SPERM MOVEMENT PROBLEMS AND OBSERVATIONS 23 



"9 + 2" 



Those interested in Hagella and cilia have spent quite a time in 

 trying to think of some explanation of the ubiquitous 9 + 2, or 

 9 + 9 _j_2, pattern of fibrils. Unless one assumes that the preparative 

 techniques for electron microscopy burn up and distort the original 

 structures to an extent which is scarcely credible, one must dismiss 

 the "commutator hypothesis" first put forward by Manton and 

 Clarke in 1952, and repeated in 1955 by Astbury et al. Nor does 

 the recent effort at explanation, if that is the right word, by Serra 

 (1960), have much to commend it. He says, for example, that one 

 explanation of 9 + 2 requires that the fibrils should follow a heli- 

 cal path along the cilium or flagellum. In fact this has nothing to 

 do with 9 + 2. The advantage of a helical arrangement of fibrils 

 is that, if it exists, bending waves can be propagated along the 

 ffaoellum without the need for individual fibrils to contract and relax 

 along their lengths. As only one spiral is needed along the whole 

 flagellum, it is not easy to disprove that such spiralization occurs. 

 Figure 3 is an electron micrograph of a longitudinal section of a 

 bull spermatozoon in which the fibrils obviously follow a straight 

 and not a spiral path; but it is only a few microns in length, whereas 

 the whole tail is fourteen times as long. If lower magnifications were 

 used so that longer lengths of the tail could be examined, the fibrils 

 would be difficult to see. Serra goes on to say (1960, p. 396) that 

 the movement of flagella and cilia "so far as is known always takes 

 place by bending in a plane perpendicular to that of the 2 central 

 fibres." Is such information available about any spermatozoon? I 

 think not. In the bandicoot spermatozoon, I believe that the bend- 

 ing waves are in the same plane as the two central fibrils (Fig. 4), 

 though Cleland, with whom I studied the ultrastructure of the 

 bandicoot sperm tail (Cleland and Rothschild, 1959) does not agree 

 with my interpretation of films of swimming bandicoot spermatozoa. 

 If I am right, the role of the peripheral fibrils in causing bending 

 waves becomes rather obscure, because the fibrils concerned, num- 

 bers 1 and 6, are atypical in not being connected to the axial ring 

 fibrils, whereas all the other peripheral fibrils are. 



I only mention these two points in Serra's paper because there 

 may be a danger of making generalizations about sperm movement 



