Hibernation. 91 



again to new supplies of food and new enjoyments. 

 Without this provision these animals would perish 

 in a single winter, and the species become extinct. 

 But Nature has not left them unprovided for. 

 Their vitality is like a burning lamp. In winter the 

 wick is turned down so that the spark of life may 

 remain, and that is all. This hibernation is no 

 ordinary sleep ; it is peculiar, and it is something 

 over which the animal has no more control than he 

 has over the change of seasons. 



In these general adaptations, we must not forget 

 the relationship of these animals to the length of 

 the year. \Yere the winter essentially longer than 

 it now is, these hibernating animals could not sur- 

 vive, excepting those rendered quite torpid like 

 some of the reptiles. Those animals that lay up 

 stores of food for winter would find themselves in 

 want. The thickening of the coat and its loss are 

 not the effect of cold and heat, but a change in the 

 'em whose machinery has been adjusted to the 

 clock-work of the stars. 



We come now to speak of a new principle of 

 adaptation which has been only incidentally re- 

 ferred to. Thus far, we have spoken mainly of 

 fixed relations ; those growing out of form, anatomi- 

 cal differences, and functional peculiarities. In 

 regard to all these, the animal is like a plant, plas- 

 tic in the hands of Nature and entirely passive. 

 He is thrown into the world with a certain struc- 

 ture, external and internal, and to this structure 

 he must conform in some measure, necessarily. 



