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A TREATISE ON ZOOLOGY

A TREATISE ON ZOOLOGY

Demy 8vo, Cloth, price 15s. net each; or in Paper
Covers, price 12s. Qd. net each.

VOLUMES READY
Part I. (First Fascicle) INTRODUCTION AND

PROTOZOA. By Sir RAY LANKESTER, K.C.B., F.R.S. ;

Prof. S. J. HICKSON, M.A., F.R.S. ; F. W. GAMBLE,

D.Sc., F.R.S. ; A. WILLEY, M.A., D.Sc., F.R.S. ; J. J.

LISTER, F.R.S. ; H. M. WOODCOCK, D.Sc. ; and the late

Prof. WELDON.
Part I. (Second Fascicle) INTRODUCTION AND

PROTOZOA. By J. B. FARMER, D.Sc., M.A., F.R.S. ;

J. J. LISTER, F.R.S. ; E. A. MINCHIN, M.A. ; and S. J.

HICKSON, F.R.S.
Part II. THE PORIFERA AND COELENTERA.

By Sir RAY LANKESTER, K.C.B., F.R.S. ; E. A. MINCHIN,

M.A. ; G. HERBERT FOWLER, B.A., Ph.D. ; and GILBERT

C. BOURNE, M.A.
Part III. THE ECHINODERMA. By F. A. BATHER,

M.A., assisted by J. W. GREGORY, D.Sc., and E. S.

GOODRICH, M.A.
Part IV. THE PLATYHELMIA, THE MESOZOA,

and THE NEMERTINI. By Prof. BENHAM, D.Sc.
Part V. MOLLUSCA. By Dr. PAUL PELSENEER.
Part VII. APPENDICULATA (Third Fascicle:

CRUSTACEA). By W. T. CALMAN, D.Sc.
Part IX. VERTEBRATA CRANIATA (First Fas=

cicle: CYCLOSTOMES AND FISHES). By E.

S. GOODRICH, M.A., F.R.S.

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TREATISE ON ZOOLOGY

K.C.B., M.A., LL.D., F.R.S.

HONORARY FELLOW OF EXETER COLLEGE, OXFORD ; CORRESPONDENT OF THE INSTITUTE

OF FRANCE ; LATELY DIRECTOR OF THE NATURAL HISTORY DEPARTMENTS

OF THE BRITISH MUSEUM

PART IX

VERTEBRATA CEANIATA

(FIRST FASCICLE: CYCLOSTOMES AND FISHES)

BY

E. S. GOODKICH, M.A., F.E.S.

FELLOW OF MERTON COLLEGE, AND ALDRICHIAN DEMONSTRATOR OF COMPARATIVE
ANATOMY IN THE UNIVERSITY OF OXFORD

LONDON

ADAM AND CHAELES BLACK
1909

AUTHOR'S PREFACE

THIS first fascicle of the Ninth Part of the Treatise deals
with the general characters of the Craniate Vertebrates and
the two Classes, Cyclostomes and Fishes. I wish here to
express my gratitude to Sir Eay Lankester, Dr. G. A. Boulenger,
Dr. A. S. Woodward, and especially to Dr. E. H. Traquair, for
the help they have given me in its preparation.

For those illustrations which are new I am directly
responsible, but for a large number of figures I am indebted
to the published works of other writers. My thanks, for
allowing me to use their blocks, are due to several authors,
publishers, and institutions. Among these may be mentioned
Dr. A. S. Woodward, Dr. B. Dean, the Trustees of the British
Museum, the India Office, the Smithsonian Institution, the
Royal Society of Edinburgh, the Zoological Society, the
Geologists' Association, the University Press of Cambridge,
Messrs. J. and A. Churchill, Messrs. Longmans, Green and Co.,
Messrs. Swan Sonnenschein and Co., Messrs. Cassell and Co.,
Messrs. Engelmann of Leipzig, and Messrs. Fischer of Jena.

EDWIN S. GOODEICH.

20th January 1909.

A TREATISE ON ZOOLOGY

PART IX

VERTEBRATA CRANIATA

FIEST FASCICLE— CYCLOSTOMES AND FISHES
BY E. S. GOODRICH.

LIST OF ERRATA AND CORRIGENDA

Page. 40. Legend of Fig. 25, for ' ol. I, olfactory lobe, ' read ' ol. I, olfactory

bulb, below which is the olfactory lobe.'

,, 50. Bottom paragraph — the Myxinoids are probably not hermaphrodite.
,, 65. 3rd paragraph, 4th line, for 'Amphidia' read 'Amphibia.'
,, -75. 8th line from top, for 'ergion ' read 'region.'
,, 99. Legend of Fig. 60, 'A' should be before Transverse section, and ' B

and C ' should take the place of 'A and B.'
,, 133. Legend of Fig. 91, first line, for ' pale ' read ' pole.'
,, 134. 2nd line, fertilisation in Laemargtis is internal.
,, 135. 10th line from bottom, for ' Fig. 52' read ' Fig. 52, C.'
,, 136. 1st line, for 'Raja' read 'Mustelus.'
,, 136. 2nd and 3rd lines, p. 156, 2nd line from bottom, and p. 159, 3rd

line from top, for ' Division ' read 'Tribe.'
,, 170. Legend of Fig. 134, 'BH' and 'HB' should be transposed; for

' hyomandibular ' read ' hyomandibular ? '
,, 201. Legend of Fig. 173, add 'p.f, pectoral fin.'

,, 247. llth line from bottom, after ' Dipnoi' add 'except in Ceratodus.'
,, 278. Last line, omit ' Dipnoi.'
,, 305. Legend of Fig. 281, add 'ep, epithelial roof; b.g, basal ganglia ; c.w,

cut wall of hemisphere ; est, epistriatum ; v, ventricle.'
,, 307. 2nd paragraph, 7th line, /or ' Catogterydae ' read ' Catopteridae. '
,, 331. 5th line from top, for ' Lophrostomus ' read 'Lophiostomus.' 2nd

line from bottom, for ' Hypsicormus ' read ' Hypsocormus. '
,, 357. Legend of Fig. 343, add ' D, section of developing lepidotrichia near

edge of fin.'

,, 358. Legend of Fig. 344, for 'Scopelius' read ' Scopclus.'
„ 360. Legend of Fig. 346, for ' B and C ' read ' C and D,' in the first line.
,, 364. Fig. 353, A, '/&' points to the epiphysis.
,, 373. Legend of Fig. 359, add 'sa, sinus endolymphaticus.'
,, 377. The first two lines apply not to Gymnotus, but to Malapterurus on

p. 383.
,, 404. For ' Gymnotus ' in 8th line read 'Malapterurus.'

116

CONTENTS

PHYLUM VERTEBRATA

PAGE

Subphylum VERTEBRATA CRANIATA i

Cephalisation, 2 ; Skull, 11 ; Brain, 13 ; Visceral arches, 18 ;
Mouth, 18 ; Lateral line, 19 ; Nerve components, 21 ; Sense-
organs, 23 ; Pineal eyes, 24 ; Alimentary canal, 26 ; Vascular
system, 26 ; Kidneys, 27 ; Gonads, 28.

DIAGRAM OF PHYLOGENY, 29.

Branch I. and Class CYCLOSTOMATA . . 30

Skeleton, teeth, 30 ; Somites and nerves, 37 ; Branchial basket,
3.8 ; Nostril, 39 ; Brain, 41 ; Gills, 41; Viscera, 43; Vascular
system, 43 ; Kidneys, 43 ; Gonads, 46.

Sub-Class 1. MYXINOIDE A . 46

Fam. Myxinidae, 51.

Sub-Class 2. PETROMYZONTIA 51

Fam. Petiomyzontidae, 54.

Affinities, 54.

INCERTAE SEDIS. Fam. Palaeospondylidae, 56.

Branch II. GNATHOSTOMATA 58

Cartilage and bone, 58 ; Skull, 67 ; Vertebral column, 68 ;
Median fins, 69 ; Concentration, etc., 71 ; Paired fins, 73 ; Muscle
and nerve, 77; Nasal sacs, 82; Viscera, 82; Sense-organs, 82;
Urinogenitals, 83 ; Chief characters, 92.

Grade I. Class PISCES 93

Gills, 63 ; Jaws, 95 ; Vertebral column, 97 ; Axial and
appendicular skeleton, 101 ; Caudal fin, 101 ; Skeleton of paired
fins, 106; Dermal rays, 109; Vascular system, 109; Yolk-sac
circulation, 114; Alimentary canal, 114; Classification, 117.
vii

CONTENTS

PAGE

Sub-Grade 1. CHONDRICHTHYES . 118

Placoid scale, 119 ; Dentine, 119 ; Ceratotrichia, 122 ; Gill slits
and rays, 123 ; Classification, 123.

DIAGRAM OF PHYLOGENY, 124
Sub-Class 1. ELASMOBRANCHII . . 125

Nostrils, 125; Lateral line, 125; Brain, 126; Pectoral fin-
skeleton and archipterygium, 127 ; Pelvic fin, 128; Claspers,
129; Urinogenitals, 131 ; Viviparity, 134.

Order 1. SELAOHII . .135

Centra, 135 ; Skeleton, 137

Group 1.

Sub-Order 1. NOTIDANI . 139

Fain. 1. Chlamydoselachidae, 142 ; Fam. 2. Notidanidae, 143.

Group 2.

Division A . . 143

Sub-Order 1. HETERODONTI .... 143

Fam. 1. Cestraciontidae, 145; Fain. 2. Cochliodontidae, 146;
Fam. 3. Edestidae, 147.

Division B .148

Subdivision 1.

Sub-Order SCYLLIOIDEI . . 148

Fam. 1. Scylliidae, 149; Fam. 2. Lamnidae, 149;
Fam. 3. Carchariidae, 150.

Subdivision 2.

Sub-Order 1. SQUALIFORMES . . 151

Fam. 1. Spinacidae, 151 ; Fam. 2. Pristiophoridae, 152.

Sub-Order 2. RAJIFORMES . . 153

Tribe 1, 155.

Fam. Squatinidae, 156.

Tribe 2, 158.

Group A. Rhitioraji, 159.

Fam. 1. Rhinobatidae, 159 ; Fam. 2. Pristidae,
160 ; Fam. 3. Rajidae, 160.

Group B, Torpedinoidei, 161.
Fam. Torpedinidae, 161.

Group C. Centrobatoidei, 163.

Fam. 1. Trygonidae, 164 ; Fam. 2. Pfcychodontidae,
165; Fam. 3. Myliobatidae, 165 ; Fam. 4. Psammo-
dontidae, 167.

INCERTAE SEDIS. Fam. 5. Petalodontidae, 167.

CONTENTS

PAGE

Order 2. HOLOCEPHALI 168

Group A • • 176

Fam. 1. Squalorajidae, 176 ; Fam. 2. Myriacauthidae, 176.

Group B . 176

Fam. 1. Callorhynchidae, 176 ; Fam. 2. Chimaeridae, 176 ;

Fam. 3. Ehinochimaeridae, 178.

INCERTAE SEDIS. Fam. 1. Ptyctodqntidae, 179 ; Fam. 2. Mena-

spidae, 180.

Sub-Class 2. PLEURACANTHODII . . 180

Fam. 1. Pleuracanthidae, 183; Fam.1 2. Cladodontidae, 183;
Fam. 3. Chondrenchelyidae, 183.

Sub-Class 3. CLADOSELACHII 184

Fam. Cladoselachidae, 187.

Sub-Class 4. ACANTHODII 187

Fain. 1. Diplacanthidae, 192 ; Fam. 2. Acanthodidae, 192.
INCERTAE SEDIS. Fam. Gyracanthidae, 192.

Sub-Grade 2. OSTRACODERMI • 194

Order 1. PTERASPIDOMORPHI . ... 195

Fam. 1. Coelolepidae, 196 ; Fam. 2. Drepanaspidae, 197 ;
Fam. 3. Psarnmosteidae, 198 ; Fam. 4. Pteraspidae, 198.

Order 2. CEPHALASPIDOMORPHI . . 200

Fam. 1. Ateleaspidae, 203 ; Fam. 2. Cephalaspidae, 203 ;
Fam. 3. Trernataspidae, 204.

Order 3. ANASPIDA . . 204

Fam. 1. Birkeniidae, 205 ; Fam. 2. Lasaniidae, 205 ; Fam. 3.
Euphaneropidae, 206.

Order 4. PTERICHTHYOMORPHI . . 206

Fam. Asterolepidae, 209.

Sub-Grade 3. OSTEICHTHYES 210

Scales, 210; Lepidotrichia, 212; Cranial bones, 213; Ganoid
scale, 214 ; Lateral line, 219 ; Air-bladder, 223 ; Nostrils, 227 ;
Chief characters, 227.

DIAGRAM OF PHYLOGENY, 228.

Group A 230

Sub-Class 1. DIPNOI 230

Scales, 230 ; Dermal rays, 232 ; Vertebral column, 233 ; Skull,
236 ; Girdles and fins, 242 ; Brain, 245 ; Gills, 247 ; Blood-
vascular system, 248 ; Urinogenitals, 253; Chief characters, 254.

CONTENTS

Sub-Class 1. 'DIPNOI— continued

Tribe 1 : Fam. 1. Phaneropleuridae, 255 ; Fam. 2. Urone-
midae, 255 ; Fam. 3. Dipteridae, 256. Tribe 2: Fam. 1.
Ctenodontidae, 257 ; Fam. 2. Ceratodidae, 257 ; Fam. 3.
Lepidosirenidae, 258.

Affinities, 258.

PAGE

Sub-Class 2. COCCOSTEOMORPHI .258

Order 1. ANARTHRODIRA . . 262

Fam. Macropetalichthyidae, 262.

Order 2. ARTHRODIRA . .262

Sub-Order 1. ARTHROTHORACI . . 262

Fam. 1. Coccosteidae, 263 ; Fam. 2. Selenosteidae, 263 ;

Fam. 3. Dinichthyidae, 263 ; Fam. 4. Titanichthyidae, 263 ;

Fam. 5. Mylostomidae, 263.

Sub-Order 2. TEMNOTHORACI 263

Fam. Homosteidae, 263.

Group B 266

Sub-Class TELEOSTOMI . • 266

Skull, 266 ; Seventh nerve, 271 ; Teeth, 272 ; Vertebral column,
273 ; Actinotrichia, 273 ; Limb-girdles, 276; Classification, 277 ;
Characters, 279.

Division 1.

Order OSTEOLEPIDOTI . . . 280

Sub-Order 1. HAPLISTIA 283

Fam. Tarrasiidae, 284.

Sub-Order 2. RHIPIDISTIA • 284

Fam. 1. Holoptychiidae, 284 ; Fam. 2. Glyptopomidae,
285 ; Fam. 3. Osteolepidae, 285 ; Fam. 4. Rhizodontidae,
285 ; Fam. 5. Onychodontidae, 286.
Division 2.
Order COELACANTHINI . 287

Fam. Coelacanthidae, 290.
Division 3.

Order POLYPTERINI . .290

Fam. Polypteridae, 300.

Division 4. ACTINOPTERYGII • 302

Paired fins, 302 ; Fulcra, 304 ; Gular plates, 304.
Subdivision 1.

Order CHONDROSTEI . . .307

Sub-Order 1. PALAEONISCOIDEI . 309

Fam. 1. Palaeoniscidae, 309 ; Fam. 2. Platysomidae,
312 ; Fam. 3. Catopteridae, 313.

CONTENTS

Sub-Order 2. ACIPENSEROIDEI 315

Fam. 1. Choudrosteidae, 316 ; Fam. 2. Polyodontidae,
317 ; Fam. 3. Acipenseridae, 318.

INCEBTAE SEDIS. Fara. Belonorhynchidae, 320.

Subdivision 2. HOLOSTEI . .321

Tail, 322 ; Otoliths, 324 ; Interorbital septum, 324 ; Myodome,
326 ; Supraoccipital, 326.

Order 1. AMIOIDEI . .327

Vertebral column, 327.

Fam. 1. Eugnathidae, 330; Fam. 2. Pachycormidae, 331;

Fam. 3. Amiidae, 333 ; Fam. 4. Semionotidae, 334 ; Fam. 5.

Macrosemiidae, 336 ; Fam. 6. Pholidophoridae, 336 ; Fam. 7.

Archaeonemidae, 337 ; Fain. 8. Oligopleuridae, 337 ; Fam. 9.

Pycnodontidae, 337.

Order 2. LEPIDOSTEOIDEI . . 340

Fam. 1. Lepidosteidae, 344.

INCEBTAE SEDIS. Fam. Aspidorhynchidae, 344.
Order 3. TELEOSTEI . 344

Chief characters, 344 ; Skull, 345 ; Vertebral column, 352 ;
Bone, 355; Scales, 356 ; Phosphorescent organs, 357 ; Lateral
line, 358 ; Gills, 358 ; Air-bladder, 359 ; Urinogenitals, 364.

DIAGRAM OF THE PHYLOGENY OF THE TELEOSTEI, 370

Division A 371

Fam. Leptolepidae, 371.

Division B . .371

Group A . . . .371

Sub-Order CYPRINIFORMES • • 371

Weber's apparatus, 373.

Tribe A. Characinoidei, 374.

Fam. 1. Characinidae, 374 ; Fam. 2. Cyprinidae, 375 ;
Fam. 3. Gymnotidae, 376.
Tribe B. Siluroidei, 377.

Fam. 1. Siluridae, 379 ; Fam. 2. Callichthyidae, 384;

Fam. 3. Loricariidae, 384 ; Fam. 4. Aspredinidae, 384.

Group B . ... 386

Sub-Group 1 . 386

Sub-Order CLUPEIFORMES • • 386

Fam. 1. Elopidae, 387 ; Fam. 2. Albulidae, 387 ; Fam. 3.

Mormyridae, 388 ; Fam. 4. Hyodontidae, 389 ; Fam. 5.

Notopteridae, 389 ; Fam. 6. Osteoglossidae, 390 ; Fain. 7.

Saurodontidae, 390 ; Fam. 8. Chirocentridae, 390 ; Fam. 9.

Phractolaemidae, 391 ; Fam. 10. Clupeidae, 391 ; Fam. 11.

Crossognathidae, 393 ; Fam. 12. Salmonidae, 393 ; Fam. 13.

Alepocephalidae, 394 ; Fam. 14. Stomiatidae, 394 ; Fam. 15.

Gonorhynchidae, 395; Fain. 16. Cromeriidae, 396; Fam.

17. Pantodontidae, 396; Fam. 18. Ctenothrissidae, 396.

CONTENTS

PAOE

Sub Group 2 . . 397

Series 1.

Sub-Order J. ESOCIFORMES . • 397

Tribe 1, 397.

Fam. 1. Galaxiidae, 398; Fain. 2. Haplochitonidae, 398.
Tribe 2, 398.

Sub-Tribe A. Fam. 1. Enchodontidae, 398 ; Fam. 2.

Esocidae, 398 ; Fam. 3. Dalliidae, 398.
Sub-Tribe B. Fam. 1. Scopelidae, 399 ; Fam. 2. Alepido-

sauridae, 399 ; Fam. 3. Cetomimidae, 399.
Sub-Tribe C. Fam. 1. Kneriidae, 399 ; Fam. 2. Chiro-
thricidae, 400 ; Fam. 3. Cyprinodontidae, 400 ; Fam. 4.
Amblyopsidae, 401.
Sub-Tribe D. Fam. Scombresocidae, 402.

INCERTAE SEDIS. Fam. Ammodytidae, 403.
Series 2.

Sub-Order 2. ANGUILLIFORMES 4O3

Division 1. Archencheli, 404.

Fam. Urenchelidae, 404.
Division 2. Neencheli, 405.
Group A. Enchelicephali, 405.

Fam. 1. Anguillidae, 405 ; Fam. 2. Nemichtbyidae, 406 ;
Fain. 3. Derichthyidae, 406 ; Fam. 4. Synaphobranchidae,
407 ; Fam. 5. Saccopharyngidae, 407.
Group B. Colocephali, 407.

Fam. Muraenidae, 408.
Series 3.

Sub-Order 3. SYMBRANCHIFORMES . 408

Fam. 1. Symbranchidae, 409 ; Fam. 2. Amphipnoidae, 409.

Series 4.
Sub-Order 4. GASTEROSTEIFORMES 410

Tribe 1. Gasterosteoidei, 411.

Fam. 1. Gasterosteidae, 412 ; Fam. 2. Aulorhyncbidae, 412.
Tribe 2. Hemibranchii, 412.

Sub-Tribe A. Protosyngnathoidei, 412. Fam. Protosyngna-

thidae, 412.
Sub-Tribe B. Aulostomoidei, 412. Fam. 1. Aulostomatidae,

413; Fam. 2. Fistulariidae, 413.
Sub-Tribe C. Gentriscoidei, 413. Fam. 1. Centriscidaje, 413 ;

Fam. 2. Amphisilidae, 413.
Tribe 3. Lophobranchii, 414.

Sub-Tribe A. Fam. Solenostomidae, 414.

Sub-Tribe B. Fam. 1. Syngnathidae, 415; Fam. 2. Hippo-
cam pidae, 415.
Tribe 4. Hypostomides, 416.
Fam. Pegasidae, 416.

CONTENTS

Series 5. PAGE

Sub-Order 5. NOTACANTHIFORMES • 416

Division 1. Fam. Dercetidae, 417.
Division 2. Tribe 1, 417.

Fam. 1. Halosauridae, 417; Fam. 2. Lipogenyidae, 417;
Fam. 3. Notacanthidae, 418.
Tribe 2. Fam. Fierasferidae, 419.

Series 6.

Sub-Order 6. MUGI LI FORMES 419

Tribe 1, 419.

Sub-Tribe A. Fam. Sphyraenidae, 419.
Sub-Tribe B. Earn. Atherinidae, 419.

Sub-Tribe C. Fam. 1. Mugilidae, 420 ; Fam. 2. Polynemidae,
420.

Tribe 2, 421.

Sub-Tribe A. Fam. 1. Tetragonuridae, 421 ; Fam. 2. Strom-

ateidae, 421.

Sub-Tribe B. Fam. Icosteidae, 421.
Tribe 3, 421.

Sub-Tribe A. Fam. Ophiocephalidae, 422.
Sub-Tribe B. Labyrinthici, 422. Fam. 1. Anabantidae, 422 ;
Fam. 2. Osphromenidae, 422.

Tribe 4, 423.

Fam. Chiasmodontidae, 423.

Tribe 5, 423.

Fam. Stephanoberycidae, 423.

Sub-Order 7. ACANTHOPTERYGII • . 424

Division 1. Salmopercae, 425.
Fam. Percopsidae, 425.

Division 2, 426.
Subdivision 1.

Tribe 1. Beryciformes, 426.

Fam. 1. Berycidae, 426 ; Fam. 2. Aphredoderidae,
427 ; Fain. 3. Pempheridae, 428 ; Fam. 4. Monocentridae,
428.
Subdivision 2.

Tribe 1. Perciformes, 428.

Sub-Tribe A : Superfamily I.

Fain. 1. Sparidae, 428 ; Fam. 2. Mullidae, 429 ; Fam.
3. Serranidae, 430 ; Fam. 4. Sciaenidae, 431 ; Fam. 5.
Pseudochromididae, 431 ; Fam. 6. Cepolidae, 431 ;
Fam. 7. Hoplognathidae, 431 ; Fam. 8. Sillaginidae,
432.

INCERTAE SEDIS : Fam. Anomalopidae, 432.

CONTENTS

Sub-Order 7. ACANTHOPTERYGII— continued

Superfamily II. Fam. 1. Scorpididae, 432 ; Fam. 2.
Caproidae, 432.

Sub-Tribe B. Chaetodontif Dimes, 433.
Division A. Squammipennes, 434.

Fam. 1. Chaetodontidae, 434 ; Fain. 2. Drepanidae,
434.

Division B. Plectognathi, 435.
Subdivision A.

Fam. 1. Teuthididae, 435 ; Fam. 2. Siganidae,
435 ; Fam. 3. Acanthuridae, 435.

Subdivision B.

Branch 1. Sclerodermi, 436.
Series 1, 436.

A. Fain. Triacanthidae, 437. B. Fam. 1.
Balistidae, 437 ; Fam. 2. Monacanthidae,
437.

Series 2, 437.

Fam. Ostraciontidae, 439.

Branch 2. Triodontes, 439.
Fam. Triodontidae, 439.

Branch 3. Gymnodontes, 439.

A. Fam. 1. Tetrodontidae, 44 T ; Fam. 2.
Diodontidae, 441. B. Fam. Molidae, 442.

Sub-Tribe C, 442.

Fam. 1. Acropomatidae, 442 ; Fam. 2. Percidae,

442 ; Fam. 3. Centrarchidae, 443 ; Fam. 4. Cyphosidae,

443 ; Fam. 5. Lobotidae, 444 ; Fam. 6. Nandidae, 445 ;
Fam. 7. Gerridae, 445 ; Fam. 8. Pristipomatidae, 445 ;
Fam. 9. Trichodontidae, 445 ; Fam. 10. Lactariidae, 445 ;
Fam. 11. Latrididae, 445 ; Fam. 12. Haplodactylidae,
445.

Sub-Tribe D, 445.

Branch 1. Fain. 1. Pomacentridae, 446 ; Fam. 2.
Cichlidae, 446.

Branch 2. Fam. Embiotocidae, 446.

Branch 3. Fam. 1. Labridae, 446 ; Fam. 2. Scaridae,
447.

Tribe 2. Gobiifwmes, 447.
Fam. Gobiidae, 448.

Tribe 3. Echeneidiformes, 448.
Fam. Echeneididae, 449.

CONTENTS

Sub-Order 7. ACANTHOPTERYGII— continued
Tribe 4. Scorpaeniformes, 449.

Sub-Tribe A. A. Fam. 1. Scorpaenidae, 449 ; Fam. 2.
Triglidae, 450. B. Fam. Agonidae, 450 ; Fam. 3. Dacty-
lopteridae, 451 ; Fam. 4. Hexagrammidae, 453 ; Fam. 5.
Comephoridae, 453 ; Fam. 6. Khamphocottidae, 453.

Sub-Tribe B. Fam. 1. Cottidae, 453 ; Fam. 2. Cyclo-
pteridae, 454.

Sub-Tribe C. Fam. 1. Platycephalidae, 454 ; Fam. 2.
Hoplichthyidae, 454.

Tribe 5. Blenniiformes, 454.

Sub-Tribe A. Fam. 1. Trachinidae, 455 ; Fam. 2. Per-
cophiidae, 455 ; Fam. 3. Leptoscopidae, 456 ; Fam. 4.
Nototheniidae, 456 ; Fam. 5. Uranoscopidae, 456.

Sub-Tribe B. Fam. 1. Callionymidae, 456 ; Fam. 2.
Gobiesocidae, 456 ; Fam. 3. Trichonotidae, 457.

Sub-Tribe C, 457 ; Fam. 1. Blenniidae, 458 ; Fam. 2.
Pholididae, 458 ; Fam. 3. Zoarcidae, 458 ; Fam. 4.
Congrogadidae, 460 ; Fam. 5. Ophidiidae, 460 ; Fam.
6. Podatelidae, 460.

Sub-Tribe D.

Division 1. Batrachi, 460.

Fam. Batrachidae, 460.
Division 2. Pediculati, 461.

1. Fam. Lophiidae, 462 ; Fam. Ceratiidae, 462';
Fam. Antennariidae, 462. 2. Fam. Gigantactinidae,
462. 3. Fam. Malthidae, 462.

Tribe 6. Scombriformes, 462.

1. Fam. Bramidae, 464. 2. Fam. Carangidae, 464;
Fam. Rhachicentridae, 464. 3. Fam. Scombridae, 465 ;
Fam. Trichiuridae, 466 ; Fam. Coryphaenidae, 466 ; Fam.
Luvaridae, 467. 4. Fam. Palaeorhynchidae, 467 ; Fam.
Histiophoridae, 467 ; Fam. Xiphiidae, 468.

Tribe 7. Kurtiformes, 468.
Fam. Kurtidae, 468.

Subdivision 3. Zeorhombiformes, 468.
Branch A.

Fam. Zeidae, 469.
Branch B.

Fam. 1. Amphistiidae, 469 ; Fam. 2. Pleuronectidae, 469.

Division 3. Lampridiformes, 475.
Subdivision 1. Selenichthyes, 475.
Fam. Lamprididae, 475.

CONTENTS

Sub-Order 7. ACANTHOPTERYGII— cottiinued
Subdivision 2, 475.

Tribe 1. Histichthyes, 476.

Fam. Veliferidae, 476.
Tribe 2. Taeniosomi, 476.

Fam. 1. Lophotidae, 476; Fam. 2. Trachypteridae, 476;
Fam. 3. Stylephoridae, 477.
Division 4. Mastacembeliformes, 477.
Fain. Mastacembelidae, 478.

Series 7. PAGE

Sub-Order 8. GADIFORMES . .478

Division 1.

Fam. Macruridae, 480.

Division 2.

Fam. 1. Gadidae, 482 ; Fam. 2. Muraenolepidae, 483.

INDEX 505

Subphylum VERTEBRATA CRANIATA

THE present work deals with the Vertebrata Craniata, that highest
branch of the Phylum Vertebrata, or Chordata, which comprises
the classes Cyclostomata, Pisces, Amphibia, Eeptilia, Aves, and
Mammalia.

Besides the Subphylum Craniata, there are included in the
Phylum Vertebrata the Cephalochorda, represented by Amphioxus and
a few allied genera, the degenerate Tunicata, and the Enteropneusta.
The latter group is an aberrant one, whose right to a position in
the Phylum is less thoroughly established.

That the six Classes of Craniata mentioned above belong to a
single branch derived from some common ancestral form, which
had acquired many new characters, and had advanced very con-
siderably beyond the grade of structure found in their nearest
allies the Cephalochorda, cannot be doubted when we study their
anatomy.

Not only do the Craniata differ from the Cephalochorda in the
possession of a large brain more or less completely enclosed in a
cartilaginous cranium, to which character they owe their name ;
but they have made a great advance in almost every detail of their
organisation. The comparison given below shows clearly the great
gap which separates the lowest known Craniate from Amphioxus.
In making this comparison it must, of course, be remembered that
Amphioxus is itself a highly specialised animal, differing in all
probability very considerably from the early vertebrate ancestor
from which both these surviving branches have diverged.

The Craniata have in common with the Cephalochorda the
fundamental characters of the Vertebrata (Chordata), such as : the
bilateral symmetry ; the pronounced metameric segmentation of the
mesoblast ; the gut opening by an anterior mouth and a posterior
anus, and provided with paired lateral gill-slits ; the dorsal tubular
central nervous system ; the supporting notochord of endodermal
origin, unsegmented and underlying the central nervous system ; the
prolongation of the body beyond the anus in the form of a metameri-
cally segmented tail, containing tissues derived from the three
germ-layers ; the well-developed coelom, and the separate blood-
vascular system.

1 i

CEP HA LISA T1ON

Among the chief features which denote the great advance in
structure of the Craniate vertebrate should first be mentioned the
pronounced cephalisation of the anterior segments. Now a typical
trunk segment of Amphioxus, besides a portion of the nerve-cord,
of the notochord, and of the gut, contains a paired coelomic cavity,
and a right and left myotome or muscle segment. Motor fibres are
supplied to these muscles direct from the nerve-cord by the ventral
'nerve-root' (Fig. 1). The separate dorsal 'nerve-root' passes
out from the nerve-cord between the myotomes to the surface,
supplying sensory fibres to the skin, and probably both sensory
and motor fibres to the viscera (Hatschek [202], Hey mans and van

- al.

TV.

FIG. 1.

Diagrams to show the relations of the dorsal and ventral nerve-roots in (A) the trunk of
Amphioxus (modified from Hatschek), in (B) the gill-region of a Gnathostome (cranial nerve),
and in (C) the tiunk-region of a Gnathostome. «Z, alimentary canal ; br, brain ; il.r, dorsal
root ; e, eye-muscle ; g, gill-slit ; I, mixed nerve to paired limb ; m, myotome ; n.c, nerve-cord ;
p, ventral branch to skin and visceral muscles; r.d, ramus dorsalis ; r.r, ramus ventralis ;
s, sympathetic ; v.r, ventral root. Fibres from the dorsal root are black.

der Stricht [213], Johnston [248]). But whereas in Amphioxus
the mesoblast is clearly segmented to the very tip of the head, and
the myotomes, developed from the second segment backwards,
persist with their corresponding nerves throughout the anterior
region, in the Craniate the segments at the anterior end of the
body are so highly modified, and their limits so obscured, that
they can only be made out with difficulty in the embryo, and are
unrecognisable as such in the adult. Two of the chief factors
in the specialisation of the head-region have no doubt been the
presence of the mouth and gill-slits, and the development of the
paired organs of sense.

The ' Vertebral ' theory of the skull, as upheld by Goethe and
Oken, and further elaborated by Owen, was upset by Huxley in

HEAD SEGMENTS

his famous Cronian Lecture in 1858 [225]. It received its final
blow from Gegenbaur (1872), and has been gradually replaced by
a ' Segmental ' theory of the Craniate head founded on sound
anatomical and embryological evidence (Gegenbaur [153, 161],
Fiirbringer [143], Froriep, Balfour [27], Marshall [292-3], van
Wijhe [495], von Kupffer [275], and others).

It is now recognised that the remote ancestor of the Craniata
must, like Ampkivxus, have been fully segmented to its anterior
extremity ; that the great differences in structure between the
head and the trunk must be considered as due to the divergent
specialisation of two regions of the body, which primitively
resembled each other closely ; and that there is no hard and fast
line between the two, the distinction having been gradually estab-
lished, and being more pronounced in the higher than in the lower
forms. The limit of the head-region varies according as we adopt
the skeleton, the nerves, or the gill-slits as our criterion.

To unravel the complex structure of the head, to enumerate
and identify the segments of Avhich it is composed, is one of the
most interesting and difficult problems of the morphology of the
Craniata.

For this purpose three chief sets of structures must be studied :
the nervous system and sense-organs ; the mesoblastic somites ;
and the gill arches and slits. Of these it is the second, perhaps,
which affords the most trustworthy evidence. It is well known
that in the trunk-region the mesoblast becomes differentiated in
ontogeny into two main divisions : the segmental dorsal somites
and the ventral unsegmented ' lateral plate.' The former may
contain segmental transient coelomic cavities (myocoel), the latter
the unsegmented coelom or permanent body-cavities. Indeed, it
is one of the main characteristics of all Craniata, as distinguished
from the Cephalochorda, that the ventral mesoblast is continuous
and has lost its segmentation, though traces of it may be seen in
the development of the trunk segments of Cyclostomes (Hatta
[202«]), and in the head region of all Craniates. The dorsal
somites become further differentiated into an outer ' cutis layer '
yielding connective tissue, an inner muscular layer forming the
true myotomes from which are derived all the segmental muscles
of the body, and a ventral inner outgrowth, the sclerotome, the
chief source of the connective tissues. From the lateral plate are
derived the coelomic epithelium and the splanchnic or visceral
muscles. Now it is important to notice that, while the myotomes
and the muscles derived from them (such as the limb-muscles) receive
their motor nerves exclusively from the ventral roots of the spinal
nerves, the splanchnic muscles, the skin, the mucous membranes,
and their sense-organs are supplied from the mixed dorsal roots
(Fig. 1).

HEAD SEGMENTS

In both the Cephalochorda and the Craniata the trunk seg-
ments are provided with corresponding segmental spinal nerves.
Originally, these were perhaps restricted in distribution to
definite segmental areas. The ventral motor root is probably
from the very first in ontogeny continuous with the myotome of
its own segment ; if not by means of nerve- fibres, at all events by
protoplasmic strands along which the fibres may grow. There is
reason to believe that they remain for ever faithful to that
segment both in individual development and in phylogeny. The
fate of the root depends on that of the muscle it supplies ; if the
latter enlarges, the motor root acquires many fibres and becomes
thick ; if, on the contrary, it dwindles, the nerve diminishes also,
and may finally vanish (Fiirbringer [142]). Anastomoses between
neighbouring motor nerves, plexus formation, can presumably
only follow on the fusion of muscle segments, a phenomenon of
frequent occurrence.

The distribution of the nerve-fibres of the dorsal mixed root is
less rigidly confined. Possibly the sensory fibres remain always
faithful to the sensory cells and organs they supply ; but these may
multiply and spread over the skin from one region to another.
Obvious traces of an originally metameric distribution of the
sensory nerves are still visible in the highest vertebrates (Bolk).
The nerve-fibres of the dorsal root which supply structures derived
from the lateral unsegmented plate are free to form an anastomosing
plexus (vagus nerve, sympathetic system).

The ventral roots are never and the dorsal roots are always
provided with a ganglion in the Craniata. Originally (Amphioxus)
the two roots were independent. But in all Craniates, with the
exception of the Petromyzontia (p. 38), the ventral root joins the
dorsal root near the ganglion to form a mixed nerve (Fig. 1).
Typically, the mixed nerve gives off four main branches : a dorsal,
a median, a ventral, and a visceral. In some fish (Selachians) the
mixing of the two sets of fibres is not very complete, and in the tail
region it may scarcely take place at all (Goodrich [176]). The spinal
ganglia and sensory nerves, originally derived from the surface,
sink inwards between the somites, and come to occupy a position
internal to the myotomes. In ontogeny the dorsal roots and ganglia
are all derived from a longitudinal neural crest, which develops on
each side of the ectodermal neural plate or thickening (the rudiment
of the central nervous system). The crest is discontinuous in the
head, but continuous at first in the trunk and tail.

Now, it is obvious that most valuable evidence with regard to
the segmentation of the head might be expected from a study of
the development of its muscles and nerves. It has been found
that in the lower Craniata there is no abrupt division between the
trunk and the head ; that as we pass forwards the segments become

HEAD SEGMENTS

on the whole less and less typically developed, more and more
specialised ; that this process of cephalisation has proceeded farther
in the higher than in the lower forms ; and finally, that it is less
pronounced in the embryo than in the adult. Observers differ as
to the exact number of somites in front of the segment corre-
sponding to the vagus nerve. The head behind that region
includes a very variable number of segments. The hind limit of
the head in fish not only may be quite indefinite, there being a
gradual transition from one region to the other, but also it does
not occupy a fixed position, and the process of cephalisation, or
assimilation of trunk segments, has gone much further in some
groups than in others.

Without attempting to give a history of the study of the
segmentation of the head, it may be mentioned that Balfour,
Marshall [292-3], Dohrn [118], van Wijhe [495], Hoffmann [216],
Braus [47], Platt [331], Koltzoff [272-3], Johnston [248a],
and numerous others, have Avorked at this difficult problem. It
has been fairly Avell established that there are 3 mesoblastic seg-
ments in front of the auditory capsule (prootic somites), and a
varying number behind (metaotic somites) ; 9 in Pristiurus, 1 0 in
Acanthias, 11 in Spinax. The fourth somite may extend below
the auditory capsule. These somites, first clearly identified by van
Wijhe [495] in Elasmobranchs, have been found in the Cyclo-
stomes (Koltzoff [272]), the Amphibia (Platt [3 3 !<?]), and the
Amniota. They appear to be strictly comparable throughout the
Oaniata (Fig. 3). A more anterior evanescent somite has some-
times been seen in front of the first of van Wijhe ; it is the
so-called 'anterior head-cavity' of Elasmobranchs (Platt [331]).

In all the Craniate vertebrates the myotomes of the first three
prootic somites are entirely subordinated to the use of the optic
capsule, and become converted into the ' eye-muscles.' Although
there are slight discrepancies between the arrangement of the six
eye-muscles of the Cyclostomes and Gnathostomes, yet their form
and innervation are remarkably constant throughout (Figs. 3 and 4).
With regard to the more posterior segments, the Cyclostomes seem
to be in a much more primitive condition than the Gnathostomes.
For, whereas in the former all the metaotic somites (from the fourth
backwards) appear to be represented in the adult by myotomes
forming a continuous series with ordinary trunk-muscles (Koltzoff
[272], Hatschek [202]), in the Gnathostomes the myotomes of
the first two or more metaotic somites vanish during ontogeny, and
the 4th somite (1st metaotic)1 never forms muscle even in the
embryo (Figs. 2 and 3).

1 Many authors, Dohrn, Kilian, Platt, Sewertzoff, etc., consider that there are
here two or more fused somites ; but the evidence, especially of the nerves, seems to
be against this view.

HEAD SEGMENTS

A varying number of somites behind the 6th grow downwards
and inwards to form the epibranchial and hypobranchial muscles,
the dorsal myotome dwindling away. A normal muscular segment,
serial with the trunk-myotomes, is generally not developed at all
in the head-region of a Gnathostome.

The anterior mesoblastic somites extend downwards to form the
lateral plate, which passes between or is pierced by the gill-slits.
From this plate are developed the muscles of the visceral skeleton

in

B.

gs.

pc:,

f Ok

a. g. v.

ack

vr. dr.

FIG. 2.

Diagrams of the segmentation of the anterior region of a Cyclostome, A, and a Gnathostome,
B. The skeleton is dotted ; the myotomes, 1-13, are shaded with lines (broken when vestigial) ;
the gill-slits (dotted) are shown below ; the dorsal root-nerves are black ; the ventral root-
nerves are represented by dotted lines, a, auditory capsule ; ad, auditory nerve ; adr,
dorsal root of anterior spinal nerve ; d.r, dorsal root ; eb, epibranchial nerve ; /, facial nerve ;
g, glossopharyngeal nerve ; g.s, branchial slit, I-VII ; l.h, limit between head and trunk ; m,
mouth ; n, nostril ; nt, notochord ; p, profundus nerve ; pe, parachordal ; s, spiracular slit ;
«c, skeletal segment or scleromere ; t, trigemlnal nerve ; tr, trabecula cranii ; v, vagus nerve ;
v.r, ventral root.

and alimentary canal, and the trapezius muscle passing to the
scapula.

The cranial nerves, which used to be considered as radically
different from the spinal nerves, have now been recognised as, for
the most part, merely modified segmental nerves, some having
dorsal and others ventral roots. The old numbering of the cranial
nerves, founded on human anatomy, is often retained for conveni-
ence, but has been replaced by an enumeration referring to their
true metameric order. Those characters which distinguish them
from the spinal nerves are partly primitive and partly secondary.

CRANIAL NERVES

Among the former may be reckoned the separate course of the
ventral motor roots (for these do not mix with the dorsal roots),
and the more superficial course of the dorsal ganglionated roots.
The cranial nerves of the Craniate, in fact, more closely resemble the
segmental nerves of Amphioxus than do the spinal nerves (Fig. 1).
The existence of a large number of motor fibres in the dorsal
nerves is correlated with the great development of the visceral
muscles in the head. This, the chief difference between the two
types of nerves, is one of degree. Likewise Avith regard to the

ffS.

FIG. 3.

Diagrams of the anterior region of a Cyclostome, A, and of a Gnathostome, B, showing'the
p< isition and development of the myotomes (numbered 1-1S). In the Gnathostome the first few
metaotic myotomes (4-6) are more or less vestigial. The sense-capsules are indicated by dotted
lines, a, auditory, n, nasal, and o, optic capsule ; g.s I- VII, gill-slits ; h.p, hypoglossal processes
of myotomes ; m, mouth ; s, spiracular slit.

position they occupy, the cranial nerves seem to lie outside the
muscles, while the spinal nerves lie mostly on the inner side of the
muscles ; this is explained by the fact that the myotomes are well
developed in the trunk and tail, but scarcely at all in the head
of Gnathostomes (Fig. 1). The position of the post - auditory
cranial nerves is normal in the Cyclostomes, where the myotomes
are present.

Setting aside the special olfactory and optic nerves, we find
that the 5th cranial nerve consists of a pair of segmental nerves
(Fig. 2). The ventral root of the first (Illrd nerve or motor oculi)
supplies eye-muscles derived from the first or premandibular somite

CRANIAL NERVES

(rectus interims or anterior, rectus superior, rectus inferior, and
obliquus inferior). Its dorsal root is the nervus ophthalmicus
profundus passing to the quite anterior region of the head. The
ventral root of the second segment (IVth nerve or patheticus)
passes to the superior oblique muscle, developed from the second
or mandibular somite. Its dorsal root is the trigeminus nerve
(Vth in part) supplying the front region of the head and the jaws.
The myotome of the third and last prootic somite (rectus posterior
or externus) is innervated by a ventral root (Vlth nerve or abdu-
cens) ; and the corresponding dorsal root is the Vllth nerve or
facialis, which has an epibranchial branch forking over the first gill-
slit or spiracle, and passing down the hyoid arch. The YHIth or
auditory nerve also represents a portion of the dorsal root of this
segment. The 4th somite, first metaotic, disappears together with
its ventral root in all except the Cyclostomes. Th£ glossopharyngeal
(IXth) nerve is the corresponding dorsal root, and supplies the second
gill-slit and first branchial arch. The dorsal root of the fifth segment
is the vagus (pneumogastric) or Xth nerve sending a branch to the
third gill-slit and second branchial arch. All the remaining gill-slits
and arches have similar epibranchial nerves which all come from
the vagus. Gegenbaur supposed the vagus to be a compound
nerve formed by the gathering together of segmental nerves equal
in number to the gill-slits they supply [156]. But this view,
that the vagus root is formed by the fusion of the dorsal roots of
several segments which have become incorporated into the hinder
region of the head, has been shown not to be in agreement with
embryology ; for there is no evidence of so complete a disappear-
ance of segments behind the first vagus root. Nor is it reconcilable
with the evidence of comparative anatomy. Not only are transi-
tory vestigial dorsal roots and ganglia found in the segments of the
gill -bearing region in Gnathostomes, but in the Cyclostomes
(Ammocoete larva of Petromyzon (Hatschek [202], Koltzoff [272])),
each of these segments is provided with a dorsal root, a ganglion,
and a dorsal branch passing to the skin between consecutive
myotomes. Nevertheless, it is possible that in the Cyclostome
one dorsal root (Hatschek [202]) and in the Gnathostome one or
more (van Wijhe) may coalesce with the vagus root.

Nor do the known facts of development and anatomy support
the view that the distribution of the branchial nerves of the vagus
is due to the branching of an originally single segmental nerve.
There remains, as the most probable explanation, the theorj7 of the
partial polymerisation of the vagus (Hatschek [202]), according to
which the original segmental dorsal branchial nerves have been
joined together by a longitudinal commissural epibranchial nerve
coextensive with the gill-bearing region, and have lost their original
connections with the spinal ganglia. In Petromyzon, indeed, the

CRANIAL NERVES

dorsal roots of the gill-region join the epibranchial nerve. Meta-
meric epibranchial placodes, or proliferations of the epidermis
(Beard [32], Koltzoff [272]), are found above each gill-slit ; from
these are derived the ganglia on the branchial nerves which become
joined together by the longitudinal connection. Similar longi-
tudinal nerves also unite the trigeminal with the facial nerve, and

Fio. 4.

A'-i'iith'n's i-i'iijm-i.t, Risso. A, outer view of muscles and nerves of right orbit, from which
the eye has been removed. B, dorsal view of right eye. ar, anterior, ir, inferior, pr, posterior,
and sr, superior rectus muscle ; ob.i, inferior, and ob.s, superior oblique muscle'; os, cartila-
ginous optic stalk ; 2, optic, 3, oculomotor, 4, pathetic, and 6, abducens nerve.

the latter with the glossopharyngeal in Petromyzon and most
Gnathostomes. The exact composition and mode of formation of
the vagus root is still far from thoroughly understood, and it is
possible that it may have been formed by a gathering together not of
whole posterior dorsal roots as Gegenbaur suggested, but of only those
components of each root which supplied the gills and alimentary
canal ; this supposition (of a slipping forward, so to speak, of

10

CRANIAL NERVES

certain portions) would avoid the assumption that new central
connections have been established with the brain (Johnston [248a]).
The intestinal branch of the vagus may perhaps have developed in
somewhat the same manner from the visceral branches of the more
posterior nerves. The sympathetic system of nerves, scarcely
recognisable as such in the Cyclostomes, would appear to be a
specialisation in the general plexus supplying the unsegmented
splanchnic structures, and is developed from the dorsal roots and
ganglia in the main. The ' dorsal ' cranial nerves are provided

mt>.

br.1

br?

FIG. 5.

Reconstruction of the head of an embryo of Acn.nthins, enlarged. (After Sewertzoff.) «.<•,
cartilage of auditory capsule; al, alisphenoid cartilage; an, auditory capsule; br1-5, tirst to
fifth branchial arches ; cp, epiphysis ; /.ft, fore-brain ; g, spinal ganglion ; It, hyoiil arch ; A. ft,
hind-brain ; in, mandibular arch ; rn.b, mid-brain ; w, nasal pit ; p, parachordal plate ; s8, eighth
scleromere ; tr, trabecula ; v.r, ventral spinal root ; 5, 7, 0, 10, roots of the trigeminal, facial,
glossopharyngeal, and vagus nerves.

with ganglia ; these generally sink deep down, and may even enter
the cranial cavity.

The ventral roots of the segments in the branchial region are
variously affected by the fate of their corresponding myotomes.
In the Cyclostomes (Petromyzon) they are normally developed
(p. 5). Since the myotomes behind the vagus root have a tendency
to disappear from before backwards in the Gnathostomes (p. 5),
the ventral roots dwindle also. They survive, however, in so far
as they supply the epibranchial and hypobranchial muscles (Fig. 5).
These are developed, as already mentioned, as ventral downgrowths
from somites of the posterior branchial segments and of a varying
number of segments farther back (from about the 8th to the 12th

SKULL n

metaotic somite in Elasmobranchs (van Wijhe [495], Neal [308«]) ;
from the 7th to the 14th in Petromyzon (Koltzoff [272]); from
the 3rd to the 5th in Necturus (Platt [33 la])). The processes from
these somites grow down behind the last gill-slit, and then pass
forwards again below to form the hypoglossal musculature, and it
is the ventral nerve -roots corresponding to them which form the
spino-occipital nerves of fish, representing the compound hypoglossal
nerve (Xllth cranial nerve) of higher forms (Fiirbringer [143]).
Thus we get a very variable number of hypoglossal constituents in
the different groups of Craniate vertebrates (Figs. 3, 44).

After Huxley's brilliant attack on the Vertebral theory of the
skull, came Gegenbaur's epoch-making work on the Elasmobranch
skeleton (1872). He showed that though the chondrocranium of
the adult Selachian forms a continuous box, yet it exhibits many
signs of an original segmental structure, at all events behind the
infundibulum and the exit of the oculo-motor nerve. This part of
the skull, including the occipital, auditory, and part of the orbital
regions, is traversed below by the notochord, gives exit to segmental
nerves, and is connected with segmental gill-arches. It was there-
fore called the ' vertebral ' region as distinct from the more
anterior part of the skull, including a part of the orbital and the
ethmoid regions. The latter was called the ' prevertebral ' region ;
it is chiefly formed by a forward growth round the nasal organs
(Gaupp [150-3]).

Following Kathke, Huxley had pointed out that the basis
cranii of all Craniata arises in the embryo as a basal or parachordal
plate embracing the extremity of the notochord, below the brain,
and two trabeculae cranii in front, one on either side of the
infundibulum. Stohr [426«] showed that, in the Urodela, the
' vertebral region ' is developed from three distinct centres —
the parachordal, the mesotic cartilage of the auditory capsule, and
an occipital segment resembling a vertebra. Subsequently Froriep
found, in the occipital region of birds and mammals, some three
metameres with distinct somites, skeletal segments, and nerves
(hypoglossal). Rosenberg [374rt], Sagemehl [379], and Gegenbaur
[160] also studied the process of assimilation of vertebral segments
(Fig. 6). This gradual inclusion of skeletal segments, sclero meres,
in the occipital region of the skull of fish has lately been followed
in great detail from embryo to adult by Sewertzoff [407],
Hoffmann, Brans [47], and Schreiner [390a]. It has now been
conclusively shown that in the Gnathostomes skeletal segments
of vertebral nature do, in the course of ontogeny, and doubtless
also in that of phylogeny, become attached to, fused with, and
finally completely embodied in the occipital region, carrying with
them their corresponding nerves. Originally spinal nerves thus

SKULL

come to pass through the cranial wall — so-called spino-occipitals.
The more anterior ventral roots only represent the hypoglossal
nerve, already described, p. 11, but more posterior and normally
developed spinal nerves may also be included, the ' occipito-spinals,'
which supply the anterior trunk, myotomes, etc. (Jackson and
Clarke [236],Gegenbaur [160], and especially Furbringer's admirable
monograph [143]).

The exact early history of the skull is sunk in the obscurity of
the past, and may perhaps never be reconstructed from embryo-

A.

B,

TIC

FIG. 6.

Diagrams illustrating the development of the skull in the Craniata. A, early stage ; B, later
stage, n, auditory vesicle; o.c, auditory capsule; e, ethmoid region ; n, nasal sac; n.c, nasal
capsule; nt, notochord ; o, optic vesicle ; o.c, optic capsule ; o.s, occipital segment or sclerotome ;
p, paracliordal region ; s, vertebral sclerotome ; /, trabecular region. The dotted areas represent
cartilage and procartilage.

logical data. That the occipital region is segmental is clear.
The parachordals themselves show but slight indications of sub-
division (Platt, in Urodela [33 la]); the trabeculae show none
whatever. How far segments in the prechordal and even in the
parachordal region of the head may have been modified and
obliterated before cartilage developed — how far, in other words,
the anterior region was ' cephalised ' before the skull arose —
in the ancestors of modern Craniates remains an unsolved
problem.

But it must be remembered that the infundibulum, to which the
notochord always reaches in Craniates, probably lies at or near the

BRAIN 13

morphological anterior limit of the head ; l and as far as this the
mesoblast is segmented. The great extension forwards beyond this
point of both the nervous system and the skull is doubtless related
to the great development of the special organs of sense, and of the
brain. Indeed, the position of the olfactory, optic, and auditory
organs must have been one of the chief factors in influencing not
only the growth of the brain, but also of the cartilaginous skull, with
its three pairs of protective capsules (Figs. 5 and 6). The nasal
capsules develop in front of the trabeculae, with which they generally
become continuous, if they are not so from the first. The optic
capsules arise independently and remain separate, partially enclos-
ing the optic vesicles. The auditory capsules either from the first
or very soon are continuous with the parachordal plates. Chondri-
fication extends up the sides and over the roof of the cranial brain-
cavity more or less completely. The skull acquires further strength
and rigidity for the support of the visceral skeleton and the attach-
ment of its muscles.

To protect and support the brain is one of the chief functions
of the cranium. The brain in even the lowest known Craniate has
made vast advances over that of Amphioxus. Into its minute
histological structure it is not possible to enter in this book ; some
day, however, the results of a more complete knowledge of the dis-
position of its cells and fibres will doubtless be of the greatest
importance in the study of phylogeny. The gross subdivisions into
which the brain becomes differentiated are of no segmental signi-
ficance. But attempts have been made to interpret local aggrega-
tions of cells, and certain transverse swellings and constrictions of the
neural tube, which appear at a very early stage in ontogeny, as true
neural segments or neuromeres (Hoffmann [216], Orr, M'Clure, Locy
[284], von Kupffer [275], Neal [308a], Johnston [248a], and others).
The observations are somewhat uncertain and contradictory, and
these neuromeres do not appear to correspond exactly with the other
evidences of segmentation. The subject is too unripe for treatment
here ; but it may be stated that if the evidence of the neuromeres
is to be trusted, there would appear to be three segments in front
of the segmented mesoblast, of which all other trace has been lost.

The embryonic brain of the Craniate is subdivided into primary
fore-brain, mid-brain, and hind-brain.

Later on the hind-brain forms a posterior myelencephalon or
medulla oblongata, and an anterior metencephalon, giving rise
above to the cerebellum (Figs. 7, 8, 9, and 10). The hind-brain is

1 Authors differ on this debatable point. Some place the anterior end of the
brain at the infundibulum, others at the edge of the neuropore. Johnston [248a]
believes it to lie at a point just behind the anterior commissure, and in front of the
optic recess and chiasma.

BRAIN

the least modified part ; it resembles the spinal cord most closely
in histological structure, and from it emerge all the cranial nerves to
which a segmental value is usually attached, except the oculomotor
and pathetic. It always retains a considerable cavity, metacoele or
4th ventricle. Its roof is never entirely nervous, and forms a
vascular membrane, the choroid plexus. The roof of the meten-
cephalon becomes thickened as the cerebellum, which acquires a

A.

copl C

ft.

B.

ol

FIG. 7.

Ventral view (A) and dorsal view (B) of the brain of Raja latis. Dorsal view (C) of the
brain of Acanthins vulgaris, showing the internal cavities shaded, a, auditory nerve ; bm,
buccal nerve ; en, cavity of mid-brain ; cct, lateral cavity of corpus restiforme ; c.fb, cavity of
fore-brain, "cerebral hemisphere" ; c.o.l, cavity of olfactory lobe ; c.op.l, cavity of optic lobe ;
cr, cerebellum ; ctf, corpora restiformia ; d.r, dorsal root of spinal nerve ; f.b, fore-brain (pros-
encephalon) ; f.v, fourth ventricle ; gl, glossopharyngeal nerve ; hm, hyomandibular nerve ; if,
infundibuluin ; l.c, lateral cavity ; l.i, lobus inferior ; l.t, lamina terminalis ; m, medulla
oblongata ; o.l, olfactory lobe ; os, olfactory tract ; op.l, optic lobe ; pr, profundus nerve ; psp,
prespiracular branches of facial ; s.op, superior ophthalmic branches of facial and trigeminal ;
.-••/ '.'.', spinal cord ; s.v, saccus vasculosus ; th, diencephalon (thalamencephalon) ; t.v, third ven-
tricle ; v, vagus nerve ; v.r, ventral root of spinal nerve.

large size and complicated structure in the higher Pisces and higher
Tetrapoda. The mid-brain remains undivided. The cavity it
encloses is known as the aqueductus of Sylvius, or mesocoele.
Above and at the sides the wall thickens into the prominent optic
lobes, from which pass fibres to the optic tract. Below, a bundle
of fibres develops into the crura cerebri. From this mesencephalon
issue the oculomotor and pathetic nerves.

BRAIN

From the primitive fore -brain are differentiated a posterior
diencephalon (thalamencephalon) and an anterior secondary fore-

JZ"'

FIG. 8.

\~ Dorsal view of the brain of Heptanehus cinereus. (From Gegenbaur, Vergl. Anat. Wirbclticre.)
Ac, aiulitory nerve; F, facial, Gp, glossopharyugeal ; H, cerebellum; M, optic lobe ; Ms, spinal
cord ; A', medulla, also nasal sac ; 0, optic nerve ; Po, olfactory tract ; Tr, trigeminal nerve ;
V, fore-brain ; Vg, vagus nerve ; Z, diencephalon ; a and b, branches of facial and trigeminal ;
ab, abducens ; Tip, (hypoglossal) occipito-spinals ; I, olfactory lobe ; om, oculomotor ; v, origin
of vagus roots.

brain, the telencephalon. The diencephalon, bounded behind by the
posterior commissure, is crossed above by the superior commissure

i 6 BRAIN

(habenular). Between these two tracts of fibres are the epiphysial
outgrowths. At the anterior limit the thin non-nervous portions
of the roof form a choroid plexus, sinking down behind the
paraphysis, and projecting into the large 3rd ventricle as a velum
transversum (permanent in the lower and transient in the higher
forms). At the sides arise the optic thalami ; above the ganglia
habenulae. Below is the large infundibular downgrowth, with the
optic chiasma and nerves immediately in front. The foremost
division of the brain is that which undergoes the most conspicuous
change in phylogenetic differentiation. Its hind limit above is
marked by the commissura habenularis, and below by the recessus

FIG. 9.

Diagram of the divisions of the brain. (After von Kuppfer, from Hertwig's Handbuch.) a, a,
'', •', /i /, limits between the regions ; Ml, myelencephalon ; Mt, metencephalon ; M, mesen-
cephalon ; D, diencephalon ; T, telencephalon ; c.c, commissura cerebellaris ; c.h, commissura
habenularis ; p.n, processus neuroporicus ; ji.r, plica rhombo-mesencephalica ; p.v, plica ence-
phali ventrali. Other letters as in Fig. 10.

opticus, marking the region from which develop the paired optic
vesicles at a very early stage. In the middle line in front the wall
forms the lamina terminalis, across which pass the anterior dorsal
and ventral commissures. The thin roof projects upwards as the
paraphysis (p. 25). This region between the recessus opticus and
the lamina terminalis is the telencephalon. But the bulk of the
secondary fore-brain becomes differentiated into large paired out-
growths, into which extends the 3rd ventricle. These are the
cerebrum (prosencephalon) and the olfactory lobe (rhinencephalon).
In the higher forms the thick-walled hollow outgrowths become
very distinctly paired cerebral hemispheres passing far in front of
the lamina terminalis. The corpus striatum is a thickening on
their outer ventral wall. The communication of their cavities on
either side with the median 3rd ventricle (prosocoele) narrows into

BRAIN

the foramen of Monro. The roof of the prosencephala becomes
the pallium which acquires such an enormous development in the
cerebral hemispheres of the highest Vertebrates. From the olfactory
lobes issue the nerves to the olfactory epithelium. The great
modifications in the shape and relative size of the different parts of
the brain in the Craniata are, of course, the outward manifestations
of the differentiation and orderly arrangement of the ganglion cells
and nerve-fibres into an elaborate system of ' tracts ' and ' nuclei,'
which cannot be described in this volume. (Brain of Fishes :
Bnrne [76], Burckhardt [70], Studntfka [429], Johnston [249].)
A new paired cranial nerve of doubtful significance has recently

to.

Longitudinal median section through the brain of an embryo Spiiiax niger. (After von
Kuppfrr, from Hertwig's llandbueh.) C, cerebellum ; c.p, posterior commissure ; eir, optic
clmsma ; «-, epiphysis ; e', paraphysis ; /.*•, rhombo-niesencephalic fissure; g.h, habenular
j::uii;lion and commissure; hy, hypophysis ; K, cartilaginous basis cranii ; /, iiifundibulum ;
/, lobus posterior ; M, mesenceplialon ; Ml, myelencephalon ; Mt, inetencephalon ; p.c, plica
cerebelli posterior ; r.o, recessus options ; ?, saccus infundibuli ; t, telencephalon ; t.o, tectum
opticum ; t.j>, tuberculum posterius ; r, valvula cerebelli posterior ; v.t, velum transversum.

been described in Elasmobranchs, Amia, and Protopterus : it is
the nervus terminalis, which issues from the fore-brain near the
olfactory nerve, bears a ganglion, and supplies the epithelium of the
nasal sac (Pinkus [329], Allis [10], Locy [284a], Johnston [248o]).
It may represent the dorsal root of the most anterior cephalic
segment.

Further evidence concerning the segmentation of the head in
Craniates niay be gained from a study of the gill-slits and visceral
arches (Gegenbaur, Koltzoff, etc.). The slits were probably
primarily intersegmental ; but their relation to the somites is not
very close. They pierce the lateral plate of mesoderm to reach the
exterior, and as they enlarge they are pushed backwards so as to

1 8 MOUTH

crush the segments behind. At the same time, the correspondence
between my ornery and branehiomery is to a great extent lost,
though evident in the nerve-supply. As the row of slits bars the
way Lo the downward growth of the myotomes, the latter have to
pass round the hinder edge of the series to form the ventral hypo-
glossal musculature (Fig. 3). A cartilaginous visceral arch develops
in front of the first or spiracular cleft, and behind this and each
succeeding cleft. Related to each arch and cleft is a segmental
branchial nerve and a blood-vascular arch.

The first or mandibular and the second or hyoid arch become
closely connected with the skull in Gnathostomes ; the mandibular
arch bends over the mouth, and becomes subdivided into the
primitive upper and lower jaws (Fig. 5). In the lips, in front and
at the sides of the mouth, labial cartilages are often present in fish,
which Gegenbaur considered to be remnants of preoral gill -arches.
Huxley suggested that the trabeculae cranii represent gill-arches.
But there is really no definite evidence that preoral gill-slits have
ever existed, and it is difficult to see how they could have been
functional. Gegenbaur subsequently abandoned this view [163],
and inclined towards that of Pollard [333]. This author
considered the labial cartilages to be remnants of a primitive
system of cirrhi, such as are found in the Myxinoids, and which he
compared with those of Amphioxus.

The nature of the mouth of Vertebrates is by no means easy
to determine. Dohrn (1882) believed it to be a new mouth
derived from a pair of anterior coalesced gill-slits [114]. Traces
of the original mouth, the palaeostome, homologous with that of
invertebrates, passing through the brain to open dorsally, were
supposed by Kolliker to be represented by the hypophysis and the
epiphysis. A less phantastic theory (Beard [33a] and von Kupfier
[275]) is that the hypophysis represents the original mouth or.
palaeostome, which opened into the alimentary canal as it still does
in Myxinoids (p. 46). This connection, however, appears to be
secondary, and at present the most reasonable view seems to be
that the ancestral vertebrate mouth has been retained, although it
may have shifted its position backwards. It is possible that during
this process of shifting some anterior gill-slits may have been
obliterated, or combined with the mouth ; but convincing evidence
of this is missing.

The upper lip is formed in fish by the junction in the middle
line below the snout of two upper-jaw processes (Fig. 117, p. 154) ;
in the Tetrapoda these lateral processes combine with the median
fron to-nasal process to complete the upper margin of the mouth.

We have briefly discussed above the subject of the segmentation
of the head in the Craniates ; but there is yet to be mentioned

SENSE-ORGANS 19

another important method of describing the nervous system, taking
account not so much of the segmental value of the nerves as of
their peripheral destination and central connections. For this
purpose, the sense-organs must first of all be considered.

Scattered sensory cells alone are found in the skin of Amphioxus,
and small simple sense-organs on the buccal cirrhi. The Craniate
vertebrates, on the other hand, especially the Gnathostomes, are
provided on the outer surface of the body and on the inner surface
of the alimentary canal with a network of free nerve-endings, and
a variety of sense-organs the structure, distribution, and nerve-
supply of which have been admirably worked out in the lower
vertebrates by numerous anatomists, whose results are of consider-
able interest for the study of phylogeny (Schulze [391-2], Leydig
[283], Strong [428], Allis [9, 10], Johnston [247-9], Herrick [210],
Ewart [133, 134], Cole [82], and many others).

In all the lower aquatic Craniata we find an important series
of sense-organs on the head and trunk constituting the 'lateral-
line system' (Figs. 11, 85). Possibly they were primitively strictly
metameric, as they are now in some fish ; at all events, these sense-
organs (neuromasts) have a definite distribution and nerve-supply,
and become of great taxonomic value in the Gnathostomes. The
less regularly arranged 'pit-organs,' ampullae, etc., of fish appear
to be related to the lateral-line system. All the nerve-fibres
derived from these lateral-line organs on the head enter the brain
by the facial, glosso-pharyngeal, and vagus nerves (and probably the
profundus also in Petromyzon}. The lateral line of the trunk is
supplied exclusively by the ramus lateralis vagi. Moreover, it has
been shown to be extremely probable (Beard [31], Ayers [22]) that
the ear and the auditory nerve represent a highly differentiated
portion of the same system. The whole forms the ' acustico-lateral
system,' whose nerve-fibres terminate centrally in the tuberculum
acusticum of the medulla and associated centres.

That a cranial nerve, the vagus, should supply a series of sense-
organs reaching to the tip of the tail strongly suggests that the
lateral-line nerve is a collector, similar to the epibranchial nerve.
Moreover, it has been observed (Alcock [7]) that in the branchial
region of the larva of Petromyzon there are a series of lateral
metameric groups of such organs, each supplied by a twig from the
branchial nerve of its own segment (this needs confirmation).
Evidence of a segmental origin may also be found in the develop-
ment of the lateral-line organs in Petromyzon. The nervus lateralis
vagi arises from a longitudinal thickening of the epiblast above the
dorsal ganglia, which is continued on the head as a series of
dorso-lateral ' placodes ' contributing to the formation of the ganglia
of the 9th, 7th, 5th, and profundus. Similar placodes occur in the
lower Gnathostomes. On the other hand, the independence of the

LATERAL LIKE

NERVE COMPONENTS 21

ramus lateralis vagi (in the adult) from the spinal nerves, and the fact
that in fish (Beard, Coilson) and in Amphibia (Harrison) the
lateral-line rudiment grows from the head backwards in a most
independent manner, have led most observers to believe that the
organs have phylogenetically been derived from the head. It is
a point still unsettled. The chief functions of the organs of the
lateral-line system are probably equilibration and orientation.

The sensory free nerve-endings scattered over the skin are
supplied by fibres belonging to the 'general cutaneous sensory
system,' and entering the central nervous system by the 5th, 7th,
9th, and 10th cranial nerves, and by the succeeding dorsal roots of
the spinal nerves. The fibres are related to the dorsal tracts of the
.spinal cord, and their prolongations in the medulla, including the
tuberculum acusticum. It is conjectured that the acustico-lateral
system is a specialised portion of this general cutaneous system.

The nerve-fibres of a similar 'general splanchnic sensory, or
coramunis, system,' in the wall of the alimentary canal, enter the
brain by the 7th, 9th, and 10th cranial nerves and by the
sympathetic fibres in the dorsal spinal nerves, and terminate in
Clarke's column, the fasciculus communis, the lobus vagi, and
associated centres. To the same centres in the brain come the
fibres from a system of gustatory 'end-bud organs,' or 'taste-
buds,' distributed over the buccal and pharyngeal cavities, and
also, in some fishes, spreading over the outer surface of the head
and body. The nerves from this 'special splanchnic or end-bud
sensory system' reach the brain by the 7th, the 9th, and the
10th cranial nerves. The end-bud system is supposed to have been
differentiated from the splanchnic general sensory system. The
taste-buds situated on the surface of the body on fins (Teleostei)
would appear to have migrated from the endoderm ; but the reverse
may possibly have occurred.

To these four sensory systems must be added the ' somatic
motor system,' communicating with their centres by the ventral
roots ; and the ' splanchnic motor system,' receiving fibres through
the dorsal roots of the cranial and spinal nerves, and the sympathetic
nerves, also from special central regions.

Thus, it has been shown that the nervous system of the
Craniates can be subdivided into several distinct components, four
sensory and two motor, each with its own type of 'end-organ,'
its own set of nerve-fibres, and its own special nerve-centres
(Strong [428], Herrick [210], Johnston [249]). It is further con-
jectured that the ' general cutaneous ' and ' splanchnic ' sensory
systems, with their more specialised derivatives, and the motor
systems, may each have originally been represented in every
segment of the body.

The size of nerve components in a given region is proportional

NERVE COMPONENTS

to the development of the 'end-organs' they supply. Some
systems may increase in importance ; others may dwindle or dis-
appear altogether. Thus, the splanchnic components, so small in
the spinal nerves, are much developed in the head-region; the
acustico-lateral system, so extensive in the fish, survives only in the
ear of the land vertebrate.

We may now briefly analyse the nerves of a fish into their chief
components (Fig. 12). A typical spinal nerve is formed by the
junction of a dorsal ganglionated root, containing a large general

pt

p/t.

MX.

md.

ff

FIG. 12.

Diagram of the nerve-components in the head-region of a lish (chiefly after the figures of
Herrick). a, ramtis lateralis accessorius (r. recurrens facialis, r, ace. vagi) ; «6, abducens
(6) ; an, anastomosis between facial and glossopharyngeal : aw, auditorius (8) ; Zm, r. buccalis
(7) ! fo, r. ophthalmicns snperficialis (7) ; rj, branchial slit ; gl, glossopharyngeus (t>) ; h, r.
hyomandibularis (7); iv, r. intestinalis (10); Iv, r. lateralis (10); mrf, r. mandibularis (5);
mx, r. maxillaris (0) ; oc, motor oculi (3) ; o?-, outline of orbit ; p, patheticus (4) ; pa, r. pala-
tinus (7) ; pr, profundtis ; prt, r. pretrematicns (10) ; psp, r. pretrematicus (7) ; pt, r. post-
trematicus (10) ; rrf, r. dorsalis ; rf, r. recurrens (7) ; f.g, spinal ganglion ; str, r. supra-
temporalis (10); tg, r. supratemporalis (9); to, r. opthalmicus snperficialis (5) ; v.r, ventral root
of spinal nerve. Between the vagus and the first spinal nerve are some spino-occipital nerves
(ventral roots). The numbers refer to the cranial nerves. For the explanation of the
components see Fig. 10(i, p. 22'2.

cutaneous component and a small splanchnic motor and sensory
component, with a ventral root of somatic motor fibres. The mixed
nerve branches, so that the general cutaneous and the somatic
motor nerve -fibres are distributed along three main trunks, the
ramus dorsalis, ram us medius, and ramus A'entralis, to the dorsal fin
muscles, dorsal somatic and ventral somatic muscles respectively,
and to the corresponding regions of the skin. The paired fins are
supplied from branches of the rami ventrales. The splanchnic
components pass into the sympathetic system by the ventral
ramus communicans.

NERVE COMPONENTS 23

In the vagus nerve the general cutaneous fibres compose the
rami cutanei dorsales passing upwards behind the skull ; the large
acustico-lateralis component forms the ramus lateralis vagi, and a
small ramus supratemporalis. The branchial nerves are chiefly
formed by the splanchnic or visceral sensory component, and some
splanchnic motor fibres, which pass into the post-trematic branches
to innervate the branchial muscles ; an intestinal and several
pharyngeal mixed branches, with splanchnic sensory and motor
components, pass inwards to the alimentary canal. The pharyngeal
taste-buds are also supplied by the branchial nerves.

The glossopharyngeal nerve has a complete set of components
distributed in much the same way. The lateralis branch, however,
is small or absent.

The facialis nerve, which is very intimately connected with
the trigeminus, has a dorsal ramus oticus, a supraorbital ramus
opthalmicus superior, and an infraorbital ramus buccalis composed
of general cutaneous and acustico-lateralis elements distributed in
the skin. A large mixed ventral hyomandibular trunk gives off
cutaneous acustico-lateralis and splanchnic motor fibres passing
behind the spiracular cleft to the hyoid region and lower jaw ; and
an internal branch, ramus palatirius, carries most of the splanchnic
sensory component to the roof of the mouth. Jacobson's anasto-
mosis of splanchnic sensory fibres generally unites the facial
(geniculate) ganglion with the jugular ganglion of the glosso-
pharyngeal. The auditory nerve represents a specialised portion
of the acustico-lateralis component.

The trigeminus nerve divides into a supraorbital branch, the
ramus opthalmicus superior, and an infraorbital ramus maxillaris,
both composed of general cutaneous fibres ; and a mixed ramus
mandibularis with a splanchnic motor component as well. The
opthalmicus profundus nerve belongs, as a rule, to the general
cutaneous system.

The three nerves to the eye -muscles represent the somatic
motor components corresponding to the three last nerves.

It is unnecessary here to enter into a detailed description of
the paired organs of sense. In front are found the olfactory sacs :
i imaginations of the ectoderm which retain their opening to the
exterior, the primitive nostrils. Next come the lateral eyes, organs
of very complex structure, derived partly from an outgrowth of the
fore-brain (p. 16), partly from an ingrowth of the outer ectoderm
(lens). Lastly, the auditory organ (concerned with equilibration
;is well as hearing) is developed from a more posterior imagination
of the ectoderm (Fig. 1 3) forming a deep sac, which remains in com-
munication with the exterior by a narrow ductus endolymphaticus
in the adult in the case of some Elasmobranch fish only. By a

SENSE-ORGANS

complicated folding of this sac are elaborated a sacculus and
utriculus, from which spring two vertical and one horizontal
semicircular canals in all Craniate excepting the Cyclostomes.

The relation these organs of special sense bear to their respec-
tive cartilaginous capsules, and their influence on the process of

adf

rns

IMC. 13.

Auditory labyrinth of Chiniacra monxt rosa, L. A, inner view ; ]{, outer view. (After
Retzius, from Gegenbaur, Vergl. A mat. H'irbeltieiv.) a, auditory nerve ; aa, iifi, (>r, ampullae;
ode, opening of ductus ; CM, anterior, c.p, posterior, and it, horizontal .semicircular eaiial : <:><.•-;
canalis utriculo-saccularis ; D.c, ductus endolymphaticns ; m.n, macula neglecta ; w.s, macula
saceuli ; m.n, macula utriculi ; pi, process of macula sacculi ; w, recessus utriculi ; .-•,
sacculus ; s.tt, sinus utriculi ; », utriculus.

cephalisation, has already been alluded to above (p. 2). No homo-
logues of these organs have been found in the Cephalochorda.

Yet another organ of sense remains to be noticed — the pineal
eye. Although it may not have a claim to the all -important
function attributed to it by Descartes, the pineal eye, or epiphysis,
is of considerable interest. Leydig in 1874 described it as a sense-
organ ; but De Graaf and Spencer, in 1886, were the first to demon-

PINEAL EYE

etrate its real significance as an eye, with both retina and lens, in
the Reptilia.

It has now been ascertained that there are two organs
developed on the roof of the diencephalon (thalamencephalon) ;
they take up a median position : the pineal behind, the parapineal
or parietal in front. In Petromyzon both are present, growing
out as hollow processes expanding into an eye-like vesicle distally,
the pineal, however, being more fully differentiated than the para-
pineal. The stalk of the former contains nerve-fibres passing to the
posterior and habenular commissure, that of the latter fibres going
to the habenular commissure (Fig. 14). In all other living Craniata
the pineal organ is in a more or less degenerate condition and the

/"•••t

I-'IO. 14.

Longitudinal section of the pineal and parapincal organs of tin1 larva of l'etromy:on, enlarged
<troin the liguivs nt' JStudniSka). ap.c, anterior dorsal commissure ; ep, epidermis ; h.c, liabeimlar
.commissure; h.g, habenular ganglion; HI, roof of mid-brain ; ?i, nerve; p, pineal eye; pp,
parapineal eye ; pi; parapliysis.

parapineal is quite vestigial, with the exception of the Reptilia, in
which it is occasionally found in a highly developed state, with
lens and retina (De Graaf [181], Spencer [412], Beraneck [35a],
iStudnicka [430]).

According to Hill and Dendy, there is reason to believe that
the dorsal eyes are of paired origin — the parapineal being the left,
and the pineal the right, each connected with the habenular
ganglion of its own side — a conclusion which is supported by
.embryological evidence (Dendy [112], Cameron [77], Hill [213«]).

The epidermis of the Craniates, unlike that of Ampldoxus,
is formed of many layers of cells continually being renewed from
the lowermost Malpighian stratum.

The alimentary canal behind the pharynx becomes differentiated

26 VASCULAR SYSTEM

into an oesophagus, a stomach, and an intestine opening to the
exterior by the amis. From the front end of the intestinal region
develop glandular outgrowths, the pancreas and the liver. The
latter is always a much more complicated structure than the
hepatic diverticulum in the Cephalochorda, the lumen of the
gland being much subdivided by the formation of an elaborate
and compact system of tubules. A specialised sacculation of the
duct, the gall-bladder, is present for storing the bile.

The ventral mesentery is always incomplete, remnants per-
sisting in front and behind. A dorsal mesentery (also generally
incomplete) supports the alimentary canal, which hangs in the
body-cavity. This cavity is continuous, all trace of segmentation
having disappeared in the abdominal coelom. In the embryo it is
in open communication with the coelom of the branchial segments ;
but later a septum is developed cutting off, completely as a rule,
an anterior cavity surrounding the heart — the pericardium.
Abdominal pores, opening from the coelom to the exterior near the
anus, are often found in fish, and occasionally in reptiles (Bridge
[53], Bles [36]).

A ventral subintestinal vein in which the blood flows forward ;
an anterior prolongation of this vessel in the gill-region (the ventral
aorta) ; a dorsal aorta, below the notochord, in which the blood
floAvs backward; a system of aortic arches carrying the
blood from the ventral to the dorsal aorta through the gill-
arches ; a longitudinal latero-dorsal cardinal vein on each side in
which the blood converges towards a transverse ductus Cuvieri join-
ing the subintestinal vein — these are the chief trunks found in the
vascular system of Amphioxus (Legros [279ft], Zarnick [511]), and
the embryo of all Craniates. In the structure of their blood-
vascular system the Craniata have again advanced far beyond the
condition found in the Cephalochorda. Not only are the arterial
and venous systems much more elaborately developed, especially the
capillary networks in the gills, liver, and kidneys ; but also the
heart makes its appearance as a special chambered muscular pump-
ing qrgan propelling venous blood through the ventral aorta into
the gills. It develops as an enlargement of the ventral vein
immediately in front of the junction of the ductus Cuvieri with
the subintestinal vein.

The blood-vascular system may communicate, but only in-
directly, with the coelom by means of the lymph-holding channels
of the lymphatic system, which branch throughout the mesoblastic
tissues. Fluid may pass into them through minute stomata in the
coelomic epithelium, and be discharged into the blood-vascular
system by a few special openings.

The blood itself consists of a colourless plasma, in which float
leucocytes and red haemoglobinous cells or corpuscles.

KIDNEYS 27

Much more radical has been the change in the excretory system.
Xo trace whatever of true nephridia, such as occur in Amphioxus
(Weiss, Boveri, Goodrich [174]), have yet been discovered in any
Craniate.

The kidney tubes of the Craniates are generally somewhat
loosely compared to the nephridia or segmerital organs of the
Annelids (Gegenbaur, Semper [404], Hatschek, etc.). Now this
comparison was first made at a time when the development of the
renal organs of the vertebrates was incompletely known, and when
both the structure and the ontogeny of the nephridia of Annelids
were very imperfectly understood. Moreover, the theory was to
some extent founded on observations which have since been shown
to be erroneous. The question now wears a very different aspect
(Goodrich [172]). Since then it has been ascertained that nephridia
are found in almost all the invertebrate Coelomata, but that they
may, or may not, be connected with the coelom ; it has been shown
that there occurs in these animals a second series of organs open-
ing to the exterior — the genital funnels or coelomostomes, which
develop from the wall of the genital or coelomic sacs ; further, the
excretory organs of Amphioxus are now known to be certainly
homologous with the nephridia of Annelids [174]. It is therefore
quite clear that if the kidney tubes of the Craniata are to be
compared to any organ in the Invertebrata, it is with the coelomo-
stomes, and not with the nephridia, that they must be homologised.
Should Boveri's suggestion, that the genital pouches of Amphiowus
represent the kidney tubes of the Craniates, prove to be true, it
will be a striking confirmation of this conclusion.

The excretory system of the Craniates is founded on a series of
paired segmental funnels and tubules derived, directly or indirectly,
from the coelomic epithelium, and leading into a longitudinal
connecting duct which opens to the exterior behind the anus. No
Craniate is known in which these tubules open independently to
the exterior, but it is reasonably conjectured that such must have
been the original state of things. The renal tubes develop from
before backwards. The earlier and more anterior become first
functional, and are succeeded by the more posterior. Thus, the
earliest set of tubes to appear occupy the pericardial region
immediately behind the gill-slits, and form the pronephros. These
subsequently become functionally replaced by the more posterior
mesonephros of the abdominal region. Finally, in the Amniota,
a separate and more posterior set of tubes, the metanephros, alone
persist as the adult kidney. A more detailed account of the
structure and development of these organs will be given later (p. 83).

There can be little doubt that originally some or all of these
tubes carried the genital products to the exterior, and this function
i> still retained by the mesonephric tubes in the male sex of all

28 GO NADS

Craniata, excepting the Cyclostomes. In the female sex are
generally found opening into the coelom a pair of oviducts, the
homology of which is still uncertain. They appear to be as a rule
connected with, if not derived from, the pronephric tubules in
development (p. 89).

As for the gonads themselves, they are originally paired organs
extending along the dorsal wall of the abdominal coelom into
which they hang, and from the epithelium of which they develop.
They form, in the embryo, two longitudinal genital ridges situated
near the base of the mesentery ; when the gonad is single in the
adult, this is due to the fusion of the two rudiments, or to the
suppression of one. Only doubtful traces of metamerism have been
described in the gonads of the Craniata.

From what has been mentioned above it is obvious that many
important characters, such as the possession of the paired sense-
organs, the extreme cephalisation of the head segments, the
structure of the skeleton, brain, heart, liver, kidneys, and gonads,
distinguish the Craniata from the Cephalochorda. They appear
to have been fully developed in the early common ancestor of the
Craniata (there is perhaps some doubt about the paired olfactory
organ, see p. 39), and these characters clearly demonstrate that the
Craniata must have travelled a long way from their common
starting-point with the Cephalochorda, and must have passed
through a long series of intermediate forms of which we have
now no trace, before they began to diverge into the various groups
included in our modern classifications of the subphylum.

Two diverging branches from the Craniate stock are repre-
sented at the present day, the Cyclostomata and the Gnathostomata.

PHYLOGENY

29

Teleosrei -

Lepidosfeoidei

Amioidei

Chondrosrei

Holosrei

Polyprerini
AcHnoprerrygii Coelacanrhini

Osreolepidori

Selachii

Teleosromi

Holocephali \ ZGoccosreomorphi

Pleuracanrhodii \ Dipnoi

Elasmobranchii \ Cladoselachii

Acanfhodii

/ "S

Chondrichrhyes

Perromyzonria
Myxinoidea

\

Cyclosk>mara

Osreichrhyes

Pisces

Gnafhosromata

Craniara

DIAGRAM I. — PHYLOGEXY OF THE VEILTEI;I:ATA CKAMATA.
The Ostracodermi have been omitted from this diagram.

Branch I. and Class CYCLOSTOMATA.

THE Cyclostomes are the lowest of existing Craniates. They
form a small group of marine and freshwater animals, widely
distributed, but containing comparatively few genera and species.
Like most isolated remnants of ancient stocks, the surviving
members are very specialised, and they appear to be also somewhat
degenerate. This, together with the absence of palaeontological
evidence, renders the interpretation of their structure very difficult.

FIG. 15.

A, Petromyzon fluaiatilis, L., the river Lamprey or Lara pern. B, Bdellostoma Vombeyi, Lac.
C, Myxine glutinosa, L., the Hag-fish, ft.o, branchial opening ; c.f, caudal flu ; d, cloacal
aperture ; d./i and d./2, first and second dorsal fin ; e, eye ; g.s, gill-slit ; m, mouth ; m.s,
mucous sac ; n, nostril ; p.f, preanal fin.

To Johannes Miiller we are indebted for an excellent account
of the anatomy of the Cyclostomes [306] ; many important additions
have been made by Furbringer [144], Parker [322], Schneider
[389], Dohrn [114«, 116, 117], Cole [83], and numerous other
authors.

The body is elongated and eel-like in shape, with an anterior,
almost terminal, mouth, and a median dorsal and ventral fin-fold
continuous round the tip of the tail (Fig. 15). No biting jaws are
present ; but from the floor of the buccal cavity protrudes a so-called
tongue, which is worked backwards and forwards so as to rasp the

30

CYCLOSTOMATA

flesh of the prey, and draw it into the alimentary canal. There are
no paired fins or girdles. The skin is very slimy.

No dermal skeleton whatever is present ; but the mouth and

Fic. 16.

Section of developing teeth of Petromyzon marinus, L. (After Warren, Q.J.M.S.) 1,
functional epidermal tooth ; 2, epidermis ; 3, dermal nutritive papilla ; 4, successional tooth
beginning to cornify.

' tongue ' are provided with large horny teeth of cornified
epidermis. The conical horny teeth when worn out are replaced
by new cones from below (Warren [480a], Beard [34] (Figs. 16 and
17)). The lateral-line organs lie superfici-
ally exposed, on the head and trunk, not
sunk in a canal. A continuous, persistent,
and unconstricted notochord extends from
the infundibular region to near the end of
the tail. It secretes two sheaths : an outer
thin elastica externa, and an inner thick
fibrous sheath without cells (Fig. 36).

The purely cartilaginous mesoblastic
skeleton is in a very rudimentary condi-
tion, and is more developed in the lampreys
than in the hag-fishes. The cartilage is of
peculiar and variable structure, with rela-
tively little matrix, Schaffer [382]. The
axial skeleton in the Petromyzontia (not in
Myxinoids) consists of a dorsal series of paired
neural arches, and of somewhat irregularly
developed interneural arches. These carti- and moutnr"(Aft'er"Heckei
lages do not meet over the neural canal in the *"".') fro
trunk-region, and alternate with the nerve -

roots. Schauinsland [384] considers that the anterior cartilage
corresponds to the intercalary (interneural or interdorsal) of higher

FIG. IT.

Petromi/zon marinus. View
of the oral sucker, horny teeth.

CYCLOSTOMATA

forms, and the posterior cartilage to the neural arch (basidorsal)
(Fig. 18). In the tail -region the arches are very irregular
and small, and finally disappear. In Myxinoids, where there are
no such arches, a continuous plate encloses both the notochord and
the nerve-chord posteriorly (Fig. 19). The median fin is continuous,
or in lampreys an anterior fin becomes separated off. In all Cyclo-
stomes the fin-web is supported by slender median rods of cartilage
(Figs. 19 and 28), separate from each other in front, but fusing at
their base behind, and then towards the tip of the tail with the
plate mentioned above in the Myxinoids. These rods or ' spines '
may branch, are several times as numerous as the segments they

/in sv

dr

rd

Petromyzon martinis, L. Left-side view of a portion of the notochord and neighbouring
organs ; the left half has been removed by a median longitudinal section in the anterior region,
an, anterior arch (jnterdorsal?) ; no, dorsal aorta ; d.r, dorsal nerve-root ; /, fatty tissue ; k. v,
kidney vein ; l.u, lateral-line nerve ; l.p.c., left posterior cardinal vein ; n.c, nerve-chord ; nt,
notochord ; pn, posterior arch (basidorsal?) ; r.d, ramus dorsalis ; r.p.c, right posterior cardinal ;
.".«, segmental artery ; .'/(, notochordal sheath ; s.i; segmental vein ; v.r, ventral nerve-root.

occupy, and are continued round the end of the tail to the ventral
region, where they develop in the same way and support the ventral
fin. Since the dorsal rods reach proximally to the connective-tissue
tube surrounding the nerve-cord, and even join together at their
bases and (in Myxinoids) with the axial plate, they should probably
be considered as forming part of the axial skeleton, as, in fact, pro-
longed neural spines. If this view be correct, there is no special
appendicular or fin-skeleton in the Cyclostomes (see p. 69).

In the Petromyzontia the brain -case is partly membranous,
especially above, being bridged over dorsally only between the-
auditory capsules (Fig. 20). These capsules alone are firmly fused
to the cranium ; the optic capsules are, of course, free, and the nasal
capsules are attached by connective tissue. The floor of the skull
is formed by the united parachordals. This plate is continuous-

SKELETON

33

with the trabeculae, which surround a basicranial fontanelle. It
is through this aperture that the large pituitary sac passes down-
wards and backwards from above to expand below the brain-
case. The trabeculae fuse in front below the pituitary sac,
expand into a wide plate, and become continuous with a lateral
subocular arch passing downwards on either side and joining the
parachordals behind. At the side, the arch sends down a styloid
process ending below in a longitudinal cornual cartilage. In front,
the trabecular plate is connected with a large median posterior
dorsal plate, overhanging an anterior dorsal plate. These, together
with lateral plates, cover and support the anterior buccal region in
front of the nostril. The sucker surrounding the mouth, and armed

a 9 uf>

Tail of M>/xine glutinosa, L. , cut so as to show the skeleton and the opening of the intestine,
etc. ; left-side view, a, anus ; c, gap behind mesentery leading from right to left coelomic
cavities; d.r, cartilage radials of dorsal median tin; g, median opening through which the
genital cells escape; i, intestine; m.tl, dorsal mesentery; m.r, ventral mesentery; n, nerve-
cord ; nt, notochord ; rk.d, left kidney duct ; «.j>, urinary papilla ; v, cartilage radials of ventral
median tin ; v.p, cartilaginous plate.

with epidermal teeth, is strengthened with an annular cartilage,
near which are placed a median ventral cartilage and a styliform
cartilage on either side (Figs. 17, 20). The rasping ' tongue' itself
is supported by large cartilages.

Behind the auditory capsule, the basal region of the cranium
and the styloid processes are continuous with a complex network
of cartilaginous bars situated in the wall of the pharynx, surround-
ing the gill-slits, and enclosing the pericardium itself. This is the
' branchial basket ' (Fig. 20).

In the Myxinoidea, both the roof and the side-walls of the
brain-case are membranous (Figs. 21, 22, 23). The nasal organ
is surrounded by an apparently median cartilaginous capsule,
attached by two strips to the trabeculae. Cartilaginous rings,
mostly incomplete, surround the long nasal tube. Between the

34

CYCLOSTOMATA

trabeculae extends a median plate below the pituitary canal. The
lateral plate, pierced by a wide fenestra, forms a subocular arch,

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and is continuous in front with two large bars which fuse to support
a powerful median ' ethmoid ' epidermal tooth. Cartilages support
the three pairs of cirrhi, and the edge of the mouth.

The branchial skeleton is represented apparently by two or

SKELETON

35

three paired bears in the wall of the pharynx behind the skull, two
of which are continued above into that part of the lateral plate
which corresponds to the styloid process of the lamprey, and one

A

t2 ophth. —

B.

FIG. 21.

Myxine glutinosa, L. A, brain, nerves, and portion of the head skeleton (dotted). B, skeleton
of the head, complete only on the right side, a.c, auditory capsule ; a. n, auditory nerve ; 6rl-3,
branchial arches ; cb, cerebellum ; co, cornual cartilage ; cr, nasal ring cart.; d.g, dorsal spinal
ganglion ; e, eye ; /, facial nerve ; fb, forebrain ; for, foramen ; hb, habenular ganglion ; hp,
hypophysial plate ; my, ' hyoid ' region ; g.g, gasserian ganglion ; gl, glossopharyngeal ; Ib, labial
cartilage ; TO'/, inidbniin ; iwl, medulla ; tia.c, nasal capsule ; n.c, nerve-cord ; nt, notochord ; ol,
olfactory lobe; ophth, ophthalmic branch of trigeminal nerve; pi, 'palatine,' and pq,
' quadrate ' regions ; sob, suborbital nerve ; sp, spinal nerve ; Z1-3, branches of trigeminal ; if,
trabecula cranii ; ts, preorbital sensory branch ; v, vagus nerve ; v.r, ventral root of spinal
nerve ; 1, 2, 3, 4, cartilages of the tentacles. For the nerves compare Figs. 22 and 25.

of which joins the cartilage of the 'tongue' below. Vestigial
cartilages are also found near the branchial external openings,
whether these are separate as in Bdellostoma or united as in Myxine
(Figs. 23, 27).

The huge rasping organ is provided with a set of large anterior

CYCLOSTOMATA

and two small posterior cartilages, while a special plate supports
the rows of horny teeth (Fig. 23).

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Many attempts have been made to compare the skull and
visceral skeleton of the Cyclostome with those of the Gnathostome ;
but none of these has proved very successful in detail. The com-

SKELETON

37

parison of the lateral cranial bars
with the trabeculae, originally
made by Agassiz [4], is doubtless
well founded. Whilst Mtiller saw
the mandibular arch represented
in the subocular bar, and the
hyoid in the styloid process,
eornual, and median ventral styli-
form cartilages, Huxley [229]
considered the latter to be man-
dibular, and the lingual to belong
to the hyoid arch. The annular
and corresponding cartilages in
Mijxine are generally compared
to the labials, and the subocular
arch to the pterygo-quadrate.
But branches of the trigeminal
nerve pass below the subocular
arch, not above as they should
if this arch were homologous with
the pterygo-quadrate bar (Figs.
20, 21, 22). It must be confessed
that the exact homology of these
cartilages is at present impossible
to determine, and that many of
them may be new formations in
the Cyclostome head.

To understand the character
of the head skeleton other systems
must be taken into consideration.
It has already been shown that
in Pdromy~»n the first meta-
otic somite, corresponding to the
glossopharyngeal nerve, develops
the first permanent myotome of
the adult (p. 5). The muscles
of the head are therefore less
specialised than in other Crani-
ates. Moreover, not only does
the notochord extend fully into
the base of the cranium, but
there is no sort of articulation
between the hind part of the
skull and the anterior region of
the vertebral column. More im-
portant still: whereas in all other

38 C YCL OS TO MA TA

Craniata apertures for the 9th and 10th cranial nerves are
included in the occipital region of the skull, in the Cyclostomata
both these nerves pass out freely behind the auditory capsule,
beyond which the cranium does not extend backwards. There
is a considerable gap, in Petromyzon, between the auditory capsule
and the large compound first neural arch through which also
pass the combined ventral roots of the first three spinal nerves
(Fig. 25).

Considerable controversy has taken place concerning the
character of the branchial basket. It is often alleged that it is
not homologous with the branchial arches of the Gnathostomes,
since it lies in too superficial a position with regard to the muscles,
nerves, and blood-vessels, and pharyngeal wall. For this reason
also it is sometimes compared to the extrabranchials of Elasmo-
branchs. This objection is, however, unconvincing, for, although
it is true that the ventral aorta lies internal to the basket, yet the
relation of the cartilage to the vagus and spinal nerves, to the
dorsal aorta, to the myotomes, and to some of the visceral muscles,
is quite similar to that of a branchial arch. The proximity of the
basket to the integument at the sides may be, to some extent, due
to the peculiar development of the large sac-like gill-pouches (Fig.
35). Moreover, in Myxinoids the relative position of the three
anterior deeply-set gill-bars is normal (Ayers and Jackson [25],
Allis [17]). The branchial arches in both Cyclostomes and Gnatho-
stomes are probably derived from the same structures (Dohrn [1 14«],
Gaupp [152]).

The myotomes stretch uniformly from head to tail, bent in
^ shape (Fig. 28), and are not subdivided into dorsal and ventral
halves by a horizontal septum as in Gnathostomes (Maurer [296]).
They are interrupted by the row of gill-openings in the lamprey
and are prolonged forward over the face above and below the eye.

An elaborate system of large muscles works the rasping
' tongue.' Since they are supplied by branches of the 5th
cranial nerve (Fig. 20), it may be concluded that they represent
the visceral muscles of the mandibular region, and that the
cartilages to which they are attached correspond to the lower part
of the mandibular arch (Meckel's cartilage), and perhaps to the
hyoid arch as well (Ayers and Jackson). Development supports
the view that the ' tongue ' cartilages correspond to the mandibular
arch (Stockard).

Some of the more interesting points in the development of the
muscles and nerves of the Cyclostomes have already been dealt
with above (p. 5, etc.). The permanent separation of the ventral
from the dorsal roots of the spinal nerves in the Petromyzon tia,
and their junction in Myxinoidea, is very difficult to explain ([341],
Figs. 18, 20, 22). On the whole, it seems probable that the fusion of

NOSTRIL

39

the roots is secondary in the latter (Koltzoff [273]), and has taken
place independently in the Gnathostomes. Petromyzon, where
they are both separate and alternate, would then retain the
primitive condition found in Amphioxus,

All the Cyclostomes differ fundamentally from the Gnathostomes
in possessing a single median nostril. Probably the nasal organ of

,nt.

rif

FIG. 24.

Median longitudinal sections of tlie head of four stages in the development of Petromyzon.
A, tin1 youngest, and D, the oldest stage. (After Dohrn.) /, opening leading to mouth ; h, hypo-
physis ; i, iniundibulum ; /, lower lip ; n, nasal pit ; nt, notochorti ; o, opening of nasal pit
and hypophysis, future median nostril ; ;i, pineal eye ; r, roof of brain ; ,«, hypophysial sac ; u,
upper lip ; r, velum ; /?, cavity of brain ; K, enteron.

the former was also originally paired (Scott), since the olfactory
lobes and nerves are paired, and pierce the capsule by paired
openings (Fig. 25). In the early embryo there is said to develop
a single terminal olfactory (?) plate (von Kupffer [275]); this later
becomes bilobed, probably incorporating two placodes, and gives
rise to the olfactory epithelium. The olfactory pit becomes involved
in the hypophysial invagination, is carried some distance back, and
finally opens dorsally into the hypophysial or nasal canal (Fig. 24).

CYCLOSTOMATA

The external opening of the hypophysial sac is single and median,
it forms the adult nostril, and it is perhaps chiefly owing to
this 'confluence of the hypophysis with the nasal pits that the

// dff

FIG. 25.

Head of Petromyson fluviatille, L., dissected ; dorsal view. The brain and nerves have been
exposed entirely on the left and partially on the right side ; the eye, pnrt of the skull, and
muscles are retained on tjie right ; and the nasal capsule has been opened in front, c, choroid
plexus on roof of 4th ventricle ; en, connection between facial and glossopharyngeal and vagus
nerves ; cr, cranium ; cr.t, anterior region of trabecula ; d.g, ganglion on dorsal spinal root ; e,
eye ; h, habenular ganglia ; I, labyrinth of ear exposed ; l.l, lateral-line nerve ; m.o, medulla
oblongata ; my, myotoine ; n.a, neural arch cut through; nc, spinal cord; n.ca, nasal capsule ;
no, nostril ; o.n, anterior oblique muscle ; o.c, auditory capsule ; o.l, optic lobe ; ol.l, ollactory
lobe ; om, olfactory fold ; ox, posterior oblique muscle; p, pineal eye; p.r, posterior rei-tus ;
ps, opening to hypophysial sac; r.a, anterior rectus ; s.r, superior rectus; vc, vagus opi-
branchial nerve lifted up above the spinals ; i:r, ventral spinal root. 1-0 the first nine cranial
nerves.

latter have come to acquire the appearance of a single median
organ.

The hypophysial sac of the Cyclostomes is unique in that it
persists in the adult opening separately and dorsally to the

BRAIN 41 '

mouth (Fig. 24). In the Petromyzontia it enlarges into a sac
below the brain (Fig. 34) ; and in the Myxinoidea it actually
opens backwards into the pharynx (Fig. 30), passing down
between the trabeculae — thus piercing the basal plate from
above.

The brain is very lowly organised (Ahlborn [5], Retzius [356],
Johnston [247]). In Pelromyzon the secondary-, fore-, mid-, and
hind-brain all have large cavities and non-nervous roofs (Fig. 25),
and do not overlap each other. The olfactory lobes are large, and
closely applied to the remarkably small cerebral hemispheres, and
the cerebellum is rudimentary. The mid-brain, on the contrary, is
unusually large. There is but a rudiment of the saccus vasculosus.
The epiphysial outgrowths consist of a pigmented pineal eye of
elaborate structure in connection Avith the commissura habenularis,
and of a smaller and simpler sac of the same nature below it, the
parapineal organ, connected also Avith the posterior commissure
(p. 24). In the larger superior vesicle not only does the outer
wall become thickened into a clear cellular lens, but the inner wall
develops into a pigmented retina of more perfect structure than
that of the smaller inferior parapineal vesicle (Beard [33], Dendy
[112], Studnicka [430]). The skull wall thins out above these
organs, which are separated from the exterior by a transparent
corneal area (Fig. 14). In the Myxinoidea the pineal organs are
less developed, and the brain is remarkable for the thickness of its
walls, and reduction of the internal cavities (Fig. 141).

The first gill-cleft, the spiracular slit between the 3rd and 4th
somites, is obliterated in the adult Cyclostome (Dohrn [1 14«], Dean
[106]). The remaining branchial slits on each side are seven in
number in the Petromyzontia, and from six to fourteen in number
among the Myxinoidea. Since, in the Gnathostomes, the pairs of
branchial slits rarely reach and never surpass the number seven,
the question arises as to whether the Cyclostomes are more
primitive in having a larger supply. At present, no definite
answer can be given ; but, as the number of slits in Amphioxus
is very large, it seems probable that it may have been gradually
reduced in the higher forms (p. 95).

The gills are distinguished by their spherical shape, being sac-
like organs, lying to a great extent surrounded by a blood-sinus,
;ui(l with gill-lamellae set all round the internal wall, scarcely
interrupted above and below (Figs. 26, 27). The lining of the gill-
sac is derived entirely from an endodermal outgrowth (Goette
[1G9]). The gill-sac communicates externally by a narrow ecto-
dermal duct, produced into a tube of considerable length in the
Hag-fishes. A narrow internal aperture opens either directly into
the pharynx, as in the Myxinoidea (Fig. 30), or into a sub-
oesophageal tube in the Petromyzontia (Fig. 34). This branchial

CYC LOS TOM ATA

tube is blind behind, but opens in front into the buccal cavity. It
is nipped off from the oesophagus in post-larval life.

A velum, probably homologous with that of Amphioxus, guards
the entrance into the pharynx in the hag-fishes, or into the branchial

VASCULAR SYSTEM 43

tube in the Lampreys. It is supported by a special cartilaginous
skeleton, elaborately developed in the Myxinoids (Figs. 30, 34).

The alimentary canal passes backwards in a straight course to
the anus. The stomach is scarcely marked, and the long intestine
has a slightly spiral " valve " in the Petromyzontia.

The liver is a large bilobed organ, provided with a gall-bladder.
A pancreas, on the contrary, is scarcely differentiated, being appar-
ently represented by small glandular tubes embedded in the liver.

The vascular system has advanced far beyond the condition
found in the Cephalochorda, but still shows primitive characters
(Miiller [306], Goette [168], Klinckowstrom [267], Jackson [235],
Vialleton [-±74]). Although large, asymmetrical, and three-
chambered, the heart is not as completely twisted as in the higher
vertebrates (Figs. 32, 34). The sinus venosus, passing across the
pericardium from the dorsal to the ventral side, opens by a narrow
neck into the large thin-walled atrium lying on the left side. This
chamber opens into the more ventral ventricle by an aperture
protected by two valves. Two valves are also placed at the
entrance of the thick-walled ventricle into the swollen base of the
ventral aorta, lying outside the pericardium.

Afferent vessels carry blood to the gills, and it is collected again
into efferent vessels, which join a longitudinal dorsal aorta begin-
ning very far forwards. Segmental somatic arteries are regularly
supplied to the myotomes from the dorsal aorta ; and a correspond-
ing series of somatic veins empty into the cardinals. There is no
renal-portal system. The kidneys are supplied with veins from the
posterior cardinals and with arteries from the aorta (Figs. 18, 32).

In the early larva of Petromyzon we find paired anterior and
posterior cardinals joining to paired ductus Cuvieri, paired inferior
jugular veins outside the branchial basket, and a complete sub-
intestinal vein (Goette [168], Cori [93], Julin, Dohrn). Soon this
latter vein breaks up in the liver into the hepatic portal capillary
system, its anterior portion forming the hepatic veins. The
inferior jugulars are replaced by a median inferior jugular below
the ventral aorta. This vein, and a ventral hepatic vein, are
peculiar to the Cyclostomes (Fig. 18). The two anterior and also
the posterior cardinals join above the oesophagus to large trunks,
which open to the right into the dorsal limb of the sinus venosus.
The ductus Cuvieri on the left side thus disappears, and all the
venous blood pours into the heart on the right side. In the
Myxinoidea, strangely enough, it is the left ductus which persists,
and the right ductus which is suppressed (Figs. 32, 34).

The pronephros nearly disappears in the adult Lamprey, but
persists as an organ of considerable size in Myxinoids (Fig. 27).
It is, however, degenerate (Weldon [483], Semon [400], Kirkaldy
[263^]), consisting of a few branching tubules, opening on the one

44

CYCLOSTOMATA

45

hand into the pericardial coelom, and on the other into discontinuous
remains of a longitudinal duct lying in a venous sinus. There is no
communication with the kidney duct. Degenerate as this organ is,
it is better developed in the Cyclostomes than in any known adult
Craniate, excepting perhaps some aberrant Teleostei (p. 364).

The permanent functional kidney, or mesonephros, is repre-
sented by a single longitudinal duct on each side, into which open
a number of tubules leading from closed renal capsules with
glomeruli (Fig. 32). In all cases the tubules have lost their primi-
tive openings into the abdominal coelom ; in Petromyzon they do

I'lti-iHi'iizi'ii m"/ '/MIX, L. Left-side view of the trunk region near the base of the dorsal Hn ;
the shin and muscles have been partially removed, o, anus ; an, dorsal aorta ; c.r, cartilage
rays suppoiting tin : <l.f, dorsal tin ; go, left genital aperture into urinogenital sinus ; i, intestine ;
/,. nicsonejihros, and kd, its duct ; ni.y, niyotome ; )(.«, neural arch ; nt, notocliord ; p.c, posterior
cardinal vt in ; r.m, radial muscles of fin ; 713.0, urinogenital opening on papilla.

not appear even during development (Wheeler [486]). While in the
Lampreys the elongated kidney consists of crowded coiled tubules
much more numerous than the segments of the body they occupy,
in the Myxinoidea the tubules preserve their original metameric
order (Miiller [306]). In this character the Myxinoids appear to be
more primitive than any other known Craniate (p. 82, where the
morphology of the excretory organs is dealt with).

The right and left kidney ducts of the adult end behind in a
common urinary sinus, which opens by a median papilla, placed in
a narrow cloacal depression at the front end of which is the anus
(Figs. 19, 28).

46 MYXINOIDEA

In Petroniyzon the anterior wall of the sinus is pierced by a
pair of genital apertures communicating with the abdominal coelom
(Fig. 28). In the Myxinoids, similar genital pores combine to open
between the anus and the kidney opening (Fig. 1 9). The genital
products in both sexes are shed into the coelom, and pass out
through these pores (Burne [74]) ; there are no other special ducts,
nor is there any communication between the testis and the kidney,
as in the Gnathostomes. The exact morphological significance of
the genital pores is unknown ; since, however, the genital ducts
may be occasionally reduced to very similar pores in the Teleostei
(p. 365), it is not impossible that these pores in the Cyclostomes
may be homologous with the Miillerian ducts of the Gnathostomes.

The Cyclostomata are classed in two very clearly differentiated
Sub-Classes. No certain traces of fossil Cyclostomes have yet been
found.

Sub-Class 1. MYXINOIDEA.

The Hag-fishes, Myxinoidea, are distinguished from the Petro-
myzontia by the following chief characters : — The single median
nostril (Fig. 29) is terminal, or slightly ventral, and the nasal canal,
strengthened by cartilaginous rings, is continued backwards below
the brain into a pituitary sac, which opens into the pharynx by a
secondary aperture pierced through in the late embryo (von KupfFer
[275]). On either side of the nostril and mouth are four tentacles,
supported by cartilages (Figs. 22, 23). They have plausibly been
compared to the oral tentacles of Amphioxus (Pollard [333]).
There is no toothed oral sucker, but a single large epidermal
' tooth ' is placed below the ' ethmoid cartilage,' on the roof of the
buccal cavity (Fig. 22). The 'tongue' is more highly developed.
No neural arches are present in the trunk, the skull is more
membranous, and the visceral skeleton, except in front near the
skull, is reduced to mere vestiges near the external gill-openings
(Figs. 23, 27). Owing, apparently, to the excessive size of the
'tongue,' the gills and heart are pushed very far back (Fig. 31).
This migration of the branchial pouches behind the first three, which
disappear in situ, occurs somewhat late in development (Dean
[106]). Consequently the gill-openings are pierced between the
dorsal and ventral somatic muscles, irrespective of their metameric
order, when the gills reach their final position (the branchial nerves,
of course, follow the gills). There is always on the left side a
simple tube leading from the pharynx to the exterior, and open-
ing in common with the last gill-pouch — it is the oesophageo-
cutaneous duct, probably a modified gill-slit (Figs. 23, 27). The
gills, in Bdellostoma, open independently to the outside, and there
may be as many as fourteen pairs. But in Myxine, where there

47

are, as a rule, only six pairs, the elongated external ducts pass
backwards, and open by a common pore on each side. The genus
ParamyxwM (Fig. 31) shows an admirably intermediate stage in
the evolution of this secondary arrangement (Dean [110]).

A.

FICJ. 29.

MI/,I hie glutinosa, L. A, left-side view of the anterior end, from which the skin has been
removed. B, ventral view of the head, a.c, dotted line indicating position of auditory capsule ;
c.r, cartilage ring of nasal tube ; m, mouth ; m.s, mucus sac ; m.t, muscles to tentacles and lip ; my,
myotome ; n.ea, nasal capsule ; no, median nostril ; o.m, oblique muscles ; op, opening of mucus
sac ; sob, stiborbital branch, and ts, preorbital sensory branch of trigeminal nerve ; v.m,
ventral muscles ; 1, 2, 3, 4, tentacles.

The adult Myxinoids differ strangely from the Lampreys and the
embryos of all other Craniates in that the afferent vessels pass to
the gill-sacs themselves, and not between successive pairs to the
gill-arches (Fig. 32).

The myomeres give rise to dorso-lateral and ventral longitudinal
muscles, outside which extends a sheet of obliquely circular muscles
(Fig. 29). The myotomes alternate from side to side as in
Amphioxus.

48

MYXINOIDEA

The anterior region of the subintestinal vein seems to persist to

nap.

ct.

Via. 30.

Median longitudinal section of the anterior region of Rdellostoma Forsterii, M. (Modified
from Parker.) b.c, buccal cavity ; b.pl, basal plate of ' tongue ' ; br, brain ; c.t, cartilage ring of
nasal tube ; et, median horny tooth ; f.t, fatty tissue ; h.p, hypophysial plate ; h.s, hypophysial
sac opening behind into pharynx ; m, mouth ; nac, nasal tube ; nap, median nostril ; n.ca, nasal
capsule, with cavity divided by median septum ; nt,, notochord ; oe, pharynx ; p.p, parachordal
plate ; pt, rasping organ with horny teeth ; sre, subnasal cartilage ; t, cartilage of ' tongue ' ;
c, velum. The cartilages are dotted.

va

CO.

FIG. 31.

Diagram of the gills and their afferent blood system in A, Bilellostoma (Homen stout i); B,
Paramyxine ; and C, Myxiiie (after Dean). Ventral view, c.o, common opening of six gill-sacs
and oesophageal duct ; b.s, gill-sac ; d, oesophageal duct ; h, heart ; o, external opening of
gill-sac ; ph, pharynx ; t, outline of rasping ' tongue ' ; t.e, tube leading to exterior ; v.a,
ventral aorta.

a considerable extent in the adult as a vessel carrying blood from
the intestine through the liver direct to the sinus venosus (Fig. 32).

MYXINOIDEA

49

MYXINOIDEA

In addition, there is a supra-intestinal vein, which, joining an
anterior vein derived from the right cardinal, swells into a pulsatile
portal heart used for pumping blood into the liver (Figs. 27, 32).
The liver is subdivided into two separate lobes. The intestine
shows no spiral valve.

The spacious pericardium surrounds the oesophagus, and remains
in open communication with the abdominal coelom on the right
side (Fig. 27). The tubules of the kidney are segmentally
arranged (p. 87, Fig. 32).

The brain differs considerably in shape, and its ventricles are
much reduced (Holm [217], Worthington [507a]. The vagus root

has apparently fused with the glosso-

A- B pharyngeal. The dorsal roots of

the spinal nerves join the ventral
roots. The small degenerate eyes
are sunk far below the skin ; both
the eye-muscles and their nerves
disappear (Figs. 21, 22). Only
one semicircular canal is present
in the ear, probably representing
the two vertical canals fused to-
gether, since there are two ampullae
(Fig. 33).

Quite recently the lateral-line
system of Bdellostoma has been de-
scribed by Ayers and Worthington
[26]; it is in a very undeveloped
condition, and consists of groups
of sensory cells lodged in the epidermis of the head. The cavities
which overlie the sense-organs are closed, and only shallow grooves
indicate their presence on the outside.

The extraordinary sliminess of the skin is principally due to the
activity of two longitudinal rows of large glandular sacs. These
are segmental, paired, lateral invaginations of the skin (Figs. 29,
32), in which are stored mucous cells (Blomfield [37«]). They are
of two kinds : granular mucous cells, and thread cells of very
remarkable structure, which may perhaps be homologous with the
club-cells in the skin of the Lamprey (Fig. 36).

