Still in the dense darkness the Beryx must surely escape? No! for, strangely enough, lights are travelling about in this midnight region. The monster

Footnote 25. See Frontispiece. 1, Chauliodus; 2, 9, 10, 11, Harpodon or Bombay Duck; 3, Plagiodus; 4, Chiasmodus, with a Scopelus in its stomach; 6, Beryx; 8, Scopelus.

himself carries lamps upon his body, and a shoal of small oblong fish, something of the size and shape of a gudgeon, come swimming by, carrying on their sides whole rows of shining spots giving out phosphorescent light; while not far off another fish, called in India the Bombay duck, glows all over, as if his whole body had been rubbed in phosphorus. Nay! so far as we know the Beryx himself is probably gleaming with light, for his body is covered with a large quantity of the same slimy fluid which makes the “Bombay duck” phosphorescent when he is freshly drawn out of the sea.

So these curious fish, living in eternal darkness except when they make an expedition to the surface, carry many of them their own lights; and as we go deeper still more and more of them are found with shining mother-of-pearl-like spots on their head, or sides, or tail, so that the very darkness is alive with light. What slaughter and hunting there is among them! for they all eat each other, and even their own young, there being no plants for any of them to feed on. There are the deep-sea cod-fish; strange forms with large heads, long tapering tails, and thread-like fins, chasing the smaller fish, and falling victims themselves to the fierce Stomias which comes sailing along with its row of glowing lights, and its huge sharp teeth, ready to seize its prey. Both these fish go down as deep as ten thousand feet and more, accompanied by another fish quite as ferocious, though only a foot long, with large teeth sticking out of its mouth like the tusks of a boar, and curious round spots, with lenses in them, on its side, which may be eyes, or may be lanterns to light it on its road; and among these luminous fishes are wriggling along the deep-sea Conger eels, with toothless mouths and elastic stomachs, swallowing large fish whole; while another curious cod-like fish, whose stomach can stretch to more than four times its natural size, draws itself over its prey just as a snake does, and carries it in the hanging bag till it is digested. And deeper yet in the dead calm water roam many fishes with delicate feelers hanging from their mouths, while their fins are slender and tapering, so that they feel their way along the still depths. Among these are the Ribbon-fish, twenty feet long but only a foot deep, and never more than two inches thick in any part, with their long rosy fins floating like ribbons back from their heads and from under the body.[26]

Strange monsters are all these deep-sea fish, some of them living as much as 16,000 feet under the surface of the sea, so that if Switzerland were turned upside down in mid-ocean, the peak of Mont Blanc would not reach down to where they swim. Yet they are only modified forms of ordinary fish from the world above, which have become fitted to live under that vast pressure of water. Their skeletons, though bony and well-knit together at that depth, are fibrous and slight compared to those of their surface relations, for although they have to resist a weight of from two to sixteen tons pressing all round them, a ton weight being added for every thousand feet, no special strength is required, because the dense water permeates their whole structure, and the pressures are everywhere equal. It is the same with them as

Footnote 26. In drawing up this sketch of the deep sea I am almost entirely indebted to Dr. Günther’s masterly sketch of the deep-sea fish in his excellent work.

with the most delicate and fragile insects living in our atmosphere, the pressure of which would tear them to pieces if unbalanced by equal pressures within and without.

But when these deep-sea fishes are brought up quickly to the surface, the outside pressure no longer balances that inside, and so their tissues loosen and their whole framework starts apart, so that they almost fall to pieces at a touch; and their air-bladder, if they have one, expands so much as to force the stomach out of the mouth, turning them almost inside out. Neither are their lanterns a special creation for their use, but merely adaptations of that slimy fluid which we saw oozing from the scales of the minnow. In some of the deep-sea fish even the outer bones are filled with this fluid, and the line of scales along the side has large openings, so that the body is bathed in glowing slime. In others it collects in glands on the sides, making the phosphorescent spots.

In this way the deep-sea fish have become fitted to make a home in the very heart of the ocean. Some with large eyes, seeing by means of their own and their neighbours’ light, others with small eyes and delicate feelers, testing each step as they go, and feeding, probably, on the shower of minute sea-animals that falls continually from above; while some, like the Beryx, the Bombay Duck, and the light-carrying Scopelus, which live nearer the top, come up on still nights to feed at the surface of the sea.

Fig. 9.

Remoras[27] clinging by their sucking-disk to the under part of a shark.—(Adapted from Brehm.)

