Glimpses of Ocean Life 30

Glimpses of Ocean Life 30

This wonderful race of animals, for their beauty of colour, elegance

of shape, and peculiarity of structure, possess a great degree of

interest, not only to the naturalist, but also to the casual observer

by the sea-side.

 

There are fourteen British species of Asteriadæ, which are arranged

under four families, namely--the Urasteriæ, the Solasteriæ, the

Gonasteriæ, and the Asteriæ. This group contains no less than eight

generic types, clearly distinguished from each other by certain

characters, 'derived from the outline of the body, the number of rows

of suckers in the avenues, and the structure and arrangement of the

spines covering the surface and bordering the avenues.'

 

There are four species of Star-fishes belonging to the genus Uraster,

the most common of which is the _Uraster rubens_, or Common Cross-fish.

 

No person in the habit of visiting the sea-shore can be unfamiliar with

the likeness of this creature, which is generally seen lying wedged

in some rocky crevice, or among the Fuci, there patiently waiting the

return of the tide.

 

At such a time, the Devil's-hand (as the Irish people term it), does

not appear by any means attractive. If placed in water, however, its

appearance becomes wonderfully improved.

 

Here is a small specimen, just brought from the sea-shore at

Cockburnspath (a most romantic and delightful locality, situated on

the coast of Berwickshire). It is neatly wrapped up in a mantle of

sea-weed. Freed of its verdant envelope, I deposit the youthful Rubens

upon his back--'willy-nilly'--in a tumbler partly filled with clear

sea-water, and then proceed to watch its movements through a magnifier.

 

At a glance we perceive that each of its five rays is grooved on its

lower surface, and filled with minute perforations, through which is

gradually protruded a multitude of fleshy suckers, knobbed at the end.

It is by aid of these organs that the animal grasps its food, and

changes its position, as we shall presently see. One of the rays is now

slowly lifted up and moved about in various directions, while from its

extreme point the suckers are extended to the utmost limit. No sooner

do they touch the side of the vessel than they are firmly fixed and

contracted. A _point d'appui_ being thus gained, the animal is enabled

by degrees to draw its body round, so as to get another regiment of

suckers into play, and, by such plan of operations being repeated,

the animal is eventually enabled to 'right itself,' and crawl up the

polished surface of the glass.

 

Generally, when the Star-fish is disturbed, or placed on a dry piece

of stone, the suckers are withdrawn into the body, leaving no signs

of their previous existence except a series of minute tubercles. In

fact, the Asterias, although enabled to adhere with great tenacity to

any foreign object when immersed in water, possesses but little power

to retain its hold if the fluid be removed. Hence the young zoologist,

keeping this peculiarity in mind, should not too hurriedly return a

verdict of 'Found dead,' when he meets with a helpless specimen upon

the beach, for in all likelihood, were the creature to be laid for a

few minutes in a rock-pool, it would soon exhibit signs of returning

animation.

 

A simpler, though not so sure a test for ascertaining whether a

Star-fish be living or not, is to handle the specimen. If it feels soft

and flabby, it is dead; but if tolerably firm to the touch, it may be

'recalled to life,' by the means pointed out.

 

It may not be out of place to chronicle here a singular circumstance

which the writer has often verified in connection with the true

Star-fishes. It is this. When any captured specimens have been placed

in confinement, no matter how large or small such might be, they never

moved through the liquid element with a tithe of the rapidity that I

well knew they were capable of. At the sea-side, I have seen a specimen

of the Cross-fish glide through the water so nimbly, yet withal so

gracefully, that I have felt inclined to rank natation among the few

other acomplishments of which the species can boast.

 

The _Uraster rubens_ is also popularly known as 'Five Fingers.' For

ages past it has been subject to the bitter denunciation of fishermen

and others, for the injury which it is said to inflict upon oysters.

At one time, according to Bishop Spratt, the Admiralty Court laid

penalties upon those engaged in the oyster-fishing who did not

tread under their feet, or throw upon the shore, a fish they call a

Five-Finger, resembling a spur-rowel, because that fish gets into the

oysters when they gape, and sucks them out. Poets have also endeavoured

to perpetuate the vulgar opinion:--

 

'The prickly Star-fish creeps with fell deceit,

To force the Oyster from his close retreat,

Whose gaping lids their widened void display;

The watchful Star thrusts in a pointed ray--

Of all its treasures robs the rifled case,

And empty shells the sandy hillock grace.'

