a use for it. If one wishes to be a new creature one must attempt a new thing. The new thing in this case was finding a way to stiffen the outside mantle with lime and make a shield against danger.

So oysters and clams and scallops grow shells as easily as we do finger nails. The rest of the body is soft and tender, but on occasion they hold their twoleaved shells tightly together.

Within the shell and mantle the soft parts of the maker are kept safe, so that the work of digesting food can go on. The stomach receives the food through something quite like a throat, and this leads to a passage for taking away what is not fit for the creature's use and pressing it out of the body. There is also an organ such as in higher animals is called. the liver, in which fluids which would be hurtful can be separated.

As this is one of the lowest of the animals which are used for food, it is interesting to know something of its nature.

The shell-bearers seem to be gifted with a number of new powers. If the lowest creatures need air they take it as they do their food into whatever they have for a stomach. Clams and oysters have a good little way of their own for breathing. Even after

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oysters have been cooked you can find frills which are the gills that let them take the air from water.

If air is needed it must be because there is blood to be kept pure. The oyster and clam have it, though it is white and cold. They have nerves also and can tell their organs what to do. People who like to watch their ways better than to get them for food tell us they can hear and smell, and that there are tiny red spots that are supposed to be eyes, but how much good they do no one can tell yet.

Oysters live in beds at the bottom of the sea, but not where the water is deep. In the open shell in the picture you can see a spot. Every oyster shell has it. It is the place where a strong muscle is joined, and below it the shell is fastened to the sea bottom. Oysters lay thousands of eggs, and there are many times as many oysters born as those that live and grow three or four years, when they become fit for food. In spite of their shells, they have many enemies among them, as you have been told, starfishes. In place of shells outside, the creatures on the ascending stairway began now to grow bony frames to support the soft flesh. They learned to defend themselves by their wits. The frog and toad, the reptiles, all the fishes, all the birds, and all the fourfooted creatures

have their places in this scale, and at the top stands the family to which you yourself belong, which is an animal family though it is also the human family.

Human beings can learn about all the things that belong to their lives, can help in the work of making them perfect, and can use them so as to be a blessing to the world.

Earth and sky were made for them and beings like them, and all things are given for their use by the Creator and Father.

You will be sure not to make the mistake of thinking that this is simply to give them a chance for a good time; it is to lead them on to something higher and greater than we can yet understand.

This is the last of the creatures we can find space for in this book. If you have been interested to see how life works in different sorts of bodies, you will watch for other ways, and all creatures will have a greater interest for you.

XXXV. GIVING AND TAKING

WHEN you see the brooks and rivers hurrying to the sea and making such a show of adding to its waters, it may please you to remember that just as much goes back, without show, to feed the springs that keep the rivers flowing and singing and sparkling.

Air will drink from anything that has moisture that it can part with. If you hang a wet handkerchief on a line or spread it upon the grass on a fair day, it will be but a few moments before the moisture will have been stolen from it.

How is it that air, which is so much lighter than water, can drink from it and bear it away? It could not do it if it were water as we see it. The water changes to vapor when the warm sun acts upon it. Passing from a liquid to this finer form is called evaporation.

There are other substances that the air takes and bears away. When you go into a garden where roses and violets and heliotrope and mignonette are in blossom, you get their perfume before you reach the place

where they are growing. They give their fragrance to the air, and the air gives it to you.

Foul smells are carried away, and unhealthy substances change to a form the air can manage, and so disappear. This makes the air a scavenger.

Our every breath gives something to the air that would be poisonous for us to go on breathing, and plants give out the part of the air they cannot use.

Do you not see that the air must have a laboratory somewhere in which it makes itself right again?

It does have such a laboratory, but we cannot see it. It makes one of its "takings" act upon another, and, if it has room to work in, sweetens everything.

If you have older brothers or sisters studying chemistry, they can tell you that there are always two parts to air besides a very little of other substances. These two are oxygen and nitrogen. The two do not unite, and it is not difficult to take them apart.

There is four times as much nitrogen in the air as there is oxygen, and the mixture always stays the same even if different parts of the two are being separately taken away. This is very important to us who depend upon it for our breath.

Nitrogen dilutes the oxygen in the atmosphere; it is a much lighter gas.