Physiology of Regeneration 639 
IX SUMMARY 
1 The rate of regeneration varies with the “level” of the 
worm’s body at which the cut has been made, being greatest 
when the cut is in the anterior region and decreasing gradually 
for cuts in more posterior regions. 
2 In the process of posterior regeneration there are certain 
definite stages whatever the level of the cut: there is invariably 
a lapse of some time, which varies with different individuals and 
under different conditions, before new tissue is proliferated; this 
is followed suddenly by a period of rapid formation of new seg- 
ments, to be in turn followed soon by a period of slower regenera- 
tion. From this time on the rate of regeneration is constantly 
decreasing until finally the process is brought to a standstill. 
3 The difference in the rates of regeneration from different 
levels appears at the very start of the regenerative process, the 
period of time during which there is as yet no regeneration taking 
place being longer in the case of worms cut near the posterior end 
than those cut nearer the anterior end;-moreover, the number of 
segments regenerating during any given period remains smaller 
in the former case than in the latter throughout the entire process 
of regeneration. ‘The difference in the rates of regeneration from 
different levels is, thus, a continuous difference, not being mani- 
fested at any particular stage in the process. 
4 The period of very rapid formation of new segments 1s 
coincident with a period of very slow growth of the existing regen- 
erated segments, while the period of slow formation of segments 
is accompanied by a vigorous growth of those already differen- 
tiated. The formation of new segments and their subsequent 
growth seem therefore to be reciprocal processes. 
5 After a second operation Podarke regenerates at a consider- 
ably slower rate than after the first operation. This slowing 
down of the regenerative process after the second operation is 
especially well marked during the first few days after the opera- 
tion, as compared with the rate of regeneration for a similar 
period of time after the first operation. After a certain time, 
however, the worm may again resume the normal rate of regen- 
eration. 
