254 Ross Granville Harrison 



tions of Rana embryos in closely graded developmental stages will 

 convince one that nerves are present in the immediate vicinity of 

 both the fore and hind limbs as soon as the limbs themselves 

 become distinguishable, and in the case of the fore limb (Fig. i), 

 even before any signs of the mesenchymatic thickening can be 

 made out. 



The specimens w^ere kept alive for a considerable length of time, 

 in m©st cases until the hind limbs, both natural and transplanted, 

 were fairly well developed and showed the various articulations. 

 In this respect my own experiments differed from those of Braus, 

 who kept none of his "aneurogenic" transplantations alive longer 

 than eight days. It is quite probable that this difference would 

 be sufficient to account for the divergence of our results. 



In the second series of experiments, which were made to test the 

 power of autochthonous development of peripheral nerves, normal 

 hind limb budswfere transplanted to nerveless organisms. Braus 

 recognized the importance of this experiment and attempted to 

 carry it out, though without results, for the reason that the nerve- 

 less tadpoles were unable to maintain themselves alive for a suf- 

 ficient length of time. This difficulty was obviated in the present 

 case by providing each nerveless individual with a nurse, i. e., by 

 uniting it to a normal larva, in the fashion of Siamese twins (Fig. 

 14). The experiments were only partially successful, however, 

 because for some unknown reason none of the transplanted limbs 

 grew well on the bodies of these nerveless larvae. 



Transplantation of Normal and Nerveless Limbs to Normal 



Individuals 



The four experiments to be considered under this heading will 

 be taken up individually. 



Experiment I ?^ The three larvae (R. sylvatica) used for this 

 experiment were reared together under the same external condi- 

 tions. On April 15, 1906, shortly after the medullary folds had 

 closed over, the medullary cord behind the vagus region was entirely 

 removed from one specimen. On April 22, the absorption of the 



^■•Record number, Tr. Ext. 7. 



