 '66 HUXLEY, Illus. of struc. of Crossopt. 4to, Lon. 
 
 NERVOUS SYSTEM, END ORGANS. '89 ALLIS, Lateral line 
 of Amia, J. of Morph. '83 CATTIE, J. T., Epiphysis, Z. wiss. 
 Zool. xxxix, 720-722, and A. de Biol. iii, 101-196. '94 COL- 
 LINGE, W. E., Sensory canals, of Polypterus, P. Birmingh. S. 
 viii, 255-262 ; of Lepid. op. cit. 263-272 ; of Polyodon Q. J. M. S. 
 xxxvi, 499-437. '83 DOGIEL, A., Retina, A. mikr. Anat. xxii, 419- 
 472, and '84 Naturf. Ges. Kasan, xi, 124 pp. '86 Geruchsorgan, Tr. 
 Kasan. Univ. xvi, 82 pp. '88 Retina, Anat. Anz. iii, 133-143. 
 '79 Gisow, A., Gehb'rorgan, Bonn. '81 Gisow, A., Gehororgan, 
 A. mikr. Anat. xviii, 484-519. '88 GORONOWITSCH, N., Gehirn 
 u. Cranialnerven v. Acip. Morph. JB. xiii, 427-514. '70 
 
BIBLIOGRAPHY: TELE OS TS 
 
 249 
 
 MIKLUCHO-MACLAY, N. v., Mittelhirn, Leip. 4to, pp. 74. '81 
 RETZIUS, Gehb'rorgan v. Polyp. Stockh. '81 SCHNEIDER, H., 
 Augenmuskelnerven, Jen. Z. viii, 215-242. '87 WALDSCHMIDT, 
 J., Centr. nerv. u. Geruchsorg. v. Polyp. Anat. Anz. ii, 308-322. 
 DEVELOPMENT. '78 AGASSIZ, A. (Larva? of Lepid.), P- Am. 
 Acad. A. and Sc. xiii, 65-76. '89 ALLIS, E. P., Lateral line, 
 Amia, J. of Morph. '81 BALFOUR and PARKER, Str. and devel. of 
 Lepid. P. Roy. S. xxiii, 112-119, an d '82 in Phil. Trans, (large 
 memoir). '89 BEARD, J., Early devel. of Lepid.. P. R. S. xlvi, 
 108-118. '95 DEAN, B., Early devel. gar and sturgeon, J. 
 Morph. xi, No. I, 1-62. '82 DUNBAR, G., Breeding of Lepid. 
 Am. Nat. May. '94 FULLEBORN, F. (Breed, habits Amia and 
 Leipd.), SB. Akad. Wiss. Berl. xl, 1-14. '67 GEGENBAUR, Wir- 
 belsaule d. Lepid. Jen. Z. iii, 359-414. '93 JUNGERSEN, H. F. E., 
 Embryonalniere d. Stors, Zool. Anz. 464, and ('94), Amia, op. cit. 
 
 No. 451. '70 KOWALEWSKY, OWSJANNIKOW, U. WAGNER, Stor, 
 
 B. Acad. St. Petersb. xiv, 287-325, and Mel. Biol. du B. Acad. 
 St. Petersb. vii, 171-183. '91 KUPFFER, K. v., Kopf. v. Acip. 
 SB. Gesell. Morph. Miinchen, 107-123, and ('93) memoir, Leh- 
 man. Munchen. '90 MARK, E. L., B. Mus. Comp. Zool. xix, 
 1-127. ' 82 PARKER, W. K., Skull of Lepid. and Acip. P. Roy. 
 S. '87 PELTSAM, E. D., Segmentation (Russian), MT. Gesell. 
 Mosc. Univ. I, Heft i, and Protocolle d. SB. Zool. Sect. 
 Mosc. ('86) I, Heft i, 206. '89 RYDER, J. A., Sturgeon, Am. 
 Nat. xxii, 659-660, and ('90) B. U. S. F. C. viii, 231-281. '78 
 SALENSKY, W., Sturgeon, SB. Gesell. Nat. Kasan ('77), 34 
 (Russian). Also Post-Emb. Entvvickel op. cit. ('78) 21 (Rus- 
 sian). (Segmentation) Zool. Anz. ('78) 243-245, and (Skeleton) 
 266-269, 288-291. (General) Mem. S. Nat. Univ. Kasan, vii 
 1-226 (Russian). '80 Pt. II, Post-Emb. and Organogeny, op. 
 cit. x, 227-545. Abstract in HOFMAN and SCHWALBE'S JB. vii. 
 213, 217-225. '81 (French), A. de Biol. ii, 233-278. 
 
 THE TELEOSTS 
 
 (Literature greatly summarized.) 
 
 GENERAL ANATOMY. '93 PARKER, T. J., Zootomy (Cod). 
 
 '88 ROLLESTON, Forms of animal life, 83-102, and '95 VOGT and 
 
 JUNG, Anatomic comparee, Vol. II. '80 EMERY, C., Fierasfer, 
 
 Fauna u. Flora d. Golfes v. Neapel, ii. 
 SKELETON. '83 BROOKS, H. S., Haddock, P. Roy. S. Dub. iv, 
 
 166-196. '90 GILL, T., Skeleton, notes, P. U. S. Nat. Mus. xiii, 
 
250 
 
 FISHES, LIVING AND FOSSIL 
 
 157-170, 231-242, 377-380. '79 GOETTE, A., Wirbelsaule u. 
 Anhange, A. mikr. Anat. xvi, 117-142. '84 GOLDI, E. A. (Derm 
 bones of Catfish, Balistes, Acipenser), Jen. Z. xvii, 401-447. '82 
 KOSTLER, M., Knochenverdickungen, Z. wiss. Zool. xxxvii, 429- 
 456. '73 VROLIK, A., Verknbckerang, Nied. Arch. Zool. 219-314. 
 
 TEETH, INTEGUMENT. '78 BOAS, J. E. V. (Scarid dentition), Z. 
 wiss. Zool. xxxii, 189-215. '78 CARLET, M., Ecailles, Ann. Sci. 
 Naturelle, viii, Art. 8. '86 SCHAFF, E., Lophobranchier, Inaug. 
 Diss. Kiel. 
 
 VISCERA, GLANDS, CIRCULATORY. '80 BOAS, J. E. V., 
 Conus, Morph. JB. vi, 527-533. '87 BROCK, J., Urogenital, Z. 
 wiss. Zool. xlv, 532-541. '91 CALDERWOOD, W. L., Head kidney, 
 J. Mar. Biol. Ass. ii, 43-46. '82 EMERY, C. (Kidney), A. Ital. 
 Biol. ii, 135-144, Atti. Ace. Rom. xiii, 43-49, ('85) Zool. Anz. 
 viii, 742-744. '77 FURBRINGER (Excretory), Morph. JB. iv, 43- 
 49. '83 MAURER, F., Pseudobranchien, op. cit. ix, 229-251. '86 
 Thymus, op. cit. xi, 129-172. '86 WEBER, M., Abdominalporen 
 (Geschlechtsorgane), op. cit. xii, 366-406. 
 
 SWIM-BLADDER. '90 BRIDGE, T. W., P. Birm. Phil. S. vii, 144- 
 187. '89 BRIDGE and HADDON, A. C., Siluroids, P. Roy. S. xlvi, 
 309-328, Phil. Trans. ('93) clxxxiv, 65-333. ' 88 CORNING, 
 H. K., Wundernetz, Morph. JB. xiv, 1-53. 
 
 NERVOUS -SYSTEM, END ORGANS. '82 CATTIE, J. T., Epiph- 
 ysis, A. Biol. iii, 101-196. '88 CHEVREL, R., Sympathetic, 
 C. R. cvii, 530-531. '91 GUITEL, F., Ligne latdrale, A. Zool. 
 expe'r. ix, 125-190, 671-697. '92 HERRICK, C. L., Fore-brain, 
 Am. Nat. xxvi, 112-120, and Anat. Anz. vii, 422-431. '87 LEN- 
 DENFELD, R. v., Phosphorescent organs, Challenger, xxii, 277- 
 329. '81 MAYSER, P., Gehirn, Z. wiss. Zool. xxxvi, 259-364. '84 
 S^DE DE LIEOUX, P. DE, Ligne laterale. Paris, 115 pp. 
 
 EMBRYOLOGY, GENERAL. '91 WILSON, H. V., Sea-bass, 
 U. S. F. C. B. ix, 209-277 (with references). '81-'91 RYDER, J. 
 A., U. S. F. C. R. and B. Larval Teleosts: '77 AGASSIZ, A., P. Am. 
 Acad. v, 117-126, ('78) xiv, pp. 25, ('82) 271-303, and Mem. 
 Mus. Comp. Zool. xiv, 1-56. '87 CUNNINGHAM, J. T., Tr. Roy. S. 
 Edinb. xxxiii, 97-136, ('91) J. Mar. Biol. Ass. ii. '83 HILGEN- 
 DORF, SB. Nat. Fr. 43-45. '90 HOLT, E. W. L., Sci. Tr. R. Dub. 
 S. 43 2 -474- '80 LUTKEN, C., Dan. Selsk. xii, 413-613. '91 
 MclNTOSH, W. C., R. Fish. Scot, ix,' 317-342. '90 MC!NTOSH and 
 PRINCE, Edinburgh, 4to. '87 RAFFAELE, F., MT. z. Stat. Neap. 
 viii, 1-84, ('90) ix, 305-329. 
 
BIBLIOGRAPHY: TELEOSTS 25 1 
 
 HERMAPHRODITISM. '91 HOWES, G. B., J. Linn. S. xxiii, 539- 
 558. '67 JACKEL, H., AH. Nat. Gesell. Num. iii, 245. '76 MALM, 
 A. W., CE. v. Ak. Forh. Stockholm. '67 SMITH, J. A., P. Roy. S. 
 Edinb. '64 '65, 300-302, ('70) J. Anat. Phys. iv, 256-258. '91 
 SMITH, W. R., R. Fish. Scot, ix, 352. '84 WEBER, M., Ned. 
 Tijdschr. Amst. 21-43, C 87 ) 128-134. 
 
 VIVIPAROUS DEVELOPMENT. '85 RYDER, P. U. S. Nat. Mus. 
 viii, 128-156 (with references) . 
 
FISHES, LIVING AND FOSSIL 
 
 CO 
 
 w 
 
 K 
 co 
 
 HH 
 fo 
 
 fe 
 
 O 
 
 ^ 
 o 
 
 H 
 
 W 
 
 hJ 
 
 w 
 w 
 
 CO 
 
 >-( o -52 
 111 
 
 wi 
 h 
 ve 
 ly. 
 
 rt ^ 
 
 rx "rt 
 
 ^t- ^*r 
 
 1-1 .H 
 IS 
 
 ^- g 
 
 pr 5 
 
 .a* g -a s 
 
 ^ +- S3 >^S 
 
 u 
 b 
 
 to 
 ro 
 d 
 iga 
 
 st 
 b 
 te 
 
 por 
 inal 
 
 <5rrt/ axis 
 sheath o 
 fins sup 
 longitudi 
 
 2 o ^"o g 
 
 If II Ml 
 iSfgSVi 
 
 *- w-~ CO <" W 
 
 5 "O w i> rt J 
 s <u oj Xi "H 
 o bf> o ^-g d 
 
 Ssflgi-S 
 oBgllfB 
 
 f'elih 
 
 2 : g " . & 
 
 ^lll-3 
 
 llp^ 
 
 |-?S|S15 
 a * .3 ^ a2 
 
 "S o C u 
 g O rt g w^g-9 
 
 l^laiii 
 
 *^ k^ 1 ' CU rt <D 
 
 3 -'*?. a,' 
 
 l.Se<^o- 
 
 ^Ssl'oS^I 
 
 .-s *a g/) 1 *- .jj w <u S 
 
 iiliP|c 
 
 tc c d QJ <s n 
 
 sjlllsll 
 
 -n'S rt o S: o e 
 
 liS: Pi 
 
 in!?m 
 
 S S S.g g c^- 
 
 fiji'Sli'l 
 
 fe S ^'3 5 
 S o^S aO 
 
 S 
 
 - 
 
 Sot 
 
SKELETON OF FISHES 
 
 253 
 
 -rt 
 
 il 
 
 . >-J3 C o 
 
 9.c $3 2 
 
 IS^II^SJ 
 
 *r* ^ C3 r> ^ "* *"-^ "-^ *^ 
 
 15 e &c 
 
 Chondr 
 and is conflu 
 massive in A 
 
 in other form 
 ossification pr 
 mouth surface 
 brane) bones. 
 
 niu 
 es ; 
 rmal 
 ener 
 nal 
 iety 
 
 Chondrocr 
 cartilage bo 
 column. D 
 reduced in g 
 often additio 
 in great var 
 tegals) . 
 
 liiiifi 
 
 c^t-p^rj^rt 
 
 ne 
 der 
 io-b 
 pec 
 
 tor 
 fin 
 to 
 
 o) " . <" ^2 in 
 
 fcJ3 "OTd O 
 
 i'SW-f- 
 
 -1 _- rt C U.5 jg w 
 
 Biis-clill 
 
 t-urti; 1 - 5 ^ rt 
 
 . ,s = 2 a 
 
 ns 
 ycer 
 y de 
 rma 
 
 Unpaired fi 
 Caudal diphy 
 Dorsal mainly 
 supports. Der 
 ized joint in a 
 fins shark-like 
 clustering roun 
 (basals). " Cl 
 tral fins of the 
 
 diphy- 
 al and 
 archip- 
 of all fins 
 ifurcating 
 
 l por- 
 ments 
 fins in 
 n) ; in 
 ls con- 
 
 o 
 adi 
 " 
 
 Unpaired fins continuous 
 cercal tail; their supports 
 basal cartilages. Paired fi 
 terygial." The outer halve 
 consisting of jointed and 
 dermal rays. 
 
 Unpaired fins shark-li 
 tions, however, enlarged 
 segmented and forked. 
 some forms shark-like (P 
 others, largely dermal, radi 
 stricted, fused, insignifican 
 
 External portion of unpaired fins sup- 
 ported by dermal rays of many types, 
 supporting parts representing mainly 
 radio-basals of older fin types ossified, 
 often with fusions. External portion of 
 paired fins dermal; radio-basals greatly 
 reduced, confluent, ossified. Tail homo- 
 cereal. 
 
 5S 
 
 ^^U 
 
 r-~ ' D. (U O 
 
 I 
 
 l-ilSMI 
 
 iss-^g-i 
 
 2 c J cs o,S 
 
 1-g c ^l| 
 Il^llfi 
 
 ^ggg 
 
 ilitlii 
 
 ^2 ^2 O U^ <U 
 
 
 2 ] 
 
 w c ~ 
 got 
 
Figs. 310-315. Skulls of fishes, to illustrate the mode of articulation of jaws and 
 branchial arches. 310. Skull of Scyllium. (After MARSHALL and HURST.) 311. Hep- 
 tanchus (Notidanus). (After HUXLEY.) 312. Chim&ra. 9 313. Ceratodus. (Slightly modi- 
 fied after HUXLEY.) 314. Polypterus. 315. Salmon. (After PARKER.) 
 
 A. Articular. AG. Angular. BR. Branchiostegal rays. CHY. Ceratohyal. D. 
 Dentary. EHY. Epihyal. EPH, LG. Epihyal ligament. EPO. Epiotic. F. Frontal. 
 GHY. Glossohyal. HHY. Hypohyal. HM. Hyomandibular. IO. Interoperculum. 
 J. Jugal. LC. Labial cartilages. MCK. Meckel's cartilage. MPT. Metapterygoid. 
 MSPT. Mesopterygoid. MX. Maxillary. N. Nasal. NC. Nasal capsule. O. Opercu- 
 lum. OC. Opercular cartilage. OR. Suborbital ring. P. Parietal. PAL. Palatine. 
 PMX. Premaxillary. PO. Preoperculum. PTO. Pterotic. PTQ. Palatoquadrate. 
 PTY. Palatopterygoid. Q. Quadrate. SQC. Supraoccipital. SE. Supra-ethmoid. SM. 
 Symplectic. SO. Supraorbital. SP. Splenial. UMC. Upper median cartilage (not 
 frontal spine of male). 
 
