6 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 fiat and gristly. It cannot move it, 

 scarce even taste its food with it, nor can it use it for making a 

 ncise. 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 ej^elids, and so, if it ever goes to sleep, it 

 must keep its eyes wide open. The iris is brown or red. 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 fr(jm the skuU 

 itself. These are called membrane bones because thev are 

 formed of membrane which has become bony by the deposition 



