The Life of the Fish § 
the lower jaw very much as a dog does. But it can move the 
upper jaw, too, a little, and that by pushing it out in a queer 
fashion, as though it were thrust out of a sheath and then drawn 
in. If we look at our dead fish, we shall see that the upper jaw 
divides in the middle and has two bones on each side. On one 
bone are rows of little teeth, while the other bone that lies behind 
it has no teeth at all. The lower jaw has little teeth like those 
of the upper jaw, and there is a patch of teeth on the roof of the 
mouth also. In some sunfishes there are three little patches, 
the vomer in the middle and the palatines on either side. 
The tongue of the fish is flat and gristly. It cannot move it, 
scarce even taste its food with it, nor can it use it for making a 
noise. The unruly member of a fish is not its tongue, but its tail. 
How the Fish Sees.—To come back to the fish’s eye again. 
We say that it has no eyelids, and so, if it ever goes to sleep, it 
must keepitseyes wide open. Theirisis brown orred. The pupil 
is round, and if we could cut open the eye we should see that the 
crystalline lens is almost a perfect sphere, much more convex than 
the lens in land animals. We shall learn that this is necessary 
for the fish to see under water. It takes a very convex lens or 
even one perfectly round to form images from rays of light 
passing through the water, because the lens is but little more 
dense than the water itself. This makes the fish near-sighted. 
He cannot see clearly anything out of water or at a distance. 
Thus he has learned that when, in water or out, he sees anything 
moving quickly it is probably something dangerous, and the 
thing for him to do is to swim away and hide as swiftly as 
possible. 
In front of the eye are the nostrils, on each side a pair of 
openings. But they lead not into tubes, but into a little cup 
lined with delicate pink tissues and the branching nerves of 
smell. The organ of smell in nearly all fishes is a closed sac, 
and the fish does not use the nostrils at all in breathing. But 
they can indicate the presence of anything in the water which is 
good to eat, and eating is about the only thing a fish cares for. 
Color of the Fish.— Behind the eye there are several bones on the 
side of the head which are more or less distinct from the skull 
itself. These are called membrane bones because they are 
formed of membrane which has become bony by the deposition 
