61] RATE OF REGENERATION— ZELENY 61 



PART III 



THE EFFECT OF LEVEL OF THE CUT UPON THE RATE AND 

 COMPLETENESS OF REGENERATION 



The present study gives a description of some experiments made to 

 define more accurately than has been done the exact relation between 

 the level of the cut and rate of regeneration and especially the relation 

 of this factor to the other factors affecting rate and completeness of 

 regeneration. The factor is one of great interest because if it is true that 

 the ratio between length regenerated per unit time and length removed 

 is a constant it follows that no matter how much material is removed 

 regeneration is always completed in the same time. It is therefore of 

 great interest to determine the extent to which this statement is true, 

 to analyze the elements of the level factor and to determine its relation 

 to other factors. 



Experiment I Rana clamitans Series 3676-3765 

 The tadpoles were collected on December 9, 1911, and first removals 

 were made in two-thirds of the individuals on December 22. A second 

 removal was made in these individuals on January 8, and at the same 

 time a first removal in the other one-third. Measurements were made 

 four, six, eight, ten, twelve and a half, eighteen and fifty-six days after 

 the operations of January 8. The first and second regenerations are 

 treated separately and the second regenerations are taken up first because 

 they have a larger number of individuals and therefore give the more 

 uniform results. 



Second Regenerations 



The different amounts removed approximate 6, 10, 18, 31, 49 and 67 

 per cent of the tail length. There are four individuals at the lowest 

 removal, averaging 1.5 mm., seven at the next, averaging 2.8 mm., five 

 at the third with an average of 4.9 mm., ten at the fourth with 8.4 mm., 

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

 data are given in tables 37 to 40 and in graphic form in figures 4 to 17. 



The regenerated lengths at ten days will be taken up first because 

 at this time the period of maximum rate has been passed and its full 

 effect is represented. Differentiation of the tissues has begun but there 



