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HIBERNATION (winter sleep)
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See also:HIBERNATION (See also:winter See also:sleep) , the dormant See also:condition in which certain animals pass the winter in See also:cold latitudes. See also:Aestivation (summer sleep) is the similar condition in which other See also:species pass periods of See also:heat or drought in warm latitudes. The origins of these kindred phenomena are probably to be sought in the regularly recurrent failure of See also:food See also:supply or of other factors essential to existence due to the seasonal onset of cold in the one See also:case and of excessively dry hot See also:weather in the other. They are means whereby certain non-migratory species are enabled to live through unfavourable See also:climatic conditions which.. would end fatally in See also:starvation or See also:desiccation were the animals to maintain their normal See also:state of activity. I. The See also:Physiology of Hibernation. Hibernation and Aestivation.—The physiology of hibernation, as exemplified in roammalia, has been worked out in detail by several observers in the case of some See also:European species, notably bats, hedgehogs, dormice and marmots. Of the physiology of aestivation nothing definite appears to have been ascertained. It seems probable, however, from observations upon the dormant animals that the physiological accompaniments of winter and summer sleep are to all intents and purposes the same. The state of hibernation. for example, in the European See also:hedgehog (Erinaceus europaeus) is not distinguished by See also:external signs from the state of aestivation of the allied Mascarene genus, the See also:tenrec (Centetes ecaudatus). The lethargy in both cases appears to be directly due to fall in the temperature of the organisms; and the fall in temperature proceeds pari passe with the slowing down and weakening of the respiration and with retardation in the circulation of the See also:blood. Similarity, moreover, between hibernation and aestivation is shown not only in their physiological accompaniments but also in the species of animals which become seasonally dormant. Birds neither hibernate nor aestivate The tenrec (Centetes) of See also:Madagascar, which aestivates, closely resembles the hedgehog (Erinaceus) in habits and belongs to the same See also:order of See also:mammalia. In the case of See also:reptiles and batrachians, See also:snakes, lizards, tortoises, frogs and toads sleep the winter through in cold countries; and some species of these See also:groups habitually See also:bury themselves in the See also:sand or mud in tropical latitudes where drought is of periodical occurrence. Terrestrial molluscs See also:lie dormant in the winter in cold and temperate latitudes and their tropical See also:allies aestivate in districts where conditions enforce the See also:habit. Some fresh-See also:water molluscs bury themselves in the mud at the bottom of pohds when the See also:surface is covered with See also:ice; others take See also:refuge in the same way when pools and tanks become exhausted during the dry See also:season in the tropics. In temperate and See also:north temperate countries See also:insects and See also:arachnida either See also:die or retire to winter quarters during the cold weather, and in the tropics they similarly disappear during times of drought. Predisposing Causes of Hibernation.—The likeness between hibernation and aestivation and the coincidence of the one with cold and of the other with heat See also:arrest the conclusion that the temperature of the surrounding See also:medium, whether atmospheric or aquatic, is the See also:prime, much less the See also:sole, cause of either. The effect of extreme cold- is to rouse the •hibernating See also:animal from its slumber; and its continuance thereafter brings about a state of torpor which proves fatal. This at least appears to be the case with mammals, where actual freezing of the tissues is followed by See also:death because the gases are expelled from the fluids as bubbles and the salts See also:separate in the See also:form of crystals, Some cold-blooded animals, however, may he cooled to o° C. See also:Fish have been resuscitated after solidification in blocks of ice, and frogs have been known to recover when ice has been formed in the blood and in the See also:lymph of the peritoneal cavity (Landois). For the reasons given, all hibernating mammals take pre-cautions against exposure to extreme cold. They either bury themselves in the See also:soil or under the See also:snow or seek the shelter of hollow trees orof caves, not infrequently congregating in the same spot so that the temperature is kept up by corporeal contact. Again the hibernating See also:instinct may be suspended unless the conditions are favourable for safely entering upon winter sleep. It is alleged that bears in Scandinavia do not hibernate unless food has been sufficiently plentiful during the summer and autumn to fatten them for their winter fast; and hedgehogs and dormice in captivity have been known to remain active in the cold until warm sleeping-quarters were insured by placing See also:hay and See also:cotton-See also:wool in their cages. Finally the See also:wood-chucks (Arctomys