sJi 



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



C. 



FallSM'l 



FallSM'l 

 HSISc't 



FIG. 455&. 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 Rives rise by rapid growth to the 

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

 At D, the barbs have grown out and become free; at E, the barbules of the 

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

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

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

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

 the horny layer HS^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 (HSt); xrr-, 

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

 From Wiedersheim, mainly after Studer. 



[To face p. 523.] 



