VARIATIONS IN SHAFT STRUCTURE — CILIA 



31 



Cirri of Euplotes are built up of 20 to 35 cilia hexagonally packed 

 in 5 to 8 rows (PI. Va), but Chen (1944) found as few as 4 cilia in 

 some cirri of Stylonychia. The membranelles of Stentor and 

 Euplotes^ shown in Fig. 8 and Plate IVa respectively, are built up of 

 2 or 3 rows of 15 to 25 cilia closely packed together, while the 

 membranelles of Epidinium may be larger, and contain up to 115 

 cilia in about 6 rows (Bretschneider, 1960). There is neither an 



Fig. 8. Diagram of the arrangement of kinetosomes in a 

 membranelle of Stentor. Each kinetosome {k) bears a ciliary 

 shaft, (c) at its distal end and a number of root fibrils (r) at its 

 proximal end. The cilia are not drawn to scale (from Randall 



and Jackson, 1958). 



interciliary matrix, nor any extraciliary membrane surrounding the 

 shafts of the component cilia and holding them together to keep 

 the shape of the compound structure. Instead, the membranes of 

 component cilia of both cirri and membranelles carry finger-like 

 projections up to 1 /x long and about 500 A in diameter which 

 ramify among the cilia of the compound structure. These projec- 

 tions are thought to help to maintain the integrity of the structure, 

 but could not maintain an absolutely rigid shape. Compound 

 cilia are also of wide occurence in metazoa, but very few have been 

 studied, e.g. the laterofrontal cilia of My^//w^ which are rather like 

 membranelles with two fairly close rows of about 20 cilia (Bradfield, 

 1955). The laterofrontal cilia of Anodonta figured in Plate lid are 

 very similar, and all the cilia are seen packed tightly together. 



