1 86 



REGENERATION 



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. 



B 



FlG. 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. 



Another series of experiments in grafting, similar to one of those 

 made by Joest and myself on the earthworm, has been made by Har- 

 rison on the tadpole. I have also later made similar experiments. 

 Two tadpoles are united by their posterior ends, as shown in Fig. 54, A, 

 and a day or two after union one of the tails is cut off near the line 

 of union. There is thus left attached to the end of the tail of one 

 tadpole a part of the tail of the other united in a reverse direction, so 

 that the exposed cut-end is the anterior end of the small piece. 

 There grows out from this cut-end a structure that resembles a tail 

 (Fig. 54, B, C, D). It contains a continuation of the notochord and 

 nerve-cord, that taper in a characteristic way to the end of the new 

 structure. The tail is flat and has a central band of muscle tissue, and 



