FOOD-REACTIONS OF AMEBA PROTEUS 401 
Except for the diatoms, we have seen that there is a wide range 
of motile food bodies to which Ameba proteus displays a general 
type of response. The following observations have been chosen 
as examples of the ameba' s second type of food reaction and also 
to display the range of adaptive modification this type of reac- 
tion may present. 
The ameba seems to have a marked preference for Chilomonas 
Paramecium. It will readily accept one of these little ciliates, 
though it has been feeding on a non-motile object or other motile 
objects. On March 19, 1919, we observed a specimen that had 
been feeding upon Oscillatoria. A Chilomonas swam into a bay 
between two stout, short pseudopods and lay in the position 
shown in figure 5. The ameba immediately sent two secondary 
pseudopods, A and B, out toward each other and behind the 
Chilomomas. These pseudopods met and fused; the ciliate was 
thus surrounded on all sides. It was next overarched by a thin 
sheet of ectoplasm. When all lines of retreat were thus cut off 
from the Chilomonas, the ameba reduced the size of the large 
vacuole, within which the prey had been captured, to that of the 
usual food vacuole. Both ectoplasm and endoplasm entered the 
formation of the pseudopods A and B in this reaction. This is 
the manner in which the enclosing pseudopods are usually con- 
structed. But even the structure of the pseudopods may be 
modified to meet the needs of a peculiar situation. 
In one instance we observed an ameba approach two Chilo- 
monases in the shallow margin of a hanging drop. In this case 
ectoplasmic pseudopods a and a' were sent out about the Chilo- 
monases (fig. 6). As a grew down to contour b, an overarching 
layer of ectoplasm, c, was formed above the prey. The internal 
margins thus formed eventually fused as b grew down to divide 
the enclosed space into two food vacuoles. The animal then 
moved out into deeper water. The unusual feature of this reac- 
tion is not that the overarching protoplasm is ectoplasmic, for 
that and the underhanging wall of the forming food vacuole are 
usually ectoplasmic. The unusual feature is the fact that the 
ectoplasm formed all sides of the forming food vacuoles. These 
vacuoles were thrown into the endoplasm when the animal moved 
