Inducing effects of the presumptive endoderm of successive stages inTriturus alpestris.

1. Using embryos ofTriturus alpestris, a piece of the endoderm of successive stages was explanted together with ectoderm of early gastrulae by the sandwich method. 2. In all series-from the uncleaved egg to the larval stage-endoderm induced mesoderm-derived organs in the ectoderm. Endoderm from uncleaved eggs and 4-cell stages induced only blood and coelomic epithelium, whereas endoderm from the other stages also induced muscle, notochord, and pronephric tubules to a varying degree. Blastula endoderm had the highest inducing activity. 3. Small amounts of intestine were also induced in the ectoderm in some cases. The explanted endoderm itself showed differentiation only when taken from the 8-64 cell stage to early gastrula stage.