Down into his burrow he cozily creeps,
And quietly through the long winter-time sleeps.”
And in Madagascar, where the heat is always great, and there is a wet and dry season, food being always in great abundance, these little bushy-tailed things go off at a certain time into a nest of leaves, and doze away for weeks, whilst their fellows are scampering around them during the moonlight nights, and imitating them in their sleep whilst all nature glows in the tropical sun. In temperate climates where there is a winter, this long sleep is called wintering, or hibernating, and in the hot climate it is called the summer sleep, or æstivation.
Why some animals should do this and others not, why some should sleep long in winter, and others in summer, and why all should be most regular in their time of taking their nap, are questions well worthy of any one’s attention, and especially because they cannot be answered. Some of the hibernating animals awake for a little time now and then, and take food, but others get quieter and quieter, their breathing becomes slower and slower, their heart beats with diminished force and rapidity, and their temperature falls; but, on the other hand, the irritability of the muscles, especially of those of the heart, increases; and in these—for instance, in many of the Bats—the hibernation is not a commonplace, long-continued slumber, but a necessary matter, and the awakened sleeper dies.
Let us notice what takes place in the hibernators. They get into a place out of the light, and where the temperature is tolerably equable, and after having got nice and fat previously, they settle down in different positions, according to their shape, and go to sleep. They avoid too cold places, and get out of the range of the action of frost. Now taking no food, breathing very slowly, with very slow pulses, and indulging in no exercise, there is very little exhaustion going on. The quantity of fat stored up by the animal in its body generally consumes away, but very tardily, for the oxygen in the blood is at its lowest ebb, and the arterial blood resembles that of the dull purple veins. Under ordinary circumstances, if the whole of the blood is in this condition, the muscles of that side of the heart which propels the pure blood throughout the frame lose their power of contraction, and death ensues. But in their hibernating condition their irritability is increased, and they pump the impure blood as well as they did the bright scarlet fluid of old. At last the fat is consumed, the animal gets thin, and by the time the spring comes it is ready for its new life.
Now the little Cheirogales of Madagascar certainly do part of all these wonderful things. They get fat, and their tails attain a most dignified size; then they retire for their summer sleep, grow thinner and thinner, and finally come forth with such miserable vestiges of tails, so thin and miserable-looking. Their time of quietude is during the hot and dry season, and is equivalent to the English winter, and they fatten up during the months when the warm rain makes everything to grow in profusion. It must be noticed that although these Cheirogales greatly resemble the Lemurs already described, they have no special construction which necessitates this sleep.
These Cheirogales resemble the Hapalemurs in shape, and may be known by their small size, their long tail, which is either conical or cylindrical, and by their face, which is scarcely narrower in front than behind. Having long ankle-bones, the back muscles of the leg have a great leverage over the foot, which enables the creature to make its easy jumps. Being nocturnal in their habits, they have very large eyes, and rounded and short, but sharp-sensed, external ears. They are vegetable feeders, yet most of them are extremely fond of something alive to eat, and, indeed, are greedy enough when they have the opportunity of catching insects. Having wonderful powers of sight, and of rapid jumping, they watch for their prey, and approach it quietly, and finally descend from some height with the stealthy swoop of an Owl, catching the Beetle, Spider, or even small bird, and tearing it to pieces with astonishing celerity. They have a shrill cry at night, which is loud for such small creatures, but their usual voice is soft.
Holes in trees are used by the Cheirogales for hiding-places and nests for their young, which do not accompany the mother at first out of their safe retreats.
Naturalists have had a vast amount of trouble in distinguishing these little Lemuroids one from the other, and there has been a vast amount of confusion about their names, but the following are interesting for many reasons.