There are several reports of electron microscopic studies on the epidermis of human fetuses and/or embryos: BREATHNACH and WYLLIE (1965a, 1965b) reported on the ultrastructure of the epidermis in human fetuses 12 and 14 weeks of menstrual age: RIEGEL

There are several reports of electron microscopic studies on the epidermis of human fetuses and/or embryos: BREATHNACH and WYLLIE (1965a, 1965b) reported on the ultrastructure of the epidermis in human fetuses 12 and 14 weeks of menstrual age: RIEGEL (1965) in human fetuse 25 to 60mm long in crown-rump length; HASHIMOTO et al. (1966) in human fetuses 12 to 22 weeks of menstrual age, 60 to 180mm in crown-rump length; FUJITA and ASAGAMI (1966) in human embryos and fetuses 6 weeks to 34 weeks of menstrual age, 5mm in total length to 42mm in foot length; HOYES (1967, 1968) in human fetuses 8 to 26 weeks of menstrual age, 26 to 230mm in crown-rump length. HOYES investigated, in the above papers, the epidermis of fetuses 26 to 50mm in crown-rump length, as the youngest group, whose menstrual ages were calculated 8 to 11 weeks on the basis of crown-rump length according to the data by AREY (1966). He found that the epidermis in the earliest developmental stage of his materials consisted of two layers of cells, the basal layer and the periderm. At the Sixth International Congress for Electron Microscopy held in Kyoto, we (FUJITA and ASAGAMI, 1966) reported that the epidermis of an embryo 5mm in total length whose menstrual age was estimated to be 6 weeks from the data of crownrump length given by NAKAMURA et al. (1955-56), consisted mainly of a single layer of cells. Though it is difficult to make an exact comparison of menstrual age between our embryos and the fetuses observed by HOYES because of the physical differencese between Japanese and English embryos it is presumed that our embryo estimated to be 6 weeks is younger than HOYES' calculated as 8 weeks. Therefore, it seems likely that judging from the findings of these two reports, the stage of a single layer epidermis may precede that of a bilayer epidermis, the latter being formed by cell multiplication at about 8 weeks of age. In the reports on the human embryonic epidermis mentioned above, the earliest epidermal melanocytes are those which were found by HASHIMOTO et al. (1966) in the scalp skin of a 12-week-old fetus. The earliest Langerhans cells in the epidermis are those which were found by BREATHNACH and WYLLIE (1965a) in the limb and face skin of a 14-week fetus. From these reports, the question arises as to whether or not each of the two types of cells appears in the epidermis of human embryonic skins earlier than the