384 



ZOOLOGY 



SECT. 



Tlie papilla becomes sunk in a sac, the fmther-foUidr (B, F), from 

 which it subsequently protrudes as an elongated feathcr-fiei^m 

 (F K), its vascular dermal interior being the feathcr-'pvlp (P). 

 The Malpighian layer of the distal part of the feather-germ pro- 

 liferates ill such a way as to form a number of vortical radiating 

 ridges (C, Fal SM') : 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 (H S (sc)) forms 

 the temporary sheath which is thrown off as the feather grows and 

 expands. The pulp of the permanent feather (D, i^) is formed 



B 

 sp.pt ^ / j ^ \ hupt 



cdpt 



Fir; 1026.— Pterylosis of Columba livia. A, ventral ; B, dor.s.al. al. pt. alar pteryla t)r wing- 

 tract ; c.j)<. cephalic i>teryUi nr liead-tnict ; erf. ^ji. caudal pteryla or tail-tract; cr. p^ cniml 

 pteryla ; cr. apt. cervical "apterium or neck-space ; j'M.pt. femoral pteryla ; hu. id. humeral 

 pteryla; lat.apt. lateral apterium; xp.pt. STpin&l pteryla; v. apt. ventral apterium; v.pt. 

 ventral pteryla. (After Xitszch.) 



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 out- 

 grow 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 1026), the feather 

 tracts ox 'pteryla'. (sp.jjt., liu. ft., &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. 



