It is not difficult to show that there are many other cases to which the stuff hypothesis does not apply. If, as Bonnet attempted to show, the regeneration is due to different stuffs, there is no explanation to account for the flow in animals of head-forming stuffs forward and tail-forming stuffs backward. In animals that regenerate laterally as well as anteriorly and posteriorly, we should be obliged to assume side-forming stuffs as well as head-forming and tail-forming stuffs; and since the kind of structures that are produced at the side are different at each level, we should be obliged to assume that there are many kinds of lateral stuffs. If regeneration can take place in a dorsal and in a ventral direction, as, for example, when the dorsal and the anal fins of teleostean fishes regenerate, there must also be stuffs to account for their development. When regeneration takes place from an oblique surface, it must be supposed that two or more of these kinds of stuff are brought into action. The regeneration of just as much of the limb of the salamander as is cut off also offers difficulties for Sachs’s view. If we assume a leg-forming substance, it fails to account for the difference in the result at each level. If we assume that different substances come into play according to the amount of the leg that has been cut off, the hypothesis becomes as complicated as the facts that it pretends to explain. A special case, to which the stuff hypothesis has been applied by Loeb and by Driesch, is that of tubularia, although the latter writer has used the hypothesis only to a limited extent as involving quantitative rather than qualitative results. There is present in the hydranth and stem of tubularia a red pigment in the form of granules in the endodermal cells. There is more of the red pigment in the stem near the hydranth than elsewhere. If a piece of the stem is cut off, it closes its cut-ends, and a circulation of fluid begins in the central cavity. In this fluid globules now appear that contain the red-pigment granules. The globules appear to be free endodermal cells, or parts of such, that have been set free in the central cavity. In the course of twenty-four hours the new hydranth begins to appear near one end of the stem, and in this region of the stem a much larger number of granules appear. A little later all the red granules disappear from the circulation.