'That man had sure a palate covered o'erWith brass or steel, that, on the rocky shore,First broke the oozy oyster's pearly coat,And risked the living morsel down his throat.'
'That man had sure a palate covered o'erWith brass or steel, that, on the rocky shore,First broke the oozy oyster's pearly coat,And risked the living morsel down his throat.'
But, 'Mandarins and Pigtails,' what was suchrisk, I ask, compared to that whichheendured, who swallowed the first mouthful of birds'-nest soup? or horror of horrors, the first spoonful of sea-snail stew? Yet we are told that both the 'mucilage' and theBêches de Merdishes are savoury and highly grateful to the palate of an appreciating gourmand.
A recent author, describing a Chinese dinner from personal observation, tells us, that when the first dish, composed of birds'-nest soup, was over, he waited the advent of the next course with very nervous excitement. 'It was a stew of sea-slugs.They are slippery, and very difficult to be handled by inexperienced chopsticks; but they are most pleasant and succulent food, not at all unlike in flavour to the green fat of the turtle. If a man cannot eat anything of a kind whereof he has not seen his father and grandfather eat before him, we must leave him to his oysters, and his periwinkles, and his craw-fish, and not expect him to swallow the much more comely sea-slug. But surely a Briton, who has eaten himself into a poisonous plethora upon mussels, has no right to hold up his hands and eyes at a Chinaman enjoying his honest, well-cooked stew ofBêches de Mer.
'During the discussion of this dish our Chinese master of the ceremonies solemnly interposed. We were neglecting the rudiments of politeness, no one had offered to intrude one of these sleek and savoury delicacies, deeply rolled in sauce, into the mouth of his neighbour. Efforts were made to retrieve the barbarian honour, but with no great success, for the slugs wereevasive, and the proffered mouthful was not always welcome.'
'In taking a review of most, if not all the actions of the animal world,it must be obvious that, whether we allow them reason or not, the actionsthemselves comprehend those elements of reason, so to speak, which wecommonly refer to rational beings, so that if the same actions had beendone by our fellow-creatures, we should have ascribed them withouthesitation to motives and feelings worthy of a rational nature.'—Schleider.
'All things are bigge with jest; nothing that's plainBut may be wittie, if thou hast the vein.'—George Herbert.
'All things are bigge with jest; nothing that's plainBut may be wittie, if thou hast the vein.'—George Herbert.
I havebeen observing for several days the movements of a Common Shore-Crab, which has been almost all his life under my protection. Although his present dimensions would render such a feat impossible, when first I shook the little fellow off a bunch ofC. officinalis, he could have crawled with the greatest of ease into the mouth of a small popgun. We all know that members of this family are bold and daring in their attacks upon their weaker neighbours; upon each and all they wage a constant predatory warfare. The poor Pholades, however, are the favourite objects of their attacks. On these innocent bivalves the Crustacea successfully prey, unless they are protected by their usual rock-bound citadel, which, of course, they cannot always be. In order to watch the Pholas at work, it is necessary that the siphons should be more or less protruding from his tubular dwelling. If supported, say, to the full depth of his valves, the animal is secure; for I notice that neither crab nor fish can tear away the gristly ends ofthe siphonal appendages when withdrawn; and when disturbed, the poor Pholas leaves only this part in view. I have frequently seen the Fiddler-Crab embrace a Pholas in his claws, and struggle to pull him from his seat. On one occasion this operation was performed successfully, much to my annoyance, as I had been at some trouble to saw the rock away in order to watch easily every movement of the animal within. At night when I looked into the tank my pet was safe; next morning it was wedged under some pebbles, and the crab was feasting leisurely upon his tender flesh.
It is most amusing to watch the Blennies, too, attack a Pholas, cast into the tank, and to witness their mode of pecking at and shaking their victim, and turning innumerable somersaults with it in their mouths. The strength they exhibit in these manœuvres is perfectly astounding.
About two hours after they had received one of their favourite 'muttons' to feast upon, I peeped into the aquarium, and found, as I expected, the Blennies hard at their work of destruction. Behind them, among some bushy tufts ofI. edulis, the little crab, before alluded to, was seated. In his arms he held an object unlike anything I had seen on sea or land. It appeared like a slender stick of beautifully iridescent opal. My amazement at this sight may readily be conceived, for I had not the remotest idea as to how he had become possessed of such a prize.
