SUPPLEMENT. I2OI 



upon the Schleswig-Holstein beds with germs of a bluish 

 colour in the mantle, even in the beginning of September, 

 then the percentage of 44*4 per cent, surely cannot be too 

 high. Oysters are hermaphrodite. In a large number of 

 oysters which I examined I found ova in the generative 

 organs, but no spermatozoa ; in many others I found sper- 

 matozoa, but no ova ; and in seven oysters which bore 

 embryos of a blue colour upon the beard, I found sperma- 

 tozoa in the generative organs. 



Three oysters with embryos of a white colour attached 

 to the beard had no spermatozoa in the generative organs. 

 Most mature oysters produce either ova or spermatozoa, 

 and not both at the same time. Of 309 oysters which were 

 dredged on the 25th of May, from four different beds along 

 the east side of the island of Svlt, and which were exa- 



^ ' 



mined from the 26th of May to the ist of June, the sex of 

 1 8 per cent, could not be determined ; of the remaining 82 

 per cent., one-half were males and one-half females. In 

 none of them were the generative products completely 

 matured. From these results I conclude that the ova and 

 spermatozoa do not arise in the generative organs of the 

 oyster contemporaneously, but that one follows the other. 

 The spermatozoa can arise very soon after the expulsion of 

 the ova, and probably one-half of the oysters of a territory 

 during any spawning period produce eggs only, the other 

 half spermatozoa only. 



If an oyster in which the embryos are in 

 this condition (ripe for expulsion) is opened, there will be 

 found upon its beard a slimy coating thickly loaded with 

 grayish-blue granules. These granules are the embryo 

 oysters, and if a drop of the granular slime be placed in a 

 dish with pure sea- water, the young animals will soon 

 separate from the mass, and spread swimming through the 