monax) in the See also:Adirondacks retire to winter quarters at about the See also:time of the autumnal See also:equinox, when the weather is warm and pleasant, and emerge at the vernal equinox before the snows of winter have vanished from the ground. These and other facts justify See also:Marshall See also: The temperature of animals in a profound state of hibernation is approximately the same as that of the surrounding medium or at most a degree or two higher. If, however, the temperature of the chosen See also:hibernaculum (winter quarters) falls as See also:low as freezing point, life is endangered at least in the case of mammals. In most cold-blooded animals, like reptiles, the temperature is normally only a little above that of the See also:atmosphere, the two rising and falling together. But, setting aside the See also:young, especially of those species in which the offspring are See also:born or hatched at a comparatively See also:early See also:stage of development, the See also:majority of warm-blooded animals are able to maintain a high and approximately - level temperature irrespective of decline in the temperature of the surrounding medium. This See also:faculty of temperature See also:adjustment, however, appears to be absent or weakened in most if not in all hibernating mammals both in their normal nocturnal or diurnal sleep and in their winter sleep. In the case of European bats it has been shown that the ordinary day sleep in summer differs only in the See also:matter of duration from the prolonged slumber of the same animals in winter. The temperature falls with that of the atmosphere, respiration practically ceases and See also:immersion in water for as many as eleven minutes has been known to prove innocuous. At moderate temperatures ranging from 45° to 50° F., dormice (Muscardinus avellanarius) and hedgehogs (Erinaceus europaeus) alternately See also:wake to feed and sink into slumber. Dormice awake once in every twenty-four See also:hours; the sleep of the hedgehogs may last for two or three days. The temperature of the hedgehog, when awake and active, rises to about 87' F., that of the See also:dormouse to 92° or 94° F.; but during sleep the temperature of both species falls to about that of the atmosphere. In other words, all the phenomena characteristic of hibernation are exhibited in these animals during the periods of sleep interrupting their periods of wakeful activity. Sleep of this nature, for which the See also:term " diurnation " has been proposed, because it has only been observed in nocturnal animals, lies phenomenally midway between the normal sleep of non-hibernating mammals and the dormant condition in winter of hibernating species. The stimulus of See also:hunger appears to be the prime cause of its periodic cessation. Since then the faculty of temperature adjustment is in See also:abeyance during the ordinary diurnal summer sleep in hibernating mammals, which in this physiological particular resemble reptiles, it seems probable that hibernation can only be practised by those species in which the See also:power to maintain, when sleeping, a permanent See also:average high temperature has been lost or perhaps never acquired. That there is no broad See also:line of demarcation between the ordinary sleep of these hibernating mammals in which the temperature is known to drop considerably and that of non-hibernating species is indicated by the fact that the temperature of human beings and possibly of all non-hibernating species falls to a certain, though to a limited, extent in ordinary sleep. The relation between the See also:internal See also:body-temperature and the See also:respiratory movements has been worked out in hibernating dormice, hedgehogs, marmots and bats. When the temperature is below 12° C., the torpid animal exhibits See also:long periods of See also:apnoea of several minutes' duration and interrupted by a few respirations. With the temperature rising above 13° C., the periods of apnoea in the still inactive animal become shorter, the respiration suddenly commencing and ceasing (See also:Biot's type), or gradually waxing and waning (See also:Cheyne-See also:Stokes' type). When the temperature is at about 16° C., the periods of apnoea in the gradually awaking animal are very See also:short and infrequent. When the temperature is about 20° and rising apace, respiration becomes continuous and rapid and the animal is awake. These stages have been especially recorded in the case of dormice. In the. last stage the respiration of hedgehogs and marmots is somewhat different, there being a See also:series of rapid respirations, often followed by a single deep sighing respiration. Respiration appears to be totally suspended in animals in a See also:complete state of hibernation, if See also:left undisturbed. It may however, be readily re-excited by the slightest stimulus; and to this fact may perhaps be attributed the belief, that breathing does not actually cease. If a hibernating hedgehog; be lightly touched it draws a deep breath, and breathing is maintained for a longer or shorter time before again ceasing; but if at the same time the temperature of the atmosphere be raised, respiration becomes continuous and lethargy is succeeded by activity (Marshall Hall). The See also:opinion that respiration is totally suspended