The Armory of the Tower of London forms, it is generally admitted, one of the most interesting sights of the great metropolis. No one can look without wonder upon that goodly array of knights and noble warriors, nor help an involuntary sigh over the degeneracy of modern humanity. Though the figures before us are technically and irreverently termed 'dummies,' the hardened shell with which their body and limbs are cased we know has felt the throb of many a true English heart, maybe, glistened beneath the sun at Cressy and Agincourt, or perhaps on the bloody fields of Worcester and Marston Moor. It requires no great power of the imagination to transport ourselves to bygone centuries, and listen to the ring of hostile arms, the sepulchral voices of men whose heads are inurned in casques of steel, blended with the clash of battle-axes, the whizz of arrows, the neighing of steeds, the rattle of musketry, and at intervals the deep booming cannon's roar.

But, asks the gasping reader, what has this parade of mail-clad warriors and old battle-fields to do with so prosaic a theme as the exuviation of crabs? I must acknowledge that the question is a very natural one, for there appears at first sight no connection between the two subjects. The analogy will not, I believe, appear so forced when I mention my possession of a smaller, although hardly less singular armory, consisting of various coats of shelly mail, each of which, at one time or other, belonged to, and was worn by a living creature, and proved as effectual a protection in many fierce though bloodless combats as any casque or helmet worn by knight. Unlike the dummies of the Tower, my specimens are perfect, and give a complete representation, more truthful than any photograph, of the defunct originals, when armed by Nature cap-a-pie.

In plain words, I own a curious collection of the cast-off shells of various crabs, which have from time to time been under my protection. From the fact that no museum in the kingdom contains a single series of such objects, exhibiting the various stages of growth in any crustaceous animal, the reader will easily conceive the difficulty there must be in procuring them, and consequently the interest that attaches to the mysterious phenomenon of exuviation.

Strange to say, the subject of this chapter is one of the least known in the whole range of natural history. The facts connected with the process are few, and far from well authenticated. This state of things appears the more extraordinary, when we remember the great facility with which specimens of crustacea may be found.

For years past I have paid much attention to the elucidation of this subject, and during that period have had to submit to numberless mishaps and disappointments. For example, perhaps after watching a 'pet' day after day for months, anxiously expecting that exuviation would take place, in nine cases out of ten,—ay, in ninety-nine out of the hundred,—I would find that the process had been completed when I was asleep, or that the animal had died suddenly. In the latter case new specimens had to be procured, and the same watching process repeated, in most cases with the like unhappy results.

I will now, however, endeavour as briefly as possible to make the reader acquainted with what has already been written upon exuviation, as far as I have been able to learn, up to the present time, interspersing the narrative with such notes as may seem necessary by way of illustration, and then proceed, in the words of Shakspeare, to lay down my own 'penny of observation.'

The first clear and satisfactory remarks on this subject were made by the celebrated Reaumur, who lived above a century ago: 'The unexampled accuracy and truthfulness of this great naturalist is attested,' says one writer, 'by the fact, that of all the observations made by himself alone, far exceeding those of any other writer of past or present times, and occupying in their published form numerous large quarto volumes, scarcely one has been contravened by subsequent credible observers, whilst they have formed the substance of half the numerous compilations on insect life, acknowledged or otherwise, which have appeared since his time.'

Goldsmith, who derived his knowledge of this subject from Reamur, tells us, in his usual free and easy style, that crustaceous animals (as crabs and lobsters) 'regularly once a year, and about the beginning of May, cast their old shell, and nature supplies them with a new one. Some days before this necessary change takes place, the animal ceases to take its usual food. It then swells itself in an unusual manner, and by this the shell begins to divide at its junctures between the body and the tail. After this, by the same operation, it disengages itself of every part one after the other, each part of the joints bursting longitudinally, till the animal is at perfect liberty. This operation, however, is so violent and painful that many die under it; those which survive are feeble, and their naked muscles soft to the touch, being covered with a thin membrane; but in less than two days this membrane hardens in a surprising manner, and a new shell as impenetrable as the former supplies the place of that laid aside.'

