Chapter XXXVI: Part II: The Inhabitants of the Sea (9)

The fragile shell of the pholades seems to have prompted them to seek a better protection in the hard rock; a similar necessity may have induced the ship-worm to drill a dwelling in wood. Its shells, which are only a few lines broad, are very small compared with the size of the vermiform body, and are therefore completely inadequate for its defence. For better security it bores deep passages in submerged timber, which it lines with a calcareous secretion, closing the opening with two small lids. Unfortunately, while thus taking care of itself, it causes considerable damage to the works of man. It is principally to guard against the attacks of this worm that ships are sheathed with copper, and the beams of submarine constructions closely studded with nails. During the last century, the Teredo caused such devastations in the dykes which guard a great part of Holland against the encroachments of an overwhelming ocean that the Dutch began to tremble for their safety; and thus a miserable worm struck terror in the hearts of a nation which had laughed to scorn the tyranny of Philip II., and bid defiance to the legions of Louis XIV.

But while blaming the teredo for its damages, justice bids us not pass over in silence the services which it renders to man. If it here and there destroys useful constructions, on the other hand, it removes the wrecks that would otherwise obstruct the entrance of rivers and harbours; and we may ask whether these services do not outweigh the harm it causes. The pholades also belong to the noxious animals; they perforate the walls and calcareous jetties which man opposes to the fury of the sea, or raises for the creation of artificial harbours and landing places, destroy their foundations, and gradually cause their destruction.

_a._ Foot.]

The foot of the lamellibranchiates presents a great variety of form, and is found in various degrees of development, gradually passing into a rudimentary state, until finally it is completely wanting in the oyster family. In most of those which live at large it is strong and muscular, serving either as an excellent spade for speedy concealment in the sand when an enemy approaches, or to dig a furrow into which the animal forces itself partially, and then advances slowly by making slight see-saw or balancing motions, or even to jump along with tolerable rapidity. Thus, the common Cockle protrudes its foot to its utmost length, bending it and fixing it strongly against the surface on which it stands; then by a sudden muscular spring it throws itself into the air, and, by repeating the process again and again, hops along at a pace one would hardly expect to meet with in a shell-bound mollusc.

Even some of those which have but a very rudimentary foot, incapable of subserving locomotion, are able to move from place to place by the sudden opening or shutting of their valves. In this manner the scallop, which inhabits deep places, where it lies on a rocky or shelly bottom, swims or flies through the water with great rapidity, and the file or rasp mussel, a closely related genus, principally occurring in the Indian Ocean, glides so swiftly through the water that the French naturalists Quoy and Gaimard were hardly able to overtake it.

_a._ Foot.]

In the stone or wood-boring bivalves the functions of the foot with regard to locomotion are much more limited than in the Cockle, or Tellina, as they merely consist in moving the animal up and down in the cavity where it has fixed its residence. In the Razor-Shells, which will sometimes burrow to the depth of two feet, and very rarely quit their holes, the cylindrical foot, no longer fit for horizontal locomotion, serves the animal for rising or sinking in the sand, for when about to bore, it attenuates it into a point, and afterwards contracts it into a rounded form so as to fix it by its enlargement when it desires to rise.

In places where the razor-shells abound, they are sought after as bait for fish, and taken in spite of their mole-like facility of concealment, for when the tide is low, their retreat is easily recognised by the little jet of water they eject when alarmed by the motion of the fishermen above. Having thus detected their burrow, the wily enemy who is well aware that, though inhabiting the salt water, the Solen does not like too much of a good thing, merely throws some salt into the hole, which, sadly irritating the nerves of the poor creature, generally brings it to the surface. He must, however, be very quick in grasping it firmly, for should he fail, the animal speedily sinks again into the sand and will remain there, being either insensible to the additional irritation or its instinct of self-preservation teaching it to remain beneath.

The pholades, which have very delicate milk-white valves, burrow holes in limestone or sandstone rocks, though occasionally they content themselves with houses of clay or turf. How creatures invested with shells as thin as paper and as brittle as glass are able to work their way through hard stone has long been a puzzle to naturalists, some of whom asserted that they attained their object by means of an acid solvent, others that they bored like an auger by revolving; but recent investigations have discovered that their short and truncated foot is the chief instrument they use in their mining operations, being provided at its base with a rough layer of sharp crystals of flint, which, when worn off, are soon replaced by others, and act as excellent files.

_a._ Foot.]

In several of the sedentary genera the rudimentary foot, though incapable of locomotion, makes itself useful by spinning a bundle of silken threads, called _byssus_, or beard, which serve to anchor the animal to any solid submarine object as firmly as a ship in harbour. Generally the connection is permanent, but some species, among others the edible mussel, are able to detach the filaments from the glandular pedicle situated at the inferior base of the foot which originally secreted them, and then to seek another point of attachment.

If the byssus be examined under a powerful lens, before any of the filaments are torn, it is easy to perceive that these are fixed to submarine bodies by means of a small disc-like expansion of their extremities of various extent, according to the genus and species. Certain genera are celebrated for the abundance and fineness of their byssus; that of the Pinnæ, or Wing-Shells, among others, which are very common in some parts of the Mediterranean, and attain a considerable size, is so long and firm that in Naples it is sometimes manufactured into gloves and other articles of dress, though more as an object of curiosity than for use.

Thus we find in the same class of animals the same organ most variously modified in form and structure; now serving as a foot, now as a spade, or as a rasp, or as a spinning machine, and, throughout all these modifications, admirably adapted in every case to the mode of life of its possessor.