 Figs. 310, 314, 315 are regarded by HUXLEY as "hyostylic" (i.e. the hyoid element, 
 HM, attached by ligaments to the jaw hinge, taking an important part in the suspension 
 of the jaw; 311, a modified hyostylic condition ; the hinder upper margin of PTQ becom- 
 ing greatly enlarged, and attached by ligaments to the skull, is spoken of as "amphistylic " ; 
 312-313, were " autostylic," i.e. the upper jaw element fused with the skull. 
 
 254 
 
A d S d S 
 
 p-sgg a-s 
 dial- 6 *! 
 |I^1,-I 
 
 ^ 3 . S: S 2 fa 
 4r.*l 
 
 ^'!l!|g 
 
 O U j3 -s; -3 ir! 
 
 255 
 
FISHMS, LINING AND FOSSIL 
 
 co 
 
 W 
 E 
 co 
 
 O 
 
 a 
 
 J 
 
 < 
 
 E 
 u 
 Sz; 
 
 < 
 ^ 
 PQ 
 
 co 
 
 W 
 E 
 H 
 
 fe 
 O 
 
 co 
 
 O 
 
 H 
 < 
 J 
 W 
 
 ^S)"l 
 ^^-Sis 
 
 
 ? 2^ 
 
 jsllll 
 
 L_, C .5 rt 
 
 olll 
 
 g ;- 
 
 
 aia>a;c c3 
 
 Ml I J 
 
 s-^? g c 
 
 3 j_i O w i2 C 
 
 fis ^8| 
 
 v* fj 
 
 <L) O 
 
 to 
 me 
 ally 
 hyal 
 ve 
 
 dibular serves t 
 he jaw; its attach 
 ll region and dist 
 mentous. Ceratoh 
 rts anteriorly the 
 branchial arche 
 rod-like oper 
 egals) . 
 
 III! H 
 
 IMS 
 
 -a +- o o w 
 
 i=|i:i 
 
 1S B t!-s 
 
 . w C o 
 
 Itf'H 
 
 N!.it* 
 
 I'llul 
 
 .| U S^S> 
 
 T3 ? J ID o 0) 
 
 ^^5^^ 
 O 1 ^^ ., J3' 
 
 i !( -3.S 2 
 
 - 
 
 l-llfll 
 
 " -> 5 '" . f 10 
 
 S. S s'-o 
 
 fl o! 
 
 ilill 
 
 liifi 
 
 >- rt " g <u 
 
 OJ 4J x> Q. 
 ^bli- ^^ 
 1H -*T3 >> ^ ^ 
 
 Blll 
 
 -I"! 1-al 
 
 >"!".i^ 
 .It I? 
 
 i T3 jj C to rt 
 -"^ K 
 
 3 S ..3^ = 
 
 a|3sl 
 
 O CJ "^ tfl 
 to 0) jn O ^^ bfl 
 
 5-Sog 
 | -s S "g & 
 
 _ 
 
 cj >, en O jj O 
 
 bo 
 te, 
 ly 
 
 o 
 
 rfl ? 
 
 fN ' TO ^ 
 
JAWS AND GILL AKCHES 
 
 257 
 
 ,11 
 
 c >.s 
 
 c 2~ 
 
 Ifli 
 
 fill 
 
 
 * 
 
 
 Oo.cr;.o 
 
 1 l|l 
 
 
 10 i^I' 
 
 o g 
 
 ' 
 
 
 -cf js a.*- <u >s 
 
 sllff^rf'8 
 IfriUsJ-Ssj 
 
 r2 .. w 55 cs rt .2 
 
 ^'3 S O'-rf "" S 
 CU-3 2 O O X 
 
 wing 
 , pter 
 d ant 
 denti 
 compo 
 e mout 
 , prem 
 kelian 
 mem 
 
 l^lpgl' 
 
 ' 
 
 ^l-i'iffl! 
 
 S IOTtlJ 
 
 .5Ert 
 
 ial. 
 
 c >%-3 -! c -d 
 8&ol-2^ 
 ^S^^g^u- 
 a" 55 .3 3 
 
 J jj <" O 
 
 ll^l- S - s & 
 
 > S S i a 
 
 a o e -61s 
 
 JilUti 
 
 p iH?.ai 
 
 ll^lli 
 
 Ig 
 
 o h-^ 
 
 111 
 
 *ti 
 
 c 2 
 51" 
 
 I 1* 
 
 I |ly 
 1, |.ix"l 
 
 ss'^JSijS 
 1 1's ?a 
 
 u -a^ a ^ 
 jl^.l^J 
 
 ii's<i 
 
 sflili 
 
 Illll 
 
 6 W 
 
 ^ y?^H' 
 r2--sS=- 
 
 WMJH 
 
 &y- 32^3 
 
 ^fll-1 
 
 .^"S o.2- IS 
 
 *!M*! 
 
 ^lllli 
 
 |r;ll 
 
 ^^ rt S " - y 
 
 !l!|l 
 
 liffi 
 
 -^-- 
 
 tli 
 
 * 
 
 lil 
 
FIG. 316 
 
 AU 
 
 318 
 
 322 
 
 320 
 
 VEN 
 
 VEN 
 
 Figs. 316-325. Heart and arterial cone of fishes. 316. Heart of shark; 317, Heart 
 of catfish, Silurus glanis ; 318, Heart of shark, shown opened at the side. 319. Conus 
 arteriosus (inner view) of Chimcera, 320. Conus of Ceratodus. 321. Conus of Protopte- 
 rus. 322. Conus of Lepidosteus. 323. Conus of Amia. 324. Conus and bulbus of the 
 Teleost, Butrinus, 325. Conus and bulbus of the Teleost, Clupea. (Figs. 316-318 
 after WIEDERSHEIM, 320-325 after BOAS.) 
 
 A. Aorta. AU. Auricle. B. Bulbus. C. Conus. V. Valves. VEN. Ventricle. 
 
 258 
 
Pigs. 9-12. Arrangement of gills of Bdellostoma (9), Myxine (10), Shark (n), and 
 Teleost (12). In each figure the surface of the head region is shown at the left. 
 
 B. Barbels. BD. Outer duct from gill chamber, BS. BO. Common opening of outer 
 ducts from gill chambers. BS. Branchial sac, or gill chamber. BS". Branchial sac, sec- 
 tioned so as to show the folds of its lining membrane. G. Lining membrane of gullet. 
 GB. Gill bar, supporting vessels and filaments of gills. GC. Outer opening of gill cleft. 
 GF. Gill filament. GR. Gill rakers. GV. Vessels of gill. J t J'. Upper and lower jaw. 
 M. Mouth opening. N,N'. Anterior and posterior opening of nasal chamber. OP. Oper- 
 culum. SP. Spiracle. ST. Tendinous septum between anterior and posterior gill filaments. 
 * Denotes the inner branchial opening; -, the direction of the water current. 
 
 259 
 
260 
 
 FISHES, LIVING AND FOSSIL 
 
 s 
 
 ! I 
 
 g >- 
 
 
 
 33 -a 
 
 s 
 
 ca, 3 
 
 W 
 PL, 
 
 O 
 
 5^2 
 
 -Ss .0 
 
 W 
 ffi 
 co 
 
 ft 
 O 
 
 S 
 
 3 
 
 ffi 
 
 w 
 
 E 
 H 
 
 b/D 
 fa 
 
 s 
 11 
 
 S| 
 
 3'S 
 .2 ? 
 
 S 
 
 T i. . 
 rt o 
 
 5 o 
 g 
 
 | 2 
 
 8<u 
 K 
 a w 
 
 = 1 
 
 SI 
 
 Ms 
 
 : g,s 
 
 S 2 
 
 r H 'rf' 
 
 gas 
 al. 
 
 N S -g 
 
 3 CS 
 
 gfll 
 '8 ^ ^.5 
 
 "o J>" S 
 42 '^ * 
 
 K^-^T; 
 
 "c "o 
 
 . ?fi| 
 
 * 
 
 B X! 
 
 - 0) 
 
 ss 
 
 ^s 
 
 sg- 
 a 
 
 I 
 I * 
 
 O > 
 
 o5 - g 
 
 rt ^ > a> OJ 
 
 tn ^ > eS w 
 
 |o^ > 
 
 3 ^ xj > 
 
 h c o *3 "*-" 
 
 8 
 
 of 
 f 
 
 s^s 
 
 Big 
 
 11". 
 
 111 
 
 *->!, 
 
 '-o c 
 
 !!>=s 
 S*ll 
 
 ^1$ 2 
 
 ^1 
 
 " 9 S op 
 
 g5J*j-g t5^ 
 
 Slll^l 
 sa* 1 6 2 
 
 O F.w.2 O.S aJ 
 
 ^ J ,o , .. 9 
 
 in 8 UJ 
 
 3 C 3 3 <J 3 
 
 C-- C C C 
 
 O in O O O 
 
 ri 
 
 s 8- I 
 f$ | I 
 
 O GO W S 
 
 till 
 
 2 "S 5* ff-S'^O 5 
 
 CU U " 
 
 CO 
 
 W 
 
 PH 
 CO 
 
 O 
 O 
 
 o 
 
 CO 
 
 O 
 U 
 
 n O 
 
 .tS oJ " 
 
 ..a M 
 
 O S 8:2.9 
 
 \ ^-g^*. 
 
 w , 1 Pi 
 
 I-) T3 I 2"X 4, 
 
 u s nr-s 
 
 
 <_, > 
 
 SB s S 
 E "SsSf 
 
 igif 
 
 ^ 
 
 "aj *-' ** ^* 
 
(7/ZZ5 
 
 DEFENCES 
 
 26l 
 
 :d to the anterior or 
 and are constantly 
 11 bars, which inter- 
 
 f'// Defences. 
 
 folds produced at 
 or margin of each 
 is sometimes sup- 
 cartilaginous rods. 
 
 i-SI s i 
 
 TI: s i 
 
 _. a, w -a ji 
 
 1S1 S a 
 
 S -a 
 
 111 * 
 
 -it | | 
 
 1 1 
 
 1 1 
 
 6 i 
 
 - s. s : s 
 
 E" E " 
 
 3 33 
 
 Jill 
 III! 
 
 "0 a, 
 
 o '5 S .3 S 
 
 <i j ! &i 
 
 OXJ U O 
 
 3 "5 2 
 
 O C O a; 
 
 S-a S.I* 
 
 o o ^ 
 
 o .5 
 
 G O'S 3 
 
 * "2 o 
 
 STH o. 
 
 - . - ; 
 
 3 " 
 
 a I 
 
 i o 
 
 *- .5 rf 
 
 ^ 
 
 c a 
 
 
 9 
 
 .1 |5 
 
 *Q & 
 
 rt 
 
 50 
 
 ' 'B 
 
 w-a Jj^ 
 
 ill 
 
 "c c I 
 
 'S 
 
 1 II 
 
 ^ P 
 
 "c? 
 
 'e <o" 
 
 1 51 
 
 "jl-d || 1^1 
 
 
 
 i2 li 
 
 c ^ g I) 
 
 1) W Q. 
 
 g "> 
 
 w 
 
 g S 
 
 rt J=.2 Q- 
 
 --" rt.2 
 
 II 
 
 b S^ 
 
 
 3 "^ T3 
 O t/5 O C 
 
 5 o = *v u 
 
 S-t 
 
 a <!! 
 
 2 \f 
 
 |IS 
 
 en = "6 "^ ' S g* "3 2 ^ K 
 
 C JX CU3 
 
 "g O .2 
 
 
 
 
 |I.1 
 
 11-1 
 
 |l F 
 
 = ^"-5 
 
 ; ^ o 
 
 ^^2 o a 
 
 *;-i! 
 si?? 
 
 =S5 
 
 2'53M 
 
 pl 
 
 rt * -5 <u <D 
 S g ^ 5 & 
 
 ||^ g 50 go 
 
 - V 3 uT 
 
 1 . 1 
 f 1 1 " 
 
 3 w C 
 
 ^2 5- 
 
 2 rt H'S 
 
 .S2 
 
 CS 2 
 
 2 ; 
 
 0) 
 
 * C S2 
 
 % 
 
 
 .2 o 
 
 Si A 
 
 o'=|u- 
 
 ^f 5 
 
 
 * S 
 
 . o O 
 
 8 M -: a 
 
 w D, - c 
 
 ?=! 
 
 li 
 
 
 &s 
 
 g^ ^ bfl 
 
 t! 3 f 
 
 |ll 
 
 : 
 
 1 . 
 
 g| = g | g g - 
 
 "* 5 i4 c 
 
 1 ^3 
 
 
 >^Q O 
 
 ^*o S* ^ S *5 
 
 5'o rt rf 
 
 i 
 
 
 0|? 
 
 ^ 13 ^* J^ Q ^ .2 
 
 5 a 
 
 J3^*o ^ 
 
 I ofi| 
 
 3 cs a; o 
 g 3 S 
 
 
 
 1 Sj 1 -p 
 
 ft ft C ft w 
 
 i||i 
 
 * I'll! 
 1 !Fi 
 
 ^ g C ^ ' 
 ^ Srt|^C 
 
 r u :; 5- rt y 
 ^ o c.E* 
 
 -0 trt 
 
 | 
 
 1 
 
 o S S "o^Tr: 
 
 = HS. n . il 
 
 g^= -gj: " g> 2 
 
 |g Is i 1^1 
 
 H232 22 ,2 If. 
 
 ^ fc - 5i|l 
 
 -3 T3 -0 rt ft 
 
 
 
 
 09 
 
 oa 
 
 
 
 1 
 
 ctf : 
 
 5 1 
 
 co 3 
 
 2 ^J S d ri 
 
 I 
 
 s 
 
 1 S 1 
 
 2 'S 
 
 s s & 
 
 -S 
 
 A *3 J 
 
 > -a .s* > 
 
 o o o B 
 CM h4 <5 CM <J H 
 
FIG. 326 
 
 Figs. 326-331. Digestive tracts of fishes. 326. Cyclostome, Petromyzon. 327. Shark. 
 328. Chimaeroid, Callorhynchus. 329. Lung-fish, Protopterus. (After W. N. PARKER.) 
 330. Ganoid, Acipenser sturio. 331. Perch. (After WlEDERSHElM.) 
 
 A. Anus. BC. Branchial chamber. BE. Bursa entiana (duodenum) . CL. Cloaca. 
 GC. Gill openings. 7. Intestine. M. Mouth. MI. Mid-gut. NN'. Anterior and poste- 
 rior nares. OE. Gullet. PC. Pyloric coeca (pancreas). PY. Pyloric end of stomach. 
 R. Rectum. RG. Rectal gland. S. Stomach. SP. Spiracle. SP. V. Spiral intestinal 
 valve. 
 
 262 
 
DIGESTIVE TRACT 
 
 263 
 
 
 
 
 : rectum with 
 into lobules, 
 percular skin 
 
 >aca. Dorsal 
 by opercular 
 
 i 
 
 o 
 
 p 
 
 
 
 3 
 
 
 
 
 
 a 
 
 _s 
 
 "B 
 . 
 
 1 
 1 
 
 ntestine, with 
 
 ^ 
 '^ 
 
 . "c 
 
 ^ 
 '5 
 & 
 
 e 
 
 i spiral valve 
 :onditions of 
 
 
 
 
 T: _ o 
 
 2 S c 
 ^ -g < 
 
 %% 
 
 3* 
 
 .1 
 1 
 
 1 
 
 3 
 
 a, 
 
 w 
 
 < 
 
 1 
 
 5 
 
 li 
 
 If. 
 
 1 
 
 tr 
 
 ^ s 
 
 
 
 
 * x 
 
 | S 5 
 
 hj 
 
 O 
 
 c o. 
 
 It 
 
 3 
 ^ 
 
 1 
 
 73 
 S2 
 o 
 
 a 
 
 1 caecum. 
 
