Terebella figulus.
(THE POTTER.)
'Whether progressing on the solid surface, or moving through the
water, or tunneling the sand, advancing or retreating in its tube,
the Annelid performs muscular feats distinguished at once for their
complexity and harmony. In grace of form the little worm excels the
serpent. In regularity of march, the thousand-footed Nereid outrivals
the Centipede. The leaf-armed Phyllodoce swims with greater beauty of
mechanism than the fish; and the vulgar earthworm shames the mole in
the exactitude and skill of its subterranean operations. Why, then,
should the "humble worm" have remained so long without a historian? Is
the care, the wisdom, the love, the paternal solicitude of the Almighty
not legible in the surpassing organism, the ingenious architectures,
the individual and social habits, the adaptation of structure to the
physical conditions of existence of these "degraded beings?" Do not
their habitations display His care, their instincts His wisdom, their
_merriment_ His love, their vast specific diversities His solicitous
and inscrutable Providence.'--DR. WILLIAMS.
[Illustration:
1 THE POTTER (_Terebella figulus_)
2 _Terebella littoralis_]
XII.
Having visited the sea-side a few weeks since, along with some
'aquarian naturalists,' among other objects we managed to capture
a very fine _Terebella Figulus_, commonly called the 'Potter.' The
specimen measured about five inches in length, and was nearly as
thick as a common drawing pencil. I could discover no signs whatever
of any tube in the rocky basin in which the Annelid was situated, a
circumstance that struck me as being rather curious.
On returning home, my much-valued prize was placed in a tumbler of
large dimensions, the base of which I strewed with newly-pounded shells
and gravel. By the following morning all the fine or powdered portion
of the 'Silver Willies' had been collected and used in the construction
of a tube, sufficient in length to cover half the contracted body of
the industrious little mason. After labouring for a fortnight, the tube
was gradually extended across the bottom of the vase in a cylindrical
form, but eventually it assumed a semi-circular shape, being built
upon the glass, and elevated by gentle stages up each side of the
vessel until the level of the water was reached, when all further
labours ceased for a time.
After the lapse of a few days the building operation was resumed,
and the tube carried fully an inch further, at right angles to its
former position. The opposite end of the structure was next extended
at an angle of 45° from the base of the vase, to a height of about two
inches. Then commenced a very curious phenomenon. Some of the tentacles
were incessantly elevated and extended across the vessel, until they
touched the opposite end of the tube, with what object I could not then
conceive. The design, however, was afterwards made evident: in less
than two days the animal succeeded _in making both ends of its tube
meet together, so as to form a continuous circle_. I happened to be
watching the mason, when the last stroke of his labial trowel was given
to the building, and shall never forget the cautious way in which the
animal crept for the first time over the newly-completed portion of the
work, and the seeming delight with which it continued to glide, hour
after hour, over the entire circuit of its dwelling-place.
Sometimes its body would be long drawn out, until the tips of the
tentacula would reach, and apparently tickle the extreme point of the
tail; then a race would commence, in character exactly resembling
that so often witnessed with the kitten, or the playful whelp, when
either of these animals foolishly imagine that the tip of their tail is
adorned with some coveted tit-bit.
The branchial organs of my specimen were very beautiful objects, being
formed of three blood-red spiral tufts, the effect of which were
heightened by their being placed in contact with the drab, coloured
cephalic[10] tentacles, which seemed to be almost innumerable. These
latter organs, although apparently so useless when seen closed, are in
reality of the greatest importance to the _Terebella_, for they not
only act as auxiliary organs of respiration, and aid most materially
in building its dwelling-place, but also constitute the real organs of
locomotion.
[10] Cephalic, belonging to the head.
'They consist,' says Dr. Williams, 'of hollow flattened, tubular
filaments furnished with strong muscular parietes. The band may be
rolled longitudinally into a cylindrical form, so as to enclose a
hollow cylindrical space, if the two edges of the band meet, or a
semi-cylindrical space if they only meet imperfectly. This inimitable
mechanism enables each filament to take up and firmly grasp _at any
point of its length_ a molecule of sand, or, if placed in a linear
series, a row of molecules. But so perfect is the disposition of the
muscular fibres at the extreme free end of each filament, that it is
gifted with the twofold power of acting on the sucking and muscular
principle.
'When the tentacle is about to seize an object, the extremity is
drawn in, in consequence of the sudden reflux of fluid in the hollow
interior. By this movement a cup-shaped cavity is formed, in which
the object is securely held by atmospheric pressure. This power is,
however, immediately aided by the contraction of the circular muscular
fibres. Such, then, are the marvellous instruments by which these
peaceful worms construct their habitation, and probably sweep their
vicinity for food.'
The foregoing beautifully and accurately describes the tentacular
cirri. The use of these organs in the formation of the tube in which
the Annelid dwells, I will now endeavour to make clear, from close
personal observation.
It is an extremely interesting sight to watch a Terebella extend its
tentacles in all directions in search of building materials, catching
up the surrounding molecules (sometimes visible along the whole length
of each filament), and then, by a strong muscular contraction, bringing
the collected atoms to the opening of the tube, around which, as is
generally supposed, they are then immediately attached by a secretion
which is exuded from the body of the animal. Such, however, is not the
case.
