154 S. R. DETWILER 



would effect a corresponding shift in its segmental nerve supply. 

 Its failure to do so in these and previous experiments on 

 Amblystoma (table 2) has suggested that other factors must be 

 considered in any attempt to interpret the character of innerva- 

 tion which these cases presented. 



The fact that the limb nerves made functional connection 

 with their proper end organ when the latter was transplanted 

 four and five segments caudal to the normal site, scarcely seemed 

 explainable on purely mechanical grounds. These nerves did 

 not terminate at the limbless area as they do upon simple ex- 

 tirpation of the limb, but they continued their growth caudally 

 until the heterotopic limb was reached and connections were 

 made. The caudo ventral elongation of the myotomes un- 

 doubtedly acts as a mechanical factor in directing the nerves 

 caudally towards the transplanted limb. Such a mechanical 

 influence would not explain why the nerves, being so directed, 

 should make functional connection with the limb after they do 

 reach it any more than mechanical agencies can determine proper 

 selective peripheral connections under normal conditions of 

 development. 



It has been shown in previous experiments (Detwiler, '20, '21) 

 that when a limb rudiment is excised, there are, in early stages 

 of development, as many motor axones passing out to the limb- 

 less area as there are on the opposite (normal) side. These ob- 

 servations, by the way, strongly contradict those of Shorey ('09), 

 who claimed that no motor axones developed in the absence of 

 the functional end organ. In the absence of the major portion 

 of their terminal musculature (limb and shoulder muscles), the 

 unsupplied fibers in such cases terminated in the general limb- 

 less area. However, when the limb was reimplanted further 

 caudally a given number of body segments, the nerves, which in 

 these cases had as many motor axones as are present after simple 

 extirpation of the limb, did not terminate in the limbless area, 

 but continued their growth and effected functional connection 

 with the heterotopic appendage. This observation alone strongly 

 indicated that the extended caudal growth of the nerves in the 

 latter case is not governed solely by the mechanical effects result- 



