520 | Charles Zeleny 
mentioned below point to the view that additional injury in 
these cases at least results in an acceleration of the rate of regen- 
eration from a particular level. They naturally led to a general 
investigation of the effect of the degree of injury upon the rate 
of regeneration. 
3 The Arms of the Brittle-star,” Ophioglypha lacertosa 
A comparison was made of the rate of regeneration of individual 
arms from cuts at their bases when one, two, three, four and 
all five arms were removed. Care was taken to make the level of 
injury the same throughout. Nine individuals were used in each 
of the five groups and no food was given throughout the experi- 
ment. Measurements of the lengths of the regenerating arms 
were made 22, 33 and 46 days after the operation. ‘The data are 
given in Table I and Figs. 2 and 3 of the Journal of Experimental. 
Zoology, vol. 11, no. 1. 
Notwithstanding the complications due to the age factor and 
the large degree of individual variation it is seen that there is an 
increase in the rate of regeneration of an arm as we pass from the 
cases with a smaller to those with a greater number of removed 
arms. ‘The series with all five arms removed is excepted in this 
statement because the animals in this lot in every instance died 
or showed evidences of decay before the completion of the experi- 
ment. ‘The difference between the series with four and that with 
only one arm removed is very evident. The intermediate cases 
with two and three arms removed show the same trend though 
somewhat obscured by individual variation. 
The general results obtained with the arms of the brittle-star 
therefore confirm the suggestion given by the opercula of the 
Serpulids that an increase in degree of injury to the individual 
leads to an increase in rate of regeneration from a particular level. 
The results suggest also that this is not true indefinitely but that 
beyond a certain optimum degree of injury further injury 1s fol- 
lowed by a decline in the rate. When all five arms are removed 
2 Biological Bulletin, 1903, and Journal Exp. Zoél., 1905, pp. 7-77. 
