Degree of Injury and Rate of Regeneration 533 
coming last. The same is true when the specific amounts of 
regeneration are compared. The comparison of individuals 
within a group is more accurate than an inter-group comparison 
because the control of the factors involved in general treatment 
of the animals is better. The dishes within a group were always 
kept together and operations were made at the same time. How- 
ever, if all the individuals of the experiment are taken without 
regard to group boundaries the same general result is obtained. 
The animals with an addiltional injury of one hind-leg show the 
greatest average amount of regeneration of the tail, those with 
both hind-legs removed nearly as great an average amount, while 
those with the tail alone removed show the least tail regeneration. 
The average specific amounts are 0.487, 0.464 and 0.436 respect- 
ively. 
The later measurements suffer considerably from the large 
number of deaths, the series with one hind-leg removed suffering 
more than the others. Ninety-nine or one hundred days after 
the operation the average specific amounts are 0.623 for the 
greatest injury, 0.572 for the medium injury and 0.616 for the tail 
alone removed. One hundred and forty-nine or 150 days after 
the operation all those with the medium injury had died. ‘The 
ones with an additional injury of both hind-legs show an average 
specific amount of regeneration of the tail equal to 0.605 as op- 
posed to 0.505 for those with the tail alone removed. ‘The appar- 
ent shrinkage in the last measurements is not real but due to 
preservation in alcohol, the other measurements having been 
made from the living animals. 
The specific amounts of regeneration are given in Table 7. 
The individuals are arranged according to magnitude of specific 
amount. 
Summary of Experiments on Animals Without a Molting Habit 
A general survey of the foregoing experiments on animals 
without a molting habit may be profitable. All my experiments 
that give any data on the problem are included. Taken as a 
whole the data are favorable to the view that within moderate 
