Glimpses of Ocean Life 13

Glimpses of Ocean Life 13

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.'

 

[4] Illustrations to Paley's Natural Theology.

 

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.

 

[5] This affords an important hint to the young aquarian to watch the

Patella, and occasionally to touch its conical house, to make sure the

proprietor is alive and well.

 

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.