THE PEARL FISHERIES OF CEYLON. 235 



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 ten to twenty 

 miles oS 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 can not 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 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 pearly 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 bodies 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 center what was undoubtedly a grain of sand; and 

 from Mr. Hornell's notes taken since I left Ceylon, I quote the follow- 

 ing passage, showing that he has had a similar experience : 



"February 16, 1903 — Ear-pearls. Of two decalcified, one from the 

 anterior ear (No. 148), proved to have a minute quartz grain (micro, 

 preparation 25) as nucleus." 



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 gain access to the interior, that 

 such inorganic particles supply the irritation which gives rise to 

 pearl formation. 



The majority of the pearls found free in the tissues of the body 

 of the Ceylon oyster contain, in our experience, the more or less easily 

 recognizable remains of Platyelmian parasites; so that the stimula- 

 tion which causes eventually the formation of an 'orient' pearl is, as 

 has been suggested by various writers in the past, due to infection by a 

 minute lowly worm, which becomes encased and dies, thus justifying. 