_c._ Pedicle from which the filaments are detached.
_d._ Inferior base of the foot.
]

The whole construction, and generally the extremely restricted locomotion, of the bivalves tells us at once that they are unable to attack their prey, but must be satisfied with the food which the sea-currents bring to the door of their shells, or within the vortex of their branchial siphons. But they have as little reason to complain as the equally slow or sessile polyps, bryozoa, and ascidians, for the waters of the ocean harbour such incalculable multitudes of microscopic animals and plants that their moderate appetite never remains long unsatisfied. The same streams which aërate their blood also convey to their mouth all the food which they require.

Deprived of more active weapons, most bivalves rely upon their shells as their best means of defence, and to answer this purpose, their stony covering must naturally increase in solidity the more its owner is exposed to injury. The pholades, lithodomes, and teredines, which scoop out their dwellings in stone or wood, and thus enjoy the protection of a retrenched camp, can do with a thin and brittle or even with a mere rudimentary shell. The solens, which at the least alarm bury themselves deeper and deeper in the sand, likewise require no closely-fitting valves; but the oysters or mussels, which have no external fortress to retire to, and are unable to move from the spot, would be badly off indeed if they could not entirely conceal themselves within their thick shells, and keep them closed by strong muscular contraction.

Bernardin de St. Pierre, in his "Studies of Nature," points out another admirable provision for the safety of molluscs. Thus, those which crawl and travel, and can consequently choose their own asylums, are in general those of the richest colours. Such, among the Gasteropods, are the gaudily-tinted Nerites, and the polished marbled Cowries, the Olives, richly ornamented with three or four colours, and the Harps, which have tints as rich as the most beautiful tulips; while among the bivalves the vivacious Pectens, coloured scarlet and orange, and a host of other travelling shells, are impressed with the most lively colours. But those which do not swim, as the Oysters, which are adherent always to the same rocks, or those which are perpetually at anchor, as the Pinnas and Mussels, or those which repose on the bosom of Madrepores, such as the Arcs, or those which are entirely buried in the calcareous rocks, as the Lithodomi, or those which immovably, by reason of their weight, pave the surface of the reefs, as the Tridacna, are of the colour of the bottoms or floors which they respectively inhabit, in order, no doubt, that they shall be less perceived by their enemies.

But even so the best guarded of the bivalves fall a prey to innumerable enemies, and when we see the strand covered for miles and miles with their débris, we may rest assured that but few of the quondam inmates of these fragmentary shells have died a natural death. Annelides and Sea-snails, crustaceans and star-fishes, strand birds and even quadrupeds, all fatten upon their delicate flesh, and man devours incalculable numbers.

In vain the Pholas buries itself in stone, or the cockle in the sand; their security was at an end as soon as man had found out that they were grateful to the palate. The former was reckoned a delicacy by the ancients, and the latter is preferred by some to the oyster itself. So much is certain, that, during the years of famine caused by the potato disease, it preserved the lives of many of the poor Shetlanders and Orcadians.

The Razor-Shells, particularly when roasted, and the Clam-Mussels, which are not only a favourite repast of the Greenlander but also of the white bear and arctic fox, are equally reckoned among the most delicate of bivalves.

The common Mussel (_Mytilus edulis_), which is found in the littoral zone on almost every rocky shore, is eaten in vast numbers by the coast inhabitants, and carried in enormous masses into the interior of the country; it furnishes an equally cheap and agreeable food, but is not easy of digestion, and sometimes produces symptoms of poisoning, which have been ascribed to the eggs of asterias, on which it feeds during the summer. In the northern countries it is also in great request as a bait for cod, ling, rays, and other large fishes that are caught by the line. In the Frith of Forth alone from thirty to forty millions of mussels are used for this purpose, and in many places they are enclosed in _gardens_, the ground of which is covered with large stones, to which they attach themselves by their byssus or beard.

It is a curious fact that the rearing of mussels should have been introduced into France as far back as the year 1235, by an Irishman of the name of Walton. This man, who had been shipwrecked in the Bay de l'Aiguillon, and gained a precarious living by catching sea-birds, observed that the mussels, which had attached themselves to the poles on which he spread his nets over the shallow waters, were far superior to those that naturally grow in the mud, and immediately made use of his discovery by founding the first "_bouchot_," or mussel-park, consisting of stakes and rudely interwoven branches. His example soon found imitators, and, strange to say, the method of construction adopted by Walton, six centuries ago, has been maintained unaltered to the present day. It may give some idea of the immense resources that might be obtained from so many utterly neglected lagunes when we hear that the fishermen of l'Aiguillon, although they sell three hundredweight of mussels for the very low sum of five francs, or four shillings, annually export or send them into the interior to the amount of a million or twelve hundred thousand francs.

The praise which Pliny bestowed on the oyster, calling it the palm or glory of the table, is still re-echoed by thousands of enthusiastic admirers. We know that this king of the molluscs congregates in enormous banks, often extending for miles and miles, particularly on rocky ground, though it is also found on a sandy or even on a muddy bottom. Along the shallow alluvial shores of many tropical lands, great quantities of oysters are often found attached to the lower branches of the mangroves, where they are so situated as to be covered when the flood sets in, and to remain suspended in the air when it retires, swinging about as the wind agitates their movable support. The oyster inhabits all the European seas from the shores of the Mediterranean to the Westenfiord in Norway, where it finds its northern boundary, lat. 68° N., but the British waters may be considered as its headquarters, for nowhere is it found in greater abundance and of a richer flavour. After the ancient Romans had once tasted the oysters of Kent--the renowned _Rutupians_--they preferred them by far to those of the Lucrine lake, of Brindisi, and of Abydos, and Macrobius tells us that the Roman epicures in the fourth century never failed to have them at table. The "Pandores" of Edinburgh, and the "Carlingfords" of Dublin, are likewise celebrated for their delicious flavour; and if we turn to the Continent, we find the Bay of Biscay, and the coasts of Brittany and Normandy, of Holland and of Schleswig-Holstein, renowned for the excellence of their oysters.

