SPERM MOVEMENT — PROBLEMS AND OBSERVATIONS 



25 



on evidence which is neither extensive nor conclusive. Another ex- 

 ample concerns the actin-myosin interdigitation hypothesis of skeletal 

 muscle contraction. In at least two papers on sperm movement, the 

 suggestion has been made that, somehow or other, the fibrils in a 

 sperm tail interdigitate in a way analogous to that which possibly 

 occurs in skeletal muscle, thereby contracting and producing bend- 

 ing waves. Leaving aside that the fibrils in a sperm tail are not in 

 hexagonal array, are not attached to anything at their distal ends, 

 and not made of actin or myosin, why should a sperm tail work in 

 the same way as voluntary muscle, which has a different job to do, 

 not unnaturally done in a different way? At the moment, it is more 

 a question of ingenuity than reasoning to think of explanations or 

 mechanisms which might be consistent with the 9 + 2 pattern. 



Fig. 4. Diagram of a transverse section of the bandicoot (Perameles 

 nasuta) sperm tail. The dorsal and ventral halves of the tail are, respec- 

 tively, at the top and bottom of the diagram. The axial ring fibrils are 275 

 A in diameter. (After Cleland and Rothschild, 1959.) 



