372 



ZOOLOGY 



SECT. 



B 



(C), in which also there is no interlocking of the barbs : when these 

 first appear each is covered by a horny sheath like a glove-finger. 

 Feathers, like scales, arise in the embryo from papillae of the 

 skin (Fig. 1036, A, Pap.), formed of derm with an epidermal covering. 

 The papilla becomes sunk in a sac, the feather -follicle (B, F), from 

 which it subsequently protrudes as an elongated feather-germ (FK), 

 its vascular dermal interior being the feather-pulp (P). The 

 Malpighian layer of the distal part of the feather-germ proliferates 

 in such a way as to form a number of vertical radiating ridges 

 (C, Fal (&M 1 )) : its proximal part becomes uniformly thickened, 

 and in this way is produced the rudiment of a down-feather, having 

 a number of barbs springing, at the same level, from the distal end 



of the quill. The 

 horny layer of 

 the epidermis 

 (HS (Sc 1 )) forms 

 the temporary 

 sheath which is 

 thrown off as the 

 feather grows 

 and expands. 

 The pulp of 

 the permanent 

 feather (D, F 1 ) 

 is formed from 

 the lower or deep 

 end of that of 

 the down- 

 feather, and its 

 development is 

 at first similar, 

 but, instead of 

 the ridges of the 

 Malpighian layer 

 remaining all of 



one size, two adjacent ones outgrow the rest and become the 

 rachis ; as the latter elongates it carries up with it the remaining 

 ridges, which become the barbs. 



The feathers do not spring uniformly from the whole surface of 

 the body, but from certain defined areas (Fig. 1037), the feather 

 tracts or pterylce (sp. pt., hu. pt., &c.), separated from one another 

 by featherless spaces or apteria (v. apt., &c.), from which only a few 

 filoplumes grow. The feathers are, however, long enough to cover 

 the apteria by their overlap, and the body is thus completely 

 covered with a thick, very light, and non-conducting investment. 



In the wings and tail certain special arrangements of the feathers 

 are to be distinguished. When the wing is stretched out at right 



FIG. 1037. Pterylosis of Columba livia. A, ventral ; B, dorsal. 

 al.pt. alar pteryla or wing-tract ; c.pt. cephalic pteryla or head- 

 tract ; cd.pt. caudal pteryla or tail-tract ; cr.pt. crural pteryla ; 

 cv.apt. cervical apterium or neck-space ; fm.pt. femoral pteryla ; 

 ku.pt. humeral pteryla ; lat.apt. lateral apterium ; sp.pt. spinal 

 pteryla ; v.apt. ventral apterium ; v.pt. ventral pteryla. (After 

 Nitzsch.) 