 1 
 
 C o" 
 
 'C c 
 >^ '~ 
 
 - 1 c 
 
 o 
 t:" 
 
 h 
 
 "c ~ 
 
 
 
 c3 
 CU 
 
 * c d 
 
 c3 2 
 
 'o ^ 
 
 2 
 
 | 
 
 1 
 
 J 
 
 - S 
 
 
 rt o 
 
 
 
 55 
 
 ' JK C3 
 
 &s o. e 
 
 4) 
 
 1 
 
 S 
 
 o 
 
 to 
 
 ui "1 ft 
 
 
 c G 
 
 
 
 2 
 
 C C/3 d 
 
 > .^ 
 
 13 
 
 CJ 
 
 ^_^ 
 
 -^ 
 
 fll 
 
 ~* 
 
 o 
 
 
 
 1 
 
 g 5 
 
 Sii 
 
 d ^ ys 
 
 ?l 
 
 a g 
 
 S 
 
 8 
 
 ! 
 
 v 
 
 9 
 
 o 
 
 1 
 
 fit 
 
 s| 
 
 li 
 
 
 
 c 
 
 
 .i: o. 
 
 
 o 
 
 o 
 
 = 
 
 C W3 r/^ 
 
 ai (/] 
 
 ^L 
 
 IX. DIGESTIVE TRACT 
 
 1 
 
 .23 
 'to 
 
 b 
 1 
 
 1 
 C^ w 
 cp _rt 
 
 vO w 
 N e 
 
 CO S 
 
 X c3 
 
 ^T^ ^ 
 
 S I 
 N ""' M 
 
 1 
 
 0> 
 
 J3 
 
 H 
 
 1 
 
 
 o 
 
 tn 
 
 d 
 
 C 
 
 ."s 
 
 .S 
 
 0) 
 
 1 
 
 1 
 
 c 
 
 CJ 
 
 1 
 
 i" 
 
 JS 
 '-o 
 
 siphonal stomach, short intestine provided with spiral valve (having 
 LI caecum; cloaca. Mesentery at beginning and end of digestive 
 ierced with 5 (6 or 7) gill clefts ; spiracle present, its gill supplied bj 
 ent in Chlamydoselache. 
 
 almost straight, no marked stomachic dilation; injestine with sp 
 y reduced to 4 string-like supports. No spiracle ; gill arches 5, com] 
 , with rudimentary cartilaginous supports. 
 
 >w gullet, tubular stomach, intestine with spiral valve of 9 turns, 
 y greatly reduced. No spiracle ; 5 gill arches ; hyoidean gill. 
 
 t straight ; stomach small ; intestine with spiral valve of 9 turns, sh 
 5 gill arches, of which the hinder 3 present external branchiae. 
 
 t ; a single pyloric caecum, spiral valve of 8 turns, no cloaca, single (or 
 odont. 
 
 stomach, recurved at end; a mass of pyloric caeca; short, twisted, s 
 
 Ive of 3 (rudimentary) turns. No cloaca. Well-marked dorsal mese 
 ial stomach ; pyloric caeca in fused mass (but separate in Polyodon) ; 
 Ive of 8-9 turns ; no cloaca. Dorsal mesentery largely fenestrated. 
 
 pouch-like stomach, no pyloric caeca; long, stout, small intestine, littl 
 Ive of 4 turns ; no cloaca. Dorsal mesentery at hind gut largely fene 
 
 ct of many types ; stomach usually recurved ; many pyloric caeca ; in 
 )heirocentrus), with little difference between anterior and posterior d 
 y. Spleen single. No spiracle. Accessory branchial apparatus. 
 
 
 
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 enibrane thrown into irregular ridges ; its vascular supply ^ 
 of efferent branchial artery, thence returns by vein to left 
 
 LIVING 
 
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 lorsal aorta (? coeliac artery) ; lining membrane regularly ^ 
 
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 lired fourth branchial artery, returns by systematic veins ; 5^ 
 
 g membrane smooth; vascular supply from dorsal aorta 
 
 ; with many diverticula ; its long air duct may connect with 
 h the throat in Physostomes ; its opening obliterated in 
 nd-producing; connected with the ear in Cyprinoids and 
 11. Its substance may be calcified Cyprinoids, Siluroids, 
 Is). 
 
 
 
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 omologous.) 
 
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 pharynx; lin 
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 ; vascular 
 
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 iary artery ; 
 
 
 
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 gos ; opens withoi 
 returns by systema 
 
 to -a 
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 Acanthopterygians 
 Siluroids, and in t 
 and in fossil Cross 
 
 
 
 3 
 
 
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LEPIDOSTEUS 
 AND AMIA 
 
 ERYTHRINUS 
 
 CERATOOUS 
 
 POLYPTERUS 
 
 AND 
 CALAMOICHTHYS 
 
 LEPIDOSIREN 
 
 AND 
 PROTOPTERUS 
 
 REPTILES 
 BIRDS 
 
 MAMMALS 
 
 Figs. 13-19. Air-bladder of fishes, shown from the front and sides. Cf. p. 
 264. A. Air- or swim-bladder. AD. Air duct. D. Digestive tube. (After WILDER.) 
 13. Sturgeon and many Teleosts. 14. Amia and Lepidosteus. 15. Erythrinus, a 
 Cyprinoid Teleost. 16. Ceratodus. 17. Polypterus and Calamoichthys. 18. Lepi- 
 dosiren and Protopterus. 19. Reptiles, birds, and mammals. The diagrams illus- 
 trate the paired or impaired character of the organ, its varied mode of attachment 
 to the digestive tube, and the smooth or convoluted condition of its lining mem- 
 brane. 
 
 26 5 
 
266 
 
 FISHES, LIVING AND FOSSIL 
 
 s 
 
 w 
 
 H 
 co 
 
 CO 
 
 J 
 < 
 
 i i 
 
 W 
 O 
 
 X 
 
 S8 
 
 R *|J** 
 
 " iffe 
 
 & || ail 
 
 i &!f 
 
 passes outward 
 urinogenital sinus; 
 Eggs pass from pair 
 ilized and receive sh 
 ard through dilated 
 us sharks the wal 
 
 - o P<o 53 
 
 alii 
 
 Mil 
 
 -E-Q'S 
 I4I-I, 
 II 8 *>l% 
 
 f r yi5 
 
 EU-St? *.S 
 
 es 
 a : 
 
 a 
 
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 8 i5*'al 
 
 &^g|<sg 
 
 aie 
 
 a pass outward thro 
 d vas deferens may 
 nd noteworthy modi 
 ns into or in front of 
 metimes be present 
 ntinued into the 
 achment and emi 
 ronectid), and he 
 erranus) appear 
 
 > e S u = o S4J^ 
 
 8 3l8-8|i| 
 
 -0-5 c ^w'S^ g 
 
 '{J |j| ]!i 
 
 |5|ls|Iil 
 
 S. S-S^oS^-w 
 
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 O) 
 
 {111 
 
333 
 
 334 
 
 UGS 
 
 AP 
 
 AP 
 
 335 
 
 336 
 
 UGS 
 
 337 
 
 / \ us 
 
 f *r% 
 
 UGP 
 
 AP 
 
 Figs. 332-337. Urinogenital ducts and their external openings. 332. Cyclostome, 
 Pctromyzon. (After W. K. PARKER.) 333. Shark, ?. 334. Chimaeroid, juv. 9. 335. 
 Cerahdus. 336. Ganoid, $. 337- Teleost (Salmonoid), ?. (After BOAS.) 
 
 A. Anus. AP. Abdominal pore. CL. Cloaca. G. Genital opening. MD, MD' . 
 Left and right Miillerian ducts. OVD, OVD'. Left and right oviducts (not Miillerian 
 ducts). R. Rectum. U, U' . Left and right ureters. UG. Urinogenital opening. UG' ', 
 UG". Left and right Urinogenital ducts. UGP. Urinogenital papilla, showing distal 
 opening. UGS. Urinogenital sinus. UP. Urinary papilla. 
 
 267 
 
268 
 
CIRCULATION IN FISHES 
 
 269 
 
 lejiln**lif"4lt 
 
 iPtMlliilPJaj^i 
 
 ^llllPPlllilFlil 
 
 *J f n-'j<.-- 1 i 
 
 sl*&|f*tf* 
 
 Sipllsi'gisljsisf 
 !i:a*llaiil3*&Mi 
 
270 
 
 FISHES, LIVING AND FOSSIL 
 
 5-3 
 
 P 
 
 
 
 HI li 
 
 s.eis To 3 
 
 68, ^ 
 
 II 
 
 
 H u 
 co ^ 
 
 12 5^ 
 'Hat? 
 
 JJ-0 
 
 rt r< 
 
 ^3 fi 
 
 
 i 
 
 
EXCRETORY SYSTEM: ABDOMINAL PORES 
 
 271 
 
 
 9 O.S. o 
 
 -32 
 
 *l 
 
 Pi tO 
 
 3 
 
 is 
 
 So, 
 
 ""2 a u 
 
 M S O fl Q 
 
 
 
 *f 
 
 CO g s 
 W 'SjT 
 
 !l? 
 
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 & Si 8 
 
 S ||| 
 
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 CG 3 o.S 
 
 ^ 
 
 511 
 
 S-5 <0 8 ^ *S & 
 
 Sgg 3 g ^" O 
 U <n,24}-i W 
 
 l|^!.st.lla 
 
 SJllinn 
 
 - 5 S . ^ S .S 
 *o" -a" '-^ tf a*. 
 11 ill" 
 
 '3 '3 o '3 
 d. CU c/3 D 
 
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 &a 
 
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 gj o P< ^ 
 
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FIG. 339 
 
 340 
 
 341 
 
 - 339-344' The brain of fishes. The dorsal view of each brain is shown in the 
 upper figure, the ventral view immediately below. 339. Bdellostoma. (After JOH. 
 MiJLLER.) 340. Petromyzon (Ammoccetes stage). (After ZlEGLER'S model.) 341. 
 Shark (angel-fish, Squatind). (After DUMERIL.) 342. Chimczra. (After WILDER.) 
 343. Lung-fish, Protopterus. (After BURCKHARDT.) 344. Perch, Perca. (After T. J. 
 PARKER.) 
 AQS. Aqueduct of Sylvius. DSE. Diverticula of saccus endolymphaticus. E. 
 
 272 
 
342 
 
 Epiphysis. EP. Epencephalon. IN. Infundibulum. LH. Lobus hippocampi. LI. Lobi 
 inferiores. LT. Lamina terminalis. M. Mesencephalon (optic lobes). ML. Myelen- 
 cephalon (spinal cord). MT. Metencephalon (medulla). MT '. Anterolateral lobes of 
 metencephalon. P. Prosencephalon (cerebral hemispheres). P T. Pituitary body. R. 
 Olfactory lobes. SV. Saccus vasculosus. T. Thalamencephalon. 4. Fourth ven- 
 tricle. Numbers I-X. Cranial nerves, i. First spinal nerve. 
 T 273 
 
274 
 
 FISHES, LIVING AND FOSSIL 
 
 
 
 'o 
 
 c 
 
 g-g 
 
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 11 
 
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 g E 
 
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 52 
 
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 '= 
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 mate ant( 
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 4) 
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 epresente 
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 111 
 
 
 15 S 
 
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 8 
 
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 ominent ; 
 alon) wide 
 
 1 | 
 
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 prominent; 
 )r plexus; 
 ning; <?/<? 
 
 'i a; 
 
 2 
 
 are scattere 
 
 ntinues an: 
 
 ventricle r 
 into which 
 
 Lindibulum 
 losus ; mes 
 
 S 
 
 a 
 1 
 
 1 
 
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 aj t* 
 
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 >-344) 
 
 rences within the g 
 
 i 
 
 a> 
 
 o 
 
 TJ 
 
 epiphysis, howev^ 
 w; medulla (mete; 
 
 1! 
 
 1! 
 
 2 
 
 ic system present, 
 ptic nerves probab 
 shable ; fore-brain 
 
 wncephalon raised 
 id plexus, lacking i 
 ! prominent centra 
 
 halon. Spinal cho 
 ntral branches, bul 
 
 ibstance the nerve 
 
 i post-olfactory lol 
 
 Ib ; prosencephalon 
 h large dorsal opei 
 
 e ventral surface a 
 ; (paired) saccus ^ 
 
 HE CENTRAL NERVO 
 
 (Cf. Figs. 339 
 V summary of the more important diffe 
 
 1 
 & 
 
 I 
 
 1 
 
 'o 
 
 'S 
 1 
 
 "o 
 
 a 
 
 vcephalon apparently greatly reduced; 
 epencephalon) with median dorsal furro 
 
 in by abrupt transverse dorsal and ven 
 interior to i posterior root ; of these t] 
 
 ior roots fuse together No sympathet 
 .nch of the vagus. A chiasma of the o 
 i in B ; its parts more readily distingui 
 
 mpi or postolfactorius ; lobes of thalan 
 \ eye 7) ; no velum (?) t a simple choroi 
 s ; mesencephalon with dorsal lobes and 
 
 ig (sinus rhomboidalis) in the metencep, 
 r roots ; both divide into dorsal and ve 
 
 M 
 C 
 
 1 
 
 <u 
 
 w 
 
 | 
 
 en 
 
 0) 
 
 c 
 o 
 
 E 
 o 
 
 E 
 
 ^ 
 
 c 
 "tu 
 
 g 
 
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 cu 
 
 "o 
 
 ^ 
 
 I 
 
 sn enlarges into a hollow olfactory bu 
 ibus hippocampi ; thalamencephalon wit 
 
 long, slender epiphysis present; on th 
 a large pituitary body, and a pad-like 
 
 H 
 
 ^S 
 
 E 
 o 
 
 o 
 
 %> ^^ 
 
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 CO t 
 
 N 
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 11 
 
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 13 
 
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 LUS Ult 
 
 0, 2 
 
 5 s 
 
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 &.S c 
 
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 S o 
 
 21 
 
 X3 rt 
 
 3 
 
 IS 
 o 
 
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 1 
 
 
 
 
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 e 
 
 
 
 
 
 
 
 
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 2 
 
 
 
 
 
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NERVOUS SYSTEM OF FISHES 
 
 27S 
 
 J3 ^ 
 
 "* J3 
 
 ||| ft'Sf J 
 
 5 let- |ll 
 itflfji; 
 
 o *5 "^ "rt *- ~ 
 
 T- o ^ - H to 
 
 2 .6 
 
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 S -S " C3 
 
 ""'* ^ 'O ~ ~ TO ^ 4) 
 
 fflll*! 
 
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 S . -S o 
 l^t-^l 2 
 
 f-?UlP 
 
 If 
 
 5 -2 
 
 S2 2 '% a 
 
 o a 55 J 
 
 :i-^ii-g 
 
 ;-= Til 
 
 S ^" S *o 5 ^ *? 
 
 !!!|ll! 
 s = 5ip 
 
 Eb B = O I jj 
 
 " &5't'8 JS l 
 
 o 1 ];*!] 
 
 ? , a "s 1 
 
 o ."2 "s T* x o 
 
 ^ ^ ^ X O 
 
 -^- S ^ I 
 
 ^j .^ 
 
 Bro^.-C^sr 
 
 S ., J g S S o 
 
 e 
 en 
 
 I -e - s 
 
 ><lylal 
 
 ^ C <" S w C 
 
 2 o li o 
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 111! 
 
 S ^ * c O * 
 > ^ a o S 
 5 5 5 to 6 g 
 
 bJO 3 C (" O u 
 
 j-s 
 
 5 '^ -s 'S. " 
 
 f.liifI11 
 
 T3 IT .S > 
 
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 S d .s a 
 
 =3 S 2 c 
 
 O c3 5 D, H 
 
 ^&o.^ 
 
 If 2 S 
 
 ^ * o , 
 
 o T sympa 
 vagus, as in sharks 
 n is non-nervous, or 
 
 5 ^ S 2 
 
 S2 -g ^ o 
 
 ^o^t_ S d 
 
 i?** t'"*| 
 illllilll 
 
 S H 
 
 to g< 
 
 c o 
 
 3 2 
 
276 
 
 FISHES, LIVING AND FOSSIL 
 
 8 fc-s 
 
 CO 
 
 O 
 
 W 
 
 CO 
 
 
 
 W 
 
 CO 
 
 W 
 E 
 H 
 
 
 I III 
 
 2 ' 
 
 p 
 
 030 
 
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 S-.s-fi 
 
 CS 4J 
 
 > ,fl 4} 
 
 m 
 II! 
 
