CHAPTER VII.

ZOANTHARIA, OR ANIMAL FLOWERS.

"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."

[Illustration: Fig. 66. Caryophillia cyathus (Lamarck).]

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).

[Illustration: Fig. 67. Flabellum pavoninum (Lesson).

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.

[Illustration: Fig. 68. Occulina virginea (Lamarck).]

[Illustration: Fig. 69. Stylaster flabelliformis (Lamarck).]

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.

[Illustration: Fig. 70. Astrea punctifera (Lamarck).]

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.

[Illustration: Fig. 71. Meandrina cerebriformis (Lamarck).]

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.

[Illustration: Fig. 72. Fungia echinata (Milne Edwards).]

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.

[Illustration: Fig. 73. Fungia agariciformis (Lamarck).]

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_.

[Illustration: Fig. 74. Dendrophyllia ramea, half natural size (De

Blainville).]

_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."

[Illustration: Fig. 75. Dendrophyllia ramea (De Blainville). Natural

size, with polypi.]

[Illustration: Fig. 76. A part magnified.]

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.

[Illustration: Fig. 77. Madrepora plantaginea (Lamarck).]

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.

[Illustration: Fig. 78. Porites furcata (Lamarck), natural size.]

[Illustration: Fig. 79. Millepora alcicornis (Linn.), one-fourth natural

size.]

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!

[Illustration: Plate IV.--Coral Island of Clermont-Tonnerre, in the

Pomotouan Archipelago.]

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.

* * * * *

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."

* * * * *

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.

* * * * *

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.

* * * * *

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.

The proportionate increase of the structures, according to Mr. Darwin,

depends at once upon the species which construct the reefs and upon

various accessary circumstances. The ordinary rate of increase of the

madrepores, according to Dana, is about an inch and a half annually;

and, as their branches are much scattered, this will not exceed half an

inch in thickness of the whole surface covered by the madrepore. Again,

in consequence of their porosity, this quantity will be reduced to

three-eighths of an inch of compact matter. It is, besides, to be noted

that great spaces are wanting; the sands filling up the destroyed part

of the polyp are washed out by the currents in the great depths where

there are no living corals, and the surface occupied by them is reduced

to a sixth of the whole coralline region, which reduces the preceding

three-eighths to one-sixth. The shells and other organic débris will

probably represent a fourth of the total produce in relation to corals.

In this manner, taking everything into account, the mean increase of a

reef cannot exceed the eighth of an inch annually. According to this

calculation, some reefs which are not less than two thousand feet thick

would require for their formation a hundred and ninety-two thousand

years.

It is necessary to add, however, that in favourable circumstances the

increase of the masses of coral may be much more rapid. Mr. Darwin

speaks of a ship which, having been wrecked in the Persian Gulf, was

found, after being submerged only twenty months, to be covered with a

bed of coral two feet in thickness; he also mentions experiments made by

Mr. Allen on the coast of Madagascar, which tend to prove that in the

space of six months certain corals increased nearly three feet.

* * * * *

We proceed to the theoretic explanation of these curious mineral

formations.

Naturalists and navigators have been much divided in opinion as to the

true origin of these madreporic islands. Most of them have admitted that

these enormous banks are composed of the mineral spoils and earthy

detritus of the madrepores and corals, which, developing themselves in

their midst, or upon the bed of the ocean, multiplying and superposing

themselves, age after age, and generation after generation, have finally

concluded by forming deposits of this immense extent. The growth of the

vast madreporic column would be finally arrested by the want of water

when its summit approached the level of the sea. It is thus that

Forster, Péron, Flinders, and Chamisso have explained the formation of

the _atolls_ and _madreporic_ reefs. This opinion has also found a

supporter, in our times, in the French admiral, Du Petit Thouars. But he

objects, with reason, that the corals cannot live at the prodigious

depth of sea at which the base of these islets lie. It has therefore

been found necessary to seek for another cause to satisfy the diverse

conditions of the phenomena, and explain, at the same time, the strange

circular arrangement of these islands, which is almost constant, and

which it is essential to keep in view.

Sir Charles Lyell was of opinion that the base of an atoll was always

the crater of an ancient submarine volcano, which, when crowned with

corals and madrepores, would naturally reproduce this circular wall

formed of heaped-up corals.

