1916] Chandler: Structure of Feathers 277 
color by reflected hght. More frequently, as in the belly of Myiarchus 
and Tyrannus verticalis, the color is a combination of yellow pig- 
ment and the same superstructure as described above. 
Orange and red, like yellow, may be produced by pigment alone, 
by a combination of red pigment and a structural modification, or 
by a structural modification with an underlying dark pigment. The 
simplest red is that produced by a diffuse red pigment in both rami 
and barbules, with no structural modification, as in Cardinalis cardi- 
nalis. A much deeper and more striking red is produced by a mere 
glazing or highly polished surface of barbules or naked barbs filled 
with red pigment, as in the deep red of Nectarinia famosa, or the 
‘“wax tips’’ of the waxwing. It is a common phenomenon for red 
feathers to be characterized by comparatively widely separated trans- 
verse ridges of one sort or another on the barbs or barbules. In 
Eudocimus ruber, Phoenicopterus ruber, and some other species, the 
barbules are inflated, possess a rather dilute red pigment, and have the 
margins of the cells conspicuously enlarged as ridges (pl. 20, fig. 26a). 
In the fiery red crest of Tyrannus verticalis the red pigmented 
barbs have similar transverse striations, produced by rudimentary 
scale-like barbules, arrested in their development, and fused with the 
ramus. In hummingbirds only, so far as I have observed, is red pro- 
duced by iridescence. In the red gorget feathers of many species of 
hummingbirds, the color is produced by the greatly developed flange, 
which is broader than the rest of the base of the barbule. and has no 
apparent striations (pl. 32, fig. 88d). The underlying color is a 
very dark olive, quite different from the fuscous brown underlying 
iridescent green or the rufous brown of iridescent blue, a phenome- 
non which may be explained by the principle of selective trans- 
mission and reflection. 
Green is produced in a very large variety of ways. In the 
Musophagidae alone there is a green pigment, turacoverdin ; in Osmo- 
treron and a few other birds, some of the feathers appear green 
from a combination of greenish yellow in the pennula, with some 
gray or blue color in the bases (pl. 29, fig. 69a). In Melopsittacus 
a delicate blue-green results from a blue refraction color in the rami, 
coupled with a greenish-yellow pigment in the barbules. In the 
vast majority of cases green is an iridescent color, and is the com- 
monest iridescent color found in birds. The variety of refrangent 
surfaces is astonishing. In the speculum feathers of ducks, for 
instance, the cells of the pennula are highly modified into flat, warped 
