96 CHARLES PACKARD 



not only its own development, but that of the egg nucleus also. 

 The number of vesicles and karyomeres differ considerably. 

 Normally there should be at most four or five vesicles with 

 twenty-eight karyomeres. Frequently the number of vesicles 

 may be as high as twenty. The appearance of such eggs recalls 

 the condition described by Lillie ('02) in the fertilized egg of 

 Chaetopterus which had been treated with KCl solutions of vary- 

 ing concentrations. He found that the nucleus broke up into 

 many fragments which were distributed irregularly through 

 the protoplasm, and were never gathered up into a single nucleus 

 again. Each particle of chromatin was surrounded by a vacuole 

 of liquified protoplasm. The appearance is similar in many 

 respects to that found in Nereis, although the mode of formation 

 of the vacoules is entirely different. Whether both of the germ 

 nuclei are concerned in this process or only one, cannot be defi- 

 nitely settled. The presence of no extra asters shows that if the 

 sperm nucleus has divided the chromatin only has been con- 

 cerned. In view of G. Hertwig's experiments on the sea urchin, 

 in which the egg nucleus divided without fusing with the sperm 

 nucleus, it seems reasonable to suppose that in Nereis also the egg 

 nucleus divides by itself. But here the division is very abnormal, 

 being due to something evidently brought in by the sperm. 



The second class of abnormalities is caused by the failure of the 

 sperm nucleus to enter the egg. There is always a fairly large 

 number of abnormalities of this type in material treated in the 

 way indicated, and each egg presents practically the same appear- 

 ance. It should be mentioned at the outset that this condition 

 is found, though rarely, in the controls. 



Although the spermatozoa that have been radiated are as active 

 as those in the controls yet some of them fail to effect a complete 

 entrance into the egg. The actual attachment of the spermato- 

 zoon is undoubtedly due to its own activity, but its subsequent 

 entrance into the protoplasm of the egg is due to the activity of 

 the egg itself. It may be inferred, therefore, that the sperm does 

 not, in these cases, call out the proper stimulus for the complete 

 reaction. The egg is able to draw the sperm head in for a short 

 distance only. The details of the entrance of such a sperm are 



