234 



ZOOLOGY 



The whitefish (Coregonus *), of which we possess many 

 species, is exclusively an inhabitant of fresh water. 2 Its 

 teeth are almost completely absent, or very small ; it feeds 

 almost exclusively upon small arthropods and mollusks. 

 It is of very great commercial importance, its fisheries 

 being valued at nearly three million dollars a year. 



Leaving now the Salmonidse, we may briefly consider 

 some of the other more important families of bony fishes. 



FIG. 214. Morone americana, the white perch. The fish is searching for food 

 along the bottom of the aquarium, an instinct which it shows in nature also. 

 About one-third nat. size. Photo, of living animal by Dr. R. W. Shufeldt, 

 from " Bull. U. S. Fish Com.," 1899. 



The darters are spiny-rayed fishes of small size, from four 

 to seventeen centimetres long, brightly colored, and with 

 well-developed pectoral fins. They live in clear streams, 

 half concealed under stones, and are most abundant in the 

 Mississippi drainage basin. 



7, the pupil of the eye ; ywvia, angle. 



2 Fig. 213. 



