Chapter VIII: Acalephæ, or Sea Nettles (2)

Having presented to the reader certain characteristic types of Medusadæ, we proceed to offer some general remark upon the organization and functions of these strange creatures. We have, in short, selected these types because they have been special objects of anatomical and physiological study to some of our best naturalists.

The Medusæ have no other means of breathing but through the skin. We remark all over the body of these zoophytes certain cutaneous elongations, disposed so as to favour the exercise of the breathing function. Certain marginal fringes of extended surface, as well as the tentacle, are the special seats of the apparatus. The organs of digestion also present arrangements peculiar to themselves; the mouth is placed on the lower part of the body, and is pierced at the extremity of a trumpet-like tube, hanging sometimes like the tongue of a bell. The walls of the stomach, again, are furnished with a multitude of appendages, which have their origin in the cavity of the organ, and which are very elastic. The stomach, furnished with these vibratile cells, appears to secrete a juice whose function is to decompose the food and render it digestible.

In some of the Medusadæ the central mouth is absent altogether. With the Rhizostoma, for instance, the stomachal reservoir has no inferior orifice; it communicates laterally with the canals which descend through the thickness of the arms, and open at their extremities through a multitude of small mouths. These are the root-like openings from which the animals derive their name of Rhizostoma, from the Greek words ῥίζα, root, and στόμα, mouth.

The arms of the Rhizostoma are usually eight in number, the free extremities of each being slightly enlarged: in these arms many small openings or mouths occur, which are the entrances to so many ascending canals communicating with larger ones, as the veins do in the higher animals: the common trunk canal is thus formed, which directs itself to the stomach, receiving in its way thither all the lateral branches.

A very distinct circulation exists in the Medusæ. The peripheric part of the stomach suffers the nourishing liquid which has been elaborated in the digestive cavity to pass: this fluid then circulates through numerous canals, the existence of which have been clearly traced.

It is also a singular fact, that organs of sense seem to have been discovered in these Medusæ, which early observers believed to be altogether destitute of organization. "During my sojourn on the banks of the Red Sea," says Ehrenberg, in his work on the _Medusa aurita_, "although I had many times examined the brownish bodies upon the edge of the disk of the Medusæ, it is only in the month past that I have recognized their true nature and function. Each of these bodies consists of a little yellow button, oval or cylindrical, fixed upon a thin peduncle. The peduncle is attached to a vesicle, in which the microscope reveals a glandular body, yellow when the light traverses it, but white when the light is only reflected on it. From this body issue two branches, which proceed towards the peduncle or base of the brown body up to the button or head. I have found that each of these small brown bodies presents a very distinct red point placed on the dorsal face of the yellow head; and when I compare this with my other observations of similar red points in other animals, I find that they greatly resemble the eyes of the Rotifera and Entomostraca. The bifurcating body placed at the base of the brown spot appears to be a nervous ganglion, and its branches may be regarded as optic nerves. Each pedunculated eye presents upon its lower face a small yellow sac, in which are found, in greater or smaller numbers, small crystalline bodies clear as water." The presence of a red pigment in very fine grains is an argument in favour of the existence of visual organs in these zoophytes, for the small crystals disseminated in the interior of the organ would no doubt perform the part of refracting light which is produced by crystalline in the eyes of vertebrated animals. Moreover, it is found that there are marginal corpuscles analogous to these brown spots in other species of Medusæ. They are of a palish yellow, or quite colourless, and enclose sometimes a single, sometimes many calcareous corpuscles. When they are colourless, some naturalists have rather taken them for ears reduced to their most simple expression.

The Medusæ are not absolutely destitute of nervous system. We have seen that they have ganglions, and probably optic nerves. Ehrenberg also states that they have ganglions at their base, which furnish them with nervous filaments.

Without entering further into the details of their delicate and complicated structure, we shall pause briefly on their mode of reproduction. We shall find here physiological phenomena so remarkable as to appear incredible, had not the researches of modern naturalists placed the facts beyond all doubt. "Which of us," says M. de Quatrefages, "would not proclaim the prodigy, if he saw a reptile issue from an egg laid in his court-yard, which afterwards gave birth to an indefinite number of fishes and birds? Well, the generation of the Medusæ is at least as marvellous as the fact which we have imagined." Let us note, for example, what takes place with the Rose Aurelia, a beautiful Medusa, of a pale rose colour, with nearly hemispherical disk, from four to five inches in diameter, whose edge is furnished with short russet-brown tentacles; taking for our guide the eloquent and learned author of the "Metamorphosis in Men and Animals," M. de Quatrefages.

The Medusa, designated under the name of Rose Aurelia, lays eggs which are characterised by the existence of three concentric spheres. These eggs are transformed into oval larvæ, covered with vibratile cells, having a slight depression in front. They swim about for a short time with great activity, much like the infusoria, which they strikingly resemble in other respects.

At the end of forty-eight hours the movements decrease. Aided by the depression already noted, the larvæ attaches itself to some solid body, fixing itself to it at this point by the assistance of a thick mucous matter. A change of form soon takes place: it becomes elongated; its pedicle is contracted, and its free extremity swells into a club-like shape. An opening soon presents itself in the centre of this extremity, through which an internal cavity appears. Four little mammals have now appeared on the edge, which are elongated in the manner of arms. Others soon follow: these are the tentacles of a polyp: the young infusoria has become a polyp!

The polyp increases by buds and shoots, just like a strawberry plant, which throws out its slender stems in all directions, covering all the neighbouring ground.

