1916] Chandler: Structure of Feathers 333 
d) Relationships 
The Cathartae show many characters in the minute feather struc- 
ture which appear to show rather close alliance with the Steganopodes, 
and in one particular, namely in the nature of the distal barbules of 
the inner vane, show an astonishing likeness to Plotus. This is a char- 
acter which could easily have arisen separately in the two groups, as 
it undoubtedly has done in other cases, e. g., the Bucerotidae, but the 
other likenesses between the Cathartae and the Steganopodes as a 
group make it more probable that Plotus and the Cathartae had a 
common ancestor. As will be shown below, the present group differs 
considerably from the Accipitres but the gap is bridged to some 
extent by the Gypogerani and Vulturidae. 
e) Summary 
The main characters of the Cathartae are as follows: 
(1) Barbules relatively widely spaced on the barb, and of large 
size. 
(2) Distals of remiges characterized by large stout base, mod- 
erate ventral teeth, heavy pennulum, and a series of progressively 
longer stout hooklets, followed by a few large, more or less appressed 
ventral cilia, the dorsal cilia being reduced to 2 stout, blunt, spine- 
like, basal ones immediately beyond which there is a conspicuous 
bend in the barbule. 
(3) Proximals with moderate base and ventral teeth, pennulum 
shorter than base, and with no cilia on either inner or outer vane. 
(4) Down barbules long and slender, with long internodes and 
very inconspicuous nodes. 
II. Suborder GyYPoGERANI 
Pl. 22, Fig. 35 
Though in general appearance the secretary birds are farther 
removed from typical Accipitres than are the American vultures, 
in feather structure they have a much closer resemblance. 
a) Gypogeranus serpentarius 
(1) Remex 
Inner vane—Distal barbules (pl. 22, fig. 35c) more or less inter- 
mediate in form between those of the other suborders of this group. 
Base and ventral teeth moderate, hooklets 5 in number, and slender 
as in Faleonidae, ventral cilia slender and rather inconspicuous, 
