Twelve birds of the Single-comb White Leghorn females were killed at various ages from the day after hatching to maturity (laying of the first egg), and the rate of increase of the ovary weight according to age was observed with reference to that of the body weight. The percentage weight (to the body weight) of the ovary increses with age. The growth period of the ovary in weight is probably analogous to that of the body, being composed of two or three cycles. The maxima of the cycles occur both in the ovary and in the body at the same ages about two and three months. There is a prepuberal period of rapid increase of the ovary weight which lasts from about four or five months of age to the laying of the first egg with the increased rate of deposition of yolk materials.