670 



COMPARATIVE ANATOMY 



feathers developed from the epidermis, although there are extremely few 

 glands. Some birds, like the ostrich, possess none, though a great many 

 species have the so-called uropygial gland at the base of the tail which 

 pours out an oily secretion for dressing the feathers. In a few rasores 

 (scratching birds), there are modified sebaceous glands near the ear. The 

 scales on the legs, as well as the claws on the feet and sometimes on the 

 wings, are often said to be derived from reptilian ancestors. 



Feathers are closely related to scales. There are several kinds of 

 feathers, conveniently grouped under three heads : 



1 



Fig. 397. 



Feathers of a pigeon. A, Down feather ; B, filoplume ; C, quill feather. a.s., 

 Aftershaft ; i.u., inferior umbilicus ; qu., quill or calamus ; rch, rhachis or shaft ; 

 s.u., superior umbilicus; vex., vexillum or' vane. (After Borradaile.) 



/, II, HI. Parts of a feather. /., Four barbs (B.) bearing anterior barbules 

 (ABB.) and posterior barbules (PBB) ; II., six barbs (B.) in section showing 

 interlocking of barbules; ///., anterior barbule with barbicels (H.) (After 

 Nitzsch.) 



(1) Filoplumes (hairy feathers). 



(2) Plumulae (down feathers). 



(3) Plumae (contour feathers). 



It is the plumae that have the typical form consisting of shaft and 

 vane. (Fig- 397.) The base of the shaft is the hollow quill in which 

 a small amount of loose pith is found. The shaft or rhachis is solid, and 



