TRANSPLANTATION OF LIMBS IN AMBLYSTOMA 155 



ing from the caudoventral elongating myotomes; otherwise, 

 upon simple extirpation of the limb, the same mechanical 

 influences should be expected to cause the limb nerves to follow 

 a similar pathway. 



The intimate developmental relationship between the limb 

 and its normal nerves, as suggested in these experiments, has 

 been more strongly brought out in the experiments in which the 

 limb was transplanted anterior to its normal position. The limb 

 nerves in these cases, in effecting connection with the appendage, 

 have had to do so under the mechanical opposition resulting 

 from the caudoventral growth of the myotomes which tends to 

 direct their growth in a caudal direction. That the nerves in 

 these experiments actually were so directed in their initial out- 

 growth is seen from the direction of their proximal portions 

 (figs. 8, 13, 16, and 18). The limbs in these cases, although 

 occupying a position from only one to two and a half segments 

 anterior to the normal site, in many cases (table 1 and fig. 3) 

 were originally reimplanted the distance of three segments 

 anterior to the normal site, so that the relative distance between 

 the transplanted limb and the normal limb nerves was greater 

 at the time when initial connections were made than is indicated 

 by the final position of the limb, the latter having migrated 

 caudally during development. 



From the examination of figure 3 it is seen that the caudal limit 

 of the transplanted rudiment in series B (table 1) extends onl}^ 

 to the anterior level of the second myotome. Under the mechani- 

 cal influence of the elongating myotomes which direct the nerves 

 caudally, we should hardly expect that the third and fourth 

 nerves would change their initial direction of growth to an an- 

 terior course unless there exists in the latter some attractive 

 influence which is responsible for the reversed course of their 

 distal portions (fig. 16). 



The orderliness of peripheral growth and terminal connections 

 in normal development offers strong evidence in favor of the 

 presence of some specific reaction between each kind of nerve 

 fiber and the particular structure to be innervated. In dis- 

 cussing the question of peripheral connections, particularly with 



