. A book of birds. Birds. INTRODUCTORY 15 so difficult to pull the barbs of a feather apart. In the vane of a Crane's quill, in a piece of web 15 inches long, no less than 650 of these barbs were counted, each of which bore about 600 pairs of barbules—that is, about 800,000 for the inner web alone, and more than a million for the whole feather : and all these are necessary to hold the vane together. This system of interlocking is most perfect in the wing and tail quills. In some feathers, such as have a loose, hairy texture, as in the body feathers of many birds, these hooklets are but feebly,
. A book of birds. Birds. INTRODUCTORY 15 so difficult to pull the barbs of a feather apart. In the vane of a Crane's quill, in a piece of web 15 inches long, no less than 650 of these barbs were counted, each of which bore about 600 pairs of barbules—that is, about 800,000 for the inner web alone, and more than a million for the whole feather : and all these are necessary to hold the vane together. This system of interlocking is most perfect in the wing and tail quills. In some feathers, such as have a loose, hairy texture, as in the body feathers of many birds, these hooklets are but feebly, if at all, developed. The loose feathers of the Ostrich tribe also lack them, but here they were once all perfectly developed ; when the R. / p. Fig. 6.—Section through two rows parallel to the Distal Radii or Barbules. (After Pycraft.) Distal Radii; Proximal Radii or Barbules. birds ceased to fly, the feathers degenerated, and the interlocking was lost. What are known as semi-plumous feathers are degenerate feathers. Down feathers differ considerably from *' contour feathers " in structure, having little or no shaft, all the barbs arising from a common base. These barbs are, further, very long, and have only very minute barbules. In the Ducks and some other birds these barbules take the form of triangular nodules ; while in other birds again they are knot-like. The iilo-plumes have a long, slender shaft with a minute vane at the tip. They are, apparently, a degenerate form of contour feather, judging from the fact that during the earlier part of their development many more barbs are present than are to be found in the fully grown 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 Pycraft, William Playne. London, Sidney Appleton
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbirds, bookyear1908
