116 Animal Intelligence 
“th, 16th, 17th, 18th and roth trials he did perform the act 
before the 10 seconds were up, then for several times went 
during the two-minute intervals without regarding the sig- 
nal, and finally abandoned the habit altogether, although 
he showed by his behavior when the signal was given that 
he was not indifferent to it. 
Dogs 1, 2 and 3 were also given 95, 135 and 95 trials, re- 
spectively, the acts done being (1) standing up against the 
wire netting inclosing the pen, (2) placing the paws on top of 
a keg, and (3) jumping up onto a box. The time intervals 
were 5 seconds in each case. |No dog of these ever per- 
formed the act before I started to take the meat to feed 
them, but they did show, by getting up if they were lying 
down when the signal was given, or by coming to me if they 
were in some other part of the pen, that something was sug- 
gested to them by it., Why these cases differ from the cases 
of Cats 3 and 4 (zo and 12 also presented phenomena like 
those reported in the cases of 3 and 4) is an interesting 
though not very important question. The dogs were not 
kept so hungry as were the cats, and experience had cer- 
tainly not rendered the particular impulses involved so 
sensitive, so ready to discharge. Dogs 2 and 3 were older. 
There is no reason to invoke any qualitative difference in the 
mental make-up of the animals until more illuminating ex- 
periments are made. 
ASSOCIATION BY SIMILARITY AND THE FORMATION 
OF CONCEPTS 
What there is to say on this subject from the standpoint of 
my experiments will be best introduced by an account of 
the experiments themselves. 
Dog 1 had escaped from AA (O at front) 26 times. He 
we 
