2Q4 ELEMENTARY ZOOLOGY. 



302. Definition of the Class Pisces. The fishes are cold- 

 blooded aquatic vertebrates, breathing by means of gills 

 throughout life. They have a two-chambered heart. 

 Their paired appendages are fin-like and do not develop 

 toes. The skin usually develops bony or horny scales 

 or plates. 



303. Key to the Common Orders. 



No operculum covering gills Order Elasmobranchii . 



Bodies elongated, and rounded in section, 



Sharks (dog-fish ; saw-fish ; etc) . 



Bodies flattened dorso-ventrally Skates and rays. 



Gills covered with an operculum. 



Body partly or wholly covered with plates, 



Order Ganoidei (Long-nosed gar; sturgeon). 

 Body not covered with plates ; skeleton bony, 



Order Teleostei. 

 Air bladder connected with intestine by open duct, 



Sub-order Physostomi. 



Marine: Smelt; salmon (Fig. 113) ; shad; herring; eels. 

 Fresh water: Trout ('Fig. 114); whitefish; suckers; carp; 

 pickerel; muskalonge; minnows; catfish. 



Air bladder when present not opening into the intestine. 

 Dorsal, anal, and pelvic fins spiny in front, 



Sub-order Acanthopteri. 



Marine: Mackerel; toad-fishes; sculpin; silversides. 

 Freshwater: Perch; stickleback; sunfish (Fig. 115); 

 darters. 

 Dorsal, anal, pelvic fins not spiny, 



Sub-order Anacanthini. 



Marine: cod; haddock; turbot; sole; and other flat- 

 fishes. 



304. Topics for Themes in Zoology and English. i. 

 Probable origin of fresh-water fishes. What forms are 

 now able to go back and forth from fresh to salt water? 

 Why may not any fish do so? 



2. Get data about the habitat, food, breeding habits, 

 distribution, economic importance (and the reasons there- 



