If the amoeba is ever to get up in the world very far, it must stop using all its parts for everything. The first little creature to make a stomach on the inside, you know very well. Or, rather, you know his empty house. A sponge is the skeleton, or bony house, where hundreds and hundreds of little animals once lived. They all live together so they can help float food to each other's mouths. You know a sponge is full of holes. These holes are long, crooked water streets of the bony town. Other sponge colonies live in glass towns. Those are very beautiful.

Bath sponges are a kind of elastic horn. Elastic means that it will stretch, like rubber. When you fill a sponge with water and squeeze it out, you make it do over again, in a way, what it does when every room in it has living baby tenants. The sponge lives by having water flow through its village. But, instead of soaking up the water and squeezing it out, the water is paddled through the little streets, by little hair-like arms.

The sponge is the lowest animal that is made of more than one cell. The sponge has a stomach on the inside and bones on the outside. By living, a great many of them, in one house or village, like those old cliff-dwellers, all the little sponges get along better. They live very close neighbors, all work for each other, buy their food of the same grocer, and pay for it in a lump. Their house is a kind of fort, too. Larger water animals could "gobble up" millions of separate little sponges, but a whole village of them, in a horny house, is too big and tough a bite. It's a great thing to be sociable, to make friends and live in peace with neighbors. That makes life easier and pleasanter for boys and girls, bees and sponges.

The holes in the sponge are little mouths that lead into the village. Inside of it, when the sponge is alive, there are little one-room houses, and in these are packed, side by side, little jelly-like cells with tails. These tails stick out into the water and, like little fishermen, catch smaller plants and animals out of the water, as it passes through the sponge. At the same time these tails, or fishing poles, catch the water as it flows through the channels. The water also carries air, and the sponge gets its oxygen out of it. You see, the sponge like the fish, must breathe under water.

While the sponge is like an animal, in eating other little animals and plants, it is like a vegetable in that it cannot move around. It is rooted to one spot. The sponges grow so thickly that they often make perfect forests on the rocks, on the bottom of the sea. When the sponge is taken from the water it is covered with what seems to be a mass of jelly. This is its flesh, and the flesh is made up of the little cells with tails that I have been telling you about.

Just as if you might forget—although it seems so plain—that this sponge is made up of little creatures like the infusoria, and has become a higher order of animal because all these little animals formed into a society and worked together, the sponges increase by laying eggs; one-celled eggs. These eggs first turn into simple little animals with paddles all around them, like the infusoria, and they swim around by themselves, for awhile, before a number of them settle down together to form a sponge. They are like boys that go out into the world awhile to learn what it is like, and then join other boys and go into business together.

As we go along you will find nature continually "saying her piece" over again, from the beginning, as if to be sure she gets it right. And, also, I think, she may do it to be sure that we catch the idea of what wonderful things all of us can do in this world, if we will do each little thing, build each little thing, as well as we can, and keep looking upward as we build.

A sponge as it appears attached to the ocean bed. The little animals inside the horny skeleton stick hairly-like tails out into the water to catch their food.

It is as if nature said, after studying the yeast plant: "This yeast plant will make something better if it can get out into the world." So she took the same sort of little cells out where they could meet the air and the sun, and there came the liver-wort, part leaf and part root, and the first plant to find out how to make spores. Next came the mosses which began to stand up; and then the ferns which gave the vegetable world its backbone. Last of all came the flower-bearing plants, and with it the great partnership between the animal and the vegetable world, each helping the other to live.

But to do all her wonderful work Nature, like you and me, had to work with two hands. While with one hand she was helping the vegetables to get up high enough to receive the help of the animal world, in getting still higher; she had to teach the amoeba how to grow into birds and butterflies and men, so that they could come into this grand plan of things, and make more and more beautiful and useful varieties of animal and vegetable life.

Now, her work with her right hand, in growing the wonderful varieties of animals from the shapeless, formless amoeba, has got along as far as the sponges, which already have mouths and "hands" and the beginnings of bones, and a hollow inside.

Not only have sponges so many more useful and interesting parts than the amoeba, but they show, again, how fast you can make differences when you have more than one part to multiply with. Sponges have many different shapes, different colors, and they live in many different kinds of places. One kind of sponge is called the finger sponge, because it has fingers like the human hand. Another is shaped like a banana. Others are almost as round as a ball. Some look like a flat red mat, spread over the rocks under the water, as if for the entrance to the doorway to some palace of the water fairies. Some are black, some yellow, some brown.

One kind of sponge looks like a beautiful vase of spun glass, and when these sponges were first brought to Europe, from their home in the South Pacific, they were not thought to be sponges at all, but vases made by very skillful workers in glass. They were known as "Venus' Flower Baskets."

The sponge itself is not only made up of other little animals living together, and getting food for one another, but other animals, of a higher order, are often found living in the cosy sponge village. In the larger sponges are found shrimps, crabs and even fishes. See Sponges, page 1801.