Next day I placed another devoted Pholas in the tank, and after a while looked in to see how its finny enemies were conducting themselves, when, what should meet my eye, but the crab, sneaking off with another opal baton in his arms! I was more puzzled than ever. It was quite certain that the object in question had been procured from the Pholas, yet I had not heard of, or ever seen anything like it in that animal.
I was 'on thorns' until next day, so that I might by watching solve the mystery. A third Pholas was flung into the den. The fishes, eager as usual, instantly attacked and pulled the mollusc to pieces. After a while the crab began to move about to and fro, evidently very restless, and anxious for my departure. I did retire, but only to such distance as would allow me a distinct view of his movements. In a few moments he stepped out mincingly on the tips of his toes, and crossed the tank to the spot where the poor Pholas lay, like some fine beau in Queen Anne's reign tripping jauntily down the Mall, or across St. James' Park, to feed the ducks in Rosamond's Pond.
The Blennies darted off at his approach. He then seated himself before the mangled corpse, and scraped at it vigorously, manifestly searching for some coveted treasure. Shortly after, perceiving him clutch at something, I quickly approached and disturbed his movements—took up the Pholas, and tomy surprise found, on drawing out an object that protruded from the foot of the animal, that I possessed the pearly and gelatinous cylinder, such as the crab had twice before devoured with such evident relish.[11]
It was plain then that the little rascal had become so dainty, that he 'turned up his nose,' or rather his 'pair of noses,' at what is vulgarly termed the 'first cut,' and condescended only upon the tit-bits, for his marine banquet. So his crabship, in order to save himself trouble, actually waited until the fishes had cut up the Pholas to a certain point, when he would rush forward and seize on his favourite fare.
Some of my readers will doubtless remember the anecdote of the crossing sweeper, whose idiosyncrasy led him to covet diurnally a mutton-chop situated in the middle of the loin. My Lady Pepys, or Mr. Saccharine, the great grocer, couldn't always procure the desired 'cut!'n'importethe knight of the besom met with no such disappointment.
This individual's place of business was luckily situated opposite to a noted butcher's shop, which circumstance easily enabled him to watch until, from the demands of sundry customers, the perspective of the loin, which lay temptingly upon the chopping block, had become adapted to his point of sight. He would then step in and meekly order a simple pound avoirdupois. With thisbonne-bouchecarefullypacked in his pocket, he would again mount guard, and remain until night. At dusk of evening he shut up shop,—that is, he swept the dirt over the parallel path that he had all day kept scrupulously clean, and then marched off to enjoy his dinner at a fashionable hour, in private.
Are not these cases palpably alike? Passing by certain details, were not the pawkiness and cunning of the epicurean beggar fully equalled by our diminutive friend,C. mænas?
'But,' you ask, 'what then was the opal stick?' Ay, there's the rub, for even the greatest naturalists cannot positively agree as to the use and purpose of this mysterious organ. Yet it is to be found (as we have seen) in the foot of the Pholas, in the Mussel, the Cockle; and, in fact, it occurs in almost all bivalves both great and small. It is termed the 'hyaline cylindrical stylet,' and is verylucidlyand scientifically described as 'an elastic spring to work the corneous plate or attritor, and by the muscular action of the foot and body, to divide and comminute the food, and especially the minute crustaceous and testaceous alimentary matters received into the stomachial cavity. It appears then that this appendage acts asa gizzard, and the bivalve mollusca are thus supplied with a masticatory apparatus very analogous to the gizzards of some of the gasteropoda.'
Now, the simple fact that I have stated above, of the hyaline stylet being found in thefoot, and notin the stomach, at once proves that it cannot possibly act as agizzardto the Pholas, or any other bivalve in which it is known to exist.
In the succeeding chapter I shall endeavour, from personal observation, to shed a slender ray of light upon the function of the stylet.
'He that of greatest works is finisherOft does them by the meanest minister.'
Atcertain parts of the Scottish coast, the 'dykes,' or walls built near the road-side, are constructed entirely of rough-hewn pieces of hard sandstone rock, brought from the neighbouring shore. Sometimes a dyke will extend for two or three miles, without presenting an isolated fragment, in which the honeycomb-like perforations of certain species of the boring Mollusca are not more or less apparent.
