TRANSPLANTATION OF LIMBS IN AMBLYSTOMA 15}5) 
riorly cannot function to any degree unless they receive innerva- 
tion from the limb level or from segments of the cord just poste- 
rior to the limb level. — 
It thus seems likely that the influence bringing about the 
posterior elongation of the nerves from the limb level, in addition 
to certain probable conditions existing within the central nervous 
system (which will be discussed later on), provide a mechanism 
whereby the transplanted limbs may, within limits, perform 
functionally adaptive movements. One cannot help but be 
impressed with the fact that the peculiar posterior elongation 
of the nerves to the transplanted limb, as is shown in figures 
10 and 11, is not the result of mere accident or the result of a 
non-directive agent. Especially is this true in those cases where 
the nerves, after having grown out posterolaterally to the body 
wall, will turn their course in a ventral direction and wind their 
way through a mass of muscle tissue to meet a limb more ventrally 
situated. 
Although further experiments are necessary to prove or dis- 
prove definitely that the transplanted limb does so exert an 
influence on the outgrowing nerves as to determine the segmental 
nerve supply and the paths taken by them in the innervation 
of the limb, this hypothesis appears at the present time to be 
the one which most nearly fits the facts. 
A brief explanation of the factors conditioning the function 
of the transplanted limbs has already been published (Detwiler, 
19), but it will be necessary to discuss this point again. 
It has previously been shown (table 2 and fig. 9) that as the trans- 
planted limbs receive less and less innervation from the normal 
limb level of the cord, there occurs a corresponding decrease in 
the ability of the limbs to exhibit movements codrdinated with 
those of the opposite intact limb, so that a position is finally 
reached (six segments posterior to the normal) in which the 
limbs receive no segmental contribution anterior to the eighth 
segment of the cord and show nothing more than greatly impaired 
movements in response to tactile stimulation. This gradual 
decrease in the function of the limbs as they become implanted 
more and more remote from the normal limb region, depends 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 31, NO. 1 
