Do you know why fishes cannot live on land? The answer to this question is very curious.
Every living thing, a man, animal or fish, must have air or die. But when the fish comes out of the water, where there is very little air, into the air, it dies for lack of air. It dies on land for lack of air, just as a man may be drowned in the water.
But why cannot the fish breathe the air when you put it on earth? Why must it die for lack of air when there is plenty of air around?
In order to breathe air one must have lungs or something like lungs, and the fish has no lungs. In order to get the air which is dissolved in water one must have something quite different from lungs, which is called gills. The fish has no lungs, but only gills. We have no gills, but only lungs. Therefore we die in the water, and the fish dies out of it.
If an animal had both gills and lungs, then it would be able to get air from the air or to get the air which is in the water; and it could live both on the land and in the water.
... if fishes close their eyes and sleep underwater? Every living thing has its time of rest. Even microbes rest, and plants, and, of course, fishes.
But fishes do not close their eyes when they sleep. Why? Because they have nothing to close their eyes with; they have no eyelids.
Not only fishes have no eyelids. If you look at the snakes in the Zoo for a minute or two, you will notice that their eyes are always wide open, though they are sleeping. This is because the snakes, like the fishes, have no eyelids.
