CŒLENTERATA.

POLYPS AND JELLY-FISHES.

Despite the low rank they occupy in the hierarchy of animal life, the Coelenterata, comprising the numerous families of the Jelly-fishes and Polyps, play a most important part in the household of the ocean, for the sea is frequently covered for miles and miles with their incalculable hosts, and whole archipelagos and continents are fringed with the calcareous structures they raise from the bottom of the deep.

Their organisation is more simple than that of the preceding classes, for they have neither the complex intestinal tube of the polyzoa or the sea-urchins nor the jointed rays or arms of the star-fishes; their whole digestive apparatus is but a simple sac, and their instincts are reduced to the mere prehension of the food that the currents bring within reach of their tentacles, or to the retraction of these organs when exposed to a hostile attack.

But, simple as they are, they have been provided by Nature with a comparatively formidable weapon in those remarkable "thread-cells," or urticating organs, which are so constantly met with in their integuments, and chiefly in their tentacles.

The thread-cells are composed of a double-walled sac having its open extremity produced into a short sheath terminating in a long thread. A number of barbs or hooks are sometimes disposed spirally around the sheath, the thread itself being often delicately serrated. Under pressure or irritation the thread-cell suddenly breaks, its fluid escapes, and the delicate thread is so rapidly projected that the eye is utterly unable to follow the process. The violent protrusion of this barbed missile, along with the acrid secretion of the cell, causes many a worm or crustacean of equal or superior strength, that might have gone forth as victor from the struggle of life, to succumb to the coelenterate, and is even in many cases exceedingly irritating to the human skin. Besides enabling its possessor to derive his subsistence from animals whose activity, as compared with his own, might be supposed to have removed them altogether out of the reach of danger, these stings serve also as admirable weapons of defence, and many a rapacious crab or annelide that would willingly have feasted upon a sea-anemone is no doubt repelled by the venomous properties of its urticating tentacles.

The Coelenterata have been subdivided into two great classes: the Hydrozoa, in which the wall of the digestive sac is not separated from that of the cavity of the body, and the Actinozoa, in which the stomach forms a distinct bag separated from the wall of the cavity of the body by an intervening space, subdivided into chambers by a series of vertical partitions. Each of these two classes comprises a number of families of various forms and habits of life. Thus among the Hydrozoa, with whom I begin my brief survey of coelenterate life, some are of a compound nature (SertularidÆ, &c.), and, having once settled, remain permanently attached to the site of their future existence; while others (RhizostomidÆ, &c.) continue freely to roam through the water, and others again appear in the various stages of their development either as sessile polyps or as free-swimming MedusÆ.

The sertularian tribes are remarkable for the elegance of their forms, resembling feathers more or less stiff and angular, more or less flexible and plumose. Their bleached skeletons are among the commonest objects thrown out by the waves, and so plant-like is their appearance and manner of growth that, like the FlustrÆ, they might easily be mistaken for sea-weeds.

Originally produced from a single ovulum, every species, by the evolution of a succession of buds, after an order peculiar to each, grows up to a populous colony, and simultaneously with its growth the fibres by which it is rooted extend, and at uncertain intervals give existence to similar bodies, whence new polypiferous shoots take their origin, for these root fibres are full of the same medullary substance with the rest of the body. Thus the graceful sea-fir (Sertularia cupressina), the largest of our native species, may attain a height of two or three feet, and bear on its branches no less than 100,000 distinct microscopical polypi, each with its own crown of tentacles, and each of these armed with numerous thread-cells, as formidable in their way as the crustacean's claw or the annelide's embrace. But though each polyp has a certain share of independence yet its body is continuous with the more fluid pulp that fills the branches and stem of the common trunk, and by this means all the polyps of it are connected together by a living thread, and made to constitute a family whose workings are all regulated by one harmonious instinct. Each of these plant-like structures may therefore be considered as one animal furnished with a multitude of armed heads and mouths, and in all the other compound coelenterates we find a similar organisation. All the soft parts of a sertularian polypary are enclosed in a horny sheath (hydrosoma) which develops peculiar cup-shaped processes (hydrothecÆ) for the protection of each individual polyp, and capsules for the reproductive bodies (gonoblastidia) in which the ova are produced. The various modifications of form and structure of the polyps, of their hydrothecÆ and gonoblastidia, give rise to a number of families, genera, and species. Thus in the SertulariÆ the polypites are sessile, biserial, alternate, or paired; sessile and uniserial in the PlumulariÆ, and stalked in the CampanulariadÆ.