Three sorts of oysters are distinguished in the trade. The first comprises those which are dredged from the deeper banks. These are the largest-sized, but also the least valued. The second consists of those that are gathered on a more elevated situation. Being accustomed to the daily vicissitudes of ebb and flood, they retain their water much longer, and can therefore be transported to much greater distances than the former. Those are preferred that grow on a clear bottom near the estuaries of rivers. The third and most valued sort of oysters are those that are cleaned and fattened in artificial _parks_ or stews.

This branch of industry was already known to the Romans, and Pliny tells us that Sergius Orata, a knight, was the first who established an artificial basin for the cultivation of oysters, and realised large sums of money by this ingenious invention. At present Harwich, Colchester, Whitstable, and many other sea-ports along our coast are famed for their oyster-stews, as are, in France and Belgium, Marennes, Havre, Dieppe, Tréport, and Ostend, where real British natives are cleaned and fattened for continental consumption.

The renowned oyster-parks of Ostend, the oldest of which celebrated its hundredth anniversary in 1860, are extensive walled basins, communicating by sluices with the open sea, so that the water can be let in and out with every returning tide. As microscopic algæ and animalculæ are produced in much greater numbers in these tranquil reservoirs than in the boisterous sea, the oysters find here much more abundant food, and being detached one from the other, they can also open and close their shells with greater facility, so that nothing hinders their growth. Thus fostered and improved by constant attention, they are greatly superior in flavour to the rough children of nature that are sent without any further preparation to market and condemned to the knife soon after having been dragged forth from their submarine abode. The highly prized _green_ oysters owe their colour to the number of ulvæ, enteromorphæ, and microscopic infusoriæ, that are abundantly generated in the parks, and communicate their verdant tinge to the animal that swallows them.

In spite of their high price, which unfortunately debars the poorer classes from their enjoyment, the consumption of oysters is immense; so that in a commercial point of view they are by far the most important of all the mollusc tribes. Of the quantities eaten in London alone, it is impossible to give even an approximate guess, as no reliable statistics can be arrived at. Exclusive of those bred in Essex and Kent, in the rivers Crouch, Blackwater, and Colne, and in the channel of the Swale and the Medway, vast numbers are brought from Jersey, Poole, and other places along the coast. The Channel Islands alone, which export about 100,000 bushels a year, send a great part of their oysters to the metropolitan market.

The luxurious tables of Paris likewise consume unnumbered millions, and when we consider that, thanks to the railroad, even the most distant inland towns of the Continent may now be supplied with Ostend oysters, we cannot wonder that their price has risen enormously with the constantly increasing demand.

This great augmentation of value has naturally directed attention to the creation of new oyster-banks, and to the better management of those already existing, and fortunately the manner in which the mollusc propagates renders its culture in appropriate localities a by no means difficult task.

The oyster spawns from June to September. Instead of immediately abandoning its eggs to their fate, as is the case with so many sea-animals, it keeps them for a time in the folds of its mantle, between the branchial lamellæ, and it is only after having thus acquired a more perfect development that the microscopic larvæ, furnished with a swimming apparatus and eyes, emerge from the shell, and are then driven about by the floods and currents, until they find some solid body to which they attach themselves for life. In this manner the oyster produces in one single summer a couple of millions of young, which, however, mostly perish during the first wandering stage of their existence. Thus we see what rich rewards may be gained by protecting and fixing the oyster-larvæ at an early date; and that this can be done in many places without any great outlay of capital is proved to us by successful examples both in ancient and modern times.

Between the Lucrine Lake, the ruins of Cumæ, where of yore the Sibyl uttered her ambiguous oracles, and the promontory of Misenum, lies a small salt-water lake, about a league in circumference, generally from three to six feet deep, and reposing on a volcanic, black, and muddy bottom. This is the old Acheron of Virgil, the present Fusaro. Over its whole extent are spread from space to space great heaps of stones, that have been originally stocked with oysters brought from Tarentum. Round each of these artificial mounds stakes are driven into the ground, tolerably near each other, and projecting from the water, so as to be pulled up easily. Other stakes stand in long rows several feet apart, and are united by ropes, from which bundles of brushwood hang down into the water. All these arrangements are intended to fix the _oyster-dust_, that annually escapes from the parental shells, and to afford it a vast number of points to which it may attach itself. After two or three years the microscopic larvæ have grown into edible oysters. Then, at the proper season, the stakes and brushwood bundles are taken out of the water, and after the ripe berries of the marine vineyard have been plucked, they are again immersed into the lake, until a new generation brings a new harvest. Thus the indolent Neapolitans have for ages given an example which has but recently been imitated by the men of the North. In 1858 a mason named Beef (a name which, if not misspelt, would seem to point out an English origin) inaugurated the modern era of oyster cultivation, at the island of Ré, near La Rochelle, by laying down a few bushels of growing oysters among a quantity of large stones on the fore shore. His success encouraged his neighbours to follow his example, so that now already upwards of 4,000 beds or _claires_ extend along the coast.

