VI 



FORM AND FUNCTION 



'47 



When the quill is dry and hollow, the feather is 

 in most ways a dead thing, but the fact that in 

 some birds there is a change of colour without a 

 moult, and without the loss of any part of the feather, 

 shows that it has not entirely lost life. The stiff rod 

 above the quill is the rachis or shaft (S). It is grooved 



-v$^§ 



^D 



Fig 38. — Contour Feathers of Heron. 



(a) plume-like feather with little or no interlocking. 



(b) pennaceous or perfect flight feather. 



B, Barb ; d, Downy ends of the lower barbs ; p, dried remains of Pulp ; Q, Quill ; 



s, Shaft or rachis ; s ?, After-shaft ; v, Vane formed of the two webs on either side ; 



u 1, Inferior umbilicus ; u 2, Superior umbilicus. 



down the under-surface. The branches on either side 

 are called barbs (B), and the barbs to right and left 

 together form the vane of the feather. The barbs 

 give rise to barbules — i.e., little barbs on either side. 

 The barbules end in barbicels— i.e., still more diminu- 

 tive barbs. The barbicels belonging to the barbules 

 on the side of the barb that is nearer to the quill 



L 2 



