First published in 1936, this book contains the text of the Terry Lectures for 1934-5, originally delivered at Yale University. Needham discusses the nature, deployment, and hierarchical continuity of biological order, as well as the history of scientific investigation into animal development through embryology, genetics and the study of mitosis. The lectures also take the opportunity to draw implicit conclusions on the nature and existence of God, or not, based on the 'oneness of inorganic and organic science'. This book will be of value to anyone with an interest in the history of science and the conjunction of science and theology.