Page:Popular Science Monthly Volume 82.djvu/549

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 (a) Black abalone shell with pearl form inserted, (b) Head of shell pearl form on inner side of black abalone shell, (c) culture pearl formed in the green abalone in seven months.

nacre which we now know serve as minute prisms to split up the white light into the rainbow tints so beautiful when reflected from the surface of the pearl. In the middle of the nineteenth century from an investigation of the fresh-water mussels of Turin Lake, Filippe proved that the stimulus for pearl formation in that species is a trematode worm. Other naturalists, Küchenmeister, 1856, Möbius, 1857, Kelaart and Humbert, 1859, Garner, 1871, Dubois, 1901, and Giard, 1903, have contributed to our knowledge of the origin of pearls from parasitic nuclei. In 1902, Jameson traced the life history of a Distomum from its first host, a duck, to a clam as its second host, and he succeeded in