LESSON XLV.
SCALES AND TEETH.
I told you that most fish had scales, and that these scales clothed them in a gleaming, flexible suit of armor. Most of the beautiful color of fish isfound upon their scales. Many of the scales are iris or rainbow hued. That is, they have the gleam of many colors, according as the light strikes them. Have you not seen such colored light in a glass prism?
The scales of different fish vary in shape, size, color, and hardness. In general, they are horny like your finger nail, but thinner. Their shape is nearly round, much like a rose petal. They are fastened by the smaller edge to the skin of the fish. Then each scale laps over the next one, and so on.
Scales are always so set that they turn or lap, from the head toward the tail. In the middle of each scale, on the lateral or side line of the fish, is a little groove or canal. It runs in the direction of a line from head to tail. Let us see what it is for.
Have you noticed how slippery fishes are? Is it not hard to hold them? If you rub your finger hard down their bodies, you rub off a quantity of slime, or stuff like glue, or thin paste. This glue-like stuff is made near the mouth of the fish. It is supplied to the scales by little tubes near the mouth. It runs through that little canal in each scale in a line upon the side of the fish.
This slimy stuff helps the fish to slide easily through the water. It keeps the scales limber and healthy.It keeps the body supple. It helps the fish to slip away from creatures that seize it. Also, I am sure, it helps the fish to slide easily down the throats of birds, animals, or fish that capture it!
The fact that the scales all lie turned from the head to the tail of the fish, also makes it easy for birds or other fish to swallow it. But if a fish is partly swallowed, it cannot be readily cast out, for its scales rising, make a rough surface, and hinder it. I suppose that was why the alwife duck I told you of could not get the partly swallowed fish out of her throat.
Each kind of fish has its own especial shape and color of scales. Some are pointed, some are rounded, some are flat, some are curved, some are three-cornered. Some fish have no scales. Some have such tiny ones that you will not notice them unless you look sharp. Some fish, as the sturgeon, have great bony plates, like large limpet shells, laid in lines up and down the body.
Fish not only have their own especial shape of scales, but their especial color, and such colors have their especial place on the fish. One flat, brown fish has all the under side of its body white, but spots of red, like sealing wax, are laid all over the brown side, as if you had dropped red wax upon it.
When you see a smoked and salted herring hung up for sale, you are not likely to guess what a beautiful thing it was, when living in its water home. It had a coat of blue, green, and silver, and gem-like eyes. The eye of a dead fish is sunken and dull. The eye of a living fish is full, and gleaming with light.
There is a little fish called a wrasse which looks as if made out of a rainbow. It is dressed in bright blue, gold, bronze, and white.
The red bream is of a fine rose-red color, with silver sides. Its luminous eyes are set in golden rings. The perch has dark, shining bands on its silver coat, and it has gay, red fins. The gray mullet is a quaker fish, trim, grave, quiet in its style, but lovely in its shape and in the rainbow lights along parts of its body.
Once I saw in the water a fish called a gurnard. He seemed to have borrowed a sunset to dress himself in. His scales were deep red and bronze. There was a vivid blue on the edges of his fins. The fins were in shape and coloring like a butterfly’s wings.
I never saw a boy who did not think that a trout was one of the prettiest things ever made. Very much of the beauty of fishes lies in the wonderful scales.
But you must examine scales for yourselves. If you have a microscope to look at them with, you will be full of delight and surprise at what you see. Once I looked through a very powerful microscope, and thought I was looking at a lump of half-melted gold set full of fine jewels. But it was the scale of a fish.
I will now leave the scales, and tell you a little about the teeth of fish. Fish have a great many teeth. Their mouths are for the most part hard and horny, and so covered with teeth that it is not likely that they have very much sense of taste. Still there are some kinds of fish that are almost, if not quite, toothless.
If you open the mouth of a sea-trout you will find that it is set entirely round, with sharp, strong teeth. Then if you stretch the mouth open and look into it, you will see that there is another row of teeth set all round a bone inside the upper jaw. Look still farther in, and you will see a row of teeth on the middle bone in the roof of the mouth. Look still beyond, and you will see a row of teeth on each side of the tongue.
Some fish, besides all these teeth, have the tongue quite covered with teeth. Others, that eat vegetables, have little fine teeth all down the sides of thethroat. The French call such teeth as these, “teeth in the velvet.” Some fish have the entire mouth and throat lined with teeth.
These teeth may all be alike, not some “double” and some “single” as you have. But sometimes fish have teeth of different patterns. The most common form of teeth in fish that live on fish or other animal food, is that of a slim cone, bent a little inward to hold firmly the fish caught, so that it cannot slip away.
The fish that feed on weeds have short, roundish teeth with a flat top, to make a good mill with which to grind or crush their food. Fish that eat insects do not need such large teeth. They have a great number of little teeth almost as fine as hairs. Rows of these teeth look like a little brush.
Some fish are said to have “mill” teeth, as the carp, because their large flat teeth roll upon each other like the stones of a mill grinding grain.
The ray fish, that feed on crabs, shell-fish, and flat fish, need very strong teeth for crushing such food. If you should look into their mouths, you would see that they are made like a mill, and the upper and under teeth roll against each other and crush fine all that is between them. By looking at the mouth of fish and examining its teeth, you canfind out what kind of food it used, just as by looking at the beak and claws of a bird, you can tell what were its habits and food.
Some fish have the inside of the stomach thick and furrowed, very like the gizzard of a fowl. This is to aid in cutting or grinding up the food. The teeth of a carp have much the appearance of the teeth of sheep and cows, only they are much smaller. They work against a plate of gristle in the roof of the mouth and reduce the food to pulp.
The strong, sharp teeth of fish are used not only for eating their food, but for biting and fighting other fish. Two great salmon have been known to fight until one was killed. The dead one was found to be badly wounded and torn by the teeth of its enemy.
Pike have very sharp, strong teeth, and a big pike has been known to seize hold of the foot or nose of a dog, fox, or other animal, that came to the water’s edge to drink.
The mouth of a dog-fish is set back on the under side of the head. This mouth has a row of strong, sharp teeth all round it. When the fish seizes its prey or its enemy with its teeth, it whirls itself over, and this action enables it to tear out a large piece of the flesh held by its teeth.