36 Transactions Tennessee Academy of Science. 



The stentor has a definite and permanent body shape which is 

 covered with small hair-like organs, the cilia, which function as 

 locomotor organs and also to create a vortex of water directed 

 toward its mouth, by means of which food and other particles are 

 brought to it. The ameba on the other hand has no definite body 

 shape, no definite organs of locomotion, no mouth ; it has, indeed, 

 no specialized organs of any sort. Another difference between 

 these two forms is that stentor frequently attaches itself to some 

 solid support, while at other times it swims freely through the 

 water. But the ameba neither fastens itself nor swims in the 

 water; it glides over the surface of submerged objects like a 

 snail does ; but unlike a snail, it changes its shape continually, and 

 what is at any given time the head end will be gradually trans- 

 formed into the tail end. 



Of these two forms the ameba is commonly regarded as stand- 

 ing much lower in the scale of living beings than stentor; indeed 

 it is frequently referred to as the simplest animal known. A refer- 

 ence to figures 1 and 2 will serve to make clear to some extent the 

 main characters of these forms. 



We shall first take up some of the experimental work on sten- 

 tor. The method of feeding was simple. A number of particles 

 of the desired kind were sucked up with some water into a pipette 

 of very small bore. The particles were then very slowly dropped 

 on the stentor 's disk and the fate of each one, whether eaten or 

 rejected, was noted and recorded. The work was done under a 

 binocular microscope magnifying sixty-five diameters. 



As a first experiment I fed a few small organisms, known under 

 the name P hoc its triquctcr, which were ingested ; then a number of 

 grains of sulphur were fed, but all of these excepting one, were 

 rejected. Then some more phacus were fed, followed by sulphur 

 grains. Again the phacus were eaten and the sulphur rejected. 

 The experiment showed that the food discriminative powers of 

 stentor as far as they apply to sulphur and food organisms, arc 

 nearly perfect. 



In other similar experiments stentor discriminated almost per- 

 fectly between food organisms and starch grains (which stentor 

 cannot digest), and between food organisms and powdered glass 

 or sand grains. The degree of accuracy in discrimination ranged 

 from about 90 per cent to 98 per cent. The same degree of dis- 



