In France oyster dredging is conducted by fleets of thirty or forty boats, each carrying four or five men. At a fixed hour, and under the surveillance of a coastguard in a pinnace bearing the national flag, the flotilla commences the fishing. In the estuary of the Thames the practice is much the same, although no official surveillance is observed. Each bark is provided with four or five dredges, resembling in shape a common clasp purse. It is formed of network, with a strong iron frame, as represented in Fig. 172, the iron frame serving the double purpose of acting as a sucker, and keeping the mouth open, while giving it a proper pressure as it travels over the oyster-beds. When the boat is over the oyster scarp, the dredge is let down, and no more attractive sight exists than that presented by the well-appointed Whitstable boats on one side of the estuary, or the Colne boats on the other, as they wear and tack over the oyster-beds, bearing up from time to time to haul in the dredge, and empty its contents into the hold. The tension of the rope is the signal for hauling in, and very heterogeneous are the contents—sea-weeds, star-fishes, lobsters, crabs, actinia, and stones. In this manner the common oyster fields on both sides of the Channel were ploughed up by the oyster dredger pretty much as the ploughman on shore turns up a field. The consequence was that, twenty years ago, the French beds were totally exhausted, and France had to look to foreign countries for its oyster. Oyster farms which had employed fourteen hundred men and two hundred boats were reduced to two hundred men and twenty boats. Similar results from over-dredging would have followed, no doubt, on this side the Channel had the mollusc not been protected by the company and private proprietors who held the oyster-beds in the large estuaries. This state of things in France led to some important discoveries in the science of oyster culture, which have produced important changes there.

The name of Sergius Orata has already been mentioned as a cultivator of oysters. He lived in the fifth century before our era, and according to Pliny he first attempted parking oysters at Baia in the times of the orator Lucius Crassus. He was the first to recognise the superior flavour of the oysters of the Lucrin Lake, the Avernus of the poets, probably for trade reasons of his own, for then, as now, Reveille-Parise remarks, writing on the subject, "tradesmen speculated on the weaknesses of human gourmandism." But Sergius really created a new industry, which is still practised in thousands of places much as he left it. As a proof of the perfection to which Sergius had brought oyster culture, his contemporaries said of him, in allusion to the hanging banks which he invented, that if he had been prevented from raising oysters in the Lucrin Lake, "he would have made them grow on the house-tops." The traveller who visits this celebrated lake finds only a miry puddle. The precious oysters placed there by Catiline's grandfather are replaced by a host of miserable eels, which leap in the mud; vile mountains of ashes, coal, and pumice-stone, which was thrown up in a night like the mushroom, having reduced the once celebrated lake into the state described.

Rondeletius also speaks of a fisherman who understood the art of oyster culture.

The Neapolitan Lake Fusaro—the terrible Acheron of the poets—is a great oyster-park, in which Art is made effectually to aid Nature in the multiplication of its products. This famous oyster-bank, which is represented in Pl. XIII., lies in the neighbourhood of Baia and Cumæ. It forms one of the most interesting spots in that beautiful bay. In the month of February, 1865, M. Figuier tells us he traversed its celebrated coast, seated himself on the banks of the historical lake, and tasted the produce of this curious manufacture of living beings, whose origin dates from the Roman period.

Lake Fusaro was in ancient times a place of evil report: Virgil immortalized it as the mythological Acheron; but its landscape had nothing of the sadness and desolation which accords with the sojourn of the dead. It is a salt pond, shaded with a girdle of magnificent trees. It is about a league in circumference, and about a fathom in depth at its deepest part; its bottom is muddy and black, like the rest of this volcanic region.

It will be understood, from what has been said, that the chief obstacle to the reproduction of oysters is the absence of any solid body to which the young spawn can attach itself, and the means of shelter from animals which prey upon them. The fishermen living on the shores of Lake Fusaro have long realized this, and provided against it by warehousing, as it were, in the lake near the sea, the oysters ready to discharge their spawn, while retaining the young generations captive in the protected basins, where they are sheltered from various causes of destruction to which oysters are exposed in the open sea.

