Part 16

Most formidable are the powers which reside in the long tentacles. Each of these is an excessively slender ribbon of contractile substance, connected at its base with a translucent bag, and carrying at short intervals throughout its length semi-rings of thread-cells (_cnidæ_), similar to those of our Sea-anemones, but of far more deadly virulence. Mr. Bennett, who, for the sake of science, ventured to test their powers, has left us a terrific account of his sufferings. “On one occasion,” he says, “I tried the experiment of its stinging powers upon myself, intentionally; when, on seizing 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, inflicted severe and peculiarly pungent pain, adhering 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 tentacula remained adherent to the skin. I soon found that the effects were not merely 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 was produced; the muscles of the chest even were affected, the same distressing pain 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 of the pain being probably longer, in consequence of the time and delay occasioned by removing the exciting and virulent tentacula from the skin, as they adhered to it, by the aid of the stinging capsules, with an annoying degree of tenacity. On the whole being removed, the pain began gradually to abate; but during the day a peculiar numbness was felt, accompanied also by an increased temperature in the limb upon which the stings had been inflicted. For some hours afterwards the skin displayed white elevations or wheals on the parts stung, similar to those usually seen 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; and 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. To remove the irritation, at first cold water was applied, but this, instead of alleviating, increased the evil: an application of vinegar relieved the unpleasant symptoms, and olive oil has produced a similar beneficial effect. I have observed 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 had been used for wiping off the adhering tentacles, when touched, still retained the pungency, although it had lost the power of producing such violent constitutional irritation.”[124]

Among the tentacles there are seen many depending organs, which take somewhat the shape of a claret-bottle, with the mouth a little expanded. These are highly moveable, turning and bending themselves in various directions. They are termed _polypites_, and are the mouths and stomachs of the animal: taking-in and digesting food, much as the protrusile lips of an Anemone do. Mr. Bennett describes the _Physalia_ as seizing and benumbing small fishes by means of the tentacles, which are alternately contracted to half-an-inch, and then shot out with amazing velocity to a length of several feet, and which drag the helpless and entangled prey to the sucker-like mouths, the stomach-cavities of which were filled while he looked-on, with atoms of the flesh absorbed.

Dr. Wallich thinks Mr. Bennett must have mistaken what he saw; because he has observed that in a great number of cases the _Physalia_ is accompanied by small fishes, which play around and among the depending tentacles without molestation. He has in so many cases seen this, and even witnessed the actual contact of the fishes with the tentacles, with no inconvenience to the former, that he too hastily concludes that “the urticating organs are innocuous.” Surely the premises by no means warrant such an inference. There is no antagonism between the two series of facts witnessed by such excellent observers; the venomous virulence of these organs has been abundantly proved by many naturalists, myself among the number, and Mr. Bennett, to his cost, as narrated above. We have only to suppose that the injection of the poison is under the control of the _Physalia’s_ will, and the impunity of the bold little fishes is sufficiently accounted for.

THE GULF-STREAM.

That wonderful river that flows with a well-defined course through the midst of the Atlantic,--the Gulf-stream,--brings on its warm waters many of the denizens of the tropical seas, and wafts them to the shores on which its waves impinge. Hence it is that so many of the proper pelagic creatures are from time to time observed on the coasts of Cornwall and Devon. The Portuguese man-of-war is among them, sometimes paying its visits in fleets; more commonly in single stranded hulks. Scarcely a season passes without one or more of these lovely strangers occurring in the vicinity of Torquay; and from one of these I took the opportunity of making the careful drawing with which I illustrate this paper.[125] The fishermen and similar persons who pick them up, always endeavour to make a harvest of their captures, not by the sale, but by the exhibition of them, sometimes carrying the specimen from door to door, sometimes erecting a temporary screen in some place of resort, exaggerating the rarity and value of the specimen outrageously. This summer (1862) I have known of three in this vicinity; and have heard of one at the Isle of Wight, in July, which forms the subject of a memoir and a coloured figure by Mr. Humphreys in the _Intellectual Observer_; also, a fleet of hundreds scattered over both sides of the same island in August, as recorded by Mr. Rogers in the _Zoologist_; and finally, one at Tenby in July, obtained by Mr. Hughes, and recorded in the last-named periodical.

Mr. Hughes in his account mentioned a circumstance as normal, which, being unknown to me, excited my curiosity. His specimen was accompanied by “its attendant satellites, two _Velellæ_.” In reply to my inquiries my friend gives me the following information:--“My authority for the association of Velella with Physalia is Jenkins, the collector at Tenby, who was attending me when they were found.

