28 
Pearl Inducing Worm 
fisheries were a considerable but intermittent source of revenue. The 
Royal Society was approached to send a Zoologist to investigate 
the Pearl Fishery problems and, as a result, Professor Herdman 
ai’rived in Ceylon in 1902. The discovery of the pearl-inducing worm 
dates from that time. Large collections of Cestode parasites from 
marine fishes were made. These were described by Dr Shipley and 
Mr Hornell (i). The larvae inhabiting the tissues of the oj^ster were 
identified as Cestode larvae, and the adult worm which was named 
Tetrarliynchus unionifactor was found in Rhinoptera javanica. 
Cysts of this worm were also obtained from certain species of fish 
of the genus Balistes but the position of these cysts with relation to 
the life history of the parasite itself was left in some doubt. In 
1905, the banks were leased to the Ceylon Company of Pearl 
Fishers Limited, and the work done since that time will be detailed 
in this paper. 
Two kinds of pearls occur in the Ceylon pearl oyster. Those pearls 
which are formed round the larvae of Tetrarliynchus unionifactor —and 
very occasionally round other nuclei—are termed “ cyst ” pearls. They 
are usually round, and if old, ai’e of considerable size. The second kind 
of pearls have a totally different origin. They almost always occur at 
the insertions of the levator and pallial muscles. They are termed 
“seed” or “muscle” pearls. They appear to have no nucleus and they 
are always very small and of irregular shape. Their origin is unknown. 
By some they are considered to be excretions caused by irritation set 
up consequent on the “shear” of muscles working in different planes. 
By others they are considered to be excretions due to a superfluity of 
lime in the organism. No nuclei have as yet been discovered in them, 
but they are believed by some to be formed round a primary limey 
nucleus which has been termed a calcospherule. 
The early stages of the life history of the pearl-inducing worm are 
not known. Herdman recorded the presence of free-swimming Cestode 
larvae in the plankton collected on the Pearl Banks, but as he 
mentioned later “ it is still uncertain whether the free-swimminsf 
larvae found on the Muttuvaratu Paar really belong to the life history.” 
Although the plankton has since been collected fairly regularly over the 
pearl banks, no Cestode larvae have been identified, and it would be 
obviously impossible at the present stage of our knowledge to identify 
an adult worm from larvae so young. 
Nothing is known as to how the larvae enter the oyster. The adult 
worm occurs in fish which live on the bottom and are bottom feeders. 