The young Medusa lives some time under this form. Then one of the polyps becomes enlarged and its form cylindrical. This cylinder is divided into from ten to fourteen superposed rings. These rings, at first smooth, form themselves into festoons, and separate into bifurcated thongs; the intermediate lines become channeled. The animal now resembles a pile of plates, cut round the edges. In a short time each ring is stirred at the free edge of its fringe: this becomes contractile. The rings are individualised. Finally, these annular creatures, obscure in their lives, isolate themselves. When detached, they begin to swim: from that time they have only to perfect and modify their form. From being flat, they become concave on the one side and convex on the other. The digestive cavity--the gastro-vascular canals--become more decided; the mouth opens, the tentacles are elongated, the floating marginal cirri become more and more numerous; and now, after all these metamorphoses, the Medusa appears: it perfectly resembles the mother.

TUBULARIDÆ.

We have already said that recent researches have led to a separation of a class of animals from the Sertularia, and to their being united with the Medusæ. Of these creatures we formerly only knew one of the forms, namely, the polyp form; or, rather, the first stage of it. During their earliest days they possess a polyp, furnished with tentacles, and a bell-shaped body. During their medusoid age, they present a central stomach, with four canals in the form of a cross, and four to eight tentacles with cirri. The animals constitute the Tubularidæ, comprehending many genera; among others the Tubularia and Campanularia, in studying which Van Beneden of Louvain discovered most interesting facts connected with the subject of alternate generation.

The class of zoophytes ranged among the Tubularia have the power of secreting an inverting tube of a horny nature, in which the fleshy body can move up and down, expanding its tentacles over the top. Others of them give forth buds, each of which takes the form of a polyp, and these, being permanent, give it a shrub-like or branched appearance; it is now a compound polyp. The tube is branched, and the orifices from which the polyps expand usually dilate into cups or cells. This is the condition of the _Tubulari-campanulariadæ_ groups, which are numerous round our own coast and in the Channel. The Tubularia are plant-like and horny, rooted by fibres, tubular, and filled with a semi-fluid organic pulp; polyps naked and fleshy, protruding from the extremity of every branchlet of the tube, and armed with one or two circles of smooth filiform tentacles; bulbules soft and naked, germinating from the base of the tentacles; embryo medusiform. "Some modern authors," says Frédol, "assure us that the tree-like form of these polyps is a degraded and transitory form of the Medusæ. The Medusa originates the polyp, the polyp becomes a Medusa." _Tubularia ramea_ so perfectly resembles an old tree in miniature, deprived of its leaves, that it is difficult to believe it is not of a vegetable origin; it is now a vigorous tree in miniature, in full flower, rising from the summit of a brown-spotted stem, with many branches and tufted shoots, terminating in so many hydras of a beautiful yellow or brilliant red. _T. ramosa_, of a brownish colour and horny substance, rising six inches, is rooted by tortuous, wrinkled fibres, with flexible, smooth, and thread-like shoots, branching into a doubly permeate form. In _T. indivisa_ the tubes are clustering; its numerous stems are horny, yellow, and from six to twelve inches in height, about a line in diameter, and marked with unequal knots from space to space, like the stalk of the oat-straw with the joints cut off. Their lower extremity is tortuous, attaching itself readily to shells and stones in deep water, flourishing in deep muddy bottoms, and upright as a flower, fixed by the tapering root-like terminations of its horny tube: a flowering animal, having, however, neither flower nor branch. At the summit of each stem, a double scarlet corolla is developed of from five to thirty-five petals, in rows, the external one spreading, those in the interior rising in a tuft; a little below, the ovarium appears, drooping when ripe like a bunch of orange-coloured grapes. After a time the petals of the corolla fade, fall, and die, and a bud replaces them, which produces a new polyp; and so on. This succession determines the length of the stem. Each apparent flower throws out a small tube, which terminates it, and each addition adds one joint more to the axis, which it increases in length.

The Campanulariæ differ considerably from the above, the ends of their branches, whence the polyps issue, being enlarged into a bell-like shape, whence their name. _C. dichotoma_ is at once the most delicate and most elegant of the species. It presents a brownish stem, thin as a thread of silk, but strong and elastic. The polyps are numerous: upon a tree eight or nine inches high there may be as many hundreds. _C. volubilis_ is a minute microscopic species, living parasitically on corallines, seaweed, and shelled animals. The stem is a capillary corneous tube, which creeps and twists itself upon its support, throwing out at alternate intervals a long slender stalk, twisted throughout or only partially, which supports a bell-shaped cup of perfect transparency, and prettily serrated round the brim. Dr. Johnston found the antennæ of a crab so profusely infested with them as to resemble hairy brushes. It is furnished, according to Hassall, with a delicate joint or hinge at the base of each little cup--a contrivance designed, it is imagined, to enable the frail zoophyte the better to elude the rude contact of the element in which it lives, by allowing it to bend to a force which it cannot resist.

The Campanulariæ increase by budding, the buds being found in much the same manner as in the Hydræ. It is a simple excrescence, which, in due time, takes the form of the branch from which it proceeds. These buds have their birth at certain distances, and form a new polyp.

SIPHONOPHORA.

