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 p. 270 — 288. 



(Genus No. 37—42.) 

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 Mag., Novbr., p. 142—144. Decbr. p. 145—148. 

 (14 n. sp.; n. g. Lilia.) 

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3. Trim. Bull. p. CXV. 

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 (Biological.) 



II. Wissenschaftliche Mitteilungen. 



1. Preliminary Abstract of Observations upon the Development of the 



American Oyster. 



By W. K. Brooks Ph.D. Associate in Biology Johns Hopkins University, 

 Baltimore U. S. A. 



The following is a statement of the more important points of a 

 paper upon the Development of the Oyster which will be printed in 

 full in the »Scientific Results of the Second Session of the Chesapeake 

 Zoological Laboratory of the Johns Hopkins University«. 



1) The American Oysters j Ostrea virginiana Lister, are unisexual. 

 Out of more than a thousand oysters which were carefully examined 

 with the microscope no hermaphrodites were found ; although in the 

 ovaries of several females which had nearly finished spawning the yolk 

 granules of ruptured eggs exhibited active brownian movements, and 

 closely resembled spermatozoa. 



2) The males and females are present in about equal numbers, 

 and the sexes, in the same depth of water, mature at the same time. 



3) The sexes are not distinguished by any external characteristics. 



4) The eggs are extruded from the ovaries very slowly, the process 

 occupying several days, and they are fertilized in the water outside the 

 shell, and none of the adult oysters examined during the breeding 

 season had any developing eggs or embryos in the mantle cavity, gills 

 or ovaries. 



The young are so very minute that it is almost impossible to find 

 them in the water, and surface collecting yielded only about a dozen 

 specimens of the early stages. The observations were accordingly made 

 upon embryos raised in aquaria from artificially impregnated eggs. 



5) As regards the age at which the Oyster can reproduce : eggs 



