66 Papers from the Marine Biological Laboratory at Tortugas. 



operation leaves the jelly-fish without marginal sense-organs and, therefore, 

 its rhythmical contractions cease until a slight epithelial rim has regenerated, 

 which serves to reestablish the pulsation. This new tissue is itself unable 

 to contract, yet it is the seat of the stimulus which causes the disk to pulsate. 

 Two jelly-fish, each about 86 mm. in diameter, were cut around their 

 entire periphery so as to remove a strip of tissue lo mm. across (fig. i). 

 Two other medusae were cut, in a similar manner as near as possible, and in 

 addition their mouth-arms were removed, so that they were entirely de- 



FlG. I. — Diagram indicating method of cutting. 



Fig. 2. — Stippled border sliows newly regenerated tissue from cut periphery. New tissue 

 widest where ends of mouth-arms [MA) press against it. 



prived of all means of obtaining food. The former are designated in table 

 I as Nos. I and ia, the latter as Nos. 2 and 2.\. By referring to this table 

 the rates of regeneration from the cut peripheries may be readily ascertained 

 for the three medusae, Nos. i, i.^, and 2; 2A died soon after the experiment 

 had started. Nos. i and ia were pulsating two days after the operation and in 

 six days they had grown a rim of new tissue 3.3 mm. wide about their cut 

 peripheries. The regenerating tissue then began to thicken and did not in- 

 crease further in width until after the tenth day. On the fourteenth day 

 the sense-organs were slightly indicated; from this time until the thirty-fifth 

 day there was only a slight increase in the radial width of the regenerating 

 rim until it reached about 5 mm. across, or was one-half as wide as the 

 piece originally removed. During this period, however, the regenerating 

 tissue was becoming thicker, until it had attained the normal thickness of the 

 disk for the given level ; further differentiation of the sense-organs was also 

 taking place. At the same time it must be remembered that the animal as 

 a whole was constantly becoming smaller for want of food, so that the disk 

 of No. I, which measured 66 mm. in diameter after the operation on June 

 13, measured only 40.6 mm. on July 18, or 35 days later. Thus the amount 

 of regenerated tissue is to the diameter of the disk almost as much as the 

 amount of tissue removed was to the original diameter after the operation 

 was performed. 



