458 Prof. E. B. Poulton on the Mimetic N. American 



of its far more isolated position, probably represents a white 

 spot, also triangular in shape, near the end of the cell in 

 Anoda. 



The marginal pattern is as in the hind-wing save that 

 the apical white spots of the innermost series lose the 

 crescentic shape and become squarish. The changes which 

 have occurred in the subapical white spots of arthemis are 

 peculiarly interesting. In arcliippus, only the costal spot 

 and the second minute spot, generally a mere point, re- 

 main distinct and clear as in the ancestral form. The others 

 — one to three in number — have become continuous with 

 and contribute to form the triangular subapical pale 

 yellowish patch which, in both mimic and model, is of 

 the same tint as the ground-colour of the hind-wing. In 

 the Limenitis, however, the outer (hind-marginal) part of 

 this pale patch exhibits, as in the hind-wing, by a deeper 

 tint, a distinct vestige of the reddish submarginal spots of 

 arthemis. The single distinct costal white spot and minute 

 second spot already referred to, appear to represent the 

 extremity of a sickle-like curve within the apical angle of 

 the fore-wing. All other parts of this curve are made up 

 of the innermost series of marginal white spots — the ones 

 which have undergone the principal increase in size in 

 archippus. The effect is heightened by the special enlarge- 

 ment of the apical spot itself. Now when we turn to the 

 model we find that the innermost series of marginal white 

 spots does actually turn inwards sickle-like within the 

 apex and that a close superficial resemblance has been 

 attained in the mimic by the fusion of two separate 

 elements. One of these has been preserved for the purpose 

 out of an ancestral marking of which the remainder has 

 been transformed in an entirely different direction. 



The utilisation of the chief black and white markings of 

 arthemis in the subapical region of the fore-wing oi archippus, 

 in order to promote the mimetic resemblance to p)lexippiis, 

 together with the value of the whitened marginal lunules 

 of both wings is fully recognised by Scudder (1. c, p. 278). 



c. The Upper Surface of Zimc7iitis archij^pus. — The 

 marginal band is much blacker and heavier looking than 

 that of the under surface, in correspondence with the Anosia 

 model. The markings in it consist only of the white sections 

 of the fringe and the spots of the innermost series, the outer 

 blue crescentic marks in the margin of arthemis having dis- 

 appeared. The innermost crescents have become white and 



