INSECTS 



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 meta- 

 morphosis. There are different degrees of such trans- 

 formation; 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 out- 

 side 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 con- 

 fronted 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 expediency, and peri- 

 odically 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 grass- 



[14] 