Upon the bottom of the lake, and on its circumference, the proprietors of Fusaro have constructed hillocks here and there, with stones heaped up, artificial rocks, raised sufficiently to shelter the depôts from mud and slime. Upon these rocks they deposit the young oysters gathered in the Gulf of Tarentum. Each of these rock-works is surrounded by a girdle of piles, driven close to each other, and raised a little above the surface of the water, as represented in Fig. 173. Other piles are distributed in long lines, and bound to each other by a cord, from which are suspended fagots of young wood. In the spawning season the oysters which have been deposited on the artificial rocks discharge the myriads of young fry which have been nurtured in the folds of their mantles. The fagots suspended from the piles arrest the germ before it is driven away by the waves, much as a swan attaches itself to the first shrub which comes in the way. By these precautions the riverains of Fusaro have provided for the preservation of the young fry, besides removing many of the natural enemies of the young oyster.

In other places the piles are distributed in long lines and bound together by strong cords, from which fagots of brushwood are suspended, on which the young spawn lay hold, as in Fig. 174.

By means of these arrangements the pregnant oyster deposits its spawny progeny in quiet repose; the young germs are intercepted by the fagots and hurdles suspended between the piles, where the young oysters develop themselves under the favourable conditions of repose, temperature, and light. When the fishing season arrives, the piles and fagots which surround the beds are removed, and the oysters are gathered suitable for market. The oysters thus selected for sale are packed loosely in osier baskets and sunk, while waiting for purchasers, into a reserve or park. This park is established on the shores of the lake. It is constructed of piles which support a gangway provided with hooks, from which the baskets filled with living oysters are suspended, ready for sale.

Some twenty years ago the oyster-beds of France had become totally exhausted under the open system of dredging; and circumstances having brought the protective system pursued at Fusaro under the notice of M. Coste, a learned academician, to whom France is indebted for the restoration of the bivalve, M. Coste reported to the Emperor in 1858 that at Rochelle, Marennes, Rochefort, at the Isles of Ré and Oleron, where there had formerly been twenty-three oyster-beds, there were now only five, and these in danger of being destroyed by the increase of mussels; that at the Bay of St. Brieuc, so naturally suited for oyster culture, the beds were reduced to three; that even on the classic oyster grounds of Cancale and Granville, it was only by the most careful administration that decay was prevented, while the increasing numbers of consumers threatened altogether to destroy an industry essentially necessary for the support of a maritime population.

The impulse given by this report has been productive of the most satisfactory results in France. All along the coast the maritime populations are actively engaged in oyster culture. Oyster parks, in imitation of those at Fusaro, have sprung up. In his appeal to the Emperor, M. Coste suggested that the State, through the Administration of Marine, and by means of the vessels at its command, should take steps for sowing the whole French coast in such a manner as to re-establish the oyster-banks now in ruins, extend those which were prosperous, and create others anew wherever the nature of the bottom would permit. The first serious attempt to carry out the views of the distinguished academician was made in the Bay of St. Brieuc. In the month of April in the same year in which his report was received, operations commenced by planting three millions of mother-oysters which had been dredged in the common ground; brood from the oyster grounds of Cancale and Tréquiers were distributed in ten longitudinal lines on tiles, fragments of pottery, and valves of shells. At the end of eight months the progress of the beds was tested, and the dredge in a few minutes brought up two thousand oysters fit for the table, while two fascines drawn up at random contained nearly twenty thousand, from one to two inches in diameter. Two of these fascines exposed to public view at Béni and Patrieux excited the astonishment of the maritime population.

This result encouraged M. Coste to pursue his experiments upon a greater scale, and he now proposed to bring the whole littoral under a regulated system of oyster culture. In the roads of Toulon and in Lake Thau, which touches this port, the same system was put in force by the Administration of Marine as had already been done in the Bay of Arcachon and in the Isle of Ré. In these localities oyster culture assumed gigantic proportions. Associations were formed for the purpose of prosecuting them and forming oyster-parks.

