214 
ZOOLOGY: C. ZELENY 
An analysis of the progress of regeneration from the time of the oper- 
ation to the completion of the process shows that the proportional in- 
crease in regenerated length with the increase in removed length and 
resultant constancy in specific regenerated length applies only to the 
material produced by active cell division. During the first four days 
in frog tadpoles, when the regenerating part is made up almost entirely 
of cells that have migrated from the old tissues without division, there 
is no such relation. The length of new material at this time is not 
strikingly different for the different levels and the process seems to be 
a local response of the cells to the injury. 
RANA CLAMITANS. SECOND REGENERATIONS. TEN DAYS 
FIG. 2. RANA CLAMITANS. SPECIFIC REGENERATED LENGTHS. TEN DAYS 
A compKcation in the relation between regeneration and level of the 
cut is introduced by the fact that the regenerated tail is not as long as 
the original one. A certain per cent only of the removed length is re- 
placed, 40% or less for all except the levels near the tip. Also, the end 
of the process is reached sooner for the shorter than for the longer re- 
movals. From the deepest levels regeneration is still proceeding when 
it has stopped from the medium and shallowest ones. When all regen- 
erations are completed the specific lengths are therefore slightly greater 
for the longest removals than for the medium ones. 
As to the cause of the greater rates at the deeper levels little more 
can be said than that it does not seem to be due to inherent differences 
