GRAFTING AND REGENERATION 185 



esculenta was united to the posterior part of Rana arvalis. 1 The blood 

 of the posterior component was driven through the vessels by the 

 action of the heart of the anterior component. The animal lived 

 for seventeen days. 



In all these combinations between different species, each develop- 

 ing part retains its specific characters, and, although in several cases 

 one part received its nourishment from the other through the com- 

 mon circulation, yet no influence of one component on the other 

 could be observed. 



Harrison has succeeded in keeping an individual made up of two 

 species, Rana virescens and Rana palustris, for a much longer time, 

 until, in fact, the transformation of a tadpole into a frog had taken 

 place. Each half retained the characteristic features of the species 

 to which it belongs. 



The absence of regeneration after the union of the pieces may 

 be attributed, in several cases, to the absence of this power in the 

 region through which the cut has been made ; but in other experiments 

 this cannot be the explanation, since the power to regenerate can be 

 shown to exist in the part. This is the case in an experiment car- 

 ried out by Harrison and repeated later by myself. If the tips of 

 the tail of two tadpoles are cut off and interchanged (Fig. 55, A, B\ 

 a perfect union takes place between the two parts, and a single tail 

 develops. Each of the cut-surfaces has the power to regenerate, 

 but the union of the parts has suppressed the regeneration. If, 

 however, like parts are not brought in contact, regeneration may take 

 place in the region of union (Fig. 55, D). 



Both Harrison and I have made a number of experiments, in 

 which the end of the tail of a tadpole of one species was inter- 

 changed with a similar part of another species. It is found that as 

 the new tail grows larger the ectoderm of the grafted piece is car- 

 ried 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 com- 

 ponent. If the tip of the tail is now cut off, as indicated by the line 

 bb in Fig. 55, C, there are left at the exposed edge two kinds of ecto- 

 derm, 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 con- 

 tact, but no influence could be detected. In another series of experi- 

 ments 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 



1 The figure was drawn fifteen days after union. 



