[Karen W. (OP)]

Well It was just one of those  lovely Snapple facts and I am curious that if they do why is that.. Is it protection from environmental things like shielding eyes from sand or something?

How do their eyelids work?

[LeeE]

Yeah - as well as the normal upper and lower eyelids, they have a third single eyelid that's used as a sort of windscreen wiper to clear the eye of sand particles.

[Karen W. (OP)]

I kinda thought that if it was true it may have been protection from sand etc.. Very cool I have looked at pictures and seen one in life as a small child, but I did not know they had three eyelids..... I have seen huge long eyelashes...

Do you think that camels originated with this third eyelid or was it something that evolved over time due to their body having to adapt to the dry sandy environment?

[LeeE]

Many different types of animal have them (see http://en.wikipedia.org/wiki/Nictitating_membrane) , which suggests that they were a feature of a common ancestor and have subsequently been lost in those animals that now don't have them.

[Karen W. (OP)]

That is a good link! Thanks...I never knew this was so common in animals etc...  Thanks for the link!