FOOD-REACTIONS OF PELO.MYXA 383 



the other hand a ciliated object may produce physical stimula- 

 tion through currents set up in the water as well as causing 

 stimulation through the products of its metabolism. Schaeffer 

 indicates that mere physical stimuli are responded to by 

 amoeba. 



Schaeffer, ('12), says: "All sorts of particles, whether digestible 

 or not, are eaten if properly agitated. Not only is it unneces- 

 sary for the agitated particle to lie in contact with the amoeba, 

 but vibrations produced by a needle are likewise reacted to 

 positively, if the needle point is one-fiftieth of a millimeter or 

 more from the amoeba. We may be certain, therefore, that 

 water vibrations proceeding from a definitely localized source 

 are an efficient cause for successful feeding," page GO. 



As a rule, the reactions of Pelomyxa to food fall into two 

 general types. These types arise out of the non-motility or 

 motility of the prey — the possibility of escape of the latter 

 presenting a contingency, which to be successfully met, has 

 led to a definite type of reaction. 



Great variability of reaction to food has been observed in 

 Amoeba proteus by Kepner and Taliaferro ('16), though but 

 two classes of stimulation, concerned in the reaction of a rhizo- 

 pod to food, can be recognized. 



We shall record at this point the following examples of the 

 first type of food reactions. These descriptions of Pelomyxa's 

 behavior are taken from notes which were made at the time of 

 observation by the authors and others who happened to take 

 turns with us at the microscope as the reactions progressed. 



OBSERVATIONS 



A. Reactions to objects not capable of retreat 



November 4, 191G. A Pelomyxa moving in the direction of 

 a green Eromosphaera encountered the spherical alga ec- 

 centrically so as to turn it counter-clock-wise (as seen under 

 the compound microscope) through about ten degrees. The 

 Eromosphaera was not moved farther than this. The tip of the 

 Pelomyxa's pseudopod next expanded to fit intimately the 



