PEARLS AND PARASITES 91 



an elaborately formed tomb or sarcophagus, in which 

 the parasite is enclosed layer upon layer. This mode ot 

 disposing of parasites and other intrusive bodies is not 

 unusual in animals. The terrible little flesh-worm 

 the Trichina which causes the death of rats, pigs, and 

 men who eat raw meat, is sometimes conquered in this 

 way. It is found in the muscles (flesh) of man and 

 animals enclosed in little pearl-like sacs, half the size of 

 a hempseed, and it dies there, unless the invaded animal 

 should die, and its flesh be eaten (as raw ham for 

 instance) by another animal. The burying of incon- 

 venient corpses in plaster of paris, corresponding to 

 pearls as we now know them, has been a method of 

 concealment occasionally adopted by criminals. On the 

 whole, pearls have not very pleasant associations. 



The history of the special parasitic worm which 

 invades the beautiful little pearl-oyster of Ceylon has 

 recently been followed out by skilful naturalists. There, 

 too, a smaller oyster-eating fish of a peculiar kind, and 

 a larger fish which eats the first fish, are necessary for 

 the reproduction and multiplication of the pearl-pro- 

 ducing parasites. The new Ceylon Pearl-Fishing Com- 

 pany has, therefore, to see to it that both these kinds of 

 fish are encouraged to live in the sea near where the 

 pearl oysters are found, and it is their object to increase 

 the parasitic disease by which pearls are formed, and 

 ensure an abundance of parasites. 



An interesting new method has been recently applied 

 to the examination of pearl oysters for pearls. The Ront- 

 gen rays are used to produce a skiagraph (such as 

 surgeons use in searching for a bullet) of the pearl oysters 

 when brought into harbour. They are thus rapidly 

 examined one by one, without injury, and the shadow- 

 picture shows the pearl or pearls inside those oysters 

 which are infected. The pearlless oysters are returned 

 to the depths of the sea, whence they came those with 

 small pearls only are kept in special reserves or sea-lakes, 



