[1] These he identifies with “those complicated mutual relations which Darwin designates as conditions of the struggle for existence.” Along with chorology--the distribution of animals--œcology constitutes what he calls _Relations-physiologie_. Haeckel, “Entwickelungsgang u. Aufgaben der Zoologie,” Jenaische Zeitschr., 1869, Vol. V, p. 353. The quotations from Brooks, on a preceding page, show even more explicitly the intimate relation which exists between biology and ecology. At first glance they may seem to prove almost too much--that biology and ecology are synonymous. They show at least that ecology is concerned with fundamental biological problems--the responses of organisms to their complete environments. The relations which different branches of ecology bear to one another may be discussed under three headings, individual, aggregate, and associational ecology. These phases are superficially so distinct that students of one branch may be almost unaware of the existence of the coördinate branches and may not realize that each is a part of the larger unit. _Individual Ecology._--The study of individual ecology is the investigation of the development (_process_ of formation) of the structure, function, and behavior of a given individual or kind of animal from the standpoint of its relations and responses to the complete environment. All ecologically significant facts should be considered. Such a study may be devoted to an animal, as, for example, a bumblebee, a crawfish, or a garter snake, and may be limited to a single habitat or locality, or extended throughout the entire geographic range of an animal. From this standpoint the individual studied becomes the hub of the microcosm, from which all relations and responses radiate. Most of the physiological studies of ecological bearing and many investigations of animal behavior have been made from this viewpoint. The organism is thus considered as an agent which, transforming and utilizing substance and energy, produces a varied number of physiological conditions and forms of activity, which in turn furnish the basis for the constant process of response between the organism and its environment.