The third eyelid on a frog is called a nictitating membrane.
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
It is called a nictating membrane.
The camel has a third eyelid.
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).
Yes because it is to help the frogs see under water
No, no fish can blink because they have no eyelids. We blink to regain moisture in our eyes and wash away dirt, but they are surrounded by moisture and water, so there is no need to blink. However, the are a few that have a nictitating membrane (also called the third eyelid) that they "blink". This "third eyelid" is used to protect the eyes.
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 often called a third eyelid or haw (and may be referred to as the plica semilunaris or palpebra tertiain scientific terminology).
eyebrows
Eyelashes.