Chapter XXXVIII: Part II: The Inhabitants of the Sea (11)

_a_ and _b_. _Vorticlava humilis._
_c._ Four polypites of _Hydractinia echinata_, growing on
a piece of shell.
_d._ Portion of _Syncoryne Sarsii_, with medusiform zoöids (ρ),
budding from between the tentacles (τ) of the polypite (ο).
--(All, except _a_, magnified.)
]

In a similar manner the Coryniadæ, a family of hydrozoic polyps, which, unpossessed of the firm investment of the sertularians, are frequently found decking sea-weeds and stones with dense arborescent structures, give birth to detached medusiform zoöids. On the other hand, many medusid forms produce organisms directly resembling their parents, and many fixed Hydrozoa, such as the Sertularidæ, do not give birth to free-swimming medusoids, but to ciliated gemmules, which, escaping from the capsules in which they had been formed, soon evolve themselves into true polyps. A great part of this "strange eventful history" is still enveloped in darkness, as the life of comparatively but few Hydrozoa has been thoroughly investigated; so much is certain that future observations will bring many new interesting relationships to light, and add new links to the chain which binds together the various members of the hydrozoic class.

Although the Ctenophora, thus named from the ciliated bands which constitute so obvious a feature in their physiognomy, closely resemble the Medusæ by their gelatinous consistence and their mode of life, yet a more complex organisation assigns them the highest rank among the Actinozoa, and approximates them to the sea-anemones. The elegant _Pleurobrachia pileus_, which in the summer so often appears on our coasts in countless multitudes, is the species that has been longest known. The melon-shaped body, from half an inch to nearly an inch in length, is clear as crystal, and divided by eight longitudinal equidistant ribs into eight equally large segments or fields. These ribs are covered with numberless flat paddles or ciliæ, placed one above another, and obeying the will of the animal. When it wishes to swim backwards or forwards, it sets all its paddles in motion, whose united power drives the living crystal rapidly and gracefully through the water; and when it wishes to turn, it merely stops their movements on one side. In sunlight, the ribs of the pleurobrachia sparkle with all the colours of the rainbow; in darkness they emit a beautiful cerulean phosphorescence.

The prehensile apparatus of the elegant little creature is no less beautifully organised than its locomotive mechanism. It consists of two long tentacles emerging from the under part of the body, and capable of so wonderful a contraction as entirely to disappear within its cavity, where they are lodged in tubular sheaths. On one side they are provided at regular intervals with shorter and much thinner filaments, which roll together spirally when the chief tentacle contracts, and expand when it is stretched forth. On the secondary branches themselves still more minute threads are said to have been observed. Words are unable to express the beauty which the entire apparatus presents in the living animal, or the marvellous ease with which it can be alternately contracted, extended, and bent at an infinite variety of angles.

Most of the Ctenophora are spheroidal or ovate, but in Cestum elongation takes place to an extraordinary extent, at right angles to the direction of the digestive track, a flat ribbon-shaped body, three or four feet in length, being the result. The Callianiræ are remarkable for having their ciliated ribs elevated on prominent wing-like appendages, and the Beroës, which have no tentacles, receive their nourishment through a widely gaping mouth, whose size makes them amends for the deficiency of other prehensile organs. Such are but a few of the varieties exhibited by the beautiful and interesting Ctenophora.

In habit they resemble the oceanic Hydrozoa, like them swimming near the surface in calm weather, and again descending on the approach of a squall. Like them also, their delicate structures rapidly disappear when removed from the sea-water and exposed to the rays of the sun, an almost imperceptible film remaining the only trace of what was erewhile an active and beautiful organism. Yet in spite of their aqueous consistence the Ctenophora are very voracious, feeding on a number of floating marine animals, among which their own kindred seem especially to be preferred. The prey once swallowed is assimilated with a rapidity which to some may seem strange when the simple structure of the digestive apparatus is considered.

_a. Cestram Veneris._ _b. Eurhamphæa vexilligera._ _c. Beroë
rufescens._ _d. Callianira triploptera._ _e. Pleurobrachia pileus._
(_a_ is considerably reduced; _b_ slightly so; _c_ and _e_ are about
the natural size; the size of _d_ is uncertain.)
]

The land has its flowers; they bloom in our gardens, they adorn our meadows, they perfume the skirts of the forest, they brave the winds that blow round the high mountain peaks, they conceal themselves in the clefts of rocks, or spring forth out of ruins; wherever a plant can find room there Flora appears with her lovely gifts.

But the ocean also has its large radiate anemones, whose lustrous petals, still more wonderful than those of the land, for they are endowed with animal life, form the chief ornament of the crystal tide-pools, or of the sheltered basins of our rock-bound shores.

More than twenty species of these marine flowers, many of them displaying a gorgeous wreath of richly coloured tentacles, are denizens of the British waters; but the finest and largest are found along the margin of the equatorial ocean, where they occasionally measure a foot in diameter. Their tints are as various as the arrangement of their prehensile crown; fiery red and apple-green, yellow and white as driven snow. Sometimes the tentacles form a gorgon's head of long thick worms, clothed in satin and velvet, and sometimes a thicket of delicate filaments.

