THE BEHAVIOR OF PROTOZOA 65 
but it is plain that their interpretation presents difficulties. 
It may be asked whether the Bodos combine designedly in 
groups of ten or twenty, understanding that they are more 
powerful when united than when divided. But it is more 
probable that voluntary combinations for purposes of attack 
do not take place among these organisms; that would be to 
grant them a high mental capacity. We may more readily 
admit that the meeting of a number of Bodos happens by 
chance; when one of them begins an attack upon a Colpod, 
the other animalcula lurking in the vicinity dash into the 
combat to profit by a favorable opportunity.” 
More recent investigations have shown that the behavior 
of protozoa gives no evidence of the high psychic develop- 
ment assumed by Binet. There has been a strong tendency 
on the part of certain investigators to explain the behavior 
of these low forms as due in large measure to comparatively 
simple physical and chemical factors. Others contend that 
the phenomena are much more complex and at present defy 
analysis into physical and chemical processes, while a few 
go further and maintain that we must assume some super- 
physical agency, a vital principle, or entelechy of some 
sort, to explain the results. 
Much attention has been bestowed upon the activities of 
Ameeba, which is generally assumed to be one of the most 
primitive of the protozoa. Ameeba is a jelly-like organism 
with a clear, outer, relatively dense layer of protoplasm, the 
ectosarc, surrounding a more fluid, granular substance, the 
endosarc, which contains the nucleus. The Amceba com- 
monly moves by sending forth blunt processes or pseudopodia 
from the side of the body; material flows into the pseudopod 
which may increase greatly in size; then other pseudopods 
are put forth on the same side, the posterior part of the body 
being pulled, in the meantime, in the direction in which the 
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