chapter I

have already briefly described the wonderful transformations of the barnacles, acorn-shells, and lerneæ, but the changes which the young crabs, lobsters, prawns, and shrimps, have to undergo ere they assume their perfect form are no less astonishing. Thus in the earliest state of the small edible crab (_Carcinus mœnas_) we find a creature with a preposterously large helmet-shaped head, ending behind in a long spine, and furnished in front with two monstrous sessile eyes like the windows of a lantern. By means of a long articulated tail the restless Chimera continually turns head over heels. Claws are wanting, and while the old crab is of course a perfect decapod, the young has only four bifid legs, armed at the extremity with four long bristles, that are continually pushing food towards the ciliated mouth. Who could imagine that a creature like this should ever change into a crab, to which it has not the least resemblance? But time does wonders. After the first change of skin the body assumes something like its permanent shape, the eyes become stalked, the claws are developed, and the legs resemble those of the crab, but the tail is still long, and the swimming habit has not yet been laid aside. At the next stage, while the little creature is still about the eighth of an inch in diameter, the crab form is at length completed, the abdomen folding in under the carapace. No wonder that these larvæ were long supposed to be distinct types, and described under the names of Zoëa and Megalops, until Mr. T. J. Thompson first discovered their real nature.

[Illustration: Metamorphosis of Carcinus mœnas.

A. First stage. B. Second stage. C. Third stage, in which it begins to assume the adult form. D. Perfect form.]

[Illustration: Phyllosoma.]

The life history of the Palinuri or spiny lobsters is equally curious. They frequently weigh ten or twelve pounds each, and are distinguished by the very large size of their lateral antennæ and by their feet being unarmed with pincers. Surely nothing can be more dissimilar than the glass crabs or _Phyllosomas_, thin as a leaf of paper, and so transparent that their blue eyes are their only visible parts while swimming in the water; and yet these flimsy creatures are nothing but the young of the large and bulky Palinuri.

Though several of the lower crustaceans ascend into the regions of eternal snow, while others hide themselves in the perpetual night of subterranean grottoes; though many delight in the sweet waters of the river or the lake, or rapidly multiply in stagnant pools, yet the chief seat of their class, which altogether comprises about 1,600 known species, is in the ocean and its littoral zone, where their numbers, their voracity, and their powerful claws, render them the most formidable enemies of all the lower aquatic animals that are not swift or cunning enough to escape them. Even the fishes and cetaceans are, as we have seen, exposed to their attacks; and as the whale, the carp, the sturgeon, the shark, the perch, have each of them their peculiar crustacean parasites, it can easily be imagined how large the number of still unknown species must be which feast on that vast host of fishes that has never yet been accurately examined. On the other hand, the crustaceans constitute a great part of the food, as well of the sea-stars, sea-urchins, annelides, and many of the molluscs, as also of the fishes and sea-birds; and as they are found of all sizes, from microscopical minuteness to the gigantic proportions of the _Inachus Kæmpferi_ of Japan, the fore-arm of which measures four feet in length, and the others in proportion, so that it covers about 25 feet square of ground, they are able to satisfy the wants or the voracity of a vast number of enemies, from the rotifer or the polyp that feed on tiny entomostraca or the larvæ of the barnacle, to man, who selects a great variety of the fat and luscious decapods for his share of the feast.

A great fecundity enables the crustaceans to bear up against all these persecutions. 12,000 eggs have been found on the lobster; 6,807 on the shrimp; 21,699 on the great crab (_Platycarcinus pagurus_). The lower orders are still more prolific, for such is the rapidity with which many of them come to maturity and begin to propagate that it has been calculated that a single female Cyclops may be the progenitor in one year of 4,442,189,120 young! Endowed with such powers, the crustaceans are not likely to be extirpated, nor to disappoint the hopes of their gastronomical admirers for many an age to come.

* * * * *

When we hear of fishes wandering about on the dry land, we cannot wonder that some insects and arachnidans should depart so strangely from the usual habits of their class as to select the sea for their habitation.

"There is a minute marine spider," says Mr. Gosse, "very common on most parts of the coast, crawling sluggishly upon the smaller sea-weeds, which seems, from its lack of centralisation, to realise our infant ideas of Mr. Nobody; but zoologists have designated him as _Nymphon gracile_. Widely different from the spiders of terra firma, in which an abdomen some ten times as bulky as all the rest of the animal put together is the most characteristic feature, the belly of our marine friend is reduced to an atom not so big as a single joint of one of his eight legs; though his thorax is more considerable, this is little more than the extended line formed by the successive points of union of the said legs. These latter, on the other hand, are long, stout, well-armed, and many-jointed; but, apparently from the lack of the centralising principle, they are moved heavily, sprawled hither and thither, and dragged about like the limbs of an unfortunate who is afflicted with the gout." This strange little creature has four eyes gleaming like diamonds, respires by the skin, and its stomach is prolonged into each of its eight legs, which are thus made the seats of digestion. Mr. Nobody and his marine relations, some of which also attach themselves to fishes, form the small group of the _Pycnogonida_ (πυκνος, _frequent_; γὁνυ _knee_) thus named from their many-jointed legs.

It is a well-known fact that the winds will sometimes waft butterflies to an immense distance from the shore. Thus _Acherontia atropos_ has been found on the Atlantic a thousand miles from the nearest land; and while Mr. Darwin was in the bay of San Blas, in Patagonia, he saw thousands of butterflies hovering over the sea as far as the eye could reach. These insects, of course, are nothing but stray wanderers on an alien and hostile element; but _Leptopus longipes_, a species of bug, makes the salt water its home; the Halobates, another hemipterous insect, faces the tranquil mirror of the tropical seas as leisurely as our water-bugs sport on the glassy surface of our ponds, and the _Gyrinus marinus_, a beetle belonging to the family of the whirligigs, ambitiously seeks a wide expanse, and may be seen curvetting about on the surface of the sea, and darting down every now and then to seize its prey.

[Illustration: Stenopus hispidus.]

CHAP. XIV.

MARINE ANNELIDES.

The Annelides in general.--The Eunice sanguinea.--Beauty of the Marine Annelides.--The Giant Nemertes.--The Food and Enemies of the Annelides.--The Tubicole Annelides.--The Rotifera--Their Wonderful Organisation.--The Synchæta Baltica.

The class of the Annelides, or annulated worms--to which also our common earth-worm and the leech belong--peoples the seas with by far the greater number of its genera and species. All of them are distinguished by an elongated, and generally worm-like form of body, susceptible of great extension and contraction. The body consists of a series of rings, or segments, joined by a common elastic skin; and each ring, with the exception of the first or foremost, which forms the head, and the last which constitutes the tail, exactly resembles the others, only that the rings in the middle part of the body are larger than those at the extremities. The head is frequently provided with eyes, and more or less perfect feelers; the mouth is armed in many species with strong jaws, or incisive teeth. The blood is red, and circulates in a system of arteries and veins.

[Illustration: Nervous Axis of an Annelidan.]

With the idea of a worm we generally connect that of incompleteness; we are apt to consider them as beings equally uninteresting and ugly, and disdain to enquire into the wonders of their organisation. But a cursory examination of the _Eunice sanguinea_, a worm about two and a half feet long, and frequently occurring on our coasts, would alone suffice to give us a very different opinion of these despised, but far from despicable creatures. The whole body is divided into segments scarce a line and a half long, and ten or twelve lines broad, and thus consists of about three hundred rings. A brain and three hundred ganglions, from which about three thousand nervous branches proceed, regulate the movements, sensations, and vegetative functions of an Eunice. Two hundred and eighty stomachs digest its food, five hundred and fifty branchiæ refresh its blood, six hundred hearts distribute this vital fluid throughout the whole body, and thirty thousand muscles obey the will of the worm, and execute its snake-like movements. What an astonishing profusion of organs! Surely there is here but little occasion to commiserate want, or to scoff at poverty!

And if we look to outward appearance, we shall find that many of the marine annelides may well be reckoned among the handsomest of creatures. They display the rainbow tints of the humming-birds, and the velvet, metallic brilliancy of the most lustrous beetles. The vagrant species that glide, serpent-like, through the crevices of the submarine rocks, or half creeping, half swimming conceal themselves in the sand or mud, are pre-eminently beautiful. The delighted naturalists have consequently given them the most flattering and charming names of Greek mythology,--Nereis, Euphrosyne, Eunice, Alciopa.

[Illustration: Nereis.]

"Talk no more of the violet as the emblem of modesty," exclaims De Quatrefages, "look rather at our annelides, that, possessed of every shining quality, hide themselves from our view, so that but few know of the secret wonders that are hidden under the tufts of algæ, or on the sandy bottom of the sea."

[Illustration: Aphrodita, or Sea-Mouse.]

In most of the wandering annelides, each segment is provided with variously formed appendages, more or less developed, serving for respiration and locomotion, or for aggression and defence; while in some of the least perfect of the class, not a trace of an external organ is to be found over the whole body. The great Band-worm (_Nemertes gigas_) is one of the most remarkable examples of this low type of annelism. It is from thirty to forty feet long, about half an inch broad, flat like a ribbon, of brown or violet colour, and smooth and shining like lackered leather. Among the loose stones, or in the hollows of the rocks, where he principally lives on Anomiæ,--minute shells that attach themselves to submarine bodies,--this giant worm forms a thousand seemingly inextricable knots, which he is continually unravelling and tying. When after having devoured all the food within his reach, or from some other cause, he desires to shift his quarters, he stretches out a long dark-coloured ribbon, surmounted by a head like that of a snake, but without its wide mouth or dangerous fangs. The eye of the observer sees no contraction of the muscles, no apparent cause or instrument of locomotion; but the microscope teaches us that the Nemertes glides along by help of the minute vibratory ciliæ with which his whole body is covered. He hesitates, he tries here and there, until at last, and often at a distance of fifteen or twenty feet, he finds a stone to his taste; whereupon he slowly unrolls his length to convey himself to his new resting place, and while the entangled folds are unravelling themselves at one end, they form a new Gordian knot at the other. All the organs of this worm are uncommonly simplified; the mouth is a scarce visible circular opening, and the intestinal canal ends in a blind sack.

Nature has not in vain provided the more perfect annelides with the bristly feet, which have been denied to the Nemertes and the sand-worm. Almost all of them feed on a living prey,--Planarias and other minute creatures--which they enclasp and transpierce with those formidable weapons. Some, lying in wait, dart upon their victims as they heedlessly swim by, seize them with their jaws, and stifle them in their deadly embrace; others, of a more lively nature, seek them among the thickets of corallines, millepores and algæ, and arrest them quickly ere they can vanish in the sand.

But the annelides also are liable to many persecutions. The fishes are perpetually at war with them; and when an imprudent annelide quits its hidden lurking-place, or is uncovered by the motion of the waves, it may reckon itself fortunate, indeed, if it escapes the greedy teeth of an eel or a flat-fish. It is even affirmed of the latter, as it is of the whelks, that they know perfectly well how to dig the annelides out of the sand. The sea-spiders, lobsters, and other crustacea are the more dangerous, as their hard shells render them perfectly invulnerable by the bristling weapons of the annelides.

While the greater part of these worms lead a vagrant life, others, like secluded hermits, dwell in self-constructed retreats which they never leave. Their cells, which they begin to form very soon after having left the egg, and which they afterwards continue extending and widening according to the exigencies of their growth, generally consist of a hard calcareous mass; but sometimes they are leathery or parchment-like tubes, secreted by the skin of the animal, not however forming, as in the mollusks, an integral part of the body, but remaining quite unconnected with it. Thus these tubicole annelides spend their whole life within doors, only now and then peeping out of their prison with the front part of their head.

As they lead so different a life from their roaming relations, their internal structure is very different, for where is the being whose organisation does not perfectly harmonise with his wants? Thus, we find here no bristling feet or lateral respiratory appendages; but instead of these organs, which in this case would be completely useless, we find the head surmounted by a beautiful crown of feathery tentaculæ, which equally serve for breathing and the seizing of a passing prey. Completely closed at the inferior extremity, the tube shows us at its upper end a round opening, the only window through which our hermit can peep into the world, seize his food, and refresh his blood by exposing his floating branchiæ to the vivifying influence of the water.

Do not, therefore, reproach him with vanity or curiosity, if you see him so often protrude his magnificently decorated head; but rejoice rather that this habit, to which necessity obliges him, gives you a better opportunity for closer observation. Place only a shell or stone covered with _serpulas_ or _cymospiras_, into a vessel filled with sea-water, and you will soon see how, in every tube, a small round cover is cautiously raised, which hitherto hermetically closed the entrance, and prevented you from prying into the interior. The door is open, and soon the inmate makes his appearance. You now perceive small buds, here dark violet or carmine, there blue or orange, or variously striped. See how they grow, and gradually expand their splendid boughs! They are true flowers that open before your eye, but flowers much more perfect than those which adorn your garden, as they are endowed with voluntary motion and animal life.

[Illustration: Serpula, attached to a Shell.]

At the least shock, at the least vibration of the water, the splendid tufts contract, vanish with the rapidity of lightning, and hide themselves in their stony dwellings, where, under cover of the protecting lid, they bid defiance to their enemies.

Not all the tubicole annelides form grottos or houses of so complete a structure as those I have just described. Many content themselves with agglutinating sand or small shell-fragments into the form of cylindrical tubes. But even in these inferior architectural labours of the _Sabellas_, _Terebellas_, _Amphitrites_, &c., we find an astonishing regularity and art; for these elegant little tubes, which we may often pick up on the strand, where they lie mixed with the shells and algæ cast out by the flood, consist of particles of almost equal size, so artistically glued together, that the delicate walls have everywhere an equal thickness. The form is cylindrical, or funnel-shaped, the tube gradually widening from the lower to the upper end. Some of these tubicoles live like solitary hermits, others love company; for instance, the _Sabella alveolaris_, which often covers wide surfaces of rock, near low-water mark with its aggregated tubes. When the flood recedes nothing is seen but the closed orifices; but when covered with the rising waters, the sandy surface transforms itself into a beautiful picture. From each aperture stretches forth a neck ornamented with concentric rings of golden hair, and terminating in a head embellished with a tiara of delicately feathered, rainbow-tinted tentacula. The whole looks like a garden-bed enamelled with gay flowers of elegant form and variegated colours.

* * * * *

If size alone were a criterion of classification, the Rotifera would have to be ranked among the microscopic Protozoa, as they are scarcely visible to the naked eye; but a more complicated organisation separates them widely from these lowest members of the animal kingdom, and entitles them to be placed next to the worms.

[Illustration: Ptygura mehcerta.--(A rotifer highly magnified.)

1. Partially expanded. 2. Completely expanded, the cilia in action causing currents indicated by the arrows. 3. Contracted. _a._ Contractile vesicle. _b._ Situation of the anal orifice. ]

They are chiefly characterised by a remarkable rotatory or ciliary apparatus, whose vibrating motions, whirling the water about in swift circles or eddies, engulf in a fatal vortex their microscopic food, or enable them to swim from place to place. Such is the crystal transparency of these curious little creatures that their internal structure can be easily recognised. The mouth is placed immediately below the rotatory apparatus, and when once an unfortunate animalcule has been driven into its gaping portals, it is presently crushed between a pair of formidable sharp-toothed jaws, which are perpetually in motion, whether the animal is taking food or not. After having undergone the action of this lively apparatus, the aliment passes into a tubular stomach surrounded by a cushion-like mass of cells commonly coloured with the hue of the food, and, therefore, concluded to be connected with the digestive system.

[Illustration: Conochilus volvox.--(Highly magnified.)

_a._ Jaws and teeth. _b._ Papillæ. _c._ Glands. _d._ Ovarium. ]

The rotifera are either naked or covered with a sheath, and many inhabit a tube formed by themselves, attached by its lower end to some water-plant, and open at the summit, from which the animal protrudes when it would exercise its active instincts, and into which it retires for repose from labour or for refuge from alarm. The majority, however, have a furcated foot, which is often capable of contraction by a set of telescopic sheathings or false joints, and by which they are enabled to secure a hold of the minute stems of water-plants. This is their ordinary position when keeping their wheels in action for a supply of food or of water; but they have no difficulty in letting go their hold, and either creeping along by alternate contractions and extensions or swimming away in search of a new attachment. From the neck projects a telescopic spur, supposed to be an organ of respiration, and just below this are seen two minute red specks, supposed to be eyes. The first rotifer was discovered by Leeuwenhoek, in 1702; now more than 180 species are known, and new discoveries are constantly adding to their numbers. They are chiefly found in sweet water, but some are inhabitants of the sea, as, for instance, the _Synchæta baltica_, remarkable for its luminous powers. It measures about 1/125 of an inch in length, and but 1/350 in width, so that it is invisible to the sharpest unassisted sight: but when viewed through a microscope, it appears as a beautiful and richly organised creature, clear as glass and perfectly colourless, except that its stomach is usually distended with yellow food, and that it carries a large red eye, which glitters like a ruby.

[Illustration: Philodina roseola.--(Highly magnified.)

_a._ Respiratory tube. _b._ Alimentary canal. _c._ Cellular mass. _d._ Terminal intestinal pouch. _e._ Anal orifice. ]

"Its motions too," says Mr. Gosse, "are all vivacious and elegant. It shoots rapidly along or circles about in giddy dance, in company with its fellows, sometimes near the surface, at others just over the bottom of the vase in which it is kept. Occasionally the foot with the tiny toes is drawn up into the body and then suddenly thrown down, and bent up from side to side as a dog wags his tail. Sometimes the rotatory organs are brought forward and then spasmodically spring back to their ordinary position, when the little creature shoots forward with redoubled energy. In all its actions it displays vigour and precision, intelligence and will."

CHAP. XV.

MOLLUSCS.

The Molluscs in general.--The Cephalopods.--Dibranchiates and Tetrabranchiates.--Arms and Tentacles.--Suckers.--Hooked Acetabula of the Onychoteuthis.--Mandibles.--Ink Bag.--Numbers of the Cephalopods.--Their Habits.--Their Enemies.--Their Use to Man.--Their Eggs.--Enormous size of several species.--The fabulous Kraken.--The Argonaut.--The Nautili.--The Cephalopods of the Primitive Ocean.--The Gasteropods.--Their Subdivisions.--Gills of the Nudibranchiates.--The Pleurobranchus plumula.--The Sea-Hare.--The Chitons.--The Patellæ.--The Haliotis or Sea-Ear.--The Carinariæ.--The Pectinibranchiates.--Variety and Beauty of their Shells.--Their Mode of Locomotion.--Foot of the Tornatella and Cyclostoma.--The Ianthinæ.--Sedentary Gasteropods.--The Magilus.--Proboscis of the Whelk.--Tongue of the Limpet.--Stomach of the Bulla, the Scyllæa, and the Sea-Hare.--Organs of Sense in the Gasteropods.--Their Caution.--Their Enemies.--Their Defences.--Their Use to Man.--Shell-Cameos.--The Pteropods.--Their Organisation and Mode of Life.--The Butterflies of the Ocean.--The Lamellibranchiate Acephala.--Their Organisation.--Siphons.--The Pholades.--Foot of the Lamellibranchiates.--The Razor-Shells.--The Byssus of the Pinnæ.--Defences of the Bivalves.--Their Enemies.--The common Mussel.--Mussel Gardens.--The Oyster.--Oyster Parks.--Oyster Rearing in the Lago di Fusaro.--Formation of new Oyster Banks.--Pearl-fishing in Ceylon.--How are Pearls formed?--The Tridacna gigas.--The Teredo navalis.--The Brachiopods.--The Terebratulæ.--The Polyzoa.--The Sea-Mats.--The Escharæ.--The Lepraliæ.--Bird's Head Processes.--The Tunicata.--The Sea-Squirts.--The Chelyosoma.--The Botrylli.--The Pyrosomes.--The Salpæ.--Interesting Points in the Organisation of the Tunicata.

