EFFECT OF RADIUM ON FERTILIZATION 107 



e. The development of eggs normally fertilized, and exposed - 



to radium 



In this series of experiments, the eggs were inseminated and 

 stirred frequently for five minutes, then put over the radium cap- 

 sule, which had an activity equal to 4 mg. of the pure bromide. 

 At intervals a small quantity was taken out, half of the eggs being 

 killed, and half put into sea water and allowed to develop. 



The early stages of fertilization are normal in all respects. The 

 jelly is extruded at once (this began before the eggs were exposed 

 to the radium) and consequentl}' only one sperm enters. The 

 external phenomena of implantation of the sperm and the rising 

 up of the entrance cone are normal. A study of the sections shows 

 that in many cases the fertilization cone does not take the usual 

 dark stain, but remains as a very light, nearly transparent vesi- 

 cle, similar to that described in the second series of experiments, 

 (fig. 15). The sperm enters normally, however, as in the former 

 case. In the meantime tlie polar bodies are normally extruded. 



The first indication of abnormal development is seen in the 

 behavior of the germ nuclei. In many instances these do not fuse, 

 but remain separated, at some distance from each other and inde- 

 pendently develop chromosomes and normal spindles. Figure 

 26 shows an early stage of the process. The nuclear walls are 

 still intact. The sperm nucleus has not developed as far as the 

 egg nucleus, being still in the closely wound spireme stage. The 

 egg nucleus with its aster has moved from its position under the 

 polar bodies, away from the approaching sperm nucleus. Figure 

 24 is a later development. Probably the structure nearer the 

 polar body is the sperm nucleus which has failed to develop much 

 further than the stage shown in the preceding figure. The egg 

 nucleus, however, has lost its nuclear membrane and has formed 

 distinct chromosomes which are not as clear cut as normal, but 

 show some evidence of becoming broken up into granules. Fig- 

 .ure 25 shows a still later development. The nuclei have migrated 

 as far from each other as appears possible and lie between complete 

 and normal asters. In each nucleus the haploid number of 

 chromosomes can be determined. In figure 27 the division has 



