CONTENTS 



HALF-VOL. II 



CHAPTER VI 



STRUCTURE AND CLASSIFICATION OF FISHES (PISCES) AND 

 PRIMITIVE VERTEBRATES (PROTOCHORDATA) 



FISHES (PISCES) 



Page 



Structure and Development of the Spotted Dog-Fish (Scyllium canicula), taken as 



a Type - 257 



Sub-Class I. LUNG-FISHES (Dipnoi) Ceratodus, Protopterus, Lepidosiren - - 264 



Sub-Class II. BONY FISHES (Teleostomi) - - 266 



Order i. GANOIDS (Ganoidei) - - 266 



(i) Fringe-finned Ganoids (2) Ray-fmned Ganoids. 



Order 2. BONY FISHES PROPER (Teleostei) - - 269 



Structure of the Common Perch (Perca fluviatilis), taken as a Type - - 269 



A, Teleosts in which the Swim-bladder (when present) has lost its con- 



nection with the Gullet. 



Sub-Order i. SPINE-FINNED FISHES (Acanthopterygii) - 273 



Sub-Order 2. TUFT-GILLED FISHES (Lophobranchii) - 276 



Sub-Order 3. FIRM-JAWED FISHES (Plectognathi) - - 277 



Sub-Order 4. SOFT-FINNED FISHES (Anacanthini) 278 



B, Teleosts in which the Swim-bladder retains its connection with the 



Gullet. 



Sub-Order 5. TUBE-BLADDERED FISHES (Physostomi) - - - 280 



Sub-Class III. SHARKS AND RAYS (Elasmobranchii) - - - 284 



Order i. SHARKS AND DOG-FISHES (Selachoidei) - - - 284 



Order 2. SKATES AND RAYS (Batoidei) - 287 



Sub- Class IV. CHIMERAS (Holocephali) 290 



Sub-Class V. ROUND-MOUTHS (Cyclostomata) - 291 



(i) Lampreys (2) Hag-Fishes. 



PRIMITIVE VERTEBRATES (PROTOCHORDATA) 



Essential Characters of the Chordata -- 292 



Sub- Class I. LANCELETS (Cephalochorda) - - 293 



Structure of the Common Lancelet (Amphioxus lanceolatus). 

 Sub-Class II. SEA-SQUIRTS OR ASCIDIANS (Urochorda or Tunicata) - - - 297 



Structure and Development of a simple Sea-Squirt (Ascidia mentula), taken 



as a Type Fixed and Free-swimming Ascidians 297 



Sub-Class III. WORM-LIKE PROTOCHORDATES (Hemichorda) - - 300 



Structure of the Acorn-headed Worm (Balanoglossus). 



5 



