ABSTRACT
In this article 108 human fetuses from 12 to 30 weeks of gestation, 3 neonates and a 1.5 years child were used for study of the histogenesis of the appendix.In 12 weeks old fetus, the appendix showed small lumen and thin wall. The mucosa presented intestinal villi and crypts. The endocrine and goblet cells could be found. The circular muscle and serous membrane had differentiated. In the specimens of 13 to 15 weeks, the lamina propria contained diffused lymphatic tissue and lymphatic follicles. On such sites, the intestinal villi were absent. The surface epithelium became attenuate and composed of cuboid or lower cuboid cells. The outer longitudinal muscle layer was evident. The scattered muscularis mucosa was found. At 16 weeks, the endocrine cells appeared and showed various forms. The open-type or closed-type endocrine cells could be distinguished easily. Under EM, based on the morphology of the basal granules, the endocrine cells might be divided into two types. The granules were cell enclosed in a limiting membrane. One type of the granules was round and various in size, and another type was irregular. In the surface epithelium covered on the lymphatic tissue, the microfold cells could be found. They showed irregular microvilli or mierofolds and numerous apical micropinocytotic vesicles. At 18.5 weeks, the villi tended to merge each other. At 20 weeks, the muscularis mucosa was formed and the 4 layers of appendix resembled those of the normal adult. We found endocrine cells aggregated into Segi's cap on the apex of the villi in 7 fetuses of 16-21 weeks. The T or B lymphocytes could be identified as early as 13.5 weeks by immunologic method. We found the percentage of the B lymphocytes decreased with the gestation age, and this fact suggested that the appendix might be a B lymphocyte pool during the fetal period.