70 PHILOSOPHY OF ZOOLOGY. 



individuals, not sufficiently cautious in choosing proper re- 

 treats, are sometimes prematurely called into action, at a 

 season when there is no food,, so that they fall a prey to 

 owls, and the cold of the evening. But what indications of 

 returning spring can be experienced by those which are at- 

 tached to the roofs of the deeper caves ? Surely no increase 

 of temperature ? 



There is another very curious circumstance attending the 

 reviviscenee of quadrupeds from their torpid state, which 

 deserves to be mentioned. As soon as they have recovered 

 from their slumbers, they prepare for the great business of 

 propagation. This is a proof, that torpidity, instead of ex- 

 hausting the energies of nature, increases their vigour. It 

 also indicates a peculiarity of constitution, to the preserva- 

 tion and health of which, a brumal lethargy is indispensably 

 requisite. 



It appears to be the general practice of modern natural- 

 ists, to treat with ridicule those accounts which have been 

 left us, of birds having been found in a torpid state during 

 winter. These accounts, it is true, have in many instances 

 been accompanied with the most absurd stories, and have 

 compelled us to pity the credulity of our ancestors, and 

 withhold our assent to the truth of many of their statements. 

 But are there no authenticated instances of torpidity among 

 birds ? 



In treating of the torpidity of quadrupeds, we were un- 

 able to detect the cause of torpidity, as existing in any cir- 

 cumstances connected with structure, or with circulation, 

 respiration, or animal temperature ; nor in the places which 

 they frequent, nor the food by which they are supported. 

 Hence we cannot expect much help from a knowledge of 

 the anatomy, physiology, or even habits of birds, in the 

 resolution of the present question. It has indeed been said, 

 that as birds can readily transport themselves from one 

 country to another, and in this manner shun the extremes 



