1919] Rhodes: Binary Fission in Collodictyon triciliatum Carter 247 



Chatton thus emphasized or summarized three categories : 



1. Division center within the karyosome (nuclear membrane persistent, 

 chromosomes organized from peripheral chromatin). 



2. Division center outside the karyosome, but within the nucleus (nuclear 

 membrane persistent, the karyosome organizing the equatorial plate). 



3. Division center extranuclear (nuclear membrane disappears, chromosomes 

 organized from nuclear chromatin). 



Collodictyon falls into none of these categories. This system is 

 based upon Amoeba and can not be extended without modification to 

 include the typical polymastigote type of mitosis, in which the nuclear 

 membrane is persistent and the division center extranuclear. Analysis 

 of the mitotic phenomena of Collodictyon may be correlated and 

 summarized here. 



1. The unequal constriction or differential division of the karyo- 

 some into microkaryosomes and macrokaryosomes, which differ at least 

 in behavior. The microkaryosome organizes directly into the segment- 

 ing skein. The macrokaryosome is: (a) extruded from the nucleus 

 and absorbed into the cytoplasm, producing an extranuclear chromidial 

 cloud ; or ( 1) ) distributed as a unit to one of the daughter nuclei ; or 

 (c) is absorbed in the intranuclear cloud and probably is involved in 

 chromosome organization. These two derivatives seem to offer good 

 examples of so-called trophochromatin and idiochromatin. 



2. The presence of an extranuclear centrosome. Intranuclear 

 chromatin cloud. 



3. The presence of a paradesmose. 



4. Nuclear membrane persistent. 



5. Successive separation of promitotic segmented skein. Indication 

 of a precocious splitting of the peripheral chromatin granules of the 

 nucleus. Evident precocious splitting of final segmented skein in 

 prophase. 



6. A well defined intranuclear spindle (of mantle-fibers). No 

 extranuclear astral rays. 



7. Definite chromosomes, organized upon equatorial plate, probably 

 derived from chromatin of the microkaryosome and the intranuclear 

 chromatin cloud formed by the going into solution of the peripheral 

 chromatin granules and probably the macrokaryosome. 



8. Apparent transverse splitting of the chromosome in metaphase. 

 That it is impossible to use Chatton 's categories, unmodified, will 



inevitably be concluded from only a slight survey of protozoan mitosis. 

 If emphasis be laid upon the division-center, accepting this as the 



