REGENERATION IN ANNELID NERVE CORD 175 
there is no bunching apparent. The strand (S) is nearly as 
long as the part of the cord removed and seems to have taken its 
place. The septa (Mes.) are also practically in their proper posi- 
tions, the middle segment of the three removed being shorter 
than normal. In the strand (S) of the cicatrix lying between 
the ends of the cord there are fewer nuclei and also there is a 
distinct difference in the staining reaction, this part being lighter 
than those each side of it. A closer study reveals the fact that 
it is the fibrillar structures which stain differently, those of the 
strand being more of a yellow with fine varicosities, while those 
of the surrounding cicatrix are brown. Comparison of the 
fibrillar structure of the strand and of the ends of the cord which 
we know to be nerve fibers shows that color and structure are 
the same, which seems to indicate a growth of nerve fibers. 
After three months’ growth others of these worms were killed 
and sectioned (fig. 17). The pieces are about ten to twelve seg- 
ments long, the cicatrix being at the center of the piece. Such 
worms show no sign of scar in epithelium, muscle, or nerve 
tissue. The septa are all nearly parallel and the coelom free 
from extra cell structures. The new ganglia are normal in 
every respect except length, two of the regenerated ganglia 
being shorter than normal. I know that two and three segments 
were removed, from actually counting the ganglia on the bit of 
cord excised. I also know, by counting back, that the part of 
the worm which was sectioned contains the excised region of the 
cord. Thus it seems that actual growth of nerve fibers takes 
place, and that all superfluous cells are again absorbed, leaving 
all the structures normal. Since the epithelium does not grow 
inward when the body wall is cut, but merely covers the plug, 
these replaced ganglion cells as well as fibers must come from 
growth in the cord. 
3. Summary of regeneration when two to four segments are 
removed. 1. There is a massing of cicatrix cells into all parts of 
the cut region as in simple regeneration. These connect all cut 
layers and either draw the ends of the cord directly together by 
means of a strand so that all the mesenteries and muscle layers 
become massed or the strand fills in the vacant place in the cord 
leaving the other layers in their normal positions. 