 

Even yet the oyster fishermen at certain localities wreak all

possible vengeance upon the 'submarine Dando's,' for their supposed

gourmandizing propensities. I say _supposed_, for although so

many naturalists have studied the question, it is not, up to the

present time, satisfactorily settled. Some deny the alleged tendency

altogether, while less sceptical observers are unable to understand

the mode in which the Star-fish could injure an animal apparently so

capable of self-defence as the oyster. According to certain authors,

the Star-fish encircles the oyster with its five fingers, and by some

clever process of suction destroys the unfortunate mollusc. Others,

again, maintain that the first step of the attack is the injection

of some marine chloroform between the shells of the oyster, and that

during the insensibility that follows, the Star-fish effects an

entrance.

 

As this is an interesting subject, perhaps the reader would like to

have the exact words which are used by two celebrated naturalists, one

of whom attempts to vindicate the character of the Asteridæ, the other

to blacken it.

 

Sir John Dalyell--a high authority upon all matters of marine

zoology--shrewdly remarks: 'I have not heard it suggested that the

Star-fish possesses any kind of solvent compelling the bivalves

to sunder. Neither can its hostility be very deadly to the larger

univalves, from the distance to which they are enabled to retreat

within their portable dwellings. Their general habits are, to force the

shells of smaller bivalves asunder, and to devour the contents; they

likewise consume the substance of ordinary fishes entire; nevertheless,

as far as I am yet aware, their destruction of oysters is destitute of

evidence. The Star-fish sometimes shows an eversion of stomach, or of

some membrane of it. Whether this may be the means of affecting their

prey, merits investigation.'

 

Professor Jones, who affirms that in the latter suggestion Sir J.

Dalyell has nearly hit upon the true solution of the problem, thus

gives what _he_ considers to be the correct mode of procedure on the

part of the Star-fish: 'Grasping its shell-clad prey between its rays,

and firmly fixing it by means of its prehensile suckers, it proceeds

deliberately to turn its stomach inside out, embracing in its ample

folds the helpless bivalve, and perhaps at the same time instilling

some torpifying fluid, for the shells of the poor victim seized soon

open, and it then becomes an easy prey.'

 

Now, many fishermen with whom I have conversed hold the same opinion as

Bishop Spratt, and believe that when the oyster is gaping the Star-fish

insinuates a finger, and hastily scrapes out the delicious mouthful;

nay, further maintain that the Star-fish is far from being successful

at all times, very often, especially when there has only been one ray

inserted, the frightened oyster grasps it with all his might, and

obliges his discomfited opponent to retire minus a limb.

 

If the writer might venture to suggest an opinion, he would express

his belief that the following is the correct account of the state of

matters. He believes with the fishermen that frequently the star-fish

begins his attack by inserting an arm, but he does not believe that the

oyster under such circumstances escapes with life. Let us suppose the

star-fish to have succeeded in insidiously introducing a ray within the

shell of the apathetic oyster, and that the oyster immediately resented

such intrusion by closing his shell with all the force he can exert.

The opposite argument at this stage is, that the intruder is obliged

from _pain_ to abandon his hold, and even pay for his audacity by the

forfeit of a limb. But against this we advance the notorious fact, that

the star-fish, like so many marine creatures of a similar organization,

is remarkably indifferent to pain. I therefore believe the true

explanation to be, that the oyster being unable to sustain such

continued muscular exertion for nearly so long a time as the star-fish

can tolerate the pressure upon its ray, the latter is consequently, in

the long run, successful.

 

The number of rays in the several genera of the true Star-fishes is

extremely various. In the genus _Uraster_, as we have seen, five is

the predominant number. If we turn to the two species which comprise

the genus _Cribella_, we still find the quintuple arrangement adhered

to. In _Solaster endeca_, on the contrary, the rays vary from nine

to eleven, and even reach as high as twelve or fifteen in _Solaster

papposa_.

 

In the genus _Palmipes_ we have the pentagonal form, it is true, but

the space between each ray is filled up, so as to resemble the webbed

foot of a bird, hence the popular title of this solitary species,

'The Bird's-foot Sea-star.' 'It is the flattest of all its class, and

when alive it is flexible like a piece of leather.' Passing by the

'Cushion-stars' (which have five _angles_--it seems a misnomer to call

them rays), which connect the true Star-fishes with the Sea-Urchins,

we come lastly to the 'Lingthorn,' _Luidia fragillisima_, with its

seven rays. This is the animal of which Professor Forbes discourses so

pleasantly about its winking derisively at his despairing endeavours

to preserve even a small portion of what at that time was his maiden

specimen. The Luidia is even more brittle--more regardless of its

wholeness, than the _Ophiuræ_, which renders the capture of a perfect

specimen a most difficult task.

 

 

 

 

CHAPTER XIX.

 

Sea-Urchins (Sea-Hedgehogs).

 

 

'Truly the skill of the Great Architect of Nature is not less displayed

in the construction of the Sea-Urchin than in the building up of a

world.'--P. FORBES.

