422 Max Mapes Ellis 
3. The time elapsing between the operation and the cessation of 
regeneration varied with the amount removed. 
4 The amount regenerated throughout the regeneration period 
was influenced by temperature. 
The only regeneration considered was that of the tail; hence the 
term “regenerated” refers to the regenerated tail. [he compari- 
son made was that of length, the length of the regenerated part 
being compared with the length of the part removed. 
FACTORS INFLUENCING REGENERATION 
Throughout the experimentation an effort was made to con- 
sider all of the factors which might influence the amount of regener- 
ation. ‘These were generally controlled directly, but if this were 
impossible, they were reduced to a constant by theintroduction of 
a “control series” of uninjured tadpoles whose reactions to the 
factors of the experiment were noted. ‘The factors of largest 
importance are here considered. 
1 Environment. The animals were kept in glass berry dishes 
containing about 150 cubic centimeters of water. [hese were of a 
uniform size and shape allowing each individual equal freedom 
and air. ‘The dishes were covered with panes of window glass so 
arranged as to permit the free circulation of air between them and 
the top of the dishes. In Experiments 2 and 3, the groups of tad- 
poles were kept in large glass battery jars. 
2 Food. ‘Three kinds of food were used: fresh Spirogyra, 
raw beef and a combination of both. Some series were not fed at 
all. When Spirogyra was used, more was placed in the dishes than 
would be eaten before the next feeding time, so that there would 
be an excess of food always present. As the food was not the 
same for all experiments, that given in each case is stated at the 
beginning of the record of the experiment. 
3 TLémperature ‘The temperature in Experiments 1, 4, and 9, 
was not controlled directly, but the average temperature of the 
water in the dishes was taken as a standard temperature for the 
experiments. [he remaining experiments were subjected to 
definite temperature conditions. ‘The jars containing the tadpoles 
