CHAPTER XX.

THE VARIETY OF MACHINERY IN ANIMALS.

You have seen what a variety of curious machinery there is in our bodies for our minds to work, besides that which is needed to keep the body in repair. But I have told you some things about other animals as I have gone along. There is in them also a great deal of machinery, and it is different in each. The variety of it is wonderful. You see that the world is every where full of many kinds of animals, making it a very busy world. I do not believe that you have ever thought how different they are from each other. I will therefore tell you a little about this.

[Sidenote: Machinery in the oyster suited to its wants.]

See what a difference there is between man and some animals. Look at the oyster. He lives in the water, shut up in his rough shell. He is no traveler. He has no eyes to see sights with. He has no sense of smell. He has taste for his food, and, no doubt, enjoys it. He has the sense of touch; this he needs, both to manage his food and to guard himself against harm. As he does not move about, and has no feet or hands, he has but few muscles. He has one to shut up his shell tight, which he does when he is alarmed. His brain and nerves are very small affairs, for he has little use for such things.

There is little machinery, then, in an oyster, as you compare it with the machinery in your body; and it is simply because he does not need so much as you do. If he had needed more, God would have given it to him. But there is, after all, considerable machinery even in the oyster. He has machinery for digesting his food. He has circulating machinery--a heart with its arteries and veins. And he has gills like fishes, by which his blood is aired by the air in the water. Then he has a few muscles, some nerves, and a sort of brain.

[Sidenote: The hydra--all stomach and arms.]

[Sidenote: How it acts when alarmed.]

Look, now, at another animal that has less contrivances in him than the oyster. Look at the hydra. This is a very little animal which is found in ponds, sticking to a straw or stick by a sort of sucker. Here is a representation of it. The small figure shows it of its natural size. The larger figure shows it as magnified by the microscope. This animal is little else than a stomach with long arms. We can turn the body of it--that is, the stomach, inside out, and the animal will do as well as before. The arms are merely to catch things, as worms and insects, which they put into the mouth of the stomach, marked _a_. One of the arms is represented as having caught something, which it is about to put into this mouth. When the little creature is alarmed, he gathers up all his arms around his stomach, and looks like a little ball. No brain has ever been discovered in him, but it is plain that he thinks some in catching his food, and in gathering himself into a ball to escape notice. He probably has a brain to think with, though it is so small that it is not to be seen with the most powerful microscope.

[Sidenote: One of the arms of the hydra magnified.]

[Sidenote: Contrivances in animals endless.]

Here is one of the arms of this animal as seen with a powerful microscope. It is made up of little cells or bladder-like things. How it is that these make the different motions of this arm we do not know.

The two animals that I have just told you about are very unlike to man, but they are not more so than a multitude of others. The variety in the shapes of animals and in the arrangements of their different parts is almost endless; but, with all this variety, all are alike in some things. All have organs to digest their food with, and organs to circulate their blood. All have brains to think with, and nerves to use in finding out about what is around them, and in making their muscles work.

The variety in the contrivances in animals is so great, that when one undertakes to study them, he continually finds something new. And one thing is always true of the machinery in animals--it is perfect. It is always exactly fitted to do just what it is made for. No machinery that man ever made is equal to it.

Animals are suited in their shapes and arrangements to the way in which they live. Some are made to fly. These have wings; and the wings exhibit great variety, as you see if you look at the birds and insects that are so busy in the air. Some animals are made to live in the water; most of these have a broad tail and fins to swim with, but some crawl, as the crab. Some float about, like the hydra, and some lie still, like the oyster.

[Sidenote: How different animals move.]

Some animals walk about on the ground. Man is the only animal that walks about erect upon two feet. The beasts, you know, are four-footed. The monkey is one of the most singular of beasts: he has neither feet nor hands, but some things which are like both. With these he is more of a climber than a walker. There are many small animals that walk on many feet. And the snakes, without any feet, crawl along the ground. Some animals hop, as the frog and toad. Some go by a long jump, as the grasshopper, and the troublesome little flea, which is here represented as magnified by the microscope. Very strong muscles must this animal have to enable it to make such leaps with its long, crooked legs.

There is great variety in the coverings of animals. But I will tell you about these in another chapter.

[Sidenote: The organs of some animals like those of man.]

Some animals are much more like man than others. The bones, and muscles, and nerves, and heart, and brain of some are very much like the same things in our bodies. This is true of many of the four-footed animals. You can therefore know how the parts of the machinery inside of you look by observing the different parts of animals at the meat-market. In a calf’s head you can see how your brain looks. Its lungs, or lights, as they are commonly called, are very much like yours, and its heart is quite like your heart. And so of other parts.

[Sidenote: Variety of motion in man.]

[Sidenote: Has more muscles than any other animal.]

The more an animal moves, the more muscles he has to make his motions with. Man has more variety of motion than any other animal, and so has more muscles. God gives to each animal just the machinery that it needs. Some have machinery that others do not have. Some have very little, while others have a great deal. In our bodies there is a great variety of machinery, for our busy minds want to know and to do very many things.

The mind of man does more things with the hand than with any other part of its machinery. I shall therefore now go on to tell you about the hand, and then about those things that, in different animals, answer somewhat in place of hands.

_Questions._--What is said about the variety of machinery in the bodies of animals? What senses has the oyster? Why does he have these? What is said of his muscles? What of his brain and nerves? Why has not the oyster as much machinery in his body as there is in yours? What machinery has he? Tell all about the hydra. What is said about his brain? What are his arms made of? In what things are all animals alike? How does the machinery in animals compare with that made by man? What are the shapes and machinery of animals suited to? Tell about animals that fly--those that live in the water--those that walk. What is said about man? What is said about the monkey? Mention some animals that hop--some that make a long jump--those that crawl without feet. What animals are much like man, and in what? Why is there so great a variety of machinery in our bodies? What part of the machinery do our minds use most?