1916] Chandler: Structure of Feathers 383 



the down is pigmented, and grayish in color. The nodes, except in 

 such unpigmented down as that referred to above, are always con- 

 spicuous, but not strikingly larger near the base of the barbule 

 than at its tip. The shape of the nodes and length of internocles 

 varies considerably in different birds, the nodes being shaped like 

 a eucalyptus fruit in Corvus (pi. 37, fig. 115), and spaced about 

 22 per millimeter; of similar shape, but about 32 per millimeter in 

 Myiarchus ; more rounded and about the same number in Menura; 

 of Coracias type (pi. 37, fig. 110) in Cinchis; exceedingly numerous 

 and prominent in the Mniotiltidae, 35 or more per millimeter, and 

 even more numerous in some of the Fringillidae (pi. 37, fig. 114). 



d) Color Modifications 



The colors of passerine birds are produced in much the same 

 way as in the Coraciiformes. Yellow is produced either by struc- 

 ture, pigment, or both. The yellowish straw color of the head and 

 neck feathers of Paradisea apoda is due almost if not entirely to 

 structure ; the yellow of the belly feathers of Myiarchus cinerascens 

 and Tyrannus verticalis to a combination of a structural modification 

 and an underlying yellow pigment; the yellows and orange yellows 

 oi Oriolus and various species of Mniotiltidae to pigment only, dis- 

 tributed in both rami and barbules. 



Red, as far as I have observed, is always the result of pigment, 

 frequently deepened in color by the high polish of the barbs in 

 which it occurs. Dull reds, such as that on the breast of Piranga 

 ruhra are produced by pigment on both rami and barbules. The 

 fiery red crests of Tyrannus and Pyrocephalus are produced by red 

 pigment in naked rami which have diagonal lines running partly 

 across them, these representing rudimentary barbules arrested in 

 their development, and fused with the ramus. Other deep and 

 intense reds are produced by naked barbs which sometimes have no 

 structural modifications. 



The deep blue of Progne suhis is due to barbules which are 

 reduced to straight flattened bands partially overlapping each other, 

 and with refrangent surfaces, the tips always broken off, leaving 

 the ends truncate. The bright blue of the lazuli bunting, Passerina 

 amoena, is produced by refraction from naked rami. 



The brilliant red and green feathers of Nectarinia famosa are 

 worthy of special mention. The tips of the rami in these feathers 

 are naked and have a deep red color, thus giving the shining red 