This theory supposes the existence of volcanic craters in the

neighbourhood of all the coral islands. It is quite certain that these

islands are often found not far from extinct volcanoes, and Sir Charles

Lyell has published a very curious map in connection with the subject;

nevertheless, the coincidence does not always exist. We have already

remarked on the theory by which Mr. Darwin seeks to explain the

complicated conditions of the phenomena. The explanation proposed

accounts for the known facts, as well as the present appearance of the

madreporic islands. The circular atolls and madreporic banks which are

disposed as a sort of girdle, are principally formed of _porites_,

_millepora_, and _astrea_, zoophytes which cannot exist at any great

depth in the ocean, but which swarm on the rocks at some few fathoms

only below the limits of the tide. These animals, by means of their

accumulated débris, soon form a sort of coating round the island, which

constitutes the littoral reefs: this marginal tongue or shoulder,

according to Mr. Darwin, is the first stage in the existence of a

madreporic island. At this point the author introduces a geological

cause, namely, a great subsiding movement of the soil, in which the

madreporic colony is sunk under the water. It is evident that after

submersion the zoophyte will only continue to develop itself on the

upper surface, and within the limits which its nature prescribes. The

madrepores exhibiting their greatest vitality at the points most exposed

to the fury of the waves, it will be near the outer edge of the reef

that the development will be most rapid. If the subsidence of the island

thus surrounded should still continue, as mountain after mountain and

island after island slowly sink beneath the water, fresh bases would be

successively afforded for the growth of the corals, and the outer edge

elevated by their continual labour, thus transforming the space into a

sort of circular lagune. The madreporic deposits would thus form an

isolated girdle, and the lagune, which occupies the centre, would become

deeper and deeper in proportion to the lowering of the soil. This is the

second stage of the madreporic isle.

The existence of the atolls are thus subordinated to two principal

conditions: the progressive subsidence of the shore washed by the sea,

and the existence of coral formed of stony cells, the growth and

multiplication of which are extremely rapid.

It follows from this that madreporic isles cannot exist in all seas;

that they only have their birth in the Torrid zone, or at least near the

Tropics, for it is only in these regions where the warmth exists, so

necessary to their development, that the madrepores show themselves in

greatest abundance.

The great field of madreporic formations, in short, is found in the warm

parts of the Pacific Ocean. It is from this point, as from a common

centre, round which are ranged the series of madreporic isles and

islets, that it will be useful, in concluding this chapter, to trace

their geographical distribution. We borrow the materials for this from

Milne Edwards's _tableaux_ of their distribution in the principal seas

of the world.

It is, as we have said, only in the warm parts of the Pacific Ocean that

the great mass of these islands are found. They give birth towards the

south to the group of atolls known as the archipelago of the Bashee

Islands, the extreme limit of the region being the Isle of Ducie. A

multitude of other islands of the same nature are sparsely scattered

over the sea, up to the east coast of Australia. There are enormous

areas here, in which every single island is of coral formation, and is

raised to the height at which the waves can throw up fragments. The

Radack group is an angular square, four hundred miles long by two

hundred and forty broad. Between this group and the Low Archipelago

itself, eight hundred and forty miles by four hundred and twenty, there

are groups and single islands covering a linear space of more than four

thousand miles. To the north of the Equator, the archipelago of the

Caroline Islands constitutes a very considerable group of madreporic

formation, comprehending upwards of a thousand, extending in a broad

belt over nearly forty degrees of longitude. On the other hand, all

along the coast of the American continent, round the Galapagos and the

Isle of Paques, we find no trace of them. The reason assigned is, that

in these regions a great current of cold water, flowing from the

Antarctic Pole, so much lowers the temperature of the sea, that the

zoophytes no longer possess the requisite vigour.

We still meet with atolls in the Chinese Seas, and madreporic barrier

reefs are abundant round the Marianne and Philippine Islands. These

marginal reefs form also an immense tract, from the Isle of Timor, along

the south coast of Sumatra, up to the island of Nicobar, in the Bay of

Bengal.

To the west of the Indian Peninsula, the Maldive and Laccadive Islands

form the extremity of another group of atolls, and important madreporic

reefs, which extend towards the south, by the Maldives and the Chagos

Islands; they consist of low coral formations, densely clothed with

cocoa-nut trees. The Maldives, the most southerly cluster, include

upwards of a thousand islands and reefs; the Laccadives, seventeen in

number, are of similar origin. The Saya de Malha bank, towards the

south-east, constitutes a further group of madreporic islets. Finally,

the coast of the Mauritius, of Madagascar, of the Seychelles, and even

the African continent, from the northern extremity of the Mozambique

Channel to the bottom of the Red Sea, are studded with numerous reefs of

the same nature. They fail, however, almost completely, along the coast

of the Asiatic continent, where, among others, the waters of the

Euphrates, the Indus, and the Ganges, enter the sea, and diversify its

inhabitants. The western coast of Africa, and the east coast of the

American continent, are almost entirely destitute of great madreporic

reefs, but they abound in the Caribbean Seas. In the Gulf of Mexico,

where the vast fresh-water current of the Mississippi debouches into the

sea, they are unknown. It is principally on the north coast and upon the

eastern flanks of the chain of West Indian Islands that the madreporic

reefs show themselves in these regions.

