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 
Trrisor, 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. Im 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 (pl. 31, fig. 81a). 
The blue-gray of Ceryle alcyon is produced, as is that of the 
gulls, by irregular distribution of black pigment (pl. 31, fig 79a). 
Blue, like green, is produced either by refraction from the rami 
accompanied by lhght 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 ease 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 (pl. 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 anas, 
the refraction is from the portion of the barbules which is not 
curved over, while in the brighter green of Hugenes fulgens, and in 
all lilac, ruby, or fiery red colors, it is from the broad, recurved 
flange (pl. 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 
