Glimpses of Ocean Life 26

Glimpses of Ocean Life 26

'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 very _lucidly_ and

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 as _a 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 the _foot_, and not in the stomach, at once proves

that it cannot possibly act as a _gizzard_ to 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.

 

 

 

 

CHAPTER XVI.

 

The Pholas, &c.

 

(ROCK-BORERS.)

 

 

'He that of greatest works is finisher

Oft does them by the meanest minister.'

 

 

 

 

XVI.

 

 

At certain 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 is manifested 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 the _debris_ of 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 the _debris_ which is deposited at

the _base_ of 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 untempting and 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 the fishes

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.

Glimpses of Ocean Life 25

Glimpses of Ocean Life 25

The same difficulty of calculation does not exist, at least to any such

extent, with the spawn of Eolis, which is laid in stringy coils. M.

Gosse mentions a specimen of _E. papillosa_ that laid nine strings of

spawn in his tank between the 20th of March and the 24th of May, all as

nearly as possible of the same length. Each string contained about a

hundred convolutions, each convolution about two hundred ova, and each

ova including, on an average, two embryos, making a total progeny of

forty thousand, produced from one parent in little more than two months.

 

I may mention that on no occasion have I ever found the spawn coils of

either Doridiæ or Eolididæ in my tanks, or at the sea-shore, except

during the months of January and February or March; neither have any

of my specimens spawned more than once during an entire season. From

noticing the same group of parent slugs congregated, and remaining,

as I can affirm, for weeks near their egg clusters, evidently in a

most enfeebled condition, it has occurred to me that on the Frith of

Forth, at least, vast numbers of these animals do not long survive the

hatching season.

 

Whether this be the case or not, it is a most singular fact that

in this locality, a Doris more than one or two inches in length is

scarcely ever to be met with.

 

There is at present in one of my tanks a specimen of the Doris of a

pearly-white colour, a second, tinted white and pink, and two others

which are quite _black_,--all being procured from the coast near

Edinburgh. The last-mentioned animals are, I think, somewhat uncommon.

When watching one of them in motion while the sun is shining down upon

it, the hue of the creature changes from a black to a very deep purple,

owing, no doubt, to its fleshy disc being many shades lighter than its

body, which, being extended, and exhibited under a full glow of light,

becomes semi-transparent. This peculiarity is not evident, of course,

when the Doris is lying in a passive state, with all its gill-plumes

closed up.

 

This sombre-coated gasteropod, although rare in some localities, is

very plentiful in foreign parts, if the following may be received as

an accurate narrative. 'On a reef of rocks near the island of Raiatea

is a huge unshapely black or brown slug, here called '_Biche_,' from

six to seven inches long, and five to six broad. Is is caught in vast

quantities, and not only regarded as a great delicacy by the natives,

but being cured, has become a valuable article of commerce in the China

market, whither it is carried from many insular coasts of the Pacific

by American ships. We have seen a number of lads fill three canoes in

two hours with these sea-snails.'

 

Thus uninviting as this slimy animal seems to our English taste, there

is evidently no doubt of its being used by the Chinese as an article of

food, and according to the evidence of certain authors, is esteemed by

the 'barbarians' a high-class luxury; but then we must remember that

the inhabitants of the land of gongs and chopsticks, have always been

famed for their singular gastronomic tastes. One poet writes:--

 

'That man had sure a palate covered o'er

With 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 such _risk_, I ask, compared

to that which _he_ endured, 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 the _Bêches de Mer_

dishes 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 of _Bêches 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 were _evasive_, and the proffered

mouthful was not always welcome.'

 

 

 

 

CHAPTER XV.

 

The Crab and the Dainty Beggar.

 

 

'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 actions themselves comprehend those elements of reason, so to

speak, which we commonly refer to rational beings, so that if the same

actions had been done by our fellow-creatures, we should have ascribed

them without hesitation to motives and feelings worthy of a rational

nature.'--SCHLEIDER.

