Threadlike structures on the surfaces of mammalian internal organs were recently observed, and they can be the anatomical basis of the meridian-like network of internal organs as detected by the Bi-Digital O-Ring test imaging method. Morphological and histological studies were performed to reveal their novel features by using confocal and electron microscopy, and there is evidence that reveals that they have a ductal structure in which some liquid flows. They form a part of the network of acupuncture meridians that is thought to be a circulatory system distributed throughout an animal body. In order to confirm further the circulatory function it was necessary to provide evidences for the existence of endothelial cells at the inner boundaries of the microchannels that form the threadlike ducts. In this work we performed immunohistochemical studies for the identification of endothelial cells. In addition, we identified the extracellular matrices between the microchannels in the threadlike structure by using antifibronectin, elastin, laminin, and collagen type IV. Since immunohistochemical data are not sufficient for definite proof we supplemented the analysis with ultra structural information by using transmission electron microscopy (TEM). Yet TEM images show only ultrathin sections (50 nm) of a specimen, we needed to take 3-dimentional images to provide a visual demonstration of the microchannels in the threadlike ducts. We conducted high voltage electron microscopic studies for this purpose and obtained corroborating tomograms that exhibit the microchannels. In conclusion, the meridian-like tissues are ducts with microchannels, which implies the circulatory function of the acupuncture meridian network.