Abstract
THE retina of the pigeon has at least four kinds of cones, which can be distinguished by the oil droplets which they contain. The colours of three of these are in the visible part of the spectrum; the fourth appears colourless or slightly green1,2. These oil droplets are found in the paraboloid of the cones and can act as sharp cut-off filters that absorb practically all visible light below 600 (red), 550 (orange), 480 (yellow) and 430 (greenish) nm respectively. The four kinds of cones are not uniformly distributed across the retina and appear in different proportions in the four retinal zones (Table 1). Different pigeons have different proportions in the different quadrants, but their relative distribution is similar to the one shown here.
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