456 CHARLES RUSSELL BARDEEN 



McGregor ('08) after exposing both parents to the X rays 

 found that the results were not markedl} different from those 

 obtained after exposing the male before fertilization. He found 

 more striking results after exposing the male than after exposing 

 the female. I endeavored in the spring of 1910 to repeat experi- 

 ments along these lines on a more extensive scale, but, unfor- 

 tunately, I used too weak a current to get very positive results. 



"in the control experiment out of 110 eggs 11 per cent showed 

 abnormalities during the period of larval and early tadpole differ- 

 entiation. This unusual percentage of abnormalities makes the 

 results of the experiments somewhat uncertain since it indicates 

 that other factors than the X rays played a part in causing ab- 

 normalities in development in the exposed specimens. 



After exposing a male to the X rays for an hour and ten min- 

 utes and then fertilizing eggs taken from the toad used for the 

 control mentioned above, out of 410 eggs all but 8 per cent devel- 

 oped into normal tadpoles. Of the abnormal specimens one died 

 before completing gastrulation. 



After exposing a female to the X rays for an hour and ten min- 

 utes and then fertilizing the eggs with sperm derived from the 

 control mentioned above, out of 190 fertilized eggs, 14 per cent 

 showed abnormalities. In three eggs gastrulation was not com- 

 pleted, in one a condition of spina bifida appeared, in the others 

 Ihe abnormalities appeared during larval differentiation. 



Out of 376 eggs taken from the exposed female and fertilized 

 by spermatozoa taken from the exposed male 21 per cent showed 

 abnormalities of development. Of the abnormal specimens 27 

 showed marked abnormalities during gastrulation and 52 during 

 larval differentiation. 



So far, therefore, as the experiments go they indicate that 

 exposure of both sex cells before fertilization gives rise to more 

 severe effects than the exposure of either alone and that weak X 

 rays filtered by the tissues affect the female sex cells more than 

 the male sex cells. The experiment must, however, be repeated 

 and extended before definite conclusions are warranted. 