These exertions roused the curiosity of foreign nations. Van Beneden, a distinguished naturalist of Louvain, and M. Eschrecht of Copenhagen, visited France to study the arrangements for oyster culture. M. Coste demonstrated that parks could be established on all places visited by the tide, and under his advice the Bay of Arcachon is now transformed into a vast field of production, which increases every day, giving the happiest presages of an abundant harvest. Already twelve hundred capitalists, associated with a similar number of fishermen, occupy a surface of nine hundred and eighty-eight acres, which emerge at low water. In this bay the State has organized two model farms for experimental purposes, in which tiles, fascines, and valves of shells are laid down with other appliances, to which the young oysters may attach themselves. These expedients have been so successful that the park, which has cost about £114, is now estimated to be worth about £8000 in money, with a total of five million oysters, large and small. The Isle of Ré, which was originally surrounded by a muddy bottom ill adapted for oyster culture, has been totally changed, so that in two years four leagues of foreshore have been turned into a rich and profitable oyster-bed; twelve hundred parks are in full activity, and two thousand others are in course of construction, the whole forming a complete girdle round the island.

Every one has heard of the green oysters of Marennes, the preservation, amelioration, and ripening of these oysters, so to speak, representing a very considerable branch of industry in France. In order to give the reader some idea of its importance, we shall give here a brief summary of M. Coste's voyage of exploration on the French littoral.

The parks at Marennes, in which the oysters are placed in order to acquire the green colour which characterises them, are basins stretching along both banks of the Seudre for many leagues. They are locally known as claires, and differ from the oyster-parks of other countries in this particular—that, while the ordinary parks are so arranged as to be submerged at every return of the tide, the basins of Marennes are so arranged that they can only be submerged at spring tides; that is, at the new and full moon, when the waters rise beyond the ordinary level.

The basins of claires occupy from two hundred and fifty to three hundred square yards of superficies; two sluices permit of the entrance and withdrawal of water at will, so as to maintain it at the level most convenient to the industrial wants of the place, or to empty it altogether when it is necessary to cleanse the basin, pave the bottom, and furnish it with a fresh supply of oysters.

When these necessary works are completed, advantage is taken of the first spring tide to fill the basin. When the tide begins to ebb, the sluices are closed, so as to retain sufficient water in the basins; and while thus shut up, salt held in solution is deposited, and qualities analogous to those of marine bottoms are produced, purged by cleansing processes of all products offensive to the bivalves.

When the basin has been filled with sea-water for the necessary time, and the bottom is sufficiently impregnated, it is emptied and left to dry; and now, the soil being prepared, it only remains to furnish it with oysters of a mellow and ripe age, in order to give them their green hue. Towards the month of September, at low water, the whole sea-side population of Marennes go to gather oysters on the pavement left uncovered by the ebbing tide, or by using a dredger in the deeper parts of the claires where the water still remains. A temporary magazine for the reception of the oysters thus gathered is erected on the banks, which the water revisits twice a day. The young are reserved for cultivation on the parks or claires; the fullest are sold for consumption in the neighbourhood; but the quantity of oysters raised at Marennes is insufficient to supply the demand. About a third of the provision intended for the claires comes from the coasts of Brittany, of Normandy, and La Vendée. "These foreign oysters," says M. Coste, "never attain the fine flavour of those bred in the locality. It is necessary to keep them for a long time in the claires before they are sufficiently ameliorated, and, even when they become green, they retain traces of their primitive nature, remaining hard, in spite of the new qualities imparted to them by cultivation; a certain bitterness remains, which is easily distinguished by the true amateur; it is the same with indigenous adult oysters. When they are taken at this stage of their existence the colouring does not succeed with them;—it is only, so to speak, the false brand used to give a speculative value to the merchandise. It is not enough that the mollusc should have a fine flavour; it must have the peculiar taste. It is not enough that it has the green hue; it is necessary that these qualities should pervade it from the earliest age, and that the culture of the claires should continue to the end." It is thus necessary that the oysters for the claires of Marennes should be selected when from twelve to eighteen months old, that the shells should be well-formed, and free from all foreign bodies adhering to the surface. Being thus carefully picked out, the oysters are distributed over the bottom of the claires with a shovel, and afterwards so arranged by the hand that they may not touch each other when they increase in size; that they do not embarrass each other by the movements of their valves; and that nothing should interfere with the regularity of their forms. The young colony reposes under a sheet of water from twelve to eighteen inches deep, which is, as we have said, only renewed at spring tides, which reach the level. Nor are the oysters abandoned to themselves in these privileged beds while they are growing and ripening. They are objects of continual care and of special manipulation. The spring tides visit the claires charged with mud, which, if deposited in the motionless basins, would act as a mortal poison to the young mollusc; hence the necessity of transporting them from one claire charged with mud into others free from such accumulations; and this is a process in constant operation until the animals are finally gathered for consumption. Oysters deposited in the claires aged eighteen months should remain two years before they are ready for use; but three and even four years are required to give them the full degree of perfection which characterises the best products of the Marennes oyster-parks.

