EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 145 



The discussion heretofore has dealt chiefly with the processes which effect 

 the final limitation and configuration of the ground color. The general tendency 

 toward the production of dark pigment in rows of scales adjacent to unpigmented 

 areas has also been noted. These streaks of dark scales, which are usually 

 transverse, and the various other characteristics, such as the apical spot, the 

 longitudinal streak of black scales in the apex and the black streak in the fold, 

 properly constitute the markings^ in distinction to the ground color, and are 

 superimposed upon it. While the progressive change in the configuration of 

 the ground color is the important factor in determining the general evolution of 

 the genus and the different stages at which development has halted form the 

 starting points for the differentiation of the different groups of species, the develop- 

 ment of the markings is the important factor in determining the phylogenetic 

 sequence of the individual species within each group. A knowledge of their 

 mode of origin and relative time of appearance is therefore essential. 



In L. tiliacella and tritcenianella, it was seen that the dark margin develops 

 first along the edge of Band IV, which is the first band to reach its adult shape. 

 In L. tiliacella, the outer edge of this band has become fixed before all of the bands 

 have even been laid down. The dark margin appears toward the costa and 

 dorsum, in places where the outer edges of the band have undergone no change 

 whatever since the first appearance of color. The dorsal margin seems to be 

 in advance of the costal. There is no darkening of pigment along the bands in 

 the apex, which appear comparatively late. From these observations, it appears 

 that in the ontogeny, the dark margin develops earliest along the edge of that band 

 which first reaches its definitive adult condition. Before dark margins can develop, 

 the edge of a band must have remained fixed for an appreciable period of time. 



In L. cratcegella, ostrycefoliella and lucidicostella, the dark margin on Band 

 IV is also the first to appear. The apparent contradiction to the principle just 

 laid down that a dark margin develops earhest along the edge of the band that 

 has first reached its definitive adult condition, lies in the fact that in these species 

 the color areas in the basal half of the wing are at the outset defined almost as 

 in the adult, while the bands in the apex repeat the racial development. It 

 might be expected, then, that the margin would appear earhest along the first 

 pair of streaks. It has, however, required a much longer time in the evolution 

 of the species for the basal half of the wing than for the apical half of the wing 

 to acquire its present aspect; the development in the apical half has come to a 

 standstill comparatively early in the phylogenetic history of the species. The 

 observed recapitulation in the apical three or four bands during the ontogenetic 

 development of the steps in the racial differentiation of the species is in harmony 

 with the conclusions of other investigators that it is only among primitive forms 

 that anything approaching a complete repetition of phylogenetic changes is to 

 be found in the ontogeny. 



The apex of the wing (in respect to the conservation of primitive color 

 areas) may be regarded as primitive in comparison to the base of the wing. In 



