160 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 
less degree of modification; the earlier evolution in this direction has halted, the 
longer will have been the time available for specific differentiation. Оп the 
other hand, species belonging to groups recently established and hence of high 
phylogenetie position, may be almost lacking in the darker colors. Actual 
examples of each of these possibilities are furnished among our species; morrisella 
(Fig. 48, Pl. П) and fragilella (Fig. 3, Pl. ПІ) are examples of the first, quercial- 
bella (Fig. 46, Pl. III) of the second possibility. 
III. GENERAL DISCUSSION. 
Ontogenetic and phylogenetic studies upon the development of the color 
pattern in Lithocolletis lead to the conclusion that evolution has taken place in 
definite directions under the action of a few definite laws; in other words, that it 
has been orthogenetie. It was shown that the primitive color pattern, the first 
to be laid down upon the white wing, is a series of seven uniformly colored, pale 
yellow transverse bands. From these, the color areas, which form the ground 
color of the various groups of species, have been derived. The first tendency 
observed is a uniform widening of the bands. Evolution in the shape and extent 
of the primitive bands of ground color, as has been shown (see page 141), has been 
brought about by three definite processes, two of which were observed in actual 
operation in the development of color in the pupal wings; the third is a necessary 
inference from the lack of agreement between the primitive positions of the bands 
and their positions in the more advanced species. The most far-reaching and 
widespread changes have taken place toward the base of the wing proximal to 
the transverse vein. 
The final result of the action of these three processes is a uniform ground 
color; this uniformity will be attained first near the base of the wing, since it is 
here that evolution has proceeded most rapidly. The color bands in the apical 
half of the wing, which were laid down later, are modified at a slower rate and 
retain more nearly their primitive shape. "These observations are in agreement 
with the general principle that development is more rapid in the anterior and 
proximal parts of an organism. 
The observed evolution in the pattern of the ground color suggests that 
the uniform yellowish ground color which suffuses the wing 1n the higher Lepidoptera, 
beginning at the base and spreading distalward, is the outcome of a phylogenetically 
older type of marking, originally banded, and later fused to a uniform color, and 
that the markings are a second series superimposed upon the first. | 
If the disposal of the transverse primitive bands of ground. color is de- 
pendent upon the positions of the nervures, as my observations on Lithocolletis 
have indicated, then in the primitive color pattern of the ancestral Lepidoptera. 
where more veins are present and their arrangement on the margins is more 
symmetrical, the number of these bands should be considerably augmented. 
As evolution has proceeded, this primitive type of color pattern would have been 
modified in various ways. Attendant upon the degradation in venation in some 
