. The bird, its form and function. Birds. 32 The Bird rows of barbules, and these give rise to a series of curved hooks, known as barbicels, which work into opposite series of grooves, so tightly that air cannot force its way through the feather. When the wings are pressed doAvn- ward, the phenomenon flight is made possible by the accumulated resistance which the flight-feathers offer to the air. At the lower end of our pigeon's feather, bar- bicels are present only near the quill. Therefore the. Fig. 20.—Two interlocked barbs from the vane of a Condor's wing-feather, show- ing barbules and ba
. The bird, its form and function. Birds. 32 The Bird rows of barbules, and these give rise to a series of curved hooks, known as barbicels, which work into opposite series of grooves, so tightly that air cannot force its way through the feather. When the wings are pressed doAvn- ward, the phenomenon flight is made possible by the accumulated resistance which the flight-feathers offer to the air. At the lower end of our pigeon's feather, bar- bicels are present only near the quill. Therefore the. Fig. 20.—Two interlocked barbs from the vane of a Condor's wing-feather, show- ing barbules and barbicels. Magnified diameters. tips of the barbs are loose and fluffy, unconnected and useless for flight. This is the condition in all down and in the feathers of the ostrich and cassowary. We might naturally think that feathers stiffened by so many close rows of interlocking barbicels w'ould be useful in many ways beside flight. But fluffy feathers are evidently just as efficient in keeping warmth in and rain out as the other kind; so Nature, economical to the most micro- scopic degree, has lessened the number of, or has never provided, barbules and barbicels wherever a feather is not needed for flight or Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Beebe, William, 1877-1962. New York, Holt
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbirds, bookyear1906
