THE MOVEMENTS AND REACTIONS OF AMCEBA. 169 



about for ten minutes at the posterior end, then finally pass upward into 

 the surface current, where they were carried to the anterior end. Even 

 when this slow current from the posterior appendage is completely 

 suspended the suspension is only temporary. The currents after a period 

 begin again, and a strongly marked warty posterior appendage may in 

 time completely disappear, its substance hav- 

 ing become mingled with that of the remain- 

 der of the Amoeba. 



Other parts of the Amoeba may become 

 temporarily immobile and thus excluded from 

 the general circulation. One often sees certain FIG. 57.* 



parts of Amoeba proteus and other similar species thus quiet, while the 

 rest of the body is inactive motion (see Rhumbler, 1898, p. 122). 



In the species with "eruptive" pseudopodia this process seems to 

 have gone farthest. Here the whole outer layer apparently becomes 

 hardened at times, so that movement occurs only when the inner sub- 

 stance bursts through this, forming "eruptive" pseudopodia. In this 

 case the pseudopodia formation apparently differs from that in A?noeba 

 proteus and its relatives, as described above, in the fact that the ectosarc 

 of the body is not transferred to the surface of the pseudopodium. I 

 have not been able to study this process in detail further than to deter- 

 mine that there is no backward current on such pseudopodia. The 

 matter is worthy of further examination. In Amoeba verrucosa, the 

 species which has been hitherto supposed to have the most immobile 

 ectosarc, we have shown that the outer layer is in continual rotary 

 motion in the progressing animal. 



GENERAL VIEW OF THE MOVEMENTS OF AMCEBA IN LOCOMOTION. 



Let us now, with the aid of a diagram, attempt to form a clear con- 

 ception of the movements occurring in an Amoeba that is progressing 

 in a definite direction, with* a view to determining the nature of the 

 forces at work. Fig. 58 may represent a longitudinal section of such 

 an Amoeba as seen in a side view. The anterior end, A, is, as we have 

 seen, very thin, and is applied closely to the substratum, while the 

 posterior end, P, is high and rounded, forming a sort of pouch. It is 

 free from the substratum, beginning at the point AT, at about the middle 

 of the body. 



At the anterior end waves of hyaloplasm are pushed forward one 

 after the other, so that the anterior end successively occupies the posi- 

 tions #, , c. As we know, it is the upper surface which thus pushes 

 out ; it rolls over, so that a point which was originally on the upper 



*FiG. 57. Diagram of the surface currents when the posterior appendage is 

 excluded from the general stream. 