A fragment of soft sandstone lies before me, measuring three and a half inches in length, and two inches in breadth, which, small though it be, contains no fewer than seventeen cylindrical tunnels. Each of these exhibits so wonderful a skill in construction, that human hands could not surpass it, though aided by 'all the means and appliances to boot,' of mechanical agency.
It is generally stated that the Pholas never intrudes itself into the apartment occupied by a neighbouring 'worker.' The Pholas, however, often intrudes on its neighbour; and such intrusion ismanifested in the small piece of stone alluded to in no less than four instances. Here let me observe, that it is not always the larger mollusc that bores through the smaller one; it as frequently happens that the latter deserves the brand of wanton aggressor. Both cases are common enough, and, indeed, must of necessity occur, wherever at any time a colony of various sized Pholades are clustered together in a small portion of rock.
A fragment of rock riddled by the Pholas is a much more pleasing sight than can be witnessed at the sea-shore in connection with that animal under usual circumstances. For this reason: When visiting the habitat of the boring bivalves, a host of small circular holes are sometimes seen; at other times the surface of the same portion of the beach appears comparatively sound, and it is only by striking a smart blow with a hammer upon the ground, that we render scores of orifices instantly observable in all directions, from each of which is thrown a small jet of water. This phenomenon is caused by the Pholades in alarm retracting their siphons, which had hitherto filled the entire extent of the tunnels. At such a locality, if a piece of rock be excavated, various specimens of these boring molluscs, shrunk to their smallest possible size, will be discovered at the base of the cavities, which are invariably of a conical form, tapered at the top, and gradually enlarging as they descend.
It must be evident, then, that neither the likeness of the animal, nor the formation of its singular dwelling-place, can be seen by the casual wanderer along the sea-shore.
It will also be apparent to the intelligent reader, that when once the Pholas is located in a certain spot, he becomes a tenant for life; for never by any chance whatever, can the poor miner leave his rocky habitation by his own unaided exertions, even were he so inclined. As he grows older and increases in size, nature teaches the animal to enlarge his habitation in a proportionate and suitable manner.
During the period of the boring process, the orifice becomes clogged above the shell with thedebrisof the rock, and this, if allowed to accumulate would speedily asphyxiate the animal. To get rid of such an unpleasant obstruction, the Pholas retracts, and closes the end of its siphons, then suddenly extends the 'double barrelled' tube to its full length, until it reaches the entrance of the tunnel. This movement often repeated, causes portions of the pulverized stone to be forced outwards at each operation.
It is interesting to watch the curious manner in which the end of the principal siphon is alternately closed and spread out when it reaches the water, like a man inspiring heavily after any unusual exertion; it is then made again to descend, and renew its task, as above described.
In extracting that portion of thedebriswhich isdeposited at thebaseof the cavity, below the body of the industrious miner, a different plan is adopted. Wherever a Pholas is at its labours, there are always deposited within a circumference of several inches round the tunnel, myriads of short thin threads, which are squirted out from the smaller siphon.
The nodules on examination are found to be composed of pulverized rock, which is drawn in at the pedal opening, and ejected in the above manner, thereby effectually clearing the lower portion of the orifice. It was suggested to me that these threadlike objects were the fœcal matters of the Pholas, but this idea was soon dispelled by the assistance of the microscope; and, moreover, from the fact that the threads are never visible when the animal is in a quiescent state, but only when it is busily engaged in its mysterious task of boring.
I was for some time puzzled to find any aperture in connection with the club-like foot of the Pholas (P. crispata), although several of the bivalves were sacrificed to the cause of science. But what the microscope and scalpel in this instance failed to unfold, attentive watching of the animal in the aquarium made palpably apparent, in the following manner.
I had on one occasion captured about a dozen Pholades, some of which were embedded in the solid rock, others detached.
The first mentioned, I knew would be quite safe among the blennies and crabs, from the untemptingand unedible nature of their siphonal tubes. Very different was the case with the defenceless, disentombed specimens. These were intended as food for their finny companions, who happened to be particularly fond of a change of diet. My 'pack' had subsisted for some time on Mussels, and on such excellent food, had become impudent, corpulent, and dainty. But overgorged epicures though they were, I knew that although everything else failed, a 'real live' Pholas placed before them would serve to speedily whet their appetites.
A splendid specimen of the siphoniferous bivalve was dropped into the tank, the base of which it had no sooner reached, than the fishes, with eager eyes and watering mouths, came hovering like a flock of vultures round the welcome meal thus unexpectedly placed before them.