Alongside the Medusæ naturalists place certain marine zoophytes which are equally remarkable for their beauty and for their curious structure, the latter being so complicated that their true organization long remained unknown. They were known, until very recently, under the designation of Hydrostatic Acalephæ, or Hydra-medusæ. They are known in our days as Siphonophoræ. These inhabitants of the deep are graceful in form, and are distinguished by their delicate tissues and brilliant colours. Essentially swimmers, supported by one or many vessels filled with air--true swimming-bladders, more or less numerous, and of variable form--they float upon the waves, remaining always on the surface, whatever may be the state of the sea. They are natural skiffs, and quite incapable of immersion. The Siphonophoræ form four orders or families; namely, the _Diphydæ_, double-bell-shaped animals, one fitting into the cavity of the other; _Physaliadæ_, having large oblong air-vessels and numerous tentacles of several forms, long, and pendent from one end of the shell, with a wrinkled crest; _Vilelladæ_, animals stretching over a cartilaginous plate with a flat body, an oblique, vertical, cartilaginous crest above, a tubular mouth below, and surrounded by numerous short tentacles; _Physophora_, consisting of a slender and vertical axis, terminating in an air-bladder, carrying laterally swimming-bladders, which lose themselves amongst a bundle of slender white filaments.

VILELLADÆ.

The Vilellæ assemble together in great shoals; in tropical seas and even in the Mediterranean they may be seen in fine weather floating on the surface of the waves. As described by De Blainville, the body is oval or circular, and gelatinous, sustained in the interior of the dorsal disk by a solid sub-cartilaginous frame, provided on the lower surface of the disk with extensible tentacular cirri. The family includes four genera; namely, _Vilella_, the Holothuria of the Chinese, which the reader will most readily comprehend from the brief description we shall give of the Mediterranean Vilella (_V. limbosa_--Fig. 93), which has been very minutely examined by M. Charles Vogt, of Geneva, from whose work on the "Inferior Animals of the Mediterranean" our details are borrowed. _V. spirans_, sometimes called _V. limbosa_, was discovered in the Mediterranean, between Monaco and Mentone, by Forskahl, who most erroneously took it for a holothuria. On the upper surface of the animal is a hydrostatic apparatus, the object of which is to maintain its equilibrium in the ambient element. This apparatus consists of a shield and a crest, organs of which M. Vogt gives a very detailed description; but it is on the under surface that the principal organs of the Vilella are exhibited. These are not seen when the animal swims, because under such circumstances the vertical, oblique crest only is visible. The lower surface is concave, with a sort of mesial nucleus, presenting at the extremity of a trumpet-like prolongation, whitish and contractile, a sort of central mouth, surrounded by tentacular cirri, the external row being much longer than the internal ones. This was formerly thought to be the stomach of the Vilella. In the present day, this appendage is known to be the central polyp around which are grouped other whitish and much smaller appendages, the base being surrounded by little yellow bunches. These are supposed to be the reproductive organs. Between the crest and the shield numerous free tentacles present themselves, vermiform in appearance, cylindrical, and of a sky-blue colour, which are kept in continual motion.

The Vilella is therefore not an isolated individual, but a group or colony, in which the individuals intended to be reproductive are the most numerous, and occupy the inferior parts.

The central polyp, by its size and structure, is distinguishable at the first glance from all the other appendages of the lower surface of the body. It is a cylindrical tube, very contractile and pear-shaped, swollen into a round ball, or considerably elongated. Its mouth is round and much dilated; it opens in the cylindrical or trumpet part, which is contained in a sac in the form of elongated fusci, clothed in the whitish integuments which formed the body of the polyp when perfect. At the bottom of the sac two rows of openings are observed, which lead to a vascular network extending over the whole body; the membranous parts, while affecting various conditions in their arrangement, are nevertheless in direct communication with all the reproductive individuals.

It is a general characteristic of all colonies of polypi that the digestive cavities of the individuals composing them meet and inosculate in a common vascular system. The Vilellæ present the same conformation. Only in their case the vascular system is extended horizontally, this being the essential character of the union of all the individuals constituting the colony, with the canals common to all, in which the nourishing fluids circulate, elaborated for all and by all. It is a true picture of social communism realized by Nature.

The central polyp is alone destined to absorb the food. M. Vogt has always found in its interior cavity fragments of the shells of crustaceans, the remains of small fishes; and he has often seen the hard parts which resist digestion discharged through the trumpet-like opening. This central polyp nourishes itself and also all the others, but is itself sterile.

The tentacles are hollow cylinders, completely closed at the extremity. These are strong muscular tubes of considerable thickness, the interior of which is filled with a transparent liquid. They are enveloped in a strong membrane of a deep-blue colour. The epidermis is furnished with small stinging capsules, formed of a sac with comparatively thick walls. If this sac is compressed under the microscope it explodes, opening at a determinate part, and throwing out an apparatus forming a long stiff filament, which is implanted on a conical channel and surrounded with points. "I know not," says M. Vogt, "if all this machinery can re-enter the capsule after it has exploded; but I presume that the animal can extend itself and withdraw at pleasure. A tentacle of Vilella sufficiently compressed presents a surface bristling with these cirri, so as to resemble a brush. The tentacles themselves are in continual motion, and I have no reason to doubt that the observation of Lesson, who saw them cover small crustaceans and fishes, may be perfectly true. These stinging organs doubtless serve the same purpose as with other animals of the same class; namely, to kill the prey which the tentacles have enabled them to secure." Thus the Vilellæ have their javelins, as the Greek and Roman warriors had, and a lasso, as the cavaliers of Mexico and Texas have.

The reproducing individuals form the great mass of the appendages attached to the under surface of the Vilella. The form of the individuals is much more varied, inasmuch as they are extremely contractile. Nevertheless, they have considerable resemblance to the corolla of a hyacinth.

