28 



AFRICAN MIMETIC BUTTERFLIES 



leads to an inference which is precisely the same as that drawn from the comparison of forms 

 from different localities under the same climatic conditions . The tropical forests of West Africa 

 and the Malayan Islands are very similar as regards climate ; in the first chrysippus occurs 

 as the white hind-winged alcippus, in the second as the type form, a peculiar dark form 

 inhabiting Java. 



Having thus thrown some doubt on the influence of climatic conditions, the author 

 proceeds to account for them by the aU-pervading influence, natural selection. He suggests 

 that the klugii (dorippus) form is a development in a procryptic direction in areas where the 

 struggle for existence is so severe that even the unpalatability of the species is an insufficient 

 protection against enemies goaded to hunger by the scarcity of insect prey. In support of 

 this assumption it is pointed out that the ground-colour of dorippus is modified in some 

 specimens to a decided sand-colour, such modification being more noticeable in Africa 

 where the type form is usually of the dark golden-brown colour already described as typical of 

 the African region. Such a view implies the assumption that dorippus has developed from 

 chrysippus and not chrysippus from dorippus, in support of which Professor Poulton con- 

 tinues as follows : ' Island individuals which are so generally ancestral are chrysippus, 

 and only very rarely klugii (dorippus), except near the metropolis of the latter form in 

 Somahland. Perfect and imperfect mimics, Batesian and Miillerian, are very large in 

 number, especially in Africa. Probably not one of these mimics klugii {dorippus) and not 

 chrysippus, a few mimic both, while the great majority mimic chrysippus alone. Again 

 klugii {dorippus) stands alone among Danainae, while the pattern of chrysippus is closely 

 related to that of several other species and genera, such as Salatura. The distribution of 

 klugii {dorippus) can be understood by supposing the desert region of Somaliland to be its 

 centre. From this point it radiates towards the east, becoming gradually rarer, although 

 it is well known in Karachi, and Col. Yerbury even captured a single specimen in Ceylon ; 

 towards the south, finally disappearing in South Africa ; towards the Nile Valley, here also 

 probably disappearing towards Central Africa. D. chrysippus, or at least forms with a black 

 and white apex to the fore-wings, on the other hand, occur over the whole vast range of 

 the species, with the exception of certain parts of Somaliland.' 



Further and still stronger arguments are deduced from consideration of some of the 

 forms of mimicking species. Marshall considers the form alcippus to be a further develop- 

 ment in the direction of still more efficient warning colours, in which view Professor Poulton 

 concurs, in view of the abundant life of Tropical West Africa, and of the fact that it is much 

 more conspicuous on the wing. 



Were alcippus to occur only in Tropical West Africa the views of the origin of the various 

 forms of D. chrysippus just explained would no doubt be much strengthened, but as Marshall 

 has pointed out, this form presents some difficulties, occurring as it does at Aden, Wadelai, 

 &c., and is also common on the Tugela River. Further difficulty is presented by the alhinus 

 form, for if the coloration of dorippus is procryptic and that of alcippus aposematic, we 

 have in albinus the simultaneous development of two features of opposing significance. There 

 is a general tendency to a more or less white suffusion, especially of the hind-wings, in 

 chrysippus, for many specimens from various localities exhibit it in a greater or less degree. 

 It would, therefore, seem reasonable to suppose that this tendency is inherent in the species, 

 and is not inhibited by the development of the other variations. If this were so, the white 

 hind-wings would become general wherever the conditions of life favoured them more than 

 the other forms, as for instance appears to be the case, from whatever cause, in West Africa. 

 In other locahties there might be no special advantage in white hind-wings over the typical 