Nothing seems more inoffensive than a sea-anemone expanding its disc in the tranquil waters, but woe to the wandering annelide, to the shrimp, or whelk, or nimble entomostracon, that comes within reach of its urticating tentacles, for, plunged into a fatal lethargy, it is soon hurried to the gaping mouth of its voracious enemy, ever ready to engulf it in a living tomb. The morsel thus swallowed is retained in the stomach for ten or twelve hours, when the undigested remains are regurgitated, enveloped in a glairy fluid, not unlike the white of an egg. The size of the prey is frequently in unseemly disproportion to the preyer, being often equal in bulk to itself. Thus Dr. Johnstone mentions a specimen of _Actinia crassicornis_, that might have been originally two inches in diameter, and that had somehow contrived to swallow a scallop-valve of the size of an ordinary saucer. The shell fixed within the stomach was so placed as to divide it completely into two halves, so that the body, stretched tensely over, had become thin and flattened like a pancake. All communication between the inferior portion of the stomach and the mouth was of course prevented; yet instead of emaciating and dying of an atrophy, the animal had availed itself of what undoubtedly had been a very untoward accident to increase its enjoyments and chances of double fare. A new mouth, furnished with two rows of numerous tentacula, was opened upon what had been the base, and led to the under stomach; the individual had indeed become a sort of Siamese twin, but with greater intimacy and extent in its unions.

From this instance we may naturally infer that the Actiniæ are no mean adepts in the art of accommodating themselves to circumstances. They may be kept without food for upwards of a year; they may be immersed in water hot enough to blister their skins, or exposed to the frost, or placed within the exhausted receiver of the air-pump, and their hardy vital principle will triumph over all these ordeals. Their reproductive powers are truly astonishing. Cut off their tentacles, and new ones sprout forth; repeat the operation, and they germinate again. Divide their bodies transversely or perpendicularly through the middle, and each half will develop itself into a more or less perfect individual.

But these apparently indestructible creatures die almost instantly when plunged into fresh water, which is for them, or for so many other marine animals, a poison no less fatal than prussic acid to man.

Though generally firmly attached by means of a glutinous secretion from their enlarged base to rocks, shells, and other extraneous bodies, the sea-anemones can leave their hold, and remove to another station, whensoever it pleases them, either by gliding along with a slow and almost inperceptible movement or by reversing the body and using the tentacula as feet; or, lastly, inflating the body with water so as to diminish its specific weight, they detach themselves, and are driven to a distance by the random motion of the waves. They are extremely sensible not only to external irritations--the slightest touch causing them to shrink into a shrivelled shapeless mass--but also of atmospherical changes. They hide their crown under a glare of light; but in a calm and unclouded sky expand and disclose every beauty, while they remain contracted and veiled in cloudy or stormy weather. The Abbé Dicquemare has even found, from several experiments, that they foretell changes of the weather as certainly as the barometer. When they remain naturally closed there is reason to fear a storm, high wind, and a troubled sea; but a fair and calm season is to be anticipated when they lie relaxed with expanded tentacula. The ova of the Actiniæ are detained for some time after their separation in the interseptal spaces, or even in the stomach, and there hatched, as it were, into their lasting form. On emerging into the open ocean, they already resemble their full-grown relatives, the only difference consisting in a smaller number of tentacles and septa. The sea-anemones were consequently supposed to be viviparous, an error which more accurate observations have fully refuted.

_a._ Branch to which the polypary is fixed.
_b._ Foot.
_c._ Trunk.
_d._ Polyp-bearing branches.
_e._ Polyps contracted within the foot.
]

Both the Ctenophora and the Sea-Anemones are single or solitary, but the vast majority of the Actinozoa consist of aggregated animals attached to one another by lateral appendages, or by their posterior extremity, and participating in a common life, while at the same time each member of the family enjoys its independent and individual existence. These compound polyps are all either _Alcyonarians_, in which each polyp is furnished with eight pinnately fringed tentacles, or _Zoantharians_, in which the tentacula are simple or variously modified, and generally disposed in multiples of five or six. The Alcyonarians are again subdivided into the four families of the Alcyonidæ, the Pennatulidæ, the Gorgonidæ, and the Tubiporidæ.

The Alcyonidæ vary much in form, being either lobed, branched, rounded, or existing in a shapeless mass or crust, while the interior substance is of a spongy or cork-like nature, surrounded by tubular rays enclosed in a sort of tough fleshy membrane. The _Alcyonium digitatum_ is one of our most common marine productions, so that on many parts of the coast scarce a shell or stone can be dredged from the deep that does not support one or more specimens. As it lies on the shore, it certainly offers few inducements from its beauty to recommend it to further notice, and seems fully to warrant the more expressive than elegant names of "cow's paps," "dead man's toes," or "dead man's hands," which the fishermen have conferred on it. On putting one of these shapeless masses into a glass of sea-water, however, and allowing it to remain for a little time undisturbed, its real nature becomes apparent, and a series of most interesting phenomena present themselves. The dull orange mass, which was at first opaque and of a dense texture, slowly swells and becomes more diaphanous, apparently by the absorption of the surrounding water into its substance, until, having attained its full dimensions, numerous dimples appear, studding its entire surface, each of which, as it gradually expands, reveals itself to be a cell, the residence of a polyp, which, gradually protruding itself, pushes out a cylindrical body, clear as crystal, fluted like a column, and terminated by a coronet of eight delicately fringed tentacula. The unsightly aspect of the trunk, which reminded us of cadaverous fingers or toes, is now forgotten, just as we forget the uncouth branches of a cactus when we see it clothed with its gorgeous flowers. All the polyp-cells are connected by a complicated system of inosculating canals, bound together by a fibrous network, and lying imbedded in a transparent jelly, which forms the fleshy part of the compound animal. The eggs are lodged in the tubes, and at length discharged through the mouth.

