124 PROTOZOOLOGY 



further in C. anodontae, C. curtus, C. magna (Kidder), Uro- 

 centrum turbo, Colpidium colpoda, C. campylum, Glaucoma 

 scintillans (Kidder and Diller), and Allosphaerium convexa 

 (Kidder and Summers). Kidder and his associates beheve that 

 the process is probably eHmination of waste substances of the 

 prolonged cell-division, since chromatin extrusion does not take 

 place during a few divisions subsequent to reorganization after 

 conjugation in Conchophthirus mytili and since in Colpidium and 

 Glaucoma, the chromatin elimination appears to be the cause of 

 high division rate and infrequency of conjugation. 



Other examples of amitosis are found in the vesicular nuclei 

 in the trophozoite of Myxosporidia, as for example, Myxosoma 

 catostomi (Fig. 54), Thelohanellus notatus (Debaisieux), etc., in 

 which the endosome divides first, followed by the nuclear con- 

 striction. In Streblomastix strix, the compact elongated nucleus 

 was found to undergo a simple division by Kofoid and Swezy. 



tf^^-j/^^ W^'^W^ f^^^^^H ffr'M^'^0 "A^S^tW 



a b c d e 



Fig. 54. Amitosis in the trophozoite of Myxosoma catostomi, 

 X2250 (Kudo). 



Indirect nuclear division. The indirect division which occurs in 

 the protozoan nuclei is of manifold types as compared with the 

 mitosis in the metazoan cell, in which, aside from minor varia- 

 tions, the change is of a uniform pattern. Chatton, Alexeieff and 

 others, have proposed several terms to designate the various 

 types of indirect nuclear division, but no one of these types is 

 sharply defined. For our purpose, mentioning of examples will 

 suffice. 



A veritable mitosis was noted by Dobell in the heliozoan 

 Oxnerella maritima (Fig. 55), which possesses an eccentrically 

 situated nucleus containing a large endosome and a central 

 centroplast or centriole, from which radiate many axopodia (a). 

 The first sign of the nuclear division is the shght enlargement, and 

 migration toward the centriole, of the nucleus. The centriole 

 first divides into two (c, d) and the nucleus becomes located be- 

 tween the two centrioles (e). Presently spindle fibers are formed 