Simple or compound, free or sessile, peopling the high seas or lining the shores, the marine Molluscs, branching out into more than ten thousand species, extend their reign as far as the waves of ocean roll. Though distinguished from all other sea-animals by the common character of a soft unarticulated body, possessing a complicated digestive apparatus, and covered by a flexible skin or mantle, under or over which a calcareous shell is generally formed by secretion, yet their habits are as various as their forms. Some dart rapidly through the waters, others creep slowly along, or are firmly bound to the rock; in some the senses are as highly developed as in the fishes, in others they are confined to the narrow perceptions of the polyp. Many are individually so small as to escape the naked eye, others of a size so formidable as to entitle them to rank among the giants of the sea; some are perfectly harmless and unarmed, others fully equipped for active warfare. It is evident that creatures so variously gifted, and consequently so widely dissimilar in structure, cannot possibly be grouped together in one description, and that each of the four orders, Cephalopoda, Gasteropoda, Pteropoda, and Acephala (Lamellibranchiates, Brachiopods, Polyzoa, and Tunicata), into which they have been subdivided, must be separately brought before the reader, in order to give him a clear and faithful picture of their organisation and mode of life.

The Cephalopods are the most perfect specimens of the molluscan type, as the decapods are the first among the crustaceans. These remarkable creatures consist of two distinct parts: the trunk or body, which, in form of a sack, open to the front, encloses the branchiæ and digestive organs, and the well-developed head, provided with a pair of sharp-sighted eyes, and crowned with a number of fleshy processes, arms or feet, which encircle and more or less conceal the mouth. It is to this formation that the cephalopod owes its scientific name, for as the feet grow from the circumference of the mouth, it literally creeps upon its head.

All the cephalopods are marine animals, and breathe through branchiæ or gills. These are concealed under the mantle, in a cave or hollow, which alternately expands and contracts, and communicates by two openings with the outer world. The one in form of a slit serves to receive the water; the other, which is tubular, is used for its expulsion.

According to the different number of their gills, the cephalopods are divided into two groups. The first, to which the poulp and common cuttle-fish belong, and which comprises by far the majority of living species, has only two sets of gills; while the second, which, in the present epoch, is only represented by a few species of Nautilus, has four, two on each side, according to the number of their arms or feet--for these remarkable organs serve equally well for prehension or locomotion. The first group is again subdivided into two orders, Octopods and Decapods, the former having only eight sessile feet, while the latter possess an additional pair of elongated tentacles, which serve to seize a prey that may be beyond the reach of the ordinary feet, and also to act as anchors to moor them in safety during the agitations of a stormy sea.

[Illustration: Poulp (Octopus).]

Both the arms and tentacles are furnished with suckers disposed along the whole extent of the inner surface of the former, but generally confined to the widened extremities of the latter, where they are closely aggregated on the inner aspect.

[Illustration: Calamary.]

In all the octopods the suckers are soft and unarmed. Every sucker is composed of a circular adhesive disk, which has a thick fleshy circumference and bundles of muscular fibres radiating towards the circular orifice of an inner cavity.

This widens as it descends, and contains a cone of soft substance, rising from the bottom of the cavity, like the piston of a syringe. When the sucker is applied to a surface for the purpose of adhesion, the piston, having previously been raised so as to fill the cavity, is retracted, and a vacuum produced, which may be still further increased by the retraction of the plicated central portion of the disk. So admirably are these air-pumps constructed, and so tenacious is their grasp, that, when they have once seized or fixed upon a prey, it cannot possibly disengage itself from their murderous embrace.

In many of the decapods, who, generally seeking their prey in the deeper waters, have to contend with the agile, slippery, and mucus-clad fishes, more powerful organs of prehension have been superadded to the suckers. Thus, in the Calamary the base of the piston is enclosed by a horny hoop, the margin of which is developed into a series of sharp-pointed curved teeth; and in the still more formidable Onychoteuthis each hoop is produced into the form of a long, curved, and sharp-pointed claw (_f_), which the predacious mollusc presses firmly into the flesh of its struggling victim, and then withdraws by muscular contraction.

[Illustration: Section of an arm and suckers of a Poulp.

_e._ Soft and tumid margin of the disk. _g._ Circular aperture. ]

Besides the hooked acetabula, a cluster of small simple unarmed suckers may be observed at the base of the expanded part. These add greatly to the animal's prehensile powers, for when they are applied to one another (_e_), the tentacles are firmly locked together at that point, and the united strength of both the elongated peduncles can be applied to drag towards the mouth any resisting object which has been grappled by the terminal hooks. There is no mechanical contrivance which surpasses the admirable structure of this natural forceps.

The size of the arms and the arrangement of the suckers differ considerably in the various species. In the octopods or poulps, which generally lead a more sedentary creeping life, and, hidden in the crevices of rocks, await the passing prey, the arms, in accordance with their wants, are with rare exceptions longer, more muscular, and stronger, than in the actively swimming decapods, where the two elongated tentacles or peduncles are the chief organs of prehension. In some species we find the arms distinct--in others they are united by a membrane. Some have a double row of suckers on each arm, others four rows, others again but one. So wonderful are the variations which nature, that consummate artist, plays upon a single theme--so inexhaustible are the modifications she introduces into the formation of numerous species, all constructed upon the same fundamental plan, and all equally perfect in their kind.

[Illustration: Arms and Tentacles of an Onychoteuthis.

_e._ Parts joined together by the mutual apposition of the armed suckers.

_f._ Terminal expanded portions bearing the hooks. ]

Thus well provided with the means for seizing and overcoming the struggles of a living prey, the Cephalopods likewise possess adequate weapons for completing its destruction; for their mouth is most formidably armed with two horny or calcareous jaws, shaped like the mandibles of a parrot, playing vertically on each other, and enclosing a large fleshy tongue bristling with recurved horny spines. Hard, indeed, must be the crab which can resist this terrible beak; and when the cuttle-fish has once fixed on the back of a fish, though much larger and stronger than himself, it is in vain for the tortured victim to fly through the water: he carries his enemy with him till he sinks exhausted under his murderous fangs.

Besides their arms, by help of which the Cephalopods either swim or creep, the forcible expulsion of the water through the respiratory tube or infundibulum serves them as a means of locomotion in a backward direction. By those which have an elongated body and comparatively strong muscles, this movement is performed with such violence that they shoot like arrows through the water, or even like the flying-fish perform a long curve through the air.

Thus Sir James Ross tells us, that once a number of cuttle-fish not only fell upon the deck of his ship, which rose fifteen or sixteen feet above the water, and where more than fifty were gathered, but even bolted right over the entire breadth of the vessel, like a sportsman over a five-barred gate. Finally, the fin-like expansion of their mantle renders the nimble decapods good service in swimming. In the Sepias this finny membrane runs along the sides of the body, while in the Calamary it forms a kind of terminal paddle.

[Illustration: Sepia.

_b._ Finny membrane running along the sides of the body. _c._ Arms with four rows of suckers. _d._ Elongated retractile tentacles. _e._ Eyes. ]

It might be supposed that the dibranchiate cephalopods, by their swiftness, their arms, and their powerful jaws, were sufficiently provided with means of attack or defence; but it must be remembered that their body is soft and naked, and that, though well armed in front, they may readily be attacked in the rear. To afford them the additional protection they required, nature, ever ready to minister to the real wants of her children, has furnished them with an internal bag communicating with the respiratory tube, and secreting a large quantity of an inky fluid, which they can squirt out with force in the face of their foe, and which, mixing readily with the water, envelops them in an opaque cloud, and thus screens them from pursuit. But this inky fluid, thus useful to its owner, is often the cause of his destruction by man, who applies it to his own purpose, for the Italian pigment, called sepia, so invaluable to painters in water-colours, is prepared from the inspissated contents of the ink bag of a cuttle-fish. Such is the durability of this colour that even the inky fluid of fossil species has been found to retain its chromatic property. We are told that grains of wheat buried with Egyptian mummies three thousand years ago have germinated; but it is surely still more astonishing that an animal secretion, the origin of which is lost in the dark abyss of countless ages, should remain so long unaltered.

The cephalopods are scattered in vast numbers over the whole ocean, from the ice-bound shores of Boothia Felix to the open main; they seem, however, to be most abundant in temperate latitudes. Some, like the common poulp, constantly frequent the coasts, creeping among the rocks and stones at the bottom; others, like the Cirroteuthis and Ommastrephes, roam about the high seas at a vast distance from the land.

They are generally nocturnal or vespertine in their habits; they abound towards evening and at night on the surface of the seas, but sink to a greater depth, or retire into the crevices of the rocks, as soon as the sun rises above the horizon. Some are of a recluse disposition, and lead a solitary life in the anfractuosities of the littoral zone; others, of a more social temper, wander in large troops along the shores, or over the vast plains of ocean.

Possessing the organs of sense, and the means of locomotion in a high degree of development, the cephalopods may naturally be expected to be far more active and intelligent than the inferior orders of the molluscs. On moonlight nights, among the islands of the Indian Archipelago, Mr. Adams frequently observed the Sepiæ and Octopi in full predatory

## activity, and had considerable difficulty and trouble in securing them,

so great was their restless vivacity, and so vigorous their endeavours to escape. "They dart from side to side of the pools," says the naturalist in his entertaining and instructive account of his journey to those distant gems of the tropical sea, "or fix themselves so tenaciously to the surface of the stones by means of their suckers that it requires great force and strength to detach them. Even when removed and thrown upon the sand, they progress rapidly, in a sidelong shuffling manner, throwing about their long arms, ejecting their ink-like fluid in sudden violent jets, and staring about with their big shining eyes (which at night appear luminous, like a cat's) in a very grotesque and hideous manner."

At the Cape de Verd islands, Mr. C. Darwin was also much amused by the various arts to escape detection used by a cuttle-fish, which seemed fully aware that he was watching it. Remaining for a time motionless, it would then stealthily advance an inch or two, like a cat after a mouse, and thus proceeded, till, having gained a deeper part, it darted away, leaving a dusky train of ink, to hide the hole into which it had crawled.

All the cephalopods are extremely voracious; they destroy on shallow banks the hopes of the fishermen, devour along the coasts and on the high seas countless myriads of young fish and naked molluscs, and kill, like the tiger, for the mere love of carnage. Thus they would become dangerous to the equilibrium of the seas if nature, to counterbalance their destructive habits, had not provided a great number of enemies for the thinning of their ranks.

They form the almost exclusive food of the sperm-whales, and the albatross and the petrels love to skim them from the surface of the ocean. Tunnies and bonitos devour them in vast numbers, the cod consumes whole shoals of squids, and man, as I have already mentioned, catches many millions to serve him as a bait for this valuable fish.

At Teneriffe, in the Brazils, in Peru and Chili, in India and China, various species of cephalopods are used as food. Along the eastern shores of the Mediterranean, the common sepia constitutes now, as in ancient times, a valuable part of the food of the poor. "One of the most striking spectacles," says Edward Forbes, "is to see at night on the shores of the Ægean the numerous torches glancing along the shores, and reflected by the still and clear sea, borne by poor fishermen, paddling as silently as possible over the rocky shallows in search of the cuttle-fish, which, when seen lying beneath the water in wait for his prey, they dexterously spear, ere the creature has time to dart with the rapidity of an arrow from the weapon about to transfix his soft but firm body."

Animals exposed to the attacks of so many enemies must necessarily multiply in an analogous ratio. Their numerous eggs are generally brought forth in the spring. In the species inhabiting the high seas, they float freely on the surface, carried along by the currents and winds, and form large gelatinous bunches or cylindrical rolls, sometimes as large as a man's leg.

The eggs of the littoral cephalopods appear in the form of dark-coloured, roundish or spindle-shaped bodies, of the size and colour of grapes, and hanging together in clusters. They are soft to the touch, with a tough skin, resembling india-rubber; one end is attenuated into a sort of point or nipple, and the other prolonged into a pedicle, which coils round sea-weed or other floating objects, and serves to fix the berry-like bag in its place. At an early stage these "sea-grapes," as they are called by the fishermen, contain a white yolk enclosed in a clear albumen, and nearer maturity the young cuttle-fish may be found within in various stages of formation, until finally, hatched by the heat of the sun, it emerges from the husk perfectly formed, and launches forth into the water.

[Illustration: Ova of the Cuttle-fish.]

Some species of cephalopods are only about the size of a finger, while others attain an astonishing size. Banks and Solander, in Cook's first voyage, found the dead carcass of a gigantic cuttle-fish floating between Cape Horn and the Polynesian islands. It was surrounded by aquatic birds, which were feeding on its remains. From the parts of this specimen, which are still preserved in the Hunterian collection, and which have always strongly excited the attention of naturalists, it must have measured at least six feet from the end of the tail to the end of the tentacles.

Near Van Diemen's Land, Péron saw a sepia about as big as a tun rolling about in the waters. Its enormous arms had the appearance of frightful snakes. Each of these organs was at least seven feet long, and measured seven or eight inches round the base. These well authenticated proportions are truly formidable, and fully justify the dread and abhorrence which the Polynesian divers entertain of those snake-armed monsters of the deep; but not satisfied with reality, some writers have magnified the size of the cephalopods to fabulous dimensions. Thus Pernetti mentions a colossal cuttle-fish, which, climbing up the rigging, overturned a three-masted ship; and Pliny notices a similar giant, with arms thirty feet long and a corresponding girth. But all this is nothing to the Norwegian kraken, a mass of a quarter of a mile in diameter, and a back covered with a thicket of sea-weeds. When it comes to the surface, which seems to be but rarely the case, it raises its arms mast-high into the air, and, having enjoyed for a time the lovely daylight, sinks slowly back again into abysmal darkness. Fishermen are said to have landed on a kraken, and to have kindled a fire upon the supposed island for the purpose of cooking their dinner. But even a kraken, thick-skinned as he may be, does not like his back to be converted into a hearth, and thus it happened that the treacherous ground gave way under the mistaken mariners, and overwhelmed them in the waters. Strange that the oriental tale of Sinbad the sailor should thus be re-echoed in the wild legends of the north.

All the dibranchiate cephalopods are destitute of an outward shell, with the sole exception of the Spirula, a small species chiefly found in the South Sea, and of the far more renowned Argonaut, which poets, ancient and modern, have celebrated as the model from which man took the first idea of navigation. Its two sail-like arms expanding in the air, and the six others rowing in the water, the keel of its elegant shell is pictured as dividing the surface of the tranquil sea. But as soon as the wind rises, or the least danger appears, the cautious argonaut takes in his sails, draws back his oars, creeps into his shell, and sinks instantly into a securer depth. Unfortunately there is not a word of truth in this pleasing tale. Like the common octopus, the argonaut generally creeps about at the bottom of the sea, or when he swims, he places his sails close to his shell, stretches his oars right out before him, and shoots backwards like most of his class by expelling the water from his respiratory tube.

[Illustration: Argonaut.]

As he sits loosely in his shell, he was supposed by some naturalists to be a parasite enjoying the house of the unknown murdered owner; but this is perfectly erroneous, as the young in the egg already show the rudiments of the future shell, and the full-grown animal repairs by reproduction any injury that may have happened to it.

[Illustration: Pearly Nautilus.]

The tetrabranchiate cephalopods, or Nautili, are very differently constructed from their dibranchiate relations. Here, instead of mighty muscular arms, furnished with suckers or raptorial claws, we find a number of small, sheathed, and retractile tentacles (_f_), surrounding the mouth in successive series, and amounting to little short of a hundred. The head is further provided with a large muscular disk (_g_), which, besides acting as a defence to the opening of the shell, serves also in all probability as an organ for creeping along the ground, like the foot in the Gasteropods. The mandibles are strengthened by a dense calcareous substance fit to break up the defensive armour of the crustacean or shell-fish on which the animal feeds. There is no ink-bag, no organ of hearing, and the eyes (_h_) are pedunculated, and of a more simple structure. The handsome pearl-mother and spirally wound shell is divided by transverse partitions (_a_), perforated in the centre, into numerous chambers (_b_). The animal takes up its abode in the foremost and largest (_b′_), but sends a communicating tube or siphon (_c_) through all the holes of the partitions to the very extremity of the spirally wound shell. Though the empty conch was frequently found swimming on the waters of the Indian Ocean, or cast ashore on the Moluccas or New Guinea, yet it was only in 1829 that the animal was known with any certainty, one having been caught alive by Mr. George Bennett, near the New Hebrides, which, preserved in spirits, is now in the museum of the College of Surgeons. Since then three different species have been found to abound in the waters of the above-named archipelago, of New Caledonia, and of the Feejee and Solomon Islands, where they principally sojourn among the coral reefs at depths of from three to six fathoms. They usually remain at the bottom of the water, where they creep along rather quickly, supporting themselves upon their tentacula, with their head downwards and the shell raised above. After stormy weather, as it becomes more calm, they may be seen in great numbers floating upon the surface of the sea with the head protruded, and the tentacula resting upon the water, the shell at the same time being undermost; they remain, however, but a short time sailing in this manner, as they can easily return to their situation at the bottom of the sea, by merely drawing in their tentacles and upsetting the shell. They are caught in baskets by the natives, who eat them roasted as a great delicacy.

What renders these animals peculiarly interesting is the circumstance that they are the only living representatives of a class which once filled in countless numbers the bosom of the primeval ocean, and whose fossil remains (Orthoceratites, Ammonites) furnish the naturalist with a series of historical documents, attesting the unmeasured age of our planet. What are the ruins, thirty or forty centuries old, that speak of the vanished glories of extinguished empires to these wonderful medals of creation that lead our thoughts through the dim vista of unnumbered centuries to the fathomless abyss of the past.

* * * * *

In point of development of organisation the Gasteropods or snails rank immediately after the Cephalopods. They also have a head plainly distinguishable from the rest of the body, and to which two brilliant black eyes give an animated expression. But their nervous system is far less developed, and while the lively cephalopod is able to swim about, and rapidly to seize a distant prey, almost all the gasteropods creep slowly along upon a flat disk or foot situated below the digestive organs, a formation to which they owe their name of gasteropods or stomach-footers.

The marine snails are divided into several groups according to the different position and arrangement of their gills. In some species these organs form naked or free-swimming tufts on the back (Nudibranchiata) but generally they are variously disposed either in special cavities or under the folds of the mantle. Thus in the Inferobranchiata they are arranged under its inferior border on both sides of the body, or upon one side only, while in the Tectibranchiata they are placed, as in the Nudibranchiata, upon the dorsal aspect of the body, but are protected by a fold of the skin. In the Cyclobranchiata they form a fringe round the margin of the body, between the edge of the mantle and the foot, and in the Scutibranchiata and Pectinibranchiata they are pectinated, or shaped like the teeth of a comb, and placed in a large hollow chamber, which opens externally at the side of the body or above the head.

[Illustration: Tiara.]

[Illustration: Glaucus.]

[Illustration: Scyllæa.]

Nothing can be more elegant or various than the form and arrangement of the gills in most of the nudibranchiate gasteropods. In the Glauci and Scyllææ, we see at each side of the elongated body long arms branching out into tufty filaments; in the Briarei a hundred furcated stems serve for the aëration of the blood. On the back of the Eolides the gills are arranged in rows; in the Dorides they form a wreath or garland round the posterior intestinal aperture.

The beauty of these animals corresponds with their charming mythological names, for every part of them which is not sparkling like the purest crystal shines with the liveliest colours, red, yellow, or azure. Some inhabit the coasts, where they creep along upon a well-developed foot, others live in the deep waters, where they cling to the stems of floating sea-weed with a narrow and furrowed foot, or swim upon their back, using the borders of the mantle and of the branchiæ as oars. Though chiefly living in the warmer latitudes, they are found in every sea, and many interesting species inhabit the British waters: such as the Sea-lemon (_Doris tuberculata_), which, when its horns and starry wreath of branchiæ are concealed, bears a curious resemblance in size, form, colour, and warty surface to the half of a citron divided longitudinally; the exquisite _Eolis coronata_, whose crowded clusters of branchial papillæ are radiant with crimson and cerulean tints; and the crested Antiopa, whose transparent breathing organs are tipped with silvery white.

[Illustration: Eolis.]

Though they have no shell to cover them, the Nudibranchiata are not left defenceless to the mercy of their enemies. The transparency of their body is a cause of safety to many of them. Some conceal themselves under stones or among the branches of the madrepores, and some on contracting cast off a part of their mantle, which they leave in possession of their hungry foe, while they themselves make their escape.

