58 CHARLES PACKARD. 



done to the egg chromatin appears at the anaphase of the first 

 cleavage. Fig. 8 shows an egg in which this is the case. There 

 has not been a complete mingling of the two nuclei for the egg 

 chromosomes are left behind in the future cleavage plane. They 

 are for the most part normal in appearance. One is stretched 

 out to an unusual length as though pulled at each end by a 

 spindle fiber. If this is the case, the spindle-fiber attachment is 

 unusual for here it is evidently terminal while in the normal 

 chromosomes it is median. The nine sperm chromosomes in 

 each group show the characteristic V-shape. Division is thus 

 regular and haploid, and the injured egg chromosomes have not 

 interfered with the oiderly division of the egg. 



A more noticeable injury to the egg chromatin is seen in Fig. 9. 

 Here again the nuclei probably fused normally to all appearances. 

 But at the anaphase, when the sperm chromosomes are moving 

 towards the poles, the egg chromatin is left behind in a very con- 

 fused condition. A few chromosomes have formed but they are 

 noticeably beaded as though on the point of breaking up into 

 fine granules. The remainder of the chromatin is in irregular 

 masses. Possibly its position outside of the spindle accounts for 

 the fact that the chromosomes show little sign of being drawn 

 towards the poles. No spindle fibers can be found attached to it. 



When the nuclei have failed to fuse, as shown in Figs. 3 and 4, 

 the further growth of the egg nucleus is greatly modified. In Fig. 

 10 the chromatin is seen to be condensed into rods and irregular 

 masses which lie wholly outside of the mitotic spindle. The 

 rod-shaped masses are beaded. Only a few of the chromosomal 

 vesicles could have migrated inward. 



A polyspermic egg in which the same type of abnormality is 

 found is shown in Fig. n. From the distribution of the chro- 

 matin it may be inferred that this condition is a further develop- 

 ment of such an egg as is shown in Figs. 5 and 6. It is interesting 

 to note that the egg chromatin which shows the greatest sign of 

 injury remains nearest to the pole. The more normal chromatin 

 has migrated inwards. The sperm chromosomes which are dis- 

 tributed very irregularly are of normal shape and size. 



These observations show that when the unfertilized eggs are 

 radiated for periods up to 30 minutes before insemination, the 



