AMEBOID MOVEMENT in 



made quickly but carefully, beginning and ending with the pos- 

 terior end of the ameba. 



One of the best examples of the sinuous path of an ameba 

 is shown in Figure 33. It is the path of an Amoeba bigeuuna 

 from a natural out-door culture. The observations were made 

 under the conditions outlined above. The temperature, which is 

 an important factor, was unfortunately not recorded, but it was 

 about 28 C. 



Practically the whole of the path of this ameba consists of 

 right and left-hand curves which are nearly uniform in length, 

 each wave being about eight to ten times the length of the 

 ameba. Since the drawings were made at intervals of a minute, 

 the waves are therefore from eight to ten minutes long in time, 

 measuring from crest to crest. Some of the waves are flatter than 

 others, for example wave No. 4, but otherwise it is like the 

 others. Wave 7 is a double wave due to a change of direction. 

 Instead of turning to the right at 9:23 the ameba changed its 

 direction and turned to the left. The smoothness with which this 

 turn was made indicates that it originated in the mechanism pro- 

 ducing the sinuous course itself, or that it proceeded from 

 a very slight stimulus external to it. At 9:49 the direction of 

 movement was changed again, but just enough to disturb the 

 formation of a smooth wave. The general direction of locomo- 

 tion was not changed. It may be assumed that this change was 

 produced by a stimulus external to the wave-producing mechan- 

 ism. The irregularity and shortness of wave 13 was probably 

 due to the same stimulus that disturbed wave n. Shortly after 

 9:58 the ameba came within sensing range of a mass of debris 

 which it pushed away and followed, thus causing a change in the 

 direction of movement. Although waves begin to appear again 

 after this, some of them very smooth, they are not typical for 

 they are too short, ranging from a little over three lengths (wave 

 16) to a little over six lengths (wave 23). It is likely that the 

 disturbance caused by the mass of debris at 9:58 together with 

 the onset of the division crisis produced the succession of atypical 

 waves. An external disturbance that is sufficiently strong to 

 change the direction of locomotion usually persists for the dura- 

 tion of at least one wave length thereafter. It will be noted that 



