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There are two elementary phases of the life process: the vegetative and the reproductive. In lower organisms which reproduce by fission, the individual expands as an integrated system, but within certain limitations beyond which it cannot maintain its integrity. Within the organism new centers of organization then arise which result in the production of two new individuals. Multicellular animals at first proceed in the same manner, but the tendency of the two new units to become completely separated or individuated is antagonized by the primary integration of the organism as a whole, with the result that two units of only partial independence cooperate in the immediate further development of the individual. The same principle of development operates also in the behavior of vertebrates. That this is more than analogy is obvious to one who has studied intensively the development of behavior as correlated with the structural development of the nervous system2.
Accordingly, the purpose of this paper is to show that there are, in the development of behavior, two essentially antagonistic principles, and that these principles prevail also in the development of