324 Darwin, and after Darwin. 



the raison cfttre of conspicuous colouring be that 

 of protecting disagreeably flavoured caterpillars 

 from any possibility of being mistaken by birds? 

 Should this be the case, of course the more con- 

 spicuous the colouring the better would it be for 

 the caterpillars presenting it. Now as soon as this 

 suggestion was acted upon experimentally, it was 

 found to be borne out by facts. Birds could not be 

 induced to eat caterpillars of the kinds in question ; 

 and there is now no longer any doubt that their con- 

 spicuous colouring is correlated with their distasteful- 

 ness to birds, in the same way as the inconspicuous or 

 imitative colouring of other caterpillars is correlated 

 with their tastefulness to birds. Here then is yet 

 another instance, added to those already given, of 

 the verification yielded to the theory of natural 

 selection by its proved competency as a guide to facts 

 in nature ; for assuredly this particular class of facts 

 would never have been suspected but for its suggestive 

 agency. 



As in the case of protective imitation, so in this 

 case of warning conspicuousness, not only colour, but 

 structure may be greatly modified for the purpose 

 of securing immunity from attack. Here, of course, 

 the object is to assume, as far as possible, a touch- 

 me-not appearance ; so that, although destitute of 

 any real means of offence, the creatures in question 

 present a fictitiously dangerous aspect. As the 

 Devil's-coach-horse turns up his stingless tail when 

 threatened by an enemy, so in numberless ways do 

 many harmless animals of all classes pretend to be 

 formidable. But the point now is that these instincts 

 of self-defence are often helped out by structural 



