Glimpses of Ocean Life 20

Glimpses of Ocean Life 20

Before each block of stone that formed the foundations of the arch

was placed a splendid frond of Lettuce Ulva, tied by a strand of

silk to a white pebble. These verdant fronds, so smooth in texture

and so gracefully convoluted, rising up from the base of the tank

and reaching to its brim,--mingling, too, with the various tufts of

corallines and other sea-weeds that jutted from each crevice, were

very pretty to look at. When disturbed by the movements of the fishes

passing in and out, the gracefulness and beauty of the sea-weed was

doubly increased.

 

In making observations upon any bivalve, such as the Mussel, it is

extremely puzzling to know what is going on _inside_ the shell.

Yet it is almost necessary to acquire this knowledge by means not

always apparent, in order to satisfy one's mind relative to certain

appearances, which we perceive going on externally. We have to form our

judgment of things we do not see from those that are apparent--at all

times a difficult task. But not often so tantalizing as in the case of

an insignificant creature like the Mussel, who lives, moves, and works

constantly before our eyes. I may add that it was not enough for me

that I saw the spinning process frequently. It all seemed tolerably

clear to my mind, but still I did not feel thoroughly satisfied. My

desire was to peep into the shell, and find out where the last spun

thread was situated; or, in other words, from what part of the trunk

the new branch sprung. On examining various specimens of the byssus,

this point was by no means apparent. Various means I adopted failed

to secure me the requisite knowledge. At length I hit upon a plan,

which, after no long time, I found opportunity to put in practice. My

largest Mussel lifted up its testaceous canopy, put aside the fringed

and fleshy veil that surrounded its edge, protruded its spinner to

make sure the ground was secure, and then withdrew it again into the

shell as usual. After the lapse of a second, the foot reappeared and

was stretched out to an unusual length. No sooner was the end of the

thread formed on the glass than immediately I firmly pressed the valves

together, and held them in this position until I had gradually worked

the Mussel up out of the vase, when I bound them close together by

means of a piece of cord. I need not describe my manœuvres further;

suffice it to say that the thread nearest to the base of the groove

was found to be the one that was spun last. This, in my opinion, is

invariably the case.

 

I may mention that the above experiment also proved to my mind that the

foot must be a most important vital organ of the Mytilus. At times, on

placing an open Mussel in my tank as food for crabs or other animals, I

have noted that if every other part were eaten, and the foot allowed to

remain attached to the muscles of the bivalve, that member would after

a lapse of several days show signs of--I do not say life--but sensation

and retractile power.

 

But when the foot is cut and otherwise injured, the animal dies

quickly. In the experiment mentioned the valves were not kept closed

for more than half an hour; yet when they were opened, vitality had

evidently ceased within. This was the more singular when we remember

that the Mytili will live for many days out of the water; the shells,

of course, during the whole period being firmly closed.

 

The Mussel, as already hinted, is very tenacious of life. I have kept

specimens by accident for several days in the pocket of my coat, but

found them quite well and lively when placed in sea-water.

 

In general the sure sign of their not being in a healthy condition is

when the shell opens; for, while the animal retains any sense whatever,

it exercises a strict and judicious 'closeness.'

 

I have found, however, on several occasions, that the shell being

contracted is not always a valid proof of its owner's convalescence,

for when placed in water the Mussel would float for several days upon

the surface like a cork, although it was near death's door.

 

This phenomenon must be caused, I should suppose, by some sudden fright

compelling the mollusc to close its shell with such rapidity as to

prevent a proper supply of water being taken in. Having only air to

exist upon, the animal then lingers on until its branchiæ become dried

up, and all moisture exhausted. In this state the Mussel opens its

shell with a deep bursting sigh, and sinks to the bottom--dead.

 

Being at the sea-side one fine summer day, I heard a little Scotch

girl cry out to her brother who was about to swallow entire, a fine

specimen of the _Mytilus edulis_, 'Eh, Willie dear, dinna ye eat that.

Dinna eat the _beard_ or ye'll dee!' Many years ago I remember a remark

to the same purport as the above being made by a poor child to its

playmate, in the neighbourhood of Gravesend.

 

I little thought at that time that the Mussel was so interesting a

shell-fish, or that I years after should spend many an anxious hour

studying the formation and nature of its despised beard.

 

I need hardly state that the idea of the beard being poisonous is a

vulgar error. In general the fish may be eaten entire with impunity.

 

Cases have occurred where persons have been taken ill after eating it,

but this result has been satisfactorily explained to have been caused

by the Mussels being procured from places such as Leith Docks, where

their food consisted chiefly of unwholesome and putrescent matters.

 

This mollusc is not used as food to any very great extent by the poorer

classes. It is employed very extensively, however, by the fishermen as

bait along all parts of the British coast. But in France it is much

esteemed both by rich and poor. The trade in them is successfully

cultivated, and affords a means of support to hundreds of industrious

and deserving men.

