button to a round or nearly round pearl, but should the pearl be taken
from the fish before the metamorphosis is completed, a depression, or
pit, would mar its contour. When borers intrude through the shell, the
presentation is at once covered with nacre, and successive deposits
are built up around it resulting in the nacreous wart known as a
baroque. The rounding action of the mollusk is clearly shown in these
excrescences, as the borer is not simply covered and levelled with
the shell, but the slight elevation above the level of the lining
receives a continuity of concentric deposits which finally raise it
very considerably above the surface and separate it in construction
from the lining to which it is attached. The shell herewith reproduced
illustrates the result. Borers pierced it at the thick part of the
hinge, and burrowing down, entered the interior at the point where
the baroque is shown. In rare instances, pearls attached to the shell
do escape the concentric deposition, for they have been found buried
under even layers of nacre, when the mother-of-pearl was cut up in the
process of manufacture.
[Illustration: VENEZUELAN PEARL-SHELL, SHOWING BAROQUE]
From the appearance of the striæ when they are divided lengthwise,
pear-shaped pearls appear to have been spherical at one time. During a
stage in the growth, the forming layer has curved away from the centre
at one section of the sphere to a point. Succeeding layers, following
the innovation, are deposited around the extension until it becomes
sufficiently elongated to give the pearl the obovoid form.
Many pearls are shaped like a capsule. The ends of most are rounded
up to a full dome; some have somewhat flatter ends; many are long and
cylindrical like an ordinary capsule; others are short and appear
in shape like two high button pearls joined at their bases; while
some resemble a cartridge, one end being almost flat and the other a
somewhat pointed dome. It is noticeable that such pearls have a chalky
line around the middle, and sometimes there is a lustrous band between
two. These chalky lines are found, on peeling such a pearl, to extend
through all the interior layers. Similarly, a high button joined at its
entire circumference to the shell, if the junction is abrupt, has an
intersecting chalky line, marking the juncture of the two, between the
luster of the pearl and the shell lining. If the base of the pearl and
the shell form a curve there is no chalky line of demarcation.
This suggests that whenever the animal is unable to envelop the thing
upon which the mantle deposits its secretions completely or is not in
touch with every part of it, there is at the extremity of its action,
an unnacreous deposit, corresponding to the deposit of conchiolin or
calcite, at the extreme edge of the shell which precedes the nacreous
layers following within and slightly back of it. As the luster of the
pearl arises from the transparency of the calcium carbonate modified
by the undulating lines formed by the edges of the wave-plates, it may
be that the lapping action of the mantle is necessary for the regular
formation and crystallization of these plates, and that at points
beyond the reach of this action, the depositions of the mantle are
therefore not pearly.
Much is necessarily conjectural as to the modus operandi by which the
shell and the pearl are formed but the invariable tendency toward
sphericity suggests that the nucleus of a pearl, when free within the
mollusk's mantle, is not only enveloped in its exudations, but is
either kept constantly moving with a rolling motion or lapped on all
sides by the membrane which exudes upon it the nacreous material.
The instances cited of the short capsule shaped pearl and the high
button joined to the shell, which seem to escape the nacreous deposit
at the basis of the domes, favor the lapping or licking method of
depositing the nacreous solution and this action by the mollusk would
result in a constant rolling or turning motion imparted to the object
if it were free within the creature's body. The licking and rolling
action of the mollusk, modified by the conceivable influences of
position in the shell, would account for the spherical form with all
the various modifications in which the pearl is found.
To account for the variation of quality which undoubtedly exists in the
successive skins of some pearls, and the imperfections in the nacre of
the same skin, the theory has been advanced that the secretions for the
lining, the shell proper, and the epidermis, are exuded by different
parts of the mantle; the pearl traverses during growth these different
bands and its skins are modified by the secretions, as they come within
the various zones of influence. But there are several facts which seem
to oppose the theory.
