Part 17
All this time the tentacles have been set around the terminal margin, but now these are absorbed, and a new set rapidly spring from the basal segment. The saucers become very loosely attached; at length the end one breaks away and swims through the sea, as a true Medusa, though no more than a sixth of an inch wide, pumping as it goes in proper parental wise. Others quickly follow, and thus a colony of tiny swimming jelly-fishes are shooting hither and thither in the liveliest manner. Strange to say, these little Medusæ, which as to details differ much from their adult form, have been again described, under the name of _Ephydra_; all these appellations indicating the assumptions of various naturalists, who found the little creatures in their respective stages, without knowing their previous history, that each was an independent form of animal life.
CYDIPPE.
As the closer and more severe scrutiny of anatomical structure has induced modern zoologists to separate the Lucernaria from its formerly assigned alliance with the Sea-anemones, and to associate it with the Medusæ, it is interesting to remark that the scales of justice have been maintained in equipoise by the like shifting of a member from the Medusæ to the Anemones. The latter animal is one familiar to most haunters of the shore, and invariably admired as one of the most charming of the many lovely forms that throng the summer seas; it is the sweet little _Beröe_, or _Cydippe_.[131] Indeed at first sight you would be little disposed to admit the propriety of the transfer in this case, for certainly the active glittering globule of pure crystal appears to possess much more resemblance to one of the smaller Medusæ, the _Sarsia_, for instance,--than to a daisy or a beadlet. But naturalists look beneath the surface: and they find that, with important peculiarities, the internal economy of the _Cydippe_, and specially its digestive apparatus, are modelled rather on the type of the latter than of the former.
We will not, however, trouble ourselves now with these elaborate matters, but rather look at the exterior and obvious characters of the charming little pet, which is disporting itself in this vase of sea-water on our table. It is a globe of pure colourless jelly, about as big as a small marble, often having a little wart-like swelling at one of its poles, where the mouth is placed. At the other end there are minute orifices; and between the two passes the stomach, of a form which is flat, or wider in one diameter than in the other.
If the stomach be considered as the axis of the globe, and the two extremities as its poles, the meridians of longitude are well represented by eight narrow bands, situated on the surface, which do not, however, reach either pole. Along the course of each of these meridional bands are fixed at close intervals minute square moveable plates, whose outer edges are set with strong cilia, like the teeth of a comb. These are the locomotive organs, and most effective they are. They are used like the paddles of a steamer, the little animal beating the water with them in rapid and regular succession, their minute subdivision causing the rays of light, especially when in the sun, to play along these bands, with the most brilliant prismatic colours; while their vigorous strokes cause the globe to shoot hither and thither through the water with remarkable power.
Within the clear substance of the _Cydippe_, on each side of the stomach, there is excavated a capacious cavity, which communicates by a canal with the surface, near the equator. Within each cavity is fixed a tentacle of great length and slenderness, which the animal can at pleasure shoot out of the orifice, and allow to trail through the water, shortening, lengthening, twisting, or coiling it at will; or, on the other hand, quickly contract it into a tiny ball, and withdraw it wholly within the proper cavity. A peculiarity, which imparts an inexpressible charm to this apparatus, is, that, throughout the length of this attenuate white thread, short threadlets are given off at regular intervals, which can be coiled or straightened, lengthened or shortened, individually. They proceed only from one side of the thread-like tentacle, though, from the slight twisting of the axis, they seem now to project on one side, now on another.
It has been well observed that of the grace and beauty which the entire apparatus presents in the living animal, or the marvellous ease and rapidity with which it can be alternately contracted, extended, and bent at an infinite variety of angles, no verbal description can sufficiently treat. Fortunately this little beauty is so common in summer and autumn on all our coasts, that few who use the surface-net can possibly miss its capture. So lovely a creature is worthy of a poet’s description: it has received it.
