Fate maps and gastrulation in Amphibia — a critique of current views

In the urodele blastula the ectomesoderm consists of a layer of cells bound to the hyaline membrane and of an aggregate of free cells lying inside the marginal zone. In the fate maps published by Vogt (1929) the chordamesoderm is located exactly above this annular aggregate, and Vogt himself realized that the mesoderm, in part at least, is derived from these inner cells.The results of several of the experiments recorded by Vogt, however, are impossible to account for on the assumption that any mesoderm is derived from the superficial membrane-bound cells, and it is therefore suggested that the mesoderm in toto is represented by the inner, free cells. Various lines of evidence support this contention, above all the fact that none of the ruptures between the germ layers implied by Vogt's fate maps has ever been observed.If the suggested origin of the mesoderm is accepted, the pre-Vogtian views on the mechanism of gastrulation are largely correct, having the consequence, among others, that the notochord can be considered to be derived from the ectoderm, and not from the mesoderm.