WHERE ee ee a Айылы ААКы — 
EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 147 
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to that of the species of the “‘flat-larval group." The margins appear almost 
simultaneously, the scales changing directly from colorless to gray and thence to 
black. These scales, at the time the yellow ground color spreads over the wing, 
are not fully formed, thus contrasting with the similarly unpigmented, but 
fully developed scales belonging to the white fascia and streaks. In all other 
species examined, the scales were all equally and fully formed at the time of the 
first appearance of pigment in any part of the wing. 
In many species, these dark streaks adjacent to white are the only defined 
dark markings present; there may be a few scattered, darker tipped scales in 
the apex. An increase in the amount of dark pigment producing additional 
dark markings manifests itself in either of two ways. (1) The number of scales 
thus affected may be increased, so that the actual extent of the wing occupied 
by dark tipped scales is greater. This is the direction that evolution has taken 
in the species of the ‘‘flat-larval group” (illustrated on Plate IV) and in a few of 
the species of the *'cylindrical-larval group” (e. g., celtisella, Fig. 56, Pl. III, and 
celtifoliella, Fig. 4, Pl. III). Often, among the more highly differentiated of the 
species of the "flat-larval group," the entire apex of the wing is covered with 
black tipped scales (e. g., agrifoliella, Fig. 79, Pl. ТУ). Similar areas may develop 
in other parts of the wing; thus a patch of dark tipped scales may extend outwards 
from the angle of a fascia (e. g., bethunella, Fig. 84, Pl. ТУ). (2) There may be a 
concentration of pigment in comparatively few scales, which with increasing 
differentiation tend to be segregated in definitely limited areas marked out by 
structural modifications of the seales (e. g., lucidicostella, Fig. 44, Pl. III, and 
crategella, Fig. 36, Pl. II). In these cases, the scales are pigmented almost to 
their bases, not merely dark tipped. With the single exception of obstrictella 
(Fig. 64, Pl. IV) among the species of the second division of the genus, this 
tendency is confined to the species of the “cylindrical-larval group," where it 
manifests itself in the apex either as an apical dot or as a somewhat elongate or 
irregular patch of scales, broadest just before the tip of the wing. А similar 
longitudinal streak of black scales is present in the fold in robiniella (Fig. 50, 
Pl. IIT), whlerella (Fig. 49, Pl. ПТ), and morrisella (Fig. 48, Pl. III). 
Finally, there may be a decided deepening of the ground color itself between 
the white streaks. This process has reached its highest development in robini- 
ella, uhlerella, and morrisella. 
In the ontogeny, the development of all of these specializations has been 
much abridged, and concomitant with this, their time of appearance has been 
pushed back farther and farther into the earlier stages of pupal development. 
The dark tipped scales remain colorless during the time the yellow scales are 
attaining their adult condition; later, they change directly to gray and black. 
The pigment in the areas of dark tipped scales in the apex and beyond the fascize 
often appears simultaneously with that of the margins. Some variation is to 
be notieed here; in L. bethunella, the gray pigment appears in all the scales 
beyond the fascia, simultaneously with the beginning of the formation of the dark 
