130 SPOLIA ZEYLANICA. 



PLACUNA FISHERY: INSPECTION OF MARCH, 1908. 



By A, WiLLEY. 



I. — Ovulation and Maturation of Placuna. 



THE Tamblegam pearl fishery, which has recently come to an 

 end, has been conducted by contractors under a lease from 

 Government, and was the second out of a series of five annual 

 fisheries contemplated by the terms of a quinquennial lease. Indis- 

 criminate fishing is reported to have occurred during the years 

 1905-1906 ; this ceased when the lease came into force at the 

 beginning of 1907. 



It was naturally supposed that the oyster beds Avould be auto- 

 matically re-stocked at least once a year during the course of the 

 lease ; but this expectation has not ])een fulfilled, since the oysters 

 which have, been taken this year helomjed to the sam,e generation as 

 those of last year, so tliat the end of the fishery means the end for 

 industrial purposes of that generation. It is fortunately impossible, 

 with the best efforts, to collect all the oysters ; some few are certain 

 to escape the vigilance of the divers ; and these are the sole hope 

 of the future, unless measures are taken, as they have been, to keep 

 a special stock of oysters in reserve for breeding. 



During my first inspection of the beds in June, 1907, I was unable 

 to determine the sexes of any of the oysters examined fresh, owing 

 to the immaturity of the gonads : and upon my second visit in 

 October, 1907, I was not able to gather much further information 

 on this matter for the same reason, even the largest specimens 

 measuring more than seven inches in long diameter and more than 

 six inches in height, being quite immature. I was able to detect 

 the presence of occasional nests of developing ova amidst an abundant 

 stroma ; but this was not sufficient to determine whether the sexes 

 were distinct, or whether the individuals were hermaphrodites ; it was 

 enough, however, to establish the fact of the commencement of 

 ovulation. In some preparations there appeared an ovarian reti- 

 culum associated with an aggregation of the brown pigment, which 

 is more or less diffused throughout the substance of the gonad. 

 The alcoholic extract of the gonads has a clear yellow colour like a 

 solution of picric acid. 



At the same time (October) I examined the gonads of other 

 Lamellibranchiate Molluscs, e.g., Venus, &c., and found them to be 

 perfectly mature, male and female in separate individuals, the 



