The ultrastructure of amphibian ectoderm treated with an inductor or actinomycin D.

Amphibian (Triturus alpestris) ectoderm was isolated and after 2-16 days in culture examined by electron microscopy. It has been shown that the ectoderm, formerly called "undifferentiated ectoderm", forms in part ciliated epithelial cells, which cannot be distiguished from the cells of the epidermis, which has developed in situ (except for the alignment of the cells which depends on the mesenchyme underlying the epidermis). The ultrastructure of the cilia is similar to that of cilia of protozoa or sperms of insects or vertebrates. A zone at the periphery of the epidermal cells, free of yolk platelets, mitochondria and pigment granules (embryonic pigment) is observed after 4 days. This area is rich in vacuolous structures and basal bodies of the cilia.Ectoderm, which was treated with the vegetalizing factor differentiates into mesodermal and endodermal tissues. Cilia, as well as the characteristic peripheral zone, are not formed in the induced ectoderm.In ectoderm treated with actinomycin D (1 μg/ml for 6 h) the differentiation of the peripheral zone and the cilia is delayed.