Feather
Collier's New Encyclopedia (1921)
a plume or quill, one of the dermal growths, multitudes of which constitute the covering of a bird. A feather is homologous with a hair from the skin of a mammal, and some of the inferior birds have imperfect feathers suggestive of hairs only. A feather consists (a) of a central shaft, which is tubular at the base. This is inserted in the skin like a plant in the earth, living and growing. (b) Of a web on either side, that on one side being often developed more than on the other other. This web oped is composed of a series of regularly arranged fibers, called barbs. In some cases, of a small supplementary shaft with barbs, called the plumule-i. e., the little plume. Feathers are of two kinds, quills on the wings and tail, and plumes generally diffused. The primary feathers rise from the bone corresponding to the hand in mammals; the secondary feathers from the distal end of the forearm; and the tertiary feathers from the proximal end of the forearm. The feathers are renewed once or twice a year; the bird is languid during the process, but, when fresh plumage is obtained, renews its youth in vigor as well as in beauty. The beard and quill of feathers have essentially the same composition, about 52.5 per cent carbon, 7.2 hydrogen, 17.9 nitrogen, and 22.4 oxygen and sulphur. Feathers owe their permanent color to peculiar pigments, of which the red, green, lilac, and yellow are soluble in alcohol and ether. Black feathers contain a pigment insoluble in alcohol and ether, but soluble in ammonia.
What Has Changed in the Last Century
Collier's in 1921 called a feather "homologous with a hair from the skin of a mammal" — a comparison now abandoned; feathers and hair arose independently, and feathers are today traced to the skin appendages of archosaurs. The great shift came from the Chinese fossil beds of Liaoning, where from 1996 onward Sinosauropteryx and dozens of other dinosaurs were found with filaments and true vaned feathers, showing that feathers long predate flight and probably began as insulation or display. Collier's also attributed all feather colour to pigments; the blues and iridescent greens of birds are in fact structural, produced by nanoscale architecture in the barbs, while the pigment granules themselves — melanosomes — have since 2010 been used to reconstruct the plumage colours of extinct dinosaurs such as Anchiornis. The account of shaft, barbs, primaries and secondaries, however, remains accurate.
Written for this edition, 2026.