1923] Hall: Binary Fission of Menoidiiim incurvum 463 



The Endosome 



The endosome, or "Binnenkorper" (Doflein, Tschenzoff), is one 

 of the least understood structures in the euglenoid nucleus. Some 

 aiithors ascribe to it an inactive role in mitosis; others believe it to 

 be active in initiating division ; while a few have described it as con- 

 taining a centriole. With a few exceptions, such as Berliner (1909), 

 Haase (1910), Schiissler (1917), all are agreed that the endosome 

 has nothing to do with the formation of chromosomes. Since Haase, 

 however, describes also the formation of gametes bj' an intrakaryo- 

 somal mitosis and the union of gametes to form a zygote, her interpre- 

 tation is open to suspicion. 



The question of the presence or absence of a centriole in the 

 endosome of euglenoids is not yet definitely settled. A centriole or 

 centrosome has been described by Berliner (1909), Hartmann and 

 Chagas (1910), Haase (1910), Belaf (1916), Schussler (1917). 

 Schiissler describes "Centren" in the middle of the. "Pseudopol- 

 korper," which are formed at the poles of the endosome; he reverts to 

 the theory of chromatic dualism when he states that in 



alien genauer untersuchten einfacher Protozoenkernen sich stets zwei gesonderte 

 Komponenten nachweisen lassen, eine lokomotorische und eine generative. 



He considers that in the phylogeny of the euglenoids the more primi- 

 tive types, represented by Scyiomonas, have both nuclear components 

 localized in the endosome, while in the higher forms such as Euglena 

 the generative function is invested in the outer chromatin. Berliner 

 (1909) believes that in the division of Copromona^ major the old 

 basal granule degenerates or is drawn back into the nucleus, and that 

 new basal granules arise from the centrioles of the daughter nuclei ; 

 from these newly produced granules the flagella of the daughter 

 flagellates grow out. This is denied by Schiissler, and Dobell (1908) 

 also fails to find any indications of such a process. The cytological 

 evidence of Haase (1910) for the presence of centrioles is quite as 

 inadequate as that for her other fanciful interpretations, so that her 

 account is of little value. Belaf (1916), however, has described and 

 figured a structure resembling a centriole in the endosome of Astasia 

 Levis, and has traced it from the prophase through the anaphase. 

 Hartmann and Chagas (1910) figure a divided centriole in the endo- 

 some of Peranema during the prophase, but they have not followed 

 this structure through mitosis, as Belaf has done in Astasia, and their 



