190 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
With regard to artificial rhythm caused by 
chemical stimuli, by far the most conspicuous 
instance that [ have observed is that of the para- 
lyzed nectocalyx of Sarsia. This consists in a 
highly peculiar motion of a flurried, shivering 
character, which is manifested by this organ when 
its marginal ganglia have been removed and it is 
exposed to the influence of faintly acidulated water. 
Now, when read in the light of the foregoing facts, 
there can be no doubt that the present one falls 
into its place very satisfactorily : it is an additional 
and very valuable instance of the display of arti- 
ficial rhythm under the influence of a constant 
stimulus of low intensity; for the shivering 
motions of the mutilated nectocalyx under these 
circumstances are most unmistakably of a rhythmic 
nature. Viewed from a little distance, indeed, these 
motions are not distinguishable from the natural 
swimming motions of the unmutilated animal, 
except that, not being of quite such a powerful 
character, they are not so effective for locomotion. 
Viewed more closely, however, it may frequently be 
seen that the whole bell does not contract simul- 
taneously, but that, as it were, clouds of contraction 
pass now over one part and now over another. 
Still, whether the contractions are partial or uni- 
versal, they are more or less rhythmical. As this 
was the only case that had ever been observed of 
too, the presence of ganglion-cells has never been observed micro- 
scopically, though specially sought for by Dr. Klein and others. 
Yet, under the influence of mechanical and other modes of stimu- 
lation, I find that I am able to make the excised organ pulsate as 
rhythmically as a heart. 
