A visualizing agent, Trypan blue, was found to be preferentially effective for Bonghan ducts (BHDs) and corpuscles compared to blood vessels or adipose tissues. By using it, we observed a weblike network of BHDs which was in various membrane structures, such as the peritoneum, and omenta. This network of BHDs in the membrane structures was connected to the freely movable BHDs which did not adhere to the surfaces or wrapping membranes of internal organs. In addition, tracing BHDs in adipose tissues became possible because Trypan blue does not stain adipose tissue.