72 Papers from the Marine Biological Laboratory at Tortugas. 



angle seem to reenforce one another in regeneration, a kind of summation 

 of regeneration occurring. Througii such a process the disk is converted 

 into a ball-shaped body with a small triangular opening at the top, where 

 the three uninjured corners are brought almost together (fig. 9). 



It will be recalled that the fins of the gold-fish and Fundulus, when cut 

 straight across, begin to regenerate their new tissues faster in the middle 

 of the cut and slower near the corners, a fashion identical with that fol- 

 lowed by the disk of the jelly-fish. 



The medusse-disks were next cut in such patterns as to give what Alor- 

 gan has termed "partial cut surfaces" (figs. 10, 11, and 12). Such cuts 

 were varied in the width of their different parts as well as in depth. Many 

 individuals were prepared in the several ways. 



The deep part of the cut shown in figure 10 must be wide, since it shows 

 a strong tendency to close its walls together after a week or two (fig. 14). 

 The history of the regeneration from such a cut surface may be recorded 

 in detail. The cut was made so that the bottom of the deep part was 23 mm. 

 from the peripheral margin at its most distant point; this part was 26 mm. 

 in width ; the lateral shallow parts of the cut were each 19 mm. wide and 

 10 mm. below the margin at their middle point. Four days after the 

 operation the regeneration was perceptibly greater from the deep-cut sur- 

 face than from the lateral shallow surfaces, and within si.x days the middle 

 part had almost overtaken the lateral surfaces (fig. 13). The regeneration 

 in the deep cut really takes place from three surfaces, the bottom and the 

 two sides of the cut, as here there is free opportunity for lateral regenera- 

 tion, thus difi'ering from the case of the fish's fin, where the fin-rays seem 

 to prevent lateral regeneration, since they are only capable of growing out 

 from the stumps of the old rays. 



Ten days after the operation there was 13 mm. of regenerated tissue 

 from the deep cut and only 10 mm. from the lateral shallow parts. After 

 14 days the deep cut had become so pulled together that there was only 5 

 mm. between its original walls. When 20 days old the regenerated tissue 

 had rounded across its free margin and was now growing out as one piece. 

 After 23 days the old sides of the deep cut were only 3.3 mm. apart; the 

 regenerated tissue over it measured only 10 mm. and over the shallow parts 

 7 mm. This loss in width may be either due to the thickening of the new- 

 tissue which is taking place, or may be on account of the general decrease 

 in size which the medusa has undergone, measuring now 63 mm. in diameter, 

 whereas it was yy mm. across when the experiment began. The new tissue 

 from the deep cut after the twenty-third day began again to increase slowly 

 in width until when 35 days old it was 14.5 mm. wide and that from the 

 shallow parts was 8 mm. The original walls of the deep cut were almost 

 drawn together, being only 2.3 mm. apart. The entire cut had tended to 

 contract, so as to take an angular form, as illustrated in figure 14. All 



