. Analysis of development. Embryology; Embryology. Fig. 167. Plan of development of the nephric sys- tem of vertebrates. A, Origin and mode of develop- ment of the nephric duct; B and C, its relations to the other parts of the system; PR. pronephric units; ND, nephric duct; NGC, nephrogenic cord; G, gonad; MRS, mesonephric units; MET, metane- phros; UR, ureter; CL, cloaca. in question lies at the future cephalic end of a band of nephrogenic tissue which, in the course of gastrulation, passes inward around the lateral lip of the blastopore toward its final position in the lateral trunk region.
. Analysis of development. Embryology; Embryology. Fig. 167. Plan of development of the nephric sys- tem of vertebrates. A, Origin and mode of develop- ment of the nephric duct; B and C, its relations to the other parts of the system; PR. pronephric units; ND, nephric duct; NGC, nephrogenic cord; G, gonad; MRS, mesonephric units; MET, metane- phros; UR, ureter; CL, cloaca. in question lies at the future cephalic end of a band of nephrogenic tissue which, in the course of gastrulation, passes inward around the lateral lip of the blastopore toward its final position in the lateral trunk region. In salamander embryos final topographic localization of the pronephric material oc- curs from late gastrula to middle neui'ula stages. In the early neurula the material has been invaginated and lies in the lateral body wall, anterior to the blastopore and below prospective somites 4 and 5 (Fig. 169, after Yamada, '37; see also Muchmore, '51). After this stage its position relative to adjacent regional structures (somites, limb area, gills, etc.) does not essentially change. By the middle neurula stage, however, as a result of posterior elongation of the body axis, the location is relatively further forward (Fales, '35; see also Yamada, '37; Nieuwkoop, '47; Muchmore, '51). At this stage transplants of a limited area (Fig. 171) always produce pronephros, and contiguous areas have no pronephric potency (Fales). Nevertheless,. Fig. 168. A, Position of the prospective pro- nephric area in the early gastrula of the axolotl, according to Pasteels ('42); B, later distribution of the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Willier, Benjamin H. (Benjamin Harrison), b. 1890. Philadelphia, Saunders
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