[The dual-nature of the retina of mammals]

Using the literary review and author's data the morphologic criterion in the distinction of cones and rods is being discussed. It is based on a distinction of the chromatin structure in the photoreceptor kernels. The rod chromatin is organized by one or a few large blocks which disguise a nucleolus. The cone chromatin is a crumbly grain. One or two nucleoli can be seen clearly. Obviously, the manner of the chromatin condensation reflects the physiological and biochemical distinctions of cones and rods. Even nocturnal or diurnal mammals have mixed double retina. These facts contradict to the Walls' theory of evolution in photoreceptors (transmutation theory) and agree to the Dollo's low. Double-natured retina is a significant condition for its plastic and private adaptation in changing of ecological conditions.