And now, as we rise again from the dark still depths up to warm layers of the tropical seas into which the sun is pouring his penetrating rays, it may

Footnote 27. Echeneis remora.

happen that a large dark body moves between us and the surface, as the Great Blue Shark, or one of his smaller relations, ploughs his way through the water. But what are these little dark brown fish, with round gaping mouths, which are hanging by the top of their head and back from under the shark’s belly? (see Fig. 9). Where he goes they go with him, and, as they are borne along, they feed upon the tiny sea-animals among which they are carried so easily. These cunning passengers, of whose very existence the shark seems unconscious, are the Remoras, or sucking-fish. You would scarcely think that they

belong by descent to the mackerel tribe, a strong-swimming, active, and almost warm-blooded group of fish, with a large supply of nerves and blood-vessels to their muscles, so that they swim boldly out to sea, and make more use of the open ocean than almost any other group. But among all tribes there will be some weak members, and these must live by stratagem. The little remora is a feeble swimmer, and, having to live out at sea, has acquired a curious sucker by which he clings to sharks, and whales, and even ships, so that he is carried along without exertion. Yet this sucker, again, is only a special adaptation of the back-fin, which, instead of being single, as in other mackerel, has its spines divided and bent, one set to the left, the other to the right, and joined by a double set of plates, surrounded by a fringe of skin. This forms an oval disk, and, as the remora glides along under the shark’s belly, he presses the damp membrane against the fish, and, drawing together the muscles of the plates, clings as firmly as a limpet to a rock.

Nor is the remora the only companion of the shark—

“Bold in the front the little Pilot glides,

Averts each danger, every movement guides;”

for the little steel-blue striped Pilot-fish,[28] another distant connection of the mackerel tribe,[29] is hovering around, feeding upon the scraps of the shark’s food, and finding protection in his neighbourhood, though in olden times he was supposed to protect the shark.

Footnote 28. Naucrates.

Footnote 29. In this description I am not alluding simply to the mackerel family Scombridæ, but to that much larger group Cotto-Scombriformes, to which so many ocean fish belong, and even the sword-fish is allied.

A brave little fish this, which has succeeded in making the shark his friend: while near him he is safe from other fishes.

And now, as we continue our way in the open sea, it is nearly always forms more or less related to the mackerel tribe which cross our path. The slender Bonito[30] and the heavier Tunny[31] sometimes ten feet long, are hunting below or on the surface, and the beautiful Dorados,[32] or gold-mackerel, as the Germans call them, with their silvery blue backs tinged with a sheen of gold, their dull-coloured fins, and their golden eyes, are driving by in large shoals in pursuit of the flying-fish. All these are powerful swimmers, and they have no air-bladder, which is an advantage to such active hunters which wish to turn rapidly, to go down deep or rise to the top, and change their position at every moment; for in all these movements a natural float inside is a hindrance to be overcome. And so we find that in fish, even of the same family, some have lost the air-bladder, while others have it enlarged to meet their wants, as in the case of the lovely blue and silver sun-fish[33] for example, which, though quite near relations of the dorado, have very large air-bladders, enabling them to float quietly on the top of the water, waving their deep scarlet fins.

Fig. 10.

Flying-Fish[34] pursued by the Dorado.[35]

But while we are watching all these large and strong swimmers an active and bloodthirsty struggle is going on, for the bonitos and the dorados are looking to make their meal upon the little Flying-fish, which are straining every nerve to escape them, while here and there

Footnote 30. Thynnus pelamys.

Footnote 31. Thynnus thynnus.

Footnote 32. Coryphæna.

Footnote 33. Lampris luna.

Footnote 34. Exocœtus.

Footnote 35. Coryphæna.

one drops down into their very mouths. Lovely little creatures these are, of the Pike family, which have taken to the open sea, where they rise with a stroke of the tail many feet out of the water, their bright purple backs and silvery sides gleaming in the sun, as, with their long transparent arm-fins outspread, they float for as much as two hundred yards before they fall back, to spring up again with another stroke. Their air-bladder, which is half as long as their body, and contains in a six-inch fish as much as three and

a half cubic inches of gas, stands them in good stead, and they rise and fall with quick rapid flights out of the reach of their foe, so that in the open sea they do fairly well on the whole, though, if they venture near land, the sea-birds persecute them in the air. Nor do they stand alone in this curious habit of flying, or rather floating, in the air, for a larger fish of quite another family, the “Flying Gurnards,”[36] with a smaller but still ample air-bladder, and long arm-fins, may also be seen rising in the Mediterranean and tropical seas, out of reach of the fish-hunters of the water.

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.

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