HYBERNATION OF INSECTS. 449 



the decomposition of the respired air — will not avail us 

 here. For, first, the hive-bee, which has the capacity 

 of evolving animal iieat in a much greater degree than 

 any other insect, is killed by a cold considerably less 

 than that of freezing. Secondly, many large larvae, j^s 

 Reaumur has observed, are destroyed by a less degree 

 of cold than smaller species whose respiratory organiza- 

 tion is necessarily on a much less extensive scale. And 

 thirdly, the eggs of insects — in which, though they pro- 

 bably are in some degree acted upon by the oxygen of 

 the atmosphere, nothing like respiration takes place — 

 can endure a much greater intensity of cold than either 

 the larvce or pupae produced from them. 



Nor can we refer the effect in question to the thinness 

 or thickness — the greater or less non-conducting power 

 — of the skin of the animal. Reaumur found that the 

 subterranean pupae of many moths perished with a cold 

 of 7° or 8° R. below zero {14° F.), while the exposed 

 pupae o^ Pontia Brassicce and other species endured 15" 

 or 16° without injury => ; (a proof, by the way, that the 

 different economy of these insects, as to their choice of 

 a situation in their state of pupae, is regulated by their 

 power of resisting cold ; ) but no difference in the sub- 

 stance of the exterior skin is perceptible. And the eggs 

 of insects have usually thinner skins than pupae, and yet 

 they are unaffected by a degree of cold much superior. 



In the present state, then, of our knowledge of animal 

 physiology, we must confess our ignorance of the cause 

 of these phenomena, which seem never to have been suf- 

 ficiently adverted to by general speculators on the na- 

 ture of animal heat. We may conjecture, indeed, either 



^ Rcaum, ii. 146 — . 

 VOL. II. 2 G 



