LESSON XL.
THE FIN FAMILY.
I remember when I thought that no living thing was of so little interest as a fish. I used to wonder how it was that the great Agassiz began his studies in Nature with fish. I did not think that fish were even pretty.
I suppose that was because I knew nothing about them. When we are quite ignorant of a subject, we are apt to think it has no interest.
One reason why, in these Nature Readers, I am telling you something of many things is, that by knowing a little of these subjects, your interest in them may be aroused. Then you will try to learn more; and the more you know, the more you will enjoy.
IN THE COOL DEPTHS.
IN THE COOL DEPTHS.
Once, if you had asked me, “What is a fish?” I should have said, “Oh, a fish is a long thing, with scales and fins; and it lives in the water!” How many of you can tell me anything more than that? Perhaps you will add that a fish is good to eat.
Well, one day I went into a house where there was a great glass tank. It was like a glass room fullof water. As I stood looking in through the glass side of this tank, I saw, gliding through the water, a large, lovely creature, in silver and rose color. It had big black eyes, set in a golden ring.
This creature seemed to move without the least effort. It made no sound. It slid by me like the figures in a beautiful dream. It rose. It turned. It sank,—and all without seeming to exert itself in the least. I saw no effort at motion; but now and then a tremor of a forked tail, and now and then the gentle wave to and fro of a pair of gleaming, thin, silken things, like fans, half unfurled.
This, then, was a fish at home! Here was a fish living in the water, and doing as it pleased. The clear water added to its beauty. It shone like a gem. Other creatures, as beautiful, but different, lived with it. They crossed and recrossed each other’s course. They left no track. They had no path. They moved on, far more easily than a bird moves in the air, or a man on the land.
From that day I loved the fin family. Let us look at this family.
I told you that a bird is built on the plan of a boat to sail in the air. The fish, also, is built on the boat plan. He is a boat to move noton, butin, the water.
Perhaps this is not a fair way of speaking; for birds and fish were made long before men. And no doubt men built their boats on the plan of the water-birds and the fish.
The fishes vary much in shape and size. We will speak now of the ordinary fish type. We will take a model or pattern fish, such as the perch or the mackerel.
The head is sharp and wedge-shaped. It serves as the prow of the boat, to divide the water. The body is long, narrow, smooth. It has scales lapping over each other, and are all turned from the head toward the tail.
The tail is like the rudder of a boat, to direct its course. It serves also as the paddle, or propeller, to drive it through the water. There is a long slim fin on each side, just below and behind the head. These serve as balances, and, also, sometimes as oars.
There is a long fin, sometimes there are two fins, on the ridge of the back. There are also two fins on the lower line of the body. These steady the fish in the water. They help to keep it, as you would say, “right side up.” There are two more fins under the body, near the tail. What you call the tail is really a fin. The true tail is the narrow end of the body, just above this final fin.
Let us look at the head. Just on the front is the mouth. It has plenty of teeth. I shall tell you of these teeth in another lesson, when I tell you about the scales. Just above and behind the mouth are the eyes, one on each side of the head. They never have any eyelids.
Below and back of the eyes are the gills and gill-covers. Gills are wonderful things, which serve the fish for lungs. These gills can take, or sift, out of the water, the oxygen of the air that is mixed with the water.
The fish takes the water in at his mouth. Then, by a motion like swallowing, he drives it out through the gills; and the gills sift out the oxygen, as the water passes through them. Fish need that part of air called oxygen to purify their blood, just as you need it.
If fish are kept in a vase where the water is not renewed, they soon die for lack of oxygen. If they are put into water which has been boiled, they die, because boiling has driven out the oxygen.
Perhaps you have been told that fish breathe water, as you breathe air. That is not true. Fish breathe air, but the air must be sifted through their fine gills. When you pull a fish out of water, he pants and struggles and cannot get his breath. Hisfine gills stick together, and cannot do their work. So the fish chokes to death. His panting action is an effort to get air.
Fish with the thinnest and finest gills, as herring, choke very soon. A carp, perch, or other fish that have gill-covers that will hold moisture, and gills that will keep wet a long time, will live one, two, or more hours in the air.
Fish have inside the body an air-bladder, or bag of air. This may help them in breathing, but its chief use is to keep them up in the water. The bladder lies under the backbone. This backbone runs from the head to the tail of the fish. It is made of little pieces like cups. Each piece has two or more long spines, like ribs, on each side of it.
The bony frame of a fish is very curious. You should try to have a fish skeleton to look at. There are little bones that extend from each division of the fins. You will see that the skeleton looks somewhat like the ribs or frame of a boat before the planks are put on.
The bright color and gleam of the fish is in the scales. I will tell you of these later. The scales are like a rich, flexible suit of armor.
Fish have cold blood, not warm like yours. They have very keen sight and smell. Probably they havegood hearing, and but little sense of touch or taste. They have small brains, and not very much intelligence.