BIVAL VES 3 8 3 



returned to the water until the images are coated with mother-of-pearl, when they 

 are taken out and sold as charms. A modification of the same plan is adopted by 

 the Japanese at the Mikomoto pearl-farm. By means of a small canula, a minute 

 mother-of-pearl bead, flattened on one side so as to lie steady on the shell, is intro- 

 duced between the valves of a pearl-oyster, which is then returned to salt-water, 

 where it is allowed to grow for six or seven years. At the end of that period the 

 batch of oysters is taken out and examined for pearls. Owing to the large number 

 of oysters thus treated, the industry is profitable, although the pearls are never 

 perfectly spherical, and are also — probably from the nature of the core— deficient 

 in lustre. Several hundreds of people are employed on the ' farm,' and the pearls 

 find a market at good prices. Indeed, some of the so-called antique jewellery 

 offered for sale at Manila has been found to be set with these artificially produced 

 Japanese pearls. The results at Mikomoto leave no doubt that the artificial 

 production of real pearls is not only practicable, but profitable. The aim is, how- 

 ever, to grow spherical, perfect pearls of fine lustre like the best natural ones, and 

 it seems probable that this can be attained only by forming them round a natural 

 nucleus. In the Philippines fully 50 per cent, of these nuclei consist of the larvae 

 of cestode tapeworms, while in a few instances they consist of eggs, probably of a 

 small crab, grains of sand, and fragments of calcareous sponges, and other organisms. 

 Other large pearl-oyster fisheries are carried on in the Persian Gulf, on the 

 western coast of central America, and off the north-western coast of Australia. 



It was formerly believed that pearls were invariably formed round grains of 

 sand and other inorganic substances, but the trend of modern research has been 

 to show, as noted above, that the nuclei generally consist of the larvae, or more 

 rarely the eggs, of parasites infesting the oysters, the most common of these being 

 worms of the cestode group. Although pearls formed round such nuclei at first 

 lie loose within the valves of the oyster, they do not always remain so, but may 

 become attached to the shells themselves, when they assume various irregular 

 shapes. 



Although it is a fact that Ceylon possesses some of the richest beds of pearl- 

 oysters in the world, it is probably little known that it owns another source of 

 pearls. This second supply is derived from the thin-shelled species of oyster 

 commonly known as the window-pane oyster, and scientifically termed Placuna 

 placenta. These oysters are found in certain backwaters, or lagoons, in the island, 

 where they are carefully and extensively cultivated for the sake of their pearls. 

 As the interior of the placuna shell does not display the brilliant iridescence of 

 the true pearl-oyster, the pearls obtained from it are probably inferior in lustre 

 to the others. 



To the same family (Aviculidce) as the pearl-oysters belong the curious 

 hammer-oyster (Malleus vulgaris) of the Indian Ocean, and the wing-shells 

 (Avicula), and the various species of the allied genus Pinna. In the last of 

 these the valves of the shell are in the shape of an isosceles triangle, and quite 

 translucent. Some pinnas grow to as much as a couple of feet in length, and in 

 life project a foot or more above the sand, in which they are partially buried, moored 

 by the silky byssus to any convenient object. 



As representing another large group, mention may be made of the Australian 



