138 MOVEMENT OF CILIA AND FLAGELLA 



it frequently looks twisted, so that this observation needs 

 confirmation. 



The anterior flagella of this trichomonad (at least in preparations 

 of animals removed from the termite and examined in a saline 

 solution) perform a cycle of beat rather like that of many cilia. 

 The four flagella frequently beat synchronously, but may move 

 separately through the characteristic cycle. At the beginning of 

 a beating cycle the flagellum is held straight out, and bends at 

 the base through an angle of about 90° vs^hile the main (distal) 

 part of the shaft remains straight. A wave of bending then 

 passes up the flagellum from the base bringing the flagellum back 

 to the starting position. This cycle of movement is illustrated 

 in PI. XVIa. 



Several species of large flagellates of the genus Trichonympha 

 are also found in this termite. The flagella of the body of 

 Trichony7npha occur in enormous numbers and are inserted on 

 the body in such a way that they are directed backwards. 

 Undulations of these flagella appear to be approximately sinusoidal, 

 and bending waves passing backwards along many flagella at the 

 same time are sufficient to move this relatively large organism 

 (see PL XVIb). Pitelka and Schooley (1958) have pointed out 

 that this flagellar beating will only move the animal forwards, 

 and that changes of direction are caused by movements of the 

 mobile anterior end (rostrum) of the body. 



2. The Form of Beat of Cilia 



The difference between the form of beat of flagella and that 

 of cilia has usually been regarded as a fairly large one, but this 

 is most probably a mistake, for the ciliary beat appears to be but 

 a modification of the flagellar beat. Gray (1955) found that the 

 beat of the sea urchin sperm tail was often asymmetrical. A 

 sperm tail with extreme asymmetry shows a beating pattern very 

 similar to that of a cilium. This is illustrated in Fig. 36, where, 

 although the positions of the flagella in parts A, B and C are 

 falsified because the head normally moves from side to side, the 

 transition from the symmetrical flagellar beat to the ciliary beat 

 is clearly shown. 



Few reliable observations of the beat of cilia have been made, 

 but they usually agree in that the beat of a cilium takes place 



