From stage 13 onward, the primordium of the dorsal vessel moves dorsally along with the overlying ectoderm (Campos-Ortega and Hartenstein 1985; Hartenstein and Jan 1992; see Bate, this volume). The two rows of cells express different characteristics: Cells of the dorsal row adopt a cuboidal shape and become perfectly aligned. These cells are the cardioblasts (car) that form the dorsal vessel proper. The lateral cells keep their rounded shape and remain more irregularly arranged. They give rise to the pericardial cells (per), large cells that flank the dorsal vessel on either side. Close to the anterior end of the developing dorsal vessel, a cluster of mesodermally derived cells that are confluent with the pericardial cells form the primordium of the lymph glands (lg).

After dorsal closure [stage 17] the rows of cardioblasts of either side meet and fuse. The double row of cardioblasts develops a central lumen through which the hemolymph circulates. Anteriorly, the dorsal vessel is attached to the dorsal pouch. More posteriorly, segmentally repeated pairs of ligament cells (alary muscles, alm) anchor the dorsal vessel to the dorsal epidermis. (as) Amnioserosa; (mus) somatic musculature; (myo) myoblasts.