Analogs in Other Species
Crustaceans have a single eye atop of the head as a nauplius (first stage larva). This eye has a lens and senses direction of light but cannot see images. Later, more sophisticated segmented eyes develop on sides of the head but the initial eye stays for some time. Hence it is possible to say that at some stage of development crustaceans have the "third eye" as well. Some species like Artemia salina, the brine shrimp, retain the primary eye, being three-eyed in the adult stage.
Many arthropods have simple eyes, frequently between the main eyes, called ocelli.
Read more about this topic: Parietal Eye
Famous quotes containing the word species:
“Prohibition will work great injury to the cause of temperance. It is a species of intemperance within itself, for it goes beyond the bounds of reason in that it attempts to control a man’s appetite by legislation, and makes a crime out of things that are not crimes. A Prohibition law strikes a blow at the very principles upon which our government was founded.”
—Abraham Lincoln (1809–1865)