Evidences of Theory of Natural Selection. 323 



Mr. Darwin's theory namely, that the more perfect 

 the resemblance is caused to become through the 

 continuous influence of natural selection always picking 

 out the best imitations, the more highly discriminative 

 becomes the perception of those enemies against the 

 depredations of which this peculiar kind of protection 

 is developed ; so that, in virtue of this action and 

 re-action, eventually we have a degree of imitation 

 which renders it almost impossible for a naturalist 

 to detect the animal when living in its natural en- 

 vironment. 



Warning Colours. 



In strange and glaring contrast to all these cases 

 of protective colouring, stand other cases of conspic- 

 uous colouring. Thus, for example, although there 

 are numberless species of caterpillars which present 

 in an astonishing degree the phenomena of pro- 

 tective colouring, there are numberless other species 

 which not only fail to present these phenomena in 

 any degree, but actually go to the opposite extreme 

 of presenting colours which appear to have been 

 developed for the sake of their conspicuousness. At 

 all events, these caterpillars are usually the most con- 

 spicuous objects in their surroundings, and therefore 

 in the early days of Darwinism they were regarded by 

 Darwin himself as presenting a formidable difficulty 

 in the way of his theory. To Mr. Wallace belongs 

 the merit of having cleared up this difficulty in 

 an extraordinarily successful manner. He virtually 

 reasoned thus. If the raison d'etre of protective 

 colouring be that of concealing agreeably flavoured 

 caterpillars from the eye-sight of birds, may not 

 Y 2 



