250 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
an exposure of ten, and generally survive an ex- 
posure of five. But although they thus continue 
to live for an indefinite time, their vigour is con- 
spicuously and permanently impaired; while in 
the fresh water irritability persists for a short time 
after spontaneity has ceased, and the tentacles and 
manubrium are strongly retracted. 
“Turning now to the case of the fresh-water 
species, when first it is dropped into sea-water at 
85° there is no change in its movements for about 
fifteen seconds, although the tentacles may be re- 
tracted. But then, or a few seconds later, there 
generally occurs a series of two or three tonic 
spasms, separated from one another by an interval 
of a few seconds. During the next half-minute the 
ordinary contractions become progressively weaker, 
until they fade away into mere twitching convul- 
sions, which affect different parts of the bell irregu- 
larly. After about a minute from the time of the 
first immersion all movement ceases, the bell re- 
maining passive in partial systole. There is now 
no vestige of irritability. If transferred to fresh 
water after five minutes exposure, there immediately 
supervenes a strong and persistent tonic spasm, 
resembling rigor mortis, and the animal remains 
motionless for about twenty minutes. Slight 
twitching contractions then begin to display them- 
selves, which, however, do not affect the whole bell, 
but occur partially. The tonic spasm continues 
progressively to increase in severity, and gives the 
outline of the margin a very irregular form; the 
twitching contractions become weaker and less fre- 
