TRANSPLANTATION OF LIMBS IN AMBLYSTOMA 153 



concentration of the rudiment into the definitive Hmb bud. This 

 is well illustrated in Amblystoma. The original limb rudiment 

 which extends from the anterior border of the third somite 

 to the posterior border of the fifth becomes innervated by the 

 third, fourth, and fifth segmental nerves. Assuming that these 

 nerves reach the rudiment when it occupies its maximal extent, 

 as they very hkely do, their convergence into a plexus (fig. 4) 

 would mechanically result from the concentration of the rudi- 

 ment into the definitive limb bud which centers ventral to the 

 fourth myotome. 



In discussing the question of variations in the segmental nerve 

 supply to the limb plexus, Harrison ('10) explained such modifica- 

 tions as due specifically to variations in the position and extent 

 of the limb rudiment, these variations are assumed to occur 

 frequently in nature. Harrison's interpretation of this condition 

 was justly made as a result of his own hmb experiments in which 

 he found that transplanted limbs received their nerve supply 

 from segments of the cord corresponding in position to that 

 occupied by the transplanted rudiment. It must be borne in 

 mind, however, that in his experiments, all of which were carried 

 out on anuran forms, the nerve paths were in part or totally laid 

 down at the period when the rudiment was transplanted. In 

 preparing the wound for the reception of the transplant, the pe- 

 ripheral ends of the nerves were severed and the rudiment placed 

 in the direct pathway of the cut ends. Furthermore in these 

 experiments, the normal limb rudiments were left intact in all 

 cases, and the transplanted Umb was developed from an additional 

 rudiment taken from another embryo. Under the conditions 

 of his own experiments, therefore, it was impossible to test the 

 effects of variations in the position of the limb upon the growth 

 of its normal nerves, since these nerves were already in connec- 

 tion with their normal intact appendages at the time of 

 the operation. 



If the position and extent of the limb rudiment alone deter- 

 mined the source and number of spinal nerves contributing to 

 its plexus, we should expect that the rudiment, when trans- 

 planted several segments caudal or anterior to its normal position, 



