Inductive Activity of the Organizer in the Morula and Blastula of Triturus pyrrhogaster

Abstract

1) A piece of the dorsal marginal zone of Triturus embryos at st. 6, 7, 8 and 9 were enclosed in pieces of presumptive ectoderm at st.11 and cultured in vitro for 9-12days. 2) The organizer at st. 6 caused little or no induction. Definite neural induction was first obtained by using the organizer at st. 7. 3) With organizer at progressively later stages, induction improved and became more frequent, and most explants involving organizer at st. 9 produced fully differentiated brain or spinal cord, often with sense organs as well. 4) It is concluded that the organizer acquires the ability to induce neural differentiation at st. 7 and this ability increases progressively to a maximum at st. 9. 5) Results do not exclude the possibility that the inductive agent comes into being or into action at a later stage during culture as a result of self-differentiation of the explanted organizer.