EXPERIMENTS ON THE FORE LIMB OF AMBLYSTOMA 459 
Splitting of the limb bud by a vertical or horizontal incision 
may cause slight delay in development, but does not produce 
reduplications. 
A single normal limb will develop from two fused limb buds 
when one is superimposed upon the other in proper orientation. 
Removal of the ectoderm covering the limb bud has no effect 
upon the development of the limb beyond causing slight delay. 
Removal of the mesoderm of the limb bud, when complete, 
prevents the development of the limb even when the proper 
ectodermal covering is healed back over the wound. 
Transplantation (inoculation) of mesoderm from the limb re- 
gion to a pocket under the skin of the flank results in many 
cases in the development of limbs. In about half the cases 
which live this inoculated tissue is resorbed or does not develop 
further. 
The limbs which develop show a large proportion of redupli- 
cations; one case was perfectly normal except for syndactyly of 
the first two digits. 
Taken together, the experiments show that while the ectoder- 
mal covering is indifferent, the mesoderm of the limb bud con- 
stitutes a specific self-differentiating system, which, however, in 
itself is an equipotential system in Driesch’s sense. 
