REGENERATION OF ARMS IN BRITTLE-STAR. 13 



of the experiment. Measurements of the lengths of the regener- 

 ating arms were taken 22, 33 and 46 days after the operation. 

 As stated above the specimens in the series where all five arms 

 were removed did not retain their vitality for a sufficient length 

 of time to allow of comparison with the others and they will 

 therefore be excluded from the following tabulation. 



As the rate of regeneration varies with the size of the animal 

 as well as with the number of removed arms the proper relations 

 can best be represented by means of curves. The figure accom- 

 panying this paper gives the average of Series I. and II. (those 

 with respectively one and two arms removed) in one curve and 

 of Series III. and IV. (those with respectively three and four arms 

 removed) in the other. The same arrangement is followed for 

 each of the three measurements taken respectively 22 days, 33 

 days and 46 days after the operation. This brings out the de- 

 sired relations more clearly than would have been possible if all 

 the individual data had been included. In the figure the abscissae 

 give the size of the animal as represented by the disk diameter 

 in millimeters. The ordinates give the length of the regener- 

 ating arm or arms, also in millimeters. In the series where more 

 than one arm was operated on the regeneration length as given 

 is an average of all the regenerating arms of the individual. As 

 the individual disk diameters are not exactly equivalent in the 

 different series it was found convenient in taking the averages for 

 the combination curves to use arbitrarily disk diameters equal to 

 whole millimeters as the points for comparison. The curves in 

 the figure are therefore constructed on this basis. The unbroken 

 line in each case gives the average of Series I. and II. (one and 

 two arms removed) and the broken line of Series III. and IV. 

 (three and four arms removed). 



Statement of Data and Discussion. The curves show very 

 distinctly the correlation between the rate of regeneration and 

 the size of the animal on the one hand and the number of re- 

 moved arms on the other. 



I. Taking up first the size correlation we find that, starting 

 with the smaller individuals, as we advance toward the larger 

 ones there is a general increase up to a maximum at a diameter 

 of i 2 to 15 mm. This is most striking in the two later meas- 



