Physiology of Regeneration 607 
died before the completion of the process, but I know from the 
results of other similar experiments that, while at the end of 36 
days the number of regenerated segments may reach eleven or 
twelve, hardly any more new segments will be found at the end 
of forty-five days. The process, then, has not merely been 
slowed down, but practically brought to a standstill by that time. 
If, now, we compare the results of the process of regeneration 
from the two different levels, we find, in the first place, that the 
number of worms which proliferate new tissue soon after the 
operation is four times as great in case of worms from which 
nearly two-thirds of the body are removed than in the case of 
worms from which only about one-third of the body is cut off. 
This difference is of some theoretical importance since it reveals 
the fact that the reaction takes place much more vigorously at 
one level than it does at the other, and therefore a greater activity 
must have ensued as the result of the operation in the worms 
cut nearer the head than in those cut near the tip of the tail. 
We shall find, furthermore, that already at the end of the first 
four days after the operation worms regenerating from a more 
anterior level are in advance of those regenerating from a more 
posterior one, and that this condition is maintained practically 
throughout the entire period of regeneration. In the diagram, 
Fig. 5, this point is illustrated by superimposing the diagram, 
Fig. 4, over the diagram, Fig. 3. 
This diagram makes it perfectly clear that there is not merely 
a difference in the rates of regeneration from two different levels - 
at some particular stage in the process, but that there is, so to 
speak, a continuous and lasting difference. This cannot be due 
to a more effective slowing down of the regenerative process in 
one case than in the other, as in either case the regenerating tail 
goes through a similar cycle of stages: a short interval of no 
apparent activity soon after the operation, then a very sudden 
rise in the regenerative activity followed by a sudden drop in 
the process, which is on the decline from this time until it reaches 
practically a standstill. But there is a constantly greater output 
at one level than at the other, as is illustrated by the diagram, 
Fig. 5, in which the obliquely striated columns correspond to the 
