244 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
observations on the physiology of this interesting 
animal, by quoting i 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 Medusze 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 marine congeners. More par- 
ticularly, these movements resemble those of the 
marine species which do not swim continuously, 
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 with 
young specimens. In colder water (65° 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 enormously 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 
