TRANSPLANTATION OF LIxMBS IN AMBLYSTOMA 125 



gills were practically normal in appearance. In case 19 an 

 appendage with a reduplicated forearm and hand developed in 

 place of the third gill. A complete limb which was normal in 

 function regenerated at the original site. The reduplicated 

 appendage exhibited only limited movements in the forearm and 

 hand. 



In cases in which complete regeneration of the gills did not 

 occur, the limb retained its transplanted position. Such rudi- 

 ments, although having a normal aspect at the beginning, soon 

 took on the typical posture of a developing gill, and in all cases 

 distorted and abortive development followed. 



In connection with the question of gill development, Ekman 

 ('13, '14) has shown that the factors for the outgrowth of the 

 external gills in various anuran forms (Rana fusca, Rana esculenta, 

 Bombinator, and Hyla) reside entirely in the ectoderm. His 

 experimental results have proved that this ectoderm, which 

 becomes localized before the closure of the medullary folds 

 (stage 1), possesses the properties of self-differentiation. He 

 has also shown that this gill-producing faculty resides not only 

 in the ectoderm of the immediate gill region, but that prospective 

 gill forming potencies extend for a considerable distance beyond 

 the limits of the immediate gill region, particularly in the region of 

 the heart and the pronephros. According to this author, the 

 capacity of the outlying ectoderm to regenerate gills is not the 

 same in all forms — it being higher, for example in Bombinator 

 than in Rana fusca. 



The equipotential properties of the gill ectoderm in 

 Amblystoma is secondarily brought out in the present experi- 

 ments, particularly in series A (table 1), in which it has been 

 shown that after complete extirpation of the tissue of the third 

 gill swelling, complete gill formation occurred in more than 50 

 per cent of the cases, and that the limb rudiment, in these cases, 

 which originally occupied the region of the third external gill, 

 underwent a caudal displacement so as to lie eventually posterior 

 to the normal gill region. 



The difficulty of making successful limb transplantations was 

 likel}' due to the presence of the inherent gill-producing property 



