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The function and morphology of retinal ganglion cells in the adult mammalian visual system has been well studied, but little is known about how the adult state is achieved. To address this question, the morphological changes that retinal ganglion cells undergo during development were studied. Ganglion cells were first identified by retrograde labeling with rhodamine latex microspheres deposited in retinorecipient targets in fetal and early postnatal cats. The structure of ganglion cells was then revealed by intracellular injection of Lucifer yellow in living retinas removed and maintained in vitro. As early as 2 weeks before birth, a morphologically diverse assortment of ganglion cells is present, some of which resemble the alpha, beta, and gamma classes found in the adult. However, in contrast to the adult, developing ganglion cells exhibit several transient features, including excessive axonal and dendritic branching and exuberant somatic and dendritic spines. These morphological features indicate that there is a transient network of connectivity that could play an important role in the final determination of retinal ganglion cell form and function.

Electrical stimulation of the centrifugal fibers to the avian retina can disturb the balance between the excitatory and inhibitory system within the receptive fields of individual retinal ganglion cells. Although the mechanisms may vary from one unit to another, the effect is always to make them fire more readily and to a wider range of visual inputs.

Magnification, the relative size of the neural representation of a portion of the visual field, decreases more rapidly with increasing visual field eccentricity in striate cortex than in the retinal ganglion cell layer of the owl monkey (Aotus trivirgatus); the proportion of the cells in striate cortex devoted to central vision is much larger than the comparable proportion of retinal ganglion cells. Magnification in striate cortex is a power function of magnification in the retinal ganglion cell layer. A formula for convergence (ganglion cells to cortical neurons) follows from this relationship.

A new type of receptive field of cat retinal ganglion cells is described and termed the "suppressed-by-contrast" type. The firing rate of these cells is suppressed by a variety of visual stimuli. However, it has not been possible to find a stimulus that increases the firing rate above the maintained level.

The percentage of bipolar and amacrine synapses onto ganglion cell dendrites of the ground squirrel has been determined by electron microscopy of cells impregnated by the Golgi method. One group of ganglion cells has mainly amacrine input (approximately 97 percent); the other group has an approximately equal bipolar and amacrine input. Morphologically distinct types of ganglion cells usually have a consistent synaptic input, but exceptions may exist.

Certain ganglion cells from the central region of dark-adapted retina of the rhesus monkey respond to stimulation of both rod and cone receptors. With dim stimuli the function of these ganglion cells is determined entirely by the rods; with brighter stimuli that affect both dark-adapted rods and cones, little evidence of rod function is detectable because a cone mechanism appears to determine both the latency and frequency of ganglion-cell firing.

A new type of cell has been found in the ganglion cell layer of the retinas of dogs and humans. Its axon and its terminal branches are intraretinal. From its structure it appears that this cell might play an associational role at the level of the ganglion cells.