One rascal, who seemed to be cock of the walk, came forward and made the first grip at the delicate fleshy foot, that in appearance was as white as a newly fallen snowflake. The pedal organ was, of course, instantly and forcibly withdrawn, so much so, indeed, as to be almost hidden from view, except at its extreme base. In this position it remained for several seconds. When the finny gourmand again boldly advanced to take a second mouthful, to my intense surprise he was, apparently, blown to a distance of several inches. I could scarcely credit the evidence of my senses. Another and another of thefishes were in their turn served in like manner as their leader. In a short time, however, the poor mollusc failed to repulse his enemies, and finally fell a passive victim to their gluttonous propensities.
Now comes the important question, 'How is the boring operation performed?' How can this simple animal, with its brittle shell, and soft fleshy body, manage to perforate the sandstone, or other hard substances, in which it lives?
For hundreds of years this query has been asked, and various are the replies which from time to time have been given. Singular to state, although specimens of the Pholas, and its allies the Saxicavæ, are to be procured in abundance in many parts of the kingdom, the subject is not even yet positively settled.
There have been many theories advanced, some the result of fancy or guess-work; others, of practical study. All these have their supporters, but none have, by common consent, been adopted by physiologists as the true one.
Having for several years made this subject a study of personal observation, I believe I may venture to state, that I have succeeded in casting a feeble ray of light upon it; and, although the result of my labours may not be deemed conclusive, I may at least claim some credit for my endeavours to clear up a most difficult, though deeply interesting point in natural history.
The various theories promulgated on this knotty point are generally classed under five heads: 1st, That the animal secretes a chemical solvent—an acid—which dissolves the substance in which it bores. 2d, That the combined action of the secreted solvent, and rasping by the valves, effects the perforations. 3d, That the holes are made by rasping effected by silicious particles studding the substance of certain parts of the animal. 4th, That currents of water, set in action by the motions of vibratile cilia, are the agents. 5th, and lastly, That the boring mollusca perforate by means of the rotation of their shells, which serve as augurs.
Of all the above, the first which is quite a fancy theory, seems to meet with greatest favour among certain naturalists. But as it is rather puzzling to find a chemical solvent, which will act equally upon sandstone, clay, chalk, wax, and wood, this hypothesis can only be looked upon by practical men as ingenious, but incorrect. Even were it proved that the animal really possessed the power of secreting an acid sufficiently powerful, the question naturally arises, How can the shell escape being affected in like manner with the much harder substance in which it is situated?
The second theory, or the combined action of rasping and the secreted solvent, is, for obvious reasons, equally objectionable.
The third theory, which endeavours to account for the wearing away of the rock by means of silicious particles situated in the foot and other parts of the animal, has been for some time proved to be erroneous, from the fact, that the combined skill of some of our best anatomists and microscopists has failed to discover the slightest presence of any particles of silex in the Pholadidæ, although these are believed to exist in other families of the boring acephala.
The fourth theory, that of ciliary currents as an accessory agent in boring, is worthy of greater consideration, chiefly from the evidence we possess of the immense power which the incessant action of currents of water possess in wearing away hard substances.
We come now to what may be considered the most important of the theories above enumerated, viz., the mechanical action of the valves of the Pholas in rasping away the rock, &c. This hypothesis is one which most naturally suggests itself to the mind of any impartial person, on examining, for instance, the rasp-like exterior of the shell ofPholas crispata.[12]But as I shall endeavour to show, although the shell forms the principal, it does not by any means constitute thesoleagent in completing the perforating process.
Mr. Clark, a clever naturalist, considers with Mr. Hancock that the powerfully armed ventral portion of themantleof the closed boring acephala is fully adequate to rub down their habitations, and that the theories of mechanical boring, solvents, and ciliary currents, are so utterly worthless and incapable of producing the effects assigned to them, as not to be worth dwelling upon for one moment. Mr. Clark, therefore, comes to the conclusion that 'the foot is the true and sole terebrating agent in the Pholas.' This 'fact' he considers to be 'incontestably proved,' for the following reason, viz., because he had discovered specimens of this bivalve with the foot entirely obliterated,—which phenomenon, Mr. Clark states, is caused by the animal having arrived at its full growth, at which period the terebrating functions cease; and as 'nature never permanently retains what is superfluous,' the foot is supposed gradually to wither away, and finally disappear.
