A net-like structure of unknown function found at the junction of the umbilical vein and the left hepatic vein of the 16-day chick embryo is described. The net consists of strands of mesenchyme tissue covered by an endothelial layer continuous with that of the blood vessels in which it is located. An unusual feature of the net is the presence, at certain points where the strands meet, of hollow spherical or ellipsoid bodies, the walls of which are formed from a layer of simple cuboidal epithelium arranged upon a well defined basal lamina. The cavity of these bodies appears to contain some non-cellular material but they have no obvious duct to their exterior. The embryological origin of the net and its possible functions are discussed.