The Sea-Pens, or Pennatulæ, are remarkable from the circumstance that, although they possess an internal calcareous support, they are not permanently attached to foreign bodies. The lower portion of the stem, which strikingly resembles the barrel of a quill, is naked, and, when found in the bays upon our coast, is generally stuck into the mud at the bottom like a pen into an inkstand, whilst the upper two thirds of the stem are feathered with long closely set pinnæ, comparable to the barbs of a quill, from the margin of which are protruded the rows of polyps which minister to the support of the common body of the compound animal. The purple-red _Pennatula phosphorea_, which is found in great plenty sticking to the baits on the fishermen's lines, especially when they use muscles to bait their hooks, is one of the most singular and elegant of the British sea-pens. Some authors believe that it is capable of using its fin-like arms like oars, but observations are wanting in corroboration. The pale orange fawn _Virgularia mirabilis_, an allied species, has a more elongated slender form than the pennatula. Its rod-like body, from six to ten inches long, is furnished with short fin-like lobes of a crescent shape, which approach in pairs, but are not strictly opposite; they are about the eighth of an inch asunder, and are furnished along the margins with a row of urn-shaped polyp-cells. These very delicate and brittle animals seem to be confined to a small circumscribed part of the coast, which has a considerable depth and a muddy bottom, and the fishermen accustomed to dredge at that place believe from the cleanness of the Virgulariæ, when brought to the surface, that they stand erect at the bottom with one end fixed in the mud or clay.

The Gorgonidæ (Gorgonia, Primnoa, Corallium, Isis, Mopsea) mainly differ from the Alcyonidæ in having an erect and branching stem, firmly rooted by its expanded base. A soft and fleshy crust, studded with numerous polyps, envelops a solid horny or calcareous axis, which serves as a support to the arborescent structure, and enables it to rise to a height of several feet, or even, if we are to credit the Norway fishermen, to rival our forest-trees in magnitude. This they conclude to be the case from their nets being sometimes entangled on the trunk or stem of the _Primnoa lepadifera_, as this large species of gorgon is called, when the united strength of several men is unable to free the nets. "They have even assured me," says Sir A. Capell de Brooke, "that the corals grow to the height of fifty or sixty feet, as they judge from the following circumstance, which seems clear and simple. The lines for the red-fish, which is found in the greatest plenty where the primnoa grows, are set in very deep water at the distance of about six feet from the bottom, and in the parts where it is flat and level, which they can tell from their soundings. On drawing up the lines at the distance of forty, fifty, or sixty feet, and sometimes even more from the bottom, they get entangled with some of the upper parts or branches of the gorgon, which are thus torn off, and hence they reasonably conclude that the animal rises to this height."

The Gorgonidæ either branch away irregularly like shrubs, or else their branches inosculate and form a kind of net or fan, as in the _Flabellum Veneris_, a beautiful Indian species, which some naturalist of more than usual fancy has appropriated to the use of Venus.

Four British species of Gorgonia are recorded. _G. verrucosa_, the commonest of these, abounds in deep water along the whole of the south coast of England. It is more than twelve inches in height, and fifteen or seventeen in breadth, and expands laterally in numerous cylindrical and warty branches. It is somewhat fan-shaped, but does not form a continuous network. Its coral has a dense black axis, with a snow-white pith in the centre, and is covered, while living, with a flesh-coloured crust. The flexible corneous stem of the Gorgonias enables them to bend beneath the passing current, and thus prevents their long and slender ramifications from breaking, while the hard calcareous branches of the valuable red coral (_Corallium nobile_) are sufficiently short and strong to resist the violence of the sea. This beautiful marine production, though also occurring in the Ethiopic Ocean and about Cape Negro, is chiefly found in the Mediterranean, on the shores of Provence, about the isles of Majorca and Minorca, on the south of Sicily, and on the coast of Africa. It grows on rocky bottoms, and frequently in an inverted position, or downwards from the under surface of stones, generally at a depth of several hundred feet.

Gorgonia nobilis. (A small detached portion magnified.)]

When alive, the soft rind which invests the valuable central stony axis is studded with snow-white polyps. The fishery is still carried on in the same way as it was described by Marsigli 150 years ago. The net is composed of two strong rafters of wood tied crosswise, with leads fixed to them; to these they fasten a quantity of hemp twisted loosely round and intermingled with some loose netting. This apparatus is let down, and while the boat is sailing or being rowed along, alternately raised and dropped so as to sweep a certain extent of the bottom and to entangle the corals in its coarse meshes. The labour, as may be imagined, is very great; frequently, after a long toil, the net is brought up empty, or filled only with other marine productions, which, however interesting they may be to the naturalist, are perfectly worthless in the eyes of the coral-fisher; and not seldom immense exertions are required to loosen it from the rocks, among which it has got entangled.

The chief seat of the coral-fishery is at present along the coasts of Algeria and Tunis, where it is almost exclusively carried on by the Italians, who fit out more than 400 small ships, or "corallines," of from five to sixteen tons, for this purpose. In spring this fleet of nut-shells leaves the ports of Torre del Greco, Sicily, Sardinia, and Genoa, and proceeds to its various points of destination, where it remains until the autumnal gales compel the fragile "corallines" to retire. Every month or fortnight the products of the fishery are delivered up to agents in Bona or La Calle, under whose direction the corals are sorted, packed in cases, and sent to Naples, Leghorn, or Genoa, where they are cut, polished, and manufactured into necklaces and other ornaments or trinkets. About 4,000 sailors are employed in the fishery, each man receiving an average pay of 380 franks for the season, which he almost entirely brings home with him, his trifling expenses on land being generally defrayed by the small pieces of coral he manages to conceal from the sharp eye of the "padrone." The average quantity of corals fished by each "coralline" amounts to about six hundredweight, and the total value of the fishery to more than 200,000_l._, without taking into account the produce of the fisheries at Stromboli, in the Straits of Messina, and other parts of the Italian coast.

