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. On the 

 other hand, species belonging to groups recently estabhshed and hence of high 

 phylogenetic 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 III) and fragilella (Fig. 3, PL III) 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 LithocoUetis 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 orthogenetic. 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 in 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 LithocoUetis 

 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 



