450 HIBERNATION OF INSECTS. 



that they are owing to some peculiar and varying attrac- 

 tion for caloric inherent in the fluids which compose the 

 animal, and which in the egg state, like spirit of wine, 

 resist our utmost producible artificial cold ; or that, as 

 John Hunter seems to infer with respect to a similar fa- 

 culty in a minor degree in the hen's egg, the whole are 

 to be referred to some unknown power of vitality. The 

 latter seems the most probable supposition; for Spallan- 

 zani found that the blood of marmots, which remains 

 fluid when they are exposed to a cold several degrees 

 below zero of Fahrenheit, freezes at a much higher tem- 

 perature when drawn from the animal a ; and it is rea- 

 sonable to conjecture that the same result would follow 

 if the fluids filling the eggs of insects were collected se- 

 parately, and then exposed to severe cold. 



Spring is, of course, the period when insects shake off 

 the four or five months' sleep which has sweetly banish- 

 ed winter from their calendar, quit their dormitories, 

 and again enter the active scenes of life. It is impossi- 

 ble to deny that the increased temperature of this season 

 is the immediate cause of their reappearance; for they 

 leave their retreats much earlier in forward than in back- 

 ward springs. Thus in the early spring of 1805 (to me 

 a memorable one, since in it I began my entomological 

 career, and had anxiously watched its first approaches 

 in order to study practically the science of which I had 

 gained some theoretical knowledge in the winter,) insects 

 were generally out by the middle of March ; and before 

 the 30th, I find, on referring to my entomological jour- 

 nal, that I had taken and investigated (I scarcely need 

 3 Rapports de V Air, $c. ii. 215. 