The manufactured articles sell of course for a much higher price, so that the "red coral" is a by no means inconsiderable article of trade. Great quantities are exported to India, and in Leghorn and Genoa several large manufactories work exclusively for that distant market, where the blood-red corals, whose colour harmonises with the dark complexion of the native ladies, are particularly in demand, while those of a roseate hue are preferred in Europe.

The fishermen have a strange belief that the corals are by nature soft, but immediately turn into stone from terror when entangled by the net. There is also a legendary tale of an enchanted coral-tree, large and powerful as an oak, which is said to grow in a deep grotto at the foot of Mont Alban, on the Ligurian coast. It extends its arms when no danger is nigh, but immediately withdraws them, like a cuttle-fish, at the approach of an insidious enemy. This superstition is so firmly rooted that, while Professor Vogt was at Villafranca in 1865, a "coralline" arrived from Torre del Greco for the purpose of fishing for this imaginary prey. The "padrone" swore he would not leave the neighbourhood before he had secured his prize, hoping to enrich himself with the spoils, but doomed, no doubt, to a grievous disappointment, and a considerable loss, on a coast where but few ordinary corals are found.

In the elegant _Isis hippuris_, which grows in the Indian Ocean, and is frequently found in cabinets of natural history, the horny and calcareous matter of the axis is disposed in alternate joints, so as to unite flexibility with firmness. A similar structure of alternately disposed calcareous and horny segments occurs in Mopsea. In Isis branches are developed from the calcareous, in Mopsea from the horny segments of the axis.

The Tubiporidæ are confined to the narrow limits of a single genus containing but few species. Here the polypary is composed of distinct calcareous tubes rising from a fleshy or membranaceous basis, and arranged in successive stages. These tubes are separated from each other by considerable intervals, but mutually support each other by the interposition of external horizontal plates, formed of the same dense substance as themselves, by which they are united together, so that a mass of these tubes exhibits an arrangement something like that of the pipes in an organ, whence the beautiful Indian species, _Tubipora musica_, has derived its name. From the upper ends of the tubes the polyps are protruded, and being, when alive, of a bright grass-green colour, they contrast very beautifully with the rich crimson of the tubes they inhabit.

In our seas, the coralligenous Zoophytarians, distinguished by the hard calcareous skeletons they deposit within their tissues are but feebly represented by a few straggling Caryophylliæ, but in the tropical ocean they branch out into numerous families, genera, and species, and play a highly important part in the economy of the maritime domain. Originally proceeding from single ova, which at first freely move by means of vibratile ciliæ, and become fixed after a short period of erratic existence, they multiply by gemmation, and grow into an immense variety of forms, of which the following description by one who has long and attentively studied them in their native haunts may serve to give an idea. "Trees of coral," says Professor Dana, "are well known; and although not emulating in size the oaks of our forests--for they do not exceed six or eight feet in height--they are gracefully branched, and the whole surface blooms with coral polyps in place of leaves and flowers. Shrubbery, tufts of rushes, beds of pinks, and feathery mosses, are most exactly imitated. Many species spread out in broad leaves or folia, and resemble some large-leaved plant just unfolding; when alive, the surface of each leaf is covered with polyp-flowers. The cactus, the lichen clinging to the rock, and the fungus in all its varieties, have their numerous representatives. Besides these forms imitating vegetation, there are gracefully modelled vases, some of which are three or four feet in diameter, made up of a network of branches and branchlets, and sprigs of flowers. There are also solid coral hemispheres like domes among the vases and shrubbery, occasionally ten or even twenty feet in diameter, whose symmetrical surface is gorgeously decked with polyp-stars of purple and emerald-green."

Under such aspects appear the living organisms whose combined efforts have mainly constructed those reefs and islands of coral origin which now lie scattered far and wide over the surface of the equatorial ocean. Words are inadequate to express the splendour of the submarine gardens with which the lithophytes clothe the rocky shores of the tropical seas.

"There are few things more beautiful to look at," says Captain Basil Hall, "than these corallines when viewed through two or three fathoms of clear and still water. It is hardly an exaggeration to assert that the colours of the rainbow are put to shame on a bright sunny day by what meets the view on looking into the sea in those fairy regions." And Ehrenberg was so struck with the magnificent spectacle presented by the living polyparia in the Red Sea that he exclaimed with enthusiasm, "Where is the paradise of flowers that can rival, in variety and beauty, these living wonders of the ocean!"

Besides the charms of their own growth, the tropical coral gardens afford a refuge or a dwelling-place to numberless animals clothed in gorgeous apparel. Fishes attired in azure, scarlet, and gold, crustaceans, sea-urchins, sea-stars, sea anemones, annelides, of a brilliancy of colour unknown in the northern seas, glide or swim along through their tangled shrubberies; and frequently the gigantic tridacna, embedded in their calcareous parterres, discloses, on opening her ponderous valves, her violet mantle tinted with emerald-green. The enchanted naturalist lingers for hours over the magnificent spectacle, and forgets the lapse of time, as wonders upon wonders crowd on his enraptured gaze.

