fishing-grounds are in water about 40 ft. deep, and the season lasts for four months. An ordinary fishing-party expects to obtain about three tons of shells per day, and it is estimated that one shell in a thousand contains a pearl. The pearls are shipped in barrels from San Francisco and Panama Some pearls of rare beauty have been obtained from the Bay of Mulege, near Los Coyetes, in the gulf of California; and in 1882 a pearl of 75 carats, the largest on record from this district, was found near La Paz in California The coast of Guayaquil also yields pearls Columbus found that pearl-fishing was carried on in his time in the Gulf of Mexico, and pearls are still obtained from the Caribbean Sea. In the West Indies the best pearls are obtained from St Thomas and from the Island of Margarita, off the coast of Venezuela. From Margarita Philip II. of Spain is said to have obtained in 1579 a famous pearl of 250 carats.
Of late years good pearls have been found in Shark’s Bay, on the coast of West Australia, especially in an inlet termed Useless Harbour. Mother-of-pearl shells are also fished at many other points along the western coast, between the 15th and 25th parallels of south latitude. An important pearl-fishery is also established in Torres Strait and on the coast of Queensland. The shells occur in water from four to six fathoms deep, and the divers are generally Malays and Papuans, though sometimes native Australians. On the western coast of Australia the pearl-shells are obtained by dredging rather than by diving. Pearl-shells have also been found at Port Darwin and in Oakley Creek, New Zealand.
River pearls are produced by the species of Unio and Anodonta, especially by Unio margaritiferus. These species belong to the family Unionidae, order Eulamellebranchia. They inhabit the mountain streams of temperate climates in the northern hemisphere especially in Scotland, Wales, Ireland, Saxony, Bohemia, Bavaria, Lapland and Canada. The pearls of Britain are mentioned by Tacitus and by Pliny and a breastplate studded with British pearlS was dedicated by Julius Caesar to Venus Genetrix. As early as 1355 Scotch pearls are referred to in a statute of the goldsmiths of Paris; and in the reign of Charles II. the Scotch pearl trade was sufficiently important to attract the attention of parliament. The Scotch pearl-fishery, after having declined for years, was revived in 1860 by a German named Moritz Unger, who visited Scotland and bought up all the pearls he could find in the hands of the peasantry, thus leading to an eager search for more pearls the following season. It is estimated that in 1865 the produce of the season’s fishing in the Scotch rivers was worth at least £12,000. This yield, however, was not maintained, and at the present time only a few pearls are obtained at irregular intervals by an occasional fisherman.
The principal rivers in Scotland which have yielded pearls are the Spey, the Tay and the South Esk; and to a less extent the Doon, the Dee, the Don, the Ythan, the Teith, the Forth and many other streams. In North Wales the Conway was at one time celebrated for its pearls; and it is related that Sir Richard Wynn, chamberlain to the queen of Charles II, presented her with a Conway pearl which is believed to occupy a place in the British crown. In Ireland the rivers of Donegal, Tyrone and Wexford have yielded pearls. It is said that Sir John Hawkins the circumnavigator had a patent for pearl fishing in the Irt in Cumberland. Although the pearl-fisheries of Britain are now neglected, it is otherwise with those of Germany. The most important of these are in the forest-streams of Bavaria, between Ratisbon and Passau. The Saxon fisheries are chiefly confined to the basin of the White Elster, and those of Bohemia to the Horazdiowitz district of Wotawa. For more than two centuries the Saxon fisheries have been carefully regulated by inspectors, who examine the streams every spring, and determine where fishing is to be permitted. After a tract has been fished over, it is left to rest for ten or fifteen years. The fisher-folk open the valves of the mussels with an iron instrument, and if they find no pearl restore the mussel to the water.
