The Sea-star might be called a flattened sea-urchin, with radiated lobes, and the Sea-urchin, a contracted or condensed sea-star, so near is their relationship. In both we find the same radiating construction, in which the number five is so conspicuous, and in both also the rows of suckers, which, starting from a centre, are set into motion by a similar mechanism, and used for the same purpose. In all the sea-urchins finally, and in many of the sea-stars, we find the surface of the body covered with numerous exceedingly minute, two- or three-forked pincers, that perpetually move from side to side, and open and shut without intermission. These active little organs, which have been named Pedicellariæ, were formerly supposed to be parasites, working on their own account, but they are now almost universally recognised as organs subservient to the nutrition of the animal, and destined to seize the food floating by, and to convey it to the mouth, one passing it to the other. Even in their outward appearance, the sea-urchins are not so very different from the sea-stars as would be imagined on seeing a Butt-thorn near a globular urchin, for both orders approach each other by gradations; thus, the Goniasters, with their cushion-shaped disks and shortened rays, approximate very much in shape to the sea-urchins; and among the latter we also find a gradual progression from the flattened to the globular form. Still there are notable differences between the two classes. Thus in the sea-urchins the digestive organs form a tube with two openings, while in the true sea-stars they have but one single orifice. Their mode of life is, however, identical.
The Echinidæ move forward by means of the joint action of their suckers and spines, using the former in the manner of the true star-fishes, and the latter as the snake-stars. They also make use of the spines, which move in sockets, to bury themselves in the fine sand, where they find security against many enemies.
Some species even entomb themselves pholas-like in stone, inhabiting cavities or depressions in rocks, corresponding to their size, and evidently formed by themselves. Bennett describes each cavity of the edible Echinus lividus as circular, agreeing in form with the urchin within it, and so deep as to embrace more than two-thirds of the bulk of the inhabitant. It is large enough to admit of the creature's rising a little, but not of its coming out easily. The echinus adheres so firmly to this cavity by its suckers, as to be forced from it with extreme difficulty when alive. On the coasts of the county of Clare thousands may be seen lodged in the rock, their purple spines and regular forms presenting a most beautiful appearance on the bottoms of the grey limestone rock-pools. How the boring is performed has, like many other secrets, not yet been settled by naturalists. The first perforation is most likely effected by means of the teeth, and then the rock softened by some secreted solvent.
Sea-urchins are found in all seas, but as they are extremely difficult to preserve, and many of them have such long and delicate spines that it is almost impossible to procure perfect specimens, probably not one tithe of their species is known.
On our coasts the common "egg-urchin" affords the poor a somewhat scanty repast; but, throughout the Mediterranean, its greater size, and also that of its allies, Echinus melo and E. sardicus, render them, when "in egg," important articles of food. In Sicily these animals are in season about the full moon of March; there the E. esculentus is still called the "King of Urchins;" whilst the larger melon-urchin is popularly considered to be its mother. The size and abundance of these edible species are among the striking peculiarities of the fish markets of the Mediterranean sea-board.
The calcareous shell of the "sea-urchin" seems, at first sight, to be composed of one simple crust, but proves, on nearer inspection, to be a masterpiece of mosaic consisting of several hundred parts, mostly pentagonal. These are so closely united that their junctions are hardly visible, but on allowing the shell to macerate for some days in fresh water, it falls to pieces. This complicated structure is by no means a mere architectural fancy, a useless exuberance of ornament, but essentially necessary to the requirements of the animal's growth. A simple hard crust would not have been capable of distension, whereas a complicated shell, such as the sea-urchin possesses, can grow in the same ratio as the internal parts, by continual deposits on the edges of the individual pieces. On closely examining a living sea-urchin, we find the whole surface of the shell and spines covered with a delicate skin, which, in spite of their close connexion, penetrates into the intervals of the several pieces. This membrane secretes the chalk of which the shell is composed, and deposits fresh layers on the edges of the plates, so that in this manner the shell continually widens until the animal has attained its perfect size. The spines are secreted in the same manner, and show under the microscope an admirable beauty and regularity of structure. So bountifully has the great Architect of worlds provided for the poor insignificant sea-urchin!
The dental apparatus of the animal—the so-called lantern of Aristotle—is another masterpiece in its way. Fancy five triangular bones or jaws, each provided with a long, projecting, movable tooth. A complicated muscular system sets the whole machinery going, and enables the jaws to play up and down, and across, so that a more effective grinding-mill can scarcely be imagined.
