No. i.] REGENERATION OF TISSUE. 9 



of normal form, and, as far as could be observed, it had the 

 characteristics of the species of the grafted stump (palustris) 

 and not those of the body (virescens). This was seen in the 

 character of the pigmentation, and especially in the absence of 

 the large black blotches along the side of the tail, which are 

 found constantly in the regenerated appendages of R. viresccus. 

 In spite of the insignificant size of the grafted stump, as com- 

 pared with the whole body, and in spite of the fact that the 

 nourishment conveyed to the growing appendage is brought 

 there in blood, which is largely derived from the body, the 

 tissues maintain their specific characters. 1 ' 1 



By using two species in which there is a marked difference 

 in the pigmentation of the ectoderm and also some distinctive 

 difference in the color of the pigment cells in the mesoderm, 

 I hoped to be able to determine more definitely the character 

 of the new part, and further, by observing the tissues of the 

 two species, where they are regenerating side by side, to see 

 if they mutually influence each other. The problem is some- 

 what different from the one Harrison examined, since I was 

 less concerned with the influence of the major component on 

 the new regenerating part than with the possibility of a mutual 

 influence of the new cells on each other. Harrison has shown, 

 with some degree of probability, that the former influence is 

 not shown in the new part, but the latter problem is not 

 specially considered. 



I have found it possible to graft together two such differ- 

 ently pigmented tadpoles as Rana (temporaries} sylvatica and 

 R. palustris. The former breeds earlier, but the development 

 will be retarded several weeks if the dishes in which the tad- 

 poles are placed be put on ice in an ice chest. It is better to 

 let the tadpoles develop as far as the stage when the tail-knob 

 is just about to appear, since at this stage they withstand better 



1 " I had hoped to obtain more definite evidence concerning the influences 

 which regulate regeneration, from experiments carried out along these lines. But, 

 owing to unfortunate circumstances, most of the larvae of this series died. 

 Besides, all regenerated tails deviate somewhat from the normal type, especially 

 as regards pigmentation, which fact would bring in a considerable element of 

 uncertainty, and in the tail I have not been able to find any other characters 

 which could with safety be considered diagnostic of either species." 



