15 THE BEHAVIOR OF LOWER ORGANISMS. 



rather difficult to see how the forward movement of the outer layer 

 would be produced. As we have seen, Blochmann found that the 

 internal and external forward currents move at the same rate and in 

 the same direction. It is difficult to explain how this should occur if 

 the two are separated by a layer moving in the opposite direction. 

 But Blochmann accepted Biitschli's suggestion, and attempted to give 

 some evidence in its favor. He says that one sees the outer current, 

 with the movement of the projections, in places where the marginal 

 current has come to rest, and that the outer and internal currents then 

 move at the same rate, separated by the resting marginal layer. Now 

 one can receive exactly this impression in Amoeba in the following 

 manner : The margins where they are pressed against the substratum 

 are at rest. Just above this region, and often visible in the same focus, 

 there is the forward current, which is visible on the one hand on the 

 surface (through the movements of the projections) ; on the other hand, 

 in the interior (through the movements of the granules of the endosarc). 

 Unless one is on his guard as to the slight difference in level, one might 

 seem to see two currents separated by a resting layer, particularly if 

 the probability that this were true had been suggested beforehand. It 

 is notable that Blochmann describes nowhere outer and inner forward 

 currents, separated by a marginal backward current, as would be 

 required by the modified surface-tension theory. 



We have demonstrated above, for Amoeba at least, that the forward 

 movement is not confined to a thin outer layer, but extends from the 

 outer surface to the endosarc (p. 142) ; in other words, that the outer 

 surface moves in continuity with the internal substance. 



Rhumbler (1898, pp. 126-130) discussed at length the possibility of 

 explaining the movement of Amoeba by means of a rolling sac of 

 ectoplasm, only to come to the conclusion that it was impossible. 

 Rhumbler's discussion of this matter is an excellent example of the 

 fact that acumen and excellent reasoning may lead one astray in scien- 

 tific matters when the observational basis for the reasoning is not 

 secure. What chiefly misled him was an incorrect idea as to the 

 direction of the currents in the substance of Amoeba, particularly his 

 assumption that there is a backward current on the upper surface. 

 The diagram which he gives of the currents as they must occur in an 

 Amoeba moving in a rolling manner (Fig. 33, A, p. 133) is, therefore, 

 much more nearly correct than that in which he shows what he con- 

 siders the really existing currents (Fig. 33, B). 



Rhumbler's conception as to the necessary movements in the sub- 

 stance of an Amoeba progressing by rotation is, however, incorrect in 

 one particular, so that his diagram (Fig. 33, A) does not correspond 

 to the facts in this point. He assumes that there must be a backward 





