Rate of Regeneration in Cassiopca xamaehana. 97 



III. Experiments were performed to test the rate of regeneration after 

 removal of different-sized pieces of oral epithelium at the same distance 

 from the center and pieces of the same size at different distances from 

 the disk center. My interpretation of Morgan's idea of " pressure " in 

 regeneration would lead one to expect greater pressure near the center and, 

 therefore, new epithelium should cover the more central wounds of equal 

 size sooner than it does those more peripherally located. The experiments 

 were not entirely satisfactory on account of a tendency of the wounds to 

 contract while healing or regenerating new tissue. Those nearest the disk 

 center seem to contract most, so that the result is difficult to interpret. It 

 was noted, however, that in the circular wounds the regenerating film was 

 widest toward the disk center, as if tissue was being proliferated out from 

 that direction at a faster rate than from any other. (See fig. 24.) 



R'. When a medusa disk is cut so that a strip wide at one end and nar- 

 row at the other is removed from the entire periphery (fig. 25) regenera- 

 tion will occur along the cut edge of the strip and also from the cut margin 

 of the remaining disk center (figs. 25, 26, and 27). In such a preparation 

 the strip has had most body-tissue removed from its narrow end ; also it 

 is least injured at the broad end, where least tissue has been removed. The 

 disk center is most injured where it was deepest cut or at that place from 

 which the wide end of the strip came and least injured on that portion from 

 which the narrow end was cut. 



The rate of generation from the strip, which when straightened would 

 form a long triangular body, is fastest at the wide end and is gradually 

 slower as the narrow end is reached. It is, therefore, fastest from the part 

 from ivhich the least tissue has been removed. The rate of regeneration 

 from the disk portion is more rapid from the deep-cut part and becomes 

 slower as the cut approaches the region of the former margin ; therefore, 

 the regeneration rate here is fastest from the portion from whieh most tis- 

 sue lias been removed. In both cases it will be observed that it is fastest 

 at the deepest or same level, and slower as the level nears the margin. It 

 is important to note that regeneration in both directions toward the periph- 

 ery and toward the disk center proceeds at almost the same rate from 

 the same level. 



This experiment may be interpreted as contrasting the influences due to 

 the degree of injury and those exerted at different levels of the animal's 

 disk-shaped body. The level at which the cut is made is shown to be the 

 more important factor of the two, and if the amount of injury exerts any 

 influence on the rate of regeneration it is probably of secondary importance. 

 One could scarcely claim that the narrow and wide ends of the strip were 

 to be compared with two animals from which many and few appendages 

 had been removed. 



\\ A ring 18 or 20 mm. in width or wider may be cut from the peri- 



7 



