g(> Papers from the Marine Biological Laboratory at Tortugas. 



SUMMARY AND CONCLUSIONS. 



I. When a peripheral ring of tissue is removed from the disk of Cas- 

 siopea the cut margin of the disk promptly begins to regenerate a new rim. 

 Tlie rate at which the new tissue is formed depends upon the width of 

 the removed ring. The wider the ring is radially, or, in other words, the 

 nearer the cut is made to the disk center, the faster will the resulting 

 regeneration take place. Cuts made deep into the body o^ the disk regen- 

 er.ite tissue which increases rapidly in radial width for about ten or twelve 

 days and then almost ceases to grow in width and begins to thicken until 

 the new tissue is as thick as the medusa disk at the given level. The cut 

 periphery from which only a narrow ring of tissue has been removed 

 regenerates slowly, but almost continuously, as this portion of the disk 

 is thin and only a slight subsequent thickening is necessary. 



A small medusa regenerates proportionately faster than a larger one. 



These facts are closely similar to those observed by Morgan on the 

 earthworm, fish, and salamander. The result is interesting in that it shows 

 that animals so distinctly different as a medusa and a vertebrate regenerate 

 new tissues at rates which differ with dift'erent levels of the body, and that 

 as in the process of embryonic growth the nearer the normal body size and 

 form is approached the slower will be the rate of regeneration. 



The disks cut nearest the center are injured to the greatest degree, and 

 thev might be expected to regenerate new tissue at a faster rate than those 

 cut further from the center or less injured, if the condition is parallel to 

 the removal of more parts. It so happens, however, that the difference 

 in level and the degree of injury often coincide. These two factors were 

 contrasted in other experiments, which seemed to indicate that the level of 

 the cut was the more important in regulating the regeneration rate of the 

 new tissue. 



II. Cassiopea regenerates new tissue from the wounded edges of straight 

 cuts, and " partial cut surfaces " in exactly the same manner as Morgan 

 found regeneration to take place from similar cuts made on the fins of 

 fishes. Such a fact is of importance; first, since it shows the same prin- 

 ciples in regeneration to apply to the proliferation of new tissue from the 

 appendages and the true body-surface of animals. Second, it indicates that 

 a common principle or law regulating the rates of regeneration from dif- 

 ferent parts of variously shaped cut surfaces runs through the animal 

 kingdom, since forms at almost opposite ends of the series, the fish and the 

 medusa, regenerate in the same manner. 



The outer corners of cut surfaces seem to exert retarding influences 

 upon the rate of regeneration at all levels. At the inner corners of " partial 

 cut surfaces " regeneration proceeds at a faster rate than on the straight 

 surface. This fact is probably due to a summation of regeneration which 

 takes place from the two sides forming the angle of the inner corner. (See 

 figs. 13, 15, and 17.) 



