SYMMETRY IN TRANSPLANTED LIMBS 105 
The secondary regulation of form may be brought about in 
one of two ways: either by rotation of the limb as a whole dur- 
ing development, whereby it is gradually brought into normal 
posture, or by a process of reduplication, which is more compli- 
cated. In the latter the original grafted limb bud gives rise 
to a secondary or reduplicating bud of mirror symmetry, which 
outstrips the former in development, reducing it to a spur or 
even practically suppressing it. The process of reduplication 
more often yields, however, actual double appendages, and there 
is no hard and fast line between the latter and the single Imibs 
with the original bud reduced to a spur. The figures given in 
the table are therefore somewhat arbitrary in this respect. 
Regulation by rotation has been noted only in the inverted 
limb buds from the same side of the body {hom.dv), and it has 
been further shown that this mode of adjustment probably occurs 
when the lunb bud at the time of operation is rotated anteriorly 
along the dorsal semicircumference somewhat less than 180° 
(p. 41). The mechanics of this process is not yet understood. 
In the other disharmonic group single limbs are very rare (only 
one case), unless reversal by reduplication and reduction occurs, 
and no cases of rotation have been observed. 
Regulation by reduplication and reduction, which is attended 
by reversal of asymmetry, has been observed in five cases out of 
thirty-one in the heteropleural dorsodorsal group, but no perfect 
cases of single limbs so produced have been found in the other 
disharmonic combination (hom.dv.). In the latter group, how- 
ever, reduplication is frequent, and the reduplicating member is 
often normally attached and assumes the same posture as the 
normal lunb, but it has never been found to begin its development 
early enough to bring about the suppression of the original bud. 
In a measure offsetting the regulative cases, there are four 
others in which the same process, reduplication, has resulted not 
in regulation, but rather in its prevention. In three cases of 
inverted buds^^^ (hom.dv.), where there was tendency to regulate 
by rotation, this regulative process was rendered futile bj^ second- 
ary budding, and also in one case of a heteropleural dorso- 
"5 I. E. SG, SS, 90 and possibly two other cases. See p. 37. 
