TRANSPLANTATION OF LIMBS IN AMBLYSTOMA 153 
govern the innervation of the limbs, when transplanted at a 
period before initial outgrowth of the nerves begins. 
Were this not so, then the limb rudiment, if displaced the 
distance of several segments should so effect the nerve contri- 
bution that the plexus ought to come from segments correspond- 
ing to the position occupied by the displaced limb rudiment. 
That is, by shifting the position of the limb bud the distance of 
two segments so that it lies ventral to the fifth, sixth, and seventh 
somites, there should be a corresponding change in the segmental 
nerve contribution so that the limb plexus should be derived 
from the fifth, sixth, and seventh nerves. However, in an 
examination of table 2 the strong tendency for the limb to receive 
innervation from the limb level is quite evident. In. fact, it 
requires a shifting of the limb rudiment the distance of three 
segments (series AS3, table 2) before a change in the segmental 
nerve contribution can be at all effected. The results of these 
experiments strongly suggest that the transplanted limb bud 
exerts a guiding influence on the segmental nerve supply and 
determines the paths taken by the spinal nerves effecting its 
innervation. The results also tend to show that the positive 
reaction toward this influence is greater in the nerves developing 
from the normal limb level of the cord. Especially is this true 
of the fourth and fifth nerves, both of which were found to elon- 
gate in a posterolateral direction a greater distance to effect 
innervation than did the third nerve or those developing from 
segments of the cord posterior to the limb level. The remarkable 
posterior elongation of the nerves to innervate transplanted 
limbs is well illustrated in figures 10, 11, and 12. Figure 11 
shows the segmental contribution to the plexus supplying the 
limb which was transplanted so as to center ventral to the eighth, 
ninth, and tenth somites. We find that this limb receives a 
considerable amount of its nerve supply from the fifth segment 
of the cord. The question arises: why should these nerves 
situated such a great distance anterior to the limb effect limb 
innervation? It is found that the nerves of the limb level do 
not grow out to the limbless area as they do upon simple extirpa- 
tion of the limb, but almost immediately after their exit from the 
