54 STRUCTURE 



The centrioles that form the basal bodies of ciHa and flagella 

 are in general similar to those which have been described from 

 other parts of cells, except for the structures which develop from 

 them. Records of dimensions are available from a wide variety of 

 animal and plant cilia, flagella and sperm (see Table 4); the 

 diameter lies between 0*12 and 0*27 /x and the length between 

 0*2 and 0*8 jit, excepting in trichonymphid flagellates and cycad 

 sperm where abnormally long structures are present (see below). 

 The ring of nine fibril triplets in the wall of the basal body has been 

 found in all the types of organelle, including the flagella of Pseudo- 

 trichonympha (Gibbons and Grimstone, 1960), the cilia of Opalina 

 Noirot-Timothee, 1959) and of the rat tracheal epithelium 

 (Rhodin and Dalhamn, 1956), the sperm of the sea urchin 

 (Afzelius, 1959) and of the toad (Burgos and Fawcett, 1956), and 

 will probably be found to be a general feature when improved 

 techniques are more widely used. The transition between this 

 triplet stracture and the fibril doublets of the shaft has been 

 described for two examples on pp. 22-26. 



In the majority of cases the cavity of the basal body is cut oflF 

 from the ciliary shaft by a transverse septum just below the 

 granule at which the central fibrils end (PI. IVb); Gatenby (1961) 

 noted that the matrix of the shaft was denser than the matrix in 

 the cavity of the basal body. The transverse septum may connect 

 with the ciliary membrane, with the plasma membrane of the cell 

 close to the base of the cilium or there may be other connexions 

 between the axial fibre bundle and the membrane at the base of 

 the cilium, both between the basal body and the membrane and 

 between the peripheral fibrils of the transition region and the 

 membrane (see pp. 23 and 25). The nine fibril groups of the basal 

 body of the mammalian retinal rod connecting cilium are each 

 linked to the cell membrane by a filament 600 to 1000 A long and 

 100 to 150 A thick (Tokuyasu and Yamada, 1959), while a pair of 

 50 A thick filaments connect each fibril group of the basal body of 

 Pseudotrichonympha flagella to the surface membrane. Filaments 

 running between the peripheral fibrils and the membrane are also 

 present in the proximal part of the shaft of both of these organelles. 



Gibbons and Grimstone (1960) found that the basal body of 

 Pseudotrichonympha flagella reaches a length of some 5 or 6 «, of 

 which the distal 0*6 /Lt differs from the proximal region in that 



