Dr. R. McDonnell ou the Urticatiiiy Power of the Actiuire. 305 



the very doubtful state of the question, I ventured to look forward to 

 the pleasure of making another communication on the subject vv^hen 

 I had had further opportunities of examining the Actiniae in health 

 and vigour. 



I have now had these opportunities, and have found that the 

 most delicate electrometers are unaffected by these animals ; and I 

 conceive that by the following simple, and indeed obvious experi- 

 ments, all idea of the Anemones of our coasts being electrical may 

 be set aside. 



A galvanoscopic frog's limb having been prepared, with the nerve 

 as long as possible, it is laid on a piece of perfectly clear glass, so that 

 the nerve hangs over the edge. The pendent nerve is lowered into 

 the water containing an Atithea, and the nerve is brought in contact 

 with a single one of the long tentacles of this creature ; immediately 

 vigorous contractions follow in the muscles of the limb ; and if every- 

 thing be left undisturbed, these twitcliings will continue for some 

 minutes after the nerve is withdrawn. 



If, however, a thread be tied round the nerve, below the point 

 where the tentacle of the Anthea had touched it, all twitchings at 

 once cease. If the portion touched by the tentacle be snipped off, 

 all twitcliings 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 re- 

 moved, 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 ])Ossible, 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 the nerve touched by the 

 tentacle be cut off. There can, it seems, no longer be any doubt that 

 the muscular contractions are excited, not by electricity, but by the 

 irritant action of the urticating organs of the Anthea, which being 

 more powerful in this respect than other Anemones, has been chosen 

 for experiment, although other varieties give similar results. 



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

 the frog's limb by the Actiniae could be transmitted along a wire. I 

 presume that in preparing the experiment alluded to, which I per- 

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

 rials 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. 



Ann. ^Mag. N.Hist. Ser. 3. Vol iii. 20 



