126 MIMICRY AND VARIATION [ch. 



selection would not come into play untU the would-be 

 mimic was sufficiently like the model to be confused 

 with it under natural conditions ^ The part now 

 often attributed to natural selection is to put a polish 

 on the resemblance and to keep it up to the mark by 

 weeding out those which do not reach the required 

 standard. It is supposed that if natural selection 

 ceases to operate the mimetic resemblance is gradually 

 lost owing to the appearance of variations which are 

 no longer weeded out. An interesting case has recently 

 been brought forward by Carpenter ^ and explained on 

 these lines: The Nymphahne Pseudacraea eurytus is 

 a poljmiorphic species found in Central Africa. In 

 Uganda it occurs in several distinct forms which were 

 originally supposed to be distinct species. Three of 

 these forms bear a marked resemblance to three species 

 of the Acraeine genus Planema. 



Mimic Model 



Pseudacraea eurytus Planema 



Form hoUeyP (PI. VII, macam to (PI. VII, fig. 2) 

 figs. 6, 7) 

 terra (PI. VII, fig. 8) tellus (PI. VII, fig. 3) 

 obscura paragea (PI. VII, fig. 4) 



These different species occur round Victoria Nyanza 

 and also on some of the islands in the lake. Some 



1 Cf. B. B. PouJton in Bedrock for Oct. 1913, p. 301. 



2 Trans. Ent. Soc. London, 1914. 



' In the female hobleyi, with rare exceptions, the orange of the 

 male is replaced by white, and it has received the name tirikensis. 

 The female of P. macarista also shews white in place of the orange of 

 the male. 