The median fin is not subdivided, and is not provided with
special muscles.

Alone among Craniate vertebrates the Myxinoids are normally
hermaphrodite. They lay eggs of large size, richly provided with
yolk, and enclosed in elaborately finished shells of horny consistency
(Fig. 91). These shells are secreted in the ovary itself, and are not
homologous with the very similar egg-cases of Elasmobranchs.

Cleavage is meroblastic ; but, unfortunately, the development of

PIG. 33.

Auditory labyrinth of Myxine glutinosa,
L. A, inner dorsal view ; B, inner ventral
view. (After Retzius, from Gegenbaur,
Vergl. Anat. Wirbeltiere.) a.a, anterior
ampulla ; n.p, posterior ampulla ; m.c,
macula communis ; r.a and r.p, ramus
anterior and posterior of auditory nerve ;
s.e, sinus endolymphaticus.

MYXINOIDEA 51

the Myxinoids is as yet but very incompletely known (Dean [106],
Price [335]).

The Myxinoids are all marine, and are unknown as fossils.

Family MJTXIXIDAE. Bdellostoma, J. Miiller (Homea, Flem.), Fig. 15 ;
Pacific. Paramyxine, Dean ; Pacific (Fig. 31). Myxine, L. ; Atlantic,
North Sea, Pacific (Fig. 15).

Sub-Class 2. PETROMYZONTIA.

The Lampreys possess the following chief distinguishing features
in their structure : —

A wide ' tooth '-bearing sucker surrounds the mouth. Since,
dorsally, it develops between the stomodeum and the hypophysis,
the nostril (hypophysial aperture) is carried up and far back on
the dorsal surface of the head (Fig. 24), and is not terminal.
Ths cartilaginous skull and neural arches are well developed ; but
it is in the presence of an elaborate branchial basket, surrounding
the gills and 'tongue/ and even enclosing the pericardium, that
they differ most from the hag-fish (Fig. 20).

The gill-pouches are seven in number on each side, open sepa-
rately to the exterior, and communicate internally with a suboeso-
phageal tube (p. 34). In the larva, however, the gill-pouches
open, as in all vertebrates, directly into the pharynx (Figs. 35
and 37). During the metamorphosis this region becomes nipped
off behind ; whilst the oesophagus grows forward and above, so as to
open into the buccal cavity in front of the gill-slits.

Other characters, such as the blind hypophysial sac, the simpler
and hollow structure of the brain, the separate course of the dorsal
and ventral roots of the spinal nerves, the normal structure of the
eyes, the presence of two semicircular canals in the ear and of a
well-developed lateral-line system of sense-organs, the closure of the
pericardium, the more complex structure of the kidney, the spiral
valve in the intestine, the subdivision of the dorsal fin, etc., have
been mentioned above.

It is in the Ammocoete larva of Petromyzon that some of the
strongest evidence of the primitive character of the Cyclostomes is
found to occur (Balfour [29], Scott [393], Dohrn [116], von Kupffer
[275], Koltzoff [273], Schneider [389], etc.).

The eggs are thin-shelled, small, with comparatively little yolk,
and undergo holoblastic cleavage. The blastopore becomes the
anus. The first three mesoblastic somites develop as outgrowths
of the archenteric wall, and contain a coelomic cavity which for a
time is in communication with the archenteron as in Amphioxus.
The embryo develops into a larva differing very considerably in
structure from the adult, and undergoes a pronounced metamor-
phosis to reach the perfect state. In this Ammocoete many

PE TROM YZONTIA

remarkable features bridge over the gulf between the Craniata
and the Cephalochorda.

The mouth is bounded by lips (Fig. 37) ; there is neither sucker

m

5 ^ "S r. 'J | 'f .

nor horny armature, nor yet any rasping 'tongue.' The buccal
cavity is separated by a velum from the pharynx, and this is limited
in front by an encircling ciliated groove (like that of Amphioxus),
which is at the level formerly occupied by the transitory first gill-

PE TROM YZONTIA

53

slit. The groove is carried back along the floor of the pharynx into
the opening of the thyroid gland. This gland develops as a mid-
ventral outgrowth of the pharynx, acquires a lumen of considerable
size, and along its folded walls become differentiated four rows of
mucous cells (Fig. 36). In fact, the whole structure bears a
striking and unmistakable resemblance to the endostyle of the

th

Fio. 35.

Transverse section of the gill-region of an Ammocoete larva, somewhat diagrammatic. (Partly
after Alcock.) a.c, anterior cardinal vein ; of, afferent artery ; 6.6, branchial basket ; d.a, dorsal
aorta ; d..«, dorsal blood-sinus ; ef, efferent artery ; g, gill-lamella ; g.o, gill-opening ; l.n, lateral-
line nerve; n, nerve-cord; nt, notochord ; th, thyroid gland; v.a, ventral aorta; v.n, vagus
nerve ; v.s, ventral blood-sinus.

Tunicate and Cephalochorda, with which it is no doubt homologous
(\\. Miiller [30 7 a]). It may also be mentioned that the liver is
composed of a mass of branching tubules, much more distinct than
in the compact liver of higher vertebrates ; in the adult it undergoes
fatty degeneration, and the gall-bladder is lost. The paired eyes
lie hidden deep beneath the skin. The pericardium opens widely
into the abdominal coelom (Fig. 37, C) ; on its dorsal wall lies the
pronephros. The median fin is continuous.

54

PE TROM YZON TIA

Both marine and freshwater Lampreys are known, but no fossil
forms have yet been discovered.

Family PETEOMYZONTIDAE. Petromyzon, Art. ; rivers and seas of
Europe, Asia, and America (Fig. 16). Mordacia, Gray, and Geotria, Gray ;
S. America and Tasmania.

B.

l-el

Ammocoete larva of Petromyzonfltiviatilis, L. A, transverse section of skin, much enlarged.
B, portion of a transverse section of the notochord, enlarged. C, transverse section of
the thyroid gland, enlarged, b, branchial basket ; c, striated club-cells ; eg, lumen of thyroid
gland, which communicates with the pharynx ; c.t, connective tissue ; el, elastica externa ; ep,
outer layer of epidermis ; f.s, fibrous sheath ; g.c, gland-cell ; gd, row of glandular cells of
thyroid ; gl.c, glandular cell ; m.j, median jugular vein ; nt, notochord ; o, opening of thyroid
gland ; v.a, ventral aorta.

AFFINITIES. — The Cyclostomes, united to the cartilaginous fish
by Cuvier, were separated from the true fish by Agassiz (1857).
That they should be definitely placed apart from the Gnathostomes
the facts mentioned above leave no doubt. Such special characters
as the rasping 'tongue,' the large sub-cerebral hypophysial sac,
etc., prove that they form a single divergent group ; on the other

PE TROM YZONTIA

55

hand, the development of the anterior myotomes, the absence of a
horizontal septum subdividing the myotomes, the cranial nerves,
the skull which does not enclose the vagus, and other points of
structure, not to mention such histological characters as the absence

of medullated nerve-fibres, etc., and the ciliated groove and thyroid
gland of the Ammocoete larva, point clearly to the conclusion that
the Cyclostome stem originated from the common Craniate trunk
at a point far below that at which the known classes of the
Gnathostomata began to diverge. Attempts have indeed been made

56 PETROMYZONT1A

(Dohrn) to show that the Cyclostomes are degenerate fish, derived
from some member of the class Pisces. The facts we have just
cited sufficiently dispose of this view ; these characters, at all events
(hypophysial sac, fully developed anterior myotomes, larval thyroid
gland, rasping ' tongue,' etc.), cannot be due to degeneration !
Nevertheless, it can hardly be doubted that the Myxinoids, if not
the Petromyzontia as well, show some signs of degeneration. In
the former group the vestigial eyes, for instance, and perhaps the
absence of median fin muscles and many characters of the skeleton,
may safely be attributed to degeneration. The total absence of
paired limbs and girdles is, of course, a very important feature ;
there is no satisfactory evidence that the Cyclostomes ever had any,
in spite of Dohrn's suggestion that the small folds at the sides of
the cloaca represent vestiges of pelvic fins. Whether the ancestral
Craniate, from which both the Gnathostome and the Cyclostome
groups diverged, possessed biting jaws or not, is a question we can
scarcely hope to solve without palaeontological evidence (Howes
[221]).

INCERTAE SEDIS.

Family PALAEOSPONDYLIDAE. This family contains only the very
interesting extinct fishlike creature from the Middle Old Red Sandstone of
Scotland, named Palaeospondylus Gunni by Traquair, who first described
it and considered it to be possibly a fossil Cyclostome. Unfortunately
Palaeospondylus is very small, its skeleton is ill -preserved, and its
structure still very imperfectly understood, in spite of the careful
researches of Traquair [463], Dean [107], and Sollas [411].

The elongated body appears to have been naked ; no trace of teeth has
been found (Fig. 38). The skull is relatively large ; it has an extensive
brain-cavity with side walls, a continuous floor marked with an infundib-
ular depression, but probably an incomplete roof. Behind the large
orbits are the auditory capsules continuous with the cranial wall, and in
front are ill-defined structures which probably represent paired olfactory
capsules. From the extreme anterior end of the skull project some
eleven slender processes attached in a circle to a basal ring ; they
seem to represent tentacles surrounding a median aperture, which
might be the nostril or the hypophysis, but much more probably the
mouth. Below the anterior region of the skull is a T-shaped element
of doubtful nature, but probably belonging to the visceral skeleton, of
which distinct traces have been described by Sollas. About four
branchial arches can be made out, and in front of them indications
of an upper and lower jaw. Attached to the hindermost arch are a
pair of large plates projecting backwards behind the skull. The vertebral
column has a large number of ring-like centra with neural arches. The
tail is diphycercal, bears a caudal fin supported by median prolongations
of both the neural and the haemal arches, forming delicate rays some-
times branched, and strikingly like those of the Cyclostomes. There are
no rib?, nor have any certain traces of paired fins been found, though it

PALAEOSPOND YL US

57

has been suggested that the pectoral fins are represented by the large
postbranchial plates mentioned above. The histological character of the
skeleton is quite unknown, but it was probably cartilaginous.

Many views have been put forward with regard to the affinities of
Palaeospondylus (Traquair, Gill [166], etc.). That it is not a larval form
seems to be proved by the presence of well-marked centra. This fact is

FIG. 38.

Palaeosfjondi/liis Gunni, Traq. ; from the Middle Old Red Sandstone of Caithness ; restored.
(After R. H. Traquair, from Brit. J/HS. (!ui<l<:)

also a very serious objection to its close association with the Cyclostomes.
While the fin-rays and the apparent absence of paired fins recall the latter,
the structure of the vertebral column, the skull, and the visceral arches
approaches that of the Gnathostomes. To which of these two Branches
Palaeospondylus belongs it is not yet possible to determine ; it may have
arisen from an extinct intermediate group.

Palaeospondylus, Traquair ; Middle Old Eed Sandstone, Caithness.

Branch II. GNATHOSTOMATA.

AMONG the many important new characters which distinguish
the Gnathostomata from the Cyclostomata, and bear witness to

the higher grade of development
of the former, may first of all be
mentioned the possession of a dermal
exoskeleton. This superficial skeleton
first appears in the form of small tooth-
like structures, or denticles, scattered
all over the skin. Since the skin
grows inwards at the mouth and gill-
slits, denticles may be found also in-
side the buccal cavity, and on the
inner surface of the gill-bars. Along
the inner edge of the jaws they become
specialised into true teeth (Fig. 39).

The Gnathostomes as a whole are
characterised by the great and diverse
development of the supporting tissues,
whether endoskeletal or exoskeletal ;
and the skeleton is of such great im-
portance in their anatomy that we
may digress at once to briefly investi-
gate the whole question of the relation
borne by the original cartilaginous
endoskeleton to the dermal denticles
and bone.

mk.''

FIG. 39.
A, diagram of a transverse section

Cartilage and bone may be looked
of the lower jaw of Seyiiium canicuia, upon as specialisations of the general

L., showing the development and sue- «••.•»•» • • t • i

cession of the teeth. B, anterior portion Scaffolding OI Connective tlSSUe, which

pervades, so to speak, the entire body
of a Craniate, affording support to and

in skin on outer surface ;' mk, Meckel's binding together the various parts of
cartilage; o.t, old worn tooth; t, time- ,, • r. • ,, .

tionai tooth at wting edge; y.t, young the organism. It is really in connec-

tooth which will succeed the older teeth t' n W1>V. 4-Up rmiopnl'ir e^erem tViaf flio
in the direction indicated by the arrow. l ;UIOT S> stem tnat tne

connective tissues have reached their
highest degree of differentiation. The Craniata are elongated

58

GNA T HO S TO MA TA

59

segmental animals, and correlated with this structure is the seg-
mentation of their muscular system. In the lower forms, and
in the embryos of the higher, the segmental character of the
somatic muscles is most distinctly shown. Now the connective
tissues are found to surround the myotomes, forming not only
closed boxes in which these lie, but also a lining to the body-wall
outside and to the body-cavity within, and a sheath surrounding
the notochord and central nervous system. Thus a system of
transverse septa (myocomata), intersegmental in position, and of

Fio. 40.

Diagram of tlie connective-tissue system in the trunk of a Craniate Vertebrate, showing the
relation borne by the axial skeleton to the transverse and longitudinal septa, n.c, wall of
abdominal coelom ; bd, basidorsal ; bv, basiventral ; 6. w, cut body- wall ; d.r, dorsal rib; i,
intcstiiH- haiijsiiiK in the codom; iv, interventral ; m, transverse septum (myocomnia) ; ms,
mesentery; m.*.<l. median dorsal septum; m.s.v, median ventral septum ; nes, neural tube ;
n.s, notochordal sheath ; p. r, ventral or pleura! rib ; s.p, neural spine ; ts, horizontal septum.
Oblique view of left side, from which the septa have been partially removed.

longitudinal, more or less tubular coverings, is formed. To these
may be added a longitudinal vertical median septum, a longitudinal
horizontal septum (in Gnathostomes), and others of minor import-
ance, completing the system of membranes in which the various
parts of the skeleton arise (Fig. 40).

The true endoskeleton, in fact, is only the local strengthening
of certain regions of the connective tissue, chiefly for the sake of
affording a firmer hold, and greater mechanical advantage to the
muscular system enclosed in it. Since the musculature is seg-
mented, we find that the skeletal system is also, as a rule, of a
segmental character. As the lateral paired limbs become differen-
tiated, and as the head becomes more and more 'cephalised'

60 GNA THOS TO MA TA

(p. 2), the primitive arrangement of both septa and muscles
becomes modified and obscured.

The skeleton of the trunk first develops in connection with the
main notochordal axis and transverse septa : vertebrae are formed
between the myotomes, where the septa meet the covering of the
notochord and neural canal ; and ribs are added where the same
septa intersect the horizontal septum and the coelomic wall
(Fig. 40).

Passing now to the origin and finer structure of the endo-
skeleton, we find that it arises in the mesoblastic tissue, and takes
the form of cartilage. Cartilage is a tissue in which the cells secrete
a firm, compact elastic matrix, more or less homogeneous and free
from fibres, the chemical basis of which yields chondrin (Fig. 41).
The cells, which are generally oval and provided with fine pom-

FlG. 41.

Section of articular cartilage of Man, showing transition of cartilage-cells, «, to brandling
connective-tissue cells, ft. (From Quain's Anatomy, by permission of the Publishers.)

municating branches, are distributed throughout the matrix, and
multiply by division. The matrix not being rigid, cartilage can
grow equally in all directions, i.e. in the three dimensions of space.
This is its most characteristic feature. Intermediate forms of tissue
are found between such typical ' hyaline ' cartilage and fibrous
connective tissue.

Bone is a form of connective tissue which develops in relation
to the endoskeleton later than cartilage. This is the case in both
phylogeny and ontogeny. In the higher vertebrates bone gradually
increases in importance as a skeletal tissue, and eventually almost
entirely supplants the cartilaginous framework on which it has been
moulded. There has been, so to speak, a struggle between cartilage
and bone, in which the latter has triumphed.

In the majority of cases, then, bone has replaced cartilage, and,
as a matter of fact, we find that in ontogeny the bony skeleton is,
for the most part, actually preformed in cartilage. The advantage,

CARTILAGE AND BONE

61

for mechanical reasons, of the retention of a cartilaginous stage of
growth in the young is obvious. In some regions, however, true
bone is developed in connective tissue without being preceded by
cartilage. This is always the case in the exoskeleton. To such
ossifications the terms ' dermal ' and ' membrane ' bone have been
given.

It was a London physician, Clopton Havers, who first began
the serious study of the structure of bone. Towards the end of the
seventeenth century he described those small canals which have
since borne his name. The Haversian canals are minute branching
channels running throughout the substance of bone, and containing

ff/

Flo. 42.

Transverse section of a human humerus showing the structure of bone, with lacunae for
bone-cells set in concentric rings round three Haversian canals. (From Quain's Anatomy by
permission of the Publishers.)

blood-vessels, lymph-spaces, and nerves. To Purkinge is due the
discovery of the microscopic cavities in which, as Virchow after-
wards showed, the cells or so-called bone-corpuscles are situated.
Among the numerous observers who have since completed our
knowledge of this complex tissue may be mentioned Tomes, Todd
and Bowman, Sharpey, and Kolliker.

Bone is constituted by lamellae formed of an organic basis,
ossein, which yields gelatine ; it is impregnated with phosphate and
carbonate of lime. Distributed throughout the matrix, between the
lamellae they have secreted, are the bone-cells (Fig. 42). These
are provided with a multitude of fine ramifications reaching from
one to the other, and ultimately to the nearest Haversian canal, or
to the surface of the bone. The lamellae are arranged concentrically

62 CARTILAGE AND BONE

round the canals, or parallel to the bone's outer surface. By
decalcifying bone, fibres were discovered by Sharpey to extend
in varying quantity through the matrix of ossein. Just as the
cartilages are surrounded by a connective -tissue covering, the
' perichondrium,' so the bones are enclosed in a connective-tissue
'periosteum,' from which blood-vessels and nerves penetrate to the
canals.

Such is the structure of typical bone in mammals, whether it
be preceded by cartilage or formed directly in connective - tissue
membranes. But the finer structure of bone may vary con-
siderably. The Haversian canals, serving chiefly for nutrition,
are found to be less numerous, or even entirely absent, in the
bones of very small animals, and in structures of small size. The
bones in the lower classes of vertebrates are often of less regular
and elaborate formation. The lamellae may be scarcely indicated,
the bone-cells scattered, and the canals in the shape of irregular
spaces. Kolliker [270] has shown that, in the Teleostei, the bone
may in some cases be poor in matrix and very rich in fibres (Xiphias,
Gadus) ; in others the bone -cells may be exceedingly rare, or
practically absent in the adult tissue (Pleuronectes) ; again, it
may acquire a structure similar to that of dentine (Stewart,
Fistularia [425]). Nevertheless, true bone is undoubtedly
developed in all the classes of the Craniata, from the fish upwards,
though not in all Craniates.

The question of the origin and growth of cartilage and bone
during individual development is important. The history of
cartilage in ontogeny is simple enough : un differentiated cells, in
certain regions of the connective - tissue system, secrete a clear
matrix round themselves, divide, and still secrete until a mass of
cartilage is formed surrounded by the perichondrium. Such a
cartilaginous skeleton can continue to grow in all its parts, either
retaining or altering its shape according to the needs of the animal.
This account, however, is based on comparatively modern investi-
gation. Before the significance of the cells in cartilage was
understood, it was for a long time held that cartilage is formed
from a fluid blastema by a process of gradual solidification. This
process, carried a step farther, was supposed to give rise to bone
with the aid of calcification.

Such a crude theory had to be abandoned when the importance
of the cells came to be appreciated. But it was still supposed, until
the middle of last century, that cartilage becomes actually con-
verted into bone by the solidification and calcification of the
existing matrix, and by the modification of the enclosed cells
into branching bone-corpuscles. This view received at first the
support of Schwann, Tomes, Virchow, Kolliker, Ranvier, and
others, and appears to be still held in a more or less modified form

CARTILAGE AND BONE 63

by some modern authors. A priori, it seems to be in the highest
degree improbable that such highly differentiated cells as those of
cartilage should be able to so entirely change their form and
function. All analogy would lead us to suppose that, as a rule,
highly differentiated tissues become very limited in their powers of
growth, and can only produce more tissue of a nature similar to
their own. Moreover, there is much evidence against this theory
of conversion.

More than a century and a half ago, Nesbitt (1736) denied, on
general grounds, the genetic connection between bone and cartilage.
Describing two species of ossification yielding the same bony
substance, one in membrane and the other in cartilage, he pointed
out that in the latter case the connection between the bone and the
cartilage is loose. It was not till the middle of the last century
that Nesbitt's speculations were placed on a sound basis of
observation by Sharpey, the founder of the modern theory of
the development of bone in cartilage by substitution. Sharpey
showed that membrane-bones are developed in connective tissue
without being preceded by cartilage ; that, in the case of cartilage-
bones, the outer layers may be deposited beneath the periosteum
without the intervention of cartilage ; and finally, that, even in the
case of true ' emlochondral ' ossification, the bone is not formed by
the conversion of previously existing cartilage, but by the invasion,
so to speak, of bone-forming tissue from without. Blood-vessels
penetrate into the cartilage, the cartilage-cells become peculiarly
modified, the original matrix becomes calcified, then destroyed and
absorbed, and finally it is replaced by a new deposit secreted by
cells brought in with the vessels (Fig. 43).

These views of Sharpey, now almost universally adopted and
much extended, met at first with g7-eat opposition. The triumph
of the new theory of ' substitution ' abroad was greatly
helped by the careful researches of H. Miiller in 1858, and of
Gegenbaur in 1864. It is now established that through the
work of active immigrating cells, which accompany the fine blood-
vessels, channels are eaten away or dissolved in the cartilage
matrix. Other immigrating cells, called 'osteoblasts' by Gegen-
baur, deposit the new matrix or lamellae of ossein on the walls of
the cavities so formed. The osteoblasts become surrounded by
their own secretion, and so converted into bone-cells united to each
other only by fine threads of protoplasm (Fig. 43). The typical
Haversian systems are not well marked at first, but generally
become developed during the latter stages of growth of the bone.

Three varieties of bone can be distinguished : the endochondral,
of which the development has just been noticed ; the sub-periosteal,
or perichondral ; and the membrane bone. To the first variety of
ossification is due very much less of the adult skeleton than was at

64

CARTILAGE AND BONE

first supposed. In ontogeny it is the latest to appear ; it is formed
chiefly in the region of the epiphyses, and is almost entirely of a
purely provisional character. By far the greatest bulk of the endo-

FIG. 43.

Enlarged view of a portion of a section through the phalanx of a mammalian foetus showin;
the development of bone (from a preparation lent by Dr. G. Mann). 1, hyaline cartilage matrix
2, cartilage cell ; 3 and 4, the same becoming modified near the region of ossification ; 5, calci
fied cartilage matrix ; 6, blood-vessels invading the cartilage ; 7, osteoblasts depositing bone
8, island of cartilage, remains of matrix surrounded by newly-deposited bone ; 9, endochondral
bone substituted for cartilage ; 10, perichondral bone deposited outside ; 11, bone-cell ; 12,
invading cells destroying cartilage.

skeleton is of the second or sub-pcriosteal variety. This is the first
bone to appear in the ossification of the limb-bones, for instance,
and is deposited layer upon layer by the osteoblasts lining the

CARTILAGE AND BONE 65

inner surface of the periosteum (perichondrium of earlier stages).
Intramembranous bones are formed, but usually to a much smaller
extent, in the region of the skull, the pectoral girdle, and exo-
skeleton generally.

How a rigid structure like bone can grow while in continuous
functional activity, and still retain its shape while increasing in
size, are questions which soon suggested themselves. Certain
authors, like Todd and Bowman, Strelzoff and Kastschenko, held
that bones enlarge by interstitial growth and expansion ; others,
like Hunter, Kolliker, and Stieda, supported the opposite, and now
generally accepted, view that bone once formed does not expand,
but grows by the deposition of new layers on its surface. While
the osteoblasts are continually adding new material in one place,
other cells, termed osteoclasts, may be destroying the older
portions in another. Thus a bone may alter in shape, or may
increase in size, retaining its form, as the needs of the animal
demand. In this way the greatest mechanical efficiency is secured,
with the least weight and expenditure of material, all superfluous
bony substance being removed in the formation of medullary
cavities.

There remain, perhaps, a few cases in which bone is formed by
the actual conversion of cartilage with its cells. It has been
described by Schmid-Monnard [388a] in Teleostean fish, by
Kastschenko in Amphidia, and by Gegenbaur [153] in Mammalia.
But even here appearances are probably deceptive. Stephan [424]
has explained how apparent conversion may be due to the gradual
change of ' perichondrium ' into ' periosteum ' ; so that if this
layer ceases to produce cartilage and takes to producing bone,
sections show a gradual transition from one to the other. Thus,
it would be the activity of the growing tissue which changes,
not the already formed skeleton which undergoes conversion.

A comparative study of the general development of the skeleton
was begun by Duges in Amphibia [123]; by von Baer, Rathke,
Reichert, Jacobson, Kolliker, Parker [323, etc.] in various groups
of vertebrates. They concluded that the history of the development
of a bone affords important evidence concerning its homology. The
'cartilage -bones,' connected with the endoskeleton, were called
' primary ' ; the ' membrane-bones,' which appeared to have been
added from without, were called 'secondary.' It was argued that
homologous bones must develop in a similar way ; in other words,
it was thought that a ' primary ' bone could not be homologous
with a ' secondary ' bone. This morphological distinction, between
bone developed inside the perichondrium and bone developed more
superficially, was found to be so strongly supported by the facts,
that it became almost a dogma that bones of unlike development
could not be homologous.

5

66 CARTILAGE AND BONE

Such hard-and-fast rules rarely, if ever, hold good in Zoology.
Gegenbaur, to whom we owe so much of our knowledge of the
morphology of the vertebrate skeleton, adopted a wider view, and
held that bone originated in the skin, and only secondarily came
into connection with the more deep-lying cartilage — that, in fact,
' secondary ' bones have become gradually converted into
1 primary.'

Both Gegenbaur [159] and Schmid-Monnard state that the
' squamosal ' (pterotic) of certain Teleostei arises as a membrane-
bone, then becomes closely connected with the cartilaginous cranium,
and finally continues to develop as an endochondral bone. Histo-
genesis would, in such a case, be no criterion for homology. In
the course of phylogeriy, bones, originally intramembranous, might
develop more and more directly as cartilage-bones, so that they
could no longer be distinguished from them (p. 266). There is also
reason to believe that, in some cases, the reverse may happen, the
cartilaginous stage being suppressed. Thanks to the researches
of Williamson [496a], Ley dig, Gegenbaur, and more especially
0. Hertwig [211-12], the ontogenetic and phylogenetic connection of
the dermal bones with denticles, like those developed in the skin of
Elasmobranch fish, has been traced. Williamson considered that the
plates and scales of fish were formed by the combination of super-
ficial denticles with underlying dermal bone. Hertwig supposed
that by the enlargement of the basal plate, whereby the hollow
tooth-like denticle is fixed in the dermis, or by the fusion of
adjacent basal plates, such superficial bones are developed as are
found covering the skull or the roof of the mouth in the lower
Gnathostomes (see, however, p. 215).

Now Hertwig contended that true dermal bones can always be
traced back, in the lower forms, to the denticles from which they
were derived ; even when in the higher vertebrates such bones
have sunk below the skin, and become closely united to the
endoskeleton. Further : that dermal bones always lie outside the
perichondrium, and may cover over cartilage-bones ; and that
cartilage-bones can never be traced back to denticles, and are
developed entirely in direct relation to the cartilaginous skeleton.
The same result, therefore, was reached on this theory, from a
study of comparative anatomy, as had previously been reached by
Kolliker and others, from a more strictly histological point of view.
These conclusions are opposed to those of Gegenbaur and his pupils.
While adhering to the view that bone was originally developed in
relation to dermal denticles, the latter school holds that in the case
of the cartilage-bones, both perichondral and endochondral, the
osteoblasts derived from the surface have migrated farther inwards,
and finally come to invade the cartilage itself. Whether ossifica-
tion extends inwards by such migration, or by a sort of infection,

SKULL 67

by a spreading inwards, as it were, of the tendency to form bone
within the connective tissue system, remains a doubtful point ; but
the main conclusion, that the phylogenetic development of the bony
skeleton has, on the whole, followed this course, is now generally
accepted.

Glancing briefly at the parts played by bone and cartilage in
the general development of the vertebrate skeleton, we find that
the eridoskeleton appeared first, and in the form of cartilage
(Cyclostomes). Subsequently, it would seem, the skin became
covered with tooth-like scales, the primitive exoskeleton of fish.
The first bone may then have been developed in relation to these,
and it is to such superficial bones that the term ' primary ' should
be applied. Owing to the necessity for further consolidation, it
became advantageous either for the cartilages to be strengthened
by an abundant deposit of lime salts (Chondrichthyes, p. 122), or
for the process of ossification to extend inwards in the connective
tissue to the deeper regions. Moreover, bony plates, superficial
in origin, may, in the course of evolution, sink so as to come into
close connection with the underlying skull and pectoral girdle
(Vrolik [476], Walther [480], Osteichthyes, p. 212). The develop-
ment of the denticles, and their relation to the bones of the skeleton,
are dealt with further on (p. 214),

The skull becomes more developed in the Gnathostomes. The
nostrils and nasal sacs are paired. The two capsules usually
develop in continuity with the trabeculae, which fuse in front into
an ethmoid cartilage forming a median nasal septum (Fig. 6). The
brain -case is more complete, though membranous fontanelles
generally remain above and below in the chondrocranium. An
occipital region is always continuous with the parachordals and
auditory capsules, and includes several ' scleromeres ' behind; so
that not only are the glossopharnygeal and vagus nerve -roots
invariably enclosed in the skull, but also one or more segmental
elements of the hypoglossal (p. 10).

The characteristic mouth is bounded above and below by the
biting jaws, developed from the first pair of visceral arches. This
arch bends over the angle of the mouth, the upper limb becoming
separated as the palato-quadrate bar, or primary upper jaw; the
lower limb forming Meckel's cartilage, or primary lower jaw
(Fig. 5). There are never more than eight pairs of gill -slits.
The first, or spiracle, is always different from the others, is
generally not pierced, and is often vestigial. It is followed by
the hyoid arch behind, and the remaining slits by corresponding
branchial arches. These visceral arches develop as paired cartilages
next to the wall of the pharnyx, internal to the muscles, nerves,
blood-vessels, and coelom. Below they join a series of median

68

SKELETON

elements lying above the ventral longitudinal blood-vessel. All
these structures become greatly modified in the higher and terres-
trial vertebrates.

While the notochord itself decreases in importance as a skeletal
axis in the adult, the vertebral column becomes more and more
developed. Vertebral centra of some sort, either within or outside
the notochordal sheaths (p. 99), are almost always formed in con-
nection with the bases of the arches. The centra are therefore
primarily intersegmental, like the neural arches (Fig. 45). In the
caudal region, behind the abdominal coelom, corresponding haemal or
ventral arches meet below, enclosing a space in which run a caudal
artery and vein. Further forward the haemal arches often tend to

Otf. tUL

hnv.

dr. vr

iruL

mdf.
FIG. 44.

Skeleton and nerves of the head of Mustelus laevis, Kisso (the nerves partly from Allis). be,
buccal nerve; d.g, dorsal branch of glossopharyngeal ; d.r, dorsal root of spinal nerve ; d.v,
dorsal branch of vagus ; e, labial cartilage ; g, glo.ssopharyngeal ; hm, hyomandibular, the
spiracle is indicated by a dotted line in front, and the prespiracular cartilage is shown in front
of the spiracle; h.n, hyomandibular nerve; hy, hypoglossal nerve; LI, lateral-line branch of
vagus ; m.c, Meckel's cartilage ; md, mandibular nerve ; md.f, mamlibular branch of facial nerve ;
n.c, nasal capsule ; opt, optic nerve ; ot.f, otic branch of facial ; p.q, palato-quadrate ; jirb,
pretrematic nerve ; pro, profundus nerve ; pt.b, post-trematic nerve ; r, dorsal rostral cartilage ;
sop, superior ophthalmic branch of trigeminal and facial ; v, ventral rostral cartilage ; r.r,
ventral root ; v.v, visceral branch of vagus.

disappear, being represented by mere stumps ; or they may be
prolonged as separate ribs embracing the abdominal cavity, the
so-called pleural or ventral ribs, lying outside the peritoneum on
the inner surface of the myotomes (Fig. 40), (Bruch [66], Dollo-
[119], Goppert [179], Glaus [79]). True or dorsal ribs, on the
contrary, are situated above in the horizontal longitudinal septum,
which in all Gnathostomes separates the myotomes into dorsal
and ventral portions (Fig. 40). It is to A. Goette that we are
indebted for the clear exposition of this important distinction
[167].

The neural arch generally meets above the neural canal a
median neural spine situated in the longitudinal median septum.
The homology of the ' neural spines ' throughout the Gnathostomes

MEDIAN FINS

69

is more than doubtful (pp. 101 and 105). The haemal arches are
similarly completed below by haemal spines.

In the lower Gnathostomes (Pisces) the median dorsal arid
ventral fins are provided with endoskeletal supports, generally in
the shape of rods known as pterygiophores, radials, or somactidia
(Lankester). Now the question arises as to the morphological

OS

SCL

av

to. at

KH;. 45.

Scyllium i-t'it<i-:ilii, L. Left-side view, enlarged, of a portion of the vertebral column and
ribs with the connective tissue septa, to show their relation to the blood-vessels and nerves.
a<i, dorsal aorta ; ax, abdominal wall ; tit, artery ; av, vein ; c, centrum ; d.n, dorsal nerve ; d.r,
ganglion of dorsal root ; tii, interdorsal ; li, dorsal ligament ; m.s, median dorsal septum ; n,
ventral nerve.; ntt, basidorsal ; n.c, nerve-cord ; r, rib ; s.a, segmental dorsal artery ; sd, supra-
dorsal ; fjit, vertical transverse septum passing between successive myotomes ; s.v, segmental
dorsal vein ; t.s, chief transverse horizontal septum in which lie the ribs ; o.s, oblique upper
longitudinal septum, a similar lower septum occurs lietween it and the transverse horizontal
septum ; v, posterior cardinal vein ; r.r, ventral spinal root ; ic, intervertebral ligament.

significance of this supporting skeleton. Is it a special appendicular
skeleton, separate from the axial skeleton (skull and vertebral
column) as held by Cuvier and Huxley 1 Or is it derived from
the axial skeleton itself (Gegenbanr) 1 In the Cyclostomes, the
cartilaginous rays of the median fins reach down to the neural
tube, and may even fuse to a continuous cartilage passing down
each side, so as to enclose the nerve-cord and notochord (p. 32
and Fig. 19). In most of the Teleostomi the dorsal fin skeleton

MEDIAN FINS

reaches, or articulates with, the neural spines (p. 105), and in the
Dipnoi there is no distinction between the two (p. 234). Moreover,
the ventral lobe of the caudal fin is almost always supported by
direct prolongations of the haemal arches ; and the dorsal lobe
in Selachians is usually borne by cartilaginous median 'spines,'
articulated to the vertebral column, yet more numerous than the
vertebrae (Fig. 46, B). All these facts seem to uphold the second
hypothesis, according to which the ' neural spines ' and the fin-
radials represent the proximal and distal regions of an originally

Fio. 46.

Diagrams showing the modifications of caudal fins, and the relations of the ondoskeletal
radials of median h'ns to the axial skeleton. A, diphycercal type, with equal dorsal and ventral
lobes (Dipnoi); B, heterocercal type (Selaehii) ; C, modified diphycercal (Coelacanthini) ; I),
heterocercal (Chbndrostei) ; E, homocercal type (Teleostei) ; F, abbreviate heterocercal type
(Amioidei). a.f, anal fin ; ax.l, axial lobe ; c.r, epichordal radial ; tlef, dorsal lobe partly
formed by epichordal lobe ; d.f, dorsal fin ; ef, epichordal lobe ; h.a, haemal arch ; hf,
hypochordal lobe ; ky, hypural arch ; n.a, neural arch ; nt, notoehord ; r, radial. The
endoskeleton is black.

continuous skeletal rod with several joints. We should not, then,
believe that the fin -skeleton has developed independently at the
base of the fin itself, and has grown inwards centripetally ; but,
on the contrary, we should consider the wide separation of the
radials from the vertebral column in some fish (Elasmobranchs) as
secondary. Thus the discrepancies in number, and the want of
concordance in position, of the arches and fin-radials would be due
to concentration and modification of the originally corresponding
elements (Fig. 46) ; the nonconformity of the two sets of supports
may be either the cause or the effect of their separation.

MEDIAN FINS 71

Since, in many fish, the unpaired fin extends uninterruptedly
along the dorsal mid-line to the tip of the tail, and along the
ventral mid-line forwards as far as the anal region or even beyond ;
and since, in many of those fish which in the adult state have
discontinuous dorsal, caudal, and anal fins, these separate fins
develop as differentiations in a continuous embryonic fin-fold,
it seems very probable that the median fins of the primitive
Gnathostomes formed continuous folds. By the obliteration of
certain regions they became subdivided. This view is further
borne out by the fact that we find quite or almost continuous
median fins amongst some of the most primitive groups of fish
(Pleuracanthini, Dipnoi). Moreover, traces of the fin-skeleton and
musculature are found between the discontinuous fins of such fish
as Acanthias, Rhino, (Figs. 50, 52), Pristis (Goette [167], Thacher
[437], Mivart [300]), and Gadus. We may conclude, at all events,
that the unpaired fins are longitudinal median structures, internally
segmented like the body itself, and involving many segments. The
metamerism is evident in the skeleton, often composed of a series
of separate jointed rods corresponding in number to the neural
arches, or a multiple thereof. The muscles also are segmented,
being as a rule developed from special outgrowths of the
myotomes, the muscle-buds (Dohrn [118], Mayer [297], Harrison
[197], Goodrich [176]) (Fig. 47). A single bud grows into the fin-
fold from each myotome on each side (Scyllium, Salmo). The
muscle-forming cells may, however, be given off not as definite
buds, but from a mere proliferation of the myotome. The nerves
which supply the fin-muscles are branches of the spinal nerves of
the segments belonging to the myotomes from which they were
developed. The buds of the right and left sides correspond in pairs,
find between each such pair is developed a skeletal radial (Fig. 47).

The exact correspondence between the body segments and the
fiu segments is usually disturbed by ' concentration ' and by
concrescence, which accompany the breaking up of the continuous
fold into separate fins. The base of each separate portion tends to
become narrower, and thus a dorsal fin which in the embryo
developed from some dozen segments, may in the adult come to
occupy only some half-dozen or fewer. As a rule, more buds arise
in the embryo than come to full development in the adult, some
being suppressed at each end, where concentration is most pro-
nounced. The skeletal and muscular elements thus become
relatively compressed, and this concentration may take place more
at one end of the fin than at the other (Fig. 47). Owing to
concentration radial fin-muscles may become more or less widely
separated from the myotomes which gave rise to them, and the
nerves are made to converge towards the narrowed base of the fin
to supply them ; thus are formed longitudinal ' collector ' nerves,

PAIRED FINS

PAIRED FINS 73

especially in front of the fins. Concrescence, the second factor,
may introduce profound modification (Thacher [434], Mivart [300]).
Not only do the skeletal radials often fuse, forming basal plates or
jointed axes of most varied shapes (Figs. 48-50, 52-54), but the
muscular segments also possibly mix to some extent in ontogeny,
and lose their primitive metamerism.

The very important subject of the origin of the paired limbs of
Gnathostomes must now be discussed. As it is generally agreed
that the primitive form of these must have been the fin-like
'ichthyopterygium/ the evolution of the fish fin only need for the
present be considered. What appear to be the less modified fish
possess a pair of pectoral fins supported by a pectoral girdle behind
the gills, and a pair of pelvic fins supported by a pelvic girdle
passing just in front of the anus.

According to one theory, that of Gegenbaur [155, 157, 162],
the paired limbs are modified gill-structures ; the girdles represent-
ing the gill-arches, and the fin-fold and the fin-skeleton representing
the gill-flap and its gill-rays. The position of the fins far back,
especially of the pelvic fins, is explained as due to the shifting
backwards or migration of these posterior arches, which have lost
their original branchial function. This may shortly be called the
gill-arch theory.

A second and rival theory, that of Balfour [27-29], Thacher
[434], and Mivart [300], holds that the paired fins are of the same
nature as the median fins, and have been developed from paired
longitudinal lateral fin-folds ; the somactidia, or endoskeletal radials,
would, in both cases, have arisen for the stiffening of the fin-folds.
The girdles would have been developed by the extension inwards
of these rays so as to afford a firm basal support to the fins. This,
the most generally accepted view, is known as the lateral-fold theory.

The paired fins develop, on the whole, just like the unpaired
fins. They appear as longitudinal folds of the body -wall into which
grows mesenchymatous mesoderm. Muscle-buds push their way
into the fin-fold from the neighbouring myotomes (Dohrn [118], Rabl
[336, 338], Mollier [301-302]), two growing out of the lower end
of each myotome in the fin region in Elasmobranchs (Fig. 47), or
one from each myotome in other forms. The buds spread outwards,
dividing into upper and lower halves, which form the dorsal and
ventral radial muscles of the adult fin. Endoskeletal radials,
somactidia, are differentiated between the upper and lower muscle-
buds. At first the girdle, basals, and peripheral radials appear as
a continuous rudiment of pro-cartilaginous cells. Later on the
individual elements seen in the adult arise as separate chondrifica-
tions, leaving non-cartilaginous joints (Balfour [28], Mollier [301],
Ruge [377fl]).

74 PAIRED FINS

Since the girdles are ingrowths from the base of the fin-skeleton,
it is natural that some of the nerves should become surrounded by
them, and in the adult pass through foramina to supply the fin.

It is difficult to find any facts which actually support the gill-
arch theory, and much evidence may be urged against it. If
developed from gill-septa, lying across the long axis of the body,
such transverse folds would rather hinder than favour progres-
sion. Moreover, the two pairs would presumably be at first close
together, behind the other gills in a position very disadvantageous
mechanically. Now, in ontogeny, a paired fin never makes its
appearance as a dorso-ventral fold ; but, on the contrary, always as
a more or less longitudinal ridge.

The position of the pelvic fins is attributed (Gegenbaur) to
their backward migration. But neither in primitive fishes
generally nor in their early fossil representatives is there any
evidence of a more anterior pelvic fin. When, as in some
Teleostei (p. 425), the pelvic fins are far forwards, their position
is on good evidence considered to be secondary.

The presence of rudimentary muscle-buds in front of the paired
fins is supposed to indicate backward migration. This, however,
can hardly be the case, since such buds are also found behind these
same fins. It has been urged that the presence of a ' nerve-plexus '
or collector nerve (Davidoff [97-99]) at and in front of the base of
the pelvic fins, and that the greater extension of the collector in
the young than in the adult, are evidence of backward migration.
But, again, such a plexus and extension are found at the posterior
end of the fins.

It is true that an attempt has been lately made (Fiirbringer
[143], Braus [48]) to account for the position of the pelvic fins by
the assumption that the primitive Gnathostomes had much more
numerous gill-arches extending much farther back than in known
forms ; but of this there is no evidence. That the paired limbs
occupy very different relative positions on the trunk is an obvious
and striking fact, which will be dealt with farther on (p. 79).

The gill -arch theory gives no intelligible account of the
participation of a large number of segments in the formation of the
musculature and nerve-supply of the paired limbs. Yet it is always
the case that a considerable, and sometimes a very large number of
nerves and myotomes contribute towards them ; and the area from
which they are supplied is wider than the actual base of the fin
(Fig. 51). Speaking quite generally, the lower the class of verte-
brate concerned, the more segments take part in the formation of
the paired limbs (Braus [46]).

If the skeleton of the paired fins were derived from gill-rays, we
should expect their muscle -supply to be drawn, not from the
myotomes at all, but from the ' lateral-plate ' musculature, inner-

PAIRED FINS 75

vated from the dorsal roots (p. 3 and Fig. 1). In the head region
although the visceral arches may be supplied with epi- and hypo-
branchial muscles derived from myotomes, yet the great bulk of
the musculature of these arches belongs to the lateral-plate
mesoblast. It is true that the trapezius muscle, attached to the
scapula, is of similar origin and is supplied from the vagus, but it
does not penetrate into the fin ; and, at all events, in the pelvic
ergion there is no trace of other than segmental muscles. Still
more inexplicable on Gegenbaur's theory is the position of the
girdles with regard to the nerves, blood-vessels, coelom, etc. For,
whereas these lie outside the gill-arches, in the case of the girdles
we find not only that the relative position of the structures is
reversed, but that the nerves often actually pierce the girdle to
reach the fin. In fact, the girdles lie in the outer body-wall, Avhile
the visceral arches lie in the wall of the alimentary canal. Finally,
this theory offers no explanation whatever of the striking
resemblance borne by the paired fins to the median fins in every
detail of structure and development— a resemblance so close that
it can only be supposed that they are organs of essentially the same
nature. Especially remarkable is the identity in structure of the
dermal fin rays (pp. 122, 212).

Turning now to the rival fin-fold theory, it is found that if
difficulties in its application do occur, yet the greater part of the
evidence of embryology and of comparative anatomy is distinctly
in its favour.

The paired limbs, especially the fins of fish, as already mentioned,
always appear as longitudinal folds. The folds may be very short.
The continuity of the folds from the pectoral to the pelvic regions
is not really an essential point. Possibly from the first the paired
fins, and indeed the median fins also, were discontinuous. Never-
theless, such facts as the great extension of the muscle-buds and of
the 'nerve-plexus' both before and behind the fins [46], the con-
centration of the fins, the frequent presence of a greater number
of buds in earlier than in later stages, the presence in some fish
(such as Pristiunis and Scyllium: Dohrn [118], Braus [47, 50])
of such buds in all the trunk segments, may be considered as
evidence supporting Balfour's view of the original continuity of the
folds.

It has been convincingly shown (Thacher [434], Mivart [300])
that the various types of the endoskeleton of the median fins of
fishes, with more or less well-developed basal plates, or rays branching
from an axis (Figs. 48-50, 52), have been formed from a series of
primitively discrete segmental radials (somactidia) by a concrescence
or fusion of their bases, often accompanied by concentration or
gathering together at the narrow base of the fin (p. 106). That the
similar manifold types of the endoskeleton of the paired fins have

76

PAIRED FINS

arisen in the same way can scarcely be doubted. Indeed, it is

B.

.ar.

abs.

fir

FIG. 48.

Dorsal fins, with the ewloskeleton exposed, of: A, Xotidanus (Heptanchus) cinereits, Gin. ;
B, Ginglymostomu clrmtum, Gm. ; C,Zygaena malleus, Risso ; D, Rhynchobatus djeddensis, Forsk.
(After Mivart.) ate, anterior radials lying on vertebral column ; a.r, anterior radial ; 6,
longitudinal basal ; bs, basal ; tl.s, distal segment of radial ; /, fin web supported by ceratotrichia ;
m.s, median segment of radial ; p.r, posterior radial ; pr.s, proximal segment of radial. These
figures illustrate the formation of ba.sals by the concrescence of radials.

FIG. 49.

Left-side view of a portion of the, tail of Raja. The vertebral column has been exposed in
front, also the endoskeleton of the two dorsal tins, showing the concrescence of the radials at
their base to form a posterior axis.

necessary to assume this even on Gegenbaur's theory, which derives
the fin-skeleton from originally separate gill-rays.

The objection often raised that, in Elasmobranchs, the fin-radials

PAIRED FINS

77

become differentiated in a continuous procartilaginous rudiment
(Balfour [28], Ruge [337a]), and not as separate rudiments, applies
equally to the median fins (Balfour, Braus [50, 176]). More-
over, in Teleosts, and possibly in many other fish, the radials are
separate from the first (Harrison [197]). It is also urged that the
metamerism of the radial muscles of the adult fin does not correspond
to that of the embryo (Braus [50]). Now, although it may be true-

hiu ca-

FIG. 50.

Acanthias vulgari*, Risso. A, dorsal fin and portion of the vertebral column which has
been cut through longitudinally in front. B, calcified cylinder of a centrum. C, transverse
section of the vertebral column, caudal region. D, surface view of denticles as disposed in
the skin, a, canal for aorta ; a.c, anterior cartilages (either modified radials or neural spines) ;
6.c, basal cartilage ; b.pl, basal plate ; ra, calcified cylinder ; ct, cartilaginous centrum ; d,f,
dorsal fin ; h.a, haemal arch ; in, interdorsal ; iv, intervertebral ligament ; li, dorsal ligament ;
n.a, neural arch ; n.e, neural canal ; nt, notochord ; s, blunt spine ; sp, fin spine, with base cut
away to expose cartilage core ; r, radial ; v, canal for caudal vein. The cartilage is dotted.

that muscle-buds fuse at their base, that a nerve-plexus is formed,
and that the substance of an adult radial muscle may not be derived
entirely from one bud, yet it is doubtless derived mainly from
that bud the position of which it continues to occupy throughout
development, and the radial muscles correspond in number and
relative position to the buds from which they have been formed
(Figs. 47, 51). In this respect also the median resemble the paired
fins. Indeed, it is very doubtful whether any fusion of neighbouring
buds takes place at all in such low forms as the Elasmobranchs

PAIRED FINS

X

m

S=s |

ill
ill

I

i~

-\

•=~;e

5 35 V

Ps 51

PAIRED FINS

79

(Goodrich [176]), and there is evidence that in Raja, for instance, the
radial muscles of the pectoral fin retain the primitive metamerism.

We have now to account for the apparent migration of the limbs.
Even if the ancestral Gnathostome had possessed continuous paired
fin-folds, the position of the paired limbs cannot be accounted for
in phylogeny merely by their persistence in certain regions and
suppression in others. In all classes there has been perpetual

-TIC.

ha- ,

FIG. 52.

Transverse section through the centre of A, a trunk vertebra of Raja. B, a caudal vertebra
of Rhinabatus granulatus, Cuv. C, a trunk vertebra of Rhino, tquatina, L. D, left-side view
of a portion of the vertebral column, and of the skeleton of the first dorsal fin of Rhino, squat inn,
L. bp, basal ; br, basiventral (haemal arch) ; c, centrum ; <:.r, calcareous ring ; d.f, dorsal tin ;
h.a, haemal arch ; in, interdorsal ; n.a, basidorsal (neural arch) ; n.c, neural canal ; n.sp, neural
spine (or anterior radial) ; 7-, distal end of radial ; r.c and v.e, radiating calcification (black) ;
sd, supradorsal.

alteration of the position occupied by the paired limbs, just as in
the case of the unpaired fins of fish (Figs. 47, 51). It has been
held (Gegenbaur) that these changes of position are due to the actual
migration of the paired limbs from one place to another. Now
embryology affords no evidence for this view. In ontogeny there is
little or no migration of the whole fin. Considerable apparent
motion is brought about by processes of concentration, growth, and
reduction. It has already been mentioned that any trunk segment

8o

PAIRED FINS

may contribute to the production of a limb (p. 75), and we find
that the segments of the region occupied by the limb in the adult
always share in its development. The limb, as a whole, retains its
position throughout ontogeny (Fig. 47). But if reduction takes
place in iront, and growth takes place behind or vice versa, if, in
other words, certain segments cease to contribute at one end, and
certain other segments begin to contribute at the other, then apparent
motion takes place backwards or forwards. This may be further
complicated by unequal concentration at the two ends. The nerve-

A.

B

FIG. 53.

Skeleton of the pectoral fin of A, Scymnus lichia, Cuv. (after Gegenbaur) ; B, Heterodontus
(Cestracion) 1'hilippi, Lac. (after Gegenbaur) ; C, Centrophorus calceus, Gthr. (after Woodland).
In the latter the web of the fin is represented. 6, basipterygium ; /, fin-web ; mt, metaptery-
giuin ; p.r, preaxial radials ; pt, propterygium ; pt.r, post-axial radials.

supply of the adult limb is a sure guide to the identification of the
segments from which the muscles have been derived. Segments
before and behind the limb-plexus may no longer enter into the
formation of the limb owing to reduction ; but the adult nerves un-
doubtedly show which segments contribute most to the musculature.
That, in a series of metameric myotomes and nerves, each motor
nerve remains, on the whole, faithful to its myotome throughout
the vicissitudes of phylogenetic and ontogenetic modifications, may
be considered as established. However, by means of a nerve-
plexus, nerves may come into secondary connection with muscles not
originally belonging to them, at all events in the higher vertebrates
(Tetrapoda). The nerve-plexus of a limb is brought about not by

PAIRED FINS

81

the nerve deserting one muscle for another, but owing to the fusion
of muscle-buds, or cells. Strictly speaking, even then the nerves
probably remain faithful to the muscle substance of their own
segment, though it may be combined in one muscle with fibres
derived from other segments supplied by other nerves. The limb-
plexus is, however, formed not so much by an intermingling of the
nerves as by a gathering together of these nerves from a number
of segments into common collector trunks (Fig. 47). This collecting
does not necessarily disturb the metameric order of the structures
concerned. It is due to concentration (Mollier [301], Goodrich [176])
in so far as it concerns the motor fibres, and alters neither their

B.

A.

mt.

FIG. 04.

Callorhynchus antarcticus, Lac. The web of the fin, and the ceratotrichia, have been cut
across. (After Mivart.) 6, basipterygium ; /, lin-web; mt, metapterygium ; p.r, preaxi;il
radiuls ; />(, propterygium ; pt.r, cartilages representing postaxial radials.

proximal roots nor their peripheral destination. Thus we find that
even in such a fin as that of Ceratodus, the development of which
is so abbreviated and obscured (Semon [400a], Braus [48]), the
preaxial and postaxial muscles are regularly supplied from nerves
belonging to segments in order from before backwards.

Now, as Furbringer has shown in his admirable works [142, etc.],
a limb-plexus shifts backwards or forwards like the limb it
supplies. Its change of position can be accounted for neither by
the theory of inter- and excalation of segments, nor by the
supposition that the nerves actually move through the segments.
It is, therefore, by progressive growth in one direction, and by
corresponding reduction in the other, that change of position takes
place. The motion is only apparent, and is not due to the

82 PAIRED FINS

actual migration of the ready-formed material from one segment on
to another, but may be said to be due to ' transposition ' from
one set of segments to another set up or down the series.

In the Teleosts, where within comparatively recent times the
pelvic fins have shifted from an abdominal to a thoracic, and from
a thoracic to a jugular position, the nerve-supply is correspondingly
modified (Guitel [187]). In the last instance it may even be
drawn to some extent from a segment supplying the pectoral fin
(Lepidoleprus [Stannius, 416], Uranoscopus [von Jehring, 245]). l

In spite of the fact that the muscles in the fins of fish are not
always attached to the cartilages, yet there is no reason to believe
that the mesenchymatous mesoblast from which the latter are
developed is not derived from the same segments. We conclude
that the limbs are always developed from the segments correspond-
ing to their position in the adult, as indicated by the nerve-
supply. Change of position is not brought about by migration,
but by progressive growth at one end accompanied by reduction at
the other. Migration is apparent, not real.

Finally, with regard to the origin of the paired fins, it may be
concluded that the position of the girdles in the body-wall, the
perforation of these girdles by a number of nerves supplying the
fins, the structure of the endoskeleton of the fins, the derivation of
their musculature and nerve-supply from a large and varying
number of segments, above all, the remarkable resemblances
between the development and adult structure of the paired and
unpaired fins, and the presence in both of exactly similar dermal
fin-rays (p. 212), that these and other facts mentioned above are
strong evidence for the lateral-fold theory, and receive their natural
explanation from it.

In the Gnathostomata, the nasal sacs and the nostrils are dis-
tinctly paired. They do not come into connection with the
hypophysis. The latter (Fig. 10) is always small and develops
as an ingrowth of the ectoderm, on the roof of the buccal cavity,
which grows towards the infundibulum. As a rule, it becomes
nipped off, and converted into a glandular mass, the pituitary
body, lying inside the cranial cavity, attached to the infundibulum.

The thyroid loses all trace of an endostylar structure, and
forms a glandular mass. A large vascular organ, the spleen, is
always present, situated near the stomach. The latter organ is
generally well differentiated and U-shaped, and the intestine to
some extent coiled. A renal portal circulation is established in the
kidneys (p. 114).

The ear has one horizontal and two vertical semicircular canals.

1 An investigation into the development of these fins is much needed, and
would be sure to yield interesting results.

URINOGENITAL ORGANS 83

The dorsal and ventral roots of the spinal nerves of the trunk
always combine to form mixed branches. The sympathetic
nervous system becomes well differentiated, with segmental and
visceral ganglia.

Other, and perhaps more important, differences are found in
the structure of the urinogenital organs (p. 27). As already
mentioned, we find a succession of excretory organs in the
ontogeny of the Craniata, which is more thoroughly carried out
in the Gnathostomes than in the Cyclostomes. Something must
here be said concerning the development of these organs in the
Craniata generally (see also p. 365).

A very large number of embryologists, among whom one may
mention Balfour [26, 29], Sedgwick [395-6], Eiickert [376-7],
Eabl [337], Semon [397], Brauer [45], Kerens [258], van Wijhe
[496], Field [137], Wheeler [486], Price [335], and Felix [135-6],
have studied this subject in various groups. Felix has recently
published an excellent summary of our present knowledge of it
[136].

A pronephros is found in the embryo of all Craniates, although
it generally appears to be incompletely developed, or degenerate.
In Elasmobranchs and Amniota it is vestigial and probably never
functional.

In the early stages of development the segmented mesoblastic
somites separate off gradually from the unsegrnented lateral
mesoblast (p. 3 ), a slender stalk alone for a time connecting
the two together. It is from this connecting stalk, gener-
ally containing a lumen whereby the myocoel communicates
with the splanchnocoel, that the pronephric tubules arise, either
directly or indirectly. This rudiment of the pronephric tubule,
the nephrotome, may be nipped off as a solid block, which subse-
quently acquires a lumen and joins on to the lateral plate, or it
may from the first be fused with the lateral plate (Teleost). In
the typical fully developed organ each tubule resembles a
mesonephric tubule, and consists of a segmental ciliated funnel
opening into the coelom, the coelomostome (outer funnel, or
primary nephrostome of the communicating canal). This leads by
a narrow canal (Erganzungskanal) to the renal chamber or capsule
(Bowman's capsule of the Malpighian body, the ' urocoele '). Into
this small chamber opens a funnel (inner funnel, or ' urostome ')
leading into the main renal canal. The renal capsule and its
canal arise as an outgrowth of the tubule. All the pronephric
tubules join a longitudinal duct, which passes backwards to open
into the cloaca. This is called the pronephric duct, or segmental
duct. Into the renal chamber projects a blood-vessel, supplied
from the aorta, known as the glomerulus.

84

KIDNEYS

Now such a complete tubule is rarely found in the pronephros
(Figs. 55, A; 56, A). It occurs, however, in Ganoids, Apoda (Gymno-

A.

ar.

pro.

OS.

cw.

ov.

FIG. 55.

Diagrams of the urinogenit.il organs of the Craniata, seen in transverse sections of the trunk.
A, pronephros ; B, mesonephros ; C, young stage in development of male ; D, adult male ; E,
female with ' free ' ovary ; F, female with closed ovisac (Lepidostens and most Teleostei). a.d,
archinephric duct (which becomes the mesonephric duct in all except A) ; ao, aorta ; or, artery
to glomerulus ; c, main tubule ; c.o, cavity of ovary closed off; e.ic, wall of coelom ; g, genital
ridge; m, mesentery; m.d, Miillerian duct; in.f, Mullerian fold (developing duct); mn.i;
mesonephric capsule; ms.d, mesonephric duct; ms.f, mesonephric funnel; nt, notochord ; o£,
ostium of oviduct ; ov, ovary ; p.f, pronephric funnel ; v.c, cardinal vein.

phiona), and less typically in Myxinoids. As a rule, the pronephric
tubules gradually dwindle at the anterior and posterior end of the
organ, and even the middle tubules are often incomplete. For

KID.\7E YS 85

instance, the renal capsule and glomerulus are only developed
in the three groups just mentioned and the Teleostei. Gener-
ally the pronephros consists merely of coiled ciliated tubules
leading from the coelom to the connecting duct. In some
cases the renal chambers may fuse into a longitudinal pronephric
chamber, and the glomeruli may also combine into a single
' glomus.'

A second set of blood-vessels may project into the coelom,
near the coelomostome ; these constitute the ' outer glomerulus '
found in Actinopterygii, Dipnoi, most Amphibia, and Amniota.
The region of the coelom surrounding the outer glomerulus may
become incompletely separated off from the abdominal coelom,
forming an ' outer chamber,' as in Ganoids, Anura, and Urodela,
and to some extent in the Amniota. On the contrary, in others
the coelomostome may, apparently, open out so that the renal
chamber merges with the general coelom (Elasmobranch ?,
Petromyzon 1 ).

It is important to notice that at first the tubules are strictly
segmental, although subsequently they may shift and become
closely packed together (Myxinoid), or even fuse to a single opening
(Elasmobranch).

In the anterior region the longitudinal canal, \vhich lies outside
the somatopleure, is formed by the fusion of the distal extremities
of the pronephric tubules (Fig. 56). Further back a region of
varying length may be developed by a direct folding off of a
longitudinal ridge of the somatopleure. Lastly, the terminal
portion of the duct, which opens into the cloaca, is usually formed
by the growing backwards of the free posterior extremity of the
duct. Here, again, we meet with great variation. While in the
Gymnophiona [45] the pronephric duct extends backwards almost
entirely by free growth, in the Anura and Teleostei it develops
to a great extent as a folding off of the somatopleure. Further, in
the Cyclostomes there is evidence of the whole duct being really
formed by the fusion of segmental rudiments representing tubules,
much reduced in Petromyzon [486], but reaching fuller development
in fidellostoma [335].

The number of distinct tubules forming the head kidney, or
pronephros, varies considerably. In the higher vertebrates it is
never large — from two to six — but the number of rudiments is
always larger. The Gymnophiona may have as many as ten [45],
and the Myxinoids about twenty tubules.

The pronephros soon loses its importance as an excretory
organ, and its function is assumed by the mesonephros (Wolffian
body). With few exceptions (Cyclostomes, p. 43 ; and Teleostei,
p. 364), the pronephric tubules disappear almost completely in the
adult, or contribute to the formation of the funnel of the Miillerian

86

KIDNEYS

duct or oviduct (p. 90). The pronephric duct, however, persists,
although it may become much modified.

There is no fundamental distinction between the pro- and the
mesonephros; in the Myxinoids [335] and Gymnophiona [45]
the transition from one to the other is gradual. Such differences
as are found in the development appear to be chiefly due to the

FIG. 5G.

Diagrams of the urinogenital system in the Craniata. A, hypothetical ancestral sta.^' with
continuous archinephros. B, Cyclostome with anterior pronephros. C, female Gnathostome
(adult). D, male Gnathostome (adult), a.d, archinephric duct ; ar.t, anterior vestigial tubule ;
a.t, archinephric tubule ; c, Malpighian capsule ; el, cloaca ; l.c, longitudinal canal ; m.d,
Miillerian duct ; ms.d, mesonephric duct; mgf, mesonephric funnel; o.f, coelomic funnel; ov,
ovary; pf, coelomostome (funnel); pr.d, pronephric duct; pr.f, pronephric funnel; pr.t,
posterior vestigial tubule ; r, vestigial network of vasa efferentia ; s.f, secondary funnel ; te,
testis ; t.t, tertiary tubule ; v.e, vas efferens. The vestigial oviduct and the embryonic
pronephros are represented by dotted lines in C and D.

fact that, as the mesonephros arises later, the mesoblastic somites
are by that time more completely differentiated.

The mesonephric tubule, like the pronephric, arises from the
mesoblastic stalk (nephrotome, intermediate cell-mass, Urseg-
mentstiel) connecting the somite with the lateral mesoblastic
plate. These rudiments generally become completely separated
off from the somite, and sometimes also from the lateral plate, at an

KIDNE YS 87

early stage. They form more or less solid masses, which may fuse
into a continuous strand on either side. Subsequently they
become hollowed out, forming coiled tubules with Malpighian
capsules (urocoeles) and glomeruli, and generally coelomostomes
(mesonephric funnels) (Fig. 55, B). The main canal of the tubule
grows outwards towards the longitudinal duct of the pronephros,
with which it fuses. This duct is now partly or entirely converted
into a mesonephric duct (Fig. 56, B). If the nephrotome has become
completely separated oft' from the lateral plate, the opening to the
coelom may be reacquired ; but as a rule it persists throughout the
development of the tubule. At first the mesonephric tubules are
strictly segmental ; in Myxinoids only do they remain so (p. 50). In
other Craniates, at all events throughout the greater length of the
mesonephros, a varying number of new tubules are formed from
masses of cells nipped off' from the first rudiment. All the
mesonephric tubules are therefore derived from the same original
series of rudiments by a sort of budding. These secondary tubules
acquire the typical structure and relations, excepting for the
coelomic funnel which is not developed. The tubules become
crowded, and their metameric order is lost. The coelomostomes
survive only in adult Elasmobranchs and Amphibia (Bles [36]).
The mesonephric tubules are developed from the anterior to the
posterior end of the abdominal cavity, but some tubules in front
and behind may degenerate.

In some fish (Elasmobranchii) and in Amphibia the posterior
region of the mesonephros is much more developed than the anterior,
and functions as the chief excretory organ. But in the Amniota the
mesonephros disappears almost entirely in the later stages of
development, and is replaced behind by the permanent kidney or
metanephros. In essential structure the metanephros resembles
the mesonephros, but it never has any coelomostomes, shows no
obvious trace of segmental order, and possesses its own duct, the
ureter. Some authors believe the metanephros to be entirely
formed by an outgrowth from the hinder end of the meso-
nephric duct (Minot, Schultze, etc.) ; but others have shown
(Sedgwick, Schreiner, Felix [135], etc.) that only the ureter
and the collecting tubes are so developed, the excretory tubules
and capsules being derived from a separate rudiment. The
metanephric rudiment is in the shape of a mass of cells continuous
with the mesonephric rudiments in front, and derived like these
from the intermediate cell-mass, but of more posterior segments.
Coelomostomes are here permanently lost.

Much controversy has taken place with regard to the
morphological significance of the three divisions of the excretory
organ. One of three views may be held : they are merely three
regions of a once continuous kidney, which have come to function,

KIDNE YS

and so to develop at different times ; or they represent three
organs ; or again three separate longitudinal series of excretory
tubules one above the other, homodynamous, but not strictly
homologous. That the first view is, at all events in a general
sense, correct can hardly be doubted now that we know that there is
no essential difference between the pronephric and the mesonephric
tubules (Sedgwick [296], Brauer [45], Price [335], Kerens [258]).
When the pronephros and mesonephros appear to overlap, as seems
to be the case in birds, for instance (Felix), the ' mesonephric '
tubules of the pronephric segments are probably comparable to the
secondary generations of tubules further back. It also seems
•clear that the metanephros represents merely the specialised and
retarded hinder end of the series (Semper [404], Balfour [29],
Sedgwick, Schreiner [390&]). The chief difficulty lies in the
relations of the ducts.

We may assume, perhaps, with Riickert [376] that there was
originally a metameric series of coelomostomes opening independently
to the exterior (p. 27). Subsequently these fused at their distal
ends to form a longitudinal duct opening behind. At this stage,
then, the ancestral Craniate possessed an archinephros (Lankester),
consisting of a continuous series of archinephric tubules opening
into a single archinephric duct on each side (Fig. 56, A). No living
Craniate presents such a structure, but obvious traces of it are seen
in the Cyclostomes (Bdellostonm, Price [335]), where a continuous
series of metameric tubule rudiments is formed, some of which
become the pronephros and others the mesonephros. Some tubules
disappear between the pro- and mesonephros ; others disappear at
the hinder end of the series. Here, in the Myxinoids, the metameric
order is preserved in the abdominal region, no secondary tubules
are formed, and the single duct persists.

In the Craniata, however, not only may several series of tubules
be produced in the abdominal region (meso- and metanephros), but
these only secondarily come into connection with the already
completely developed longitudinal duct of the pronephros. If,
as seems certain, this duct was originally formed by the fusion all
along its course of archinephric rudiments, it would appear that the
process of formation of the hinder region of the duct by the free
growth backwards of the anterior portion is due to secondary
modification, correlated with the late development of the hinder
tubules. The pronephric tubules, together with the first series
of mesonephric tubules (metamerically arranged and provided with
coelomic funnels), would thus represent the original archinephric
series. Possibly this series has been suppressed in the metanephric
region. The limit between the pro- and mesonephros is not fixed,
and differs considerably in the various classes ; it is quite indefinite
and has doubtless been gi-adually established. The front end of

GENITAL DUCTS 89

the mesonephros and its duct may exactly resemble the pronephros
both in structure and development

We may conclude, then, that all the kidney tubules and their
ducts are derived from one source, the nephrotome or intermediate
cell-mass, that the multiplication of tubules takes place by a
budding process from this rudiment, the earlier being more ventral
and the later more dorsal ; that the pro-, meso-, and metanephros
are not so many regions of one single continuous series, but that, in
the Petromyzontia and Gnathostomata, the mesonephros is formed
of one primary and several generations of secondary tubules, the
hindmost of which become further specialised as the metanephros.

The archinephric longitudinal duct (provisional pronephric)
becomes bodily converted into the mesonephric duct, except in
the Elasmobranchs, where a splitting takes place resulting in the
formation of a Miillerian duct and a mesonephric duct. The
significance of this fact is discussed below.

Some very important differences between the systems of
excretory and genital ducts in the Cyclostomes and in the
Gnathostomes must now be considered. As already mentioned
(p. 45), in the former the excretory duct on each side remains
single, and the generative cells escape to the exterior through
paired short funnel-like openings at the hinder end of the abdominal
coelom. The coelomostomes, in the Gnathostomata, retain to some
extent their original function as genital ducts, and the single
longitudinal archinephric duct is always replaced by two ducts.
Where a metanephros occurs it also acquires its own special duct,
probably by the gradual separation of the distal end of its tubules
from those of the mesonephros, and their union to a common canal
opening separately into the cloaca. Of the two ducts mentioned
above the first is the Miillerian duct, which functions in the adult
female as the oviduct ; the second is the Wolffian duct, which, in the
male sex, acts as a sperm-duct or vas deferens in all Gnathostomes,
and also as a urinary duct jn those Gnathostomes in which the
mesonephros (Wolffian body) represents the adult kidney (Pisces
and Amphibia).

In the male sex of all Gnathostomes the testis is shut off from
the coelom, and (except in some Teleostomes in which the conditions
are highly specialised, p. 364) its products are poured by means of
fine canals, the vasa efferentia, into the tubules of the mesonephros,
through these into the mesonephric duct, and so to the exterior
(Figs. 55, D ; 56, D). Originally the vasa efferentia probably
extended along the whole length of the gonad (Ceratodus, Lepi-
dosteus) ; later they became restricted to the anterior (Elasmo-
branch), or to the posterior region (Lepidosire,n, etc.).

As in the case of the ovary, so in that of the testis, the primary

9o GENITAL DUCTS

germ-cells sink below the coelomic epithelium, and give rise to a
system of canals which generally join to a longitudinal testis-canal.
From this runs the network of transverse canals, vasa efferentia ;
and these usually join again near the base of the mesonephros
(Fig. 56) to a longitudinal canal, into which open the mesonephric
tubules leading to the Malpighian capsules. This plan of structure
is found throughout the Gnathostomes, with slight modifications,
being only secondarily altered in some specialised groups (Teleo-
stomes, p. 364 ; Anura). Thus, the spermatozoa are never shed
into the body-cavity in the Gnathostomes.

The network of canals joining the testis to the mesonephros is
derived from three sources in ontogeny : the testis canals, the fold
of coelomic epithelium closing in the longitudinal canal (and vasa
efferentia) near the base of the testis, and the kidney tubules which
open into it. These three factors may contribute in varying
proportions. The continuous system of canals in the male is, then,
formed from a longitudinal chamber of the coelom closed off near
the base of the genital ridge, into which open, on the one hand, the
testicular canals, and, on the other, the mesonephric funnels (Fig.
55, C and D). Rudiments of these ducts may be present in the
female (Spengel [414], Mihalkovics).

The female sex in the Gnathostomata presents a more primitive
condition (again with the exception of some Teleostomes, which
will be dealt with later, p. 367). The ova are shed into the
abdominal coelom, and are carried out by the open -funnelled
Miillerian ducts (Figs. 55, E; 56, C).

Much controversy has taken place concerning the exact homology
of the genital ducts ; into the details of the question we need not
enter here. Putting aside for the present the Teleostomes (p.
367), it may be pointed out that both the Miillerian and the
Wolffian duct are present in both sexes ; and that, while the latter
is clearly the mesonephric duct, the real difficulty lies in determining
the homology of the former.

That the oviducts in the Elasmobranch, the Dipnoan, the
Amphibian, and the Amniote are homologous structures cannot be
doubted on the evidence of comparative anatomy ; the position of
the ostium abdominale, the course of the duct running along the
abdominal wall outside the mesonephros, the posterior opening into
the cloaca — these and other characters are essentially similar in all
the Gnathostomes mentioned above. Yet on the uncertain evidence
of embryology this conclusion is sometimes denied.

It has been clearly demonstrated (Balfour [27], Kabl [337])
that the archinephric duct, in the Elasmobranch embryo of both
sexes, becomes split into two from before backwards, in such a
way that the pronephric tubules remain connected with one of
the resulting tubes (the ' pronephric ' or Miillerian duct), and

GENITAL DUCTS 91

the mesonephric tubules with the other (the mesonephric or
Wolffian duct). Meanwhile the pronephric funnels fuse to a single
opening (ostium abdominale), which shifts backwards to open at the
anterior end of the abdominal coelom (p. 132). In the male the
Miillerian duct undergoes more or less complete degeneration,
especially in its middle region. On the contrary in the female,
the Miillerian duct enlarges into the oviduct of the adult. From
this it was concluded that the pronephric duct became modified
into the oviduct.

In the Amniota, however, no such intimate connection between
the developing oviduct and the pronephros can be traced. As a rule,
the duct arises in front from a groove or outgrowth of the coelomic
epithelium, along the mesonephric ridge, Avhich then grows freely
backwards to open into the cloaca. The groove, which is not
directly derived from pronephric funnels, gives rise to the abdom-
inal funnel ; the free process to the tube of the oviduct. At
first sight these facts seem quite irreconcilable with the account of
the development of the duct in the Elasmobranch ; but, if we reflect
that the kidney tubules and ducts are themselves outgrowths of the
coelomic epithelium, the difference does not appear so fundamental.
In the Elasmobranch the rudiments of both the pronephric tubules
and oviduct come off together and separate later ; in the Amniote
they appear separate from the first. Moreover, the distinction be-
tween the two modes of development is to some extent broken down
by what we know of the ontogeny of these organs in the Amphibia.
Here the Miillerian duct is formed to a greater extent from a groove-
like outgrowth, which grows backwards close to the pronephric
duct, and possibly to some extent is derived from the latter. The
oviducal funnel has been shown (Rabl [339], Hall [192«]) to be
either partly derived from (Salamandra) or developed in close
connection Avith the pronephric funnels (Amblystoma).

It should not be overlooked that most of the speculations on
the homology of the oviduct have been biassed by our knowledge
of its development in the Elasmobranch, which is more complete
and was earlier acquired than that of the origin of the oviduct in
other forms. The derivation of the Miillerian from the archinephric
(pronephric) duct may not be primitive at all, and it might well be
held that, whereas in all other Gnathostomes the oviduct develops
more or less directly from the coelomic epithelium, in the Elasmo-
branch alone has its rudiment become secondarily involved with the
rudiment of the pronephros.

A knowledge of the development of these organs in the lowest
Teleostomes, and especially in the Dipnoi, would doubtless shed
great light on the subject. In conclusion it may be said that :
throughout the Craniata the mesonephric duct is the converted
archinephric (pronephric) duct ; and that the oviduct (Miillerian

92 CLASSIFICATION

duct) is directly or indirectly derived from the coelomic epithelium,
and may be connected in development with the pronephros. All
these ducts and tubules, whether urinary or genital, being coelomo-
stomes in origin. Provisionally one may suppose that the function
of carrying the ova to the exterior early became restricted to the
more anterior coelomostomes, belonging probably to the pronephric
region, and that the spermatozoa, on the other hand, passed out
through the coelomostomes of the mesonephric region.

The chief characters which distinguish the Gnathostomata from
the Cyclostomata may be summarised as follows : — There is a general
advance in the complexity of the various systems of organs, and in
histological differentiation. The primitive metamerism is more
completely obscured by specialisation, especially in the head region,
where several postauditory myotomes become reduced, and several
occipital segments are added from behind to the skull. The vagus
and some components of the hypoglossal nerve thus come to pass
out through the skull wall. A dermal exoskeleton arises super-
ficially, and the whole endoskeleton becomes much more developed ;
true teeth are present. The pituitary ingrowth is small, and
remains below the infundibulum. The nostrils and nasal capsules
are paired ; the ear has three semicircular canals. The first
visceral arch forms an upper and a lower biting jaw. Paired
pectoral and pelvic limbs are developed (in fish similar in structure
to the unpaired fins). A renal portal system occurs in the kidney.
A spleen is present. The genital products are carried to the
exterior by ducts. In the female an oviduct is developed from the
coelomic epithelium. The spermatozoa of the male are never shed
into the body-cavity, but escape through the mesonephric tubules
and duct to the exterior.

The Branch Gnathostomata, including the five Classes Pisces,
Amphibia, Keptilia, Aves, and Mammalia, was divided by Huxley
[229] into the Ichthyopsida (Pisces and Amphibia), the Saurop-
sida (Reptilia and Aves), and the Mammalia. Since this
classification expresses rather the existence of three grades of
structure than of three divergent phylogenetic lines of develop-
ment, it will not here be adopted. The Reptiles must be placed
next to the Amphibians in any phylogenetic scheme.

The Gnathostomes might be divided into the Ichthyomorpha
(Pisces) and the Tetrapoda (Amphibia, Reptilia, Aves, Mammalia).
But, again, there are serious objections to the isolation of the first
group, although the second seems genuine enough. For the Class
Pisces includes a heterogeneous assemblage of sub-classes, from
some one of which, no doubt, the Tetrapoda have been derived.
Therefore, until our knowledge of the internal relationships of the

PISCES 93

Class Pisces is more advanced, until it can be split up into its
phylogenetic constituent branches, it is best to preserve it as a
provisional group of convenience, representing the first Grade of
the Gnathostomata.

Grade I. Class PISCES.

This, the lowest Class of the Gnathostomata, contains all the
true fish. Like the Cyclostomes, they are still adapted to an
aquatic life, and preserve many primitive points of structure which
must have characterised the early ancestors of all Gnathostomes.

Throughout life the Pisces breathe by means of gills borne on
the visceral arches. The gill-slits are formed by ectodermal pits
meeting endodermal outgrowths. But whereas in the Cyclostomes
the inner pouches are large, and give rise to the gill-lamellae by a
folding of their endodermal lining, in the Pisces the ectodermal
pits are relatively more developed. Their -gill -slits are closely
approximated and transversely elongated ; and open, as a rule, widely
both inwards and outwards. The gill-lamellae tend to grow towards
the exterior ; and, indeed, arise in the embryo of the higher fish (and
Amphibia) as projections of the ectoderm, into which pass branches
of the primary aortic arch. But the difference is more apparent
than real, and even in these cases the endoderm seems to grow out-
wards be.low the ectoderm, forming a gill-lamella with merely a
superficial covering of ectoderm (Greil [185-6]).

Goette [169] considers that the gill-lamellae of the Cyclostomes
and of the Gnathostomes are not homologous (except perhaps the
spiracular gill). There can be little doubt, however, that the gills of
all the Craniate, are really derived from some common origin (Dohrn
[1 14«, 115]). Possibly they are divergent forms from some original
less specialised gill in the covering of which both the ecto- and the
endoderm took a share (Moroff [303]). The ectoderm spreading
inwards seems to have gradually encroached upon the endoderm ;
less, however, in the gill-slits of Elasmobranchs than in those of
higher fish.

The structure of a free branchial bar is very constant in the
Pisces. Along its inner edge is the skeletal arch (Fig. 57) ; out-
side this in the embryo is the coelomic canal, opening below into
the pericardial cavity. From the walls of this canal (lateral plate)
are developed the visceral muscles. The primitive aortic arch
passes along the posterior face of the bar; but in the adult it
becomes variously broken up into an efferent (branchial vein) and
one or two afferent vessels (branchial arteries), communicating with
each other through the lamellae. The vessels run up the outer side

94

PISCES

of the skeletal arch, the efferent being always the innermost next
to the arch.

Since, in each gill-pouch, the branchial lamellae are usually
distinctly grouped in an anterior row on the posterior face of one
bar, and a posterior row on the anterior face of the next bar (Fig.
26), each complete gill is said to consist of two hemibranchs.

FIG. 57.

Sections across the gill-arch of A, Mustelus ; B, Ceratodus ; C, Acipenser ; D, Lepidosteus ;
E, Salmo ; F, 1'olypterus. a, skeletal arch ; «/, afferent artery (black) ; e, septum reaching
external surface ; e/, efferent artery (cross hatched) ; g.l, gill-lamellae ; g.r, supporting gill-ray ;
r, gill-raker ; s, septum, largest in A, and smallest in E. Anterior lamellae to the right.

In the reduced first or spiracular gill-slit is present never more
than one hemibranch, the anterior or ' mandibular,' borne on the
mandibular arch. The hyoid bar may bear a posterior ' hyoidean '
hemibranch ; and the succeeding bars may each have a complete
gill (or holobranch). The last bar, embedded in the body-wall, can,
of course, never bear more than an anterior hemibranch, and is

GILLS 95

generally gill-less. The way in which the gills and the visceral
arches become specialised is of great importance in classification.

Primitively, no doubt, each gill-pouch opened independently
to the exterior,' as is still the case in most Elasmobranchs. The
region between consecutive gill-pouches became narrowed to a thin
septum bearing the gill -lamellae (Fig. 26). The skin, with its
exoskeleton, was still continuous along the outer edge of the
septa.

In most fish, however, the free edge of the hyoid gill-flap, the
septum of the hyoid arch, grows backwards as an opercular flap
covering the branchial openings. Accompanying the development
of this operculum (Figs. 26, 57) is a reduction of the other septa, so
that the gill-lamellae come to project freely at their outer ends in
the branchial chamber.

It is impossible as yet to decide what was the original number
of gill-slits and arches in the common ancestor of the Pisces, But,
since seven branchial slits and arches are found behind the hyoid
arch in some living Selachians (Heptanclms, p. 140), and traces of
a seventh arch may be identified in the larynx of Amphibia,
it seems probable that the early forms had at least eight
gill-slits (counting the spiracle). This conclusion is supported
by the discovery of vestiges of gill-clefts, behind the normal six,
in some living fish, and by the fact that the number of clefts
becomes progressively reduced from behind forwards in more
specialised forms (five branchial slits in most fish, four in
Holocephali, three in many Teleosts).

The primitive jaws, derived from the first visceral arch (p. 18),
become directly or indirectly attached to the skull. In front, the
upper or palato-quadrate bar is generally movably connected with
the lateral ethmoid region of the skull by the palato-basal or
ethmoid process. Behind, the quadrate region of the bar may either
be directly fused to the auditory capsule (Dipnoi, Fig. 206), or it
may be supported away from the skull by the dorsal element of the
hyoid arch, the hyomandibular (Selachii, Teleostomi, Figs. 58, 59),
or again it may be connected with the auditory capsule both by an
articulation above and by the hyomandibular (Notidani, Fig. 59).
Huxley [230] named these three types of skull and jaw suspension
autostylic, hyostylic, and amphistylic respectively. In the autostylic
type the hyomandibular becomes much reduced, and may disappear.
In the hyostylic type, on the contrary, it becomes very large, and
may give rise to a separate ventral element, the symplectic. The
amphistylic type appears to be the least specialised of the three,
and here the hyomandibular is only moderately developed. The
structure of the suspensorial apparatus is of great importance in
classification, but it must be borne in mind that convergence may
occur. For instance, a pseud-autostylism has been almost certainly

96

PISCES

developed in at least two cases, i.e. the Holocephali and the
Teleostei (p. 437).

ea.

ncu.

nc.

p

nik.

Fu.. 58.

,

el's cartilage ; na, nasa capsue ; n.c, nasa carage p, aa-uarae ; pc, prespracuar ;
pi, palatine region ; 7, quadrate region ; t, trabecula. A dotted ring indicates the spiraclelin A.

To grasp the full significance of Huxley's comparisons of these
various modes of attachment of the jaws, we must briefly refer

JAWS

97

A.

cr e> pop.

/ ,•' '

cr.

ink.

FIG. 50.

Diagrams of, A and D, an amphistylic skull (Ileptuiidi «*), B and E, an autostylic skull (Euna),
and C and F, a hyostylic skull (Seym-urn). A, B, and C, left-side views. D, E, and F from
behind (the niandibular arch being dotted, and the cranium shaded), c, columella auris ; ch,
ceratohyal ; er, cranium ; e, junction of ethmoid and palatine cartilages ; e.p, ethmoid process ;
h, hyomandibular branch of facial nerve ; h.a, hyoid arch ; hm, hyomandibular ; I, labial ; mk,
Meckel's cartilage ; nn, nasal capsule ; o.o, junction of otic process of quadrate with the auditory
capsule ; o.p, otic process ; pd, palato-basai process ; pi, palatine region ; p.n, palatine brancli of
facial nerve ; po, preorbital process ; po.p, postorbital process ; pt, palato-quadrate cartilage ; q,
quadrate region ; r, rostral process ; up, spiracle ; t, tympanum.

98 PISCES

to the condition found in the lower Pentadactyle vertebrates
(Amphibia and most Reptilia). In these the palato-quadrate arch
is not only continuous in front with the ethmoid region of the
cranium, but also behind with the auditory region. The quadrate
is forked proximally ; the lower limb, or pedicle of the suspensorium,
is usually fused with, or firmly fixed to, the anterior outer region of
the ear capsule ; the upper limb, or otic process, is fused to this
capsule above. In the canal so formed, between the limbs of the
quadrate and the capsule, the hyomandibular branch of the facial
nerve passes backwards to its peripheral destination, crossing over
the spiracular gill-cleft (or Eustachian tube and tympanic cavity,
Fig. 59, B). The postspiracular hyomandibular cartilage takes no
share in the support of the upper jaw. This is the typical
autostylic attachment, which among the Pisces is found in the
Dipnoi only.

In the amphistylic Notidanidae, the superior otic process (Fig.
59, A) would appear to be represented by the large upgrowth of the
quadrate region of the upper jaw, which articulates with the post-
orbital process of the auditory capsule, and passes outside and
above the hyomandibular nerve. In the anterior palato- basal
process, which articulates more ventrally with the cranium behind
the optic foramen, Huxley saw the representative of the 'pedicle
of the suspensorium.' The relation this process bears to the
nerves, however, shows that this view is untenable. Possibly the
pedicle is not represented at all in Elasmobranchs, and the anterior
process probably represents merely the ethmoid process, found
articulating in front of the orbit in most fish. It has shifted
back in the Notidanidae, which are provided with an exceptionally
wide gape.

Gegenbaur looked upon the articulation of the otic process as
representing the primitive attachment of the arch [153]. Huxley,
on the contrary, considered it to be secondary [230]. It would
certainly seem that the mandibular arch must have been originally
attached more ventrally, below the nerve exits (by the palato-basal
process) like the other visceral arches. Nevertheless, the otic
articulation appears to have been established very early, since
there is reason to believe that it existed not only in the Jurassic
Cestraciontidae (ffybodus, p. 144), but also in the Cladoselachii
(p. 185), Acanthodii (p. 189), and Pleuracanthodii (p. 180).

The notochord secretes an outer thin elastica externa and an
inner fibrous sheath, often very thick (Hasse [201], Klaatsch [265],
Schauinsland [384]). Outside there is the mesoblastic skeletogenous
layer (Fig. 60). Neural arches develop in this layer, and also
haemal arches, which in the trunk are represented by lateral basal
processes (parapophyses). In some fish, Polypteridae and the

VERTEBRAL COLUMN

99

Actinopterygii, the notochordal sheaths remain unbroken through-
out ontogeny, the vertebral centra being formed round them inter-
segmentally. Generally the vertebral rings, or half-rings, developed
in connection with the arches constrict the notochord, so as even to
obliterate it in the middle of each centrum (Fig. 94).

In other fish, the Dipnoi, the mesoblastic cells of the skeleto-
genous layer at the base of the arches pierce the thin elastica

V *>- .

nu, v. .

Bv' • •• . '<
- -'

FIG. 00.

.Si'i/Hiid/i (itn'miild, L. Transverse section of the vertebral column of the tail of a young
embryo. A, the base of the neural arch in an older embryo ; B, of a later stage ; C, all magnified,
a, caudal artery; c, cartilage; e.i, 'elastica interim* or inner layer of the fibrous sheath ; el,
elastica externa ; /.$, fibrous sheath which becomes invaded by mesoblastic cells ; h.a, haemal
arch ; n.n, neural arch ; n.e, nerve-cord ; nt, notochord ; nt.ep, notochordal epithelium ; MM,
nuclei of mesoblastic cells passing through the broken elastica externa ; v, caudal vein.

externa, and invade the fibrous sheath into which they migrate at
four points in its circumference in each segment. Here they give
rise to a small amount of cartilage ; without, however, forming dis-
tinct centra (Fig. 204). But in the Elasmobranchs the invasion is
much more thorough. Almost the whole thickness of the wide
sheath is formed of intrusive mesoblastic tissue in late stages. The
original fibrous sheath often remains next to the notochord as a
clear thin layer, the so-called elastica interna (Fig. 60). Both

ioo PISCES

inside and outside the elastica externa the mesoblastic tissue may
develop into cartilage, continuous with the arches, and forming
hour-glass-shaped centra constricting the notochord segmentally.
The remains of the ruptured elastica may thus become buried in
the centrum.

Such centra, formed at all events partly inside the sheaths, are
called chordal centra, in contrast to those of the first type, the
perichordal centra, which develop outside the sheaths.

The structure of the vertebral column is by no means uniform.
A varying number of elements may serve to arch over the neural
and haemal canals, and the centra themselves may show traces of
a complex build. Attempts have been made to reduce the various
types of structure of the vertebral column, not only of the Pisces,
but also of the Tetrapoda, to a single scheme of homologous parts
(Gadow and Abbott [146], Schauinsland [384]). But it is doubtful
whether such a proceeding is really justifiable, since the different
types may well have been independently developed. Moreoverr
when comparing different regions of the vertebral column
together, authors often try to interpret the structure in agreement
with some artificial scheme uniform throughout ; but it should be
remembered that there is no reason to believe that the arrangement
of the dorsal elements was ever exactly like that of the ventral, or
that of an anterior segment ever exactly like that of a posterior.

The elements entering into the composition of a single vertebral
segment are very variable, both in number, in size, and in shape.
Yet it appears to be possible to reduce them to the following
common plan of four chief paired elements. The neural canal is-
arched over by two elements: the neural arch (basidorsal [146],
caudal arch [384]) behind, and the intercalary arch (interdorsal [146],
cranial arch [384]) in front. Below are found corresponding elements
enclosing the haemal canal: a haemal arch (basiventral [146],
caudal arch [384]), and an interhaemal arch (interventral [146],
cranial arch [384]). The interdorsals, and especially the inter-
ventrals, are liable to reduction. It is very difficult in ontogeny
to follow the exact limits between consecutive segments, since
the myocommata spread out when they reach the vertebral
column, and the myotomes become very much bent. But the
blood-vessels passing upwards from the aorta and cardinal veins
may be taken to indicate the original anterior limit of a segment.
The spinal nerves pass out in front of the vessels to reach the
myocommata (Fig. 45). The neural arch lies between the nerve
and the vessel. The basidorsals and interdorsals vary greatly in
relative development; they frequently surround the nerve-roots.
The roof of the neural canal may be closed above (as in Elasmo-
branchs) by a row of median or paired elements, the supradorsals.
On the top of these runs the longitudinal ligament. Above this

TAIL 101

ligament generally occur a row of spinal elements. These median
spines form the connecting link between the axial skeleton of the
vertebral column (see pp. 69 and 105) and the appendicular skeleton
of the median fins ; possibly (Goette [167]) they should be reckoned
rather with the latter than with the former.

Assuming that the different types of vertebral arches found in
fish have been evolved from such a primitive complex structure, we
find that in the course of specialisation the basidorsals and basi-
ventrals persist generally as the most important elements, while the
others tend to disappear, or to fuse with them.

Both the dorsal ribs and the pleural ribs may be considered as

LUrneu up ui LIIU uuMJUJJUfu . r, en<iuhi\eieuii iciuicii , sc, sr-aies. -iiie pruAimui cnua ui cue

<li;rmal rays have been cut off to expose the nulials and tip of the uotochord. This tail is prob-
ably secondarily diphycercal.

prolongations of the basiventrals ; these basals may remain separate
or ' autogenous ' when ossified (in many primitive Teleostei (Figs.
336, 358), tail of Arnia, etc.), or they may fuse with the centra.
Either the ribs or the basiventrals may undergo reduction and
disappear.

In the formation of the haemal canal behind the abdominal
region it is the basiventral, not the pleural rib which becomes the
haemal arch. The haemal spine is sometimes separate (Amia), but
often appears to be merely a prolongation of the arch (most
Teleosts, Fig. 63), and the ribs may persist as well (Fig. 336).

In no fish with a heterocercal or homocercal tail are the haemal
spines and radials typically represented in the hypochordal fin (p. 104).

102

PISCES

nsp. r

FIG. 62.

Dissected tail of Lepidostctts. (After Kolliker.) d.f.s, dorsal fulcral scales; h.a, expanded
haemal arcli ; h.f, hypochordal tin ; n.np, neural spine ; i>t, upturned tip of the notochord ; r,
dorsal radial ; v.c, vertebral centrum ; r./.s, ventral fulcral scales. The proximal ends of the
dermal rays have been cut off to expose the endoskeleton.

nsp. pi.

ef.

nt

Fia. 63.

Dissected tail of Sahno. (After, Kolliker.) c, centrum of caudal vertebra ; ef, epichordal
dermal ray ; h.a, haemal arch ; h.f, hypochordal fin ; lip, expanded haemal arch or hypural ; I,
dermal ray of opposite (right) side ; n.?p, neural spine ; nt, upturned extremity of the
notochord ; pi, covering bony plate (modified neural arch ?).

TAIL

103

This ventral lobe is invariably supported by single rigid skeletal
pieces, the haemal arches. Some traces of subdivision may be
found in Elasmobranchs, and distal nodules of cartilage may be
present in these and other fish ; but it is still an open question

d.

A, endoskelcton of the tail ofl'ottux ijolio, L. (After I.otz.) B, tail of Puchycormus Jietenmts,
AH., showing the last external trace of the heterocercal structure, a, bony sheath of tip of
note-chord ; «.«, scales covering the upturned tip of notochord ; (/, dorsal radials(?) ; <l.l, dorsal
lobe of hypochordal fin ; /, fulcra; h, hypural bone; h.a, haemal arch ; n.a, neural arch and
spine ; v.c, vertebral centrum ; v.l, ventral lobe of hypochordal tin.

whether the radials have fused with the arches, are represented by
the nodules, or are altogether absent (Fig. 46).

Doubtless the notochordal axis primitively extended in a
straight line to the extremity of the tail, as it still does in Cyclo-
stomes and Cephalochordates. The median fin fold probably
stretched continuously along the dorsal edge to the tip of the tail,
and again ventrally from the tip to near the anus (p. 71). But
such a simple structure is rarely if ever found in either living or

IO4

PISCES

extinct Pisces. It is generally represented by one or two dorsal
fins, one anal (post-anal) fin, and a caudal fin formed of a dorsal
(epichordal) and a ventral (hypochordal) lobe. The name diphy-
cercal has been given to the primitive symmetrical caudal fin ; and

it has been shown that the
asymmetrical, heterocercal,
caudal fin could be derived
from it by a bending upwards
of the notochordal axis, ac-
companied by a reduction of
the epichordal and an enlarge-
ment of the hypochordal lobe
(Fig. 46). A further step in
specialisation gives rise to the
homocercal type, found in the
Teleostei, by the shortening of
the axis, the more complete
suppression of the dorsal lobe,
and the greater development
of the ventral lobe (Figs. 63,
64). The homocercal caudal
fin acquires a secondary out-
ward symmetry. As Huxley
[226] and Agassiz [2] long ago
showed, fish with the more
specialised tails pass through
the more primitive stages in
development : from the di-
phycercal to the heterocercal,
and thence to the homocercal
type (Fig. 65). But in the
process the middle or axial
lobe, in which runs the noto-
chord, becomes relatively re-
duced ; so that, whereas in
primitive diphycercal and
heterocercal tails the noto-
chord reaches to or near the
tip (Elasmobranchs, Dipnoi, Chondrostei), in the more abbreviate
heterocercal and homocercal tails of the Holostei the hypochordal
fin projects far beyond it (Figs. 61-66).

As will appear later, it seems probable that the heterocercal tail
has been independently acquired in more than one group (p. 233) ;
and that, in some cases, fish whose ancestors possessed asymmetrical
caudal fins have reacquired an outward symmetry, making them
superficially similar in appearance to the primitive diphycerca

FIG. 65.

Successive stages in the development of the
homocercal tail of the Flounder, Plewroncctes flesus,
Ii., showing the disappearance of the axial lobe, c,
and growth of the hypochordal fin, h.f. ac, actino-
trichia ; h.a, haemal arch ; hy, hypural cartilage ; I,
dermal ray ; n.sp, neural spine ; nt, notochord.
(After A. Agassiz.)

MEDIAN FINS

105

type (p. 480). The name gephyrocercal has been applied to these
pseudo-diphycercal tails.

Turning now to the relation between the axial and the appen-
dicular skeleton of the median fins, which has already been alluded
to above(pp. 69 and 101), wefind that in the Pleuracanthids amongst
the Chondrichthyes, in the Dipnoi, and in many Teleostomes (Coela-
canths, many Teleosts) the radials of the fins correspond to, and
may articulate with, the neural and haemal spines. As a rule, the
more complete is the fin, the more thorough is the continuity

etff

c.

The development of the caudal liii of Lrp'ulosteus. (After A. Agassiz.) A, young larva with
.interior sucker, s; yolk-sac, y.s; continuous dorsal and ventral tin folds, d.f and v.ff; and
straight notochord. The latter stages, B, C, and L>, show the upbending of the notochord,
the dwindling of the axial lobe, o, which disappears in the adult (cp. Fig. 65), and the
great development of the hypochordal tin, h.f. n.f, anal, d.f, dorsal, ec.f, epichordal, and pt.f,
pectoral tin.

between the two sets of skeletal rods. Now it is important to
notice that in the Elasmobranchs, where the median fin breaks up
into isolated dorsal and anal fins, the neural spines above the longi-
tudinal ligament and the haemal spines tend to disappear com-
pletely (except perhaps in the epichordal lobe of the caudal fin), and
the radials are free to concentrate and coalesce far from the vertebral
column (Fig. 46, B). Traces of the spines remain only in such forms
as the liajiformes, where the fin skeleton is closely connected by
them to the arches (Fig. 52). On the contrary, in the Teleostomi
the series of neural and haemal spines usually remains complete
and unaffected by the concentration of the fin-radials. These may

106 PISCES

either articulate with (caudals of Eusthenopteron, Coehicanthns,
etc.) or alternate with the spines (majority of Teleostei). In the
Teleostomi, then, the division between the axial and the fin skeleton
takes place at the distal end of the spines (p. 69).

The skeleton of the paired fins differs considerably, not only
among the larger groups of the Pisces, but even among closely
allied families and genera. That the various types have been
derived from some common ancestral form, by the fusion and
modification of originally separate and uniform elements, is most
probable (p. 73) ; but what that original type may have been it is
at present impossible to say for certain. Palaeontological evidence
alone could enable us to decide this question.

According to Gegenbaur [157, 162], the original type resembled
the skeleton of the pectoral and pelvic fins of Ceratodus (Fig. 213).
Such an ' archipterygium ' consisted of a median axis, articulating
with the girdle, and provided with an anterior preaxial and a
posterior postaxial series of radials. The radials were arranged in
pairs, diminishing in size towards the tapering distal extremity.
The archipterygium may be described as ' mesorachic ' and
' rachiostichous ' (Lankester). That such a ' biserial ' fin skeleton
is a very ancient type can hardly be doubted. It is found not only
in archaic living fish (Ceratodus, Howes [218], Braus [48]), but also
there is evidence that it was possessed by the Dipnoi and the
Osteolepidoti (Crossopterygii) of the Devonian epoch (p. 282).
Moreover, it is also found in the pectoral fin of the Carboniferous
Pleuracanthodii (p. 181, Fig. 148).

As Gegenbaur has shown [158, 162], the various types of the
paired-fin skeleton found in the Teleostomi may be derived from the
archipterygium on the supposition that the axis has become much
shortened, that the radials have been reduced in number, and that
the postaxial radials have almost or entirely disappeared (Fig. 68),
The ' rhipidostichous ' type of skeleton of the paired fins of Elasmo-
branchs, in which the radials have a fanlike arrangement, may be
deduced in much the same way from the archipterygium. But here
the reduction has been less complete (Figs. 96, 134) ; and it is
unnecessary to assume that the pelvic fins of the Chondrichthyes
have ever fully conformed to the rachiostichous type, since even in
the Pleuracanthodii the pelvics are monostichous (Fig. 150), i.e. have
only one series of radials.

The origin of the archipterygium itself remains to be explained.
The objections to Gegenbaur's theory of its derivation from gill-
rays has been dealt with elsewhere (p. 74). Following Haswell
[198«] and Mollier [301], Ave may suppose that it has been formed
by the great concentration of a large number of radials to a very
narrow base, giving rise to a central axis, and leaving their distal

PAIRED FINS

107

ends diverging on either side (Fig. 67).1 The view that the
nrchipterygium represents the ancestral form of the pelvic fin of the
Osteichthyes, and of the pectoral fin of both the Osteichthyes and
the Chondrichthyes, is thus quite reconcilable with a 'lateral-fold
theory.' But even so, it is probable that the ancestral type was
not as perfectly mesorachic as the modern Ceratodus fin, and that
a certain number of preaxial rays (pro- and mesopterygium)

A, JL

Diagrams to show the result of concentration on the skeleton and nerve-supply of a paired
tin. A, 15, C lead towards the Selachian type of fin ; A, 15, 1) towards the Dipnoan type.
nl-°, nine spinal nerves supplying the fin ; n.c, nerve-cord ; r, radials represented as seen in
an early embryonic stage ; pr, preaxial, and pt, postaxial radials ; /./, fin fold.

remained articulating with the girdle (as in Plewacanthus and
Cladodus, p. 183).

The other theory, favoured by Balfour [28], Thacher [434], A.
Smith Woodward [503], and others, is that the originally separate

1 If it is objected that in Ceratodus, where the adult fin has about thirty radials
and radial muscles, only about three segments have been shown to contribute muscle-
buds in the embryo (Semon [400«]), it must be answered that this result is not trust-
worthy, since Davidoff [99] and Braus [46] have found twelve motor nerve-roots con-
tributing to the limb-plexus. With regard to the development of the cartilages, it
has already been shown that, in Elasmobranchs, the originally separate radials become
differentiated in a continuous procartilaginons rudiment, somewhat as in Ceratoili'*
(P- 73).

io8

PISCES

And parallel (orthostichous) somactids or radials of the paired-fin
folds, becoming concentrated, fused at their base, giving rise to a
' pleurorachic ' and ' monostichous ' type of skeleton (Fig. 68).
In such a fin, the axis lay in the body-wall, and bore a single row
of radials along its outer edge. This type of fin skeleton may be
found in the median fins of Elasmobranchs and other fish (p. 75
and Figs. 87, 1 50), but not in the pectoral fin of any living form. The
pelvic fins, however, in Elasmobranchs and the lower Actinopterygii
very nearly conform to it (Fig. 96). But among the early fossil

FIG. 68.

Diagrams showing the possible derivation from each other of the various types of pectoral
fin skeleton in the Osteichthyes. A, pleurorachic type (Cladodiis). B, hypothetical stage leading
to the mesorachic type C (Ceratodits). D, hypothetical type leading to E (Acipenser, Amid). F,
teleostean type, reached either from A through E, or from C through D and E. a, segment of
axis ; b, basal of axis ; g, pectoral girdle ; pr.r, preaxial radial ; pt.r, postaxial radial.

Chondrichthyes (Cladoselachii, Fig. 155) pectoral fins are found
which possibly have a skeleton of this character (Dean [104]).
Philogenetically, the pleurorachic fin could become mesorachic by
the freeing of its hinder edge from the body-Avail, and by the
shifting of the axis towards the centre of the fin-lobe, so that
radials should come to develop on the growing postaxial side.1
The rhipidostichous fins would be, to some extent, intermediate
forms (Fig. 68). The chief objection to this view, and it is a

1 The ontogenetic formation of the axis in one region of the fin or another is, as
Mollier has shown [301], due to the concentration of the radials about a different ideal
axis. In the Rajidae there may be two axes in one fin (p. 128 and Fig. 121 ).

PAIRED FINS 109

weighty one, is that it becomes difficult to avoid the supposition
that the archipterygial type of fin has been independently
developed in the Pleuracanthodii and the Dipnoi (p. 244).

The development of an outstanding basal stem, or axis, bearing
peripheral radials, is clearly seen in the median fins of certain fossil
and living fish (A. Smith Woodward [503], Thacher [434], Mivart
[300], and Figs. 251, A ; 147). The dorsal fins of the Rajidae (Fig.
49) and the anal fins of the Pleuracanthodii are good examples.
The orthostichous arrangement of the radials in the paired fins of
the higher Teleostomes (p. 302 and Fig. 243) is almost certainly
secondary, and due to the reduction of the axis.

It is important to notice, as a general primitive character, that
the endoskeleton of the fins typically has no articulations ; that is
to say, it moves as a whole, being articulated to the girdle, but is
not subdivided into regions moving on each other, as is the case
with the limbs of the Tetrapoda. Further, we find that, in the
more specialised fish, the endoskeleton has a tendency to become
reduced, and the exoskeletal dermal rays, on the contrary, become
increasingly important as supporters of the web of the fins. These
dermal fin-rays, or dermotrichia [175], are found in both the paired
and the unpaired fins of all Pisces. They form a very characteristic
innovation diagnostic of the Class, and will be described below
(pp. 122 and 212).

Turning to the vascular system, we find a symmetrical heart lying
in a pericardium, situated ventrally, between the pectoral girdle and
the basibranchial plate underlying the oesophagus (Fig. 303). The
pericardial coelom is almost (Chondrichthyes, Chondrostei) or quite
(Teleostei, Lepidosteidae, Amiidae) closed off from the abdominal
coelom by a transverse septum. Here the right and left ductus
Cuvieri and the hepatic veins join to enter the sinus venosus. This
leads into a thin-walled atrium, opening into a muscular thick-
walled ventricle. There are two sinu-atrial and two atrio-
ventricular valves. The ventricle is prolonged forwards into a
contractile conns arteriosus, leading to the ventral aorta (Stohr
[426], Boas [38-39], Rose [373]). Inside the conus are rows of
semi-lunar valves (Fig. 69). In the more specialised Teleostei the
base of the aorta is swollen into a non-contractile bulbus, and the
conus is reduced to a narrow strip supporting only one row of
valves (p. 363).

As a primitive type of circulation we may take that of a
Selachian (Hyrtl, Balfour [27], Hochstetter [214-15], Dohrn
[114], Rabl [336], Parker [314-15]). The median ventral aorta,
morphologically a forward prolongation of that longitudinal ventral
' subintestinal ' vessel of which the heart itself is a specialised
portion (p. 26), and like that vessel developing from originally paired

PISCES

•^ "^ C.

t-, ^ tr oj

IlsFf

"I

». 25 rt -3 °

I -f *5

w <c o "

O ~ O Q OJ

'

VASCULAR SYSTEM

rudiments (Mayer [29 la]},
runs forward below the
branchial skeleton (Fig. 71). It
provides five afferent branchial
arteries, the first of which
passes up the hyoid arch
to supply its posterior hemi-
branch. These afferent vessels
and the efferent vessels are
partially derived from, and
replace, the embryonic com-
plete aortic arches, six in
number, running up the man-
dibular, hyoid, and succeeding
four branchial arches. The
paired rudiments of the dorsal
aorta unite to form a single
median vessel behind ; but in
front they diverge and join
again below the brain to form
in the embryo a complete
circle, the circulus cephalicus
(Fig. 72). It is this region
which receives the efferent or
epibranchial vessels. The con-
tinuity of the circulus is usu-
ally interrupted behind the
hyoid arch in later develop-
ment in Selachians, and indeed
in all Gnathostomes except
the Teleostei (Fig. 72). In
Selachians the circulus dis-
appears, the aorta becoming
single and median to below
the base of the skull (Fig. 71).
The mandibular arch also is
broken off below, with the

...ks.

rpv. -

rf)c.

intv.

FK.;.

Diagram of the venous system of Musteluis
antarcticiis (after T. J. Parker), ventral view, a,
atrium ; c, conus ; co.s, orbital sinus ; c.v, caudal
. , vein ; d.c, ductus Cuvieri ; d.c.v, hinder portion

development Of the ]aws, and of dorsal cutaneous vein ; /.», vein from pelvic fin ;

,1 j , • /• ,1 • i h.p.v, hepatic portal vein passing up into liver;

the reduction Of the SpiraCUlar ,Jt hyoid sinus; i.j, inferior jugular; «.», iliac

vein ; int.v, intestinal vein ; j.v, jugular vein ; k,
kidney ; I.e. v, right lateral cutaneous vein ; l.p.c, left
posterior cardinal ; l.v, lateral vein ; p.v.c.i>,posterior
ventral cutaneous vein ; r.p.e, right posterior car-
dinal; r.p.v, right renal portal vein; s, hepatic

slit, so that
region of the
much

vessels in this
head become
In most

tliP hvm'rl irrh i<? sinus; «p, spermatic vein ;" s<, stomach ;«, testis ;
u.7 ul a v, ventricle ; vn, vein joining portal to posterior

likewise interrupted below, cardinal.

and the hyoidean hemibranch

then receives blood only from the efferent vessel of the next

112

PISCES

branchial arch (p. 258 and Figs. 72, 220). The dorsal portion of
the mandibular aortic arch (anterior carotid) having lost its

artery; li.a, hyoid efferent vessel; up, nepauc veins; nt, IIBHIV, JI.K, uuavon
posterior efferent vessel ; s, spiracle ; v.a, ventral artery ; I-V, branchial slits.

connection with the ventral aorta, acquires a new supply of blood
for the spiracular gill from the efferent vessel of the hyoid arch.
It passes thence across the floor of the orbit, through the lateral

of3

Diagram of the branchial circulation of a Teleostean lish (modified from T. J. Parker), a. 6,
artery to air-bladde/- ; af 3-6, four afferent vessels from ventral aorta ; c.a, carotid artery ; c.c,
circulus cephalicus ; cl, coeliac artery ; d, ductus Cuvieri ; d.a, dorsal aorra ; efs, efferent vessel
of first branchial arch ; ep, epibranohial artery ; h.a, hyoidean artery (afferent vessel of pseudo-
branch) ; hp, hepatic vein ; ht, heart ; mis, mesenteric artery ; o.a, ophthalmic artery (efferent
vessel of pseudobranch) ; p$, pseudobranch (hyoidean gill, possibly with spiracular gill) ; s,
position of spiracle (closed) ; v.a, ventral'artery ; I-V, live branchial slits.;

carotid foramen, into the cranial cavity, where it joins its fellow
from the other side (front end of the original circulus cephalicus),
and gives off paired cerebral arteries and a median spinal artery.

VASCULAR SYSTEM

From the efferent vessel of the hyoicl arch springs also a posterior
carotid (internal carotid), which gives off a branch to the orbit, and
piercing the base of the skull, enters the pjtuitary depression of the

V,c.a*

>V.v.

IV'out

V.c.1.

y.a.

Veau.

\ ' cJO.

V.ccue,

V.cau

Diagrams of the development of the Venous System in the Selachian. (After Rabl and
Hochstetter, from Hertwig's Hundbuch.) Six stages. V.v, vitelline vein running into the left
omphalo-niesfinteric ; V.si, subintestinal vein ; F.cuu, caudal vein ; V.ca, anterior cardinal vein ;
l'.'-p, posterior cardinal vein ; I'.sy', vein of spiral valve ; ]'.d, external jugular vein ; }'s, sub-
clavian win ; Vir, interrenal vein.

cranial cavity. It joins the cerebral artery of the opposite side.
Segmental parietal vessels are given off by the aorta, and branches
to the limbs and viscera. Among the latter the coeliaco-mesenteric,
the coeliac, the lieno- gastric, the anterior, and the posterior
mesenteries are the most important.

8

ii4 PISCES

The post-cardiac portion of the embryonic subintestinal vein
contributes to the formation of the hepatic portal and renal portal
systems. It runs below the intestine, bifurcates to surround the
rectum, and joins again to a median caudal vein. This posterior
portion comes into connection with the hinder ends of the posterior
cardinals, and separates off from the intestinal portion (Fig. 73).
In front the subintestinal vein joins the paired omphalo-mesenteric
veins, forming a complete loop, which subsequently becomes broken
up into capillaries in the liver. The anterior ends of the loop
form the hepatic veins ; the posterior ends form the portal veins,
receiving blood from the remains of the subintestinal and from
other newly formed veins of the alimentary canal.

The cardinal veins receive the segmental parietal veins and
enter the ductus Cuvieri. The anterior cardinal of the embryo,
running ventrally below the spinal nerves, is partially replaced by
a large jugular vein (anterior cardinal sinus) passing forwards
outside the nerves to the head. This sinus sends a branch down
the hyoid arch, which joins the ventral inferior jugular vein (Fig.
70). The posterior cardinals, having joined the caudal vein, break
up in the adult kidney, or mesonephros, into the renal portal system
of capillaries. Two ventral longitudinal epigastric or lateral veins
unite just above the pelvic girdle, receive the iliac veins, then run
forward to open into the ductus Cuvieri, near which point they
receive the brachial veins (Figs. 70, 74).

A special yolk-sac circulation is established in the embryos of
those fish whose eggs are supplied with a very large quantity of
yolk. It may be entirely venous and derived from the sub-
intestinal vein (Teleostei, Fig. 75), or partly arterial and partly
venous (Elasmobranchs, Fig. 76). In the latter case are found a
vitelline artery — a branch of the aorta passing out to the yolk-sac
on one side — and a vitelline vein returning behind to the hepatic-
portal region of the subintestinal vein (Balfour [29], Ziegler [512],
Wenckebach [485]). In the Elasmobranch the stalk of the yolk-
sac comes off from the gut in front of the hepatic diverticulum ; in
the Teleostomes the yolk is situated farther back, on or behind the
diverticulum.

In the intestine of all living Pisces, excepting the Teleostei
(p. 362), is found a 'spiral valve'; it is a spiral infolding of the
wall provided with blood-vessels, and serving to increase the
absorptive surface (Figs. 77, 78 [Parker, 313]). Another primitive
structure is the cloaca — formed partly by the expansion of the
posterior end of the enteron, partly by an imagination from the
exterior. Into the cloaca open the rectum by the anus in front,
and the urinary and genital ducts farther back (Fig. 90).

