Euploeines forming Mimetic Groups 17 



A.— KEY ISLANDS GROUP. (Plate Ia.) 



The Key Islands combination shows the greatest development of 

 white markings. There is no such dominant white coloration in the 

 species of the Aru Islands, where the tendency is in the other direction, 

 and the forms are dark. The development of white coloration in the 

 Key Islands is also noticed in Danais plexippus hyllene Fruh., in 

 Cethosia chrysippe insulata Butl., and in the female of Troides hecuba. 

 The pattern of these forms is quite unlike that of the Euploeines, but 

 the Cethosia mimics the Danais. Some other species of Euploea, which 

 would form excellent members of the Key Island group, exist in places 

 where no other white-banded butterfly is known to occur, as in New 

 Guinea and the Solomons. Such species must presumably have derived 

 their pattern from their progenitors in a locality where the mimetic 

 stimulus was in operation. It may be that in some past epoch, this 

 white-banded combination was spread over a larger land area, and that 

 ultimately some members of it were cut off from their associates by 

 geographical changes. 



The allies of these white-banded Key Island forms all exhibit some 

 tendency to white scaling in the distal area of the wings. It may be 

 inferred, therefore, that given the existence of a common white-banded 

 Euploea, as assimilata Hopff., on Key, other species with this colour- 

 tendency would develop it. 



On an island, mimetic likeness should be more readily attained. 

 If a conspicuous species becomes common, the limit to its range 

 determined by the sea would serve to render the species more con- 

 spicuous owing to the occurrence of more individuals in any part of the 

 island. Just as species become changed by long continued isolation in 

 islands, so mimetic likeness should undergo a similar change and become 

 more intensified. 



It is possible that the large white patch of the Danaine and the 

 white patches on the wings of the Troides hecuba female, have some 

 biological connection with the prevailing white coloration in the 

 Euploeines and Hypolimnas, and we may perhaps look to the inten- 

 sifying insular factor for an explanation. We must also not overlook 

 the possibility that these forms may have derived their white colora- 

 tion, or at least the tendency, from more ancient forms under different 

 conditions. Both suggestions may be combined in seeking for a 

 solution to the problem, for selection in the direction of mimicry would 

 utilize all suitable variations, including those which are atavistic, 



