FERTILIZATION ON PARTHENOGENESIS. 157 



difference between sperm within the cytoplasm and those re- 

 maining outside the egg but in contact with the surface is the 

 absence of a tail. No tail has ever been observed within the 

 cytoplasm of these eggs. 



Thirty minutes after insemination we see no evidence of any 

 change on the part of the sperm within the egg. The egg nucleus 

 however has begun to change somewhat. The nuclear wall has 

 disappeared in some and chromosomes are definitely formed 

 usually lying scattered, or more aggregated in the cytoplasm. 

 Slight radiations have begun to appear centering indistinctly 

 near the nucleus or chromosomes. In a few eggs, the per- 

 centage increasing at a later stage, chromosomes are dispersed 

 along the rays that diverge from the center of the egg. Prac- 

 tically no amphiasters have ever been found in these series. 1 



During all this change on the part of the egg pronucleus the 

 sperm heads have given not the slightest indication of any 

 change. They lie in the cytoplasm very much as if they were 

 foreign bodies. 



From Hindle's cytological study of artificial parthenogenesis 

 in Strong! yocentrot us purpuratus 2 we know that essentially the 

 same nuclear changes are present after butyric acid treatment 

 alone that we have in the above lot of eggs. Monasters are 

 formed but not amphiasters. And in the absence of any indi- 

 cation of a reaction due to the presence of sperm we necessaiily 

 must conclude that these changes have been induced as a result 

 of the butyric acid treatment and not by the effect of sperm. 

 There has been no fertilization; the character of the egg has 

 become changed to such an extent that no activation whatever 

 so far as one may judge from experiments and sections, has been 

 effected by the spermatozoon. The ovogenous substance has 

 once been activated (i. e., by butyric acid) and further activation 

 by sperm is just as impossible as it is after normal fertilization. 



B. Over-Exposure to Butyric Acid Partial Fertilization. 

 Again referring to the curve of fertilization we notice that 

 exposure to butyric acid slightly above the optimum does not 



1 In one series of preserved eggs, two containing amphiasters were found; but 

 the control of the experiment eggs inseminated without the membranes being 

 destroyed showed 6 per cent, of cleavages. 



2 Archiv. fur entV Mech., Bd. 31. 



