METABOLIC GRADIENTS IN AMOEBA 83 



later that most of them had already been recorded by Jennings in 

 his 1904 publication to which the reader is referred. It will be 

 sufficient for me to mention that the method of disintegration 

 of the amoeba in cyanide, as described earlier in this paper, 

 points to the same conclusion ; and to report an interesting case 

 of an ingestion of a rotifer by an amoeba. The amoeba had 

 assumed a nearly spherical form following its capture of the roti- 

 fer; the rotifer, which appeared to be quite intact, was thrashing 

 about vigorously within the amoeba, doubling and straightening 

 itself. The endoplasm offered no obstacle whatever to the fran- 

 tic movements of the rotifer but all its struggles did not enable 

 it to pierce the ectoplasm or to produce any effect upon it. The 

 ectoplasm offered a seemingly solid barrier to its escape, behaving 

 indeed like a 'skin' containing the much more fluid endoplasm. 



Another line of evidence is afforded by those Rhizopoda which 

 habitually produce permanent long and slender pseudopodia, as 

 the Foraminifera and the Radiolaria. Even Amoeba may give 

 rise to quite slender pseudopodia. I find it impossible to under- 

 stand how a fluid could be drawn out into such long processes 

 without breaking, and, how, if this were possible, it could main- 

 tain these processes against the surface forces. As Rhumbler has 

 quite readily admitted, one is compelled to recognize that the 

 protoplasm of these organisms is to some degree solidfied, as the 

 presence of a visibly solid axis in many cases testifies. Perhaps 

 the most remarkable case of this kind is that of the Foramini- 

 feran Astrorhiza, described by Schultz ('15), whose long thread- 

 like pseudopodia, after becoming fastened at their tips, exhibit- 

 tensile and contractile properties very much like those of stretched 

 rubber bands; if cut, they retract instantly, just like stretched 

 rubber, and they contract normally with sufficient force to draw 

 the animal along. 



The actual method of locomotion in amoebae and related forms 

 furnishes further excellent evidence against the correctness of 

 the assumptions of the surface tension theory. Amoeba does not 

 move in complete contact with the substratum as supposed by 

 Berthold, Rhumbler and others, nor in the rolling manner de- 

 scribed by Jennings ('04), except in the case of Amoeba verru- 