is supported by a number of facts. Hibernating marmots and bats, for example, have been known to live four hours in See also:carbon dioxide, a See also:gas which proves almost instantly fatal, to mammals in a state of normal activity (See also:Spallanzani). A hedgehog which may be drowned in about three minutes when awake and active, has been removed from water uninjured when in deep winter sleep after twenty-two and a half minutes' submergence. A hibernating noctule See also:bat, when similarly treated, survived sixteen minutes' immersion. Further See also:proof of the suspension of respiration has been furnished by experiments upon a bat which while in a deep and undisturbed. state of lethargy was kept in a pneumatometer for ten hours without appreciably affecting the percentage of See also:oxygen in the See also:air. The same animal, when active, removed over 5 cub. in. of oxygen in the space of one See also:hour from the See also:instrument. As in the case of respiration, alimentation and See also:excretion are suspended during hibernation. The circulation of the blood, on the other See also:hand, continues without interruption, though its rapidity is greatly retarded. This fact may be observed by microscopic examination,of the wings of bats in a state of winter sleep. Moreover, in the case of a hedgehog lethargic from hibernation, it was experimentally shown that when the See also:spinal See also:cord was severed behind the occipital foramen, the See also:brain removed and the entire spinal cord gently destroyed, the See also:heart continued to See also:beat strongly and regularly for several hours, the contraction of the auricles and ventricles being quite perceptible, though feeble, even after the See also:lapse of ten hours. After eleven hours the See also:organ was motionless; but resumed its activity when stimulated by a See also:knife-point. Even after twelve hours both auricles responded to the same stimulus, though the ventricles remained motionless. Shortly afterwards the auricles gave no response. On the other hand, when the spinal cord of a hedgehog in a normal state of activity was severed at the occiput, the left ventricle ceased to beat almost at once, and the left See also:auricle in less than fifteen minutes; the right auricle was the next to cease, whereas the right ventricle continued its contraction for about two hours. Experiments upon marmots have yielded very similar results. The heart of a See also:marmot decapitated in a state of lethargy continued to beat for over three hours. The pulsations, at first strong and frequent and varying from 16 to i8 per See also:minute, became gradually weaker and less frequent, until at the end of the third hour only 3 were recorded in the same length of time. Excised pieces of voluntary See also:muscular See also:tissue contracted vigorously three hours after death See also:tinder electric stimulus. Only at the end of four hours did they cease to See also:respond. The heart of an active marmot killed in the same way contracted about 28 times a minute at first, the number of pulsations falling to about 12 at the end of fifteenminutes, to $ at the end of See also:thirty minutes, and ceasing altogether at the end of fifty minutes. Similarly the response of the muscles to galvanic See also:shock failed at a correspondingly rapid See also:rate. It is evident, therefore, that during hibernation the irritability of the heart is augmented in a marked degree, and that the irritability of the left See also:side of the organ is scarcely less pronounced than that of the right side. Similar reduction in the rate of the circulation has been demonstrated in certain hibernating See also:mollusca, Mr C. See also:Ashford having proved experimentally that the number of pulsations of the heart per minute gradually lessens with a falling temperature. At a temperature of 52° F. the number was 22 in the See also:common See also:garden See also:snail (See also:Helix horlensi t), and 21 in the cellar slug (Hyalinia cellaria). At a temperature of 3o° F. the pulsation See also:fell to 4 in the former and t© 3 in the latter animal. The nature of hibernation, and, probably also of aestivation, and the See also:principal physiological phenomena connected with them, may be briefly summarized as follows: i. During hibernation death from starvation and wasting of the tissues is prevented by the absorption of See also:fat, which; at least in the case of mammalia, is stored in considerable quantities, sometimes in definite parts of the body, during the See also:weeks of activity See also:im mediately preceding the See also:period of winter sleep.: 2. Every gradation seems to exist between ordinary sleep and hibernation; the See also:differences between the ordinary diurnal' or nocturnal sleep in summer of hibernating 'animals and their See also:pro-longed and lethargic quiescence in winter are merely differences of degree, differences, that is to say, of intensity and duration. 