382 WM. A. KEPNER AND J. GRAHAM EDWARDS 



Wilson ('00) says: " Occasionally a Pelomyxa was observed 

 in the remarkable attitude shown in figure 5, a portion of the 

 body resting on the bottom, while the rest of the animal divided 

 into pseudopodia projected freely upward in the water. In 

 this condition, Pelomyxa appears for the time being as an 

 attached rhizopod with tentacle-like pseudopods, the nearest 

 analogue to which is the interesting minute form, Hylamoeba 

 sessilis, found by Frensel in Cordova, in Argentina." In this 

 connection Wilson shows in his figures variously curved regions 

 of the body, which suggest that there might have been local 

 torsion or bending. Such torsion was observed by Mr. Conway 

 Zirkle in this laboratory. He saw a specimen "sway one of 

 its longer pseudopods through an arc of nearly 90 degrees back 

 toward the thicker region of the body. There was no percep- 

 tible flow of the endoplasm in this pseudopod." 



One of us has observed an arched specimen attached at its 

 two ends standing with the plane of the arch at right angles 

 to the surface. This attitude has been described by Wilson 

 ('00). But in this case, the animal swaj^ed to and fro upon the 

 two bases of the arch, so that at one end of the oscillation it 

 lay with the plane of the arch horizontal and directed toward 

 the right, then after swaying through 180°, the plane of the 

 arch lay horizontal and directed towards the left. More re- 

 markable than this, however, has been the behavior of the 

 specimen which was fixed by one pseudopod such as Wilson 

 ('00) described. This specimen, standing upon the end of 

 its body with its free end bearing three stout pseudopods, had 

 its free end turn so as to inscribe a circular orbit counter-clock- 

 wise. These observations indicate a differential contraction 

 of the protoplasm, most likely the ectoplasm, which approxi- 

 mates muscular activity and could scarcely be explained in 

 terms of surface tension. 



There are obviously two classes of stimuli — chemical and 

 physical — concerned in the response of rhizopoda to food. 

 When, for example, an amoeba reacts to a desmid, that lies in 

 the light, the stimulus arises from the oxygen and other ele- 

 ments or compounds given off by the plant's metabolism. On 



