7o Papers from the Marine Biological Laboratory at Tortugas. 



will be the rate of the regenerating growth. Miss King (1898) finds in 

 Asterias that the rate of regeneration is greatest from the disk and decreases 

 directly towards the tip of an arm. It is also true that those medusa-disks 

 cut nearer the center are the greatest injured and according to Zeleny 

 would be expected to regenerate their removed tissue fastest, just as they 

 really do. It so happens that the difference in level and the amount of in- 

 jury are often closely associated. I shall, however, cite an experiment be- 

 low which serves to contrast the two and shows the level of the cut to be 

 the more important factor in regulating the rate of regeneration. 



RATE OF REGENERATION FROM DIFFERENT PARTS OF VARIOUSLY 



SHAPED CUT SURFACES. 



For the study of problems relating to the rates of growth from surfaces 

 partially cut as compared with those entirely cut, and the rates of growth 

 from diiTerent parts of the same cut surface, Cassiopea oflfers exceptional 

 opportunity, since the disk-body itself may be cut in sundry patterns and the 

 regeneration rate observed in the several cases. Morgan (1902 and 1906), 

 from a study of regeneration in the fish's fin, has contributed a number of 

 valuable observations bearing on the question in point. The caudal fins of 

 Fuiiduhts and Carassius were trimmed in different ways, and it was found 

 that partially cut surfaces regenerated slower than entire surfaces cut at 

 the same level ; also that new tissue grew out at a faster rate from certain 

 parts of all cut surfaces than from other parts. Since Morgan's experi- 

 ments were confined to the manner of regeneration from fins or appendages, 

 I determined to make similar cuts upon the disk or " body " of the medusae 

 to ascertain whether the same principles in regeneration would hold. The 

 results show not only that the same manner of regeneration is adhered to 

 in the body and in the appendages of the two animals, but further, that the 

 forces controlling or determining the regeneration rate on various parts of 

 the cut surfaces act similarly in animals as different as fish and medusae, 

 almost at the opposite ends of the animal series. 



Straight cuts were made upon the disks of medusae in the following 

 ways : First, a single piece was cut from the disk, as shown in figure 4. 

 Second, two such pieces were cut off as indicated in figure 5, and lastly 

 three pieces were removed as in figure 6. Five individuals were cut in each 

 way and different-sized pieces were removed. The course of regeneration 

 followed by each of the cuts in all of the 15 meduste was practically the 

 same. The history of one set, consisting of one of each kind of individual, 

 will answer for all. 



The specimen having one cut will be designated as A, the two cuts as 

 B, and the three cuts as C. From A a portion of the disk was removed 

 that measured 32 mm. wide at its broadest place and included 6 of the 16 

 marginal sense-organs. Four days later the regenerated tissue from the cut 



