In 1912 Carl von Hess, Professor of Ophthalmology in Munich, published the first comprehensive monograph on color vision in animals. He concluded that fish and all invertebrates are color-blind. At the same time, Karl von Frisch demonstrated that fish and honeybees can see and distinguish colors. The theory of trichromacy (Young-Helmholtz) is valid only for primates and some (e.g., bees) but not all insects. Almost all animals can see colors, and the eyes of some invertebrates contain up to 11 types of spectrally different receptor cells. Most animals - with the exception of mammals and cephalopods - can see ultraviolet and/or far red light. Therefore, many animals perceive more colors than human beings.