112 
W. GLEN LISTON ANI) C. H. MARTIN. 
the culture-medium it made its way by extruding two distinct 
types of pseudopodia, viz. (1) coarse lobose pseudopodia, 
consisting almost entirely of ectoplasm, were extruded for 
the most part in the direction of movement, and (2) fine, 
needle-like, short, pointed pseudopodia extended out from 
the lobose pseudopodia as well as from other parts of the 
body. A nucleus and contractile vacuole were plainly visible. 
The vacuole contracted rhythmically and fairly regularly 
almost every two minutes. The amoeba moved over the 
medium at about the rate of 160 fx in thirteen minutes. As 
it progressed it encountered in its path little groups of cocci 
which were growing with it on the culture-medium. During 
one hour and thirty-eight minutes before the amoeba divided 
into two individuals, one hundred and eight cocci were 
ingested by the amoeba under observation. The cocci 
were taken into the protoplasm of the amoeba in groups of 
two or four. When larger groups of cocci were encountered 
the amoeba broke them up into smaller groups and then 
ingested them. Four minutes after ingestion the cocci were 
seen to be contained within a vacuole. The vacuoles con- 
taining the cocci moved about through different parts of the 
protoplasm, and as digestion proceeded they at first became 
larger, then, becoming smaller, they slowly disappeared. (On 
a neutral-red medium it was easy to demonstrate that the 
contents of the vacuoles had an acid reaction.) The cocci 
within the vacuoles for a time remained visible, but gradually, 
in the course of fifteen minutes, melted from view. After 
watching the amoeba for one hour and thirty-eight minutes, 
it gradually became more and more sluggish and the 
contractile vacuole contracted less and less frequently. These 
changes occurred immediately after the amoeba had engulfed 
piecemeal a group of thirty cocci, the amoeba appearing to 
be satiated with this big meal. The amoeba had meanwhile 
assumed a rounded form, withdrawing all lobose pseudopodia, 
but still the fine needle-like pseudopodia projected from its 
surface. The movements of the protoplasm, which up to 
this time had been active, gradually ceased altogether, and 
