THE GEOGRAPHICAL DISTRIBUTION OF MARINE LIFE.

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]

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.

"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.

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.

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]

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."

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 Amoeba,[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.

Living among and upon this Bathybius we find a multitude of other protozoa, foraminifera and other rhizopods, radiolarians, and sponges.

Such is the countless number of the Foraminifera inhabiting the deep seas, that their remains form the chief mass of the soft oozy bottom of the ocean. In the surface layer of the deposit the shells of Globigerina bulloides, the prevailing species, are found fresh, whole, and living, and in the lower layers dead and gradually crumbling down by the decomposition of their organic cement and by the pressure of the layers above. Countless generations are thus piled one upon the other; and each successive stratum, weighing upon those of older date, is laying the foundation of future rocks, which subsequent revolutions may perhaps heave out of the deep and raise in towering pinnacles to the skies.

Sponges[Y] of wonderful beauty and lustre appear to extend in endless variety over the whole of the bottom of the sea. Some (Holtenia Carpenteri) anchor in the ooze by means of a perfect maze of delicate glassy filaments, like fine white hair, spreading out in all directions through the sea's fluid mud; while others (Hyalonema) send right down a coiled whisp of strong spicules, each as thick as a knitting-needle, which open out into a brush as the bed gets firmer, and fix the sponge in its place somewhat on the principle of a screw-pile. "A very singular sponge, from deep water off the Loffoden Islands, spreads into a thin circular cake, and adds to its surface by sending out a flat border of silky spicules, like a fringe of white floss silk round a little yellow mat; and the lovely Euplectella, whose beauty is imbedded up to its fretted lid in the grey mud of the seas of the Philippines, is supported by a frill of spicules standing up round it like Queen Elizabeth's ruff."[Z]

The stalked sea-stars, which, as the fossil pentacrinites and encrinites testify, abounded in the past periods of the earth's history, were, until now, supposed to be on the verge of extinction; but when we consider that the first few scrapes of the dredge at great depths have brought new species to light, we are entitled to believe that they constitute an important element in the abyssal fauna, and probably pave large tracts of the sea-bottom with a carpet of animated flowers. Freely-moving sea-stars and sea-urchins have likewise been hauled up in great numbers from abyssal depths; crustaceans have not been found wanting, and the captured shell-fish have shown that the deep-sea molluscs are by no means deficient in colour, though as a rule they are paler than those from shallow water.

Dacrydium vitreum, dredged from 2,435 fathoms, a curious little mytiloÏd shell-fish, which makes and inhabits a delicate flask-shaped tube of foraminifera and other foreign bodies cemented together by organic matter and lined by a delicate membrane, is of a fine reddish-brown colour dashed with green, and the animals of one or two species of Lima from extreme depths are of the usual vivid orange scarlet.

Some of the abyssal molluscs have even been found provided with organs of sight. A new species of Pleurotoma, from 2,090 fathoms, had a pair of well-developed eyes on short foot-stalks, and a Fusus from 1,207 fathoms was similarly provided. The presence of organs of sight at these great depths leaves little room to doubt that light must reach even these abysses from some source, and as from many considerations it can scarcely be sunlight, Professor Wyville Thomson throws out the suggestion "that the whole of the light beyond a certain depth may be due to phosphorescence, which is certainly very general, particularly among the larvÆ and young of deep-sea animals."

Thus many of the creatures dredged in the Northern Atlantic, off the west coast of Ireland,[AA] in depths varying from 557 to 584 fathoms, were most brilliantly phosphorescent. In some places nearly everything brought up seemed to emit light, and the mud itself was perfectly full of luminous specks. The alcyonarians, the brittle-stars, and some annelids were the most brilliant. The PennatidÆ, the VirgulariÆ, and the GorgoniÆ shone with a lambent white light, so bright that it showed quite distinctly the hour on a watch, while the light from Ophiacantha spinulosa was of a brilliant green, coruscating from the centre of the disk, now along one arm, now along another, and sometimes vividly illuminating the whole outline of the star-fish. While the Ophiacantha shines like a star of the most vivid uranium green, the sea-pen (Pavonaria quadrangularis) is resplendent with a pale lilac phosphorescence like the flame of cyanogen gas, not scintillating like the green light of Ophiacantha, but almost constant, sometimes flashing out at one point more vividly, and then dying gradually into comparative dimness, but still sufficiently bright to make every portion of the polyp visible.

Such numbers of the Pavonaria were brought up at one haul of the dredge in the Sound of Skye, that the "Porcupine" had evidently passed over a forest of them. While the darkness of winter frowns over the surface of the Northern Atlantic, the animated shrubs at its bottom are thus glowing with light, and a kind of magical day prevails in depths which were supposed to be shrouded with perpetual night. But it might have been better for many of the luminous denizens of the abyss if a more obscure existence had been their lot; for in a sea swarming with predaceous crustaceans with great bright eyes phosphorescence must surely be a fatal gift.

Off the coast of Portugal there is a great fishery of sharks (Centroscymnus Coelolepis), carried on at a depth of 500 fathoms. If an animal so highly organised as a shark can thus bear without inconvenience the enormous pressure of more than half a ton on the square inch existing at that depth, it is a sufficient proof that the pressure is applied under circumstances which prevent its affecting it to its prejudice, and there seems to be no reason why it should not tolerate equally well a pressure of one or two tons, or why many other fishes—though the dredge, in consequence of their facility of locomotion, will hardly ever be able to bring them to light—should not abound in the still waters of the abyssal deep.

The "Challenger" Exploring Expedition will no doubt reveal to us still many an unknown wonder of those interesting regions, and make us acquainted with a world of new animals which even the profundity of the ocean vainly strives to hide from the curiosity of man.