c a B e h t n i Eyes January 1987, page 6 FF feber State College Comment, am ae —_— ome reptiles and amphibians have an eye in the back of their head, and a Weber State zoologist is trying to find out why. The question is, what is the third eye doing, and how important is it for the organism to have one?” Dr. Gloria Z. Wurst, an associate professor of zoology, said. The blue-bellied lizard has the best known third eye, but frogs and toads grow them as well. Roughly 60 percent of all reptiles have the third eye, and Dr. Wurst wonders what happened to the other 40 percent. SR “It doesn’t make sense to me that some species have enough variability in their genes to allow for third eyes, and others do not,” she said. The “eyes” are simple photo cells that detect different colors and different patterns of light. They are located on top of the head, midway between the two, more fully developed eyes. The third eye is small, and looks more like a round scale than an actual eye. “The eye is not anywhere near the size of regular eyes. It has a cornea, lens, retina and nerve, but no eye lid or tear ducts,” Dr. Wurst said. The extra eye seems to mostly measure sunlight. Lizards apparently use the eye to take weather readings from sunlight so as to know when the optimal time comes to reproduce. Another theory says that the head-top eye is used by lizards as a homing device. The reptile uses light polarization to keep an eye on the way back home. “The lizards read the polarization vectors and orient their changes with an internal clock. They know how the polarization looks at 10 a.m., and _ they. seem_to. know when it’s 2 p.m. and can adjust for the changing polarizations and know where home is at any time of the day. They cannot do that when the third eye is removed,” she said. The more pronounced the seasons the more likely lizards are to have a third eye. On the other hand, Dr. Wurst is close to half-way through background research on amphibians, and as yet has found no pattern predicting third eye development for frogs and toads, Genetically the lizards, frogs and toads have the ability to form third eyes, but various, and as yet unknown, factors either encourage or discourage the eye’s development, Dr. Wurst said. “Something seems to happen to change the development schedule,” she said. Despite what grade school children may think about their teachers Dr. Wurst said that during the evolutionary process mammals lost the ability to develop third eyes, but if humans did have a third eye it would be located in what is commonly referred to as the soft spot on the top of the head, most easily seen in newborns. “But the reason the soft spot is there is just a reflection of the way bones grow, and not because of any evolutionary mark,” she said. Dr. Wurst is currently raising a colony of 35 lizards to use as research subjects in order to see how changing development times affect third eye formation. Dr. Wurst will also soon begin similar research with tadpoles, which are much easier to observe and manipulate, she said. “If I can unlock one system from another then we will begin to see what is happening,” she said. When Dr. Wurst was young she was afraid of lizards, frogs and the like. Now she is raising a colony of lizards (top left) to see why some have third eyes and others do not. Third eyes (shown in top right photo as a white spot in the middle of the lizard’s head) show up about 60 percent of the time in lizards. ; Dr. Wurst holds one of the Egyptain lizards (bottom right) she is raising for research on third eyes. : | ; | . q :