PLATE IV 



TRACK OF THE SPERM-HEAD 



Cinematograph of a bull spermatozoon (in semen diluted 1 : 450) moving 

 forward at a speed of about 0-15 mm. /sec. Photographic plate 

 exposed for 1 sec, using dark ground illumination. Mag. x 673. Only 

 the projection of the movement of the sperm-head is seen, the tail 

 leaving no track. As the sperm-head is shaped like an elliptical disc, 

 intense light scattering occurs only when the thin edge of the head 

 is visible; during 1 sec. exposure ten images of the head were recorded 

 which means that it rotated or oscillated backwards and forwards 

 ten times. 



(By courtesy of Lord Rothschild) 



