136 



Notes on the Artificial Fertilization of the Eggs of the 

 C^OMMON (/LAM, {yoDi.s Mciccnaria) . 



H. E. Knders and H. D. Aller. 



In view of the ecoiiDiiiic iiuiiorljuice of the eominon ehiin we endeavored 

 to artitii-ially fertilize its e.iigs dnriuy tlie ])nst sninnier* at the United States 

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

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

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

 NoveJiiber 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 segiuentation, and the early trochophore stage. In 

 one instance (August 1. 10(»(i) 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 spherical fifteen or 

 twenty minutes after the addition of a< five spermatozoa. The eggs then 

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

 tion of spemn. 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 unecpial divi- 

 sion. The next division occurs lii a plane at right angles to the first and 

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



The cells divide synchyonously uji to the thirty-two-celled stage but 

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



The percentage of eggs fiat could be fertilized was small during July: 

 it increased during August and September, but during Xovenibei' the sjK'r- 

 matozoa were not at live and the (>ggs could not be fertilized. 



While we have not ri'acheil a detinite conclusion regarding the breeding 

 habits of the conuiion <hnn we feel tb;it these data are themselves signifi- 

 cant. 



'■'■'Sunmier of 1905. 



