HIBERNATION IN COLD-BLOODED ANIMALS

While hibernating mammals seek caves, dens or hollow logs, usually making themselves dens of dry leaves or grass to sleep through the winter, the lower orders remain buried throughout the winter with the body temperature approximately that of the external environment, and with great decrease in metabolism. Reptiles hide away among stones or pits or caves, often coiling together, to form a huge, inert mass. Frogs, lizards, salamanders and certain fishes bury themselves in the earth below the reach of frost, the aquatic (forms digging into the mud at the bottom of the stream. The few fishes which are known to lie dormant and take no food, sink into the mud of the streams or of the sea. Some fish, as the carp, lie quiet on mud bottoms. The horseshoe crab buries into the mud beyond the reach of oyster dredges in November, remaining in deep water until the middle of Spring. Because snakes hibernate so deep below the ground that frost never reaches them, they live further north than any other reptile. Spiders and snails hibernate under stones, moss, etc., while slugs bury themselves in the mud and muscles and other molluscs living in the streams and lakes, descend into the mud.

As cold weather comes and winter approaches the purely aquatic species of frogs take to the water and burrow into the moist mud at the bottom of the ponds below the frost line. Here they hibernate throughout the winter, becoming cold and dormant, where the climate is severe, until revived in the Spring. Others bore into the soil, or beneath the fallen leaves, or into the rotting stumps, etc., and exist quietly and dormant until the coming of warm weather and food. During this period, most of the life activities of the frog cease. The heart beats very slowly and there is little evidence of life. The frog does not breathe through its lungs during this period but takes in oxygen through its skin. Toads also hibernate through winter. Hibernating frogs and toads take no food, being dependent during this time on the food reserves stored in their bodies as fat and glycogen. All activities are suspended except those necessary to maintain life, such as the beating of the heart. Metabolism is much reduced, little oxygen is required, and respiration takes place entirely through the skin. Many other amphibians bury themselves in mud, this being particularly true of those that estivate during the dry season.

Lizards residing in the temperate zones hibernate during the winter. Here in the Southwest, the great variety of lizards, some brilliantly colored, others dull and drab, like the noted horned toad, that one sees in the Summer months, is almost bewildering. Upon the approach of Winter they disappear. They may be found under boards, piles of straw, logs, etc., dormant and almost incapable of activity. If placed near a fire and made warm, they become as active as in the Summer months.

Newts are more difficult to find than lizards, but if one digs into the hole, often far down into the ground, where a newt is spending the winter, one may find a black shriveled object that is scarcely recognizable.

The snail prepares a really tough defense for itself. It seeks a hiding place, preferring a damp and rather warm atmosphere, and when ensconced in its new home, manufactures from its own juices a chalky secretion covering the mouth of its cell. By puffing from its lungs it separates this covering from contact with itself. This defensive covering is porous to the air so that the sleeping snail can breathe. It then shrinks into the deep recesses of its shell instead of filling out the whole of it. Here it spends the winter in sleep, taking no food during the whole of this period.

Date: 2015-01-11; view: 782