6Q PEARLS [CH. 



one of the lines along which biological science has 

 at various times exerted its influence. As a matter 

 of fact, the artificial production of pearls has so far 

 proved a greater commercial success than the culti- 

 vation of the pearl oysters. Great care must be 

 taken, however, to distinguish between true pearls 

 and blisters, and most, if not all, of the artificially 

 stimulated pearls are really only blisters, and so of 

 comparatively little value/. 



The natives of the far East recognised many years 

 ago that if a foreign body was insinuated between 

 the shell and the mantle of nacre-producing mol- 

 luscs, the irritating object would be covered with 

 a layer of nacre. Sometimes small worms or even 

 fish get into this strange position, and become 

 coated with nacre (fig. 8). A beautiful specimen of 

 this is to be seen in the British Museum. Hague 

 describes how the Chinese carried on a manu- 

 facture of pearls in this way in the fresh-water bivalve 

 Dipsas plicatns. The shellfish were collected and 

 kept living in lakes for this purpose. They were 

 first opened (usually by children) and then objects 

 of various kinds (grains of sand, pellets of nacre, or 

 images of Buddha) were inserted between shell and 

 mantle. After about ten months or longer, up to 

 three years, the shellfish were fished up and the 

 nacre-covered objects removed and sold. 



The nacre-covered pellets were naturally the most 



