16 LORD ROTHSCHILD 



Unfortunately, spermatozoa are rather an awkward shape for such 

 measurements. 



To return to the morphology of sperm movement, things are less 

 clear in the bull than the sea urchin spermatozoon. When swimming, 

 at any rate under optimal conditions, the head often rotates or oscil 

 lates; this is easy to see only because the bull sperm head is shaped 

 like a thin elliptical disk, which makes it look quite different down 

 the microscope according to its orientation relative to the optical axis 

 of the microscope. One might easily miss the rotation or oscillation 

 of the sperm head in cases where the head is pear-shaped. Partly be- 

 cause of this rotation or oscillation, the suggestion has been made that 

 the distal part of the tail propagates a helical wave, whereas the an- 

 terior part does not. This suggestion was, I think, first made by Gray 

 (1958), who also raised the question whether the distal part of the bull 

 sperm tail might not be twisted. The helical wave proposition has 

 been faithfully repeated by other workers in the field, though, as men- 

 tioned earlier, there is not much objective evidence for the existence 

 of helical waves in any part of the bull sperm tail and some evidence 

 to the contrary. 



One observation many gametologists must have made on bull 

 spermatozoa is rather difficult to interpret: if one makes dead bull 

 spermatozoa flow along a tube, one can often see their heads flashing, 

 oscillating, or rotating in the way live ones do. Does this mean that 

 the whole spermatozoon is rotating or oscillating, or can the head do so 

 by itself? There is a curious structure in the neck of the bull spermato- 

 zoon, Fig. 1, and, for that matter, in that of man, which sometimes 

 looks like a pile of circular disks, though its geometry has not yet been 

 completely elucidated. Can the bull sperm head oscillate or rotate 

 around these disks independently of the tail? Of course, a torque 

 must be applied to effect such a rotation. But where does the torque 

 come from when a dead bull spermatozoon is flowing along a glass 

 tube? Perhaps someone should make a large model of a bull spermato- 

 zoon, drop it down a tube of treacle (molasses), and see what happens. 

 One must use treacle, because a real spermatozoon thinks it is swim- 

 ming in treacle, not water, when in its normal medium. This ex- 

 periment would, of course, bring us into the realm of hydrodynamics 

 or fluid dynamics, about which I would like to say a few words. 



