XI] CONCLUSION 151 



in the Pierids as compared with other butterflies, there 

 would seem to be no reason why the same factors 

 governing the distribution of black should not be 

 common to members of different groups. A distri- 

 bution of black pigment similar to that found in a 

 model and its mimic may occur also in a non-mimetic 

 ally of the mimic. Dismorphia astynome, for example, 

 resembles the Ithomiine Mechanitis lysimnia (PI. XV, 

 fig. 8) both in the distribution of black as weU as 

 of yeUow and bright brown pigments. A similar 

 distribution of the black pigment is also found in 

 Dismorphia avonia, but the yellow and bright brown 

 of the other two species is here replaced with white. 

 By a slight though definite alteration in chemical 

 composition this white pigment could be changed into 

 bright brown and yellow with the result that D. avonia 

 would closely resemble D. astyno^ne in its colour scheme 

 and would in this way also become a mimic of Mecha- 

 nitis lysimnia. Another good instance is that of the 

 females of Perrhybris demophile and P. lorena, the 

 former being black and white, whereas in the latter 

 the white is replaced by yeUow and bright brown, 

 giving the insect a typical Ithomiine appearance^. 

 Here again a definite small change in the composition 

 of the pigment laid down in the scales would result in 

 the establishing of a mimetic likeness where there would 

 otherwise be not even a suggestion of it. It is in 

 accordance with what we know to-day of variation 



1 Coloured representations of these two species will be found on 

 PL 20 of Seitz, Macrolepidoptera of the World, Fauna Americana. 



