Influence of the Nervous System 697 
Head not Regenerated 
As none of the worms were amputated posterior to the 5th 
segment, the lack of regeneration could not have been due to the 
fact that the level had been reached beyond which no anterior 
regenerationtakes place. Norwasit due tolengthof cord removed, 
for in other cases as much or more of the cord was extracted, yet a 
head appeared. | 
Histologic examinations of these worms at different periods 
gave the following results: 
No. 1.79. The 3 head segments were removed. The ventral 
Fig. 17. Cross section through’ 8th segment, i. e., through old cord. Sheath is present. Gan- 
glion cells more numerous and arranged around periphery. Letters as in Figs. 15 and 16, 
nerve cord was extracted from the next 3 segments. Preserved 
12 days later. 
Segments 4 to 6’ inclusive contain no trac of the cord or bases of 
the lateral branches. Fig. 15 is a cross-section through the 6th 
segment showing the ventral portions of the worm and the com- 
plete absence of the cord. ‘Toward the 7th segment the ventral 
7 The original number of the segment will be used, thus, if 3 segments were removed and none regen- 
erated, then the first segment of the headless animal is the original fourth segment and will be so 
designated. 
