032 The Outline of Science 



thoracic appendages, and strong, hard jaws well suited for gnaw- 

 ing green food. Its business in life is to feed and to grow, and 

 it feeds rapidly and almost continuously. It may eat many 

 times its own weight in a day, but probably only digests the fluid 

 part of the food. It outgrows its inexpansible chitinous cover- 

 ing, and has to moult it, an exhausting and dangerous process. 

 Then it feeds and grows and moults again, until at its limit of 

 growth it passes into a resting phase. It becomes a pupa, or 

 chrysalis. 



The Cabbage White Butterfly larva suspends itself in a 

 quiet corner by a silken thread, with its tail against a support, 

 and the larval skin forms the pupa case, but many other pupa? 

 (e.g. many moths) have the additional protection of a cocoon, 

 either of pure silk secreted at the jaws, or of silk mixed with 

 leaves, moss, or other extrinsic matter. The larva (i.e. the cater- 

 pillar) now undergoes the great change which is called meta- 

 morphosis. Within the cocoon the body of the larva is broken 

 down and is built up again on a new architectural plan. When 

 the reconstruction is completed the fully-formed insect emerges. 

 What a contrast ! It is now an intensely active butterfly, having 

 left behind it the shrivelled skin of the creeping caterpillar, and 

 for a brief season it lives its aerial life, growing not at all, feed- 

 ing but little, and then only on liquid nectar by means of the 

 long sucking- tube so different from the strong biting jaws of the 

 caterpillar: hunger is no longer the preoccupation; the butter- 

 fly lives for love, and before it dies it deposits its eggs on the 

 green plant which it cannot itself eat, but which forms the right 

 food material for the offspring it does not survive to see. 



Beetles 



Beetles are essentially biters, with very strong and hard 

 mouth-parts, one pair of which, the mandibles, are sometimes 

 of relatively enormous size, with sharp saw-like edges. Many 

 of them, such as the Weevils, are vegetarians, feeding on green 



