TRANSPLANTATION OF LIMBS IN AMBLYSTOMA 119 
This leaves open the question of whether or not the limb rudi- 
ment, either in the normal or the heterotopic position, exerts 
any directive influence upon the segmental contribution of the 
spinal nerves or upon the final path taken by them in the inner- 
vation of the limb. The possibility of the limb’s exerting any 
such influence on the developing peripheral nerves could hardly 
be adequately tested by transplanting limb buds to larvae in 
which the peripheral nerve paths have already been formed, 
such as in the experiments hitherto described. As we have seen, 
limb buds in these cases are placed in the direct pathway of a 
number of already formed spinal nerves, the peripheral ends of 
which are severed in preparing the wound, and it is expected 
that these nerves should continue their growth into the rudi- 
ment so placed. 
Evidence as to whether or not the limb rudiment does exert 
any influence on the segmental contribution and on the path of 
the spinal nerves entering into the formation of the nerve plexus 
ought to be obtained by transplanting limb rudiments in embryos 
at a period before the spinal nerves have begun to develop. 
Then, any possible influence on the part of the end organ can 
exert itself on the nerve fibers at a time when initial outgrowth 
takes place. In the Urodele, Amblystoma punctatum, the an- 
terior limb rudiment can readily be transplanted at such a period. 
In the present paper, which contains a description of a series of 
both autoplastic and homoplastic transplantations on this form, 
certain findings are set forth which strongly suggest such an 
influence on the part of the limb. 
Another very important question on which the experimental 
results contained in this paper throw some light deals with the 
part played by functional activity of the limb on the differentia- 
tion of neuroblasts. 
The general problem of the effect of functional activity of an 
end organ on the differentiation of neuroblasts is one which has 
been tested but little by the experimental method, and the re- 
sults of different investigations as they stand to-day are not en- 
tirely compatible. 
