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REGENERA TION 



species, even when they belonged to different genera. It is found, 

 however, that some of these combinations can be more easily made 

 than others, but it is not clear whether the difference depends upon 

 differences in the sizes of the pieces, or the rate of growth of the ecto- 



FlG. 54. A. After Harrison. Union of two tadpoles by posterior ends. Two days after opera- 

 tion. The line to the left of plane of union indicates where the two were cut apart. B. Tail 

 of right-hand tadpole in A. Five days after cutting apart. C. Same. Nine days after cut- 

 ting apart. D. Same. Ninety-five days after cutting apart. E. After Born. Combination 

 of Rana esculenta (anterior) and Rana arvalis (posterior) . Thirteen days after the operation. 



derm over the cut-surfaces, or to a deeper-lying lack of affinity between 

 the tissues. A combination of Rana esculenta (anterior) with Bombi- 

 nator igneus (posterior) was made. The combination lived for ten 

 days, and then showing pathological changes, it was killed. Another 

 combination is shown in Fig. 54, E, in which the anterior part of Rana 



