ESTIVATION, the dormancy or ((summer sleep," induced in some of the lower plants and animals by heat and drought, and the means by which in summer they resist these unfavorable conditions, as they do others in winter by hiber nation. The two states are comparable, though induced by opposite conditions. In summer the principal danger to which such organisms are exposed is the deprivation of water. Some of the lowest are able to endure this to an extreme degree. Certain bacteria and other low plants and various animalcules will survive prolonged baking and may blow about in the dust of dried-up ponds for a long period, ready to revive when dampened. Among land-snails estivation is a common phenomenon, the snails protecting themselves from excessive loss of moisture, not only by burrowing into the ground, but by throwing one or several epiphragms of hard ened, sometimes chalky, mucus across the aper ture of the shell, thus shutting themselves into an air-tight case, where they, remain inactive until better conditions arrive. In a similar man
ner certain fishes and amphibians bury them selves in the muddy bottom of ponds or river pools evaporated by drought, where they preserve sufficient dampness about them to keep alive. Turtles, on the other hand, are often compelled to leave their pools in the tropics, because the water becomes so hot and full of fermentation and seek cool spots under rocks, and the like, where they sleep torpidly until autumn. Even a few mammals of extremely hot regions, such as the deserts of Australia, go into a summer-sleep during the height of the hot season, substantially as their congeners hibernate in the midwinter of northern climates.
See HIBERNATION.