218 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
both fore and hind wings are very similar, In order to exhibit this 
fact graphically, the color-variations have been laid off upon the 
diagram, Fig. 97, Plate 9. The base line is marked at equal inter- 
vals with the words “rufous,” “translucent rufous,” “translucent, 
slightly rufous,” “ transparent,” ete, and the ordinates show the 
number of species which exhibit the various colors, rufous, trans- 
lucent rufous, ete. For example, at the point “translucent rufous ” 
we find that the ordinate is 23; this indicates that in 23 species 
the area is translucent rufous in color. The points thus found 
upon the ordinates are successively joined by straight lines form- 
ing a zig-zag figure. ‘The full line represents the fore wing, and 
the dotted line the hind wing, and it becomes clearly evident from 
the closeness of these two zig-zag lines that the color of the inner 
rufous area of the fore wing (area I, Plate 4) is almost always 
sure to be identical with that of the inner rufous area of the hind 
wing (area X, Plate 4). We see, therefore, that whatever color- 
variation affects the inner rufous area of the fore wing, this area 
in the hind wing is almost always affected in the same manner. 
Fig. 99, Plate 9, is derived from Tables 15 and 24, which show 
the color-variations in the fore and hind wings of the genera Helico- 
nius and Eueides. It is seen that here also the colors of these two 
areas in both the fore and hind wings are almost always identical. 
We here meet with one of those interesitng physiological laws 
which are independent of Natural Selection, and the meaning of 
which remains a mystery, for surely we can see no reason on the 
ground of adaptation why similar areas upon both fore and hind 
wing should bear similar colors. 
(2) The “ Inner Black” Spot. Table 2 shows the presence or 
absence of the “inner black” spot in the Danaoid Heliconidae. 
This spot is marked II in the figures upon Plate 4. When pres- 
ent, it is always black in color and is usually found occupying the 
middle region of the cell of the fore wing. The table shows that 
it is about an even chance whether it be present or not, for it is 
absent in 210 species and present in 190, In the genus Ithomia, 
however, it is present in only one third of the species. What is 
most worthy of note concerning it, is the fact that it almost always 
appears, when present, as a single spot. Indeed, it appears as a 
double spot in only 7 species, and 5 of these belong to the genus 
Melinaea. A good example of its appearance as a double spot is 
found in Melinaea paraiya (Fig. 48, Plate 4). It will be remem- 
