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) : 



^^(a) 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 one end. 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 



