4 o THE PSYCHIC LIFE 



memory and volition. We shall group our remarks 

 under the two following heads: 



a. The choice of food; and 



b. The movements necessary for the prehension of 

 food. 



The Micro-organisms do not nourish themselves 

 indiscriminately, nor do they feed blindly upon every 

 substance that chances in their way. Also, when they 

 ingest food through some point or other of their bodies, 

 they understand perfectly how to make a choice of the 

 particles they wish to absorb. This choice is some- 

 times quite well defined, for there are species which 

 feed exclusively upon particular foods. Thus, there 

 are herbivorous Infusoria and carnivorous Infusoria. 

 Among the herbivorous ones may be classed the chilo- 

 dons which feed upon small Algae, Diatomaceae, and 

 Oscillaria. The parmecia live principally upon Bac- 

 teria. The Leucophrys is a specimen of the carnivo- 

 rous class; it devours even the smaller animals of its 

 own kind. The Cyrtostomum leucas eats everything, 

 as do the Rotifers. 



Though the fact of an exercise of choice in taking 

 food is settled beyond question, yet the interpreta- 

 tion of this phenomenon is a matter of much uncer- 

 tainty. Some writers, as Charlton Bastian for in- 

 stance, explain this choice of food as an affinity of 

 chemical composition existing between the organism 

 and the nutriment. This idea does not lead to any- 

 thing. Others compare the discrimination made by 

 the Proto-organism between objects presented to it, 

 to the action of a magnet which in some way selects 

 particles of iron that have been mixed with particles 

 of other substances. ' The latter interpretation is an 

 evidence of the tendency evinced by some naturalists, 



