In summer the rivers in which it lives often dry up altogether, and the mud at the bottom is baked as hard as a brick by the rays of the sun. So, as soon as the water begins to get shallow, the animal burrows deep down into the mud, curls itself up like a fried whiting, and falls fast asleep for several months, just as hedgehogs and dormice do during the winter in cold countries. Then, when the rainy season comes and the rivers fill up again, it comes out from its retreat and swims about as before. It is from this habit that it gets its name of mud-fish. Now we come to the true fishes; and perhaps our best plan will be to read about some of the fresh-water fishes first, and afterward about some of those which live in the sea. STICKLEBACKS Let us begin with a little fish which is very common in almost every pond, but is nevertheless very curious and very interesting. When fully grown, the stickleback is about three inches long, and you can tell it at once by the sharp spines on its back, which it can raise and lower at will. It uses these spines in fighting. For the male sticklebacks, at any rate, are most quarrelsome little creatures, and for several weeks during the early part of the summer they are constantly engaged in battle. At this season of the year they are really beautiful little fishes, for the upper parts of their bodies are bright blue and the lower part rich crimson, while their heads become pale drab, and their eyes bright green! And apparently they are very jealous of one another, for two male sticklebacks in their summer dress never seem able to meet without fighting. Raising their spines, they dash at one another over and over again with the utmost fury, each doing his best to swim underneath the other and cut his body open. When one of them is beaten he evidently feels quite ashamed of himself, for he goes and hides in some dark corner where nobody can see him. And, strange to say, as soon as he loses the battle his beautiful colors begin to fade, and in a very few hours they disappear altogether. About the beginning of June, all the male sticklebacks which have not been beaten set to work to build nests. These nests are shaped like little tubs with no tops or bottoms, and they are made of tiny scraps of grass and cut reed and dead leaf, neatly woven together. As soon as they are finished the female sticklebacks lay their eggs in them. Then the males get inside, and watch over the eggs until they hatch. [Illustration: NORTH AMERICAN FOOD AND GAME FISHES] PERCHES Another very handsome fresh-water fish is the perch, which is plentiful in almost every river and lake in the warmer parts of the whole world. In color it is rich greenish brown above and yellowish white below, with from five to seven upright dark bands on either side of its body, while the upper fins are brown and the lower ones and the tail bright red.