Amount of Tail Regenerated to Removed in Tadpoles 439 
other series operated upon as follows: one-fourth of the tail was 
removed from eight; one-half of the tail from another eight; and 
three-fourths of the tail from a third eight. This experiment was 
unexpectedly brought to a close on the fourth day after the opera- 
tion, and is mentioned here for but two things. (1) During the 
four days of the experiment some of the individuals of the series 
which had lost one-fourth of the tail, regenerated more than 100 
per cent of the partremoved. This is the only case in these 
experiments, in which all of the removed part was regenerated. 
It must be noted, however, that during these four days the con- 
trol series grew from 12.2 mm. to 16 mm., body length. (2) 
Almost all of the animals with three-fourths of the tail removed, 
died. 
DISCUSSIONS AND CONCLUSIONS 
Tem perature 
‘Temperature was found to influence the amount of regeneration, 
Its effect is direct, and the amount of regeneration varies in the 
same direction as the temperature, between two thermal limits. 
In Experiments 2 and 3, tadpoles regenerated the tail at 66° F. 
but did not regenerate at 57° F. even though the other conditions 
of the experiments were the same. As the temperature factor 
was the only variable in these two experiments, the lack of regenera- 
tion at 57° F. must be ascribed to the effect of temperature upon 
the processes producing regeneration. ‘This lack of regeneration 
at 57° F. is of particular interest since the animals did not die, 
although they did not regenerate. “he minimum temperature at 
which regeneration takes place, although not absolutely deter- 
mined, is between 66° and 57° F. for the type of tadpoles used. 
Considering the other temperatures in Experiments 2 and 3, it 
is seen that tadpoles regenerated readily at 76° F. while they 
died in less than twenty-four hours at 96° F. ‘The temperature at 
which most of the experiments in this work were maintained, was 
78° F. ‘Tadpoles regenerated readily at that temperature. ‘The 
highest temperature used, at which regeneration took place, was 
82° F. in Experiment 6. On the contrary, tadpoles were kept at 
47° F., 19° below the lowest temperature at which they regenerated, 
