The Mental Life of the Monkeys 205 
ideas of the signals and clean-cut associations with those 
ideas. The other records check such a conclusion. 
In studying the figures we should remember that occa- 
sional mistakes, say 1 in ro trials, are probably not significant 
of incomplete learning but of inattention or of precipitate 
action before the shutter had fairly exposed the card. We 
must not expect that a monkey who totally fails to discrimi- 
nate will always respond wrongly to the ‘no’ signal, or that 
a monkey who has come to discriminate perfectly will always 
respond rightly. A sudden drop from an average high level 
of error to an average low level will signify sudden learning. 
Where the failure was on the first trial of a series a few hours 
or a day removed from the last series, I have generally repre- 
sented the fact not by a column 1 mm. high and 1 mm. 
broad, but by a single 10 mm. perpendicular. See i and A. 
Such cases represent probably the failure of the animal to 
keep his learning permanent rather than any general in- 
ability to discriminate. 
K was to some extent a memory trial of d (after over half 
a year). 
The experiment with zo and 110 is noteworthy. Al- 
though, as can be seen from the figures, the difference is ob- 
vious to one looking at the white part of the figure, it is not 
so to one looking at the black part. No. 1 failed to improve 
appreciably in fifty trials, probably because his previous 
experience had gotten him into the habit of attending to the 
black lines. 
Before arguing from the suddenness of the change from 
failure to success we have to consider one possibility that I 
have not mentioned, and in fact for the sake of clearness in 
presentation have rather concealed. | It is that the sudden 
change in the records, which report only whether the animal 
did or did not go down, may represent a more gradual 
