SYMMETRY IN TRANSPLANTED LIMBS 43 
Since these differences can scarcely be accounted for on the ground 
of different degree of rotation of the Umb buds at operation (p. 
40), it would seem that the few mesoderm cells remaining in the 
wound bed must have exerted some influence upon the develop- 
ing limb. This does not mean that the limbs which do develop 
in such cases arise solely by a process of regeneration from the 
host. In fact, the rate of development, which is only slightly 
retarded below the normal, precludes such an interpretation. 
What probably does take place is an intermingling of cells from 
the host and the graft, with the result that the former, acting in 
the same sense as the environment with which they are in har- 
monic relation, counteract the tendency of the inverted elements 
to reverse their asjanmetry. This was, however not shown to 
the same degree in the corresponding experiments with super- 
posed limbs (p. 65). 
9. Heteroplewal transplantations, dorsodorsal orientation. For- 
ty-nine cases were operated upon in this way and thirty-one 
lived long enough to yield definite results (table 2). By far the 
largest number of these (twenty-five) developed reduplications of 
one kind or other. Five cases gave rise to limbs with reversed 
asymmetry, i.e., to limbs which developed to fit their new sur- 
roundings, though one of these was considerably underdeveloped. 
One yielded a somewhat imperfect non-reversed limb and four 
were rudimentary. These results seem altogether divergent from 
the corresponding heterotopic transplantations. An examina- 
tion of them shows, however, that fundamentally they accord 
with the latter, complete agreement being modified, by a second 
factor, which may suppress the original bud in favor of the 
reduplicating member. The normal environment of the trans- 
planted bud and the concomitant normal functioning seem to 
facilitate this transformation. Moreover, there is no hard and 
fast line between the different results just enumerated, and the 
individual cases may be taken as forming a series, beginning with 
the single non-reversed and ending with the single reversed limb. 
The reduplications are intermediate. They will be considered in 
this order. 
