The development of a new head in pieces cut to one side of the old median line offers some facts of interest. A piece may be cut from the side of a planarian of such a shape that it has no anterior surface at all (Fig. 19, _A_); yet a head develops at the anterior end of the new material that appears at the side. It stands at first to one side, later it assumes an anterior position. In this case an axial structure arises in a lateral position, unless we look upon the new head as arising at the anterior end of the new part, rather than at the side of the old, but there is no evidence in favor of such an interpretation, since the head arises at the same time as does the rest of the new material at the side. In a small piece all of the new material at the side may be used to form the new head (Fig. 19, _d_). Sometimes two heads develop (Fig. 19, _e_). _REGENERATION FROM AN OBLIQUE SURFACE_ There are also certain important facts connected with the regeneration from an oblique surface. The first case of the sort was described by Barfurth. He found that if the tail of a tadpole is cut off obliquely, as shown in Fig. 20, _B_, the new tail that develops stands at first at right angles to the oblique surface. The angle that the new tail makes with the axis of the old tail will be in proportion to the obliquity of the cut-surface. The notochord that occupies the centre of the new tail begins at the end of the old notochord, and extends to the tip of the new tail, dividing it in the same proportionate parts as does the notochord of the normal tail. The other organs occupy corresponding positions. As the new tail becomes larger it slowly swings around into line with the old part. This phenomenon of regeneration from an oblique surface has been found in a number of other forms. It has been described by Hescheler, and by myself [Illustration: FIG. 20.--_A, A¹._ After Driesch. _A._ Piece of stem of tubularia cut off obliquely, showing oblique position of tentacles. _A¹._ Same, later stage. _B._ After Barfurth. Tail of tadpole regenerating from oblique surface. _C._ Tail of fundulus regenerating from oblique surface. _D._ After Hescheler. Anterior end of allolobophora regenerating from oblique surface. _E._ Piece of planaria, cut off by two oblique cuts, regenerating new head and tail. _F, F¹, F²._ Three stages in the development of a new head (of a piece of bipalium) at anterior end of oblique surface.]