162 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 
The great diversity to be observed in the position, shape and extent of the 
dark markings in the various groups of Lepidoptera, is due to differences in the 
direction of evolution of the pattern of the ground color, and the different levels 
at which it has halted, permitting the dark markings to develop. 
The actual appearance of dark pigment in certain defined positions is prob- 
ably due to physiological factors; just why these processes should occur con- 
tiguous to unpigmented areas is largely a matter of conjecture. It is possible 
that the chemical changes involved are oxidative in their nature; the presence 
of air in the unpigmented hollow scales may possibly accelerate chemical proc- 
esses along this line. This supposition will however not account for the phylo- 
genetic permanency of such markings after the ground color covers the wing 
uniformly. 
The investigations of previous workers upon the color patterns of Lepi- 
doptera have been limited to the markings, that is, to that series which I have 
designated as secondary and superimposed upon an original primary color 
pattern. In as much, however, as these markings have originally been deter- 
mined by the configuration of the pattern of the ground color, the laws con- 
cerning their places of appearance should agree with my observations on the 
evolution of the pattern of the ground color; it is on the contrary not to be 
expected that these laws concerning behavior of the markings will apply in their 
entirety to the comparatively primitive and phylogenetically older type of 
markings in this genus. The laws governing the color pattern have been based 
upon more highly developed markings often of comparatively recent origin 
phylogenetically. For convenience in comparison a statement of some of these 
laws of coloration follows. The following are those advanced by Mayer (97): 
“ (а) Any spot found upon the wings of a moth or butterfly tends to be 
bilaterally symmetrical, both as regards form and color, the axis of symmetry 
being a line passing through the center of the interspace in which the spot is 
found, and parallel to the direction of the longitudinal nervures. (b) Spots 
tend to appear not in one interspace only, but as a row occupying homologous 
places in successive interspaces. Indeed we almost always find spots arranged 
in linear series, each similar in shape and color to the others and occupying the 
center of its interspace. (c) It is interesting to notice that bands of color are 
often made by the fusion of a row of adjacent spots; and conversely, chains of 
spots are often formed by the breaking up of bands, leaving a row of spots 
occupying the interspaces. (d) The most common method of disappearance 
is a shrinking away of the band at one end. It is very common to find bands 
shrinking away at oneend. This is a special case of Bateson’s law that the ends 
of a linear series are more variable than the middle. Sometimes however they 
shrink away at both ends, and very often, they break up into a row of spots, 
which may then contract into the centers of their interspaces and finally dis- 
appear. It is worthy of note that it is very rare to find a band breaking at the 
middle of its length and each half receding from the other. (e) The position of 