 

 

 

 

[Illustration:

 

1 THE APLYSIA or SEA-HARE

2 PURPLE-TIPPED SEA-URCHIN

3 Spine of PURPLE-TIPPED SEA-URCHIN

4, 5 Suckers of PURPLE-TIPPED SEA-URCHIN

6 COMMON SUN-STAR]

Glimpses of Ocean Life 29

Glimpses of Ocean Life 29

The instruments can all be withdrawn into the body of the animal at

will, but we can easily conceive that such formidable weapons being

retracted into its flesh would not add to the creature's comfort--in

fact they would produce a deadly effect, were it not for the following

simple and beautiful contrivance.

 

Each spine is furnished with a double sheath composed of two blades,

between which it is lodged; these sheaths closing upon the sharp points

of the spear when the latter is drawn inwards, effectually guard the

surrounding flesh from injury.

 

The shape of this animal is oval, the back convex, while the under part

presents a flat and curious ribbed-like appearance. Its length varies

from three to five inches; specimens, however, are sometimes to be

procured, even on our own shores, of much larger dimensions.

 

 

 

 

CHAPTER XVIII.

 

Star-fishes.

 

(OPHIURIDAE AND ASTERIADAE.)

 

 

'As there are stars in the sky, so there are stars in the sea.'--LINK.

 

 

 

 

XVIII.

 

 

There are not a few persons still to be met with, who believe that

man and the lower animals appeared simultaneously upon the face of

the earth. Geology most forcibly proves the error of such an idea,

for although the fossilized remains of every other class of organized

beings have been discovered, human bones have nowhere been found.

This fact, though deeply interesting, is perhaps not more so than

many others which this wonderful science has unfolded. What can be

more startling to the student for instance, than the information that

for a long period, it may be thousands of years, no species of fish

whatever inhabited the primeval seas? True it is that certain creatures

occupied the shallows and depths of ocean, but these were of the lowest

type. The most conspicuous were the coral polypes, which even then as

now were ever industriously building up lasting monuments of their

existence, as the Trilobites, a group of Crustacea, and the Crinoids,

or Lily-stars.

 

The last-mentioned group of animals were analogous to the present tribe

of Star-fishes, and are now nearly extinct. The body of the Lily-star,

which resembled some beautiful radiate flower, was affixed to a long,

slender stalk, composed of a series of solid plates superposed upon

one another, bound together by a fleshy coat, and made to undulate

to and fro in any direction at the will of the animal. The stalk

was firmly attached to some foreign substance, and consequently the

Crinoid Star-fish, unlike its modern representative, could not rove

about in search of prey, but only capture such objects as came within

reach of its widely expanded arms. 'Scarcely a dozen kinds of these

beautiful creatures,' observes Professor Forbes, 'now live in the seas

of our globe, and individuals of these kinds are comparatively rarely

to be met with; formerly they were among the most numerous of the

ocean's inhabitants,--so numerous that the remains of their skeletons

constitute great tracts of the dry land as it now appears. For miles

and miles we may walk over the stony fragments of the Crinoidae,

fragments which were once built up in animated forms, encased in

living flesh, and obeying the will of creatures among the loveliest

of the inhabitants of the ocean. Even in their present disjointed and

petrified state, they excite the admiration not only of the naturalist,

but of the common gazer; and the name of stone lily, popularly applied

to them, indicates a popular appreciation of their beauty.' Each

wheel-like joint of the fossil Encrinite being generally perforated

in the centre, facility is thus afforded for stringing a number of

these objects together like beads, and in this form the monks of old,

according to tradition, used the broken fragments of the lily-stars as

rosaries. Hence the common appellation of St Cuthbert's Beads, to which

Sir Walter Scott alludes,--

 

'On a rock by Lindisfarn

St. Cuthbert sits, and toils to frame

The sea-born beads that bear his name.'

 

One solitary species of the Crinoid Star-fishes has of late years been

found to flourish in our own seas; it is, however, affixed to a stalk

(pedunculated) only in the early periods of its existence.

 

When first discovered by Mr. Thompson in its infant state, the

_Pentacrinus Europæus_ was believed to be a distinct animal. It was

taken attached to the stems of zoophytes of different orders, and

measured about three-fourths of an inch in height. In form it resembled

a minute comatula mounted on the stalk of a Pentacrinus. Subsequent

research has proved that the little stranger was merely the young state

of the feather star _Comatula rosacea_, and that although for a certain

period attached to a slender waving stem, the Pentacrinus, when arrived

at a certain stage of development, feels fully able to start life on

its own accord, and hence takes opportunity to break off its early

ties, and become a free animal, dependent upon its own exertions for

subsistence.

