The development of the spleen in the Australian lungfish, Neoceratodus forsteri Krefft, with special reference to its relationship to the "gastro"-enteric vasculature.

The spleen of Neoceratodus forsteri Krefft grows in the shape of a " boomerang " on the left lateral-dorsal-right lateral part of the borderline between the foregut and the yolkgut . Development of the spleen follows the following stages: 1) appearance of the splenic primordium as a mesenchymal condensation in a limited portion of the region supplied by the third and fourth vitelline arteries on both sides, 2) development of the splenic sinuses within the primordium, 3) formation of the "gastric" and enteric splenic portal systems and 4) growth of the spleen along the anterior extremity of the spiral valve. The blood vascular dynamics of the foregut and the yolkgut are intimately involved with the formation of the spleen in this species. These processes were, therefore, compared with similar processes in other animals, and the characteristics of this organ common to vertebrates were investigated.