Rhodes: Binary Fission in Collodictyon triciliatum Carter 227 



only the chromatin encrusted upon the nuclear membrane remains 

 outside of it. As to the behavior of this peripheral chromatin, there 

 is some doubt. It may pass into solution and become a part of the 

 metaphase chromosomes, or spread out upon the nuclear membrane, 

 making this appear heavier and darker, or it may be extruded into 

 the cytoplasm. There is an indication in a few individuals of a 

 peculiar splitting of peripheral encrusted chromatin bodies (pi. 11, 

 fig. 46). I can not verify this as a regular occurrence nor can I 

 regard it as typical. This splitting is prior to the metaphase and 

 may be closely correlated with the precocious splitting of the seg- 

 mented spireme (pi. 12, fig. 47). 



The microkaryosome elongates and divides, the separation being 

 characterized by connecting fibrils somewhat resembling spindle 

 fibers, rather than a dumb-bell constriction as in differential division 

 of the primary karyosome (pi. 10, figs. 34, 35, 36). A chromatin cloud 

 forms immediately around this elongating microkaryosome and fills 

 up the intervening space, almost obliterating the fibers (pi. 11, figs. 37, 

 38). This cloud expands until the whole area within the kinetic 

 membrane becomes diffusely filled with fine granules. 



This early microkaryosome organization is exceedingly complex 

 for microscopic analysis, but it soon becomes evident that instead of 

 having divided simply into two masses, the microkaryosome is under- 

 going a segmenting process (pi. 11, 'figs. 39, 40, 41, 42, 44, 45), pre- 

 liminary to a final prophase spireme (pi. 12, fig. 47). The first division 

 is followed by a second elongation of each mass, apparently passing 

 through a tripod and ring stage, in time forming two crescentic 

 masses or a segmented skein (pi. 11, figs. 40, 41, 42, 44). This retains 

 terminal chromatin masses or knobs which probably form the basic 

 elements of the future chromosomes. The next phase is a longitudinal 

 splitting of each segment (pi. 11, fig. 45). If all terminal knobs 

 divide at this time, eight chromatin masses would result and this 

 would probably determine the correct count of chromosomes. It is 

 possible that one of the four terminal knobs fails to divide, and this 

 would give but seven chromatin masses as many chromosomes as I 

 have been able to count (pi. 12, fig. 50). Such a phenomenon is 

 common in mitoses of higher animals (Wenrich, 1916; Carothers, 

 1917), but it must be admitted that the evidence here is not con- 

 clusive (pi. 11, fig. 45). The middle and final prophase stages are 

 characterized by an active organization of chromatin upon the 

 segmenting skein. That there is some chromatin in the original 