 

It is no uncommon thing, as a late writer forcibly remarks, in the

inferior classes of the animal kingdom, to find animals permanently

attached from the period of their birth, and during all their

existence. Familiar examples of this occur in the oyster, and various

other bivalve shell-fish, as well as in numerous compound zoophytes. We

likewise meet with races which are free and locomotive in their first

stages, and afterwards become permanently fixed; but an animal growing

for a period in the similitude of a flower on a stem, and then dropping

from its pedicle, and becoming during the remainder of its life free

and peripatetic, is not only new, but without any parellel in the whole

range of the organized creation.

 

The Comatula, or as it is commonly called, the Rosy Feather-star, is

allowed to be without exception the most lively of all the star-fishes.

Its movements in swimming are said to resemble exactly the alternating

strokes given by the medusa to the liquid element, and have the same

effect, causing the animal to raise itself from the bottom, and to

advance back foremost even more rapidly than the medusa. It has ten

very slender rays with numbers of long beards on the sides. The body,

which is of a deep rose colour, is small and surrounded with ten little

filiform rays. The extremities of these organs are shaped like claws,

by means of which the animal attaches itself to various kinds of

sea-weed, and other submarine objects.

 

The adult Comatula generally measures about five inches across its

fully expanded rays.

 

Before treating of what are termed the _true_ Star-fishes, we require

to dwell briefly upon an intermediate family named by Professor Forbes

the _Ophiuridæ_, 'from the long serpent or worm-like arms, which are

appended to their round, depressed, urchin like bodies.... They hold

the same relation to the Crinoidea that the true Star-fishes hold to

the Sea-Urchins. They are spinigrade animals, and have no true suckers

by which to walk, their progression being effected (and with great

facility) by means of five long flexible-jointed processes placed at

regular distances around their body, and furnished with spines on the

sides and membraneous tentacula. These processes are very different

from the arms of the true Star-fishes, which are lobes of the animal's

body, whereas the arms of the Ophiuridæ are super-added to the body,

and there is no excavation in them for any longation of the digestive

organs.'[16]

 

[16] British Star-fishes.

 

The British Ophiuridæ are now classed under two genera; of the Ophiuræ,

or Sand-stars only two species (_O. texturata_ and _O. albida_) are

found on our shores; and the Ophicomæ, or Brittle-stars, of which there

are ten.

 

An extraordinary feature, characteristic of all the above-mentioned

animals, is the great tendency which they have to mutilate themselves,

and throw their limbs about in fragments on the slightest provocation.

If a specimen be handled, a certain number of fragments will assuredly

be cast off. If the rays become entangled in sea-weed, or even if the

water in which the animal resides happens to become impure, the same

disastrous result follows, until nothing but the little circular disc

remains. As a set off against this weakness, both the Ophiuræ and the

Brittle-stars possess reproductive powers of a high order. Hence it not

unfrequently happens that if each and all the rays of a specimen be

rejected, the animal will live on, and eventually, perhaps, become a

complete and perfect star-fish.

 

The best means of preserving an Ophiura is to let the devoted animal

remain for a time expanded in sea-water, then with a small pair of

forceps lift it carefully up, and plump it into a bath of cold 'fresh'

water, letting it lie there for about an hour. The animal speedily

dies, as if poisoned, in the fresh liquid, in a state of rigid

expansion. Some writers recommend that, at this stage, the specimen

should be dipped for a moment into boiling water, and then dried in a

current of air; but I have never been able to detect any great benefit

arising from the adoption of the process.

 

When examining any of the Brittle-stars, I have always found it an

excellent plan to raise them up by aid of the forceps applied to the

disc. By this means a specimen may be moved about without any fear

of mutilation; whereas if the fingers be used as forceps, an unhappy

result will assuredly follow.

 

The _Ophiocoma rosula_, figured on Plate 9, will serve to convey to

the reader a general idea of this class of animals. Its popular title

is the Common Brittle-star, indicative of the inherent fragility of the

species, as also of their prevalent appearance at the sea-shore; but,

though so exceedingly 'common,' we must at the same time in justice

add, that the _O. rosula_ exceeds in beauty many other species which

are rare, and consequently more highly prized by the collector.

 

It is very abundant on all parts of the British coast, and is often

found in clusters upon the stems of _L. digitata_, and as frequently

upon the under side of boulders. In dredging, the Brittle-star is an

unfailing prize. It is a marvellous sight when the scrapings of the

ocean bed are spread out upon the dredging-board for examination,

to see hundreds of these singularly delicate creatures twisting and

twining about in all directions,--over each other's bodies, through the

weed, sand, shells, and mud, and strewing fragments of their snake-like

arms upon every surrounding object.

 

At the mere mention of 'Star-fishes,' the most uninitiated reader will

at once realize in his mind's eye a tolerably correct notion of the

form of these curious productions of the marine animal kingdom, even

although he had never seen a living or dead specimen.

