THE BIOLOGY OF THE CELL SURFACE 



in cells generally, if we can base these conclusions only on 

 the nuclear behavior and state of sea-urchins' eggs. 



Besides, as I stated above, many cells lack asters, many 

 others lack well-defined centrospheres though they possess 

 asters. Certain eggs, such as those of Ascaris^ of Ciona, 

 of Phallusia, of Amphioxus, etc., have no asters at the 

 spindle-ends in the maturation-divisions. Yet they divide. 

 Many plant-cells go through mitotic division; their mitotic 

 figures are without asters. Asters and centrospheres are 

 not essential for mitotic divisions. 



Also we should not forget that in many eggs repeated 

 mitotic divisions ensue without cleavage of the cyto- 

 plasm. Take eggs of insects, for example: many nuclear 

 divisions ensue before the cytoplasm divides. Nuclear 

 division without cleavage of the cytoplasm is not limited 

 to eggs. It obtains among unicellular animals and among 

 multicellular, including man, and among plants, in such 

 protoplasmic systems that contain many nuclei, the syn- 

 cytia. That nucleus and cytoplasm may divide a-syn- 

 chronously constitutes the strongest evidence against the 

 proposition that in mitosis lies the cause for the sundering 

 of the cytoplasmic mass. 



Finally, an explanation of cell-division founded upon the 

 mitotic complex as a whole or upon any component of it, 

 falls to the ground for it can not encompass division of 

 cells whose nuclei divide amitotically. Whatever the 

 biological significance of amitosis, be it a primitive or a 

 degenerate process, undubitable cases of amitosis are on 

 record. Whatever the conditions responsible for its occur- 

 rence, we must reckon with this as fact. Even if the 

 mitotic complex were always uniform and cell-division 

 with mitosis were identical in all cells, we still could not 

 explain by reference to mitosis the division of the cell-mass 

 where amitosis prevails. 



266 



