Abstract.In an investigation of the incidence of the sex chromatin of intermitotic nuclei in the various tissues (skin, stomach and muscle) of 37 human embryos (crown-rump length 7.9-318mm) and the ventral abdominal skin of 20 patients (10-80 years old), the following results were established. 1. In the early stages of 7.9-35.6mm crown-rump length (4-9 weeks), the sex can not be determined from the form of external genitals, without error, but it is

Type II at 36.2% and Type III at 1.2% in the average.3. In the middle and the later fetal stages, however, positional changes of the sex chromatin as to different organs occur, so that the organs, mentioned above, group themselves in two main classes.a. The frequency of nuclei of Type IV is remarkably higher than that of Type II, as seen in most organs: oral and nasal mucosa, esophageal epithelium, tracheal and alveolar epithelium, uterine and vaginal lining and inner zone of adrenal cortex.