4 PEARLS AND PARASITES 



enables us to do much to ensure steady success in 

 a very speculative industry ; and with complete 

 knowledge there is no reason why pearl fisheries 

 should not be under as good control as oyster 

 fisheries now are. 



It was about fifty years ago (1857-1859) that 

 the problem of the Ceylon pearl-oyster fishery was 

 first attacked in a thoroughly scientific spirit by a 

 certain Dr. Kelaart. His reports to the Govern- 

 ment of the island contain the following suggestive 

 sentences : 



' I shall merely mention here that M. Humbert, a Swiss 

 zoologist, has, by his own observations at the last pearl 

 fishery, corroborated all I have stated about the ovaria or 

 genital glands and their contents ; and that he has discovered, 

 in addition to the Filaria and Circaria (sic), three other para- 

 sitical worms infesting the viscera and other parts of the pearl- 

 oyster. We both agree that these worms play an important 

 part in the formation of pearls ; and it may be found possible 

 to infect oysters in other beds with these worms, and thus 

 increase the quantity of these gems. The nucleus of an 

 American pearl drawn by Mobius is nearly of the same form 

 as the Circaria found in the pearl-oysters of Ceylon. It will 

 be curious to ascertain if the oysters in the Tinnevelly banks 

 have the same species of worms as those found in the oysters 

 on the banks off Arripo.' 



Unfortunately Dr. Kelaart died shortly after making 

 this report, leaving his investigations incomplete. 



Some seven years before, in 1852, Filippi had shown 

 that the pearls in our fresh-water mussel {Anodonta) 

 were formed by the larvae of a fluke (a trematode), 

 to which he gave the name of Distomum duplicatum. 

 Many students of elementary biology, as they pain- 

 fully try to unravel the mystery of molluscan mor- 

 phology, must have come across small pearls in the 

 tissues of the fresh-water mussels {Unio or Anodonta) ; 

 but these are said to have less lustre and to be more 