The Holothuriæ, or Sea-cucumbers, may be regarded in one light as soft sea-urchins, and in another as approximating to the Annelides or worms. Their suckers are similar to those of the true star-fishes and sea-urchins. Besides progression by means of these organs, they move, like annelides, by the extension and contraction of their bodies. The mouth is surrounded by plumose tentacula, the number of which, when they are complete, is always a multiple of five. They all have the power of changing their shapes in the strangest manner, sometimes elongating themselves like worms, sometimes contracting the middle of their bodies, so as to give themselves the shape of an hour-glass, and then again blowing themselves up with water, so as to be perfectly globular.
The great Sea-cucumber is the largest of all the known European species, and probably one of the largest Cucumeriæ in the world, measuring when at rest fully one foot, and capable of extending itself to the length of three. Under the influence of terror, it dismembers itself in the strangest manner. Having no arms or legs to throw off, like its relations the luidia and the brittle-star, it simply disgorges its viscera, and manages to live without a stomach; no doubt a much greater feat than if it contrived to live without a head. According to the late Sir James Dalyell, the lost parts are capable of regeneration, even if the process of disgorgement went so far as to leave but an empty sac behind. Considering the facility with which the sea-cucumber separates itself from its digestive organs, it is the more to be wondered how it tolerates the presence of a very remarkable parasite, a fish belonging to the genus Fierasfer, and about six inches long. This most impudent and intrusive comrade enters the mouth of the cucumber, and, as the stomach is too small for his reception, tears its sides, quartering himself without ceremony between the viscera and the outer skin. The reason for choosing this strange abode is as yet an enigma.
The Holothuriæ, which in our part of the globe are very little noticed, play a much more important part in the Indian Ocean, where they are caught by millions, and, under the name of Trepang or Biche de mer, brought to the markets of China and Cochin-China. Hundreds of praos are annually fitted out in the ports of the Sunda Islands for the gathering of trepang; and sailing with help of the western monsoon to the eastern parts of the Indian Archipelago, or along the northern coast of Australia, return home again by favour of the eastern monsoon. The bays of the inhospitable treeless shores of tropical New Holland, the abode of a few half-starved barbarians, are enlivened for a few months by the presence of the trepang fishers.
"During my excursions round Raffles Bay," says Dumont d'Urville, ("Voyage to the South Pole,") "I had remarked here and there small heaps of stones surrounding a circular space. Their use remained a mystery until the Malayan fishers arrived. Scarce had their praos cast anchor, when without loss of time they landed large iron kettles, about three feet in diameter, and placed them on the stone heaps, the purpose of which at once became clear to me. Close to this extemporised kitchen they then erected a shed on four bamboo stakes, most likely for the purpose of drying the holothurias in case of bad weather. Towards evening, all preliminaries were finished, and the following morning we paid a visit to the fishermen, who gave us a friendly reception. Each prao had thirty-seven men on board, and carried six boats, which we found busily engaged in fishing. Seven or eight Malays, almost entirely naked, were diving near the ship, to look for trepang at the bottom of the sea. The skipper alone stood upright, and surveyed their labours with the keen eye of a master. A burning sun scorched the dripping heads of the divers, seemingly without incommoding them; no European would have been able to pursue the work for any length of time. It was about noon, and the skipper told us this was the best time for fishing, as the higher the sun, the more distinctly the diver is able to distinguish the trepang crawling at the bottom. Scarce had they thrown their booty into the boat when they disappeared again under the water, and as soon as a boat was sufficiently laden, it was instantly conveyed to the shore, and succeeded by another.
"The holothuria of Raffles Bay is about six inches long, and two inches thick. It forms a large cylindrical fleshy mass, almost without any outward sign of an organ, and as it creeps very slowly along is easily caught. The essential qualities of a good fisherman are great expertness in diving, and a sharp eye to distinguish the holothurias from the similarly coloured sea-bottom.
