64 STRUCTURE 



of such ciliates as Stentor, but, although they occupy a similar 

 position, the detailed structure is certainly different. In the 

 somatic kinetics of Stentor, according to Randall and Jackson 

 (1958), the non-striated fibril which leaves each basal body runs 

 out and turns posteriorly (PL Xlllb) to join the " kinetodesma", 

 which is a stack of 1 3 to 24 sheets of fibrils, with 24 to 30 apparently 

 tubular fibrils about 200 A in diameter in each sheet. Near their 

 termination at the basal body, the fibrils bifurcate to run to either 

 side of the basal body, and many thin filaments connect the two 

 branches ; it is thought that several of these fibrils may connect to 

 each basal body. The ** kinetodesmata " of Spirostornum seem to 

 have a similar arrangement (Randall, 1957). 



Unstriated fibrils with diameters between 150 and 300 A, and 

 with a tubular appearance in transverse section, are frequently 

 found in protozoa, not only in association with basal bodies, but 

 also in other structures, e.g. the pellicular ridges of Opalina 

 (Noirot-Timothee, 1959), the trichites of Prorodon and Coleps 

 (Rouiller, Faure-Fremiet and Gauchery, 1957), the contractile 

 vacuole canal of Tokophrya (Rudzinska, 1958) and in other places 

 (see Roth, 1958a). In Colpidium, Pitelka (1961) has described two 

 sets of such fibrils (about 200 A in diameter) which arise '' in 

 intimate association with the kinetosomes." Fibrils of both groups 

 run close enough to make contact with a group of longitudinal 

 fibrils of similar dimensions, although connexions have not been 

 seen (Fig. 14). The bands of short but overlapping longitudinal 

 fibrils run parallel to the pellicle and just beneath it, superficial 

 to and perhaps slightly to the right of the kinetodesmata. A group 

 of 7 or 8 postciliary fibrils arises immediately posterior to each 

 basal body, and runs posteriorly to the right and towards the 

 surface to end near the band of longitudinal fibrils. Another 

 group of about 6 transverse fibrils arises at the left side of each 

 basal body and runs to the left towards the longitudinal band of 

 fibrils of the adjacent kinety. Could it be that the postciliary and 

 longitudinal fibrils of such a system have been elaborated to make 

 the '' kinetodesmal " structure found in Stentor} 



The roots connected to the bases of the membranelles of 

 Stentor are quite different from the somatic " kinetodesmata", 

 although the fibrils concerned are of a similar size. Each mem- 

 branelle is composed of 2 or 3 rows of 20 to 25 cilia, and the basal 



