PHYTOFLAGELLATES 127 



The structure of the pellicle is complex. Striae are evident in 

 profile as strongly skewed ridges with an abrupt, even concave, 

 slope on one side and a gradual one on the other. In fragments, 

 it appears that a prominent fiber, about 30 m^ in diameter, runs 

 along the peak of each ridge. The thin membranous band between 

 fibers contains fine diagonal fibrils or folds, visible only on the 

 outer surface of the pellicle (Fig. 45, PL XII). The pellicle most 

 iiequently tears along the bases of the grooves, suggesting that 

 these are the weakest sites. 



Examination of sectioned E. gracilis does not suffice yet to 

 explain entirely the structure of the isolated pellicle strips. The 

 same slanted or hooked profiles appear in cross-sectioned ridges. 

 Running longitudinally within the overhanging peak of each 

 ridge (Gibbs, 1960; de Haller, 1959, 1960) are two or three tubular 

 fibrils, 18 to 25 m/x in diameter, which probably represent the 

 continuous fibers seen in fragments (Fig. 47, PL XII). The diagonal 

 markings on the outer pellicle surface are not explained. The 

 surface seems to be limited by two membranes about 8 m^ apart ; 

 the outer is a typical three-ply membrane, the inner often is less 

 distinct. At a level slightly below the bottoms of the grooves, a 

 single layer of fine vesicles appears, slightly humped beneath 

 the ridges. 



In the reservoir, the inner one of the pellicle membranes seems 

 to be absent. Fibrils similar to those in the pellicle crests but 

 regularly spaced at shorter intervals run longitudinally in the neck 

 of the reservoir and all around its bulb, immediately beneath the 

 limiting membrane. In addition Wolken and Palade (1953) and 

 Roth (1958a) found close-set fibrils situated deeper in the cyto- 

 plasm, encircling the neck, but not the bulb, of the reservoir 

 (Fig. 46, PL XII). 



E. gracilis is commonly pictured as having a single flagellum 

 with a bifurcated base inside the reservoir. Electron micrographs 

 leave no doubt that two flagella are present basally, but no 

 observations are reported to indicate whether or not the short one 

 actually attaches at its tip to the long one. Both flagella arise from 

 conventional kinetosomes, located just below the reservoir 

 membrane. The basal 1 \x of each flagellum, above the kinetosome, 

 is swollen and the central fibrils arise distal to this swelling. 

 Higher in the reservoir, near the presumed point of junction of 



