684 A. . Goldfarb 
cluded), the missing parts of the leg were readily regenerated in 
almost every instance. 
The elements of the leg, foot and toes were differentiated in a 
perfectly typical manner. Certain malformations made their 
appearance and these were perhaps more numerous than among 
the control animals. But these were due in largest part to mechan- 
ical stresses or other indirect effects of paralysis. Many of the 
paralyzed legs, even at a late stage, could not be distinguished 
from controls of the same degree of differentiation. 
The tal. ‘The facts appeared at first to point to the conclusion 
that regeneration of the tail in Diemyctylus viridescens 1s directly 
dependent on motor innervation of the amputated end. ‘This con- 
clusion is contrary to that obtained in the regeneration of the limb 
of this animal, in the tail of the tadpole, and in the head of the 
earthworm,—to be hereafter described—and it seemed to follow 
either that the role of the motor nerve system was different in 
different parts of the same organism, and different in different 
animals, or, that there were some other factor or factors in the 
regeneration of the tail of the newt that I had not yet discovered. 
A detailed study of many more animals showed that the first 
alternative was wholly untenable. 
It was found that at each level the normal tail is supplied by 
nerves that take their origin in the cord and dorsal ganglia of the 
next two or three anterior vertebra, i.e., a distance of about 4 to 
44mm. From this it followed that the destruction of less than 44 
or 5 mm. of the cord removes only a part of the motor supply while 
the removal of more than 5 mm. prevents all motor impulses from 
reaching the cut surface. Generally speaking the destruction of less 
than 5 mm. of the cord did not prevent the regeneration of the 
tail, destruction of more than 7 mm. nearly always inhibited the 
development of the tail. | 
After the operation, the end of the cord nearest the amputated 
surface undergoes degenerative changes of both fibrous and cellu- 
lar layers. ‘The changes cease and are superseded by construct- 
ive changes whereby either abnormal structures such as multiple 
cords are formed, or a new cord is developed. The rate of regener- 
ation of the new cord varies considerably with the extent of the 
