132 University of California PuhUcations in Zoology [Vol. 16 



The nucleus is comparatively large, with a very distinct nuclear 

 membrane and the chromatin more or less diffused throvighout its 

 extent (text-fig. A), less frequently with a karyosome (pi. 16, figs. 

 4, 7), or granules lying on the periphery. In some specimens a slender 

 rhizoplast may be noted connecting the nucleus and the blepharoplast 

 (text-fig. A, nuc. rhiz.) This structure, as in the case of Trichomonas 

 (Kofoid and Swezy, 1915?)), and perhaps most other flagellates, is 

 probably normally present but, owing to its lack of affinity for most 

 of the stains used, is difficult to demonstrate. 



Below the nucleus and partly surrounding it, is the parabasal 

 body (text-fig. A, par. h.). This is quite variable in its appearance, 

 as is evident from the figures shown. The form which it assumes in 

 most of the individuals is that of a band extending partly around the 

 cell immediately below the nucleus. Figure 6, plate 16, looking at 

 the flagellate from the anterior end, shows the entire structure. This 

 exhibits a heavy band across the flagellate below the nucleus when 

 viewed from one side (pi. 16, fig. 7) or, viewed from the opposite 

 side, two shorter bands (pi. 17, figs. 10, 13). Extending upward 

 from one end of the parabasal body is the slender rhizoplast of this 

 structure (text-fig. A, -par. rhiz.) which joins the blepharoplast. This 

 like the nuclear rhizoplast, is usually difficult to demonstrate, yet it is 

 very definite in a number of cases (pi. 16, figs. 5, 7 ; pi. 17, figs. 13, 15). 



The parabasal body was not figured by Dobell (1909) in his de- 

 scription of this flagellate as Monocercomonas huforiis. Alexeieff 

 (1911) figured this structure, terming it the "corps siderophile, " and 

 later Janieki (1915) homologized it with the parabasal bodies of the 

 Trichonymphida, a conclusion which I had reached before the appear- 

 ance of his paper (Swezy, 1915&). 



The protoplasm is more or less alveolar, sometimes filled with large 

 vacuoles (pi. 16, fig. 4; pi. 17, fig. 20), but more frequently these are 

 small and indistinctly marked off (pi. 16, fig. 5). 



There is no cytostome present nor are food bodies commonly found 

 in the cytoplasm, though not infrequently vacuoles are observed which 

 have a minute granular mass in the center, suggesting partly digested 

 food substance (pi. 17, fig. 19). 



Mitosis 

 Mitosis in Polymastix lufonis is initiated by a splitting of the 

 blepharoplast (pi. 16, figs. 8, 9). At the same time the chromatin of 

 the nucleus becomes condensed into a number of granules, the intra- 



