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 internodes 
varies considerably in different birds, the nodes being shaped like 
a eucalyptus fruit in Corvus (pl. 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 (pl. 37, fig. 110) in Cinclus; exceedingly numerous 
and prominent in the Mniotiltidae, 85 or more per millimeter, and 
even more numerous in some of the Fringillidae (pl. 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 
of 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 
rubra 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 subis is due to barbules which are 
reduced to straight flattened bands partially overiapping each other, 
and with refrangent surfaces, the tips always broken off, leaving 
the ends truncate. The bright blue of the lazuli bunting, Passerina 
amoena, 1s 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 
