108 ILLINOIS BIOLOGICAL MONOGRAPHS [108 



PART IV 



THE CHANGE IN RATE OF REGENERATION DURING THE 



REGENERATIVE PROCESS 



The present experiments were undertaken in extension of previous 

 studies on the change in rate throughout the regenerative cycle. This 

 previous work showed that the increase in amount of material during 

 regeneration follows the general rule of increase during an ordinary 

 life cycle. The rate is at first very slow, then increases very rapidly 

 to a maximum, then declines rapidly at first and then more and more 

 slowly as zero is approached. 



Frog tadpoles and salamander larvae were used in the present 

 study. Large tadpoles of Rana clamitans which remained fairly con- 

 stant in size during the course of the experiments were found to be the 

 most satisfactory. The results obtained from them were uniform enough 

 for an analysis of the change in rate. The salamander larvae showed 

 a great variation in rate from day to day apparently associated with 

 external factors such as food and temperature. The data obtained from 

 them are however of interest in comparison with the frog tadpole results. 



The experiments will be taken up in turn beginning with the series 

 containing the largest number of individuals and giving the most uni- 

 form results. 



Experiment I Rana clamitans Second regenerations of the 

 tail Series 3676-3765 



The tadpoles were collected on December 9, 1911 and first remov- 

 als were made on December 22 and second removals on January 8. 

 Measurements were taken 4, 6, 8, 10, 12y 2 and 56 days after the opera- 

 tion. The operations were made at six different levels, the removals 

 approximating 6, 10, 18, 31, 49 and 67 per cent of the tail length. The 

 first of these removals averaged 1.5 mm. and four individuals with 

 completed measurements are available, the next averaged 2.8 mm. with 

 seven individuals, the third 4.9 mm. with five, the fourth 8.4 mm. with 

 ten, the fifth 13.1 mm. with eight and the sixth 18.1 mm. with ten 

 individuals. The rates per day for each level during each period are 

 given in table 55 and in graphic form in figure 52. The maximum 



