SKIN TRANSPL.\NTATION IN FROG TADPOLES 389 



also showed no changes. All of the autotransplants of back skin 

 on the back (thirty cases) gave the same result. No antagonistic 

 interaction between the grafted and the host cells was indicated. 



Having proved that tail skin transplanted to the back, and that 

 back skin transplanted to a new position on the back always 

 retain their individuality, logically the next experiment was to 

 make reciprocal grafts; that is, to transplant integument from the 

 back on to the tail. There are some mechanical difficulties in 

 making such grafts. The back skin may be rolled into a cyhn- 

 drical mass after healing has begun, or may become so wrinkled 

 that union is prevented. However, when the wrinkling is not 

 too great and union is once established, the graft persists. Seven 

 cases were observed. In every one the difference in appearance 

 between the two kinds of skin was very marked, and all of them 

 continued to maintain this difference for months after the opera- 

 tion. The results were so uniform that the making of more 

 grafts of this kind was not deemed necessary. The conclusion is 

 inevitable that back skin, as well as tail skin, will retain its indi- 

 viduality when transplanted into a strange region of the same 

 animal, indicating that there is no effective interaction between 

 host and graft tissue. 



The only other region of the tadpole in which the skin is charac- 

 teristically different from those already considered is the venter. 

 From nearly the whole of that region melanophores are absent, 

 and the number of xantholeucophores greatly exceeds that in 

 any other part of the animal. As a result, the color of the venter 

 is white or cream. When transplanted on to the back, belly- 

 skin grafts present an excellent opportunity for studying any 

 changes in structure or pigmentation that may result. The skin 

 heals readily and firm union is established within twenty-four 

 hours. Such grafts, ten of which were made, are always sharply 

 delimited and never become indistinguishable from the surround- 

 ing skin. Because of the transparency of the epidermis, the 

 deeper layers of dermis may be seen with the aid of the micro- 

 scope, and months after the operation the dermis appears charac- 

 teristically different from the dermis of back skin. In a very 

 old graft even a casual observer would notice the difference. All 



