 The extensive empirical researches on the generation of birds and mammals carried out by William Harvey (1578–1657), and published late in his life in his Exercitationes de generatione animalium (Observations on the Generation of Animals) in 1651, proved to be a bombshell in this discussion. Harvey’s careful studies claimed to refute on empirical grounds both the Aristotelian form-matter theory of sexual generation as well as the rival “two-seeds” theory based on the assumption of equivalent male and female semen. This latter theory had been embraced by ancient atomists, by Galenic and Hippocratic medical theorists, and by the majority of Renaissance physicians. The two-seeds theory had also been accepted by early-modern atomists such as Pierre Gassendi (1592–1655) and Nathaniel Highmore (1613–85) (Fisher 2006). As a consequence, when Descartes’s own speculations on embryonic formation were finally published posthumously in 1677, in which he had also relied on the combination of male and female semina organized by laws of nature and the vortex theory, they commonly met with derision (see quote from Garden below). Harvey’s detailed embryological enquiries of 1651 had already seriously undermined the empirical bases of these claims. It is difficult to find any author who endorsed the solution as offered by Descartes.