A cheap imitation pearl is made of opal glass, a bluish-white milky appearing material, to which a pearly effect is given by treating it with fluoric acid. Imitation black pearls are made from hematite, but as they require careful finishing to hide the metallic luster and are much heavier than pearls, they are seldom used. The Chinese and Japanese have been much more ingenious in their methods and have long produced, with enforced aid from the animal, imitations which are in part real pearl. The former insert in the Chinese pearl-mussel (anodonta herculea) small figures of Buddha upon which the fish proceeds to deposit its nacre. When they are coated, which occurs in from one to two or three years, the pearly figures are extracted and sold to the devout. The Japanese do more. They attempt to produce a marketable gem and have so far succeeded that a considerable number have been sold of late in the United States and in many cases the public buy them not knowing that they are an artificial production. The base upon which the nacre is deposited appears to be composed of a substance resembling porcelain shaped like a low dome hollowed out on the under side and having a hole in the centre of the cavity. As there is no nacre on the under side, it must, when the button is placed in the mussel, be thereby protected from the action of the fish except at the edges where the nacreous deposit probably joins it to the shell but in such a manner that it can be easily detached. The pearl covered button is then fitted to a piece of polished mother-of-pearl of the same exterior size and shape and the two are neatly joined, forming a double low domed piece of pearl on one side, and mother-of-pearl on the other. These Japanese pearls as they are called, when mounted in a setting constructed to hide the under side, have the appearance of imperfect spheres of natural pearl. The beds where the culture of these artificial pearls is carried on, are situated in the Bay of Ago, a few miles south of the Temple of Ise, in central Japan on the Pacific side. It is a quiet piece of water, in a coast broken by numerous inlets and coves. A little north of the centre of the bay is a small island called Tadoko where the necessary buildings and the men connected with the industry are. Around the island and near it, about 1,000 acres of sea bottom are leased and used for the pearl oyster cultivation. The water is about five to seven fathoms deep. The oyster used is the one common to the waters of Japan, the Avicula martensii Dunker. In May and June, stones weighing six to eight pounds are scattered over the bottom of the sheltered shallows which run up into the land, where the spat is collected. The breeding season is in July to August and in the latter month very tiny shells attached to the stones by the byssus may be seen already.