Although it is not possible to give a satisfactory definition of
a large group like the Pisces, exhibiting such a wide range of

CHIEF CHARACTERS

structure, yet their chief diagnostic characters may be summarised

as follows : — The dermal
.dcv. skeleton is in the form of

denticles and scales. There
are median fins supported
by endoskeletal radials (som-
actidia) ; and paired limbs
of similar structure. All
these limbs are fins adapted
to aquatic life, and have
the web strengthened with

Transverse section of the trunk of Mnstelus
I'ntiif-tii-uf, Gthr. (after T. J. Parker), showing the
veins, i; abdominal coelorn ; cv, posterior car-
dinal; <?.((, dorsal aorta; d.c.v, dorsal cutaneous
vein ; d.i.v, dorsal intestinal vein ; i.i.v, internal
intestinal vein at edge of spiral valve ; l.c.v,
lateral cutaneous vein; l.v, lateral vein; m.v,
elonic vin.

H

FIG. 75.

Embryo of Gdbius. (After Wencke-
bach, from Hertwig's Handbuch.) A,
aorta ; H, heart ; V.c.a, vena cardinalis
anterior ; V.si, vena subintestinalis ; D.C,
cluctus Cuvieri.

dermal fin-rays (dermo-
trichia). An elaborate
system of lateral -line
organs extends over the
head and trunk. The
heart retains an un-
divided atrium, and
pumps venous blood into
the branchial lamellae
of the gill-arches. Not
more than eight gill-slits
are pierced, of which the
first is the relatively
small spiracle. As char-
acters which are con-
sidered primitive, but
are often lost through
specialisation, may be
mentioned : an uncon-
stricted notochord, a
diphycercal tail, a large
number of radials in the
median and paired fins, an amphistylic attachment of the jaws, a large

FIG. 76.

Torpedo embryo with yolk-sac. (After Riickert, from
Hertwig's Handbuch.) 1, vitelline artery; 2, vitelline
vein ; 3, remains of the peripheral sinus.

ii6 PISCES

number of uniform teeth succeeding each other throughout life, a
separate opening for each gill-slit, an optic chiasma, a contractile
conus arteriosus, a purely venous heart, a pericardium communicat-

B.

FIG. 7t.

A, stomach and intestine of Chiroccntrus dorab, Forsk., opened up to show the spiral valve.
B, three portions of the intestine of Alopius wipes, M. and H., cut longitudinally, c, caecum ;
c.w, cut wall ; e, entrance of pyloric end ; i, intestine ; p, pyloric end of stomach ; st, stomach ;
s.v, spiral valve. The upper piece is cut through on the near side of the middle line ; the
lower pieces through the middle line.

ing with the abdominal coelom, a spiral intestinal valve, a ' free *
ovary, a well-developed oviduct, and a cloaca.

The Pisces are such an ancient class, their remains having been
found even in the LoAver Silurian rocks, and so many side twigs of

CLASSIFICA TION

117

their phylogenetic tree have been pruned off by natural selection,
that the branches which survive to the present day can be easily
classified into well-defined groups. But when we come to deal with
the extinct forms, we are at once met with the familiar difficulties
in the construction of a phylogenetic system : the discovery of
intermediate forms ; apparent primitive simplicity due to degenera-
tion ; apparent close relationship due
to convergence.

In the eighteenth century, Artedi,
a friend of Linnaeus, founded the
modern classification of fish bydividing
them into three groups : the Chon-
dropterygii, the Malacopterygii, and
the Acanthopterygii. A great advance
was made in the first half of the nine-
teenth century in our knowledge of
the structure and classification of fish
by the publication of Cuvier and Valen-
cienne's Histoire Naturelle des Poissons
[95]. These authors separated all
the ' bony fish ' as one group from
the Chondropterygii. But among the
latter were still included the Cyclo-
stomes and the Sturgeons, with the
Elasmobranchs. A third epoch was
marked by the appearance of the
work of L. Agassiz on fossil fish [4].
Relying chiefly on the characters of
the exoskeleton, he divided the true
Pisces into Placoidei, Ganoidei,
Cycloidei, and Ctenoidei. The skin
of the first division is provided with
' placoid ' denticles ; that of the
second, with thick shiny bony scales ;
the third, with rounded, thin, over-
lapping, concentrically lined scales ;
the fourth, with similar scales bear- up

ing Spiny processes behind. Although T- J- Parker.) at, attachment of spiral
or<ji e valve ; c, rectal gland ; i, intestine ; i.f,

AgaSSlZ greatly forwarded the Study inner free edge of valve ; st, stomach.

both of living and of extinct fish,

yet his classification in these four orders is not natural. The
order Ganoidei included several unrelated but convergent forms,
such as Polijpterus, Acipenser, Ostracion, and Lepidosiren ; and
the separation of the Cycloidei from the Ctenoidei was very
artificial. Johannes Muller [307] united these two orders in the
sub-class Teleostei ; and purged the Ganoidei of the Dipnoi and of

Fio. 78.

Intestine of Zygaena malleus, opened
show the spiral valve. (After
- - 1

ii8 PISCES

the armour-bearing Teleosteans. Huxley [227-8], Cope [91], Zittel
[512], and others have since made important contributions. To
A. Giinther we are indebted for many improvements, especially in
the detailed classification of modern fish [189, 191]. His grouping
of the Pisces in the two sub-classes Palaeichthyes and Teleostei
does not express a phylogenetic division. The Palaeichthyes are
characterised by the possession of an optic chiasma, a contractile
conus arteriosus, and a spiral intestinal valve, as was shown by
J. Miiller, C. Vogt, and others. Now these are all primitive
ancestral characters in the class. They appear to have been lost
by the Teleostei, not to have been acquired by a diverging single
branch giving rise to the Palaeichthyes.

Modern advances in the taxonomy of fish are chiefly due to
Traquair [441-469], Smith Woodward [505], Gill [164-5], Boulenger
[40-42], and others.

Following, rather, the example of Cuvier, Valenciennes, and
Dum6ril [124], we divide the Pisces into two main groups, corre-
sponding to two diverging sub -classes, the Elasmobranchii and the
Teleostomi (see Table of Contents, p. vii). Undoubtedly the Dipnoi
either are a specialised branch of the Teleostomi or have, at all
events, been derived with these from a common ancestral stock.
The sub-classes Dipnoi and Teleostomi, therefore, form one division,
the Osteichthyes. With the Elasmobranchii are associated two
extinct sub-classes (Pleuracanthodii and Cladoselachii) ; together
these make up the second great division, the Chondrichthyes.
Between these two divisions may provisionally be placed an
assemblage of extinct fish, the Ostracodermi, whose affinities are
very imperfectly known. Another group of doubtful origin, the
Acanthodii, is provisionally retained with the Chondrichthyes
(Stannius [417], Huxley [229], Bridge [57], Brown Goode [64],
Jordan [250], Gregory [184], Hay [204]).

Sub-Grade I. CHONDRICHTHYES.

This is a provisional assemblage of fish which, speaking
generally, are lowly organised, and preserve several primitive
features. The normal optic chiasma, the contractile conus
arteriosus, and the spiral intestinal valve are all present in the
living forms.

True bone is never developed, either in connection with the
endoskeleton or in the form of superficial plates and scales. The
dermal exoskeleton is entirely composed of ' placoid ' scales or
denticles (except for the dermal fin-rays, p. 122, and Acanthodii).
Very rarely (Acanthodii, p. 189) bone-like tissue occurs, but it
appears to be merely calcified connective tissue. Occasionally the

DENTINE

119

bases of neighbouring denticles may fuse; in this way have probably
arisen the dermal plates sometimes found in fossil Chondrichthyes
(p. 168). The placoid scales (Williamson [496a], Hertwig [211],
Klaatsch [264]) are essentially hollow cones of dentine surround-
ing a pulp-cavity. Dentine, which forms the bulk of the hard

FIG. TO.

Successive stairs in the development of the denticles of the Dogfish, Scyllium canicula, L.
In A is seen the first gathering of the soleroblasts, sc, below the basement membrane, b.m ; in
C, the first deposition of dentine, d (black) ; in E, three stages (from right to lelt) in the
formation of the basal plate, it.jt. <-t, connective-tissue deep layer of cutis ; e, "enamel"
(white) ; ml, modified epidermal cells ; p, pulp-cavity. A-D, transverse, E. longitudinal
section, enlarged.

tissue of the teeth of all Gnathostomes, is of mesoblastic orgin.
It is secreted by the odontoblasts lining the pulp -cavity, and
consists of a hard calcified matrix traversed by a multitude of
minute nearly parallel canaliculi (dentinal tubules) with delicate
branches. No cells are included in the dentine, but fine processes
of the odontoblasts extend up the canaliculi (Figs. 79, 81). The

120

CHONDR1CHTH YES

first appearance of dentine takes place immediately beneath the
epidermis, in direct continuity with the basement membrane, of
which it may be considered to be a thickening (Fig. 79, A-D). It
is secreted by a group of mesoblastic cells (odontoblasts), the rudi-
ment of the future dental papilla or pulp. Dentine differs from
bone not only in that it contains no cells, but also in that it grows
on one surface only — the surface next to the dentinal pulp. As
a rule, the base of the dentine cone spreads inwards into the
underlying connective tissue, and may change in structure from
true dentine to a looser kind of trabecular calcified tissue. A
'basal' plate' is thus formed, which tends to cut off the pulp-
cavity below, leaving only one or two narrow openings whereby

B

FIG. so.

Median dorsal denticle of Raja tlamla. A, left-side view. B, section much enlarged. 6,
basal plate ; d, dentinal tubules ; o, opening of pulp-cavity, p.c ; s.p, projecting spine ; tr,
modified trabecular dentine.

the blood-vessels, nerves, and lymph-channels can pass through.
The distal region of the denticle breaks through the epidermis and
emerges freely on the surface. It is covered with a shiny enamel-
like layer. Of the real nature of this layer observers are still
uncertain. According to Leydig and Rose [372], it is a special
outer zone of vitrodentine, with very fine canaliculi. It does
not appear to be true enamel, secreted by the epidermal cells, such
as is found on the teeth of higher vertebrates. Tomes [439]
believes it to be formed by the combined action of the epidermis
without and the odontoblasts within.

We may here briefly describe the chief varieties of dentine found
in fish (Tomes [438, 440], Rose [372], Owen [31 la]). They may
be classified as follows : typical dentine, with numerous canaliculi
radiating from a central pulp-cavity (Fig. 79); plicidentine,

TEETH

121

folded dentine developed round a pulp with outstanding ridges
(Lepidosteus, Fig. 81, B) ; vasodentine, with branching pulp-
channels, but few or no canaliculi (Merlucius, Fig. 81, A); osteo-
dentine, or trabecular dentine, with anastomosing branches of
the pulp-cavity (Esox, Fig. 81, C; Lamna) ; vitrodentine is
the name given to the outermost enamel-like layer generally
found on Elasmobranch teeth and denticles, as described above.
Intermediate forms exist between these varieties, and occasionally

FIG. 81.

A, section through a tooth ami jaw of the Hake, Mfiinrlux i-iili/nri*. (Partly after Tumi's.)
H. transverse section of the tooth of l.i'ii!ilii*t<'tix. C. enlarged view of a small piece of the tooth
of Esox 7('i'iii.«. 1, enamel tip; 2, vasodentine; 3, elastic ligament; 4, bone of jaw; 5, free
outer edge of tooth-base ; 6, bone of attachment forming socket for tooth-base ; 7, pulp-cavity;
S, dentine layer at .surface of tooth ; 9, osteodentine canals ; 10, folded wall of dentine.

dentine may come to resemble bone, with laminae and enclosed
cells.

The placoid scales do not indefinitely increase in size. New
denticles may develop from fresh ' germs ' between the old ones,
and these when old and worn out may be shed (Steenstrup).

Along the inner margin of the jaws, the teeth, which are merely
specialised denticles, arise at the bottom of a deep dental groove
(Fig. 39). Here new generations of teeth are continually being
produced, and as they grow older they move up to the biting edge
of the jaw, pushing the older teeth before them. Thus the old

122

CHONDRICHTH YES

Fio. 82.

Baja tlanda, Holt. c;>, surface of the cartilage,
showing prismatic calcifications, ct.

and Avorn teeth drop off, and are replaced from behind by new
ones.

The teeth, in Elasmobranchs, and indeed in all Chrondrichthyes
excepting the Acanthodii, are not firmly fixed to the jaw, but are
merely attached to the cartilaginous jaws by connective tissue.
They may become much specialised in structure and disposition,
leading to the development of a highly characteristic dentition in
various groups. Occasionally several tooth-germs may fuse to form
compound teeth. Large specialised denticles may also be found on
the body. Among these are to be reckoned the powerful spines,

which often occur in front
of the fins (Markert [291]).
In some cases (dcanthias,
Fig. 50) these are merely
large hollow cones of the
ordinary structure, resting on
a cartilaginous radial.

The endoskeleton remains
cartilaginous ; but is often
strengthened, especially on
its surface, by the deposition

c palpa,,prmg colfe rypnprallv

cAicaieous salts, generally
in the form of prismatic plates
(Fig. 82). In living Chondrichthyes the notochordal fibrous sheath
is always invaded by the surrounding mesoblastic layer (p. 99,
Fig. 60). The median fin-folds are always more or less subdivided,
and the caudal fin usually becomes heterocercal. The vertebral
column extends to the extremity of the dorsal lobe.

Both the median and the paired fins are provided with very
numerous horny fin-rays, or ceratotrichia. This is one of the most
characteristic features of the group (Mayer [297], Klaatsch [264],
Goodrich [175]). The ceratotrichia are slender, unjointed rods of
homogeneous fibrous substance secreted by the mesoblastic cells.
As a rule, they are very much more numerous than the underlying
somactidia. At the growing distal edge of the fin they are seen to
originate immediately below the basement membrane. But later on
they sink into the connective tissue, and to their proximal ends
are attached the radial muscles of the fins. The ceratotrichia are
developed on both sides of the fins, and proximally embrace the
ends of the median cartilaginous radials (Fig. 83).

In all the living Elasmobranchs, except the highly specialised
Holocephali, the gill-slits always open to the exterior independently.
This was probably also the case in the extinct Chondrichthyes (with
the possible exception of the Acanthodii). Where the gill-septum
reaches the surface, a strip of the ordinary denticle-bearing skin
passes between the openings (Figs. 26, 57).

CLASSIF1CA TION

123

d

The number of branchial slits is larger in some Chondrichthyes
(Xotidani) than in any other Pisces, and this may be a primitive
character. We find, also, that
among the least differentiated and
earliest representatives the upper
jaw(palato-quadrate) is of ten broad
behind, and articulated by an otic
process to the auditory capsule.
It is possible that this amphistylic
type of jaw-articulation was pos-
sessed by the common ancestor
of the whole group of Chondrich-
thyes (p. 95). In the Elasmo-
branchii, and apparently also in
the Pleuracanthodii, the gill-septa
are supported by a single posterior
series of cartilaginous gill-rays
(Figs. 57, 99). If, as seems prob-
able, a similar single series of rays
existed in the Cladoselachii, this
character might distinguish the
whole Division from the Osteich-
thyes, in which there are two
series. But there is some reason
to believe that this was not the case
in the Acanthodii (p. 190).

The Chondrichthyes retain
most of the structures mentioned

1 , . i ...

above as being Characteristic OI

primitive fish; the absence of true
bone, of scales other than den-
ticles, and the formation of the jaws from the palato-quadrate bar
and Meckel's cartilage, distinguish them from the rest of the Pisces.
The classification of the Chondrichthyes still presents many diffi-
culties. The first two sub-classes described below (Elasmobranchii
and Pleuracanthodii) have many characters in common, and are
distinguished from all other Pisces by the development in the male
of copulatory 'claspers.' These are specialised posterior portions
of the pelvic fins. It seems very unlikely that the claspers should
have been developed independently in the Elasmobranchs and in
the Pleuracanthodians.1 At the same time, to unite these two
groups into one sub-class would perhaps be to separate them too far
from the Cladoselachii. Until the structure and affinities of the
latter are better understood, it cannot be decided whether they are

1 For a discussion of the morphology of the skeleton of the paired fins, see
pp. 73, 106 ; for the copulatory claspers, see p. 129.

FIG. 83.

Diagram of a section through the dorsal
tin of >'<•!/// ijnn. ct, ceratotrich ; <?, denticle ;
•c, emloskeletal radial. (From Quart. Journ.

I24

CHONDRICHTH YES

Elasmobranchs which have lost the claspers, or an early offshoot

II! fJI/g^ jfi/ t /
/'''' / If /as ///'''''' ^ / I

-J~--

-ill Pleuracanrhodii
- /Cladoselachii

Acanrhodii

Chondrichrhyes

DIAGRAM II.

Diagram illustrating the Phytogeny of the Chondrichtliyes, and their distribution in the
:eological strata. Ihe actual range of distribution is shown in black ; the dotted lines indicate
hypothetical connections.

sprung from the Chondrichthyan stem before claspers were developed.
The affinities of the Acanthodii are still less clear.

ELA SMOBRANCHII 1 2 5

Sub-Class 1. ELASMOBRANCHII.

The mouth is never quite terminal, a rostrum of considerable
size, supported by cartilaginous processes of the skull, being
generally produced in front. The two palato-quadrate cartilages
meet below the skull in front. The nostrils are more or less
ventral, in front of the mouth, and are incompletely subdivided
into anterior and posterior openings by a small flap (Figs. 114,
117). They lead into wide nasal cavities with two rows of olfactory
folds. A fronto-nasal process grows down between the nostrils in
the embryo, and either fuses with the upper lip so as completely to
separate the nostrils from the mouth (Fig. 114) or its edges form

Fio. S4.

Portion of the snout of tri/llium in .section, showing unpnllaxy tubes. (After GegenUant.
from Sedgwick's Zoology.) «, ampulla ; id, passage of a tutu- through the dermis ; <•, epidermis ;
c1, derrnis ; n, nerve; n, external openings of tu lies ; /, tube.

two deep grooves running from the mouth to the nostril on each
side (Fig. 103). The latter system, with 'confluent' nostrils,
appears to be the most primitive, and is found both in the Selachii
and in the Holocephali. The auditory vesicle often remains open
to the exterior by a narrow ductus endolymphaticus, even in the
adult (Fig. 13), and the sacculus contains a mass of small otoliths.
The eye, enclosed in a cartilaginous sclerotic, has a pigmented
tapetum, but the ventral ciliary process attached to the lens is
small ; it contains a muscle for accommodation (Fig. 346).

The distribution of the lateral-line system on the head, fairly
constant among the Selachii, may here be described (Figs. 11, 85).
The main lateral line of the trunk runs forward on to the head,
where it may give off a transverse occipital branch ; continuing as
a short temporal canal and a postorbital canal, it divides into a
dorsal supraorbital and a ventral suborbital branch extending on
to the snout. Portions of a hyomandibular and mandibular canal
are also present, though generally interrupted (cp. p. 220, and Figs.

126

ELASMOBRANCHII

85 and 196, where the nerve-supply of these canals is given). The
very characteristic groups of sensory ampullae, supplied by the
facial nerve (Fig. 84), are distributed on the head, as shown in
Figs. 11 and 85. These deep-seated organs communicate with the
exterior by long tubes opening by conspicuous pores on the surface
(Fig. 84).

Among the characteristic features of the brain one may mention
the following. The prosencephalon (Fig. 7) is large, of paired
origin, and may contain paired cavities, but shows little or no sign
of external division, especially in the Rajiformes. The thickened
floor and wall of the telencephalon merges in front with that of the

trf. gl.

scf.

soa.

iba.

nc

f.ba. nix.

FIG. 85.

Diagram of the head of Laemargus, showing the cranial nerves and sense-organs. (After.Ewart
and Mitchell.) The lateral-line canals are indicated as in Fig. 196, p. 222. a, auditory labyrinth ;
ad, auditory nerve ; 6, bnccal branch of facial ; c, ciliary ganglion on branch of oculomotor ;
e, eye ; g, epibranchial ganglion on branch of vagus ; gl, glossopharyngeal ; li.u, hyoid group
of ampullae of Lorenzini ; hm, hyomandibular branch of facial ; i.ba, inferior group of ampullae ;
i.v, intestinal branch of vagus ; l.l, lateral-line canal of trunk ; l.v, lateral-line branch of vagus ;
m.a, mandibular group of ampullae ; mx, maxillary branch of trigeminal ; n.c, nasal sac ; ob.a,
suborbital group of ampullae ; p.o, pit-organ ; pr, profundus ; p.tr, post-trematic branch of
branchial nerve ; s.o, superior ophthalmic branch of trigeminus ; s.o.a, superior group of
ampullae ; s.o./, superior ophthalmic branch of facial ; sp, spiracle ; st.v, supratemporal branch
of vagus ; t.r.f, roots of trigeminus and facial ; v, vagus root ; I-V, five branchial slits.

prosencephalon, obliterating the thin lamina terminalis, and forming
a mass of nervous tissue covering the sides, front wall, and roof of
the telencephalon (Figs. 7, 86). It is into this often immensely
developed prosencephalic mass that the lateral ventricles project.
At the sides, or in front, arise large diverging olfactory lobes ; these
may either be near the cerebrum or they may be drawn out into
long olfactory tracts, expanding anteriorly into olfactory bulbs close
to the nasal capsules. The epiphysis is long, and reaches forwards
in Selachians to below the superior fontanelle of the skull ; but
there is no pineal eye. As in many other fish, the lobi inferiores and
saccus vasculosus are well developed in the infundibular region.
The cerebellum is very large and often convoluted ; the restiform
bodies, at the sides of the medulla, may also be prominent.

PAIRED Fh\S

127

The phosphorescence of Elasmobranchs, mentioned by Aristotle,
appears to be clue to special little organs scattered over the skin
(Burckhardt [71], Johann [246]).

The median fins are always subdivided; the caudal is heterocercal
in internal structure, though the axis is almost straight in many
living sharks.

The endoskeleton of the paired fins is very variable in detail,
owing to concentration and fusion of the radials (somactidia). A
large number of segments contribute to their formation — generally
ten or more. The pectoral fins have a well-marked outstanding
muscular lobe, supported by a rhipidostichous skeleton (p. 106).

Gegenbaur, in 1865, attempted to show, in an important work

cer

.III

fel

.te

tuberculuni acusticum ; tel, telencephalon ; t.m, tectum mesencephali ; v, velum transversum

[153], that the ground-plan of the pectoral-fin skeleton consisted of
three basal pieces, the pro-, meso-, and metapterygium, articulated
to the girdle, and each bearing a number of radials. Later, he
compared this skeleton to the ' archipterygium ' of Ceratodus [157].
The pro- and mesopterygium were considered to be formed by
the fusion of the basal joints of the preaxial radials. The meta-
pterygium, on the contrary, with sometimes some distal elements,
was supposed to represent the original axis. Vestiges of postaxial
rays are occasionally found (Fig. 53). The metapterygium was held
by Gegenbaur not to be formed by concrescence.

This distinction, drawn between the posterior and largest basal
(the metapterygium) and the others, does not seem to be justified
either by comparative anatomy or by embryology. Indeed, Huxley
[230] identified the original axis in the mesopterygium. All the
basals are probably formed by concrescence, and an endless variety

128

ELA S MO BRA NCHII

of detail is presented by the different families and genera. There
may be a single basal, as in Scymnus (Fig. 53, A); two basals, as in
Heterodontus and Chimaera (Fig. 54, A) ; three, as in Scyllium or
Acanthias ; or five, as in Myliobatis. In the Rajidae, also, an anterior
axis develops quite similar to the metapterygial axis (Fig. 121).

The pelvic fin is much less completely constricted off than the
pectoral ; its skeleton is simpler. In the Selachii, the fanlike

A.

B

pro. '

prr.

pr.

Skeleton of the pectoral arch and fin of A, Clatlod-us Neilsoni, Iraq. ; B, Chlamytloselachus
anguineus, Garman ; and C, Symmorium reniforme, Cope. (A restored from Traquair's figure, B
and C after Braus.) c, coracoid region ; d.b, distal basal or 3rd segment of metapterygial axis ;
d.n, diazonal nerve foramen ; /, problematical fin outline ; j, joint between girdle and tin ; ms,
mesopterygium ; mt, inetapterygium ; n, nerve foramen; p.r, posterior preaxial radial ; pro,
propterygium ; pr.r, anterior preaxial radial ; pt.r, possibly postaxial radial ; s, scapular region ;
ta, distal segment of metapterygial axis.

arrangement of the radials, although to some extent visible at
the posterior end, is never as pronounced as in the pectoral fin.
Except for a few radials which may articulate with the girdle,
the single series is attached to one longitudinal basal, the basiptery-
gium, lying in the body -wall. Postaxial rays, if ever present,
have disappeared, leaving but occasionally a doubtful remnant
(Figs. 96, 101). The pelvic fin is almost or quite monostichous.

The articulation of radials to the pelvic girdle in front of the
metapterygium is doubtless a primitive character ; it is an indication

CLASP ERS

129

of the derivation of the girdle from the base of the radials, and is
conspicuous in the Pleuracanthodii (p. 181), in the Notidani, and
to a less extent in many sharks, but is lost in the Dipnoi. The
Holocephuli, however, have the radials of the pelvic fin radiating
from the edge of a single basal plate, like a fan (Fig. 54, B).

The fossil Elasmobranchs give little or no help for the interpre-

bw.

,P

sty-.

Dorsal view of the i*lvie girdle ami tins of a male Ai-iuithing i-ul<niri*, Ki.sso ; the skeleton
has been exposed on the right side. />, axial cartilage of clamper ; b}>, basipterygitim ; l>.w, cut
body-wall ; o, dorsal covering plate ; e, ventral plate ; h, hook ; os, opening of glandular sac ;
]>, pelvic girdle ; pr, propterygial, or anterior basal ; pt, posterior radial ; fir, pelvic fin ;
r, modilied radial ; .«, outline of glandular sac embedded in body-wall dorsal to girdle ; sty,
hard style.

tation of the skeleton of the paired fins. The fact that the pectoral,
as a rule, differs so much from the pelvic, shows that one, or
both, have departed considerably from the primitive type
(p. 108).

AVe may here describe the modifications of the skeleton of
the pelvic fin brought about by the development of the " clasper,"
mixipterygium, or copulatory appendage of the male (Gegenbaur
[155], Petri, Jungersen [254-5], Huber [222]). The pelvic fin-

9

ELA SMOBRA NCH1I

fold is produced at its hinder margin into an outstanding lobe. The
basipterygium is continued backwards into this lobe as a cartilage
rod, consisting, as a rule, of two short anterior and one long
posterior segment. A dorsal groove carrying the skin with it is

sty

FIG. 89.

Raja Wanda, Holt. Dorsal view ; the cartilaginous skeleton has been completely exposed
on the right side, a, b, c, d, f, cartilages of clasper ; a.l, anterior lobe of pelvic fin; '//>.
basipterygium ; d, clasper ; c.p, covering-plate ; i.p, iliac process ; o.s, opening of sac ; p, pelvic
girdle ; p.p, prepubic process ; pr.r, enlarged preaxial radial ; pt, posterior preaxial radial ; x,
dotted line indicating ventral glandular sac ; st, second segment of basipterygial axis ; sty,
styliform cartilage.

developed along this terminal piece, which becomes hollowed out to
receive it. The edges of the cartilage are rolled round so as almost
completely to enclose the groove in a split tube open at both ends
(Fig. 88). Spermatozoa may pass in at the front and out at the
hind end. The internal tegumentary tube projects forward as a
blind sac, and from its wall develops a special gland. The main

I'RINOGENITAL ORGANS

cartilage is usually produced into a sharp calcified style, near which
terminal pieces are developed (Fig. 88).

Among the Selachii, Huber distinguishes three main types of
modification of some importance in classification. Type A : with

Kic. IK).

B.

A, Urinogenital system of the female, 1), of the male dogfish (.s-r//Mi<u;i). ali.fi, abdom-
inal pores ; d, cloaca ; <-i>, claspors of the male ; /, rudiment of the oviducal opening in
the male ; Ifd, metutephiic ducts ; mtn, metanepbros ; od, oviduct; oe, cut end of oesophagus ;

o.g, oviducal gland; oi>, ovary; /'./, pelvic fins; ;;, rectum; x.x, sperm-sacs ; T, testis ; «.//.
urinary papilla in the female ; ug.p, urogenital papilla in the male ; u.s, urinary sinus ; ii.e, vasa
ril'i'nnitia ; r.x, v.'sicula seminalis ; H'.rf, Wolttian duct: II'.;;, Wolllian gland or mesone[iliros.
< After <;. C. Hourne.)

n prominent hard terminal style, piercing the skin ; a tegumentary
fold partially covering the groove ; and the whole internal cavity
glandular. Type B differs from the former in having the tegu-
mentary fold inside, the overlapping edges of the main cartilage
more developed and turned in, and the terminal cartilages reaching
to or beyond the end of the style. Type C : the gland is
specialised and of tubular structure ; and one, two, or three of the
accessory pieces form flattened sheathing-plates (Fig. 89). Type A

I32 ELASMOBRANCHII

occurs in the Notidani, Heterodonti, and Squaliformes ; Type B
in the Scillioidei ; Type C in the Rajiformes. The copulatory
appendage of the Pleuracanthodii seems to have been of very
similar structure ; but that of the Holocephali acquires a trifid
instead of a tubular main cartilage (p. 174).

The primitive optic chiasma, conus arteriosus with valves, and
spiral valve are all retained in living Elasmobranchs. Except in
Chlamydoselachus, which retains a single efferent A'essel as in the
embryo (Ayers [24]), the gill-bearing branchial arches are provided
with two efferent vessels. The posterior of one arch joins the
anterior of the next, above the slit, to form the epibranchial artery
(Fig. 71).

The mesonephric kidneys are differentiated into an anterior
' genital ' region and a posterior excretory region (Fig. 90). The
latter, which is sometimes called the metanephros, is large and
normally developed ; but its collecting ducts become to a great
extent separated off from that of the front tubules, and in the
male may join to a single duct or ureter on each side. They open
into the base of the mesonephric ducts, which join to a median
sinus in both sexes (Fig. 90). The excretory tubules of the
anterior region of the kidney are relatively unimportant. In
the male the mesonephric duct swells to a seminal vesicle behind,
and forms a coiled epididymis in front, receiving the vasa
efferentia from the testis. The urinogenital sinus receives the
seminal vesicles and the ureters in the male, and in the Selachii
is continued forwards in paired blind 'sperm-sacs.' The urino^
genital papilla opens into the cloaca behind the anus.

The large oviducts of the female open independently into the
cloaca between the anus and the urinary papilla (Fig. 90). Their
anterior coelomic funnels join to a common ostium on the ventral
surface of the oesophagus and in front of the liver.

The Mullerian duct (oviduct) is developed in both sexes, re-
maining as a vestige in the adult male. It is derived from the
pronephros (Balfour [27], Rabl [337]). The rudimentary pronephric
funnels combine to one opening, shifting backwards to a position
behind the pericardial septum (p. 90). The duct is split off from
the archinephric duct, which thus becomes divided into an oviduct
or Miillerian duct, and a mesonephric or Wolffian duct. As a rule,
the egg is large, heavily laden with yolk ; fertilisation is internal,
and cleavage meroblastic. A large narrow-stalked yolk-sac remains
for a considerable time protruding from the ventral surface of the
embryo, often even after birth. A lobe of the yolk-sac may also
lie in the abdominal coelom. The vitello-intestinal duct arises from
the anterior end of the intestine.

A characteristic horny case, secreted by a special glandular
region of the oviduct (Fig. 91), and containing an albuminous

DE VELOPMENT

'33

FIG. 01.

K^.us ami egg-cases of iishe<. (l-'pjm Dean.) A. ]}iii!ln*tiniin, ex.--''ase : B, upper pale of
Ilic same shouin- hooks and inirropyli.' (after Avers): ('. J/./wine (after Steeristrup) ; D, a
prut-ess of the same: K. retrunin-.im mnrinus; F. >'••/////«»( (after (liintlier); G, Raja; H,
//•(< i-iMliiiitna (after Gunther) ; 1. t'«U<n'h fim-lt »>• (after Gunthi-r) ; ,J. ' V ;•<«/, »/».< (after Semon) ;
K. Li'iiidnxt: Kg; i.. .l,-;,i, •„>•, ,• ; M , .lri»v. showing larva (after G anther) ; X, Sc minus ', O, .-(Zosa ;
P, Bleaiii".--. e^-.capsnlcs attai-hed : Q, the sanu- enlarged (aftei- Guitel).

'34

ELASMOBRANCHII

fluid, surrounds the egg when it is laid. In Laemargus, however,
fertilisation appears to be external, and the eggs are comparatively
small. This is probably a secondary modification.

Many Selachians are viviparous. In these, the egg-case becomes
reduced to a thin membrane (Mustdus) or disappears altogether
(Torpedo), and the wall of the oviduct develops bunches of
secreting villi or cotyledons (Dnme'ril [124]). While the embryo
Trygonid or Myliobatid takes in the nutritive fluid through its

V:

cw.'

-sp.

IV.

c.

FK;. !>•_>.

I'tcroftfatea micrvra, Bl. Sclin. Portion of oviduct opened to show the embryo insitir.
c.ic, cut Avail of oviduct; t, embryo; i.v, internal wall with villi ; od, oviduct : .«;•, spiracle of
embryo ; v, long villi entering spiracle.

mouth or spiracles, in Pteroplatea (Wood-Mason and Alcock [6,
498]) the maternal villi actually penetrate through the spiracles
into the alimentary canal of the embryo (Fig. 92). In some of the
Selachians with villate oviducts (Mustelus, Carcharias) an intimate
connection is established between the wall of the oviduct and the
highly vascular yolk-sac. A placenta is thus formed in which
maternal villi fit closely into corresponding crypts in the embryonic
yolk-sac (J: Muller).

A number of gill-lamellae become elongated into threads,
projecting to the exterior as transitory larval external gills, and
may serve as organs of absorption (Fig. 76).

S EL AC H II 135

The Elasmobranchs are distinguished by the possession of a
heterocercal tail, ventral nostrils only incompletely subdivided by a
flap, a single series of cartilaginous branchial rays on each arch,
ampullary organs, a brain in which the front wall becomes much
thickened, a copulatory clasper in the male, an oviducal gland in
the female which secretes a horny egg-capsule.

The sharply divided orders, Selachii and Holocephali, into
which the Elasmobranchii are at the present day classified, appear
to have been already well marked in Devonian times. The
modern Holocephali are highly specialised in many respects, but
possess all the essential characteristics of Elasmobranch structure.
On the other hand, they differ fundamentally from the Dipnoi,
with which they have sometimes been associated on account of
a vague resemblance between the two groups in the skull and
vertebral column.

Order 1. SELACHII.

In this order, which includes the most primitive of living fish,
the spiracle, and the hemibrauch on its front wall, are generally
preserved. The branchial slits always open independently to the
exterior, and are placed primitively in front of the pectoral girdle.

The cartilaginous brain-case is large and very complete, except-
ing for an anterior dorsal fontanelle (Fig. 93). The two orbits
often communicate by a canal through the floor in the pituitary
region. The optic capsule may be connected with the cranium by
a cartilaginous peduncle. The intracranial notochord is usually
much reduced and a definite occipital joint becomes established
(Gegenbaur [153], Parker [318]).

The notochord becomes much constricted by the mesoblastic
cells invading the sheath (p. 99), and vertebral centra are almost
always developed (Goette [167], Hasse [200], Klaatsch [265])..
These are usually strengthened by special calcifications, which
first take the form of a constricted cylinder (Fig. 50) developed* in
the inner layer near the notochord. There may be added radi-
ating longitudinal lamellae between the bases of the arches (Fig. 94),
or concentric cylinders outside the original one (Fig. 52). Hasse
called these three types the cyclospondylous, asterospondylous, and
tectospondylous respectively, and classified the Selachii accordingly
(Fig. 95). That these characters of the centrum are of consider-
able taxonomic value there can be no doubt, but the distinction
between the various types does not seem to be as clear and sharp
as was supposed. Both radiating and concentric calcifications may
be plainly shown in the same vertebra (Cetwhinus). The radiat-
ing calcifications may be developed centrifugally from the primary
cylinder (most Scyllioidei), or they may grow inwards centripetally

136

SELACHII

from the outer layer (Raja). This outer layer is sometimes, at all
events, formed outside the elastica externa, by a spreading out of

IV.

ecu.

FIG. 03.

Inner view of the right half of the skull of Hexanchns. (After Gegenbaur.) a/-, foramen for
auditory, gp, for glossopharyngeal, o, for optic, ocn, for spino-occipital, om, for oculomotor,
tg, for trigeminal, tr, for troclilear, vg, for vagus, and vs, for occipit.o-spinal nerve ; a.p,
antorbital process ; t, carotid foramen ; en, interorbital canal ; MI, membrane over fontanelle ;
r, rostrum.

the bases of the arches, which finally meet round the notochordal
centrum. A compound centrum is thus formed, partly 'perichordal'

rU dr.

FIG. 04.

LaniiM cornubicu, Gm. A, portion of the vertebral column of the trunk, partly cut longi-
tudinally (right-side view). B, transverse section of the same through the middle of a centrum.
c, centrum ; cu, calcareous constricted ring ; d.r, foramen for dorsal nerve-root : ]ia, basiventra] :
in, interdorsal ; iv, interventral ; li, ligament ; na, basidorsal ; n.c, neural canal ; nt, notocliord ;
r.ca, radial calcifications ; v.r, foramen for ventral root ; w, intervertebral ligament.

and partly 'chorda!' (p. 100). The ventral root of the spinal
nerves, as a rule, comes out either behind or through the neural
arch (basidorsal) ; the dorsal root either behind or through the

SKELETON

137

intercalary (interdorsal). In the caudal region there are generally
two centra and two sets of arches to each segment (marked by one
pair of myotomes and
of spinal nerves) ; this
diplospondyly probably
ensures greater flexibility
in the tail (Hasse [200],
Kidewood [361]).

The dorsal ribs are
often well developed in
the horizontal septum :
of separate pleural ribs
only traces are perhaps
found in the anterior

Caudal region (p. bb). Diagrammatic transverse sections of vertebrae, to

illustrate the, A, cyclospondylous, B, tectospondylous,
and ,C, aateroapondylona condition. C, notochord ; D,
central calcareous ring; E, elastica externa ; N, neural,
and 11, haemal arch. (After Hasse, from Sedgwick's
Zoology.)

l-'ic;. 95.

fins

The dorsal tins are
always much concen-
trated ; the skeleton may
be either far removed

from the vertebral column (Sci/Uimn) or closely connected with it
(Raja, Fig. 49 and p. 105).

The pectoral girdle consists of a cartilaginous bar with a well-
developed dorsal scapular region and a ventral coracoid region.
Ventrally the two halves are either fused or joined together by
fibrous connective tissue. A varying number of diazonal nerves
pass through the girdle to the fin.

The two halves of the pelvic girdle fuse together in the mid-
ventral line to form a transverse bar (Fig. 96), generally pierced by
nerves. The pelvic girdle, on the whole, appears to have undergone
reduction, and almost all trace of a dorsal iliac process has vanished
in the sharks.

The hyomandibular is large. The jaws are movably articulated
to the cranium, the suspensorium being hyostylic, in all modern
forms except the Notidani (p. 96).

The lateral-line system of sense-organs, on the head and trunk,
sinks below the skin into a tube, which remains in communication
with the exterior by short canals between the sense-organs
(Fig. 97) (Kwart and Mitchell [134], Garman [148]).

A dorsal thick-walled coecum, the rectal gland (Fig. 78), is
present at the hind end of the intestine (Howes [220]).

Except in Chlamydoselachus, the branchial arches of the Selachii,
like those of the Dipnoi, have two efferent arteries (Fig. 57),
and, further, the epibranchial arteries differ from those of other
Pisces in that they correspond to the slits and not to the bars, being
formed by the union of a posterior efferent vessel of one bar with
an anterior efferent vessel of the bar next behind (Fig. 71).

138

SELACHII

One may diagnose the Selachii as : Elasmobranchs with sub-
divided and much concentrated median fins ; a constricted noto-

. %.

Ventral view of the pelvic girdle and fins of //<>/".«•/, us ,-;,iei-Kit.t, (Jin. Tlie .skeleton is com-
pletely exposed on the left side. 6, basipterygium ; tir, web of (in supported by ceratotrichia ;
fi, pelvic cartilage ; pr.r, series of preaxial radials. (From Quart. Jonrn. Micr. >SVi.)

chord, an invaded notochordal sheath, and centra, if present, of
chordal origin ; dorsal ribs ; the two halves of the pelvic girdle

FIG. 97.

Diagram of the lateral-line canal of a Selachian seen in a section vertical to the surface.
ep, epidermis; l.c, longitudinal canal; I.n, lateral-line nerve; <>, opening of branch canal on
surface ; s.o, sense-organ.

fused together ; a wall between the cavity of the auditory capsule
and of the brain-case, a large hyomandibular cartilage ; epibranchial
arteries corresponding to the branchial slits ; gill-slits opening
separately to the exterior ; and a rectal gland.

The Selachii may be divided into two groups. In the first, the

NOTIDANi

139

attachment of the jaws is more or less amphistylic, the branchial
slits are six or seven in number, and there is only one dorsal fin.
In the second group, the jaws are attached in modern forms on the

Diagram of the branchial circulation of an Elasmobranch fish (modified from T. J. I'arker).
/'.'i, median anterior prolongation of aorta; n,.r, anterior carotid, efferent v.-ssel of spiracular
-ill (pseudobranch) ; n.ef, efferent vessel from last hemibranch ; «./, anterior efferent vessel ;
a/--8, live afferent vessels from ventral aorta ; a/.ci, afferent artery of spiracular gill : <:, conns
leading to ventral aorta ; <•/, coeliac artery ; d, ductus Cuvieri ; d.a, dorsal aorta ; </, epi branchial
artery; //.". hvnid efferent vessel; hp, hepatic veins; lit. heait; />.c, posterior eurotid ; ;>.'•/,
l>osteri">r efferent vessel ; s, spiracle: c.«, ventral artery ; I-V, branchial slits.

hyostylic plan, there are not more than live branchial slits (with one
exception, p. 152), and there are two dorsal fins (Miiller u. Henle

D

Diagram showing the principal modifications in tlx- arrangenifiit of the hyoid arch in th«
Si lachii. (After Gegenbaur, from Sedgwick's Zwlogy.) A, in Htptaildnu ; B, in a shark ;
C', in Torpedo; D, in Rnj«. llm, hyornandibular ; Ini, lower part of hyoid arch; ;>, prwcss
support ing .jaw --articulation ; r, branchial rays.

[308], A. 8. Woodward [505], Dunu-ril [124], Regan [346], Jaekel
[238], etc.).

GROUP I.

Sub-Order 1. NOTIDANI.

These sharks have a skull and jaw apparatus built on the
amphistylic plan. In Heptanchus, the palato-quadrate is firmly

140 SELACHII

articulated to the auditory capsule by its otic process (Fig. 59, A) ; in
HexancJms, the articulation is looser; finally, in Cklamydoselachns,
the otic process, though large, does not quite reach the skull.
The gape of the jaws is very wide ; the hyomandibular is elongated
and directed backwards. The palato-quadrate bars have a basal
process placed far back, and are only loosely joined together in front.
There is a long occipito-spinal region, behind the vagus foramen,
the skull not being clearly marked off from the vertebral column
(Fig. 93). There is no triradiate rostral cartilage, and the floor of
the orbit is not cartilaginous. The nostrils are not confluent with

pb.

eb

FIG. 100.

Branchial arches of Heptanchus. (After Gegenbaur.) lib, basibranclii.il : rn, basiliyal ; cl l~7,
ceratobranchials ; cj>, fused 6th and 7th basi branchial* ; eb, epibranchial : h, hypobranchial ;
hy, ceratohyal ; j>6, pharyngobraiichlaL

the mouth. The spiracle is small. There are six branchial arches
and slits in Hexanchus and Chlamydoselachus, seven arches and slits
in Heptanchus (Fig. 100). ' The slits remain widely open externally.
One moderately concentrated dorsal fin alone is present. There
is an extensive anal fin. The radials in the median fins are
numerous, and tend to fuse into elongated basal pieces (Fig. 48).
The tail is but slightly heterocercal. The notochord is largely
persistent, vertebral centra being feebly developed, especially in
Chlamydoselachus, where the notochord remains quite unconstricted
in the anterior region (Fig. 101). Heptanchus and the fossil
Notidanus, however, have well -developed centra behind, where
calcifications of the asterospondylous type may occur. A consider-

NOTIDANI

141

142

SE LAC HI I

able transitional region is found between the trunk and the posterior
diplospondylous part of the vertebral column ; here the arches are
double in each segment, but not the centra.

The copulatory appendages (p. 131) resemble those of the
sub-orders Heterodonti and Squaliformes, but they are smooth.

The rostrum is small in Heptanchus, scarcely at all developed
in Hexanchus and Chlamydoselachus. The skull and visceral arches
aftbrd evidence that the Notidani are the most primitive group of
the Selachii.

FIG. 102.

Dentition of Heptaii-hvs (Notiilanitx) itulieus, Guv. a, teetli in function ; >>, teetli in reserve ;
w, upper, and I, lower tooth of natural size. (After Giinther.)

FAMILY CHLAMYDOSELACHIDAE. One of the most remarkable of
living sharks, Chlamydoselachus, is isolated in this family (Fig. 101, A).
The mouth is nearly terminal, and the nostrils are more lateral than
ventral. The edges of the gill-septa are expanded into overlapping folds.
The groove-like structure of the lateral line of the trunk is perhaps
secondary (Fig. 101, E). The teeth, with three long cusps developed
separately (Rose [374]), ha%-e a striking resemblance to those of the
Pleuracanthodii, which appears to be due to convergence. The pelvic
girdle is unusually long, and pierced by a double series of nerve foramina
(Fig. 101, G) (Garman [147]).

Chlamydoselachus, Garman ; Pacific and Atlantic Oceans, and Pliocene
of Europe.

HETERODONTl 143

FAMILY NOTIDANIDAE. These typically amphistylic sharks have a
more normal Selachian structure, and have diverged chiefly in their
dentition. In modern genera the teeth are very unlike in the two jaws.
In the lower jasv they are long, very compressed, and with a saw-like
edge (Fig. 102). The gradual differentiation of this type of tooth, from
one with a broad base supporting a large cusp and a few small ones, and
closely resembling that of Hybodus (p. 144), can be traced in the fossil
genus Notidanus (A. Smith Woodward [505]). The upper teeth have
departed much less from the primitive type.

The fact that in the Jurassic N. eximius, Wagn., the centra are more
calcified even than in Heptanchus points to the modern forms being
somewhat degenerate.

Notidanus, Cuvier ; Jurassic and upwards, Europe and New Zealand.
Heptanchus, Raf. ; Atlantic and Mediterranean Seas. Hexanchu*, Raf. ;
warm and tropical seas.

GROUP II.

In these Selachians the number of branchial slits does not
exceed five (except in Pliotrema, p. 152); the notochord becomes
much constricted by usually well -developed centra ; the occipital
region of the skull is clearly marked off from the column, and
the occipito-spinal region very much shortened ; a cartilaginous
floor is formed below the orbit, except in the Rajiformes. The
external branchial openings are, as a rule, considerably diminished
in length by the overgrowth of the skin above and below.

An anal fin is present, except in the Subdivision 2 (p. 151,
Squaliformes and Rajiformes), where it appears to have been lost.
There are two dorsal fins.

DIVISION A.

With little or no rostrum and no triradiate supporting cartilage,
the mouth being almost terminal. The attachment of the jaws of
the early forms is amphistylic ; that of the later forms hyostylic.

Sub-Order 1. HETERODONTl.

An ancient sub -order dating back beyond the Carboniferous
epoch, probably to the Devonian, but surviving at the present day
in one genus only, Heterodontus (Cesf radon). In this modern
Port Jackson shark the notochord is much constricted by well-
developed asterospondylous centra; the jaws are hyostylic, but
with a very extensive palato-basal articulation, so that the
hyomandibular scarcely acts as a real support (Fig. 58). The
teeth of Heterodontus are highly modified in both jaws, those
towards the centre being small and pointed, those towards the
sides being blunt and flattened into crushing plates. Several
rows of teeth are functional at the same time (Fig. 107).

144

SE LAC HI I

Early fossil forms arc found, such as Hybodus (A. S. Wood-
ward [500], Brown [63]), in which the teeth are much less
specialised, resembling those of the early Notidanids. The teeth
of Hybodus are nearly uniform, with a long cusped crown and a
sharp central cusp. Those of Sijnechodus and Acrodus become
blunter at the sides than towards the middle of the jaws (Fig. 104).
Finally, the dentition of Asteracanthus closely resembles that of
Cestradon and Heterodontus (Fig. 105). In the Cochliodontidae
it is still further specialised by fusion. The teeth are very solid,
being formed of vasodentine with fine branching pulp-canals.

The vertebral centra of Palaeospinax and Syneckodm were

Tlie Port .JarkMMi shark, llrti-rutlontttx (I'estracioti) /Vii7i/i/<i. l.ac. (After Carman, IVoin
Dean.) A, ventral, 15, front, and C', dorsal view ot'licad.

well-developed and calcified, with distinct radial calcifications in the
latter genus ; but Hybodus shows no centra at all, and possibly
had a primitive unconstricted notochord ; nor have centra been
found in Acrodus and Asteracanthus.

Most important of all, however, is the development of the jaws ;
for it is well established [500] that Hybodus and St/necliotlii*
had typical amphistylic skulls, with the palato - quadrate and
hyomandibular as in the Notidanidae and other primitive
Elasmobranchs (p. 97). Now if this series of Heterodonts is
correctly associated as a monophyletic group, it must be supposed
that the hyostylic arrangement has been developed independently
in the Heterodonti and in the members of Division B (p. 148). The
Heterodonti must, if Ave accept this view, be definitely separated
off from the other sharks, as a distinct offshoot from a more primitive

HETERODONTI

|

s

H

en

*•-.«
XS

amphistylic stock. In this connection it is interesting to notice
that the hyostylism of Heterodontus differs considerably from that
of other sharks (Huxley [230], Gegenbaur [153], and Fig. 58).

Family CESTRACIONTIDAE. The dorsal fins are armed with strong
spines on the anterior edge, immediately in front of the endoskeletal

146

SELACHII

radials, which are much concentrated, and fused proximally to a large
basal. In Hybodus the spines have a serrated posterior edge apparently
formed by the fusion on to the spine of a double
series of denticles (Fig. 106).

The nostrils are confluent with the mouth. A
strong supraorbital crest is developed, bearing two
pairs of specially enlarged spines in the male
Hybodus, Acrodus, and Asteracanthus. The spiracle
is very small, and placed below the eye. The base
of the pectoral fin grows forward below the last three
branchial slits. The pectoral girdle is very powerful.
The teeth become differentiated into grinding plates
at the sides, but do not fuse. The egg - case of
Heterodontus is provided with a peculiar spiral lamina
(Fig. 91, H).

Hybodus, Ag. ; Triassic and Jurassic, Europe.

Sphenacanthus, Ag., Tristychius, Ag., from the

FIG. 105.

Portion of the lower jaw and teeth of Aster-
acanthus (Strophodus) medius, Owen ; Great
Oolite, Caen. (From Brit. Mus. Guide.)

Fio. 106.

Spine of Hybodus
subcarinatus, Ag.
(After Owen.)

Carboniferous of Europe. Orodus, Ag. ; Carboniferous of Europe and
America. Wodnika, von Munst. ; Permian. Acrodus, Triassic to Cretaceous.
Asteracanthus (Strophodus), Ag., Palaeospinax, Eg., Cestracion, Cuv. ; Jurassic,
Europe. Synechodus, A. S. W. ; Cretaceous, Europe and New Zealand.
Heterodontus (Cestracion}, Blainv. ; Port Jackson shark, Pacific (Fig. 103).

Family COCHLIODONTIDAE. Incompletely known fossils chiefly from
Carboniferous strata (Davis, Owen, A. S. Woodward). Helodus had an
anal fin and a spinous dorsal. The teeth resemble those of Cestracion,
but are farther modified. Not only do neighbouring teeth tend to fuse
at the sides, but also successive generations ; so that paired crushing plates
are produced, the worn outer edge of which is coiled inwards.

Helodus, Ag., with detached teeth ; Psephodus, Ag., with the two outer
rows fused; Pleuroplax, A. S. W. ; Deltodus, Ag. ; Cochliodus, Ag., with a

HETERODONTI 147

small inner and larger outer plate ; Paecilodus, M'Coy; Deltoptychius, Ag.,
both plates join to a single large plate on each side ; Diplacodus, Davis —
all from the Carboniferous of Europe. Xystrodus, Ag., Sandalodus, N.
and W. ; Carboniferous of N. America and Great Britain.

Family EDESTIDAE. Certain peculiar coils of teeth in a single row
have been found, which have been variously interpreted by palaeontolo-
gists as compound spines, as the armature of a twisted snout (Karpinsky
[256]), or as a spirally coiled row of median symphysial teeth of the
lower jaw of a fish allied to the Cestraciontidae (A. S. "Woodward [503],
Eastman [127]).

The last interpretation certainly is most in harmony with what we

FIG. 107.
Upper jaw of Heterodontus (Ccstmclon) Philifpi, Lac., the Port Jackson shark. (After Owen.)

know of the succession and position of the teeth in other Selachii.
Already in the Cochliodonts the inrolling of the worn edge of the com-
pound tooth-plates is seen ; and the little Devonian Selachian Protodus
seems to show the initial stage in the formation of a spiral coil of a single
row of teeth (A. S. Woodward). In Campodus the median teeth, which
.are not much compressed, form a short coil of about thirteen teeth,
and there are series of lateral teeth resembling those of the Cestraciont
Orodus (Eastman). Only the median coil is known in the more
modified Edestus and Helicoprion. Here the teeth are much compressed,
and there may be as many as 150 in a single coil (Fig. 108).

Protodus, A. S. W. ; Devonian, England and Canada. Campodus,
Kon., Carboniferous ; Edestus, Leidy, Carboniferous ; Helicoprion, Karp. ;
>Carboniferous and Permian — Europe and North America.

148

SELACHII

•"<*

\

FIG. 108.

Spiral row of teeth of Helicoprion bessonovi, Karp. ; Permo-Carboniferous, Uussiu. A, new
teetli being formed ; B, teeth in use ; C, old teeth passed out of use. (After Karpinsky, from
Brit. Mas. Guide.)

DIVISION B.

Only the hyostylic type of jaw attachment is known to occur
in these fish. The notochord is always constricted.

A rostrum is present, generally strengthened by cartilage ; it
appears, however, to have been lost in the Squatinidae and
Centrobatidae.

SUBDIVISION 1.

Sub-Order 1. SCYLLIOIDEI.

An anal fin is present and the dorsal fins are spineless. The
centra are generally asterospondylous ; concentric calcifications may
appear (Cetorhimis), as well as the more usual radial calcifica-
tions, but there are generally four 'radiating wedge-shaped
masses of uncalcified cartilage converging towards the centre from
the bases of the arches (Fig. 94). The rostrum is supported by
three cartilages, which generally meet at a point in front (Fig. 59,
C). The palato-basal articulation is loose, and the process reduced.
The teeth remain fairly simple, the median cusp enlarging to a
sharp piercing cusp (Sphenodus), or a flattened conical cutting blade
(Carcharodon). The spiracle is small, or may be closed up.

SCYLLIOIDE1

149

Family SCYLLIIDAE. With nasal grooves nearly or quite reaching
the mouth, and small sharp teeth. The extinct Mesitda had calcified
rings supporting the lateral-line canal, resembling those of the Holocephali
(p. 169, A. S. Woodward [499]).

Some of the Orectolobinae are adapted to a bottom-living habit ; the
rostrum is reduced, the head and trunk depressed, and the spiracles
enlarged (especially in Eucrossorhinus).

FIG. 100.
Cetorhinus maximus, Gun. (From Jordan and Evermann.)

SUB-FAMILY 1. SCYLLIINAE. Palaeoscy Ilium, Wagn.; Jurassic, Bavaria.
Mesiteia, Kromb. ; Cretaceous, Asia. Scyllium, Cuv. (Scylliorhinus) ; widely
distributed, occurs in the Cretaceous strata of Europe and Asia. Pristiurus,
Bon. ; European coasts, and Jurassic, Bavaria.

Fio. 110.

A, portion of a branchial arch of Cetorhinus (Selache) maximus, Cuv. 13, head of a Mackerel,
Scomber scomber, L., from which the left opercnlum has been remove*?, br, gill-ray ; c, cut
surface of ceratohyal ; g.u, gill-arch ; g.f, gill-lamella ; i, inner surface of gill-arch ; op, cut
»>dge of operculum ; r, anterior gill-raker ; s, outer septum ; t, posterior gill-raker.

SUB-FAMILY 2. ORECTOLOBINAE. Chiloscyllium, M. and H. ; Indian
Ocean and Pacific, and Miocene, Europe. Ginglysmostoma, M. H., tropical
seas ; and Eocene, Europe and N. America. Stegostoma, M. and H. ;
Indian Ocean. Orectolobus, Bon. (Crossorhinus, M. and H.) ; Pacific.
Eucrossorhinus, Regan.

Family LAMNIDAE. Large sharks without naso-oral grooves, with
wide external gill-slits, and with spiracles minute or closed. A lateral

150

SELACHI1

keel is developed on each side of the tail. A pit is present at the base
of the caudal fin. The large pointed teeth are filled with osteodentine.

In Cetorhinus (which is sometimes placed in a separate family) the
teeth are small and very numerous, and the branchial arches are provided
on both sides with a comb-like series of gill-rakers (Fig. 110). These
are enormously elongated denticles, uncalcified, and of horny consistency
(Turner [470]). Although strikingly like the gill-rakers of certain

Fio. 111.
Lamna cornitbica, Gm. (From Jordan and Evermann.)

Teleostei, yet they are of quite different origin. The deep-sea genus
Mitsukurina has a protractile mouth and spatulate snout.

SUB-FAMILY 1. LAMXINAE. Orthacodus, A. S. TV. ; Jurassic, Europe.
Scapanorhynchus, A. S. W., Cretaceous, Europe and Asia, is perhaps the
same as the living Mitsukurina, Jordan, Japan. Odontaspis, Ag., Lamna,
Cuv. (Fig. Ill), and Oxyrhina, Ag., in tropical and temperate seas,

Fio. 112.
Alopecias (Alopias) vulpes, Gm, (After Day, Fish&s of India.)

extend down to Cretaceous ; Alopecias, M. and H. (Fig. 112), and
Carcharodon, M. and H., to Eocene. Cetorhinus, Blainv. (Selache, Cuv.)
(Fig. 109) ; Atlantic, and Pliocene, Belgium.

SUB-FAMILY 2. RHIXODONTIXAE. Khinodon, one of the largest sharks,
reaching the length of some 70 feet, has gill-rakers like Cetorhinus. The
nostrils are near the margin of the mouth, which is almost terminal.
The minute conical teeth are very numerous.

Rhinodon, Smith ; southern and tropical seas.

Family CARCHARIIDAE. Usually pointed hollow teeth. No oro-
nasal grooves. The spiracle may be absent (Carcharias, Sphyrninae).

SQ UAL1FORMES \ 5 r

A third eyelid, or nictitating membrane, is present (Fig. 113); it
appears to be a specialised anterior region of the lower lid.

SUB-FAMTLY 1. CARCHARINAE. With an elongated rostrum. Mustelus
has acquired a blunt crushing dentition.

Carcharias, Guv., and Galeocerdo, M. and H., of world-wide distribution,
extend down to Eocene in the Old and the New World. Galeus, Cuv.,
and Mustelus, Cuv. ; distribution ^

general, and to Eocene, Europe.
Hemipristis, Ag. ; to Eocene, -...

Europe, Asia, and N. America.

SUB-FAMILY 2. SPHYRNINAE.
Specialised forms in which the
head is produced at the sides ,
into flat processes carrying the ^ ''

eyes and nostrils outwards. The
cartilaginous skull is correspond-
ingly modified, large extensions if,

of the pre-andpostorbital regions Fm. 113.

supporting the eyes. Left eye of Mustelus laevis, Risso. II, lower

In Sphyrna the process is eyelk' > SP> sP!7racle : ". tt»rd eyelid or nictitating

«l membrane ; u.l, upper eyelid,

only moderately developed, but

in the "Hammer-headed" Zygaena it is extraordinarily large (Fig. 114).

Sphyrna, Raf., and Zygaena, Cuv. (sometimes united in one genus) ;
tropical and subtropical seas, Miocene, Europe, and N. America.

SUBDIVISION 2.

Without anal fin. The vertebral centra are often cyclospondylous,
with a simple constricted calcified cylinder (Acanthias, Fig. 50).
Sometimes they are tectospondylous, with numerous complete con-
centric cylinders (Ehina, Fig. 52) ; or again they may have radiating
calcifications (Raja). Only the hyostylic type of skull is known.
The spiracle is well developed. The nostrils are usually separated
from the mouth.

Sub-Order 1. SQUALIFORMES.

These retain the shark-like body, with its large swimming tail.
The branchial slits are never ventral.

Family SPINACIDAE. The gill-slits extend not more than half-way
below the level of the pectoral girdle. Vertebrae cyclospondylous
(Acanthias, Fig. 50 ; Spinax, etc.) ; or uncalcified, and with very large re-
mains of the notochord (Laemargus, Echinorhinus [487]). The teeth are
generally of moderate size ; frequently they are more modified in the
lower than in the upper jaw (Spinax, Laemargus) ; and their points
are often turned aside so that the inner margin forms the cutting edge
(Fig. 39).

A large hollow spine, fixed on the anterior cartilaginous radial, is

152

SE LAC MIL

developed in front of the dorsal fins in Centrina, Centroscyllium, Acanthias,
and CentropJwrus. The radials of these fins are much concentrated, and
fused proximally to a large basal resting on the vertebral column, as in
Cestraciontidae (Fig. 50). In the other genera the fin - skeleton is
similarly modified, but the spines appear to have been lost. Occasionally
(Acanthias, Fig. 50) may be seen in front of the dermal spine traces
of radials, or perhaps of neural spines. The Spinacids are mostly
viviparous (p. 134). Laemargus, on the contrary, lays its eggs before
they are fertilised (Burckhardt [72], Helbing [206-7]).

Acanthias, Risso (Squalus, L.), and CentropJwrus, M. and H., widely
distributed in temperate seas, date back to the Cretaceous epoch.

,df.

FIG. 114.

A, Acanthias vulgaris, Risso; and B, ventral view of the head of the same (after Day,
modified). C, Zygaena tildes, Val. a./, anal, c./, caudal, d.f, dorsal, p.f, pectoral, and pv, pelvic
fin ; cl, clasper ; d.s, dorsal spine ; e, eye ; m, mouth ; n, nostril ; sp, spiracle.

Centrina, Cuv. ; Mediterranean and Atlantic ; Miocene, Europe. Spinax,
Cuv., Scymnus, Cuv., Echinorhinus, Blainv. ; Atlantic and Mediterranean ;
Pliocene, Europe. Centroscyllium, M. and H., Laemargus, M. and H. ; N.
Atlantic.

Family PRISTIOPHORIDAE. Pristiophorus has an elongated, flat
rostrum armed with a series of large denticles, or teeth, at its edge,
reaching to the angles of the mouth (Fig. 115). Below the rostrum
hang two pairs of sensory tentacles. The large spiracles are crescentic.
Pliotrema is remarkable in the possession of six pairs of branchial slits
(Regan [347]). The teeth are small and conical. The pectoral fins are
large, but well marked off at their base from the body. The vertebrae
are tectospondylous, and the tail has lateral keels.

The remarkable resemblance between this family and the Pristidae
is considered to be due to convergence (Jaekel [237ti]). A detailed
comparison of the two would be sure to yield interesting results. Fossil

RAJIFORMES

»53

remains, of simpler structure than the modern species, are found in the
Cretaceous of Mount Lebanon (A. S. Woodward [503]).

Pristiophorus, M. and H. ; Pacific ; Cretaceous, Mt. Lebanon. Plio-
trema, Regan, S. African.

Pristlophoi '(',-• I'h-

FIG. 115.
K, Lath., 9- (After Jtu'kel, from Dean.)

Sub-Order 2. RAJIFORMES.

The body becomes more or less depressed. The branchial slits
take up a distinctly ventral position ; while the large crescentic
spiracle, which is now inhalent, remains near the eye, on the dorsal
surface. A movable valve, containing the prespiracular cartilage,

A.

7. ad.

FIG. 116.

A, Zygaena tude.s, Cuv. (After Cuvier.) B, dorsal view, ;ind C, ventral view of Jthina
•/uiitiiia. ad, lirst dorsal tin ; c.f, caudal tin ; g, gill-slit; n, nostril; p./, pectoral fin; pv,
pelvic fin ; r, rostrum with lateral teeth ; up, spiracli1.

is formed on its anterior face (Division 2). The movable eyelids
.are lost. The tail becomes reduced in size, less heterocercal ; and
the dorsal fins shift backwards, even the first being always behind
the pelvic, on the tail. The trunk appears to spread outwards,
chiefly owing to the enormous development of the pectoral fins.
These not only may extend backwards so as to meet the pelvic

SELACHII

fins, but also grow forwards, passing above the branchial slits
(Squatinidae, Division 1). Further, the pectoral fins fuse with the
sides of the head (Division 2), and may grow forwards, below the
eyes and above the mouth and nostrils, to meet in the middle line
at the front end of the rostrum. This remarkable development of
the pectoral fins can be followed in the ontogeny of young skates
(Fig. 117). By the coalescence of radials an anterior endoskeletal
axis is developed in the pectoral fin, similar to the original posterior
axis (Fig. 121) (Gegenbaur [153], Howes [219]). To support these

B

A

C.

Flft. 117.

A, B, and C, three successive stages in the development of Torpedo ocellata, Kaf. The external
gill-filaments have been removed on the left side, ap, anterior region of pectoral fin growing
forward ; b, region of fore-brain ; lr, fourth branchial arch ; d, cloacal aperture ; e, eye ; e.g,
external gills ; l.j, lower jaw ; n, opening of nasal sac ; p, pectoral tin ; pv, pelvic fin ; «, ridge
along which the pectoral fin will grow ; sp, spiracle ; tt.j, upper jaw ; y, stalk of yolk-sac.

huge fins, the anterior vertebrae become fused into a continuous
tube (Fig. 1 1 8), the pectoral girdle becomes firmly attached to it
above, by a specially differentiated suprascapula (Fig. 118), and
greatly strengthened and widened at the sides for the reception
of the basals. The lateral -line system becomes much modified,
spreading over the expanded pectoral fins (Fig. 127). The
ampullae, also, may be extended over their surface. A very definite
articulation, by means of two condyles, is established between the
occipital region of the skull and the rigid vertebral column (Fig. 119).
The preorbital process of the skull may become very large, forming
a separate jointed piece attached to and supporting the pectoral fin
(Fig. 120). The mouth becomes transverse, and the two halves of

RAJ1FORMES 155

the jaws fuse together across, the palato-basal articulation being lost.
The attachment is hyostylic. The hyoid arch, however, becomes
peculiarly modified ; for, while the hyomandibular is specialised to
support the jaws only, losing its branchial rays, the remainder of
the arch becomes separately attached to the skull by a ligament
and a small epihyal (Raja, Fig. 99). The basal elements of the
branchial arches come to form a slender anterior transverse bar, and
a large posterior plate (Fig. 120). The last (5th) branchial arch be-
comes firmly attached to the pectoral girdle behind (Fig. 125).
Along the dorsal edge of the vertebral column large median
cartilages are often present ; they appear to be true neural spines
(p. 105), and accordingly the radials of the dorsal fins (which are

SC.

~f

vc.

Fin. 118.

Pectoral girdle and portion of the vertebral column of Raja blanda, Holt ; oblique left-
side view. ar, articular facets for pectoral lin ; c, coracoid region ; d.p, dorsal plate ; /, foramen ;
li, ligament ; sc, scapular region ; v.e, vertebral column.

much concentrated), when present, reach down to the neural arches
(Fig. 49).

The ribs tend to disappear. In the depressed forms the
ventral surface of the body becomes smooth and white, while the
dorsal surface, on the contrary, may be highly coloured and armed
with large sharp denticles.

Almost all the divergences mentioned above from the normal
and more primitive type of Selachian structure may be directly
correlated with the habit of swimming, not with the tail, but with
the pectoral fins, and of living on the sea-bottom.

TRIBE 1.

The large pectoral fins are produced forwards, but not fused
to the head. The branchial slits are partly ventral, partly lateral,

1 56

SELACHII

and not visible from above. The skeleton preserves many of its
shark-like characters, and in all essentials resembles that of the
Squaliformes.

Family SQUATINIDAE. The body and head are considerably depressed,
but the tail is still powerfully developed (Fig. 116). It has lateral keels.

A.

fnv

.ret

FIG. 119.

A, occipital region of the skull of Raja from behind. B, skull and anterior portion of
pectoral-fin skeleton of Trygon tuberculata, Lac., ventral view. (Both after Gegenbaur.) ex,
anterior axis of lin ; b, basihyal ; c, occipital condyle ; cf, nasal flap ; e, endolymphatic foramen ;
l.c, lateral condyle; l.l, foramen for lateral-line canal; m.k, Meckel's cartilage; p.q, palato-
quadrate ; r, vestigial rostrum ; rd, radial ; vg, vagus foramen.

The mouth is very far forward, there being no rostrum. The teeth are
small and conical. The anterior vertebrae may be slightly modified, but
not fused. The centra are typically tectospondylous (Fig. 52). Neural
spines are well represented (Fig. 52). In the form of the palato-
quadrate cartilage, with its powerful palato-basal process, of the hyoid
arch, and of the pectoral girdle, the Squatinidae differ from the next
Division, and resemble the Squaliformes. Obviously they are more
closely related to the latter than to the Scyllioidei. In the structure of

RAJ I FORMES

157

its pelvic ' claspers ' Rhina distinctly resembles the Kajidae, and differs
from the Squaliforrnes. On the whole, it is a beautifully intermediate
form between the shark-like and ray -like families. Many authors place
the ' Angel-fish ' with the sharks ; however, it is scarcely possible to
believe that so many skate -like characters have been independently

Fu;. 120.

Skull and visceral arches of Raja, ventral view. (After Gegenbaur.) a.p, antorbital process ;
lib, compound basibranchial ; c, basihyal ; cb5, fifth ceratobranchial ; hb, hypobranchial ; hm,
hyomandibular ; I, labial ; m.k, Meckel's cartilage ; »«, nasal capsule ; pb, pharyngobranchial ;
'j><l, palato-quadrate ; r, rostrum.

acquired, and it seems more reasonable to suppose that the Squatinidae
represent an early offshoot from near the base of the Rajiform stem.
They were represented in Upper Jurassic times by a well- differentiated
species, Squatina spcciosa, differing from the modern Rhina chiefly in
the possession of fewer calcined concentric lamellae in the vertebrae
(A. S. Woodward [503]).

Squatina, Bel. ; to Jurassic, Europe.

llhina, Angel-fish, Klein ; tropical and temperate seas.

I58

SELACH11

TRIBE 2.

The pectoral fins fuse in front with the sides of the head, and
the branchial openings are quite ventral. The rostrum, as a

FIG. 121.

Skeleton of Raja balls, L. (From Owen, Anal, of Vertebrates, by permission of Messrs. Long-
mans and Co.) 7, scapular region of pectoral girdle ; 8, 9, 10, segments of anterior axi»«of
pectoral fin; 11, posterior axis ; 12, radials of expanded pectoral fin; 10, preorbital process ;
52, cartilage plate joining scapula to vertebral column ; 55, posterior outgrowth of pectoral
girdle; 63, pelvic girdle ; 68, basipterygium ; c, anterior enlarged radial ; v, pelvic-fin radials.

rule, is much developed. In this division most of the changes in
the skeleton described above (p. 154) are carried out. Extra-
branchials are preserved in the Rhinobatidae and in Trygon. The
iliac process may be much developed ; since it is large in the
Holocephali and in the Tetrapoda, this is possibly a primitive
character.

RAJ/FORMES 159

Except in the first two families, the nostrils are confluent with
the mouth, there being a well-marked fronto-nasal process.

Although the main trend of the evolution of this Division has
been towards adaptation to a bottom-living habit, yet divergencies
can be traced amongst the various families. Accordingly, we divide
it into three groups (Jaekel [238]). In Group A, Khinoraji, are
developed a large median rostral cartilaginous process, and a pelvic
girdle with paired prepubic processes. Group C has no cartilaginous
rostrum, and a median prepubic process. Group B, containing the
Tropedinidae, is perhaps an offshoot from Group A, having the same
type of pelvic girdle, but losing the rostrum almost completely.
It is, however, quite possible that the more shark-like Pristidae
and Khinobatidae represent a primitive group from which the

FIG. 122.

Khynchobatus djeddemis, Forsk. Dorsal view, and ventral view of the head. (After Day,
Fishes of India.)

Rajidae, the Torpedinidae, and the Centrobatoidei have arisen us
three diverging branches.

GROUP A. RHINORAJI.

The rostrum is supported by a large median cartilaginous
process of the skull (Fig. 120). The tail becomes slender and the
dorsal fins shift back towards its tip. Two longitudinal keels
develop along its sides. Paired prepubic processes are present on
the pelvic girdle (Fig. 121).

Family RHINOBATIDAE. The head and trunk are much depressed,
forming a ' disk ' produced forwards into a large rostrum ; the very large
pectorals do not yet reach the snout (Fig. 122). Their endosfceletal radials
attain neither the rostrum nor the large preorbital processes in the Jurassic
species. The tail is relatively small, is losing its heterocercal shape
by the reduction of the ventral lobe, but still blends in front with the
trunk. The blunt teeth are closely set on the jaws, and may form an

i6o

SELACHII

undulating grinding pavement (Fig. 123). In the Jurassic species the
anterior vertebrae remain free, or are less fused than in the modern species.
No oro-nasal grooves, except in Trygonorhina, which with its confluent
nostrils is so skate-like that it is difficult to say whether it should be
put here or in the family Rajidae.

Rhinobatus, Black ; tropical and temperate seas ; to Upper Jurassic,
Europe, and Cretaceous, Syria. Rhynchobatus, M. and H. (Fig. 122) ;
Indian seas and Pacific. Trygonorhina, M. and H., Platyrhinoidia, Gar. ;
Pacific.

Family PRISTIDAE. The body is shark-like and little depressed,
with a well- developed caudal region and slight longitudinal keel (Fig.
116). The first dorsal is almost on a level with the pelvic. The pectorals
are large, but do not reach the skull, although passing forwards into a
fold on the head. The teeth are numerous, small, and blunt.

FIG. 123.
Dentition of Ithynchobatus sp. (After Giinther.)

Ill the modern Saw-fish, Pristis, the rostrum is drawn out into a long
flattened blade bearing a single series of large teeth along its lateral edge
(Fig. 116). Each of these modified denticles has a persistently growing
base deeply embedded in a socket in the hard calcified cartilage of the
rostrum. The Cretaceous genus Sclerorhynchus (A. S. Woodward [503])
shows a more primitive condition, in which the rostral teeth are smalt
and lie in the skin. Jaekel [238] considers that the shark- like
shape of the body has been secondarily acquired, and that the Pristidae
are derived from the Rhinobatidae. In no other way can we account
for the condition of the pectoral fins, branchial slits, and vertebral
column, characters acquired apparently in adaptation to a mode of life
which the Pristidae have abandoned.

Sclerorhynchus, A. S. W. ; Cretaceous, Syria. Propristis, Davis ;
Eocene, Egypt. Pristis, Lath. ; tropical and subtropical seas ; Eocene,
Europe and N. America.

Family RAJIDAE. The adaptation to boltom living is carried to

RAJIFORMES

161

If.

.el.

almost its extreme condition (Fig. 129, A). The slender tail is sharply

marked off from the large ' disk.' Small dorsal fins are usually carried

near its extremity, and the caudal is much reduced or absent. The tail is

triangular in section, with

paired longitudinal keels ; d nc

some of its muscles are

usually converted into an

electric organ (Fig. 124)

(Ewart[132]). Therhombic

disk is formed chiefly by

the huge pectoral fins, whose

anterior axis and radials

reach forward to the pre-

orbital process and beyond.

In Platyrhina they almost,

and in Sympterygia they

., , • ,1 ™'^Ji vertebral centrum ; <?, dorsal denticle ; el, electric organ ;

quite meet in the middle Lfj longitudinal fold ; m, my otome; H.C, nerve-chord.
line. The basihyal is a

very slender transverse rod, and the basibranchials are fused to a simple
broad plate, perhaps including some hypobranchials.

The pelvic girdle bears a pair of prepubic processes. In Cyclolatis
not only these but also the iliac processes are very long. The pelvic
fins are deeply notched, an anterior lobe being developed which is
supported by specially enlarged anterior radials (Fig. 89). The ribs
are very short. The teeth are small, blunt or pointed, and may differ in
the two sexes. The dorsal surface is frequently armed with very large
denticles, which may fuse into compound plates (Acanthobatis).

Eelemnobatis, Tlnoll.jAsterodermus, Ag.; Jurassic, Europe. Acanthobatis,
Larr. ; Miocene, Europe. Oncobatis, Leidy ; Pliocene, N. America. Cyclo-
batis, Eg. ; Cretaceous, Syria. Raja, Cuv. ; temperate and tropical seas,
to Cretaceous in Syria, and Eocene in Europe. Platyrhina, M. and H. ;
Pacific, and to Eocene, Europe. Sympteryyia, M. and H.

Fie. 1 •_>-».
Transverse section of the tail of Raja duruta. c,

GROUP B. TORPEDINOIDEI.

The family Torpedinidae is perhaps an oft'shoot from Group A,
which it resembles in the structure of the pelvic girdle. It differs,
however, in the loss of the median rostral process and in the
development of anterior electric organs. The ceratotrichia are lost.

Family TORPEDINIDAE. In general structure the electric rays
resemble the Rhinobatidae, but the tail is more distinctly marked off from
the disk. The caudal fin is usually little developed, and the body is
smooth. The disk is very rounded ; the median rostral cartilage has'
been lost in Torpedo, but in Narcine a considerable rostrum remains.
The edge of the disk is supported by the expanded pectorals, which do
not nearly meet in front, the wide intervening space being filled by
paired rostral processes, and the greatly enlarged preorbital cartilages
articulating in front of the nasal capsules (Fig. 125). In Torpedo,

1 62

SELACHII

while the hyoid copula has disappeared, the basal elements of the
branchial arches fuse to a single large plate. But the hypobranchials are
more distinct than in the Rajidae. The ceratohyal is articulated to the
hyomandibular (Torpedo), or to the first branchial arch (Hypnos). The
jaws become very slender and crescentic, and bear small teeth.

Fie. 125.

Ventral view of the skull and visceral arches of Torpedo. (After Gegenbaur.) ao, enlarged
antorbital process ; h, fused basibranchials ; c, spiracular cartilage ; hrn, hyomandibular ;
hy, hyoid arch: m.k, Meckel's cartilage; n.c, nasal cartilage ; r, rostral process; s, base of
cranium ; 1-4, first four branchial arches ; 5, fifth branchial arch, which abuts against the
pectoral arch.

The two halves of the pectoral girdle are not firmly fused ventrally,
neither do they articulate as in the Rajidae with the vertebral column,
but join above it to a median piece. The pelvic girdle has paired pre-
pubic processes. The ribs are well developed. A large electric organ,
supplied by a branch of the facial, and by four branches of the vagus
group of nerves, is situated between the branchial pouches and the
pectoral fin, on each side of the head (Fig. 126). This organ, formed of
vertical prismatic columns of tissue, is probably a greatly enlarged and

RAJIFORMES

163

modified portion of the visceral muscles, and of totally different origin
from that of the Rajidae (Fritsch [141]).

The Torpedinidae appear to be much more closely allied to the
Rajidae than to the Centrobatoidei. Yet there is reason to believe that
they should be derived independently from some Rhinobatid-like ancestor

EO

Tr

Fio. 126.

Torpedo with electric organ, E.O, and brain exposed ; dorsal view. On the right side only
the dorsal surface of the organ is exposed ; on the left tin- nerve> which supply it are shown.
Br, branchial sacs ; GB, sensory canals of lateral-line system ; Lr, electric lobe of brain ; <i, eye ;
Tr, trigeminal nerve ; V, vagus nerve. (After Gegenbaiir. from Sedgwick's Zoology.)

(Jaekel). Of living genera Narcine is perhaps the most primitive, and
Torpedo one of the most specialised.

Torpedo, Burn. ; Mediterranean, Atlantic, and Indian Ocean, to Eocene,
Europe. Hypnos, Dum. ; Australian. Narcine, Henle ; tropical seas, and
Eocene, Italy. Astrope, M. and H. ; Indian Ocean. Temem, Gray ;
Indian seas.

GROUP C. CENTROBATOIDEI.

The rostral cartilage is usually lost, but the skeleton of the pec-
toral fins grows forward to meet in front of the skull (Fig. 119, B).

164

SELACH11

The tail becomes very distinctly marked off, and slender ; the single
dorsal fin which alone remains not moving down towards the tip of
the tail, but being situated near its base. The pelvic girdle has
a median and no lateral prepubic process.

Family TRYGONIDAE. The large rhombic disk is completed in front
of the skull by the pectoral fins, which meet in the "nddle line.
Their anterior axis rests on the preorbital process. The skeletal rostrum
is represented only by a median strand of connective tissue (Fig. 119).
A slender horseshoe-shaped basihyal is present ; but the basibranchials
are fused into a single large plate, apparently together with the hypo-

FIG. 127.

Dorsal view of Iteroplatm Valeneicnnii, Duni. (after Carman), showing the extensive
development of the lateral-line organs, dc, endolymphatic openings ; pv, pectoral fin • plv
pelvic fin ; sc, spine ; up, spiracle.

branchials. The ceratohyal is attached either to the skull directly or
to the base of the hyomandibular. The stout transverse jaws bear
numerous small and usually sharp teeth. The tail is slender, varying
much in development. In Urolophus it bears a terminal fin, and
in Tryyonoptera a dorsal fin ; but as a rule it is whip-like, and has
lost almost all trace of the fins. On the other hand, it is generally
provided with one or more large serrated spines (Fig. 127), whence their
name Sting-Rays. These spines are placed behind the fins, not in front
as in other Selachians.

Xyphotrygon, Cope ; Eocene, N. America. Urolophus, M. and H., and
Trygon, Ad. ; warm seas, and to Eocene, Italy. Urogymmis, M. and H. ;
Indian seas. Pteroplatea, M. and H. (Figs. 92, 127); temperate and
tropical seas. Tr$gonoptera, M. and H. ; Australian.

RAJIFORMES

165

Family PTYCHODONTIDAE. A group of Cretaceous fish of which
little is known except the teeth. The dentition somewhat resembles
that of the Myliobaticlae, there being longitudinal rows of teeth, of which
the middle row is the largest (Fig. 128). The large teeth are nearly
square in shape, and composed of thick vasodentine, with a ridged
surface (Owen [31 la], A. S. Woodward [505«]). In the shape of the jaw
they approach the Trygonidae.

Ptychodiis, Ag. ; Cretaceous, Europe and N. America.

Family MYLIOBATIDAE. As in the last family, the pectoral fins
generally meet in front of the skull ; but their anterior, preorbital

12S.

Lower jaw of Ptyehodus dwurrens, Ag. ; Cretaceous, Sussex. (After A. S. Woodward,
from Brit. Mus. Guide.)

portions become separated off from the rest of the fin, so as to form a
special anterior cephalic fin, median in the Myliobatinae (Fig. 129, B).
In the Dicerobatinae this fin is developed as paired horn-like projections
(Fig. 129, C).

The head, with its large protruding eyes, projects dorsally above the
level of the disk. The skeleton resembles that of the Trygonidae ; but
the ceratohyal is attached to the first branchial arch. The skin is smooth,
excepting for a strong serrated spine which generally lies behind a single
email dorsal fin, near the base of the elongated whip-like tail (Fig. 129).

SUB -FAMILY 1. MYLIOBATINAK! With a median 'cephalic fin,'
quite continuous with the pectorals in Promyliobatis. The teeth form a
flat grinding pavement (Fig. 130), of which the central row becomes

1 66

SELACH1I

greatly enlarged and transversely elongated. They form a mosaic of
closely fitting blocks of vasodentine.

A

,
pv, pelvic tin ; .?, spine ; sp, spiracle.

FIG. 130.
Jaws and teeth of the Eagle-Ray, Myliolmti*

iln, L. (After Owen.)

Myliobatis, Cuv., and Aeobatis, M. and H., warm seas ; to Eocene,
Europe and N. America. Promyliobatis, Jaekel ; Eocene, Italy.

SUB-FAMILY 2. DICEROBATIXAE. With paired cephalic-fin processes.
The teeth, which are closely set in many rows, may be small and almost

RAJIFORMES

167

uniform, or some middle rows may be enlarged (Figs. 131, 132). In
Ceratoptera, they are absent from the upper jaw.

Dicerobatis (Cephaloptera), Blainv., Ceratoptera, M. and H., and
lihinoptera ; warm seas ; the latter to Eocene, Europe.

Family PSAMMODOXTIDAE. Known only from fossil teeth, which
are transversely elongated, flattened, and adapted for grinding. They are

Khinojitem Woodvardi, Ag
(After Owen.)

Teeth of Ithinopte m polymloii, Gthr.
(After Giinther.)

133.

Tooth of Foliirhizoilus /»»•;//».•;,
M'Coy ; Carboniferous Limestone,
Armagh. (After M'Coy.) c, outer
.^limling surface ; r, basal root.

closely set in longitudinal rows, somewhat as in the Myliobatidae, with
which this family is generally associated.

Copodus, Davis, Psammodus, Ag. ; Lower Carboniferous, Europe and
X. America. Archaeobatis, Newb. ; Lower Carboniferous, N. America.

INCEUTAE SEDIS.

Family PETALODONTIDAE. These palaeozoic Selachians are chiefly
known from remains of the dentition, which is much specialised. In the
case of Janassa it has been ascertained that the body was depressed and
expanded, with large pectoral fins reaching forward and perhaps fusing with
the head (Miinster, Jaekel [240]). The jaAvs were wide and strong,
bearing powerful grinding teeth set one behind the other in regular rows.
Apparently the old teeth remained to support the newer growing up
from behind. As a rule, each tooth has a distinctly marked crown and
root. In Polyrhi::oJ.us the root is subdivided (Fig. 133). The affinities

168 HOLOCEPHALI

of this family are still obscure ; usually they are associated with the
Myliobatidae, but possibly they are more closely related to the Squatinidae
(Jaekel).

Petalodus, Owen ; Potyrkizodus, M'Coy ; Janassa, Miinster ; Carboni-
ferous, Europe and North America.

Order 2. HOLOCEPHALI.

The Holocephali, a very ancient group of highly specialised
marine fish, date from the Devonian, and flourished especially in the
Mesozoic times. At the present day they are represented only by
a few genera scattered over the world.

In their general organisation they closely resemble the
Selachians : the skeleton is mainly cartilaginous and without true
bone ; the two dorsal, the anal, the caudal, and the paired fins are
all provided with typical ceratotrichia ; there are pelvic ' claspers '
in the male. Moreover, in living forms the egg is large, heavily
laden with yolk, and laid in a horny capsule secreted by the oviduct
(Fig. 91, I). The alimentary canal with its spiral valve, the heart
with its contractile conus and several rows of valves (Lankester [277]),
the urinogenital organs, in fact, all the viscera, are built on the
Selachian plan. But the Holocephali have become much specialised
in many respects, though in some few points they have perhaps
preserved some very primitive characters.

They differ from the Selachian, in the absence of a rectal
gland, which may, however, be represented by glandular patches ;
in the absence of an attenuated anterior ' genital ' portion of the
female meson ephros ; in the slight differentiation of the stomach,
and the small number of turns made by the spiral valve. Lastly,
the development is in the main quite Selachian in character ; but
the cleavage is of the holoblastic type.

The skin in the adult of modern genera is smooth over the
general surface of the body. A covering of powerful denticles was
present in such early forms as Squaloraja and Chimaeropsis (Fig.
137, B) ; they are usually preserved in living Holocephali only
on the claspers and frontal prehensile process of the male, and may
also be present in rows on the head and back of the young as in
Callorhynchus.

They have no enamel, but an outer layer of vitrodentine as
in Selachians, and the pulp-cavity is almost filled up. The large
spine, almost universally present on the front edge of the first
dorsal fin, may be considered as a modified denticle ; it consists of
vasodentine. In the Myriacanthidae dermal plates of similar
structure are developed on the head ; these have also probably
been derived from denticles (A. S. Woodward [506]).

HOLOCEPHALI 169

The lateral-line system is very well developed (Garman [148,
149], Collinge [90]). As a rule, the canal is an incompletely closed
or a widely open groove, and its wall is strengthened by crescentic
ossicles or small plates, probably modified denticles (Fig. 135, B).
Deeply embedded ampullary organs are present on the head.

A peculiar rostrum supported by cartilage processes is developed
-on the snout. In living genera the nostrils are found to be ventral
with grooves leading to the mouth, as in many Selachii. The lips
Are strengthened with large complex labial cartilages (Fig. 134).
The gape of the mouth is small (Fig. 144).

The eyes become very large, and the orbits tend to come close
together in the middle line. The membranous side-walls of the
brain-case, near each other in Callorhynchus, in Chimaera form an
interorbital septum above the brain, which throws backwards and
downwards the diminished brain- cavity (Fig. 135). Thus the
brain lies below the septum. The branchial slits are reduced, in
modern forms, to four, and are covered over by a membranous
operculum borne by the hyoid arch and its well-developed branchial
•rays. The gill-slits and arches are drawn close together as in the
higher operculate fish, and the septum between the gill-lamellae
is considerably reduced as in the Dipnoi (Fig. 57), no doubt owing
;to the development of the operculum. The spiracular slit has
been lost. There is no spiracular gill, but a posterior hyomandibular
ihemibranch, three holobranchs, and an anterior hemibranch on the
fourth branchial arch.

The whole structure of the jaws and skull has been profoundly
modified in connection with the development of permanent paired
grinding plates. There are generally a small anterior ' vomerine '
plate and a posterior large ' palatine ' plate on the upper jaw, and a
.corresponding large plate on the lower jaw (Fig. 141) (Jaekel [241],
Dean [llOa, etc.]). These plates are generally differentiated into
An extensive flattened basal region, and more prominent grinding
ridges or tritoral areas ; the former of trabecular or vasodentine,
the latter with a covering of vitrodentine (Fig. 141). They have
persistently growing bases, are not shed and replaced, and in the
embryo show no distinct signs of having been formed by the
fusion of separate denticles. Yet they must be considered as the
modified derivatives of the teeth of the upper and lower jaws,
and the tubercles often present on the ' tritors ' may represent
originally separate elements. To support the grinding plates
the jaws are strengthened and shortened. The two rami of the
lower jaw are fused in front, while the palato-quadrate cartilage
is fused to the ethmoid region of the skull in front and to the
auditory capsule behind (Fig. 135) (Huxley [230], Dean [IKk],
Schauinsland [383]). The branchial arches are normal ; the
hyoid arch, however, shows no large hyomandibular element, but

i ;o

HOLOCEPHALI

ends above in an epihyal and a minute pharyngohyal. Most
authors believe the hyomandibular to be represented by the small

??4*S?

b2 g

S'S-SSsf

.£•-=• 2 r

1) X >> ' • - JL

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cartilage at the top of the hyoid arch ; but from the evidence
of embryology and the course of the hyomandibular branch of the

SKULL

171

facial nerve, it would appear more probable that the hyomandibular
is indistinguishably fused both with the auditory capsule and with
the quadrate, the spiracle being suppressed (Fig. 135). If this
interpretation is correct, the autostylism of the Holocephali differs
radically from that of the Dipnoi, and has probably been derived
from a hyostylic structure. Cartilaginous branchial rays are
present in single series, as in the Selachii (p. 123), and are much
developed on the hyoid arch to support the operculum (Fig. 134).
One of the most characteristic organs of the Holocephali is the

vr.

CaUorhyncht'S antarcticus, Lac. A, skeleton anil nerves of the head of a young specimen
(after Schauinsland's figures). (n>, auditory capsule ; b, buccal branch of facial nerve ; clu; :>th
ceratobranchial ; c/i, ceratohyal ; dr, dorsal median rostral cartilage ; eh, epihyal ; gp, glosso-
pharyngeal nerve ; ml,', Meckel's cartilage ; p, palato-quadrate region ; jih, pharyngohyal ; q,
quadrate, or probably hyomandibular, region ; #, interorbital septum ; sp, spinal nerve-roota ;
cb, i-i, fl, bnuichial, intestinal, and lateral -line branches of vagus nerve ; v.r, ventral paired
rostral cartilage ; 2, optic, 3, oculomotor, 4, pathetic, 5, trigeminal, (3, abducent, and 7, facial
nerves. B, calcilied skeletal supports of the lateral line.

frontal clasper, or tenaculum, found in all undoubted members of
the group from the Jurassic time onwards, but in the male sex
only. It is a movable median process, supported by a cartilaginous
axis articulated to the skull above and in front of the orbit
(Figs. 141, 144). Long and pointed in the Myriacanthidae and
Squalorajidae, short and with a swollen tip in the later forms, it
is always armed with denticles. The origin of the tenaculum is
unknown ; its derivation from the front end of the dorsal fin has
been suggested by Dean ([llOrt], Reis [351rt]).

The cartilaginous auditory capsule, unlike that of the Selachian,
is widely open to the cranial cavity internally, and the basicranial
axis is strongly bent upwards. The skull extends backwards so as

172

HOLOCEPHALI

to enclose several occipito-spinal nerves. There is a well-defined
convex condyle .articulating with the vertebral column.

The notochord in the Holocephali (Hasse [200], Schauinsland
[383], Klaatsch [265]) is persistent and unconstricted. It is

surrounded by a thick fibrous sheath
into which mesoblastic skeletogenous
cells migrate through the ruptured
elastica externa (Fig. 136). These
cells form complete rings, which
acquire a calcified bone-like struc-
ture, and are much more numerous
than the segments of the body. Tn
Callorhynchus the rings are not de-
veloped ; they are, on the contrary,
very strong and closely packed in
the extinct Squaloraja (Fig. 137).
True centra never occur. There
are no ribs. Normal cartilaginous
neural and haemal arches are present
and do not meet round the noto-
chord, except in the modified anterior
region. Interneurals (interdorsals)
and rarely interhaemals (inter-
ventrals) occur, and supradorsals
complete the neural tube above.
Immediately behind the skull (Fig.
134) some dozen or more vertebral
segments are fused below the anterior
dorsal fin ; here is formed a con-
tinuous cartilage enclosing the noto-
chord and nerve-cord, and stretching
upwards into a dorsal process with

Chimaera monstrosa, L. Vertebral VvViipVi artirnlafp<j tVip r-irfiliio-p nf tViA

column: A, transverse section ; B, side Wnl ' Cartilage (

view ; and C, longitudinal median section, fin. The axial Cartilage tube and

(All after Hasse, slightly modified.) 1, . , , . . .

interdorsal ; 2, basiventral ; 3, notochord ; its dorsal process may be Considered

4, elastica externa and connective tissue ; rnarlp nn of fnsipH vprrr>Virap • in

5, fibrous sheath ; 6, calcified ring ; 7, basi- as Hiaue Up OI lUSCQ ^ ertCDiae ; 111
dorsal ; 8, dorsal nerve-root foramen ; 9, living genera its Compound StrUC-
ventral nerve-root foramen ; 10, supra- • i

dorsal. ture is shown by the numerous

nerve apertures, and in the extinct

Squaloraja and Myriacanthus traces of segmentation appear in it
(Fig. 141, B) (Dean [llOa]).

The first dorsal fin is characteristically modified, the radii
being represented by the single cartilaginous plate just mentioned,
to which is firmly fixed the dorsal spine. The whole fin, spine
and all, is movable and can be folded back or erected. In
Myriacanthus two or three cartilages support the spine. The

. • .•.

^v/T^g|$ 3

FIG. 136.

SKELETON

173

second dorsal fin is extended, and its simple rod-like radials appear
to be in a primitive undifferentiated condition. The dorsal (axial)
lobe of the heterocercal caudal fin is much elongated and tapers

A.

B

FIG. 137.

,s'///(ir7,,, 17/n polyspondyla, Ag. Enlarged views of, A, vertebral rings ; B, denticles, b.p,
basal plate ; c, projecting spine ; -no, cavity for notochord ; v, vertebral ring.

into a long whip-like end. In Harriotta the long tail is straight,
and scarcely betrays its original heterocercal character (Fig. 145).
The anal fin shifts far back to near the caudal ; it is often very
small, and is not present in Harriotta.

FIG. 13S.

Ventral view of the pelvic girdle and tins of Chinuum monstrosn, L., 9 • The skeleton is com-
pletely exposed on the left side. l>, basipterygium ; </>•, web of light tin with ceratotrichia ; p,
pelvic cartilage ; pi-.i; preaxial radials ; jit.r, postaxial radials. (From Quart. Joiirn. Mies. .Sri.)

The pectoral girdle is formed of stout cartilages fused in the
middle ventral line. They support the skeleton of the fin, which
is essentially of the typical Selachian kind, with many fan-like rays
attached to a nietapterygium (Fig. 134). The pelvic fin has a very
similar but smaller skeleton (Fig. 138). The pelvic girdle, on the

174

HOLOCEPHALI

other hand, differs considerably from that of the Selachian, in that
the two halves are not fused and the iliac process is Avell developed.
In the male an anterior clasper, armed with denticles and lodged in

FIG. 139.

Chiinaera tnongtrota, L. A, ventral view of the right pelvic fin of a male. B, ventral
view of the left half of the pelvic girdle and pelvic fin of a male (after Davidotf). C, diagram
showing the opening of rectum and urinogenital sinus in the female, a.c, anterior clasper
armed with denticles ; an, anus ; a.p, abdominal pore ; b, basipterygium ; d, posterior clasper ;
il, iliac process ; k.d, kidney duct ; od, oviduct ; p, pelvic cartilage ; p.f, pelvic fin ; pt, pocket
into which the anterior clasper can be withdrawn ; r, radial ; rt, rectum ; tr, tritid extremity
of clasper ; tr.c, its cartilage cut short ; ug, urinogenital papilla ; ttg.h, its opening ; itg.s,
urinogenital sinus.

a pouch, is borne by a cartilage attached to the girdle, at all events
in living Holocephali and in Squaloraja (Figs. 139, 141). This
anterior clasper, unique amongst fish, is doubtless formed by the

HOLOCEPHALI

175

modification of the front end of the pelvic fin, just as the posterior
clasper is formed from the hind end ; in Squaloraja its isolation is
less pronounced, since intermediate radials are preserved articulat-
ing Avith the pelvis (Dean [llOa]).

The brain, while resembling that of a shark in its general
structure, is remarkable for the great development of the restiform
bodies, the relatively small olfactory bulbs, and
more especially for the great elongation of the
diencephalon (thalamencephalon) widely separating
the cerebral hemispheres from the optic lobes, a
stretching of the mid-brain which is related to the
formation of an interorbital septum. The cerebral
hemispheres are more distinctly paired than is
usual among Selachii (Fig. 140).

It may be concluded that the Holocephali are
the descendants of some primitive form of shark
with unconstricted notochord, which diverged from
the main stem in pre-Devonian times, and became
specialised in the loss of the denticles, spiracle,
and cloaca, and in the acquisition of a spine-bearing
dorsal fin close behind the head, of a cephalic
prehensile organ in the male, of a pronounced
rostrum, of peculiar vertebral rings, of an opercular
flap, and above all of a fixed upper jaw and grinding
plates. It is in the elaboration of these grinding
plates that progress has been most marked up to
the present day.

The chief characters of the Holocephali may
be enumerated as follows : the gill-openings are ^™™tro°* L''"/^"^
covered by a hyoid opercular flap, the spiracle Owen,.4*a*. qf rcrte-
being closed ; a rostrum is present, the mouth is of Mewn.'taiigmaiM
small, and the teeth specialised into permanent i&^&$SS™-,
grinding plates ; the palato-quadrate is fixed to the c1, cerebellum ; ./,/,
skull, the hyomandibular reduced, and an inter- mrelencephaioD • o,
orbital septum developed dorsal to the brain ; the ?!£!£: $?%£.
lateral line is incompletely closed ; the notochord |ated di*-ncepiiaion,
is unconstricted, the sheath invaded, but no centra
are formed ; the first dorsal fin is specialised to support a spine,
the second remains unconcentrated ; a cephalic tenaculum, and an
anterior and a posterior clasper, are present in the male ; the cloaca
is absent (Fig. 139).

The earliest remains of true Holocephali occur in Jurassic
strata. These fossils are in all essentials like the modern forms,
yet in some few points they show a more primitive structure. For
instance, as already mentioned, the covering of denticles is more
complete, the anterior end of the vertebral column less fused up,

Dorsal viewer the

1 76 HOLOCEPHALI

and the pelvic girdle and fin more normal. Unfortunately, palaeon-
tology throws but little light on the ancestry of Chimaeroids ; for
the genera from Devonian rocks, which are only very doubtfully
referred to this Order (Ptyctodontidae), are much too imperfectly
known to afford any trustworthy evidence on the subject.

GROUP A.

Where known, the body is found to be covered with denticles,
the rostrum long and depressed, the tenaculum straight and pointed,
the dental plates thin and without well-defined grinding areas.

Family SQUALORAJIDAE. Large denticles are scattered over the elon-
gated and depreased body. The head appears to have been flattened and
expanded with a long depressed rostrum. Above the latter was a long
movable tenaculum, or frontal clasper, armed with denticles (Fig. 141, B).
No dorsal fin spine is known. The tooth-plates, four above and two
below, are thin and without well-differentiated tritoral areas (Fig. 141, D).

Squaloraja, Riley ; Lower Lias, England.

Family MYRIACANTHIDAE. The head bears several tuberculated
paired dermal plates, of vasodentine, which may have projected from
the sides of the head and lower jaw (Fig. 142). There is a large com-
pressed rostrum with bent tip as in Callorhynckus. Long calcified rods
are generally interpreted as labial cartilages. The teeth, consisting of
paired palatine, vomerine, and prevomerine plates above, and two man-
dibular and a presymphisial tooth below, are thin and have ill-defined
tritoral areas (Fig. 141, A). A tuberculated dorsal-fin spine is present.

Myriacanthus, Ag. ; Lower Lias, England. Chimaeropsis, Zittel ;
Lower Kimmeridgian, Bavaria.

GROUP B.

With a quite or almost scaleless body, and a short tenaculum
bearing denticles on its swollen extremity. The teeth become
thicker, and usually have distinct grinding patches (Fig. 141).
The dorsal fin spine is smooth.

Family CALLORHYNCHIDAE. The rostrum has an expanded end. The
large teeth have well-marked tritoral areas. No calcareous rings are
present in the notochordal sheath. The cartilaginous support of the
mixipterygium is comparatively simple. The lateral -line canal is a
closed tube opening by pores in the adult.

Callorhynchus, Gronow ; Pacific, and Cretaceous, New Zealand (Fig.
143).

Family CHIMAERIDAE. The rostrum is quite short. Anterior tritors
are present on the teeth. The notochordal sheath has small calcified
fibro-cartilage rings ; and the clasper divides into three branches, each
with a cartilage axis (Fig. 139). The lateral-line organs are in an open
groove [281].

Chimaera, L. ; widely distributed iu the deep seas ; Pliocene, Italy

HOLOCEPHALI

177

B

,-vt

pvt.

si

St.

Fit;. 111.

A, dentition of M\ii-w-m\.thut. B, dorsal view of Squaloraja polyspondyla, Ag. C,
dentition of Cattorh yiwhux ; D, of S'lualorajn ; E, of Rhynchodus ; F, of Harriotta degans. D
uml G, Elasmodus JIunteri, EJJJ. (All after Dean.) a.d, anterior clasper ; c, paired cartilage ;
t-', clasper; f.v, fused postoccipital vertebrae ; pst, ' predentary ' tooth ; pt, ' palatine' tooth-
1'late; pv.t, ' prevoinerine ' tooth ; r, rostrum; st, tooth-plate of lower jaw; t.n, tritoral area;
/(, tentaculuin ; t'.c, vertebral column ; v.t, ' vomerine' tooth.

12

1 78

HOLOCEPHALI

(Fig. 114). Ganodus, Ag. ; Jurassic, England. Ischyodus, Eg. ; Jurassic
and Cretaceous, Europe and New Zealand. Elasmodectes, Newt. ; Creta-
ceous, England. Elasmodus, Eg. ; Eocene, Europe (Fig. 141, G).

FIG. 142.

Restored mandible of Myriacanthits. (After Dean.) j, jaw ; pi, dermal plate ;
pst, presymphysial tooth ; t, niandibular tooth.

Family RHINOCHIMAERIDAE. The proboscis is very long and pointed.
Narrow calcined rings are present round the notochord, the clasper is
long but of simple structure, the olfactory bulbs are remote from the

FIG. 143.

Callorhynclius antarcticus, Lac. (After Garman, from Dean.) A, dorsal aspect ; B, ventral

view of head.

cerebrum, and the lateral-line canal opens only by a very narrow slit.
The teeth have cutting edges, but no tritors in Rhinochimaera ; and
tuberculated tritors in Harriotta (Fig. 141, F).

Rhinochimaera, Garman, and Harriotta, G. and B. ; Pacific (Fig. 145).

HOLOCEPHALI

179

IXCERTAE SEDIS.

Family PTYCTODOXTIDAE. Scarcely anything but the dental plates
with tritors is known (Fig. 141, E). There appear to have been one pair
in each jaw meeting at the symphysis and beak-like [125].

FIG. 144.

Chimaera moiistrosa,;'L., <J. (After Gannan, from Dean.) A, ventral, and B, frout view of

head.

Eecently, however, Jaekel [242a, 243a] has described some dermal
plates in association with Ptyctodont teeth (Rhamphodus). In this genus,
according to Jaekel, the dermal armour forming a pectoral girdle points

FIG. 145.
llamotta llaUifjhana, G. and B. (From Jordan and Evermann.)

to an affinity with the Acipenseroidei ; but Dollo (12 la) contends with
justice that the armour of Rhamphodus resembles rather that of the
Coccosteomorphi, with which he would associate them. The Ptycto-
dontidae, like the Menaspidae, were almost certainly devoid of the spine

i8o HOLOCEPHALI

BO characteristic of the dorsal fin of the Holocephali. A better knowledge
of the histological structure of the dermal plates of these families is much
needed.

Ptyctodus, Pander, Bhynchodus, Newb. ; Devonian, Europe and N.
America. Palaeomylus, A. S. W. ; Devonian and Carboniferous, N.
America. Rhamphodus, Jaekel ; Devonian, Germany.

Family MENASPIDAE. In this family may be provisionally included
certain incompletely known fossil fish the affinities of which are still very
uncertain, but which appear to be more closely related to the Holo-
cephali than to any other order.

Menaspis has a general covering of denticles strengthened into a sort
of cephalic shield bearing a series of paired lateral spiny processes, per-
haps homologous with the spiny plates of Myriacanthus. Three unequal
pairs of long curved rods of calcified fibrocartilage may be compared to
the so-called labial cartilages of the same genus. The dentition consists
of four grinding plates like those of Rhynchodus. Such remains of the
paired fins and mucus canals as have been found resemble those of
Chimaerids. Menaspis seems to be allied to Myriacanthus (Dean [1106]).
It is possible that the Devonian fossil described by Traquair under the
name Gemundina Sturtzii [467] belongs to this group.

Menaspis, Ewald ; Permian, Europe.

Sub-Class 2. PLEURACANTHODII (Ichthyotomi).

Of all the Palaeozoic Chondrichthyes the Pleuracanthodii are
by far the best known, their skeleton having been described in full
by Brongniart [62], Koken [269], Doderlein [113], Reis [353], and
others, and especially in the admirable work of Fritsch [139].

Pleuracanthus is shark-like in shape, with a large nearly terminal
mouth, a powerful median occipital spine, well-developed paired
fins, a long tapering tail, almost if not quite diphycercal, and
elongated median fin-folds. The dorsal fin is almost continuous,
begins but a short way behind the head, and is only separated by
a notch from the caudal. The median ventral fin is subdivided
into two anal lobes and a long caudal (Fig. 146).

The dermal skeleton is little developed, being represented by
small denticles near the mouth, along the back, and on the clasper
of the male. Large pointed tricuspid teeth arm the jaws ; like the
occipital spine they are formed of vasodentine (Fig. 148).

The endoskeleton was entirely cartilaginous, with well-
developed prismatic calcifications. The skull and jaws resemble
those of the Notidanidae ; the pre- and postorbital processes are
large, and the attachment of the jaws is of the amphistylic type.
Five branchial arches, subdivided like those of the Selachii, are
present (bearing small teeth) ; the median basibranchials seem to
be somewhat reduced in number. The notochord was persistent,
and probably quite unconstricted ; no distinct centra are found

PLE URA CA NTHODII

181

(Fig. 146). W ell-developed arches
occur above and below, but the
intercalaries are small or absent ;
there are short ribs. The neural
spines articulate with a series of
dorsal radials formed of three seg-
ments. In the caudal fin these radials
are segmental ; but in the dorsal fin
they are twice as numerous as the
arches. No such radials have been
found in the ventral lobe of the
caudal, a fact which argues against
the fin being truly diphycercal.

In the region of the anal fins the
radials, still articulating with the
haemal arches, become fused in a
variable manner, showing most
clearly how such concrescence may
lead to the formation of a fin-axis
(Fig. 147).

Behind the occipital spine, which
seems to have been movable, the
neural arches point forwards.

The two halves of the pectoral
girdle remain separate, and each has
a small dorsal and ventral segment
(Fig. 148). Most interesting is the
skeleton of the fin, which is built
on the archipterygial or mesorachic
plan, with a tapering jointed axis
bearing a preaxial series of radials
in front and a postaxial series behind.
The preaxial are the more numerous,
and some of them may be articulated
to the girdle itself. The pelvic girdle
is formed of two separate cartilages
(Figs. 149, 150, 151). The skeleton
of the pelvic fin never appears to
be of the mesorachic type; although
the radials have evidently been con-
centi-ated in much the same manner
as in the pectoral to form a seg-
mented axis, there is no series of
postaxial radials. One postaxial
radial has, however, been described
(Fig. 150). In the male the axis

PLE URA CA NT HOD II

is modified and prolonged, much as in the Selachians, to form a

clasper armed with sharp hooks.

Ceratotrichia are present in all the fins of Xenacanthus, but

have not been described in Pleura-
canthus. There is evidence from
the fossilised faeces of the pres-
ence of a spiral valve.

Cladodus (Traquair [464]),
which seems to be allied to Pleura-
canthus, and has a similar dentition
and head -skeleton, differs con-
siderably in the structure of the
pectoral fin. The pectoral girdle
is of the typical form (Fig. 87).
The fin -skeleton consists of a
number of anterior radial s, whose
proximal joints are incompletely
fused to a basal articulating with
the girdle ; behind it articulates a
second basal formed by the coales-
ce- 147. cence of more posterior radials.

Skeleton of anal fins of I'lcurarantlni* It is the base of a loilff many-
(Xenacanthits) Decheni, Goldf. a, ft, c, haemal • • , j • r • i_ . /

arches; 1-6, segments of fin-radiais. Right jointed axis, wnicn represents the

border preaxial, and left postaxial. (After mpfor^fprvcrinm ami mav Vmvp

Fritsch, from A. s. Woodward.) letapterygiui may na\ e

been lodged in the body -wall.

This axis has presumably arisen from the bases of a single
series of radials, which have almost disappeared behind ; in this
case the fin is strictly uniserial. On the other hand, it may have
been derived from a mesorachic fin, like that of Plewacanthus,
by the suppression of the postaxial radials. This on the whole
seems to be the more probable explanation of its structure.

The pectoral-fin skeleton of Symmorium, which is supposed to
be allied to Cladodus, has been described by Cope [92] ; but it is
much more like that of a Selachian (Fig. 87).

That the Pleuracanthodii are closely related to the Selachii is
shown by the structure of the skull and visceral arches, and the
presence of a pelvic clasper ; but the unconcentrated character of
the radials of the median fins, and the persistence of the girdles in
two halves, point to their having been derived from a common
ancestral form more primitive than any known member of that
Order. In these two respects they approach the Holocephali. The
ancestral Chondrichthyan, parent both of the Elasmobranchii and
of the Pleuracanthodii, must have had an amphistylic skull, and
paired fins with concentrated radials forming a fairly well-defined
axis. Whether a postaxial series of radials was present in the

PLE URA CANTHODII

183

pectoral fin at this stage remains doubtful, but there is little
evidence of their existence in the pelvic fin (p. 181). The reduc-
tion of the dermal skeleton, and the development of a large occipital
spine in the first family, are signs of specialisation. Possibly
the Pleuracanthodii are related to the Cladoselachii through the
Cladodontidae (Dollo [121], etc.). The Pleuracanthodii appear
in the Devonian epoch, and seem to die out in the Permian.

Family PLEURACANTHIDAE. Pleuracanthus, Ag. ; Lower Permian,
Europe. (Xenacanthus, Beyr. ; Carboniferous and Permian, Europe ;
possibly the same as Pleuracanthus.) Diplodus, Ag. ; Carboniferous and

Fio. 148.

Left pectoral girdle anil fin-skeleton of 1'leuracantJnis Gaudryi, Fr. «, segmented axis of
tin ; c, coracoid region ; d.c, dorsal cartilage ; pr, preaxial radial ; pt, postaxial radial ;
a, scapular region ; v.c, ventral cartilage. On the right three teeth of Orthacanthiis (from
Fritsch), t.

Permian, N. America. Diacranodus, Garm. ; Permian, N. America
[61].

Family CLADODONTIDAE. With teeth having many small lateral cusps,
jind uniserial pectoral-fin skeleton (Fig. 87). The rest of the skeleton is
scarcely known at all (Traquair [464], Braus [49]).

Cladodus, Ag. ; Devonian, Carboniferous, and Permian of N. America,
and Europe. Symmorium, Cope, Carboniferous, N. America, possibly
belongs to this sub-class (Fig. 87) (Cope [92]). Dicentrodus, Traq. ; Mid.
Carboniferous, Scotland. Phaebodus, St. J. and "W. ; Devonian, N.
America.

Family CHONDRENCHELYIDAE. An incompletely known fossil
described by Traquair [452a] ; it is like Pleuracanthus, but lacks the
dorsal spine, and has only one* dorsal radial to each segment.

Chondrenchelys, Traq. ; Lower Carboniferous, Dumfriesshire.

184

PLE URA CA NTHODII

FIG. 149.

Pelvic girdle of Pleuracantlu/s
Gaudryi, Brogn. (From Quart.
Journ. Micr. Sci.)

FIG. 150.

Ventral view of the pelvic girdle and
right fln of a female Pleuracanthus Oelber-
gensis, Fr. a, jointed axis ; p, pelvic carti-
lage ; pr.r, preaxial radial; pt.r, postaxial
radial. (After Fritseh, from Quart. Journ.
Micr. Sci.)

FIG. 151.

Pelvic girdle and fin-
skeleton of a male Pleuracun-
thtis Oelbergcnsis, Fr. (After
Fritseh.) a.r, anterior preaxial
radial resting on girdle ; bp,
segmented basipterygial axis ;
cl, modified radials of clasper ;
p, pel vie girdle (left half) ; p.r,
preaxial radials.

Sub-Class 3. CLADOSELACHII.