Among the British Inferobranchiata we find the rare golden or orange-coloured _Pleurobranchus plumula_, thus named from its branchiæ projecting like a plume from between the mantle and foot in crawling; and among the Tectibranchiata the common sea-hare (_Aplysia punctata_), which resembles a great naked snail; its back opening with two wide lobes, which can be expanded or closed over the opening at the animal's will. When open, they expose to view on the right side the finely fringed and lobed branchiæ, seated in a deep hollow beneath a fold of the mantle. The uncomely creature glides along over the stones upon its flat fleshy foot and up the slender stems of sea-weeds by bringing the borders of the same locomotive apparatus to meet around the stem, thus tightly grasping it as if enclosed in a tube. While progressing, the fore part is poked forward as a narrow neck furnished with two pair of tentacles, one pair of which, standing erect and being formed of thin laminæ, bent round so as to bring the edges nearly into contact, look like the ears of the timid quadruped, from which the Aplysia has derived its common name. The colour is a dark-brownish purple studded with rings and spots of white. On being disturbed, the sea-hare pours out from beneath the mantle-lobes a copious fluid of the richest purple hue, which however quickly fades, and is of no value in the arts.

More than forty species of Aplysiæ are known, most of them inhabitants of the warmer seas. The acrid humour exuded by the depilatory aplysia, or _Aplysia depilans_, of the Mediterranean is still supposed by the Italian fishermen to occasion the loss of the hair, and was used by the ancient Romans in the composition of their venomous potions--though it is by no means poisonous. Such are the prejudices resulting from the propensity of man to associate evil qualities with an unprepossessing appearance.

[Illustration: Chiton squamosus.]

To the Cyclobranchiate order belong the Limpets and the Chitons. The latter, which are the only multivalve shells among the Gasteropods, are spread in more than two hundred species over every shore from Iceland to the Indies, but they are particularly abundant on the coasts of Peru and Chili. Some of the smaller species inhabit our coasts, where they may be found adhering to stones near low water mark. They are coated with eight transverse shelly plates, folding over each other at their edges like the plates of ancient armour, and inserted into a tough marginal band, so as to form a complete shield to the animal. Thus encased in coat of mail, the chitons have the power of baffling the voracity of their enemies by rolling themselves up into a ball like the wood-louse or the armadillo: they are also able to cling with such tenacity to the rock that it is difficult to detach them without tearing them to pieces. The Limpets, or Patellæ, likewise attach their shield-like shell so firmly to a hard body that it requires the introduction of a knife between the shell and the stone to detach them. It has been calculated that the larger species are thus able to produce a resistance equivalent to a weight of 150 pounds, which, considering the sharp angle of the shell, is more than sufficient to defy the strength of a man to raise them. They often congregate in large numbers in one place, and an old writer compares them to nail-heads struck into the rock. More than a hundred species are known; one of which, the _Patella cochlear_ of the Cape, is almost invariably found squatting upon the shell of another species of limpet. The finest and largest varieties abound on the shores of the Oriental seas and the coasts of the Mediterranean, but several of the smaller species are very numerous in our littoral or sub-littoral zone, where they either feast on the green sea-weeds that we find covering at ebb-tide the stones with a thin emerald layer, or upon the coarser olive-coloured algæ. Thus _Patella pellucida_ and _Patella lævis_, both remarkable for longitudinal streaks of iridescent colours on an olive-shell, may generally be found feeding either on the broad fronds or on the roots and stems of the Laminariæ, or Oar-weeds. To their labours may indeed be partly attributed the annual destruction of these gigantic algæ, for, eating into the lower part of the stems, and destroying the branches of the roots, they so far weaken the base that it is unable to support the weight of the frond, and thus the plant is detached and driven on shore by the waves.

[Illustration: Limpet and Shell.]

The beautiful Sea-ear, or Haliotis, is the chief representative of the scutibranchiate gasteropods. The flattened shell, perforated with small holes on one side, is characterised by a very wide mouth or aperture, the largest in any shell except the limpet. The outside is generally rough, or covered with marine substances; the inside presents the same enamelled appearance as mother-of-pearl, and exhibits the most beautiful colours. The holes with which the shell is perforated serve to admit water to the branchiæ, and are formed at regular intervals as it increases in size. The foot is very large, having the margin fringed all round, and is able, like that of the chiton or the limpet, to cling firmly to the rock. More than seventy species of Haliotis are known, the greater part occurring in the Pacific Ocean.

[Illustration: Haliotis.

_c._ Series of perforations. _d._ Eye peduncles. _e._ Tentacles. _g._ Foot. ]

[Illustration: Carinaria.]

To the scutibranchiate gasteropods also belong the strangely formed Carinariæ, which seem to be made up of disjointed parts. The gills (_g_) project from under a thin vitreous shell (_f_), which projects from the dorsal surface, and has a form not unlike that of the Argonaut or of a Phrygian cap. The foot (_b_) is not formed for creeping, but constitutes a muscular vertical paddle or fin, that serves them for swimming on the back, and is furnished with a sucking disk (_c_), with which they are enabled to attach themselves to floating objects.

The Pectinibranchiata comprise all the spiral univalve shells, and are by far the most numerous of all the gasteropods, as their species are not counted by hundreds, but by thousands. If their calcareous garment could be drawn out, it would be found to consist of a tube gradually widening from the apex to the base; but what an immense variety of form and ornaments, what a prodigality of splendid tints, has not Nature spread over this interminable host! The same fundamental idea appears to us in thousands of modifications, one yet more elegant and capricious than the other. Thus the passion of the shell collector is as conceivable as that of the lover of choice flowers, and when we read that rich tulip-amateurs have given thousands of florins for one single bulb, we cannot wonder that many of the Volutes, Cones, Mitres, and Harps, are worth several times their weight in gold; that more than a hundred pounds have been paid for a Chinese wentle-trap, and that the _Cypræa aurora_, which the Polynesian chiefs used to wear about the neck, is valued at thirty or forty guineas.

[Illustration: Orange Cone-Shell.]

[Illustration: Mitre-Shells.]

[Illustration: Harp-shell.]

The mode in which these beautifully painted structures are formed is very similar to what takes place among bivalve shells. They are secreted by the glandular margin of the mantle or soft skin which clothes the upper part of the body of the snail, and their form depends on the shape of the body they are destined to cover, while the outline of the border is alike regulated by that of the mantle. In the border of the mantle are placed the glands through which colouring matter is added to the lime of which the shell consists, and here also the whole of the outer coat of the shell is formed by constant annual additions to the lip. The after-growth of the shell proceeds, layer over layer, from the general surface of the mantle, so that the calcareous robe constantly increases in thickness with the age of the animal.

[Illustration: Chinese Wentle-trap.--(Scalaria pretiosa.)]

However different the form of a shell may be, its use is invariably the same, affording the soft-bodied animal a shield or retreat against external injuries. In this respect it is not uninteresting to remark that those species which inhabit the littoral zone, and are most exposed to the violence of the waves, have a stronger shell than those which live in greater depths, and that the fresh-water molluscs have generally a much more delicate and fragile coat than those which live in the ocean. The greater the necessity of protection the better has Nature provided for the want. Thus most of the gasteropods, besides possessing a stone-hard dwelling, are also furnished at the extremity of the foot with an operculum, or calcareous lid, which fits exactly upon the opening of their house, and closes it like a fortress against the outer world. But no animal exists that is safe against every attack, for the large birds sometimes carry the ponderous sea-snails, whose entrance they cannot force with their beaks, high up into the air, and let them fall upon the rocks, where they are dashed to pieces.

The ordinary mode of locomotion of the testaceous sea-snails is by creeping along on their foot: those that have a very heavy house to carry, such as the Cassis or the Pteroceras, generally move along very slowly, while others, such as the Olivæ, that are possessed of a comparatively strong and broad foot, have rapid and lively movements, and quickly raise themselves again when they have been overturned. The Strombidæ and Rostellariæ place their powerful and elastic foot under the shell in a bent position, when suddenly by a muscular effort they straighten that organ and roll and leap over and over. The structure of the foot of the _Tornatella fasciata_, an inhabitant of our coast, is most remarkable: beaten incessantly by the waves, in the cavities of rocks which it frequents, nearly on a level with the surface of the sea, to the violence of which it is always exposed, it has need of additional powers for retaining its hold; its foot is therefore divided into two adhering portions, placed at each extremity, and separated by a wide interval; when it crawls, it fixes the posterior disc and advances the other, which it attaches firmly to the place of progression, and this being effected, the hinder sucker is detached and drawn forwards, locomotion being accomplished by the alternate adhesion of these two prehensile discs. In Cyclostoma the foot is likewise furnished with two longitudinal adhering lobes, which are advanced alternately. But the foot of the marine snails is not merely an instrument of progression on a solid surface, for in many species it is convertible at the will of the animal into a boat, by means of which the creature can suspend itself in an inverted position at the surface of the water, where by the aid of its mantle and tentacles it can row itself from place to place.

[Illustration: Pteroceras scorpio.]

[Illustration: Oliva hispidula.]

[Illustration: Strombus pes pelicani.]

[Illustration: Ianthina communis.]

The Ianthinæ, or purple Sea-Snails, carry under their foot a vesicular organ like a congeries of foam-bubbles, that prevents creeping, but serves as a buoy to support them at the surface of the water.

[Illustration: Murex haustellum.]

When the sea is quiet, these little creatures,

Like little wanton boys that swim on bladders,

appear in vast shoals on the surface, but as soon as the wind ruffles the ocean, or an enemy approaches, they at once empty their air-cells, contract their float, and sink to the bottom, pouring out at the same time a darkened fluid like that of the Aplysia or the Murex, which no doubt serves them as a defence against their foes, and, according to Lesson, furnished the celebrated purple of the ancients. The Ianthinæ inhabit the Mediterranean and the warmer regions of the Atlantic, but especially towards the close of summer they are frequently drifted by the Gulf Stream to the west coast of Ireland.

[Illustration: Magilus antiquus.]

[Illustration: Worm-Shell.]

While the vast majority of the gasteropods either creep or swim, some are doomed to the sedentary life of the oyster, and remain for ever fixed to the spot where they first attached themselves as small free-swimming larvæ. Thus the _Magilus antiquus_, which in its young state presents all the characters of a regular spiral univalve, establishes itself in the excavations of madrepores, and as the coral increases around it, the Magilus is obliged, in order to have its aperture on a level with the surrounding surface, to construct a tube, lengthening with the growth of the coral. As the tube goes on increasing, the animal abandons the spiral for the tubular part of the shell, and in the operation it leaves behind no partitions, but secretes a compact calcareous matter which reaches to the very summit of the spiral part, so that in an old specimen the posterior part of the shell presents a solid mass.

The Siliquariæ are generally found embedded in a similar manner in sponges or other soft bodies, while the Vermetus, or Worm-Shell, usually attaches itself, like the Serpulæ, to rocks, coral-reefs, or shells.

In these genera, which have been arranged by Cuvier in a separate order (Tubulibranchiata), the foot is naturally reduced to the state of an adhesive organ, its chief functions consisting in opening and closing the lid.

The sea-snails are either predaceous or herbivorous; among the pectinibranchiates, those with circular mouths to the shell are vegetable feeders, while such as have an aperture ending in a canal are animal feeders. Considerable modifications of internal structure indicate this difference of food; and the external organs, particularly about the mouth, exhibit a corresponding variety of form. In those which feed on vegetables the mouth is generally a slit furnished with more or less perfect lips, armed with a simple cutting apparatus, which is often powerful enough to divide or dismember comparatively hard substances.

In most animal feeders the mouth presents the appearance of a proboscis that can be protruded or shortened at the will of the animal, and which, grasping the food, conveys it to a spine-armed tongue, by the aid of which it is propelled into the gullet without mastication or any preparatory change.

In the Whelk and its shell-boring allies, the alternate protrusion and retraction of the proboscis, which is here of a much more complicated structure, causes the sharp tongue to act as a rasp or auger, capable of drilling holes into the hardest shells. It is this circumstance which renders the whelk so formidable an enemy to mussel and oyster banks. During the erection of Bell Rock lighthouse, an attempt was made to plant a colony of mussels on the wave-beaten cliff, as they were likely to be of great use to the workmen, and especially to the light keepers, the future inhabitants of the rock; but the mussels were soon observed to open and die in great numbers. "For some time," says Mr. Stevenson in his interesting narrative, "this was ascribed to the effects of the violent surge of the sea, but the Buccinum lapillus having greatly increased, it was ascertained that it had proved a successful enemy to the mussel. The buccinum was observed to perforate a small hole in the shell, and thus to suck out the finer parts of the body of the mussel; the valves of course opened, and the remainder of the shell-fish was washed away by the sea. The perforated hole is generally upon the thinnest part of the shell, and is perfectly circular, of a champhered form, being wider towards the outward side, and so perfectly smooth and regular as to have all the appearance of the most beautiful work of an expert artist. It became a matter extremely desirable to preserve the mussel, and it seemed practicable to extirpate the buccinum. But after we had picked up and destroyed many barrels of them, their extirpation was at length given up as a hopeless task. The mussels were consequently abandoned as their prey; and, in the course of the third year's operations, so successful had the ravages of the buccinum been that not a single member of the imported mussel colony was to be found upon the rock." Thus the engineer, whose skill and perseverance had gained so proud a triumph over the waves of the stormy ocean, was defeated by an ignoble whelk.

[Illustration: Limpet's tongue.]

In the genera which have no proboscis, the tongue, acting as a prehensile and rasping or abrading organ, is frequently of considerable length; thus, in the Ear-shell, it is half as long as the body, and in the common Limpet even three times longer than the entire animal. From the two cartilaginous pieces (_b b_), placed on each side of its root, arise the short and powerful muscles which wield the organ. The surface of this curious piece of mechanism, a magnified view of which is given at B, is armed with minute, though strong, teeth, placed in transverse rows, and arranged in three series; each central group consists of four spines, while those on the sides contain but two a-piece. It is only at its anterior extremity (_d_), however, that the tongue, so armed, presents that horny hardness needful for the performance of its functions, the posterior part being comparatively soft; so that, probably in proportion as the anterior part is worn away, the parts behind it gradually assume the necessary firmness, and advance to supply its place. In the upper part of the circumference of the mouth, we find a semicircular horny plate, resembling an upper jaw, and the tongue, by triturating the food against this, gradually reduces substances however hard. On opening the limpet, the tongue is found doubled upon itself, and folded in a spiral manner beneath the viscera.

Many of the Gasteropods which live on coarse and refractory materials are provided with several digestive cavities, resembling in some degree the stomachs of the ruminating quadrupeds; and frequently the triturating power of these organs is still further increased by their being armed with teeth variously disposed.

[Illustration: Bulla.]

In the Bulla, for instance, a genus belonging, like the sea-hares, to the tectibranchiate order, the gizzard, or second stomach, contains three plates of stony hardness attached to its walls, and so disposed that they perform the part of a most efficacious grinding mill.

On opening the gizzard of the Scyllæa, it is found to be still more formidably armed, for in its muscular walls there are embedded no less than twelve horny plates (_e_), which are extremely hard and as sharp as the blades of a knife.

[Illustration: Gizzard of Bulla.]

[Illustration: Gizzard of Syllæa.]

The Sea-hare, however, furnishes us with the most curious form of these stomachal teeth, for here we see not only the gizzard (_b_) armed with horny pyramidal plates, whose tuberculated apices, meeting in the centre of the organ, must necessarily bruise by their action whatever passes through that cavity, but the third stomach (_d_) is also studded with sharp-pointed hooks (_c_), resembling canine teeth, and admirably adapted to pierce and subdivide the tough leathery fronds of the olive sea-weeds on which the animal feeds. Thus these deformed and disgusting molluscs afford us one of the most interesting examples of the adaptation of organs to their functions, which an enlightened research is continually finding in creation.

[Illustration: Compound stomach of Sea-Hare.]

Though not so gifted as the cephalopods, many of the gasteropods possess all the organs of sense. Like them, they have an apparatus specially calculated to appreciate sonorous undulations, and consisting of a membranous vesicle attached to an auditive nerve, and containing either a single spherical otolithe or a larger number of similar smaller calcareous bodies, which by their vibrations communicate the impression of sound to the nerve. Their minute eyes are short-sighted, it is true, and frequently either entirely wanting or, as in the Nudibranchiates, scarcely able to distinguish light from darkness; but their inactive habits require no wide field of vision, and thus they see as much of the external world as is necessary for their humble sphere of existence. The organs of sight are generally situated either on a prominence at the base of the superior pair of tentacles or, as, for instance, in the Murex, at the extremity of these organs (_a_, _b_), a position which enables the animal to direct them readily to different objects.

[Illustration: Tentacles and eye of Murex.

_c._ Eye highly magnified.]

Many of the Gasteropods are evidently capable of perceiving odours; thus, animal substances let down in a net to the bottom will attract thousands of Nassæ in one night. We also may infer that they are not deficient in taste from the presence of papillæ at the bottom of their mouth, analogous to those found on the tongue of other animals; but, of all their senses, that of touch is undoubtedly the most perfect. The whole soft surface of the body is indeed of exquisite sensibility, but more especially the vascular foot, and the tentacles, or horns, which vary both in number and in shape in different genera. Yet, in spite of this delicacy in the organisation of the skin, which makes it so sensible of contact, it appears to have been beneficently ordered that animals so helpless and exposed to injury from every quarter are but little sensible to pain. Although they are deprived of all higher instincts, we find among the Gasteropods a few examples of concealment under extraneous objects, which remind us of the masks and artifices frequently employed by the insects and crustaceans.

The Agglutinating Top (_Trochus agglutinans_) covers itself with small stones and fragments of shells, and thus shielded from the view escapes the voracity of many an enemy but little suspecting the savoury morsel hidden under the mound of rubbish which he disdainfully passes by.

In animals which are only provided with passive means of defence, we may naturally expect a considerable degree of caution, and in this respect the gasteropods might give many useful lessons to man. How carefully they protrude their tentacles as far as possible to sound every obstacle in their way, before they creep onwards, and how rapidly they withdraw into their shell at the least symptom of danger! What an example to so many of us that leap before they look, and frequently break their necks in the fall!

Yet, in spite of all their prudence and of the protection of their stony dwellings, they serve as food to a host of powerful enemies. The sea-stars, their most dangerous foes, not only swallow the young fry but also seize with their long rays the full-grown gasteropods, and clasp them in a murderous embrace.

They are preyed upon by fishes, crustaceans, and sea-birds, who pick them up along the shores; but it will sometimes happen that a crow, while endeavouring to detach a limpet for its food, is caught by the tip of its bill, and held there until drowned by the advancing tide.

Man also consumes a vast number of sea-snails, for on every coast there are some edible species; and it may be said that, with the exception of very few that have a disagreeable taste, they are all of them used as food by the savage. The miserable inhabitants of Tierra del Fuego chiefly live upon a large limpet that abounds on the rocky shores of their inhospitable land, and but for this resource would most likely long since have been extirpated by hunger.

Many of the univalve shells are, moreover, highly prized as objects of ornament or use both by savage and civilised nations. The South Sea Islander makes use of a Triton as a war conch; the Patagonian drinks out of the Magellanic volute, the Arab of the Red Sea employs a large Buccinum as a water-jug, and the _Cypræa moneta_ is well known in commerce as the current coin of the natives of many parts of Africa. In Europe the iridescent Haliotis is frequently used for the inlaying of tables or boxes, and various species of Helmet-shells and Strombi (_Cassis rufa madagascariensis_, _Strombus gigas_), peculiar as being formed of several differently coloured layers, placed side by side, are in great request for the cutting of cameos, as they are soft enough to be worked with ease, and hard enough to resist wear. More than two hundred thousand of these shells are annually imported into France, and the value of cameos produced in Paris alone amounts to more than a hundred thousand pounds. A large number are also cut in the small town of Oberstein on the Nahe (a river flowing into the Rhine at Bingen), which has long been famous for the manufactory of agate ornaments and trinkets, and has now added this new branch of industry to the more ancient sources of its prosperity.