Between March and May 1859 a quantity of oysters taken from different parts of the sea were distributed in ten longitudinal beds in the Bay of St. Brieux, on the coast of Brittany. The bottom was previously covered with old oyster-shells and boughs of trees arranged like fascines, which afford a capital holding-ground for the spat. In 1860 three of the fascines were taken up indiscriminately from one of the banks, and found to contain about 20,000 oysters each, of from one inch to two inches in diameter. The total expense for forming the above bank was 221 francs, and reckoning the number of oysters on each of the 300 fascines laid down on it at only 10,000, these sold at the low price of 20 francs a thousand would produce the sum of 60,000 francs, thus yielding a larger profit than any other known branch of industry.

Encouraged by these successful examples, an English company has obtained a grant by Act of Parliament of a piece of fore shore lying between the Whitstable and Faversham Oyster Companies' beds, and thus admirably situated for receiving a large quantity of floating spawn from these establishments. There can be no doubt that oyster cultivation will spread further and further, and that ultimately all the worthless bays and lagunes along our coasts will be converted into rich oyster-fields, yielding a good profit to their owners and enjoyment to millions of consumers.

A shell nearly related to the oyster produces the costly pearls of the East that have ever been as highly esteemed as the diamond itself. The most renowned pearl-fisheries are carried on at Bahrein, in the Persian Gulf, and in the Bay of Condatchy, in the island of Ceylon, on banks situated a few miles from the coast. Before the beginning of the fishery, the government causes the banks to be explored, and then lets them to the highest bidder, very wisely allowing only a part of them to be fished every year. The fishing begins in February, and ceases by the beginning of April. The boats employed for this purpose assemble in the bay, set off at night at the firing of a signal-gun, and reach the banks after sunrise, where fishing goes on till noon, when the sea-breeze which arises about that time warns them to return to the bay. As soon as they appear within sight, another gun is fired, to inform the anxious owners of their return. Each boat carries twenty men and a chief; ten of them row and hoist up the divers, who are let down by fives,--and thus alternately diving and resting keep their strength to the end of their day's work. The diver, when he is about to plunge, compresses his nostrils tightly with a small piece of horn, which keeps the water out, and stuffs his ears with bees'-wax for the same purpose. He then seizes with the toes of his right foot a rope to which a stone is attached, to accelerate the descent, while the other foot grasps a bag of network. With his right hand he lays hold of another rope, and in this manner rapidly reaches the bottom. He then hangs the net round his neck, and with much dexterity and all possible despatch collects as many oysters as he can while he is able to remain under water, which is usually about two minutes. He then resumes his former position, makes a signal to those above by pulling the rope in his right hand, and is immediately by this means hauled up into the boat, leaving the stone to be pulled up afterwards by the rope attached to it. Accustomed from infancy to their work, these divers do not fear descending repeatedly to depths of fifty or sixty feet. They plunge more than fifty times in a morning, and collect each time about a hundred shells. Sometimes, however, the exertion is so great that, upon being brought into the boat, they discharge blood from their mouth, ears, and nostrils.

While the fishing goes on, a number of conjurors and priests are assembled on the coast, busily employed in protecting the divers by their incantations against the voracity of the sharks. These are the great terror of the divers, but they have such confidence in the skill or power of their conjurors that they neglect every other means of defence. The divers are paid in money, or receive a part of the oyster-shells in payment. Often, indeed, they try to add to their gains by swallowing here or there a pearl, but the sly merchant knows how to find the stolen property. The oysters, when safely landed, are piled up on mats, in places fenced round for the purpose. As soon as the animals are dead, the pearls can easily be sought for and extracted from the gaping shells. After the harvest has been gathered, the largest, thickest, and finest shells, which furnish mother-of-pearl, are sorted, and the remaining heap is left to pollute the air. Some poor Indians, however, often remain for weeks on the spot, stirring the putrid mass in the hopes of gleaning some forgotten pearls from the heap of rottenness. The pearls are drilled and stringed in Ceylon, a work which is performed with admirable dexterity and quickness. For cleaning, rounding, and polishing them, a powder of ground pearls is made use of.

The Pacific also furnishes these costly ornaments to wealth and beauty, but the pearls of California and Tahiti are less prized than those of the Indian Ocean.

Pearl-like excrescences likewise form on the inner surface of our oysters and mussels, and originate in the same manner as the true pearls. The formation of the pearl, however, is not yet quite satisfactorily accounted for. Some naturalists believe that the animal accumulates the pearl-like substance to give the shell a greater thickness and solidity in the places where it has been perforated by some annelide or gasteropod; and according to Mr. Philippi, an intestinal worm stimulates the exudation of the pearl-like mass, which, on hardening, encloses and renders it harmless.

Brilliancy, size, and perfect regularity of form are the essential qualities of a beautiful pearl. Their union in a single specimen is rare, but it is of course still more difficult to find a number of pearls of equal size and beauty for a costly necklace or a princely tiara.

