398 WM. A. KEPNER AND J. GRAHAM EDWARDS 



be crowded towards one of the pseudopods by the expansion 

 of one of them until the inter-pseudopodial space is reduced 

 when the two pseudopods take part in the formation of the 

 food-vacuole; and (5) finally, even a foreign body, such as a 

 desmid may become a conditioning factor in the reaction of the 

 Pelomyxa in meeting the contingency of the escape of the prey. 

 This variability of reaction to food of Pelomyxa stands in 

 sharp contrast to that of a more highly specialized protozoan 

 such as paramaecium. Similarly there is a contrast between 

 types of food eaten by the two animals. A Pelomyxa' s food 

 varies in quality greatly, for it includes plants and animals; 

 in size this food varies from nematodes to very minute ciliates 

 and flagellates. A paramaecium's food, on the other hand, 

 consists solely of bacteria and its size is determined by the car- 

 rying capacity of the vortex created by its peristonial cilia. 

 Hence we find Pelomyxa having two types of food-reaction 

 and presenting great variation in the details of one of these; 

 whereas, paramaecium has but one type of food reaction and 

 that showing little if any variation. 



SUMMARY 



1. There are two general types of food-reaction. 



2. The contingency presented by the possible escape of motile 

 objects of prey appears to condition the more complex type of 

 food-reaction. 



3. The paths of possible retreat of motile objects present 

 a wide range of variability, so that, though we may predict 

 what in general the type of reaction may be to such objects, 

 yet the details of such reactions cannot be predicted. Slight 

 variability of contingent conditions is presented by non-motile 

 objects of food, and to these we find Pelomyxa responding 

 with very little variability of reaction. 



4. No hypothesis, yet advanced to explain the movement of 

 Rhizopoda, can be applied to the solution of the problem of 

 Pelomyxa's movement about the food-bodies. 



