In zoology, one of the paired structures certain animals use for flying. Bat and bird wings are modifications of the vertebrate forelimb. In birds, the fingers are reduced and the forearm is lengthened. The primary flight feathers propel the bird forward, and the secondaries (on the upper wing) provide lift. Bat wings consist of a membrane stretched over slender, elongated arm and hand bones. Insect wings are folds of integument (“skin”). Most insects have two pairs of wings; dipterans (flies) have only one developed pair, and beetles have two but use only one for flying. The two wings on a side usually move together, but dragonfly wings work independently.

This entry comes from Encyclopædia Britannica Concise.
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