Did you know...
The tuatara (a lizard-like reptile from New Zealand) possesses an organ called a parietal eye on the top of its head, with a degenerate lens, cornea and retina. Though incapable of forming an image, but it can apparently detect light and dark (in young tuatara, anyway; it becomes covered over with skin and bone in the adults), and may have even functioned as a normal eye at some point in the tuatara's evolutionary history.