[Experimental studies on competence in early development of amphibian ectoderm]

The inductive effect of lithium chloride was examined on isolated presumptive ectoderm from different developmental stages (16-32-cell stage up to the early middle gastrula stage) of Triturus vulgaris and Ambystoma mexicanum. The following results were obtained: 1. Nearly the same temporal sequence of differentiation tendencies were found for treated ectoderm of comparable stages of Ambystoma- and Triturus ectoderm. The lithium treatment brought about mesodermal differentiations in the morula stage up to the early gastrula stage (at Triturus also two cases in the 16-32-cell stage). The most frequent and largest mesodermal inductions were obtained in the middle and late blastula. 2. In both species entodermal differentiations were formed in all examined stages. Entodermal inductions decreased in the late blastula to the early middle gastrula. In the morula, early blastula and in the early middle gastrula ectoderm of Ambystoma and Triturus entodermal differentiations appeared independent of mesodermal tissues. 3. There are clear differences in the degree of the differentiation of entodermal structures in relation to the developmental stage. Intestine and peripheral entoderm were more frequent in the older stages than in the earlier ones. 4. Comparing the results of Ambystoma and Triturus there are significant differences with respect to the regionality of the induced tissue complexes. Ambystoma ectoderm forms entodermal and spinocaudal structures, while Triturus ectoderm brings about entodermal, mesodermal and deuterencephalic inductions. The parts and the composition of the analyzed tissue formations correspond with certain regions of the young larva. Thus the treated ectoderm of Ambystoma forms tissues corresponding to the region of the tail, while Triturus ectoderm produces differentiations of the posterior and middle part of the trunk of the young larva.