3. The physiological accompaniments of hibernation are: (a) Cessation of all activities associated, with alimentation and excretion; (b) lowering of the body temperature to that of the surrounding medium or to within a few degrees of it; (c) See also:total or almost total cessation of respiration, accompanied by power to survive immersion for a considerable time in water er asphyxiating gases, which prove rapidly fatal to the same animals when `normally active; (d) marked increase in the irritability of the' muscles, especially of those of the left side of the heart, whereby the •pulsations of that organ, although retarded, are uninterruptedly maintained; (e a slight See also:exchange of gases in the lungs, is kept up by the See also:car iopneumatic See also:movement. 4. Amongst cold-blooded animals, both vertebrate and invertebrate, devoid of the faculty of temperature adjustment, the pheno. menon of hibernation or aestivation is of See also:general occurrence wherever the conditions of existence accompanying the onset of cold or drought are inimical to active life. In hot-blooded vertebrates, on the contrary, the phenomena are non-existent so far as birds are concerned; aestivation is of very rare occurrence in mammalia, while hibernation is practised by a comparatively small number of species; and in these the faculty of temperature adjustment appears to be temporarily at all events in abeyance. II. The See also:Zoology of Hibernation and Aestivation.—Owing to the extreme difficulty of keeping See also:wild animals under observation in their natural haunts for any lengthened time, it is almost impossible to get accurate knowledge of the details of this state of existence. In a general way it is known, or assumed from their disappearance, that certain species retire to winter quarters in particular districts, but on such important points as whether the winter sleep is continuous or interrupted, See also:light or,profound, assured See also:information is for the most See also:part not forthcoming. This is true even of See also:familiar species inhabiting See also:Europe and North See also:America, which have been See also:objects of study for many years. It is still more true of species occurring in countries: uninhabited and rarely visited, especially in winter, by naturalists interested in such questions. The See also:Chiroptera (bats) furnish an See also:illustration of this truth. It was formerly assumed that the winter sleep of these animals in north and temperate Europe was complete and uninterrupted. Marshall Hall, for example, remarked that " perhaps the bat may be the only animal which sleeps profoundly the winter through without awaking to take,food." It was known, it is true, that in countries where gnats and other winged insects disappear with the first frosts of winter, bats which feed upon them retire to winter quarters in hollow trees, caves, sheds or other places likely to afford them sufficient shelter. Here they hang suspended, solitary or in companies according to the species. But a mild spell of weather in mid-winter will .sometimes entice a few to take wing while it lasts, although they never appear in any See also:numbers until See also:crepuscular and nocturnal insects are plentiful. But Mr T. A. See also:Coward has recently shown in the case of the greater and lesser horseshoe bats (Rhinolophus ferrum-equinum and R. hipposiderus), that during the early period of their occupation of the winter See also:retreat, hibernation, in the strict sense of the word, does not take See also:place, and that even later in the season the sleep is constantly interrupted, especially when the temperature of the air rises above 46° F., and that during their wakeful intervals they crawl about and feed apparently upon the insects which live throughout the See also:year in the caves. This is also true of the long-eared bat (Plecotus auritus), and probably of other species of this See also:group. At See also:Mussoorie in the Himalayas, and in other parts of See also:northern See also:India, insectivorous bats, such as Rhinolophus luctus and Rh. affinis, pass the winter in a semi-torpid state, and are rarely seen abroad during the cold season. The See also:fruit-eating bats, on the contrary (Pteropidae), which are more See also:southern in their See also:distribution and are restricted in the Himalayas to the warmer valleys and See also:lower slopes of the mountains, are as active in the winter as at other times of the year (See also:Blanford). Although almost as exclusively insectivorous as bats, moles and shrews do not, so far as is known, hibernate. This distinction between two groups so nearly alike in See also:diet, no doubt depends upon the difference in their habitats and in those of the creatures they live upon. By tunnelling deeper in winter than in summer, moles are still able to find See also:worms and various insects buried in the See also:earth beyond the reach of See also:frost; and shrews See also:hunt out spiders, centipedes and insects which in their larval, pupal or sexual stages have taken shelter and lie dormant in holes and crannies of the soil, beneath the leaves of ground See also:plants or under stones and logs of wood. In view of the perennially active life of the two insectivora just mentioned, it is a singular fact that the common hedgehog (Erinaceus europaeus)—the only member of this order besides genera referable to the moles (Talpidae) and shrews (Soricidae) that inhabits temperate and north-temperate latitudes in Europe and See also:Asia—passes the winter in a state of torpor unsurpassed in profundity by that of any species of mammal so far as is known. Possibly the explanation of this