196 JELLY-FISH, STAR-FISn, AND SEA-URCHINSw 



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 ot 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, i.e. in a shorter 

 time than is required for the first appearance of 



