466 University of California Publications in Zoology [Vol.20 



somes occurs. His views are such a radical departure from the com- 

 monly accepted conception of the status of the chromosomes that 

 they must be considered at present with some degree of skepticism, 

 but they are, to say the least, very interesting and should provide 

 an impetus to further critical investigation. His account, however, 

 does not seem to be supported by the mitotic phenomena described for 

 euglenoids. 



The Metaphase 



In Euglena viridi-s, according to Tschenzoff, the chromosomes, 

 after being parallel to the endo.some, come together in a thick equa- 

 torial zone, in which they are arranged at random with respect to 

 the axis of the endosome. Separation of the double chromosomes 

 observed at this stage begins at one end of the pairs, while the free 

 ends begin to migrate toward opposite ends of the endosome. Dehorne 

 (1920) finds in Euglena, at a stage approximating an early metaphase, 

 distinct longitudinal cleavage of separate chromosomes — " Le clivage 

 est tres surprenant chez un tel noyau, mais indubitable." At this 

 stage he is unable to find a continuous spireme, but he believes that 

 the free ends of the chromosomes later fuse again to form a single 

 thread. This formation of separate chromosomes, their longitudinal 

 cleavage, and the re-formation of the spireme occur prior to the 

 anaphase, so that the separation of the equatorial belt into two 

 daughter groups is due to a "division transversale " of the spireme. 

 This interpretation of Dehorne is in marked contrast to that of 

 Tschenzoff (1916), who finds in Euglena viridis longitudinal division 

 of the chromosomes in a true mitosis, and no indications of a con- 

 tinuous spireme. When one considers that Dehorne, in the paper 

 under consideration, is bent upon tracing similarities in the nuclei 

 of ciliates, euglenoids, and Cyanophyceae, his interpretations may 

 be suspected to have been influenced somewhat by his underlying 

 hypothesis. 



From the behavior of the chromosomes in Menoidium, it is con- 

 cluded that the procedure in the metaphase is slightly different from 

 that described by Tschenzoff for Euglena. The thickened chromo- 

 somes of the late prophase appear to remain radially arranged with 

 respect to the axis of the elongating endosome. In the early meta- 

 phase, splitting apparently begins at one pole of these thick chromo- 

 somes and proceeds toward the other, while the free ends of the 

 daughter chromosomes begin to move toward opposite ends of the 

 endosome. Although no evidence for such a condition has been 