* * * * *

The Pteropods, or Wing-footers, move about by means of two fin-like flaps, proceeding wing-like from the fore part of the body. They have no disk to walk upon, nor arms for the seizure of prey, like the cephalopods and gasteropods, but resemble them by the possession of a head distinct from the rest of the body, which some, like the Hyaleas and Cleodora, conceal in a thin transparent or translucent shell, in which they also hide their head and wings at the approach of danger, and immediately sink to the bottom; while others, like the blue and violet Clios, beautifully variegated with light red spots, are perfectly naked. They generally inhabit the high seas, and are but rarely drifted by storms or currents into the neighbourhood of the land. They mostly swim about freely, but sometimes also they are found clinging by their wings to floating sea-weeds. They are small creatures, but propagate so fast that the _Clio borealis_ and _Limacina arctica_ form the chief food of the colossal whale.

[Illustration: Hyalea globulosa.]

While these two little pteropods, in spite of their minute proportions, deserve to rank among the most important inhabitants of the northern seas, the Mediterranean species belong mainly to the genera Hyalea, Cleodora, and Criseis--forms wholly unknown to our own fauna except as waifs. Vast shoals of these animals frequent the deeper parts of that sea, leaving their remains strewed over its bed, between depths of from one hundred to two hundred fathoms; they are short-lived creatures, and have their seasons, being met with near the surface during spring and winter, sparkling in the water like needles of glass.

"The pteropods are the winged insects of the sea," says M. Godwin-Austen, "reminding us, in their free circling movements and crepuscular habits, of the gnats and moths of the atmosphere; they shun the light, and if the sun is bright, you may look in vain for them during the life-long day--as days sometimes are at sea; a passing cloud, however, suffices to bring some Cleodoræ to the surface. It is only as day declines that their true time begins, and thence onwards the watches of the night may be kept by observing the contents of the towing-net, as the hours of a summer day may be by the floral dial. The Cleodoræ are the earliest risers; as the sun sets, _Hyalæa gibbosa_ appears, darting about as if it had not a moment to spare, and, indeed, its period is brief, lasting only for the Mediterranean twilight. Then it is that _Hyalæa trispinosa_ and _Cleodora subula_ come up; _Hyalæa tridentata_, though it does not venture out till dusk, retires early, whilst some species, such as _Cleodora pyramidata_, are to be met with only during the midnight hours and the darkest nights. This tribe, like a higher one, has its few irregular spirits, who manage to keep it up the whole night through. All, however, are back to their homes below before dawn surprises them."

* * * * *

The lamellibranchiate Acephala, or headless molluscs with comb-like gills, are distinguished from the preceding orders of molluscs by a more simple organisation and the peculiar formation of their external coverings. They are all contained within a bivalve shell, articulated after the manner of a hinge, and to which some of their families are attached by one strong muscle (Monomyaria), others by two (Dimyaria). In this shell, which is secreted by two large flaps or folds of their skin or mantle, they generally lie concealed like a book in its binding, and bid defiance to many of their enemies. When danger menaces, the sea-snail withdraws its head and closes the entrance of its hermitage with a lid, but the bivalve shuts its folding-doors when it wishes to avoid a disagreeable intruder. A strong elastic ligament connects the two valves, and opens them wide as soon as the muscular contraction which closed them ceases to act.

While the sea-snail creeps along upon a mighty foot, the bivalve is frequently doomed to a sedentary life, and the former protrudes from its shell a well-formed head, while the latter, like many a biped, has no head at all. The lamellibranchiate Acephala have, however, been treated by nature not quite so step-motherly as might be supposed from this deficiency, for many of them have eyes, or at least ocular spots, which enable them to distinguish light from darkness; and even auditory organs have been discovered in many of them. Their circulation is performed by a heart generally symmetrical, and their respiration by means of four branchial leaflets equal in size, and symmetrically arranged on either side of the body. The mouth is a simple orifice without any teeth, bordered by membranous lips, and placed at one end of the body between the two inner leaves of the branchiæ. The digestive apparatus consists of a stomach or intestine of different lengths, a liver, and several other accessory organs. A simple nervous system brings all the parts of the body into harmonious action.

[Illustration: Bivalve deprived of shell, to show its various openings.]

In many lamellibranchiates the folds of the mantle are disjoined, as, for instance, in the oyster, which, on opening its shell, at once admits the water to its delicately fringed branchiæ; in others they are more or less united, so as to form a closed sack with several openings, an anterior one (_h_) for the passage of the foot, and two posterior ones (_g_, _f_) for the ingress and egress of the water which the animal requires for respiration. These posterior openings are often prolonged into shorter or longer tubes or siphons, sometimes separate, and sometimes grown together so as to form a single elongated fleshy mass. The use of these prolongations becomes at once apparent when we consider that they are chiefly developed in those species which burrow in sand, mud, wood, or stone, and which therefore require to be specially guarded against the danger of suffocation. The interior of these siphonal canals is lined with innumerable vibratory cilia, by the action of which the water is drawn towards the branchial orifice and conveyed in a current through the canal over the surface of the gills; then, having been deprived of its oxygen, it is expelled by a similar mechanism through the other tube; and it is by the force of this anal current that the passage is kept free from the deposit of mud or other substances, which would otherwise soon choke it up. The cleaning action of the anal current is assisted by the faculty the burrowing molluscs possess of elongating and contracting their siphons, and the degree to which this may be accomplished depends on the depth of the cavity which the species is accustomed to make. Yet since many particles of matter float even in clear water, which from their form or other qualities might be injurious to the delicate tissue of the viscera to be traversed, how is the entrance of these to be guarded against in an indiscriminating current? A beautiful contrivance is provided for this necessity. The margin of the branchial siphon, and sometimes, though more rarely, of the anal one, is set round with a number of short tentacular processes, endowed with an exquisite sensibility and expanding like feathery leaves. In _Pholas dactylus_ this apparatus, which is here confined to the oral tube, is of peculiar beauty, forming a network of exquisite tracery, through the interstices or meshes of which the water freely percolates, while they exclude all except the most minute floating atoms of extraneous matter. Thus admirably has the health and comfort of the lowly shell-fish been provided for that spend their whole life buried in sepulchres of stone or sand.

[Illustration: Donax.

_a_, _b_. Siphons.]

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.

[Illustration: Pholas striata.]

[Illustration: Ship-worm.--(Teredo navalis.)]

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.

[Illustration: Petunculus.

_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.

[Illustration: Cockle.

_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.

[Illustration: Solen, or Razor-Shell.

_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.

[Illustration: Pinna.

_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.

[Illustration: Edible Cockle.]

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.

[Illustration: Edible Mussel.]

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.

[Illustration: Ceylon Pearl-Oyster.]

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.

[Illustration: Tridacna gigas.]

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.

[Illustration: Hippopus maculatus.]

* * * * *

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."

* * * * *

[Illustration: Leaf-like Sea-Mat.]

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.

[Illustration: Flustra in its cell. (Highly magnified.)]

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.

[Illustration: Eschara cervicornis. (Natural size.)]

[Illustration: Portion of a branch of the polypary of Eschara cervicornis, magnified twenty diameters, to show the form and arrangement of cells.]

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.

[Illustration: An individual of Eschara cervicornis, highly magnified.

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

[Illustration: Retepora cellulosa. (Neptune's Ruffle.)]

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.

[Illustration: A. Portion of a Cellularia, magnified.

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!

[Illustration: Clavellina producta. Group of two adult and several young individuals, magnified about five times.

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

[Illustration: Ascidia mammillata.

_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."

[Illustration: Chelyosoma Macleayanum.

_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.

[Illustration: Botryllus violaceus. Two of the stems magnified.

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

[Illustration: Diazona violacea (magnified).]

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.

[Illustration: A single individual of Pyrosoma giganteum, cut out of the common test and magnified.

_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.

[Illustration: Salpa maxima.

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

[Illustration: Salpæ, isolated and associated.

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.

[Illustration: Inner or under side of the superior plated surface of Chelyosoma Macleayanum.

_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.

Every one knows the common Star-fish, with its lanceolate arms; its generally orange-coloured back, thickly set with tubercles, and the pale under-surface, with its rows of feet, feelers, or suckers, which serve both for locomotion and the seizure of food.

When one of these creatures is placed on its back, in a plate filled with sea-water, it is exceedingly curious to watch the activity which those numberless sucking feet display. At first the star-fish is motionless; for, offended by the rough handling it has undergone, the feet have all shrunk into the body; but soon they are seen to emerge like so many little worms from their holes, and to grope backwards and forwards through the water, evidently seeking the nearest ground to lay hold of. Those that reach it first immediately affix their suckers, and, by contracting, draw a portion of the body after them, so as to enable others to attach themselves, until, pulley being added to pulley, their united power is sufficient to restore the star-fish to its natural position.

[Illustration: Star-Fish.

The upper tuberculated surface is shown, with some of the spines of the under surface projecting at the sides of the rays. At one of the angles between the rays, on the right side, is seen the eccentric calcareous plate, or madreporic tubercle, which indicates the existence of a bilateral symmetry.]

This act of volition is surely remarkable enough in so simple an animal, which scarcely possesses the rudiments of a nervous system, but the simple mechanism by which the suckers are put into motion is still more wonderful. Each of these little organs is tubular, and connected with a globular vesicle filled with an aqueous fluid, and contained within the body of the star-fish immediately beneath the hole from which the sucker issues. When the animal wishes to protrude its feet, each vesicle forcibly contracts, and, propelling the fluid into the corresponding sucker, causes its extension; and, when it desires to withdraw them, a contraction of the suckers drives back the fluid into the expanding vesicles. The internal walls of the suckers and their vessels are furnished with vibratory cilia, and by this simple means a continual circulation of the fluid they contain goes on within them.

[Illustration: Lily-Encrinite.]

Numerous species of star-fishes are so very common in our waters, that in many places the sea-bottom is literally paved with them. They likewise abounded in the primeval ocean, for deep beds of carboniferous limestone and vast strata of the triassic muschelkalk are often formed by the accumulation of little else than the skeletons of Encrinites and Pentacrinites, which, unlike the sea-stars which every storm drifts upon our shores, did not move about freely, but were affixed to a slender flexible stalk, composed of numerous calcareous joints connected together by a fleshy coat. The feathered bifurcated arms of the Crinoids are unprovided with suckers, which would have been perfectly useless to creatures not destined to pursue their game to any distance, but passively to receive the nutriment which the current of sea-water set in motion by their richly-ciliated pinnules conveys to the mouth. These beautiful creatures were formerly supposed to be nearly extinct, for up to within the last few years only two living stalked crinoids were known in the ocean of the present period, but the dredge has latterly brought up new and remarkably fine species from depths of more than 2000 fathoms, and there is every reason to believe that these animals still form an important element in the abyssal fauna.[S]

[Footnote S: See page 420.]

[Illustration: Portion of the Pentaorinus Briareus. (Fossil.)]

Of freely-swimming Crinoids but one single representative is known in the northern seas, the Rosy Feather-star (_Comatula rosacea_), whose long and delicately fringed rays and deep rose colour dotted with brown may serve to give us an idea of the beauty of the submarine landscapes where _Pentacrinus Wyville-Thomsoni_ or _Bathycrinus gracilis_ abound. During the earlier stage of its existence, the comatula is attached to a stalk; a discovery for which science is indebted to Mr. T. V. Thompson, who in 1823 dredged in the Cove of Cork a singular little pedunculated crinoid animal (_Pentacrinus europæus_), which he found attached to the stems of zoophytes. It measured about three-fourths of an inch in height, and resembled a minute _comatula_ mounted on the stalk of a _pentacrinus_. When this pygmy representative of the ancient lily-stars was first dragged up from its submarine haunts, it created a great sensation among naturalists, as it was the first recent animal of the encrinite kind which had ever been seen in the seas of Europe. At first it was supposed to be a distinct species, but Mr. Thompson, by carefully following it through all the stages of its growth, succeeded in proving that it was merely the hitherto unnoticed young of the rosy feather-star.

This elegant crinoid is found all round our coasts, and its range extends from Norway to the shores of the Mediterranean. In swimming, the movements of its arms exactly resemble the alternating stroke given by the medusa to the liquid element, and have the same effect, causing the animal to raise itself from the bottom and to advance back foremost, even more rapidly than the medusa. When dying, either in fresh water or in spirits, it emits a most beautiful purple colour, which tinges the liquid in which it is killed.

The _Ophiuridæ_, or _snake-stars_, are essentially distinguished from the true _star-fishes_ by the long serpent or worm-like arms, which are appended to their round, depressed, urchin-like bodies. They have no true suckers with which to walk, their progression being effected (and with great facility) by the twisting or wriggling of their arms, which are moreover in many species furnished with spines on the sides, assisting locomotion over a flat surface. These arms are very different from those of the true star-fishes, which are lobes of the animal's body, whereas the arms of the Ophiuridæ are mere processes attached or superadded to the body.

These animals are very generally distributed through the seas of our earth, both of its northern and southern hemispheres, but are found largest in the tropical ocean. In our own waters they are very abundant, and are among the most curious and beautiful game pursued by the dredger.

[Illustration: Sand-star.]

The British Ophiuridæ belong to two generic types, that of the _Ophiuræ_ and that of the _Euryales_. The former, to which the sand and brittle-stars belong, have simple arms; the latter, arms ramifying into many processes.

The rays of the Sand-stars have a whip-like or lizard-tail appearance, while those of the Brittle-stars look like so many centipedes or annelides attached at regular distances round a little sea-urchin. We have ten native brittle-stars, the most common of which (_Ophiocoma rosula_, Forbes) is also one of the handsomest, presenting every variety of variegation, and the most splendid displays of vivid hues arranged in beautiful patterns. Not often are two specimens found coloured alike. It is the most brittle of all brittle-stars, separating itself into pieces with wonderful quickness and ease. Touch it, and it flings away an arm; hold it, and in a moment not an arm remains attached to the body. "The common brittle-star," says Edward Forbes, "often congregates in great numbers on the edges of scallop-banks, and I have seen a large dredge come up completely filled with them; a most curious sight, for when the dredge was emptied, these little creatures, writhing with the strangest contortions, crept about in all directions, often flinging their arms in broken pieces around them; and their snake-like and threatening attitudes were by no means relished by the boatmen, who anxiously asked permission to shovel them overboard, superstitiously remarking that the things weren't altogether right."

Fancy the naturalist's vexation, who has no other means of preserving a brittle-star entire than by quickly plunging it into cold fresh water, which acts as a poison on the Ophiuræ as well as on most other marine animals, and kills them so instantaneously that even the most brittle species have no time to make the contraction necessary to break off their rays.

The _Ophiocoma rosula_ seems to be equally abundant on all parts of the coast of Britain and Ireland. It is fond of rocky places, and grows in Shetland to a much larger size than elsewhere. It is said to prey on little shells and crabs, and is greatly relished by the cod in its turn, great numbers being often found in the stomach of that voracious fish.

[Illustration: Warted Euryale.]

The Scotch or Shetland Argus (_Euryale verrucosum_, Lamarck), a very rare animal, of which the adjoining wood-cut represents a segment, is the only British _Euryale_. It measures a foot or more across, and its singular aspect has long excited admiration among naturalists. "So odd a creature as this," remarks Bradley in his "Works of Nature," "is well worth the contemplation of such curious persons as live near the sea, where every day they have subjects enow to employ their curiosity and improve their understanding." Grew says that "as he swims he spreads and stretches out all his branches to their full length, and so soon as he perceives his prey within his reach, he hooks them all in, and so takes it as it were in a net."

The British species of true star-fishes may be arranged under four families. The _Urasters_ are distinguished from all others by having four rows of suckers in each of the avenues which groove the under surface of their rounded rays. In consequence of the great number of these singular organs, the under surface of a living cross-fish presents a sight truly curious and wonderful. Hundreds of worm-like suckers, extending and contracting, coiling and feeling about, each apparently acting independently of the others, give the idea rather of an assemblage of polypi than of essential parts of _one_ animal. They are sensitive in the extreme, for, if we touch one of those singular tubes when outstretched, all those in its neighbourhood are thrown into a state of agitation; and when it shrinks from our touch, changing from a lengthy fibre to a little shrunk tubercle, some of its neighbours, as if partaking in its fears, contract themselves in like manner.

[Illustration: Common Cross-fish.]

The common Cross-fish (_Uraster rubens_) abounds on most parts of our shores, so as in some places to be used for manure in large quantities. "It is a sworn enemy to oysters, and as it is frequently found with one or more of its rays broken off, the fishermen fancy that it loses them in consequence of its oyster-hunting propensities; that it insinuates an arm into the incautious oyster's gape, with the intent of whipping out its prey, but that sometimes the apathetic mollusk proves more than a match for its radiate enemy, and closing on him, holds him fast by the proffered finger; whereupon the cross-fish preferring amputation and freedom to captivity and dying of an oyster, like some defeated warrior flings his arms away, glad to purchase the safety of the remaining whole by the reparable loss of a part, as it has the power of reproducing the broken rays.

"There is, however, reason to think that the cross-fish destroys his prey in a very different manner from that just narrated; for star-fishes are not unfrequently found feeding on shell-fish, enfolding their prey within their arms, and seeming to suck it out of its shell with their mouths, pouting out the lobes of the stomach, which they are able to project in the manner of a proboscis. Possibly the stomach secretes an acrid and poisonous fluid, which, by paralysing the shell-fish, opens the way to its soft and fleshy parts."--_Forbes's Star Fishes._

The _Solasters_ are "suns in the system of sea-stars," and are entitled to this distinguished rank among the marine constellations by their many rays and brilliant hues. The _Solaster papposa_, or common Sun-star, with rays varying in number from twelve to fifteen, is one of the commonest, and at the same time handsomest, of all the British species. Sometimes the whole upper surface is deep purple, and frequently the disk is red, and the rays white tipped with red. It grows to a considerable size, having been found eleven inches broad.

The Goniasters, or Cushion-stars, are distinguished from the allied species by their pentagonal form. One of the most singular of our native species is the Birdsfoot Sea-star (_Palmipes membranaceus_), being the thinnest and flattest of all its class. When alive it is flexible, like a piece of leather, and a person who had never seen it before would be apt to mistake it for the torn off dorsal integument of some gibbous goniaster. The colour is white, with a red centre and five red rays, proceeding one to each angle. The whole upper surface is covered with tufts of minute spines arranged in rows.

The Asteriæ, with their stellate body and flat rays, are very different in aspect from the Goniasters. The Butt-thorn (_Asterias aurantiaca_) owes its name to one of those strange superstitions which originate in some inexplicable manner, and are handed down by one credulous generation to the next. "The first taken by the fishermen at Scarborough is carefully made a prisoner, and placed on a seat at the stern of the boat. When they hook a butt (halibut) they immediately give the poor star-fish its liberty and commit it to its native element; but if their fishery is unsuccessful it is left to perish, and may eventually enrich the cabinet of some industrious collector."

To the family of the Asteriæ belongs also the Ling-thorn (_Luidia fragilissima_), the largest, and one of the most interesting of our British species. When full grown, it measures two feet across, and would appear to exceed that size occasionally, judging from fragments. The rays are from five to seven in number, quite flat, and generally five times as long as the disk is broad. The colour is brick-red above, varying in intensity, the under surface being straw-coloured. The wonderful power which the Luidia possesses, not merely of casting away its arms entire, but of breaking them voluntarily into little pieces with great rapidity, approximates it to the brittle-stars, and renders the preservation of a perfect specimen a very difficult matter.

