Architectonics of the Mesonephros of the Senegal Bichir (Polypterus senegalus (Cuvier 1829), Polypteriformes)

Layer-by-layer serial histological sections were used to reconstruct the mesonephros of P. senegalus. The distribution pattern of the structure of both nephron and hematopoietic tissue was shown to be similar to the general structure observed in actinopterygians. Most of the hematopoietic tissue of animal origin was revealed to be located at the cranial–ventral pole of the organ. The largest number of renal corpuscles, all with the smallest surface area and located at the greatest distant from one another, was found in the caudal part of the mesonephros. Such an arrangement of the structural units of the kidney, coupled with the high vascularization level of the organ (the position of extraorganic and multiple branching intraorganic vessels), makes it possible to create a sufficiently increased pressure to determine the destination, thus bringing the P. senegalus kidney closer to the amphibian mesonephros. These features could have been evolutionarily fixed in the basal groups of actinopterygians and preserved in the process of evolutionary development, manifesting themselves in evolutionarily young species of this group.