The Sea-Mouse
Looking far more like a hairy slug than a worm, the sea-mouse also belongs to the class of the annelids. You can easily find this creature by hunting in muddy pools among the rocks just above low-water mark; and most likely you will consider it as one of the dingiest and most unattractive-looking animals that you have ever seen. But if you rinse it two or three times over in clean water till every atom of mud has been washed out of its bristly coat, you may change your opinion. For now you will see all the colors of the rainbow playing over it—crimson, purple, orange, blue, and vivid green—just as if every hair were a prism. It would be difficult, indeed, to find any creature more beautiful in the waters of the sea. This bristly coat is really a kind of filter, which strains out the mud from the water that passes to the gills.
Leeches
Leeches, too, are annelids, living in fresh water instead of salt water. They are famous for their blood-sucking habits, and when we examine their mouths through a microscope we find that they are provided with three sets of very small saw-like teeth, which are set in the form of a triangle. When a leech wants to suck the blood of an animal, it fastens itself to the skin of its victim by means of its sucker-like lips, and then saws out a tiny triangular piece of skin. That is why it is so difficult to stop the bleeding after a leech has bitten one. An actual hole is left in the skin, which does not heal over for some little time. And a great deal of blood is generally taken by the leech itself, which will go on sucking away until its body is stretched out to at least double its former size.
That is rather a big meal to take, isn't it? But then such meals come very seldom. Indeed, when a leech has once gorged itself thoroughly with blood, it will often take no more food at all for a whole year afterward!
Leeches lay their eggs in little masses, called cocoons, which they place in the clay-banks of the pools in which they live. In each of these cocoons there are from six to sixteen eggs.
We now come to the last great class of animals about which we shall be able to tell you—that of the cœlenterates. It contains three most interesting groups of creatures.
Jellyfishes
You may have seen plenty of jellyfishes if at any time you have been staying at the seaside, for they are often flung up on the beach by the retreating tide. But if you were to go and look for them two or three hours after seeing them, on a bright sunny day, you would find that they had disappeared. All that would be left of them would be a number of ring-like marks in the sand, with just a few threads of animal matter in the middle of each. The reason would be that they had evaporated! That sounds rather strange, doesn't it? But the fact is that the greater part of the body of a jellyfish is nothing but water! It is quite true that if you cut it in half the water does not run away. But then that is equally true of a cucumber; and cucumbers, too, are made almost entirely of water. The reason is the same in both cases. The water is contained in a very large number of tiny cells; and when you cut either the animal or the vegetable across, only a few of these cells are divided, and only a small quantity of the water escapes.
Round the edge of the disk of a jellyfish which has just been flung up by the waves you will find a number of long, slender threads. These are its fishing-lines, with which it captures its prey, and they are made in a very curious manner. All the way along they are set with a double row of very tiny cells, in each of which is coiled up an extremely sharp and slender dart. These cells are so formed that at the very slightest touch they fly open, and the little darts spring out; and, besides this, the darts are poisoned. So as soon as any small creature swims up against these threads a number of the venomed darts bury themselves in its body, and the poison acts so quickly that in a very few seconds it is dead. Then other threads come closing in all round it, and in a very short time it is forced into the mouth and swallowed.