THE CAUSE OF MIMETIC RESEMBLANCE. 611 



in the Itliomiinm (figs. 2 & 3). The scales on the opaque border of 

 the transparent area are almost uniform in appearance, forming the 

 sharpest contrast with those of the IthomiincB. In the transparent 

 part the individual scales are but little changed in appearance or 

 size, but they are immensely reduced in number, so that the light 

 freely passes between them. The scales which remain merely cause 

 the appearance of a grey dusting over the transparent surface. Ituna 

 ilione was drawn for this figure, the other species, I. ^henarete, only 

 differing in this respect by its even more complete transparency in 

 consequence of a still greater suppression of the scales. 



Thus the course of development leading to superficial resemblance 

 has been entirely difi'erent in the species of these two sub-families — 

 tlie IthotniincB and BanaincB. 



Plate 44. 



Further divergent methods by which the transparency necessary for the 

 likeness has been attained in other members of the group shown on 

 Plate 42, viz. in the Pierince, and among moths in the Pericopidce and 

 CastniidcB. 



Fig. 1. About \ natural size. On the right side is seen the single Pierine 

 species which enters into this group, viz. Bismorphia arise. The 

 two upper figures are male and female of the type form found in 

 many parts of tropical South America. Opposite them on the left 

 is a male and female of the type form of Meihona confusa. The 

 specimen represented in the lowest position on each side is a form 

 which occurs in Ecuador, in which the transparency is increased at 

 the expense of the black bars and border. It is very interesting that 

 this form of Methona should thus have been followed by the Pierine 

 butterfly in the same area. The former has recently been distin- 

 guished as Methona 'psamathe (Godm. & Salv.). 



Fig. 2. X about 15. The scales on the transparent part of the left apical patch 

 on the fore wing of Bismorphia orise, the opaque border being repre- 

 sented at the lower part of the circle. In this case a third method 

 has been adopted. In IthomiincB the widely different scales were 

 I'educed in size and simplified in shape: in Banainm the uniform 

 scales were reduced in numbers rather than in size : while here in the 

 Pierinm they have been reduced in size rather than in numbers, but 

 remain almost unchanged in shape. The amount of reduction in size 

 in this species is better seen by comparison with other parts of the 

 opaque surface upon which the scales are far larger than those of the 

 border which are shown in this figure. 



Fig. 3. About ^ natural size. A set of day-flying tropical South -American 

 moths which fall into this group. The two left-hand rows are 

 five species of the genus Anthomyza. The upper pair are A. brotes 

 (Druce), male left, female right ; the nest A. Buckleyi (Druce), male 

 left, female right ; the next A. Swainsoni (Druce), both female ; the last 

 pair being A. praxilla (Druce) on the left, and A. tiresia (Or.) on the 

 right. The two lowest moths of the figure are Hyelosia tiresia (Cr.). 



