 In 1859, Darwin focused on embryos and their usefulness for understanding evolutionary relationships. Ernst Haeckel brought the study of embryos to popular attention. And histologists and embryologists, especially in Germany and the United States, used rapidly improving microscopic techniques to observe far more than had been possible before. These observations, in the context of evolutionary interpretations, raised new questions and provoked new answers. The understanding of both epigenesis and preformation underwent transformation so that the debates brought new questions along with the traditional differences.