DEVELOPMENT OF GALLUS 225 



The nestling- down feathers are carried out on the tip of 



Fig. 107. — Sections and diagrams showing the development of feathers. 



A, section through an early papilla ; F, slightly later stage in which the 

 sides of the papilla are beginning to sink beneath the surface ; C, longitudinal 

 section through a young feather in which the epidermal thickenings are 

 present, but the feather-sheath has not yet disappeared ; D, transverse 

 section of C ; E, the feather-sheath has been shed from the end of the 

 feather and the barbs are freed ; F, diagram showing the relations of the 

 rachis, barbs, and aftershaft ; G, view of an adult feather, a, aftershaft ; 

 b, barbs ; c, calamus ; e, ectoderm ; fs, feather-sheath ; iu, inferior um- 

 bilicus ; m, mesoderm ; p, papilla ; r, rachis ; su, superior umbilicus ; t, 

 ectodermal thickenings (which will give rise to the barbs) ; v, vane. 



the adult feathers, for the latter grow from the same papillae 



Q 



