TRANSPLANTATION OF LIMBS IN AMBLYSTOMA 157 



nerve, provided the latter be isolated. The susceptibiHty of 

 muscle to additional motor innervation is undoubtedly ter- 

 minated when its initial motor connection is established in 

 development. Such stabilization, however, does not perma- 

 nently preclude the possibility of a muscle's being functionally 

 innervated by other nerves. 



The experiments under consideration in this paper offer no 

 explanation of the nature or character of the stimuli which bring 

 about the proper peripheral connections in the embryo. They 

 do suggest more strongly, perhaps, than have previous observa- 

 tions, the possibility that there does exist in the embryo pref- 

 erential selectivity at the periphery, possibly of a chemotactic 

 nature, which may largely account for the constancy of connec- 

 tions. Kappers ('17) has offered a rational electrochemical 

 theory in explanation of the dynamic polarization of the neurone 

 and of the selectivity within the central nervous system, and it 

 is possible that peripheral selectivity may be determined in a 

 similar manner. 



The initial outgrowth of the peripheral nerve in a straight line 

 and at right angles to the central nervous system as was first 

 observed by His ('88) falls in line with the stimulogenous fibrilla- 

 tion concept of Bok ('15) and meets an explanation on galvano- 

 tactic grounds as presented by Kappers (op. cit.). That the 

 nerve fibers in the embryo have only very short distances to 

 grow before connecting with their proper end organs was brought 

 out by Harrison ('10). Thus the principal nerve paths which 

 grow out from the central nervous system are at first relatively 

 short and only later become lengthened out by the shifting of 

 parts which accompanies the development and growth of the 

 organism. Thus we see that, although the final paths of the 

 nerve fiber are purely subsidiary to the growth and shifting of 

 the organ innervated, initial connection cannot be explained on 

 purely mechanical grounds, and it is very probable that there 

 exists, at the periphery, forces of a chemotactic or galvanotactic 

 nature which bring about orderly selectivity just as these same 

 forces appear to underly the process of selectivity within the 

 central nervous system. 



