136 



MOVEMENT OF CILIA AND FLAGELLA 



It is a pity that Lowndes was not able to substitute for these 

 diagrams an equally clear picture of the movement of a flagellum 

 from his own observations. He can not be blamed for this, 

 however, for the movements are evidently not simple, and two 

 features in particular complicate the picture very considerably. 

 The first is that the movements are three-dimensional in that the 

 body of the organism rotates even though the flagellar beat may 

 be more or less in a single plane. Secondly, the flagellum projects 

 from the anterior end of the body as the organism moves, and 

 the movement of the water is bound to bend the flagellum back 

 and distort the movement of bending waves propagated from the 

 base of the flagellum to the tip. 



Euglena viridis. 



Fig. 35. Movement of Euglena, showing two waves of con- 

 traction passing along the flagellum in the direction indicated 

 by the arrow. The movement of these contraction waves tends 

 to move the organism towards the dotted figure (from Lowndes, 



1941). 



In all cases Lowndes found that the flagellum is moved by 

 waves of bending that pass from the base of the flagellum to the 

 tip, there being sometimes one and sometimes several waves in 

 the length of the flagellum, depending on the length of the 

 flagellum and on the rate of propagation of the bending wave. 

 The flagellum is bent back to lie roughly parallel to the body, 

 and waves of bending propagated along the flagellum were found 

 by Lowndes to cause a rotation of the flagellar tip, because the 

 long distal part of the flagellum was not easily moved in the 

 water, and the most stable position was that in which the 