* * * * *

The polyps which have produced these vast ranges of islands would be set

down, at first sight, as the most incapable objects in creation for

accomplishing it. In the case of the _Pennatulidæ_, the case is

coriaceous, strengthened with calcareous particles; the interior is a

fibrous network containing a transparent jelly in the squares, and

permeated by a certain number of longitudinal cartilaginous tubes; the

soft part is uniformly gelatinous, but the skin is also coriaceous, with

a great number of calcareous spicula placed parallel to one another,

adding greatly to its strength and consistency.

The polyps are placed in this external fleshy crust; their position

being marked by an orifice on the surface, distinguished by eight

star-like rays, which open when the upper portion of the body is forced

outwards, in which state it resembles a cylindrical bladder or nipple

crowned with a fringe of tentacula, which surround the mouth. Under this

orifice is the stomach, occupying the centre of the cylinder. The space

between this stomach and the outer envelope is divided into eight equal

compartments or cells by as many thin septa, originating in a labial rim

or lip between the basis of the tentacula, which descend through the

cylinder attached on the one side to the inner tunic of the body, and on

the other to the stomach, which is thus retained in its position.

The protruding portion of the polyp is very delicate, the internal

viscera being, as it were, enclosed in a bladder formed of two very thin

membranes in intimate union, so transparent as to permit a view of their

arrangement. At the base of the body, where thickest, it coalesces with

the base of the adjacent polyp; thus constituting the common cortical

portion into which each animal retreats at will, by a process in many

respects resembling that by which a snail draws in its horns. In the

greater number of _Asteroidæ_ this common portion secretes carbonate of

lime, which is deposited in the meshes of its tissues either in granules

or in crystalline spiculæ, which imparts a solid consistency to the

whole. The inner tissue meanwhile continues unaltered, being prolonged

throughout the polypiferous lining of the cell, the abdominal cavity,

and the longitudinal canals which permeate the whole polyp, as well as

the tubular network with which the space between the canals is occupied.

It is among these inner tissues that the buds or gemmæ are generated, by

whose increase and evolution the polyp mass is enlarged, the shape and

size depending on the manner in which the buds are evolved; for in some,

as in the _Pennatulidæ_, determinate spots only have the appropriated

organization, while in others, as in _Alcyonium_, the generative faculty

appears to be undefined and more diffused.

THE ACTINIARIA.

Here we leave the group of polyps which form united families. The Sea

Anemones, of which the _Actinia_ are the type, consist of _Zoanthaires_,

which produce no corals, that is to say, of polyps whose covering

remains always soft, and in whose interior nothing solid is produced.

This order is usually divided into two families--the _Actiniadæ_, having

the tentacles in uninterrupted circles, with no corallum, and the

_Minyadinæ_, having globose bodies, and very short tentacula.

The modern aquarium exposes the spectator to many wonderful surprises.

Coiled up against the transparent crystal walls of the basin, he

observes living creatures of the most brilliant shades of colour, and

more resembling flowers than animals. Supported by a solid base and

cylindrical stem, he sees them terminate like the corolla of a flower,

as in the petals of the anemone: these are the animals we call _Sea

Anemones_--curious zoophytes, which, as all persons familiar with the

sea shore may have observed, are now seen suspended from the rocks, and

presently buried at the bottom of the sea, or floating on its surface.

These charming and timid creatures are also called _Actinia_, as

indicating their disposition to form rays or stars, from the Greek

ἀκτὶν, a ray.

The body of these animals is cylindrical in form, terminating beneath in

a muscular disk, which is generally large and distinct, enabling them to

cling vigorously to foreign bodies. It terminates above in an upper

disk, bearing many rows of tentacles, which differ from each other only

in their size. These tentacles are sometimes decorated with brilliant

colours, forming a species of collarette, consisting of contractile and

often retractile tubes, pierced at their points with an orifice, whence

issue jets of water, which is ejected at the will of the animal.

Arranged in multiples of circles, they distribute themselves with

perfect regularity round the mouth. These are the arms of this species

of zoophyte.

The mouth of the Actinia opens among the tentacles. Oval in form, it

communicates by means of a tube with a stomach, broad and short, which

descends vertically, and abuts by a large opening on the visceral

cavity, the interior of which is divided into little cells or chambers.

These cells and chambers are not all of the same dimensions; in parting

from the cylindrical walls of the body, they advance, the one

increasing, the others getting smaller, in the direction of the centre.

