G. Mayr, Die Gesetzmässigkeit im Gesellschaftsleben, 1877, p. 240.
Edward Smith (Health and Disease), who attributes this to the lessened vitality of offspring at that season. Beukemann also states that children born in September have most vitality.
Westermarck has even suggested that the December maximum of conceptions may be due to better chance of survival for September offspring (Human Marriage, Chapter II). It may be noted that though the maximum of conceptions is in May, relatively the smallest proportion of boys is conceived at that time. (Rauber, Der Ueberschuss an Knabengeburten, p. 39.)
Krieger found that the great majority of German women investigated by him menstruated for the first time in September, October, or November. In America, Bowditch states that the first menstruation of country girls more often occurs in spring than at any other season.