442 Charles R. Stockard 



V RELATION OF THE LEVEL OF THE CUT TO THE RATE OF 

 REGENERATION 



Experimenters have found that the rate of regeneration varies 

 with the level of the cut in such widely different animals as the 

 medusa, earthworm, starfish, fish and amphibians. The nearer 

 the periphery of the body or distal end of an appendage the ampu- 

 tation is made the slower will be the rate of ensuing regenerative 

 growth. The rate of regeneration, therefore, varies directly 

 with the depth of level, the deeper the more rapid will be the rate. 

 A similar principle is found in embryonic growth, the nearer the 

 adult body size is attained the slower is the rate of growth until in 

 many animals growth finally stops entirely. In regeneration the 

 more the normal size or body limit is disturbed by the opera- 

 tion the more rapid will be the growth to reform it and the slower 

 this growth becomes the nearer the regenerating part approaches 

 the original size. 



My former paper on regeneration in Cassiopea presented many 

 facts in favor of this principle. It was shown that cut surfaces 

 on the same disk when at different distances from the center regen- 

 erate new tissue at rates depending upon the level of the cut. In 

 this circular disk-shaped body one is able to compare the rates from 

 different levels on the same individual and so eliminate the com- 

 mon source of error due to individual differences. 



The differences in rates of regeneration from different parts 

 of variously shaped cuts in the bodies of these medusae are com- 

 parable to those differences in rates found by Morgan ('06) in 

 similar cuts on the fins of fishes. 



To test further the relation of the level of injury to the rate of 

 regeneration additional experiments have been performed on 

 the body of Cassiopea and on the arms of the two species of 

 ophiurans, Ophiocoma riisei and Ophiocoma echinata, with the 

 decidedly positive results given below. 



The peripheral borders were cut from ten medusa disks so as 

 to remove strips 10 mm. wide from one-half and 20 mm. from the 

 other (Fig. 7). After regeneration had proceeded for seven days 

 the new tissue was measured. In all specimens it was readily 



