It is generally considered that animal cloning by nuclear transfer originated in proposals made by Hans Spemann (1936), following his experiments on delayed nucleation in the newt egg, which were preceded by similar attempts using the sea-urchin egg (Loeb, 1894). Briggs and King (1952) were the first to succeed in transplanting blastula and gastrula nuclei into the enucleated frog egg and in obtaining a significant number of normal tadpoles by means of this technique. We present evidence that much earlier (1895) Yves Delage (1854-1920), a French biologist, had clearly formulated the same experimental project of nuclear transfer, as a means to test Weismann's theory of cell differentiation during embryonic development. This was also Spemann's motivation. Both Delage and Spemann were aware of Loeb's experiments (1894), in which delayed nucleation in the sea-urchin egg was found to result in twin larvae. It is difficult to decide whether Delage's project was influenced by Loeb's findings. On the other hand, it seems that Spemann was not aware of Delage's proposal, since he did not express his own ideas on extended nuclear transfer before 1936. Finally, neither Delage nor Spemann imagined that nuclear transfer could be a means of obtaining groups of genetically identical animals (reproductive cloning). KEY WORDS: nuclear transfer, cloning, Delage, SpemannAlthough it is commonly believed that Hans Spemann, in the early decades of the 20 th century, pioneered the ideas of nuclear transplantation and reproductive cloning, a French biologist, Yves Delage (1854-1920), had proposed much earlier (1895) the concept of nuclear equivalence and suggested experiments of nuclear transfer.

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The effect of lithium (Li) on gastrulation movements was investigated during the development of the urodele amphibianPleurodeles waltl. Attention was focused on mesodermal cell migration. Under conditions of Li treatment providing a maximal enhancement of dorsoanterior structures, it was found that the dorsoventral polarity of gastrulation was abolished. In particular, vital staining and scanning electron microscopy observations on embryo fractures showed that mesodermal cells migrated radially after Li treatment, which led to the formation of rounded embryos. Epiboly movements thus were accelerated. Nevertheless, contrasting with the precocious disappearance of the early-formed yolk plug, archenteron invagination was constantly retarded and commenced with a delay of several hours as compared to control gastrulae. Cell-lineage analysis of the progenies from ventral or dorsal equatorial blastomeres of 32-cell-stage embryos provided evidence that both dorsal and ventral mesoderm contributed to notochordal tissue after Li treatment. Dorsalization of the entire marginal zone was confirmed by the ability of the entire mesoderm rudiment to behave as a dorsal organiser after Li treatment. Comparison of the migratory behaviour of isolated animal hemispheres from Li-treated or control embryos cultured on fibronectin-coated substrate indicated that all marginal cells acquired the autonomous capacity for migration of dorsal marginal cells under the action of lithium.