1916] Chandler: Structure of Feathers 277 



color by reflected light. More frequently, as in the belly of Myiarchus 

 and Tyr annus 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 ruher, 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 (pi. 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 fiange, 

 which is broader than the rest of the base of the barbule. and has no 

 apparent striations (pi. 32, fig. 88(^). 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 (pi. 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 



