Reinvestigating the work of the anatomist Wilhelm His (1831-1904) shows how engaging with models in three dimensions can revise our accounts of scientific change. His is known to historians of biology for articulating a mechanical approach to embryology and for inventing a section cutter, or microtome. Focusing on the wax models that he also made in the late 1860s shows how the other two innovations were linked; reconstructing embryos from the sections, His claimed, provided compelling evidence for mechanical views. The (...) next generation of embryologists appropriated His's work selectively. In the 1880s anatomists took up "plastic reconstruction" to visualize the complex forms of higher vertebrate, especially human, embryos. An increasingly dominant experimental embryology, by contrast, drew on His's mechanical approach but had little use for the waxes and effaced them from the history of his work. Recovering these models offers a fresh perspective on the transformation of a central science of animal life and enriches our understanding of the relations between representation in two dimensions and three. (shrink)