The fine structure of the amphibian lymph sac.

The fine structure of lymph sacs in the amphibian was observed by transmission electron microscopy. The wall was lined by endothelial cells which were similar to those of the endothelium of lymph capillaries in mammals, but with many more abluminal projections and a much more prominent basement membrane--especially centrally, near the lymph hearts. There were four types of intercellular junctions: open, overlapping, end-to-end, and interdigitating or complex. Specialized complexes were seen in 50% of the junctions. The cytoplasm frequently projected from the lumen and abluminal surfaces. Many thin filaments anchored the abluminal endothelial wall to the surrounding connective tissue. There were numerous small vesicles in the cells and opening onto both surfaces.