But the tropical coral-gardens serve not only as a harbour of refuge to the numberless creatures that frequent their labyrinthine recesses, for many annelides, crustaceans, asterias, and even fishes, feed upon their animal flowrets. Among these, the Scari are provided with a very remarkable dental apparatus to protect their mandibles from injury while biting the calcareous corals. These fishes have their jaws, which resemble the beak of a parrot (whence they receive their usual appellation "parrot fishes"), covered externally with a kind of pavement of teeth, answering the same purpose as the horny investment of the mandibles of the bird. The teeth that form this pavement are perpetually in progress of development towards the base of the jaw, whence they advance forward, when completed, to replace those which become worn away in front by the constant attrition to which they are subjected. Thus armed, the Scari browse without difficulty on the newest layers of the stony corals, digesting the animal matter therein contained, and setting free the carbonate of lime in a chalky state. Many of the Diodons, Chætodons, and Balistæ or file-fishes, of which Kittlitz saw some new species, one still more splendid than the other, in every lagoon-island he visited in the long range of the Carolines, likewise feed upon corals, and possess a dental apparatus fit for masticating their refractory aliment. The Diodons have grooved teeth, excellently adapted to crush and bruise, and the Balistæ have eight strong conical teeth in every jaw, with which they easily nip off the shoots of the coral bushes.

Of the reef-building corals it may well be said that they build for eternity. The bones of the higher animals vanish after a few years, but the stony skeleton of the polyp remains attached to the spot of its formation, and serves as a basement or stage for new generations to build upon. Life and death are here in concurrent or parallel progress; generally the whole interior of a corallum is dead. The large domes of the astræas are in most species covered with a hemispherical living shell, about half an inch thick; and in some porites of the same size the whole mass is lifeless, except the exterior for a sixth of an inch in depth.

We are astonished when travellers tell us of the vast extent of certain ancient ruins; but how utterly insignificant are the greatest of these when compared with the piles of stone accumulated in the course of ages by these minute, and individually so puny architects! The history of the formation of coral-reefs is no less wonderful than their extent. They have been divided, according to their geological character, into three classes. The first fringes the shores of continents or islands (shore-reefs); the second, rising from a deep ocean, at a greater distance from the land, encircles an island, or stretches like a barrier along the coast (encircling-reefs, barrier-reefs); the third, enclosing a lagoon, forms a ring or annular breakwater round an interior lake (atolls, or lagoon-islands).

Many of the high rocky islands of the Pacific lie, like a picture in its frame, in the middle of a lagoon encircled by a reef. A fringe of low alluvial land in these cases generally surrounds the base of the mountains; a girdle of palm-trees, backed by abrupt heights, and fronted by a lake of smooth water, only separated from the deep blue ocean by the breakers roaring against the encircling reef; such, for instance, is the scenery of Tahiti, so justly named "the queen of islands." But the encircling reefs are often at a much greater distance from the shore. Thus in New Caledonia they extend no less than 140 miles beyond the island.

As an example of barrier-reefs, I shall cite that which fronts the north-east coast of Australia. It is described by Flinders as having a length of nearly a thousand miles, and as running parallel to the shore at a distance of between twenty and thirty miles from it, and in some parts even of fifty and seventy. The great arm of the sea thus inclosed, has a usual depth of between ten and twenty fathoms. This probably is both the grandest and most extraordinary reef now existing in any part of the world.

The atolls, or lagoon-islands, are numerously scattered over the face of the tropical ocean. The Marshall and Caroline islands, the Paumotic group, the Maldives and Lacadives, and many other groups or solitary islets of the Pacific or Indian Ocean, are entirely built up of coral; every single atom, from the smallest particle to large fragments of rock, bearing the stamp of having been subjected to the power of organic arrangement. A narrow rim of coral-reef, generally but a few hundred yards wide, stretches around the enclosed waters. When a lagoon-island is first seen from the deck of a vessel, only a series of dark points is descried just above the horizon. Shortly after, the points enlarge into the plumed tops of cocoa-nut trees, and a line of green, interrupted at intervals, is traced along the water's surface.

The long swell produced by the gentle but steady action of the trade wind, always blowing in one direction over a wide area, causes breakers which even exceed in violence those of our temperate regions, and which never cease to rage. It is impossible to behold these waves without feeling a conviction that a low island, though built of the hardest rock, would ultimately yield, and be demolished by such irresistible forces. Yet the insignificant coral-islets stand and are victorious; for here another power, antagonistic to the former, takes part in the contest. The organic forces separate the atoms of carbonate of lime one by one from the foaming breakers, and unite them in a symmetrical structure. Let the hurricane tear up its thousand huge fragments, yet what will this tell against the accumulated labours of myriads of architects at work night and day, month after month. Thus do we see the soft and gelatinous body of a polyp, through the agency of vital laws, conquering the great mechanical power of the waves of an ocean, which neither the art of man nor the inanimate works of nature could successfully resist.

The reef-building corals, so hardy in this respect, are extremely sensitive and delicate in others. They absolutely require warmth for their existence, and only inhabit seas the temperature of which never sinks below 60° Fahr. They also require clear and transparent waters. Wherever streams or currents are moving or transporting sediment, there no corals grow, and for the same reason we find no living zoophytes upon sandy or muddy shores.

As within one cast of the lead coral-reefs rise suddenly like walls from the depths of ocean, it was formerly supposed that the polyps raised their structures out of the profound abysses of the sea; but this opinion could no longer be maintained, after Mr. C. Darwin and other naturalists had proved that the lithophytes cannot live at greater depths than twenty or at most thirty fathoms.

Hereupon Quoy and Gaimard broached the theory that corals construct their colonies on the summits of mountain ridges, or the circular crests of submarine craters, and thus accounted both for the great depths from which the coral-walls suddenly rise, and the annular form of lagoon islands. Yet this theory, ingenious as it was, could not stand the test of a closer examination: for no crater ever had such dimensions as, for instance, one of the Radack Islands, which is fifty-two miles long by twenty broad; and no chain of mountains has its summits so equally high, as must have been the case with the numerous reef-bearing submarine rocks, considering the small depth from which the lithophytes build. Another seemingly inexplicable fact was, that, although corals hardly exist above low-water mark, reefs are found at Tongatabu or Eua, for instance, at elevations of forty and even three hundred feet above the level of the ocean.

