246 University of California Publications in Zoology [Vol. 19 



Promitose vor. " Plemming (1882) suggested the terms, "amitosis" 

 and "mitosis," and defined the former as a nuclear division without 

 formation of chromosomes and a spindle, while in mitosis these are 

 more or less evident. Nagler (1909, p. 46) thinks amitosis would be 

 better characterized "durch die unregelmassige Durchschnurung des 

 Kernes (Fragmentierung)." He concludes that an extreme instance 

 of amitosis is not known in the Protozoa, instances so interpreted, with 

 division of centriole within the karyosome and the apparent division of 

 the whole chromatin mass, being more analogous to mitosis than amitosis. 

 Chatton (1910) distinguished three types of mitosis, which, as he 

 characterized them, may be analyzed as follows : 



Promitosis. — (Protokaryon type of nucleus, consisting of a fundamental 

 mass of plastin, impregnated with chromatin, and containing a centriole). 



1. Nuclear membrane is persistent and division is intranuclear. 



2. Karyosome is the equivalent, morphologically and physiologically of the 

 centrosome. 



3. Equatorial plate (chromosomes?) organized from peripheral chromatin 

 material. 



4. Chromatin is not distributed equally by the nuclear mechanism. 



5. Achromatic separation fibers are apparent when the karyosome divides. 



Thus all essential elements and the primitive substances, except 

 peripheral chromatin (which may be most important), are condensed 

 within the karyosome. In higher forms of mitosis these tend to 

 separate. "In proportion as the karyosome loses its plastin and 

 chromatin elements, and becomes reduced to the centriole alone, so the 

 primitive promitosis will approach more and more to the type of an 

 ordinary mitosis" (Minchin, 1912, p. 110). This reduction of the karyo- 

 some may be either temporary, taking place only during the process of 

 mitosis, or permanent, as is characteristic of higher types of mitosis. 



Mesomitosis. — 



1. Nuclear membrane persistent and division intranuclear. 



2. Centriole, more or less separated from the karyosome, rests within the 

 nucleus. 



3. Chromosomes derived from the karyosome. 



4. Chromosomes (equatorial plate) organized upon a spindle. 



5. Plastin is reduced or disappears. 

 Metamitosis. — 



1. Nuclear membrane disappears during process of mitosis, the mitotic figure 

 resting in the cytoplasm. 



2. Centriole, separate from the karyosome, may be intranuclear (as in 

 Pelomyxa), but is generally extranuclear. 



3. Evident chromosomes splitting longitudinally upon an equatorial plate. 



4. "With the zones of differentiated, surrounding cytoplasm the centriole 

 forms the centrosome. Polar asters are usually present. 