 

The body of the animal is divided into rays, like the pictured form of

one of the heavenly stars, and the fancied resemblance is most apparent

in the Asteridæ, or true Star-fishes, of which we are now about to speak.

Glimpses of Ocean Life 28

Glimpses of Ocean Life 28

Perhaps some of my readers would like to know how to procure a sight

of the stylet; if so, their wishes may be easily gratified. Take up a

disentombed Pholas in your hand, and with a sharp lancet or point of a

pen-knife, briskly cut a slit in the extreme end of the foot, and, if

the operation be done skilfully, the object of your search will spring

out of the incision to the extent, it may be, of a quarter of an inch.

If not, a very slight examination will discover the opal gelatinous

cylinder, which may be drawn out by means of a pair of forceps.

 

When extracted and held between the finger and thumb by its smaller

end, the stylet will, if struck with a certain degree of force, vibrate

rapidly to and fro for some seconds, in the same manner as a piece of

steel or whalebone would be affected, under like circumstances.[14]

 

[14] In the _Athenæum_ (Nos. 1632 and 1636), were kindly published two

letters from the author on the above subject, under the respective

dates January 26th, and February 28th, 1859.

 

So long as a Pholas exhibits only the ends of its siphons to the eyes

of a greedy crab, it is perfectly safe from attack. It is only when

the fleshy foot is unprotected that it falls a prey to some hungry

crustacean.

 

The toughness of the siphonal orifices is, I believe, a most important

point, for, as I shall endeavour to explain, the siphonal tubes

constitute important accessory excavating agents, to those already

enumerated.

 

We all know that the hole which each young Pholas makes, when first

he takes possession of his rocky home, is extremely minute,--not

larger than a small pin's head; now, it stands to reason, that if the

shell was the only terebrating agent, the opening of the cavity in

question would always remain of the same size, or, perhaps, on account

of the action of the water, a slight degree larger than its original

dimensions. Such, however, is not the case.

 

Here is a fragment of rock exhibiting several Pholas holes. The

aperture of one of these, which I measure, is nearly half-an-inch in

diameter, while in juxtaposition with it is situated another cavity,

measuring across the entrance less than the eighth part of an inch.

The reader will at once perceive, if the foot and shell were the sole

augurs, that as the animal descended deeper into the rock, the siphonal

tube, as it enlarged in proportion to other parts of the animal, would

have to be drawn out to an extremely fine point to fit the opening of

the tunnel. But as this is not the state of matters, the conclusion

forces itself upon us, that that portion of the orifice situated above

the shell of the animal must be enlarged by the constant extension and

retraction of the siphons, aided by currents of water acting on the

interior surface of the cavity.

 

This same theory will also serve to explain how it is that all Pholades

situated at the same depth in the rock, are not all of a uniform size.

I have frequently seen a piece of rock exhibit the peculiarity of two

burrows of vastly different proportions as regards breadth, being

precisely the same depth from the surface of the stone. This appears

to me equally wonderful and puzzling at first sight, as the 'boring'

question.

 

What age is attained by any species of the rock-borers before they

arrive at full growth, there are no means of knowing. This point,

like several others in the history of these animals, still remains a

mystery, nor is it likely soon to be cleared up. The largest specimen

of _P. crispata_ that I have seen is at present in my possession. Each

valve measures three and a half inches in length, by two inches in

breadth. Some foreign specimens of this species, and especially of _P.

dactylus_, are, however, frequently found of much larger dimensions.

 

On no occasion have I ever examined any Pholas excavation that had lost

its conical shape, a fact that seems to prove that the successive

stages of the boring operation must have taken place solely in

consequence of the animal not having reached its adult form.[15] For

had the shell attained its full development, and its owner continued

to labour, and rasp away the rock, the sides of the cavity at its base

would necessarily present a parallel appearance--a phenomenon which is

never witnessed.

 

[15] The above remark holds good, even although (_as is frequently the

case_) the animal wilfully deviates from the straight path, and bores

its tunnel in a curved form.

 

From this we may conclude that the depth of the perforation, which is

seldom many inches, depends entirely upon the growth of the mollusc.

 

When keeping specimens of the Pholas for observation, the usual plan is

to chip away the rock to the level of the valves, so that the whole of

the animal's siphonal tubes may be distinctly seen, however slightly

these organs may be extended. This plan, I found, did very well for a

time, but I was annoyed to witness, that in the course of a few months,

the siphons ceased to be either advanced or retracted,--they having

become, as it were, rudimentary.

 

To obviate such contingency, the writer adopted the following scheme.

 

To place in the tank a Pholas completely embedded in a fragment of

rock, so that nothing but the tips of its siphons, when extended to the

utmost, were visible, would not afford much pleasure to the student. I

therefore managed to saw away the rock in such a manner, as to leave a

narrow slit along the entire length of the tunnel, so as to expose the

slightest movement of the animal within. Having natural support for its

siphons, I expected that these organs would be constantly retracted and

extended; but such was not the case; at least for so long a period as I

had anticipated.

