1920] KofoidSwezij : Morphology and Blitosis of Chilomastix 133 



cavity of the oral pouch. The same structural peculiarities which exist 

 in the neuromotor apparatus in the free flagellate are present in the 

 cj'st except for the free flagella. There is little if any change in the 

 size of its constituent elements in the cyst. 



The spiral groove of the body (tig. B, spir. (jr.) loses its spiral 

 course and becomes a faint meridional shadow at the right of the 

 cytostome, distinguishable in the iron haematoxylin preparation as a 

 narrow, clear region extending from the anterior end of the encysted 

 flagellate nearly to its posterior end (pi. 16, figs. 10-14). 



MITOSIS 



Binary fission in the free flagellates has not been found in our 

 stained faecal smears, though constant watch has been maintained 

 for it. In the encysted stages, however, we have been more fortunate 

 in that we have been able to secure a fairly representative series show- 

 ing the main steps in the mitosis of this form in the first two divisions 

 in the cyst. Many of the minute details of this process have thus far 

 eluded us, as well as the plasmotomy of the two or more daughter 

 flagellates thus formed and their liberation from the cyst. 



The onset of mitosis is apparently not foreshadowed in the behavior 

 of the chromatin contents of the nucleus, since this retains its usual 

 structure until the new neuromotor organelles are at least partially 

 developed (pi. 16, figs. 10, 11, 13, 14). The process is begun by the 

 division of the centrosome and blepharoplasts. The earliest stages 

 we have been able to find (pi. 16, fig. 13) show these granules dupli- 

 cated and each set of blepharoplasts connected by the normal com- 

 plement of rhizoplasts to the as yet undivided nucleus. The origin 

 of the rhizoplasts appears to be by division of the original rhizoplasts. 

 The centrosomes spin out between them as they separate a darkly 

 staining thread, the paradesmose (pi. 16, figs. 13, 14), which lies 

 on the nuclear membrane. 



The duplication of other parts of the neuromotor apparatus occurs 

 by outgrowth and not by division, as seems to be the case with the 

 blepharopla.sts and rhizoplasts. The new cytostome, and its peri- 

 stomal fiber and associated parabasal, parastyle, and cytostomal 

 flagellum, arise as outgrowths of the new secondary and tertiary 

 blepharoplasts, appearing at first as minute loops and threads (pi. 16, 

 fig. 13) which gradually enlarge until, in the final stages, they equal 



