12 ILLINOIS BIOLOGICAL MONOGRAPHS [12 



distances of the new cut surface from the dividing line between the old 

 and the new tissue. The regenerated lengths as given are the living 

 lengths. Measurements were made on material killed in Gilson's mer- 

 curo-nitric fluid and preserved in 85% alcohol. Sets I and IX were 

 measured both when alive and after killing and preserving. From them 

 the shrinkage coefficient was obtained and this made possible the reduc- 

 tion of all the data to the living basis. The averages include only the 

 sets in which both individuals are present. The specific amount of 

 regeneration is the amount regenerated per unit of removed length. It 

 has been shown that within wide limits this is a constant if the only 

 variable in the experiment is the amount removed. This statement holds 

 for all levels in the present experiment. 



The table shows that the average amount regenerated at the end 

 of six days is 2.16 mm. from the old tissue levels and 2.15 mm. 

 from the new tissue levels. The new tissue levels however rep- 

 resent the shorter amount removed, 10.7 mm. as opposed to 11.3 

 for the old tissue levels. This gives an average specific rate of 0.204 

 for the new levels and 0.196 for the old levels. The difference is proba- 

 bly not significant. The individual specific amounts in pairs, putting 

 the old tissue first and the new tissue second in each case, are 0.17 and 

 0.18, 0.16 and 0.18, 0.16 and 0.20, 0.15 and 0.24, 0.19 and 0.15, 0.21 

 and 0.21, 0.18 and 0.23, 0.26 and 0.23, 0.17 and 0.20, and 0.31 and 0.22. 

 The old tissue is ahead three times, the new six times and there is a tie 

 in one case. 



At the end of eight days the result is similar. There is a slight 

 advantage in favor of the new tissue level but this cannot be considered 

 as significant. The average amount regenerated is 3.19 mm. from old 

 tissue levels and 3.12 mm. from new tissue levels. The specific 

 amount regenerated is 0.303 for the old and 0.310 for the new level. 

 The individual amounts by pairs putting the old tissue level first as 

 before are 0.27 and 0.24, 0.25 and 0.29, 0.28 and 0.31, 0.36 and 0.34, 

 0.25 and 0.28, and 0.41 and 0.40. Each level is ahead of the other in 

 three of the six cases. 



Experiment II Series 3676-3765 



Tadpoles of Rana clamitans with an average length of forty 

 mm. were used. The experiment was designed for a study of the 

 effect of successive removal on the rate of regeneration but incidentally 

 furnishes valuable data for the present problem. In removing the re- 

 generated portion, the cut in most cases did not come exactly at the 

 border. In some cases it was too near the base of the tail and therefore 

 the cells at the cut surface were old unregenerated cells. In other cases 



