58 STRUCTURE 



flagellum forms from the basal body, while the ring centriole, 

 which marks the posterior end of the mid-piece of the sperm tail, 

 moves posteriorly as a ring surrounding the axial fibre bundle, 

 drawing out the cytoplasm to form the sheath of the mid-piece. 

 The ring centriole, which is perhaps more correctly regarded as a 

 centriole derivative, is seldom obvious in the adult sperm, and may 

 only have a function in spermatogenesis. The arrangement of 

 distal centrioles is similar in the grasshopper Melanoplus (Tahmis- 

 ian and Devine, 1961), although in this and some other inverte- 

 brates there is no proximal centriole. Burgos and Fawcett (1956) 

 found that in the toad Biifo there seems to be no ring centriole; 

 the distal centriole forms the tail flagelhun, while the proximal 

 centriole is associated with the dense material of the tail fin. 

 Gatenby (1961) believed that a third, unattached, centriole is also 

 present in the amphibian sperm. 



One important function of centrioles is the organization of 

 fibrous structures. Thus, the basal bodies of cilia and flagella 

 seem to be responsible for the production of the characteristic 

 arrangement of tubular fibrils in the ciliary shaft. They also act 

 as centres for the development of the various root systems in the 

 cytoplasm of the cell which are described below (pp. 61-73). 

 Rouiller and Faure-Fremiet (1958) have found that root fibres are 

 formed at the same time as the ciliary shafts when aboral cilia of 

 the peritrich Ophrydium develop from resting kinetosomes. It is 

 interesting that the basal body of the locust scolopale cilium 

 produces nine normal fibril doublets outwards into the ciliary 

 shaft, and nine striated root fibres into the dendrite cytoplasm, so 

 that the two ends of the centriole are capable of producing different 

 structures (Gray, 1960). On the other hand, the root structures 

 produced by some basal bodies are tubular and not unlike the 

 shaft fibrils in appearance and dimensions (see below). The 

 stalks of the peritrich ciliates Opercularia and Zoothatnnium 

 (p. 36) are believed to be formed from modified ciliary shafts 

 which develop a transverse striation, so that normal fibrils may 

 be transformed into striated ones during development, and the 

 basic structure of the two may not be very different. 



The second important function of centrioles, that has been 

 implicit in the theory of ciliate protozoan kinetosomes, as well as 

 in the classical cytological picture of centrosomes, is their self- 



