CELL-DIVISION 



surface which accompany cell-division. They are also 

 well defined in other living cells when freshly dissected out 

 of the organism. We need not, therefore, confine our 

 explanation of cell-division to eggs of sea-urchins. We 

 dismiss as cause for cell-division division of the nucleus, by 

 mitosis with or without asters, and by amitosis, whether 

 occurring simultaneously with cytoplasmic division or not, 

 since no constant relation between nuclear division and that 

 of the cell-body can be established. Since not all cells are 

 spherical and not all spherical ones elongate during the 

 cycle, we dismiss also elongation of the cell as a factor. 

 Movement in the cytoplasm depends upon ectoplasmic 

 activity; it is thus not a primary factor. There remains 

 the ectoplasm found in all cells. 



Cells do not extend indefinitely into space. They possess 

 surfaces. Cell-division means that one cell becomes two 

 by the rise of a new partition. Does this arise within the 

 cytoplasm or does it come about through the extension of 

 the ectoplasm inward .^ Until we know more concerning 

 the origin of cleavage by cell-plates, we may only hazard 

 conjectures as to the formation of cell-walls within the 

 cytoplasm as found in plants. For animal cells, generally, 

 we must seek the cause of cell-division in ectoplasmic 

 activity. 



28' 