The extinct family Cladoselachidae contains some of the earliest
and most interesting of the fossil Chondrichthyes. Isolated sharp-
cusped teeth have long been known, under the name Cladodus,
from Devonian and Lower Carboniferous strata ; but it is only lately
that more or less complete fossils have been found (Newberry [309],
Dean [102, 104]).

In general shape Cladoselache resembles a Notidanid except
that the tail ends in a sharply upturned tip (Fig. 152). The
caudal fin has a large ventral lobe. Horizontal keels extend along

PLE URA CANTHODII

185

the tail. Two dorsal fins are present, but apparently no anal.
There are paired pectoral and pelvic fins of remarkable structure.
No rostral process projects beyond the mouth ; the orbits are
surrounded by a double ring of dermal plates, probably formed of
fused denticles. Small denticles are distributed over the body ;
their histological structure has unfortunately not yet been described.
The lateral line runs between two rows of denticles. Broad-based
teeth, with a large median and smaller lateral cusps, are closely

FIG. 152.

'•'r'c/.).«e?oc/ie Fyleri, Newb. ; Upper Devonian, Ohio. A, right-side vif\v ; 15, ventral view;
C, front view ; restored. (After Dean, from A. S. Woodward, 7Vor. (led. Assoe.)

set in rows transverse to the jaws (Fig. 153). The skull resembles
that of the Notidanidae ; also the jaws, which are amphistylic,
with a broad palato-quadrate cartilage and long back ward ly directed
hyomandibular. The branchial arches were five, or possibly six or
seven, in number. The
notochord was probably
unconstricted ; no centra,
but neural and haemal
arches without inter-
•calaries, have been found.
The endoskeletal supports
of the median and paired

«no afo iitiim'nt-o/1 ovf^nrl Teeth of Cladoselachf, from different regions of the jaws.

tins are unjomtecl, extend (After Deailj Fishcs Living and Fossii.)

to near the edge of the

fin-web, and the ceratotrichia are but little developed. Possibly
this extension is primitive; but it must be noted that it occurs
also in the Rajiformes and certain other Selachians. The dorsal
lobe of the caudal fin is borne by segmental radials, and the ventral
by numerous slender cartilages crowded in its lower half (Fig. 154).

FIG. 153.

1 86

PLE URA CANTHOD1I

The chief points of interest in the paired fin are the breadth of the
base, which shows no sign of constriction
from the body -wall either in front or
behind ; and the correlated slight con-
centration of the radials. Yet the radials
are numerous, and are stouter at the pre-
axial border than at the postaxial, where
considerable concentration may have taken
place without producing the posterior
notch characteristic of the fins of most
other fish. Only vague indications of
girdles can be made out ; the pelvic
radials seem to have remained separate
in the body -wall without fusing to a
basipterygium (Fig. 155); the pectoral
radials fuse to some extent, at all events,
to form basal pieces.

No claspers have been found in the
Cladoselachii ; we must therefore suppose
that this sub-class diverged from the main
stem before the Chondrichthyes had ac-
quired them. The antiquity of the strata
in which the Cladoselachii occur, their
general proportions and simplicity of
structure, their dentition, amphistylic
jaws, and paired fins, all favour the view
that they are primitive. The strongly
heterocercal tail, and the circumorbital

Fio. 1.54.

Cladosflache Fi/lcri, Kewb.
Caudal lin. (After Dean, from
A. 8. Woodward.) D, fin-mem-
brane with dermal rays ; N, neural
.spines; R, endoskeletallradials.

FIG. 155.

Clailoselaelie Fi/leri, Newb. Left pectoral and pelvic fins. (After Dean, from A. S. Wood-
ward.) B, basal cartilages within the body-wall ; D, dermal fin-membrane with dermal rays ;
R, endoskcletal radials.

CLADOSELACHII

187

ring, are the only clearly specialised characters they possess ; and
in these they approach the Acanthodii. Another point of resem-
blance is the manner in which the paired fins merge posteriorly
into the body-wall. Important differences, however, separate these
two sub-classes.

Family CLADOSELACHIDAE. Cladoselache, Dean ; Cleveland Shale
(Upper Devonian or Lower Carboniferous).

Sub-Class 4. ACANTHODII.

Among the earliest known fossil Vertebrata are certain spiny
fish, which are generally associated with the Elasmobranchii.

B

FK;. 1 •"•!'>.

A, restoration otDtpUuxinihvistriahu, Ag. (after Traquair). B, scaling of Acanthoiles gracilia,
Beyr., enlarged (after Zittel). C, scales of the lateral line otProtaeanthodet pin nut us, Fr., enlarged
(after Kritsch). c.f, anal, c.f, caudal, d.f, dorsal, p.f, pectoral, and pv, pelvic fin ; 1 .1, lateral-line

scales ; .«j», spine.

These Acanthodians extend from the Upper Silurian to the
Permian epoch ; their structure has been studied of late more
especially by Fritsch [139], Reis [351-2], A. S. Woodward [505],
Traquair [462, 460], Dean [111], and others. Shark-like in general
shape, they have a fusiform body, blunt snout, and distinctly
heterocercal tail. The hypochordal lobe of the caudal fin is large,
the epichordal scarcely developed.

An anal and one or two dorsal fins are present, each with a
powerful spine at its anterior edge ; these spines are single
structures of vasodentine, as in the Holocephali, and probably are
enlarged denticles (Fig. 1 58). The web of the fin is attached in front
to the hinder edge of the spine, and along its whole extended base to

1 88

ACANTHODII

the body. The paired fins are of similar form, with a strong anterior
spine and thin membranous web, supported, however, in some cases
by ceratotrichia with calcified base (Reis [352]). The mouth is
wide, the orbit far forward, and the nostrils were probably placed
as in Selachians. The five gill-slits opened independently to the
exterior.

The whole body is covered with minute closely fitting dermal
scales (Fig. 156). These scales, which are generally loosely com-
pared to placoid scales, differ fundamentally from the denticles of
Elasmobranchs (Reis [352], Goodrich [178]). They have a deep-
lying solid base expanding superficially into a more or less quad-
rangular shiny plate sometimes ornamented, or produced to a point.
There is no pulp-cavity ; the scale is made up of concentric layers

.9

-dt

FIG. 157.

Transverse section of the scale of AcantJiades sp. ; Lower Carboniferous, Edinburgh.
dt, branching canaliciili ; g, outer shiny layer ; I, inner more opaque layer.

of bony substance without bone-cells ; minute branching canaliculi
penetrate into this substance from the outside, and it therefore
has some resemblance to dentine (Fig. 157). The outer layers
resemble ganoine, and there is no enamel. In fact, the Acanthodiau
scale, except for the absence of cells and vascular channels, is just
like a small ganoid scale (especially like the scale of Cheirolepis,
p. 311). It differs so markedly from the denticle that it is
impossible without intermediate forms to say whether it has been
derived from the Elasmobranch placoid scale. On the other hand,
the resemblance it bears to the ganoid scale is very possibly clue to
convergence.

The scales spread on to the caudal fin, in rows simulating
lepidotrichia, and to a less extent on to the other fins also. On
the head they increase in size and form a covering of close-fitting
plates. Four or more similar plates surround the orbit. The

ACANTHODI1 189

scales and the spines are probably of similar origin ; and ridge-
scales, somewhat intermediate in shape, may extend from the base
of the dorsal fin on to the head (Pare.nis).

A varying number of spines may also be found between the
pectoral and the pelvic fin (Figs. 156, 164); their presence has
been taken to indicate the former continuity of these two fins (Cope,
A. S. Woodward [503]). It is to be noticed that there is no con-
centration of the base of the fins, no notching of the posterior edge
such as is found in other fish, with the exception of the Clado-
selachidae, the fin passing gradually into the body behind.

The lateral line runs usually between two rows of scales, as in
Elasmobranchs (Fig. 156, C). But in Euthacanthus gmcilis it was

cr

Fie. 158.

Restoration of Cheiracanthus Mtm-hisinii, Ag. (After Traquair.) ('./, anal, c./, caudal,
d.f, dorsal, jw.f, pectoral, and p.f, pelvic tin ; c.r, circumorbital ring ; g, five branchial slits.

covered over and enclosed by double rows of modified scales
(Dean [111]).

Of great interest is the skeleton, which shows certain unexpected
points of resemblance to that of the Osteichthyes. The notochord
appears to have been persistent and unconstricted ; there are
slender neural arches, and similar haemal arches thickened at the
base of the hypochordal fin. Traces have also been found
(Dean [111]) of dorsal radials forming a row separate from the
vertebral column. Eadials also appear in the front region of the
hypochordal fin strengthened with dermal scales. The skull and
visceral arches seem to have closely resembled those of the
amphistylic Elasmobranchs (Fig. 159). The palato-quadrate has
a large otic process, the hyomandibular is elongated, the five
branchial arches have the usual epi-, cerato-, hypo-, and basi-
branchial elements. Most remarkable is the strengthening of the
primary upper and lower jaws with hard bone-like tissue. This
tissue is probably never typical bone ; but it resembles it very closely,

190

ACANTHODII

and contains numerous cells which may have branching processes.
The marginal teeth of the jaws, sometimes large and multicuspid,
are firmly fixed to these 'bones' in some genera (Fig. 160).
As a rule, the teeth are small, or absent. Sometimes, however,

Vm. 150.

Diagram of the skull and visceral arches of an Acanthodian. l>r, fifth branchial arch ; 7im,
hyomandibular ; h.p, calcified plate bearing similar branchial rays (?) ; m, Meckel's cartilage ;
o.p, otic process of the palato-quadrate ; po, ethmoid process.

they are of considerable size, and Dean has described in Ischna-
canthus rows of teeth, with large central and small lateral cusps,
resembling those of primitive sharks (Cladoselachians, etc.). The
ceratohyal seems to be covered with a plate bearing a series (or
two series, Eohon [367]) of long branchial rays, all of similar hard

st

FIG. 160.

Portion of lower jaw of Isehnacanthus, L. Devonian, Forfar ; outer view.
b, bone-like tissue ; st, inner teeth ; t, marginal tooth.

tissue or of dentine (A. S. Woodward [505], Eeis [352]). Long
branchial rays also occur on the branchial arches ; but whether in
single or in double series is not yet clear. Perhaps more peculiar
still is the structure of the pectoral girdle. It remains in some of
the fossils (Acanthodes, Fig. 162), in the shape of a rod fixed to the
base of the spine; in others (Parexus, Fig. 161), a broad clavicular

ACANTHOD1I

191

plate is added above ; while in the Diplacanthidae a girdle is com-
posed of two ventral claviculars and two larger dorsal supra-
claviculars, all of bone-like tissue (Fig. 163). The endoskeleton of
the fins must have been very much reduced or absent in most
cases, in correlation with the great development of the dermal
spines ; but Acanthodes is said (Reis [352]) to possess some short
radials at the base of the pectoral fin.

The Acanthodii were placed with the 'Ganoids' in the older
classifications; Huxley [227] considered them to be rather
intermediate between these and the Elasmobranchs ; A. S.
Woodward places them with the Elasmobranchs [505]. That

FIG. 10--'.

.

E^. ; Upper Carbonif.,
Staffordshire. Skele-
ton of pectoral tin
and girdle. //, ' supra-
clavicular'; r, cerato-
trichia ; .-., tin -spine.
(From A. S. Wood-
ward, Urit. Mtts.C'atcl.)

xti-in.titx, Ag. ; Lower Old
1 :.-il Sandstone, Scotland." Skeleton of
pectoral arch and fin. d, ' supraclavicnlar ' ;
ii-l, 'clavicular' plate ; h, basal region of
pectoral fin ; s, anterior, and m, posterior
.spine. (From A. S. Woodward, lirit. Mas.
GUaL)

Fin. 101.

rnrexus fi.ili-ntii.--,
Powrie ; Lower Old
Red Sandstone, Scot-
land. Skeleton of pec-
toral girdle and lin.
li, ' supraclavicular ' ;
d, ' clavicular ' plate ;
x, tin-spine. (From
A. S. Woodward,
Urit. Mus. Catal.)

they are far removed from any known Osteichthyes is shown by
the absence of an operculum, of marginal jaw-bones, etc. (for it
must be remembered that the jaws of the Acanthodii represent
the palato-quadrate and Meckel's cartilage) ; affinity, on the other
hand, is shown in the structure of the scales, and the development
of hard tissue which bears some resemblance to bone. On the
whole, the Acanthodii seem to be nearer to the Chondrichthyes,
with which we shall place them on account of the general form of
the body, structure of the skeleton, the amphistylic character of
the jaws, the position of the lateral line, and the presence of
ceratotrichia. They resemble the Cladoselachii in general shape,
in the jaws, fins, and heterocercal tail, and in the circumorbital ring
of plates. It would be interesting to compare the finer structure
of the scales in these two groups. Dean [103] considers the Acan-
thodii to be related to, but more specialised than, the Cladoselachii.

192

ACANTHODII

Family DIPLACANTHIDAE. The spines are much developed, may be
serrated and grooved ; they usually occur between the pectoral' and
pelvic fins. In Diplacantlms there are two pectoral spines on each side
(Fig. 163). There are two dorsal fins, and usually clavicular plates.

Diplacanthus, Ag. (Fig. 156, A); Parents, Ag. ; Mesacanthus (Fig.
164, B) ; Ischnacanthus, Eg.; Devonian, Scotland. Climatius, Ag.
(Fig. 164, A); Devonian, Scotland and England.

Family ACANTHODIDAE. The intermediate spines are vestigial or
absent ; the remaining spines are more slender ; there is only a single

FIG. 104.

A, CUmatius scutiger, Eg., Lower Old Red Sandstone, Forfarshire ; B, Mesacanthus Mitchell!,
Eg., ibid. ; C, Acanthodes sulcatus, Ag., Lower Carboniferous, Edinburgh ; D, Acanthodes (tracilis,
Roemer, Lower Permian, Bohemia ; restored outlines. (A after A. S. Woodward, B and C
after Traquair, D after Fritsch, from A. 8. Woodward, Proc. Geol. Assoc.) a, anal, d, dorsal,
p, pectoral, and v, pelvic fins ; i.sp, paired ventral spines.

dorsal fin ; and the pelvic fin tends to dwindle in size as the pectoral
becomes larger.

Acanthodes (Acanthoessus), Ag. ; Devonian, Europe and N. America
(Fig. 164, C and D) ; Carboniferous and Permian, Europe. Cheir acanthus,
Ag. (Fig. 158); Devonian, Scotland. Acanthodojisis, H. and A.; Car-
boniferous, Great Britain. Protacanthodes, Fr. ; Permian, Europe.

INCERTAE SEDIS.

Family GYRACANTHIDAE. Isolated large spines and small tubercles,
found in Palaeozoic deposits, and to which the names Gymcanthus and
Oracanthus have been given, have long been a puzzle to palaeontologists.
Quite recently, A. S. Woodward has shown that they belong to a fish

G YRA CANTHIDAE

193

apparently allied to the Acanthodii [507]. The body of Gyracanthides
seems to have been broad, short, and somewhat depressed ; the tail well-
developed and heterocercal. An
anal and a dorsal fin are found ;
each provided with a strong anterior
spine, from which the membrane
stretched back along the body as in
Acanthodians. Very large pectoral
and smaller pelvic spines indicate
the paired fins ; a groove along the
hind edge of these spines probably
marks the attachment of the fin-
web, which, however, is unknown
(Fig. 165). The head, trunk, tail,
and fins are all covered with
closely fitting quadrangular scales
of small and nearly uniform size.
Unfortunately the minute structure
of these scales is still unknown ;
but there is said to be a small
pulp-cavity, which would point to
their being flattened den tides, rather
than true Acanthodian scales [507].
The fin -spines, composed of vaso-
dentine, have a hollow base, and
are superficially ornamented with
grooves and tubercles. Neither
endoskeleton, nor teeth, nor circum-
orbital plates have been found ;
but there are " two pairs of hollow,
broad, triangular, free spines, of
fibrous texture, fixed near the in-
sertion of the pectoral fin-spines " ; FIG. 165.
these also have a tuberculated or-
namentation on one surface.

cf.

Gyracanthus Murmyi, A. S. W. ; Carboni-
ferous, Victoria ; restored. (After A. Smith
Woodward.) Ventral view, with the tail twisted
The systematic position of the so as to show the dorsal fin. a, anterior, and
ftvrapintliirlnp is l>v rm mpaTi<? clpar *' Posterior paired body-spines; a./, anal, c.f,

uyracantmaae is oy no means uear. caudal) an(j ^ dorsal fin . pspi pectoral spine ;
While resembling the Acanthodii in pv-sp, pelvic spine,
many characters [507], these interest-
ing fossils show some affinity to the Ostracodermi (more especially the
Pteraspidomorphi) in the structure of the dermal spines and plates.
Possibly they form a connecting-link between these two groups, and will
afford a valuable clue to the real position of the Acanthodii.

Gi/racanthus, Ag. (Fig. 165); Lower Devonian, Canada; Carboni-
ferous, Europe, N. America. Oracanthus, Ag. ; Carboniferous, Europe,
N. America.

Sub-Grade 2. OSTRACODERMI.

THIS is a merely provisional group, in which are gathered some
of the oldest and least satisfactorily known Palaeozoic fish. So
aberrant are they in structure that their very 'right to be placed
among the Pisces at all has been disputed (Cope, A. S. Woodward
[503, 505]). Cope, indeed, suggested that they are allied to the
Cyclostomes. While the relationship to each other of the various
orders included in this Division remains almost as obscure as ever,
the affinities of the Pteraspidomorphi to the Elasmobranchii, through
the Coelolepidae, seem to be now well established by the researches
of Traquair. On the other hand, the presence in the Cephalaspido-
morphi and Pterychthiomorphi of true bone in the exoskeleton, and
of fin-rays and fulcra having considerable resemblance to the lepi-
dotrichia and fulcra of the Osteichthyes, points doubtfully to some
connection with the latter. The fact that true jaws have not yet
been detected has little weight, since no remains of any part of the
endoskeleton have been preserved in these very ancient fossils
(except, perhaps, in the tail of some Anaspida, p. 206). The
Ostracodermi have very few characters in common beyond the
possession of a single dorsal fin, a heterocercal tail, and a
tendency, so to speak, for the head and trunk to become enclosed
in dermal shields. In all, except the Anaspida, the lateral -line
system has been described. The mouth is ventral, and some sort
of branchial opening can generally be made out. No very definite
traces of nasal or of auditory organs can be seen, though there are
occasional vague indications of their presence. Paired orbits and
a median pore or depression, probably due to a pineal organ, are
generally, if not universally, present. It is to be noted that normal
paired limbs have never been found in any member of the group ;
but in some the body expands at the sides into a longitudinal fold
(Coelolepidae), or distinct flap (Cephalaspidae), or jointed appendage
(Pterychthyidae), which may represent a pectoral limb. Of a
separate pelvic limb there is not the slightest trace.1

1 The very interesting fragments from the Lower Old Red Sandstone described by
Traquair under the name Farnellia tttberculata possibly belong here. This fossil has
polygonal scutes and ring -like centra. Similar scutes have been found in the
Silurian Ludlow bed (A. S. Woodward).

194

PTERASPIDOMORPHI 195

Order 1. PTERASPIDOMORPHI (Heterostraci).

It is chiefly to the works of Lankester [276J and Traquair that
we are indebted for our knowledge of the strange fossils included
in this Order. The anterior region of these fish, including the
head and trunk, is broad and dorso-ventrally depressed. Behind,
they usually narrow rapidly to the distinctly heterocercal tail, with
a ventral caudal fin-lobe. A single median dorsal fin is sometimes
(Coelolepidae), perhaps always, present. A longitudinal fold or
ridge on each side may possibly represent the paired fins (Traquair
[465-9]). Small lateral orbits are found near the anterior margin.
They are situated wide apart, unlike those of the Cephalaspido-
morphi. The mouth was probably in the form of a transverse
ventral slit. There is no trace of teeth or jaws. A cloacal
aperture has been found in Drepanaspis (Fig. 169). Thelodus
and Cyathaspis show signs of some six or seven branchial pouches
(Fig. 172). In Pteraspis, also, there is a pair of small lateral
apertures near the edge of the dorsal shield, which may represent
spiracles (Fig. 170). The exoskeleton varies from a covering of
scattered denticles in the Coelolepidae to plates and scales of complex
structure in the other families. But it is characteristic of the
whole group that true bone-corpuscles are never present (Huxley
[224]).

The origin of the dermal plates, according to Traquair [466], is
as follows : — In Lanarkia the whole body is covered with spine-like
denticles ; cones of dentine without basal plate, and with tubules
radiating from a central pulp-cavity, which is Avidely open below
(Fig. 167). The shagreen of Thelodus consists also of separate
denticles ; but they are broader and flatter, and the opening of
the pulp-cavity is generally narrowed to a small central aperture,
although no distinct basal plate is developed. These placoid scales
of typical dentine, with perhaps a superficial enamel, are set nearer
together, and may fit closely together by their crenulated edges
(Fig. 166). Now in the Psammosteidae the plates and scales have
a superficial covering of exactly similar closely fitting denticles with
crenulated edges, which, however, are fixed to an underlying layer
of spongy bone-like substance (Fig. 166, D, H). The inner surface
of these plates may be strengthened by a laminated layer of similar
substance. Thus the primitively isolated denticles appear to have
become connected together by a secondary development of ' bone '
in the deeper layers of the connective tissue. The compound plates,
then, acquire a structure bearing a striking resemblance to that of
the cosmine-covered scales of the Osteolepidoti (p. 217). The
denticles, already much elongated in Psamrnosteus, become converted
into smooth ridges of dentine, forming a nearly even layer over

196

P TERA SPID OMORPHI

the entire surface of the scales and plates of the Pteraspidae
(Fig. 166, E, I).

Thus we seem to be able to trace a genetic connection between
the very aberrant Pteraspids and some early kind of shark, through
the Coelolepidae ; but whether the four families given below really
form a phyletic series remains doubtful.

The Pteraspidomorphi are among the most ancient of vertebrate

FIG. 166.

Diagrams of the structure and development of the dermal skeleton of A, an early stage, and
B, later stages of Elasmobranchs ; C, Thelodtis ; D, Psamrnostev.s ; E, Pteraspis, all in section
at right angles to the surface ; the dentine is black. F-I, enlarged views of the outer
surface of the dermal skeleton of, F, Thelodus head ; G, Thelodus tail ; H, Psammosteus shield ;
and I, Pteraspis shield. 6/j expanded basal plate ; b.m, basement membrane ; c.t, connective
tissue ; d.c, dentine cap ; ep, epidermis ; I, bony lamellae ; p, pulp-cavity ; 7', surface ridge ; tr,
bony trabeculae of vascular layer.

animals ; they flourished in Upper Silurian and Devonian times,
beyond which they do not appear to have survived.

Family COELOLEPIDAE. The body is flattened dorso-ventrally, and
expanded on each side into a longitudinal flap of considerable size. A
single dorsal fin is present. The exoskeleton is in the form of numerous
scattered placoid scales ; either sharp, conical, and tooth-like as in
Lanarkia (Fig. 167), or more flattened and closely fitting as in Thelodus
(Fig. 168). No lateral-line system has been made out (Traquair [466],
Kohon [371]).

Thelodus, Ag. ; Coelolepis, P. ; Upper Silurian and Devonian, Europe.
Lanarkia, Traq. ; Upper Silurian, Scotland.

P TERA SPIDOMORPHI

197

Family DREPANASPIDAE. The expanded depressed body is shaped
much as in Thelodus ; but the tail, although heterocercal, is not so
distinctly bilobed, and no dorsal fin has been found (Fig. 169). The
whole animal is covered with plates and scales, ornamented with stellate

"~"°" " :

FIG. 167.

Diagrammatic restoration of Lanarkla spinosa, Traq. Dorsal view with the tail twisted to
show the heterocercal caudal fin. The eyos appear near the anterior border. (After Traquair,

'J'l-i'n*. Roil. >'<»•. l'.ilin.)

tubercles or ridges. A large median dorsal plate is situated above, two
' rostral ' plates at the anterior edge ; a large median ventral plate occurs
below, with a median ' mental ' in front. The mouth was situated in
the transverse slit between the rostrals and the mental ; and a cloacal
aperture seems to have been placed behind the ventral. Anterior and

FIG. 168.

Diagrammatic restoration of Thelwlus scollom, Traq. Dorsal view with the tail twisted to
show the caudal and dorsal (ins. Tin; eyes are shown near the anterior border. (After Traquair,

TI-HHS. H<>U. >'"<-. l-'.ilin.)

posterior ventro-lateral plates occur, also a pair of lateral plates are
pierced by a hole, which probably represents the orbit. The eyes were,
then, rather ventral than dorsal, and far apart. The lateral flaps, the
expanded edge of the body, are enclosed in long ' postero-lateral ' plates.
The spaces between the large plates are covered with a mosaic of smaller
polygonal plates, which are continued on to the tail and caudal fin, where
they acquire the shape of imbricating scales diminishing in size behind.

198

The dorsal and the ventral edge of the tail are strengthened with a
median series of stout fulcral scales (Traquair [467-8]).

Drepanaspis, Schliiter ; Lower Devonian, Prussia.

Family PSAMMOSTEIDAE. Incompletely known fossils, represented
by large convex plates, isolated fragments apparently the posterior
corners of the lateral naps, scales, and fulcra. All these are covered
with an outer layer of denticles, often with closely fitting crenulated
edges, strikingly like those of Thelodus. The denticles are fixed on an

FIG. 169.

Restoration of Drepanaspis gemiindencnsis, Schl. Dorsal (A) and ventral view (B). Lower
Devonian, Bundenbach. (After Traquair, from Brit. Mus. Guide.) a.v.l, anterior ventro-lateral ;
e.l, external labial ; TO, mental, behind the mouth ; m.d, median dorsal ; m.v, median ventral ;
p.l, postero-lateral ; p.v.l, posterior ventro-lateral ; r, rostral ; x, orbital plate with orbit ;
cloacal aperture behind the median ventral plate.

underlying layer of bony substance with large vascular spaces (Fig.
166, D and H). The plates are frequently marked with superficial
polygonal areas, somewhat like those of the Cephalaspid armour
(Traquair [466]).

Psammosteus, Ag. ; Devonian, Europe.

Family PTERASPIDAE. The head and body are narrower, and the
lateral flaps are but little developed (Fig. 171). The exact shape of the
tail is unknown, but there is reason to believe that it was heterocercal.
No dorsal fin has been observed (Lankester [276], Traquair [466],
Drevermann [122], Alth [19a]).

The best-known genus, Pteraspis, has the entire dorsal region of the
head and body covered by a bony shield, projecting into a rostrum in

P TERA SPIDOMORPHI

199

front, and a sharp median spine and two lateral angles behind (Fig. 170).
This shield appears to be made up of seven plates, distinct only in the

A.

Fio. 170.

A, dorsal view of the shield of Pteraspis rostrata, showing the openings of the lateral-line
system. B, transverse section (after Patten). C, ventral view of the same, with the ventral

lit-st.. ration of l'trraf)>ix rostrata, Ag. ; Lower Old Red Sandstone. (After A. S. Woodward,
Brit. Ma.-: I'ntnl.) Left-side view ; the tail and fin only in outline.

young. The rostral plate surrounds a preoral projection, two orbital
plates are pierced with holes which presumably harboured the eyes, a

200

P TERA SPIDOMORPHI

very large convex dorsal plate bears the spinal plate behind, and is flanked
on either side by a cornual or postero-lateral plate. The latter doubtless
represents the lateral flap in the Coelolepidae and
Drepanaspidae. A median internal depression be-
tween the orbits is taken to mark the position of
the pineal body ; and an oblique slit in each cornual
may represent a gill-opening.

Fitting below the dorsal shield is a large convex
ventral shield formed of a single piece (Fig. 170, C).
The mouth was between it and the rostral. The tail-
region is covered with imbricating scales. An elabo-
rate system of lateral-line canals, opening to the
exterior by a double series of pores, is present in the
dorsal shield (Fig. 170, D, E) (A. S. Woodward
[503]).

In microscopic structure the plates resemble those
of Psammosteus (p. 195); but the superficial placoid
scales have become converted into long ridges. The
caudal scales are of the same nature.

In Cyathaspis the rostral shield is quite short,
ouki and the orbits do not appear to have been enclosed in
from visceral surface of the carapace (Fig. 172).
dorsal shield. (After m, V, 11

A. s. Woodward.) au, I he Pteraspidae would seem to represent an ex-

o?Kan(?)°n br Tmpres^ */reme stage in specialisation, in which the dorsal and
sions of 'branchial ventral median plates, already present in Drepanaspis,
have extended and fused with neighbouring plates, the
small intervening plates or scales having disappeared.
Pteraspis, Kner ; Devonian, Europe. Palaeaspis (Holaspis), Clay p. ;
Silurian, N. America ; Devonian, Europe. Cyathaspis, Lank. ; Silurian
and Devonian of Europe.

FIG. 172.

pineal beefy7??).

Order 2. CEPHALASPIDOMORPHI (Osteostraci).

Like the Coelolepidae, these Palaeozoic fish have an expanded
depressed head-region, which narrows behind to a heterocercal tail-
(Fig. 173). There is a single dorsal fin. The lateral edge of the
broad front region, which probably includes at least the most
anterior portion of the trunk, extends into a longitudinal flap in the
Ateleaspidae. This lateral expansion closely resembles the similar
flap in the Coelolepidae. It may represent a paired fin-fold, for in
the Cephalaspidae it is developed into a well-defined outstanding
scaly lobe with a narrow base (Fig. 173).

The mouth was ventral, and what appears to be a ventral
cloacal slit has been described in Cephalaspis at the root of the tail
(Patten [326]). Traces of six gill-pouches have been seen in
Cephalaspis (Jaekel [243]) on the under surface of the head-region ;
a number of ventral paired openings in Tremataspis possibly indicate
branchial openings (Fig. 176) (Rohon [371]).

CEPHALASPIDOMORPHI

2OI

The orbits are placed close together on the top of the head
(Figs. 174, 175), roofed over by a thin bony plate, and separated
only by a narrow bridge. The orbits are partially floored by bone
in Tremataspis. The interorbital space is occupied by a plate, which

dsc

ma

rf.

Restoration of Crphalaspis Li/Ml, a, lateral area with polygonal plates ; c, cornu of cephalic
shield ; c/, caudal fin ; el, position of cloaca ; c.s, cephalic shield ; d.f, dorsal fin ; d.sc, dorsal
ridge scales ; c, orbit ; m.a, median area with polygonal plates ; p, position of antorbital fossa.

may be quite free (Tremataspis) and bears on its inner surface a
median depression possibly for a pineal body. In front of the
orbits is an internal cavity opening, at all events in some genera
(Tremataspis), by a median
pore to the exterior. It
has been suggested that
this aperture represents
an olfactory organ,1 or a
median eye. A series of
pits in the cephalic shield
of Tremataspis indicates
the presence of a lateral-
line system of sense-organs
(Patten [325]).

The Cephalaspido-
morphi are, for the most
part, entirely covered
over with plates and
scales consisting of three
layers. The outer layer
of dense dentine-like sub-
stance bears spinelets or
tubercles. The middle

layer is pierced with vascular spaces ; the inner layer is lamellated.
True bone-cells are found in all three (Huxley [224], Lankester
[276]).

1 Some authors believe the Cephalaspids to be monorhinal, and allied to the
Cyclostomes.

FIG. 174.

Transverse sections of Cephalaspls. (After Patten.) A,
through the cephalic shield and eyes ; B, through the
trunk, d, dorsal ridge scale ; e, ocular scale ; ie, inturned
margin ; La, lateral area of small scutes ; v, ventral scales.

202

CEP HAL A SPIDOMORPHI

In the Ateleaspidae the scales on the sides of the body are set
in transverse rows, which fuse at the sides to transverse plates in

Cephalaspis Lyelli, Ag. ; restoration of dorsal shield. (After Lankester, from A. S. Wood-
ward.) a./, antorbital fossa ; a.p, antorbital prominences ; i.g, interorbital groove ; i.p, inter-
orbital plate; m.c, 'marginal cells'; o.r, orbital rim; p.a, posterior angle; p.c, posterior
cornu ; p.ov, postorbital depression ; p.r, posterior ridge ; p.s, posterior spine ; r, rim.

ma.

-\-~pa.

FIG. 176.

Tremataspis Schmidti, Rohon, enlarged. A, ventral, and B, dorsal view of the shields.
(After Patten.) a.a, anterior area with polygonal plates ; a.m.o, anterior median opening ; d.s,
dorsal shield ; l.l, pits of lateral line ; m, mouth ; m.a, median area with plates ; or, orbit ; p.a,
posterior area with plates ; pl.o, lateral opening ; v.o, ventral openings, probably branchial ;
v.p, ventral plates ; v.s, ventral shield.

CEPHALASPIDOMORPHI 203

the Cephalaspidae. Small scales like those of Thclodus are also
present in certain regions.

In the Cephalaspidae the scales also extend on to the fins,
forming linear series closely resembling the lepidotrichia of Teleo-
stome fish ; and a ridge of strong scales is present along the back,
and along the sides of the trunk, which thus acquires a triangular
section (Fig. 174). The tail of the Tremataspidae is unknown,' and
may have been naked. The expanded anterior region in the Atele-
aspidae is covered with a flexible armour of small polygonal plates ;
but in the Celphalaspid these fuse together over the head-region, so
as to form a large rigid dorsal shield with rounded anterior border,
and two posterior horns (Fig. 175). The compound origin of the
shield is betrayed by the persistence of polygonal areas, marked out
by vascular channels in the middle layer ; also by the presence of
an oval postorbital depression, and paired lateral spaces, in which
the polygonal plates remain separate (Fig. 173). These probably
indicate flexible areas over the brain and gill - chambers. The
cephalic shield of the Tremataspidae is still more thoroughly fused,
extending round to the ventral surface, so as to form an almost
complete box (Fig. 176).

These dermal structures have probably been formed by the fusion
of small denticles and an underlying plate, as in the case of the
Pteraspids ; but the stages in the process have not yet been so
clearly demonstrated, nor has the presence of bone-cells in the
superficial layer been explained.

The structure of the exoskeleton of the Cephalaspidomorphi is
now very thoroughly known, thanks to the labours of Lankester,
Rohon, A. S. Woodward, Patten, and Traquair. Yet their affini-
ties remain obscure. They differ markedly from thePteraspidomorphi
in the position of the orbits, and in the presence of bone-cells in
the exoskeleton. The resemblance in shape between Thelodus and
Ateleaspis seems, however, to point to some relationship between the
two orders (Traquair [466]).

Family ATELEASPIDAE. The head -region has a rounded margin
expanding into a rounded flap on each side. There are no shields, but
polygonal plates and scales, bearing sharp spinelets on their surface [466,
469].

Ateleaspis, Traquair; Upper Silurian, Scotland (Fig. 177).

Family CEPHALASPIDAE. The head -region is covered dorsally by a
large shield with inturned edge, and ventrally with polygonal scales.
The shield may bear a posterior median spine, and its posterior corners
may be produced backwards into immense cornua (Eukeraspis). In
Auchenaspis (Thyestes) the shield extends on to the trunk, several series
of trunk-scales having apparently been incorporated into its hinder region.
The interorbital plate is fixed. The cephalic shield is generally orna-
mented with tubercles, and may bear tooth-like spines along its edge. A

2O4

CEPHALA SPIDOMORPHI

large fin-like lobe, covered with scales continuous with the shield at its
base, projects from each side of the body behind the cephalic shield in
Cephalaspis (Fig. 173 [505, 276, 326]).

Cephalaspis, Ag., and Auchenaspis, Ag. (Thyestes, Eich.) ; Upper Silurian
and Devonian, Europe. Eukeraspis, Lank., Silurian, and Didymaspis,
Lank., Devonian, England.

Fio. 177.

Diagrammatic restored outline of Ateleagpis tcssellata, Traq., the tail being turned so as to
appear in profile. The orbits are shown near the middle of the head-shield, and in front of
them the antorbital fossa and median pore. (After Traquair.)

Family TREMATASPIDAE. The almost smooth cephalic shield is con-
tinuous round the sides on to the ventral surface. Ventrally, behind the
mouth, is an area covered by closely fitting plates, and between these and
the edge of the shield are a series of apertures, presumably branchial.
The interorbital plate is free ; the orbits roofless. No lateral flaps are
known [371, 325].

Tremataspis, Schmidt ; Upper Silurian, Russia (Fig. 176).

Order 3. ANASPIDA.

An order founded by Traquair [466] for the reception of two
genera of very aberrant structure from the Silurian rocks of Scot-
land, Lasanius and Birkenia, to which has been added a less well-

FIG. 178.

Birkenia elegans, Traq. ; restored. (After Traquair.) c.f, caudal fin ; d.f, dorsal fin ;
l.o, lateral openings, possibly branchial ; o, orbit ; i:s, large ventral scales.

AN ASP ID A

205

\J

known genus, Euphanerops, from the Upper Devonian of Canada
(A. S. Woodward [503a]). They are fish-like in shape, with fusiform
body and heterocercal tail (Figs. 178,
179). The ventral lobe of the caudal
fin is well marked. They have hard
exoskeletal scales, the histological char-
acters of which are not thoroughly known,
and in which no bone -cells have been
found ; and both Birkenia and Lasanius
have a median ventral row of strong pro-
jecting scales. Birkenia and Euphanerops
have a small median dorsal fin ; but in
none of the Anaspida is there any trace
of paired fins or flaps.

The mouth appears to have been
ventral, below the rounded snout. Neither
nostrils nor orbits can be certainly identi-
fied, although a pair of rounded spaces in
Birkenia and two skeletal rings in Eupha-
nerops may possibly indicate the position
of the eyes on each side of the head. In
the former genus, also, is seen a row of
eight small holes set obliquely on each
side at the back of the head, which are
supposed to represent gill-openings, and
recall similar apertures in Tremataspis
(p. 204). The systematic position of the
Anaspida remains quite uncertain. The
heterocercal tail and the dorsal fin they
possess in common with other Ostra-
codermi ; in the disposition of the scales
on the trunk, and in the presence of a
row of branchial (?) openings, they approach
the Cephalaspidomorphi.

Family BIRKENIIDAE. Birkenia is com-
pletely covered with scales, small on the head,
larger on the trunk, and smaller again on
the caudal tin. On the body they are chiefly
set in regular oblique rows inclined forwards and downwards (Fig. 178).
The scales have a slightly tuberculated surface [466].

Birkenia, Traq. ; Silurian, Scotland.

Family LASANIIDAE. A single row of small scales followed by a set
of eight parallel oblique rods placed on either side behind the head, together
with a ventral row of very uniform recurved scutes, seem to represent all
that remains of the bony exoskeleton in Lasanius. Possibly the parallel
rods passed between gill-slits. There are indications of rays on the caudal
fin [466, 469].

206

ANASP1DA

Lasanius, Traq. ; Silurian, Scotland (Fig. 179).

Family EUPHANEROPIDAE. Small scattered shagreen granules are
found on the head, enlarging on the trunk into narrow scales disposed
much as in BirJcenia ; towards the tail are some quadrangular scales
with enamel-like surface. The granules extend on to the fins, in which
traces of dermal rays and also of endoskeletal supports can be made
out. The ventral row of scutes is less marked than in the other families
[503a].

Euphanero2)s, A. S. Woodward ; Upper Devonian, Canada.

Order 4. PTERICHTHYOMORPHI (Antiarchi).

This is a small compact group of Ostracodermi, remarkable for
the great development of the dermal armour. The plates and scales
are of true bone, with bone -cells throughout; their surface is or-
namented with tubercles and ridges, but bears no distinct evidence
of having been formed of fused denticles (Fig. 180). Vascular

ol.

FIG. ISO.

Enlarged view of a small piece of the shield of Bothriolepis canadensis, \Vht. ; Upper
Devonian, Canada, i, inner bony lamellae ; l.v, large vascular space ; m.l, middle vascular
layer ; o.l, outer bony lamellae ; s, surface ornament.

cavities are developed in the middle layer, and the inner layer is
lamellated as usual. • A very complete and accurate knowledge of
the outer structure of these Palaeozoic fish has been obtained of
late years from the researches of Pander [312], Traquair [452, 461],
A. S. Woodward [503, 505], Patten [328], and Rohon [370].

The broad rounded head is covered with a shield, which articu-
lates behind with a larger trunk shield or cuirass, completely
surrounding the body. Both are composed of closely united plates,
separated by fine sutures. The tail-region bears a dorsal fin and
an unforked heterocercal fin (Fig. 181). An anterior dorsal fin-fold
has been described in Bothriolepis immediately behind the carapace

PTERICHTHYOMORPHI 207

(Patten [328]). In Asterolepis and Pterichthys the tail is covered
with imbricated scales, smaller scales extend in rows on to the fins,
and powerful fulcral scales lie along the mid-dorsal line and the
anterior edge of the fins. Bothriohpis has an almost naked caudal
region. The lateral-line system is represented by grooves running
round the cephalic shield, passing ventrally in front of the mouth,
and down the sides of the trunk- cuirass on to the tail. The course
of these grooves on the head is very different from that pursued
in typical Pisces.

In front of the mouth below are placed two dermal ' maxillary '
plates, with toothed edges, which seem to represent jaws. On the
outer edge of each is a notch, perhaps indicating a nostril (A. S.
Woodward [503]). The mouth is limited behind by two small
semilunar plates at the edge of the ventral trunk-shield. The two
orbits are situated close to each other near the middle of the
cephalic shield. Each is protected by a thin, convex, bony plate ;
and between them is a free quadrangular plate, with a deep inner
excavation, possibly for a pineal organ.

The plates composing the cephalic shield do not agree in
number or disposition with the normal structure of the skull of
a Teleostome. Their arrangement, and also that of the plates
forming the trunk-cuirass, will best be understood by consulting
Fig. 181. A large plate on each side of the head appears to have
been movable and with a free edge — it may represent an operculum.
The one median and four paired plates composing the ventral trunk-
shield bear a remarkable resemblance to the plastron of the
Coccosteids (p. 261). According to Patten [328] the cuirass had
a free membranous edge behind, leaving a branchial opening
between it and the trunk. But the position of the branchiae, and
indeed their very presence, has not yet been definitely determined.
Probably they were within the cephalic shield.

Articulating near the front edge of the cuirass are two most
remarkable two-jointed, freely movable appendages, with serrated
anterior edge. They are completely encased in long plates. The
cavity inside the appendage communicates with that of the body
by an aperture in the cuirass. Most authors compare these
appendages to pectoral fins (Fig. 181).

So striking is the resemblance between the Pterichthyomorphi
and the Coccosteomorphi, not only in the general shape of the body
and the development of the cephalic and trunk shields, but also
in the minute structure of the dermal skeleton, that they were for
a long time associated by the older authors. Yet the two groups
differ in several fundamental characters. The presence of pectoral
appendages in the former, their absence in the latter ; the presence
of pelvic fins in the latter, their absence in the former ; and above
all, the possession of recognisable upper and lower toothed jaw-bones

208

P TER1CHTH YOMORPHI

in the Coccosteomorphi, are evidence of wide divergence. On the
other hand, the Pterichthyomorphi have much in common with the

( occ

Fio. 181.

Pteriehthys Milleri, Ag. Dorsal (A), ventral (B), and left lateral aspects (C); restored.
(After Traquair, from A. S. Woodward, Proc. Geol. Assoc.) a.d.l, anterior dorso-lateral,; ag,
angular ; a.m.d, anterior median dorsal ; a.v.l, anterior ventro-lateral ; c, central ; d.a, dorsal
anconeal ; d.ar, dorsal articular ; e.l, extra-lateral ; e.m, external marginal ; i.m, internal
marginal ; I, lateral ; l.oce, lateral occipital ; m, median ; m, in, in, in, marginals ; m.occ, median
occipital ; m.v, median ventral ; inx, maxilla ; o, ocular ; p.d.l, posterior dprso-lateral ; pm, pre-
median ; p.m.d, posterior median dorsal ; ptm, posthiedian ; p.i'.l, posterior ventro-lateral ; si,
semilunar ; t, terminal; v.a, ventral anconeal ; v.ar, ventral articular. Dotted lines indicate
the course of lateral-line canals.

PTERICHTH YOMORPHI

209

Cephalaspidomorphi. Especially important is the position and
structure of the orbits — so peculiar amongst Pisces, and so essentially
similar in both cases. The pectoral appendages may, moreover,
be compared with the paired flaps of Cephalaspis, also covered with
dermal armour.

cf

nv.

Fia. 1SU.

s ; restored. (After Patten.) c, cephalic shield ; cf, ventral lobe of caudal tin ;
c.v, dorsal lobe of caudal fin ; d./, second dorsal fin ; e, eye ; m, mouth ; p, pectoral jointed
appendage ; .-/(?, fold of skin (pelvic tin ?) ; t.x, thoracic shield.

Family ASTEROLEPIDAE. Asterolepis, Eich. ; Pterichthys, Ag. ; Micro-
Irachius, Traq. ; Devonian, Europe. Hothriolepis, Eich. ; Devonian, Europe
and Canada.

Sub-Grade 3. OSTEICHTHYES.

The remainder of the true fish are included in this sub-grade.
Many important characters distinguish them from the Chondrich-
thyes, which remain at a lower grade of organisation. The cartila-
ginous endoskeleton becomes to a considerable extent reduced in
the adult, and replaced by true bone, or some bone-like tissue
derived from true bone (p. 355).

The exoskeleton is also modified and strengthened by the
development of bony tissues. Whilst the primitive placoid scales
(denticles) may remain, at all events in certain regions, the body
is protected by the development of a new kind of bony scale or

FIG. 182.

Leuciscus rutilus. Right-side view, showing the scales. Some of the lines of scales have been
marked in black, to demonstrate their correspondence with the myotomes. 6', lateral line.
(After A. Hase.)

plate below them. The structure of these plates is very variable ;
and their exact ontogenetic and phylogenetic relation to the over-
lying denticles is often difficult to understand. On the trunk and
tail of the lower Osteichthyes are generally found thick, shiny,
more or less rhomboid scales in oblique rows corresponding numeri-
cally to the myotomes (Figs. 182, 183, 193). Each scale to some
extent overlaps its neighbours from before backwards like the tiles
of a roof, and the anterior deep -lying edge is often produced into
an articulating process. In the higher forms the scales become
thinner, more deeply imbricating, less closely articulated, and may
lose their metameric disposition.

Agassiz [4] classified the fish into the groups Placoidei,
Ganoidei, Cycloidei, and Ctenoidei, according to the character of

210

DERMAL SKELETON

211

their scales. The first have only 'placoid' scales (denticles,
see p. 119). The second have the flat rhombic shiny scales
mentioned above. The third have thin rounded scales. Lastly,
the Ctenoidei have similar thin scales, but provided with spiny

Fio. 183.

Ltin-isriin rutilus. Left-side view, showing the myotomes, two of which are marked in black.
E, longitudinal transverse septum ; S, lateral line. (After A. Hase.)

projections. Kecent work tends to show that the ' cycloid ' and
' ctenoid ' scales are closely allied forms derived from the more
primitive ' ganoid ' scale, and that they all three differ very

Fio. 184.

Dermal lin-ray of Polypterus bichir, Geoflr., enlarged. A, surface view of a few segments.
H. longitudinal section of the same, ct, connecting ligament ; d, denticle ; cp, epidermis ; si;
bony plate or segment of lepidotrich.

fundamentally from the 'placoid' type (Williamson [496«], Hertwig
[212], Klaatsch [264], A. S. Woodward [505]).

The true scale (as distinguished from the placoid denticle) of
the Osteichthyes sinks deep into the connective tissues, it is rarely
shed, and generally grows throughout life by the addition of
successive layers of bony substance. Scales differ, however, very

OSTEICHTHYES

considerably both in their mode of growth and histological structure
(p. 214). In the more specialised fish they undergo modification
in diverse ways — becoming spine - like (Gymnodontes), or few,
large, and plate-like (Acipenser, Loricariiclae), or sometimes dis-
appearing altogether.

Besides these body-scales are found scale-like exoskeletul
elements set end to end in rows, and forming jointed dermal
fin-rays, called lepidotrichia (Goodrich [175]), supporting the web

of both the paired and the
median fins (Figs. 184, 185,
186, 187). The minute struc-
ture of these fin-rays is almost
or quite identical with that of
the scales of the fish to which
they belong. This is true more
especially of the lower forms.
In some, such as Amblypterus,
there is a perfect gradation in
form and arrangement between
the body-scales and the fin-ray
elements. But, as a rule, the
transition is more abrupt, the
segments of the rays acquiring
a squarish or oblong shape, and
not overlapping (Fig. 249).
Both the scales and the seg-
ments of the lepidotrichia are
embedded in the dense con-
nective tissue, the fibres of
which enter the substance of
the bone. Movable joints are
formed by the fibrous matrix

remaining unossified between1
them (see pp. 214 and 356).
Large superficial dermal

Diagram of a section through the dorsal fin of , •, , , ,

Aeipenser. a, actinotrich ; I, lepidotrich ; r, plates are developed in the

Fid. 185.

(FromQvart- Osteichthyes on the head and
shoulder - girdle, which also

resemble the scales in structure and development. There can be
no doubt that these bones are of the same nature as the scales
on the body, though probably they were never exactly like them in
shape or disposition. In the course of the differentiation of the
now widely divergent groups included in the Osteichthyes the
dermal bones have undergone many important changes, yet a
fundamental plan can be made out which is common to all the
more primitive forms (Figs. 236, 240, 250-51).

DEKMAL SKELETON

213

The bones covering the head consist essentially of a paired
series of f rentals between the orbits, nasals in front and parietals
behind. Circumorbital bones surround the eye-sockets ; a trans-
verse row of small bones (often called supratemporals) covers
the occipital region, and forms a transition between the cranial
plates and the scales of the body ; and the sides of the cranial
roof are completed over the auditory region by paired pterotics
(squamosals) overhanging the articulation of the jaws. The upper
jaw is bounded on either side
by a toothed premaxillary and
maxillary. Each ramus of the
lower jaw is provided with an
outer toothed dentary and pos-
terior lower angular ; to these
should be added a dermal articular
and a coronoid (complementary).
The dermal articular plate seems
to be the last element of a series
of infradentaries found in certain
early forms (Megalichthys, etc.).
Ventrally the space between the
rami is covered with gular plates,
of which a row extends upwards
on either side on to the hyoidean
opercular Hap, where they expand
into the subopercular and oper-
cular bones.

On the roof of the buccal
cavity are a median posterior
parasphenoid underlying and
supporting the basis cranii, and
paired anterior vomers. Large
pterygoids and smaller palatines
cover the palato-quadrate arches, FIG. ise.

which do not form the biting Diagram of a section through the dorsal fin
<ulcrA nf flip TTIV nnrl nrr> iieii'illT' of Lepidosteus. a, actinotrich ; ft, scate ; d,

ifljaw, ana an suaiiy denti£le. lt lepidotrich; r> radi'al. (From
separated in the middle line in Quart. Joum. Micr. sn.)
front. A splenial on either side

lines the inside of the lower jaw. All these internal bones may
be toothed, and are indeed to a great extent formed by the
cementing together of numbers of small teeth (p. 217). Similar
bony plates with teeth may be found on the gill-arches. To this
list of primitive cranial dermal bones should perhaps be added a
median ethmoid in front, a median occipital behind, and a median
gular below.

Limiting the branchial chamber behind is the dermal shoulder-

214

OSTEICHTHYES

girdle (Figs. 241, 263). This consists of a series of paired bones : the
clavicle below overlies the coracoid ; the cleithrum strengthens the
region where the pectoral fin articulates, covering the scapula ; the
uppermost is the post-temporal (suprascapular), which in all typical
Osteichthycs unites the dermal shoulder-girdle firmly with the
otic region of the skull (Fig. 302). A supratemporal (extrascapular)
may occur between the pterotic and the post-temporal.

All these scales, bones, and lepidotrichia are in primitive forms

of similar structure, and are pre-
sumably of homologous nature.
Lying in the connective tissue
of the dermis outside the
muscles, they are covered
over by a layer of mesoblastic
tissue and the unbroken epi-
dermis. Only the larger bones
extend into the deeper layers
of the connective-tissue system.
True denticles (dermal teeth),
similar in structure and develop-
ment to those of the Elasmo-
branch, are found in some living
Teleostomes scattered over the
surface of the scales and lepido-
trichia. They are either fixed
(Lepidosteus, Polypterus, Figs.
184, 264) or movably attached
to the underlying bone (Silti-
roids, Fig. 373). Some fossil
forms (Coelacanthidae,Fig. 262)
are known to have possessed
an abundant supply of similar
denticles, and possibly they were
widely distributed among early

Diagram of a section through the dorsal fin of TeleOStomi.
a Teleost. a, actinotrich ; I, lepidotrich ; in,
radial muscle ; r, endoskeletal fin-radial ; .«,

scale. (From Quart. Joimi. Micr. Set.) What has been the history

of the ' ganoid ' scale is still an

undecided question. Since such bony scales occur even in Silurian
rocks, it is doubtful whether the clue to their origin will be found
in any known fossil. The most favoured theory is that of
Williamson [49 60], which has been extended by the researches of
O. Hertwig [212] and others (Rohon [369, 371], Pander [312],
Gegenbaur [163], etc.). According to Hertwig's view, the history
of the scales and plates has been as follows. Starting from a condi-
tion, such as still persists in modern Elasmobranchs, where the body

Fio. 187.

SCALES

215

is covered with isolated placoid scales, it is supposed that the
denticles developed extensive basal plates in the dermis ; by the
coalescence of adjoining basal plates were formed larger plates or
scales studded on their outer surface with small denticles. The
modification, spreading out, or fusion of the denticles then gave
rise to the ganoine, and the ornamentation of tubercles and ridges
found on the surface.

This theory is open to several objections. Firstly, the ' placoid '
denticle is never found separate from its basal plate, which is merely

skn

Fio. 188.

Lepidosteus osseus, L. A, surface view of trunk-scales from which the skin and connective
tissue have been removed on the left side. B, longitudinal section through the skin and
scales, a.p, anterior articulating process ; c.t, connective tissue of cutis ; rf, denticle ; d.p,
dorsal articulating process; ep, epidermis; g, ganoine layer; sk, scale; skn, skin covering
scales ; v.c, vascular canal.

an extension of it inwards. In the Osteichthyes, on the contrary,
denticles are developed separately, often later than the underl} ing
bony plate, and only secondarily become connected with it.
Secondly, the basal plate of a placoid scale is never formed of true
bone, but either of dentine or of some allied substance. Thirdly,
the scale often sinks away from the epidermis, and grows by the
addition of new layers over its surface (cp. p. 356). The shiny
ganoine layer of the scales of the Osteichthyes, being formed by the
mesoblast, must not be confused with true enamel deposited by the
epidermis.

216

OS7EICH7HYES

SCALES

217

According to Williamson's original theory the scales and plates
of the Osteichthyes have been formed by " the confluent aggrega-
tion and superficial depression of a number of placoid teeth " over-
lying and becoming fused Avith a lower bony plate. We have seen
how admirably this theory accounts for the structure of the
exoskeleton of the Pteraspidomorphi (p. 195); will it equally well
.account for that of the ganoid scale 1

We must carefully distinguish between two very different kinds of
scales hitherto called ' ganoid ' (Goodrich [1 78]). The first, which is
the true ganoid scale, occurs in the Actinopterygii. The second may

ff-

FIG. 190.

Scale of Megaliehthys llibberti, A£. ; Carboniferous, England. A, piece of a thick transverse
section, much enlarged. B, section through the hind edge, enlarged. C, outer view of a scale.
•ac, anterior region covered by next scale ; c, large vascular cavity ; ch, chamber of cosmine
layer ; dt, canaliculi of cosniiue ; g, thin outermost shiny layer ; h, irregular vascular canals ;
;, bony inner layer or isopedine ; o, opening of chamber on surface ; p.c, pulp-cavity from
which canaliculi radiate ; i-.c, vertical canal.

be called the cosmoid scale, and is found only in the Dipnoi and Osteo-
lepidoti (Figs. 189, 190). The latter is formed of three layers: a
middle layer of bone with large vascular anastomosing channels ; an
inner layer of bony "isopedin," in which the matrix is deposited in
successive laminae, and the cells are arranged in parallel planes ; and
an outer layer of " cosmin " (Williamson [496«]). This cosmine is of
complex structure, being formed of cell-less matrix in which vertical
vascular spaces alternate with ' pulp-cavities ' from which radiate
fine canaliculi. It resembles dentine (Fig. 1 90). A thin layer of
enamel or vitrodentine covers its outer surface.

The ' ganoid ' scale, on the other hand, consists of concentric
layers of skeletal substance, passing both above and below. Two

218

OSTEICHTHYES

distinct types of true ganoid scales can be distinguished [178], The
first — the Palaeoniscoid type — has four layers : isopedine below, a
vascular layer, a layer with canaliculi branching from a horizontal
system of canals (comparable to the cosmine layer), and lastly, a
layer of successive lamellae of enamel-like, cell-less substance — the
ganoine (Fig. 191). The second — the Lepidosteoid type — has the
ganoine above and the isopedine below, but only a few irregular
transverse vascular channels; there is no real cosmine-like layer,
and the scale is characterised by a number of small tubules passing

FIG. 191.

Eurynotus crenatus, Ag. ; Lower Carboniferous. A, diagrammatic and much enlarged view of
a piece of the scale. 13, enlarged outer view of a scale. C, transverse section of a scale, en-
larged, a, anterior covered region ; a.p, articulating process ; c, tine canaliculi of cosmine
layer ; g, ganoine layer ; h, system of horizontal canals ; i, isopedine layer ; o, opening on
outer surface of vertical canals ; p, posterior exposed shiny surface ; s, outer surface ; v.c,
vertical canal.

inwards at right angles to the lines of growth from the lower and
lateral surfaces (Fig. 192) (Reissner [355], Scupin [394]).

Whilst the cosmoid scale grows only by the addition of new
cosmine round its edge, and of new layers of isopedine on its under
surface, the ganoid scale grows by the addition of concentric layers
over its entire surface, each of which contains elements of all the
strata of the scale. No living fish has a cosmoid scale. It is
probable that the ganoid is derived from the cosmoid type of scale,
which may be supposed to have sunk away from the epidermis,
becoming inclosed in a mesodermal pocket by which the new com-
plete concentric layers are deposited. If, as Williamson suggested,
the cosmine or dentine layer represents an original set of super-

SCALES

219

ficial placoid scales fused together, the presence of denticles on the
top of modern ganoid scales can only be explained as a new set
developed after the scale has sunk below the surface (see Figs. 188-9).
On the other hand, it is, of course, possible that the cosmine is only
a peculiarly specialised layer of the independently formed scale,
since intermediate stages in its formation have not yet been found.
The different varieties of scales described above are of great taxo-
nomic importance.

In the primitive Pisces the organs of the lateral -line system
have become distributed over the head and body according to a
definite pattern (p. 19), and have sunk in a subdermal tube open-
ing on the surface by pores (p. 220 and Fig. 195). The pattern of

ff

Fio. 192.

Much enlarged view of a piece of the scale of Lepiiiosteits osseus, L. d, superficial denticles ;
g, ganoine layer ; i, inner bony layers, or isopedine ; t, tubules with branching inner ends ; v.c,
vascular canal.

the lateral line remains very constant, on the whole, throughout the
Osteichthyes, though it undergoes secondary modification in detail.
But the tube in which the sense-organs have sunk necessarily
becomes inclosed in the dermal plates of the head and scales of the
body. There is thus established a definite relation between the
exoskeleton and the lateral line, which is often of great service in
tracing the homologies of the various bones concerned. In all
primitive Osteichthyes the lateral-line canal on the body pierces
through every scale along its course, passing from its upper surface
in front to its lower surface behind (Fig. 194). A sense-organ is
situated between each pair of scales, and a tube leads to a pore
approximately above the centre of each scale. Secondary lateral
lines may be developed dorsally and ventrally essentially similar to
the main line, of which they are branches. In front the line passes
through the dorsal elements of the shoulder-girdle (post-temporal)

220

OSTEICHTHYES

on to the head. By a subdivision and branching of the pore canal
a number, of small pores may replace the original primary pore.

We have already seen (p. 125) that the canals of the lateral-
line system follow a fairly uniform course on the head in the
various groups of fish. The Elasmobranchii and Osteichthyes agree
well in this respect (Allis [9, 19], Garman [148], Clapp [78], Herrick
[210], Collinge [85-89], etc.). Now the connection established
with the cranial bones is as follows (Figs. 196, 500, A). The trunk
lateral line passes by means of the post-temporal on to the supra-
temporal or the pterotic (squamosal) ; from this point a transverse

lac

FIG. 193.

Leuciscus ccphalus, L. A, longitudinal section through the skin, scales, and muscles. 15,
surface view of body-wall ; the skin has been removed on the left, and the myotomes exposed
below on the right, c.t, connective tissue ; op, epidermis ; l.sc, lateral-line scale : w, myotome ;
o, opening of lateral-line canal ; ae, scale in connective-tissue pocket ; .</,•, skin.

branch is often sent off towards the middle line running as a rule in
the supratemporal bones — it may be called the supratemporal or
occipital branch. The organs in this region of the canal are supplied
by the supratemporal twig of the vagus. The main line then con-
tinues horizontally through the pterotic, forming a short temporal
canal supplied by the otic branch of the glossopharyngeal (this
short region does not always occur). The canal is prolonged
forward to behind the orbit — postorbital line — through the pterotic
and post-frontal. It is supplied by the otic branch of the facialis.
Next it passes below the orbit and forwards to the nostrils ; the
ramus buccalis facialis supplies this infraorbital canal, which passes
through the post-, infra-, and preorbital ('lachrymal') bones.
Starting from the junction between the postorbital and infra-

LATERAL LINE

221

A.

so

c},.

ps.

Fio. 195.

Gadm nioi-i-ltiiii, I.. .Surface view of the skin, enlarged, showing the lateral line, c.o, cut
wall of canal to opening; c.ir, cut wall of main canal; o, opening; s, scale; s.o, sense-organ
<ueuroinast).

222

OSTE1CHTHYES

orbital canals is the supraorbital canal, which passes through the
frontal and nasals to the snout, where it may join the infraorbital. It
is the superior ophthalmic branch of the facialis which innervates
the supraorbital canal. Lastly, the ramus hyomandibularis facialis
supplies a hyomandibular canal, which passes down the preopercular
and forwards through the dermarticular to the dentary.

It frequently happens that, in the more specialised fish, where
the cranial bones and scales become thin, lose their superficial
layers, and sink far below the surface, the system of canals again

fiO.

oc.

sof.

SOQ.

md.

Fie.. 196.

Diagram of the head of Amia calva, L., showing the system of lateral-line canals and pit-
organs, and their nerve-supply (from Allis). b, buccal branch of facial nerve ; g, dorsal branch
of glossopharyngeal ; /(, hyomandibular branch of facial ; l.l, lateral line of trunk ; J.v, lateral-
line branch of vagus ; md, mandibular canal ; o.c, occipital or supratemporal canal ; p, pit-
organs on trunk ; po, postorbital canal ; ps, pit-organs on Head ; sob, suborbital canal ; so.c,
supraorbital canal ; s.o.f, superior ophthalmic branch of facial ; t, temporal canal. The system
of distinguishing the canals is indicated on the right of the figure : 1, supraorbital, and main
canal of trunk ; 2, postorbital ; 3, suborbital ; 4, hyomandibular (the same system is used
in Fig. 85).

becomes free. Every stage in the process of the liberation of the
canals from the underlying bones may be traced in the Teleostei.
Special tubular bones often become separated off, and are left in
these fish to protect the sensory canals (Figs. 328, 456). Lastly, in
both the Teleostei and Dipnoi the lateral line may so far degenerate
that the sense-organs remain, at all events along the body, exposed
on the surface, and no longer sink in a tube at all.

The chondrocranium, well developed in many Osteichthyes, is
much reduced in the more specialised groups, and is distinguished
in all by the disappearance of the cartilaginous wall separating the
cavity of the skull from that of the auditory capsule (Figs. 303, 358).

AIR-BLADDER 223

The ossification of the endoskeleton, so characteristic of these fish,
has already been dealt with in a general way above (p. 60). Most
Teleostomes have a number of endochondral bones in the cranium
and visceral arches, which are comparable with those found in the
terrestrial vertebrates ; but since they are mostly absent from the
modern Dipnoi, and many of them have not yet been shown to
occur in extinct Dipnoi, it cannot be asserted that they were
present in primitive fish ancestral to these sub -classes. The
description of these bones of the endoskeleton may therefore be
left till later (p. 266). We may mention, however, that ventral (or
pleural) ribs are present throughout the Osteichthyes.

In all the Osteichthyes an operculum is present on the hyoid
arch. It covers the branchial apertures, never more than five in
number, and is supported by bones the largest of which, the
opercular, is articulated to the hyomandibular.

The air-bladder is one of those important structures which
distinguish the Osteichthyes from the Chondrichthyes. Some kind
of air-bladder is found in all the divisions of the former group, and
it can hardly be doubted that it is only absent in those Teleostomes
in which it has been lost. But in size, structure, disposition, and
blood-supply the air-bladder is so variable, that it is by no means
certainly homologous throughout the Osteichthyes.

The air-bladder always develops as a diverticulum of the
alimentary canal — generally from the oesophagus, but sometimes
farther back from the stomach. In Polypterus it is ventral and
bilobed, lying below the alimentary canal (Fig. 197, A) ; the large left
and smaller right lobe unite, and open through a muscular vestibule,
or rudimentary ' larynx,' by a median ventral aperture into the
oesophagus far forward. A somewhat similar muscular vestibule
opens ventrally into the oesophagus (either in the middle line or
slightly to the right) in the Dipnoi. But here the vestibule leads
into a ductus pneumaticus which passes round the right side of the
alimentary canal to expand dorsally into the air-bladder, a median
(Ceratodus, Fig. 197, B), or bilobed sac (Protopterus, Fig. 198).
Blood is supplied to the bladder in Polypterus and in the Dipnoi by
paired afferent ' pulmonary arteries,' derived from the last (fourth)
branchial arch, the sixth of the embryonic series (Fig. 197). The
blood is returned to the heart in Polypterus by paired efferent vessels,
opening into the hepatic vein near the sinus venosus ; in the Dipnoi
by paired vessels uniting and passing directly to the sinus venosus
itself on the left side. That the air-bladder of the Dipnoi was
originally ventral, and that its dorsal position has been secondarily
acquired, is clearly shown by the course of the ductus pneumaticus,
and of the left afferent and the left efferent vessels which pass round

224

OSTEICHTHYES

below the oesophagus towards the right side (Parker [324], Spencer
[413]). Moreover, in the embryo, the bladder develops as a
median ventral outgrowth (Semon [399], Neumayer [308ft]).

In all the Actinopterygii the air-bladder is essentially a median
dorsal organ, lying below the vertebral column and aorta and above

A. B.

d.

d

FIG. li'7.

Diagrams illustrating the blood-supply of the air-bladder in A, 1'olyiittntx, B, Cemtodus, C,
Amia, and D, a Teleost. The blood-vessels are seen from behind, and cat short in transverse
section, a, dorsal aorta ; a.a.d, anterior dorsal artery from the coeliac; a.a.v, ant. ventral
artery ; a.b, air-bladder ; a.v.d, anterior dorsal vein to the cardinal ; fca6, 4th aortic arch (6th
of the series); cv, coeliac artery ; d, ductus Cuvieri ; la, left pulmonary artery ; oc, oesophagus ;
pr, portal vein receiving posterior vein from air-bladder ; r.n, right ' pulmonary ' artery ;
r.p. v, right (branch of) ' pulmonary ' vein ; IT, right vein from air-bladder ; ^•1 left ' pulmonary '
vein.

the alimentary canal, often outside the abdominal coelom. The
communicating ductus pneumaticus passes down the dorsal
mesentery to open into the oesophagus. The ductus is
short, and the opening wide in the more primitive forms (Lepi-
dosteus, Amia, Acipenser). But although the bladder is dorsal in
the Actinopterygii, the opening of the ductus varies considerably
in position. In the Chondrostei, Amia, Lepidosteus, and the
majority of the Teleostei, it is quite or nearly median and dorsal ;

AIR-BLADDER

225

but in others, such as Salmo, the Siluridae, Cyprinodontidae, Per-
copsidae, and Galaxiidae, it opens more or less on the right. On
the contrary, in the Mormyridae, Notopteridae, Gymnotidae,
Cyprinidae, and Characinidae, it opens somewhat on the left (Fig.
199), and in some genera of the last family, such as Erythrimts
and Maerodon, the ductus passes down to open quite on the left
side of the oesophagus (Rowntree [375]).

The evidence of ontogeny seems to show that the difference in
the position of the opening is due rather to secondary shifting than

ao

FIG. 198.

Diagram showing the relations of the oesophagus, of, the pneumatic duct, p.d, the bilobed air-
bladder and its blood-supply in Protopteru*, seen from behind, no, junction of aortic arches to
dorsal aorta ; ?./, left lobe of air-bladder ; l.p.u, left pulmonary artery ; p.v, pulmonary vein ;
r.l, right lobe of air-bladder ; r.p.a, right pulmonary artery.

to the retention of a more primitive position in the aberrant fish
(Moser [304], Piper [330]).

AVith regard to the original condition of the air-bladder,
attempts have been made to derive these various organs found in
the Osteichthyes from some single ancestral form.

Boas suggested that the bladder was originally dorsal and
median ; that, together with its duct, it split into right and left
halves ; that these separated, passed round the oesophagus, and
reunited ventrally to open finally by a median ventral glottis.
This explanation, however, cannot be applied to the Dipnoi (p. 223),

'5

226

OSTEICHTHYES

and there is nothing in Polyptems to support it. According to
Sagemehl [379], the bladder, originally ventral and bilobed, has
shifted round the right side in the Dipnoi, and the left side in the
Actinopterygii. The median dorsal sac of the latter would represent
the left lobe only, and such genera as Erythrinus would show an
intermediate stage in the shifting. This theory is inconsistent
with the structure of Amia, where not only are the bladder and its
opening median and dorsal, but the bladder receives a right and a
left afferent vessel directly from the last branchial arch (sixth of
the embryonic series), and the nerve -supply is also paired and
symmetrical. It is true that the right and left efferent vessels join
and, passing to the left of the oesophagus, enter the left ductus

FIG. 199.

A, air-bladder of Lebiasina limanulata, opened to show internal cells. B, stomach of
Ichthyoborus niloticus, showing entrance of pneumatic duct, ab, anterior division ; ce, cellular
wall ; oe, oesophagus ; pb, posterior division ; p.d, pneumatic duct ; s.p, pyloric end of stomach ;
st, stomach. (After Rowntree.)

Cuvieri (Fig. 197, C) ; but it is easier to suppose that the return
stream of the blood has been diverted to the left side, than that
the arterial and nervous supply have been entirely readjusted after
the shifting of the air-bladder from a ventral to a dorsal position.
In all the Actinopterygii (excepting Amia) the blood-supply of the
air-bladder resembles that of the other abdominal viscera (Figs. 197,
351). As a rule, there appears to be a double arterial supply, from
the coeliac artery in front and from the dorsal aorta behind ; the
blood is returned to the cardinal veins from behind, and the portal
vein from in front (Corning).

A third possibility remains to be considered. According to
this the most plausible theory, the air-bladder may be derived from
paired outgrowths, possibly a posterior pair of modified gill-pouches
(Spengel [415], Goette [170]). The ventral union of such out-

NOSTRILS 227

growths, supplied from the aortic arches, might give rise to the
bladder of Polyptems; while from their more complete fusion
dorsally might be formed the bladder of Amia, etc. The return of
the blood to the veins behind the heart is difficult to explain on
this hypothesis, and it must be confessed that the problem of the
homology of the air-bladder is not yet satisfactorily solved.

The primitive position of the nostrils seems to have been in the
Osteichthyes, as in the Chondrichthyes, on the ventral surface of
the snout. Such it was apparently in the early Teleostomes (Osteo-
lepidae), and such it remains in the Dipnoi. But in all the living
Osteichthyes, with the exception of a few specialised genera (p. 445),
the nostrils are double. The groove on either side of the fronto-
nasal process, already described in the Elasmobranchs (p. 125),
closes over to form a complete canal in the Dipnoi ; so that in the
adult the nasal sac communicates with the exterior by an external
anterior nostril, and with the buccal cavity by an internal posterior
nostril, as in Pentadactyle vertebrates (Fig. 207). In the Acti-
nopterygii and Polypteridae the nostrils remain separated from the
mouth, and migrate towards the dorsal surface of the snout. No
distinct fronto-nasal process, and no groove to the mouth develop ;
but the nostril becomes subdivided into two by a narrow bridge.
The two openings so formed are probably homologous with the
internal and external nostrils of the Dipnoi. There are no movable
eyelids.

The Osteichthyes, with the exception of the specialised Teleostei,
retain many primitive characters such as the spiral valve in the
intestine, the contractile conus of the heart with many rows of
valves, and the chiasma of the optic nerves. The urinogenital
organs, also, are built on much the same plan in the primitive
forms as in the Elasmobranchs ; but the cloaca is lost in all living
forms except the Dipnoi.

We conclude that the development of true bone in the
endoskeleton, of scales on the body, of lepidotrichia on the fins, of a
special set of bony plates on the head and shoulder-girdle, of marginal
jaw-bones, of a connection between the dermal shoulder- girdle and
the skull, of pleural ribs, of an operculum covering the gill-openings,
of an air-bladder, and of double nostrils, justify the inclusion of
the Dipnoi and Teleostomi in a separate sub-grade — the Osteichthyes.

228

OSTE1CHTHYES

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Coccosreomorphi

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Osfeichrhyes

DIAGRAM III.

Diagram illustrating the Phylogeny of the Osteichthyes, and the distribution of the
Families in the geological strata.

OSTEICHTHYES

229

i ;/// ? 1

' ii'/ lepidosteoidei
* ."// — ~» — 7

Acrinoprerygii
Teleosromi

Osreichrhyes

DIAGBAM III. (continued).

GKOUP A.

IN this group may be provisionally associated the two sub-
classes Dipnoi and Coccosteomorphi. Some authors (A. S.
Woodward [503, 505], Eastman [128-9]) definitely place the extinct
Coccosteus and its allies in one sub -class with the Dipnoi ; this
step seems, however, to be premature, considering how incomplete
is our knowledge of the former, and how much the two groups
differ from each other. It still remains to be proved whether the
Coccosteomorphi were truly autostylic, and even then whether they
were more nearly related to the Dipnoi than to the Teleostomi.
The affinities of these sub -classes is discussed in greater detail
below.

Sub-Class 1. DIPNOI.

The Dipnoi are among the most interesting of fish. On the
one hand, they have a close affinity to the Osteolepidoti ; on the
other, they present many striking points of resemblance to the
Amphibia, which cannot all be put down to convergence.

For the correct delimitation of this group we are chiefly
indebted to Huxley [230], Giinther [190], and Traquair [447].
Already in the Devonian epoch two strongly marked types of
structure are found among the Dipnoi, exemplified by Dipterus and
PhoMeropleuron, showing that, even then, considerable divergence
had taken place. First founded by J. Miiller for Lepidosiren, the
group of living Dipnoi was shown by Huxley to be characterised
by the autostylic attachment of the jaws. Subsequently Traquair
demonstrated that the fossil forms were likewise autostylic.

The scales are cycloid and overlapping. In modern genera they
are thin, and embedded below the surface in pockets in the con-
nective tissue of the dermis (Fig. 200). Dipterus has thick scales,
with a shiny pitted surface. In microscopic structure they closely
resemble the scales of the Osteolepidoti, with an outer layer of
typical cosmine, separated by a trabecular layer of bone from an
underlying sheet of isopedine. Smaller elongated quadrangular
scales of the same structure extend in rows over the median and
paired fins to their very edge -(Fig. 202). This scaling of the fins
is characteristic of the sub-class.

230

SCALES

231

There are no true fulcra in any Dipnoi. The head and shoulder
of Dipterus are provided with plates of a structure similar to that

B.

A.

t:

FIG. 200.

A, scale of Ccratoihts Forstfri, Kroft't. 15, enlarged view of a portion of the outer surface of
the scale of Protopterus annectens, Owen, a, anterior edge ; /, front limit of exposed region of
scale ; p, posterior edge ; s, spine ; t, layer of bone-like tissue.

of the scales. The lateral-line canals are embedded in these plates
and scales in the early forms.

A minute comparison of the exoskeleton of the fossil and living
Dipnoi yet remains to be made. In the more modified forms the

vc.

Fid. 201.

Enlarged view of a small portion of the scale of Phaneropkuron curium, Wht. ; Upper
Devonian, Canada. i, inner bony layer ; s;i, surface spinelet ; re, vascular space.

ganoid surface disappears from the plates, leaving only sheets of
bone, sunk far below the surface in living genera. The scales also
lose their cosmine layer, which appears to be represented by numerous

232

DIPNOI

small spine-like processes, highly characteristic (Fig. 200, B), and not
to be confused with denticles. This spiny covering is found in all
the living genera, and even in the Devonian Phaneropleuridae
(Fig. 201) ; it is therefore an important and old-established form of
not found in any other sub-class. The trabecular and

isopedine layers remain,
though in living genera
bone - corpuscles are no
longer present (Wieders-
heim [490], Klaatsch
[264], Goodrich [178]).

The dermal fin -rays
are always jointed, gener-
ally branched, and are
formed of a bony sub-
stance containing bone-
cells (Fig. 203). They
are slender, much more
numerous than the endo-
skeletal radials, with an
unjointed proximal piece
deeply embedded in the
connective tissues and
muscles, so as to con-
siderably overlap the
radials [175]. In the
modern degenerate Dipnoi
the dermal rays, or camp-
fitfrichia, become fibrous
and little calcified, thus

FIG. 202.

somewhat resembling the

Diagram of a section through the dorsal fin of ceratotrichia
Dipterus. b.sc, body-scales ; (Hst.r, distal jointed region •, i -p, , .

of the camptotrich ; efr, radial of fin ; pr.r, proximal Ol'ancnS. iSUt in the early
unsegmented region of the camptotrich ; s.sc, scale over-
lying dermal ray. (From Quart. Joitrn. Micr. Sci.)

of Elasmo-
branchs.

fossils they are thoroughly
bony, and approach lepi-
dotrichia in structure. The distal- jointed region of the camptotrichia
is, however, always covered over externally by true scales ; and in
Dipterus these fit closely in rows along the rays (Figs. 202, 226).
It is, therefore, possible either that in Dipnoi we have lepidotrichia,
which have sunk deep below the surface, and been covered over by
a new set of scales ; or that the camptotrichia really are modified
ceratotrichia, with which the more superficial true scales are be-
coming associated. A still closer union of these two elements might
have given rise to the typical lepidotrichia of primitive Teleostomes.
Whatever may have been the history of the camptotrichia, they
differ considerably from the dermal rays of other fish [175].

VER TEBRA L COL UMN

233

sc

No actinotrichia have been observed in young, or adult,
Dipnoi (pp. 212, 273).

The vertebral column has a persistent unconstricted notochord.
Although, judging from living forms (Fig. 204, A), the elastica
externa is ruptured, and the mesoblastic cells invade the thick
fibrous notochordal sheath to some extent, yet complete vertebral
bodies are never formed so as to constrict the notochord in the
typical manner. But in Ceratodus the notochord is pushed inwards
alternately, above and below, by the
cartilaginous masses, which grow from
the basidorsals and basiventrals (Fig.
204, B). The extreme tip may be
entirely surrounded by cartilage.

There is, then, a thick fibrous sheath
in which are partially embedded cartila-
ginous basidorsals and basiventrals. Small
and irregular intercalaries (interdorsals
and interventrals) are occasionally present.
The basidorsals extend upwards as ossified
neural arches meeting above the nerve-
cord ; along the top of these arches runs
a longitudinal ligament, above which
again are a series of neural spines. The
latter may be fused to the arches in
the hinder region. Similarly the caudal
region is provided with haemal spines
and arches, continued in front into
basal cartilages and pleural or ventral
jribs (Fig. 204, C) lying just outside
the peritoneum. There are no true
ribs.

All living Dipnoi are provided with
a diphy cereal tail, and continuous dorsal
and ventral median - fins (Fig. 205).
Dipterus, however, has two separate dorsal
and one anal fin, and a heterocercal tail
.(Fig. 226). In Phaneropleuron with a
separate anal only, and Seaumenacia with
an anal and two dorsal fins, we have

intermediate conditions (Fig. 227). Dollo [120] has very plausibly
argued that these Dipnoi represent a degenerating series leading
to an extreme form like Lepidosiren, in which the body becomes
more elongated and eel-like, the tail becomes straightened, and the
median fins fuse together. It must be remembered, however, that
the Carboniferous genus Uroncnms already has continuous median

FIG. 203.

Diagram of a section through
the dorsal fin of O/-"f"<7".--. r,
camptotrich; r, endoskeletal radial :
s, body • scale ; fc, superficial fin-
scale. (From Qui'i-t. /burn. .V<Vv.

DIPNOI

fins and a diphycercal tail. The Dipnoi may well have been derived
from some earlier form of similar shape (Fig 227).

It is important to notice that the fin -supports, radials or
somactids, are segmented and intimately connected with the axial
skeleton (Fig. 205). The radials and neural spines together form
continuous three-jointed ossified rods. When the dorsal and anal
fins are separate, the proximal segments may be concentrated
and fused (Scaumenacia, A. Smith Woodward [503]). This tendency
is also seen in the anal region of the continuous fin of Ceratodus.

That the ventral caudal lobe in modern Dipnoi is supported by
separate radials, and not by rigid unjointed haemal spines, would

nc..

Fio. 204.

A, transverse section of vertebral column of a young Protopterus, showing the invasion of
the fibrous notochordal sheath by the mesoblastic cells. B, left-side view of a portion of the
vertebral column (abdominal region) of Ceratodus Forsteri, Krefft., of which the anterior half
has been cut longitudinally. C, view of the same cut across, bd, basidorsal cartilage ; liv,
basiventral cartilage ; cJ, canal for ligament ; e, elastica externa ; f.sh, fibrous sheath ; h.a,
haemal arch (basiventral) ; h.c, haemal canal ; n.a, neural arch ; H-.C, nerve-cord ; n.cl, neural
canal ; »..«/>, neural spine ; nt, notochord ; p.r, pleura! rib.

seem to be due to the genuine diphycercal character of the tail,
and not, as Balfour supposed [30], to the loss of the caudal fin
itself. This character indicates a primitive structure (p. 101), and
weighs against Dollo's theory.

The notochord extends to near the pituitary region ; there i&
no distinct joint between the skull and the vertebral column, which
pass gradually into each other. Several vestigial vertebral segments
seem to be incorporated into the hind part of the skull behind the
vagus nerve. In Ceratodus, besides the hypoglossal roots, two
complete spinal nerves pass through this region ; three neural
arches and spines are found attached to it above, and a pair of
enlarged 'cranial ribs ' articulate to it at the sides (Figs. 206, 209).
Such cranial ribs are found in all living Dipnoi, and even in such

SKELETON

235

early genera as the Devonian Scaumenacia. The bone described

by Huxley as an exoccipital, the only endochondral ossification
in the skull of living Dipnoi, appears to represent the first of the

236

DIPNOI

occipital neural arches, since it is placed between the hypoglossal
and the first occipitospinal nerve (Fiirbringer [14 la]).

The chondrocranium, complete, thick, and without fontanelles
Ceratodus (Fig. 206), is less complete in the Dipneumones,

in

d.

a- it T"" '! 4 5*7~ * 9

bh. hr2, so'*: \ | /

JO

mp.

eo.

Fio. 20tj.

Ceratodus Forsteri, Krefft. A, outer view of left half ; B, inner view of right half, a, angular ;
lih, basihyal ; br, fifth branchial arch ; ch, ceratohyal ; c.r, ' cranial ' rib ; d, dentary ; eo,
' exoccipital ' ; 7im, hyomandibular ; h.n, hyomandibular nerve ; hr, hypohyal ; l.p, lateral plate ;
ra.a, median anterior, and m.p, median posterior plate ; n.a, neural arch ; n.v.e, cartilage of
neural arch ; n.s, notochordal sheath ; n.sp, neural spine ; lit, notochord ; o, opercular, and oc,
its cartilage ; pa, parasphenoid ; pf, postfrontal ; p.p, pterygo-palatine; p.t, palatine tooth ;
pto, pterotic (?) ; and q, its downward process covering the quadrate cartilage, q.c ; s, sub-
opercular ; so, suborbital ; sp, isplenial ; s.t, splenial tooth ; v.t, vomerine tooth.

where the trabeculae remain recognisable, and the wall of the brain-
case is to some extent formed by membrane bones above, below,
and at the sides (Fig. 209). The cavity of the auditory capsule
is widely open to the interior as in Teleostomes. Fenestrated
cartilaginous nasal capsules are present ; also separate nasal
cartilages, at all events in Ceratodus (Fig. 207).

SKULL

237

It is in the connection of the skull with the visceral arches
the Dipnoi have diverged most conspicuously from other fish.

«k

that
The

II -IP

T3 E 2 3

I&J.S-J3

2 o 3 t. s 3
S-.-n-g.3S
8fll^

lslli.5

modern genera are completely autostylic (p. 95). The ptery go-
quadrate bar is firmly fused to the cranium in front and behind.
The spiracle disappears ; and the hyoid arch is well developed, with
i\ median basihyal, paired hypohyals, and large ossified ceratohyals

238 DIPNOI

(Fig. 206). But the hyomandibular takes no share in the support
of the jaws. It disappears, indeed, entirely in the Dipneumones,
where the ceralohyals alone remain, and, as Huxley showed [230]
(Ridewoo'd [358], Sewertzoff [408]), is represented in Ceratodus by a
minute vestigial cartilage, overlying the hyomandibular branch of
the seventh nerve (Fig. 206). Of the structure of the hyoid and
branchial arches in the fossil forms we know practically nothing, but
there is no reason to think that it differed essentially from that of
modern Dipnoi. Traquair has shown that Dipterus was autostylic
[447]. The branchial arches in Ceratodus are fairly well developed
with epibranchial elements, and even some pharyngobranchials ;
but in the Dipneumones they are reduced to mere unsegmented
cartilaginous rods. On the other hand, a small cartilage in front
of the first branchial slit led some observers (Wiedersheim [489],
Bridge [56a]) to believe that there are six branchial arches in the
Dipneumones, one gill-cleft having disappeared behind the hyoid
arch. But the distribution of the nerves, blood-vessels, etc.,
does not support this view, and the cartilage rod appears to be
a secondary development from the base of the gill -rakers (K.
Fiirbringer [141rt]).

Among the chief characters of the dermal bones of the skull
which distinguish modern Dipnoi from the more primitive early
Osteichthyes, we may mention the sinking of the bones beneath
the surface, leaving the sensory canals in the skin, the overgrowth
of these bones by scales, and their reduction in number ; the pre-
ponderance of large median elements, the loss of the nasals,
premaxillae, and maxillae, and the great reduction or entire dis-
appearance of the dentary ; the correlated absence of teeth on the
margin of the mouth ; the presence of a pair of strong pterygo-
palatine bones, bearing large compound palatine teeth ; the
development of corresponding large teeth below on the splenials ;
the absence of the ventral and lateral gular series, the small size of
the opercular and subopercular, and the absence of a pineal foramen.
So far have these Dipnoi departed from the normal type, that the
homology of the cranial bones cannot yet be determined with
certainty.

Passing backwards to the Devonian forms, we find skulls more
nearly resembling those of the primitive Teleostomes. In the
Phaneropleuridae (Fig. 208) are large paired f rentals and parietals,
meeting in the middle line, followed behind by a median occipital.
The supraorbital sensory canal is carried by a row of plates, the
prefrontal, supraorbitals, and postfrontal. It is continued back-
wards through two posterior bones, probably representing the
squamosal (pterotic) and supratemporal. A chain of bones, enclos-
ing the infraorbital canal, passes below the orbit from the post-

SKULL

239

frontal behind to the prefrontal in front. The eye is surrounded
by an inner ring of circumorbital bones. Two large ventral gular
plates are present, but no lateral gulars. The operculum • is
supported by a large opercular and what is probably a subopercular.
Unfortunately the cheek region is still incompletely known, and
the course of the opercular sensory canal remains to be determined.
In Ctenodus (Fig. 209) the paired frontals and parietals are
smaller, and a median plate appears between them. This plate
becomes larger in Diptems, where the frontals and parietals are

FIG. 208.

Restoration of the head of Phaneropleuron. co, circumorbital; /, frontal ; /»•, pterotic (?) ;
m.s, median supratemporal (occipital) ; op, opercular ; pa, parietal ; pf, posterior snpraorbital ;
prf, prefrontal ; pt, small lateral plate ; ptf, postfrontal ; so, supraorbital. The course of the
lateral-line canals is indicated by a dotted line on the right side.

smaller (Fig. 210). The superficial cranial bones of Diptents
become more numerous and often strangely irregular, suggesting a
secondary subdivision of the lateral plates, somewhat as in the
Sturgeons among the Actinopterygii. Ceratodus has diverged in a
different direction (Figs. 206-7) : the parietals and frontals are no
longer recognisable as such ; the anterior median bone (ethmoid)
meets the large posterior occipital (fronto-parietal) ; the supra-
orbital and lateral series of bones seem to be represented by
two large 'lateral' plates (dermal -lateral ethmoid of Bridge),
outside which lie the postfrontal and the ' squamosal.' The latter
bone, with the ' lateral ' and the occipital, forms a roof over the

DIPNOI

jaw muscles. Now this ' squamosal ' is generally likened to that of
the Amphibia, to which it bears a remarkable resemblance. Since,
in Ceratodus sturii (Teller [433]), it harbours the postorbital sensory
canal, it is probably the homologue of the pterotic (squamosal) of
the hyostylic fishes. As it spreads downwards over the quadrate
it appears to be a prespiracular bone, and therefore can hardly
represent, as has been suggested, the preopercular of other Osteich-
thyes. For, in these, the hyomandibular sensory canal, supplied by
the post-spiracular hyomandibular branch of the seventh nerve, is
lodged in the preopercular. In fact, a true preopercular has never

pm.

m

f

sc.

--pa.

FIG. 2<K>.

Restoration of the head of Ctenodiis. in, maxilla; pm, premaxilla ; j>, median plate; other
letters as in Fig. 208.

been shown to exist in the Dipnoi. The two opercular bones are
small, but retain on their inner surface small cartilages, which
appear to be remnants of branchial rays of the hyoid arch. Bran-
chial rays, however, are not found on the gill-arches of modern
Dipnoi (Fig. 97).

The Dipneumones differ from Ceratodus chiefly in the further
modification of the dermal bones. The postorbitals and suborbitals
are gone. The ' ethmoid ' remains in front, and a large median
bone lying on the chondrocranium, and partly below the muscles,
probably represents the occipital. The ' laterals ' project freely
behind over the muscles (Fig. 211). It is obvious that the cranial
bones of the modern Dipnoi are in a very specialised condition.

TEETH

241

The nostrils in all Dipnoi are on the ventral surface of the snout.
There are separate anterior or external nares leading into the
nasal chambers, and posterior or internal nares opening from these
into the mouth (Fig. 207). These separate openings are formed in
the embryo by the arching over of the nasal grooves, and are doubt-
less correlated with the air-breathing function of the oesophageal
bladder.

In the Devonian forms the nostrils are in the same position,
and the blunt snout is covered dorsally by a bony shield, probably

...m

Fio. 210.

Restoration of the head of Dipteriis. m, maxilla ; pm, premaxilla ; p, median plate ; the
other letters as in Fig. 208.

representing the fused premaxilla and maxilla, with, perhaps, the
nasals as well. In modern Dipnoi these bones have disappeared.

The palate is characteristically simple and very uniform in
structure. A large expanded parasphenoid is flanked on both sides
by a ptery go-palatine bone, bearing in front a large grinding tooth.
Two much smaller and simpler ' vomerine ' teeth are generally
situated in front (Figs. 207, 210A). These tooth-plates are developed
in the embryo from rows of separate denticles which become fused
together by their bony bases (representing the palatine and vomer)
(Fig. 21 OB).

In the lower jaw Meckel's cartilage persists, covered by an
angular behind, and by a large toothed splenial internally. The
dentary has disappeared in the Dipneumones, is vestigial in Ceratodus,

16

242

DIPNOI

ail.

but larger in the early fossils (Figs. 206-7, 225). The jaws of the
Dipnoi have undergone profound modification in connection with the

development of the great compound
tooth-plates. Correlated with this
are the complete fusion of the pteiy go-
quadrate bar in front and behind with
the skull, the reduction of the hyo-
mandibular and of the marginal teeth
and bones of the jaws, and the growth
of the splenial and pterygoid bones.
It can scarcely be doubted that the
Dipnoi have been derived in remote
pre- Devonian times from ancestors
possessing a more normal palatal
dentition, marginal teeth and bones,
a detached quadrate, and a hyoman-
dibular of moderate size.

J

The two halves of the simple
ventral view of the palate of Dipterus cartilaginous pectoral girdle fuse

restored, a.n, anterior nostril ; p, palato- . . *• . fe

pterygoid bone ; pa, parasphenoid ; p.n, in the middle line in CemtoUUS

posterior nostril ; p.t, palatine tooth : v.t, /-n- mn\ T ^.u- j ii_

vomeiine tooth. (Fig. 212). In this and other

primitive Dipnoi there are paired
ventral clavicles overlying the coracoid region, and paired cleithra

Fio. 210a.

Upper dentition of a young Ceratodus Forsteri. (After Semon, from Gegenbaur, I'ergl. Anal.)
V, vomerine plate ; P, palatine plate. The denticles are joined at their base by a delicate bony
network.

over the scapular region. The cleithrum is connected with the
skull by a post-temporal. In the Dipneumones the shoulder-girdle

SKELETON

243

is reduced; the post-temporal is vestigial, and suspended in a
ligament ; a very small cleithrum surmounts the clavicle, and the

FIG. 212.

Pectoral girdle of A, Ceratodtis ; B, Polypterus. Ventral view. (From Gegenbaur, Vergl.
Aiiat.) Cl, clavicle ; Cl', cleithrum ; g, articular facet for fin-skeleton.

cartilage is subdivided into a ventral median piece, and two more
.dorsal pieces supporting the fins.

244

DIPNOI

The pelvic girdle, unossified and known only in living genera,
is remarkably amphibian. It consists of a median ischio-pubic
cartilage. There are paired lateral or prepubic processes, and

a large median epipubic process
(Fig. 213).

The fin -skeleton has already
been mentioned (p. 106). In
Ceratodus both the pectoral and
the pelvic fins are leaf -shaped,
covered with scales, and with
dermal rays set all round both
along the preaxial and the post-
axial edges. They are provided
with a tapering segmented median
skeletal axis (Fig. 213). The first
segment articulates proximally
with the girdle and distally with
the second segment by means of
a true joint. In G. sturi it was
ossified. From the second out-
wards some twenty segments bear
preaxial and postaxial radials, of
which the latter are the smallest
and most numerous. When at
rest the preaxial margin of the
pectoral fin is borne upwards ; the
reverse is the case with the pelvic-
fin. Lepidosiren and Protopterus
have much reduced filamentous
paired fins, with a slender jointed
cartilaginous axis. The former
has lost all trace of lateral radials ;
but small preaxial radials remain
in Protopterus (Fig. 205).

Ventral view of the pelvic girdle and fins The fin-skeleton is entirely

of Ceratodus Forsteri, Kr. The skeleton of pnrHlao-inrm<j in livino- Dinnni anrl

the right fin is completely exposed, a, jointed Cartilaginous in living JJipnOl, ana

axis ; d.r, , dermal rays ; l.p, lateral process ; scarcely any traces of it remain

m.c, median process; p, pelvic cartilage; . i r o-

pr. r, postaxial radials ; pt.r, preaxial radials; in any known foSSllS. binCC,

s, scaly covering of axial region. (Partly i ,1 i 11 i i j

after Davidoff, from Quart. Journ. Micr. Sci.) however, these have all lobate

fins like those of Ceratodus, there

can be hardly any doubt, judging from the scale -covered axial
region, the dermal rays, and what remains of the axis in some
fossils, that the endoskeleton in the extinct Dipnoi was of essen-
tially similar character. It may safely be assumed that the
early forms had typical rachiostichous and mesorachic paired
fins.

FIG. 213.

BRAIN

245

The brain deserves particular notice :
few organs in the Dipnoi so clearly show
the isolation of this sub-class from other
fish. On the whole, the brain is primitive
in structure ; it lacks the special character-
istics of the Elasmobranch or of the Teleo-
stome ; so far as it is distinctly advanced,
it approximates to the Amphibian type
(Beauregard [35], Burckhardt [69], Bing
and Burckhardt [73]). The brain is long
and narrow, and has large ventricles. A
large and simple medulla is followed by a
very small cerebellum (Figs. 214-15). The
mid-brain is long and fully exposed ; the
optic lobes are fused in Protopterus. There
is a velum transversum. Most remarkable
are large paired cerebral prolongations
projecting far beyond the lamina terminalis.
These ' hemispheres ' are separate, and in
the Dipneumones have thickened nervous
walls above and at the sides as well as
below (Fig. 281); in Ceratodus, however,
which has a less developed and perhaps
somewhat degenerate brain, the roof of the
prosencephalon is epithelial, like that of the
greater part of the brain. In the Dipneu-
mones the relatively small olfactory lobes
are attached in front to the cerebral hemi-
spheres ; but the rhinencephalon of Cera-
todus is drawn out into a tract expanding
into a large hollow olfactory bulb near the
nasal capsule. The ganglion cells are
stratified in the fore-brain.

The dentition is most characteristic.
The dental plates, already described, are
firmly fused to the underlying bones, and
not replaceable. They are composed of
thick dentine, round numerous tubular and
often branching pulp-cavities. The grind-
ing surface, in modern forms, is provided
with high radiating ridges. These ridges
are really formed in the embryo by the
growth and fusion of originally distinct
small conical teeth (Fig. 210A, Semon [401],
Fig. 21 OB). All external trace of their

-10

-12
-U

1O

|-—-- 9

m

-m — 4.

<— -a

i

Fio. 214.

Dorsal view of the brain of
1'rotoptervg anncctens, Owen.
(After Burckhardt, from Sedg-
wick's Zoology.) 1, spinal cord ;
2, dorsal root of first spinal
nerve ; 3, rtiverticula of 4, the
saccus endolymphaticus ; 0,
medulla oblongata ; 6, fourth
ventricle ; 7, cerebellum ; 8,
mesencephalon (fused optic
lobes) ; it, stalk of pineal body ;
10, thalamencephalon ; 11, velum
transversum; 12, pineal body; 13,
lobus hippocampi ; 14, choroM
plexus ; 15, cerebral hemisphere
(prosenccpTiclmi) ; 10, olfactory
lobe,

246

DIPNOI

compound nature is lost in recent Dipnoi ; but in the early fossils
the ridges are set with conical tubercles (Fig. 210A); and in

some, such as Uronemits and perhaps Conclwpoma (Traquair [458]),
the separate conical teeth are not fused even in the adult. Much

GILLS

247

smaller compound vomerine teeth are set on the ethmoid cartilage
in front. They probably drop off in fossils, where they have never
actually been found.

The pharynx leads into an oesophagus, stomach, and straight
intestine, fastened by an incomplete ventral as well as dorsal
mesentery. A well-developed spiral valve is present (Giinther [190],
Parker [324], Hyrtl [232]). The cloaca receives the anal, genital,
and urinary openings. Paired abdominal pores are present.

Ceratodus has five open branchial slits. The first, behind the
hyoid arch, has a hyoidean hemibranch. It is a pseudobranch
supplied indirectly from the first epibranchial artery (Spencer [413],

c.l.o

FIG. 216.

Larva of Ltpiiinxlrfn y/«rf«/<//i', Nat. (After Kerr, from Sedgwick's Zoology.) rl.o, cloacal
opening ; four external gills are shown, also the rudiments of the paired limbs, anrl the adhesive
organ. below the head.

Kellicott [257]). The following four arches bear complete gills
(Figs. 207 and 220).

Protopterus has also five open clefts, with a hyoidean hemi-
branch, two complete gills on the third and fourth arches only,
and a few gill-lamellae (an anterior hemibranch) on the fifth arch
(Fig. 221). Only four open gill-clefts remain in the adult Lepidosireii,
where the hyobranchial slit is closed.

Larval gills are present in all recent Dipnoi ; in Protopterus and
Lepidosireii (Kerr [259], Budgett [67a], Semon [399]) they extend
freely to the exterior as branching processes from several gill-
arches (Fig. 216). In the former genus they may remain outside
the operculum in the adult (Fig. 221), and are supplied with
afferent and efferent vessels from the last three aortic arches.

The complete gill-arches show in section (Fig. 57) a broad
septum beyond which the lamellae project a little. There are a
single afferent and two efferent vessels j but there is reason to
believe that the latter are not strictly comparable to those of
Elasmobranchs. Alone among the Osteichthyes, the Dipnoi have

248

DIPNOI

no branchial rays on the
branchial arches. Gill -rakers
with cartilaginous supports are
present.

An opercular fold from the
hyoid arch completely covers
the gill-clefts ; and in the Dip-
neumones the external opening
is narrowed down to a small
aperture.

As the importance of the
gills diminishes that of the air-
bladder increases. As described
above (p. 223), it is morpho-
logically ventral, arising as a
median ventral outgrowth of
the oesophagus (Fig. 217).
While the muscular glottis re-
mains ventral, the posterior
saccular dilatation shifts round
to a dorsal position. It is highly
vascular and functions as a lung
(Gunther [190], Spencer [413]),
the deeply folded inner wall
being cellular in structure.

The vascular system is of
great interest, showing many
points of resemblance to that
of the Amphibia as well as
primitive characters (Owen
:311], Lankester [277], Boas
:38], Spencer [413], Parker
:324], Kellicott [257], Rose
'373]). The heart, unlike that
of other fish, is in a thin-walled
pericardium. It is completely
twisted, so that the sinus venosus
lies dorsal to the atrium which
passes in front of the conical
ventricle (Figs. 218-19). the
sinus receives all the venous
systemic blood from the two
ductus Cuvieri, the vena cava
posterior, and the hepatic veins.
But the pulmonary vein, coming

HEART

249

from the air-bladder, passes right through the sinus venosus to
the left side of the atrium, and discharges the arterial blood
.almost straight into the ventricle. This incipient division of

-rd

y

PIG. 218.

Heart of Protopterus anneetens, Owen. A, dorsal view. B, opened, ventral view. C, the
sinus venosus opened, a, cut arterial arches ; a 1 and 2, entrance from conns to lirst two
arches ; a 3 and 4, entrance to last two arches ; at, atrium ; c, conus arteriosus ; o.w.e, cut wall
ofconus; c. w. v, cut wall of ventricle ; /, fibrous plug closing the passage from ventricle to
atrium and passing into the sinus ; I, dorsal attachment to pericardial wall ; l.d, left ductus
Cuvieri ; Iv, longitudinal ridge ; p, small portion of pericardial wall ; p.v, pulmonary vein ; r.d,
right ductus Cuvieri ; sv, longitudinal compound valve ; v, ventricle ; v.c, vena cava inferior ;
vv, row of small valves ; w, dotted line indicating course of venous blood from the shallow
sinus venosus, through the atrium (C) into the ventricle on the right of the plug (B). In C the
dotted lines Id, rd, and vc pass into the sinus venosus ; the lines x and y into the cavity of the
.atrium opening widely into the sinus ; the line p.v passes down the pulmonary vein to enter
the ventricle on the left of the plug (Z in B).

the heart into a venous and an arterial channel is continued in the
atrium, where an incomplete interauricular wall is developed as a
thick projecting plug, and is even carried on into the ventricle. Of
the four main longitudinal rows of valves found in the spirally

250

DIPNOI

-a2

- a3

twisted conns of Ceratodus, one is so enlarged as to longitudinally
divide the cavity into two channels. In the Dipneumones, and

especially in Lepidosiren,
where this subdivision
of the cavities of the
heart is more completely
carried out, these valves
fuse to a longitudinal
fold. The pulmonary
blood entering the left
side of the atrium is
thus borne forward to
the first two aortic
arches, and the venous
blood to the last two
(Figs. 218, 221).

From the truncus
arteriosus, the short
remnant of the ventral
aorta, spring four pairs
of afferent branchial
vessels, passing up the
first four branchial
arches. Four corre-
sponding pairs of epi-
branchial arteries are
formed by the junction
of two efferent vessels-
in each arch in Ceratodus
(Fig. 2 20). They join the
dorsal aorta. From the
posterior epibranchial,
the sixth aortic arch,
counting the mandibular
as the first, is given off
a pulmonary artery to
the air-bladder. The

eraot's orsteri, ret. enra vew o e ear , ,„

dissected so as to expose the inside of the ventricle and presence 01 tWO eiterent
conns, and the disposition of the aortic arches, ai-4, four . _pi_ in „„,.}, Kranphial
aortic arches, a dotted line passes up the base of the 1st ' es

and combined 3rd and 4th ; at, atrium ; c, cut wall of Ij^r in both the Dipnoi
conus ; /, plug tilling the atrio-ventricular opening ; Iv, .....

small posterior valves ; p, portion of wall of pericardium ; and the Selachii is prob-
s.v, specialised row of enlarged valves; t, truncus; r, •> , c 1,1

anterior valve, also cut wall of ventricle ; TO and z, dotted ably OI no pnylOgenetlC
lines^passing into the sinus venosus. (Compare Fig. 218, signjficance . jn the rela-
tion of the epibranchial

arches to the bars the Dipnoi are the more normal (p. 111). On
the other hand, the reduction of the ventral aorta, the gathering

4)''

Fio. 219.
CeraMt'x Forsterl, Kreflt. Ventral view of the heart

VASCULAR SYSTEM

together of the epibranchial vessels to form the dorsal aorta, the

mes

la'.

of?

fit:.

Fio. 2-20.

Branchial circulation of Ceratoiliix (from Spencer's figures). I-V, five branchial slits ; abr,
anterior efferent vessel; a.c, anterior carotid; o/3-6, four afferent vessels (corresponding to
the original arches 4-6) ; c, conns ; d, coeliac artery ; d, ductus Cuvieri ; eb ?-4, second and fourth
epibranchial arteries; h.a, hyoid artery (from original 2nd arch); L, air-bladder ; I. a, lingual
artery ; mes, mesentric artery ; p.a, pulmonary artery ; pbr, posterior efferent vessel ; p.c,
posterior cardinal ; p.v, pulmonary vein ; s, position of closed spiracle ; v.a, ventral artery ;
r.f, vena c-ava inferior. The gills are represented on the hyoid and next 4 branchial arches.

ca

ma,

VCLO.

FIG. 221.

Branchial circulation of Protopterus (from Parki-r's figures), a/2-8, afferent branchial
arteries ; nf.tj, afferent vessel to external gill ; ca, carotid ; d, coeliac artery ; c.t, left branch of
dorsal aorta formed by .junction of branchial efferent vessels ; d, ductus Cuvieri ; ef.g, efferent
vessel of external gill ; e.ij, external gill ; ep, epibranchial region of arterial arch of first gill-less
branchial arch ; cp.h, epibranchial vessel of hyoid arch ; lit, heart ; L, lung ; m.a, median
artery ; p.a, pulmonary artery ; p.v, pulmonary vein ; v.ao, ventral aorta ; v.c, vena cava
posterior. The five branchial slits are shaded ; the first two branchial arches are without gills.
A dotted line indicates the position of the obliterated spiracle.

structure of the conus, and the position of the auricles, are features
in which they distinctly approach the Amphibia.

The aortic arches of the first two jnll-less branchial bars of the

252

DIPNOI

Dipneumones pass directly, without breaking up into capillaries, to
the aorta, as in terrestrial vertebrates. In Ceratodus, but not in the

-ptv.

cv.

FIG. -l-l-l.

Diagram of the venous system of Ceratodus Forxteri, dorsal view. (After Spencer.) a , atrium ;
«!>, anterior abdominal vein ; br, branchial vein ; c, con us; c.v, caudal vein ; h.p, hepatic portal
vein ; i.j, inferior jugnlar vein ; il, iliac vein ; A4, kidney ; I, liver ; l.c, lateral cutaneous vein ;
l.p.c, left posterior cardinal ; p, pulmonary vein ; pt.v, posterior vein from body-wall ; p.v, pelvic
vein ; r.p, renal portal vein ; r.p.c, right posterior cardinal ; «<•, subclavian vein sj, jugular
vein ; t, testis v ventricle ; v>c, vena cava.

Dipneumones, the hyoidean hemibranch is a pseudobranch, receiving
blood only from the efferent system (Spencer, Parker, Figs 220-21).
Three chief points of interest are found in the venous system
(Figs. 222-4). Firstly, the pulmonary blood is returned directly to
the heart by a vein passing to the left side of the sinus venosus, as

VASCULAR SYSTEM

253

mentioned above. Secondly, the right posterior cardinal is interrupted

in front, and contributes to the formation

of a posterior vena cava, carrying blood

from the caudal vein and kidney directly

to the sinus venosus. Thirdly, in Cemtodus

at all events, an anterior abdominal vein

opens into the right ductus Cu'vieri ; it

is formed by the junction of two pelvic

veins, themselves derived from iliac and

renal portal veins. This epigastric, or

anterior abdominal vein, so amphibian in

appearance, is probably homologous with

the lateral veins of Elasmobranchs.

The kidneys, the gonads, and their
ducts differ but little in Ceratodus from
those of other primitive fish, such as the
Elasmobranchs (Giinther [190], Semon
[402-3], Kerr [260-61], Parker [324]).
An elongated mesonephros, which loses
its coelomic funnels in the adult, pours
its secretion into a duct opening into a
median cloacal caecum. The caecum,
derived from the fused bases of the
ducts, is placed above the rectum. Long
oviducts, in the female, having open
funnels in the front region of the
abdominal cavity, pass back to open into
the cloaca (Fig. 355).

In the male Ceratodus the semen is
carried by numerous vasa efferentia into
the kidney, passes through certain of the
renal capsules and tubules to the meso-
nephric duct, and thereby reaches the
cloaca (Fig. 356).

Lepidosiren is more specialised in that
the vasa efferentia are few in number,
arise from a sterile tubular posterior
portion of the testis, and pass into the
posterior region of the kidney. Finally,
in Protopterus one vas efferens alone

plv.

FIG. 223.

Diagram of the venous systent
of Protopterus annectens, Owen,
ventral view. (After W. N. Parker.)'
us, anastomosis between posterior
cardinals; c, conns; u.v, caudal
vein ; g.b, gall-bladder ; h.p, hepatic
remains On each Side, leading into the portal vein ; h.v, hepatic vein ; i,
TC j , i i • e ,i i • i intestine ; i. j, inferior jugular vein ;

modified tubular region of the kidneys, j, jugular vein ; k, kidney ; i, liver j.

l.p.c, left posterior cardinal ; o,
otrium ; oes, oesophagus ; o.v,
ovarian vein ; p, pericardium ; p.v,

,, i T\- • • parietal vein; r.p, renal portal;

111 the adult male Dipnoi, Opening in- r.p.e, right posterior cardinal

which meet in the middle line. The
Miillerian ducts persist to a great extent

dependently into the cloaca.

pcrcrc
egoS,

scl,

subclavian "vein ; st, stomach ; r,
ventricle ; v.c, vena cava.

254

DIPNOI

provided with a considerable amount of yolk, and surrounded by a
gelatinous coat secreted by the oviduct, undergo total but unequal
cleavage. The larvae, except in Ceratodus, have feathery external
gills and a ventral sucker of attachment below the head (Fig. 216).

The structure of the Dipnoi may be summarised as follows : —
As primitive characters : the spiral valve, the contractile conus, the
cloaca, the unconstricted notochord, the ventral nostrils. As specialised

Flo. 224.

Diagrams illustrating the formation of the veua cava iu the Dipnoi and Amphibia (after
Kellicott). A, Ceratodus, early larva ; B, Ceratodus, later stage ; C, Ceratodus, adult ; D,
Protoptems ; E, Scdamandra ; F, Eana. a.c, anterior cardinal ; d.c, ductus Cuvieri ; It, hepatic
veins ; l.p.c, left, and r.p.c, right posterior cardinal ; v.c, vena cava.

characters : the camptotrichia, the loss of the spiracle and pineal eyes,
the reduction of the hyomandibular, the autostylism, the loss of the
marginal jaw-bones and teeth, the permanent grinding plates formed
from coalesced internal teeth, the median pelvic cartilage, the twist-
ing of the air-bladder to a dorsal position, the special pulmonary
circulation, the incipient vena cava inferior, the large paired cerebral
hemispheres. It must be mentioned also that the scales are rounded,
the notochordal sheath is invaded, the median fin-radials articulate
with the axial skeleton, pleural ribs only are present, the paired
fins have a jointed median axis, and the air-bladder has a ventral
opening.

DIPNOI

255

TRIBE 1.

Family PHANEROPLEURIDAE. With -a diphycercal, or very slightly
heterocercal tail. The anal fin is separate in Phanerofileuron, and in
Scaumenacia there are two

dorsal fins as well (Fig. 227). .d

There are large paired parietals
and frontals. The median
cranial bones are little de-
veloped (Fig. 208). Two large
inferior jugular plates are
present. The scales are thin,
with bone-cells, and are covered
with spinelets as in Ceratodus
(Fig. 201). The dermal fin-
rays are strong and bony in
this and the next two families.
The teeth have tuberculated
ridges (Huxley [227-8], Miall
[299],Whiteaves [488], Jaekel
[237], Traquair [459, 462]).

Phaneropleuron, Huxley ;
Upper Old Red Sandstone,

FJpvnnian Pannda

Devonian, uanacta.

Dorsal view Of the lower jaw of Dipterus. a,

articular . on> angular . d> dentary ; spt spienial tooth
Scaumenacia, Traquair ; De- onithe spienial bone.
vonian, Canada.

Family URONEMIDAE. The median fins are continuous, and the tail
is diphycercal (Fig. 227). The palatine and spienial groups of teeth are
not fused into dentary plates. The cranial bones are numerous, and

FIG. 226.

Dipterus Valenciennesli, Sedgw., restored. (After Traquair, slightly modified.) o.d.f, anterior
dorsal fin ; a.f, anal lin ; c.f, caudal fin ; op, operculum ; p.f, pectoral fin ; pv, pelvic fin.

disposed as in Dipterus ; the presence of gular plates is doubtful. The
scales are thin (Traquair [458]).

In the continuity of the median fins and the simple condition of the
teeth these fossils are perhaps the most primitive Dipnoi known. In the

256

DIPNOI

structure of the skull, with large median elements, they approach
Dipterus.

Uroncmus, Ag. ; Carboniferous, Scotland. Probably also Conchopoma,
Kner ; Permian, Germany.

Family DIPTERIDAE. A heterocercal tail, and two dorsal and one
anal fin (Fig. 226). The superficial cranial bones and the scales are
thick, and covered with an outer layer of cosmine (Figs. 202, 210, 225).
The head-plates are numerous, the median series large, and the parietals
and frontals small. The ossification of the endoskeleton seems to be more
complete than in modern Dipnoi ; the auditory capsule, the quadrate, and

" hf.

•of.

FIG. 227.

Restorations from Traquair of A, Uronemus lobatus, Ag., Lower Carboniferous ; B, Phanero-
pleuron Andersoni, Huxley, Upper Devonian ; C, Scaumeiiacia curta, Whiteaves, Upper Devonian.
u.d.f, anterior dorsal fin ; a./, anal fin ; d.f, dorsal fin ; «/, epichordal lobe, and h.f, hypochordat
lobe, of caudal fin ; p.d.f, posterior dorsal fin ; p.f, pelvic fin ; pt.f, pectoral fin ; v.f, ventral fin.

the articular are bony. Paired ventral gular plates are present. The
teeth have tuberculated ridges [299, 312, 447, 505].

