the former experiment do not apply, and the same sort of a structure, namely, a tail, is produced. [Illustration: FIG. 5.--_Hydra viridis_. _A._ Normal hydra. Lines indicate where piece was cut out. _B_, 1-4. Changes in a piece of _A_, as seen from the side. _C_, 1-4. Same as seen from the end. _D, E, F._ Later stages of same piece, drawn to same scale.] In the earthworm also we find some interesting facts connected with the regeneration of the terminal pieces. If one, two, three, four, or five segments are cut from the anterior end, they will die without regenerating. Pieces that contain more segments, six to ten, for example, may remain alive for a month or longer, but do not regenerate (Fig. 3, _A_, _B_). That this lack of power to regenerate at the posterior end is not due to the smallness of the piece can be shown by removing from a piece of five segments one or two of its anterior segments. These will be promptly regenerated. Another experiment has shown, however, that if these small pieces can be kept alive for a long time, and also supplied with nourishment, regeneration will take place at the posterior end. If, for instance, a small piece of eight or ten segments has its anterior three or four segments cut off, and is grafted by its anterior end to the anterior end of another worm, as shown in Fig. 3, _F_, the piece will begin, after several months, to regenerate at its exposed posterior end, but in the one instance in which this experiment has been successfully carried out, a new head, and not a tail, appeared on the exposed free end. The result is not due to the grafting, or to the anterior position of the posterior end, but to some peculiarity in the piece itself. We find the converse of this result in an experiment with the tail region of the earthworm, where the outcome is more clearly seen to be connected with the nature of the piece itself. If a piece less than half the length of the worm is cut off from the posterior end, there is generally formed from its anterior cut-surface, not a head, but another tail (Fig. 2, _I_). The result is similar to that described by Bonnet for one of the fresh-water annelids. A parallel case to that of the head of the earthworm is found in one of the planarians. If the head of _Planaria lugubris_ is cut off just behind the eyes (Fig. 4, _F_), there is produced, at the posterior cut-edge of the head, a new head turned in the opposite direction, as shown in Fig. 4, _F¹_. _REGENERATION BY TRANSFORMATION OF THE ENTIRE PIECE_ [Illustration: FIG. 6.--_A._ Piece of _Bipalium kewense_. Middle pigment stripe injured at two points (see circles in _A_). _B._ Regeneration of same piece.]