96 PEARLS [CH. 



which build up tlie pearl. It will be quite clear then 

 that if we can say definitely in every case how and 

 Avhy the pearl sac has been formed, Ave shall have 

 solved the problem of the oiigin of pearls. 



The Italian scientist, Filip]>i, is usually credited as 

 being the originator of the vieAv that the nucleus of 

 pearls is an entombed parasite. 



This investigator, whilst examining fresh-Avater 

 mussels (Anodouta — quite common in our ponds and 

 streams) in the royal parks near Turin (1852) was 

 surprised at tlie large number of pearls found therein. 

 At the same time the abundance of pearls Avas 

 attended by the presence of large numbers of a 

 parasitic flat worm {Distoina duplicatum). Filippi 

 next examined the pearls, Avhich Avere of various ages 

 and sizes, and found ahvays an organic nucleus. It 

 Avas apparently impossible to recognise definitely in 

 the entombed organic matter the form of the Avorm, 

 but arguing from the abundance of both pearls and 

 Avorm parasites (and the organic nuclei) Filippi did 

 not hesitate to suggest that the Avorm parasites had 

 caused pearl formation. Later, Filippi recognised 

 certain parasitic remains in other pearl nuclei — re- 

 mains of other species of Avorms. 



In 1856, Kiichenmeister found in both Anodouta 

 and Unio (both common shellfish of fresh-Avater ponds 

 and streams in the British Isles) the remains of an 

 arthropod in the nuclei of pearls. 



