Other jelly-fish have a motion more like the opening and closing of the hands. Some have little oars, paddles, or hairs on the edge of the disk. Some seem to open and close as you would slowly open and shut an umbrella.
The swimming-bell of the jelly-fish is often called the umbrella from its shape. This bell has little fine muscles through it, by which it can spread out and draw together. You know you have muscles by which you can move the parts of your body.
On the under side of the swimming-bell, is a flap called the veil. This flap turns inward, and the little fine muscles spread over it. This veil is pulled together in the act of swimming, and pushes out the water from the bell. Then the bell spreads and takes in more water, and again it is driven out. A boy in swimming parts and pushes the water back with his arms, the jelly-fish has no arms or legs, but still it moves about easily.
I told you that jelly-fish could sting. They can also shine. They can make a fine bright light, something as glow-worms or fire-flies do, but more steady. From this power, they have been called Lamps of the Sea. I have seen the ocean bright with them for miles. It looked as if all the stars had fallen from the sky, and were glowing in the water.
When the jelly-fish shine so, the light is like a ball. It is not in straight lines, long, or square. It is round, like fire-balls, or balls of melted iron, or of glass. These balls are sometimes red, or blue, or white, or green, or yellow.
Jelly-fish differ much in size. Some are so small that you can hardly see them; some are as large as a split pea. Then some are the size of a dime, of a dollar, of a plate, and so on, up to the size of a huge wheel.
As they are of many sizes, so they are of many shapes, as I told you at first. They are like balls, fans, bells, bottles, plumes, baskets, cups, flowers.
And now, here is another odd thing to tell you. You know that when Mr. Barnacle is young he swims about. When he is grown up, he settles down to stay in one place. The jelly-fish stays in one place, and grows fast, when he is young, but when he has grown up he swims about wherever he chooses. I wonder which is the better way! Which way would you children like best?
Some of the jelly-fishes come from an egg. Some of them come from what is called a bud. Let us look at them from the bud or from the egg. The egg at once fastens to some solid thing on the sea-bottom. It grows into what looks like a plant with stems and branches.
On these branches are little cup-shaped buds. These buds are so many little jelly-fish growing on one stem. This is the larva state. After a time, these buds open, and a young jelly-fish breaks from the slender stem, and at once goes swimming away, as happy as a jelly-fish knows how to be.