THE AMERICAN NATURALIST. [Vol. XXXVI IL 



Concerning- the first, it required but few experiments to deter- 

 mine very clearly the existence of such a capacity, though its 

 progress was somewhat more slow than had been anticipated. 

 Various rents of the umbrella were soon healed, but excisions 

 of the margins of the body were regenerated much more slowly. 



Concerning the second class, the responses were similarly 

 slow. An excised oral arm required several weeks to completely 

 regenerate, as was also the case with excised portions of the 

 gastric pouches. 



Concerning the third class I had entertained some doubt, 

 namely the power to reproduce the more specialized organs, 

 such as rhopalia or sensory bodies. The experiments were 

 an agreeable disappointment, as these organs were quite as 

 promptly regenerated, if not indeed more so than had been the 

 case with the former. In some cases the first signs of regener- 

 ation were noted within five days of their excision, and in 

 from eight to twelve days their functional power was clearly 

 recovered, as was proved by details of experimentation imprac- 

 ticable to describe here. The associated organs, such as lap- 

 pets, hood, etc., were also quite as fully regenerated as the other. 



Histological examinations show beyond any doubt the opera- 

 tion of typical histogenic processes, various phases of the regen- 

 erating organ being easily traceable from stage to stage to perfect 

 maturity of form and structure. 



In earlier experiments of a similar sort made upon Cyanea 

 and Aurelia by the writer it was found impossible to maintain 

 the normal vitality of the animals for sufificient time to secure 

 any conclusive results. Rhizostoma, however, lends itself most 

 remarkably to experimentation of various sorts and for continu- 

 ous periods of from four to six weeks without material loss of 

 vigor or regenerative power. It was found, however, that this 

 was somewhat dependent upon the size and, presumably, age of 

 the specimens. Those of large size, 75 to 125 mm. in diameter, 

 proving much less hardy under an aquarium environment than 

 specimens of smaller size; though very small specimens also 

 proved less satisfactory. Specimens of from 40 to 60 mm. in 

 Tieter proved much the better, not only from the apparently 

 lience for experimentation and 



