MAYER: COLOR AND COLOR-PATTERNS. 181 



ino- from one to two weeks only, according to the temperature to 

 which the chrysaUs is exposed. For the first few days the wings are 

 ])erfectly transparent, but about five days before the butterfly issues 

 thev become pure white. An examination of the scales at this 

 period shows that they are completely formed and merely lack 

 pigment. In about 48 hours after this (see Fig. 42) the ground 

 color of the wings changes to a dirty yellow. It is interesting to 

 note that the white spots which adorn the mature wings remain 

 pure Avhite. Fig. 43 illustrates the next stage, where the black has 

 begun to appear in the region beyond the cell. The nervures them- 

 selves, however, remain Avhite. Fig. 44 shows a still later condi- 

 tion, where the dirty j^ellow ground color has deepened into rufous, 

 and the black has deepened and increased in area and has also 

 begun to appear along the edges of the nervures. In Fig. 45 the 

 black has finally suffused the nervures, the base of the wing and 

 the submedian nervure being the only parts that still remain dull 

 yellow. ■ It is apparent that in Danais plexippus, as in Callosamia 

 promethea, the central areas of the wings are the first to exhibit the 

 mature colors, and that the nervures and costal edges of the wings 

 are the last to be suffused. 



IV. The Laws avhich govern the Color-Patterns of Butter- 

 flies AND Moths. 



(1) Historical Account of precious liesearches. The earliest 

 paper upon this subject is by Higgins ('68). He came to the 

 conclusion, that "the simplest type of color presents itself in the 

 plain uniform tint exhibited when the scales are all exactly alike." 

 He also thought it probable that "the scales growing on the mem- 

 brane upon or near the veins would be distinguished from the 

 scales growing on other parts of the membrane by a freer develop- 

 ment of pigmentary matter, and that in this manner would arise 

 a kind of primary or fundamental color-pattern, namely, a pale 

 ground with darker linear markings following the course of the veins, 

 e. (J. Pieris crataegi." He also attempted to explain the formation of 

 eye-spots by assuming that crescent-shaped markings migrate out- 

 wards from the sides of the nervures and meet so as to inclose a 

 space. 



