no EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 



exceedingly elongate, linear scales, so that toward their bases they appear 

 almost as fine as the ciha themselves. Such a scale, one of the blue iridescent 

 scales in the cilia of L. cratcegella, is illustrated by Fig. 5. The scales forming 



the apical spot, a characteristic of a considerable group 

 ^_^ ^ '^ of species, are smaller than the average and proportion- 



ately broader and are of almost uniform size. The scales 

 in the black patch before the apex of such species as L. 

 cratcegella are very similar to these. 



All of the scales just described are marked with a 

 Fig. 4. Wing scales. serics of nearly parallel strise, there being six or eight 

 such ridges extending into each tooth. 

 In a few species, which for additional reasons to be adduced later are to be 

 regarded as among the farthest advanced phylogenetically, a peculiar highly 

 specialized type of scale has developed. The 

 extremel}^ brilliant luster of the white mark- 

 ings of L. morrisella and ostensackenella and t^ r a • , • 



^ . -TIG. 5. Apical wmg scale. 



P. desmodiella and of the bronzy purple me- 



taUic reflections on the thorax and base of the wings of P. desmodiella is pro- 

 duced by these scales. These white scales, one of which is illustrated by Fig. 

 6, are broader than the usual type, and the sides curve outward from the base. 

 The outer edge of the scale, instead of being coarsely and acutely dentate as in 

 the ordinary scales, is obtusely dentate or, sometimes, the teeth 

 are entirely absent. The edge then appears scalloped, in a man- 

 ner similar to the edge of a pec ten. The depressions between 

 the strise, which appear rather broader and more widely sepa- 

 T. . ...... • ^^^^^ ^^^^ usual, are concave. The concavities between these 



Fig. 6. White wmg ^ . . „ „ ^ , ^ . 



scale oiL. morrisella. strisB appear as it tormcd by a slopmg out of the sides of the 

 strise. The assumption of a concave surface will explain the 

 brilliant and slightly opalescent luster of these scales; the various colors being 

 produced by essentially the same processes as they are in a soap film. These 

 scales contain no pigment whatever; the effects observed are due entirely to 

 the effect of light passing through a medium of varying thickness. It may be 

 noted here that in L. rohiniella, a species very closely related to L. morrisella, 

 this differentiation has not reached the same degree of perfection. The white 

 scales are, however, broader and with fewer strise than those of the more typical 

 species. The metahic purple scales of the base of the wings and thorax of P. 

 desmodiella are very similar to the white scales structurally but differ in that 

 they contain a brownish pigment. Their metafile iridescence may undoubtedly 

 be ascribed to the same agencies. 



(c) Comparative Study of the Adult Markings. 

 The following study of the adult markings was instituted for the purpose 

 of discovering whether, as was suggested earfier in the paper, the primitive 