“The Physalia was taken by me first; and, while I was admiring it, I noticed that Jenkins continued searching for something. Immediately afterwards he came up with the Velella in his hand, at the same time stating they were generally found with the Portuguese man-of-war. As I had found the man very honest and truthful in his dealings with me (and not previously being familiar with either of the creatures), I accepted the information as correct.”

VELELLA.

The _Velella_ is a creature closely allied to the _Physalia_, having the same essential structure, but differing greatly in form and appearance. It consists of a flat disk of thin cartilaginous shell, of a long rectangular outline, on which stands erect another similar plate somewhat triangular, extending across from corner to corner. One large polypite or mouth hangs down from the centre of the under side, and short tentacles project on all sides from the edges of the horizontal plate. The internal structure is very complex. The whole is enclosed in a thin layer of flesh, which is tinged of a fine blue colour, sometimes varied with purple and green. It is generally about two inches long, and the erect plate rather less in height. As the little creature floats on the waves, this plate forms a sail, and the breeze playing upon it, imparts to the whole animal, according to Mr. Bennett, a rotatory motion.[126]

STEPHANOMIA.

Both these oceanic forms of the class _Hydrozoa_ agree in being quite unprovided with any apparatus for locomotion. Though their parts can be moved among themselves, and sometimes with much vigour, as we have seen in the case of the tentacles of the _Physalia_, yet the whole organism would be absolutely confined for life to one spot, were the elements motionless around it: it is merely passively driven hither and thither by the winds and waves. But there are other members of the class, and even some belonging to the same order, which have express organs of locomotion. A most exquisite example is found in _Stephanomia_, of which a specimen was taken in Kingstown harbour in July 1856, by Mr. Joseph Greene, and described and figured in the “Proceedings of the Dublin University Zoological Association” for that year. The float (_pneumatocyst_) is a small bladder, which is filled with air, and which has the appearance, when alive, of a globule of quicksilver; while the slight inequalities of its surface reflect the light in such a manner that it often looks as if a fine network of crimson veins ramified over its surface. From the end of this oval bladder a long fleshy tube hangs down in the water to the distance of six or seven inches, the upper part of which is surrounded by a number--seven to ten--of little clear transparent bells, looking very much like the blossoms of our common Arbutus, and crowded, like flowers with short footstalks, on the stem. These swimming bells (_nectocalyces_) are true organs of locomotion; for by their contraction they drive out the water contained in their cavities, and by their combined impulse, all acting together, shoot the whole creature forward. This action I will explain more in detail presently.

The long tube or common stem is very irritable, and under stimulus is coiled up in a spiral, then gradually relaxed, and allowed to hang loosely down. Attached to it throughout are the _polypites_, or stomach-mouths, protected by leaf-like organs, which overlap them. Numerous tentacles, too, of exceeding length and tenuity, and throwing off branches, spring from the stem throughout its length, all the extremities of each forming tiny oval knobs of spiral coils, the whole capable of being thrown into the most beautiful and graceful convolutions, now bent at right angles, and again thrown out in a series of light airy-looking arches.

The exquisitely beautiful specimen described was taken in sultry weather, when the sea was perfectly calm. “It lived in a large globe of sea-water for several days, and was a most striking and beautiful object: it generally lay quite upright in the water, the slightest ripple upon the surface of which set it in motion; and immediately coiling up its fishing lines, and shortening the length of its stolon by about one-third, it threw its set of little balloons into strong pulsations, until, weary of descending, it submitted to be guided by its brightly glittering head, and soon ascended to the surface. When subjected to examination it soon died, and was not long until it had completely broken itself up.”[127]

SARSIA.

The _nectocalyx_ or swimming-bell is, however, seen in a much more developed condition in the delicate forms which swarm in our harbours and about our rocky coasts in summer and early autumn, and are known by the name of Naked-eyed Medusæ. A common and very characteristic example of this order is the Tongued Sarsia,[128] in which a single swimming-bell forms the greatest portion of the whole creature. It is a tall dome of crystalline colourless flesh, thick at the summit and thinning off at the edges; about half an inch in height. From the interior of this dome hangs the single polypite, exactly as the clapper hangs from the top of a bell. It is long and cylindrical, abruptly attenuated at the upper part into a sort of foot-stalk, and at the extremity enlarging into four fleshy, very protrusile, lips, capable of seizing and sucking in an object much larger than the diameter of the whole polypite. I have seen a Sarsia, in confinement in a tank, lay hold of, and swallow, a newly-hatched fish, notwithstanding the activity of the latter. For hours afterwards the little green-eyed fry was visible, the engulphment being a very slow process; the Medusa, however, never let go its hold; and gradually the tiny fish was sucked into the interior, and passed up the cavity of the polypite, becoming more and more cloudy and indistinct, as digestion in the stomach gradually dissolved its tissues.

