NATURE presents no greater or more curious phenomenon than the habit of certain animals to conceal themselves and lie dormant, in a lethargic sleep, for weeks and months. It is known that in perfect hibernators the processes of nature are interrupted during the period of this long insensibility. Breathing is nearly, and in some animals, entirely suspended, and the temperature of the blood even in the warmer blooded animals, falls so low that how life can be maintained in them is a great mystery.

A variety of Rocky Mountain ground squirrels, when in perfect hibernation, says an observer, has a temperature only three degrees above freezing point of water, and when taken from their burrows are as rigid as if they were not only dead, but frozen. But a few minutes in a warm room will show that they are not only alive, but full of life.

As to the suspension of breathing in hibernators, the fact is proved sufficiently in the instances of the raccoon and the woodchuck. When they have laid themselves away for the winter sleep they roll themselves up comfortably and press their noses in such a position against their hinder parts that it would be an absolute impossibility for them to draw a breath. It is generally supposed that the bear rolls itself up in this way and does not breathe, but the holes melted in the snow beneath which the animal frequently stows itself, under a covering of leaves, prove that it does breathe while in its lethargy.

The marmot family produces the soundest winter sleepers. When the marmot is in its peculiar state of hibernation the electric spark will not rouse it. The most noxious gases do not affect it in the slightest. If its temperature is raised above that at which the animal breathed in its natural state it will die almost immediately.

Our own familiar wild animals, the bear, the raccoon, and the woodchuck—the so-called ground-hog—are classed as perfect hibernators, because they store no food for winter, but have acquired or provided themselves with a thick, fatty secretion between the skin and flesh, which, it is supposed, supplies them with sustenance. As a matter of fact, although dormant animals absorb fat, it does not enter into their digestive organs. Food introduced into the stomach of a hibernating animal, or reptile, by force or artificial means, will be found undigested at all stages of its lethargy, for it invariably goes into its peculiar state on an empty stomach. That is one of the mysteries of the phenomenon, not so great, however, as the fact that bears and woodchucks produce their young during their winter sleep. The male bear is frequently roused from his sleep and is found by the woodsman roaming about in mid-winter, but they have never known, they say, a female bear to be killed after the season for hibernation has set in.

Squirrels are only partial hibernators, from the fact that they work all summer and fall storing great quantities of food to supply them when hunger wakes them up during the winter, some of them, no doubt, spending very little time in a lethargic sleep.

The common land tortoise, no matter where it may be, and it is a voracious feeder, goes to sleep in November and does not wake up again till May, and that curious animal, the hedgehog, goes to sleep as soon as the weather gets cold and remains in unbroken slumber six months.

Bats, at the beginning of cold weather, begin to huddle together in bunches in hollow trees, dark corners in deserted houses, and in caves and crevices in the rocks. They gradually lose all sensibility, and continue in a comatose state until the return of genuine warm weather. When you see the first bat of the season fluttering at nightfall you can be sure that warm weather has come to stay. The little hooks at the end of one of the joints of each wing are what the bat hangs itself up by when it goes to sleep, whether for a day or for months. When the bats are clustering for hibernation one of the number hangs itself up by its hooks, head downward, and the others cling to it. It is on record that sixty bats have been found in one cluster, the entire weight of the lot being sustained by the one bat clinging with its hooks to whatever it had fastened them to at the start—a weight of at least ten pounds. The position of the central bat in such a cluster would be like that of a man hanging by his thumb-nails and supporting the weight of fifty-nine other men. So completely is animation suspended in the bat during the cold months that no test yet applied has induced it to show the least sign of life. Torpid bats have been inclosed by the hour in air-tight glass jars and not a particle of oxygen in the jars has been exhausted when they were taken out, showing that the bats had not breathed.

As cold drives certain animals, insects, and reptiles to a state of torpidity, so heat and lack of water bring about the same condition in others. The animal or reptile that hibernates, or goes to sleep in cold weather, arranges its body so that it will conduce to the greatest warmth, while those that estivate, or become torpid in warm weather, place themselves in positions that show that they want all the coolness the climate will permit. The tenric, a tropical animal, carnivorous and insectivorous, becomes torpid during the greatest heat, and lies on its back with its body drawn to its greatest length, and its limbs spread wide apart. Snakes estivate in the South, all kinds together, just as snakes hibernate in the North, but instead of rolling themselves in great balls, as the northern snakes do, they lie singly, and stretched to their full length.

Want of water will cause the common garden snail to go into a state of the most complete and curious lethargy. This is the snail of the genus Limax, not the larger one of the genus Helix. In the latter the phenomenon of hibernation is especially remarkable. In November the snail forms just a soft, silky membrane across the external opening of its shell. On the inner surface of that it deposits a coating of carbonate of lime, which immediately hardens the gypsum. This partition is again lined with a silky membrane. The snail then retires a little further into the shell and forms a second membranous partition, retiring again and again until there are six of these partitions between the snail and the lime-coated door at the entrance of the shell. In the recess behind all these partitions the snail lies torpid until May. All this time it lives without motion, without heat, without food, without air, without circulation or the exercise of any of its functions. If this snail is prevented from hibernating for several seasons by keeping it in a warm room, it will gradually waste away and die. A case is known where several snails of this genus were shut in a perforated box without food or water. They retired into their shells and closed them with a thin membrane. They remained so for three years, but revived when put into torpid water. They had been driven into torpidity by drought. The blood of this animal is white.

It may be of interest to state in connection with these animals who pass half the year, or less, in sleep, that there are several species of fish, reptiles, and insects which never sleep during their stay in this world. Among fish it is now positively known that pike, salmon, and gold-fish never sleep at all. Also that there are several others of the fish family that never sleep more than a few minutes during a month. There are dozens of species of flies which never indulge in slumber, and from three to five species of serpents which the naturalists have never been able to catch napping.