This, I suspect, is another 'fancy' theory. Although I have excavated hundreds of Pholades, some of giant-like proportions, it has never been my lot to witness the foot otherwise than in a healthy and fully developed condition.
Another writer, having no opportunity of viewing the living animal, does not consider it difficult to imagine the Pholas 'licking a hole' with its foot, from the fact that he (Mr. Sowerby) managed to make 'a sensible impression' upon a piece of kitchenhearthstone. 'I had,' he says, 'not patience to carry the experiment any further, but as far as it went, it left no doubt on my mind that, with the foot alone, and without any silicious particles, without a chemical solvent, and without using the rasping power of its shell, our little animal could easily execute his self-pronounced sentence of solitary confinement for life.'
Such an inconclusive statement as this would, I feel certain, never have been penned, had its author been so fortunate as to have had opportunity of watching a Pholas at work.
But, as Professor Owen truly observes, 'Direct observation of the boring bivalves in the act of perforation has been rarely enjoyed, and the instruments have consequently been guessed at, or judged of from the structure of the animal.' Such, evidently, is the case with Mr. Sowerby, and several other writers who treat on this subject.
Here we may call attention to the folly of naturalists endeavouring to tag a pet theory upon all the boring acephala, to the exclusion of every other. Such a system is defended upon the principle that, 'it is much more philosophical to allow that animals, so nearly allied as these in question, are more likely to effect a similar purpose by the same means, than that several should be adopted. Surely this is more consistent with the unity of the laws of nature, and that beautiful simplicity which is everywhere prevalent in her works.'
How much more shrewd and philosophical are the opinions of such a man as Professor Owen, who, when speaking of the mechanical action of the valves ofP. crispata, says, 'To deny this use of the Pholas shell, because the shell of some other rock-boring bivalves is smooth, is another sign of a narrow mind.' Again, this learned author forcibly remarks, in direct opposition to the writer previously quoted, 'The diversity of the organization of the boring molluscs plainly speaks against any one single and uniform, boring agent at all!'
The more I study this subject, the more does the truth of the last-mentioned statement become apparent to my mind.
An examination of engravings of the shells, or even of the Pholas itself, when lying loose in the tank, or quietly seated in the rock, extending and retracting its siphons, fails to give one the slightest idea of its extraordinary appearance when enlarging its dwelling. At such times it seems to be a totally different animal, and to have suddenly acquired a most marvellous degree of power, energy, and perseverance, forming a striking contrast to its usual quiet, passive habits.
In the first place, as I have elsewhere written, it retracts its tube to, and even under, the level of its shell, just as a man, about to urge onwards some heavy mass with his shoulders, would depress his head to increase and concentrate his muscular power.Then follows an expansion of the neck or upper part of the ventral border, from whence the siphons protrude. This movement closes the posterior portions of the valves below the hinge, and brings their serrated points together. The next act on the part of the animal is to place its foot firmly at the base of the hole; when leaning forward, it makes a sweeping movement fully half round the cavity, pressing firmly-upon the umboes, which nature has strengthened for the purpose by two curved teeth fixed on the inside of the valves. At this stage it again reclines on its breast, and tilting up the shell as much as possible, it makes another motion round to its former position, leaning upon its back. By these intricate movements, which the Pholas appears to accomplish by a contraction almost painfully strong, it opens the rasping points of the valves. These execute a very peculiar scooping movement at the base of the cavity, and the animal having got so far, prepares itself for further exertion by a short rest.
The specimen whose movements I have attempted to describe, lived in my possession for a considerable time. It bored so completely through the piece of rock in which it was embedded, that the whole of its foot dropped through the aperture, and remained in this position for months, the animal, in consequence, being unable to change its position even in the slightest degree. Each movement of this specimen,both before and while the hole at the base of the cavity was gradually being enlarged, was watched, and every striking and interesting feature that occurred noted down at the moment. Various queries were put and answered, as far as possible, by direct ocular demonstration of the labours of the animal in the vase before me.
I consider myself to have been singularly fortunate in being able to view the actions of the creature from beneath, in consequence of the hole being bored through the rock. This circumstance allowed me distinctly to see what was going on at the base of the orifice.
My early observations have fortunately been confirmed in other captive Pholades, which at various periods have been domesticated in my tanks.
