EFFECTS OF INJURY UPON SPERM. 253 



Lillie's experiments by the removal of the sperm cell at this stage. 

 Since the formation of attachment granules and a fertilization 

 cone is not in itself necessary for membrane formation, matura- 

 tion and other visible cytoplasmic changes, as is shown by my 

 experiments, and since their presence without the sperm head, 

 does not lead to a greater visible change than does their absence, 

 there is good reason to believe that they function solely in the 

 attachment, penetration, and revolution of the sperm head. 

 After these functions have been performed they cannot be 

 traced much farther. They are probably dedifferentiated and 

 behave as ordinary cytoplasm. I am inclined to think that in 

 Nereis the mere penetration of the egg cytoplasm by the sperm 

 head is insufficient although the observations on this point are 

 not entirely satisfactory. The experiments of Ziegler ('98) and 

 Wilson ('03) support this view. Ziegler succeeded in producing 

 a constriction in the egg of the sea urchin in such a way that it 

 separated the egg nucleus from the sperm nucleus. The part 

 containing the sperm nucleus segmented. The remainder failed 

 to segment, but gave indication that the presence of the sperm 

 nucleus was not without effect, by dissolving and reappearing 

 several times. 



Wilson cut the eggs of Cerebratulits in two, shortly after the 

 penetration of the sperm cell. When the cut separated the two 

 nuclei the part containing the sperm nucleus segmented and the 

 other part formed polar bodies but refused to cleave. 



Even in cases where the germ nuclei of Nereis copulate there 

 is not necessarily a complete stimulus to development. F. R. 

 Lillie thinks that the partial sperm nuclei produced by centri- 

 fuging at the proper time do not cause normal cleavage. Some- 

 times a partial cleavage results and sometimes cleavage ceases 

 in the two-cell stage. In my experiments many eggs either 

 attempted to cleave and failed or stopped after cleaving once. 

 This indicates that the mere presence of the germ nuclei is 

 insufficient as an internal stimulus for development. The normal 

 interchange between the nucleus and cytoplasm is not neces- 

 sarily brought about. Although the nucleus of the sperm 

 succeeds in producing aster formation yet the rate of metabolism 

 is so low that normal cleavage cannot take place or can take place 



