Part 16

CRABS.

But now the tide has reached its lowest mark; and as we wander over the wet sand at its very verge, our attention is attracted by every tiny object that breaks the uniform level, even at a considerable distance. Some of these are worm-casts thrown up by busy Annelids, working away in the sand to reach a lower and therefore a wetter level, as the upper stratum dries in the sun. But others are Crabs, of two or three species. One of them is the somewhat uncommon and very beautiful Portumnus variegatus, of which a great number are left by the sea, but all of them dead; some of them, however, from their freshness, only recently defunct. The shape of the carapace, or body-shell, is very elegant, and the colours, though sober--a light drab, mottled and pencilled with pale lilac--are pleasing: the hindmost pair of feet terminate in thin swimming-plates, but they are narrow, and exhibit the natatory character in only a subordinate degree.

Other Crabs are alive and active, though, to be sure, in a somewhat sluggish way. Here we catch sight of a slight movement in the wet sand, and, stooping, we perceive a pair of antennæ, much beset with short bristles, projecting from the surface. They wag to and fro, and presently up pushes a shelly head, with its pair of stalked and jointed eyes, and two tremendously long angular arms, furnished with awkward-looking nippers at their extremities. Another effort, and the whole Crab emerges from his sandy burrow, and displays his pale buff-coloured shell, wrinkled across, and armed with sharp spiny points at its front and edges. We easily take him up, for his means of escape are feeble, as he uncouthly shuffles on his short legs over the sand; and his bellicose instincts are not strongly developed, nor, if they were, have those long levers of arms any formidable powers of offence. Latreille gave to the genus the title of Corystes; which signifies a warrior armed for battle, from κόρυς, a helmet, but its inoffensiveness belies the appellation. Pennant had already conferred on the species the name of Cassivelaunus, the ancient British chief immortalized by Cæsar. If you were to ask me why this obscure crab should bear a name so renowned, I can answer only by conjecture. The carapace is marked by wrinkles, which, while in some specimens they suggest nothing, in others, especially old males, bear the strongest and most ludicrous resemblance to the face of an ancient man. I have taken specimens in which the vraisemblance was so perfect as to strike me, and others to whom I showed it, with amazement. Now Pennant, as is well known, had strong sympathies with his British ancestry; and perhaps, by a not extravagant stretch of imagination, his playful fancy saw the features of the grand old Celtic warrior perpetuated on this Crab, which he first met with, too, be it remembered, on the Welsh coast.

PLATE 14.

P. H. GOSSE, del. LEIGHTON, BROS.

MASKED CRAB. ]

USE OF THE ANTENNÆ.

Mr. Couch, in his Cornish Fauna, notices the unusual length of the antennæ. “These organs,” he says, “are of some use beyond their common office of feelers; perhaps, as in some other crustaceans, they assist in the process of excavation; and, when soiled by labour, I have seen the Crab effect their cleaning by alternately bending the joints of their stalks, which stand conveniently angular for this purpose. Each of the long antennæ is thus drawn along the brush that fringes the internal face of the other, until both are cleared of every particle that adhered to them.” This suggested use of the antennæ does not seem to me to be a very felicitous guess of the excellent Cornish naturalist: I should fancy them to be somewhat inefficient instruments in excavation: perhaps I can help him to a better. I have observed that, when these Crabs are kept in an aquarium, they are fond of sitting bolt upright, the antennæ placed close together, and also pointing straight upward from the head. This is, doubtless, the attitude in which the animal sits in its burrow, for the tips of the antennæ may often be seen just projecting from the sand. When the chosen seat has happened to be so close to the glass side of the tank as to bring the antennæ within the range of a pocket lens, I have minutely investigated these organs, without disturbing the old warrior in his meditation. I immediately saw, on each occasion, that a strong current of water was continuously pouring up from the points of the approximate antennæ. Tracing this to its origin, it became evident that it was produced by the rapid vibration of the foot-jaws, drawing in the surrounding water, and pouring it off upwards between the united antennæ, as through a long tube. Then, on examining these organs, I perceived that the form and arrangement of their bristles did indeed constitute each antenna a semi-tube, so that when the pair were brought face to face the tube was complete. It is difficult to make this arrangement intelligible by mere words; but I may say that if either of the antennæ were broken off in the middle and viewed vertically, the bristles would be seen to project from each side of the inner face, in a curved form, each making about a fourth of a circle, so that the two corresponding bristles enclose, with the body of the antenna, a semicircle. Of course, those of the opposite antenna make another semicircle, and, when placed face to face, the points of the bristles just cross each other, and a circle is enclosed. Now, the whole length of the antennæ (about an inch and a half) is closely beset with these bristles, and thus a long row of rings is formed with very narrow interspaces between them; and these rings do in effect constitute a tube quite sufficient to retain the stream of water that is poured through it.

