vi] "MIMICRY RINGS" 65 



In this way was offered a comparatively simple 

 method of getting over the difficulty of applying 

 the principle of natural selection to the initial varia- 

 tions in a mimetic approach on the part of one species 

 to another. But it did not escape Darwin's penetra- 

 tion that such an argument would not always be 

 easy of application — that there might be cases where 

 a given model was mimicked by members of several 

 groups of widely differing ancestral pattern, and that 

 in these cases it would be difficult to conceive of 

 members of each of the several groups shewing simul- 

 taneous variations which would render them liable to be 

 mistaken for the protected model. The difficulty may 

 perhaps be best illustrated if we consider a definite case. 



It is a feature of mimetic resemblances among 

 butterflies that a given species in a given locality 

 may serve as a model for several other species belonging 

 to unrelated groups. Generally such mimics belong 

 to presumably palatable species, but other presumably 

 unpalatable species may also exhibit a similar colora- 

 tion and pattern. In this way is formed a combine 

 to which the term "mimicry ring" has sometimes 

 been applied. An excellent example of such a mimicry 

 ring is afforded by certain species of butterflies in 

 Ceylon, and is illustrated on Plate IV. It is made 

 up in the first place of two species belonging to the 

 presumably distasteful Danaine group, viz. Danais 

 chrysippus and D. plexippus. The latter is a rather 

 darker insect but presents an unmistakable general 

 likeness to D. chrysippus. Those who believe in 



P M. 



