Effect of Successive Removal upon Regeneration 505 
mean an acceleration of the rate in the first case and a slowing of 
the rate in the second case as compared with a first removal. 
Data. ‘The data are given in Table 15 which includes in the 
first column the final thoracic lengths, in the second and third 
columns the first regenerations and in the fourth and fifth columns 
the second regenerations. 
General Result. \n the thirty-one valid individuals, the average 
length for first regenerations is 2.20 mm. and for the second 2.17 
mm. an advantage in favor of the first regenerations of 0.03 mm. 
or 1.4 per cent. This difference, though very slight, may be 
valid when we consider that in twenty-two of the thirty-one cases, 
the first regeneration is greater than the second. In only six is the 
reverse true while three are equal. 
» IV DATA FROM OTHER SOURCES 
The data from the literature of the subject may be grouped 
under two heads: 
1 Data bearing on the effect of successive removal on the rate 
of regeneration, which is of special interest in connection with the 
present paper. 
2 Data showing an effect upon other features of regeneration. 
The first may be subdivided into three heads: 
a Data showing no change in rate as a result of successive 
removal. 
b Data showing a decrease in rate with successive removal. 
c Data showing an increase with successive removal. 
1-a The firstof these are by far the most frequently mentioned, 
though without the data giving actual measurements. ‘The general 
statement is made that an organ may be removed and regenerated 
several times in succession without influencing its rate of regenera- 
tion. Spallanzani (1769) says: “If the four reproduced legs be cut 
off again, four new legs will make their appearance the second 
time as they did the first; and this is repeated several times. In 
fact, when the salamanders were quite young, at which time the 
reproduction is soonest performed, I have obtained in the course 
of the months of June, July and August, six successive reproduc- 
