INSECTS IN GENERAL 11 



festly enslaved by the impulses of instinct. What 

 instinct is we do not know, but we may see it 

 working in numberless ways on any summer day. 

 Without instruction or opportunity for imitation, 

 insects perform all manner of intricate tasks for their 

 own or their offspring's good. The only possible in- 

 ference is that each succeeding generation of insects 

 inherits from its parents a self-acting nervous machin- 

 ery, comparable to an elaborate piece of clockwork, 

 wound up and ready to perform its destined move- 

 ments as soon as the spring is released. The release 

 of the spring in the case of the insect appears to be 

 effected by some simple stimulus, due either to internal 

 or external causes, of which we know next to nothing. 

 In this way the wheels are set going, so to speak, 

 and the whole marvellous sequence of the creature's 

 inherent skilfulness is reeled off. 



We must now turn our attention to the growth and 

 development of insects. With few exceptions, insects 

 lay eggs. In the case of some lowly kinds, the young,, 

 when they hatch, are miniature reproductions of their 

 parents. They simply increase in size as they grow 

 from youth to maturity. But in the vast majority of 

 insects growth and development involve a more or 

 less marked form-change, or metamorphosis. The 

 growing insect, in fact, casts its outer cuticle at stated 

 intervals in its life-history ; and in most instances each 

 succeeding moult renders it less like its pristine self 

 and more like its adult forbears. Take, for example, 

 the cockroach and the mole-cricket. In each case the 

 newly hatched insect has much the same form as 

 its parents, but is destitute of wings. These organs 

 develop gradually as growth proceeds, becoming more 

 and more noticeable after each moult, but remaining 



