Originally published in 1927 as the third instalment of the Cambridge Comparative Physiology series, this book examines the role of hormones in 'co-ordinating the activities of the organism'. Hogben illustrates the text with charts to illustrate key points, as well as photographs of animal specimens to demonstrate the role of certain secretions in processes such as growth and colour development. This book will be of value to anyone with an interest in the history of science.