392 WM. A. KEPNER AND J. GRAHAM EDWARDS 



a and a' (fig. 13 B) about the ciliate. The prey now escaped, 

 but a' was advanced to b and an overarching thin pseudopod 

 c arose from between the bases of the two encircling pseudopods. 

 The formation of the food vacuole did not advance beyond 

 this state. Pseudopods a, b-a' and c were then retracted. 



Pelomyxa may also modify its reaction to a given stimulus 

 as though a summation of stimuli, or a change of physiological 

 state had taken place. This is shown in the following obser- 

 vation in which the Pelomyxa was reacting to a Paramaecium 

 caudatum. 



November 14, 1916. The Pelomyxa in this case moved 

 past a quiet paramaecium, which lay almost parallel to and with 

 its oral or ventral side directed away from the rhizopod. After 

 the Pelomyxa' s anterior half had passed the ciliate it reacted 

 by sending a small pseudopod a (fig. 14) to the paramaecium 

 at position 1. The contact with the paramaecium caused it 

 to take position 2. The narrow pseudopod followed the ciliate 

 and made a second contact at b. Again the paramaecium re- 

 treated. It was followed to its third position 3 and contact 

 c was made. Paramaecium next took position 4. The taper- 

 ing pseudopod followed it to d and again caused it to move off; 

 this time to position 5. At this point the advancing pseudopod, 

 a, b, c, d, was modified so that it grew laterally as it advanced 

 towards position 5 of the paramaecium, and when it came close 

 to this animal it spread anteriorly and posteriorly along the 

 dorsal side of the prey. In the meantime the entire pseudopod 

 widened as the anterior portion of the Pelomyxa' s body flowed 

 back into it. This widened pseudopod (shown by the broken 

 contours) now gave rise to pseudopods / and /', these in turn 

 advanced to g and g' when the paramaecium escaped from the 

 mouth of the enclosed bay. After this the large bifurcated 

 pseudopod was slowly withdrawn. 



