Studies on the formation and state of determination of the trunk organizer in the newt,Cynops pyrrhogaster.

The exact localization of the presumptive trunk organizer was determined by means of vital staining at the initiation of gastrulation (0 h embryo) and subsequently in 6, 9, 12 and 24 h embryos.The progressive changes in the self-differentiation and inductive capacity of the trunk organizer were studied in isolation cultures (sitting drop) and in sandwich cultures with competent gastrula ectoderm. In the 0 and 6 h embryo cultures the excised trunk organizer predominantly formed atypical ectoderm. A dramatic change in differentiation and inductive capacity occurred in the 9 h embryo. The positive cases - 83% of the isolation and 50% of the sandwich cultures - mainly formed notochord and somites, accompanied by spinal cord and hindbrain in the sandwich cultures. Although no further change in self-differentiation occurred from that time onwards, a gradual increase in inductive capacity was recognized.