EXTERIOR PARTS OF BIRDS 



125 



such a substance as a solution of gelatine, and withdrawn to cool, 

 until its whole surface was covered with an even coat of that sub- 

 stance, it is clear that the gelatinous coat would be thickest at the 

 basal or anterior end of the median groove, at the median ends of 

 the lateral furrows, and at those ends of the minor grooves which 

 open into them ; while it would be very thin at the apices of the 

 median and lateral grooves, and between the ends of the minor 

 grooves. If, therefore, the hollow cone of gelatine, removed from 

 its mould, were stretched from within ; or if its thinnest parts be- 

 came weak by drying \ it would tend to give way, along the inferior 

 median line, opposite the rod-like cast of the dorsal median groove 

 and between the ends of the 



casts of the lateral furrows, , <^-': : ''1 „ r 



as well as between each of /'"' 



the minor grooves, and the / 



hollow cone would expand 

 into a flat, feather-like struc- 

 ture Avith a median shaft, as 

 a ' vane ' formed of ' barbs ' 

 and 'barbules.' In point of 

 fact, in the development of 

 a feather such a cast of the 

 dermal papilla is formed, 

 though not in gelatine, but 

 in the horny epidermic layer 

 developed upon the mould, 

 and, as this is thrust outward, 

 it opens out in the manner 

 just described. After a cer- 

 tain period of growth the 

 papilla of the feather ceases '\.'=s-r .- _^' 



to be grooved, and a continu- ■^-iiv-. , ^^ 



ous horny cylinder is formed, ^ " 



whiVh pon«titiifp« flip'rniill ' " Fia.l9.— A partly pennaceous, partly plumulaceous 



wmon OOUbUlLUUeb uue qum. feather from Ai-gus pheasant; after Nitzsch. o.d, 



(Introd. L'UiSSif. ^■In'uil. p. 71.) liia'H stem; d, calamus ; a, rhachls ; c, c, c, vanes, 



^ ' • ' ' " ■'■ ' '' cut away on left side in order not to interfere with h, 



Structure or Feathers. the after-shaft, the whole of the right vane of winch 



A perfect feather, possessing '« "kewise cut away. 



all the parts it can develop, consists of a main stem, shaft or scape (Lat. 

 scapus, a stalk ; Fig. 19, ad), and a supplementary stem or after-shaft 

 {hyporhacMs ; Gr. viz 6, hupo, under, pdxfi, rhachis, a spine or ridge; 

 Fig. 1 9, h), each bearing two webs or vanes (Lat. vexillum, pi, vexilla, 

 a banner ; Fig. 1 9, c, c, c), one on either side. The whole scape is 

 divided into two parts : one, nearest the body of the bird, the tube 

 or barrel or " quill " proper (Lat. mlanms, a reed), Avhich is a hard, 

 horny, hollow, and semi-transparent cylinder, containing a little pith 



