

INTEGUMENT. 



21 



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

 pocket the feather-follicle (F 9 F 1 ). 



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

 (8c, SM) extends into the base of the follicle, and thence into the 

 feather-germ (Sc\ AM 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 



FIG. 12. Six STAGES IN THE DEVELOPMENT OF THE FEATHER. 

 (Mainly after Th. Studer.) 



rv, derma ; SM, stratum Malpighii ; Se, stratum eorneum ; SM 1 , Sc 1 , extensions of 

 these tissues iota the feather-papilla, Pap ; FK, feather-germ ; F, F\ feather- 

 follicle ; P, pulp ; Fed (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) ; sec, sec, secondary rays (barbules) 

 arising from the latter ; , 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 ,long a central axis, which extend inwards towards the 

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

 Fal (SM 1 ) and HS (Sc 1 ). These folds then become cornified and 

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