Moreover, they have many kinds of cells, which dispose themselves in

their different relations with great regularity--their tentacula, which

correspond with them, being arranged in circles radiating more or less

from the centre.

The stomach of the sea anemones fulfils a multitude of functions. At

first, it is the digestive organ; it is also the seat of respiration;

and is unceasingly moistened by the water, which it passes through,

imbibes, and ejects. The visceral cavity absorbs the atmospheric air

contained in the water; for the stomach is also a lung, and through the

same organ it ejects its young! In short, the reproductive organs, the

eggs, and the larvæ, are all connected with the tentacles or arms. In

the month of September the eggs are fecundated, and the larvæ or embryos

developed. As Frédol says in "La Monde de la Mer," "These animals bear

their young, not upon their arms, but in their arms. The larvæ generally

pass from the tentacula into the stomach, and are afterwards ejected

from the mouth along with the rejecta of their food--a most singular

formation, in which the stomach breathes, and the mouth serves the

purposes of accouchement--facts which it would be difficult to believe

on other than the most positive evidence."

"The Daisy-like Anemones (_Sagartia bellis_--Gosse), in the Zoological

Gardens of Paris," says Frédol, "frequently throw up little embryos,

which are dispersed, and attach themselves to various parts of the

aquarium, and finally become miniature anemones exactly like the parent.

An actinia which had taken a very copious repast ejected a portion of it

about twenty-four hours later, and in the middle of the ejected food

were found thirty-eight young individuals." According to Dalyell, an

accouchement is here a fit of indigestion.

The lower class of animals have, in fact, as the general basis of their

organization, a sac with a single opening, which is applied, as we have

seen, to a great variety of uses. It receives and rejects; it swallows

and it vomits. The vomiting becomes necessary and habitual--the normal

condition, in short, of the animal--and is perhaps a source of pleasure

to it, for it is not a malady, but a function, and even a function

multiplied. In the sea anemone it expels the excrement, and lays its

eggs; in others, as we have seen, it even serves the purposes of

respiration; so that the animal flowers may probably be said to enjoy

their regular and periodical vomit.

The sea anemones multiply their species in another manner. On the edge

of their base certain bud-like excrescences may often be observed. These

buds are by-and-by transformed into embryos, which detach themselves

from the mother, and soon become individuals in all respects resembling

her. This mode of reproduction greatly resembles some of the vegetative

processes. Another and very singular mode of reproduction has been noted

by Mr. Hogg in the case of _Actinia oeillet_. Wishing to detach this

anemone from the aquarium, this gentleman used every effort to effect

his purpose; but only succeeded, after violent exertions, in tearing

the lower part of the animal. Six portions remained attached to the

glass walls of the aquarium. At the end of eight days, attempts were

again made to detach these fragments; but it was observed, with much

surprise, that they shrank from the touch and contracted themselves.

Each of them soon became crowned with a little row of tentacula, and

finally each fragment became a new anemone. Every part of these strange

creatures thus becomes a separate being when detached, while the

mutilated mother continues to live as if nothing had happened. In short,

it has long been known that the sea anemones may be cut limb from limb,

mutilated, divided, and subdivided. One part of the body cut off is

quickly replaced. Cut off the tentacles of an actinia, and they are

replaced in a short time, and the experiment may be repeated

indefinitely. The experiments made by M. Trembley of Geneva upon the

fresh-water polypi were repeated by the Abbé Dicquemare on the sea

anemones. He mutilated and tormented them in a hundred ways. The parts

cut off continued to live, and the mutilated creature had the power of

reproducing the parts of which it had been deprived. To those who

accused the Abbé of cruelty in thus torturing the poor creatures, he

replied that, so far from being a cause of suffering to them, "he had

increased their term of life, and renewed their youth."

The _Actiniadæ_ vary in their habitat from pools near low-water mark to

eighteen or twenty fathoms water, whence they have been dredged up.

"They adhere," says Dr. Johnston, "to rocks, shells, and other

extraneous bodies by means of a glutinous secretion from their enlarged

base, but they can leave their hold and remove to another station

whensoever it pleases them, either by gliding along with a slow and

almost imperceptible movement (half an inch in five minutes), as is

their usual method, or by reversing the body and using the tentacula for

the purpose of feet, as Réaumur asserts, and as I have once witnessed;

or, lastly, inflating the body with water, so as to render it more

buoyant, they detach themselves, and are driven to a distance by the

random motion of the waves. They feed on shrimps, small crabs, whelks,

and similar shelled mollusca, and probably on all animals brought within

their reach whose strength or agility is insufficient to extricate them

from the grasp of their numerous tentacula; for as these organs can be

inflected in any direction, and greatly lengthened, they are capable of

being applied to every point, and adhere by suction with considerable

tenacity, throwing out, according to Gaertner, of their whole surface a

number of extremely minute suckers, which, sticking fast to the small

protuberances of the skin, produce the sensation of roughness, which is

so far from being painful that it even cannot be called disagreeable.

