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 devel- 

 oped; 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 transfor- 

 mations. 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 rela- 

 tionships 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 imper- 

 fect 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 



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