Like the Eye of Sauron, this eye never sleeps. The Red-eyed tree frog (Agalychnis callidryas) from Costa Rica has the upper part of the lower eyelid translucent, allowing the frog to see its surrounding even with the eyes closed. The eyelid carries a pattern of golden lines that obscure the normally highly visible red iris of the eye.

(This image is now available as a high quality print from my new image collection.)