210 BULLETIN : MUSEUM OF COMPARATIVE ZOÖLOGY. 
ment within them. Figure 55 represents a scale from one of the light- 
drab colored areas of the mature wing, and upon comparing it with Fig- 
ure 54 it becomes apparent that it is much darker in color, and yet it is 
taken from the lightest colored area of the wing. Figure 56 is a view 
of the under surface of the hind wing of a male, and Figure 57 of the 
under surface of the fore wing of a female moth. "Phe two figures illus- 
trate a very early stage of color development, and from them it will be 
seen that the colors first appear, as I have stated, between the nervures. 
The upper surfaces of the wings are as yet of a uniform dull yellow color. 
Figures 58-64 show successive stages in the color development in the 
male, and Figures 65—70 the same for the female. In the stages repre- 
sented in Figures 60 and 67 the male and female wings are very similar 
in appearance, except that the general tone of the male wing is grayish, 
that of the female cinnamon-brown. The ground color of the male 
wings, however, soon deepens into jet black, as is shown in Figures 61 
and 62. 
Figures 71-74 show successive stages in the color development of the 
fore wing of Danais plexippus. In Figure 71 is seen the wing in the 
dull yellow stage, showing the white spots already standing out against 
the dull yellow background. In Figure 72 the black coloration has be- 
gun to appear near the centre of the wing, and in Figure 73 this black 
coloration has spread along the edges of the nervures, and the rufous 
ground color of the mature wings has begun to appear in places between 
the nervures. In Figure 74 the black color has finally suffused the 
nervures. The base of the wing and the submedian nervure are the 
only parts that still remain dull yellow. It is evident 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 of all to be affected. 
These results confirm and amplify the previous researches of Schäffer 
(89) upon Vanessa urticee ; van Bemmelen (89) upon Vanessa urtice, 
Pyrameis cardui, and Pieris brassicæ ; Urech (91) upon several Vanes- 
sas; and Haase (92) upon various species of Papilio. 
The primary object of the present research is to determine the man- 
ner in which the wing scales of the Lepidoptera acquire their pigmental 
colors. I have also traced the general development of the wings from 
the condition found in the mature larva up to that of the imago. The 
paper will be divided into four parts: (1) The General Development of 
the Wings and Scales ; (2) The Development of the Pigment within the 
