Читать книгу The Book of the Pearl. The history, art, science, and industry of the queen of gems онлайн

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In examining a species of fresh-water mussel, the Anodonta cygnea, occurring in ponds near Turin, and especially the many small pearly formations therein, Filippi observed that these were associated with the presence of a trematode or parasitic worm, which he named Distomum duplicatum, and which appears to be closely allied to the parasite which causes the fatal “rot” or distemper in sheep. Under the microscope, the smallest and presumably the youngest of these pearls showed organic nuclei which appeared undoubtedly to be the remnants of the trematode. In Anodonta from other regions, which were not infested with the distoma, pearls were very rarely found by Filippi. In a paper,^[55] published in 1852, containing a summary of his observations, he concluded that a leading, if not the principal, cause of pearl-formation in those mussels was the parasite above noted; and in later papers^[56] he included such other forms as Atax ypsilophorus within the list of parasitic agencies which might excite the pearl-forming secretions, comparing their action to that of the formation of plant-galls.