These reproductive individuals are, then, at the same time nurses. The Medusæ originating by budding in the case of those reproductive individuals, constitute the sexual state of the Vilellæ. They exist, in short, in two alternate states: the one sexual, producing eggs; in this state they are isolated individuals of the Medusadæ, which never group themselves or form colonies: the other aggregate state is non-sexual, and in it they form swimming colonies, under the special designation of _Vilellæ_.

The Vilellæ, so called by Lamarck, are found widely diffused in the seas of Europe, Asia, America, and Australia. One species, _V. limbosa_, is often taken on the southern coast of England. The animals are also met with far at sea, and often huddled together in considerable masses, old and young together.

Such is a brief account of the strange facts to which the careful study of the lower class of marine animals initiates us. Naturalists range along with them the _Rataria_ and _Porpita_.

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The Rataria have the body oval or circular, sustained by a compressed sub-cartilaginous framework, much elevated, having a muscular, movable, longitudinal crest below, and provided in the middle with a free proboscidiform stomach and a single row of marginal tentacular suckers. De Blainville was inclined to consider the very small animals which Eschscholtz termed Ratariæ as young and undeveloped _Vilellæ_. M. Vogt doubts not that the Ratariæ are young Vilellæ which have acquired, by little and little, the elliptical form, but that the limb is only furnished at a later period to the reproductive individuals. These Ratariæ are engendered, according to Vogt, by the naked-eyed Medusæ born of the Vilellæ, and owe their existence to the eggs produced by these Medusæ.

* * * * *

The Porpitæ constitute, like the Vilellæ, colonies of floating animals furnished with a cartilaginous, horizontal, and rounded skeleton, but they are destitute of crest or veil. The body is circular and depressed, slightly convex above, with an internal circular cartilaginous support, having the surface marked by concentric striæ crossing other radiating striæ, the upper surface being covered by a delicate membrane only. The body is concave below; the under surface is furnished with a great number of tentacles, the exterior ones being longest, and also with small cilia, each terminating in a globule, which sometimes contains air; the interior tentacles are shorter, simple, and fleshy. In the centre of these tentacula is the mouth, in form of a small proboscis, leading to a simple stomach surrounded by a somewhat glandular substance. The editors of the last edition of the "Règne Animal" only mention one species--_P. Gigantea_, a native of the Mediterranean and other warm seas, of a beautiful blue colour. Lamarck gives four species. De Blainville and others consider with Cuvier that they are only varieties, which Eschscholtz reunites under one species. In Fig. 94 we have represented _P. Pacifica_ (Lesson), the disk of which is twelve lines in diameter, without comprehending the tentacles. This disk is finely radiated on the under surface with a brilliant argentine nacre. The membranous fold which surrounds it is cut into, leaving light and perfectly straight festoons. It is of a clear celestial blue colour, and very transparent. The tentacles are much compressed, very thin and cylindrical, of a light blue, and the glands are of an indigo blue colour. All the reproductive individuals, which are placed in the lower part of the body, are of a perfect hyaline white.

This beautiful Porpita was discovered by Lesson on the Peruvian coast, where it occurs in swarms closely packed on the surface of the sea. "Its manner of life," says Lesson, "is perfectly analogous to that of the Vilella. Their locomotion on the sea is purely passive, at least in appearance. Their disk laid flat on the surface upon the water-line, leaves them to float freely and in a horizontal direction, the irritable arms hanging all round them."

PHYSOPHORA.

This family includes the _Physophora_, properly so called, the _Agalina_, and the _Stephanomina_, for the history of which we are indebted to the curious observations of M. Vogt. Fig. 95 is a representation of _Physophora hydrostatica_, after M. Vogt's memoir. We see that the animal is composed of a slender vertical axis, terminating in an aërial bladder, carrying laterally certain vesicles, known as swimming-balls, which terminate in a bundle of whitish slender threads.

The aërial bladder is brilliant and silvery, punctured with red spots. The swimming-bladders are encased in a transparent and somewhat cartilaginous capsule, which is continued into the common median trunk, the latter being rose-coloured, hollow, and very contractile; in short, it presents very delicate muscular fibres, which expand themselves on the external fan of the capsule, and is closed on all sides.

The swimming-bladders are of a glass-like transparency, and of a firm, compact tissue. They are attached obliquely and alternately upon a common axis, presenting an exterior curvature, a round opening, furnished with a fine, muscular, and very contractile limb, and arranged like the iris of the eye. Their power of resistance is increased by certain horny hollow threads, which are in direct communication with the cavity of the vertical trunk, and have their origin in a common circular canal.

"The animal," says Vogt, "is enabled to guide itself in any direction by means of the swimming apparatus or air-bags. These, on opening, are filled with water, which is again ejected in the contractile movement, for their movements may be compared to that of the umbrella of the Medusæ. It is the violent expulsion of this liquid which enables the animal to advance diagonally through the water, a kind of motion which is the consequence of its organization; for where both rows of air-bags are working in the direction of the axis of the trunk, the organism will incline to the side which works most, but always in such a manner that the aërial vesicle will be borne forward."

In its lower parts the trunk expands, becomes flat, and winds itself in a spiral. It is hollow, and encloses a transparent viscous liquid, in which very small granules are observed, which appear to be the result of digestion. This disk is attached to three different sorts of appendages; we shall first address ourselves to the tentacles.

These form a crown or bundle of vermiform appendages, of a reddish colour, over an inch in length, and which are kept continually in motion: these are formed of a glass-like cartilaginous substance; they are conical tubes, closed on all parts except at the point where the tentacle is attached to the disk. Their cavity is filled with the granulous liquid already mentioned. On the under surface of the disk, and to the inside of these tentacles, the polyps and fishing-lines are attached.

