After some years he was a very queer-looking fish. Finally, some men were making an embankment, and they came upon this fish-home in the roots of the tree. They took the fish out with care, and sent him to a pond. I fancy it seemed odd to him to swim at first, after being so long a prisoner. There are some kinds of fish that live and thrive in the icy-cold waters of polar seas. There are other fish that live in hot springs or ponds, where the water is so hot that you can hardly bear your hand in it. Some fish can live only in very clean water. Others live in black and muddy streams, and their flesh takes the dark hue of their home. In fact, there seem to be some kinds of fish made to suit every kind of water. This is very fortunate, as so many birds and beasts and so many people eat fish. FOOTNOTES: [31] The dolphin of the Mediterranean is of the whale family, and is not a true fish. The dolphin of the Atlantic is a true fish. The porpoise is of the whale family, not a true fish, but a mammal. LESSON XLIII. HOW THEY BEHAVE. [Illustration: ABOVE THE WAVE.] Birds, beasts, and insects live where we can easily watch them. Wherever we go, they are our near neighbors. We can easily find out many facts about their way of living. For this reason, many people, from the earliest times, have observed these creatures, and have written down what they learned about them. But of fish, people have been able to see and know much less. It has taken much longer to learn about creatures that hide in the waters, and are, for the most part, out of our sight. Seeing fish so much less often, people took less interest in them. Since great aquariums were built with glass tanks, in which fish can live at ease and behave in a natural way, we have learned more of their habits. These tanks are filled with salt or fresh water, as the fish may require. The floor of the tank is covered with sand, rock, shells. Then crabs and small “shell-fish” of many kinds, and larvæ and worms are put in, such as the fish would find in their native homes. Caves and grottos, lined with moss and weeds, are built; and the tank looks like a true part of a river, pond, or sea. Then the water is kept at the right warmth, and fresh air is driven in as I have told you. The light is made just right for the fish in the tank, and proper kinds of fish are put together. When you go and stand outside of one of these great tanks, this water world is before you from top to bottom. Now I shall tell you some of the things which I learned about how fish behave at home. By such a tank I first learned that nothing can be more easy and full of grace and majesty than the motion of a fish in the water. I watched a great fish swimming. I could not see the motion of a muscle, or the least quiver of fin or tail. His great round eyes shone; his splendid red fins were still; his spotted back glistened through the waves; his broad sides gleamed in silver mail.