THE FORM OF BEAT OF FLAGELLA 135 



and gyration of this end of the animal, such that the animal 

 *' screws " its way through the water by the principle of the 

 rotation of an inclined plane (Fig. 34). The mode of movement 

 of the organism need not be considered at length here, but the 

 motion of the flagellum is of interest. 



Lowndes (1944) has pointed out that the description of flagellar 

 movement of Monas given by Krijgsman (1925) in his figures 

 A and B, and since copied many times, does not give a good idea 

 of the normal movement of the flagellum of this organism. In 

 the first place, Krijgsman stated that his figures were diagrammatic 

 or semi -diagrammatic, which Lowndes interpreted to mean that 



Ettglena viridis. 



Fig. 34. Movement of Euglena, showing the successive 



positions taken up by the organism in swimming along the 



line A-B (from Lowndes, 1941). 



they were Krijgsman's impressions of the way in which the 

 flagellum moves. Secondly, the movement of Monas is inhibited 

 by strong light, in which the organism executes only rather feeble 

 ** kicking movements ", so that, under the illumination necessary 

 for normal high magnification investigation of movement, Monas 

 showed a maximum swimming speed of about 10 jit/sec. In 

 feebler illumination it was found by Lowndes to swim at about 

 260 /x/sec, so that it is unlikely that Krijgsman was in fact seeing 

 Monas moving forward at maximum speed. In any case, one 

 could not watch the flagellum of an animal that was moving at 

 that speed under the high magnification necessary to see it. It 

 is rather sad that these diagrams, which have been used so often 

 to convey an idea of the movement of a flagellum, should be found 

 to show an abnormal mode of movement, but they have had their 

 value in showing movements that flagella can perform, and indeed 

 they show a cycle of movement not unlike that of many cilia. 