 

'All things are bigge with jest; nothing that's plain

But may be wittie, if thou hast the vein.'

 

--GEORGE HERBERT.

 

 

 

 

XV.

 

 

I have been 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 of _C. 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 of the

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 of _I. 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 to my 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]

 

[11] My first introduction to the Hyaline stylet as above narrated,

occurred in October 1858.

 

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'importe_ the 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 this _bonne-bouche_ carefully packed 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_?

Glimpses of Ocean Life 24

Glimpses of Ocean Life 24

These wrinkles, or rings, which frequently amount to thirty or forty

in number, are first formed at the top, and slowly extend downwards.

Gradually as these furrows become deeper, the tentacula waste away, and

upon the margin of the upper ring eight equi-distant rays are formed.

The process continuing, in the space of a fortnight or so each groove

or ring is in like manner furnished with rays. The Medusæ now present

an appearance exactly resembling a series of cups piled up one within

the other. Strange to state, each little cup becomes eventually endowed

with life! As the uppermost segment is completely developed, it rests

upon the slender lips of the one beneath. It then glides off from its

old resting-place, and swims freely about in the water. Quickly it

aspires to the rippling surface above, and by a series of graceful

evolutions accomplishes its object. Once among the dancing waves and

exposed to the rays of a cheering sun, our little Medusa assumes its

complete form; and as a beautiful _Modecra formosa_, it may be destined

at some time or other to be the prize of an ardent zoologist, who, I

venture to assert, could not compliment it in more poetical language

than Professor Forbes has already done. This delightful author,

describing the little gem in question, says, 'It is gorgeous enough

to be the diadem of sea fairies, and sufficiently graceful to be the

night-cap of the tiniest and prettiest of mermaidens.' Or as an adult

_Cyanea capillata_, our once insignificant jelly-bag may perhaps

appear, and by an exercise of its urticating powers, send some unhappy

swimmer smarting and trembling to his home.

 

While the Medusæ column proceeds to throw off from its uppermost part

living segments of itself, its lower half, or stem, continues to grow,

but does not become ringed, for as the budding process ceases, the last

formed cup rests on newly-formed tentacula! Then again stolens are

thrown out, on which young Medusæ are formed, as before described.

 

Contemplating such mysteries as these, the mind becomes bewildered and

the spirits humbled.

 

'Imagination wastes its strength in vain,

And fancy tries and turns within itself,

Struck with the amazing depths of Deity.'

 

The above may be deemed one of the most interesting zoological theories

that has ever been promulgated in modern times. It was founded by

Chamisso, and termed the 'alternation of generation,' but was much

improved and extended by the researches of Steenstrup. Professor Owen,

however, had previously reduced the theory to a fixed and definite

scientific form, under the title of '_Parthenogenesis_.' Another

author, not viewing the Medusæ in the various stages of development

as an aggregation of individuals, 'in the same sense that one of

the higher animals is an individual,' proposes that each Medusa be

considered as an individual, developed into so many 'zooids.'

 

Into this abstract question, of course, I cannot enter. The reader who

would wish to know more of the subject than I have faintly shadowed

forth in this chapter, may consult Steenstrup's Memoir, published

by the Ray Society; Dr. Reid's admirable papers in the 'Magazine of

Natural History' 2d series; Lewes' 'Sea-Side Studies;' and the learned

works of Professor Owen.

 

 

 

 

[Illustration: MEDUSÆ IN VARIOUS STAGES OF DEVELOPMENT.]

 

 

 

 

CHAPTER XIV.

 

Doris, Eolis, &c.

 

 

'The inhabitants of the watery element were made for wise men to

contemplate and fools to pass by without consideration.'--ISAAK

WALTON.

 

 

 

 

XIV.

