SYMMETRY IN TRANSPLANTED LIMBS 73 
that when half the disc is excised, complete suppression of 
development may sometimes result, probably through accidental 
injury to the remaining part. The result of the former contin- 
gency would be confusing, owing to the de\'elopment of a normal 
limb in place of a reduplication. 
In connection with these questions it must also be borne in 
mind that the cases of union of two disharmonic halves differ, 
with respect to the disharmony of the combination, from those 
in which the limb-bud has been transplanted as a whole. In 
the former only one half of the rudiment is involved, the other 
being in all cases harmonic with the surrounding tissues. We 
are, therefore, dealing with a rudiment that is disharmonic in 
itself, while in the case of the whole limb the transplanted bud is 
harmonic in itself, though disharmonic with respect to the organ- 
ism as a whole. This might possibly give rise to some differences 
in the results in the two classes of experiments. 
In view of these considerations, we should not expect the trans- 
plantation of half buds to give such clear-cut results as the 
experiments with whole ones. On the other hand, it must not 
be overlooked that the sources of confusion above enumerated, 
while accounting for nearly all of the anomalies, also render less 
cogent the cases which conform to the rules. Nevertheless, 
after taking all circumstances into consideration, it can scarcely 
be doubted, that the experiments with half discs do afford a 
valuable confirmation of the results obtained from the other 
experiments. 
18. Homopleural transplantations, dorsodorsal orientation. The 
eight cases of homopleural grafts in upright orientation (hom.dd), 
two involving each half of the bud, all resulted in normal limbs, 
as was to have been expected, for this operation is nothing more 
than replacing an excised portion with one exactly similar. Only 
slight retardation of development is recorded in some of the cases. 
19. Homopleural transplantations, dorsoventral orientation. The 
nineteen experiments with homopleural grafts in inverted posi- 
tion {hom.dv) resulted, in accordance with expectation, in a 
large number (fifteen) of duplicities^^ (figs. 121 and 122). The 
78 H. E. 29 and 31. 