"The first time I ever took one of these creatures," says Edward Forbes, "I succeeded in getting it into the boat entire. Never having seen one before, and quite unconscious of its suicidal powers, I spread it out on a rowing-bench, the better to admire its form and colours. On attempting to move it for preservation, to my horror and disappointment I found only an assemblage of rejected members. My conservative endeavours were all neutralised by its destructive exertions, and it is now badly represented in my cabinet by an armless disk and a diskless arm. Next time I went to dredge on the same spot, determined not to be cheated out of a specimen in such a way a second time, I brought with me a bucket of cold fresh water, to which article star-fishes have a great antipathy. As I expected, a luidia came up in the dredge, a most gorgeous specimen. As it does not generally break up before it is raised above the surface of the sea, cautiously and anxiously I sunk my bucket to a level with the dredge's mouth, and proceeded in the most gentle manner to introduce luidia to the purer element. Whether the cold air was too much for him, or the sight of the bucket too terrific, I know not, but in a moment he proceeded to dissolve his corporation, and at every mesh of the dredge his fragments were seen escaping. In despair I grasped at the largest, and brought up the extremity of an arm with its terminating eye, the spinous eyelid of which opened and closed with something exceedingly like a wink of derision."

[Illustration: Goniaster.]

The Sea-star might be called a flattened sea-urchin, with radiated lobes, and the Sea-urchin, a contracted or condensed sea-star, so near is their relationship. In both we find the same radiating construction, in which the number five is so conspicuous, and in both also the rows of suckers, which, starting from a centre, are set into motion by a similar mechanism, and used for the same purpose. In all the sea-urchins finally, and in many of the sea-stars, we find the surface of the body covered with numerous exceedingly minute, two- or three-forked pincers, that perpetually move from side to side, and open and shut without intermission. These active little organs, which have been named _Pedicellariæ_, were formerly supposed to be parasites, working on their own account, but they are now almost universally recognised as organs subservient to the nutrition of the animal, and destined to seize the food floating by, and to convey it to the mouth, one passing it to the other. Even in their outward appearance, the sea-urchins are not so very different from the sea-stars as would be imagined on seeing a Butt-thorn near a globular urchin, for both orders approach each other by gradations; thus, the Goniasters, with their cushion-shaped disks and shortened rays, approximate very much in shape to the sea-urchins; and among the latter we also find a gradual progression from the flattened to the globular form. Still there are notable differences between the two classes. Thus in the sea-urchins the digestive organs form a tube with two openings, while in the true sea-stars they have but one single orifice. Their mode of life is, however, identical.

[Illustration: Shell of Echinus, or Sea-Urchin.

On the right side covered with spines, on the left the spines removed.]

The Echinidæ move forward by means of the joint action of their suckers and spines, using the former in the manner of the true star-fishes, and the latter as the snake-stars. They also make use of the spines, which move in sockets, to bury themselves in the fine sand, where they find security against many enemies.

Some species even entomb themselves pholas-like in stone, inhabiting cavities or depressions in rocks, corresponding to their size, and evidently formed by themselves. Bennett describes each cavity of the edible _Echinus lividus_ as circular, agreeing in form with the urchin within it, and so deep as to embrace more than two-thirds of the bulk of the inhabitant. It is large enough to admit of the creature's rising a little, but not of its coming out easily. The echinus adheres so firmly to this cavity by its suckers, as to be forced from it with extreme difficulty when alive. On the coasts of the county of Clare thousands may be seen lodged in the rock, their purple spines and regular forms presenting a most beautiful appearance on the bottoms of the grey limestone rock-pools. How the boring is performed has, like many other secrets, not yet been settled by naturalists. The first perforation is most likely effected by means of the teeth, and then the rock softened by some secreted solvent.

[Illustration: Mammillated Sea-Urchin.]

Sea-urchins are found in all seas, but as they are extremely difficult to preserve, and many of them have such long and delicate spines that it is almost impossible to procure perfect specimens, probably not one tithe of their species is known.

On our coasts the common "egg-urchin" affords the poor a somewhat scanty repast; but, throughout the Mediterranean, its greater size, and also that of its allies, _Echinus melo_ and _E. sardicus_, render them, when "in egg," important articles of food. In Sicily these animals are in season about the full moon of March; there the _E. esculentus_ is still called the "King of Urchins;" whilst the larger melon-urchin is popularly considered to be its mother. The size and abundance of these edible species are among the striking peculiarities of the fish markets of the Mediterranean sea-board.

[Illustration: Edible Sea-Urchin.]

The calcareous shell of the "sea-urchin" seems, at first sight, to be composed of one simple crust, but proves, on nearer inspection, to be a masterpiece of mosaic consisting of several hundred parts, mostly pentagonal. These are so closely united that their junctions are hardly visible, but on allowing the shell to macerate for some days in fresh water, it falls to pieces. This complicated structure is by no means a mere architectural fancy, a useless exuberance of ornament, but essentially necessary to the requirements of the animal's growth. A simple hard crust would not have been capable of distension, whereas a complicated shell, such as the sea-urchin possesses, can grow in the same ratio as the internal parts, by continual deposits on the edges of the individual pieces. On closely examining a living sea-urchin, we find the whole surface of the shell and spines covered with a delicate skin, which, in spite of their close connexion, penetrates into the intervals of the several pieces. This membrane secretes the chalk of which the shell is composed, and deposits fresh layers on the edges of the plates, so that in this manner the shell continually widens until the animal has attained its perfect size. The spines are secreted in the same manner, and show under the microscope an admirable beauty and regularity of structure. So bountifully has the great Architect of worlds provided for the poor insignificant sea-urchin!

[Illustration: Dental Apparatus of the Sea-urchin, viewed from above.]

The dental apparatus of the animal--the so-called lantern of Aristotle--is another masterpiece in its way. Fancy five triangular bones or jaws, each provided with a long, projecting, movable tooth. A complicated muscular system sets the whole machinery going, and enables the jaws to play up and down, and across, so that a more effective grinding-mill can scarcely be imagined.

[Illustration:

A. Two sockets with teeth, of Echinus esculentus. B. Single socket with its tooth viewed on the outside.]

The _Holothuriæ_, or Sea-cucumbers, may be regarded in one light as soft sea-urchins, and in another as approximating to the Annelides or worms. Their suckers are similar to those of the true star-fishes and sea-urchins. Besides progression by means of these organs, they move, like annelides, by the extension and contraction of their bodies. The mouth is surrounded by plumose tentacula, the number of which, _when they are complete_, is always a multiple of five. They all have the power of changing their shapes in the strangest manner, sometimes elongating themselves like worms, sometimes contracting the middle of their bodies, so as to give themselves the shape of an hour-glass, and then again blowing themselves up with water, so as to be perfectly globular.

[Illustration: Fierasfer.]

The great Sea-cucumber is the largest of all the known European species, and probably one of the largest _Cucumeriæ_ in the world, measuring when at rest fully one foot, and capable of extending itself to the length of three. Under the influence of terror, it dismembers itself in the strangest manner. Having no arms or legs to throw off, like its relations the luidia and the brittle-star, it simply disgorges its viscera, and manages to live without a stomach; no doubt a much greater feat than if it contrived to live without a head. According to the late Sir James Dalyell, the lost parts are capable of regeneration, even if the process of disgorgement went so far as to leave but an empty sac behind. Considering the facility with which the sea-cucumber separates itself from its digestive organs, it is the more to be wondered how it tolerates the presence of a very remarkable parasite, a fish belonging to the genus _Fierasfer_, and about six inches long. This most impudent and intrusive comrade enters the mouth of the cucumber, and, as the stomach is too small for his reception, tears its sides, quartering himself without ceremony between the viscera and the outer skin. The reason for choosing this strange abode is as yet an enigma.

[Illustration: Eatable Trepang.]

The _Holothuriæ_, which in our part of the globe are very little noticed, play a much more important part in the Indian Ocean, where they are caught by millions, and, under the name of _Trepang_ or _Biche de mer_, brought to the markets of China and Cochin-China. Hundreds of praos are annually fitted out in the ports of the Sunda Islands for the gathering of trepang; and sailing with help of the western monsoon to the eastern parts of the Indian Archipelago, or along the northern coast of Australia, return home again by favour of the eastern monsoon. The bays of the inhospitable treeless shores of tropical New Holland, the abode of a few half-starved barbarians, are enlivened for a few months by the presence of the trepang fishers.

"During my excursions round Raffles Bay," says Dumont d'Urville, ("Voyage to the South Pole,") "I had remarked here and there small heaps of stones surrounding a circular space. Their use remained a mystery until the Malayan fishers arrived. Scarce had their praos cast anchor, when without loss of time they landed large iron kettles, about three feet in diameter, and placed them on the stone heaps, the purpose of which at once became clear to me. Close to this extemporised kitchen they then erected a shed on four bamboo stakes, most likely for the purpose of drying the holothurias in case of bad weather. Towards evening, all preliminaries were finished, and the following morning we paid a visit to the fishermen, who gave us a friendly reception. Each prao had thirty-seven men on board, and carried six boats, which we found busily engaged in fishing. Seven or eight Malays, almost entirely naked, were diving near the ship, to look for trepang at the bottom of the sea. The skipper alone stood upright, and surveyed their labours with the keen eye of a master. A burning sun scorched the dripping heads of the divers, seemingly without incommoding them; no European would have been able to pursue the work for any length of time. It was about noon, and the skipper told us this was the best time for fishing, as the higher the sun, the more distinctly the diver is able to distinguish the trepang crawling at the bottom. Scarce had they thrown their booty into the boat when they disappeared again under the water, and as soon as a boat was sufficiently laden, it was instantly conveyed to the shore, and succeeded by another.

"The holothuria of Raffles Bay is about six inches long, and two inches thick. It forms a large cylindrical fleshy mass, almost without any outward sign of an organ, and as it creeps very slowly along is easily caught. The essential qualities of a good fisherman are great expertness in diving, and a sharp eye to distinguish the holothurias from the similarly coloured sea-bottom.

"The trepang is first thrown into a kettle filled with boiling sea-water. After a few minutes, it is taken out of its hot-bath and ripped open with a knife to cleanse it of its intestines. It is then thrown into a second kettle, where a small quantity of water and the torrefied rind of a mimosa produce dense vapours. This is done to smoke the trepang for better preservation. Finally, it is dried in the sun, or in case of bad weather under the above-mentioned shed. I tasted the trepang, and found it had some resemblance to lobster. In the China market the Malays sell it to the dealers for about fifteen rupees the picul of 125 pounds. From the earliest times, the Malays have possessed the monopoly of this trade in those parts, and Europeans will never be able to deprive them of it, as the economy of their outfit and the extreme moderation of their wants forbid all competition. About four in the afternoon the Malays had terminated their work. In less than half an hour the kettles and utensils were brought on board, and before night-fall we saw the praos vanish from our sight."

The inhabitants of the island of Waigiou, to the north of New Guinea, prepare the trepang in the Malay manner, and barter it for cotton and woollen stuffs, which are brought to them by some Chinese junks. "In every hut," says Lesson, "we found great heaps of this dried leathery substance, which has no particular taste to recommend it, and is so highly esteemed by the Chinese for no other reason than because they ascribe to it,--as to some other gelatinous substances, as agar-agar, shark-fins, and edible bird's nests,--peculiar invigorating properties, by means of which their enervated bodies are rendered fit for new excesses."

The Feejee islanders have the reputation of being the greatest cannibals and the most perfidious savages of the whole Pacific, yet the trepang fishery attracts many American and European speculators to that dangerous archipelago. Captain Wilkes, of the United States Exploring Expedition, found there a countryman, Captain Eagleston, who had been successful in more than one of these expeditions, and obligingly communicated to him all the particulars of his adventurous trade. There are six valuable sorts of biche de mer, or trepang; the most esteemed is found on the reefs one or two fathoms deep, where it is caught by diving. The inferior sorts occur on reefs which are dry, or nearly so, at low water, where they are picked up by the natives, who also fish the biche de mer on rocky coral bottoms by the light of the moon or of torches, as they come forth by night to feed. The most lucrative fisheries are on the northern side of Viti Levu. They require a large building for drying, with rows of double staging, on which reeds are placed. Slow fires are kept up by natives underneath, about fifteen hands being required to do the ordinary work of a house.

Before beginning, the services of some chief must be secured, who undertakes the building of the house, and sets his dependants at work to fish. The usual price is a whale's tooth for a hogshead of the animals just as they are taken on the reef; but they are also bought with muskets, powder, balls, vermilion, blue beads, and cotton cloth of the same colour. When the animals are brought on shore, they are measured into bins containing about fifty hogsheads, where they remain until next day. They are then cut along the belly for a length of three or four inches, taking care not to cut too deep, as this would cause the fish to spread open, which would diminish its value. They are then thrown into boilers, two men attending each pot, and relieving each other, so that the work may go on night and day. No water need be added, as the fish itself yields moisture enough to prevent burning. After draining on a platform for about an hour, they are taken to the house and laid four inches deep upon the lower battens, and afterwards upon the upper ones, where they remain three or four days. Before being taken on board they are carefully picked, all damp pieces being removed. They are stowed in bulk, and sold in Manilla or Canton by the picul, which brings from fifteen to twenty-five dollars. In this manner Captain Eagleston had collected in the course of seven months, and at a trifling expense, a cargo of 1200 piculs, worth about 25,000 dollars. The outfit is small, but the risk is great, as no insurance can be effected; and it requires no small activity and enterprise to conduct this trade. A thorough knowledge of native character is essential to success, and the utmost vigilance and caution must always be observed to prevent surprise, or avoid difficulties.

No large canoes should ever be allowed to remain alongside the vessel, and a chief of high rank should be kept on board as a hostage. That these precautions are by no means unnecessary, is proved by the frequent attempts of the savages to cut off small vessels trading on their coasts. One of the most frequent methods is to dive and lay hold of the cable; this, when the wind blows fresh to the shore, is cut, in order that the vessel may drift upon it, or in other cases a rope is attached to the cable by which the vessel may be dragged ashore. The time chosen is just before daylight. The moment the vessel touches the land, it is treated as a prize sent by the gods, and the crew murdered, roasted, and devoured.

[Illustration: Sea-horse.]

CHAP. XVII.

CŒLENTERATA.

POLYPS AND JELLY-FISHES.

Thread-cells or Urticating Organs.--Sertulariæ.--Campanulariadæ.--Hydrozoie Acalephæ.--Medusidæ.--Lucernariadæ.--Calycophoridæ.--The Velella.--The Portuguese Man-of-war.--Anecdote of a Prussian Sailor.--Alternating Fixed and Free-swimming Generations of Hydrozoa.--Actinozoa.--Ctenophora.--Their Beautiful Construction.--Sea-anemones.--Dead Man's Toes.--Sea-pens.--Sea-rods.--Red Coral.--Coral Fishery.--Isis hippuris.--Tropical Lithophytes.--History of the Coral Islands.--Darwin's Theory of their Formation.--The progress of their Growth above the level of the Sea.

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

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

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

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

[Illustration: Urticating Organs of Cœlenterata.

_a_, _e_, _f_. Threads and thread-cells of _Caryophyllia Smithii_. _b._ Thread-cell of _Corynactis Allmani_. _c._ Peculiar receptacle of _Willsia stellata_, containing thread-cells. _d._ A single thread-cell of the same. _g._ Thread-cell of _Actinia crassicornis_.--(All magnified.) ]

The Cœlenterata have been subdivided into two great classes: the Hydrozoa, in which the wall of the digestive sac is not separated from that of the cavity of the body, and the Actinozoa, in which the stomach forms a distinct bag separated from the wall of the cavity of the body by an intervening space, subdivided into chambers by a series of vertical

## partitions. Each of these two classes comprises a number of families of

various forms and habits of life. Thus among the Hydrozoa, with whom I begin my brief survey of cœlenterate life, some are of a compound nature (Sertularidæ, &c.), and, having once settled, remain permanently attached to the site of their future existence; while others (Rhizostomidæ, &c.) continue freely to roam through the water, and others again appear in the various stages of their development either as sessile polyps or as free-swimming Medusæ.

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

[Illustration: Sertularia tricuspidata.

_a._ Skeleton (natural size). _b._ Portion of the same, highly magnified. _κ._ _Cœnosarc_, or common trunk. _π′._ _Hydrotheca_, or protective envelope of individual polyp. _ρ′._ _Gonoblastidium_, or reproductive germ or body. ]

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

[Illustration:

_a._ _Laomedea neglecta_, natural size. _b._ Portion of the same, magnified. _c._ Reproductive body of _Campanularia volubilis_. _e._ Reproductive body of _C. syringa_. ]

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

[Illustration:

_a._ Medusid seen in profile. _b._ The same viewed from below. _c._ Its polypite. _d._ Part of its marginal canal, and other structures in connection therewith. ν. Disk or swimming organ. π. Polypite. ψ. Veil. τ. Tentacle. χ. Radiating canal. χ′. Marginal canal. ω. Reproductive organ. ο′. Coloured spot. ο″. Marginal vesicle. ]

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

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

[Illustration: Various forms of Medusidæ.

_a._ _Aequorea formosa_, seen in profile. _b._ The same, viewed from above. _c._ Upper view of _Willsia stellata_. _d._ _Slabberia conica._ _e._ Portion of the marginal canal of _Tiaropsis Pattersonii_. _f._ Polypite of _Bougainvillea dinema_. _g._ Part of its marginal canal. _h._ _Steenstrupia Owenii._ (_a_, _b_, and _d_ are about the natural size; the others are magnified.) ]

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

## active for the welfare of the community.

[Illustration: Oceanic forms of Lucernaridæ.

_a._ _Rhizostoma pulmo._ _b._ _Chrysaora hysoscella._ _c._ Its lithocyst.--(All reduced.) ]

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

[Illustration: Lucernalia auricula. (Natural size.)]

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

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

[Illustration: _a._ Diphyes appendiculata.]

[Illustration: _b._ Vogtia pentacantha. (Natural size.)]

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

## action of the currents. Again two or three days elapsed, and as the

surface of the sea occupied by both species of animals extended at the least over four degrees of latitude, a faint idea may be formed of their numbers. Shoals of dolphins and sperm-whales were busy exterminating the barnacles, as these had devoured the Velellæ. The whole scene was an example on the grandest scale of the destruction and regeneration perpetually going on in the wastes of the ocean.

[Illustration:

_a_. _Velella spirans_, somewhat enlarged. _b._ One of its smaller polypites, much magnified. ν. Crest. λ. Liver. ο. Mouth of polypite. δ. Its digestive cavity. φ′. Rounded elevations, containing thread-cells. ρ. Medusiform zoöids. ]

[Illustration: Physalia caravella.--(Considerably reduced.)

α. Pneumatophore, or float-bladder. π. Polypites. τ. Tentacles. ]

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

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

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

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

[Illustration: Physophora Philippii.

α. Pneumatophore. ν. Swimming-bells. φ. Hydrocysts. π. Polypites. τ. Tentacles. ]

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

[Illustration: Development of Chrysaora hysoscella.

_a._ Ova with gelatinous investment. _b_ and _c_. Free ova. _d._ Young Hydratuba developed therefrom. _e._ The same with eight tentacles. _f._ Hydratuba in its ordinary condition. _g_, _h_. More advanced forms, with constrictions. _i._ A specimen undergoing fission, in which the tentacles are seen to arise from below the constricted portion, while its upper segments separate and become free-swimming zoöids (_k_). ]

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

[Illustration: Various forms of Coryniadæ.

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

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

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

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

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

In habit they resemble the oceanic Hydrozoa, like them swimming near the surface in calm weather, and again descending on the approach of a squall. Like them also, their delicate structures rapidly disappear when removed from the sea-water and exposed to the rays of the sun, an almost imperceptible film remaining the only trace of what was erewhile an

## active and beautiful organism. Yet in spite of their aqueous consistence

the Ctenophora are very voracious, feeding on a number of floating marine animals, among which their own kindred seem especially to be preferred. The prey once swallowed is assimilated with a rapidity which to some may seem strange when the simple structure of the digestive apparatus is considered.

[Illustration: Various forms of Ctenophora.

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

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

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

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

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

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

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

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

[Illustration: Alcyonidium elegans.

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

Both the Ctenophora and the Sea-Anemones are single or solitary, but the vast majority of the Actinozoa consist of aggregated animals attached to one another by lateral appendages, or by their posterior extremity, and

## participating in a common life, while at the same time each member of the

family enjoys its independent and individual existence. These compound polyps are all either _Alcyonarians_, in which each polyp is furnished with eight pinnately fringed tentacles, or _Zoantharians_, in which the tentacula are simple or variously modified, and generally disposed in multiples of five or six. The Alcyonarians are again subdivided into the four families of the Alcyonidæ, the Pennatulidæ, the Gorgonidæ, and the Tubiporidæ.

