224 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
movements are interrupted by a violent spasm, 
on which strong shuddering contractions are super- 
imposed. 
8. Nicotun.—On dropping Sarsia into a sea-water 
solution of nicotin of appropriate strength, the 
animal immediately goes into a violent and con- 
tinuous spasm, on which a number of rapidly suc- 
ceeding minute contractions are superimposed. 
The latter, however, rapidly die away, leaving the 
nectocalyx still in strong and continuous systole ; 
tentacles and manubrium are retracted to the 
utmost. Shortly after cessation of spontaneity, 
the bell is no longer responsive to tentacular stimu- 
lation, but remains for a considerable time respon- 
sive to direct stimulation of its own substance; 
eventually, however, all irritability disappears, 
while the tentacles and manubrium relax. On 
transferring the animal to normal water, muscular 
irritability first returns, and then central, as shown 
by the earlier response of the bell to direct than to 
tentacular stimulation ; but if the animal has been 
poisoned heavily enough to have had its muscular 
irritability suspended, it is a long time before 
central irritability returns. Soon after central 
irritability has returned, the animal begins to show 
feeble signs of spontaneity, the motions being 
exceedingly weak, with long intervals of repose ; 
but the degree of such feebleness depends on the 
length of time during which the animal has pre- 
viously been exposed to the poison; thus in a speci- 
men which had been removed from the poison 
immediately after the disappearance of reflex 
