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.
The hydra—all stomach and arms.
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.
One of the arms of the hydra magnified.
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.