We know from our experimental work that many, if not all, of the elementary organs in ontogeny show one and the same prospective potency distributed equally over their elements. If we now borrow a very convenient term from mechanics, and call any part of the organism which is considered as a unit from any morphogenetic point of view, a morphogenetic “*system*,” we may sum up what we have learnt by saying that both the blastoderm of the echinoderms, at least around its polar axis, and also the germ-layers of these animals, are “systems” possessing an equal potentiality in all of their elements, or, in short, that they are *equipotential systems*. But such a term would not altogether indicate the real character of these systems. Later on we shall analyse more carefully than before the distribution of potencies which are the foundation both of regeneration proper and of adventitious growth, and then we shall see that, in higher plants for instance, there is a certain “system” which may be called the organ proper of restitutions, and which also in each of its elements possesses the same restoring potency; I refer to the well-known cambium. This cambium, therefore, also deserves the name of an “equipotential system.” But we know already that its potencies are of the complex type, that they consist in the faculty of producing the *whole*, of such a complicated organisation as a branch or a root, that the term “equipotential system” is here only to signify that such a complicated unit may arise out of each of the cells of the cambium. The potencies we have been studying in the blastula or gastrula of echinoderms are not of the complex type: our systems are equipotential to the extent that each of their elements may play every *single* part in the totality of what will occur in the whole system; it is to this *single* part that the term “function of the position” relates. We therefore might call our systems equipotential systems with single potencies; or, more shortly, singular-equipotential systems.