In 1967, the present author published as a monograph "Histological studies of the human thyroid gland observed from the viewpoint of its postnatal development" based upon the quantitative measurements of thyroid tissue compo­ nents in 326 cases ranging in age from immediately after birth to 88 years. Through successive intermediate zones, newborn, infant, child and pubertal on one hand and through a transitional zone presenile on the other hand, the realm of interest concerning in medicine recently has been extended from the main trunk of the adult towards two poles, senile (gerontology) and embryonic (prena­ talogy). The problem of the thyroid gland is no exception to this recent trend (Boyd, 1950) and also seems to be one of the most topic endocrine subjects from the standpoint of this view (Russel et at., 1957; Carr et at., 1959; Smith et at., 1961; Pickering, 1964; Pickering et al., 1958, 1961, 1963; French et al., 1964). A survey of the literature shows considerable numbers of papers dealing with the developmental histology of the prenatal human thyroid gland. Earlier, Dr.