THE MOVEMENTS AN1> REACTIONS OP AMCEBA. 233 



(20) The currents in the positive and negative reactions are not 

 similar to the currents in a drop of inorganic fluid moving toward or 

 away from an agent which causes a local decrease or increase in the 

 surface tension. In Amoeba the currents on the surface and in the 

 interior are congruent ; in the inorganic fluid they are opposed. 



(21) In the taking of food the protoplasm and the food body in 

 many cases do not tend to adhere, so that the Amoeba is compelled to 

 overcome considerable mechanical difficulty before the food can be 

 inclosed. Frequently the food body rolls away from the animal as soon 

 as it is touched (pp. 193, 196). The difficulty is overcome by sending 

 out pseudopodia on each side of the body and inclosing it, together with 

 a certain amount of water. In Amceba verrucosa and its relatives food- 

 taking is aided by the tendency of foreign bodies to adhere to the body 

 surface. Amoebae frequently prey upon each other, and this often gives 

 rise to a long and complex train of reactions (pp. 198-202, and Fig. 76). 



CONCLUSIONS. 



(22) The chief factors in locomotion seem to be as follows: (i) At 

 the anterior edge of the Amoeba a wave of protoplasm pushes out, rolls 

 over, and becomes attached to the substratum ; (2) This pulls on the 

 upper surface of the Amoeba, causing it to move forward ; (3) The 

 hinder portion of the Amoeba becomes released from the substratum, 

 and contracts slowly ; (4) As a result of the strong pull from in front 

 and the slight contraction from behind the posterior end moves forward ; 

 (5) The internal substance must flow forward as a result of the pull on 

 the upper surface, the movement forward of the posterior end, and the 

 pressure due to the pulling from in front and the contraction behind. 

 The movement of the internal fluid is comparable to that in a sac or 

 bladder half filled with water and rolled along a surface (pp. 146, 149, 



171). 



(23) There is no continuous transformation of endosarc into ectosarc 

 at the anterior end, and of ectosarc into endosarc behind this (Rhum- 

 bler's ento-ectoplasm process), as a necessary feature of locomotion, 

 since the ectosarc of the upper surface rolls over to the under surface 

 at the anterior end (p. 148). Nevertheless, ectosarc and endosarc are 

 mutually interconvertible when need arises for the change of one into 

 the other. 



(24) It results from paragraphs (i), (2), (n), above, that the loco- 

 motion of Amoeba cannot, with fidelity to the results of the physical 

 experiments, be accounted for by a decrease in surface tension at the 

 anterior end. 



(25) From (3), (4), (12), above, we must conclude that the sending 

 out of pseudopodia cannot, without violence to the results of the phys- 

 ical experiments, be accounted for as due to a local decrease in surface 

 tension at the point of the pseudopodium. 



