Ill] OF REGENERATION 277 



of a size, about 40 mm. ; the average length of tail was very near 

 to 26 mm., or 65 per cent, of the whole body-length; and in four 

 series of experiments about 10, 20, 40 and 60 per cent, of the tail 

 were severally removed. The amount regenerated in successive 

 intervals of three days is shewn in our table. By plotting the 

 actual amounts regenerated against these three-day intervals of 

 time, we may interpolate values for the time taken to regenerate 

 definite percentage amounts, 5 per cent., 10 per cent., etc. of the 

 amount removed; and my diagram is constructed from the four 

 sets of values thus obtained, that is to say from the four sets of 

 experiments which differed from one another in the amount of tail 

 amputated. To these we have to add the general result of a fifth 

 series of experiments, which shewed that when as much as 75 per 

 cent, of the tail was cut off, no regeneration took place at all, but 

 the animal presently died. In our diagram, then, each curve 

 indicates the time taken to regenerate n per cent, of the amount 

 removed. All the curves converge towards infinity of time, when 

 the amount removed approaches 75 per cent, of the whole; and all 

 start from zero, for nothing is regenerated where nothing had been 

 destroyed. 



The rate of regenerative growth in tadpoles' tails 

 (After M. M. Ellis, Journ. Exp. Zool. vii, ^.421, 1909) 



* Each series gives the mean of 20 experiments. 



The amount regenerated varies also with the age of the tadpole, 

 and with other factors such as temperature; in short, for any given 

 age or size of tadpole, and for various temperatures, and doubtless 

 for other varying physical conditions, a similar diagram might be 

 constructed!. 



The power of reproducing, or regenerating, a lost limb is par- 



t Cf. also C. Zeleny, Factors controlling the rate of regeneration, Illinois Biol- 

 Monographs, iii, p. 1, 1916. 



