148 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 



margin; in L. carywfoliella, the dark margin of the fascia is complete before any 

 pigment has developed in the area beyond it. In the imago, the patch of dusting 

 beyond the fascia is an estabhshed constant character in hethunella; in carycejo- 

 liella, the amount of such dusting is very variable, indicating its recent appearance 

 in the species. 



It would seem then that only those characters permanently established and of 

 long standing in a species exhibit this precocity of development; recently acquired or 

 variable characters appear ontogenetically in the order of their phylogenetic sequence. 



This conclusion is confirmed by observations upon the mode of development 

 ontogenetically of other analogous dark markings. Comparison of imagoes 

 indicates that the apical spot and the black patch in the apex have originated 

 phylogenetically earher than the streak of brown scales along the middle of 

 the wing but later than the dark internal margins of the white fascise and streaks. 

 In L. crata^gella, the pigment in the scales of the black patch before the apex, 

 which is unquestionably a characteristic only acquired through differentiation 

 extending over a long period of time, appears earlier than that in the brown 

 scales extending along the middle of the wing and reaches its definitive adult 

 condition while the latter are still wholly unpigmented. In L. hageni also, the 

 apical spot appears sooner than the dark scales in the middle of the wing beyond 

 the tip of the first dorsal streak. 



Such specializations as these cannot, however, have originated very early 

 in the evolution of a species, and the observed phenomenon of their unduly 

 precocious appearance and rapid development in the ontogeny requires additional 

 explanation. In L. cratcegella, ostryoefoliella, lucidicostella, hageni and morrisella, 

 these were the first dark markings to appear. The first tinge of gray appeared 

 before the ground color itself had reached its adult shade or rarely even before 

 it had reached its adult configuration. It is possible that physiological causes 

 act directly toward this end. In the racial development, the segregation of 

 black scales over a limited area and the later modification of these scales structur- 

 ally has been accomplished gradually; the results have become permanent in 

 the species, and the scales, when first formed before any pigment has entered 

 them, have a structure identical with that acquired late in phylogenetic develop- 

 ment. It is suggested, in explanation of the phenomenon of the early appearance 

 of black pigment in them, that the concentration of pigment-forming substances 

 within a smaller space — the interior of these smaller scales — results in a more 

 intense chemical action over a locahzed area and thus hastens development. 



The general conclusions which have been drawn from the study of pupal 

 development may be summarized as follows : 



1. The primitive type of color pattern consists of a series of seven trans- 

 verse bands, which, except the first, cross the wing perpendicular to the costal 

 margin and are not wider than the unpigmented fasciae between them. Their 

 positions are determined by the course of the longitudinal nervures. 



2. In the evolution of the genus, changes in extent alone of bands are 