Mr. Charles Darwin was the first to give a satisfactory explanation of all the phenomena of coral formations, by ascribing them to the oscillations of the sea bottom, to its partial upheaving or subsidence.

It is now perfectly well known that large portions of the continent of South America, Scandinavia, North Greenland, and many other coasts, are slowly rising, and that other terrestrial or maritime areas are gradually subsiding. Thus on every side of the lagoon of the Keeling Islands, in which the water is as tranquil as in the most sheltered lake, Mr. Darwin saw old cocoa-nut trees undermined and falling. The foundation-posts of a store-house on the beach, which, the inhabitants said, had stood seven years before just above high water, were now daily washed by the tide.

Supposing on one of these subsiding areas an island-mountain fringed with corals, the lithophytes, keeping pace with the gradual sinking of their basis, soon raise again their solid masses to the level of the water; but not so with the land, each inch of which is irreclaimably gone. Thus the fringing reef will gradually become an encircling one; and, if we suppose the sinking to continue, it must by the submergence of the central land, but upward growth of the ring of coral, be ultimately converted into a lagoon-island.

The numerous _atolls_ of the Pacific and Indian Ocean give us a far insight into the past, and exhibit these seas overspread with lofty lands where there are now only humble monumental reefs dotted with verdant islets. Had there been no growing coral, the whole would have passed away without a record; while, from the actual extent of the coral-reefs and islands, we know that the entire amount of the high land lost to the Pacific was at least 50,000 square miles. But as other lands may have subsided too rapidly for the corals to maintain themselves at the surface, it is obvious that the estimate is far below the truth.

As living coral-reefs do not grow above low-water mark, it may well be asked how habitable islands can form upon their crests. The breakers are here the agents of construction. They rend fragments and blocks from the outer border of the reef and throw them upon the surface. Corals and shells are pulverised by their crushing grinding power, and gradually fill up the interstices. In this manner the pile rises higher and higher, till at last even the spring tides can no longer wash over it into the lagoon, on the border of which the fine coral sand accumulates undisturbed. The seeds which the ocean-currents often carry with them from distant continents find here a congenial soil, and begin to deck the white chalk with an emerald carpet. Trees, drifting from the primeval forest, where they have been uprooted by the swelling of the river on whose banks they grew, are also conveyed by the same agency to the new-formed shore, and bring along with them small animals, insects, or lizards, as its first inhabitants. Before the stately palm extends its feathery fronds sea-birds assemble on this new resting-place, and land-birds, driven by storms from their usual haunts, enjoy the shade of the rising shrubbery. At last, after vegetation has completed its work, man appears on the scene, builds his hut on the fruitful soil which falling leaves and decaying herbs have gradually enriched, and calls himself the master of this little world. In this manner all the coral-reefs and islands of the tropical seas have gradually become verdant and habitable; thus has arisen the kingdom of the Maldives, whose sultan, Ibrahim, glories in the title of sultan of the thirteen atolls and twelve thousand isles. May his shadow never be less!

CHAP. XVIII.

PROTOZOA.

The Foraminifera.--The Amœbæ--Their Wonderful Simplicity of
Structure.--The Polycystina.--Marine Infusoria.--Sponges--Their
Pores--Fibres and Spiculæ--The Common Sponge of Commerce.

Think not, reader, that the life of the ocean ends with the innumerable hosts of fishes, molluscs, crustacea, medusæ, and polyps we have reviewed, and that the waters of the sea or the sands of the shore have now no further marvels for us to admire. The naked eye indeed may have attained the limits of life, but the microscope will soon reveal a new and wonderful world of animated beings.

Take only, for instance, while wandering on the beach, a handful of drift-sand, and examine it through a magnifying glass. You will then not seldom find, among the coarser grains of inorganic silica, a number of the most elegant shells; some formed like ancient amphoræ, others wound like the nautilus, but all shaped in their minuteness with a perfection which no human artist could hope to equal in the largest size.

_a._ Natural size.
_b._, _c._ The same, highly magnified.
]

The knowledge of these charming little marine productions is of modern date, for they were first observed in the sand of the Adriatic by Beccaria in 1731, and for some time believed to belong exclusively to that gulf. At a later period some species were discovered here and there in England and France, but their universality and importance in the economy of the ocean were first pointed out in 1825, by the distinguished French naturalist Alcide d'Orbigny.

The sand of many sea-coasts is so mixed with Foraminifera, as they have been called from the openings with which their shells are pierced, that they often form no less than half its bulk. Plancus counted 6000 in an ounce of sand from the Adriatic, and d'Orbigny reckoned no less than 3,849,000 in a pound of sand from the Antilles. Along the whole Atlantic coast of the United States, the plummet constantly brings up masses of foraminiferous shells from a depth of ninety fathoms, so that the vast extent of ocean-bottom, which itself forms but a small part of the domains they occupy, is literally covered with their exuviæ.

Thus their numbers surpass all human conception, nor can any other series of beings be compared to them in this respect; not even the minute crustaceans which colour thousands of square miles on the surface of the sea, and, according to Scoresby, form almost exclusively the food of the huge Greenland whale; nor the infusory animals of the fresh-water, whose shields compose the Bilin slate quarries in Bohemia; for these are limited in their distribution, whereas the Foraminifera occur in all parts of the world.

