2 20 DARWINISM AND THE PROBLEMS OF LIFE 



whose tentacles are small. Here the constructive 

 instinct differs for the two sexes. But in neither case 

 can we suppose that the larva knows what sort of 

 tentacles it will have. The clay-ball, moreover, is only- 

 formed once in life, and there is no possibility of 

 practice. 



One of the most complicated pupa-coverings is the 

 web of the small nocturnal peacock's eye. In this case 

 there is a hole for creeping out in the spun capsule, but 

 in order that the enemies of the pupa may not crawl 

 in by it a bundle of stiff silk-bristles, with points directed 

 outwards, is spun over the hole, and acts as a weel. 

 The bristles are easily pushed aside by the butterfly 

 when it issues forth, but they prevent an entrance from 

 without. Here, again, there can be no question of 

 practice, as the caterpillar only makes the web once 

 in its life, and makes it — must make it — correctly on 

 this single occasion. The intelligence of the caterpillar, 

 moreover, has certainly nothing to do with the work, 

 as it cannot know that it will need special protection 

 during the pupa stage, and that this complicated 

 structure on its home will keep off its enemies. 



We see, therefore, that the Lamarckian principle 

 entirely fails to explain many instincts. There are 

 instincts that can never have been acts of will and 

 intelligence, and others in which the element is entirely 

 wanting to make them instinctive even if they had 

 once been voluntary actions — namely, practice or 

 repetition — as they are only performed once during 

 life.-*^ If the complex instincts we have described cannot 



" Instincts of this kind are Weismann's chief objection to Lamarckism. 



