EFFECT OF RADIUM ON FERTILIZATION 95 



the usual attachment granules. The cone itself develops normally, 

 and its behavior in drawing in the spermatozoon is normal. 



When the sperm head is in the process of being drawn in by the 

 fertilization cone the first abnormality makes its appearance. 

 The chromatin of the head, instead of forming an unbroken band, 

 as in the normal process may now become broken up into irreg- 

 ular masses (fig. 6) . Occasionally, in the normal sperm head as it 

 is drawn through the egg membrane, one finds some evidence 

 of segmentation, but in no case is there so marked a breaking 

 up of the chromatin as is found here. About 10 per cent of the 

 eggs show this abnormality. 



From this stage the subsequent behavior of the sperm heads 

 may differ. The further entrance and development of the sperm 

 nucleus may be normal, or the sperm may entirely fail to gain 

 further entrance. In the first case, the sperm head, preceded by 

 the fertilization cone, penetrates further into the egg, revolving 

 meanwhile. After complete revolution the sperm aster develops. 

 The division of the sperm centrosome was found in only a few 

 instances, but was normal when found. The chromatin becomes 

 vacuolated and later forms into the haploid number of karyomeres. 

 At this stage it may normally fuse with the egg nucleus, or else 

 undergo a curious development which results in its failure to fuse 

 with the latter. When fusion occurs the cleavage nucleus divides 

 normally with twenty-eight chromosomes present. There is, 

 then, either a complete fusion with subsequent normal division, 

 or else no fusion at all, and no division of either germ nucleus. 



In the latter instances the germ nuclei remain in the karyomere 

 stage. The sperm asters which at first are present now gradually 

 dwindle and finally disappear altogether. Figure 7 illustrates this 

 point. The two asters are hardly as large as the smaller of the 

 original sperm asters. At this time the egg aster has normally 

 disq,ppeared. This case and others to be described are not due to 

 polyspermy, for such eggs are readily recognizable. The number 

 of karyomeres present also shows that only one sperm has entered. 

 Figure 8 shows an egg in which no trace of astral radiations can be 

 found. There are many such eggs in the preparations. The 

 action of the radiation on the sperm, then, has been to prevent 



