9y 



On Scale Evolution in the Lepidopterous Genus Ithomia. 



By W. H. Nunney. 



{Communicated by J. E. Ingpen, May 17th, 1895.) 



In taking advantage of Mr. Ingpen's wish that I should supple- 

 ment his paper from the comparative and systematic aspect in 

 contradistinction to the purely histological, and his most interest- 

 ing observations having apparently opened up a new field of 

 inquiry, it was, of course, necessary for me to overlook a great 

 number of butterflies and moths for purposes of comparison. My 

 observations are, I believe, in the main correct, but it is possible 

 from their extent, and the little time I was able to devote to the 

 matter, that certain of them may need future modification, more 

 especially as I did not intend to render them exhaustive. 



The question of scale evolution is one which unfortunately has 

 attracted little attention, notwithstanding its great interest. 

 Nowhere can it be more effectively studied than in butterflies and 

 moths. The occurrence in that order of every variety of scale 

 form, from the almost filamentous to the broadened plate known 

 as the " battledor," affords the widest possible scope for theory. 

 Till of late we needed to search through numerous species to 

 discover transition forms between hair and scale. The discovery 

 of nearly all the varieties on the wings of a single species of 

 Ithomia has, however, placed the matter in a better light, and 

 gives additional verification to the theory of the evolution of the 

 true scale from the simple hair. 



The Ithomiae are an exceedingly concrete group of American 

 butterflies, characterized by the possession of clear or semi-trans- 

 parent wings, the lower ones provided with scent pouches, as in the 

 whole of the sub-family Danainee to which they belong. These 

 scent sacs during the insect's life diffuse an odour objectionable to 

 most insect-eating birds and reptiles, the species being thus 

 rendered less likely to be preyed upon. The whole group is 

 usually placed in an intermediate position between the white tribj 



