12 ROSS G. HARRISON 
as their direction of 'pointing' is determined principally by the 
bud itself. In two of the combinations (homopleural dorsoven- 
tral and heteropleural dorsodorsal) , they point anteriorly or 
dorsoanteriorly ; in the other two (homopleural dorsodorsal and 
heteropleural dorsoventral) posteriorly or dorsoposteriorly like 
the normal. The subsequent development in the latter case is 
normal, but in the former there is a tendency for the limb to stick 
out more sharply to the side or to rotate more or less from the 
position in which it would be found were the position determined 
entirely by the orientation of the bud itself. Nevertheless, the 
palm tends to face ventromedially, or else the limb is so rotated 
that it faces more ventrally or anteriorly. In order to determine 
whether the limb is right or left, it is necessary to be able to dis- 
tinguish between the palm and the back of the hand, which is 
not always so simple as it might seem. It can usually be done, 
however, by noting the digits, which are frequently slightly 
flexed. When there is uncertainty, it is necessary to resort to 
sections, in which case there is no difficulty in distinguishing be- 
tween the two faces, because of the much greater thickness of 
the soft parts on the flexor surface of the skeleton. 
The duplicities that arise are of all grades and kinds, and occur 
in very different proportions in the several experiments. Some- 
times they make their appearance very early, sometimes late in 
development. In the orthotopic grafts reduplication is far more 
common when the developing limb and the substratum are of 
opposite sides. In such cases the doubling member nearly always 
appears as a bud posterior to the main limb, growing there into 
a limb of proper asymmetry. The extent of reduplication may 
include the whole limb from the shoulder down, or only certain 
of the digits. The duplicate limb is as if it were mirrored from 
the original in a plane which is perpendicular to the plane of the 
proximodistal axes of the two lunbs^ and which cuts the axes 
of the two limbs at their junction, at an angle which varies from 
almost 0° to 90°. In the former case the two members are 
almost parallel, in the latter they diverge in the opposite direction 
at almost 180°, the mirror plane bisecting the angle between them 
8 Bafcesou, Materials for the Study of Variation, p. 479. 
