534 HYBERNATION OF INSECTS. 
are constantly taking place in many European carnivorous perfect insects in summer 
when their food is abundant, lead them then, in Europe as in tropical countries, to 
seek out or prepare a suitable retreat? Yet, however full fed insects in temperate 
climes may be in summer, we know that they do not retire to become torpid at that 
period. All, therefore, that the present state of our knowledge seems to entitle us to 
say, is, as expressed in the close of the above letter, written thirty years ago, that 
the act of hybernation is dependent on the instinct of the insect, and that though 
this instinct may be, and probably is, excited by some bodily sensation, we as yet 
know no more of the precise nature of this than of that of a thousand other sensa- 
tions which may give rise to the endless instincts of different kinds observed in the 
insect tribes. F 
