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Which animals have three eyelids?

Find out which animals have three eyelids.

The camel's third eyelid is technically called a
©Jupiter Images, 2009
The camel's third eyelid is technically called a "nictitating membrane."

In many Eastern spiritual traditions, the "third eye" is a metaphysical gate into the higher realms of inner consciousness. Now, we're not saying that camels are enlightened beings, but they do have a third eyelid. It seems like that should be worth at least a few karma points.

The camel's third eyelid is technically called a "nictitating membrane," which is a thin, clear sheath that can open and close behind the outer eyelids. This is especially helpful for desert-dwelling camels, protecting them from the blowing sands of their native habitat while allowing enough light to see where they are going, almost like a pair of built-in sunglasses.

The third eyelid is a pretty cool feature, but what's even cooler is that nictitating membranes open and close horizontally, like a sliding glass door.

Actually, nictitating membranes are more common then you might think. A large number of animal species feature a third eyelid, including polar bears, beavers, and many birds and reptiles. In fact, humans once had a nictitating membrane -- if you look in the inner corners of your eyes you can still see their vestigial remains. It seems a shame, considering all the useless features evolutionary forces chose to keep for us (body hair), that we couldn't keep this one.

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