The anterior part of the polyp is formed of a glass-like substance, which changes its form in the most varied and surprising manner. It bears a roundish mouth at its summit. In its posterior part the polyp presents a straight hollow stem, of reddish colour; but near to this red stem we find a thick tuft of cylindrical appendages, from the middle of which springs the extensible and contractile filaments which Vogt calls the _fishing-lines_ (fil pêcheur), and of which he has given the following very strange account:

"Each of these appendages consists of an assemblage of cylindrical tubes somewhat resembling and analogous to a filament of confervæ. All these tubes are traversed by a continuous canal, which originates in the internal cavity of the stem of the polyp. Each fragment of the line is capable of a prodigious extent of elongation and contraction; but where completely drawn back the pieces fold themselves up somewhat in the manner of a pocket foot-rule. It is to the combined effect of contraction and the unfolding of the pieces that these lines owe the marvellous changes of length which they present." In Fig. 96 are represented the polyps and fishing-lines of _P. hydrostatica_, with a portion of the disk and two pairs of reproductive clusters.

In this figure it will be observed that each fragment or joint has implanted, near the articulation, a secondary line, which bears the stinging organ. Each of these filaments consists of three parts: a straight stem, muscular, contractile, and hollow, the cavity of which communicates with that of the trunk which carries it; a middle part, a sort of tube containing, in a considerable internal cavity, a transparent liquid; finally, an inflated stinging organ, which terminates the apparatus. This last is egg-shaped, and consists internally of a hyaline substance of cartilaginous consistence, in the interior of which we find a great cavity, which opens from within, near the base of the capsule; to the inside of this cavity a second muscular sac is attached all round the opening of the capsule, in such a manner that the opening leads directly into the cavity of the sac. This cavity conceals in its interior a long filament usually rolled up in a spiral, as illustrated in Fig. 97, where the two urticant capsules of the stinging apparatus of _Physophora hydrostatica_ are represented, one of them being a section, magnified by twelve diameters. This spirally rolled-up filament consists of a large quantity of very small, hard, sabre-shaped, corpuscular bodies, supported the one against the other, and having their points turned inwards. These objects Vogt terms "_urticant sabres_:" the extremity of the filament consists of curved corpuscles, larger, of a brownish yellow, very strong, and with a double point. M. Vogt had also opportunities of observing the action of these stinging capsules. He has seen them burst naturally, and he has also obtained artificially the same result. In the former case the filament issues from the opening left at the base of the capsule with a sort of explosion. "The use," he says, "of the fishing-lines" becomes evident when we see a Physophora in repose in a vase large enough for its full development; then it takes a vertical position; the lines elongate themselves more and more, by unfolding one by one the secondary lines with stinging capsules, and the Physophora now resembles a flower posed upon a tuft of roots, with extremely long and delicate rootlets reaching the bottom of the vase. But in the case of the Physophora the living roots are in continual motion. Each line is elongated, foreshortened, and contracted in a thousand ways. The least movement of the water causes the stinging capsules to be suddenly drawn up, the lines hauled in most rapidly being those near the crown of tentacles. This continuous play of the lines has no other object than to attract the prey destined to feed the polyp, and we cannot find any better comparison for them than the fishing-lines to which they have been compared. The moment that some small microscopic medusæ, larvæ, or crustaceans come within the sphere of those redoubted lines, it is at once surrounded, seized, and led with irresistible force towards the mouth of this polyp by a gentle and gradual contraction of the line; the stinging organs, complicated as we have seen them to be in the Physophora, thus serve the same purpose as the stinging organs disposed on the arms of the Hydræ, or on the external surface of the tentacles and prolific polyps of the Vilellæ.

Can there be any animal form more graceful than _Agalma rubra_, which is reproduced in Plate VII. from Vogt's Memoir? This beautiful creature is common in the Mediterranean, on the coast near Nice, from November till the month of May. Towards the middle of December Vogt found nearly fifty individuals in the space of an hour, opposite to the Port of Nice, all following the same current, a prodigious quantity of Salpæ, Medusæ, and small Pteropodean Mollusks accompanying them.

"I know nothing more graceful," says Vogt, "than this Agalma as it floats along near the surface of the waters, its long, transparent, garland-like lines extended, and their limits distinctly indicated by bundles of a brilliant vermilion red, while the rest of the body is concealed by its very transparency; the entire organism always swims in a slightly oblique position near the surface, but is capable of steering itself in any direction with great rapidity. I have had in my possession some of these garlands more than three feet in length, in which the series of air-bags measured more than four inches, so that in the great vase in which I kept them the column of swimming bags touched the bottom, while the aërial vesicle floated on the surface. Immediately after its capture the columns contracted themselves to such a point that they were scarcely perceptible, but when left to repose in a spacious vase, all its shrunken appendages deployed themselves round the vase in the most graceful manner imaginable, the column of swimming-bladders remaining immovable in their vertical position, the air-bags at the surface, while the different appendages soon began to play. The polyps, planted at intervals along the common trunk of rose-colour, began to agitate themselves in all directions, taking a thousand odd forms; the reproductive individuals, like the tentacles, were contracting and twisting themselves about like so many worms; the tentacles were stirred, the ovarian clusters began to dilate and contract, the spermatic air-bells agitated the waters with their umbrellas, like the Medusæ; but what most excited my curiosity, was the continuous action of the fishing-lines, which continued to unroll and contract in a most surprising manner, retiring altogether sometimes with the utmost precipitation. All who have witnessed these living colonies detach themselves reluctantly from the strange spectacle, where each polyp seems to play the part of the fisherman who throws his line, furnished with baited hooks, withdrawing it when he feels a nibble, and throwing again when he discovers his disappointment. These efforts continue in full vigour for two or three days, and I have succeeded sometimes in feeding them with the small crustaceans which swarm on our coasts."

