Abstract
The relative proportion of rods and cones (single and double) in the chicken retina was determined by counting these elements in each of nine pre-determined segments prepared as periodic acid-Schiff serial sections for rod (hyperboloid glycogen) and double cone (accessory cone paraboloid glycogen) identifications and as unfixed, flat preparations for cone determinations (colored oil droplets). Periodic acid-Schiff preparations revealed that rods and accessory cones were equal in number in all retinal segments except those located directly posterior to the posterior extremity of the pecten where the double cones out-numbered the rods in a ratio of 14 : 10. On the basis of oil-droplet pigmentation, double cones housing a golden-yellow droplet in their chief component and a small yellowish-green droplet in their accessory members were constantly observed to be twice as numerous as single cones (red droplet) in all retinal segments. These data reveal that the proportion of rods to double and single cones is 2 : 2 : 1, respectively, in all areas of the chicken retina except a posterior (lateral) segment where the ratio is 10 : 14 : 7. This area of greater cone concentration corresponds to the site of the temporal fovea of some birds and may represent the area of most acute vision in the fovea-free chicken retina.
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