THE MOVEMENTS AND REACTIONS OF AMCEBA. 163 



formed the anterior boundary of the hyaloplasm (that is, of the Amoeba 

 as a whole) at a previous pause. The reason for this is as follows : 

 The lower surface of the Amoeba, as we know, is at rest ; here the 

 protoplasm has become modified to form a sort of membrane. This 

 membrane extends up a very little distance at the sides and ends (as 

 is shown by the fact that the protoplasm at the sides is at rest). Thus 

 at the anterior end there is, after a pause, a low barrier formed by this 

 membrane. The next wave of advancing hyaloplasm arises just behind 

 this barrier, overleaps it, and pushes forward (the conditions being 

 essentially the same as in Amoeba verrucosa, already described). This 

 advancing wave when first formed is very thin, forming a mere sheet 

 lying on the substratum. This is shown by the fact that when the out- 

 line of the remainder of the Amoeba is sharply in focus, the anterior 

 portion is often undefined, and one is compelled to focus lower to get 

 its outline sharply. The thin sheet of hyaloplasm which has just pushed 

 forward is bounded behind by a low wall, formed from the membrane 

 which previously limit- 

 ed it in front (Fig. 53, 

 x). Now the granules 

 of the endosarc flow for- 

 ward until they reach ~ 

 this boundary ; there FlG * *~ 



they stop and become 



heaped up against it (Fig. 53). After a time the membrane forming 

 this barrier, since it is now completely enveloped by protoplasm, be- 

 comes dissolved and gives way in the manner described above ; the 

 granules then flow forward. Meanwhile, a new partial boundary 

 has been left in front by the hyaloplasm ; this again stops the endosarc, 

 and the whole process is repeated many times. 



Of course, when the anterior boundary advances uniformly, without 

 pauses, no anterior membrane is formed, and there is nothing to hold 

 back the granules of the endosarc ; hence there is no reason for a separa- 

 tion of hyaloplasm and endosarc, and we find that none exists. On the 

 other hand, when the Amoeba has paused for a long time the anterior 



* FIG. 53. Diagram of a longitudinal section of the anterior edge of Amoeba, 

 to show the cause of the stopping of the granules of the endosarc some distance 

 behind the anterior margin. The line beneath represents the substratum to 

 which the Amoeba is attached. The anterior hyaloplasm at first moves forward to 

 the line x-x ; stopping there it becomes covered with a firmer wall, as represented 

 by the heavy black line. Now the hyaloplasm pushes forward from above the 

 anterior edge x-x, forming a thin sheet closely applied to the substratum, as 

 shown in the figure. The endosarcal granules flow forward, but are stopped by 

 the barrier x-x (the former anterior boundary of the Amoeba); they cannot flow 

 forward till this boundary is liquefied. 



