But even this terminology would fail to touch precisely the very centre of facts: it is not only the simplicity or singularity of their potencies which characterises the rôle of our systems in morphogenesis,[57] but far more important with respect to the production of form are two other leading results of the experimental researches. The proper act to be performed by every element in each actual case is in fact a single one, but the potency of any element as such consists in the possibility of many, nay of indefinitely many, single acts: that then might justify us in speaking of our systems as “indefinite equipotential,” were it not that another reason makes another title seem still more preferable. There are indeed indefinite singular potencies at work in all of our systems during ontogeny: but the sum of what happens to arise in every case out of the sum of the single acts performed by all of the single equipotential cells is not merely a sum but a unit; that is to say, there exists a sort of harmony in every case among the *real products* of our systems. The term *harmonious-equipotential system* therefore seems to be the right one to denote them. [57] The name of singular-equipotential systems might also be applied to elementary organs, the single potencies of which are awaked to organogenesis by specific formative stimuli from without; but that is not the case in the systems studied in this chapter. We now shall try first to analyse to its very extremes the meaning of the statement that a morphogenetic system is harmonious-equipotential. *The “Harmonious-Equipotential System”* We have an ectoderm of the gastrula of a starfish here before us; we know that we may cut off any part of it in any direction, and that nevertheless the differentiation of the ectoderm may go on perfectly well and result in a typical little embryo, which is only smaller in its size than it would normally be. It is by studying the formation of the highly complicated ciliary band, that these phenomena can be most clearly understood. Now let us imagine our ectoderm to be a cylinder instead of being approximately a sphere, and let us imagine the surface of this cylinder unrolled. It will give us a plane of two definite dimensions, *a* and *b*. And now we have all the means necessary for the analytical study of the differentiation of an harmonious-equipotential system.