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distinctness of the side-swimmers. The
effect of an apparition of plaice in a sandy
pool, is comparable to the surprise given by
wrens, or tom-tits, when they flit across the
path of a lonely wood. The play of colours
heightens the effect. Just such a coloration
ie needed by them to enable them to escape
the observation of their enemies, and make
it difficult to distinguish them from the sand
plants, or stones, near them. The young side-
swimmers are symmetrical, while the old
have their necks twisted until both eyes are
upou the dark, or uppermost side. According
to the simple physiology of the Scottish
fishermen, side-swimmers wring their necks
by their long and anxious lookings upward
for their food and their enemies.

An incident, which surpasses in interest
all the others in the olive zone, is of constant
occurrence, the squirtings of pholades. As
the tide recedes, sand and water are seen in
all directions spurting up a foot high into the
air. When a novice commences a scientific
investigation into the cause of these mysterious
spurtings by putting his finger into the
hole, a fierce squirt of sand and sea-water,
three or four feet high, bespatters his face,
and blinds his eyes.

No question in conchyliology has been more
keenly discussed for centuries, than the puzzle
how the pholades perforate the rocks? Over-
impressed with a just admiration of the
marvellous secretions of the mantle of the
mollusks, learned conchyliologers maintained it
was by means of a dissolving acid unknown
to chemistry. In eighteen hundred and fifty-
one, an amateur exhibited half a score of
pholades in the Pavilion, Brighton, before
the Provincial Medical Association, perforating
lumps of chalk by mechanical operations.
Every witness could see the rotations
of the valves as rasps, and the squirtings
of the branchial siphon as a syringe. Dr.
Mantell as the mouth-piece of the numerous
spectators, exclaimed, "Mechanically after
all!"

The old English students of shells called the
hole-lurker, or pholas, the stone-piercer, but
there are many conchylions which bore stones,
and the pholas perforates chalk, sand-stone,
gneiss, and wood. Restrict the genus of the
Hole-hides (the word is the exact translation
of the Greek pholadidæ, and in using the
word hide, to signify the one who hides, I
follow the excellent usage of the children in
the game of hide-and-seek), restrict the
genus of the hole-hides as we may, by the
exclusion of gastrochenes, myæ, solens,
fistulanes, and cloissonaires, there will still remain
considerable variety in the ancient genus
pholas. There will remain pholades, whose
valves remind one of the spiny leaves of the
acanthus, with which the ancient Greeks
adorned the capitals of their Corinthian columns,
and copies of which were embroidered
upon their richest robes. The monster
pholades from the Molucca Islands will remain,
whose shells alone are known, and whose
animals and habits are entirely unknown.
But the most singular of all are the spherical
pholades, which, in size and roundness, are
bigger than cricket-balls.

It was on the pholas dactylus (the finger-
like hole-hide, which is most common upon
our coasts) that the physiology of the pholades
was discovered. Professor Flourens taught it
to his class at the Jardin des Plantes, in
eighteen hundred and fifty-three; and an
account of it appeared in the Journal de la
Conchyliologie in the same year. M. Emile
Blanchard describes it minutely, and
illustrates it with splendid plates, in a recent
livraison of his vast and admirable work
L'Organization du Règne Animal.

The pholas is a living combination of three
instruments: he is a hydraulic apparatus, a
rasp, and a syringe. Working in a narrow
hole, under water, the pressure of the water,
which is proportional to the depth and
narrowness of the hole, gives him, at will, the
command of a powerful hydraulic force. His
two siphons are united into one tube, and by
sucking in water with the one, and blowing
out air with the other, he establishes currents
in the water, which float food into the mouth,
or among the tentacles of the prisoner in his
hole. To the hole-hide, his hydraulic apparatus
is, what his spinning machinery is to
the spider; and the currents serve the
mollusk as the web serves the arachnida in the
capture of his food.

The pholas is a rasp. His valves look
like two bits broken off from the end of a
rasp. When examined under the microscope,
the shell is seen to be a collection of
crystallised chalk, covered by a thin organic
membrane or skin. The shell is thick, and
the teeth on it are strong and sharp at the
lower extremity. Inside the shell are two
little levers. The muscular system of the
pholas explains how the double rasp is
brought to bear upon the sides of the hole.
The organ which the anatomists have called
a foot is really a motor or moving power.
Issuing from the wide opening at the lower
end of the shell, the motor-foot presses
against the side of the hole, the muscles
which command the levers are successively
contracted and distended, and the valves
rasp by demi-rotations. The machinery
consists of a motor, ropes, levers, and rasps.
M. Blanchard's beautiful plates of the pholas
dactylus illustrate all this strikingly. But
several difficulties remain to be explained.
How does the pholas get rid of the raspings?
and how did he first get into the rock? The
answer isthe pholade is a syringe. There
is no doubt about it among the persons who
have been blinded by his squirtings. The
organ called a foot, the motor of the rotatory
rasp, is the piston of the syringe. Resembling
in shape a rose-leaf, the piston is capable
of very sudden and very considerable
expansion. When the raspings accumulate,

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