220 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



areas Avhicli surround it ; for example, while the middle yellow is 

 rufous in color in only 14 species, the inner 3'ellow is rufous in 56; 

 also the inner yellow area, being usualh' smaller and less conspicuous 

 than the middle yellow, is less important in cases of mimicry, and 

 the diagi-am P^ig. 98, Plate 9, shows that it is much more variahle 

 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-variations displayed hy each of these two areas, 

 and as there are 400 species of the Danaoid Heliconidae recorded 

 b}' me, it becomes evident that, if there irere no color preferences 

 displayed by these areas, there would probably be about aoo.^ 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. Xow 

 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, Avhich 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 intei*esting, 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 j^hysiological 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- 

 ation s.- 



1 This is not true for one color, white. 



- 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 

 <mly VI 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 chemicaUy. 



