ZOOFLAGELLATES 165 



Grooves in which the kineties lie are wider and shallower than 

 the others. Each cilium arises at the base of a cylindrical depres- 

 sion in the bottom of the groove (Fig. 67, PL XVIII). The two 

 central fibrils of the ciliary axis begin in a dense spherical granule 

 from which a short sleeve extends distally for about 100 m/z. The 

 kinetosomes in some of Noirot-Timothee's micrographs show 

 clearly the skewed triplet fibrils in their proximal portions. 



From the anterolateral margin of each kinetosome, near its 

 base, arises a pair of slender bands which converge and pass 

 anteriad towards, but rarely reach, one side of the next kinetosome 

 (whether this is the right or the left side could not be determined, 

 although the anterior direction is clear [Pitelka, 1956]). Each band 

 appears to be composed of short cross-fibrils. This structure, as 

 seen in the micrographs of Pitelka and of Noirot-Timothee, thus 

 seems to differ from the solid cross-striated and the tubular fibrils 

 of many flagellates and ciliates, but the position of the bands in 

 Opalina is very similar to that of kinetodesmal fibrils in some 

 ciliates, which will be discussed in the next chapter. 



The cortical cytoplasm of Opalina shows a number of remark- 

 able differentiations of unknown significance. Running between 

 the rows of kinetosomes, and perpendicular to them or slightly 

 oblique, are regularly spaced zones packed with minute, rod-shaped, 

 club-shaped, and ovoid, membrane-limited bodies. The number 

 and sequence of these transverse zones clearly do not correspond 

 to the number and spacing of kinetosomes. In the clear cytoplasm 

 separating the bands are rows of larger, dense-walled, spherical 

 profiles. Inspection of appropriate tangential sections shows that 

 these are diverticula of the cell membrane at the bottoms of the 

 grooves between pellicular ribs. Noirot-Timothee concluded that 

 the diverticula were being pinched off as vesicles, and suggested 

 a process of pinocytosis occurring here in an exceptionally 

 orderly fashion. 



Just a little farther below the surface, the bands of minute 

 membranous bodies lose their regular orientation and spread out 

 as a subcortical layer of varying thickness, mingled with spherical 

 vesicles perhaps formed by pinocytosis. Below this layer the 

 ectoplasm is extremely alveolar, containing thin-walled vacuoles 

 of all sizes and shapes, usually with diffusely granular contents. 

 Also in this region of the ectoplasm are abundant, very distinct 