 

 

One fine morning during the month of January, on peering into my

largest tank I perceived, attached to the upper portion of the marble

arch (centre piece), a peculiar object that had evidently been

deposited during the preceding night, but by whom or by what means I

knew not. It resembled a fungoid growth, or riband of flesh, plaited up

and attached at one edge to the stone. At every undulation of the water

the object moved to and fro with an extremely graceful motion.

 

By careful and close examination it was seen to be covered with a film,

that gradually expanded until it burst, and thus gave means of escape

to thousands of minute white granules. On submitting these to the

microscope, a most wondrous sight met my astonished eyes. Each dot or

granule proved to be a transparent shell, resembling the periwinkle or

rather the nautilus in shape; containing an animal whose excited and

rapid movements were amusing to witness. From out the opening of the

shell appeared now and again two rings of cilia. When these organs

were about to be put into action, they reminded me of two circular

tubes of gas connected together, and each containing innumerable

perforations, which were sometimes suddenly and entirely lit up by a

torch being applied to one end.

 

The _cilia_ may be distinctly seen to play at a certain point, and then

gradually extend round the circumference of the rings. When the whole

are in full action their movements are so extremely swift _as to appear

devoid of motion_, and thus bear a resemblance to rings of flame.

 

The result of the movements of the cilia was always evident in

the vigorous evolutions of the little embryos, for the microscope

filaments, while in action, caused the animal to roll about in all

directions in a confined circle. When this envelope burst, the little

nautiline dashed out, and then--then it was of little use attempting to

get a view of the animal again, so rapid and violent were its movements

to and fro, never resting for one instant on any spot, and least of

all the spot wished. By the aid of blotting-paper, I sometimes reduced

the quantity of water in the watch glass; and the animal, thus being

compelled to confine its evolutions to a narrower stage, was more often

within the field of view.

 

On visiting the sea-shore shortly after the discovery of the egg

cluster just described, I perceived attached to numberless stones and

large boulders thick clusters, composed of the self-same objects!

Beside them were lying confused heaps of _sea-slugs_, evidently

exhausted with their hatching exertions. Anything more repulsive to

the eye than those animal heaps exhibited it would be difficult to

conceive. Yet, at the same time, I know of no sight more pleasing than

to watch the _Doris_ in its healthy state, gliding along with outspread

plume on the under surface of the water, or up the sides of the tank,

more especially if it be observed through a powerful hand lens.

 

These remarks will perhaps convey some new information to the young

naturalist, embracing as they do the leading facts connected with the

wondrous embryotic development of many marine animals. The reader will

already be prepared to learn that the vivacious little animal, moving

by aid of cilia and enclosed in a _shell_, was in reality the youthful

stage of that slow creeping gasteropod the _Doris_, which, in its

mature form, is possessed of no cilia, nor any shelly covering whatever.

 

I should not have introduced this subject so familiarly did I not feel

anxious to make my readers aware how easy it is for each of them to

conduct experiments in the early stages of embryotic development, and

to gain practical evidence of the wonders which this study unfolds.

 

'What,' eloquently asks Mr. Lewes, 'can be more interesting than to

watch the beginnings of life, to trace the gradual evolution of an

animal from a mass of cells, each stage in the evolution presenting

not only its own characteristics, but those marks of affinity with

other animals which make the whole world kin? To watch the formation

of the blood-vessels, to see the heart first begin its tremulous

pulsations, to note how life is from the first one incessant struggle

and progress--these keep us with fascinated pertinacity at our studies.'

 

The remarkable fact above mentioned, of the young of the Nudibranchiate

Gasteropoda being furnished with a shell is exhibited not only in

Doris, but in Eolis, Tritonia, Aplysia, &c., while the embryos of the

Purpura, Nerita, Trochus, &c., are likewise in their youthful state

furnished with cilia, by the agency of which these animals swim freely

about in their native element.

 

There is one exception to this, which occurs in _Chiton_, the early

stage of which has recently been shown by the observations of Mr.

