A common object found within medical museums is the developmental series: an arrangement of embryos depicting the transformation of an unremarkable blob into an anatomically organized and recognizable organism. The developmental series depicts a normative process, one where bodies emerge in reliable sequential stages to reveal anatomically perfect beings. Yet a century before the developmental series would become a visual model of embryological development, the very process of development itself was discerned through the comparative study of preserved human fetuses—specifically, those (...) deemed “monstrous” or characterized as “malformations.” This article examines how anatomically diverse fetal bodies were reformulated from singular curiosities into alternative developmental pathways whose characteristics testified to the laws of nature and to the primordial, physical relationship between humans and other species. In early nineteenth century Amsterdam, the father-son team of physicians Gerard and Willem Vrolik built up an internationally renowned anatomical museum famous especially for Willem’s collection of fetal malformations. Physical preparations of fetal malformations play a central role in Willem’s monumental handbook on developmental embryology: comparing human embryos against one another and the embryos of other species, Willem plots out a sequence of embryological development in which a body’s form marks its place within the ever-unfolding natural order. In conversation with the literature on model organisms, this article explores how the “monstrous” gets standardized and, in doing so, contributes to the scientific production of a normative physiological process. (shrink)