The camel has a third eyelid.
The third eyelid on a frog is called a nictitating membrane.
A nictitating membrane The nictitating membrane is the THIRD eyelid, the SECOND eyelid that you asked about is just that, the eyelid, just like in humans
the 3 eyelids work together to create a constant barrier against the saltwater
Nictitating Membrane
Yes because it is to help the frogs see under water
The third eyelid in the cat (and dog) is found in the lower corner of the eye on the side near the nose. It can be visualized on occasion as it may partially elevate and partially cover the eye. In birds, the third eyelid is very functional and sweeps across the entire eye. It too is located in the same spot as the cat and dog. Even humans have a third eyelid, however, it is vestigial (a small non-functional remnant).
Seeing your cat's third eyelid is a common sign of disease in cats. To answer your question, yes, it is very possible it means that your cat is sick.
It is called a nictating membrane.
Depends on how serious the tear is. This is a question for a VETERINARIAN
manatees have a third eyelid ,which is clear, to protect it from water getting into it.
the second one is. the first one is the furry one, the second one is the white one and the third is invisible