seeming See also:anomaly may be found in the bionomial differences between the three animals. The subterranean feeding habits of the See also:mole render hibernation unnecessary on his part. Therefore the See also:shrew and the hedgehog, both surface feeders for the most part, need only be considered in this connexion. As compared with shrews, amongst the smallest of palaearctic mammals, the hedgehog is of considerable See also:size. Moreover, in point of vivacious See also:energy it would be difficult to find two mammals of the same order more utterly unlike. Hence in winter when insects are scarce and demand active and diligent See also:search, it is quite intelligible that the shrews, in virtue of their smallness and rapidity of movement, are able to procure sufficient food for their needs; whereas the hedgehogs, requiring a far larger quantity and handicapped by lack of activity, would probably starve under the same conditions. Like the common hedgehog of Europe, the long-eared hedge-hog (Erinaceus megalotis) hibernates in See also:Afghanistan from See also:November till See also:February. The tenrec (Centetes ecaudatus), a large insectivore from Madagascar, aestivates during the hottest weeks of the year; and specimens exhibited in the Zoo-logical Gardens in See also:London preserved the habit although kept at a See also:uniform temperature and regularly supplied with food. Amongst the See also:Rodentia, no members of the Lagomorpha (See also:hares, rabbits and picas) are known to hibernate, although some of the species, like the See also:mountain See also:hare (Lepus timidus), extend far to the north in the palaearctic region, and the picas (Ochotona) live at high altitudes in the Himalayas and Central Asia, where the cold of winter is excessive, and where the snow lies deep for many months. It is probable that the picas live in fissures and burrows beneath the snow, and feed on stores of food accumulated during the summer and autumn. The Hystrico-morpha also are non-hibernators. It is true that the common See also:porcupine (Hystrix cristata) of See also:south Europe and north See also:Africa is alleged to hibernate; the statement cannot, however, be accepted without See also:confirmation, because the cold isseldom excessive in the countries it frequents, and specimens exhibited in the Zoological Gardens in London remain active throughout the year, although kept in enclosures without artificial heat of any See also:kind. Even the most northerly representative of this group, the See also:Canadian porcupine (Ereihizon dorsatus), which inhabits See also:forest-covered tracts in the See also:United States and See also:Canada, may be trapped and shot in the winter. Some members of this group, like capybaras (Hydrochaerus See also:capybara) and coypus (Myocastors coypus) which live in tropical America, are unaffected by the winter cold of temperate countries, and live in the open all the year See also:round in parks and zoological gardens in See also:England. Several of the genera of Myomorpha contain species inhabiting the northern hemisphere, which habitually hibernate. The three European genera of dormice (Myoxidae), namely Muscardinus, Eliomys and Glis, sleep soundly practically throughout the winter; and examples of the South See also:African genus Graphiurus practise the same habit when imported to Europe. If a warm spell in the winter rouses dormice from their slumbers, they feed upon nuts or other food accumulated during the autumn, but do not as a See also:rule leave the nests constructed for shelter during the winter. According to the weather, the sleep lasts from about five to seven months. In the See also:family Muridae, the true mice and rats (Murinae) and the voles and lemmings (Arvicolinae) seem to remain active through the winter, although some species, like the lemmings, range far to the north in Europe and Asia; but the See also: All the true marmots (Arctornys), a genus of which the species live at tolerably high altitudes in Central Europe, Asia and North America, appear to spend the winter in uninterrupted slumber buried deep in their burrows. They apparently See also:lay up no See also:store of food, but accumulate a quantity of fat as the summer and autumn advance, and frequently, as in the case of the See also:woodchuck (A. monax) of the Adirondacks, retire to winter quarters in the autumn long before the onset of the winter cold. The See also:prairie marmots or prairie See also:dogs (Cynomys ludovicianus) of North America, which live in the plains, do not hibernate to the same extent as the true marmots, although they appear to remain in their burrows during the coldest portions of the winter. Beavers (See also:Castor), although formerly at all events extending in North America from the tropic of See also:Cancer up to the Arctic circle, do not hibernate. When the ground
is deep in snow and the See also:river frozen over, they are still able to feed on aquatic plants beneath the ice.
