HIBERNATION, in zoology, that pe culiar condition of sleep in which certain animals, chiefly cheiroptera and rodentia, pass the winter season. The bat, the hedgehog, and the dormouse are the most striking examples of this phenom enon.
During dormancy the animal functions are all but suspended. Respiration and circulation are reduced to a minimum. The air of a closed jar containing a hibernating dormouse is unaltered. Others can survive long in an atmos phere deprived of oxygen. A bat in a lethargic condition has remained 16 min utes under the water. Hibernators lose weight, often to the extent of 30 and 40 per cent., in this respect resembling starving animals.
.All reptiles and batrachia become tor pid during cold weather, snakes passing the winter in tangled knots as if for warmth; if the viper is aroused at this ;eason its venom is said to be inert. Alligators creep into holes in the river banks, and frogs lie dormant in the mud at the bottom of ponds. Many fishes
(carp, roach, chub, minnows, eels, the lediterranean inurna, etc.) also retire into some deep recess, or into the mud, though their condition at this period is not that of the true hibernators. Their vitality only is lowered. In winter all land-snails hibernate by closing the mouths of their shells with a plate (the epiphragm), leaving only a little hole in the middle of it for breathing. Slugs also become torpid in holes in the ground, and the fresh-water mussels (Unio, Anodonta, Dreissena) bury them selves in the pond and river mud till the cold months are over. The torpidity of insects in the pupa and other stages is well known. Individuals belonging to the Vanessa group of butterflies which hibernate in the imago stage occasionally emerge during mild winter days. But hive-bees do not hibernate, food being necessary for their subsistence during the flowerless season.