CENTRIOLES AND BASAL BODIES 55 



only the latter contains a central '* cartwheel *' structure of fila- 

 ments. The distal region may perhaps be equivalent to the whole 

 basal body of other organelles. Fibril triplets continue through 

 the whole structure, and, in both regions, the outer (C) subfibril 

 of one triplet is connected to the inner (A) subfibril of the next 

 triplet in an anticlockwise direction (looking outwards from the 

 inner end) by a filament or lamella about 45 A thick (PI. I). Some- 

 times thinner filaments connect all the A subfibrils at the extreme 

 distal end of the basal body. The central part of the distal region 

 of the basal body is occupied, according to the position on the 

 body, by regularly arranged granules or a group of three cylinders 

 about 400 A in diameter ; the latter run from the cartwheel 

 structure of the proximal region of the basal body to the transverse 

 septum at the base of the shaft, and can be seen in transverse 

 section in Plate I. At the centre of the longer proximal region of 

 the basal body is a system of 45 A thick filaments (or perhaps 

 lamellae) forming a " hub " and '* spokes ". The hub is a ring 

 about 250 A in diameter from which nine spokes run out to 

 connect with the inner subfibril of each triplet. A similar cart- 

 wheel structure is present in the basal bodies of Trichonympha 

 flagella, but is absent in the flagellar base of HolomastigotoideSy 

 which is otherwise similar (PL Xllla). 



The centriole of an early spermatocyte of the snail Viviparus 

 was found by Gall (1961) to show both fibrils connecting adjacent 

 triplets and a central cartwheel structure with hub and spokes. 

 Gall suggested that the hub and spoke structure is characteristic 

 of the inner or proximal end of the centriole or basal body. A 

 cartwheel structure has been found in the basal bodies of flagella 

 of Blastocrithidia (Vickerman, 1962) and cilia of Paramecium 

 (Gibbons, 1960), but was not revealed in a study of Anodonta 

 cilia by the latter author (Gibbons, 1961b). 



The basal bodies of flagella (or cilia?) of spermatozoids of the 

 cycads Zamia and Cycas are structures of even greater length. 

 Barton (1962) has found basal bodied 16 to 20 /Lt long extending 

 from the cell surface to a thick fibrous band underlying the spiral 

 flagellar tract. Throughout most of the length of the basal body a 

 spiral filament (or a succession of transverse annular filaments) was 

 found just inside the ring of peripheral fibrils. This structure 

 appears in transverse sections as rings rather less than • 1 /x in 



