266 ADOLF H. SCHULTZ. 



course for seven days following menstruation. Lorenz ('98), 

 Lenhossek and Orschansky ('03) are of the opinion that sex is 

 subject to hereditary influences, inasmuch as they found families 

 in which males predominated and those in which females appeared 

 in excessive numbers. Newcomb, Woods ('06) and Heron ('06) 

 deny this and show that inheritance plays no part in the sex- 

 ratio. Numerous authors attribute its variations to the absolute 

 and relative ages of the parents. According to Rosenfeld ( T oo) 

 there is a decided preponderance of male children born to young 

 and old fathers, as compared with those of middle age. Francke, 

 from the statistics of Norway, found this to be true in respect to 

 young fathers, but reached an opposite conclusion as regards old 

 ones. Dumont ('94) found for Paris a sex-ratio of 101.9 when 

 the fathers were from 1 8 to 25 years; 104.2 when the fathers were 

 between 26 and 50 years and 97.5 when the fathers were over 51 

 years. According to E. Bidder ('78), the sex-ratio of births by 

 mothers under 18 years and over 40 years is especially high. 

 Sadler ('30) stated that the relative ages of the parents deter- 

 mines the sex-ratio; the latter is 86.5 when the father is younger 

 than the mother, 94.8 when both are of equal age, and reaches 

 163.2 when the father's age exceeds the mother's by 16 or more 

 years. Kollmann ('90) obtained an opposite result. He there- 

 fore draws the conclusion, based upon extensive material, that 

 the sex-ratio is high when the father is younger, and low when he 

 is older than the mother. At the same time he opposes the view 

 that the absolute age of the mother has any influence whatever 

 upon the sex-ratio. Stieda, on the basis of his investigations, 

 reaches the conclusion that any influence of the absolute ages of 

 the parents is out of the question, as he noted the highest sex- 

 ratio when the parents were of equal age. Numerous other 

 authors have occupied themselves with the question of parental 

 age as an influence upon sex-ratio, but only two additional ones 

 will be mentioned, Boudin ('62) and Stadler ('78). The con- 

 flicting views which have been presented suffice to show that 

 nothing definite is known concerning a correlation between the 

 age of parents and sex-determination; in fact such a correlation 

 is hardly to be expected. Pearl ('08) in a very careful study 

 demonstrated that there are more males produced when the 



