136 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 



is, however, prolonged outwardly at its angle along the wing to a position between 

 the third pair of streaks. A comparison with the adult shows that the pro- 

 longation of the fascia is occupied by dusting on a whitish ground; that is, these 

 j.^^^ ni jy- y^y^ white scales are destined to become black tipped. 



The third pair of streaks are situated normally over 



I veins 10 and 2 respectively. There is no white spot 



^ over the tip of vein 9 on the costa. Bands V and VI 



Fig. 20. Early stage in the havc fuscd. A quadrate area in the apex remains 



orZtZ*;°'"^ '-^ *'^ ^'"^ ««loriess; the portion directly over vein 7 corre- 



sponds to the white streak normally situated here, 

 the remainder will be occupied by dark dusting in the adult. The scales 

 around the margin at the apex are yellow; these in the adult will be brown 

 tipped yellow scales. 



In a wing at a somewhat later stage, there has been some deepening of the 

 ground color. There is a small patch of scales just beyond vein 7 which are 

 brown tipped and darker than any other scales on the wing. In the extreme 

 apex, the scales extending over the cilia are not noticeably dark tipped. Dorsal 

 to the dark patch of scales, the scales over the formerly colorless area become 

 gradually paler, until near vein 5 their tips show just a faint tinge of gray. All 

 the scales in the prolonged portion of the fascia are becoming pale gray tipped. 

 There is also a faint gray tinge to the scales just below the tip of the dorsal 

 arm of the fascia, continuous with the gray in the prolonged portion of the fascia. 

 All of these scales are much paler than those in the apex just beyond vein 7 but 

 approach in color those near vein 5. 



The margins of the remaining streaks soon make their appearance; the 

 dusting of the apex reaches the adult condition earliest. 



A contrast in the sequence of development of dark marks is afforded by 

 L. carycefoliella Clem. In this species, the margins of the first and second fasciae 

 develop contemporaneously with a small patch of dusting at the extreme apex, 

 and the margin of the second fascia is entirely complete, though not as dark as 

 in the adult, at a stage when there is no indication of dark dusting beyond its 

 angle. This dusting is very variable even in the adult, sometimes being very 

 slight. The significance of the difference in development will be discussed later. 



LithocoUetis ulmella Cham. 



In this species, the pale yellow color appears simultaneously over all those 

 areas which are to remain yellow in the adult (Fig. 95, PI. IV) or in which the 

 scales are yellow with brown or blackish tips. The white streaks and the white 

 dusted portions of the wing remain colorless. Thus, the second costal streak is 

 produced for a short distance along the cell, and the wing from vein 7 to the 

 apex is colorless, but the scales around the apex and below the oblique dorsal 

 streak, which are yellow with brown tips in the adult, have already acquired the 

 pale yellow color. 



