Both Harrison and I have made a number of experiments, in which the end of the tail of a tadpole of one species was interchanged with a similar part of another species. It is found that as the new tail grows larger the ectoderm of the grafted piece is carried out to the tip of the new tail, as shown in Fig. 55, _C_, and does not cover all the inner tissues that belong to the same piece, the rest of the tail being covered by the ectoderm of the major component. If the tip of the tail is now cut off, as indicated by the line _b-b_ in Fig. 55, _C_, there are left at the exposed edge two kinds of ectoderm, and from the cut-edge a new tail regenerates, covered in part by each of the two kinds of ectoderm. I made this experiment in order to see if the new ectoderm would show any influence of its dual origin, especially along the line where the two kinds are in contact, but no influence could be detected. In another series of experiments the grafted tail was cut off, as shown in Fig. 55, _A_, or in Fig. 55, _B_, or in Fig. 55, _C, a-a_. In these cases there is left exposed, at the cut-edge, the internal tissues of the two species. The new tail that regenerates is composed in part of material derived from one species and in part from that of the other, but each tissue remains true to its kind, and there is found no evidence of an influence of one on the other (Fig. 55, _E_). These experiments show that even when the two kinds of tissue regenerate side by side, and unite to form a single morphological organ, there is no influence of a specific kind of one tissue on the other. [Illustration: FIG. 55.--_A._ _Rana sylvatica_ with grafted tail of _Rana palustris_. Line _a-a_ indicates where tail was cut off. _B._ _Rana palustris_ with grafted tail of _Rana sylvatica_. Line _a-a_ indicates where tail was cut off. _C._ Older stage of a graft like _B_. Lines indicating two possible operations. _D._ Another individual with two tails, one composed of both components. _E._ Later stage of last, when tail was cut off at level _a-a_.]