CILIATES 213 



precise groupings on the ventral surface of a flattened, semi-rigid 

 cell, and used as legs in the ciliate's characteristic crawling 

 locomotion. The adoral band of membranelles is well developed 

 and functions importantly in swimming. Light microscopists 

 have described intracellular "neuromotor" fibers interconnecting 

 the cirri, the membranelles, and a motorium, and a net-like 

 silverline system occurs in constant and species-specific patterns 

 (see recent revision of the genus Euplotes by TurTrau, 1960). 



The pellicle of Euplotes patella (Fig. 85, PL XXIII) consists of 

 at least two unit membranes, the outer one being continuous over 

 the surfaces of the cilia and the inner one forming a thickened ring 

 about the cilium bases. Beneath the inner layer are two mutually 

 perpendicular systems of fine tubular fibrils about 22 m/x in 

 diameter. Cirri arise from depressions in the cell surface and are 

 composed of groups of about 27 cilia arranged with great 

 precision in five to eight parallel rows. Frequent tubular out- 

 pocketings of the ciliary membrane are the only structures seen 

 that could, if they intertwine, account for the adhesion of cilia 

 within a cirrus or a membranelle. Internally, the kinetosomal 

 fibers end at dense granular thickenings, and similar granules 

 occur around the kinetosomes in a plane about half-way distally. 

 At both these levels, fibrils may interconnect adjacent kinetosomes 

 directly or may pass them tangentially in a manner rather suggest- 

 ing the orientation of kinetodesmal fibrils. 



The membranelles are similar in structure to the cirri, except 

 that each membranelle consists of two rows of 15 to 25 cilia, 

 occasionally with an additional short row. From the proximal 

 ends of some kinetosomes of both cirri and membranelles arise 

 rootlet fibrils — several fibrils per kinetosome but not from every 

 kinetosome in the group. These are, again, tubular 21-m^ fibrils. 

 They may pass vertically into the cytoplasm, laterally in bundles 

 toward other ciliary organelles, .or peripherally toward the 

 pellicular fibril systems. In the region of the cytostome appears 

 an aggregation of fibrils running in several directions within the 

 mass and extending from it at least toward the buccal cavity wall 

 and toward neighboring membranelles. Roth identifies this mass 

 with the light microscopist's motorium and the bundles of tubular 

 fibrils with their neuromotor fibers. In addition, ill-defined tracts 

 of similar fibrils were seen adjacent to the micronucleus. 



