CONCLUSIONS 229 



the difference may be insignificant. At any rate, periodic fibers 

 reappear with a vengeance in the metamonads. 



A search for evidences of relationship between the bodonids 

 and the trichomonads, supposed to be successive stem groups in 

 the zooflagellate series, is not particularly rewarding at the 

 moment. For one thing, the mysterious kinetoplast-mitochon- 

 drion of the bodonid-trypanosomid appears to be a unique 

 structure. For another, the pellicular fibril system does not 

 reappear in similar form anywhere among the higher zooflagellates 

 yet seen. 



With the trichomonads, there is a sudden flowering of zoo- 

 flagellate architectural ingenuity. They have the striated parabasal 

 fibril seen again in Trichonympha (the axial ribbons of Pyrsonjmpha 

 and Joenia probably are the same thing put to a slightly different 

 use) ; the fibrillar axostyle wall found in l^ophomonas and Holomasti- 

 gotoides; and the beautifully periodic costa, whose suspected 

 counterparts occur in some other metamonads not yet studied. 

 The occurrence of a centriole separate from the flagellum- 

 producing ones has not been demonstrated by electron microscopy 

 in Trichomonas, but is suggested in Foaina. Higher metamonads 

 work with essentially the same construction units as do the 

 trichomonads, but have conceived some astonishing ways of 

 putting them together. 



On the rhizopod side of flagellate relationships, the scarcity of 

 evidence concerning flagellate stages makes speculation nearly 

 impossible. Polyphyletic origin of various rhizopod and actinopod 

 groups, as well as of slime molds, sporozoa, and fungi, is probable. 

 The pellicular fibril system of Tetramitus, suggestively similar to 

 that of euglenoids and bodonids, is noteworthy and needs study. 



Not surprisingly, the study of ciliate ultrastructure does not 

 yet offer any clues to ciliate origins. The simplest forms (if indeed 

 there are any simple enough) have not been examined. Once 

 again, their banded fibrils are conspicuously linked to kinetosomes. 

 The fibrils look remarkably like the parabasal fibrils of some 

 zooflagellates, but if there is any homology here it must be 

 peculiarly devious, the ciliate kinetodesmal fibril having come 

 unhooked from Golgi apparatus or nucleus and assuming instead 

 a peripheral linear disposition. Perhaps a more direct homology 

 is to be sought in the banded root fibrils of phytoflagellates. In 



