190 JELLY-FISH, STAR-FISH, AND SEA-UECHINS. 



With regard to artificial rhythm caused by- 

 chemical stimuli, by far the most conspicuous 

 instance that I 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 eftective 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 souglit 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. 



