Chapter VII: Zoantharia, or Animal Flowers (1)

"I saw the living pile ascend
The mausoleum of its architects,
Still dying upwards as their labour closed:
Slime the material, but the slime was turned
To adamant by their petrific touch."

MONTGOMERY'S _Pelican Island_.

The zoophytes which constitute the class _Zoantharia_ are quite great personages. Some of them are eighteen or twenty inches long; at the same time, others scarcely exceed the eighth part of an inch in length. They live in all seas, and seem to have existed through many ages of the earth's history; they appear at an early geological period, and they have performed an important part in its formation; we shall see that, with great numbers of them, parts cut off from their bodies continue to live and become new individuals.

The name of _Zoantharia_ was first given to the class by Gray; but here we give it a somewhat wider signification, embracing under it the madrepores and starred stones of Lasueur, who is reminded of a field enamelled with small flowers when he sees the little polyp of _Porites Astroïdes_ in full blow. "But it is only," says Johnston, "when they lie with their upper disk expanded, and their tentacula displayed, that they solicit comparison with the boasts of Flora; for, when contracted, the polyp of the madrepores conceal themselves in their calcareous cups, and the actiniæ hide their beauty, assuming the shape of an obtuse cone or hemisphere of a fleshy consistence, or elongating themselves into a sort of flabby cylinder that indicates a state of relaxation and indolent repose."

These zoophytes are flesh-eaters, and consume quantities truly prodigious, of animals such as the crustaceans, worms, and small fishes. They are all marine, nearly all attached to the same spot for life, and they live in colonies. Some few are isolated and live by themselves, either free or attached to the soil. They differ altogether from the animals belonging to the _Alcyonaria_ by their disposal of, and mode of multiplying, tentacula. These appendages in the _Zoantharia_ never present the _bipinnate_ arrangement which is observable in the _Alcyonaria_. They are habitually simple, and, if they present ramifications, these are only exceptional. In nearly every instance, the tentacles exist to the number of twelve, eighteen, twenty-four, and even larger numbers, which form a sort of concentric crown to the animal.

_Zoantha thalassanthos_ (Lesson), which has given its name to the group, consists of large turf-like tufts of coral attached to a rock. Its animalcules are packed closely together, and their expanded flower-like heads have a curious resemblance to a mass of flowers in full bloom. They are borne on bending root-like stems of pure white, interlacing one with the other, surmounted by a fusiform or spindle-shaped body, pediculate and swelling towards the middle, but truncate at the summit, of a reddish-brown colour, marked with longitudinal stripes more highly coloured; its consistence is firm and parchment-like. From the body issues a tube, narrow, muscular, contractile, and red in colour, terminating at the summit in eight elongated arms or tentacula, of a pure yellow, traversed by a nervure of the same colour. The edges of these arms are fringed with fine pinnæ, parallel to each other, of a bright maroon colour, and resembling the barbs of a feather. According to Lesson, the arms of this _Zoantha_ are kept unceasingly in motion, which produces in the water small oscillating currents, in the course of which the animalcules on which the polyps feed are precipitated into the stream leading to their mouths.

The tendency to produce a calcareous polypidom is a property almost universal with animals of this class. Zoologists are agreed in dividing them into three very distinct orders--namely, the ANTIPATHIDÆ, consisting of the genera _Antipathes_, _Cirripathes_, and _Seipathes_, in which the polypidom is of a horny consistence; the MADREPORIDÆ, in which the polypidom is calcareous and stony; finally, the ACTINIDÆ, which produce no polypidom.

ANTIPATHIDÆ.

We need not dwell upon this group, which is comparatively uninteresting. They correspond with the family of _Gorgonidæ_ among the _Alcyonaria_, which they resemble in having the central axes branching after the manner of a shrub; but the polyps have the mouth surrounded with a crown of six simple tentacula. The axis is of a harder and denser tissue than that of the Gorgons, and presents on its surface small spiniform projections. The polypiferous crust, with which they are covered, is in general very arenaceous, and is so easily detached, that it is rare to see in collections anything but the denuded skeleton of the colony. In _A. arborea_, the polypidom is fragile and brittle; when dry, the branches, always slender and delicate, resemble the barbs of a feather. The colour is of a deep black, or rather bistre and _terra de sienna_ tint. Under a powerful lens, the extremities of the branches appear to be covered with small spines, and the trunk is formed of oval and irregular concentric beds, which are the zones of growth. Its consistence is firm, so that it can be worked up and converted into chaplets for pearls and other bijouterie: it is known in commerce as _black coral_.

MADREPORIDÆ.

The _Madrepora_ are better known than their congeners. They are sometimes, but erroneously, designated corals, since the coral forms no part of this group.

The Madrepores are remarkable for the calcareous crust which always surrounds their tissue, and determines the formation of their polypidom. They are in other respects easily recognized by the star-like structure of their polypidom, in which may always be distinguished a visceral chamber, the circumference of which is furnished with perpendicular laminæ or partitions, which are always directed towards the axis of the body. When sufficiently developed they constitute, by their assemblage, a star-like body formed of a great number of rays. The polypidom is always calcareous. The consolidation of the envelope of each polyp produces at first a kind of sheath, to which Milne Edwards has given the name of the wall. The partitions which proceed from the interior towards the axis of the visceral chamber occupy the subtentacular cells; the terminal and open portion designated the calyx is in organic continuity with the polyp, which has retired thither more or less completely as into a cell.

