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
Retina of the forkhead transcription factors FOXD1 and FOXG1. Additional gradients are formed within the retina that aid in proper targeting of RGC axons that function to establish the retinotopic map. The retina is stratified into distinct layers, each containing specific cell types or cellular compartments that have metabolisms with different nutritional requirements. To satisfy these requirements, the ophthalmic artery bifurcates and supplies the retina via two distinct vascular networks: the choroidal network, which supplies the choroid and the outer retina, and the retinal network, which supplies the retina's inner layer. At first glance, one may think that the vertebrate retina