Chapter VIII: Part 8

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.

PLATE 30.

P. H. GOSSE, _del._ LEIGHTON, BROS.

CYDIPPE. COMMON MEDUSA. LARVAL FORMS.
]

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_.

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.

PLATE 31.

P. H. GOSSE, _del._ LEIGHTON, BROS.

PYRGOMA ON A CORAL. SCALPELLUM. LOBSTER-HORN. NECKED BARNACLE.

COMMON BARNACLE. PORCATE BARNACLE.
]

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.

PLATE 32.

P. H. GOSSE, _del._ LEIGHTON, BROS.

SCARLET SERPULA.
]

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.

The protrusion of the fore parts, which takes place in a much more leisurely manner, is performed by quite another set of instruments, formed on a totally different principle. Their action is a pushing or shoving. The instruments for effecting this are the fine but strong bristles which run through the feet. Each bristle is composed of a strong rigid unyielding shaft, having an expanded shoulder drawn out into a point. On one side of this pointed shoulder may be remarked a double row of fine teeth, admirably calculated to catch against any roughnesses of the surface with which they come into contact, against which they then push with the force of the proper muscles. Acting diagonally backwards, from the two sides of the animal, the result of the combination of the forces is that the animal itself is pushed forwards, and so protruded from the mouth of the tube. The feet on the hinder portion of the body are, according to Dr. Williams,[142] modified in structure with express reference to the duties of mopping, sweeping, scraping, and wiping the inferior closed end of the habitation. I think, however, he has forgotten that this end, formed by the animal in its infant state, must now be very much too strait to be reached by any portion of the body, or by any of its organs.

Dwelling in a tubular house, the Serpula would find its breathing organs scarcely available, if these were placed, as in most _Annelida_, in pairs on the body-segments. They are therefore much modified, and that not only in position but in form. They consist of most elegant comb-like filaments, richly coloured, arranged in two rows around the front extremity, one row on each side of the mouth. They are graduated in length, and are so affixed, that, where the rows meet behind, they can be thrown-in, so that a vertical view of the circular coronet shows a great sinus in it. These brilliant gill-tufts form the most attractive feature in these elegant Worms, and are individually most exquisite examples of mechanical contrivance. Examined under a low microscopic power, they present a most charming spectacle. Each filament consists of a pellucid cartilaginous stem, from one side of which springs a double row of secondary filaments like the teeth of a comb. Within both stem and filaments the red blood may be seen, with beautiful distinctness, driven along the artery, and back by the vein (which are placed close side by side) in ceaseless course, constituting a very striking spectacle.

The exterior of these organs is set with strong cilia, so arranged that the water-current is vigorously driven upward along one side of the filament, and downward along the other. Yet the combined result of all the branchial currents is to bring a powerful vortex into the enclosed funnel, the bottom of which terminates in the mouth. The food which sustains nutrition is thus brought to be swallowed, a large quantity of water being at the same time constantly poured into the body; this is discharged (by the agency of a ciliated lining of the hinder parts) in the form of a strong current, which, impinging against the closed end of the tube, is turned upward, carrying with it all extraneous or fœcal matters, and is ever pouring out of the frontal extremity around the neck of the creature. What a beautiful and effective contrivance is this for constantly keeping in a state of the most unsullied cleanness the interior of the house! It reminds one of the fabled Hercules cleansing the Augean stable by driving the river Peneus through it.

ITS STOPPER.

On each side of the mouth there springs a lengthened horny thread, appearing to answer to the antennæ which in other Worms, as well as in Insects and Crustacea, project from the front of the head. Such seems their true relation considered structurally, but in function and office they are very remarkable and quite peculiar. To these organs is assigned the duty of closing up the tube when the animal has withdrawn its gaily-coloured plumes; and for this end, one of these antennæ is much lengthened, and at the end is expanded into a broad trumpet-shaped club, the extremity of which is somewhat concave, and is delicately marked with radiating grooves. This organ is usually painted with the same brilliant colours as the gill-tufts, and by its length, size, and form, makes a very conspicuous feature in the charming Serpula. Its length is such, that when the gill-filaments are rolled up and withdrawn, the conical club enters after all, and is found accurately to fit the trumpet-like orifice of the tube, just as a cork fits tightly into the mouth of a bottle.

