Van Den Bergh, Jr., which was invaluable. The former aided me most
intelligently in the care of the animals and the construction of
apparatus; and the latter, especially, was of very real service in
connection with many of my experiments.

The collection of animals which Doctor Hamilton placed at my disposal
consisted of ten monkeys and one orang utan. The monkeys represented
either _Pithecus rhesus_ Audebert (_Macacus rhesus_), _Pithecus irus_ F.
Cuvier (_Macacus cynomolgos_), or the hybrid of these two species
(Elliot, 1913). There were two eunuchs, five males, and three females.
All were thoroughly acclimated, having lived in Montecito either from
birth or for several years. The orang utan was a young specimen of
_Pongo pygmaeus_ Hoppius obtained from a San Francisco dealer in
October, 1914 for my use. His age at 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