452 CHARLES RUSSELL BARDEEN 



tilized although the subsequent effects of irradiation were marked, 

 indicates quite clearly that irradiation of mature eggs has little 

 or no effect on their capacity for fertilization. 



2. Period of cleavage 



The early cleavage stages appeared to be normal. No speci- 

 mens were seen to stop segmenting early, as in the case of the 

 two atypical experiments with exposed sperm. (See Experi- 

 ments 2 and 7, table 1.) We have, however, seen reason to be- 

 lieve that in the latter the effects were due to other causes than 

 irradiation. 



3. Period of gastrulation 



In a considerable number of instances, 5 . 7 per cent in Experi- 

 ment 6, and 9 per cent in Experiment 7, gastrulation did not ad- 

 vance far and left a mass of yolk protruding through a large blas- 

 topore. Some of these specimens were very abnormal. Similar 

 forms were found in two of the experiments on the exposure of 

 sperm, but in considerable numbers merely in the atypical Expe- 

 riment 2, table 1, in which they formed 9.1 per cent of the 

 fertilized eggs. 



In Experiment 6, table 2,1.3 per cent of the ova gave rise to 

 hemi-larvse, and in Experiment 7, 2 . 3 per cent. This percentage 

 is larger than that found in either of the two experiments with 

 the exposed sperm which resulted in the production of forms of 

 this character. 



In Experiment 6, table 2, 17 per cent of the ova developed into 

 more or less highly differentiated types of spina bifida, and in 

 Experiment 7, 6.2 per cent. Spina bifida specimens were found 

 in two of the experiments on exposure of the sperm, but in con- 

 siderable numbers only in the more atypical one. Experiment 2, 

 table 2. 



In Experiments 1 and 2, table 2, no eggs, and in Experiments 

 3 and 5, but few eggs ceased development before the completion 

 of gastrulation. In Experiment 4 a very large percentage of 

 eggs ceased development during gastrulation or showed marked 



