the water, regeneration takes place at the cut-ends. If a piece is suspended with its apical end upwards (Fig. 14, _B_), a new stem develops at the upper cut-end, and new roots from the lower cut-end. If a piece is suspended with its basal end upwards (Fig. 14, _C_), there is formed at its upper (basal) end a new stem with its branches also slanting upwards as shown in the figure. Roots appear at the lower (apical) end. Since gravity is the only force that acts in a vertical direction under the conditions of the experiment, Loeb concluded that it plays an important rôle in determining the kind of regeneration that takes place. Its action is of such a nature that a new stem develops from the upper cut-end, and roots from the lower end, regardless of whether the upper end is the basal or the apical end of the piece. Similar results are also obtained, according to Loeb, if the pieces are suspended obliquely. In a piece of this sort, it is found that new stems arise along the upper surface of the old stem, and roots from the lower surface as well as from the lower cut-end (Fig. 14, _D_, _E_). If a piece of the stem is placed horizontally on the bottom of an aquarium, the branches that come off from the under surface of the stem begin to grow downwards at their ends, and where they come in contact with a solid body they fasten themselves to it, thus showing that they are true roots (Fig. 14, _F_). One or more stems may arise from the upper side of the main stem. These stems grow vertically upwards, and produce lateral branches. Only in one case did a new stem, or stem-like structure, arise from one of the vertical branches, as shown to the left in Fig. 14, _F_. Loeb found it also possible to change the character of the growth of the apex of the normal stem and to transform it into a root. A long piece of the hydroid was cut off and suspended vertically with the basal end upwards. From the upper end a new stem began to grow, and then the entire piece was reversed, so that the new stem pointed downwards. Under these circumstances the young stem did not bend around and begin to grow upwards, as a young plant might have done, but it ceased to grow as a stem, and at its apex one or more roots developed. Loeb concludes: “I cannot imagine by what means the place of the formation of organs in antennularia is determined in connection with the orientation of the animal except by means of gravity.”