INSECTS
plained, and if a writer often does not succeed so well with the reader in this undertaking, the reader should remember that his own difficulties of reading are perhaps no greater than the difficulties of the writer in writing. With a little extra effort on both sides, then, we may be able to arrive at a mutual understanding.
In the first place, let us see in what particular manner the young and the adults of insects differ from each other. The adult, of course, is the fully matured form, and it alone has the organs of reproduction functionally developed; but this is true of all animals. The caterpillar and the moth, the grub and the beetle, the maggot and the fly, however, differ widely in many other respects, and are so diverse in appearance and in general structure that their identities can be known only by observing their transformations. On the other hand, the young grasshopper (Fig. 8), the young roach (Fig. 51), or the young aphis (Fig. 97) is so much like its parents that its family relationships are apparent on sight. Still, in the case of all winged insects, there is one persistent difference between the young and the adult, and this is with respect to the development of the wings. The wings are always imperfect or lacking in the young. The inability to fly puts a limitation on the activities of the immature insect and compels it to seek its living by more ordinary modes of progression. It may inhabit the land or the water; it may live on the surface; it may burrow into the earth or into the stems or wood of plants—in short, it may live in a thousand different places, wherever legs or squirming movements will take it, but it can not invade the air, except as it may be carried by the wind.
As a first principle in the study of metamorphosis, then, we must recognize the fact that only the adult insect is capable of flight.
Let us now turn back to the grasshopper (Chapter I); it furnishes a good example of an insect in which the adults differ but little from the young, except in the matter of
[ 232 ]
