Insects, with the exception of certain species giving birth to living young, are reproduced from eggs laid by the females; with few exceptions, the latter take no further interest in the eggs beyond placing them in surroundings offering the most favourable conditions for their well-being, and a sufficient food supply for the forthcoming young; each egg is protected by a delicate shell, through which the young insect makes its way on hatching. On emerging from the egg, the young insect commences to feed and grow in size, until very soon a stage is reached when the cuticle or shell becomes too small for the enclosed insect; a fluid then collects between the cuticle and the underlying skin, and a new and more roomy cuticle is secreted by the latter; on this process being completed, the old chitinous covering splits, and the insect withdraws itself. This moulting takes place several times, until the body is fully grown, when the cuticle formed at the last moult is retained by the now adult insect for the rest of its life. The different stages through which an insect passes from egg to adult constitute its life history, or life cycle, and the relation of the latter to the seasons, its seasonal history. According to the species, a full twelve months or even more may be necessary for the complete life cycle, or the cycle may be repeated several times within the year; when the cycle occupies twelve months, the insect is single-brooded; but two, three, or four-brooded, etc., when the cycle is repeated two, three, or four times, respectively, in the year. Climatic and food-supply conditions have a distinct influence on the number of broods, the one species in many cases being single-brooded in colder, and two or three-brooded in warmer climates. During the winter, when the temperature is low enough, insects are more or less dormant in some stage of their life cycle; such a state is the period of hibernation. [Illustration: FIGURE 4. 1, Silverfish. 2, Earwig; a, young larva; b-d, later stages; e, adult. 3, Cicada; f, young larva; g, resting stage prior to emergence of adult; h, adult. 4, Thrips; i and j, larvae; k, first stage pupa; l, second stage pupa; m, adult. 5, Aphis-lion; n, larva; o, pupa; p, adult. 6, Moth; q, egg; r-t, larvae; u, pupa; v, adult. 7, House-fly; w, egg; x-z, larvae; aa, puparium; bb, adult. NOTE: Developing wings shown in black.]