I am convinced, then, that the shell forms theprincipalagent in boring the animal's dwelling, without either acid or flinty particles. The late lamented Professor Forbes held that if this were the case, the rasping points on the surface of the valves would soon be worn down,—an appearance which, he says, is never seen. With all respect for such an eminent name, I must state that he was in error. Not only are the edges at certain times worn, but the rough surface is worn nearly smooth, appearing in certain parts of a white colour, instead of a light drab, as usual.
But the reader may ask, if certain parts of the valves are occasionally worn smooth, and the animalworks so vigorously, how is it that they are never rasped through? This is a very natural question, and one that I put to myself repeatedly.
I have made frequent and careful observations while the animal was actually at work, in order to satisfy myself upon this point, and have always perceived that the particles of softened rock fell from, and on each side of, the large and well-developedligamentthat binds the hinge, and extends to the lowest points of the valves. Moreover, this leathery substance always seemed scraped on the surface. I cannot, therefore, but believe that the ligament aids very materially in rubbing off the rock, or at all events, in graduating the pressure of the valves during the process, and that this curious organ, instead of being worn away, may, like the callosity upon a workman's hand, increase in toughness the more labour it is called upon to perform.[13]
The reason why so few specimens of the Pholades exhibit a worn shell may be thus explained: As the animal only bores the rock in sufficient degree to admit of its increased bulk of body, it only requires to bore occasionally, and there may be often an interval of many months, during which time naturemay have renewed the serrated edge and rough surface of the valves, and thus enabled the creature to renew its wondrous operations.
We now come to a consideration of the foot, which, as many writers aver, forms the 'sole terebrating agent.'
Although this sweeping statement is incorrect, I will freely admit that the foot constitutes an agent second only in importance to the shell of the animal. A casual examination of any Pholas perforation will show that the foot could not have been the only instrument by which the cavity was formed, from the peculiar rings that line the lower portion of its interior. These rough appearances, I feel convinced, could be formed by no other means than the rotatory motion of the shelly valves.
The valves, however, could not rotate and press against the surface of the rock, were it not for the aid which the foot affords to the animal, by its being placed firmly at the base of the hole, and thus made to act as a powerful fulcrum.
This supposition fully accounts for the lowest extremity of the rocky chamber being always smooth, and hollowed out into a cup-like form by the action of the fleshy foot above alluded to.
The foot for a long time was a complete puzzle to me: I was unable to satisfy my mind as to how it acquired its seeming extraordinary power. The phenomenon was fully explained when I becameaware of the presence of that mysterious organ the hyaline stylet, situatedin the centre of the foot. The use of this springy muscle, which is, as we have shown in the previous chapter, by naturalists erroneously considered to be the gizzard of the animal, is, I believe,solely to assist the Pholas in its boring operations.
Perhaps some of my readers would like to know how to procure a sight of the stylet; if so, their wishes may be easily gratified. Take up a disentombed Pholas in your hand, and with a sharp lancet or point of a pen-knife, briskly cut a slit in the extreme end of the foot, and, if the operation be done skilfully, the object of your search will spring out of the incision to the extent, it may be, of a quarter of an inch. If not, a very slight examination will discover the opal gelatinous cylinder, which may be drawn out by means of a pair of forceps.
When extracted and held between the finger and thumb by its smaller end, the stylet will, if struck with a certain degree of force, vibrate rapidly to and fro for some seconds, in the same manner as a piece of steel or whalebone would be affected, under like circumstances.[14]
So long as a Pholas exhibits only the ends of itssiphons to the eyes of a greedy crab, it is perfectly safe from attack. It is only when the fleshy foot is unprotected that it falls a prey to some hungry crustacean.
The toughness of the siphonal orifices is, I believe, a most important point, for, as I shall endeavour to explain, the siphonal tubes constitute important accessory excavating agents, to those already enumerated.
We all know that the hole which each young Pholas makes, when first he takes possession of his rocky home, is extremely minute,—not larger than a small pin's head; now, it stands to reason, that if the shell was the only terebrating agent, the opening of the cavity in question would always remain of the same size, or, perhaps, on account of the action of the water, a slight degree larger than its original dimensions. Such, however, is not the case.
