"Here it is. Now look at these long slits, just behind the jaws. Lift up one of them, and inside you will see the red gills. The gills are the lungs ofthe fish, for fishes have no lungs such as we have. Fishes cannot live without breathing air any more than we can. We breathe by means of lungs, the fish by means of gills.""But I can"t see how a fish can breathe air," said Norah, "while it is living and moving about in the water.""Ah," said Fred, "that is the wonderful part of it. You remember that water is porous, and that it absorbs air. Water, in fact, always contains air. The fish lives by robbing the water of some of the air, which it breathes in through its gills.
"If you notice a fish swimming in the water, you will see that it is constantly opening and shutting its mouth, as if it were drinking. It is not drinking. It takes the water into its mouth, but only to pass it backwards over the gills, and so out again through the slits at the sides.
"Teacher explained what all this means. He pointed out the redness of the gills, and he told us that, if our eyes were sharp enough, we should find these gills crowded with tiny blood-vessels. It is the blood in these vessels which gives the gills their red color.
