82 PHILOSOPHY OF ZOOLOGY. 



sitical on one species of animal. The distribution of such 

 animals is thus dependent on their food. 



The same remark is generally applicable to carnivorous 

 and phytivorous animals. But, in many species, though the 

 restriction is absolute as to the nature of the food, it admits 

 of a considerable range with regard to the variety or kind. 

 Thus, though the lion is restricted to flesh, his cravings are 

 equally satisfied with the carcase of a horse, a cow, or even 

 of man. The hog in general feeds on roots, but it is not 

 confined to those of one kind of plants ; hence it can sub- 

 sist wherever the earth is clothed with verdure. 



The seasons exercise a powerful influence on animals, 

 directly, in reference to their temperature, and, indirectly, 

 with regard to the production of their food. Thus, the 

 insect that feeds on the leaves of a particular tree, can only 

 enjoy its repast during that part of the season when this 

 tree is in leaf. How, then, is life preserved during the re- 

 maining portion of the year ? The resources are numerous. 

 It either exists in the form of an unhatched egg, an inac- 

 tive pupa, in the imago state, requiring little food, or ac- 

 tually becoming torpid. 



The birds which feed on insects in summer, in this cli- 

 mate, are, from the absence of this kind of sustenance in 

 winter, obliged to have recourse to various kinds of vege- 

 table food during that season. Should this change of diet 

 be unsuitable, migration to other districts, where a proper 

 supply can be obtained, becomes indispensably requisite. 



In compliance with these regulations, we observe numer- 

 ous mammalia, birds, and fishes, accompany the shoals of 

 herrings in their journeys ; and the grampus and seal enter 

 the mouths of rivers in pursuit of the salmon *. The bats, 



* The seal sometimes enters fresh water-lakes in pursuit of his favourite 

 repast. In the account of the parish of North Knapdale, by the Reverend 



