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 producing 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 locomotion was not changed. It may be assumed that this change was produced by a stimulus external to the wave-producing mechanism. The irregularity and shortness of wave 13 was probably due to the same stimulus that disturbed wave 11. 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 duration of at least one wave length thereafter. It will be noted that [Illustration: Figure 33. Illustrating the path of an _Amoeba bigemma_ under controlled conditions, in ordinary diffuse light from a north window. For convenience of reference the waves in the path are numbered from 1 to 23. The figures were drawn with the aid of a camera lucida at intervals of one minute. The path was recorded from 8:58 to 10:26, when fission occurred. After fission, the path of one of the daughter cells was followed for a short time, but the ingestion of a mass of debris destroyed the regularity of the path. The vertical lines at the point where fission occurred indicate that the figures _above_ the lines were moved up the length of the lines. The first figure beyond wave 13 was influenced in its movements by a mass of debris lying to its left. Average length of the ameba, 150 microns.]