156 ILLINOIS BIOLOGICAL MONOGRAPHS [156 



ment may therefore be made that within limits the regeneration of a part 

 is not retarded by simultaneous removal and regeneration of material in 

 other parts of the body. When this additional material is of the same 

 kind as that whose rate is being studied there may even be an acceler- 

 ation of regeneration. 



In comparison with such a factor as level of the cut this difference 

 in rate is slight and no such quantitative relation as in that case can be 

 made out. It must however be considered that the principal object of the 

 original experiments was to show that additional injury within the given 

 limits tends to increase rather than decrease the rate of regeneration. 

 This has been proved for these experiments. The evidence in favor of 

 a definite increase in rate with any certain increase in degree of injury 

 is not so conclusive. It is obvious that in many series of experiments 

 factors whose influence is greater than that of the factor under discus- 

 sion may obscure the result. 



Emphasis should again be placed on the fact that all data obtained 

 by the writer are included. That some of the series, especially those with 

 a few individuals, diverge from the general result is to be expected by 

 anyone in similar work who has attempted to eliminate entirely all of the 

 factors except the one under observation at a particular time. 



Summary 



1. A comparison was made of the rate of regeneration of a leg or 

 of the tail of an Amblystoma larva when the part alone is removed 

 with its rate when similar or dissimilar parts of the individual are 

 removed at the same time. The data are derived from two principal 

 Experiments, I and II, and from a few scattered observations listed as 

 Experiments III to VI. 



2. In Experiment I a comparison was made of the rate of regener- 

 ation of the right fore-leg when it alone is removed with its rate when 

 the other fore-leg is removed at the same time and when the other fore- 

 leg and one half of the tail are removed. The result obtained from forty 

 individual comparisons made at different times shows that the rate of 

 regeneration of the right fore-leg in each of the series with additional 

 injury is greater than in the series without additional injury. 



3. The rate of regeneration of a right fore-leg when its mate plus 

 one-half of the tail is removed is not essentially different from the rate 

 when its mate alone is removed. The addition of the injury to a dissimilar 

 organ, the tail, does not alter the rate of regeneration of the fore-legs. 



4. In Experiment II it is shown that there is no significant differ- 

 ence between the rate of regeneration of a tail one-half of which has been 



