The histological structure of the thyroid gland is relatively simple, but the interpretation of the histological picture of individual glands examined is not always easy. The structural relation is so variable that it is often difficult to determine whether the gland is within normal range or not, so that interpreta. tion tends to beeome more or less subjective and empirie. As stated by WEGELIN (1926), the variation may depend upon the characteristic state of the thyroid gland as a ductless gland, closely resembling an alveolar gland with a collecting duct system and accumulating colloid in the follicles. The colloid contained may be abundant or searee, depending upon the requirement of the animal body and the intensity of secretory stimulation, resulting in the pattern of the parenehyma, especially the follicles, to be also variable. This state is particularly exaggerated in the human thyroid gland (HINTON, 1931; BIANCHEDI, 1934; ROSENKRANZ, 1935), and influenced by different eomplieated eonditions of individual life, it be comes very difficult to analyze the histological pietures presented. Notwith standing eurrent interest in the physiology of the human thyroid gland in relation to pathology and disease, little work has been done to elucidate its histology, especially its developmental histology.

Material and Methods

Observations
Discussion
Summary.