46 



STRUCTURE 



the fibrous sheath, inside which is a normal 9-plus-2 bundle of 

 fibrils surrounded by nine very large outer fibres (Fig. 11a). 

 These large fibres have a homogeneous dense appearance in 

 sections, and vary in size, shape, distance from the centre of the 

 tail and connexions to other components of the tail, seven of them 

 being joined to corresponding peripheral fibrils of the axial bundle 

 by connecting laminae. Six of these laminae are double, with two 

 longitudinal rows of nearly transverse filaments, 200 to 250 A in 

 diameter and about 250 A apart, embedded in a matrix that is 

 slightly denser than the other non-fibrous part of the axis; a 

 seventh lamina is single with only one row of filaments. The 



Fig. 1 1 . Diagrams of transverse sections of some mammalian 



sperm tails. 

 a : Section through the principal-piece of the tail of the sperm 

 of the bandicoot (Peranieles), omitting the outer sheath struc- 

 tures (see text) (from Cleland and Rothschild, 1959). 

 b: Section through the mid-piece of the tail of the rat sperm. 

 Note the differentiation in size of the outer fibres, the largest 

 (1, 5 and 6) being those furthest from the plane through the 

 central fibrils. Around these fibres is the mitochondrial sheath. 

 c: Section through the principal-piece of the sperm tail of 

 the rat. There is still a marked difference in size between the 

 outer fibres, the two in the plane of the central fibrils have 

 disappeared and their place has been taken by laminae projecting 

 inwards from the fibrous sheath (cf. Plate XIc). 

 Figs, b and c constructed from several sources referred to in 



the text. 



