164 DUBLIN UNIVERSITY 



ings at once cease. If the portion touched by the tentacle be snipped 

 off, all twitchings also cease. 



Having thus repeatedly observed that contact between the nerve and 

 a single tentacle was followed by muscular contractions, which at once 

 ceased as soon as the portion of the nerve which had been in contact 

 with the tentacle was removed, it occurred to me to try the effect of 

 applying to the nerve a single tentacle removed from the body of an 

 Anthea. I therefore had recourse to the following experiment : — 



The hind leg of a frog is separated from the body ; the sciatic nerve 

 dissected out carefully, so that the nerve be not crushed or injured; and 

 the thigh cut away. The limb, with the nerve thus dissected out as 

 long as possible, is to be laid on a plate of clean glass. A silk thread is 

 tied round the base of one of the tentacles of an Anthea, and the tentacle 

 snipped off. The mere tentacle, separated from the animal to which it 

 belonged, is drawn gently across the nerve, or laid upon it at the upper 

 part. Immediately muscular contractions follow in the leg. These con- 

 tractions cease at once if the portion of nerve touched by the tentacle be 

 cut off. 



There can, it seems, no longer be any doubt that the muscular con- 

 tractions are excited, not by electricity, but by irritant action of the 

 urticating organs of the Anthea, which, being more powerful in this 

 respect than the Actinia or other genera, has been chosen for experi- 

 ment, although other species give similar results. 



I now see that I was in error in supposing that the effect produced 

 on the frog's limb by the Actinia) could be transmitted along a wire. I 

 presume that in preparing the experiment alluded to, which I performed 

 in the open air at the sea-side, some of the irritant materials of the 

 Anemones, which I had possibly handled, had been brought by my 

 fingers in contact with the nerves, and I was thus deceived. I am very 

 happy, however, that I am myself the first to perceive and correct this 

 error. 



The Rev. Eugene O'Meara, A. M., read the following — 



NOTES ON THE ENCYSTED CONDITION OF DIATOMA VULGARE. (PLATE XVII.) 



I have the gratification of bringing before this Meeting a series of ob- 

 servations recently made by me on the encysted condition of Diatoma 

 vulgar -e, calculated to throw some light on the nature of this pheno- 

 menon in the Diatomacese. 