“Now o’er the stern the fine-mesh’d net-bag fling, And from the deep the little Beroë bring; Beneath the sunlit wave she swims conceal’d By her own brightness;--only now reveal’d To sage’s eye, that gazes with delight On things invisible to vulgar sight. When first extracted from her native brine, Behold a small round mass of gelatine, Or frozen dew-drop, void of life and limb: But round the crystal goblet let her swim ’Midst her own element; and lo! a sphere Banded from pole to pole; a diamond clear, Shaped as bard’s fancy shapes the small balloon To bear some sylph or fay beyond the moon. From all her bands see lucid fringes play, That glance and sparkle in the solar ray With iridescent hues. Now round and round She wheels and twirls; now mounts, then sinks profound. Now see her like the belted star of Jove, Spin on her axis smooth, as if she strove To win applause--a thing of conscious sense Quivering and thrilling with delight intense. Long silvery cords she treasures in her sides, By which, uncoil’d at times, she moors and rides; From these, as hook-hairs on a fisher’s line, See feathery fibrils hang in graceful twine, Graceful as tendrils of the mantling vine These swift as angler by the fishy lake Projects his fly the keen-eyed trout to take, She shoots with rapid jerk to seize her food, The small green creatures of crustaceous brood; Soon doom’d herself a ruthless foe to find, When in Actinia’s arms she lies entwined. Here, prison’d by the vase’s crystal bound, Impassable as Styx’s nine-fold round, Quick she projects, as quick retracts again, Her flexile toils, and tries her arts in vain; Till languid grown, her fine machinery worn By rapid friction, and her fringes torn, Her full round orb wanes lank, and swift decay Pervades her frame, till all dissolves away. So wanes the dew conglobed on rose’s bud; So melts the ice-drop in the tepid flood: Thus, too, shall many a shining orb on high That studs the broad pavilion of the sky,-- Suns and their systems fade, dissolve, and die.”[132]
FOOTNOTES:
[123] _Physalia pelagica_, of which a representation is given in the centre of Plate XXVIII. Some naturalists make two or three other species, but I do not think that their distinctive characters can as yet be depended on.
[124] _Gatherings of a Naturalist_, p. 7.
[125] I ought to say that, as usual in these stranded examples, the tentacles and suckers were so mutilated by washing on the shore, that I have been compelled to aid my observation by the figures of Eschscholtz and Huxley, on whose correctness I could depend.
[126] See his _Gatherings in Australasia_, for much interesting information on both these animals.
[127] _Op. cit._
[128] _Sarsia tubulosa_; a group is represented of the size of life, in the lower right-hand corner of Plate XXVIII.
[129] _Æquorea Forbesiana_; this fine species forms the subject of Plate XXIX.
[130] _Aurelia aurita_, represented (about one-fourth of the natural size) in Plate XXX. On the extreme right and left are seen the young, in the stages of _Hydra_, _Strobila_, and _Ephydra_.
[131] _Cydippe pileus_, seen, of the size of life, near the upper left-hand corner of Plate XXX.
[132] Dr. Drummond, in Trans. Roy. Irish Acad. for 1839.
XI.
NOVEMBER
If we could roam at pleasure over the bottom of the sea, with the privilege of using all our senses as effectually and as comfortably as in the air, we should doubtless see some wonderful things. We might not, indeed, find all the useful and ornamental articles that drowning Clarence saw in his dream, but doubtless we might substitute for them things that he never dreamed of, things that the eye of man was not as yet cultivated to see. What opportunities for enlarging the bounds of science are possessed by the engineers that have been working many hours a day, for years past, at the great Breakwater in that prolific field of marine life, Weymouth Bay!--working in a capacious diving-bell at the bottom of the sea. But there are many reasons why we can expect nothing in the way of natural history from them. Perhaps not one of them has ever been taught to think upon any of the strange forms that might occur, which do not commonly minister to the pocket of man in the market, as anything but mere rubbish not worth a second glance, or something hurtful or nasty to be crushed beneath the heel. Or if, perchance, an observer of nature’s beauties be engaged in such an occupation, his time would be so fully taken up with his urgent duties, as to preclude attention to such amenities. Besides which, the loads of enormous blocks of stone already shot down on the sea-floor, which he is there to arrange and settle, must pretty well have smashed and covered everything which had revelled in dull enjoyment there, before his arrival. Still I fancy I should like to borrow his diving-bell on a holiday, and roam a little beyond those wildernesses of broken stone, picking up treasures here and there such as the scraper of the dredge has never yet been able to gather out of the crevices and crannies of those deep-water rocks.
