Cumulative Record. Chapter 45: John Broadus Watson, Behaviorist. Quote 2

In establishing the continuity of species Darwin had attributed mental processes to lower organisms . . . The inevitable reaction was epitomized in the writings of Lloyd Morgan, who argued that such evidences of mental processes could be explained in other ways. A third step was inevitable, and it was Watson who took it: If there were other explanations of mental processes in lower organisms, why not also in man? (p. 601)