The founding of the Carnegie Institutes Department of Embryology in 1913, alongside its systematization of embryo staging, contributed to the mechanization of developmental stages of embryo growth in the early 20th century. For a brief period in the middle of the century, attention to the detailed interrelation between embryo development and time made pre-existing ideas about pregnancy ends less determinative of ideas about that developmental course. However, the turn to the genetic scale led to the disappearance of this attention, replaced by a sense of biological life as seamlessly scripted. This study examines the history of what I refer to as temporal attention: attention to the live, unfolding potentialities within vital matter. The reintroduction of temporal attention to discussions of development allows us to more fully consider non-human vitality and the experiences of beings that house or otherwise intimately intersect with that vital tissue, regardless of outcomes.