INTEGUMENT. ai 
glands near the ear in some rasores. The scales on the legs and the 
claws on the feet and occasionally on the wings, are derivatives from 
reptilian ancestors. The feathers are also derived from scales, but are 
greatly modified. 
Feathers.—There are several kinds of feathers but all may be 
grouped under three heads: hair feathers (filoplumes), down feathers 
(plumulz), and contour feathers (plume). The latter have all of the 
feather features (fig. 22) and in the typical form consist of shaft and 
vane. The basal part of the shaft is the hollow quill, in which is a 
Fic. 23.—Feather tracts of Geococcyx californianus, after Shufeldt. 
small amount of loose pith. In the region of the vane the shaft, here 
called rhachis, is solid, and running the length of its lower surface is a 
groove, the umbilicus. The vane consists of lateral branches (barbs) 
on either side, which have, in turn, smaller side branches (barbules), 
these with small hooks at their sides and tips (B). Interlocking of 
these hooks gives firmness and continuity to the whole vane. In down 
feathers the barbs arise directly from the end of the quill, and as hooks 
are lacking, the barbs do not interlock and no vane is formed. Hair 
feathers are merely long and slender shafts with no barbs, the simplest, 
if not the most primitive kind of feather. It is still a question as to 
