CHAPTER XVII 

 SUBPHYLUM VERTEBRATA: CLASS III. PISCES 



THE PISCES are the true fishes. The class includes the com- 

 mon fishes and the lung-fishes. They are aquatic animals and 

 are, therefore, adapted to life in the water. The respiratory 

 organs of fishes are gills. Usually a dermal exoskeleton of scales 

 or bony plates furnishes a protective covering for the body. 

 Living fishes are grouped into two subclasses. 



Subclass I. TELEOSTOMI. - - Fishes with a skeleton consist- 

 ing wholly or partially of bone, usually wjth scales (never placoid 

 scales), and a well-developed operculum covering the gills. 



Subclass II. DIPNOI. - - Fishes with a skeleton of cartilage 

 and bone, a single or double lung, and an operculum covering 

 the gills. 



i. A BONY FISH- -THE PERCH 



External Features. - - The yellow perch, Perca flavescens (Fig. 

 368), inhabits the fresh-water streams and lakes of the north- 



FIG. 368. Perch, Perca fiavescens. (From Dean, after Goode.) 



432 



