1916] Chandler: Structure of Feathers 377 



mented and almost transparent. Gentle scraping or light pressure 

 destroys the superstructure of the rami, leaving the purple hue, 

 while crushing destroys this color also and the barb appears 

 blackish. The beautiful light blues and purples of the Old World 

 kingfishers and rollers are produced in this way. 



Dull or olive-green, as in the back and breast of species of 

 Merops and Momotus, is always the result of structural color in the 

 rami and black or brown pigment color in the barbules, while 

 bright, metallic, or iridescent greens, such as that of the back of 

 Jacamerops, the breast and plumes of many trogons, the breast of 

 Irrisor, and of many other species, are the result of refraction 

 from the barbules. In Jacamerops and Irrisor it is produced by 

 the slightly modified bases of the barbules. In the trogons the 

 brilliant green is produced by barbules which are entirely meta- 

 morphosed into color-producing structures which are non-coherent 

 and do not lie flat, the result being the beautiful effect of tinsel 

 so characteristic of these birds (pi. 31, fig. 81a). 



The blue-gray of Ceryle alcyon is produced, as is that of the 

 gulls, by irregular distribution of black pigment (pi. 31, fig 79a.). 

 Blue, like green, is produced either by refraction from the rami 

 accompanied by light or dark pigment color in the barbules, or 

 by refraction from the latter. 



The brilliant iridescent gorget feathers of hummingbirds are 

 among the most interesting color-producing structures to be found. 

 In this case^ the color is produced by barbules the flanges of which 

 are very broad and recurved, being in some cases wider than the 

 portion of the feather not turned over (pi. 32, fig. 88d). These 

 barbules, like those of the back and breast feathers which are not 

 modified for the production of color, have broad pennula which lie 

 in a line on the outer edge of the vanule, parallel with the ramus, 

 and are unpigmented, and therefore inconspicuous. In the iri- 

 descent color-producing feathers, the bases of the barbules are so 

 broadened as to produce a solid vanule, i. e., without spaces between 

 the barbules. In the green and blue colors of Petasophora anais, 

 the refraction is from the portion of the barbules which is not 

 curved over, while in the brighter green of Eugenes fulgens, and in 

 all lilac, ruby, or fiery red colors, it is from the broad, recurved 

 flange (pi. 32, fig. 88d), the latter being also produced medially in 

 order to cover the ramus and meet its fellow from the opposite side. 



In hummingbirds alone are there to be found red, lilac, or ruby 



