266 THEORIES OF MIMICRY 



guished as M. psamathe, Godm. and Salv., are much 

 narrower than in the type form, and we find that 

 the Dismorphia from the same locality has followed in 

 the same direction. Microscopic examination reveals 

 that in Dismorphia the transparency is attained, unlike 

 Ituna, by a reduction in size of the scales ; while, unlike 

 the Ithomiinae, the normal shape and outline are pre- 

 served almost unchanged. 



It is a little remarkable that in this large, dominant, 

 and widely distributed group, no member of the 

 Heliconinae has yet been shown to find a place. 



We now pass to the Heterocerous members of the 

 group. Microscopic examination proves that the moths 

 become transparent in two ways, which differ entirely 

 from each other, and from any of the methods already 

 described in the butterflies. The scales of Castnia are 

 not reduced in size, but they have lost their pigment 

 and are transparent ; they are furthermore set up on 

 edge so that the light freely passes between them. The 

 scales towards the centre of the transparent patches are 

 much more upright than those of the margin, where they 

 are transitional into the opaque border. The arrange- 

 ment in Hyelosia is closely similar to that of Castnia, 

 save that the scales are much reduced in number. The 

 scales of Anthomyza, on the other hand, are normal in 

 arrangement as well as in size. They lie flat on the 

 wing-membrane with the usual overlap, but are so 

 devoid of pigment that the light passes through them. 

 Although transparent, they retain a more or less faint 

 yellow or greenish-yellow tinge, but this is also to be 

 noticed in the transparent part of the wings of Methona, 

 Dismorphia, &c. 



The comparison of these details is almost a demon- 

 stration of the operation of the Darwinian theory. We 

 cannot conceive of Natural Selection acting other than 

 along some such lines as those which have here been 

 shown to exist ; for it is impossible to believe that very 

 different species with very different natures would 

 present anything but very different variations for its 

 action. On the other hand, we cannot conceive of any 



