The little fish, from the time they are out of the egg, until they are about half grown, are called fry. Some fish, as the salmon, get different names at different periods of their growth. A great many fish together are called a school. Thousands of fish will come leaping, rolling, and tumbling along in the water, and we say it is a school of fish. FOOTNOTES: [33] Nature Reader, No. 1, Lesson 3. LESSON XLV. SCALES AND TEETH. I told you that most fish had scales, and that these scales clothed them in a gleaming, flexible suit of armor. Most of the beautiful color of fish is found upon their scales. Many of the scales are iris or rainbow hued. That is, they have the gleam of many colors, according as the light strikes them. Have you not seen such colored light in a glass prism? The scales of different fish vary in shape, size, color, and hardness. In general, they are horny like your finger nail, but thinner. Their shape is nearly round, much like a rose petal. They are fastened by the smaller edge to the skin of the fish. Then each scale laps over the next one, and so on. Scales are always so set that they turn or lap, from the head toward the tail. In the middle of each scale, on the lateral or side line of the fish, is a little groove or canal. It runs in the direction of a line from head to tail. Let us see what it is for. Have you noticed how slippery fishes are? Is it not hard to hold them? If you rub your finger hard down their bodies, you rub off a quantity of slime, or stuff like glue, or thin paste. This glue-like stuff is made near the mouth of the fish. It is supplied to the scales by little tubes near the mouth. It runs through that little canal in each scale in a line upon the side of the fish. This slimy stuff helps the fish to slide easily through the water. It keeps the scales limber and healthy. It keeps the body supple. It helps the fish to slip away from creatures that seize it. Also, I am sure, it helps the fish to slide easily down the throats of birds, animals, or fish that capture it! The fact that the scales all lie turned from the head to the tail of the fish, also makes it easy for birds or other fish to swallow it. But if a fish is partly swallowed, it cannot be readily cast out, for its scales rising, make a rough surface, and hinder it. I suppose that was why the alwife duck I told you of could not get the partly swallowed fish out of her throat. Each kind of fish has its own especial shape and color of scales. Some are pointed, some are rounded, some are flat, some are curved, some are three-cornered. Some fish have no scales. Some have such tiny ones that you will not notice them unless you look sharp. Some fish, as the sturgeon, have great bony plates, like large limpet shells, laid in lines up and down the body.