FOOD-REACTIONS OF PELOMYXA 395 



a convergence of the growing pseudopod. Here food-vacuoles 

 were thus formed in a complex fashion despite the fact that the 

 reaction had advanced to form only b and b' when the ciliates 

 had all escaped. This might suggest a strong physiological 

 momentum causing, by a flood-like process, the completion of 

 the encircling movements. However, but a little later in the 

 same forenoon this same animal had almost completed the en- 

 circling movement about a paramaecium indicated at figure 

 13, B-a and b, and had also formed an overarching pseudopod 

 c over the enclosed bay before the paramaecium escaped. The 

 entire reaction, therefore, in this second instance was much 

 more advanced than in the first (fig. 13, A), and yet after the 

 escape of the prey the currents in pseudopods a, b, c, figure 13, B 

 were reversed at once and the pseudopods withdrawn. 



In the second place, there is yet another method of surround- 

 ing an animal that can hardly have the conception of physio- 

 logical momentum applied to it. Kepner and Taliaferro ('16) 

 saw that in Amoeba proteus, when a Chilomonas stimulated 

 the rhizopod in the narrow angle between two pseudopods that 

 lay close to each other, a small pseudopod was given off behind 

 the Chilomonas from the mesial side of each large pseudopod. 

 We have seen something somewhat like this in Pelomyxa. In 

 figure 12 there is shown a reaction to an object that was stimu- 

 lating the mesial side of one of two adjacent pseudopods (A 

 and B). Here, pseudopod A, after it had by expanding mesially, 

 crowded the small ciliate over closer to pseudopod B, threw 

 out to each side of the possible prey a small secondary 

 pseudopod; while pseudopod B threw out a secondary 

 pseudopod c toward b of A. Before the secondary pseudopods 

 b and c had closed to cut off the ciliate' s retreat the latter es- 

 caped along the path y. After this escape the entire reaction 

 of Pelomyxa was reversed. Here we have a greatly agitated 

 body causing an encircling movement. More than that, after 

 the escape of the prey, though the reaction was well advanced, 

 it was reversed at once. The sudden reversal of relations, more 

 advanced than others which completed the formation of food- 

 vacuoles, suggests that physiological momentum can hardly be 

 invoked to explain the reaction of Pelomyxa towards motile food. 