The resemblance of the Foraminifera to the nautili and ammonites at first led naturalists to suppose that they formed part of the same class, which in a long course of centuries had dwindled down in less congenial seas to almost invisible dimensions; but a closer investigation proved them to belong to a much lower order of beings, nearly related to the Amœbæ, which likewise occur all over the ocean. Other animals excite our wonder by their complicated structure, but the amœba raises our astonishment by the excessive simplicity of its organisation. The amœba is nothing more than a living globule of mucus, a transparent, colourless, contractile substance, or plastic mass, the individual life of which shows itself in manifold changes of form, bearing the character of voluntary motion. When an amœba approaches another minute animal or plant unable to move out of its reach, it sends out extemporaneous feet, which soon clasp the prey on all sides, and the prisoner lies embedded in the living mucus until all his soluble parts have been absorbed. There is absolutely no trace of particular organs in the amœba; all its constituent particles may be used for any purpose, all equally move and digest, and each can at any time perform the organic functions pertaining to the whole.

The shell is perforated with holes, through which the different lobes of the animal communicate, and thread-like portions are protruded externally.]

In their internal simplicity the Foraminifera are on a par with the amœbæ, and differ from them only in respect of their outward form. The amœbæ are naked, while the Foraminifera are covered with a shell, out of which, through one or numerous openings, the animal protrudes the processes which it requires for creeping or seizing its prey. These processes or filaments of mucus frequently ramify, closing as they spread, and sometimes covering an area of several lines in diameter, in the centre of which the animal inclosed in its shell waits for its prey, like a spider in its net.

The extended filaments appear to have something venomous about them; for Dr. Schultze, to whom we owe an interesting monograph on the Foraminifera, frequently saw small and sprightly parameciæ, colpodes, and other infusoria drop down paralysed as soon as they touched the net.

_a. Lagena striata._
_a′. Nodosaria rugosa._
_b. Marginulina raphanus._
_b′._ Longitudinal section of shell of ditto.
_c. Polystomella crispa_, with its pseudopodia protruded.
_d. Nummulites lenticularis_, shown in horizontal section.
_e. Cassidulina lævigata._
_f. Textularia globulosa._
_g. Miliolina seminulum._
_g′._ Animal of Miliolina removed from its shell.
]

The amazing variety of form of the Foraminifera is no less remarkable than the elegance of their delicately chiselled shells, and may well be called immense, as no less than 2,400 living and fossil species have already been distinguished by naturalists, and a far greater number is probably still nameless and unknown. Though generally so minute that the diameter of the pores through which they protrude their filaments usually only ranges from 1/3000 to 1/10000 of an inch yet the diminutive world of the Foraminifera has also its giants, particularly among the fossil species, such as the Nummulites, which occur in such prodigious numbers in the limestone of the Egyptian pyramids, and whose flattened lenticular coin-like forms (d) attain the comparatively gigantic diameter of several inches. Thus the material with which the proud Pharaohs of the Nile constructed their colossal tombs was originally piled up at the bottom of the sea by countless generations of shell-cased Protozoa.

The Foraminifera are among the oldest inhabitants of our globe,[T] and as the present ocean contains them in countless multitudes, thus have they swarmed in the waters of the primeval seas from the first dawn of creation, and piled up the monuments of their existence in vast strata of limestone. A great part of the rocky belt from Rügen to the Danish isles, the white chalk cliffs which, beginning in England, extend through France as far as Southern Spain, are chiefly composed of the shells of Foraminifera, and the zone of Nummulite limestone, which served to build the huge quadrilateral monument of Cheops, forms a band, often 1,800 miles in breadth, and frequently of enormous thickness, from the Atlantic shores of Europe and Africa through Western Asia up to North India and China; enough to satisfy the most extravagant architectural folly of millions of despots. So important is the part which these beings, individually so minute, have performed and still perform in the geological annals of the globe.

[Footnote T: The _Eozoon canadense_, the oldest of known organic remains, found in the Upper Laurentian series, which preceded the Cambrian formation, is a Foraminifer. Millions of years must have passed since it first felt and moved.]

Many of these "minims of nature" consist of only one chamber, and hence are called unilocular or monothalamous; but a vast proportion consist of several chambers, and hence are called multilocular or polythalamous. The latter, however numerous their chambers or seemingly complex their structure, always originate as a single shell. The primitive jelly-sphere, or first sarcode segment, secretes around itself its appropriate calcareous envelope. Having grown too large for its habitation, it protrudes a portion of itself without, and thus forms a second segment. If by a process of spontaneous fission this segment becomes quite detached from its parent, and repeats the life and method of reproduction of the latter, a series of monothalamous shells will be formed. But if by means of a sarcode band the primitive segment maintains its connection with its immediate offspring, and this, repeating the reproductive process, does the same, a compound shell will, of course, be the result.

Among the microscopic denizens of the ocean, the Polycystina rival the Foraminifera both by their number and their wonderful elegance of form and structure. Their body consists of the same viscid homogeneous plastic mass, termed "sarcode" by the naturalists; like them they are capable of protruding it through the foramina with which their shell is pierced, and consequently they are ranked with them among the Rhizopods, or root-footed animalcules, that form the lowest order of the Protozoa, the lowest class of the animal world.

