( xl ) 



Mr. Grose-Smith informs me that he possesses an allied un- 

 described species from the same island with even broader 

 bands, especially upon the posterior wings. Furthermore 

 Neplis vielella, D. and H., is represented in Madagascar by 

 the form gratilla, Mab., in which, as in saclava, the white 

 markings are larger than in the African form. Another black 

 and white species, N. sextilla, Mab., is unknown to me. There 

 is therefore clear evidence of the existence in Madagascar of 

 a powerful combination in which the white markings are 

 especially well developed. 



2. The Tawny Markings of the Island Species. — It is diffi- 

 cult to decide between the two alternative interpretations of 

 the difference in colour between saclava and the four species 

 in the outlying islands. If white markings are ancestral in 

 saclava it follows that the tawny colour has been evolved 

 independently in the north-western and eastern species. 

 Furthermore we have no cause to assign for the change except 

 the vague and unsatisfactory one of isolation. The relation- 

 ship of the two north-western species is also opposed to this 

 interpretation. We may infer from the differences between 

 them that comorarum has been isolated for a much longer period 

 than mayottensis, and yet the tint of their yellowish markings 

 is almost precisely the same. It therefore appears to me more 

 likely that saclava formerly possessed in Madagascar, and 

 probably also in Africa, markings of a tawny colour, and that 

 these have been gradually changed to white on both areas 

 as the result of a synaposematic approach to other black 

 and white species of Neptis. The four outlying species did 

 not encounter any such causes of change. According to this 

 hypothesis the eastern species represent an early emigration 

 when the markings of saclava were of a deep tawny tint, 

 while the north-western species represent a much later phase 

 when they were far advanced towards white. Mimetic 

 approach commonly advances more rapidly in the female sex ; 

 and the faint cream tint of the male saclava may be a lingering 

 trace of an earlier tawny shade. The difference between the 

 pale markings of male and female is, however, so minute that 

 a long series of fresh specimens should be compared before it 

 can be accepted as firmly established. If the suggestion made 



