Tetrachromacy class eventually lose two of their four cones. The normal explanation of tetrachromacy is that the organism's retina contains four types of higher-intensity light receptor (called cone cells in vertebrates as opposed to rod cells, which are lower intensity light receptors) with different absorption spectra. This means that the animal may see wavelengths beyond those of a typical human being's eyesight, and may be able to distinguish between colors that, to a normal human, appear to be identical. Species with tetrachromatic color vision may have an unknown physiological advantage over rival species. The goldfish ("Carassius auratus auratus") and zebrafish ("Danio
Retinal precursor cells retina is generated from the precursor cells within the inner layer of the optic cup, as opposed to the retinal pigment epithelium that originate from the outer layer of the optic cup. In general, the developing retina is organized so that the least-committed precursor cells are located in the periphery of the retina, while the committed cells are located in the center of the retina. The differentiation of retinal precursor cells into the mature cell types found in the retina is coordinated in time and space by factors within the cell as well as factors in the environment of the