Of the "personelle" of these colonies a few words will not be misplaced. The common axis of the _Agalma_ is a hollow muscular tube, the length of which may be three feet, and its breadth an eighth or tenth of an inch; it is traversed by a double current of granulous liquid; at its summit is the aërial vesicle; beneath are the swimming vessels. These are disposed along the trunk in a double series, attaining sometimes the number of sixty; their structure is analogous to the same organs in the Physophora.

In examining the posterior portion of the trunk, traversing polyps are observed at intervals, whose base is surrounded by a cluster of reddish grains, each of which is armed with a _line_, and with its surrounding filament, terminating in a tendril of a red vermilion colour, which is a perfect arsenal of offensive and defensive arms. There we find "_sabres_" of divers sizes, and poniards of various forms, the whole constituting a truly formidable stinging apparatus.

These warlike engines, these arms of attack and defence with which man surrounds himself, Nature has freely bestowed on these little creatures with which the ocean swarms in some places. It might be said that, after having created these graceful creatures to ornament and decorate the depths of the ocean, the Creator was so pleased with His work that He furnished them with arms for their protection and defence against all attacks from without.

Among these creatures we may note the pretty _Apolemia contorta_ of Milne Edwards (Fig. 98), which also inhabits the Mediterranean, and particularly the coast of Nice, and is no less admirable in its structure than _Agalma rubra_. This elegant species is often met with in the Gulf of Villafranca, near Nice, and has been figured and described by Milne Edwards, Charles Vogt, and also by M. de Quatrefages, who asks the reader "to figure to himself an axis of flexible crystals, sometimes more than a mètre (forty inches), all round which are attached, by means of long peduncles or foot-stalks equally transparent, some hundreds of bodies, sometimes elongated, sometimes flat, and formed like the bud of a flower. If we add to this garland of pearls of a vivid red colour, an infinity of fine filaments, varying in thickness, and give life and motion to all these parts, we have even now only a very slight and imperfect idea of the marvellous organism." The air-bells in _Apolemia contorta_ consist of a mass having the form of an elongated egg cut in the middle. They are arranged in a vertical series of twelves, and the axis which supports them is terminated by the aërial vesicle. This axis is always arranged in a spiral form, even in its greatest expansion, is of a fine rose tint, and flattened into the form of a ribbon; it is marked in all its length with asperitics or hollow dimples, in which the filamental appendages originate.

The nursing polyps have been called _poboscidiferous_ organs by Mr. Milne Edwards, who has studied them carefully. They are rendered conspicuous at a glance by the bright-red colour of their digestive cavity and their extreme dilatability. At the base of their stems the very delicate filaments called fishing-lines are attached, which are furnished with a multitude of stinging tendrils of a reddish colour. These tendrils slightly resemble those of the Agalmæ, and the sabre-like weapons are not wanting.

Between the nursing polyps are placed in pairs the reproductive individuals, having the form of an elongated tube very dilatable, and closed at the free end. They have, then, no mouth! Milne Edwards calls these "vesicular appendages," and M. Koelliker, tentacles. The buds arranged at the base of each prolific individual vary; but, according to M. Vogt, they are always there in pairs--a male and female at the base of each stem. Figs. 99 and 100 represent the colony we have endeavoured to describe, 99 being the nursing individual of _Apolemia contorta_ magnified twelve times, 100 representing the reproductive pair under the same magnifying power.

THE DIPHYDÆ.

We have seen that the _Physophora_, the _Agalma_, and the _Apolemia_ have for the use of the colony a vast number of swimming vesicles and a terminal aërial vesicle. It is much the same in the _Prayæ_ or Diphydæ. In this family a great number of natatory vesicles are connected with the terminal aërial vesicle, as in Fig. 101, _Praya diphys_. This species is widely diffused in the sea which bathes the Nicean coast, but it is very difficult to procure perfect specimens. M. Vogt found fragments more than three feet long which swam on the surface, and was in its state of contraction not more than a finger's length. This species has been met with at Porta della Praya and at San Yago, one of the Cape de Verde islands.

The colony of the Praya presents two great locomotive bell shaped masses, between which the common trunk is suspended, and to which it can retire. This cylindrical trunk, which is thin and transparent, carries from space to space certain groups very exactly circumscribed and individualised. Each of these groups consists of a nursing polyp, having its fishing-line with a special floating air-bladder, a reproductive bud male or female, and a protecting casque enveloping the whole.

Another species having a great resemblance to the _Praya_ is _Galeolaria aurantiaca_ (Plate VIII.), or orange Galeolaria, which is represented on the opposite page, borrowed from the fine "Memoir of the Inferior Animals of the Mediterranean," by Carl Vogt. Here we find only two great floating bladders placed at each extremity of a common trunk, and serving the purpose of a locomotive apparatus to the whole colony. This trunk carries in like manner polyps placed at regular intervals forming isolated groups, provided each with its protecting plates. But there is no special swimming apparatus for each of these groups. Moreover, each colony is either male or female.

PHYSALIA.

