FOOD-REACTIONS OF PELOMYXA 393 



DISCUSSION 



The reaction to food on the part of Pelomyxa involves pri- 

 marily a differential contractility. The ability to exercise 

 local contraction of the body is displayed by the observation 

 of H. V. Wilson ('00), Mr. Zirkle and one of us. Such con- 

 duct could not be expected to be explained through surface 

 tension phenomena and brings to bear upon the problem of 

 food-vacuole formation evidence somewhat of the sort that Mast 

 and Root ('16) so ingeniously derived from the reaction of 

 Amoeba proteus to paramaecia. 



Moreover, the formation of food-vacuoles does not involve 

 adhesion as Bayliss ('15) suggests in the following: when the 

 surface of an amoeba or other rhizopod "comes into contact 

 with food, it appears to soften and become sticky so that the 

 food adheres and is more readily taken in," page 22. No evi- 

 dence of adhesion has been encountered in either type of food 

 reaction of Pelomyxa. 



Schaeffer ('16), in some of his observations on amoeba came 

 upon reactions closely resembling the two general types we 

 have been able to record above. He says "a small organism 

 like the flagellate Chilomonas is ingested in a food-cup nearly 

 always large enough to accommodate easily the ciliate Coleps. 

 But particles of isolated proteins are frequently ingested in 

 food-cups scarcely larger than the particles themselves," page 

 545, "and actively moving objects such as organisms, and me- 

 chanically agitated particles are eaten with more water than quiet 

 objects," page 547. If this were all that he was able to record 

 concerning the amoeba's reaction to moving and non-moving 

 objects, his records would closely agree with our observations of 

 Pelomyxa's two types of reactions to food. He goes on to say, 

 however, that "Some objects such as isolated proteins are 

 sometimes ingested apparently without any water; sometimes 

 with just a slight amount of water. On other occasions again, 

 the same kind of objects are ingested in food cups with larger 

 amounts of water," page 547. In Pelomyxa we have found no 

 such variability. When non-motile food was ingested there 



