EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 149 



brought about by the uniform spreading of the pigment toward the base, the 

 edges of the bands remaining straight. Changes in the extent and form of these 

 bands have taken place through the action of any or all of the three following 

 dynamic processes : (a) The middle portion of a band may be produced distally 

 until it comes in contact with the band beyond it. (b) The extremities of a 

 band may be broadened by being produced proximally. (c) The extremities 

 of a band may be narrowed by the retraction of pigment from their outer edges. 

 The action of the first two may be observed directly, the third is an inference 

 from a comparison of adult markings. 



3. The bands, either in their primitive shape or as modified through the 

 course of evolution, constitute the ground color upon which a second darker 

 series of transverse characters is superimposed. These are properly termed the 

 markings and appear at the limits between ground color and unpigmented areas. 

 Their relative time of appearance, ontogenetically, is dependent upon the time 

 when that portion of the edge of a band has become fixed phylogenetically. 



4. Later in the ph3dogenetic history, spots and longitudinal black markings 

 may appear. For reasons not fully understood, certain of these markings appear 

 earliest in the ontogeny. 



5. Recapitulation in the ontogeny is at most only partial and is confined 

 to those species or to those parts of the wings in which there has been the least 

 advance from a primitive condition. Here also a distinction must be made 

 between ground color and markings. 



(e) Phylogenetic Development of the Color Pattern. 



From the previous discussion, it was seen that a few definite processes, 

 identical in all of the species, have acted to produce modifications in the extent 

 and configuration of the areas of ground color. Later, a set of darker transverse 

 markings has been superimposed upon the ground color. The dark pigment 

 appears in rows of scales contiguous to unpigmented areas. There are two 

 possibilities in regard to the place of its first appearance, namely, the outer or 

 the inner edge of a band. 



While the evolution of the pattern of the ground color has taken place in 

 the same directions in both divisions and in the two subgenera of the genus, 

 the development of the dark markings has followed different directions. In the 

 division whose larvse are of the ordinary cylindrical type and in Porphyrosela, 

 the dark markings appeared first on the outer edges of the bands: in the division 

 whose larv2e are of the modified flat type and in Cremastobombycia, the margins 

 appeared first on the inner edges of the bands. 



Two different inherent tendencies in development are therefore exhibited. 

 These two lines of development must have diverged early in the phylogeny, 

 while the only color pattern was still that blocked out on the white wing by the 

 shape of the areas of ground color and before any of the dark markings had 

 appeared, since neither type of marking can be derived from the other, and the 