Ordinarily those organs which appear in pairs are formed so as to be the counterparts of each other. But here is an exception. One only, sometimes the right, sometimes the left, indifferently, takes the remarkable form that I have been describing, the other being much shorter, and terminating only in a small knob, like the head of a pin. Why should there be this difference? Why this exception to an all but universal rule? The reason is obvious. Yes, obvious enough when seen and noticed; but it tells an eloquent tale of the Divine forethought and care. If both of the antennæ were furnished with the terminal cone, one would interfere with the other in the performance of their closing, corking-up function; they would jam in the doorway, and the tube would be left open. Hence the one is left undeveloped, yet retaining, as I believe, the latent power of expanding into a cone, if it should ever be needed by the accidental loss of the fellow now so furnished. I thus judge, because experience shows me that the conical club is occasionally thrown off, and quickly renewed, in captivity.

My esteemed friend, the Rev. Sir Christopher Lighton, has indeed put on record an example of a Serpula of this species possessing two equal antennæ, that had replaced the single one accidentally lost. They were both perfectly developed, and joined together near the base. Each was decidedly smaller than the single one that had formerly occupied their place.[143] This exceedingly interesting case can, of course, only be regarded as a monstrosity of redundancy, as children are sometimes born with a superfluous finger. But it is valuable as showing that there is a power of development latent in the crownless antenna. I wish very much that the excellent observer had added a note, telling us to what extent the tube was closed, and how the work was performed without mutual interference.

It has been sometimes brought as an objection to our assigning a certain service to certain organs, that the necessity for such service is a gratuitous supposition, since other creatures similarly formed in most respects, and in which we might infer a like need, have no such supply. We may admit the facts, but refuse the reasoning. There can be no manner of doubt that the conical antenna does act as a stopper to the Serpula, as our eyes can see; and surely it would be most unphilosophical to suppose that the function so performed is not serviceable to the creature. Yet its near cousins, the Sabellæ, similarly constructed, and of similar habits of life, and as we should have _à priori_ supposed, quite as liable to injury in the same direction, are entirely destitute of this contrivance for protection, and of anything compensating for it, so far as is known. Why the need of one should be met by such a beautiful contrivance, while the same need in the other is wholly unmet, though both are formed by the same Infinite God, is one of those unanswerable questions which, while they leave unimpeached His wisdom, make us deeply conscious of our own ignorance.

We find numerous examples of this genus _Sabella_ in our confused heap of tangled life and death. By their vigour and their abundance we have proof enough that their wants _are_ supplied, though they do not enjoy this special contrivance: they manage to live and thrive and enjoy themselves, with open doors, taking all risks of insidious robbers,--such, for instance, as that vile burglar, the Longworm,[144] that we found under a stone the other day; which is ever on the watch to insert its snaky head within the unprotected tube, and to tear away with merciless clutch the beauteous gill-tufts.

PLATE 33.

P. H. GOSSE, _del._ LEIGHTON, BROS.

SABELLÆ.
]

One species of this genus[145] can by the cursory observer be distinguished from the Serpulæ, only by this absence of the antennal stopper. For it dwells in a shelly tube, essentially resembling those which we have just been examining. It has peculiarities of detail, however. It is never found associated with numbers of its fellows in agglutinated groups, but always, so far as my experience goes, singly. It is more common on shells than on stones, generally attached to the old valve of some cockle or scallop. It is straight or nearly so, never at least contorted. Attached only for a very short portion of its smaller end, perhaps for an inch or so, for which it creeps along the surface, it then rises into a more or less erect position, extending sometimes to a height of seven or eight inches perfectly free. The tube is of about the same diameter as that of the Serpula, but is slighter in structure, or perhaps it appears so, because it is destitute of those expansions which here and there in that species indicate the trumpet-lips of successive stages of development. The extremity of the tube here is simple, not expanding. Slight annular rings, however, do here and there vary the shelly surface of the tube.

The gill-tufts are ample; they are two, considerably infolded, consisting of about forty-five filaments each, which are much longer and slenderer than those of the Serpula, the last filaments of the volutions diminishing rapidly. The secondary filaments, or pinnæ, are very fine and very numerous, so set on the main stem that the two rows form the sides of a narrow groove, facing inwards. The whole is yellowish-white with eight or ten bright scarlet dots set with intervals all along the back or outer side of the stem. When fully protruded, the base of the gills, and even a good deal of the neck, lolls out of the tube. If the animal be removed, the body is seen to be white, elegantly banded with scarlet, and furnished with a broad translucent collar, edged with scarlet: this collar ordinarily lines the mouth of the tube.

