MAYER: COLOR AND COLOR-PATTERNS. 181 
ing from one to two weeks only, according to the temperature to 
which the chrysalis is exposed. For the first few days the wings are 
perfectly transparent, but about five days before the butterfly issues 
they 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 white. 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 white. Fig. 44 shows a still later condi- 
tion, where the dirty yellow 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. Tue Laws wuich GOVERN THE CoLor-PaTrTEeRNS oF BuTrrer- 
FLIES AND Morus. 
(1) Historical Account of previous Researches. 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. g. 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 neryures and meet so as to inclose a 
space. 
