SHOULDER GIRDLE AND ANTERIOR LIMB 519 
TABLE 8 
Showing the results of transplantation of the limb mesoderm from embryos in the 
stage of high medullary folds 
FOSION | = 7c 
NOR | eee Leeper wire [AON Bs ee 
ORIENTATION MAL | ~ PLICA=| NOR- |). ie 
LIMBS nye TIONS MAL pies Kees rite D 
LIMB LIMBS | SORBE 
Homopleural dorso-dorsal.............. 8 2 10 id 2 3 
Homopleural dorso-ventral............. 2* 1 2 Z 1 0 
Heteropleural dorso-dorsal............. 2t 1 1 1 4 0 
* Laterality reversed. 
} Original laterality retained. 
abnormalities, the transplants were later placed at the posterior 
end of older embryos. In such cases the transplant was of suffi- 
cient distance from the normal limb to allow independent develop- 
ment of the two systems. 
The region in the stained embryo from which the transplant 
had been taken was in many cases covered with unstained ecto- 
derm taken from a third embryo. This unstained insert now 
occupied the place from which the transplant had been taken 
and its position in the embryo, when the somites became visible, 
served to indicate whether the limb rudiment had been entirely 
or only in part transplanted. Z 
The results of the transplantation experiments are given in 
table 8. 
The posture of the normal limbs is in accord with the funda- 
mental rules 1 and 2 underlying the determination of laterality 
(Harrison, ’17). When the transplant is grafted on the same side 
from which it is taken (homopleural) and not inverted (dorso- 
dorsal), original laterality is retained (rule 1), but when inverted 
(dorso-ventral) a limb of opposite laterality results (rule 2). 
When transplanted to the side opposite to that from which it is 
taken (heteropleural) and not inverted, original laterality is 
retained (rule 1). 
While the number of experiments is small, the results show 
that the fundamental asymmetry of the limb mesoderm is already 
determined in embryos with high medullary folds. 
Just how early the limb rudiment is determined cannot be said 