Clarke and Professor Loven to be peculiar, and more resembling that

of an annelid than of a mollusc. In this case the animal can scarcely

be said to undergo a metamorphosis; for the embryo, even within the

egg, has nearly the form of the parent, and the appearance of the

shell-plates is a mere matter of development.

 

I have never attempted to count the ova that were contained in any

single riband of Doris spawn, in fact I considered the task an

impossibility; but at a rough calculation, I concluded there would not

be less than a million. Dr. Darwin, however, travelling in the Falkland

Isles, met with a riband of spawn from a white Doris (the animal itself

was three and a half inches long), which measured twenty inches in

length, and half an inch in breadth! and by counting how many balls

were contained in a tenth of an inch in the row, and how many rows in

an equal length of riband, this gentleman reckoned that upon a moderate

computation there could not be less than six millions of eggs. Yet, in

spite of such amazing fecundity, this Doris was not common. 'Although,'

says Dr. Darwin, 'I was searching under the stones, I saw only seven

individuals. No fallacy is more common with naturalists, than that the

numbers of an individual species depend on its powers of propagation.'

 

This apparent paradox is not difficult of explanation when we consider

the number of enemies which are always hovering near, and ready with

hungry mouths to snap up the infant embryos as soon as they begin

to show signs of vitality. The Hermit-Crabs are especially fond of

Doris spawn, so much so, indeed, that the writer could never retain

any for hatching purposes while any of the Paguri were near. Mr.

Peach says they (the young Dorides) have myriads of enemies in the

small _Infusoria_, which may be noticed, with a powerful microscope,

hovering round them, and ready to devour them the instant weakness or

injury prevents their keeping in motion the cilia, which serve both

for locomotion and defence. Let them cease to move, a regular attack

is made, and the animal is soon devoured; and it is interesting to

observe several of the scavengers sporting with the empty shell, as if in derision of the havoc they have made.

Glimpses of Ocean Life 23

Glimpses of Ocean Life 23

Hugh Miller also gives a beautiful prose description of the luminosity

of our own seas, but we must resist the temptation to introduce it here.

 

The appearance of the Greenland Seas is principally owing to the

presence of the minute species of Acalephæ, but there are many others

that grow to an immense size. Specimens of these may be frequently seen

cast on the sea-beach by the force of the waves. When in their native

element they form the swimmer's dread, owing to a peculiar stinging

power which they possess.

 

The Medusæ have been divided into groups, and distinguished according

to their different organs of locomotion. The common idea is that all

jelly-fishes are like mushrooms or miniature umbrellas. Such, it is

true, is their general form, but others abound both in our own and

in foreign seas, that possess a totally different appearance. For

instance, some move by means of numerous cilia, or minute hairs that

are attached to various parts of their bodies. By the exercise of these

organs the creatures glide through the water, and hence they are called

_ciliograde Acalephæ_.

 

One of the most remarkable examples of this class is seen in the

Girdle of Venus (_Cestum veneris_). 'This creature is a large, flat,

gelatinous riband, the margins of which are fringed with innumerable

cilia, tinted with most lively irridescent colours during the day,

and emitting in the dark a phosphorescent light of great brilliancy.

In this animal, too, which sometimes attains the length of five or

six feet, canals may be traced running beneath each of the ciliated

margins.'

 

This animal, as it glides rapidly along, has the appearance of an

undulating riband of flame. Most likely it is the species to which

Coleridge alludes in the following passage:--

 

'Beyond the shadow of the ship

I watched the water snakes

They moved in tracks of shining white,

And when they reared, the elfish light

Fell off in heavy flakes.

* * * * *

Within the shadow of the ship

I watched their rich attire--

Blue, glossy green, and velvet black,

They curled and swam; and every track

Was a flash of golden fire.'

 

Another of this class is the common Beroë (_Cydippe pileus_); its body

is melon-shaped, and covered over by rows or bands of cilia, placed

similarly to the treads on a water wheel, one above another. These are

entirely under the will of the little gelatine. It can use each or

all of them, and thus row itself along at pleasure. But perhaps the

most singular portion of this creature is what has been termed its

fishing apparatus, though by some writers it is considered merely to

be the means by which the Beroë anchors its body to any desired spot.

