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 accumulated a large mass of the most valuable and interesting observations on the behavior of monkeys, and he more thoroughly understands them than any other observer of whom I have knowledge. Much to my regret and embarrassment in connection with the present report, he has thus far published only a small portion of his data (Hamilton, 1911, 1914). In his most recent paper on "A study of sexual tendencies in monkeys and baboons," he has given important information concerning several of the monkeys which I have observed. For the convenience of readers who may make use of both his reports and mine, I am designating the animals by the names previously given them by Hamilton. The available and essential information concerning the individuals is presented below. _List of animals in collection_ Skirrl. _Pithecus irus_. Adult male. Sobke. _P. rhesus_. Young adult male. Gertie. _P. irus-rhesus_. Female. Born November, 1910. Maud. _P. rhesus_. Young adult female. Jimmy II. _P. irus_. Adult male. Scotty. _P. irus_ (?). Adult male. Tiny. _P. irus-rhesus_. Female. Born August, 1913. Chatters. _P. irus_. Adult eunuch. Daddy. _P. irus_. Adult eunuch. Mutt. _P. irus_. Young adult male. Born August, 1911. Julius. _Pongo pygmaeus_. Male. Age, 4 years to 5 years. When I arrived in Santa Barbara, Doctor Hamilton was about to remodel, or rather reconstruct, his animal cages and laboratory. This gave us opportunity to adapt both to the special needs of my experiments. The laboratory was finally located and built in a grove of live oaks. From the front it is well shown by figure 10 of plate III, and from the rear, by figure 11. Its location was in every way satisfactory for my work, and in addition, the spot proved a delightful one in which to spend one's time. [Illustration: FIGURE 12.--Ground plan of Montecito laboratory and cages. Scale 1/120