But such a desire is at present hopeless; and we must be satisfied with such resources as are at our command, thankful that the dredge, and the trawl, and the keer-drag, the fisherman’s deep-sea line, the lobster-pot, and the sounding-lead--are all contributing to our acquaintance with the curious, the uncouth, the wondrous, the beautiful, that lurk far down _in profundis_.
Let us then go back to the results of our dredging day that we so much enjoyed a few weeks ago. A portion of its produce yet remains in buckets and pans, waiting for a further overhauling; and it will doubtless yield us some objects worthy of an hour or two’s investigation.
LOBSTER-HORN CORALLINE.
The first thing that our fingers pull up is a great tangled group of Sertularian _Hydrozoa_, of which the finest part consists of some half-dozen stems of _Antennularia_, called, from obvious resemblance, the Lobster-horn Coralline.[133] These are nearly straight, somewhat stiff, unbranched stems, a foot or more in length, with an uniform thickness of about a line, of a buff-yellow hue, closely divided into short joints. Each of the joints gives origin to a whorl of very delicate bristles, giving a hairy appearance to the whole affair, but which under magnifying power are discerned to be colourless, jointed filaments, bearing on the inner shoulder of each joint a tiny glassy cup (_hydrotheca_), within which resides a minute many-tentacled polype. The stems spring in close groups from an obscure root-mass of tangled threads, which cling to stones and shells, and afford a mooring to the Lobster-horn, which in its turn affords support to miniature forests of other _Hydrozoa_, slenderer than the finest hair--_Laomedea_, _Campanularia_, etc., which crowd together on it, especially around the bottom, and make the investigation of any one specimen very difficult. These have their polype-cups of exquisitely elegant forms, and I see on the latter many of the urn-shaped vessels (now called _gonotheca_), out of which issue what appear to be distinct and independent forms of life, as unlike the parent as can well be imagined, but exactly like the little naked-eyed Medusæ that we lately looked at. This, however, is not properly an animal at all, but only an organ (the _gonophore_) which has the faculty of maintaining a separate existence, and which is destined to give birth to ciliated embryos, like the _planula_ of the _Aurelia_, that attach themselves, and develop into new _Campanulariæ_. Most wonderful are the processes and phases of life which have been discovered in these zoophytic forms.[134] A volume might be written on them, full of praise to the all-wise God.
SCALPELLUM.
Now, however, we must turn aside to look at other objects. Attached to the base of the Lobster-horn, we find several examples of an interesting Cirripede.[135] It is of a dirty buff, or drab hue, semi-transparent, in outline something like a butcher’s cleaver, handle and blade, or still more like a silver butter-knife, but much thicker in proportion; the handle represented by the cartilaginous and flexible stalk, the blade by the compressed valves. These vary much in regularity of form, some being nearly oval, little wider than the stalk, others angular and much wider. The body throws itself vigorously about on the stalk, when disturbed. The valves open, and out comes a widely radiating hand, of brilliantly glassy fingers, the joints and comb-like bristles of which glitter and sparkle as I hold it up in a tumbler of sea-water, examining it with a lens, with a lamp behind. It remains some seconds expanded, as if enjoying contact with the water; or perhaps, if I may draw inferences from some slight twitchings, feeling and testing for the accidental presence of invisible atoms that might serve it for food; then suddenly the fingers close together, and the hand is drawn in with a snap, as if it had taken some prize, though the lens had revealed nothing there. Soon it opens again, and exhibits the same manœuvres. A front view of the hand, the bristle-like fingers radiating in all directions, is a very attractive object for a low magnifying power. There are several tiny ones in another group, the bodies of which are not bigger than hempseed; these make their grasps apparently at random, with regular alternation, much as the commoner Barnacles do.