This, then, was and is to a great extent, up to the present time, the universally adopted explanation. Goldie, of course, could not afford time, and it may be doubted if he possessed the requisite amount of patience, to confirm what he wrote by actual observation. Seeing that the statement was graphic in its details, and evidently either wholly or in part the result of personal observation, he very naturally gave it full credence. But what shall we say of a noted writer (Sir C. Bell)[4] who apparently half doubts the truth of exuviation, for although he mentions the particular account which Reamur gives, yet tells his readers that 'naturalists have not found these cast off shells.' After such a remark as this, we need no longer sneer at the compilations of the author of the 'Vicar of Wakefield.'

I need hardly state, that at certain seasons of the year almost every rock-pool at the sea-shore will exhibit to the observant eye scores of 'these cast off shells' in a perfect state. The writer above quoted also remarks, 'We presume the reason that the shells of the crustacea are not found in our museums, is because they are not thrown off at once, but that the portions are detached in succession.' An ill-founded presumption this, the fact being that the inelastic integument is invariably (in all the Decapoda at least) thrown off entire, the eyes and long antennÆ sheaths, the claws with the hair attached, even the gastric teeth, all remain with wonderful exactness.

To look at the rejected shell, indeed, any person not previously acquainted with the fact would naturally suppose that he saw before him the living animal, a close inspection being necessary to dispel the illusion. As soon as the crab has emerged from its old covering, it increases with such astounding rapidity, that at the end of one or two days it can grow no larger until the next moulting time.

In referring to my own introduction to the subject of exuviation, I may be allowed to notice the annoyance a young aquarian experiences from the rapidity with which the tank water is apt to become opaque. As such a state involves considerable trouble, especially when the occupants of the tank are the subjects of continued observation, I may mention, in passing, that the means I adopted to correct this state of matters was either to syringe the water frequently, or what seemed to answer still better, to permit it to run off by a syphon into a basin on the floor.

When the opacity of the tank is occasioned by decaying animal matter, the only remedy is to remove the offending 'remains.' But with many of the common inhabitants of the tank—the crustaceans, for example—great difficulty is often experienced in ascertaining their state of health, with a view to sanitary investigation. As these creatures, instead of boldly exhibiting themselves during the day, generally hide under pebbles or pieces of rock, or are buried in the sand, it is sometimes necessary to submit the contents of the mimic rock-pool to a process of 'putting things to rights,' as the ladies say when about doing a kindness,—oh, horror!—to our books and papers.

It happened on a certain occasion that my aquarium was in an unsatisfactory condition. A nasty vapour arose from the base, and diffused itself over nearly the entire vessel. My fishes disliking their usual haunts, were all spread out at full length high and dry upon a ledge of rock-work, projecting above the surface of the water. The little Soldier-Crab had managed to drag his body and heavy tail piece up the brae, hoping to breathe the fresh air in safety. His big brother was not so successful, and despite his efforts speedily came to grief. Finding he could not drag his carriage up the rock, he stepped out of the lumbering vehicle. His appearance soon became woe-begone in the extreme. In a few minutes he expired. The buckies, too, with singular instinct, had collected in a row along the dry ledge of the tank.

Upon counting the numbers of my little colony, I found all right, excepting C. mÆnas; him I could not discover, and I soon began to suspect that he was defunct. No time, therefore, was to be lost, so a diligent search for his remains was instantly commenced. Fishes, Buckies, Hermits, &c., were speedily placed in safety in an extemporaneous tank—nothing else than an old pie-dish. This receptacle, when partly filled with sea-water, admirably answered the required purpose.

The water in the large vase was gently run off, and on approaching the base I found, as I expected, the dismembered carcase of the crab. One leg lay here, and another there, while the body was snugly esconced beneath a stone, on which sat my favourite limpet with its curiously formed shell, profusely decorated with a plume of sea-grass and infantile D. sanguinea. Here, then, I thought, was the mystery explained. It was from this spot that the noxious vapour must have emanated. Of course, the body of the crab was removed; but in performing this necessary act I tilted the stone, and so disturbed the Limpet. Guess my surprise at observing the overturned shell of the Patella to be quite empty, and its former occupant lying before me a mass of putrefaction.[5] It now began to dawn upon me that I must have libelled C. mÆnas. A few moments served to confirm this opinion, for on lifting the stone, there darted out a—I could scarcely believe it was the crab, who instantly went through a circus-like performance around the circumference of the vessel.

