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

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Blister pearls are also caused by the defensive or protective action of the mollusk in resisting the intrusion of some animal, as a boring sponge or a burrowing worm, which has begun to penetrate the outer layers of the shell. This stimulation causes the mollusk to pile nacreous material upon the spot, thus making a substantial mound closely resembling a segment of a large pearl. This walling-out of intruders is not the result of intelligent forethought or of instinct, analogous to the repairing of a damaged web by a spider, or the retunneling of a collapsed gallery by ants; it is a pathological rather than an intelligent action.

BROOCHES MADE OF PETAL, DOG-TOOTH, AND WING PEARLS

From the Upper Mississippi Valley

When the nucleus of a pearl is large and very irregular, it necessarily follows that the deposited nacre roughly assumes the irregular outline of the inclosed object. This is strikingly shown in pearls covering a minute fish, a crayfish, or a small crab. Several specimens have been found in which the species could be identified by examination through the nacreous coating.