32 ILLINOIS BIOLOGICAL MONOGRAPHS [32 



Experiment II Rana clamitans Series 3676-3765 



Material and Method Ninety tadpoles with an average total length 

 of about 40 mm. and an average tail length of 27 mm. were used in the 

 experiment. The plan consisted in the removal of a portion of the tail 

 in a part, S, of the individuals, the remaining part, F, being left un- 

 injured at the time. After S had been regenerating a new tail for 

 twenty-two days both S and F were operated upon. In S the regen- 

 erating tails were removed by a cut which came at the border line be- 

 tween the old and the new tissues. In F an operation was made similar 

 to the original one on S and leaving the same amount of old tail in both 

 S and F. The procedure is similar to that shown in Figure 1. S and 

 F were now allowed to regenerate and a direct comparison is possible 

 between a second regeneration in S and a first regeneration in F. 



Measurements were made of regenerated lengths at 4, 6, 8, 10, 12y 2 , 

 18 and 56 days. The operations were made at six levels corresponding 

 approximately to the removal respectively of a / 18 , Vio> %> %> Y2 

 and % of the tail. Four of these levels, 1 / 10 , %, ^ and %, had at 

 least five individuals each for each regeneration. The other two levels, 

 1 / 18 and %, had less than five individuals per regeneration but are 

 included in the tables though their averages are not as reliable as those 

 of the others. 



The method as described agrees in principle with that pursued in 

 Experiment I. It has a decided advantage over a direct comparison 

 within a single individual because it eliminates the age factor as well as 

 the effects of change in external conditions such as temperature and 

 food. 



Data The results of the experiment are given in Tables 21 to 30 

 an<^ in Figures 2 and 3. The data show on the whole a tendency for 

 the second regeneration to remain in advance of the first for eight or 

 ten days after the operation. The first regeneration then catches up 

 and even slightly surpasses the other; this is apparent both when the 

 regenerated lengths are taken directly and when they are corrected for 

 difference in level of the cut and put in terms of specific regenerated 

 length or the length regenerated per unit of removed length. 



In making the comparisons certain general features must be borne 

 in mind. The maximum rate of regeneration is reached on or near the 

 seventh day, earlier for the smaller removals and later for the larger 

 removals. The whole regeneration, in so far as it is completed, is 

 finished in nearly all cases at 12^ days, again somewhat earlier for the 

 smaller and somewhat later for the larger removals. In the tadpoles 

 used in the present experiment about four-tenths in length of the re- 

 moved tail is replaced before regeneration stops. This was found to be 



