PLATE II 



ELECTRON MICROGRAPH OF SPERM-TAIL 



Broken end of tail from a bull spermatozoon, showing the tuft of fibrils 

 of the axial filament, and the helical structure of the tail sheath; 

 I 1 indicates 1 /x. 



(By courtesy of Prof. L. H. Bretschneider and Dr. Woutera van Iterson) 