 

After repeated experiments, I have now discovered that whether the

siphons be protected as above described or not, they will always be

vigorously exercised if the animal be placed in shallow water, so that

its tubes when fully extended will reach the surface of the fluid.

 

The conclusion, from what has been stated, is, that the Pholas can

no longer be considered a weak and helpless animal. Possessed of a

rasp-like shell, a horny ligament, retractile tubes, a strong muscular

foot, and a powerful spring or stylet, it is not by any means difficult

to conceive that these agents when they are all brought into play, are

fully equal to the task of excavating the rocky chamber in which the

animal lives.

 

 

 

 

CHAPTER XVII.

 

The Sea-Mouse.

 

(APHRODITE ACULEATA.)

 

 

'For seas have ...

As well as earth, vines, roses, nettles, melons,

Mushrooms, pinks, gilliflowers, and many millions

Of other plants, more rare, more strange than these,

As very fishes living in the seas.'

 

 

 

 

[Illustration:

 

1 THE SEA MOUSE (_Aphrodite aculeata_)

2 THE DORIS

3 YOUNG OF THE DORIS

4 EOLIS PAPILLOSA]

 

 

 

 

XVII.

 

 

Beauteous stars also the sea contains, as numberless, though not so

brilliant in appearance as those which stud the firmament of heaven;

flowers, too, grow beneath the wave, and rival in loveliness the gems

which adorn our fields and hedge-rows. Nay, more, like the land, the

ocean owns its various grasses, its lemons, and cucumbers, its worms,

slugs, and shelly snails, its hedgehogs, its birds, its ducks and geese

(_anatidæ_), its dogs, its hares, and lastly its _mice_ (_aphroditæ_.)

The latter objects, despite their unprepossessing name, being in no

wise less interesting than those above mentioned.

 

The _Aphrodite aculeata_ is, perhaps, one of the most gorgeous

creatures that inhabits the seas of our British coast. Its body is

covered with a coating of short brown hairs, but as these approach the

sides of the animal, they become intermixed with long dark bristles,

the whole of which are of an iridescent character. In one respect

this creature bears no resemblance to its namesake of the land, being

extremely slow and sluggish in its movements (at least according to

our experience) when kept in confinement. Some writers, however, affirm

that the Aphrodite possesses the power, although seldom exercised, of

both running and swimming through the water with considerable speed.

 

In general the animal loves to tenant the slimy mud, and wherever the

writer has happened to come upon a specimen at the sea-shore, its back

has always been thickly coated with sand or dirt. The Sea-Mouse, then,

unlike the peacock, can never be deemed an emblem of haughty pride,

yet has nature in her lavish beauty endowed this humble inhabitant of

the deep with a richness of plumage, so to speak, fully equal in its

metallic brilliancy to that which decorates the tail of the strutting

bird we have mentioned. As the bristles of the Aphrodite are moved

about, tints--green, yellow, and orange, blue, purple, and scarlet--all

the hues of Iris play upon them with the changing light, and shine with

a metallic effulgence. Even if the animal, when dead, is placed in

clear water, the same varied effect is seen as often as the observer

changes his position.

 

Not only are the _Setæ_ worthy of notice on account of their lustrous

beauty, but also for their shape, and the important part they play in

the economy of the animal. These lance-like spines seem to be used by

the Aphrodite as weapons of defence, like the spines of the hedgehog

or porcupine. In some species they are like harpoons, each being supplied with a double series of strong barbs.

Glimpses of Ocean Life 27

Glimpses of Ocean Life 27

Of all the above, the first which is quite a fancy theory, seems to

meet with greatest favour among certain naturalists. But as it is

rather puzzling to find a chemical solvent, which will act equally upon

sandstone, clay, chalk, wax, and wood, this hypothesis can only be

looked upon by practical men as ingenious, but incorrect. Even were it

proved that the animal really possessed the power of secreting an acid

sufficiently powerful, the question naturally arises, How can the shell

escape being affected in like manner with the much harder substance in

which it is situated?

 

The second theory, or the combined action of rasping and the secreted

solvent, is, for obvious reasons, equally objectionable.

 

The third theory, which endeavours to account for the wearing away of

the rock by means of silicious particles situated in the foot and other

parts of the animal, has been for some time proved to be erroneous,

from the fact, that the combined skill of some of our best anatomists

and microscopists has failed to discover the slightest presence of any

particles of silex in the Pholadidæ, although these are believed to

exist in other families of the boring acephala.