 ^51 
 
 V 
 
 4.8 8 ri 
 
 III1I 
 
 rt S fX 
 .C O g w 
 
 T3 c P- 1 *O O 
 T3 rt c C i- 
 rt o .S cS W 
 
 oid 
 us 
 
 iaticus (My 
 , with a bu 
 
 all s 
 si* | 
 
 "M = - 
 
 II 6 S "I- 
 
 l!i--lf 
 fiilllll 
 
 ' 5 M B 2 S 
 
 <Uj3CgriPJ<U 
 
 1 1 1 S 1 1 J I 
 
 T2 C t* ^ "7^ 
 
 t* (> 
 
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 c 'o 
 
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 c g 
 M d" o 
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 e 
 
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 a) a) <u o 
 
 S e c -2 -2 
 
 ^ c -S -5 -3 <*- u 
 
 ^ 2 I-, o 3 
 
 G, JD O 8 w 
 
 C3 OJ 
 
 *3 hn ^ '" W 
 
 ^ 
 
 ^3 
 
 .- ._. XI 
 
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 O "T-; TO t ^- 
 
 & * a 
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 CX T3 
 
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 S "2 o 
 
 55 S S 
 
 j3 bJO ^ i 
 
 I -I a i 
 
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 Sf.il 
 
 o -= u c 
 
 c 3 o ^ 
 
 I 1 '!." 
 
 s ^ 
 
 o js 
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 e s -o S 
 
 O *C ^ cs 
 
 oil 
 
 rt 3 3 3 
 
 j/2 a; <" S c 
 
 C -5 .2 -a -E 
 
 s : .-2 
 
 E? -s 
 
THE SENSE ORGANS 
 
 277 
 
 - t/> 
 
 w 3 
 
 S 
 
 its nerve supply 
 bulb of greatly 
 ngs become ex- 
 ecialized labio- 
 aris is somewhat 
 e to 
 
 s ; 
 ry 
 ni 
 sp 
 
 sark 
 olfacto 
 sal op 
 by the 
 anterio 
 
 rt " rt H 
 
 3 I Us 
 
 S, ^ P & 
 
 c , -2 5 
 "< 
 
 ^ -2 o ^ o 
 
 iorly close to its opposite 
 tip ; the posterior naris is 
 n at the juncture of pala- 
 dental plates. 
 
 r, opening ante 
 under the snou 
 h the lip marg 
 id " vomerine " 
 
 g^ 
 
 <" w rt 
 
 - 
 
 C 
 
 ule shallow, flattened, small, with 
 nsory septa; its nerve supply is 
 adacent greatly reduced nasal bulbs ; 
 
 o-do 
 re 
 
 separate, 
 tube-like. 
 
 aps 
 t se 
 djac 
 is 
 d ; 
 ect 
 
 is usually on the late 
 the nasal openings ar 
 al rims often produced 
 
 c 
 t 
 
 o 
 e 
 
 a 
 ir 
 
 5 S 
 
278 
 
 FISHES, LIVING AND FOSSIL 
 
 NTEGUMENTARY SENSE ORGANS 
 
 Dermal Sensory Organs. 
 
 
 
 
 j, 
 
 3 
 
 U> 
 
 a 
 '6 
 
 a 
 
 TJ 
 
 2 
 
 -d 
 
 o 
 
 P 
 
 tributed. In Petromyzon nerve end buds sunken in pits, 
 
 are arranged in an upper and lower lateral line, and in three 
 
 typical lines on the head. Myxinoids are lacking in these 
 structures, but are remarkable in a sub-connective tissue, 
 
 I 
 I 
 
 c 
 
 
 
 i 
 Q 
 
 | 
 
 % 
 
 SI 
 
 '-5 
 
 
 1 
 
 ^ 
 
 i 
 
 || 
 
 W) C 
 
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 >^ 
 
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 1 
 
 
 .SS 
 
 ^, 
 
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 33 w 
 
 5| 
 
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 ll 
 
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 8 
 
 
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 5 v 
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 CD 
 
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 t/5 J2 
 
 fc 
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 M 
 
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 x 
 
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 e? J= 
 5 
 
 
 1 '^ 
 
 . 13 . 
 
 [ARACTERS OF INTEGUM 
 
 I 
 
 <D 
 >^ 
 
 -7 
 
 6 
 | 
 
 j>v 
 
 IS c3 
 ^ "o 
 
 ^ 
 _o 
 
 >, 
 
 1 
 
 
 
 2 
 u 
 
 1) 
 
 c 
 
 is composed of large and definite cellular e 
 ferentiated into monocellular glands (goblet 
 
 o 
 
 5 
 jj 
 
 c' 
 rt 
 
 O 
 O 
 
 o 
 
 I 
 
 V 
 
 33 
 
 E 
 
 "3 
 
 o 
 
 2 
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 00 
 
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 15 
 53 
 
 c 
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 73 
 
 tn 
 
 C 
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 3 
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 n 
 
 
 
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 1 
 
 3 
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 '5 
 c 
 'x 
 
 5' 
 
 ^0 
 
 1 
 
 rt 
 
 c 
 
 2 
 
 H 
 
 layers are composed notably of goblet ce 
 these are other large granular cells, which c< 
 
 and discharge their contents, as thread 
 the network to retain the mucous secretion 
 
 ?. 
 '5 
 
 iz: 
 
 'rt 
 c 
 o 
 u 
 
 
 
 shaped cells (which rise to the surface and 
 granular cells, whose processes are connecte 
 its cuticular border is pierced with fine pores, 
 
 K 
 U 
 
 
 
 
 
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 hH 
 
 
 
 
 
 1 
 
 
 
 
 
 
 
 X 
 
 
 
 
 
 U 
 
 
 
 
 
 
 
INTEGUMENT AND SENSE ORGANS 
 
 279 
 
 w 3 w > 
 
 _u rt _O 
 
 rt i tuo JJ 
 
 1/3 Cu O rt 
 
 O _ P 2 
 
 .S ^ 
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 c 
 
 4-1 0) 
 
 S^ C 
 
 Q. f ! 
 
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 S o 
 
 
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 - 
 
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 8 
 
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 s (?) ; no scattered 
 
 l|;a 
 
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 lidermis does not present a sharply 
 
 lenna; its elements are relatively 
 
 .ilar, without flask-shaped mucous 
 
 sum, and is partly shed during the L 
 
 idermis with striate cuticular bord 
 
 8 
 
 (ft 
 
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 = 
 -_ 
 
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 :nt, and, as in Amphibia, muticellul; 
 
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 reen and dermal plates. 
 
 lidermis of well-marked polygonal c 
 border ; sharply marked off below 
 iful goblet mucous cells, which di 
 e surface; branched cells plentifu 
 ented. Derma of widely differe 
 
 idean or horn-like scales. 
 
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280 
 
 FISHES, LIVING AND FOSSIL 
 
 FISHES 
 
 si 
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 After extrusion, 
 
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 Number 
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EARLY DEVELOPMENT 
 
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2 32 FISHES, LIVING AND FOSSIL 
 
 XIX. THE SUPPOSED DESCENT 
 
 Interrelationships and lines of descent as suggested by a number of 
 noted on each scheme. * Denotes that the diagram is the present writer's 
 
 Howes ('91) * 
 
 (On TJrino Genital System) 
 
 Smith Woodward ('92)' 
 (On Palaeontology) 
 
 Nephrorchidic 
 
 (Elasmobranchs 
 
 Batraehians 
 
 Amniotes) 
 
 L A 
 
 thorchidic 
 
 (Ganoids 
 
 Teleosts 
 
 Marsipobranchs 
 
 Dipnoans) 
 
 Haeckel('93)* 
 
 (On General Anatomy) 
 
 Ci ossopterygiana 
 
 Rays 
 
 Cycles tome 
 
 Selachian 
 
 Palaedipneusten 
 
 Proganoid \ 
 
 . Dipnoau ' 
 
 \ \ 
 
 Ganoid and \ 
 
 Teleost Amphibian 
 
 lUy 
 
 Klaatsoh ('93) 
 
 (On Axial Skeleton) 
 
 Cartilaginous 
 Chordal Verte- 
 brae 
 
 Perichordal Cartilaginous 
 Vertebrae 
 
 W.N. Parker ('92)* 
 (On General Anatomy) 
 
 Shark Acipenser \ Teleost 
 
 Lepidosteus 
 Cope ('85)* 
 (On General Anatomy and Palaeontology) 
 
 Chimaeroid 
 
 Ichthyotome 
 
 Burekhardt ('92) 
 (On Central Nervous System) 
 Selachian / v Petromyzon 
 
 7 
 
 Retziua ('98) 
 
 (Nervous System and End Organs) 
 
 Ceratodus 
 
 Dipnoan 
 
 \ 
 
 Protopterua 
 
 Reptile 
 
 Myxine 
 
 Proganoid A 
 Acipenser 
 
 Amphibia 
 
 Teleosts 
 
 Bony Ganoids 
 
 Petromyzon 
 
SUPPOSED DESCENT OF GROUPS 
 
 283 
 
 OF THE GROUPS OF FISHES 
 
 observers ; their views have been based on the different lines of investigation 
 interpretation of the text of the author cited. 
 
 Balfour ('80) 
 (On Embryology and Anatomy) 
 
 Giinther ('80)* 
 
 \" V 
 
 rcnlatory System) includes Lancelet and Cyclostomes 
 / as 2 Sub classes of Fishes 
 
 
 / V Palaekhthys 
 
 / 
 
 ay Ganc 
 
 ids N. \ \ 
 
 . 
 
 \\ Ganoids 
 \Amphibia ^-^ Di pIJOans ) 
 Protopterus 
 Chondrosteans 
 ratodus (Sharks and Chimaeroids) 
 
 leiewu 
 
 
 Gill ('95) 
 
 
 (On Structural Characters) 
 
 
 //j\\ avldoff('80) 
 
 / 1 \ \\vV Pleuracanthid (On Extremities and Girdles) 
 
 ,, . / / / \\V Primitive Gnathostome 
 Wynne 7 / | \ \\Teleostome | 
 
 Petromyion' J \ \Dipnoan 
 
 I 1 
 
 Chimaeroid Elasmobranch 
 
 Scaphyrhynchus 
 
 
 | Selachian 
 
 Bridge C?8) 
 
 JVcipcnccr 
 
 (On Osteology of Ganoids) 
 
 I Shark Rays(!) 
 
 1 
 
 Polyodon | "Chimaeroid 
 
 Apneumato- | 
 coela Pneuma 
 | coela 
 
 Heptanchus Acanthias 
 
 1 
 
 Polypterus 
 
 .hlasmobrancn 
 
 Amia Lepidosteus 
 1 | 
 
 ~1 
 
 1 Amphib 
 
 ia , o 
 
 Selachoidei 
 
 
 Teleosteoidei 
 
 (On Embrj'olog}-) ' 
 
 c 
 
 ^X . 
 
 
 (On Anatomy of Head) 
 
 Beard ('90) 
 
 \Shark 
 
 (On Embryology and Brain) 
 
 Selachians Crossopterj-gian 
 
 / 
 
 Ctenodipterini N. 
 
 Selachodichthyidae 
 
 Ganoids (Devon) N^^ 
 
 I Tel 
 
 /\ ^ hlb " 
 
 eosts \AmpTiibia Ceratodus 
 
 
 andProtamnia / (Trias) 
 
 ^r ^W 
 
 ~~*7 1 '\. 
 
 / N. 
 
 Ischyodus/ / Ceratodus 
 
 / ^v 
 
 (Jura)/ / 
 
 Selachians >v 
 
 / pL 
 
 >. Holocephali 
 Dipnoans and 
 
 Amphibia 
 
INDEX 
 
 Abdominal pores, 271. 
 
 Acanthias, larva of, 21 6 (Figs. 288, 
 289). 
 
 Acanthodes, gill shields, 20; a fossil 
 shark of the Coal Measures, 79; 
 structure of, 80, 8i; A. wardii, 81 
 (Fig. 87) ; shagreen and denticle of 
 A. gracilis, 8 1 (Fig. 88); affinities 
 of, 95; diagram of affinities, 98 
 (Fig. 103) ; gill arches, 1 14. 
 
 Acanthodians, antiquity of, 9; fin 
 spine and pectoral fin, 28, 29 (Fig. 
 32); pectoral fin of Parexus, 42 
 (Fig. 51), 44. 
 
 Acanthodopsis wardii, teeth of, 82 
 (Fig. 88 A}. 
 
 Acanthopterygian, 166 (Fig. 171 A). 
 
 ACANTHOPTERYGII, in classification, 9 ; 
 as a subdivision of Teleocephali, 174. 
 
 Acipenser, in classification, 8; antiquity 
 of, 9, 1 66 (Fig. 171 A}; swim-blad- 
 der of, 22 (Fig. 1 3) ; description of, 
 159-161; A. sturio, 160 (Fig. 165); 
 eggs and breeding habits, 181 (Fig. 
 194), 185; fertilization, 187; devel- 
 opment of eggs, 203 (Figs. 249- 
 264), 207; larval development of, 
 221-223 (Figs. 296-302); heart, 
 oonus and bulbus arteriosus, tables, 
 260; gills, spiracle, gill rakers and 
 opercula, tables, 261 ; digestive tract, 
 tables, 262 (Figs. 326-331); swim- 
 bladder, tables, 264, 265 (Fig. 13); 
 genital system, tables, 266; urino- 
 genital ducts and external openings, 
 tables, 267 (Figs. 332-337) ; excre- 
 tory system and urinogenital ducts, 
 tables, 271. 
 
 ACTINOPTERYGII, in classification, 8, 
 147; description of, 155-178 (Figs. 
 157-185 A)\ Chondrosteans (Gan- 
 oids), 155; fossil forms, 155-159 
 (Figs. 158-164); living types, 159- 
 178 (Figs. 165-185 A}. 
 
 Actinotrichia, 31, 33 (Fig. 39). 
 
 dZtheolepis, ganoid plates of, 24 (Fig. 
 
 25), 25. 
 
 Agassiz, L., 37, 66, 107, ill. 
 Agassiz, A., 224. 
 Air-bladder, v. Swim-bladder. 
 Allis, E. P., 50, 51. 
 Alopias,%<); A.vulpes (thrasher shark), 
 
 89 (Fig. 95). 
 Alosa, eggs and breeding habits, 181 
 
 (Fig. I97)> 186. 
 
 American Arthrodirans, 130. 
 
 American Geologist, 80. 
 
 Amia, in classification, 8; antiquity 
 of, 9, 1 66 (Fig. 171 A); swim-blad- 
 der of, 21, 22 (Fig. 14) ; sensory 
 tracts in head dermal plates, and 
 scales of, 50-52 (Figs. 64-68) ; A. 
 calva, 51 note; a Ganoid with her- 
 ring-like scales, 145 ; description of, 
 163-165 (Figs. 167, 168); Mesozoic 
 forms, 164, 165 (Figs. 169-171); 
 heart, conus and bulbus arteriosus, 
 tables, 260; gills, spiracle, gill rakers, 
 and opercula, tables, 261 ; digestive 
 tract, tables, 263; swim-bladder, 
 tables, 264, 265 (Fig. 14); genital 
 system, tables, 266; excretory sys- 
 tem and urinogenital ducts, tables, 
 271. 
 
 Amiurus, barbels of, 46, 47 (Fig. 58). 
 
 Ammoccetes, head of, 61 (Fig. 72 C"), 
 
 285 
 
286 
 
 INDEX 
 
 62; development of egg, 189 (Fig. 
 
 215)- 
 Amphibian affinities of the shark, 98 
 
 (Fig. 103). 
 AMPHIOXUS, in classification, 7; gills 
 
 of, 1 6. 
 
 ANACANTHINI, 174. 
 Anal fins, v. Fins. 
 Anatomy, v. Shark, Cladoselache, Acan- 
 
 thodes, Climatius, Pleuracanthus, 
 
 Chondrenchelys, Chimcera, Dipnoan, 
 
 etc. 
 
