ANIMAL BIOLOGY. [Part I. 



is herbivorous ; the frog insectivorous ; the pigeon gramini- 

 vorous ; and the rabbit herbivorous ; and their mouths are 

 to some extent fitted for their special food. The cod has 

 powerful crushing jaws and pharyngeal teeth ; the tadpole, 

 horny jaws for cropping the weeds; the frog, a protrusible 

 tongue for catching prey, and minute teeth for holding the prey 

 when caught; the rabbit, special gnawing and grinding teeth, 

 in relation to its mode of feeding; but the beak of the pigeon 

 cannot be said to be specially modified in relation to its peculiar 

 diet, though its stomach is specially modified, being converted 

 into a gizzard, with thick callous walls, in which the grain is 

 triturated by the aid of small stones swallowed for that purpose. 

 Finally, in the temperature of the body there is a marked differ- 

 ence. The temperature of the cod and of the frog varies with 

 the temperature of the water or the air by which they are bathed. 

 Hence the hibernation of the frog in winter, and its renewed 

 activity in the warmth of spring. The temperature of the 

 rabbit's body is constant at about 98 Fah., its clothing of hair 

 enabling it to maintain this temperature even in winter. The 

 temperature of the pigeon's body is 104 or 105 Fah., its thick 

 clothing of feathers, in which is entangled much air an 

 excellent non-conductor of heat aiding it in maintaining this 

 temperature. 



The student is advised to lose no opportunity of comparing 

 the structures of different animals, and ascertaining for himself 

 how far they resemble in the external characters we have now 

 considered, and in the internal structure, on the study of which 

 we have next to enter the cod, the frog, the pigeon, and the 

 rabbit ; and how far they differ from these types. 



