Fio. 455o. Feather, s/i, shaft; v, vanes; A, barbule, with (be) the barbicels. 



FIG. 4556. Six stages in the development of the feather. Feathers arise in 

 pits of the dermis lined by the epidermis; at the bottom of the pit is a papilla 

 (A, Pap) the epidermal investment of which gives rise by rapid growth to the 

 feather. FK in B is the germ of the feather; C, section showing the horny layer. 

 At >, the barbs have grown out and become free: at E, the barbules of the 

 down-feather; F, the rudimentary feather; Cu, derma; SM. Malpighian layer; 

 Sc, horny layer; SM , Sc l . extensions of these tissues into the feather-papilla, 

 Pop; FK, feather-germ; F. F l . feather-follicle; P, pulp: Fal (SM 1 ), folds of the 

 Malpighian layer extending into the feather-germ, and enclosed externally by 

 the horny layer H^Sc 1 ); both layers are seen in the transverse section (C); FSp, 

 quill of feather, which breaks up above into a tuft of rays or barbs (HKty. sec, 

 sec, secondary rays (barbules) arising from the latter; R, rachis; V, vexillum. 

 Prom Wiedershei'm, mainly after Studer. 



[To face p. 523.] 



