ZOOLOGY: S. R. DETWILER 
325 
of the elements has been obtained by making a count of the ganglion 
cells. 
Although diligent search has been made, no evidence has as yet 
been obtained to show that the functional activity of the transplanted 
limb has effected a hyperplasia of the peripheral somatic motor neurones, 
there being no constant differences in size between the motor horn 
areas supplying the heterotopic limb and the opposite side where the 
limb is not present. 
The experiments were carried out upon embryos in the so-called tail 
bud stage (stage 29). In the majority of the experiments the anterior 
limb rudiment was excised and re-implanted in the same embryo at dis- 
tances ranging from one to seven segments posterior to the normal posi- 
tion (autoplastic transplantation). Other experiments consisted of 
transplanting an additional anterior limb rudiment to an embryo in 
which the normal limb rudiments were left intact (homoplastic trans- 
plantations). The larvae were preserved at intervals from thirty to 
eighty days after the operation, the majority of cases being under 
observation for about sixty days. 
The results of the transplantations are presented in table 1. The 
figures in table 1 A illustrate the significant fact, that, as the limbs are 
implanted farther and farther away from the normal situation, there 
occurs a corresponding decrease in their ability to function until a posi- 
tion is reached (six segments posterior to the normal, series AS6) in which 
all exhibit very imperfect movements, there being no cases with perfect 
adaptive function. 
Additional anterior limbs transplanted successively three, four and 
five segments posterior to the normal intact limb of the host (table 1 B), 
while exhibiting slight twitching movements in cases, never attain the 
completeness of function reached by autoplastic limbs implanted in the 
same relative position. 
The gradual decrease in the function of the autoplastic limbs as they 
are implanted more and more remote from the normal limb region 
seems to be directly correlated with the segmental nerve contribution 
(table 2). 
The normal anterior limb is supplied by a plexus composed of the 
third, fourth and fifth spinal nerves (fig. 1). In the tail bud stage of 
embryonic development the anterior limb rudiment constitutes a slightly 
thickened region of somatopleural mesoderm lying just ventral to the 
pronephros and extending from the anterior border of the third somite 
to the posterior border of the fifth. 
