142 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 
the others toward the adult condition; as in tiliacella, development must take 
place more rapidly, since its margins reach their adult condition before those 
of the other bands. Here, also, is the first manifestation of that tendency, so 
charaeteristie of all the more highly differentiated species of the genus, toward 
the darkening of seales in the apex. In this species, these scales are scattered 
over the entire apex, instead of being limited to a definitely defined area where 
the scales are modified structurally. This species does not, at any stage, show 
the primitive type of marking; a considerable amount of development is, however, 
necessary before the color areas attain their definitive final extent. 
In L. crategella (Fig. 36, Pl. IIT), ostryefoliella (Fig. 23, Pl. ПІ), lucidicostella 
(Fig. 44, Pl. П), hageni (Fig. 17, Pl. III) and morrisella (Fig. 48, Pl. ПІ), in the 
basal half of the wing, where in the adult there is the greatest divergence from a 
transversely banded type of marking, the color areas, upon the first appearance 
of a uniform pale yellowish, have almost exactly the same shape and extent as 
in the adult. They undergo very little change during development, except that 
in these species, as well as in tiliacella and tritenianella, there is a progressive 
and gradual deepening of the ground color. In the youngest specimens of 
ostryefoliella observed (Fig. 14), the first pair of streaks are still connected; 
very soon, however, they become separated by the union of Band III with IV. 
In the apical half of the wing, Bands V, VI and VII appear as straight 
transverse bands (except in morrisella); the transformation of the unpigmented 
fasciæ between them and between IV and V into pairs of opposite streaks is 
brought about by the outward extension of Bands IV, V and VI along the cell 
in a manner similar to that previously observed for Band IV in tiliacella and 
tritenianella. The obliteration of a white streak is brought about by the inward 
extension of the extremity of a band to meet the outer edge of the preceding 
band. In morrisella, the pattern is predetermined from the outset, the white 
fascia and streaks being produced by structurally modified scales, which are 
destined never to acquire pigment. 
There are no reasons favoring the view that such a type of marking as that 
found in crategella (Fig. 36, Pl. III) is primitive: there are many reasons for re- 
garding it as having been produced through a long process of evolution. It is a 
matter of general observation that the pale colors appear first ontogenetically, 
black of the pigmental colors being last to appear; it has been inferred that the 
same is true also for the phylogeny. In the adults of these species, there have 
developed, in addition to the usual dark markings adjacent to the unpigmented 
areas, definitely limited black spots and streaks in the apex. The scales thus 
pigmented are also differentiated structurally from the surrounding scales by 
their smaller size. There is no such structural modification of the dark tipped 
scales in the apex of tritenianella. Obviously a considerable period of time 
must have been required for the final differentiation of such characters as these. 
That these species have undergone an extensive process of differentiation in the 
production of certain characters of a kind which can only be acquired late in 
