EFFECT OF RADIUM ON DEVELOPMENT OF CH.ETOPTERUS- 57 



matin follows the shape of the nuclear vesicle; a little is still in the 

 polar position. This condition prevents the egg nucleus from 

 flattening out against the sperm nucleus. The latter is seen 

 normally developed with its astral rays extending far out into the 

 protoplasm. 



A more pronounced case of the same sort is seen in Fig. 4. 

 Here the egg nucleus has hardly moved at all but has developed 

 in approximately its original position. Its inner end has come 

 under the influence of a sperm aster, and some of its chromatin is 

 evidently polarized. Its outer end is attached to the second 

 polar body by chromatin threads and the whole nucleus has the 

 appearance of being anchored to it. 



Modifications of this condition are seen in the polyspermic egg 

 shown in Fig. 5. Most of the egg nucleus has migrated away 

 from the pole but a small piece about the size of a single chromo- 

 somal vesicle is still attached to the second polar body by deli- 

 cate strands. Two sperms have entered; one of them has en- 

 tirely fused with the egg nucleus, and the other is about to fuse. 

 Only three asters can be found in this case. In Fig. 6 two sperms 

 have fused with the egg nucleus which, as in the preceding case, 

 is still attached to the polar body. Five asters can be found in 

 connection with this cleavage nucleus. The number of instances 

 in which three or five asters appear make it evident that the 

 original egg aster may persist. 



A final stage showing how the egg nucleus in the vesicular con- 

 dition may fail to fuse normally with the sperm nucleus appears 

 in Fig. 7. The latter nucleus is about fully grown and its asters 

 are well developed. The egg nucleus is developed only in part. 

 The two small vesicles contain numerous chromatin granules. 

 Between them the remainder of the egg chromatin lies free in the 

 protoplasm in the form of rods and spheres. These masses are 

 not chromosomes for they have not the typical size or appearance. 

 The curious positions which they have assumed indicate that the 

 force drawing them inward is not normal. 



Those eggs which were radiated for periods up to 25 minutes 

 do not show many of the abnormalities just described. In such 

 eggs the pronuclei develop normally to all appearance and fuse 

 with each other. The first indication that any injury has been 



