Amphibia and Reptilia.—All the animals belonging to these classes hibernate in cold or temperate climates. Land tortoises bury themselves in holes in the ground, and fresh-water tortoises in the banks or at the bottom of lakes und rivers. Lizards and snakes retire to holes in trees, under stones, or among dead leaves, where many species congregate in large numbers, and pass the winter closely entwined, and in a still more torpid condition than that of the hibernating mammals, their digestion and respiration being entirely suspenderl. Many tortoises, crocodiles, and serpents bury themselves in mud in both South America and Africa, and testivate in the hard-baked ground during the dry season of the year. When the viper is disturbed daring the winter its bite is harmless ; but this is not ths case- with the venomous serpents which activate in tropical countries.
Frogs generally hibernate in masses in the mud at the bottom of the water, and if awakened from hibernation by warmth can remain eight times longer under water without drowning than frogs in the breeding season. We should hardly expect the habits of such an animal as the frog to be greatly affected by domestication, but Professor Bell was acquainted with a gentleman living at Kingston, whose kitchen was built on the banks of the Thames, and whose servants made a pet of a frog which had his hole in the skirting. It was unnecessary for the frog to hibernate, and instead of doing so he came out of his hole every evening to bask before the kitchen fire for three successive winters. It is impossible to say how long frogs and toads may continue to retain a dormant life, if the mud in which they bury themselves should become hardened around them during hibernation. Too many circumstantial accounts of the discovery of live toads embedded in solid rock, and even in coal, have been published to allow us to dismiss them all as fabulous, notwithstanding the difficulty and obscurity in which this subject is still involved.
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Mollusca.—Many species hibernate. The land-snails bury themselves in the ground, or conceal themselves under the bark of trees, in holes in walls, or even in the stems of large umbelliferous plants. They close the mouth of the shell with a calcareous plate, technically called an epiphragm, which they secrete by means of their mantle, and which is perforated by a small hole to admit the air. In winter they bury themselves with the head upwards, and do not grow at all during the winter; but while growing they bury themselves in summer, with the head downwards, at occasional intervals, for several days together, and then grow very rapidly. Snails are not considered in season at Paris till after the first frost, when they are closed with a white epiphragm. In dry weather, and during the heat of summer, snails also close their shells with an epiphragm, to protect themselves from drought, but this covering is thinner than that which they construct during the winter. In the British Museum is preserved the shell of a specimen of Helix desertorum, from Egypt, which revived after having been gummed to a board for four years in the Museum, and lived .for Two years afterwards. Other instances of the revival of land-shells after a still longer period are equally well authen ticated. Some species retire to winter quarters earlier than others, and their pulsation, which ranges from 30 to 110 during summer, ceases entirely in winter. Slugs also bury themselves in the ground, and become torpid during frosts or droughts, but it is doubtful whether their condition is that of genuine hibernation. The fresh-water mussels (Anodonta) hibernate before the close of autumn, and bury themselves in the mud till the beginning of spring. It is believed that many of the marine Mollusca also hibernate, but very little is known of their habits at present.
Insecta.—Most of the insects which pass the winter as larvee or perfect insects hibernate during the period that they can obtain no food. Larvae which are full grown in autumn frequently lie dormant during the winter, and do not assume the pupa state till spring. In the case of insects which have more than one brood in the year, the last brood gene rally hibernates, sometimes retiring to winter quarters quite early in the autumn, while the perfect insects of the pre vious brood are still flying about, and while the weather is still fine and warm. Insects which hibernate in the perfect state do not pair till spring, and are probably not fully developed till after hibernation. Hive-bees probably do not hibernate, and it is well known that they require food during the winter. It is asserted that the aphides, on whose sweet secretion ants chiefly subsist in inclement weathar, become torpid at exactly the same low temperature as the ants themselves.
Concluding Remarks.—The seeds of many plants, and the eggs of many of the lower forms of animal life, may remain dormant for years in cold or dry climates, until heat or moisture awakes them to vitality. Many plants die down in winter, the roots remaining in the ground, while many trees then shed their leaves, the sap retiring to the roots. Similar phenomena take place in tropical countries during the hot, dry season, wherever the amount of humidity in the atmosphere is insufficient to maintain a perennial vegetation during the year. These phenomena in the vegetable world are regarded as analogous to those of hibernation in animals, and the term "hibernation of plants " is sometimes applied to them.
Dr Marshall Hall, in Todcl s Cyclopaedia of Anatomy and Physiology, art. " Hibernation " ; Braid s Observations on Trances or Human Auction to Entomology, &c.
