34 



ROBERT RIKMENSPOEL 



Fig. 2. Enlarged reproduction of die image of a rotating cell; at the 

 points P the tail has moved out of the plane of focus. 



as shown in Fig. 1, has also been observed by Gray (1955). The tail 

 wave of the rotating cells is three-dimensional. Figure 2 illustrates 

 a rotating cell where the image of the tail is blurred in two places, 

 owing to the fact that it has moved out of the plane of focus. 



An attempt was made to measure the "vertical" amplitude from 

 the amount of blur of the tail image. Figure 3 represents the meas- 

 ured width of the image on a film of the tail of a dead sperm cell as 

 a function of the distance to the focal plane. Unfortunately no quan- 

 titative data can be obtained in this way, chiefly because a well- 

 focused tail is blurred to about three or four times its diameter by 

 spherical aberration from the 1-mm-thick cover slide and by the grain 

 of the emulsion. Qualitatively, however, the fact that rotating cells 

 have a three-dimensional (helical) zuave is firmly established. 



The forward movement of the sperm, measured as the distance 



