THE MOVEMENTS AND REACTIONS OF AMCEBA. 139 



on this point are those of Schulze (1875), Berthold (1886, p. 109), and 

 Biitschli (1892, p. 220). These authors all agree that the backward 

 current visible at the sides of the anterior end in Pelomyxa are clearly 

 also present on the upper surface. It is not usually possible to observe 

 particles moving backward on the upper surface of Amoeba, nor even 

 particles at rest, though this might be due to the fact that the granules 

 have sunken downward, leaving the upper surface clear. But to 

 decide whether the currents in Amoeba are essentially like those pro- 

 duced in a drop of fluid by a local change in surface tension, it is most 

 important to determine with certainty what is taking place on the upper 

 surface. 



Evidently the most natural way of doing this is to cause, if possible, 

 some small object to rest upon or become attached to the upper surface 

 of Amoeba, then to observe the movement of this object. This can be 

 done by mingling a considerable quantity of soot with the water in 

 which the Amoebae are found. Some of the soot particles settle on the 



FIG. 38.* FIG. 39. t 



upper surface of the Amoebae, and in some species they adhere to this 

 surface. 



I was quite unprepared for the results of this experiment. The 

 upper surface of Amoeba moves forward, not backward, as required 

 by the surface tension theory ; nor is it at rest like the lower surface. 



* FIG. 38. Movements of a particle attached to the outer surface of Amoeba 

 verrucosa. When first seen the particle was at the posterior end (/) ; it then 

 moved forward, as shown by the arrows, until it passed around the anterior end 

 (a) to the under side. (The Amoeba itself of course moved forward at the same 

 time; no attempt is made to represent its movement in the figure.) 



f FIG. 39. Diagram of the movements of a particle attached to the outer 

 surface of Amoeba verrucosa, in relation to the movements of the animal. The 

 Amoeba is seen from above. In the position i the particle is at the anterior end 

 of the Amoeba. As the Amoeba moves forward, it passes over the particle, 

 which retains its place. Thus when the Amoeba has reached the position 2 the 

 particle is at the middle of its lower surface; when it reaches 3 the particle is at 

 its posterior end. The particle then passes upward and forward, as shown by 

 the arrows, so that when the Amoeba reaches the position 4 the particle is in 

 front of the middle, on the upper surface. 



