Evolution of the eye Early stages of eye evolution
 Eyespots are found in nearly all major animal groups. The 'Euglena's eyespot, called a 'stigma', is at the front. Its red pigment shades a collection of light sensitive crystals. Together with the leading flagellum, the eyespot allows the organism to move in response to light to assist in photosynthesis, and to predict day and night, the primary function of circadian rhythms.