Milne Edwards remarks that the polypidom of the _Madrepora_ present in their structure five principal modifications, due in part to the fundamental number of which the chambered cells are the multiple, and in part to the mode of division in the visceral chamber, and finally to the manner in which its tissue is constituted. M. Edwards avails himself of this peculiarity of structure in order to divide the Madrepores into fixed sections; namely, _Madrépores apores_, _Madrépores perforés_, _Madrépores tabulés_, _Madrépores tuberleux_, and _Madrépores rugueux_. In the group of Aporous Madrepores, the polypidom is perhaps the most highly organized. We find there a well-developed and very perfect wall, and a well-developed visceral apparatus. The calyx is neatly starred; the number of rays in the earlier stages being six, which soon afterwards reach from twelve to twenty-four. The cells between the chambers are sometimes open in all their depth, sometimes more or less shut up by transverse plates; these, being independent of each other, are never reunited in the breadth of the visceral cavity, so that they constitute discoid plates such as we find in _tabular_ and _rugose_ Madrepores.

The animals belonging to this group, which may be characterised as _stelliform_ or star-like, are very abundant in every sea, and in several geological formations. They constitute many families, among which may be noted the MILLEPORINA of Ehrenberg, the polypidom of which Dr. Johnston describes as "calcareous, fixed, plant-like, branching or lobed, with cells scattered over the whole surface, distinct, sunk in little fosses, obscurely stellate, the lamellæ narrow and almost obsolete." (JOHNSTON'S _Zoophytes_, vol. i. p. 194.) In _Turbinolia_, the animal is simple, conical, striped, furrowed externally with larger and smaller ribs, the mouth surrounded by numerous tentacula, and solidified by a calcareous polypidom, which is free, conical, and also furrowed externally; attenuated at the base, but enlarged at the summit, and terminating in a shallow radiated lamellar cup or cell. Several species have been dredged off the coast of Cornwall, and the west coast of Scotland and Ireland.

_T. melletiana_ is described as coral-white, wedge-shaped, somewhat compressed, with interspaces or ribs equidistant, smooth, and glossy. Above, the ribs turn over the edge, and are continued into the centre of the enlarged cup, forming its lamellæ. "That the zoophyte must have lived for some time after having become a movable thing, is proved," says Dr. Johnston, "by the ribs being continued beyond or round the point of attachment." The specimen here described was dredged alive, and Professor Forbes says of it that "it is a most interesting and beautiful species, the more so as it is certainly identical with Defrance's _Turbinolia melletiana_, found in both the crag formations."

The _Caryophilliæ_ (Lamarck), from καρύα, a nut, and ϕύλλου, a leaf, have the polypidom permanently fixed, simple, striated longitudinally, and the summit hollowed into a lamellated star-like cup; the animal, actinia-like, is provided with a simple, or double crown of tentacula, projecting from the surface of star-like, cylindrical, cone shaped cells. In _C. cyathus_ (Lamarck) (Fig. 66), which inhabits the Mediterranean, the polyps are of a greyish colour, the tentacula streaked with black. The polypidom is erect and upright, sometimes cylindrical, and generally so firmly attached to the rock as to seem a part of it. The lamellæ are of three kinds: one large and prominent, between every pair of which there are three, sometimes five, smaller ones, the centre one being divided into two portions forming an inner series. The lamellæ are arched entire and striated on the sides, whence the margin appears somewhat crenelated. "It is found," says Mr. Couch, "of all sizes, from a mere speck to an inch in height. In a very young state, it is sometimes found parasitical on _Alcyonium digitatum_, on shells, and on the stalks of sea-weeds; but as these substances are very perishable, and offer no solid foundation, large specimens are never found on them. In its young state the animal is naked, and measures about the fifteenth of an inch in diameter, and about the thirty-second of an inch in height. In the earliest state in which I have seen the calcareous polypidom, there were four small rays, which were free or unconnected down to the base; in others I have noticed six primary rays, but in every case they were unconnected with each other. Other rays soon make their appearance between those first formed; they are mere calcareous specks at first, but afterwards increase in size. The first union of rays is observed as a small calcareous rim at the base of the polyp, which afterwards increases in height and diameter with the age of the animal."

The animals of this interesting polypidom are vividly described by Dr. Coldstream, in a communication to Dr. Johnston, as he observed them at Torquay:--

"When the soft parts are fully expanded," he says, "the appearance of the whole animal closely resembles an actinia. When shrunk, they are almost entirely hid amongst the radiating plates. They are found pendent," he adds, "from large boulders of sandstone, just at low-water mark. Sometimes they are dredged from the middle of the bay. Their colour varies considerably. I have seen the soft parts white, yellowish, orange-brown, reddish, and of a fine apple-green. The tentacula are usually paler."

The _Caryophilliæ_ are sometimes dredged from great depths; Professor Travers dredged one in eighty fathoms, and Dr. Johnston remarks that the existence of an animal so vividly coloured at so great a depth is worthy of remark. "When taken," says the professor, "the animal was scarcely visible, being contracted; when expanded, the disk was conspicuously marked by two dentated circles of bright apple-green, the one marginal and outside the tentacula, the other at some distance from the transverse and linear mouth. In the dark, the animal gave out a few dull flashes of phosphorescent light."

In addition, we may mention the assertion of Mr. Swainson, that _C. ramea_, common in the Mediterranean, is occasionally found on the Cornish coast; but Dr. Johnston thinks it improbable that it could have escaped the attention of Mr. Couch and Mr. Peach, had it been so.

As belonging to this family, we present here illustrations of _Flabellum pavoninum_, Lesson (Fig. 67).