The free-swimming Jelly-fishes, or AcalephÆ, as they have been named by Aristotle on account of the stinging properties due to their urticating cells, are likewise among the commonest objects left upon our shores by the retreating tide. When stranded, they appear like gelatinous masses, disgusting to the sight; but these shapeless objects were beautiful while they moved along in their own element, and their simple organisation shows no less the masterhand of the Creator than the complex structure of the higher stages of animal existence. With the exception of the Ctenophora, they all belong to the hydrozoic class, and from the great diversity of their structure have been ranged under four orders, MedusidÆ, LucernaridÆ, CalycophoridÆ, and PhysophoridÆ.

The MedusidÆ are distinguished by their globular or bell-shaped disc, which by its alternate contractions and expansions forces them forward through the water. By contracting the whole or only part of its disc, the medusa has it in its power to direct its movements, and while thus swimming along with the convex side of the disc directed forwards, and its oral lobes and tentacles following behind like "streamers long and gay," it may well rank among the most elegant children of the sea.

From the roof of the disc a single polypite is suspended, whose mouth, generally produced into four lobes, though in some forms it is much more divided, passes into the central cavity (stomach) of the swimming organ, from which canals (either four in number, or multiples of four) radiate to join a circular vessel surrounding the margin of the bell. A shelf-like membrane or veil, extending around the margin, and highly contractile, assists locomotion by narrowing more or less the aperture of the bell, and thus concentrating its efforts upon a narrower space. More or less numerous tentacles generally depend from the margin, and around it are disposed two kinds of remarkable bodies—"vesicles" and "pigment spots," or "eye-specks"—which are supposed to be able to communicate the impressions of light and sound. This complexity of organisation in creatures which RÉaumur contemptuously styled mere lumps of animated jelly is all the more wonderful when we consider that they consist almost entirely of water, and shrink to a mere nothing when abandoned by their vital power. Thus of a medusa originally weighing many pounds but few traces remain after death; the ground is covered with a light varnish; all the rest has been absorbed by the thirsty sands.

The oceanic or free-swimming forms of the LucernaridÆ resemble the MedusidÆ by their bell-shaped umbrella, but differ from them by their internal structure, by the absence of a marginal veil, by the nature of their canal system and marginal bodies, and by their mode of development. The radiating canals, never less than eight in number, send off numerous branches, which form a very intricate network, and the vesicles and pigment-spots, here united into a single organ, termed the lithocyst, are each protected externally by a sort of hood, whence these jelly-fishes have been named "Stegonophthalmia," or "covered-eyed," by Forbes, to distinguish them from the naked-eyed "Gymnophthalmia," or MedusidÆ. The PelagidÆ (Chrysaora), which form one of the divisions of this group, are simple, and have their margin surrounded with tentacles like the MedusidÆ, while the RhizostomidÆ have no marginal tentacles, and consist of numerous polyps studding the trunks of a dependent tree. These animals have consequently no central mouth, but hundreds of little mouths all active for the welfare of the community.

The sessile LucernaridÆ differ from the other members of the order by the narrow disc or stalk which serves to fix their body when at rest. Their quadrangular mouth is in the centre of the umbrella expansion, and round the margin of the cup arise a number of short tentacles, disposed in eight or nine tufts in Lucernaria, and forming one continuous series in Carduella.

