The visual responses have been studied, by recording with tungsten micro-electrodes, in the nucleus interlaminalis medialis, the superior colliculus, the cerebellar visual area of the cat, and the superior colliculus of the baboon. • A. THE NUCLEUS INTERLAMINALIS MEDIALIS.OF'THE L.G.N. #1. The secondary retinal representation has been determined on the cat's L.G.N., and the observation of Seneviratne and Whitteridge (1962) that the upper visual field is represented in the posterior part of the nucleus has been confirmed. In addition, the representation of the lower field has also been found in the anterior part of the nucleus. Some degree of retinotopic organization on the N.I.M. has been shown. #2. Twelve single units were observed and these had either 'on' or 'off' center with receptive fields larger than in the main nucleus. • B. THE SUPERIOR COLLICULUS OF THE CAT #1. The retinotopic organization has been described on the surface of the superior colliculus which has been flattened out and the ratio 1.5 :1 of the surface areas between the lower and the upper field quad- rants was obtained. There is a close correlation between the magnification factor and a centro- peripheral retinal ganglion cell density (Stone, 1965) along the horizontal meridian. #2. 150 units have been classified into 5 groups according to the size of the receptive fields and the optimum responses to moving stimuli (small receptive field unit, medium receptive field unit, large receptive field unit, directionally selective unit, and specific orientation unit). The majority of units responded only to movement and required different velocities as their optimum stimuli. In general, the velocity increased as the receptive field increased in size. The functional significance of units in the superior colliculus concerned with eye movement control has been discussed. #3. The influence of the visual cortex upon single units in the superior colliculus has been studied by cooling the corresponding parts of the visual cortex and the visual responses of 7 units were found to be abolished. • C. THE BABOON'S SUPERIOR COLLICULUS #1. The retinotopic projection on the surface of the superior colliculus, which has been flattened out, has been mapped. In general, the pattern of projection is similar to that in the cat, but there is no disparity between the areas of the superior colliculus devoted to the upper and lower visual field quadrants. There is evidence of macular representation on the anterior pole of the superior colliculus. The magnification factor along a horizontal meridian has been measured and a close correlation with a centro- peripheral retinal ganglion cell density was obtained. #2. Eight single units, which were similar in behaviour to those in the cat, have been observed. Apart from the non - directional units, two specific orientation units have been found. • D. THE CEREBELLAR VISUAL AREA OF THE CAT #1. The visual responses in the cerebellum have been studied by moving stimuli, and the extent of the visual responsive area is confined to the Declive (lobule VI) and Folium -Tuber vermis (lobule VII). #2. The visual responses of 104 units, which were classified into 4 groups according to the behaviour of the units in responding to moving stimuli, have also been studied. Most of the units responded to movements, usually of fast speed, and showed habituation to repeated stimuli. One type of directionally sélective unit, "the centrifugal unit", showed a preferential response to movement in a centrifugal direction (moving away from the center of fixation). The possible role of the units in the cerebellar visual area in the mechanism of eye movements has been discussed.