WALLACE AND FEMALE MIMICEY 133 



(e. g. the Nymphaline genus Euripm) resembles 

 a very different model. On the other hand, a 

 non-mimetic female accompanied by a mimetic 

 male is excessively rare. An example is afforded 

 by the Oriental Nymphaline, Cethosia, in which 

 the males of some species are rough mimics of 

 the brown Danaines. When both sexes mimic, it 

 is very common for the females to be better and 

 often far better mimics than the males. 



Predominant female Mimicry is character- 

 istic of butterflies and very rare in moths. If 

 examples occur at all among the numberless 

 mimetic Diptera, Coleoptera, &c., they are 

 probably excessively scarce. In some of the orb- 

 weaving spiders, however, the males mimic ants, 

 while the much larger females are non-mimetic. 



Although still believing that Wallace's 

 hypothesis in large part accounts for the facts 

 briefly summarized above, the present writer has 

 recently been led to doubt whether it offers a 

 complete explanation. Mimicry in the male, 

 even though less beneficial to the species than 

 Mimicry in the female, would still surely be 

 advantageous. Why then is it so often entirely 

 restricted to the female ? While the attempt to 

 find an answer to this question was haunting 

 me, I re-read a letter written by Darwin to 

 Wallace, April 15, 1868, containing the following 

 sentences : — 



'When female butterflies are more brilliant than their 

 males you believe that they have in most cases, or in all 



