Does the proud beauty who glories in the possession of a pearl condescend to imagine that she flaunts on her bosom just so many tombs containing the dust of the germs of a parasite? Does she not rather love to think of the gems as emblems of almost celestial purity, and to dwell on the fable of the Persians rather than the audacious modern fact?
Addison has set the fable in imperishable gold: A drop of water fell out of a cloud into the sea, and finding herself lost in such immensity of fluid matter, broke out into the following reflection: “Alas! What an inconsiderable creature am I in this prodigious ocean of waters; my existence is of no concern to the universe; I am reduced to a kind of nothing, and am less than the least of the works of God.” It so happened that an oyster which lay in the neighbourhood chanced to gape and swallow it up in the midst of this its humble soliloquy. The drop, says the fable, lay a great while hardening in the shell, until by degrees it was ripened into a pearl, which, falling into the hands of a diver after a long series of adventures, is at present that famous pearl which is affixed on the top of the Persian diadem.
Though one may count his pearls by the score, the hoard may be valueless. Upon such examples entertaining, if not valuable, experiments may be made without affectation or giving hostages to fortune. In all the little deformed specimens thus dissected the core has been found to consist of a foreign substance, generally what seemed under a microscope of limited power a speck of dirt. The heart of one was a blob of mud, which gave off a most baleful vapour. This was the result of the house-cleaning of a common, edible rock oyster, and the pearl, dirty green and lustreless, merely a thin casket, for the noisome mud had not solidified. The care with which the impurity had been rendered innocuous demonstrated the correct ideas of the oyster on sanitation. No doubt the germ of the special form of tape-worm which troubles oysters, irritates to pearl-making, and passes through other transformations in other hosts, and completes its cycle in the body of a shark, would be too minute for inexpert detection. The fact that molluscs do intern foreign and obnoxious substances is testimony to their decency and love of cleanliness, and so may the pearl be still accepted as the embodiment of purity. Though all its little soul be dirt, the pearl is pure, and but for the dirt or the germ of a filthy ailment it would not be pearl.
So many molluscs produce pearls that it would be absurd for the great oyster family to set up exclusive rights. They do not, for your oyster is ever humble even when tenanted with a rivalless pearl. On the coast of North Queensland, within the Great Barrier Reef, pinnas of at least two species are among the producing agents, which, covering a wide range, seem to meet in two distinct genera, far apart in appearance and habit. There is the frail, flat, translucent “window-shell” (Placuna), the valves of which fit so closely that the poor little inhabitant is squeezed to a wafer, a film, a fragment of muscle. Yet in some localities nearly every individual has a pearl, pretty in tint, but too minute to be of value. An allied species is common on the coast of China, where the pearls are collected for export to India, to be reduced to lime by calcination for the use of luxurious betel-nut chewers. These almost microscopic pearls are also burnt in the mouths of the dead who have been influential and wealthy.
Coal-black pearls occur in one of the pinnas, the interior of which is sooty, shot with iridescent purple, and since the pearl, whether produced by oyster, mussel, pinna, or window-shell, is generally more brilliant than the containing shell, that of the black pinna, with the high lights of its environment concentrated, may be a gem of surpassing novelty and beauty. But the habitual product of this pinna is small, dull, mud-tinted or brown, and of no value whatever. Another of the genera grows “seed” of excellent lustre, corresponding with the azure brightness of the shell.
The chief source of orient pearls on the coast of North Queensland is the gold-lip mother-of-pearl PINCTADA MAXIMA, while the black lip PINCTADA MARGARITIFERA occasionally yields fine and flawless specimens of a silvery lustre. One which is still lovingly remembered was of pale blue and wonderfully lighted. The commonest of the giant clams TRIDACNA GIGAS sometimes betrays evidence of past internal trouble by the presence of a concretion of porcelain whiteness and of porcellaneous texture, but such are not to be described as pearls and to be prized as rarities only.
That some huge molluscs produced pearls before man, with his faculty for admiration, came on the scene is proved by their existence as fossils in chalk. Hemispherical specimens have been found on the inner surface of a shell which has no living representative—viz., the Inoceramus (some of which attained a length of two feet)—and spherical ones of the same prismatical structure occur detached in the chalk. It were curious to let the imagination run over the fact that the hosts of these uncommended gems died ages before the advent of man. The best of modern prizes may be puny in comparison with those which caused distress to the giant molluscs of the age when the Ichthyosaurus, Plesiosaurus, and Pterodactylus were the aristocrats of the animal world. Such gems have gone for ever, and even during this age of insatiable and adventurous search man does not secure a tithe of the ocean's tribute, for, since a pearl is a source of discomfort to its host, the unceasing effort of the animal is towards expulsion. The greatest and possibly the most magnificent are cast out as rubbish on the ocean floor, or are retained within the valves when the animal dies of old age.
So-called pearls have been found in elephants' tusks and semi-adherent to the bones of fish, and concretions—hard, smooth, and round, and of the flat hue of skimmed milk—in coconuts and in the cavities of bamboos; but in the production of the real gem neither oyster nor mussel nor pinna need fear the rivalry of anything on the earth's surface. The pearl belongs to the sea.
Completely spherical pearls can be formed only loose in the mantle or soft parts of the body of the animal; but intrusions incite a deposit of nacre in the form of a projection on the interior, which projection, often a mere bubble, but sometimes semi-detached, may take the shape and dimensions of the foreign substance. Or an inoffensive mollusc may be goaded by the piercing of its shell from the exterior to create that for which men venture into the depths of the sea. If a pearl-secreting oyster be inherently robust, its defence against assault from without may consist of the strengthening of the interior at the point of attack by deposits of nacre. Thus, a slight protuberance arises which becomes the base of a blister or button or the starting-point of a pear-shaped gem. Many a lovely gem is, therefore, nothing more than the imperishable record of aggression on the part of a flabby sponge on a resourceful oyster. Occasionally valuable pearls are found within huge blisters. Such pearls originate, no doubt, in the ordinary way, but, becoming an intolerable nuisance on account of increasing size, are confined in nacre.
One of the accompanying illustrations shows the fate which befell an infant chiton upon intrusion on a small black-lip oyster, and coincidentally the origin of a blister. The chiton family being notorious for stolidity, the infant could not have realised the risks of its trespass until the strait-jacket made its retirement impossible. The nacre has reproduced the details of the chiton's exterior with the fidelity of a casting, and further reveals the fact that it was alive when entombed, for its struggles to escape are solidified.