60 M. L. Shorey 
days after the removal of the limb. In this specimen the normal 
nerve roots can be traced but a short distance beyond the spinal 
cord (Fig. 30), and I cannot demonstrate with certainty the pres- 
ence of any motor fibers, but there is some evidence of the begin- 
ning of the formation of the ventralhorn. Only five days elapsed 
between the time when this larva was killed and the one in Experi- 
ment 27. There is no sign of degeneration in the latter case, and 
when it is remembered that, so far as is known, the atrophy of 
tissue requires a longer period of time than its formation (compare 
surgical literature and experiments described by Bethe and others, 
and Experiment 5 on the chick embryo, for this point) there seems 
little possibility that, at the rate of development of this animal, 
these cells could have been formed and completely degenerated. 
Moreover, as the extent of the defect is continually increasing, if 
all the motor nerves are self-differentiating, there must be a con- 
tinual degeneration, and tissue in the process of destruction is so 
apparent that it could not have escaped detection in some of 
the specimens studied. I can therefore see no reason for believing 
that the defects in the nervous system of the specimens studied is 
due to degeneration. 
D_ Experiments on Bufo lentiginosus Americanus 
Little need be said in regard to the experiments on the toad, for 
they furnish no new points of interest. ‘The presence of some 
muscles, and the fact that regeneration occurs, makes it impossible 
to study the behavior of the nerves in the absence of all the organs 
which they normally innervate. But in one specimen preserved 
nine days after the removal of a hind limb, there was a defect in 
the motor horn, although it was not yet completely formed on the 
normal side. Examination of several specimens showed that the 
motor horn and ventral root are always smaller if there is a marked 
loss in the mass of musculature, and no evidence of degeneration 
could be found. The toad, therefore, confirms the results obtained 
by experiments on amblystoma. 
