1916] Chandler: Structure of Feathers 335 
a) Buteo borealis 
(1) Remiges 
Shaft about as wide as deep, quadrangular, with well-developed 
ventral groove. Vanes notched or incised on outer vanes, the rami 
of outer vane beyond point of incision as wide as shaft is deep, 
the pith more than one cell in thickness, with moderate ventral 
ridge, with villi on ventral edge. Proximal vanule with over two- 
thirds as many barbules as distal vanule, there being 28 to 30 distal 
barbules and 22 to 23 proximals per millimeter, the latter small 
relative to distals. 
Inner vane-—Distal barbules (pl. 23, fig. 38a) with long, slender 
base, about 0.38 by 0.06 mm., with relatively small, but broad and 
lobate ventral teeth; pennulum much longer than base, with 5 
slender, moderately long hooklets, which progressively increase in 
length, a well-developed series of slender, filamentous ventral cilia, 
and a series of slender dorsal cilia, the basal ones stouter and 
more spinelike, but not lobate as in the Cathartae. Proximal bar- 
bules (pl. 23, fig. 38b) with base relatively small as compared 
with distals, about 0.75 by 0.07 mm., with 4 or 5 short, poimted 
ventral teeth and moderately slender pennulum, a little over half 
as long as base. 
Outer vane—Distal barbules much like those of inner vane, but 
base shorter and relatively stouter, pennulum shorter, the hooklets 
usually 6 in number, and relatively longer, and no dorsal cilia. 
Proximal barbules (pl. 23, fig. 38¢) on terminal portion of barbs 
with a series of highly developed hooked ventral cilia, basal ones, 
representing ventral teeth, short and triangular, middle ones almost 
like hooklets of distal barbules, outer ones smaller, weak, and _fila- 
mentous. 
(2) Other Feathers 
Back feathers have structure differing from remiges chiefly in 
simplification. Barbules more slender, especially base, all the barbi- 
cels considerably reduced and vanules open, 1. e., with spaces 
between barbules, which stand in vertical plane relative to surface 
of barb (see plate 23, figures 41a and 41b, representing barbules 
from back feather of Falco rusticola). Breast feathers similar, but 
still more simplified, the bases of barbules very elongate and slender 
and all barbicels greatly reduced. 
b) Other Types 
Examination of a large number of species of different sections 
of the suborder shows that there is little variation in the form of 
the barbules. Feathers of species of Buteo, Circus, Haliastur, 
Archibuteo, Spizaetus, Haliaeétus, Aquila, Elanus, Falco, Pandion, 
Polyborus, and Gyps have been examined, and no striking devia: 
tions from the type described have been found. In the distal bar- 
bules of Falco peregrinus (pl. 23, fig. 36a) the pennulum is rela- 