Oysters placed in the reservoirs in an adult state become green, it is true, in a very few days, but they never attain the exquisite flavour of those which have been bred in the parks, and have undergone the costly manipulation described from their earliest years.

The question arises, What is the colouring principle which is here in operation? The green colour is not general; it is shown principally on the branchiæ, upon the labial feelers and intestinal canal; it is rather undecided; and the colouring matter appears to differ chemically from all other known pigments of green colour. Must it be attributed to the soil of the claire? This is its most probable origin. But many naturalists insist that the colouring matter proceeds from an infusorial animalcule, the green-coloured Vibrion. Others have hazarded the opinion that it is a disease of the liver in our unfortunate bivalve which produces the colour. Bile secreted in excess by a diseased liver would give a green hue to the parenchyma of the respiratory organs of an animal rendered sick by the exceptional treatment to which it has been subjected. Of these three opinions, says M. Figuier, the first, as we have said, presents the greatest appearance of probability.

The system of oyster farms, which has worked admirably for the companies themselves, has proved of doubtful utility, so far as the oyster-eating public is concerned, as the following sketch of the Whitstable oyster farms will show. The oyster farm at Whitstable is co-operative in the best sense of the term, and has been in operation for many years. The Company possesses large oyster grounds, and a fine fleet of boats kept for the purpose of dredging and planting the beds; it is established under the Joint Stock Companies Act, but there is no other way of entrance into it but by birth, as none of the free dredgermen of the town can hold shares. "When a man dies his interest in the Company dies with him, but his widow, if he leaves one, obtains a pension. The affairs of the Company are managed by twelve directors, who are called "the jury."

"The layings at Whitstable," to summarise Mr. Bertram, "occupy about a mile and a half square; and the oyster-beds have been so prosperous as to have obtained the name of the 'happy fishing grounds.' Whitstable lies in a sandy bay, formed by a small branch of the Medway, which separates the Isle of Sheppey from the mainland. Throughout this bay, from the town of Whitstable at its eastern extremity to the old town of Faversham, which lies several miles inland, the whole of the estuary is occupied by oyster farms, on which the maritime population, to the extent of three thousand people and upwards, is occupied; the sum paid for labour by the various companies being set down at £160,000 per annum, besides the employment given at Whitstable in building and repairing boats, dredges and other requisites for the oyster-fishing. The business of the various companies is to feed oysters for the London and other markets, to protect the spawn or floatsome, as the dredgers call it, which is emitted on their own beds, and to furnish, by purchase or otherwise, the new brood necessary to supply the beds which have been taken up for consumption."

We have hinted above that in oyster, as in other fisheries, a wasteful spirit of extravagance has hitherto prevailed. It appears, however, that no rule can be laid down even as to the particular year in which the oysters will spawn, much less where it will be carried to; for, although the artificial contrivances adopted by Sergius Orata for saving the spawn are perfectly well known to the parties interested here, they have not hitherto been imitated; the practice of the companies and private owners of oyster-layers being to purchase their young brood from the dredgers and others who fish along the public foreshore and open grounds on the Kent and Essex coasts, and even as far north as the Frith of Forth. The little bay of Pont, for instance, on the Essex coast, which is an open piece of water sixteen miles long and three broad, free to all, and which formerly yielded considerable supplies to Billingsgate, now gives employment to a hundred and fifty boats, each with crews of three or four men, who are wholly employed in obtaining young brood—that is, oysters from eighteen months to two years old, which they sell to the oyster farmers. The result is, that the oyster farms have become a vast monopoly. By tacit consent they agree to feed the market at some eight pounds sterling per bushel; they pay the dredger one-fourth of that sum; and as the common fishing grounds are thus rendered mere nurseries of young brood, the lover of the bivalve must reconcile himself to pay a monopoly price for the precious morsel.

