FISHES COKSIDEKED AS A CLASS. 



247 



Fishes feed mainly upon smaller members of their own 

 class, and upon other smaller animals. Some kinds, how- 

 ever as the Lancet-fishes of the tropical seas are vegeta- 

 ble feeders. Most kinds swallow their prey whole. Some, 

 which feed on shell-fish, crush their food by means of the 

 powerful crushing and grinding teeth in the gullet. Di- 

 gestion is performed very rapidly. The blood is red, and 

 the globules are large and elliptic. 



The heart of fishes contains only two cavities, corre- 



