HIBERJSTATIOlSr. 
809 
to survive after more tliau five years’ abstinence from food ; even 
our Hdiv neniundis has been recorded as having endured more 
than tliree years’ starvation, and many other striking examples of 
this faculty are known. 
Hibernation (Jdherno, to spend the winter), or winter torpor, is 
induced in the mollusca and other organisms by the advent of cold, 
and is obviously related to sleep, of which it seems but an intensifica- 
tion, enabling the mollusk to successfully resist the extreme reduction 
of temperature and the absence of accustomed food. 
At the approach of winter and in the more sensitive species often 
as early as October, the mollusks, being then plumper and better 
nourished than at other times, gTadually become less voracious and 
more sluggish and lethai'gic, the terrestrial species retiring to their 
accustomed or temporary places of shelter, frecpiently clustering 
together in the crevices of walls, rocks, and trees, or ensconcing 
themselves deeply amongst dead leaves or in the earth, in which latter 
case the mouth of the shell is invariably directed upwards and often 
level with the surface of the soil, the epiphragm or cover to the 
mouth of the shell (see p. 1.80) being then secreted, to protect the 
animal from the weather and other dangers and to prevent the 
evaporation of its natural moisture, the activity of their respiration 
also diminishing as the temperature becomes lower and lower, until 
the animals fall into a hibernal sleep or die. 
This comatose state may be partial or complete according to the age 
of the animal, the hardihood of the species and the character of the 
winter, whether it lie continuously severe or present comparatively 
mild intervals ; as during such intervals, if sufficiently mild, the 
winter sleep, especially of the more immature individuals, may be 
broken and the mollusk wander about in search of food. 
In a hard winter the animal contracts more and more closely 
within the spire of the shell, forming any additional epiphragms 
necessitated by the smaller compass into which the mollusk has com- 
pressed itself ; the young individuals are, however, less susceptible 
to cold than mature animals, retiring later into winter (quarters and 
re-appearing earlier and perhaps only becoming reall)' torpid during 
the continuance of actual frost, this superior hardihood of the 
younger animals being possibly due to their more active circulation. 
Many of the fluviatile species during severe weather bury them- 
selves in the mud of the })0uds or rivers they inhabit, and even 