 

From the learned author of the "Rambles of a Naturalist" we learn

that at the village of Esnandes, on the coast of France, the Mussel

trade, commenced about eight hundred years ago, has assumed a gigantic

extent. Both here and at the neighbouring villages of Charron,

Marsilly, Mussels are bred in an ingenious and systematic manner. At

the level of the lowest tide short piles or stakes are driven into the

mud, in a series of rows about a yard apart. This palisade is then

roughly fenced in with long branches. On this structure the Mussel

spawn is deposited, and it is found that the molluscs thus produced in

the open sea are much finer than those which are bred nearer the shore.

 

These artificial Mussel beds are termed 'bouchots.' The fishermen who

engage in this branch of industry are known as 'boucholeurs.'

 

'The little Mussels,' continues M. Quatrefage, 'that appear in the

spring are known as _seeds_. They are scarcely larger than lentils,

till towards the end of May, but at this time they rapidly increase,

and in July they attain the size of a haricot bean. They then take

the name of _renouvelains_, and are fit for transplanting. For this

purpose they are detached from those _bouchots_, which are situated

at the lowest tide mark, and are then introduced into the pockets or

bags made of old nets, which are placed upon the fences that are not

quite so far advanced into the sea. The young Mussels spread themselves

all round the pockets, fixing themselves by means of those filaments

which naturalists designate by the name of byssus. In proportion as

they grow and become crowded together within the pockets, they are

cleared out and distributed over other poles lying somewhat nearer

to the shore, whilst the full-grown Mussels which are fit for sale

are planted on the _bouchots_ nearest the shore. It is from this part

of the Mussel bed that the fishermen reap their harvest, and every

day enormous quantities of freshly gathered Mussels are transported

in carts or on the backs of horses to La Rochelle and other places,

from whence they are sent as far as Tours, Limoges, and Bordeaux....

The following data, which were collected by M. D. Orbigny more than

twenty years ago, will show how important this branch of industry

must be to the district in which it is cultivated. In 1834 the three

communes of Esnandes, Charron, and Marsilly, representing a population

of 3000 souls, possessed 340 _bouchots_, the original cost of which

was valued by M. D. Orbigny at 696,660 francs; the annual expenses of

maintaining them amounted to 386,240 francs, including the interest of

the capital employed, and the cost of labour, which, however, is spared

to the proprietor who works on his own account. The nett revenue is

estimated at 364 francs for each _bouchot_, or 123,760 francs for the

three communes. Finally, the expense of the carts, horses, and boats,

employed in transporting the Mussels, then amounted annually to 510,000

francs; but these numbers are far from representing the expenses

or profits at the present day. At the time M. D. Orbigny lived at

Esnandes, the _bouchots_ were only arranged in four rows; now however,

there are _no less than seven rows, and some of them measure more than

1000 yards from the base to the summit_. The whole of these _bouchots_,

which were at first limited to the immediate neighbourhood of the three

villages, of which I have already spoken, extend at the present day

uninterruptedly from Marsilly far beyond Charron, and _form a gigantic

stockade for two miles and a half in breadth, and six miles in length_.'

 

A curious circumstance connected with the Mytilus remains to be

described. Let the reader, who may be so fortunate as to possess a

good microscope, cut away a portion of the fleshy part of the Mussel,

then place it in a watch glass, and examine it through that 'portal

to things invisible,' and, unless I am much mistaken, he will own the

sight to be supremely wonderful. Some water being deposited in the

glass the fleshy object will be seen to swim about in a most singular

and mysterious manner, while a close inspection shows every portion of

it to be in active motion.

 

This motive power is caused by countless cilia, the rapid vibration of

which creates constant currents. This action preserves the health of

the poor mollusc by ærating the water which passes over his respiratory

organs.

 

That some such wonderful contrivance is adopted, for conveying food

within the valves, too, is evident, when we consider that the Mussel

is always affixed to some foreign substance, that it cannot hunt after

prey, and therefore can subsist only upon whatever nutritious particles

may be contained in the element in which it lives. These consist of

minute animalculæ, principally crustacea, which are drawn within the

shell by powerful currents.

 

I have often watched this phenomenon through a hand lens, and have

seen the young shrimps and skip-jacks, for instance, notwithstanding

the nimbleness of their movements, irresistibly drawn into the gulf

of destruction. Even tolerably sized specimens that were seated in

fancied security upon a valve of the Mussel, have suddenly been drawn

in, out of sight. As an instance of the power of these currents, I may

state that the water in a small aquarium is often seen to be affected

by the respiratory action of a single bivalve. The same thing has even

been apparent to the writer, while watching the movements of a colony

of Barnacles attached to a Limpet, the most distant part of the fluid

being gradually drawn near, in obedience to the beck of these delicate and graceful little creatures.