The reader will be prepared to learn that what I had at first observed were portions of the exuvium, which had by some means been distributed over the tank.

Many months did I wait with nervous anxiety to see the exact process of exuviation, but, except in the instances I am now about to chronicle, my wishes were never gratified.

I had at one time in my possession six little vases, each containing a crab measuring about one inch across the back (carapace). By constant watchfulness, morning and evening, for several months, I naturally entertained a confident hope of being favoured with a sight of the moulting operation in at least a single instance. But no; persevering though my endeavours were, I was always disappointed. The exuviÆ were cast regularly enough, but the crabs so managed matters, that the process was completed either when I was asleep, or had just gone away. I could almost have sworn that the whole pack had entered into a league to annoy me.

On one occasion I sat up all night, feeling confident, from symptoms which a certain Cancer mÆnas exhibited, that he was speedily about to exuviate. Alas! I was mistaken. On my endeavouring to expedite the event by lifting up the carapace of the crab, I received a nip on my finger so severe, that I shall never forget it.

But at length in the early portion of last year (1859), I, most happily for my own peace of mind, did actually witness the entire process of exuviation in a tolerably large specimen of the Common Shore Crab. The animal in question, who was domiciled in a crystal vase, or, in common language, a glass tumbler, rendered himself a favourite from his constant habit of poking part of his head and his entire claw (he had got but one), out of the water whenever he caught sight of me. Who could resist such a powerful, though silent appeal to 'the generous impulses of one's nature' as this? Certainly I could not, and therefore, once a day at least, gave Master Cancer the half of a newly-opened mussel, a tit-bit that was greatly relished. He would sometimes get a grip of the valve, and allow himself and the Mytilus to be entirely raised out of the water. Improving upon this, he would then partly finish his meal while seated in my hand. On the morning of the above mentioned eventful day, I gave the crab a portion of a Pholas, but to my surprise, the heretofore high-class dainty remained untouched. I was in ecstasies! for I felt morally certain that the grand event, so long looked for, was soon to take place. Consequently, I took out the crab, cleaned the windows of his dwelling in order that I might the better see what was going on within, treated him to some fresh water, as well as a new frond of sea-weed, and then again introduced my pet to his old apartment.

Before doing this I had the animal closely examined, to see if any signs of the approaching moult could be detected, but none were visible, except that the glassy bags, if I may so call them, which for some weeks had been gradually thrown out from the stumps of the three mutilated limbs, appeared finer in texture than usual. Indeed, so transparent had they become, that I could distinctly see the contour of the new limb about to be reproduced, folded up within each capsule.

A few minutes after the crab had been placed in the tumbler, I gave a peep to see how he was getting on. To my intense surprise, I observed that his shell had just opened near the tail! My first feeling was one of sorrow, thinking that in handling the specimen I had been too rough, and had perhaps injured it. This apprehension was soon changed to delight, as I became by degrees aware that exuviation had actually commenced.

The operation did not extend beyond five minutes (although the time appeared much longer to me), and was carried on by gentle, and at first almost imperceptible degrees. The shell, or carapace, was slowly raised over the back, and gave one the idea of the rear view of a lawyer's white wig when tilted over his brow, thus exposing the natural black hair on the occiput below; for, as the body of the animal came forth, it was very dark in colour, while the old case assumed a whitish hue. I need hardly say, the leg sheaths of the crab did not split open, and yet the corresponding limbs were drawn out with the greatest ease. Moreover, they did not appear in view one by one, but in a cluster, as it were, and packed close to the bent body of the crab.

During the entire process the animal appeared to use scarcely any exertion whatever, certainly not half so much as any human being would exhibit in throwing off the most trifling garment. In fact, the crab seemed to swell painlessly, and gently roll or glide out in a kind of ball. Until it had completely escaped from its old shell, I was somewhat puzzled to guess what shape it would eventually assume. The eyes and antennÆ, so soon as they left their old sheaths, commenced, together with the flabellÆ, to work as usual, although as yet they were still inside the exuvium. This circumstance was distinctly visible by looking through the side of the half-cast shell.

