152 S. R.. DETWILER 
being more perfect when innervated from the limb level of the 
cord. 
It has hitherto been stated that in the tail-bud stage, the 
period of development in which the experiments were carried 
out, the anterior limb rudiment constitutes a region of somato- 
pleural mesoderm extending from the anterior border of the 
third somite to the posterior border of the fifth. The normal 
anterior limb is supplied by a plexus composed of the third, 
fourth, and fifth spinal nerves (fig. 2). These nerves, effecting 
connection with the limb rudiment at a period when it occupies 
its maximum extent (anterior border of third somite to posterior 
border of fifth), become converged into a plexus as a result of 
concentration of the rudiment into the definitive limb bud which 
centers under the fourth myotome. Such convergence having 
taken place, a typical normal plexus as illustrated in figure 2 
would be produced. In the normal position, the number of 
segments occupied by the limb rudiment apparently serves as 
an index of the number of segments which will contribute nerves 
to the appendage. 
The results of homoplastic experiments carried out by Braus 
(05) and Harrison (’07), as have already been pointed out, show 
that transplanted limbs also received innervation from segments 
corresponding to the extent and position of the rudiment. In 
the majority of their experiments, all of which were carried out 
on anuran embryos, 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 
peripheral ends of the nerves were severed and the rudiment 
placed in the direct pathway of the cut ends, which were found 
to continue their growth into the rudiment so placed. Any 
influence which the limb might have on the segmental nerve 
contribution and the direction of the nerve paths could not be 
adequately tested by these experiments; since, in order to do 
so, the rudiment would have to be transplanted at a period before 
initial outgrowth of the nerves begins. The results of the auto- 
plastic limb experiments in Amblystoma show that other factors, 
in addition to the position and extent of the limb rudiment, 
