EVOLUTION 375 



definite bearing on the problem of selection. Planema is a 

 genus of Acraeine butterflies with a wide range over tropical 

 Africa, comprising a number of species whose wing patterns 

 are predominantly black and white in the female, black and 

 tawny with red markings in the male. Pseudacraea is a 

 nymphaline genus closely akin to our south English Limenitis 

 Sibylla (" White Admiral "), it appears through Africa in a 

 number of forms, the males and females closely mimicking 

 the various Planema *' models," not only in wing-pattern 

 but in the constant sexual difference of narrower forewings 

 in the male than in the female (Plate XIV, B). 



The various mimetic forms of Pseudacraea received 

 distinctive names and were all regarded as distinct species, 

 until Jordan's studies of the variations convinced him that 

 most of them were referable to the Linnean Pseudaa'aea 

 eurytus. This view has been confirmed by Hale Carpenter's 

 success in breeding and rearing various forms from the 

 same parents. He has also demonstrated the selection- 

 value of mimicry by statistical records, taken on the shores 

 and islands of the Victoria Nyanza, of the numbers of the 

 Planema models and of the Pseudacraea mimics as compared 

 with intermediate forms which show no close resemblance 

 to any Planema. In localities and seasons when the pro- 

 portion of Planema to the total number of butterflies 

 captured is high, the proportion of the intermediates to the 

 total number of Pseudacraea is low ; but when the Planema 

 models are relatively few, the number of intermediate 

 Pseudacraea becomes relatively high. From these figures 

 it is inferred that the intermediates ** were apparently 

 destroyed wliile the models exercised their protection to the 

 mimetic forms," but that they had ** an equal chance of 

 survival . . . when the protection of the models was in 

 abeyance." 



From the facts of insect life summarised in the preceding 

 pages, and from many others that could be adduced, it 

 seems certain that natural selection has played a large part 

 in the evolution of insect races, and in the fixation of specific 

 characters so far as these are themselves adaptive, or 



