294 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
areas which surround it; for example, while the middle yellow is 
rufous in color in only 14 species, the inner yellow is rufous in 56 ; 
also the inner yellow area, being usually smaller and less conspicuous 
than the middle yellow, is less important in cases of mimicry, and 
the diagram Fig. 98, Plate 9 , shows that it is much more variable 
in color than the middle yellow. The full zig-zag line in this figure 
represents the color-variations of the inner yellow, while the dotted 
zig-zag line gives the color-variations of the middle yellow. As 
there are nine color-variation^ displayed by each of these two areas, 
and as there are 400 species of the Danaoid Heliconidae recorded 
by me, it becomes evident that, if there were no color preferences 
displayed by these areas, there would probably be about or 44.4, 
species which would display it as rufous, 44.4 translucent, 44.4 yellow, 
etc. The heavy, straight, dotted line (Fig. 98, Plate 9 ) represents 
this ideal condition, which would be approximately realized were 
one color as likely to occur as another in the respective areas. Now 
it is evident from an inspection of the figure, that the full zig-zag 
line, which represents the color-variations of the “ inner yellow,” 
approaches the straight line condition more nearly than does the 
dotted zig-zag line, which represents the middle yellow. 1 The 
inner yellow is therefore more liable to color-variations than the 
middle yellow; and this is what we should expect on account of 
its comparatively small size and its consequent inconspicuousness 
as a characteristic marking in cases of mimicry. 
A comparison of Figs. 97 and 98, Plate 9 , is interesting, for it 
shows that the color-variations of the inner rufous are quite similar 
to those of the inner yellow and middle yellow. This serves to 
illustrate the close physiological relationship which exists between 
rufous and yellow. The two pigments are probably closely related 
chemically, for every ordinarily rufous area is sometimes found to be 
yellow, and vice versa. Yellow areas also often change to white. 
Rufous, yellow, and white are evidently closely related color-vari¬ 
ations. 2 
iThis is not true for one color, white. 
2 It may be well to mention here that the black areas upon the wings are subject to 
very little color-variation. In some cases, however, especially upon the under surfaces 
of the wings in Ithomia, the black has changed to a rufous or russet color. For example, 
Table 4 shows that the middle black area (IV in the figures upon Plate 4) is rufous in 
only 12 species out of the 400 which are recorded, and all of these 12 are Ithomias. Also 
Tables 7 and 13 show that the outer black of the fore wing, and the outer black of the 
hind wing are russet in 22 and 11 species, respectively. Evidently, black is a far more 
conservative color than rufous, yellow, or white. Probably black is also quite different 
from the other pigments chemically. 
