In this fish there is a well-developed light reflex. On illuminating one eye, the pupil narrows on this side only; there is no true consensual reflex. However, after cutting one optic nerve, bilateral illumination causes constriction in both pupils. Electrical stimulation of the 3rd or 4th spinal roots, or of the sympathetic chain more anteriorly, or. of the long or short ciliary nerves causes narrowing of the pupil. Stimulation of the oculomotor nerves causes dilatation of the pupil. After the animal has been killed by removal of the heart and viscera, the pupils become narrowed; they are released from this constriction by cutting the 3rd and 4th spinal roots, or the sympathetic chains anterior to these roots, or by pithing the cord. They are not released by destruction of the medulla oblongata. There is therefore a cilio-spinal centre, responsible for constriction of the pupil. After unilateral section of the 3rd and 4th spinal roots of the living animal the light reflex is no longer manifested on this side, and the eye is more protruded than the control. After section of one oculomotor nerve in the living animal the corresponding pupil narrows more readily and completely than the control. By means of local applications and injections of nicotine it has been shown that there is a synapse of the constrictor fibres in the trigeminal sympathetic ganglion and of the dilatator fibres in the ciliary ganglion. There is thus shown to be in this fish a well-developed nervous mechanism for the control of the pupil, resembling that of mammals in general plan, but with the functions of the "antagonistic" nerves reversed. The pharmacological reactions of the m. sphincter iridis of Uranoscopus resemble those of the corresponding mammalian muscle.