The system pursued at Whitstable, and other oyster-parks in the estuary of the Thames and Medway, is most efficient. The oysters reared in them, called "natives," in contradistinction to those called "commons," which are bred in their natural beds, are justly considered to be very superior in flavour, although they are a mixed breed, being brought from every quarter to augment the stock.

The Thames, or "native" system, is as follows: Every year each layer is gone over and examined by means of a dredge, successive portions being done day by day, till it may be said that each individual oyster has been examined; the young brood is detached from its bed, the double oysters are separated, and all kinds of enemies killed. During three days in each week dredging is pursued for "planting;" that is, for transference from one bed to another more suitable for their growth or fattening, and for the removal of the dead or sickly oysters and mussels. On the other three days dredging for market takes place, when the more mature beds are dredged, and as many are lifted as are required. Not only is this constant dredging of the beds themselves necessary, but the public beds immediately outside require the same care to keep them in a fit state, and free from enemies.

The same story of over-fishing and improvidence extends round our whole coast. The far-famed Pandores obtained at Preston Pans, near Edinburgh, once so cheap, are becoming scarce and dear. The brood is caught and barreled for export to Holland and other places, especially the Thames oyster farms. English buyers pick the grown oysters for Manchester and other large provincial markets, and the Corporation of Edinburgh, the Duke of Buccleuch, and other proprietors of the foreshore, have just interfered in time to prevent the total destruction of the trade, when the wild song of the Cockenzie dredgerman might have been left to charm some future antiquary, as it is now said to charm the oyster into the dredge with its refrain:

The Scallop-shell (Pecten) is round, nearly equal-sided, resting on the right valve, which is more convex and marked with radiating ribs. Linnæus made the mistake of confounding with the Ostrea a great number of shells, which, by their channeled edges and surfaces, strongly reminded one of the arrangements of the teeth of a comb, whence their name of Pecten. They were well known to naturalists long before the time of Linnæus, under the name of Pilgrims' shells, a name which came into use from the practice which prevailed among pilgrims in the middle ages—we know not why—of ornamenting habits and hats with the valves of some of the species.

The shell of the Pecten is in general nearly circular, more or less elongated, and terminated towards the summit in a straight line, forming a sort of triangular appendage called the ear, to which the hinges are attached. The valves are very regular, but with no resemblance to each other. In some species, the shell of which is closely shut, the lower valve is more or less convex than the upper one. In others, both valves are convex. The hinge is without teeth, and the ligament, which is intended to close the shell, is inserted into a triangular depression or dimple. The retractile muscle is unequal, and nearly central. The valves are not nacred inside, and are formed on their exterior surface of numerous fluted channels, which spring from a lobe more or less pointed at the summit, diverging towards the circumference. The edges are sometimes smooth, as in the Watered Pecten (P. pseudamussium, Fig. 175), but more frequently they are formed in strips or scales, as in the Smooth-shelled Pecten (P. glaber, Fig. 176). Upon the whole, however, the Pectens are very variable, but always elegant in form; the colours are frequently lively and brilliant. In Pl. XIV., some of the most striking forms are represented, as in Fig. I., the Ducal Mantle (Pecten pallium), an inhabitant of the Indian Ocean, remarkable for its elegant form, its twelve radiating stripes, diverging towards the circumference, the horizontal furrows of its salient scales, and the striking distribution of its white spots upon a bed of red and brown marble; Fig. II., the Purple Pecten; Fig. III., the Coral Pecten; Fig. IV., the Tiger Pecten; Fig. V., the Foliaceous Pecten; and Fig. VI., the Northern Pecten.

The animal which inhabits the Pecten shell has the general form of the oyster, differing however from it in a remarkable manner. The edges of the mantle are furnished with multiplied fringes of simple tentacles, between which we find other tentacular appendages a little thicker, each terminating in a sort of small pearl, vividly coloured, to which is attached a nervous thread, which has been taken for an eye. Another difference: the branchiæ, in place of being connected by a striated lamina, as is the case in the oyster, are cut into parallel capillary filaments, forming a free and floating fringe, and the mouth is surrounded by salient many-cleft lips.

