Some time ago I went to an aquarium; it was close to the sea, so that there was no want of water to fill the tanks. At the bottom there was sand, and there were bits of rock, among which brown and green seaweeds were growing, in order that the prisoners might forget that they were shut up in a glass prison-house, and feel as much at home as possible in their captivity. There they were, big fish and little fish, flat plaice and long serpent-like eels--fish of all sorts, of all shapes and sizes. There were other creatures as well as fish; lobsters and crabs and star-fishes; and the anemones, which "blow flower-like," and have such lovely colours that they are sometimes called "sea-roses," were waving their bright fringes to and fro, and catching the shrimps for their dinner with those same soft fingers of theirs. I should like you to see an aquarium such as this was; but if you cannot just now, I daresay you may have the chance of watching a gold-fish in a globe of water, and noticing how it uses its fins to balance itself and steer its way through the water, and its tail to move itself along so gracefully and swiftly; how it has two pairs of fins, which serve for legs and arms, besides three others, the use of which you cannot so well make out; and how the boat-like shape of the fish helps it to cut its way so rapidly through the water. If you keep drilled those two bright eyes over which God has made you officer, you will notice something near the fish's eye which keeps opening and shutting like a little door. That little door covers the gills, and it opens and shuts every time the fish breathes. But now comes a question which used to puzzle me--that is, What does a fish breathe? [Illustration: A CRYSTAL-WALLED PRISON] When I heard, long ago, that fishes cannot breathe if they are taken out of the water, I used to think that they breathed the water; for then I knew no better than the boy who, when he had at last caught a minnow, put it into a bottle with plenty of water, and corked it up tight, in order to keep his prize safely. Of course the poor little fish was dead before he got home. It died, not from want of water, but from want of air; for fishes draw in and send out the air through their gills, which are to them what your lungs are to you.