A 5A HYBERNATION OF INSECTS. 
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 frozen. 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 has the capacity 
of evolving animal heat ina much greater degree than 
any other insect, is killed by a cold considerably less 
than that of freezing. Secondly, many large larve, as 
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 larvae or pupz 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 pupze of many moths perished with a cold 
of 7° or 8° R. below zero (14° F.), while the exposed 
pupze of Papilio Brassice 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 pupze, is regulated by their 
power of resisting cold ;) but no difference in the sub- 
stance of the exterior skin is perceptible. And the eggs 
4 Reaum, i. 146— 
