The author sets out and critically examines the main theoretical provisions of ethology in connection with the achievements of modern physiology and related sciences. A large place in the book is occupied by questions of the origin of innate and acquired forms of behavior, their study in nature and experiment. Techniques for investigating not only innate behavior, but also the so-called early memory in animals, which is of exceptional importance for understanding the development of behavior, upbringing and learning, are highlighted.