Published with permission of the author and the translators, Howard E. Gruber and Jacques Voneche; it is an excerpt from The Essential Piaget, edited by Itoward E. Gruber and Jacques Voneche (Basic Books, in press). I n a work called Biology and Knowledge we sought to show the relationship and functional continuity that connect the process of the formation and development of knowledge to the biological mechanisms of autoregulation peculiar to the organism. In this brief article we should hke to adduce a new example of these fundamental analogies. In order to facilitate this comparison, we will be using a terminology upon which it would be well to agree. In biology we can call "exogenous" a variation imposed by the environment, thus phenotypical and not hereditary, while we reserve the term "endogenous" for genotypical variations. The resulting phenotype is always dependent on the "norm of reactions" of the corresponding genotype but always with a momentary action by the environment as well. In psychology, in the same way, we will call "exogenous" the information drawn from experience and thus empirical, although it always presupposes an assimilative framework of endogenous origin. On the other hand, we will generalize the term "endogenous" when applying it to the knowledge which, without being innate, is drawn from the internal and necessary coordinations of actions, since these coordinations are the product of interior structurations and not of exogenous experience. The purpose of this essay is, first, to show that one of the most general processes in the development of cognitive structures consists in replacing exogenous knowledge by endogenous reconstructions that reconstitute the same forms but incorporate them into systems whose internal composition is a prerequisite. Second, we will seek to demonstrate the biological equivalent of this process in the mechanism ofphenocopy: an exogenous phenotype is neither interiorized nor fixed, but followed by and entirely replaced by a genotype of the same form, now reconstructed by purely endogenous mechanisms. The convergence of these two processes, cognitive and biological, perhaps indicates a broader role for the phenocopy than has generally been granted particularly in those widespread realms where modifications of organs and behavior are necessarily interdependent.