Organ of vision. A pair of eyes is placed on the first somite ( = first cephalon somite). In most cases the eye is movably connected with the body and consists of a stalk of one or two segments, the distal of which carries the cornea. The cornea consists of the optical elements and usually is pigmented. In some species the eye is reduced, the optical elements may be few or entirely absent, and also the pigment can be absent; the eye then usually becomes small and bullet-shaped and may even become immovably fused to the body.