Plasticity and rigidity of differentiation of brain vesicles studied in quail-chick chimeras.

Transplantation of a piece of the alar plate of the prosencephalon or of the rhombencephalon of quail embryos into the roof of the mesencephalon of chick embryos was carried out at 7-10 somite stage. Results obtained were: the transplanted alar plate of the prosencephalon differentiated into tissue closely resembling the tectum when the transplants were integrated into the host mesencephalon; in all the cases, the alar plate of the rhombencephalon did not differentiate into tectum-like structure, but into rhombencephalic descendants. We conclude that the alar plate of the prosencephalon at 7-10 stage is not definitively determined and may retain an ability to differentiate into the optic tectum, whereas the prospective fate of the rhombencephalon has already been determined at 7-10 stage.