456 University of California Puhlications in Zoology [Vol.20 



toward opposite poles of tlie endosome. In the next stage observed, 

 the chromosomes are arranged in the so-called equatorial plate (pi. 41, 

 figs. 16, 17, 20, and 21), in which they are grouped around the endo- 

 some parallel to its long axis. From the observed behavior of the 

 chromosomes, it seems probable that the equatorial plate is formed 

 by an unfolding of the V-shaped chromosome pairs, the free ends 

 of which have migrated to opposite poles of the endosome while the 

 other ends remain attached in the plane of the equator. 



Anaphase 



In the early anaphase (pi. 41, fig. 18) the daughter chromosomes 

 begin to separate in the eijuatorial plane, resulting at a slightly later 

 stage (pi. 41, fig. 19) in complete separation of the two groups of 

 daughter chromosomes. Further elongation of the nucleus now 

 begins, with the chromosomes .still retaining their parallel relation 

 to the endosome. Constriction of the nucleus into two daughter 

 nuclei occurs and these begin to pull apart, still connected by the 

 middle portion of the endosome (pi. 41, figs. 22 and 23). This con- 

 necting portion becomes thinner and thinner as the nuclei become 

 further separated, until finally constriction is completed at the end 

 of the anaphase (pi. 41, fig. 24). The nuclear membrane remains 

 intact throughout this stage. 



Telophase 



After the connecting thread of the endosome has broken (pi. 41, 

 fig. 24), the daughter nuclei begin to round up (pi. 41, fig. 25). The 

 two new endosomes shorten and reassume their spherical shape, and 

 the parallel arrangement of the chromosomes is replaced by a spiral 

 organization comparable with that of the prophase. This reorgan- 

 ization process is continued until typical resting nuclei are formed 

 in the daiighter flagellates with the completion of binary fission. 



There is no adequate evidence here for a precocious splitting of 

 the chromosomes in either the anaphase or the late telophase, as in 

 Euglena (Tschenzoff, 1916). If such were the ease, the metaphase 

 phenomena would involve merely the separation of previously formed 

 daughter chromosomes; but in Blenoidium incurvum the actual split- 

 ting seems to occur in the metaphase. 



