494 Charles Zeleny 
molting period may differ considerably in length without greatly 
affecting the amount of regeneration taking place within the period. 
In other words, all or nearly all of the regeneration that is to occur 
during a molting period occurs during the first few days. It is 
obvious in connection with this statement that the rate of regener- 
ation may be accelerated or retarded as far as the active regener- 
ating period is concerned without any visible external evidences as 
long as the total amount regenerated during the molting period is 
unaltered. ‘This possibility must be borne in mind in comparing 
data on the Crustacea with data on other forms. 
3 The Chele of the Crayfish, Cambarus bartoni 
Method. A female crayfish with young attached to her swim- 
merets was collected on December 14, 1906. ‘The young, fifty 
in number, were kept together until February 11, 1907, when they 
were put into individual dishes. The water was changed fre- 
quently. ‘The food consisted of Tubifex worms, the supply of 
which in each dish was never allowed to be exhausted. All shed 
skins were preserved in 85 per cent alcohol, and all operations were 
made two days after a molt. The autotomy of the chelaz was 
effected by injuring the nerve with a needle. 
The experiment consisted in the repeated removal and regenera- 
tion of a single or both chelz in about one-half the crayfish. The 
regenerating chelz on the average attained about three-fourths of 
their original length before a new removal. No operation was 
made on the second half of the individuals until the first ones were 
ready to begin their third or fourth regeneration. Their chela- 
were then removed for the first time. A direct comparison was 
thus made possible of the first and third or fourth regenerations. 
In the tables of data (Tables 11 and 12) the chela length is the 
length in millimeters of the propodite. The thoracic length is the 
length of the cephalothorax to the tip of the rostrum. 
Because the molting periods did not coincide in the different 
crayfish only a small number of individuals is available for any one 
comparison. 
The young crayfish were probably in their fourth molt when 
the observations were begun on February 11. The internal evi- 
