[26] A change of the position of the cell is of course effected by each variation of the direction of the cut, which is purely a matter of chance. *The Potencies of Elementary Organs in General* Before dealing with other very young germs, I think it advisable to describe first an experiment which is carried out at a later stage of our well-known form. This experiment will easily lead to a few new concepts, which we shall want later on, and will serve, on the other hand, as a basis of explanation for some results, obtained from the youngest germs of some other animal species, which otherwise would seem to be rather irreconcilable with what our Echinus teaches us. You know, from the second lecture, what a gastrula of our sea-urchin is. If you bisect this gastrula, when it is completely formed, or still better, if you bisect the gastrula of the starfish, either along the axis or at right angles to it, you get complete little organisms developed from the parts: the ectoderm is formed in the typical manner in the parts, and so is the endoderm; everything is proportionate and only smaller than in the normal case. So we have at once the important results, that, as in the blastula, so in the ectoderm and in the endoderm of our Echinus or of the starfish, the prospective potencies are the same for every single element: both in the ectoderm and in the endoderm the prospective value of each cell is a “function of its position” (Fig. 9). [Illustration: Fig. 9.--The Starfish, *Asterias*. *a*^1. Normal gastrula; may be bisected along the main axis or at right angles to it (see dotted lines). *a*^2. Normal larva, “*Bipinnaria*.” *b*^1. Small but whole gastrula that results by a process of regulation from the parts of a bisected gastrula. *b*^2. Small *but whole* “*Bipinnaria*,” developed out of *b*^1.] But a further experiment has been made on our gastrula. If at the moment when the material of the future intestine is most distinctly marked in the blastoderm, but not yet grown into a tube, if at this moment the upper half of the larva is separated from the lower by an equatorial section, you will get a complete larva only from that part which bears the “Anlage” of the endoderm, while the other half will proceed in morphogenesis very well but will form only ectodermal organs. By another sort of experiment, which we cannot fully explain here, it has been shown that the endoderm if isolated is also only able to form such organs as are normally derived from it. And so we may summarise both our last results by saying: though ectoderm and endoderm have their potencies equally distributed amongst their respective cells, they possess different potencies compared one with the other. And the same relation is found to hold for all cases of what we call elementary organs: they are “equipotential,” as we may say, in themselves, but of different potencies compared with each other. *Explicit and Implicit Potencies: Primary and Secondary Potencies*