In this chapter, the author presents the formal mechanism which seems to his to control all morphogenesis. He explains that an elementary fashion, using an analogy between the development of an embryo and a Taylor series with indeterminate coefficients. The author describes the overall development of the embryo in the following way: a totipotent egg divides, in the course of time, into masses of cells which acquire special and irreversible functions. But there always exists in the animal a germinal line of totipotent cells which will result in the formation of reproducing cells in the adult individual. The structural stability of functional operators has never been the subject of a systematic study. In the case of partial differential equations the equivalent problem is almost exactly that of the well-posed problem, of which many classical examples are known, such as Dirichlet's problem for elliptic operators and Cauchy's problem for parabolic and hyperbolic operators.