610 PROP. E. B. POTJLTON : NATURAL SELECTION 



Plate 43. 

 The divergent methods by which the transparency — an important element in 

 the resemblance between the members of the group shown on Plate 42 — 

 has been attained in Ithoiniinm and BanaincB. 

 Fig. 1. About I natural size. The two central Ithomiine species round which 

 the group has in all probability converged. The extraordinarily close 

 resemblance between these butterflies belonging to entirely different 

 genera is a very fine example of common warning colours. The 

 next two figures will show that so close a resemblance is quite super- 

 ficial ; for there is a very wide difference between the shapes of the 

 scales on the transparent areas of the two species. 

 Fig. 2. X about 15. In this and all the other figures of scales on Plates 43 

 and 44, a portion of the transparent patch at the apex of the left 

 fore wing has been figured, including a small part of the opaque 

 margin, so as to show the manner in which the transition is effected. 

 The scales of butterflies and moths overlap from the base of the wing 

 towards its apex, and therefore in the arrangement here adopted the 

 uppermost part of each figure lies in the direction of the apex of the 

 wing. On this Plate a portion of the opaque border on the outer side 

 of the transparent patch, viz. towards the apex, is represented, and is 

 therefore uppermost in each of the three figures. In Plate 44 a 

 portion of the border towards the base has been drawn, and therefore 

 occupies the lowest part of each of the four figures. 



The magnification was as nearly as possible equal in all the seven 

 figures representing the scales. All the specimens which were thus 

 drawn belong to the Hope Department. Fig. 2 represents the scales 

 of Methona confusa, and it is seen in the upper part of the circle that 

 the opaque surface of the wing is covered with broad forked scales 

 regularly alternating with long and narrow ones. On the transparent 

 part the latter are reduced to extremely fine hairs, the former to 

 minute bifid structures. 

 Fig. 3. X about 15. The scales oi Thyridia psidii. The scales of the border in 

 this species are seen to differ somewhat in form from those of Methona, 

 while the difference on the transparent part of the wing is very marked, 

 the narrow scales being far broader and the bifid ones of a different 

 shape. The method by which transparency is attained is however 

 the same although the details differ. A method similar in all 

 essential respects was found in all the Ithomiine species shown on 

 Plate 42. fig. 2. In certain species, however, the process was carried 

 further : thus in Dircenna the broader scales were reduced to Y-shaped 

 hairs, as well as the others to simple hairs. 

 Fig. 4. About ^ natural size. The two species of the Danaine genus Ituna, 

 I. ilione and /. phenarete, which enter the group. The Ithomiina 

 were formerly classed witJi the BanaincB, but the important differences 

 between them are now generally recognized as justifying their separa- 

 tion into two distinct sub-families. 

 Fig. 5. X about 15. The method by which transparency is attained in the 

 Danaine genus Ituna is seen to be entirely different from that followed 