Here is a fragment of rock exhibiting several Pholas holes. The aperture of one of these, which I measure, is nearly half-an-inch in diameter, while in juxtaposition with it is situated another cavity, measuring across the entrance less than the eighth part of an inch. The reader will at once perceive, if the foot and shell were the sole augurs, that as the animal descended deeper into the rock, the siphonal tube, as it enlarged in proportion to other parts of the animal, would have to be drawn out toan extremely fine point to fit the opening of the tunnel. But as this is not the state of matters, the conclusion forces itself upon us, that that portion of the orifice situated above the shell of the animal must be enlarged by the constant extension and retraction of the siphons, aided by currents of water acting on the interior surface of the cavity.
This same theory will also serve to explain how it is that all Pholades situated at the same depth in the rock, are not all of a uniform size. I have frequently seen a piece of rock exhibit the peculiarity of two burrows of vastly different proportions as regards breadth, being precisely the same depth from the surface of the stone. This appears to me equally wonderful and puzzling at first sight, as the 'boring' question.
What age is attained by any species of the rock-borers before they arrive at full growth, there are no means of knowing. This point, like several others in the history of these animals, still remains a mystery, nor is it likely soon to be cleared up. The largest specimen ofP. crispatathat I have seen is at present in my possession. Each valve measures three and a half inches in length, by two inches in breadth. Some foreign specimens of this species, and especially ofP. dactylus, are, however, frequently found of much larger dimensions.
On no occasion have I ever examined any Pholas excavation that had lost its conical shape, a fact thatseems to prove that the successive stages of the boring operation must have taken place solely in consequence of the animal not having reached its adult form.[15]For had the shell attained its full development, and its owner continued to labour, and rasp away the rock, the sides of the cavity at its base would necessarily present a parallel appearance—a phenomenon which is never witnessed.
From this we may conclude that the depth of the perforation, which is seldom many inches, depends entirely upon the growth of the mollusc.
When keeping specimens of the Pholas for observation, the usual plan is to chip away the rock to the level of the valves, so that the whole of the animal's siphonal tubes may be distinctly seen, however slightly these organs may be extended. This plan, I found, did very well for a time, but I was annoyed to witness, that in the course of a few months, the siphons ceased to be either advanced or retracted,—they having become, as it were, rudimentary.
To obviate such contingency, the writer adopted the following scheme.
To place in the tank a Pholas completely embedded in a fragment of rock, so that nothing but the tips of its siphons, when extended to the utmost, were visible, would not afford much pleasure to the student.I therefore managed to saw away the rock in such a manner, as to leave a narrow slit along the entire length of the tunnel, so as to expose the slightest movement of the animal within. Having natural support for its siphons, I expected that these organs would be constantly retracted and extended; but such was not the case; at least for so long a period as I had anticipated.
After repeated experiments, I have now discovered that whether the siphons be protected as above described or not, they will always be vigorously exercised if the animal be placed in shallow water, so that its tubes when fully extended will reach the surface of the fluid.
The conclusion, from what has been stated, is, that the Pholas can no longer be considered a weak and helpless animal. Possessed of a rasp-like shell, a horny ligament, retractile tubes, a strong muscular foot, and a powerful spring or stylet, it is not by any means difficult to conceive that these agents when they are all brought into play, are fully equal to the task of excavating the rocky chamber in which the animal lives.
'For seas have ...As well as earth, vines, roses, nettles, melons,Mushrooms, pinks, gilliflowers, and many millionsOf other plants, more rare, more strange than these,As very fishes living in the seas.'
'For seas have ...As well as earth, vines, roses, nettles, melons,Mushrooms, pinks, gilliflowers, and many millionsOf other plants, more rare, more strange than these,As very fishes living in the seas.'
The Sea-Mouse
1 THE SEA MOUSE (Aphrodite aculeata)2 THE DORIS3 YOUNG OF THE DORIS4 EOLIS PAPILLOSA
Beauteousstars also the sea contains, as numberless, though not so brilliant in appearance as those which stud the firmament of heaven; flowers, too, grow beneath the wave, and rival in loveliness the gems which adorn our fields and hedge-rows. Nay, more, like the land, the ocean owns its various grasses, its lemons, and cucumbers, its worms, slugs, and shelly snails, its hedgehogs, its birds, its ducks and geese (anatidæ), its dogs, its hares, and lastly itsmice(aphroditæ.) The latter objects, despite their unprepossessing name, being in no wise less interesting than those above mentioned.
