661 



nordiciisi and in hiiiiiettes (Homo alpinus). A still more convincing 

 proof can be drawn from Table V, for this table shows that if the 

 menarche appears at an early age in tlie mother, this is, on an 

 average, also the case in the danghter. I have on |)urpose arranged 

 the data in this table according to the age of the mother. 



A simple calculation siiows iis the following: the average age of 

 the menarciie of those daughters, whose mothers began to menstruate 

 in the IJ"', 12"' and 13"' year, is 12 years and 10 months; of the 

 mothers whose first menses appeared in the 14"' , 15"' and 16"' jear, 

 the daughters were, on an average, 13 years 7 months old, and 

 finally this mean age was 14 years and 11 months in those daughters 

 whose mothers fust menstruated in their 17"', 18'*', or 19''' year. 

 These ages prove that a retarded menarche in the mother is inherited 

 by the daughter. 



Among the external factors which are of influence on the menar- 

 che, tiie temperature, as has been remarked already, is regarded as 

 being of great significance. This opinion was, up till now, only 

 grounded on the fact that the menarche arrives at an earlier age 

 in the population of a warmer zone than in that of a colder climate. 

 Now I can prove from my investigation that this external influence 

 can be demonstrated even in the population of our country. I put 

 the question whether the menarche appears with equal frequency 

 in the ditlerent months of the year; and it became clear that this 

 is not the case. The frequency-curve of the menarche, arranged 

 according to the months of the year, has a most typical direction, 

 as may be seen from Table VI. In this table the frequency for 

 each montii is expressed in percentages of the whole. 



TABLE VI. 



January. . . 8.2 "/q 



February . . . 5. — „ 



March .... 7.— „ 



April .... 8.8 „ 



May 

 June . 

 July . 

 August 



10.8 "/„ 

 10.- „ 



9.5 „ 



10.9 „ 



September 

 October . 

 November 

 December 



. 6.9 o/o 



• 6.2 „ 



7.8 „ 



. 8.6 „ 



This table shows that a first menstruation appears more frequently 

 during the warmer months (May, June, July, and Aug.) than during 

 the rest of the year; for the total frequency during these 4 months 

 is 41.3"/, to 29.5°/. during the first and 29.7 7„ during tiie last 

 4 montiis of tiie year. 



The monthly course, however, is somewhat more complicated. 

 Besides the greater frequency during the summer months there is 



