442 



EXTINCTION OF SPECIES. 



[Ch. XLII, 



every class, as, for example, where some of onr English hawks 

 or buzzards {Buteo) devour not only small quadrupeds, as rab- 



mice 



the profusion of any one of these last may cause all such 

 general feeders to subsist more exclusively upon the species 

 thus in excess, by which means the balance may be restored. 

 Agency of omnivorous animals. — The number of species 

 which are nearly omnivorous is considerable ; and although 

 every animal has, perhaps, a predilection for some one de- 



some 



doms of the o: ^ 

 Thus, when the racoon of the West Indies can procure 

 neither fowls, fish, snails, nor insects, it will attack the sugar- 

 canes, and devour various kinds of grain. The civets, when 

 animal food is scarce, maintain themselves on fruits and roots. 

 IS'umerous birds, which feed indiscriminately on insects and 

 plants, are perhaps more instrumental than any other of the 

 terrestrial tribes in preserving a constant equilibrium between 

 the relative numbers of different classes of animals and veo^e- 

 tables. If the insects become very numerous and devour the 



immediately 



from 



Hottentots 



crops 



ifluence of 



The 



intimate relation of the inhabitants of the water to those of 

 the land, and the influence exerted by each on the relative 

 number of species, must not be overlooked amongst the com- 

 plicated causes which determine the existence of animals and 

 plants in certain regions. A large portion of the amphibious 

 quadrupeds and reptiles prey partly on aquatic plants and 



animals, and in nart on tprrpstrial : and a deficiencv of onp kind 



them 



exam 



is confined to the water during one stage of their transfor- 

 mations, and in their perfect state to the air. Innumerable 

 water-birds, both of rivers and seas, derive in like manner 

 their food indifferently from either element ; so that the abun- 

 dance or scarcity of prey in one induces them either to forsake 



