108 THE STRUCTURE OF THE FOWL 



The epidermic nature of the feathers is 

 very evident when their development is watched 

 (Fig. 53). The first indication of feather- 

 formation is an upward gro^vth of the dermis 

 or sensitive and vascular part of the skin, 

 and the consequent production of a papilla. 

 Next, the skin immediately around the papilla 

 sinks downwards as a moat - like depression, 

 so that before long the papilla comes to be 

 enclosed in a follicle in the skin. The epidermis 

 over the papilla, like that over the rest of the 

 skin, consists of two layers : — {a) a horny outer 

 layer, and (b) a deep germinative layer com- 

 posed of cells which are soft at first but finally 

 become horny. The horny outer layer of 

 epidermis forms a protective sheath for the 

 growing feather and is cast off when the 

 feather is formed. The feather itself develops 

 from the underlying germinative layer, which, 

 as it grows, forms a cylinder of cells. The 

 lower part of this cylinder embraces the dermic 

 papilla, and, retaining its cylindrical form, 

 ultimately becomes the calamus or quill : while 

 the upper part of the cylinder develops ridges, 

 these subsequently separating to form the 

 barbs of the vane. When the feather is fully 

 grown the dermic papilla upon which it has 



