“…Some neuroepithelial sites in the neighborhood of secondary organizers nevertheless revealed low levels of AChE activity. Comparison with published reports using other markers of postmitotic neurons corroborated earlier accounts (e.g., Gerebtzoff, 1959;Filogamo and Marchisio, 1971;Drews, 1975;Miki et al, 1981aMiki et al, , 1981bMiki and Mizoguti, 1982;Mizoguti and Miki, 1985;Layer, 1983; see also Layer and Sporns, 1987;Layer, 1990Layer, , 1991Schlaggar et al, 1993) indicating that most young neurons initiate AChE expression shortly after exiting the ventricular zone (sometimes even whilst still inside it). We found the patchy and heterochronic emergence of the earliest neurons, and the subsequent sequential tangential spread and radial accumulation of neurogenesis at different parts of the neural wall, to be informative about basic anteroposterior (AP) and dorsoventral (DV) subdivisions already presumed to be induced by earlier genetic patterning of the neuroepithelial progenitors.…”