In the first place all these parts of the mantle which supply the
material for the epidermis, the middle shell, and the lining, are
enclosed within the shell and in touch with the lining yet each
receives the exudations of that part of the mantle which supplies the
material suitable for it, the mantle invariably pushing the coarser
excretions outwardly to the shell's exterior. Again, whatever the
quality of the skin of the pearl may be, it is never of conchiolin
like the outer epidermis and though sometimes similar to the plates,
of which the conchiolin is the exposed fringe, it always contains
sufficient nacre to render the surface smooth. The fact that the skins
of a pearl do sometimes correspond with the different parts of the
shell, and that the same skin on the surface is occasionally partly
nacreous and unnacreous, in connection with the variation of quality
which exists in the internal composition of the skin, favors an idea
that the mixed and variable quantity of nacre in the skins may be
caused by the abnormal position of the mantle wrapped about the growing
pearl which would thereby come more or less under the influence of the
calcite and conchiolin zones distorted from their normal extension and
action.
It has also been suggested that the oyster deposits the nacreous
layer in a fluid state and then rests until the deposit hardens, when
the process is repeated. To a certain extent this may be true though
apparently it could not be a yearly process as pearls found in the
small varieties of the avicula which mature in four to six years and
die out in seven years, often contain a greater number of layers than
the years of the mollusk's life, and no pearl is ever found with a soft
exterior, though it seems possible that pearls with a dead white chalky
exterior are taken from the oyster at a period when the crystallization
of the outer skin has not been perfected, or that they have escaped
some action, chemical or of the animal, necessary for the formation
of the lustrous waves of nacre. Mr. Ludwig Stross, who has had much
experience at the pearl fisheries, says that he has frequently found
pearls of fair size in shells of the Lingah type which could not be
over twelve to fifteen months old. Some of these pearls weighed fully
three grains. As there are many apparent skins in a pearl of that
size, the divisions could not mark either years, seasons, or breeding
periods. In some experiments made by Mr. Stross, he found that borings
made to the interior of a living mollusk's shell were closed by a film
of hard nacre in two days.
The known facts about a pearl are these. It is composed of about
ninety-two per cent. carbonate of lime, about six per cent. organic
matter and a little over two per cent. water in combination almost
identical with the lining of the shell in which it grows and similar
to the mineral aragonite. In construction it is usually a series
of layers, which can sometimes be peeled off entirely, each one
successively enveloping its predecessors apparently as an independent
structure though itself composed of a number of thin lapping waves.
Upon cutting through these layers the divisions appear as a series
of rings and the intervals, though composed of many thin waves,
appear compact. It grows spherically or with such modifications as
the exigencies of position in the shell would reasonably account for.
These facts seem to justify the hypothesis that a foreign substance
upon entering the shell of a pearl oyster is at once enveloped or
washed in the creature's exudations; that the organic matter of the
secretions forms a filmy envelope in which the mineral contained in
them is precipitated or crystallizes in wave-like layers of crystals
of great tenuity, and that as these layers harden the process is
repeated, and that during the process the creature either revolves
the object, or about it, as it is free, or fastened to the shell. It
is also possible that changes in the organic matter interwoven with
the calcium carbonate may produce some chemical action resulting in
the crystallization of the lime, and the crystallization in turn be
provocative of another deposit, each process in turn being almost
simultaneous and that the process is continued until a paucity of
mineral in the exudations induces a rest for recuperation, after which
the process is repeated, the result being a succession of composite
skins as we find them. Whatever the cause, it is evident in all parts
of the shell and in the pearl that continuity of construction is
periodically arrested to be resumed upon exactly the same plan, except
that the material used in the succeeding layer of the pearl may be
formed occasionally like another of the shell sections though usually
it is like the preceding one.
Marked differences in the same skin occur more frequently in the pearl
formations of univalves. The skins of the abalone pearl especially, are
frequently nacreous in part only.
Pearl oysters are found in immense numbers on banks having a calcareous
foundation. They are extraordinarily prolific, the spat of one oyster
being estimated at upwards of several hundred thousands to millions,
so that were it not for the natural enemies of their young and the
liability of being swept away and scattered by storms before they have
anchored, the banks would be over-crowded with the myriads produced.
Some idea of the numbers may be gained from the fact that during the
fishing season the Ceylon divers raise about one million each day.
