454 THE WONDER OF LIFE 



brown in colour, with a large head and a small body, with 

 anterior breathing tubes, and no open mouth. After a 

 few days the pupa husk sphts and the winged gnat escapes. 

 Other Insects. — ^No Hfe-history is more marvellous 

 than that of a moth or butterfly. Out of the egg, after a 

 very remarkable development, there emerges a minute 

 worm-hke caterpillar, usually active, voracious, and of 

 rapid growth. Typically, it shows a hard head with biting 

 mouth-parts, with very minute antennae, and with several 

 pairs of simple eyes — ^in every respect as different as possible 

 from the full-grown insect's head. The body consists of 

 thirteen or so segments, of which the first three bear jointed 

 clawed legs, corresponding to, though they do not become, 

 the three pairs of thoracic legs in the adult. Posteriorly 

 there are four or five pairs of unjointed, unclawed, leg-Uke 

 structures — ^the so-called ' pro-legs ' — ^which are not repre- 

 sented in the winged insect. As it eats it grows, and 

 growth involves moulting — ^the thoroughgoing casting of 

 the cuticle. There may be five of these moults, each marked 

 by respiratory and other difficulties, and followed by rapid 

 growth. Finally, having reached its limit of growth, 

 the caterpillar becomes quiescent ; it often surrounds itseH 

 with a cocoon, sometimes silken, and passes into the 

 chrysaHs or pupa state. Serious respiratory and other 

 difficulties beset the pupa ; a process analogous to inflam- 

 mation pervades it ; the old structure is broken down and 

 groups of formative cells of an embryonic character proceed 

 to build up the adult body on a new architectural plan. 

 Everything is changed — ^mouth-parts, antennae, food-canal,, 

 muscles, everything. New structures, such as wings and 

 compound eyes, make their appearance. By and by there 

 struggles painfully out of the imprisoning husk an 



