The average age at which menstruation begins in the negro women of Africa is from 10 to 13. In Algeria puberty occurs at 9 or 10 years. Among the Australian indigens, menstruation commonly begins as early as 8 years, and at the very latest at the age of 12 years. The data available concerning the indigens of the Oceanic Archipelago are extremely variable and inexact, but we cannot go far astray in stating the age of puberty among these to be from 10 to 13. In tropical South America girls begin to menstruate from the age of 9 to 14 years. The Indian women of North America begin to menstruate at the ages of 12, 13, 14, or even as late as 18 or 20. In the Arctic zone of North America and in Greenland the onset of menstruation is delayed till 17 and even till 23 years. As regards the position in life and the upbringing years it has been shown by numerous observers that among the well-to-do classes, whose mode of living is luxurious, and whose social circumstances allow free play to the imagination, menstruation begins at an earlier age than among the working classes, whose life is one of want and privation. According to the statistical data of _Mayer’s_ regarding 6,000 women, menstruation began: _In women of the upper _In women of the lower classes._ classes._ At the age of 13 years 11.73 per cent. 7.06 per cent. At the age of 14 years 23.90 per cent. 13.33 per cent. At the age of 15 years 22.83 per cent. 14.56 per cent. At the age of 16 years 14.10 per cent. 16.53 per cent. At the age of 17 years 9.60 per cent. 13.33 per cent. From this table we learn that in nearly one-fourth of the girls of the upper classes puberty occurs at the age of 14, whilst in girls of the lower classes barely one-sixth begin to menstruate at this age. The average age at the first menstruation in girls belonging to the upper classes is seen to be 14.69 years, but in girls belonging to the lower classes, 16.00 years. According to other observers the average age at the first menstruation is: _Brierre de _Tilt._ _Krieger._ _Ravn._ Boismont._ (_London._) (_Berlin._) (_Copenhagen._) (_Paris._) Amongst gentle folk 13y. 8m. 13y. 5½m. 14y. 1m. 14y. 3m. and the rich Amongst the 14y. 5m. 14y. 3½m. 15y. 5m. 15y. 5½m. well-to-do middle classes Amongst the lower 14y. 10m. 16y. 8m. 16y. 5½m. classes Comparative observations on women living in towns and women living in the country show also that in the former, menstruation begins on the average at an earlier age. According to _Brierre de Boismont_, the average age at the first menstruation is: