INTRODUCTION. 9 



To the biologist two dangers are, however, evident, and, paradoxical as it may 

 seem, these are overcrowding and overfishing. 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 someone who has had sufficient biological training to understand the life-problems 

 of the animal, and who will therefore know when 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 as to 

 structure, reproduction, life-history, growth and habits of the oyster which we had 

 to deal with, 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, in the south of Ceylon. 



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 Kondatchi 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 satisfactorily at Galle than 

 anywhere in the Gulf of Manaar. 



Turning now from the health of the oyster population on the " paars " to the 

 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 pearlv excrescences on the interior of the shell 

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

 grains of sand and other foreign particles gaining access to the body inside the shell, 

 which are popularly supposed to form the nuclei of pearls, only do so, in our experience, 

 under exceptional circumstances. Out of the many pearls I have decalcified, only one 

 contained in its centre what was undoubtedly a grain of sand ; and from Mr. Hornell's 

 notes taken since I left Ceylon, I truote the following passage showing that he has 

 had a similar experience : "February 16th, 1 ( J03. 'Ear-pearls,' of two decalcified, 

 one from the anterior ear (No. 148) proved to have a minute quartz grain (micro- 

 preparation 25) as nucleus." Since then he has found one more. 



It seems probable that it is only when the shell is injured, as, for example, by the 

 breaking off or crushing of the projecting "ears," thereby enabling some fine sand to 