These little creatures are endowed with very effective powers of locomotion. In the unbounded freedom of their native sea, and in the limited dimensions of a glass vase, they are alike sprightly. By rapid pump-like contractions of their _nectocalyx_, they dart through the water, and shoot round and round, almost with the force and swiftness of a swimming fish. The summit of the bell always goes foremost, whether the direction of the movement be vertical, horizontal, or, as is most commonly the case, oblique; and the tentacles, and the long white polypite, drag behind in trailing lines. Now and anon, the shooting is suddenly suspended, the bell hangs over and remains awhile motionless, the tentacles are allowed to depend like spiders’ webs, or are suddenly drawn up into shrivelled puckers, become mutually entangled and intertwisted, then slowly free themselves, and hang down again. Sometimes the motionless bell itself sinks very gradually, and the tentacle-threads take the most elegant curves and arches in their descent.

The manner in which the strong pulsating movements of the Medusæ are performed depends on the position and action of certain bands of muscular tissue. Four of these radiate from the centre of the dome to the margin. This course is not a straight but a curved one. When, therefore, these bands are simultaneously and forcibly contracted in length, they are drawn from a curved into a straight line, and the cavity, which was bell-shaped, becomes more conical, and its capacity is considerably diminished; a portion of the water which it before held is therefore driven out at the mouth, and by its reaction forces the animal forward with a jerk in the opposite direction. Besides these radiating muscles, there are circular bands which pass round the margin and the interior walls of the dome. These by their contraction diminish the volume of the cavity, and aid the action described above.

FORBES’S ÆQUOREA.

The tiny Sarsia has but four tentacles, which spring from as many equidistant points on the margin of the bell. But in the genus _Æquorea_, of the same family, these organs are far more numerous, two species which I first discovered at Ilfracombe having, the one thirty-six, the other about two hundred tentacles. The former of these, which I have honoured with the name of the late Edward Forbes,[129] differs much in general appearance from the little Sarsia, being a cake-shaped segment of a globe, about three or four inches in diameter, and an inch and a half in thickness. The roof of the interior is low and nearly flat, or indeed dropping slightly in the centre.

The polypite is peculiar, and would scarcely be recognised as of the same nature with the lively bottle-shaped organs of the Portuguese man-of-war, or the long nimble tongue of the Sarsia. It forms a very wide circle on the flat roof of the bell, whence the four large triangular lips descend, which are cut into a minutely divided fringe of filaments, that wave loosely in the water. There are about seventy slender vessels which radiate from the polypite circle along the roof to the margin, where they join the circular marginal vessel. I have said that the tentacles are about thirty-six in all; that is, about half as many as the radiating vessels, though the relation of number is not exact. They hang down in the usual form, to the unassisted eye appearing as excessively slender whitish or flesh-coloured threads, capable of great elongation, or of contraction into ovate spiral masses, hardly perceptible. But by the aid of the microscope we discern that each tentacle consists of a lengthened fleshy tube, on which are set at pretty regular intervals thickened semi-rings, or knobs, very much like the knobs on the horns of an antelope in appearance. They do not quite encircle the tentacle, and thus one side for the entire length is smooth and straight. These thickened swellings are collections of thread-capsules (_cnidæ_), which are packed as close as they can lie in them, and give to the tentacle that power of adhering by a touch to any animal whose tissues are penetrable, and of benumbing and destroying its vitality, in the manner which I have already, on more than one occasion, alluded to.

I have not yet described the colours of this _Æquorea_; they are, however, exceedingly lovely and beautiful. The crystalline translucency of most of these Medusæ, when they are colourless, and of the colourless parts of such as have bright hues, is exquisite in its glass-like purity; in this example the whole of the peripheral portion of the dome is of this hyaline character; but the lower part, which lies just above the flattened roof, is of a lively azure blue, seen to great perfection, when the animal is relieved by a dark background: the colour is gradually lost at about a quarter of an inch from its bottom. Then the radiating vessels are of a bright rose-colour, drawn in lines along the colourless surface of the roof; and the marginal vessel is of the same hue, as are also the four triangular lips of the polypite, with their ciliary fringes. These, as they depend, often extending below the level of the margin, waved about in various directions by the motion of the sea, or by the animal’s own movements, add greatly to its elegance.

