Regeneration in Rhizostoma Piilmo. 8i 



organs which among the Hydromedusae are most promptly re- 

 generated are here among the most slow to develop ; such, for 

 example, as the oral arms and gastric lobes. The fact that in the 

 rhizostomous medusae these organs have no very active function 

 in the capture of food might apparently afford some plausible 

 reason for this difference in the rate of regeneration. In Goni- 

 onemus the gastric and oral organs are among the most prompt 

 in regeneration, and are, of course, also among the most important 

 in the functional activities of the animal. That this, rather than 

 liability to injury, should be a predisposing factor in regeneration 

 would seem to be confirmed in the case of Rhizostoma, for as will 

 appear in later experiments there seems to be no good reason to 

 suppose that the liability to injury, to which these organs are 

 constantly exposed, has anything to do with the capacity for rapid 

 or perfect regeneration. 



Additional experiments were begun on May 28th and 30th. In 

 this series the specimens varied in size from 20 to 60 m/m in 

 diameter. As remarked above there was in these cases the same 

 degree of promptness in the responses, which was markedly in 

 contrast with that shown by specimens of considerably larger 

 size, but in the present cases there was also apparent a somewhat 

 less favorable response In the very small specimens. This fact 

 considered in connection with the difficulty of operating easily 

 upon small specimens, emphasizes the value of animals of medium 

 size for such experiments. This conclusion was emphasized 

 throughout the entire course of experimentation. 



In part of the specimens of this series only three rhopalia were 

 excised, in others four, in others five. In some the rhopalia were 

 all removed from one side, while in others only alternate organs 

 were removed. In some specimens the same order was observed 

 as to excision of mouth arms and other similar operations. One 

 of the specimens of the series had only one full-sized mouth arm, 

 while the others were in what seemed to be various stages of 

 regeneration. As is well known these organs among medusae of 

 this type are among the most open to accident from attack of 

 fishes or other predatory enemy. The specimen under considera- 

 tion would seem to confirm the results of these experiments that 



