426 Mr. G. A. K. Marsliall on 



made for the fact that the border represented in Fig. Ih, 

 Plate XII, is exceptionally broad, and is still more excep- 

 tional, indeed transitional towards sesamus, in the size of 

 the blue markings in it. But the lighter character of the 

 markings and the more conspicuous appearance of the 

 under-side border is perfectly clear in Fig. 1, Plate XIII. 

 And there is one other point not expressly mentioned 

 although probably implied by Mr. Trimen, which is I 

 think the most convincing evidence of .all in favour of 

 adaptation in the direction of conspicuousness ; — the fact 

 that the spots of ground-colour included in the basal black 

 patch of the hind-wing, and absent from the upper-side, 

 are distinctly lighter in tint than the rest of the ground- 

 colour, and thus afford a far more effective contrast with the 

 hlacl'. This difference in tint is well seen in Fig. 1, Plate 

 XIII. The spot in the basal black of the fore-wing which 

 represents a similarly-placed spot on the upper-side, is 

 also often lighter than the rest of the under-side ground- 

 colour, but the difference is far less marked than in the 

 hind-wing and is sometimes absent. 



Now the basal area of the under-side of butterflies' 

 wings and especially of the exposed hind-wing is a part 

 specially seized upon by natural selection for the display 

 of conspicuous warning characters. It is seen in the red 

 patches of many Pierine genera, especially the distasteful 

 Delias (appearing also in its Chalcosid mimics) in the Old 

 World, and several Pierinie in the New, where Dr. F. A. 

 Dixey has shown that the character has probably been 

 adopted by Heliconinm in Miillerian association with them, 

 the relationship — an important discovery first made in 

 1894 by Dixey — being one of "reciprocal assimilation " or 

 " diaposematic resemblance " (Trans. Ent. Soc. Loud., 1894, 

 pp. 290-298 ; 1896, pp. 72-74 ; 1897, pp. 326, 327, 331 ; 

 Proc. Ent. Soc, 1897, p. xxix). A stripe of bright yellow 

 or red bordering the basal part of the costal margin of the 

 under-side of the hind-wing of a large number of distaste- 

 ful tropical American butterflies of different .sub-families 

 is another very characteristic syna,poseme, rendering the 

 same part of the wing especially conspicuous. And in 

 Africa itself we have the most remarkable case of all, in 

 the triangular golden-brown, black-marked synaposeme 

 which is discussed at some length on pages 488 to 490 

 of the present memoir. Furthermore, there is the group 



