THE hibernation of animals is one of the most interesting phenomena of nature. The word "hibernation" comes from the Latin hibernare, meaning to go into winter quarters, but it has come to have a more restricted meaning, and we understand by it a protracted condition of lethargy, during which the vital activities of an animal are more or less completely suspended.
Some of the simplest or one-celled animals, the infusoria, have the ability to withstand extremes of cold and drouth for long periods by forming hard coverings or cysts about themselves and in this condition they may be completely dried up and blown about by the wind, reviving when favorable conditions return, perhaps months afterward.
This condition corresponds to the hibernation of higher animals about as closely as any of the other activities of these simple organisms correspond with the more complex life of the higher species.
As far as I have been able to learn, there is nothing corresponding to hibernation in those animals that are nearest the infusoria in the scale of life, the sponges, corals, jelly-fishes, starfishes and the hosts of other marine invertebrates. However, practically all insects in temperate climates (excepting some that live in the water) pass the winter in a dormant state. In some species the adult insect lives through the winter, in others only the eggs, the larvæ or the chrysalides survive. In some cases the insect burrows into the ground or seeks protection elsewhere; in others, the egg, larva, chrysalid or adult insect remains in the most exposed situations in temperatures at times many degrees below freezing point.
Without attempting to enumerate all the kinds of animals that hibernate or to discuss the general features of the phenomenon, I shall merely call attention to the well-known fact that frogs, toads, snakes, lizards and turtles, in temperate climates, seek protection during the winter months in crevices among rocks or buried in the soil or mud according to their especial habits. We will now pass on to a discussion of the hibernation of certain well-known species of the highest class of the animal kingdom, the mammals.