"The size of the prey is frequently in unseemly disproportion to the

preyer, being often equal in bulk to itself. I had once brought me a

specimen of _A. crassicornis_, that might have been originally two

inches in diameter, which had somehow contrived to swallow a valve of

_Pecten maximus_ of the size of an ordinary saucer. The shell, fixed

within the stomach, was so placed as to divide it completely into two

halves, so that the body, stretched tensely over, had become thin and

flattened like a pancake. All communication between the inferior portion

of the stomach and the mouth was of course prevented; yet, instead of

emaciating and dying of atrophy, the animal had availed itself of what

undoubtedly had been a very untoward accident to increase its enjoyment

and its chance of double fare. A new mouth, furnished with two rows of

numerous tentacula, was opened up on what had been the base, and led to

the under stomach; the individual had indeed become a sort of Siamese

Twin, but with greater intimacy and extent in its unions!"

The sea anemones pass nearly all their life fixed to some rock, to which

they seem to have taken root. There they live a sort of unconscious and

obtuse existence, gifted with an instinct so obscure that they are not

even conscious of the prey in their vicinity until it is actually in

contact, when it seizes it in its mouth and swallows it. Nevertheless,

though habitually adherent, they can move, gliding and creeping slowly

by successive contractile and relaxing movements of the body, extending

one edge of their base and relaxing the opposite one.

At the approach of cold weather the _Actiniadæ_ descend into the deepest

water, where they find a more agreeable temperature.

We have said that the sea anemones are scarcely possessed of vital

instinct; but they are capable of certain voluntary movements. Under the

influence of light, they expand their tentacles as the daisy displays

its florets. If the animal is touched, or the water is agitated in its

neighbourhood, the tentacles close immediately. These tentacles appear

occasionally to serve the purpose of offensive arms. The hand of the

man who has touched them becomes red and inflamed. M. Hollard has seen

small mackerel, two to three inches long, perish when touched by the

tentacles of the Green Actinia (_Comactis viridis_--Allman). This is a

charming little animal. "The brilliancy of its colours and the great

elegance of its tentacular crown when fully expanded," says Professor

Allman, "render it eminently attractive; hundreds may often be seen in a

single pool, and few sights will be retained with greater pleasure by

the naturalist than that presented by these little zoophytes, as they

expand their green and rosy crowns amid the algæ, millepores, and plumy

corals, co-tenants of their rock-covered vase."

The toxological properties of the Actinia have been attributed to

certain special cells full of liquid; but M. Hollard believes that these

effects are neither constant enough nor sufficiently general to

constitute the chief function of these organs, which are found in all

the species and over their whole surface, external and internal. Though

quite incapable of discerning their prey at a distance, the sea anemone

seizes it with avidity when it comes to offer itself up a victim. If

some adventurous little worm, or some young and sluggish crustacean,

happens to ruffle the expanded involucrum of an actinia in its lazy

progress through the water, the animal strikes it at once with its

tentacles, and instinctively sweeps it into its open mouth. This habit

may be observed in any aquarium, and is a favourite spectacle at the

"Jardin d'Acclimatation" of Paris, at noon on Sunday and Wednesday, when

the aquatic animals are fed. Small morsels of food are thrown into the

water. Prawns, shrimps, and other crustaceans and zoophytes inhabiting

this medium, chase the morsels as they sink to the bottom of the basin;

but it is otherwise with the Actinia; the morsels glide downwards within

the twentieth part of an inch of their crown without its presence being

suspected. It requires the aid of a propitious wand, directed by the

hand of the keeper, to guide the food right down on the animal. Then its

arms or tentacles seize upon the prey, and its repast commences

forthwith.

The Actinia are at once gluttonous and voracious. They seize their food

with the help of the tentacula, and engulf in their stomach, as we have

seen, substances of a volume and consistence which contrast strangely

with their dimensions and softness. In less than an hour, M. Hollard

observed that one of these creatures voided the shell of a mussel,

and disposed of a crab all to its hardest parts; nor was it slow to

reject these hard parts, by turning its stomach inside out, as one might

turn out one's pocket, in order to empty it of its contents. We have

seen in Dr. Johnston's account of _A. crassicornis_ that when threatened

with death by hunger, from having swallowed a shell which separated it

into two halves, at the end of eleven days it had opened a new mouth,

provided with separate rows of tentacula. The accident which, in

ordinary animals, would have left it to perish of hunger, became, in the

sea anemone, the source of redoubled gastronomical enjoyment.

