Submarine Appliances And Their Uses
Deep Sea Diving, &c., &c.

SUBMARINE COMMERCIAL INDUSTRIES. PEARL, SPONGE, CORAL AND AMBER FISHERIES. The pearl fisheries of Australia have developed greatly during the past twenty- five years, until at the present time several thousands of men, with from 800 to 900 luggers are engaged in the industry, the annual yield of Mother-o’-I’earl shell alone being valued at considerably over a quarter of a million pounds sterling. The principal fisheries are on the north-west and north-east coasts, Broome, W.A., being- the centre of the former, and Thursday Island, Torres Straits, of the latter. There are smaller fisheries with stations respectively at Onslow, Shark’s Bay and Cossack on the West Coast, and Port Darwin in the Northern Territory. The luggers are of 10 to 12 tons, each carrying one Japanese or Manila diver, with a mixed crew of four or five, and are worked in groups of six to eight attended by schooners of 60 to 120 tons, from which the luggers are provisioned weekly. The Pearl Oyster (classified as the Avicula Margaritijerd) is an oyster slightly larger than the European congener, and is valuable for the pearl it bears, the shells themselves being of no commercial value. These are found more or less in all parts of the world, but principally on the Coasts of Ceylon, Western Australia, 1 anama, and some parts of Mexico and California. THE PEARL. The peari is really a tiny nucleus coated with films of carbonate of lime. Ihe oyster is well provided with this secretion, with which it lines its shell, and which, in its hardened state with which we are familiar, is called nacre, or mother-of-pearl. Now, the oyster is extremely sensitive to irritation, and the tiniest grain of sand or other foreign particle that may find its way into the valves causes the mollusc to exude its secretion and cover the intruding particle with layer upon layer till it is as smooth as the inside of the shell itself. Similarly, when a “borer" worm or other prey of the oyster has succeeded in boring through the shell, the mollusc will plug up the hole with nacre, continuing to spread layer upon layer until the aperture is made impregnable. If now we opened the shells, we should find a pearl adhering to one of them. C4