STUDY OF CELL MECHANICS 477 



R humbler ('96) finds in the growth of the membrane (gestei- 

 gertes Membranwachstum) a factor which assists the asters 

 in cell division. This phase of cell division is more fully elabo- 

 rated in a later paper (Rhumbler '99). 



Zeigler ('98 b) interpreted the swelling of the ectoplasmic 

 layer in ctenophores in a different way, as I pointed out on 

 page 466. 



More recently we have works which approach the problem 

 from the standpoint of physical chemistry. Foremost among 

 these is Lillie's work, who finds that there is a distinct change 

 in the permeability of the cell during each division cycle, and 

 as he points out, this would be accompanied by changes in 

 surface tension (Lillie '16). 



A moment's consideration will show that these three widely 

 differing views on cell division may be united by this study of 

 monaster eggs. The swelling of the ectoplasmic layer is just 

 the same phenomena described by Rhumbler and Zeigler. No 

 where is the "vortical flow of cell substance" more clearly seen 

 than in monaster eggs. And finally the great changes in sur- 

 face tension which monaster eggs undergo indicate a difference 

 in density (and of necessity permeability) on the several sides of 

 the egg. In monaster eggs, however, these phenomena follow 

 each other in regular order, and appear to be due either to a 

 single factor, or several factors working together. Perhaps 

 the whole series of events may be traced to a difference in the 

 density of the protoplasm on the side of the egg opposite the 

 chromosomes in monaster eggs, or to a dense girdle of proto- 

 plasm in the case of normal eggs. Later researches must throw 

 light here. But a distinct advance has been made, I believe, 

 when we are able to harmonize the discordant views of so many 

 investigators, and show, as I think the above analysis does, that 

 they were all dealing with different expressions of the same 

 force. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 24, NO. i 



