CHARACTERS OF VERTEBRATE ANIMALS 



in the general form of the body. Hair is practically absent in 

 the adult, though there may be a few stiff bristles in the neigh- 



Fig. 67. — The Porpoise {Phocana coimnwiis) 



bourhood of the mouth, but the lack of a protective external 

 covering is fully compensated by the thickness of the skin and by 



the presence of a thick layer of fat (blub- 

 ber) underneath it. A tail fin is present, 

 but this, instead of being flattened from, 

 side to side, as in a fish, is flattened from 

 above downwards. The fore-limbs have 

 been converted into paddles, presenting 

 externally no trace of digits, and the hind- 

 limbs have disappeared, though traces of 

 them are to be found on dissection. There 

 may be one or two nostrils, situated, for 

 convenience in breathing, on the top of 

 the head. Cetacea feed on other animals, 

 ranging from comparatively large forms 

 to small creatures which are found in huge shoals. 



The Porpoise {Phoccena communis) (fig. 67), which possesses 



rig. 68. — Baleen in the 

 Upper Jaw of Whale 



a. Section, of a portion of the palate of 

 a whalebone whale, showing three baleen 

 plates, b. The arrangement of the baleen 

 plates on opposite sides of the jaw. 



