12 EMBEYOLOGY OF THE LOWEE VEETEBEATES ch. 



ment— the unincised basal portion forming the quill of the feather. 

 The horny sheath becomes strongly cornilied and then breaks open 

 and the longitudinal thickenings of the epidermis, now also strongly 

 cornified, break- away from the sparse cornified dermal tissue of the 

 axis and form the fluffy barbs of the down feather. 



In the basal quill portion of the feather the epidermis immedi- 



Fig. 42. — Illustrating the development of feathers. (After Davies, 1889.) 



A, B, C, longitudinal sections'; D, E, F, transverse sections (D, E, down feather ; F, flight feather) ; 

 G, longitudinal section through barb rudiment showing developing harbules ; H, longitudinal section 

 through base of feather, b, barb ; 66, barbule ; o, horny septa ; c.e, layer of cylindrical epithelium ; 

 /, feather rudiment ; g, germinal region ; p, pulp ; q, quill ; r, rachis ; s?t, sheath. 



ately covering the outer end of the axial dermal tissue or pulp forms 

 a thin strongly cornified superficial layer which separates off as a 

 septum cutting across the cavity of the quill. This process being 

 repeated periodically gives rise to a series of horny caps fitting one 

 over the other, in the interior of the quill (Fig. 42, H, c). 



The flat feathers, found as contour feathers arranged in patches 

 over the general surface and as Eemiges and Eectrices in the wings 



