One for the upper eye, one for the lower eye, and on like ours...covering it all. Without eyelids, their eyes would dry up. Try going for an hour without blinking. Is it not a natural instinct to blink? :)
Yes because it is to help the frogs see under water
Ur in Oms Mr Hopkins class I am creepy
The camel has a third eyelid.
The third eyelid on a frog is called a nictitating membrane.
No, frogs do not have eyelashes. A frog does have eyelids. They have both an upper and lower eyelid. The upper eyelid on the frog is a skin fold and the lower eyelid is a translucent membrane.
A cat's third eyelid becomes more visible when they are sleepy because their eye muscles relax, allowing the third eyelid to move across the eye and become more noticeable.
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
They have webbed feet,moist skin and an extra eyelid. random
Nictitating Membrane
Cats sometimes have their third eyelid showing when they are sleeping because it helps protect their eyes and keep them moist while they are resting.
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.