16 



Closely allied with the Eastern Xejihernnia, are the [jeucerouia 

 of Africa. In two of these Leucemnia we find forms of the female 

 differing widely from the male, and bearing a close resemblance to 

 other butterflies which are believed on good grounds to be distaste- 

 ful. I shall return to these later. 



In the New World we have other instances of the kind. 

 Perciite c/iarnps, a Pierine from Central and South America, the 

 male of which is on the upper side a black butterfly with a powdering 

 of bluish grey, has a female whose upper side is dark brown with 

 no grey powdering, but crossed on the forewing by a diagonal band 

 of bright scarlet. This brings it into mimetic relation with a large 

 assemblage of butterflies, all characterised by the same general type 

 of coloration, including many members believed on good evidence 

 to be immune. Other examples are plentiful ; tlius we have in 

 Central America Pieris viarJi, the male of which is a w^hite butter- 

 fly of quite ordinary aspect, while the female is furnished with black 

 and yellow streaks which assimilate it in aspect to the very 

 conspicuous insect Heliconiiis r/iaritonia. 



There is a curious set of instances belonging to the mimetic 

 category, but differing in one respect from those that we have just 

 been considering. In these, though dimorphism still obtains as 

 between the sexes, both sexes are mimetic, but in unequal degree. 

 In Verrhyhris pyrrha, for example, a Pierme from Brazil, the female 

 belongs, by its coloration on both surfaces, to a group of 

 protected insects which includes a large number of members from 

 different subfamilies of butterflies and even of moths. The male 

 on the other hand is on its upper surface simply a white butterfly 

 with a black apex to the forewings. The same applies to the under 

 surface of the forewings ; but on the under surface of the hindwings 

 there is displayed a mimetic pattern like that of the female, though 

 a less perfect copy of the original. In another case, that of Dis- 

 viorphia praxino'e from Central America, which is also one of the 

 Pierinoi or " white " butterflies, the female is completely mimetic 

 on both surfaces ; while the male though for the most part exhibit- 

 ing an imitative pattern like that of the female, retains, on the under 

 surface of the forewing and upper surface of the hindwing, a con- 

 siderable area of the original white. 



We have added then to our stock of data this further fact ; that 

 even when both sexes are mimetic in some degree, the female 

 frequently displays a far more perfect imitation of the distasteful 

 model than does the male. 



Let us now turn back for a time to those cases where the female 

 is mimetic and the male shows no trace of imitative assimilation. 

 The instances that we have examined hitherto belong to the sub- 

 family of Pierince, of which our common whites, brimstones and 

 clouded yellows are members. But the phenomenon is by no means 

 confined to butterflies of this group. Many probably of my hearers 

 are acquainted with the common tropical butterfly Daiiaida 



