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FRANK W. BANCROFT 



body (fig. 2) and extends posteriorly along the ventral side; not 

 anteriorly as ndicated in Jennings's ('04, '06) figures. That this 

 s the actual position of the flagellum was determined by watching 

 the motion of india ink particles which had been added to the 

 culture fluid (fig. 3) ; and also by observing the flagellum directly 

 after adding the viscid Irish moss solution'^ (fig. 2, a). When the 

 fluid was made so viscid that the Euglenae cou'd barely swim some 

 of the flagellae ceased beating continuously and in these indi- 



Fig. 2 Diagram showing the position of the flagellum as seen in a viscid me- 

 dium; a, when Euglena is swimming forward in a narrow spiral; h, when swerving 

 sharply towards the dorsal side; c, when moving backwards. 



Fig. 3 Dotted area, shows the position of the moving india ink particles. 

 a, when Euglena is swimming forward in a narrow spiral ; h, when swerving towards 

 the dorsal side during a shock-movement. 



viduals it could occasionally be seen that loops were formed near 

 the proximal end of the flagellum, which loops then rapidly pro- 

 gressed towards the tip. It seems, then, that the flagellum goes 

 through about the same motions as a rope one end of which is free, 

 and the other end held in a hand which from time to time describes 

 small quick cii-cles in a plane perpendicular to the rope (Biitschli) . 

 It will be seen that such a motion would furnish both a forward 

 component and one which would tend to rotate the Euglena on 

 its long axis. It is also evident that the Euglena can never swim 



^Normally the flagellum seems to work as close to the ventral side of the organ- 

 ism as it is possible for it to do; for india ink particles that are in contact with the 

 ventral surface are set in motion by its vibrations. When swimming in a narrow 

 spiral unilateral stimulation does not diminish the slight swerving towards the 

 dorsal side. 



