Blood cell formation in the River lamprey, Lampetra fluviatilis

Abstract

Haemopoiesis has been studied throughout the life cycle of the parasitic lamprey, Lumpetra fluviatilis, with supplementary data being provided by its nonparasitic derivative, Lampetra planeri. Attention was paid to the location of the principal haemopoietic sites in both the larval and post‐larval stages and to the mode of differentiation of the blood cells. In the prolarva, the formation of blood cells takes place initially in the blood islands but, at the time when the gut starts to rotate, this role is taken over by the typhlosole. After the ammocoete has reached about 20 mm in length, division and maturation of blood cells were also clearly detected in the intertubular and fat cell region of the nephric fold. Both the typhlosole and nephric fold discharge blood cells into the circulation and throughout the rest of larval life constitute the main sites of lymphopoiesis, erythropoiesis and granulopoiesis. At the beginning of transformation, however, both these structures undergo involution and by the end of metamorphosis the haemopoietic function has been assumed by the fat column. This latter organ remains active throughout the adult phase until near the end of the spawning run at which time it undergoes massive degenerative changes. Differentiation of blood cells from the fixed cells of haemopoietic tissues occurs only in the blood islands of the prolarva and in the typhlosole during the very earliest stages of its development. Throughout the rest of the life cycle, the mode of formation of blood cells was the same in haemopoietic tissues containing a reticular network (typhlosole, fat cell region of the nephric fold and fat column) as in haemopoietic tissue where there was no such fibrous arrangement (the intertubular tissue of the more ventral regions of the opisthonephric kidney). Haemopoietic tissues could be seen to be formed in all the above structures by the accumulation of immature cells in tissue spaces which form a suitable environment for cell division and maturation. Descriptions are given of lineages leading from small lymphocyte‐like stem cells to erythrocytes and to eosinophilic and neutrophilic granulocytes, and from large lymphocytes to macrophages. Copyright © 1976, Wiley Blackwell. All rights reserved