It was a curious and extraordinary sight to see the eyes gradually lose their brilliancy, and exhibit the filmy, lack-lustre-like appearance of death, while the act of exuviation was being accomplished. I may add that the tumbler which held my little captive stood upon a table near a large window, and that the sloughing operation was watched through a powerful hand lens.

On an after and well-remembered occasion, I saw a moderate-sized Partane standing on the top of a bush of Chondrus Crispus that grew in my aquarium. The fronds were attached to a piece of sandstone, placed uppermost upon a cluster of rock-work, situated, as before mentioned, in the centre of the vessel, and rising slightly above the level of the water. Thinking he was planning means of escape, I turned away for a few moments to procure a simple instrument wherewith to carry him to a less elevated position. On my return I saw him in the act of backing out of his shell. It was a singular circumstance that I should have just risen from the perusal of a talented author, who informed me that 'the crab hitches one of its claws into some crack or fissure, and from this point of resistance gives more power in emerging and withdrawing itself from between the carapace and the tail.'

Certainly no statement could more inadequately describe what I had witnessed in both of my crabs. Not only was the whole operation performed with perfect ease, but I am much inclined to believe with a degree of pleasure. For a while one of my crabs stood in juxtaposition to the shadow of its former self, and rubbed his antennÆ and wee peeping eyes as if awakening from a sleep. He had been lately, there was no doubt, living in an oppressed state, and might probably have surveyed things around him somewhat darkly, but now all was bright and clear again. On turning, the first object that caught his awakened eye was his cast-off vestment, which he seemed to scan as dubiously as a grown man would an exhumed pair of boyish corduroys, and mutter musingly, while stroking his chin, 'Well, come what will, it can never be my case again.'

On taking it in my hand, the Partane felt quite soft and velvetty to the touch, and exhibited no signs of alarm.

Since then I have repeatedly had shells of crabs cast in smooth glass globes, containing nothing else but clear salt water. This fact, in my opinion, completely subverts the statements of certain writers, who assert that these animals require extraneous assistance when about to exuviate.

Some writers have questioned the truth of the generally-received opinion that the new parts of the crab are derived from the old: that, for instance, a claw is regenerated within a claw, a limb within a limb, eyes within the eyes, and that on exuviation each is withdrawn from the pre-existing organ as from a sheath. But my operations tend fully to confirm the popular and existing belief.

There is yet one curious point connected with this subject which requires explanation, as it is not generally understood. I allude to the apparent disproportionate smallness of the 'glassy bag,' situated at the stump, as compared with the size of the regenerated limb, which is supposed to be folded up within the bag previous to exuviation. On looking at the newly-formed member, we can scarcely believe it possible that the transparent case could by any possibility have held it. The mystery vanishes if the new limb or claw be examined; for, although in shape it is perfect, even to the most minute particular, it remains for a certain period comparatively useless to the animal, from the fact of its being utterly devoid of flesh.

The new limb, therefore, can be considered merely as an expanded case, which, by a wonderful law of nature, becomes slowly filled up and completed. Immediately after exuviation has taken place, and a claw is introduced in the place of some mutilated stump, if any one will pull off the new member, he can readily confirm the truth of what I have stated, and, moreover, be able to test into how very small bulk the new limb may be rolled.

As the reader may remember, Goldsmith states that the crab casts its shell 'regularly once a-year, at the beginning of May.' Professor Owen fixes the date in the month of August. Professor Bell states, that 'there is no doubt exuviation takes place annually with great regularity, until the growth is completed, which, in many species, is not before the animal is many years old.' Another professor, treating on the same subject, thus writes, 'We are told that all this coat of mail is annually thrown off in a single piece by the contained animal,—the great proficient in Chinese puzzles may well be posed at this greater puzzle.' In fact, all writers whose works I have had opportunity of examining repeat the statement. Mr. Ball, who writes from personal observation, apparently confirms beyond a doubt, the annual moult of Crustacea. This gentleman, we learn, kept a Cray-fish alive for two years in a vase, and found that during each year its exuvium was shed but once.