 Angel-fish, v. Rhina. 
 Anguilla, v. Eel. 
 APODES, 173. 
 
 Aquatic breathing, 1 6-23 ; modes of, 20. 
 Archipterygium, 39. 
 Arius, eggs and breeding habits, 181 
 
 (Fig. 195), i85 l86 - 
 
 Armour plates, 23; evolution of, 25. 
 
 ARTHRODIRA, in classification, 8; de- 
 scribed, 129-138 (Figs. 130-144); 
 geological position of, 9, 129; asso- 
 ciated with Pterichthys by Traquair, 
 130; American, described by New- 
 berry and by Claypole, 130; Din- 
 ichthys, 130 (Frontispiece and Figs. 
 I 33~ 1 37) ; varying size of, 136; den- 
 tition, jaws, and mandibles, 136, 137 
 (Figs. 138-144) ; affinities, 136-138; 
 differing from lung-fishes and from 
 sharks, 136 note. 
 
 Aspidorhynchiis, 157; A. acutirostris, 
 158 (Fig. 162). 
 
 Aspredo, eggs and breeding habits, 186. 
 
 Authors, comparison of phylogenetic 
 tables of, 282, 283; v. Bibliogra- 
 phy. 
 
 Ayers, H., 57, 60, 181. 
 
 Balfour, F. M., 40, 193, 216; phylo- 
 genetic table of, compared, 283. 
 
 Barbels, 46-48 (Figs. 55-60). 
 
 Basking shark, v. Cetorhinus. 
 
 Bass, striped, numerical lines of, 5 
 (Fig. 8). 
 
 Bathyonus compressus, 1 68 (Fig. 172). 
 
 Batrachus, eggs of, 1 86. 
 
 Bdellostoma, gills of, 17 (Fig. 9); 
 anatomy and general description of 
 B.dombeyi, 57, 58 (Fig. 69 A}, 59, 
 60 (Fig. 70), 61 (Fig. 72 A}\ eggs 
 of, 1 80, 181 (Fig. 1 86); genital sys- 
 tem, tables, 266; excretory system 
 and urinogenital ducts, tables, 270; 
 brain of, tables, 272 (Fig. 339) ; cen- 
 tral nervous system, tables, 274. 
 
 Bean, T. H., 103, 108, no. 
 
 Beard, J., 57, 61, 146, 217; phylo- 
 genetic table of, compared, 283. 
 
 Berycids, antiquity of, 9. 
 
 Bibliography, 231-251. 
 
 Blenniids, eggs of, 185 (Figs. 198- 
 199), 186. 
 
 Blenny, v. Blenniids. 
 
 Blood-vessels, v. Fishes, circulation in, 
 Heart, Chimaeioids, etc. 
 
 Boas, J. E. V., phylogenetic table of, 
 compared, 283. 
 
 Bohm, A. A., 187. 
 
 Bolau, H., 185. 
 
 Bony fishes, v. Teleosts. 
 
 Bow-fin, v. Amia calva. 
 
 Brain, of Chimaeroids and sharks, 114; 
 resemblances between lung-fishes 
 and Elasmobranchs, 128; compari- 
 son tables of, 272 (Figs. 339-341), 
 273 (Figs. 342-344), 274-275. 
 
 Branchial arches, table of relations of, 
 254 (Figs. 310-315). 256-257. 
 
 Breathing, aquatic, 1623. 
 
 Breeding habits, 180-186; table of the 
 early development of fishes, 280-281. 
 
 Brevoortia (menhaden), gills of, 20. 
 
 Bridge, T., phylogenetic tables of, 
 compared, 283. 
 
 Bulbus arteriosus, comparative tables 
 of, 258 (Figs. 316-325), 260. 
 
 Bull-head, v. Catfish. 
 
 Burkhardt, R., 128; phylogenetic 
 table of, compared, 282. 
 
 Butrinus, heart, conus and bulbus ar- 
 teriosus, 258 (Fig. 323) ; compari- 
 son tables of, 260. 
 
 Calamoichthys, swim-bladder of, 22 
 
INDEX 
 
 287 
 
 (Fig. 17); median fins of, 31; an- 1 
 tiquity of, 148; described, 150; 
 C. calabaricus, 147, 150 (Fig. 150). 
 
 Calberla, E., 187. 
 
 Caldwell, W. H., 125. 
 
 Callichthys, respiration of, 20; ganoid 
 plates. of, 24 (Fig. 26), 26; origin 
 of dermal cusps, 30; C. armaius, 
 172 (Fig. 178); eggs and breeding 
 habits, 1 86. 
 
 Callorhynchus, lateral line lost, 49; 
 description of, 104, 109; mandibu- 
 lar, 106 (Fig. no); bottle-nosed 
 Chimsera, 109 (Fig. 1 1 8); eggs 
 and breeding habits of, 181 (Fig. 
 191), 185. 
 
 Canals, v. Lateral line. 
 
 Carassius aurattis, 170 (Fig. 176). 
 
 Carp, scales of, 26 (Fig. 31 A}; eggs 
 of, 187. 
 
 Catfish, barbels of, 46, 47 (Fig. 58) ; 
 description of, 171, 172; Amiurus 
 me/as, 171 (Fig. 177). 
 
 Cattie, J. T., 54. 
 
 Caturus, 164-165; C. furcatus, 164 
 (Fig. 169) ; Mesozoic caturid, 166 
 (Fig. 171.4). 
 
 Caudal fins, 35; evolution of, 35-39 
 (Figs. 44-48). 
 
 Central nervous system, v. Nervous 
 system. 
 
 Cephalaspis, antiquity of, 9; described, 
 67; C.lyetti, 66 (Figs. 78, 79). 
 
 Cephaloptera, v. Dicerobatis. 
 
 Ceratodus, antiquity of, 9, 10; swim- 
 bladder of, 22 (Fig. 1 6); archip- 
 terygial pectoral fin of, 39, 40, 42 
 (Fig. 54), 44, 45; description of, 
 123 (Fig. 127), 124; skeleton of, 
 123 (Fig. 128); skull of, 124 (Fig. 
 128^4); embryonic stages, 125; 
 eggs and breeding habits, 181 (Fig. 
 192), 185; development of egg, 
 198-202 (Figs. 231-248); larva of, 
 218-221 (Figs. 290-295); skeleton 
 of, tables, 253; jaws and branchial 
 arches, tables, 254 (Fig. 313), 257; 
 .heart, conus and bulbus arteriosus, 
 
 tables, 258 (Fig. 320) ; comparison 
 tables of heart, etc., 260; gills, 
 spiracle, gill rakers, and opercula, 
 tables, 261; digestive tract, tables, 
 263; swim-bladder, tables, 264, 265 
 (Fig. 16); genital system, tables, 
 266; urinogenital ducts and external 
 openings, tables, 267 (Fig. 335); 
 excretory system and urinogenital 
 ducts, tables, 270; abdominal pores, 
 tables, 271. 
 
 Cestracion, antiquity of, 10; jaw of, 
 24 (Fig. 27); caudal fin, 36, 37 
 (Fig. 45), 38; anatomy of, 85 (Fig. 
 91), 86; Port Jackson shark, 181 
 (Fig. 190), 183. 
 
 Cestraciont, antiquity of, 9, 10; gills 
 of, 1 6 note; anatomy of, 85, 86; 
 dentition of, 86; affinities of, 95, 
 96; dental evolution, 112. 
 
 Cetacean, fish-like form of, 5 (Fig. 
 7), 6. 
 
 Cetorhinus, 90 (Fig. 96 A). 
 
 Challenger report, quoted, 87, 103. 
 
 Characteristic structure of fishes, 14. 
 
 Cheirodus, 157; C. granulosus, 157 
 (Fig. 1 60). 
 
 Cheiropterygium, 39. 
 
 Chilomycterus geometricus, 175, 176 
 (Fig. 184). 
 
 Chimcera, sensory canals of the head, 
 30; lateral line of, 49, 51 note; 
 affinities to shark, 98 (Fig. 103); 
 anatomy of, 99-101 (Fig. 104); 
 skeleton of, 101-103; skeleton of 
 C. monstrosa, 102 (Fig. 105) ; genus, 
 104; mandibular, 106 (Fig. 109); 
 palatine plate, 106 (Fig. 109 A); 
 clasping spine of forehead, 107 (Fig. 
 113); ventral fin and clasping organ, 
 107 (Figs. 1 1 6, 117); bottle-nosed 
 Chimaera, 109 (Fig. 118); general 
 description, no (Fig. 119), in 
 (Fig. 120); dermal plates, 113 (Fig. 
 104) ; comparison tables of skeleton 
 of, 253; jaws and branchial arches, 
 tables, 254 (Fig. 312), 256; urino- 
 genital ducts and external openings, 
 
288 
 
 INDEX 
 
 tables, 267 (Figs. 332-33?) 5 ab ' 
 dominal pores, tables, 271; brain 
 of, 273 (Fig. 342). 
 
 CHIM^ROIDS, in classification, 7, 8; 
 antiquity of, 9, 10; gill shields, 20; 
 affinities to shark, 96; general de- 
 scription of, 99-115 (Figs. 104- 
 120); anatomy of, 99-101 (Fig. 
 104); skeleton of, 101-103 (Fig. 
 105); embryology and larval his- 
 tory of, 103; fossil Chimseroids, 
 103, 104 (Fig. 105^); living Chi- 
 mseroids, description of, 104-111 
 (Figs. 117-120); spines and clasp- 
 ing organs, 107 (Figs. 113-116); 
 affinities, 111-115; dental plates, 
 in (Fig. in); history of fossil 
 forms, 112; dental evolution, 112; 
 structural affinities to shark, 112- 
 115; divergences from elasmo- 
 branchian structure, 113; skull and 
 mandible of, 1 13; fins and fin spines, 
 113; skin defences and teeth, 113; 
 gill arches, 114; brain of, 114; lat- 
 eral line, 114; clasping spine, 114; 
 descent of, 115; diphycercal tail 
 compared with that of sharks, 115; 
 separated from Arthrodirans, 136; 
 eggs and breeding habits, 181 (Fig. 
 191), 184, 185; list of authors and 
 works on the Chimaeroids, 244; 
 gills, spiracle, gill rakers, and oper- 
 cula, tables, 271; genital system, 
 tables, 266; circulation in, tables, 
 269; central nervous system, 
 tables, 275; sense organs of, 
 tables, 277; integument and in- 
 tegumentary sense organs, 279; 
 early development of, tables, 280- 
 281. 
 
 Cklamydoselache, antiquity of, 10; gill 
 shields, 20; lateral line, 49, 50 (Fig. 
 61); C. anguineus, 87 (Fig. 92); 
 affinities to shark, etc., 96; gill 
 arches, 114. 
 
 Chondrenchdys, 78; anatomy of, 85. 
 
 CHONDROSTEI, in classification, 8, 
 161, 162. 
 
 Chondrosteus, 161, 162; C. acipense- 
 roides, 161 (Fig. 165^). 
 
 Chordates, ancestors of, 16 note; de- 
 scription of, 63-65. 
 
 Christiceps, eggs of, 1 86. 
 
 Circulatory characters in Dipnoans, 
 129. 
 
 Cladodus, teeth of, 80 (Fig. 86^). 
 
 Cladoselache, in classification, 8; an- 
 tiquity of, 9; gill slits, 16; gill 
 shields, 20; dorsal fins of, 33 (Fig. 
 41) ; caudal fin of, 36, 37 (Fig. 46), 
 38; pectoral and ventral fins of, 42 
 (Figs. 49, 50), 43-46; a primitive 
 form of, 78; description of, 79; 
 anatomy of, 79 (Figs. 86 and 86,4 
 and 86.5); dentition of, 86; affini- 
 ties of, 95, 98 (Fig. 103); gill 
 arches, 114. 
 
 Clark, W., 130, 133 note, Frontispiece. 
 
 Clasping spine of Chimaeroids, 114; 
 absence of, in Dipnoans, 129. 
 
 Claypole, E. W., 66, 67, 71, 80, 130. 
 
 Climatius, anatomy of, 82 (Fig. 89). 
 
 Clupeoid, antiquity of, 9; heart, conus 
 and bulbus arteriosus, 258 (Fig. 
 320) ; heart, etc., comparison tables 
 of, 260. 
 
 Coccosteus, in classification, 8; locali- 
 ties, 130; anatomy of C. detipiens, 
 I 3 I ~I33 (Figs. 130-132); dermal 
 and ventral plates of, 132 (Figs. 
 131, 132); lateral line in, 135; eyes 
 of, 135- 
 
 Cochliodonts, 86; dental evolution of, 
 
 112. 
 
 Cod, barbels of, 46, 47 (Fig. 55 ), 
 171; description of Gadus morrhua* 
 174 (Fig. 182); circulation in r 
 tables of, 269. 
 
 C&lacanthus, in classification, 8; dor- 
 sal fin of, 33, 34 (Fig. 43), 43; de- 
 scription of, 87 (Fig. 92), 153; as 
 a Crossopterygian, 147; C. elegans, 
 153 (Fig. 155). 
 
 Columbia College Museum, 130, 135,. 
 Frontispiece. 
 
 Conus arteriosus, comparison tables of,. 
 
INDEX 
 
 289 
 
 258 (Figs. 316-325), 260; v. Sharks, 
 etc. 
 
 Cope, E. D., 8, 10; phylogenetic 
 table of, compared, 282. 
 
 Cricotus, 54; parietal foramen of, 54. 
 
 CROSSOPTERYGII, in classification, 8; 
 antiquity of, 9; unpaired fins of, 33 
 (Fig. 43); affinities to shark, 96; 
 included in the term Ganoid, 139; 
 ancestry of, 147; a group of Teleo- 
 stomes, 147; description of, 148- 
 155 (Figs. 148-156,4); habits of 
 living and breeding, 150; fossil 
 forms, 150-155 (Figs. 151-156^); 
 pakeozic, 166 (Fig. 171 A}. 
 
 Ctenodus, in classification, 8; median 
 foramen of, 5 5 ; affinity to Cerato- 
 dus t 122, 124; ancestry of, 147. 
 
 Ctenolabrus cceruleus, larval develop- 
 ment of, 224 (Figs. 303-309), 225. 
 
 Curves of fishes, 5, 6. 
 
 Cusk, barbels of, 46, 47 (Fig. 55). 
 
 Cusps, v. Derm cusps. 
 
 CYCLOSTOMES, in classification, 7, 8; 
 antiquity of, 9; metamerism in, 14- 
 16; gills of, 18; lampreys, 57-63; 
 their affinities^ 63-65; palaeichthyic 
 affinities, 70; eggs and breeding 
 habits of, 180, 181 (Figs. 186, 187); 
 fertilization of eggs, 187 note; larval 
 development, 214, 215 (Figs. 212, 
 215, p. 189, and 72, p. 60) ; names of 
 authors and works, list of, 234-238; 
 skeleton of, tables, 252; heart, conus, 
 and bulbus arteriosus, tables, 260; 
 gills, spiracles, gill rakers, and oper- 
 cula, tables, 260; digestive tract, 
 tables, 262 (Fig. 326), 263; swim- 
 bladder, tables, 264; genital system, 
 tables, 266; urinogenital ducts and 
 external openings, tables, 266, 267 
 (Fig. 332) ; abdominal pores, tables, 
 271, 272 (Fig. 340); central ner- 
 vous system, tables, 274; sense or- 
 gans, tables, 276; integument and 
 integumentary sense organs, tables, 
 278. 
 
 Cyprinodonts, eggs of, 185. 
 
 Davidoff, M., phylogenetic table of, 
 compared, 283. 
 
 Davis, J. W., 84. 
 
 Dean, B., 8, 78, 128, 132. 
 
 Deep-sea fishes, lateral line in, 49. 
 
 Defences, v. Dermal and Teeth. 
 
 Dental plate, of Sandalodus, 24 (Fig. 
 28), 28; of sting-ray, 24 (Fig. 29); 
 of eagle-ray, 24 (Fig. 30), 27; of 
 Arthrodirans, 136, 137 (Figs. 138- 
 144); of Dinichthys, 136-138. 
 