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

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

[Illustration: Grey Sea-Pen.]

[Illustration: Virgularia mirabilis.]

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

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

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

[Illustration: Red Coral.

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

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

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

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

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

[Illustration: Isis hippuris.]

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

[Illustration: Tubipora Musica.]

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

[Illustration: Caryophyllia.]

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

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

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

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

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

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

[Illustration: Astræa.]

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

[Illustration: Stone Corals.]

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

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

[Illustration: Stone Corals.]

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

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

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

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

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

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

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

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

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

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

CHAP. XVIII.

PROTOZOA.

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

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

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

[Illustration: Nummulina discoidalis.

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

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

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

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

[Illustration: Amœba.]

[Illustration: Amœba, showing the extemporaneous feet formed by evanescent projections of the general plastic mass of the animal.]

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

## particular organs in the amœba; all its constituent particles may be used

for any purpose, all equally move and digest, and each can at any time perform the organic functions pertaining to the whole.

[Illustration: A Compound Foraminiferous Protozoon, magnified.

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

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

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

[Illustration: Various forms of Foraminifera.

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

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

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

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

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

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

[Illustration: Polycystina.

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

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

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

[Illustration: Marine Infusoria.

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

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

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

[Illustration: Single interspace or open cell, and surrounding finer meshwork of the skeleton of a sponge.]

[Illustration: Needle-like and starred spicula of a Tethea. (Highly magnified.)]

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

[Illustration: Minute portion of the surface of Tethea Cranium, magnified, spicula projecting beyond the surface.]

[Illustration: Halina papillaris.

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

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

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

Subsequent observations have proved that the living sponge has the power of opening and closing at pleasure its oscula, which are capable of

## acting independently of each other, thus fully establishing the animal

nature of these simple organisations, in whom latterly even traces of sensibility have been detected, such as one would hardly expect to meet with in a sponge. For these creatures, as we are entitled to call them, are able to protrude from their oscula the gelatinous membrane which clothes their channels, and on touching these protruded parts with a needle, they were seen by Mr. Gosse to shrink immediately--a proof that the sponge, however low it may rank in the animal world, is yet far from being so totally inert or lifeless as was formerly imagined.

The propagation of the sponges is provided for in a no less wonderful manner than their respiration and nourishment. Minute globular particles of sarcode sprout forth as little protuberances from the interior of the canals. As they increase in size, they are gradually clothed with vibratile cilia, and, finally detaching themselves, are cast out through the oscula into the world of waters. Here their wanderings continue for a short time, until, if they be not devoured on the way, they reach some rock or submarine body on which, tired of their brief erratic existence, they fix themselves for ever, and, bidding adieu to all further rambles, lead henceforth the quiet sedentary life of their parents. In this manner the sponges, which otherwise would have been confined to narrow limits, spread like a living carpet over the bottom of the seas, and in spite of their being utterly defenceless, maintain their existence from age to age. At the same time they serve to feed a vast number of other marine animals, for the waters frequently swarm with their eggs, and these afford many a welcome repast to myriads of sessile molluscs, annelides, polyps, and other creatures small or abstemious enough to be satisfied with feasting on atoms.

Sponges inhabit every sea and shore, and differ very much in habit of growth. For whilst some can only be obtained by dredging at considerable depths, others live near the surface, and others, again, attach themselves to the surfaces of rocks and shells between the tide marks. Like the corals, they revel in every variety of shape and tint, imitate like them every form of vegetation, and adorn like them the submarine grounds with their fantastic shrubberies. The fine collection of West Indian sponges exhibited in the Crystal Palace, but to which fancy must add the additional ornament of colour, may serve to give some idea of their prodigal versatility of growth. More than sixty different species have been discovered in the British waters alone, and as they go on increasing in numbers, size, and beauty, until they attain their highest development along the shores of the tropical ocean, they no doubt hold a conspicuous rank among the living wonders of the sea. The branched sponges, with a compact feltred tissue, are more common than others in the colder maritime domains, where the species of a loose texture, which grow in large massive forms, either do not exist or are very rare. Many sponges are of considerable size, such as the vase-like tropical species known under the name of Neptune's cup; others are almost microscopical; and while by far the greater number grow superficially from a solid base, some penetrate like destructive parasites into the texture of other animals. Thus the _Halichondria celata_ establishes itself in the small holes which some of the smaller annelides drill in the shell of the oyster, eat further and further into the unfortunate mollusc's vitals, causing the softer parts of the shell to rot away, and spread through its whole substance, like the dry-rot fungus through a solid beam of timber, until, sinking under the weight of his misery, the poor victim perishes, and his loosened shell is cast to the mercy of the waves. On the other hand, some marine Acorn-shells nestle habitually in a sponge, the normal construction of the base of the shell being altered to suit the peculiarities of its habitation, so that in this instance, as in many others, there is a foreseen relation between two very dissimilar animals. Amongst the reticulated fibres of its spongy dwelling, the Acorn-shell finds a secure refuge in its infant state, and is soon enclosed by the growing fabric of the sponge-animal, except a small opening, which is kept clear by the vortex occasioned by the constant motion of its feelers or tentacula.

But very few of the manifold species of sponges are of any use to man. The common sponge of commerce (_Spongia communis_), so serviceable in our households, is most abundant in the Lycian seas, where it is found attached to rocks at various depths between three fathoms and thirty. When alive, it is of a dull bluish black above, and dirty white beneath. There are several qualities, possibly indicating as many distinct species.

"The most valued kinds," says Edward Forbes, "are sought for about the Gulf of Macri, along the Carian coast, and round the opposite islands. The species which live immediately along the shore near the water's edge, though often large, are worthless. These are of many colours; some of the brightest scarlet or clear yellow form a crust over the faces of submarine rocks; others are large and tubular, resembling holothuriæ in form and of a gamboge colour, which soon turns to dirty brown when taken out of the water; others are again lobed or palmate, studded with prickly points, and perforated at intervals with oscula. These grow to a considerable size, but, like the former, are useless, since their substance is full of needles of flint."

Large quantities of excellent sponge (_Spongia usitatissima_) are likewise imported from the West Indies.

CHAP. XIX.

MARINE PLANTS.

The Algæ.--Zostera marina.--The Ulvæ and Enteromorphæ.--The Fuci.--The Laminariæ.--Macrocystis pyrifera.--Description of the Submarine Thickets at Tierra del Fuego.--Nereocystis lutkeana.--The Sargasso Sea.--The Gathering of edible Birds'-nests in the marine Caves of Java.--Agar-Agar.--The Florideæ.--The Diatomaceæ.--Their importance in the economy of the Seas.

The dry land develops the most exuberant vegetation on the lowest grounds, the plains and deep valleys, and the size and multiplicity of plants gradually diminish as we ascend the higher mountain regions, until at last merely naked or snow-covered rocks raise their barren pinnacles to the skies: but the contrary takes place in the realms of ocean; for here the greater depths are completely denuded of vegetation, and it is only within 600 or 800 feet from the surface that the calcareous nullipores begin to cover the sea-bottom, as mosses and lichens clothe the lofty mountain-tops. Gradually corallines and a few algæ associate with them, until finally about 80 or 100 feet from the surface begins the rich vegetable zone which encircles the margin of the sea. The plants of which it is composed do not indeed attain the same high degree of development as those of the dry land, being deprived of the beauties of flower and fruit: but as the earth at different heights and latitudes constantly changes her verdant robe, and raises our highest admiration by the endless diversity of her ornaments, thus also the forms of the sea-plants change, whether we descend from the brink of ocean to a greater depth, or wander along the coast from one sea to another; and their delicate fronds are as remarkable for beauty of colour and elegance of outline, as the leaves of terrestrial vegetation.

The difference of the mediums in which land- and sea-plants exist naturally requires a different mode of nourishment, the former principally using their roots to extract from a varying soil the substances necessary for their perfect growth, while the latter absorb nourishment through their entire surface from the surrounding waters, and use their roots chiefly as holdfasts.

The constituent parts of the soil are of the greatest importance to land-plants, to whose organisation they are made to contribute; while to the sea-plant it is generally indifferent whether the ground to which it is attached be granite, chalk, slate, or sandstone, provided only its roots find a safe anchorage against the unruly waters.

Flat rocky coasts, not too much exposed to the swell of the waves, and interspersed with deep pools in which the water is constantly retained, are thus the favourite abode of most algæ, while a loose sandy sea-bottom is generally as poor in vegetation as the Arabian desert.

But even on sandy shores extensive submarine meadows are frequently formed by the Grass Wrack (_Zostera marina_), whose creeping stems, rooting at the joints and extending to a considerable depth in the sand, are admirably adapted for seeming a firm position on the loose ground. Its long riband-like leaves, of a brilliant and glossy green, wave freely in the water, and afford shelter and nourishment to numerous marine animals and plants. In the tropical seas it forms the submarine meadows on which the turtles graze, and in the North of Europe it is used for the manufacture of cheap bedding. It also furnishes an excellent material for packing brittle ware.

Sea-weeds are usually classed in three great groups, green, olive-coloured, and red; and these again are subdivided into numerous families, genera, and species.

On the British coasts alone about 400 different species are found, and hence we may form some idea of the riches of the submarine flora. Thousands of algæ are known and classified, but no doubt as many more at least still wait for their botanical names, and have never yet been seen by human eye.

The _Green_ sea-weeds, or Chlorospermeæ, generally occur near high-water mark, and love to lead an amphibious life, half in the air and half in salt-water. The delicate Enteromorphæ, similar to threads of fine silk, and the broad brilliant Ulvæ, which frequently cover the smooth boulders with a glossy vesture of lively green, belong to this class. Many of them are remarkable for their wide geographical distribution. Thus the _Ulva latissima_ and the _Erderomorpha compressa_ of our shores thrive also in the cold waters of the Arctic Sea, fringe the shores of the tropical ocean, and project into the southern hemisphere as far as the desolate head-lands of Tierra del Fuego. But few animals or plants possess so pliable a nature, and such adaptability to the most various climates.

The _Olive-coloured_ group of sea-weeds, or Melanospermeæ, plays a much more considerable part in the economy of the ocean. The common fuci, which on the ebbing of the tide impart to the shore cliffs their peculiar dingy colour, belong to this class; as well as the mighty Laminariæ, which about the level of ordinary low water, and one or two fathoms below that limit, fringe the rocky shore with a broad belt of luxuriant vegetation.

The first olive-coloured sea-weed we meet with on the receding of the flood is the small and slender _Fucus canaliculatus_, easily known by its narrow grooved stems and branches, and the absence of air-vessels. Then follows _Fucus nodosus_, a large species, with tough thong-like stems, expanding at intervals into knob-like air-vessels, and covered in winter and spring with bright yellow berries. Along with it we find the gregarious _Fucus vesiculosus_, with its forked leaf traversed by a midrib, and covered with numerous air-vessels situated in pairs at each side of the rib. Finally, about the level of half-tide, a fourth species of fucus appears, _Fucus serratus_, distinguished from all the rest by its toothed margin and the absence of air-vessels.

These four species generally occupy the littoral zone of our sea-girt isle, being found in greatest abundance on flat rocky shores,

## particularly on the western coasts of Scotland and Ireland, where they

used formerly to be burnt in large quantities for the manufacture of kelp or carbonate of soda, which is now obtained by a less expensive process. In Orcadia alone more than 20,000 persons were employed during the whole summer in the collection and incineration of sea-weeds, a valuable resource for the poverty-stricken islanders, of which they have been deprived by the progress of chemical science.

The fuci are, however, still largely used, either burnt or in a fermented state, as a valuable manure for green crops. Thus every year several small vessels are sent from Jersey to the coast of Brittany, to fetch cargoes of sea-weeds for the farmers of that island.

A RUSSIAN OFFICIAL, ATTENDED BY A SOLDIER, COLLECTING ALGÆ ON THE SHORES OF THE NORTH PACIFIC.

The annexed plate is taken from the frontispiece of the magnificent folio volume by Messrs. Ruprecht and Postels, on the Algæ of the North Pacific. This work, in which even the largest of the marine plants of that region are represented of their natural size, was published at the expense of the Russian Government, and copies were presented to some of the principal libraries of Europe.

In the middle distance, a Russian official belonging to one of the settlements is seen gathering algæ, attended by a soldier.

In the front of the picture the water is supposed to be so clear as to show distinctly the growth of sea-weeds of various kinds, which clothe the submarine rocks in that region. Some species of these have been added to the number shown in the original composition.

In the centre, with the light fully upon them, are streaming plants of a gigantic _Alaria_, whose fronds sometimes extend to a length of 40 feet. Immediately beneath it, to the right, is the curiously perforated _Agarium Gmelini_, the singular perforations of which are indicated by small white patches.

To the right is the curious "flower-bearing" sea-weed known as the Sea Rose, _Constantinea Rosa marina_, the flower-like growth of which, combined with the pink colour of its seeming flowers, is very remarkable.

In front, and rather to the right of the last, is a dark mass of the splendid _Iridæa Mertensiana_, the dark velvety masses of which, of a deep crimson colour, are often more than a foot across.

To the right of the last, in the corner, is one of the most beautiful of the ulvæ, _Ulva fenestrata_, a name which may be popularised as the "windowed" ulva, in allusion to its extremely perforated character, the openings being of considerable size, and often separated from each other only by the slenderest divisions, thus forming a kind of vegetable lace-work.

[Illustration: A RUSSIAN OFFICIAL ATTENDED BY A SOLDIER COLLECTING ALGÆ ON THE SHORES OF THE NORTH PACIFIC.]

The largest of indigenous sea-weeds are the _Laminaria saccharina_ and _digitata_, or the sugary and fingered oar-weeds. Their stout woody stems, and broad tough glossy leaves of dark olive-green, often twelve or fourteen feet long, must be familiar to every one who has sojourned on the coast. When gliding over their submerged groves in a boat, their great fronds floating like streamers in the water afford the interesting spectacle of a dense submarine thicket, through whose palm-like tops the fishes swim in and out, emulating in activity the birds of our forests.

But our native oar-weeds, large as they seem with regard to the other fuci among which they grow, are mere pygmies when compared with the gigantic species which occur in the colder seas.

None of the members of this family grow in the tropical waters, but they extend to the utmost polar limits, and seem to increase in size and multiplicity of form as they advance to the higher latitudes. The northern hemisphere has generally different genera from the southern. To the former belong the gigantic Alarias with their often forty feet long and several feet broad fronds, the singularly perforated Thalassophyta, and the far-spreading Nereocystis, which is only found in the Northern Pacific; while the genera Macrocystis and Lessonia are denizens of the Southern Ocean.

In the numerous channels and bays of Tierra del Fuego, the enormous and singular _Macrocystis pyrifera_ is found in such incredible masses as to excite the astonishment of every traveller. "On every rock," says Mr. Darwin, perhaps the best observer of nature that ever visited those dreary regions, and certainly their most poetical describer, "the plant grows from low-water mark to a great depth, both on the outer coast and within the channels. I believe, during the voyages of the Adventure and Beagle, not one rock near the surface was discovered which was not buoyed by this floating weed. The good service it thus affords to vessels navigating near this stormy land is evident, and it certainly has saved many a one from being wrecked. I know few things more surprising than to see this plant growing and flourishing amidst those great breakers of the western ocean, which no mass of rock, let it be ever so hard, can long resist. The stem is round, slimy, and smooth, and seldom has a diameter of so much as an inch. A few taken together are sufficiently strong to support the weight of the large loose stones to which in the inland channels they grow attached; and some of these stones are so heavy, that when drawn to the surface they can scarcely be lifted into a boat by one person."

"Captain Cook, in his second voyage says, that 'at Kerguelen's Land some of this weed is of most enormous length, though the stem is not much thicker than a man's thumb. I have mentioned that, on some of these shoals on which it grows, we did not strike ground with a line of twenty-four fathoms; the depth of water, therefore, must have been greater. And as this weed does not grow in a perpendicular direction, but makes a very acute angle with the bottom, and much of it afterwards spreads many fathoms on the surface of the sea, I am well warranted to say that some of it grows to the length of sixty fathoms and upwards.'

"Certainly at the Falkland Islands, and about Tierra del Fuego, extensive beds frequently spring up from ten and fifteen fathoms water. I do not suppose the stem of any other plant attains so great a length as 360 feet, as stated by Captain Cook. Its geographical range is very considerable; it is found from the extreme southern islets near Cape Horn, as far north on the eastern coast as lat. 43°, and on the western it was tolerably abundant, but far from luxuriant, at Chiloe, in lat. 42°. It may possibly extend a little further northward, but is soon succeeded by a different species.

"We thus have a range of 15° in latitude, and as Cook, who must have been well acquainted with the species, found it at Kerguelen's Land, no less than 140° in longitude.

"The number of living creatures, of all orders, whose existence intimately depends on the kelp, is wonderful. A large volume might be written, describing the inhabitants of one of these beds of sea-weed. Almost every leaf, except those that float on the surface, is so thickly incrusted with corallines as to be of a white colour. We find exquisitely delicate structures, some inhabited by simple hydra-like polypi, others by more organised kinds and beautiful compound ascidiæ. On the flat surfaces of the leaves, various patelliform shells, trochi, uncovered mollusks, and some bivalves are attached. Innumerable crustacea frequent every part of the plant. On shaking the great entangled roots, a pile of small fish, shells, cuttle-fish, crabs of all orders, sea-eggs, star-fish, beautiful holothuriæ (some taking the external form of the nudibranch mollusks), planariæ, and crawling nereidous animals of a multitude of forms, all fall out together. Often as I recurred to a branch of the kelp, I never failed to discover animals of new and curious structure. In Chiloe, where, as I have said, the kelp did not thrive very well, the numerous shells, corallines, and Crustacea were absent, but there yet remained a few of the Flustraceæ, and some compound ascidiæ; the latter, however, were of different species from those in Tierra del Fuego. We here see the fucus possessing a wider range than the animals which use it as an abode.

"I can only compare these great aquatic forests of the southern hemisphere with the terrestrial ones in the intertropical regions. Yet, if the latter should be destroyed in any country, I do not believe nearly so many species of animals would perish, as under similar circumstances would happen with the kelp. Amidst the leaves of this plant numerous species of fish live, which nowhere else would find food or shelter; with their destruction the many cormorants, divers, and other fishing-birds, the otters, seals, and porpoises, would soon perish also; and lastly the Fuegian savage, the miserable lord of this miserable land, would redouble his cannibal feast, decrease in numbers, and perhaps cease to exist."

For many a day's sail before reaching Cape Horn, large bundles of the macrocystis detached by the storm announce to the navigator that he is approaching the desolate coasts of Tierra del Fuego.

"We succeeded," says Professor Meyen, in his _Reise um die Welt_, "in getting hold of one of these floating islands, which, amid loud acclamations, was hauled upon deck by the exertions of five men. It was quite impossible to disentangle the enormous mass; we could only detach, to the length of about sixty feet, what we considered to be the chief stem; the branches were from thirty to forty feet long, and as thick as the principal trunk from which they sprang. We estimated the total length of the plant at about two hundred feet; the pear-shaped air vessels at the basis of the leaves were often six or seven inches long, and the leaves themselves measured seven or eight feet. On these swimming fucus-islands lived a vast multitude of various animals; thousands upon thousands of barnacles and sertulariæ, of crustaceans and annelides.

"The admiration which the gigantic sea-weeds of Tierra del Fuego excited in our minds equalled that which had been raised by the exuberant vegetation of the virgin forests of Brazil. One single plant of the _Macrocystis pyrifera_ would suffice, like one of the mammoth-trees of those luxuriant woods, to cover a large space of land with its leaf-like substance. The quantity of small algæ, of sertularias, cellarias, and other minute animals dwelling on these swimming islands, surpasses in variety the multitude of parasitical plants bedecking the trees in a tropical forest. It seems as if, in these desolate and dreary regions, the generative powers of the planet were solely confined to the gigantic growth of submarine vegetation."

