SKIN TRANSPLANTATION IN FROG TADPOLES 367 



like those of a normally regenerated tail (fig. 11). Harrison 

 states definitely that in his grafts the nerve cord was never 

 regenerated, although the notochord was. It may be that the 

 production of nerve cord in the grafts described here was due to 

 conditions of age or environment or both, different from those 

 under which Harrison made his grafts. In several cases prolifera- 

 tion from the originally anterior and posterior ends consisted 

 chiefly of the new notochord with a very thin connective-tissue 

 layer between it and the epidermis. Such outgrowths were 

 cylindrical, from 1 to 6 mm. long, and usually twisted in various 

 ways (fig. 5). 



MECHANICAL ADJUSTMENT OF GRAFTS 



1. Grafts over eyes kept in the light (series LN), or in darkness 



(series DN) 



a. Tail skin. The first transplantations consisted of tail skin 

 placed over the eyes of animals kept in light. Due to the presence 

 of some muscle tissue and the notochord, and to the presence of 

 the melanophores of the skin, the transplants were usually opaque 

 enough to conceal the eye and, presumably, to inhibit vision. 

 They were grafted in four different orientations, viz., with the 

 originally anterior end either, 1) on the anterior side of the 

 wound; 2) on the ventral side of the wound; 3) on the posterior 

 side of the wound, or 4) on the dorsal side of the wound (table 1). 

 No relation between the orientation of the transplant and its 

 behavior could be determined. The source of the skin was 

 usually the animal's own tail. A few homoiotransplants were 

 made, but they exhibit no differences in the adjustment process. 

 It should be borne in mind throughout the following descriptions 

 that any graft over an eye of a tadpole is necessarily concave on 

 its under side, conforming to the shape of the eye. The history 

 of each transplant may be divided into three periods, according 

 to the changes which are taking place in it. 



(1) First or healing period. The first period covers the time 

 of healing and the establishment of union with the host integu- 

 ment, and its duration depends primarily upon the accuracy 



