412 EDITH PINNEY 



The whole phenomenon is one that is concerned with develop- 

 mental rather than with hereditary factors. 



If, as was originally suggested by Biitschli (18, 2), protoplas- 

 mic currents are concerned in the movements of chromosomes, 

 we might have in the specific character of such currents the 

 physical factor necessary to regulate chromosome division in these 

 cases. The results of Chambers (3) and Heilbrunn (6) are highly 

 suggestive in this connection. Both of these workers have 

 demonstrated changes in the viscosity of the cell protoplasm 

 during mitosis. Specific viscosity differences in the eggs at the 

 anaphase period may cause the abnormal division of chromo- 

 somes occurring in some heterogeneric hybrids. The conditions 

 of viscosity that prevail during the cleavage of these hybrids are, 

 I believe, the normal conditions always present in the egg and 

 are not deviations from the normal caused by the foreign sperm. 

 I infer this from the fact that the egg cytoplasm exerts a differ- 

 ential effect toward the two sorts of chromosomes which it con- 

 tains. The egg chromosomes divide normally. The sperm 

 elements show abnormal behavior. 



There are two exceptions to this. Doncaster and Gray (4) 

 consider that the abnormally behaving chromatin in the cross 

 Echinus acutus 9 X Echinus esculentus cf is of maternal ori- 

 gin. The phenomenon described by them for that cross, how- 

 ever, is of an apparently different nature and need not be con- 

 sidered in this category. The other exception occurred in the 

 cross, Arbacia 9 X Toxopneustes cf , in which Tennent (16) 

 observed the ehmination of chromosomes of both species from 

 the nucleus. These eggs were, however, given rather drastic 

 treatment to cause penetration of the foreign sperm. The eggs 

 stood in sea-water for four hours and were then treated with 

 alkahne sea-water. If this treatment in any way changed the 

 egg cytoplasm, the results are no longer inconsistent, but follow 

 the expectations of the hypothesis expressed here. The point 

 could be tested perhaps by self-fertiHzing Arbacia eggs treated 

 in the same manner. 



