2o6 DARWINISM AND THE PROBLEMS OF LIFE 



However, we need not linger with these objections to 

 the theory. There are certain facts that completely 

 demolish it. These facts are the casting of the skin 

 of beetles, flies, wasps and butterflies. In all these 

 animals the coat of the imago is formed underneath 

 the pupa-cover. The legs are pressed against the 

 body, the wings folded, and everything enclosed by 

 the pupa-skin as in a parcel. But the pupa scarcely 

 moves, and so there can be no pressure to act through 

 its shell on the underlying imago skin. And even if a 

 pupa happened to be exposed to pressure, the stimulus 

 would act equally on all parts of it, as in the pupa 

 they are all folded together, though in the adult insect 

 they must be wide apart and differ very much in thick- 

 ness, as they do in point of fact. Finally, it is precisely 

 the thin parts of the imago coat that lie directly under- 

 neath the pupa skin ; many of the thick parts are 

 protected from pressure by the overlying wings. 



It is clear, therefore, that in the secretion of the 

 imago coat the skin cannot possibly be influenced by 

 pressure. Nor even immediately after the emergence of 

 the insect. The imagines of the insects enumerated 

 may expose their coat to all kinds of pressure, as much 

 as they will, the underlying skin will never be caused 

 thereby to secrete a stronger coat, because in these 

 insects it has no further activity in the imago. No 

 butterfly ever casts its skin ; this is done by it several 

 times as a caterpillar, and once as a pupa. None of 

 the characteristics of the coat of a bee, the wing- 

 nervures, the thick and thin parts, the various kinds 

 of hairs, the eye-facets — none of these things can 



