284 Professor W. A. Herdman [IVtarcli 27, 



11. Probably the majority are killed by overcrowding. 



12. They should therefore be thinned out and transplanted. 



13. This can be easily and speedily done, on a large scale, by 

 dredging from a steamer, at the proper time of year, when the young 

 oysters are at the best age for transplanting. 



14. Finally there is no reason for any despondency in regard to 

 the future of the pearl oyster fisheries, if they are treated scientific- 

 ally. The adult oysters are plentiful on some of the Paars and seem 

 for the most part healthy and vigorous ; while young oysters in their 

 first year, and masses of minute spat just deposited, are very abund- 

 ant in many places. 



To the biologist two dangers are however evident, and, paradoxical 

 as it may seem, these are overcrowding and overfisJiing. But the 

 superabundance, and the risk of depletion are at the opposite ends of 

 the life cycle, and therefore both are possible at once on the same 

 ground — and either is sufficient to cause locally and temporarily a 

 failure of the pearl oyster fishery. What is required to obviate 

 these two dangers ahead, and ensure more constancy in the fisheries, 

 is careful supervision of the banks by some one who has had sufficient 

 biological training to understand the life-problems of the animal, 

 and who will therefore know wLen to carry out simple measures of 

 farming, such as thinning and transplanting, and when to advise as 

 to the regulation of the fisheries. 



In connection with cultivation and transplantation, there are 

 various points in structure, reproduction, life-history, growth and 

 habits of the oyster which we had to deal with, and some of which 

 we were able to determine on the banks, while others have been the 

 subject of Mr. Hornell's work since, in the little marine laboratory 

 we established at Galle. 



Although Galle is at the opposite end of the island from the pearl 

 banks of Manaar, it is clearly the best locality in Ceylon for a marine 

 laboratory— both for general zoology and also for working at pearl 

 oyster problems. Little can be done on the sandy exposed shores of 

 Manaar island or the Bight of Condatchy — the coasts opposite the 

 pearl banks. The fisheries take place far out at sea, from 10 to 20 

 miles off shore ; and it is clear that any natural history work on the 

 pearl banks must be done not from the shore, but, as we did, at sea 

 from a ship during the inspections, and cannot be done at all during 

 the monsoons because of the heavy sea and useless exposed shore. 

 At such times the necessary laboratory work supplementing the 

 previous observations at sea can be carried out much more satis- 

 factorily at Galle than anywhere in the Gulf of Manaar. 



Turning now from tlic hcaUh of tlic oyster population on the 

 " paars," to tLe subject of pearl formation, which is evidently an 

 unhealthy and abnormal process, we find that in the Ceylon oyster 

 there are several distinct causes that lead to the production of pearls. 

 Some pearls or pearly excrescences on the interior of the shell are 

 due to the irritation caused by boring sponges and burrowing worms. 



