The thinner the successive coats the finer the lustre. Pearls have even been discovered embedded in the animal itself. The number of pearls found in a shell depends on the number of times the living host was compelled to seal up some irritant object, and may vary from one up to the eighty-seven which are said to have been found in an Indian oyster. That an oyster thus distinguished has not led a happy existence is testified by the distorted shape of its shell, a clue that guides the pearl-fishers in their search. Moreover, pearl-oysters never have thick nacreous shells, and on the other hand molluscs with fine mother-o’-pearl seldom contain pearls. Beautiful white and silvery pearls are found in a small oyster that lives at a depth of 6 to 13 fathoms (11-24 m.) in the Gulf of Manaar, off the coast of Ceylon. About seven-eighths, however, of the pearls that come into the market are obtained from a larger oyster which has its home on the Arabian coast of the Persian Gulf. These famous fisheries have been known since very early times. The pearls found here are more yellowish than those from Ceylon, but are nevertheless of excellent quality. The pearl fisheries off the north-west coast of Western Australia and off Venezuela are also not unimportant, and fine black pearls have been supplied by molluscs from the Gulf of Mexico. [Illustration: _PLATE XXXI_ METAL FIGURES OF BUDDHA INSERTED IN A PEARL-OYSTER] [Illustration: _PLATE XXXII_ FIG. 1 FIG. 2 SECTIONS OF CULTURE PEARL FIG. 1. IN THE OYSTER. FIG. 2. WHEN FINISHED. A. PEARLY DEPOSIT. B. PIECE OF MOTHER-O’-PEARL INSERTED IN THE OYSTER. C. OUTER SHELL OF THE OYSTER. D. MOTHER-O’-PEARL BACK ADDED.] The Chinese have long made a practice of introducing into the shell of a pearl-oyster little tin images of Buddha in order that they may be coated with the nacreous secretion. The Japanese have during recent years made quite an industry of stimulating the efforts of the mollusc by cementing small pieces of mother-o’-pearl to the interior surface of the shell (Plate XXXII, Fig. 1); these ‘culture’ pearls, as they are termed, are recognizable by examination of the back. About a year has to elapse before a coating of a tenth of a millimetre is formed, and another two years must pass before the thickness is doubled. After removal the piece of mother-o’-pearl, which is now coated with several nacreous layers, is cemented to a piece of ordinary mother-o’-pearl, and the lower portion is ground to the usual symmetrical shape (Plate XXXII, Fig. 2). Blister pearls are often similarly treated. In both cases, however, the ‘orient’ is deficient in quality. The finest mother-o’-pearl is supplied by a mollusc found in the sea near the islands lying between Borneo and the Philippines, and fine material is found at Shark Bay and off Thursday Island. CORAL