Reexamination of the 'regulative development' of amphibian embryos.

In this article, we have reviewed a series of our recent results of isolation, defect and transplantation experiments on early embryos of Xenopus laevis. The results show that as early as the 8-cell stage an embryo consists of several kinds of cells which differ distinctly in developmental capacities and that their capacities are much more restricted than previously thought. Thus, for the formation of complete embryos a certain set of cells is necessary; and no regulation occurs whenever any one of the necessary cells is lacking.