The How and Why Library/Life/Animals-Section VIII
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VIII. How the Worm in Armor Counts by Twos and Threes
Like ourselves, the crawfish is divided into three main parts, but differently.
The front third of him carries his brain, his arms and legs, his eyes and feelers. The second third is his abdomen. The third part is his tail.
Look at this picture of the inside of a crawfish. Notice where his stomach, and that long earthworm intestine, are. Now, imagine where they would be and what they would look like, if the brain of the crawfish should grow and grow, until it was as large, in proportion to the rest of his body, as your brain is.
Wouldn't the stomach be crowded into the abdomen, to make room for the brain? And wouldn't that long, earthworm intestine be doubled and folded, back and forth, just as you see the intestines of human beings, in the picture in your big brother's physiology?
Section showing inside of crawfish: a, intestine; s, stomach; c, brain.
Even in the spider, which, on the outside, is so much like the lobster, the intestine instead of being one long tube, begins to be folded, because the growth of the brain crowds it into a smaller space. The spider is much "smarter" than the lobster. She (for it is the lady spider that is so "smart") has to be much cleverer than the lobster, to catch food for herself and her little ones. She must catch flying insects with a web that she must make for herself. She must do this, not only for herself but for her babies. The lobster and crawfish lay their eggs and then go away and leave them. If they had to support their families they would have to learn to bebrighter, too. We learn in doing things for ourselves; but we learn the most and the fastest when we do things for others. That's nature's way of teaching living things multiplication.
Now, notice how nature does "examples" in addition, in making plants and animals. She seems, in her counting, to be like the funny old colored man, who was set to counting sheep.
As the flock began passing through the gate, he said:
"One, two, three—dar goes anoder, dar goes anoder, dar goes anoder!"
He couldn't count above three! Nature seems to do a good deal of her counting in that way. She fits the parts of things together by ones and twos and threes. Plant and animal life begin with just one cell. The growth of a plant begins with just one shoot. Sometimes there are already two leaves on it when it comes above ground. But it always begins, either above or below ground, with a single shoot. Then come two leaves, making three parts. As it branches, each branch begins as a single shoot. It adds its leaves in the same way— in pairs, like your paired eyes and ears and nostrils, and hands and feet. After the first two leaves, come two more, making, with the shoot, five. Then two more—making seven; and so on. So the petals of most flowers are five in number. We have five senses and five fingers and five toes. The starfish eats with five fingers. Nature seems to enjoy doing things with "fives." So don't be ashamed if you still have to count on your five fingers.
Now listen to the crawfish say his addition and multiplication table:
"I have two eyes, two feelers, two claw feet. Each of these feet has two claws. I have four pairs of legs—four on each of two sides. My body is divided, as you see, into three parts. Each of these three parts is made up of seven parts; seven rings like the earthworm's, hinged together. Seven, as you see, is 1+2+2+2."
In a few members of the crawfish family, some of these seven parts have grown together. But still, even these members of the family show each of the seven rings plainly, while they are babies. There, you see, is nature's same old way of having her little ones tell the story of their grandparents. Perhaps you have read Scott's "Tales of a Grandfather." This grandfather tells the tales to the children. But in the story of the world, as we find it written in the Book of Nature, it is the children who first tell the story, if we will only look and listen very closely.Even the crawfish's legs and the spider's legs have seven joints. In those members of the crawfish and lobster family where there are fewer than seven joints, either some of these joints have grown together, or they have shrunk up, from not being used, until they don't look or act like joints at all. Sometimes we find them turned into little thread-like legs or feelers. You can see these feelers fringing the crawfish's jaw-feet, and the end of his flipper tail.
Why and how did Nature get into this way of counting by the odd numbers, I, 3, 5, 7? There is a reason given for this which you could not understand now. But you can easily understand it when you are older, if you keep on studying this wonderful Nature book which you see open all around you—in the woods, the water, the fields and the air.
This you can easily understand now: That, having begun with one part, then having added two to this one, as you see in the growing plant to keep it balanced, things must go on by adding twos if they are to grow sym-met'ri-cal-ly. That is a long word, but you should learn to use it. Look it up in a dictionary and see how much it means. In plants and animals Mother Nature, whatever else she does, always builds sym-met'ri-cal-ly.