According to Dollo, Dipterus represent the most primitive Dipnoan
type (see p. 233). The presence of typical cosmine is a striking
point of resemblance with the Osteolepidoti. The more pronounced
ossification may perhaps also be primitive. But the arrangement of the
cranial covering bones points rather to the Dipterids being a highly
specialised offshoot from the base of the Dipnoan stem.

Dipterus, Sedg. and Murch. Conchodus, M'Coy ; Devonian, Europe.
Palaedaphiis, v. Ben. and de Kon. Ganorhynchus, Traq. ; Devonian,
Europe, and N. America.

DIPNOI

257

TRIBE 2.

In the following three families the gular plates and the cosmine layer
are lost ; the dermal bones sink beneath the skin ; in the living genera
the lateral-line system is in the skin, the organs being quite superficial
on the body, and sunk in canals only on certain regions of the head ; the
tail is diphycercal, and the median fins are continuous. They show
progressive specialisation and degeneration, though probably not forming
a true monophyletic series.

Family CTEXODONTIDAE. The covering bones of the skull resemble
those of Dipterus ; but the frontals and parietals are of considerable size,

vf

FIG. 228.

A, Cerutodus Fm-xtei-i, Krrtt't. B, Protopterusannectent:, Owen (after Lankester). C, Lepidosiren
iHtrmiuxa, Fitz. (after Lankester, modified). 6.0, branchial opening ; /, median tin ; p.f, pectoral
fin ; pv, pelvic fin ; vf, va.scular villi present on the male.

and the anterior median plate is small (Fig. 209). The ridges of the
teeth are set with tubercles.

Ctenodus, Ag. ; Carboniferous, Europe and N. America. Sagenodus,
Owen ; Carboniferous, Europe.

Family CERATODIDAE. The cranial bones are thin and much reduced
in number. Two large median bones, 'ethmoid' and 'occipital' (p. 238),
and two large paired 'lateral' bones, probably including the frontals
and parietals, cover the head, and are themselves overlaid with scales.
Circumorbital bones, postfrontals and 'squamosals,' complete the covering.
The chondrocranium is thick, complete, and unossified (Figs. 206-7).
The hyomandibular persists as a vestige ; the hyoid and branchial arches
are better developed than in the Lepidosirenidae. The gills are well
developed, and the air-bladder or lung is a median sac.

The paired fins have an endoskeleton with biserial radials, and are
covered with scales (Fig. 213). The ridges on the teeth have lost the
tubercles.

17

258 DIPNOI

Ceratodus, Ag. (Fig. 228) ; Triassic and Jurassic, Europe, N. America,
Africa, Asia, Australia ; Cretaceous, C. Africa, Patagonia. Ceratodus
(Neoceratodus\ living in Queensland. Gosfordia, A. S. W. ; Triassic,
N.S. Wales.

Family LEPIDOSIRENIDAE. The most specialised and degenerate of
Dipnoi. The body becomes much elongated, especially in Lepidosiren,
the scales are reduced in size, the naked filamentous paired limbs are
vestigial (Fig. 228). The dermal fin-rays are soft, scarcely jointed, and
with few cells.

The head is covered with soft, scale-bearing skin, and the dermal
bones are deeply sunk, and still further reduced in number. Two large
median bones cover the incomplete chondrocranium above ; two elongated
lateral bones pass back from the orbits at the sides • and two ' squamosals '
cover the quadrates (Fig. 209). The dentaries and post-temporals are
lost ; the opercular bones are very small. The branchial arches are much
reduced, and all trace of the hyomandibular has gone.

As described above, the teeth, gills, heart, and male genital ducts are
highly specialised. The lung-sac is bilobed. A remarkable growth of
vascular filaments develops during the breeding season on the pelvic
limbs of the male Lepidosiren (Fig. 228). They appear to function as
accessory gills (Lankester [278], Kerr [259]).

Lepidosiren, Nath. ; South America ; Protopterus, Owen ; Tropical
Africa.

Affinities. — It is clear that the early Dipnoi approach closely
to the primitive Teleostomes in general structure. Moreover, in
both them and the Osteolepidae we find similar lobate fins, large
paired inferior gulars, a layer of typical cosmine, powerful palatine
and splenial teeth, and a blunt snout with ventral nostrils. The
Dipnoi are probably a specialised offshoot from the base of the
Teleostome stem, which acquired an autostylic structure before the
hyomandibular had become very large, and before the hyostylism
of the ancestor had become fully established. But such a pre-
Devonian ancestral form must have differed so considerably from
any known genus that it seems better for the present to keep the
Dipnoi separate from the Teleostomi in our classification.

Sub-Class 2. COCCOSTEOMORPHI (Arthrodira).

A group of heavily armoured Palaeozoic fish, which often
attained a formidable size. The large broad head has the orbits
placed very far forwards, and apparently two small nasal openings
near the extremity of the blunt snout. The pineal eye is indicated
by a foramen, or an internal depression, in a median cranial plate.
Both the head and the anterior region of the trunk are covered
with a shield of closely fitting or fused bony plates. Those on the
trunk encircle it in a complete cuirass, which usually articulates
with the cranial shield by means of a pair of elaborately differen-

COCCOSTEOMORPHI 259

tiated ginglymoid joints. The trunk tapers into a tail, quite or
very nearly diphycercal. There is a single dorsal fin. Of pectoral
tins there is no definite trace, and the pelvic fins are only known
from rare remains of the endoskeleton. The body was apparently
naked in most cases, though scattered tubercles have been found in
Selenosteus (Dean [109]), and thin cycloid scales are stated to
occur in Coccosteids (Jaekel [244]). The structure of the dermal
bones is very like that of Asterolepis. They have, in the more
primitive genera, a tuberculated surface ; in others, such as
Titanichthys, the ornamentation has gone, the bones having
probably sunk below the skin. The dermal plates are formed of
true bone with bone-cells, an internal lamellated layer, a middle
vascular trabecular layer, and an external layer of denser substance.
Neither typical ganoine nor cosmine, neither denticles nor even
dermal fin -rays have been described. An elaborate and fairly
normal system of lateral-line canals is indicated on the cranial
shield by grooves ; they extend on to the lateral, and even on to
the ventral, regions of the body -cuirass. In the Anarthrodira
(Dean [109]) the canals are sunk below the surface of the bones.

The endoskeleton is scarcely known except in Coccosteus (Fig.
232). The notochord appears to have been persistent and uncon-
stricted ; no remains of centra are found. There are no ribs, but
well-developed haemal and neural arches are present. The dorsal
fin is supported by a series of two -jointed radials attached to and
corresponding with neural arches. A skeletal plate possibly belongs
to an anal fin (Fig. 232). Two basal pieces, with traces of radials,
seem to represent a pelvic girdle and pelvic fins. These endoskeletal
structures are of calcified cartilage.

The dermal plates are best known in Coccosteus (Pander [312],
Traquair [454, 457], A. S. Woodward [505]). An anterior ethmoid
(rostral) between the nares is followed by a ' posterior ethmoid '
or pineal plate. There is a large median occipital behind ; paired
' preorbitals ' ( = prefrontals + frontals ?) and ' centrals ' ( = parietals)
cover the skull above ; circumorbital plates surround the eye ;
' postorbitals ' ( = postfrontals) and ' marginals ' ( = pterotics) cover
the sides ; ' external occipitals ' (supratemporals) complete the shield
behind (Fig. 229). Toothless premaxillae and maxillae (suborbitals)
are found on the upper jaw ; the latter expands behind to cover
the cheek, and bears on its posterior edge a crescentic plate, which
is supposed to have supported a movable operculum. As indicated
above, these plates can, with more or less certainty, be homologised
with the bones of more normal Osteichthyes.

The solid trunk-cuirass may represent a much-modified dermal
pectoral girdle (Figs. 229, 229A). The ventral shield consists of
four paired and two median plates, of which the anterior is compared
to an interclavicle. In front are two elongated inter-lateral bones

26o

COCCOSTEOMORPHI

( = clavicles 1) ; and at the sides are an anterior lateral ( = cleithrum)
and anterior and posterior dorso-laterals ( = supra-clavicles ?). A
median dorsal completes the arch above. It is the anterior dorso-
lateral which articulates with the external occipital by the character-
istic joint. On the whole, the arrangement of the dermal plates is
very uniform throughout the sub-class. In some genera the outer
end of the interlateral is produced into a prominent spike, Avhich
may be formed of a separate plate (Phlyctaenaspis [Traquair, 459],

Brachydirus [v. Koenen], Pholi-
dosteus [Jaekel, 244]). These
paired fixed or movable processes
have been compared to the limbs
of Asterolepis and the cornua of
Cephalaspids(Figs. 230A and 231).
The jaws have no marginal
teeth ; but there are vomerine and
palatine teeth supported by palatal
bones above, and corresponding
teeth on a bone of the lower jaw,
which is probably the splenial
(Figs. 232, 234). The Coccosteo-
morphi become greatly specialised
in their dentition. The teeth,
indeed, appear to have always been
continuous with the supporting
bone, and possibly are merely
tooth-like processes. Whereas in
Coccosteus the teeth are of normal
conical shape, in Titanichthys they
v, are developed into formidable

quair, from A. S. Woodward.) a.dl, anterior piercing and Cutting deiltal plates,

dorso-lateral ; a.l, anterior lateral ; c, central ; t ,° , „ V

e, ethmoid; e.o, external occipital; m, lOrmcd merely OI dense bone, not
marginal; m.d, median dorsal; m.o, median t Hpntinp /Tlnvnnlp FftO/j^

occipital; mx, maxillo-suborbital ; », nostril; ° dentine (Ulaypoie [oUrtj;.

If the description by Jaekel
[242, 244] of an angular and an
articular bone in the lower jaw be
confirmed, all doubt will be set

aside as to whether the Coccosteomorphi are true Teleostomes
(Fig. 230) — a conclusion which is further strengthened by his
discovery of thin cycloid scales on the body.

For the view advocated by some authors (Newberry, A. S.
AVoodward, Eastman [128]) that the Coccosteomorphi are specialised
Dipnoi, it must be confessed that there is no convincing evidence.
One may note a general similarity in the disposition of the cranial
bones, with large median plates ; the structure of the tooth-bearing
bones resembles that of the Dipnoi, and is consistent with the view

Fio. 22P.

o, orbit ; p, pineal ; p.dl, posterior dorso-
lateral ; p.l, posterior, lateral; pmx, pre-
maxilla ; [>o, preorbital ; pto, postorbital ; r,
opercular (?). Dotted lines indicate the
course of the lateral-line canals.

COGCOS TEOMORPHI

261

that the jaws were autostylic in their attachment, but such has not

yet been proved to be the case. The only character in which the

two groups resemble each other

and diverge from other Osteich-

thyes is the dentition : the

reduction of the marginal teeth,

and the special development of

vomerine, palatine, and splenial

tooth-plates. In the Dipnoi,

however, these plates are of true

dentine (p. 245).

The Coccosteomorphi so far
known differ greatly from the
Dipnoi in the absence of true
bone in the endoskeleton, of
dermal fin-rays, and of normal
pectoral fins.

On the other hand, they have
in common with the Pterichthyo-

. * restored.

morphi, with which they were

associated by the earlier observers

(Agassiz, Hugh Miller, Zittel,

Jaekel), the structure of the

dermal plates, and the cuirass encircling the trunk. Its ventral shield

especially is very like in both cases ; and the lateral processes of

.art

-tiny.

FIG. 229A.

* ili-i'ijiii'ns, Ag. Ventral shield,
(After Traquair, from A. S. Wood-
ward.) a.m. i', anterior median ventral ; a.v.l, an-
terior ventro-lateral ; i.l, inter-lateral (clavicle?) ;
m.v, median ventral ; p.v.l, posterior ventro-
lateral. Dotted lines indicate the course of
lateral-line canals.

ang

FIG. 230.

Lower jaw of rhdidoxteuis FriVtH/, Jkl. A, outer view ; B, inner view (after Jaekel).
a » 3, angular : art, articular ; xpl, splenial.

Phlyctacnaspis, mentioned above, may conceivably represent the
pectoral limbs of Ptnichthys. Such resemblances may, however,
very well be due to convergence, and so do not outweigh the

262

COCCOS TEOMORPHI

many important differences. The real affinities of the Coccosteo-
morphi are still obscure.

The Sub-Class may be divided into two Orders — the Anarthro-
dira (Dean [109]) and the Arthrodira.

Order 1. ANARTHRODIRA.

A small group of incompletely known fish, perhaps representing
a less specialised type than the Arthrodira. Large sculptured
plates extend dorsally from the cranial shield over the trunk.
There appears to be no differentiated joint between the armour of
the two regions, the limit being marked only by an internal shelf of
bone. But perhaps the whole shield belonged to the skull, and there
was no trunk-armour (Eastman [129]). The lateral-line canals are
sunk below the superficial ornamental layer and open by a double
series of pores. There is no separate pineal plate, and the frontals
are widely separated by the median occipital which meets the ethmoid.

Family MACROPETAUCHTHYIDAE.
Devonian, N. America and Europe.
America.)

Order 2. ARTHRODIRA.

Macropetalichthys, Norm . and Owen ;
(? Asterosteus, Newb. ; Devonian, N.

The cranial shield is movably jointed with the cuirass of the
trunk. The ' centrals ' (parietals) touch in the middle line, separ-
ating, as a rule, a pineal from the median occipital plate. Super-
ficial grooves indicate the position of the lateral-line canals.

Sub-Order 1. ARTHROTHORACI.

The two joints between the shields are typically developed.
Doubtless in correlation with the powerful dentition there is

generally a con-
siderable space be-
tween the two
dorsal shields
above, allowing
the cranial shield
to be uplifted ; the
lower jaw appears
to have but little
play, being closely
followed by the
ventral plates. The
orbits were bound

Coccosteus bickensis, v. Keen. Restoration ofhead ami trunk shields, behind and below

vs.

FIO. 230A.

pa, pectoral spine; v.s, ventral shield. (After Jaekel.)

hv A mayi'lli

orbital). Except in the Coccosteidae, the preorbitals do not exist.

CO CCO S TEOMORPHI

263

Family COCCOSTEIDAE. The preorbitals (frontals) meet behind the
pineal. The teeth are conical and of moderate size. The statement
that they extend on to the symphysis is probably erroneous (Jaekel
[244]). In some the ventral shield is produced at each side into a
process bearing a spine (Traquair [459]), which in others may be long
and movable (Fig. 231).

Coccosteus, Ag., Brachydirus, v. Koen ; Devonian, Europe. Phlyc-
taenaspis, Traq. ; Devonian, Europe and N. America. Acanthaspis,
Pholidosteus, Jaekel ; Devonian, Europe.

Family SELENOSTEIDAE. The mandibular bones bear a row of
conical teeth along the anterior and the symphysial edge (?). The cranial
shield has no orbital notches, and two
diverging posterior wings (Fig. 233).

Selenosteus, Dean, Diplognathus,
Newb. ; Cleveland shale, N. America.

Family DINICHTHYIDAE. With
three pairs of biting bony plates, on
the vomers, palatines, and splenials
with anterior beak -like processes
(Fig. 234).

Dinichthys, Newb. ; Devonian, N.
America and Europe.

T-. -i PTI IT Acanthaspis decipiens ; Devonian, Spitz-

ramiiy UTAXICHTHYIDAE. Very bergen. Ventral view of body-shield, restored.

large fish, with slender toothless jaws (After A. S. Woodward, Vert. Palaeontology.)

' J ap, lateral spine ; pr, process supporting it.

and very broad head.

Titanichthys, Newb. ; Devonian, Carboniferous, N. America.
Family MYLOSTOMIDAE. The teeth are in the form of crushing
plates (Dean [108]).

Mylostoma, Newb. ; Devonian, N. America (Fig. 233).

Fio. 231.

FIG. 282.

Coccosteus decipien.i, Ag. ; Lower Old Red Sandstone. (After A. S. Woodward,
J!i it. Mint. Cittitl.) Left-side view, with dermal shields and endoskeleton.

Sub-Order 2. TEMNOTHORACI.

The very extensive and broad cranial shield is closely but

movably joined to the trunk-armour. The orbits are surrounded

by the post- and preorbitals ; the latter do not meet behind the
pineal (Fig. 235).

Family HOMOSTEIDAE. Homosteus, Asmuss ; Devonian, Europe.

264

COCCOSTEOMORPHI

'§ 1

^i = '~
' I § 2 ~
o>5 ^-«2r

COCCOSTEOMORPHI

265

FIG. -234.

Outer view of right jaws of DiniMhys Intermeilius, Newb. ; Upper Devonian, Ohio, n, anterior
Tipper piercing plate ; mil, lower piercing and cutting plate ; p, posterior cutting plate ; so, sub-
orbital, showing lateral-line groove. (From Jlrit. Mus. Guide.')

//..„!, ,..(i 1 ix riiillfi-i, Ti;iq. Cranial and dorsal shit-Ids, etc.. restored. (After Traquair, from
A. S. Woodward.) A. B, C, undetermined bones ; a.ill, anterior dorso-lateral ; at, ethmoid ;
e, central; e.o, external occipital; m, marginal; ia.<l, median dorsal; m.o, median occipital;
o, orbit ; p.'ll, posterior dorso-lateral ; po, preorbital ; jitr, piiu-al ; pto, postorbital. Double
dotted lines indicate the course of lateral-line canals.

GKOUP B.

Sub-Class TELEOSTOMI.

ON the head of the Teleostomi are usually to be noticed a pre-
ponderance of the paired cranial bones (a pineal foramen), and the
strengthening of the margins of the jaws with well -developed
tooth-bearing premaxillae and maxillae above, and dentaries below.
The outer, biting edges of the mouth and the main rows of functional
teeth are no longer supported by the palato-quadrate arch and
Meckel's cartilage ; the latter dwindles in importance anteriorly,
and the former becomes chiefly concerned in the roofing of the
palate. The cartilaginous cranium becomes very completely ossified,
not only by the development of endochondral bones in the deeper
parts, but also by the ingrowth from the surface of certain of the
dermal bones. It is sometimes difficult to decide to which of
these two categories some of the bones belong. Transition stages
from the dermal or membrane bone to the endochondral, and
perhaps also from the endochondral to the dermal, are frequently
found (p. 66). It also may happen that the main plate of a
given bone develops independently from that part which protects
the lateral line, the two often only fusing in the adult ; thus a
bone may acquire the appearance of having been originally formed
by the combination of two really distinct elements, whereas in
reality, as explained above (p. 222), the separation is secondary.

The periotic capsule becomes invaded by the postfrontal
(sphenotic) from in front, and the pterotic (' squamosal ') from behind
(Figs. 237-8, 303-5). The former bone helps eventually to lodge the
anterior vertical semicircular canal of the ear, gradually encroaching
on the upper and anterior region of the auditory capsule. In the
more specialised fish (most Teleostei), the postfrontal abandons the
surface and sinks below, becoming a purely ' cartilage bone,'
except for the lateral -line element which may remain above. In
Amia the two portions are sometimes well developed and separate
(Allis [12]). Similarly, the pterotic invades the posterior upper
region of the auditory capsule, and lodges the horizontal semi-
circular canal. A bone known as the epiotic (external occipital)
develops on the upper posterior and inner region of the capsule,

266

SKULL

267

sharing in the protection of the horizontal semicircular canal and
the posterior vertical canal. This epiotic, like the opisthotic and
prootic, arises in close relation with the cartilage, and probably
has never been superficial. The prootic (petrosum) occupies
the anterior ventral region of the auditory capsule, generally

ctk

firnsc.

a.n.

Dorsal view of the skull of Amia calm, L. (After Allis.) The course of the lateral-line system
is indicated by a dotted line on the left side, cm, adnasal ; d, dentary ; efh, inesethmoid ;
/, frontal; I, lachrymal or first suborbital ; no., nasal; np, opercular; j), parietal; pmsc,
premaxilla ; pobd and pobv, dorsal and ventral postorbitals ; pop, preopercular ; pp, supra-
temporal ; pt, post-temporal ; s, pterotic ; so, suborbitals.

surrounds the exit of the facial nerve, and lodges the anterior
semicircular canal. The opisthotic (intercalare), situated behind it,
may cover the outer horizontal canal ; but is often small, and
sometimes absent (many Teleostei). As Huxley showed [229],
the number and disposition of these ' otic ' bones is very constant
among Teleostomes, and many if not all of them can be identified
in the terrestrial Vertebrates.

268

TELEOSTOMI

The foramen magnum is bounded by paired exoccipitals at the
sides, and a median basioccipital below. In the Teleostei (Figs.
305, 381) a median supraoccipital appears above (p. 326). The
exoccipitals, which are pierced by the glossopharyngeal, the vagus,

sm.

obs. Of

FIG. 237.

Ania calva, L. (After Allis, slightly altered.) A, left-side view of the skull. B, left-side
view of the cranium, from which the dermal bones have been removed. Cartilage is dotted.
a.c, auditory capsule ; an, adnasal ; ar, dermarticular ; as, alisphenoid ; 60, basioccipital ; bst,
branch! ostegal ray ; c, cartilaginous cranium ; d, dentary ; ep, epiotic ; eth, mesethmoid ; ex,
exoccipital ; /, frontal ; fa, foramen for facial nerve ; ff, foramen for vagus ; h, hyomandibular ;
iop, interopercular ; I, lachrymal ; in.g, median gular ; m.l, lateral line in mandible ; inx,
maxilla ; n, neural arch ; lui, nasal ; n.sp, neural spine ; o, opisthotic ; obs, orbitosphenoid ;
oc.n, foramen for spino-occipital nerve ; o./, vacuity with optic foramen in front ; olf, olfactory
capsule ; op, opercular ; p, parietal ; pf, prefrontal ; pmx, premaxilla ; po, prootic ; pob, post-
orbital ; pop, preopercular ; pp, supratemporal ; pt, post - temporal ; ptf, postfrontal ; q,
quadrate; s, pterotic ; s.a, supra-angular; sm, septomaxillary ; so'p, subopercular ; apm, supra-
maxilla ; t.f, trigeminal foramen ; v.c, vertebral centrum.

and the occipito - spinal nerves, replace cartilage of compound
segmental origin (p. 12). The basioccipital forms the floor of the
brain-cavity behind, develops round the anterior end of the noto-
chord, and corresponds to the vertebral centra situated farther back

SKULL

269

(p. 11). Generally, it has a concave posterior face, just like that
of a centrum, to which the vertebral column is attached without
distinct articulation. Paired basisphenoids appear in the region of

pa.

FIG. 238.

Arnic. culm, L. A, ventral view of skull and upper jaw. B, posterior view of skull, an,
articular surface of quadrate, ap, of symplectic ; bo, basioccipital : enpt, entopterygoid ; ••/..
epiotic ; ept, ectopterygoid ; ex, exoccipital ; /, posterior temporal fossa ; h, hyomandibular ;
mp, rnetapterygoid ; mx, maxilla ; n.a, neural arch, whose centrum is fused to basioccipital ;
o.c, occipital cartilage ; op, opisthotic ; p and pa, palatine bones ; pm, premaxilla ; po, pro-
otic ; pp, supratemporal ; pr, parasphcnoid ; pt, i»ost - temporal ; sq, pterotic ; v, vomer ;
c./, vagus foramen.

the pituitary fossa, and may fuse to a median bone. The lateral
wall of the brain-case between the orbits is strengthened by an
alisphenoid in the region of the trigeminal foramen, and by an
orbitosphenoid near the optic foramen. The antorbital cartilage

270

TELEOSTOMI

is invaded by the prefrontal (lateral ethmoid), originally a superficial
bone, which may sink below the surface in higher forms (p. 345).
A median ethmoid may grow into the cartilaginous internasal
septum from above, and sometimes the vomer also from below.
Little paired septomaxillaries (Fig. 237) may occasionally be found
in the nasal capsule near the articulation of the maxilla (Parker
[319], Bruch [65], Sagemehl [379], etc.).

Accompanying the great development of the bones of the skull
is a corresponding reduction of the chondrocranium (Parker [319],
Swinnerton [431], Gaupp [151«]). The cartilaginous walls of the
brain-case are, as a rule, very incomplete. A large fontanelle is
found above, limited behind by an arch, the tectum synoticum,

FIG. 230.

Amia calva, L. Skeleton of the left jaws and byoid arch, from which the dermal bones of
the lower jaw have been removed. (After Allis, slightly modified.) The cartilage is dotted, cup,
endochondral palatine ; 6, process articulating with prootic ; c.p, coronoid process ; enpt,
endopterygoid ; eph, epihyal ; ept, ectopterygoid ; h, hyomandibular ; h.a, its articular head ;
lih, hypohyal ; i.c, ventral segment of ceratohyal; I, ligament; in, Meckel's cartilage; m.m,
mento-Meckeliau ; mp, metapterygoid ; n, foramen for hyomandibular nerve ; o.o, articular
head for opercular ; p, palatine (dermal) ; pg, palato-pterygoid cartilage ; q, quadrate ; sy,
symplectic ; w.c, jipper segment of ceratohyal.

between the auditory capsules. A hypophysial space below
separates the two trabeculae, which fuse in front to form the
nasal and antorbital cartilage, but hardly contribute at all to the
closure of the side walls (Fig. 58).

The attachment of the jaws is always of the hyostylic type.
The hyomandibular is large, and supports the quadrate some
distance from the cranium (Figs. 239, 302, 456). At its anterior
end the palato-quadrate bar has a palatine bone ; it often bears teeth
and may be subdivided into an endochondral and a dermal element
(Amia, Allis [10], Fig. 239 ; Lepidosteus, van Wijhe [494]). Usually
it articulates with both the ethmoid region of the skull and the
maxilla. There follow behind a dermal ectopterygoid (pterygoid)

VISCERAL ARCHES 271

and endopterygoid (mesopterygoid) ; bones which often are toothed.
An endochondral quadrate bears the lower jaw ; and an endo-
chondral metapterygoid joins on to the hyomandibular above it.
Thus the hyomandibular, symplectic (when present), and palato-
ptery go-quad rate usually form one rigid arch. How far these
three pterygoid bones are all present in primitive and early forms
is uncertain.

The palato-pterygoid arch articulates in front with the ethmoid
cartilage laterally, by an ethmo-palatine articulation. The right
and left arches do not, therefore, meet below the snout as in
the Chondrichthyes (except in the Acipenseroidei). It is interest-
ing to notice that in certain (perhaps in all the primitive forms) of
the lower Teleostomes (Pycnodontidae, Aspidorhynchidae, Macro-
semiidae, Pholidophoridae, Lepidosteidae, Lepidotidae, Amiidae) the
metapterygoid sends inwards a process (Fig 239), which quite or

Inner view of the lower jaw of Amia calva, L. (After Alli.s.) a, articular ; an, angular ;
ar, dermarticular ; a.sp, anterior splenials ; cp, coronoid cartilage ; d, dentary ; sa, supra-
angular ; sm, mento-Meckelian ; sp, splenial with minute teeth ; t, marginal tooth.

/

nearly articulates with the trabecular region of the skull between
the optic and the trigeminal foramina (van Wijhe [494], Reis [349]) ;
a vestige of this process appears in the embryos of some Teleostei
(Salmo, Swinnerton [431], Winslow). This connection may
perhaps represent the lower articulation of the quadrate in auto-
stylic skulls — the pedicle of the suspensorium (p. 9?J! In that
case it would point to the Teleostomi having preserved a trace
of the original connection between the mandibular arch and the
cranium (p. 97).

The large cartilaginous hyomandibular generally ossifies in two
pieces — a hyomandibular bone above articulating with the skull,
and a symplectic below, connected with the quadrate (Fig. 239).
In Pdypterus, however, there is no symplectic (see p. 295) ; and
in some Teleosts, such as the Siluridae and Anguillifermes (Apodes),
it appears to have been lost.

The different relation of the seventh nerve to the hyomandibular
is of some interest (van Wijhe). Whereas in Selachians the main
hyomandibular branch issues from the skull in front of the articula-

272 TELEOSTOM1

tion and passes outwards and backwards over the hyomandibular
cartilage, in the Acipenseridae it issues below and passes behind the
hyomandibular ; in Amia, Lepidosteus, and the Teleostei it passes
through it. Polypterus displays an intermediate condition in which
the mandibular branch passes in front and the hyoid branch behind
the hyomandibular. Doubtless these differences are due to the
shifting forward and upward of the articulation.

Epihyal (interhyal), ceratohyal, hypohyal, and basihyal elements
are generally present (Fig. 331). The basibranchials are usually
well represented, and many of the branchial arches may have infra-
and suprapharyngeals. As a rule, the branchial arches are
extensively ossified.

There are some interesting points to be noticed concerning the
teeth of the Teleostomes which may be mentioned here. As a
rule, they develop regularly in a dental fold, succeeding each other
throughout life ; but they differ much in size, shape, and mode of
attachment (Tomes [440]). While in the Selachii the teeth are
merely bound by connective tissue to the jaws, in the Teleostomes
they usually become firmly fixed and cemented on to the dermal
jaw-bones by bony substance, which is reabsorbed when the tooth
is shed. Frequently, however, some of the teeth (Esox, Gadus,
Lophius) are movably attached by means of an elastic ligament on
the inner side, allowing them to be folded back when food is taken
in (Fig. 81). Rarely the teeth are planted in sockets (Sauro-
dontidae), to the sides of which they may become anchylosed
(Scomber). Sometimes they are placed in a deep groove. The
normal process of succession may become much modified. In many
fish the new tooth grows underneath the old one so as to replace
it 'vertically' (Fig. 448). In others, successive generations of
teeth may become cemented together, forming a beak-like covering
to the jaws, with cutting edge or grinding surface ; such compound
teeth have been independently developed in several families (Dio-
dontidae, Figs. 451, 453, p. 440 ; Hoplognathidae, Fig. 439, p. 431).

Correlated with the presence of a complete opercular flap, we
find the septum supporting the branchial lamellae undergoing
greater and greater reduction in the Teleostomes. It is short in
the Chondrostei, and almost absent in the Teleostei. The lamellae
project, therefore, more and more freely into the branchial cavity,
and the branchial rays supporting them invariably form a double
series on each arch, not a single series as in Selachians (Fig. 57).

Breathing valves are often developed on the jaAvs, serving to
direct the stream of water through the gills (Dahlgreen [96],
Allis [13]).

The axial and appendicular skeleton become very thoroughly

SKELETON 273

ossified in the Teleostomes. True bone is present in the earlier and
more primitive forms ; but it may become much modified later, and
in many Teleostei may lose all trace of bone-cells (p. 355). A
return to the cartilaginous condition may, on the other hand, have
taken place in certain degenerating groups (Chondrostei).

The vertebral column differs markedly in structure from that
of other fish, more especially the Elasmobranchs, in that the
notochordal sheaths remain throughout growth intact (Fig. 338).
However much the notochord may be constricted, the mesoblastic
cells never pass through the elastica externa to invade the fibrous
sheath [265, 471a, 130]. The early and primitive Teleostomes
may have possessed permanently unconstricted notochords, as is
still the case with the living Chondrostei ; but even amongst the
Devonian genera annular bony vertebral bodies are found. The
vertebral centra, Avhether simple or complex, are formed in connec-
tion with the neural and haemal arches in the connective-tissue
skeletogenous layer outside the notochordal sheaths, and are dis-
tinguished as perichordal centra from the chordal centra of the
Elasmobranchs (p. 100).

As a rule, the neural and haemal spines form a very complete
series, and fuse with the corresponding arches (p. 352). The
median fin-radials are present either in equal number or a multiple
thereof. As already mentioned (p. 109), the radials (somactidia),
both in the paired and the unpaired fins, project as a rule but little
into the fin -fold, which becomes more and more completely
supported by the dermotrichia. The endoskeletal radii, then,
diminish and retreat to the base of the fins as the lepidotrichia in-
crease in importance. At the same time, each radial becomes more
definitely related to individual lepidotrichia, in the dorsal and anal
fins only, of the higher Teleostomi (p. 321 ; Bridge [56],
Harrison [196], Goodrich [175]). Whereas in the lower forms
the dermal rays are much more numerous than the endoskeletal,
in the higher fish they come to correspond in position and
number, each double (right and left) lepidotrich forming an
elaborate articulation with its supporting radial (Figs. 301 A, 311).
The median fins of the Actinopterygii are thus beautifully adapted
to folding, being capable of erection or depression at the will of
the animal. Similar articulations for the lepidotrichia occur in the
paired fins.

Lepidotrichia are found on the fins of all Teleostomi ; but the
presence of small actinotrichia at the edge of all the fins in the
adult is quite characteristic of the group (Harrison [196], Goodrich
[175]) (Figs. 186, 187). These delicate unjointed horny fibres are
the only dermotrichia in the embryonic fins. They closely resemble
the ceratotrichia of Elasmobranchs, with which they are in all
probability homologous (p. 122). The actinotrichia develop in the

18

274

TELEOSTOMI

mesoblastic cells below the epidermis, and they remain at the

.-scl.

pel.

FIG. 241.

Skeleton of the right, pectoral flu and right half of the pectoral girdle of Amia calm, L.,
seen from within, rf, cleithrum ; co, coracoid ; dr, lepidotrich ; /, nerve foramen ; m.co, ineso-
coracoid arch ; mt, metapterygium ; p.cl, postclavicle ; p.t, post-temporal : p. to, its lower process
to opisthotic ; rd, distal preaxial radial ; rp, proximal preaxial radial ; sc, scapula ; s.d, supra-
clavicle ; s.f, scapular foramen. The cartilage is clotted.

FIG. L'4-J.

Left pectoral girdle of Atipenser sturlo. A, oblique view from behind. B, inner view.
(From Gegenbaur, Vergl. Anat.) cl, cleithrum; d', clavicle ; g, articular facets for pectoral
fin-skeleton ; o, «, open channel ; ss, dorsal cartilage.

growing edge of the fin-web, sinking deeper into the connective
tissue, while , the less numerous but more important lepidotrichia

SKELETON

275

are formed outside them in the now more superficial mesoblastic

layers (Fig. 343). Only in the

fatty or adipose fin of certain

Teleostei (Salmonidae, Siluridae,

etc.) do the actinotrichia acquire

considerable size in the adult, and

in these fins they form the sole

organs of support.

The skeleton of the paired
fins has already been discussed
above (p. 106), and will be further
dealt with below (p. 302) ; but
we may here consider the structure
of the limb-girdles.

The endoskeletal pectoral
girdle consists of a bar of cartilage,
extending dorsally as the scapular . }nilt:r vie.w °f *!"» ri&ht, lialf °f *he en,d°-

° * - * skeletal pectoral girdle and tin of Salmo salar.

region and ventrally as the cora- L. c, coracoid : a.c, distal cartilages of

• j • /T:V ,,i 0\ mi radials ; nic, mesocoracoid arch; r. fifth

COld region (-blgS. 2±\-6). Ihe radial ; ,s scapula ; s./, scapular foramen.

two halves do not fuse ventrally,

and as a rule are widely separated, resting on the dermal covering

bones (clavicle and cleithrum, p. 214). Among living Teleostomi

Ventral view of the ]«-lvic girdle and tins of ButfkenovttfOH Fwrili, Wht. : restored. The
skeleton of the right fin is completely exposed, o, jointed axis. (From Qtm.rt. Jvurn. Micr.
Sci.)

276

TELE OS TO MI

the girdle is ossified, except in Amia and the Chondrostei. A
bony coracoid appears below, and a bony scapula above, generally
pierced by a large foramen. In all the lower sub-orders, and in
some of the less specialised Teleostei, we find a third inner
anterior process differentiated from the coracoid, known as the
mesocoracoid (precoracoid of Parker [317], Fig. 243), which may
be separately ossified. This mesocoracoid arch, although absent in
Polypterus, is probably a primitive structure inherited from a

common ancestor. A more
detailed study of the fossil
genera would throw light on
this question, which is of con-
siderable importance in class-
ification (Gegenbaur [153],
Boulenger [42]).

The essential features of
the dermal pectoral girdle
have been described above
(p. 214). It becomes much
modified in the higher Actino-
pterygii.

The two halves of the
originally cartilaginous pelvic
girdle ossify, except in the
Chondrostei, in the form of
two horizontal bones lying
in the abdominal wall, meet-
ing ventrally in front, and
bearing the fin-skeleton at
their hinder end (Figs. 244-
248). The dorsal iliac process
is scarcely if at all repre-
sented. Small cartilages may
remain at the anterior ends
of the bones, and rarely the
may fuse to a small median cartilage

FIG. 245.

Ventral view of the pelvic girdle and fins of Amid
cnlva, Bon. The skeleton of the right fin is com-
pletely exposed, dr, web of left tin with lepido-
trichia ; }>, pelvic bone ; pr.r, preaxial radial, or
remains of axis. (Partly from Uavidoff, from Quart.
Journ. Micr. Sci.)

girdle

two halves of the
(Gadus, Fig. 247).

On very insufficient evidence it has been argued that the
occasional small anterior cartilages represent the true girdle, and
that the large pelvic bones are the modified basipterygia of the fins
(Davidoff [97-9], Gegenbaur [163], Wiedersheim [491-2]). While
Wiedersheim considered these cartilages to represent the first rudi-
ments of a developing girdle, Gegenbaur, on the contrary, looked
upon them as its last vestiges. Since, however, the pelvic bones
are found normally developed in Teleostomes from the Devonian
to the present epoch (Evsthenopteron, Fig. 244, Goodrich [1 73]), there-

CLASSIFICA TION

277

is no reason for rejecting the old view that they are the two halves
of the girdle, comparable to those found in Holocephali and
Pleuracanthodii. In the Dipnoi and Elasmobranchii only the two
halves become intimately fused together, as in the higher terrestrial
Vertebrates.

The living Teleostomes differ from the Dipnoi (and the
Chrondrichthyes) in several important respects besides those
mentioned above : the branchial lamellae are supported by a double
series of rays on each arch ; the brain is characterised by the pre-
ponderance of the hind- and
mid-brain over the fore-brain and
the small development of the
anterior region of the fore-brain
(telencephalon), which retains a
simple epithelial roof (Figs. 283,
353). The basal ganglia thicken
below; but there are no paired
cerebral outgrowths. There is
no cloaca, the urinogenital open-
ing being behind the anus.

The ova are relatively small,
and generally extremely numer-
ous. Those of the lower Teleo-
stomes (Polyptems, Lepidosteus,
Adpcnser, Amia] are provided
with comparatively little yolk,
and are quite or nearly holo-
blastic in cleavage. The larvae
have organs of fixation, in the
shape of paired suckers in front
of the mouth, unlike those of

,•1 -rv • 14 i -i • 1-1 ineieiy exi>oseu on i/ne ieio siue. cir, weu ui

the Dipnoi and Amphibia which [eft fin with lepidotnchia ; p, pelvic bone;

are ventral and behind the mouth.
In the Teleostei the yolk is rela-
tively very large in amount and the cleavage meroblastic. Fre-
quently their eggs float freely in the sea with the help of an oil-
globule of light specific gravity (Dean [105], Agassiz [3], Balfour
[30], etc.).

The orders Ganoidei, Ctenoidei, and Cycloidei of Agassiz
(p. 210), founded merely on 'the structure of the scales, were shown
by Johannes Miiller to be to a great extent artificial. Following
rather the example of Cuvier, and trusting chiefly to distinctions of
internal anatomy, Miiller determined the limits of the group
Ganoidei anew [307], purging it of its foreign elements. He
divided Agassiz's three orders into two sub-classes, the Ganoidei

Fio. 246.

Ventral view of the pelvic girdle and fins
of Lc[ii<lo*ti:t'.< OASCH*', L. The skeleton is com-
pletely exposed on the left side, ilr, web of

.r, preaxial radial, or remains of axis. (Partly
after Davidoff, from Quart. Joiirn. Mier. Sci.)

TELEOSTOMI

and Teleostei, placing two orders in the former, the Holostei
(Lc/>i<}<>,<fcn.< iind Polypterw) and the Chondrostei (Acipenserini and
Spatulariae). Thus was laid the foundation of our modern classifica-
tion. Mullet's Ganoidei are distinguished from the Teleostei by
the possession of a valvular contractile conus, a spiral valve, and an
optic chiasma. C. Vogt [474«] subsequently showed that Amia
belongs to this group.

The next great step was made by Huxley [227]. Treating the
fossil in conjunction with the living fish, he subdivided the
Ganoidei into Amiadae, Lepidosteidae, Crossopterygidae, Chon-
drosteidae, and Acanthodidae. The foundation of the group
Crossopterygidae Avas a great advance, for in it were gathered

together with Polypterus a
number of related but hitherto
scattered genera clearly dis-
tinguished from the remainder
of the Ganoidei. On the
other hand, the work of Cope,
A. S. AVoodward, and others
on extinct fish has tended to
break down the distinction

between the Ganoidei and
Teleostei. It is now coming
to be recognised that none of
these older classifications is
strictly in accordance with
a phylogenetic scheme.

The reunion of the Amia-

Ventr.1 view of the pelvic girdle ami .ins of dae> Lepidosteidae, and Choil-

Gad us >,w,Thti <:,}.. ,1. r, dermal rays (lepidotrichia) ; drOSteidaC into the One group

m.f, median cartilage; p, pelvic bone; posterior , .. , ^ *?_., n

process. (From Quart. Jo«rn. Mirr. >Vf.) ActinOpterygll by Cope [91flJ

\vas the next important move

towards a more natural classification. But the Crossopterygidae
of Huxley, the only common and diagnostic character of which
is the possession of a pair of large gular plates, tend now
to fall apart into a number of diverging groups whose mutual
affinities are very doubtful. The Dipnoi have been separated oft'
as a specialised offshoot, related to but probably not derived from
any known Osteolepidotid (p. 258). It is true that the Crosso-
pterygidae have more or less ' lobed ' paired fins fringed with dermal
rays, but so have many other fish ; and the supposition that the
endoskeleton of these fins has been derived from the rachiostichous
and mesorachic type found in Dipnoi rests on speculations which
are neither firmly established nor generally accepted (p. 282).

The Teleostomi, as originally defined by Owen, included the
Ganoidei, Dipnoi, and Teleostei. We now use the term in a more

CHARACTERS

279

restricted sense as comprising the Actinopterygii and three other
orders, Osteolepidoti, Coelacanthini, and Polypterini. All these
orders, except the last, were already represented in Devonian times.
Their exact relationship to
each other remains a problem
to be solved.

The chief characters of the
Teleostomi maybe summarised
as follows : The paired series
of bones preponderate on the
cranial roof. The pineal fora-
men is often preserved. Teeth
are borne on marginal dermal
bones on the jaws ; the skull is
hyostylic, the hyomandibular
large ; there is a palatal ptery-
goid compound plate. The
lateral gular plates are usu-
ally present. The notochordal
sheaths remain intact, although
generally the notochord is
constricted, and perichordal
vertebrae developed. The
series of neural and haemal
spines remains little, or not at
all, affected by the subdivision
and concentration of the
median fins. The two halves
of the endoskeletal pectoral
girdle remain separate and
tend to dwindle in importance,
being to a great extent re-
placed by dermal bones; the fin of .S«/mo salar, L. (Modified from Bruch.) a.r,

pelvic girdle is in the form
of paired ventral bones, or
cartilages. The skeleton of the paired fins may show distinct
signs of being built on the ' archipterygial ' plan ; but the
axis is generally posterior, and much reduced, or altogether absent
(Teleostei). All the fins are provided with lepidotrichia and
marginal actinotrichia. Besides the cosmoid, ganoid, or teleostean
scales which clothe the body, there is frequently preserved a
general superficial covering of dermal denticles.

Living Teleostomes have the branchial rays supporting the gill-
lamellae in a double series ; a brain in which the prosencephalon is
not differentiated ; a separate anus and urinogenital aperture ; and

FIG. 24S.
Ventral view of the pelvic girdle and left pelvic

posterior radial or remains of basipterygium ; I,
lepidotrich ; p, pelvic bone ; r, radial.

280

OSTEOLEPIDOTI

comparatively small ova. (The nostrils usually are dorsal ; but this
was certainly not always the case in the extinct Osteolepidoti ; sec
below.)

Division 1.
Order OSTEOLEPIDOTI (Crossopterygii, Osteolepida).

The Osteolepidoti flourished from the Middle Devonian to the
end of the Carboniferous epoch ; only one genus is known to extend
into the Permian, Megalichthys, the largest of this order. Thanks
to the researches of Pander [312], Huxley [228], Traquair [443,
445, 450]), Whiteaves [488], A. S. Woodward [505], and others,

our knowledge of the ex-
ternal form and internal
skeleton of the Osteolepidoti
is fairly complete.

The scales vary in shape
from the rhomboid (Osteo-
lepis, Fig. 250) to the cycloid
i(yrm(Hdoptychiu&, Fig. 253).
They are never, strictly
speaking, ' ganoid ' (p. 218);
but may be thick and shiny,
or thin and unpolished. In
the first case their exposed
surface is covered with a
layer of typical cosmine
(Fig. 1 90 and p. 217), which
in others seems to be
reduced, or to disappear

entirely, leaving the bony layers exposed (Fig. 249). The cranial
plates and the lepidotrichia agree in structure with the scales.
True denticles have not yet been definitely shown to exist.

The proximal end of each lepidotrich extends inwards below
tlie body-scales, just as these overlap each other (p. 210). In
OsteoUpis the scales overlap the dermal ray to a slight degree, in
Glyptoltpis for a considerable length, still further in Gbtptopomins,
and finally, in Holoptychius the unjointed proximal segment of the
lepidotrich is almost as deeply embedded as in Dipnoi (p. 232).

The orbit is small and situated far forward. The anterior
cranial bones (premaxillae, nasals, ethmoid, and even frontals and
prefrontals) tend to fuse to a continuous shield covering the snout,
especially in the Osteolepidae (Figs. 250, 257). It is the presence of
this shield, sometimes with paired notches below, which leads to
the conclusion that the nostrils were ventral, unlike those of living

FIG. 249.

Anterior edge of the dorsal fin of Eusthenopteron
Foordi, Wht. ps, base of dermal ray ; r, endoskeletal
radial ; sc, scale ; si, thickened scale-like segment of
anterior dermal ray.

OSTEOLEPIDO 77

281

Fio. 250.

Restoration of Glyptopomm. A, ventral, and B, dorsal view of the head, (After Huxley,
Slightly modified.) c, clavicle ; d, cleithrum ; e, ethmoid ; fr, frontal ; I, lower jaw ; l.y, lateral
gular ; rn.s, median supratemporal : 'nix. maxilla ; np, opercular ; p, pineal foramen ; pa, parietal ;
I if, prefrontal ; ;>»i, premaxilla ; pn. preopercular; ytf, postf'rontal ; jito, pterotic; s, supra-
temponil ; sel, supraclavicle ; xop, subopercular ; r.g, ventral gular.

pto.

Tilt.

St.

f

pnix

9 S°P

FIG. 251.

Restored head of Iliiloptyi.-hiusAndersoni, Ag. ch, cheek-plates ( = preopercular ? ) ; el, cleith-
rum ; civ, clavicle ; ri. dentary ; c, mesethmoid ; /, frontal : g, paired ventral gular ; ioj>, inter.
opercular ; l.g, lateral gular: nt.t, median supratemporal ; op, opercular ; p, parietal ; pmx,
premaxilla ; pi, ix>st-teinporal ; pt<>, pterotic ; fip, suboperculum ; sp, notch, possibly indicat-
ing spiracle ; st, supratemporal.

282

OSTEOLEPIDOTI

Teleostomes (Polypterini and Actinopterygii). The extensive
cheek region is covered partly by the postorbitals and partly by
one or more large plates representing the preoperculum (Fig. 251).
Sometimes a normal preoperculum is present, with separate cheek-
plates in front (Fig. 256). A row of three supratemporal plates
covers the occipital region.

The lower jaw is provided, as a rule, with a series of infra-

dentaries. On either side of
the large paired inferior gular
plates a series of lateral gulars
extends upwards to the sub-
opercular and opercular bones
(Fig. 250). The interoper-
cular has not been identified
for certain. The anterior
median gular, if present, is
small. On the inner side
of the mandible, the splenial
bears large teeth, and may
be subdivided into several
ossicles. Large teeth are
also present above in the
vomerine and palatine regions.
The wall of these teeth tends
to become much folded
(p. 285).

The paired fins have an
outstanding scale-covered lobe
of considerable size. In some
(Holoptychiidae) this central
axial region is elongate and
tapering, 'acutely lobate,' with
a fringe of lepidotrichia on
FIG. 252. either side, thus closely re-

A, en.loskeleton of the second dorsal fin of Sembling the fin of CeratoduS

Glyptokpis leptojitei-iis, Ag. B, skeleton of the left /]?:„ 9^X\ TTnfnrtnnarplv

pectoral lin of Em>thenvpteronVoonn,\{\\t.; restored. Vrl§- ^Ot). U n] tely>

«, segment of longitudinal axis ; a.b, basal segment the internal skeleton is UU-
of axis ; 6, basal; d.r, dermal rays; p.p, postaxial . .

process (radial?); pr.r, preaxial radial ; r, radial. known in these forms ; but it

would appear to have been

built on the mesorachic plan, with a jointed central axis bearing
preaxial and postaxial radials. In the Osteolepidae the fins, especi-
ally the pelvics, are shorter, and less acutely lobate ; in these also
the endoskeleton is unknown. The Rhizodontidae have lobate fins-
departing from the mesorachic type : here the preaxial edge and its
dermal rays are becoming stronger than the postaxial, as in the
Actinopterygii, while the skeletal axis is somewhat posterior (Fig,

\N< . ?

V v N

prr.

Willfe

!' >\\\\V\^v '

dr.

OS TEOLEPIDO 77

283

258). In this family the endoskeleton is well ossified, and has
been described (Traquair [443], A. S. Woodward [505]). The
pectoral fin has a jointed bony axis of from three to five segments,
bearing each a well -developed preaxial radial ; large posterior
processes from some of the axial segments may possibly represent
postaxial radials (Fig. 252).

The skeleton of the pelvic fin (Traquair [459], Goodrich [173])
is less well developed, but is built on the same plan, with three
to four axial segments bearing preaxial radiais (Fig. 244). The
asymmetrical (pleurorachic) fins of the Ehizodonts are supposed to
be developed from the mesorachic (archipterygial) type (p. 106) ;

al.

of.

kf.

FIG. 2^3.

A, Osteoleph mucrolepidotn?, Ag. ; restored. (After Traquair.) c.f, anal fin ; c.f, caudal lin ; d.f,
second dorsal fin ; op, opercular; pc.f, pectoral lin ; p.f, pelvic (in. B, restoration of Tri*ti<-h<t-
pterus alattis, Eg. ; Old Red Sandstone, Caithness. (After Traquair.) c.f, anal, d.f, dorsal,
e.f, epichordal, h.f, hypocliordal, p.f, pelvic, and pt.f, pectoral fin ; c .1, axial lobe of caudal tin.

but it must be remembered that there is as yet no proof of the
existence of a typical mesorachic endoskeleton in the paired
fins of any Teleostome.

The tail is either diphycercal or more or less heterocercal ; but
the upper epichordal lobe never quite disappears, and is supported
by dermal rays. Such tails, in which the epichordal lobe is only
somewhat smaller than the hypochordal, may be called hetero-
diphy cereal.

Sub-Order 1. HAPLISTIA.

This sub-order contains only the single species described by
Traquair under the name Tcrrasius problematicus from the Lower
Carboniferous rocks of Glencartholm, Scotland [449, 455]. It

284

OSTEOLEPIDOTI

differs from the other Osteolepidoti in the possession of continuous
dorsal and ventral median fins.

Family TARRASIIDAE. The dermal bones of the skull and operculum
appear on the whole to resemble those of the Osteolepids. The front
region of the trunk is naked ; but the caudal region is covered with small
quadrangular scales, which scarcely overlap and have a superficial resem-
blance to the scales of an Acanthodian. The tail is diphicercal, and the
notochord was persistent, there being no centra. A series of radials,
more numerous than the vertebral arches, supports the median fins. The
pectoral fin has a small rounded basal lobe ; no pelvic fin has been found.
This important genus is still incompletely known ; its affinities are still
very uncertain. In this connection it would be most interesting to
ascertain the structure of the outer shiny layer which covers the dermal
skeleton.

Tarmsins, Traq. ; Lower Carboniferous, Dumfriesshire.

Sub-Order 2. RHIPIDISTIA.
With subdivided median fins.

Family HOLOPTYCHIIDAE. The pectoral fins are acutely lobate, and
the pelvic fins rather less acutely lobate. The tail is heterocercal, with a
large lower and smaller upper lobe. There is no pineal foramen. The

FIG. 204.

A, lloloptychius Flemingi, Ag. ; Upper Old Red Sandstone, Dura Den ; restored. (After
Traquair, from A. S. Woodward.) B, restoration ofGlyptopomus Kinnairdi, Huxley ; Devonian.
(After Huxley, modified.) a./, anal, d.f, dorsal, c./, epichordal, /;./, hypochordal. /)./, pelvic,
and pt.f, pectoral fin.

OSTEOLEPIDOTI 28:

vertebrae appear never to have been ossified. The notochord was possibly
unconstricted. The scales are cycloid, and deeply overlapping ; their
exposed surface covered with a modified cosraoid layer sculptured in
ridges and knobs (Rohon [369]). The teeth acquire a marvellous com-
plexity of structure owing to the infolding of the wall, especially near
the base ; it is owing to this feature that the family has been named
Dendrodontidae (Owen [31 1«, 368, 453, 462]).

Glyptolepis, Ag., and Holoptychius, Ag. (Fig. 254) ; Devonian, Europe
and America. Dendrodus, Owen ; Devonian, Europe.

Family GLYPTOPOMIDAE. Like the preceding family ; but the paired
fins less acute, the tail diphycercal, and the scales mostly rhomboidal
and only slightly overlapping, though sculptured. There is a pineal
foramen [228].

Glyptopomus (Glyptolaemus}, Ag. (Fig. 254) ; Devonian, Europe and
North America.

Family OSTEOLEPIDAK. The scales are rhomboid, and, like the cranial
plates, have a thick layer of shiny cosmine. There are large strong
scales at the base of the fins, and a
median anterior gular. The cranial
roof bones are often fused together,
especially in front. A pineal foramen
is preserved, except in Meyalichthys.
The teeth are but little folded. The
paired fins have a short and some-
what obtuse lobe. The tail may be
very slightly heterocercal (hetero-
diphy cereal) as in Diplopterus (Fig.
255), or quite heterocercal as in FlG- 255-

Osteolepis (Fig. 253) [312, 227-81. Tail of DiptnpterusA<j"xx!iii:, Traill. (After

. 7 • -tr i /-A- n~n\ rrii Traquair.) ax, extremity of axis ; o./, anal

Osteolepis, Val. (.big. 253) ; llmr- tin ; cf, hypochordal tin; <?./, dorsal fin.

.-•/((.•>, Traquair ; Diplopterus, Ag.

(Fig. 255) ; Devonian, Scotland. Meyalichthys, Ag. ; Carboniferous and

Lower Permian, Europe and North America.

Family RHIZODONTIDAE. The scales overlap deeply, and are gener-
ally thin, cycloid, sculptured, and without cosmine. A shiny cosmine
layer is, however, preserved in Gyroptychius, in which genus the scales
are somewhat rhomboid. The caudal fin is diphycercal or hetero-
diphycercal (Tristichopterus). Usually there are three well-marked lobes,
into, the middle one of which projects the extremity of the notochord
(Figs. 253 and 258). The paired fins are obtusely lobate, and not strictly
mesorachic ; the fin-lobe is somewhat triangular and the anterior edge is
strengthened (p. 282). There is in some a small median anterior gular
plate, and the teeth are considerably folded at their base. The endo-
skeleton is generally well ossified, bony, ring-like centra being frequently
present [488, 445, 450].

It is evident from the structure of the paired fins that the Rhizodonts
ditt'er considerably from the previous three families, and they should
perhaps not be included in the same Order (Figs. 244, 252).

Gyroptychius, M'Coy ; Tristichopterus, Eg. (Fig. 253); Devonian,

286

OSTEOLEPIDOT1

Scotland. Sauriptenis, Hall

FIG. 25t>.

Rhizodopsis sauroldef, Will. Right-side view of
head, restored. (After Traquair, from A. 8.
Woodward.) ag, angular ; d, dentary ; /, frontal ;
i.d, infradentary ; j, jwiired inferior gular ; l.j,
lateral gulars ; m.j, median inferior gular ; ma1,
maxilla ; op, opercular ; or, orbit ; />/, post-frontal ;
pmx, premaxilla ; pop, preopercular ; pa, parietal ;
x.o, suborbitals ; s.oj>, subopercular ; st, supra-
temporals ; s«, pterotic (squamosal) ; *, *>, cheek- England and North America.

Cricodus, Ag. ; Upper Devonian,
Europe and North America.
Eusthenopteron, Whiteaves (Fig.
258) ; Upper Devonian, Canada.
Rhizodus, Owen ; Strepsodus,
Young ; Rhizodopsis, Young (Fig.
256); Carboniferous, Europe and
North America.

Family ONYCHODOXTIDAE. In-
completely known Osteolepidoti
with tuberculated cycloid scales,
and mandibular teeth with
folded base, of which some very
large ones are situated at the
symphysis.

Onychodus, Newb. ; Devonian,

FIG. 257.

lihizodopsis saui-oides, Will. A, dorsal view of skull, restored. (After Traquair, from
A. S. Woodward.) /, frontal ; or, orbit ; pa, parietal ; p/, post-frontal ; pmx, premaxilla ;
.«/, pterotic ; st, supratemporals. B, ventral view of head, restored. (After Traquair, from
A. 8. Woodward.) j, paired inferior gular ; l.j, lateral gulars ; m.j, median gular ; ran, man-
dible ; sop, subopercular.

FIG. 258.

Eusthenopteron Foordi, Whiteaves; restored. (After Whiteaves, from A. S. Woodward.)
el, cleithrum (clavicle) ; /r, frontal ; i.d, clavicle ; run, mandible ; mx, maxilla ; op, opercular ;
pa, parietal ; sd, supraclavicle ; sop, subopercular ; st, supratemporal ; sbo, suborbital ; x,
cheek-plate.

COELA CA NTH INI

287

Division 2.
Order COELACANTHINI.

These remarkable fish appear first in the Devonian and persist
in the Cretaceous rocks. They are very uniform in structure
throughout this long period, and are clearly marked off from

Fig. 259.

Vndino gido, Eg.; Lower Jurassic, Dorset. Restoration, omitting scales and supraclavicle,
and showing the calcified air-bladder. (Prom A. S. Woodward, lirit. MH*. C<<M.)

related Teleostomes by well-defined characters. Huxley [228],
Miinster, Wellburn [484], Winkler, Willemoes-Suhm, Reis [350,
354], and other authors have given us a
very complete description of their skeleton.
The notochord appears to have been
persistent and unconstricted ; at all events,
no trace of centra is found. The tail is
diphycercal, and subdivided into three
lobes, of which the central one projects
far beyond the epi- and hypochordal lobes,
and has no ossified endoskeletal supports.
The neural arches, haemal arches, and
pleural ribs are well developed and ossified.
The arches are fused to the spines, and

,v , • i , i • .1 j i • girdle and (ins of Holophmius gulo,

to these are articulated in the caudal region Huxley. P. pelvic bone -V, out-
a corresponding series of somactidia or Jj& aJj ' (Ro* g"*^ •*"*
radials, supporting the lepidotrichia of the

epi- and hypochordal fins (Fig. 259). Unlike what occurs in all
Teleostomes excepting the higher Actinopterygii (p. 321), these
lepidotrichia agree in number with the endoskeletal radials, and are
closely connected with them. One anal and two dorsal fins are
present ; they have remarkable projecting, scale-covered lobes, with

ventral view of the pelvic

288

COELACANTH1NI

numerous dermal rays ; but the endoskeletal supports are preserved
only in the shape of peculiar forked bones near the base of the anal
and second dorsal fins, and of a bony plate below the anterior dorsal
fin. These bones seem to represent the coalesced inner segments of

h.

•ep.

eh'.

FIG. 2C1.

Macropoma Muntelli, Ag. ; Cretaceous, England. Restoration of the skull, side-view (A),
aud ventral view (B); left palato-quadrate and hyoid arch (C). an, angular; ch, ceratohyal ;
cl, clavicle ; ct, cleithrum ; d, dentary ; ep, epihyal ; eth, ethmoid ; fr, frontal ; g, paired gular ;
h, hyoniandibular ; Iw.r, parasphenoid ; mx, maxilla; n, nasal; o<", occipital region; o)>,
opercular ; or, orbit ; os, row of supraorbitals ; p, parietal ; JKI, palatine ; pmx, premaxilla ; p<i,
postorbital ; pop, preopurcular ; ps.t, post-temporal ; pt, pterotic (in A), pterygoid (in Band C) j
</, quadrate; sor, suborbital ; sp, splenial ; -v, voiner.

the concentrated radials. The paired fins are of the obtusely lobate
type. In the only case where the skeleton of the pectoral fin is
known, it is in the form of a posterior short basipterygium and
four preaxial radii (A. S. Woodward [288]). The endoskeleton
of the pelvic fins is not preserved, excepting for two elongated
bones representing the pelvic girdle (Fig. 260).

COELA CA NTH IN I

' < The skull is well ossified both outside and in (Figs. 259, 261, A).
The ossified prootics and opisthotics show that the cranium closely
resembled that of the lower Actinopterygii. The orbit is large, not
far forward, and surrounded by a ring of plates. The exact position
of the nostrils is unknown. There appears to be no separate row
of supratemporals ; and a peculiar series of small parafrontals passes
above the orbit towards the snout. The hyomandibular is closely
connected with the quadrate and pterygoid plate in a very Teleost-
like manner (Fig. 261, C). Teeth are distributed over the roof
of the mouth, small ones on the pterygoids and the expanded
anterior end of the parasphenoid, and larger teeth on the palatines
and vomers. The maxillae and premaxillae are toothed, but the
dentary is small and usually toothless. A large splenial bears the

Fir:. -26-2.

Two scales of .V<!iv«yi"»/« Mantelli, At;, a, anterior smooth region ; d, denticle fixed on
posterior excised region.

teeth of the lower jaw. There are large paired gular plates, but
no lateral gulars, nor is any subopercular or preopercular found.
A large opercular is present. Post-orbitals cover the cheek. The
epihyal, ceratohyal, and five branchial arches are ossified, also a
median forked bone below, which may represent the basibranchials.
Clavicles, cleithra, and post-temporals (or supraclavicles ?) can be
made out in the dermal shoulder-girdle. The scales are thin, deeply
imbricated, and either cycloid or with a pointed posterior border.
They are composed of the usual inner bony layers, over which is
found in some genera (Coelacanthus) a striated enamel-like ornamenta-
tion of doubtful significance ; in other genera (Macropoma) the
exposed surface of the scales is studded with fixed denticles of
typical structure (Fig. 262). Similar denticles are found on the
lepidotrichia, and, in more or less modified form, on all the dermal
bones of the head (Williamson [496a]).

The large air-bladder is conspicuous in fossil Coelacanths owing
to the calcification of its wall (Fig. 259).

19

290

POL YPTERINI

Family COELACANTHIDAE. Coelacanthus, Ag., ; Devonian to Permian,
Europe ; Carboniferous, North America. Undina, Munster (Hol&phagiis,
Eg.) (Fig. 259) ; Libys, Munster ; Coccoderma, Quenst. ; Heptaiiema, Bell ;
Jurassic, Europe. Diplurus, Newb. ; Trias, North America. Macropoma,
Ag. (Fig. 261) ; Cretaceous, Europe.

Division 3.
Order POLYPTERINI.

This Order includes only two genera of living African fish,
Polypterus and Calamoichthys, of great interest and importance. No
fossil representatives of the Order have yet been found, and

upc.

r' dc. f.

FIG. 263.

Skeleton of the right half of the pectoral girdle and of the right I'm of Polypterus bichir,
Geoffr. ; inner view, cl, cleitlmim ; co, coracoid ; cv, clavicle ; d.c, distal radial cartilage ;
/, dermal rays ; l.pc, lower postelavicle ; -in, inesopterygial bony plate ; m.c, inesopterygial
cartilage ; mt, metapterygium, or postaxia^ radial ; n.f, nerve-foramen ; p.ra, preaxial radial ;
pst, post-temporal; r, radial; sc, scapula; sc.f, scapular foramen; scl, supraclavicle ; ii.pc,
upper postelavicle.

although Huxley showed some points of resemblance between the
Polypterini, the Osteolepidoti, and the Coelacanthini, and united
them in the one group Crossopterygidae [227], yet it must be
confessed that the living forms remain very isolated, and that their
systematic position is still very uncertain. J. Miiller [307], Huxley
[227], Leydig [282], Traquair [441-2], Allis [13, 14], Boulenger [41],
Pollard [334], and Bridge [54] have studied the anatomy and

POLYPTERINI

291

osteology of the Polypterini ; Steindachner [4226], Budgett [67-8],
and Kerr [263] have contributed valuable knowledge of the larval
development of Polypterus. The two genera are essentially similar,
and since Polypterus is better known and appears to be less
specialised than Calamoichthys, it will here receive greater attention.
The body of Polypterus is fusiform ; that of Calamoichthys eel-

A

I'li'ni'tenis bichir, Geoffr. A, two dorsal finlets and neighbouring scales. B, much enlarged
view of a fragment of a scale with denticles. C, outer view of scale, enlarged, a.p, anterior
articulating process ; a.s, surface covered by next scale ; b.s, basal scale of linlet ; d, denticle ;
<?./), dorsal articulating process ; h.c, vascular canals ; I, lepidotrich ; p, lateral-line pore ; p.s,
exposed posterior surface bearing minute denticles ; r, endoskeletal radial ; sc, scale ; w, web
of fin ; y.d, detached dentine cap of young denticle.

like (Figs. 274, 275). In both the pectoral fin has a narrow base,
and a prominent lobe covered with scales on its outer side. The
lobe has a fringe of numerous lepidotrichia. It was to this superficial
structure that Huxley gave the name ' Crossopterygian ' ; but the
outward shape of the fin is of minor importance, and in its internal
skeleton it differs greatly from that of the acutely lobate fins of
Ceratodus, or even from the fin of Eusthenopteron (p. 282). The
pelvic fin has been lost in Calamoichthys. In Polypterus it is very

POLYPTERIN1

like that of the Actinopterygii, with a very small lobe. The tail is
outwardly diphycercal (p. 104). The median dorsal fin, continuous
in the larva with the epichordal lobe of the tail [42 2b, 67], becomes
broken up in the adult into a series of finlets of peculiar structure
(Figs. 264, 272) (Steindachner, Traquair [441]). Each is supported
in front by a strong movable elongated scale of paired origin, bear-
ing at its distal end a number of normal lepidotrichia. There is
an anal fin. The body is covered with thick rhomboid shiny scales,
with a small articulating superior and a larger anterior process
(Fig. 264). The scales differ markedly in their finer structure
from those of the Osteolepidoti, and are built on essentially the
same plan as the true ganoid scales of the Actinopterygii (p. 217).
They consist of three principal layers passing into each other at

d

Portion of a thick transverse section of the scale of 1'oli/ftti-rus bicltir, Geoft'r., much
enlarged. 6, inner bony or isopedine layer ; e, canaliculi of the cosmine layer ; <?, superficial
denticle ; g, ganoine layer ; h, system of horizontal vascular canals ; o, opening of vertical
canal on outer surface ; v.c, vertical canal.

the sides : bony lamellae below, ganoine lamellae above, and a
layer with vascular canals and dentinal tubules between these two
(Fig. 265). The dentinal tubules are chiefly, if not exclusively,
given off by fine canals derived from the vascular channels ; this
intermediate layer obviously corresponds to the middle layer in the
scales of the Palaeoriiscids (Fig. 288). The scales grow by the
addition of concentric layers, and are, in fact, typical ganoid scales
(p. 218). Moreover, to their outer surface are generally fixed small
sharp denticles, sometimes scattered over the whole exposed surface
of the scale, more often restricted to its free edge. The lepido-
trichia are of the same structure (Fig. 184), and also the dermal
bones of the shoulder-girdle and skull, but on the latter the denticles
are absent.

The skull has no pineal foramen ; the orbits are small and far
forward. The double nares are on the dorsal surface of the snout,

POLYPTERINI

293

and the anterior nostril has a tubular prolongation,
cranial bones depart consider-
ably from the typical Teleostome
arrangement (Figs. 265A, 266).
On the one hand, some bones
seem to have fused together ; on
the other, a large number of small
additional plates are present (Allis
[13, 14], Collinge [87], etc.). The
pterotics (squamosals)and parietals
are represented by a single pair
of bones in which run the lateral-
line canals. Behind these parietals
is a transverse row of paired supra-
temporals. The post-frontal is
hidden below the frontal, and the
post-orbital is the first of a long
series of small ossicles extending
back to the operculum. Some of
these are movable and cover the
external opening of the persistent
spiracle, situated at the outer side
of the parietal (Fig. 266, A). The
cheek is protected by a large pre-
opercular plate, harbouring the
hyomandibular sensory canal. An
opercular and a subopercular are
present in Polypterus, but no inter-
opercular ; in Calamoichthys neither
subopercular nor interopercular
are found. There is a pair of
large ventral gular plates only ;
the lateral gulars have been lost
(Fig. 273). In the lower jaw are
found an articular, a dentary, and
an angular (dermarticular 1} ex-
ternally, and a toothed splenial
internally. The latter has a strong
coronoid process, near which lies
a labial cartilage. The palate has
a large parasphenoid, spatulate in
front, paired vomers, ectoptery-
goids, and endopterygoids, all
covered with small teeth. A small
endochondral palatine hidden be-
hind these articulates with the prefrontal.

The dermal

A metapterygoid is

294

POLYPTERINI

also present. The quadrate is only loosely connected with the
hyoid arch, and bears the articulation for the lower jaw (Figs. 266-7).

pm

,-ecpt

Skull of Polypterus bichir, Geoft'r. A, dorsal, and C, lateral view. (Modified from J. Miiller
and Allis.) B, ventral view, without the lower jaw. an, adnasal ; any, angular ; boce, basi-
occipital ; ri, dentary ; e, mesethnioid ; ecpt, ectopterygoid ; ept, endopterygoid ; /, frontal ;
g, paired gular ; gop, subopercnlum ; hy, hyomandibular ; TO, maxilla ; 11, nasal ; o, opisthotic ;
op, opercular ; orb, orbit ; p, labial cartilage (dotted) ; pa, parietal ; par, parasphenoid ; pm,
premaxilla; po, postorbital; pop, preopercular ; pt, post-temix>ral ; qvad, quadrate ; soj>, sub-
operculuni ; sp, spiracle ; spo, spiracular plate ; st, suprateinporal ; ro, vomer. A dotted line
indicates the course of the lateral-line canal.

The palato-pterygoid bar is, in fact, chiefly connected to the skull
by the palatine and long pterygoid articulation. The hyomandibular

POLYPTERIN1

295

is an elongated bone sharing but little in the support of the jaws.
There is no symplectic. Stylohynls, ceratohyals, and hypohyals are
present. There are only four branchial arches, all with cerato- and
hypobranchial, some with epibranchial, pharyngo- and supra-
pharyngo- branchial as well. The basibranchials are, however,
fused to a single plate. All the visceral arches are well ossified.
A pair of bones, analogous to and perhaps homologous with the
urohyal (p. 350), extend backwards from the ceratobranchials.
The chondrocranium is extensively preserved even in the adult. A
single ossification behind seems to represent the combined basi-
occipital and exoccipitals. In the auditory capsule are a large
opisthotic, probably including the epiotic, and a small prootic closely

d

Flo. -'< 7.

1'iiti/iitri'n* hii.'hir, Geottr. Inner view of the lower jaw and hyoid arch, a, articular; c,
ceratoiiyal ; <?, dentary ; e, epihyal ; ;/, inferior gular ; h, hyoinandibnlar ; o, small dermal
ossicle ; op, opercular ; j«>, preopercnlar ; so, subopercnlni1 ; .•••]), splenial.

connected to the parasphenoid (van Wijhe [494]). The cranial
walls between the orbits are strengthened by two peculiar bones
which surround the pituitary fossa and fuse ventrally ; these
' sphenoids ' probably represent both the alisphenoid and the orbito-
sphenoid of other fish.

The dermal pectoral girdle consists of paired clavicles, cleithra,
postclavicles, and supraclavicles (Fig. 212); the post-temporals are
closely connected with the skull (Figs. 265A, 263). The endo-
skeletal girdle has an ossified scapula and coracoid, but no meso-
coracoid arch (p. 276). This, and the small size of the 'primary'
pectoral girdle, are points of resemblance with certain Teleosts. The
skeleton of the pectoral fin is very peculiar (Gegenbaur [153, 162],
Klaatsch [266]). It consists of two ossified basal rods, articulating
with the girdle, between which is a wide cartilaginous plate with a
bony centre. Attached to these is a row of distal ossified radials

296

POLYPTERINI

and outer cartilage nodules (Fig. 263). Budgett [67] has shown
that the fin-skeleton is really of the pleurorachic rhipidostichous
type (p. 106), similar to that of the Selachii and lower Actino-
pterygii (Amia, p. 302). The posterior basal represents the axis
or metapterygium; the anterior basal, the median plate, and the
distal elements being derived from the preaxial radials partially
fused at their base (Fig. 268). Still more Actinopterygian is the
skeleton of the pelvic fin ; here only four bony radials are preserved,
separately articulating with the pelvic girdle. Two long bones
with some small anterior cartilages represent the girdle (Fig.
•269).

The axial endoskeleton is well ossified. The notochord is very
much constricted by the solid bony amphicoelous centra (Fig. 265A).

The neural arches are continuous
with the neural spines above.
Throughout the abdominal region
each centrum bears a pair of true
dorsal ribs stretching outwards in
the transverse septum to the skin,
and a pair of ventral or pleural
ribs below (p. 68) ; the former
increase in length forwards, the
latter increase in length back-
wards, and pass gradually into
haemal arches. The extremity of
the vertebral column stops far-
short of the edge of the caudal
fin ; it is almost, but not quite,
perfectly straight, the end of the
notochord being just a little turned
upwards both in the larva and in

Reconstruction of the pectoral girdle ami the adult (Koelliker [271], Blldgett

fin-skeleton of a larval Polj/pterus, enlarged. [67]), and enclosed with the nerve-

( After Budgett.) c, coracoid region ;/, iora- L J . ., ,

men ; in, mesopterygial cartilage plate ; mi, COI'd in a Cartilage sheath, as in

metapterygium ; pr, propterygium ; r, radial ; r -j i i ^ • A lii, i

sc, scapular region. LepWOSieUS KDBL'AmtO, Although

the tail is outwardly symmetrical,

there is reason to believe that it is not truly diphycercal, but has
been derived from a more heterocercal form. For, while the dorsal
spines are separate from the radials in the epichordal lobe, in the
hypochordal lobe the lepidotrichia rest on direct prolongations of
the haemal arches as in typical heterocercal fins (Fig. 61, p. 101).
Two points of interest are to be noticed in the anal fin : the proximal
segments of the radials still articulate for the most part with the
haemal spines, and some of them fuse together, as in the median
fins of some Osteolepidoti (Fig. 252) ; and the dermal rays are still
much more numerous than the radials (Fig. 2 65 A). In the caudal

FIG. 268.

POLYPTERINI

297

and dorsal fins each lepidotrich is related to one radial. The
radials supporting the dorsal finlets are each formed of a single
piece, which, as in the Holostei (p. 322), projects not at all beyond
the body into the base of the fin (Bridge [56]).

There are four branchial slits, and neither mandibular nor
hyoidean gill. The gill-lamellae project freely at their end into the
gill-chamber ; but there is more septum preserved than in the
higher Actinopterygii (p. 95 and Fig. 57). A double series of
cartilaginous rays supports the lamellae. A remarkable pinnate
external gill is developed
on the hyoid arch of the
larva (Fig. 272). The ven-
tral air-bladder, with cellular
walls, and a symmetrical
arterial blood -supply from
the last branchial arch,
has already been described
(p. 223). The teeth are of
simple conical shape, without
foldings. There is a gastric
caecum, and the intestine
bears a single pyloric caecum
(Fig. 270).

The brain of Polypterus
shows many generalised char-
acters (Bing and Burckhardt
[73], Kerr [263]). The
medulla is primitive in its
form, the thinness of its walls,
the large size of its ventricle,
and the structure of its roof.
The small cerebellum has

a thin median ZOne, with Ventral view of the 'pelvic girdle and fins of
,i • i , ,1 -i , ]'iliiiitcrn> • bicliir, Geott'r. The skeleton of the right

tniCKeningS at ine Slues, pro- t\n \s completely exposed. >•, anterior cartilage ; di-,

iVotino- forwards hplnw rpitrp- lepMotrk-hia supporting \veb of Jin ; p, pelvic bone ;
J6C ,mg lorwara 1OW, repl( ^ preaxial ra(lials . .Sj scale-covered lobe. (From

senting the valvula so much tf<«"-'. </<>«<•"• M '•-•)•• •*•(.)
developed in the higher

Actinopterygii (p. 305). The optic lobes are of moderate size and
paired. The roof of the fore-brain is epithelial and crossed
by a deep velum trans versutn ; large corpora striata are de-
veloped below. There are no cerebral hemispheres. In the
young P. palmas the olfactory bulbs are sessile ; but in the adult
P. bichir they are stalked. On the whole, the brain of the
Polypterini represents a primitive low stage of differentiation
leading towards the Actinopterygian type (Fig. 271). With the
brain of the Dipnoi or Amphibia it shows no particular affinity,

POLYPTERINI

and it differs markedly from that of the Elasmobranch. In the
sacculus of the membranous labyrinth is found a large solid

otolith, like that of the Actino-
pterygii Holostei.

The urinogenital organs of
the female are normal. Each
oviduct opens into the coelom in
front, and into the base of the
mesonephric duct behind ; the
ova thus pass to the exterior by a
median urinogenital pore behind
the anus (Fig. 355). In the male
the ducts are more specialised
(Budgett [68]). The testis sac
passes directly into a tube leading
backwards to open into the urinary
sinus, formed by the junction of
the mesonephric ducts (Fig. 356,
C and F). The spermatozoa pass
out through the median urino-
genital pore without entering the
kidney. This separation of the
vas deferens from the mesonephros
is probably secondary, and may be
considered to have been brought
about by the same gradual process
as in the Dipnoi (p. 253). The
freeing of the vas deferens from
the mesonephros, however, is not
evidence of any close relationship
with the Dipnoi, since it is found
to have taken place independently
in the Teleostei (p. 366) and in
the Amphibia (some Anura).

Owing to the presence of lobate
paired fins, of paired gulars, of
rhomboid scales, and of an out-
wardly diphycercal tail, and to a
considerable similarity in the dis-
FIO. 270. position of the roofing cranial

Alimentary canal of A, Polyjiterti.s ; and bones, Huxley placed the Pol}'-
B, Lenidosteus. (From Gegenbaur, Vergl. ... , . , , ~

Anat-.) ap, caecum ; c.p, pyloric caeca ; dc, pterilll in his sub-Order Cl'OSSO-

pterygidae [227]. Comparing the
living with the fossil genera, the
resemblance of the paired fins is merely superficial, that of the
cranial bones only general ; the tail is probably secondarily sym-

POLYPTERINI

299

metrical, and the scales are of very different structure. Of all
this evidence the presence of paired gulars is the only item

pin.
cer. f 0 / d.s.

vel.

a.c.

Median longitudinal section of the brain of I'diii'tiTim liJi-hir. (From Kerr, Budgett Jli-in.
Vol.) t/.c, anterior commissure ; c, posterior commissure ; cer, cerebellum ; ch, optic chiasma ;
'/..<, dorsal sac ; h.c, habenular connnissure ; i.g, infundibular gland ; pin, pineal body ;
s. v, saccus vasculosus ; t.o, tectum opticum ; r.Ili, third ventricle; v.lV, fourth ventricle;
vel, velum.

above suspicion. The preopercular spreading over the cheek
resembles that of certain Osteolepidoti (Osteolepis, Eusthenopteron),
but is not a character of much importance. The bones of the
palate are remarkably like those of the Coelacanths ; and there is

Fio. •>-•>.

Larva of Polypi crus laprodei, Stein. (After Budgett, Trans. /Cool. Soc.) 1, external gill ;
2, pectoral, 3, pelvic, 4, dorsal, and o, anal tin.

also a resemblance with the latter in the agreement between the
lepidotrichia and the radials in the caudal fin, in the shape of
the pelvic bones, and in the absence of lateral gulars. On the
other hand, many characters point to a closer affinity with the

3°°

POLYPTERINI

Actinopterygii : the formation of the scales, the skeleton of
the paired fins, the presence of double dorsal nostrils, the otolith.
Excepting for the ventral opening of a bilobed air-bladder, the
viscera also resemble those of the lower Actinopterygii ; the
structure of the brain, heart, and alimentary canal supports this
view.

These facts would hardly justify us in placing the Polypterini
among the known Actinopterygii ; but they necessitate the

brm.

Fio. 273.

1'olypterus lapradii, Stdr. Ventral view of head, b, barbel ; br.m, brancliiostegal membrane ;
cl, clavicle ; /, pectoral fin ; g, paired ,gular plate ; m, intergular membrane ; op, opercular
region.

separation of the Order from the fossil forms generally associated
with it.

The peculiar subdivision of the dorsal fin is the most distinctive
newly acquired character of the Polypterini ; presumably the
finlets have been derived from a continuous dorsal fin, and this
alone is a serious difficulty in the way of deriving these fish from
any known extinct forms, except perhaps Tarrasius, A more
detailed knowledge of this interesting fossil genus is greatly
needed (p. 283).

Family POLYPTERIDAE. Polypterus, Geoffr. (Fig. 274) ; Calamoichthys,
Smith (Fig. 275) ; Equatorial Africa.

POLYPTERIM

302

A CTINOPTER YG1I

FIG. 276.

Division 4.
ACTINOPTERYGII.

The paired fins are non-lobate, the radials having been so much
reduced that they scarcely project beyond the body-wall, and the

web of the fin is almost

Pia Pm " ''* entirely supported by

the dermotrichia. The
same is the case in the
median fins. It cannot
be said that there is any
evidence of a biserial
arrangement of the
radials in the paired fins
of the Actinopterygii,
yet it is usually sup-
posed that they have
been derived from such
an archipterygium by

Ventral view of the cartilaginous skeleton of the pelvic . , c t M

girdle and fin of Sco.phirhynclius. (After Rautenfeld.) the lOSS OI the post-axil
P/n, median, and I'd, dorsal process of girdle; F, nerve- j- i /pt_., u [~i KO

foramen ; i-9, radials. radials (Gegenbaur [158,

162], Braus [48]; see

p. 108). All distinct trace of an axis has disappeared in the pelvic
fin of the Holostei, f.

where the few remain- *• t* A* ?

ing radials articulate
directly with the pelvic
bone (Figs. 245 - 8).
This is also the case
with the pectoral fin
of the Teleostei (Figs.
243,480). Butin^Trcm
and Lepidosteus a basal
element persists, bear-
ing several radials (Fig.
241); and here the fin
appears to be built on
the rhipidostychous
plan, with a post-axial

n-vic VOT-TT- intorootinrr Ventral view of the endoskeleton of the pelvic girdle

fixiss. vei_y uiMUTBBUUg and fin of Pofyodou /oZiim, Lac. (After Rautenfeld.) Pm,

and important is the median, and Pel, dorsal process of girdle ; F, FI, and J*"2,

. i-i • i nerve-foramina; 1-13, radials.

skeleton of the paired

fins in the Chondrostei (David off [98], Wiedersheim [492],

Eautenfeld [343], Thacher [434], Salensky [380], Mollier [301]).

FIG. 277.

ACTINOPTERYGII

3°3

The pectoral fin has a fairly normal skeleton, conforming to the
rhipidostychous plan, with
a postaxial axis (Fig. 279);
but the pelvic fin has a
remarkable structure, differ-
ing from that of all other
Osteichthyes. No definite
line of demarcation exists
between the pelvic girdle
and the skeleton of the fin
itself (Figs. 276-8). The
radials, forming a single
series, are articulated to
basals, Avhich are more or
less independent posteriorly,
but become fused to the
girdle in front. A skeleton
is thus formed somewhat
resembling that of Clado-
selache, and suggesting a
derivation from a primitive
orthostichous type (Wieders- Ai..Jteiuer Sturi0t L. The s-keieto,rof the right im is

heim [4921, Regan [3451) completely exposed. </r, lepidotrichia supporting
' , \veb of fin ; p, pelvic cartilage ; }//•. r, preaxial radials.

rather than irom an out- (From Quart. Jovm. Micr. ad.)

standing axis in a projecting

Dorsal processes, analogous if not homologous
with the iliac process, are
developed along the basal
region of the fin of Polyo-
don. In Scaphirhynclws
cataphmctus the internal
end of the pelvic cartilage
may be segmented off as a
separate element. So far
as is known, the radials
of the dorsal and anal fins
undergo little concentra-
tion, and do not tend to
fuse together proximally

Ventral view of the pelvic girdle and fins of

lobe (see p. 108).

a

FIG. 27?.

as in the lower Teleostomi

Pectoral girdle and fins of Acipenscr sturio. Ventral and the Dipnoi. The tail
lew. (From Gegenbaur, Vergl Anal) IS, iwstaxial . v.f .„„._„_ i hnmn^pr^l

edge of fin-skeleton ; d, clavicle ; d', cleithrum ; F,

base of left fin ; m, muscle ; R, enlarged preaxial dermal Qr geph VTOCercal never

ray ; r, endoskeletal radials. o 1 J

truly diphycercal (Belono-

rhynchidae ?). When the median fin is subdivided, as is the
case in all except some Teleostei, a single • anal and a single

A CTINOPTER YGII

dorsal separate from the
appear to be two or more
dorsals (Teleostei, p. 480)
are probably due to
secondary modification.
In all the more primitive
groups fulcral scales are
found on the extreme
anterior edge of some or
all of the fins, especially
on the dorsal edge of the
caudal. The fulcra are
quite peculiar to this
Division, and consist of
a double series of elon-
gated scales (Fig. 286) ;
often the opposing scales
fuse to V-shaped fulcra
(Fig. 280). In the gular
series of plates the most
anterior median is gener-
ally large and the paired
series become very numer-
ous and narrowed (Figs.
285-7). They are con-
verted into freely movable
branchiostegal rays. The
two foremost may be
longer than the others,
but never occupy the
space between the two
rami as in the Osteo-
lepidoti, Coelacanthini,
and Polypterini, and are
probably not homologous
with the paired gulars of
the first two Orders. The
body -scales and dermal
plates of the more primi-
tive forms are of the true
ganoid structure (p. 2 1 8).
Usually the scales have
peg and socket articula-
tions, and the peg often
appears as the continua-
tion of an inner thicker. ed

caudal. Those cases in which there

-S3

i!

ridge. But these scales, like

ns
the

A CT1NOP TER YGII

305

branchiostegal rays and the fulcra, may in the course of divergent
evolution undergo great modification and reduction. In the primi-
tive forms the cranial bones conform to the ordinary Teleostome
plan ; the preoperculum does not cover the cheek, as is so often the
case in the Osteolepidoti.

The brain in the Actinopterygii acquires a very characteristic
structure. The preponderance of the hind- and mid-brain over the
fore-brain, which has already been noticed in the Teleostomes in
general, becomes more pronounced, especially in the Teleostei.
There is a large cerebellum, which, instead of bulging almost entirely
on the surface, as, for instance, in the Selachian, extends forwards
and inwards into the ventricle of the mesencephalon. In the

Diagrams of transverse sections through the secondary fore-brain of A, 1'oli/^tenis (after
Burckhardt); B, AapenaKi- (after Goronowitsch) ; C, Amia; D, Salmo; E, Protoptenis (after
Burckhardt).

Chondrostei the solid cerebellum projects but little into the
mesocoele, and forms but a rudiment of this valvula cerebelli (Fig.
282), which becomes very large in the Teleosts, filling almost
completely the cavity of the mid-brain (Fig. 352). Large paired
hollow optic lobes are conspicuous, except in the Chondrostei, their
roof (tectum opticum) covering the valvula. The diencephalon
becomes shortened and partially hidden above ; below there is
a large infundibular outgrowth, with very well developed lobi
inferiores and saccus vasculosus (Figs. 282-3, 353). The fore-brain
is remarkably undeveloped ; no cerebral hemispheres are formed,
the lamina terminalis becomes almost horizontal, the basal ganglia
(corpus striatum and epistriatum) are the only conspicuous paired
thickenings, and the whole of the roof remains epithelial (Fig. 281).
A large velum transversum is present, but the ventricle remains
undivided in the middle line. The olfactory lobes are sessile in the

306

ACTINOP TER YG1I

lower forms, but may be stalked in the Teleostei. The ganglionic
cells become clearly stratified (Goronowitsch [180], Mayser [298],
Rabl-Riickert [340], Johnston, Mihalkowikz).

Fio. 282.

Median longitudinal section of the brain of Acipenser ruthenus. (After Goronowitsch, from
Sedgwick's Zoology). Cb, cerebellum ; c7i, optic ehiasma ; ep, pineal tody ; hy, pituitary body ;
pi, roof of telencephalon with choroid plexus ; M, roof of mesencephalon ; pi, roof of myelen-
cephalon ; s.r, saccus vasculosus ; V. cavity of telencephalon ; z, cavity of thalamencephalon.

Fio. 283.

Left-side view of brain of A, Aeipenser ruthenus ; and B, Amia calm. (After Goronowitscli,
from Gegenbaur, Vergl. Anat.) ac, auditory nerve ; Ep, epiphysis ; F, facial nerve ; (?;>, glosso-
pharyngeal nerve ; h and hy, hypophysis ; Hh, cerebellum ; L.i, lobus inferior ; L.ol, olfactory
lobe ; M, mesencephalon ; N, myelencephalon ; o, optic nerve ; pi, choroid plexus ; Tr' and
2Y", trigeminal nerve ; s.v, saccus vasculosus ; Vg, vagus nerve.

The urinogenital organs are discussed elsewhere (p. 365) ; but
it may here be mentioned that the cloaca is lost, the anus opening
separately in front, and the genital and urinary ducts lead into a

ACTINOPTERYGII 307

sinus opening behind. In the Teleostei, however, the sinus may
disappear, all the openings coming to the surface (Fig. 354).

The Actinopterygii first appear in early Devonian strata, and
have since become the dominant group of fish. The recent
advances in our knowledge of the structure and classification of
the more primitive fossils formerly included in the Ganoidii are
due to Wagner, Vetter, Thiolliere, Pictet, Heckel, Zittel, Pander
[312], Traquair [446, 448, etc.], and A. S. Woodward [505]. They
are now generally subdivided into four sub-orders of equal rank ;
but the Lepidosteidae and Amiidae are so closely related to the
Teleostei, that we prefer to unite these three groups in one Sub-
division, the Holostei, to be distinguished from the Chondrostei
(Heckel [205a], Pictet, Wagner [477], Vetter [473], Davis [100],
Thiolliere [473], Zittel [513], Crook [94], Kner and Steindachner
[268], Loomis [285]).

SUBDIVISION 1.
Order CHONDROSTEI.

This group contains the most ancient and the most primitive
known Actinopterygii. The definite association of the Palaeoniscidae
and Platysomidae with the Acipenseroidei is due to Traquair [446,
448] (one of the Palaeoniscids, Cheirolepis, is found as the first
representative in Lower and Upper Devonian rocks). They seem
to have diverged in three principal directions, leading to the
Platysomidae, Chondrosteidae, and Catopterydae. The affinities
of the Belonorhynchidae are very doubtful, and they are only
provisionally placed here. The degenerate Chondrostei are con-
sidered to be the only direct survivors at the present day of the
sub-order ; but it must be remembered that the belief in their close
affinity to the Palaeoniscids rests on slender evidence. The whole
endoskeleton is very incompletely ossified, remaining for the most
part cartilaginous, and in consequence is very incompletely known
in the extinct species.

The notochord in living forms is quite unconstricted, and
surrounded by a very thick sheath outside which are no true
centra. The vertebral column was presumably of the same
structure in the fossils ; but traces of centra have been described
in Pygopterus and PJianerosteon (Traquair [446], Fritsch [139]). Only
pleural ribs occur in the living Chondrosteidae ; but they are
unknown in the extinct families. The dorsal ribs are absent.

In Acipenser the persistent notochord, surrounded by its thick
fibrous sheath and its thin elastica externa, bears along its dorsal
surface a cartilaginous neural tube formed by a series of large

308

CHONDROSTEI

basidorsals (neural arches) and small interdorsals (Figs. 280, 284).
The former have ossified dorsal extremities embracing the powerful

B.

,nt.

nt.--

he.

FIG. 284.

mg.

Vertebral column of Acipenser sturio, L., from the trunk region. A, left-side view of a piece
partly cut through longitudinally ; B, the same cut transversely, bv, basiventral ; h.c, haemal
canal; id, interdorsal ; it; interventral ; li, longitudinal ligament; na, basidorsal ; n.c, neural
canal ; n.sp, neural spine ; nt, notochord ; r, pleural rib ; sh, notochordal fibrous sheath bounded
outside by the elastica externa.

longitudinal ligament, and to which articulate the long neural
spines. Ventrally runs a cartilaginous haemal tube formed by

a corresponding series of basi-
^ ventrals and interventrals, and

surrounding the aorta. The
neural arches and spines of
the Palaeoniscids seem to
have been similar (Coccolepis).
The endoskeleton of the
median fins resembles rather
that of the Selachian than
that of the Holostei (Fig. 280),
In the dorsal and anal it is in
the form of segmented rods,
of which the two proximal
pieces are long and sometimes
ossified, while the distal seg-
ments are very much shorter
(Bridge [56]). There is little
concrescence, but probably
considerable concentration, as
the radials are more numerous
than the segments in which
they lie. Primitive character

is also shown in the overlapping of the distal ends of the radials by
the base of the lepidotrichia, which are much more numerous. In

Oblique ventral view of the head of Gonatodus
jmnctatus, Ag. ; Calciferous Sandstone, Wardie.
(After Traquair.) a.g, enlarged anterior lateral
gular; cl, clavicle ; ct, cleithrum ; l.g, lateral gtilar ;
m.g, median gular ; «, nostril ; o, orbit.

CHONDROSTEI 309

Coccolepis, however, they only slightly exceed the radials in number
(A. S. Woodward [501]). The tail is typically heterocercal, and
generally distinctly forked owing to the great development of the
anterior region of the hypochordal lobe. Along the upper edge of
the dorsal lobe (Fig. 280) runs the vertebral column, the epichordal
fin being represented externally only by the row of fulcra — it is this
which distinguishes the heterocercal tail of the Chondrostei from
that of other fish.

There is no interoperculum, and no large paired inferior gulars,
although in Palaeoniscids the first pair of lateral gulars may be
enlarged. The anterior median gular is small or absent. The scales
vary from the rhombic to the cycloid type, or persist as large plates.
The articulating peg projects from the dorsal edge. They often
differ considerably in structure on various parts of the body, and it is
characteristic that while on the trunk the scales are disposed in
the usual oblique rows bending backwards and downwards, this
disposition is suddenly reversed on the tail, where they pass down-
wards and forwards (Fig. 290). Elongated rhomboid scales are
preserved on the tail even when they are lost on the trunk.

The frequent presence of a hyoid demibranch, of a spiracle,
and of a spiracular pseudobranch, indicates primitive structure.
It has been noticed above that the brain shows certain primitive
characteristics ; the same may be said of- the urinogenital organs
and other viscera.

Sub-Order 1. PALAEONISCOIDEI.

In which the scales are of the palaeoniscoid type of structure
(p. 218), with ganoine and cosmine (Figs. 191, 288).

Family PALAEONISCIDAE. These are the most primitive and earliest
of the Actinopterygii. They appear in the Lower Devonian, are abundant
in the Carboniferous and Permian, and die out in the Jurassic times.
The dermal skeleton is covered with ganoine. The scales are usually
rhomboid, with articulating pegs ; but in some (Coccolepis, Cryphiolepis)
the scales are cycloid and deeply imbricating on the trunk, and in
Phanerosteon the trunk is almost scaleless.

The orbits are far forward and the snout blunt, so that the nostrils
are lateral, or even ventral, rather than dorsal. The superficial cranial
bones differ but little in plan from those of the normal Teleostome. The
opercular, subopercular, and lateral gulars form a very continuous series.
The preopercular is narrow and bent forwards, the maxilla spreads back-
wards over the cheek ; the premaxilla is small ; a large median ethmoid
probably includes the nasals. The orbit is surrounded by a narrow ring
of few bones. The supratemporals are a narrow row of transversely set
bones ; the post-temporal is large (Figs. 285-7).

PALAEONISCOIDEI

The hyomandibular is elongated backwards and connected with a
broad pterygoid plate. A symplectic has not been found. The lower
jaw has dentary, angular, splenial, and articular bones.

Numerous radials occur in the pelvic fin of Coccolepis (A. S. Woodward
[501]), the only genus in which the endoskeleton of the fins is known.

FIG. 286.
Palaeoniscus macropomus, Ag. ; restored. (After Traquair, from A. S. Woodward.)

Sub -Family CHEIROLEPIDINAE. The Devonian Cheirolepis in the
minute size of its scales fitting close together, but scarcely overlapping,
approximates to the Acanthodii (Fig. 288) ; but otherwise it is a genuine
Palaeoniscid. The proximal lengthened segment of the lepidotrichia passes
inwards below the body-scales, overlapping the endoskeletal radials. The

FIG. 287.

Head of Palaeoniscus macropomiia, Ag. ; restored. (After Traquair, from A. S. Woodward.)
«/, prefrontel ; ag, angular ; br, branchiostegals (lateral gulars) ; d, cleithrum ; rf, dentary ; e,
ethmoid ; /, frontal ; i.d, clavicle ; i.op, subopercular ; mx, maxilla ; n, narial opening ; op,
opercular ; p, parietal ; p.d, post-clavicle ; p. op, preopercular ; pt, post-temporal ; pmx, pre-
maxilla ; q, pterotic (squamosal) ; sd, supraclavicle ; so, circumorbital ring and postorbitals ;
st, supratemporal. Dotted lines indicate the course of lateral-line canals.

anterior paired gulars are large, and there are large laniary teeth on the
jaws (Traquair [444]).

Cheirolepis, Ag. ; Devonian of Europe and Canada.

Sub-Family PALAEOXISCIDINAE. The paired gular plates are not
much enlarged, the scales are of normal size, the lepidotrichia scarcely
extend inwards, and the teeth are usually. quite small [446].

Canobius, Traq. ; Cryphiolepis^Traq.; Gonatodus, Traq. ; Nematopiychius,

PA LA EONISCOIDEI

Iraq. ; Khadinichthys, Traq. ; Holurus, Traq. ; Phanerosteon, Traq. ; Car-
boniferous, Europe. Eurylepis, Newb. ; Carboniferous, N. America.
Pygopterus, Ag. ; Palaeoniscus, Bl. (Fig. 286) ; Permian, Europe.

IV.

c

FIG. 288.

Cheirohpis, sp., L. Devonian. A, transverse section of scalp. B, outer view of scales
enlarged. C, much enlarged view of a piece of a scale cut transversely. D, a fragment of the
inner bony layer, magnified, dt, canaliculi of cosmine layer ; /, vertical blind canals (pulp-
cavities) ; g, ganoine layer ; h, system of horizontal vascular canals ; i, inner bony layer,
isopedine ; s, shiny outer surface ; c.c, vertical canal.

Fio. .'80.

Restoration of Trissolepis KmmoviensU, Fr. (After Fritsch.) a.f, anal fin ; «x, scale-covered
tail ; c./, hypochordal fin ; d.f, dorsal, p.f, pelvic, and pt.f, pectoral fin ; /, fulcral scale.

Amblyptenu, Ag. ; Europe. Acrolepis, Ag. ; Europe and N. America ;
Permian and Carboniferous. Elonichthys, Geibel ; Carboniferous in
Europe and N. America ; Permian in Europe. Gyrolepis, Ag. ; Trias,
Europe. Apateolepis, A. S. W. ; Atherstonia, A. S. W. ; Myriolepis, Eg. ;

PALAEONISCOIDEI

Trias, N.S. Wales. Coccolepis, Ag. ; Trias, N.S. Wales, and Lower Lias,
England. Oxycjnathus, Ag. ; Gentrolcpis, Eg. ; Lower Lias, England.

Sub -Family TRISSOLEPINAE. Very like Palaeoniscinae ; but there
are no fulcra except on the upper caudal lobe, the lepidotrichia are

unbranched, and the scales behind the head have toothed edges, while those
on the hinder trunk-region are cycloid, and those on the tail remain
rhomboid. The palate is strongly toothed (Fritsch [139]).

Trissolepis, Fritsch ; Permian, Bohemia (Fig. 289).

Family PLATYSOMIDAE. In everything but the shape of the head

PA LAEONISCOIDEI 3 1 3

and trunk, which become very much compressed and deepened, and the
accompanying extension of the dorsal and anal fin, the Platysomidae
closely resemble the Palaeoniscidae (Fig. 290). Eurynotus, Mesolepis, and
Platysomus are three stages in change of form. As the body deepens the
scales become transversely elongated, the articular pegs being at their
upper end (Fig, 191). The jaws become more pointed, and the pelvic fins
become reduced in size (Platysomus), or apparently disappear altogether as
in Cheirodus. No symplectic is known, the hyomandibular becomes nearly
vertical, and the mouth is diminished (Fig. 291). The teeth may be
considerably modified, becoming swollen and tritoral. In Cheirodus and
Cheirodopsis the palatal and splenial teeth fuse to grinding plates. This
family is found in Carboniferous and Permian strata [444, 448].

C.

-or

FIG. 291.

Cheirodut granulosus, Young. Restoration showing the bones associated with the mandibular
.and hyoid arches. (After Traquair.) og, angular; or, articular; (?, dentary ; kiti, hyomandi-
bular; m-pt, inetapterygoid ; 71, position of nostril ; o, orbit ; op, opercular ; pop, preopercular ;
pt, pterygoid ; q, quadrate ; fop, subopercular ; .<••;>> splenial.

Eurynotus, Ag. ; Mesolepis, Young (Fig. 290) ; ll-'anlichthys, Traq. ;
Cheirodus, M'Coy ; Cheirodopsis, Traq. ; Carboniferous, Great Britain.
Globulodus, Miinster ; Permian, Europe. Platysomus, Ag. ; Carboniferous
and Permian, Europe.

Family CATOPTERIDAE. A triassic family of fusiform fish resembling
the Palaeoniscidae in general structure ; but with an abbreviate hetero-
«ercal tail, and lepidotrichia which only slightly exceed the radials in
number. The latter also appear to be formed chiefly of one long
proximal segment. In the characters just mentioned the Catopteridae
undoubtedly approach the Holostei, with which they should possibly be
classified. The head and shoulder girdle are quite Palaeoniscid. The
ganoid scales are rhombic; the teeth slender and conical [505].

Catopterus, Redf. ; Trias, N. America. Dictyopyge, Eg. (Fig. 292);
Trias, N. America and Europe.

PALAEONISCOIDEI

^ttir^yj.**??* ,v.r— v ,, •-<-'<",! '" -'••'•

A CIPENSEROIDEI

315

Sub-Order 2. ACIPENSEROIDEI.

According to the researches of Traquair [451] and A. S.
Woodward [505], the families in this group form a degenerating
series starting from a type similar to the Palaeoniscids ; they reach
the highest degree of differentiation in the Acipenseridae.

The body remains fusiform with a typical bifurcated hetero-
cercal tail. The dorsal and anal fins are moderately short. The
orbits are far forward, near the olfactory capsules, but the snout
becomes greatly prolonged beyond them and the mouth.

This rostrum is borne by a prolongation of the median ethmoid
cartilage (Fig. 293). The cartilaginous cranium is, indeed, in living
forms massively developed, and extends far back, passing gradually

Left-side view of tlie skull ami vertebral column of Aeipenser. The branchial arches have
been removed. (From Owen, Anatomy of Vertebrates, by permission of Messrs. Longmans and
Co.) a, notochordal sheath ; b and c', basiventral ; c, pleural rib ; il, basidorsal ; il', inter-
dorsal ; e, neural spine; f, cartilage cranium; /, anterior neural arches fused on behind;
9> &> Q'"> parasphenoid ; g", articulation of hyomandibular ; 3"", vomerine plate ; »', orbit ; /,',
nasal capsule; m, hyomandibular ; o, maxilla; p, palatine; .«, 'jugal'; 20, pterygoid carti-
lage ; 2(1, hyon:andibular cartilage ; 28, symplectic ; 32, dentary.

into the vertebral column. Some half-dozen sclerotomes are more or
less completely fused with the back of the skull behind the vagus
(Sewertzoff [406]) ; there is no break between the skull and the verte-
bral column, and the notochord passes uninterruptedly forwards to
the pituitary region (Fig. 293).

The whole cranium is supported below by an immense para-
sphenoid, and the vomers are pushed forwards to below the
rostrum. The palato-quadrate arches meet in the middle line, which
is exceptional among Teleostomes, and lose their articular connec-
tion with the ethmoid and sphenoid regions of the skull. The jaws
are weakened, become freed from the skull, and lose the premaxilla.
The large hyomandibular is only loosely connected with the jaws
by means of ligaments and a large symplectic. The five branchial
arches are well developed. The frequent presence of a hyoid
demibranch (opercular gill), of an open spiracular cleft, and of a
spiracular pseudobranch, indicates primitive structure. The gill-

A C1PENSEROIDE1

lamellae are attached to a septum for about half their length
(p. 95). The brain and other internal organs are of generalised
structure (p. 305).

The scales possibly preserve some true ganoine in some of the
early genera ; but they never show any trace of the cosmine or of the
network of vascular canals seen in Palaeoniscids. In Adpenser
they are formed merely of concentric layers of bone.

The chief degenerate characters of the more recent forms are
shown by the loss of the ganoine on the dermal skeleton, the loss of

hnv.

pst.

op.

FIG. 294.

Polyodon folium, Lac. (After Traquair.) A, left-side view of skull, .jaws, and pectoral girdle ;
B, inner view of right jaws, c, coracoid ; ch, ceratohyal ; c/, clavicle ; dt, cleithrum ; rf, dentary ;
he, postclavicle ; hm, 'liyomandibular ; Lm, levator muscle ; rn, Meckel's cartilage ; mx, maxilla ;
«, olfactory capsule ; o, optic capsule ; op, opercular ; pa, palatine ; ps.t, post-temporal ; ;>/,
pterotic ; so, subopercular ; spl, splenial ; sy, syniplectic.

scales on the trunk, of branchiostegal rays, of the median gular, and
the reduction of the opercular bones ; the loss of fulcra, except on
the tail ; the irregularity and subdivision or loss of the dermal
cranial bones ; the loss of the premaxillae and reduction of the
teeth ; the appearance of a median series of bones on the skull ; the
relative lack of ossification in the endoskeleton. There seems, on
the other hand, to be a compensating recrudescence of cartilage.

Family CHONDROSTEIDAE. The trunk appears to be scaleless; rhombic
ganoid scales are found on the tail only. The paired frontals, parietals,
postfrontals, and pterotics (squamosals) are still normally developed, and
not separated by a median series (Fig. 295).

A CIPENSEROIDEI

317

Four paired and one median (occipital) suprateniporal are present ;
also an opercular, a large subopercular, and numerous branchiostegal rays.
The exact condition of the rostrum and of the sides of the head is not
known, but a suborbital and a small 'jugal' (preopercular ?) are found.
There is no median gular ; but about ten branchiostegal rays (Fig. 295).
The pterygoids, palatine, dentary, angular, and articular are still present.
The jaws are rather small and apparently toothless. The rest of the
skeleton closely resembles that of the sturgeons. The Chondrostei are the
earliest of this group and occur in the Lias (Egerton, Traquair [451]).

8.

Chondrosteus, Ag., Lower Lias, and Gyrostens, Ag., Upper Lias —
England.

Family POLYODOXTIDAE. These fish have minute scales on the
trunk ; small and separate in Crossopholis, quite vestigial in Polyodon.
A Cretaceous genus, Pholidurus, alone retains the ganoine (A. S. Wood-
ward). An enormous flattened rostrum without barbels is developed in
Polyodon. The roofing bones of the skull are very incomplete and more
modified even than in the next family ; few can be recognised (Fig. 294).
On the other hand, the mouth and jaws with minute teeth are more
normally developed (Bridge [52], Allis [18]). Elongated frontals,
parietal.*, and nasals cover the cranium above ; an interrupted series of
median bones runs forwards on the rostrum, but not behind the orbits.

A C1PENSEROIDEI

The postfrontals and pterotic seem to have fused, and behind them
comes an enormous post -temporal. The bones at the side are still
further reduced than in Acipenser. The operculum and suboperculum
are vestigial and the iuteroperculum and branchiostegals have disappeared.
The palatopterygoid cartilage has only one ossification in front (palatine ?).
There are no ribs, and the endoskeleton is very little ossified. The lateral-
line canals on the head are to a great extent freed from the large bones
and enclosed in special ossicles (Allis [18]).

Polyodon has a spiracle and a pseudobranch, but no hyoidean hemi-

Fio. 296.

The spoon-bill sturgeon, Polyodon folium, Lac. Ventral and side view. (After Goode,

from Dean.)

branch. The gill-rakers are especially developed. The air-bladder is
cellular.

In the mouth and jaws the Polyodontidae are less, in the rostrum
and bones of the head they are more, specialised than the Acipen-
seridae.

Pholidurus, A. S. W. ; Upper Cretaceous, England. Crossopholis, Cope ;
Eocene, N. America. Psephurus, Giinther (Fig. 297) ; China. Polyodon,
Lac. (Spatularia) ; Mississippi (Fig. 296).

FIG. 297.
Psephurus gludius, Mart. (After Gunther.)

Family ACIPENSERIDAE. The typical arrangement of the cranial
roof-bones is much disturbed by the disappearance of some and the sub-
division of others. The paired dorsal series can still be recognised
(Fig. 298), but they are separated by a number of median osteoscutes,
of which a large posterior occipital probably represents the median
supratemporal of Chendrosteus. Small scutes cover the very prominent
rostrum, below which hangs a transverse series of four sensory barbels
(Fig. 300). The mouth becomes peculiarly modified, suctorial, protrusible,

A C1PENSEROIDEI

3'9

and reduced in size. The small jaws, toothless in the adult, together
with the palato-quadrate arch, form a specialised apparatus connected with
the powerful hyomandibular by a large symplectic (Fig. 293). A maxilla
and a 'jugal' are present as in Ckondrosteus, also ossifications probably
representing the palatine, ectopterygoid, metapterygoid, and quadrate in
the expanded cartilage of the palato- quadrate arch. A single bone is
supposed to represent the
vomers. Only a dentary is
developed on Meckel's carti-
lage. In old specimens of
Acipenser- ossifications appear
in the chondrocranium, which
probably represent the opis-
thotics, prootics, orbito-
sphenoids, and two lateral
ethmoids. The visceral arches
are partly ossified (Parker
[321], van Wijhe [494], Col-
linge [86]). Supra-, post-,
and suborbitals persist, also a
large opercular, an inter-
opercular, and a subopercular ;
the opercular membranes are
confluent below. There are
no branch iostegals. In Aci-
penser, but not in Scaphi-
rhyndius, the spiracle persists,
with a pseudobranch. A
hyoidean hemibranch is
present.

On the trunk are five
longitudinal rows of large
rhombic plates, and some
scattered small irregular
spines (Fig. 299). The front
edge of the pectoral fin is
strengthened by a powerful
spine rigidly attached to the

pst

FIG. 298.

Skull of Acipenser sturio, L. ; dorsal view. A dotted
small first radial articulating line indicates the lateral line according to Collinge.
. ,. a.n, anterior nostril; fr, frontal ; j, junction of post-

Wlth the shoulder - girdle ; orbital, occipital, and trunk branches of lateral-line

this <?ninp rpnrpspnrs n mnrVi sygtem ! °P> opercular; pa, parietal; p.n, posterior

spine repre 1 nostril . poC) postoccipital ; prf, prefrontal ; pst, post-

enlarged pair of lepidotrichia temporal ; py, postfrontal ; pto, pterotic ; r, rostral

•L. i ii . . , V -L plates ; so, supraorbital ; soc, supraoccipital ; sr>,

in which the joints have been spiracle; st, ropratemponi

obliterated. No ganoine is

found on the exoskeleton ; it is merely replaced by layers of bone, of
which the scales and plates are entirely composed. The internal organs
are of generalised character (p. 309). The air-bladder is simple (p. 223).
Acipenser, L. (Fig. 299) ; freshwater and marine, Europe, Asia, and N.
America ; Lower Eocene, England.

320

BELONORH YNCH1DAE

Scaphirhynchtis, Heckel (Fig. 300) ; rivers of N. America and Central
Asia.

FIG. 299.

Wiixti' rutheiius, L. ; the Sterlet. (After Cuvier.) 1, rostrum ; 2, mouth ; 3, pectoral,
4, pelvic, 5, anal, (i, caudal, and 7, dorsal liu ; 8, dorsal bony scute ; 9, nostrils.

IXCERTAE SEDIS.

Family BELOXORHYNCHIDAE. An extinct family of fish from
Triassic and Liassic deposits, which have been placed sometimes with
the 'Ganoids' (Heckel [205«]), at other times with the Teleostei (Pictet,
Ltitken, Zittel [512]). They have been placed by A. S. Woodward
[505] among the Chondrostei ; but their real position seems so uncer-
tain, that it is better not to include them in that sub-order for the
present. The presence of clavicles and the possession in the median
fins of lepidotrichia which are more numerous than the supporting
radials, the most important characters they have in common with the
Chondrostei, are after all but signs of primitiveness ; which evidence is,
moreover, somewhat invalidated by the fact that the radials resemble
rather those of higher Actinopterygii in being mainly composed of a

FIG. 300.
Sixiphirhynchtis platorhynchus, Raf. (From Jordan and Evermann.)

long proximal segment. The symmetrical caudal fin is apparently of
the abbreviate diphycercal type, quite unlike that of any Chondrostean
or primitive Holostean, and suggesting affinity with the Osteolepidoti.
The dermal bones of the skull form ~a continuous shield in the adult,
extending far back over the occiput, over the sides of the head, round
the orbit, and forwards projecting into a greatly elongated pointed snout
(Fig. 301). The lower jaw is similarly drawn out ; it is very deep
behind. The dentition consists of large and small conical teeth. There
appear to be no median or lateral gulars, and only one large opercular.

BELONORHYNCHIDAE

321

No scales occur on the body, but generally a dorsal, a ventral, and two
lateral longitudinal rows of scutes. The fulcra are vestigial or absent.

A.

FIG. 301.

Belonorhynchus, (After A. S Woodward.)

The notochord was persistent. There are no centra, but well-developed
bony ribs, haemal and neural arches and spines. As in the higher
Holostei, the neural arches bear articulating zygapophyses. This most
puzzling assemblage of characters
has not yet been satisfactorily
explained.

Belonorhynchus^ Bronn (Fig.
301); Trias, N.S. Wales; Juras-
sic, Europe. Saurichthys, Ag. ;
Trias, Europe. ? Saurorliamphus,
Heckel ; Cretaceous, Europe.

d

Subdivision 2. HOLOSTEI.

