Measurements of the pupillary light reflexes, in a pure strain of mice which never develop rods in the retina, showed that the iris under photo-stimulation dilates and contracts independently of the functional capacity of the retina. (The author had previously satisfied himself from a detailed series of behavior experiments that these animals were completely devoid of vision.) In these rodless mice, a longer time than in the normal was required for the response of the iris to light of the same intensity, and the actual degree of contraction was less than normal. The author believes that these experiments prove that in mammals the iris may function independently of vision.