192 DARWINISM AND THE PROBLEMS OF LIFE 



reflection. We do not see why the light does not 

 cause light colours such as those hidden in the folded 

 wings. How, moreover, can we suppose it to create so 

 intricate a colour-design? And if the skin has the 

 capacity to bring about a protective colouring, we may 

 very well ask what was the origin of this capacity, as 

 very few animals possess it. But we need not delay 

 with these theories ; they are completely refuted by one 

 single fact. The protective colouring does not arise 

 when the animal exposes its wings to the light, but in 

 the earlier stage of the pupa. Long before it issues 

 from the pupa all the colours are present on the wings 

 folded up under the pupa-shell. And in the pupa the 

 position of the wings is reversed ; the front wings 

 always cover the hind wings, in such a way that the 

 protectively coloured under-side of the front wings is 

 turned away from the light. Hence the light does not 

 touch any of the protectively-coloured parts during the 

 development of the colours. We may add that the 

 thick, dark pupa-covering does not admit the penetration 

 of the rays of light ; and that many caterpillars pass the 

 pupa-stage underneath stones, and the night-butterflies 

 even underground. 



We must therefore exclude the action of light 

 altogether in the formation of the colours of butter- 

 flies. The fact that their front wings have protective 

 colouring just in so far as they are visible can easily be 

 explained by natural selection. We know that selection 

 only continues its action until what is necessary has 

 been attained. Those butterflies survived which had 

 the most deceptive colouring ; but the variations that 



