Let me transport you for a few moments into the midst of the Indian Ocean! The sultry sun of February has been basking all day upon the heated waters from a brassy sky without a cloud—the vapors of the upper regions resembling a thin veil of dust, fiery and glowing, as if recently ejected from the mouth of some vast furnace! But the tyrant has gone to his repose, and we enjoy some respite from his scorching influence. It is not cool, but the temperature is tolerable, and this is much! Leave the observation of the barometer to the captain! You cannot prevent a hurricane, should it be impending. Then trust such cares to those in whom is vested the responsibility, and come on deck with me.
There is no moon—but the “sentinel stars” are all at their post. Observe those broad flashes reflected upward from beneath the bows, and playing brightly upon the jib! At every plunge of the vessel, as she sinks into the trough of the sea, you might read a volume fluently by that mild radiance; and beautiful indeed is the view from the fore stay-sail nettings, looking down upon the curling wreaths on either side of the cut-water, and the long lines of foam thrown off by the swell as the vessel gracefully breasts the coming wave, all glowing like molten silver intermingled with a thousand diamonds!
But I will not lead you thitherward—a noble sight awaits us in our wake. Step to the stern and lean with me over the taffrail. What a glorious vision! For miles abaft, our course presents one long and wide canal of living light—the clear, blue ocean, transparent as air, filling it to repletion; while the darker waters around appear like some dense medium through which superior spirits have constructed this magic path-way for us and us alone, so nicely are its breadth and depth adjusted to the form of our gallant bark. Has not the galaxy been torn from heaven, and whelmed beneath the waves to form that burning road? No! no! Though thousands of bright orbs are set in that nether firmament to strengthen the delusion, yet it cannot be. Night’s stormy cincture never gleamed like this, nor bore such dazzling gems. There it still glimmers with its myriad sparks, athwart the dark blue vault, paled by the radiance of its sea-born rival, while huge globes of fire roll from beneath the keel, and blaze along the silvery track like showers of wandering meteors, but all too gentle in their aspect to be deemed of evil-augury.
Those stars are literally living stars,—that ocean galaxy is formed of living beings only,—and even those meteors, invisible by day, except when they approach unusually near to the surface, are active in pursuit of prey. Observe one closely, and you perceive its motions. Formed like a great umbrella of transparent jelly, with fibres, yards in length, trailing from its margin, and the handle carved into a beautiful group of leaves, it flaps its way regularly through the water with a stately march, and wo to the unfortunate creature that becomes involved in the meshes of its stinging tendrils.
This is no exaggerated picture, for such are the beautiful phenomena occasionally witnessed in the Indian and Pacific Oceans. The animals upon whose agency they are dependent, generally become invisible by daylight in consequence of their transparency; but there are certain tribes among them whose peculiar structure renders them conspicuous: and of these one of the most remarkable is known to naturalists by the title of Salpa.
There are many species of the salpæ, but they bear a closer likeness to each other than do most of these simple tribes of being. In form they all resemble diminutive purses, composed of highly transparent jelly, with wide mouths like the ordinary clasp—and strengthened by a net-work of ribbons interwoven with the general texture of the purse. These are designed to supply the place of muscles. The salpæ move through the water by contracting the net-work, so as to render the cavity smaller and expel the water from it with some force; then, relaxing the fibres, they allow their natural elasticity to expand them to their original form; thus drawing in a fresh supply of fluid with which to renew the effort. In this manner they are driven onward, always retreating from the principal orifice of the sac. But I will not detain you with a detailed description of their singular organization. It is enough for our present purpose to state that near the bottom of the purse, within the thickness of its walls, there is a golden spot, as if a solitary coin was there deposited. This spot alone enables us to see the animal distinctly when floating in the water.
When young, these little creatures adhere together in strings or cords arranged like the leaflets of a pinnated leaf, in consecutive pairs, to the number of twenty or more. At that period, the most common species in the South Atlantic rarely exceed one half an inch in length, and the yellow spot hardly equals in size an ordinary grain of sand; yet, in certain regions of the ocean these salpæ swarm in such inconceivable multitudes that the sea assumes the appearance of a sandy shoal for miles in length and breadth. To the depth of many fathoms their delicate bodies are closely huddled together, until the constant repetition of the diminutive colored spots renders the water perfectly opaque, and so increases its consistence that the lighter ripple of the surface breaks upon the edge of the animated bank, while the heavier billows roll on smoothly, with the regular and more majestic motion of the ground swell. In passing through such tracts the speed of the vessel is sometimes sensibly checked by the increased resistance of the medium in which she moves; and when a bucket full of brine is lifted from the sea, it may contain a larger portion of living matter than of the fluid in which it floats.
There can be no reasonable doubt that most of those false shoals which disfigure the older charts—their existence proved upon authorities of known veracity and denied by others no less credible—have really been laid down by navigators who have met with beds of salpæ, and were ignorant of their true nature.
I have never seen these animals emitting light, but it is well known that many phosphorescent animalcules shine only in certain stages of the weather or at certain seasons of the year: and as several distinguished travellers have spoken of their luminous properties, it is at least probable that they or their congeners act an important part in dramas similar to that which has been just described. At all events, their history clearly shows the vastness of the scale of animal existence in the superficial waters of the ocean. But for the little yellow spot within their bodies, they would be totally invisible at the distance of a few feet in their native fluid, and could not interfere appreciably with the progress of the rays of light.
If further proof were necessary to show the incalculable increase of many oceanic tribes, it might be found in the history of living beings much more familiar to the mariner. Most persons have met with notices of the Portuguese man-of-war, called, by naturalists physalia, a living air sac of jelly provided with a sail, armed with a multitude of dependant bottle shaped stomachs, all capable of seizing prey, and colored more beautifully than the rainbow. This splendid creature pursues its way over the waves with all the skill of an accomplished pilot, and furnishes, when caught, one of the most astonishing examples of the adaptation of animal structure to the peculiar wants, and theatre of action of living beings, one of the most striking evidences of Omniscient Wisdom which nature offers to the moralist. The physalia rarely sails in squadrons, but wanders solitary and self-dependent over the tropical seas, a terror even to man, by the power which it possesses of stinging and inflicting pain upon whatever comes in contact with its long, trailing cables.