it, surrounds it, and gradually that morsel has passed inside the amoeba. There by degrees it grows smaller, fading from sight, and we know that the amoeba has captured its prey, has swallowed and digested it, and is ready for more. If any part of the food is indigestible, it will be seen to pass out of the body later.

Naturally enough, the more an amoeba eats the larger it grows to be; and then, after a while, comes the dividing and the multiplying. If you should have the good fortune to see this done, the chance is that you would carry on a series of exclamations which would correspond with each step of the dividing process.

First of all, however, notice the spot in the body of the amoeba. Such a vital point exists in every amoeba that lives to-day. It is the nucleus - the very center of life, as we shall learn later. Here, now, are the exclamations which a person is apt to make as he looks through a microscope and for the first time sees an amoeba divide. "What a queer little creature!" Why, it's stretching itself out!" "It's turning into a dumb-bell!" "It's actually pulling itself in two!"

"Yes, it has done it! There are two of them nowtwins, but they act as if they didn't know each other by sight!" The slow-moving, tireless activity of this living creature is indeed an ever-fascinating study for those who watch him through the microscope.

The amoeba has but three rules to live by:

1. Adding food to itself.

2. Dividing the protoplasm, nucleus and all.
3. Multiplying itself by two.

After the dividing, each newly made amoeba owns its fraction of the nucleus and is a separate, living creature. It falls to creeping and eating and growing as its parent did. It is, indeed, as we have seen, a part of its parent. Soon it has reached full size. Then it, too, divides and multiplies. Thus does amoeba life and history go on through the ages.

As for any sign of a nervous system in the body of the small animal, what does the scientist find? Just one important fact. When the end of an outstretched arm of protoplasm is touched it swells a trifle, and the impulse, as it is called, seems to move as a sort of wave across the body of the amoeba. Not a thread of nerve is to be found in the bit of protoplasm; no sign of brain anywhere; no spinal cord; nothing definite to carry any sort of stimulus in a straight line from one point to another. In place of all this there is the slowly moving wave which affects the whole of the amoeba as far as the wave travels.

We see, then, that just as any part of this surprising protoplasm may, at a moment's notice, become arm or leg, body or stomach, so any part may also be the nervous system itself, carrying messages across from side to

side. This is the special reason why a book on control must start with protoplasm in the shape of an amœba, for many scientists spend their lives in tracing the road that leads from sensation in an amoeba to sensation in man. At each end of the road is a living machine amoeba at one end, man at the other. One is a single cell of protoplasm which, through all its eating, creeping, dividing, and multiplying, never increases the number of its cells. The other is made up of cells by the countless million.

Side by side with the amoeba in the world of living animals is his legion of single-celled relatives. Some are larger, some are smaller, but not a creature of this host has either head or tail, either bones, muscle, sight, hearing, or smell. Nevertheless, like the amoeba, they all live, grow, divide, and prolong their days beyond the reach of our imagination. On the other hand, in contrast to this fascinating group of single-celled animals, stands every other living thing from microbe to man and elephant that is composed of more than one cell. Of every size and shape, scattered wherever they may be, in water, earth, or air; whether they are worms, birds, beasts, or men- any living creature that has more than one cell belongs to the many-celled group.

We shall yet see how our knowledge of the amœba makes the structure of the nervous system of man easier to understand.

On the mantelpiece of the room in which I sit there is a small Japanese bronze box. It is an inch and a quarter long, almost square, and decorated on the outside with queer Japanese figures. Inside, in a vial an inch long, very slender and filled with alcohol, is a curved white object, with what seems to be a dark shadow running along through its center from one end to the other.

This object has neither head nor tail, neither wings nor bones of any sort; but four years ago it was a living, darting thing that found food for itself in the sand on the seashore of Formosa. It buried its body in the sand and appeared to be nothing but a water tube, for a small, round opening at one end was surrounded by a waving fringe of fibers. This opening served for mouth, and into it the water went. On the under side of the body was another opening out of which the water flowed. The animal lived on the food which it caught from the water that passed through its body.

With all that it lacks then, this small creature is entirely different from the amoeba, for it has at least a

mouth and a stomach. It has indeed much more than this, for the shadow which we see stretching from end to end is the simplest and the earliest style of backbone that scientists have ever found in an animal of any sort.

And because of this backbone the amphioxus is a relative of every other creature that has a backbone — human beings included. Scientists, therefore, study it carefully with their microscopes, and they discover what they call the nerve tube. This stretches through the

b

AMPHIOXUS, THE SIMPLEST VERTEBRATE

a, where water goes in; b, where water escapes; c, nerve tube; d, backbone little fish close above the backbone. In fact, there is a groove on the upper side of the backbone just deep enough to serve for a nerve canal in which the nerve tube rests. Slender nerves stretch from this tube to different parts of the body.

Even as they study the backbone and the nerves of the amphioxus, so also do scientific students follow the history of the animal from the time it begins its life as an egg until it is full grown-two inches long and laying eggs on its own account.

Amphioxus is its name-too long a name for so short a thing, but learned men do the naming, and