While the oyster shell is completely fixed to its bed, the Pecten is, on the contrary, perfectly free, and shifts from place to place, moving in the water even with a certain amount of agility; by smartly closing its half-opened valves and forcibly expelling the water, it moves backward by a sort of reaction; this action, repeated many times, compels the animal to move almost in spite of itself, and enables it to avoid danger, or directs its steps towards the spot it wishes to reach. Some naturalists even assert that, when raised to the surface, the Pecten half opens its shell in such a manner that the upper valve serves the purpose of a sail.

The Pectens, of which a hundred and seventy-six species are described, are inhabitants of every known sea. Twenty species belong to Europe, among which we may mention P. opercularis, represented in Fig. 177; P. glaber, and P. nivea. Fig. 178 represents the White-mantled Pecten (P. plica, Linn.) of the Indian Ocean, and Fig. 179, the Concentric Pecten (P. Japonica) of the Japan seas.

Among the Ostreadæ the shells of Spondylus are distinguished for their variety of form and the brilliant colours with which they are decorated. This makes them much sought after by amateur collectors, and procures for them a high price. The shell of Spondylus is solid and thick, with unequal adherent valves, nearly always bristling with spines, forming a very peculiar kind of ornamentation to the valves; the hinges have two very strong teeth. The animals which inhabit this shell resemble the oyster in many respects, but they still more closely resemble the Pectens. The edges of the mantle are provided with two rows of tentacles, the exterior row being, many of them, furnished at their extremities with coloured tubercles. As examples, we note several species of these bivalves for representation. Spondylus regius (Pl. XV. Fig. I.) is, perhaps, the most remarkable for its immense spines. Spondylus radians, Lamarck (Fig. III.), is noted for its elegant form. Spondylus avicularis (Fig. IV.) shows remarkable inequality in the valves. Spondylus imperialis, Chenu (Fig. II.), has long projecting spines, like feet, and the Scaly Spondylus (S. crassisquama, Fig. V.) is covered with scales arranged like so many roofing-tiles.

Like oysters, the genus Spondylus is frequently found firmly rooted to rocks and other submarine bodies, and, oftener still, heaped one upon the other, like herrings in their barrel.

These animals belong essentially to the seas of warm countries. We find them, however, occupying considerable space in the Mediterranean, where (Fig. VI.) the Ass-footed Spondylus (S. gæderopus) abounds.

But the most remarkable species of all is assuredly Spondylus regius (Pl. XV. Fig. I.). This species is a native of the Indian Ocean, and there scarcely exist three fragments of this rare shell in the museums of Europe. M. Chenu relates in one of his books an anecdote which would prove—if any proof were necessary—how far the desire of a collector to obtain possession of some rare and costly specimen will carry him in order to attain his object. "M. R——," says M. Chenu, "was Professor of Botany to the Faculty of Paris, and was, as some times happens, more learned than rich; he wished, on the invitation of a stranger, to purchase one of these shells at a very high price, which might be from 3000 to 6000 francs; the bargain was made, and the price agreed upon; it was only necessary to pay. The money in the professor's hands made only a small part of the sum the merchant was to receive for his shell, and he would not part with it without payment. M. R——, now consulting his desire to possess the shell more than his weak resources, made up secretly a parcel of his scanty plate, and went out to sell it. Without consulting his wife he replaced his silver plate by coverings of tin, and ran to the merchant to secure his coveted Spondylus, which he believed to be S. regius.

"The hour of dinner arrived, and we may imagine the astonishment of Madame R——, who could not comprehend the strange metamorphosis of her plate. She delivered herself of a thousand painful conjectures on the subject. M. R——, on his part, returned home happy with his shell, which he had committed to the safe custody of a box placed in his coat pocket. But, as he approached the house, he paused, and began for the first time to think of the reception he might meet with. The reproaches which awaited him, however, were compensated when he thought of the treasure he carried home. Finally, he reached home, and Madame R——'s wrath was worthy of the occasion; the poor man was overwhelmed with the grief he had caused his wife; his courage altogether forsook him. He forgot his shell, and, in his trepidation, seated himself on a chair without the necessary adjustment of his garment. He was only reminded of his treasure by hearing the crushing sound of the broken box which contained it. Fortunately, the evil was not very great—two spines only of the shell were broken; but the good man's grief made so great an impression on Madame R——, that she no longer thought of her own loss, but directed all her efforts to console the simple-minded philosopher."