 Denticle, v. Dermal defences. 
 
 Dentine, v. Shark, skin of. 
 
 Derm cusps, origin of, 30. 
 
 Dermal defences of fishes, 23-30; of 
 shark, 23, 24 (Figs. 30, 31); evolu- 
 tion of, 24 (Figs. 24-26), 25; of 
 Chimaeroids, 113; of Coccosteus de- 
 cipiens, 132 (Fig. 131); v. Fin 
 spines. 
 
 Dermal sense organs, v. Sensory or- 
 gans, integumentary. 
 
 Development, v. Fishes, Eggs, larval, 
 etc. ; comparison table of early, 280, 
 281. 
 
 Devil ray or mantis, v. Dicerobatis. 
 
 Dicerobatis, 95, 96 (Fig. 102^4). 
 
 Digestive tract, comparison tables of, 
 263 (Figs. 326-331). 
 
 Dinichthys, Frontispiece; pineal fun- 
 ne l> 55 > general description, 130- 
 138; type specimens in Columbia 
 College Museum, 130 (Frontispiece 
 and Figs. 133-137); fin and fin 
 spine, 131; D. intermedius, resto- 
 ration of by Newberry, 133 (Fig. 
 133 and Frontispiece); elater-joint 
 of, 134; dermal, ventral, and pineal 
 plates of, 133 note; dorsal plates in 
 Columbia College Museum, 135; 
 jaws of, 136, 137 (Figs. 138-144); in- 
 ter movement of dental plates of, 1 38. 
 
 Diphycercal-shaped fin, 35, 37 (Fig. 
 
 47). 
 Diplognathus, jaw of, 136, 137 (Figs. 
 
 141-143). 
 Diplurus, 147, 153,154; D.longicau- 
 
 datus, 154 (Fig. 156). 
 
290 
 
 INDEX 
 
 DIPNOANS, in classification, 7, 8; an- 
 tiquity of, 9, 10, 147; swim-bladder 
 of, 21; affinities to shark, 96, 98 
 (Fig. 103); general description of, 
 116-129 (Figs. 121-129); structural 
 characters and general anatomy of, 
 116-120 (Fig. 121); skeleton of, 
 118 (Fig. 122), 119; fossil forms, 
 120-124 (Figs. 123-126); living 
 forms, 123-127 (Figs. 127-129^); 
 relationships, 127-129; amphibian 
 characters of, 127, 129; kinship to 
 sharks, 127; the advancing struc- 
 tures of, 1 29 ; the Arthrodiran lung- 
 fishes, 129-138 (Figs. 130-144); 
 arthrodiran affinities, 136; eggs and 
 breeding habits, 181 (Fig. 192), 
 185; larval development of, 218- 
 221 (Figs. 290-295) ; names of 
 authors and works on, list of, 244- 
 246; comparison tables of skeleton, 
 253; skeleton of Protopterus annec- 
 tans, 119 (Fig. 122); skull and 
 branchial arches, table of relations 
 of, 257; heart, conus and bulbus 
 arteriosus, tables of, 258 (Figs. 320, 
 321 ); comparison tables of heart, etc., 
 260; digestive tract, 262 (Fig. 329) ; 
 comparison tables of digestive tract, 
 263; genital system, tables, 266; 
 urinogenital ducts and external 
 openings, tables, 267 (Figs. 332- 
 337); circulation in, tables, 269; 
 brain, 272 (Fig. 343) ; central ner- 
 vous system, tables, 275; sense or- 
 gans, tables, 277; integument and 
 integumentary sense organs, tables, 
 279; early development of, compari- 
 son tables, 280-281. 
 
 Dipterus, in classification, 8; antiquity 
 of, 9; description of, 121 (Figs. 
 123-125), 122. 
 
 Dohrn, A., 40, 63. 
 
 Dolphin, fish-like form of, 6. 
 
 Dorsal fin, v. Fins. 
 
 Drum-fish, barbels of, 46, 47 (Fig. 
 56). 
 
 Dugong, fish-like form of, 6. 
 
 Eagle-ray {Myliobatis) , dental plates 
 of, 24 (Fig. 30), 27. 
 
 Early development, v. Development. 
 
 Edestus heinrichsii, fin spine of, 28-30 
 (Figs. 35-38). 
 
 Edinburgh Society, Transactions of, 
 quoted, 70. 
 
 Edwards, V. N., 184. 
 
 Eel, movement of, 2 (Fig. 2) ; gills of, 
 18; median fins of, 31; description 
 of Anguilla vulgar is, 171, 173 (Fig. 
 1 80). 
 
 Eggs of fishes, 180-186 (Figs. 186- 
 199)1 v - Comparison tables of the 
 early development of fishes, 280. 
 
 ELASMOBRANCHII, in classification, 8, 
 9; antiquity of, 9; description of, 
 72-97 (Figs. 83-102); affinities of, 
 95 ; resemblances to lung-fishes, 1 28, 
 129; to Athrodirans, 136, v. Shark; 
 eggs and breeding habits of, 183, 
 184 (Figs. 189,189^); circulation 
 in, 268 (Fig. 338), 269; central ner- 
 vous system, tables of, 274, 275. 
 
 Elonichthys, 156; E. (Rhabdolepis) 
 macropterus, 156 (Fig. 158). 
 
 Embiotocids, eggs of, 185. 
 
 Emery, C., 169, 170. 
 
 Enamel of shark skin, 23, 24 (Fig. 
 20) ; enamel organ of shark, 23, 24 
 (Fig. 20). 
 
 Entering angle of fishes, 5, 6. 
 
 Environment, changes due to, 167- 
 169 (Figs. 172-174). 
 
 Erythrinus, swim-bladder of, 22 (Fig. 
 
 15)- 
 Eurynotus, 157; E. crenatus, 156 
 
 (Fig. 159). 
 Eusthenopteron.) 151153; E. foordi, 
 
 152 (Fig. 154). 
 Evolution, of fishes, slowness of, 1 1 ; 
 
 of fins, 30-46; of unpaired fins, 31- 
 
 39 (Figs. 39-43) ; of paired fins, 39- 
 
 46 (Figs. 49-54)- 
 Excretory system, tables of, 270, 271 
 
 (Figs. 332-337, P- 267). 
 Exoskeletal specializations of Dip- 
 
 noans, 129. 
 
INDEX 
 
 2 9 I 
 
 Eye, v. Pineal eye. 
 
 Feeling, sense of, 46-48. 
 
 Fertilization phenomena, 186, 187, v. 
 comparison tables of the early devel- 
 opment of fishes, 280. 
 
 Fierasfer, 169, 170; F. acus, 169 (Fig. 
 
 175). 
 
 Fins, location of, 3, 4; evolution of, 
 30-46 (Figs. 39-54); unpaired, 31- 
 39 (Figs. 39-43); dorsal and anal, 
 31-35 ( Fi g s - 39-43); caudal, 35- 
 39 (Figs. 44-48); paired, 39-46 
 (Figs. 49-54); pectoral, 41-43 (Figs. 
 49, 5 T -54); ventral, 41-43 (Fig. 
 50); of Chimaeroids, 113; primitive 
 dermal, 31 ; of Cladoselache, 33 (Fig. 
 41) ; of Ccelacanthus, 34 (Fig. 43) ; 
 of Crossopterygian (Holopty chins) t 
 
 33 (Fig- 43)- 
 
 Fin spines, 23; description of, 28-30 
 (Figs. 32-38) ; of Acanthodian, 29 
 (Fig. 32); of Hybodus, 29 (Fig. 
 33) ; of sting-ray, 28, 29 (Fig. 34) ; 
 of Edestzis heinrichsii, 28, 29 (Figs. 
 35-38); of Chimaeroids, 113. 
 
 Fishes, defined, i; movement of, I, 2 
 (Figs, i, 2); type of swift swim- 
 ming fish, 3, 4 (Fig. 3) ; balanced 
 in water, i, 4; symmetry of, 4; nu- 
 merical lines of, 5, 6 (Figs. 5-8); 
 effect of environment of, 7; classifi- 
 cation of, 7, 8; geological distribu- 
 tion of, 9; importance of group, IO; 
 permanence of, IO; evolution of, II ; 
 generalized, 1 2 ; characteristic struc- 
 ture of, 14-56 (Figs. 9-60) ; meta- 
 merism, 14-16; aquatic breathing, 
 gills, etc., 16-23 (Figs. 9-19); der- 
 mal defences of, 23-30 (Figs. 20- 
 38) ; teeth in highly modified fishes, 
 28; development of, 179-225 (Figs. 
 186-309); embryology of, 1 79 ; eggs 
 and breeding habits of, 180-186 
 (Figs. 186-199); fertilization of 
 eggs of, 1 86, 187; development of 
 eggs of, 187-214 (Figs. 200-283); 
 larval development of, 213-225 
 
 (Figs. 284-309) ; names of authors 
 and works, on the general subject, 
 231-234; skeletons, table of, 252, 
 253 (Figs. 69, 84, 105, 122, 146, 
 147, and 310-315); skull, jaw, and 
 branchial arches, tables, 254 (Figs. 
 310-315); heart of, 258 (Figs. 
 316-325), 260; comparison tables 
 of heart of, 260; gills, spiracles, 
 gill rakers, and opercula, tables, 
 259 (Figs. 9-12), 260, 261; di- 
 gestive tract, tables, 262 (Figs. 326- 
 331), 263; swim-bladder, tables, 
 264, 265 (Figs. 13-19); genital 
 system, tables, 266, 267 (Figs. 332- 
 337); circulation in, tables, 268 
 (Fig. 338), 269; excretory system 
 and urinogenital ducts, 270, 271 
 (Figs. 332-337, p. 267) ; abdominal 
 pores, 271 ; brain of, 272 (Figs. 339- 
 341), 273 (Figs. 342-344); central 
 nervous system, tables, 274, 275; 
 sense organs, tables of, 276, 277; 
 characters of integument and in- 
 tegumentary sense organs, 278, 
 279; early development, compari- 
 son tables of, 280, 281. 
 
 Flounder, 171; description of, 174, 
 175; Pseudopleuronectes america- 
 nus, 172 (Fig. 183). 
 
 Fossil forms, v. Sharks, Chimaeroids, etc. 
 
 Fraas, 157. 
 
 Fric, 102, 119. 
 
 Frilled shark, v. Chlamydoselache, etc. 
 
 Fritsch, A., 42, 83. 
 
 Gadoid, 9. 
 
 Gadus, v. Cod. 
 
 Gage, S., 182. 
 
 Ganoid plates, in jQLtheolepis, 24 (Fig. 
 25); in Lepidosteus, 24 (Fig. 24); 
 in Callichthys, 24 (Fig. 26). 
 
 GANOIDS, in classification, 8, 148; an- 
 tiquity of, 9; dermal plates, 24 (Fig. 
 25), 25; Ganoid includes the Cros- 
 sopterygians, 139 note; the term 
 " Ganoid " used in the popular sense 
 to denote the Teleostomes, 139; con- 
 
2 9 2 
 
 INDEX 
 
 trasted with Teleost, 144 (Fig. 147) ; 
 air-bladder like that of a Dipnoan, 
 145; J. Miiller as to structural differ- 
 ences between Ganoids and -Tele- 
 osts, 145; recent Ganoids, 159; 
 Mesozoic, 166 (Fig. 171 A); eggs 
 and breeding habits, 181 (Figs. 193, 
 194); fertilization of eggs of, 187; 
 development of eggs of, 202-207 
 (Figs. 249-268) ; larval development, 
 211-223 (Figs. 296-302); names of 
 authors and works on, 246-249; 
 skeleton, tables of, 253 ; skeleton of 
 Polypterus bichir, 144 (Fig. 147); 
 digestive tract, tables, 262 (Figs. 
 326-331); urinogenital ducts and 
 external openings, tables, 266, 267 
 (Figs. 332-337) ; abdominal pores, 
 tables, 271; tables of early devel- 
 opment, 280, 281. 
 
 Ganoine, 166 note. 
 
 Carman, 87, 93, 109, no. 
 
 Gar-pike, v. Lepidosteus. 
 
 Gegenbaur, C., 39, 40, 42, 146. 
 
 Generalized fishes, defined, 12. 
 
 Genital system, comparison tables of, 
 266 (Figs. 332-337) , 2 7. 27 1 - 
 
 Geological distribution of fishes, 9. 
 
 Geologist, American, quoted, 80. 
 
 Gill, T., no; phylogenetic table of, 
 compared, 283. 
 
 Gill rakers, 20; comparison tables of, 
 260. 
 
 Gill shields, 20 ; v. Sharks, Chimaeroids, 
 etc. 
 
 Gills, 16-23; evolution of, 18; of 
 Amphioxus, 16; of Bdellostoma, 17 
 (Fig. 9); of Myxine, 17 (Fig. 10); 
 of shark, 17 (Fig. n); of Teleost, 
 17 (Fig. 12); of Cyclostomes, 18; 
 of Heptanchus, 1 6, 19; of mullet, 
 20; of Brevoortia (menhaden), 20; 
 of Selache, 20; number of gill slits, 
 1 6, note; table of comparison of, 
 260, 261 (Figs. 9-12, p. 259). 
 
 Goette, A., 189. 
 
 Goldfish, 170; Carassius auratus, 170 
 (Fig. 176). 
 
 Goode, G. B., 3, 47, 89, 90, 92, 94, 95, 
 103, 108, 155, 160, 162, 163, 171, 
 
 1 73- 1 77- 
 
 Graf, A., 75, 102, 119. 
 Greenland shark, v. Lamargus. 
 Guitel, F., 181. 
 Gunn, M., 70. 
 GUnther, A., 60, 90, 96, 103, 123, 125, 
 
 146, 162, 168, 170, 172, 178, 181; 
 
 phylogenetic table of, compared, 
 
 283. 
 
 Gurnard, v. Prionotus. 
 Gyroptychius, 150, 151 (Fig. 151). 
 
 Haeckel, 146; phylogenetic table, 
 
 compared, 282. 
 
 Hagfish, in classification, 8; v. Myxine. 
 Harriotta, 103, 104, 108 (Fig. 117); 
 
 clasping spine of, 115. 
 Heart, v. Sharks, etc. 
 HEMIBRANCHIATES, 176. 
 HemitripttruS) barbels of, 46, 47 
 
 (Fig. 57). 
 
 Heptabranchias, v. Notidanus. 
 
 Heptanchus, v. Notidanus. 
 
 Hertwig, O., 54, 204. 
 
 Heterocercal caudal fin, 35, 37 (Figs. 
 4546). 
 
 HETEROSOMATA, 175. 
 
 Hippocampus, 176; H. heptagonus, 
 177 (Fig. 185) ; eggs and breeding 
 habits, 1 86. 
 
 Hofer, B., 24. 
 
 Hoffman, 187 note. 
 
 HOLOCEPHALI, v. Chmueroids; heart, 
 conus and bulbus arteriosus, tables, 
 260; digestive tract, tables, 263; 
 swim-bladder, tables, 264. 
 
 Holoptychius, in classification, 8; un- 
 paired fins of, 33 (Fig. 33) ; ances- 
 try of, 147; description of, 150; H. 
 andersoni, 151 (Fig. 153). 
 
 Homocercal caudal fin, 35, 37 (Fig-48). 
 
 Howes, G. B., 42; phylogenetic table 
 of, compared, 282. 
 
 Huxley, 131, 257. 
 
 Hybodus, number of gill slits, 1 6 note; 
 fin spines of, 28, 29 (Fig. 33). 
 
INDEX 
 
 293 
 
 Hydrolagus colliei, general anatomy 
 
 of, 100 (Fig. 104), no. 
 HYPERORARTIA, 62. 
 
 ICHTHYOMI, in classification, 8. 
 
 Innes, W., 149. 
 
 Integument, v. Shark, sense organs, 
 
 etc. 
 
 Intestine, v. Digestive tract. 
 Ischyodus, 103 (Fig. 1 06) ; mandibular 
 
 of, 106 (Figs, in, 112), 112. 
 
 Jaekel, O., 92, 113. 
 
