198 Animal Intelligence 
of an actual retrograde as the trials concerned followed an 
eight days’ cessation of the experiments. 
I next tried No. 1 with an apparatus exposing sometimes 
a card with a diamond-shaped piece of buff-colored paper 
on it and sometimes a card with a similar black piece. 
The black piece was three fourths of an inch farther behind 
the opening than the other. The light color was the ‘yes’ 
signal. The error curves for both signals are given, as No. 1 
at the beginning of the experiment did not go down always 
(Fig. 30, 6 and 6,). 
I next tried No. 1 with the same apparatus but exposing 
cards with YES and N in place of the buff and black dia- 
monds. The record of the errors is given in Fig. 30, ¢ and ¢. 
At ‘the start he came down halfway very often. This I 
arbitrarily scored as an error no matter which signal it 
was in response to. It should not be supposed that these 
curves represent two totally new associations. It seems 
likely that the monkey reacted to the position of the N 
card in the apparatus (the same as that of the black dia- 
mond card) rather than to the shape of the letters. On 
putting the black diamond in front he was much confused. 
Inext gave No. 1 the chance to form the habits of coming 
down when I rapped my pencil against the table twice and 
of staying where he was when I rapped with it once. He 
had go trials of each signal but failed to give evidence of 
any different associations in the two cases. 
Experiments of this sort were discontinued in the summer. 
In October I tried No. 1 with the right and left hand ex- 
periment, he being in a new room and cage, and I being 
seated in a different situation. He came down at both sig- 
nals and failed to make any ascertainable progress with the 
no signal in 80 trials. (October 20-24.) 
I then tried him with the black and buff diamonds, the 
