Symmetry in a receptor mosaic demonstrated in the chick from the frequencies, spacing and arrangement of the types of retinal receptor

The mean percentages of receptors in the central retina were 14% rods, 32% double cones and 54% single cones. The mean percentages in the periphery were 33% rods, 30% double cones and 37% single cones. Single cones were classified into type I, type II and type III and the ratio of these types was about 5:2:1, respectively, in both central and peripheral retina. A statistical analysis showed that each type of receptor was evenly spaced in the receptor mosaic, but single cone type I tended to occur in pairs. The types of receptor were arranged in a pattern which was in the form of a hexagonal lattice. The pattern in the mosaic is regarded as the outcome of an evenly spaced distribution of the types of receptor. Perhaps pattern in the receptor mosaics of other vertebrate retinae should be interpreted as evenly spaced distributions of the types of receptor present. A method for detecting pattern in receptor mosaics, in which pattern is obscure, is described. A scheme accounting for the formation of the pattern in the chick retina during development is proposed.