1923 J Hall: Binary Fission of Mennidiwm vncurvum 467 



found, these chromosomes of the late prophase might, in reality, be 

 paired chromosomes which have already split at an earlier stage, as 

 described bj' Tschenzoff in Euglena viridis; if such were the case, 

 the metaphase "splitting' would be merely the separation of pre- 

 viously formed daughter chromosomes. Tschenzoff finds that in 

 Euglena the chromosomes split in the telophase or late anaphase, 

 while the daughter chromosomes so formed pair in the prophase of 

 the next mitosis and are permanently separated in the metaphase. 

 Such a process could not be confirmed in Menoidium; however, it 

 should be stated that the nucleus of this flagellate is much smaller 

 than that of Euglena, so that it may be that such a process occurs 

 and has not yet been detected. 



The migration of the free ends of the V-shaped chromosome pairs 

 during the metaphase in Menoidium results in the formation of the 

 ring of chromosomes parallel to the endosome ("equatorial plate 

 stage") ; in such a case the ring is formed by the paired daughter 

 chromosomes which have unfolded but still remain attached at the 

 equator. This is supported by the condition shown in plate 41, 

 figures 16 and 17, in which a split has not yet appeared in the plane 

 of the equator through the end-to-end union of the daughter chromo- 

 somes. In slightly later stages (pi. 41, figs. 18 and 19) a split appears, 

 while the chromosomes are still parallel to the endosome. A similar 

 process of equatorial plate formation is described by Kofoid and 

 Swezy (1919&) in Trichonympha campanula: 



. . . with the beginning of the formation of the spindle fibres, or somewhat 

 earlier, another change takes place in the chromosomes, the loops straightening 

 out so that the chromosomes come to lie parallel to the paradesmose. . . . The com- 

 pletion of this gives the equatorial plate phase, with the chromosomes still joined 

 by an end to end union in the equatorial plane. 



Anaphase and Telophase 



Tschenzoff 's description of the later stages of mitosis in Euglena is 

 in accord with the observed phenomena in Menoidium, except for the 

 fact that a splitting of the chromosomes in the telophase or late 

 anaphaise could not be determined in the latter. Dehorne (1920) 

 states that, in the late anaphase, the separate segments of the spireme 

 produced by the transverse division of the metaphase stage reunite 

 to form the continuous spireme characteristic of the prophase ; in such 

 flagellates as Euglena, however, where the chromosomes are closely 

 massed together in the anaphase, it is difficult to understand how one 

 could be certain that such a structure exists. 



