196 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
epithelial surface has become opalescent to a con- 
siderable degree. 
In the case of stimulation by glycerine, the be- 
haviour of the manubrium is more unequivocal 
than it is in the case of stimulation by acid. I 
have therefore reserved till now my description of 
the behaviour of this organ under the influence of 
constant chemical stimulation. This behaviour is 
of a very marked though simple character. The 
manubrium is always the first to respond to the 
stimulation, its retraction preceding the first 
movements of the bell by an interval of several 
seconds, so that by the time the bell begins its 
rhythmic response the manubrium is usually re- 
tracted to its utmost. The initial response of the 
manubrium is also rhythmic, and the rhythm 
which it manifests—especially if the glycerine 
solution be not over-strong—is of the same slow 
character which has already been described as 
manifested by this organ when under the influence 
of mechanical stimulation. The rhythm, however, 
is decidedly quicker in the former than in the latter 
case. 
Lastly, with regard to the marginal ganglia, it is 
to be observed that in the case of all the chemical 
irritants I have tried, if unmutilated specimens of 
Sarsia be immersed in a sea-water solution of the 
irritant which is of a sufficient strength to evoke 
artificial rhythm in paralyzed specimens, the spon- 
taneity of the ganglia is destroyed in a few seconds 
after the immersion of the animals, 2.e. in a shorter 
time than is required for the first appearance of 
