The conception of mental disorder here presented inevitably leads to certain views regarding the causes which give rise to it. Since mental health is dependent on capacity for adjustment being equal to the demands made upon it, mental disorder must always be due to failure to maintain this relationship between capacity and needs. The causes of insanity must therefore be of two kinds: First, those which make the task of adjustment so difficult as to overtax the capacity. Second, those which lessen the capacity so that it is unequal to the demands made upon it. The third section of the paper is a brief discussion of what these causes are and how we should deal with them. Author's Abstract. A STUDY OF SEXUAL TENDENCIES IN MONKEYS AND BABOONS. By G. V. Hamilton. Journal of Animal Behavior, September-October, 1914, vol. 4, No. 5, pp. 295-318. The writer asserts that the work and problems in sexuality in human beings place upon the animal behaviorist an obligation to lay the necessary foundations for a scientific and thoroughly comprehensive investigation of sexual life. This has led him to formulate the following two problems in animal behavior: (1) Are there any types of infra-human primate behavior which cannot be regarded as expressions of a tendency to seek sexual satisfaction, but which have the essential objective characteristics of sexual activity? (2) Do such sexual reaction-types as homosexual intercourse, efforts to copulate with non-primate animals and masturbation normally occur among any of the primates, and if so, what is their biological significance? The author presents a list of the subjects (monkeys and baboons) employed in his study; gives a description of the environmental conditions in his laboratory which is in the midst of a live oak woods In Montecito, California, about five miles from Santa Barbara; gives a list of the types of situations that were arranged by the observer or encountered by the subjects in consequence of their spontaneous activities, and under each description of a typical situation one or more detailed descriptions of typical responses thereto; and finally offers the classification of sexual tendencies as expressions of reactive tendencies observed. The author then enters into a discussion of the use of the term reactive tendency, and explains that this term, according to his definition, is meant to explain something more specific than an inclination to direct activity toward one of a limited number of general ends, and to include both the innate and the acquired features of an individual's reactive mechanism.