The oysters are seldom found in water with a temperature below 75
degrees and they seem to thrive best in warm sheltered bays and inlets,
especially when the banks are situated far from the equator. They
attach themselves to the beds by a bunch of tough threads which pass
out through an aperture in the shells, near the hinge, and fasten on
the rocks and stones; consequently the oysters do not lie flat, as
might be supposed, but maintain an upright position, hinge down, lip
end up, and the shell slightly open for the passage of the food-laden
water, as the fresh-water mussels do. These threads are called the
beard or byssus, and are composed of material similar to the epidermis
of the shell.
The abalone, which is a univalve, holds on to the rocks by the foot, a
flat muscular appendage used for locomotion and also as an anchor on
the principle of the leather toy known to boys as a sucker.
Although pearls of value are found only in shells containing
mother-of-pearl, a small proportion only of the mother-of-pearl shells
contains pearls, and many varieties in which pearls are found do
not yield enough nacre to make the shells valuable. The size of the
meleagrina in some seas is remarkable. That at page 127, photographed
from a Tuamotu shell, measures 8-7/8 inches by 6-7/8 inches and weighs
twenty-eight ounces troy.
It is of the black-edge variety, contains a large quantity of fine
quality mother-of-pearl, and has a beautiful small pearl attached to
the lining near the center of the shell. Though large, it is not full
grown. It is probably twelve to fourteen years old and would continue
to lay on mother-of-pearl and so grow thicker and heavier until sixteen
to eighteen years of age, when the oyster would reach maturity. The
Australian white shell at page 129 is a young shell—that is, it has not
attained the full thickness and weight of a mature shell. The shells at
pages 131 and 161 are from the coast of Venezuela; they measure 2-1/4
by 2-1/4 inches and weigh seven pennyweights each.
The common form of the pearl-bearing fresh-water mussel unio
(nigger-head) is illustrated at page 146. This shell measures 3-3/4 by
2-3/4 inches and weighs 3-1/2 ounces. It is from the Middle West of
the United States. In construction it resembles the meleagrina, the
epidermis being dark, though not as rough as that of the oyster, and
the lining white, showing slight iridescence around the lip-edge and
to a greater degree on the adductor muscle scar. The mother-of-pearl
under the epidermis at the thick or hinge end is quite iridescent, and
the lines which make the color play are plainly discernible under the
loup.
The largest and finest pearls, also the greatest number, are found
usually in distorted shells. This has given rise to the idea that they
are a symptom of disease in the fish, but having in mind the functions
of the three zones of the creature's mantle by which they supply
separately material for the epidermis, middle shell and lining, one
may conceive that if, by some extraordinary cause, the secretions of
one of these is largely withdrawn from the natural channel, the losing
part of the shell would warp the normal growth of the others to its own
dwarfage.
When the nacre grows to a pearl, contrary to the intent of nature,
instead of a lining for the shell endeavoring to keep pace with the
growing oyster, the full-growing exterior is distorted in accommodating
itself to the undersized lining. In view of the fact that an oyster
sometimes contains a large number of pearls (one shell in New Caledonia
contained 256) the diversion of nacre sufficient to cover them, or
to produce one large pearl, might reasonably be expected to result
in a considerable distortion of the shell. It may also be that the
displacement of the mantle, caused by the wrapping of itself about the
growing pearl, interferes with the even deposit of shell material about
the edges of the shell and so distorts it.
Because deformed shells are more fruitful of pearls some have advocated
the practice of throwing perfectly-formed shells back into the sea
unopened, but, inasmuch as the mother-of-pearl of the shells often
exceeds in value the pearls found in them, this is not likely to
happen. Few fisheries could be made to pay if they were fished for the
pearls alone. In many of them the shells yield 90 per cent. of the
total value and are in fact the sole incentive for the investment of
the necessary capital.
Luckily for the world's supply of pearls, however, the disturbers of
the mollusk which cause these gems by their intrusions appear to be
more abundant in waters where the shell is valueless, the banks about
Ceylon especially being infested with the cestodes which are commonly
the nuclei of Indian pearls. It is interesting also to learn that Mr.
