TRANSPLANTATION OF LIMBS IN AMBLYSTOMA 117 



medullary folds (Detwiler, '17, '18), and it can be transplanted 

 prior to the period when outgrowth of the spinal nerves begins. 

 Here it is possible, therefore, to test whether or not the trans- 

 planted end organ (limb) exerts any directive influence on the 

 normal limb nerves at a time when the latter undergo their 

 initial outgrowth. 



The fact that limb nerves made connections with their proper 

 end organ when the latter was transplanted four and five seg- 

 ments caudal to the normal site scarcely seemed explainable on 

 purely mechanical grounds any more than proper selective periph- 

 eral connections under normal conditions of development can 

 be explained solely by mechanical agencies. These nerves did 

 not terminate at the limbless area as they did upon simple extirpa- 

 tion of the limb, but they continued their growth caudally until 

 the heterotopic limb was reached and connections were made. 

 The caudoventral elongation of the myotomes undoubtedly acts 

 as a mechanical factor in directing the nerves in this game general 

 course, since they lie in grooves between the elongating muscle 

 segments. 



We might conceive of the extended caudal growth of these 

 nerves as due in part to an insufficient number of muscles in the 

 general limbless region for the accommodation of all of their 

 axones. The non-supplied fibers, being directed by the caudo- 

 ventral elongation of the myotomes, would continue to grow 

 until the limb muscles were reached and connections were made. 

 An interpretation of this nature, however, would not explain why 

 the nerves should finally enter the limb when they do reach it, 

 nor why they should take priority over the nerves coming from 

 segments of the cord corresponding to the position now occupied 

 by the transplanted limb. This evidence, pointing to the direct- 

 ive influence of the transplanted limb upon its normal nerves, 

 suggested the experiments which are taken up in the present 

 paper. 