"The trepang is first thrown into a kettle filled with boiling sea-water. After a few minutes, it is taken out of its hot-bath and ripped open with a knife to cleanse it of its intestines. It is then thrown into a second kettle, where a small quantity of water and the torrefied rind of a mimosa produce dense vapours. This is done to smoke the trepang for better preservation. Finally, it is dried in the sun, or in case of bad weather under the above-mentioned shed. I tasted the trepang, and found it had some resemblance to lobster. In the China market the Malays sell it to the dealers for about fifteen rupees the picul of 125 pounds. From the earliest times, the Malays have possessed the monopoly of this trade in those parts, and Europeans will never be able to deprive them of it, as the economy of their outfit and the extreme moderation of their wants forbid all competition. About four in the afternoon the Malays had terminated their work. In less than half an hour the kettles and utensils were brought on board, and before night-fall we saw the praos vanish from our sight."
The inhabitants of the island of Waigiou, to the north of New Guinea, prepare the trepang in the Malay manner, and barter it for cotton and woollen stuffs, which are brought to them by some Chinese junks. "In every hut," says Lesson, "we found great heaps of this dried leathery substance, which has no particular taste to recommend it, and is so highly esteemed by the Chinese for no other reason than because they ascribe to it,—as to some other gelatinous substances, as agar-agar, shark-fins, and edible bird's nests,—peculiar invigorating properties, by means of which their enervated bodies are rendered fit for new excesses."
The Feejee islanders have the reputation of being the greatest cannibals and the most perfidious savages of the whole Pacific, yet the trepang fishery attracts many American and European speculators to that dangerous archipelago. Captain Wilkes, of the United States Exploring Expedition, found there a countryman, Captain Eagleston, who had been successful in more than one of these expeditions, and obligingly communicated to him all the particulars of his adventurous trade. There are six valuable sorts of biche de mer, or trepang; the most esteemed is found on the reefs one or two fathoms deep, where it is caught by diving. The inferior sorts occur on reefs which are dry, or nearly so, at low water, where they are picked up by the natives, who also fish the biche de mer on rocky coral bottoms by the light of the moon or of torches, as they come forth by night to feed. The most lucrative fisheries are on the northern side of Viti Levu. They require a large building for drying, with rows of double staging, on which reeds are placed. Slow fires are kept up by natives underneath, about fifteen hands being required to do the ordinary work of a house.
Before beginning, the services of some chief must be secured, who undertakes the building of the house, and sets his dependants at work to fish. The usual price is a whale's tooth for a hogshead of the animals just as they are taken on the reef; but they are also bought with muskets, powder, balls, vermilion, blue beads, and cotton cloth of the same colour. When the animals are brought on shore, they are measured into bins containing about fifty hogsheads, where they remain until next day. They are then cut along the belly for a length of three or four inches, taking care not to cut too deep, as this would cause the fish to spread open, which would diminish its value. They are then thrown into boilers, two men attending each pot, and relieving each other, so that the work may go on night and day. No water need be added, as the fish itself yields moisture enough to prevent burning. After draining on a platform for about an hour, they are taken to the house and laid four inches deep upon the lower battens, and afterwards upon the upper ones, where they remain three or four days. Before being taken on board they are carefully picked, all damp pieces being removed. They are stowed in bulk, and sold in Manilla or Canton by the picul, which brings from fifteen to twenty-five dollars. In this manner Captain Eagleston had collected in the course of seven months, and at a trifling expense, a cargo of 1200 piculs, worth about 25,000 dollars. The outfit is small, but the risk is great, as no insurance can be effected; and it requires no small activity and enterprise to conduct this trade. A thorough knowledge of native character is essential to success, and the utmost vigilance and caution must always be observed to prevent surprise, or avoid difficulties.
No large canoes should ever be allowed to remain alongside the vessel, and a chief of high rank should be kept on board as a hostage. That these precautions are by no means unnecessary, is proved by the frequent attempts of the savages to cut off small vessels trading on their coasts. One of the most frequent methods is to dive and lay hold of the cable; this, when the wind blows fresh to the shore, is cut, in order that the vessel may drift upon it, or in other cases a rope is attached to the cable by which the vessel may be dragged ashore. The time chosen is just before daylight. The moment the vessel touches the land, it is treated as a prize sent by the gods, and the crew murdered, roasted, and devoured.
CŒLENTERATA.
POLYPS AND JELLY-FISHES.
Despite the low rank they occupy in the hierarchy of animal life, the Cœlenterata, 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 cœlenterate, 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 Cœlenterata 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 cœlenterate 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 cœlenterates 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 (ν, ν′′) 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 (π), 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 (ν) is produced into five points, of which the three upper are much longer and stronger than the two lower. The individual polyps (π), 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.