Nature has given the bivalves the same beauty of colouring and wonderful variety of elegant or capricious forms as to the sea-snails; so that they are equally esteemed in the cabinets of wealthy amateurs. Among the most costly are reckoned the Spondyli, which are found in the tropical seas, where they grow attached to rocks. They are distinguished by the brilliancy of their colours, but particularly by the long thorny excrescences with which their shells are covered. A Parisian professor once pawned all his silver spoons and forks to make up the sum of six thousand francs which was asked for a _Royal Spondylus_; but on returning home was so _warmly_ received by his lady that, overwhelmed by the hurricane, he flung himself on a chair, when the terrific cracking of the box containing his treasure reminded him too late that he had concealed it in his skirt-pocket. Fortunately but two of the thorns had been broken off, and the damage was susceptible of being repaired; his despair, however, was so great that his wife had not the heart to continue her reproaches, and in her turn began to soothe the unfortunate collector.

The gigantic Tridacna, which is now to be found in the shop of every dealer in shells, was formerly an object of such rarity and value that the Republic of Venice once made a present of one of them to Francis I., who gave it to the Church of St. Sulpice in Paris, where it is still made use of as a basin for holy water. The tridacna attains a diameter of five feet, and a weight of five hundred pounds, the flesh alone weighing thirty. The muscular power is said to be so great as to be able to cut through a thick rope on closing the shell. It is found in the dead rocks on the coral reefs, where there are no growing lithophytes except small tufts. Generally only an inch or two in breadth of the ponderous shell is exposed to view, for the tridacna, like the pholas, has the power of sinking itself in the rock, by removing the lime about it. Without some means like this of security, its habitation would inevitably be destroyed by the roaring breakers. A tuft of byssus, however strong, would be a very imperfect security against the force of the sea for shells weighing from one to five hundred pounds. It is found in the Indian Ocean and the Pacific as far as the coral zone extends. The animal of the tridacna, and of the nearly related Hippopus, distinguishes itself by the beauty of its colours. The mantle of the _Tridacna safranea_, for instance, has a dark blue edge with emerald-green spots, gradually passing into a light violet. When a large number of these beautiful creatures expand the velvet brilliancy of their costly robes in the transparent waters, no flower-bed on earth can equal them in splendour.

* * * * *

Like the Lamellibranchiate Acephala, the Brachiopods are covered with a bivalve shell, but their internal organisation is very different. Instead of being disposed in separate gills, their respiratory system is combined with the ciliated mantle on which the vascular ramifications are distributed, but their most striking feature is the possession of spiral fringed arms or buccal appendages which serve to open the shell and occupy the greater part of its cavity. These curious organs are in some Brachiopods quite free, in others attached to a complicated cartilaginous or calcareous skeleton. None of the existing molluscs of this class are capable of changing place, but are either fixed to extraneous substances by the agglutination of one of their valves or by a muscular peduncle passing through a perforation of their shells. There are no more than forty-nine living species, chiefly belonging to the genera Terebratula and Crania, and generally found at great depths in the Southern Ocean; but the fossil remains of 1,370 species prove their importance in the primitive seas, where they rivalled the lamellibranchiates in numbers and variety. Though now so rare or so local in the British seas that ordinary collectors are not likely to meet with any, they abound in many of our oldest rocks. "A visit to the quarries at Dudley," says E. Forbes, "or an Irish lime-kiln, or an oolitic section on the Dorsetshire coast, or a green sand ravine in the Isle of Wight, will afford more information about the Brachiopods than an examination of the finest collection of the living species. In each of the above excursions a different set of forms would be collected, for many of the palæozoic genera have altogether disappeared when we rise among the secondary rocks, and in the latter we find forms which closely remind us of existing species, but which, though very near, are yet unquestionably distinct. In formations of all epochs, a few generic types are common, and the Lingulæ of the earliest sedimentary formations, presenting traces of organic life, strikingly remind us of the species of that curious group living in exotic seas at the present day."

* * * * *

At the lower extremity of the great series of molluscous animals we find the Polyzoa (Bryozoa, or Sea-Mosses) and Tunicata. The former, which comprise the Sea-Mats (Flustræ, Escharæ), the Sea-Scurfs (Lepraliæ), the Retepores, the Cellulariæ, and several other families, were formerly reckoned among the polyps, whom they greatly resemble in appearance and mode of life, but far surpass by the complexity of their internal organisation. The Sea-Mats are among the commonest objects which the tide casts out upon our shores, for you will hardly ever walk upon the strand without finding their blanched skeletons among the relics of the retiring flood. Their flat leaf-like forms might easily cause them to be mistaken for dried sea-weeds, but a pocket-lens suffices to show that they are built up of innumerable little oblong cells, placed back to back like those of a honey-comb, and each crowned by four stout spines, which give their surface a peculiarly harsh feel when the finger is passed over it from the apex to the base. "The individual cells," says Mr. Gosse, "are shaped like a child's cradle, and if you will please to suppose some twenty thousand cradles stuck side to side in one plane, and then turned over, and twenty thousand more stuck on to these bottom to bottom, you will have an idea of the framework of a flustra. And do not think the number outrageous, for it is but an ordinary average. I count in an area of half an inch square sixty longitudinal rows, each of which contains about twenty-eight cells in that space; this gives 6,720 cells per square inch on each surface. Now a moderate-sized polyzoary contains an area of three square inches, i. e. six on both surfaces, which will give the high number of 40,320 cells on such a specimen. Many, however, are much larger."

Before the stormy tide detached them from the bottom of the sea, and left them to perish on the shore, each of the cells contained a living creature whose mouth was surrounded by a coronet of filiform and ciliated tentacles, destined to produce a vortex in the water, and thus to provide the tiny owner with its food. The body was bent on itself somewhat like the letter V, the one branch (_a_) being the mouth and throat, the other (_b_) the rectum, opening by an anus, and the middle part (_c_) the stomach. Each of these tiny members of the flustra colony possessed a considerable number of muscles; each was furnished with a movable lip or lid to block up the entrance of his cell when he courted retirement; each had his individual nerves, and consequently his individual sensations, though feeling and moving simultaneously with his fellow citizens by the agency of a system of nerves common to the whole republic, and sending forth a delicate filament to the inmate of each cell.