 Janassa, 86. 
 
 Jaws of fishes, 24, 27; of Port Jackson 
 
 shark, 24 (Fig. 27), 27; table of 
 
 relations of, 254 (Figs. 310-315), 
 
 256, 257. 
 Journal of Morphology, quoted, 51 
 
 note, 1 60. 
 
 Kepler, W., 130. 
 
 Klaatsch, phylogenetic table of, com- 
 pared, 282. 
 Kner, 82. 
 Kreft, 125. 
 Kupffer, K. v., 187 note, 189, 222. 
 
 Labrax lineatus, v. Bass. 
 
 Lczmargus, shagreen denticle of, 24 
 (Fig. 21), 25; described, 90 (Fig. 
 96 B*} ; breeding habits of, 183 and 
 note. 
 
 Lagocephalus, description of Z. kzvi- 
 gatus, 176 (184^). 
 
 Lamna, 89, 90 (Fig. 96). 
 
 Lamprey, classified, 8; metamerism 
 in, 14-16; gills of, 17; v. Petromy- 
 zon, Cyclostomes, etc. 
 
 Lampreys, v. Cyclostomes, etc.; com- 
 parison table of the early develop- 
 ment of, 280, 281. 
 
 Lankester, E. R., 66. 
 
 Larva, v. Fishes, larval development 
 of. 
 
 Lateral line, 48-53 (Figs. 61-68); of 
 Chimaeroids and shark, 114; in Coc- 
 costeus, 135. 
 
 Lepidosiren, in classification, 8; swim- 
 bladder of, 22 (Fig. 1 8); account 
 of, 125 (Fig. 129), 126; swim- 
 bladder, tables of, 264, 265 (Fig. 
 18). 
 
 Lepidosteus, in classification, 8; an- 
 tiquity of, 9, 1 66 (Fig. 171 A}\ 
 swim-bladder of, 21, 22 (Fig. 14); 
 ganoid dermal plates of, 24, 25 (Fig. 
 24) ; especial interest of gar-pike in 
 connecting the Ganoids with the 
 Crossopterygians, 159; gar-pike, Z. 
 platystom us, described , 1 5 9- 1 60 ( Fig. 
 I 57); e gg s and breeding habits of, 
 181 (Fig. 193), 185; fertilization 
 of, 187; development of egg of, 203 
 (Figs. 265-268), 207; heart, conus 
 and bulbus arteriosus, 258 (Fig. 
 322); comparison tables of heart, 
 etc., 260; gills, spiracle, gill rakers, 
 and opercula, tables, 261 ; digestive 
 tract, tables, 263; swim-bladder, 
 tables, 264, 265 (Fig. 14); genital 
 system, tables, 266; excretory sys- 
 tem and urinogenital ducts, 271. 
 
 Leptolepis, 165; Z. sprattiformis, 165 
 (Fig. 170). 
 
 Leydig, F., 51 note. 
 
 Limb structure in Dipnoans, 129. 
 
 List of names of authors and of their 
 works, 231-251. 
 
 List of the derivations of proper 
 names, 227-230. 
 
 LOPHOBRANCHII, 1 66 (Fig. 171 A}, 
 178. 
 
 Lung-fishes, v. Dipnoans. 
 
 Lungs, v. Swim-bladder. 
 
 Mackerel shark, v. Lamna. 
 
 Mackerel, Spanish, movement and fins 
 of, 2, 3 (Fig. 3); front view of, 4 
 (Fig. 4); lines of, 5 (Fig. 6). 
 
 Macropetalichthys, eyes of, 135. 
 
 Manatee, fish-like form of, 6. 
 
 Mandibles of Chimseroids, 113; articu- 
 lation of in Dipnoans, 129. 
 
 Mantis, or devil-ray, v. Dicerobatis. 
 
 Marey, 2. 
 
294 
 
 INDEX 
 
 MARSIPOBRANCHS, v. Cyclostomes ; 
 
 tables of the early development of, 
 
 280, 281. 
 McClure, 182. 
 Mechanical adaptation of the fish's 
 
 form, 5> 6. 
 
 Median fins, v. Fins. 
 Megalurus, 165; M. elegantissimus, 
 
 165 (Fig. 171). 
 Megaptera, v. Whale; M. longimana, 
 
 numerical lines of, 5 (Fig. 7), 61. 
 Menaspis, skin defences of, 113. 
 Menhaden, v. Brevootia. 
 Metamerism, vertebrate, of fishes, 14- 
 
 16; of lampreys, 15; of sharks, 16. 
 Miall, L., 126. 
 Microdon, 157; M. wagneri, 158 
 
 (Fig. 163). 
 Mivart, St. G., 40 
 Modern fishes, v. Teleostomes. 
 Mollier, S., 39. 
 Monk-fish, v. Rhina. 
 Mormyrus, 171, 172; M. oxyrhynchus, 
 
 172 (Fig. 179). 
 Morphology, Journal of, quoted, 51 
 
 note. 
 Mouth of fishes, v. Jaws, Teeth, etc. ; 
 
 of catfish (a Teleostome), 64 note. 
 Movement in water, I, 2 (Figs, i and 
 
 2). 
 
 Mucous canal system, v. Lateral line. 
 
 Miiller, Johannes, 145. 
 
 Mullet, gills of, 20. 
 
 Murtena, 173. 
 
 Myliobatis, v. Eagle-ray. 
 
 Mylostomids,'\T\ classification, 8; trunk 
 of, 136; jaws of Mylostoma varia- 
 bilis, 136, 137 (Fig. 138). 
 
 Myriacanthus, in classification, 8 ; 
 restoration of, 104; head region of, 
 105 (Fig. 106) ; dermal plates of 
 head and snout, 105 (Figs. 106, 
 A and B), 113; mandibular, 106 
 (Fig. 107); dorsal spine, 107 (Fig. 
 114); dental evolution, 112; sha- 
 green tubercles and dermal bones 
 and plates, 105 (Fig. 106), 107 
 (Fig. 114), 113. 
 
 Myxine, classification, 8; gills of, 17 
 (Fig. 10), 18; general description, 
 of M. glutinosa, 59, 60 (Fig. 71), 
 61 (Fig. 72 j); eggs of, 180-182 
 (Fig. 187); genital system, tables 
 of, 266; excretory system and urino- 
 genital ducts, 270. 
 
 Myxinoid, Californian, gills of, 18; 
 teeth of, 57; eggs of, 182 (Figs. 186 
 A and 187 A} ; comparison tables 
 of the early development, 280, 281. 
 
 Names, list of authors and their 
 
 works, 231-251. 
 
 Names, list of derivations of, 227-230. 
 Nares, in Dipnoans, 129. 
 Natterer, J., 125. 
 Necturus, swim-bladder of, 21. 
 Nervous system, central, 272 (Figs. 
 
 339-340! 2 73 (Figs. 342-344), 
 
 274, 275. 
 Newberry, J. W., 78, 106, 120, 130, 
 
 131, 132, 136. 
 Newton, 106. 
 Nicholson, H. A., 125. 
 Notacanthns sexspinis, 168 (Fig. 174). 
 Notidanus, antiquity of, 9; gill slits, 
 
 1 6, 19; pectoral fin, 40-42 (Fig. 
 
 52), 44, 45; described, 87-89 (Fig. 
 
 93); affinities, 96; skull, jaws, and 
 
 branchial arches of, 254 (Fig. 
 
 Numerical lines of fishes, 5, 6 (Figs. 
 5-8). 
 
 Onychodus, in classification, 8. 
 Operculum of Teleosts, 19; comparison 
 
 tables of, 260. 
 Ophidium, barbels of, 46, 47 (Fig. 
 
 55)- 
 
 Opisthure, in. 
 
 Osteolepis, in classification, 8; descrip- 
 tion of, 150, ^51 (Fig. 152). 
 
 OSTRACODERMS, classified, 8; antiquity 
 of, 9; description of, 65-71; types 
 of, 67; affinities of, 66 (Fig. 77), 
 70; list of authors and works on 
 Ostracoderms, 238. 
 
INDEX 
 
 295 
 
 Paddle-fish, v. Polyodon. 
 
 Palaaspis americana, 67 (Fig. 75) ; 
 paired fins or spines, 71 note. 
 
 Paltzdaphus, median foramen, 55. 
 
 Palaoniscus, in classification, 157, 158 
 (Fig. 164); Palseozic, 166 (Fig. 
 171,4). 
 
 Palaospondylus, in classification, 8; 
 antiquity of, 9, 71 ; P. gunni, 65 
 (Fig. 73), 70; palseichthyic affini- 
 ties, 70; list of authors and their 
 works on Pal&ospondylus, 238. 
 
 Pander, 121, 151. 
 
 Paraliparis bathybius, 1 68 (Fig. 172). 
 
 Parexus, pectoral tin of, 42 (Fig. 51), 
 
 44- 
 
 Parker, W. N., 7, 117, 127, 128. 
 , T. J., 41, 58. 
 
 Parsons, 5, 6. 
 
 Perca, v. Perch. 
 
 Perch, antiquity of, 9; scales of, 25 
 (Fig. 31 A}, 26, 171; described, 
 174; Perca americana (= fltivia- 
 talis?}, 173 (Fig. 181); digestive 
 tract, tables of, 262 (Figs. 326-331). 
 
 Petalodonts, 86. 
 
 Petromyzon, 61 ; P. marinus, 60 (Fig. 
 72), 61 (Fig. Z>), 62; skeleton of, 
 58 (Fig. 69); eggs of, 180-183; 
 eggs of P. marinus, 181 (Fig. 
 188); fertilization of eggs, 187; 
 development of, 188-192; develop- 
 ment of P. planeri, 189 (Figs. 200- 
 214); digestive tract, tables of, 262 
 (Fig. 326) ; genital system, tables 
 of, 266; urinogenital ducts and ex- 
 ternal openings, 267 (Fig. 332); 
 excretory system and urinogenital 
 ducts, 270 ; brain of, 272 (Fig. 
 340) ; central nervous system, 274. 
 
 Phaneropleuron, in classification, 8; 
 description of, 122 (Fig. 126). 
 
 Phoctzna lineata, v. Porpoise. 
 
 Phylogeny, tables of, 98 (Fig. 103), 
 166 (Fig. 171 A}\ comparison of 
 the phylogenetic tables of the differ- 
 ent authors, 282, 283. 
 
 Phyllopteryx, 178. 
 
 PHYSOSTOME, 166 (171 A). 
 
 Pineal eye, 53-56. 
 
 Pipe-fish, v. Syngnathus. 
 
 PISCES, v. Fishes. 
 
 PLECTOGNATHI, 176. 
 
 Pleuracanthus, in classification, 8; 
 gill slits, 16; a fossil shark, 78; 
 anatomy and skeleton of, 83 (Fig. 
 90); dermal bones of head roof, 
 84 (Fig. 90 A) ; teeth of, 84 (Fig. 
 90 .5); affinities of, 95, 98 (Fig. 
 103); anterior spine of dorsal fin, 
 114; tail of, 115; Coccosteus com- 
 pared with, 131. 
 
 PLEUROPTERYGII, in classification, 8. 
 
 Pogonias, v. Drum-fish. 
 
 Pollard, H. B., 64, 113, 132. 
 
 Polyodon, barbels of, 46, 47 (Fig. 59), 
 48; described, 160-163; P. spatula, 
 162 (Fig. 1 66.5); gills, spiracle, 
 gill rakers, and opercula, tables of, 
 261. 
 
 Poly pier us, swim-bladder of, 21, 22 
 (Fig. 17) ; origin of derm cusps, 30; 
 caudal fin of, 36, 37 (Fig. 47) ; tail 
 of, 115; skeleton of P. bichir, 144, 
 
 147 (Fig. 147) ; contrasted with 
 Teleosts, 144; P. bichir described, 
 
 148 (Fig. 148), 149 note; P. lap- 
 radei, 149 (Fig. 149); in table of 
 phylogeny, 166 (Fig. 171^); skull 
 and branchial arches, 254 (Fig. 
 314) ; table of relations of skull and 
 branchial arches, 257; comparison 
 tables of gills, spiracle, gill rakers, 
 and opercula, 261 ; digestive tract, 
 tables, 263; swim-bladder, tables, 
 264, 265 (Fig. 1 7) ; excretory system 
 and urinogenital ducts, tables, 270. 
 
 i Porcupine-fish, v. Chilomycterus. 
 ! Porpoise, striped, lines of, 5 (Fig. 5). 
 Port Jackson shark, v. Cestracion. 
 Powrie, 82. 
 Prionotus, barbels of, 46, 47 (Fig. 60), 
 
 48. 
 
 Pristiophorus, antiquity of, 9 ; descrip- 
 tion of, 92 (Fig. 99) ; affinities of, 
 96-98 (Fig. 103). 
 
296 
 
 INDEX 
 
 Pristis, antiquity of, 9; description of, 
 91 (Figs. 98 and 98^4); affinities 
 of, 96-98 (Fig. 103). 
 
 Pristiurus, larval development of, 215, 
 216 (Fig. 284). 
 
 Protocercy, 35. 
 
 Protopterus, swim-bladder of, 22 (Fig. 
 18); anatomy of, 116 (Fig. 121); 
 paired fin structure, 118 (Fig. 122), 
 119; jaws and skull, 119 (Fig. 
 122 A}; account of, 126 (Fig. 
 129^); Coccosteus compared with, 
 131; heart, conus and bulbus arte- 
 riosus, 285 (Fig. 325) ; comparison 
 tables of heart, etc., 260 ; gills, 
 spiracle, gill rakers, and opercula, 
 tables, 261; digestive tract, tables, 
 262 (Fig. 329), 263; swim-bladder, 
 tables, 264, 265 (Fig. 18); circula- 
 tion in, tables, 269; excretory sys- 
 tem and urinogenital ducts, 270; 
 abdominal pores, 271; brain of, 273 
 (Fig. 343) ; central nervous system 
 tables, 275. 
 
 Psammodus, dentition, 86. 
 
 Psephurus, 160-163; P- gladius, 162 
 (Fig. 166,4). 
 
 Pseudopleuronectes, v. Flounder. 
 
 Pteraspis, antiquity of, 9; described, 
 67 (Figs. 74, 76, 77). 
 
 Pterichthys, antiquity of, 9; described, 
 69 (Figs. 80-82) ; Arthrodira associ- 
 ated with by Traquair, 1 30. 
 
 Putnam, 182. 
 
 Pycnodont, 157, 158. 
 
 Rabbit-fish, v. Lagocephalus. 
 
 Rabl, C., 146; phylogenetic table of, 
 compared, 283. 
 
 Raja, v. Ray. 
 
 Rat-fish, v. Chimcera. 
 
 RAY, in classification, 8; antiquity of, 
 9; shagreen of, 24 (Fig. 23); de- 
 scription of, 93-95 (Figs. 100-102) ; 
 barn-door skate (^?. Icevis}, 94 (Fig. 
 101): affinities, 95, 96, 98 (Fig. 
 I0 3) ; eggs and breeding habits, 181 
 (Fig. 189,4), 183, 184. 
 
 Recent sharks, v. Sharks. 
 
 Relationships, v. Affinities, under the 
 family and species. 
 
 Respiration, v. Aquatic breathing. 
 
 Retzius, G., phylogenetic table of, com- 
 pared, 282. 
 
 Rhina, 91 (Fig. 97); affinities to 
 shark, 96, 98 (Fig. 103) ; brain of, 
 tables of, 272 (Fig. 341). 
 
 Rhinobatus, antiquity of, 9; descrip- 
 tion of, 93 (Fig. 100) ; affinities to 
 shark, 98 (Fig. 103). 
 
 Rhyncodus, mandibular of, 106 (Fig. 
 in), in. 
 
 Ruckert, J., 187. 
 
 Ryder, J. A., 31, 37, 115. 
 
 Salensky, W., 214 note. 
 
 Salmonid, antiquity of, 9; eggs and 
 breeding habits, 186; skull and 
 branchial arches, table of, 254 (Fig. 
 3i5)i 257. 
 
 Sandalodus, dental plates of, 24 (Fig. 
 28), 28. 
 