Though generally preferring to lie at anchor, the LucernaridÆ are able to detach themselves, and to swim in an inverted position by the slowly repeated movements of their cup-like umbrella. When in a state of expansion, few marine creatures exceed them in beauty and singularity of form; when contracted, they are shapeless, and easily overlooked. "Their mode of progression," says Mr. Couch, "differs under different circumstances. If intending to move to any great distance, they do so by loosening their attachments, and then, by various and active contortions, they waft themselves away till they meet with any obstruction, where they rest; and if the situation suits them, they fix themselves; if not, they move on in the same manner to some other spot. If the change be only for a short distance, as from one part of a leaf to another, they bend their campanulate rims, and bring the tentacula in contact with the jaws, and by them adhere to it. The foot-stalk is then loosened and thrown forward and twirled about till it meets with a place to suit it; it is then fixed, and the tentacula are loosened, and in this way they move from one spot to another. Sometimes they advance like the ActiniÆ, by a gliding motion of the stalk. In taking their prey, they remain fixed with their tentacula expanded, and if any minute substance comes in contact with any of the tufts, that tuft contracts, and is turned to the mouth, while the others remain expanded watching for prey."

The CalycophoridÆ are distinguished by the cup-shaped swimming organs, which form the most prominent part of their body. Generally transparent like glass, their course upon distant inspection is only revealed by the bright tints of some of their appendages. In Diphyes, the type of the group, the two cups (?, ?'') fit into each other so as to form a more or less perfect close canal. The common stem of the numerous polyp colony freely glides up and down the chamber thus formed, into which it can be completely retracted, and along its sides are placed the several appendages of the compound creature, consisting chiefly of polypites (p), tentacles, and organs of reproduction. Large specimens of Diphyes attain, when fully extended, a length of several inches, the stem giving support to at least fifty different polypites. The other genera of the order exhibit a great variety in the form and arrangement of their various parts; thus, in Vogtia, each of the swimming organs (?) is produced into five points, of which the three upper are much longer and stronger than the two lower. The individual polyps (p), large in size, but few in number, are congregated immediately under the swimming apparatus, and are provided with long and formidable tentacula.

In the PhysophoridÆ the basal end of the common polyp stem is modified so as to form a float or aËriform sac, which is, however, extremely different in shape, structure, and size in the various families. In the VelellÆ, the float, whose under surface is studded, besides one larger central polypite, with numerous small nutritive, reproductive, and tentacular bodies, forms a horizontal disc traversed by a diagonal triangular crest, and divided into numerous hollow chambers. Thus equipped, the semi-transparent velella, beautifully tinged with ultramarine, sails on the surface of the warmer seas, but the currents of the Gulf Stream, and the westerly winds, frequently drift it to the coast of Ireland, where it is often found on the beach, entangled in masses of sea-weed. Of the vast numbers in which it sometimes occurs, Herr von Kittlitz relates an interesting instance in his "Travels to Russian America and Micronesia." "Having passed 30° N. lat. in the Pacific, the sea was suddenly found covered with myriads of VelellÆ, of a size somewhat greater than the Atlantic species." Two days long the ship sailed through these floating masses, when suddenly the scene changed, and large clusters of barnacles appeared, which, having no doubt devoured the soft parts of the VelellÆ, now invested their horny skeletons. As the ship advanced, the number of the barnacle clusters augmented, which, to judge from the various sizes of the individuals, must have taken some time for their formation, and were apparently destined to increase until the final destruction of the VelellÆ hosts, into which, from their greater weight, they were continually drifting deeper and deeper by the action of the currents. Again two or three days elapsed, and as the surface of the sea occupied by both species of animals extended at the least over four degrees of latitude, a faint idea may be formed of their numbers. Shoals of dolphins and sperm-whales were busy exterminating the barnacles, as these had devoured the VelellÆ. The whole scene was an example on the grandest scale of the destruction and regeneration perpetually going on in the wastes of the ocean.