1. Vertical position.
2. Upper edge, with its plates and median thread.
3. Form of the animal.
]

Of the _Occulinæ_, the animal is unknown, but it is contained in regular round radiated cells, more or less prominent, and scattered on the surface of a solid, compact, fixed tree-like coral. The individuals dispose themselves in ascending spiral lines, and appear to be regularly dispersed on the surface of the several branches. The typical species, _O. virginea_, formerly known as the White Coral, although it differs widely in reality from the true Coral, both in its structure and by its star-like polypiferous cells (Fig. 68), is found in the Mediterranean and also in the equatorial seas. Over the specimen we see (2) a portion of a branch magnified, in order that the reader may appreciate numerically the form of polype over its cells.

The species formerly named _Occulina flabelliformis_, and which now bears the name of _Stylaster flabelliformis_, which is represented in Fig. 69, will give an excellent idea of these arborescent zoophytes. The polypidom is in the form of a fan, with many very unequal branches; the larger branches are smooth, the middle-sized are covered with small points. This fine zoophyte is found in the seas which surround the Isle of Bourbon and the Mauritius, a fine example of which is to be seen in the collection of the Museum of Natural History of Paris.

ASTRÆACEA.

How diversified are the forms of aquatic life! "Nature revels in these diversities," to paraphrase the saying of one of the ancient kings of France. Here are animals, the frame of which might have been designed by a geometrician. They are called Star Corals (_Astrea_). Their resemblance to the well-known figure was too striking to escape the observation of naturalists; but the organization of these creatures of the ocean is far from being rigorously regular, for Nature rarely employs perfectly straight lines, giving an evident preference to circles and waving lines.

The _Astrea_ are inhabitants of the Indian Ocean, where they are found in a great variety of forms, which has led to their subdivision into many genera by Messrs. Milne Edwards and J. Haime. The animals are short, more or less cylindrical, with rounded mouth placed in the centre of a disk, covered with a few rather short tentacula; the cells are shallow, with radiating lamellæ in _Astrea punctifera_ (Fig. 70), forming by their union a many-formed coral, which often encrusts other bodies. In short, this polyp may be described as a parasite, for it generally attaches to some other bodies, and it is by no means unusual to meet with it attached even to shells.

The _Meandrina_ differ from the _Astreas_ in having the surface hollowed out into shallow sinuous elongated cells, furnished on each side of the mesial line with hooked lamellæ, ending against one or other of the ridges with separate valleys; the polypidom, which is calcareous, being fixed, simple, and inversely conical when young, and globular when old. The animals have each a distinct mouth, and lateral series of short tentacula; they are contained in shallow cells, meeting at the base, and forming by their union long and tortuous hollows. _Meandrina cerebriformis_ (Fig. 71), so called from its resemblance to the folds of the brain, is a native of the American Seas.

The _Fungia_, so called by Lamarck from their resemblance to the vegetable Fungi, are too remarkable in their appearance to be passed over in silence. The major part of the species only occur in recent geological strata. Nevertheless some of the species were very numerous in the Cretaceous period, and even find representatives in the Silurian period; it is this group in which Madrepores of great size are found.

The family, as we have already said, take their names from their supposed resemblance to the Mushroom. "But," says Peyssonnel, "there is this difference between terrestrial and marine mushrooms--that the former have leaflets below, and those of the ocean have them above (Fig. 72). These leaflets are only expansions of the Madrepores. Now, although I have not actually examined these petrified Mushrooms of the sea, I have no reason to doubt but that they are true genera or species of Madrepores, containing, like others, the zoophytes which form them. In my travels in Egypt, in 1714 and 1715, I never heard it said that the Nile could produce them." In this last remark, Peyssonnel makes allusion to the opinion entertained by many ancient authors, that the Fungia were productions of the Nile.

The animal is gelatinous or membranous, generally simple, depressed, and oval, with mouth superior and transverse, in a large disk, which is covered by many thick cirrhiform tentacula; the polypidom is rendered solid internally by a calcareous solid deposit of a simple figure, having a star of radiating, acutely-pointed lamellæ above, and simple rays, full of wrinkles, beneath. There are nine species, mostly natives of the Indian Seas, which De Blainville arranges in three groups, according as they are simple and circular, simple and compressed, or complex and oblong. In _Fungia echinata_, represented in Fig. 72, we have a species which inhabits the Indian and Chinese Seas. It belongs to the last group, being oblong in form, convex above, and concave below. The hollow, from which the lamellæ or chamber-walls proceed, are of considerable length; the toothed partitions are very irregular, thin and prickly, resting upon their lower edge, in order to leave the concave portion of the field free to a host of excrescences, resembling the roof of a grotto studded with small stalactites.

The conformation of the softer parts of this polypus has been described by many travellers. The upper portion of the body of the animal, corresponding to the lamelliform part of the polypus, is furnished with scattered tentacula, very long in some species, and remarkably short in others. These tentacula appear to terminate in a small sucker, and the animal seems to recover its position with difficulty, when overturned. In order to complete our description of these curious madrepores, we may refer to _Fungia agariciformis_, represented in Fig. 73. This remarkable species inhabits the Red Sea and the Indian Ocean, and is here represented with its polyps.

* * * * *

De Blainville gave the name of MADREPORÆA to the second group of his stony _Zoantharia_, placing them after the _Madrephylliæ_. The products of this section are generally arborescent, with small, partially lamelliform cells, which are constantly porous in the interstices of the walls of the cells, this being its most important characteristic. Thus the visceral apparatus constitutes the essential part of the polypus, presenting no side plates, the visceral chamber being open from the base to the summit, and neither filled with dissepiments, pulpy matter, nor with plates.

The history of these inhabitants of the deep is extremely obscure, and will probably always remain so; the most beautiful of their productions are intertropical, and consequently beyond the reach of discriminating observers during the life of the animal. Solander proposed to divide the genus according to certain characteristics in the growth of the coral, and De Blainville has rearranged the groups formed by Lamarck, Lamouroux, and Goldfuss, with special reference to the soft parts of the animals figured by Lesueur, Quoy, Gaimard, and others, who have observed them in their native state.