I think then that we may, with an approach to certainty, conclude that the long antennæ are intended to keep a passage open through the sand, from the bottom of the burrow to the superincumbent water, for the purpose of pouring off the waste water, rendered effete by having bathed the gills: and it is one of those exquisite contrivances and appropriations of structure to habit which are so constantly exciting our admiration in the handiwork of the ever blessed God, which cannot be predicated by the à priori reasoner, however astute, but are ever rewarding the research of the patient observer.

Our walk along the sands with steady downcast poring gaze suddenly ends, and we find ourselves among low ledges of black rock (ruddy, however, in its recent fractures, for it is the old red sandstone), clad with sweltering weed, and intersected by little sparkling pools and basins, in which the tiny fishes and entangled prawns shoot hither and thither at our approach. It is the low-lying ridge in the midst of the broad sandy bight that I have already spoken of. Well, n’importe; there is plenty of game to be obtained here, and all is fish that comes to our net. What have we here, creeping over the broad brown leathery leaf of this Laminaria? Is it a little scrap torn from an old newspaper? It looks like it at the first glance, only that it moves steadily onward with a smooth gliding motion, which shows that it possesses a life of its own. Examine it closely: it is exactly like a bit of white paper, about as large as a rose leaf, and cut into that shape, only with an even edge, its clear white surface marked all over with black parallel lines, some thinner, some thicker, running lengthwise, and as clear as if drawn with a pen. What answers to the base of the leaf is the head of the creature, the pointed end being the tail, where the two most strongly marked black lines meet; from the head end arise two curious ear-like leaflets, which are studded with crowded black dots, and are thrown back upon the general surface. With a lens we may discern on the surface of the body, just between these ear-like tentacles, a group of black specks. These are ascertained to be veritable eyes, notwithstanding their number, for they have a cornea, a light-refracting body surrounded with pigment, and a nerve-bulb.

LINED EURYLEPTA.

As the animal glides over the surface of the smooth weed, or over the inequalities of the rough rock, we see that its thin papery margin is frequently thrown up into waves, or folds, more or less distinctly revealing the inferior surface. The movement is very even and uniform, but the mode by which it is effected has not been satisfactorily explained. It has been asserted that certain staff-like bristles which project from the skin are used as oars, but this seems doubtful. It is certain that the whole body of the animal, as of the entire class to which it belongs, is densely clothed with minute vibratory cilia; and these, while they probably serve as organs of locomotion in freely swimming, do also without doubt make the whole skin a highly delicate and sensitive organ of touch.

It is asserted of the near allies of this species, and probably is equally true in this case, that if an individual be cut to pieces, every portion continues to live and feel, from whatever part of the body it may be taken; and what is not a little remarkable, each piece, even if it be the end of the tail, as soon as the first moment of pain and irritation has passed, begins to move in the same direction as that in which the entire animal was advancing, as if the body were actuated throughout by the same impulse; and, moreover, every division, even if it is not more than the eighth or tenth part of the creature, will become complete and perfect in all its organs.

You would naturally expect to find the creature’s mouth at the front end, where the two tentacles are placed, and the group of eyes, but you would search for it there in vain. It is, in fact, situated most strangely in the very midst of the belly; that is, at the very centre of the inferior surface. And its structure is not less peculiar than its locality. It consists of an orifice, in the midst of which lies a sort of trumpet of enormous extent when opened, but when not in active use thrown into many folds, which, when the animal wishes to seize prey, are thrust forth, and being partly opened, take the appearance of many irregular tentacles radiating in all directions, at the centre of which is the œsophagus, leading immediately into a much ramified intestine. The name which is given to this elegant and interesting creature is Eurylepta vittata.

PLATE 15.

P. H. GOSSE, del. LEIGHTON, BROS.

BANDED FLAT-WORM. LONG-WORM. ]

But here is another member of the same class of strange creatures. On turning up a large flat stone, we expose to the light of day what might readily be mistaken for a very long thong of black leather, or rather a narrow strip of Indian-rubber, twisted and tied together, and coiled in all possible contortions. If you take hold of it, you find it not so easy to secure it as you expected, for it is excessively lubricous and soft, and withal so extensile and so tough, that you may pull one of the coils to almost any length without lifting the rest of the creature. However, you at last contrive to raise the slippery subject, and commit it safe to your tank at home, in which it will live an indefinite while; often invisible for weeks at a time, lying concealed under some of the stones, then seen perhaps in every corner of your aquarium at once, stretching from one stone to another, and coiling around every groin and projection, folded back upon itself, until in the multitude of convolutions you despair of finding head, tail, or any end at all to the uncouth vermin. You may soon discover the signs of its presence, however, in another way, for its voracity is great, and it is a ferocious foe to the tube-dwelling worms; such as the lovely Sabellæ and Serpulæ, thrusting its serpent-like head into their tubes, and dragging out the hapless tenant to be quickly swallowed.

