EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 141 



4. Discussion and Conclusions. 



In general, I have found that the action of three processes is sufficient to 

 explain the transformation of the seven primitive bands into the several existing 

 patterns of the ground color. These three processes may be 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. These three processes may act 

 separately or in combination; the particular pattern produced is the resultant 

 of their combined activity. The first two of these laws are based chiefly upon 

 the changes observed during pupal development, the third law is deduced 

 from adult characters, since the changes are such as cannot be observed directly. 

 The evidence in detail is as follows : 



In L. tiliacella {Fig. 7), seven distinct transverse bands of ground color 

 are laid down; of these, those numbered II, III and IV appear first; following 

 these, Band I, at the base of the wing, appears continuous in the costal half of 

 the wing with II; it is, however, sufficiently separated from it by the difference 

 in time of appearance. The three bands in the apex of the wing appear last and 

 undergo no change; the connection of Band V with IV is brought about entirely 

 by the extension outwardly of IV along the middle of the wing. The changes 

 in Bands II and III are brought about by the spreading of the color onto areas 

 formerly unpigmented; that is, the fascia between II and III is narrowed by 

 the very slight growth distally of II along the middle of the wing, its extremities 

 remaining fixed, and by the extension proximally of III, chiefly along the margins. 

 Band IV reaches its adult configuration earhest; it is also the earhest to acquire 

 the black pigment on its outer edge. This does not appear in the middle of the 

 wing, where the band has extended outwardly uniting with V. The outer 

 edges of the extremities of Band III have remained constant in position, and the 

 dark scales appear first here. In Band II, there has been the least change in 

 shape; the deepening of the pigment along its outer edge occurs more uniformly. 

 From this, it follows that while the general tendency is for dark pigment to develop 

 along the outer edges of hands adjacent to unpigmented areas, the precise time of its 

 appearance along any hand or portion of a hand in relation to other hands or portions 

 of the same hand is determined hy the time when such hands or portions of hands 

 reach their adult shape and color. The outer edge of a hand in direct contact with 

 another hand acquires no dark pigment. It would appear from the observations 

 on this species that the hands in their primitive condition are narrower than they 

 are in the adult. A fascia may he narrowed hy the uniform spreading of a hand 

 toward the hase. 



These conclusions are corroborated by the observations on L. tritcenianella 

 (Fig. 5, PI. Ill) ; all the bands, however, appear simultaneously, and at this time 

 all are straight. There is, however, a reduction in the apparent number of bands, 

 V and VI being completely united. Band IV seems no further advanced than 



