[Differentiation behavior of the mesodermal germinal sone of differently old pregastrulation stages of Ambystoma mexicanum. Cultivation of untreated and lithium-treated isolates].

Isolates from the dorsal, lateral and ventral area of the marginal zone are showing differentiation capacities already in the stage of early morula. The composition of the differentiation pattern alters: ecto- and mesodermal tissues are realized until the late morula. Beyond these, endodermal structures are visible with the stage of early blastula. After a mild Li treatment of the isolates the differentiation pattern of the marginal zone shows significant modifications. Ectodermal organs are registered to a lesser degree. Gut-structures are already visible within the stage of middle morula. The capacity for gut-differentiation is not restricted to only the lateral and ventral areas but is also observed in the dorsal region of the marginal zone. The results of experiments are discussed on the basis of Nieuwkoop's formation of the mesoderm in urodelean amphibians.