438 CHARLES RUSSELL BARDEEN 



were fertilized they were more deeply affected by the X ray 

 sperm than are normal ova. Unfortunately my notes on the 

 control of this experiment were misplaced before the marked 

 difference between this lot of eggs and other lots fertilized by 

 exposed sperm was noted. In cases in which development ceased 

 in the late cleavage stages the cleavage cavity was, in the eggs 

 examined, of at least normal size. Hertwig, 1910, has found that 

 long exposure of the sperm of sea urchins and amphibians to 

 radium gives rise to disturbances manifest in the early cleavage 

 stages. 



3. Gastrulation 



In most of the experiments all of the eggs externally appeared 

 normal during the period of gastrulation. In three experiments 

 marked abnormalities appeared during this period in some of 

 the eggs. The percentage of eggs thus affected was much the 

 greatest in the atypical experiment mentioned above, (Expt. 2.) 

 In this experiment in 9 . 1 per cent of the eggs gastrulation was 

 abortive and development ceased after the production of a large 

 blastopore through which a large yolk mass protruded, (figs. 1, 

 6, and 7, plate 1). In 0.7 per cent of the eggs a hemi-embryo 

 was formed similar to those artificially produced by Roux and 

 others by injuring one of the blastomeres in the two cell stage, 

 (figs. 4 and 5). In 12 .2 per cent of the eggs more or less typical 

 spina bifida specimens were produced similar to those produced 

 by Hertwig and others in eggs placed in NaCl solutions, (figs. 

 2 and 3). Marked abnormalities of this kind were much rarer 

 in the other two experiments mentioned. In one of these. Experi- 

 ment 4,0.5 per cent of the eggs produced hemi-embryos and . 1 

 per cent of the specimens were of the spina bifida type. In the 

 other experiment (Expt. 8,) 1.7 per cent of the specimens showed 

 an irregular cap of cells surmounting a protruding yolk mass. 



In a considerable number of instances in all of the experiments 

 eggs which on external appearance seemed normal during the 

 period of gastrulation, internally suffered more or less well 

 marked abnormalities of structure. In the atypical experiment, 

 (Expt. 2,) 11.7 per cent of the eggs ceased development soon 



