VERTEBRATA 



183 



single in the porpoise are on the top of the head. All 

 are carnivorous, and essentially marine, a few dolphins 

 only being found in the great'rivers. In the whalebone 



FIG. 170. Outline of the sperm whale (Physeter). The blowhole is seen at the extreme 

 tip of the head. In this region the spermaceti is found. Maximum length, eighty- 

 five feet. South Atlantic. 



whales, the teeth are absorbed, and disappear before 

 birth, and their place is supplied by horny "baleen" 

 plates (Fig. 228). " The whale feeds by putting this 



FlG. 171. Greenland whale (Baleena mystzcetns} . North Atlantic. 



gigantic strainer into operation, as it swims through the 

 shoals of minute mollusks, crustaceans, and fishes, which 

 are constantly found at the surface of the sea. Open- 



