PROF. LIPSCHÜTZ in a feuminating review of current work on this subject in Biological Reviews, vol. 2, pp. 263-280, gives concrete expres sion to some of themain results which have emerged from the study of ovarian dynamics. In the first place, the author shows that the number of primary follicles which enters into follicular development, the degree of follicular ripening which is attained, and the further fate of the follicle, depend not upon the total number of primary follicles present, but upon general internal factors outside the ovary. This he terms the law of follicular constancy, and there is a constancy for each species.