James Hornell (inspector of the pearl banks) finds these worms in
another stage in the file-fish, which frequents the banks to prey upon
the oysters, and confidently expects to find them in the adult stage in
the shark, which in turn devours the file-fish.
It is the opinion of Jameson of London and others, that the parasite
which causes the formation of pearls in the mussels of Europe is
frequently the larva of distomum somaterœ, from the eider-duck and
scoter, and that the larva first inhabits Tapes, or the cockle, before
getting into the mussel.
Generally the nuclei appear to be the bodies or eggs of minute
parasites—distoma, filaria, bucephalus, etc., and they vary in
different localities according to the animal life of the neighborhood.
In the still parts of the river Elster, where water-mites (Limnochares
anodontœ) were abundant, Kuchenmeister found that the mollusks
contained more pearls.
METHODS OF FISHING
The beds of the marine shell-fish from which pearls are taken lie
always under water. Unlike others which are sometimes left exposed by
the tides, to be gathered by man without difficulty, the pearl oyster
is never left uncovered by the sea. It is found usually on shoals some
distance from shore, sometimes but five to seven feet from the surface;
more frequently fifteen to forty feet deep, and often one hundred to
one hundred and twenty-five and even one hundred and fifty feet deep.
Everywhere, then, man's quest for pearls is confronted by the heaving,
restless waters of the sea, for the greater part of the year rough and
turbulent, frequently lashed to furious racing by tropic tempests but
through which he must in any case go to get them. In a few places where
the beds lie in shallow inlets and sheltered bays they can be dredged,
but almost universally the oysters are gathered by divers. During the
greater part of the year, when storms rage, diving is very dangerous
if not quite impossible; but when the song of the sea is hushed to low
crooning, and the gentle roll of the waves does no more than playfully
slap the boats in passing, then in the seas where men dive for pearls
they gather to the harvest of gems.
There are two ways of diving—naked, and with dress. The former is the
common method throughout the Orient and is practised to-day after the
same manner that it was in the days of the Pharaohs and the Cæsars,
for the primitive method survives with few variations wherever eastern
people control the fisheries.
In the fishing season one sees now in the Red Sea and the Persian Gulf
and about Ceylon, the same scenes as they were enacted there before
Rome was a city, or France a nation, or the Macedonians overran Egypt.
Naked divers, diving into fifteen to forty feet of water, use few aids.
They grease their bodies, put greased cotton in the ears and a forked
stick, or tortoise-shell clip, upon the nostrils to compress them, hang
a wide-mouthed wicker basket or net at the waist, and they are ready.
There are several methods of naked diving: head-first from a
spring-board attached to the side of the boat, as the Malabar coast
Hindus and some of the Egyptians do; swimming to the bottom, as
practised in the deep waters of the South Sea; and dropping to the
oyster bed with a stone. The latter is the most common way in Indian,
Egyptian, and Arabian waters, especially where the banks lie in forty
to fifty feet of water.
Standing on the spring-board a few seconds to fill his lungs, the
head-first diver suddenly plunges overboard and passes smoothly and
rapidly through the water straight to the shoal below. Gathering
quickly as many oysters as possible while his breath lasts, he
places them in the net at his waist, attaches them to a convenient
rope hanging from the boat's side and shoots to the surface. There
he recuperates by lazily floating about if the water is shallow, if
deeper, by climbing back into the boat for his next plunge. If diving
in pairs, one rests while his partner dives.
Expert divers who dive singly have an attendant, a manduck, who
attends to the lines and looks out for his interests generally. The
manduck drops a line with the oyster basket overboard and attaches to
it another weighted with a forty to fifty pound stone. These are so
fastened that they can be quickly released. The diver then drops into
the water feet first and placing his foot in a loop in the line over
the stone puts the basket on it, and releasing the lines, sinks to the
bottom. Disengaging himself, he proceeds to fill his basket while the
attendant pulls up the stone and adjusts it for the next descent. When
ready to return he signals his attendant, and holding on to the line
with the basket is drawn to the surface, occasionally accelerating his
own return by climbing the rope hand over hand at the same time. He
rests in the water by the boat's side until ready to dive again, making
seven or eight descents before climbing into the boat for a longer rest
and sun-bath.
