NUCLEAR DIVISION. 5 



the nucleus, which stain deeply, closely resembling the chromatin 

 granules. In the meantime the chromosomes increase in size, and it 

 seems reasonable to suppose that the nucleolar substance contributes 

 materially to their growth. The development of the nucleolus in the 

 daughter nucleus and its behavior during the following, or second 

 mitosis, seem to strengthen this theory. The chromosomes, when 



FIG. a. Spindle and telophase of first mitosis in the tetraspore mother-cell of Dictyota dickotoma. 



E, spindle nearly mature ; nuclear membrane has disappeared at poles. 



F, mature spindle ; the small lumpy chromosomes are regularly arranged in equatorial plate ; nuclear 



membrane persists at sides. 



G, daughter nuclei still connected by strand of connecting fibers ; at poles of each nucleus is a well- 

 developed centrosphere. 



arranged in the equatorial plate, appear, especially when crowded to- 

 gether a phenomenon of frequent occurrence as rounded lumps 

 (Fig. 2, E, F). A careful study in favorable cases shows clearly that 

 each chromosome is either in the shape of a ring, or so contracted as 

 to leave scarcely any central space, such, for example, as occurs in 

 some higher plants (Podophyllum, Helleborus} . In such cases each 



