EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 161 



of the lower groups, there must have been immediate and complete fusion of 

 bands occupying adjacent interspaces, when the vein which separated them was 

 lost. Modification in the shape of the wings, resulting in changes in the relative 

 positions of the nervures, must also have been an important factor in producing 

 correlated changes in the primitive color pattern by bringing about displacement 

 and fusion of some of the bands. Just what modifications in the color pattern 

 would have been produced by the direct action of these conditions, could only 

 be determined by a complete knowledge of the actual series of changes which 

 have taken place in the wings of Lepidoptera. Beyond, and apparently inde- 

 pendent of these factors, there is the evolution in the shape and extent of the 

 color areas themselves. 



It was found that dark markings, properly so-called, appeared at the limits 

 between ground color and unpigmented areas. Increase in breadth of a dark 

 marking takes place away from an unpigmented area. The dark markings do 

 not appear until the edge of a color area has remained constant for an appreci- 

 able length of time. Since they appear at the edges of color areas, their shape 

 and position are in great part determined by the same laws which control the 

 evolution of the pattern of the ground color. Markings once formed tend to 

 become permanent and immovable. Thus we find that the suffusion of an un- 

 pigmented area with ground color subsequent to the formation of a dark streak 

 does not affect its permanency; the shrinking away of ground color leaves a dark 

 streak or line isolated in an otherwise unpigmented area. Therefore, although, 

 during the early stages of evolution, the development of markings was entirely de- 

 pendent on the configuration of the ground color, these markings once permanently 

 established in the race, tend to reappear independently of the ground color. When 

 this level has been reached in racial history, we have a series of transverse markings 

 appearing on a uniform ground color. This is the condition in all of the higher 

 Lepidoptera. In the ontogeny of such groups, there is no evidence to show that 

 these markings are a second series superimposed upon the earlier primitive one. 



If the theory of the origin of dark markings on opposite edges of primitive 

 bands of ground color is a valid one, we should expect to find in the higher types, 

 that there is a tendency for dark stripes to recur in pairs, and that fusions at any 

 single period would be more apt to occur between any two consecutive stripes 

 than between three consecutive stripes. Observations confirm this hypothesis. 

 Among many of the Pyralids, the dark markings are formed of two dark lines 

 connected by a paler color; each of these marks is separated from a similar pair 

 of lines by ground color. Even in the butterflies, the tendency toward grouping 

 of dark marks in pairs is witnessed. Elmer's ('97) series of adult forms of Papilio 

 and von Linden's ('98, '02) figures of the pupal development illustrate this 

 principle. In the pupal development of the wings of Papilio machaon, the 

 tendency for the dark scales to appear first at the edges of bands was noted; 

 bands thus formed have, on my hypothesis, originated from the fusion of dark 

 stripes situated on either side of a primitive band. 



