156 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 
white fascia. If the outward growth of Band П 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 tvpe of morrisella 
(Fig. 48), uhlerella (Fig. 49) and robiniella (Fig. 50) wil 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 robiniella 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 uAlerella 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 crategella (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 
Вапа IV toward the base, angulated fascize will result; apicinigrella (Figs. 
55a, 55b) 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 
Cremastobombycia and the “‘flat-larval group,” is illustrated on Plate IV. 
The species of Cremastobombycia and of the “flat-larval group" have fol- 
lowed very similar lines of development. In Cremastobombycia the result has 
been modified somewhat by the shorter and very oblique, almost horizontal 
position of the white streak separating Bands I and II. A white basal streak 
