PROF. SHELFORD is one of the best-known American students of animal ecology. It will be remembered that, more than twenty years ago, he published a number of studies on the relations between the larvae of tiger-beetles and the soil and vegetation on the shores of lakes near Chicago, and that more recently he and his associates have been concerned in the study of the relation between the codlin moth and climate. From field work of this type he has progressed in the direction of controlled work in the laboratory. He has not tried to study the animals as a physiologist would, by isolating factors and devising ‘good experiments’ in which one factor only is allowed to vary. On the contrary, he holds that the ecologist in his laboratory should aim at reproducing the complex, varying, cyclic conditions of Nature. This is a legitimate view, but it is not in accordance with the general scientific maxim that work should proceed from the analysis of simple controlled experiments to the synthesis of more complicated conditions. Parts of Prof, Shelford's book describe the extremely complex and expensive plant, designed to give complete control of temperature, atmospheric humidity, and other factors, and to provide a great variety of combinations of them.