 The concrete manifestation of Buffon’s combination of novel methodology and empirical inquiry is first displayed by his treatment of embryological generation in the second volume of his Natural History (1749). These principles also underlie his unusual analysis of the meaning of “species” in natural history. In both instances, the notion of epistemic certitude gained from a “constant recurrence” of events seems to have played a fundamental role in his reflections. Following the lead of his friend Maupertuis, Buffon also endorsed the theory of the male and female seeds to explain sexual generation, deriving the origin of the embryo from the mechanical mixture of these ingredients. Amplifying upon Maupertuis’s prior speculations (see above  Section 2.4),  he explained the organization of the particles of these two seeds into a structured whole through microforces closely identified with Newtonian attractive forces that formed an organizing force-field, an “internal mold”, that assimilated matter in the proper order for embryological development. Viewed in longer historical perspective, Buffon’s theory of the internal mold functioned in a way similar to Aristotle’s notion of an immanent substantial form, and was likely influenced by Aristotle’s discussions in De generatione animalium (see above  Section 1.1).  This “mold” serves as an immanent principle of organization that acts in company with matter to structure the unified organism by gradual development. The internal mold also guaranteed the perpetuation of like by like over time. Unlike Aristotle’s substantial form, however, Buffon’s internal mold is without an internal finality in its action. It is also not a principle of vitalization.