It consists of two exceedingly slender filaments or streamers, which

measure many times the length of the Beroë itself. Some writers, again,

fancy that these organs are used to propel the animal. This must be an

erroneous notion, for if they were cut off, the creature would still

continue to move with the same power as before. Nay more, if the little

Cydippe be cut into pieces, and the ciliated bands be attached to

each fragment, the latter will swim about with the same power as when

connected with the entire animal.

 

From the filaments here described, others more slender still depend at

regular intervals, which curl up like vine tendrils upon the principal

stem. The whole can be spontaneously elongated or slowly withdrawn

within the body of the Beroë, where they lie enclosed in two sheaths

until again required for use.

 

These interior 'sheaths,' which resemble in shape the drone of a

bag-pipe, are easily seen, being almost the only parts which are not

perfectly transparent. They are whitish in colour, and semiopaque.

(Plate 6 contains a sketch of the Beroë, drawn from nature.)

 

I may mention that the paddles, with their comb-like array of cilia,

flap successively in regular order from the top to the bottom of each

row. This wave-like movement takes place simultaneously in all the

rows, when the animal is in full vigour.

 

The organs of progression in the _Pulmonigrade_ Acalephæ, as their name

imports, bear certain resemblance to the lungs in respiration. They

move by the expansion and contraction of their umbrella-shaped bodies.

Graceful and elegant indeed are the motions of these creatures. I have

seen small specimens about the size of a sixpence, advance, in three

springs, from the bottom to the top of a large vase in which they were

confined.

 

In descending they turn over and allow themselves to sink gradually as

if by their own weight.

 

The third division of the Acalephæ is termed _Physograde_. The most

common member of this group is the _Physalus_, so well known to all

sailors under the name of the Portuguese Man-of-War. It is buoyed up

by air bladders--in fact, its entire body appears as one bladder, which

the animal is enabled to contract or expand at will. At first glance

the _Physalus_ appears to belong to quite a different family--suffering

under some maltreatment; for from its lower side, what seem a number of

entrails, of all shapes and sizes, hang down. When the upper surface

or crest of its swimming bladder projects above the waves, it has a

beautiful appearance, spangled with rays of purple, blue, and gold.

This formation acts as a kind of sail, by means of which the creature

is enabled to glide along with considerable speed.

 

This Physalus is a somewhat mysterious being, and zoologists have not

as yet been able to determine many points connected with its structure

and development.

 

The _Cirrigrade_ Acalephæ, too, are a singular family. They exhibit a

higher stage of development than those already alluded to, and possess

a kind of skeleton embedded within their gelatinous bodies.

 

The _Porpita_ and _Velella_ are examples of this class, but for

detailed descriptions I must refer the reader to larger works which

treat on the subject.

 

I cannot conclude this brief and imperfect sketch of the Acalephæ

without noticing their singular mode of reproduction. Nothing can

appear more marvellous than this process when first brought before

one's attention. It far excels the wildest dreams of fiction; and were

it not so well authenticated by naturalists who have devoted labour and

valuable time to gain ocular demonstration of the fact, we might well

hesitate to believe the statements laid before us in their works.

 

For example, a Polype, as _Hydra Gelatinosa_ or _Hydra Tuba_(found

on buoys, oyster shells, &c., long submerged), will, it may be in a

simple aquarium, produce a number of small objects which, on being

examined through the microscope, are found to be, not young Polypes,

but Jelly-fish! In process of time, the latter, by a wondrous law of

nature, will produce in their turn, not Medusæ, but Polypes!

 

'Imagine,' says Mr. Lewes, 'a lily producing a butterfly, and the

butterfly in turn producing a lily, and you would scarcely invent

a marvel greater than this production of Medusæ was to its first

discoverers. Nay, the marvel most go further still, the lily must first

produce a whole bed of lilies like its own fair self before giving

birth to the butterfly, and this butterfly must separate itself into a

crowd of butterflies, before giving birth to the lily.'

