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.
Those fringes which you see when the little doors open, are the gills. They are so red because they are filled with blood; indeed, they are made of a great number of little blood-vessels. As the fish swims along with its round mouth open, it does not swallow the water, but lets it run over its gills, and then out it comes at the little doors; the red fringes take the oxygen out of the water, and it goes into the fish's blood. The water is the fishes' atmosphere, and it is only from it that they can get air to breathe; so that if the glass globe were broken, and the pretty goldfish were let fall upon the carpet, unless they were quickly put back into water they would gasp and die from want of air; just as you would, if someone held your head long under water.
So you see that the home of the fish is perfectly suited to it. In the aquarium you would observe that while most of the fishes dart hither and thither, there are some which never rise to the surface of the water. These are the flat-fish; and they keep at the bottom, because for some wise purpose God has made them without the power of rising and sinking like others.
Inside most fishes there is a bag filled with air, as is the india-rubber ball which you delight to bounce so high. The fish can make this little balloon larger or smaller, just as it wishes to be itself lighter or heavier. As it swims along, it is usually about the same weight as the water; but when it wants to dive, the fish squeezes its air-bag tightly together, which causes its body to become heavier than the water—for air pressed closely together becomes heavy, and its own weight sinks it down. When it wants to rise again to the surface, it ceases to squeeze this bag, the air in the little balloon expands, and the diver rises again and floats or swims because its body is now lighter than the water.
Is not this a very perfect and beautiful plan? How true it is that God has provided for the wants of all His creatures, and fitted them for the life designed for them!
But besides rising or sinking when they please, fishes can turn themselves about very quickly. To understand how they do this, you must look at the long bone which runs right through the body, from head to tail. You will see that it is made, like your backbone, of a number of small bones which move upon each other so easily that they enable the fish to turn itself rapidly, as you see it does. The wonderful way in which these tiny bones are fitted together by what is called the "ball and socket arrangement" may best be seen in a large fish, such as the salmon; but a sardine's frame is made in the same beautiful way.