BRAIN DUMP
Jun 11, 2020
3 minutes
Why do some animals have a third eyelid?
Alec Bruce
■ Birds, reptiles and some mammals have an extra eyelid to protect the eye from dust and dryness. Its technical name is the nictitating membrane. It has its own gland that generates up to half the tears an animal’s eye needs. This is particularly important for birds to keep their vision sharp when flying high up. Unlike our eyelids, this secret bonus lid is translucent and sweeps left and right like windscreen wipers. AG
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