268 Charles Zeletzy 



gins was studied with respect to the question of relation of degree 

 of injury to the rate of regeneration, but because of distortions 

 involving the whole umbrellar region, no adequate data were 

 obtained. 



2 The Effect of Successive Injury on the Rate of Regeneration 



The study of successive injury was confined to the margins. 

 As in the last mentioned case there was considerable trouble with 

 distortion of the disk. Eight individuals however were without 

 distortion and could be used for the present purposes. The 

 experiments on successive injury come under two heads. In one 

 series a number of individuals of a size were chosen. In half of 

 these the whole margin was removed and allowed to regenerate for 

 twenty-nine days, at the end of which time it had nearly completed 

 its regeneration. This margin was then removed for the second 

 time at the same hour that it was removed for the first time in the 

 others. After twelve days the animals were killed and a measure- 

 ment of the new margins gave a direct comparison of first and 

 second regeneration as shown in Table 11. 



TABLE n 



Width of regenerated margin in millimeters 

 First regeneration Second regeneration 



•S 



1.6 



Average . 



The second regeneration shows a decided advantage over the first. 



In a second series the first, and second regenerations were com- 

 pared within single individuals. A part of the margin of each 

 individual was removed, and after it had nearly completed its 

 regeneration it was removed again at the same time that a similar 

 segment from another part of the circumference was removed 

 for the first time. A direct elimination of indviduality was thus 

 obtained. 



On account of individual differences in the method each case 

 is described separately. In each, how,ever, the first operation 



