. The structure and life of birds . our 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 sideare called barbs (B), and the barbs to right and lefttogether form the vane of the feather. The barbsgive rise to barbules—, little barbs on either barbules en
. The structure and life of birds . our 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 sideare called barbs (B), and the barbs to right and lefttogether form the vane of the feather. The barbsgive rise to barbules—, little barbs on either barbules end in barbicels—, still more diminu-tive barbs. The barbicels belonging to the barbuleson the side of the barb that is nearer to the quill L 2 148 THE STRUCTURE AND LIFE OF BIRDS chap- are smooth and hairlike, with only an occasional im-perfect hook near the edge of the vane. Those onthe further barbules end, many of them, in perfectlittle hooklets. By means of these the barbules oftwo neighbouring barbs are locked Fig. 39 (after Pycraft).To show method of and B, Barhicels running in grooves ; c, Barhule on near side of barb :on further side. Barbule If you look at a feather under the microscope, usinga not very high power, you will see that the barbuleson the distant side of the barb are not only hookedbut waved, and the smooth hairlike endings of theopposite set that meet them are neatly tucked under-neath into the hollow of the wave. It is not the case, vi FORM AND FUNCTION 149 as is sometimes stated, that the barbules themselvesinterlock. It is the hooklets that fasten one barbuleto another, and this they do in such a way that, whilekeeping a firm grip, they increase the elasticitynatural to the material of which the feather is made(Fig. 39A). The edges of the barbules, that have tobe laid hold of by the hooklets of those opposite tothem, are folded over. Below this folded edge is achannel between the two adjacent barbules that lieparallel t
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