In eighteenth-century French natural history, the notion of preformation was not only a model for a small preexisting embryo that gradually extended its shape through the influx of particles, but also for an order that coordinated the dynamic relation between organic parts. Preformation depended therefore also on a hidden order behind the continuity of visible forms. Louis Bourguet, Charles Bonnet, and Georges Cuvier distinguished three organizational levels: First, the synchronic or functional order of organic systems; second, the diachronic order of the initiation of mechanical processes; and third, the hierarchical order that regulates the interaction of organic parts. In this essay, I reconstruct and compare the three organizational levels in the writings of Bourguet, Bonnet and Cuvier, relate their models of organic unity to the principle of perfection, and contrast these models with Georges Buffon's critique of system theories.