52 



THE STUDY OF INSECTS. 



terflies, beetles, bees, and flies, leave the egg in an entirely 

 different form from that which they assume when they reach 

 maturity. A butterfly begins its active life as a caterpillar. 

 It feeds and grows, and when full grown changes to a chrys- 

 salis. In this stage it has very little resemblance to a cater- 

 pillar. After a time there bursts forth from the chrysalis 

 shell the butterfly, which looks very little like the chrysalis, 

 and still less like the caterpillar from which it came. In a 

 similar way, from the egg laid by a fly upon a piece of meat 

 there hatches, not a fly, but a footless, worm-like maggot. 

 This when fully grown changes to a quiescent object corre- 

 sponding to the chrysalis of a butterfly. Later from this ob- 

 ject there escapes a winged fly like that which laid the egg. 

 Those insects, like the butterflies and flesh-flies, which when 

 they emerge from the egg bear almost no resemblance in 

 form to the adult insect, are said to undergo a complete met- 

 amorphosis. In other words, the change of form undergone 

 by the insect is a complete one. 



How Insects groiv — Molting. — The skin of an insect is hard- 

 ened more or less by a horny substance known as cliitine 

 (chi'tine). This hardening usually occurs to a much greater 

 extent in adult insects than it does in 

 the young. But in all the skin becomes 

 so firm that it cannot stretch enough to 

 allow for the growth of the insect. The 

 result is, that from time to time an in- 

 sect's skin becomes too small for it, and 

 must be shed. But before this is done 

 a new skin is formed beneath the old 

 one; then the old skin bursts open, and 

 the insect crawls forth, clothed in a soft 

 skin, which stretches to accommodate 

 the increased size of the animal. Very 

 soon, however, this new skin becomes 

 hardened with chitine, and after a time 

 it in turn must be shed. This shedding 

 of the skin is termed moltiiig, and the cast skin is some- 



Fig. 62a.— Exuviae of 

 nymph of Dragon-fly. 



