But the third change is the strangest of the three. One of the eyes would now seem to be useless, since it is on the lower surface of the head as the fish lies on the sea-bottom, and would be completely buried in the mud. But as soon as the fish goes and lies down at the bottom of the sea, this eye actually begins to travel along the lower surface of the head, till at last it works its way round and settles down by the side of the other! If you look at the flounders the next time you pass by a fish-market, you will observe that both eyes are placed quite close together above the same corner of the mouth. That is because the lower eye traveled round the head till it found a resting-place by the side of the other. In habits, all these fishes are very much alike. They are found in almost all seas, except those of the polar regions, and in most parts of the world are exceedingly plentiful, and everywhere form a cheap and excellent food. THE SWORDFISH A very odd-looking creature is this. It abounds in the Atlantic and also in the Mediterranean. Its chase affords one of the finest summer sports to be enjoyed along the south coast of New England, where it is taken by spearing from swift sailboats. In this fish the upper jaw, which has hardly any teeth in it, is drawn out into a long, slender, pointed beak. With this "sword" the fish impales its victims, which are often of considerable size; but how it gets them off its beak again in order to eat them nobody seems to know. This fish sometimes drives its way through the water with such tremendous force that it has been known to pierce the planking of a boat with its sword, which it had to snap short off in order to release itself. In the Natural History Museum at South Kensington, London, there is part of a beam taken from the hull of a ship, into which one of these fishes had driven its sword to a depth of twenty-two inches. MACKEREL One of the best known of all the salt-water fishes is the mackerel. This fish lives in enormous shoals, which are always traveling from place to place, and visit the same parts of our coasts at about the same season in every year. Sometimes they are caught in most extraordinary numbers, so that they can be purchased at very small prices. In some cases, indeed, the catch has been so heavy that it has been found quite impossible to draw in the nets, which had to be allowed to sink to the bottom with the fishes still in them. These nets are generally made with rather large meshes, not quite wide enough to allow the fishes to swim through. When the mackerel are caught they try to force their way through the meshes, but find that they cannot do so. They then attempt to back out. In doing this, however, the thin twine of which the net is made is almost sure to become entangled with their gill-covers, so that they are held prisoners until the net is lifted from the water. When fully grown the mackerel is about sixteen inches long, and weighs perhaps two pounds.