ZOOLOGY: C. ZELENY 
213 
In order to test further the view that the accelerating effect may be 
confined to additional removal of a similar organ a comparison was 
made of the regenerating tail lengths following removal of one-half of 
the tail under the two degrees of no additional injury and of removal 
of the two fore-legs. In such a case there is no difference in rate of re- 
generation of the tail. 
These experiments, together with others that have been made, when 
taken as a whole show that a part regenerates slightly more rapidly 
when additional material of the same kind is removed than when the 
part alone is removed. Simultaneous removal of tail material, how- 
ever, may not accelerate the regeneration of a leg and simultaneous 
removal of a leg may not accelerate the regeneration of the tail. The 
rate in these cases is, however, not decreased by the additional injury. 
The statement may therefore be made that within limits the regener- 
ation of a part is not retarded by simultaneous removal and regenera- 
tion of material in other parts of the body. When this additional mate- 
rial is of the same kind as that whose rate is being studied there may 
even be an acceleration of regeneration. 
2. Level of Cut. — That the level of the cut has an important influence 
upon the rate of regeneration has been made out by a number of inves- 
tigators. Their work indicates that regenerations from deeper levels 
are on the whole more rapid than from more superficial ones. The pres- 
ent data confirm this conclusion and make possible a further analysis 
of the relation. They show that within wide limits the length regen- 
erated in the tail of an Amphibian larva is directly proportional to the 
length removed. Within these limits therefore the length regenerated 
per unit of removed length is a constant. 
First and second regenerations of the tail in the tadpoles of Rana 
clamitans and first regenerations in the salamander, Amblystoma 
punctatum, give essentially the same results. Second regenerations 
of the frog will be taken as an example. The removed tail lengths were 
1.5, 2.8, 4.9, 8.4^ 13.1 and 18.1 mm. or respectively 6, 10, 18, 31, 
49 and 67% of the original tail lengths. The regenerated lengths for 
these six levels ten days after the operation were respectively 1.0, 1.3, 
1.4, 2.3, 3.7, and 5.1 mm., an increase for each increase in depth of 
the level of injury. 
The specific lengths or lengths regenerated per unit of removed 
length as calculated from these values are respectively 0.67, 0.46, 
0.29, 0.28, 0.28 and 0.28, a close approach to constancy for removed 
lengths of 4.9 to 18.1 mm. Figures 1 and 2 give graphic representa- 
tions of these results. 