The variation in the number and direction of the spines is a striking feature in Spondylus. When the whole lower surface adheres to branches of coral, a very frequent occurrence, they are confined to the upper valve, but when a part only of the valve, the whole surface becomes covered.

Having finished our short sketch of the Conchifera, we shall now treat of the singular group, Brachiopoda,[11] which some place nearer to the Gasteropoda than the Pteropoda, giving them, in fact, their place. It is out of the province of this work to enter into the physiological arguments of such a question. The days of the Brachiopoda or short-footed animals are past. Of the 1842[12] species formerly known, a few types of a small number of genera only are left, numbering in all 102. The Terebratulidæ are best represented; there were once 300 or 400 species; there are now not more than 67 in the seas of the world. The difference between the past and the present is especially striking, when we compare the recent and fossil species of Europe. Among no other class of shells has there been such a wholesale extinction of species. The great family of Spiriferæ are wholly extinct, and of 400 Rhynconella only four are now living. The curious Crania, Discina, and Lingula are still living, and are mostly found in the seas of the southern hemisphere.

CEPHALOUS MOLLUSCA.

CHAPTER XIII.

The third is æolidæ, types Glaucus and Æolis.

The fourth is Tritoniadæ, types Scyllæa and Tritonia.

The fifth is Doridæ, types Idalia and Doris, the curious sea-lemon.

The first family of the second division, Tectibranchiata, is Phyllidiadæ, types Diphyllidia and Phyllidia.

The second family is Pleurobranchidæ, types, Umbrella, in form resembling a limpet, and Pleurobranchus.

The third family is Aplysiadæ, types, Dolabella and Aplysia.

The fourth family is Bullidæ, types, Scaphander, Acera, and Bulla.

The fifth family is Tornatellidæ, types, Tornatina and Tornatella.

The third order is the Pulmonifera, and the fourth is the Prosobranchiata; we shall speak of them in the next chapter.

In this family we reach a group of Gasteropods much more numerous, both in species and in special types, which respire by the aid of branchiæ, or gills. Cuvier divides them into many orders, based chiefly upon their respiratory organs.

The Tectibranchiata have the gills attached either to the right side of the body or upon the back, arranged in the form of leaflets, more or less divided, but not symmetrical, and nearly covered by the mantle. Bulla and Aplysia are the two principal genera of the group, and may be considered as the type of two small families.

The Aplysiæ were known to the ancients under the name of sea-hares (Lepus marinus), from some fancied resemblance to the terrestrial hare. They were objects of profound horror, inspired either by their singular form, or from an acrid, caustic, and inodorous liquid which they secrete. A magic influence was attributed to them; they were supposed, for instance, to have influence over the female heart. It is not easy, however, to explain the evil renown acquired by an animal which is known to be gentle and even timid. They are naked and fat, somewhat resembling the Limnæa in their oval, elongated form, their thickness in the dorsal region, and their posterior locomotion. Their head, which is very indistinct, is furnished with four tentacles, the anterior two of which are the largest, and somewhat resemble the ears of a hare. The eyes are found at the base of the posterior tentacles. These characters are observed in Aplysia depilans (Fig. 180). Aplysia inca shows also the same arrangement (Fig. 181). In this family the mollusc is much more important from its volume than from its internal, rudimentary, and horny shell, which is contained in the branchial shield. In Fig. 182 we have the small and thin cartilaginous shell which exists in the interior of the animal.

The Aplysiæ are found nearly in every region of the globe, not only upon the shores of the Continent, but on every island shore. They commonly inhabit sandy and muddy shores of small depths, or even the rocky recesses, or under shelter of the stones which have fallen from the cliffs. Their eggs consist of those long filaments which are discharged in immense numbers, and which fishermen call sea-worms.

They feed upon certain algæ, with which the bottom of the sea is covered; but they eat, also, small marine animals, such as the naked molluscs, annelids, and crustaceans.

We are the less astonished to see the Aplysiæ so gluttonous when we learn how liberally Nature has accorded to them organs of mastication, trituration, and digestion. Their mouth is formed of thick and muscular lips; a very long œsophagus or gullet succeeds, and this œsophagus does not communicate with a single stomach, but with four—one enormous membranous crop, an exceedingly muscular gizzard, with two accessary pockets, one of which terminates in the form of a sac. The gizzard has thick walls, and is furnished on the internal wall with cartilaginous quadrangular pyramids, the summits of which intertwine. This apparatus is intended to bruise the food when it reaches the third stomach. It is also armed with little hooks, the curvature of which is directed towards the entrance of the gizzard.

