Influence of the Nervous System 699 
cord is marked by the termination of the cord sheath, as well as 
by the absence of the typical ganglionic cells. ‘These have divided 
into smaller ones by active division. ‘The minute cells also appear 
to have multiplied rapidly and collected at the anterior end. 
Many stages in the development from these minute cells,almost to the 
typical ganglion cells, may be seen in Fig. 18. Another pointof par- 
ticular interest is the forward migration of this whole mass of cells. 
In 1.8 the cord was extracted from 5 segments. ‘Time 68 days. 
Though the time was twice as great as the preceding, constructive 
changes have gone no farther. 
The forward growth of the cord is even more pronounced in No. 
1.16. From the anterior end of the old cord, nerve cells of all 
sizes and all stages of differentiation, from minute cells, difficult 
to distinguish from surrounding cells, to typical ganglion cells have 
pushed forward tothe amputated end, yet no regenerationof a head 
was induced. These changes required 82 days fortheir completion. 
The worms next to be considered have regenerated even a 
greater length of cord than any of the preceding. 
No. 1.107. Cord extracted from 3 segments. ‘Time, 28 days. 
From the end of the old cord at the 6th segment, the new cord has 
grown anteriorly about one segment. It tapers and loses itself 
among a mass of fibers and connective tissue. “The new cord con- 
tains cellular and fibrous layers, though very primitive. 
Though No. 1.7 was preserved 61 days, after the operation, the 
characters are essentially the same as 1.107. 
In No. 1.4 after 79 days the new cord has grown a trifle over I 
segment in length. 
No. 1.33. Cut off 3 segments. Extracted cord from 4segments. 
Time, 35 days. The old cord is normal until the gth segment. 
From this level the cord quickly shrinks, owing largely to the 
diminution of the fibrous layer. Beginning at the middle of 
the 7th segment the new cord has grown into the 6th and 5th 
segments. Along the new cord are very many minute nerve cells 
that cluster into primitive ganglionic masses in the middle of 
the 6th and 5th segments. At these places the cells assume more 
of the typical appearance of the ganglion cell. 
No. 1.40. Three segments removed. Cord removed from 3 
