From Spermatic Animalcules to Sperm Cells: The Reconceptualization of Generation in the 19th Century. At the end of the 18th and still at the beginning of the 19th century most naturalists considered spermatic animalcules to be parasites of the seminal fluid that played no role in procreation. This view was progressively questioned by 19th century physiologists. They gradually redefined the spermatic animals as (cellular) products of the male organism, as agents of fertilization and bearers of the male heredity material. This (...) article discusses this change from two different perspectives: on a microhistorical level, it analyzes the experimental research of the naturalist Lazzaro Spallanzani (1729–1799) and of the physiologist Albert Kölliker (1817–1905) in order to show how spermatozoa were turned into a new epistemic object of biology – the sperm cell. Further, it asks how the role of the reconceptualization of spermatic animalcules affected the long‐term transformations that gave rise of our modern understanding of heredity, generation and the sexed body. By combining these two perspectives, the article aims to connect historiographies that are often kept separate: the macrohistorical narratives about gender and the body in the modern age and the microhistorical studies of biomedical practices and objects. (shrink)