FOOD-REACTIONS OF PELOMYXA 397 



to terms of equilibration between the organism and its environ- 

 ment, or in the words of Lillie ('15): "In any stable or well- 

 adapted species the total action of the environment upon the 

 organism is exactly counterbalanced by the total activities of 

 the organism. The interaction is reciprocal, and normally 

 results in an adjustment which renders prolonged equilibrium 

 possible. . . . Each organic feature has its complement in 

 some feature of the environment. The complexity of the or- 

 ganism is thus the correlative or mirrow-image of the complexity 

 of external nature." Our own work, on the other hand, in- 

 dicates that a striking characteristic of the food-reactions of 

 Pelomyxa is their adaptability to varying present conditions 

 which involve contingencies. Lillie says also: "It is these 

 externally directed actions which form the greater part of what 

 is known as ' animal behavior,' and they represent an important 

 though not the only, means by which the animal adapts itself to 

 its environment. 



"Ordinarily we class such actions partly as 'instinctive' 

 partly as 'intelligent'; perhaps their most remarkable feature 

 is that they often have reference to a future more or less remote 

 — they can not be understood by taking to account present con- 

 ditions alone." The contingency of escape of the possible prey 

 contrasted with no such contingency are factors in differentiat- 

 ing the two general types of reaction. Moreover, the relative 

 position of the animal that is likely to escape presents condi- 

 tions that are met in a highly variable manner. For example: 

 (1) When the motile prey lies below the Pelomyxa, a curtain 

 of protoplasm is dropped down about the prey and then even- 

 tually the margin of the curtain closes beneath it to complete 

 the formation of the f ood-vacuole : (2) When the motile prey 

 lies above the rhizopod a cylindrical cup arises about it, the 

 lips of this cup eventually closing above the captured animal: 

 (3) When the motile prey lies in the plane through which the 

 Pelomyxa is advancing pseudopods are first sent out to each 

 side of the prey and when it is quite surrounded in this plane, 

 overarching pseudopods form and finally the protoplasm closes 

 in beneath it: (4) If the prey lies between pseudopods it may 