Let us finally note among the Siphonophoræ a zoophyte which has attracted great attention, and has been described under many names. Sailors call it the sea-bladder, from its resemblance to that organ; it is also known as the Portuguese man-of-war, from its fancied resemblance to a small ship as it floats along under its tiny sail. Naturalists after Eschscholtz call it _Physalia utriculus_, from the Greek word φυσαλὶϛ, a bubble, and utriculus from its stinging powers. It was long thought that the Physalia was an isolated individual. But, according to recent researches, they form, like the species already described, an animal republic.

Let us imagine a great cylindrical bladder dilated in the middle, attenuated and rounded at its two extremities, of eleven or twelve inches in length, and from one to three broad. Its appearance is glassy and transparent, its colour an imperfect purple, passing to a violet, then to an azure above. It is surmounted by a crest, limpid and pure as crystal, veined with purple and violet in decreasing tints. Under the vesicle float the fleshy filaments, waving and contorted into a spiral form, which sometimes descend perpendicularly like so many threads of celestial blue. Sailors believe that the crest which surmounts the vesicle performs the office of a sail, and that they tell the navigator "how the wind blows," as they say. With all respect to the sailors, the bladder-like form, with its aërial crest, is only a hydrostatic apparatus, whose office is to lighten the animal, and modify its specific gravity. Mr. Gosse thinks otherwise, however.

"This bladder," says Gosse, in his "Year by the Sea-side," "is filled with air, and therefore floats almost wholly on the surface. Along the upper side, nearly from end to end, runs a thin edge of membrane, which is capable of being erected at will to a considerable height, fully equal at times to the entire width of the bladder, when it represents an arched fore-and-aft sail, the bladder being the hull. From the bottom of the bladder, near the thickest extremity, where there is a denser portion of the membrane, depends a crowded mass of organs, most of which take the form of very slender, highly contractile movable threads, which hang down into the deep to a depth of many feet, or occasionally of several yards.

"The colours of this curious creature are very vivid; the bladder, though in some parts transparent and colourless, and in some specimens almost entirely so, is in general painted with richest blues and purple, mingled with green and crimson to a smaller extent, these all being, not as sometimes described, iridescent or changeable, but positive colours independent of the incidence of light, and, for the most part, possessing great depth and fulness. The sail-like, erectile membrane is transparent, tinted towards the edge with a lovely rose-pink hue, the colours arranged in a peculiar fringe-like manner. When examined anatomically, the bladder is found to be composed of two walls of membrane, which are lined with cilia, and have between them the nutritive food which supplies the place of the blood. Besides this, the double membrane is turned in or inverted like a stocking prepared for putting on; and thus there is a bladder within a bladder, both having double walls; the inner (_pneumatocyst_) much smaller than the outer (_pneumatophone_), and contracted at the point where it is turned into the almost imperceptible orifice. The inner sends up closed tubular folds into the crest, which, being arrested by the membranous walls of the outer sac, give to the sail that appearance of vertical wrinkles which is so conspicuous."

When it is filled with air the body is almost projected out of the water. In order to descend it is necessary to compress itself or dispel the air, in part, for the centre of gravity in the animal is displaced according as the air is in the vesicle or in the crest. When the last is distended it rises out of the water, and becomes nearly vertical; in short, it then becomes a sort of sail. The floating appendages beneath the body are of divers kinds. Some of these are reproductive individuals; some are nurses; some are tentacles; finally, there are organs designated under the name of _Sondes_ by French naturalists; probes or suckers, we may call them, forming offensive and defensive arms truly formidable; for these elegant creatures are terrible antagonists. Dutertre, the veracious historian of the Antilles, relates the following: "This 'galley' (our Physalia), however agreeable to the sight, is most dangerous to the body, for I can assert that it is freighted with the worst merchandise which floats on the sea. I speak as a naturalist, and as having made experiments at my own personal cost. One day, when sailing at sea in a small boat, I perceived one of these little 'galleys,' and was curious to see the form of the animal; but I had scarcely seized it, when all its fibres seemed to clasp my hand, covering it as with birdlime, and scarcely had I felt it in all its freshness (for it is very cold to the touch) when it seemed as if I had plunged my arm up to the shoulder in a caldron of boiling water. This was accompanied with a pain so strange that it was only with a violent effort I could restrain myself from crying aloud."

Another voyager, Leblond, in his "Voyage aux Antilles," relates as follows: "One day I was bathing with some friends in a bay in front of the house where I dwelt. While my friends fished for sardines for breakfast, I amused myself by diving, in the manner of the native Carribeans, under the wave about to break; having reached the other side of one great wave, I had gained the open sea, and was returning on the top of the next wave towards the shore. My rashness nearly cost me my life: a Physalia, many of which were stranded upon the beach, fixed itself upon my left shoulder at the moment the wave landed me on the beach. I promptly detached it, but many of its filaments remained glued to my skin, and the pain I experienced immediately was so intense that I nearly fainted. I seized an oil flask which was at hand, and swallowed one half, while I rubbed my arm with the other: this restored me to myself, and I returned to the house, where two hours of repose relieved the pain, which disappeared altogether during the night."