[Illustration: Plate V.--Sea Anemones.

1, 2, 3. A. sulcata.

4. Phymactis sanctæ Helenæ.

5. Actinia capensis.

6. A. Peruviana.

7. A. sanctæ Catherinæ.

8. A. amethystina.

9. Comactis viridis.

]

"The anemones," Frédol tells us, "are voracious, and full of energy;

nothing escapes their gluttony; every creature which approaches them is

seized, engulfed, and devoured. Nevertheless, with all the power of

their mouth, their insatiable stomachs cannot retain the prey they have

swallowed. In certain circumstances it contrives to escape, in others it

is adroitly snatched away by some neighbouring marauder more cunning and

more active than the anemone."

In PL. IV. are represented the principal species of Anemone usually

observed in the aquarium. Figs. 1, 2, and 3, _A. sulcata_, is surmised

by Johnson to be the young of _A. effoeta_ (Linn.). It is also quoted as

a synonyme of _Anthea cereus_, from Drayton's stanza:

"Anthea of the flowers, that hath a general charge,

And Syrinx of the weeds, that grow upon the marge."

Fig. 4, _Phymactis Sanctæ Helenæ_ (Edw.); Fig. 5, _A. Capensis_

(Lesson); Fig. 6, _A. Peruviana_ (Lesson); Fig. 7, _A. Sanctæ

Catherinæ_; Fig. 8, _A. amethystina_ (Quoy); Fig. 9, _Comactis viridis_

(Milne Edwards).

"It is sometimes observed in aquariums that a shrimp, which has seen the

prey devoured from a distance, will throw itself upon the ravisher, and

audaciously wrest the prey from him and devour it before his eyes, to

his great disappointment. Even when the savoury morsel has been

swallowed, the shrimp, by great exertions, succeeds in extracting it

from the stomach. Seating itself upon the extended disk of the anemone,

with its small feet it prevents the approach of the tentacles, at the

same time that it inserts its claws into the digestive cavity and seizes

the food. In vain the anemone tries to contract its gills and close its

mouth. Sometimes the conflict between the sedentary zoophyte and the

vagrant crustacean becomes serious. When the former is strong and

robust, the aggression is repelled, and the shrimp runs the risk of

supplementing the repast of the anemone."

If the actinias are voracious, they can also support a prolonged period

of fasting. They have been known to live two and even three years

without having received any "nourishment."[7]

Although the sea anemone is said to be delicate eating, man derives very

little benefit from them in that respect. In Provence, Italy, and

Greece, the Green Actinia is in great repute, and Dicquemare speaks of

_A. crassicornis_ as delicate food. "Of all the kinds of sea anemones, I

would prefer this for the table; being boiled some time in sea water,

they acquire a firm and palatable consistence, and may then be eaten

with any kind of sauce. They are of an inviting appearance, of a light

shivering texture, and of a soft white and reddish hue. Their smell is

not unlike that of a warm crab or lobster." Dr. Johnston admits the

tempting description, and does not doubt their being not less a luxury

than the sea urchins of the Greeks, or the snails of the Roman epicures,

but he was not induced to test its truth. Rondeletius tells us, having,

as Dr. Johnston thinks, _A. crassicornis_ in view, that it brings a good

price at Bordeaux. _Actinia dianthus_ also is good to eat, quoth

Dicquemare, and Plaucus directs the cook to dress it after the manner of

dressing oysters, with which it is frequently eaten. _Actinia coriacea_

is found in the market at Rochefort during the months of January,

February, and March. Its flesh is said to be both delicate and savoury.

With these general considerations, we proceed to note some of the more

remarkable genera and species of these interesting creatures. Among

these, the species represented in PL. IV. are those usually seen

collected in such aquariums as those of the Zoological Gardens of London

and the Gardens of Acclimatization of Paris.

The first section of the _Actiniadæ_, according to Milne Edwards,

includes the Common Actinia, the feet of which are broad and adherent,

the lateral walls soft and imperforate. To this section belongs, among

others, the genera _Anemonia_, _Actinia_, and _Metridium_.

[Illustration: Plate VI.--Sea Anemones.