The perforated _Zoantharia_ form three very natural families: the _Eupsammidæ_, the _Madreporidæ_, and the _Poritidæ_. The first have the solid parts of the polyps, simple or complex, with well-developed lamellar portions, the central column spongious, walls granular, semi-ribbed, and perforated. The second are composite, increasing by gemmation; walls spongy and porous; septa lamellous, and well developed. In the third the visceral chambers are divided into two equal parts by the principal septa, which are more developed than the others, meeting by their inner edge. The _Dendrophylliæ_ (Fig. 74) are conspicuous among the _Eupsammidæ_.

We shall describe three genera, the two first of which belong to the MADREPORÆA, and the last of the family of the _Porides_.

_Dendrophyllia ramea_, represented in Figs. 75 and 76, is an elegant madrepore of the Mediterranean. Its polyp presents a very large trunk charged with short ascending branches; it usually attains to about a yard and a half in height. The polyps are provided with a great number of tentacula, in the centre of which the mouth is placed. They are deeply buried in the cells, which radiate from numerous unequally _saillant_ plates. Peyssonnel, who had seen the polyps of this colony, says: "I may observe that the extremities or summits of the branching madrepore, the species in question, which in the Provencal we call Sea-fennel, is soft and tender, filled with a glutinous and transparent mucous thread, similar to that which the snail leaves on its path. These extremities are of a fine yellow colour, five or six lines in diameter; soft, and more than a finger's breadth in length. I have seen the animal nestling in them; it seemed to be a species of cuttle-fish or sea-nettle. The body of this sea-nettle must have filled the centre; the head being in the middle, surrounded by many feet or claws, like those of the cuttle-fish. The flesh of this animal is very delicate, and is easily reduced to the form of a paste, melting almost under the touch."

The madrepores abound in all intertropical seas, taking a considerable part in the constitution of the reefs which form the coral and madreporic islands so conspicuous in the ocean. The tree-like _Dendrophyllia_ (_D. ramea_, Figs. 75 and 76) have cells of considerable depth, radiating into numerous lamellæ, forming a widely-branching arborescent coral, externally striated, internally furrowed, and truncate at the extremities. The animals are actiniform, furnished with numerous cleft tentacula, in the centre of which is the polygonal mouth. In the _Lobophyllia_, the tentacula are cylindrical, the cells conical, sometimes elongated and sinuous, with a sub-circular opening terminating the few branches of the polyp, which is fixed, turbinate, and striated. The Plantain Madrepore, _M. plantaginea_ (Lamarck), is an interesting example, the polyp presenting itself, as in Fig. 77, in tufts, with slender and prolific branches.

In _Madrepora palmata_, vulgarly named Neptune's Car, we have a large and beautiful species, whose expanding branches are flat, round at the base, and forming in lobes, whose length is often as much as three feet high, with a breadth of twenty inches, and a thickness of two to two and a half: this fine madrepore is found in the Caribbean Sea and among the Antilles.

PORITES.

The Porites are madrepores produced by a pitcher-shaped fleshy animal, with twelve short tentacula; the cells are unequally polygonal, imperfectly defined, slightly radiating by thread-like pointed rays, with prickles placed at intervals. The polypus is polymorphous or many-formed, composed of a reticulated and porous tissue, the individuals forming it being always completely united together. Externally it presents the figure of an irregular trellis-work, more or less loosely connected in its meshes. As a type of this organization, we give a figure of the Forked Porites (_P. furcata_, Fig. 78), of the natural size. The branches are generally dichotomous, that is, rising in pairs obtusely lobed. In some of the species the rays are more fully marked, and resemble a bed of miniature anemones thickly crowded together, as in _Gonispora columna_, in which the polypi have a central mouth, round which the twelve short tentacula radiate; the coral is stony, fixed, branched, or lobed, having a free surface covered with a great number of regular stars, which are highly characteristic, and cannot be confounded with those of an astrea or madrepore.

In the Tabulate Madreporides, the polyp is essentially composed of a highly-developed mural system. The visceral chambers are divided into a series of stages or stories, by perfect diaphragms or plates placed transversely, the plates depending from the walls and forming perfect horizontal divisions, extending from one wall of the general cavity to the other. In order that the reader may form some idea of the Tabulate Madrepores, one of the polyps known as _millepores_ is here represented. The millepores were first separated from the madrepores by Linnæus, along with a great number of species distinguished by the minuteness of their pores or polypiferous cells (Fig. 79), represented above, as nearly allied, and perhaps identical with Dr. Johnston's _Cellepora cervicornis_, a species found in deep water on the Devonshire and Cornwall coasts, and, indeed, all round our west coast. "A single specimen of this millepore is about three inches in height," says Dr. Johnston, "and somewhat more in breadth. It rises from a broad flattened base, and begins immediately to expand and divide into kneed branches or broad segments, many of which anastomose, so as to form arches and imperfect circles. The extreme segments are dilated and variously cut, sometimes truncate, both sides being perforated with numerous pores just visible to the naked eye, and arranged in rows; the pores circular, and level with the surface on the smooth and newly-formed parts; but in the older parts they form apertures of urceolate cells, which appear to be formed over the primary layer of cells, giving to the surface a roughish or angular appearance. The orifice is simple, contracted, with a very small denticle on one side; the thickness of the branches varies from one half to two lines; the interior is cellular; the new parts are formed of two layers of horizontal cells, but the older parts are thickened by cells superimposed on the primary layers."

