530 HYBERNATION OF INSECTS. 



obvious that something more than the sensation of heat is the regulator of 

 the movements of each. Not, however, to detain you here unnecessarily, 

 I shall not enlarge 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 1 re- 

 ferred them to the operation of cold upon the animals in which they are 

 witnessed, but acting in a different manner. Some conceive that cold, com- 

 bined with a degree of fatness arising from abundance of food in autumn, 

 produces in them an agreeable sensation of drowsiness, such as we know, 

 from the experience of Sir Joseph Banks and Dr. Solander in Terra del 

 Fuego, as well as from other facts, is felt by man when exposed to a very 

 low temperature ; yielding to which, torpidity ensues. Others admitting 

 that cold is the cause of torpidity, maintain that the sensations which 

 precede it are of a painful nature ; and that the retreats in which hyber- 

 nating animals pass the winter are selected in consequence of their endea- 

 vours to escape from the disagreeable influence of cold. 



I have before had occasion to remark the inconclusiveness of many of 

 the physiological speculations of very eminent philosophers, arising from 

 their ignorance of Entomology, which observation forcibly applies in the 

 present instance. The reasoners upon torpidity have almost all confined 

 their view to the hybernating quadrupeds, as the marmot, dormouse, &c., 

 and have thus lost sight of the far more extensive series of facts supplied 

 by hybernating insects, which would often at once have set aside their 

 most confidently-asserted hypotheses. If those who adopt the former of 

 the opinions above alluded to had been aware that numerous insects retire 

 to their hybernacula (as has been before observed) on some of the finest 

 days at the close of autumn, they could never have contended that this 

 movement, in which insects display extraordinary activity, is caused by the 

 agreeable drowsiness consequent on severe cold ; and the very same fact 

 is equally conclusive against the theory that it is to escape the pain arising 

 from a low temperature that insects bury themselves in their winter 

 quarters. 



In fact, the great source of the confused and unsatisfactory reasoning 

 which has obtained on this subject is, that no author, as far as my know- 

 ledge extends, has kept steadily in view, or indeed has distinctly perceived, 

 the difference between torpidity and hybernation ; or, in other words, 

 between the state in which animals pass the winter, and their selection of a 

 situation in which they may become subject to that state. 



That the torpidity of insects, as well as of other hybernating animals, is, 

 with us, caused by cold, is unquestionable. However early the period at 

 which a beetle, for example, takes up its winter quarters, it does not suffer 

 that cessation of the powers of active life which we understand by tor- 

 pidity, until a certain degree of cold has been experienced ; the degree of its 

 torpidity varies with the variations of temperature ; and there can be no 

 doubt that, if it were kept during winter from the influence of cold, it 



1 Here must be excepted my lamented friend the late Dr. Reeve of Norwich, 

 who, in his ingenious Essay on the Torpidity of Animals, has come to nearly the 

 same conclusion as is adopted in this letter : but, by omitting to make a distinction 

 between torpidity and hybernation, he has not done justice to his own ideas. 



