These swimmerets are used for another purpose as well, however, for the mother lobster always glues her eggs to the hairs with which they are fringed, and carries them about with her for some little time. Haven’t you noticed, when you have had shrimps for tea, that a good many of them had clusters of eggs underneath their bodies? Well, if you had put one of those shrimps under a microscope, and examined it very carefully, you would have found that every one of the eggs was firmly glued down to one of the hairs on its swimmerets, where it would have remained until it was hatched. And lobsters carry their eggs about with them in just the same way.
If you go down among the rocks when the tide is out, and look into the shallow pools which have been left among them by the retreating waves, you are quite sure to see numbers of shadowy forms darting to and fro through the water. A good many of these will be prawns, and if you catch one or two of them in a small net, and examine them carefully, you will find that they are very much like tiny lobsters. Indeed, if you could magnify a prawn to the size of a lobster, or reduce a lobster to the size of a prawn, it really would not be very easy to tell the one from the other.
But you will be surprised to see how different live prawns look from the dead ones which you may see in a fishmonger’s shop. The fact is that, like the lobster, they change colour when they are boiled. When they are alive, indeed, they hardly have any colour at all, and are nearly transparent. That is why it is so difficult to see them in the water. And if you keep them in an aquarium, all that you can see of them, very often, as they dart to and fro is just their glowing eyes, which gleam in the water like tiny balls of fire.
There are two facts about prawns which I am sure you will be interested to know.
The first is that they are extremely useful little creatures, for they feed upon the bodies of the various small animals which die in the sea, and so prevent them from becoming putrid and poisoning the water. And the second is that they always take the greatest possible care to keep themselves clean. If you take a few live prawns home, and put them in an aquarium, you may often see them performing their toilets. Their front legs are covered with stiff little hairs which stand out at right angles, so that these limbs really form a pair of brushes. And with them the prawn will clean its body most diligently, rubbing itself all over until every little speck of dirt has been removed. And if any object should cling to its body which these tiny brushes cannot rub away, it will pull it off by means of the strong little pincers on the second pair of legs.
Do you want to know how to tell a prawn from a shrimp?
Well, all that you have to do is to look in front of its head. There, projecting from the edge of the “carapace,” or shield which covers the back, you will see a long spike, something like a beak. Just put your finger upon this, and feel the edge. If it is set with sharp little teeth, like those of a saw, the animal is a prawn. But if the spike is perfectly smooth, it is a shrimp.
This is a much prettier creature than the common prawn, for its transparent body is covered with scarlet lines, while its long thread-like feelers have rings of the same colour round them at regular distances apart. It is called the “Æsop” prawn because it has a big hump on its back, just like the writer of the famous fables.
If you want to catch an Æsop prawn you must look for it in the summer, for it always spends the rest of the year in deeper water. But as soon as the weather becomes really warm it travels up and down with the tide, and you may find it in plenty in the pools which are left among the rocks at low-water.
I told you that a good many of the shadowy forms which you may see darting to and fro in the rock-pools are those of prawns. The rest are quite sure to be shrimps, which are very much more common. Indeed, in most of the rock-pools you will find at least ten shrimps for every prawn. But they are very difficult to see, for they are partly transparent when they are alive, so that they are scarcely visible when they are swimming. And when they are resting at the bottom of the pool their speckled bodies look almost exactly like the sand on which they lie. Besides this, they have a way of nearly burying themselves, by scooping out a kind of furrow with their hind limbs, sinking into it, and then covering themselves with sand by means of their feelers. So the fishermen often call them “sand-raisers.”