 

Let me now, by entering briefly into detail, endeavour to make the

reader acquainted with the leading features of this mysterious subject,

known as 'the alternation of generations.'

 

The adult Medusæ, then, gives birth to a number of oval gemmæ or buds,

appropriately so called by most writers, which appear like minute

jelly bubbles, covered with numberless vibratile cilia. These organs,

ten thousand times more delicate, we may imagine, than the eyelashes

of some infant member of fairy land, are ever in constant motion. The

currents produced thereby serve to propel the little animal to some

stray pebble or stalk of sea-weed, situated at a respectful distance

from its gelatinous relative. On some such object the young bud

attaches itself, and proceeds to vegetate.

 

The body gradually lengthens, and becomes enlarged at its upper

extremity; from this portion of the animal four arms appear surrounding

a kind of mouth. The arms lengthen, and are soon joined by four others.

These organs, as also the inner surface of the lips and of the stomach,

are covered with cilia, and become highly sensitive. They are used

in the same manner as the tentacula of the Actiniæ, namely, for the

capture of food. There is this difference, be it observed, between the

two animals, that while the infant Medusæ labours incessantly to gain

its daily meals, the zoophyte remains still, and trusts to chance for

every meal that it enjoys.

 

Fresh sets of arms continue to be developed successively upon the

little jelly fish, until the whole amount in number to twenty-five or

thirty. 'And the body, originally about the size of a grain of sand,

becomes a line, or the twelfth part of an inch in length.'

 

Thus far there appears nothing particularly striking or improbable in

the history of the Medusæ; the next stage, however, exhibits matter for

our 'special wonder.'

 

The young Acaleph now throws off its animal existence, and sinks into a

plant or compound polype.

 

The lower part of the body swells, and from thence, what may be termed

a _stolen_, is thrown out. On the upper surface of the stolen one

and even two buds are often formed. 'As the bud enlarges it becomes

elongated, and bends itself downwards to reach the surface of the stone

to which the elongated extremity adheres; after this the attached end

is gradually separated from the body of the parent. When thus detached,

a small opening presents itself at its upper end, its interior

gradually becomes hollowed out, and cilia grow upon it, and tentacula

begin to sprout around the mouth, exactly in the same manner as in the

buds formed on the upper surface of the stolens.'

 

Thus, from a single bud numberless other buds are formed, each being

endowed with equally prolific powers. If the parent be cut in half

transversely, the cut will close in, attach itself to some object, and

produce stolens and buds! If cut longitudinally, and the cut edges

be allowed to touch each other, they will again adhere, and exhibit

no trace of their ever having been divided. If the cut edges of each

division be not kept apart they will approximate and adhere together,

and thus two separate animals will be produced, each gifted with the

power of throwing out stolens and buds with the same prodigality as if

they had never been disunited!

 

How long this budding process of necessity continues we cannot tell. It

may be only during the winter season. These creatures in their perfect

condition are generally found crowding our seas during the summer

months; most probably, therefore, as Sars and Steenstrup state, it is

at the commencement of spring that they undergo the last portion of

this 'transformation strange.'

 

Still, this cannot be taken as a general rule. Dr. Reid, who for a

period of two years kept colonies of Medusæ, and assiduously watched

the various stages of their development, found that the larvæ of

one colony, which was obtained in September 1845, did not split

transversely into young Medusæ in the spring of 1846, as he expected

them to do, but continued to produce stolens and buds abundantly.

 

On the other hand, the larvæ of the other colonies, which this

gentleman obtained in July, began to yield young Medusæ about the

middle of March. This process takes place in the following manner:

A 'bud' having arrived at maturity, it becomes 'cylindrical,'

considerably elongated, and much diminished in diameter, its outer

surface being marked with a series of transverse wrinkles.