 Scales, 23; of Teleost, 24 (Fig. 31); 
 degeneration of, 26. 
 
 Scaphaspis, 66 (Fig. 77), 67. 
 
 Scaphirhynchus, 160; S. platyrhyncus, 
 162 (Fig. 1 66). 
 
 Scomberomorus maculatus, 2, 3 (Fig. 
 3) ; front view of, 4 (Fig. 4) ; lines 
 of, 5 (Fig. 6). 
 
 Sculpin, barbels of, 46, 47 (Fig. 57). 
 
 Scyllium, shagreen of, 24 (Fig. 22), 
 25> 90; eggs of, 181 (Fig. 189), 
 183, 184 and note; development of 
 egg of, 193 (Figs. 216-230); larvae 
 of, 215, 216 (Figs. 285-287); skull, 
 jaw, and branchial arches of, 254 
 (Fig. 310), 256. 
 
 Sea-bass, v. Serranus. 
 
 Sea-cat, v. ChinHzra and Callorhyn* 
 chus. 
 
 Sea-horse, v. Hippocampus. 
 
 Sea-raven, v. Hemitripterus. 
 
 Sea-robin, v. Prionotus. 
 
 Seal, fish-like form of, 6. 
 
 Selache, gills of, 20. 
 
INDEX 
 
 297 
 
 SELACHII, in classification, 8. 
 Semionotus, 157; S. kapjfi, 157 (Fig. 
 
 161). 
 
 Semon, R., 125, 181, 199, 200, 219. 
 Sense organs, characters of, 4656; 
 
 tables of, 276-277; integument and 
 
 integumentary sense organs, tables 
 
 of, 278, 279. 
 Sense of feeling, 46-48. 
 Sensory canals in head of Chimaera, 
 
 3- 
 
 Sensory tubules, v. Lateral line. 
 
 Serranus, eggs of, 181 (Fig. 196), 186; 
 development of egg of S. atrarius, 
 208 (Figs. 269-283). 
 
 Shad, v. Alosa. 
 
 Shagreen denticle of shark, 23-25 
 (Figs. 20-22) ; of sting-ray, 24 (Fig. 
 23), 25. 
 
 SHARKS, movement of, 2; in classifi- 
 cation, 7, 8; antiquity of, 9, 10, 72; 
 gills of, 17 (Fig. n), 19; spiracle 
 of, 19; gill shields of, 20 ; skin, 
 enamel, and dermal denticle of, 23- 
 26 (Figs. 20-22) ; shagreen denticle 
 of the Greenland shark (Ltsmargus), 
 24 (Fig. 21); jaw of Port Jackson 
 shark (Cestracimf)^ 24 (Fig. 27), 
 27; evolution of the dermal armour- 
 ing, 25, 26 (Figs. 25, 26) ; unpaired 
 fins of, 33, 34 (Figs. 39-43) ; caudal 
 fin of, 36-39 (Figs. 45-47) J lateral 
 line of, 49, 50 (Figs. 6 1, 62), 51, 76; 
 description of, 72-98 (Figs. 83-103) ; 
 position of, 72; general anatomy of, 
 73 (Fig. 83); skeleton of, 74-76 
 (Fig. 84); sub-notochordal rod in 
 skeleton, 76 (Fig. 85); integument 
 of, 76; brain of, 76; nasal organ, 
 eye, and ear, 76; renal and repro- 
 ductive system of, 76; digestive 
 tube, viscera, 77; heart, 77; clasp- 
 ers, 77; fossil sharks described, 77- 
 86 (Figs. 86-91) ; teeth of fossil, 86; 
 recent sharks, 87-95 (Figs. 92-101) ; 
 affinities of, 95-98 (Fig. 103) ; eggs 
 and breeding habits, 181 (Figs. 189- 
 190), 183, 184; fertilization of eggo, 
 
 187 note; development of egg of, 
 194-198 (Figs. 216-230); larval de- 
 velopment of, 215-218 (Figs. 284- 
 289); list of authors and their works 
 on sharks, 238-244; comparison 
 tables of the skeleton of, 252; skel- 
 eton of Cestracion galeatus, 75 (Fig. 
 84), 255; skull, jaws, and branchial 
 arches, tables, 256; heart, tables, 
 258 (Fig. 317), 260; gills, spiracle, 
 gill rakers, and opercula, tables, 262 
 (Fig. u, p. 259); swim-bladder, 
 tables, 264; genital system, tables, 
 266; urinogenital ducts and exter- 
 nal openings, 267 (Fig. 333), and 
 tables, 270; plan of circulation in, 
 tables, 268 (Fig. 338), 269; ab- 
 dominal pores, tables, 271; brain of, 
 272 (Fig. 341); sense organs of, 
 tables, 276; integument and integ- 
 umentary sense organs, tables, 279; 
 comparison tables of the early devel- 
 opment of, 280, 281. 
 
 Siluroid, antiquity of, 9; affinity and 
 phylogeny of, 147, 166 (171 A}, 
 171; South American Siluroid {Cal- 
 lichthys armatus), 172 (Fig. 178); 
 eggs and breeding habits of, 181 
 (Fig. 195), 185, 186 and note; 
 heart, conus and bulbus arteriosus, 
 tables of, 258 (Fig. 318). 
 
 Siphostoma, eggs and breeding habits 
 of, 1 86. 
 
 SIRENOIDEI, in classification, 8. 
 
 Skates, description of, 93-95 (Figs. 
 100-102) v. Ray. 
 
 Skeleton, v. Shark, Pleur acanthus, Chi- 
 mseroid, Dipnoan, Ceratodus, etc. 
 
 Skin defences, v. Dermal and Teeth. 
 
 Skull of fishes, dermal bones of head 
 root of Pleuracanthus, 84 (Fig. 90 
 A}-, of Chimaeroids, 113; resem- 
 blances of skull of lung-fishes to 
 Elasmobranchs, 128; of Dinichthys 
 intermedius, 133 (Fig. 133 and Fron- 
 tispiece) ; table of relations of skull, 
 jaws, and branchial arches of, 254 
 (Figs. 310-315), 256. 
 
298 
 
 INDEX 
 
 Smithsonian Institution, Heptanchus, 
 88 (Fig. 93). 
 
 Solenostoma, eggs and breeding habits, 
 1 86. 
 
 South American lung-fish, v. Lepido- 
 siren. 
 
 South American Siluroid, v. Callichthys. 
 
 Spatularia, v. Polyodon. 
 
 Specialized fishes, defined, 12. 
 
 Spines, 23; v. Fin spines, Clasping 
 spines. 
 
 Spiracle of shark, 18; comparison 
 tables of, 260. 
 
 Spook-fish, v. Chimsera and Chimae- 
 roids. 
 
 Spoon-bill sturgeon, v. Polyodon. 
 
 Squaloraja, in classification, 8; affini- 
 ties of, 98 (Fig. 103) ; restoration of, 
 104, 105 (Fig. io6,4); mandibular 
 of, 106 (Fig. 108) ; frontal spine of, 
 107 (Fig. 115); dental evolution of, 
 112; skin defences of, 113. 
 
 Sgualus, 89 (Fig. 94). 
 
 Squatina, v. Rhina. 
 
 Steindachner, F., 149, 150. 
 
 Sticklebacks, v. Hemibranchiates. 
 
 Sting-ray, shagreen of, 24 (Fig. 23); 
 dental plates of jaw, 24 (Fig. 29), 
 25; fin spine of, 28, 29 (Fig. 34). 
 
 Stomach, v. Digestive tract. 
 
 Strong, O. S., 112. 
 
 Structure, characteristic, of fishes, 14. 
 
 Sturgeon, v. Acipenser ; spoon-bill 
 sturgeon, v. Polyodon and Psephu- 
 rus ; shovel-nose sturgeon, v. Sea- 
 phirhyncus ; a Liassic sturgeon, 
 v. Chondrosteus. 
 
 Swim-bladder, hydrostatic, I, 21, 22 
 (Figs. 13-19); of Amia, 21, 22 
 (Fig. 14); of gar-pike, 21, 22 (Fig. 
 14) ; of Dipnoans, 21 ; of Polypterus 
 and Calamoichthys, 21 , 22 (Fig. 17) ; 
 of Necturus, 21; of sturgeon, 22 
 (Fig. 13) ; of Teleosts, 22 (Fig. 13) ; 
 of Erythrinus, 22 (Fig. 15); of 
 Ceratodus, 22 (Fig. 1 6); of Lepido- 
 siren, 22 (Fig. 1 8); of Protopterus, 
 22 (Fig. 1 8) ; of Dipnoans, 129 ; 
 
 compared with reptiles, birds, and 
 mammals, 20 (Fig. 19); comparison 
 tables, 264, 265 (Figs. 13-19). 
 
 Swimming: eel, shark, mackerel, 2. 
 
 Symmetry of fishes, 4. 
 
 Synechodus, dentition of, 86. 
 
 Syngnalhus, 1 66 (Fig. 171 A] ; de- 
 scription of, 177, 178; S. acus, 178 
 (Fig. 185 A}\ eggs and breeding 
 habits of, 186. 
 
 Tail, v. Caudal fins. 
 
 Teeth, general, 23, 24 (Figs. 27-30) ; 
 description and evolution of, 27, 28; 
 of Port Jackson shark, 24 (Fig. 27), 
 27, 86; of highly modified fishes, 
 28; of Myxinoids, 57; of Cladodus, 
 80 (Fig. 86 B} ; of Acanthodopsis, 
 82 (Fig. 88 A} ; of Pleur acanthus, 
 84 (Fig. 90 B} ; of fossil sharks, 86; 
 of Chimseroids, 113; resemblances 
 of lung-fishes to Elasmobranchs as 
 to teeth, 128. 
 
 TELEOCEPHALI, included in Actinop- 
 terygians, 8, 148; description and 
 phylogeny of, 165, 166 (Fig. 171 A). 
 
 TELEOST, antiquity of, 9, 147; gills of, 
 17 (Fig. 12), 19; operculum of, 19; 
 gill rakers of, 20; swim-bladder of, 
 22 (Fig. 13) ; swim-bladder of Ery- 
 thrinus, 22 (Fig. 15); scales of, 24 
 (Fig. 31); caudal fin of, 36, 37 
 (Fig. 48) ; the term " Teleost " used 
 in the popular sense to denote the 
 modern " bony fish," 139; the perch 
 a convenient type, 139; general 
 anatomy of, 141-145 (Figs. 145, 
 146) ; skeleton of Percafluviatilis, 
 142 (Fig. 146) ; relationship and 
 descent, 145-147; description and 
 phylogeny of, 165, 166 (Fig. 171 A)\ 
 modified conditions of, 167-171; 
 eggs and breeding habits, 181 (Figs. 
 196-199), 185, 186; fertilization of, 
 187 and note; development of egg, 
 207-212 (Figs. 269-283) ; larval 
 development, 223-225 (Figs. 303- 
 309); list of authors and their 
 
INDEX 
 
 299 
 
 works, 249-251; comparison tables 
 of the skeleton of, 253; heart, conus 
 and bulbus arteriosus, tables, 258 
 (Figs. 324, 325), 260; digestive tract, 
 tables, 262 (Fig. 331), 263; urino- 
 genital ducts and external openings, 
 267 (Fig. 337), and tables, 271; 
 circulation in, tables, 269; abdomi- 
 nal pores, tables, 271; brain of, 273 
 (Fig. 344) ; central nervous system, 
 tables, 275; comparison table of the 
 early development of, 280, 281. 
 
 TELEOSTOMES, in classification, 7, 8; 
 antiquity of, 9, IO; mouth of, 64 
 note; opercular apparatus of, 114; 
 tail of, 1 1 5 ; affinities to Arthrodirans, 
 ^36; general description of, 139- 
 178 (Figs. 145-185 A); skeleton 
 of, 141-143 (Fig. 146); visceral 
 parts of, 143; contrasted with 
 Ganoids, 144 ( Fig. 147) ; Teleosts 
 and Ganoids merged into one group 
 by Prof. Owen, 146; descent of, 
 146; affinities with the Dipnoans 
 generally admitted, 146; Rabl de- 
 rives them from a selachian stem, 
 146; Beard and Woodward as to 
 their descent, 146; two principal 
 subdivisions of, 147; phylogeny, 
 scheme of, 165, 166 (Fig. 171 A)-, 
 comparison tables of skeleton of, 
 253 ; table of relation of skull, jaws, 
 and branchial arches, 257; heart, 
 conus and bulbus arteriosus, tables, 
 260; gills, spiracle, gill rakers, and 
 opercula, tables, 261 ; digestive 
 tract, tables, 263; swim-bladder, 
 tables, 264, 265 (Fig. 13); genital 
 system, tables, 266; sense organs, 
 tables, 277; integument and integu- 
 mentary sense organs, tables, 279. 
 
 Telescope-fish, v. Carassiits. 
 
 Terrell, J., 130. 
 
 Thacher, J., 40. 
 
 Thiolliere, 58. 
 
 Thrasher shark, v. Alopias. 
 
 Tissues, cellular elements of, in Dip- 
 noans, 129. . . 
 
 Titanichthys, pineal foramen of, 55, 
 56, 135; size and localities of, 130; 
 lip-like mandibles of, 136; mandi- 
 bles of T. clarki, 136, 137 (Fig. 
 
 139). 
 
 Torpedo, 95 (Fig. 102). 
 Trachosteus, jaws of, 136, 137 (Fig. 
 
 140). 
 Transactions of Edinburgh Society, 
 
 quoted, 70. 
 Traquair, R. H., 65, 68, 70, 71, 78,. 
 
 128, 130, 132, 156, 157, 159. 
 Trygon, dental plates of jaw of, 24 
 
 (Fig. 29); fin spine of, 28, 29 (Fig. 
 
 34). 
 Turner, W., 217. 
 
 Undina, 147, 153; U. gulo, 154 
 (Fig. 156.4). 
 
 United States Fish Commission Re- 
 ports, quoted, 3, 89, 90, 92, 94, 95, 
 155, 160, 162, 163, 171, 173-177. 
 
 United States National Museum, Pro- 
 ceedings of, quoted, 103. 
 
 Urinogenital system, comparison tables 
 of, 266, 267 (Figs. 33 2 -337)> 2 7 
 271. 
 
 Urogymnus, shagreen of, 24 (Fig. 23). 
 
 Ventral plates of Coccosttus decipiens^ 
 132 (Fig. 132). 
 
 Vertebral axis of lung-fishes, resem- 
 blance to Elasmobranchs, 128. 
 
 Vienna collection, 149 note. 
 
 Visceral characters, resemblance be- 
 tween lung- fishes and Elasmo- 
 branchs, 128; of Teleost, 143; of 
 Ganoids, 145. 
 
 Walcott, 65. 
 
 Ward, H. A., 75. 
 
 Whale, fish-like form of, 6. 
 
 Whale, humpback, numerical lines of, 
 
 5 (Fig- 7)- 
 Whiteaves, 152. 
 Whitman, C. O., 187 note. 
 Wiedersheim, R., 40, 113. 
 Willey, A., 16. 
 
300 
 
 INDEX 
 
 Wilson, H. V., 208. 
 
 Woodward, A. S., 8, 10, 24, 25, 33, 
 42, 66, 68-71, 80, 81, 106, 107, 
 112, 121, 127, 129, 131, 132, 135, 
 136, 146, 151, 154, 161, 164, 165; 
 phylogenetic table, compared, 282. 
 
 Works on the general subject, fishes, 
 231-234; on the Cyclostomes, 234- 
 238 ; on the Ostracoderms and 
 Palaosp.ondylm, 238 ; on the sharks, 
 238-244; on the Chimgeroids, 244; 
 on the lung-fishes, 244-246; on the 
 
 Ganoids, 246-249; on the Teleosts, 
 249-251. 
 
 Xenacanthus, pectoral fin of, 39, 40, 
 42 (Fig. 53), 45; v. Pleuracan- 
 thus. 
 
 Zittel, K. v., table of geological dis- 
 tribution of fishes, 9; quoted, 81, 
 82, 104, 124, 157, 158, 164, 165. 
 
 Zoological Society, Proceedings of, 
 257 note. 
 
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