464 University of California Publications in Zoology [Vol. 20 



eytological evidence seems insufficient; Alexeieff (1913) even accuses 

 Hartmann and Chagas of arbitrarily selecting a pair of granules and 

 calling them " centrioles, " as other centriolists are said to have done. 



The structure of the endosome in Menoidium supports the views 

 of Tschenzoff and others, since there is no evidence at all of a centriole 

 in the endosome. Since the only account ^yorthy of careful consider- 

 ation is that of Belaf (1916), the probabilities seem rather against 

 the presence of a centriole in the endosome of all euglenoids. 



Fragmentation of the endosome occurs in the mitosis of some 

 euglenoids, such as Euglena (Haase, 1910; Dangeard, 1902) and 

 Heteronema (Rhodes and Kirby, MSS) but such a phenomenon has 

 not been discovered in Menoidium. The significance of such a process 

 is not known. 



Another interpretation of the endosome — the theory of the 

 nucleolo-centrosome — was advanced by Keuten (1895). He com- 

 pared the endosome (" Nucleolo-centrosom") with the centrosome and 

 central spindle of the diatoms, and with the intranuclear centrosome 

 of Ascaris (Brauer, 1893). This theory was supported by Schaudinn 

 (1896), who cited an interesting experiment on Oxyrrkis marina as 

 evidence of the nature of the endosome. In the nucleus of this form 

 there is normally a large endosome ; when the flagellates were placed 

 in diluted sea-water the endosome left the nucleus and behaved as an 

 extranuclear centrosome. Steuer (1904) accepts the term nucleolo- 

 centrosome, but the more modern investigators have discarded this 

 conception, employing such terms as karyosome, " Binnenlidrper" 

 (Tschenzoff, Doflein), and endosome (Minchin). 



It has been suggested to me by Dr. Kofoid that a solution of the 

 endosome problem is to be sought in connection with the intranuclear 

 rhizoplast (Kofoid and Christiansen, 1915& ; Boeck, 1917). In many 

 flagellates activity within the nucleus is apparently correlated with 

 the activity of the extranuclear centrosome ; the physical bond between 

 these two structures is the intranuclear rhizoplast, connecting the 

 centrosome with the karyosome. There is a possibility that the endo- 

 some of the euglenoids may, in some way, be comparable with this 

 intranuclear rhizoplast ; future investigation may perhaps throw some 

 light upon this phase of the question. 