River pearls are found in many parts of the United States, and have been systematically worked in the Little Miami river, Warren county, Ohio, and also on the Mississippi, especially about Muscatine, Iowa. The season extends from June to October. Japan produces fresh-water pearls, found especially in the Anodonta japonica. But it is in China that the culture of the pearl-mussel is carried to the greatest perfection. The Chinese also obtain marine pearls, and use a large quantity of mother-of-pearl for decorative purposes. More than twenty-two centuries before our era pearls are enumerated as a tribute or tax in China; and they are mentioned as products of the western part of the empire in the Rh’ya, a dictionary compiled earlier than 1000 B.C. A process for promoting the artificial formation of pearls in the Chinese river-mussels was discovered by Ye-jin-yang, a native of Hoochow, in the 13th century; and this process is still extensively carried on near the city of Teh-tsing, where it forms the staple industry of several villages, and is said to give employment to about 5000 people. Large numbers of the mussels are collected in May and June, and the valves of each are gently opened with a spatula to allow of the introduction of various foreign bodies, which are inserted by means of a forked bamboo stick. These “matrices” are generally pellets of prepared mud, but may be small bosses of bone, brass or wood. After a number of these ob]ects have been placed in convenient positions on one valve, the unfortunate mollusc is turned over and the operation is repeated on the other valve The mussels are then placed in shallow ponds connected with the canals, and are nourished by tubs of nightsoil being thrown in from time to time. After several months, in some cases two or three years, the mussels are removed, and the pearls which have formed over the matrices are cut from the shells, while the molluscs themselves serve as food. The matrix is generally extracted from the pearl and the cavity filled with white wax, the aperture being neatly sealed up so as to render the appearance of the pearl as perfect as possible. Millions of such pearls are annually sold at Soo-chow. The most curious of these Chinese pearls are those which present the form of small seated images of Buddha. The figures are cast in very thin lead, or stamped in tin, and are inserted as previously described. Specimens of these Buddha pearls in the British Museum are referred to the species Dipsas plicata. It should be mentioned that Linnaeus, probably ignorant of what had long been practised in China, demonstrated the possibility of producing artificial pearls in the fresh-water mussels of Sweden.
Pink pearls are occasionally found in the great conch or fountain shell of the West Indies, Strombus gigas, L.; but these, though much prized, are not nacreous, and their tint is apt to fade They are also produced by the chank shell, Turbinella scolymus, L.[1] Yellowish-brown pearls, of little or no value, are yielded by the Pinna squamosa, and bad-coloured concretions are formed by the Placuna placenta.[2] Black pearls, which are very highly valued, are obtained chiefly from the pearl oyster of the Gulf of Mexico. The common marine mussel Mytilus edulis also produces pearls, which are, however, of little value.
According to the latest researches the cause of pearl-formation is in most cases, perhaps in all, the dead body of a minute parasite within the tissues of a mollusc, around which nacreous deposit is secreted. The parasite is a stage in the life history of a Trematode in some cases, in others of a Cestode; that is to say of a form resembling the common liver-fluke of the sheep, or of a tapeworm. As long ago as 1852 Filippi of Turin showed that the species of Trematode Distomum duplicatum was the cause of a pearl formation in the fresh-water mussel Anodanta. Kuchenmeister subsequently investigated the question at Elster in Saxony and came to a different conclusion, namely that the central body of the pearl was a small specimen of a species of water mite which is a very common parasite of Anadonta. Filippi however states that the mite is only rarely found within a pearl, the Trematode occurring in the great majority of cases. R. Dubois and Dr H. Lyster Jameson have made special investigations of the process in the common mussel Mytilus edulis. The latter states that the pearl is produced in a sac which is situated beneath the epidermis of the mantle and is lined by an epithelium. This epithelium is not derived from the cells of the epidermis but from the internal connective-tissue cells. This statement, if correct, is contrary to what would be expected, for calcareous matter is usually secreted by the external epidermis only. The sac or cyst is formed by the larva of a species of Trematode belonging to the genus Leucithodendrium, a species closely resembling and probably identical with L. somateriae, which lives in the adult state in the eider duck. At Billiers, Morbihan, in France, the host of the adult Trematode is another species of duck, namely the common Scoter, Oedemia nigra, which is notorious in the locality for its avidity for mussels. Trematodes of the family Distomidae, to which the parasite under consideration belongs, usually have three hosts in each of which they pass different stages of the life history. In this case the first host at Billiers is a species of bivalve called Tapes decussatus, but at Piel in Lancashire there are no Tapes and the first stages of the parasite are found in the common cockle. The Trematode enters the first host as a minute newly hatched embryo and
- ↑ Strombus gigas, L., is a Gastropod belonging to the family Strombidae, of the order Pectinibranchia. Turbinella scolymus, Lam, is a Gastropod of the same order.
- ↑ Placuna placenta, L., belongs to the family Anomiidae; it is found on the shores of North Australia. Pinna squamosa, Gmelin, belongs to the Ostreacea; it occurs in the Mediterranean. Both are Lamellibranchs.
