30 
Pearl Inducing Worm 
of Placuna are the same as those found in the Ceylon pearl oyster. 
We shall however return to this subject later. Haswell and Hill (1894) 
also recorded a similar case of endogenous multiplication in Polycercus 
—the bladder stage of Taenia nilotica from Giirsorius europaeus. 
This globular cyst then, found in the pearl oyster, is the first 
known stage in the life history of the pearl-inducing worm. It is 
round these larvae that cyst pearls are formed. The remains of the 
larva have been identified in the centre of sections of decalcified pearls. 
It appears that although cyst pearls almost invariably originate in this 
way, other nuclei may very occasionally lead to pearl formation. 
Hornell records two cases in which grains of sand have been found to 
act as nuclei. 
The outstanding feature in connexion with these larvae, and their 
relation to pearl formation, is, that so few pearls are found, although the 
larvae are so abundant. A normal oyster may contain as many as 200 
larvae and not a single pearl may be present. One is well within the mark 
in stating that not O'OOl of the larvae present in the Pearl oyster ever 
become pearl nuclei. It seems likely that cyst pearls are only formed 
round such parasites as for some unaccountable reason die in the tissues 
of the oyster and thus set up local irritation, resulting in a migration 
of ectodermal cells which eventually cover the irritating particle with 
pearly matter. This pearly matter is secreted round the parasite in 
layers, simulating the underground leaves of an onion. 
It would appear possible, and even likely, that future scientific 
investigation will be directed towards enquiring more fully into this 
question and, should it be found possible to treat oysters in such a way 
that a large percentage of these larvae become pearl nuclei, pearl fishing 
in Ceylon will be revolutionised. A few experiments of this kind have 
been carried out on the Ceylon Pearl Banks but with only a little 
success. The operations were severely hampered by the almost 
complete absence of oysters. 
Up to the present, all the methods of culture in Ceylon have been 
directed towards the preservation of beds of oysters, and no attempts 
have been made to enhance the pearl-yield of the individual oyster. It 
is obvious that the pearl-yield bears some relation to the degree of 
infection, but instead of leaving the results to nature, something may 
be done in the future to assist nature in the way indicated. 
A form of pearl culture is extensively carried on in Japan, which 
consists of the introduction of small leaden images of the Buddha or other 
nuclei between the mantle and the shell. In a short time these nuclei 
