All insects do not follow the same method of development from egg to adult, and the adaptations of structure and habit are many and varied as well as simple and complex. Species having a complex development, during which they pass through stages, each differing in form from its predecessor, undergo what is known as a metamorphosis; contrasted with such insects are those developing in a simple manner without pronounced differences in the form of successive stages, the young resembling the adult in most features except size and maturity--these insects are without a metamorphosis. Intermediate between these two extremes are other insects with a partial metamorphosis. A consideration of the life cycle of some common insects will serve to illustrate the principles of development discussed above. Firstly, will be taken examples of complex development or complete metamorphosis; secondly, examples of simple development or absence of metamorphosis, followed by a review of species having a partial metamorphosis, thus linking the first two types. A convenient type of insect undergoing a complete metamorphosis is any common moth (Fig. 4); one of the most suitable, most easily obtained in all stages and commonest in any part of the country from spring to autumn, is the magpie moth (_Nyctemera annulata_) and its caterpillar, the “woolly bear.” The moth, unlike most of its kind, is a day-flying species, and is very conspicuous owing to its black colour relieved by white wing spots, and orange-yellow bands on the abdomen; the equally conspicuous caterpillar, feeding on groundsel, ragwort and cineraria, is black, with a very hairy body marked with narrow brick-red lines. The eggs are laid in clusters by the female moth on the under side of the leaves of the caterpillars’ food-plant; at first the eggs are of a pale green colour, but assume a darker yellowish tint within a few hours, and finally a leaden colour some time later. These colour changes are due to the developing embryo, and just before the young insect (the caterpillar in this case) hatches, its outline as it lies curled within the egg is easily seen through the transparent egg-shell; near the top of the egg is a black spot marking the position of the caterpillar’s head, while the numerous delicate black lines below the egg surface are the black hairs with which the caterpillar is clothed. According to temperature and humidity, the incubation period--that is, the period between egg-laying and the hatching of the young caterpillar--varies from eight days to three weeks. The process of hatching occupies about two hours, the young insect using its jaws to eat an exit hole through the egg. The caterpillar stage--indeed, the first stage of all insects--is known as the larva.