The stem barnacles have long, flesh-like stems which move and sway with the motion of the water. They look much like a little, queer, pale plum hung by a thick stem.
The end of the barnacle, which clings to the stone, log, shell, or fish on which it has fastened itself, is the head end. The two feelers, which all these animals have, are turned into two fine tubes, or pipes. These feelers have little glands or sacs which make a strong cement. Cement is like glue, but much more strong and stiff.
This cement fastens Mr. Barnacle to his place. So after he has settled himself in life, he never wanders about any more.
Did Mr. Barnacle ever go abroad? Oh, yes! When he was young he swam about the water-world, in a very brisk way. Let us hear about that.
Mr. Barnacle makes the same changes of life that an insect does. First he is an egg, then a larva, then a pupa, and at last a steady old barnacle. But the larva barnacle makes two or three changes of shape before it turns into a pupa.
Barnacles grow fast. They change their coats often when they are young.
Here is an old acorn barnacle fast upon a stone. It is about as big as the end of your little finger. It has some eggs which it packs into the shape of a small leaf. It tucks this leaf of eggs into a fold of the thin skin that lines the thick shell.
As the eggs get ready to hatch into larvæ, the old barnacle is also growing, and making more shell. Soon it is ready to enlarge the outer shell. So the inside skin cracks apart and falls off. By degrees some barnacles become quite large as fresh shell grows from within.
When the old inside skin falls off, the eggs are set free. Out of them come the larvæ. The larvæ are active, hungry little fellows, who know how to swim as soon as they are loose in the water.