SUSCEPTIBILITY OF AMPHIBIAN OVA TO X-RAYS 453 



abnormalities in the process. In this lot the female was pithed, 

 the abdominal cavity opened and some eggs were removed several 

 hours before exposure so that the eggs remaining in the abdominal 

 cavity at the time of exposure were probably somewhat injured. 

 The current used was weaker than in Experiments 6 and 7. 



Many .specimens in which externally gastrulation appeared 

 normal, and in which the yolk was completely covered by pig- 

 mented cells, undoubtedly internally deviated markedly from the 

 normal course of development. Of the specimens of this char- 

 acter a considerable number (see Experiments 3-7, table 2), 

 ceased development as soon as the blastopore was closed, while 

 others made abortive attempts at larval differentiation before 

 dying. In the experiments with exposed sperm specimens ceas- 

 ing to live as soon as the blastopore was closed were found only 

 in the atypical Experiment 2, table 1, where they formed 11.7 

 per cent of the total number of eggs fertilized. For a description 

 of the internal changes in eggs of this tj^pe see the description 

 of this latter experiment. 



4. Period of larval differentiation 



(a) Early stages. In Experiment 6, 35.6 per cent of the fer- 

 tilized eggs ceased developing after giving rise to abnormal forms 

 without distinct heads or tails; in Experiment 7, 21.5 per cent; 

 in Experiments 3, 4 and 5, 24 . 7 per cent, 26 . 8 per cent and 38 . 3 

 per cent respectively. In the experiments with the exposed sperm 

 in which the proportion of abnormal forms of this type was deter- 

 mined the number was found to be less than 10 per cent of the 

 fertilized ova, except in the atypical Experiment 2, table 1, in 

 which the number reached 20 per cent. The types of abnormal- 

 ities corresponded with those described in connection with the 

 sperm experiments. 



(6) Later Stages. In Experiment 6, 34.9 per cent, and in 

 Experiment 9, 48 per cent of the fertilized eggs developed into 

 monstrous forms in which rudiments of the heads and tails were 

 fairly distinct. In Experiments 3, 4 and 5, 36.4 per cent, 31 

 per cent and 40 . 2 per cent respectively. In Experiment 2, 50.9 



