308 PROTOPLASM 



to the streaming drops of oil-lather described before in fact 

 so entirely their exact counterpart in all important points 

 that I am completely convinced of the agreement of the 

 forces at work in the two instances. In these Amoebae also 

 we find an axial stream which passes through the axis 

 towards the progressing anterior end, there bends round on 

 each side, though certainly in other directions also, 1 flows on 

 the exterior of the body for usually a relatively short distance 

 backwards, and then comes to rest. The axial stream draws 

 protoplasm to itself from all sides at the posterior end, and 

 in the same measure that this protoplasm from behind passes 

 into the current, the quiescent lateral protoplasm is carried 

 farther backwards, and then by degrees passes into the axial 

 stream again. The single essential difference, which is usually 

 shown between such Amoebae and streaming drops of oil- 

 foam, is this, that the extension-current of the anterior 

 end for the most part only extends, as has been said, a 

 comparatively short distance backwards, and that it comes 

 to rest relatively quickly. In the drops of oil-froth, how- 

 ever, the extent of the current in question also depends, on 

 the one hand, upon the intensity of the forces at work, on 

 the other hand, upon the viscidity of the oil. It can often 

 be observed that feeble extension-currents are only continued 

 a little way towards the hinder end, so that the conditions 

 become quite similar to those of the Amoebae described. I 

 am hence convinced that the explanation of the phenomena 

 of streaming in these Amoebae must be the same as that we 

 put forth for the froth-drops. 



If we wish to apply the explanation given for foam- 

 drops to the phenomena of movement in Amoebae, it will be 

 necessary, in the first place, to examine into the nature of 

 protoplasmic substance a little. The aggregate condition has 

 already been briefly considered above, from which it resulted 

 that both the framework and the intervening substance must 



1 It is easy to convince oneself in Pelomyxa of the fact that the back cur- 

 rent at the progressing anterior end, or at the tip of a pseudopodium, as the 

 case may be, goes on over the entire free surface, and not merely at the two 

 sides, where it usually conies into view. With a suitable focus it can 

 always be plainly seen that the back current stretches over the whole free 

 surface. 



