Incubation, THE PERIOD OF, during which birds sit on their eggs before the young are hatched varies in different species, but is nearly constant in each. In the humming-birds it is only 12 days; in canaries it is from 15 to 18 days; in the raven and in the common fowl it is 21 days; in the duck it is from 28 to 30 days; in the pheasant and in the guinea-fowl it is 28 or 29 days; in the turkey, 30 days; and in the swan, from 40 to 45 days. The degree of heat (about 40° C., 104° F.) necessary for the development of the young is usually supplied by the mother-bird; but in some cases the sunshine (as in ostriches during the day), or the warmth of a nest of decaying plants (as in the Megapodes), is relied upon; nor must it be forgotten that in many Passerine and Running Birds the males take their share, or it may be the entire responsibility of incubation. While the patience of incubation is most emphasised and rewarded among birds, hints of it appear in reptiles—witness the female python; and analogous processes are seen in a few amphibious fishes, and even Invertebrates.
Incubators, or devices for artificial hatching, are used both for practical and scientific purposes at the poultry farm and in the embryological laboratory. From time immemorial the Egyptians have hatched eggs by artificial warmth in peculiar but comparatively simple ovens, and thirty millions of chickens per annum are said to be thus hatched in Egypt. In 1777 Bonnemain devised a hatching apparatus which supplied the Parisian markets with poultry. In 1825 D'Arceut obtained chickens from artificial incubation by means of the thermal waters at Vichy. The Eccaleobion, invented by Mr Bucknell, was said to possess a perfect control over temperature from 300° F. to that of cold water for any length of time. The modern incubator consists essentially of a large water-bath and a gas regulator for automatically preventing the rise of temperature above 40° C. The eggs are placed in a tray or drawer, so arranged that the products of the gas combustion are kept away from the eggs, but a supply of fresh air and moisture secured. For embryological purposes the form most used in Great Britain is probably that of the Cambridge Scientific Instrument Company. See OSTRICH-FARMING, POULTRY; also PISCICULTURE.
Incubus. See DEMONOLOGY.