Abstract
The material employed consists of 9 human embryos which range from 4.5 to 20mm length and belong to the Streeter's 5 developmental stages horizon XIV-XVIII. The beginning of the metanephros is observed in 4.5mm long embryo, which belongs to the horizon XIV. It appears as a form of 95μ long so-called Nierengang and projects dorsal and cranial from the dorsal and a little medial wall of the Wolffian duct 133μ cranial from the opening to the cloaca. The metanephric tissue layer is already in contact with the cranial end of this ureterir bud.
In the next stage of horizon XV, to which belong 6mm (K) and 10mm (F) long specimens, the cranial end of the ureteric bud enlarges and becomes the pelvic portion, while the rest part remains ureter; the length of the latter is 190μ on both sides in these 2 specimens. The metanephric tissue of the enlarged pelvic portion differentiates in two layers; the inner layer contacts with the pelvic portion, the outer covers this inner layer.
In 7.5mm long embryo of the horizon XVI the pelvic portion enlarges craniocaudal two-fold to the preceeding stage and differentiates into cranial and caudal portions which may correspond to the two future major calyces. These two cranial and caudal portions are covered with the inner layer of the metanephric tissue respectively, the intermediate portion between these two only with the outer layer directly, so that the inner layer is separated into two cranial and caudal portions. Its ureter is 323μlong on the right, 285μ long on the left.
To the next horizon XVII belonging embryos are 9.5mm, 10mm (U), and 14mm long. By the former 2 earlier specimens comes the opening of the Wolffian duct to the cloaca near that of the ureter; that portion of the Wolffian duct caudal to the opening of the ureter seems to become the wall of the cloaca. The pelvic portions of these specimens situate cranial to A. iliaca communis. The length of the ureter is 835 in 10mm (U) long one on both sides. In the pelvic portion there appear except cranial and caudal divisions two ventral and one dorsal so that there are 5 divisions on both sides of 9.5mm long one, while they are in 10mm (U) long one 6 (ventral and dorsal each 2) on the right, 7 (ventral 2 and dorsal 3) on the left side to be observed. The number of these di visions becomes 10 in elder 3 specimens, 14mm-(late XVII stage), 18mm (a) and 20mm (XVIII stage) long ones. In these specimens there are except cranial and caudal always 4 ventral and 4 dorsal divisions, and they correspond to the Felix's collecting tubules of a first generation The collecting tubules of a second generation begins to form only at the caudal division on both sides of 10mm (U) long specimen. Such subdivision increases in 14mm long one, 9 among 10 on the right, 8 on the left, but there is no subdivision of a third generation. The latter occurs 5 among 10 on the left, 4 on the right in 18mm (a) long embryo. There is not yet subdivisions of a fourth generation. The latter appears in 20mm long embryo 4 among 10 on the right side, 2 on the left. By this specimen there is no primary division already, the subdivision of a second generation 2 on both sides, that of a third generation 4 on the right, 6 on the left. These subdivisions progress always dichotomic.