Such are the wonders which but for the microscope would for ever have remained unknown to man.

The Escharæ greatly resemble the Flustræ, for here also the cells are disposed side by side upon the same plane, so as to form a broad leaf-like polyzoary, which, however, is not of a horny or coriaceous texture, as in the latter genus, but completely calcified, so as to present something of the massiveness of the stony corals. The annexed wood-cuts, showing us _Eschara cervicornis_, first A, in its natural size; then B, a few cells magnified twenty diameters, and ultimately C, a single individual so highly magnified as to reveal some of the details of its otherwise invisible structure, give us a good idea of the truly remarkable organisation of the Polyzoa.

In the Escharæ and Flustræ the cellular extension of the common stock or polyzoary is unbroken, and opening on both surfaces, while in the Retepores we find the cells opening only on one side, and the leaf-like expansion pierced like network.

In cabinets of natural history, the species commonly called Neptune's ruffles will rarely be found wanting. It is a native of the Mediterranean, but individuals of a smaller size are also found in the British seas.

_a._ Tentacula
_b._ First digestive cavity.
_d._ Stomach.
_f._ Anus.
]

The Lepraliæ, or Sea-Scurfs, form thin calcareous crusts of a white-yellow or reddish colour on rocks, shells, and sea-weeds. To the naked eye they appear as rude unsightly eruptions, so as to justify their name derived from the hideous leprosy of the East, but, when magnified, their cells, generally disposed in regular concentric rows, exhibit a surprising diversity and elegance of structure. Forty species are found in the North Sea alone; hence we may judge how great the number of still unknown forms must be that spread their microscopic traceries over the algæ and shells of every zone.

It would lead me too far were I minutely to describe the Cellulariæ with their cells disposed in alternating rows on narrow bifurcated branches; the Tubulipores, with their mouths at the termination of tubular cells without any movable appendage or lip; the Bowerbankias and Lagunculas, with their creeping stems and separate cells; suffice it to say that a wonderful exuberance of fancy displays itself in the structure of the numerous varieties of the Polyzoa.

B. A Bird's Head Process, more highly magnified, and seen in the act of grasping another.]

But a closer inspection reveals still greater miracles to the marine microscopist, for most genera, and chiefly the Cellulariæ, possess very remarkable appendages, or processes, presenting the most striking resemblance to the head of a bird. Each of these processes, or "aviculariæ," as they have been named, has two "mandibles," of which one is fixed like the upper jaw of a bird, the other movable like its lower jaw; the latter is opened and closed by two sets of muscles, which are seen in the interior of the head, and between them is a peculiar body, furnished with a pencil of bristles, which is probably a tactile organ, being brought forwards when the mouth is open, so that the bristles project beyond it, and being drawn back when the mandible closes. During the life of the polyzoon, these tiny "vulture-heads," which are either sessile or pedunculated, keep up a continual motion, and it is most amusing to see them see-sawing and snapping and opening their jaws, and then sometimes in their incessant activity even closing upon the beaks of their neighbours.

It is still very doubtful what is their precise function in the economy of the animal; whether it is to retain within reach of the ciliary current bodies that may serve as food, or whether it is like the pedicellariæ of the sea-urchins to remove extraneous particles that may be in contact with the surface of the polyzoary. The latter would seem to be the function of the "vibracula," which are likewise pretty generally distributed among the polyzoa. Each of these long bristle-shaped organs, springing at its base out of a sort of cup, that contains muscles by which it is kept in almost constant motion, sweeps slowly and carefully over the surface of the polyzoary, and removes what might be injurious to the delicate inhabitants of the cells, when their tentacles are protruded. So carefully have these lowly molluscs been provided for!

The polyzoa can neither hear nor see, at least as far as we are able to ascertain, but the delicacy of their sense of touch is very great. "When left undisturbed in a glass of fresh sea-water," says Dr. Johnston,[R] "they push their tentacula beyond the mouth of the cell by straightening the body, and then expanding them in the form of a funnel or bell, they will often remain quiet and apparently immovable for a long time, presenting a very pretty and most interesting object to an observer of the 'minims of nature.' If, however, the water is agitated, they withdraw on the instant, probably by aid of the posterior ligament or muscle; the hinder part of the body is pushed aside up the cell, the whole is sunk deeper, and by this means the tentacula, gathered into a close column, are brought within the cell, the aperture of which is shut by the same series of actions. The polyzoa of the same polyzoary often protrude their thousand heads at the same time, or in quick but irregular succession, and retire simultaneously, or nearly so, but at other times I have often witnessed a few only to venture on the display of their glories, the rest remaining concealed, and if, when many are expanded, one is singled out and touched with a sharp instrument, it alone feels the injury, and retires, without any others being conscious of the danger, or of the hurt inflicted on their mate. The polyzoa propagate by gemmation and by ova or eggs, which, germinating on the inner surface, escape at a later period into the visceral cavity, and are finally discharged into the wide sea, so to fulfil their mission in creation, and people the shores of every clime with myriads of busy workers in horn and in lime, which, with subtle chemistry, they draw from a fluid quarry and build up in textures of admirable beauty and heaven-ordered designs."

