48 STRUCTURE 



types of mammalian sperm (e.g. Fig. lib) the outer fibres are seen 

 in transverse sections to be drawn out into a daisy-petal shape, 

 with the points touching the axial doublets, e.g. in the rat 

 (Yasuzumi, 1956). 



Differentiation in size of the outer fibres, which was also found 

 in Perameles, is of more widespread occurrence. The most com- 

 mon pattern is that found in ram and bull sperm (Bradfield, 1955), 

 where the three fibrils furthest from the plane through the two 

 central fibrils (numbers 1, 5 and 6) are considerably larger than 

 the other six. Similar differences in size are found in the rat 

 (Yasuzumi, 1956) and guinea pig (see PI. XIc) (Fawcett, 1958a), 

 and Fawcett also found three slightly larger fibrils in monkey and 

 human sperm, although Anberg (1957) believed all nine to be of 

 similar size. In human sperm (and also guinea pig sperm) the 

 two outer fibres nearest to the plane through the central fibrils 

 (3 and 8) are shorter than the other seven; this may be just as good 

 an indication of their lesser importance as their smaller diameter 

 might be. In rat sperm outer fibres 3 and 8 are again the shortest, 

 fibres 4 and 7 end next, then 2 and 9, and fibres 1, 5 and 6 are the 

 longest (Fawcett, 1961). 



4. Centrioles and Ciliary Bases 



The centrosome region has been known to have an important 

 function in dividing animal cells for nearly a century, and the 

 centriole granule in this region is regarded as the centre of produc- 

 tion of the spindle fibres in mitotic and meiotic division of cells. 

 The same structure is known to be important in spermatogenesis, 

 where it is found at the base of the tail, again associated with 

 fibrogenesis. It appears, then, as if the centriole may be function- 

 ally concerned with fibre production, at least as an organizing 

 centre. Henneguy (1898) and von Lenhossek (1898) discussed the 

 idea that the basal bodies of ciliary organelles were of centrosomal 

 nature or origin. Support for this came from the finding, in several 

 groups of fiagellated protozoa, that the basal bodies of some 

 flagella are centro-blepharoplasts which act as centrioles in 

 mitotic division while the flagellar shafts are still attached (see the 

 review by Belaf (1926) or the description of division in Trichomonas 

 by Hawes (1947)). The remarkable similarity between the fairly 

 elaborate structure of the centriole of non-ciliated cells and the 



