t that time, as judged by his size
and the presence of milk teeth, was not more than five years. So far as
I could discover, he was a perfectly normal, healthy, and active
individual. On June 10, 1915, his weight was thirty-four pounds, his
height thirty-two inches, and his chest girt twenty-three inches. On
August 18 of the same year, the three measurements were thirty-six and
one-half pounds, thirty-three inches, and twenty-five inches.

For the major portion of my experimental work, only three of the eleven
animals were used. A growing male, _P. rhesus_ monkey, known as Sobke; a
mature male, _P. irus_, called Skirrl; and the young orang utan, which
had been named Julius. Plates I and II present these three subjects of
my experiments in characteristically interesting attitudes. In plate I,
figure 1, Julius appears immediately behind the laboratory seated on a
rock, against a background of live oaks. This figure gives one an
excellent idea of the immediate environment of the laboratory. Figure 2
of the same plate is a portrait of Julius taken in the latter part of
August. By reason of the heavy growth of hair, he appeared considerably
older as well as larger at this time than when the photograph for figure
1 was taken. In plate II, figure 3, Julius is shown in the woods in the
attitude of reaching for a banana, while in figure 4 of the same plate
he is represented as walking upright in one of the cages.

Likenesses of Sobke are presented in figures 5 and 6 of plate II. In the
latter of these figures he is shown stretching his mouth, apparently
yawning but actually preparing for an attack on another monkey behind
the wire screen. Figure 7 of this plate indicates Skirrl in an
interesting attitude of attention and with an obvious lack of
self-consciousness. The same monkey is represented again in figures 8
and 9 of plate II, this time in the act of using hammer and saw.

EXPLANATION OF PLATE II

FIGURE 3.--Orang utan, Julius, reaching for banana.

FIGURE 4.--Julius walking across his cage.

FIGURE 5.--_P. rhesus_, Sobke.

FIGURE 6.--Sobke stretching his jaws (yawn?) preparatory to a fight.

FIGURE 7.--_P. irus_, Skirrl.

FIGURE 8.--Skirrl using hammer and nail.

FIGURE 9.--Skirrl using a saw.

All of the animals except the orang utan had been used more or less for
experiments on behavior by Doctor Hamilton, but this prior work in no
way interfered with my own investigation. Doctor Hamilton has
accumul