A comparative study of the area of acute vision in vertebrates

who has found a fovea in the cat.Gamer (19) and Chievitz (31) have found only an area.Chievitz has described and pictured the area and fovea centralis in many animals, and put his results in a concise tabulated form.Other investigators of this period will be mentioned later in a similar tabulation.Many obscure points were made clear by these numerous investigators.However, two points still remained unsolved : the structure of the molecular layers and the endings of the fine branches of the retinal cells.The solution of these points depended on a new method of research.This new method was inaugurated by Tartuferi (21) in 1887, who used the quick method of GoIgi and succeeded in showing that the cell processes end in more or less fine tufts which did not anastomose with other bunches.Later on he discovered and described the structure of the molecular layers.Dogie1 ( 2 2 ) in 1888 so modified the Ehrlich method that it would stain the fresh retina.He was thus able to confirm almost all the results of Tartuferi.He found that the branches from different cells anastomose, but other investigators have not confirmed this.The works of Baquis (23) and Ramon y Cajal (24), who used the Golgi method, in general confirm the results previously obtained.Ramon y Cajal has made clear the endings of the rod and cone fibres in the outer molecular layer.He finds that there are certain cells of the inner nuclear layer which are related to the cones.That is, their terminal branches come in contact only with the processes from the cones, while other cells of this layer send their dendrites to the rods.In general, each cell communicates with many rods or cones, excepting in the fovea, where the process from each cell branches very little and comes in contact with but one cone.METHODS.