. The bird, its form and function . Fig. 20.—Two interlocked barbs from the vane of a Condors wing-feather, show-ing barbules and barbicels. Magnified 25 diameters. tips of the barbs are loose and fluffy, unconnected anduseless for flight. This is the condition in all down andin the feathers of the ostrich and cassowary. We mightnaturally think that feathers stiffened by so many closerows of interlocking barbicels would be useful in manyways beside flight. But fluffy feathers are evidently justas efficient in keeping warmth in and rain out as theother kind; so Nature, economical to the most mi
. The bird, its form and function . Fig. 20.—Two interlocked barbs from the vane of a Condors wing-feather, show-ing barbules and barbicels. Magnified 25 diameters. tips of the barbs are loose and fluffy, unconnected anduseless for flight. This is the condition in all down andin the feathers of the ostrich and cassowary. We mightnaturally think that feathers stiffened by so many closerows of interlocking barbicels would be useful in manyways beside flight. But fluffy feathers are evidently justas efficient in keeping warmth in and rain out as theother kind; so Nature, economical to the most micro-scopic degree, has lessened the number of, or has neverprovided, barbules and barbicels wherever a feather isnot needed for flight or steering. Feathers 33 The two lines of barbs which grow out on each sideof the quill are very elastic and so intimately hooked toeach other that they will bend some distance before sepa-rating. If we ever tried to force our way through a. Fig. 21.—Model showing interlocking barbules and barbicels of feather,greatly enlarged. bramble of sweet-brier or blackberry-vines, we can morereadily appreciate how these barbs and the interlockingbarbules clutch each other. The thorns in the bramblecatch our clothes and, when we move, the elasticity of thelong stems tends to make them hold the tighter. We notice that one line of barbs—that along theinner curve of the quill—is much longer than that on theouter curve and we might think the air would force this 34 The Bird upward and escape beyond the edge. So it would, if itwere not for the arrangement of the feathers on the wing,which overlap like the tiles on a roof, each vane over-lying and holding down the long barbs of the featherin front, while, above and below, other shorter feathershelp to bind the whole tightly, thus enabling the bird atevery stroke to whip a wingful of air downward andbackward. A feather and its parts, like all the rest of the bird, iscomposed of cells
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbirds, bookyear1906
