Microscopic erai-iir.E,tion of -oreserved ;naterir2 sho\;ed. that ovaries raid testes of 

 the pearl oysters v;ere ripe. Some of the oysters had already spavraed, and maay of their 

 ovarian tutules v.-ere empty. The gonad of one oyster v/as fotrnd to "oe herr.ap?iroditic 

 (Fig. 27) . As one can see from the photogra-Vn, ripe eggs and ripe spena were present. The 

 fenale tuTjules v;ere ohviotisly in the after-spavniing stage vrhich suggested that sex reversal 

 took place inmediately after the discharge of eggs. The picture greatly reseir."oles that of 

 the gonad of hermaphroditic Ostrea lurida as descrioed "oy Coe (1932). 



The finding of one hermaphroditic oyster out of only eight speciiiens ezaiiined 

 histologically su^ests the possilsility that in Pinctada raasatlanica the chajage from female 

 to male phase taJces place imnediately follov/ing the shedding of eggs. It is ohvious that 

 more detailed studies are needed to thro\\r more light on this interesting point in the 

 "biology of pearl oysters. In the studies of the pearl oyster of Cej'lon, Herdmaii (I903) 

 found no evidence of change in their sex. He stated that "in no cases v/ere even stray ova 

 found in the gonads that were determined as male, nor any spermatozoa in the females - 

 elthou^ such traces of hermaphroditism were carefully looked for." 



Ho hermaphrodites v;ere found among the Hawaiian oysters, Pinctada galtsoffi , 

 v/hich I examined in 1930» 



Sex reversal is known to occur, however, in the Japanese oyster, Pinctada 

 martensi (ihaiker) , and in the Australian white pearl oyster, Pinctada maxima Janeson. This 

 fact v;as established hy Japanese scientists, R. Wada and S. Vfada ( 1939 > 19^2) , who made 

 ohservations with oysters of known sex marked vfith lead tags. In both species, the change 

 took place either from female to male or from male to female. 



There is no evidence at present that sex reversal has any effect on the reproduc- 

 tion and fertility of pearl oysters. 



MkiA k^ 



yigure 27 Photomicrograph of a hermaphroditic gonad of Pinctada nagatlanica . 



Eark mass in the center consists of ripe spermatozoa surrounded hy 

 eggs. Prom a preparation stained v/ith haemato3!ylin-cosin, x I50. 



^3 