The three sub-orders in-
cluded in this subdivision
belong to a higher grade of
organisation than the fish we
have hitherto dealt with.
They have certain characters
in common which at once
distinguish them. The endo-
skeleton is very thoroughly
ossified. In the anal and
dorsal fins the lepidotrichia
correspond in number to the
radials. In the caudal fin of
the Amioidei and Lepido-
steoidei the correspondence is

incomplete, and in the caudal FIG. sou.

of the Teleostei the dermal , &?* '«?''«•. L- A> : t.w.° rad,ia's of «•« do™al fl?»

_ left-side view. B, radial and dermal ray from in

raVS Still greatly exceed the front, d, distal cartilage ; TO, median segment, and

° i • i p.r, proximal segment of radial ; I, lepidotricli,

haemal arches m number broken short in A.

322

HOLOSTEI

(Figs. 62-3). The lepidotrichia can be erected aud depressed in all
the fins except the caudal (Fig. 301 A). The median radials pro-
ject not at all beyond the level of the body-wall, and are composed
of three-jointed rods as a rule ; the proximal segment is long (inter-
spinous bone), the two distal segments short, the outer one being
rigidly fixed in the bifurcated base of the lepidotrich. The tail
is abbreviate heterocercal, homocercal, or of some more modified
type (p. 353) ; but the hinder end of the upper lobe of the hetero-
cercal tail of the larva (the axial lobe) is always lost during

paisc

FIG. 302.

Skull of Salmo solar, L., cut longitudinally. (After Bruch.) a, angular; al, alisphenoid ;
ar, articular ; bo, basioccipital ; bsp, basisphenoicl ; d, dentary ; e.c, ethmoid cartilage ; no,
exoccipital ; h, hyomandibular ; li, ligament ; m.c, Meckel's cartilage ; mpl, metapterygoid ;
nipt, mesopterygoid ; mx, maxilla; osp, orbitosphenoid ; p, post-temporal; pa, palatine; pmsc,
premaxilla ; pro, prootic ; ps, paraspheroid ; pt, pterygoid ; q, quadrate ; so, stipraoccipital ;
sth, stylohyal ; sy, symplectic ; vo, vomer.

development, and the notochord does not reach the extremity of
the tail in the adult. Therefore the adult caudal fin is formed
chiefly from the hypochordal lobe, but also to a small extent from
the epichordal lobe (Fig. 46). The radials of the paired fins are
still more reduced than in the Chondrostei. The clavicle is lost,
its place being taken by the cleithrum, and the endoskeletal pectoral
girdle is relatively small (Fig. 241). The maxilla generally both
acquires a free posterior end and bears one or two supra-
maxillary bones. In the two first sub-orders the lower jaw is still
provided with a dentary, angular, supra-angular (coronoid), splenial,
and articular (Figs. 237-240). Of the inferior gulars only a single

HOLOSTEI

323

median one may persist (Amioidei and some Teleostei). The hyoid
arch is formed of five cartilages : hyomandibular, interhyal, hypo-
hyal, and basihyal ; but the ceratohyal always ossifies in a main
inferior ' ceratohyal ' and a smaller superior ' epihyal.' Since,
however, the interhyal (stylohyal) probably corresponds to the epi-
branchial in the posterior arches, and should be called epihyal, it
is possible that the ' epihyal ' ossification below it does not represent

[in

FIG. 303.

Median longitudinal section through the head of Salmo solar, L. (Modified, after Brnch.)
at, atrium ; 6, but bus arteriosus ; 66, basibranchial, br.m, branchiostegal membrane ; b.s,
branchial slit ; cr, cranial cartilage ; c.v, vertebral centrum ; d, dentary ; d.a, dorsal aorta ;
f.n, facial nerve ; k, kidney ; I, liver ; n.ar, neural arch ; n.sp, enlarged nerral spine ; ol.n,
olfactory nerve ; o.n, optic nerve ; p, pericardium ; pa, parasphenoid ; pw, septum between
pericardial and abdominal coelom ; s.c, anterior vertical semicircular canal ; s.o.m, superior
oblique muscle of eye ; sp, neural spine ; s.v, sinus venosus ; tth, urohyal ; v, ventricle,
valves separate its cavity from that of atrium above and bulbus in front ; va, vagus nerve ;
r.rto, ventral aorta ; vm, rectus muscle of eye in eye-muscle canal ; vo, vomer.

an element found separate in the lower forms (Figs. 239, 322,
331). The basibranchials are usually well represented, though
often the two last, and sometimes others, are fused together. In
Lepidosteus and most Teleostei the basihyal projects forwards and
is known as the ' glossohyal.' In the Holostei the pharyngeal
teeth are usually very numerous, and may be attached to dermal
bony plates which overlie and become very closely connected with
the gill-arches, basibranchials, and basihyal. A symplectic bone is

324 HOLOSTEI

present with rare exceptions. The preoperculum serves to bind
the hyomandibular, symplectic, and quadrate bones into a rigid arch
supporting the jaws (Figs. 360, 456).

Whereas in the Elasmobranchii, Dipnoi, and Chondrostei the
otolithic masses in the auditory labyrinth are aggregates of small
separate nodules or crystals, in the Holostei (and also in Polypterus,
p. 298) they form large solid calcareous structures. The spiracle
opening never persists, though a pit is found in Amia and Lepidosteus
(Wright [509]), which opens into the pharynx and lies near the
auditory capsule ; it probably represents the ' auditory ' diverticulum
of the spiracle of Selachians [359].

Of these characters the arrangement of the lepidotrichia and
the loss of the clavicle point most clearly to an advance over the
Chondrostei, and seem to prove that the three next sub-orders
must have branched off from a common ancestor.

The structure of the skull in the Teleostomes has already been
dealt with in a general way above (p. 266); it will be convenient
here to describe certain modifications of importance which occur in
the Holostei, and are of some taxonomic significance although they
may possibly have arisen independently in several groups through
convergence.

In the lower fish the cranial cavity, often but very incompletely
filled by the brain, extends forwards between the orbits, and the
olfactory nerve reaches the nasal organ directly by piercing the
cranial wall. In the Holocephali alone among the Chondrichthyes
is an interorbital septum formed between the huge orbits, and it is
above the brain. There is a tendency among the Holostei for the
brain-case to become more and more narrowed between the orbits,
until finally the two sides come together in the mid-line, giving rise
to a septum as. a rule partly membranous (Fig. 304). The septum
forms usually from below upwards ; thus the optic foramina become
closely approximated, or even confluent. The narrowing in front
obliges the brain to retreat to the hinder region of the cranial
cavity. Now since the nasal sacs are situated in front of the
orbits, either the olfactory bulbs remain near them or they retreat
with the brain. In the first case the bulbs give off short olfactory
nerves and retain their connection with the prosencephalon by
means of greatly drawn-out olfactory tracts. In the second, more
usual, case the bulbs cling close to the brain and the olfactory
nerves are lengthened out; they are then compelled to pass on
either side of the very thin septum, and reach the nasal capsules in
front by crossing more or less freely through the orbit (Figs. 304y
508). Intermediate conditions are found within certain families, as,
for instance, in the Characinidae (Sagemehl [ 379]), where Citharinuz
has a moderately long tractus and short olfactory nerves inside-

HOLOSTEI

325

the cavum cranii, and piercing the prefrontal ; Hydrocyon, whose
nerves are longer and crossing the front of the orbit, has the
bulbus further back ; and finally, Erithrinus, with sessile bulbs, has

A.

pmx

A, Salmo s<tlar, L. ; longitudinal sectioTi through the head exposing the sen
brain-cavity viewed from above (after Bruch). B, transverse section of the lit

Salmo trutta, L., in the region of the fore-brain.

osp, orbitosphenoid ; p, palatine ; pf, prefrontal ; pmx, preinaxilla ; p.o, ossification of optic
capsule ; pro, prootic ; ptf, postfrontal ; r, cranial roof ; s.o, superior oblique muscle ; s.r,
superior rectus muscle ; tr, trabecula.

olfactory nerves passing out of the orbitosphenoid freely across the
orbit. The septum in the Gadiformes, on the other hand, is formed
below the brain-case, and the narrow brain-cavity is continued for-

326 HOLOSTEI

wards to the nasal sacs (Figs. 353, 508); in it run the olfactory
tracts (Gadidae) or nerves (Macruridae). It is probable that similar
modifications have taken place independently in several families ;
but what is not likely is that fish which have once reached one
extreme form (with sessile bulb) should be able to give rise to genera
which exhibit the other extreme. In the classification of such a
modern group as the Teleostei, where every scrap of evidence is of
value, the relation of the brain to the septum is therefore of great
importance. The median septum of the Lepidosteoidei, chiefly in
front of the orbits, is probably due to the elongation of the snout
(ethmoid septum), and not strictly homologous with that of the
Teleostei.

Another new formation in the Holostean skull is the so-called
eye-muscle canal, or myodome (Figs. 302-5, 358). In all fish the four
recti muscles are attached close together to the inner wall of the orbit
near the basis cranii in the basisphenoid region. Now in Amia and
many Teleostei these muscles pass farther inwards and backwards
into a space hollowed out in the floor of the cranium. This canal is
arched above by transverse wings of the prootics, and its roof is
completed by membrane in front and at the sides, so that it does not
really open into the cavum cranii. Its floor is formed either by
the prootics (Amia) or, when these fail to meet in the middle-
below, by the parasphenoid (many Teleostei). Moreover, in the
latter case when the canal extends far back it may be closed
above by the alisphenoid, prootic, and basioccipital, below by the
parasphenoid ; but in the dried skull the canal may open behind
between the basioccipital and the parasphenoid (Cliipea, Elops,
Salmo, etc.).

Lastly, the occipital region is of interest. In no fish below the
Teleostei is a median supraoccipital bone known to occur (Figs. 238,
305, 329). Superficial dermal occipital plates are often found, and
may possibly have given rise to the supraoccipital, but there is no
evidence that it is derived from such plates. Rather does the
supraoccipital seem to have been developed from the neural spines of
one or more of those vertebrae that have last been incorporated in
the occipital region of the skull ([497] and p. 11). A difficulty
encountered by this view is the fact that already in Lepidosteus
(Shreiner [390«]) some six or seven sclerotomes have been included
in the skull without the appearance of a bony supraoccipital, and
there is no evidence that the Teleostean skull holds more segments
(Fig. 322). Ontogeny supports the view that it is an endo-
chondral bone. The limit between the skull and the vertebral
column in the lower Holostei is somewhat indefinite : in Lepidosteiis
and many Teleosts one, and in Amia two occipital neural arches
remain separate while their corresponding centra fuse with the
occipital region. It is, of course, quite possible that the supra-

HO LOST El

327

occipital is derived from neither of these sources, but is a new
ossification.

The intestinal spiral valve is already much reduced in Amia and
Lepidosteus ; in the Teleostei it usually disappears altogether.

Via. 305.

Salnto solar, L. (After Uruch.) A, skull from behind. B, transverse section of the trunk.
C, transverse section of a trunk vertebra, bo, basioccipital ; bi\ basiventral ; c, centrum ; ep,
Kpipk-iiral ; epo, epiotic ; exo, exoccipital ; f.m, foramen magnum ; li, longitudinal ligament ; my,
myotome ; n.e, neural canal ; n.s, neural spine ; op, opisthotic ; pa, parasphenoid below the
myotlome ; p.r, pleural rib ; pto, pterotic ; r, rib ; so, supraoccipital.

Order 1. AMIOIDEI.

The three sub-orders of the Holostei differ in the structure of
the vertebral column. In the Amioidei the notochord is sharply
constricted by well-formed centra in the only living species, Amia,
calca, but in the earlier, more primitive forms it appears to have
persisted to a much greater extent. The Amioidei are distinguished
by the presence of separate pleuro- and hypocentra, at all events
in a certain region. In the Actinopterygii we have hitherto

328

A MI O WEI

dealt with, the vertebral centra, formed in the skeletogenous layer
in connection with the bases of the neural and haemal arches,
are derived almost equally from the dorsal and the ventral
elements ; with the help of bony tissue these are bound together
into a single ring-like or biconcave centrum. Now in Amia well-
developed bony centra occur along the trunk region, each bearing

FIG. 306.

A, B, C, diagram of three regions of the vertebral column of Ktiriiaoi-iiin.<. (From A. S
Woodward, Vert. Palaeontology.) h, haemal arch ; he, hypocentrum ; n, neural arch ; pi, pleuro
centrum. D, left-side view of three segments of the vertebral column of a 7 '5 cm. long Am it
calva, taken at the junction between trunk and tail. 1, basidorsals (neural arches) ; 2, inter
dorsals; 3, basiventrals ; 4, interventrals. (After Schauinsland, from Hortivig's Ilinnilimli.)

a neural arch surmounted by a spine, and, except in the first two
segments, basiventrals which carry the long pleural ribs. The
neural arches are separated from the centra by cartilage, and a pair
of cartilaginous nodules are found between them (the interdorsals).
Farther back, in the caudal region (except at its extremity), there
appear to be alternate centra with and without arches. Here occur
anterior centra bearing a pair of vestigial cartilaginous interdorsals
and a pair of similar interventrals, followed by posterior centra

AM 10 ID El

329

bearing separate arches above and below (Fig. 311). At the
junction between the two regions may be found intermediate con-
ditions, incompletely divided centra (Fig. 306, D). Each pair of
centra belongs to one segment and corresponds to one spinal nerve.
They therefore represent one normal centrum divided into a pre-
and postcentrum (pleuro- and hypocentrum) (Schmidt [388],
Schauinsland [384], Hay [203]). The extinct Amioidei show
great variety in the structure of the centrum. Eurycormus has
pre- and postcentra as in Amia; but in the anterior region each
segment is composed of an upper crescentic piece and a ventral
rather larger piece ; the series of dorsal crescents are wedged in

IUI.

FIG. 307.

Vertebra of Osteorha<:his Itxdsi, A. S. W. ; Oxford Clay, Peterborough. A, oblique side view
from behind ; B, front view, h.c, hypocentrum ; n.a, neural arch ; nt, aperture for notochord ;
pic, pleurocentmm ; r, parapophysis for rib.

between the ventral crescents (Fig. 306, A, B, C). In Cat urns the
whole length of the vertebral column contains complex centra.
In Euthynotus the ventral are much larger than the dorsal crescents.
From the structure of Eurycormus it would appear that the dorsal
wedges represent incomplete precentra formed chiefly by the inter-
dorsals, while the ventral and generally larger wedges represent the
postcentra formed by the basiventrals. The basidorsals form
typical arches, but in these genera appear to contribute little to
the centra. Thus, some of the elements which go to make up a
centrum in a typical vertebra (p. 100) seem to remain separate
throughout life in these fish. A somewhat similar but not identical
splitting of the centrum takes place in the Amphibia.

The skull and visceral arches in Amia are perhaps less specialised
than in any other living Teleostome (Figs. 236-240); the chondro-

330 AMIOIDEI

cranium persists to a considerable extent, yet most of the bones
typical of this group are well represented (Allis [10, 11], Franque
[138], Bridge [51], Shuffelt [409]). In the extinct genera the cheek
is usually covered by special plates, and the circumorbital bones are
more complete. There is a small eye-muscle canal in Amia and the
Semionotidae, and only two supratemporals (extra-scapulars). Two
free occipital neural arches overlie the foramen magnum, the
corresponding centra of which have been included in the basi-
occipital. The maxilla projects freely backwards and bears a
supra-maxilla. The opercular bones are well developed. There
is a single median gular, possibly homologous with the large paired
inferior gulars of the lower Osteichthyes (Fig. 312). The scales
are of the lepidosteoid type.

Amia has no spiracular opening or gill, nor any opercular gill.
There is a considerable bulbus arteriosus (Fig. 69, p. 110), and paired
pulmonary arteries (p. 226). The viscera in Amia remain in an
unspecialised condition. The air-bladder is cellular, there are no
pyloric caeca. The urinogenital organs will be dealt with below
(p. 366). The cleavage of the egg is holoblastic, and the larva
has preoral adhesive organs.

According to A. S. Woodward, the Amioidei include several
families which have diverged along two different main lines. The
oldest, the Semionotidae, and the possibly related Macrosemiidae,
would lead to the highly specialised Pycnodontidae with deep com-
pressed bodies and grinding teeth. From the other branch would
arise the predaceous sharp-toothed families Eugnathidae, Pachy-
cormidae, and Amiidae. That the last three families are closely
related there can be scarcely any doubt ; the general proportion of
the body, the fins, the vertebral column, the skull, etc., all support
this view. But the affinities of the Pj-cnodontidae are very doubtful.
It may also be doubted whether the Semionotidae are really more
closely related to the Amioidei than to the Lepidosteoidei ; certain
specialisations in the structure of the skull would seem to bring
them nearer to the latter. Lepidotus is possibly not an Amioicl,
but a primitive Lepidosteoid.

Family EUGNATHIDAE. Triassic, Jurassic, and Cretaceous fish of
elongate shape, with deeply forked caudal and short dorsal and anal.
The mouth is wide and the hyomandibular directed backwards. The
scales and cranial bones are ' ganoid,' there are small teeth on the palate,
large pointed teeth on the jaws and the vomers (sometimes fused).
The fulcra are biserial, the scales thick and rhomboid, with a dorsal
articular peg (Eugnathus), or thin and almost cycloidal (Caturus, Eury-
cormus). The notochord may be persistent, without centra (Caturus) ; but
generally with vertebrae composed of separate post- and precentra (hypo-
and pleurocentra). The centra of Neorhombolepis and others are probably
formed by the fusion of these elements.

AMIO1DEI

Allolepidodtis, Deeke ; Trias, Europe. Heterolepidotus,~Eg.; Ptycholepis,
Ag. ; Caturus, Ag. (Fig. 309) ; Triassic and Jurassic, Europe. Callopterus,

Fin. 308.
l-:»tlii.athu.s orthostoiimx, Ag. , Lower Jurassic, Dorsetshire ; restored. (After A. S. Woodward.)

Tliiol. ; Osteorhachis, Eg. (Fig. 307) ; Earycormus, Wagner ; Eugnathus,
Ag. (Fig. 308) ; Jurassic, Europe. Neorhombolepis, A. S. W. ; Jurassic
and Cretaceous, England. Lophtoetorma, Eg. ; Cretaceous, England.

FIG. 300.

i 'iiini-n.-tfin-catits. A#. ; Upper Jurassic, Bavaria ; restored, without scales.
(After A. S. Woodward.)

Family PACHYCORSIIDAE. They are similar in outward shape to the
last ; but the ethmoid and vomer combine to form a prominent rostrum
which separates the premaxilhie, especially in Protosphyraena. The

FIG. 310.

ii.-i iiifii/hi", Wanner: Upper Jurassic, Bavaria; restored, without scales.
(After A. S. Woodward.)

liranchiostegals become very numerous ; pointed teeth arm the jaws,
vomer, and splenial ; in Hypsicormus there is a very large pair on the
last two bones. The fulcra are vestigial. The scales thin" and rhombic,

332

U

AM 10 ID El

333

or with rounded hinder edge ; they are small or absent. As a rule,
there are no distinct vertebral bodies. The pectoral and caudal fins are
very large, and the hypochordal lobe is supported by a much-expanded
haemal arch. The pelvics are small and far forwards.

Euthynotas, Wagner ; Sauropsis, Ag. ; Asthenocormus, A. S. W. ;
Pachycormus, Ag. ; Hypsocormus, Wagner (Fig. 310) ; Jurassic. Europe.
Protosphyraena, Leidy ; Cretaceous, Europe and North America.

Family AMIIDAE. These fish differ from those of the previous family
chiefly in external shape. The body is fusiform, the dorsal and anal fins

\-u

\-lff

FIG. 31±

Head of Amla calva, L. ; oblique ventral view, e, eye ; /, pectoral (in ; y, median gular
plate ; l.g, lateral gulars or branchiostegal rays ; l.j, lower jaw ; m, mouth n, nostril • oj> ,
operculum ; s.a, serrated appendage.

become lengthened, and the caudal, which is little if at all forked, shows
no external sign of heterocercy. Fulcra, small on the median, are absent
from the paired fins. The scales are th"in, squarish, and deeply over-
lapping. The ganoine is represented in Amia only by the surface orna-
mentation on the scales, and this genus has lost all fulcra [508]. There
are vestigial cheek - bones, but a large median gular remains. Amia
h;is a special serrated bony plate projecting into the branchial chamber
(Fig. 312). The hypo- and pleurocentra form complete alternating
rings in the caudal region (Fig. 311). In Liodesmus the notochord was
persistent.

334

AMIOIDEI

Liodesmus, Wag. ; Jurassic, Bavaria ; Megalurus, Ag. ; Jurassic,
Europe ; Cretaceous, Brazil. Amiopsis, Kner ; Cretaceous, Europe. Amia,
L., living, North America ; Miocene and Eocene, Europe.

Fio. 313.

Dapedius politus, Leach ; Lower Jurassic, Dorsetshire. (After A. S. Woodward,
Vert. Palaeontology.)

Family SEMIONOTIDAE. The trunk becomes deepened, especially in
Dapedius, where it is much compressed, and there is a corresponding
extension of the dorsal and anal fins. The mouth is small, and the teeth
differentiated into an outer pointed series on the jaws, and inner grinding
teeth, often very massive and rounded, on the splenial pterygoids and

FIG. 314.

Dapedius politus, Leach ; restored, with scales removed. (After A. S. Woodward,
Vert. Palaeontology.)

vomers. The latter may fuse to a single bone (Lepidotus). In the more
specialised forms the grinding teeth form a pavement. The head is
completely covered by plates with ganoid ornament (Figs. 315, 316). A

AMIOIDEI

335

ring of many circumorbitals, several supratemporals, and a number of
small cheek-plates occur, but the median gular may be absent (Lepidotus).

scl.

"lop

FIG. 315.

Left-side view of the head of Dapedius. (After Traquair.) a, angular ; d, dentary ; co, post-
orbital ; eth, ethmoid ; /, frontal ; g, median gtilar ; top, interopercular ; mx, maxilla ; n. nostril ;
na, nasal ; op, opercular ; p, parietal ; •/>/, postfrontal ; pmx, premaxilla ; pop, preopercular ;
ps, supratemporal (?) ; pt, post-temporal ; pto, pterotic (squamosal) ; scl, supraclavicle ; so,
cheek-plates ; sop, subopercular ; st, supratemporal.

In these characters, and in the formation of an interorbital septum, and
especially in the position of the nostrils at the end of an elongated snout,
Lepidotus resembles the Lepidosteoidei.

FIG. 316.

Lepidotus minor, Ag. ; Upper Jurassic, Dorsetshire ; restored. (After A. S. Woodward,
Vert. Palaeontology.)

The vertebral arches, spines, and ribs are well developed ; but the
notochord appears to have been persistent, at all events only ring-like
centra are found. The fulcra are large, in single or double rows, the

336 AM I OI DEI

scales rhombic with slight peg and socket articulations ; but they may
become cycloid on the tail (Aetheolepis).

Semionotids are found in Permian, Triassic, and Jurassic rocks. The
most specialised are the latest. Acentropliorus and Semionotus are still
fusiform.

Acentropliorus, Traq. ; Permian, Europe and North America. Serro-
lepis, Quend. ; Saryodon, PI. ; Colobodus, Ag. ; Triassic, Europe. Semionotus,
Ag. ; Triassic, Europe, Soutli Africa, North America. Lepidotus, Ag.
(Fig. 316); Khaetic to Wealden, Europe; Jurassic, India; Cretaceous,
Brazil. Cleithrolepis, Eg. ; Triassic, N.S. Wales, South Africa. Aetheolepis,
A. S. W. ; Aplmelepis, A. S. W. ; Jurassic, N.S. Wales. Dapedius, Leach
(Figs. 313-15); Lias, Europe. Tctrayonolepis, Bronn ; Jurassic, Europe
and India.

Family MACROSEMIIDAE. This family of Mesozoic fish is probably
allied to the Semionotidae and Eugnathidae. The body is elongate with
a usually much lengthened dorsal fin, which is divided in Propterus and
Notayoyus. The scales are rhombic, but may become very thin in the
later Jurassic forms (Macrosemius). They are provided with peg and
socket articulations. The fulcra also are somewhat degenerate, being
present on the caudal fin only in some (Macrosemius). Although delicate,
the skeleton is well ossified. The mouth is small, the hyomandibular
vertical or inclined forwards. The sides of the cranium are incomplete.
The opercular bones are complete, the branchiostegals numerous, and a
median gular has been found in Opliiopsis. A notochord of considerable
size persisted, since the centra are in the form of rings, which may be
double in the tail-region (Ophiopsis). Nine radials have been counted
at the base of the pectoral fin. The teeth are usually strong, pointed or
styliform, on the jaws and inner bones of the mouth [505, 512].

Legnonotus, Eg. ; Rhaetic, England. Ophiopsis, Ag. ; Histionotus,
Ag. ; Petalopteryx, Pidet, Macrosemius, Ag. ; Propterus, Ag. ; Notayoyus,
Ag. ; Jurassic, Europe.

Family PHOLIDOPHORIDAE. Amioids of elongate shape. No coronoid
has been found in the lower jaw, but there may be a vestige of the splenial.
There are fulcra and more or less rhombic deeply overlapping scales, with
peg and socket articulations. The scales are of the lepidosteoid structure,
with fine canaliculi. The vertebral centra are often divided horizontally
into upper and lower elements (hypo- and pleurocentra), which, however,
never form double rings or crescentic wedges. It is chiefly on account of
the structure of the lower jaw that this and the next two families have
been removed from the Amioidei, by A. S. Woodward, and placed at the
base of the Teleostei. The allied Oligopleuridae bridge over the gap
between them and the next Order in some respects.

The remarkable genus Thoracopterus, with huge pectoral fins and
a large and powerful ventral lobe of the caudal fin, was a ' flying fish '
of the Triassic age. Giyantopterns, of similar form, is closely allied
(Abel [1]).

Pholidophorus, Ag. ; Triassic and Jurassic, Europe ; Trias, Australia.
Thoracopterus, Bronn ; Giyantopterus, Abel ; Peltopleurus, Kner ; Trias,
Europe. Pleuropholis, Eg. ; Jurassic, Europe.

AMIOIDEI

337

Family ARCHAEOXEJIIDAE. Differing from the last in the possession
of thin cycloid scales, and ridge scales along the mid-dorsal and ventral
lines. '•

Archcieonemus, A. S. W. ; Jurassic, N.S. Wales.

Family OLIGOPLEURIDAE. In these the ganoine is vestigial, the scales
thin, overlapping, and more or less rounded, the centra annular or
amphicoelous, and generally well ossified. The first centrum has two
disks.

Oligopleitrus, Thiol. ; Jurassic, Europe. Oenoseopus, Costa ; Jurassic
and Cretaceous, Europe. Spathiuru*, Davis ; Cretaceous, Mt. Lebanon.

I-'lc. 317.

a, transverse section of the jaws of a Pycnodont, showing tlie two halves of the spleniul
dentition opposing the vomerine teeth above ; 6, vomerine and splenial teeth of Microdon ; c,
vomerine and splenial teeth of Coelodus ; <l, portion of vertebral column of Cocloihis, showing
the persistent notochord (shaded) and the expanded bases of the neural and haemal arches ; «,
the same of Pycnothis ; f, inner view of scales, showing mode of interlocking by pegs and
sockets, continued as longitudinal ribs. (After J. J. Heckel, from A. S. Woodward.)

Family PYCNODOXTIDAE. This is a highly specialised family of deep-
bodied compressed fish found in deposits from the Lower Lias to the
Eocene. The dorsal and anal fins are greatly extended backwards, the
pectorals small, and the pelvics vestigial (Fig. 319). The caudal fin,
externally symmetrical, is of the abbreviate heterocercal type and often
strongly forked. Fulcra are absent or vestigial. The scales are rhombic"
but greatly lengthened transversely (Fig. 317). They usually have a
large internal keel which projects above and below, forming articulating
pegs, or may fit closely by irregular sutures (Mesturus). The scales may
be absent from the tail, and sometimes appear to grow only on the
anterior half of the body (Mesodon, Microdon}. There is a covering of
ganoine. The arrangement of the cranial bones is remarkable and
inconstant; it has been variously interpreted (Zittel [512], A. S. Wood-
ward [502-3], Henning [208]). The orbits are high up in the head,

338

AMIOIDEI

and the facial region descends very suddenly to the small mouth with its
pointed jaws (Fig. 318). There is reason to believe that many of the

A.

FIG. 318.

Mesturus leedsi, A. S. W. Restoration of head, A, from above ; B, from the side. (After
A. S. Woodward, Vert. Palaeontology.) ag, angular ; br, branchiostegals ; d, dentary ; eth,
ethmoidal plates ; /, frontal ; m, median plate ; mx, maxilla ; op, operculum ; orb, orbit ; pop,
preoperculum ; pa, parietal plates ; pmx, premaxilla ; socc, snpraoccipital plate ; st, supra-
temporals ; spl, splenial bearing tritoral teeth ; sq, pterotic (squamosal) ; v, vomer bearing
tritoral teeth ; x, small plate.

usual bones have by a process of degeneration been split up into a
number of small irregular plates, as in the Acipenseridae.

Taking Mesturus as an example (A. S. Woodward [502]), we find

AM JO WEI

339

the snout covered with numerous plates ; two large frontals partly
separated by a median bone ; irregular small bones representing the
parietals, separated in the mid-line by a large occipital plate ; several
small supratemporals ; a single bone representing the pterotic and post-
frontal ; the orbit limited below by small plates which extend over the
sub- and preorbital region. There appears to have been a small oper-
cular and a large preopercular extending over the cheek, an exceptional
thing amongst Actinopterygians ; no sub- or interoperculum. Only two

FIG. 319.

Mesodon macropterus, Ag. ; Upper Jurassic, Bavaria ; restored. (After A. S. Woodward,
Vert. Palaeontology.) fr, frontal ; meth, mesethmoid ; md, mandible, showing narrow dentary in
front ; op, opercular ; orb, orbit ; pop, preopercular ; pa, parietal ; pmx, premaxilla ; socc,
supraoccipital ; sq, pterotic (squamosal) ; v, vomer. The caudal region is destitute of scales.

branchiostegal rays remain, and the place of the median gular is taken
by a mosaic of small plates. The gill-opening is small. The jaws and
palate are much specialised to bear a grinding dentition. The maxilla
ia slender and toothless. Sharp prehensile teeth occur on the small
premaxilla and dentary ; the slender toothless palato - quadrate arch
becomes fixed for a considerable length to the basis cranii. On the
splenials and opposing fused vomers are longitudinal rows of blunt
enlarged grinding teeth. As specialisation increases the rows become
fewer and more regular, and the teeth larger (Fig. 317).

\
340 AMIOWEI

The notochordal axis shows no trace of centra, and was probably per-
sistent and unconstricted. The neural and haemal arches are well ossified
and continuous with the spines, become greatly expanded, and develop
articulating processes (Fig. 317). The pleural ribs expand in the same
way. The bases of these arches tend to grow round the notochord to a
small extent in Coelodus, to a great extent in Pycnodus, where the dorsal
almost meet the ventral.

Many of the most important structural characters of the Pycnodontidae
are correlated with the development of a grinding dentition. Although
their systematic position cannot be considered as definitely established,
yet their removal from the Platysomatidae by Traquair and A. S. Wood-
ward has brought to light their affinity to the Semionotidae. In the
structure of the vertebral arches they approach the Teleostei.

Mesodon, Wagner (Fig. 319); Mesturus, Wagner; Microdon, Ag. ;
Jiirassic, Europe. Athrodon, Sauvage ; Gyrodus, Ag. ; Coelodus, Heckel ;
Jurassic and Cretaceous, Europe. Coccodus, Pictet ; Xenopholis, Davis ;
Cretaceous, Mt. Lebanon. Pycnodus, Ag. ; Cretaceous and Eocene, Europe.
Palaeobalistum, Blainv. ; Cretaceous and Eocene, Europe and South
America.

Order 2. LEPIDOSTEOIDEI.

This order dates only from Eocene times, and contains a single
genus, Lepidosteus (J. Miiller [307], Balfour and Parker [30 and 320],
van Wijhe [494], Kolliker [271], Collinge [85], Allis [19]). The
body is elongate, the dorsal and anal fins short, and the caudal
abbreviate-heterocercal (Figs. 324, 62). Thick rhombic ganoid
scales cover the trunk and tail. These scales may bear numerous
small true denticles on their surface (Fig. 192), and are provided
with peg and socket articulations. The dermal bones have a similar
layer of ganoine. A long snout is produced by the elongation of
the jaws in a manner which is quite characteristic in that the
nostrils and nasal sacs are carried to the extremity. It is therefore
the ethmoid region which is lengthened, and the olfactory nerves
reach the nasal capsules through long canals in the ethmoid cartilage.
Paired fulcra arm the edges of the fins (Fig. 62). On the skull
are to be noticed the usual paired supratemporals, parietals, and
f rontals ; the pterotics are large, and the nasals are represented by
elongated ethmo-nasals and small anterior nasals. There is no
pineal foramen. A long preoperculum runs along the ventral edge
of the operculum, most of the cheek region being covered by
numerous irregular plates (Fig. 320). Characteristic of the upper
jaw is the subdivision of the maxilla into a row of several toothed
bones. The teeth are strong and pointed, with the wall radially
folded at the base (Fig. 81, B). There is an extensive interorbital
septum, the large exoccipitals meet above the foramen magnum,
and no myodome is developed (Fig. 321). An articulation takes
place between the prootic and the meta-pterygoid. The hyoquadrate

LE FIDOS TEOIDEI

arch is very long, the articulation of the lower jaw being in front

of the orbit. There is no median gular, and the branchiostegal
rays are reduced to three.

342

LEPIDOS TEOIDEI

The vertebral centra (Gegenbaur [154], Balfour and Parker
[30]) are quite exceptional among fishes for having a concave
posterior and a convex anterior face ; they are thus opisthocoelous
(Fig. 322). The skeleton of the paired fins resembles that of
Amia, though more reduced.

The spiracle is closed, but a well -developed opercular gill
persists (hyomandibular posterior demibranch), Miiller [305]. The
pyloric caeca are numerous, and the median dorsal air-bladder is

sq. c/

A h > e/i

"' \ i r*'

f

FIG. 3-21.

Lepidostevs osseus, L. A, oblique view of the skull from behind ; B, inner view of the right
opercular bones and upper ,jaw broken short in front ; C, inner view of the hind end of the
lower jaw ; D, lower portion of hyoid arch, belonging to 13. an, angular ; ar, articular ; ar.p,
articular process for metapterygoid ; bh, basihyal ; bo, basioccipital condyle ; br, branchiostegal ;
ch, ceratphyal ; (/, dentary; da, posterior splenial; dp, palatine; eh, epihyal; ep, epiotic ; ex,
lateral wing of basioccipital (fused neural arches) ; /, frontal ; h, hyomandibular.; hh, hypohyal ;
iop, interopercular ; ink, Meckel's cartilage ; ms, endopterygoid ; int, metapterygoid ; op,
opercular ; opo, exoccipital (probably including opisthotic) ; p, parietal ; pa, parasphenoid ; pop,
preopercular ; pro, prootic ; pt, ectopterygoid ; pto, postfrontal ; 7, quadrate ; s, symplectic ;
set, supra-angular ; sop, subopercular ; sp, splenial ; sq, pterotic ; st, supratemporal.

lung-like with cellular walls (p. 224). The conus arteriosus is very
long, with very many rows of valves (Fig. 323). In the presence of
a closed ovisac, communicating only to the exterior by the oviducts,
Lepidosteus shows a remarkable resemblance to the Teleostei (Fig.
355, D, and p. 3G6). The genital ducts in both sexes open together
with the kidney ducts by a median pore. The cleavage of the
egg is meroblastic. The larva has preoral adhesive organs.

In many respects, such as the elongation of the snout, the
position of the nostrils, the forward position of the articulation

LEPIDOSTEOIDEI

343

of the jaw, the covering of the cheek with small plates, the presence

A.

B

Fio. 3:22.

Lrpulostevs osseus, L. A, vertebra from in front ;
I!, vertebral column of trunk, right-side view. (After
Balfour and Parker.) 1, convex anterior surface of
centrum ; 2, concave posterior surface of centrum ;
3, neural arch (basidorsal) ; 4, neural canal ; 5, inter-
dorsal cartilage ; 6, longitudinal ligament ; 7, neural
s-pine; s. transverse process of centrum (parapophysis).

FIG. 323.

Heart of Ispidosteus osscus, L. I,
ventral view. II, conns arteriosus
opened, a, atrium ; 6, conus ; c, /, g,
transverse rows of valves in conus ; h, k,
I, m, four afferent branchial vessels; v,
ventricle. (From Giinther.)

Fio. 3->4.

f.i-i'i'l".<ti'"-- MM *», L. 1, nostrils ; 2, pectoral, 3, pelvic, 4, anal, 5, caudal,
and 0, dorsal fin.

of an interorbital septum and of paired fulcra, and the absence
of a median gular, Lepidofus approaches the structure of this

344

A SPIDORHYNCHIDAE

order ; very possibly Lepidoateus is merely a specialised late
remnant of the family Semionotidae.

Family LEPIDOSTEIDAE.

Lcpidosteus, Lac. ; Eocene, Europe ; Eocene and living, North
America (Fig. 324).

IXCERTAE SEDIS.

Family ASPIDORHYXCHIDAE. Certain Mesozoic fishes, with very
elongate body (Fig. 320), and a sharp long snout formed by the upper
and lower jaws, are included in this family (Reis [349], A. S. Woodward
[505], Assmann [21]). There are deep rhombic ganoid scales, with peg
and socket articulations. Ganoid bones cover the skull ; a large cheek-
plate protects the side of the head; there are several lateral but no
median gulars. The very long upper jaw is formed by the premaxillae
and a portion of the maxillae which are in several pieces. The shorter
lower jaw is provided with a distinct predentary bone. Sharp teeth are
set on the jaws and palate. The nostrils are immediately in front of

Kin. 325.

AspidorhyiicUus acutirostris. Blainv. ; Upper Jurassic, Bavaria ; restored.
(After A. S. Woodward.)

the orbit. A short dorsal fin is opposed to a similar anal, and the caudal
is quite homocercal in appearance (Fig. 325). Small fulcra are found
only on the median fins. The Aspidorhynchidae are placed as a rule
near the Lepidosteidae, which they resemble in the subdivision of the
maxilla and absence of a median gular plate. But they differ from
them in many important characters, such as the position of the nostril,
the shape of the tail, and the possession of simple annular vertebral centra.
On the other hand, they approach the Pholidophoridae in these same
characters, and they also have a median vomer as in all Teleostei.
Possibly they represent a specialised offshoot from some eai'ly Amioid stock.
Aspidorhynchus, Ag. (Fig. 325) ; Jurassic, Europe. Belonostomus, Ag. ;
Cretaceous, Europe, Asia, America, Australia.

Order 3. TELEOSTEI.

Almost all the living Osteichthyes are included in this the
highest Order of fish. The typical Teleostei are characterised by
certain modifications of which the chief are the following : the loss
of the ganoine covering the exoskeleton ; the rounded thin over-
lapping scales ; the simple annular or amphicoelous bony vertebral

TELEOSTEI

345

centra ; the intermuscular bones ; the homocercal tail with hypural
bones ; the further reduction of the radials of the paired fins ; the
spine-like postclavicle ; the supraoccipital (p. 326); the unpaired
vomer ; the simplification of the lower jaw, which loses the supra-
angular and splenial, preserving only the dentary angular and
articular ; the absence of special cheek-plates, and loss of the
median gular ; the median urohyal ; the reduction of the conus
and its valves, and compensating development of the truncus
arteriosus ; the loss of the optic chiasma and of the spiral valve ;
the special vas deferens, and ovarian sac.

Many of these characters are not possessed by the lower forms,

cor

n,

pm

sop

TX>P wp

FIG. 326.

Eight-side view of the skull of Slops saurus, L. (From Ridewood, Proc. Zool. .S'oe.) cor, cir-
cumorbitals ; d, dentary; fear, dermarticular ; /, frontal; hm, hyomandibular ; iop, inter-
opercular ; rnx, maxilla ; n, nasal ; ope, opercular ; pm, preniaxilla ; pop, preopercular ; pt, post-
temporal ; q, quadrate ; sm, supramaxillaries ; soji, subopercular ; .-.•?, snpratemporals.

either because the new structures have not yet become developed
or because certain ancestral characters are not yet lost. The
Teleostei are the "most recent of all the Actinopterygian Orders;
they are not known to occur below the Jurassic, and thus offer to
the systematist at once the best opportunity for tracing out
phylogeny, and a most confusing number of intermediate forms.
For the most recent advances in the classification we are chiefly
indebted to Gill [165], Giinther [151-92], Sagemehl [379], Jordan
[250-51], A. S. Woodward [505], and Boulenger [40-42].

In the skull we notice a general tendency, already referred to
(p. 222), for the dermal bones to sink deep below the surface,
leaving lateral-line ossicles in the skin (Allis [16, 19]), Parker [319],
.Schleip [387], Gaupp [151rt]. The prefrontal (ectethmoid,

346

TELEOSTEI

parethmoid) and post-frontal (sphenotic), and even the pterotic
(' squamosal '), may thus become converted into entirely cartilage
bones. The parietal region often becomes grown over by the
trunk myotomes from behind (as in the Gadidae, Fig. 328), and
the supraoccipital then develops a vertical crest. The muscles
may simply cover the parietals or they may project into a post-

.1 pmx

ptc

pa-

epc

spt

FIG. 3:27.

Dorsal view of the skull of Cyprinvs earpio, L. A dotted line indicates the lateral-line
canals on the left side, epo, epiotic ; eth, pre-ethmoid (rostral) ; /c, frontal ; I, lachrymal ;
meth, inesetlnnoid ; inx. maxilla ; op, opercular ; pa, parietal ; pal, palatine ; pf, prefrontal ;
pmx, premaxilla ; pop, preopercnlar ; ptf, postfrontal ; pto, pterotic ; nob, supraorbital ;
soc, supraoccipital ; spt, suprateniporal ; st, anterior supratemporal.

temporal foramen, as in Amia, tending to separate the parietals from
the cranial wall. This post-temporal fossa is often present in the
lower families (Elopidae, Albulidae, Osteoglossidae, Clupeidae, etc.).
It may be roofed over by the epiotic and pterotic as well as the
parietal. A supratemporal (extrascapular) is often present, but is
lost in the higher sub-orders (Figs. 329-31).

The position of the parietals is important. It may safely

SKULL

347

be assumed that the condition in which the parietals meet in
the middle line and are not separated by the supraoccipital is
primitive ; it is found in the lower Teleostomes, where, indeed,
the supraoccipital has not yet appeared (p. 326). But, although it
is the rule in the lower sub-orders that the parietals meet, yet even
in the Clupeiformes there are genera in which the supraoccipital
touches the frontals underneath the parietals (Slops, Alhila, Chanos),
and among the Acanthopterygii the parietals may sometimes meet

fr.

t>f.

so.

n

FIG. 32S.

Left -side view of the skull of Gadus morrhna, L. The branches of the facial nerve
are shown, and the course of the lateral-line system (by a series of dots), partly after Cole.
an, angular ; art, articular ; 6, barbel ; b.c, buccal branch of facial supplying suborbital canal ;
d, dentary ; fr, frontal ; Jim, hyomandibular ; hm.f, hyomandibular branch of facial supplying
its lateral-line canal ; iop, interopercular ; 1, ' lachrymal ' ; I.I, lateral-line branch of vagus ;
l.o, lateral -line ossicles; mpt, metapterygoid; mx, maxilla; n, nasal; oc, crest of supra-
occipital ; op, opercular ; pf, prefrontal ; pmx, premaxilla ; pop, preopercular ; pst, post-
temporal ; 7, quadrate ; r.d, branch of facial supplying region of dorsal fin ; r.fv, dorsal
recurrent branch of facial ; rv, branch of facial supplying region of pectoral fin ; s.o, superior
ophthalmic branch supplying supraorbital canal ; sob, suborbital ; sop, subopercular.

(Cyttidae, Scorpaenidae, Triglidae (Boulenger [42], Eidewood
[362-65])). Their union in such cases may be secondary.

Frequently, especially in the higher forms (Acanthopterygii),
not only the basioccipital, but the exoccipitals as well, bear articular
facets for the vertebral column, and join below the foramen
magnum.

Two more characteristics of the Teleostean skull may be
noticed : the presence of a supraoccipital bone, the origin of which
has already been discussed (p. 326) ; and the fact that the vomer
is single and median, not paired as in almost all lower forms.

No certain trace of either the splenial or the coronoid has been
found in the lower jaw of a Teleost ; but the median gular is preserved

348

TELEOSTEI

in one family only of living Teleostei, the Elopidae (Fig. 376).
In others the right and left branchiostegal membranes either are

soc

parietal ; pof, postfrontal ; prf, prefrontal ; pro, prootic ;
(squamosal) ; v, vomer.

confluent in the mid-ventral line below the isthmus, or, in the more
modified forms, they may run forwards without meeting. The
branchial slits are continued ventrally far forwards between the

JAWS 349

rami of the lower jaw, and separated by a narrow ' isthmus '
supported by the basibranchials and urohyal.

The opisthotic varies in a remarkable manner, being very large
in some (Gadidae), small in others (Esocidae, etc.), or absent
(Mormyridae, etc.). An interorbital septum is present (p. 324),
except in the Cypriniformes (Ostariophysi ; see, however, the
Galaxiidae and Gadidae). In what is probably its more primitive
condition it is formed partly by cartilage, partly by the orbito-
sphenoids meeting and fusing in the middle line (Salmonidae) ; in
other cases it is entirely bony (Allula, Fig. 329), or almost entirely
membranous (Elopidae, Gadidae, etc.). The basisphenoid, paired
or median, is always small and often absent. The orbitosphenoid

Albula conorhynchuis, B. and S. Left hyopalatiue arch, etc. ; inner view. (From Ridewood,
Proc. Zool. Soc.) an + tear, angular fused to dermal articular; </, dentary ; ewr, dermal
articular; ecp, ectopterygoid ; cnar, articular (endosteal) ; cup, endopterygoid ; hm, hyomandi-
bular ; iop, interopercular ; mpt, metapterygoid ; oj«-, opercular ; pi, palatine ; pop, pre-
opercular ; q, quadrate ; s.ar, sesamoid articular ; sop, subopercular ; sy, symplectic.

is rarely found outside the lowest sub-orders. The palatine
articulates in front either by a single large head with the ethmoid
cartilage or the prefrontal bone, or by two heads as in the
Salmonidae and others (Swinnerton [431]); or the anterior
articulation alone remains (Gasterosteus, Belone, etc.). Various and
peculiar are the modifications undergone by the mouth and jaws in
the Teleostei. The premaxillae become very movable, free behind,
and loosely articulated in front in the higher forms. The maxilla
loses its teeth and ceases to occupy the margin of the mouth.
The two bones come to lie parallel to each other ; the former
articulating with the anterior mesethmoid region, the latter with
the vomer and lateral ethmoid region and palatine (Fig. 456).
Frequently the jaws are protrusible (p. 375), in which case the
dorsal process of the premaxilla is usually much elongated and

350

TELEOSTEI

slides backwards and forwards over the ethmoid, the maxilla being
pushed forward by the palatine (Figs. 333," 441). An accessory

Albula conorhynchus, B. and S. (From Ridewood, Proc. Zool. Soc.) Dorsal view of the

a mill uasi oranomais iiiseu auu covereu wiui sinaii ueaugaruua piai/e ; gn, uim oony piauj
vering the basihyal (glossohyal) ; hi 3, third hypobranchial ; hh, hypohyal ; pb ! and pb 3, first

masticating apparatus is often developed on the branchial arches
(Fig. 460).

The median urohyal, attached in front to the hypohyals and

FIG. 332.
Erythrichthys nitidus, Rich. (After Gunther.)

passing back between the sternohyoid muscles, is quite peculiar to
the Teleostei (Figs. 303, 358) ; similar but paired bones occur in
Polypterus.

FINS

35'

The dermal pectoral girdle is generally remarkable for the
backward and inward prolongation of a styliform postclavicle deeply

FIG. 333.
Head of Erythrichthys nitidus, Rich., with mouth protracted. (After Giinther.)

embedded in the body-wall (Fig. 452). Almost always the radials of
the pectoral fin are reduced to three or four short radii and one very

PIG. 334.

Skeleton of the right half of pectoral girdle and right
fin of Fierasfer aevs, L. (After Emery.) c, coracoid ; clt,
cleithrum ; I, lepidotrich ; pr, ventral process ; ps.t,
post - temporal ; r, 5th radial ; s, scapula with small
foramen ; set, supraclavicle. The cartilage is dotted.

Endoskeleton of the pectoral
girdle and fin of Malapterurus
clectricus. (After Sagemehl, from
Gegenbaur, Vergl. Anat. \\~irbel-
tiere.) N, scapular foramen ; A"i,
nerve foramen ; RI-H, radials ; Sch,
girdle ; Sp, mesocoracoid.

small radial fixed to the base of the anterior dermotrich. There
may be a few distal nodules of cartilage. All trace of an axis has
vanished, and the radials appear to be all of preaxial origin.

352

TELEOSTEI

However, a ventral process of the coracoid present occasionally
in the adult (Fig. 324), but more frequently in the early stages
of development, has been supposed to represent the fin axis
(Swinnerton [432], Haller [194]). But in some few cases
there is a greater number of radials (Anguilla, Malapterurus (Fig.
335), Mumenohpis). Whether this larger number really represents
the survival of a more primitive condition, as Sagemehl supposed,
it is difficult to say ; on the whole, it seems more probable that it
does not. Vestiges remain of the pelvic radials only in lower

bdi.

FK:. 33<>.

A, left-side view of two trunk vertebrae of Esox Indus, L. B, vertical median section of the
same. D, C, and B, Thynnus vidgaris, Cuv. C, anterior trunk region ; D, posterior trunk
region ; E, caudal region, ltd, basiventral (haemal arch) ; bd.o, basidorsal cartilage ; bv.c,
basiventral cartilage ; c, centrum ; d.r, dorsal rib (epipleural) ; epn, epineural ; li, longitudinal
ligament ; n.a, basidorsal (neural arch) ; n.a.c, its cartilage (interdorsal V) ; n.a.l, left neural arch ;
n.c, neural canal ; nt, notochord ; p.r, pleural rib ; prz, anterior articulating process ; ptz,
posterior articulating procr-s.

forms. The pelvic girdle consists of two bones sometimes united
in front by cartilage (Gadtis, p. 276), sometimes expanding behind
into large plates spreading towards the middle line (Siluroids, etc.,
Fig. 365).

The vertebral centra show no signs of compound structure. As
a rule, they are more or less solid and biconcave (Figs. 336, 337),
the notochord in living genera being usually constricted to a mere
fibrous thread (Goette [167], Grassi [182], Scheel [385]). The
centra are generally, but not always, co-ossified with the arches and
these with the spines. Intervertebral articulations are formed by

VER TEBRA L COL UMN

353

the development of anterior zygapophyses on the neural or haemal
arches which rest on corresponding processes in front, or these may
be supplemented by processes dorsal and ventral from the centra
themselves (Fig. 339). The basiventrals in the abdominal region
form outstanding processes of the centrum (parapophyses, 'trans-
verse processes '), to which the pleural ribs may be articulated.
More dorsal ribs (epipleurals) generally are attached near the

FIG. 337.

Longitudinal section through the vertebral column of A, licrbus viilgufia; and 15,
ifaitierates ilii'-tm: (From Gegenbaur, Vergl. Aitat.) c, notochord ; c.s, notochordal sheaths ;
ek, outer, and ik, inner bony layer ; jch, intervertebral ligament ; /•, space ; s, axial strand ;
v, centrum.

parapophysis ; as they extend outwards in the horizontal septum
they are analogous, if not homologous, Avith the dorsal or true ribs
of Elasmobranchs, etc. Slender intermuscular bones (Fig. 305)
also frequently extend into the connective tissue septa from the
centra (epicentrals), or neural arches (epineurals). The tail in all
but the lowest families is completely homocercal (Figs. 63-65). As
a rule, the haemal arches of one or more of the most posterior
vertebrae become greatly expanded and are known as hypural bones
(Huxley [226], Kolliker [271], Ryder [378], Dollo [120]). The
hypurals may coalesce. In many groups, however, the tail tapers
to a symmetrical end, and acquires the appearance of a diphycercal

23

354

TELEOSTEI

FIG. 338.

Transverse section of the vertebral column in the trunk of a very young Trout (Sulino),
enlarged, a.b, dorsal wall of air-bladder ; a.c, abdominal coelom ; lid, basidorsal cartilage ;
bv, basiventral cartilage; e, posterior cardinal vein; el, elastica externa ; /.«, fibrous sheath
surrounding notochord ; g.r, genital ridge ; li, dorsal longitudinal ligament ; m.d, niesoneplnio
duct ; n.c, nerve-chord ; r, rib ; d, skeletogenous tissue.

A.

B.

no,

Fio. 33t>.

Caudal vertebrae of Thynnus vulgaris (Cuv. and Val.). A, right-side view ; B, left-side
view of the same cut in half, a.v, anterior ventral process ; a.z, anterior 'zygapophysis' ; o,
centrum; h.at haemal arch; n.a, neural arch; p.v, posterior ventral process ; p.z, posterior
'zygapophysis'; r place of attachment of rib.

BONE

355

structure (Figs. 340, 341). This is brought about by the reduction
of the extreme tip of the heterocercal or homocercal fin in the later
stages of development ; such a false or secondary diphycercal fin is
called gephyrocercal (Ryder [378]). The structure of the actual
upturned tip of the notochord varies greatly, being naked in Eso?,
with a cartilaginous sheath in Salmo, Slops, etc., a bony urostyle in

FIG. 340.

Skeleton of the extremity of the tail of Fierasfer dentatus, Cuv. (After Emery.)
/, lepidotrich ; v, last vertebra.

Acanthopterygii and others. Special bony plates may lie on each
side of it (Fig. 63) (Lotz [286]).

It is to be noticed that although the caudal fin is chiefly of
hypochordal origin (p. 104), yet a considerable portion of the upper
lobe may be derived from the epichordal fin (Fig. 46). The
composition of the caudal fin thus varies in different families, and
ii more exact study of its development might yield useful results.

FIG. 341.

Callionymm lyra, L. Left-side view of the two last caudal vertebrae, enlarged, a.p, anterior
articulating process ; c, centrum ; h, hypural expansion ; t, outline of tail.

In a large number of the more primitive Teleostei the bone in
the adult is of normal structure with branching bone-cells, vascular
canals, and a lamellated matrix (p. 61) ; but in many others it
becomes strangely modified (Kb'lliker [270], Schmidt-Monard [388«],
Stewart [425]). For instance, in Salmo and Thymallus the cells lose
their branching processes ; in Xiphias gladius the lamellated matrix
is deposited round vascular canals some of which give off fine
tubules ; but the bone-cells are very scarce or altogether absent.
Fistulariii and the Plenronectidae have likewise lost the cells and

356

TELEOSTEI

the bone somewhat resembles dentine ; while in Gadus the skeleton
is formed of bony matrix with irregular spaces, but neither
Haversian canals nor bone-cells.

The scales also almost always lose their bone-cells, and the
lower lamellae become transformed into thin, tough, and pliable
layers of crossing fibres without any vascular canals, over which is
deposited a more calcified layer (Fig. 193). The varied ornamenta-
tion on the surface of Teleostean scales is due to modifications in
this outer layer, in the form of ridges, spines, etc. (Figs. 342, 441, C).
In the ctenoid variety of scale it grows out into sharp spines situated
on the posterior free border (Gobius, Holocentrum, etc.) ; or over the
whole exposed surface (Solea, Mugil, etc.). Lens -shaped calcifica-
tions are sometimes scattered in the inner regions of the scale.

Both the outer and the inner
layers grow by the addition of
new lamellae on the outside.
No trace of true ganoine is
found in modern Teleostei ; but
it is possible that the outer cal-
careous layer has been derived
from it. In some families the
scales become modified into
spines, either small and em-
bedded in the skin, or large
and freely projecting (Diodon-
tidae). Such spines do not re-
present modified denticles, from
which they differ fundamentally.
True denticles with dentine cone and pulp -cavity do, however,
occur in large numbers on the dermal skeleton of the Siluroids,
where they are movably articulated to the underlying bones (Fig.
373). This puzzling fact can at present only be accounted for on the
supposition that the Siluroidei have been derived from ancestral
Teleosts in which the dermal denticles were still present, as they
are in Polyptenis and Lepidosteus.

The Teleostean scale develops like the ganoid (Hofer [215«],
Klaatsch [264], Ussow [471], Hase [198]). Mesoblastic cells gather
together below the basement membrane, forming papillae which
project slightly into the epidermis. In the middle of each mass
of scleroblasts as it spreads out appears a thin lamella of skeletal
substance (Fig. 343, A). This increases in size and thickness by the
addition of new layers, the scleroblasts covering its entire surface.
The surrounding tissue becomes the loose packet in which the
adult scale is lodged (Fig. 193). The front edge of the scale
grows inwards; the hinder edge outwards, carrying the epidermis,
with it.

FIG. 342.

Ctenoid scale of Erythriehthys nitidus, Rich.
(After Giinther.)

PHOSPHORESCENT ORGANS

357

Deep-sea Teleostean fish are variously modified in adaptation to
their peculiar environment, and among the most characteristic
structures developed in them are the phosphorescent organs.
These differ considerably in the various genera and in the
different parts of the same animal. The more elaborate phos-

Fio. 343.

A, early stage in the development of the scales of the Minnow, Leitciscus phoxlnus, L. B,
portion of the free edge of the dorsal fin of a young Siluroid, showing the actinotrichia
underlying the lepidotrichia at the growing margin. C, transverse section of the developing
lepidotrichia of the Trout, Salmo truta, L. All enlarged. «, actinotrich ; b.m, basement
membrane; c.t, connective tissue; e, growing edge; I, lepidotrich ; s, pocket lined with
scleroblasts enveloping the developing scale, sc ; w, web of fin.

phorescent organs have a cellular lens set in the opening of a cup,
which contains an epithelium of large cells. These are the cells
which secrete the light-giving substance, and the walls of the cup,
generally covered with pigment, act as a reflector (Fig. 345).
Organs of this character may be present on the head or body, and
may be distributed in regular lines, or scattered over the whole

358

TELEOSTEI

surface more or less evenly (Fig. 344). Occasionally they occur
near the eyes, and so placed as to direct the light inwards. Some-
times they appear to be directly derived from the lateral line on the
body, and may be lodged in a specially enlarged series of scales
(Fig. 417). The interesting suggestion has been made that, since
they give out light of various colours, these luminous organs fulfil
the same function among deep-sea fish living in the dark as do pig-
ments among animals in daylight (Brauer [43-44], Lendenfeld [280]).

The lateral line is often excessively developed on the head,
large mucus cavities being excavated in the bones (Scorpenidae).
On the trunk the canal may be obliterated so that the organs lie
in the skin (p. 222).

The Teleostei never have more than four complete gills, and

adf.

A.

FIG. 344.

A, Scopelius engrcmlis, Gthr. B, Polylpnus spinosus, Gthr. (After Giinther.) «./, anal lin ;
ad/, adipose fin ; d.f, dorsal fin ; p.f, pelvic' fin ; ph, phosphorescent organ ; pt.f, pectoral tin.

often less in the specialised groups. Frequently there is a pseudo-
branch of variable structure and doubtful morphological signi-
ficance. It may be well developed and in the form of gill-lamellae,
as in the Pleuronectidae ; or it may be more or less completely
hidden below the skin or even deeply sunk in the tissues. In many
cases it is said to be altogether absent. The blood -supply is
derived from the efferent system of vessels, and usually from the
hyoidean artery (second vascular arch) ; while it leaves the pseudo-
branch by the ophthalmic artery (Fig. 72). It has not yet been
determined for certain whether this pseudobranch is derived from
the mandibular or the hyoidean gill ; the latter seems to be its
place of origin in many cases, but in others it may develop from
both sources. (Allis [15], Cole and Johnstone [84], Dohrn [115],
Maurer [294-95]).

AIR-BLADDER

359

The sclerotic of the eye may be ossified. The ventral muscle
of accommodation is present as usual ; but there projects besides,
to the back of the lens, a vascular process from the choroid fissure,
the characteristic campanula Halleri (Fig. 346). A very large solid
otolith usually occurs in the saculus of the ear, and smaller ones in
the utriculus and lagena (Retzius [356]).

The duct of the air-bladder, always dorsal except in some

—r

Section through epidermis and phosphorescent organ of M<iiiii»x. (After Brarrer.) <//•,
glandular cells which secrete the light-producing substance ; y, transparent gelatinous tissue ;
I, lens ; r, reflector ; pigment surrounds the organ except on the surface turned towards the
epidermis.

Characinids (p. 225), is generally longer and has a much narrower
lumen than in the lower Teleostomes ; the lumen may become
reduced or disappear, and the air-bladder be quite cut off in the
adult from the alimentary canal — a fact which led authors to divide
the Teleostei into Physostomi with open, and Physoclisti with closed
pneumatic duct.

The shape of the air-bladder undergoes all sorts of modifications :
in the Cyprinidae it is constricted into a small anterior and a larger

360

TELEOSTE1

posterior chamber ; in OtoUthus a median chamber has paired lateral
prolongations (Fig. 349) ; in the Sciaenidae and Polyxeiridae in-
numerable branching diverticula are given off (Fig. 348) ; in
Callichthys the complication is still greater. The cavity of the air-
bladder is sometimes divided into compartments (Siluridae (p. 377)),
or small alveoli (Erythrinus). In the Herring (Fig. 383) a special
opening to the exterior is formed behind the anus (Weber) ; while
a communication is established with the right branchial cavity in
the physoclistous Caranx trachiurus (Moreau). The bladder is a

Kio. 346.

A and B, eye of AcawthUis vul&mii, Risso. B and C, eye of Salmosnlar, L. A and C, section
of eye vertical to surface, leaving the lens intact. 13 and D, inner view of the outer half of the
eyeball, showing the lens in position. 1, lens; 2, cut surface of retina ; 3, retina : 4, anterior
chamber or aqueous humour ; 5, posterior chamber or vitreous humour ; (>. pigment layer ; 7,
cut edge of sclerotic ; 8, iris ; 0, ora serrata ; 10, optic nerve ; 11, cornea ; 12, ventral accom-
modating muscle (ciliary process) ; 13, vascular ridge from choroid tissure ; 14, vascular process
(campanula Halleri). (Goodrich and Gradon.)

hydrostatic organ, is never supplied direct from the aortic arches
(p. 226), and never functions quite as a lung ; but on its inner wall
are developed retia mirabilia, highly vascular patches, which secrete
the gases in the bladder (Hasse [199]).

Caecal outgrowths towards the head and tail occur in a large
number of families (Berycidae, Siluridae, Clupeidae, etc.). A con-
nection between them and the ear is often established. In the
simpler cases a diverticulum on each side abuts against a
membranous fenestra of the periotic capsule, so that pressure or
vibrations can be communicated from the bladder to the perilymph

AIR-BLADDER

FIG. 347.

Chatoessun. (After Hyrtl,
from Gegeiibaur.) Oesophagus,
a ; stomach, l> ; and intestine,
c ; with pyloric appendages,
up and ap'.

FIG. 349.

Air-bladder of Otolithus sp.
(After Giinther.)

FIG. 348.
Air-bladder of Pogonias chromis, L. (After Giinther.)

362

TELEOSTEI

surrounding the labyrinth of the ear (Mormyridae, Serranidae,
Berycidae, Sparidae, Gadidae, Notopteridae ; Bridge and Haddon
[58]). The diverticulum in other genera may penetrate the prootic
and pterotic bones and may
touch the labyrinth (most Clu-
peidae, Hyodontidae ; Kidewood
[357]). The most complex
arrangement is that found only
in the Cypriniformes, as de-

c.

Oe—

[>CV:

V5.

FIG. 350.

Alimentary canal and air-bladder of
Alosa mdgar'ix. (From Gegenbaur, Vergl.
Anat.) A.p, pyloric appendages ; tl.p,
ductus pneumaticus ; AI, stomach ; Mil,
intestine ; Oe, oesophagus ; V5, air-
bladder.

FIG. 351.

Diagram of the venous system of a Teleost,
ventral view, c, superior .jugular vein ; c.v,
caudal vein ; d.c, ductus Cuvieri ; h, heart ;
h.v, hepatic vein ; i, intestine ; j, inferior
jugular vein ; fc, kidney ; I, liver ; p.c.r, pos-
terior cardinal vein ; p.v, portal vein ; r.p,
renal portal vein ; so.v, somatic vein ; sp,
spermatic vein ; s.v, subclavian vein ; v, vein
uniting caudal with portal (not always
present) ; v.b, vein from air-bladder.

scribed below (p. 373). Often the air-bladder is lost (among
the Scopelidae, Symbranchiidae, Pleuronectidae, Lophiidae, etc.).

The spiral valve of the intestine has disappeared in all living
Teleosts except Chirocentrus (Cuvier and Valenciennes [95] (Fig.
77, A)). Vestiges of it may perhaps remain in some Salmonidae

HEART

363

(Kathke) and Gymnarchus (Assheton). The intestine becomes
lengthened and sometimes much coiled. The pancreas almost dis-
appears. The pyloric caeca vary greatly in development (Fig. 350).

Already in Amia the bulbus arteriosus (base of the truncus) of
the heart is large and the conns small, in the Teleostei the non-
contractile bulbus is still larger and the conns reduced to a mere
vestige bearing a single row of valves. A larger remnant of the conns
with two rows of valves occurs in Albula (Butirimis) and Osteoglossum
(Boas [39]), and in Tarpon and Megalops (Senior [405]) (Figs. 69, 303).

Many variable and minor differences occur in the vascular
system [8, 314, 131, 417, 360]. The lateral epigastric veins dis-
appear, or may be represented by a prolongation of the hepatic

Fio.

.Median longitudinal section of tin' brain of a Trout (>Wm..). AH, aqueduct.!!* Sylvii ; Bo,
olfactory lobe ; Cbl, cerebellum; C.c, central canal of spinal cord; Cm, anterior commissure;
Cho, optic nerve ; Ci, inferior commissure ; <;t/i, pineal body ; Ily and Hy', hypophysis ; J,
infundibulum ; Nol, olfactory nerve ; Pa, roof of telencephalon ; pf, velum transversum ; S.v,
saccus vasculosus ; 2Vo, pia mater ; Ti, roof of mid-brain ; tr, crossing fibres of fourth nerve ;
V.c, valvula cerebelli ; !'••/». ventricle of telencephalon; I';/, fourth ventricle; Vt, third
ventricle. (After Rabl-Riickhani. from Sedgwick's Xnnlng-ii.)

portal into the caudal vein. Direct communicating vessels through
the kidneys to the posterior cardinals tend to reduce the renal
portal system (Fig. 351). The vascular supply of the air-bladder
has been described above (p. 226).

The chief modifications in the brain have already been men-
tioned (p. 305). It is to be noticed that it is much concentrated,
and in spite of the great development of the hinder parts, the
prosencephalon is scarcely differentiated and has an epithelial roof.
The valvula cerebelli attains its greatest development, and the optic
lobes may be huge. The Teleostei are distinguished by the absence
of an optic chiasma, the optic nerves crossing each other outside the
brain without mixing (Figs. 352-53).

364

TELEOSTEI

The mesonephric kidneys, without coelomic funnels, are often
enlarged in front into a mass of lymphatic tissue developed in con-
nection with the larval pronephros (Balfour [29]) ; behind they
give off two mesonephric ducts which join together and open behind
the anus by a median pore. The sinus formed at their junction
may be produced into a mesoblastic urinary bladder, which, of course,

B.

mx
md .

FIG. 353.

Brain of Ksox lucivs. Dorsal view (A). Brain of Gadus rnorhun, dorsal view (B); ventral
view (C). 1, olfactory, 2, optic, 3, oculomotor, 4, pathetic, 5, trigeminal, 6, abducens, 7,
facial, 8, auditory, i>, glossopharyngeal, and 10, vagus nerve, ac, accessories, 6, buccal, h,
hyomaudibular, mil, mandibular, mx, maxillary, oph, superior ophthalmic, and r, dorsal
recurrent nerve branch ; r, cerebellum ; fb, forebrain ; l.i, lobus inferior ; m, myelencephalon ;
o.l, olfactory lobe ; op, optic lobe ; os, olfactory tract ; pt, pituitary body.

is not homologous with that of the terrestrial vertebrates (Fig.
354).

In Fierasfer and Zoarces (Emery [131]), and to a less extent
in Lepadogaster (Guitel [188]), the pronephros functions in the
adult.

Never do the generative products of the male pass through the
kidney (p. 89). The elongated testes, which are shut off from
the abdominal coelom as in all other Gnathostomes, are directly

365

prolonged backwards into ducts which join and open to the exterior,
or open into the base of the urinary ducts (Figs. 354, 356, B).

A few Teleosts have free ovaries which shed the ova into the
coelom in the normal manner. In these cases the OAra are carried
out either by oviducts of considerable length (Osmerus) or very
short (other Salmonidae) (Fig. 355, E), or again they may pass out
by mere pores representing the last stage of degeneration of the
oviduct (Anguillidae, Galaxiidae, Notopteridae, Hyodontidae, Osteo-
glossidae, and Misgurnus, a Cyprinid) (Hyrtl [232a], Rathke [342],
MacLeod [288]).

The opening of the genital ducts to the exterior varies much in

FIG. 3o4.

Left-side view of a dissection of a male Eso.i Im-it/*. I.., showing tin- median ai«'rtures of
the rectum, genital ducts, and kidney ducts. «, anus ; a.h, air-bladder, blind hinder end ; an,
dorsal aorta ; '/', urinary bladder; ci; yil, vas dfiferens ; g.o, genital opening; /, intestine; /,-,
kidney (meeonephros) ; m.d, mesonephric duct; p.c, posterior cardinal; t, testi.s ; lit.o,
urinary opening.

position among the Teleostei. As a rule, the oviducts or pores open
l)y a median aperture between the anus and the urinary pore (Fig.
354, 356, E). The cloaca has been lost, though traces of it may
perhaps be seen in some lower forms. The sperm-ducts may open
into the base of the mesonephric ducts or bladder, as in Eels,
Analleps, Perca, Zoarces, Cycloptems, etc. ; or by a special opening,
Clupea, Scants, Trigla, Tinea, etc. ; or together with the anus, Lota ;
or with both the anus and the kidney, Lophobranchii (Hyrtl,
Stannius [417]).

The urinogenital organs of the Teleostei present features which
are very difficult to explain and have given rise to much contro-
versy (Rathke [342], Huxley [231], Waldeyer [478], Semper [404],
Balfour [29, 30], Brock [59, 60], Weber [482], Jungersen [253],

366

TELEOST.EI

Haller [193], Howes, Felix [136]). We may here briefly discuss
their morphology. In both sexes the goriads arise as a longitudinal
thickening of the coelomic epithelium, near the base of the mesentery,
which hangs in the body -cavity as the genital ridge (Fig. 338).
On the outer side of this fold the genital cells are developed.

First of all with regard to the absence of a direct communi-

msd.

Fio. 355.

Diagrams of the female urinogenital ducts in the Dipnoi and Teleostomi derived from the
figures of various authors. A, Protopterus (after Ayers and W. N. Parker). B, Pclypterus (after
Budgett). C, Amiti (after Hyrtl and Huxley). D, I^epidosteus (after Balfour and Parker). E,
a Teleost with closed ovisac. F, a Salmonid (after Weber). a.p, abdominal pore ; c, cloaca!
bladder ; d, cloaca ; /, open funnel of oviduct ; k, mesonephros ; mf.d, mesonephric duct ; o,
ovary ; od, oviduct ; op, genital papilla and pore ; ocs, closed ovisac ; r, rectum ; ug.p, urino-
genital papilla ; u.p, urinary pore. In all the figures, except F, only the right oviduct is com-
pletely drawn.

cation between the testis and the mesonephros, characteristic of all
the Teleosts. This is doubtless secondary. A system of spaces and
canals develops from the testis, and from these is formed near the
base of the peritoneal fold supporting the testis a longitudinal duct
which grows back to the external opening (Fig. 356, B). It seems
very probable that this sperm-duct represents the longitudinal canal
found in other Gnathostomes uniting the testicular canals, and into

URINOGENITAL ORGANS

367

which open the mesonephric tubules (p. 89). Primitively vasa
efFerentia stretched across from testis to collecting duct, and from
duct to kidney along the whole length of the two organs, as in the
Chondrostei and Lepidosteus (Fig. 356). But whereas in the
Elasmobranchs the vasa efFerentia became restricted to the anterior
end (p. 132), in the Dipnoi they became restricted more and
more to the posterior end (p. 253). Independently the same
specialisation seems to have taken place in the Teleostomes, both in

A.

..k.

o&ULitUMUi u.uuv ] 7/w?.(*, uiamuio|Piuiu uuui/ , "•/'» uviuuwoi puic , •/, icuuum , t., teni/ia , «-(/•/',

uriuogenital pore ; u.pt urinary pore ; u.s, uriuogenital sinus ; v.d, vas deferens ; v.e, vas efferent.

the Polypterini (p. 298) and the Teleostei. The longitudinal duct
has, in these, lost all connection with the kidney, and shifted its
opening Farther and farther backwards, finally becoming quite
independent (Budgett [68]).

Turning now to the female organs, several questions arise :
Which is the primitive condition among the Teleostei, the closed
ovarian sac or the free ovary 1 the long oviduct of Osmerus or the
genital pore of Anguilla 1 are the oviducts homologous with the
Mullerian duct of other forms or with the sperm-duct of Teleosts 1
The oviduct may be distinguished into two portions : an anterior

r

368 TELEOSTEI

ovarial part in connection with the ovary itself ; and a posterior part,
passing back behind to the pore. In the Anguilliformes the genital
ridge remains as a simple band, with ova on its outer side. In
many Teleosts, such as ItJiodeus, Gobio, Cobitis, Esox, Clupea, and the
Cyprinidae. this genital fold bends upwards and outwards, thus
fusing with the coelomic wall (Fig. 55, F), so as to form an ovarian
sac with a lateral ' parovarial ' canal, blind in front. Or there may
appear on the outer surface of the genital ridge itself a groove,
which folds round so as to form when closed up a central or
'entovarial' canal. The genital surface of the ovary so en-
closed may become much folded (Perca, Acerina, etc.). That the
parovarial and the entovarial ducts are not fundamentally distinct
seems clear ; moreover,~in Salmo the ovary is folded to form a par-
ovarial canal in front and a short open entovarial canal behind,
which is not produced backwards (Felix [136]).

The posterior duct is formed by a backward growth of the wall
of the ovisac and of its lumen. There is no sharp distinction
between the two, but a gradual passage from the fertile wall of the
ovary to the sterile wall of the duct. In some fish, as Zoarces and
Cyclopterus, the ovary reaches to quite near the pore.

As to the first question, whether the free ovary is primitive or
not in the Teleostei, Balfour inclined to the view that it is secondary,
since already in Lepidosteus there is a closed ovisac [30]. Brock, on
the other hand, holds it to be primary [60]. The sporadic occur-
rence of this character among Teleosts of different families is very
strong evidence in favour of Balfour's view that it is a return to
the primitive condition. Much more difficult is it to determine
the homology of the oviduct. Waldeyer and Semper held that it
represents the Miillerian duct of other Gnathostomes, the whole
ovary having been enclosed by the tube, in forms with a closed sac.
Rathke and others have held that the oviduct is entirely derived
from the ovary, the posterior portion being a backward prolongation.
Jungersen adopts Balfour's suggestion that the closed sac is formed
by a junction of an ovarian canal with the open mouth of a short
Miillerian duct. The free condition in Teleosts would be brought
about by the failure of these two structures to fuse.

The oviducts and sperm-ducts are so similar in the Teleostei,
that they are generally considered to be homologous with each
other and not with the Miillerian duct. In Polypterus and Lepido-
steus the anterior region of the oviduct develops as a parovarial
canal, into which open, in early stages only, the mesonephric funnels
(Fig. 55). The comparison with the longitudinal duct of the male
is obvious (Budgett [68]). But the homology will not apply in the
case of the Chondrostei (Fig. 356, A), where (Miillerian ]) ducts with
open funnels exist in both sexes, and the male has a longitudinal
testicular canal as well (Hyrtl [233a], Semon [398]).

CYPRINIFORMES 369

In conclusion, it must be remembered that, in all Gnathostomes
except perhaps the Teleostei, the relative position of the organs in
([uestion when enumerated from the middle line outwards is as
follows : the genital ridge near the base of the mesentery, the meso-
nephric ridge with the peritoneal funnels, then the Mullerian duct
(Fig. 55). When the latter develops as a closing groove it is in that
position. Now in the Chondrostei there are short open-mouthed
ducts, leading behind into the base of the mesonephric ducts ; these
oviducts appear to be genuine Miillerian ducts. The short wide-
mouthed oviducts of the Salmonidae and the pores of the Anguil-
liformes are probably of the same nature (Fig. 355). At all events,
no other representatives of the Mullerian ducts can be found in these
fish. We may suppose, then, that in Polypterus, Lepidosteus, and most
Teleosts the Mullerian groove (developing duct) has shifted to the
base of the ovary, so as to occupy the same place as the male
collecting duct of the testis ; or that the short Mullerian duct has
combined with the homologue of the testicular duct in front, thus
forming the parovarial portion of the oviduct, which remains open
in Polypterus and closes in Lepidosteus and the majority of the
Teleostei. This latter view seems the more probable (Fig. 355). x

To classify the Teleostei according to a phylogenetic scheme is
a very difficult matter. The more highly specialised forms fall into
groups which are fairly well defined, but the position of less
differentiated families is not yet well determined owing to lack of
palaeontological evidence. If we were to attempt the reconstruc-
tion of a primitive Teleost ancestral to all living forms, we should
have to attribute to it the following characters : a skull with typical
superficial covering bones, with no interorbital septum, with a
median gular plate ; a mesocoracoid ; a homocercal tail ; one dorsal
and one anal fin ; a spiral valve ; a conus provided with two rows
of valves ; cycloid scales and superficial denticles.2

No living fish is known to combine these characters, though,
except the last, all appear scattered among certain members of the
lowest division of the Teleostei as given in modern classifications —
the Isospondyli (Cope, A. S. Wood ward), Malacopterygii (Boulenger),
or Clupeiformes (p. 386). This sub-order represents not a well-
defined branch, but at most an assemblage of divergent families,
from some one or more of which the other more specialised families
may have arisen. Further, if, following A. S. Woodward, we
include with them the Pholidoplioridae and their immediate allies,

1 We cannot hope to reach a definite conclusion on this difficult subject until the
development of the ducts in such forms as Osmertts, Amia, Acipenser, and the Dipnoi
has been made known.

2 It is, of course, possible that the denticles on the surface of the body of the
Siluridae have been, so to speak, reacquired ; the bony plates on which they rest seem
to be secondary, since they often overlie the normal bones of the skull.

24

370

TELEOSTEI

possessing compound vertebrae, abbreviate heterocercal tail, ganoid
scales with peg and socket articulation, fulcra, and possibly a
splenial and supra - angular, it becomes obvious that the group
( Isospondyli) can no longer be fitted into any phylogenetic scheme.
The Leptolepidae, however, may be classed as primitive Teleosts,
and the remaining families can be grouped together into various
sub-orders with considerable confidence, but of the relationship
between these sub-orders, of their exact position on the phylogenetic
tree, we know as yet comparatively little.

Order 3. TELEOSTEI.

b-Order GADIFORMES.

Series 2
Sub-Order 2 ANGUILLIFORMES.

Divitmo I. ArJm:

•clock/I, ^W

Sub-Order 4. CASTER
Tribe 1. GruUroittndei,

Divi.ion ! NancM, Trilj«

Orou|. A. i'nc/iriieq'koli, Tribe *• i«P*<*'ow»:

Group B. Caloaphnlt, Trib« <

Tribe 6. Scombriforma,
Tribe 7 *r«rHfr™o,

DIAGRAM IV. — PHYLOGENY OF THE TELEOSTEI.

C YPRINIFORMES

37i

Division A.

Although preserving the ganoine, the scales in these fish are
never of a rhombic ganoid character, but of the cycloid type. The
splenial and fulcra have disappeared, the centra are undivided. The
tail is scarcely yet homocercal, and there are no expanded hypurals.

Family LEPTOLEPIDAE. The tail is still much as in the Ainioidei.
The scales are cycloid and thin, but ganoine covers both them and the
•cranial dermal bones. The annular bony centra are pierced by the noto-
chord ; the neural arches remain separate from the centra and spines in

Fio. 357.

Leptolepis dubius, Blainv. ; Upper Jurassic, Bavaria; restored, without scales.
(Atln A. S. Woodward.)

the abdominal region. There is no median gular. The Leptolepidae
.appear in the Trias and die out in the Cretaceous epoch, when the
modern Teleostean types begin to dominate over all others.

Leptolepis, Ag. (Fig. 357) ; Lias to Cretaceous in Europe ; Trias in
N.S. Wales. Aethalion, Mu'nster ; Europe. Lycoptera, J. M. ; Jurassic,
Asia. Thrissops, Ag. ; Jurassic and Cretaceous, Europe.

Division B.

The tail is truly homocercal, with expanded hypurals, or it is
gephyrocercal. The ganoine has vanished, and the centra are
always well ossified and amphicoelous, except in degenerate forms.
Frequently the hinder region of the dorsal fin is differentiated as
an adipose fin (p. 275), in the older families. The scales are of the
cycloid or ctenoid type, or derived therefrom.

Group A.
Sub-Order CYPRINIFORMES (Ostariophysi).

This group is remarkable for the absence of the interorbital
septum, which appears to some extent only in certain Characinidae,
and for the presence of a superficial covering of denticles in the
Siluroidei. The dermal bones of the head still, for the most part,
lie near the surface and harbour the lateral-line canals (Fig. 327).
Very generally there is a fontanelle between the parietals. Usually

372

TELEOSTEI

the pseudobranch is absent ; the mesocoracoid arch and the closed
ovarian sac are preserved.

iijrttii

t ~ ~ "'C.-Z
:-» =. ~ Z

15 III ill

ll^p

§ = 2 "8 . - «-•§ I

IllPill

^ ^ j5 >. s" "' ~ 3

.irSi

From all other fish this sub-order is distinguished by the pos-
session of a most remarkable apparatus, connecting the ear with

C YPRINIFORMES

373

sc.

the air-bladder, first described by Weber [481]. It is essentially
the same in all the families (Sagemehl [379], Wright [510],
Bridge and Haddon [58], Bloch [37], Grassi, Storensen). The
right and left membranous labyrinths join across below the
medulla by a transverse canal, from which pass backwards a
pair of sacculi and a median sinus endolymphaticus. The latter
lies in the atrium, an extension of the perilymph cavity lodged
in the basioccipital (Fig.
358). On each side, from
a membranous fenestra of
the atrium, stretches a
chain of four ossicles to
the air-bladder. The
largest and hindmost
ossicle, the tripus (mal-
leus), lies on the anterior
wall of the air-bladder ;
the foremost and smallest,
the claustrum, on the
membranous wall of the
atrium ; the scaphium
(stapes), with a process
fitting over the atrial
fenestra, and the inter-
calarium (incus) complete
the chain (Fig. 359).
Observers differ as to
the exact homology of
Weber's ossicles. The
tripus is believed to

..ut.

represent the rib of the
third vertebra (Sage-
mehl) ; the ii

re.

FIG. 359.

Macroms nemwus. A, the Weberian ossicles. B, por-
tion of the skull, the labyrinth, and Weberian apparatus
diagrammatically represented from above (from the
the neural arch of the nRtires of Bridge and Haddon). tt.ft, air-bladder ; a.r,
T /ITT • i \ anterior vertical canal of the ear ; d, claustrum ; to,
Second Vertebra ( Wright) ; exoccipital ; h, horizontal canal ; in, intercalarium ; pto,
4.1 „ ™.,v.;,,^ 1 pterotic ; n, sacculus ; sc, scaphium ; tr, tripus ; vt, utri-

the SCaphllim the neural culus ; r.c, Vertebral column.

arch, and the claustrum

the spine of the first vertebra (Wright). Sagemehl and Grassi
consider that the claustrum is derived from the skull. More
probably the two last ossicles represent the first neural arch and
rib. The anterior vertebrae are much modified in connection with
Weber's apparatus.

The air-bladder often comes quite close to the skin, just
behind the pectoral girdle, forming a sort of tympanum, in many
Cyprinidae, Characinidae, and Siluridae.

An adipose fin is found in all the families excepting the

374

TELEOSTEI

Cyprinidae. Often there are spinous serrated anterior dermal rays
on the median and paired fins ; such spines are formed by the
enlargement and ankylosis of the segments of the lepidotrichia
from the base outwards, unfused segments frequently remaining at
the tip. In the pectoral girdle, besides the mesocoracoid arch, must
be noticed the great development of the coracoids, which often meet
in a ventral suture (Fig. 365). The Cypriniformes have diverged
in two chief branches : the Characinidae depart least from the
primitive type, and lead to the Cyprinidae and eel-like Gymnotidae ;
the other branch includes the Siluroidei, among which are some of
the most specialised of Teleosts.

pmx

.—pro.

TRIBE A. CHARACINOIDEI.

This includes the more generalised forms, with parietals distinct and
not separated by the supraoccipital, well-developed opercular bones, three

to five branchiostegals,

A- , and a symplectic. Ex-

cept on the first four
segments', the anterior
parapophyses are usu-
ally short, separate from
the centrum, and bear-
ing pleural ribs. The
second and third centra
become fused and the
parapophyses of the
fourth vertebra en-
larged, bent downwards,
and applied to the air-
bladder, which is gener-
ally subdivided into an
anterior and a posterior
chamber (Fig. 199).
From the latter comes
the pneumatic duct.
Epipleurals and epi-
neurals are present.

Family CHARACINI-
DAE. The scales are
cycloid or with a hinder
ctenoid edge. The max-
illa may be toothed as
well as the premaxilla
and dentary ; the teeth
may be powerful and

(Fig. 360). Sometimes an incomplete interorbital
The anterior chamber of the air-bladder may be

-pro.

FIG. 360.

Left jaw-bones of A, Erythrinus unitaeniatits, Spix. ; and
B, Cithariniis Geoffroyi, Cuv. (After Sagemehl.) an, angular ;
art, articular ; </, dentary ; ect, ectopterygoid ; cut, entoptery-
goid ; /, foramen ; hm, hyomandibular ; mt, metapterygoid ;
mx, maxilla ; pi, palatine ; pmx, premaxilla ; pro, preopercular ;
q, quadrate ; s, cartilage ; sy, symplectic.

with several cusps
septum is present.

C YPRINIFORMES 37 5

cellular as in Erythrinus ; in Citharinus there is an accessory respiratory
diverticulum of the gill-cavity. There are many pyloric caeca and an
adipose fin [379].

Tetrayonopterus, Ag. ; Tertiary, Brazil. Hydrocyon, Cuv. ; Alestes,
M. and T. — Africa. Crenuchus, Giinth. ; Brycon, M. and T. ; Chakeus,
Cuv. ; Serrasalmo, Lac. ; Piabucina, C. and V. — America. Dislichodns, M.
and T. ; Citharinus, Cuv. — Africa. Macrodon, M. and T. ; Erythrtnns,
Gron. — America. Phago, Giinth. ; Neoborus, Blgr. ; Xenocharaz, Giinth.

Family CYPRINIDAE. The scales are cycloid ; sometimes they are
absent, and in the leather carp variety of Cyprinus they are represented
by only a few very large scales on the body. Barbels are often present.
The mouth has a small gape, is usually protractile, toothless, and
margined only by the premaxilla (Figs. 327, 358). The protractility
of the jaw in the Cyprinoid has doubtless been acquired independently
of that of the Acanthopterygii, and differs fundamentally from it in the
manner in which it is brought about (Sagemehl [379]). In the Carps the
dorsal processes of the premaxillae are short, do not reach the cranium,
but are joined to it by a ligament in which lies a median 'rostral' bone
(Fig. 327). It is by the stretching of the ligament and motion of the
rostral that the jaw is brought forward. The rostral is a specialised
portion of the ethmoid cartilage. In the Catostominae the maxilla still
contributes to the margin of the mouth. A fenestra is present in the
exoccipital. The lower pliaryngeals (fifth branchial arches) are strong
and armed with powerful teeth, which in many genera bite against a
horny pad borne on a ventral process of the basioccipital (Fig. 358).
A sensitive palatal organ is situated in front of this masticator.

The second and third dermotrich of the dorsal and pectoral fins are
often serrated spines. There are no pyloric caeca.

In Cobitis, Homaloptera, and their near allies the air-bladder is small,
with a subdivided cavity, and is partially or entirely enclosed in a bony
capsule, apparently formed by the ossification of its walls. This affords
a very interesting case of parallelism when compared with certain of the
Siluroidei (p. 377), in which the reduced air-bladder is also encapsuled,
but by very different means. Gastromyzon is remarkably flattened
ventrally, its expanded paired fins contributing to form a sucker-like
surface of attachment.

Rhodeus, and allied genera, are remarkable for the development of a
long ovipositor, a tubular outgrowth from the urinogenital opening of tlie
female.

SUB-FAMILY 1. CATOSTOMINAE: The 'Suckers.' Sclerognathus, Gthr. ;
Catostomus, Le S. (Fig. 361) ; Carpioides, Raf. ; Moxostoma, Raf. — N.
America ; some in Tertiary deposits.

SUB- FAMILY 2. CYPRININAE : The Carps. Carp, Cyprinus, L. (Fig,
362) ; Barbel, Barbus, Cuv. ; Gudgeon, Golrio, Cuv. ; Minnow, Leuciscus,
Klein ; Tench, Tinea, Cuv. ; Rhodeus, Ag. ; Aspius, Ag. — Europe, and
to Miocene or Oligocene. Catla, C. and V. ; E. Indies. Labeo, Cuv. ;
Africa and Asia. Itohteiclithyx, Bleek ; Leptobarbus, Bleek. — E. Indies,
Luciosoma, Blkr. ; Hypophthalmichthys, Blkr. — China. Bream, Abramis,
Cuv. ; Alburnus, Heck. — Northern hemisphere.

376

TELEOSTEI

SUB-FAMILY 3. COBITIDINAE : The Loaclies. Botia, Gray ; E. Indies.
Misgurnus, Lac. ; Cobitis, Art. — Europe and Asia. Acanthopsis, van H. ;
Apua, Blyth — E. Indies.

SUB-FAMILY 4. HOMALOPTEHINAE. Homaloptera, van H. ; Helgia, Vin. ;
Glaniopsis, Blgr. ; Gastromyzon, Gtbr. — Asia.

Family GYMNOTIDAF. This family has undergone great specialisation.

FIG. 301.
Catostomus occidentcdis, Ayres. (From Jordan and Evermann.)

These fish acquire an eel-like body, covered with cycloid scales or naked.
The dorsal fin disappears or remains only as an adipose strip. The
caudal region is mnch elongated, and also the anal fin ; the caudal is

Fio. 302.
Cyprinus carpio, L., the Carp. (From Seeley, Freshwater Fishes of Europe.)

reduced or absent. The small mouth is frequently borne at the end of a
long snout. A shortening of the abdominal cavity takes place, accom-
panied by the shifting forward of the anus even to below the snout.
The gill-opening is reduced in size.

The Electric Eel (Gymnotus electricus) has a powerful electric organ
formed by the modification of the myotomes along the caudal region ; it

CYPRINIFORMES 377

is also remarkable for the possession of a large number of pectoral radials
(8), like Anguilla (Sagemehl [379] and Fig. 363).

FIG. 363.

Gymnotus eleetrieus, L., dissected so as to show the electric organs on the right side, k
and ?; h, reflected body-wall. (From Owen, Anatomy of Vertebrates, by permission of
Messrs. Longmans and Co.)

Gymnotus, Cuv. ; Campus, M. and T. ; Sternopygus, M. and T. ;
Sternarchus, Cuv. ; lihamphichthys, M. and T. — S. America.

TRIBE B. SILUROIDEI.

Normal Teleostean scales are never present, the body being either naked
or covered with overlapping plates, or armed with a stiff cuirass. Possibly
both these are modified scales (Fig. 373). On the head and shoulder
region the dermal skeleton is usually very well developed ; the bones
being generally ornamented, close-fitting, and expanded so as to form a
cephalic shield, in which may become involved the post-temporal and
supraclavicle (Fig. 366). The cleithrum may also develop a large dermal
plate. The postclavicle is absent. There is no eye-muscle canal ; and
no distinct parietals, these bones being probably fused with the supra-
occipital, formed by the combination of a large dermal plate with an
endochondral element (unless the parietals are represented by two small
supratemporal bones pushed outwards and backwards). Only one ptery-
goid persists ; there is no symplectic bone, and the palatine is toothless,
often rod-like, and sometimes vestigial. The subopercular has the
appearance of a branchiostegal ray, and the maxilla generally becomes
converted into a small ossicle supporting the cartilaginous axis of the
barbel (Figs. 364, 366, 367). The prernaxilla, dentary, vomer, and
generally the pterygoid, are toothed [252, 274, 286, 290, 332, 410].

The anterior vertebrae are more modified than in the Characinidae.
A complex vertebra, behind the small first centrum, is made up of three,
four, or even five centra, forming a single mass which may be co-ossified
with the first centrum and the basi occipital. The parapophyses are long,
especially in front, and those of the fourth, and sometimes also of the
fifth vertebra, are immensely enlarged and project outwards to articulate
with the massive post - temporal (Fig. 367). The latter has one limb
articulating with the basioccipital, and another with the epi- and pterotic.
The enlarged parapophyses more or less thoroughly invest the anterior
chamber of the air-bladder, sometimes in a complete bony capsule [58].

The air-bladder is typically subdivided internally into an anterior
transverse chamber and paired posterior chambers. In many cases it
undergoes degenerative changes, becoming very small and almost solid, the

378

TELEOSTEI

epo

Fio. 364.

A, dorsal view, and B, left-side view of the skull and pectoral girdle of Silunts glanis, L.
(After Juge, slightly altered.) art, articular ; 6, barbel ; br, brancliiostegal ; cl, oleithrum ; d,
dentary ; epo, epiotic ; cth, mesethmoid ; fr, frontal ; Jim, liyomandibular ; iofi, interopercular ;
mx, maxilla ; na, nasal ; op, opercular ; pmx, premaxilla ; pop, preopercular ; pst, post-
temporal ; pt, pterygoid ; ptf, postfrontal ; pto, pterotic ; ij, quadrate ; r, radial ; sob, sub-
orbital ; soc, supraoccipital ; t.r, transverse process of the compound first vertebra abutting
against the cleithrum.

379

front chamber alone persisting (Clarias, Saccolranchus, Bagarius, Loricariidae,

etc.). In some (Aucheniptems, etc.) a peculiar elastic spring apparatus is

developed from the expanded parapophysis of the fourth vertebra, which

acquires a thin pliable base, ami can be moved by muscles so as to alter

the pressure in the bladder and produce a sound (J. Mu'ller, Bridge and

Haddon [58]). There are no pyloric caeca. Accessory respiratory organs

are sometimes developed. Certain anterior lepidotrichia in the dorsal and

pectoral fin may become modified

into powerful spines (Bagrinae,

Doradinae, etc.), connected by an

elaborate locking joint. InAmiums,

for instance, the first interspinal

plate is a small ossicle with its

dermal ray a small scute ; the

second ray is a U-shaped bone

at the base of the large defensive

spine, which is the third dermo-

trich resting on a large plate

belonging to the third radial. In

the Bagrinae and Doradinae there

is a regular dorsal buckler thus

formed in connection with the

dorsal fin (Fig. 366).

Callomysta.'- produces a stridu-
lating sound by the scraping of the
first dorsal radial between the
ridged laminae of the deep cleft of
the combined fourth and fifth
neural spines (Haddon).

The Siluroidei present some
most striking superficial resem-
blances to the extinct Cephalaspidae
and Coccosteidae. So close is the
likeness (especially among the
Clariinae and Loricariidae) as even
to deceive so acute an observer
as Huxley [227]. It is now FIG. 865.

generally admitted that the resem- . Auchenogianis biscutatis, Geoifr. A, ventral

, view of the pectoral girdle ami left pectoral hn.

blance between these Siluroidei B, ventral view of the pelvic girdle and left

ind the Dpvoninn fossils is dnp tn Pelvic fln- clt> cleithrum ; co, coracoid ; msr,

3 mesocoracoid ; p, pelvic bone ; pf, pelvic lepido-

COllVergence. trichia; .*;>, pectoral spine or first lopidotrich.

Family SILURIDAE. These fish

usually have an adipose fin. The tail region is extremely long in the
Clariinae, where both the anal and the dorsal fins are extended ; and in
the Silurinae, where the dorsal is very short and the anal very long.
The opercular bones are somewhat reduced.

Clarias has accessory respiratory organs in the branchial cavity
(Fig. 368) ; and in Saccobranchus a large diverticulum, supplied
with blood from the aortic arches, extends back from the branchial

380

TELEOSTEI

cavity below the trunk - muscles and acts as a lung (Fig. 369)
(Burne [75]).

Sub-Family DIPLOMYSTACIN^E. In which the maxilla is still toothed,
and of considerable size. Diplomystax (Diplomystes), Dum. ; Chile.

Sub- Family CI,ARIINAE. Clarias, Gron. ; Heterobranchus, St. H.
— Africa and Asia ; Pliocene, India. Copidoglanis, Gthr. ; Asia,

pmx

mxt>

i op

pfsp

Fro. 366.

Synodontis schal, Schn. (After Briihl, modified). Skull, pectoral girdle and fin, anterior
vertebrae, and dorsal fin. d, expanded cleithrum ; eth, mesethmoid ; /, prefrontal ; fr, frontal :
iop, interopercular ; l.b, lower barbels; mx.b, maxillary barbel ; n.ar'2, neural arch of second
vertebra ; op, opercular ; p.f.sp, pectoral-fm spine ; pi, lateral bony plate ; pmx, premaxilla ;
ptf, postfrontal ; pst, post-temporal ; pts, pterotic ; r, dorsal radial ; s, first dorsal spine ? ; sen-,
supraoccipital plate ;"sp 2 and 3, second and third spines ; v*, fourth vertebra fixed to anterior
vertebrae,

Australia. Cnidoylanis, Gthr. ; Australia. Channolabes, Gthr. ; Clariallabes,
Blgr. — Africa.

Sub-Family SILUBINAE. Silurus, L. (Fig. 370) ; Europe and Asia,
and Tertiary. Saccobranchus, C. and V. ; Helicopliagus, Blkr. — Asia.
Pseudeutropius, Bl. ; Asia, and Tertiary. Eutropius, M. and T. ; Schilbe,
Guv. — Africa. Eumeda, Cost. ; Neosilurus, Stnd. — Australia.

Sub-Family BAGRINAE. Macrones, Dum. ; Rita, Bl. — Asia, and
Pliocene. Arius, C. and V. ; tropics ; Eocene, Europe. Amiurus, Bl. ;
Asia, America ; Miocene, N. America. Rhinetutcr, Cope ; Eocene,
N. America. Buddandium, Konig ; Eocene, England. Chrysichthys,

C YPRINIFORMES

eth

Skull and anterior vertebrae of Glorias magur, H. U. A dotted line indicates the course of

FIG. SOS.

I.i'l't-side view of head of Clarias lazera, C. and V., with branchial chamber exposed by
removal of operculum. a, accessory respiiatory organs attached to top of gill -arches ; an,
anterior nostril ; b, barbel ; br, gill-lamellae ; pn, posterior nostril.

382

TELEOSTEI

Bl. ; Auchenoglanis, Gthr. — Africa. Pimelodu*, Lac. ; Callophysus, M. and

FIG. 369.

Left-side view of Saeeobmnchus fossilis, L., dissected to show the air-sac. 1, barbel; 2,
pectoral, 3, pelvic, 4, dorsal, 5, anal, and 6, caudal (in; 7, branchial sac; 8, its opening
into branchial chamber.

FIG. 370.
SUimis glanis, L. (From Seeley, Freshwater Fishes of Europe.)

FIG. 371.
Malaptcrurus elcctricus, Gin. (After Giinther.)

T. ; Nannoylanis, Blgr. ; Conorhynclius, Blkr. ; Notoylanis, Gthr. — America.
Nedystoma, Og. ; Pachyula, Og. — Australia.

Sub-Family DORADINAE. Synodontis, Cuv. ; Phractura, Blgr. ;
Euchilichthys, Blgr. — Africa. Bayarius, Bl. ; Asia, and Tertiary. Sisoi;

C YPRINIFORMES

383

H. B. ; Chaca, C. and V. — Asia. 'Doras, Gthr. ; Oxydoras, Kner ;
Callomystax, Gthr. Glanidium, Liitk. ; Cetopsis, Ag. — America.

Section of Muluiiterurus clectricus, Gm., showing the electric organ, A. B, vascular layer :
K, adipose tissue ; G, muscles. (From Owen, Anatomy of Vertebrates, by permission.)

-de.

FIG. 373.

Plecostomus Commersonii, Yal. A, piece of lepidotricli, enlarged. B, several scales, from
which the skin has been removed on the left. C, small piece of the surface of a scale, much
enlai-ged. D, section through a developing denticle of Hypostoma (D, after Hertwig). u.s,
smooth anterior region ; d, denticle ; d.c, dentine cap ; en, enamel cap ; c;i, epidermis ; l.c,
lateral-line canal ; m, enamel organ ; p, pulp ; so, scale ; *./, segment of lepidotrich.

Sub-Family MALAPTERURINAE. Malaptcrurus, Lac. ; Africa ; with
a large electric organ (Figs. 371, 372) (Fritsch [141]).

384 TELEOSTEI

Family CALLICHTHYIDAE. The small mouth is ventral and provided
with minute teeth. The body is armoured with two rows of overlapping
bony plates which, like the surface of the cranial bones, are beset at
their hinder edge with movable denticles (p. 369). There is a strong
pectoral spine and an adipose fin.

Callichthys, L. ; Corydoms, Lac. — S. America.

Family LORICARIIDAE. These are closely allied to the last, but
(except in Arges) the bony plates are more numerous and form a com-
plete rigid armour on the head and body. The dermal bones are
studded with denticles and the small teeth resemble these in structure.
It is curious to note that the denticles may be much larger in the male
than in the female. The modified suctorial mouth is below the flattened
head, which generally develops a prominent lateral edge and snout (Figs.
374, 375). The orbits shift dorsally, the posterior nostrils moving close
to them. The parapophyses have disappeared, the pleural ribs are sessile,
and the anterior neural spines bifid. There is no adipose fin and the

FIG. 374.
Loricaria lanceolata, Gthr. Upper Amazons. (After Giiuther.)

gill-opening is small, the opercular bones being also much reduced. The
pectoral spine is usually very large. The intestine becomes much
coiled.

Sub-Family ARGINAE. With a naked body and strong ribs.

Arges, C. and V. ; Astroblepus, Humb. — S. America.

Sub-Family LORICARIINAE. With complete bony armour and
slender ribs.

Plecostomus, Gthr. ; Chaetostomus, Heck. ; Loricaria, L. (Fig. 374) :
Acestra, Kner — S. America.

Family ASPREDINIDAE. The head is wide and depressed, the body
naked and tapering to a long tail ; the gill-opening minute. The large
air-bladder is not enclosed by bone. The pectoral spine is very powerful.
Although the skelton resembles that of the Loricariidae in many points,
yet there is a leaning towards the Siluridae. There is a small dorsal
shield ; the bones of the operculum are vestigial, the opercular disappear-
ing altogether. The female carries the eggs embedded in the skin
below the head and belly.

Aspredo, L. ; Bunoceplialiis, Kner ; Dysichthys, Cope — S. America.

C Yl'RINI FORMES

Upper ami lower .side of the head of Aiwistrus (Chaetottomtu) heteraixmthus, Gthr. Upper
Amazons. (After GUn!h"r.) Tufts of enlarged denticles are shown at the sides.

386 TELEOSTEI

Group B.

The lower members of this group preserve many primitive
characters, such as the median gular, mesocoracoid arch, spiral valve,
conus with two rows of valves, all of which are found in the first
sub-order only ; moreover, the oviducts may have open internal
funnels (p. 367). There is an interorbital septum, not always
completely formed, however (Osteoglossidae, Galaxiidae, Gadidae).
With the single exception of the Gadiformes (p. 478), these fish
have the cranial cavity shortened, the brain situated far back, the
olfactory lobes lying immediately in front of the fore-brain, and the
elongated olfactory nerves passing forward on either side of the
interorbital septum when present (p. 324). There are neither
denticles nor Weberian ossicles. The lines of divergence among
the lower forms are too indistinct to be followed out with certainty.
The group may be divided into eight sub-orders, of which two, the
Esociformes and the Mugiliformes, seem to lead towards the
Acanthopterygii.

Sub-Group 1.
Sub-Order CLUPEIFORMES (Isospondili, Malacopterygii).

This is a purely artificial assemblage of lowly organised families
retaining the mesocoracoid arch, pneumatic duct, a comparatively
large number of vertebral segments, and numerous lepidotrichia in
the paired fins. The scales are cycloid as a rule.

The segments of the lepidotrichia are not co-ossified into spines ;
neither is the head, as a rule, overgrown with scales, and the dermal
cranial bones frequently remain in their primitive position near
the surface (p. 213).

It should be noticed that in the skull the parietals usually, but
by no means always, meet in a median suture ; the eye-muscle
canal is generally present ; the maxilla always, except in the
Albulidae, forms the posterior margin of the upper jaw ; and the
symplectic is absent in the Mormyridae, Phractolaemidae, and
Cromeriidae. The hypural bones may remain unfused (Elopidae,
Saurodontidae, etc.). Epineurals are generally and epipleurals
rarely present. A complete scapular foramen is usually developed.
The number of pelvic lepidotrichia varies from as many as sixteen
in the Elopidae to as few as five in the Osteoglossidae and
Stomiatidae.

The Clupeiformes might perhaps be subdivided into two
groups, one containing the Elopidae, Albulidae, Osteoglossidae,
Mormyridae, Notopteridae, Hyodontidae, and Halosauridae, in
which the parietals meet in the middle line, and the other the

CLUP El FORMES

387

remainder of the families; but it is very doubtful whether such

a division is natural (p. 346).

Ridewood has recently given an

account of the skull of these fish

[363].

Family ELOPIDAE. Both the
maxilla and premaxilla enter the
margin of the upper jaw. The
parietals meet in spite of the
junction below of the frontal with
the supraoccipital. The two supra-
temporals are large and meet (Elops)
(Fig. 326). It is remarkable that
the median gular plate is preserved
(Fig. 376), though often in a
vestigial condition. Small teeth
are present not only on the marginal
jaw-bones but also on all the bones
of the palate including the para-
sphenoid, and on the glossohyal
and pharyngeals. The eye-muscle
canal is present. There is a scapular
foramen, and three of the radials
rest on the coracoid. Usually there
are enlarged axillary scales (Fig.
376).

Elops, L. (Fig. 377) ; tropical
seas ; Eocene, Europe. Megahps,
Lac. ; Tarpon, J. and E. ; S.
American Atlantic Coast, Indo-
Pacific ; Eocene, Europe. Elopopsis,
Heckel ; Esocelops, A. S. W. ;
Europe ; Osmeroides, Ag. ; Europe,
Asia ; Notelops, A. S. W. ; lihacolepis, Ag. ; S. America — all Cretaceous.

tuc

FIG. 370.

Head of Elops saurus, L. ; oblique ventral
view, a.sc, axillary scale ; b.r, branchiostegal
ray ; ch, preopercular region ; t, fold of skin
over eye ; g, lower jaw ; g.p, gular plate ; iop,
interopercular region ; mx, maxilla ; op, oper-
cular ; pj, pectoral fin ; sop, subopercular.

Fio. 377.
Elops saurus, L. (After Day, Fiches of India.)

Family ALBULIDAE. This family dates from Cretaceous times like

388 TELEOSTEI

the Elopidae, to which they are doubtless closely allied. The skeleton
differs in the absence of a gular plate, in the partial or complete with-
drawal of the maxilla from the margin of the mouth, which is small,
in the presence of a third, pterotic, branch to the post- temporal, in the
articulation of only two radials with the coracoid, and in the larger size
of the postclavicle, which is formed of three pieces. The parasphenoid
is expanded, and bears numerous grinding teeth opposed to a similar
patch of teeth on the basibranchials (Figs. 330-31). Two rows of valves
remain in the conus (p. 363).

Albula has a flattened transparent larva very similar to the Lepto-
cephalus larva of the Anguillifornies.

Albula, B. and S. (Butirinus) ; tropical seas. Anoymius, Cope ;
Cretaceous, N. America. Pterothrissus (Bathythrissa), Hlg., deep-sea,
Pacific.

Family MORMYRIDAE. A most remarkable family of freshwater
African fish, highly specialised in some respects. In the Mormyrinae
the head may become drawn out into a long decurved sriiout carrying

FIG. 378.
Mormyrus oxyrhynchus, Geoff. (After Giinther.)

the small mouth at its extremity, and sometimes provided with a ventral
appendage (Fig. 378). The premaxillae fuse and the maxilla, palatal,
and pharyngeal bones are toothless. The large scale-like supratemporal
covers a wide lateral fossa. The opisthotic, symplectic, entopterygoid,
and supramaxilla are absent. The hyopalatine arch is firmly fixed to
the skull, the palatine being fused to the vomer. Paired tendon bonesy
comparable to those of Polypterus, project backwards from the hypo-
branchials. The suboperculum is small, concealed below the operculum,
or absent. The branchial opening is narrowed. Diverticula are given
off by the air-bladder to the auditory capsules, and the bladder is cellular
in Gymnarchus. A peculiar diverticulum grows on the bulbus arteriosus.
The brain of these fish is remarkable for its large size, owing chiefly
to the great dorsal development of the tuberculum impar and vagus
centres. A thick glandular skin covers the head and even the eyes, which
are often somewhat degenerate. In most genera the caudal region is
long, and the anal fin considerably lengthened ; Gymnarchus acquires an
eel-like shape with tapering tail, while the pelvic, anal, and caudal fins
disappear.

All the Mormyridae seem to have electric organs developed in the

CLUPE I FORMES

389

caudal muscles ; they are especially powerful in Gymnarchus. This genus
is also remarkable for its larval stage with a large yolk-sac and external
gills (Fig. 379, Budgett [67a], Assheton [20]). All African.

Sub-Family MORMYRINAE. Differs from Gymnarchus in having a simple
air-bladder, toothed parasphenoid and glossohyal, special bones alongside
the electric organs, a foramen

in the scapula, or between it ^

and the coracoid, and complete
fins.

Mormyrops, J. M. ; Petro-
cephalus, Marc. ; Mormiirn*,
L. ; Gnathonemus, Gill ; Stoma-
torhinus, Blgr. ; Marcuson'm,
Gill.

Sub - Family GYMNAR-
CHIDAE. Gymnarclms, Cuv.

Family HYODOXTIDAE.
Hyodon seems to be related
both to the Notopteridae and
to the Mormyridae. It differs
from the latter in possessing
a wide mouth, with strong
teeth on the maxillae as well

as the premaxillae, a symplectic, and in the absence of a closed ovisac
(p. 368). There is the same lateral temporal fossa covered over by an
expanded supratemporal, and vesicle of the air-bladder, which here lies
against a fenestra of the auditory capsule. The pterygoids are separate,
and the hyopalatine arch movably articulated. A prominent toothed

FIG. 370.

Larva of '///""'«'v'i»'.< nHoi'tru*, Cuv. (After Budgett,
Trant. Zool. Soc.) 1, yolk-sac; •_', external gills ; 3
and 4, subintestinal vein.

FIG. 380.

Koto]>t' r»* l;«j>ii-nt, Luc. (After Day, Fishes o/Iii'lin.)

ridge is formed by the parasphenoid. The very large coracoids meet
ventrally in a keel. The body is elongate and compressed.

Hyodon, Le S. ; rivers of N. America.

Family NOTOPTERIDAE. Another small family, allied to the two last.
These highly specialised fish have a very compressed body, a very short
trunk followed by a long tapering caudal region, with a dorsal fin small
or absent. The tail is gephyrocercal, and the caudal fin continuous with
the very long anal (Fig. 380). The pelvic fins are reduced or absent.

390 TELEOSTEI

The supratemporal does not cover the lateral fossa, and there is no sub-
opercular, but in most other respects the bones of the skull resemble those
of Hyodon. The upper branch of the post-temporal is incomplete or absent,
paired bones are attached to the basibranchials as in Mormyrus, and mid-
ventral adpleurals form a keel joining the pleural ribs below. As in
Hyodon, the ovaries are ' free,' that is, not closed off from the abdominal
coeloni.

Notopterus, Lac. ; Africa and E. Indies ; Tertiary, Asia. Xenomystus,
Gthr. ; Africa.

Family OSTEOGLOSSIDAE. The skull [55, 364] has a distinctly
primitive appearance, the superficial bones being close to the skin and
having a sculptured surface. The wide nasal?, frontals, and parietals
meet in the middle line, and the supraoccipital scarcely reaches the
surface. As in most primitive Teleosts, there is an eye-muscle canal,
blind behind, an opisthotic, and, as a rule, a toothed parasphenoid, which,
moreover, sends out a process to articulate with the entopterygoid (p. 271).
Both the premaxilla and maxilla are toothed, and share in forming the
margin of the mouth ; there is no supramaxilla. The interorbital septum
is but incompletely formed ; the orbitosphenoid when ossified is paired
(Arapaima, Ridewood). The dermal articular may be distinct from the
endosteal articular. The subopercular is small, often hidden behind
the preopercular, and likewise the interopercular. The scales are large,
thick, and cycloid. In Heterotis, at all events, the ovaries are free, and
the larva has external gills (Budgett [67a]). The Osteoglossidae are
an ancient family dating from Eocene times ; they seem to be more
closely allied to the Albulidae than to any other family. In the more
specialised genera the caudal region is generally much developed, the
dorsal and anal fins may be extended, so that the pelvics are relatively
far forward. Heterotis has a spiral suprabranchial accessory breathing
organ (Hyrtl [233c]).

Dapedoylossus, Cope ; Eocene, N. America. Brychaetus, A. S. W. ;
Eocene, England. Osteoglossum, Vand. ; Arapnima, Mull. — S. America.
Heterotis, Ehr. ; Africa. Scleropages ; Indo-Pacific.

Family SADRODONTIDAE. An extinct family closely allied to the
Chirocentridae, but rather more primitive. An eye-muscle canal and a
normal symplectic are present. The parietals are separated. The riba
are sessile, the neural arches separate from the centra, and there are no
compound hypurals. Characteristic of the family is the setting of the
teeth in deep sockets. Sometimes a predentary bone is present (Sauro-
cephalus, Saurodon).

Saurocephalits, Harlan ; Saurodon, Hays — Cretaceous, Europe and
N. America. Cladocyclus, Ag. ; Cretaceous, Europe and S. America.

Family CHIROCENTRIDAE. This family, present in Cretaceous strata,
but also surviving at the present day, is possibly derived from the
Saurodontidae, but differs from them in having the large teeth not in
regular sockets, the symplectic hidden by the quadrate and hyomandi-
bular.

A normal postclavicle is not present. There is a large axillary
scale above the level of the pectoral fin. The large coracoids

CLUPEIFORMES 391

meet below to form a ventral keel. The pelvics are very small. Both
epineurals and epipleurals are present. The air-bladder is partly cellular,
the pseudobranch and pyloric caeca have disappeared ; but most remarkable
of all is the retention of a distinct though rudimentary spiral valve in the
intestine (Fig. 77).

Platinx, Ag. ; Eocene, Italy. Chiromystus, Cope ; Brazil ; Chiro-
centrites, Heckel ; Istria — Cretaceous. Ichthyodectes, Portheus, Cope ; N.
America and Europe ; Cretaceous. Chirocentriis, Cuv. ; Indo - Pacific ;
and Lignite, Sumatra.

