COLOR IN MOTHS AND BUTTERFLIES. i6l 



ground-color of the wings of Peiris rapae consists of sixty per 

 cent white, seventeen per cent black, thirteen per cent emerald 

 green, and ten per cent lemon yellow. Furthermore, a spectro- 

 scopic examination of the colors shows that they are generally 

 compound, i.e., composed of several distinct colors. It appears, 

 then, that natural selection has not been very severe with color 

 in Lepidoptera, for the colors are neither very pure nor intense. 



When we examine the color patterns displayed by the wings 

 of butterflies and moths, it appears that the spots show a strong 

 tendency to be bilaterally symmetrical, both as regards form 

 and color ; and the axis of symmetry for each spot is a line 

 passing through the center of the interspace in which the spot 

 is found parallel to the trend of the nervures. A good illus- 

 tration of this law is afforded by the case of "eye spots," 

 where the center of the spot is always at the center of the 

 interspace in which the spot is found. This was pointed out 

 by Bateson in 1894. In addition to this law we notice that 

 spots of similar form and color tend to form a row by appear- 

 ing in homologous places in a series of adjacent interspaces. 

 A study of the color patterns shows that they follow these sim- 

 ple laws quite rigidly, and that there is surprisingly little 

 diversity among them. Natural selection has not been severe 

 with color patterns in these respects, and as a consequence 

 many patterns which we could easily picture to ourselves are 

 never seen in nature. For example, a very striking color effect 

 might be produced were a series of adjacent interspaces to dis- 

 play alternate colors, say red, yellow, red, yellow, red, yellow, 

 etc. ; but this is never seen in nature. 



Considering the color patterns from another point of view, 

 however, we cannot fail to be struck with wonder and admira- 

 tion at the remarkably close resemblance between the wings of 

 many moths and their surroundings. And the reason for this 

 appears to be that such resemblance affords protection to the 

 insect possessing it, and that natural selection has perfected it 

 until now we find moths whose outspread wings almost exactly 

 match the colors of the bark of the tree upon which they rest, 

 etc. Even more remarkable are the numerous cases where an 

 edible species resembles almost exactly the form and color of 



