136 



Notes on the Aettficial Fertilization of the Eggs of the 

 Common Clam, { Venus Mercenaria). 



H. E. Enders and H. D. Aller. 



In view of the economic imyortauce of the common clam we endeavored 

 to artificially fertilize its eggs during the past suimiier* at the United States 

 Fisheries Laboratory, at Beaufort, North Oarolina. Many clams were full 

 of eggs or contained active spermatozoa when we tirst examined them in 

 July. This condition prevailed till the 12th of September, but early in 

 November of this year the spermatozoa were not active. 



Several times during July and August we fertilized the eggs by the 

 addition of active spermatozoa from several males and observed the matura- 

 tion of the egg. the segmentation, and the early trochophore stage. In 

 one instance (August 1, ]0()(5) the development continued to the young 

 veliger stage. 



The female sexual element is a pear-shaped cell in which a large 

 germinal vesicle is found. Many of the cells become si^herical tifteen or 

 twenty minutes after the addition of active spermatozoa. The eggs then 

 show no further evidence of being fertilized till two hours after the addi- 

 tion of sperm, when the first polar body is cast off and this followed by the 

 second at an interval of twenty or thirty minutes. Thirty minutes later 

 the egg i)asses into the two-celled stage by a holoblastic and unequal divi- 

 sion. The next division occurs in a plane at right angles to the tirst and 

 this is followed by division in a plane at right angles to the other two. 



The cells divide synchyonously up to the thirty-two-eelled stage but 

 we were unable to determine whether this continues beyond this stage. 



The percentage of eggs that could be fertilized was small during July ; 

 it increased during August and September, but duriug November the sper- 

 matozoa were not active and the eggs could not be fertilized. 



While we have not reached a definite conclusion regarding the breeding 

 habits of the connnon clam we feel that these data are themselves signifi- 

 cant. 



^Summer of 1905. 



