REGENERATION IN ANNELID NERVE CORD Rio 
The regeneration in the nerve cord consists, then, of two steps, 
first, the formation of a strand of plug cells which unites the 
ends of the cord and, second, a growth of fibers from the original 
cord through the strand uniting the cells of the two ganglia 
which were separated by the cut. 
3. Summary of sumple regeneration. We may then summarize 
the steps in the process when a simple cut is made in the body 
wall of the earthworm and the nerve cord sectioned. 
1. In a very short time (forty-five minutes to two and a 
quarter hours) the wound is closed. This is accomplished by 
means of a plug which fills all the spaces between the cut ends of 
the tissues. The meshes of the plug are filled with corpuscles 
and large clumps of agglutinated cells. 
2. In this same short period of time a strand of the cicatrix 
material unites the ends of the nerve cord, which may be as 
much as the width of two metameres apart, due to the elasticity 
of its fibers. 
3. Shrinkage of the cells of the strand draws the oe of the 
cord nearer and nearer together. 
4. A growth of characteristic fibers takes place from both 
ends of the cord as regeneration progresses, finally bridging the 
gap. If the cut be through a ganglion, large nerve cells may 
migrate into the connecting material reconstructing the destroyed 
ganglion. 
5. In the final stages the different layers are connected and 
functioning, the muscle layers by a strand of the differentiated 
plug cells, and the nerve stumps by a growth of fibers from the 
old cord. 
D. Regeneration when two to four segments are removed 
1. Former work. In connection with my former study of the 
time required for a simple cut to regenerate, I operated on sev- 
eral worms, taking out from two to four segments of the cord. 
Some very striking results weré apparent, but it was impossible 
to verify these on account of lack of material. At that time I 
allowed regeneration to progress to the point at which loco- 
