Fig. 4.

Conflicting hypotheses of the origin of the neural crest and kidney duct. (A) Plate V, fig. 69 in Remak (1855). Transverse slice (possibly from a fresh embryo) through the trunk of a chicken embryo viewed with transmitted light. Individual cells are not shown; the tissue is simply block‐shaded, with selected mesodermal derivatives shown in a paler shade. (B) Fig. IVa, p. 32 in Hensen (1903) showing a transverse section with what Hensen believed to be the precursor of the nephric duct arising from a cell mass in the ectoderm; the mass grows ventrad towards the mesoderm and then becomes detached (our boxes a and b). (C) Plate XI (III) in His (1865a) A–D (from bottom to top) are sections from the same chicken embryo showing what His thought was the precursor of the nephric duct (Urnierenfalte, Unf.). (D) Plate VI, fig. III (4) in His (1868b). Transvere section through a chicken embryo showing the intermediate groove (Zr), the supposed precursor of the peripheral ganglia. (E) Plate VII, box I, figs 2, 4 in (His, 1868b). Our box a shows detail of intermediate cord (Z); our box b shows precursors of the ganglia as an inverted pyramid of tissue (arrowhead). Note that His's figures show individual cells, a reflection of his improved histological techniques.