The retina of a painted turtle
Birds and some reptiles are known to have the most sophisticated color vision systems of any vertebrate. In the eye, light is focused onto the retina, which contains cone cells responsible for sensing color. In this retina from a painted turtle, cone cells contain oil droplets colored with carotenoids. These droplets act like tiny lenses, filtering specific colors onto cone cells. The amount of carotenoid in each droplet determines if the cone senses red, blue, green, or ultraviolet light.
Image by Dr. Joseph Corbo, Washington University in St. Louis School of Medicine.
(元記事： microscopyu.com (freshphotonsから))