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feather
An outgrowth of the epidermis of birds. Feathers are composed of the protein keratin. They provide heat insulation and waterproofing, give the body its streamlined shape, and those of the wings and tail play a crucial role in flight.
Feathers come in a variety of forms. A typical vaned feather features a main shaft, called the rachis, to which are fused a series of branches, or barbs. The barbs themselves are also branched and form the barbules. These barbules have minute hooks called barbicels for cross-attachment.
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• ZOOLOGY
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