164 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



Opalina bears orderly, longitudinal ridges or ribs running parallel 

 to the kineties (Text-fig. 11). From one to 24 ribs are present 

 between adjacent kineties — fewer anteriorly where kineties are 

 more numerous and close-set, and more posteriorly. The number 



Text-figure 11. Diagrammatic reconstruction of the pellicle of 

 Opalina. fl, flagella; p, plasma membrane; f.p., peripheral fibrils of 

 flagellum; f.a., central fibrils of fiagellum; r.p., longitudinal ribs 

 formed by folds of cell membrane over f.r.p., fibrils of the pellicular 

 ribs; c.f., cylindrical extension from g.a., axial granule at top of 

 bl., kinetosome; f.c, fibrils composing band comparable in 

 position to kinetodesma of ciliates. From Noirot-Timothee, 1959. 



of ribs may be reduced by fusion near the posterior tip of the cell. 

 Ribs are about 50m/* in thickness, about 600m/x high, and separated 

 from adjacent ribs by grooves about lOOm^ wide. Each rib con- 

 sists of a fold of the cell membrane enclosing a single row of 20 

 to 25 parallel, longitudinal, tubular fibers about 17m/z, in diameter, 

 embedded in a structureless matrix. 



