How far degeneracy may turn back the page of evolution is excellently illustrated in the cyclopian descendants of degenerate families elsewhere cited from Kiernan, of Chicago. While there is a seeming conflict as to the primitive eye type of vertebrates between morphologists represented by Howard Ayres[203] (who claims that the eyes were derived from the median eye of the ascidian lancelet) and Semper[204] (who is of the opinion that the existing vertebrate eyes represent the paired eyes of a hypothetical annelid precursor); still both opinions are fully reconcilable through the results of study of the ascidian and lancelet eye collated with cyclopian and triophthalmic (three-eyed) degeneracies in man, the human eye and the third eye of reptiles like the hatteria of New Zealand. The eye of the ascidian tadpole agrees fundamentally with the type of eye peculiar to the vertebrates in that the retina is derived from the wall of the brain. On this account it is called a myolonic eye. In the typical invertebrate eye, on the contrary, the retinal cells are differentiated from the external ectoderm. The ascidian eye, however, differs, as Osborn[205] remarks, essentially from the paired eyes of the craniate (skulled) vertebrates in that the lens as well as the retina is derived from the wall of the brain. The lens of the lateral eye of the vertebrates is derived by an invagination of the ectoderm, which meets and fits in the retinal cup at the end of the optic vesicle. The ascidian eye, however, agrees in respect to the origin of its lens with the parietal or pineal eye of the lizard, in which the lens is likewise derived from cells which form part of the wall of the cerebral outgrowth which gives rise to the pineal body. The pineal body is another of those remarkable rudimentary structures whose constant presence in all groups of vertebrates forms such an eminently characteristic median outgrowth from the dorsal wall of the brain (thalamencephalon), the distal extremity of which dilates into a vesicle and becomes separated from the proximal portion. The distal vesicle becomes entirely constricted off from the primary epiphysial (pineal) outgrowth of the brain, and the parietal nerve does not represent the primitive connection of the pineal eye with the roof of the brain, but arises quite independently of the proximal portion of the epiphysis.