52 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



orientation in all cilia of a field, and that a line connecting the two 

 fibers was perpendicular to the plane of beat of the cilia. More 

 recently Afzelius (1961) found a consistent bilateral arrangement 

 of accessory lamellae in the packed swimming-plate cilia of a 

 ctenophore, and established that the direction of active beat of 

 the cilia was toward the single fibril bisected by the medial plane. 



This consistency in orientation may be a general rule, although 

 the high-resolution pictures required to demonstrate it are not 

 always available. But it seems to apply frequently to ciliates as 

 well as to ciliated epithelia, and in these protozoa the cilia are 

 capable of bending in any direction, and commonly do deviate 

 from the beating plane on their recovery stroke — a fact too often 

 ignored but clearly demonstrated by Parducz (1954). The orienta- 

 tion of the central fibers might still be associated with a preferred 

 beating direction, a relationship that remains to be explored. 



The fundamental asymmetry of the flagellum may perhaps be 

 related to another observation on ciliary movement by Parducz 

 (1954). Ciliate cilia may under certain circumstances cease their 

 directed, locomotor beating and move instead in a simple, 

 ineffectual conical path, which the author considers to be a 

 primary movement related to the simplest form of beat in a 

 flagellum. In all of the many ciliate species examined this is a 

 counter-clockwise sweep when the viewer observes the ciliated 

 surface from above. As noted earlier, Gibbons and Grimstone 

 (1960) and Gibbons (1961) found that the arms on the peripheral 

 flagellar fibrils point counterclockwise if the flagellum similarly 

 is viewed from its distal end. 



Finally, one aspect of the problem that has not received much 

 recent attention is that of polarity of the whole flagellar apparatus 

 and the polarity imposed by it on the cell. In flagellates there 

 typically is a spatial association, intermittent with mitosis or 

 continuous, between nucleus and flagellar basal bodies. Golgi 

 elements, contractile vacuoles, and other organelles occupy fixed 

 positions also near the basal bodies. In ciliates, individual ciliary 

 rows, as well as the whole body, are strongly polar and asym- 

 metric. In all these organisms, kinetosome duplication precedes 

 the visible inception of mitosis. Sequence and synchrony in 

 morphogenetic events require some sort of directional informa- 

 tion transfer among the various organelles involved ; the cell and 



