g2 Miscellaneous. 



Observations upon the Artificial Fertilization of Oyster-eggs, and on 

 the Embryology of the American Oyster. By W. K. Brooks, 

 Associate in Biology, Johns Hopkins University. 



All the writers upon the development of the oyster, from Home 

 (Phil. Trans. 1N27) to Mobius (Austern und Austernwirthschaft, 

 L877), state that the eggs are fertilized inside the shell of the 

 parent, and that the young are carried inside the mantle-cavity 

 until they are provided with shells of their own, that they leave 

 the parent in a somewhat advanced state of development, and that 

 their free-swimming lite is of short duration and lasts only until 

 they find a suitable place to attach themselves. 



Misled by these statements, which do not apply to our species, I 

 opened a number of oysters during the summer of 1878 and exa- 

 mined the gills and the contents of the mantle-chambers for young, 

 but found none, and concluded that the time during which the 

 young are carried by the parent must be so short that I had missed 

 it. 1 undertook the same investigation this May, with the deter- 

 mination to examine adult oysters for young every day during the 

 breeding-season, and at the same time to try to raise young for 

 myself by the artificial fertilization of eggs taken from the ovaries. 

 1 had complete success with the second method from the first, and 

 succeeded in raising countless millions of young oysters, and in 

 tracing them through all their stages of development up to the 

 time when they had acquired all the characteristics which Salensky, 

 Lacaze-Duthiers, Mobius, and others have figured and described in 

 the young European oyster at the time it leaves its parent. I also 

 made careful examination of the gills and mantles of more than a 

 thousand oysters, but never found a single fertilized egg or embryo 

 inside the mantle-cavity of an adult, although I found females with 

 the ovaries full of ripe eggs, others with the ovaries half empty, 

 others with them almost entirely empty, and others at all the inter- 

 mediate stages ; and I therefore feel sure that my examinations were 

 made upon spawning oysters. 



While this evidence is only for one season and one bed, I think 

 that, until it is shown to be exceptional, we must conclude that 

 there is an important difference in the breeding-habits of American 

 and European oysters, and that the eggs of the American oyster are 

 fertilized outside the body of the parent — that during the period 

 which the European oyster passes inside the mantle-cavity of the 

 parent, the young American oyster swims at large in the open 

 ocean. 



The more important points in the development of the oyster 

 are: — 



1. The oyster is practically unisexual, since at the breeding- 

 season each individual contains either eggs or spermatozoa exclu- 

 sively. 



'l" Segmentation takes place very rapidly, and follows substan- 

 tiallv the course described for other Lamellibranchs by Loven and 

 Fleming. 



