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 grow — Molting .—The skin of an insect is hard¬ 
ened more or less by a horny substance known as chitine 
(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 molting , and the cast skin is some- 
