Influence of the Nervous System 683 
incite the regeneration of the tail. In the series wherein the verte- 
bral canal was plugged at the end, the ganglia were undisturbed, 
yet here also no regeneration took place. In the last series the 
presence of the ganglia did not stimulate the formation of the tail, 
when the essential factors were not present. Finally in a small 
number of animals the ganglia on both sides, together with the 
cord were destroyed for about 5 mm., yet the regeneration of the 
tail was not inhibited. In. other words sensory stimuli are not 
responsible for the regeneration or lack of regeneration of the tail. 
Summary. 
The limbs. Having determined the course of the nerves in the 
rear limbs and tail, the animals were operated in such a way that 
the nerve cord was completely destroyed in the tail, in the lumbo- 
sacral plexus and from one to six vertebrz anterior thereto. 
Study of serial sections established the equally important fact that 
at the level of the plexus no regeneration of the nerve cord took 
place. In consequence the rear limbs were permanently deprived 
of all motor innervation. Ina number of other animals the dorsal 
or sensory ganglia of the plexus nerves were likewise destroyed. 
‘The limbs were amputated either before or immediately after the 
removal of the cord or after intervals sufficiently long to permit 
the nerves of the leg to degenerate more or less completely. 
Special attention was given to the nerves of the leg. Degenera- 
tive changes took place very slowly, about 150 days being required 
for the complete degeneration of the motor fibers. ‘These were 
never regenerated. ‘The sensory fibers however—where the dorsal 
ganglia had not been destroyed—degenerated but for a short dis- 
tance from the amputated end, and then grew down into the regen- 
erated leg. 
In a number of animals the legs were able to move more or less 
completely, but in every such instance at least one of the plexus 
nerves was found connected with the nerve cord. In no case was 
there any movement after the whole of the cord had been destroyed 
from the plexus region. 
Regardless of the nature of the operation, and regardless of the 
subsequent degeneration of the various tissues (nerve fibers in- 