The genus Bulla differs materially from the Aplysiæ. They have a well-developed shell, the form of which is elegant; they are delicate in structure; their brilliant colours, consisting of red, black, or white bands, separated by many varied tints, cause these little molluscs to be much sought after for ornamental collections. The shell itself is oval or globulous, rolled up in a scroll, smooth, spotted, very thin and fragile, with a concave spiral, umbilicate, open in all its length, with a straight, wide, and cutting edge.

Obtuse at its two extremities, neither the head of the animal nor the tentacles are very apparent. The gills are placed under the back, a little to the right and behind; its stomach, which alone fills a great part of the cavity of the body, presents the peculiarity, already noted in the Aplysia, of being furnished with bony pieces, evidently intended to grind the food.

The Bullæ can swim with facility in deep water, but they evidently prefer the shallows and a sandy bottom, feeding upon smaller molluscs. They are found in every sea, but they abound chiefly in the Indian Ocean and Oceania. Some species, however, such as Bulla ampulla (Figs. 183 and 184), the shell of which is shaded grey and brown, and the Water-drop (Bulla hydratis), inhabit European seas. Bulla oblonga and Bulla aspersa (Adams), and Bulla nebulosa (Gould), represented in Figs. 185, 186, and 187, are also well-known species.

We take leave of our little friends the Headless Mollusca or Acephalæ, and direct our attention to those molluscs to which Nature has been more generous, and furnished with a head. This head, however, is still carried humbly; it is not yet os sublime dedit; it is drawn along an inch or so from the ground, and in no respect resembles the proud and magnificent organ which crowns and adorns the body of the greater and more perfectly organized animals.

The organization of the Cephalous Mollusca present three principal types, which has led to their being divided into three classes, after their more salient characteristics of form and locomotive apparatus; namely, Gasteropoda, Pteropoda, and Cephalopoda.

In the class Gasteropoda (from γαστὴρ, belly, ποῦϛ, gen.ποδὸϛ, foot) the locomotive apparatus consists of a flattened muscular disk, placed under the belly of the animal, aided by which it creeps. The Snail (Helix), the Slug (Limax), and the Cowrie, (Cyprea), are types of this class.

In the Pteropoda, from πτερὸν, wing, and ποῦϛ, foot, the locomotive apparatus assumes the form of wings, or membranous swimming-fins, placed on each side of the neck. The Hyalea and Clio are types of this class.

In the Cephalopoda, from κεφαλὴ, head, and ποῦϛ, foot, the locomotive apparatus consists of arms, or tentacles, which surround the mouth in numbers more or less considerable. The Cuttle-fish (Sepia), and the Poulpes (Octopoda) are types of this last class.

The Molluscous Gasteropoda have the organs of respiration formed for aerial respiration, or for respiration under water.

This physiological arrangement involves important differences in internal organization in these molluscs, and renders it convenient to divide them into two secondary groups; namely, Pulmonary Gasteropods, which breathe in the air, and by a species of lung, and Non-pulmonary Gasteropods, which breathe in the water, by means of branchiæ or gills.

CHAPTER XIV.

Limnæidæ.

The Limnæidæ, Aquatic Pulmonary Gasteropods, is the second family of the series. They belong to the group that come to the surface of the water to breathe, as do the cetacea and phocas among the Mammifera. The Limnæa, Planorbis, and Physa are the principal members of this group.

Limnæa lives in great numbers in the stagnant waters of all countries, particularly of temperate climates. It cannot remain long under water, being compelled frequently to rise to the surface in order to breathe atmospheric air. It is even observed, by a mechanism not very well understood, to turn itself upside down, in such a manner as to present itself feet uppermost, and to move slowly along in this position, creeping, as it were, through the water. It is difficult to comprehend how the movable liquid bed upon which the animal operates can offer resistance enough to permit of its creeping as if it were on a solid resisting body; it seems to produce the movement with the assistance of its foot, which is broad and thick, and shorter than the shell.