164 ADA R. HALL 
segments when the muscles are dead and are fixed to prevent 
‘pull.’ Bovard (17) says that not only does the nerve cord 
carry impulses through several ganglia, but that muscle pull 
reinforces these impulses in each segment so that the message 
goes a long distance without losing its force. He has also in 
his histological studies shown that when the nerve cord is cut 
regeneration is very rapid, and that the fibers which are regen- 
erated bear a very direct relation to the movements of the 
worm, the locomotor movements depending on the fine central 
fibers, which regenerate first, and the general collapsing move- 
ments depending on the giant fibers which recover about twenty- 
four hours later. My problem has been to discover in the proc- 
ess of regeneration, a single cut having been made: 1) what 
cells form the cicatrix region and unite the ends of the nerve 
cord and, 2) whether nerve fibers actually grow through this 
region from the ends of the nerve cord before impulses can pass 
from one end of the worm to the other, or whether the muscle 
layers serve as a bridge to get the impulses past the gap. In 
connection with this, I have also studied different periods of 
regeneration in worms from which two or three segments of 
cord have been removed, in order to see if this process will throw 
any light on simple regeneration. 
DISCUSSION OF THE PROBLEM 
A. Materials and methods 
The worm used in these experiments is Helodrilus caliginosa, 
commonly found in our fields and meadows, especially where 
there is turf. They are kept several days between moist cloths 
to free them from as much grit and dirt as possible. Cloths are 
preferable to filter-paper, as they can be sterilized frequently 
and they also prevent the fillmg of the digestive tract with 
paper pulp—a hindrance in sectioning. When ready to operate, 
the worms are anesthetized by placing them in 5 per cent alcohol 
until movements practically cease; left longer they are not 
strong enough to recover and may die before regeneration is 
complete. The worm is next laid over a rounded surface, such 