From the length and isolation of its shelly tube this is a remarkable species: the great tenuity of its filaments, however, requires a lens to bring out their beauties; but with this aid, the arrangement of the rich scarlet bands and spots on the pale yellow ground cannot fail to evoke admiration.

SABELLÆ.

In general, the Sabellæ inhabit tubes which are not calcareous or shelly; they are composed of a soft flexible substance somewhat resembling wet parchment, made of a secretion from the animal’s body, in which the impalpable muddy sediment which the waves agitate, consisting of decomposed organic matter for the most part, is interwoven. The tissue so made is sufficiently tough and enduring, retaining its form long after the animal has died out of it.

In our dredge-hauls we find a pretty little kind[146] common enough, which lives in association, the tubes apparently from half-an-inch to an inch in length, forming dense masses on stones and shells, and projecting in every direction. A dozen or more may be in one group, and when all are alive, one or another protruding or retiring every moment, it makes a pretty object.

The gill-filaments are nine to eleven in each row, of a yellowish white, occasionally patched with dead-white, or red-brown: delicately and densely pinnate. The filaments, in the act of protruding, are closed together like a straight bundle of rods which suddenly fall open at the ends. In this moment of unfolding, their tips are seen to be a little hooked inwards. The tube is about as large as a crow-quill; under a lens it appears speckled, as if the inorganic matter imbedded in it were grains of the finest sand. On carefully removing all the surrounding tubes and other objects so as to isolate one, we see that it is truly about three inches in length, but that two-thirds of the whole are prostrate and adherent; this basal portion is horny and pellucid, no mud entering into its texture. The animal when extracted is an inch in length, of which the gill-tufts form one-third.

Mingled with these there are one or two specimens of a much more imposing species, the Hook-plumed Sabella.[147] It grows to a large size, the crown of gill-filaments sometimes attaining a height of an inch, and the same diameter. The two rows are incurved in regular spirals of half a turn, each consisting of about eighteen filaments, which are rather stout, the whole crown sometimes taking the form of a funnel, sometimes that of a cup, often arching inward at the tip. Their pinnæ are long and close, the two rows forming a groove, but nearly parallel. Each primary stem is set along the back with twelve pairs of feather-like processes, hooked downwards;--a very remarkable character, and one by which this species may be in a moment distinguished. Their colour is pale red-brown, mottled irregularly with deep brownish purple and with white; there is a pair of brown specks at the origin of each pair of hooks. The base of the crown is always concealed in the mouth of the tube, but it springs from a narrow frilled membrane of pure white. The body is destitute of a thoracic shield, or conspicuous collar. The tube is largely composed of soft homogeneous mud, usually of a pale purplish hue, of about the thickness of the shelly tube of _S. tubularia_.

TUBE-BUILDING.

The process of building the mud tubes of the Sabellæ is a very interesting one. It is performed, according to my own observations,[148] mainly by means of the gill-filaments and their pinnal grooves. The filaments are bent-over, till the inner or grooved face comes in contact with the soft mud on which the animal is lying, when the sensitive pinnæ close on a minute portion of the mud, taking it up in a pellet, which is then fashioned by the form of the groove; the filament is now erected, and the pellet, passing down the groove to the bottom by means of the cilia, is delivered to the care of two delicate moveable organs, like leaves or flaps, which place it on the edge of the tube, and then shape and mould it, smoothing both surfaces. Doubtless, either from these organs, or from some other part of the circumjacent region, the glutinous secretion is at the same time poured out, which consolidates the mud, and forms the true basis of the tube.

FOOTNOTES:

[133] _Antennularia antennina_, figured in Plate XXXI., springing from the lower left corner. It will be easily recognised from the description.

[134] For details and figures of these developments, I beg to refer the reader to my _Naturalist’s Rambles on the Devonshire Coast_.

[135] _Scalpellum vulgare_, seen in Plate XXXI., in the position described in the text.

[136] _Balanus balanoides_, of which a group is seen in the extreme left of the foreground in Plate XXXI.; _B. porcatus_, a single specimen, is a little to the right.