Amongst the terrestrial See also:carnivora hibernation appears to be practised, with one possible exception, only by species belonging to the group Arctoidea. In north temperate latitudes both in Europe and Asia, as well as in the Himalayas, See also: Their See also:absence during the winter from particular spots in the Arctic regions where ice-See also:bound See also:ships have spent the winter, and the occasional See also:discovery of specimens buried beneath the snow, have led to the belief that these animals habitually retire to winter quarters through the cold sunless months of the year. This may possibly be the true explanation at least for certain districts. But it has been alleged that bears, both adult and half-grown, may be seen throughout the winter; and it is known that pregnant See also:females bury them-selves in the autumn under the snow, where they remain without feeding with their newly-born young until the spring of the following year. Hence the absence of hears in the winter from the neighbourhood of icebound ships may be explained on the supposition that the adult females alone hibernate for breeding purposes, while the full-grown males and half-grown specimens of both sexes migrate in the winter to the edges of the ice-floes and to See also:coast lines, where the water is open. Before retiring to winter quarters the pregnant females store up sufficient quantity of fat in their tissues not only to sustain themselves but also to supply See also:milk for their cubs. In the Adirondack region and probably in other districts of the same or more northern latitudes in North America, raccoons (Procyon lotor) retire in the winter to some sheltered place, such as a hollow See also:tree-See also:trunk, and pass the severest part of the season in sleep, emerging in February or See also: If, however, food has been scarce, this dog is compelled to remain active all through the winter. The Arctic See also:fox (Vulpes lagopus), although considerably more northern in range than the raccoon dog, does not hibernate. It was long a See also:mystery how these animals obtained food in winter, but it has been ascertained that in some districts they migrate southwards in large numbers in the late autumn, whereas in other districts apparently they lay up stores of dead lemmings or hares, for food during the winter months. In See also:Australia the porcupine See also:ant-eater (See also:Echidna aculeata) hibernates; and the habit is retained by specimens imported to Europe if exposed to the cold in outdoor cages.
Instances of quasi-hibernation have been recorded in the case of See also:man. For example, in the See also:government of See also:Pskov in See also:Russia, where food is scarce throughout the year and in danger of exhaustion during the winter, the peasants are said to resort to a practice closely akin to hibernation, spending at least one-half of the cold weather in sleep. From time immemorial it has been the See also:custom when the first snows fall for families to shut themselves up in their huts, huddle round the See also:stove and lapse into slumber, each member taking his turn to keep the See also:fire alight. Once a day only do the inmates rouse themselves from sleep to eat a little dry See also:bread.
Reptiles in which the body-temperature falls with that of the surrounding medium pass the winter in temperate countries in a state of lethargy; and specimens exported from the tropics into northern latitudes become dormant when exposed to cold in virtue of their inability to maintain their temperature at a higher level than that of the atmosphere. The common land See also:tortoise (Testudo graeca) of South Europe buries itself in the soil during the winter in its natural See also:habitat, and even when imported to England is able, in some cases at least, to withstand the more rigorous winter by practising the same habit, as See also: Carolina, retires into the muddy See also:banks to spend the cold months of the year. In certain parts of the tropics tortoises protect themselves from the excessive heat by burrowing into the soil which afterwards becomes indurated. When drought sets in with the dry season and the tanks become exhausted and food unobtainable, crocodiles and alligators sometimes wander across country in search of water, but more commonly bury themselves in the mud and remain in a state of quiescence until the return of the rains; and according to See also:Humboldt, large snakes, anacondas or See also:boa constrictors are often found by the See also:Indians in South America buried in the same lethargic state. Snakes and lizards in all countries where there is any considerable seasonal variation in temperature become dormant or semi-dormant during the colder months. Batrachians, like reptiles, hibernate in Europe and other countries situated in temperate latitudes. Frogs bury them-selves in the mud at the bottom of tanks and ponds, often congregating in numbers in the same spot. Toads retire to burrows or other secluded places on the land, and newts either bury themselves in the mud of ponds, like frogs, or lie up beneath stones and pieces of wood on the land. According to Mr G. A. Boulenger, however, European frogs and toads do not pass the winter in profound torpor, but merely in a state of sluggish quiescence. In tropical countries, where wet and dry seasons alternate, frogs which, like the See also:rest of the batrachians, are for the most part intolerant of See also:great heat, especially when accompanied by dryness of atmosphere, bury themselves deep in the soil during the time of drought and emerge from their retreats in numbers with the breaking of the rains. This habit of passing the