TheAphrodite aculeatais, perhaps, one of the most gorgeous creatures that inhabits the seas of our British coast. Its body is covered with a coating of short brown hairs, but as these approach the sides of the animal, they become intermixed with long dark bristles, the whole of which are of an iridescent character. In one respect this creature bears no resemblance to its namesake of the land, being extremelyslow and sluggish in its movements (at least according to our experience) when kept in confinement. Some writers, however, affirm that the Aphrodite possesses the power, although seldom exercised, of both running and swimming through the water with considerable speed.
In general the animal loves to tenant the slimy mud, and wherever the writer has happened to come upon a specimen at the sea-shore, its back has always been thickly coated with sand or dirt. The Sea-Mouse, then, unlike the peacock, can never be deemed an emblem of haughty pride, yet has nature in her lavish beauty endowed this humble inhabitant of the deep with a richness of plumage, so to speak, fully equal in its metallic brilliancy to that which decorates the tail of the strutting bird we have mentioned. As the bristles of the Aphrodite are moved about, tints—green, yellow, and orange, blue, purple, and scarlet—all the hues of Iris play upon them with the changing light, and shine with a metallic effulgence. Even if the animal, when dead, is placed in clear water, the same varied effect is seen as often as the observer changes his position.
Not only are theSetæworthy of notice on account of their lustrous beauty, but also for their shape, and the important part they play in the economy of the animal. These lance-like spines seem to be used by the Aphrodite as weapons of defence, like thespines of the hedgehog or porcupine. In some species they are like harpoons, each being supplied with a double series of strong barbs.
The instruments can all be withdrawn into the body of the animal at will, but we can easily conceive that such formidable weapons being retracted into its flesh would not add to the creature's comfort—in fact they would produce a deadly effect, were it not for the following simple and beautiful contrivance.
Each spine is furnished with a double sheath composed of two blades, between which it is lodged; these sheaths closing upon the sharp points of the spear when the latter is drawn inwards, effectually guard the surrounding flesh from injury.
The shape of this animal is oval, the back convex, while the under part presents a flat and curious ribbed-like appearance. Its length varies from three to five inches; specimens, however, are sometimes to be procured, even on our own shores, of much larger dimensions.
'As there are stars in the sky, so there are stars in the sea.'—Link.
Thereare not a few persons still to be met with, who believe that man and the lower animals appeared simultaneously upon the face of the earth. Geology most forcibly proves the error of such an idea, for although the fossilized remains of every other class of organized beings have been discovered, human bones have nowhere been found. This fact, though deeply interesting, is perhaps not more so than many others which this wonderful science has unfolded. What can be more startling to the student for instance, than the information that for a long period, it may be thousands of years, no species of fish whatever inhabited the primeval seas? True it is that certain creatures occupied the shallows and depths of ocean, but these were of the lowest type. The most conspicuous were the coral polypes, which even then as now were ever industriously building up lasting monuments of their existence, as the Trilobites, a group of Crustacea, and the Crinoids, or Lily-stars.
The last-mentioned group of animals were analogous to the present tribe of Star-fishes, and are now nearly extinct. The body of the Lily-star, which resembled some beautiful radiate flower, was affixed to a long, slender stalk, composed of a series of solid plates superposed upon one another, bound together by a fleshy coat, and made to undulate to and fro in any direction at the will of the animal. The stalk was firmly attached to some foreign substance, and consequently the Crinoid Star-fish, unlike its modern representative, could not rove about in search of prey, but only capture such objects as came within reach of its widely expanded arms. 'Scarcely a dozen kinds of these beautiful creatures,' observes Professor Forbes, 'now live in the seas of our globe, and individuals of these kinds are comparatively rarely to be met with; formerly they were among the most numerous of the ocean's inhabitants,—so numerous that the remains of their skeletons constitute great tracts of the dry land as it now appears. For miles and miles we may walk over the stony fragments of the Crinoidae, fragments which were once built up in animated forms, encased in living flesh, and obeying the will of creatures among the loveliest of the inhabitants of the ocean. Even in their present disjointed and petrified state, they excite the admiration not only of the naturalist, but of the common gazer; and the name of stone lily, popularly applied to them, indicates a popularappreciation of their beauty.' Each wheel-like joint of the fossil Encrinite being generally perforated in the centre, facility is thus afforded for stringing a number of these objects together like beads, and in this form the monks of old, according to tradition, used the broken fragments of the lily-stars as rosaries. Hence the common appellation of St Cuthbert's Beads, to which Sir Walter Scott alludes,—