The development and morphology of the gonads of the mouse.— Part I. The morphogenesis of the indifferent gonad and of the ovary

The work described in this series of papers was carried out with a view to furnishing controls of the experiments on the mouse undertaken in collaboration with Dr. A. S. Parkes and others. This paper deals with the development of the indifferent gonad of the mouse, up to the stage at which it differentiates into an ovary or a testis. This takes place on the 12th day post coitum, when the testis can first be distinguished. The ovaries remain in the indifferent stage for some time longer, but can be identified by a process of elimination. The present paper is concerned also with the development of the ovary from the time when sex can be distinguished until sexual maturity (8 weeks post partum). It is not proposed to consider here the structure of the maturing follicle, the process of atresia, or the formation of the corpus luteum. These problems will be reserved for a subsequent paper on the adult ovary of the mouse.