PHYSIOLOGY 



107 



tion of flagellum is accomplished by a slow forward movement, 

 while undulation along the entire length by a rapid forward move- 

 ment. Recently Krijgsman (1925) studied Monas sp. (Fig. 44) 

 which he found in soil cultures, under the darkfield microscope 

 and stated: 1) when the organism moves forward with the maxi- 

 mum speed, the flagellum starting from cl , with the wave begin- 

 ning at the base, stretches back (c 1-6), and then waves back {d, 

 e), which brings about the forward movement. Another type is 



Fig. 44. Diagrams illustrating flagellar niovemengs of Monas sp. 

 (Krijgsman). a-g, rapid forward movement (a, b, optical image of 

 the movement in front and side view; c, preparatory and d, e, effective 

 stroke; f, preparatory and g, effective stroke); h-j, moderate forward 

 movement (h, optical image; i, preparatory and j, effective stroke); 

 k-o, undulator}' movement of the flagellum in backward movement; p, 

 lateral movement; q, turning movement. 



one in which the flagellum bends back beginning at its base (/) 

 until it coincides with the body axis, and in its effective stroke 

 waves back as a more or less rigid structure (g) ; 2) when the or- 

 ganism moves forward with moderate speed, the tip of the flagel- 

 lum passes through 45° or less (h-j); 3) when the animal moves 

 backward, the flagellum undergoes undulation which begins at 

 its base (k-o) ; 4) when the animal moves to one side, the flagellum 

 becomes bent at right angles to the body and undulation passes 

 along it from its base to tip (p); and 5) when the organism under- 

 goes a slight lateral movement, the distal end of the flagellum 

 only undulates (q). 



