INTEGUMENT. 



deeper into the derma, and thus becomes surrounded by a sort of 

 pocket the feather-follicle (F, F 1 ). 



The horny, as well as the Malpighian layer of the epidermis 

 (fc, J/) extends into the base of the follicle, and thence into the 

 feather-germ (Sc l , &J/ 1 ), the interior of which is throughout filled 

 by cells of the derma, which give rise to the pulp (P). As the 

 feather-germ keeps on growing, the cells of the Malpighian layer 



c: 



FaliSW 



Tal/SU'l 

 HSISc 1 ) 



.'OJ -I' 



FIG. 12. Six STAOE.S ix THE DEVELOPMENT OF THE FEATHER. 

 (Mainly after Th. Studer.) 



Cti. derma ; .S.I/, stratum Malpighii : Sc, stratum corneum : SM 1 , .S'f 1 , extensions of 

 these tissues into the feather-papilla, Pop ; FK, feather-germ ; F, F 1 , feather- 

 follicle ; P, pulp ; Fal (SM 1 ), folds of the Malpighian layer extending into the 

 feather-germ, and enclosed externally by the horny layer, HS (%') : both layers 

 are seen in the transverse section (C) ; PSp, quill of feather, which breaks up 

 above into a tuft of rays or barbs (HSt) ; sec, sec, secondary rays ^barbules) 

 arising from the latter ; S, rachis ; V, vexillum. 



For further details as to the different stages A-F, compare text. 

 If one supposes that in Fig. A the papilla grows and becomes flattened and 

 bent downwards posteriorly, and that ossification occurs in the dermal portion, 

 the essential mode of development of a scale would be arrived at. 



begin to proliferate rapidly, giving rise to a series of radial folds 

 arranged along a central axis, which extend inwards towards the 

 pulp, and are immediately bounded by the horny layer (Fig. 12, C, 

 Fal (<S'J/ 1 ) and HS (& 1 ). These folds then become cornified and 

 separated from the surrounding cells, and, by a gradual drying of the 



