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1. Three distinct morphological types of cat retinal ganglion cells have been identified and categorized as α, β and γ. Alpha ganglion cells have dendritic field diameters from 180 to 1000 μm; β, about 25 to 300 μm; γ, 180 to 800 μm, possibly more. 2. The dimensions of the α and β ganglion cell dendritic fields increase monotonically from the central area outwards to the periphery; those of the γ cells do not. Seemingly a spectrum of sizes of the γ cells is found at most locations in the retina. 3. All three morphological types of ganglion cells are found in the central area. 4. Possible further anatomical types of ganglion cells are discussed. Correlations are suggested between the morphological category α cells and the physiological class Y cells; between β cells and the X cells and between the γ cells and the W cells.

Bipolar cells were studied in Golgi - Colonnier-stained whole mounts of macaque monkey retinae. A piece of retina, at 6 - 7 mm eccentricity, was particularly well stained for the analysis of the different bipolar cell types. Many midget bipolar cells were encountered and the dichotomy into flat and invaginating midget bipolars was confirmed. Six types of diffuse cone bipolar cell are distinguished. They differ in their dendritic branching pattern, in the number of cones contacted-usually between five and ten-and in the shape and branching level of their axons. The size, shape and stratification of the axons were found to be the most reliable distinguishing features for classifying diffuse cone bipolar cells. The stratification of the axons in the inner plexiform layer (IPL), whether closer to the amacrine or ganglion cells, was used to name diffuse cone bipolar cells in the order DB1 to DB6. Blue cone and rod bipolar cells were confirmed as distinct types. Axon terminals of diffuse cone bipolars were found to tile their sublamina of the IPL in a territorial manner. From this the density of each type could be estimated, and it is shown that a single cone is likely to be in contact with as many as 15 individual diffuse bipolar cells, as well as two midget bipolars. The diffuse bipolar cells observed contact all the cone pedicles in their dendritic fields. It is, therefore, unlikely that they carry a chromatic signal into the inner retina. The presence of many midget bipolar cells, which make contact with one cone pedicle only, suggests that midget bipolars provide chromatic input to ganglion cells in peripheral retina as well as in the fovea. The data show that the P- and M-cell pathways of the primate visual system are, to a significant extent, already anatomically discrete at the photoreceptor synapse.

AII-amacrine cells were characterized from Golgi-stained sections and wholemounts of the macaque monkey retina. Similar to other mammalian retinae, they are narrow-field, bistratified amacrine cells with lobular appendages in the outer half of the inner plexiform layer (IPL) and a bushy, smoother dendritic tree in the inner half. AII cells of the monkey retina were stained immunocytochemically with antibodies against the calcium-binding protein calretinin. Their retinal mosaic was elaborated, and their density distribution across the retina was measured. Convergence within the rod pathway was calculated. Electron microscopy of calretinin-immunolabelled sections was used to study the synaptic connections of the AII cells. They receive a major input from rod bipolar cells, and their output is largely onto cone bipolar cells. Thus, the rod pathway of the primate retina follows the general mammalian scheme as it is known from the cat, the rabbit, and the rat retina. The spatial sampling properties of macaque AII-amacrine cells are discussed and related to human scotopic visual acuity.

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