[137] _Lepas anatifera_. A group, the size of life, is seen depending in the upper right-hand corner of Plate XXXI.

[138] _Pyrgoma Anglicum_, of which three specimens are seen attached to a _Caryophyllia Smithii_, at the left side of Plate XXXI.

[139] _Zoologist_, pp. 7054, 7111.

[140] _Serpula contortuplicata_, a mass of which forms the subject of Plate XXXII., mingled with _S. triquetra_.

[141] Some in this infant state are seen in Plate XXXIII.

[142] Brit. Annelida, in _Rep. Brit. Assoc._, 1851.

[143] _Zoologist_, p. 5976.

[144] _Vide supra_, p. 135.

[145] _Sabella tubularia_, represented as occupying the foreground and the left-hand side of Plate XXXIII.

[146] I have figured a group in the centre of Plate XXXIII. I cannot satisfactorily identify it with any species described in Grube’s _Fam. der Anneliden_. It has some affinities with the _Sabella penicillus_ of Müller; and still more with _S. gracilis_ of Grube. This latter is defined, however, as wanting the two naked threads by the mouth, which in my little species are sufficiently conspicuous. I must leave it undetermined.

[147] _Sabella bombyx_, represented in Plate XXXIII., towards the right hand, springing out of a group of Serpula tubes.

[148] _Intellectual Observer_, vol. iii. p. 77.

XII.

DECEMBER.

December is here, with its short days, its feeble watery sunshine, its frequent gloom and mist, its hanging leaden skies; in short, as the poet describes it,--

“Sullen and sad, with all his rising train;
Vapours and clouds and storms.”

It requires some zeal in the pursuit of scientific lore to leave the glowing fire and the pleasant book, the luxurious arm-chair and the elastic carpet, and to venture down to the wild sea-beach, to poke and peer among the desolate rocks. Yet even now we may find a few bright days, when Nature abroad looks inviting, and when an hour’s marine research will prove neither unpleasant nor unsuccessful.

SQUIRTERS.

On such a noon, then, calm and quiet, the sun bright and cheerful, if low and feeble, the tide tolerably low and the rocks accessible, we hie down to some one or other of those ledges which have so often already yielded their treasures to our search, and begin our wonted labours at turning over the heavy angular masses. We soon find, attached to the under surfaces of these, what seem to be irregular blobs of coloured jelly of somewhat firm consistence, as if an invalid had been here eating his calves’-foot jelly, whose trembling hand had dropped sundry spoonfuls on the stones. Some appear as flattish shapeless drops, but others take more elevated forms, like sacks set on end, and usually displaying two mouths. One of these is of a pellucid yellowish green, or olive hue, with a cloudy spot of rich orange in the interior. A slight shrinking from the touch, a yet closer contraction of the projecting points, is the only token of life that we can discern in it now; but if we place it in an aquarium,--not forcibly removing it from its attachment, but lifting the shell or stone on which it rests; or, if this be too large, detaching the fragment with a chisel,--and allow it to remain a few hours undisturbed, we shall see evidences of a vitality, indubitable if not very active.

The whole creature is now much plumper and more pellucid; it stands up boldly from its base on the stone; its upper portion is much lengthened, and the two wart-like eminences have become two short tubes with gaping extremities, appearing as if they had been soldered together side by side, of which the one is considerably higher than the other.[149]

We have before us one of the _Tunicata_, an order of molluscous animals which are closely allied to the _Conchifera_ or bivalves, but somewhat lower in the scale than they. It has no shell; that is to say, lime is not deposited in the outer investment, so as to give it the hard, rigid, solid texture of shell; but the internal organs, which are essentially similar to those of an Oyster or a Sand-gaper, are enclosed in a tough leathery coat, known as the _test_, which is in fact a closed shell destitute of lime. The eminent physiologist, John Hunter, who had dissected some of these homely Squirters, as they are familiarly called, recognised, with his wonted acumen, the structural similarity of their leathery envelopes to the stony shells of the lower bivalves; and, associating them in a group, called them “soft-shells.” The naturalness of this group, since called _Tunicata_ by Lamarck, has been recognised by modern zoologists.

PLATE 34.

P. H. GOSSE, _del._ LEIGHTON, BROS.

ORANGE-SPOTTED SQUIRTER. FOUR-ANGLED SQUIRTER. CURRANT SQUIRTER. ]

THE GILL-SAC.