This volume, which is based on the Terry Lectures delivered at Yale University in 1935, deals with the problem of the unity of natural knowledge. It considers the cleavage between the inorganic and biological sciences, and between the theology of intelligibility and that of inexplicability. Under the heading “The Nature of Biological Order” it considers some of the opinions which biologists, physicists, and philosophers hold regarding the form of organization which living things exhibit. The discussion is continued under the headings “The Deployment of Biological Order” and “The Hierarchical Continuity of Biological Order,” and the conclusion is reached that “the profounder our insight into the nature of organic form, the clearer does the unity of science become.”