Regeneration in Rhizostoma Puhno. 75 



their greater mass, are inclined in most cases to sink toward the 

 bottom of the tanks, where after a time certain disorganizing 

 influences appeared to set up pathologic conditions which seemed 

 to deplete their vigor and at the same time render their regen- 

 erative processes less satisfactory. 



The experiments were directed to three ends, namely to deter- 

 mine: I, The capacity of the medusae to reproduce lost parts, or 

 to recover from such Injuries as might ordinarily happen to them 

 in a state of nature, such as the battering effects of waves, the 

 injuries inflicted by enemies, etc. 



2, The comparative powers of the various regions to regenerate, 

 or In other words, the relation of the regenerative capacity to 

 liability to Injury. 



3, The capacity to regenerate such highly specialized organs as 

 rhopalla, or other sensory structures. 



The experiments included specimens of sizes from about 20 

 m/m to 125 m/m In diameter, and while all proved to have 

 unexpected powers of regeneration those of medium size, from 

 40 to 70 m/m, proved very much more satisfactory than those of 

 larger size both in convenience and In their promptness In re- 

 sponding to the several sorts of operations, and they apparently 

 were more healthy and vigorous during the progress of the ex- 

 periments than were those of larger size. Those having a size 

 of 100 m/m or more In diameter proved to be much less prompt 

 In regeneration and, as will be seen in the records of experiments, 

 were much more liable to deteriorate or utterly collapse than were 

 the smaller specimens. This is only what might be more or less 

 expected, and Is quite In keeping with observations on other 

 classes of organisms. The same tendency was more or less evi- 

 dent in specimens on exhibition in the public aquarium in which 

 of course no mutilations or similar Injuries had occurred. In this 

 connection may be noted a somewhat anomalous pathological phe- 

 nomenon observed in large specimens both in the exhibition aqua- 

 ria and in the small aquaria during the course of experlmentaton, 

 namely, the appearance of whitish blotches, or patches of disin- 

 tegrating tissues at various places on the exumbrella of the animal 

 which sooner or later affected its health and general behavior. 



