Differentiation in small grafts of the median region of the presumptive prosencephalon.

In early neurulae of Triturus alpestris the cranio-caudal distribution of differentiation tendencies in the presumptive prosencephalon was tested. Small grafts made from a median strip excised from the region of the neural plate and transverse neural fold were transplanted to a pocket made under the cranio-ventral ectoderm of early neurulae. Grafts made from the middle portion of the strip showed almost exclusively eye differentiation, whereas more cranial as well as more caudal grafts showed relatively more telencephalic differentiation, and only little diencephalic differentiation. The results indicate that the process of pattern formation in the central region of the prospective prosencephalon is advanced with respect to the surrounding areas.