A synthesis of classic and modern neurobehavioral literature dealing with the principles by which complex, purposive, and intelligent behavior is generated, this book features: * papers by C.S. Sherrington, E. von Holst, D.M. Wilson, G. Fraenkel, H. Mittelstaedt, and P. Weiss * clear descriptions of three types of elementary units of behavior -- the reflex, the oscillator, and the servomechanism * a review of the diverse manifestations of hierarchical structure in the neural mechanisms underlying coordinated action. This volume has proven to be of great value to psychologists, neurobiologists, and philosophers interested in the problem of action and how it may be approached in light of modern neurobehavioral research. It has been designed for use as a supplemental text in courses in physiological psychology, neurobiology and behavior, and those courses in cognitive and developmental psychology that place particular emphasis on understanding how complex behavior patterns are implemented.