[Footnote R: "History of the British Zoophytes," 2nd edit. vol. i. p. 259.]

Each polyzoon begins with a single ovum. The original or seminal cell of a flustra or lepralia has no sooner fixed itself upon some stone, shell, or alga, than new buds begin to shoot forth, which in their turn produce others from their unattached margins, so as rapidly to augment the number of cells to a very large amount. Thus a common specimen of _Flustra carbasea_ presents more than 18,000 individual polyzoa, and as each of these has about twenty-two tentacula, which are again furnished with about a hundred ciliæ a piece, the entire polyzoary presents no less than 396,000 tentacula and 39,600,000 ciliæ. The Rev. David Landsborough calculated that a specimen of _Flustra membranacea_ five feet in length by eight inches in breadth had been the work and the habitation of above two millions of inmates, so that this single colony on a submarine island was about equal in number to the population of Scotland. As the tentacula are numerous in this species, four thousand millions of ciliæ must have provided for its wants, about four times the number of the inhabitants of this globe!

_c._ Branchial orifice.
_e._ Branchiæ.
_i._ Anal orifice.
_l._ Stomach.
_o._ Heart.
_u_, _u′_, _u″_. Reproductive
buds, springing from the abdomen of the adults.
]

_a._ Branchial orifice, open.
_b._ Anal orifice, closed.
]

The Tunicata are so called because their soft parts are not enclosed in a calcified shell such as invests the majority of their class, but in a more or less coriaceous envelope or tunic which is either bag-shaped, and provided with two apertures, or tube-shaped, and open at the ends. They present a strong resemblance to the Polyzoa, not merely in their general plan of conformation, but also in their tendency to produce composite structures by gemmation; they may, however, be at once distinguished from them by the absence of the ciliated tentacula which form so conspicuous a feature in the external aspect of a flustra or a retepore. Their branchiæ, which have generally the form of ridges (_e_), occupy a large sac, forming, as it were, the antechamber of the alimentary canal, which is barely distinguishable into gullet, stomach, and intestine, and always convoluted or folded once on itself. The Tunicata are exclusively marine, and widely spread from the arctic to the tropical seas. All of them are free during the earlier parts of their existence; some remain permanently so (Pyrosomidæ, Salpæ), but the generality (Ascidiæ, Botrylli) become fixed to shells and other marine bodies; some exist as distinct individuals (Ascidiæ, Cynthia), whilst various degrees of combination are effected by others (Botryllus, Clavellina, Pyrosoma), and some are simple in one generation and combined in the next (Salpæ).

Thus the whole family is divisible into two groups, the _simple_ and the _aggregate_; both branching out into numerous genera, of which my limits only allow me to mention some of the most remarkable. The simple Ascidiæ, or Sea-Squirts, are very common on our shores. "Rarely," says Forbes, "is the dredge drawn up from any sea-bed at all prolific in submarine creatures without containing few or many of their irregularly shaped leathery bodies, fixed to sea-weed, rock, or shell, by one extremity, or by one side, free at the other, and presenting two more or less prominent orifices, from which, on the slightest pressure, the sea-water is ejected with great force. On the sea-shore, when the tide is out, we find similar bodies attached to the under surface of rough stones. They are variously, often splendidly, coloured, but otherwise are unattractive or even repulsive in aspect. Some are of a large size, several inches in length. As may easily be imagined, they lead a very inactive life, except in the young state, when by means of a long tail they rapidly swim about, until finally settling in some convenient spot, they gradually assume the form and adopt the quiet life of the parent from which they sprang."

_a._ Branchial orifice.
_b._ Anal orifice.
_c._ Coriaceous envelope of the sides.
_d._ Stone to which the animal is fixed.
]

To the simple Tunicata belong also the Chelyosomata, whose coriaceous envelope, consisting of eight somewhat horny angular plates, reminds one of the carapace of the turtle. Their small and prominent orifices, perforating the plated surface, are each surrounded by six triangular valvules.

Some species of simple Ascidians on the coasts of the Channel and the Mediterranean are valued as articles of food. At Cette sea-squirts are taken regularly to market, and _Cynthia microcosmus_, although so repulsive externally, furnishes a very delicate morsel.

_a._ Common test.
_b._ Some of the branchial orifices.
_c._ The common anal orifice of one of the systems.
]

While in the Clavellinidæ the animals are connected by creeping tubular prolongations of the common tunic through which the blood circulates, the Botrylli form translucent jelly-like masses of various hues of orange, yellow, purple, blue, grey, and green; sometimes nearly uniform in tint, sometimes beautifully variegated, and very frequently pencilled as if with stars of gorgeous device; now encrusting the surface of the rock, now descending from it in icicle-like projections. They are also frequently attached to the broad-leaved fuci, investing the stalks, or clothing with a glairy coat the expanse of the fronds. "In examining their bodies," says the distinguished naturalist previously quoted, "we find that it is not a single animal which is before us, but a commonwealth of beings bound together by common and vital ties. Each star is a family, each group of stars a community. Individuals are linked together in systems, systems combined into masses. Few bodies among the forms of animal life exhibit such exquisite figures as those which we see displayed in the combinations of these compound Ascidians."

In the genus Diazona, which has its chief seat in the Mediterranean, the animals, which are very prominent and arranged in concentric circles, form a single system expanded into a disc like that of a flower or of an Actinia. The anal orifices, it will be seen, are situated close to the branchial apertures at the free end of the single animals, while in the Botrylli they open into a central excretory cavity.

