Pearls are found in several molluscs inhabiting shallow seas and sandbanks in the old and new world, but the most productive mollusc is the Meleagrina margaritifera or Avicula margaritifera, the pearl oyster ; and the best known localities are the Persian Gulf, the west coast of Ceylon in the Gulf of Manaar, Panama, the shores of Califor nia, Australia, Red Sea, Arabian coasts, the Aru Islands, Zebu, the Sulu Archipelago, Mindanao, coast of New Guinea, Torres Straits, Gulf of Omra, and coasts of Japan.
Friar Jordanns, a quaint old missionary bishop, who was in India in 1330, says that 8000 boats were engaged in this fishery and that of Ceylon, and that the quantity of pearls was astounding and almost incredible. 'the headquarters of the fishery was then, and indeed from the days of Ptolemy to the 17th century continued to be, at Chayl or Coil, literally, the temple, on the sandy promon tory of Ramnad, which sends off a reef of rocks towards Ceylon, known as Adam's Bridge. And Ludovico di Varthema mentions having seen the pearls fished for in the sea near the town of Chayl, in about A.D. 1500 ; and Barbosa, who travelled about the same time, says that the people of Chayl are jewellers who trade in pearls. This place is, as Dr. Vincent has clearly shown, the Koru of Ptolemy; the Kolkhi of the author of Periplus, the Coll or Chayl of the travellers of the Middle Ages, the Ratnana-Koil (temple of Rama) of the natives, the same as the sacred promontory of Ramnad and isle of Rameswararn, the headquarters of the Indian pearl fishery from time immemorial.
In Arabic poetry, pearls are fabled to be drops of vernal rain congealed in oyster shells. Benjamin of Tudela says that in the month of March the drops of rain-water which fall on the surface of the sea are swallowed by the mothers-of-pearl, and carried to the bottom of the sea, where, being fished for and opened in September, they are found to contain pearls. The Hindus poetically describe them as drops of dew falling into the shells when the molluscs rise to the surface of the sea in the month of May, and becoming, by some unexplained action of the sun's rays, transformed into pearls. Pliny and Dioscorides believed that
pearlswere productions of dew ; but that observant old Elizabethan navigator, Sir Richard Hawkins; shrewdly remarked that 'this must be some old philosopher's conceit, for it cannot be made pro bable how the dew should come into the oyster.' Modern writers suggest various causes for the intrusion of the nucleus round wilich the pearl is formed. The free border of mantle lining each valve of the shell dips downwards to meet a similar edge on the opposite side, thus forming a double-fringed veil. The tentacles of this fringe consist of long and short flat filaments, which are exceedingly sensitive, so that even the approach of a foreign substance makes them draw forwards and shut out the intruder. They doubtless prevent the pearls from dropping out of the shell, and preserve the fish from the host of carnivorous creatures which infest its place of abode ; and if it be true that particles of sand form the nuclei of pearls, they must run the gauntlet of these ever watchful sentinels before they can intrude them selves amongst the interstices of the mantle. The food of pearl-oysters consists of foraminifera, minute algae, and diatoms; and Dr. Kelaart has suggested that the silicious internal skeletons of these microscopic diatoms may possibly permeate the coats of the mantle, and become nuclei of pearls.
It is suggested that pearls are produced when the transparent envelope of the animal, called the mantle, is wounded or irritated. That small boring worms pierce the shell and penetrate to the body of the animal. The mantle then sends forth a quantity of pearly matter over the wounded spot, and this becomes a little knob or pearl. This is supported by the fact that nearly all the shells in which pearls are found are outwardly contorted, and that a smooth regular shell is a pretty sure sign of the absence of the pearl.