VI] "MIMICRY RINGS" 63 



by a trifling patch of colour while the main ground 

 of the insect was still white. But unless they avoided 

 those with the small colour patch there would be an 

 end of natural selection in so far as the patch was 

 concerned, and it would have no opportunity of 

 developing further through the operation of that 

 factor. This is the difficulty of the initial variation 

 which has been clearly recognised by most of the 

 best known supporters of the theory of mimicry. 

 Bates himself offered no suggestion as to the way 

 in which such a form as a Pierid could be conceived 

 of as beginning to resemble an Ithomiine^. Wallace 

 supposed that the Ithomiines were to start with 

 not so distinct from many of the edible forms as they 

 are to-day, and that some of the Pierines inhabiting 

 the same district happened to be sufficiently hke some 

 of the unpalatable forms to be mistaken for them 

 occasionally ^. 



The difficulty of the initial variation had also 

 occurred to Darwin, and he discusses it in an interesting 

 passage which is so important that we may quote 

 it here in f uU : 



It shoidd be observed that the process of imitation probably 

 never commenced between forms widely dissimilar in colour. But 

 starting with species already somewhat like each other, the closest 

 resemblance, if beneficial, could readily be gained by the above 

 means ; and if the imitated form was subsequently and gradually 



1 "In what way our LepfaUs {—Dismorphia) originally acquired 

 the general form and colour of Ithomiae I mtist leave undiscovered." 

 Trans. Linn. Soc. vol. 23, 1862, p. 513. 



2 Darwinism, 1890, pp. 242-244. 



