278 Unwwersity of California Publications in Zoology  \Vou. 13 
structures with a very dark pigment (pl. 21, fig. 287) ; in the green 
feathers of pheasants and roosters the pennula are modified into 
spoon-shaped, flat structures with deep pigmentation, with no warp- 
ing of the individual cells, or constrictions between them (pl. 24, 
fig. 429g) ; in the peacock, green is produced by barbules which are 
conspicuously ringed or cross-ridged in both base and pennulum; 
in hummingbirds by the greatly developed flange of the bases of 
the barbules (pl. 32, fig. 88d); in trogons by smooth, curved bar- 
bules (pl. 31, fig. 8la), more or less triangular in cross-section, 
devoid of barbicels of any kind, and entirely given over to the 
production of color, the effect of tinsel being consequent upon the 
broken surface, resulting from the irregular curving of the bar- 
bules; in Nectarinia famosa by short, flattened barbules, with no 
barbicels whatever, the entire barbule very closely resembling the 
pennulum of a green duck feather; and in parrots, coraciids, ete., 
by the rami alone, in which the greatly developed dorsal ridge is 
refrangent, the tone of the color varying with the amount of black 
or brown pigment in the non-refractive barbules. Bronze is produced 
in manners very similar to those of refraction greens. 
Blue, except the slate blue of Gouwra, or bluish-gray as of herons 
and pigeons, is always a refraction color, produced in nearly all 
the same ways as 1s green, but always underlaid by a warmer brown 
pigment in accordance with the principle of selective reflection. The 
pretty light blue of Coracias affinis and some other species is pro- 
duced by a deep violet refraction color in the hexagonal cells of 
the ramus, each hexagon, or sometimes only scattered ones, being 
overlaid by a whitish film which is destroyed by scraping or by 
crushing which is insufficient to destroy the deeper refraction color. 
In the case of the hight blue, the barbules are transparent. 
Various delicate and unusual colors are produced by a combina- 
tion of structural color in the ramus with a pigment color in the 
barbules, e. ¢., in Melopsittacus, already cited, and in the blossom- 
headed parakeet, Palaeornis cyanocephalus, in which the delicate 
changeable color, ‘‘resembling the bloom of a peach’’, is the result 
of a combination of a blue refraction color in the rami, and a red 
pigment in the barbules. 
It is apparent from this that a great many different methods 
have been employed in nature in the acquisition of similar results, 
totally independent of each other, as much so as are the various 
types of wings produced in insects, reptiles, birds and mammals. 
