Rate of Regeneration in Cassiopea xaviaehaua. 



79 



THE RATE OF REGENERATION FROM DIFFERENT AREAS ON TAPERING 

 PERIPHERAL STRIPS AND REMAINING PART OF DISK - CONTRAST- 

 ING THE LEVEL OF THE CUT AND EXTENT OF INJURY. 



The circular medusa disk offers exceptional material for certain opera- 

 tions that could not be carried out on animals having a differently shaped 

 body. It has been found difficult to perform an experiment which would 

 clearly contrast the rate of regeneration from certain levels with the rate 

 from parts more or less injured. According to Zeleny the rate of regenera- 

 tion will be faster the greater the injury up to a reasonable limit, and ac- 

 cording to Morgan's pressure and growth idea the rate varies at different 

 levels, being slower as the level is nearer the normal body limits. The con- 

 ditions are usually open to either interpretation, since the least injured ani- 

 mals are the ones with less body tissue removed and necessarily nearer the 

 normal bodv limits than those with more tissue removed. 



Fig. 25. — Manner of cutting bias strip 

 from periphery of medusa disk. 



Fig. 26. — Such strip if straightened 

 would form a long triangle with 

 sense-organs, SO, along its base. 



Fig. 27. — Manner of regeneration from 

 cut edge of the disk center. 



If a medusa disk is so cut that a strip wide at one end and narrow at 

 the other is removed from the entire periphery, then regeneration will take 

 place from the entire cut surface of the strip and also from the cut margin 

 of the remaining disk center (fig. 25). The strip is most injured, one may 

 say, at its narrow end, as obviously here more of the disk has been re- 

 moved from it, and it is least injured at its broad end, as here less tissue 

 has been cut away. The wide end of the strip, however, has more raw 

 tissue exposed by the cut, as the disk is thicker near the center and gradu- 

 ally thinner toward the periphery. One might claim that those portions 

 with the most raw tissue exposed were the most injured; therefore the 

 strip and disk center were equally injured along corresponding regions 

 of the cut. It seems more logical, however, to consider the object most 

 injured from which a greater amount of its original body tissue has 

 been separated. The remaining disk center is most injured where it was 

 deepest cut or on that part from which the wide end of the strip came, and 

 it is least injured where the narrower part of the strip came from. 