On the rocky coasts of the Falkland Islands are found no less astonishing masses of enormous sea-weeds, chiefly belonging to the genera Macrocystis, Lessonia, and Durvillea. Rent from the rocks to which they were attached, and cast ashore, they are rolled by the heavy surf into prodigious vegetable cables, much thicker than a man's body and several hundred feet long. Many of the rarest and most beautiful algæ may be here discovered, which have either been wrenched from inaccessible rocks far out at sea, along with the larger species, or have attached themselves parasitically to their stems and fronds. Many of them remind the botanist, by some similarity of form, of the sea-weeds of his distant home, while others tell him at once that he is far away in another hemisphere. The gigantic lessonias particularly abound about these islands. Their growth resembles that of a tree. The stem attains a height of from eight to ten feet, the thickness of a man's thigh, and terminates in a crown of leaves two or three feet long, and drooping like the branches of a weeping-willow. They form large submerged forests, and, like the thickets of the macrocystis, afford a refuge and a dwelling to countless sea animals.

A similar abundance of colossal algæ is found in the Northern Pacific, about the Kurile and Aleutic Islands, and along the deeply indented and channel-furrowed north-west coast of America.

Thus the _Nereocystis lutkeana_ forms dense forests in Norfolk Bay and all about Sitcha. Its stem, resembling whipcord, and often above 300 feet long, terminates in a large air-vessel, six or seven feet long, and crowned with a bunch of dichotomous leaves, each thirty or forty feet in length. Dr. Mertens assures us that the sea-otter, when fishing, loves to rest upon the colossal air-vessels of this giant among the sea-weeds, while the long tenacious stems furnish the rude fishermen of the coast with excellent tackle. The growth of the nereocystis must be uncommonly rapid, as it is an annual plant, and consequently develops its whole gigantic proportions during the course of one brief summer.

Before proceeding to the third chief group of marine plants, the red sea-weeds, or Rhodosperms, I must mention the enormous fucus banks, or floating meadows of the Atlantic, which form undoubtedly one of the greatest wonders of the ocean.

We know that the mighty Gulf Stream, which rolls its indigo-blue floods from America to the opposite coasts of the Old World, flows partly southwards in the neighbourhood of Azores, and is ultimately driven back again to America. In the midst of these circuitous streams, from 22° to 36° N. lat., and from 35° to 65° W. long., extends a sea without any other currents than those resulting from the temporary action of the winds. This comparatively tranquil part of the ocean, the surface of which surpasses at least twenty times that of the British Isles, is found more or less densely covered with floating masses of _Sargassum bacciferum_. Often the sea-weed surrounds the ship sailing through these savannas of the sea, in such quantities as to retard its progress, and then again hours may pass when not a single fucus appears. While Columbus was boldly steering through the hitherto unknown fields of the Sargasso Sea, the fears of his timorous associates were increased by this singular phenomenon, as they believed they had now reached the bounds of the navigable ocean, and must inevitably strike against some hidden rock, if their commander persevered in his audacious course.

It is an interesting fact that the Sargasso Sea affords the most remarkable example of an aggregation of plants belonging to one single species. Nowhere else, according to Humboldt, neither in the savannas of America, nor on the heaths or in the pine forests of Northern Europe, is such a uniformity of vegetation found as in those boundless maritime meadows.

"The masses of sea-weeds," says Meyen, "covering so vast an extent of ocean have ever since the time of Columbus been the object of astonishment and inquiry. Some navigators believe, that they are driven together by the Gulf Stream, and that the same species of Sargassum plentifully occurs in the Mexican Sea; this is however perfectly erroneous.

"Humboldt was of opinion that this marine plant originally grows on submarine banks, from which it is torn by various forces; I for my part have examined many thousands of specimens, and venture to affirm that they never have been attached to any solid body. Freely floating in the water, they have developed their young germs, and sent forth on all sides roots and leaves, both of the same nature."

Thus the Sargassum seems to be the indigenous production of the sea where it appears, and to have floated there from time immemorial. Its swimming islands afford an abode and nourishment to a prodigious amount of animal life. They are generally covered with elegant sertularias, coloured vorticellas, and other strange forms of marine existence. Various naked or nudibranchiate mollusks and annelides attach themselves to the fronds, and afford nourishment to hosts of fishes and crustaceans, the beasts of prey of this little world.

Similar aggregations of sea-weeds are also met with in the Indian and Pacific Oceans, in the comparatively tranquil spaces encircled by rotatory currents. Their rare occurrence on the surface of the sea may serve as a proof of the restless motion of its waters. Were the ocean not everywhere intersected by currents, it would most likely be covered with sea-weeds, opposing serious, if not invincible obstacles to navigation.

The _Red_ sea-weeds, Rhodosperms or Florideæ, are by far the most numerous in species, and undoubtedly the most beautiful and perfect of all the algæ. They love neither light nor motion, and generally seek the shade of larger plants on the perpendicular sides of deep tide-pools removed from the influences of the tides and gales. They mostly grow close to low-water mark, and are to be seen only for an hour or two at the spring-tides, during which, as is well known, the deepest ebbs take place. To this group belong the wonderfully delicate polysiphonias, callithamnias, plocamias, and delesserias, whose elegant rosy scarlet or purple leaves are the amateur's delight, and when laid out on paper resemble the finest tracery, defying the painter's art to do justice to their beauty. It likewise numbers among its genera the chalky corallines and nullipores, which on account of the hardness of their substance were formerly considered to be polyps, but whose true nature becomes apparent on examining their internal structure.

The _Chondrus crispus_, or Carrigeen, which grows in such vast quantities on the coasts of the British Isles, also belongs to the rhodosperms, though when growing, as it frequently does, in shallow tide-pools, exposed to full sunlight, its dark purple colour fades into green or even yellowish white. When boiled it almost entirely dissolves in the water, and forms on cooling a colourless and almost tasteless jelly, which of late years has been largely used in medicine as a substitute for Iceland moss. Similar nutritious gelatines, which also serve for the manufacture of strong glues, are yielded by other species of rhodosperms, among others by the _Gracillaria spinosa_ of the Indian Ocean, which the Salangana (_Hirundo esculenta_), a bird allied to the swallow, is said principally to use for the construction of her edible nest.

The steep sea-walls along the south coast of Java are clothed to the very brink with luxuriant woods, and screw-pines strike everywhere their roots into their precipitous sides, or look down by thousands from the margin of the rock upon the unruly sea below. The surf of incalculable years has worn deep caves into the chalk cliffs, and here the Salangana builds her nest. Where the sea is most agitated whole swarms are observed flying about, and purposely seeking the thickest wave-foam. From a projecting cape, on looking down upon the play of waters, may be seen the mouth of the cave of Gua Rongkop, sometimes completely hidden under the waves, and then again opening its black recesses, into which the swallows vanish, or from which they dart forth with the rapidity of lightning. While at some distance from the coast the blue ocean sleeps in undisturbed repose, it never ceases to fret and foam against the foot of the mural rocks, where the most beautiful rainbows glisten in the eternally rising vapours.

Who can explain the instinct which prompts the birds to glue their nests to the high dark vaults of those deep, and apparently so inaccessible, caverns? Did they expect to find them a safe retreat from the persecutions of man? Then surely their hopes were vain, for where is the refuge to which his insatiable avidity cannot find the way? At the cavern of Gua-gede, the brink of the precipitous coast lies eighty feet above the level of the sea at ebb-tide; the wall first bends inwards, and then, at a height of twenty-five feet from the sea, throws out a projecting ledge which is of great use to the nest-gatherers, serving as a support for a rotang ladder let down from the cliff. The roof of the cavern's mouth lies only ten feet above the sea, which, even at ebb-tide, completely covers the floor of the cave, while at flood-tide the opening of the vast marine grotto is entirely closed by every wave that rolls against it. To penetrate into the interior is thus only possible at low water, and during very tranquil weather; and even then it could not be done, if the rugged roof were not perforated and jagged in every direction. The boldest and strongest of the nest-gatherers wedges himself firmly in the hollows, or clings to the projecting stones, while he fastens rotang ropes to them, which then depend four or five feet from the roof. To the lower ends of these ropes long rotang cables are attached, so that the whole forms a kind of suspension bridge throughout the entire length of the cavern, alternately falling and rising with its inequalities. The cave is 100 feet broad and 150 long as far as its deepest recesses. If we justly admire the intrepidity of the St. Kildans, who, let down by a rope from the high level of their rocky birthplace, remain suspended over a boisterous sea, we must needs also pay a tribute of praise to the boldness of the Javanese nest-gatherers. Before preparing their ladders for the plucking of the birds' nests, they first offer solemn prayers to the goddess of the south-coast, and sometimes deposit gifts on the tomb where the first discoverer of the caverns and their treasures is said to repose. Thus in all zones and in every stage of civilisation, man is directed by an inward voice to seek the protection of the invisible powers when about to engage in a great and perilous undertaking.

As I have already mentioned, the Salangana builds her nest of sea-weeds, which she softens in her stomach and then disgorges. During its construction new layers, which soon grow hard in the air, are continually deposited on the margin, until it has attained the proper size. When gathering time approaches, some of the pluckers daily visit the cavern to examine the state of the brood. As soon as they find that most of the young are beginning to be provided with feathers, their operations commence. These nests form the first quality; those in which the young are still completely naked, the second; while those which only contain eggs, and are consequently not yet ripe, rank third. The nests with young whose feathers are completely developed are over-ripe, black, and good for nothing. All the young and eggs are thrown into the sea. The gathering takes place three times a year; the birds breed four times a year. In spite of these wholesale devastations their numbers do not diminish; as many of the young have no doubt flown away before the day of execution, or other swallows from still unexplored caverns may fill up the void. In this manner about 50 piculs are annually collected, which the Chinese pay for at the rate of 4000 or 5000 guilders the picul. Each picul contains on an average 10,000 nests. Dividing these 500,000 nests among three gatherings, and reckoning two birds to each nest, we find that more than 333,000 swallows inhabit at the same time the Javanese coast caverns.

In the interior of the island, in the chalkstone grottos of Bandong, the Salangana also breeds, but in far inferior numbers, as here the annual collection amounts on an average to no more than 14,000 nests. In these inland caves swallows and bats reside together, but without disturbing each other, as the former when not breeding leave their caverns at sunrise, disappear in the distance, and only return late in the evening, when the bats are already enjoying their vespertine or nocturnal flight.

In Sumatra and some other islands of the Indian archipelago, birds'-nests are likewise collected, but nowhere in such numbers as in Java. They are brought to the Chinese market, where they are carefully cleaned before being offered for sale to the consumer. The addition of costly spices renders them one of the greatest delicacies of Chinese cookery, but as for themselves they are nothing better than a fine sort of gelatine.

The Japanese have long been aware that these costly birds' nests are in fact merely softened algæ. They consequently pulverise the proper species of sea-weeds, which are abundantly found on their own coasts, boil them to a thick jelly, and bring them to market under the name of _Dschin-schan_, as artificial birds'-nests. The Dutch call it Agar-agar, and make great use of it; simple boiling sufficing to convert the dried substance into a thick uniform jelly, which is both nourishing and easy of digestion. Thus we see that the algæ, which the Romans considered so perfectly worthless that, when they wished to express their utter contempt of an object, they declared it to be still viler than the vile sea-weed, are by no means deserving of so hard a sentence. Man himself might be much more justly reproached for neglecting the abundant stores of nourishment which nature has gratuitously provided for him on all flat and rocky coasts. For not only the species I have mentioned are eatable, but also some of the commonest fuci of our seas (_Fucus nodosus_, _F. vesiculosus_, _Laminaria saccharina_), as well as the gigantic alarias and durvilleas of the colder oceanic regions. And yet how rare is their use, notwithstanding the increasing wants of a rapidly growing population!

[Illustration: Surirella constricta.

A. Front view. B. Binary subdivision.--(Highly magnified.)]

Besides the larger forms of vegetation, the ocean contains a vast number of microscopical plants. Among these the most remarkable are the Diatomaceæ, simple vegetable cells enclosed in a flinty envelope, consisting of two plates closely applied to each other like the two valves of a mussel. The forms of these minute organisms are no less curious than those of the Foraminifera, for they exhibit regular mathematical figures, and their surface is often most delicately sculptured. Multiplying by spontaneous fissure, many of the Diatoms are met with entirely free after the process of duplicative subdivision has once been completed, while others, such as the Licmophora, or Fan-bearer, an elegant native species, habitually remain coherent one to another, producing clusters or filaments of various shapes, connected by a gelatinous investment or by a stalk-like appendage, which serves to attach them to other plants or to stones and to pieces of wood. Though individually invisible to the naked eye, they appear, when thus congregated, as patches of a green or brownish slimy mass, or as little glittering tufts a line or two in height. Some of their numerous species are natives of fresh water, but by far the majority are denizens of the sea, where they are found from the equator to the poles. The brown scum floating upon the surface of the antarctic waters near the mighty ice barrier which arrested Sir James Ross's progress to the south pole was found to consist almost solely of Diatomaceæ, and they are equally abundant in the Arctic Ocean.

It is remarked by Dr. Hooker that the universal presence of this invisible vegetation throughout the South Polar Seas is a most important feature, since there is a marked deficiency in this region of higher forms of vegetation, so that without the Diatoms there would neither be food for aquatic animals nor (if it were possible for these to maintain themselves by preying on one another) could the ocean waters be purified of the carbonic acid which animal respiration would be continually imparting to it. Thus it is not in vain that they abound in the most inhospitable seas, where but for them no sea-bird would flap its wings, and no dolphin dart through the desert waters.

[Illustration: Licmophora flabellata. (Highly magnified.)]

From the indestructible nature of their flinty coverings the Diatoms play a no less conspicuous part in the geological history of our globe than the calcareous Foraminifera.

Extensive rocky strata, chains of hills, beds of marl--once deposited at the bottom of the ocean, and raised by subsequent changes of level from the depth of the waters--contain the remains of these little plants in greater or less abundance. No country is destitute of such monuments, and in some they constitute the leading features in the structure of the soil. Under the whole city of Richmond, in Virginia, and far beyond its limits, over an area of unknown extent, they form a stratum of eighteen feet in thickness, and similar deposits are found to alternate in the neighbourhood of the Mediterranean with calcareous strata chiefly composed of Foraminifera. At first sight it may seem a gross exaggeration to attribute so vast an agency to beings individually so minute, but when we recollect how quickly they multiply by division, and how their activity dates from the first dawn of organic creation, their architectural powers no longer seem incredible. In forty-eight hours a single diatom may multiply to 8,000,000, and in four days to 140,000,000,000,000, when the silicious coverings of its enormous progeny will already suffice to fill up a space of two cubic feet. No wonder, then, that during the course of ages these microscopic plants have been able to form prodigious strata wherever circumstances favoured their propagation. In no case is the power of numbers more forcibly exemplified, for where can we find results more vast, proceeding from the infinite multiplication of the smallest individuals, than that whole tracts of country should literally be built up of the skeletons of Foraminifera and Diatomaceæ?

[Illustration: Hooded Merganser.]

CHAP. XX.

THE GEOGRAPHICAL DISTRIBUTION OF MARINE LIFE.

The Dependence of all created Beings upon Space and Time.--The Influences which regulate the Distribution of Marine Life.--The four Bathymetrical Zones of Marine Life on the British Coasts, according to the late Professor Edward Forbes of Edinburgh.--Abyssal Animals.--_Bathybius Haeckelii._--Deep-Sea Sponges and Shell-Fish.--Vivid Phosphorescence of Deep-Sea Animals.--Deep-Sea Shark Fishery.--The "Challenger."

The wanderer to distant lands sees himself gradually surrounded by a new world of animals and plants. On crossing the Alps, for instance, the well-known vegetable forms of our native country leave us one after the other; the beech, the fir, the oak, no longer meet the eye, or appear but rarely, and of more stunted growth, while in their stead citron and olive-trees decorate the landscape; and finally, on the shores of the Mediterranean the world of palms begins to disclose its beauties.

Thus during a long journey our early companions drop off one after the other, until at last we see ourselves surrounded by a crowd of new associates, who were strangers to us at the beginning of our pilgrimage.

We may cross the earth from pole to pole, or follow the sun in his diurnal course; in all directions, from north to south and from east to west, Nature will be found to change her garments as we proceed, and never to resume again those she has once cast off. The plants and animals of the temperate and cold regions of the north are different from those of the analogous regions in the southern hemisphere; and in the tropical zone each part of the world nourishes its peculiar inhabitants.

Similar changes meet our eye on ascending from the plains to the summits of high mountains. At the foot of Etna flourishes the luxuriant vegetation of a warmer sky, the palmetto (_Chamærops humilis_) and the pomegranate, even the cotton shrub and the sugar-cane; higher up, the cool shade of magnificent chestnut woods refreshes our path; then follows the stately oak; until finally we attain the dreary height where all vegetation ceases in the dreadful cold of an eternal winter. With every thousand feet we rise above the level of the sea, we seem to have advanced nearer and nearer to the pole.

This wonderful change of form, which decorates the various regions of the earth with such an endless variety of organised existence, alike prevails in the realms of ocean. Here we find every larger sea-basin nourishing its peculiar inhabitants, and discover at various vertical distances beneath the surface of the sea, changes in organic nature similar to those we observed at different distances above its level.

Thousands of extinct animal and vegetable forms, which have successively flourished and disappeared, teach us the important lesson, that all created beings are made but for a season. It is only during a determined epoch of planetary life that each genus or species finds that combination of outward circumstances, under which it is able to attain its highest perfection. But imperceptibly, in the course of ages, the external world modifies its nature; families once flourishing in a different atmosphere decline and wither; they are no longer able to maintain themselves against new forms of life starting up in all the vigour of youth, and disappear from the scene, supplanted by races which must one day vanish in their turn.

Organic life is no less dependent on place than it is on time. Of the numberless animal and vegetable forms that people the earth, each finds in only one spot the scene of its greatest size and its greatest profusion. Some endowed with a more pliable or energetic nature occupy a large space upon the surface of the globe; we find them in the enjoyment of healthy existence scattered far and wide over whole hemispheres, while others are obliged to content themselves with the narrowest birthplace, and are not seldom confined to a single bay, or a single mountain side.

A great part of the magic charm of nature is owing no doubt to this deep and mysterious connexion between the soil and its productions. Here all is harmony; we feel it in our hearts; and our eye delights in the consonance of forms and colours, as our ear in the concord of sweet sounds. And where is the mortal artist whose paintings could rival the ever-changing panorama which the Master of all worlds unfolds through all zones, from pole to pole? His pictures constantly fade away; but they are perpetually succeeded by new creations of equal beauty. Happy the man whose eye is open to their charms! Every ramble through the woods and fields is to him a banquet of pure and inexhaustible delight.

The causes which confine the life of animals and plants to circumscribed localities are in many cases easily to be traced. The warmth or coldness of the sea, resulting from currents, geographical position, and depth; tranquil or disturbed, pure or troubled waters; abundance or scarcity of food, solidity or softness of the ground, sufficiently explain why many species of marine animals appear in some places in considerable numbers, while in others they are totally wanting. A superficial view of their organisation often shows us at once the physical properties their _habitat_ must necessarily possess. By looking at a fucus we immediately see whether it requires the protection of tranquil waters, or is able to bid defiance to the floods; whether it is made to anchor upon the rock, or to sink its roots into a more yielding soil.

In many cases, however, the causes which regulate the distribution of the sea-animals are still enveloped in darkness, and we no more know why the tropical seas bring forth in some places numerous coral-reefs, and none at all in other to all appearance just as favourably situated localities, than we do why the tea-plant is confined to a small corner of Asia, or the Peruvian cinchonas to a narrow girdle on the Andes.

Evidently, besides the influences known to us, there are many other hidden ones at work, whose conflicting powers draw round every living creature a mysterious circle, whose bounds it is unable to transgress. Their discovery belongs to the future, and certainly forms one of the most interesting subjects for the naturalist's inquiries.

