Studies on the histogenesis of Wolffian body and the differentation of erythrocytes in chick embryos have been carried out. The results obtained in these studies may be summarized as follows: (1) Erythrocytes in the Wolffian body in chick embryo show transitional phases into the several sorts of elements of Wolffian body, such as small lymphoid cell, the cell resembling with fat-laden cell, fibroblast or connective tissue cell, eosinophilic granulocyte and mesenchymal cell. (2) The primordium of glomeruli begins its development. by -condensation of erythrocytes. but there-after the erythrocytes included in that anlage gradually decreasing in number, on the contrary, the small lymphoid cells increase in number and there can be seen transitional forms between these two elements. (3) The development of Wolffian tub ules begins, at first, by condensation of so-called nephrogenous tissue cells, but then they are formed from condensed mass of erythrocytes by means of the differentiation of erythrocytes, formation of lumen in the center of mass and fusing together with these masses, thus cord like tubule may be formed. (4) Formation of Wolffian tubules of chick embryos does not cease on the 10 to 11 days of incubation, but continue to the later embryonic stage. (5) The mitotic indices in glomeruli, Wolffian tubules and intertubular region are so small in valtie that mitosis can hardly be seen to be the chief factor of vast increase of cells in these tissues, on the contrary, there are many evidences that the leading factor of increasing in number of cells in developing mesonephros rests on the basis of the migration, and differentiation of erythrocytes into the fixed elements of Wplffian body. (6) T h e experimental results show that the erythrocytes actually differentiate into small lymphoid cells in Wolffian bodies which were transplanted or received certain treatment.
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