THE MOVEMENTS AND REACTIONS OP AMCEBA. 149 



Dr. Wallich shared the correct opinion of Lachmann and Perty. 

 This excellent observer unfortunately often gave his results in the form 

 of mere brief general statements, so that one cannot judge how much 

 evidence he had for them, and little attention has, therefore, been paid 

 them. But it is singular how many of these statements show them- 

 selves to be correct, even in opposition to later work. Concerning 

 the matter in question, Wallich has the following : 



In short the effect is similar to that which would be produced were an empty 

 and transparent bladder or caoutchouc sac, containing granular bodies of greater 

 specific gravity than the viscid fluid within which they were sustained, to be 

 rolled along a plain surface. (Wallich, 1863, b, p. 331.) 



He makes no attempt to demonstrate the truth of this correct com- 

 parison, and does not develop the matter beyond the mere statement 

 given above. 



Schulze (1875), Berthold (1886), and Butschli (1892), as we have 

 seen, agree in stating that the currents on the upper surface at the 

 anterior end in Pelomyxa are backward. In view of the great authority 

 of these writers we should be compelled to suppose that the movement 

 in this animal is of an entirely different character from that found in 

 the various species of Amoeba, but for a most fortunate circumstance. 

 The only previous demonstrated observation of the forward movement 

 of the upper surface in the Rhizopoda relates precisely to Pelomyxa, 

 and was made by an investigator closely associated with Butschli. 

 It was not until my work was finished and the present paper written 

 that I came across the note of Blochmann (1894) on the movements of 

 Pelomyxa. Blochmann shows that the movement of substance on the 

 upper surface of Pelomyxa is forward, just as we have found it to be 

 in Amceba. The outer surface of Pelomyxa is covered with fine cilia- 

 like projections. By observing these projections Blochmann had no 

 difficulty in seeing that they move forward on the upper surface. The 

 rate of movement was the same as that of the internal forward current. 

 Butschli (1892, Appendix, p. 220) had already observed, greatly to his 

 surprise, that there is a forward current in the water next to the sur- 

 face of an advancing Pelomyxa, this current being exactly the reverse 

 of that called for by the theory that the motion is due to a lowering of 

 the surface tension at the anterior end. 



Butschli (/. .) attempted to save the surface tension theory by sug- 

 gesting that it was only a thin outer layer that moves forward. The 

 currents in the moving animal would then be as follows : A forward 

 current within, a backward current just beneath the surface, a forward 

 current in a thin layer on the surface. It is possible that this compli- 

 cated arrangement of currents might be brought into harmony in some 

 way with the surface-tension theory of the movement, though it is 



