128 



MOVEMENT OF CILIA AND FLAGELLA 



pattern ; if the tail were considerably longer, this form of beating 

 would have the appearance of what has been regarded as the 

 '* typical flagellar beat ". 



When bending waves of this form are passed backwards along 

 a flagellum, the water exerts forces against the tail in such a way 



Fig. 30. Simplified diagram of forces exerted by the water on 

 two elements of a sperm tail of a sea urchin. The elements 

 X and Y are being moved transversely because the bending 

 waves in which they occur are moving backwards. Thus, 

 element X is moving to the left and element Y to the right. 

 The forward components Fx and Fy act together, but the 

 transverse components Tx and Ty are in opposition. (The 

 forward movement of the sperm is neglected.) 



that the whole body is moved forwards. The forces acting on 

 various parts of the body will differ, and at any instant they will 

 have both transverse and longitudinal components for all elements 

 of the tail that are moving (i.e. excepting those at the crests of 

 the waves). The maximum longitudinal forces will be exerted 

 on those elements of the tail which are moving at a maximum 



