4O2 EDWIN G. CONKLIN. 







and where every chromosome may give rise to a separate chromo- 

 somal vesicle (Fig. 7). As the cell passes into the resting phase, 

 these vesicles fuse together more or less completely, giving rise 

 to vesicles of varying sizes. Other things being equal, the 

 later the stage in the resting period the smaller the number of 

 separate vesicles. If the separate vesicles were formed by divi- 

 sion of an originally single vesicle, exactly the reverse would be 

 the case. 



2. The presence of centrospheres and spindle remnants in 

 many cases shows conclusively that division has taken place 

 by mitosis, and the position of these structures indicates the 

 location of the mitotic figure (Figs. 8-12 ~et seq.}. 



3. The elongation of daughter nuclei in the position of the 

 plate of daughter chromosomes of normal division figures indi- 

 cates that such elongated nuclei are formed by the partial 

 fusion of the chromosomes of the daughter plate (Figs. 4-6). 



These considerations make it absolutely certain that these 

 peculiar nuclear forms are due to a partial or incomplete union 

 of chromosomes into a single nuclear vesicle in the final phase of 

 mitosis; they represent modified mitosis and not amitosis. 

 And it is practically certain that many of the cases of so-called 

 amitosis described by several of the authors mentioned above 

 are of this same character. 



It is not easy to determine exactly the mechanism by which 

 these modifications have been produced. As already mentioned 

 they may be caused by abnormally high temperature (Figs. 1-12) 

 or by hypertonic sea-water (Figs. 19-29). It is well known that 

 when the daughter chromosomes approach the poles of the 

 spindle they are normally closely crowded together and it seems 

 probable that this is due to linin connections within the spindle 

 or between the chromosomes. In the development of the daugh- 

 ter nucleus each chromosome absorbs achromatic material 

 from the cytoplasm and becomes a vesicle with chromatic walls. 

 The material thus absorbed is probably chiefly water though it 

 doubtless contains dialyzable proteins and other substances 

 which may be assimilated into the chromatin and linin of the 

 nucleus. It is probable that there is a real membrane sur- 

 rounding each chromosome (Conklin, 1902, 1912) and that the 



