Buccal organogenesis in Pleurodeles waltlii Michah (urodele amphibian). Study by intrablastocelic transplantation and in vitro culture.

Various embryonic areas liable to take part in the mouth's formation are extirpated from neurulae of Pleurodeles at stages 15 and 18 and tested either separately or in association with others. The comparison of the results obtained by the transplantation into the gastrula blastocele of the same species and in vitro culture allows us to define the conditions for organogenesis of buccal structures. The formation of complete mouths can be obtained by association of the stomodeal area with neural fold, precordal mesoderm and lateral cephalic mesoderm. The formation of opening alone can only be obtained in transplantation through interaction of stomodeum with lateral mesoderm of the host. The mouth opening and complete mouth formation therefore can be dissociated and seem to be two different steps. The buccal structures (bones, cartilages and teeth) were never produced separately. Their differentiation depends on interactions of the stomodeal endoderm together with the neural fold. The neural crest is the source of the one hand of mesenchyme operating in the formation of the buccal opening and on the other hand of cells predetermined to provide chondroblasts and odontoblasts. The differentiation of chondroblasts and odontoblasts is dependent on the stomodeal endoderm. The latter also induces the ectoderm to form a buccal opening. The schema of the Pleurodeles buccal organogenesis we propose is compared to that of Cusimano (1972) for Discoglossus.