_a. Podocyrtis Schomburgkii. b. Haliomma Humboldtii._]

It is a peculiar feature of these beautiful little shells (whose delicate sculpture frequently reminds the observer of the finest specimens of the hollow ivory balls carved by the Chinese) that they are usually surmounted by a number of spine-like projections, very frequently having a radiate disposition. Some have an oblong shape (Podocyrtis), others a discoid form (Haliomma), from the circumference of which the silicious spines project at regular intervals, so as to give them a star-like aspect. They are generally of a smaller size than even the Foraminifera, appear to be almost as widely diffused, and have also largely contributed to the structure of the earth-rind. They were first discovered by Professor Ehrenberg at Cuxhaven, on the North Sea; they were afterwards found by him in collections made in the antarctic seas, and have been brought up by the sounding lead from the bottom of the Atlantic at depths of from 1,000 to 2,000 fathoms.

The term Infusoria, which formerly comprised a most heterogeneous assemblage of minute plants and animals, is now confined to the highest order of the Protozoa, distinguished from the Rhizopods by the possession of a mouth and of ciliary filaments, whose vibrations serve them both for progression through the water and for drawing alimentary particles into the interior of their body. Though most of the Infusoria live in ponds, morasses, pools, wells, or cisterns, yet many are marine, as, for instance, the _Carchesium polypinum_, which is frequently found attached to corallines, and the _Vaginicola valvata_, which from its sheath and valve strongly reminds one of a tubicolar annelide.

_a._ _Vaginicola valvata_, showing animal extended, and
valve (φ) raised.
_a′._ The same, showing animal contracted within its sheath, and
valve (φ′) shut down.
_b._ _Lagotia viridis_, showing rotatory organ (ξ).
_b′._ Young animal of preceding.
]

The wide diffusion both in time and space of the marine Protozoa, and chiefly of the Foraminifera and Polycystina, is a sufficient proof of their vast importance in the household of the seas. Along with the Diatoms and other microscopical forms of vegetation on which their own existence depends, they evidently constitute the basis on which the superstructure of all the higher orders of the animal life of the ocean reposes. Hosts of minute crustaceans, annelides, acalephæ, and molluscs, feed upon their inexhaustible legions, and serve in their turn to sustain creatures of a larger and still larger size until finally Man is enabled to feast on the abundance of the seas.

The Porifera, or Sponges, were formerly supposed to belong to the vegetable kingdom, but their animal nature is now fully ascertained, for modern researches have proved that the soft glairy substance with which their skeleton is invested during life consists of "sarcode," similar to that which forms the soft parts of the Foraminifera and Polycystina. It is by this animated or organic gelatine, which can generally be pressed out with the finger, and in some species is copious even to nauseousness, that the solid parts of the sponge are deposited, and from it the whole growth of the mass proceeds. The framework or skeleton of the Porifera is usually composed of horny fibres of unequal thickness, which ramify and interlace in every possible direction, anastomosing with each other so as to form innumerable continuous cells and intricate canals, the walls of which in the recent sponge are crusted over with the gelatinous living cortex.

Generally this fibrous mass is interwoven with numerous mineral spicules of a wonderful elegance and variety of forms, for their shapes are not only strictly determinate for each species of sponge but each part of the sponge, it is believed, has spiculæ of a character peculiar to itself. Sometimes they are pointed at both ends, sometimes at one only, or one or both ends may be furnished with a head like that of a pin, or may carry three or more diverging points, which sometimes curve back so as to form hooks. Sometimes they are triradiate, sometimes stellar; in some cases smooth, in others beset with smaller spinous projections like the lance of the saw-fish. In many species they are embedded in the horny framework; in others, as, for instance, in Tethea Cranium, or in Halichondria, they project from its surface like a tiny forest of spears. They are generally composed of silex or flint, but in the genus Grantia they consist of carbonate of lime. Though the skeleton of most sponges is formed both of horny fibres and of mineral spicules yet the proportions of these two component parts vary considerably in different species. In the common sponge, for instance, the fibrous skeleton is almost entirely destitute of spicules, a circumstance to which it owes the flexibility and softness that render it so useful to man, while they predominate in the Halichondriæ, and sometimes even, as in the Grantiæ, completely supersede the horny fabric.

Currents passing inwards through the pores (_a a_), traversing the internal canals (b), and escaping by the larger vents (_c_, _d_).]

On examining a sponge, the holes with which the substance is everywhere pierced may be seen to be of two kinds; one of larger size than the rest, few in number, and opening into wide channels and tunnels which pierce the sponge through its centre; the other minute, extremely numerous, covering the wide surface, and communicating with the innumerable branching passages which make up the body of the skeleton. Through the smaller openings or pores the circumambient water freely enters the body of the sponge, passes through the smaller canals, and, ultimately reaching the larger set of vessels, is evolved through the larger apertures or oscula. Thus by a still mysterious agency (for the presence of cilia has as yet been detected but in one genus of full-grown marine sponges) a constant circulation is kept up, providing the sponge with nourishing particles and oxygen, and enabling its system of channels to perform the functions both of an alimentary tube and a respiratory apparatus.

Dr. Grant describes in glowing terms his first discovery of this highly interesting phenomenon: "Having put a small branch of sponge with some sea-water into a watch-glass, in order to examine it with the microscope, and bringing one of the apertures on the side of the sponge fully into view, I beheld for the first time the spectacle of this living fountain, vomiting forth from a circular cavity an impetuous torrent of liquid matter, and hurling along in rapid succession opaque masses, which it strewed everywhere around. The beauty and novelty of such a scene in the animal kingdom long arrested my attention, but after twenty-five minutes of constant observation, I was obliged to withdraw my eye from fatigue, without having seen the torrent for one instant change its direction or diminish in the slightest degree the rapidity of its course. I continued to watch the same orifice at short intervals for five hours, sometimes observing it for a quarter of an hour at a time, but still the stream rolled on with a constant and equal velocity."