 Darwin was not an embryologist, and he did not contribute to our understanding of embryogenesis as such. Nor did Haeckel, really. But while Darwin’s use of the embryo in supporting evolutionary theory and in helping to interpret evolutionary relationships was consistent with various versions of either epigenetic or preformationist development, Haeckel’s view was decidedly preformationist. Here, then, was a preformationist interpretation based not on additional embryological observations but on adherence to Haeckel’s own metaphysical view—monistic materialism—and to his desire to provide evidence for evolution. The Haeckelian approach reflected the context in which those studying cells and embryos worked at the end of the nineteenth century.