340 Annals Entomological Society of America  [Vol. VII, 
famine, build a fire in a huge stove which serves as a resting 
place and lying upon this, keep as quiet and warm as possible 
and thus reduce their need of food. Among the Mammals, 
the marmot has been the most studied of the hibernating forms. 
Cleghorn lists a number of animals that hibernate—he states 
that bats of different species hibernate at different times of the 
year—that when disturbed for a time, they breathe almost 
normally and then again, the respiration goes down almost to 
zero. If awakened suddenly by great heat, death always 
ensues. He says that bears are as fat after hibernation as when 
they go into it in the fall and that female bears even raise their 
young while not obtaining any food and still show very little 
change in condition. Bears and badgers of the North do not 
go into any true state of hibernation but sleep lightly through 
the winter. The black bear, however, is aroused with difficulty 
from the winter sleep—the woodchuck of Canada, the European 
hedgehog, chipmunks and ground squirrels, all hibernate. 
Frogs hibernate in mud at the bottom of pools and if awakened 
by warmth can remain much longer under water without being 
drowned than during the active season. Some fish survive long 
draughts by burial in the mud. - Baker (5) states that during 
some seasons of draught, Lymnzidze bury themselves and form 
an epiphragm inside the outer lip as is common with Helix 
during hibernation and estivation. Plants have a similar 
phenomenon also known as hibernation which is closely con- 
nected with lowering of temperature and shows itself in the 
decreased rate of the metabolic processes. 
The physiology of hibernation has best been studied by 
Bellion in the European edible snail (1’ escargot). Bellion (6) 
finds that the moisture content of the air and not temperature 
is the essential external factor of hibernation—when the mois- 
ture content is low, and epiphragm is formed in spite of low or 
high temperature and the snail is plunged into a condition of 
lethargy. If moisture content is high, no epiphragm is formed 
and activity is at its height even at a low temperature. Car- 
bon dioxide content of the tissues increases towards the end 
of hibernation while the oxygen content diminishes in propor- 
tion. Dubois (16) has found in the marmot that when carbon 
dioxide is present in a certain proportion in the blood, torpor 
sets in. At moment of awakening, carbon dioxide is high— 
it is very probable that the carbon dioxide and rehydration 
