The organization of inputs establishes two functional and morphologically identifiable classes of ganglion cells in the retina of the turtle.

Analyses of the photoresponses and morphologies of ganglion cells in the turtle retina suggests that these cells are of two types: type A ganglion cells receive predominantly bipolar inputs, while type B ganglion cells receive a mixture of inputs from bipolar and amacrine cells. According to these classification criteria, ganglion cells may reflect either activities of the outer or of the inner plexiform layer, respectively. To corroborate the validity of this classification a number of basic properties of ganglion cells were analysed. It was found that double colour opponency was characteristic of type A cells and directional selectivity was performed only by type B cells. In addition, the absolute sensitivity and the firing rate of type A cells were significantly higher than those of type B cells.