This article explores the collaborative research of the Nobel laureate Hans Spemann (1869–1941) and the Swiss zoologist Fritz Baltzer (1884–1974) on problems at the intersection of development and heredity and raises more general questions concerning science and politics in Germany in the interwar period. It argues that Spemann and Baltzer’s collaborative work made a significant contribution to the then ongoing debates about the relation between developmental physiology and hereditary studies, although Spemann distanced himself from _Drosophila_ genetics because of his anti-reductionist (...) position. The article analyzes how Spemann framed the issues of heredity in terms of an epigenetic principle in the context of his work on the “organizer,” and it explores the experimental dynamics of research on newt merogones carried out by Baltzer in a methodological development of Spemann’s constriction experiments. Finally, these research attempts are discussed as part of a broader “prehistory” of the mid-twentieth century cell nuclear transplantation experiments, which provided the basis for later animal cloning. (shrink)