Abstract
1. The blood cells of trout and roach consist of nucleated erythrocytes and reticulocytes, nucleated thrombocytes, coarse and fine granulocytes, and lymphocytes of varying sizes. It is difficult to distinguish any cells showing characteristics similar to those of the monocytes of mammals. Immature cells occur more frequently in the blood than is the case in mammals.
2. The coarse granulocytes very commonly escape from the blood vessels, and have been observed in large numbers in the intestinal mucosa and submucosa, in the gill epithelia, and in the peritoneum. These cells migrate to the epithelial surface, where they undergo changes in structure leading to the formation of a characteristic discharge pattern of their granules. It is proposed that the "granules" are in reality vesicles with fluid contents, which are ultimately discharged at epithelial surfaces.
3. The hematopoietic organs of these fishes are chiefly the intertubular tissues of the kidneys; in the trout the spleen is also active; in the roach, only the kidney is active; in the perch, only the spleen is active.
4. Two alternative hypotheses of blood cell formation are proposed. On the first hypothesis, the common stem cell is described as a "large lymphoid hemoblast," which gives rise to granulocytes by direct transformation and undergoes mitotic division to give rise to "small lymphoid hemoblasts." From the latter develop the erythrocytes, thrombocytes and blood lymphocytes.
On the second hypothesis, the large lymphoid hemoblast, derived by transformation of reticular cells is the precursor solely of the granulocytes, and the small lymphoid hemoblast is to be derived from endothelial cells and is the precursor of erythrocytes and thrombocytes. In this case the large cell is to be compared with the "primitive white cell" of Doan, Cunningham and Sabin, and the small cell with the "megaloblast" of the same authors. No evidence however is available of the derivation of small hemoblasts from endothelial cell components of the reticulo-endothelium.
5. In the maturation of the erythrocyte in teleost fishes, there is a progressive increase in the size of the cell; in mammals and birds there is a decrease in size. In both cases there is a decrease in size in granulocyte maturation.
6. There are no essential differences between the blood cells and hematopoietic processes of the freshwater and marine teleost fishes examined.