Family PHRACTOLAEMIDAE. A small family founded for a single
highly specialised African genus. The head is very small and the
toothless jaws protractile, the mouth when at rest being folded back on
to the top of the snout. The nostril is single on each side, with a barbel
in front. The intestine is very long and convoluted. Phractolaemus
appears to be allied to the Osteoglossidae (Boulenger [42]), but it has lost
the symplectic, the myodome, and the postclavicle. The interoperculum is
enormous ; moreover, the parietals are widely separated by the frontals
meeting the supraoccipital. The caudal region is very short.

Phractolaemus, Blgr. ; W. Africa.

Family CLUPEIDAE. The Herrings form a large family already well
represented in Cretaceous times. On the whole, they are of a generalised
structure ; but the small parietals are separated by the prominent supra-
occipital (Fig. 381). A superior temporal fossa, between the frontal and
parietal, and a pre-epiotic fossa are characteristic of almost all Clupeid
skulls (Fig. 381, B). Prootic and pterotic bullae, in which is lodged the
diverticulum of the air-bladder, and an auditory fenestra are usually
present. The eye-muscle canal is generally open behind. The upper
jaw is of very variable structure ; one or two supramaxillae are usually
present ; teeth may be placed on both the premaxilla and maxilla
(Engraulis), or on the former only (Pellonula), or on neither (Chatoessus) ;
the maxilla may be large and firmly fixed to the premaxilla (Thris-
sopatrinae), or movably articulated to the ethmoid behind (Clupeinae).
In some the maxilla is prolonged backwards beyond the angle of the
mouth, a peculiarity which is carried to an extreme in Coilia.

The number of branchiostegal rays varies from thirteen in Dussumieria
to four in CJianos ; and of pelvic lepidotrichia from eleven to six. The
hypural bones remain simple. There is a remarkable development of
intermuscular bones, epineurals, epipleurals, and adpleurals ; and usually
the pleural ribs are joined below by a series of median V-shaped scales
so as to form complete hoops ; similar dorsal ridge scales may be present.
The coracoids join to a ventral keel ; and the postclavicle is quite
peculiar in that it overlaps outside the clavicle.

Caecal prolongations of the air-bladder rest against the auditory
fenestra, and the pneumatic duct opens into the stomach. In Clupea
the hinder end of the air-bladder opens directly to the exterior by a
pore on the left of the anus, a quite unique arrangement among fish
(Fig. 383).

Chanos is the type of an aberrant sub-family, sometimes associated
with the Albulidae (A. S. Woodward [505]), in which the cranial fossae,

392

TELEOSTE1

auditory bullae, and fenestra are absent, and the maxilla excluded from
the gape of the small mouth.

soc

ct

pro

FIG. E81.

Skull of Clnpcujintu, Cuv. (From Ridewood, Proc, Zool. Soc.) A, dorsal view; B, left-side
view ; C, view from behind, ^w, parasphenoid ; t.f. temporal fossa. Other lettering as in Fin.
329, p. 348.

Sub-Family THRISSOPATRINAE. Thrissopater, Gthr. ; Cretaceous,
England.

Sub-Family ENGRADLINAE. Spaniodon, Pictet ; Cretaceous, Asia.
Enyraulis, Cuv., Anchovy ; warm seas ; Eocene, Europe. Cetenyraulis,
Gthr. ; Diissumieria, C. and V. ; Coilia, Gray (Fig. 384) — Indo-Pacific.

CLUPE1 FORMES

393

Sub -Family CLUPEINAE. Pseudoberyx, P. and H. ; Histivthrissa,
A. S. W. Scombroclupea, Kner ; Eocene, Europe and Asia Minor.
Clupea, L. ; recent ; and Eocene, Europe. Diplomystus, Cope, Pacific ;

FIG. 382.
Clupea alosa, L., the Shad ; with caudal scales. (From Seeley, Freshvut' i I'i.-ln .- "/ /•>

Eocene, Europe, Asia, N. America. Pellonula, Gthr. ; Atlantic. Odaxo-
thrissa, Blgr. ; Africa. Chatoessus, C. and V. ; Pacific and C. America.

Sub-Family CHAXINAE. Clianos, Lac. — Indo- Pacific ; CJianoides,
A. S. W. — Eocene, Europe. Prochanos, Bass. ; Cretaceous, Europe.

Family CROSSOGNATHIDAE. An extinct group of imperfectly known
Cretaceous fish probably related to the Clupeidae.

Crossognathus, Pictet ; Scyllaemus, Cope ; Cretaceous, Europe.

Family SALMONIDAE. Although the parietals are often separated by

I'd

Fio. 383.

Clupea harengiis, L., with the viscera exposed. (After Brandt, from Clans and Sfd^wick.) A,
anus ; Ap, pyloric appendages ; /?»•, gills ; D, intestine ; Dp, pneumatic duct ; G.p, genital pore ;
Oe, oesophagus ; S, spleen ; T, testis ; V, stomach ; I'll, vas dciVrt-ns ; I'/i, air-liladder.

the supraoccipital meeting the frontals, yet they sometimes spread over
and join above in a median suture. On the whole, the skeleton i.s
primitive, and the chondrocranium is particularly well preserved (Fig. 302).
There is an adipose fin ; pyloric appendages vary in number from 200
to a few, or may be absent (Microstoma) • the air-bladder, which is

394

TELEOSTEI

usually large and simple, may also be lost (Salanx). The ovary is free,
the oviducts being short (Osmerus), or reduced to mere pores (p. 367).

Salmo, L., Salmon and Trout (Fig. 385) ; Northern hemisphere ;
Pleistocene. Mallotus, Cuv. ; N. Asia and N. America ; Pleistocene.
Coreyonus, Art., Whitefish ; Osmerus, L., Smelt ; Thymallus, Cuv., Gray-

FlO. 3b4.

CoiUa ilumnnieri, C. and V. (After Day, Fishes of India.)

ling — Northern hemisphere. Argentina, Art. ; Europe. Salanx, Cuv. ;
China. Suciotrutta, Gthr. ; Caspian Sea, Russia, N. America. Opistho-
proctus, Peters (Fig. 401, A).

Family ALEPOCEPHALIDAE. A family of deep-sea fish apparently
related to the last, but with neither adipose fin nor postclavicle. All
have lost the air-bladder ; Platytroctes the pelvic fins ; and some, like
Aleposaurus, have lost the scales.

Alepocephalus, Risso; Bathytrodes, Gthr. ; Aleposomus, Gill; Leptoderma,
Vaill. ; Platytroctes, Gthr.

Family STOMIATIDAE. Specialised deep-sea fish, with very delicate
scales or naked skin, and usually numerous well-developed phosphorescent

FIG. 385.
Salmo salar, I.,. ; tlie Salmon. (From Seeley, freshwater Fishes of Europe.)

organs. The maxilla is large and toothed ; the parietals meet in a
median suture (Chauliodus). The branchial opening is very wide, the
post-temporal being attached near the middle line. There is often a
hyoid barbel and an adipose fin. The air-bladder may be absent and the
paired fins reduced. In this one family Boulenger has united the
Stomiatidae and Sternoptychidae of Giinther.

CL UPEIFORMES

395

Sub-Family CHAULIODONTINAE. Elongated, with the dorsal fin far
forwards, a very wide gape, and formidable dentition.

Chauliodus, B. and S.

Sub-Family GONOSTOMATINAE. Elongate, with the dorsal fin far
back ; sometimes a barbel (Astromethes).

Astromethes, Rich. ; Gonostoma, Raf. ; Maurolicus, Cocco ; Photichthys,
Hut*.

Sub-Family STERNOPTYCHINAE. The body is very short and deep,
the pelvic fins vestigial or absent.

Argyropekcus, Cocco; Sternoptyx, Herm.; Polyipnus, Gthr. (Fig. 344, B).

A.

B.

FIG. 386.
A. Mcilitcostcus indi':us, Gthr. (After Gitnther.) B, Itliacunthiisferox, Gthr. (After Giinther.

Sub-Family STOMIATINAE. Elongate, with the dorsal far back, a wide
gape, and large pointed teeth. Often there is a barbel, and the pectoral
fins may be vestigial or absent.

Stomias, Cuv. ; Macrostomias, Br. ; Photonectes, Gthr. ; Malacosteus,
Ayres (Fig. 386, A). Stylophthalmus, Br. (Fig. 401, B). Idiacanthus, Gthr.
(Fig. 386, B).

Fio. 387.
Gonorlii/ni-hn.-: in'1'i/i, Rich. (After Giinther.)

Family GONORHYNCHIDAE. An ancient family dating from Eocene
times, and represented at the present day by a single specialised genus,
Gonorhynchus, which has the head and body covered with small ctenoid
scales, and carries a ventral barbel on the prolonged snout. The supra-
occipital separates the parietals, the premaxilla articulates with the
maxilla and excludes it from the margin of the small mouth. Teeth are
absent (Notoyoneus), or present on the palate only. There is no myodoine
and no air-bladder. These fish are possibly related to the Scopelidae
(A. S. Woodward).

Gonorhynchus, Gronov (Fig. 387) ; Indo-Pacific. Notogoneus, Cope ;
Eocene, Europe and N. America. Charitosomus, Marck ; Cretaceous,
Europe and Asia Minor.

396

TELEOSTE1

Family CROMERIIDAE. Including the minute fish, Cromeria, from the
White Nile. The small inferior mouth is toothless, the maxilla not
excluded, the parietals separated, the branchial opening narrow, the body
scaleless. There is no postclavicle, no symplectic, and no myodome.

Cromeria, Blgr. ; Africa.

Family PANTODONTIDAE. A little African freshwater flying-fish,
Pantodon, seems to be closely related to the Osteoglossidae, although it
has become highly specialised in the development of its paired fins.
The slender curved mesocoracoids meet in the middle line. The large
pectorals have the postaxial edge prolonged into a soft web joining on to
the side of the body ; and the pelvics, bearing only seven dermotrichia,
some of which are filamentous, are placed far forwards almost under

FIG. 388.

Ctetiothrtusu vexillifcr, Pictet ; Upper Cretaceous, Mount Lebanon ; restored ; left-side view.
(After A. S. Woodward, Proc. Geol. Assoc.)

the pectorals. They are thoracic in position, although the girdle is not
fixed to the pectoral arch. The cranial bones are not sculptured, yet
they resemble those of the Osteoglossidae except in the fusion of the
premaxillae, and the loss of the sub- and interopercular. The auditory
capsule is swollen into a thin -walled bulla (Peters, Boulenger [42],
Ridewood [364]).

Pantodon, Peters ; W. Africa.

Family CTENOTHRISSIDAE. A small extinct group of obscure
affinities, with very large pelvic fins (with eight dermotrichs) placed far
forward. The anterior dermal rays of the dorsal fin are unjointed.
Premaxillae and large maxillae, with small teeth, border the gape. The
parietals meet.

Like the Pantodontidae, which they resemble sdmewhat in structure,

CLUPEIFORMES 397

the Ctenothrissidae are placed in the Clupeiformes chiefly on account of
their osteology ; yet in the position of their pelvic fins and the spine-
like dorsal rays, they approach the Acanthopterygii, with which they are
possibly related.

Ctenothrissa, A. S. W. (Fig. 388), and Aulolepis, Ag. ; Cretaceous,
Europe and Asia Minor.

Sub-Group 2.

In which the mesocoracoid arch is lost and a higher level
of general specialisation is reached, usually accompanied by the
closure of the pneumatic duct, the development of spines and
ctenoid scales, and the modification of the maxilla into a toothless
bone, separately articulated, and lying behind the premaxilla.
This last character has been independently developed in the
Cypriniformes and probably also in several of the following
sub-orders. Except in the Berycidae (Starks [421]) and Lampridi-
formes (Regan [344]), the orbitosphenoid is lost. Seven sub-orders
are included, some of which are merely provisional assemblages of
families, whose affinities are by no means clearly established.
Indeed, the origin of the Anguilliformes, for instance, is quite
unknown ; but, since the Acanthopterygii appear to be more
closely related to two of the sub-orders than to the others, we
can distinguish five divergent series which may be of some phylo-
genetic value.

Series 1.
Sub-Order 1. ESOCIFORMES (Haplomi).

This is a provisional sub-order containing some of the least
specialised forms of Sub-Group 2 (Starks [420]). They are with-
out true spines, and are usually physostomouS (with an open pneu-
matic duct). As a rule, the parietals are separated and the
orbitosphenoids absent. The pelvic fins are abdominal, and may
have numerous dermal rays ; the dorsal fin single, though occa-
sionally followed by an adipose fin.

In general structure the Esociformes resemble the Clupeiformes,
the Cyprinodontids lead towards the Mugiliformes, while the
Scopelids and Stephanoberycids approach the Acanthopterygii
(Boulenger). Fossil forms are known from the Eocene upwards.

TRIBE 1.

The parietals meet, separating the frontals from the supraoccipital ;
the post-temporal is simple ; the neural arches and parapophyses generally
autogenous (Swinnerton).

398 TELEOSTEI

Family GALAXIIDAE. The toothless maxillary, though behind the
premaxillary, shares in the margin of the mouth. There is no eye-
muscle canal, and the interorbital septum is but incompletely formed.
Neochanna has lost the pelvic fins. Scaleless.

Flo. 389.
Galaxias truttaceus, Cuv. (After GUntheri)

Galaxias, Cuv. (Fig. 389) ; rivers of S. Africa, S. Australasia, and
S. America. Neochanna, Gthr. ; New Zealand. .

Family HAPLOCHITONIDAE. Differ from the former in the exclusion
of the maxillary from the margin of the jaw, the presence of an eye-
muscle canal, and an adipose fin. Prototrodes has small scales.

Haplochiton, Jen.; S. America. Prototrodes, Gthr. ; Australasia.

TRIBE 2.

The frontals join the supraoccipital so as to separate the parietals, the
parapophyses when present are fused to the centra, and usually there is
no eye-muscle canal.

SUB-TKIBE A. The maxillae are not excluded from the margin of
the mouth ; there are no parapophyses on most of the precaudal vertebrae.

Family ENCHODONTIDAE. An extinct family from the Cretaceous,
related to the Scopelidae, naked or with small scales, and sometimes with
dermal scutes. Usually an adipose fin. The maxilla may be toothed,
the preopercular may have a spine (Halec, Eurypholis), and the pelvic
fins may be far forward.

Enchodus, Ag., Europe, Asia, N. America ; Eurypholis, Pict. ; Halec,
Ag., Europe, Asia ; Cimolichthys, Leidy, Europe, N. America ; Leptecodon,
Will., N. America ; Pantopholis, Davis, Asia — all from Cretaceous strata.

Family ESOCIDAE. The Pikes are among the least specialised of this
sub-order, except in their dentition, which is composed of numerous
powerful sharp teeth on the jaws, palate, and visceral arches. The
forked post-temporal rests on the epiotic and exoccipital. There is no
adipose fin, and the pelvic may have eleven dermal rays. The vertebral
arches are autogenous. There is a prenasal bone.

Esox, Cuv. ; Europe, Asia, N. America ; and Miocene, Europe. Umbra,
Kram. ; Europe, N. America.

Family DALLIIDAE. Specialised fish, closely related to the Esocidae,
in which the skeleton is thin and soft, the post-temporal incompletely
ossified, the pectoral fin has lost its radials, and the pelvics preserve only
three dermal rays (Starks).

Dallia, Bean (Fig. 390) ; Siberia and N. America.

ESOCIFORMES 399

SOB-TRIBE B. The mouth margined by the premaxilla only. An
adipose fin usually present.

Family SCOPELIDAE. A large and important family of marine fish,
dating from Cretaceous times. Many of them are deep-sea forms with
brilliant phosphorescent organs (Fig. 344, A). The pelvic fins, with from
seven to ten dermal rays, may be placed far forwards.

Ipnops has lost its eyes, and acquired two large cephalic phos-
phorescent organs ; Odontostomus is scaleless and has enormous eyes and
barbed teeth ; Bathypterois has lengthened sensitive filaments borne by
specialised lepidotrichia (Fig. 512, A). The air-bladder may be lost.

Sardinoides, van der M. ; Acrognathus, Ag. ; Leptosomus, van der M.,
Europe and Asia ; Rkindlus, Ag. ; Sardinius, van der M., Europe and
N. America ; Nematonotus, A. S. W., Syria ; Scopeloides, Wettstein ;
Dactylopoyon, van der M. ; Parascopelus, Sauv. ; Anapterus, Sauv. ;
Apateodus, Ag., Europe ; all from the Cretaceous. Scopelus, Cuv. ;

FIG. 390.
Dallia pectoralis, Bean. (From Jordan and Evermann.)

Ipnops, Gtlir. ; Sudis, Raf. ; Paralepis, Risso ; Bathypterois, Gthr. ;
Harpodon, Les. ; Odontostomus, Cocco ; Bentlwsaurus, G. and B.

Family ALEPIDOSAURIDAE. Powerfully toothed elongated fish, with
an immense dorsal fin, no scales, no air-bladder, and a simple post-
temporal attached to the opisthotic. The single genus appears to be
closely allied to the Scopelidae.

Alepidosaurus, LoAve (Fig. 391) ; Atlantic and Pacific.

Family CETOMIMIDAE. Deep-sea fish, whose affinities are very uncer-
tain, with a huge mouth, small teeth, and no scales. Cetomimus has lost
the pelvic fins, and has very small eyes.

Cetomimus, G. and B. (Fig. 392) ; Ronddetia, G. and B.

SUB-TRIBE C. The maxillae are excluded from the margin of the
mouth, which usually has a small gape, with the suspensorium produced
forwards ; and the centra have well-developed parapophyses. Without
an adipose fin.

Family KNERIIDAE. With toothless non- protractile jaws, small
scales, opercular membranes confluent, a narrow gill -opening, pelvic
fins with nine dermotrichs.

Kneria, St. ; rivers of Tropical Africa.

400

TELEOSTEI

Family CHIROTHRICIDAE. Premaxillae very slender. Teeth small
or absent ; sometimes dermal scutes. The fins are remarkably large,
the pelvics being of enormous size, with some eighteen dermal rays, and
placed far forwards quite near the pectorals. The family is known from
the Cretaceous only.

Fio. 391.
Alepidoscmnis ferox, Lowe. (From Jordan and Evermann.)

Chirothrix, P. and H. ; Telepholis, van der M. ; and Exocaetoides,
Davis — Cretaceous, Europe and Asia Minor.

Family CYPRINODONTIDAE. The mouth is protractile ; teeth are
present on the jaws and pharyngeals, but rarely on the palate ; the
palato- quad rate arch is more or less reduced. Not more than seven
pelvic dermal rays. The air-bladder may be lost.

FIG. 392.
Cetomimus Gillii, G. and B. (From Jordan and Evermann.)

The Cyprinodonts, which are often of extremely small size,
frequently exhibit remarkable sexual differences, the male being
smaller and more brilliant in colouring. In the male the anal fin
may be modified to serve as an intromittent organ (Fig. 393). They
are often viviparous.

Procatopus is distinguished by having the pelvic fins far forward
below the pectorals, and Anableps by a remarkable adaptation of its
eyes for seeing both in the air and in the water as it swims at the
surface, the cornea being divided into two dissimilar halves (Fig. 394).

ESOCIFORMES

401

GROUP A. Carnivorous ; with strong jaws and short intestine.
Anableps, Art. (Fig. 394); America. Gambusia, Poey (Fig. 393) ; America.
Orestias, C. and V. ; mountains of S. America. Prolebias, Sauv. ; and
Pachylebias, A. S. W. — Miocene, Europe. C'yprinodon, Lac. ; America and

Fm. 393.
Gambusia affinit, Brcl. and (ir«l., male. (From Jordan and Evermaim.)

Mediterranean region. Haplochilus, M'Cl. ; America, India, Africa.
Fundulus, C. and V. ; Europe, America, Africa.

GROUP B. Mud-eating ; with long convoluted intestine and weak
jaws. Poecilia, Gthr. ; Mollienesia, Les. ; Platypoecilus, Gthr. ; Girardinus,
Poey — S. America.

Family AMBLYOPSIDAE. Closely related to the Cyprinodonts • but
with a scarcely protractile mouth, and pelvic fins vestigial or absent.
The anus moves forward to near the head. Viviparous.

vii, Gill. (From Jordan and Evermaim.)

Some, like Choloyaster, live in the open, and are pigmented and
provided with normal eyes. Others, like Amblyopsis and Typhlichthys,
live in caves, and lose their colour and their eyes.

Chologaster, Ag. ; AmUyopsis, De Kay (Fig. 395) ; Typhlichthy*,
Ger. — N. America.

SUB -TRIBE D. The air-bladder is closed, the lower pharyngeals

26

402

TELEOSTE1

are fused, long parapopbyses bear ribs, and there are lateral longi-
tudinal rows of ridged scales.

FIG. 305.
AvMyopgis sjielaeus, De Kay. (From Jordan and Evermann.)

Family SCOMBRESOCIDAE. The air-bladder may be cellular, the
stomach is indistinctly marked, and the maxilla is not excluded.
The post-temporal is simple, and the post-clavicle lost. Scales cycloid.
Sometimes there is a series of dorsal finlets (Scombresox}. In Hemirhannphus

Fio. 396.
Exocoetus callopterus, Gtlir. (After Giinther.)

the lower jaw, and in Belone and Scombresox both jaws are prolonged into
a slender beak. The pectoral fins acquire a large size, especially in the
Flying-Fish Exocoetiis (Fig. 396) ; and the pelvic fins may also be enlarged.
It is interesting to compare these modifications with those 'Flying- Fish'

Fio. 397.
llemirhamphus brasiliensis, L. (From Jordan and Evermann.)

belonging to other groups (Pholidophoridae, Semionotidae, Dactylopteridae ;
Abel [1]). Hemirhamphus is sometimes viviparous, and the anal fin may
be modified into a copulatory organ, as in Cyprinodonts.

ESOCIFORMES 403

SUB-FAMILY 1. BELONINAE, with zygapophyses, and the maxilla fused
to the premaxilla ; Belone, Guv., Gar-Fish. SOB-FAMILY 2. EXOCOETINAE,
with separate maxilla, no zygapophyses, and enlarged third upper
pharyngeals ; Scombresox, Lac. ; Hemirhamphus, Cuv. (Fig. 397) — tropical
and temperate seas ; and Eocene, Europe. Arrhamphus, Gthr. ; Pacific.
Exocoetus, Art. (Fig. 396) ; tropical seas.

INCERTAE SEDIS.

Family AMMODYTIDAE. A small family of elongated marine fish,
whose systematic position is very uncertain ; they are placed near the
Scombresocidae by Boulenger, in the Ophidiidae by many authors.

In the extinct Cobitopsis the pelvic fins are present and abdominal,
in the modern forms they are lost. The parietals are separated, the

FIG. 398.
americanus, De Kay. (From Jordan and Evermanu.)

maxillae excluded from the margin of the mouth, which is protractile,
the scales small and cycloid, the teeth small or absent, the air-bladder
absent, and there are no parapophyses.

Ammodytes, L. (Fig. 398), Sand Eel ; Northern hemisphere.
Hypoptyehus, Steind. ; Japan. Cobitopsis, Lorn. ; Oligocene, France.

Series 2.
Sub-Order 2. ANGUILLIFORMES (Apodes).

The Eels are a highly specialised group. They acquire a very
elongated shape ; the median fins are extremely long and usually
confluent behind ; the tail is truncated, both hypural bones and
caudal fin being lost, and ends in a symmetrical gephyrocercal tip
{Fig. 400). The paired fins also tend to disappear, traces of the
pelvics being found only in the extinct Urenchelys, which is also
remarkable for the possession of a caudal fin (A. S. Woodward
[504-5], Hay [205]). As a rule, the number of vertebrae is greatly
increased, and the notochord persists more than usual among
modern Teleosts. The parietals meet above. It is in the visceral
skeleton that the modifications are most conspicuous. Normal
premaxillae are never found ; either they have been lost or they
have fused with the ethmoid and vomer (Fig. 402) ; these two bones
coalesce. The maxillae themselves may be absent (Muraenidae) ;
.and even the ptery go -quadrate arch may become discontinuous

404

TELEOSTEI

(Muraenidae), or disappear (Synaphobrauchidae, Saccopharyngidae).
In fact, the interpretation of the bones of the upper jaw is often
doubtful. The symplectic is absent, and the mandible contains
only an articular and a deritary.

The pectoral girdle has become freed from the skull, there
being no post-temporal (Fig. 399). Often more than five radials
are found in the pectoral fin, a peculiarity which is to be noticed
in Gymnotus and the Muraenolepidae.

'f.

r.

Fia. 399.

Skeleton of the left half of the pectoral girdle and of the tin of Anguillu vulgnris, L.
c, coracoid ; cl, cleithrum ; /, foramen ; r, eighth radial ; s, scapula ; scl, supraclavicle. The-
cartilage is dotted.

The scales are rudimentary or absent. -The branchial opening
becomes much narrowed ; the air-bladder has an open duct and
there are no pyloric caeca. The ova are discharged through mere
genital pores (p. 367).

The remarkable deep-sea form, long known as Leptocephalus, has
been shown to be the larval stage of the Anguilliformes, which
metamorphoses into the elver ; the latter grows into the adult
form (Delage [Ilia], Grassi [182o]).

Division 1. ARCHENCHELI.

The caudal fin and hypural bones are still present, also the-
pelvic fins. The jaws are toothed, and the palatopterygoid arch
is normally developed. The scales are vestigial or absent.

Family URENCHELIDAE. Represented by extinct genera from Cre-
taceous strata.

Urenchelys, A. S. W. ; Cretaceous, England and Mt. Lebanon.
Anguillavus, Hay ; Cretaceous, Mt. Lebanon.

ANGUILLIFORMES

405

Division 2. NEENCHELI.
The pelvic and caudal fins have been lost.

GROUP A. ENCHELICEPHALI.

Toothed maxillae are present, and the palatopterygoid arch is
usually complete.

Family ANGUILLIDAE. The skull is well ossified ; but the bones are
sunk deeply, and only one of the circumorbital series remains in front.
The opercular bones are of moderate size, and the branchial arches well

Fio. 400.
Labichthys carinatus, G. and R. (From Jordan and Evermann.)

developed (Fig. 402). The branchiostegal rays long and curled inwards.
Anguilla, Sinenchelis, and Ilyophis have vestigial scales.

Eomyrus, St. ; Ehynchorhinus, A. S. W. ; Eocene, England. Anyuilla,
Shaw ; widely distributed, and Eocene, Europe. Nettastoma, Kaf. ;

FIG. 400*.
Derichthys serpentinitf, Gill. (From Jordan and Evermann.)

Pacific, Mediterranean ; and Eocene, Europe. Sinenchvlys, Gill ; Ilyopliys,
Gilbert — deep-sea. Conger, Kp. ; Congromuraena, Kp. ; Uroconger, Kp. ;
Myrus, Kp. ; Ophichthys, Gthr. ; Moringna, Gray.

406

TELEOSTE1

Family NEMICHTHYIDAE. Small and extraordinarily slender deep-
sea eels with the anus near the head, and often the jaws produced into
delicate diverging points.

NemichthySj Rich. ; Dysomma, Ale. ; Spinivomcr, G. and II. ;
Labichthys, G. and B. (Fig. 400) ; GavMiceps, Ale. ; warm seas.

Family DERICHTHYIDAE. Another small deep-sea eel with a snake-like
neck. The maxillae are fused to the skull.

Derichthys, Gill (Fig. 400A) ; Atlantic.

A NG UILLIFORMES

407

Family SYNAPHOBRANCHIDAE. Deep-sea forms in which the pterygo-
palatine arch is lost, and the branchial openings are confluent below.
There are small scales.

Synaphobranchus, Johns.

Family SACCOPHARYNGIDAE. Extraordinarily modified deep-sea eels
with a much-reduced skeleton. The mouth is enormously enlarged, the
palato-quadrate arch incomplete, the hyomandibular very movable, and
the jaws greatly lengthened (Fig. 401, D). Mere loose rods represent the
gill-arches, and the branchiostegals have been lost.

A small flexible snout overhangs the mouth, and close behind it are
the small eyes.

Saccopharynx, Mitch. (Fig. 401, D); Ewypharynx,Vai\\. ; Macropharynx,
Br. ; Gastrostomns, G. and R. — Atlantic.

2 3

20

Fiu. 40:?.

Left-side view of skull and hyoid arch of the Conger Eel, Conger vulgaris, Cuv. 1, vomer ;
2, preorbital ; 3, na.sal ; 4, ethmoid ; 5, frontal ; (5, postfrontal ; 7, parietal ; 8 and !>, supni-
occipital ; 10, pterotic ; 11, hyomandibular ; 12, epibranchial ; 13, opercular ; 14, branehiostegal ;
15, subopercular ; 10, interopercular ; 17, preopercular ; 18, angular ; 19, urohyal ; 20, cerato-
hyal ; 21, articular ; 22, basihyal ; 23, dentary ; 24, maxilla; 25, pterygoid ; 26, quadrate ; 27,
parasphenoid.

GROUP B. COLOCEPHALI.

The head is much compressed, the palatal bones very abnormal,
and the place of the premaxilla and maxilla seems to be taken by
the toothed ethmo - vomer and pterygoid. Behind the palato-
pterygoid arch is incomplete ; the hyomandibular bearing the
quadrate is firmly attached to the skull. The opercular bones
are all present, but very small. The mouth is often provided
with very formidable teeth pointing backwards. The branchial

408

TELEOSTEI

apparatus is usually reduced, and the branchiostegals delicate
or absent. The gill-opening is narrowed to a small round aperture,
and the gill-clefts small. The pectoral fins, and even the girdle,
may be lost.

Family MURAENIDAE. The body is scaleless and generally conspicu-
ously coloured. The tail is very long (Fig. 403).

FIG. 403.
Mtiraena pieta, Alii. (After Giinther.)

Muraena, L. ; Thyrsoidea, Kp. ; Myroconger, Gthr. ; Enchelycore, Kp. ;
Lycodontis, McCl. ; Channomuraena, Rich.

Series 3.
Sub-Order 3. SYMBRANCHIFORMES.

A small group of very highly specialised fish whose affinities
cannot yet be determined. They have a superficial resemblance to
the Eels, from which they differ in many important osteological
characters, and in the possession of closed ovisacs. The air-bladder
is absent.

The skull is like that of the Clupeiformes ; the parietals
meet, the maxillae, however, are almost excluded from the margin
of the mouth, and the hyopalatine arcade is closely fitted to
the narrow, firmly ossified cranium. The trunk being much
lengthened and the tail short, the anus is usually far back, and
there are a large number of vertebrae. In Ckilobranchus the tail
is long. Strong parapophyses bear short ribs. The centra are
slightly opisthocoelous.

S YMBRANCHIFORMES

409

The branchial openings have joined in a single ventral
opening (Fig. 405) ; the opercular bones, and especially the gills,
become reduced, respiration is carried on chiefly in the wall of
the buccal cavity and intestine,

conse-
(Hyrtl

and the circulation is
quently much modified
[233i], Volz [475]). The
dorsal aorta is formed by the
junction of the last pair of
aortic arches, which are complete
(Fig. 404) ; the jugulars return
the blood from the head and
other arches directly to the
heart.

The scales are either minute
(Amphipnoidae) or altogether
absent (Symbranchidae). Dermal
folds without lepidotrichia alone
represent the vestiges of the
median fins ; and the paired fins
have been lost, leaving only a
slender pectoral girdle, attached
to the skull in the Symbranchi-
dae, but free in the Amphipnoi-
dae.

Unknown in the fossil state,
these peculiar fish, which have
now been separated from the
Anguilliformes and placed in a
special sub -order, may have
been derived from some primi-
tive group which had lost
the mesocoracoid arch, or
perhaps even from some
member of the Clupeiformes
or Esociformes (Boulenger
[42]).

t---Acf

FIG. 404.

Diagram of the circulation in Monopterus
/«r««f »-;.s, Lac. The right kidney and its veins
have been removed ; the right jugular vein is
incomplete. Arrows show the direction of the
blood-stream. White vessels contain arterial
blood, shaded vessels mixed, and black vessels
venous blood. I-IV, four gill-arches; A.c,
coeliac artery ; A.<!, dorsal aortii ; HA, bulbus :
c, carodid ; C.V, caudal vein; D, gut; D.C,
ductus Cnvieri ; L, liver ; X, kidney ; R.A = IV,
radix aorta; V, ventricle; V.r, cardinal vein;
I'.li, hepatic vein; V.jd, right jugular vein;
V.js, left jugular vein ; V.fi, portal vein ; x,
attrrent vessel of third gill-arch. (From W.
Volx.)

Family SYMBRANCHIDAE. The

, . .,, ,

post-temporal is still present and

attached to the skull. Symbranchus

has well-developed gills ; but Monopterus has only vestigial gill-lamellae

on three arches.

Symbranchus, Bl. (Fig. 405) ; America, E. Indies. Monopterus, Lac. ;
E. Indies and Archipelago.

Family AMPHIPNOIDAE. The slender pectoral girdle is free, the post-
temporal having been lost. Gill-lamellae are found on the second arch

410

TELEOSTE1

only, and are supplemented by two extensible lung-like air-sacs, backward
prolongations of the branchial chamber.
Amphipnous, Mull. ; E. Indies.

AAV

5 * ****'

.11 V

Fie. 40-5.
Symbranchus bengalensi*, M'Cl., ami upper teeth. (After Day, Fishes o////<'i<<.)

Series 4.

Sub-Order 4. G AST EROST El FORMES (Catosteomi, Hemibranchii,
Lophobranchii).

This sub-order is an assemblage of fish for the most part highly
specialised, which were first brought together by A. S. Woodward.
The Flute-mouths (Fistulariidae) and Sticklebacks (Gasterosteidae),
which Cope had already united in the group Hemibranchii, and the

d.

sc.

br. pop.iop. scf)

FIG. 40ti.

Skull and pectoral girdle atGasterottetugpinaekla. an, angular ; ar, articular ; a.so, anterior
suborbital ; br, branchiostegal ; cl, cleithnim ; co, coracoid ; d, dentary ; d.c, dermal coracoid
plate ; d.f, dorsal fin spine ; d.pl, dorsal dermal plate ; fr, frontal ; 1. pi, lateral dermal plate ;
mx, maxilla ; n, nasal ; no, nostril ; op, opercular ; pa, parietal ; pmx, premaxilla ; pop, pre-
opercular; prf, prefrontal ; p&t, post-temporal ; ptf, postfrontal ; ptn, pterotic ; q, quadrat*- ;
r, radial of pectoral fin ; so, scapula ; so./, scapular foramen ; so, suborbital ; soc, supraoccipital ;
sop, subopercular ; st, supratemporal.

Pipe-Fishes (Lophobranchii of Cuvier), have been shown to be
related (A. S. Woodward [505], Swinnerton [431], Starks [419],
Gill [164]).

The snout becomes greatly produced by the elongation of the
region between the orbit and the mouth ; the nostrils remain near

GASTEROSTEIFORMES

411

bm

the eye, and the mouth becomes terminal (Figs. 410-13). The
maxillae are toothless, and almost or quite excluded from the margin
of the gape. The branchial apparatus becomes reduced. The
cranial bones remain superficial ; the frontals joining the supra-
occipital, and separating the parietals when these are present
(M'Murrich [289]). Ectopterygoids are generally absent. A short
eye-muscle canal may be present, but it is usually vestigial or
absent. The post-temporal is never typically forked, and is usually
fixed to the skull. The supra- and postclavicle are generally absent.
A foramen is present in the scapula, or between it and the cleithrum.

The paired fins are often reduced, especially the pelvics, which
are abdominal in position. Typical scales are rarely present, being
generally represented by rows of scutes of an osseous substance
without bone-cells. These scutes
may be ankylosed to the endo-
skeleton, and may form a complete
armour in Lophobranchs. Large
paired scutes come into secondary
connection with the limb -girdles,
and are almost always present,
firmly fused in the adult to the
ventral edge of the coracoids (Figs.
406, 407). It is these bony plates
which were formerly supposed to
represent ' infraclavicles ' (true
clavicles), homologous with those
of the Chondrostei and Osteolepi-
doti. Spines are sometimes pre-
sent in the fins (Gasterosteoidei).
The canal of the lateral line, the
mesentery, and the pyloric caeca
are lost as a rule. The gills are
reduced to four or less.

Most of the families of the
Gasterosteiformes can be traced back-
to Eocene deposits. The origin of
the sub-order is still quite unknown.

FIG. 407

TRIBE 1. GASTEROSTEOIDEI (Hemi-
branchii, in part).

Ventral view of the trunk of Gasteroste us
spinachia, L. a, anus ; n.f, spine of anal
fin ; b.m, confluent branchiostegal mem-
1 , branes ; dc, dermal plato attached to pec-
1 toral girdle ; l.pl, lateral dermal plates ; op,

The Sticklebacks are the

modified of this sub-order. The skull operculum ; p, dermal plate attached to
e f • i , pelvic girdle ; p.f, pelvic fin spine ; pt.f.

IS Ot iairly normal structure, the an- pectoral fin ; «-, uriuogenital opening.

terior region not excessively prolonged

(Fig. 406). The body is elongated, scaleless, and usually provided with

412

TELEOSTEI

lateral and dorsal rows of scutes. Large paired scutes are attached to
the pelvic as well as to the pectoral girdles (Fig. 407). The pelvic fina

FIG. 408.
Gasterosteus aculeaius, L. (After Heckel and Kner, from Clans and Sedgwick.)

have one or two spines, and sometimes one or two jointed dermotrichs.
The pectoral radials are quite short (Fig. 406). The anterior region of
the dorsal fin is represented by a series of finlets with
isolated spines (Fig. 408). The anal fin has an anterior
spine.

Family GASTEROSTEIDAE. The ribs are slender and
free, and the pelvic fins have not more than two
jointed dermotrichs.

Gasterosteus, Art., Sticklebacks (Fig. 408) ; Apeltes,
De K. ; Eucalia, Jord. ; Spinachia, L. — Northern
hemisphere.

Family AULORYXCHIDAE. With a longer and more
tubiform snout, an elongated body, and four jointed
dermotrichs in the pelvic fin. The ribs are expanded
and fixed to the lateral scutes.
•A ulorhynchus, Gill ; N. Pacific.

\

TRIBE 2. HEMIBRAXCHII.

FIG. 409.
Ankylosed anterior

The snout is extremely long and tubiforni, the
skull consequently much modified, the symplectic
and neighbouring bones being much lengthened. The
pelvic fins are spineless, with from three to six
lepidotrichia. The ribs are reduced or absent, but
parapophyses are usually present. This Tribe is
distinguished by the specialisation of the anterior
vertebrae, four of which generally become enlarged,
fou r vertebrae of Fiatu- elongated, and often fused together (Fig. 409).

!Anaiomylfyfrtelnttel', SUB-TRIBE A. PROTOSYNGNATHOIDEI. Slender free

by permission.) r;bs are present, and the anterior vertebrae are

slightly elongated. This extinct group is less
specialised than the next.

Family PROTOSYXGNATHIDAE. Protosyngnathus, v. d. M. ; Tertiary of
Sumatra.

SUB -TRIBE B. AULOSTOMOIDEI. The body is very elongate ; the occip-
ital condyle becomes distinctly convex, and long ossified ligaments extend

GA S TEROS TE I FORMES

413

backwards from the epiotic region and the pectoral girdle, somewhat as in
the Mugilidae. The pectoral radials are of normal shape and rather large.

Family AULOSTOMATIDAE. The body is covered with small ctenoid
scales, and there are isolated dorsal fin spines. The suborbitals are lost,
and the palatines united and fused to the skull. Each of the transverse
processes is formed from two adjacent vertebrae.

Aidostoma, Lac. ; Atlantic ; Eocene, Europe.

FIG. 410.
Fistularia serrate, Cuv. (After Day, Fishes of India.)

Family FISTULARIIDAE. The body is quite naked or with vestigial
scutes, and without dorsal fin spines. The caudal fin bears a long fila-
ment supported by the middle lepidotrichia.

Fistularia, L. (Fig. 410) ; tropical Atlantic and Indo- Pacific Oceans ;
and Eocene, Europe.

FIG. 411.
Centriscus humerosvs, Rich. (After Giiuther.)

SOB-TRIBE C. CEXTRISCOIDEI. With a comparatively short compressed
body, an anterior dorsal fin with a stout spine, very short pectoral
radials, no ribs, no suborbital?, and no teeth.

Family CENTRISCIDAE. The body is covered with rough scales, and
scutes, some of which are fused to the neural spines and to the transverse
processes of the modified anterior vertebrae.

Rharnphosus, Ag. ; Eocene, Italy. Centriscus, Cuv. (Macrorhamphosus,
Lac.) (Fig. 411); Atlantic and Pacific.

Family AJIPHISILIDAE. Scaleless, but with a complete armour of
scutes fixed to the endoskeleton. The tail is shortened and twisted
ventrally, the dorsal fin projecting beyond it.

414 TELEOSTEI

Amphisile, Guv. (Fig. 412) ; Indo-Pacific Ocean ; and Eocene and
Oligocene, Europe.

Amphisile scutate, L. (After Day, Fishes of Iiulict.)

TRIBE 3. LOPHOBRANCHII.

Toothless elongate fish, with scutes, very small pectoral radials, no
air-bladder, and gill-laniellae in the form of rounded lobes.

SUB-TRIBE A. The anterior division of the dorsal fin is spiny. The
pelvic fins of the female coalesce to form an egg-pouch.

Family SOLENOSTOMIDAE. Solenostomus, Lac. ; Indian and Pacific
Oceans.

SOB-TRIBE B. With spineless fins and scaleless body, enclosed in seg-
mental rings of armour formed by overlapping scutes attached to the vertebral

Fio. 413

Syngnathus acus, L. A, left-side view of the anterior region ; B, the left branchial chamber
exposed by the removal of its outer wall ; C, enlarged view of a portion of a branchial arch ; D,
skeleton of the right half of the pectoral girdle and fin, inner view ; E, portion of the tail— a
caudal vertebra is shown behind, and a portion of the notochord is exposed. 6;-, branchial
lamella ; c, coraco-scapular cartilage ; d, cleithrum ; c.o, cut opercular wall ; d.c, distal
cartilage supporting lepidotrich ; e, eye; g, gill; g.b, gill-bar; g.r, gill-raker; m, mouth; n,
nostril ; nt, persistent constricted notochord ; op, operculum ; p.f, pectoral iin ; pi, bony
dermal plate ; r, 5th radial ; sp, opening of branchial chamber ; v, vertebra.

GA S TEROS TEf FORMES

415

processes. The pectoral radials are very small, with a row of distal cartilages
(Fig. 413, D). The pelvic fins are absent in the adult, though traces of

FIG. 414.
Sijnyni'thux I"'**, L., &, with subcaudal brood-pouch. (After Giinther.)

them appear in the embryo Nerophis (Huot [233]). The tail is attenuated
with a small fin, or it is prehensile and finless (Nerophis, Hippocampus}.
The skeleton is to a great extent cartilaginous, and the notochord
largely persistent, though constricted. The
visceral skeleton is much reduced, and the
four gills are considerably modified. The
lamellae have lost their pectinate character,
become less numerous, and acquired a
rounded shape- (Fig. 413, B, C). The
branchial openings are narrowed to small aper-
tures dorsally placed (Fig. 413, A). Brood-
pouches are generally developed in the male.

Family SYNGNATHIDAE. With a very
elongated body. The pectoral fins have been
lost in Nerophis and Gastrotoceus. The latter
carries its eggs in a soft abdominal mem-
brane, and Synynathus on its belly without
pouch ; but in others the eggs are carried in pec-
toral, abdominal, or subcaudal ventral pouches.

Synrjnathus, L. (Fig. 414), temperate and
tropical seas ; and Eocene, Europe. Siphono-
stoma, Kaup., Atlantic ;- Miocene, Europe.
Calamostoma, Ag. ; Pseudosyngnathus, K. and
S. ; Eocene, Europe. Nerophis, Kp.; Atlantic,
Indian. Ocean.

Family HIPPOCAMPIDAE. The scutes are
buttressed, and immovable sideways. The
head is bent at right angles to the body, and ventral brood-pouch.* (From ciaus

, ., . i. -i rni and Sedgwick.)

the tail is curved and prehensile. There

is a ventral ovisac. The ' Sea-Horses ' are among the most specialised of
fish in general structure, and sometimes they are further provided with
branching dermal processes simulating seaweed (Phyllopteryx).

Hippocampus, Leach (Fig. 415) ; temperate and tropical seas.

Phyllopteryx, Svv., and Gastrotoceus, Kp. ; Pacific.

FIG. 415.
Male of Hippocampus sp.

4i6

TELEOSTEl

TRIBE 4. HYPOSTOMIDES (Incertae sedis).

A small group of highly specialised fish the systematic position of
which is very uncertain, although they are usually associated with the
Lophobranchs.

The body is short and depressed; the head produced into a long
snout beyond the mouth, which is small, ventral, and toothless. Rings

FIG. 416.
Pegasus natans, L. (After Giinther.)

of scutes cover the body. The gill-opening is very small. The enlarged,
horizontal pectoral fins bear five spinous dermotrichs. Pelvic fins are
represented by a few dermal rays behind the pectoral. There are no
ribs, no air-bladder, no symplectic, and no preopercular.

Family PEGASIDAE. Pegasus, L. (Fig. 416) ; Indo-Pacific.

Series 5.
Sub-Order 5. NOTACANTHIFORMES (Heteromi).

This is a group of highly specialised, mostly deep-sea fish, of
somewhat doubtful affinity, to which have been added the extinct
Dercetidae. In the modern forms the caudal region is relatively
long, with a tapering extremity from which the caudal fin has dis-
appeared. A snout is usually present (especially in the Halosauridae
and Notacanthidae). The pelvic fins are abdominal, and the median
fins may be spiny. The duct of the air-bladder is closed. The
parietals meet in a median suture, and the pectoral girdle is joined
to the skull by a reduced simple post-temporal, attached to the
supraoccipital, or by a mere ligament. When present, the scales
cover the head as well as the body.

This sub -order was founded by Boulenger [42] to include
the Lyopomi and Heteromi of Gill, highly specialised deep-sea fish,
and a few other doubtfully related genera.

NOTACANTHIFORMES 417

DIVISION 1.

There are separate dorsal, anal, and caudal fins.

Family DERCETIDAE. An extinct family of fish with elongate body,
extended dorsal and short anal fin, seven or eight dermal rays in the
pelvic fin, and no spines. The scales are vestigial, either very small or
absent ; but a row of large scutes extends along each side. There is a
snout, a large mouth bordered by the premaxillae, and small teeth.
These Cretaceous fossils possibly represent a stage in phylogeny before
the caudal fin was lost.

Dercetis, Ag. ; Europe. Leptotrachelus, van der M. ; Europe and
Asia. Pelargorhynchus, van der M. ; Stratodus, Cope — North America.

DIVISION 2.

The tail is pointed, and the caudal fin has been lost, while the
anal has become very long. The pectoral fins are generally inserted
high up, especially in the Notacanthidae and Halosauridae.

TRIBE 1.

There are cycloid scales, and the anus is normally situated.

Family HALOSAURIDAE. The border of the small mouth is formed
by the premaxillae and maxillae, both provided with minute teeth. The
preopercular is vestigial. All the dermal rays are soft, the dorsal fin is
short. A canal for the notochord pierces the centra. The ova are shed
freely into the coelom. Halosauropsis has phosphorescent organs along
a series of enlarged lateral scales.

FIG. 417.

HulifiKii-Hjms nigerriinus, showing the phosphorescent organs lodged in the large
scales of the lateral line. (After Alcock, Katuralist in Indian SKI*.)

Echidnocephalus, van der M. ; Enchelurus, van der M. — Cretaceous,
Europe and Mount Lebanon. Halosaurus, Johnson ; Halosauropsis, Coll.
— deep-sea (Fig. 417).

Family LIPOGENYIDAE. The genus Lipogenys differs from the pre-
ceding family chiefly in the possession of spines in the anal fin and three
spines in the pelvic fin, and in the modification of the mouth, which is
small, suctorial, and ventral. The jaws are toothless and specialised.
Small scales cover the body.

Lipogenys, G. and B. ; North Atlantic (Fig. 418).

27

4i8

TELEOSTEI

Family NOTACANTHIDAE. The dorsal fin is represented by a series
of separate spines. Spines are also found in the anal and pelvic fins.

FIG. 418.
Lipogenys Gillii, G. and B. (From Jordan and Evermann.)

Fio. 419.
Notacanthus analis, Gill. (From Jordan and Evermann.)

The preraaxillae alone enter the margin of the small inferior mouth.
The suborbitals and post-temporal have been lost.

Notacanthus, Bl. ; depths of the Mediterranean, Atlantic, and Pacific
(Fig. 419).

TRIBE 2.

Scaleless fish, with the anus near the head ; a situation which may
be related to their habit of living inside other animals, such as Bivalves
and Holothurians.

FIG. 420.

t'icrasfer acus, Kaup ; one specimen emerging from a holothurian.
(After Emery, from Dean.)

NOTACANTHIFORMES 419

Family FIERASFERIDAE. The dorsal fin is elongated like the anal.
Only the premaxillae border the small inferior mouth. Special muscles
are developed for dilating the front end of the air-bladder. Neither
pelvic fins, nor spines, nor pyloric caeca, nor suborbitals are present.
There are exoccipital paired condyles, not found in other Xotacanthi-
formes (Emery [131]). Possibly belonging to the Zoarcidae.

Fierasfer, Cuv. ; widely distributed (Fig. 420).

Series 6.

In these fish the air-bladder loses its open communication with
the gut, except in the Stephanoberycidae and some of the lowest
Acanthopterygians (p. 426) ; the toothless maxilla is usually com-
pletely excluded from the margin of the mouth ; the supraoccipital
meets the frontals so as to separate the parietals ; and several
anterior dermal rays of the dorsal and of the anal fin, and the
front dermal ray of the pelvic fins, as a rule, become converted into
jointless spines (p. 424).

Sub-Order 6. MUGILIFORMES (Percesoces).

The families included in this sub-order form an assemblage of very
doubtful phylogenetic value (Starks [418]). They are not bound
together by any very distinctive characteristics, and most of those
modifications which do occur — such as the development of spines, and
the moving forward of the pelvic girdle, which may become joined
to the pectoral girdle by ligament — are approximations to the Acan-
thopterygian type of structure. Again, the constant presence of
one spine and five (or not more than five) jointed dermotrichs
in the pelvic fins, except in the Ophiocephalidae and aberrant
Icosteidae, strongly suggests affinity with the Perciformes. As a
rule, scales completely cover the head. The Mugiliformes are not
known for certain to occur below the Eocene strata.

TRIBE 1.

With two separate dorsal fins, the anterior with spines. Except in
the Sphyraenidae, the pelvic bones are attached by ligament to the
symphysis of the cleithra, and ribs are borne by strong parapophyses.

SUB-TRIBE A. Family SPHYRAENIDAE. With free pelvic bones, and
sessile anterior ribs. The large mouth is armed with formidable teeth.
With cycloid scales.

Sphyraena, Bl., Sch. ; warm seas ; Eocene, Europe and N. America.

SUB-TRIBE B. Family ATHERINIDAE. The pelvic bones are connected
by ligament to the cleithra. The pectoral fins are inserted high up.
With cycloid or ctenoid scales.

420

TELEOSTEI

Atherina, L. ; Atlantic, Mediterranean ; Eocene, Europe. Rhampho-
gnathus, Ag. ; Eocene, Europe. Chirostoma, Sw. ; Labidesthes, Cope ;
Menidiu, J. and G. — America.

SUB-TRIBE C. Closely related families distinguished by a strange modi-
fication of the girdles : the pelvic bones are not attached to the cleithra,

FIG. 4-21.
Mugil cephalus, L. (From Jordan and Evermann.)

but are firmly connected with, and supported by, the postclavicles, a
very peculiar modification paralleled only in the Centriscidae.

Family MUGILIDAE. The Mullets are distinguished by the possession
of a very perfect filtering apparatus on the gill-arches, formed by the gill-
rakers ; and peculiarly modified pharyngeals. The oesophagus has long

FIG. 4-22.
Pentanemus quinquarius, L. (After Giinther.)

thin internal papillae, and there is a muscular gizzard -like stomach.
The scales are cycloid, and the pectoral fins are inserted high up.

Mugil, L. (Fig. 421), Grey Mullets ; wide range ; Oligocene, Europe.
Myxus, Gthr. ; Anostomus, Gron. ; Joturus, Poey.

Family POLYNESIIDAE. The scales are ctenoid, and the pectoral fins-
are low down. The pectoral fin radials appear to have fused with the

MUG1LIFORMES 421

scapula to form a ventral prolongation, supporting a fascicle of fila-
mentous dermal rays separate from the main fin (Fig. 422) ; a highly
specialised condition.

Pentanermis, Art. ; Polyncmus, L. ; Galeoides, Gthr. — tropical seas.

TRIBE 2.

With one dorsal fin, of which the front portion may be spinous.
The anterior vertebrae without parapophyses and with sessile ribs.

SUB-TRIBE A. The dentition is very feeble ; the pseudobranch is
provided with a row of gill-rakers ; and the oesophagus has two lateral
pouches beset with internal papillae.

Family TETRAGONURIDAE. With a pair of lateral keels near the end
of the tail ; specialised rhomboidal scales set in obliquely transverse
rows, in each of which the scales are connected together ; and with free
pelvic girdle. The air-bladder is lost.

Tetragonurus, Risso ; warm seas.

Family STROMATEIDAE. These are closely related to the preceding ;
but they have cycloid scales, the pelvic bones may be attached by liga-
ment to the cleithra ; and the body becomes very deep and compressed,
much as in Lampris. The air-bladder and the pelvic fins may be lost.

Nomeus has enormous pelvic fins, which fold in ventral grooves.

Platycormus, V. D. M. ; Homosoma, Eocene. Nomeus, Cuv. ; Cubiceps,
Lowe ; Stromateus, Art. ; Centrolophus, Lac.

SUB-TRIBE B. Family ICOSTEIDAE. Although lacking both spines
and oesophageal pouches, the aberrant Rag-Fish are probably allied to
the Tetragonuridae, which they resemble in the possession of gill-rakers
near the pseudobranch. The vertebrae have increased in number (70) ;
the scales when present are cycloid, and the pelvic bones are free.

Icosteus, Lock ; Icichthys, J. and G. ; Acrotus, Bean — Pacific American
coast.

TRIBE 3.

The head is covered with large scales ; there are generally para-
pophyses bearing the ribs ; and a distinguishing character is the

FIG. 4:23.
Ophiocephalus striatus, India. (After Giinther.)

possession of an accessory suprabranchial chamber. The branchiostegal
membranes are confluent below the isthmus. The pelvic bones are joined
by ligament to the cleithra.

422

TELEOSTEI

SCB-TRIBE A. Without spines, and with pelvic bones some way behind
the cleithra.

Family OPHIOCEPHALIDAE. With large suprabranchial cavities, into
which project vascular folds from the wall (Fig. 424). Cycloid scales.
Channel has lost the pelvic fins.

Ophiocephalus, Bl. (Fig. 423) ; Asia. Channa, Grom. ; Africa.

SUB-TRIBE B. LABYRIXTHICI. With ctenoid scales, and a more or less
spiny border to the opercular bones ; the pelvic bones quite near the
cleithra ; and the broad intergular membrane covered with large scales.

Into the suprabranchial chamber
project thin vascular lamellae sup-
ported by bone from the first
branchial arch (Fig. 425) (Hen-
ninger [209], Cuvier [95], ZografF
[514], Day [101]). Spines occur
on the anal and dorsal fins. The
body is broad and compressed.

Family ANABANTIDAE. The
vascular lamellae are most elabo-
rate, the pelvic girdle only loosely
attached ; the pelvic fins have a

FIG. 424.

Ventral view of left half of head of Ophioce-
phctlus striatus, BL, from which the lower jaw,
etc., have been cut away to expose the gullet and
the branchial cavities. 1, accessory branchial
cavity into which project respiratory folds ; 2,
operculum ; 3, branchial cavity ; 4, toothed
superior pharyngeal plate ; 5, oesophagus.

Head of Ancbas scandens, Dald. (After
Cuvier, from Sedgwick's Zoology.) The
operculum has been removed to show the
excavated superior pharyngeal (fharyngo-
branchiate).

spinous and five soft dermal rays, and the cranial bones have a smooth
surface forming a complete covering to the head and cheeks. The
preopercular is movable, and said to be used in climbing.

Anabas, Cuv. ; E. Indies, Africa.

Family OSPHROMENIDAE. The cranial bones are more irregularly
sunk ; and the pelvic bones point upwards to the cleithra, with which
they are closely bound. The pelvic fins are modified ; the outer dermd-
trich being excessively long and jointed, while the others become reduced
(Fig. 426). The anal fin reaches far forwards.

Helostoma, K. and H. ; Betta, Blk. ; Osphromenus, Com. ; Trichogaster,

MUGIL1FORMES

423

FIG. 426.
OspTiromenits olfax, Comm. (After Giinther.)

Schrn. — E. Indies. Micracanthus, Sauv. ; Africa. Luciocephalus, Blk. ;
Polyacanthus, K. and H.

TRIBE 4.

Family CHIASMODONTIDAE. Of very doubtful relationship are these
voracious deep-sea fish. The skeleton resembles that of the Atherinidae,
but the operculum is reduced. The scales are small or absent.

Chiasmodon, Johns. ; Pseudoscopelus, Gthr. ; Champsodon, Gthr.

FIG. 427.

iasiMdon niger, Johns. ; obtained in the North Atlantic at a depth of 1500 fathoms ;
the specimen has swallowed a large tieopelus (s) ; o, pelvic fin. (After Giinther.)

TRIBE 5.

Family STEPHANOBERYCIDAE. The affinities of this family are yet
more uncertain. The pneumatic duct remains open ; the median fins
are spineless ; the pelvic fins are abdominal, and provided with 1 spine

424

TELEOSTEI

and 5 jointed dermal rays ; but the cranial bones are spiny, the scales
sometimes ctenoid (Stephanoberyx), and sometimes cycloid (Malacosarcus).
Stephanoberyx, Gill ; Malacosarcus, deep-seas (Fig. 428).

FIG. 428.
Stephanoberyx monae, Gill. (From Jordan and Evermann.)

Sub-Order 7. ACANTHOPTERYGII.

The cranial dermal bones are mostly deeply sunk and often
covered over with scales (Fig. 434 A). The parietals are separated
by the supraoccipital in the middle line, with rare exceptions
apparently due to secondary growth (Scorpaenidae, Cottidae, Trig-

Fio. 429.
Scorpaenopsis rosea. Day. (After Day, Fishes of India.)

lidae, and Zeidae (Ridewood [362]). The toothless maxilla is almost
or completely excluded from the margin of the mouth (Fig. 456).
The scales are ctenoid, and spines are generally developed on the
median and paired fins, and spiny processes on the opercular bones
(Fig. 429) ; the fin-spines show no sign of segmentation, unlike
those of the Ostariophysi they are rigid to the extreme tip ( Vaillant).
Perhaps the most remarkable and constant characteristic of the

A CA NTH OP TER YGII

425

sub -order is the fact that the pelvic fins are always very far
forward. Except in the Salmopercae, the pelvic bones' are attached
to the cleithra, and the pelvic fins are 'thoracic' or 'jugular,'
with usually much less than eighteen dermal rays. Excepting in a
few of the lowest genera, the pneumatic duct is closed. Among
more primitive characters may be mentioned a continuous dorsal
fin, the presence of a toothed palate, an eye-muscle canal, a scapular
foramen, both pleural ribs and epipleurals attached to them, and
four complete gills with five branchial slits. All these characters,
however, are liable to great modification in the more specialised
families, and it is in this sub-order that the Teleostei attain their
highest development.

Extremely numerous and diversified at the present time, the
Acanthopterygii make their appearance only in the Cretaceous
epoch. They may be classed in two Divisions, to the second of
which most of the modern forms seem to belong.

Division 1. SALMOPERCAE.

The pelvic fins are, strictly speaking, abdominal, not being
closely attached to the cleithral symphysis.

Family PERCOPSIDAE. An interesting intermediate family of dis-
tinctly perch-like structure ; but the pelvic fins are not attached to the

FIG. 430.
Columbia transmontana, Eig. (From Jordan and Evermann.)

pectoral girdle, although close to it, and there is an adipose fin. The
scales are strongly ctenoid, and do not cover the head. The air-bladder
has an open duct. The bones of the skull have large mucous cavities.
The myodome and epipleurals are absent. One radial rests on the

426

TELEOSTEI

coracoid. Spines occur in the dorsal and anal, but not in the pelvic fin,
which has 9 jointed lepidotrichs.

Percopsis, A. G. ; Columbia, Eig. (Fig. 430) ; N. America.

Division 2.

The pelvic fins are thoracic or jugular, closely attached to the
pectoral girdle. The pneumatic duct may remain open in a few
Berycidae, Serranidae, and Sparidae, but disappears in the others.

The Division may be classified into six Subdivisions, chiefly
according to the structure of the fins and girdles.

Subdivision 1.

The pelvic fins are thoracic. A perforate scapula and a
coracoid are present, only one or two of the pectoral radials being
articulated to the latter. Except in a few cases, there is an
eye-muscle canal.

TRIBE 1. BERYCTFORMES.

The pelvic fins are thoracic, with one spine, and usually many dermal
rays. The dorsal and anal fins are spiny, the teeth small, villiform.

FIG. 431.
Bcryx decadactylus, C. and V. (After Gunther.)

Family BERYCIDAE. This the most ancient family of the Acantho-
pterygii persists at the present day, and is distinguished by the possession
of from six to thirteen soft rays on the pelvic fins. The jaws are pro-
tractile ; the myodome and subocular shelf of the suborbitals are present.

BERYC1FORMES

427

The Beryeiclae preserve the orbitosphenoid, as well as the alisphenoicl and
basisphenoid (Starks [421]).

Hoploptcnjs., Ag. (Beryx} (Fig. 432) ; SphenocepJialus, Ag. — Cretaceous,
Europe. Acrogaster, Ag. ; Holopteryx, Ag. — Cretaceous, Europe and Mt.

Restoration of Iloplopteri/x kwesiensis, Mantell ; from tlie English Chalk.
(After A. S. Woodward, from Brit. Mus. Guide.)

Lebanon. Dinopteryx, A. S. W. ; Cretaceous, Mt. Lebanon. Myripristis,
Cuv. ; Holocentrum, Guv. — tropical seas ; and Eocene, Europe. Beryx,
Cnv. (Fig. 431) ; Gephyroberyx, Blgr. ; Polymixia, Lowe ; Plectromus,
Gill ; Caidolepis, Gill ; Trachichthys, Shaw — tropical seas.

Fio. 433.
Pempherls russelli, Day. (After Day, Fishes of India.)

Family APHREDODERIDAE. Perhaps allied to the last, but with non-
protractile jaws, and the anus very far forwards. They have no myodome,
no orbitosphenoid, and no subocular shelf.

Aphredoderus, Les. ; North America. Asineops, Cope ; Eocene,
North America.

428 TELEOSTEI

Family PEMPHERIDAE. The soft pelvic rays are reduced to five.
Baihydupea preserves the open pneumatic duct, has no median spines,
and has subjugular pelvic fins. The family's systematic position is very
doubtful.

Pempheris, C. and V. (Fig. 433) ; Bathyclupea, Ale. ; Parapriacanthus,
Steind. — tropical seas.

Family MOXOCENTRIDAE. The snout is very obtuse, the ribs are lost

FIG. 434.
Monocentris japonicus, Htt. (After Giinther.)

on the first half-dozen vertebrae, only two or three soft dermal rays
remain on the pelvic fin, and the scales are closely set in a rigid armour.
Monocentris, Sch. (Fig. 434) ; Indo-Pacific.

Subdivision 2.

This is founded chiefly on the structure of the pelvic fins. If
the persistent occurrence of one spine and not more than five
jointed 'soft' dermal rays in these fins is of any phylogenetic
significance, all or some of these families must have been derived
from a common ancestor which branched off from the Beryciform
stock.

TRIBE 1. PERCIFORMES.

Spines are usually well developed, and the pelvic fins are thoracic
and provided with one spine and four or five jointed rays. The subocular
shelf is not always present ; it is an ingrowth, from one or more of the
suborbitals, supporting the eyeball (Fig. 436, B). The pectoral radials
are generally flattened and expanded at each end. It is scarcely possible
as yet to attempt to group phylogenetically the numerous families included
in this Tribe.

SUB-TRIBE A. I. With a subocular shelf (Fig. 436, B).

Family SPARIDAE. The Sea -Breams, are deep -bodied fish, with a

PERCIFORMES

429

continuous dorsal fin and from five to seven branchiostegals. The
palate is usually toothless ; but the teeth on the jaws become very
powerful, those in front being modified as incisors and those farther back
as flat grinders (Fig. 435). Rarely hermaphrodite (Chrysophrys).

Fig. 434 A.

.S>, •//(!,,• ovi*, Mitch., the Sheep's-head. Right-side view and dentition. (After Giinther.)

Sparnodus, Ag. ; Trigonodon, Sism. — Eocene, Europe. Sargus, Cuv.
(Fig. 434A) ; Sparus, Kl. ; Pagrus, Cuv. ; Pagellus, C. and V. — widely
distributed, and Miocene. Dentex, Cuv. ; Caesio, Com. ; Box, Cuv. ;
Chrysophrys, Cuv.

A, dorsal view of the lower jaw of Sargux rufesce,ns, C. and V. (After Owen.) B, front view
of the upper jaw of Sc.rgus.vetula, C. and V. (After Owen.) i, incisiform teeth ; g, grinding
teeth ; y, young teeth.

Family MULLIDAE. Closely related to the preceding ; but with a
feeble dentition, only four branchiostegals, and with two scapular
foramina. The dorsal is subdivided.

Upeneoides, Blk. ; Mullus, L., Red Mullet ; Mulloides, Blk. ; Upeneus,
C. and V. ; widely distributed in warm seas.

430

TELEOSTEI

Family SERRANIDAE. Very like the Sparidae
toothed palate, and sometimes with the lower

but usually with a
pharyngeals united

._.- YfC

FIG. 436.

A, left half of the pectoral girdle, left pectoral fin, and pelvic girdle of Serranvs cabrilla, L.
B, suborbitals of the same, showing the subocular shelf, enlarged, c, coracoid ; d, cleithruni ;
Ic, lateral line suborbital canal ; p, right pelvic bone ; pc, postclavicle ; p.f, left pelvic fin ; p.t,
post-temporal ; pt.f, pectoral fin ; r, radial ; s, scapula ; sc, supraelavicle ; s.f, scapular foramen ;
so 1-3, suborbitals ; so.s, suborbital shelf; v.pc, ventral postclavicle.

Fio. 437.
Serranvs altivelis, C. and V. (After Giinther.)

(Centrogenys). The spinotis dorsal may be separate. Often hermaphrodite.
The male Chilodipterus and Apogon carry the developing eggs in their mouth.

PERCIFORMES

43i

Prelates, Prieny. ; Upper Cretaceous, France. Morone, Mitch. ;
Serranus, Cuv. (Fig. 437) ; Percichthys, Ger. ; Anthias, Schn. ; Apogon,
Lac. (Fig. 438) — of wide distribution, and Eocene. Grrammistes, Art. ;
Priacanthus, C. and V. ; Centropomus, Lac. ; Pomatomus, Eisso ; Ambassis,

FIG. 438.
Apogon frenatas, Val. (After Giiiither.)

Com. ; Chilodipterus, Lac. ; Cirrhites, Lac. : Pentaceros, C. and V. ;
Mesoprion, Cuv. ; Ce?itrogenys, Rich.

Family SCIAENIDAE. With a separate spinous dorsal fin ; the lower
pharyngeals often united ; and very large slime - cavities in the
cranial bones. The palate is usually
toothless, and the large air-bladder often
has many diverticula.

Pogonias, Cope ; Atlantic ; Miocene,
N. America. Umbrina, Lawley ; widely
distributed, and Lower Pliocene, Italy.
Arripis, Jen. ; Sciaena, Art. ; Ancylodon,
C. and V. ; Eques, Bl. ; Otolithus, Cuv.

Family PSEUDOCHROMIDIDAE. Differ-
ing from the Sciaenidae chiefly in the
feeble development of the spines on the
lengthened dorsal and anal fins.

Pseudochromis, Riipp. ; Gichlops, M.
and T. ; Lopholatilus, G. and B., Tile-
Fish ; Opisthognathus, Cuv. ; Latilus, C.
and V. ; Bathymaster, Cope — widely dis-
tributed, marine.

Family CEPOLIDAE. Like the preceding ; but with a very elongated
tail, and dorsal and anal fins. Only a few feeble spines.

Gepola, L. ; Acanthocepola, Blk. — widely distributed.

Family HOPLOGNATHIDAE. Differing from the Serranidae in having
a toothless palate, and the teeth of the jaws fused to a strong beak.

Hoplognathus, Rich. ; Pacific (Fig. 439).

FIG. 439.

Dentition of Hoplognathus sp.
(After Giinther.)

432

TELEOSTE1

Family SILLAGINIDAK. With a toothed palate, but a separate spinous
dorsal and elongate soft dorsal and anal.
Sillago, Cuv. ; Indo-Pacific.

INCERTAE SEDIS.

Family ANOMALOPIDAE. Two genera of deep-sea Perciform fish may
be provisionally placed here ; their osteology is still unknown. They
are remarkable for the possession of a large movable phosphorescent
organ below the eye ; it can be turned outwards when lit up and in use,
and turned back into the orbit when extinguished.

Anomalops, Kner (Heterophihalmus, Bleeker) ; Photoblepharon, Weber ;
S. Pacific.

FIG. 440.
Psettus argenteus, L. (From Gunther.)

SuB-TKlBE A. II. With a subocular lamina. The body tends to-
acquire a very flattened rhombic shape, with the elongated dorsal arid
anal fins along the hinder edges. The pelvics become vestigial. The
mouth becomes very protractile, and the teeth very small, villiform.

Family SCORPIDIDAE. The post-temporal is normal.

Aipichthys, Stein. ; Cretaceous, Europe (?). Scorpis, C. and V. ;
Atypichthys, Gthr. ; Atyposoma, Blgr. ; Psettus, Com. (Fig. 440) — Indo-
Pacific.

Family CAPROIDAE. The post- temporal is fused to the skull. The
mouth is very protractile. They clearly approach the Chaetodontidae in
structure, and perhaps should be placed in the next sub-tribe.

PERCIFORMES

433

Protantiyvnia, Kr. ; Miocene, Europe. Antiyonm, Lowe ; tropical seas.
Cupros, Lac. (Fig. 441) ; Atlantic, Mediterranean.

SUB-TRIBE B. CHAETODONTIFORMES. The following are some of
the chief characters which appear in this sub-tribe : the jaws become

FIG. 441.

C<ijirii.i n'l'i'i-. L. A, head \vith jaws retracted, li, head with jaws protracted. C, scale,
enlarged. <>,-, articular ; h.m, confluent branchiostegal membranes ; d, dentary ; t, eye ; l.j,
lower jaw ; /./(, anterior nostril ; m, mouth ; rnb, membrane ; mr, maxilla ; pmx, premaxilla ; so,
anterior smootli region ; .</<, spim-s on posterior exposed region ; u.j, upper jaw ; «.-«, posterior

uostiil.

shortened, the mouth small, the palate toothless, the gill -membranes
confluent below ; the post- temporal becomes firmly fixed to the skull,
losing its forked character ; the pelvic bones meet, and tend to fuse in the
middle line ; the pelvic fins acquire a jugular position ; the scales become
modified into plates or prominent spines ; the intestine becomes long and
coiled ; the vertebrae are reduced to never more than twenty -five in

28

434

TELEOSTEI

number. The head is more or less completely covered with the scale-
bearing skin. Among the Chaetodontiformes are some of the most
specialised of Teleostean fish ; they diverge
greatly from the Perciform stock from which
they appear to have arisen.

DIVISION A. SQUAMMIPENNES. These still
preserve many of the primitive characters :
there are a subocular shelf, ctenoid scales,
four gills, paired and median fins with spines,
and well -developed pleural ribs. The body-
scales extend between or over the dermal rays
of the median fins. They are probably more
closely related to Sub-Tribe B than to any
other Perciformes.

Family CHAETODONTIDAE. The body
becomes very compressed and deep, the mouth
produced forward, the 'face' more vertical,
and a very high supraoccipital crest is con-
tinued at the sides into the pterotic crest ;
it is enormously enlarged in Ephippus (Fig.
442) ; the minute setiform teeth are set in
bands. The opercular bones may be armed
with spines ; in Holocanthus there is a pro-
minent preopercular spine.

Chaetodon, Art. (Fig. 443) ; Holacanthus,
Lac. ; Pomacanthus, Lac. ; Ephippus, Cuv. ;

Platax, C. and V. (Fig. 444) — tropical seas ; Eocene, Europe. Chelmo,

Cuv. ; Parapsettus, Stnd.

FIG. 442.

Skull of Ephippus fabcr, Br.
«, enlargement of frontal, and 6,
/>f supraoccipital ; c, interorbital
septum ; <?, basis cranii. (After
Giinther.)

FIG. 443.
Chaetodon ephippium, C. and V. (After Giinther.)

Family DREPANIDAE. Very like the last, but having lost the sub-
ocular shelf, and with very long specialised pectoral fins.
Drepane, C. and V. ; Indian Ocean.

PERCIFORMES 435

DIVISION B. PLECTOGNATHI. Here the maxilla becomes fixed to, and
generally fused with, the premaxilla ; the jaws become short and stout,
and the upper jaw does not slide forwards, but becomes hinged on the
ethmoid so as to bite up and down (Fig. 453). The subocular shelf is
lost ; the post- temporal loses its lower branches and fuses with the
supratemporal. The pelvic bones become firmly united, narrow, and
elongated. The gill-membranes fuse with the isthmus, and the branchial
opening becomes restricted.

SUBDIVISION A. Family TEUTHIDIDAE. The body is compressed, the
tail armed with movable lateral spines fitting in a groove, the dorsal and
anal fins with many spines, the small jaws provided with a single row of

Fin. 444.
Platax teira, Forsk. (After Day, Fishes of India.)

incisiform teeth, the palate toothless, the gill-membranes attached. The
post-temporal is still forked.

Teuthis, L. (Fig. 445) ; Indo-Pacific. Archaeoteuthis, Wettst. ; Eocene,
Europe.

Family SIGANIDAE. The post- temporal is not rigidly fixed, the
suborbital shelf is lost, but the myodome is present. The parietal is
lost. The pelvic fin has 6-7 spines, and the pelvic is peculiar in having
a posterior as well as an anterior spine, and four soft rays (Starks [422a]).

SiganuSj Forsk. ; Pacific.

Family ACANTHUIUDAE. The body is compressed, covered with
minute ctenoid or spinous scales. One spine and five jointed dermo-

436

TELEOSTE1

trichs in the pelvic fin. The teeth vary, but are generally incisiforin.
Parapophyses are present bearing ribs and epipleurals. The tail is pro-
vided usually with lateral plates or sharp defensive spines. Bony plates
near the base of the dorsal spines. A median bony horn develops above
the eyes in Naseus.

FIG. 445.
Teuthis nebuloM, Q. and G. (After Giinthcr.)

Naseus, Cuv. ; Acanthurus, Forsk. (Fig. 446) — -tropical seas ; Eocene,
Europe. A ulorhamphus, de G., Eocene; and Apostasis, Kr., Miocene,
Europe. Zanclus, C. and V. ; Colocopus, Gill ; Prionurus, Lac. — tropical
seas.

SUBDIVISION B. The opercular bones become reduced, the myodome
and the ribs are lost ; if present the pelvic bones are fused in the middle

line ; also the pelvic fins,
which are reduced to a spine
and a few small dermal ray.s,
may disappear altogether.
The gill -opening is very
narrow (Regan [344]).

FIG. 440.
Acanthurus leucosternifin , Uenn. (After Giiiithfr.)

BRANCH 1. SCLERODERMI.
The supraclavicle is vertical
and the pectoral radials
normally developed (Fig.
452, B). The dentary is
fused to the articular, and
the teeth usually strong and
incisor-like (Fig. 448). Four

complete gills are present. The orbit is carried very high up on the

skull.

SERIES 1. The spinous dorsal consists of one or more spines, of which
the first immediately behind the skull is generally very large, and, when
erect, may be locked by the second. There are generally only about nine-
te^n vertebrae. The teeth are conical or incisiform. Branchial opening
small.

A. The pelvic bones are fixed ; but there are still vestiges of paired

PERCIFORMKS

437

pelvic fins in the form of two large spines and a few jointed dermal rays.
The scales are rounded and spiny.

Family TRIACANTHIDAE. The premaxilla is protractile, and remains
.separate. The hyopalatiue arch is firmly fixed. From three to six dorsal
spines. The deep-sea genus Halimochirurgus has a long tubular snout.

Acanthopleurus, Ag., Oligocene ; Spinacanthus, Ag., Eocene — Europe.
Triacanthus, Ctiv. (Fig. 447) ; TriacantJiodes, Blkr. ; Halimochirurgus,
Ale. — Indo-Pacific.

B. Tlie body is somewhat compressed, and covered with spiny scales
or scutes. The co-ossified pelvic bones bear only a single median spine
suspended in a scaly fin-fold ; but even this spine may be lost (Mona-
canthidae). The premaxilla is firmly fixed to the maxilla.

Triaeamtku

KM:. -147.
/'/*, T. and S. (After Day, h'i*k<*

Family BALISTIDAE. The 'Trigger-Fishes' have two or three dorsal
spines, and generally large scales or scutes.

Acanthoderma, Ag. ; Oligocene, Europe. Batistes, Cuv. (Figs. 448-9) ;
J'araluteres, Blkr. ; Aluteren, Cuv. ; Ps&ocephalut, Sw. — warm seas.

Family MONACANTHIDAE. The 'File-Fishes' have one strong dorsal
spine, and generally a second vestigial spine behind it. The pelvic tin
is vestigial or absent. The body is covered with small spiny scales.

Monacanthus, Cuv. (Fig. 450).

SERIES 2. (OSTRACODERMI). There is no spinous dorsal fin, and the
whole body, excepting the. jaws, base of the fins, and caudal pedicle, is
encased in a rigid carapace of hexagonal plates. The vertebrae are reduced
to 16-14 ; the epipleurals and the pelvic girdle and fins have disappeared.
The clavicles, coracoid, and postclavicle are greatly expanded below the
carapace. The hyopalatine arch is fixed. The premaxilla is firmly
united to the maxilla.

438

TELEOSTEI

.-7*

FIG. 448.

Balistcs viri descent, Bl. Schn., File fish, from specimens in British Museum. A, lower jaw,
inner view ; B, lower jaw, outer view; C, upper .jaw (premaxilla), inner view; D, upper Jaw,
outer view, ar, articular ; d, dentary ; e.s, empty socket from which the growing tooth has
been removed ; f.t, tooth of first row ; o.t, older worn tooth ; s.t, tooth of second row ; y.t,
younger tooth about to replace the older one.

Fio. 440.
- Minna, B. and S. (After Day, Fishes of India.)

PERCIFORMES

439

ac

FIG. -T.O.
MiiHiii'iiiitlni.-: 1-1,11, 1'ni-i fiki'his, Blkr. (After Day, Fishes of India.)

Family OSTRACIOXTIDAE. 'Trunk'- or ' Coffer -Fish,' with long
narrow teeth. The carapace
has an almost vertical front edge,
angular sides, and often large
frontal and anal horns.

Ostracion, L. ; tropical seas ;
Eocene, Europe. Aracana, Gr. ;
Lactophrys, Sw. — tropical seas.

BRANCH 2. TRIODONTES.
Family TRIODONTIDAE. A family
intermediate between the first
and third sub-groups, whose exact
position it is difficult to deter-
mine. The teeth coalesce into a
beak, single below but paired
above. The spinous dorsal and
the pelvic fins have disappeared,
there is a dilatable oesophageal
sac. Yet a movable pelvis is
present as in the Balistidae, which
they resemble in many characters
of the skeleton. There are twenty
vertebrae, and the body is covered
with small spiny plates.

m • j -rr - -n T T ClMomycterus reticulatus, L. Porcupine fish;

1 notion, Kemw. ; E. Indies. from specimens in British Museum. Vertical

"RRVXTPII 1 Pvurv/Ynrwrira median section of both jaws, a.c, alveolar cavity

* 'TES- in which young teeth develop; i.o.t, grinding

There are no normal Scales, no surface formed by inner set of old tooth-plates ;

dorsal spinous fin, no pelvic fin

FIG. 451.

440

TELEOSTEI

or girdle, no epipleurals, and no parapophysee. The teeth when present-
are fused into plates in which vertical succession takes place (Figs. 451,
453). The basis cranii is simple ; the interoperculum rod-like and con-
cealed ; the suture between the dentary and articular remains, also ;i

A

scl.

Inner view of right half of pectoral girdle with pectoral fin of (A), />;</</.>« /.n/ir/cMiis. Kp. ;
and (B), Balistes verrucosus, L. cl, clcithruin ; cor, coracoid ; /«7. postclavicli1 ; f>tr, radial ; tc,
scapula ; scl, supraclavicle. (After Kegan, I'ro<: Xml. Soc.)

Of)

sop

Skull and jaws of Dieotulickthys ptin,etiiliitn.<, Kaup. «g, angular; nr, articular; <?, dentary ;
//•, frontal; hm, hyomandibular ; iop, interopercular ; mp, mesopterygoid ; mf , metaptetygoid :
mx, maxilla; op, opercular; pint;, premaxilla; pop, preopercular ; prf, prefrontal ; jrf, pterygoid ;
ptf, postfrontal ; pto, pterotic ; '/, quadrate ; sop, subopercular ; sy, syinplectic.

separate angular. The spines of the anterior vertebrae are bifid. The
supraclavicle is usually oblique (Fig. 452, A).

A. In which the crushing beak is very massive, the skull is broadened,
and the hyopalatine arch very firmly fixed or fused to the skull, the
palatine being generally continuous with the vomer (Fig. 453). The
gills are reduced to three in number, and one branchiostegal is much

PERC1FORMES

44i

enlarged. The nostrils are often modified ; the nasal sacs may protrude
as a papilla, the nostrils become confluent, and finally the sac open
freely to the exterior (Regan [344]). The papilla then becomes a mere

Fir.. 404.
Ditdon moetciottu, Gthr. (After Giinther.)

appendage in which end the olfactory nerves. The oesophagus is provided
with a large diverticulum, which on being filled with water inflates the
fish to an almost spherical shape, the defensive spines scattered over the
body thereby being erected (Thilo [435]). These spines, fixed in the skin
by three basal processes, may acquire a very large size, and are the modified
scales (Figs. 454-5).

Fio. 400.
Dioili'H iii"i-iiliiinf:J Gtlir., inflated. (After Giinther.)

Family TETRODONTIDAE. The beaks are divided by a median suture.
There may be as many as twenty-nine vertebrae, and small plates are
rarely found in the skin.

Telrodon, L. ; tropical seas and African rivers ; Eocene, Europe.
Bpkippion, Bibr. ; Tropidichthya, Blkr. ; Xenopterus, Holl. ; Chonerhrnn*.
Blkr. — tropical seas.

Family DIODONTIDAE. The 'Porcupine Fish' have beaks without
suture, the vertebrae reduced to twenty-two, and the skin armed with
spines only.

Diodon, L. (Figs. 454-5) ; tropical seas ; Eocene, Europe ; Miocene,
Java, N. America. Dicotylichthys, Kaup ; Chylomycterus, Blkr. (Fig. 453) ;
Trichocydus, Gthr. — tropical seas.

442

TELEOSTEI

B. Family MOLIDAE. The beaks have no median suture ; the body is
compressed and truncated behind, the vertebrae numbering seventeen, and
the caudal being replaced by the dorsal and anal fins which join posteriorly.
There are no inflatable sacs, the skin is naked or with small spines. The
skeleton is very fibrous, and very imperfectly ossified.

Orthagoriscus, B. and S. (Mola, Guv.) ; Ransannia, Nardo — Atlantic.

mi

Ssc

Brs-

Fid. 456.

Skeleton of head and .shoulder-girdle of Perca fluvintilis, L. (After Cuvier, from Clans and
Sedgwick.) Ac, postclavicles ; AJs, alisphenoid ; An, angular; Ar, articular; B.rs, branchio-
stegal rays ; Cl, cleitbrum ; Cor, coracoid ; D, dentary ; Ekp, ectopterygoid ; Enp, endo-
pterygoid ; Ethi, mesethmoid ; EM, prefrontal ; Fr, frontal ; Frp, postfrontal ; hm, hyo-
mandibular ; Hy, hyoid arch ; Jm, premaxilla ; JOp, interopercular ; Mty, metapterygoid ; MX,
maxilla ; Oex, epiotic ; Op, opercular ; Os, supraoccipital ; Pal, palatine ; Par, parietal ; POp,
preopercular ; l'r.0, prootic ; Ps, parasphenoid ; Q, quadrate ; S, symplectic ; Se, scapula; Sop,
subopercular ; $rj, pterotic ; S'«c, supraclavicle and post-temporal ; Vo, vomer.

SCB-TRIBE C. The subocular shelf has been lost.

Family ACROPOMATIDAE. Somewhat intermediate between the
Serranidae and the Percidae.

Acropoma, Schlg. ; Dinolestes ; Malacichihys, Dod. ; Propoma, Gthr. ; •
Synagrops, Gthr. — Pacific.

Family PERCIDAE. Chiefly freshwater fish, with not more than three
anal spines, a mouth at most feebly protractile (Fig. 456), and a divided
dorsal fin.

Prelates, Pr. ; Cretaceous, Europe. Cyclopoma, Ag. ; Eocene, Europe,

PERC1FORMES

443

Mioplosus, Cope ; Eocene, N. America. Smerdis, Ag. ; Oligocene, Europe.
Lates, C. and V. ; Africa, Asia, Australia ; and Eocene, Europe. Labrax,
C. and V., ' Bass,' Atlantic ; Eocene, Europe. Perca, L. ; Liicioperca,
Cuv. ; Acerina, Cuv. (Fig. 457); Boleosomn, Dk. — N. America. Aspro,
Cuv. ; Europe.

Fio. 457.
Acerina cernua, L., the Pope. (From Seeley, Freshienter Fit-lies of Europe.)

Family CENTRARCHIDAE. Freshwater fish differing from the last
chiefly in the larger number of anal spines (3-14), the deeper body, and
the undivided condition of the dorsal fin.

Lepomis, Raf. ; Micropterus, Lac. ; Centrarchus, Cuv. ; Pomotis, C. and
V. ; Pomoxys, Raf. — N. America.

FIG. 468.
Daseijllus aruanus, L. (After Gunthcr.)

Family CYPHOSIDAE. With incisiform teeth and densely scaled fins.
Cyphosns, Lac. ; Medialuna, J. and F. ; Sectator, J. and F. — Indo-
Pacific.

444

TELEOSTEI

Family LOBOTIDAE. "With conical teeth, a toothless palate, and very
protractile mouth.

FIG. 450.

Ditrema argentei/m, dissected to show the fully developed young, ready for expulsion
by the genital orifice, o. c, folds of the ovarian sac ; r, anus. (After Gvinther.)

6r.

Fl<;. 4C.O.

T.abrus maculatus, Bl. (Wrasse, from specimens in British Museum.) A, ventral view of
skull, with dorsal portion of branchial arches. 15, dorsal ,view of lower jaw and ventral
portion of branchial arches, ar, articular ; 6 !-2, two basibranchials ; bh, basihyal ; br, fourth
ceratobranchial,; eh, ceratohyal ; d, dentary ; eb !••*, pharyngobranchials ; lib, hypobranchial ;
l.ph, lower pharyngeal (5th ceratobranchials) ; mx, maxilla ; op, opercular ; jta, parasphenoid ;
pal, palatine ; pmx, premaxilla ; pnp, preopercular ; q, quadrate ; t, pharyngeal teeth.

PERCIFORMES

445

Catopr«, Blk.— S. E. Asia. Poly-

A

ot ,

Lobotes, Cuv. ; Atlantic, Mediterranean, Indp-Pacific. Datnioides,
Blk. ; E. Indian Ocean and rivers.

Family NANDIDAE. With a vi'i-y protractile mouth, very slender
maxilla, and no endopterygoid.

Nandtts, C. and V. ; Kadis, Blk. ;
centropsu, Blgr. ; W. Africa. Mono-
cirrus, Hekl. ; Polycentrus, M. and T.
— S. America.

Family GERRIDAE. With a very
protractile mouth, toothless palate,
premaxilla with an upward process,
and lower pharyngeals more or less
coalesced.

Equula, Cuv. ; Ga::~M, Hupp. ;
Gerres, Cuv. — tropical seas.

Family PRISTIPOMATIDAE. With
toothless palate, small teeth, and
undivided dorsal.

Pristipoma, Cuv. ; Haemulmi,C\\v. ;
Diafframma, Cuv. ; Pentapus, Cuv. —
tropical seas.

Family TRICHODONTIUAE. Scale-
less marine fish, with very upturned
mouth, toothless palate, divided dorsal
and elongated anal.

Trichodon, Cuv. ; Ardoscopus, J.
and E.— N. Pacific.

Family LACTARIIDAE. With
toothed palate, small deciduous cycloid
scales, and short spinous dorsal fin.
The scapula has two foramina.

Ladarius, C. and V. ; S. Asiatic
coast.

Family LATKIDIDAE. With small
scales, villiform teeth, and the pelvic
fins relatively far back. i'seiui<>»-<irti* ,ini.,-i<-i<tus, c. and v., from

T . • -n- i L i- T -VT s])i'c-ii(iens in tlie British Museum. A, upper.

Latns, Rich.; Australia and .New and B, lower pharyngeals. «, ith cerato-

401.

Zealand.

Family HAPLODACTYLIDAE. With
the pelvic fins relatively far from the

branchial ; n.<; alveolar cavity in which
teeth develop ; h, right pharyiigobranchial ;
<>.t, ol<l teeth lixedaud worn down ; p, grind-
ing plate : y.t, young teeth succeeding th&
old teeth. Succession is from before back-

pectorals : a large soft portion of the wards above, and from behind forwards

below.

dorsal.

Haplodactylus, C. and V. ; Chironemus, Cuv.
Pacific and southern seas.

Chilodactylu*, Lac.-

SUB-TRIBE D. (PHARYNGOGNATHI). The palate is toothless, but the
pharyngeals strongly toothed, and the lower pharyngeals are firmly
united (Fig. 461). The body is usually somewhat deepened, and the
dorsal fin remains continuous.

1. With a single nostril on each side.

446

TELEOSTEI

Family POMACENTRIDAE. The subocular slielf is preserved. Brilliantly
coloured marine fish, with gills reduced to three and one heniibranch.
Outwardly they resemble the Chaetodontidae.

Heliastes, C. and V. ; Azurina, J. and E. ; Pomacentrus, Lac. ;
Dascyllus, Cuv. (Fig. 458) ; Amphiprion, Bl. Schn. — warm seas.

Family CICHLIDAE. Freshwater fish, without subocular shelf or
supramaxilla, and with a suture separating the pharyngeals.

Tilapia (Chromis), Smith ; Tropheus, Blgr. ; LamprolOffiu, Schilt. ;
Hemichromis, Pet. ; Asprotilapia ; Plccodus, Blgr. ; Pseudetroplus — Africa.

B.

FIG. 462.

Pseudoscarus muricatiis, C. and V. Parrot fish ; from specimens in British Museum. The
upper and lower jaws. A, outer left-side view ; B, view of the jaws cut vertically, a.c, alveolar
cavity in which young teeth develop ; d, dentary ; o.t, old worn teeth near edge of jaws, firmly
held in bony cement ; pin, premaxilla ; y.t, loose young teeth about to replace older teeth.

Chaetobranchus, Hekl.
E. Indies.

Acara, Hekl. ; Heros, Hekl. ; Ciclila, Cnv.
Geophagus, Hekl. — America. Etroplus, C. and V

2. With normal nostrils and subocular shelf.

Family EMBIOTOCIDAE. Viviparous fish, with deep furrows along
the base of the dorsal fin. The anal may be peculiarly modified in
the male.

Abeona, Gir. ; Cymatogaster, Gibb. ; Embiotoca, Ag. ; Ditrema, Schl.
(Fig. 459) ; Hysterocarpus, Gibb. — Pacific.

3. With normal nostrils, and no subocular shelf. Gills reduced to
three and one hemibranch.

Family LABRIDAE. The Wrasses are brilliantly coloured marine fish,

PERC1FORMES

447

with strong pointed teeth on the jaws, and conical or tubercular teeth on
the pharyngeals (Fig. 460).

Phyllodus, Ag. ; Pseudosphaerodon, Ntlg. ; Eyertonia, Coc. ; Platy-
laemus, Dix. — Eocene, Europe. Labrodon, Gerv.; Eocene, Europe and New
Zealand. Jtdis, Cuv. ; tropical seas ; Miocene, Europe. Labms, L. ;
Mediterranean, Atlantic ; Miocene. Europe. Ctenolabrus, C. and V. ;
Chaerops, Riipp. ; Tautoga, Mitch. ; Chilinus, Lac. ; Cossyphus, C. and V. ;
Platyglossus, Kl. ; Epibulus, Cuv. ; Novacula, C. and V.

Family SCARIDAE. Closely related to the preceding family, the Parrot-
Wrasses differ chiefly in having expanded pharyngeals bearing tessellated
flattened teeth, and the teeth of the jaws more or less completely fused
into a firm beak (Fig. 462). Generally brilliantly coloured.

Scarus, Forsk. ; Mediterranean, Atlantic ; Eocence, Europe. Coridodax,
Gthr. ; Callyodon, C. and V. ; Scarichthys, Blkr. ; Pseudoscarus, Blkr. ;
Odax, C. and V. ; Siphonognathus, Rich. — chiefly tropical seas.

TRIBE 2. GOBIIFORMES.

The skull is usually somewhat depressed, with a blunt snout, the
bones not serrated, and there is no eye-muscle canal. The base of the
pectoral fin is generally extended and almost at right angles to the
vertebral column, the scapula and coracoid more or less reduced or
vestigial, so that the radials may touch the cleithrum. The four or five

Fio. 463.

Pectoral endoskeleton and cleithrum of A, Peristedion cataphractum ; B, Trigla hirundo ; C,
Jlemitriptenis acadianus ; D, Gobius guttatus. d, cleithrum ; m, coracoid ; n, scapula ; :i-/>,
radials. (From Gegenbaur, Vergl. Anat. Wirbeltiere.)

radials, of which one to two rest on the coracoid, are much flattened,
forming a narrow plate (Fig. 463, D). Characteristic is the modification
of the pelvic fins : they are thoracic, close together, and expanded so as
to form an adhesive disc, often completed by a transverse membrane
joining the fins behind. Usually there are several flexible spines in the
dorsal, one in the anal, and one spine and four or five soft lepidotrichia
in the pelvic fins. As a rule, there are no pyloric caeca and no air-bladder.

448

TELEOSTEI

Family GOBIIDAE. The dorsal fin has a separate soft hinder portion ;
the anterior portion is supported by flexible spines, and may be reduced.
The dentition and scaling varies ; the scales may be smooth, ctenoid, or
absent. There is no lateral line, and usually a large anal papilla.

Periophthalmus is modified for progression on land, and has powerful
pectoral tins, and protruding eyes brought up on to the top of the head.
Fossil forms have not yet been determined with certainty. Marine and
freshwater, widely distributed.

Gobius, Art. ; widely distributed. Eleotris, Gron. ; freshwater, tropics.
Benthophiius, Eisch. ; Caspian. Periophthalmns, Schn. ; tropics.

TRIBE 3. ECHENEIDIFORMES (Discocephali).

Distinguished by the extraordinary modification of the separate
anterior dorsal fin, which extends on to the head as far as the snout, and
becomes flattened out into an oval sucking disc with transverse ridges,

FIG. 404.
Remora brachyptera, Lowe. (From Jordan and Everniann.)

strengthened by a double series of serrated plates seemingly the modified
lepidotrichia (Figs. 464-5) (Storms [427]). The skull is correspondingly
flattened, its bones are deeply sunk and smooth, and there is no eye-muscle

Sucking disc of Bemofa brachyptera, Lowe. Dorsal view. (From Jonlan and Everniann.)

canal. The supraelavicle is reduced. The scapula perforate, and three
radials rest on the coracoid. Already in the Eocene fully differentiated
representatives of this family are found. It appears to have no close
affinity to the Scombriformes, with which it was long associated.

ECHENEIDIFORMES

449

Family ECHENEIDIDAE. The scales are small, cycloid, the suborbital
arch slender, the maxilla fixed to the premaxilla. The pectoral fin is
placed high up, beneath the disc. The posterior dorsal and anal fins
are spineless. There are pyloric caeca, but no air-bladder. The Eocene
genus Opisthomyzon has a quite small sucker.

Opisthomyzon, Cope ; Eocene, Europe. Echeneis, Art., ' Sucking-
Fish' ; Remora, Gill. (Fig. 464) — warm seas.

TRIBE 4. SCORPAENIFORMES (Scleroparei).

A natural group of fish, which appear to have been derived from
some primitive Perch-like form, and have diverged in several special
directions. They are distinguished by the possession of an enlarged
posterior suborbital (3rd), which spreads backwards over the cheek (Fig.
466), sometimes becoming firmly fixed to the preoperculum (Scorpaena,
etc.). This characteristic ' suborbital ' stay is not fully developed in the
more primitive genera, and may be again reduced in the more specialised.
The parietals often meet in the
middle line ; and the gills may
be reduced to three and a half.
The pectoral radials are gener-
ally in the form of flattened
plates.

The fins and scales are
generally very spiny, also the
head, which tends to become
covered with a bony cuirass.
Some of the anterior dermal
rays of the pectoral fin rest
directly on the scapula, with
which one or more of the
radials seem to have fused

fFicr 4fi7^ WliiUt ahmil- thirtv Sebastes percoides, Sol. (After Gunther.) Rigl.t-

lJng.4B7;. W Illlbt about tnirty slde Viewof-skull. pr, preopercular ; so, suborbital ;

vertebrae Occur in the less st> bony stay from third suborbital.

specialised families (Scorpae-

nidae), the number increases to fifty or sixty in the Comephoridae and

Cottidae.

SUB-TRIBE A. The pectoral arch has the perforate scapula and the
coracoid normally disposed, and with the latter articulate two of the
flattened radials (Figs. 463, 467).

A. Family SCORPAENIDAE. The cephalic cuirass is incomplete ; the
spinous portion of the dorsal is armed with strong spines, often provided
with poison glands, but is not separate. The anal generally has three
spines. The cranial bones are usually very spiny, often distorted, and
fleshy processes may be developed on the head. The myodome is present.
The base of the pectoral fin is broad and vertical, and one or two lower
dermal rays may be separate. The radials are constricted. The scales
may be lost, and the gills reduced to three and a half, one slit being

29

Fio. 466.

450

TELEOSTEI

. 7

closed. The air-bladder may be lost. An eye-muscle canal is present,
and the parietals may meet above the supraoccipital (p. 347). The dorsal

spines are often provided with
poison-glands.

Ampheristus, Koenig ; Histio-
cephalus, A. de Z. — Eocene,
Europe. Scorpaena, Art. (Fig.
468) ; warm seas ; Miocene,
Europe. Sebastes, C. and V. ;
Setarclies, Johns. ; Pterois, Cuv. ;
Apistus, C. and V. ; Agriopus,
C. and V. ; Chorisinodadylus,
Rich. (Fig. 469) ; Pelor, C. and
V. — warm seas.

Family TRIG LID AE. The head
is completely covered by a cuirass,
formed partly by the suborbitals
(Fig. 470). The anal fin is spine-
less, the dorsal fin becomes sub-
divided, and the pelvic fins are
widely separated. Two or three
of the ventral (anterior) dermal
6 pectoral rays become specialised

Fio. 467. as independent feelers capable of

Skeleton of left half of pectoral girdle and fin separate movement (Hamburger
of Pterois voliUms. 1, post-temporal; 2, supra- [195]). The pectoral fin is
clavicle; 3, scapular; 4, coracoid ; 5, radial; 6, L J ,, , , , .,,. ,,

lepidotrich ; 7, postciaviele ; 8, cleithrum. generally large and brilliantly

coloured. The post-temporal is

fused to the skull, and the myodome is present. The body is covered
with rough scales, or sometimes with an armour of bony plates (Peristediori)
(Fig. 472).

Fio. 468.
Scorpaena bynociisis, Rich. (After Gunther.)

Trigla, Art. (Fig. 471) ; warm and temperate seas ; Miocene, Italy.
Lepidotrigla, Gthr. ; Prionotus, Lac. • Peristedion, Lac. — warm seas.

B. Family AGONIDAE. The cephalic cuirass is complete, and usually

SCORPAENIFORMES

451

spiny. The myodome is lost ; the post-temporal fixed, the pelvic fins
close together with one spine and two soft rays, and the anal spineless.
Bony plates cover the body.

Agonus, Bloch, the ' Pogge,' widely distributed.

FIG. 469.
Chwismodactylus midtibnrbis, Rich. (After Giinther.)

.8

23

22

20 19

15 14 l3

FIG. 470.

Trigla gurnardus, L. Left-side view of skeleton of head and pectoral girdle. 1, nasal ; 2,
nasal capsule ; 3, prefrontal ; 4, preopercular ; 5, opercular ; 0, pterotic ; 7, subopercnlar ; 8,
supraclavicle ; 9, cleithrum ; 10, scapula; 11, lepidotrichia ; 12, three free specialised lepido-
trichia ; 13, radial ; 14, coracoid ; 15, subopercular ; 16, cleithrum ; 17, interopercular ; 18,
.angular ; 19, articular ; 20, maxilla ; 21, enlarged suborbital ; 22, dentary ; 23, premaxilla.

C. Family DACTYLOPTEKIDAE. Resembling the preceding family in
the complete armature of the head, the subdivision of the dorsal fin, and
the fusion of the post-temporal ; but the myodome is lost. The head is
short ; the cephalic cuirass extends far back. The dorsal fin is preceded

452

TELEOSTEI

by free spines ; the pelvics are close together ; and the pectorals are
enormously developed in the adult, and subdivided into a shorter anterior

Fio. 471.
Trigla pleuracunthicu, Rich. (After Giinther.)

Fio. 472.
Peristedion miniatum, Goode. (From Jordan and Evermami.)

Fia. 473.
Dactylopterus volitans, L. (After Gitnther.)

and a longer posterior division. The supraclavicle has been lost, and the
postclavicle is reduced. The three posterior radials rest on the coracoid,
and are peculiarly lengthened. The Flying Gurnard, Dactylopterus, and

SCORPAENIFORMES 453

the flying-fish, Exocoetus, present a most interesting case of convergence of
structure (p. 402).

Dactylopterus, Lac., the Flying Gurnard (Fig. 473) ; Atlantic and
Indian Ocean.

Family HEXAGRAMMIDAE. With an eye-muscle canal, rather smooth
cranial bones, few spines, and a continuous or incompletely divided
dorsal. The posterior nostril is reduced to a minute pore. Scales small.

Hexagrammus, Steller ; Pleuroyrammus, Gill ; Ophiodon, Gir. ; Zanio-
lepis, Gir.- — N. Pacific.

Family COMEPHORIDAE. Without eye-muscle canal, with few and
feeble spines. With very large pectoral, and small or no pelvic fins.
Comephorus, adapted to deep waters, is colourless, and has very large
eyes ; moreover, the suborbital stay is reduced, and the whole skeleton
very delicate.

Anoplopoma (Scombrocottus), Ayres ; N. Pacific. Triglopsis, Gir. ;
deep Canadian lakes. Comephorus, Lac. ; Gottocomephorut, Pell. — Lake
Baikal.

PIG. 474.
Cottus gobio, Cuv., the Miller's Thumb. (From Seeley, Freshwater Fishes of Europe.)

Family RHAMPHOCOTTIDAE. With spiny cranial bones and incom-
plete cuirass, no myodome, and gills reduced to three and a half, with
narrowed opening. The flat post-temporal is fixed to the skull. Small
spiny scales. Vertebrae few (24).

Rhamphocottus, Gthr. ; Pacific coast of N. America.

SUB-TRIBE B. The scapula is widely separated from the coracoid, so
that some of the flat plate-like radials rest on the cleithrum. The scales
tend to disappear, or to be modified into spines embedded in the skin.
The myodome is present.

Family COTTIDAE. The spinous dorsal is usually separate ; but the
scales and spines on the fins and head are less developed than in the
Scorpaenidae, as a rule. The eyes are generally placed high and close
together, the teeth small, the gills sometimes reduced to three and a half,
the anal spineless. The vertebrae may be numerous, especially in later
forms.

Eocottus, A. S. W. ; Eocene, Italy. Lepidocottus, Sauv. ; Miocene
and Oligocene, Europe. Cottus, Art. (Fig. 474) ; Icelm, Kr. ; Jordania,

454

TELEOSTE1

Stks. ; Triglops, Reinh. ; Blepsias, C. and V. ; Scorpaenichthys, Gir. —
Northern seas. Sclerocottus, Fisch. ; Antarctic. Psychrolutes, Gthr. ;
N. Pacific.

FIG. 475.
Liparis Dennyi, J. and 8. (From Jordan and Evermann.)

Family CYCLOPTERIDAE. Differing from the closely allied Cottidae
in the reduction of the size of the branchial opening, the spines, and
scales, and in the formation of a sucking disc by the pelvic fins (Fig.

476). There is no myodome. The
thick skin is naked or with scattered
embedded spines and tubercles.

Cyclopterus, Art., the Lump-Sucker;
Liparops, Garni . ; Liparis, Art. (Fig.
475); Paraliparis, Coll. — marine,
widely distributed.

SUB-TRIBE C. With a very de-
pressed spiny head, no eye -muscle
canal, well -developed scapula and
coracoid, and very flattened radials,
widely separated pelvic fins, and
spineless anal.

Family PLATYCEPHALIDAE. With
small scales.

Platycephalus, Schn. ; Indo-Pacific.
Family HOPLICHTHYIDAE. With an incomplete cuirass, the post-
temporal fused to the skull, and an armour of bony spiny plates.
Hoplichthys, C. and V. ; Bembras, C. and V. — W. Pacific.

Fio. 470.

Liparis Dennyi, J. and S. Ventral view,
showing sucker formed by the united pelvic
tins. (From Jordan and Evermann.)

TRIBE 5. BLENNIIFORMES (Jugulares + Pediculati).

The families contained in this fifth Tribe, which seem to have
started from some primitive Perch-like fish with pelvics bearing one
spine and five dermal jointed rays, and a subocular shelf at least on the
second suborbital, form perhaps but an artificial assemblage. The
second and third divisions (B and C) are doubtless related to each
other, and perhaps also to some of the more specialised Perciformes ;

BLENNIIFORMES

455

but the position of Sub-Tribe A
their allies were for long associ-
ated with the Gadiformes, from
which theyhavebeen distinguished
by Boxilenger [40].

The pelvic fins are placed in
front of the pectorals, being
'jugular' or even 'mental' in
position. The base of the pectoral
fin is usually vertical and ex-
tended. Frequently the foramen
lies not in the scapula, but between
it and the coracoid (Fig. 477, A).
The spines and scaling are gener-
ally reduced ; the more specialised
families become much modified
and give rise to some of the most
phantastic forms of fish.

SUB-TRIBE A. Two of the
short flattened pectoral radials
rest on the coracoid, and some of
the anterior dermal rays on the
scapula, as in the Scorpaeniformes
(Fig. 477, A).

Family TRACHINIDAE. The
Weevers have a subocular lamina
on the second subdrbital, well-
developed pleural ribs and epi-
pleurals, the foramen between the
scapula and coracoid, and a long
opercular spine. The mouth is
large and protractile, the snout
very short, the spinous dorsal short
and separate, the tail lengthened
with a long soft dorsal and anal.
The pelvic fins have one spine and
five jointed dermotrichs. The air-
bladder has been lost, and the
small cycloid scales are set in
oblique bands.

Trachinus, Art., the Weever ;
Mediterranean and E. Atlantic ;
Miocene, Europe.

Family PERCOPHIIDAE. Differ
from the preceding in the disposi-
tion of the scales, the wide separa-
tion of the pelvics, and the position
of the foramen in the scapula (Fig.
477, B).

is less certain. The Trachinidae and

3C

Skeleton of the pectoral and pelvic girdles and
tins of (A) Trnchiniis draco, L. ; (B) Percophis
brtuilieiuis. Q. and G. ; (C) Caulolatilus princeps.
Left-side view. (After Boulenger.) d, cleithrum ;
cor, coracoid ; pelv, pelvic girdle ; pt, radial ; ptcl,
postclavicle ; pte, post-temporal ; so, scapula ; scl,
supraclavicle.

456 TELEOSTEI

Percophis, C. and V. ; coast of Brazil. Bleekeria, Gthr., and Embo-
lichthys, J. and E., Indo-Pacific, are perhaps of this family.

Family LEPTOSCOPIDAE. Like the foregoing, but without subocular
lamina.

Leptoscopus, Gill. (Fig. 478) ; Bembrops, Std. ; Parapercis, Std. ;
Neopercis, Olg. ; Chimarrhichthys, Sauv. ; Pleuragramma, Blgr. — Southern
hemisphere.

Family NOTOTHEXIIDAE. Like the Trachinidae ; but without sub-
ocular shelf, and sometimes with a scapular foramen (Trematomus} ; the
scales, also, are ctenoid, though they may disappear, as well as the
spinous dorsal. The pelvic fins are wide apart, and the nostril is
usually single.

Notothenia, Rich. ; Acanthaphritis, Gthr. ; Cliaenichthys, Rich. ; Cryo-
draco, Dollo ; Bovichthys, C. and V. ; Gymnodraco, Blgr. ; Gerlachia,
Dollo ; Bathydraco, Gthr. ; Racovitzia, Dollo ; Trematomus, Blgr. —
Southern seas.

FIG. 478.
Leptoscopus macropygus, Rich. (After Giinther.)

Family URANOSCOPIDAE. Like the Trachinidae ; but the foramen
is in the scapula, and the reduced radials are fused to the scapula and
coracoid. The head is much modified, very broad, with the eyes on the
top, a very short snout, and an almost vertical mouth. The spinous
dorsal may be lost, also the scales.

Uranoscopus, L. ; Anema, Gthr. ; Ariscopus, J. and S. ; Kathetostoma,
Gthr. — Mediterranean and tropical seas.

SUB-TRIPE B. The subocular shelf is absent, and the suborbital
arch generally not ossified. The entopterygoid, the eye-muscle canal,
and the epipleurals are lost.

Family CALLIONYMIDAE. Scaleless marine fish with a protractile
mouth, widely separated pelvic fins with a spine and five soft dermotrichs,
and a separate spinous dorsal. The vertebrae are few, the two last are
enlarged, and many neural spines are bifid. The forked post -temporal
is fixed to the skull. A fenestra is present between the scapula and
coracoid, and the three broad radials rest on the latter. The gill-opening
is reduced to a small aperture above the operculum. The sexual colora-
tion of the male is often very vivid.

Callionymus, L., the Dragon et ; widely distributed. Vulsus, Gthr.,
Celebes.

Family GOBIESOCIDAE : The Cling-Fishes, are scaleless and spineless,
with a protractile mouth and simple post-temporal. The ventral

BLENNIIFORMES

457

surface of the abdomen is occupied by a large complex sucker formed

k

pel

FIG. 479.

Oblique ventral view of f^padogaster gouanii, Lac. a, anus ; br, branchial opening ; n,
nostril ; p, left pectoral fin which joins the right to form the edge of the pectoral sucker, p.s;
pv, pelvic fins combined to form the pelvic sucker, pv.s.

partly by the pelvics widely separated, and partly by the pectoral fins
(Fig. 479) ; the pelvic bones, cleithra, and postclavicles are expanded to
support it, and the whole
pectoral girdle is much
modified. The median fins
are spineless.

Gobiesox, Lac. ; Choriso-
c/mraus, Barn. ; Lepadogaster,
Gowan ; Leptopterygius, Tr. ;
Diplocrepis, Gthr. — widely
distributed, marine.

Family TRICHOXOTIDAE.
Resembling the Callionymi-
dae, but with an ossified
suborbital arch, a more
normally forked post -tem-
poral, wide gill-openings, a
single dorsal, and scales.
Numerous vertebrae.

Trichonotus, Schn. ;

Taeniolabrus, St. — Indian
Ocean. Hemerocoetes, C. and
V. ; N. Zealand.

SUB-TIUBE C. The pec-
toral dermal rays all rest Fl(i- 48°-

O11 the radials, of which Left pectoral girdle and fin-skeleton of lilennius

rViprp arp apnprallv fnur r,r- 9attoru<jine, Bl. cl, cleithrum ; co, coracoid ; l.c, lateral-

tnere are generally lour or line cana] . ^ postclavicie ; pst, post-temporal ; r,

five, two 01' three tOUChin" 4th radial ; sc, scapula ; sri, supraclavicle ; AT./, scapular
,, i mi i -° foramen,

the scapula. The scapula is

usually perforate, but often much reduced (Fig. 480). The pelvic fins
have a spine and four derrnotrichs, but are liable to reduction. The
body has a short trunk, large head, and long tapering tail ; both the
anal and the dorsal fin are usually lengthened, the latter often reaching
to the head and giving rise to separate cephalic rays.

458

TELEOSTEI

Family BLENNIIDAE. The subocular shelf is usually developed. The
maxilla contributes to the margin of the protractile mouth. Generally
with many dorsal spines, and a distinct caudal fin. The dentition is
sometimes very formidable, as in Anarrhichas (Fig. 483). Some genera
(Alticus) become adapted to progression on land, and closely resemble the
Gobiid Periophihalmm.

FIG. 481.
Blennius vulgarls, Poll., the Blenny. (After Seeley, Freshwater Fishes of Europe.)

Pteryyocephalus, Ag. ; Eocene, Italy. Clinus, Cuv. ; Blennius, Art.
(Fig. 481) — temperate and tropical seas ; Miocene, Europe. Anarrhichas,
Art. ; Chasmodes, C. and V. ; Petroscirtes, Riipp. ; Salarias, Cuv. ; Stichaeus,
Kroyer ; Blenniops, Nils. ; Pataecus, Rich. ; Gadopsis, Rich. ; Opistho-
centrus, Kner ; Xiphasia, Blk. (Fig. 482) — widely distributed, chiefly
marine.

FIG. 482.
Xiphasia setifer, S\v. (After Day, Fishes of India.)

Family PHOLIDIDAE. Differing from the preceding in the absence
of a subocular shelf, and of parapophyses on the precaudal vertebrae.
Pelvics absent or vestigial. Only spines in the dorsal. The lips are
thickened.

Pholis (Centronotus), Fl. ; Apodichthys, Gir. — Northern seas.

Family ZOARCIDAE. Degenerate forms, separated by Jordan and
Evermann from the Gadidae, with which they used to be associated,
but from most of which they differ by the possession of a perforate
scapula, and usually well developed pseudobranch, and homocercal tail.

BLENNIIFORMES

459

The caudal fin may, however, disappear from the tip of the tapering
tail, and the very elongate dorsal and anal fins may then meet. There
is no subocular shelf, and the pelvics are often vestigial or absent, and

Fio. 483.

Dentition of the Wolf-fish, Anarrlii'-hris lupus, L. (After Giinther.) Upper teeth on the
right, lower teeth on the left.

also the scales. As a rule, there are no spines, except sometimes in the
hinder regions of the dorsal. The gill-membranes fused to the isthmus.

