REGENERATION IN ANNELID NERVE CORD 167 
C. Regeneration after a simple cut 
1. The source of the cicatrix cells. In studying the source of 
the plug cells formed when a cut is made in the body wall, all 
of the tissues of the normal worm should be considered (fig. 1) 
and comparison made with these same tissues in the regenerat- 
ing worms. 
The epithelium of the normal worm is of the simple columnar 
type. Its appearance varies somewhat according to its position 
on the metamere. On the outer rounded parts of the metamere 
is a high columnar epithelium with many gland cells, large 
rounded bodies closely packed with granules. In the furrows 
are the low columnar type with few or no gland cells. When a 
cut is made in the body wall the epithelium is one of the first 
tissues to regenerate. Worms killed within a few minutes after 
section show the edges of the epithelium turned inward (fig. 2). 
This is due to the contraction of the circular muscles. In a very 
short time—forty-five minutes to two and a quarter hours—the 
wound is filled with a mass of cicatrix cells which extends up, 
nearly to the digestive tract and fills all the space between the 
cut ends of the different layers (fig. 3). The inturned edges of 
the epithelium may be imbedded in this mass, but the epithelial 
cells which are covered thus break down and degenerate without 
leaning toward or migrating into the plug. Figure 13 shows 
_ such a condition (D. Ep.). The cells at the outer edge lean out, 
and by proliferation give rise to the new epithelium (R. Ep.). 
More often the skin is not turned in so deeply and the growth 
is from the cut end of the epithelial layer (fig. 14). 
An early stage in the process is shown in figure 12. Here the 
plug (P1.) fills the cut area, with a few strands of circular muscle 
imbedded in it. The new low epithelial cells extend out a short 
distance, but the central part of the plug is directly exposed. 
As regeneration progresses the whole plug shrinks and the 
epithelial cells grow entirely across (figs. 14 and 15). Rand (01) 
has shown that these arise from the old epithelium and migrate 
across the cicatricial area. Although the old cells tend to lean 
in the direction of growth, yet there seems to be no proliferation 
