36 STRUCTURE 



peritrich ciliates have been found to have ciUary origin by Rouiller, 

 Faure-Fremiet and Gauchery (1956). The stalks of the non- 

 contractile types Campanella and Opercularia and the contractile 

 Zoothamnium are long cylindrical structures, with a central 

 contractile " spasmoneme " in the third-named genus. An aboral 

 scopula of cilia forms a fibrous skeleton in the stalk, while other 

 parts of the peritrich surface produce matrix material to fill the 

 interstices. The detailed structure is different in all three genera. 



The cilia which elongate into the stalk of Campanella have a 

 normal fibrillar structure near the base, but soon widen out and 

 lose all the inner fibrils. The cilium continues down the stalk as a 

 hollow cylinder formed from the ciliary membrane which is 

 interconnected with other similar cylinders by oblique trellis-like 

 fibrils about 50 to 100 A thick. In the other two genera the cilia 

 again elongate into the stalk, but the peripheral fibrils form the 

 skeletal structure, the ciliary membranes disappearing. In 

 Opercularia the nine peripheral fibrils diverge somewhat near the 

 base and become striated, the striations having a period of about 

 440 A in the fully developed stalk. The nine peripherals of 

 Zoothamnium again diverge, but then fuse to form a single cylinder 

 about 3500 A in diameter with a striated wall having a 470 A 

 period. Although central fibrils are absent in Opercularia, a non- 

 striated structure which may represent the central fibrils has been 

 seen in Zoothamnium. 



These details of structure found by Rouiller, Faure-Fremiet 

 and Gauchery form a coherent picture of stalk structure in these 

 three peritrichs, but Randall (1962) has studied a wide variety of 

 peritrich stalks and believes the picture described above to be an 

 over-simplification. He has obtained striking electron micrographs 

 which show that the striated fibres are not continuous with the 

 peripheral fibrils of the scopula basal bodies. Further work is ob- 

 viously necessary before we can fully understand these structures. 



Flagella 



A variety of modifications of the flagellar shaft have been 

 described ; most of them have the result of increasing the effective 

 diameter of the flagellum. Hairs or scales may be present on the 

 flagellar surface, the membrane may be expanded, or additional 

 material may be longitudinally disposed either inside or outside 



