416 Marion L. Durbin 
they quickly revive and wriggle violently until exhausted. ‘The 
most specific evidence in favor of the view that the rate of the 
initial period is low, because the animals during that time, are 
laboring against the inhibiting effects of the shock of operation, 
lies in two facts: (1) The greater the amount removed from the 
tail of a tadpole of given size, the longer the interval of slow regen- 
eration preceding the interval with a maximum rate; in other 
words, the more severe the operation the more concave the curve, 
from its beginning to its greatest height; (2) if the amount of 
tail removed is too large the animal dies soon after the operation. 
Fig. V shows the curves of rate drawn from the data, collected 
by Ellis in his “Experiment 4.” The tadpoles of this set were 
37-42 mm. long. ‘Three millimeters were removed from each 
animal in one series; 5 mm. from those in another; Io mm. from 
those of a third; 15 mm. from the fourth and 20 mm. from the 
fifth. ‘The curves for the series with 3 and 5 mm. removed show 
little or no inhibition in the rate during the first period. ‘The 
curve for the series from which 10 mm. were removed shows that 
the rate at the end of the first period is very little below what it 
would have been, had it increased uniformly from the time of 
operation to the time of maximum regenerating speed. The 
curve for the series with 15 mm. removed shows that the rate in 
the first period is very low in comparison with that attained 
during the second period. The maximum rate for this series was 
not reached until three days after it had been reached by the 
animals in the three preceding series. Eighty per cent of the 
series, with 20 mm. removed died soon after the operation. ‘The 
four that did survive did not begin to regenerate until after the 
third day. On the ninth day they reached their maximum rate, 
but the new tails that were being formed were stunted and crooked. 
However well these facts support the idea that the shock of 
operation is responsible for the low rate in the initial period, 
they are not opposed to the view that time is spent, previous to 
the beginning of rapid regenerations, in building up a layer of 
embryonic tissue, which serves as a basis for the subsequent regen- 
eration. Sections of a tail, after it has been regenerating for 
three days, show that all of the cells in the new organ are undiffer- 
