68 "MIMICRY RINGS" [ch. 



to change one unprotected condition for another. 

 Probably all adherents of the mimicry theory would 

 be agreed in regarding the male of Elymnias undularis 

 as shewing the ancestral coloration of the species, and 

 in looking upon the female as having been modified to 

 her own advantage in the direction of D. plexippus. 

 The question that we have to try to decide is how 

 this has come about — whether by the accumulation 

 of shght variations, or whether by a sudden change 

 or mutation in the pattern and colour of the female 

 by which she came to resemble closely the Danaine. 

 It is clear that if D. plexippus were what it is to-day 

 before the mimetic approach on the part of E. undularis 

 began, small variations in the latter would have been 

 of no service to it. The difference between the two 

 species would have been far too great for individuals 

 exhibiting slight variation in the direction of D. 

 plexippus to stand any chance of being confused 

 with this species. And unless such confusion were 

 possible natural selection could not work. There is, 

 however, an immediate way out of the difficulty. 

 We may suppose that the coloration of the male 

 of the mimic, E. undularis, is not only the ancestral 

 colour of its own species but also of the model. D. 

 plexippus on this supposition was very like E. undularis, 

 of which both sexes were then similar to what the 

 male is to-day. The pattern is, however, an incon- 

 spicuous one, and it can be imagined that it might 

 be to the advantage of D. plexippus to don a brighter 

 garb for the advertisement of its unpleasant qualities. 



