74 Charles W . Hargitt. 



The earlier references of Haeckel to the capacity of larvae of 

 certain medusae to regenerate entire organisms are likewise in- 

 definite. Morgan in referring to the subject in his recent book on 

 "Regeneration," 'oi, merely remarks that among Scyphozoa 'the 

 jelly-fishes belonging to this group have a limited amount of re- 

 generative power." 



I very much regret that an unusual scarcity of material compels 

 me to leave several points somewhat less fully considered than is 

 desirable, but I trust they are not of sufficient gravity to seriously 

 mar the general value of the results as a whole. 



In one respect this scarcity of material, making necessary suc- 

 cessive experiments on the same specimen in many cases, proved 

 fortunate rather than otherwise, since facts of importance were 

 thus brought to light which might otherwise have been overlooked. 

 Some of these will be referred to specifically in another connec- 

 tion. 



.II. EXPERIMENTAL. 



The experiments were performed upon Rhizostoma pulmo, one 

 of the most common of the Mediterranean medusae. Both in 

 size and vigor this medusae affords one of the most satisfactory 

 forms for experimentation which has come under my observation. 

 It seems likewise to suffer less under the somewhat artificial con- 

 ditions of the aquarium than any other which I have had occasion 

 to use. As compared with Aurelia and Cyanea of New England 

 waters it is incomparably superior in every way, but particularly 

 in its ability to thrive for weeks in an environment which would 

 prove fatal to the others in as many days. With the single excep- 

 tion of Gonionemus I know of no other medusa which affords 

 so good a type for this sort of observation and experimentation. 

 It was not unusual to have specimens under direct observation in 

 the ordinary aquaria of the laboratory rooms for from four to 

 six weeks and without apparent deterioration, even in some cases 

 under the severe tax of extensive mutilation made necessary by 

 the experiments to which they were subjected. It should be stated 

 however that as a rule younger and smaller specimens proved 

 much better than those of larger size; the latter, on account of 