_Millepora moniliformis_ is a species which attaches itself to the branches of the gorgons, and forms there a series of little rounded or lateral lobes. The animal is unknown, the cells very small, unequal, completely immersed, obsoletely radiate and scattered; the polypier fixed, cellular within, finely porous and reticulated externally, extending into a palmated form.

Of tuberous or wrinkled madrepores, which consist almost entirely of fossil species chiefly belonging to the Silurian formation, we shall only note _Cyathophyllum_ as one of the best known species.

* * * * *

There is no spectacle in Nature more extraordinary, or more worthy of our admiration, than that now under consideration. These zoophytes, whose history we are about to investigate--wretched beings gifted with a half-latent life only--these animalcules so small and so fragile--labour silently and incessantly in the bosom of the ocean, and, as they exist in innumerable aggregated masses, their cells and solid axes finish by producing in the end enormous stony masses. These calcareous deposits increase and multiply with such incalculable rapidity, that they not only cover the submarine rocks as with a carpet, but they finish by forming reefs, and even entire islands, which rise above the surface of the ocean in a manner remarkable at once for their form and the regularity with which they repeat themselves.

In noting the Indian and Pacific Oceans, navigators had long been struck with the appearance of certain earthy bases, which presented a conformation altogether singular. In 1601, Pyrard de Laval, speaking of the Malouine (now the Falkland) Islands, said: "They are divided into thirteen provinces, named _atollons_, which is so far a natural division in that place, that each atollon is separated from the other, and contains a great number of smaller islands. It is a marvel to see each of these atollons surrounded on all sides by a great bank of stone--walls such as no human hands could build on the space of earth allotted to them. These atollons are almost round, or rather oval, being each about thirty leagues in circumference, some a little less, others a little more, and all ranging from north to south, without any one touching the other. There is between them sea channels, one broad, the other narrow. Being in the middle of an atollon, you see all around you this great stone bank, which surrounds and protects the island from the waves; but it is a formidable attempt, even for the boldest, to approach the bank and watch the waves as they roll in and break with fury upon the shore."

Since the publication of Laval's description, many circular isles, or groups of islands, analogous to these atollons, since called _atolls_, have been discovered in the Pacific Ocean and other seas. The naturalist Forster, who accompanied Cook in his voyage round the world, first made known the more remarkable characteristics of these gigantic formations. He perfectly comprehended their origin, which he was the first to attribute to the development of the calcareous zoophytic polypier.

After Forster, many other naturalists--Lamouroux, Chamisso, Quoy, Gaimard, Ehrenberg, Ellis, Darwin, Couthony, and Dana--have furnished Science with many precious lessons on the natural history of coral islands and madreporic reefs. We can only glance at a few of the more remarkable genera of these interesting creatures.

"Those occupying the same Coral," says Frédol, "live in perfect harmony; they constitute a family of brothers, physically united in the closest bonds of union. They occupy the same dwelling, each having its separate chamber; but the power of abandoning it is denied them. Attached each to its cell, they are driven to trust in Providence for the food which never fails them; moreover, what is eaten by each mouth profits the whole community. Urged on by a wonderful instinct, the polypes labour together at the same work; isolated, they would be weak and helpless; in combination, they are strong." M. Lacaze-Duthiers has even demonstrated that _Antipathes glaberrima_, _Gorgonia tuberculata_ (Lamarck), _Leiopathes glaberrima_ (Gray), and _Leiopathes Lamarckii_ (Haime), were present on the same coral, the _Gerardia_ of Lamarck. It is thus recognized that, under the general denomination of polyps, very distinct genera are found, some being of the _Hydra_ type, others belonging to the _Plumularia_. The first are very common on our coast: they include the _Tubularia_, the _Campanularia_, and the _Sertularia_.

The Reed Tubularia (_T. indivisa_) is remarkably curious: its numerous stems are horny, yellow, and marked at intervals with irregular knots, resembling the joints of a straw. Their lower extremity is tortuous, and apt to adhere to foreign bodies; the upper part is nearly upright, and slightly flexuous, the whole resembling some flowering plant, without leaves or lateral branches. The _Campanularias_ are altogether different; the end of the branches whence the polyps issue are broad and bell-shaped, _C. dichotoma_ presenting a stem of brownish colour, thin as a silken thread, but strong and elastic. The polyps are numerous, a branch eight inches in height being inhabited by as many as twelve hundred individuals.

The _Sertularias_ have a horny stem, sometimes simple, sometimes branching, and may easily be mistaken for small plants. Their name is derived from the Latin _sertum_, a bouquet; and, indeed, they can only be described as trees in miniature, with branches yellow and semi-transparent, each tree having seven, eight, twelve, or twenty small panicles, each of which will contain about five hundred animals, the tree itself containing probably an association of ten thousand. Occasionally _Sertularia argentea_ is said to afford shelter and employment for a hundred thousand of these creatures. _S. falcata_, having all the grace and elegance of the delicate and slender Mimosa, is now placed among the Bryozoares.

The minute cells in which the polyps are lodged are not always arranged in the same manner. Sometimes the cells occupy one side only; in other instances they occupy both; sometimes they are grouped like the pipes of an organ, at others they are ranged spirally round the stem, or arranged at intervals, forming horizontal rings round it.

The _Alcyonaria_ are very common on some parts of our coast, where scarcely a stone or shell is dredged up that does not support one or more specimens known to the fishermen as "cow's paps," "dead men's fingers," and other popular names. This round and lobed fleshy mass is quite a colony in itself; placed in pure sea water, it very soon presents certain yellow or grass-like points, which gradually expand and display themselves in their native transparent and animated coralline. Each of these polyps have eight dentate petals, in the centre of which is the mouth; the body of the polyp is tubular, varying externally in length, traversed internally throughout its entire mass by a tissue studded with reddish spiculæ, and furrowed with small reed-like ribbons, common to all the individuals of the association.

