The How and Why Library/Life/Animals-Section VII
VII. The Earthworm Puts on Armor
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You needn't be afraid of him, little friend Earthworm. This armored monster, with his long feelers, his stalk eyes and his great crooked arms with battle axes on the end of them!
"Worse than that," you say, "they're battle scissors!"
So they are, battle scissors. Did I say battle axes?
Well, you needn't be afraid of him, anyhow. He doesn't do half the good in the world that you do. You help make the soil that grows things to eat, while he goes swaggering around—this fierce Mr. Crawfish, and his fiercer big brother, Mr. Lobster—fussing and fighting, and tearing into pieces everything they can lay their scissors on.
We're not afraid of them, are we? "Booh, Mr. Crawfish! Booh, Mr. Lobster!" We'll show them they're only worms, after all.
Why, just look at your insides, Mr. Crawfish. You needn't try to hide them under your jointed armor. We can see right through you!
See that tube running from his stomach to the end of his tail? If that tube didn't swell out into a stomach at one end, and if it wasn't inside of such a queer, armored man-of-war, wouldn't you say he was simply an earthworm? The earthworm lives on very simple breakfast food, the earth he burrows in, and he doesn't need a big stomach to keep it in until it is digested, as the crawfish does; so he doesn't have such a stomach. The earthworm's food passes right through him and digests all the way down—tastes good all the way down, too, very likely, for he doesn't have any special tongue to taste with, either.
But the crawfish and the lobster and all their near relations, eat various things. They eat little fish, scales and all; pieces of each other, shell and all, when they get to fighting, for they are cannibals. So, having many different and very tough things to grind up and digest in their stomachs, they must have a big, strong mill to do it with. Like all fighting animals, they are large eaters. When men spent much of their time in fighting, they spent the most of the rest of it in eating strong meats and drinking strong drinks—which made them want to fight still more. And so they went from bad to worse, just as the crawfish and the lobster do, and died, at last, "with their boots on." Few of the lobsters die in their beds.See that little northeast room of the crawfish's stomach? It is not quite shut off from the main living-room. In that room are his stomach teeth. He has to have teeth to grind with, just as a hen does. But the hen, poor thing, has to use false teeth. You have seen her picking them up around the yard—little stones and bits of shell and such things, that she swallows.
The crawfish and his kind have three of these teeth in their stomachs. With these teeth they grind finer the food that they have first torn to pieces with their pincher claws.
The underside of a crawfish, showing the eyes, two long feelers, the large two-claw feet, four pairs of legs, and the tail with its fringe of little hairy feelers.
The crawfish seems to have started, as a baby, to divide his stomach into three rooms. When he gets to be a bossy cow, eating clover in the pasture, he really does divide it into four stomachs, as you know. The cow stops the food that needs the most digestion in the first stomach. The food that needs less grinding stops in the second stomach. Real fine, partly digested food, like bran-mash, goes straight through, "by express," into the third stomach. All of the food finally goes into the fourth and last stomach. The first stomach rolls the coarser food into little balls. These the cow brings up into her mouth again, and chews them over. Haven't you seen cows chewing their cuds?
In the crawfish there is a big front stomach, you see, like the first stomach of the cow, that we call the paunch. In the chicken it is the crop. Next comes the grinding mill in the northeast room, which works like the chicken's gizzard. Beyond this is the back room stomach that opens into the long, worm-like hallway that runs clear down to the tail.
This back stomach of the crawfish is lined with little things sticking out from its walls. These hold back all the food that is too large to go through. Without this "strainer," pieces of undigested food would get into Mr. Crawfish's little insides, and make him doubleall up—like a boy who has been eating green apples. Isn't it queer that the stomach of the crawfish in the creek, and of the cow in the pasture, should be so much alike? This just goes to show again that you can't judge by outside appearances alone.
The blood of the crawfish circulates very much as the blood of the earthworm does. He has two long tubes for carrying it. One of these tubes runs along his back, the other along the underside of him.
The tube at the top is a vein; the one at the bottom an artery. The vein carries the blood to his heart; the artery carries blood away from his heart. This, you know, is just what your veins and arteries do for you. You can feel the blood beating in one of your arteries by holding the thumb of one hand on the wrist of the other.
As it is much more dangerous to cut an artery than a vein, your arteries are better protected than your veins. For instance, there are veins on the back of your hand, which is always bumping into things, but you have an artery on the inside of your arm and wrist where you seldom get hurt. Mr. Crawfish seems to know he must be more careful of his artery than of his vein. Look at the picture and see where he puts his artery.
Mr. Crawfish seems to be a little careless about the way in which he carries his heart. You see, he has it away up on his back, between his shoulder blades, as it were. But, then, in changing and shifting parts in animals, Mother Nature seems to be a good deal as your mama is with the Spring house cleaning; she can't get everything into the right place at once. But Mr. Crawfish has made the four hearts that he had when he was an angle worm into one heart, and that's a very great improvement.
Now here is a curious thing; the earthworm has four hearts, the crawfish has only one. You have only one; but just look at a picture of a human heart (See Heart, Vol. II, page 853) and see how many parts it has. Four? Yes, just four!
Running along the underside of the earthworm you will notice a little white cord. It is like a thread with knots in it. This is his nervous system; his telegraph line. And the knots are the stations. In the crawfish and his family, there are two of these knotted cords running side by side, and joined together, at the points where the knots are. As Mr. Crawfish thinks mostly about eating and fighting he uses his nerves mostly to run his eating and fighting machines. So we find these little white telegraph wires running around his gullet.In his head you will find several of these nerve knots grown together. And that's little Mr. Crawfish's little brain.
Mother Nature doesn't "cross bridges" until she comes to them; that is, she takes care of the business of every day without bothering herself too much about what she is going to do a long way ahead. She's not like the little girl who got to dreaming how much money she was going to get for her eggs, and then how, by and by, she was going to sell more eggs, and so finally get enough to buy a silk dress. You know, while she was going along thinking of everything but where she was going, she tripped and fell.
And the eggs—!
Mother Nature always has her mind on her day's work. She says: "Give us this day our daily duty, and the doing of it will keep us happy and get us ready for the next duty."