138 THE BEHAVIOR OF LOWER ORGANISMS. 



and must therefore spread out ; it would not be unnatural for the 

 currents to flow even backward a little, as in Schulze's figure (Fig. 

 37), in order to fill the area just in front of the resting portion of the 

 protoplasm (at x, Fig. 37). As we shall see, such movement is 

 sometimes to be observed in inorganic fluids under similar conditions 

 (p. 21 1). Whatever the explanation of the difference between my 

 observations and those of the investigators named, the point of impor- 

 tance is that the backward current is not a constant nor an essential 

 part of the locomotion of Amoeba, so that it does not form a fitting 

 basis for a theory of locomotion. Further, as we shall see, I am able 

 to demonstrate conclusively the incorrectness of that conception of the 

 nature of amoeboid movement for which alone the account of the 

 currents given by Butschli and Rhumbler is significant. 



It is evident that the method of movement here described is better 

 adapted to the production of locomotion in a given direction than that 

 which Butschli and Rhumbler describe (see Figs. 30-33), since accord- 

 ing to their account a portion of the substance of the body is first trans- 

 ported forward, then backward. In the locomotion as I observed it 

 there is no such useless transportation of substance in a direction 

 opposed to that in which the animal is traveling. 



On the other hand, the movements as I have described them bear 

 much less resemblance to those produced in drops of fluid by local 

 changes in surface tension (Fig. 34). There is only the slight turning 

 outward at the anterior end that can be at all compared to the backward 

 flow of an outer layer in the inorganic drop. Rhumbler himself notes 

 that in Amoeba angulata there is often no such backward current to 

 be seen (Rhumbler, 1898, p. 120), but bases his theory of the forward 

 movement entirely on the cases where it (supposedly) does occur. In 

 Amoeba angulata^ A. verrucosa, and A. sphceronucleolus, according 

 to my observations, there is often no indication even of the turning 

 out of the particles in a fanlike manner ; they merely flow forward and 

 stop for a time. Butschli (1892, p. 199) notes that the backward cur- 

 rent at the anterior end of Amoeba, required by the surface tension 

 theory, is very slight, but conceives it to be sufficient to fulfill the 

 requirements of the theory. 



MOVEMENTS OF UPPER AND LOWER SURFACES STUDIED EXPERIMEN- 

 TALLY ROLLING MOVEMENT IN AMCEBA. 



Thus far we have left out of consideration the movement of substance 

 on the upper surface of the Amoeba. It is usually assumed that the 

 condition here is the same as at the sides and on the under surface ; 

 thus Rhumbler gives a diagram, reproduced in my Fig. 33, B, showing 

 the backward current of the upper surface. The positive observations 



