HYBERNATION OF INSECTS, 459 
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 drowsi- 
ness consequent on severe cold; and the very same fact 
is equally conclusive against the theory, that it is to es- 
cape the pain arising from a low temperature that in- 
sects bury themselves in their winter quarters. 
In fact, the great source of the confused and unsatis- 
factory reasoning which has obtained on this subject, is, 
that no author, as far as my knowledge 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 hy- 
bernating animals, is caused by cold, is unquestionable. 
However early the period at which a beetle, for exam- 
ple, takes up its winter quarters, it does not suffer that 
cessation of the powers. of active life which we under- 
stand by torpidity, 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 would not become torpid at all—at least this has 
proved the fact with marmots and dormice thus treated ; 
and the Aphis of the rose (4. Rose), which becomes tor- 
