EXPERIMENTS ON THE FORE LIMB OF AMBLYSTOMA 445 
posited in the ectoderm. A few experiments have been made 
by grafting markers in the form of pieces of notochord, which 
could readily be recognized, in the mesoderm of the different 
quadrants of the limb bud, in the hope that they might be lo- 
cated after the limb was developed. As yet these have resulted 
negatively. 
ATTEMPTED SPLITTING OF THE LIMB BUD 
Some years ago, in experimenting with larvae of the anuran, 
Pelobates, Tornier (’05) found that by making a deep incision 
through the hind-limb rudiment and the base of the tail he 
could prod*ce double appendages. 
A few experiments have been made for the same purpose in 
connection with the present study. The material has necessi- 
tated, however, a rather different mode of operation, and the 
results have proved to be different. 
The limb bud was deeply incised through the middle, either 
dorso-ventrally or antero-posteriorly, and a narrow strip of 
tissue including both ectoderm and mesoderm was removed. 
Thirteen experiments were made. Six were lost by accident 
eleven days after the operation, but all of them had at that time 
normal limbs on the operated side. The other cases were kept 
for sixteen or eighteen days and again all had normal limbs, 
though in four cases development was somewhat retarded. Nine 
of the embryos were in the oldest stage used (fig. 3) at the time 
of operation. The wound usually left a distinct scar or groove 
running across the limb bud, which, however, was obliterated 
after several days. In no ease did the operation result in redu- 
plications. The difference between these results and those of 
Tornier may be ascribed to the fact that in the case of the latter 
the operation was more radical and done upon older embryos, so 
that the chance of the divided limb rudiment healing together 
completely was much less. 
EFFECT OF SUPERIMPOSING LIMB BUDS 
In experiments upon early embryonic stages the most usual 
test of equipotentiality of the parts has been the development 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 25, No. 2 
