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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. Eimer’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. 
