structural:expansion, information:classification
History

Walter Baldwin Spencer at the University of Oxford gave the first description of the pineal gland in lizards. In 1886, he described an eye-like structure, which he called the pineal eye or parietal eye, that was associated with the parietal foramen and the pineal stalk. The presence of a pineal body was already discovered by German zoologist Franz Leydig in 1872, in European lizards. Leydig called them the "frontal organ" (German stirnorgan). In 1918, Swedish zoologist Nils Holmgren described the "parietal eye" in frogs and dogfish. He discovered that the parietal eyes were made up of sensory cells similar to the cone cells of the retina, and suggested that it was a primitive light-sensor organ (photoreceptor).