Of these latter we have no lack, many of the rough shells and small pebbles being incrusted with crowded colonies of the commonest Acorn Barnacle.[136] We see the same species, by tens of thousands, covering roods and roods of the seaward surfaces of our rough rocks between tide-marks. They rarely exceed one-third of an inch in diameter at base; but there is a much more massive kind, rough with ridges and furrows, and hence called _porcate_, occasionally found adhering to the jutting angles of rocks hereabout, and much more commonly on the coast of South Wales, around Tenby.
These Acorn Barnacles have no foot-stalk, but adhere by the whole broad base to the rock or shell, on which a floor either of strong stone, or of thin membrane is formed, and from whose margin the stony plates arise, enclosing a more or less conical chamber, with an orifice at the summit. If we look in at this during the life of the animal, we discern, a little below the rim, some angular valves, which meet with a straight suture, and close the interior. These are moveable, however; and under water they open like folding-doors, and a hand of many fingers, each composed of many joints, modelled on the same plan as that of the _Scalpellum_, but less delicate, protrudes, which makes its cast for prey, and is withdrawn beneath the again-closed valves.
NECKED BARNACLES.
The winds and waves not unfrequently bear into our harbours fragments of spars, old water-casks, or planks, from the hull of some ill-fated ship foundered in the inhospitable ocean, which are teeming with life. Conspicuous on such “flotsam and jetsam,” as our ancient maritime law-codes term these relics, we mark the Necked Barnacles,[137] so long believed by our ancestors, with a most implicit credence, to be legitimately descended from, and to be in turn the regular and normal parents of, a certain species of goose, common enough on our northern shores. That myth may, however, be dismissed with a mere recollection.
In this form the neck or stalk is greatly developed, frequently reaching to eight inches and upwards in length, with a thickness of half an inch. Externally it is very tough and leathery, yet it is sufficiently flexible to be jerked vigorously in various directions, and thrown into contorted curves, by means of muscles that run through it. The lower part adheres firmly to the support, which is generally wood, and I believe only in a floating condition. The bottoms of ships in warm climates are generally much infested with these parasites, which acquire a great size in the course of a voyage of only a few months.
The valves resemble delicate shells, and are elegantly painted with various tints of light blue varied with white, the edges of the valves being often rich scarlet or orange. The hand is deep purplish black, the fingers stout and massive; but not differing in their structure or in their mode of use, from those of their sessile fellows.
Perhaps the most interesting of all our native forms of these Cirripedes--for true parasitism is always a subject of peculiar interest--is that little species[138] which invariably selects as its support the stony walls of a coral. Our beautiful Cup-coral, so common at extreme low-water level on both the north and south coasts of Devon and Cornwall, is the favourite species of the _Pyrgoma_. So far as my experience goes, extending over a very extensive series of specimens, I think about one in six of these corals carries the parasite, generally situated either on, or just without, the margin of the cup. I say, “generally,” because Mr. Guyon has lately recorded what he thinks an exception to the rule, in two _Pyrgomata_ situated on the rock close to the base of the coral. But Mr. Holdsworth, an excellent authority, considers that the exception is more apparent than real. The number of these little intruders varies from one upwards. I possess specimens, one of which carries nine, the other eleven; the appearance of the ovate barnacles, each with its conspicuous orifice, crowded all round the edge of the coral, is exceedingly curious and novel. Mr. Holdsworth mentions, however, that he has seen fourteen _Pyrgomata_ attached to a single _Caryophyllia_, which was dredged in Plymouth Sound.[139]
CIRRIPED TRANSFORMATIONS.
