74 Papers from tlie Marine Biological Laboratory at Tortugas. 



We may now consider regeneration from surfaces cut in practically the 

 opposite manner from those just recorded. The lateral cuts are deep, with 

 a high middle tongue-piece (fig. ii). Many medusas cut in this fashion 

 regenerated tissue in a similar way. The exact history of one of the indi- 

 viduals is as follows: The disk was cut so that the lateral surfaces were 26 

 and 41 mm. wide, respectively, and the high tongue-piece between them 

 was 14.5 mm. wide and 10 mm. high, or above the level of the side cuts 

 (fig. 11). Six days after the operation the newly proliferated tissue was 

 widest on the two side portions and narrow from the middle piece. The 

 corners of the high middle part seemed to exert a retarding influence on the 

 regenerative processes, as did also the outer or marginal corner of the lateral 

 cuts. The inner corners of the side cuts were, on the other hand, the places 

 of greatest regeneration, as no doubt the lateral and basal surfaces both con- 

 tributed to the process (fig. 15). Nine days after the operation the re- 

 generated tissue from the lateral cuts was 5 mm. wide, while that from the 

 middle piece was only half as much. On the twelfth day the conditions were 

 about the same. The fifteenth day gave the side parts 7 mm. of new tis- 

 sue, while the middle part had proliferated tissue only 2.3 mm. wide. At 

 this time the old border of the middle piece is 8 mm. wide, while the lateral 

 parts are 16 and 5 mm. respectively. When 21 days old the regenerated 

 tissue had rounded its border (fig. 16) and measured 7 mm. deep over the 

 side cuts and 3.5 mm. over the middle part. From this time until the twenty- 

 seventh day the middle part continued to grow out new tissue, while the side 

 portions seemed to have completed themselves. 



Regeneration from such a cut surface may be thus summarized. The 

 lateral cut surfaces produce new tissue faster than the high middle piece. 

 The outer corners of all the cut surfaces seem to exert a retarding influence 

 on the rate of regeneration, while from the inner corners of the lateral cuts 

 new tissue is formed at a very rapid rate, which is probably due to a sum- 

 mation of regeneration. It will be again recalled that an identical condition 

 exists in the regeneration from similar cuts on the fish's tail. 



Medusae were also cut in such a way as to test the rate of growth at dif- 

 ferent levels on one and the same individual. Here, obviously, the conditions 

 of nutrition and vigor must be as nearly identical as possible. At one place 

 on the rim of the disk a piece was cut out which was 10 mm. deep at its 

 broadest part. Opposite this cut, or 180° away, a second piece of the disk, 

 including an arc of the same extent, was cut away to a depth of 16 mm. 

 from the highest point of the arc (fig. 12). When one cut is narrower 

 peripherally than the other, the rates of regeneration are not readily com- 

 pared, since regeneration proceeds more rapidly from a narrow cut than 

 from a wide one at the same level. 



After six days the regenerating tissue was broader from the deep than 

 from the shallow cut, although here it has a thicker base of tissue to grow 



