the term employed by naturalists to denote that state in which certain animals pass a portion of each year in a more or less complete suspension of their active functions; and as this state has most frequently been observed during the rigour of winter, it has been designated Hybernation, from the Latin word hyberna.

The continued application of cold to such animals will induce a suspension of their active faculties, and artificial heat will dissolve their hybernation; yet this state cannot be altogether the consequence of a low temperature; for hybernation is observed, in tropical climates, in some insectivorous mammals and reptiles, when the dry heats of those regions abridge the supply of suitable food. These facts would show that hybernation is also caused, and perhaps chiefly so, by the want of due aliment to keep up or renovate the irritability of the vital organs. Without some such law, the existence of insectivorous animals, both in high latitudes and in tropical climates, would have been impossible; and we must regard hybernation as one of those admirable adaptations of special means to an important end, which the history of animated nature so frequently presents.

In the most complete hybernation the animals, on the approach of that season, retreat to their places of temporary concealment, their vital functions begin to be more slowly performed, they cease to eat, breathe more slowly, and finally their respiration would appear to be totally suspended, while the movements of the heart become more languid, and are performed at much longer intervals of time; the animal heat is much diminished, and finally, insensibility is profound. In such cases the small degree of oxygenation necessary to maintain sufficient irritability in the muscles of the heart to prevent their absolute rest is probably supplied by the dermoid surface of the animal.

In our climates the bat and the hedgehog present the best known instances of hybernation among mammals. In them all the vital functions, except a very languid circulation of the blood, appears to be totally suspended at that season, when a want of insect food would condemn them to starvation. In some other European mammals the hybernation, though somewhat analogous, is less complete. This is the case with certain frugivorous species that lay up stores of vegetable food in their winter domiciles; as the dormouse, the squirrel, and the marmot. In them the insensibility would appear to be less profound, and the respiration never wholly suspended, though much diminished in frequency. A good observer of the habits of the Alpine marmot, Professor Mangili, calculates that during its six months of torpidity, this animal only makes 71,000 inspirations; while, in its active state, it makes no less than 72,000 in 48 hours. The large collection of dried grass which the marmot lays up in its hybernaculum is probably intended for consumption in its occasional revivals during its long hybernation; although Schinz supposes that this ample store of food is untouched until its full restoration to activity on the return of warm weather in April, which he supposes to take place before the new grass is sufficient for its wants. It is certain, however, that tame marmots, when awakened by artificial heat, eat whenever they are roused up. Mammals of other countries, that lay up similar stores of food, have similar habits and hybernations; as various genera of the family Mus.—Merion canadensis, and M. leporinus; Aricola economica, or economic mouse; Cricetus vulgaris, or hamster, &c. These animals probably have the same kind of hybernation as the marmot. The common bear, the teeth of which prove it to be chiefly a vegetable feeder, passes a considerable portion of the winter without food, and in profound sleep. All these animals become fat in autumn, which seems to be intended to supply the waste of the system during their hybernation.

In hot climates certain mammals also undergo hybernation. Thus the three species of Centetes or tearee of Madagascar, which have much analogy with our hedgehog, being like it furnished with a spiny covering, and living on insects, sustain a torpidity of three months, according to Brugiere, at the season when the dry heats of that climate cut off their supply of insect food.

Insectivorous birds are less subject to hybernation than mammals in cold climates, because they possess the power of an easy migration to regions where insect food is easily procured. Such birds are migratory; as are many of our land birds. Yet the writer of this article has known instances in these islands of the hybernation of Rollus crez, or land rail, and the swallow. Cuvier not only mentions the hybernation of Hirundo riparia or sand martin, but expresses his belief of that bird being found hybernating below the surface of water in marshes.

The hybernation of many cold-blooded animals is with us very complete. Snakes, lizards, toads, and frogs lie in a state of complete torpor during the winter months, while the lips of the latter are glued together, and they are buried in mud at the bottom of stagnant water at that season. They cannot breathe during that process; but probably the small quantity of oxygenation required by their system is sufficiently obtained through their skin.

In North America, as with us, snakes are hybernating animals, though in warmer regions they are active throughout the year. The same takes place with lizards. In these cases, hybernation seems rather, however, the consequence of the want of due nutriment than of mere cold. A fact mentioned by Von Humboldt confirms this. The largest species of serpent, the Boa murina, during the long rains that inundate the immense deserts of Central South America, remains buried in the soil until the mud, dried by the heats which invariably succeed the rainy season, cracks, and emancipates the imprisoned monster from his earthly tomb. Yet in Surinam and Brazil, this boa, like other serpents there, passed the whole year in uninterrupted activity.