336 University of California Publications in Zoology I Vol. 13 



tively short, but the proximals, (pi. 23, figs. 366, 36t;) almost exactly 

 as in But CO. Falco sparverius, again, has a long pennulum on 

 the distal barbules. In Haliaeetus leucocephalus the pennulum of 

 the distals is short, and the basal dorsal cilia unusually stout 

 (pi. 23, fig. 39a). The proximals (pi. 23, fig. 386) have longer 

 and more prominent ventral teeth than in Buteo. Polyhorus cheri- 

 way agrees with Haliaeetus in the small pennulum and spinelike 

 dorsal cilia of the distal barbules (pi. 23, fig. 40a). 



The structure of the feathers of Circus hudsonius was worked 

 out in detail by me (1914) ; they agree with Buteo in all important 

 details. 



In Oyps fulvus, representing the Vulturidae, the barbules of 

 the outer vane of the remiges dififer considerably from the type, as 

 shown by plate 22, figures 33c and 33(^. The distal barbules have 

 enormously developed booklets and ventral cilia, giving the barbule 

 a very unique appearance. The proximal barbules on the terminal 

 portion of the barbs do not acquire hooked cilia as in other Accip- 

 itres, but differ from those of the inner vane merely in the slight 

 proliferation of the ventral teeth, which are only partially trans- 

 formed into cilia, as shown in plate 22, figure 33(i. The back 

 feathers of this species differ from those of more typical accipitrines 

 only in the great width of the pennulum of the distal barbules 

 (pi. 22, figs. 33a, 33&). 



c) Down 



The down barbules are very variable, even within a single genus. 

 In the majority of the group, e. g., Accipiter cooperi, Pandion 

 carolinensis, Circus hudsonius, Buteo horealis, and Gyps fulvus, 

 the barbules are elongate and very slender, with very slight swell- 

 ings at the nodes, and short prongs toward the tip. In Falco, how- 

 ever, the nodes are more enlarged, not conspicuously so in F. rusti- 

 cola or F. peregrinus but strikingly so in F. sparverius where the 

 pigmentation is in deep nodular spots. As shown in plate 35, figure 

 105, the internodes are very slender and frequently wavy, the latter 

 condition being very unusual in down barbules. 



d) Relationships 



The microscopic morphology of the feathers of the Accipitres 

 presents many points which are difficult of interpretation. Admit- 

 ting their relationship with the Cathartae, which seems to be 



