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CHAELES RUSSELL BARDEEN 



1 Period of fertilization 



According to Helen Dean King ('01) the second polar body is 

 given off about ten minutes after the entrance of the spermatozoon 

 into the toad's egg and the two pronuclei fuse about thirty-five 

 minutes later. In table 3 we have summarized the results of 

 exposure of toad's eggs during the first hour after fertilization. 



In Experiments AO a string of fifty-four eggs was exposed 

 for forty-five minutes beginning immediately after fertilizing 

 fresh ova with fresh sperm. Practically all of the batch of eggs 

 from which this string was derived were fertilized. It is, there- 

 fore, possible although not certain, that the exposure to the rays 

 prevented development in the two eggs in the string which failed 

 to show any signs of cleavage. Forty-nine eggs failed to develop 

 past the early gastrulation stages. Of these forty-one ceased 



TABLE 3 

 Irradiation of eggs during fertilization 



Figures in brackets indicate percentage of eggs discarded because of lack of 

 fertilization. 