dry season in the hardened mud forming the bottom of exhausted pools and See also:rivers is practised by several species of tropical See also:freshwater fishes, belonging principally to the family Siluridae. The members of this group are able to exist and thrive in moist mud, and can even support life for a comparatively long time out of water altogether. The instinct is exhibited by species occurring both in the eastern and western hemispheres, as is shown by its record in the case of species of Callicthys and Loricaria in See also:Guiana and by Clarias lazera in See also:Senegambia. It is also met with, according to See also:Tennent, in a species of climbing See also:perch (Anabas oligolepis) found in See also:Ceylon and belonging to the family Anabantidae, all the species of which are able to live for a certain length of time out of water, and may sometimes be found crawling across land in search of fresh pools. The habit is also common to some species of mud fishes of the order Dipneusti, in which the air See also:bladder plays the part of lungs. Protopterus, from tropical Africa, for instance, burrows into the mud and remains for nearly half the year coiled up at the bottom in a slightly enlarged chamber. The walls of this are lined with a layer of slime secreted from the fish's skin, and the orifice is closed with a lid the centre of which is perforated and forms an inturned See also:tube by means of which air is conducted to the fish's mouth. The aestivating burrow of the Brazilian mudfish (Lepidosiren) is similar, except that the lid is perforated with several apertures. The Australian mudfish (Ceraiodus) is not known to hibernate or aestivate. In countries where winter frosts arrest the growth of vegetation terrestrial mollusca seek hibernacula beneath stones or fallen tree trunks, in rock crannies, holes in walls, in heaps of dead leaves, in See also:moss or under the soil, and remain quiescent until the coming of spring. Amongst pulmonate gastropods, most species of snails (Helix, Clausilia) See also:close the mouth of the See also:shell at this period with a membranous or calcified See also:plate, the epiphragm. Slugs (Limax, See also:Arion), on the contrary, lie buried in the earth encysted in a coating of slime. Similarly in the tropics members of this group, such as Achatina in tropical Africa and Orthalicus in See also:Brazil, aestivate during the dry season, the epiphragm preserving them against desiccation; and examples of two species of Achatina from See also:east and See also:west Africa exhibited in the Zoological Gardens in London remained concealed in their shells during the winter, although kept in an artificially warmed See also:house, and resumed their activity in the summer. Freshwater Pulmonata do not appear to hibernate, such forms as Limnaea and Planorbis having been frequently seen crawling about beneath the ice of frozen ponds. During periods of drought in England, however, they commonly bury them-selves in the mud, a habit which is also practised during the dry season in the tropics by species of Prosobranchiate Gastropods belonging to the genera Ampullaria, Melanin and others, which lie dormant until the first rains rouse them from their lethargy. Freshwater Pelecypoda (Anodonta, Unio) spend the European winter buried deep in the muddy bottom of ponds and streams. In cold and temperate latitudes a great majority of insects pass the winter in a dormant state, either in the larval, pupal or imaginal (reproductive) stages. In some the state of hibernation is complete in the sense that although the insects may be roused from their lethargy to the extent of movement by spells of warm weather, they do not leave their hibernacula to feed; in others it is incomplete in the sense that the insects emerge to feed, as in the case of the See also:caterpillar of Euprepia fuliginosa, or to take the wing as in the case of the midge Trichocera hiemalis. Others again, like Podura nivalis and Boreus hiemalis, never appear to hibernate, at least in England. The insects which hibernate as larvae belong to those species which pass more than one season in that stage, such as the See also:goat-See also:moth (Cossus ligniperda), cockchafers (Melolontha), stagbeetles (Lucanus) and See also:dragon-flies (Libellula), &c.; and to some species which, although they only live a few months in this immature state, are hatched in the autumn or summer and only reach the final stage of growth in the following spring, like the butterflies of the genus Argynnis (paphia, aglaia, &c.) in England. As aninstance of species which survive the winter in the pupal or chrysalis stage may be cited the See also:swallow-tailed butterfly of Europe (Papilio machaon); while to the See also:category of species which hibernate as perfect insects belong many of the See also:Coleoptera (Rhyncophora, Coccinellidae), &c., as well as some See also:Hemiptera, See also:Hymenoptera, See also:Diptera and See also:Lepidoptera (Vanessa io, urticae, &c.). In the case of the social Hymenoptera it is only the fertilized See also:queen See also:wasp out of the See also:nest that survives the frost of winter, all the workers dying with the onset of cold in the autumn; the common hive bees (Apia mellifica), although they retire to the hive, do not hibernate, the numbers and activity of the individuals