METABOLIC GRADIENTS IN AMOEBA 95 



great elastic tension, so that if they are cut they retract and 

 shorten like stretched rubber bands when cut. With the develop- 

 ment of this tension there appears in each pseudopodium, an axial 

 fibril, obviously indicative of coagulation. The animal moves by 

 the contraction of the pseudopodia, drawing itself along, and in 

 this contraction, the axial fibril shortens and does not wrinkle, 

 indicating that it is the contractile element. When the pseu- 

 dopodia are withdrawn the fibrils vanish completely. This ap- 

 pears to me to be excellent case of coagulation accompanying 

 contractility. 



In conclusion, I wish emphatically to disclaim any originality 

 or priority for the explanation of amoeboid movement which I 

 have presented, although I should perhaps state that it arose in- 

 dependently in my mind as a result of my observations on the 

 axial gradient. I found in the literature that a number of in- 

 vestigators had made similar suggestions, particularly Jennings, 24 

 and further that Rhumbler as far back as 1898 had given the 

 same explanation of the movement of certain amoebae with 

 ' hautartigem' ectoplasm, such as A. verrucosa. He states that 

 in amoebae with solidified ectoplasms "die Bewegung des 

 Pseudopodiums erfolgt dadurch dass lokale 'Verflussigungen bez. 

 Herabminderungen der Spannkraft der Haut .... her- 

 beigefuhrt werden" (Rhumbler, '98, p. 195). In later papers 

 ('05, '10) he has given a more complete statement of the method 

 of locomotion in amoebae with gelatinized surfaces, and in 

 various places he has discussed the futility of attempting to 

 draw any line between the liquid and solid state in emulsoid 

 solutions, and has emphasized that in protoplasm the state is 

 always changing. I believe that Rhumbler has been mistaken 

 merely in assuming that most amoeboid organisms have fluid 

 surfaces, and in failing to realize that the spumoid structure is 

 evidence of the loss of fluid properties and the gain of solid 

 properties. The * Schaumspannung' to which he frequently 

 refers is identical with the contractile tension on the surface of 

 amoeboid organisms of which I have spoken. It is a matter of 



24 Even Biitschli had. a very similar theory ('94, p. 314); also Montgomery 

 (Pfliiger's Archiv, vol. 25, 1881). 



