When Cambarus clarkii is exposed to a source of light so that both eyes are equally illuminated, leg movements of the two sides are equal in frequency and amplitude. On covering one eye and exposing the uncovered eye to light, leg movements on the side of the uncovered eye are more frequent and are of greater amplitude than on the side of the covered eye. On covering the exposed eye also the leg movements on the two sides again tend to become equal in frequency and amplitude. When one eye is lost and the other remains functional, the leg movements on the side of the lost eye will be similar to those on the side of a normal, covered eye.