“We are apt to contrast the extremes of instinct and intelligence, to emphasize the blindness and inflexibility of the one and the consciousness and freedom of the other. It is like contrasting the extremes of light and dark and forgetting all the transitional degrees of twilight.... Instinct is blind; so is the highest human wisdom blind. The distinction is one of degree. There is no absolute blindness on the one side, and no absolute wisdom on the other.”--C. O. WHITMAN (1899). The precedence here given to _changes in behavior_ is in harmony with the emphasis which is put upon _processes_ and genetic phases or sequences throughout this book. As Holmes (1905, p. 108) has well pointed out, behavior consists of relatively fixed and relatively changeable responses, with intergradations. There are thus two avenues of approach which he sums up as follows (p. 112): “In the trial and error method the random character of the movement impresses us most; in the tropisms, the element of direct determination by the environment. Both of these factors run through the behavior of all animals, but they are mingled in various proportions in different forms. In the lives of most, if not all animals both are essential elements in the adjustment of the organism to its conditions of existence.” And in regard to those responses which do not change in form with experience, he says (p. 106): “The element of spontaneous undirected activity is one of vast if not essential importance in the life of nearly all animals. The simpler animals profit by their varied experience, although they may not learn, and thus secure some of the advantages which it is generally considered the special function of intelligence to confer.” Thus to the ecologist studying the sequences of changes in the environment, and changes in the organism, it is but natural and consistent for him to apply the same methods to behavior, in order to facilitate their mutual relations and aid in their interpretation. In a study of the environment we also have the relatively stable elements and the relatively rapidly changing ones, and any adequate understanding of animals must correlate these four variables: two relatively changing, one in the organism and one in the environment; and two others relatively stable, one in the organism and the other in the environment. JENNINGS, H. S. 1905. The Method of Regulation in Behavior and in Other Fields. Jour. Exp. Zoöl., Vol. II, pp. 473-494. HOLMES, S. J. 1905. The Selection of Random Movements as a Factor in Phototaxis. Jour. Comp. Neurol. and Psychol., Vol. XV, pp. 98-112. JENNINGS, H. S. 1905. Modifiability in Behavior. I. Behavior of Sea Anemones. Jour. Exp. Zoöl., Vol. II, pp. 447-472. 1906. Modifiability in Behavior, II. Factors Determining Direction and Character of Movement in the Earthworm. Jour. Exp. Zoöl., Vol. III, pp. 435-455. 1906. Behavior of the Lower Organisms, pp. 366. New York.