It may readily be believed, with such a formidable array of contrary evidence, that I offer my own observations with modesty. But at the same time, I feel justified in confidently stating that the moult of the crab, (in its comparatively youthful state, at all events), takes place not only once, but many times during each year of its existence. My specimens may, perhaps, be considered exceptions to the general rule, but the facts I relate cannot by any possibility admit of doubt. The cast-off shells lie before me as I write.

Here is a set of three belonging to the same animal, exhibiting with marvellous exactness the gradual development of a broken claw. In the first the member appears very diminutive, in the second it is nearly twice its size, while in the third it has advanced to its natural form and bulk. To my regret, I cannot state the exact period that elapsed between each successive moult, but I am confident that the trio were cast in the course of a very few months.

I may here take the liberty of informing the uninitiated, that the appearance of the above objects is extremely pleasing; for, as the exuvium becomes dry, its colour changes to a bright scarlet, somewhat resembling that which the crab assumes when placed for a time in boiling water.

The next series of specimens, five in number, possess even still greater interest than the first examples. They were produced by a youthful C. mÆnas, at the following consecutive intervals:—

The first moult took place on 11th April 1858; the second on the 22d of May following; the third on July the 3d; the fourth on the 30th of August; and the fifth on the 26th of September in the same year. So that between the first and second period of exuviation there was an interval of forty-one days, between the second and third forty-two days elapsed, between the third and fourth fifty-eight days, but, singular to state, between the fourth and fifth moult only twenty-seven days intervened.

My first impression was, that as the creature grew older, its shell would be renewed less frequently, and the dates of the sloughings seemed to support this idea—until the fourth moult. It had occurred to me that perhaps the operation might be accelerated by the amount of diet which the crab consumed. In order to test this, I fed the animal carefully every day, as though he were a prize beast about to be exhibited at some Christmas show. Nothing loath, he ate of everything that was placed before him with a gusto that would have done credit to an alderman. The result was, that the shell was renewed in less than half the time that elapsed between the preceding moults.

These interesting investigations, which had been conducted thus far so satisfactorily, were suddenly brought to a close by the death of my protÉgÉ. This sad event occurred unexpectedly, not from overfeeding, as some persons may suppose, but from natural causes.

Whether increase of food always produces a like effect to that mentioned, is a point that I hope some of my brother naturalists will be able to determine. That the moult was accelerated by such means in my own specimen I have not the slightest doubt, for, on no other grounds can I explain its unusually speedy occurrence.

I may here assure my readers that the above dates may be confidently relied upon as correct, and also that each exuvium was produced by the same crab—one specimen only being in the tank during the whole period.

Since the foregoing was written, I have again been fortunate enough to have ocular demonstration of the phenomenon of exuviation, as occurring in a Cancer Pagurus, about as large as a moderate-sized walnut.

While watching this crab, it flashed across my mind that it would be a happy circumstance if by any means I could arrest the process then going on before my eyes, while it was yet only half completed, in order that others might also be enabled to witness the marvellous act of exuviation.

But how to carry out this scheme was the rub. I knew that—

'If 'twere done, then 'twere well it were done quickly.'

One minute passed,—two minutes flew by;—the crab would speedily complete his labours; still was I perplexed.

To plump it into fresh water would, I knew, be fatal to the animal, but not in such a speedy manner as was desirable. Boiling water next suggested itself, and doubtless would have answered the purpose effectually, had a supply been near at hand at the time, but such was not the case. I then thought of spirits. Ah! capital idea.... Before the third minute had passed, I might be seen to rush frantically to the sideboard, pour something into a glass, then dart back to the tank, dive down my trembling hand, bring up the poor unfortunate crab, and drop it into a fatal pool of pure "Glenlivet."

The animal appeared to die quickly, and was next day transferred to a vessel filled with Mythilated spirits. As it luckily turned out, the whisky answered the intended purpose remarkably well.

