132 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 



The darkening of scales in the ciha around the apex and just below it on 

 the termen and the dark margins of the first costal and dorsal streaks are the 

 next characters to appear. A wing examined at this stage shows the scales in 

 the ciha brownish with scarcely a tinge of gra}^, the margin of the first dorsal 

 streak somewhat paler and brownish yellow, extending from the ciha to vein 2, 

 and the margin of the first costal streak pale and scarcely distinct. These 

 observations are in agreement with those made on L. cratcegella and ostrycefoUella; 

 namely, that the dark markings appear earliest in the apex of the wing on Band 

 VII and soon after on Band IV. 



The process of development consists now merely of the gradual appearance 

 and darkening of the margins of the other streaks and the extension of the line 

 in the ciha to the first dorsal streak. 



LithocoUetis morrisella Fitch. 



At a period when the entire wing, viewed by transmitted hght, seems uni- 

 formly colorless, the white markings as seen by reflected light are definitely laid 

 down as they will appear in the adult (Fig. 48, PI. Ill) and have already acquired 

 the lustrous pearly tint characteristic of the adult. This white appearance is 

 due entirely to the structural modification of the scales described earher in this 

 paper and cannot be in any way ascribed to a precocious development of the 

 scales over these areas, since, when examined, all of the scales of the wing are 

 seen to be fully developed. 



With the first appearance of pigmentation, a pale yellow suffuses those 



portions of the wing only which are destined to be yellow in the adult {Fig. 16). 



,,, ir V yt^yj, In the basal half of the wing, therefore, the yellow is 



confined mainly to the region above the fold; there is, 



however, a faint yellow tinge just before the dorsal arm 



of the fascia. There is a scarcely discernible tinge of 



Fig. 16. Early stage in gray at the basc of the dorsum below the basal streak 



the development of color in ^^^ ^^^^^^ ^^iQ first dorsal streak. At the tip of the wing, 



the wmg 01 L. morrisella. i o; 



over the area to be occupied by the apical dot, the scales 

 are beginning to turn gray, those outermost being the deepest. Otherwise, the 

 areas occupied by gray and black in the adult and by the white streaks appear 

 by transmitted light uniform and colorless. Examination by reflected light 

 shows that these two kinds of areas are not homologous, since the white streaks 

 stand out clearly as structural modifications, while the scales margining them 

 and those below the fold are duller and lack the pearly luster. The bands and 

 the white fascia and streaks occupy their normal positions. The absence of a 

 white streak over the apex of vein 7 is accounted for when it is seen that the 

 apical spot has acquired such proportions as to cover the tip of vein 7, which in 

 this and related species reaches the margin nearer to the apex than usual. 



In the next stage examined {Fig. 17), the ground color has deepened some- 

 what, and decidedly more of the grayish tint has developed. The dorsal part 



