Page:Insects - Their Ways and Means of Living.djvu/44

 form of a caterpillar, has no resemblance to its parent, and the same is true of a young fly, which is a maggot, and of the grublike young of a bee. The changes of form that insects undergo during their growth are known as metamorphosis. There are different degrees of such transformation; the grasshopper and its relatives have a simple metamorphosis.

An insect differs from a vertebrate animal in that its muscles are attached to its skin. Most species of insects have the skin hardened by the formation of a strong outside cuticula to give a firm support to the muscles and to resist their pull. This function of the cuticula, however, imposes a condition of permanency on it after it is once formed. As a consequence the growing insect is confronted with the alternatives, after reaching a certain size, of being cramped to death within its own skin, or of discarding the old covering and getting a new and larger one. It has adopted the course of expedlency, and periodically molts. Thus it comes about that the life of an insect progresses by stages separated by the molts, or the shedding of the cuticula.

The grasshopper makes six molts between the time of hatching and its attainment of the final adult form, a period of about six weeks, and goes through six post-embryonic stages (Fig. 9). The first molt is the shedding of the embryonic skin, which, we have seen, takes place normally as soon as the young insect emerges from the earth. The grasshopper now lives uneventfully for about a week, feeding by preference on young clover leaves, but taking almost any green thing at hand. During this time its abdomen lengthens by the extension of the membranes between its segments, but the hard parts of the body do not change either in size or in shape. At the end of seven or eight days, the insect ceases its activities and remains quiet for a while until the cuticula opens in a lengthwise split over the back of the thorax and on the top of the head. The dead skin is then cast off, or rather, the