THE BEHAVIOR OF PROTOZOA 89 
give the motor reflex with no apparent cause. After a time 
their actions become slower and more sober. Have we any- 
thing essentially different in the experiments of Mr. Smith? 
Possibly so, but I cannot convince myself of it from the 
results described. 
Hodge and Aikins in their study of the daily life of a 
Vorticella observed that one individual, after having en- 
gulfed yeast cells for some time, refused them and persisted 
in so doing for several hours. What this fact signifies can- 
not be decided from the single observation reported; there 
are a number of possibilities, and the correct interpretation 
can be made only after carefully planned experiments. 
There have been few systematic investigations with the 
end of testing the educability of the protozoa, and while 
granting the possibility that future work may compel us 
to modify our conclusion, it may be said that, thus far, there 
is no unmistakable evidence that the protozoa are capable 
of forming true habits or of learning by association. 
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