162 Harry Lewis Wieman. 



in the nuclei, amitosis is here certainly concerned with cell multi- 

 plication. This protracted form of cell division is quite different 

 from Preusse's descriptions, nor is it necessarily at variance with 

 the observations of other authors ; for unless a continuous series of 

 stages are studied, it would never be suspected that the amitotic 

 divisions which are at first confined to the nucleus, later extend 

 to the cytoplasm. 



The striking feature of the amitotic figure is the fact that the 

 nuclear membrane does not disappear, but remains intact through- 

 out the entire process of division. This fact together with the 

 staining reactions serves to throw some light on the fundamental 

 difference between mitosis and amitosis. 



It has long been recognized that the dissolution of the nuclear 

 membrane is in some way associated with a well defined alteration 

 in the capacity of the egg for further development. From the 

 observations of Delage ('01), it would appear that the essential 

 feature of maturation is not so much the separation of the polar 

 bodies as the removal of the barrier between the nuclear and cyto- 

 plasmic areas. The critical event which causes a change in the 

 cytoplasm is the passage of nuclear constituents into it. The 

 result may be a change in the osmotic pressure of the cytoplasm 

 or in its rate of oxidation. Delage also observed that enucleated 

 egg fragments of Asterias are incapable of fertilization before the 

 germinal vesicle has broken down, but that very soon after the 

 membrane shows signs of dissolution, merogonic cleavage becomes 

 possible. 



In his study of the karyokinesis of the Crepidula egg, Conklin 

 ('02) arrived at conclusions which are important in this connec- 

 tion. ''The nuclear membrane appears to permit the passage 

 of materials inward, but not outward during the resting period, 

 whereas the escape of nuclear material into the cell is brought 

 about by the disappearance of the membrane during karyokine- 

 sis. " He also determined cy tologically ' ' a very extensive exchange 

 of material between the nucleus and cytoplasm. A large part of 

 that most characteristic nuclear substance, the chromatin, passes 

 into the cytoplasm during every cell cycle, while a relatively 

 small part is reserved for the purpose of reproducing the daughter 



