408 WM. A. KEPNEE AND W. CARL WHITLOCK 
phenomena of spreading and surface tension are adequate for the 
explanation of the movement and food getting of this rhizopod. 
Hynian ('17) says ''I am in favor of Clowes's" (16' a, '16 6) 
''interpretation, aheady referred to, that in passing from the 
surface of the protoplasm to the interior, a reversal of phase 
occurs, the colloidal material forming the outer phase, or dis- 
perse medium, in the surface layers, while in the interior it forms 
the disperse phase and water containing a variety of materials 
in solution and suspension, is the disperse medium" (p. 87). 
It appears to us that even colloidal phenomena cannot be 
called upon to exjDlain the phenomena involved in the food reac- 
tions of this ameba, because of their qualitative character. The 
qualitative nature of these phenomena becomes apparent when 
w^e compare the reactions of ameba to various quiet paramecia. 
In these reactions there appears a marked disparity between 
their variability and the degree of variability of the stimuli 
arising from the quiet animals that are about to be captured. 
An ameba may react to a quiet Paramecium in tkree ways: 
1) by forming a pocket within its own body within which the 
cihate will be driven (figs. 9, 10, 11); 2) by sending encircling 
pseudopods about the prey and then roofing over and flooring 
the enclosed space with ectoplasm before disturbing the prey, 
and, 3) by closing in upon the Paramecium with the advancing 
tips of two pseudopods until the prey is held fast in a grip of the 
pseudopods' ends. After the Paramecium is thus caught, it is 
very tightly closed in upon and constricted (figs. 13 to 18). 
Paramecia concerned in 2 and 3 should not in a highly variable 
manner stimulate the ameba. It might be held that the feeding 
vortex of a Paramecium lying with its ventral side directed toward 
a mass of detritus, as in 1, is of a different character from that of 
a Paramecium lying free in the open. Then, too, the disturbance 
of the water by Paramecium that had been caught at its girdle 
would be changed as soon as the vortex became divided by the 
advancing tips of the pseudopods and thus set up a new type of 
stimulation. There is weight to these possible objections that 
may be raised against the idea that the ameba's reactions toward 
paramecia are quahtative. 
