A small constellation north of Aquila; the Arrow.

The distance from a point in a curve to the chord; also, the versed sine of an arc; -- so called from its resemblance to an arrow resting on the bow and string.

a small constellation in the northern hemisphere between Cygnus and Aquila and crossed by the Milky Way

A genus of transparent, free-swimming marine worms having lateral and caudal fins, and capable of swimming rapidly. It is the type of the class Chætognatha.

any arrowworm of the genus Sagitta

The keystone of an arch.

the radius minus the apothem

The vertical depth of the curve of a spherical mirror. Lay your mirror on its back. Carefully lay a ruler across its diameter. The distance, at the center of the mirror, from the ruler to the mirror surface is the sagitta.

See vertex depth.

The larger of the two otoliths, or ear bones, found in most fishes.