68 



Papers from the Marine Biological Laboratory at Tortugas. 



ner at these places where the mouth-anns pressed. Regeneration also pro- 

 ceeded at a faster rate in the irregularities of the cut surface. This case will 

 be fully considered in a following section. 



No. 2, which was cut in the same way as Nos. i and ia and in addition 

 had all of its mouth-arms removed, regenerated somewhat more slowly at 

 first, although obviously the most injured of the three. Later, however, 

 it showed almost as much regenerated tissue as either of the other two. 

 During the observations this medusa showed a ver)^ peculiar condition ; the 

 periphery of the disk became arched aborally and the regenerating tissue 

 was thus also directed aborally, being finally so folded over that the animal 

 became cup-shaped ( fig. 3 ) . The regenerating tissue then grew toward the 

 center, and by fusing the edges of its periphery changed the cup into a hol- 

 low sphere. This condition was also observed in several other experiments 

 and may be explained thus : The muscles being slightly out of the nor- 



Fic. 3. — .1, top view of aborally arched disk; new tissue (/?) regenerating from cut 

 periphery grows toward center. B, cross-section of such specimen. C, new tissue 

 completely fused over top, converting former disk into hollow sphere. 



mal condition of coordination, those expanding the disk act more strongly 

 than the oral contractors and the periphery is thus gradually directed more 

 and more aborally. The new regenerating tissue has a tendency to fuse if 

 two of its surfaces are brought together so that when its periphery is folded 

 aborally and the edge-^ come together they fuse and form the hollow sphere. 

 A similar balloon-like condition has been recorded by Hargitt (1899) in 

 Gonionemus. Hargitt was unable to produce such a condition artificially, 

 although he tried in several waj's to do so. 



Two other medusa, designated in the table as Nos. 3 and 3.\, had a strip 

 16.5 mm. wide taken from the peripheries of their disks. These disks are, 

 therefore, more injured than the first and they are also cut at a deeper level. 

 After 6 days they had regenerated a rim of tissue slightly wider than that 

 of Nos. I and i.\, and after 10 days the rims of the latter were only half 

 as wide as those of Nos. 3 and t,.\. From this time the periphery of No. 3 

 became abnormally arched and its regeneration was slightly modified, yet it 

 continued ahead of Nos. i and i.\. The disk of 3.^ remained flat and the 

 regenerated border here increased rapidly in width for 12 days and then 

 commenced to thicken and ceased to grow in width ; the sense-organs began 



