In all social circumstances, and in all times the great principle of sexual morality must dominate the sexual life of woman. As the ethical characteristics of the three great epochs in that sexual life we recognize the purity of the maiden, the faithfulness of the wife, and the love of the mother. But within the limits imposed by these demands it is still possible to satisfy the modern claim for a free development of the personality, and to accommodate the circumstances of the sexual life to the individual vital needs and vital claims of the present day. I. THE SEXUAL EPOCH OF THE MENARCHE. (PUBERTY.) The term _menarche_ (μήν, a month, ἀρχή, the beginning) was introduced by me into medical literature to denote the period of life in which, as a sign of puberty, menstruation first makes its appearance. The age at which this occurs is subject to variations depending upon race, occupation, hereditary tendencies, and climate; but in Germany and Austria the average age at puberty is 14 or 15, the extreme limits being 12 to 19. Until about the age of 13, the physical differentiation of the sexes, except for the anatomical peculiarities of the genital organs, is in our climates a trifling one. But at puberty the important changes occur by which the sexes are so strikingly differentiated. Whereas in the growing boy all physical change takes the form of increasing strength and energy, in the development of the girl, we note the appearances of the rounded outlines so characteristic of womanhood. At the same time the voice alters, becoming less sharp, with a softer quality, and yet a fuller tone; and we may observe that young brunettes have commonly a contralto voice, young blondes, more often a soprano. The intellectual changes undergone by the girl at puberty are no less extensive and characteristic than the physical changes. In brief, the undifferentiated, neuter girl is transformed into a young woman, endowed with all the attributes, mental and bodily, characteristic of femininity. As regards the age at which the menarche usually occurs, and the manner in which its occurrence is anticipated or retarded by the various influences already mentioned, the following propositions may be put forward, based on the available statistics and observations: 1. Climate is an important factor. In the torrid zone, menstruation appears at a very early age, on the average from 11 to 14; in the temperate zone, it appears later, on the average from the age of 13 to 16; in the frigid zone, later still, on the average from the age of 15 to 18. The mean temperature of the atmosphere appears to have a direct influence on the age at which menstruation begins, the hotter the climate, the earlier being the menarche. The height of the place of residence above the sea level and its distance from the coast also have a certain influence.