338 THE PLACE OF MIMICRY 



Planema poggei. This black butterfly with a broad orange 

 bar across the fore wing, and a white bar across the hind 

 wing, appears to the east of the Victoria Nyanza, but has 

 become far more dominant on the west shore, and thence 

 extends to the west coast of the continent. The models 

 overlap for some distance on both sides of the lake, and 

 as far as Toro in Western Uganda. A new female form 

 of P. dardanus, planemoides, beautifully mimetic of the 

 Planema, appears on the east side, becomes common on 

 the west, and extends to the coast. I have specimens of 

 the cenea female up to the north-eastern shore of the 

 lake, but not beyond. If they occur at all, they probably 

 quickly cease westward, and the form has never been 

 seen anywhere near the West Coast. In the case just 

 described, one very different model replaces the other, 

 leading to an equally wide divergence between a mimetic 

 form and its substitute. It is more usual for the changes 

 to be less abrupt, both models and mimics being replaced 

 by closely allied representative species or sub-species. 

 Thus we find the eastern Amauris niavius (form domini- 

 canus), with an immense white patch, replaced on the west 

 by A. niavius, with a considerably smaller white patch. 

 The two sub-species meet, as described on pp. 68-9, on 

 the eastern shores of the Victoria Nyanza, and there 

 interbreed, if we may so conclude from the number of 

 intermediate examples. Another of the mimetic females 

 of Papilio dardanus (merope), the black and white 

 hippocoon form, undergoes corresponding changes in 

 pattern, and here, too, intermediate varieties are found in 

 the neighbourhood of the lake. The equally beautiful 

 Nymphaline mimic Hypolimnas (Eur alia) wahlbergi of the 

 east is similarly replaced at about the same point by the 

 closely allied H, anthedon with a smaller white patch. Such 

 examples might be multiplied almost indefinitely. Those 

 here brought forward are, however, especially striking, 

 being large insects with a bold and simple pattern. A 

 succession of such replacements in an outlying member 

 of a Mullerian combination, in correspondence with the 

 successive changes in its other members, is described in 

 the tropical American genus Protogonius, on, pp. 350-2. 



