454 HYBEIliNATION OF INSECTS. 



regard to the source of the power which many Insects 

 in some states, and almost all in the egg- state, have of 

 resisting intense degrees of cold without becoming fro- 

 zen. It is clear that the usual explanation of the same 

 faculty to a less degree in the warm-blooded animals — 

 the constant production of animal heat from the caloric 

 set free in the decomposition of the respired air — will 

 not avail us here. For, first, the hive-bee, which ha? 

 the capacity of evolving animal heat in a much greater 

 degree than any other insect, is killed by a cold consi- 

 derably less than that of freezing. Secondly, many 

 large larvfe, as Reaumur has observed, are destroyed 

 by a less degree of cold than smaller species whose re- 

 !?piratory organization is necessarily on a much less 

 extensive scale. And thirdly, the eggs of insects — in 

 which, though they probably are in some degree acted 

 upon by the oxygen of the atmosphere, nothing like re- 

 spiration takes place — can endure a much greater in- 

 tensity of cold tlian either the larvae or })upae produced 

 from them. 



Nor can we refer the effect in question to the thin- 

 ness or thickness — the greater or less non-conducting 

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

 the subterraiiean pupa? of many moths perisJied with a 

 cold of 7^ or 8" R. below zero (14" F.), while the ex- 

 posed pups o^ Papilio Brassicce and other species en- 

 dured \b° 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 substance of the exterior skin is perceptible. And 

 ■ Reaum. ii. 146 — 