Among the _Tubiporidæ_ may be noted _Tubipora musica_ (Linnæus), from the Indian Ocean, characterised by its stony tubes, simple, numerous, straight or flexible, parallel, and slightly radiating, of a fine purple, and united together at intervals by transverse bands, so as to resemble the pipes of an organ. The polyp is a brilliant grass green, according to Péron; the tentacula furnished on each side with two or three rows of granulous fleshy papillæ, to the number of sixty to eighty (Lesson).

The _Gorgonia_ is studded with calcareous or siliceous spiculæ which form a crust in drying. This crust is friable, and frequently preserves the colours more or less brilliant which characterise it. Their cells are sometimes hollowed out of the plain surface; sometimes they occur in the projecting mammals; these are smooth, rough, or scaly--sometimes pendent the one from the other.

These animals attach themselves to solid bodies, sometimes even to each other, grafting themselves or interlacing each other in all directions. In colour they are whitish, pure white, yellow, and apple-green; their shades, passing from olive-brown to deep blue, from vermilion to violet, and from pale yellow to pearly-grey. Each tube or cell contains an individual. The cells are more or less deep, according to the species. The polyps are composed generally of a hidden portion more or less tubular, and of a star-like portion more or less displayed. This latter portion presents from eight to twelve soft and granulous wattles, susceptible of expansion, like the petals of a flower. When these appendages are displayed, they often attain twice the height of the body; in this state they are nearly transparent, except towards the extremity. They extend or compress these wattles, dilate or contract the mouth according to their wants; but their digestive tube is firmly soldered to the cell, while the axis which supports the cells is motionless. What a singular combination is here presented! Trees, one-half of which are animated, growing at the bottom of the sea; polyps, one-half of which is imprisoned, and riveted to their person; their stomachs in the bark, their arms on a branch, their movements perfect repose!

These minute silent workers are active and indefatigable; their task is to separate the salt and other chemical particles from the waters of the ocean, and, while feeding themselves, secrete and organise the axis which bears their lodging. They love the warmer regions of the ocean; in colder regions, the results of their labours are extremely limited: the one forms a sward of submarine life, which carpets the rocks; the other produces animated stalactites, great shrubs, whole forests of small trees. The electric cable which unites Sardinia to the Genoese fort was so encrusted with corals and bryozoares, that certain portions taken from the water for repairs had attained the size of a small barrel.

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The atolls present three unfailing and constant peculiarities. Sometimes they constitute a great circular chain, the centre of which is occupied by a deep basin, in direct communication with the exterior sea, through one or many breaches of great depth. These are the _atolls_, described more than two centuries ago by Pyrard de Laval; sometimes they surround, but at some distance, a small island, in such a manner as to constitute a sort of skeleton or girdle of reefs; finally they may form the immediate edging or border of an island or continent. In this last case they are called fringing littorals, or edging reefs. At the distance of a few hundred yards only from the edge of some of these reefs, the sea is of such a depth that the sounding-lead has failed to reach the bottom.

In order to give an idea of the general form of these atolls, although they are rarely so regular, the reader is referred to PL. III., which represents one of these islands of the Pomotouan Archipelago, in the Indian Ocean. It represents the island of Clermont-Tonnerre, figured by Captain Wilkes in the American Exploring Expedition. The exterior girdle of rocks here surrounds a basin nearly circular. Such is the general form--the typical form, so to speak--of the coral isles, of which this is a fair representation.

The zoophytes which form these mineral accumulations belong to diverse groups, and nowhere have the results of observations made upon these atolls been more minutely described than in Mr. Darwin's remarks on the grand Cocos Island situated to the south of Sumatra, in the Indian Ocean.

No writer, it seems to us, has reasoned on these atolls more comprehensively than the author of the "Origin of Species." "The earlier voyagers," he says, "fancied that the coral-building animals instinctively built up their great corals to afford themselves protection in the inner parts; but so far is this from the truth, that those massive kinds, to whose growth on the exposed outer shores the very existence of the reef depends, cannot live within the lagoon, where other delicately-branching kinds flourish. Moreover, in this view, many species of distinct genera and families are supposed to combine for one end; and of such a combination not a single instance can be found in the whole of nature. The theory that has been most generally received is, that atolls are based on submarine craters, but when the form and size of some of them are considered, this idea loses its plausible character. Thus, the Suadiva atoll is forty-four geographical miles in diameter in one line by thirty-four in another; Rimsky is fifty-four by twenty miles across; Bow atoll is thirty miles long, and, on an average, six miles broad. This theory, moreover, is totally inapplicable to the Northern Maldivian atolls in the Indian Ocean, one of which is eighty-eight miles in length, and between ten and twenty in breadth."

The various theories which had been propounded failing to explain the existence of the coral islands, Mr. Darwin was led to reconsider the whole subject. Numerous soundings taken all round the Cocos atoll showed that at ten fathoms the prepared tallow in the hollow of the sounding rod came up perfectly clean, and marked with the impression of living polyps. As the depth increased, these impressions became less numerous, but adhering particles of sand succeed, until it was evident that the bottom consisted of smooth sand. From these observations, it was obvious to him that the utmost depth at which the coral polyps can construct reefs is between twenty and thirty fathoms. Now, there are enormous areas in the Indian Ocean in which every island is a coral formation raised to the height to which the waves can throw up fragments and the winds pile up sand; and the only theory which seems to account for all the circumstances embraced, is that of the subsidence of vast regions in this ocean. "As mountain after mountain and island after island slowly sunk beneath the water," he says, "fresh bases would be successively afforded for the growth of the corals. I venture to defy any one to explain in any other manner how it is possible that numerous islands should be distributed throughout vast areas, all the islands being low, all built of coral absolutely requiring a foundation within a limited depth below the surface."

