Up to this time all investigations concerning the fusion of identical objects have been conducted with stimuli which had a simultaneous effect on the fovea of one eye and on certain surrounding areas located near the fovea of the other eye. Previously, no attempt had been made to learn how identical objects imaged on strictly peripheral disparate points of the retinas can affect the relative position of the two eyes. For an investigation of this kind a haploscope, such as Bielschowsky and Hofmann used in their fundamental work on fusion, is inadequate. One needs an instrument which permits the stimulation of any desired areas of the two retinas with identical stimuli, the relative position, size, shape and brightness of which can be controlled. An arrangement of several projection lanterns and polarizing material, which allows the dissociation of the two eyes, fulfils these conditions and has proved to be satisfactory. Two