Ravn Copenhagen 3,840 16 years, 9 months. Frugel Christiania 157 16 years, 6 months. Dubois Russia 600 16 years, 8 months. Faye Norway 100 15 years, 6 months. Lundborg Esquimaux 16 15 years, 6 months. Wistrand Stockholm 100 15 years, 7 months. from these observations we obtain an average of 16 years and 3 months. III. IN HOT CLIMATES: _Observer._ _Place._ _No. of _Average Age._ Cases._ Goodeve Calcutta 239 12 years, 5 months. Lith Deccan 217 13 years, 5 months. Robertson Calcutta 540 12 years, 6 months. Webb Calcutta 39 12 years, 5 months. Dubois Asia 600 12 years, 11 months. from these observations we obtain an average of 12 years and 7 months. In 6,550 cases collected by _Krieger_ menstruation first appeared: At the age of: 9 years in 1 instance. 10 years in 7 instances. 11 years in 43 instances. 12 years in 184 instances. 13 years in 605 instances. 14 years in 1193 instances. 15 years in 1240 instances. 16 years in 1026 instances. 17 years in 758 instances. 18 years in 582 instances. 19 years in 425 instances. 20 years in 281 instances. 21 years in 111 instances. 22 years in 55 instances. 23 years in 15 instances. 24 years in 15 instances. 25 years in 1 instance. 26 years in 4 instances. 27 years in 2 instances. 28 years in 1 instance. 29 years in 1 instance. From these figures it appears that in the 6,550 cases under consideration, the age 15 was that at which the first appearance of menstruation was most frequently observed, namely in 1,240 instances, or 18.9 per cent. The age 14 comes next, with 1,193 instances, or 18.2 per cent. The case in this series in which menstruation appeared earliest, namely in the ninth year, was observed by _Mayer_, the girl being a blonde of average height, good family, and German descent; the case in which menstruation appeared latest, namely in the twenty-ninth year, was that of a woman living in Berlin, who was sickly and chlorotic up to the time of her marriage, and in whom menstruation did not appear until some years after that event.