LUMINOSITY.

That strange and at times magnificent and imposing phenomenon, the luminosity of the sea, is certainly due in part to some of the Medusæ. Members of perhaps all the classes of marine invertebrate animals are at one time or other engaged in the illumination, and no doubt the most wide-spread production of spontaneous light, and the most effective, is due to creatures which are individually unrecognisable by the eye. When the ship ploughing through the tropical sea, turns luminous furrows on each side of her prow, and leaves a long wake of curdling light astern, or when the steamer dashes the water of our own estuaries into cascades of fire and showers of coruscating sparks, it is doubtless to the microscopic _Infusoria_, _Annelida_, and _Entomostraca_, that we are mainly indebted for the charming spectacle. Still, many of the Medusæ are conspicuously luminous under certain conditions, generally displaying the phenomenon at the moment of irritation; the light being evolved, not apparently by any proper organs, but either by the whole of the marginal ring, or by the (often coloured) swellings that are seated at the base of the tentacles.

The following appearances proved the luminosity of this beautiful _Æquorea_, on being subjected to experiments in the dark. When with my finger-nail I tapped the glass jar in which two specimens were floating at the surface, instantly each became brilliantly visible as a narrow ring of light, the whole marginal canal becoming luminous. On my touching them with the end of a stick, the light became more vivid, and round spots appeared here and there in the ring, of intense lustre and of a greenish-blue tint. These were, I doubt not, the tentacle-bulbs; and any one of them would be excited to this intensity by my touching that part of the margin with the stick. The luminosity of the ring was not so evanescent as in some species, lasting several seconds, and continuing to be renewed as often as I molested the animal. The two circles of light, two inches or more in diameter, were very beautiful as they moved freely in the water, sinking or rising according as they were touched, now seen in full rotundity, now shrinking to an oval, or to a line, as either turned sidewise to the eye, and reminded me of the _coronæ_ of glory in the pictures of the Italian school, round the heads of saints.

CRIMSON-RINGED JELLY-FISH.

Most of the larger Medusæ of our coasts belong to another order, including those which have covered eyes, and some other peculiarities, chiefly connected with reproduction. The _Lucernariæ_, which I have already noticed, formerly associated with the Anemones, are now united with this order. A very familiar example we may see in our harbours and tidal rivers in summer, the common Crimson-ringed Jelly-fish.[130] It is a hemisphere of colourless jelly, some six or eight inches in diameter, which is usually well marked by four imperfect rings of purplish crimson--the reproductive organs--seen through the transparent flesh. The radiating vessels are often tinged with the same colour.

INFANT FORMS.

The most interesting circumstances in the history of this large jelly-fish are the wonderfully varied phases through which it passes in the earlier stages of its existence. Along the margins of the lengthened flaps of the polypite there are found remarkable pouches, within which the ova are placed, and whence they are hatched in the form of soft flat animalcules, capable of swimming by means of cilia. This has been called a _planula_. After swimming a while, it alters its form to that of a pear, and presently adheres by its slender end to a sea-weed or rock under water, hanging downward. A depression now appears in the larger end, which deepens and forms a mouth and stomach, and the little _planula_ has assumed a polype-form. Four tiny warts now spring from the margin of the mouth, which lengthen into tentacles; four more then shoot in the interspaces; these eight increase to sixteen, then to thirty-two, all at the same time acquiring great length. In this stage, in which it is very common in our aquaria, it has been supposed a new animal, and has been named _Hydra tuba_. The space between the margin and the mouth has widened into an “umbrella,” and the mouth has protruded into a polypite. The whole is of a translucent white hue, and the body without the tentacles is ordinarily about one-sixth of an inch high.

This stage sometimes lasts for years without further change, except that creeping root-threads shoot from the attached base, which send up at intervals buds that grow into _Hydræ_; and buds break out from different parts of the body itself, which likewise develop themselves, the form in both cases being exactly similar to that of the present _Hydra tuba_. Thus we frequently find numerous colonies of these tiny creatures crowded together.

At length a change takes place. The body enlarges both in length and thickness, and begins to show traces of rings or segments, as if it had been tied tightly round with threads at regular intervals. In this stage it has been described under the name of _Scyphistoma_. These cuts deepen, and the segments thus marked off become hollow; and so they resemble a pile of tiny saucers set one within another, each of which is now divided at its rim into eight teeth. In this stage it has been once more named, as if an independent animal, _Strobila_.