44 Papers from the Marine Biological Laboratory at Tortugas. 



when the removal of legs was not followed by regeneration such speci- 

 mens grew in size faster than the regenerating individuals, and in most 

 instances actually faster than the control. These observations clearly 

 show that the process of regeneration itself, and not the injury inflicted, 

 is responsible for the retardation of growth in the regenerating lobsters.' 



The experiments here recorded were performed upon the Scypho- 

 medusa Cassiopea xamachana, which may be so readily obtained at the 

 Tortugas Islands. Healthy individuals of medium size were selected 

 and operated upon as described below. 



The first experiment consisted of two groups of 20 individuals of 

 the same average size. Group A had 5 of the 8 oral-arms cut from each 

 specimen (fig. i). Group B also had 5 oral-arms cut in a similar manner 

 from each of the 20 individuals, and in addition each medusa had a 



Fig. I. — Medusa with s oral-arms cut away at their bases. 



Fig. 2. — Medusa with s oral-arms cut away and a peripheral strip cut from the disk. 



Fig. 3. — Medusa disk after all of the oral-arms and the stomach have been removed. 



peripheral strip cut from its body disk which included one-third of the 

 circumference and in width extended in beyond the oral, zigzag, muscular 

 layer shown in fig. 2. The specimens were then allowed to regenerate 

 for 34 days, their disk diameters being measured at intervals so as to 

 determine the differences in decrease of body size in the two groups. 



Table I. — Record of disk diamclcrs and regeneration of oral-arms in Cassiopea, ivhen 5 arms 



are reinoved {in miUimeters). 



