200 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



species of covered-eyed Medusae 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 Medusa3, 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 Medusae 

 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 rhytlimic 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 cir- 

 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 foro'otten 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 nuich importance to the ganglionic 



