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-finned 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 1. — 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. Chim^eras (Holocephali) 290 



Sub-Class V. Round-Mouths (Cyclostomata) 291 . 

 (i) Lampreys — (2) Hag-Fishes. 



PRIMITIVE VERTEBRATES (Protochordata) 



Essential Chai-acters of the Chordata 292 



Sub- Class I. Lancelets (Cephalochorda) 293 



Structure of the Common Lancelot (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). 



