660 



then llie developuieni aleo undergoes the influence of tlie ovarial 

 function. Tliat this latter should have a retarding inflnence. on the 

 growth of the girl is doubtful, considering the fact that the full- 

 grown daughters of the youngest generation generally surpass their 

 mothers in height. 



A second question concerns the cause of the phenomenon; is this 

 early appearance of the menarche a reaction on external stimuli, or 

 is it a primary change in the developing process? That we should 

 have to do with a primary biological phenomenon, with the effect 

 of an internal cause, is doubtful. I cannot imagine that an internal 

 factor could, as it were suddenly, so hasten a developmental pheno- 

 menon as appears to be the case in the menarche. If this was an 

 individual phenomenon, an exception, this could be possible, but it 

 is a general thing, which makes it necessary lo acce[)t some external 

 influences as cause. 1 will not enter into speculations as to what 

 these are, but will close this part of my communication with a last 

 remark. 



The question can be raised whether, in this considerable precipi- 

 tation of the menarche, one has to do with a phenomenon which 

 falls beyond the limits of normal physiology. I cannot ascribe such 

 a significance to it, and may venture the following idea. I have on 

 purpose often drawn the attention to the fact that in all the groups 

 which I examined (brunettes, blondes, Jewesses, older and younger 

 generations), the variability curve of the menarche begins at 10^ 

 years; that is the threshold-age of sexual maturity. In every girl 

 who has passed this age the sexual sphere can be awakened, though 

 in the one it remains latent longer than in the other. The duration 

 of this period of latency is determined by hereditary factors and 

 by external circumstances. While the part determined by the former 

 is an unvariable one, that dependent on external circumstances is 

 on the contrary very variable. It depends on and changes with the 

 external conditions of life, with the mode of living, nature of food, 

 temperature etc. Whether it is advantageous for the individual or 

 not that the sexual sphere is awakened early under the inflnence 

 of those circumstances, is a question difficult to answer; but its 

 activation after having once crossed the threshold of maturity, falls 

 within the limits of the physiological norm. 



The time of activation of the sexual functions is, as just remarked, 

 dependent on hereditary and external factors. The material I have 

 collected enables me to furnish a proof for both influences. 



The significance of the heriditary factor has already been shown 

 by comparing the average age of the menarche in lilondes (Homo 