FIG. -is4.

Zoarces viviparus, L. (From Clans and Sedgwick.) A, anus ; V, urinogenital aperture.
The jugular pelvic fins are seen below the head.

Zoarces and others are viviparous. Some deep-sea forms lose their eyes,
as Typhlosus, Aphyonus ; also the cave-forms Ktyrjicola and Lucifuga.

Via. 485.
Lycodes perspiciHum, Kr. (From Jordan and Evermaim.)

Zoarces, Cuv. (Fig. 484) ; Lycodes, Eeinh. (Fig. 485) ; Lamproyrammus,
Ale. ; Lycocara, Gill ; Gymnelis, Reinh. ; Melanostigma, Gthr. ; Neobythites,
G. and B. ; Typhlonus, Gthr. ; Rhodichthys, Coll. ; Aphyonus, Gthr. ;
Brotula, Cuv. — marine. Stygicola, Gill ; Lucifuga, Poey (Fig. 48G) —
caves of Cuba.

46o TELEOSTEI

Family CONGROGADIDAE. Spineless, eel-shaped Blennies, with thick-
ened lips, a suborbital shelf, and the small post -temporal fixed to the
skull. No pelvic fins ; gill-membranes united, but free from the
isthmus.

Congrogadus, Gthr. ; Indo-Pacific. ? Hierichthys ; Japan.

Family OPHIDIIDAE. Degenerate fish, allied to the Zoarcidae, which
have lost the caudal fin, and have the pelvics placed very far forward
below the mouth, and reduced to a forked filament. Many from the
deep seas.

Ophidium, L. ; Lepophidium, Gill; Genypterus, Phil. — Atlantic, Indian,
and Pacific Oceans.

Family PODATELIDAE. Specialised forms perhaps allied to the Blen-
niidae. The protractile mouth is inferior, with minute teeth or toothless.
The pelvic fins are reduced to a filament with two rays. The long anal
is continuous with the caudal, the dorsal is short. Scaleless and spine-
less. The post-temporal is loosely attached and the perforate scapula
remains cartilaginous ; the radials are represented by a small plate of
cartilage.

Podateles (Ateleopus\ Blgr. ; deep seas near Japan and India.

FIG. 486.
Lucifuga dentatus, Poey ; from the Caves of Cuba. (After Giinther.)

SUB-TRIBE D. The trunk, and especially the head, becomes widened
and depressed, the mouth, as a rule, very large, the teeth sharp, the gill-
opening narrow, and the gills reduced. Neither a suborbital arch nor
an eye-muscle canal is present. The pleural ribs are lost in all, and the
epipleurals in all but the Batrachidae. The post-temporal is flat and
fixed to the skull, while the supraclavicle becomes much lengthened.
The scapula and coracoid are modified, and the radials tend to become
lengthened, expanded distally, and reduced in number. The scales are
generally absent or modified into spines or tubercles.

DIVISION 1. BATRACHI. The scapula and coracoid are reduced, and
there are four or five radials. The gill-opening is moderately large and
normally situated.

Family BATRACHIDAE. With a very large mouth and depressed head ;
a small spinous dorsal, and pelvic fins with one spine and two or three
jointed rays ; naked or with small scales. Thalassophryne has perforated
poisonous opercular and dorsal spines. Batrachus tau has eggs relatively
very large for a Teleost.

Opsanus (Batrachus), Raf. ; Porichthys, Gir. ; Thalassophryne, Gthr. ;
Thalassothia, Berg. — tropical and temperate seas.

BLENNIIFORMES

461

DIVISION 2. PEDICCLATI. The scapula and coracoid are lengthened
and project outwards, and the two or three elongated radials loosely
articulated with them ; a more or less prominent and jointed or genicu-
lated lobe is thus formed by the base of the pectoral fin. Although the

FIG. 487.
Ogcoeephalus vespertilio, L. Dorsal view. (From Jordan and Evermann.)

opercular bones remain large, the branchial opening is reduced to a pore,
generally behind the attachment of the pectoral. The caudal fin is well
developed, the tail as a rule not lengthened, and the anal and soft dorsal
fins short. The spinous dorsal becomes peculiarly modified into one or
more separate spines extending on to the snout. Here the anterior spine

FIQ. 488.
Ogcoeephalus vespertilio, L. Anterior view. (From Jordan and Evermann.)

is developed into a movable lure, often with a fleshy terminal appendage,
which can be dangled in front of the mouth (Fig. 489). Branching fleshy
outgrowths simulating seaweed, etc., are often distributed over the body.
So strangely modified is the structure of these fish that they are often
placed in a separate sub-order ; they appear, however, to be merely
specialised Blenniiformes.

462 TELEOSTEI

1. With a very wide head and large mouth, terminal, or directed
upwards ; and the gill-opening below or behind the base of the pectoral.

Family LOPHIIDAE. In these Fishing-Frogs, or Anglers, the pectoral
fin is scarcely geniculated, and has two radials. The pelvic has one
spine and five jointed rays, and is not much modified.

Lophitis, Art., ' Angler ' ; tropical and temperate seas ; Eocene, Italy.
Ghirolophis, Sw. ; Lophiomus, Gill.

Family CERATIIDAE. The scarcely geniculated pectoral has three
radials. The pelvics have disappeared, also the scales. They inhabit
the deep seas, and the skeleton is imperfectly ossified.

Ceratias, Kroy. ; Aceratias, Br. ; Himantolophus, Rhdt. ; Melanocoetus,
Gthr. ; Onirodes, Liitk. (Fig. 489) ; Liocetus, Gthr. ; Linophryne, Coll.

Family ANTENNARIIDAE. The lobe of the pectoral forms a distinct
angle or geniculation, and has three radials. The pelvics have four or five
rays, and project outwards. As a rule, two large fleshy processes project

above the head. Chaunax
lives in the deep sea and
can innate its abdomen
like a Gymnodont.

Antennarius, Com. ;
Chaunax, Lowe ; Saccarius,
Gthr. ; Pterophryne, Gill ;
Brachionichthys, Blkr. —
warm seas.
PIG. 489. 2. The gill - pore is

Onirodes glomerosns, deep-sea Angler from the Indian below and behind the base
Ocean with rudimentary subcutaneous eyes. (After Alcock, np ii,p •npPtrirn'| . fhp mmifh
Naturalist in Indian Seas.) Ot ttle Pectoral » tlae mOUttl

of moderate size becomes

inferior, while the snout is produced into a long tentacle provided with a
phosphorescent organ at its tip.

Family GIGANTACTINIDAE. A deep-sea fish resembling the Ceratiidae
in structure, but covered with small spines. The pelvics are absent.

Gigantactis, Brauer ; Indian Ocean.

3. A rather small and more or less inferior mouth. The gill-opening
is above the base of the pectoral, which is strongly geniculated. The
pelvic fins, with five derrnotrichs, project strongly outwards, and like the
pectorals are adapted for walking (Figs. 487-8). Usually there is a long
snout, below which may be lodged the lure, the only remains of the
spinous dorsal. The body in the pectoral region becomes greatly
expanded, and is covered with tubercles or spines.

Family MALTHIDAE. There are three pectoral radials ; the teeth may
be villiform. The gills may be reduced to two.

Malthe, Cuv. ; Malthopsis, Ale. ; Coelophrys, Br. ; Dibranchus, Ptrs. ;
Ogcocephalus, Fisch. (Figs. 487-8) — chiefly deep-sea, tropical.

TRIBE 6. SCOMBRIFORMES.

Although difficult to distinguish by definition from the closely allied
Perciformes, this appears to be a natural assemblage of related families.

SCOMBRIFORMES

463

The dorsal and anal spines are few and feeble ; there is no subocular
shelf. The most distinctive character is seen in the caudal fin : the
caudal pedicle is constricted, and the vertebral column ends in a very
symmetrical hypural bone ; the fin is deeply forked, and supported by
lepidotrichia conspicuously symmetrical about the median axis, with
closely approximated bases, forked, and embracing the hypurals, which

Fio. 490.

A, skeleton of the tail of Thynnus vulgaris, Cuv. and Val., Tunny fish. 14, terminal caudal
vertebrae of Scomber scomber, L., Mackerel, c, centrum ; h.a, haemal arch ; hy, hypural com-
pound bone, partially concealed in A by the dermal rays ; no, neural arch ; sp, spine.

they may almost completely conceal (Fig. 490). The tail is often keeled,
and the hypural spine strongly developed. The pelvic fins, except when
reduced, have the usual single anterior spine, and five lepidotrichia. The
scales are cycloid as a rule and tend to disappear. Usually the gill-
openings are very wide, the gill - membranes free from the isthmus,
the gill-rakers very well developed, the opercular bones unarmed in the
adult, the air-bladder large, and the pyloric caeca numerous.

1. The premaxillae are at most slightly protractile. With a deep

464 TELEOSTEf

body, elongate dorsal and anal fins without distinct spinous portions, and
usually large cycloid scales often connected together by processes.

Family BRAMIDAE. With about forty-five vertebrae. In Pteradis
and its allies the median fins may be greatly expanded. The pleural ribs
often are much widened, and the coracoid becomes very large. Pteradis
has enormous dorsal and anal fins.

Brama, B. and S. ; Bentenia ; Pteradis, Gron. ; Pterycombus, Fries.

2. The premaxillae are protractile ; and the cycloid scales small or
absent, except along the lateral line, where they may be enlarged into
scutes. Generally there is a special spinous division of the dorsal and
anal fins ; the latter may be detached. The body is slightly deepened,
and there are about twenty-five vertebrae.

FIG. 491.
Caranx ferdatt , Forsk. (After Giinther.)

Family CARANGIDAE. The spinous dorsal is often much reduced, and
the spines vestigial. Sometimes free spines in front of the anal. The
scales may be lost.

Vomeropsis, Heck. ; Carangopsis, Ag. ; Semwphorus, Ag. (Fig. 492) ;
Ductor, Ag. — Eocene, Italy. Caranx, Lac. (Fig. 491) ; Seriola, Guv. ;
Lichia, Cuv. ; Mene, Lac. — wide range ; and Eocene, Italy. Selene, Lac. ;
Naucrates, Cuv. ; Trachynotus, Lac. ; Paropsis, Jen. ; Chorinemus, C. and
V. ; Vomer, C. and V.

Family KHACHICEXTRIDAE. Differing from the preceding chiefly in
the absence of parapophyses. There are small scales.

Mhachicentrus, Kp. ; Atlantic and Indian Ocean.

3. Mouth not protractile, the cycloid scales are usually small or
absent, the body becomes elongated, and there are no free spines, but there
may be a separate spinous dorsal fin. No parapophyses, except in the
Xiphiidae.

SCOMBRIFORMES

465

Family SCOMBRIDAE. The anal and posterior dorsal tins are broken
up behind into a series of finlets each supported by a radial. The spinous
dorsal folds back into a groove. From thirty to fifty vertebrae, and the
pectoral fins inserted high up. Gastrochisma has enormous pelvics, which
fold into a ventral groove (Fig. 494).

FlO.'4'.iL'.

Semlophorus velicann, Bl. ; Upper Eocene, Monte Bolca. (From Giinther, after Agassi/.)
A, anal, C, caudal, and D, dorsal lin.

laurickthys, A. S. W. ; Palimphyes, Ag. — Oligocene, Europe. Eothynnus,
A. S. W. ; Scombrinus, A. S. W. ; Sphyraenodus, Ag. — Eocene, Europe.
Cijbium, Cuv. ; Auxis, Cuv. ; Thynnus, Guv. (Fig. 493) — Atlantic, Indian
Ocean ; and Eocene, Europe. Scomber, L. ; warm and temperate seas ;
and Oligocene, Europe. Sarda, Cuv. ; Acanthocybium, Gill ; Gastrochisma,
Rich. (Fig. 494).

30

466

TELEOSTEI

Family TRICHIUBIDAE. The pectoral fins are inserted low clowu, and
the body much compressed. Starting from Mackerel-like forms, such as
Thyrsites, the body gradually acquires a very elongate, band-like shape.
At the same time the vertebrae increase in number, and the originally

FIG. 493.
Thynnus thynnv.s, L. (After Giinther.)

distinct spinous portion becomes continuous with the soft portion of the
dorsal, the tail tapers to a point, while the caudal fin finally disappears, as
in Trichiurus. The pelvics? are likewise lost. The teeth become very
powerful and sharp.

Fio. 494.

r it*. 41*-*.

Gastrochisma melampus, Rich. The lower figure shows the groove into which the pelvic fins
can be folded. (After Giinther.)

Tkyrsitocephalus, von K. ; Oligocene, Europe. TJiyrsites, C. and V. ;
L&pidopus, Gou. (Fig. 495) — widely distributed ; Oligocene, Europe.
Epinnula, Poey ; Nealotus, Johns. ; Dicrotus, Gthr. ; Trichiurus, L. (Fig.
496) ; Benthodesmus, Goode ; Eupleurogrammus, Gill ; Gempylus, C. and V.

Family CORYPHAENIDAE. The body is elongate, compressed, with
very blunt snout, and large deep head, on to which extends the un-

SCOMBRIFORMES

467

divided dorsal. The pectorals are small. The pelvics fold into a groove.
About thirty vertebrae. Small cycloid scales, and large teeth. No air-
bladder.

Coryph&na, Art. 'Dolphin' ; warm seas.

KKJ. 49 "i.
oi'ii'* i-aiul"tii$, Euplir. (After Giiiitlier.)

Family LUVARIDAE. With a large head and very short snout, but
the dorsal fin tar back, and a very feeble dentition. About twenty-three
vertebrae. The pelvic bones are fused, and the pelvic fins small. There
is a small gill-opening. The post-temporal is enormous.

Luvarus (Ausonia), Raf. ; Mediterranean, Atlantic, Pacific.

4. The body becomes much lengthened, and the jaws produced into
a sharp rostrum. The dorsal and haemal spines expand into flattened
plates. The teeth are minute or absent.

Trifhiurux

<;. 4'.'t5.
s, L. (From Jordan and Evermann.)

Family PALAEORHYNCHIDAE. The ribs completely encircle the
abdomen. The pectoral fins are small, and the pelvic fins large. From
fifty to sixty vertebrae.

Hemirhynchus, Ag. ; Eocene, Europe. Palaeorhynchus, Bl. ; Oligocene,
Europe.

Family HISTIOPHORIDAE. The lengthened lower jaw bears a pre-
dentary bone. The dorsal and anal fins more or less subdivided ; the

468 TELEOSTEI

dorsal often of huge size. The upper jaw is produced into a long spear-
like ' sword.' The teeth are small, the air-bladder large and sacculate,
the scales elongate. About twenty-four vertebrae. The pelvic fins are
reduced, having only one to three dermal rays.

Xiphiorhynchus, van Ben.; Ancestrus, A. S. W. — Eocene, Europe.
Histiophorus, Lac. (Fig. 497) ; warm seas; Eocene, Europe. Tetrapterus, Raf.

FIG. 497.
Histiophorus pulchellits, C. and V. (After Gujitlier.)

Family XIPHIIDAE : The Sword -Fish, has twenty -six vertebrae, no
teeth, a very long flattened rostrum formed chiefly by the upper jaw,
and 110 pelvic fins. The young have both teeth on the jaws and granula-
tions in the skin.

Xiphias, Art. ; world-wide range.

TRIBE 7. KURTIFORMES.

This tribe contains a single aberrant genus, Kurtus, witli a short
dorsal and long anal fin, each having a few small spines ; pelvic fins
thoracic in position, and provided with one spine and five jointed rays ;
and small pectorals supported by four radials on the coracoid. The
scapula is absent. Most of the ribs are fixed to the ossified wall of the
air-bladder. There is no subocular shelf, and the occipital crest is
developed into a remarkable hook-like process. Minute scales cover the
compressed body. The teeth are villiform.

Family KURTIDAE. Kurtiis, Bl. ; Indian and Pacific Ocean?.

Subdivision 3. ZEORHOMBIFORMES.

In this group are placed the asymmetrical Flat -Fish, and two
families supposed to represent remnants of the symmetrical ancestral
forms which gave rise to them. The body is always much com-
pressed, and very deep ; the dorsal and anal fins are elongate ; the
abdominal region is shortened and the caudal lengthened ; the
caudal fin is normal, without, however, the spine usually found on
the side of the hypural bone ; and the pelvic fins have from seven
to nine dermal rays. Transverse purapophyses, pleural ribs, and

ZEORHOMBIFORMES 469

epipleura are generally present ; and some of the anterior radials
of the anal are usually fused to a single strong bone connected
with the haemal arches, as is often the case in deep-bodied fish.
The air-bladder is closed. On the whole, the symmetrical forms
resemble in structure the Berycidae ; but the Pleuronectidae be-
come much modified, and lose all trace of spines on the fins.
Owing chiefly to this fact, they were classed with the Gadidae as
Anacanthini by J. Miiller [306] ; but there can be no doubt that
they have no special affinity with the Cods. Whether the Zeiclae
and Amphistiidae, as suggested by Thilo [436] and Boulenger [40],
are really closely related to them must not be considered as defin-
itely established. Both the Amphistiidae and the Pleuronectidae
appear in Eocene deposits.

BRANCH A.

Symmetrical fish retaining well-developed spines in the fins, and an
eye-muscle canal. The gills become reduced to three and a half.

Family ZEIDAE (Cyttidae). The mouth is protractile ; the spinous
dorsal well differentiated, but not quite separated ; the anal with a
detached front portion bearing from one to four spines ; the pelvics with
one spine and six to eight jointed rays. Very variable is the squamation,
which may consist of small scales joined together in transverse rows, or
of larger scales, sometimes with bony scutes at the base of the dorsal and
ventral fins and along the edge of the body (Zeus). The post-temporal
is forked, but fixed to the skull ; three out of four of the pectoral
radials rest on the perforate scapula. The vertebrae are numerous, from
thirty to forty-six.

Cyttoides, "VVett. ; Oligocene, Europe. Zeus, Art., 'John Dory';
warm seas ; Pliocene, Europe. Cyttus, Gthr. ; Cyttopsis, Gill ; Zenion,
3. and E. — warm seas.

BRANCH B.

In which the spinous portions of the very elongated median fins become
reduced, and evenly continuous with the posterior soft portions (Fig. 498).
While the more primitive forms retain their symmetry (Amphistiidae),
the Pleurouectidae undergo modifications related to their habit of swim-
ming and resting on the sea-bottom on one side.

Family AMPHISTIIDAE. This extinct family distinctly approaches
the Fiat-Fish in structure, but retains the bilateral symmetry. There are
twenty -four vertebrae, small spines on the dorsal and anal fins, one spine
and eight soft rays in the pelvic, and the scaling is normal.

Amphistium, Ag. (Fig. 498) ; Eocene, Europe.

Family PLEURONECTIDAE. The spines, the eye-muscle canal, and the
air-bladder are lost. The changes which bring about the secondary
asymmetry of the adult affect many organs in the body, and are effected
during the lifetime of every individual. The embryo Pleuronectid and

470

TELEOSTEI

FIG. 498.
Restoration of Amphistium paradoxum, Ag. ; Upper Eocene. (After Boulenger.)

FIG. 490.

Enlarged views of three successive stages in the development of Pleuroiiectes pMessa, L.
(After Cole and Johnstone.) Stages A and B are still symmetrical, a, anus ; a.f, anal fin ; d.f,
dorsal tin ; e, ear ; hy.f, hypochordal caudal fin ; I, left eye, which migrates ; p.f, pectoral tin ;
r.e, right eye, which remains on the ' ocular ' side ; y.s, yolk-sac.

ZEORHOMBIFORMES

jF§8

?4J ~

elB«s

°. S u ~- =

2 f-5.0'-

-L. S 5 '^ <D

IS..1

g S— • *"

472

TELEOSTEI

even the free-swimming larva are structurally symmetrical ; but in later
stages the eye of one side is brought round until it occupies a position
above the eye of the other side. Thus in the adult the two eyes lie
on the same side, which is now carried upwards, and the lower side

A.

B.

rna.

rnac

rna

vo.

-op.

FIG. 501.

Flevroneutes platessa, L. (After F. J. Cole and J. Johnstone.) A, dorsal, and B, ventral view
of skull, showing the torsion of the front region, ar, large process of right side ; as, alispheroid ;
60, basioccipital ; eo, exoccipital ; ep, epiotic ; et, ethmoid cartilage ; /.c, carotid foramen ; f.g,
glossopharyngeal foramen ; f.j, jugular foramen ; f.t.f, trigeminal and facial foramen ; f.v, vagal
foramen ; h, socket for hyomandibular ; l.f, left frontal ; Lie, left lachrymal ; l.pf, left prefrontnl ;
me, mesethmoid ; op, opisthotic ; pa, parietal ; pro, prootic ; ps, parasphenoid ; pto, pterotic ;
rf, right frontal ; r.lc, right lachrymal ; r.nn, right nasal ; r. na.c, right nasal cavity ; r.pf, right
pre frontal.

is left 'blind.' The migrating eye may remain near the dorsal edge
of the head, as in the more primitive genus Psettodes (Fig. 502) ; or
it may move farther down on the ' ocular ' side (Pleuronectes, Solea,
Fig. 503). In this case the eye of that side also moves down, so as to
allow more room ; and sometimes, as in Synaptura (Fig. 504), the two
eyes may come very close together, and the orbits become confluent near

ZEORHOMB1FORMES 473

the middle of the lateral surface of the head. The dorsal fin may now
grow forward in a straight line on to the head (Pleuronectes, etc.) ; or
even to near the end of the snout (Rhombosolea, Cynoglossus). The line
marked by the fin on the head is not the true dorsal mid-line, for this
has become distorted on to the ocular side, as is shown by the course of
the lateral-line canals, and the bones of the skull (Fig. 500). The orbits
are far forward, and as the eye shifts, the front end of the skull (and
even the brain) becomes correspondingly distorted ; the relations of the
bones are considerably altered. For instance, the frontal of the blind
side is twisted round, loses its original connection, and acquires a new
connection with the prefrontal below, or dorsal to, the shifted eye (Fig.
501). The mouth, still wide and symmetrical in Psettodes, becomes
smaller, and more and more distorted on to the blind side, on which alone
the teeth may be developed. As was first clearly explained by Traquair
[44 1«], the shifting of the eyes is brought about, not by one eye leaving

FIG. W-2.
Psett&les erumci, 13. and S. (After Day, Fiahes of India.)

its socket to move across to the opposite side, but by the twisting of the
whole anterior region of the head — an adaptation to a peculiar mode of
life which affects almost all the other organs as well. The branchial
opening becomes more restricted. The median fins become longer, ex-
tending forwards and backwards ; in the most specialised genera, like
Cynoglossus, the tail tapers to a point, the dorsal and anal fins being con-
fluent at the tip. Asymmetry is not pronounced in the pectoral fins ;
but the radials are reduced generally to mere cartilaginous vestiges, and
the post- temporal may lose its inner limb. The pelvic fins, bearing
from five to seven dermotrichia, may be distorted ; that on the ocular
side becoming elongated in the same line as the anal '(Fig. 502). The
behaviour of the nostrils during torsion varies in different genera : in
some, Solea, the nostrils retain their position on the blind side ; in
Pleuronectes they migrate with the eye, but remain near the dorsal edge
of the lower side ; Arnoylossus has the dorsal fin passing forward below
them. The anus is very far forward and median ; but the urinogenital
papilla of the male and urinary papilla of the female are brought on

474

TELEOSTEI

to the ocular side. Owing to the forward growth of the anal fin, the
radials of which meet the haemal arches, the abdominal cavity becomes
excessively shortened, and the viscera may extend backwards on either
side in blind coelomic diverticula (Solea). The pyloric caeca may be
absent. The scales are cycloid or ctenoid. The vertebrae, twenty-four
in number in Psettodes, may be much more numerous in higher genera.

'$JF®:

FIG. 503.
Solea lietcrorhinc, Blkr. (After Day, Fixhcn of India.)

Concerning the asymmetry it is interesting to note that in Psettodes
the eyes may be either on the right or on the left side ; while in some
genera like Hippoglossus, Pleuronectes, and Solea, they are on the right ;
and in others, like Psetta, Arnoglossus, and Cynoglossus, the left is the
ocular side. Always there is a difference in colour between the two
sides, the lower being white and the ocular strongly pigmented.

FIG. 504.
Synaptura albomcculnta, Kp. (After Day, Fixhts of India.)

\ (Psetto) Rhombus, Kl. ; N. Atlantic, Mediterranean; and Eocene. Solea,
Guv. (Fig. 503) ; wide range, Miocene. Psettodes, Benn. (Fig. 502) ;
Ammotretis, Gthr. ; Achims, Lac. ; Hippoylossus, Guv. ; Pleuronectes, Art. ;
Citharus, Blkr. ; Rhomboidichthys, Blkr. ; Arnoglossus, Blkr. ; Zeuyopterus,
Gotzsch; Synaptura, Ctr. (Fig. 504) ; Cynoglossus, H. B. ; Symphurus
(Plagusia) — all marine.

LAMPRIDIFORMES 475

Division 3. LAMPRIDIFORMES (Allotriogmathi).

Quite recently the Taeniosomi of Gill have been joined with
the Lamprididae and the Veliferidae to form this Division by
Regan [348]. It is characterised by the compression of the body,
the peculiar mechanism of the protractile mouth, and the presence
of an orbitosphenoid (except in Sti/lephoms), a bone which has been
lost in all the Acanthopterygii except the Berycidae.

The scales are reduced, being either very small or absent. The
covering bones of the skull are, for the most part, deeply sunk ;
there is usually a remarkably large occipital crest. Whilst in
other Acanthopterygii it is the premaxilla alone which slides
forwards on the ethmoid, when the maxilla is pushed forwards by
the palatine to protrude the mouth, in the Lampridiformes the
maxilla itself moves forwards, sliding on the vomer and ethmoid.
There is no supramaxilla, no subocular shelf, a short eye-muscle
canal, and no opisthotic. The paired fins are spineless, and the
pelvics may have as many as seventeen rays. The pelvic girdle is
more or less closely connected to the coracoids. The air-bladder
is closed, the dentition feeble.

The Lampridiformes are all marine, of either pelagic or deep-
sea habit ; they are unknown as fossils. They appear to be
specialised forms derived from ancestors resembling the Berycidae,
and have now diverged in two directions.

SUBDIVISION 1.
TRIBE SELENICHTHYES.

Lampris (Fig. 401, C) has a very deep compressed body and spineless
fins ; the pelvics may have seventeen dermal rays. The pelvic bones
articulate with the very large expanded coracoids. Only three short
pectoral radials are present, one of which rests on the coracoid ; and the
dermal rays partly spring from the scapula. There are forty-six vertebrae,
without parapophyses, the ribs being strong and sessile. The maxillaries
take a share in the margin of the toothless mouth.

Family LAMPRIDIDAE. Lampris, Retzius, the brilliantly coloured
King-Fish ; Mediterranean, Atlantic, and Pacific (Fig. 401, C).

SUBDIVISION 2.

The mesethmoid is behind the prefrontals, and the frontals
cover an anterior chamber on the skull. The two pelvic bones
project upwards between the coracoids.

476

TELEOSTEI

TRIBE 1. HISTICHTHYES.

The body is deep and compressed ; there are two spinous rays in the
dorsal fin, and eight or nine rays in the pelvic, and the pectoral dermal
rays rest partly on the scapula and partly on the four radials ; one of
these articulates with the coracoid. The ribs are attached to parapophyses ;
there are thirty-three vertebrae.

Family VELIFERIDAE. Velifer, Schleg.

TRIBE 2. TAENIOSOMI.

The very compressed body is elongated, and may attain a length of
20 feet, with some ninety vertebrae. The dorsal fin is very long, and is
supported by unjoin ted dermal rays. The anal is short or absent.
Parapophyses are present, but the ribs are more or less completely
reduced. Of the three pectoral radials at least two rest on the coracoid.
The post-temporal has become simple.

FIG. o05.
gle*ne, Asc. (From Jordan and Evennami.)

Family LOPHOTIDAE. The pelvic fins, if present, are small, widely
separated, and with five or six dermotrichs. The anus is near the hind
end of the body, with a small anal fin just behind it. A long spine
represents the first dorsal ray.

Lophotes, Giorna ; warm seas. Eiimecichthyes, Regan.

Family TRACHYPTERIDAE. The pelvic fins are close together, but
the dermal rays may be reduced to one (Regalecus). The anus is about

LA MPRIDIFORMES

477

half-way up the body, and the anal fin has been lost. The caudal tin
has disappeared in Regalecus, but in Trachypterus is strangely modified,
the dermal rays being separated into two diverging fascicles (Fig. 506).

Trachypterus, Gouan (Fig. 506), and Kegalecus, Briinn (Fig. 505) —
widely distributed.

Fie. 506.

Ti-iii-lii/iiti-i-ii.*- tii' i, in, Schn. (After Giinthcr.)

Family STYLKPHORIDAE. The deep-sea genus Stylephorus is very
much specialised, having lost the pelvic fins, the arches of the vertebral
column, the orbitosphenoid, and the greater part of the pterygo-palatine
bar. The ceratohyals are widely separated below, the ethmoid is carried
by the parasphenoid far from the vomer, and the lower jaw has acquired
a huge size in spite of the presence of a very small tubular mouth
(Stark s).

Stylephorus, Shaw ; Pacific.

Division 4. MASTACEMBELIFORMES (Opisthomi).

A small group of Acanthopterygian fishes which have acquired
a deceptive resemblance to the Eels, not only in outward shape but
also in internal structure. The body is elongate, the tail gephyro-
cercal, the long dorsal and anal fins confluent at its tip ; the snout
is prolonged as a pointed movable appendage ; the pelvic fins have
been lost. The dorsal fin is continued forwards as a series of
detached spines, and spines are also present in the anal fin. The
scales are very small. The nostril is single on each side, the non-
protractile mouth is bordered by the premaxillae. The parietals
are separated by the supraoccipital which joins the frontals ; and
the pectoral girdle is attached, not to the skull, but to the vertebral
column. The numerous trunk vertebrae bear transverse processes
and ribs. The air-bladder is closed. These fish are adapted to
air-breathing, the branchial opening being small and ventral.

478 TELEOSTEI

The affinities of the Mastacembeliformes are obscure ; but they
appear to be highly specialised forms allied perhaps to the
Blenniidae, with which they are frequently associated.

Fit;. 507.
MastcKembelus argus, Gthr. (After Giinther.)

Family MASTACEMBELIDAE. Mastacembelus, Gron. (Fig. 507), and
lihynchobddla, Schn. — tropical Asia and Africa.

Series 7.
Sub-Order 8. GADIFORMES (Anacanthini).

Whilst showing many points of resemblance to some of the
Acanthopterygii (Blenniiformes), this sub-order preserves certain
apparently primitive characters which seem to indicate that it
branched off at an early time, and that the resemblances are due
more to convergence than to close affinity (Bouleriger [42] ;
Regan [344a]).

The cranial bones are mostly deeply sunk below the surface ;
the frontals are often fused ; the supraoccipital is well developed,
with a high median crest, and separates the parietals (Fig. 328) ;
the opisthotic is peculiarly large, growing downwards so as to
separate the prootic from the exoccipital. There is no eye-muscle
canal, and no basisphenoid. But by far the most important char-
acteristic of the Gadiform skull concerns the interorbital region.
Here the interorbital septum is membranous, and really only
developed below the cranial cavity ; for the narrow channel in
which run the olfactory nerves or tracts is a continuation of the
cranial cavity itself (Fig. 508). Indeed, in the Gadidae, alone
among the living Teleostei with the exception of the Cypriniformes,
the brain is continued far forwards, the olfactory bulbs being close
to the nasal sacs (Fig. 353). The olfactory nerves or tracts, then,
do not pass through the orbital cavities as in the higher Teleostei
(with the exception of the Galaxiidae). This peculiar relation of
the septum points to the origin of the Gadiformes from some remote
ancestral fish, possibly even outside the Group B in which they
are here provisionally included. Spinous rays are found only in the
dorsal fin of some Macrurids. The scapular foramen is between
the scapula and the coracoid, or rarely in the scapula (Gadomus).
The coracoid is imperforate. The number of pectoral radials varies

GADIFORMES

479

from three in Gadomus to six in Macrurus and ten in Muraenolepis.
This increase above the usual number, five, is probably secondary
(p. 404). The pelvic fins, which may have as many as twelve
dermal rays, are very far forward, anterior to the pectorals in the

FIG. .008.

tract in A ; op, optic nerve ; s, membranous interorbital septum.

Gadidae, but the girdle is only loosely attached to the cleithra.
Usually pleural ribs as well as epipleurals are present on the trunk
vertebrae, except the first two.

Scales generally cover the head ; they are cycloid in the

vl. hy.

FIG. 509.

Tail of a young Coil. (After A. Agassiz.) d, dorsal cartilage (neural arch ?) ; d.l, lepidotrichia of
dorsal lobe of caudal tin ; li.u, haemal arch ; hy, hypural ; n.sp, neural spine ; nt, notochord.

Gadidae and some Macruridae ; but in the latter family they
become spinous (Fig. 512, B). The air-bladder is closed, and the
pseudobranch usually sunk and glandular. Often a mental barbel
is present. The Gadiformes have not been found below the
Miocene and Oligocene rocks.

480

TELEOSTEI

The median fins become outwardly subdivided in a very char-
acteristic manner : in the Macruridae there is a small anterior
dorsal, as in all Gadiformes, and the long posterior dorsal and anal
dwindle gradually to the end of the tapering tail ; but in the
Gadidae these two fins become differentiated from a pseudocaudal,
and again subdivided into two dorsals and two anals (Fig. 514).
The tip of the tail is produced to a fine straight point in Macruridae

de

YLCL

hcu.

FIG. 510.

Tail end of the vertebral column of Gctdvs morrhua, L. Only tin1 base of the dermal rays
is indicated, c, centrum; d.e, dorsal (epichordal) dermatrichia ; d.li, ventral (hypochordal)
dermatrichia ; ha, haemal spine ; hy, hypural ; na, neural spine ; g, detached spine (or radial).

(gephyrocercal) ; but the homocercal tip is merged, in Gadidae,
with portions of the dorsal and anal fins contributing to form a
pseudocaudal, having the outward appearance of a diphycercal fin.
This tail fin, however, differs considerably in internal structure
from that of all other fish ; it has a large dorsal lobe similar to the
ventral lobe, and like it supported by the prolongations of a large
number of vertebral arches (Figs. 509, 510).

DIVISION 1.
The first vertebra is normally joined to the skull.

Family MACRURIDAE. Modified deep-sea fish in which the trunk
becomes shortened, the tail tapers to a filament, the dentition becomes

GADIFORMES

481

reduced, the mouth, which is protractile, diminishes in size, and a pro-
minent rostrum develops above it (Fig. 511). The rostral process is sup-
ported by the enlarged nasals and preorbitals. The eyes are very large.

Macrurtis australis, Rich. (After Giinther.)

Aii anterior spinous ray is found in the dorsal of the sub-family Mac-
rurinae. There is a specialised larval form (Krohnius) with filamentous
extensions of the pelvic fins.

A.

af

FIG. 512.

A, lln.tlti/iiti.'i-oin longicaiula, Gthr. B, Macnirus JUicuuda, Gthr. (After Giinther.) adf,
adipose, a./, anal, d.f, dorsal, p.f, pelvic, and pt.f, pectoral h'n ; Z,|lilament, probably elongated
lepidotricliia of anterior dorsal tin.

Sub-Family BATHYGADINAE. Such primitive genera as Gadomus have
a terminal mouth, no rostrum, nearly continuous dorsal fins, a scapular
foramen, and cycloid scales.

Gadomus • Bathyyadus, Gthr.

Sub-Family MACRURINAE. With a spine on the first dorsal fin, and
the first gill-slit narrowed to a small aperture.

Macrurus, Bl. ; widely distributed in deep seas (Figs. 511-12).

482

TELEOSTEI

DIVISION 2.

The first neural arch is sutured to the exoccipitals, and its spine
attached to the supraoccipital crest. The pelvic fins are farther
forward.

FIG. 513.

Lota vulgaris, Cuv., the Burbot. (After Cuvier.) 1, barbel ; 2, pelvic, 3, pectoral, 4, anal,
5, caudal, C, first dorsal, and 7, second dorsal flu.

Family GADIDAE. The Cods have small cycloid scales, the pseudo-
caudal fin described above, jugular pelvic fins, with from one to nine
dermal rays, a wide mouth, bordered above by the premaxilla ; powerful
teeth on the premaxilla, dentary, and palate.

FIG. 514.

Gadus morrhua, L., the Cod. (After Cuvier.) 1, nostrils ; 2, barbel ; 3, pelvic, 4, pectoral,
5, first anal, 6, second anal, 7, caudal, S, first dorsal, 9, second dorsal, and 10, third dorsal fin.

Nemopteryx, Ag. ; Oligocene. Gadus, Art. (Fig. 514); Brosmius, Cuv.
— Northern hemisphere ; Miocene. Merluccius, Cuv. ; Motella, Cuv. ;
Lota, Cuv. (Fig. 513) ; Raniceps, Cuv. ; Phycis, Cuv. ; Molva, Nils. ;
Haloporphyrus, Gthr. ; Bregmaceros, Th.

GADIFORMES

483

Family MUKAENOLEPIDAE. Represented by a single genus, differ-
ing from the Gadidae in the absence of a separate pseudocaudal, the
narrowness of the gill-openings, the very large number of pectoral radials,
and the disposition of the oblong scales in rows crossing at right angles.

Muraenolepis, Gthr. ; Kerguelen.

Synancidiinn horridum, L. (After Day, Fishes of India.)

484 LITERA TURE

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493. - Uber d. Kehlkopf der Ganoiden u. Dipnoer. Anat. Auz. vol. xxii.,

1903.

494. Wijlis, J. W. van. Uber das Yisceralskelet u. die Nerven des Kopfes der

Ganoiden u. von Ccratodus. Niederl. Arch. f. Zool. vol. v., 1879-1882.

495. Ueber d. Mesodermsegmente . . . d. Selachierkopfes. Verh. K.

Acad. Wet. Amsterdam, vol. xxii., 1882.

496. - Uber d. Mesodermsegmente des Ruinpfes u. d. Entw. d. Exkretions-

syst. Arch. f. mikr. Anat. vol. xxiii., 1889.

496a. Williciinson, W. C. The Structure of the Scales of Fishes, etc. Part I.
Phil. Trans, vol. cxl., 1849. Part II. ibid. vol. cxli., 1850.

504 L1TERA TURE

497. Willcox, M. A. Notes on the Occipital Region of the Trout, Trutta Fario.

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498. Wood-Mason, J., and Alcock, A. On the Uterine Villiform Papillae of

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INDEX

Figures given in thick type refer to the systematic position.
/. refers to an illustration. All the numbers refer to pages.

Abeona, 446
Abramis, 375
Acanthaphr&it, 456

Acantfw.spis, 263 ; A.

ilfi'ipiens, 263 /.
Acunthias, 5, 10/., 71, 122,

127 /., 128, 151, 152 ;

A. vulgnrts, 9 /"., 14 /'.,

58/., 77/., 12¥/., 152 V.,

360 /.

Acanthobatis, 161
A'-fint/mcepnla, 431
J cnnthoci/biu/ii, 465
Acdiif/iix/i'i-iiia. 437
Acantfiniles, 188 /., 190,

191, 192 ; .1. gracilis,

187 f., 192 f. ; .4. s«/-

ciitnx, 192 /'. ; .1. ir«/v//,

191 /.

Acantliodi, 187
Acanthodidae, 192 ; skull,

190 /.

Antiif/nx/ii/ixis, 192
Acant/ioessus, 192
AeanAoplearut, 437
Acanthnpxis, 376
Acanthoptervfiii, 424
Acantli undue, 435
Ai-ii/if/ninis, 436 ; .1. /<'"

i-nxli'i'ituin, 436 /.
Acara, 446
Acentrojifxinix, 336
Aceratinx. 462
4eeriflo, 368, 443; <4.

ivriiin.i, 443
Acestra, 384
Acliirux, 474
Acipenser, 94 /"., 108 /..

117, 133 /., 212 /, 224.

277, 305 h, 307, 315 /"..

316, 318, 319, 367/., 369;

^4. riMenus, 304 f.,

306 /"., 320 /: ; A.ttvrio,

110' /'., 274 /., 303 /..

308 ^'., 319 /'.

Acipeuseridae, 318

Acipenseroidei, 315

Acroduis, 144, 146

Acrogaster, 427

Acrognathux, 399

Acrolepis, 311

AI-/-II/III/IIII, 441

Acropoinatidae, 441

Acrotva, 421

Actinoptyrygii, 302

actiiiotrichia, 273

adipose fin, 275

Aeobatit, 166

Aethelii'tt, 371

Aftheolepis, 336

Agonidae, 450

Agonm; 451

Ai/rin/iiin, 450

Aipic/tt/n/s, 432

air-bladder, 223, 359 ;
auditory caeca, 360 ; cal-
cified, 289 ; bony, 377

.I//W«, 347, 349,363,388;
.1. coiitirhi/Hchus, 110 /".,
348 /., 349 /., 350 /. '

Albulidae, 387

Alburn us, 375

Alepidosauridae, 399

Alepulosaurns, 399; .-).
/e>m-, 400/.

Alepocephalidae, 394

Alepocephaltix, 394
riix, 394
i<K, 394

.•t/f.s-to, 375

alimentary canal, 2»i

AHiilt-pi'loilus, 331

Allotriogmatlii, 475

Al<i]tr<-Inx, 150: .1. f
ISO./.

Alupiiix. 150/'. ; .1.
110/., 116/.

Aloxu, 133/. ; ^4
362 /'.
.i, 458
505

Aluteres, 437

Ambossis, 431

Amblyopsidae, 401

Amblynpsis, 401 ; ^4.
spdaeus, 402. /'.

Amblyplerus, 212, 311

.4 ?« a(', 17, 101, 108 /'.,
224 /., 226, 227, 266,
270, 272, 276, 277, 278,
296, 302, 305 /., 316/.,
324, 326, 327, 328, 329,
330, 333, 334, 342, 346,
363, 367 /., 369; ^1.
caZra, 110 /., 222 /'..
267 /., 268 /., 269 /'.',
270 /., 271 /., 274 /.,
276/., 306 /:, 328. 332 /.,
333 /.

Amiidae. 333

Amioidei, 327

Amiopxis, 334

A miv.i-iis, 379. 380

Ammocoete larva. See !'<•-
tromyzon

. 1 niiiiiMiyteSi 403 ; A . «u«'ri-
cainifi, 403 /'.

Ammodytidae, 403

Ammotretis, 474

A iii/i/n r/xti/s, 450

AMftliio.a'ft, 1, 2, 2/., 3, 4,
7. 13. 18, 19, 25. 26, 27,
39, 42, 46, 47, 51, 52

Amphipnoidae, 409

Amphipnout, 410

Amphipi'ioit, 446

Amphisile, 414: A. XI-H-
tata, 414/.

Amphisilidae, 413

Amphistiidae, 469

. I iiifthlythim, 469 : . I . ^«w-
il«.'->(»i, 470 f.

amphistylic jaws, 95, 139,
144

ampullae, 19, 125

Anabantidae, 422

5o6

INDP:X

Aiiabas, 422 ; A. scandens,

Ariscopus, 456

438 /. ; i'. rci-i-ncosus,

422 /.

.'Irms, 133 /., 380

440 /'. : /J. riridescem,

Anableps, 365, 400, 401 ;

Arnoylossus, 473. 474

438 /.

• A. Dovii, 40 If.

Arrhamjihuy, 403

Halistidae, 437

Anacauthini, 478

Arripis, 431

IS(ii-bns, 375 ; />. nd<jarist

Anapterns, 399

Arthrodira, 258, 262

353 /.

A tutrrhichatjiM ; . I . !nj>ns,

Arthrothoraci, 262

hasidorsal arch, 100

469 f.

.Isyieojw, 427

basiventral arch, 100

Anarthrodira, 262

Aspidorhyuchidae. 344

Bathydupea, 428

Anaspida, 204

Aspidorhynchus, 344 ; *•!.

Rathydracn, 456

Ancestrus, 468

acutirostris, 344 /.

Bathygadiuao, 481

A ncistrus lieteraca nth us,

Aspius, 375

Bathygadtu, 481

385 f.

Aspredinidae. 384

Bathi/iitaxti'i; 431

Ancylodon, 431

Aspredo, 384

Jfathyplt-i-oia, 399

Aiiema, 456

Aspro, 443

BathythrixsK, 388

Anguilla, 352, 367, 377,

Atprotttapia, 446

Bathyt roctes, 394

406 ; -1. rulyaris, 404

Astemcantlius, 144, 146 ;

Hatrachi, 460

Angutittavus, 404

.1. medius, 116/.

Batrachidae, 460

Anguillidae. 405

Astermlernnig, 161

Katracht'x, 460 ; /»'. ^««,

Auguillifornies, 403

Asterolepidae, 209

460

Anogmii's. 388

Asterolepis, 207, 209, 250.

Uddlostmna, 35, 42 /., 46,

Auomalopidae, 432

260

48/., 49/., 50, 51, 85,

Anomalopt, 432

Asterosteus, 262

88, 133 A ; 7J. Dwnbeyi,

Anoplopoma, 453

Asthenocnrmus, 333

30 /., 49 /. ; ^. /V-

Anostomvs, 420

Astroblepua, 384

ste/'t'i, 48 /.

Antennariidae, 462

Astromethes, 395

Belemnobatis, 161

A ntennarius, 462

Astrope, 163

fieto/ze, 349, 402, 403

Anthius, 431

asymmetry, 469

Beloninae, 403

Antiarchi, 206

Ateleaspidae, 203

Belonorhynchidae, 320

Antv/onia, 433

Ateleaspis, 203; J. /<:wt-

Belon&rhynchus, 321 /.

aortic arches, 47, 111

lata, 204 /.

Relonostomus, 344

Apatemlns, 399

Atdeopus, 460

Beiribras, 454

Apatcolepis, 311

Atherina, 420

Bembrops, 456

Apeltes, 412

Atherinidae, 419

Bentenia, 464

Aphnelepis, 336

Atherstonia, 311

Bcnthodesmit.t, 466

Aphredoderidae, 427

Athrodon, 340

Benthophilu-s, 448

- 1 phredoderus, 427

Atypichthys. 432

Beiithosaunifi, 399

Aphyonus, 459

Afi/posoiiic, 432

Berycidae, 426

Apistus, 450

Auclwnaspis, 203, 204

Beryciformes, 426

Apodes, 403

Auchenoylanis, 382 ; -1.

Beryx, 427 ; />'. decadac-

A/>"i/ii-]itJi>/8, 458

biscutatis, 379 /.

tylus, 426 /.

A /Hymi, 430.431 ; ,l.//v>-

auditory capsule, 11 ;

7}c«rt, 422

narns, 43 1/.

ossifications in, 266

Birkenia, 204, 205, 206 ;

Apostasin, 436

auditory organ, 23

73. elegans, 204 ./;

Apua, 376

. 1 idolepis, 397

Birkeniidae, 205

.lraca/i«, 439

- 1 ulorhampJi " ••••, 436

Bleekeria, 456

Arapaima, 390

Aulorliynchidae, 412 Blenniidae, 458

.1 rchaeobatis, 167

Aulorhynchvs, 412

Bleiiuiiformes, 454

Archaeonemidae, 337

Aulnstnmci, 413

Blenniops, 458

. 1 rcharoaeni n.s, 337

Anlostoinatidae, 413

Blennius, 133 /., 458 ; A'.

A i-chaeotf.uthis, 435

Aulostonioidei. 412

gattoriif/ine, 457 /. ; Ti.

Archenclifli, 404

Ausoniii, 467

nttgaris, 458 /.

archipterygium, 106 ; of

autostylic jaws, 95, 171,

Blepsias, 454

Pleuracantfhus, 181 ; of

237

Boleosoma, 443

Cemtodus, 244; of Osteo-

^4 «a;is, 465

bone, 60 ; primary and

lepidoti, 282

Azuriitn, 446

secondary, 65, 67 ; car-

Arctoscoptis, 445

tilage-bone, 65 ; mem-

Aryenti/1", 394

7J<M«s, 445

brane-bone, 6"> ; dermal

.1 i^res, 384

/Sagarins, 379, 382

bone, 66 ; modified, of

Argiuae, 384

Bagrinae, 380

Teleostei, 355 ; section,

. 1 ryy ropeJecus, 395

llnlixtf*, 437 ; />. stellaris,

61/., 64 /.

INDEX

507

bone-like tissue, of Acan-

464 /. ; C'. trachiunts,

241, 242, 243 /"., 244,

thodii, 189 ; of Ptera-

360

245, 247, 250, 251 /.,

spidomorphi, 195

('<II-<II/HS, 377

252, 253, 254 /., 255,

llothnxlepis, 206, 207, 209 :

<.'a<-f]><i<-inx, 134, 150, 151

258, 282 ; C. Fontcri,

B. canadeiusis, 206 /.

Carcharidae, 150

231 /., 234 /., 236 /.,

Botia, 376

Carchariuae, 151

237 /., 242 /•., 244 /.,

Bovichthyt, 456

<',in-liiii-iHliiii. 148, 150

248 /., 250 /., 252 /.,

/I".-; 429

fi'i-Jiinilffn. 375

257 /. ; C. sturii, 240

llfn.ch imi it-Jithi/x, 462

cartilage, 31, 60 ; articular,

Cemtoptera, 167

llriic/ii/diriis, 260, 263

of man, 60 /.

ceratotrichia, 122

brain, 13, 16 /. ; of Acti-

cartilage and bone, 58 ;

cerebellum, 13

nopterygii, 305 ; of

substitution theory, 63

Cestradon, 80 /., 96 /.,

Dipnoi, 245 ; of Elas- ; Catta, 375

143, 144, 146, 147/.

niobrancliii, 126 ; of

Oatopra, 445

Cestracioutidae, 145

Teleostei, 363 ; of Teleo-

Catopteridae, 313

Cetengraulis, 392

stomi, 277

t'lifii/ifi'i-iix, 313

Cetomimidae, 399

n,-nmn, 464

Catosteomi, 410

Cetdmi iints, 399; '-'. (fillii,

Bramidae, 464

Catostoniinae, 375

400 /.

branchia, 41, 93, 272

Catostomiis, 375 ; (J. occi-

Cetopsis, 383

branchial bar, 93

dental in, 376 /.

Ceturhinv.s, 135, 148, 150 ;

branchiostegal rays, 304

Caturus, 329,' 331 ; C.

C. ma.cimus, 149 /.

breathing valves, 272

fnrcatus, 331 /.

Chaca, 383

firegmaceros, 482

Caulolatili(sprinceps,455f.

Chaenichthys, 456

Pu-ihim ins, 482

(Jaulohpis, 427

Chaerops, 447

Brotula, 459

Centrarchidae, 443

Chaetobranchus, 446

Brydiaetus, 390

Centrurckus, 443

Chaetodon, 434 ; C. ephip-

Brycon, 375

(A'liti-iitn, 152

pium, 434 f.

Hi/cMandium, 380

Centriscidae, 413

Chaetodontidae, 434

Bunocephaltu, 384

Centriscoidei, 413

Chaetodontiformes, 433

Butirinus, 363, 388

Centriscvx, 413 ; ^*. humer-

ChaetostonntK, 384, 385 /.

osiis, 413 /.

Chalceus, 375

Caesio, 429

Centrobatoidei, 163

Clifiiiiji.iiidi'ni, 423

Calamoichthys, 290, 291,

Centr»(jeiiiix, 431

Chaninae, 393

293 ; O.calabaricus, 301 /.

Oentrdepis, 312

Channa, 422

Calamostomo., 415

Centrolophus, 421

Channolabex, 380

Callichthyidae, 384

('i-iitrniiiifiix, 458

Channomumenn. 408

Callichthys, 384

Centrophoriis, 152 ; C*. rci'-

Chanoides, 393

Callionymidae, 456

c«w, 80 /.

Glianos, 347, 391, 393

Oattionymiu, 456 ; O. lyra,

CentrojMmun, 431

Characiuidae, 374

856 /.

' 'fiitrtwi/lliiiiii. 152

Characinoidci, 374

(\illnii Hxttu-, 379, 383

centrum, 68, 100 ; astero-

<'liitrit<is<-»inis, 395

<\i.llii]ilnjsus, 382

spondylous, cyelospon-

Chasmodes, 458

Calloptcrus, 331

dvlous, tectospondylous,

Chatoessus, 361 /., 391, 393

Callorliynchidae, 176

135 ; divided, 328

Chauliodontinae, 395

Oaliorhynektu, 133 /:, 168,

Cephalaspidae, 203

<'h<niU(«lns, 394, 395

169, 172, 176, 177 /. ;

( 'c])halaspidomorphi, 200

C'Jutunax, 462

','. aiitarcticus, 81 /..

(.'eplutlanpin, 200, 201 /.,

' ' Jhciracanthus, 192 ; ''.

171/., 178/.

204, 209 ; f,'. Ijf^t,

Murchisoni, 189/'.

C'allyodon, 447

20 1/., 202 /.

C/ii-iroilnpsis, 313

campanula Halleri, 359

L-t-phalisation, 2

C/ieirodus, 313; f. <//•»/ //*/-

Campodus, 147

('?/>lmlt>ptera, 167 ; C.yiov-

/(»«M«, 313/.

camptotricliia, 232

nae, 166/.

Cheirolepidinae, 310

canal of a Selachian,

' (7«-/(/, 431

Cheirolepis, 188, 307, 310,

lateral-line, 138/.

Cepolidae, 431

31 1/.

C'ttnobius, 310

fi'i-c.tiii.-i, 462

Chdmo, 434

C.iproidae, 432

Ceratiidae, 462

Ckiasmodon niijtr, 423 /.

('iipro.t, 433; C. aper,

Ceratodidae, 257

Cliiasmodontidae, 423

433 /.

('.•/•ri t<«f HX, 81, 89, 94 /.,

Chiasmodus, 423

Caraugidae, 464

106, 107, 108 /., 127, Chilinus, 447

(Juranffopsis, 464

133/"., 223, 224 A. 233/., Chilobranchus, 408

Caraax, 464; l'.f<f>l«n.

234! 236, 238, 289, 240, ('hilmlacfi/lits, 445

5o8

INDEX

Chilodiptems, 430, 431

Cladoselauhidae, 187

Coiiorhynchii?;, 382

Chilomy stems reticulatus,

Cladoselachii, 184

Gopidoyliniis, 380

440 /.

Clariallabes, 380

Copodus, 167

Chiloscyllium, 149

Clarias, 379, 380 ; C'.

Coregonus, 394

Chimaera, 128, 169, 176;

lazera, 381 /.; f '. magur,

Coridoi.in.i-, 447

C. monstrosa, 24 f. , 110

381 /.

Corydorvx, 384

/., 170/1, 172/1, '173 /,

Clariinae, 380

Coryphaena, 467

174 /., 175 /, 179/.

clasper, 129 ; anterior,

Coryphaenidae, 466

Chimaeridae, 176

174 ; frontal, 171

cosmiue, 217

Chimaeropsis, 168, 176

Cleithrolejjis, 336

cosmoid scale, 217. 230

Chimarrhiclithys, 456

Clim-atius, 192 ; C'. srutiger,

Uossyphus, 447

Chirocentridae, 390

192/.

Cottidae, 453

Chirocentrites, 391

Cliniis, 458

Cottocotnephoni.s, 453

Chirocentrus, 362, 391 ; r.

cloaca, 114

CM«s,453 ; ''. 70610, 103 /I,

dorafi, 116 /.

C/7/pe«, 326, 365, 368, 391,

453 /.

Ghirolopkis, 462

393 ; (7. refcwa, 393 /'. ;

cranial nerves, 6

(Jhirmnystus, 391

G, ' /iMto, 392 /. ; r.

Qrenuclnt.x, 375

Chirotiemus, 445

harengus, 393 /.

Cncodus, 286

Chirostoma, 420

Clupeidae, 391

Cromeria, 396

Chirothricidae, 400

Clnpeiforuies, 386

Cromeriidae, 396

Chirothrkc, 400

Clupeinea, 393

Crossognathidae, 393

Chlamydoselachidae, 142

Onidoglanis, 380

Crossognathuft, 393

Chlamydoftelachus, 132, 137,

Cobitidinae, 376

Crossopholis, 317, 318

140, 142 ; C'. anguineus,

(7oAt<w, 368, 375, 376

Crossopterygian, 291

128 /., 141/.

Cobtiopsis, 403

Crossopterygii, 280

Ohologaster, 401

Coccoderma, 290

Crossorhinus, 149

Chondrenchelyidae, 183

Coccodus, 340

Oryodraco, 456

Chondrenchelys, 183

Coccolepis, 308, 309, 310,

Cryphiolepis, 309, 310

Chondrichthyes, 118

312

Cteuodontidae, 257

chondrocranium, 11

Coccosteidae, 263

Ctenodus, 239, 240 /., 257

Chondrostei, 307

Coccosteomorplii (Arthro-

Ctenolabrus, 447

Chondrosteidae, 316

dira), 258

Ctenothrissa, 397 ; C*.

C/wndrostei/s, 317, 318. 319 ;

Coccosteus, 230, 259, 260,

vexillifer, 396/1

(7. acipenseroides, 3 1 7 /.

263 ; C'. decipiens, 260 /".,

Ctenothrissidae, 396

Clwncrhinus, 440

26 1/., 263/1

Cubiceps, 421

Chorinemus, 464

Cochliodontidae, 146

Cyathaspis, 195, 200

Chorismodactylftf, 450 ; C.

Cochliodus, 146

Cybium, 465

mnltibarbis, 451/1

Coelacanthidae, 290

Cyclobatis, 161

Ckorisochismus, 457

Coelacanthini, 287

Cyclopoma, 441

(Jhromis, 446

Coelacanthus, 106, 289, 290 Cyclopteridae, 454

Uhrysichthys, 380

Codmlus, 337/1, 340 Cydopterus, 365, 368, 454

Ckrytopftryg, 429

Coelolepidae, 196 Cyclostomata, 30

Chylomycterus, 440

Coelolepis, 196 Oyclostome, 6/., 7/.

C'ic/tfo, 446

coelom, 3, 26 Cymatogaster, 446

Cichlidae, 446

Coelophi-ys, 462 Cynoglossux, 473, 474

Uicltlopit, 431

Co-Hid; 391, 392 ; ('. t/nxfn<- Cyphosidae, 443

Cimolichthi/f:, 398

wu'm, 394 /. Cyprinidae, 375

circulation, branchial, 112

Colobodus, 336 Cypriniformes, 371

/, 139 /.

Colocephali, 407

Cyprininae, 375

Cirrhites, 431

Colocopvs, 436

Cyprinodon, 401

Cithariwts, 325, 375 ; C.

Columbia, 426 ; C. trans- Cyprinodontidae, 400

Geo/royi, 374 /

montana, 425/1 d/prinns, 375 : C. i-nrji/n,

Citharus, 474

Comephoridae, 453 '346/., 372 /., 376/1

Cladocydns, 390

Gomephorus, 453

Cytloides, 469

Cladodontidae, 183

Concliodiis, 256

Cyttoj/sis, 469

Cladodu*, 107, 108 /., 182,

Conchopoma, 246, 256

C^tttM, 469

183. 184 ; (7. Neilsoni,

Conger, 405 ; C'. vttlgaris,

128 /.

407 /.

Dactylqpogoii, 399

Cladosdaclie, 184, 185 /.,

Congrogadidae, 460

Dactylopteridae, 451

187 : r. 7-ym', 185/.,

Congrogailus, 460

Ihtctyloptems, 452, 453 ;

186 /'.

Congromuraena, 405

/>. rotifans, 452/.

INDEX

509

Ihtllia, 398 ; D. pectoralis,

399 /.

Dalliidae, 398
Dapedius, 334, 335 /.,

336 ; D. politus, 334 /.
Dapedoglossus, 390
JJascyllus, 446 ; 1). aruanus,

443 /.

Datnioides, 445
lieltodus, 146
Iteltoptychiux, 147
llendrodus, 285
Dentex, 429
denticle, 66, 118, 168 ; of

Teleostei, 356, 384
dentine, 119
Dereetidae, 417
Dercetis, 417
Derichthyidae, 406
Jierichthys, 406 ; Z). serpe/i-

tinus, 405 /.
dermal fin-rays, 109, 122,

212, 230
dermal plates of Ostraco-

dermi, 195, 206 ; of

Osteichthyes, 212
dermotrichia,109,122, 212,

230

JJiacranodus, 183
Diagramma, 445
Dibranchns, 462
Dicentrodus, 183
Dicerobatinae, 166
Dicerobatis, 167
IHcotylichthys, 440 ; /A

punctulatus, 441 /.
Dicrotus, 466

Didyopyge, 313 ; 7). wi«c-
, 314 /.
iispis, 204
diencephalon, 15
Dinichthyidae, 263
Dinichthys, 263 ; ./>. iWc/1-

medius, 265 /.
Dinolestes, 441
Dinopteryx, 427
iJiodon, 440 ; Z>. mucu-

latus, 441 /., 442 /. ; Z).

punctulatKs, 440 /.
Diodontidae, 440
diphycercal tail, 104
Diplacanthidae, 192
Dip! acanthus, 192 ; Z>.

striatus, 187 /., 191 /.
Diplacodus, 147
Diplocrepis, 457
Diplodus, 183
Diplognathus, 263
Diplomysta.i; 380
Diplomystacinae, 380
Diplomystes, 380

, 393

Diplopterus, 285

diplospondyly, 137

J)ij>/»i'ux, 290

Dipnoi, 230, 366 /. ; affini-
ties, 258

Dipteridae, 256

Dipterus, 230, 231, 232 /'.,
233, 238, 239, 241 /.,
242 /., 255 /., 256,257 ;
Z). Valenciennesii , 255 /.

Discocepliali, 448

Distichodus, 375

Ditrema, 446 ; />. argen-
teiim, 444 /.

Doradinae, 382

Doras, 383

Drepanaspis, 195, 198 ; />.
gemundi'iiensifi, 198 /.

Drepanasj>idae, 197

JJrepane, 434

Ductor, 464

Dussumieria, 391, 392

Dysichthys, 384

Dysomma, 406

Echeneididae, 449

Echeneidiformes, 448

Echeneis, 449

Echidnocephalus, 417

Kchinorhinus, 151, 152

Edestidae, 147

Edestus, 147

Egertonia, 447

egg-case, horny, 132, 168

egg-shell, 50

Elasmobranchii, 125

Elasmodectes, 178

Elasmodus, 178 ; A'. //"/(-
<m, 177/.

electric organ, of Raja, 161 ;
of Torpedo, 162 ; of
fiymnotus, 377; of Main-
pterurus, 383 ; of Mor-
myridae, 388

Eleotris, 448

Elonichthys, 311

Elopidae, 387

Elopopsis, 387

fifops, 326, 347, 355, 387 ;
.#. saurus, 345 /., 387 /.

Embiotoca, 446

Embiotocidae, 446

Embolichthys, 456

Enchelicephali, 405

Enchelunis, 417

Enchelycore, 408

Enchodontidae, 398

Enchodus, 398

Engranlinae, 392

Engranlis, 391, 392

Eocottus, 453
Eomyrus, 405
Eothynnus, 465
Ephippion, 440
Ephippus, 434 ;

434 /.

Epibulus, 447
epicentral, 353
epidermis, 25
epineural, 353
Epinnula, 466
epiphysis, 16, 24
Eques, 431
Equula, 445
Eritkrinus, 326
Eryihrichthys nitidt'.*, 350

/., 351 /., 356 /.
Erythrinus, 225, 226, 360,

375 ; A', unitaeniatus,

374 /.

Esocelops, 387
Esocidae, 398
Esociformes, 397
^soa;, 121, 272, 355, 368,

398 ; .& foetus, 121 /.,

321 /., 352 /., 364 /.,

365 /.

Etroplits, 446
Eucalia, 412
Euchilichthys, 382
Eucrosscrrhinus, 149
Eugnathidae, 330
Eugnathus, 331 ; A', oi'tho-

stomus, 331 /,
Euceraspis, 203, 204
Eumecichthyes, 476
Eumeda, 380
Enphaneropidae, 206
Euplianerops, 205, 206
Eupleurogrammus, 466
Eurycormns, 328 /., 329,

331

Eurylepis, 311
Eurynotus, 313 ; A', or-

woiws, 218/.
Eurypharynx, 407
Eurypholis, 398
Eusthenopteron, 106, 276,

286, 291, 299; A'.

Foorrff, 275 /., 280 /:,

282 /., 286 /.
Euthacanthus gracilis,

189

Euthynotus, 329, 333
Eutropius, 380
excretory system, 27, 83
Exocoetinae, 403
Exocoetoides, 400
Exocoetus, 402, 403, 453 ;

.B. callopterus, 402/.
external gills, 134, 247

5io

INDEX

eye, 23; ot'Elasmobranchii,

Gasterosteidae, 412

Gobiesocidae, 456

125 ; of Teleostei, 359

Gasterosteifornies, 410

Gubtesox, 457

eye-muscle canal, 326

Gasterosteoidei, 411

Gobiiformes, 447

eye-muscles, 5

Gasterosteus, 349, 412 ; G.

Gobio, 368, 375

aculeatus, 412 /. ; G.

Gobius, 115 /., 356, 448 ;

FnrneUia luberculata, 194

spinach ia, 410 /., 41 If.

G. guttatus, 447 /.

Fieratfer, 364, 419 ; F.

Gastrochisma, 465 ; G.

gonad, 28

acus, 351 /., 418 /. ; F.

melai/tjjus, 466. /'.

Gonatodus, 310 ; G. punc-

dentatus, 355 /.

Gastromyzon, 375, 376

tatus, 308 /. -

Fierasferidae, 419

Gastrostomits, 407

Gonorhynchidae, 395

tin, dorsal, 214 /.

Gastrotoceus, 415

Gonorhynektu, 395 ; '»•'.

fin - ray. See radial and

Gavialiceps, 406

grey I, 395 /.

dermal fin-ray

Gazza, 445

Gonostoma, 395

fin - skeleton, mesorhachic,

Gempylus, 466

Gonostomatiuae, 395

monostichous, ortho-

Gemundina Sturtzii, 180

Gosfordia, 258

stichous, pleurorachic,

genital duct, 27, 89 ; of

Grammisles, 431

rachiostichous, rhipido-

Elasmobranchii, 132 ; of

gular plates, 213, 304

stichous, 106-8

Dipnoi, 253 ; of Teleo-

Gymnarchidae, 389

fin, skeleton, 69, 106 ;

stomi, 366

Gymnarchus, 363, 388, 389

concrescence, 75 ; con-

genital pore, 46, 367

Gymnelis, 459

centration, 71, 75, 105 ;

Genypterus, 460

Gynmodontes, 439

migration, 79; of Elasmo-

GeopJuigus, 446

Gymnodraco, 456

branchii, 127

Geotria, 54

Gymnotidae, 376

fin-spines, 374, 424

Gephyroberyx, 427

Gijmnotus, 377, 404 ; G.

fins, lateral-fold theory, 73 ;

gephyrocercal tail, 355

electricus, 376, 377 /.

gill-arch theory, 73

Gerlachia, 456

Gyracanthidae, 192

fins, median, 32, 69, 70/.;

Gerres, 445

Gyracanthus, 192, 193 ; G.

development of, 71

Gerridae, 445

Murray i, 193/.

fins, paired, development

Gigantactinidae, 462

Gyrodus, 340

and origin of, 73, 107 /. ;

Gigantactis, 462

Gyrolepis, 311

of Elasmobranchii, 127 ; Gigantopterus, 336, 337

Gyroptychius, 285

of Pisces, 106 ; of Acti- gills, of Cyclostomes, 41 ;

Gyrostem, 317

nopterygii, 302 ; jugular,

of Pisces, 93 ; of Teleo-

425 ; thoracic, 425

stomes, 272

Haemulon, 445

Fistiilaria, 62, 355, 412 /,

gill-arch, 17 ; mandibiilar,

Halec, 398

413 ; F. serrata, 413/.

18; hyoid, 18

Halimoehirwrgiu, 437

Fistulariidae, 413

gill-rakers, 150, 248 llaluporphyrus, 482

fulcra, 304

gill-rays, 73, 123, 272

Halosauridae, 417

Fun</ulus, 401

gill-slits, 17, 93, 122

Halosattt'opsis, 417 ; H.

Ginglysmostoma, 149 ; G.

nigcrri'i/ius, 417

Gadidae, 482

cirratum, 76 /.

Haloscownu, 417

Gadiformes, 478

Girardinus, 401

Haplistia, 283

Gculomus, 478, 479, 481

girdle, pectoral, 73, 75 ;

Haplochilus, 401

Gadop.ii.t. 458

dermal bones of, 213 ; of

JJajilochiton, 398

Gadus, 62, 71, 272, 276,

Teleostome, 275

Haplocliitonidae, 398

352, 356, 471 /., 479 /.,

girdle, pelvic, 73, 75 ; origin

Haplodactylidae, 445

482 ; O. morrhua, 221 '/.,

of, in Teleostomi, 276 ; of

Haplodactyliu, 445

278 /., 347 /., 364 /.,

Actinopterygii, 302

Haplomi, 397

480/., 482 /.

Glanidium, 383

Harpodon, 399

Gal«xut.s,398; G. truttaceus,

Glaniopsis, 376

Harriotta, 173, 178 ; H.

398 /.

Globulodits, 313

elegans, 177 /. ; H.

Galaxiidae, 398

Glyptolaemus, 285

RaUighana; 179 f.

Galeocerdo, 151

Glyptolepis, 280, 285 ; G.

heart, of Cyclostome, 43 ;

Galeoides, 421

leptopterus, 282 f.

of Dipnoi, 249 ; of

Galeus, 151

Glyptopmnidae, 285

Pisces, 109 ; of Tele-

Gambusia, 401 ; G. affinis,

Glyptopomus, 280, 281 /.,

ostei, 363

401 /.

285; G. Kinnairdi, 284 1/.

Helgiu, 376

Ganodus, 178

Gnathonemus, 389

Heliastes, 446

ganoid scale, 217

Gnathostomata, 58

Helicoplagus, 380

ganoine, 218

Gnathostome, 6f., If.

Helicoprion, 147 ; //. besso-

Ganwhynchus, 256

Gobidae, 448

novi, 148/.

INDEX

Jlelodus, 146

Homalopterinae, 376

Jii/tc.ftm, 167, 168

J/elostuiiui, 422

Homea, 51 ; //. Stouti,

jaws, 18 ; of Pisces, 95 ; of

Hemerocoetes, 457

48 /.

Dipnoi, 237 ; of Teleo-

hemibraiich, 94

homocercal tail, 101, 104

stonii, 266 ; of Teleostei,

Hemibranchii, 410, 411,

Jtomosoma, 421

349

412

Homosteidat', 263

Joi'daiilc, 453

Jfemich fumis, 446

Hamasteus, 263 ; //. milleri,

Joturus, 420

JJemiprixtis, 151

265 f.

Jugulares, 454

llemirhamphus, 402, 403 ;

Hoplichthyidae, 454

yi//i's, 447

//. tii-iixilii-ioiiti, 402 f.

Jfoplichthys, 454

lli'/ni ili i/Hchi(s, 467

Hoplognathidae, 431

Kathetostoiita, 456

//<•/// i t r i i>tei"iis acadianus,

Jloploynat/nts, 431

kidney, 27 ; of C'yclosto-

447 /.

Hoplopteryx, 427 ; //.

mata, 45 ; of Dipnoi,

Jfeptanclnts, 76/., 95, 98 A,

leu'esiensis, 427/.

253; of Elasiiioliranchii,

139 /., 140 /., 142, 143 :

horny teeth, 31

132 ; of Pisces, 83

H. cinereus, 15/, 138/. ;

Hybodns, 97, 143, 144,

Knma, 399

H. indlcus, 142 /.

146 ; //. fnihi'i/ri/tatu^,

Kneriidae, 399

JIept<tnen>((, 290

146/.

Krohnius, 481

Hems, 446

Ili/tli-ix-imn. 325, 375

Kurtidae, 468

Jlt'ti-ftibrtHicfiiix, 380

Hyodon, 389, 390

KnrtiforuiL's, 468

heterocercal tail, 101, 104

Hyodontidae, 389

/fM;-<«.s, 468

Heterodonti, 143

Iiyostylic jaws, 95

Kyphosus, 443

I/etei-odontits, 128, 133 /.,

llypnos, 162, 163

143, 144, 145, 146 ; 11.

hypocentruni, 328

Labeo, 375

I'/n'/ippi, 80 f., 96/.,

hypochordal fin, 101, 104

Labichthyx, 406 ; //. Cfert-

147 /.

hypoglossal muscles, 11 ;

natus, 405 f.

lletefolfpidntus, 331

nerve, 11

Labidesthet, 420

Heteromi, 416

Hypophthalmichthys, 375

Ac///-".,-, 443

Hettrophthalm ".v, 432

hypophysis, 18, 39

I^aliridae, 446

Hetero.straci, 195

Bypoptycfius, 403

Liitii-otttHi, 447

Heterotis, 390

Hypo.stoini<k's, 416

Latifiiit, 447 ; /.. macii-

Hexagrammidae, 453

Hypsoconnus, 333 ; ^. iw-

latvs, 444/.

Hexagraasauu, 453

signis, 331 /.

Labyrinthici, 422

Hexanchvs, 136 /., 140,

hypnral, 353

F.actariidae, 445

142, 143

llt/xti'i-i'i'iirin'x, 446

Laclo fiiis, 445

llii'i-ii-lithi/.f, 460

Lnctoph fi/x, 439

Himant<ili'i>hn.i. 462

Laemargus, 126 /., 134,

Hippocanipidae, 415

Icelus, 453

151, 152

Ifi//jn>i;ii,ijiiis, 415 /.

Ichthyoborus nilotiais,

Lamna, 121, 150 ; Z.

Bippofflosfue, 474

•2-2(5 /.

cornubica, 136 /., 150, /'.

Histichthyes, 476

Ichthyoilecti-*, 391

Lamnidae, 149

Jlistiocephalun, 450

ichthyopterygiam, 73

Laiiininae, 150

Histionotvs, 336

Ichthyotomi, 180

Laniprididae, 475

Histiophoridae, 467

Ichyndus, 178

Lanipridilbrmes, 475

Histiophoms, 468 ; //. /<"/-

fctcWAy*, 421

Lmnpi-is, 421, 475 ; /,.

eAetfws, 468 /.

Icosteidae, 421

yuttatus, 406 /.

Histiothrissd, 393

Icosteiis, 421

Lamprogrammus, 459

llohii-iiitthiix, 434

Idiacanthus, 395 ; I.ferw;

Lamproloyus, 446

holobraucli, 94

395 /.

Luiuirkia, 195, 196 ; />.

Holocenti'um, 356, 427

Ilyophys, 405

spinosa, 197 /.

Holocephali, 168

infandibulnm, 12, 16

Lasaniidae, 205

Holophagus, 290 ; £f. </«/£>,

interdorsal arch, 100

Lasanius, 204, 205, 206

287 /.

iuterorbital septiiin, 169 ;

lateral line, in scales and

ffoiopteryx, 427

in Holostei, 324, 390,

plates, 219

Holoptychiidae, 284

398, 478

lateral-line system, 19 ; of

Holoptychius, 280, 285 ;

interventral arch, 100

Elasmobranchii, 125 ; of

#. Anderson i, 281 /. ;

Ipnops, 399

Osteichthyes, 220

//. Flemingi, 284 /.

Ischnacanthus, 190 /., 192

lateral-plate mesoblast, 3

Holostc-i, 321

isopedine, 217

Lates, 443

Holurus, 311

Isospondili, 386

Latilus, 431

Homaloptero, 375, 376

Isurichthys, 465

Latrididae, 445

512

INDEX

Latris, 445

Lobotidae, 444

Mastacembelidae, 478

Lebiasina limuculuia, 226 f.

Lophiidae, 462

Mastacembeliforme.s, 477

Leyiwnotus, 336

Lophiomus, 462

Mastacembdus, 478 ; 3/.

Lepadogaster, 364, 457 ; L.

Lophius, 272, 462

argus, 478 f.

gouanii, 457 f.

Lophobrancliii, 410, 414

Maurolicus, 395

Lepidocottus, 453

Lopholatilus, 431

Medialuna, 443

Lepidoleprus, 82

Lophotes, 476

medulla oblougata, 13

Lepidopus, 466 ; L. cauda-

Lophotidae, 476

Megalichthys, 280, 285 ;

tus, 467 f.

Lophrostomus, 331

3/. Hibberti, 217 f.

Lepidosiren, 89, 117, 230,

Loricaria, 384 ; Z. lancen-

Jkfegalops, 363, 387

233, 244, 247, 250, 253,

tata, 384 /.

Afegalur-us, 334

258 ; L.paradoxa* 243 f.,

Loricariidae, 384

Melanocoetus, 462

246 /., 247 /., 257 f.

Loricariinae, 384

Melanostigma, 459

Lepidosirenidae, 258

Zoto, 365, 482 ; Z. r"/-

Menaspidae, 180

Lepidosteidae, 344

garis, 482 /.

Menaspis, 180

lepidosteoid scale, 218

Lucifuga, 459; Z. detitatus,

Mene, 464

Lepidosteoidei, 340

460 /.

Afenidia, 420

Lepidosteus, 84/., 89, 94/.,

Luciocephalns, 423

Merluccius, 482

102 /., 105 /., 121 /.,

Lucioperca, 443

Merlucius, 121 ; J/. tnti-

133 /., 213/., 214, 224,

Luciosoma, 375

gram, 121 /.

270, 272, 277, 278, 296,

Luvaridae, 467

Mesacanthus, 192 ; 3f.

298 /., 302, 324, 326,

Luvarus, 467

Mitchelli, 192/.

327, 340, 342, 344, 356,

Lycocara, 459

mesencephalon, 14

366 /., 367 /., 368,369;

Lycodes, 459 ; L. perspicil-

Mesiteia, 149

L. osseus, 215 f., 219 /.,

lum, 459 /.

Mesodon, 337, 340 ; J/.

277 /., 314 /., 342 /.,

Lycodontis, 408

macropterus, 339 /.

343 /. ; L. viridis, 341/.

Lycoptera, 371

Mesolepis, 313 ; J/. sc«-

lepidotrichia, 212, 273, 322

lymphatic system, 26

toris, 312/.

Lepidotrigla, 450

mesonephros, 27, 45, 86

Lepidotus, 335, 336, 343 ;

«

Mesoprion, 431

L. minor, 335 /.

Macrodon, 225, 375

Mesturns, 337, 338, 340 ;

Lepomis, 443

Macrones, 380 ; 3/. 7ie-

Af. Ze«fci, 338 /.

Lepophidium, 460

murus, 373 /.

metanephros, 27, 87

Leptecodon, 398

Macropetalichthyidae, 262

metencephalon, 13

Leptobarbus, 375

Macropetalichthys, 262

Micracanthus, 423

Leptocephalus, 388, 404

Macropluirynx, 407 ; J/.

Microbrachius, 209

Leptoderma, 394

longicaudatus, 406 /.

Microdon, 337 /., 340

Leptolepidae, 371

Macropoma, 289, 290 ; 3/.

Micropterus, 443

Leptolepis, 371

Mantelli, 288 /., 289 /.

Alicrostoma, 393

Leptopterygius, 457

Macrorhamphosus, 413

Mioplosus, 443

Leptoscopidae, 456

Macrosemiidae, 336

Misgumus, 365, 376

Leptoscopus,156; L.macro-

Macrosetnius, 336

Mitsukurina, 150

pygus, 456 f.

Macrostomias, 395

mixipterygium, 129

Leptosomus, 399

Macruridae, 480

Jfote, 441

Leptotrachelus, 417

Macruriuae, 481

Molidae, 440

Leuciscus, 375 ; L. ceplialus,

Macrurus, 479, 481 ; Jf.

Mollienesia, 401

220 /. ; L. phoxinus,

australis, 481 /.

Molva, 482

357/. ; L. rutilus, 210/.,

Malacichthys, 441

Monacanthidae, 437

21 If.

Malacopterygii, 386

Monacanthus, 437 ; J/.

Libys, 290

Malacosarcus, 424

chaerocephalus, 439 /.

Lichia, 464

Malacoste.us, 395 ; J/. in-

Mouocentridae, 428

Linophryne, 462

rf/CMs, 395 /.

Monocentris, 428 ; Jf.

Liocetus, 462

Malapterurinae, 383

japonicus, 428 /.

Liodesmus, 334

Malapterurus, 352, 383 ;

Monocirrus, 445

Liparis, 454 ; L. Dennyi,

J/. electricus, 351 /.,

Monopterus, 409 ; M.java-

454 /.

382 /., 383 /.

nensis, 409 /.

Liparops, 454

Mallotus, 394

Mordacia, 54

Lipogenyidae, 417

Malt/ie, 462

Moringua, 405

Lipogenys, 417 ; Z. Gillii,

Malthidae, 462

Mormyridae, 388

418 /.

Malthopsis, 462

Mormyrinae, 389

Lobotes, 445

Marcusenius, 389

Mormyrops, 389

INDEX

513

Mvrmyrus, 389, 390 ; AI.

Necturus, 11

Odontaspis, 150

oxyrhynchus, 388 /.

Nedystoma, 382

Odontostomus, 399

Morone, 431

Neencheli, 405

Oenoscopus, 337

Motella, 482

yematonotus, 399

Ogcocephalus, 462 ; 0. ves-

mouth, 18, 67

Nematoptychius, 310

pertilio, 461 y.

Moxostoma, 375

Nemichthyidae, 406

olfactory organ, 23

mucous glands, 50

Nemichthys, 406

Oligopleuridae, 337

Afugil, 356, 420 ; AI.

ffemopteryx, 482

Oligoplenrus, 337

cephalus, 420. /'.

Neoborus, 375

Oncobatis, 161

Mugilidae, 420

Xeobythitcs, 459

Onirodes, 462 ; 0. glome-

Mugiliformes, 419

iVeoceratodns, 258

rovus, 462 /.

Mnllidae, 429

Neochannn, 398

Onychodontidae, 286

Mulliniles, 429

Neopercis, 456

Onychodus, 286

AIullus, 429

NeorhomboUpis, 331

operculum, 169, 223

Muraena, 408 ; M. pida,

y<'tixiliirus, 380

Ophichthys, 405

408 ./: '

nephriilia, 27

Ophidiidae, 460

Muraenidae, 408

Xerophis, 415

Ophidium, 460

Muraenolepidae, 483

nerve-components, 19, 22

Ophiocephalidae, 422

Muraenolepis, 352, 479,

/. ; acustico-lateral, 19

Ophiocephahis, 422 ; 0.

483

general cutaneous, 21

striatus, 421 /., 422 /.

muscles, 3 ; of eye, 5 ;

general splanchnic, 21

Ophiodon, 453

epibranchial, 6 ; hypo-

somatic motor, 21

Ophiopsis, 336

branchial, 5 ; trapezius, 6

splanchnic motor, 21

fyristhocentrus, 458

Mustelus, 94/., 134, 151 :

splanchnic sensory, 21

Opisthognathus, 431

M. autarcticus, 111 /. ,

nerve-roots, 2, 4

Opisthomi, 477

115/. ; M. laevis, 20 f.,

nerve supply, 78 /.

Opisthomyzon, 449

68 /.

Xettastoma, 405

Opisthoprocttis, 394 ; 0.

inyelencephalon, 13

nictitating membrane, 151

soleatus, 406 /.

Myliobatidae, 165

Xomeus, 421

Opsam(s, 460

Myliobatinae, 165

Nostril, median, 39 ; paired,

Oracanthus, 192, 193

Alylinbatis, 128, 166 ; M.

82

Orectolobinae, 149

ar/i/ila, 166 f.

nostrils of Elasmobranchs,

Orectolobus, 149

Alylostirmn, 263 ; Al. mri-

125 ; of Dipnoi, 241 ;

Orestias, 401

abilis, 264 /.

of Osteichthyes, 227

organs, urinogenital, 84 /.

Mylostomidae, 263

Notacanthidae, 418

Orodus, 146, 147

myodome, 326

Notacanthiformes, 416

Orthacanthus, 183/.

myotome, '2

Xotacanthus, 418 ; *V.

Orthacodns, 150

Myriaeanthidae, 176

ininlis, 418 /.

Orthagoriscus, 441

Ali/riacanthns, 172, 176.

Notagogus, 336

Osmeroides, 387

177/., 178/., 180

Notelops, 387

Osmerus, 365, 367, 369,

Ali/riolepis, 311

Notidani, 139

394

Myripristis, 427

Notidanidae, 143

Osphromenidae, 422

Mi/riirungei; 408

AW«toniw,l40,142/,148;

Osphromenus, 422 ; 0.

Alyrun, 405

^.V. cinereus, 76 f.

o//aa;, 423 /.

Alyxine, 35, 42 /., 46,

notochord, 1, 68, 97

Ostariophysi, 371

48 /., 51, 133 /. ; M.

notochordal sheaths, 31,

Osteichthyes, 210

(jlutinosa, 33 /., 35 /.,

97, 273

Osteoglossidae, 390

44/., 47/., 50 /.

Notoglanis, 382

Osteoglossum, 363, 390

Myxinidae, 51

Notogoneus, 395

Osteolepida, 280

Myxinoiilea, 46

Notopteridae, 389

Osteolepidae, 285

J///./V/X. 420

Xotopterus, 390 ; iV. J:n/>i-

Osteolepidoti, 280

rat, 389 /.

Osteolepis, 280, 299 ; O.

Xotothenin, 456

macrolepidohis, 283 /.

Naudidau, 445

Nototheniidae, 456

Osteorhachis, 331 ; 0. /ee<?s/,

Nandus, 445

Novacula, 447

329 /.

Nannoglanis, 382

Osteostraci, 200

Narcine, 161, 163

Ostracion, 117, 439

Naseus, 436

occipital region, 11

Ostraciontidae, 439

Naucrates, 464 ; N. ductor,

occipito-spinal nerves, 12

Ostracodermi, 194, 437

353 /.

Odax, 447

otic process, 97, 139, 144

Nealotv.s, 466

Odaxothrissa, 393

otoliths, 298, 324

33

INDEX

Otolithus, 360, 361 /.,

Pempheridae, 428 Selachii, 127 ; of Tele-

431

Pempheris, 428 ; P. r«s-

ostei, 357, 394, 399

Oxydoras, 383

se«i, 427 /.

Photichthys, 395

Oxygnathvs, 312

Pentaceros, 431

Photoblepharon, 432

Osyrhiiia, 150

Pentanemiis, 421 ; P. <?*mi-

Pfwtonectes, 395

quarius, 420 /.

Phractolaemidac, 391

Pachycormidae, 331

Pentapus, 445

Phractolaemus, 391

Pachycimnus, 333 ; P.

Perai, 365, 368, 443,

Phractura, 382

heterurus, 103/.

479 /.; P. fiuvialilis,

Phycis, 482

Pachylebias, 401

221 /., 442 /.

Phyllodus, 447

Pachyula, 382

Perccsoces, 419

Phyllopteryx, 415

Paecttodus, 147

Percichthys, 431

phylogeny of the Chon-

Pagettus, 429

Percidae, 441

drichthyes, 124 /. ; of

Pagrus, 429

Perc-i formes, 428

Osteichthyes, 228, 228/.,

Palaeaspis, 199/1, 200

Percophiidae, 455 229/. ; of Teleostei, 370 :

Palaedap/ms, 256

PercopMs, 456 : P. brasili- of Vertebrate Craniatsi.

Palaeobulistum, 340

e?ms, 455 /. '29

Palaeomylus, 180

Percopsidae, 425 Physoclisti, 359

Palaeoniscidae, 309

Perco2)sis, 426

Physostomi, 359

Palaeoniscidinae, 310

pericardium, 26 ; of Myxi- Piubuciiia, 375

Palaeoniscoidei, 309

noid, 50 ; of Pisces, 109 Pi'cfcJ, 336

Palaeoniscoid scale, 218

Periophthalmus, 448, 458 Pimelmlns, 382

Palaeoniscus, 311 ; P. OT«C-

Peristedion, 450 ; P. »n'«/- pineal eye, 24

ropomus, 310/.

atom, 452 /. ; P. c«/«- Pisces, 93

Palaeorhynchidae, 467

phractum, 447 /. placoid scale, 118, 121,

Palaeorhynchus, 467

Petalodontidae, 167 356

Palaeoscyllium, 149

Petalodus, 168 J'lng-usiu. 474

Palaeospinax, 144, 146

Petalopteryx, 336 I'lutn.i-, 434

Palaeospondylidae, 56

Petrocepludiis, 389 Platinx, 391

Palaeospondylus, 56, 57 ;

Petromyzon, 8, 9, 10, 11, i Platyceplialidae, 454

P. Gwrwit, 56, 57 /. -

19, 25, 25 /., 38, 39,

Platycepkahu, 454

palato-basal articulation,

39 /., 41, 43, 45, 51,

Platycoi-mnx, 421

97, 271

54, 85 ; P. flwriatilui,

Platyglossus, 447

Palimphyes, 465

SO/., 40/., 53./1, 54/.,

Platylaemiis, 447

Palmas, 297

55/. ; P. marinus, 31 /'.,

Platypoecilutt, 401

Pantodou, 396

32/., 34/., 45/., 52/.,

Platyrhina, 161

Pantodontidae, 396

133 /.

Platyrhinoiclia, 160

Pantopholis, 398

Petromyzontia, 51

Platysomidae, 312

Pamlepis, 399

Petromyzontidae, 54

Platysoiinis, 313

Paraliparif, 454

1'etroscirtes, 458

Platytroctes, 394

Paraluteres, 437

Pliaebodus, 183

Plecodus, 446

Paramyxine, 47, 48/1, 51

Phago, 375

Plecostomus, 384 ; P. Co?«-

Parapercis, 456

Phaneropleuridae, 255 mersonii, 383 ./I

Paraphysis, 16

Phanerqpleuron, 230, 233, Plectognathi, 435 .^'

Pampriacanthus, 428

239/., 255; P. --l/c/'V- I'tectronm.a, 427

Parapsettus, 434

soni, 256 /. ; P. I'ti.'ti/in. Pleuracanthidae, 183

Parascopeliis, 399 | 231 /. Pleuracanthodii, 180

Parexus, 189, 190, 192 ;

Phanerosteon, 307, 30!». Pleuracanth/us, 107, 180,

P. falcatus, 191 /.

311 182, 183; /'. il ?<•]„•,<!,

Paropsis, 464

pliaryngeals, upper and

181 /., 182 /.; /'. &««-

Pataecvs, 458

lower toothed, 44.". «V.y/, 183/1, 184. /I ; /'.

pedicle of suspensoriimi,

Pharyngognatlii, 445 Odberyensis, 184/1

97, 271

Pklyctaenaspis, 260, 263 I'li-tint'ii-amiim, 456

Pediculati, 454, 461

Pholiilidae, 458 plenrocentrum, 328

Pegasidae, 416 ,

Pholidopboridae, 336 /'Icurogrammus, 453

Pegasus, 416 ; P. natuns,

Phdidophorus, 337 Pleonnectes, 62, 472, 473,

416 /.

Phdidosteus, 260, 262/1, 474; P. Jtesus, 104 /.:

Pelargorhynchus, 417

263 ; P. Friedeli, 261 /I

P. platessa, 470/1, 471 /I,

Pellonula, 391, 393

Pholidurits, 317, 318 472 /.

Pefor, 450

Pholis, 458 Pleuronectidae, 469

Peltopleums, 337

phosphorescent organs of Pleuropholis, 337

INDEX

515

Pleuruplu.'.; 146 Pi-i>/nnna, 441

Pterothi-issus, 388

Pliotremu, 143, 152, 153 P,':>pris.tis, 160

Plerichthys, 207, 209

/Wr/iVA'*-, 460 I'/'upterus, 336

Pterycombus, 464

Podatelidae, 460 pvosencephalon, 16, 245 f.

Pteri/gocejjlialns, 468

I'ni'ciliii, 401 I'rntacanthodes pinnattis,

Ptycliodontidae, 166

pui/fniHis, 431; P. chi-omia, 187 /., 192

/'tychoilim, 166 ; P. decur-

361 /. I ' rotantigonia, 433

n-iis, 165 /.

Polyacaitt/iux, 423 I'rutodits, 147

Ptycholepis, 331

Polycentmiifiix, 445 I'rotopterus, 17, 223, 225/.,

I'tyctodontidae, 179

Poli/centni.s, 445 234 /"., 244, 245, 247,

I'lyctodii'S, 180

Polyipnus, 395 ; P. .sy///*o- ' 251 /., 253, 254 /, 268,

I'yenodontidae, 337

SKA', 358 /.

305, 366 / ; P. annec-

I'l/ciuidux, 340

Piili/iiiicia, 427

te»w, 231 /., 235 /.,

Pygopterus, 307, 311

Polynemidae, 420

245 /., 249 /., 253 /.,

l>yloric caeca, 297

Piili/ufiimx, 421

257 ./'.

I'u! ,/,„/,, ,t, 303, 317. 318 ;

PrutuSfjhyrae/ta, 333

P./WHMB, 802/., 816/.,

Protosyngnathiihu', 412

Racovitzia, 456

318 /.

Protosyngnathoidei. 412

radial, 69

Polyodontidae, 317

Protoayngnatktu, 412

AVya, 76 /'., 79/., 133/.,

Polypteridae, 300

/'folotroctes, 398

136, 137, 139 /., 155,

Polypterus, 94/., 117,214,

protractile jaws, 349, 375

156 /., 157 /:, 161 ; 7f.

223, 224, 226, 227, 243,

Psammodoutidae, 167

&«*<«, 14 /, 158 ; /,'.

271, 272, 276, 277, 278,

/'xitii/iiitidu-s, 167

W«/«?fl, 120 /., 122 /.,

290, 291, 293, 296 /.,

Psammosteidae, 198

ISO/., 166/. ; A ctettite,

297, 298 /., 300, 305 /.,

/ '.•<'! /a niosteus, 195, 196 /.,

161 /., 166/.

324, 350, 356, 366 f.,

198, 200

liajidae, 160

367 /., 368, 369, 388 ;

/'xi'ji/iodita, 146

Rajifonnes, 153

P. bickir, 101 /., 21 1/.,

I'.icphurus, 318 ; P.ijladius,

ftimo, 98/., 254 /.

269 f., 290 /., 291 /'.,

318 /.

/tttitici'jts, 482

292 '/, 293 f., 294 /.,

/'.seii!rt, 474

1'anzannia, 441

295 /., 297 /., 299 /.,

I'settodes, 472, 473, 474;

ivctal gland, 137

301 f. ; P. laprudei, 299

P. erumei, 473 /.

Regalecus, 476, 477 ; -ft.

/, 300 /.

Psettus, 432 ; P. aryenteus,

glesne, 476 /.

Polypterini, 290

432 /.

Renwra, 449 ; ^. braehy-

Polyrhizodus, 167, 168 : P.

Pseudetroplus, 446

ptera, 448 /.

pusillus, 167 /.

Pseudeutropius, 380

respiratory organs, acces-

Pomacanthus, 434

Paevdobei-yx, 393

sory, 379, 409, 422

Pomaceutridae, 446

pseudobraucli, 111, 258 I Rliachicentridae, 464

Pomaceiitri'fi, 446

Psendochroroidldfte, 431

Rhachieentrus, 464

PmiMtoiinix, 431

Ptettdochromu, 431

Rhacn/ejtis, 387

PoitHillx, 443

Pseudoscarus, 447 : /'.

Rhadi,»irlitli>is, 311

Pvin.<>.<:iix. 443

nntricatvx, 446/.

Itii'iiii/i/iifhthys, 377

Poricldhys, 460

Pseudoscopdus, 423

Rliamphocottidae, 453

Portheus, 391

Paevdotphaerodon, 447 ll/iam/>/t<i<-i't/<tx, 453

/'/•/'acanthus, 431

Paeitdofyngnathiia, 415 RAomphoehu, 179, 180

Priotiotus, 450

PsiloeepholMB, 437 Rhamphognat// vn, 420

Priomrrus, 436

I'xi/i-hrohitfx, 454

Rha.mphosus, 413

Pristidae, 160

Pteradit. 464

/?/u'na, 71, 151, 157 : /^.

Pristioplioridai'. 152 Pteraspidae. 198 squatina, 79/., 153 /.

Pristwphorus, 152, 153 ; I'tcraspidomorplii, 195

RAuutute/r, 380

P. cirratus, 153 /. /'/,•,•«*/<(*, 195, 196 /., 198,

Ithiuellus, 399

/ 'n'x/ ijiOHia, 445 200 ; P. rostrata, 19»/.

rhinencephalon, 16

I'ristiiioiiiatidae, 445 I'ti-richthyoniorphi, 206

Rhiuobatidae, 159

Pristis, 71, 160 I'tfricltt.hys* 261 ; A

I'liiiinhii.tus, 160 ; R.grann-

Pristiurus, 5, 75, 149 MHIeri, 208 /.

lutiix, 79 f.

Pi-i>ca/<'j»ift, 400 /'ffi-nis, 450 ; /'. BoKfolM,

Rhinochimaera, 178

/'mrlianvs, 393

450 /.

Rhiuochimaeridae, 178

relates, 431, 441

Pterophri/ne, 462

I ih 'modem, 150

Prolebins, 401

Ptei'i.>i>I«.t.e« iiiicri'fu. 134 /.

Rhinodontinae, 160

Promyliobatis, 165. 166

Pteroplalca, 164; P. Firfcn-

Rhinoptera, 167 ; R.polyo-

pvonephros, 27, 43, 83

ciennii, 164 /.

don, 167 /.

5i6

INDEX

Rhinoraji, 159

216/., 217; ganoid, 217;

segments, of head, 3 ; of

Rhipidistia, 284

lepidosteoid, 216/., 218 ;

trunk, 2

Rhizodontidae, 286

palaeoniscoid, 216 /., Selache, 149 /., 150

Rhizodopsis, 286 ; R.

218; Rhizodont, 216/. ; Selachii, 135

sauroides, 286 /.

Teleostean, 356 Selene, 464

RJiizodiis, 286

Scapanorhyrukut, 150 > Selenichthyes, 475

Rhodeus, 368, 375

Scaphirhynchus, 302 /.,

Selenosteidae, 263

Rlwdichthys, 459

319, 320 ; S. cdtu-

Selenosteus, 259, 263 ; .S'.

RlwmboidicMhys, 474

phractus, 303 ; S. plato- Kepleri, 264 /.

Rhombosolea, 473

rhyuchus, 320 /. Semiouotidae, 334

Rhombus, 474 ; R. maxi-

Scarichthys, 447 Semionotus, 336

mus, 471 /.

Scaridae, 447 Semiophorux. 464 ; &

Rhynclwbatus, 160 /.; R.

Scarus, 365, 447 velicans, 46o./'.

djeddensis, 76 /., 159 /.

Scaumenacia, 233, 2-">4.

sense-organs, 19

Rhynchobdella, 478

255 ; & cjtrto, 256 /.

Feriola, 464

Rhynclwdus, 177 f., 180

Hckilbe, 380

Serranidae, 430

Rhynchorhinus, 405

ticiaena, 431

Sernums, 133 /., 431 ; £.

rib, plenral and dorsal, 68,

Sciaenidae, 431

altivelis, 430 /'. ; .S. «/6-

101

Sclerocottus, 454

ri«a, 430 /.

.fti'to, 380

Sclerodernii, 436

Sermsaliiw, 375

Rohteichthys, 375

Sclerognathus, 375

^i'1-rolepift, 336

Rondeletia, 399

scleromere, 11

Setarches, 450

Scleropages, 390

Siganidae, 435

Saccarius, 462

Scleroparei, 449

Siganus, 435

Saccobranchus, 379, 380 ;

Sclerorhynchus, 160

Sillagiuidae, 432

S^fossilis, 382 /.

selerotome, 3

81 Hugo, 432

Saccopharyugidae, 407

Scomber, 465 ; £ scomber,

Siluridae, 379

Saccopharynx, 407

149/.

Silurinae, 380

Sagenoilus, 257

Scombresocidae, 402

Siluroidei, 377

Salamandra, 254 /.

Scombresox, 402, 403

Silurus, 380 ; S.ylunis, 378

Salanx, 394

Scombridae, 465

/., 382 /.

Salarias, 458

Scombrifonnes, 462

Sinenchelys, 405

-SWww, 71, 94 /., 96 /.,

Scombrinus, 465

Siphonognatlms, 447

102 /., 225, 271, 305,

Scombrodupea, 393

Siplwnostuiiw, 415

326, 354, 363, 367, 368,

Scombrocottus, 453

5«'s(w, 382

394 ; & safer, 110 /.,

Scopelidaer 399

skull, dermal bones of,

275 /., 279 /., 322 /.,

Scopelius engraulis, 358 /.

213 ; development of,

323 /., 325 /., 327 /.,

Scopeloides, 399

12 /. ; bones of, 267 ;

360 /., 394 /.; S. truta,

Scopelus, 399, 423 /.

segmental theory of, 11 ;

357 /.

Scorpaena, 450 ; <S. 6y/io-

vertebral theory of, 2, 1 1

Salmonidae, 393

e»isw, 450 /.

Smerdis, 443

Salmopercae, 425

Scorpaenichthys, 454

>We</. 356, 472, 473, 474 :

Sandalodtfs, 147

Scorpaenidae, 449

& heterorhini', 474./.

Sarda, 465

Scorpaeniformes, 449

Soleuostomidae, 414

Sardinius, 399

Scorpaenopsis rosea, 424 f.

Solenostomoidei, 414

Sardinoides, 399

Scorpididae, 432

Solenostomiis, 414

Sargodon, 336

SCOT pis, 432

somactidium, 69

.Sanfus, 429 ; 6'. ott's, 429 A;

Scyllaemus, 393

somites, 3 ; prootic, 5 ;

& rufescens, 429 /. ; £

Scyllidae, 149

metaotic, 5

?-«<wte, 429 /

8cyllinae, 149

sound-producing organ, 379

Saurichthys, 321

Scyllioidei, 148

Xpaniudoii, 392

Sauripterus, 286

Scylliorhinus, 149

Sparidae, 428

Saurocephalus, 390

Scyttium, 71, 75, 98/., 123,

Sparnodus, 429

Saurodon, 390

125 /., 128, 133/..137,

Spar us } 429

Saurodoutidae, 390

149 ; ^. canicula, 58/.,

Spathiurus, 337

Sauropsis, 333

69 /, 72/., 99/., 119 /.

SpJienacanthus, 146

Saurorhamphus, 321

Scymnus, 128, 152 ; <S.

Sphenoceplialvs, 427

scales, ctenoid, cycloid,

/i'c/u'a, 80 /.

SpJienodus, 148

ganoid, and placoid, 210,

Sebastes, 450 ; <S. percoides,

Sphyraena, 419

217 ; development of,

449 /.

Sphyraenidae, 419

119, 214, 356 ; cosmoid,

Sectator, 443

Sphyraenodus, 465

INDEX

517

Sphyrna, 151

XymitHji-ittiit, 182, 183 ; .S.

Thy r sites, 466

Spliyrninae, 151

•reniforme, 128/.

Thyrsitocephalut, 466

tipinacantlms. 437

^i/i/tpltni-ua, 474 Thyrsoidea, 408

Spinackia, 412

Xympteryyiu, 161 Tilupui, 446

Spinacidae, 151

Si/nai/ropn, 441

futeo, 365, 375

spinal nerve, 2, 4. 22, 83

8ynnncidii(m horrid i* /// .

Titanichthyidae. 263

Spinaz, 5, 151, 152 ; X

483/. TitiiHichMii/x, 259, 260,

niger, 17 f.

Synaphobrancliidae, 407 263

Spine, vertebral, neural, and

SynaphobrtOichus, 407 Torpedinidae, 161

haemal, 32, 100, 101.

Synaptura, 472, 474 ; X Torpediiioidei, 161

105

albv'iiutculata, 474/. Toiyedu, 115/., 134, 139 /.,

Sjii/iiroi/ter, 406

Ki/itevhodttis, 144, 146; X 161, 162 /., 163 /. ; T.

spino-occipital nerves, 11

dabi-isiensis, 145 /. ocellata, 154/.

spiral valve, 43, 114 ; of

.Sj-ngnathidae, 415 Trachichthys, 427

Teleostei, 327, 362

.*t/ni/inithns, 415 : X. «(.•('.<. Trachinidae, 455

Squaliformes, 151

414/., 415/. Truchiniis, 455 ; T. <//-«fo,

Squaloraja, 168, 172, 174,

SyitOiloiiti*, 382 ; X. .vt7/«/, 455 /.

175, 176, 177 /. ; X.

380 /. Trackynotiu, 464

jjolyspondyki, 173 /.,

Trachypteridae, 476

177 /.

Tutiiiolali-Hx, 457

Ti-arhypterus, 477 ; 7".

Squalorajidae, 176

Taeuosonii, 476

taenia, 477 /.

Sqtialus, 152

Tarpon, 363, 387

Treniataspidae, 204

Squammipennes, 434

Tarrasiidae, 284 Trtmataspis, 200, 201, 204,

rtjuutina, 157 ; S. speciosa,

Tti.nvstHs, 284, 300; 7'. 205 ; 71. Sckmldti, 202 /.

157

problematicug, 283 Tremutdmitg, 456

Squatinidae, 156

Tautoga, 447

Triacanthidae, 437

titegostoma, 149

teeth, 121 ; horny, 31 ; of

Triacantkodes, 437

Stephanoberycidae, 423

Teleostomes, 272

Trincanthus, 437 ; 7*. i/-«-

Stephemoberyx, 424 ; x.

telencephalon, 15

virosti'is, 437 /'.

mtmae, 424/.

Teleostei, 344

Trichiuridae, 466

Sternarchu*, 377

Teleostomi, 266, 366 /.

r,-l<-hiiirus, 466 ; T. /«/)-

Sternoptychinae, 395

Tdephulla, 400

titrus, 467 /.

Xtent'ijiti/,'-, 395

Temera, 163

Trichdcydus, 440

Stemopygua, 377

Temnothoraci, 263

Trichodon, 445

Sticluwttg, 458

Tetragoiinlepis, 336

Trichodontidae, 445

Stniiiittiii-ltiiuis, 389

Tetrago'iHijjterus, 375

Trichogastti; 422

Slomius, 359 /., 395

Tetragonuridae, 421

Trichonotidae, 457

Stomiatiilae, 394

Tetragoituruti, 421

Ti-ichonotits, 457

Stoiniatinae, 395

Telrapterus, 468

'/'/•/</;</, 365. 450 ; 7'.

titratodus, 417

Tetrodun, 440

if a i-iid ril a x, 451 /. ; T.

Xtrepswluis, 286

Tetrodontidae. 440

hirundo, 447 /. ; 3T.

striclulating organ, 379

Teuthidae, 435

pleur(i<'</ii///if<>, 152 /.

Stroinateidae, 421

T<-nthii<, 436 ; T. nebn/'^n.

Triglidae. 450

Stromateus, 421

436 /.

Triylopx, 454

$ti-(>i>ln>dus. 146/

tlialanieucephalon, 15

Trlylopisix, 463

Xtygicolo. 459

Tltalassophryne, 460

Trigonodo/i, 429

Stylepboridae. 477 Thalassnt/tia, 460

Triodon, 439

Htylephorus, 475, 477 Thdodus, 195, 196/., 197,

Triodontes, 439

Stylophthalmuf, 395; X. 198, 203; T. scoticus,

Triodontidae, 439

paradojus, 406/.

197 /.

Trissolepinae. 312

anbocolar shelf, 428

T/ioraci>f>terus, 336. 337

Trissdepis, 312 : 71. A'OK-

Snciotrutta, 394

Tkrissopater, 392

noviensis, 31 1./'.

sucker, cephalic, 44s :

Tlirissopatrinae, 392

Ti-ixtichopterus, 285

larval, 247, 277 ; ventral,

Thrissopx, 371

Tristych it'*, 146

455, 457

Tlnifsius, 285

ZVqpAtftw, 446

Xndis, 399

Tliyestes, 203, 204

Trojiufu-htlii/s. 440

Supraoccipital, 326

T/iyiHiilli/x, 355, 394

7Y//.v<;/i, 158, 164; T.

Symbranchidae, 409

Thy nuns, 465 ; T. tlii/mni*.

tuberctilata, 156 /.

Syiiibrancliiforines, 408

466 /'. ; f. rulgarift, 352

Trygonidae, 164

Xi/Hibmnchus, W9 ; X. /«•//-

/., 354 /., 463 /.

Tryyonoptera, 164

galensis, 410 /.

thyroid gland, 53. 82

Trii'tonofh intt, 160

5i8

INDEX

Typhlichthys, 401

148 ; of Teleost, 363 ;

Xenochafcu;, 375

TypMonus, 459

of Alonoptenis, 409

Xenoiiiystus, 390

Typhlosus, 459

veins, 43, 48, 114

Xenopholis, 340

Vdifer, 476

Xenopterus, 440

Umbra, 398

Veliferidae, 476

Xiphasia, 458 ; X. sdifer,

Umln-iiiM, 431

vertebrae, transverse sec-

458 /.

Undina, 290

tions of, 137/.

Xiphias, 62, 468 ; X.

Undino gulo, 287 f.

vertebral arches. 31, 68 ;

yladii'.s, 355

Upeneoides, 429

neural, haemal, and in-

Xiphiidae, 468

Upeneus, 429

tercalary, 100

XipliiurhyncJins, 468

Uranoscopidae, 456

vertebral centra, 68, 135 ;

Xyphotrygon, 164

Uranoscopus, 82, 456 chordal, 100 ; perichor-

Xystrvdus, 147

Urenchelidae, 404 dal, 100

Urenchdys, 403, 404 : vertebral column, 31, 68,

yolk-sac, 114, 132; cir-

urinogenital organs, 27, 83,

97, 135, 233, 273,

culation, 114

86/., 131 /. ; of Selachii, 327, 352; elements of

132 ; of Dipnoi, 253 ; of segment, 100

Zaiidus, 436

Teleostei, 365

viviparity of Elasmo-

Xaniolepis, 453

Uroconger, 405

branchs, 134 ; of Teleosts,

Zeidae, 469

Urogymnus, 164

415, 446, 459

Zenion, 469

Urolophus, 164

Vorner, 464

Zeorhombiformes, 468

Uronemidae, 255

romefopsis, 464

Zeugoptents, 474

Uronemus, 233, 246, 256 ;

Vulsvs, 466

Zeus, 469

U. lobatus, 256 /.

Zoarces, 364, 365, 368,

Wardichthys, 313

459 ; Z. viciparus, 459/.

vagus nerve, 8, 19

Weber's apparatus, 373

Zoarcidae, 458

vascular system, 26 ; of

\Vodnika, 146 Zygaena, 151 ; Z. malleus,

Cyclostomes, 43, 47 ; of

76/., 117/. ; Z. tudes,

Pisces, 109 ; of Dipnoi.

Xenacanthus, 182 /., 183 152 /., 153 /.

Printed by R. ^i R. CJ.AKK, LIMITED, Edinburgh.

STUDIES

IN

FOSSIL BOTANY

BY

DUK1NFIELD HENKY SCOTT

M.A., LL.D. Pu.D., F.R.S.

Second Edition, containing 212 Illustrations

DKMY 8vo. PRICE IO/6 NET BOUND IN CLOTH

(Post free, jn-ici: I I/-)

OR IN TWO VOLUMES
Vol. I., price 6 /- net. Vol. II., price 5 = net.

(Pout free, prices 6/4 and 5/4 resjwt.irrl i<

NOTE

THIS book, originally founded on a course of lectures delivered at University
College, London, has been completely revised, and to a considerable extent
rewritten, in order to bring the new edition into harmony with the results
of important recent research. The "Studies" are concerned essentially with
those morphological and evolutionary aspects of Fossil Botany on which so
much light has been thrown by the work of the last few years.

AN INTRODUCTION

TO

STRUCTURAL BOTANY

BY D. H. SCOTT

M.A., I.I..1), PH.D., Klf.S.

In Two Parts. Crown 8vo, Cloth. Price 36 each.

PART I.— FLOWERINd PLANTS I PART II. — FLOWKRLKSS PLANTS

Sixth Edition
Illustrated with 118 Figures

Fifth Edition
Illustrated with 120 Figures

" In noticing elementary books in these pages, we have l;iiiieiit<-<] nothing more than the want of
a book which should do for structural botany what Prof. Oliver's • Lessons ' has lonj: done for tin-
study of the principal natural orders. It seems hard to realise that this grievance is no more, and
that we possess such a Iwok in our own language, and a book that no honest critic will fail to assess
at a higher value than any known book in any language that has UIP same scope and aim. Nothing
could well be more plain and simple, or more severely accurate or better judged from beginning to
end." — Jwirnvl nf Rnim>>i.

PUBLISHED BY

ADAM AND CHARLES BLACK, 4, 5, & 6 SOHO SQUARE, LONDON

THE SENSE OF TOUCH IN MAMMALS
AND BIKDS

WITH SPECIAL KEFEKENCE TO THE PAPILLARY RIDGES

BY WALTER KIDD, M.D., F.Z.S.,

Author of ' Use Inheritance,' 'Direction of Hair in Animals and Mau,' etc.

Demy 8vo, Cloth, containing 174 Illustrations. Price 5s. net.
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" This is, for the purposes of exact science, undoubtedly a valuable book. ... As regards the
highest mammal, man, it is well pointed out that the sense of touch has been from the very first of
extreme importance, and that ' such use of this sense in man must have contributed greatly to
his better equipment for the struggle of his life, and thus in a broad way have been governed by
a slow, remorseless process of selection.' The book is eminently one for specialists, but the
excellence of the numerous illustrations makes it also interesting to the general reader." — London
Quarterly Review.

"Dr. Kidd's book is the most important contribution to the matter since 3tiss Whipple's paper
was published."— The Spectator.

BY THE SAME AUTHOR

USE-INHEBITANCE

ILLUSTRATED BY THE DIRECTION OF HAIR OX
THE BODIES OF ANIMALS

Demy 8vo, Paper Covers. Price 2s. 6d. net.

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"Such a book as this is calculated, a.t least, to give pause to the Weismannians. Dr. Kidd has
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— The Irish Naturalist.

" This is an interesting contribution to the dynamic or Lamarckian principles of evolution. . . .
The author seems to have made out a good case ami to have been led by the legitimate use of the
inductive method to what seem to be valid and natural conclusions."— Science.

" It is urged that . . . the doctrine that acquired characters are never inherited does not hold
good, and hence a Lamarckian explanation of the phenomena must be accepted. The case, as
argued by Dr. Kidd, appears to be a strong one. and it will be curious to note what the Weisman-
nists will have to say in reply." — Ktwivledge.

THE DIEECTION OF HAIR IN ANIMALS

AND MAN

Demy 8vo, Cloth, Illustrated. Price 5s. net.

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" Dr. Kidd shows much ingenuity in explaining the various causes which, in his opinion, have
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are of considerable assistance to the reader."— Westminster Review.

" The description of the facts can be commended. There is evidence that considerable care has
been taken iu the collection of observations, and the illustrations are excellent." — Mani-hester
Guardian.

" That the direction of the hair-slope in mammals varies much is a fact well known to zoologists ;
but we are not acquainted with any general work, such as the present, in which the facts are put
together within one cover. The author has, therefore, in any case, accomplished a piece of work
which supplies a definite want in the literature of zoology. The usefulness of this general summary is
furthermore enhanced by numerous clear figures which show at a glance the essential facts."— Lancet.

PUBLISHED BY

ADAM AND CHARLES BLACK, 4, 5, & 6 SOHO SQUARE, LONDON