370 MUSCARDINIDAZ—MUSCARDINUS 
quite likely that in many mammals the accumulation of fat,’ 
which in temperate and arctic climates is usual in autumn, 
causes a progressive decrease of metabolic activity, and that 
the advent of a certain degree of cold, which is no doubt fairly 
definite for each species, consummates the matter by bringing 
the vital processes almost to a standstill. Add to this the 
effect of long custom regulating by inheritance the exact time 
or conditions under which the machinery shall slow down, and 
we seem nearer to a satisfactory explanation. But the actual 
process is in life influenced by questions of food and of 
individual differences. Thus, while dormice seem to have 
acquired such similarity of constitution that all the individuals 
may be said to become “ripe” for hibernation at about the same 
time, the same process in hedgehogs is spread over a much 
longer period, and the “ripening” is reached in a much more 
uncertain manner. The difference is probably connected with 
the more abundant food and the greater hardiness of hedge- 
hogs; it also indicates a higher degree of specialisation in 
dormice. Both animals agree in that hibernation, having been 
once properly started, runs a more or less normal course until 
the body, having absorbed the fat by which its vital processes 
have been clogged, is stimulated to fresh activity by the warmth 
of spring, a warmth coincident with a renewed food-supply. 
Bats exhibit two forms of hibernation. Some species, such 
as Leisler’s Bat, are highly specialised and experience a regular 
and normally continuous torpidity, and probably in these the 
process has been so ingrained by inherited habit that the 
stimulus of temperature and fat accumulation are hardly 
needed. In other species, such as the Pipistrelle, hibernation 
is intermittent, and here temperature would seem to be the sole 
stimulus—the temperature at which the food-supply disappears. 
In this respect the Pipistrelle is less specialised than bats which 
hibernate more regularly. 
Hibernation may, therefore, be of two kinds—continuous, as 
in the Dormouse; intermittent, as in the Pipistrelle. It does not 
preserve the animal from cold, since it will die if not sheltered 
1 As suggested for Glis by Aug. Forel, who likened hibernation to catalepsy and 
hypnotic sleep (Révue de Phypnotism, translated in Zoologist, 1887, 281); and by 
W. L. Hahn (see above, Vol. I., 29) for bats. Thin animals certainly cannot 
hibernate successfully. 
