EFFECT OF RADIUM ON FERTILIZATION 109 



with the chromatin, and that the fertilized eggs in the two cases 

 respond in very different ways. 



/. Subsequent development of the embryo 



The great majority of the eggs do not divide. In some cases 

 they may divide into three or four blastomeres at once, as would 

 be expected from the division figures already described. Very 

 few of the eggs continued to divide after ten hours of development. 

 A small number of early trochophores developed but no pigment 

 formed in them, and the cilia were abnormal. No embryos sur- 

 vived after twenty-four hours. 



g. Development of eggs radiated before and after fertilization 

 with normal sperm 



The early phenomena of fertilization in eggs radiated for two 

 hours before fertilization and for varying periods after fertilisation, 

 do not differ to any extent from those described in the second 

 series. In some lots of eggs the alveolar layer is extruded nor- 

 mally in almost every instance, while in other lots it is retained for 

 some time after the implantation of the sperm. In the latter case 

 polyspermy invariably occurs, as many as ten sperms entering 

 at practically the same time and developing at the same rate. 



The mode of entrance of the sperm in either case is the same as 

 that described in the second series. In many instances the fer- 

 tilization cone is an almost transparent vesicle. But, as in the 

 previous cases, this change in the staining reaction does not indi- 

 cate any change in function, for the spermatozoon is drawn in 

 normally, and the whole process is without any other indication 

 of abnormality. The further development of the sperm head is 

 normal. The head and cone revolve, and an aster forms at the 

 base of the head. The chromatin, as the head enlarges, collects 

 into a few karyomeres. But the number of vesicles which contain 

 these structures may be very large. In some eggs there may be 

 as many as forty, indicating that each sperm has broken up into 

 at least four. Their subsequent development will be described 

 after the behavior of the egg nucleus has been traced. 