within the hive being sufficient to keep up the temperature above soporific point. Ants also remain actively at See also:work underground unless the temperature falls several degrees below zero. Spiders, like nearly all insects, hibernate in cold temperate latitudes. Burrowing species like See also:trap-See also:door spiders of the family Ctenizidae and some species of Lycosidae See also:seal the doors of their burrows with See also:silk or close up the orifice with a See also:sheet of that material. Other non-burrowing species, like some species of Clubionidae and Drassidae, lie up in silken cases attached to the underside of stones or of pieces of loose bark, or buried under dead leaves or concealed in the cracks of walls. Other species, on the contrary, pass the winter in an immature state protected from the cold by the silken cocoon spun by the See also:mother for her eggs before she See also:dies in the late autumn, as in the " garden spider" (Aranea diadema). Commonly, however, when the cocoons are later in the making, or the cold weather sets in early, the eggs of this and of allied species do not See also:hatch until the spring; but in either case the young emerge in the warm weather, become adult during the summer and die in the autumn after pairing and oviposition. Some members of this family, nevertheless, like Zilla x-notata, which live in the corners of windows, or in outhouses where the habitat affords a certain degree of See also:protection from the cold, may survive the winter in the adult stage and be roused from lethargy by breaks in the weather and tempted by the warmth to spin new webs. Typical members of the Opiliones or See also:harvest spiders, belonging to the family Phalangiidae, do not hibernate in temperate and more northern latitudes in Europe and America, but perish in the autumn, leaving their eggs buried in the soil to hatch in the succeeding spring. During the early summer, therefore, only immature individuals are found. Other species of this order, belonging to the family Trogulidae, spend the winter in a dormant state under stones or buried in the soil. False scorpions (Pseudoscorpiones) also hibernate in temperate latitudes, passing the cold months, like many spiders, enclosed in silken cases attached to the underside of stones or loosened pieces of bark. Centipedes and millipedes bury themselves in the earth, or lie up in some secluded shelter such as stones or fallen tree trunks afford daring the winter; and in the tropics millipedes lie dormant during seasons of drought. What is true of the dormant condition of arthropod life in the winter of the northern hemisphere is also true in a general way of that of the southern hemisphere at the same season of the year. This is proved—to mention no other cases—by the observations of Darwin on the hibernation of insects and spiders at Montevideo and Bahia Blanca in South America, and by Distant's See also:account of the paucity of insect life in the winter in South Africa; by his discovery under stones of hibernating semi-torpid Coleoptera and Hemiptera at the end of August in the See also:Transvaal, and of the See also:gradual increase in the ;numbers of individuals and species of insects in that country as the spring advanced and the dry season came to an end. Teleostei " in See also:Cambridge Natural See also:History, vii. 541-727 (1904) ; T. W. See also:Bridge, " Dipneustei " in Cambridge Natural History, vii. 505-520 (1904) ; A. H. See also:Cooke, " Molluscs " in Cambridge Natural History, iii: 25-27 (1895) ; T. A. Coward, P.Z.S. pp. 849-855 (190), and pp. 312-324 (1907); C. Darwin, A Naturalist's Voyage Round the See also:World, pp. 97-98 (1907 ed.); W. L. Distant, A Naturalist in the Transvaal, ch. iii. (1892); Marshall Hall, " Hibernation, " in Todd's Cyclopaedia of See also:Anatomy and Physiology, pp. 764-776 (1839) (Bibliography); Phil. Trans. See also:Roy. See also:Soc. (1832); See also: 17, pp. 517-533 (1856) ; L. Landois, A See also:Text-See also:book of Human Physiology, translated by W. See also:Stirling, i. 410 (1904); V. See also:Laporte, " Suspension of Vitality in Animals," Pop. Sci. Monthly, See also:xxxvi. 2J7-259 (New See also:York, 1889-1890) ; Mangili, " Essai sur la lethargic periodique," Annales du Museum, x. 453-456 (1807); C. See also:Hart Merriam, North American See also:Pocket Mice (See also:Washington, 1889); \V. See also:Miller, " Hibernation and Allied States in Animals," Trans. See also:Pan-Amer. Med. Congr. (1893), pt. ii. pp. 1274-1285 (Washington, 1895) ; M. S. Pembrey and A. G. Pitts, The Relation between the Internal Temperature and the Respiratory Movements of Hibernating Animals," Journ. Physiol. (London, 1899), pp. 305-316 ; Prunelle, " Recherches sur See also:les phenomenes et sur les causes du sommeii hivernal," Annales du Museum, xviii.; J. A. Saissy, Recherches sur les animaux hivernans (1808); L. Spallanzani, Memoires sur la respiration (1803); J. See also:Emerson Tennent, Sketches of the Natural History of Ceylon, pp. 351-358 (1861); Volkov, " Le Sommeil hivernal chez les paysans russes,"See also:Bull. Mem. Soc. Anthropol. (See also:Paris, 1900), i. 67; abstract in Brit. Med. Journ. (1900), i. 1554• (R. I. Additional information and CommentsThere are no comments yet for this article.
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