REGENERATION AFTER EXARTICULATION 123 
physis and the skeleton of the new foot is formed. This is 
followed by growth in a proximal direction to form the new fibula 
(centripetal regeneration). Apparently the energy of regenera- 
tion is not always sufficient to produce a complete fibula even 
in a year’s time although it may do so in two months as in the 
first specimen described (sixty-six days). 
A tendency to regenerate centripetally was also noted in 
experiment four, where both leg bones were removed and the 
foot allowed to remain. In this case however it was limited to 
the formation of a mass of cartilage (fig. 7, T.c.) uniting the proxi- 
mal surfaces of the tarsalia. Wendelstadt (’01) obtained centri- 
petal regeneration in the axolotl by extirpating the upper ends 
of the radius and ulna. In three animals, the bones were com- 
pletely restored after fifteen to eighteen months. There was 
apparently no tendency to regenerate centrifugally from the 
femoral epiphysis. 
Morgan (’08) using Plethodon and Diemyctylus tried to dis- 
cover what kind of a structure would regenerate from the proxi- 
mal end of a limb. For this purpose the limb was cut off and 
grafted onto the stump in reverse position. Regeneration oc- 
curred but results were complicated, due to mixing of old and 
new material and to the turning of the graft in the skin-pocket. 
This method was discarded in favor of the following: The 
hind leg was cut off at the knee. Then the femur was cut off 
high up in the thigh and the distal portion reversed in position. 
A new limb regenerated. Its skeleton was composed of (1) 
proximal stump of femur, (2) connecting cartilage, (3) piece of 
reversed femur, (4) new tibia and fibula, and (5) foot. There 
was considerable evidence of absorption and in only a few cases 
did it seem probable that the material for the new limb came 
from the exposed proximal end of the grafted piece. In some 
cases the new cartilage from the proximal stump grew past the 
graft. On the whole it is not quite clear from Morgan’s account 
what part the graft played in regeneration, as histological de- 
tails are not given. 
Reed (’03) performed a series of experiments somewhat similar 
to those just described (Exp. 5) except that the distal end of the 
