1923] Hall: Binary Fission of Menoidium incurvmn 453 



gullet of Euglena is for the admission of liquid food. Wager (1899), 

 however, considers this hypothesis as unproved, and states that the 

 gullet and reservoir are excretory organelles, serving as outlet for 

 substances discharged by the contractile vacuole. The regular occur- 

 rence of a number of paramylum bodies at the anterior end in 

 Menoidium suggests that the gullet is in some way connected with 

 metabolism, possibly through the admission of liquid food; for the 

 liquid medium would probably enter the gullet unless there is some 

 undiscovered means of keeping the cytostome closed. But whatever 

 the function of the gullet and reservoir, the structure of these organ- 

 elles is essentially similar in the holozoic, the saprozoic, and the holo- 

 phytic euglenoids. 



The Nucleus 



The nucleus of Menoidium is visually situated near the center of 

 the body, although frequently posterior and sometimes at the extreme 

 posterior end. In structure the nucleus (fig. A) is quite typical for 

 the euglenoids. Thei-e is a homogeneous, heavily-staining endosome 

 (the " Binnenkorper" of Doflein and Tschenzoff) located usually near 

 the center; the term endosome is used in the sense ascribed to it by 

 Minchin (1912) and is not to be confused with the "entosome" of 

 Prowazek (1901). Around the endosome, in the resting nucleus 

 (pi. 40, fig. 7), chromatin granules occur apparently in the nodes 

 of a linin network: in mitosis, the chromatin forms distinct chromo- 

 somes surrounding the endosome. In a few cases twelve have been 

 counted, but this is only a tentative determination since the exact 

 limits of the chromosomes are usually difficult to determine. A fairly 

 distinct nuclear membrane is present, and persists throughout mitosis. 



HABITS AND ACTIVITIES 



The method of nutrition in Menoidium is probably saprozoic, since 

 the evidence at hand favors such a conclusion ; observation of the 

 living organism has failed to reveal any ingestion of solid food 

 particles, and no such particles have been seen in stained material. 

 Lemmermann (1913) also regards Menoidium incurvum as "meso- 

 saprob. " Menoidium is preyed upon by the Euplotes, Stylonychia, 

 and Amoeia which have usually been present in the cultures. The 

 amoebae are especially voracious, often engulfing several of the 

 flagellates, which persist for some time during digestion. 



