ee ADA R. HALL 
2. Growth of nerve fibers. ‘The next point to be considered is 
the further growth in connection with the nerve cord. Does 
the cicatrix strand, mesodermal in origin, differentiate into 
nerve material, thus bringing about the early functioning of 
that organ, or is there a growth of nerve fibers from the cord 
itself? This mesodermal strand does form a bridge between 
the cut ends of the cord which rapidly shortens through shrink- 
age, but it seems more probable that the original nerve should 
furnish the material for nerve connections. In a study of the 
cord we find confirmatory evidence for this. The first step in 
the process is seen in figure 4, two and a quarter hours’ regen- 
eration. Here the cord has been cut between ganglia and is 
now united by a definite strand. The cells of the ganglia at 
either side have the appearance of leaning toward the cut region 
and the fibers are thinner at each end of the cord where the 
strand attaches, as if they were stretching also to fill the gap. 
This region is characterized by few nuclei. The central part of 
the strand, however, shows a large number of round nuclei, 
indicating a comparatively small amount of fibers. This is the 
region of the strand formed by the agglutinated blood-cells, 
while the clearer, non-nucleated strand region is formed by 
fibers from the nerve cord. As regeneration progresses the 
strand shortens through shrinkage, and these fiber areas extend 
farther and farther across this bridge. Now the nuclei, of 
necessity, appear fewer, since the fiber growths have usurped 
their place. In figure 5 this further fiber growth is seen, causing 
the nerve part of the strand to appear lighter in color than the 
muscle part. ‘The fibers in the cord also show varicosities which 
are characteristic of nerve but not of muscle. When the cut is 
through a ganglion the large ganglion cells move out into the 
cicatrix at the same time as the fiber growth takes place, thus 
building up again the ganglion which was destroyed. This 
process shows even more clearly in the study of the regenera- 
tion, when several segments are removed. This will be dis- 
cussed more fully later. When the normal functions have been 
recovered, the fibers extend clear across through the central 
region and a different more hollow part appears dorsally connect- 
ing the ends of the giant fiber (fig. 11). 
