14 PEARLS AND PARASITES 



which feeds largely on oysters, the cestodes exist in 

 swarms in the stomach, and the eggs make their way 

 from the fish into the oysters, and there some of them 

 grow up, but most of them perish in their pearly casket. 

 If, as I beHeve, this is the history of the pearl-forming 

 organism, we must regard the Rhinoptera as a friend 

 to the industry, and not, as hitherto, an enemy which 

 helps to destroy the oyster-beds. 



The discovery of the cestode larva as a real cause 

 of pearl-formation received an interesting confirmation 

 shortly after it had made it. M. G. Seurat, working 

 independently at Rikitea on the island of Mangareva, 

 in the Gambler group, discovered a very similar larva 

 in the local pearl-oyster around which pearls are 

 formed ; this larva, if we may judge from pictures, is 

 almost certainly the same as the one from Ceylon. 

 Professor Giard regards it as belonging to a tape- 

 worm of the genus Acrobothrium ; and, if he be right, 

 then Professor Herdman's larva is an Acrobothrium 

 too. We have so little knowledge of the early forms 

 of cestodes that we cannot accept this attribution as 

 final. We may, however, hope for further informa- 

 tion, for a French zoologist, M. Boutan, started some 

 little time ago for the East to work at the problem ; 

 Mr. Hornell is still at work in Ceylon; and Mr. C. 

 Crossland, who has had much experience in marine 

 work in the tropics, has been appointed, at the request 

 of the Soudan Government, to investigate the pearl- 

 oyster beds of the Red Sea. Finally Dr. Willey, of 

 the Colombo Museum, has recently described similar 

 larvae in the pearls of the ' window-pane ' oyster, 

 Placuna placenta, from the eastern shores of Ceylon. 



In 1904 it was again found possible to hold a fishery 

 in Ceylon. It was held at a place called Marichikaddi, 

 also on the north-west coast. In the course of thirty- 

 eight days over 41,000,000 oysters were taken. The 

 trade was very brisk; the prices paid were un- 



