CENTRIOLES AND BASAL BODIES 



57 



the function of forming the sperm aster in the fertiUzed egg. The 

 second, or distal, centriole divides into two parts — one is a 

 normal cylindrical group of tubular fibrils which forms the basal 



Head x^////^-^ 

 Neck 



Mid-piece 



Principal- 

 piece 



Fig. 13. Diagram showing the relationship between the 

 centrioles, axial fibrils, mitochondrial sheath and fibrous sheath 

 in a mammalian spermatozoon. 

 AT., nucleus; P.c, proximal centriole; D.c.y distal centriole; 

 C.f.y central fibril; P./., peripheral fibrils; O./., outer (coarse) 

 fibres; M., mitochondria; R.c, ring centriole; F., fibrous sheath. 



body of the sperm flagellum, while the second part is a short 

 cylinder of centriole matrix material, lacking fibrils, which forms 

 the ring centriole. After the division of the distal centriole the 



