278 University of California Puhlications in Zoologij [Vol.13 



structures with a very dark pigment (pi. 21, fig. 2Hi) ; in tlie 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 (pi. 24, 

 fig. 42gr) ; 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 (pi. 32, fig. S8d) ; in trogons by smooth, curved bar- 

 bules (pi. 31, fig. 81fl), 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 irregTilar 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, etc., 

 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 Goura, or bluish-gray as of herons 

 and pigeons, is always a refraction color, produced in nearly all 

 the same ways as is 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 light 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. g., in Melopsittacus, already cited, and in the blossom- 

 headed parakeet, Palaeornis cyanoceplialus, 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. 



