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This is the second edition of this popular volume on the discipline of ethology. The book had its origins in lectures delivered at Cambridge and Harvard Colleges. Ethology is derived from the Greek, ethos, which means custom or habit. It is based upon the extensive and meticulous observations of the behavior of animals. The authors have evolved a large body of data which has implications concerning evolution, phylogenesis, and instinct theory.
Instinct is defined as "a hierarchically organized nervous mechanism which is susceptible to certain priming, releasing, and directing impulses of internal as well as external and which responds to these impulses by coordinated movements that contribute to the maintenance of the individual and the species." The central nervous system is not only responsible for the regulation of the conditions and requirements of the internal milieu, but also controls the organism's transactions with his environment. This means that each fragment