LONG-WORM.

The animal is named Nemertes Borlasii, or sometimes Borlasia longissima, in allusion to Dr. Borlase, the historian of Cornwall. It is also occasionally termed the Long-worm, par excellence, a name whose appropriateness will appear from the fact that it sometimes reaches a length of thirty feet, with a breadth of an eighth of an inch.

Mr. Kingsley has drawn the portrait of this ciliated worm; and if he has painted it in somewhat dark colours, and manifested more than a common measure of antipathy to it, we must confess that the physical and moral lineaments of the subject do in some degree justify the description. I will quote his vivid words.

ITS FORM AND HABITS.

“There are animals in which results so strange, fantastic, even seemingly horrible, are produced, that fallen man may be pardoned if he shrinks from them in disgust. That, at least, must be a consequence of our own wrong state; for everything is beautiful and perfect in its place. It may be answered, ‘Yes, in its place; but its place is not yours. You had no business to look at it, and must pay the penalty for intermeddling.’ I doubt that answer: for surely, if man have liberty to do anything, he has liberty to search out freely his Heavenly Father’s works; and yet every one seems to have his antipathic animal, and I know one bred from his childhood to zoology by land and sea, and bold in asserting, and honest in feeling, that all without exception is beautiful, who yet cannot, after handling, and petting, and admiring all day long every uncouth and venomous beast, avoid a paroxysm of horror at the sight of the common house-spider. At all events, whether we were intruding or not, in turning this stone, we must pay a fine for having done so; for there lies an animal, as foul and monstrous to the eye as ‘hydra, gorgon, or chimera dire,’ and yet so wondrously fitted for its work, that we must needs endure for our own instruction to handle and look at it. Its name I know not (though it lurks here under every stone), and should be glad to know. It seems some very ‘low’ Ascarid or Planarian worm. You see it? That black, slimy, knotted lump among the gravel, small enough to be taken up in a dessert-spoon. Look now, as it is raised and its coils drawn out. Three feet! Six--nine at least, with a capability of seemingly endless expansion; a slimy tape of living caoutchouc, some eighth of an inch in diameter, a dark chocolate-black, with paler longitudinal lines. Is it alive? It hangs helpless and motionless, a mere velvet string across the hand. Ask the neighbouring Annelids and the fry of the rock fishes, or put it into a vase at home, and see. It lies motionless, trailing itself among the gravel; you cannot tell where it begins or ends; it may be a strip of dead sea-weed, Himanthalia lorea, perhaps, or Chorda filum; or even a tarred string. So thinks the little fish who plays over and over it, till he touches at last what is too surely a head. In an instant a bell-shaped sucker mouth has fastened to its side. In another instant, from one lip, a concave double proboscis, just like a tapir’s (another instance of the repetition of forms), has clasped him like a finger, and now begins the struggle; but in vain. He is being ‘played’ with such a fishing-rod as the skill of a Wilson or a Stoddart never could invent; a living line, with elasticity beyond that of the most delicate fly-rod, which follows every lunge, shortening and lengthening, slipping and twining round every piece of gravel and stem of sea-weed, with a tiring drag such as no Highland wrist or step could ever bring to bear on salmon or trout. The victim is tired now; and slowly, yet dexterously, his blind assailent is feeling and shifting along his side, till he reaches one end of him; and then the black lips expand, and slowly and surely the curved finger begins packing him end foremost down into the gullet, where he sinks, inch by inch, till the swelling which marks his place is lost among the coils, and he is probably macerated into a pulp long before he has reached the opposite extremity of his cave of doom. Once safe down, the black murderer contracts again into a knotted heap, and lies like a boa with a stag inside him, motionless and blest.”

FOOTNOTES:

Trachinus vipera, represented by the lower figure in Plate XIII.

So old Drayton, in his “Polyolbion” sings, quaintly enough, and with a noble defiance of grammar:--

“The Weever, which, although his prickles venom be, By fishers cut away, which buyers seldom see, Yet for the fish he bears, ’tis not accounted bad.”

Since the above was written, the question has been set at rest, by Dr. Günther’s and Mr. Byerley’s actual discovery of poison-glands in connexion with these spines.