_a._ Branchial or external orifice.
_b._ Anal or internal orifice.
_d._ Stomach.
_e._ Liver.
_f._ Branchiæ.
]

In the Pyrosomes we find large colonies of small individuals aggregated in the form of a cylinder open at one end. Their mouths or anterior extremities are situated on the exterior of this hollow body, which they bristle with large and longish tubercles (_a_), whilst the opposite or anal orifices (_b_) open into the cavity of the cylinder, whose smooth wall they perforate with numerous small holes. By a simultaneous action the central cavity is either narrowed or enlarged, and by this means the strange social republic glides slowly through the waters.

The Pyrosomes inhabit the Mediterranean and the warmer parts of the ocean. In the former at times their abundance is a source of great annoyance to the fishermen, sometimes even completely clogging their nets, and on the high seas they are not seldom met with in almost incredible profusion. Their delicate and transparent forms, their elegant tints, and their unrivalled phosphorescence render them objects of admiration to the voyager, and entitle them to rank amongst the most resplendent living gems of the ocean.

_a._ Upper lip or posterior orifice.
_b._ Anterior orifice.
_c._ Prolongations of the test by which the
animal is adherent to its neighbours.
]

A. _Salpa runcinata_, solitary.
B. _Salpa runcinata_, associated.
C. _Salpa zonaria_, aggregated.
]

While the sessile Ascidiæ remind one of the polyps, the transparent Salpæ, freely swimming in the sea, bear a great resemblance to the pellucid jelly-fishes. Each resembles a crystalline tube, through which one can distinctly see the internal coloured parts. Sometimes these animals, which abound in the warmer seas, are found solitary, at other times associated in circular or lengthened groups, termed garlands, ribands, and chains; but, strange to say, these two forms so different in outward appearance are only the alternating generations of one and the same animal. The chained Salpæ produce only solitary ones, and the latter only chains, or, as Chamisso, to whom we owe the discovery of this interesting fact, expresses himself, "a salpa mother never resembles her daughter, or her own mother, but is always like her sister, her grand-daughter, or her grand-mother." When Chamisso first made known his discovery, he was laughed at as a fanciful visionary, but all later observations have not only fully confirmed his statement but also discovered similar or even more wonderful metamorphoses among the jelly-fish, polyps, crustacea, sea-urchins, and other marine animals. Thus Chamisso gave the first impulse to a whole series of highly interesting observations, and his rank is now as well established among naturalists as it has long been among the most distinguished poets of Germany. The Salpæ progress by the alternate contractions and dilatations of their tubular body. In this manner the chains, as if obeying a common impulse, glide along with a serpentine movement, and are often regarded by sailors as sea-snakes.

_a._ Branchial orifice.
_b._ Anal orifice.
_c._ Muscles bordering the carapace-plates.
_d._ Central hexagonal plate.
_e._ Surrounding plates.
_f._ The nerve-ganglion and nerve-fibres.
_g_, _h_. Auditory apparatus.
_i._ Row of tentacles, anterior to the œsophagus.
_j._ Stomach.
_k._ Part of the intestine.
]

Before quitting the Tunicata, a few points of interest in their simple history remain to be noticed. Despite their humble organisation, they have a heart which, as may easily be ascertained in the transparent species, is subject to strange alternations of action. For after having received for a minute or two the blood _from_ the branchiæ, and propelled it _to_ the system at large, it will at once cease to pulsate for a moment or two, and then propel the blood _to_ the branchial sac, receiving it at the same time _from_ the system generally. After this reversed course has continued for some time, another pause occurs, and the first course is resumed. It is very probable that many of the Tunicata are able to hear and to see. In Chelyosoma, organs have been discovered whose structure seems to indicate that they are destined for the transmission of sound, and the Ascidiæ have frequently around the extremity of their tubes a row of coloured points similar to the imperfect organs of sight present in the majority of the bivalve Acephalans. Thus a closer examination of the lower animals is constantly bringing new faculties to light, and the further we penetrate into the secrets of their life the more we find occasion to admire the power and wisdom of their Maker!

CHAP. XVI.

ECHINODERMATA.

STAR-FISHES, SEA-URCHINS, AND SEA-CUCUMBERS.

The Star-Fishes.--Their Feet or Suckers.--Voracity of
the Asterias.--The Rosy Feather-Star.--Brittle and
Sand-Stars.--The real Sea-Stars of the British Waters.--The
Sea-Urchins.--The Pedicellariæ.--The Shell and the Dental
Apparatus of the Sea-Urchin.--The Sea-Cucumbers.--Their strange
Dismemberments.--Trepang-fishing on the Coast of North Australia.--In
the Feejee Islands.

"As there are stars in the sky, so are there stars in the sea," is the poetical exordium of Link's treatise on Star-fishes, the first ever published on the subject; and James Montgomery tells us in rather bombastic style, that the seas are strewn with the images of the constellations with which the heavens are thronged.

This is no doubt highly complimentary to the star-fishes, but is far from being merited by any particularly shining or radiant quality; as they occupy a very inferior grade among the denizens of the sea, and merely owe their stellar name to their form, which somewhat resembles the popular notion of a star.

But if they are of an inferior rank to most marine animals; if even the stupid oyster boasts of a heart, which they do not possess; yet a closer inspection of their organisation shows us many wonderful peculiarities, and proves to us once more that nature has impressed the stamp of perfection as well upon her lowest and most simple creations, as upon those beings that rank highest in the scale of life.