The preparation in question is, as far as I can discover, unique; at least I have neither read nor heard of another such existing in any private or public museum in the kingdom.[6]

It shows at a glance the increase that instantaneously takes place in the size of the crab after the act of exuviation is performed, the portion exuded being on a scale considerably larger than the old covering, which, however, is capacious enough to hold that half of the animal that had not effected its deliverance at the moment when the novel arrestment was so unceremoniously served.

The fourth and fifth pair of legs are free, while the eyes and antennÆ are also drawn out of their sheaths. (This is not very evident now, but such is really the fact, I having distinctly seen those organs in motion when the animal was in the living state.) The chelÆ, or large claws, being still undetached, serve to bind the crab to its old integument, and thus enable the act of exuviation, or one phase of it at least, to be distinctly apparent.

I know of no work on Natural History that speaks of the Hermit-Crabs (Anomoura) casting their shells, and on this account I have given some attention to them. These animals being so common, I kept by me at least a dozen specimens for the purpose of observing some of them, if possible, in the act of exuviation. The result of my labours has not been so satisfactory as I could wish, from my not having been able to collect any 'sets' of exuviÆ. I cannot, therefore, speak with certainty as to the frequency of this phenomena. By this time my readers will know that the tail of the Hermit-Crab is very tender and fleshy, being covered merely with an extremely delicate membraneous skin, while the carapace, claws, and antennÆ of the animal are protected by a hard crust, similar to the Lobster, Cray-fish, &c.

From this peculiar formation of the crab, I was not at all surprised to find, on several occasions, the upper part of its body alone cast off, and therefore came to the very natural conclusion, that as the tail was soft, it would grow and increase in proportion to the other parts of the animal, without ever needing the skin to be changed.

Each morning and evening during the time my experiments were being conducted, I examined all the tanks attentively, to see whether an exuvium had been cast. If visible, the object was picked out and gummed in a box, and a date placed above it for future reference. After having performed an operation of this kind one afternoon in October 1858, I saw a Hermit-Crab (who had cast his shell on the previous day) hurriedly leave his testaceous dwelling, then scrape away at his tail, and after a moment's interval, leap into his old seat again. On inspection, I found to my surprise that he had actually slipped off the skin of his tail![7] much in the same fashion as we would draw off a well-fitting glove. Here was a strange and unexpected discovery.

On submitting the exuvium to the microscope, we find that the covering of the false feet, and the cilia attached to the same, all remained fixed in their natural position to the tail-piece. Although in several cases I have had no difficulty in discovering the rejected cuticle of the tail, at other times it has eluded my search. The cause of this I cannot explain. It may be that the animal, adopting the habits of the toad, swallows a portion of its exuviÆ as soon as cast. On two occasions I found the slough of the body and claws of a crab, and waited patiently for several days, without success, expecting to get the tail portion. Growing impatient, it occurred to me that it would be a curious experiment to try and draw off the exuvium with my fingers. This was easy to talk about, but difficult to perform.

In the first place, the crab would not, if he could help it, allow himself to be handled even in the most gentle manner. To overcome this difficulty the shell had to be broken. This was done; but, alas! the shock nearly killed the poor little Hermit. After some trouble, I carefully unwound his body from the whirls of the Top Shell, and proceeded to perform the intended operation. Reader, have you ever seen a child take a rose-bud in his hands, and force open its half-pouting blossom, in the belief that by so doing he was assisting nature? If so, you must have watched the puzzled expression of the boy's countenance when he beheld the leaves fall one by one at his feet, and the bud itself exhibit evident signs of approaching decay.

In just such a position did I stand with regard to the poor Hermit-Crab, for, in spite of all my care in manipulation, the skin of the animal was so tender and delicate that the first gentle pinch caused a puncture which proved fatal; and as to drawing off the covering, the thing I now believe to be impossible, even under the most favourable circumstances.

The upper portion of the Soldier-Crab, I may mention, is cast off in one piece, while the animal is seated in its turbinated dwelling. The act is performed with the most perfect ease. Unlike the Brachyura, the Anomoura do not exhibit signs of such rapid growth immediately after exuviation, but increase in size very gradually indeed.