Certain of the working concepts developed by Clements and Shelford in "Bio-Ecology" are restated in a rigorous fashion. These selected concepts then are illustrated in detail by choosing examples of work done on laboratory populations cultured under carefully controlled conditions. The flour beetle Tribolium confusum and the fruit fly Drosophila melanogaster are used in most cases as illustra tive material. Exptl. examples of the following concepts are presented: action and reaction; aggregation; co-operation; disoperation, and competition. Reproduction, mortality and metamorphosis are the biological end-responses most dealt with. There is a general discussion of laboratory as contrasted with natural (field) populations. A bibliography of 104 titles is appended.