The _Porites_, according to Mr. Darwin, form the most elevated deposits of those which are situated nearer the level of the water: _Millepora complanata_ also enters into the formation of the upper banks. Various other branched corals present themselves in great numbers in the cavities left by the _Porites_ and _Millepora_ crossing each other. It is difficult to identify species occupying themselves in the deeper parts, but, according to Darwin, the lower parts of the reefs are occupied by polyps of the same species as in the upper parts; at the depth of eighteen fathoms and upwards, the bottom consists alternately of sand and corals. The total breadth of the circular reef or ring which constitutes the atoll of the Keeling or Cocos Island varies from two hundred to five hundred yards in breadth. Some little parasitic isles form themselves upon the reefs, at two or three hundred yards from their exterior edge, by the accumulation of the fragments thrown up here during great storms. They rise from two to three yards above the sea level, and consist of shells, corals, and sea urchins, the whole consolidated into hard and solid rock.

Mr. Darwin's description of a kind of Sea-pen, _Virgularia Patagonia_, throws some curious light on the habits of these creatures. "This zoophyte consists of a thin, straight, fleshy stem, with alternate rows of polypi on each side, and surrounding an elastic stony axis, varying in length from eight inches to two feet. The stem at one extremity is truncate, but at the other is terminated by a vermiform fleshy appendage. The stony axis, which gives strength to the stem, may be traced at the extremity into a mere vessel filled with granular matter. At low water, hundreds of these zoophytes might be seen projecting like stubble, with the truncate end upwards, a few inches above the surface of the muddy sand. When touched or pulled, they suddenly drew themselves in with force, so as nearly, or quite, to disappear. By this action, the highly elastic axis must be bent at the lower extremity, where it is naturally slightly curved; and I imagine it is by this elasticity alone that the zoophyte is enabled to rise again through the mud. Each polyp, though closely united to its brethren, has a distinct mouth, body, and tentacula. Of these polyps, in a large specimen there must be many thousands, yet we see that they act by one movement. They have also one central axis connected with a system of obscure circulation, and the ova are produced in an organ distinct from the separate individuals. For," adds Mr. Darwin, in a note, "the cavities leading from the fleshy compartments of the extremity were filled with a yellow pulpy matter which, under a microscope, consisted of rounded semi-transparent grains aggregated together into particles of various sizes. All such particles, as well as separate grains, possessed the power of rapid motion, generally revolving round different axes, but sometimes progressive."

The description of the Island of Cocos or Keeling is as follows:--"The ring-formed reef of the lagoon island is surmounted, in the greater part of its length, by linear islets. On the northern, or leeward side, there is an opening through which vessels can pass to the anchorage within. On entering, the scene was very curious, and rather pretty; its beauty, however, entirely depended on the brilliancy of the surrounding colours. The shallow, clear, and still water of the lagoon, resting in its greater part on white sand, is, when illumined by a vertical sun, of the most vivid green. This brilliant expanse, several miles in width, is on all sides divided, either by a line of snow-white breakers from the dark heaving waters of the ocean, or from the blue vault of heaven by the strips of land crowned by the level tops of the cocoa-nut tree. As a white cloud here and there affords a pleasing contrast to the azure sky, so in the lagoon bands of living coral darken the emerald-green water.

"The next morning I went ashore on Direction Island. The strip of dry land is only a few hundred yards in width; on the lagoon side there was a white calcareous beach, the radiation from which, under this sultry climate, was very oppressive. On the outer coast, a solid broad flat of coral rock served to break the violence of the open sea. Excepting near the lagoon, where there is some sand, the land is entirely composed of rounded fragments of coral. In such a loose, dry, stony soil, the climate of the intertropical regions alone could produce so vigorous a vegetation. On some of the smaller islets, nothing could be more elegant than the manner in which the young and full-grown cocoa-nut trees, without destroying each other's symmetry, were mingled into one wood. A beach of glittering white sand formed a border to those fairy spots.

"The natural history of these islands, from its very paucity, possesses peculiar interest. The cocoa-nut tree, at the first glance, seems to compose the whole wood; there are, however, five or six other trees. One of these grows to a very large size, but, from the extreme softness of its wood, it is useless; another sort affords excellent timber for shipbuilding. Besides the trees, the number of plants is exceedingly limited, and consist of insignificant weeds. In my collection, which includes, I believe, nearly the perfect Flora, there are twenty species, without reckoning a moss, lichen, and fungus. To this number two trees must be added, one of which was not in flower, and the other I only heard of. The latter is a solitary tree of its kind, and grows near the beach, where, without doubt, the one seed was thrown up by the waves.

"The next day I employed myself in examining the very interesting yet simple structure and origin of these islands. The water being unusually smooth, I waded over the flat of dead rock as far as the living mounds of coral, on which the swell of the open sea breaks. In some of the gulleys and hollows there were beautiful green and other coloured fishes, and the forms and tints of many of the zoophytes were admirable. It is excusable to grow enthusiastic over the infinite number of organic beings with which the sea of the Tropics, so prodigal of life, teems; yet I must confess, I think those naturalists who have described in well-known words the submarine grottoes, decked with a thousand beauties, have indulged in rather exuberant language.

