Sperm Tail Structure in Relation 

 to the Mechanism of Movement* 



DON W. FAWCETT 



Department of Anatomy, Harvard Medical School, Boston, Massachusetts 



Efforts to relate sperm tail structure to the mechanism of sperm 

 locomotion are complicated by the lack of unanimity as to whether 

 the tail movements are planar undulations or three-dimensional gy- 

 rations. The intermittent flashing of the flattened heads of free 

 swimming bull sperm, when observed in dark-ground illumination, 

 was interpreted to mean that the heads rotated as the sperm swam 

 (Rothschild, 1953). This fostered the belief that the tails execute 

 spiral movements. More recent dark-ground cinephotographic stud- 

 ies of the simple flagellate sperm of invertebrates by Gray (1955) 

 have shown that with slow shutter speeds a luminous region is re- 

 corded behind the head which delimits the area within which the 

 tail movements occur. As the sperm head oscillated about its long- 

 axis in swimming, this "optical envelope" of the tail alternated be- 

 tween an elliptical and a linear configuration. Since the optical en- 

 velope of a tail executing helical movements would be expected to 

 approximate a cylinder, it was thought that the observed alternation 

 of its shape during swimming could best be explained on the basis of 

 a two-dimensional wave motion. Similar studies on bull sperm, which 

 have a more complex tail structure, yielded results which suggested 

 that in this species, too, the movements were predominantly two di- 

 mensional, but there appeared to be a slight torsional component 

 such that points near the tip of the tail followed a flat figure-of-eight 

 path (Gray, 1958). Other analyses of cinematographic and photo- 

 electric measurements on bull sperm (Rikmenspoel, 1958) have led 

 to very different conclusions, namely, that the sperm cell does rotate 



* Supported by grant RG-6729 of National Institutes of Health, United States 

 Public Health Service. 



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