Mr. Bennett, who accompanied the exploring expedition under Admiral Fitzroy, as naturalist, ventured to test the powers of the Physalia. "On one occasion," he says, "I tried the experiment of its stinging powers upon myself, intentionally. When I seized it by the bladder portion, it raised the long cables by muscular contraction of the bands situated at the base of the feelers, and, entwining the slender appendages about my hand and finger, inflicting severe and peculiarly pungent pain, it adhered most tenaciously at the same time, so as to be extremely difficult of removal. The stinging continued during the whole time that the minutest portion of the tentacular remained adherent to the skin. I soon found that the effects were not confined to the acute pungency inflicted, but produced a great degree of constitutional irritation: the pain extended upwards along the arm, increasing not only in extent but in severity, apparently acting along the course of the absorbents, and could only be compared to a severe rheumatic attack. The pulse was accelerated, and a feverish state of the whole system produced: the muscles of the chest, even, were affected; the same distressing pain being felt on taking a full respiration as obtains in a case of acute rheumatism. The secondary effects were very severe, continuing for nearly three-quarters of an hour; the duration being probably longer in consequence of the time and delay occasioned by removing the tentacula from the skin, to which they adhered, by the aid of the stinging capsules, with an annoying degree of tenacity. On the whole being removed, the pain began to abate; but during the day a peculiar numbness was felt, accompanied by an increased temperature in the limb on which the sting had been inflicted. For some hours afterwards the skin displayed white elevations or weals on the parts stung, similar to those resulting from the poison of the stinging nettle. The intensity of the pain depends in some degree upon the size and consequent power of the creature. After it has been removed from the water for some time, the stinging property, although still continuing to act, is found to have perceptibly diminished. I have observed, also, that this irritative power is retained for some weeks after the death of the animal, in the vesicles of the cables, and even linen cloth which has been used for wiping off the adhering tentacles, when touched, still retained the pungency, although it had not the power of producing such violent constitutional irritation."

The question has been much agitated, without being positively resolved, whether the Physalia are venomous or not: if they can kill or make sick the man or animal which swallows them. Listen to the opinions of M. Ricord-Madiana, a physician of Guadaloupe, who made direct experiments with a view to settling the question. "Many inhabitants of the Antilles," he says, "say that the 'galleys' are poisonous, and that the negroes make use of them, after being dried and powdered, to poison both men and animals. The fishermen of the islands also believe that fish which have swallowed them become deleterious, and poison those that eat them, a prejudice which has been adopted by many travellers, and has even found its way into scientific books. We can state as the result of direct experiment, that though the 'galley,' will burn the ignorant hand which is touched by its tentacles, when dried in the sun and pulverized, it becomes mere grains of dead matter, producing no effect whatever upon the animal economy."

On the other hand, we read in P. Labat's Voyage, vol. ii. p. 31, "that the bécune should not be eaten without some precaution, for this fish being extremely voracious, greedily devours all that comes within its reach in and out of the water, and it often happens that it meets and swallows 'galleys,' which are very caustic, and a violent poison. The fish does not die, but its flesh absorbs the venom, and poisons those who eat it." "There is every reason to believe," says M. Leblond, in the work already quoted, "that the sardine, as well as many other species of fish, after having ate the tentacles of the 'galley,' acquires a poisonous quality. Supping at an auberge on one occasion, with other persons, a bécune was served up, of which gastronomers are very fond, and which is usually perfectly harmless: five persons partook of it, and immediately afterwards exhibited every symptom of being poisoned. This was manifested by a burning heat in the region of the stomach. I bled two of them: one was cured by vomiting; one other would take nothing but tea and some culinary oil. The colic continued during the night, and had disappeared in the morning, but he entertained so great a horror of water, that during the remainder of the voyage a glass of it presented to him made him turn pale." M. Leblond concludes, from this and other facts, that the fishes which eat the Physalia become a poison for those who eat them, although it does not appear that he had any evidence of the fish having ate the "galley," or any other poison.

"Let us report our own experiments," continues M. Ricord-Madiana.

"I. I had placed a 'galley' in the sun, in order to dry and pulverize it. A nest of ants were there, who devoured the whole of it. Now, many persons in the islands think that these insects will not touch venomous fishes.

"II. Another 'galley,' which I had left on the table in my laboratory, was attacked by a number of great flies, who deposited their eggs there; these were duly hatched, and the larvæ fed on the decomposed zoophyte.

"III. On the 12th of July, 1823, I saw on the sands in the bay between Saint Mary and La Goyave, at Guadaloupe, many Physalia recently cast ashore. Having a dog with me, with the assistance of my servant, I made him swallow the freshest of them, with all its filiform tentacles, pushing it down his throat, while my servant held his mouth open; five minutes after, the dog exhibited symptoms of great pain on the edges of its lips; it foamed at the mouth and rubbed it in the sand, or upon the grass, leaping about, passing its paws over its jaws, and exhibiting every symptom of excessive pain. I mounted my horse, and, in spite of its sufferings, the poor animal followed me as it was wont. After twenty minutes, when its sufferings seemed over, I had a piece of bread which I gave it, and it ate it with appetite, swallowing it without any difficulty; it only seemed to feel the pain on the edges of its mouth: it was well enough all day, and had evacuations which gave no indication that the Physalia had any influence over the digestive organs. Next day, and the day following, it was as well as usual, exhibiting no signs of inflammation either in the mouth or throat.

"IV. On the 20th of the same month, I took two 'galleys' on the sea-shore and cut them in pieces; then, with a spoon, I had them forced down the throat of a puppy, which still sucked its mother; this strong dose of Physalia had no effect upon it, the tentacles having probably been surrounded by the fleshy parts of the animal in dividing it, so as not to touch the mouth: it seems probable, therefore, that the internal mucus is capable of subduing the irritation, which is so distressing when applied to membranes exposed to the external air. We swallow some things with impunity, which we could not support in the mouth if the burning substance remained there.