Another very typical case of a morphogenetic system of the harmonious type is supplied by the phenomena of restoration in the ascidian *Clavellina*. I cannot fully describe the organisation of this form (Fig. 13a), and it must suffice to say that it is very complicated, consisting of two very different chief parts, the branchial apparatus and the so-called intestinal sac; if these two parts of the body of *Clavellina* are separated one from the other, each may regenerate the other in the typical way, by budding processes from the wound. But, as to the branchial apparatus, there may happen something very different: it may lose almost all of its organisation and become a small white sphere, consisting only of epithelia corresponding to the germ-layers, and of mesenchyme between them, and then, after a certain period of rest, a new organisation will appear. Now this new organisation is not that of a branchial apparatus but represents a very small but complete ascidian (Fig. 13). Such a fact certainly seems to be very important, not to say very surprising; but still another phenomena may be demonstrated on the animal which seems to be even more important. You first isolate the branchial apparatus from the other part of the body, and then you cut it in two, in whatever direction you please. Provided they survive and do not die, as indeed many of them do, the pieces obtained by this operation will each lose their organisation, as did the whole branchial apparatus, and then will each acquire another one, and this new organisation is also that of a *complete* little *Clavellina*. So we see that not only is the branchial apparatus of our animal capable of being transformed into a whole animal by the co-operative work of all its parts, but even each part of it may be transformed into a small *whole*, and it is quite at our disposal how large this part shall be, and what sort of a fragment of the original branchial apparatus it shall represent. [Illustration: Fig. 13.--Clavellina. *a.* Diagram of the normal animal: *E* and *J* = openings; *K* = branchial apparatus; *D* = intestine; *M* = stomach; *H* = heart. *b.* The isolated branchial apparatus. *c-e.* Different stages of reduction of the branchial apparatus. *f.* The new *whole* little ascidian.] We could hardly imagine a better instance of an harmonious-equipotential system. I cannot give you a description of all the other types of our systems subservient to restitution, and I can only mention here that the common hydra and the flatworm *Planaria* are very fine examples of them. But to one special case of harmonious equipotentiality you must allow me to direct your further attention.