SOME PROBLEMS OF CILTARY STRUCTURE AND CILIARY FUNCTION 559 



sperm tail, but at the end of the life span of the spermatozoon the flagelhim 

 mav perform asymmetrical twitches of a non-propagating type. A twitch 

 consists of a slower bending phase and a more rapid straightening phase 

 which is directed towards the asymmetrical midpiece [3]. F'igure i shows 

 two squid spermatozoa in which the section includes the two midpieces 



Fig. I. Cross-section of two squid spermatozoa {Lolign pea/ii). The respective 

 midpieces (m) and tail flagella (/) are included in the section but not the heads. 

 There is a marked separation between the midpieces and the tail flagella owing to 

 an asymmetrical position of the midpiece in relation to the centre axis (i.e. the tail). 

 It is of interest that the arrangement of the 9 + 2 tail filaments is fairly constant in 

 relation to the micipiece : a line through the two central filaments is at right angles 

 to the line connecting midpiece and tail ; the outer nine filaments are unevenly 

 spaced in the ring around the central ones as the two filaments located away from 

 the midpiece are closer together than any other two peripheral filaments. Magnifi- 

 cation 57 500 X . 



and below them the respective flagella. It can be noted that the arrange- 

 ment of the flagellar filaments is fairly constant and that the unpaired 

 filament i is closest to the midpiece. It mav be inferred from pictures like 

 this that the arrangement of the filaments is fixed in relation to the mid- 

 piece and that thus, the direction of the flagellar twitch is fixed in relation 

 to the arrangement of the filaments. 



The interest in Fig. 2 lies in the two tail cross-sections that are properly 



