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OBSERVATIONS AND EXPERIMENTS ON THE 



LIFE-HISTORY AND HABITS OE THE 



PEARL OYSTER. 



I. Determination op Sex. 



At an early date in the investigation it became clear that the pearl oyster is dioecious 

 or of one sex only whether permanently so or only temporarily was a matter that 

 could not be settled in one season, but which Mr. Hornell determined later on in the 

 Galle laboratory. The dissections made during the cruises of the " Lady Havelock" in 

 the Gulf of Manaar and in Trincomalee showed that each mature individual functions 

 as male or female only. In no cases were even stray ova found in the gonads that 

 were determined as male, nor any spermatozoa in the females although such traces 

 of hermaphroditism were carefully looked for. 



In the Gulf of Manaar, during February and March, 1902, our dissections showed 

 a considerable preponderance of males over females, and further work by Mr. Hornell 

 at Galle showed the same disproportion, to the extent of about 10 per cent, of the 

 total number examined, during other parts of the year. We have several lists, of 

 which the following may be taken as a sample. Here out of 210 oysters from four 

 distinct localities the sex of 158 was determined, 87 being male and 71 female the 

 remainder were indeterminable owing either to immaturity or their spent condition. 



The further question the permanence of the sexual condition was one of those 

 points which could only be settled in a marine laboratory, where the animals could be 



