Aggregation of the smooth muscle cells found in certain hemopoietic organs and tissues of the stingray, Dasyatis akajei (Elasmobranchii, Chondrichthyes).

A combined light and electron microscopic study revealed that there are conspicuous aggregations of smooth muscle cells in several hemopoietic organs and tissues such as in the Leydig (esophageal) and epigonal organs, diencephalic choroid plexus and perihypophyseal connective tissue sheath of the stingray, Dasyatis akajei. These cells were gathered in bundles of varying caliber or arranged concentrically around a central focus, but neither innervation nor gap junction was found. In some of the concentrically arranged cells, signs of degeneration were noticed. The possible origin of these structures is discussed in relation to the vascularity of the loose connective tissue.