Influence of the Nervous System 701 
farther than 1.40, or, more correctly, the elementary cord has 
assumed more of the characters of the original cord. From the 
15th to the gth segment, the cord is normal. From hereto the 
8th segment it tapers, due to the degeneration of the fibrous layer. 
The attenuated cord reaches almost to the 4th segment. ‘The new 
cord is considerably wider than in 1.40, the cluster of cells in each 
segment approach more closely the typical ganglia, and the constit- 
uent cells resemble more and more the ganglia cells of the normal 
cord. Ee 
It has been pointed out that the removal of the cord from the 
two segments nearest the cut end sufhced to prevent any motor 
nerve stimuli from reaching that end. ‘In the preceding experi- 
ments, the whole cord,’ together with the bases of the lateral 
branches, was removed from the 3d, 4th and 5th anterior segments. 
The length of the extracted cord was made doubly certain, first by 
examination under the microscope immediately after the operation, 
secondly by subsequent study by serial section. In none of the 
instances given was there any sign of the regeneration of the head, 
though the time in some cases at least was more than three times 
what is ordinarily required for a head to regenerate. 
Of the early changes near the broken end of the cord three 
deserve special consideration: 
1 Degeneration of the fibrous layer of the cord does not extend 
over one segment from the broken end. 
2 Acap of small cells develops at the broken end of the cord. 
3 The large nerve cells disappear and are replaced by large 
numbers of smaller cells. 
Subsequently the nerve fibers in the cord grew forward to and 
beyond the broken end, pushed aside the cap of cells and carried 
forward the numerous small nerve cells. These tended to form 
clusters of primitive ganglionic masses in the middle of each seg- 
ment. In the latest stages this anterior growth had extended over 
several segments, to within one segment of the amputated end. 
There is no evidence whatsoever of growth of the cord from the 
ectoderm. 
The question arises whether the lack of regeneration of the head 
may not have been due to the failure of the nerve cord to grow for- 