When the filaments bring their 'subscriptions,' the material thus
gathered, instead of being used at once for building purposes, _is,
in reality, first eaten by the animal, and, after undergoing a kind
of mastication, becomes coated with a salivary secretion, and is then
ejected in mouthfuls at the extremity of the tube_, which, by such
means, becomes gradually elongated. The shell work, when deposited as
above mentioned, is held in position, and prevented from falling over
the outside of the cavity, by the filaments which are made to hang
down in a most ingenious manner; the animal, at the same time, putting
itself in motion, allows the slimy surface of its body to press and
rub against the new addition to the tube, which is thus effectually
strengthened and soldered together.
The animal does not always wait until the opening of the tube is
reached, but gently disgorging while lying at its ease, it then pushes
forward by aid of its head and tentacles the mass of building material,
which soon becomes distributed and moulded to its proper shape.
If your specimen should happen to build a complete tube, its mode of
working cannot be well seen; but should it economize its labours, and
run its house up in a semi-circular form against the transparent side
of the vessel, as the animal I write of did, you will be enabled to see
distinctly every movement that goes on in the interior.
It seems somewhat singular that the Terebella should possess the power
of turning itself within its tube, so as to be able to extend its
habitation from either end at will. I have very often watched the
operation with emotions of pleasure, not unmixed with wonder.
Wishing to test the powers and intelligence of my specimen, I
dropped within its tube, which was curved in shape lengthways, some
particles of sand, and a pebble which nearly filled up the 'bore' of
the cylinder. The great annoyance occasioned by this intrusion to
the master of the house was painfully evident. For a whole day the
Terebella endeavoured to push out the objectionable matter by means of
its head and cephalic tentacula, but without success; for although the
mass frequently neared, it never touched or toppled over the mouth of
the aperture, and consequently fell to its original position at the
bottom of the tube as soon as the animal removed the pressure.
Apparently despairing of its efforts, though still oftener repeated,
being eventually prosperous, the poor Annelid literally 'turned tail,'
and very coolly proceeded to elongate the opposite end of its dwelling.
This operation did not last long; for in the course of a few hours, on
peering again into the vessel, I saw that the humble and insignificant
worm had mustered up courage to 'face the enemy' once more, and had,
in fact, apparently conceived a new idea, the wisdom of which was
soon made palpable; for slowly, but surely, most of the arenaceous
particles were eaten, and nothing being left but the pebble, it was
speedily and triumphantly ejected from the tube, and the sand soon
after employed for building purposes. The Terebella having completed
its laborious and well-executed task, seemed to be quite exhausted, and
lay to all appearance lifeless for the succeeding four and twenty hours.
When walking along the sandy beach, myriads of peculiar objects may be
seen swayed to and fro by the roll of the waves. Frequently, when the
tide has receded, these tubes remain sticking out of the sand to the
height of two or three inches, each terminating in a tuft, like the end
of a piece of cord that had been teazed out.
Within such a fragile habitation dwells the _Terebella littoralis_,
the most common species of the marine tubiculous Annelids. I have very
often tried, by aid of my fingers only, or a strong spade, to capture
one of these creatures, but have never been successful, even in a
solitary instance. Yet several authors tell their readers the task is
perfectly easy. Mr. Lewes, for instance, made me feel ashamed of my
previous manipulative efforts when I read his vivid description of a
Terebella hunt, and caused me lately to journey a distance of six miles
to try my hand again, with no better result than hitherto.
I have lately seen a specimen of _T. littoralis_ which a friend of
mine was so fortunate as to capture. The tube of the animal, instead
of being in its usual position, was situated in a pool, and offered a
most rare prize to its discoverer, it being the only one he had ever
caught. The tube, being of great length, was cut down to about six
inches and transferred to a shallow glass tank, in which was introduced
some pounded shells. The beautiful Annelid soon made itself at home,
and commenced to repair the damage done to its habitation by collecting
these particles, by means of its tentacula, which were thrown out to an
extraordinary distance in all directions.
The result of the animal's labours was soon apparent by a most amusing
white patch being added to each end of its dark tube.
As soon as this operation was completed _mon ami_ carefully tore up
the patched garment, and ejected the defenceless Terebella into the
vessel, wherein was placed a piece of glass tube that measured an
inch in length. Strange to state, the animal instantly crept into
this object, and soon made itself quite at home and comfortable. When
the building materials were placed near, they were collected and
_attached to each end of the glass cylinder_ by the little architect,
who doubtless was the first of its 'family' who could boast of such a
noble mansion,--which ultimately assumed a very remarkable aspect from
the variously-coloured 'mortar' that was employed in its construction.
Above and below the transparent centre came patches of red, white, and
blue material, composed respectively of broken tile, pounded shells,
and coloured glass. Such a 'concourse of atoms' was surely never before
combined, either 'fortuitously' or otherwise, in the construction of so
common an object as the tube of an Annelid.
The branchiæ of the above mentioned specimen presented a most exquisite
appearance, resembling the perfect skeleton of a leaf, supposing that
to be dyed a brilliant crimson colour, and made to exhibit incessant
life-like motion even in its most delicate and minute ramifications.