Abstract

PIP: In this histological analysis of 1452 human embryonal gonads on a large scale, embryos were obtained from mothers whose pregnancies were interrupted by curretage mainly for social reasons. The ratio of male to female embryos was fairly constant at and after Streeter's Horizon 20 at values of about 130. At Horizons 18 and 19 a remarkably high sex ratio was obtained: 385 and 212, respectively. From these data it may be conceivable that the earlier the gestational stage, the higher the sex ratio of conceptuses, i.e., contrary to theoretical calculation, the primary sex ratio may not be 100, but may be even higher than the secondary ratio of 106 males to 100 females at birth.