1916] Chandler: Structure of Feathers 335 



a) Buteo horealis 



(l) 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 harhules (pi. 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 booklets, 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 har- 

 hules (pi. 23, fig. 38&) with hase relatively small as compared 

 with distals, about 0.75 by 0.07 mm., with 4 or 5 short, pointed 

 ventral teeth and moderately slender pennulum, a little over half 

 as long as base. 



Outer vane. — Distal harhules much like those of inner vane, but 

 base shorter and relatively stouter, pennulum shorter, the booklets 

 usually 6 in number, and relatively longer, and no dorsal cilia. 

 Proximal harhules (pi. 23, fig. 38c) 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 booklets 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, i. e., with spaces 

 between barbules, which stand in vertical plane relative to surface 

 of barb (see plate 23, figures 41a and 415, 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. 



h) 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, 

 Archihuteo, Spizaetus, Haliaeetus, Aquila, Elanus, Falco, Pandion, 

 Polyhorus, 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 (pi. 23, fig. 36a) the pennulum is rela- 



