RESUMO
The gravid uterus with zygotes and microfilariae in utero of Brugia pahangi, a rich source of antigen as revealed by a recent immunofluorescent technique, were studied ultrastructurally. The epithelial cells of uterus show ultrastructural features of synthetically active cells. Their secretions may provide nutrients for the egg in utero. On the basal side, the uterine epithelial cells may also secrete substances to form the basal lamina of the uterus which is rather thick and irregularly fused with the basal lamina lining the body wall where the pseudocoelomic cavity is obliterated. For the most part, the uterine basal lamina contains uniform granular material of moderate electron density. There are also elongated visceral muscle cells embeded in it, and which surround the uterus, with adjacent cells overlapping. The gravid uterus contains several stages of developing microfilariae within its lumen, the cleaving zygotes are also present at another level. The morula of zygotes are composed of several closely packed cells surrounded loosely by their own egg shell membranes. The egg shell becomes more convoluted as development proceeds. The egg shell surrounding the developing microfilariae in utero is secreted by the uterine epithelium. This structure later becomes the sheath of circulating microfilariae, and is highly antigenic as indicated by intense labeling with fluorescent antibodies.