156 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 



white fascia. If the outward growth of Band II along the cell is comparatively 

 rapid, a pair of opposite streaks will be produced at the basal fourth. These 

 changes have taken place very early in the phylogenetic history, and if evolution 

 of the pattern of the ground color ceases here, species of the type of morrisella 

 (Fig. 48), uhlerella (Fig. 49) and rohiniella (Fig. 50) will develop. The 

 laws governing specific differentiation have had an opportunity to operate 

 over a long period of time, and very highly specialized individual characters 

 have developed. In rohiniella evolution of the pattern did not cease quite as 

 soon as in the other two species, the fascia has been narrowly separated into 

 two streaks and all of the streaks have become more oblique. In consequence 

 of the later beginning of specific differentiation, the individual characters are 

 not as highly specialized as in uhlerella and morrisella. 



If the edges of the first pair of streaks move toward the base, and there is 

 no corresponding extension of the extremities of Band III toward the base, 

 species of the type of lucetiella (Fig. 51) will be produced. 



Where Band III has been extended to the base, there is a basal streak very 

 similar to that of cratcegella (Fig. 36) and the other species of that group. 

 Martiella (Fig. 52), gemmea (Fig. 53) and symphoricarpella (Fig. 54) have 

 originated thus. In symphoricarpella the basal streak is very small — ^the ground 

 color has shortened and narrowed it. 



If the outer edge of Band III instead of remaining straight has grown distally 

 along the cell and at the same time the movement of its extremities toward the 

 base has been accompanied by a compensating extension of the extremities of 

 Band IV toward the base, angulated fasciae will result; apicinigrella (Figs. 

 55a, 556) and celtisella (Fig. 56) have been thus differentiated. Finally 

 this angulated fascia may become very acutely angled through the shrinking 

 away of Band III and the white may be extended along the margins to the base 

 of the wing. At this stage a very slight outward growth of the middle of Band III 

 will divide the fascia into very oblique streaks; basistrigella (Fig. 57) has 

 been thus produced. In this species the separation of a white fascia into a 

 pair of streaks was the last step in evolution; in the other species characterized 

 by opposite streaks, this process has been one of the earliest events in evolution. 



Bataviella (Fig. 58) is an early isolated offshoot from the main stem; 

 it alone of all the species has preserved, in some of its varieties, Band I at the 

 base of the wing distinctly separate from II. Specific differentiation has ex- 

 tended over a length of time sufficient for all of the scales of the ground color 

 to become dark tipped. 



The second main stem of the phylogenetic tree, which has given rise to 

 Cremastohomhycia and the ^^flat-larval group," is illustrated on Plate IV. 



The species of Cremastohomhycia and of the ^^flat-larval group'' have fol- 

 lowed very similar lines of development. In Cremastohomhycia the result has 

 been modifled somewhat by the shorter and very oblique, almost horizontal 

 position of the white streak separating Bands I and II. A white basal streak 