The PhysaliÆ, which far surpass the VelellÆ in size and beauty, are also inhabitants of the warmer seas, where the Physalia caravella, or "Portuguese man-of-war," is the mariner's admiration. On a large float-bladder eight or nine inches long and three inches broad, whose transparent crystal shines in every shade of purple and azure, rises a vertical comb, the upper border of which sparkles with fiery red. This beautiful float has a small opening at either end, and strong muscular walls, so that by their contraction its cavity can be considerably diminished. And thus partly by the escape of air forced out through the openings, and partly by the compression of what remains, the specific gravity is so much altered as to admit of the animal's sinking into the deep when danger threatens. Numerous polyps proceed from the lower surface, accompanied by tentacles having a sac-like extension at their base, and hanging down in beautifully blue and violet coloured locks or streamers. When fully extended, these tentacles form fishing lines fifteen or sixteen feet long, which, as their thread-cells are uncommonly large, at once paralyse the resistance of the fish or cephalopod they meet with. Then rolling together, they convey the senseless prey to the numerous mouths of the compound animal, which, sucking like leeches, pump out its nutritious juices. In this manner the greedy physalia devours many a bonito or flying-fish of a size far superior to its own, and such is the corrosive power of its tentacles that even man is punished with excruciating pains when heedlessly or ignorantly he comes within their reach. "One day," says Dutertre in his "History of the Antilles," "as I was sailing in a small boat, I saw a physalia, and as I was anxious to examine it more closely, I tried to get hold of it. But scarcely had I stretched out my hand when it was suddenly enveloped by a net of tentacles, and after the first impression of cold (for the animal has a cold touch) it seemed as if my arm had been plunged up to the shoulder in a caldron of boiling oil, so that I screamed with pain." In his journey round the world, Dr. Meyen also relates the case of a sailor who jumped overboard to catch a physalia. But scarce had he come within reach of its tentacles when the excruciating pain almost deprived him of sensation, and he was with great difficulty hauled out of the water. A severe fever was the consequence, and his life was for some time despaired of.

Several of the PhysophoridÆ are provided, besides the float, with swimming-bells (nectocalyces) and peculiar appendages or bracteÆ (hydrophyllia), which, overlapping the polypites, serve for their protection. The graceful Athorybia rosacea possesses from twenty to forty of these organs inserted in two or three circlets immediately below the pneumatocyst, and above a much smaller number of polypites.

It has the power of alternately raising and depressing them so as to render them agents of propulsion.

The PhysophorÆ have no hydrophyllia, but their swimming-bells are considerably developed, and serve as powerful instruments of locomotion. They are also provided with certain processes termed "hydrocysts," which some observers appear disposed to regard as organs of touch. Such are but a few of the numerous genera of the PhysophoridÆ.

Of the jelly-fishes in general it may be remarked that, though they are denizens of the frigid as well as of the temperate and tropical seas, their beauty increases on advancing towards the equator, for while the MedusÆ in our latitudes are generally dull and obscure, those of the torrid zone appear in all the splendour of the azure, golden-yellow, or ruby-red tints which distinguish the birds and fishes of those sunny regions. They are indeed of no immediate use to man, but their indirect services are not to be despised. They partly nourish the colossal whale, and thus, converted into oil, attract thousands of hardy seamen to the icy seas; numberless Crustacea and molluscs also live upon their hosts, and are in their turn devoured by the mighty herring shoals, whose capture gives employment and wealth to whole nations of fishermen.

Armed with that wonderful instrument, the microscope, naturalists have been taught to disunite in many cases animals which from their external resemblance were formerly supposed to belong to the same class or family; and to join others to all appearances extremely dissimilar. Thus the Bryozoa have been detached from the polyps, in spite of their similitude of growth, while the roaming and fixed Hydrozoa have been found in many cases to be but alternating generations or various phases of development of the same animal. Take, for instance, Chrysaora hysoscella (see preceding figure, page 351), one of our commonest jelly-fishes. The ova this free-swimming creature produces might naturally be supposed to develop themselves into equally free-swimming ChrysaorÆ; but instead of this they soon become attached, and grow into a colony of sessile HydratubÆ, as, at this stage of their career, they have been termed. For years they may thus continue, but then the evolutions shown in the annexed illustration take place until free-swimming zoÖids are detached, which eventually become similar to the huge Chrysaora, from one of whose ova the primitive hydratube was produced.

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.

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.

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.

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 200,000l., 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!