1. Actinia dianthus.

2. Cereus gemmaceus.

3. Actinia bicolor.

4. Sagartia viduata.

5. Cereus papillossus.

6. Actinia picta.

7. Actinia equina.

8. Sagartia rosea.

9. Sagartia coccinea.

]

The Green Actinia (_A. viridis_) has very numerous tentacula, sometimes

as many as two hundred, exceeding in length the breadth of the body, of

a fine brownish or olive green, and rose-coloured at the extremity. The

trunk is of a greyish green or brown; the disk is brown with greenish

rays. This species is plentiful in the Mediterranean and in the Channel.

When attached to the vertical sides of a rock, a little below the

surface of the water, in which position it is often seen on the shores

of the Mediterranean, the tentacles hang suspended as if the animal had

no power to display them in their radiate form; but when fixed

horizontally in a calm sea, they are spread out in all directions, and

are kept in a state of continual agitation; its long, mane-like

tentacula, fully expanded, float and balance themselves in the water in

spite of the action of the waves, presenting a most interesting

spectacle as it displays its beauties a few feet below the passing boat.

_A. dianthus_ (Ellis), having a number of synonymes, is represented in

PL. V. Fig. 1; its body is smooth and cylindrical; the disk marked in

the centre with clavate radiating bands; tentacula numerous, irregular,

the outer small, and forming round the margin a thick filamentous

fringe. This species attaches itself to rocks and shells in deep water,

or within low-water mark, to which it permanently attaches itself, and

cannot be removed without organic injury to the base. When contracted,

the body presents a thick, short, sub-cylindrical form, about three

inches long, and one and a half in diameter, and about five inches when

fully expanded; the skin is smooth, of an uniform olive, whitish, cream,

or flesh colour. The centre of the disk is ornamented with a circle of

white bands, radiating from the mouth, the lamellæ running across, the

circumference being perceptible through the transparent skin. From the

narrow, colourless interspaces between the lamellæ the tentacula

originate. "They are placed," says Dr. Johnston, "between the mouth and

the margin, which is encircled by a dense fringe of incontestable

beauty, composed of innumerable short tentacula or filaments, forming a

thick, furry border." In PL. V. Fig. 2, we have probably Gaertner's

_Anthea cereus_, the body of which is a light chestnut colour, smooth,

sulcated lengthwise, with tentacula rising from the disk to the number,

in aged animals, of two hundred. _Sagartia viduata_--Gosse (Fig. 4) has

the body adherent, cylindrical, without a skin, destitute of warts,

emitting capsuliferous filaments from pores; nettling-threads short,

densely armed with a brush of hairs; tentacles conical. _A. picta_ (PL.

IV. Fig. 6), which Professor Edward Forbes changes to _Adamsia

palliata_, is described by Mr. Adams, who first discovered it, "as

longitudinally sulcated, having the edges of the base crenated; the

lower part an obscure red, and the upper part transparent white, marked

with fine purple spots; the outer circumference of the aperture has a

narrow stripe of pink. When expanded, the superior division of the body

seems formed of membrane. From perforated warts placed without order on

the outer coat, issued white filamentous substances variously twisted

together. I have observed," he adds, "similar bodies ejected from the

mouths of all the species of this genus which have fallen within my

notice."

_A. mesembryanthemum_ (Johnston).--The _A. equina_ of Lesson (PL. IV.

Fig. 6), known in France as the _Cul d'ane_, is extremely common in the

Channel on rocks between the tide marks. It attaches itself chiefly to

rocks beaten by the waves and exposed to view at the moment of reflux.

The body is from two to three inches in height, and from an inch to an

inch and a half in diameter; hemispherical when contracted, it resembles

a bell perforated at the summit, dilated into a cylinder. When fully

extended the tentacula are nearly equal to the height of the body, of a

uniform liver colour, or olive green, and sometimes streaked with blue,

having a greenish line either continuous or in spots, the base generally

of a greenish colour encircled with an azure blue line, often streaked

with red. The tentacula are terminated by a small pore. Its colour is

variable, but generally it is of a violet-red. Sometimes it presents

round spots of a fine green; at other times it is only of a greenish

hue; the edge of the feet have a narrow border of red, with green and

blue beneath.

_Metridium dianthus_ has a thick body with russet grey skin, the disk

strongly lobed, thin and transparent round the mouth; the tentacula very

numerous, very short, and occupying a broad, strong zone upon the disk.

The mesial lines are whitish and wide apart; externally they are closer,

papiliform, and brown. This species is found on stones and shells in the

North Sea and in the Channel.

* * * * *

The verrucous, or warty section of the _Actiniadæ_, have the lateral

walls of the body covered with agglutinated tubercles, and

well-developed feet. To this section belong the Coriaceous Cereus,

_Actinia crassicornis_ (Johnston), and _A. senilis_ (Hollard and

Dicquemare), which seem to vary in habit. Hollard describes them as

frequently buried in the sands on the shore, while Cocks describes them

"as attaching themselves to shells and stones in deep water, or attached

on the littoral to the sides of rocks, in crevices, or on the face of

clean stones in sheltered places." The body is variegated, green, and

red; the tentacles thick, short, and greyish, with broad roseate bands.

