134 University of California Puhlications in Zoology [Vol. 20 



the old organelles in size (pi. 17, fig. 24). The old cytostome, with 

 its peristomal fiber, parabasal, parastyle, and cytostomal flagellum, 

 remains intact throughout the process of mitosis, though later stages 

 would seem to indicate that the entire complex is somewhat reduced 

 in size and its cytostomal flagellum can no longer be found (pi. 17, 

 figs. 22, 23). It retains its original position while the new cytostome, 

 with its related orgajielles, follows the migrating centrosome and 

 eventually comes to lie at the opposite end of the body (pi. 17, figs. 

 18-22). With thie completion of mitasis and the disappearance of 

 the paradesmose, the activity of the encysted flagellate somatella may 

 bring the second neuromotor complex and nucleus back to their orig- 

 inal anterior position, so that the two groups of organelles come to 

 lie side by side (pi. 17, fig. 24). The mobility which we have observed 

 in the dividing schizonts in binary and multiple fission in free 

 trichomonad flagellates (see Kofoid and Swezy, 1915) appears to 

 occur, to some extent, in the schizonts of Chilomastix while still within 

 the cyst. 



During the development of the new neuromotor organelles the 

 daughter centrosomes move farther apart on the nuclear membrane 

 (pi. 16, figs. 13-15; pi. 17, figs. 16-17) until they come to lie at 

 opposite poles of the nucleus (pi. 17, fig. 18), drawing out between 

 them the slender thread which forms the paradesmose. This may be 

 seen in stained preparations as a dark line which follows the contour 

 of the nucleus but may not be attached to it (pi. 17, fig. 20). In later 

 stages, it extends through the cytoplasm between the centrosomes on 

 the nuclear membrane of the two daughter nuclei (pi. 17, fig. 23). 



The nuclear membrane is retained intact throughout the entire 

 process of mitosis. It loses its encrusted chromatin before the forma- 

 tion of the spindle, becomes considerably enlarged and is drawn out 

 into a spindle shape as mitosis progresses, and is finallj' parted by 

 equatorial constriction into the two daughter nuclei. 



The behavior of the chromatin and its formation into chromosomes 

 we have not been able to follow in all details. The amount of chro- 

 matin apparently increeises considerably with the onset of mitotic 

 phenomena and decreases in the final phases, as may be noted by a 

 comparison of figures 17 to 20 on plate 17 with the other figures given 

 on the same and preceding plates. A spireme is formed as a rather 

 thick, continuous thread (pi. 17, fig. 17) coiled in the axis of the 

 nucleus. This spireme later shows transverse constriction into five 

 unequal masses prior to its movement into the equatorial plate (pi. 17, 



