200 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
species of covered-eyed Medusze that I have met 
with. In order to evoke any response at all, 
stronger solutions of the irritants require to be em- 
ployed in the case of the covered than in that of the 
naked-eyed Medusze, and when the responses do occur 
they are not of so suggestive a character as those 
which I thought it worth while so fully to describe. 
Nevertheless, even in the covered-eyed Medusze 
well marked, though comparatively brief, displays 
of artificial rhythm may often be observed as the 
result of constant chemical stimulation. Thus, for 
instance, in the case of Aurelia, if the paralyzed 
umbrella be immersed in a solution of glycerine 
(ten to twenty per cent.), a few rhythmic pulsa- 
tions of normal rate are usually given; but shortly 
after these pulsations occur, the tissue begins to go 
into a tetanus, which progressively and rapidly 
becomes more and more pronounced until it ends in 
violent tonic spasm. So that the history of events 
really resembles that of Sarsia under similar eir- 
cumstances, except that the stage of artificial 
rhythm which inaugurates the spasm is of a 
character comparatively less pronounced. 
Thus far, then, I have detailed all the facts which 
I have been able to collect with reference to the 
phenomena of artificial rhythm, as produced by 
different kinds of constant stimulation. It will not 
be forgotten that the interest attaching to these 
facts arises from the bearing which they have on 
the theory of natural rhythm. My belief is that 
hitherto the theory of rhythm as due to ganglia has 
attributed far too much importance to the ganglionic 
