[Movements of cellular material of the dorsal wall in clawed-toad embryos during gastrulation and neurulation].

The pieces of dorsal ectoderm of the Rana temporaria embryos at the early and midgastrula stages were transplated onto the dorsal surface of the X. laevis embryos of the same age and the movements and changes in the form and area of the transplants were followed from early gastrula to neurula. During the first period (early--midgastrula) all movements of the transplants were directed towards the blastopore and related ma- In the beginning of the second period the transplants moved toward the blastopore only in the most caudal region, whereas in all other regions the material was markedly displaced craniad. Until the early neurula stage these movements were related to the longitudinal expansion of the material in the dorsal area and later, during neurulation, to its transverse compression. The head region material was first markedly expanded in the transverse direction and then also contracted. Alternation of active contractions and expansion of the suprablastopore material has been revealed and mediocaudal (gastrulation) vs. craniopetal (neurulation) cell movements were distinctly shown.