'2H JELLY-FISH, STAU-FJSH, AND SEA-URCHINS. 



observations on the pliysiology of this interesting 

 animal, by quoting in extenso my original paper 

 upon the subject {Nature, June 24, 1880). Before 

 doing so, however, I may state that Professors A. 

 Agassiz, Moseley, and others have since informed us 

 that sundry species of sea- water Medusae have been 

 observed by them living and thriving in the brackish 

 waters of estuaries — a fact which strongly corrobo- 

 rates the inference at the end of the present paper. 



" The natural movements of the Medusa precisely 

 resemble those of its maiine congeners. More par- 

 ticularly, these movements resemble those of the 

 marine species wdiich do not swim continuous^, 

 but indulge in frequent pauses. In water at the 

 temperature of that in the Victoria lily-house (85° 

 Fahr.), the pauses are frequent, and the rate of the 

 rhythm irregular, suddenly quickening and suddenly 

 slowing even during the same bout, which has the 

 effect of giving an almost intelligent appearance to 

 the movements. This is especially the case wdth 

 young specimens. In colder water {Qb° to 75°) the 

 movements are more regular and sustained; so 

 that, guided by the analogy furnished by my ex- 

 periments on the marine forms, I infer that the 

 temperature of the natural habitat of this Medusa 

 cannot be so high as that of the water in the 

 Victoria lily-house. In water of that temperature 

 the rate of the rhythm is enoimously high, some- 

 times rising to three pulsations per second. But 

 by progressively cooling the water, this rate may 

 be progressively lowered, just as in the case of the 

 marine species ; and in water at 65°, the maximum 



