AMITOSIS IN CELLS GROWING IN VITRO. 457 



hardly be explained by the assumption of an increased emigration 

 of these forms during the second day; it is more probable that 

 some of these bipartite nuclei have originated in the new 

 growth, and the observation of this process here confirms this 

 conclusion. 



Mitosis, too, cannot account for the formation of these bi- and 

 multipartite nuclei, for in all the cases of mitosis followed through 

 in the living condition the end result has always been two 

 daughter cells, quite separate except for a narrow connecting 

 process, and each containing a single centrosphere. The only 

 theories remaining for consideration are those of nuclear origin 

 de novo, or from chromidial extrusions, and these suppositions 

 are too improbable to discuss here. No other process than that 

 of nuclear amitosis, therefore, can account for the production 

 of bi- and multinucleate cells in the cultures examined. 



Though the amitotically-divided parts of the nucleus seem 

 to possess metabolic independence, as noted, they do not appear 

 to have reproductive independence, for the reason that they are 

 never dissociated one from the other to become the nuclei of 

 separate cells. Furthermore they show only one type of cell 

 division, viz., mitosis, in which the process begins coincidently 

 in the two nuclear parts, manifested by the simultaneous appear- 

 ance in each part of a similar spireme. Although in amitosis 

 there is a mass division of the nuclear material there is no 

 meristic division, and it appears that before a cell containing an 

 amitotically divided nucleus can divide it is necessary that the 

 separated chromatin moieties should recombine. This was done 

 in the specimen examined during life, for the combined product 

 of the two nuclear sacs formed a single equatorial plate of chro- 

 mosomes. Such a type of amitosis, therefore, is not incompatible 

 with the chromosome hypothesis. 



Spiremes in bipartite nuclei, and in dumb-bell-shaped nuclei 

 evidently undergoing amitosis, are not confined to the cells of 

 tissue cultures, for Maximow ('08) has described them in the 

 normally-developing mesenchyme cells of the embryo rabbit, and 

 this author refers to similar cell configurations which Karpow 

 ('04) describes in the leucocytes of urodele amphibia. 



