Below and back of the eyes are the gills and gill-covers. Gills are wonderful things, which serve the fish for lungs. These gills can take, or sift, out of the water, the oxygen of the air that is mixed with the water. The fish takes the water in at his mouth. Then, by a motion like swallowing, he drives it out through the gills; and the gills sift out the oxygen, as the water passes through them. Fish need that part of air called oxygen to purify their blood, just as you need it. If fish are kept in a vase where the water is not renewed, they soon die for lack of oxygen. If they are put into water which has been boiled, they die, because boiling has driven out the oxygen. Perhaps you have been told that fish breathe water, as you breathe air. That is not true. Fish breathe air, but the air must be sifted through their fine gills. When you pull a fish out of water, he pants and struggles and cannot get his breath. His fine gills stick together, and cannot do their work. So the fish chokes to death. His panting action is an effort to get air. Fish with the thinnest and finest gills, as herring, choke very soon. A carp, perch, or other fish that have gill-covers that will hold moisture, and gills that will keep wet a long time, will live one, two, or more hours in the air. Fish have inside the body an air-bladder, or bag of air. This may help them in breathing, but its chief use is to keep them up in the water. The bladder lies under the backbone. This backbone runs from the head to the tail of the fish. It is made of little pieces like cups. Each piece has two or more long spines, like ribs, on each side of it. The bony frame of a fish is very curious. You should try to have a fish skeleton to look at. There are little bones that extend from each division of the fins. You will see that the skeleton looks somewhat like the ribs or frame of a boat before the planks are put on. The bright color and gleam of the fish is in the scales. I will tell you of these later. The scales are like a rich, flexible suit of armor. Fish have cold blood, not warm like yours. They have very keen sight and smell. Probably they have good hearing, and but little sense of touch or taste. They have small brains, and not very much intelligence. LESSON XLI. OUTSIDE AND INSIDE. If I ask you what is the largest of all fish, you will say “a whale.” But let me tell you that a whale is not a fish. A whale is an animal that spends all its time _in_ the water, but cannot live constantly _under_ water. If cast ashore it will die, because it has no means of getting back into the water, and no food on the land. [Illustration: QUEER NOSES.] But whales have no gills, and they breathe air as you do. They are so made that they can, with safety, remain under water for a much longer time than you can. If a whale is kept under water too long, he drowns. So we must leave whales, nar-whales, and porpoises out of our account of fishes.