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ZOOLOGY: R. a HARRISON 
dd.), result primarily in limbs that are not normally placed in relation 
to the cardinal points of the embryo, and may be termed disharmonic. 
In comparing the distribution of single and reduplicated appendages 
in the various groups a remarkable result becomes apparent. In the 
heterotopic group, where function is excluded, the harmonic combina- 
tions yield a relatively large proportion of reduplications (about 54%), 
while the disharmonic combinations yield a far greater proportion of 
single limbs (about 87%). In the orthotopic group, on the other hand, 
the harmonic combinations yield in overwhelming proportion (96%) 
single limbs which are functional and perfectly normal with respect 
to their surroundings, while the disharmonic combinations yield about 
96% of reduplications. 
Experiments with superimposed limb buds and with transplanted 
half-buds confirm the above results. The harmonic combinations 
yield single limbs while the disharmonic combinations result in re- 
duplications. 
All double formations do not remain as such, however, for it is possible 
to achieve a normal result from at least one of the disharmonic com- 
binations (het. dd.) by the reduction of the original limb of the pair and 
the preponderance of the other, which then becomes a normal single limb 
of reversed laterality (3c) corresponding, therefore, to the laterality of its 
new surroundings. On the other hand, in the only case in which a single 
normal limb of opposite laterality (2a) developed in the orthotopic 
position, it functioned perfectly. This shows that when innervation 
and vascularization are sufficient, a functional condition may arise 
which is independent of the harmony of the combination. 
It would be premature to discuss the bearing of the experiments upon 
the question of adaptation. It may be pointed out, however, that the 
fundamental rules of laterality, as stated above, lead as often to dis- 
harmonic as to harmonic results. On the other hand the secondary 
factors, especially those which determine whether a reduplicated or a 
single appendage shall arise and those which lead to the resorption of 
one of the two members of a pair, show a tendency to produce a pre- 
ponderance of adaptive results. To determine the exact nature of these 
factors will require further investigation, pending which it seems un- 
wise to appeal to mysticism for the explanation. 
1 Braus, H., Miinchener med. Wochenschr., 1903. 
2 Harrison, R. G., these Proceedings, 1, 1915. 
3 The shoulder girdle rudiment is itself such a system according to Braus, Experimentelle 
BeitrSge zur Morphologie, 1, 1909 (400). Also Morph. Jahrh., Leipzig, 39, (271). 
< Harrison, R. G., Anat. Rec, Philadelphia, 10, 1916. 