The geographical distribution of the terrestrial plants and animals is undoubtedly much easier to be ascertained than that of the denizens of the ocean. The naturalist is able to climb the highest mountains beyond the extreme limit of vegetation, and far above their most towering peaks his eye, piercing the transparent atmosphere, sees the condor soar in solitary majesty; he can wander through the deepest glens, or even, penetrating into the bowels of the earth, examine and collect the forms of the subterranean flora; but it has not been given him to perambulate the submarine meads, or to force his way leisurely through dense thickets of algæ, and explore their hidden wonders.

Yet, in spite of these natural impediments, his inventive genius, fired by his insatiable avidity of knowledge, has given him the means of interrogating the abyss, and partly raising the veil behind which marine life conceals its secret operations. Armed with a dredge, he fetches from the bottom of the sea plants, polypi, mollusks, and annelides, and learns to distinguish the various depths assigned for their abode; or he puts on the helmet of the submarine diver, and passes whole hours in collecting and observing beneath the clear waters of the sea; or he drops the plummet hundreds of fathoms deep into the ocean, and draws it up again coated with specimens of corals or Foraminifera.

To the late Professor Edward Forbes of Edinburgh science is indebted for the first investigations of this nature that have been undertaken on a greater scale; and, to give the reader some idea of the causes which regulate the distribution of marine life, I cannot do better than cite a few of the general results of that eminent naturalist's researches.[U]

[Footnote U: Natural History of the European Seas, by the late Professor E. Forbes. Edited by R. Godwin Austen, 1859.]

As the animals and plants of the land are grouped together into distinct zoological and botanical provinces, so likewise is the population of the sea gathered into geographical groups, which, though well marked in their more central and most developed portions, imperceptibly merge at their margins into those of neighbouring realms. "These submarine provinces have a more or less direct correspondence with those of the neighbouring lands, though sometimes they differ very considerably from the latter in their extent; since the physical features which may constitute boundaries in the one, may not be sufficiently extended or developed in the other to impede the spread of peculiar species of animals or plants. Marine creatures, owing to their organisation and the transporting powers of the element in which they live, are much more capable of diffusion, as a whole, than the terrestrial organisms; hence we should expect to find the regions they respectively inhabit, beneath the waves, of much vaster dimensions than those occupied by similar geographical assemblages of their terrestrial brethren; and such is to a great extent true. Nevertheless, the inequalities of the sea-bed, the modifications of the temperature of the ocean produced by currents pouring through it like mighty rivers, the projection of promontories, and the more important interruptions caused by the great gulfs and abysses of the deep, or by vast and comparatively desert tracts of unprolific sand, which in many places are spread out in extensive shallows, are all-powerful influences, determining their diffusion within certain and more or less defined limits."

The _structure of the coast_, as far as the mineral character of its rocks is concerned, may seriously affect the distribution of particular tribes. Since many shell-fish, for instance, bore only in limestone or rocks containing abundance of lime, a very ordinary difference in the nature of the strata must necessarily determine their presence or absence.

The _outline of a coast_ has also great influence in regulating the diffusion of species. A much indented region is very favourable to submarine life; a straight coast-line, exposed to the full rolling of the surf, is usually unfavourable, though there are a few creatures which delight in the dash of the waves, and hardily, though some of them are small and exceedingly delicate, brave the full force of the ocean storms, reminding us, as Mr. Godwin Austen quaintly remarks, "of those sturdy people, not uncommon in this stormy life, who thrive best in troubles, and feel happiest under conditions that make most men miserable."

The _nature of the sea-bottom_, according as it consists of mud, sand, gravel, nullipore, broken shells, loose stones, or rock, determines, to a great extent, the presence or absence of peculiar forms of shell-fish and other invertebrata, and of fish also, since the distribution of the food regulates that of the devourers.

The _rise and fall of the tides_ are most important in determining the presence or absence of the species inhabiting the littoral zone. The _currents_, besides their agency as modifiers of climate, act as means of transport, by carrying the germs and larvæ of numerous creatures from region to region.

The _influence of climate_ is conspicuously manifested in the diminution of the number of genera and species as we proceed northwards to the Icy Ocean.

The _composition of the waters_ has also a most important effect on the distribution of aquatic animals, as the degree of saltness or freshness determines the presence or absence of numerous forms of both fishes and invertebrate animals; and last, not least, the _influence of depth_, in which _pressure_ and the _diminution of light_ are doubtless important elements, is everywhere manifest over the ocean, "for everywhere we find creatures, whether animal or vegetable, distributed in successive belts or regions, from high-water mark down to the deepest abysses from which living beings have been drawn up. Peculiar types inhabit each of the zones, and are confined within their destined limits, whilst others are common to two or more, and not a few appear capable of braving all bathymetrical conditions. Nevertheless, so marked is the appearance of the inhabitants of any given region of depth, that the sight of a sufficient assemblage of them from any one locality will enable the naturalist at once to declare the soundings within certain limits, and without the aid of line or plummet."

In the British seas _four_ distinct and well-marked zones of life succeed each other in vertical extension. The first of these is the _littoral zone_, equivalent to the tract between tide-marks, but quite as manifest in those portions of the coast-line where the tides have a fall of only a foot or two, or even less, as in districts where the fall is very great. This important belt, which again forms four subdivisions, and is inhabited by animals and plants capable of enduring periodical exposure to the air, to the glare of light, the heat of the sun, the pelting of rain, and often to being more or less flooded with fresh water when the tide has receded, claims many genera as well as species peculiar to itself. "The verge of continual air is generally distinguished by the abundant presence of _Fucus canaliculatus_, among whose roots may be found crowds of small varieties of the periwinkle, called _Littorina rudis_, which indeed range out of the water considerably, and may be found adhering to rocks many feet above high-water mark." The second sub-region is marked by the abundance of a small dark rigid sea-weed, called _Lichina_, painting the rock sides as if with a dingy stripe. With it we find the larger forms of _Littorina rudis_, abundance of the common limpet (_Patella vulgata_), the common mussel (_Mytilus edulis_), and myriads of small seaside barnacles, often striping the sea-wall in a broad white band. "Where the shore shelves a little, and rocky ledges decline gradually into the sea, the common mussel delights to live, firmly anchored by its byssal cable in the crevices of rocks or among masses of gravel, the pebbles of which are tied together by its silky filaments." The rock sides and the floors of transparent pools are here often thickly coated with a nullipore, forming a hard pale red crust. The region of half-tide forms a third subdivision of the littoral zone, and is exceedingly prolific in marine animals and plants. "Here we find _Fucus articulatus_, with its graceful even-edged rich brown fronds, mingled occasionally with the less elegant _Fucus nodosus_. Here limpets throng, and dog-periwinkles (_Purpura lapillus_) crawl observantly, seeking to bore more passive mollusks and extract their juicy substance. This is the home of the best of periwinkles, the large black _Littorina littorea_, gathered in thousands for the London market. On our western coasts we find it in company with the purple-striped top-shell (_Trochus umbilicatus_), and towards the south with the larger _Trochus crassus_. Here also sea-anemones love to expand their many-armed disks, often glowing with the most brilliant colours." A fourth sub-region succeeds, the lowest belt above low-water mark, and is distinguished by the presence of the black saw-toothed sea-weed (_Fucus serratus_), so much used in the packing of lobsters for market. On its fronds creeps the lowest in grade of the periwinkles, the variously tinted _Littorina neritoides_, exhibiting every colour in its obtuse and thickened shell.

[Illustration: Limpet.]

[Illustration: Periwinkle.]

"At the verge of low-water mark, immediately below it, wherever the coast is rocky, there are all round the British shores, within a space of a few inches, a remarkable series of more or less distinctly defined belts, each consisting of a different species of sea-weed. These in succession are, the _Laurencia pinnatifida_ uppermost; then the green _Conferva rupestris_; then the elegant and firm, often iridescent, fronds of _Chondrus crispus_; and, lowermost, the thong-weed or _Himanthalia lorea_."

Succeeding the shore-band, or littoral zone, we have the _region of the great laminaria or tangle forests_, or in sandy places the waving meadows of zostera, or grass-wrack. It extends from the edge of low water to a depth varying in different localities, but seldom exceeding fifteen fathoms, and is itself divided into sub-regions, marked by belts of differently tinted algæ. This zone above all others swarms with life, and is the chief residence of fishes, mollusks, crustaceans, and invertebrata of all classes, remarkable for brightness and variety of colouring. "Here," says Mr. Godwin Austen, "is the chosen haunt of the nudibranchiate mollusks, animals of exceedingly delicate texture, extraordinary shapes, elegance of organs, and vividness of painting. Their bodies exhibit hues of a brilliancy and intensity such as can match the most gorgeous setting of a painter's palette. Vermilion red, intense crimson, pale rose, golden yellow, luscious orange, rich purple, the deepest and the brightest blues, even vivid greens and densest blacks, are common tints, separate or combined, disposed in infinite varieties of elegant patterns, in this singular tribe. Our handsomest fishes are congregated here, the wrasses especially, some of which are truly gorgeous in their painting. Here are gobies and more curious blennies, swimming playfully among these submarine groves. Strange worms crawl serpent-like about their roots, and formidable crustacea are the wild beasts who prowl amid their intricacies. The old stalks, and the surfaces of the rocky or stony ground on which they usually grow, are incrusted like the trunks of ancient trees or faces of barren rocks with lichenous investments. But whereas in the air these living crusts are chiefly if not all of vegetable origin, in the sea they are more often constructed out of animal organisms. Some of them are sponges, others are true zoophytes, others polyzoa or bryozoa, beings that have proved to belong to the class of mollusks, however unlike they may seem to shell-fish.

"In the middle and lower part of the Laminarian region around our shores the tangles become less plentiful as we descend, and at last become exceptional and disappear. But other sea-weeds are very abundant, especially those that delight in red or purple hues. Tender sea-mosses, exquisitely delicate in form and colouring, abound. Where none of these are very plentiful, we often find the coral-weed or nullipore in vast quantities, and assuming many strange modifications of form. Among these vegetable corals numbers of shells and articulate animals delight to live, and probably not a few feed upon their stony fronds. The Lima, a shell-fish related to the scallop, gathers the broken branches by means of prehensile tentacles, and constructs for itself a comfortable nest lined with a woven cloth of byssal threads. Numerous fishes resort to these rugged pastures in order to deposit their spawn among the gnarled branchlets."

To the laminarian succeeds the _coralline zone_, extending in most places some thirty fathoms or more. Plants, indeed, are rare, but here the horny plant-like sertularias love to rear their graceful feathery branches, and form miniature gardens of fairy-like delicacy and beauty; and here carnivorous mollusks, whelks above all, prowl in great numbers. Bivalves of remarkable elegance, especially clams and scallops, are found buried in multitudes beneath its gravels and muddy sands; and no less plentifully congregate the spider-crabs, with many other peculiar crustaceans. As a natural consequence of this well-furnished table, fishes abound, and many of our deep sea and white fisheries owe their value to the zoological features of the coralline zone.

Last and lowest of our regions of submarine existence is that of _deep-sea corals_, so named on account of the great stony zoophytes characteristic of it in the oceanic seas of Europe. Many sea-stars and sea-urchins are likewise found in this region, in the depths of which the number of peculiar creatures is few, yet sufficient to give it a marked character.

[Illustration: Whelk.]

[Illustration: Gurnard.]

The aspect of the British submarine fauna is in general more remarkable for elegance of form and neat simplicity than for glaring or vivid hues. "The smaller kinds of sponges are not seldom brilliantly dyed, but the more conspicuous kinds are tawny or brownish. The sea-anemones are elegantly variegated with rich colours, but the majority of zoophytes are not strikingly tinted. The star-fishes, as a group, are most remarkable among the invertebrata for gorgeous painting, but our sea-urchins are sombre when compared with their relatives from warmer seas. The jelly-fish are occasionally tinged with delicate hues, and some of the smaller kinds even showily ornamented; but those which most figure in our waters are not conspicuous on account of colour, however elegant in their contours. Our marine shells, though often pretty, are not gaudy or attractive, except in rare instances. The same may be said with almost equal truth of our marine crustaceans, though, on close inspection, the elegance of device on the carapaces of many species is exceedingly admirable."

Our fishes are not distinguished by brilliancy of colour. "Their hues are quaker-like, though sufficiently lustrous for sober tinting. The cod and flounder tribes are among the most characteristic, and such of the more common fishes as belong to families of which we have but few representatives are in most instances clothed in sober grey and silver. Beauty of no mean description may, however, be displayed by these modest vestments; as, for instance, in the mackerel and the herring. Our gorgeously decorated wrasses form the chief exception to the general rule, but these belong to a family more characteristic of the southern seas. A like deficiency in the numbers of the gurnard and mackerel tribes seriously affects the aspect of our piscine fauna when compared with denizens of the Mediterranean." The sharks and rays too are comparatively deficient, although a few species, as we have seen in a former chapter, are, to the great annoyance of our fishermen, over-abundant. The sea-eels are also few, though in the common conger and the larger sand-eel (_Ammodytes lancea_) we have two very conspicuous species.

[Illustration: Sand-Eel.]

[Illustration: Grey Mullet.]

[Illustration: Red Mullet.]

[Illustration: Salmon.]

As the surface of the British islands exhibits a transition as it were from a northern to a southern character, from the firs of Scotland to the free-growing myrtles of the Devon coast, so the inhabitants of our seas pass through a great variety of form, from a northern to a southern type. While the rorqual of the Frozen Ocean not seldom strands on our northern and eastern coasts; the flying-fish of the equinoctial seas sometimes appears within view of our southern shores; and it is this peculiar position of our insular empire, fronting the colder and the warmer seas, which enriches its waters with such a variety of marine life. "Several characteristic boreal forms find their southern limit within the northern half of our waters, and there some of the most striking and abundant kinds are chiefly developed in numbers, such as the cat-fish or sea-wolf (_Anarhicas lupus_), the scythe (_Merlangus carbonarius_), the ling (_Lota molva_), the cod (_Gadus morrhua_), the lump-sucker (_Cyclopterus lumpus_), and even the herring (_Clupea harengus_). On the other hand, along the southern shores of England we find fishes becoming frequent which are distinctly of a southern type, such as the grey and red mullets (_Mugil cephalus_ and _Mullus barbatus_), the sea-bream, and, far more plentifully, the John Dory (_Zeus aper_) and the pilchard (_Clupea pilchardus_)."[V]

[Footnote V: Godwin Austen, Natural History of the European Seas, pp. 103, 104.]

Although very inferior in beauty to the tropical fishes, our finny tribes are far superior in flavour, and may well challenge the world to produce their equals for the table. The turbot, cod, whiting, herring, whitebait, mackerel, sole, and even the salmon, though it belongs rather to fluviatile history than to the chronicles of the sea, may fairly be cited to testify to the truth of this assertion; so that surely we have no reason to complain of having been but indifferently provided for in the geographical distribution of fishes, which of all marine productions are the most important to man.

The researches of Forbes led him to believe that "as we descend deeper and deeper, the denizens of the sea become fewer and fewer, indicating our approach towards a silent and desolate abyss, where life is either extinguished or exhibits but faint glimmerings to mark its lingering presence;" but subsequent deep-sea soundings, performed with improved dredging apparatuses, have led to the surprising result that the bottom of the ocean, even in its abyssal depths, far from being a dreary void, as was formerly imagined, is in reality a busy scene, absolutely teeming with life. And in this case, as in so many others, we have a fine instance of the truth of the observation that every new invention or discovery casts a new light upon some other province of human knowledge; for to the submarine telegraph we are indebted for the first certain proof of the existence of highly organised animals living at abyssal depths.

In 1860 the submarine cable between Sardinia and Bona, on the coast of Africa, having completely failed, was picked up from a depth exceeding one thousand fathoms, and found encrusted with various shells and corals. All previous observations with reference to the existence of living creatures at extreme depths had been liable to doubt from two sources. In the first place the methods of deep-sea soundings were still so imperfect that there was always a possibility, from the action of deep currents upon the sounding-line or from other causes, of a greater depth being indicated than really existed; and, secondly, there was no absolute certainty that the animals entangled on the sounding instrument had actually come up from the bottom. They might have been caught on the way.

But now all doubt was removed. A submarine cable lies on the ground throughout its whole length. Before laying it, its course is carefully surveyed and the real depth accurately ascertained. Fishing it up is a delicate and difficult operation, and during its progress the depth is checked again and again. When, therefore, as in this case, the animals dragged up with a cable from depths of upwards of one thousand fathoms are found, not sticking loosely to it, but moulded upon its outer surface, or cemented to it by horny or calcareous excretions, it is evident that they must have lived and grown upon it at the bottom of the deep sea.

The subsequent dredging cruises of H.M.SS. "Porcupine" and "Lightning" in 1868, 1869, and 1870, under the scientific direction of Dr. Carpenter, Professor Wyville Thomson, and Mr. Gwyn Jeffreys, afforded additional and convincing proofs that life abounds in the abyssal regions of the ocean. During these several cruises 57 hauls of the dredge were taken at depths beyond 500 fathoms, and 16 at depths beyond 1,000 fathoms, and in all cases life was abundant. In 1869 two casts were taken in depths greater than 2,000 fathoms, and proved equally successful in bringing up specimens of deep-sea life. With the deepest cast, 2,435 fathoms, off the mouth of the Bay of Biscay, living, well-marked, and characteristic specimens of all the five invertebrate sub-kingdoms were taken. "And thus," says Professor Wyville Thomson,[W] "the question of the existence of abundant animal life at the bottom of the sea has been finally settled, and for all depths, for there is no reason to suppose that the depth anywhere exceeds between three and four thousand fathoms; and if there be nothing in the conditions of a depth of 2,500 fathoms to prevent the full development of a varied fauna, it is impossible to suppose that even an additional 1,000 fathoms would make any great difference."

[Footnote W: The Depths of the Sea. London, 1873.]

It may be asked how the deep-sea animals bear the enormous pressure at these great depths, which seems at first sight alone sufficient to put any idea of life out of the question? There was a curious popular notion that on descending deeper and deeper the sea water became gradually, under the pressure, heavier and heavier, so that at last it became more weighty than molten gold. But water is, in fact, almost incompressible; so that its density at 2,000 fathoms is scarcely appreciably increased. Any free air suspended in the water, or contained in any compressible tissue of an animal at 2,000 fathoms, would of course be reduced to a mere fraction of its bulk; but the animals subject to the pressure of the deep seas, being permeated throughout their whole organisation by incompressible fluids at the same pressure, are consequently as capable of bearing it as we do the pressure of the atmosphere. The absence of light seemed another circumstance incompatible with the existence of animal life at abyssal depths, as all plants depend upon light for their growth, and their absence apparently involves that of vegetable food, which, as we all know, forms everywhere the substratum of animal existence. We have as yet very little exact knowledge as to the distance to which the sun's light penetrates into the water of the sea. According to some recent experiments it would appear that the rays capable of affecting a delicate photographic film are very rapidly cut off, their effect being imperceptible at the depth of only a few fathoms; and though probably some portions of the sun's light possessing certain properties may penetrate to a much greater distance, it is certain that, beyond the first fifty fathoms, plants to whose existence light is essential are barely represented, and after two hundred fathoms entirely absent.

But though plant-life is thus limited to the more superficial parts of the ocean, the analysis of sea water, taken in all localities and at all depths, has shown that it everywhere contains a very appreciable and very uniform quantity of organic matter in solution and in suspension. It is thus quite intelligible that numberless protozoa--whose distinctive character is that they are capable of being supported by the absorption of organic matter through the surface of their bodies--are able to exist in the dark abysses of the sea, and in their turn afford nourishment to more highly organised animals.

After these general remarks on the creatures of the deep, I will now give a brief account of their various groups.

Over an enormous extent the abyssal ocean bottom is found covered with a sheet of almost formless beings, absolutely devoid of internal structure, and consisting merely of living and moving expansions of jelly-like matter. Whether this form of life, still more simple than the Amœba,[X] to which Professor Huxley has given the name of _Bathybius Haeckelii_, be continuous in one vast sheet or broken up into circumscribed individual

## particles, it is equally an object of wonder; and as no living thing,

however slowly it may live, is ever perfectly at rest, it shows us that the bottom of the sea is, like its surface, the theatre of perpetual change.

[Footnote X: See