J 



66 TME PLACK OF MnilCRY 



better mimic. Tyochiliu))i (Scsia) crabrtvuforvw'^ {btnibcci- 

 fornie), the)- are far more degenerate, in accordance with 

 the presumption that they have been useless to the species 

 for a longer period of time. It is interesting to note that 

 these degenerate scales have not been reduced in size in 

 either species, but are, on the contrary, much larger than 

 the scales which are retained for the whole life of the 

 moth. It is probable that the increase of size renders it 

 even more difficult for the degenerate stalks to retain the 

 scales durin-' llii-ht. In certain allied ' Clearwinos' of the 

 genus Scsia [Troi/n7iu))i) the transparency of the fore 

 wing has been attained by the transparency of scales 

 which are retained, as well as by the loss of scales.^ 



6. Mimetic Resouhlancc bcHvcoi Species of very 

 Different Size. — It has been observed for many years 

 that close mimetic likeness maybe found between species 

 of very different size. One of the most striking examples 

 is to be seen in Papilio ( Prurya) antiuiachus, an immense 

 West African swallow-tail butterfly with an obvious 

 Acraeoid appearance. The J\xpilio appears to form one 

 of a complex mimetic group of which the centre is 

 composed of many comparatively small but dominant 

 species of Acraea.- When the members of this mimetic 

 combination were exhibited, Mr. F. A. Heron suggested^ 

 an interpretation of such remarkable cases of the want of 

 accord between size and the other elements which sio to 

 make up a likeness. Size, as correlated with the idea of 

 distance, was, he pointed out, extremely difficult of 

 estimation. In fact the huge a)itij)iacJius, seen far off, 

 may well appear to be smaller than the comparatively 

 insignificant Acraeas at a much less distance. Especially 

 is this likely to be true of young and inexperienced 

 enemies, and it is precisely these which IMiillerian Resem- 

 blances are in large part adapted to meet. This interest- 



' See also pp. 264-6 for other examples of transparency attained in 

 a variety of ways. Consult also \V. J. Kaye in Eut. Record^ vol. xvii, 

 nos. 4 & 5, and Mark L. Sykes in Tratis. blanch. I\Iitrosc. Soc. 1901, 

 p. 82. 



' Proc. Eiit. Soc, Lond., 1903, Nov. 18, pp. Ixiii-lxv. 



' Ibid., p. Ixv. 



