EXPERIMENTS ON THE FORE LIMB OF AMBLYSTOMA 455 
ably shorter than normal. Examination of frontal sections shows that 
only the coracoid portion of the girdle is developed. Shoulder muscles 
are present, but no nerves have been found. ‘There are two ulnae, one 
on each side of the somewhat thickened radius. 
Experiment Tr. Mes. 19. March 3, 1915. Mesoderm of right limb 
to left side. 
March 16. Growth of transplanted tissue has been comparatively 
slow, though in the past three days considerable. 
March 19. Limb still short, though showing beginning of digita- 
tions. 
March 29. Arm very short; three long digits, of which the most 
ventral and posterior is probably a reduplication. On the dorso- 
anterior border the third and fourth digits show, the latter but very 
slightly. 
April 12. Specimen preserved. 
This is similar to the previous case (Tr. Mes. 18), but the limb is 
shorter and the elbow bend more distinct. There is an approximately 
symmetrical radial reduplication of the hand, which is broad and paddle- 
like. The arm points posteriorly and laterally. The posterior mem- 
ber is probably the primary one and has had its laterality reversed, 
being a left. The digits are further developed in this hand, both the 
third and fourth being distinguishable (Fig. 45). 
In viewing the above seven cases as a whole, it is seen that, 
while no one is absolutely normal, they are all sufficiently de- 
veloped to show their specific form. One alone is badly de- 
ficient, two show reduplications which are slight, three others 
reduplications which are more marked, involving in one case the 
whole forearm and hand. One case (Tr. Mes. 5) has no re- 
duplication and is normal except that the first two digits are held 
together by a web throughout their length. This abnormality is, 
however, not infrequently found in limbs that have not been 
operated upon. 
These results show clearly that the specific limb-forming 
tissue is the mesoderm of a certain region of the body wall 
and not the ectoderm. When it is considered that there is much 
loss of tissue in the operation and that what remains must 
often be to a great extent mixed up, the most striking thing is 
that the limbs which develop from such inoculations should be 
so nearly normal. These experiments thus afford additional 
evidence for the equipotentiality of the elements constituting 
the limb bud. 
