TORPIDITY. 81 



fishes, and even some species that inhabit the sea, subsist, 

 at the season of the year when a supply of food cannot be 

 procured. A similar condition prevails among the fresh 

 water mollusca, and also among many species of Annelides. 

 But we must observe, that accurate observations on this 

 branch of the subject are still wanting. 



We have thus endeavoured to trace the various means 

 by which animals are enabled to counteract the baneful 

 effects of the varying temperature of the seasons. This 

 end is accomplished, in some, by a change in the quantity, 

 or the colour, of their dress, by which its conducting and 

 radiating powers are regulated. The inconveniences of 

 excessive heat or cold are avoided by others, by their perio- 

 dical migrations ; while, in a third class, the body, during 

 the cold season, falls into a lethargic state, from which it 

 recovers with the return of spring. But there are other 

 circumstances which influence the distribution of animals, 

 besides those connected with temperature. 



II. FOOD. 



Although temperature appears to exercise a very power- 

 ful controul over the geographical distribution of animals, 

 yet it is likewise indispensably necessary that they be pro- 

 vided with an abundant supply of suitable food. When this 

 supply is deficient in quantity j both the size and shape of 

 the animals are altered. The frame becomes diminished in 

 stature, its symmetry is marred, and its feebleness indicates 

 the scantiness of its nourishment. 



The dependence of the geographical distribution of ani- 

 mals on the supply of nourishment, is most conspicuously 

 displayed in those species which are destined to feed on 

 particular kinds of food. Thus many species of insects are 

 restricted in their eating to one kind of plants, or are para-* 



VOL. II. F 



