THE MOVEMENTS AND REACTIONS OF AMOEBA. 15! 



current on the lower surface, as indicated by the lower (heavier) arrows 

 in his diagram (Fig. 33, A). This backward current does not exist, 

 and is theoretically unnecessary, as may be seen by making a cylinder 

 of cloth and moving it in the manner described above (p. 145). The 

 under surface remains at rest until it passes upward at the posterior 

 end (cf. Fig. 40) . Rhumbler held that this backward current below, 

 with the forward current above (Fig. 33, A], must set the endosarc 

 in rotation ; u the endoplasma granules would themselves necessarily 

 all move, like the particles of the ectosarc, in circular or elliptical 

 courses " (p. 128). The absence of such circular or elliptical paths for 

 the granules of the endosarc would then speak against the method of 

 movement by rotation of the ectoplasm. But since there is no such 

 backward current as Rhumbler assumes, and not even the particles of 

 the ectosarc move in circular or elliptical courses, this objection falls 

 to the ground. 



Further, Rhumbler seems to assume that for locomotion by a rotary 

 movement of the ectosarc, the latter must necessarily be a "sharply 

 defined persistent organ," and that its contractions could only be due 

 to preformed, permanent fibers, in a definite arrangement. Rhumbler 

 is able to show of course that these two assumptions are probably incor- 

 rect, and considers that this weighs against the possibility of movement 

 in the manner characterized. But both these assumptions are unneces- 

 sary. The rotation demonstrably does occur, yet the permanent, sharply 

 defined ectosarc with definitely arranged persistent fibers does not exist, 

 as Rhumbler has set forth, and as must be evident to anyone who 

 studies for a long time the changes of form and movement in Amoeba. 

 As we shall see later, a simple drop of fluid, with no differentiated outer 

 layer, may move in the same manner. 



Penard (1902) also discusses the possibility of movement by rotation 

 of the ectosarc in Amoeba verrucosa ( A. terricold). His study of 

 the movements is excellent and he gives as a possibility on p. 115 what 

 is really in its main features a nearly accurate statement of the method 

 in which locomotion actually occurs, only to reject this possibility later. 

 The ground for this rejection is as follows : The posterior end of the 

 Amoeba often bears an irregular saclike projection (what Penard calls 

 the u houppe" ) ; this may be much wrinkled or covered with projec- 

 tions. This wrinkled sac retains its position ; in Amceba verrucosa it 

 is covered, like the rest of the body, with a resistant cuticula, which can 

 be dissolved only with great difficulty and very slowly. 



If the Amoeba rolled on itself in progressing, the posterior part of this mem- 

 brane would necessarily follow the movement and pass little by little forward, 

 which is contrary to the facts. The best manner of assuring one's self of the 

 immobility of the pellicle is to look very attentively at the surface of the con- 



