And now we must leave the open sea and steer for the shore. It is true that many other fish are wandering in the broad watery main, but many of them, such as the globe-fish, feeding on the small crustaceans and the sea-horses,[37] whom we shall meet nearer shore, are feeble forms carried hither and thither by currents or on floating banks of seaweed, while others have no special interest. The sharks, the mackerel, and the flying-fish, are the most remarkable colonisers of the ocean-surface, for even the enormous Sword-fish,[38] which attacks the bonitos and whales with its long wedge-shaped bony jaw, and is said to sail by raising his back-fin, is a distant off-shoot of the mackerel tribe. So we cannot do better than follow our own common Mackerel, as they migrate in shoals out of the deep sea to feed on the fry of the herring or the pilchard in shallower water, or to leave their eggs floating not many miles from land, so that the tiny mackerel, when hatched, may live in the quiet bays till their strength comes. But stop! Long before we have come so far as this, and while we are still a hundred miles or more from the shore, let us peep down into the sea-valleys, where forests of seaweed and marine plants are growing, and myriads of tiny sea-lice and crustaceans throng the water. What is that army of thin spindle-shaped forms rising and falling in such numbers? It is a shoal of herring, which have come there to feed upon the sea-animals, keeping out of sight of the sea-birds above, and the cod and sharks and ravenous fish which hunt them without mercy, so that they only venture to come to the surface on calm dark nights. It was in valleys such as these that the herrings were living when the older naturalists thought they were gone away to the Polar Seas, because they only saw them in spring and autumn, when they come into shallower water to drop their myriads of eggs,[39] which sink down, and stick to the seaweed and stones below. But now they are revelling in the deep ocean, rising and falling with ease, for their air-bladder has two openings, one to the stomach and one to the outside of the body, so that the gas can adjust itself to their movements; and surely if the shark is the type of the old, lumbering, powerful, slow-breeding fish, the herring, with its narrow lissome body, light playful movements, and myriads of young, is the type of the new and active race. They are as truly social animals as any herds on land, for they travel in shoals of many hundreds of millions; and as they can squeak, and have a very good apparatus for hearing, it is more than likely that they call to each other. They make both the salt and fresh water their own; for when the eggs are hatched at the mouths of rivers the tiny fish take refuge there from the violent persecutions of the cod and mullet and haddock, flat-fish and whiting, and, together with the small fry of other fish, stroll up the rivers, where we call them “white-bait.”