The transformations of these animals, as investigated by Mr. Darwin, are of great interest. The Cirripede, whatever its genus, and whatever its peculiarities of adult existence, begins its life in a form exactly like that of a young Entomostracous Crustacean, with a broad carapace, a single eye, two pairs of antennæ, three pairs of jointed, branched, and well-bristled legs, and a forked tail. It casts off its skin twice, undergoing, especially at the second moult, a considerable change of figure. At the third moult it has assumed almost the form of a _Cypris_, or _Cythere_, being enclosed in a bivalve shell, in which the front of the head with the antennæ is greatly developed, equalling in bulk all the rest of the body. The single eye has become two, which are very large, and attached to the outer arms of two bent processes like the letters U U, which are seen within the thorax.
In this stage the little animal searches about for some spot suitable for permanent residence; a ship’s bottom, a piece of floating timber, the back of a whale or turtle, or the solid rock. When its selection is made, the two antennæ, which project from the shell, pour out a glutinous gum or cement, which hardens in water, and firmly attaches them. Henceforth the animal is a fixture, glued by the front of its head to its support. Another moult now takes place; the bivalve shell is thrown off, with the great eyes, and their U-like processes, and the little Cirripede is seen in its true form. It is now in effect a Stomapod Crustacean, attached by its antennæ, the head greatly lengthened (in _Lepas_, etc.), the carapace composed of several pieces (valves), the legs modified into cirri, and made to execute their grasping movements backwards instead of forwards, and the whole abdomen obliterated, or reduced to an inconspicuous rudiment.
SERPULA.
Let us resume our grubbing in the heterogeneous heap of matters with which the dredge has enriched us. The tube-dwelling _Annelida_ are generally prominent in such collections, and accordingly we see conspicuous here great and small heaps of contorted tubes, that look as if a batch of tobacco-pipe stems had become agglutinated together, and strangely twisted in the baking. These are the shelly tubes of the beautiful scarlet Serpula,[140] a general favourite in our aquaria, easily and abundantly procured, and readily maintained in health and beauty for a considerable period. I need scarcely describe the general appearance of an object so commonly kept, and so frequently gazed upon. Many tubes are usually found growing together, adhering to the same shell, bit of broken pottery, or small stone; all much intertwined, and mutually adherent, so that it is practically hopeless to attempt to isolate one. Yet by studying many specimens we are able to ascertain that each individual is at first a very slender tube of white calcareous shell, not thicker than sewing-cotton;[141] this rapidly increases both in thickness and in length, soon rising from its support, to which it at first adhered by the lime deposited in a soft state, and continuing the rest of its growth free, in a direction forming various angles with the ground line, and most irregularly twined and contorted. For the final half of its length, or thereabout, the tube attains a diameter of one-fourth of an inch, the walls being sufficiently thick to be solid, yet leaving an ample cavity for the residence of the industrious mechanic, who thus skilfully builds up his own house.
If we carefully break, by a moderated blow with a hammer, the shelly tube, so as not to crush the tenant, we are able to expose the latter to view. We then see that its length is by no means commensurate with the length of its house, of which indeed it inhabits only the last-made portion, having behind a roomy space into which to retire in case of need. It is not more than an inch or an inch and a quarter long, rather wide in proportion, and flattened, with a well-marked distinction between the corslet and the abdomen. The former carries on each side prominent foot-warts, which are vigorously protrusile, and within which bundles of strong bristles are thrust to and fro. On the upper part of each foot, extending half across the back, is a row of microscopic hooks, wielded by long thread-like tendons, which are fixed, on mechanical principles, to the attached end of each hook. By the aid of these, the Serpula so cleverly withdraws with lightning-like rapidity on alarm. By the action of muscles of indescribable delicacy, the hooks are projected to some distance beyond the surface of the body. These organs are formed on the model of a hedger’s bill-hook, only that the edge is cut into long teeth. Carefully counting them I have found that each Serpula carries about 1900 such hooks on its corslet, and that each of these being cut into seven teeth, there are between 13,000 and 14,000 teeth employed in catching the lining membrane of the tube, and in drawing the animal back.