vI FORM AND FUNCTION 147 
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 
Fic 38.—Contour Feathers of Heron. 
‘a) plume-like feather with little or no interlocking. 
6) pennaceous or perfect flight feather. 4 
B, Barb; p, Downy ends of the lower barbs ; p, dried remains of Pulp; Q, Quill; 
s, Shaft or rachis ; s 2, After-shaft ; v, Vane formed of the two webs on either side ; 
ux, Inferior umbilicus ; uv 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—zz., little barbs on either side. 
The barbules end in barbicéls—zz., still more diminu- 
tive barbs. The barbicels belonging to the barbules 
on the side of the barb that is nearer to the quill 
Te 2 
