Degree of Injury and Rate of Regeneration 551 
17 Cambarus propinquus. Nos. 2309-2378 
The present experiment and the following one (No. 18) were 
planned for a study of other factors than that of degree of injury. 
However, since they give some data on the problem in hand they 
are included. 
The individuals in Experiment 17 come from a single mother 
collected with a mass of eggs in April,1g07. All the living young, 
seventy in number, were taken from the mother on May 12 and 
put into seventy separate dishes. All but seven of the crayfish 
had molted twice since hatching. The others molted their 
second time on May 13. The experiment was planned in part 
for a study of the effect of the time of the operation with respect 
to a molt upon the time of succeeding molts. ‘Thirteen individ- 
uals are available for the purposes of the present paper. All 
these were operated upon two days after the third molt. In seven 
one chela was removed and in six both chela were removed. 
In all except one individual in each set the molt came on May 
21 and the operation on May 23. In the exceptional ones the 
molt came on May 20 in No. 2343 and on May 22 in No. 2358. 
The crayfish were killed in 85 per cent alcohol on June 20, 
twenty-eight days after the operation. The data are given in 
Tables 24, 25, 26 and 27. Tables 24 and 25 include the indi- 
viduals in which three molts occurred during the regenerating 
period and Tables 26 and 27 those in which four molts occurred. 
The young crayfish were so nearly equal in size that separate 
measurements of cephalo-thoracic length and removed chela 
lengths were not taken. It is, therefore, not possible as in the 
case of the data of the preceding experiment to give the specific 
amount and specific rate of regeneration. ‘The absolute amounts 
and the rates per day are given in the tables. Of special value 
is the fact that the molting periods show only slight differences 
in length so that two compared groups are nearly equal in abso- 
lute time as well as in number of molts. 
The data show an advantage in favor of the crayfish with two 
regenerating chele both in absolute amount and in rate per day 
For the three-molt cases the removed single chelaz have an abso- 
