SHORT HISTORICAL SURVEY OF PATTERN-FORMATION IN THE ENDO-MESODERM ANDTHE NEURAL ANLAGE IN THE VERTEBRATES - THE ROLE OF VERTICAL AND PLANAR INDUCTIVE ACTIONS

After some introductory remarks about vertical versus horizontal induc tive interactions and about planar versus homoiogenetic induction, the author discusses: a) the historical development of the more recently studied endo-mesoderm induction in the Urodeles and in the anuran Xeno pus laevis, b) the possible causal relationship between endo-mesoderm induction and the initiation of the gastrulation process, and c) the o lder history of the regional neural induction as initially studied in the Urodeles and only recently analysed in the anuran Xenopus laevis. The essential vertical interaction in the neural induction process bot h in urodelian and in anuran amphibians is emphasized.