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 in "Retina der Wirbelthiere" ("The Retina of Vertebrates"). George Wald, Haldan Keffer Hartline, and Ragnar Granit won the 1967 Nobel Prize in Physiology or Medicine for their scientific research on the retina. A recent University of Pennsylvania study calculated that the approximate bandwidth of human retinas is 8.75 megabits per second, whereas a guinea pig's retinal transfer rate is 875 kilobits per second. MacLaren & Pearson and colleagues at University College London and Moorfields Eye Hospital in London, in 2006, showed that photoreceptor cells could be transplanted successfully in the mouse retina if donor cells were at a critical developmental