Biology of Gestation, Volume I: The Maternal Organism, is the first of a two-volume treatise that aims to fill the void which exists among the various disciplines that deal with the process of gestation. This work brings together in a comprehensive form basic knowledge acquired through intensive research work carried out by many investigators in the various disciplines that deal directly or indirectly with the process of gestation. Hence, it should prove to be of great interest to the student, the research worker, and the academically oriented individual in the general field of reproduction and in the specific fields of obstetrics and pediatrics. The treatise should also provide a source of basic information to the clinician in obstetrics and pediatrics which should assist him in the interpretation and understanding of the underlying. The present book deals with the maternal organism and the changes that occur during gestation. It opens with a chapter on the mechanism of ovulation and its control. Subsequent chapters deal with the problems of gametogenesis, fertilization, migration, and implantation of the ovum; and various morphological and physiological aspects of the placenta. The final two chapters discuss the physiological and biochemical changes that occur in labor, the puerperium, and lactation; and the physiological processes that adjust the maternal organism to pregnancy.