164 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 



been produced are the result of different combinations of three general processes 

 already discussed. 



IV. SUMMARY. 



Observations on the development of color in the pupal wings and a com- 

 parison of the color pattern in adult forms of Lithocolletis have shown that in 

 his group the primitive color pattern is a series of seven uniformly colored pale^ 

 yellow transverse bands, separated from one another by unpigmented areas. 

 The disposal of these bands is dependent upon the course of the longitudinal 

 nervures, since the points of origin or the tips of the veins mark the positions of 

 the unpigmented fasciae between the bands. 



From this primitive color pattern, the several different types of color pattern 

 in this genus have been derived. Evolution has taken place in definite direc- 

 tions, under the action of three general processes, which were found to be suf- 

 ficient to explain the origin of the different color patterns. These processes have 

 been stated thus: (a) The middle portion of a band may be produced distally 

 until it comes in contact with the band beyond it. (6) 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 particular result in any case, that is, the configuration of the color areas, 

 is due to the manner and extent of the action of these processes. 



During pupal development, these phylogenetic changes are repeated only 

 to a very limited extent; recapitulation is confined to those species or to those 

 portions of the wing in which there has been the least modification of the primi- 

 tive transversely banded type of marking. 



These bands either in their primitive or modified shape, constitute the 

 ground color. Upon this ground color, a second darker series of elements, the 

 markings proper, also usually transverse, are superimposed. The different levels 

 at which evolution in the pattern of the ground color has halted, that is, the 

 configuration of the areas of ground color, are the important factors in deter- 

 mining the phylogenetic sequence of large groups; the particular colors and the 

 markings determine the positions of the species within those groups. 



These markings appear at the limits between ground color and unpigmented 

 areas, as one or more lines of dark scales along the edge of a band adjacent to a 

 white fascia or streak. Their appearance then is probably due to physiological 

 factors within the organism itself, and is independent of external conditions. 

 In the ontogeny, the relative time of appearance of the dark margin of any band 

 is dependent upon the time when the edge of that band became fixed in the 

 phylogeny. Before dark margins can develop, the edge of a band must have 

 remained fixed for an appreciable time. Hence, where bands have been laid 

 down late or have reached their present configuration late in racial development, 

 the dark margin will develop at a correspondingly late period in ontogenetic 

 development. 



