118 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 



the dorsal arm of an angulated fascia. In ulmella (Fig. 95) and conglomeratella 

 (Fig. 94), the white streak extends almost to the tornus, where it connects with 

 a dorsal streak running obliquely into the apex. 



A rather noteworthy feature common to both divisions of the genus is this : 

 the third white fascia or the third pair of streaks, whose extremities are placed 

 over the tips of veins 2 and 10, are never displaced from their normal position, 

 and only in rare instances are they much oblique. These instances are almost 

 entirely confined to Division 11. In such case, the impression of length and 

 obliquity is gained through the fact that the more apical portion of this streak 

 is homologous with the white streak over vein 5. The greatest changes have 

 taken place in the positions of the first two pair of streaks, resulting in their 

 displacement toward the base. 



In either of the two divisions of the genus, the greatest number of more or 

 less distinct bands of ground color has been seven. The first of these crosses the 

 base of the wing and is usually confluent with the second in the costal half of 

 the wing. The position of the white unpigmented areas separating these bands 

 of ground color appears to be determined by the points of origin or by the tips 

 of the longitudinal nervures. The question to be decided is whether such a 

 banded arrangement of pigment areas represents the primitive type of colora- 

 tion, and if so, how has evolution acted in bringing into existence the present 

 great complex of species. 



A group of species (Figs. 59a, 596, 60, 61, 62, 63) more primitive in 

 generic structure, namely, Cremastobomhycia, shows a type of coloration strik- 

 ingly similar to that of some of the species of the ^^flat-larval group." An 

 examination of this group discloses the fact that nowhere are there more than 

 four costal white streaks as compared with five or six in some of the species 

 of the more recent branches of the genus. Apparently, then, because of the 

 fewer separate bands of ground color present in species of this group, the primitive 

 type of marking is not to be sought for among the species of the ancestral group. 



The observations that have been made point to the conclusion that the 

 primitive type of coloration is made up of seven distinct transverse bands. The 

 results of the investigations upon the development of color in the pupal wings, 

 now to be presented, confirm this view and, in addition, furnish evidence of the 

 means by which transformation of the bands into the various types of color 

 pattern has been accomplished. 



(d) Ontogenetic Development of the Color Pattern. 



1. Historical. 

 Tower ('06) has summarized the general results of researches upon the de- 

 velopment of colors in pupal wings as follows : 



^^The studies upon the origin of color in the wings of Lepidoptera have 

 shown that there is a regular order of development, not only of colors but also 

 of the areas in which spots and stripes appear. The wings, which are colorless 