[Illustration: Fig. 80. Edwardsia Calimorpha (Gosse).]

The Anemones belonging to the fourth section, or tap-rooted actinia,

have the base small, and terminating in a rounded point, and the body

much elongated, as in _Edwardsia Calimorpha_ (Fig. 80), in which the

body is non-adherent, somewhat worm-like, having the mouth and tentacula

seated on a retractile column, the lower extremity inflated, membranous,

and retractile.

In the great family of the Actiniarians, Milne Edwards forms a special

group of the Phyllactinæ. In this group the polyps are simple, fleshy,

and present at once simple and composite tentacula. Such is _Phyllactis

prætexta_ (Fig. 81), which is found in the neighbourhood of Rio Janeiro.

The zoophyte fixes itself upon the rocks on the sea shore, and covers

itself with sand. Its trunk, of cylindrical form, is of a flesh-colour,

with vertical lines, having red points. The interior tentacles form two

simple elongated rows; the exterior tentacles are spatulate and lobed,

not very unlike the leaves of the oak.

Another group, that of the Thalassianthidæ, is distinguished from the

preceding by having all its tentacula short, pinnate, and branching, or

papilliferous. One species only is known, _T. aster_, of a slate colour,

which inhabits the Red Sea.

[Illustration: Fig. 81. Phyllactus prætexta (Dana), natural size.]

In the last group of Actiniadæ, as arranged by Milne Edwards, the

polypes occur in clusters, and are multiplied by buds, rising from a

common creeping, root-like, fleshy base; they thus present a sort of

coriaceous polypier, as in _Zoanthus socialis_ (Fig. 82). In the British

Channel this species, which Dr. Johnston has named _Z. Couchii_, after

Mr. Couch, jun., is found along the Cornish coast, on flat slates and

rocks, in deep water, and from one to ten leagues from the shore. It is

very small, resembling, both in shape and size, a split pea. When

living, its surface is plain but glandular, becoming corrugated when

preserved. When semi-expanded, which is its favourite state, it elevates

itself to twice its ordinary height, becoming contracted about the

middle, like an hour-glass. When the creature is fully expanded, the

tentacula become distended and elongated to about the length of the

transverse diameter of the body; and they are generally darker at their

extremities than towards the base. Like all the Actiniadæ, the present

species possess a power of considerably altering their shape; sometimes

the mouth is depressed, and at others it is elevated into an obtuse

cone. "This is one of the most inactive of its order," says Mr. A.

Couch; "for, whether in a state of contraction or expansion, it will

remain so for many days without apparent change. In its expanded state a

touch will make it contract, and it will commonly remain so for many

days." The trailing connecting-band is flat, thin, narrow, glandular,

and of the same texture as the polyp, sometimes enlarging into small

papillary eminences, which, as they become enlarged, become developed

into polyps.

[Illustration: Fig. 82. Zoanthus socialis (Cuvier), natural size.]

MINYADINIANS.

[Illustration: Fig. 83. Blue Minyade. Minyas coeulea (Cuvier), natural

size.]

The Minyadinians seem to represent among the Zoanthairia the form

peculiar to the Pennatula among the Alcyonians. In the case of these

animals, the base of the body, in place of extending itself in a

disk-like form, in order to grapple with the rock and other projections

at the bottom of the sea, turns itself inwards, forming a sort of purse,

which seems to imprison the air. From this results a sort of hydrostatic

apparatus, aided by which the animals can float in the water and

transport themselves from one place to another. The Blue Minyade

(_Minyas cyanea_--Fig. 83) will serve as a type of this family; its

globose, melon-like form is of azure blue, studded with white wart-like

excrescences; it is flattened at its two extremities in its state of

contraction, and it has three rows of tentacula, which are short,

cylindrical, and white. The internal organs are of a delicate rose

colour. Cuvier places this species among the Echinodermata, but the

observations of Lesueur and Quoy, who were acquainted with the living

animal, place it among the Actiniadæ. Many of the species, which are

usually fixed, are still capable of swimming and of inflating their

suctorial disks; therefore it is by no means certain that the free habit

of _Minyas cyanea_ is constant.

FOOTNOTES:

[Footnote 6: "Cours de Paleontologie Stratigraphique."]

[Footnote 7: "On en a vu vivre deux et même trois ans, sans recevoir de

nourriture."--_Vie des Animaux_, p. 117.]