The need to develop a common terminology to describe the components of the ovary has been felt for some time (Gatz, 1955; Wischnitzer, 1966). A standard nomenclature would greatly facilitate the comparison of results relating to the development of the ovary and follicle growth under normal as well as experimental conditions. Various classifications have been used to describe stages of oocyte and follicle development. Some authors use the shape of the granulosa cells and the number of layers surrounding the oocyte as the main characteristic (Engle, 1927; Mandl & Zuckerman, 1950; Adams & Hertig, 1964; Hadek, 1965). Others take the largest diameter or the volume of the follicles as the distinguishing criterion (Boling, Blandau, Soderwall & Young, 1941; Paesi, 1949), while still others use a combination of the number of cell layers and follicle diameter to describe the stage