 

The fourth theory, that of ciliary currents as an accessory agent in

boring, is worthy of greater consideration, chiefly from the evidence

we possess of the immense power which the incessant action of currents

of water possess in wearing away hard substances.

 

We come now to what may be considered the most important of the

theories above enumerated, viz., the mechanical action of the valves of

the Pholas in rasping away the rock, &c. This hypothesis is one which

most naturally suggests itself to the mind of any impartial person, on

examining, for instance, the rasp-like exterior of the shell of _Pholas

crispata_.[12] But as I shall endeavour to show, although the shell

forms the principal, it does not by any means constitute the _sole_

agent in completing the perforating process.

 

[12] Specimens of this species, I may mention, have always formed the

subject of my experiments, and therefore are alone alluded to in the

following remarks.

 

Mr. Clark, a clever naturalist, considers with Mr. Hancock that the

powerfully armed ventral portion of the _mantle_ of the closed boring

acephala is fully adequate to rub down their habitations, and that the

theories of mechanical boring, solvents, and ciliary currents, are

so utterly worthless and incapable of producing the effects assigned

to them, as not to be worth dwelling upon for one moment. Mr. Clark,

therefore, comes to the conclusion that 'the foot is the true and

sole terebrating agent in the Pholas.' This 'fact' he considers to

be 'incontestably proved,' for the following reason, viz., because

he had discovered specimens of this bivalve with the foot entirely

obliterated,--which phenomenon, Mr. Clark states, is caused by

the animal having arrived at its full growth, at which period the

terebrating functions cease; and as 'nature never permanently retains

what is superfluous,' the foot is supposed gradually to wither away,

and finally disappear.

 

This, I suspect, is another 'fancy' theory. Although I have excavated

hundreds of Pholades, some of giant-like proportions, it has never

been my lot to witness the foot otherwise than in a healthy and fully

developed condition.

 

Another writer, having no opportunity of viewing the living animal,

does not consider it difficult to imagine the Pholas 'licking a hole'

with its foot, from the fact that he (Mr. Sowerby) managed to make 'a

sensible impression' upon a piece of kitchen hearthstone. 'I had,' he

says, 'not patience to carry the experiment any further, but as far

as it went, it left no doubt on my mind that, with the foot alone,

and without any silicious particles, without a chemical solvent, and

without using the rasping power of its shell, our little animal could

easily execute his self-pronounced sentence of solitary confinement for

life.'

 

Such an inconclusive statement as this would, I feel certain, never

have been penned, had its author been so fortunate as to have had

opportunity of watching a Pholas at work.

 

But, as Professor Owen truly observes, 'Direct observation of the

boring bivalves in the act of perforation has been rarely enjoyed, and

the instruments have consequently been guessed at, or judged of from

the structure of the animal.' Such, evidently, is the case with Mr.

Sowerby, and several other writers who treat on this subject.

 

Here we may call attention to the folly of naturalists endeavouring

to tag a pet theory upon all the boring acephala, to the exclusion of

every other. Such a system is defended upon the principle that, 'it

is much more philosophical to allow that animals, so nearly allied as

these in question, are more likely to effect a similar purpose by the

same means, than that several should be adopted. Surely this is more

consistent with the unity of the laws of nature, and that beautiful

simplicity which is everywhere prevalent in her works.'

 

How much more shrewd and philosophical are the opinions of such a man

as Professor Owen, who, when speaking of the mechanical action of the

valves of _P. crispata_, says, 'To deny this use of the Pholas shell,

because the shell of some other rock-boring bivalves is smooth, is

another sign of a narrow mind.' Again, this learned author forcibly

remarks, in direct opposition to the writer previously quoted, '_The

diversity of the organization of the boring molluscs plainly speaks

against any one single and uniform, boring agent at all_!'

 

The more I study this subject, the more does the truth of the

last-mentioned statement become apparent to my mind.

 

An examination of engravings of the shells, or even of the Pholas

itself, when lying loose in the tank, or quietly seated in the rock,

extending and retracting its siphons, fails to give one the slightest

idea of its extraordinary appearance when enlarging its dwelling. At

such times it seems to be a totally different animal, and to have

suddenly acquired a most marvellous degree of power, energy, and

perseverance, forming a striking contrast to its usual quiet, passive

habits.

 

In the first place, as I have elsewhere written, it retracts its tube

to, and even under, the level of its shell, just as a man, about to

urge onwards some heavy mass with his shoulders, would depress his

head to increase and concentrate his muscular power. Then follows an

expansion of the neck or upper part of the ventral border, from whence

the siphons protrude. This movement closes the posterior portions of

the valves below the hinge, and brings their serrated points together.

