CHAPTER IX 



INTRODUCTION TO THE VERTEBRATA : DESCRIPTION OF THE 

 DOGFISH AS ILLUSTRATING THE GENERAL STRUCTURE OF 

 A VERTEBRATE 



SCHEME OF CLASSIFICATION 



Cephalochorda — Amphioxus. 



Cyclostomata — Lampreys (Petromyzon) ; Hagfish {Myxine) and Borers 



{Bdellostomd). 

 Elasmobranchii — Sharks and Dogfish ; Rays and Skates. 

 Teleostomi — 



I. Crossopterygii — Polypterus, Calamichthys. 

 II. Actinopterygii — 



A. Ganoidei — Sturgeons {Acipenser), Garpike {Lepidosteus) , 



Bowfin (Amia). 



B. Teleostei — Herring, Salmon, Carp, Catfish, Eel, Pike, Cod, 



Perch, Flounder, Sole, and the great majority of ordinary 

 fishes. 



Dipnoi — -Lungfish (Lepidosiren, Protopterus, Ceratodus). 



Amphibia — Urodela (Newts, Salamanders), Anura (Frogs, Toads), Apoda 

 or Gymnophiona. 



Reptilia — Rhynchocephalia (Sphenodon), Lizards (Lacertilia), Snakes 

 (Ophidia), Tortoises and Turtles (Chelonia), Alligators (Crocodilia), 

 and many interesting extinct groups known from the fossil remains 

 of their skeletons. 



AvES — Birds. 



Mammalia — Mammals, including all Vertebrates with hair and milk- 

 glands — from the Duckbill and Opossums and their allies up to and 

 including Man. 



A GLANCE through the list given above will show that the phylum Verte- 

 brata includes a large proportion of the most familiar and best-known 



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