THE FORM OF BEAT OF FLAGELLA 137 



contracted region of the flagellum was twisted into a loop (Fig. 35). 

 The result of the passage of these bending waves is to spin the 

 organism on its axis, and to cause the anterior end of the animal 

 to gyrate in such a way as to cause forward motion. These 

 findings have been confirmed by the observations of Brown (1945). 



The movement of the anterior flagellum of Peranema deserves 

 special mention because it has often been misunderstood; in spite 

 of the fact that Verworn (1899) and Lowndes (1936) have described 

 it correctly, many authors have given incorrect accounts. In the 

 normal forward '' ghding " movement, the long anterior flagellum 

 is held straight out in front, and undulations are found only at 

 the tip, passing in the direction from base to tip. The anterior 

 flagellum is unlikely to cause this gliding component, whose 

 mechanism is still not understood, although we now know that 

 there is a second flagellum passing along the body surface. The 

 second type of activity shown by Peranema is a writhing movement 

 with active lashing of the anterior flagellum, which results only 

 in a circling movement with little or no forward component, and 

 may result from stimulation of the animal. These flagellar 

 contractions are more like those of typical flagellates and show 

 two interesting features. Lowndes (1941) found that the velocity 

 of propagation of the contraction wave increases along the 

 flagellum from base to tip, and the amplitude of the waves also 

 increases. The change in form of the bending wave as it passes 

 along this flagellum may be connected with its complex structure 

 (p. 39), for the tapered intraflagellar strand could give a decreased 

 resistance to bending towards the tip, and the striated sheath 

 may also modify the movement. 



Patterns of beating from a more or less pure sine wave to a 

 unilateral ciliary beat are found among the more complex 

 flagellates. Two examples from the gut of the termite Zooter- 

 mopsis will serve to illustrate this. Trichomonas termidopsis has 

 four free flagella and a fifth, recurrent flagellum forms part of 

 the undulating membrane. In life, the undulating membrane 

 almost encircles the body and waves of contraction pass along 

 the recurrent flagellum from base to tip in continuous succession, 

 causing the body to rotate. The bending waves of the recurrent 

 flagellum appear sinusoidal, with the plane of bending roughly at 

 right angles to the plane of the undulating membrane, although 