The next act on the part of the animal is to place its foot firmly

at the base of the hole; when leaning forward, it makes a sweeping

movement fully half round the cavity, pressing firmly-upon the umboes,

which nature has strengthened for the purpose by two curved teeth

fixed on the inside of the valves. At this stage it again reclines on

its breast, and tilting up the shell as much as possible, it makes

another motion round to its former position, leaning upon its back. By

these intricate movements, which the Pholas appears to accomplish by

a contraction almost painfully strong, it opens the rasping points of

the valves. These execute a very peculiar scooping movement at the base

of the cavity, and the animal having got so far, prepares itself for

further exertion by a short rest.

 

The specimen whose movements I have attempted to describe, lived in

my possession for a considerable time. It bored so completely through

the piece of rock in which it was embedded, that the whole of its foot

dropped through the aperture, and remained in this position for months,

the animal, in consequence, being unable to change its position even in

the slightest degree. Each movement of this specimen, both before and

while the hole at the base of the cavity was gradually being enlarged,

was watched, and every striking and interesting feature that occurred

noted down at the moment. Various queries were put and answered, as

far as possible, by direct ocular demonstration of the labours of the

animal in the vase before me.

 

I consider myself to have been singularly fortunate in being able

to view the actions of the creature from beneath, in consequence of

the hole being bored through the rock. This circumstance allowed me

distinctly to see what was going on at the base of the orifice.

 

My early observations have fortunately been confirmed in other captive

Pholades, which at various periods have been domesticated in my tanks.

 

I am convinced, then, that the shell forms the _principal_ agent in

boring the animal's dwelling, without either acid or flinty particles.

The late lamented Professor Forbes held that if this were the case,

the rasping points on the surface of the valves would soon be worn

down,--an appearance which, he says, is never seen. With all respect

for such an eminent name, I must state that he was in error. Not only

are the edges at certain times worn, but the rough surface is worn

nearly smooth, appearing in certain parts of a white colour, instead of

a light drab, as usual.

 

But the reader may ask, if certain parts of the valves are occasionally

worn smooth, and the animal works so vigorously, how is it that they

are never rasped through? This is a very natural question, and one that

I put to myself repeatedly.

 

I have made frequent and careful observations while the animal was

actually at work, in order to satisfy myself upon this point, and have

always perceived that the particles of softened rock fell from, and on

each side of, the large and well-developed _ligament_ that binds the

hinge, and extends to the lowest points of the valves. Moreover, this

leathery substance always seemed scraped on the surface. I cannot,

therefore, but believe that the ligament aids very materially in

rubbing off the rock, or at all events, in graduating the pressure of

the valves during the process, and that this curious organ, instead

of being worn away, may, like the callosity upon a workman's hand,

increase in toughness the more labour it is called upon to perform.[13]

 

[13] Mr. Clark says, 'M. Deshayes, in his comment on Pholas, in the

last edition of Lanarck, mentions the hinge as scarcely existing, and

not being _a veritable ligament_.' How different from the fact; and

I will observe, that '_if there is a genus better provided than any

other of the bivalves with ligamental appendages, it is Pholas.... The

Pholas is iron-bound as to ligament_, which in it is far more powerful

in securing the valves, than is the shell of any other group of the

acephala, of similar fragility and tenuity!'

 

The reason why so few specimens of the Pholades exhibit a worn shell

may be thus explained: As the animal only bores the rock in sufficient

degree to admit of its increased bulk of body, it only requires to bore

occasionally, and there may be often an interval of many months, during

which time nature may have renewed the serrated edge and rough surface

of the valves, and thus enabled the creature to renew its wondrous

operations.

 

We now come to a consideration of the foot, which, as many writers

aver, forms the 'sole terebrating agent.'

 

Although this sweeping statement is incorrect, I will freely admit that

the foot constitutes an agent second only in importance to the shell of

the animal. A casual examination of any Pholas perforation will show

that the foot could not have been the only instrument by which the

cavity was formed, from the peculiar rings that line the lower portion

of its interior. These rough appearances, I feel convinced, could be

formed by no other means than the rotatory motion of the shelly valves.

 

The valves, however, could not rotate and press against the surface of

the rock, were it not for the aid which the foot affords to the animal,

by its being placed firmly at the base of the hole, and thus made to

act as a powerful fulcrum.

 

This supposition fully accounts for the lowest extremity of the rocky

chamber being always smooth, and hollowed out into a cup-like form by

the action of the fleshy foot above alluded to.

 

The foot for a long time was a complete puzzle to me: I was unable to

satisfy my mind as to how it acquired its seeming extraordinary power.

The phenomenon was fully explained when I became aware of the presence

of that mysterious organ the hyaline stylet, situated _in the centre of

the foot_. The use of this springy muscle, which is, as we have shown

in the previous chapter, by naturalists erroneously considered to be

the gizzard of the animal, is, I believe, _solely to assist the Pholas in its boring operations_.