The divers of India, Arabia and the Red Sea are natives of the Madras
Presidency, descendants of Arab fishers at Jaffna in Ceylon, Arabs, and
Egyptian Negroes. They travel long distances to the fisheries and there
are many of them between the Red Sea and Ceylon. At the last fishing
in the Gulf of Manaar there were about forty-five hundred. Their dress
during the time of the fishing consists of a loin cloth only. They have
many hereditary and class superstitions, chief of which is their faith
in shark-charmers. While waiting for the fishing to begin they also
seek to get from the fates an inkling of the luck which will attend
them. One common method is by breaking a cocoanut on the diving stone;
the more clean and even the break, the better the luck.
The mortality among divers at the fisheries is not great in Asiatic
waters. Pneumonia is the greatest scourge, fatalities in diving being
few. It is necessary however to select robust men for depths beyond
forty feet; comparatively few can work without injurious effects below
that.
Some curious mixtures of ancient days and present times, of the
Pharaohs and infant industries, are seen. One may see a black slave
diver in the Red Sea hanging over the edge of his boat taking
observations through an old tin kerosene can with a bit of glass in one
end of it. This he sinks a little way in the water and gazes through
it below. Presently the can is discarded, over he goes and returns
shortly with a few shells; while near by a clumsy monster emerges and
a diver in dress climbs into his boat. This use of modern tin cans and
glass is adopted in seas where the shells are scattered and is common
to pearl-divers the world over.
The Moros have a method of fishing in very calm weather peculiar to
themselves. They drop a three-prong catcher attached to a rattan rope
upon the oyster bunches and so haul them up to the boat. This can only
be done when the sea is perfectly still, as even a ripple would render
a sight of the oysters impossible. Ordinarily they dive to any depth
down to twenty fathoms.
Many attempts have been made to introduce dress-diving among the
natives of the east but so far few have been successful. Results from
experiments have not compared favorably with naked diving and so,
with few exceptions, naked diving is still the rule in the east where
natives control the fishings.
But of all, the Polynesians, both male and female, adhere most closely
to the old way. Most of them will not even use a stone to assist the
descent, and they probably reach greater depths than the naked divers
of any other sea. Travellers report that, at a coral atoll in the
Southern Pacific owned by the French government and known as Hikuereu,
where the natives of Tahiti and other islands flock during the season
to fish for pearls, the boys and girls and women are almost as expert
as the men.
Whole families congregate here, remaining during the season housed in
huts framed of light cocoanut palms roofed with leaves. These they
bring with them, some coming several hundred miles. The shells are
mostly in sixty to seventy feet of water; some however are brought
from a depth of one hundred feet. It is reported that a boy, on an
exhibition dive, remained under water for two minutes and forty
seconds, going to a depth of a little over one hundred feet. He was
in sight all the time, the water being so transparent that he could
be seen on the bottom, leisurely selecting pieces of coral for the
officers of the ship above. These divers hang in the water by one hand
grasping the gunwale of the boat while they examine the bottom for
oysters through a glass which they hold below the surface in the other
hand.
When shells are sighted the glass is discarded, the lungs are filled
several times and the air expelled slowly. Upon reaching a certain fit
condition a long breath is taken until the lungs are inflated to their
utmost capacity; the diver then suddenly lets go, sinks a few feet
below the surface, turns quickly and head-first swims rapidly to the
bottom.
Arriving there, he pulls himself along by grasping the coral branches
and breaking the shells loose from their anchorage with his right
hand, which is protected by a cloth wrapping, and stows them away
in a cocoanut fibre basket slung over the shoulder. This done, he
straightens himself and shoots to the surface with astonishing
rapidity, seeming to leap up from the water as he arrives with almost
sufficient impetus to carry him into the waiting canoe. In a few
minutes he is ready to dive again. In some localities where divers were
employed the women were preferred, not because they could do better
work always, but one could depend on them more safely. This was true of
the divers in Torres Straits between Queensland and New Guinea.