452 HYBEUNATION OF INSECTS. 



is yet in fact different, that of the one being constituted 

 so as to be acted upon by a less degree of heat tlian that 

 of the other : and this solution would be satisfactory if 

 the torpidity of these larvae were uninterrupted up to 

 the very period at which they quit their nest. But facts 

 do not warrant any such supposition. You have seen * 

 that the temperature of a mild day even in winter awakens 

 many insects from their torpidity, though without indu- 

 cing them to leave their hybernacula; and it is therefore 

 highly improbable that the larvae of ^. chrysorrhea should 

 not often have their torpid state relaxed during the 

 month of March, when we have almost constantly occa- 

 sional bright days elevating the thermometer to above 

 50°. Yet as they still do not, like the larvae of M. Cinxia, 

 leave their nest, it seems obvious that something more 

 than the sensation of heat is the regulator of the move- 

 ments of each. Not, however, to detain you here unne- 

 cessarily, I shall not enlarge at present on this point, but 

 shall pass on, in concluding this letter, to advert to the 

 causes which have been assigned for the hybernation and 

 torpidity of animals, and to state my own ideas on the 

 subject, which will equally apply to the termination of 

 this condition in spring. 



The authors who have treated on these phenomena 

 have generally'' referred them to the operation of cold 

 upon the animals in which they are witnessed, but act- 



' See above, 438-. 



^ Here must be excepted my lamented friend the late Dr. Reeve 

 of Norwich, who, in his ingenious Essay on the Torpiditij of A)dnials, 

 has come to nearly the same conclusion as is adopted in this letter; 

 but, by omitting to make a distinction between torpidity and hyber- 

 nation, he has not done justice to his own idea--. 