"I accompanied Captain Fitzroy to an island at the head of the lagoon; the channel was exceedingly intricate, winding through fields of delicately-branched corals. At the head of the lagoon we crossed a narrow islet, and found a great surf breaking on the windward coast. I can hardly explain the reason, but there is, to my mind, much grandeur in the view of the outer shores of these lagoon islands. There is a simplicity in the barrier-like beach, the margin of green bushes and tall cocoa-nuts, the solid flat of dead coral-rock, strewed here and there with great loose fragments, and the line of furious breakers, all rounding away towards either hand. The ocean, throwing its waters over the broad reef, appears an invincible, all-powerful enemy; yet we see it resisted and even conquered by means which at first seem most weak and inefficient. It is not that the ocean spares the rock of coral; the great fragments scattered over the reef, and heaped on the beach whence the tall cocoa-nut springs, plainly bespeak the unrelenting power of the waves. Nor are any periods of repose granted; the long swell caused by the gentle but steady action of the trade-winds, always blowing in one direction over a wide area, causes breakers almost equalling in force those during a gale of wind in the temperate regions, and which never cease to rage. It is impossible to behold these waves without feeling a conviction that an island, though built of the hardest rocks--let it be porphyry, granite, or quartz--would ultimately yield and be demolished by such an irresistible power. Yet these low, insignificant coral islets stand, and are victorious; for here another power, as an antagonist, 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 into a symmetrical structure. Let the hurricane tear up its thousand huge fragments, yet what will that tell against the accumulated labour 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 the 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."

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We have said that madreporic or coralline formations affect three forms, to which the names of _atolls_, _barrier reefs_, and _fringing reefs_ have been applied. We have spoken of atolls; we shall now say a few words on barrier and fringing reefs.

Barrier reefs are formations which surround the ordinary islands, or stretch along their banks. They have the form and general structure of atolls. Like atolls, the barrier reefs appear placed on the edge of a marine precipice. They rise on the edge of a plateau which looks down on a bottomless sea. On the coast of New Caledonia, only two lengths of his ship from the reef, Captain Kent found no bottom in a hundred and fifty fathoms. This was verified at Gambier Island in the Pacific Ocean, in Qualem Island, and at many others.

According to Mr. Darwin, the barrier reef situated on the western coast of New Caledonia is four hundred miles long; that along the eastern coast of Australia extends almost without interruption for a thousand miles, ranging from twenty or thirty to fifty or sixty miles from the coast. As to the elevation of the islands thus surrounded with reefs, it varies considerably. The Isle of Tahiti rises six thousand eight hundred feet above the level of the sea; the Isle of Maurua to six hundred; Aituaki to three hundred; and Manonai to about fifty feet only.

Around the Isle of Gambier the reef has a thickness of a thousand and sixty feet, at Tahiti of two hundred and thirty. Round the Fiji Islands it is from two to three thousand.

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The _fringing reefs_ immediately surrounding the island, or a portion of it, might be confounded with the barrier reefs we have been describing, if they only differed in their smaller breadth; but the circumstance that they abut immediately on the coast in place of being separated by a channel or lagoon more or less deep and continuous, proves that they are in direct communication with the slope of the submarine soil, and permits of their being distinguished from the barrier reefs. The dangerous breakers which surround the Mauritius are a striking example of the fringing reef. This island is almost entirely surrounded by a barrier of these rocks, the breadth of which varies from a hundred and fifty to three hundred and thirty feet; their rugged and abrupt surface is worn almost smooth, and is rarely uncovered at low water. Analogous reefs surround the Isle of Bourbon; all round this island the polyps construct on the volcanic bottom of the sea detached mammalons, which rise from a fathom to a fathom and a half above the water.

Madreporic coasting reefs present themselves also on the eastern coast of Africa and of Brazil. In the Red Sea, reefs of corals exist which may be ranked among the madreporic coasting reefs, in consequence of the limited breadth of the gulf. Ehrenberg and Hemprich examined a hundred and fifty stations in the Red Sea, all of which had outlying fringing reefs of this description.

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It may be asked, With what rapidity are these coral and madreporic banks formed, so as to become _atolls_ and _fringing reefs_? To answer this question even approximately is very difficult. On the coast of the Mauritius, according to M. d'Archaic,[6] the learned professor of the Jardin des Plantes, the edge of the reef is produced by _Madrepora corymbosa_, _M. pocillifera_, and two species of _Astrea_, which pursue their operations at the depth of from eight to fifteen fathoms. At the base is a bank of _Seriatopora_, from fifteen to twenty fathoms in height. At the bottom, the sand is covered with _Seriatopora_. At twenty fathoms we also meet with fragments of _Madrepora_. Between twenty and forty fathoms the bottom is sandy, and the sounding-rod brings up great fragments of _Caryophylla_. According to MM. Quoy and Gaimard, the _Astreas_, which, as these naturalists consider, constitute the greater part of the reefs, cannot live beyond four or five fathoms deep. _Millepora alcicornis_ extends from the surface to the depth of twelve fathoms; the _Madrepores_ and _Seriatopores_ down to twenty fathoms. Considerable masses of _Meandrina_ have been observed at sixteen fathoms; and a _Caryophylla_ has been brought up from eighty fathoms in thirty-three degrees south latitude. Among the polyps which do not form solid reefs, Mr. Darwin mentions _Cellaria_, found at a hundred and ninety fathoms deep, _Gorgonia_ at a hundred and sixty, _Corallines_ at a hundred, _Millepora_ at from thirty to forty-five, _Sertularias_ at forty, and _Tubulipora_ at ninety-five fathoms.

According to Dana, none of the species which form reefs--namely, _Madrepora_, _Millepora_, _Porites_, _Astreas_, and _Meandrineas_--can live at a greater depth than eighteen fathoms. It is only near the surface of the water that the zoophytes which produce minerals and form madreporic banks put forth their powers; the points most exposed to the beating of the waves is that which is most favourable to their growth; it is there that the _Astreas_, _Porites_, and _Millepores_ most abound.