In Polyptems senegalus a peculiar venous system exists. The pattern is symmetrical in embryos and in early-larval stages, but soon the asymmetrical development of the Cuvierian ducts, originating from vitelline veins, causes a predominance of the system to the right side. The two posterior cardinal veins coalesce except in the anterior region, where the right vein becomes the direct continuation of the single vein; in later stages the single posterior cardinal vein acquires a peculiar disposition, partially in the left and partially in the right kidney. The inferior jugular veins become asymmetrical as well. The anterior cardinal veins are replaced by lateral cephalic veins. A special vein in the abdomen may be considered as being a vena cava. Other peculiar items are the pulmonary veins. Other veins are more or less similar to those of other fishes.